Detection of starting motor position in a brushless DC motor

• US 5,569,990 A
• Filed: 03/31/1995
• Issued: 10/29/1996
• Est. Priority Date: 03/31/1995
• Status: Expired due to Term

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Seagate Technology plc (Seagate Technology Holdings Plc)
• Inventors: Dunfield, John C.
• Primary Examiner(s): SALATA, ANTHONY J
• Application Number:
  US08/414,289
• Time in Patent Office: 578 Days
• Field of Search: 318/254, 318/439, 318/138
• US Class Current: 318/400.33
• CPC Class Codes: H02P 6/185 using inductance sensing, e.g. pulse excitation
• CPC Class Codes: H02P 6/20 Arrangements for starting H02P6/08 takes precedence

Abstract

A microprocessor-controlled-circuit applies pulses to a standing motor whose rotor position is to be determined. The time required for the injected current to reach a predetermined threshold in a comparator is measured. The pulses are long enough to effectuate an accurate measurement, but not so long that the rotor moves. The pulse is applied twice to each phase, once with a positive polarity and once with a negative polarity, for a total of six measurements. The positive and negative rise times are subtracted from each other to determine whether the positive or negative current rise time was greater. Based upon the differences in the readings for all of the phases, the position of the rotor is known. There are differences in which the difference is zero or negligible. There are at least two methods to determine rotor position when there are ambiguities in the sign of the difference. In one method, the combination of the sign of the rise time difference or its absence plus the magnitude of the rise time can be used along with look-up tables to determine the rotor position. Another method is to resolve a position uncertainty by changing the effective rotor position. This is done by pulsing all three phases actively. Instead of leaving a phase open during pulsing, the third phase is tied high or is tied low. Once start-up ambiguities are resolved, control of acceleration from stand-still through medium speed to constant, nominal speed is provided.

Claims

1. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet and a stator current excitation winding, a method for controlling ordered application of electrical current to the phase windings and measuring responses thereto to determine an initial position of said rotor, said method comprising the steps of:

coupling circuit means to the phase windings for providing control signals for selectively establishing current paths through at least one selected winding;

applying short duration current pulses of first and second opposite polarities to each said selected winding for providing at least one energized winding, leaving a predetermined phase winding open during pulsing;

detecting a voltage corresponding to each of said applied current pulses of opposite polarities as converted by a current to voltage converter connected to the energized winding;

determining a magnitude for each rise time of each of said responses to said current pulses from zero amplitude to a fixed reference level;

subtracting at least one of said rise times from one associated one of said rise times to provide at least one rise time difference;

determining a magnitude of at least one of each of said rise time for each said rise time difference;

determining ambiguity in sign for each said rise time difference;

retesting with said predetermined phase winding tied so as to change effective rotor position; and

identifying the initial position of said rotor relative to said phase windings based on the sign of the rise time difference between the rise time of the responses to said pulses applied to the selected winding and based on the changed effective rotor position.

2. The method of claim 1 wherein the predetermined phase winding is tied high.

3. The method of claim 2 further comprising the step of:

using the initial position of said rotor as identified for determining both polarity and duration of at least one drive pulse for starting the motor, the duration of the drive pulse moving the rotor up to but not passed an initial commutation location.

4. The method of claim 3 further comprising the step of:

controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed.

5. The method of claim 4 further comprising the step of:

regulating a total of said current pulses to said phase windings to accelerate the rotor from the medium speed to a desired operating speed.

6. The method of claim 1 wherein the predetermined phase winding is tied low.

7. The method of claim 6 further comprising the step of:

using the initial position of said rotor as identified for determining both polarity and duration of at least one drive pulse for starting the motor, the duration of the drive pulse moving the rotor up to but not passed an initial commutation location.

8. The method of claim 7 further comprising the step of:

controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed from the initial position.

9. The method of claim 8 further comprising the step of:

regulating a total of said current pulses to said phase windings to accelerate the rotor from the medium speed to a nominal speed and to maintain said rotor revolving at said nominal speed.

10. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet and a stator current excitation winding, a method for controlling ordered application of electrical current to the phase windings and measuring responses thereto to determine an initial position of said rotor, said method comprising the steps of:

coupling circuit means to the phase windings for providing control signals for selectively establishing current paths through at least one selected winding;

applying short duration current pulses of first and second opposite polarities to each said selected winding for providing at least one energized winding, leaving a predetermined phase winding open during pulsing;

detecting a voltage corresponding to each of said applied current pulses of opposite polarities as converted by a current to voltage converter connected to the energized winding;

determining a magnitude for each rise time of each of said responses to said current pulses from zero amplitude to a fixed reference level;

subtracting at least one of said rise times from one associated one of said rise times to provide at least one rise time difference;

determining a magnitude of at least one of each of said rise time for each said rise time difference;

determining ambiguity in sign for each said rise time difference;

retesting with said predetermined phase winding tied high so as to change effective rotor position; and

identifying the initial position of said rotor relative to said phase windings based on the sign of the rise time difference between the rise time of the responses to said pulses applied to the selected winding and based on the changed effective rotor position;

controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed from the initial position; and

regulating a total of said current pulses to said phase windings to accelerate the rotor from the medium speed to a nominal speed and to maintain said rotor revolving at said nominal speed.

11. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet and a stator current excitation winding, a method for controlling ordered application of electrical current to the phase windings and measuring responses thereto to determine an initial position of said rotor, said method comprising the steps of:

coupling circuit means to the phase windings for providing control signals for selectively establishing current paths through at least one selected winding;

applying short duration current pulses of first and second opposite polarities to each said selected winding for providing at least one energized winding, leaving a predetermined phase winding open during pulsing;

detecting a voltage corresponding to each of said applied current pulses of opposite polarities as converted by a current to voltage converter connected to the energized winding;

determining a magnitude for each rise time of each of said responses to said current pulses from zero amplitude to a fixed reference level;

subtracting at least one of said rise times from one associated one of said rise times to provide at least one rise time difference;

determining a magnitude of at least one of each of said rise time for each said rise time difference;

determining ambiguity in sign for each said rise time difference;

retesting with said predetermined phase winding tied low so as to change effective rotor position;

identifying the initial position of said rotor relative to said phase windings based on the sign of the rise time difference between the rise time of the responses to said pulses applied to the selected winding and based on the changed effective rotor position;

controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed from the initial position; and

regulating a total of said current pulses to said phase windings to accelerate the rotor from the medium speed to a nominal speed and to maintain said rotor revolving at said nominal speed.

12. In a brushless DC motor having n phases corresponding to phase windings arranged as a stator and a rotor for n an integer greater than zero, a method for starting the motor in a predetermined direction of rotation of the rotor, the method comprising the steps of:

initializing a threshold induced voltage level;

mapping electrical position of the rotor including the steps of;

pulsing a phase of the n phases with positive current to provide positively induced voltage without appreciably altering the electrical position of the rotor and to provide a positively pulsed phase;

measuring a first rise time for the positively induced voltage for the positively pulsed phase to reach the threshold induced voltage level;

again pulsing the phase of the n phases but this time with negative current to provide negatively induced voltage without appreciably altering the electrical position of the rotor and to provide a negatively pulsed phase;

measuring a second rise time for the negatively induced voltage for the negatively pulsed phase to reach the threshold induced voltage level;

determining a difference between the first and the second rise time as measured in each of the measuring steps;

determining whether the difference does not provide sufficient information to ultimately resolve the electrical position of the rotor;

tying, if the difference does not provide sufficient information to resolve the electrical position of the rotor, one of the n phases not the phase currently being tested;

retesting, if the difference does not provide sufficient information to resolve the electrical position of the rotor, by repeating the step of mapping;

storing a sign of the difference; and

repeating the steps of the step of mapping until each of the n phases is processed; and

recalling and using the sign of the difference for each of the n phases as compared with predetermined stored motor electrical position information to energize at least one of the n phases to start the motor in the predetermined direction.

13. The method of claim 12 wherein the step of tying is selected from the group consisting of the steps of:

tying high, if the difference does not provide sufficient information to resolve the electrical position of the rotor, one of the n phases not the phase currently being tested; and

tying low, if the difference does not provide sufficient information to resolve the electrical position of the rotor, one of the n phases not the phase currently being tested.

14. The method of claim 13 further comprising the step of:

accelerating the motor to revolve at a medium speed.

15. The method of claim 14 further comprising the steps of:

accelerating the rotor from the medium speed to revolve at a nominal speed; and

maintaining the rotor revolving at the nominal speed.

