Method for linearization of an actuator via force gradient modification

• US 6,753,664 B2
• Filed: 03/22/2001
• Issued: 06/22/2004
• Est. Priority Date: 03/22/2001
• Status: Expired due to Fees

• Current Assignee: Creo Products Incorporated
• Original Assignee: Creo Products Incorporated
• Inventors: Trautman, Christopher Earl, Neufeld, Richard David
• Primary Examiner(s): TAMAI, KARL I
• Application Number:
  US09/813,839
• Publication Number:
  US 20020135329A1
• Time in Patent Office: 1,188 Days
• Field of Search: 310/309, 318/116, 318/119, 318/460, 385/18, 345/85, 359/290, 359/291
• US Class Current: 318/116
• CPC Class Codes: H02N 1/008 Laterally driven motors, e.g. of the comb-drive type

Abstract

In accordance with the present invention, the control over a high- speed non-linear actuator is improved by linearizing the relationship between the actuating impetus and the feedback control signal via a method that employs the separate and concurrent control of the static and dynamic characteristics of the device without resorting to the use of force-feedback or field-strength feedback. The resonant frequency of the plunger of the actuator is manipulated during operation such as to maintain it at a substantially fixed optimal value. The method is particularly advantageous in devices where space is at a premium and force-feedback or field-strength feedback mechanisms are difficult to implement.

Claims

1. A method for controlling a position of a plunger of an actuator within an actuation range, said actuation range including at least a portion of a snap-down region of said actuator, said method comprising manipulating a forced resonant frequency of said plunger of said actuator, such that said plunger is prevented from entering a snap-down condition.

2. A method according to claim 1, wherein manipulating said forced resonant frequency comprises maintaining said forced resonant frequency at a substantially constant value over a fractional actuation range of said plunger.

3. A method according to claim 2, wherein maintaining said forced resonant frequency comprises maintaining said forced resonant frequency at a maximum maintainable value over said fractional actuation range.

4. A method according to claim 1, wherein manipulating said forced resonant frequency comprises maintaining said forced resonant frequency substantially at a value of a natural mechanical resonant frequency of said plunger, said forced resonant frequency being maintained at the value of said natural mechanical resonant frequency over said actuation range.

14. A method as in any of claims 1 to 11 or 12 wherein said actuator is a microelectromechanical actuator.

16. A method as in claim 14, wherein said fractional actuation range includes at least a portion of a snap-down region of said actuator.

5. A method for controlling a position of a plunger of an actuator over an actuation range including at least a portion of a snap-down region of said actuator, said method comprising:

a. employing an actuating impetus that is non-linear with displacement;

b. using displacement as the only measured feedback signal; and

,

c. keeping forced resonant frequency of said plunger of said actuator substantially constant under actuation,

whereby said plunger is prevented from entering a snap-down condition.

6. A method as in claim 5, wherein said actuating impetus is controlled by a software control algorithm.

7. A method as in claim 5, wherein said forced resonant frequency is kept substantially at a constant value over a fractional actuation range, said constant value being substantially equal to a maximum attainable oscillation frequency of said plunger under actuation over said fractional range.

8. A method as in claim 5, wherein said forced resonant frequency is maintained substantially equal to the natural mechanical resonant frequency of said plunger.

9. A method as in claim 6 comprising imposing a constant actuation gradient on said actuator as long as a desired actuating signal to said actuator is constant.

10. A method as in claim 9, wherein the forced resonant frequency is substantially equal to a maximum attainable oscillation frequency of said plunger under actuation over a fractional actuation range.

11. A method as in claim 9 wherein said forced resonant frequency is substantially equal to a natural resonant frequency of said plunger.

17. A method as in claim 5 wherein the plunger comprises a cantilever and controlling the actuator comprises deflecting the cantilever.

18. A method as in claim 17 wherein the cantilever comprises a micromachined cantilever and deflecting the cantilever comprises applying an electrostatic potential between the cantilever and an electrode.

19. A method as in claim 5 wherein controlling the actuator comprises separately and concurrently controlling a displacement of the plunger and a slope of the actuating impetus with respect to the displacement of the plunger.

12. A method for controlling an actuator over an actuation range, said method comprising

actuating the plunger of said actuator using one of electromagnetic and electrostatic force to provide an actuating force;

measuring a plunger displacement as a feedback signal;

obtaining a first calibration relationship of plunger displacement as a function of activating impetus;

obtaining a second calibration relationship of an actuation gradient as a function of the plunger displacement, said actuation gradient being chosen to impose a constant forced resonant frequency on said plunger at each displacement; and

,

keeping said forced resonant frequency of said plunger substantially constant over said actuation range.

13. A method as in claim 12 wherein at least one of said first calibration relationship and said second calibration relationship comprises a one-dimensional look-up table.

15. A method as in claim 12, wherein said fractional actuation range includes at least a portion of a snap-down region of said actuator.

20. A method of controlling a position of a plunger of an actuator,

wherein the plunger is subject to a linear restoring force acting to bias the plunger toward a rest position and a nonlinear actuating force acting to move the plunger away from the rest position, and the plunger is movable over an actuation range including at least a portion of a snap-down region of the actuator,

wherein, when the plunger is at an equilibrium position in the snap-down region, for a time invariant actuating force, a small displacement of the plunger away from the equilibrium position causes an increase in the actuating force greater than a corresponding increase in the restoring force,

and the method comprises:

monitoring a position of the plunger;

supplying the position of the plunger as input to a control algorithm;

dynamically varying the actuating force based on an output of the control algorithm;

wherein the dynamically varying actuating force causes a forced resonant frequency of the plunger to be such that the plunger is prevented from entering a snap-down condition.

21. A method as in claim 20 wherein monitoring a position of the plunger comprises:

measuring a plunger displacement from the rest position as a feedback signal; and

the method comprises;

obtaining a first calibration relationship of plunger displacement as a function of the actuating force; and

,

obtaining a second calibration relationship of an actuation gradient as a function of plunger displacement, the actuation gradient being chosen to impose a constant forced resonant frequency on the plunger at each displacement.