INFLUENCE OF THE ROTATION OF INKJET PRINTING HEADS ON THE PRINT QUALITY

Christophe Mercier

Co-authors

Dr Olivier Morel and Dr James FoxXennia Technology Ltd

Pr Lindsay MacDonald and Dr Ron Todd London College of Communication

Knowledge Transfer PartnershipUK program

Problematic

Print quality / material deposition Printing parameters, Accurate dot positioning

Printer design and mechanical tolerances:

Print head angles: Accuracy of the system of control

Objective:

To determine, for a four colors ink-jet printing system, single pass, the angular range of the print heads which does not impact the perceived print quality

Plan

Problematic / objectives Literature review One colour Four colours Conclusion/perspectives

Perceived print quality

Print quality attributes: ISO 13660 etc Line raggedness, blurring, Colour uniformity

Visibility threshold Line raggedness, blurring; 1.6 m (Svanholm) Colour, in CIE Lab 1976 system, ∆E=4

Misregistration

Quality vs acceptability

IMAGE QUALITY METRICS NORMAN BURNINGHAM, ZYGMUNT PIZLO, JAN P. ALLEBACH

Two colour full tones

Numerical application, print head 70 mm

Half cone

Cone(degree)

Colour misregistrati

on(m)

1 10

2 42

3 96

Colour misregistration

Two colour full tones

Numerical application, print head 70 mm

Half cone

Do you need tighter tolerances, if we consider text or colour reproduction ?

Cone(degree)

Colour misregistrati

on(m)

1 10

2 42

3 96

Colour misregistration

Hypothesis

Nozzle plate geometry

If the print head is rotated

a phenomena called, nozzle pairing appears: the resolution is halved: density issues, line/text discontinuities

Then, isolated nozzles appear at the edge of the print head: stitching and density issues

This phenomena is periodic

Numerical values

Formula

For a distance of 4900 m between the two rows, the angle is 0.81 degree.

If that distance is 4200 m, the angle becomes 0. 94 degree.

)distance2*Stagger -distanceRows inter

cingnozzle spaatan(angle

Experimentation

Experimental tool

Paper

Print head + head mounting

Micrometric Screw

Static arm

Spring

Mobile carriage

Effect on a line

Reference: 0 degree Maximum distance between dots

Printing direction

Effect on text

Reference: 0 degree Maximum distance between dots

Printing direction

Plan

Problematic / objectives Literature review One colour Four colours Conclusion/perspectives

Four colour lines(1)

Objective: cone angle between the four print headsTheoretical four colour lines

Real four colour lines

Four colour lines(2)

Approach: colour of a four colours dot, at one end of the print head

Maximum deviation of the four dots

Printing direction

Position of reference

Colour model

Yule-Nielsen modified Neugeubauser

Reflectance spectrum Ri() and ai Demichel equation n factor

Algorithm

The standard deviation around the ideal position is increases linearly, enabling to get a position for the four heads

The maximum lateral displacement is measured for each state

The dots are projected on a grid to compute the ai and measuring the Delta E with the ideal case: complete overlapping between CMYK.

Complete Overlapping CMYK

No overlapping CMYK

Maximum lateral displacement For 75% overlapping, 15 microns for the

lateral displacement is desirable

Cone angle

For 75% overalpping, 0,04 degree for the cone is desirable

Conclusion

We used an progessive approach

Solid block, no specific head, 3 degrees,

One colour, specific nozzle layout , less1 degree

Four colours, specific head , less 0.3 degree to control an accurate colour reproduction

Furthers developments

Others mechanical misalignments Print raster Printing parameters: Printing speed,

throw distance, dot gain Image – pre-visualization Colour gamut volume/homogeneity