Control circuits, electronically commutated motor systems and methods

• US 5,023,527 A
• Filed: 04/18/1990
• Issued: 06/11/1991
• Est. Priority Date: 06/24/1974
• Status: Expired due to Term

• Current Assignee: Regal Beloit Electric Motors Inc (Regal Rexnord Corp.)
• Original Assignee: General Electric Company
• Inventors: Patel, Amritlal H., Erdman, David M., Beatty, James A.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US07/515,317
• Time in Patent Office: 419 Days
• Field of Search: 318/138, 318/254, 318/439
• US Class Current: 318/400.34
• CPC Class Codes: F23N 2233/04 with variable speed
• CPC Class Codes: F23N 3/082 using electronic means
• CPC Class Codes: F25B 2600/021 Inverters therefor
• CPC Class Codes: F25B 49/025 Motor control arrangements
• CPC Class Codes: G05D 23/19 characterised by the use of electric means G05D23/1393 takes precedence
• CPC Class Codes: H02K 29/06 with position sensing devices H02K29/03 takes precedence
• CPC Class Codes: H02K 29/10 using light effect devices
• CPC Class Codes: H02P 6/085 in a bridge configuration
• CPC Class Codes: H02P 6/14 Electronic commutators
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position
• CPC Class Codes: H02P 6/182 using back-emf in windings

Abstract

Control circuit for an electronically commutated motor which has a rotatable assembly and further has a stationary assembly with a plurality of winding stages having terminals for energization, and switches for applying a voltage to one or more of the terminals of the winding stages at a time and commutating the winding stages in a preselected sequence to rotate the rotatable assembly. A preselected sequence of winding stages are left correspondingly unpowered so that a plurality of the winding stages are unpowered at some time. The winding stages generate back emf signals and also couple electrical signals from each energized winding stage to the unpowered winding stages which signals can interfere with detection of back emf for position sensing purposes. The control circuit includes a first circuit for selecting at least two of the unpowered winding stages which have electrical signals coupled to them that have a predetermined relationship in polarity and magnitude. A second circuit produces an electrical output from the voltages on the winding stage terminals of the winding stages selected, so that the electrical signals coupled from each energized winding stage are substantially canceled when they have the predetermined relationship while the back emf is preserved for position sensing substantially free from interference from the electrical signals that are coupled from each energized winding stage to the unpowered winding stages. Other control circuits, electronically commutated motor systems and methods of control and operation are also disclosed.

Claims

1. A control circuit for an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages having terminals for energization, and switching means for applying a voltage to one or more of the terminals of the winding stages at a time and commutating the winding stages in a preselected sequence to rotate the rotatable assembly, leaving a preselected sequence of winding stages correspondingly unpowered so that a plurality of the winding stages are unpowered at some time, wherein the winding stages generate back emf signals and also couple electrical signals from each energized winding stage to the unpowered winding stages which signals can interfere with detection of back emf for position sensing purposes, the control circuit comprising:

means for selecting at least two of the unpowered winding stages which have electrical signals coupled to them that have a predetermined relationship in polarity and magnitude; and

means for producing an electrical output from the voltages on the winding stage terminals of the winding stages selected, so that the electrical signals coupled from each energized winding stage are substantially canceled when they have the predetermined relationship while the back emf is preserved for position sensing substantially free from interference from the electrical signals that are coupled from each energized winding stage to the unpowered winding stages.

2. A control circuit as set forth in claim 1 wherein said means for producing includes means for providing the electrical output as a function of the difference of the voltages on the terminals of a pair of the winding stages selected.

3. A control circuit as set forth in claim 1 wherein said means for producing includes means operable generally for integrating a function of the difference of the voltages on the winding stage terminals of a pair of the winding stages selected so that the back emf is integrated substantially free of interference from the electrical signals coupled from the energized winding stages and the integrated output is generally representative of the angular position of the rotatable assembly.

4. A control circuit as set forth in claim 1 further comprising means for establishing a first electrical level representative of a first angular position of the rotatable assembly at which an energized winding stage is to be deenergized, and a second electrical level representative of a second angular position of the rotatable assembly at which the switching means is to advance in the sequence, and comparing means, connected to said means for producing, for comparing the electrical output with the first and second electrical levels to produce first and second control signals for the switching means when the first and second angular positions are respectively reached by the rotatable assembly.

5. A control circuit as set forth in claim 4 wherein said means for establishing includes means for varying at least one of the first and second electrical levels as an inverse function of speed of the rotatable assembly.

6. A control circuit as set forth in claim 5 wherein said means for varying includes means for generating the first electrical level to represent a varying value beginning with an initial value and for resetting the first electrical level to the initial value in response to the second control signal whereupon said means for generating resumes generating the varying first electrical level.

7. A control circuit as set forth in claim 5 wherein said means for varying includes a capacitor and means for repeatedly charging and discharging said capacitor, to vary the first electrical level.

8. A control circuit as set forth in claim 1 wherein said means for selecting includes controlling means responsive to an input signal for generating a sequence of control signals representing a sequence of winding stages to be energized by advancing in the sequence upon each occurrence of the input signal, comparing means for supplying the input signal by comparing with an electrical level the electrical output of said means for producing, and electronically controlled switch means responsive to said controlling means to connect a pair of unpowered winding stages in sequence to said means for producing.

9. A control circuit as set forth in claim 1 wherein said means for producing has two inputs for the winding stages selected by said means for selecting, and said means for selecting includes electronically controlled switch means for selectively connecting to a given winding stage either of said two inputs of said means for producing to maintain the same polarity of the back emf across said two inputs for position sensing purposes.

10. A control circuit as set forth in claim 1 further comprising shift register means having a serial input, a set of parallel inputs, a control input to select the serial input or the parallel inputs for entry, and a set of outputs for supplying a parallel digital signal representing a commutation in the sequence, said shift register to be protected from electrical interference which could cause the outputs to supply a parallel digital signal unrepresentative of any commutation in the sequence, further means for supplying a parallel digital signal representing a particular commutation in the sequence to the set of parallel inputs of said shift register means, and means for clocking said shift register means in response to said means for producing, said control input of said shift register means connected to respond to at least one of the outputs and said serial input connected to respond to at least one of the outputs so that if any unrepresentative parallel digital signal appears which does not represent any commutation in the sequence at the outputs of said shift register, the unrepresentative parallel digital signal is replaced by another parallel digital signal representing a commutation in the sequence when said means for clocking next clocks said shift register means.

11. A control circuit as set forth in claim 1 wherein the voltage for the motor comprises a source voltage which should be in a range between a lower voltage limit and a higher voltage limit, the control circuit further comprising first means for deriving a first voltage from the source voltage as a first function of the source voltage, second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit, and means, connected to said first and second means for deriving, for comparing the first and second voltages to produce a disabling signal for the switching means when the source voltage is outside the range.

12. A control circuit as set forth in claim 1 further comprising oscillator means for producing oscillator pulses;

means for frequency dividing the oscillator pulses to supply lower frequency pulses, said means for frequency dividing having a reset input for repeated resetting by said means for producing, so that when the rotatable assembly is turning at least as fast as a predetermined spin rate, the electrical output is generated at a repetition rate for resetting said means for frequency dividing that prevents the lower frequency pulses from being supplied and otherwise allows the lower frequency pulses to be supplied when the electrical output is generated at a lower repetition rate;

means responsive to the lower frequency pulses when they occur for producing an electrical signal generally representing an accumulated number of the lower frequency pulses; and

means for supplying a disabling signal for a predetermined period of time for the switching means when the electrical signal representing the accumulated number of the lower frequency pulses reaches a predetermined value.

13. A control circuit as set forth in claim 1 for use with a voltage source and external control devices for setting speed and further comprising means responsive to said electrical output for operating the switching means, and means for supplying an analog speed control signal to said means for operating the switching means, said means for supplying including a capacitor and active device circuit means having an output resistively connected to said capacitor, and also having an input resistively connected to a terminal for the voltage source, so that said capacitor develops the analog speed control signal when the input of said active device circuit means is connected to any of the following external control devices:

A) pulse generator with variable duty cycle representing desired speed, B) variable voltage source representing desired speed, or C) variable resistance representing desired speed.

14. A control circuit for an electronically commutated motor to be energized from a power source and including a stationary assembly having a plurality of winding stages connected to a neutral adapted to be electronically commutated in a preselected sequence, and a rotatable assembly associated in selective magnetic coupling relation with the winding stages, each winding stage having a terminal and a terminal voltage associated therewith, the control circuit comprising:

commutating means for applying a voltage from the power source to energize the motor so that a winding stage is temporarily powered and another winding stage is temporarily unpowered, terminating the application of voltage to a temporarily powered winding stage in response to a first control signal and advancing in the sequence in response to a second control signal to effect rotation of the rotatable assembly;

means responsive to the terminal voltage of a temporarily unpowered winding stage for producing a sensing output which is a function of angular position of the rotatable assembly;

voltage divider means for the neutral for providing a voltage generally proportional to the voltage on the neutral to said means for producing the sensing output;

means for establishing a first electrical level representative of a first position of the rotatable assembly at which a temporarily powered winding stage is to be deenergized, and a second electrical level representative of a second position of the rotatable assembly at which said commutating means is to advance in the sequence; and

means for comparing the sensing output with the first and second electrical levels to produce the first and second control signals for said commutating means when the first and second positions are respectively reached by the rotatable assembly.

