| In the aerospace industry, Chemical milling technology is usually used in the processing of large thin-walled parts, due to the characteristics of weak rigidity and large scale. The mirror milling technology which is proposed in recent years is considered to replace chemical milling technology and it is seen as the main method of the large thin-walled parts processing in the future, due to the characteristics of good generality and high efficiency, and it will bring great changes to the of large thin-walled parts processing. The core control problems are studied in this work according to the control requirements of the mirror milling system. Aiming at the characteristics of large thin-walled parts and the actual processing system, the control strategy is determined and the control algorithm is designed.Aiming at the end structure characteristics of the actuator in the mirror milling system, a simple and intuitive method for defining the spatial pose is proposed. Based on the spatial geometry relation and the vector chain method, the inverse kinematics analysis of the series machine tool in the milling side and the Tricept hybrid mechanism in the supporting side is carried out, which provides the kinematics basis for the control of mirror milling system.According to the constant supporting force control requirement and the easy deformation characteristic of large thin-walled parts, a compliant control method is proposed: position-based explicit force control strategy based on an online trajectory premodification(OTP) force controller. The OTP force controller comprises an integral separated PID module and an online trajectory premodification module for precise adjustment and coarse adjustment respectively to improve the response speed and control precision of the system. Numerical simulation of compliant control algorithm is earried out by MATLAB. Compared with typical feedback force controller, the proposed force controller has better supporting force tracking performance in machining process. The maximum and the root mean square value of the supporting force error has been reduced by 60% and 75% respectively.Aiming at the requirement of synchronization between the supporting side and the milling side, a synchronization control method is proposed:joint space cross coupling control method of mirror milling system.According to the geometric characteristics of the actuator in the mirror milling system, the reasonable definition of joint space synchronization error is given. And the cross coupling control structure of the mirror milling system is designed. Numerical simulation of compliant control algorithm is carried out by MATLAB. Compared with parallel control mode, the proposed cross coupling mode has better synchronization performance between the supporting side and the milling side, under the premise that it won't reduce the tracking performance of the actuators. The maximum and the root mean square value of the synchronization force error has been reduced by 84% and 78%.To verify the proposed Compliant control method and synchronization control method, the experiment platform based on CNC cross slide system is designed and established. Based on the LabVIEW software environment, the control algorithm is programmed and tested.The experimental results are in agreement with the numerical simulation results, and it verifies the effectiveness of the proposed compliant control method and the synchronization control method. |
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