Printing apparatus

A printing apparatus (10) adapted for printing a plurality of imprints (12) onto a sheet (14) divided into a plurality of sequentially longitudinally spaced printing fields (16) having a selected field length, said printing fields (16) each being divided into a plurality of longitudinally and laterally spaced printing domains (18), comprising:

• a plurality of spaced printing rolls (20a-20f) having peripheral cylindrical surfaces (24a-24f) having image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) adapted to print said imprints (12) onto said sheet (14), said rolls (20a-20f) each having circumferences (28a-28f) which are different integral multiples of said field length and which are not integral multiples of one another, each of said cylindrical surfaces (28a-28f) having a subset of said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) positioned to print said imprints (12) on said printing fields (16), said printing fields (16) having a null set intersection;
• means (30) for rotating said rolls (20-20f) about said axes (22a-22f) at a velocity such that said cylindrical surfaces (24a-24f) have equal tangential velocities;
• means (32) for transferring an image reproducing medium onto each of said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f);
• means (36) for longitudinally moving said sheet (14) generally tangentially sequentially adjacent each of said cylindrical surfaces (24a-24f) at a velocity such that said sheet (14) and said cylindrical surfaces (24a-24f) have zero relative velocity difference;
• and
• means (40a-40f) for transferring said image reproducing medium from said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) to said longitudinally and laterally spaced printing domains (18) as said sheet (14) moves opposite said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f), said image reproducing medium being selected to be of a different color for each of said rolls (20a-20f), each of said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f), printing like sized and shaped imprints (12) as does each other of said subsets of said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) with said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) on each of said rolls (20a-20f) producing imprints (12) having selected densities of minute dots of each of said colors, image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) on different of said rolls (20a-20f) printing overlapping upon one or more of said imprints (12) to produce mixtures of said colors.

A method of printing a plurality of imprints (12) onto a sheet (14) divided into a plurality of sequentially longitudinally spaced printing fields (16) having a selected field length, said printing fields (16) each being divided into a plurality of longitudinally and laterally spaced printing domains (18), comprising:

• feeding said sheet (14) past a plurality of spaced printing rolls (20a-20f) having peripheral cylindrical surfaces (24a-24f), each of said rolls (20a-20f) having image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) adapted to print said imprints (12) onto each of said printing fields (16) on said sheet (14), said rolls (20-20f) each having circumferences (28a-28f) which are different integral multiples of said field length and which are not integral multiples of one another, each of said cylindrical surfaces (28a-28f) having a subset of said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) positioned to print said imprints (12) on said printing fields (16) each of said subsets of said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) on each of said rolls (20a-20f) being positioned to print said imprints (12) on only a selected subset of said longitudinally and laterally spaced printing domains (18), said printing fields (16) having a null set intersection with one another and said selected subsets of said printing domains (18) having a null set intersection with one another;
• rotating said rolls (20a-20f) about said axes (22a-22f) at a velocity such that said cylindrical surfaces (24a-24f) have equal tangential velocities;
• transferring an image reproducing medium onto each of said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f);
• and
• transferring said image reproducing medium from said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f) to said printing fields (16) as said printing fields (16) pass opposite said image transfer regions (26a.sup.1 -26f.spsp.n.sup.f).