Study On Real Time Motion Control Technology Of Five-axis Parallel Machine Tool With Constraints

In recent years,the design of aircraft structure parts are moving in the direction of integration,the overall structure parts has a characteristics of large,thin,cavitation number and flat shape.Generally the five-axis series CNC gantry machine tool for processing,but the traditional machine tools as the speed limit of rotation axis lead to low efficiency.In order to improve the machining efficiency,it is proposed to use parallel machine tool instead of series machine tool to process.Aiming at the structure characteristics and motion of parallel machine tool,this paper studies algorithm on the motion control which satisfies the real-time requirement.In this paper,the inverse solution of parallel spindle head is obtained by using the constraints and matrix transformation method,and an indirect numerical method is proposed for solving the problem of the forward kinematics.The three spherical hinges of parallel moving platform position as a positive solution object,due to the kinematic pair constraints,the initial position of spherical hinges can be determined through the machine tool structure parameters and drive displacement,the initial position of spherical hinges are used as the iterative initial value,which let the numerical method converge rapidly.It is easy to realize the indirect solution method by using three spherical hinges in the moving platform to get the pose of the end of the tool.Besides,the kinematics of the five-axis parallel machine is obtained by combining kinematic pair constraint and superposition method,the method of virtual axis programming to control parallel machine tool are realized.The geometrical error caused by the actual manufacturing and installation will lead to the deviation pose of the end-effector.In order to ensure the accuracy of the pose,the geometric error should be compensated.In this paper,the error compensation model is established based on the vector method,and the geometric error terms are determined by the method of motion equivalence and first-order differential approximation.DFP quasi-newton method is applied to solve the motion control equations of the strong coupling,which include geometric error compensation parameters,DFP algorithm is improved from two aspects of initial value and the number of iterations to meet the real-time compute requirements.The small angular velocity of the virtual rotation axis will be mapped to being the high speed the linear axis,when the virtual axis programming is using to control parallel machine tool,which exceeds the real axis speed limit.In order to keep the machine tool cutting stability,the feedrate was optimized based on the drive constraints of axis,which ensures axis speed of every pose to be within the limits.Based on the above research,a special CNC system for five-axis parallel machine tool is developed.The feasibility of parallel machine tool motion control technology was proved by simulation experiment which was done through using interpolation data of five-axis machining tool path to drive simulation model.