Abstract
In recent years, the SPBM has been applied to the milling machine. A new approach is proposed to bypass the singular position appeared on the cutting path of a Stewart-Platform-Based Milling Machine (SPBMM) called in this study. Due to the offset between the contact point of the cutter and the center of the SPBMM, the SPBMM can adjust it posture to both bypass the singular position and keep the contact point on the planned cutting path to satisfy the requirement of the geometric constraint. For SPBMM, it can increase its working space dramatically in so doing. But how to find an optimal posture of the SPBMM efficiently in an infinite set of possible ones is a problem. The Genetic Algorithm (GA) is used in this study.Three themes are introduced here. For the first one, the ball mill is used as the cutter of SPBMM. Because of the symmetry of the sphere, it is convenient for us to handle all the geometric data in all direction for the same way under all circumstances.For the second theme, the end mill is used as the cutter of the SPBMM. By the adjustment of two rotational angles and of the cutter, we can control the geometry characteristics of the projected ellipse to fit both the curvature and the change of the curvature of the workpiece at the contact point to get the maximum cutting width without undercut.For the third theme, the end mill is still used as the cutter of the SPBMM. For the previous case, only one degree of freedom is allowed bypass the singular position, the SPBMM get an over-accumulated rotational angle to shift from singular position. Therefore, we only match the curvature of the workpiece at the contact point, and the degrees of freedom not constrained are used to bypass the singularity in the iso-scallop cutting path generation.In the process of numerical simulation, the satisfying results can be achieved to find the optimal posture of the SPBMM after using GA for all cases. Especially, an excellent result is shown in the case of the third theme to prevent from over-accumulated rotational angle for SPBMM to bypass the singular position.