Nozzle misalignment compensation in a drop on demand printhead

Details Nozzle misalignment compensation in a drop on demand printhead Nozzle misalignment compensation in a drop on demand printhead

2002-10-15

2004-12-28

Nguyen, Lamson D (Department: 2861)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S041000, C347S017000

Reexamination Certificate

active

06834932

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of ink jet printing and in particular discloses a method and apparatus for the compensation for the time varying nozzle misalignment of a print head assembly having overlapping segments.
CO-PENDING APPLICATIONS
Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending applications filed by the applicant or assignee of the present invention simultaneously with the present application:
09/575,197
09/575,195
09/575,159
09/575,132
09/575,123
09/575,148
09/575,130
09/575,165
09/575,153
09/575,118
09/575,131
09/575,116
09/575,144
09/575,139
09/575,186
09/575,185
09/575,191
09/575,145
09/575,192
09/575,181
09/575,193
09/575,156
09/575,183
09/575,160
09/575,150
09/575,169
09/575,184
09/575,128
09/575,180
09/575,149
09/575,179
09/575,133
09/575,143
09/575,187
09/575,155
09/575,196
09/575,198
09/575,178
09/575,164
09/575,146
09/575,174
09/575,163
09/575,168
09/575,154
09/575,129
09/575,124
09/575,188
09/575,189
09/575,162
09/575,172
09/575,170
09/575,171
09/575,161
09/575,141
09/575,125
09/575,142
09/575,140
09/575,190
09/575,138
09/575,126
09/575,127
09/575,158
09/575,117
09/575,147
09/575,152
09/575,176
09/575,151
09/575,177
09/575,175
09/575,115
09/575,114
09/575,113
09/575,112
09/575,111
09/575,108
09/575,109
09/575,182
09/575,173
09/575,194
09/575,136
09/575,119
09/575,135
09/575,157
09/575,166
09/575,134
09/575,121
09/575,137
09/575,167
09/575,120
09/575,122
The disclosures of these co-pending applications are incorporated herein by cross-reference.
BACKGROUND OF THE INVENTION
In the applicant's co-pending application PCT/AU98/00550, a series of ink jet printing arrangements were proposed for printing at high speeds across a page width employing novel ink ejection mechanisms. The disclosed arrangements utilized a thermal bend actuator built as part of a monolithic structure.
In such arrangements, it is desirable to form larger arrays of ink ejection nozzles so as to provide for a page width drop on demand print head. Desirably, a very high resolution of droplet size is required. For example, common competitive printing systems such as offset printing allow for resolutions of one thousand six hundred dots per inch (1600 dpi). Hence, by way of example, for an A4 page print head which is eight inches wide, to print at that resolution would require the equivalent of around 12800 ink ejection nozzles for each colour. Assuming a standard four colour process, this equates to approximately fifty one thousand ink ejection nozzles. For a six colour process including the standard four colours plus a fixative and an IR ink this results in 76800 ink ejection nozzles. Unfortunately, it is impractical to make large monolithic print heads from a contiguous segment of substrate such as a silicon wafer substrate. This is primarily a result of the substantial reduction in yield with increasing size of construction. The problem of yield is a well studied problem in the semi-conductor industry and the manufacture of ink jet devices often utilizes semi-conductor or analogous semi-conductor processing techniques. In particular, the field is generally known as Micro Electro Mechanical Systems (MEMS). A survey on the MEMS field is made in the December 1998 IEEE Spectrum article by S Tom Picraux and Paul J McWhorter entitled “The Broad Sweep of Integrated Micro Systems”.
One solution to the problem of maintaining high yields is to manufacture a lengthy print head in a number of segments and to abut or overlap the segments together. Unfortunately, the extremely high pitch of ink ejection nozzles required for a print head device means that the spacing between adjacent print head segments must be extremely accurately controlled even in the presence of thermal cycling under normal operational conditions. For example, to provide a resolution of one thousand six hundred dots per inch a nozzle to nozzle separation of about sixteen microns is required.
Ambient conditions and the operational environment of a print head may result in thermal cycling of the print head in the overlap region resulting in expansion and contraction of the overlap between adjacent print head segments which may in turn lead to the production of artifacts in the resultant output image. For example, the temperature of the print head may rise 25° C. above ambient when in operation. The assembly of the print head may also be made of materials having different thermal characteristics to the print head segments resulting in a differential thermal expansion between these components. The silicon substrate may be packaged in elastomer for which the respective thermal expansion coefficients are 2.6×10
−6
and 20×10
−6
microns per degree Celsius.
Artifacts are produced due to the limited resolution of the print head to represent a continuous tone image in a binary form and the ability of the human eye to detect 0.5% differences in colour of adjacent dots in an image.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide for a mechanism for compensating for relative displacement of overlapping print head segments during operation in an effective and convenient manner.
In accordance with a first aspect of the invention there is provided in an ink ejection print head comprising a plurality of overlapping print head segments, wherein the spatial relationship between adjacent segments is variable with time, a method for controlling the firing of nozzles within the overlapped segments comprising the steps of: (a) determining a measure of the overlap between adjacent print head segments; (b) creating a half toning pattern for the nozzles in the region of overlap of the overlapping segments; and (c) adjusting said half toning pattern as a function of said measure in the overlapping regions of said print head segments to reduce artifacts produced by the overlapping of said print head segments.
Preferably, the step for determining a measure of overlap employs a measure of temperature of the print head segments The half toning patterns are preferably produced by means of a dither matrix or dither volume and the alteration can comprise adding an overlap value to a current continuous tone pixel output value before utilizing the dither matrix or dither volume. In place of a measure of temperature a measure of distance can be provided by the use of fiduciary strips on each of the segments and using an interferometric technique to determine the degree of relative movement between the segments.
In accordance with a further aspect of the present invention, there is provided an ink ejection print head system comprising: a plurality of spaced apart spatially overlapping print head segments; at least one means for measurement of the degree of overlap between adjacent print head segments; means for providing a half toning of a continuous tone image and means for adjusting said half toning means in a region of overlap between adjacent print head segments to reduce artifacts between said adjacent segments.
The means for adjusting the half toning means can include a continuous tone input, a spatial overlap input and a binary input, the half toning means utilizing the spatial overlap input to vary the continuous tone input to produce a varied continuous tone input for utilization in a look-up table of a dither matrix or dither volume so as to produce output binary values to adjust for the regions of overlap of print head segments. The means for adjusting the half tone or dither matrix may be implemented in hardware or by means of software employing an algorithm.


REFERENCES:
patent: 4272771 (1981-06-01), Furukawa
patent: 5717448 (1998-02-01), Inada
patent: 6464332 (2002-10-01), Silverbrook et al.
patent: 6679576 (2004-01-01), Crivelli

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