GB849315A - Improvements in or relating to precision optical measuring devices - Google Patents

Abstract

849,315. Verniers. SIMPSON OPTICAL MANUFACTURING CO. Oct. 25, 1957 [Oct. 31, 1956], No. 33429/57. Class 106 (2). [Also in Groups XX and XXII] A precision optical measuring device comprises in combination a scale having uniformly spaced marks and an optical reader for reading the scale and comprising a mask having a viewing window, optical means for projecting an image of the scale on the window and a rotatable light transmitting member adjacent the mask and carrying a visible spiral and radial graduations, the distance between the radially overlapping portions of the spiral being equal to the distance between the projected images of adjacent scale marks, the graduations enabling a reading to be made of the lateral travel of the spiral necessary to bring it into a predetermined fixed relation to the projected scale marks. As shown in Fig. 12, a linear scale 15 on the movable part of the instrument is illuminated by the lamp 36 via a condenser 38 and a mirror 35. An image of the scale is projected through a magnifier 30 comprising elements 31, 32 and is reflected by mirrors 39, 40, 41, 42, 44 and 45 on to the viewing window 20 in the mask 60, for observation by the operator. The reading appears in the window 20 and the indicator mark associated with the reading at a point in a second window 22 as shown in Fig. 2. A vernier is provided by a lens 70 rotatably mounted coaxial with the mask 60 and having a scale on its periphery and a spiral engraved upon it comprising two parallel lines as shown in Fig. 7; the lens 70 is rotated with respect to the mask 60 until the indicator mark lies between the parallel lines of the spiral and the vernier reading is read at the window 25 in the mask 60- which may also be illuminated by the lamp 36- and added to the coarse reading. As shown in Fig. 10, the mask 60 is fixed to upper part 49 of the viewer housing 50, and the lens 70 is mounted in a rotatable cap 92 provided with a hinged lid 81 having a mirror to allow oblique viewing of the scale. The projecting mirrors 40- 45 are fixed to a plate 46 attached to the viewer housing; the lamp 36 being mounted in the housing for easy replacement. In the milling machine shown in Fig. 1 a reader 10 operates in conjunction with the feed scale 15 and a second reader 10 operates in conjunction with the cross feed scale 16.