Velocity planning in multi-axis EDM based on a coder-player architecture

Abstract

With a higher requirement on machining accuracy in electrical discharging machining (EDM), there is a drastically increased number of multi-axis line segments for machining complex workpieces. High speed jumping is needed for a conducive discharge gap status. The increased number of line segments, however, makes the implementation of high-speed jumping difficult. To alleviate the online computational burden for velocity planning, this paper proposes a multi-axis velocity planning based on a coder-player architecture. Under this architecture, a multi-axis feeding trajectory is represented by a series of double non-uniform rational B-spline (NURBS) curves, which are then interpolated by the unit arc length increment interpolation (UALII) method. Based on the interpolation points with a resolution of a basic length unit (BLU), a velocity limit curve is generated by considering simultaneously the constraints on chord error, acceleration and jerk. The velocity planning is implemented under a coder-player architecture. As a trajectory represented by a double-NURBS curve has C2 continuity, velocity losses can be avoided at junctions between line segments, thus smoothing of line segments at junctions is unnecessary in jumping. Machining tests showed that by the use of the velocity planning based on double-NURBS curves, the machining time for one channel of a shrouded blisk can be decreased by 29.38%.