A positioning error self-correction method for image measuring instrument

Image measurement based on machine vision is a promising method for the precise measurement of workpiece. As for a large sized workpiece that exceeds the FOV (field of view) of the lens, series of images have to be taken and image mosaic must be performed to implement measurement. When the large workpiece to measure is lack of characteristics, we have to rely on the precise motion control system to locate the camera. However, positioning error will be introduced into the system because inaccuracy will inevitably exist in design and installation mechanically and this will lead to the inaccuracy of panorama after image mosaic. A camera positioning error was self calibrated through image mosaic operation for large workpiece with abundant characteristics. Because the image measuring instrument usually use close loop control system which has high repetitive positioning precision, the system can compensate the positioning error using self calibrated data. Consequently, image mosaic for large workpiece which has few characteristics can obtain high accuracy using corrected positioning error motion control system and experiments proved this conclusion.