Electronically commutated motor and method of making same

• US 4,005,347 A
• Filed: 06/24/1974
• Issued: 01/25/1977
• Est. Priority Date: 06/24/1974
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Erdman, David M.
• Primary Examiner(s): Rubinson, Gene Z.
• Application Number:
  US05/482,409
• Time in Patent Office: 946 Days
• Field of Search: 318/138, 318/254
• US Class Current: 318/400.4
• 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: H02K 29/10 using light effect devices
• CPC Class Codes: H02P 2209/07 Trapezoidal waveform
• CPC Class Codes: H02P 6/16 Circuit arrangements for detecting position

Abstract

A brushless DC motor is constructed with photosensitive devices for detecting rotor shaft position. Arcuate permanent magnets on the rotor provide a DC flux field while distributed stator windings, each spanning a fixed number of slots in the armature assembly, provide mutually perpendicular magnetic fields. A logic circuit comprising NOR gates and transistor switches and drivers activated in response to signals from the shaft position sensors are utilized to control current switching in the stator windings of the motor. A light interrupting shutter mounted to the rotor cooperates with the light sensitive devices which are mounted to a supporting bracket fixed to the stator assembly in a manner to selectively preset advancement of commutation of the stator windings.

Claims

1. A brushless DC motor having a stationary armature comprising an armature core and a plurality of winding turns disposed on said armature core, a permanent magnet rotor adapted to rotate about a longitudinal axis in response to magnetic fields established by said armature, means for developing position control signals indicative of the rotational position of said rotor and operative for causing commutation of each of the windings at an advancement angle before the rotor rotates to a position such that the center of a magnetic pole thereof of a first polarity is displaced 135 electrical degrees from the center of a magnetic pole of a polarity opposite to said first polarity and established by the winding being commutated.

2. A brushless DC motor as set forth in claim 1 further including fixed and movable position sensing elements with at least one of such elements including a source of energy, said source of energy comprising a first and a second light source spaced from each other;

said motor further including sensing means coupled to receive energy from the energy source and comprising first and second light sensors associated with each light source, said light sources each being a light emitting diode and said light sensors each being a phototransistor, and said movable element including a flange that is supported to said rotor such that said flange passes between the diodes and phototransistors to effect periodic interruption of the energy coupled therebetween upon rotation of the rotor.

3. A brushless DC motor having a stationary armature comprising an armature core and a plurality of winding turns disposed on said armature core, a permanent magnet rotor adapted to rotate about a longitudinal axis in response to magnetic fields established by said armature, means for developing position control signals indicative of the rotational position of said rotor including at least one fixed element and at least one movable element, said at least one movable element being rotatable relative to said fixed element, one of said elements including an energy transmitter and sensing means coupled to receive energy from the energy transmitter, the other of said elements including means for periodically interrupting the energy transmitted from the transmitter, a bracket mounted in fixed predetermined relation to said armature for supporting said fixed element in fixed relation to said armature, said movable element being mounted to said rotor for rotation therewith, said bracket being positioned with respect to said stationary armature and to said rotor such that said movable element periodically interrupts the energy coupled between said fixed element and said movable element so as to provide position control signals and establish advancement of commutation of the armature winding turns;

said bracket comprising a first segment fixed to said stationary armature and a second segment supported radially inward of the first segment for supporting said fixed element; and

said motor further including means for interconnecting said first and said second segments, said interconnecting means being shaped to pass over at least some of the end turns of the winding turns such that said fixed element is positioned within said end turns.

4. A brushless DC motor having a stationary armature including a core and at least two windings disposed on said core to produce at least two separate magnetic fields, a permanent magnet rotor adapted to rotate about a longitudinal axis in response to the at least one magnetic field established by said armature, means for providing control signals indicative of the angular position of said rotor relative to the armature;

said means for providing being operative to provide commutation signals that effect commutation of a given winding at a predetermined electrical advancement angle before the rotor rotates to a position such that the center of a magnetic pole thereof of a first polarity is displaced 135 electrical degrees from the center of a magnetic pole of a polarity opposite to said first polarity and established by said given winding.

5. A brushless DC motor as set forth in claim 4 wherein said motor includes position sensing means that include light source means comprising a first and a second light emitting diode, and further includes receiver means comprising first and second phototransistors, each associated with a light source in light coupling relationship therewith;

one source and receiver pair being spaced from another source and receiver pair by an arc length of 90 electrical degrees.

