Theoretical And Experimental Investigation Of 5-Dof Parallel Machine Tool With Redundant Actuation

Parallel Machine Tool (PMT) is the production of many subjects, including parallel robotics, mechanical manufacturing, computer technology and so on. As a useful complement of conventional NC machine tools, PMT has splendid future and high scientific research value. Redundant actuation has become the hot topic because that it can help parallel manipulators eliminate the singular configurations, enlarge effective workspace, and improve its dynamic performance, the precision and bearing capacity. This paper focuses on the research of correlated aspects of the 5-UPS/PRPU PMT with redundant actuation. The main contributions are as follows:Redundant actuation is introduced into the 5-UPS/PRPU PMT. The inverse kinematic solution and the velocity solution are analyzed. The velocity Jacobian matrix of the PMT with redundant actuation is established.The static equilibrium equation of the PMT with redundant actuation is established. Based on the force Jacobian matrix, the influence of the redundant actuation to the UPS limbs is studied by means of the influence coefficient method, which provides theoretical basis to improve the mechanical performance of UPS limbs. Take static equilibrium equations as the constraints, the forces and constraint couple is optimized by means of pseudo-inverse method.The dynamic equation of this PMT with redundant actuation is built by Lagrange Equation. A novel force distribution method is proposed for redundant actuation. The constraint couple of the PRPU limb to the moving platform is deduced with the D'Alembert's principle. Consequently, the dynamic calculation of the redundant actuation limb is performed, base on which the redundant driving force used in real-time force control can be obtained.The virtual prototype of PMT is established in ADAMS. Then, the motion controlling model, the friction force model and the cutting force model are created according to numerical control (NC) files and cutting parameters. Importing these models to the prototype of this PMT, the dynamic simulation of the cutting process is carried out by ADAMS software. The joint friction which affects the driving force most is analyzed. At the same time, the simulation results and theoretical results of the dynamics are compared, which showed the correctness of models.Based on the kinematics and dynamics analysis, the control system is developed for the PMT with redundant actuation. Open architecture composed of PC and PMAC is adopted for the system hardware, which is a parallel double-CPU NC system. The open CNC system software is developed on base of Windows, adopting modularization in Visual Basic 6.0. The system consists of human-machine-interfaces, security assurance, motion force/position hybrid control, calibration, file management and some other function module. Torque sensor is installed on the redundant actuation driving limb to realize real time feedback of torque signal, which realizes the compliance control of PMT primarily.A series of experimental investigation for the PMT with redundant actuation are carried out, including the detection for the positioning accuracy of each axis in Cartesian coordinates of the machine, the dynamic performance, and the machining experiments. The experimental result shows that the redundant actuation can eliminate the creeping phenomenon of the slider in the middle constraint limb, improve the positioning accuracy and the dynamic performance. The PMT with redundant actuation achieved smooth moving and the curved surface machining.