A control system architecture for three-axes coordinate-measuring machines, using hierarchical task-decomposition techniques, is described. This architecture is based on real-time, sensory-interactive control concepts developed at the National Bureau of Standards (NBS). An inspection program consists of a series of high-level goals to be satisfied. Goals are satisfied when specified information has been obtained regarding the part. There is a decision hierarchy, each level of which provides logic for partially decomposing goals into simpler goals. The control system executes the inspection program by interpreting the decision hierarchy logic. The lowest level of the decision hierarchy generates primitive coordinate-measuring machine actions, which are directly executed. A world model hierarchy executing in parallel with the task decomposition hierarchy provides information which aids in the decomposition decisions at each level. The world model is derived from a combination of prior knowledge of the part and observations gathered during inspection. The use of a world model allows an inspection task to adapt to the particular part being inspected.
It is expected that control architecture described here will provide new research opportunities in various areas of computer-aided design/computer-integrated manufacturing (CAD/CAM). The experience at NBS in using a similar architecture for robot control systems indicates that this system can naturally incorporate new inspection technology such as continuous tracing and vision. The system will also be used in various research efforts in the area of standards. These include the development of techniques for incorporating quality assurance standards into inspection tasks, development of languages for communicating inspection programs between different systems, and identifying n new data requirements for CAD representations of parts.