Moment Compensated Bending Beam Sensor for Load Measurement on Platform Supported by Bending Beams

• US 20150116260A1
• Filed: 03/15/2013
• Published: 04/30/2015
• Est. Priority Date: 05/03/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Augenbergs, Peteris K., Harley, Jonah A., Hoen, Storrs T., Brock, John M., Sarcia, Sam Rhea
• Granted Patent: US 10,088,937 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G01L 1/22 using resistance strain gauges
• CPC Class Codes: G06F 2203/0338 Fingerprint track pad, i.e. fingerprint sensor used as pointing device tracking the fingertip image
• CPC Class Codes: G06F 2203/04103 Manufacturing, i.e. details related to manufacturing processes specially suited for touch sensitive devices
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• CPC Class Codes: G06F 2203/04105 Pressure sensors for measuring the pressure or force exerted on the touch surface without providing the touch position
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: G06F 3/0414 using force sensing means to determine a position
• CPC Class Codes: H05K 13/00 Apparatus or processes specially adapted for manufacturing or adjusting assemblages of electric components
• CPC Class Codes: Y10T 29/49117 Conductor or circuit manufacturing

Abstract

A method is provided for fabricating a bending beam sensor coupled to a touch input device. The method includes providing a bending beam. The method also includes placing a first strain gauge and a second strain gauge on a surface of the beam near a first end of the beam, and aligning the first strain gauge and the second strain gauge with the beam along an axis. The first end is attached to a base. The method further includes coupling the first strain gauge and the second strain gauge to a plate of the touch input device and electrically connecting the first strain gauge and the second strain gauge such that a differential signal is obtained from the first strain gauge and the second strain gauge when a load is applied on the plate of the touch input device.

Claims

1. A method for fabricating a bending beam sensor coupled to a touch input device, the method comprising:

providing a bending beam;

placing a first strain gauge and a second strain gauge on a surface of the beam near a first end of the beam;

aligning the first strain gauge and the second strain gauge with the beam along an axis, the first end being attached to a base; and

coupling the first strain gauge and the second strain gauge to a plate of the touch input device;

wherein the first strain gauge and the second strain gauge are electrically connected such that a differential signal is obtained from the first strain gauge and the second strain gauge when a load is applied on the plate of the touch input device.

2. The method of claim 1, further comprising attaching a bottom surface of the plate to the top of the beam at the second free end by using a viscoelastic polymer.

3. The method of claim 1, wherein the beam is configured to bend near the second free end of the beam such that the second free end is angled from the first end of the beam.

4. A method for fabricating a touch input device coupled with bending beam sensors, the method comprising:

providing at least three bending beams;

placing a first bending beam sensor on a surface of the first bending beam;

aligning the first bending beam sensor with the first beam between a first end and a second free end of the first beam, the first end of the first beam attached to a first beam base;

placing a second bending beam sensor on a surface of the second bending beam;

aligning the second bending beam sensor with the second beam between a first end and a second free end of the second beam, the first end of the second beam attached to a second beam base;

placing a third bending beam sensor on a surface of the third bending beam;

aligning the third bending beam sensor with the third beam between a first end and a second free end of the third beam, the first end of the third beam attached to a third beam base;

coupling the first, second, and third bending beam sensors to a plate of the touch input device; and

electrically connecting each of the first, second, and third bending beam sensors to output signals to a processor.

5. The method of claim 4, further comprising:

attaching a second sensor for position to a bottom surface of the plate; and

attaching the second sensor for position to the top surface of each beam at the second free end by using a viscoelastic polymer, wherein the first end is attached to a beam base.

6. The method of claim 4, the operation of placing a first bending beam sensor on a surface of each beam comprising:

placing a first pair of strain gauges on a surface of each beam near one end of the beam;

placing a second pair of strain gauges on the surface of the beam near a free end of the beam; and

electrically connecting the two pairs of strain gauges as a Wheatstone bridge such that the first bending beam sensor outputs a signal when a load is applied on the plate.

7. The method of claim 4, wherein each of the first, second, and third bending beams is configured to bend near the second free end of the beam such that the second free end is angled from the first end of the beam.

8. A moment compensated bending beam sensor device for a plate coupled to a bending beam, the plate configured for applying a force on a top surface of the plate, the sensor device comprising:

a bending beam having a first end attached to a beam base; and

a bending beam sensor attached to the bending beam, wherein the bending beam sensor comprises a first strain gauge and a second strain gauge, each strain gauge being aligned with the bending beam and being placed between the first end and the second free end.

9. The sensor device of claim 8, wherein the first strain gauge and the second strain gauge are electrically connected to generate a differential output when the force is applied on the plate.

11. The sensor device of claim 8, wherein the bending beam is coupled to the plate through a viscoelastic polymer near a second free end of the beam, the bending beam sensor being at a further distance from the second free end than the viscoelastic polymer.

12. The sensor device of claim 8, wherein the bending beam sensor comprises a carrier, the first strain gauge and the second strain gauge being placed on the carrier.

13. The sensor device of claim 8, wherein the beam is configured to bend near the second free end of the beam such that the second free end is angled from the first end of the beam.

14. A touch input device, the device comprising:

a plate configured for applying a force on a top surface of the plate;

a position sensor attached to the plate;

four bending beams coupled to the plate and the position sensor, each bending beam having a first end attached to a beam base; and

a bending beam sensor attached to each bending beam, wherein each bending beam sensor comprises a first pair of strain gauges and a second pair of strain gauges being aligned with the bending beam and placed between the first end and the second free end, and the first pair of strain gauges and the second pair of strain gauges.

15. The device of claim 14, wherein the first pair of strain gauges and the second pair of strain gauges are electrically wired as a Wheatstone bridge such that the each bending beam sensor outputs a signal when the force is applied.

16. The device of claim 14, wherein the bending beam sensor comprises a carrier, the first pair of strain gauges and the second pair of strain gauges being placed on the carrier.

17. The device of claim 14, wherein each beam is configured to bend near the second free end of the beam such that the second free end is angled from the first end of the beam.

18. A method for determining a force on a plate, the method comprising:

sensing a voltage change at a first strain gauge

and a second strain gauge, the first and the second strain gauges are positioned on a common side of a single beam coupled to the plate;

obtaining a differential voltage between the first strain gauge and the second strain gauge;

transmitting the differential voltage to a processor; and

converting the differential voltage to a force on the plate.

19. The method of claim 18, further comprising determining the location of the force.

20. A touch input device, comprising:

a platform;

at least one bending beam supporting the platform; and

at least one force sensor disposed on the at least one bending beam, the force sensor operative to measure a force exerted on the platform, wherein the at least one force sensor is operative to output at least three distinct force levels.

21. The touch input device of claim 20, further comprising a position sensor coupled to the platform.

22. The touch input device of claim 20, wherein the at least one force sensor comprises at least one strain gauge, and the position sensor comprises capacitive measuring electrodes.