15. A control circuit as set forth in claim 14 wherein said commutating means includes a set of bistable means for the winding stages, each bistable means having a first state for powering a respective winding stage and a second state for terminating the application of voltage to the same winding stage in response to the first control signal, and controlling means for generating a sequence of electrical signals to determine which of said bistable means shall receive the first control signal, said controlling means being responsive to the second control signal to advance in the, sequence upon each occurrence of the second control signal.

16. The control circuit as set forth in claim 15 further comprising electronically controlled switch means, responsive to the electrical signals from said controlling means for selectively connecting at least one unpowered winding stage at any given time to said means for producing the sensing output.

17. A control circuit as set forth in claim 14 further comprising means for supplying an analog speed control signal with respect to a common to said commutating means, said means for supplying including a capacitor and active device circuit means having an output resistively connected to said capacitor, and also having an input resistively connected to a terminal for the power source, so that said capacitor develops the analog speed control signal when the input of said active device circuit means is connected to any of the following external control devices:

A) pulse generator with variable duty cycle representing desired sped, B) variable voltage source representing desired speed, or C) variable resistance representing desired speed.

18. A control circuit as set forth in claim 14 wherein said means for establishing includes means for varying at least one of the first and second electrical levels as an inverse function of speed of the rotatable assembly.

19. A control circuit as set forth in claim 14 wherein said means for establishing includes a capacitor and means for charging said capacitor, to produce the first electrical level.

20. A control circuit as set forth in claim 19 further comprising means for discharging said capacitor in response to the second control signal whereupon said means for charging resumes charging said capacitor to produce the first electrical level.

21. A control circuit as set forth in claim 14 wherein said commutating means includes shift register means having a serial input, a set of parallel inputs, a control input to select the serial input or parallel inputs for entry, and outputs for supplying a parallel digital signal representing a commutation in the sequence, said shift register means to be protected from electrical interference which could cause the outputs to supply a parallel digital signal unrepresentative of any commutation in the sequence, further includes means for supplying a parallel digital signal representing a particular commutation in the sequence to the set of parallel inputs of said shift register means, and means for clocking said shift register means in response to the second control signal, said control input of said shift register means connected to respond to at least one of the outputs and said serial input connected to respond to at least one of the outputs so that if any unrepresentative parallel digital signal appears which does not represent any commutation in the sequence at the outputs of said shift register means, the unrepresentative parallel digital signal is replaced by another parallel digital signal representing a commutation in the sequence when said means for clocking next clocks said shift register means.

22. A control circuit as set forth in claim 14 wherein the power source for the motor should have its source voltage in a range between a lower voltage limit and a higher voltage limit, the control circuit further comprising first means for deriving a first voltage from the source voltage as a first function of the source voltage, second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit, and means, connected to said first and second means for deriving, for comparing the first and second voltages to produce a disabling signal for said commutating means when the source voltage is outside the range.

23. A control circuit as set forth in claim 14 further comprising oscillator means for producing oscillator pulses;

means for frequency dividing the oscillator pulses to supply lower frequency pulses, said means for frequency dividing having a reset input for repeated resetting responsive to the second control signal, so that when the rotatable assembly is turning at least as fast as a predetermined spin rate, the second control signal is generated at a repetition rate for resetting said means for frequency dividing that prevents the lower frequency pulses from being supplied and otherwise allows the lower frequency pulses to be supplied when the second control signal is generated at a lower repetition rate;

means responsive to the lower frequency pulses when they occur for producing an electrical signal generally representing an accumulated number of the lower frequency pulses; and

means for supplying a disabling signal for a predetermined period of time for the commutating means when the electrical signal representing the accumulated number of the lower frequency pulses reaches a predetermined value.

24. A method of operating an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages having terminals and terminal voltages, and solid state switching means for applying a source voltage to one or more of the terminals of the winding stages at a time, the solid state switching means having a saturation voltage depending on current flowing through them when conducting, the method comprising the steps of:

generating commutation pulses in a preselected sequence to make the solid state switching means conduct and commutate the winding stages in the preselected sequence to rotate the rotatable assembly, the repetition rate of the commutation pulses being related to the speed of the rotatable assembly;

supplying a variable electrical level which varies in magnitude as a function of the repetition rate of the commutation pulses, the electrical level representing a current limit for the motor as a function of motor speed; and

suspending the commutating step when the saturation voltage across the switching means exceeds the variable electrical level in magnitude whereby current for the motor is limited as a function of motor speed.

25. A control circuit for an electronically commutated motor to be energized from a power source and including a stationary assembly having at least first, second and third winding stages adapted to be electronically commutated in a preselected sequence, and a rotatable assembly associated in selective magnetic coupling relation with the winding stages, each winding stage having a terminal and a terminal voltage associated therewith, the control circuit comprising:

commutating means for applying a voltage from the power source to temporarily power the first winding stage while the second and third winding stages are temporarily unpowered, initiating the application of voltage to the second winding stage in response to a first control signal and terminating the application of voltage to the first winding stage in response to a second control signal, and advancing in the sequence in response to a third control signal to effect rotation of the rotatable assembly;

means responsive to the terminal voltage of the temporarily unpowered third winding stage for producing a sensing output which is a function of angular position of the rotatable assembly;

means for establishing a first electrical level representative of a first position of the rotatable assembly at which voltage is to be applied to the second winding stage, a second electrical level representative of a second position of the rotatable assembly at which voltage to the first winding stage is to be terminated, and a third electrical level representative of a third position of the rotatable assembly at which said commutating means is to advance in the sequence; and

means for comparing the sensing output with the first, second and third electrical levels to produce the first, second and third control signals for said commutating means when the first, second and third positions are respectively reached by the rotatable assembly.

26. A control circuit as set forth in claim 25 wherein said commutating means includes a set of bistable means for the winding stages, each bistable means having a first state for powering a respective winding stage in response to the first control signal and a second state for terminating the application of voltage to the respective winding stage in response to the second control signal, and controlling means for generating a sequence of electrical signals to determine which of said bistable means shall receive the first control signal and which of said bistable means shall receive the second control signal, said controlling means being responsive to the third control signal to advance in the sequence upon each occurrence of the third control signal.

27. A control circuit as set forth in claim 26 further comprising electronically controlled switch means responsive to the electrical signals from said controlling means for selectively connecting at least one unpowered winding stage at any given time to said means for producing the sensing output.

28. A control circuit as set forth in claim 25 wherein said winding stages are connected at a neutral, the circuit further comprising voltage divider means for the neutral for providing a voltage generally proportional to the voltage on the neutral to said means for producing the sensing output.

29. A control circuit as set forth in claim 25 wherein said means for establishing includes means for varying at least one of the first and second electrical levels as an inverse function of speed of the rotatable assembly.

30. A control circuit as set forth in claim 25 wherein said means for establishing includes a capacitor and means for charging said capacitor, to produce the first electrical level.

31. A control circuit as set forth in claim 30 further comprising means for discharging said capacitor in response to said third control signal whereupon said means for charging resumes charging said capacitor to produce the first electrical level.

32. A control circuit for an electronically commutated motor to be energized from a power source and including a stationary assembly having at least first, second and third winding stages adapted to be electronically commutated in a preselected sequence, and a rotatable assembly associated in selective magnetic coupling relation with the winding stages, each winding stage having a terminal and a terminal voltage associated therewith, the control circuit comprising:

commutating means for applying a voltage from the power source to temporarily power the first winding stage while the second and third winding stages are temporarily unpowered, terminating the application of voltage to the first winding stage in response to a first control signal and initiating the application of voltage to the second winding stage in response to a second control signal, and advancing in the sequence in response to a third control signal to effect rotation of the rotatable assembly;

means responsive to the terminal voltage of the temporarily unpowered third winding stage for producing a sensing output which is a function of angular position of the rotatable assembly;

means for establishing a first electrical level representative of a first position of the rotatable assembly at which voltage to the first winding stage is to be terminated, a second electrical level representative of a second position of the rotatable assembly at which voltage to the second winding stage is to be applied, and a third electrical level representative of a third position of the rotatable assembly at which said commutating means is to advance in the sequence; and

means for comparing the sensing output with the first, second and third electrical levels to produce the first, second and third control signals for said commutating means when the first, second and third positions are respectively reached by the rotatable assembly.

33. A control circuit as set forth in claim 32 wherein said commutating means includes a set of bistable means for the winding stages, each bistable means having a first state for powering a respective winding stage in response to the second control signal and a second state for terminating the application of voltage to the respective winding stage in response to the first control signal, and controlling means for generating a sequence of electrical signals to determine which of said bistable means shall receive the first control signal and which of said bistable means shall receive the second control signal, said controlling means being responsive to the third control signal to advance in the sequence upon each occurrence of the third control signal.

