Modeling and Experimental Evaluation of a Pneumatic Variable Stiffness Actuator

The variable stiffness actuator (VSA) can absorb and reuse positive–negative power between the load and the motor, which can enhance the actuating efficiency of robotic joints and improve their impact resistance. Typical VSAs mainly adopted a motor-mechanism system into the elastomer in addition to the main actuating motor to adjust elastomer stiffness, which might limit practical effects due to large mass and inertial of the variable stiffness elastomer. This article proposes a new type of a pneumatic variable stiffness actuator (PVSA), which uses a rotating cylinder and compressed gas to form a lightweight pneumatic elastomer, the stiffness of which could be adjusted via a remote pressure controlling system, thus improving the mass distribution of the VSA in lightweight space-constrained actuation. In addition, the PVSA could also be integrated with metal springs to increase its stiffness range and torque bandwidth, further improving its practical application prospect. The influence of the friction, the backlash, and the temperature on PVSA performance are theoretically and experimentally analyzed, and its position, torque, and stiffness control performance under variable situations are tested and verified through multiple simulations and experiments. The results indicate that the PVSA can provide expected actuation performance with effective remote stiffness adjustment capability.