| Summary: | 碩士 === 國立中正大學 === 機械工程學系暨研究所 === 99 === This thesis is to study the contouring control of 5-axis machine tools with S-type acceleration/deceleration. Due to the additional rotation axes, it is more difficult to achieve high speed and high accuracy for 5-axis machine tools, compared to the conventional machine tools. The main difficulties include: (1) the contouring controller is difficult to design; (2) in a 5-axis machine tool, the velocity profile of the machining path possesses complicated relationship with that of each axis, and hence is difficult to design.
For the contouring controller design, the method of equivalent errors is adopted in this thesis. The method can be applied to general multi-axis motion systems with complicated nonlinear dynamics, which is perfectly suitable for 5-axis machine tools. Virtually all existing results take the viewpoint of the Cartesian 3-D space, i.e., the contour error of a 5-axis machine tool is decomposed into the usual contour error and orientation error. Then, two contouring controllers are designed for reducing these two types of errors separately. In this thesis, the machining path (including tool center point and tool vector) is described as a trajectory in a 5-D space formed by generalized coordinates. Then, the method of equivalent errors is used to perform the contouring control in the 5-D space. In doing so, the usual contour error and orientation error are integrated.
For the acceleration/deceleration, the S-type acceleration/deceleration is employed to yield smooth velocity profile and hence reducing contour errors. In a 5-axis machine tool, the effect of rotation axes makes the machining path in the task space significantly different from the path formed by the 3 linear driving commands (called driving path). Based on the curvature of the driving path, we propose a systematic design method for planning the acceleration/deceleration of a 5-axis machine tool, so that both tangential and centrifugal accelerations along the driving path satisfy the physical limits of the machine. The method will lower down the feed rate where the curvature of the driving path is large. In doing so, the contour errors can be reduced, resulting in better contouring performance.
In this thesis, numerical simulations for contouring a circular path with the proposed method and the conventional contouring control method are presented. The results show that the proposed method of equivalent errors can achieve better performance. In addition, the proposed S-type acceleration/deceleration planning and the usual S-type acceleration/deceleration planning are numerically compared, and the results show that the proposed planning can indeed reduce the error.
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