Diagnostic test for a resonant micro electro mechanical system

• US 6,792,792 B2
• Filed: 05/31/2002
• Issued: 09/21/2004
• Est. Priority Date: 06/04/2001
• Status: Expired due to Fees

• Current Assignee: Kelsey-Hayes Co. (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Original Assignee: Kelsey-Hayes Co. (Zeppelin - Stiftung der Stadt Friedrichshafen)
• Inventors: Babala, Michael L.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): FAYYAZ, NASHMIYA SAQIB
• Application Number:
  US10/161,411
• Publication Number:
  US 20020178813A1
• Time in Patent Office: 844 Days
• Field of Search: 73/13--, 735/041.2, 735/041.6, 735/040.2
• US Class Current: 73/1.38
• CPC Class Codes: G01C 19/5607 using vibrating tuning forks double-ended tuning forks using planar vibrating masses suspended at opposite ends G01C19/5719
• CPC Class Codes: G01C 25/00 Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass testing, calibrating or compensating compasses G01C17/38

Abstract

A balanced resonant micro electromechanical system angular rate sensor includes a feedback control loop that generates a null signal to rebalance the sense element to cancel any a Coriolis force induced displacement of the proof mass. The null signal is proportional to the Coriolis force and is used as the sensor output signal. A test signal is injected into the null signal feedback control loop. The resulting sensor output signal is a function of the test signal. If there is no change in the output signal following the injection of the test signal or if the output signal resulting from the test signal exceeds a predetermined threshold, the sensor is defective. Because the test signal is used to cancel the proof mass displacement, the test verifies operation of the sensor element.

Claims

1. A device for measuring angular rate comprising:

a resonant sensor element;

a first feedback control device connected to said resonant sensor element, said first feedback control device operative to resonate said resonant sensor element;

a second feedback control device connected to said resonant sensor element, said second feedback control device operative to sense the presence of a secondary mode signal generated by said resonant sensor element in response to a Coriolis force, said second feedback control device being responsive to said secondary mode signal to generate a null signal that cancels said secondary mode signal and to generate a first output signal that is proportional to said null signal; and

a test device connected to said second feedback control device, said test device operative to inject a test signal to said second feedback loop that is passed through said resonant sense element, said test signal causing a second output signal that is proportional to said test signal, said test device further operative to compare said first and second output signals and to set an error flag if there is no difference between said first and second output signals resulting from said test signal.

2. The angular rate measuring device according to claim 1 wherein said test device is further operative to compare said second output signal resulting from said test signal to a first predetermined threshold and to set an error flag if said second output signal exceeds said first threshold.

3. The angular rate measuring device according to claim 2 wherein said first threshold is function of said test signal.

4. The angular rate measuring device according to claim 2 wherein said test device is included in an electronic control unit for a vehicle stability system.

5. The angular rate measuring device according to claim 1 wherein said test device is further operative to calculate a change between said first and second output signals due to said test signal and to set an error flag if the absolute value of said change is greater than a second predetermined threshold.

6. A method for testing an angular rate measuring device comprising the steps of:

(a) providing a resonant sensor element, a first feedback control device connected to the resonant sensor element that is operative to resonate the resonant sensor element, and a second feedback control device connected to the resonant sensor element that is operative to sense the presence of a secondary mode signal generated by the resonant sensor element in response to a Coriolis force, the second feedback control device being responsive to the secondary mode signal to generate a null signal that cancels the secondary mode signal and to generate an output signal that is proportional to said null signal;

(b) resonating the resonant sensor element to produce a first output signal;

(c) injecting a test signal into the second feedback control device that is passed through the resonant sense element to produce a second output signal;

(d) comparing the resulting first output signal to the second output signal produced in step (c) to determine a change between the first and second output signals; and

(e) setting an error flag if any change between the first and second output signals is less than a predetermined minimum threshold.

7. A device for measuring angular rate comprising:

a resonant sensor element;

a first feedback control device connected to said resonant sensor element, said first feedback control device operative to resonate said resonant sensor element;

a second feedback control device connected to said resonant sensor element, said second feedback control device operative to sense the presence of a secondary mode signal generated by said resonant sensor element in response to a Coriolis force, said second feedback control device being responsive to said secondary mode signal to generate a null signal that cancels said secondary mode signal and to generate a first output signal that is proportional to said null signal; and

a test device connected to said second feedback control device, said test device operative to inject a test signal in to said second feedback loop that is passed through said resonant sense element, said test signal causing a second output signal that is proportional to said test signal, said test device further operative to compare said first and second output signals and to set an error flag if a difference between said first and second output signals resulting from said test signal is less than a predetermined minimum threshold.

8. A method for testing an angular rate measuring device comprising the steps of:

(a) providing a resonant sensor element, a first feedback control device connected to the resonant sensor element that is operative to resonate the resonant sensor element, and a second feedback control device connected to the resonant sensor element that is operative to sense the presence of a secondary mode signal generated by the resonant sensor element in response to a Coriolis force, the second feedback control device being responsive to the secondary mode signal to generate a null signal that cancels the secondary mode signal and to generate an output signal that is proportional to said null signal;

(b) resonating the resonant sensor element to produce a first output signal;

(c) injecting a test signal into the second feedback control device that is passed through the resonant sense element to produce a second output signal;

(d) comparing the resulting second output signal to the first output signal produced in step (b) to determine a change between the first and second output signals; and

(e) setting an error flag if the output signal change is zero.

9. The method according to claim 8 further including, subsequent to step (e), comparing the absolute value of the second output signal to a first predetermined threshold and then setting the error flag if the absolute value of the second output signal exceeds the first predetermined threshold.

10. The method according to claim 9 wherein the first threshold is a function of the test signal.

11. The method according to claim 8 further including, subsequent to step (e), comparing the absolute value of the change between the first and second output signals to a second predetermined threshold and then setting the error flag if the absolute value of the output signal change exceeds the second predetermined threshold.

12. The method according to claim 9 wherein the angular rate measuring device is included in a vehicle stability system.