34. A control circuit as set forth in claim 33 further comprising electronically controlled switch means responsive to the electrical signals from said controlling means for selectively connecting at least one unpowered winding stage at any given time to said means for producing the sensing output.

35. A control circuit as set forth in claim 32 wherein said winding stages are connected at a neutral, the circuit further comprising voltage divider means for the neutral for providing a voltage generally proportional to the voltage on the neutral to said means for producing the sensing output.

36. A control circuit as set forth in claim 32 wherein said means for establishing includes means for varying at least one of the first and second electrical levels as an inverse function of speed of the rotatable assembly.

37. A control circuit as set forth in claim 32 wherein said means for establishing includes a capacitor and means for charging said capacitor, to produce the first electrical level.

38. A control circuit as set forth in claim 37 further comprising means for discharging said capacitor in response to said third control signal whereupon said means for charging resumes charging said capacitor to produce the first electrical level.

39. A control circuit for an electronically commutated motor to be energized from a power source and including a stationary assembly having at least three winding stages adapted to be electronically commutated in a preselected sequence, and a rotatable assembly associated in selective magnetic coupling relation with the winding stages, each winding stage having a terminal and a terminal voltage associated therewith, the control circuit comprising:

a set of bistable means for the winding stages, each bistable means having a first state for powering a respective winding stage in response to a first control signal and a second state for terminating the application of voltage to the same winding stage in response to a second control signal;

electrical signals to determine which of said bistable means shall receive the first control signal and which of said bistable means shall receive the second control signal, wherein at least one winding stage is temporarily unpowered, said controlling means being responsive to a third control signal to advance in the sequence;

means responsive to the terminal voltage of at least one temporarily unpowered winding stage to produce a sensing output which is a function of angular position of the rotatable assembly; and

means for comparing the sensing output with first, second and third electrical levels to respectively produce the first and second control signals for said bistable means and the third control signal for said controlling means.

40. A control circuit as set forth in claim 39 further comprising means for varying at least one of the first and second electrical levels relative to the other so that at least two of the winding stages variably overlap in a time period of energization or variably in time to terminate the voltage applied to one of the winding stages before a time when the second of the two winding stages has voltage applied to it.

41. A control circuit as set forth in claim 39 further comprising means for varying at least one of the first and second electrical levels as a function of speed of the rotatable assembly.

42. A control circuit as set forth in claim 39 further comprising means for varying at least one of the first and second electrical levels as an inverse function of speed of the rotatable assembly.

43. A control circuit as set forth in claim 39 further comprising a capacitor and means for charging said capacitor, to produce the first electrical level.

44. A control circuit as set forth in claim 43 further comprising means for discharging said capacitor in response to the third control signal whereupon said means for charging resumes charging said capacitor to produce the first electrical level.

45. A control circuit for an electronically commutated motor to be energized from a power source and including a stationary assembly having a plurality of winding stages, a rotatable assembly associated in selective magnetic coupling relation with the winding stages, and commutating means for electronically commutating the winding stages in a preselected sequence in response to at least one control signal, each winding stage having a terminal and a terminal voltage associated therewith, the control circuit comprising:

means responsive to the terminal voltage of at least one winding stage for producing a sensing output which is a function of angular position of the rotatable assembly, the sensing output having a variable frequency which depends on the speed of the rotatable assembly;

means for comparing the sensing output with a first electrical level to produce a first control signal for the commutating means; and

means for generating a varying second electrical level representing a varying value beginning with an initial value, for resetting the second electrical level to the initial value in response to the first control signal and for resuming the generation of the varying second electrical level which thereby depends on the frequency of the sensing output that results from the speed of the rotatable assembly, said comparing means including means for also comparing the sensing output with the second electrical level to produce a second control signal for the commutating means.

46. A control circuit as set forth in claim 45 wherein said means for generating the varying second electrical level includes means for restraining the second electrical level from varying beyond a predetermined value provided it reaches the predetermined value before the first control signal next occurs, whereby the second electrical level reaches and is limited to the predetermined value at speeds of the rotatable assembly less than a predetermined speed.

47. A control circuit as set forth in claim 45 wherein said means for generating the varying second electrical level includes a capacitor, means for charging said capacitor to produce the second electrical level, and means for discharging said capacitor in response to the first control signal whereupon said means for charging resumes charging said capacitor to produce the second electrical level.

48. A control circuit as set forth in claim 47 wherein said means for generating the varying second electrical level further includes a high impedance buffer circuit means connected across said capacitor for producing a buffer output to provide the second electrical level, and zener diode means for limiting the buffer output provided it reaches a predetermined level.

49. A control circuit as set forth in claim 47 wherein said means for generating the varying second electrical level further includes voltage division means connected between the power source and said capacitor, said means for comparing having an input connected to said voltage division means.

50. A control circuit as set forth in claim 49 wherein said voltage division means includes two independently adjustable potentiometers, and said means for comparing includes means connected to adjustable points on both potentiometers for comparing the voltages thereat to the sensing output for turn-on and turn-off purposes of the commutating means in commutating the winding stages of the electronically commutated motor.

51. A control circuit as set forth in claim 49 wherein said voltage division means includes an adjustable potentiometer for setting a firing angle for the motor at slower speeds, and said means for charging said capacitor includes variable resistor means for controlling angle advance of the firing angle at speeds beyond the slower speeds.

52. A control circuit as set forth in claim 45 wherein said means for producing the sensing output includes means for integrating, the control circuit further comprising electronic switch means for selectively connecting the winding stage terminals to said means for integrating.

53. Control circuit for an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages, and switching means for commutating the winding stages in a preselected sequence to rotate the rotatable assembly, the control circuit comprising:

shift register means having a serial input, a set of parallel inputs, a control input to select the serial input or parallel inputs for entry, and outputs for supplying a parallel digital signal representing a commutation in the sequence, said shift register means to be protected from electrical interference which could cause the outputs to supply a parallel digital signal unrepresentative of any commutation in the sequence;

means for supplying a parallel digital signal representing a particular commutation in the sequence to the set of parallel inputs of said shift register means; and

means for clocking said shift register means, said control input of said shift register means connected to respond to at least one of the outputs and said serial input connected to respond to at least one of the outputs so that if any unrepresentative parallel digital signal appears which does not represent any commutation in the sequence at the outputs of said shift register means, the unrepresentative parallel digital signal is replaced by another parallel digital signal representing a commutation in the sequence when said means for clocking next clocks said shift register means.

54. A control circuit as set forth in claim 53 wherein said shift register means has at least first, second, and third outputs, said second output connected to said control input.

55. A control circuit as set forth in claim 53 wherein said shift register means has at least first, second and third outputs, the control circuit further comprising inverting means for supplying the logical complement of the first output of said shift register means to said serial input of said shift register means.

56. A control circuit as set forth in claim 53 wherein said shift register means has at least first, second, and third outputs, said second output connected to said control input, further comprising inverting means for supplying the logical complement of the first output of said shift register means to said serial input of said shift register means.

57. A control circuit as set forth in claim 53 wherein said means for supplying a parallel digital signal representing a particular commutation in the sequence to the set of parallel inputs of said shift register means includes means for supplying the parallel digital signal to have one bit with a first logic state and two further bits with the complementary logic state.

58. A control circuit as set forth in claim 53 wherein said means for supplying a parallel digital signal representing a particular commutation in the sequence to the set of parallel inputs of said shift register means includes means for supplying the parallel digital signal in a fixed form with one bit high and two further bits low.

59. A control circuit as set forth in claim 53 for use with a power source and further comprising means for resetting the outputs of said shift register means when power from the power source is interrupted and resumes.

60. A control circuit as set forth in claim 53 wherein said means for clocking includes means for comparing an externally derived signal generally representative of angular position of the rotatable assembly with an electrical level, and means for supplying a clock pulse to said shift register means when said externally derived signal reaches the electrical level.

61. A control circuit as set forth in claim 60 wherein said means for clocking further includes means for generating a series of pulses for starting the motor, and said means for supplying a clock pulse to said shift register means when said externally derived signal reaches the electrical level includes a one-shot circuit means having an input connected to said means for comparing and having an output for supplying a clock pulse, OR-gate means having a first input connected to said output of said one-shot circuit means and a second input connected to said means for generating a series of pulses for starting the motor, the OR-gate means having an output connected to clock said shift register means.

62. A control circuit as set forth in claim 53 further comprising a set of logic gate means respectively connected to the outputs of said shift register means, and means for supplying pulse width modulated pulses to said logic gate means, said logic gate means producing respective outputs for the switching means to commutate the motor.

63. A control circuit as set forth in claim 62 for use with a power source for the motor having a source voltage which is supposed to be in a range between a lower voltage limit and a higher voltage limit, the control circuit further comprising first means for deriving a first voltage from the source voltage as a first function of the source voltage, second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit, and means, connected to said first and second means for deriving, for comparing the first and second voltages to prevent the pulse width modulated pulses from activating the switching means when the source voltage is outside the range.

