Two-color printer

A two color parallel printer for impact printing alfa-numeric symbols on a printing line, comprising a frame, a hollow character drum rotatable on said frame and extending through the entire length of said line, said drum carrying a plurality of characters disposed on the outside surface of the drum at a constant angular spacing on a plurality of pairs of adjacent circumferences axially spaced by a constant pitch in confronting relation with said printing positions, inking means for alternately inking the characters of the circumferences of each one of said pairs with a first and second color, a plurality of hammer elements selectively operable for printing said characters in said printing positions and mounted on said frame and linearly arranged inside said hollow drum parallel to said printing line, drum supporting means comprising a first and a second cylindrical element respectively mounted at the ends of said drum and rotatable on said frame, said first element driving said drum at a rotational speed twice the rotational speed of said second element, said second element being connected with the drum for an axial displacement thereof and comprising a continuous cam element divided into a first and a second cam portion connected to each other and axially spaced therebetween by said pitch, each cam portion extending over 180.degree. on the outside surface of said second cylindrical element, and color selecting means comprising a cam follow member selectively engageable with said first and said second cam portions to axially shift said drum during a second revolution thereof by one pitch in a first direction and respectively in an opposite direction with respect to a central position, whereby said hammer elements are so operable as to print characters of said first color successively in odd positions and in even positions of said printing line during two subsequent revolution of said drum when said cam follower member engages said first cam portion, while said hammer elements are so energized as to print characters of said second color successively in said even and in said odd positions during two subsequent revolutions of the drum when said cam follower engages said second cam portion.