6. A brushless DC motor having a stationary armature including a core and at least two windings disposed on said core to produce at least two separate magnetic fields, a permanent magnet rotor adapted to rotate about a longitudinal axis in response to the at least one magnetic field established by said armature, shaft position sensing means for providing position control signals indicative of the angular position of said rotor relative to the armature;

said position sensing means being positioned relative to said armature so that commutation signals are provided to effect commutation of a given winding at a predetermined electrical advancement angle before the rotor rotates to a position such that the center of a magnetic pole thereof of a first polarity is displaced 135 electrical degrees from the center of a magnetic pole of a polarity opposite to said first polarity and established by said given winding;

said position sensing means including optical sensing means and a shutter that includes a flange extending axially from the rotor and movable therewith, said sensing means including light source means comprising a first and a second light emitting diode, and further including receiver means comprising first and second phototransistors, each associated with a light source in light coupling relationship therewith, with one source and receiver pair being spaced from another source and receiver pair by an arc length of 90 electrical degrees;

said windings including end turns extending beyond at least one end face of the armature core, and said motor further including a bracket mounted to support the light source and receiver means within an envelope established by said end turns.

7. A brushless DC motor having a stationary armature including a core and a plurality of stator windings disposed on said core to produce angularly directed magnetic fields;

a permanent magnet rotor adapted to rotate about a longitudinal axis in response to magnetic fields established by said armature;

said stator windings including end turns extending beyond at least one end face of the core, shaft position sensing means supported at one end of said rotor and within the end turns at that end for providing position control signals indicative of the angular position of said rotor relative to the armature;

said sensing means including an energy source and a receiver positioned to be coupled with and to receive energy from said source;

a bracket mounted in fixed predetermined relation to said armature for supporting said sensing means; and

a shutter mounted for movement with said rotor and positioned with respect to said sensing means such that said shutter periodically decouples the energy source and receiver during rotation of the rotor.

8. A DC motor comprising a stationary armature comprising a core having a longitudinal axis and at least two windings disposed on said core to produce differently directed magnetic fields, a permanent magnet rotor adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, means for providing signals indicative of the relative rotational position of said rotor, and circuit means responsive to said signals for energizing said stator windings in a predetermined sequence, said means for providing being operative to cause advancement of commutation of the windings by an angle alpha of from about five to about 25 electrical degrees to aid the build-up of current when the windings are energized during running condition.

9. A DC motor as set forth in claim 8 wherein said stator windings include at least four effective windings;

said circuit means comprises a first signal conditioning circuit responsive to the position signals for developing position control signals and a second signal conditioning circuit responsive to said control signals to control current switching in the stator windings; and

said second conditioning circuit includes independent switching means connected to each winding, and each said switching means is responsive to said control signals to control current switching in the associated winding.

10. A DC motor as set forth in claim 8 wherein said permanent magnet rotor comprises a core of magnetic material and a pair of diametrically opposed arcuate magnetic regions disposed on the periphery thereof, the arc length of each said magnetic region being within a preferred range of 120 and 170 electrical degrees.

11. A DC motor comprising a stationary armature comprising a core having a longitudinal axis and at least two windings disposed on said core to produce differently directed magnetic fields, a permanent magnetic rotor adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, means for providing signals indicative of the relative rotational position of said rotor, and circuit means responsive to said signals for energizing said windings in a predetermined sequence, said means for providing being operative to cause advancement of commutation of the windings by an angle alpha of from about five to about 25 electrical degrees to aid the build-up of current when the windings are energized during running condition, said windings comprising at least two concentrically disposed coil groups each having a predetermined span and mutually establishing a predetermined spread of conductive segments in slots of the core.

12. A DC motor as set forth in claim 11 wherein each said predetermined spread is in a preferred range of from about thirty electrical degrees to about one hundred and twenty electrical degrees.

13. A DC motor as set forth in claim 11 wherein the coil groups are arranged in pairs and each pair is formed of bifilar strands that share common slots.

14. A DC motor as set forth in claim 13 wherein said windings are connected in a star configuration.

15. A DC motor as set forth in claim 11 including means for interconnecting said windings and said circuit means in a bridge configuration.

16. A DC motor comprising a stationary armature comprising a core having a longitudinal axis and at least two windings disposed on said core to produce differently directed magnetic fields, a permanent magnet rotor adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, means for providing signals indicative of the relative rotational position of said rotor, and circuit means responsive to said signals for energizing said windings in a predetermined sequence, said means for providing being operative to cause advancement of commutation of the windings by an angle alpha of from about five to about 25 electrical degrees to aid the build-up of current when the windings are energized during running condition;

said windings including at least four effective windings;

said circuit means comprising a first signal conditioning circuit responsive to said signals for developing relative position control signals and a second signal conditioning circuit responsive to said control signals to control current switching in the windings; and

said second signal conducting circuit including independent switching means connected to each winding, and each said switching means being responsive to said control signals to control current switching in the associated winding;

said second signal conditioning circuit including a plurality of signal channels, one for each winding, each said channel including a first stage responsive to the level of at least two position control signals to develop a control output signal and switching means responsive to said control output to effect current switching in the winding associated with that channel.

