Drum printer with helically arranged type sets

A line printer for impact printing upon a recording medium, comprising:

• a type drum having a first set of type faces formed on an outer cylindrical surface thereof comprising a first group of characters, said first set of type faces being arranged in a clockwise helical path with respect to the axis of said type drum, with the pitch of said helical path of the first set of type faces being equal to twice the lateral offset between adjacent columns to be printed on said recording medium, a second set of type faces formed on said cylindrical surface of the type drum comprising a second group of characters, said second set of type faces being arranged in a clockwise helical path with respect to said drum axis, the pitch of said helical path of the second set of type faces being equal to the pitch of said helical path of the first set of type faces, and said helical path of the second set of type faces being displaced along the drum axis relative to said helical path of the first set of type faces by an amount which is equal to said lateral offset between said adjacent printed columns, a third set of type faces formed on said cylindrical surface of the type drum comprising a third group of characters, said third set of type faces being arranged in a counter-clockwise helical path with respect to the drum axis, with the pitch of said helical path of the third set of type faces being equal to the pitch of said helical paths of the first and second sets of type faces, a fourth set of type faces formed on said cylindrical surface of the type drum comprising a fourth group of characters, said fourth set of type faces being arranged in a counter-clockwise helical path with respect to the drum axis, with the pitch of said helical path of the fourth set of type faces being equal to the pitch of said helical path of the third set of type faces, and said helical path of the fourth set of type faces being displaced along the type drum axis by an amount which is equal to said lateral offset between printed columns;
• means for continuously rotating said type drum about its axis while alternately and repetitively traversing the type drum in opposite directions along the drum axis;
• a plurality of hammers arranged adjacent to said type drum, in a line parallel to said type drum axis with a fixed offset provided between said hammers, said fixed offset being equal to said pitch of the helical paths of the first, second, third and fourth sets of type faces;
• hammer shift means for selectively shifting said plurality of hammers collectively to a first shift position and a second shift position, said shifting being performed in a direction parallel to the type drum axis upon completion of a first traverse of said type drum in a first axial direction and before initiation of a second traverse of said type drum in a second axial direction opposite said first axial direction, said hammer shifting means holding said plurality of hammers stationary in said first and second shift positions with respect to movement parallel to the type drum axis during each traverse of the type drum in said first and second axial directions, said first and second shift positions being arranged such that each of the type faces of said first type face set becomes successively aligned opposite each of said hammers during a traverse of said type drum in said first axial direction while said plurality of hammers are in said first shift position, each of said type faces of said second set of type faces becomes successively aligned opposite each of said hammers during a traverse of said type drum in said first axial direction while said plurality of hammers are in said second shift position, each of said type faces of said third set of type faces becomes successively aligned opposite each of said hammers during a traverse of said type drum in said second axial direction while said plurality of hammers are in said first shift position, and each of said type faces of said fourth set of type faces becomes successively aligned opposite each of said hammers during a traverse of said type drum in said second axial direction while said plurality of hammers are in said second shift position;
• and
• hammer actuating means operated in cooperation with said type drum rotation and traversing means for actuating selected ones of said hammers to impact selected ones of said first set of type faces through the intermediary of said recording medium during a traverse of said type drum in said first axial direction while said plurality of hammers are in said first shift position, to impact selected ones of said second set of type faces during a traverse of said type drum in said first axial direction while said plurality of hammers are in said second shift position, to impact selected ones of said third set of type faces during a traverse of said type drum in said second axial direction while said plurality of hammers are in said first shift position, and to impact selected ones of said fourth set of type faces during a traverse of said type drum in said second axial direction while said plurality of hammers are in said second shift position.

A line printer for impact printing upon a recording medium, comprising:

• a type drum having a first plurality of sets of type faces formed on an outer cylindrical surface thereof, each of said first plurality of type face sets comprising a group of characters common to each of said type face sets and being arranged on said cylindrical surface in a clockwise helical path with respect to the axis of said type drum, with a fixed offset in a direction along the type drum axis being provided between each of the helical paths of said first plurality of type sets, said fixed offset being equal to the lateral offset between adjacent columns of a print line to be printed on said recording medium, said type drum further having a second plurality of sets of type faces formed on said cylindrical surface, each of said second plurality of type face sets comprising said group of characters common to each of said second plurality of type face sets and identical to said group of characters of said first plurality of type face sets, each of said second plurality of type face sets being arranged on said cylindrical surface in a counter-clockwise helical path, with a fixed offset in the axial direction being provided between each of said helical paths of the second plurality of type face sets that is equal to said fixed offset provided between each of said first plurality of type face sets;
• means for rotating said type drum about its axis while alternately and repetitively traversing the type drum in opposite direction along the type drum axis;
• a plurality of hammers arranged in a line parallel to said type drum axis adjacent to said type drum, with a fixed offset in the direction of said type drum axis being provided between said hammers, said fixed offset of said hammers being equal to said fixed offset provided between the helical paths of said first plurality of type face sets, each of said hammers being positioned with respect to the axis and circumference of said type drum such that type faces of a corresponding one of said first plurality of type face sets successively become aligned opposite thereto during a traverse of said type drum in a first axial direction and type faces of a corresponding one of said second plurality of type face sets become successively aligned opposite thereto during a traverse of said type drum in a second axial direction opposite to said first axial direction;
• and
• hammer actuating means for actuating selected ones of said hammers to impact selected type faces of said first plurality sets of type faces through the intermediary of said recording medium during a first traverse of said type drum in said first axial direction, to thereby perform printing of a first line of print, and for actuating selected ones of said hammers to impact selected type faces of said second plurality of set of type faces during a second traverse of said type drum in said second axial direction immediately subsequent to said first traverse, to thereby perform printing of a second line of print, said hammer actuating means being operated in cooperation with said means for rotating and traversing the type drum.