Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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A-3645
A-3645
METHOD OF DETERMINING THE RELATIVE POSITION OF A FIRST AND A
SECOND IMAGESETTING DEVICE WITH RESPECT TO EACH OTHER
The invention relates to a method of determining the relative
position of a first imagesetting device with respect to a
second imagesetting device by setting images on an associated
imagesetting medium. zt further relates to a method of
correcting the position of a point of projection of a first
imagesetting device with respect to a point of projection of a
second imagesetting device by changing the relative posii~ion
of the point of projection of the first imagesetting device
with respect to the point of projection of the second
imagesetting device from an actual position to an intended
position, in particular, in a printing form exposer or in a
printing unit of a printing press.
In order to set an image on a two-dimensional surface of an
imagesetting medium using one or more imagesetting devices,
the surface is scanned in two linearly independent coordinate
directions which cover the area, by a relative movement
between the surface anal the imagesetting device or devices
being produced by a suitable actuator mechanism. The scanning
is typically carried out in a so-called fast scanning
direction and a so-called slow scanning direction, in such a
way that all the points to be imaged on the surface are swept
over by the imagesetting devices, more precisely by a number
of imagesetting beams. Here, an imagesetting beam can be a
light beam, in particular a laser light beam, be it in the
infrared, visible or ultraviolet spectra7_ range, a heat pulse,
a gas jet or a droplet of a chemical substance or the like. An
imagesetting device, also referred to as an imagesetting
module, may have one or more imagesetting beams. In this case,
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imagesetting media comprise printing forms, printing plates,
so-called printing form precursors, films or the like. For
setting images on imagesetting media in the graphical
industry, be it at the pre-press stage ~.n printing form
exposers or in the printing stage in printing units (on-press
imagesetting or direct imaging printing units), laser light
sources in particular are particularly widespread in
imagesetting devices. Laser light sources are frequently diode
lasers or solid body lasers, such as lasers with reinforcing
media of Ti: sapphire or Nd:YLF, preferably pumped by a diode
laser. A plurality of laser light sources may be located on
one or more assembled diode laser bars in one imagesetting
device.
An imagesetting device can comprise one imagesetting channel
or a group of imagesetting channels. A plurality of
imagesetting devices can be integrated to form a block. For
the purpose of imagesetting or labeling, the imagesetting
channels are switched on and off (timed triggering). Depending
on the imagesetting method selected, while at least one
imagesetting is switched on, a relative movement may take
place between the point of projection and imagesetting medium,
or not. Using an imagesetting medium on which an image has
been set or written, an image can be transferred to a printing
material. Typical printing materials are paper, board, organic
polymer films or the like, be they sheets or webs.
If a number of imagesetting devices are used, be it in a
printing form exposer or a printing unit, it is very important
that the relative positions of the imagesetting devices with
respect to one another and, presupposing the case of a
plurality of imagesetting beams from one imagesetting device,
that the imagesetting beams from an imagesetting device are
aligned with one another. If appropriately accurate imaging
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optics is used on the imagesetting medium, it is consequently
then possible for the relative position of the imagesetting
beams on the imagesetting medium to be set up or calibrated
with great precision in relation to one another. As a result,
without restricting the general number of imagesetting beams
in an imagesetting device, merely to simplify the illustration
and description, let it be assumed that each imagesetting
device has one imagesetting beam each. Furthermore, without
restricting the general number of the imagesetting devices,
likewise to simplify the illustration, 1_et the description
below be aimed at a first and a second imagesetting device, in
the knowledge that the number of imagesetting devices can also
be more than two.
The procedure for setting up or calibrating the relative
position of a first with respect to a second imagesetting
device (of a first with respect to a second imagesetting
channel or of a first group of imagesetting channels with
respect to a second group of imagesetting channels) can be
required firstly in tree assembly of the imagesetting devices
and secondly in the event of maintenance of the apparatus or
the press with which the imagesetting devices are associated,
be it in a workshop or at the customer. According to a
widespread procedure, therefore, a considerable amount of
effort is associated i.n particular with the installation of
printing presses with on-press imagesetting printing units.
For each printing unit, test imagesetting of a printing form
(imagesetting medium) is carried out, part of the printi~,g
form with an image set on it is cut out and the part is
examined by a reader, so that correction values for the
relative position can be determined. The correction values are
used to make changes to the relative position, for example,
this information is made available to the control system, and
the imagesetting devices are adjusted with respect to one
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another. The abovedescribed method for the relative position
determination is iterated until the desired or required
precision has been reached. The relative position deviation
can be determined both for the fast scanning direction and for
the slow scanning direction, and the relative position can
consequently be adjusted. However, the high outlay on material
and time is a drawback when this method is used.
For instance, the document DE 44 37 284 A1 discloses the fact
that a calibration of a control system for the diffraction of
a laser beam can be performed as follows. A light-sensitive
medium is irradiated by the laser beam in order to produce a
test image, and digitized image sections which are recorded by
a CNC-controlled camera are then generated from said test
image. A calculation of correction data for the control system
for the diffraction of the laser beam is carried out on the
basis of a comparison between the actual positions of the
laser beam, measured by recording the image sections, with
predefined intended positions. The drawback when this method
is used is likewise tree outlay on material and the requirement
to use a precise CNC control system for the camera, which is
consequently expensive.
The document DE 197 32 668 A1 reveals that a calibration
device for a beam scanning device can have a surface with
defined markings. Using a detector device, the light reflected
from the surface or transmitted and belonging to the beam.
scanning over the surface is registered. When the beam strikes
a marking, only a low intensity is reflected or transmitted.
