Automatic alignment of print heads

A method for selecting a density region from among N regions of superimposingly printed alignment patterns in which the N regions vary in density cyclically from a lightest region through a darkest region and thence back to a lightest region, the selected density region corresponding to good alignment between the superimposingly printed alignment patterns, comprising the steps of:

• measuring density of each region;
• obtaining density difference data between density readings for pairs of regions, wherein each pair of regions is separated by N/2 regions;
• determining which density difference is largest;
• and
• selecting one region from the region pair having the largest density difference, the selected one region having good alignment between the superimposingly printed alignment patterns.

A method for printing an image using multiple printing passes, comprising the steps of:

• printing one band of the image at a first printing pass;
• and
• printing another band of the image at a second printing pass;
• wherein starting positions of the first and second printing passes are shifted relative to each other in a same printing direction.

An apparatus for determining misalignment between first and second printed alignment patterns comprising:

• a memory for storing executable process steps;
• and
• a processor to execute said process steps stored in said memory;
• wherein said process steps include steps to (a) print the first alignment pattern, the first alignment pattern being comprised by a repetitive pattern in which not all pixels of printed portions of the pattern are printed, (b) print the second alignment pattern in superimposed relationship over the first alignment pattern, the second alignment pattern being comprised by the same repetitive pattern as the first alignment pattern in which not all pixels of printed portions of the pattern are printed but with phase thereof being shifted gradually with respect to the first alignment pattern, and (c) measure print density of the superimposition of the first alignment pattern over the second alignment pattern so as to determine misalignment between the first and second alignment patterns.

An apparatus for selecting a density region from among N regions of superimposingly printed alignment patterns in which the N regions vary in density cyclically from a lightest region through a darkest region and thence back to a lightest region, the selected density region corresponding to good alignment between the superimposingly printed alignment patterns, comprising:

• a memory for storing executable process steps;
• and
• a processor to execute said process steps stored in said memory;
• wherein said process steps include steps to (a) measure density of each region, (b) obtain density difference data between density readings for pairs of regions, wherein each pair of regions is separated by N/2 regions, (c) determine which density difference is largest, and (d) select one region from the region pair having the largest density difference, the selected one region having good alignment between the superimposingly printed alignment patterns.

An apparatus for superimposed printout of first and second alignment patterns, each alignment pattern being comprised by repetitive patterns with the phase of the second alignment pattern being shifted at a low cycle with respect to phase of the first alignment pattern, comprising:

• a memory for storing executable process steps;
• and
• a processor to execute said process steps stored in said memory;
• wherein said process steps include steps to print the first alignment pattern on a recording medium in multiple passes and print the second alignment pattern on a recording medium in multiple printing passes.

An apparatus for superimposed printout of first and second corresponding respectively to first and second different printings by at least one print head mounted on a carriage, comprising:

• a memory for storing executable process steps;
• and
• a processor to execute said process steps stored in said memory;
• wherein said process steps include steps to print the first pattern on a recording medium in multiple passes and print the second pattern on a recording medium in multiple passes.

An apparatus for printing an image using multiple printing passes, comprising:

• a memory for storing executable process steps;
• and
• a processor to execute said process steps stored in said memory;
• wherein said process steps include steps to print one band of the image at a first printing pass, and to print another band of the image at a second printing pass and wherein starting positions of the first and second printing passes are shifted relative to each other in a same printing direction.

Computer-executable process steps stored on a computer readable medium, said process steps for determining misalignment between first and second printed alignment patterns, said process steps comprising:

• a printing step to print the first alignment pattern, the first alignment pattern being comprised by a repetitive pattern in which not all pixels of printed portions of the pattern are printed;
• a printing step to print the second alignment pattern in superimposed relationship over the first alignment pattern, the second alignment pattern being comprised by the same repetitive pattern as the first alignment pattern in which not all pixels of printed portions of the pattern are printed but with phase thereof being shifted gradually with respect to the first alignment pattern;
• and
• a measuring step to print density of the superimposition of the first alignment pattern over the second alignment pattern so as to determine misalignment between the first and second alignment patterns.

Computer-executable process steps stored on a computer readable medium, said process steps for selecting a density region from among N regions of superimposingly printed alignment patterns in which the N regions vary in density cyclically from a lightest region through a darkest region and thence back to a lightest region, the selected density region corresponding to good alignment between the superimposingly printed alignment patterns, said process steps comprising:

• a measuring step to measure density of each region;
• an obtaining step to obtain density difference data between density readings for pairs of regions, wherein each pair of regions is separated by N/2 regions;
• a determining step to determine which density difference is largest;
• and
• a selecting step to select one region from the region pair having the largest density difference, the selected one region having good alignment between the superimposingly printed alignment patterns.

Computer-executable process steps stored on a computer readable medium, said process steps for printing an image using multiple printing passes, said process steps comprising:

• a printing step to print one band of the image at a first printing pass;
• and
• a printing step to print another band of the image at a second printing pass;
• wherein starting positions of the first and second printing passes are shifted relative to each other in a same printing direction.