Global smoothing of short line segment toolpaths by control-point-assigning-based geometric smoothing and FIR filtering-based motion smoothing

摘要

The toolpaths for curved surfaces generated by most existing computer-aided-manufacturing applications are always consisted by short line segments. Due to the first-order discontinuity of the short line segment toolpath, the precise following of them must result in frequent acceleration/decelerations, which is easy to excite structural vibration of the machine tools, thus degrading the machining quality. To solve this problem, local corner rounding approaches are widely researched, however, most areas on the tool-path after corner rounding remains linear segments, unlike the global smoothing method who replaces all short line segments to spline curves thus obtaining smoother feed motion. Compared with the local corner rounding method, the global smoothing always requires iterative computes to satisfy the accuracy requirement, which makes it so time consuming that can hardly be utilized in CNC systems. To deal with above problem, this paper proposes a highly stable global smoothing method which does not need iterative computations. This is realized by a control-point-assigning-based global geometric smoothing algorithm and a FIR (Finite Impulse Response) filtering-based global motion smoothing algorithm. During global geometric smoothing, the short line segment toolpath is replaced by piecewise B-spline curve segments whose control points are directly assigned under the error tolerance constraint. During the global motion smoothing, a fast spline interpolation method based on FIR filtering is provided to generate smooth axial position references of the piecewise B-spline curve segments under the axial drive constraint. The whole global smoothing approach does not require pre-processing or iterative computation, which makes it easy to be applied. Extensive illustrations including numerical tests and experimental verification/comparison tests demonstrate the favorable effects of the proposed method in real-time capability and motion smoothing performance. Comparing with typical local corner rounding approach, the proposed global smoothing approach results in shorter motion time and better smoothness. Comparing with typical existing global smoothing method, the proposed method performs better in no required pre-processing and high-order motion smoothness.