Optical path design of the external diameter measurement system based on CCD and parallel light projection method with double light paths - art. no. 66251U

The principle of parallel light projection method for diameter measurement is to image the workpiece on the photosensitive units of CCD by parallel light. The object size can be obtained according to the shadow area projected on CCD. Considering the limitation of the lens' caliber and the effective length of CCD, the single light path system is incapable to measure a large size. Hence the double light paths method is presented. The left and right edges of the workpiece are respectively imaged on two CCDs. The diameter is achieved by calculating the length of the shadow field on two CCDs, plus to the distance between two parallel light paths. In order to make the object illuminance uniform, and to diminish the influence of optical errors on the measurement accuracy, the Kohler telecentric illumination system and the object plane telecentric imaging system are applied. The parallel light projection method with double light paths can amplify the measurement range while ensuring the measurement accuracy. The optical measurement theory, the parameter design and adjustment of the system will be introduced in detail.