Piezoelectric tactile sensor

• US 5,760,530 A
• Filed: 12/22/1992
• Issued: 06/02/1998
• Est. Priority Date: 12/22/1992
• Status: Expired due to Fees

• Current Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Kolesar, Edward S.
• Primary Examiner(s): BUDD, MARK OSBORNE
• Application Number:
  US07/995,230
• Time in Patent Office: 1,988 Days
• Field of Search: 310/316-319, 310/338, 310/339, 310/800, 310/330-332, 310/328, 345/365 A, 73/862.04, 414/730, 364/558, 901/46, 901/33
• US Class Current: 310/339
• CPC Class Codes: H10N 30/302 Sensors
• CPC Class Codes: H10N 39/00 Integrated devices, or assemblies of multiple devices, comprising at least one piezoelectric, electrostrictive or magnetostrictive element covered by groups H10N30/00 – H10N35/00

Abstract

A two-dimensional, electrically-multiplexed robotic tactile sensor realized by capacitively coupling a piezoelectric film such as a polyvinylidene fluoride (PVDF) polymer film to a monolithic silicon integrated circuit. The disclosed integrated circuit incorporates 64 identical sensor electrodes arranged in a symmetrical 8×8 matrix and physically adjacent electronic amplification for each sensor electrode signal. The response of a typical tactile sensor is linear for loads spanning the range of 0.8 to 135 grams of force and provides a response bandwidth of 20-25 Hz. Stability and response reproducibility limitations often associated with piezoelectric-based tactile sensors are resolved by a pre-charge voltage bias sequence for the PVDF film which initializes the pre-and post-load sensor responses. Recognition of sharp-edge, square, trapezoid, isosceles triangle, circle, toroid, slotted screw, and cross-slotted screw shapes using the sensor is also disclosed.

Claims

1. Force magnitude and force pattern responsive tactile sensing apparatus comprising the combination of:

a two-dimensional array of electrode elements disposed in electrical and physical isolation across a planar surface area portion of a semiconductor substrate member;

a force responsive physically deformable film of piezoelectric effect material disposed over said array of electrode elements and said substrate member surface area portions, in electrical capacitance coupling with said electrode element array;

an electrically conductive common electrode member disposed over a second distal surface portion of said film of piezoelectric effect material and connected with a common return electrical node of said sensing apparatus;

electronic amplifier means, including a plurality of high input impedance electronic amplifier circuits physically disposed adjacent to said array of electrode elements with each said amplifier circuit having respective input nodes connected with one of said electrode elements and with said common return electrical node for amplifying a piezoelectric effect electrical charge signal received on said electrode element during sensed tactile force physical deformations of said film of piezoelectric effect material;

low voltage electrical charge generating means temporarily connected with each said electrode element of said array for pre-conditioning said piezoelectric effect material to a substantially uniform signal generation state prior to each said tactile force physical deformation.

2. The sensing apparatus of claim 1 wherein said physically deformable film of piezoelectric effect material is disposed in thickness deformable covering over said array of electrode elements.

3. The sensing apparatus of claim 2 wherein said piezoelectric effect material is an organic polymer material.

4. The sensing apparatus of claim 3 wherein said film of piezoelectric effect material is comprised of polyvinylidene fluoride and has a thickness between 15 μ

m and 100 μ

m.

5. The sensing apparatus of claim 4 wherein said film of polyvinylidene fluoride material is adhesively bonded to said substrate member, and said adhesive bonding includes a film of dielectric urethane inclusive adhesive material.

6. The sensing apparatus of claim 4 wherein said electrical charge signal is of a transient signal nature in response to a continuous thickness deformation of said polyvinylidene fluoride film by said sensed force.

7. The sensing apparatus of claim 4 wherein said pre-conditioning of said piezoelectric material includes a physical thickness altering response to said temporary connection of said electrical charging means.

8. The sensing apparatus of claim 4 wherein said substrate member is comprised of silicon and said electrode elements are comprised of metallic film attached to said substrate member.

9. The sensing apparatus of claim 8 wherein said electrode elements comprise a square shaped array of square shaped individual electrodes.

10. The sensing apparatus of claim 9 wherein said square shaped individual electrodes are separated by a substrate surface interval that is at least 75% of the size of each said electrode.

11. The sensing apparatus of claim 4 wherein said electronic amplifier circuits each have an input impedance of ten raised to the exponent of twelve ohms.

12. The sensing apparatus of claim 11 wherein said substrate member is comprised of one of the materials silicon and gallium arsenide and said electronic amplifier circuits each have a metal oxide-semiconductor field-effect transistor input stage with a gate electrode thereof being connected with one of said electrode elements in said array.

13. The sensing apparatus of claim 1 wherein said electronic amplifier circuits are also disposed on said semiconductor substrate member.

14. The sensing apparatus of claim 1 wherein said electrical charge generating means is electively connected with each said electrode element via an electronic multiplexer switching circuit.

15. The sensing apparatus of claim 14 wherein said electronic multiplexer switching circuit has an off state electrical resistance characteristic of ten raised to the exponent of twelve ohms.

16. The sensing apparatus of claim 1 wherein said electrical charge generating means is electively connected with each said electrode element via a mechanical switching element.

17. The sensing apparatus of claim 1 further including detection threshold selecting circuit means responsive to an output signal of at least one of said amplifier circuits for determining presence and absence of significant force magnitude at each of said electrode elements.

18. The sensing apparatus of claim 1 further including an additional electrode element disposed in electrical isolation on said substrate member and also isolated from said sensed forces for generating a sensing apparatus temperature responsive electrical reference signal.

19. The sensing apparatus of claim 1 wherein said substrate member is comprised of ten to the exponent of fourteen ohm centimeter resistivity, silicon dioxide material of three microns thickness dimension.

20. The method of tactile force sensing comprising the steps of:

generating a spatial map related array of discrete electrical signals each representing a force magnitude at a predetermined planar location within an applied force field;

said signal generating step including capacitively sensing local quantums of electrical charge displaced to surface adjacent portions of a piezoelectric film by physical deformation of said film from said applied force field;

each said signal generating step being preceded by a temporary low voltage electrical signal induced output signal range limiting physical preconditioning of said piezoelectric film; and

amplifying each said discrete electrical signal of said array in an amplifying each said discrete electrical signal of said array in an amplifying location disposed adjacent said spatial map signal location.