Patent GB-937453-A (GB)
Title: Improvements relating to apparatus for indicating small movements
Inventor: DYSON JAMES
IPC: G01B11/00
Filed: 1959-11-17
Abstract: 937,453. Indicating small movements. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Nov. 17, 1960 [Nov. 17, 1959], No. 38979/59. Class 40 (3). Apparatus for indicating small lateral movements of a body from a straight line reference axis comprises an optical object attached to the body, an optical system arranged to cause a beam of light from said object to tend to form an image coincident with a reference position fixed relative to said object for all positions of said object on the optical axis of said optical system, a light-responsive device positioned to receive light from said image when it coincides with said reference position and means for laterally displacing and rotating said beam at a steady speed in a cylindrical path so that the said lightresponsive device receives only pulses of light from said image, and the arrangement is such that when the body is on the reference axis the time intervals between successive pulses are equal, but lateral movements of said body from said axis cause the time intervals between successive pulses to vary, and means are included for indicating the variations in the lengths of said time intervals and, in consequence, the movements of the body from the reference axis. In the diagrammatic arrangement, Fig. 1, identical curved mirrors 1, 2 are spaced apart a distance equal to their radius of curvature so that the image and object are coincident for all positions of an object on the optical axis X, Y. Semi-transparent mirrors 5, 6 are disposed in an enclosure 9 movable along the axis X, Y so that the image 8 is at a fixed position relative to an object 7, when the object 7 remains at a fixed distance from the axis X, Y during movement of the enclosure 9. In the arrangement shown, Fig. 2, the object 7 of Fig. 1 is represented by an illuminated slit 11 in an opaque screen 12, and the light beam representing the optical path, after traversing the optical axis X, Y and reflection at the semi-transparent mirror 6 forms the image of the slit 11 at a slit 16 in an opaque screen 15 behind which is located a photo-electric cell 17. A plate glass member 18 is rotated about an axis 19 joining the slit 16 and the intersection of the mirror 6 by the axis X, Y, and for the disposition shown in Fig. 2, with the image of slit 11 passing to the slit 16, the rotation of the plate 18 produces during each revolution two equally spaced pulses from the photo-cell 17. If during the movement of the enclosure 9 along a line or surface to be tested, the relative distance of the object slit 11 from the fixed optical axis X, Y is changed, the image is no longer formed in the path 19 coincident with the slit 16, but is displaced to the left or right so that by the rotation of the plate 18 two unequally spaced pulses are derived during each of its revolutions. The difference in the intervals between the pulses is detected by a circuit which may be of the form described in Specification 937,454, and is utilized to provide an indication of the movement of a body on which the enclosure 9 is mounted relative to the fixed reference axis. The arrangement may be extended to detect movement in two directions at right angles by providing two initially perpendicular slits in the screen 12 and two associated slits in the screen 15. The arrangement may be utilized to correct the movement of a lathe tool in relation to a fixed straight lathe bed. Specification 870,461 also is referred to.