Patent GB-730285-A (GB)
Title: Improvements in or relating to linear dimension gauging instruments
Inventor: HAMILTON JOHN HUNTER
IPC: G01B7/00
Filed: 1951-12-22
Abstract: 730,285. Electric indicating-systems. SIGMA INSTRUMENT CO., Ltd. March 23, 1953 [Dec. 22, 1951], No. 27431/51. Class 40 (1). A linear-dimension gauging-apparatus comprises two displaceable finger elements engaging, respectively, a gauging and a reference anvil of a gauging fixture when in measuring position, carriers for co-operating sensing means, the first carrier mounted on the second and the second on a base for parallel relative movements, relative movement between the sensing means corresponding to relative movement between the two carriers, connections causing each finger to move in unison with a carrier and indicating means responsive to the relative positions of the sensing means. As shown, the invention is applied to mounting and relatively displacing the plates of a differentiallyvariable inductance as described in Specification 666,824 placed in the circuit of Specification 616,978, which is arranged to include a galvanometer housed in a hollow base 1, Fig. 2, for indicating by pointer 2 and scale 3 through a window 4, a linear dimension as gauged by anvils 65, 66 of a gauging fixture described in Specification 730,333, [Group XIX], being one of a plurality of such fixtures carried by a turret T described in Specifications 730,334 and 730,335, [both in Group XIX], and pivotally secured to the front of an upright 5, the inductance being located in a housing 6 behind the upright 5. The lower plate 7 of the inductance is mounted by stiff spring strips 12, 13 on a block 14 attached to a supporting plate 15 which is itself mounted by reinforced spring strips 48, 49 on a block 50 attached to the base 51 with a compression spring 52 engaging spigots 53, 54. The block 14 also supports by means of spring strips 40, 41 a frame 34 in which lies the upper plate 28 of the inductance which is carried by the lower plate 7 by means of reinforced spring strips 42, 43. A sapphire secured to the upper plate 28 is urged into contact with the hardened polished hemispherical portion of an adjusting screw 36 threaded in the frame 34 and relative movement between the upper and lower plates 28, 7 is limited by adjustable stop-screws 46, 47 threaded in webs 10, 11 of the lower plate in the path of movement of lugs 44, 45 depending from the upper plate. Relative adjustment between the lower plate 7 and supporting plate 15 may be obtained by removing a plug 23 in the side of the case 6 and entering the socketed end of the shank of a control knob 24 over a pin 23 so that external teeth on the shank engage the teeth of a wheel 21 fixed on a screw 16 threaded in an element 17 upstanding from the block 14 and abutting a flat sapphire 18 let into the lower part of the web 11 of the lower plate 7. The supporting plate 15 is urged towards the upright 5 by two springs 56 attached to triangular brackets 57 secured to the base 51 which brace the upright 5, an adjustable stop 59 limiting movement of the plate 15 towards the upright and the housing 6 limiting opposite movement. A finger 63 with a tungsten carbide tip projecting through the upright 5 is rigidly connected to a wall element 62 supported by two triangular cheeks 60 provided at one end of the block 14. Another similar finger 64 is secured to the frame 34 and coil-springs 64B attached between pegs on the upper side of the wall 62 and the remote end of the frame 34 urge the latter toward the upright and hence urge the finger 64 through the upright. A stop-plate 34A secured to the block 14 limits movement of the frame 34 away from the upright. To set the apparatus for gauging any particular dimension, the turret T is turned to bring the appropriate gauging head to a position where hardened polished heads 67, 68 in gauging and stationary anvils 66, 65 respectively register with the fingers 64, 63, the head 68 moving the finger 63 to the right thus moving the supporting plate 15 and the pair of inductance plates 7, 28 as a whole to set a reference position. A master slip gauge is then introduced at P and the head 68 moves the finger 64, frame 34 and upper inductance plate 28 to the right, thus reducing the air gap between poles 31, 26 and increasing that between poles 30, 27. The inductance plates are then centralized again by adjusting the head 67 and, if necessary, by means of the control knob 24. Thereafter the galvanometer will indicate the oversize or undersize of any work-piece inserted at P within the limits set by the stops 46, 47.