Development of a 2-d.o.f. finger using load-sensitive continuously variable transmissions and ultrasonic motors

This paper presents a 2-d.o.f. finger using ultrasonic motors and load-sensitive continuously variable transmissions (CVTs) we proposed previously, which consist of a five-bar linkage and a torsion coil spring. The proposed CVT is remarkably simple and enables a finger joint to exert a large fingertip force and to move quickly. For the two joints of the 2-d.o.f. finger, we designed five-bar linkage CVTs which are more compact than the previous ones so that they can be installed on its base. Taking advantage of the geometric feature that ultrasonic motors are thin, we can arrange the drive systems for the two joints, including the two CVTs and the two ultrasonic motors, in a parallel configuration. The experimental results verify that the maximum fingertip force of the finger is as large as 30 N and the maximum angular velocity of its joints is more than 400°/s. These performance results would be impossible without the CVTs. We also verify that the finger can lift up a 1.5-kg load.