Force compensated comb drive

• US 7,302,848 B2
• Filed: 03/10/2005
• Issued: 12/04/2007
• Est. Priority Date: 03/10/2005
• Status: Active Grant

• Current Assignee: Charles Stark Draper Laboratory Incorporated
• Original Assignee: Charles Stark Draper Laboratory Incorporated
• Inventors: Elliott, Richard, Weinberg, Marc S., Kourepenis, Anthony S., Daley, Steven
• Primary Examiner(s): Williams; Hezron
• Assistant Examiner(s): BELLAMY, TAMIKO D
• Application Number:
  US11/076,649
• Publication Number:
  US 20060201250A1
• Time in Patent Office: 999 Days
• Field of Search: 735/041.6, 735/041.8, 735/041.4, 735/143.2
• US Class Current: 73/504.16
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: H02N 1/008 Laterally driven motors, e.g. of the comb-drive type

Abstract

A force compensated comb drive for a microelectromechanical system includes a MEMS mechanism for providing an output signal representative of a physical quantity; a comb drive for actuating the MEMS mechanism; a comb drive circuit for providing a drive signal to the comb drive for developing a predetermined displacement applied by the comb drive to the MEMS mechanism; an automatic gain control responsive to a change in the force to provide a correction signal to the comb drive circuit to maintain the predetermined motion; and a compensation device responsive to the correction signal for adjusting the output signal of the MEMS mechanism to compensate for errors in the output signal due to a change in the predetermined force.

Claims

1. A force compensated comb device for microelectromechanical system (MEMS) comprising:

a MEMS mechanism for providing an output signal representative of a physical quantity;

a comb drive for actuating said MEMS mechanism;

a comb drive circuit for providing a drive signal to said comb drive for developing a force applied by said comb drive to said MEMS mechanism to effect a predetermined amplitude of displacement;

an automatic gain control responsive to a change in said predetermined force to provide a correction signal to said comb drive circuit to maintain said predetermined force; and

a compensation drive responsive to said correction signal for adjusting the output signal of said MEMS mechanism to compensate for errors in said output signal due to a change in said force.

2. The MEMS system of claim 1 in which said MEMS mechanism is a gyroscope.

3. The MEMS system of claim 1 in which said MEMS mechanism is a tuning fork gyroscope.

4. The MEMS system of claim 1 in which said MEMS mechanism is a temperature sensor.

5. The MEMS system of claim 1 in which said MEMS mechanism is a pressure sensor.

6. The MEMS system of claim 1 in which said compensation device includes microprocessor for executing an nth order constant coefficient equation.

7. The MEMS system of claim 6 in which said microprocessor is programmed to solve the equations wherein a rate output compensated for AGC effects is a function of uncompensated output voltage and an automatic gain control measured voltage.

8. The MEMS system of claim 7 in which said microprocessor is programmed to solve the equations

{circumflex over (Ω

)}₁=B(V_AGC)+S(V_AGC)V_g

where {circumflex over (Ω

)}₁ is a rate output compensated for AGC effects, V_g is raw (uncompensated) gyroscope output voltage, and V_AGC is an automatic gain control measured voltage;

B(V_AGC)=B₀+B₁V_AGC+B₂V_AGC²+B₃V_AGC³+ . . .

where B(V_AGC) is a modeled bias, a function of the measured AGC voltage; and

S(V_AGC)=S₀+S₁V_AGC+S₂V_AGC²+S₃V_AGC³+ . . .

where S(V_AGC) is a modeled scale factor, a function of the measured AGC voltage.