Compliant actuation of parallel-type variable stiffness actuator based on antagonistic actuation

For a service robot requiring physical human-robot interaction, stable contact motion and collision safety are very important. To accomplish these functions, we propose a novel design for a parallel-type variable stiffness actuator (PVSA). The stiffness and position of a joint can be controlled simultaneously using the PVSA based on an antagonistic actuation inspired by the musculoskeletal system. The PVSA consists of a dual-cam follower mechanism, which acts like a human muscle, and a drive module with two motors. Each cam placed inside the dual cam-follower mechanism has two types of cam profile to provide a wide range of stiffness variation and collision safety. The use of the PVSA enables position and stiffness control to occur simultaneously. Furthermore, joint stiffness instantly decreases when the PVSA is subject to a high torque exceeding a pre-determined value, thereby improving collision safety. Experiments showed that the PVSA provides effective levels of variable stiffness and collision safety.