Compliant Control On The Supporting Side Of Mirror Milling System

With the rapid development of aerospace technology,the requirements for rocket carrying capacity are also increasing.In processing of large-thin wall parts(such as fuel tank wall of rocket),the mirror milling method has advantages of higher efficiency,simpler equipment,higher precision than the traditional milling methods.Hence,the mirror milling is supposed to replace the traditional processing methods.Large-thin wall parts have the characteristics of low rigidity,easy chatter,and easy deformation.So the supporting mechanism is supposed to provide enough and proper supporting force to ensure the processing stability and accuracy.In addition,since the supporting process involves the interaction of the supporting end-effector and the large-thin parts,only motion control is not enough to ensure the safety and accuracy of the system.Based on the requirements of supporting in the mirror milling system,this paper focuses on the compliance control studying of the supporting mechanism during processing the large-thin parts.Firstly,the structure of the mirror milling system is analyzed,as well as the supporting side kinematics and the mathematical model of axes.Based on that,a simulation model is bult in MATLAB/Simulink.A simplified dynamic model is given to facilitate the stability analysis of the impedance control system.Analysis of the hybrid impedance control is carried out,which the following control strategies proposed are both based on.In the analysis,the influence of impedance parameters on control performance is studied,which is verified by a series of simulations and provides theoretical basis for the subsequent control strategies.Secondly,in order to get the reference supporting position,a positioning strategy based on accurate force-tracking is proposed.An adaptive impedance control is improved through a fuzzy algorithm,so that the supporting end-effector maintains a constant supporting force during the its moving along the workpiece surface.The proposed strategy can ensure both small overshoot and high force-tracking accuracy,which is verified by simulation and experiment.In the experiment,the force-tracking error of the improved algorithm is reduced by 58.2% and 5.7% compared to the hybrid impedance and adaptive hybrid impedance control,respectively.And the settling time is reduced by 34.2% and 28.4%,respectively.The overshoot of the improved algorithm is reduced by 92.4% compared to the adaptive hybrid impedance control.Finally,for the control needs of the support side in the mirror milling,a fuzzy adaptive hybrid variable impedance control strategy is proposed.The strategy can regulate force and position by setting parameters according to the specific requirements.Moreover,it has the advantages of small overshoot,short settling time and easy implementation on the mirror milling system.The effectiveness of the strategy is verified in simulation and experiment.In the experiment,compared with the hybrid impedance control,the proposed control strategy reduces the overshoot by a maximum of 87.5% and the settling time by a maximum of 67.7%.The strategy can also regulate force-position relationship in different ranges.