A knowledge-navigation system for dimensional metrology

Journal of Research of the National Institute of Standards and Technology, March-April, 2002 by Howard T. Moncarz

By direct interaction with the tolerance entities, the user can obtain an intuitive feel for the meaning of different types of tolerances and how those tolerances are determined. The intuitive feel can be supplemented by displaying appropriate text and diagrams in other windows (1) for the particular tolerance being studied.

2.3 Inspection Process

The control of the inspection process can be represented as a hierarchical task decomposition. That means that a high-level command is decomposed into simpler commands at each successive level of the hierarchy. For example, Messina, et al. (6) developed a demonstration implementation of an open-architecture, knowledge-based controller for an inspection workstation (IWS). In their IWS, the tasks for the control of the inspection process are decomposed, from the top, as manufacturing cell, workstation, equipment task, elemental move, primitive move, and servomechanism. A command from the cell to the workstation level to inspect a particular part is decomposed, ultimately, to commands to the servo controls of a coordinate measuring machine. In addition to commands and statuses sent up and down the control hierarchy, data are retrieved and stored at each level, measurements are taken at the lower levels and processed up the hierarchy, and judgements are made to intelligently account and adapt to the measurements taken after comparison with the world model (i.e., the currently estimated state of the system) while the inspection is in process. Much of the diverse information involved in the inspection process can be associated with a representation of the task decomposition of the IWS control process (6).

A 2D diagram can represent the task decomposition and even show the commands, statuses, and data flows, although the density of that information would be great. If you add in the interface standards and attempt to show how they are associated with the already dense information, it is evident that two dimensions are not sufficient to show that information clearly. Consequently, it was decided that three dimensions can show more information and show it more clearly. The thought process described in this paragraph led to the idea of "concept planes."

"Concept planes" is the idea of arranging 2D diagrams that are hierarchically structured and related to each other in a stack so that the relationship of a component in one plane relative to a component in another can be inferred by their spatial relationships. The whole stack can be rotated and various components and planes can be made invisible to allow the individual components and spatial relationships among them to be seen. Any component may be selected to retrieve the information linked to it and display it in another window.

Three concept planes are used to implement the concept described here for the inspection process. The three individual planes are shown in Fig. 4. In the left frame is the IWS control hierarchy, consisting of Cell, WS, Task, Emove, Prim, and Servo, which are acronyms that correspond to the control levels specified above. The figure could have included the commands sent down the hierarchy and the statuses sent up in response but were excluded here for simplicity. The middle frame shows the information stored or retrieved at each level of the control hierarchy. The information includes the final part specifications (FP), the workpiece (WP), access volumes (AV), setup data (SetUp), features (Feat), surfaces (Surf), edges (Edge), target points (TP), and intermediate points along the path that are referred to as way points (WPt). The right frame shows three of the interoperability standards used in the inspection process. The standards include the dimensioning and tolerancing standard, "Y14.5" (3), the standard t hat includes representation of machining features, "AP224" (10), and the dimensional inspection standard, "DMIS" (7). Note that the Y14.5 and AP224 standards are elongated to fit in more than one control level to indicate that they are used to support information exchanges in multiple levels of the control hierarchy.