Temperature compensated force sensor

• US 9,003,897 B2
• Filed: 05/10/2012
• Issued: 04/14/2015
• Est. Priority Date: 05/10/2012
• Status: Expired due to Fees

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Wade, Richard, Ricks, Lamar Floyd
• Primary Examiner(s): Martin, Laura
• Assistant Examiner(s): DUNLAP, JONATHAN M
• Application Number:
  US13/468,899
• Publication Number:
  US 20130298688A1
• Time in Patent Office: 1,069 Days
• Field of Search: 737/56, 737/21, 737/27, 737/08, 737/20, 737/26, 738/626.23, 738/626.27
• US Class Current: 73/862.623
• CPC Class Codes: G01L 1/18 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 Class Codes: G01L 1/26 Auxiliary measures taken, or devices used, in connection with the measurement of force, e.g. for preventing influence of transverse components of force, for preventing overload

Abstract

A force sensor may include a housing having a cavity enclosing a sense die, an actuating element and an elastomeric seal. The sense die may have a force sensing element for sensing a force applied to a surface of the sense die, and a temperature compensation circuit. The temperature compensation circuit may be located on the surface of the sense die and may be configured to at least partially compensate for the temperature sensitivity of the force sensing element. The actuating element may extend outside the housing and be used to transfer a force applied externally from the housing to the sense die. The elastomeric seal may include one or more conductive elements separated from the edge of the elastomeric seal by an insulating elastomeric material.

Claims

1. A force sensor comprising:

a housing having a cavity and a plurality of terminals, the plurality of terminals including a power supply terminal, a ground terminal, and at least one signal terminal;

a sense die located within the cavity of the housing, the sense die having;

a diaphragm with at least two piezoresistive sensing elements for sensing a deflection of the diaphragm;

a temperature compensation circuit in electrical communication with at least one of the at least two piezoresistive sensing elements;

a number of pads including a power supply pad, a ground pad and at least one signal pad;

an actuating element operably coupled to the diaphragm of the sense die, the actuating element configured to transfer a force to the diaphragm in a contact area from a source external to the housing, wherein the force applied to the diaphragm of the sense die by the actuating element is substantially non-uniform across the diaphragm, wherein a center of the contact area is not precisely aligned with a center of the diaphragm; and

an elastomeric seal positioned between the sense die and the housing, the elastomeric seal having at least two conductive regions separated by an insulating elastomeric material, wherein the at least two conductive regions are spaced from an outer peripheral edge of the elastomeric seal, at least one of the conductive regions connecting the power supply pad of the sense die with the power supply terminal of the housing, and at least another one of the conductive regions connecting the ground pad of the sense die with the ground terminal of the housing.

2. The force sensor of claim 1, wherein the temperature compensation circuit includes at least one trimmable resistor between the power supply pad of the sense die and at least one of the piezoresistive sensing elements and at least another trimmable resistor between the ground pad of the sense die and at least one of the piezoresistive sensing elements.

3. The force sensor of claim 1, wherein the temperature compensation circuit includes at least one trimmable resistor that is in series with at least one of the piezoresistive sensing elements.

4. The force sensor of claim 1, wherein the temperature compensation circuit includes at least one trimmable resistor that is in parallel with at least one of the piezoresistive sensing elements.

5. The force sensor of claim 1, wherein at least another one of the conductive regions connecting one of the at least one signal pad of the sense die with one of the at least one signal terminals of the housing.

6. The force sensor of claim 1, wherein the housing includes a base and a cover, wherein the base and cover collectively define the cavity that houses the sense die.

7. The force sensor of claim 6, wherein the cover includes an opening, wherein the actuating element extends from the diaphragm of the sense die and through the opening in the cover.

8. The force sensor of claim 1, wherein the plurality of terminals of the housing are surface mount technology (SMT) terminals.

9. The force sensor of claim 1, wherein the actuating element is spherically shaped.

10. The force sensor of claim 1, wherein the actuating element has a first end that engages the diaphragm of the sense die, wherein the first end is semi-spherical in shape.

11. The force sensor of claim 1, wherein the actuating element has a first end that engages the diaphragm of the sense die, wherein the first end is curved in shape.

12. The force sensor of claim 1, wherein the sense die includes a circuit section laterally spaced from the diaphragm of the sense die, wherein at least part of the temperature compensation circuit is located in the circuit section of the sense die.

13. The force sensor of claim 12, wherein the at least two conductive regions of the elastomeric seal are located near the corners of the elastomeric seal.

14. The force sensor of claim 1, wherein the at least two piezoresistive sensing elements are connected in a Wheatstone bridge configuration, and the temperature compensation circuit includes a first trimmable resistor in series with a first power input of the Wheatstone bridge and a second trimmable resistor in series with a second power input of the Wheatstone bridge.

15. The force sensor of claim 14, wherein at least one of the first resistor and the second resistor is trimmable.

16. The force sensor of claim 1, wherein the at least two conductive regions are spaced from all outer peripheral edges of the elastomeric seal.

17. A temperature compensated force sensor comprising:

a housing including one or more electrical connections;

a sense die having a first side and a second opposite side, the sense die defining a diaphragm with a center, the first side of the sense die supporting at least one force sensing element for sensing a force applied to the diaphragm, one or more electrical connecting pads, and a temperature compensation circuit that includes one or more trimmable resistors that are in electrical communication with one or more of the force sensing elements;

an actuating element movable along an axis of movement for transferring an external force to the diaphragm, wherein the axis of movement of the actuating element is not precisely aligned with the center of the diaphragm; and

an elastomeric seal having two or more conductive regions, wherein the conductive regions are configured to provide an electrical connection between the one or more electrical connecting pads of the sense die and the one or more electrical connections of the housing.

18. A force sensor comprising:

a housing having a surface mount technology (SMT) package including electrical connections;

a sense die housed by the housing, the sense die configured to sense a force and communicate at least partially temperature compensated information about the sensed force to one or more of the electrical connections of the housing;

a rigid actuator for transferring a force applied to the actuator to the sense die; and

an elastomeric seal having a top surface, a bottom surface and outer peripheral side walls extending between the top surface and the bottom surface, the elastomeric seal having conductive regions, with each of the conductive regions spaced inward from all outer peripheral side walls of the elastomeric seal and recessed from at least a portion of the top surface and the bottom surface of the elastomeric seal, at least one of the conductive regions communicating the information about the sensed applied force to at least one electrical connection of the housing.

19. The force sensor of claim 18, wherein the sense die includes a temperature compensation circuit that includes at least one configurable element.

20. The force sensor of claim 19, wherein the at least one configurable element is one or more of a fuse and a trimmable resistor.