Self-testable micro-accelerometer and method

• US 5,445,006 A
• Filed: 10/18/1993
• Issued: 08/29/1995
• Est. Priority Date: 06/22/1989
• Status: Expired due to Fees

• Current Assignee: IC Sensors, Inc. (TE Connectivity Limited)
• Original Assignee: IC Sensors, Inc. (TE Connectivity Limited)
• Inventors: Terry, Stephen C., De Bruin, Diederik W., Allen, Henry V.
• Primary Examiner(s): RAEVIS, ROBERT R
• Application Number:
  US08/138,349
• Time in Patent Office: 680 Days
• Field of Search: 73/1 D, 73/1 DV, 73/2, 73/517 R
• US Class Current: 73/1.38
• 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, means for producing 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. A method of testing the temperature insensitivity of an accelerometer having a housing, a deformable member formed in said housing movable relative to said housing in response to an applied force, said deformable member including a conductive mass formed thereon, 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 attached to said housing and said deformable member for sensing movement of said mass, comprising the steps of:

subjecting said accelerometer to a plurality of different temperatures over a substantial range of temperature,

maintaining a predetermined initial distance between said capacitive plate and said mass, and

applying a predetermined potential difference between said capacitive plate and said mass producing substantially the same electrostatic acceleration between said capacitive plate and said mass for each of said plurality of temperatures.

2. A method of testing the damping characteristic over frequency of an accelerometer having a housing, a deformable member formed in said housing movable relative to said housing in response to an applied force, said deformable member including a conductive mass formed thereon, 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, at least one piezoresistive element attached to said housing and said deformable member for sensing movement of said mass, and a frame for supporting said deformable member and said mass, a base supporting said frame underlying said deformable member and having a first air gap therebetween, a cap overlying said deformable member and having a second air gap therebetween, and said first and second air gaps providing squeeze film damping for movements of said mass, and further being sized so that said base and said cap provide mechanical stops for movements of said mass, comprising the steps of:

applying a potential difference between said mass and said capacitive plate to produce movement of said mass at a predetermined frequency; and

measuring the degree of movement of said mass over time.

3. A method of testing the frequency response of an accelerometer having a housing, a deformable member formed in said housing movable relative to said housing in response to an applied force, said deformable member including a conductive mass formed thereon, 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, at least one piezoresistive element attached to said housing and said deformable member for sensing movement of said mass, the housing comprising a frame for supporting said deformable member and said mass, a base supporting said frame underlying said deformable member and said mass, a base supporting said frame underlying said deformable member and having a first air gap therebetween, and a cap overlying said deformable member and having a second air gap therebetween, wherein said first and second air gaps provide squeeze film damping for movements of said mass, and further being sized so that said base and said cap provide mechanical stops for movements of said mass, comprising the steps of:

applying a potential difference between said mass and said capacitive plate to produce movement of said mass at a predetermined frequency; and

measuring the degree of movement of said mass over time.

4. A method of testing frequency response in accordance with claim 3 wherein said applying step applies a potential difference signal to produce movement of said mass over a predetermined range of frequencies.

5. A method of testing frequency response in accordance with claim 4 wherein said applying step causes the movement of said mass to sweep in frequency over said predetermined range of frequencies.

6. A method of testing frequency response in accordance with claim 5 wherein said measuring step measures the degree of movement of said mass over said sweep of frequencies.

7. A method of testing frequency response in accordance with claim 4 wherein said measuring step measures the degree of movement of said mass over said range of frequencies.

8. A method for determining the operability of an accelerometer having a housing, a deformable member formed in said housing movable relative to said housing in response to an applied force, said deformable member including a conductive mass suspended by flexures formed in said housing, means for electrostatically moving said mass with respect to said housing, and means for sensing a movement of said mass, the method comprising the steps of:

(a) applying an operability testing potential difference between said mass and said housing, thereby electrostatically moving said mass with respect to said housing; and

(b) sensing the movement of said mass.

9. A method for determining the operability of an accelerometer having a housing, a diaphragm in said housing movable relative to said housing in response to an applied force, said diaphragm including a conductive mass suspended by flexures, means for electrostatically moving said mass with respect to said housing, and means for sensing a movement of said mass, the method comprising the steps of:

(a) applying an operability testing potential difference between said mass and said housing, thereby electrostatically moving said mass with respect to said housing; and

(b) sensing the movement of said mass.

10. A method for determining the operability of an accelerometer having a housing, a conductive mass suspended in said housing movable relative to said housing in response to an applied force, said conductive mass being suspended with flexures, means for electrostatically moving said mass with respect to said housing, and means for sensing a movement of said mass, the method comprising the steps of:

(a) applying an operability testing potential difference between said mass and said housing, thereby electrostatically moving said mass with respect to said housing; and

(b) sensing the movement of said mass.