GB898502A - Improvements in or relating to magnetic devices - Google Patents

Abstract

898,502. Magnetic holding devices; eddy current brakes. SOC. D'ELECTRO-CHIMIE, D'ELECTRO-METALLURGIE ET DES ACIERIES ELECTRIQUES DE UGINE. Feb. 6, 1959 [Feb. 8, 1958; May 6, 1958; Nov. 5, 1958], No. 4298/59. Class 35. A magnet assembly, e.g. for an eddy current brake or lifting magnet, comprises at least one pair of permanent magnets 1, 2 (Fig. 1a) the polarization of one of which is reversible by a current pulse through winding 7 so that the flux follows either the closed circuit 1, 3, 2, 4, as shown or a circuit which includes an air gap 5. The magnet material preferably has a coercivity only slightly higher than " soft " magnetic material and may be grain oriented. In the eddy-current brake shown in Fig. 11 eight pairs of stationary permanent magnets 63, 64 are disposed between rotatable discs 62 secured to a common shaft 61. Each pair of magnets is short-circuited by soft iron yokes 65, 66 when in the "off " polarization shown, but by applying a short pulse of D.C. to coils 68, 69 so as to reverse the polarity of magnets 63 while maintaining that of magnets 64, a magnetic circuit is established between diametrically opposite pairs of magnets through the discs 62, and eddy current braking of the discs results. Any number of diametrically opposite magnet pairs may be rendered operative providing a graded torque. In an alternative brake construction (Figs. 5-7, not shown) arcuate magnets spaced by soft iron bars, form a cylindrical structure at the ends of which segmental pole pieces, attached to the soft iron bars, define air gaps which are bridged by eddy-current discs pivoted coaxially with the cylinder. In the " off " state the magnets are short-circuited by the bars, whereas when " on " the flux traverses the discs. Alternatively the magnets may be straight instead of arcuate to give a " box " structure (Fig. 8, not shown) and they may be divided into three sets for sequential operation (Fig. 9, not shown), and one disc only may be provided. A lifting device (Fig. 14, not shown) incorporating the invention comprises two permanent magnets arranged between two plate-like pole pieces which either short-circuit the magnets or conduct the flux to magnetic material, e.g. a tube, to be lifted.