Electro-optic force and pressure transducer and sensor

• US 4,814,562 A
• Filed: 11/13/1987
• Issued: 03/21/1989
• Est. Priority Date: 11/13/1987
• Status: Expired due to Term

• Current Assignee: University of Arkansas (University of Arkansas System)
• Original Assignee: University of Arkansas (University of Arkansas System)
• Inventors: Langston, Marcus C.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Allen, Stephone B.
• Application Number:
  US07/119,952
• Time in Patent Office: 494 Days
• Field of Search: 250/227, 250/231 R, 250/231 P, 73/705, 73/862.04, 350/96.1, 901/33
• US Class Current: 250/227.14
• CPC Class Codes: G01L 1/24 by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
• CPC Class Codes: G01L 1/243 using means for applying force perpendicular to the fibre axis
• CPC Class Codes: G01L 1/247 using distributed sensing elements, e.g. microcapsules along a single optical fibre G01L1/242

Abstract

A pressure sensor includes at least one light conducting opening extending generally parallel to a pressure receiving face of a deformable body and a light emitting and a light receiving device at opposite ends of the light transmitting opening. A cross sectional area of the light transmitting opening, and correspondingly the light transmitting capability of the opening, vary in response to changing pressures applied to the pressure receiving face, which is determined by the light receiver. A measuring circuit for the light receiver is also provided.

Claims

1. An apparatus for measuring pressure, comprising:

a deformable elastic body having a pressure receiving surface and at least one opening extending generally parallel to and spaced form said pressure receiving surface, said at least one opening being variable in cross-sectional area in response to pressure applied to said pressure receiving surface;

means for transmitting light through said at least one opening; and

means for receiving light transmitted through said at least one opening, said light receiving means including signal generating means for detecting variations in said light transmitted through said at least one opening as said at least one opening varies in cross-sectional area as a function of the pressure applied to said body.

2. An apparatus as claimed in claim 1, wherein said at least one opening is a plurality of openings extending substantially parallel to one another, and including

a like plurality of transmitting means and receiving means to detect variations in transmittal light through each of said plurality of openings as each respective opening varies in cross-sectional area.

3. An apparatus as claimed in claim 1, wherein said at least one opening extends in a straight line through said deformable body.

4. An apparatus as claimed in claim 1, further comprising:

a reflective coating on an inside surface of said at least one opening.

5. An apparatus as claimed in claim 1, further comprising:

a deformable light conductor extending through said at least one opening, said light conductor being deformable in cross-sectional area t ovary the quantity of light transmitted therethrough.

6. An apparatus as claimed in claim 1, further comprising:

means for measuring variations in said transmitted light detected by said light receiving means.

7. An apparatus as claimed in claim 4 wherein said at lest one opening extends along a curved path.

8. An apparatus as claimed in claim 5, wherein said deformable light conductor extends in a generally S-shaped path generally parallel to said pressure receiving surface.

9. An apparatus as claimed in claim 6, wherein said measuring means is an electrical circuit connected to an output of said receiving means, said circuit including:

a selectively variable amplifier having an input connected to said output of said receiving means, and

a latch connected to an output of said amplifier.

10. An apparatus as claimed in claim 6, wherein said measuring means includes:

a comparator having a first input connected to an output of said receiving means; and

means for setting a threshold level at a second input of said comparator.

11. An apparatus as claimed in claim 9, wherein said selectively variable amplifier is a negative feedback amplifier having a variable feedback resistance, and

said latch is a logic flip-flop having a clock input connected to said output of said amplifier.

12. An apparatus as claimed in claim 10, wherein said means for setting a threshold level is a selectively variable voltage divider.

13. A pressure sensor for use in sensing forces applied to a surface, comprising:

a deformable body of flexible material having a pressure sensing surface, said deformable body having at least one transversely extending light conducting opening with first and second ends, said light conducting opening being of a ross-sectional area to transmit a quantity of light, said deformable body deformable in response to forces applied to said surface to vary said cross-sectional area and correspondingly vary the quantity of light transmitted by said opening;

an LED light source mounted at said first end of said light conducting opening to transmit a light signal through said light conducting opening;

a photo-transducer mounted at said second end of said light conducting opening to receive said light signal transmitted through said light conducting opening, and

circuit means connected to an output of said phototransducer for measuring for measuring variations in said light signal received by said photo-transducer as a result of pressure on said pressure sensing surface.

14. A pressure sensor as claimed in claim 13, wherein said deformable body is mountable in a robotic gripping apparatus to provide tactile sensing.

15. The method of control in response to pressure variations as a controlling variable which includes the steps of:

directing a force along a prescribed path intersecting a deformably elastic body having at least one through opening therein having an inlet and an outlet;

selectively changing the quantum of force so applied to correspondingly change the compressibility of the body and the cross-sectional size of the opening;

continuously directing rays of light into the inlet;

receiving light from the outlet in variable amounts as the cross-sectional size of the opening changes; and

converting the light at the outlet to an electric control signal for transmission to a point of utilization.

16. A tactile-touch sensor for providing analog feedback to a controller, comprising:

a body of elastic material through which extends an opening having a light inlet and a light outlet through which the passage of light is accommodated;

a light source at said inlet to transmit light into said through said opening

analog feedback means including;

a photo-cell means at said outlet to receive light transmitted through said opening; and

said body having a surface intersecting a force transmitting axis so that a cross-sectional area of said opening varies as a function of the force, thereby to control the quantum of light received at said photo-cell means for generating a controlling variable signal to drive the analog feedback means as a function of the variable pressure.

17. In an electro-optic force and pressure transducer and sensor, the improvement of

a sensor body of elastic material having a light conducting opening extending therethrough between first and second spaced apart points and having an intermediate portion of a selected cross-sectional configuration of predetermined cross-sectional area,

force applying means for engaging said body of elastic material and indenting said light conducting opening at said intermediate portion and reducing the cross-sectional area in proportion to the amount of deformation,

and means including light sensing means for transmitting and receiving rays of light through said opening between said first and second spaced apart points to generate a control signal proportional to the reduction of cross-sectional area of said opening and hence a function of the force exerted against said sensor body.