# US 4,398,417 A · Three-axis accelerometer having flexure bearing with overload protection

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- Number: US 4,398,417 A
- Document ID: US4398417A
- Status: Granted
- Kind: A
- Application number: 06/292,543
- Filed: 1981-08-13
- Granted: 1983-08-16
- Earliest claimed: 1981-08-13
- Assignees: Rockwell International Corporation
- Inventors: Sidney G. Shutt
- Web page: https://patentgrep.com/patent/US4398417A

## CPC

- G01P 15/132: {with electromagnetic counterbalancing means}
- G01P 15/125: by capacitive pick-up
- G01P 15/18: in two or more dimensions
- G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G})

## Abstract

A proof mass for an accelerometer is electromagnetically constrained in three orthogonal directions. An array of filaments forms an elastic suspension for the proof mass to constrain it in the remaining degrees of freedom. The resulting instrument has the potential for low cost and high-accuracy operation over a wide temperature range without the use of temperature controls. The array of filaments becomes relatively compliant in all six degrees of freedom when loading exceeds a selected design load. This provides overload protection since the proof mass can be brought to a practical mechanical stop for support before excessive stress can fracture a filament.

## Claims

### Claim 1

An instrument, comprising:
a base member;
a suspended member;
elastic suspension means for maintaining the position of said suspended member relative to said base member, wherein said elastic suspension means is relatively compliant in three degrees of freedom and relatively stiff in the remaining three degrees of freedom at loads on said elastic suspension means within a selected design load; and
a mechanical stop disposed on said base sufficiently displaced from the null position of said suspended member to avoid interference between said mechanical stop and said suspended member at loads on said elastic suspension means within the selected design load;
wherein said elastic suspension means has sufficient compliance in all six degrees of freedom at loads on said elastic suspension means in excess of said selected design load to permit said suspended member to reach said mechanical stop for support without causing structural breakdown or significant bias shift in said elastic suspension means.

### Claim 2 (depends on 1)

The instrument recited in claim 1, wherein said elastic suspension means comprises a plurality of filaments held in tension between said base member and said suspended member.

### Claim 3 (depends on 2)

The instrument recited in claim 2, wherein said plurality of filaments comprises:
a set of support filaments mounted between said base and suspension members, wherein said support filaments are disposed for minimum displacement in response to lateral tensile loading; and
a set of compliant filaments mounted between said base and suspension members, wherein said compliant filaments are spring-loaded to maintain said support filaments in tension at loads on said suspension within said design load.

### Claim 4 (depends on 3)

The instrument recited in claim 3, wherein at least one of said support filaments is not in tension at loads in excess of said selected design load.

### Claim 5 (depends on 4)

The instrument recited in claim 4, wherein said filaments are disposed in pairs, each pair consisting of a support filament and a compliant filament.

### Claim 6 (depends on 5)

The instrument recited in claim 5, wherein said compliant filament is mounted substantially parallel to said support filament.