Improved Performance of Soft Robotic Artificial Muscles Through Compositing High Dielectric Polymeric Materials

Electrically driven artificial muscle soft actuators assist in propelling automotive companies closer to the lightweighting of equipment while moving the environment closer to carbon neutrality. The innovativeness of this technology stems from muscles found in the natural world. Electrostatically based artificial muscles have not previously performed at an advantageous level that could adequately challenge electric motors. Artificial muscles are electrically driven flexible capacitors. A hydraulic response (muscle flexing) is yielded after a voltage is applied to the electrodes causing the attractive forces between them to move the internal dielectric fluid. The dielectric constant between the two-electrodes of this parallel plate capacitor dictates the capacitance of the artificial muscle, and therefore, the attractive force between the electrodes. In our soft robotics actuator, this translates directly as output force. Numerous polymeric insulating materials have been investigated as coatings for these electrodes. High dielectric constant PVDF-TrFE-CFE has always been an attractive candidate material because of the correlation of dielectric constant to higher output forces. Prior to this phase in our research, integration of this material into an artificial muscle has proven daunting. However, through compositing with PVDF-HFP, the integration of this material into the fabrication of artificial muscles was successful. A performance improvement of 4.5x was demonstrated using a composite insulating layer of PVDF-TrFE-CFE and PVDF-HFP versus a control muscle that used only 12 μm PVDF-HFP electrical insulation. An 800 g load was lifted with ~150% stroke using only an applied application voltage of 2,250 V, by an artificial muscle made with 10 μm PVDF-TrFE-CFE and 4 μm P-VDFHFP electrical insulation. This substantial improvement is ascribed to the influence of the high dielectric constant of PVDF-TrFE-CFE (50) compared to that of PVDF-HFP (10). Additionally, it was found that adding a ~10 N force to the edge of the artificial muscles’ electrodes acted as a closing assistance, increasing the weight the muscle could lift while maintaining ~150% stroke. This led to the optimization of the electrode design with the aforementioned composite insulation. A series of artificial muscle electrode designs were fabricated using various thicknesses of PVDF-TrFE-CFE composited with 4 μm PVDF-HFP to optimize the ratio of relative polymer thicknesses necessary to maximize performance. Our results demonstrated that a 3:1 ratio (13 μm PVDF-TrFE-CFE: 4 μm PVDF-HFP) performed consistently with ~150% stroke lifting up to 700 g. Such results show how manipulation of capacitive effects can be achieved in layering of different polymeric materials and achieve manipulation of soft robotic artificial muscle output force. These artificial muscles are currently being tested for use in a device that will act as a suction cup that will be applied in existing robotic equipment.