Patent GB-869289-A (GB)
Title: Optical device for a correct adjustment and reading of the extent of the displacement of a slidable carriage
IPC: G01B11/00
Filed: 1959-02-02
Abstract: 869,289. Optical gauging-apparatus. HENSOLDT & SOHNE OPTISCHE WERKE A.G., M. Feb. 2, 1959 [Feb. 10, 1958], No. 3546/59. Class 106 (2). [Also in Groups XX and XXII] An apparatus, such as a length measuring machine, radial drilling machine, or other machine tool having a carriage slidable on a guideway in a base, and an optical device for projecting an image of a part of a measuring scale on to a reticle, so that displacement of the carriage may be determined, incorporates optical means whereby tilt of the carriage, due to inaccuracies in the guideway, is compensated. The optical means may be (a) a mirror fixed to the base so as to be parallel to the guideway; (b) a mirror movable by the carriage parallel to the guideway; (c) pendulously suspended lenses on mirrors; or (d) a fixed mirror arranged to form a virtual image of the scale on the plane where measurement takes place. In the arrangement of Fig. 1 for determining the length of a workpiece 110 by measuring the displacement of a movable carriage 114 from a zero position, there is provided on the machine body 117 a guideway for the carriage and also a fixed measuring scale 118. Fixed to the carriage is an objective 119 having its front focal plane in the plane of the scale 118 so that parallel light emerges from the objective and after lateral deflection by orthogonal mirrors 121 is deflected at 122 on to a mirror 123. This mirror is fixed to the machine body 117 alongside the measuring scale 118 and has a length substantially equal to this scale. As the carriage 114 slides along the guideway an image of the graduations on scale 118 is focused by the lens 124 on a scale reading device 125 such as that described in Specification 810,820 after reflection at the fixed mirror 123 which thus compensates for small tilts in the carriage due to inaccuracies in the guideway. In an alternative form the long mirror 123 is replaced by a small mirror slidably mounted on an accurate guideway within the machine body 117 or carried by a cable connected for movement with the carriage 114. The tilt compensating mirror may be provided by the upper surface of the fixed measuring scale. Tilt compensation may also be provided by a reflector 416, Fig. 6, which is pivoted about an axis transverse to the direction of movement of the carriage and receives light from the objective 414, and directs such light on to a scale reader 418, 419. In further forms tilt compensation is provided by a pair of lenses, one of which is pendulously mounted so that on a tilt of the carriage the lens pair acts as an optical wedge (Fig. 7, not shown); or by a pendulously mounted prism 442, Fig. 8, which directs the light received from the measuring scale after reflection at a prism 441, through lenses 443, 444 and mirror 445 on to a scale reader 446. A further form is shown in Fig. 9, where a workpiece 451 is carried on a base 452, including a measuring scale 450 and a mirror 453 which projects a virtual image of this scale on to the workpiece, so that this image can be seen in a microscope 454. This microscope is mounted in a carriage 454<SP>11</SP> slidable in a guideway 4541 on the base 452, as also is a microscope 455 which via reflectors 456, 457 views the workpiece 451. The microscope 455 may be omitted and mirror 453 made semitransparent so that an image of the scale 450 superposed on an image of the workpiece 451 can be seen in the microscope 454. As shown in Fig. 10, the workpiece 470 is on a base 471 carrying a slidable part 471<SP>1</SP> bearing a semireflecting cube 472 and a mirror 476, which forms at M<SP>11</SP> a virtual image of a measuring scale 475. The cube 472 forms a virtual image of M<SP>11</SP> at M<SP>1</SP> on the workpiece 470, this image and an image of the workpiece being projected on to a microscope having a reticle 479 by objective 477, the microscope being movable in a guideway 491 in a slidable base part 471<SP>1</SP> and also being movable vertically in another guideway for focusing purposes.