Method and apparatus for brushless DC motor speed control

• US 4,876,491 A
• Filed: 02/26/1988
• Issued: 10/24/1989
• Est. Priority Date: 07/01/1986
• Status: Expired due to Term

• Current Assignee: Seagate Technology LLC (Seagate Technology Holdings Plc)
• Original Assignee: Conner Peripherals Incorporated (Whitehouse Group Ltd.)
• Inventors: Squires, John P., Shrinkle, Louis J.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US07/163,222
• Time in Patent Office: 606 Days
• Field of Search: 318/254, 318/439, 318/138
• US Class Current: 318/400.33
• CPC Class Codes: H02P 6/06 Arrangements for speed regulation of a single motor wherein the motor speed is measured and compared with a given physical value so as to adjust the motor speed
• CPC Class Codes: H02P 6/185 using inductance sensing, e.g. pulse excitation
• CPC Class Codes: H02P 6/22 in a selected direction of rotation

Abstract

Control and synchronization of a polyphase, brushless DC motor (used for a hard-disk system) during initial start-up of the motor, is effected by monitoring rotor position using a high-frequency commutation: A short current pulse is applied to each power phase of the motor, and motor current conducted in response thereto, is measured to determine therefrom positional information of the rotor. From such positional information the identity of the appropriate motor phase to which is applied a torque-producing current is determined. Cycles of high-frequency commutation and application of torque-producing are performed, until the rotational speed of the rotor has attained a predetermined RPM. Motor speed is controled in synchronized, increasing fashion by continued monitoring of the motor current and back-EMF, until a desired rotational RPM is attained, whereupon torque-producing current is sequentially applied to each motor phase in synchronization with the rotor position by deriving positional information from the disk.

Claims

1. In a brushless DC motor having multiple stator windings and a rotor, apparatus for controlling ordered application of electrical current to the stator windings, comprising:

circuit means coupled to the stator windings for selectively creating current paths there through in response to control signals;

sensing means coupled to the DC motor for producing a sense signal indicative of current conducted by the DC motor; and

control means coupled to the circuit means and to the sensing means for providing the control signals in a manner to cause current to flow through the current paths selectively formed by the circuit means in response to the control signals, effecting rotation of the rotor;

the control means including means for producing pulse signals to cause selective application of high-frequency current pulses to the stator windings and means for monitoring the pulse signals to determine which of the high frequency current pulses produces a high amplitude pulse signal relative to those of the other high frequency current pulses, the control means being operable in response to a determination by said monitoring means to provide the control signals to the circuit means.

2. A method of initiating and controlling the rotation of a rotor of a brushless DC motor of the type having multiple windings, related as phases, for conducting torque-producing current therethrough, comprising the steps of:

sequentially powering each phase of the DC motor for a short predetermined time period;

obtaining a peak amplitude value of the current conducted by the motor when a phase is powered during each corresponding short predetermined time period;

determining a one-peak amplitude value having a magnitude greater than the other peak amplitude values; and

applying a torque-producing current to the DC motor in a phase determined by the determined one-peak amplitude value.

3. The method of claim 2 including the step of:

deriving the rotational speed of the rotor from successive ones of the determined peak amplitude value.

4. The method of claim 3 including the steps of:

terminating the sequentially powering, obtaining, determining, applying, and deriving steps at a predetermined rotational speed of the rotor;

ascertaining a static motor current value;

supplying a motor current to the predetermined power phase of the motor;

measuring the motor current; and

switching application of the motor current to the next sequential power phase of the motor when the measured motor current exceeds the static motor current value.

5. A commutatorless direct current motor having a rotor for rotating with respect to a stator, said motor comprising:

(a) means, provided on the rotor, for establishing a plurality of first magnetic fields;

(b) means, provided on the stator, for inducing a second magnetic field; and

(c) control means, coupled to said inducing means, for directing a discrete short-period inducement of said second magnetic field and a discrete long-period inducement of said second magnetic field wherein said discrete short period inducement is insufficient to cause rotation of said rotor and said discrete long-period inducement is sufficient to cause rotation of said rotor, said control means including means for monitoring the interaction of said discrete short-period induced second magnetic field with said first magnetic fields.

6. The motor of claim 5 wherein said control means identifies the rotational orientation of said discrete short-period induced second magnetic field with respect to a specific one of said first magnetic fields.

7. The motor of claim 6 wherein said control means, in response to said monitoring means, identifies a subset of the possible rotational positions of said establishing means with respect to said inducing means and wherein said control means further includes microprocessor means for identifying the one rotational position of said establishing means from said subset of possible rotational positions that corresponds to the rotational position of said specific one of said first magnetic fields.

