Browse Prior Art Database

High Resolution and Accuracy Registration Measurement for Laser Printers

IP.com Disclosure Number: IPCOM000121445D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 5 page(s) / 138K

Publishing Venue

IBM

Related People

Findley, GI: AUTHOR [+2]

Abstract

The new generation of electrophotographic page printers is used to print a variety of subject matter including text, graphics, and electronically generated forms. Printing images and lines requires accurate registration of the printed image with respect to the edges of the paper. The scales or registration targets disclosed herein were developed to facilitate both accurate and easy measurement of that registration in test and service environments.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

High Resolution and Accuracy Registration Measurement for Laser Printers

      The new generation of electrophotographic page printers
is used to print a variety of subject matter including text,
graphics, and electronically generated forms.  Printing images and
lines requires accurate registration of the printed image with
respect to the edges of the paper.  The scales or registration
targets disclosed herein were developed to facilitate both accurate
and easy measurement of that registration in test and service
environments.

      The dictionary defines "scale" as "a series of marks along a
line used in measuring (the scale of a thermometer)" among other
definitions.  The term vernier scale is defined as "a short scale
used to indicate fractional parts of divisions of a longer scale".  A
printed scale including a vernier scale used to measure the
image-to-paper registration very accurately and very easily was
developed.

      The fundamental concept was to print a scale across the edge of
the paper and then visually determine how much of the scale was on
the paper (as opposed to off the edge). Previous products used a
simple linear scale much like shown on a ruler.  This works fine but
has a resolution and accuracy of about one-half the smallest scale
division.  The best practical resolution with a simple linear scale
was about 5-6 pels (picture elements - 1.106 mm each).

      A more sensitive scale was needed.  To be able to measure and
adjust printers, a scale resolution and accuracy of 1 pel was
required.  Actually, a "vernier" was needed to further subdivide the
5-6 pel resolution achievable with a simple linear scale.  The stair
step vernier scale discussed herein met this objective.

      Using several of these stair step scales at various locations
on the page enables accurate measurement of the axial registration in
both the X and Y directions, and skew (angular rotation) of the
printed image on both sides of the sheet of paper.

      This measurement technique was used extensively during the
development and testing of printers and then became the basis for the
service procedures used to adjust the registration in the customer
environment.

      The fundamental linear scale depicted in Fig. 1 is a 5 pel
black, 5 pel white repeating pattern for 200 pels.  In the ideal
situation, 100 of these 200 pels will show on the paper and 100 would
be off the edge.

      In Fig. 1, the precise location of the edge of the paper cannot
be measured without an external measuring device to an accuracy
better than about 5-6 pels.  By adding a stair step vernie...