# US 7,466,095 B1 · Voice coil motor control system and method using pulse width modulation

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- Number: US 7,466,095 B1
- Document ID: US7466095B1
- Status: Granted
- Kind: B1
- Application number: 11/455,476
- Filed: 2006-06-19
- Granted: 2008-12-16
- Earliest claimed: 2005-11-28
- Assignees: Marvell International Ltd.
- Inventors: Siew Yong Chui
- Web page: https://patentgrep.com/patent/US7466095B1

## CPC

- H02P 6/182: using back-emf in windings
- G11B 5/5526: {Control therefor; circuits, track configurations or relative disposition of servo-information transducers and servo-information tracks for control thereof (G11B5/556 takes precedence)}
- H02P 25/034: Voice coil motors (voice coil motors driven by DC H02P7/025)
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

A system and method for controlling an actuator includes a control module that communicates with a plurality of switching devices to generate current through a voice coil motor during a first time period so that an actuator arm rotates in a first rotational direction in response to the current. The control module controls the switching devices to discharge the current from the voice coil motor during a second time period less than the first time period so that the first rotational direction of the actuator arm is maintained after discharging the current. The control module further includes a back electromagnetic force (bemf) module for determining a bemf voltage after controlling the switching devices to discharge the current, and an actuator arm speed control module for determining an actuator arm speed in response to the bemf voltage.

## Claims

### Claim 1

A system comprising:
a control module that communicates with a plurality of switching devices to generate current through a voice coil motor during a first time period so that an actuator arm rotates in a first rotational direction in response to the current, that controls the switching devices to discharge the current from the voice coil motor during a second time period that is less than the first time period so that the first rotational direction of the actuator arm is maintained after discharging the current, and that generates a control signal when a predetermined time has elapsed after the current is discharged;
a back electromagnetic force (bemf) module for determining a bemf voltage based on the control signal; and
an actuator arm speed control module for determining an actuator arm speed in response to the bemf voltage.

### Claim 2 (depends on 1)

The system of claim 1 further comprising:
the plurality of switching devices;
the voice coil motor; and
the actuator arm.

### Claim 3 (depends on 2)

The system of claim 2 wherein the plurality of switches form an H bridge.

### Claim 4 (depends on 2)

The system of claim 2 further comprising an energy storage device, wherein the control module controls the plurality of switches so that the current is drawn from the energy storage device.

### Claim 5 (depends on 4)

The system of claim 4 wherein the energy storage device comprises a capacitor.

### Claim 6 (depends on 2)

The system of claim 2 further comprising an energy storage device, wherein the control module controls the plurality of switches so that discharging the current charges the energy storage device.

### Claim 7 (depends on 2)

The system of claim 2 further comprising an energy storage device, wherein the plurality of switches comprises:
a first switch and a second switch in communication with a first side of the voice coil motor; and
a third switch and a fourth switch in communication with a second side of the motor,
wherein the first switch and the third switch are in communication with the energy storage device and the second switch and the third switch are in communication with a reference voltage.

### Claim 8 (depends on 7)

The system of claim 7 wherein, during the first time period, the control module controls the first switch and the fourth switch to a conducting state and the second and fourth switch to a non-conducting state and, during the second time period, the control module controls the first switch and the fourth switch to a non-conducting state and the second and fourth switch to a conducting state.

### Claim 9 (depends on 7)

The system of claim 7 wherein, during the first time period, the control module couples the first side to the energy storage device and the second side to a reference voltage and, during the second time, the control module controls couples the first side to ground and the second side to the energy storage device.

### Claim 10 (depends on 7)

The system of claim 7 further comprising a resistor that communicates with the first side and second side.

### Claim 11 (depends on 7)

The system of claim 7 further comprising a gain and level shifting circuit that communicates with the first side and the second side forming a raw bemf voltage signal.

### Claim 12 (depends on 11)

The system of claim 11 further comprising a sample and hold circuit that samples the raw bemf signal to generate a sampled bemf voltage signal.

### Claim 13 (depends on 12)

The system of claim 12 further comprising a converter module that converts the sampled back emf voltage signal into a digital speed signal.

### Claim 14 (depends on 1)

The system of claim 1 further comprising a time constant adjustment module that adjusts a sampling interval of the control module in response to a time constant.

### Claim 15 (depends on 14)

The system of claim 14 wherein the time constant is based on motor inductance and motor resistance.

### Claim 16 (depends on 2)

A hard disk drive comprising the system of claim 2.

### Claim 17 (depends on 1)

The system of claim 1 wherein the back electromagnetic force (bemf) module determines a bemf voltage signal.

### Claim 18 (depends on 17)

The system of claim 17 further comprising an analog to digital control module converting the bemf voltage signal into a digital voltage signal.

### Claim 19 (depends on 18)

The system of claim 18 further comprising a decoder module converting the digital voltage signal into a speed signal.

### Claim 20 (depends on 19)

The system of claim 19 further comprising a pulse width generator module generating a pulse width modulated motor control signal.

### Claim 21 (depends on 20)

The system of claim 20 further comprising a time constant adjustment module in communication with the pulse width generator module for adjusting the pulse width motor control signal.

### Claim 22

A method of operating an actuator comprising:
generating a current through a voice coil motor in a first direction for a first time;
rotating the actuator in a first rotational direction in response to the current;
discharging the current from the voice coil motor and charging an energy storage device for a second time that is less than the first time;
maintaining first rotational direction of the actuator after discharging the current,
generating a control signal when a predetermined time has elapsed after the current is discharged;
determining a back electromotive force (bemf) voltage based on the control signal; and
determining an actuator speed in response to the bemf voltage.

### Claim 23 (depends on 22)

The method of claim 22 wherein generating a current comprises generating the current from the energy storage device.

### Claim 24 (depends on 22)

The method of claim 22 wherein the energy storage device comprises a capacitor.

### Claim 25 (depends on 22)

The method of claim 22 further comprising determining the current as a function of an inductance of the voice coil motor, a resistance of the voice coil motor and a voltage of the energy storage device.

### Claim 26 (depends on 22)

The method of claim 22 further comprising determining the first time as a function of an inductance of the voice coil motor and a resistance of the voice coil motor.

### Claim 27 (depends on 22)

The method of claim 22 further comprising controlling the voice coil motor in response to the actuator speed.

### Claim 28 (depends on 22)

The method of claim 22 further comprising amplifying and level shifting the bemf voltage to form a raw bemf signal.

### Claim 29 (depends on 28)

A method as recited in claim 28 further comprising after amplifying and level shifting, sampling the raw bemf signal and holding the raw bemf signal to form a bemf voltage signal.

### Claim 30 (depends on 29)

The method of claim 29 further comprising converting the bemf signal, into a digital signal and converting the digital signal into the actuator speed.

### Claim 31 (depends on 22)

The method of claim 22 further comprising performing the steps of generating, rotating, discharging, maintaining and determining during a parking mode.

### Claim 32 (depends on 22)

The method of claim 22 further comprising controlling the generating and discharging of the current using pulse width modulation (PWM).

### Claim 33 (depends on 32)

The method of claim 32 further comprising adjusting a switching frequency of the PWM based on a time constant of the motor.

### Claim 34 (depends on 22)

The method of claim 22 further comprising:
generating speed information based on the bemf voltage and a target speed of the motor; and
determining the first time, the second time, the predetermined time, and a period of the control signal based on the speed information.