Performance Study And Structure Design For The Traveling-wave USM Using A Space-contracted Model

This dissertation is supported by the National Science Foundation(No51575288).Ultrasonic Motor(USM)has many advantages,for example,high torque with low speed,compactness in size,absence of electromagnetic interference,and a fast response characteristic,a good stopping performance at switch—off power,etc.Recently,many prototypes of the ultrasonic motor have been developed successfully,and among them,ring type traveling-wave ultrasonic motor(RTWUSM)has found wide applications in auto-focus mechanism of Canon cameras,the drive of a watch,aeronautic and astronautic fields,automobile etc..The main work accomplished is summarized as follows:(1)The selection of piezoelectric materials is the key step in the initial design of ultrasonic motor structure,which requires the comprehensive consideration of the piezoelectric properties,process performance economic performance and environmental properties of materials,and so on.Therefore,the process of determination involves the decision-making of multi-criteria,multi-objective and multi-scheme.In view of the fuzziness of decision making of the deciders,the paper proposes a multi-objective solution based on fuzzy analytic hierarchy process(AHP)solution.Using the method of ? scale method,a fuzzy judgment matrix was constructed.Combined with the Delphi method and AHP method,the weight of each index parameter was determined to implement the quantitative evaluation of the selection scheme.Aiming at the piezoelectric ultrasonic motor needed by a certain electric vehicle,an instance analysis of four typical piezoelectric materials was introduced in the paper.With the aid of the quantitative selection method,the paper calculated the comprehensive evaluation index,and thus found the optimal theoretical scheme of piezoelectric materials.(2)For a traveling wave ultrasonic motor,the contact between the stator and the rotor was usually described by the plane contact model with a simple sliding.But the theoretical analysis using this traditional model may have an inevitable deviation from the motor's real output.Therefore,a variable friction spatial contact model is proposed.The friction-deformation angle was used to define the friction state in different contact properties.By the kinematics and dynamics analyzed on this 3dimensional model,the mathematical functions for the motion,force and energy loss are derived.Using software MATLAB,the motor's drive torque,the tangential velocity on the contact point,the output efficiency were simulated.Besides,the relationship between the friction interface efficiency and the stator-rotor distance are analyzed.The test results indicate,that this new model could offer a more accurate reflection to the motor's actual working condition than the traditional one.(3)The electric control model of ultrasonic motor is established,and the performance parameters such as current,input power and power factor of ultrasonic motor are simulated and analyzed.The principle suggestions of ultrasonic motor optimization design are put forward.Ultrasonic motor stator,contact surface and piezoelectric diaphragm and other modules were initially optimized design.In particular,the proposed stator and rotor flexible contact structure can ensure that the contact surface and the drive particle trajectory to maintain the vertical state,effectively reducing the relative sliding between the rotor and the stator,improve the overall energy conversion efficiency of the motor.