Design and application of a new CNC command generator for CAD/CAM integration.

摘要

The interpolator, an essential component in CNC machines, generates commands for tool motion between CAD data points according to given accuracy requirements. Increasing demands on precision in machining of 3-D free-form surfaces requires the tool to move not only with very small position error, but also with smoothly varying feedrates.; To achieve this, a "Parametric Curve Interpolator (PCI)" is proposed. This interpolator can be used for machining any free-form surface represented in a parametric form. When compared with the existing linear interpolator, the proposed interpolator is superior in position accuracy, feedrate smoothness and acceleration continuity. Moreover, in comparison to the recently developed cubic spline interpolator, the PCI has the capability of handling higher order parametric curves and also ensures precise tracking in the velocity domain. In addition, for third- or higher-order parametric curves its transition between segments is velocity-continuous and acceleration-continuous. Results from real-time simulations and experiments on open-architecture CNC machines equipped with the proposed interpolator are presented to demonstrate its practical feasibility.; Several applications illustrate the advantages of this interpolator. Its capability of interpolating all types of parametric curves is suitable, in particular, for high-precision mechanical cam manufacturing; its ability to accept variable feedrate commands can be applied to implement adaptive force control in machining and robotic arc welding; and its ability to calculate present and future velocity and acceleration along a desired path makes it an ideal command generator for feedforward torque control.; We believe that the combination of the proposed interpolator and the open architecture machine controller further advances the state of the art in the area of command generation which is an important aspect of CAD/CAM.