PIEZORESISTIVE LOAD SENSOR

• US 20130239700A1
• Filed: 02/07/2012
• Published: 09/19/2013
• Est. Priority Date: 02/07/2011
• Status: Active Grant

• Current Assignee: The Governors of the University of Alberta (University of Alberta)
• Original Assignee: The Governors of the University of Alberta (University of Alberta)
• Inventors: Moussa, Walied Ahmed Mohamed, Benfield, David
• Granted Patent: US 9,261,423 B2
• Time in Patent Office: Days
• US Class Current: 73/862.044
• 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 5/162 of piezoresistors

Abstract

A three-axis load sensor utilizing four piezoresistive devices on a flexible silicon membrane is provided. The load sensor further includes a mesa disposed on the membrane substantially equidistant from the piezoresistive devices. A six-axis load cell is provided by placing a plurality of load sensors disposed on a substrate, the substrate configured to attach to an object wherein forces applied to the object can be measured and/or determined. The load sensors can be manufactured using bulk microfabrication techniques on a single crystal silicon wafer, and can detect normal and shear loading applied to the membrane.

Claims

1. A microelectromechanical system (“

MEMS”

) load sensor for detecting loads in three axes, the load sensor comprising;

a) a flexible silicon membrane substrate comprising a top surface; and

b) a plurality of piezoresistive devices disposed on the top surface, the piezoresistive devices disposed in a spaced-apart configuration around a perimeter of the top surface, each piezoresistive device configured to produce an output voltage.

2. The load sensor as set forth in claim 1, further comprising a mesa disposed on the top surface.

3. The load sensor as set forth in claim 2, wherein the mesa is disposed substantially equidistant from each of the plurality of piezoresistive devices.

4. The load sensor as set forth in claim 2, wherein the mesa further comprises a rectangular solid member.

5. The load sensor as set forth in claim 2, wherein the mesa further comprises a cylindrical solid member.

6. The load sensor as set forth in claim 1, wherein the membrane substrate is rectangular thereby defining four edges, and wherein the plurality of piezoresistive devices is further comprised of four piezoresistive devices disposed about the perimeter of the membrane substrate, each piezoresistive device disposed substantially near the middle of each edge.

7. The load sensor as set forth in claim 1, wherein the membrane substrate is further comprised of n-type silicon.

8. The load sensor as set forth in claim 1, wherein one or more of the plurality of piezoresistive devices further comprise a four-terminal piezoresistive gauge.

9. The load sensor as set forth in claim 1, wherein one or more of the plurality of piezoresistive devices further comprise a two-terminal piezoresistor.

10. The load sensor as set forth in claim 1, wherein one or more of the plurality of piezoresistive devices are further comprised of p-type silicon.

11. A load cell for detecting loads in six axes, the load cell comprising:

a) a load cell substrate configured for disposition on an object;

b) a plurality of microelectromechanical system (“

MEMS”

) load sensors for detecting loads in three axes disposed on the load cell substrate, each load sensor further comprising;

i) a flexible silicon membrane substrate comprising a top surface, and

ii) a plurality of piezoresistive devices disposed on the top surface, the piezoresistive devices disposed in a spaced-apart configuration around a perimeter of the top surface, each piezoresistive device configured to produce an output voltage.

12. The load cell as set forth in claim 11, wherein one or more load sensors further comprise a mesa disposed on the top surface.

13. The load cell as set forth in claim 12, wherein the mesa is disposed substantially equidistant from each of the plurality of piezoresistive devices of the one or more load sensors.

14. The load cell as set forth in claim 12, wherein the mesa further comprises a rectangular solid member.

15. The load cell as set forth in claim 12, wherein the mesa further comprises a cylindrical solid member.

16. The load cell as set forth in claim 11, wherein the membrane substrate is rectangular thereby defining four edges, and wherein the plurality of piezoresistive devices is further comprised of four piezoresistive devices disposed about the perimeter of the membrane substrate, each piezoresistive sensor disposed substantially near the middle of each edge.

20. The load cell as set forth in claim 11, wherein one or more of the plurality of piezoresistive devices are further comprised of p-type silicon.

21. The load cell as set forth in claim 11, wherein the load cell substrate is comprised of silicon.

17-19. -19. (canceled)

22. A load cell system for detecting loads in six axes, the system comprising:

a) a load cell substrate configured for disposition on an object;

b) a plurality of microelectromechanical system (“

MEMS”

) load sensors for detecting loads in three axes disposed on the load cell substrate, each load sensor further comprising;

i) a flexible silicon membrane substrate comprising a top surface, and

ii) a plurality of piezoresistive devices disposed on the top surface, the piezoresistive devices disposed in a spaced-apart configuration around a perimeter of the top surface, each piezoresistive device configured to produce an output voltage; and

c) means for combining or multiplexing the output voltages from the plurality of piezoresistive devices.

32. The system as set forth in claim 22, wherein the load cell substrate is comprised of silicon.

23-31. -31. (canceled)