中文摘要：

多自由度超声波球电机适用于机器人的肩腕关节驱动．文中分析了三自由度超声波球电机的原理和结构，指出其存在的基本问题；建立了三自由度超声波球电机的坐标变换关系，通过转子受力的力平衡方程，给出转子球心的位移和定转子接触面转子形变量及其力分布的关系式，以此为基础讨论了这种电机的基本关系．

英文摘要：

Multi-degree-of-freedom motor is the advanced field in the research of motor. The paper discusses working mechanism and structure of traveling type multi-degree-of-freedom ultrasonic motor, and sets up the coordinate transfer model of spherical ultrasonic motor. Based on the force balance equation of its stator, the paper presents the displacement of the center of rotor and distribution equation of rotor on the contact area. Finally, the basic relation of this kind of spherical motor has also been presented.