3D MEASUREMENT CONTROLLED BY A CAD MODEL-BASED MEASUREMENT PLANNING AND VISION SYSTEM

Optical coordinate measurement systems will benefit from developments similar to those taking place in robots, namely off-line programming capability and intelligent sensors. Research work towards these goals is reported here. An experimental system with CAD model-based measurement planning and vision control has been constructed and its feasibility demonstrated. The system comprises a measurement planning tool, a measurement robot with vision guidance and a means of visualizing and comparing the measured results with the design data. The measurement planning tool is based on a commercial CAD system and enables the use of existing CAD models of the objects to be measured as a basis for planning. It generates a measurement model file (MMF) containing instructions for controlling the measurement robot, which is an optical coordinate measurement device based on the laser rangefinder principle and supplemented with a vision system for guiding the measurement to planned target points. The measured coordinate values can be compared with design values either graphically or numerically. The performance of the experimental system was demonstrated and evaluated. In the demonstration case a measurement sequence was planned and saved in the form of a MMF, whereupon the measurement robot was able to execute the sequence reliably according to the MMF and measure the planned target points with vision guidance. The pointing repeatability of the vision guidance function was 0.019 mRad (standard deviation), which is equal to 0.19 mm at a distance of 10 meters, and the corresponding pointing accuracy was better than 0.04 mRad. The 3D measurement had an average repeatability of 0.3 mm (standard deviation), and the absolute accuracy of averaged measurement results was better than ±1 mm (for x, y and z) in 81% of the cases. The next phase of the work will include piloting the system in an industrial application.