Sliding filament joint mechanism: Biomimetic artificial joint mechanism for artificial skeletal muscles

Soft linear actuators (SLAs) make linear displacement by shrinkage and relaxation like skeletal muscles, so they can be called as artificial skeletal muscles (ASMs). They deform their body to create displacement. However, the restoring force generated by the deformation of their soft body reduces the force available from the SLA. This actuation structure is a critical drawback in the application of SLAs. In a living body, skeletal muscle is the main actuator to make movement. In order to make meaningful movements, skeletal muscles of a living body require bones and joints. Thus, as well as ASMs, artificial joints are surely required for developing robotic applications such as robotic prosthetics and bionic body parts. This paper introduces a biomimetic artificial joint mechanism that can improve the drawback of SLA. The basic performance and usefulness of the joint mechanism was confirmed by using shape-memory-alloy actuators (called SMA in general). In addition, the joint control strategy of the joint mechanism by adopting the joint control principle of a living body was proposed and its performance was experimentally validated.