Research On Position Control Error Compensation Technology Of Full-closed Loop Servo Drive System

The high-end CNC machine tools are significant parts to the manufacturing industry,the cornerstone to achieve advanced and modernized manufacturing and the key procedure for high precision techniques and national defense modernization.Full-closed loop servo drive system,as the most important control link and actuator of the high-end machine tools,its position control error directly affects the machining accuracy of the machine tools.So it is of great significance to conduct more detailed research on the control error compensation strategy of the full-closed loop servo drive system,thus pushing forward the nationalization of high-end CNC machine tools and to improve the autonomy of high-end manufacturing equipment.In this dissertation,originated from the abovementioned backgrounds,we take the full-closed loop servo drive system as the research object,and the key technologies of the following four aspects are researched to compensate for the position control error:(1)Study on vibration suppression of control loop in the full-closed loop and improvement of full-closed loop stabilization in the servo drive system;(2)Study on the decrease of speed control error that is induced by position control error,and modification on speed /rotation angle estimation methods;(3)Study on suppression of contour error that is induced by nonlinearity factors,analysis of the influence of backlash on contour error,and optimization of quadrant error compensation strategies.And(4)Consideration of numerical/ servo system communication delay,modifying the gain margin of position control loop under high feeding rate.Detailed contents of the dissertation are in the following:For methods in position loop control,since to the inherent elastic link in the position loop control,vibration is easily induced,the full closed-loop is studied in detail in this dissertation due to its superior performance in position control,the vibration suppression methods based on full-closed loop is studied in this dissertation.First,originating from the mechanical parts and electrical control parts of the servo drive system,the model of full-closed loop position control system is established.Based on this,the transfer function of the full-closed loop control is derived,reasons that why the full-closed loop control is more easily to induce the position vibration than the semi-closed loop control is analyzed by frequency analysis.Next,by introducing the shaft position information to the potion control,the high gain margin of semi closed-loop control and high control precision of the full-closed loop are combined to construct the dual-position loop control.Finally,in order to solve the resonant frequency variation under different servo drive systems,the filter is introduced in the feedback loop to realize a feedback control method that can choose the resonant frequency,which improves the feasibility and simplicity of dual position loop control.For speed estimation method,aimed at the issues of mechanical noise or torque disturbance that is exist during low speed and fine processing.The speed/ angle estimation methods are studied in detail.The speed loop and the current loop,as the inner loops of the tri-closed loop system,their performances directly determine the position loop control.The speed estimation error will rise servo speed control error under the low speed condition,the drawbacks of two different traditional estimation methods are analyzed,in this dissertation and an effective method that can accurately estimate the speed and angle information from positon feedback is proposed.First,by combining kinetic equations,position signal reconstruction algorithm,that is based on polynomial fitting is established,and the issues about algorithm execute efficiency is solved by derivation of polynomial coefficients using the least square method,also,the proposed methods provide optimized solutions to solve the rotation angle estimation amplification during speed zero crossing.Then,the delivery form of rotation angle sampling in the digital control is analyzed,by establishing the speed observer based on the dual sampling rate,the estimated speed can be smoother.In order to make the estimated speed convergence to its real value faster and decrease the complexity of the design of observer parameters,the discretization equation of linear reduced-order observer is established,by using the zero-pole configuration methods,the reasonable observer parameters are derived.In this dissertation,the generation mechanism of transient backlash error(a typical contour error)in the full-closed loop is studied in detail,and it is aroused by multiple nonlinear factors(backlash,friction and deformation).First,the simplified model of full-closed loop servo shaft is established,on this basis,the mechanism of transient backlash error in linear machining and circular machining is demonstrated,and analytical expression of the transient backlash magnitude is derived.Noticing the fact that the backlash meshing process can be regarded as an integral process,with the help of speed reference compensation method,the amplitude of compensation signal and its duration is combined with the backlash width,and an adaptive transient backlash compensation strategy based on torque feedforward signal is proposed.The proposed compensation method doesn't need to measure the backlash in advance,and the compensation value can be generated automatically.Its structure is simple,effective and easy and fast to implement,it can decrease the delay time and transient backlash error caused by backlash,and considers both the issues of system accuracy and stability caused by the existence of backlash.An in-depth study on the delay issue of the fully closed-loop CNC system is conducted in this dissertation.For high speed feeding occasions,since the modernized numerical system usually adopts concept of the CNC is responsible for computation and the servo driver is responsible for the execution,there is inevitable communication delay between the two during the bus data interaction.In order to avoid the overshot and control accuracy deterioration caused by communication delay,the delay issues in full-closed loop control are studied in detail.First,based on the dual-position feedback control structure,the servo driver system model,that integrates the communication delay,is established,and by adopting the frequency root locus analysis method,the influence from communication delay to system stability is analyzed,and it points out the significance of delay compensation.For a better communication delay compensation,the Smith Predictor is researched and designed accordingly,and problems of model mismatch in application of Smith Predictor are analyzed,on its basis,the model error sources are summarized.Finally,the communication disturbance observation compensation is solved by combining the disturbance observer theory,the problems of model mismatch in communication delay is solved,thus the feasibility and simplicity of the delay compensation is improved.