16. The method of claim 15 wherein n is equal to three.

17. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet and a stator current excitation winding, apparatus for controlling ordered application of electrical current to the phase windings and measuring responses thereto to determine an initial position of said rotor, said apparatus comprising:

circuit means coupled to the phase windings for selectively establishing current paths through at least one selected winding in response to control signals;

means for successively applying short duration current pulses of opposite polarities to each said selected winding, leaving a predetermined phase open during pulsing; and

processing means, having storage means for storing information included therein, for determining and storing each magnitude for each rise time of each of said responses to said current pulses from zero amplitude to a fixed reference level, for subtracting at least one said rise times from another opposite said rise times to provide at least one rise time difference, for determining each sign or absence thereof of each said rise time difference, for determining ambiguity based on each said sign or absence thereof of each said rise time difference, for retesting with said predetermined phase tied high so as to change effective rotor position, and for identifying the initial position of said rotor relative to said phase windings based on the sign of the rise time difference between the rise time of the responses to said pulses applied to the selected winding and based on the changed effective rotor position as applicable.

18. The apparatus of claim 17 further comprising:

means for controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed from the initial position.

19. The apparatus of claim 18 further comprising:

means for regulating a total of said current to said phase windings to accelerate the rotor from the medium speed to a nominal speed, and for maintaining said rotor revolving at said nominal speed.

20. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet and a stator current excitation winding, apparatus for controlling ordered application of electrical current to the phase windings and measuring responses thereto to determine an initial position of said rotor, said apparatus comprising:

circuit means coupled to the phase windings for selectively establishing current paths through at least one selected winding in response to control signals;

means for successively applying short duration current pulses of opposite polarities to each said selected winding, leaving a predetermined phase open during pulsing; and

processing means, having storage means for storing information included therein, for determining and storing each magnitude for each rise time of each of said responses to said current pulses from zero amplitude to a fixed reference level, for subtracting at least one said rise times from another opposite said rise times to provide at least one rise time difference, for determining each sign or absence thereof of each said rise time difference, for determining ambiguity based on each said sign or absence thereof of each said rise time difference, for retesting with said predetermined phase tied low so as to change effective rotor position, and for identifying the initial position of said rotor relative to said phase windings based on the sign of the rise time difference between the rise time of the responses to said pulses applied to the selected winding and based on the changed effective rotor position as applicable.

21. The apparatus of claim 20 further comprising:

means for controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed from the initial position.

22. The apparatus of claim 21 further comprising:

means for regulating a total of said current to said phase windings to accelerate the rotor from the medium speed to a nominal speed, and for maintaining said rotor at said nominal speed.

23. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet and a stator current excitation winding, an apparatus for controlling ordered application of electrical current to the phase windings and measuring responses thereto to determine an initial position of said rotor, said apparatus comprising:

circuit means coupled to the phase windings for providing control signals for selectively establishing current paths through at least one selected winding;

means for applying short duration current pulses of first and second opposite polarities to each said selected winding for providing at least one energized winding, leaving a predetermined phase winding open during pulsing;

means for detecting a voltage corresponding to each of said applied current pulses of opposite polarities as converted by a current to voltage converter connected to the energized winding;

means for determining a magnitude for each rise time of each of said responses to said current pulses from zero amplitude to a fixed reference level;

means for subtracting at least one of said rise times from one associated one of said rise times to provide at least one rise time difference;

means for determining a magnitude of at least one of each of said rise time for each said rise time difference;

means for determining ambiguity in sign for each said rise time difference;

means for retesting with said predetermined phase winding tied so as to change effective rotor position; and

means for identifying the initial position of said rotor relative to said phase windings based on the sign of the rise time difference between the rise time of the responses to said pulses applied to the selected winding and based on the changed effective rotor position.

24. The apparatus of claim 23 wherein the predetermined phase winding is tied high.

25. The apparatus of claim 24 further comprising:

means for controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed from the initial position.

26. The apparatus of claim 25 further comprising:

means for regulating a total of said current pulses to said phase windings to accelerate the rotor from the medium speed to a nominal speed and to maintain said rotor revolving at said nominal speed.

27. The apparatus of claim 23 wherein the predetermined phase winding is tied low.

28. The apparatus of claim 27 further comprising:

means for controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed from the initial position.

29. The apparatus of claim 28 further comprising:

means for regulating a total of said current pulses to said phase windings to accelerate the rotor from the medium speed to a nominal speed and to maintain said rotor revolving at said nominal speed.

30. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet and a stator current excitation winding, an apparatus for controlling ordered application of electrical current to the phase windings and measuring responses thereto to determine an initial position of said rotor, said apparatus comprising:

circuit means coupled to the phase windings for providing control signals for selectively establishing current paths through at least one selected winding;

means for applying short duration current pulses of first and second opposite polarities to each said selected winding for providing at least one energized winding, leaving a predetermined phase winding open during pulsing;

means for detecting a voltage corresponding to each of said applied current pulses of opposite polarities as converted by a current to voltage converter connected to the energized winding;

means for determining a magnitude for each rise time of each of said responses to said current pulses from zero amplitude to a fixed reference level;

means for subtracting at least one of said rise times from one associated one of said rise times to provide at least one rise time difference;

means for determining a magnitude of at least one of each of said rise time for each said rise time difference;

means for determining ambiguity in sign for each said rise time difference;

means for retesting with said predetermined phase winding tied high so as to change effective rotor position; and

means for identifying the initial position of said rotor relative to said phase windings based on the sign of the rise time difference between the rise time of the responses to said pulses applied to the selected winding and based on the changed effective rotor position;

means for controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed from the initial position; and

means for regulating a total of said current pulses to said phase windings to accelerate the rotor from the medium speed to a nominal speed and to maintain said rotor revolving at said nominal speed.

31. In a brushless DC motor having multiple phase windings arranged as a stator and a rotor having a permanent magnet and a stator current excitation winding, an apparatus for controlling ordered application of electrical current to the phase windings and measuring responses thereto to determine an initial position of said rotor, said apparatus comprising:

circuit means coupled to the phase windings for providing control signals for selectively establishing current paths through at least one selected winding;

means for applying short duration current pulses of first and second opposite polarities to each said selected winding for providing at least one energized winding, leaving a predetermined phase winding open during pulsing;

means for detecting a voltage corresponding to each of said applied current pulses of opposite polarities as converted by a current to voltage converter connected to the energized winding;

means for determining a magnitude for each rise time of each of said responses to said current pulses from zero amplitude to a fixed reference level;

means for subtracting at least one of said rise times from one associated one of said rise times to provide at least one rise time difference;

means for determining a magnitude of at least one of each of said rise time for each said rise time difference;

means for determining ambiguity in sign for each said rise time difference;

means for retesting with said predetermined phase winding tied low so as to change effective rotor position; and

means for identifying the initial position of said rotor relative to said phase windings based on the sign of the rise time difference between the rise time of the responses to said pulses applied to the selected winding and based on the changed effective rotor position;

means for controlling ordered periodic application of the electrical current to said phase windings and measuring the responses thereto to accelerate the rotor to a medium speed from the initial position; and

means for regulating a total of said current pulses to said phase windings to accelerate the rotor from the medium speed to a nominal speed and to maintain said rotor revolving at said nominal speed.

32. In a brushless DC motor having n phases corresponding to phase windings arranged as a stator and a rotor for n an integer greater than zero, a method for starting the motor in a predetermined direction of rotation of the rotor, the method comprising the steps of:

initializing a threshold induced voltage level; and

mapping electrical position of the rotor including the steps of;

pulsing a phase of the n phases with positive current to provide positively induced voltage without appreciably altering the electrical position of the rotor and to provide a positively pulsed phase;

measuring a first rise time for the positively induced voltage for the positively pulsed phase to reach the threshold induced voltage level;

again pulsing the phase of the n phases but this time with negative current to provide negatively induced voltage without appreciably altering the electrical position of the rotor and to provide a negatively pulsed phase;

measuring a second rise time for the negatively induced voltage for the negatively pulsed phase to reach the threshold induced voltage level;

determining a difference between the first and the second rise time as measured in each of the measuring steps;

determining whether the difference does not provide sufficient information to ultimately resolve the-electrical position of the rotor;

tying, if the difference does not provide sufficient information to resolve the electrical position of the rotor, one of the n phases not the phase currently being tested;

retesting, if the difference does not provide sufficient information to resolve the electrical position of the rotor, by repeating the step of mapping;

storing a sign of the difference to build up a lookup table, the table for providing a reference for which of the n phases need to be energized to begin rotating the rotor in the predetermined direction; and

repeating the steps of the step of mapping until each of the n phases is completely processed.

33. The method of claim 32 wherein the step of tying is selected from the group consisting of the steps of:

tying high, if the difference does not provide sufficient information to resolve the electrical position of the rotor, one of the n phases not the phase currently being tested; and

tying low, if the difference does not provide sufficient information to resolve the electrical position of the rotor, one of the n phases not the phase currently being tested.

