Development And Research Of CNC System For A Novel3-DOF PKM Module

This dissertation deals with the key issues of high-speed and high-precisioncontrol of a novel3-DOF PKM (parallel kinematics machine) module named the A3head which is employed for large aluminum structural components high-speedmachining, covering a complete spectrum in terms of kinematic modeling, trajectoryinterpolation, development of CNC system, dynamic identification and torque controlmethod. The following contributions have been made.(1) By means of vector chain method, the kinematic models of the A3head areformulated for position, velocity and acceleration analyses. The mapping relationsbetween Euler angles and A/B angles are established in terms of angular position,angular velocity and angular acceleration. The above work provides necessarymathematical models for trajectory planning and torque control.(2) According to the characteristics of the open CNC system, the trajectoryinterpolation is studied on the basis of two-step interpolation strategy. Based on thelinear acceleration profile and the coordinate axis decomposition principle, thepoint-vector synchronous interpolation algorithm is studied systematically. Aiming atthe situation of tool rotating around the reference point, the vector interpolationalgorithms is accomplished by setting of the second feedrate, which improve theeffectiveness of interpolation computation.(3) Based on “IPC+Turbo PMAC” architecture, an open CNC systemframework of the A3head is proposed. Integrated with various peripheral equipments,the hardware platform is constructed. Adopting the modularization and hierarchydesign idea, the software architecture for five-axis machining is proposed andessential functions are developed in the circumstance of LabVIEW.(4) With the aid of the virtual work principle, the inverse dynamic model isformulated, allowing the model suitable for dynamic parameter identification to beestablished. Considering the characteristics of the load torques under differentworking conditions, a hierarchical strategy is proposed for dynamic parameteridentification. The merit of this strategy lies in that it enables the influences due to theCoulomb frictions to be counteracted or eliminated via proper path planning, therebythe identification accuracy to be significantly improved. The experiments under different working conditions are carried out to verify the validity and effectiveness ofthe proposed approach.(5) The dynamic torque compensation model is formulated by using the result ofdynamic parameter identification. On the basis of single-axis PD control, an approachfor feed-forward control is proposed at the coarse interpolation stage. Experimentalresults show that the proposed approach can effectively reduce the servo trackingerrors in the joint space in comparison with the single-axis kinematic control method.The outcomes lay a solid foundation for the development for the novelhigh-speed five-axis machine based on the A3head.