Measurement method of repeated positioning accuracy of pinhole runnerbased on combination of laser and CCD

The pinhole runner is the key component of the optical-path automatic calibration system of an experimental device, and the repeated positioning accuracy is one of its important indexes. In order to effectively measure the repeated positioning accuracy of the pinhole runner in vacuum environment, a measurement method based on the combination of laser and charge coupled device (CCD) was proposed, and the position repeatability of laser spot center of runner filtering pinhole was taken as the evaluation index of its repeated positioning accuracy. A complete set of measurement system was built, the laser spot filtered through the runner filtering pinhole was collected by CCD, and the laser spot image was preprocessed by the image processing methods, such as filtering and noise reduction, threshold segmentation, binarization and edge detection. The least square method was used for circle fitting of the laser spot, and the center coordinates of laser spot were obtained. Compared with laser interferometer in non- vacuum environment, the angular deviation between them was only 11″, which showed that the measurement method had high accuracy and met the measurement requirements. Finally, the repeatability measurement of the pinhole runner in vacuum environment was carried out for about 60 times forward and backward reciprocation in about 6 hours. The results show that the method can effectively measure the repeated positioning accuracy of the pinhole runner in vacuum environment.