64. A control circuit as set forth in claim 62 for use with a voltage source and further comprising means for supplying an analog speed control signal to said means for supplying the pulse width modulated pulses, including a capacitor and active device circuit means having an output resistively connected to said capacitor, and an input resistively connected to a terminal for the voltage source, so that said capacitor develops the analog speed control signal when the input of said active device circuit means is connected to any of the following external control devices:

A) pulse generator with variable duty cycle representative of desired speed, B) variable voltage source representative of desired speed, or C) variable resistance representative of desired speed.

65. A control circuit as set forth in claim 53 further for use with position sensing means for repeatedly generating a sensing signal generally representative of rotation of the rotatable assembly, the control circuit further comprising oscillator means for producing oscillator pulses;

means for frequency dividing the oscillator pulses to supply lower frequency pulses, said means for frequency dividing having a reset input for repeated resetting by the sensing signal, so that when the rotatable assembly is turning at least as fast as a predetermined spin rate the sensing signal is generated at a repetition rate for resetting that prevents the lower frequency pulses from being supplied and otherwise allows the lower frequency pulses to be supplied when the sensing signal is generated at a lower repetition rate;

means responsive to the lower frequency pulses when they occur for producing an electrical signal generally representing an accumulated number of the lower frequency pulses; and

means for supplying a disabling signal for a predetermined period of time to prevent the pulse width modulated pulses from activating the switching means when a predetermined value is reached by the electrical signal representing the accumulated number of lower frequency pulses.

66. A control circuit as set forth in claim 53 wherein said shift register means has at least first, second and third outputs, said second output connected to said control input, and the control circuit further comprises inverter means for supplying the logical complement of the first output of said shift register means to said serial input of said shift register means, said means for supplying a parallel digital signal to the set of parallel inputs including means for supplying the parallel digital signal to have one bit with a first logic state and two further bits with the complementary logic state, said means for clocking including means for comparing an externally derived signal generally representative of angular position of the rotatable assembly with an electrical level, and means for supplying a clock pulse to said shift register means when said externally derived signal reaches the electrical level.

67. A control circuit as set forth in claim 66 further comprising a set of logic gate means respectively connected to the outputs of said shift register means, and means for supplying pulse width modulated pulses to said logic gate means, said logic gate means producing respective outputs for the switching means to commutate the motor.

68. Control circuit for an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages, position sensing means for repeatedly generating a sensing signal generally representative of rotation of the rotatable assembly, and commutating means responsive to the sensing signal for commutating the winding stages in a preselected sequence to energize the winding stages and thereby rotate the rotatable assembly, the control circuit comprising:

oscillator means for producing oscillator pulses;

means for frequency dividing the oscillator pulses to supply lower frequency pulses, said means for frequency dividing having a reset input for repeated resetting by said sensing signal, so that when the rotatable assembly is turning at least as fast as a predetermined spin rate the sensing signal is generated at a repetition rate for resetting that prevents the lower frequency pulses from being supplied and otherwise allows the lower frequency pulses to be supplied when the sensing signal is generated at a lower repetition rate;

means responsive to the lower frequency pulses when they occur for producing an electrical signal generally representing an accumulated number of the lower frequency pulses; and

means for comparing with a predetermined value the electrical signal representing the accumulated number of the lower frequency pulses, and for supplying a disabling signal for a predetermined period of time for the commutating means after the predetermined value is reached by the electrical signal, to prevent energization of the motor during that predetermined period of time.

69. A control circuit as set forth in claim 68 wherein said means for frequency dividing includes a binary counter having an output for supplying the lower frequency pulses.

70. A control circuit as set forth in claim 68 wherein said means for frequency dividing includes a binary counter having a first output for supplying the lower frequency pulses and the counter additionally including means for frequency dividing the lower frequency pulses to produce a series of start pulses at a second output for the commutating means.

71. A control circuit as set forth in claim 68 wherein said means for frequency dividing includes a binary counter having a first output for frequency division of the oscillator pulses by a factor at least equal to the ratio of the repetition rate of the oscillator pulses to the repetition rate of the sensing signal at the predetermined spin rate of the motor above which the lower frequency pulses are prevented.

72. A control circuit as set forth in claim 68 wherein said motor has a first number of pairs of magnetic poles and a second number of winding stages, wherein said means for frequency dividing includes a binary counter having a first output for frequency division of the oscillator pulses by a factor of two-to-a-power-Q (2^Q) where the power Q at least equals the logarithm-to-the-base-2 of the ratio of the repetition rate of the oscillator pulses to the product of the predetermined spin rate with the first and second numbers.

73. A control circuit as set forth in claim 68 wherein said means for comparing includes means for temporarily isolating said means for producing the electrical signal representing the accumulated number of the lower frequency pulses from said means for frequency dividing, when the electrical signal reaches the predetermined value.

74. A control circuit as set forth in claim 73 wherein said means for temporarily isolating includes a diode network interconnecting said means for frequency dividing, said means for producing the electrical signal representing the accumulated number, and said means for comparing.

75. A control circuit as set forth in claim 68 wherein said means for producing the electrical signal generally representing an accumulated number of the lower frequency pulses includes a resistance-capacitance (RC) charging network connected between said means for frequency dividing and said means for comparing, so that the lower frequency pulses charge the capacitance in the RC charging network to a voltage representing an accumulated number of the lower frequency pulses when they occur.

76. A control circuit as set forth in claim 75 wherein said means for comparing includes a comparator with hysteresis having an input connected to said RC network.

77. A control circuit as set forth in claim 75 wherein said means for comparing includes a diode network, a voltage divider for establishing a reference voltage representing the predetermined value, a comparator having a first input connected to said RC network for sensing the voltage to which said capacitance is charged, a second input connected to said voltage divider, and a comparator output for providing the disabling signal, said diode network connecting said comparator output to said voltage divider to reduce the reference voltage when the disabling signal occurs, said diode network further interconnecting said means for frequency dividing to said RC network and to said comparator output so that said RC network is isolated from said means for frequency dividing when said disabling signal is produced, said RC network including resistive discharging means for discharging the capacitance over the predetermined period of time to the reference voltage so reduced whereupon the comparator output ceases to produce the disabling signal and said RC network is again chargeable by said means for frequency dividing.

78. A control circuit as set forth in claim 68 for use with a power source for the motor having a source voltage which is supposed to be in a range between a lower voltage limit and a higher voltage limit, the control circuit further comprising first means for deriving a first voltage from the source voltage as a first function of the source voltage, second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit, and second comparing means, connected to said first and second means for deriving, for comparing the first and second voltages to produce a second disabling signal, on a line shared with the disabling signal for said first-named means for comparing, for the commutating means to also prevent energization of the motor when the source voltage is outside the range.

79. Control circuit for an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages, and switching means for commutating the winding stages in a preselected sequence to rotate the rotatable assembly, the control circuit comprising:

first means for comparing an externally derived signal generally representative of angular position of the rotatable assembly with an electrical level and for supplying a sensing signal when said externally derived signal reaches the electrical level;

means for generating clock pulses;

means for generating pulse width modulated pulses for causing the switching means to energize the motor;

means for frequency dividing the clock pulses to produce lower frequency pulses, said means for frequency dividing being reset by the sensing signal from said first means, so that unless the rotatable assembly is turning at least as fast as a predetermined spin rate, the sensing signal is produced at a sufficiently low repetition rate for resetting said means for frequency dividing to permit the lower frequency pulses to be produced;

means for producing an electrical signal generally representing an accumulated number of the lower frequency pulses when they occur; and

means for comparing with a predetermined value the electrical signal representing the accumulated number of the lower frequency pulses, said means for comparing connected to said means for generating pulse width modulated pulses to prevent the generation of the pulse width modulated pulses for a predetermined period of time after the predetermined value is reached by the electrical signal.

80. A control circuit as set forth in claim 79 wherein said means for frequency dividing includes a binary counter having a first output for supplying the lower frequency pulses and the counter additionally including means for frequency dividing the lower frequency pulses to produce a series of start pulses at a second output.

81. A control circuit as set forth in claim 79 wherein the predetermined period of time exceeds a period of the lower frequency pulses and the control circuit further comprising means operative during the predetermined period of time for resetting the electrical signal representing the accumulated number to represent a lower number instead.

82. A control circuit as set forth in claim 79 wherein said motor has a first number of pairs of magnetic poles and a second number of winding stages, wherein said means for frequency dividing includes a binary counter having a first output representing frequency division of the clock pulses by a factor of two-to-a-power-Q (2^Q) where the power Q at least equals the logarithm-to-the-base-2 of the ratio of the repetition rate of the clock pulses to the product of the predetermined spin rate with the first and second numbers.

83. A control circuit as set forth in claim 79 wherein said means for comparing includes means for temporarily isolating said means for producing the electrical signal representing the accumulated number of the lower frequency pulses from said means for frequency dividing, when the electrical signal reaches the predetermined value.

84. A control circuit as set forth in claim 83 wherein said means for temporarily isolating includes a diode network interconnecting said means for frequency dividing, said means for producing the electrical signal representing the accumulated number, and said means for comparing.

