Trajectory Description And Interpolation In Networked Motion Control System

Along with the rapid development of equipment machining in China, the requirement for CNC machining, especially multi-axes CNC machining has been increasing day after day. While at the same time, the correlated research has being studied, including motion control system, distributed networked system, clock synchronization, CNC automatic programming, etc. Usually, CNC maching systems make use of automatic programming based on G-Code for the enhancement of efficiency. On the other hand, however, such approach introduces the "twice interpolation" problem, which reduces machining precision.Solution was proposed in this paper for the reduction of machining precision caused by "twice interpolation" problem, that makes use of the description of AutoCAD to program the cutting path directly rather than transform into G-Code, and then implements the machining based on the distributed networked motion control system. Therefore the reliability, automation and precision of CNC machining could be advanced. Multi-axes interpolation algorithms would be completed within the motion controllers in the network, which requires a synchronized clock to ensure that all controllers in the motion control network could be running and finish the designed motion trajectory simultaneously.The distributed networked motion control system in this paper is consisted of supervisor computer, motion controller PEC8000, AC servo driver and motor and chief clock. Data exchange between devices is done via Ethernet. This paper analyzed the structure of DXF file of AutoCAD in depth and programmed to read, abstract and analysis graphics within the file. Then the description of AutoCAD graphics would be transformed into the self-developed local description, distributed into the controllers in network. Simplification was considered when describing the complex free curves and surfaces, using NURBS method, to enhance the efficiency of data transmission and calculation. Motion controllers in network take charge of the implementation of interpolation algorithm independently, with the help of clock synchronization based on IEEE1588. Also crystal oscillator difference was introduce to improve the precision of clock synchroniation. A 3-axes motion control platform was established, on which validation for interpolation algorithms were carried on. Result illustrated that the precision of CNC machining would be controlled under 3um.