Motion control for 2-DOF tendon-driven spherical joint mechanisms

This research treats a tendon-driven spherical joint mechanism. At most, tendon-driven spherical joint mechanisms have three rotational degrees of freedom in one joint. Moreover, the mechanisms are lightweight and simple. As a result, the mechanisms are suited for transmission of force sensation by bilateral control. In conventional researches about the mechanisms, transmission of force sensation was difficult. In this research, tension control, position control, force control, and bilateral control is proposed for spherical joint mechanisms. The proposed control utilizes projected force on an imaginary plane which touches the sphere. In addition, a spherical joint mechanism with three linear motors is developed. The mechanism has two rotational degrees of freedom achieved by three tension-controlled strings. To simplify the mechanism, sensors are not attached to the spherical joint. Only encoders attached to linear motors are used as sensors. Rotation angles of the sphere are estimated by position responses of linear motors. Results of experiments shows that force sensation was transmitted without strings slacking.