GB1213164A - Measuring instrument - Google Patents

Abstract

1,213,164. Indicating devices. K. J. WILLIAMS. 19 April, 1968 [19 April, 1967; 18 July, 1967; 26 Sept., 1967], Nos. 18013/67, 32904/67 and 43793/67. Heading B3B. Apparatus for measuring displacement between two relatively movable members such as parts of a machine tool comprises a rotatable drum 27 mounted in a housing secured to a stationary part 56 first and second flexible elongate members 47 and 90 respectively one end of each being secured to the drum and the other end of each being secured to a movable part 57 of the machine, the second flexible member being tensioned by a spring 91 and each member being respectively windable and unwindable with respect to a helical track 49 on the drum when relative movement occurs between the drum housing and the part 57 of the machine, the angle of inclination of the first and second elongate members remaining constant and equal to the angle of the helical track. The rotation of the drum is transmitted, through gearing driven from the drum shaft 28, to calibrated dials 20, 21, 22 and the displacement between the parts is indicated on the dials by pointers 33, 39 and 42, respectively. The flexible members are enclosed by telescopic sheaths 50 connected between the housing and the mountings 51, 51a of the respective flexible members on the part 57 and the members are enclosed by the sheaths during all working conditions. In order to reduce inaccuracies in measurement due to clearances in bearings and gearing backlash, friction means is provided in the form of a spring device as in Fig. 7 (not shown) or alternatively a compressed air device as in Fig. 5 (not shown) in which a rotary disc incorporated in the gearing and which is urged in one direction by air pressure to eliminate backlash. The flexible members may be in the form of wires or tapes.