Continuous mode velocity control of voice coil motor
View Patent ↗A method of controlling the velocity of a voice coil motor (VCM), including sensing a voltage difference between the VCM and a sense resistor and driving a velocity control loop (VCL) based on the voltage difference. There is also a control loop circuit, including a current output connected to drive a voice coil motor, the voice coil motor producing a back electromagnetic field (BEMF) voltage. The circuit also includes a sense resistor connected to the BEMF output, and a BEMF resistive network comprising a first resistor and a second resistor. The circuit also includes a velocity control loop (VCL) connected to control the voltage output according to a voltage difference between (i) a junction of the sense resistor and the current output and (ii) a junction of the first resistor and the second resistor.
1. A method of controlling the velocity of a voice coil motor (VCM), the method comprising:
driving a voice coil motor (VCM) with a current output, wherein the VCM produces a back electromagnetic field (BEMF) voltage output sensed by a BEMF resistive network comprising a first resistor and a second resistor;
sensing a voltage difference between (i) a junction of a sense resistor connected to the BEMF voltage output and the current output and (ii) a junction of the first resistor and the second resistor; and
driving a velocity control loop (VCL) connected to control the BEMF voltage output according to the voltage difference.
2. The method of claim 1 further comprising:
controlling a direction of the VCM with a digital-to-analog converter (DAC) in the VCL.
3. The method of claim 2 , wherein a polarity of the DAC controls the direction of the VCM.
4. The method of claim 2 , wherein the DAC is programmable to attain a desired VCM velocity.
5. The method of claim 1 , wherein the sense resistor comprises a back electromagnetic field (BEMF) resistive circuit.
6. The method of claim 1 , wherein the VCL is in a continuous mode.
7. A control loop circuit, comprising:
a current output connected to drive a voice coil motor, the voice coil motor producing a back electromagnetic field (BEMF) voltage;
a sense resistor connected to the BEMF output;
a BEMF resistive network comprising a first resistor and a second resistor; and
a velocity control loop (VCL) connected to control the voltage output according to a voltage difference between (i) a junction of the sense resistor and the current output and (ii) a junction of the first resistor and the second resistor.
8. The control loop circuit of claim 7 , further comprising a digital-to-analog converter (DAC) connected to control a magnitude of the current output.
9. The control loop circuit of claim 7 , further comprising a digital-to-analog converter (DAC) connected to control a polarity of the current output.
10. The control loop circuit of claim 9 , wherein a polarity of the current output controls the direction of the voice coil motor.
11. The control loop circuit of claim 8 , wherein the DAC is programmable to attain a desired voice coil motor velocity.
12. The control loop circuit of claim 7 , wherein the VCL is in a continuous mode.
13. The control loop circuit of claim 8 , further comprising a velocity command amplifier connected to level-shift and output of the DAC to produce a target voltage.
14. The control loop circuit of claim 7 , further comprising first and second driver amplifiers connected to produce the current output.
15. A hard disk drive, comprising:
a storage disk;
a voice coil motor (VCM) connected to operate a VCM arm for reading the storage disk; and
a VCM control circuit including a control loop circuit connected to control the VCM, wherein the control loop circuit includes
a current output connected to drive the VCM, the VCM producing a back electromagnetic field (BEMF) voltage;
a sense resistor connected to the BEMF output;
a BEMF resistive network comprising a first resistor and a second resistor; and
a velocity control loop (VCL) connected to control the voltage output according to a voltage difference between (i) a junction of the sense resistor and the current output and (ii) a junction of the first resistor and the second resistor.
16. The hard disk drive of claim 15 , further comprising a digital-to-analog converter (DAC) connected to control a magnitude of the current output.
17. The hard disk drive of claim 15 , further comprising a digital-to-analog converter (DAC) connected to control a polarity of the current output.
18. The hard disk drive of claim 17 , wherein a polarity of the current output controls the direction of the VCM.
19. The hard disk drive of claim 16 , wherein the DAC is programmable to attain a desired VCM velocity.
20. The hard disk drive of claim 15 , further comprising first and second driver amplifiers connected to produce the current output.