Speed control method for dual-flexible manipulator with a telescopic arm considering bearing friction based on adaptive PI controller with DOB

A dual-flexible manipulator with a telescopic arm is affected by joint flexibility, load flexibility, and bearing friction, which will cause angular velocity fluctuation. Besides, the motion of the telescopic arm leads to dynamic parameters of the flexible load in the servo system time-varying. The variation of dynamic parameters increases fluctuations of angular velocity. Fluctuations in angular velocity will aggravate the vibration of the manipulator and affect the control accuracy of end-effectors. In this paper, the adaptive PI control strategy with the disturbance observer (DOB) suppresses the vibration of the manipulator by weakening the angular velocity fluctuations. Firstly, dynamics equations of the dual-flexible manipulator servo system considering the bearing friction are established by using the assumed mode method. Next, the low-pass filter in DOB is designed according to the robust stability theorem, so that the servo system can satisfy the stability under dynamic parameters time-varying and friction torque simultaneously. Then, the adaptive law and the over-load compensation control law are designed by Lyapunov’s stability theorem. Finally, numerical simulation analysis and control experiments of the manipulator are carried out. The simulation and experimental results show that: 1) The bearing friction torque can cause angular velocity fluctuations, but the DOB can effectively reduce the influence of the disturbance torque. 2) The adaptive control strategy can effectively reduce angular velocity errors under conditions that the telescopic arm is in different lengths. Therefore, the adaptive PI control strategy with the DOB can effectively suppress angular velocity fluctuations of the manipulator.