CAD model-based planning and vision guidance for optical 3D co-ordinate measurement

Controlling the geometric accuracy of manufactured products is seen as an important issue, since it affects both production costs and quality. Optical measurement technology has been found suitable for various geometric control applications, and laser rangefmder devices in particular are now being used to measure large objects and structures. This thesis describes the development of a concept of CAD model-based automated 3D measurement and the evaluation of its feasibility in cases drawn from industrial needs. Automated 3D measurement can be seen as comprising two steps: measurement planning and measurement execution. Measurement planning takes place interactively using the information contained in the CAD model of the object, to yield a measurement plan in a form readable by the measurement system. In the second step, the planned measurement sequence is executed automatically under computer control using sensory feedback. The analysis and use of the results, e.g. for quality control or for guiding parts assembly, which is naturally the following step, is touched on only briefly in this work. The concept was evaluated by implementing a graphical measurement planning tool and two automatic measurement systems. The tool was built using the development environment of a commercial CAD package, which ensured compatibility with existing CAD data. The experimental automatic measurement systems were based on optical co-ordinate measuring devices and were equipped with vision systems for sensory feedback. The operation chain from CAD model-based measurement planning to comparison between the measured and designed geometries was demonstrated. Successful experiments with automatic operation controlled by the measurement plan and vision guidance were carried out and the key performance criteria were met.