Browse Prior Art Database

Force Sensor

IP.com Disclosure Number: IPCOM000093272D
Original Publication Date: 1967-Aug-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 94K

Publishing Venue

IBM

Related People

Stewart, WR: AUTHOR [+2]

Abstract

In A, the force sensor is an accelerometer contained in hermetically sealed housing 1. Mass 2 is supported by flexure member 3. Mass 2 mechanically loads AT-cut twin crystals 4 and 5 along their respective edges by point contacts 6 and 7, respectively. Mass 2 and member 3 are arranged in a T-bar relationship which is biased by spring bias assembly 8 to preload crystals 4 and 5 symmetrically under no-load conditions, i.e., zero applied external forces. This configuration provides a lever arrangement shown schematically in B. W equals weight of proof mass. L1 equals lever arm, pivot to proof mass center of gravity. L is force exerted by crystal 4. R is force exerted by crystal 5. L2 and L3 equal lever arms, pivot to crystals. R is preload force.

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Force Sensor

In A, the force sensor is an accelerometer contained in hermetically sealed housing 1. Mass 2 is supported by flexure member
3. Mass 2 mechanically loads AT-cut twin crystals 4 and 5 along their respective edges by point contacts 6 and 7, respectively. Mass 2 and member 3 are arranged in a T-bar relationship which is biased by spring bias assembly 8 to preload crystals 4 and 5 symmetrically under no-load conditions, i.e., zero applied external forces. This configuration provides a lever arrangement shown schematically in B. W equals weight of proof mass. L1 equals lever arm, pivot to proof mass center of gravity. L is force exerted by crystal 4. R is force exerted by crystal 5. L2 and L3 equal lever arms, pivot to crystals.

R is preload force. Crystals 4 and 5 provide output signals which are fed to an A to D frequency converter show n as modules 9 and
10. The converter measures the frequency difference between the output signals of crystals 4 and 5.

Under no-load conditions, crystals 4 and 5 provide equal, nominal high- frequency output signals. Consequently, no output signal appears at output 11. When the sensor experiences a force along direction 12, mass 2 is displaced about pivot 13 and in a direction proportional to the magnitude and direction of the applied force. Thus, the load on one crystal is increased and the load on the other is creased. As a consequence, the output signal of one crystal decreases in frequency and the other increases pro...