Studies on the Exchangeability of Different APT Interpreters for 5-Axis Machine Tool Applications

Abstract

Generally, the NC format is the description for the positioning and/or the movement of its linear and rotary axes. As the multi-axis machine tools have a variety of configurations, their NC codes are not exchangeable. This issue leads to some inconvenience and confounding in the manufacturing processing schedule. Furthermore, when the specifications of tool such as length, diameter or shape are reset, the NC program must be regenerated accordingly. That is to say, the exchangeability of NC program among different five-axis machine configurations is an important issue in making better usage of industrial five-axis machine tools for efficient applications. An APT program records the tool path, tool vector and cutting information, etc. In particular, the recent development of APT format can provide the capability recording the motion posture of the tool such as the tool orientation, the position and its normal vector of the tool contact point. Therefore, it can solve the problems of the exchangeability for the different machine tools as well as the online resetting of tool specifications, even the tool posture. In this paper, a new method was proposed to interpret the APT code into tool movement data including toolpath, location, tool orientation, the contact point and its contact vector, etc., which can be applied to the conversion of different NC codes, or be connected to the controller of the machine tool so as to proceed the interpolation calculation for directly machining control. Moreover, the application scope can be extended to the verification of machining and to drive a virtual machine tool for previewing. Since the APT format varies according to different CAD/CAM systems, a common intermediate interchange standard (CMIS) was proposed, designed and verified in this paper as a feasible solution for the exchangeability of different APT formats. The process of the proposed method includes interpreting a variety of APT program into a common standard format, and then transforming this intermediate standard code into various NC programs for the corresponding machine configurations. An example was used to demonstrate how to convert an APT generated by CATIA software into intermediate code for a Table-Table five-axis machine tool with two rotary axes attached on table (XYZAC configuration). As the APT contains the definition of inclined plane, so the homogeneous coordinate transformation was adopted to transform the coordinate system of the inclined plane into the work coordinate system; it was further transformed into the corresponding NC program via an inverse kinematics transformation. This example has shown the feasibility of the method proposed. Moreover, the research can be applied not only to the exchangeability of different APT format but also to the other related applications such as the verification of machining error and the drive of virtual machine tool.