Speed control of an electromechanical integrated harmonic piezodrive system

In Japan, a travelling-wave ultrasonic motor was developed (Sashida, 1984). After it, a ring-shaped travelling-wave ultrasonic motor was proposed in which the teeth were manufactured on the vibrator. It enlarged the vibrating amplitudes of the vibrator and the motor efficiency was increased (Akira, 1987). Using the finite element method, an optimal design methodology for the ultrasonic piezoelectric motors was presented (Rho. 2007). Using analytic method combined with numerical method, an analysis and design method for the ultrasonic motors was proposed (Rho, 2008). The material characteristics of ultrasonic motors were investigated as well (Rho, 2008 and Liu, 2011). However, the sliding friction between the stator and the rotor limits the output torque and the operating life of the motors. Hence, a non-contact ultrasonic motor was proposed in which the fluid between the stator and the rotor is used to transmit torque (Yamayoshi, 1992). A small sized non-contact ultrasonic motor was proposed in which the radiation pressure of the sound wave is used to transmit torque (Hirose, 1993). Based on it, a number of the non-contact ultrasonic motors were proposed and investigated (Isobe, 2005, 2007 and Stepanenko, 2012). Besides it, a rolling-contacting ultrasonic motor was proposed in which the rollers are located between the grooves of stator, and the rollers drive the rotor to rotate (Hojiat, 2010). The non-contact and the rolling-contacting ultrasonic motors have high operating life and efficiency. However, their output torque is small and only proper for the application of the high speed and small load. Therefore, the Authors proposed an electromechanical integrated harmonic piezodrive system in which the piezodrive principle is combined with the harmonic drive and the movable tooth drive principles, and a reduction ratio is realized (Xu, 2014). Compared with other piezoelectric motors, the system has three main advantages: rolling contact, transmitting load by meshing, and reduction speed. It makes the drive system have high operating efficiency and large output torque. For the novel drive system, the bifurcation and the chaotic vibration were investigated (Li, 2016).