摘要
当今世界各国制造业广泛采用数控技术提高制造能力和水平。大力发展以数控技术为核心的先进制造技术已成为世界各发达国家加速经济发展、提高综合国力和国家地位的重要途径。X-Y平台系统的精密轮廓跟踪控制在数控机床中具有代表性,对提高数控系统加工精度和性能具有重要的作用。随着高精度复杂型面零件加工要求的不断增长,轮廓精度已成为数控系统的重要精度指标。
本文针对永磁同步直线电机(PMLSM)直接驱动X-Y平台系统易受到系统动态的非线性、系统不确定性因素以及曲线轨迹的轮廓误差模型相对复杂等问题的影响,建立实时轮廓误差模型,采用一种交叉耦合控制器(CCC)结合位置误差补偿器(PEC)的控制方法,减小系统的轮廓误差。位置误差补偿器通过预先补偿的方式达到同时降低轮廓误差及位置误差的目的。并采用PDFF控制设计单轴速度控制器,间接减小轮廓误差。
首先,本文介绍了直接驱动X-Y平台的发展应用、结构及工作原理,建立了单轴永磁同步直线电机与X-Y平台的数学模型,并且根据X-Y平台系统特点分析了影响其轮廓精度的因素。直接驱动技术消除了传统伺服系统中间传动环节,具有推力大、摩擦力小、动态刚度和定位精度高等特点。但是,系统对扰动等不确定性更为敏感,且受系统非线性因素影响,使其伺服性能大大降低,需要通过设计伺服控制器来提高系统的鲁棒性和轮廓精度。
其次,本文在描述X-Y平台轮廓误差概念的基础上,计算了直线运动轨迹、圆形运动轨迹和任意曲线运动轨迹的轮廓误差模型。总结了可以提高轮廓精度的几种方法。然后分别设计了单轴速度控制器和位置控制器,单轴控制器侧重于通过单轴跟踪控制以减小位置跟踪误差,进而减小轮廓误差。并对仿真结果进行了比较和分析。
最后,本文采用一种改进的交叉耦合控制结构,设计了交叉耦合控制器。同时设计了位置误差补偿器,该控制器可根据实时轮廓误差、当前进给速度和两轴的跟踪动态特性计算出来,结构简单易实现。并通过预先补偿的方式可以同时降低系统的轮廓误差及位置误差。
本文以日本Yokogawa LM110系列永磁同步直线电机直接驱动X-Y平台为研究对象,并用Matlab7.0软件进行仿真试验及分析。仿真的结果表明,采用PDFF控制器可以有效提高单轴控制精度;交叉耦合控制器和位置误差补偿器相结合的控制结构,能有效提高直接驱动X-Y数控平台伺服系统的鲁棒性和轮廓精度。
Nowadays, CNC technology is widely used to improve manufacturing capacity and the level. It is important way to accelerate economic development, enhance the comprehensive national strength and the national status that developed countries vigorously develop with numerical control technology as the core of the advanced manufacturing technology. There are the vital role and representation to improve the machining accuracy, performance and precise contour tracking control of CNC in X-Y table. With the growing of high accuracy complex surface parts processing requirements, contour precision has become an important precision index in CNC system.
To weaken the influences of nonlinear system dynamic, uncertainties, and complex contour error model of curve trajectory for direct drive numerical control X-Y table servo system driven by Permanent Magnet Linear Synchronous Motors (PMLSM), the real-time contour error mode is established and a method of Cross-Coupled-Control(CCC) combined with Position Error Compensator(PEC) is used to reduce contour error. Rather than focusing only on contour error reduction, the approach can reduce position error. And the PDFF control is used to design the single axle speed controller, indirect to reduce the contour error.
Firstly, the development, application, construction and work principles of direct drive X-Y table were introduced in this paper. Mathematical models of single axis permanent magnet synchronous linear motor (PMLSM) and X-Y table were established. According to the characters of X-Y table, the factors that affect the contour precision were analyzed. Direct drive technology eliminates the middle transmission parts and has the merits of large thrust, low friction, high dynamic stiffness and high positioning precision. However, X-Y table is sensitive to the uncertainties and nonlinear factors that its servo performance decreased, so it is necessary to design servo controllers to improve the robustness and contour precision.
Secondly, based on describing the concept of X-Y table contour error, contour error model of the linear path, the circular path and the free-form path were calculated. Several methods of improving contour precision were summarized. Then the single axis speed controller and the position controller are designed respectively. Single axis controllers emphasizes on reducing the contour error through reducing single axis position errors. Then simulate and analysis the result.
Finally, the article used a structure of modified CCC and designed the CCC. Simultaneously the position error compensator is used. It is calculated easily by the real-time contour error, current federate command and tracking dynamics of each axis. Rather than focusing only on contour error reduction, the approach can reduce position error.
Yokogawa LM110 permanent magnet linear synchronous motor X-Y table is considered as the controlled object, and used the Matlab7.0 to simulate and analysis the result. The simulation result indicated that the PDFF controller improved the single-axis precision effectively. The structure of the Cross-Coupled-Controller and the position error compensator can enhance the robustness and the contour precision of X-Y table effectively.
引文
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