85. A control circuit as set forth in claim 79 for use with a power source for the motor having a source voltage which is supposed to be in a range between a lower voltage limit and a higher voltage limit, the control circuit further comprising first means for deriving a first voltage from the source voltage as a first function of the source voltage, second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit, and second comparing means, connected to said first and second means for deriving, for comparing the first and second voltages to produce a disabling signal for said means for generating the pulse width modulated pulses when the source voltage is outside the range.

86. A control circuit for use with an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages to be powered by a power source having a source voltage which is supposed to be in a range between a lower voltage limit and a higher voltage limit, the control circuit comprising:

first means for deriving a first voltage from the source voltage as a first function of the source voltage,

said first means for deriving including means for providing the first voltage so that it varies with a first slope substantially linearly with the voltage of the power source to a value whereupon the first voltage varies with a second slope greater than the first slope;

second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit;

means, connected to said first and second means for deriving, for comparing the first and second voltages to produce a control signal for the winding stages to be powered, the control signal indicating whether the source voltage is within or outside the range;

means, connected to said means for comparing, for generating pulse width modulated pulses when the control signal indicates that the source voltage is within the range; and

switching means responsive to the pulse width modulated pulses for commutating the winding stages in a preselected sequence to energize the winding stages and thereby rotate the rotatable assembly.

87. A control circuit as set forth in claim 86 wherein said first means for deriving includes a voltage divider connected across the lower source.

88. A control circuit as set forth in claim 86 wherein said first means deriving includes a voltage divider having a first resistor and a second resistor connected across the power source, the second resistor connected at one end to said second means for deriving and connected at another end to said means for comparing, and a zener diode connected across the first resistor.

89. A control circuit as set forth in claim 86 wherein said second means for deriving includes means for providing the second voltage to be relatively low for source voltage up to a first value and to increase with the source voltage to a second value and then to be substantially constant for source voltage above the second value.

90. A control circuit as set forth in claim 86 wherein said second means for deriving includes means for providing the second voltage to be relatively low for source voltage up to a first value and to vary with a first slope substantially linearly with the source voltage to a second value and then to vary as a function of source voltage with a second slope less than the first slope.

91. A control circuit as set forth in claim 86 wherein said second means for deriving includes means for providing the second voltage to be substantially constant for source voltage up to a first value and to increase with the source voltage to a second value and then to be substantially constant for voltages of the power source above the second value.

92. A control circuit as set forth in claim 86 wherein said first means for deriving includes means for providing the first voltage to exceed the second voltage when the source voltage is outside the range between the lower and higher voltage limits and said second means for deriving includes means for providing the second voltage to exceed the first voltage when the source voltage is within the range between the lower and higher voltage limits.

93. A control circuit as set forth in claim 86 wherein said means for comparing includes means for producing the control signal as a first, output level when the first voltage exceeds the second voltage and a second output level when the second voltage exceeds the first voltage.

94. A control circuit as set forth in claim 93 wherein said first means for deriving includes means for providing the first voltage so that it varies with a first slope substantially linearly with the source voltage to a value whereupon the first voltage varies with a second slope greater than the first slope.

95. A control circuit as set forth in claim 94 wherein said second means for deriving includes means for providing the second voltage to be relatively low for source voltages up to a first value and to increase with the source voltage to a second value and then to be substantially constant for source voltages above the second value.

96. A method of operating a control circuit for an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages for energization, and switching means for applying a voltage from a voltage source to one or more of the winding stages at a time and commutating the winding stages in a preselected sequence to rotate the rotatable assembly at a speed dependent on the energization applied to the winding stages, the method to be compatible with utilization of alternative external control devices for desired speed and comprising the steps of:

resistively supplying an input of an active device circuit means from a terminal for the voltage source, the input also for connection to any of the external control devices;

averaging an output of the active device circuit means to produce an analog speed control signal when the input of the active device circuit means is connected to any of the following external control devices;

A) pulse generator with variable duty cycle representing desired speed, B) variable voltage source representing desired speed, or C) variable resistance representing desired speed; and

generating pulse width modulated pulses to control the switching means for the motor, the pulses modulated in width as a function of the analog speed control signal.

97. A method of protecting an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages, position sensing means for repeatedly generating a sensing signal generally representative of rotation of the rotatable assembly, and commutating means responsive to the sensing signal for commutating the winding stages in a preselected sequence to energize the winding stages and thereby rotate the rotatable assembly, the method comprising the steps of:

producing oscillator pulses;

frequency dividing the oscillator pulses by a frequency dividing means to supply lower frequency pulses, said frequency dividing means having a reset input for repeated resetting in response to the sensing signal, so that when the rotatable assembly is turning at least as fast as a predetermined spin rate, the sensing signal is generated at a repetition rate for resetting that prevents the lower frequency pulses from being supplied and otherwise allows the lower frequency pulses to be supplied when the output signal is generated at a lower repetition rate;

responding to the lower frequency pulses when they occur to produce an electrical signal generally representing an accumulated number of the lower frequency pulses; and

supplying a disabling signal for a predetermined period of time for the commutating means when a predetermined value is reached by the electrical signal representing the accumulated number, to prevent energization of the motor during that predetermined period of time.

98. A control circuit for an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages for energization, and switching means for applying a voltage from a voltage source to one or more of the winding stages at a time and commutating the winding stages in a preselected sequence to rotate the rotatable assembly at a speed dependent on the energization applied to the winding stages, the control circuit to be compatible with alternative external control devices indicating desired speed, and the control circuit comprising:

means for generating pulse width modulated pulses to control the switching means, the pulses modulated in width as a function of an analog speed control signal; and

means for supplying the analog speed control signal with respect to a common to said means for generating the pulse width modulated pulses, said means for supplying including a capacitor and active device circuit means having an input resistively connected to a terminal for the voltage source, said input also for connection to any of the external control devices, and an output resistively connected to said capacitor so that said capacitor develops the analog speed control signal when the input of said active device circuit means is connected to any of the following external control devices;

A) pulse generator with a duty cycle representative of desired speed, B) variable voltage source representative of desired speed, or C) variable resistance representative of desired speed.

99. A control circuit as set forth in claim 98 further comprising inverting circuit means and means for selectively connecting said inverting circuit means in the control circuit so that said capacitor further develops the analog speed control signal when the input of said active device circuit means is connected to D) a pulse generator as external control device with a variable duty cycle inversely related to the desired speed.

100. A control circuit as set forth in claim 98 wherein the voltage source has a source voltage which should be in a range between a lower voltage limit and a higher voltage limit, the control circuit further comprising first means for deriving a first voltage from the source voltage as a first function of the source voltage, second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit, and means, connected to said first and second means for deriving, for comparing the first and second voltages to produce a signal for said means for generating pulse width modulated pulses to prevent the pulse width modulated pulses from controlling the switching means when the source voltage is outside the range and otherwise to permit the pulse width modulated pulses to control the switching means.

101. A control circuit as set forth in claim 98 further for use with position sensing means for repeatedly generating a sensing signal generally representative of rotation of the rotatable assembly, the control circuit further comprising oscillator means for producing oscillator pulses;

means for frequency dividing the oscillator pulses to supply lower frequency pulses, said means for frequency dividing having a reset input for repeated resetting by the sensing signal, so that when the rotatable assembly is turning at least as fast as a predetermined spin rate the sensing signal is generated at a repetition rate for resetting that prevents the lower frequency pulses from being supplied and otherwise allows the lower frequency pulses to be supplied when the sensing signal occurs at a lower repetition rate;

means responsive to the lower frequency pulses when they occur for producing an electrical signal generally representing an accumulated number of the lower frequency pulses; and

means for supplying a disabling signal for a predetermined period of time for the means for generating pulse width modulated pulses when a predetermined value is reached by the electrical signal representing the accumulated number of the lower frequency pulses.

102. A control circuit for an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages for energization, and switching means for applying a voltage from a voltage source to one or more of the winding stages at a time and commutating the winding stages in a preselected sequence to rotate the rotatable assembly at a speed dependent on the energization applied to the winding stages, the control circuit to be compatible with alternative external control devices indicating desired speed, and the control circuit comprising:

means for generating pulse width modulated pulses to control the switching means, the pulses modulated in width as a function of an analog speed control signal; and

means for supplying the analog speed control signal with respect to a common to said means for generating the pulse width modulated pulses, said means for supplying including a transistor having a collector, an emitter and a base, the collector connected to the common, a capacitor connected to the common and resistively connected to the emitter of said transistor, and the emitter and the base both resistively connected to a terminal for the voltage source, so that said capacitor develops the analog speed control signal when the base of the transistor is connected to any of the following external control devices;

A) pulse generator with variable duty cycle to indicate desired speed, B) variable voltage source to indicate desired speed, or C) variable resistance to indicate desired speed.

