Silicon force sensor

• US 9,383,270 B1
• Filed: 10/28/2013
• Issued: 07/05/2016
• Est. Priority Date: 10/28/2013
• Status: Active Grant

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Crenshaw, Thomas B., Nishida, Erik E., Burnett, Damon J., Galambos, Paul C., Lantz, Jeffrey W.
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): Plumb, Nigel
• Application Number:
  US14/064,573
• Time in Patent Office: 981 Days
• Field of Search: 738/620.45, 738/62
• US Class Current: 1/1
• 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
• CPC Class Codes: G01L 5/0028 Force sensors associated with force applying means G01L5/0052, G01L5/0057, G01L5/0061 take precedence

Abstract

The various technologies presented herein relate to a sensor for measurement of high forces and/or high load shock rate(s), whereby the sensor utilizes silicon as the sensing element. A plate of Si can have a thinned region formed therein on which can be formed a number of traces operating as a Wheatstone bridge. The brittle Si can be incorporated into a layered structure comprising ductile and/or compliant materials. The sensor can have a washer-like configuration which can be incorporated into a nut and bolt configuration, whereby tightening of the nut and bolt can facilitate application of a compressive preload upon the sensor. Upon application of an impact load on the bolt, the compressive load on the sensor can be reduced (e.g., moves towards zero-load), however the magnitude of the preload can be such that the load on the sensor does not translate to tensile stress being applied to the sensor.

Claims

1. A load sensing system, comprising:

a load sensor comprising a piezoresistive sensor; and

a load application component configured to;

locate the load sensor on a supporting structure;

apply a compressive preload to the load sensor resulting in application of a compressive load to the piezoresistive sensor; and

under an operational load, effect a relaxation in the compressive load on the piezoresistive sensor.

2. The load sensing system of claim 1, wherein the load application component comprises a nut and a bolt, the bolt comprising a bolthead, a boltshaft and a threaded portion of the boltshaft onto which the nut can be attached.

3. The load sensing system of claim 2, further comprising a first washer, a second washer and a third washer located on the boltshaft.

4. The load sensing system of claim 3, wherein:

a hole extends through the supporting structure from an outer to an inner surface of said structure;

the bolt is positioned such that the bolthead is situated proximal the outer surface and the boltshaft extends through the hole beyond the inner surface;

the first washer is situated between the bolthead and the outer surface;

the load sensor is situated on the boltshaft between the nut and the inner surface;

the second washer is situated on the boltshaft between the inner surface and the load sensor; and

the third washer is situated on the boltshaft between the load sensor and the nut.

5. The load sensing system of claim 1, wherein the piezoresistive sensor comprises a plate of silicon.

6. The load sensing system of claim 5, wherein the silicon plate includes a central region that has been thinned such that in use, strain is concentrated therein.

7. The load sensing system of claim 6, wherein the piezoresistive sensor includes at least one conductive pattern forming a Wheatstone bridge.

8. The load sensing system of claim 7, wherein the conductive pattern is composed, at least in part, of polysilicon.

9. The load sensing system of claim 7, wherein the conductive pattern is conformed such that a difference between the compressive preload and the operational load causes a measurable change in resistance across the Wheatstone bridge.

10. The load sensing system of claim 1, wherein the load sensor further comprising at least one washer, a die mount, and an outer shell, the die mount and outer shell are formed from steel, and the at least one washer is formed from at least one of aluminum, copper, nylon, a glass-reinforced epoxy laminate sheet, or a polyimide.

11. The load sensing system of claim 10, wherein the washer is located between the die mount and an inner surface of the outer shell, and the die mount includes an opening, the piezoresistive sensor is located in the opening such that a portion of the piezoresistive sensor extends beyond an outer surface of the die mount and contacts the at least one washer.

12. The load sensing system of claim 1, further comprising a load measurement component configured to measure a difference between the compressive preload and the operational load.

13. A load sensing system comprising:

a load sensor setup; and

a load application component configured to;

apply a compressive preload to the load sensor setup resulting in an application of a compressive load to the sensor; and

under an operational load, effect a relaxation in the compressive load on the sensor.

14. The load sensing system of claim 13, wherein the load application component comprises:

a bolt, wherein the bolt comprises a bolthead and a boltshaft;

a housing, wherein the bolthead rests on a portion the housing and the boltshaft extends through a hole in the housing; and

at least one nut, wherein the load sensor setup is between the bolthead and the at least one nut, and wherein the at least one nut is fastened to the boltshaft such that the bolt is secured to the housing.

15. The load sensing system of claim 14, further comprising a first washer between the bolthead and the portion of the housing.

16. The loading sensing system of claim 14, further comprising a second washer between a terminus of the housing and the at least one nut.

17. A load sensing system comprising:

a load sensor setup comprising a sensor; and

a load application component configured to;

induce a compressive load to the sensor; and

under an operational load, effect a relaxation in the compressive load on the sensor.

18. The load sensing system of claim 17, wherein the load application component comprises:

a bolt, wherein the bolt comprises a bolthead and a boltshaft;

a housing, wherein the bolthead rests on a portion the housing and the boltshaft extends through a hole in the housing; and

at least one nut, wherein the at least one nut is fastened to the boltshaft such that the bolt is secured to the housing,

wherein the load sensor setup is between the bolthead and the at least one nut.

19. The load sensing system of claim 18, wherein a magnitude of the compressive load induced to the sensor setup by fastening the at least one nut to the boltshaft such that the bolt is secured to the housing is greater than a magnitude of the operational load.

20. The load sensing system of claim 18, further comprising a washer between the bolthead and the at least one nut.