Patent GB-631887-A (GB)
Title: Improvements in and relating to wire grid strain gauges and the manufacture thereof
IPC: G01L1/22
Filed: 1947-01-07
Abstract: 631,887. Coiling ; making metal fabric. ASHBY, R. J. Jan. 7, 1947, No. 513. [Classes 83 (ii) and 83 (iv)] [Also in Group XXXVI] The Specification describes a machine for manufacturing a strain gauge in the form of a helix, the top layers of which are flattened to lie between the lower. The helix is then pasted to a strip of paper, the bights of the helix projecting over the edge so that they carry no stress. Wire is fed through a counterbalanced tensioning sleeve and a feed tube 20 and is wound over cam - shaped spindles mounted in a coiling head 2 (Fig. 5). Rotation of the head is effected by a main driving shaft 18 and gearing 17, 16 and 15. At the same time a further wheel 13 on the same shaft, which carries on its inward surface four face cams A, B, C and D is rotated. Cam A recedes as rotation commences, allowing a spring plunger 22b (Fig. 2) to cause a feed-carriage 22 on which the feed tube 20 is mounted to move'in a direction parallel to the axis of rotation of the coiling-head 2, thereby forming a helix. The coiling-head 2 is supported in a rockable carrier 3, a small sector 4a fastened to a sleeve 4 forming part of the carrier riding on the surface of cam B and holding the carrier in the upward position. The carrier is formed with a sleeve 4 which slides on a shaft 12 spring loaded at one end and riding on the face of the cam C at the other. A spring-loaded ball 14 holds the sleeve 4 in one of two positions. After the predetermined number of revolutions of the coiling- head have taken place, cam C recedes and spring 12e moves forward the shaft 12, and a stop 12c on it causing the carrier and winding- head to be displaced to a position over a paper strip 19a. Cam B now disengages segment 4a which is engaged by cam D rotating the carrier 3 so that the spindles 10 lie on the paper, the lower half of the winding in contact with a prepared area of cement. The method of advancing the paper and depressing the upper half of the helix to a position between the spaces of the lower half is shown in Fig. 1. A lever 38 is caused to rock to and fro between stops 29a and 29b by a pin carried on the wheel 13 and a link 38a. This lever moves a sliding carriage 28b and at the commencement of coiling brings this carriage towards stops 29a advancing the paper by means of a piece of spring material 30. When the carriage reaches stops 29a a " trigger " 35 is rotated so that the spring 30 leaves the paper. When the carriage reaches the stops at the other end a pair of fingers 26 are rotated downwardly and at the same time their lower ends are given a transverse movement so that the upper coils of the helix are pressed into the spaces between the lower. The transverse movement is obtained by causing the lower ends of the levers to move in a groove 28a, Fig. 2. The cement is applied by a roller which moves in a direction perpendicular to the bed of the machine and is operated by a cam carried on the outward face of wheel 13. The ends of the gauge are severed by a glass hand wheel operated as the roller by a further cam on the wheel 13. The spindles 1c, Fig. 5, are of approximately elliptical section and are weighted by collars 1e. These collars also carry a tongue which is operated by a swinging plate 5. These plates 5 are made to swing by an axially movable shaft 6 operated by the shaft 12 by the stop 12e of the shaft 12. At the commencement of coiling, the ellipses are held approximately vertical. At the end, they are released so that the pressure of the fingers 26 maintains the tension on the wire against the weight of the collars. After pasting, the ellipses are moved to a horizontal position and withdrawn from the wire.