103. A control circuit as set forth in claim 102 further comprising inverting circuit means having an output connected to said capacitor and an input connected to the base of said transistor and means for selectively connecting the capacitor resistively either to the emitter of said transistor or to the output of said inverting circuit means, whereby said capacitor further develops the analog speed control signal when the base of the transistor is connected to an external control device comprising a pulse generator with variable duty cycle inversely related to the desired speed.

104. A control circuit for use with an electrical load and a power source with switching means therebetween, the power source having a source voltage which is subject to a transient substantially in excess of a normal value of the source voltage, the control circuit comprising:

first control means, including means for producing control pulses and logic gate means responsive to the control pulses, for producing a varying first electrical signal for the switching means to make the switching means repeatedly connect and disconnect the electrical load to and from the power source in normal operation; and

second control means responsive to the transient in the source voltage when the transient occurs and connected to said first control means for overriding said first control means so that the first electrical signal is forced to a level to make the switching means connect the electrical load to the power source for the duration of the transient, said logic gate means responsive to said second control means;

said second control means including means for sensing the source voltage and comparator means, responsive to said means for sensing, for producing an override signal for said first control means.

105. A control circuit as set forth in claim 104 wherein said second control means includes a zener diode connected to sense said source voltage, said second control means producing an override signal when the transient substantially exceeds a predetermined voltage for said zener diode.

106. A control circuit as set forth in claim 104 wherein said means for sensing includes a zener diode connected to sense the source voltage, and wherein said comparator means is connected oppositely to said zener diode for producing an override signal for said first control means.

107. A control circuit as set forth in claim 104 for use with an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of electrical loads comprising winding stages having terminals for energization, said first control means including means for generating commutation pulses in a preselected sequence as the first electrical signal.

108. A control circuit as set forth in claim 107 wherein electrical signals from each energized winding stage can be coupled to and interfere with a back emf of each unpowered winding stage of the electronically commutated motor and said first control means further includes means for selecting at least two unpowered winding stages at a time which have electrical signals coupled to them that have a predetermined relationship in polarity and magnitude, and means for producing an electrical output from the voltages on the winding stage terminals of the winding stages selected, so that the electrical signals coupled from each energized winding stage are substantially canceled when they have the predetermined relationship while the back emf is preserved, said means for generating commutation pulses being responsive to the electrical output so produced for advancing in the preselected sequence.

109. A control circuit as set forth in claim 107 for use with an electronically commutated motor wherein each winding stage has a terminal voltage associated therewith, and said means for generating commutation pulses in the preselected sequence includes commutating means for supplying commutation pulses so that a winding stage is temporarily powered and another winding stage is temporarily unpowered, terminating a commutation pulse in response to a first control signal and advancing in the sequence in response to a second control signal;

and wherein said first control means further includes means responsive to the terminal voltage of a temporarily unpowered winding stage for producing a sensing output which is a function of angular position of the rotatable assembly, means for establishing a first electrical level representative of a first position of the rotatable assembly at which a temporarily powered winding stage is to be deenergized and a second electrical level representative of a second position of the rotatable assembly at which said commutating means is to advance in the sequence, and means for comparing the sensing output with the first and second electrical levels to produce the first and second control signals for said commutating means when the first and second positions are respectively reached by the rotatable assembly.

110. A control circuit as set forth in claim 107 wherein each winding stage has a terminal voltage associated therewith and said means for generating commutation pulses in the preselected sequence includes means for initiating each commutation pulse in response to a turn-on signal, the control circuit further including means responsive to the terminal voltage of at least one winding stage for producing a sensing output which is a function of angular position of the rotatable assembly, the sensing output having a variable frequency which depends on the speed of the rotatable assembly, means for comparing the sensing output with a first electrical level to produce a first control signal to make the commutating means advance in the sequence, further means for generating a varying second electrical level representing a varying value beginning with an initial value, and means responsive to the first control signal for resetting said further means for generating so that the second electrical level is returned to the initial value whereupon said further means for generating resumes generating the varying second electrical level which thereby depends on the frequency of the sensing output that results from the speed of the rotatable assembly, said comparing means including means for also comparing the sensing output with the second electrical level to produce the turn-on signal for initiation of each commutation pulse by said means for generating the commutation pulses.

111. A control circuit as set forth in claim 107 wherein said means for generating commutation pulses in the preselected sequence includes shift register means having a serial input, a set of parallel inputs, a control input to select the serial input or parallel inputs for entry, and outputs for supplying a parallel digital signal representing a commutation in the sequence, said shift register means to be protected from electrical interference which could cause the outputs to supply a parallel digital signal unrepresentative of any commutation in the sequence, means for supplying a parallel digital signal representing a particular commutation in the sequence to the set of parallel inputs of said shift register means, and means for clocking said shift register means, said control input of said shift register means connected to respond to at least one of the outputs and said serial input connected to respond to at least one of the outputs so that if any unrepresentative parallel digital signal appears which does not represent any commutation in the sequence at the outputs of said shift register means, the unrepresentative parallel digital signal is replaced by another parallel digital signal representing a commutation in the sequence when said means for clocking next clocks said shift register means.

112. A control circuit as set forth in claim 107 further comprising position sensing means for repeatedly generating a sensing signal generally representative of rotation of the rotatable assembly, oscillator means for producing oscillator pulses, means for frequency dividing the oscillator pulses to supply lower frequency pulses, said means for frequency dividing having a reset input for repeated resetting by said sensing signal, so that when the rotatable assembly is turning at least as fast as a predetermined rate the sensing signal is generated at a repetition rate for resetting that prevents the lower frequency pulses from being supplied and otherwise allows the lower frequency pulses to be supplied when the sensing signal is generated at a lower repetition rate, means responsive to the lower frequency pulses when they occur for producing an additional electrical signal generally representing an accumulated number of the lower frequency pulses, and means for comparing the additional electrical signal with a predetermined value to prevent said means for generating the commutation pulses from doing so for a predetermined period of time after the predetermined value is reached by the additional electrical signal.

113. A control circuit as set forth in claim 107 the control circuit to be compatible with alternative external control devices indicating desired speed of the rotatable assembly, further comprising means for modulating the commutation pulses in width as a function of an analog speed control signal, and means for supplying the analog speed control signal to said means for modulating, said means for supplying including a capacitor and active device circuit means having an input resistively connected to a terminal for the power source, said input also for connection to any of the external control devices, and an output resistively connected to said capacitor so that said capacitor develops the analog speed control signal when the input of said active device circuit means is connected to any of the following external control devices:

A) pulse generator with a duty cycle representative of desired speed, B) variable voltage source representative of desired speed, or C) variable resistance representative of desired speed.

114. A control circuit as set forth in claim 104 wherein the normal value of the source voltage is supposed to be in a range between a lower voltage limit and a higher voltage limit, the control circuit further comprising first means for deriving a first voltage from the source voltage as a first function of the source voltage, second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit, and means, connected to said first and second means for deriving, for comparing the first and second voltages to produce a disabling signal for said first control means to make the switching means disconnect the electrical load from the power source when the source voltage is outside the range, subject to overriding by said second control means.

115. A method of operating a control circuit for an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages, and switching means for commutating the winding stages in a preselected sequence to rotate the rotatable assembly, the method comprising the steps of:

providing shift register means having a serial input, a set of parallel inputs, a control input to select the serial input or parallel inputs for entry, and outputs for supplying a parallel digital signal representing a commutation in the sequence, said shift register means to be protected form electrical interference which could cause the outputs to supply a parallel digital signal unrepresentative of any commutation in the sequence;

supplying a parallel digital signal representing a particular commutation in the sequence to the set of parallel inputs of the shift register means;

supplying the control input of the shift register means with at least one of the output sand supplying the serial input with a signal depending on at least one of the outputs; and

clocking and shift register means so that if any unrepresentative parallel digital signal appears at the outputs of the shift register means which does not represent any commutation in the sequence, the unrepresentative parallel digital signal is replaced by another parallel digital signal representing a commutation in the sequence when the shift register means is clocked.

116. A method of operating a control circuit for an electronically commutated motor to be energized from a power source and including a stationary assembly having a plurality of winding stages, a rotatable assembly associated in selective magnetic coupling relation with the winding stages, and commutating means for electronically commutating the winding stages in a preselected sequence in response to at least one control signal, each winding stage having a terminal and a terminal voltage associated therewith, the method comprising the steps of:

producing a sensing output which is a function of angular position of the rotatable assembly, the sensing output having a variable frequency which depends on the speed of the rotatable assembly;

comparing the sensing output with a first electrical level to produce a first control signal;

generating a varying second electrical level representing a varying value beginning with an initial value;

resetting the second electrical level to the initial value in response to the first control signal and resuming the generating step, the varying second electrical level thereby depending on the frequency of the sensing output that results from the speed of the rotatable assembly; and

comparing the sensing output with the second electrical level to produce a second control signal for the commutating means.

