Piezopolymer actuators

• US 4,879,698 A
• Filed: 11/03/1988
• Issued: 11/07/1989
• Est. Priority Date: 11/03/1988
• Status: Expired due to Fees

• Current Assignee: Sensor Electronics Corp.
• Original Assignee: Sensor Electronics Corp.
• Inventors: Langberg, Edwin
• Primary Examiner(s): Jordan, Charles T.
• Assistant Examiner(s): Eldred, J. Woodrow
• Application Number:
  US07/266,864
• Time in Patent Office: 369 Days
• Field of Search: 367/140, 367/191, 340/407, 73/862.04, 901/33, 901/46, 414/5, 310/800, 310/348
• US Class Current: 367/140
• CPC Class Codes: H04R 17/005 using a piezoelectric polymer
• CPC Class Codes: H10N 30/206 using only longitudinal or thickness displacement, e.g. d33 or d31 type devices
• CPC Class Codes: H10N 30/506 of cylindrical shape with stacking in radial direction, e.g. coaxial or spiral type rolls
• CPC Class Codes: Y10S 310/80 Piezoelectric polymers, e.g. PVDF

Abstract

Piezopolymer actuator, wound in a bifilar fashion on two pins, is operated in a compressive mode without buckling. In addition to constraining motion of the winding along the surface of the pins, the pins also provide wide area electrical contacts with conductive electrodes on the surfaces of the piezopolymer strip. The electrodes consist of a thin film of metallization coated with graphite. Graphite coating heals microcracks in metallization, adds body to the piezopolymer strip, and lubricates winding-pin interfaces. Modular linear arrays of actuators are readily built from a single strip of piezopolymer. Linear array modules are in turn clamped together to form a two-dimensional array. Typical application is a tactile array for the blind.

Claims

1. An actuator comprising

a base;

a first and a second pin made from electrically conducting material, said first pin and said second pin fastened parallel to each other at the base;

a means for applying a driving voltage to said pins at the base;

a winding, slidably disposed with respect to the pins, comprising a strip of piezopolymer film, said strip having a distension direction coincident with an axis of the winding and said strip comprising a first electrode on a first face of said piezopolymer strip and a second electrode on a second face of said piezopolymer strip, said winding following a path between and around said first pin and said second pin, for providing a sliding surface contact between said first electrode and said first pin and between said second electrode and said second pin, whereby the driving voltage applied thorough the pins and through a sliding contact between pins and the electrodes, to the electrodes, causes a distension of the piezopolymer winding with respect to and along the pins, said distension constituting a mechanical response of the actuator to the driving voltage; and

a means for coupling a mechanical load to the distension of the winding.

2. An actuator in accordance with claim 1 comprising a coating of conductive lubricant between said first pin and said first electrode and said second pin and said second electrode for enhancement of electrical sliding contact between said electrodes and said pins.

3. An actuator in accordance with claim 1 wherein the means for applying said driving voltage to said pins comprise conductive traces on a printed circuit board in registration with and contacting the pins protruding beyond said base.

4. An actuator in accordance with claim 1 comprising a coating of graphite between adjoining electrodes.

5. An actuator in accordance with claim 1 comprising a coating of mercury between adjoining electrodes.

6. An actuator in accordance with claim 1 comprising an elastic bonding layer between adjoining electrodes.

7. An actuator in accordance with claim 1 comprising a stretchable and electrically conductive coating between adjoining electrodes.

13. An actuator in claim 1 wherein said first and said second pins are made from steel plated with transition metal.

8. An array of actuators comprising

a base;

a plurality of electrically conducting parallel pins, ordered in pairs, and held and constrained by the base;

a means for applying electrical driving potential to each pair of said pins;

a plurality of windings made from a strip of a piezopolymer film intercalated between a pair of electrodes,

said windings slidably supported by a pair of said pins, for constraining the expansion and contraction of said strip of piezopolymer film in the winding to a single, sliding degree of freedom along a surface of said pins, and for providing a sliding electrical contact between each said electrode and corresponding said pin; and

means for mechanically loading the expansion and contraction of the piezopolymer film, caused by the electrical driving potential, connected through the pins and through the sliding electrical contact between the pair of pins and the corresponding pair of electrodes, to said electrodes.

9. An array of actuators comprising

a base made from an electrically insulating material;

a plurality of parallel pins made from an electrically conducting material, supported and constrained by the base;

an electrical connector means located below the base for applying driving voltages to the pins;

a plurality of windings, located above the base, said windings made from a metallized piezopolymer strip,

said metallization forming two electrodes on each face of said strip,

said strip slidably wound in a bifilar fashion around two adjacent pins, with a direction of distension of the piezopolymer strip substantially parallel to axes of the pins for allowing a sliding motion of said strip with respect to said supporting pin and resulting in sliding electrical contact between the pins and a corresponding said electrode,

whereby driving voltages applied through the electrical connector means to said pins, and from the pins, over a surface contact area, to the electrodes cause a distension of the piezopolymer, said distension confined by the pins to a sliding motion along the surface of the pins, in response to the applied driving voltage; and

means for applying mechanical loads to said sliding distension motion of said windings.

10. An array of actuators in accordance with claim 9, wherein said base further comprises a first perforated plate and a second perforated plate, both plates exhibiting a matching pattern of holes, each pin threaded through a corresponding hole in the first plate and in the second plate, said plates separated by a distance of an order of a centimeter, and said separation filled with an encapsulant.

11. An array of actuators in accordance with claim 10, wherein said base further comprises a metal rail housed between said first and said second plates with one pin per winding electrically connected to said metal rail, said metal rail connected to the electrical ground return, and a remaining pin per winding protruding below said base and contacting said connector.

12. An array of actuators in accordance with claim 9 wherein the means for applying mechanical loads comprises keys attached to an end of the windings opposite the base, said keys transmitting the sliding motion of the windings to skin in touch with said keys for producing a tactile sensation in the skin.