| Summary: | 碩士 === 國立中正大學 === 機械工程學系暨研究所 === 100 === This study investigates the designs of five-axis machine tools in different non-smooth paths. 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. So we start with the two-axis machine tool to do the contour controlling in non-smooth path because it is easier to analyze. And we apply the results in the five-axis machine tools finally.
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 non-linear dynamics, which is perfectly suitable for 5-axis machine tools. The equivalent errors include equivalent contour error and tangent error. The system will build the equivalent error model, and make steady error the new controlling target.
The main contribution is that we study the switching ways of the contour controllers from a smooth path to another smooth path, and the effects of contour controlling performance. In fact, the non-smooth path consists of lots of smooth paths, like straight lines cascaded by an arc or arcs of different radiuses. If a curve indicated by NURBS includes knots, it usually has finite smoothness in the turning points, so it is one kind of path mationed. We will divide the switching regions by the tangent directions to express the equivalent contour errors. While the tangent errors have relations of commands, and we switch it with time to reach the contour controlling in non-smooth paths.
To ensure the practicability of the controller, we get the dynamic equations by system identification of the 5-axis machine tools, and we verify the switching ways of the designed contour controller by numerical simulations. Then we set up the PC-Based controller to simulate immediately by dSPACE/ControlDesk DS1103, and we connect it with the 5-axis machine tools to verify the results. The experiment results show that the switching ways we proposed do work.
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