Generating Microgroove Arrays On Ultrasonic Motor's Friction Surfaces And Research On The Tribological Properties

Ultrasonic motors have become promising precision driving components due to their unique piezoelectric transduction and friction drive mechanisms.Since ultrasonic motors are typically driven by the dry friction force between the rotor and the stator,high friction coefficient and low wear rate of the friction pairs are two essential elements for improving the operating stability with longer service life.Surface textures have obvious advantages on improving the friction coefficient and the wear performance of the contact surfaces under the dry friction conditions,which provides the possibility of optimizing the output performance of the ultrasonic motors.Microgroove arrays,as a common form of surface textures,can meet the goals of increasing the friction coefficient while decreasing the wear rate.It has been verified that photoetching electrochemical micromachining and laser bean machining are two effective methods for generating micro-groove arrays.In this paper,high precision microgroove arrays were fabricated on the stator and rotor surfaces of TRUSM60 ultrasonic motor with the usage of these two methods.Meanwhile,dry friction tests were also conducted to provide a basis for optimizing the friction pairs' tribological properties in ultrasonic motors.The main contents of the dissertation are as follows:(1)Photoetching electrochemical micromachining was used to generate microgroove arrays on the surface of phosphor bronze,the ultrasonic motor's stator material.Parameters,namely,the electrolyte inlet pressure,applied voltage,pulse duty cycle and frequency were varied to investigate their influence on the dimensions and morphology of the microgrooves.Also,a new method was proposed to uniform electric field and suppress the edge effect during the machining process,which can greatly improve the machining accuracy.Finally,a special fixture was designed and high precision microgroove arrays were successfully obtained with the usage of the optimized machining parameters,and they were shown in two types: single microgroove and double microgrooves on each tooth.The microgrooves' average width and depth of the former type were 295.2 and 40.5 ?m,respectively while the latter type were 155.8 and 41.5 ?m,respectively.(2)Snice the friction layer of ultrasonic motor's rotor was made of polyimide,a kind of polymer material,laser bean machining was applied to fabricate microgroove arrays on it.The effects of machining parameters on the dimensions and morphology of microgrooves were investigated,including the machining times,the pump current value,the pulse frequency and the marking speed.A best combination of these parameters was then selected to generate microgroove arrays with high machining precision on the friction layer surface of ultrasonic motor's rotor.The average width and depth of these microgrooves were 169.5 and 94.1 ?m,respectively.(3)The dry friction and wear test between the friction material of the stator and the rotor was carried out.Firstly,the friction mechanism of ultrasonic motor was analyzed,and the effect of groovetextured surface on the tribological properties was discussed during the traveling wave transmission process.Secondly,the dry friction tests between the stator and the rotor's friction layer materials were carried out on different surface conditions such as smooth surfaces,single-side and double-side textured surfaces.Comparisons on the friction coefficient and the wear were conducted between the surfaces with and without microgroove arrays.Meanwhile,the experiment investigated the effect of microgrooves' width,area ratio and the double-side texturing parameters on the friction pairs' tribological properties.According to the principle of the highest friction coefficient and the lowest wear,the optimal combination parameters were obtained as follows: textured phosphor bronze surface with the microgrooves' average width of 200 ?m and the area ratio of 10%,and textured polyimide surface with the microgrooves' average width of 150 ?m and the area ratio of 40%.Microgrooves were distributed at an angle of 0° on two specimen surfaces and perpendicular to the sliding direction.The friction coefficient was 0.368,which increased by 50.2% compared to the smooth surfaces,and the wear weight of the phosphor bronze and polyimide surface were 0.8 and 1.0 ?g,respectively.The experiment conclusion provided a basis for improving the tribological properties of the ultrasonic motor.