Print hammer with moving coil

Claim 1

In printing apparatus a plurality of movable print hammers, a relatively flat operating coil secured to each of said print hammers, each such coil having relatively straight spaced apart leg portions connected together at each end, means for providing a plurality of pairs of parallel air gaps to receive said leg portions of said coils including a magnetic structure having elongated coextensive spaced apart north and south pole plates of magnetic material each having a plurality of alternately long and short relatively thin pole pieces projecting laterally to one side of said pole plate with end portions of the pole pieces of each pole plate inturned toward the pole pieces of the other pole plate and said end portions being arranged in interleaved relation with a long pole piece of said north pole plate lying in the same plane but spaced from a short pole piece of said south pole plate, and a first air gap between said long pole piece of said north pole plate and an adjacent long pole piece of said south pole plate, and a second coplanar air gap between a corresponding short pole piece of said north pole plate and the adjacent short pole piece of said south pole plate, said coil being positioned with one of said spaced apart leg portions in each of said first and second coplanar air gaps, means positioned between said north and south pole plates for producing a magnetic flux field in said pairs of parallel air gaps and means providing electrical connections to said coil for selectively energizing said coil to operate said print hammer.