GB989062A - Improvements in or relating to magnetic structures particularly applicable for use in magnetic catches - Google Patents

Abstract

989,062. Magnetic catches. R. CHARPENTIER. July 25, 1961 [July 29, 1960; Dec. 22, 1960], No. 26823/61. Heading E2A. [Also in Division H1] A magnetic structure, particularly for use in a magnetic catch, comprises a permanent magnet having polepieces arranged to provide a fixed gap in a magnetic circuit in shunt with the magnet, the length L of the magnet lying within the range #S/2 and #SS, the dimensions of the fixed gap satisfying the following conditions: L/15 # e # L/3 5S/12 # S<SP>11</SP> # 3S where S is the area of contact of the magnet with the polepieces, L is the length of the magnet between the surfaces of contact with the polepieces, e is the width, i.e. the length in the magnetic circuit, (or sum of the widths) of the fixed gap or gaps, s" the surface area of each of those parts of the polepieces which form the fixed air gap. The magnet is made from material having a de-magnetization curve such that the induction B drops sharply from a critical point (B<SP>1</SP>, H<SP>1</SP>) in the demagnetizing field H when the field rises. The material may be an iron base alloy containing cobalt, nickel and aluminium and known by the Trade Mark "Ticonal". In the absence of an armature the permeance is such that the BH product is approximately maximum, part of the iron is close to saturation but considerable leakage flux is present. When the armature is relatively close to the polepieces a new circuit is offered for the passage of flux, the available magnetomotive force diminishes and the total permeance of the circuit increases. The leakage diminishes proportionally to the reduction of the magnetomotive force. The flux in the fixed gap becomes reduced proportionally to the reduction of magnetomotive force so that the attractive force on the armature is thus a maximum. Preferably, where s<SP>1</SP> represents the area of contact of each of the polepieces with the armature. As shown in Fig. 2, the magnet has soft iron polepieces 2 co-operating with an armature 3 and providing an air gap 4. In Fig. 3, a double fixed gap is provided between a soft iron member 5 and polepieces 2. Fig. 5 shows an arrangement in which the polepieces 2 form a cylindrical structure having fixed gaps and capable of attracting an armature, not shown, in the direction perpendicular to the plane of the paper. Figs. 7-10 (not shown) relate to other cylindrical constructions combining the features of Figs. 2, 3, 5. Figs. 13, 14 show two views of a magnetic structure having part cylindrical polepieces 2, the fixed gap being formed between the polepieces 2 and a soft iron sleeve 8. In Figs. 17, 18 the fixed gaps are formed between the polepieces 2 and a U-shaped soft iron member 9. Figs. 19, 20 show a similar construction in which a cylindrical magnet 1 carries polepieces 2, the U-shaped member being replaced by a sleeve 10. Figs. 21, 22 (not shown) relate to a structure similar to that of Fig. 19 but having only one fixed gap.