17. A DC motor as set forth in claim 16 including protective means connected across each said switching means for shunting current developed in the windings due to a decaying magnetic field of a disconnected winding and further including means for absorbing energy released by the decaying magnetic field of a de-energized winding and returning said energy to the next energized winding.

18. A DC motor comprising a stationary armature comprising a core having a longitudinal axis and at least two windings disposed on said core to produce differently directed magnetic fields, a permanent magnet rotor adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, means for providing signals indicative of the relative rotational position of said rotor, and circuit means responsive to said signals for energizing said windings in a predetermined sequence, said means for providing being operative to cause advancement of commutation of the windings by an angle alpha of from about five to about 25 electrical degrees to aid the build-up of current when the windings are energized during running condition;

said windings including at least four effective windings;

said circuit means comprising a first signal conditioning circuit responsive to said signals for developing relative position control signals and a second signal conditioning circuit responsive to said control signals to control current switching in the windings; and

said second signal conditioning circuit including independent switching means connected to each winding, and each said switching means being responsive to said control signals to control current switching in the associated winding;

said second signal conditioning circuit including protective means for shunting current developed in the windings due to a decaying magnetic field of a de-energized winding.

19. A DC motor comprising a stationary armature comprising a core having a longitudinal axis and at least two windings disposed on said core to produce differently directed magnetic fields, a permanent magnet rotor adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, means for providing signals indicative of the relative rotational position of said rotor, and circuit means responsive to said signals for energizing said windings in a predetermined sequence, said means for providing being operative to cause advancement of commutation of the windings by an angle alpha of from about five to about 25 electrical degrees to aid the build-up of current when the windings are energized during running condition;

said windings including at least four effective windings;

said circuit means comprising a first signal conditioning circuit responsive to said signals for developing relative position control signals and a second signal conditioning circuit responsive to said control signals to control current switching in the windings; and

said second signal conditioning circuit including independent switching means connected to each winding, and each said switching means being responsive to said control signals to control current switching in the associated winding;

said motor further including means for absorbing energy released by a decaying magnetic field of a disconnected winding.

20. A DC motor as set forth in claim 19 wherein said means for absorbing energy is a capacitor.

21. A DC motor comprising a stationary armature comprising a core having a longitudinal axis and at least two windings disposed on said core to produce differently directed magnetic fields, a permanent magnet rotor adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, means for providing signals indicative of the relative rotational position of said rotor, and circuit means responsive to said signals for energizing said windings in a predetermined sequence, said means for providing being operative to cause advancement of commutation of the windings by an angle alpha of from about five to about 25 electrical degrees to aid the build-up of current when the windings are energized during running condition;

said motor further including means for recovering energy released by a decaying magnetic field of a winding when it is de-energized.

22. A DC motor comprising a stationary armature having a longitudinal axis and including a plurality of stator windings, for producing spaced apart magnetic fields, a permanent magnet rotor adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, a predetermined number of sensors for sensing positions of the rotor with adjacent sensors spaced from each other by approximately 90 electrical degrees;

the number of sensors being equal to the number of binary digits, minus one, that are descriptive in binary notation of the number of switching positions of the motor for each 360 electrical degrees of rotor rotation;

circuit means responsive to said position signals for providing switching signals associated with said windings, and including switching means responsive to said switching signals for energizing said stator windings in a predetermined sequence;

said armature comprising a low reluctance magnetic member having a plurality of axially extending slots, and said stator windings comprising a plurality of concentrically disposed winding turns.

23. A DC motor comprising a stationary armature having a longitudinal axis and including a plurality of windings, for producing spaced apart magnetic fields, a permanent magnet rotor adapted to rotate about said longitudinal axis in response to magnetic fields established by said armature, a predetermined number of sensors for sensing positions of the rotor with adjacent sensors spaced from each other by approximately 90 electrical degrees;

the number of sensors being equal to the number of binary digits, minus one, that are descriptive in binary notation of the number of switching positions of the motor for each three hundred and sixty electrical degrees of rotor rotation;

circuit means responsive to said position signals for providing switching signals associated with said windings, and including switching means responsive to said switching signals for energizing said stator windings in a predetermined sequence;

said circuit means further including protective means for recovering energy released by a decaying magnetic field of a disconnected winding.