| Parallel mechanism has the advantages of high speed, high precision, high stiffness theoretically, which are attractive for CNC machine tools, so parallel machine tools is praised as the CNC of the 21st century. But nowadays the parallel machine tools haven't exerted their theoretical performances at most, so it is very crucial to improve performances of the hybrid machine tools with the merits of the serial and parallel mechanism for accelerating their practical procedure.Incorporating the research and development of the six-axis 6PM2 hybrid boring and milling NC machine tool, The theory and application have been investigated thoroughly and systematically on the kinematic simulation analysis, the singularity and the kinematic calibration of the 3-RPS parallel mechanism and the open NC system for the hybrid NC machine tool, etc. The 3-RPS parallel mechanism is the kernel part of the 6PM2 abovementioned.The main work and innovation in this dissertation are as follows:1. The kinematics of the 3-RPS parallel mechanism is analyzed and corresponding analytical equations of position, velocity and acceleration are derived. The kinematic simulation for posture, velocity and acceleration of the motion platform is given, which provides the theoretical basis for the follow-up control. A solution method for the angles of passive joints in the 3-RPS parallel mechanism is brought up, which dissolves the assembly angles of passive joints. And principles for confirmation and design of assembly angles are given out, which handles the problem of little revolute ranges of the 3-RPS parallel mechanism, which are taken as the designing rules.2. Based on the theory of reciprocal screws the Jacobian matrix including information of the architecture and the constraint singularities is proposed in this paper as well as the educing method. The singularities of the 6PM2 hybrid machine tool are analyzed using the two methodsrespectively and gives the basis for avoiding singular configuration in engineering applications.3. The experimental calibration of the 6PM2 hybrid machine tool is accomplished by gradual approaching calibration using the indirect measuring method. The initial values of the rod length of the parallel mechanism are decided by the position trigger lock function integrated in the PMAC. The disturbing factors of measuring noise are settled by the matrix regrouping method and the ill effects of non-structural parameter factors on the calibration are eliminated through reasonable treatment of measuring data according to the practical characteristics of the calibrated object. And the comparison between experimental data got before and after the calibration shows that the motion precision is enhanced. So it provides a method to deal with the problem that the practical motion precision of parallel mechanism is lower than the theoretical one.4. A new kind of measuring device for revolute precision is developed and manufactured aiming at the characteristic of variable special position while the parallel mechanism rotates, which provides a measuring device for direct measuring the posture of the motion platform.5. The motion control algorithm of hybrid machine tools is given out and corresponding control system software is programmed. The CNC software hides the motion of the real axis and put the trajectory on the interface with motion of the virtual axis, which accords with the traditional usage of CNC.The above studied achievements are successfully applied to the six-DOF hybrid cutting machine tool - 6PM2 composed of serial and parallel mechanisms developed by the author's institute and upstanding results are achieved.
|
PDF Full Text Request