Printing head for wire dot printer

Claim 1

A printing head for wire dot printer comprising: a plurality of printing wires having front and back end portions arranged in a predetermined distribution, respectively; and wire driving means for driving the back ends of said printing wires to move said printing wires both in a dot printing direction and in a returning direction, each of said wire driving means including an armature moved in a first direction so as to drive the back end of said printing wire, a magnetic frame comprising a plurality of magnetic members arranged in a reference plane including said first direction and having at least one permanent magnet and at least one soft magnetic member, said plural magnetic members being connected in series to form a magnetic circuit provided with an air gap, at least one connecting portion of said plural magnetic members included in said magnetic frame being defined by two of said magnetic members which are slidable relative to one another in the first direction, at connecting sliding surfaces so that the length of the air gap may be adjusted by the sliding movement, said sliding surfaces defining sliding planes including both a second direction perpendicular to the reference plane and the first direction, said connecting portion having screws arranged substantially perpendicular to said sliding surfaces and pressing said two magnetic members one against the other and substantially perpendicular to said both of said sliding surfaces, an exciting coil wound around said magnetic frame and generating a magnetomotive force, when excited, to substantially off-set the magnetomotive force of said permanent magnet, and an armature support means attached to said magnetic frame to resiliently support said armature movable in the air gap in the first direction, said armature support means being slidable in both the first and second directions relative to said magnetic frame, to thereby adjust the free position of said armature in the air gap.