CLOSED-LOOP MOTOR DRIVER COMPENSATION

• US 20100127655A1
• Filed: 11/26/2008
• Published: 05/27/2010
• Est. Priority Date: 11/26/2008
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Haas, David J., Ward, Michael G.
• Granted Patent: US 8,138,708 B2
• Time in Patent Office: Days
• US Class Current: 318/621
• CPC Class Codes: G05B 11/011 details of the correcting means

Abstract

A control loop circuit for use in a closed-loop control system that controls a system such as a linear motor is presented. The control loop circuit includes a lead-lag compensator that features a lead compensation network configured to reduce output noise without substantially changing the effect of the lead compensation in the control system'"'"'s frequency response.

Claims

1. A circuit comprising:

an error amplifier having a first input to receive a reference signal, a second input and an output to produce an error signal based on the first input and the second input;

a lead-lag compensator comprising a lead portion and a lag portion, the lead portion being connected between the second input of the error amplifier and a feedback path from an external controlled system of a closed-loop control system having an associated frequency response, and the lag portion being connected between the second input and the output of the error amplifier; and

wherein the lead portion comprises a network of passive elements connected to provide a high frequency zero for lead compensation and a high frequency pole to reduce the effect of the high frequency zero on the frequency response.

2. The circuit of claim 1 wherein the lead portion comprises a first resistor, a second resistor and a capacitor, the second resistor and the capacitor being connected in series as a series resistive-capacitive (RC) circuit, and the first resistor being connected in parallel with the series RC circuit to form a parallel RC circuit.

3. The circuit of claim 2 wherein inclusion of the second resistor in the parallel RC circuit operates to introduce the high frequency pole.

4. The circuit of claim 2 wherein the lead portion further comprises a third resistor connected in series with the parallel RC circuit.

5. The circuit of claim 4 wherein the second and third resistors inclusion have values smaller than that of the first resistor.

6. The circuit of claim 4 wherein the third resistor has a value that is substantially smaller than that of the first resistor.

7. The circuit of claim 4 wherein the lag portion comprises a capacitor to provide a dominant low frequency pole.

8. The circuit of claim 7 wherein the lag portion comprises a resistor connected in series with the capacitor.

9. The circuit of claim 7 wherein the lag portion comprises a resistor connected in parallel a second capacitor to form a parallel RC network and the parallel RC network is connected in series with the capacitor.

10. The circuit of claim 9 where inclusion of the parallel RC network of the lag portion operates to introduce a high frequency pole.

11. The circuit of claim 1 wherein the second input comprises a signal produced by a sensor operable to detect movement by the external controlled system.

12. A device comprising:

a driver to drive a movement by a motion device;

a sensor to detect the movement and to produce an output in response thereto;

a control loop circuit coupled between the sensor and the driver, the control loop circuit configured to receive as inputs the magnetic field sensor output and an input provided by an external controller, and to produce an output signal based on the received inputs as an input to the driver; and

wherein the control loop comprises;

an error amplifier having a first input to receive the external controller input as a reference signal, a second input and an output to produce an error signal based on the first input and the second input;

a lead-lag compensator comprising a lead portion and a lag portion, the lead portion being connected between the second input of the error amplifier and the sensor output, and the lag portion being connected between the second input and the output of the error amplifier; and

wherein the lead portion comprises a network of passive elements connected to provide a high frequency zero for lead compensation and a high frequency pole.

13. The device of claim 12 wherein the lead portion comprises a first resistor, a second resistor and a capacitor, the second resistor and the capacitor being connected in series as a series resistive-capacitive (RC) circuit, and the first resistor being connected in parallel with the series RC circuit to form a parallel RC circuit.

14. The device of claim 13 wherein inclusion of the second resistor in the parallel RC circuit operates to introduce the high frequency pole.

15. The device of claim 13 wherein the lead portion further comprises a third resistor connected in series with the parallel RC circuit.

16. The device of claim 15 wherein the second and third resistors inclusion have values smaller than that of the first resistor.

17. The device of claim 15 wherein the third resistor has a value that is substantially smaller than that of the first resistor.

18. The device of claim 15 wherein the lag portion comprises a capacitor to provide a dominant low frequency pole.

19. The device of claim 18 wherein the lag portion further comprises a resistor connected in series with the capacitor.

20. The device of claim 18 wherein the lag portion comprises a resistor connected in parallel a second capacitor to form a parallel RC network and the parallel RC network is connected in series with the capacitor.

21. The device of claim 20 where inclusion of the parallel RC network of the lag portion operates to introduce a high frequency pole.

22. The device of claim 12 wherein the sensor comprises a magnetic field sensor.

23. The device of claim 22 wherein the magnetic field sensor comprises at least one active element to sense the magnetic field and the at least one active element element is a selected one of a Hall-effect element and magnetoresistive (MR) element.

24. The device of claim 22 wherein the driver is a coil driver and the movement is a linear movement.

25. The device of claim 12 wherein the driver, the sensor and the control loop circuit are integrated as a semiconductor integrated circuit.

26. A system comprising:

a controller; and

a linear motion control device, coupled to the controller, comprising;

a coil driver to drive a coil that, when driven, effects a linear movement by a motion device having a magnet;

a magnetic field sensor to detect a magnetic field associated with the linear movement and to produce an output in response thereto;

a control loop circuit coupled between the magnetic field sensor and the coil driver, the control loop circuit configured to receive as inputs the magnetic field sensor output and an input provided by the controller, and to produce an output signal based on the received inputs as an input to the coil driver; and

wherein the control loop circuit comprises;

an error amplifier having a first input to receive the controller input as a reference signal, a second input and an output to produce an error signal based on the first input and the second input;

a lead-lag compensator comprising a lead portion and a lag portion, the lead portion being connected between the second input of the error amplifier and magnetic field sensor output, and the lag portion being connected between the second input and the output of the error amplifier; and

wherein the lead portion comprises a network of passive elements connected to provide a high frequency zero for lead compensation and a high frequency pole.

27. The system of claim 26 wherein the lead portion comprises a first resistor, a second resistor and a capacitor, the second resistor and the capacitor being connected in series as a series resistive-capacitive (RC) circuit, and the first resistor being connected in parallel with the series RC circuit to form a parallel RC circuit.

28. The system of claim 27 wherein inclusion of the second resistor in the parallel RC circuit operates to introduce the high frequency pole.

29. The system of claim 27 wherein the lead portion further comprises a third resistor connected in series with the parallel RC circuit.

30. The system of claim 29 wherein the second and third resistors inclusion have values smaller than that of the first resistor.

31. The system of claim 29 wherein the third resistor has a value that is substantially smaller than that of the first resistor.

32. The system of claim 29 wherein the lag portion comprises a capacitor to provide a dominant low frequency pole.

33. The system of claim 32 wherein the lag portion further comprises a resistor connected in series with the capacitor.

34. The system of claim 32 wherein the lag portion comprises a resistor connected in parallel a second capacitor to form a parallel RC network and the parallel RC network is connected in series with the capacitor.

35. The system of claim 26 wherein the controller is configured to use the linear motion control device to focus the lens of a camera.

36. The system of claim 26 wherein the coil driver, the magnetic field sensor and the control loop circuit are integrated as a semiconductor integrated circuit.

37. The system of claim 26 wherein the semiconductor integrated circuit and the controller reside on a camera lens focusing module.

38. The system of claim 26 wherein the motion device comprises a linear motor.

39. The system of claim 26 wherein the motion device comprises a voice coil actuator.

40. The system of claim 26 wherein the linear motion control device has a sleep input to enable operation of the linear motion control device in a low power mode.