Development Of Micro-scaled Tribometer For MEMS Device

Those equipments used in micro friction research in MEMS are chiefly designedby researchers for their specific application. As high-speed microactuators springingup, and there is no friction and abrasion testing instrument for high-speedmicroactuators exist in domestic, a micro friction tester imitating the workingcondition of high-speed microactuators has been developed. It can be used to researchfriction, abrasion and lubrication of high-speed microactuators.The tester is designed as a pin-on-disk tester in order to imitating Slide frictionand wear in MEMS, in which normal load and friction are respectively measured byuse of displacement method and optical lever. Further, the overall structure of thetester is designed, and it’s principle of measurement is discussed in detail. In order toimprove the test accuracy and increase the measurement range of the tester, afeedback system with a piezoelectric actuator employed.A dynamometric cantilever is designed, with a vertical elastic sensitive elementfasten to the head of the cantilever to measure normal load, and an axial elasticsensitive element fasten to the end of the cantilever to measure friction. The stiffnessand maximum stress of the sensitive elements are analyzed through theoreticalcalculation and strength check of the vertical elastic sensitive element is carried on bythe Creo Simulate software. The sensitive elements and test specimens are fabricatedbymicrofabrication technology.A friction disk is drove by a motor taken from a hard disk. The motor is chargedby a full-bridge circuit and only two phases work at each state. Rotor position isdetected through zero crossing point detection. An ATmega8is used to control themotor. A PWM generator of upper computer is written by Delphi software. Therelationship between motor speed and duty cycle of PWM waves is measure by aHY-441digital tachometer.Measure the displacement of the vertical elastic sensitive element with a laserdisplacement detector. Ameasuring system with feedback consisted of a laser, mirrors,a quad detector and a piezoelectric actuator is built for torsion measurement. Theapplication method and steps of the mentioned device are described, and the controlparameter of the system is set according to its structure feature.The run-out error of the friction disk is detected, and the results show that whenthe motor speed ranges from4000to7000, the run-out error of the friction is acceptable. The stiffness of the vertical elastic sensitive element is demarcated and thecalibration value is in accord with the theoretical calculation and simulation. Theresults of static analysis indicate: the hysteresis of friction measurement is about6%,the repeatability is about0.6%, and the definition is0.011mN. actual tests show thatthe micro friction tester comply with the design requirements and can be used to testhigh speed micro friction efficiently.