Study On Key Issues Exsisted In The Rod-type Ultrasonic Motor With MDOF For Robot Wrist Joint

With the progress of science and technology,aerospace and medical treatment have become the two important technical fields of robot application.The characteristics of its unconventionality and extreme environment put forward higher requirements to robots,such as light weight,small size,low noise and no electromagnetic interference,etc.Wrist joints are the basic components of robots,so it is of great significance to explore the simple and stable structure of the wrist joint for the miniaturization and lightweight of the robot and the further application of the robot.The Rod-type ultrasonic motor with MDOF is one kind of ultrasonic motor,having new principle,simple structure and three degrees of freedom.That makes it has incomparable advantage in the construction of the robot wrist joint with simple structure and compact structure.In this paper,modeling and analysis of the Rod-type ultrasonic motor based on bolted-joint nonlinear system as well as the construction of wrist joint have been conducted by means of combining finite element analysis simulation with experimental test.1)According to the principle of the rod-type ultrasonic motor,the continuum finite element model of the stator is completed by using finite element analysis software ANSYS.The prototype is built on the basis of the relevant structural design parameters.The deficiency by adopting continuous composite structure style in the dynamic characteristics of motor,is discovered in the analysis of prototype test.2)The computation accuracy is often insufficient in the rod-type ultrasonic motor design because of the adopted continuum finite element model.The method for modeling the rod-type ultrasonic motor vibrator based on bolt pretension is presented and the influence of bolt pretension and contact surface friction coefficients on modal frequency is also analyzed.3)Studies on the construction of robot wrist joint structure based on the Rod-type ultrasonic motor with MDOF are carried out from these aspects: the mechanism to ensure the three degrees of freedom movement of the motor sphericalrotor in the joint structure,and pre-tightening force loading between stator and rotor.In the structural design of wrist joint,the three degrees of freedom movement of joint and pre-tightening force loading between stator and rotor are perfectly realized by the vertical cross arrangement between the steering ring and spherical rotor shaft.According to the dimension parameters of the prototype motor,the wrist joint structure is made.