Abstract:The direct drive XY motion platform can realize the movement of multi axis high-end CNC machine tools in the XY coordinate system. It has the advantages of fast response speed and high machining accuracy, and is the key component to achieve precise contour control. However, since the direct drive XY motion platform uses two permanent magnet linear synchronous motors as the power source, the nonlinear dynamics in the system will directly affect the motion of the platform without attenuation of the transmission links. In addition, the matching and coordination of the two feed drive axes in the motion process will also reduce the contour machining accuracy of the system. Therefore, in order to solve the problem that the precision direct drive XY motion platform is vulnerable to the influence of the system uncertainty dynamics and the dual axis coordination matching when performing the machining tasks, an adaptive nonlinear sliding mode contour control (ANSMCC) method based on the reference adjusted contour error (RACE) model and uncertainty compensator (UC) is proposed in this paper. Firstly, the dynamic model of the direct drive XY motion platform is established, which includes the uncertainty factors such as parameter variations, external disturbances and nonlinear friction forces. Next, because the traditional method of regarding the normal component of the tracking error as an approximate contour error is not applicable to the large curvature contour machining path, a RACE model is established to calculate a more accurate contour error by using coordinate transformation and equivalent contour error theory. Since the direct drive XY platform servo system will be affected by the nonlinear dynamics in the operation process, the ANSMCC method and UC method are designed for the linear reference model and the nonlinear dynamics respectively to control. Based on the designed RACE model, an ANSMCC is designed. The nonlinear sliding mode surface is introduced in ANSMCC to replace the traditional linear sliding mode surface, which can guarantee that the system has a fast dynamic response speed while reducing the contour tracking accuracy. At the same time, aiming at the uncertain dynamics in the system, the UC method and linear sliding mode controller are designed to reduce the error between the reference model and the actual object, and compensate the influence of uncertain dynamics on the contour accuracy. Finally, in order to test the effectiveness of the contour control method proposed in this paper, three comparative experimental conditions including no-load low-speed condition, no-load high-speed condition and load condition are conducted under the three contour control methods of adaptive sliding mode contour control (ASMCC), ANSMCC based on RACE, and ANSMCC based on RACE and UC. In order to ensure the fairness of the comparison experiments, all parameters in the experiment are repeatedly debugged, and appropriate parameters are selected to meet the dynamic and static performance of the system. It can be seen from the experimental results that the ANSMCC based on RACE and UC method proposed in this paper can reduce the contour error of the direct drive XY motion platform to -2.5~2.5μm. Compared with the other two methods, the contour tracking accuracy is significantly improved, which can meet the contour machining accuracy requirements in practical applications. The following conclusions can be drawn from the experimental analysis: (1) Compared with the traditional method of approximating the contour error by the normal component of the tracking error, the RACE model is more suitable for the reference trajectory with large curvature, which is simple and accurate; (2) By introducing nonlinear sliding surface, ANSMCC method can effectively improve system response speed and contour machining accuracy; (3) UC can compensate the influence of uncertain dynamics on the system, so that the direct drive XY motion platform servo system has strong robustness.
金鸿雁, 宫艳书, 赵希梅. 基于参考调整轮廓误差的直驱XY运动平台自适应非线性滑模轮廓控制[J]. 电工技术学报, 0, (): 59-59.
Jin Hongyan, Gong Yanshu, Zhao Ximei. Adaptive Nonlinear Sliding Mode Contour Control for Direct Drive XY Motion Platform Based on Reference Adjustment Contour Error. Transactions of China Electrotechnical Society, 0, (): 59-59.
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