Research On The Drive Control Techniques Of Ultrasonic Motors

As a kind of micro machines which are based on piezoelectricity, ultrasonicmotors (USMs) cause no electromagnetic interference, and can achieve high outputtorque at low speed. The special features have enhanced the studies on ultrasonicmotors. The traveling-wave rotary ultrasonic motor (TRUSM) is an iconic family ofUSMs. Due to the complexity of multi-variable, strong coupling and time-varyingcharacteristics, it is difficult to build models for USMs. The performance of USMsdepends on the characteristics of the driving control system. For the purpose of drivecontrol studies, in this article, a simulation model is built, a drive circuit along withthe speed regulating method is designed, and then a drive controller is actualized.At first a simulation model specially for drive control studies was built. Theinput of the model is two-phase driving voltage and the load torque. The output ofthe model is the speed of the USM. This new model is possessed with the equivalent-circuit model and the analytical model, so that it provides a facility for drive controlstudies.A drive circuit for USMs consists of four parts: the signal generator, the poweramplifier, the matching network and the the power supply. This artical analyzed thecharacteristics of different power inverter topology, demonstrated the feasibility of athree-phase bridge inverter for two-phase drive. Then the functions and features ofdifferent matching circuit were analyzed, and the parameter design method of seriesmatching inductance and LLCC-resonant network was presented.The relationship between the controlled PWM variable and voltage modulation,frequency modulation as well as phase modulation was described. The speedregulating method of three-phase bridge inverter was designed in detail. Thedynamics of feedback voltage from the isolated pole while speed regulating wasdiscussed. Then a general plan for isolated pole feedback was introduced, so as torealize frequency tracking.Finally, a drive controller based on FPGA was designed and actualized. Itcontains the three-phase bridge power inverter and the LLCC-resonant network. Itcan automatically collect the feedback voltage from the isolated pole achievingfrequency tracking. The software and hardware design details were presented.Experimental test was carried out to validate the general functions of the drivecontroller.