8. A commutatorless direct current motor having a rotor for rotating with respect to a stator, said motor comprising:

(a) means, provided on the rotor, for establishing a plurality of first magnetic fields;

(b) means, provided on the stator, for inducing a second magnetic field, said inducing means including a plurality of windings; and

(c) control means, coupled to said inducing means, for directing a short-period inducement of said second magnetic field, said control means including means for monitoring the interaction of said short-period induced second magnetic field with said first magnetic fields, wherein each short-period inducement of said second magnetic field is obtained by the application of a current pulse through a respective phase pair of said windings as selected by said control means, wherein said monitoring means monitors the current pulse response of each said phase pair of said windings.

9. The motor of claim 8 wherein said monitoring means detects a peak voltage obtained in response to the application of each current pulse to each said phase pair of said windings.

10. A commutatorless direct current motor including an armature having a plurality of windings, each winding having first and second ends and wherein the first ends of the windings are connected together, and a plurality of magnets supported in a rotor so as to be rotatable with respect to the armature through a plurality of discrete rotational commutation positions, said motor comprising:

(a) control means, coupled to the respective second ends of the windings, for providing commutation power to the windings; and

(b) means for applying a pulse of commutation power to the windings, where said pulse of commutation power is sufficient to alter the rotational position of said rotor, to determine the rotational position of the magnets with respect to the windings.

11. The motor of claim 10 wherein said pulse applying means is coupled to each of the second ends of the windings to enable the application of said pulse of commutation power to each of the windings.

12. The motor of claim 11 further comprising means, coupled to each of the second ends of the windings, for measuring the response of the windings to the application of said pulse of commutation power.

13. The motor of claim 12 wherein said measuring means measures the peak value of a return high-frequency signal obtained in response to the application of said pulse of commutation power to the windings.

14. The motor of claim 13 wherein said pulse applying means selectively applies said pulse of commutation power to pairs of the second ends of the windings such that said pulse of commutation power is serially conducted through pairs of the windings via their respective first ends.

15. The motor of claim 14 wherein said control means, responsive to said measuring means, selectively determines the commutation order of applying commutation power to the windings to rotate the plurality of magnets in a predetermined direction.

16. The motor of claim 15 wherein said control means is capable of relying exclusively on said measuring means for determining the rotational position of the plurality of magnets with respect to the armature.

17. In a commutatorless direct current motor having an armature and a multiple-magnet rotor, wherein said armature includes a plurality of windings for generating torque-inducing magnetic fields in response to current pulses and wherein:

said multiple-magnet rotor is caused to rotate between rotational positions relative to said armature in response to the application of long-duration current pulses to the windings, an improvement permitting the unique armature relative rotational position of said multiple-magnet rotor to be identified exclusively through the use of said windings as positional sensors, said improvement comprising;

(a) control means for applying a a respective short-duration current pulse to each phase pair of said windings, said short-duration current pulses being insufficient to rotate said multiple-magnet rotor between rotational positions; and

(b) means for detecting the respective response of the phase pairs of said windings to said short-duration current pulse.

18. The motor of claim 17 wherein said control means selectively applies said short-duration current pulse to the phase pairs of said windings, wherein said detecting means detects a distinguishing response from the phase pairs of said windings and wherein said control means, responsive to said detecting means, determines the unique armature relative rotational position of said multiple-magnet rotor.

19. The motor of claim 18 wherein said control means monitors a peak voltage developed across said windings in response to the application of short-duration current pulse, the winding for which a highest peak voltage is detected being associated with a specific location on said multiple-magnet rotor.

20. The motor of claim 19 wherein said control means applies said short-duration current pulse to each phase winding of said motor and wherein said short-duration current pulse has a predetermined duration insufficient to alter the rotational position of said multiple-magnet rotor with respect to said armature.

21. A commutatorless direct current motor comprising:

(a) an armature including a plurality of windings having first and second ends, said first ends of said windings being connected together, whereby sets of two said second ends define phase pairs of said windings;

(b) a permanent magnet motor assembly including a plurality of magnets and rotatable with respect to said armature; and

(c) control means, coupled to said respective second ends of said windings, for directing the operation of said motor, said control means including means for selectively providing commutation power to phase pairs of said windings, means for successively applying a short-duration current pulse to each phase pair of said windings, means for detecting a peak voltage developed across said second ends of each phase pair of said windings, means for comparing the detected peak voltages of each phase pair of said windings, and means for identifying a specific one of said magnets as being positionally related to the one of the phase pairs of said windings corresponding to a largest phase pair peak voltage detected.

22. A system for controlling the rotation of a motor having a rotor with multiple magnetic poles and a stator with a plurality of windings permitting the conduction of torque inducing current therein, said system comprising:

(a) means for selecting windings for the conduction of current to cause rotation of the rotor;

(b) means for applying a short-duration current pulse to selected ones of the windings; and

(c) control means, responsive to the characteristics of the response of the windings to the application of the short-duration current pulse, for controlling said selecting means and said applying means to determine the unique position of the magnetic poles of the rotor with respect to the windings, said control means including means for sensing the peak voltage developed by the selected ones of the windings in response to the application of the short-duration current pulse.

23. The system of claim 22 wherein the selected ones of the windings are related in groups or phases, wherein each short-duration current pulse is applied to a respective phase and wherein said control means further includes means for comparing the peak voltage sensed by said sensing means for each phase.

