A look-ahead transition algorithm for jump motions with short line segments in EDM

Abstract

Most electrical discharge machining (EDM) machines provide only linear or circular interpolations. To machine a workpiece with a complex geometry, a large number of line segments in terms of G01 codes are used to represent a feeding path in EDM. Periodic jump motions of an electrode are adopted such that the debris concentration in the discharge gap can be reduced and clean dielectric can enter into the discharge gap, thus increasing the effective discharge ratio and improving the machining stability. In the conventional way, the electrode will experience a deceleration to zero, and then an acceleration at junctions connecting two adjacent line segments. To solve this problem, a real-time look-ahead transition algorithm and a motion planning scheme for jump motions with short line segments are proposed. A parametric spline curve is used to blend adjacent short line segments. A transition curve can use the discharge gap as the approximation error tolerance for jump motions in EDM. Analytical calculations for the curvature extrema, real-time performance are also considered in the transition scheme. The motion planning with a look-ahead function for jump motions is developed to obtain a feedrate profile of jump motion. This motion planning scheme includes a path-smoothing, a bidirectional scanning, and a jerk-limited feedrate scheduling. Simulation results show that the velocity profile of the proposed motion planning is smoother. Machining tests for a workpiece with complex curves shows that the proposed method can reduce the machining time by 12.16 % as compared with the traditional method.