Self-testable micro-accelerometer

• US 5,253,510 A
• Filed: 07/17/1992
• Issued: 10/19/1993
• Est. Priority Date: 06/22/1989
• Status: Expired due to Fees

• Current Assignee: I C Sensors
• Original Assignee: I C Sensors
• Inventors: Allen, Henry V., Terry, Stephen C., De Bruin, Diederik W.
• Primary Examiner(s): RAEVIS, ROBERT R
• Application Number:
  US07/915,792
• Time in Patent Office: 459 Days
• Field of Search: 73/515, 73/516 R, 73/516 LM, 73/517 R, 73/517 A, 73/517 B, 73/526, 73/1 D, 73/1 B, 73/1 C, 73/1 DV
• US Class Current: 73/514.18
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

An apparatus and method of operation for a self-testable accelerometer having a housing, a diaphragm for detecting movement in response to an applied force, a mass on the diaphragm, at least one capacitive plate attached to the housing and disposed such that a potential difference between the capacitive plate and the mass causes a movement of the mass, electrodes for applying a potential difference between the mass and the capacitive plate, and at least one piezoresistive element attached to the housing and the diaphragm for sensing movement of the mass. The accelerometer'"'"'s housing comprises a frame, a base and a cap with air gaps providing squeeze film damping and mechanical stops for inhibiting movements of the mass. The combination of the capability to electrostatically produce a movement of the mass and the piezoresistive sensing of that movement allows testing and calibration of the accelerometer at any stage in its manufacture or deployment without the need for external equipment such as shakers.

Claims

1. An accelerometer comprising:

a housing;

a beam mounted in said housing movable relative to said housing in response to an applied force, said beam including a conductive mass formed on said beam;

at least one capacitive plate attached to said housing and disposed such that a potential difference between said capacitive plate and said mass causes a movement of said mass;

means for producing a potential difference between said mass and said capacitive plate; and

at least one piezoresistive element connecting said housing and said beam for sensing movement of said mass relative to said housing wherein said housing comprises;

a frame for supporting said beam and said mass;

a base supporting said frame underlying said beam and having a first air gap therebetween;

a cap overlying said beam and having a second air gap therebeween; and

said first and second air gaps providing squeeze film damping for movements of said mass on said beam, and further being sized so that said base and said cap provide mechanical stops for movements of said mass.

2. The accelerometer of claim 1 further comprising at least one electrode mounted on said base.

3. The accelerometer of claim 1 wherein said cap and said base are electronically isolated from said conductive mass and wherein said base is electrically grounded.

4. The accelerometer of claim 1 wherein said beam is connected to said frame by at least one flexure, said beam and said flexure being disposed so that a straight line through the center of mass of said mass and the center of said flexure is approximately 3°

to 8°

from flat.

5. An accelerometer comprising:

a housing;

a beam mounted in said housing movable relative to said housing in response to an applied force, said beam including a conductive mass formed on said beam;

at least one capacitive plate attached to said housing and disposed such that a potential difference between said capacitive plate and said mass causes a movement of said mass;

at least one piezoresistive element connecting said housing and said beam for sensing movement of said mass relative to said housing;

means for producing a first potential difference and a second potential difference, different from said first potential difference, between said mass and said capacitive plate;

means for sampling an output generated by said at least one piezoresistive element during the production of said first potential difference between said mass and said capacitive plate; and

means for sampling an output generated by said at least one piezoresistive element during the production of said second potential difference between said mass and said capacitive plate.

6. An accelerometer comprising

a housing;

a beam mounted in said housing movable relative to said housing in response to an applied force, said beam including a conductive mass formed on said beam;

at least one capacitive plate attached to said housing and disposed such that a potential difference between said capacitive plate and said mass causes a movement of said mass;

means for producing a first potential difference between said mass and said capacitive plate;

means for producing a second potential difference, different from said first potential difference, between said mass and said capacitive plate; and

at least one piezoresistive element connecting said housing and said beam for sensing movement of said mass relative to said housing caused by a change of applied potential difference from said first potential difference to said second potential difference.