Study On The Motion Control System Of The Series-Parallel Hybrid Polishing Machine Tool

At the present, with the competitive manufacturing market, the need for high accuracy, high speed and low-cost machines is demanding. Thereby, the disadvantage of traditional serial machine becomes obvious. The serial-parallel hybrid polishing machine tool is developed by introducing the parallel system into traditional serial system. The distinguish advantages of spacious work room, flexibility, high speed, high rigidity, and low cost make it become new trend.The integration of parallel and serial structure determines the complicity of electrical control. It is significant to design a good motion control system, which is also core technology of the serial-parallel hybrid polishing machine tool, the"brain"and"heart"of the machine tool. Compared to mechanical design of machine, the development of motion control system in China is relatively slow. In this dissertation, the theories and experimental results of a novel motion control system for a serial-parallel hybrid polishing machine tool-JDYP51, developed by University of Jilin, is discussed. This project is tested on"Embedded Motion Control System for High Efficient Free-Form Surface Grinding and Polishing (20040325)"supported by Science and Technology Development Plan of Jilin Province.JDYP51 serial-parallel hybrid polishing machine tool is composed of multiple close-loop subsystems, whose of core parts is 3-PTT parallel structure. The close-loop constraints generate the strong coupling relationship of each joint. The dynamic characteristics of parallel structure determine the performance of the machine. Therefore, it is significant to study the dynamic characterization, structure design, and rigidity and control methods for the machine. In this dissertation, the positioning of the serial structure is first analysis using a dynamic model of multiple rigid systems. The motion relationship of independent substructures, either of sliding rod, balance support and motion stage of the machine is solved using Lagrange function. The open-loop dynamic equations are derived without considering the structure coupling caused by close-loop constraints. After taking the constraints of the subsystems into the open-loop dynamic model, a simplified dynamic model for serial-parallel system is established by transforming independent coordinate systems to contradict the constraints.The key design for the serial-parallel hybrid polishing machine tool motion control system is to choose the proper motion control methods and to design the controller. The controller design consists of motion and dynamic control. For better performance the dynamic control system controls the entire parallel system based on the dynamic characteristics of the machine, especially at high speed control, required stricter dynamic control compared to motion control. Based on the dynamic model for serial-parallel hybrid polishing machine tool's system proposed in this dissertation, the PD control, calculated matrix control, fuzzy control-compensated calculated matrix control, and high-accuracy fuzzy control-compensated calculated matrix control are discussed and used for simulation. The simulation results indicates that the conventional calculated matrix control can efficiently track the system input, but high static error presents due to the parametric errors in the model. Fuzzy control algorithm can reduce the track error, but is limited in static control. The improved fuzzy control algorithm can achieve the relatively ideal track by introducing non-linear quantization.In order to improve the positioning accuracy of the motion control system, the high accuracy interpolation algorithm is required for motion tracking. NURBS method is widely adopted for free-form curve and surface interpolation. But the NURBS interpolation demands the high-speed digital system to process. To speed up the interpolation, a fast improved NURBS curve interpolation based on Newton iterative method is used. In this method, the iteration is used to replace the complicated differential process so as to realize the embedded system. The increment through the interpolation method can be output to control motion through DDA. In addition, the points interpolated by NURBS algorithm are located onto the curve, no radical error. The interpolation profile error is generated from the normal distance error by approximating the small segments to real curve. The error is also anglicized for improving the response speed and accuracy of the motion control.The motion control system is digital controlled. The noise and interference, the common issues in the digital system, cause the big static errors, or even unsteady vibration. To remove the noise online, a fast discrete wavelet algorithm is proposed. With the fast development of VLSI technology and mature of FFT-based DSP technology, the wavelet transformation algorithm can be easily implemented on hardware configuration.The motion control can efficiently realize the motion tracking or parametric motion control through real-time controlling the location and speed of motors in the transmission mechanism. In order to realizing high-speed, high-accuracy simulation and testing motion control algorithm, the multi-processing is used in the motion controller. It separates the logic functionality and motor real-time control. A multi-axis motion control PCI card is designed with TMS320F2812 in DSP chip, expandable motor control interfaces, high accuracy DDA interpolation circuit, encoder signal processing, DAC interface circuit, and I/O level processing.The multi-axis motion control PCI card can be remotely controlled by PCI device driver program developed on Window environment. The device driver program varies with Window operating system. Window driver model (WDM), an upgraded WinNT drive program, is used in this project. It can be applied to Win98, Win200, and WinXP operating system, supports power management, auto-configuration, and plug and play. The driver development wizard provided by WinDriver can make the PCI9052 driver development easy and realize the remote control via PC.The motion and dynamical control design proposed in this dissertation is tested and analyzed on the JDYP51 serial-parallel hybrid polishing machine tool, Panasonic servo adaptor controller MADDT1207N, Panasonic servo motor MSMD022P, the home-developed motion controller for parallel structure and PC. The testing results indicate that the proposed motion control system has the advantages of high accuracy, high response speed, and flexibility and realize the design requirement.