Load cell

Patent metadata

Field	Value
Publication number	US-11156511-B2
Application number	US-201916379604-A
Country	US
Kind code	B2
Filing date	Apr 9, 2019
Priority date	Apr 9, 2019
Publication date	Oct 26, 2021
Grant date	Oct 26, 2021

Abstract

The load cell for measuring a force in both push and pull includes a body assembly having a body element defining a measurement chamber with a closed end and an opposite open end, a protruding member positioned within the measurement chamber and extending from the closed end toward the open end. The load cell also includes a base assembly secured at the open end of the body element, including a base element; and a sense die attached to the base element and aligned with the protruding member, where a top surface of the sense die supports a Wheatstone bridge circuit configured to generate a signal based on a force exerted by the protruding member on the sense die. The body element, the protruding member and the base element are integrally formed from a common material which has a CTE close to the CTE of the sense die.

First claim

What is claimed is:

1. A load cell, comprising:
a body assembly comprising:
a body element defining a measurement chamber having a closed end and an opposite open end, wherein the body element comprises a protruding member positioned within the measurement chamber and extending from the closed end toward the open end,
wherein the body assembly further comprises an attachment element, wherein the attachment element, the body element, and the protruding member are integrally formed from a common material; and

a base assembly secured at the open end of the body element, wherein the base assembly comprises:
a base element; and
a sense die attached to the base element and aligned with the protruding member, wherein a top surface of the sense die supports a Wheatstone bridge circuit configured to generate a signal based at least in part on a force exerted by the protruding member on the sense die.

2. The load cell as in claim 1 , wherein the protruding member defines a first end secured at the closed end of the body element and an opposite distal end positioned adjacent the sense die, and wherein the distal end has a round and smooth tip.

3. The load cell as in claim 1 , wherein the attachment element defines a threaded portion to engage an external measurement fixture.

4. The load cell as in claim 1 , wherein the common material is characterized as having a Coefficient of Thermal Expansion (CTE) at least substantially matching a CTE of the sense die.

5. The load cell as in claim 4 , wherein the common material is Invar 42.

6. The load cell as in claim 1 , wherein the sense die comprises a single crystal silicon wafer.

7. The load cell as in claim 1 , wherein the sense die is attached to the base element with a thermally or UV cured adhesive.

8. The load cell as in claim 1 , wherein the sense die stress is recorded in the Wheatstone bridge circuit, wherein the Wheatstone bridge circuit comprises of four piezoresistive sensors, wherein an output of the Wheatstone bridge circuit is calibrated into force stored in an electrical circuitry.

9. The load cell as in claim 1 , wherein the electrical circuit is defined on one or more Printed Circuit Boards (PCBs), wherein the one or more PCBs are mounted on the base element with an adhesive.

10. The load cell as in claim 9 , wherein the one or more PCBs are mounted on the base element within the measurement chamber, and wherein the base assembly further comprises one or more electrical leads extending from the one or more PCBs and through apertures within the base element to an exterior of the load cell.

11. The load cell as in claim 1 , wherein the protruding member causes a stress in the sense die, and wherein the stress in the sense die is correlated to a force.

12. The load cell as in claim 11 , wherein the stress in the sense die correlates to both push forces and pull forces exerted from the protruding element.

13. The load cell as in claim 11 , wherein the load cell is prestressed by the protruding member exerting a force on the sense die in a zero force condition, and wherein the load cell is electronically calibrated to correlate a decrease in stress within the sense die to a pull force exerted on the load cell, and an increase in stress within the sense die to a push force exerted on the load cell.

14. The method of measuring a force of claim 11 , further comprising calibrating the base assembly by moving the protruding member to exert the force stressing the sense die at least substantially at the middle point of full sense die stress range and storing a result of calibration into an electrical circuitry.

15. The method of measuring the force of claim 14 , wherein correlating the stress to a push force or a pull force applied to the body element relative to the base assembly comprises comparing the movement with the result of calibration in the electrical circuitry.

16. A method of measuring a force, comprising:
providing a load cell comprising:
a body assembly comprising:
a body element defining a measurement chamber having a closed end and an opposite open end, wherein the body element comprises a protruding member positioned within the measurement chamber and extending from the closed end toward the open end, wherein the body assembly further comprises an attachment element, wherein the attachment element, the body element, and the protruding member are integrally formed from a common material; and

a base assembly secured at the open end of the body element, wherein the base assembly comprises:
a base element; and
a sense die attached to the base element and aligned with the protruding member, wherein a top surface of the sense die supports a Wheatstone bridge circuit configured to generate a signal based at least in part on a force exerted by the protruding member on the sense die;

monitoring a stress of the sense die caused by the force exerted by the protruding member on the sense die; and
correlating the stress to a push force or a pull force applied to the body element relative to the base assembly.

17. The method of measuring the force as claim 16 , wherein monitoring the stress of the sense die caused by a pull force comprises measuring a movement of the protruding member away from the sense die.

18. The method of measuring the force of claim 16 , wherein monitoring the stress of the sense die caused by a push force comprises measuring a movement of the protruding member toward the sense die.

19. The method of measuring the force of claim 16 , wherein the stress of the sense die is linearly proportional to the force exerted on the sense die in the full sense stress range.

Assignees

• Honeywell Int Inc

Inventors

• Wade Richard

Classifications

• G01L5/0038

  applying a pushing force · CPC title

• G01L1/18

  using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material · CPC title

• G01L9/08

  by making use of piezoelectric devices {, i.e. electric circuits therefor} · CPC title

• G01L1/2293 Primary

  of the semi-conductor type · CPC title

• G01L5/0033

  applying a pulling force · CPC title