117. A method of operating an electronically cummutated motor to be energized from a power source and including a stationary assembly having at least three winding stages adapted to be electronically commutated in a preselected sequence, and a rotatable assembly associated in selective magnetic coupling relation with the winding stages, each winding stage having a terminal and a terminal voltage associated therewith, the method comprising the steps of:

commutating the motor under control of a set of bistable means for the winding stages, each bistable means having a first stage for powering a respective winding stage in response to a first control signal and a second stage for terminating the application of voltage to the same winding stage in response to a second control signal;

generating a sequence of electrical signals to determine which of the bistable means shall receive the first control signal and which of the bistable means shall receive the second control signal, advancing in the sequence in response to a third control signal;

producing a sensing output which is a function of angular position of the rotatable assembly; and

comparing the sensing output with first, second and third electrical levels to respectively produce the first, second and third control signals.

118. A control circuit for use with an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages having terminals and terminal voltages, and solid state switching means for applying a source voltage to one or more of the terminals of the winding stages at a time, the solid state switching means having a saturation voltage depending on current flowing through them when conducting, the control circuit comprising:

commutating means for generating commutation pulses in a preselected sequence to make the solid state switching means conduct and commutate the winding stages in the preselected sequence to rotate the rotatable assembly, the repetition rate of the commutation pulses being related to the speed of the rotatable assembly;

means responsive to said commutation pulses for supplying a variable electrical level which varies in magnitude as a function of the repetition rate of the commutation pulses, the electrical level representing a current limit for the motor as a function of motor speed; and

means for producing a disabling signal for said commutating means when the saturation voltage across said switching means exceeds the variable electrical level in magnitude whereby current for the motor is limited as a function of motor speed.

119. A control circuit as set forth in claim 118 wherein said means for supplying the variable electrical level includes means for producing the variable electrical level as a direct function of the repetition rate of the commutation pulses.

120. A control circuit as set forth in claim 118 wherein said means for supplying the variable electrical level includes a voltage divider connected to a terminal for the source voltage, a capacitor connected across part of the voltage divider, and means resistively connected between said commutating means and said capacitor for charging said capacitor from the commutation pulses whereby said capacitor has a speed-dependent voltage comprising the variable electrical level.

121. A control circuit as set forth in claim 118 further comprising means connected to said commutating means and operable when the commutation pulses are absent for preventing production of the disabling signal by said means for producing the disabling signal.

122. A control circuit as set forth in claim 121 wherein said commutating means includes first logic means for supplying the commutation pulses on a set of lines for the solid state switching means and said preventing means includes second logic means connected to said first logic means to supply a preventing signal to said means for producing the disabling signal so that preventing signal is supplied when all of said lines have the same level for making the solid state switching means nonconductive.

123. A control circuit as set forth in claim 122 wherein said preventing means further includes slow-charge, fast discharge resistance-capacitance network means for coupling the preventing signal to said means for producing the disabling signal.

124. A control circuit as set forth in claim 118 wherein said means for producing the disabling signal includes a set of comparator means equal in number to the number of winding stages, each of said comparator means having a first input connected to said variable electrical level and having second input connected to a respective terminal of the winding stages.

125. A control circuit as set forth in claim 124 wherein said means for producing the disabling signal further includes a protective network including diodes respectively connected from each second input of said comparator means to a zener diode.

126. A control circuit as set forth in claim 118 wherein electrical signals from each energized winding stage can be coupled to and interfere with a back emf of each unpowered winding stage of the electronically commutated motor, the control circuit further including means for selecting at least two unpowered winding stages at a time which have electrical signals coupled to them that have a predetermined relationship in polarity and magnitude, and means for producing an electrical output from the voltages on the winding stage terminals of the winding stages selected, so that the electrical signals coupled from each energized winding stage are substantially canceled when they have the predetermined relationship while the back emf is preserved, said commutating means including means responsive to the electrical output so produced for advancing in the preselected sequence.

127. A control circuit as set forth in claim 118 wherein said commutating means includes means for supplying the commutation pulses so that a winding stage is temporarily powered and another winding stage is temporarily unpowered, terminating a commutation pulse in response to a first control signal and advancing in the sequence in response to a second control signal, and wherein the control circuit further includes means responsive to the terminal voltage of a temporarily unpowered winding stage for producing a sensing output which is a function of angular position of the rotatable assembly, means for establishing a first electrical level representative of a first position of the rotatable assembly at which a temporarily powered winding stage is to be deenergized and a second electrical level representative of a second position of the rotatable assembly at which said commutating means is to advance in the sequence, and means for comparing the sensing output with the first and second electrical levels to produce the first and second control signals for said commutating means when the first and second positions are respectively reached by the rotatable assembly.

128. A control circuit as set forth in claim 118 wherein said commutating means includes means for initiating each commutation pulse in response to at least one control signal, the control circuit further including means responsive to the terminal voltage of at least one winding stage for producing a sensing output which is a function of angular position of the rotatable assembly, the sensing output having a variable frequency which depends on the speed of the rotatable assembly, means for comparing the sensing output with a first electrical level to produce a first control signal to make the commutating means advance in the sequence, further means for generating a varying second electrical level representing a varying value beginning with an initial value, and means responsive to the first control signal for resetting said further means for generating so that the second electrical level is returned to the initial value whereupon said further means for generating resumes generating the varying second electrical level which thereby depends on the frequency of the sensing output that results from the speed of the rotatable assembly, said comparing means including means for also comparing the sensing output with the second electrical level to produce a second control signal for initiation of each commutation pulse by said commutating means.

129. A control circuit as set forth in claim 118 wherein said commutating means includes shift register means having a serial input, a set of parallel inputs, a control input to select the serial input or parallel inputs for entry, and outputs for supplying a parallel digital signal comprising the commutation pulses and representing each commutation in sequence, said shift register means to be protected from electrical interference which could cause the outputs to supply a parallel digital signal unrepresentative of any commutation in the sequence, means for supplying a parallel digital signal representing a particular commutation in the sequence to the set of parallel inputs of said shift register means, and means for clocking said shift register means, said control input of said shift register means connected to respond to at least one of the outputs and said serial input connected to respond to at least one of the outputs so that if any unrepresentative parallel digital signal appears which does not represent any commutation in the sequence at the outputs of said shift register means, the unrepresentative parallel digital signal is replaced by another parallel digital signal representing a commutation in the sequence when said means for clocking next clocks said shift register means.

130. A control circuit as set forth in claim 118 further comprising position sensing means for repeatedly generating a sensing signal generally representative of rotation of the rotatable assembly, oscillator means for producing oscillator pulses, means for frequency dividing the oscillator pulses to supply lower frequency pulses, said means for frequency dividing having a reset input for repeated resetting by said sensing signal, so that when the rotatable assembly is turning at least as fast as a predetermined rate the sensing signal is generated at a repetition rate for resetting that prevents the lower frequency pulses from being supplied and otherwise allows the lower frequency pulses to be supplied when the sensing signal is generated at a lower repetition rate, means responsive to the lower frequency pulses when they occur for producing an additional electrical signal generally representing an accumulated number of the lower frequency pulses, and means for comparing the additional electrical signal with a predetermined value to prevent said commutating means from generating the commutation pulses for a predetermined period of time after the predetermined value is reached by the additional electrical signal.

131. A control circuit as set forth in claim 118, the control circuit to be compatible with alternative external control devices indicating desired speed of the rotatable assembly, further comprising means for modulating the commutation pulses in width as a function of an analog speed control signal, and means for supplying the analog speed control signal to said means for modulating, said means for supplying including a capacitor and active device circuit means having an input resistively connected to a terminal for the power source, said input also for connection to any of the external control devices, and an output resistively connected to said capacitor so that said capacitor develops the analog speed control signal when the input of said active device circuit means is connected to any of the following external control devices:

A) pulse generator with a duty cycle representative of desired speed, B) variable voltage source representative of desired speed, or C) variable resistance representative of desired speed.

132. A control circuit as set forth in claim 118 wherein the source voltage is to be in a range between a lower voltage limit and a higher voltage limit, the control circuit further comprising first means for deriving a first voltage from the source voltage as a first function of the source voltage, second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit, and means, connected to said first and second means for deriving, for comparing the first and second voltages to produce a disabling signal for said commutating means when the source voltage is outside the range.

133. A control circuit as set forth in claim 118 wherein the source voltage is subject to a transient substantially in excess of a normal value of the source voltage, and further comprising control means responsive to the transient in the source voltage when the transient occurs and connected to said commutating means for overriding the commutation pulses to make at least one of the solid state switching means conduct for the duration of the transient.

134. An electronically commutated motor system comprising:

an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages connected together at a neutral for energization, the winding stages having terminals for switching;

switching means connected to the terminals for applying a voltage to one or more of the winding stages at a time;

commutating means, connected to control said switching means, for commutating the winding stages in a preselected sequence to rotate the rotatable assembly, leaving a preselected sequence of winding stages correspondingly unpowered so that at least two of the winding stages are unpowered at some time, wherein the winding stages generate back emf signals and also couple electrical signals from each energized winding stage to the unpowered winding stages which signals can interfere with detection of back emf for position sensing purposes;

means for selecting a pair of the unpowered winding stages which have electrical signals coupled to them that are substantially the same in polarity and magnitude; and

means, connected to control said commutating means, for producing an electrical output which is a function of the difference of the voltages on the winding stage terminals of the pair of the winding stages selected, whereby the electrical signals coupled from each energized winding stage are substantially canceled while the back emf is preserved and the electrical output varies as a function of the position of the rotatable assembly substantially free from interference from the electrical signals that are coupled from each energized winding stage to the unpowered winding stages.

