Study On Chaotic Operation Of Ultrasonic Motor System

Ultrasonic motor (USM) is a new kind of micro-motor, whose operation principleis very different from conventional electromagnetic motors. Inverse piezoelectriceffect of piezoelectric ceramic is used to incite elastomer’s supersonic tiny oscillation,then the friction between stator and rotor is changed into macroscopical beeline orrolling movement. Because of USM’s strong nonlinearities and coupling, there may besome chaotic behaviors when it is moving. Experimental results indicate that when thecontrol parameters changes, USM will appear some anomalistic movement whichseems to be chaotic but bounded. This kind of movement will make speed or torquecause intermittent vibrancy, which will waste lots of power and influence USM’sstability. So it has practical significance for USM’s control system to decisivelyanalyze and control this anomalistic movement.First, preliminary study for the chaos phenomenon is carried on in the ultrasonicmotor drive system. A kind of ultrasonic motor speed closed-loop control experimentis designed to obtain groups of sampling time sequences of driving voltage amplitudevariation. The phase-space reconstruction is used to analyze the chaos characteristicsof these time sequences. The largest Lyapunov exponent, calculated by the small datasets method, is a positive number, which shows that in certain working condition,traveling wave ultrasonic motor will show chaotic characteristics. Based on above,USM’s kinetic model and speed close-loop control system are designed to buildsimulation model which is appropriate to analyze USM’s chaotic characteristic. USM’smovement characteristic is studied across adjusting controlling parameters. Based onsimulation data, speed’s Lyapunov exponent spectrum, bifurcation diagram and thetrace which speed concerns the voltage are obtained when the parameters changes.Based on Lyapunov exponent spectrum, USM’s chaotic range is obtained. Finallybased on USM’s chaos model, proportion-delayed feedback controller is designed, inwhich conventional method and fuzzy control are respectively used to calculate thedelay time, and the control stiffness is calculated by parameter adaption. It is indicated by simulation results that both of methods can eliminate USM’s chaotic behavior.Because of the self-adaption and robustness，fuzzy delay feedback control is betterthan conventional method.