Control of a 2-DOF ultrasonic piezomotor stage for grommet insertion

The treatment of a common disease called “Otitis Media with Effusion (OME)” involves the surgeon inserting a grommet in the eardrum to bypass the Eustachian tube for draining fluid when medication fails. In this paper, a novel device for myringotomy and grommet insertion is first designed and introduced. Due to the advantages of high precision and fast response, a 2-DOF ultrasonic piezomotor (USM) stage is chosen to provide the motion sequences of the device, especially a precise path tracking during the grommet insertion. This paper briefly presents the mechanical design of the device and the configuration and control of the 2-DOF USM stage. The model of the USM consisting of a linear and nonlinear term is built. A PID controller is used as the main controller and tuned with the help of LQR technique. Since there are nonlinear dynamics caused by friction and hysteresis existing in the system, a nonlinear compensation including a sign function and sliding mode control is designed to reject the nonlinearity. Moreover, a decoupling controller is designed to eliminate the coupling effects between the two USM stages. The experimental results show that the LQR-assisted PID controller with compensation can achieve very good system performance and the decoupling controller can further improve the performance.