34. The method of claim 33 wherein n is equal to three.

35. The method of claim 33 wherein the motor is a spindle motor for a hard disk drive.

36. The method of claim 33 wherein the n phases are pulsed in a sequential order.

37. The method of claim 33 wherein the n phases are pulsed in an arbitrary order.

38. In a brushless DC motor having n phases corresponding to phase windings arranged as a stator and a rotor for n an integer greater than zero, a method for determining an initial position of the rotor, the method comprising the steps of:

initializing a threshold induced voltage level;

mapping electrical position of the rotor including the steps of;

pulsing each phase of the n phases with a first polarity current to provide first polarity induced voltages without appreciably altering the electrical position of the rotor and to provide first polarity pulsed phases;

measuring a first set of rise times for each of the first polarity induced voltages for a one-to-one correspondence with each of the first polarity pulsed phases to reach the threshold induced voltage level;

pulsing each said phase of the n phases with a second polarity current to provide second polarity induced voltages without appreciably altering the electrical position of the rotor and to provide second polarity pulsed phases;

measuring a second set of rise times for each of the second polarity induced voltages for a one-to-one correspondence with each of the second polarity pulsed phases to reach the threshold induced voltage level;

determining a set of differences between the first set and the second set of rise times as measured in each of the measuring steps;

determining which, if any, difference in said set of differences does not provide sufficient information to ultimately resolve the electrical position of the rotor;

tying, for each said difference which does not provide sufficient information to resolve the electrical position of the rotor, one of the n phases not the phase currently being tested;

retesting, for each said difference which does not provide sufficient information to resolve the electrical position of the rotor, by repeating the step of mapping; and

storing each sign of each said difference; and

recalling and comparing each said sign of each said difference for each of the n phases with predetermined stored motor electrical position information to determine the initial position of the rotor.

39. The method of claim 38 wherein the step of tying is selected from the group consisting of tying high and tying low.

40. The method of claim 39 further comprising the step of:

determining a duration and a polarity of at least one pulse for starting the motor in the predetermined direction of rotation, the duration of said pulse sufficient for moving the rotor up to but not passed an initially encountered commutation region.

41. The method of claim 40 further comprising the step of:

accelerating the motor to resolve at a medium speed.

42. The method of claim 41 further comprising the steps of:

accelerating the rotor from the medium speed to revolve at a nominal speed; and

maintaining the rotor revolving at the nominal speed.

43. The method of claim 42 wherein n is equal to three.

44. The method of claim 42 wherein the first polarity current is negative polarity direct current, and the second polarity current is positive polarity direct current.

45. The method of claim 42 wherein the first polarity current is positive polarity direct current and the second polarity current is negative polarity direct current.

46. In a brushless DC motor having n phases corresponding to phase windings arranged as a stator and a rotor for n an integer greater than zero, a method for starting the motor in a predetermined direction of rotation of the rotor, the method comprising the steps of:

initializing a threshold induced voltage level;

mapping electrical position of the rotor including the steps of;

pulsing a phase of the n phases with a first polarity current to provide a first polarity induced voltage without appreciably altering the electrical position of the rotor and to provide a first polarity pulsed phase;

measuring a first rise time for the first polarity induced voltage for the first polarity pulsed phase to reach the threshold induced voltage level;

again pulsing the phase of the n phases but this time with a second polarity current to provide a second polarity induced voltage without appreciably altering the electrical position of the rotor and to provide a second polarity pulsed phase;

measuring a second rise time for the second polarity induced voltage for the second polarity pulsed phase to reach the threshold induced voltage level;

determining a difference between the first and the second rise time as measured in each of the measuring steps;

determining and storing any sign of the difference;

determining if the difference is too small to resolve the electrical position of the rotor;

determining and storing, if the difference is too small to resolve the electrical position of the rotor, a magnitude of one of the first and the second rise time associated with the difference;

determining whether the magnitude does not provide sufficient information to ultimately resolve the electrical position of the rotor;

tying, if the magnitude does not provide sufficient information to resolve the electrical position of the rotor, one of the n phases not the phase currently being tested;

retesting, if the magnitude does not provide sufficient information to resolve the electrical position of the rotor, by repeating the step of mapping;

storing a sign of the difference; and

repeating the steps comprising the step of mapping until each of the n phases is processed; and

recalling and comparing the sign of the difference plus the magnitude of an associated one of the first and the second rise time, if the electrical position is ambiguous with only the sign of the difference, with predetermined stored motor electrical position information to energize at least one of the n phases to start the motor in the predetermined direction of rotation.