Research On Sliding Mode Control Strategy Of Ball Screw Driver Of The Chip Monter

Industrial demands for higher productivity rates and more stringent part tolerancesrequire faster production machines that can produce, assemble, or manipulate parts athigher speeds and with better accuracy than ever before. In a majority of productionmachines, such as machine tools as well as Chip Mounter, ball screw drives are used asthe primary motion delivery mechanism due to their reasonably high accuracy, highmechanical stiffness, and low cost. This brings the motivation for the research in thisthesis, which has been to develop new control techniques that can achieve highbandwidths near the structural frequencies of ball screw drives, and also compensate forvarious imperfections in their motion delivery, so that better tool positioning accuracycan be achieved at high speeds.A precision ball screw drive has been designed and built for this study. Detaileddynamic modeling and identification has been performed, considering rigid bodydynamics, nonlinear friction, torque ripples, axial and torsional vibrations, lead errors,adn elastic deformations. Adaptive Sliding Mode Controller(ASMC) is designed basedon the rigid body dynamics and notch filters are used to attenuate the effect of structuralresonances. Feedforward friction compensation is also added to improve the trackingaccuracy at velocity reversals.This thesis follows a systematic approach in modeling the dynamics of ball screwdrives and introduces new control techniques that deliver higher motion accuracy atelevated speed. All modeling and control work is based on a high precision ball screwdrive of Chip Mounter which was built at the Harbin Institute of Technology University.Henceforth, the proceeding chapters in this thesis are organized as follows:In Chapter1, the background of ball screw is introduced, as well as a literaturereview on the existing modeling and control techniques for ball screw drives ispresented.In Chapter2, Basic dynamics of the ball screw drive are modeled and identified inChapter2, comprising of rigid body motion, nonlinear friction characteristics. Thecurrent loop dynamics are ignored as well as the torsional and axial vibrations in thethesis. The models and parameters identified in this chapter are used in the followingchapters for controller design and stability analyses.In Chapter3, the basic control methodology chosen in this thesis, which isAdaptive Sliding Mode Control(ASMC), is introduced and used for controlling the rigidbody dynamics. The general ASMC formulation, developed by Slotine and Li and further improved by Zhu et al., is presented. As a special case, the control of a rigidbody based plant with an unknow external disturbance is studied. This case boil down tothe well-know PID controller with feedforward compensation terms.In Chapter4, the Chip Mounter which was built at the research laboratory ofHarbin Institute of Technology University is introduced.In Chapter5, by the use of MATLAB, the sliding mode controller which isproposed in chapter3is simulated, which is very useful in corresponding engineeringpratice.