Research On Startup Characteristics Of Ultrasonic Motor

Ultrasonic motor(USM) is a new principle motor which is being developed since 1980s, USM have a simple structure, high precision of position, low noise emission, high ratio of torque to weight, so that it gains an advantage in the application of servo control systems, especially in some applications such as auto focus camera lenses, precise positioning and aerospace. We find that sometimes USM can not start when we use it, if the USM have this phenomenon, it will seriously affect the reliability of the machine that has used the USM, also it will go against industrial and national defense. So it is of great significance to analyze the reason of the phenomenon that USM can not start and resolve it.In this paper, based on the test such as stator's resistance test, electrode feedback voltage test and static torque of contact interface test, we've analyzed the phenomenon why the USM can't start and we can believe that under suitable working conditions, the changing of the interface lead to the difficulty of ultrasonic motor's start. When ultrasonic motor works, the sliding friction heat causes the change of rotor's material performance of the contact interface. After stopping USM, the inlay or even bond of the stator tooth and rotor surface lead the increase of stator's resistance and the aggrandizement of resonant frequency, so using the foregoing frequency to trigger off the stator can't work, at the same time, the rotor can't work either. Based on the traveling wave ultrasonic motor linear elastic contact model, mathematical expressions of the ultrasonic motor's start performance are derived.To meet the requirements of ultrasonic motor's startup characteristics, speed-test principles and methods for ultrasonic motor are investigated. To gain the speed, we choose T method of optical encoder with fast output response and high testing precision. We've built a platform for the ultrasonic motor performance test, developed a set of test system for ultrasonic motor start-up characteristics, designed the upper and lower machine and compiled the driver software. This test system, which can be used for many types of ultrasonic motor start characteristics, consists of motor, encoder, coupling, test boards and so on. Using signal generator and oscilloscope to calibrate the test system, the results show that it can meet the test accuracy and can be used to test the motor's startup characteristics.We've studied several factors on the start of USM, such as ultrasonic motor's work and contact parameters, friction materials and state of the environment. The ultrasonic motor's start time after different interval is tested, which shows that as the interval increased ultrasonic motor start-up time comes longer, but steady-state speed is almost the same. We've researched the influence of parameters, which include the pre-pressure, the stiffness of the elastic element and voltage, on the characteristics of ultrasonic motor start, and compared it with simulation results, gaining a agreement in qualitative and confirming the validity of the simulation analysis. Also we've tested the influence of parameters, which include the thickness of friction material and different types of paste, and built a temperature and humidity environment test system to examine the startup characteristics under different temperature, humidity and other environmental factors, which provides the experimental basis for the ultrasonic motor applications in unmoral state environment.