Patent GB-1144133-A (GB)
Title: Optical multi-purpose measuring device
IPC: G01D5/38
Filed: 1966-04-19
Abstract: 1,144,133. Photo-electric measurement. ERNST LEITZ, G.m.b.H. April 19, 1966 [April 24, 1965], No.17178/66. Heading G1A. [Also in Division G2] Apparatus for measuring the movement, position &c. of an object includes means causing a light beam to be scanned over the object under investigation, the light reflected at the object being directed by a beam splitting device, through which light from the scanning means has reached the object, to a photo-electric and visual investigation arrangement. The embodiment of Fig. 1 shows a measuring microscope investigating the position along a predetermined path of a workpiece to which is attached a reflector. As shown, the reflector is a cylindrical object 26 with its axis parallel to a slit 12a in the microscope optical system. Light from a source 10 is transmitted by the slit 12a which either oscillates across the optical axis or moves angularly about an axis parallel to the instrument axis. A beam splitting plate 13 transmits light to an objective lens 14 and the cylinder 26 from which light is reflected back to the beam splitter, which directs it through a carrier 16 having a number of reference marks. The light reaching the photo-cell 19 via a polarizing or dichroic beam splitter 17 is thus dependent on the properties of carrier 15 and the position of cylinder 26. The carrier may be viewed by eyepiece system 18 to aid setting up of the apparatus. Other reflecting objects may be used instead of the cylinder 26. Examples are a reflector (22) Fig. 2 (not shown) with groove-like marks, which member reflects light only from the plane surfaces; a reflector (23) having a transparent plate attached to it carrying light absorbing marks; a concave mirror (24); a prism with a grooveshaped reflecting surface; and a convex mirror. In another embodiment, Fig. 3 (not shown), the angular deviation of an autocollimating mirror (35) is determined, the mirror being associated with an object the angular position of which is to be determined, the reference mark carrier 16 being calibrated in angles. This embodiment can be adapted for use as a refractometer by inserting a prismatic test cell between the mirror and the instrument, or the reflector may in fact be the rear surface of the cell. In a further embodiment, Fig. 4 (not shown) one or more Wollaston prisms are introduced into the light path to split up the beam into two or more parts, together with any optically active elements required. The reflector used is one with a plurality of marks. This arrangement enables light beams polarized perpendicularly with respect to one another, to be used, and respective detectors for each beam. An alternative type of scanning arrangement which can be used in all the embodiments is a light-emitting semi-conductor diode shaped like the slit 12a of Fig. 1 and oscillating in the same manner. This enables a higher frequency of modulation of the light to be used. The scanning frequency may be adjustable. Additional optical elements e. g. 70, 71, Fig.1, reflecting light lost from the beam splitter 13 back into the system, or reflecting unused light from the source back into the system, Fig. 3 (not shown), may be used to increase illumination of the reference mark carrier 16 to aid visual observation, or an additional source, Fig. 4 (not shown) may be used. Auxiliary masks may be imaged on to the carrier by projection. The masks may be in coded formation. In an alternative system arrangement, the photo-cell 19 may be dispensed with, and the marks on the reference mark carrier may be photosensitive elements.