Distributed NURBS interpolator for high-speed and high precision machining

NURBS interpolation is very important for high-speed and high-precision five-axis machining. In order to get a small chord error with high precision and high speed machining, a short interpolation cycle T is necessary. But short interpolation cycle will lead to high CPU load of the CNC controller. This paper tries to solve this conflict with “Distributed interpolator”, which assigns five-axis NURBS interpolation to the intelligent servo drives. Firstly, the NURBS curve in machining space is transformed to a new NURBS curve in axis space, and consequently discomposed to independent NURBS curve for every axis individually. In the real time running stage, the CNC system just needs to convert the prepared axis curve data and trigger the interpolators on the servo drives. The synchronization of the interpolators in the individual servo drives is critical for the contour error. The paper use EtherCAT as the data exchange protocol between CNC controller and servo drives. The EtherCAT controller can provide highly synchronized signal to trigger the servo drives for interpolation and servo control loops. This paper also introduced an experimental system.