24. A control system for providing rotation control of a hard-disk drive spin motor wherein the spin motor includes a rotor having a plurality of permanent magnet poles and a stator having a plurality of windings, each winding having first and second ends with the first ends of the windings being interconnected, said control system comprising:

(a) a spin motor driver coupled to the second ends of the windings for conducting current pulse through phase pairs of the windings defined by pairs of second ends, said spin motor driver providing a sense signal proportional to the magnitude of the current pulse conducted through the windings;

(b) a control circuit coupled to said spin motor drive to provide control signals for the selection of phase pairs of windings for the conduction of the current pulse, said control circuit including timing means for establishing the period of the application of respective current pulses to phase pairs of windings including a long-duration period current pulse to induce the rotation of the rotor to a different pole position with respect to the windings and a short-duration period current pulse wherein the short-duration current pulse conducted by a selected phase pair of windings is less than sufficient to induce rotation of the rotor to a different pole position with respect to the windings, said control circuit including microprocessor means, responsive to said sense signal as respectively produced in response to the conduction of current pulse for a short-duration period by each of the phase pairs of windings, for determining the unique pole position of the rotor with respect to the phase pairs of windings.

25. The control system of claim 24, wherein said microprocessor means includes means for detecting a peak voltage across each phase pair of windings developed in response to the conduction of current pulse for the short-duration period through the respective phase pairs of windings, said microprocessor means being responsive to said detecting means for identifying the phase winding pair for which a largest magnitude peak voltage is detected.

26. The control system of claim 25 wherein the motor operates to rotate a hard disk media and wherein said control circuit includes means for monitoring the back-EMF developed in the phase pairs of windings in response to the rotation of the rotor and means for obtaining rotation rate feedback information from the hard disk media.

27. A method of operating a control system for providing rotation control of a hard-disk drive spin motor, wherein the spin motor includes a rotor having a plurality of permanent magnet poles and a stator having a plurality of windings, each winding having first and second ends with the first ends of the windings being interconnected and wherein a spin motor drive current circuit is coupled to the second ends of the windings for switching current through phase pairs of the windings as defined by pairs of said second ends, said spin motor drive current circuit providing a sense signal proportional to the magnitude of the current conducted through the phase pairs of windings, the method comprising the steps of:

(a) applying a short-duration period current pulse to each phase pair of windings, where said short-duration current pulse is insufficient to cause rotation of said rotor to the next pole position relative to said stator;

(b) acquiring the sense signal produced by said spin motor drive current circuit in response to the respective application of the short-duration period current pulses;

(c) comparing the sense signals acquired to identify a phase pair of windings corresponding to an acquired sense signal distinguishable from the remaining acquired sense signals; and

(d) selecting a phase pair of windings for the conduction of a long-duration period current pulse to induce rotation of the rotor.

28. The method of claim 27 further comprising the step of substantially maintaining a predetermined level of current conducted through the phase pairs of windings in response to the long-duration period current pulses as the rotational speed of the rotor increases.

29. A method of operating a control system in hard-disk media for providing rotation control of a hard-disk drive spin motor, wherein the spin motor includes a rotor having a plurality of permanent magnet poles and a stator having a plurality of windings, each winding having first and second ends with the first ends of the windings being interconnected and wherein a spin motor drive current circuit is coupled to the second ends of the windings for switching current through phase pairs of the windings as defined by pairs of said second ends, said spin motor drive current circuit providing a sense signal proportional to the magnitude of the current conducted through the phase pairs of windings, the method comprising the steps of:

(a) initiating the rotation of the rotor to a first predetermined rotation rate by repeating the steps of;

(i) applying a short-duration period current pulse to a phase pair of windings, where said short-duration current pulse is insufficient to cause rotation of said rotor to the next pole position relative to said stator;

(ii) acquiring the sense signal produced by said spin motor drive current circuit in response to the application of the short-duration period current pulse;

(iii) comparing the sense signals acquired for each phase pair of windings to identify a phase pair of windings corresponding to an acquired sense signal distinguishable from the remaining acquired sense signals; and

(iv) selecting a phase pair of windings for the conduction of current to induce rotation of the rotor;

(b) increasing the rotation rate of the motor to a second predetermined rate by repeating the steps of;

(i) sensing the back-EMF developed in the phase pairs of windings; and

(ii) providing current to a next phase pair of windings selected from a predetermined series of phase pair winding commutation states in response to the sensing of a predetermined level of back-EMF; and

(c) maintaining the rotation race of the rotor at a third predetermined rate by repeating the steps of;

(i) receiving rotation rate feedback information from the hard disk media; and

(ii) adjusting the level of current provided to the phase pairs of windings to compensate for deviation of the rotation rates of the rotor from the third predetermined rate.

30. The method of claim 29 further comprising the step of maintaining a predetermined level of current conducted through the phase pairs of windings as the rotational speed of the rotor increases.