Research On Friction Compensation For Eccentric Control System Of Helical Milling

Helical milling technology, which is at a big advantage for drilling the difficult-to-machine materials, has broad application prospects in aviation manufacturing. The novel helical milling device, which succeeds to adjust the hole diameter automatically by hollow DDRM cooperating with eccentric sleeves, is firstly designed by the plane digital assembly group of ZJU. However, the high-precision positioning and low-velocity performance of eccentric control system is influenced by the friction of eccentric sleeves. In this dissertation, the simulation and application research of adaptive friction compensation method is studied to solve the problem about the nonlinear friction of eccentric sleeves.The dissertation consists of the following five chapters:Chapter 1 details the research background of friction compensation for eccentric control system of helical milling. The development of friction model and the friction compensation methods are reviewed. In the last section of the chapter concludes with a brief summary of the main research contents of this dissertation.Chapter 2 introduces the helical milling technology and the comparison with traditional drilling technology. Then the chapter details the end-effector of helical milling, which is composed of function theory, hardware and software. The eccentricity adjustment mechanism, the driving elements and the control difficulty of eccentric control system are analyzed. And the system dynamics is modelled based on the course of generating holes.Chapter 3 studies the design of adaptive controller. According to the special friction characteristics of eccentric control system of helical milling, the adaptive controller with the friction parameter variations are uniform and the adaptive controller with the friction parameter variations are completely non-uniform are designed, respectively. The friction characteristics are described by LuGre friction model. And the unmeasurable internal state of LuGre model is estimated by designing the state observer. The adaptive controller is designed based on backstepping method, and the stability of the system is proved by Lyapunov theorem. Comparative simulation results validate the effectiveness of the proposed controller.Chapter 4 validates the adaptive control system through experiment. The DDRM experimental platform is set up, which is mentioned from hardware system and software operating system. Then the detailed MechaWare modelling theory and implement are introduced. The experimental parameters are confirmed, including the identification of friction parameters and the optimization of control parameters. Compared with PID control, the effectiveness of the controller is validated by position servo and tracking performance. The results show that the adaptive friction compensation method can effectively suppress the nonlinear friction interference on eccentric control system. The system achieves tracking the desired position at the speed of 0.1 °/s and the tracking error decreases from 0.03° to 0.01° or less. That is to say, the proposed controller significantly improves the low-speed tracking ability.Chapter 5 summarizes main research work that has been done and draws conclusions. And some possible further research directions are discussed.