Electroadhesive Polymers and Clutch Using the Johnsen-Rahbek Effect
US20260031747A1
Abstract
A polymeric material having a volume resistivity appropriate for use as an electroadhesive (EA) material is described. The EA polymer may include ionic additives that may be used to tune the electrical resistivity of the EA material within a range such as 109-1013 Ω·cm allowing for electroadhesion using the Johnsen-Rahbek effect (JR effect). The EA force is orders of magnitude greater than that typically observed for so-called coulomb-only EA materials while operating at lower voltages. The EA polymer produces a strong EA pressure for very little power relative to overall system power, shows fast and reversible adhesion, is lightweight, and may be easily tailored for a specific application. The electrical resistivity of the EA polymer may be easily tuned by altering the weight fraction of ionic additive. The polymeric material may be easily cast into sheets, films, or molded for specific applications.
Description (excerpt)
GOVERNMENT INTEREST The invention described herein may be manufactured, used and licensed by or for the U.S. Government. BACKGROUND OF THE INVENTION Existing electroadhesive (EA) materials may be difficult to tune and may only be available in limited form factors such as ceramics. Thus there is a need for an EA material that is easily tuned and able to be deployed in various form factors. BRIEF SUMMARY OF THE INVENTION Some embodiments of the present invention provide a polymeric material having a volume resistivity appropriate for use as an EA material, referred to herein as an EA polymer. The EA polymer may include ionic additives that may be used to tune the electrical resistivity of the EA material within a range such as 10 9 -10 13 Ωcm allowing for electroadhesion using the Johnsen-Rahbek (JR) effect. The EA force is much greater than that typically observed for so-called coulomb-only EA materials while operating at lower voltages (e.g., less than one thousand volts versus five thousand volts or greater). The EA polymer produces a strong EA pressure for very little power relative to the overall system power, shows fast and reversible adhesion, is lightweight, and may be easily tailored for a specific application. The electrical resistivity of the EA polymer may be easily tuned by altering the weight fraction of ionic additive in the final composition. The polymeric material may be easily cast into sheets, films, or molded for specific applications as opposed to ceramic materials used in other devices. The EA polymer represents the first polymeric material with the requisite mechanical and electrical properties for use as a JR type EA. The JR effect has not been previously achieved using a polymeric material. The effect is primarily described for doped ceramics. Unexpectedly, polybenzimidazole (PBI) doped with a small weight fraction (or mass fraction) of ionic additive (e.g., less than five percent weight by weight (w/w)) was found to produce the JR effect. PBI polymers are primarily used for flame retardant clothing, high strength components, and as a membrane separator in fuel cells. The EA polymer may include an ionic additive and/or low vapor pressure solvent (e.g., dimethylacetamide) to lower the volume resistivity to within the 10 9 -10 13 Ωcm range. The ionic additives may include, for example, alkali/alkaline earth metal halide, alkyl halide, aryl halide, and/or ionic liquid. The EA polymer may be cast into a film, sheet, tube, or may be coated on a conductive substrate. An electric potential may be applied across the material in contact with another conductive surface, producing a strong electrostatic attraction. The EA material of some embodiments is polymeric, in contrast to existing solutions that use doped ceramic as dielectric materials used to produce the JR effect. As such, the properties of the EA material may be easily tuned and spray coated, dip coated, or processed to provide a variety of form factors for a given application. The material density is two to five times lower than ceramic-based EAs, thus providing significant size and weight savings. The EA material may be utilized as a component of EA brakes and clutches, variable stiffness dampers, morphing wing structures, telescopic robotic limbs, passive energy recovery, electroactive gripper surfaces, wall-climbing robots, launch and/or perching pads for unmanned aerial vehicles (UAVs), haptic feedback devices, variable stiffness structures, exoskeletons, robotic end effectors, and quick-release attachment points, among other applications. A clutch of one or more embodiments may include a housing and stator shaft which may include many separate braking faces and/or clutch plates. In the case of one braking face, one stator plate may include, for example, a carbon fiber shim to which a film of the EA polymer may be coupled. The stator plate may clutch to a metal layer of, for example, stainless steel shim or sputter-coated conductive metal on polymer film (e.g., aluminized polyethylene terephthalate) embedded within the housing. The metal layer and EA film may be electrically isolated from one another so that free flow of electrical current is not possible unless the two surfaces are in close contact. When an electrical potential is applied, the two surfaces may be strongly bonded together due to the JR effect, thus locking the stator to the housing. The holding force of the clutch may be tuned by the driving potential when in DC mode, or the clutch may act as a mechanical damper when driven with a bipolar DC waveform across various frequencies and amplitudes. The clutch stack may include discrete braking faces having multiple layers of EA polymer and metal. In this way, the braking force may scale approximately linearly with the number of braking faces. <description-of-
Filing details
- Inventors
- Jeffrey T. Auletta
- Assignee
- U.S. Government, as Represented by Secretary of the Army
- Filed
- Jul 26, 2024
- Granted
- Application pending
Bibliographic data and excerpted text sourced from Google Patents (public record) as part of IP TechMatch's current-filings monitor. This filing is not part of the 2019 historical archive. For the authoritative full text, drawings, and legal status, see the source links above or consult USPTO records directly.