Dimensional Inspection Planning for Coordinate Measuring Machines

S. N. Spitz

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This thesis documents the development of a fully automated dimensional
inspection planner for coordinate measuring machines (CMMs). CMMs are
very precise Cartesian robots equipped with tactile probes. Given a
solid model of a manufactured part, the goal of dimensional inspection
is to determine if the part meets its design specifications. The
planner first generates a high-level plan that specifies how to setup
the part on the CMM table, which probes to use and how to orient them,
and which measurements to perform. This plan is then expanded to
include detailed path plans and ultimately a program for driving the
CMM.
The planner has been implemented and includes an accessibility
analysis module, a high-level planner, a plan validator (through
collision detection), a simulator, and a path planner. We tested the
planner on real-world mechanical parts and it is sufficiently fast for
practical applications.
The accessibility analysis module provides a suite of algorithms to
compute global accessibility cones (GACs). GACs are sets of
directions along which a probe can contact given points on an object's
surface, and are used by the planner to determine part setups and
probe orientations. The GAC algorithms make use of widely available
computer graphics hardware, and are very efficient and robust.
The high-level planner generates plans by solving a constraint
satisfaction problem (CSP), where hierarchical constraints define the
requirements of good plans. Plans are extracted using efficient
clustering techniques. High-level planning by clustering and without
backtracking is a novel approach.
The path planner finds an efficient and collision-free path for the
CMM to inspect a set of points. We use a roadmap method to connect
the points through simple paths. Then, we find an efficient tour of
the roadmap by solving a traveling salesperson problem. The path
planner easily integrates CMM heuristics and is probabilistically
complete.