Patent GB-1505928-A (GB)
Title: High operating speed solenoid controlled by multiple springs
IPC: B41J2/285
Filed: 1975-07-30
Abstract: 1505928 Electromagnets CENTRONICS DATA COMPUTER CORP 30 July 1975 [22 Aug 1974] 31871/75 Heading H1P In a high operating speed solenoid driving a print wire (Fig. 1), a solenoid assembly comprises a ferromagnetic hollow cylinder 11 whose internal surface 11alpha is stepped at 11b to form a recessed shoulder spaced inwardly from one end while the opposite end is threaded at 11c to engage portion 12a of end cap 12 and an internal shoulder 11e supports ferromagnetic flux ring 13. The case is slotted at 11f to admit sleeve insulated leads 14A of solenoid 14, and the slot is epoxy resin filled. A ferromagnetic core 17 has an elongate threaded portion 17alpha engaging an aperture of a wall of a print head housing (not shown) and secured by locknut 18, and an intermediate flanged portion 17b fitting within increased diameter portion 11alpha of casing 11 and resting against a circular flange 19alpha of solenoid bobbin 19; the flange being spotwelded to the casing after assembly and sealed with epoxy resin. An inner portion 17c of the core extends through bobbin 19, and has an axial bore therein of which portion 17d of increased diameter connects to portions 17e of reduced diameter. A hollow tubular elongate non-magnetic guide 20 is inserted up to shoulder 17g, and is sealed with epoxy resin to core 17 at 20a, while its interior is coated with a dry lubricant to minimize wear of a stiff print wire 21 inserted therein. This is slidable in the guide to enter the reduced portion 17e and extends out of the stem with its free end positioned in opening 22a of headed armature 22 to which it is soldered. The latter is spaced from the core stem with a cylindrical extension 22b engaging a central opening 26alpha of circular spring 26 surrounding the armature extension and annular retainer 25, to which the extension is swaged at 22c. (Fig. 1alpha). A ferromagnetic flux ring 13 concentrating flux in armature 22 abuts shoulder 11e and is recessed at 13a, 13b to support the respective peripheries of steel springs 26, 27 while a further recess 13c provides a space under spring 27, whose central opening spacedly surrounds the extension of armature 22. Spring 26 is a circular lamina with central opening 26a and radial tapering spokes 26 terminating in arcuate segments extending circumferentially of each spoke and spaced from adjacent segments; these resting in annular recess 13a of flux ring 13. Spring 27 is also a circular lamina with central opening 27a and tangentially truncated at 27b, 27d, 27c to reduce bending stresses. The end cap 12 carries a screwdriver slot 12b for adjustment of armature by a projection abutting retainer ring 25 to flex spring 26. After adjustment the slot is sealed by epoxy resin. In operation the armature is at rest with coil 14 de-energized, and retainer 25 abuts end cap 12 with spring 26 preloaded. On energization the armature is attracted by flux across airgap G and spring 26 is further flexed by its axial motion. Flange 22c then abuts the inner edge of spring 27 having a stiffer characteristic than spring 26, just prior to impact of wire 21 with the surface to be printed; so that spring resistance rapidly increases towards impact. The solenoid is energized and then de-energized by a square wave pulse and on release spring 27 produces a rapid movement towards the rest position and the opening of projection 22b cooperating with the inner surface 1 of end cap 12 produces a dashpot effect reducing bounce. In a modification (Fig. 2, not shown) the armature is loaded with three spaced wheel shaped spring members in combination; stressed in succession between curved surfaces of a flux ring engaging their outer peripheries and of a flange of the armature engaging their inner peripheries. In a further modification (Fig. 3, not shown) the core stem is positioned inwardly of the bobbin and the armature has a projection extending inwardly to meet it. In a further modification (Fig. 4, not shown), the armature has a projecting member meeting the core stem within the bobbin, and is movable against a first spring resting on a surface of the flux ring and backed by a second spring of weaker strength, subsequently engaging a further surface of the flux ring. In a further modification (Fig. 5, not shown), there are provided first and second flux rings which grip the outer periphery of a circular spring, while the armature is controlled by other circular springs one retained by a surface of the first flux ring and backed up by the other which has a smaller diameter. On deflection by energization, the outer periphery of the backing spring engages the inner periphery of the spring retained between the flux rings. In a further modification (Fig. 6, not shown), a single flux ring having an inwardly directed shoulder is provided such that its surface first engages the larger of the two armature springs, while the shoulder then engages the smaller of the springs on armature deflection. The springs may alternatively comprise an annular portion with radial outwardly extending spokes (Fig. 7, not shown) or a solid apertured disc (Fig. 8, not shown) or an outer ring with inwardly directed spokes (Fig. 9, not shown). A force to deflection characteristic is given (Fig. 1d, not shown).