P3M-7 A Multi-Degrees-of-Freedom Ultrasonic Motor Design for Robotics Applications

The sphere of robotics is widely spreading in many fields, such as medical field, an amusement field, industrial robot and so on. As such a tendency growing, the motion patterns of the robots are required to be more human-friendly. For designing the motion unit capable of generating a multi-degree-of freedom (MDOF) motion, the volume of each actuator and the work condition have to be considered. Ultrasonic motor is thought as a good one for robot finger design. In this paper, a new design of hybrid MDOF piezoelectric ultrasonic motor is presented. We utilize a column vibrator as a stator which is fixed on a base body for practical mounting. In the stator, two PZT annular disks and a four-divided bronze electrode are sandwiched by the base body and a top metal with a bolt, which can generate two orthogonal bending vibrations. A multi-layered piezoelectric actuator is also installed in the stator to produce a large longitudinal vibration velocity at low driving voltage less than 10V. The motor's vibration modes are analyzed by finite element method. The first longitudinal vibration mode and the second bending vibration mode are used to generate the elliptic motion on the stator's surface. A ball rotor of 25mm in diameter can rotate in three directions at large rotation velocity. The rotation direction can be controlled by changing the phase of the driving signal. The vibrator has the size approximate to the human finger. We try to simulate the motion of finger's joint and discuss on the holding mechanism of the ball rotor suitable for the finger motions