Multi-mode accelerometer

• US 5,452,612 A
• Filed: 11/30/1993
• Issued: 09/26/1995
• Est. Priority Date: 12/23/1991
• Status: Expired due to Fees

• Current Assignee: Measurement Specialties Limited (TE Connectivity Limited)
• Original Assignee: The Whitaker Corporation (Meggitt PLC)
• Inventors: Smith, Peter R., Henry, John C.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): Brock, Michael J.
• Application Number:
  US08/159,350
• Time in Patent Office: 665 Days
• Field of Search: 73/517 R, 73/517 A, 73/517 AV, 310/328, 310/329, 310/330, 310/338, 310/366, 360/60, 369/33
• US Class Current: 73/514.34
• CPC Class Codes: G01P 15/0922 of the bending or flexing mode type
• CPC Class Codes: G01P 15/18 in two or more dimensions

Abstract

An accelerometer has a piezoelectric transducer which produces electrical signals in response to its deflection and comprises an elongated, continuous beam of generally flat configuration and narrow cross section to provide a bending axis which facilitates deflection of the free ends in response to shock in either or both of the linear and torsional modes. The beam is supported intermediate its ends by a mount, with the free ends of the beam preferably extending equidistantly in opposite directions from the mount so that the free ends of the beam deflect in the same direction in response to shock in the linear mode, e.g., along the X axis, and they deflect in opposite directions in response to shock in the torsional mode, i.e., about the Z axis.

Claims

1. A sensor for an accelerometer responsive to shock in a first linear mode along an X axis, and in a torsional mode about a Z axis perpendicular to said X axis, said sensor comprising:

a) an elongated beam structure extending longitudinally in a direction perpendicular to said X and Z axes, said beam structure comprising a piezoelectric transducer which produces electrical signals in response to its deflection,

b) a mount fixedly supporting said beam structure at a point intermediate its ends, the free ends of said beam structure extending equidistantly in opposite directions from said mount, said free ends of said beam structure deflecting in the same direction in response to shock in said first linear mode and deflecting in opposite directions in response to shock in said torsional mode,

c) said beam structure comprising a piezoelectric material and having a pair of output electrodes on one side thereof, and a continuous, electrically conductive member extending along the length of said beam structure on the other side thereof providing a common conductor, said common conductor extending on both sides of the mount,

d) said mount including conductive elements for the respective output electrodes and common conductor in electrical contact therewith, said conductive elements engaging said beam structure on opposite sides thereof,

e) whereby different signals are produced in response to linear acceleration and torsional acceleration.

2. A sensor as in claim 1 wherein the beam structure is of generally flat configuration and narrow cross section to facilitate deflection of the free ends in response to shock in said linear and torsional modes.

3. A sensor as in claim 2 wherein said X axis is in a plane normal to said Z axis, wherein the respective said sides of said beam structure are at an acute angular inclination to said plane, whereby said beam structure is also responsive to shock in a linear mode along said Z axis.

4. A sensor as in claim 1 wherein said conductive elements are fingers clasping said beam structure when engaging the said opposite sides thereof.

5. A sensor as in claim 1, wherein said sensor is within a housing and said mount is secured in stationary position on said housing, said housing being fixedly mountable on a non-rotating object exposed to shock for monitoring the acceleration of said object in said linear and torsional modes.

6. A sensor as in claim 1 wherein said piezoelectric material is a polymer material.

7. A sensor as in claim 1 wherein the electrically conductive member comprises beryllium copper material.

8. A sensor as in claim 7 wherein the electrically conductive member and piezoelectric polymer material comprise a laminate, and said output electrodes on said one side of said beam structure are formed at both opposite end portions thereof by spaced-apart depositions of electrically conductive material on one surface of said laminate.

9. A sensor as in claim 8 wherein there are two conductive elements on said mount to engage and provide leads to said output electrodes, and a third conductive element to engage and provide a lead to said common conductor.

10. A sensor according to claim 1 wherein said mount comprises three orthogonally oriented mounting surfaces for the respective X, Y and Z axes, and wherein there are three beam structures, each comprising an element of continuous piezoelectric polymer material mounted at a point intermediate its ends on one of the respective mounting surfaces.

11. A sensor for an accelerometer responsive to shock in a first linear mode along an X axis, and in a torsional mode about a Z axis perpendicular to said X axis, said sensor comprising:

a) an elongated beam structure extending longitudinally in a direction perpendicular to said X and Z axes, said beam structure comprising a piezoelectric transducer which produces electrical signals proportional to its deflection,

b) a mount supporting said beam structure intermediate its ends, the free ends of said beam structure extending in opposite directions from said mount, said free ends of said beam structure deflecting in the same direction in response to shock in said first linear mode and deflecting in opposite directions in response to shock in said torsional mode,

c) said beam structure comprising a piezoelectric polymer material, one side thereof having spaced-apart deposits of electrically conductive material at its end portions providing a pair of output electrodes, and the other side thereof having on its surface for the length thereof a continuous layer of conductive material providing a common conductor,

d) said mount comprising conductive elements engaging the respective electrodes and common conductor to provide electrical leads thereto and for securely clasping said beam structure,

e) said beam structure producing signals with voltage potential proportional to linear acceleration in response to shock in the direction of the X axis, and producing signals with voltage potential proportional to angular acceleration in response to torsional shock about said Z axis,

f) whereby different signals are produced in response to linear acceleration and torsional acceleration.

12. A sensor in accordance with claim 11 wherein the piezoelectric polymer material comprises a piezoelectric polymer sheet material.

13. An accelerometer sensor comprising:

a) an elongated beam structure comprising a central portion disposed between two outboard portions, said beam structure comprising a piezoelectric transducer which produces electrical signals in response to deflection, said transducer extending across the central portion into both outboard portions;

b) said beam structure comprising a pair of output electrodes on one side thereof, and a continuous, common conductor on the other side thereof, said output electrodes each positioned on a respective one of the outboard portions, said common conductor extending across the central portion into both outboard portions;

c) a mount comprising first, second and third conductive elements, said first and second conductive elements in electrical contact with the respective output electrodes at said one side of the beam structure, said third conductive element in electrical contact with the common conductor at said other side of the beam structure, opposite said first and second conductive elements, said conductive elements fixedly supporting the beam structure in position.

14. A sensor as in claim 13 further comprising a housing comprising a base, wherein the conductive elements each comprise respective first and second portions, said first portions extending adjacent the base, said second portions extending away from the base and engaging the beam structure therebetween to mount the beam structure in position in the housing.

15. A sensor as in claim 14 wherein the second portions comprise respective fingers which grip the beam structure therebetween.