GB541947A - Improvements in or relating to micrometer mechanisms - Google Patents

Abstract

541,947. Micrometer mechanisms for theodolites &c. COOKE, TROUGHTON & SIMMS, Ltd., and TAYLOR, E. W. Aug. 14, 1940, No. 12992. [Class 97 (ii)] A micrometer mechanism for theodolites and other instruments comprises two parallel glass or like plates 9, 27 angularly movable together about a common axis V ... V, a fine reading scale 12 movable in a plane parallel to the plane of movement of the parallel plates (as by a knob 40), the fine reading scale and the plates being mechanically coupled together (as by a pin and slot connection) in such a manner that movement of the scale imparts a predetermined angular movement to the plates, the arrangement being such that light rays passing through the plates will, on angular movement thereof, be displaced to effect a displacement of image in a field of view, the displacement being proportional to the movement of the scale. As shown in connection with a theodolite, light reflected from a mirror 1 is divided between two optical systems, one system including a horizontal graduated circle 24 and the parallel plate 27, and the other system including a graduated vertical circle 5 and the parallel plate 9. After passing through the parallel plates, the light is reflected from a prism 10 to form magnified images of the circle graduations adjacent to a field lens 13 and mask 47, Fig. 6. The images, and also the graduations on the fine reading scale 12 are viewed through the eye lens 19, the graduations on the circles 5, 24 and scale 12 being observed respectively through the mask openings 48, 49, 50. In taking readings, the knob 40 is rotated until one of the graduations in the mask opening 49 coincides with its index pointer, the reading then being the sum of this graduation and the minutes indicated at the opening 50. The same procedure is then adopted in connection with the openings 48, 50.