GB1239512A - - Google Patents

Abstract

1,239,512. Selective printing. PHILIPS ELECTROLOGICA G.m.b.H. 3 Sept., 1969 [31 Oct., 1968], No. 43625/69. Heading B6F. [Also in Division H1] An electromagnet operating e.g. a mosaic printing needle comprises a coil wound on a cylindrical magnet core 1 in housing 3; a yoke section 4 abutting on one end of the core and a yoke section 5 on the other end thereof, while a stator 6 within yoke 4 protrudes into core 1; 4 and 6 being threaded at 9 for rotary adjustment h 1 between stator 6 and armature 10. A tube 7 of antifriction non-magnetic material within stator 6 guides a printing needle 8 of a mosaic printing unit (not shown); the yoke 5 projecting into the core to reduce stray flux and constituting a stator. Opposite surfaces of the armature have differing areas and are respectively conical and annular in shape, and it is shown that the forces exerted in opposite directions of the armature differ by F D =F 1 cos 2α (where F 1 is the force exerted on the annular surface and 2α is the apex angle of the conical surface) and urge the armature towards stator 6 on energization of the coil. The airgap h 1 is displaced slightly from the centre of core 1, and the armature 10 and axial tube 11 are fixed to needle 8, which is turned over at its inoperative end for attachment to spring 13 returning the armature on de-energization; a disc 15 attached to tube 11 limiting return stroke so that working stroke h 2 <h 1 . The end stop 12 is of damping material. In a modification (Fig. 3, not shown), operation is in the reverse sense; the armature and printing needle being displaced on energization to a rest position against a return spring, and the printing needle operated on de-energization by the spring; a limit stop being screw adjustable to prevent contact between armature and stator.