A Framework for Representing and Computing Tool Accessibility

Abstract One of the criteria used to assess whether a particular tool can be feasibly used to machine all or a portion of a part is that of accessibility. This paper is the result of research efforts to develop a comprehensive view of accessibility that supports manufacturability evaluation (ME). Accessibility is defined here as a descriptive characteristic that is applied to a region of the surface of a part. It indicates the orientations that a tool can have so that the cutting portion of the tool can reach the entire region while avoiding collision between the part and the tool. An Accessibility Framework is presented that defines four forms of accessibility for an entity-tool pair: full section accessibility (FSA), partial section accessibility (PSA), full tool accessibility (FTA), and partial tool accessibility (PTA). For entities possessing FSA or FTA relative to a particular tool, there are two possible types of accessibility: open and controlled. An A-cone (accessibility cone) represents the set of all directions from which a face is openly accessible. Controlled accessibility uses an implicit form of representation. A computational approach that uses the framework to assess accessibility in support of ME is also presented. The approach is based on the idea of analyzing the compatibility of an entity-tool section pairs in broader and broader contexts. From the narrowest to the broadest the contexts are: local compatibility (LC), neighborhood compatibility (NC), and global compatibility (GC). The rationale for multiple contexts is that it enables a partitioning of the accessibility problem which can reduce computation time by quickly discarding cases of inaccessibility. The approach was implemented in a module as a part of an integrated ME system.