Bilateral control using two-stage series-elastic actuator

This paper proposes a bilateral control system for master-slave devices using a compliant mechanism that allows an operator to finely handle an object when the stiffness of the object varies from low (soft) to high (hard). The proposed system consists of a two-stage series-elastic actuator (SEA) that has two springs with different stiffness. In the proposed system, a force control system, which controls the displacement of the springs so as to control the force applied to the environment, is implemented. The softer spring in the SEA mainly works when the applied force is small, and as the force becomes larger, the two-stage mechanism seamlessly changes to a single one so that the harder spring can mainly function. By structuring a force projection type bilateral control using the proposed SEA, high transparency is achieved even if the handled object is soft or hard. To show the validity of the proposed system, experiments were conducted to measure frequency responses of environmental mechanical impedance that the operator feels at the master side. The experimental results showed that the proposed two-stage SEA system achieved higher transparency than that of a single SEA case.