Wire matrix printing apparatus

A matrix print head including:

• a base plate;
• a nose piece secured to the base plate and extending from one face of the base plate;
• a first wire guide secured to a first end of the nose piece remote from the base plate;
• second wire guides secured to the nose piece intermediate the base plate and said first end;
• a plurality of printing wires supported for lengthwise movement by said first and second guides, each printing wire having a printing end projecting from said first end of the nose piece and a ferrule mounted on a second end remote from the printing end;
• spring means operating between the ferrules and the nose piece to urge the printing wires to a retracted position;
• a plurality of U shaped magnetic yoke assemblies each including a pair of parallel limbs, said yoke assemblies being mounted on said base plate in a ring around a second end of the nose piece remote from said first end with said limbs extending from a second face, opposite said first face, of the base plate;
• a pair of coils for each yoke assembly, the coils being mounted one on each limb of the yoke assemblies and electromagnetically coupled thereto;
• a plurality of magnetic armatures each provided with a pair of oppositely extending pivots;
• a frame including a plurality of radially outwardly extending fingers, one for each magnetic yoke, and having apertures adjacent radially inner ends of the fingers;
• a pair of spaced lugs on a radially outer end of each said finger having recesses receiving said pair of pivots of said armatures respectively to pivotally support the armatures for magnetic cooperation one with each magnetic yoke, the armatures extending radially inwards from the pivots and being provided with a projection on radially inner ends thereof engaging one with each ferrule on the printing wires;
• a non-magnetic member extending between the armatures and free ends of all the limbs of the magnetic yokes effective upon energisation of said coils to maintain the armatures spaced from the yokes;
• a plurality of resilient backstop buffers disposed one in each aperture in the frame for engagement by the armatures when the coils are un-energised and the printing wires are retracted;
• and means adjacent the frame mounting adjustment screws engaging the backstop buffers operable to adjust the position of the backstop buffers individually in the frame.