Friction Identification And Compensation In An AC Servo Worktable Based On Torsion Measuring

The precision and ultra-precision processing technology is an important research direction in the machining field, where the most important factor to realize ultra-precision processing is the ultra-precision machining equipment. An AC servo feed worktable, as a very important part of the NC machine tool, is an exact tracking and positioning system, whose kinematic precision and positioning accuracy is directly relate to the CNC machining precision and surface quality and production efficiency of the CNC systems.As for a high precision feed worktable, especially in the low speed stage, the improvement of the AC servo feed worktable's kinematic accuracy is limited by the disturbances in the system, mainly by the friction. Friction may cause bad performance of control system, which embody phenomenon such as the position error, limit cycle, stick-slip etc. So it is an obstacle to improve the kinematic control accuracy. Friction is affected by the mechanical structure, the lubrication, the load and the speed, moreover it may also change with the position and time. As the decrease of the friction is restricted by the technics level and the funds, this dissertation is devoted to study the friction characteristics, friction modeling and compensation control in the AC servo feed worktable system with the ball screw from the economical and practical aspect.The development of the research on tribology is reviewed, the achievements on the research of friction model and friction control are summarized, and especially the research of friction on the AC servo system is introduced.In order to analyze the impact of the friction on the worktable's positioning accuracy; it is necessary to eliminate the positioning errors caused by the error of the ball screw pitch at first. The dynamic measurement of the pitch error has been done with the laser interferometer and raster. The periodic erroneous ingredient and the gradual erroneous ingredient of the ball screw pitch error are extracted and shape into the fitting curve of error. The influence of pitch error on position accuracy of worktable is weakened through error feedforward compensation.To measure the transmission torque of the AC servo motor, a strain torque sensor is designed. Through the analysis of mathematical model of the AC servo worktable's feed system, kinetic equation of the mechanical drive and vector control model of the AC motor are established, and then the mathematical expression of the friction in the system is obtained by means of the transmission torque. The experiment of torque...