ACCELERATING TOOL PATH COMPUTING IN TURNING LATHE MACHINING Antonio Jimeno, Sergio Cuenca, Antonio Martínez, Jose Luis Sánchez Romero Computer Science Technology and Computation Department University of Alicante Apdo. Correos 99 03080 Alicante, Spain email: {jimeno, sergio, amartinez}@dtic.ua.es ABSTRACT Tool path generation is one of the most complex problems in Computer Aided Manufacturing. Although some efficient strategies have been developed, most of them are only useful for standard machining. The algorithm called Virtual Digitizing avoids this problem by its own definition but its computing cost is high and make it difficult for being integrated in standard machining in order to adopt the new ISO standard 14649. Presented in the paper there is a Virtual Digitizing architecture that takes the advantages of Reconfigurable Computing (using Field Programmable Gate Arrays) in order to improve the algorithm efficiency. FPGAs are used as low cost and low frequency coprocessor to accelerate the calculation of tool path, meeting the actual restrictions of the Computer Numeric Controls (CNCs) at the same time. A prototype has been implemented to measure the real impact on the total computing time. 1. INTRODUCTION In order to machine a surface by means of a cutting tool on a CNC machine tool, a series of 3D or 2D coordinates that define its motion must be supplied. These points are usually referred to as tool centre positions. In this way, the problem can be expressed as obtaining a trajectory of tool centres that defines the desired object to be machined with a given precision, in literature the problem is also known as the tool compensation problem [1]. With a given object and tool, a solution cannot always be found because of the curvature of the surfaces [2]. In these cases, the problem is redefined in order to obtain a trajectory that defines the closest surface that contains the desired object (that is, without collision). Figure 1 shows the trajectory (tool path) of a circle centre point in order to define a surface. In this case, for the sake of simplicity, the problem is presented in 2D. For 3D surfaces the problem becomes more complex. Partial solutions to this problem use surface offsets generated by different methods [2,3,4]. However, these offset-surfaces are restricted to one-radius tools (i.e spherical, cylindrical and conical) and are not valid for more complex tools, such as toroidal ones with two radii. Moreover, in most cases, self-intersection problems arise according to the surface curvature. Thus, more sophisticated and higher cost computing techniques are needed to detect and solve these problems. The Virtual Digitizing algorithm [5] computes the tool path by means of a “virtually digitised” model of the surface and a geometry specification of the tool and its motion, so can be used even in non-standard machining (retrofitting). This algorithm was developed by one member of our research group and is included in commercial shoe last CAD/CAM software called Forma3D® (from the Spanish Footwear Research Institute, INESCOP). This software is currently a world leader in the CAD/CAM software for shoe lasts. The Virtual Digitalization is simple, robust and avoids the problem of tool-surface collision by its own definition, but its computational is higher than the others approaches. On the other hand, the idea of integrating trajectory generation into the numerical control itself is now becoming more common. The new ISO standard 14649 (also called STEP-NC) remedies the shortcomings of ISO 6983 by specifying the machining processes rather than machine tool motion by means of machining tasks. Fig.1. Circle trajectory in order to get a rectangle