Patent GB-1254856-A (GB)
Title: Bright line reticle apparatus and optical alignment methods
IPC: E06B9/80
Filed: 1968-12-19
Abstract: 1,254,856. Indicating alignment photoelectrically. ITEK CORP. Dec. 19, 1968 [Jan. 5, 1968], No.60410/68. Heading G1A. [Also in Division G2] Optical alignment apparatus comprises a brightline reticle 18 with a dark field background, condenser means 22 for directing radiant energy, e. g. from lamp 20 through said reticle, reference reticle 42 optically aligned with a reference axis 30, and image projection and return means 24, 26, 28 for projecting an image 10 of reticle 18 to the alignment telescope 14 and for receiving the projected image reflected back from said telescope through image 10 and transmitting the reflected image to the reference reticle to provide a quantitative representation of the misalignment of the reflected image and the reference reticle. Preferably means are provided for sensing the intensity of the reflected image at the reference reticle 42, comparing this sensed intensity with a reference level, and for rotating the bright-line reticle 18 to a position where the intensity of the reflected image is maximized. In an embodiment for aligning a body having an anti-reflective surface, e.g. a workpiece, the image 10 is formed by lenses 24, 28 and prism 26. The prism 26 serves to effectively turn reference axis 30 through 90 degrees. The telescope 14 has a focusing scale 33 for determining the location of the image 36 reflected from body 34. Two optical micrometers 50, 52 independently moveable on orthogonal X, Y axes move the reference axis relative to the body 34 to bring the image of bright-line reticle into alignment with reference reticle 42. If desired the bright-line reticle 18 may be non-symetrical in shape, have certain distinguishing features 54, 58 and may be rotatably mounted in a ring 62 about a scale 68. In a further embodiment the apparatus may be used to measure the evolute of a curved surface. The image of reticle 18 at 80 is projected by telescope 14 to 84 on reference axes 30 which also passes through the apparent centre of concave surface 88 of lens 82. The reflected image 90 is displaced from image 84 and this displacement measured as a 1 , a 2 , a 3  from the image 10 centre is found from micrometers 50, 52 and scale 33. To overcome the problem of other reflected images giving spurious results, the measurement is made when the intensity of the reflected image at the reference reticle is maximized. This has particular application with anamorphic components, e.g. cylindrical lens surfaces. In such application tilt, decentre and rotational errors in the alignment of a cylindrical lens are measured. If desired alignment can be made automatically. The reference reticle 42 is formed in a circular sensed 120 composed of photo-detectors 122. Sensor 120 is divided into four quadrants 124, 126, 128, 130; vertical position of an image 36<SP>1</SP> is controlled by Y axis micrometer 52 and horizontal position by X-axis micrometer 50. The zones 124, 126, 128, 130 have the following designations X(-)Y(-); X(-)Y(+); X(+)Y(-); X(+)Y(+). The outputs from detectors 122 are fed to appropriate comparator 138, 142, 146, 150 associated with each quadrant. A displaced image 36<SP>1</SP> causes a signal from a given quadrant to pass to its comparator which produces an X or Y output. This output is fed to the appropriate micrometer drive, 154, 156. The outputs of detectors 122 are also fed to a brightness summer 158 which feeds a signal both to a brightness indicator 160 and a comparator 162. The output from comparator 162 activates through switch 164, motor 170 which turns the ring 62 in which brightline reticle 18 is located, to give maximum brightness of the reflected image. Switch 164 is enabled by two coincident signals from null comparators 172, 174 indicating nulling of motors 154, 156 and alignment of image 36<SP>1</SP> with reticle 42. Also output of comparator 162 is suppled to a fine control 176 along with a signal from a program control 178. Program control also operates a coarse control 180 which adjusts the telescope range ring 32 on scale 33. On switching off coarse control 180 the program control utilizes the fine control to train for maximum brightness. When this is reached a switch 152 is closed and image 36<SP>1</SP> is again centred on reticle 42. The appropriate settings can then be stored by association with encoders 190, 192, 194, 196 and connecting their outputs together with those from indicator 160 to a recorder 198.