Active microaccelerometer

• US 5,233,874 A
• Filed: 08/19/1991
• Issued: 08/10/1993
• Est. Priority Date: 08/19/1991
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Eddy, David S., Hicks, David B., Putty, Michael W., Chang, Shih-Chia
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US07/746,548
• Time in Patent Office: 722 Days
• Field of Search: 73/517 AV, 73/517 R, 73/DIG. 1
• US Class Current: 73/514.29
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/097 by vibratory elements
• CPC Class Codes: G01P 15/133 with piezoelectric counterbalancing means

Abstract

A microaccelerometer is provided for use in on-board automotive safety control and navigational systems. The microaccelerometer includes a central support body which is supported upon a backing chip, a peripheral proof mass which circumscribes the central support body, and at least one pair of microbridges, each of which are attached to both the central support body and the peripheral proof mass. The pair of microbridges extend outwardly in opposite directions from the central support body such that a longitudinal axis through each of the microbridges forms a common axis through the central support body. The microbridges are attached to the peripheral proof mass at the end opposite the central support body so as to suspend the peripheral proof mass circumferentially about the central support body and above the backing chip. Piezoelectric drivers and sensors are provided, respectively, for exciting the microbridges at their resonant frequencies, and for detecting changes in the resonant frequencies of the microbridges which occur as a function of acceleration of the peripheral proof mass. The sensors are connected to a feedback circuit which amplifies and buffers their output and provides feedback to the drivers to properly maintain the microbridges at their resonant frequencies.

Claims

1. An accelerometer comprising:

a backing chip, said backing chip having at least one upwardly extending support means;

a central support body supported by said support means above said backing chip;

a peripheral proof mass circumscribing said central support body with a gap provided along the entire perimeter between aid central support body and said peripheral proof mass;

at least two pairs of bridges for suspending said peripheral proof mass from said central support body, each bridge of said pairs of bridges spanning said gap between said central support body and said peripheral proof mass, each said pair of bridges having a first bridge with one end attached to one side of said central support body and second bridge attached to an opposite side of said central support body, said first and second bridges extending oppositely from said central support body and being attached at an opposite end to said peripheral proof mass so as to suspend said peripheral proof mass circumferentially around said central support body and above said backing chip, said first and second bridges being positioned on said central support body such that a longitudinal axis through each said first and second bridges forms a common axis through said central support body, said common axis of a first pair of bridges being perpendicular to said common axis of a second pair of bridges;

a piezoelectric drive means on one end of each said bridge, each of said piezoelectric drive means vibrating at the resonant frequency of the bridge on which it is disposed, said resonant frequency changing as a function of an extension or compression of said bridge as a consequence of acceleration of said peripheral proof mass, said piezoelectric drive means being part of a film of piezoelectric material on said central support body and said bridge;

a piezoelectric sensing means on the opposite end of each said bridge, said piezoelectric sensing means detecting a change in resonant frequency of each said bridge as a function of an extension or compression of said bridge as a consequence of acceleration of said peripheral proof mass, said piezoelectric sensing means being part of a film of piezoelectric material on said central support body and said bridge;

circuitry means for amplifying and buffering said output of each said piezoelectric sensing means, said circuitry means providing an indication of acceleration in a direction along each said common axis, each said circuitry means providing feedback to each said piezoelectric drive electrode for compensating for said change so as to maintain each said bridge at its corresponding resonant frequency;

at last one stop to prevent deflection of said peripheral proof mass beyond a predetermined distance in a direction perpendicular to said common axes; and

a plurality of constraining bridges extending between said central support body and said peripheral proof mass, said plurality of constraining bridges acting to suppress rotation of said peripheral proof mass relative to said central support body and to help suppress displacement of said peripheral proof mass in said direction perpendicular to said longitudinal axes.

2. An accelerometer as recited in claim 1 wherein said pairs of bridges are disposed on a first surface of said accelerometer, and said plurality of constraining bridges are disposed on a surface of said accelerometer opposite said first surface.

3. An accelerometer as recited in claim 1 wherein said central support body is formed from single crystal silicon.

4. An accelerometer as recited in claim 1 wherein said piezoelectric drive means and said piezoelectric sensing means comprise a film of zinc oxide.