GB1225054A - Limit switch - Google Patents

Abstract

1,225,054. Non-contact-making switches. R. KREEB, and A. OSTERTAG, [trading as RAFI RAIMUND FINSTERHOLZEL ELEKTROTECHNISCHE SPEZIALFABRIK]. 14 Aug., 1968 [10 Feb., 1968], No. 38842/68. Heading H3B. A limit switch comprises a magnetoresistive element and a magnetic structure which includes a permanent magnet, a change of resistance of the element being produced by relative movement between at least a part of the magnetic structure and the element. As shown in Fig. 1, a plastics casing 1 supports a magnetoresistive element 3 which is positioned in an air gap of a magnetic structure comprising a permanent magnet 5 and polepieces 6. The resistance of the element 3 is reduced by pressing a push-rod 2 against the action of a restoring string 8 so as to move a magnetic plate 7 towards the polepieces, the flux due to the permanent magnet being diverted from the air gap to the plate. In a modification, Fig. 5, the whole of the magnetic structure comprising a permanent magnet 32 and polepieces 33 is moved so as to introduce a fixed magnetoresistive element 3 into the air gap, the resistance being increased in this case. In a further modification, Fig. 3, both the magnetoresistive element 3 and the magnetic structure comprising polepieces 17 and a permanent magnet are fixed, the air gap flux being diverted by movement of a polarized structure 18 in the direction P<SP>1</SP>. By reversing the direction of polarization of the magnet 15 or one of the polarizing magnets of the structure 18, the switch is sensitive to movement of the structure 18 in the direction P. Springs are omitted in the Fig. 2 arrangement, restoration of the push-rod being effected by the repulsion between two magnets 11, 12. One magnet may be reversed, and an attractive force between the push-rod structure and the fixed structure having a magnetoresistive element 3 in its air gap is obtained. A quick-to-break action is obtained in the Fig. 4 arrangement in which a relay-like magnetic structure 21-25 with a permanent magnet core 20 is provided, the magnetoresistive element being located in an air gap which is formed whenever a rocker 24 is moved away from a stop 23. This gap is formed whenever push-rod 2 is depressed to an extent sufficient for the rocker to be moved by the action of a spring 28 on a pin 29. In all the foregoing embodiments an electronic amplifier system 30 may be accommodated in a chamber 4. Fig. 5 shows an adjustable stroke limit switch in which pressure on a push-rod against a spring 45 rotates a shaft 41 through a rack and pinion linkage 42, 43, 44. Rotation of the shaft 41 moves a magnetoresistive element 3 into the air gap of a fixed magnet 37 or 38, the electrical connection to the element 3 being through a restoring spring 46. The magnets are mounted on a rotatable disc 39 which is preset into a position with respect to the element 3 such that the required operating stroke is obtained.