135. An electronically commutated motor system energizable from a power source and comprising:

an electronically commutated motor including a stationary assembly having a plurality of winding stages adapted to be electronically commutated in a preselected sequence, and a rotatable assembly associated in selective magnetic coupling relation with said winding stages, each of said winding stages having a terminal and a terminal voltage associated therewith;

commutating means for applying a voltage from the power source to energize the motor so that a winding stage is temporarily powered and another winding stage is temporarily unpowered, terminating the application of voltage to the temporarily powered winding stage in response to a first control pulse and advancing in the sequence in response to a second control pulse to effect rotation of said rotatable assembly;

means operable generally for integrating for terminal voltage of the temporarily unpowered winding stage to produce an integrated output generally representative of angular position of said rotatable assembly;

means for establishing a first electrical level representative of a first angular position of the rotatable assembly at which the temporarily powered winding stage is to be deenergized, and a second electrical level representative of a second angular position of said rotatable assembly at which said commutating means is to advance in the sequence; and

means for comparing the integrated output with the first and second electrical levels to produce the first and second control pulses for said commutating means when the first and second angular positions are respectively reached by said rotatable assembly.

136. An electronically commutated motor system energizable from a power source and comprising:

an electronically commutated motor including a stationary assembly having at least three winding stages adapted to be electronically commutated in a preselected sequence, and a rotatable assembly associated in selective magnetic coupling relation with said winding stages, each of said winding stages having a terminal and a terminal voltage associated therewith;

bistable means for each winding stage and having a first state for powering a respective winding stage in response to a first control signal and a second state for terminating the application of voltage to the same winding stage in response to a second control signal;

controlling means for generating a sequence of electrical signals for said bistable means to determine which of said winding stages shall be powered in response to the first control signal and which of said winding stages shall have voltage terminated in response to the second control signal, said controlling means being responsive to a third control signal to advance in the sequence upon each occurrence of the third control signal;

means responsive to the terminal voltage of at least one temporarily unpowered winding stage to produce a sensing output which is a function of angular position of said rotatable assembly; and

means for comparing the sensing output with first, second and third electrical levels to respectively produce the first and second control signals for said bistable means and the third control signal for said controlling means.

137. An electronically commutated motor system energizable from a power source and comprising:

an electronically commutated motor including a stationary assembly having a plurality of winding stages, and a rotatable assembly associated in selective magnetic coupling relation with said winding stages;

means for electronically commutating said winding stages in a preselected sequence in response to at least one control signal, each said winding stage having a terminal and a terminal voltage associated therewith;

means responsive to the terminal voltage of at least one said winding stage to produce a sensing output which is a function of angular position of said rotatable assembly, the sensing output having a variable frequency which depends on the speed of said rotatable assembly;

means for comparing the sensing output with a first electrical level to produce a first control signal for said means for electronically commutating; and

means for generating a varying second electrical level representing a varying value beginning with an initial value, for resetting the second electrical level to the initial value in response to the first control signal and for resuming the generation of the varying second electrical level which thereby depends on the frequency of the sensing output that results from the speed of the rotatable assembly, said comparing means including means for also comparing the sensing output with the second electrical level to produce a second control signal for said means for electronically commutating.

138. An electronically commutated motor system comprising:

an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages;

switching means for commutating said winding stages in a preselected sequence to rotate said rotatable assembly;

shift register means having a serial input, a set of parallel inputs, a control input to select the serial input or parallel inputs for entry, and outputs for supplying a parallel digital signal representing a commutation in the sequence, said switching means responsive to the outputs and said shift register means to be protected from electrical interference which could cause the outputs to supply a parallel digital signal unrepresentative of any commutation in the sequence;

means for supplying a parallel digital signal representing a particular commutation in the sequence to the set of parallel inputs of said shift register means; and

means for clocking said shift register means to cause its outputs to supply a parallel digital signal representing a commutation in the sequence, said control input of said shift register means connected to respond to at least one of the outputs and said serial input connected to respond to at least one of the outputs so that if any unrepresentative parallel digital signal appears which does not represent any commutation in the sequence at the outputs of said shift register means, the unrepresentative parallel digital signal is replaced by another parallel digital signal representing a commutation in the sequence when said means for clocking next clocks said shift register means.

139. An electronically commutated motor system comprising:

an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages;

position sensing means for repeatedly generating a sensing signal generally representative of rotation of said rotatable assembly;

commutating means responsive to the sensing signal for commutating said winding stages in a preselected sequence to energize said winding stages and thereby rotate said rotatable assembly;

oscillator means for producing oscillator pulses;

means for frequency dividing the oscillator pulses to supply lower frequency pulses, said means for frequency dividing having a reset input for repeated resetting by the sensing signal from said position sensing means, so that when said rotatable assembly is turning at least as fast as a predetermined spin rate the sensing signal is generated at a repetition rate for resetting that prevents the lower frequency pulses from being supplied and otherwise allows the lower frequency pulses to be supplied when the sensing signal occurs at a lower repetition rate;

means responsive to the lower frequency pulses when they occur for producing an electrical signal generally representing an accumulated number of the lower frequency pulses; and

means for supplying a disabling signal for a predetermined period of time to said commutating means after a predetermined value is reached by the electrical signal, to prevent continued energization of the motor during that predetermined period of time.

140. An electronically commutated motor system for use with a power source having a source voltage which is supposed to be in a range between a lower voltage limit and a higher voltage limit, the system comprising:

an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages;

position sensing means for repeatedly generating a sensing signal generally representative of rotation of said rotatable assembly;

commutating means responsive to the sensing signal for commutating said winding stages in a preselected sequence to energize said winding stages and thereby rotate said rotatable assembly;

first means for deriving a first voltage source voltage as a first function of the source voltage;

second means for deriving a second voltage from the source voltage as a second function of the source voltage, wherein the second voltage is equal to the first voltage only at the lower voltage limit and the higher voltage limit; and

means, connected to said first and second means for deriving, for comparing the first and second voltages to produce a disabling signal for said commutating means when the source voltage is outside the range.

141. An electronically commutated motor system for use with a voltage source and with alternative external control devices for desired speed, and comprising:

an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages for energization;

switching means for applying a voltage from a voltage source to one or more of said winding stages at a time and commutating said winding stages in a preselected sequence to rotate said rotatable assembly at a speed dependent on the energization applied to said winding stages;

means for generating pulse width modulated pulses to control said switching means, the pulses modulated in width as a function of an analog speed control signal; and

means for supplying the analog speed control signal to said means for generating the pulse width modulated pulses, said means for supplying including a capacitor and active device circuit means having an input resistively connected to a terminal for the voltage source, said input also for connection to any of the external control devices, and an output resistively connected to said capacitor so that said capacitor develops the analog speed control signal when the input of said active device circuit means is connected to any of the following external control devices;

A) pulse generator with variable duty cycle representative of desired speed, B) variable voltage source representative of desired speed, or C) variable resistance representative of desired speed.

142. An electronically commutated motor system comprising:

an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages;

solid state switching means for applying a source voltage to one or more of said winding stages at a time, said solid state switching means having a saturation voltage depending on current flowing through them when conducting;

commutating means for generating commutation pulses in a preselected sequence to make said solid state switching means conduct and commutate said winding stages in the preselected sequence to rotate said rotatable assembly, the repetition rate of the commutation pulses being related to the speed of said rotatable assembly;

means responsive to said commutation pulses for supplying a variable electrical level which varies in magnitude as a function of the repetition rate of the commutation pulses, the electrical level representing a current limit for said motor as a function of motor speed; and

means for producing a disabling signal for said commutating means when the saturation voltage across said solid state switching means exceeds the variable electrical level in magnitude whereby current for said motor is limited as a function of motor speed.

143. A method of operating a control circuit for an electronically commutated motor having a rotatable assembly and further having a stationary assembly with a plurality of winding stages having terminals for energization, and switching means for applying a voltage to one or more of the terminals of the winding stages at a time and commutating the winding stages in a preselected sequence to rotate the rotatable assembly, leaving a preselected sequence of winding stages correspondingly unpowered so that a plurality of the winding stages are unpowered at some time, wherein the winding stages generate back emf signals and also couple electrical signals from each energized winding stage to the unpowered winding stages which signals can interfere with detection of back emf for position sensing purposes, the method comprising the steps of:

selecting at least two of the unpowered winding stages which have electrical signals coupled to them that have a predetermined relationship in polarity and magnitude; and

producing an electrical output from the voltages on the winding stage terminals of the winding stages selected, so that the electrical signals coupled from each energized winding stage are substantially canceled when they have the predetermined relationship while the back emf is preserved for position sensing substantially free from interference from the electrical signals that are coupled from each energized winding stage to the unpowered winding stages.