Hardware approach to tool path computation for STEP-NC enabled CNC: A case study of turning operations

Abstract

Tool path generation is an important task that must be supported by the controller of a STEP-NC compliant CNC machine tool. However, these algorithms demand higher computation performance, which makes the implementation on many existing systems very slow or even impractical. This fact is one of the main barriers for the adoption of the STEP-NC standard for CNC machines. Hardware acceleration is an incremental solution that can be cleanly added to these systems while keeping everything else intact. It is completely transparent to the user. The cost is much lower and the development time is much shorter than replacing the computers by faster ones. The resulting system is much more robust. This paper presents a hardware solution for the implementation of a highly accurate and robust tool path generation algorithm, called virtual digitizing. This algorithm has multiple advantages when compared to traditional algorithms and can be applied to standard, as well as non-standard machining (retrofitting). We have run a series of experiments to explore the design space and show different hardware/software solutions, as well as the performance, cost and precision trade-offs. Our hardware has been implemented with Xilinx FPGAs and coded with a high level hardware description language (Handel-C). The execution time is two orders of magnitude faster than legacy CNC systems and one order of magnitude faster than modern PCs.