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Alignment and Angle Measurement Techniques
Published in Rajpal S. Sirohi, Mahendra P. Kothiyal, Optical Components, Systems, and Measurement Techniques, 2017
Rajpal S. Sirohi, Mahendra P. Kothiyal
An autocollimator is a collimator with an eyepiece for viewing the autoreflected image of its graticule for measurement of small angles. In Fig. 5.11, G is the illuminated graticule projected by the objective O. Light reflected back from a mirror M set normal to the collimated bundle is focused by the objective lens and forms an image of the graticule directly superimposed on the graticule itself. If the mirror is rotated slightly about any axis perpendicular to the autocollimator’s optical axis, the return image of a point K will be formed at K′ on the graticule displaced by a linear distance s proportional to the angle rotation 0 and given by s = 2fθ
Straightness and Alignment
Published in Toru Yoshizawa, Handbook of Optical Metrology, 2015
In optical alignment systems, the datum or reference line is defined by the optical axis of a precision optical instrument. In different configurations of a telescope, a collimator, and targets, it may be made sensitive to position or angle: Alignment telescope: An alignment telescope establishes an accurate line of sight. The optical system has the essential feature that the direction of the optical axis is precisely conserved during focusing. With the wide setting range of objective distances from the tube ending to infinity, these instruments serve to determine the deviation of targets with respect to the reference line (Figure 17.2) and are used for the alignment of bore holes, guides, axes, planes, etc.Alignment collimator: An alignment collimator serves to project the image of a reticle along a reference line over a range of distances. In combination with an alignment telescope (Figure 17.3), this has, in fact, the effect that the target is moved to infinity. Due to the parallel beams between the telescope and the collimator, the system becomes insensitive to a lateral displacement of the optical axes and thus insensitive to the targets’ lateral position, but sensitive to the angle and thus to the tilt of the collimator. This configuration therefore serves the alignment of the direction and is used for aligning bore holes, shafts, guides, etc. with respect to a reference line.Autocollimator: In an autocollimator setup, the collimator is also used as the observation telescope. This is achieved by introducing a beam splitter close to the front focal plane of the collimator optics (Figure 17.4). In a photoelectric instrument where visual observation is superseded by an electronic readout, the illuminated reticle is replaced by a back-lighted slit or crossed slits for a two-axis instrument or an LED or laser diode. The setup from Figure 17.4 is, in fact, obtained by folding Figure 17.3 and replacing the collimator by a mirror. Consequently, the configuration serves in the alignment of the direction of the mirror mount with respect to an optical reference line.Alignment autocollimator: Alignment autocollimators are a combination of the foregoing variants. They offer the possibility to measure both, the lateral displacement (straightness deviation) and the direction (tilting) of the target (Figure 17.5). The target is thus a combination of a mirror reflector and a reticle.
Small-angle measurement in laser autocollimation based on a common-path compensation method
Published in Journal of Modern Optics, 2019
Yan Guo, Haobo Cheng, Yongfu Wen, Hengyu Wu, Yumin Wu
Small-angle measurement is of great importance in industrial production and quality inspection, such as in the profile measurement of optical surfaces, precision alignment of mechanical systems, motion control of machine tools, and calibration of angle standards (1–4). Among many angle measurement methods, laser interferometry (5,6), total internal reflection (7), and autocollimation (8,9) have made great progress over the past few decades, owing to the advantages of non-contact and high precision. However, a laser interference system with bulky structure and environmental susceptibility is not suitable for workshop measurement. The total internal reflection method is very sensitive to the intensity fluctuation of a light source. An autocollimator is an angle measuring apparatus that projects a collimated laser beam onto a plane mirror and can obtain the rotation angle of the mirror by calculating the deviation between the reflected beam and the incident beam. Because the autocollimator has a simple structure and high accuracy, its use in the angle measurement field has become more widespread (10).