Spider-Inspired Pneumatic Folding Membrane Soft Actuator

Soft pneumatic joints are the main driving components of soft arthropod robots, but the problems of high start-up air pressure and low rotation angle limit the range of motion, control accuracy, and flexibility of the robots. Inspired by the hydraulic joints of spider leg, an innovative folding membrane soft joint actuator is designed to achieve an 80° rotation angle at 5.25 kPa air pressure, with an angle density of 15.23°/ kPa and a fatigue life of more than 10,000 times, significantly improving the output characteristics of pneumatic joints. This actuator's folding membrane is made of silicone-coated fiber fabric and is manufactured via integrated molding method. Furthermore, regarding the issue of ineffective expansion in actuators, the effects of various constraint layer materials on the actuator's output performance are investigated and discussed. It is found that the TPU-constrained actuator has a maximum output torque of 0.307 N·m, which is 7.7% and 13.7% greater than that of the fiber-constrained and unconstrained actuators, respectively. Meanwhile, the rebound time was 1.25 seconds, which was reduced by 0.23 seconds and 0.22 seconds respectively. Soft actuators can benefit from the design technique of the folding membrane soft joint actuator presented in the study, which can provide significant torque output at low air pressure and has superior fatigue characteristics.