From the registered intensity variation of the radiation in
reflection or transmission, the actual position of the laser
beam is determined and, in a control system, is compared with
the intended position envisaged for this point. From this
comparison, a correction value can be determined and made
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available to the control system, for example stored as a
tabular entry in a memory. One disadvantage of this
calibration device is that a surface with precise markings
must be made available. However, such a surface is sensitive
and little suited to be moved to various locations or to be
accommodated in different machines, frequently with changes in
shape, which may possible lead to distortions of the
coordinate system.
It is an object of the present invention to specify a method
of determining the relative position of a first, with respect
to a second imagesetting device which makes it possible in a
simple way to detect maladjustment of the imagesetting devices
with respect to one another, that is to say the deviation
between an actual distance and an intended distance.
According to the invention, this object is achieved by a
method of determining the relative position of a first
imagesetting device with respect to a second imagesetting
device having the features as claimed in claim 1 or as claimed
in claim 17. Advantageous developments of the invention are
characterized in the dependent and in the equivalent claims.
According to the invention, a determination of the deviation
between the position of the first imagesetting beam, which is
associated with the first imagesetting device, and the
position of the second imagesetting beam, which is associated
with the second imagesetting device, is carried out by means
of a tonal value comparison or area coverage comparison
between specific patterns, in particular grid or line
patterns, directly on the imagesetting medium on which an
image is set or on a test image printed with said imagesetting
medium. According to the invention, the relative position of
the first imagesetting device (imagesetting beam) with respect
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to a second imagesetting device {imagesetting beam) which
functions as a so-called master, is determined. By means of a
suitable selection of the orientation or. direction of the
patterns, in particular line grids, registration of the
position deviations or beam tolerances in the fast scanning
direction and slow scanning direction is possible, the
orientation of the patterns, in particular of the direction of
the lines, in the case of line grids, preferably being at
right angles to the direction of the dimensional tolerance, of
the position deviation. A precondition for the use of the
method according to the invention is precise generation of
defined, pixel-accurate patterns, in particular line grids, on
the imagesetting medium.
The method according to the invention of determining the
relative position of a first imagesetting device with respect
to a second imagesetting device by setting images on an
associated imagesetting medium comprises at least the
following steps: an image is set of a group of mutually
different reference patterns and a basic pattern by means of
the second imagesetting device which serves as a master, each
reference pattern from the group being assigned uniquely to
one relative position. An image of at least one test pattern
is set by means of the first imagesetting device, whose
relative position is to be determined, over the basic pattern,
so that a combination pattern is produced. A reference
pattern, from the group, whose area coverage coincides with
the area coverage of the combination pattern is determined.
Since the identified pattern from the group is assigned in a
unique way to one relative position, the relative position of
the first with respect to the second imagesetting device is
identified.
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Expressed in other words, the method according to the
invention for determining the relative position of two
imagesetting devices (imagesetting modules or imagesetting
beams) with respect to each other comprises setting images
over one another or writing patterns over one another, a
number of reference patterns being written by the second
imagesetting device, functioning as a master, and at least one
test pattern being written by the first imagesetting device
whose relative position deviation is to be determined, so that
at least one combination pattern is produced for the purpose
of comparing the area coverage or the tonal value by an
optical route (measurement) either on the imagesetting medium
or on a test image on a printing material printed by using the
imagesetting medium.
The method according to the invention for determining the
relative position of a first imagesetting device with respect
to a second imagesetting device, the first imagesetting device
being associated with a first imagesetting medium and the:
second imagesetting device being associated with a second
imagesetting medium, comprises at least the following steps:
an image is set of a group of mutually different reference
patterns and a basic pattern by means of the second
imagesetting device on the second imagesetting medium
associated with the second imagesetting device, each reference
pattern from the group being assigned uniquely to one relative
position. An image of at least one test pattern is set by the
first imagesetting device on the first imagesetting medium
associated with the first imagesetting device. The first and
second imagesetting media on which images are set by the first
and the second imagesetting device are printed off onto a
printing material in such a way that the test pattern whose
image is set by the first imagesetting device is printed off
over the basic pattern,, so that a combination pattern is
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produced. A reference pattern, from the group, whose area
coverage coincides with the area coverage of the combination
pattern is identified. Since the identified pattern from the
group is assigned a relative position in a unique way, the
relative position of the first with respect to the second
imagesetting device is identified.
It is particularly advantageous if the reference patterns from
the group, the basic pattern and the test pattern are two-
dimensional, but are uniform or translation-invariant in one
of the two linearly independent directions. Expressed in other
words, the patterns can have an orientation or direction. The
uniformity, in particular for line patterns or line grids, can
particularly advantageously extend at right angles to the
direction of the relative position deviation to be determined,
so that precise detection of the relative position in
combination patterns is made possible, since even a small
deviation in a direction not parallel to the uniformity can
lead to a large change in the area coverage of the combination
pattern.
The basic pattern can advantageously comprise a group of
mutually identical control patterns. These can be arranged at
various locations on the two-dimensional area of the
imagesetting medium. These control patterns can, but do not
have to be, overwritten by one and the same test pattern. In
the case of a test pattern, the result is redundancy of the
information, so that statistical or other error sources can
advantageously be avoided. In the case of a plurality of test
patterns, different combination patterns are produced, so that
additional information can be obtained by optical comparison.
It is also advantageous if the number of reference patterns in
the group and the number of control patterns is the same and
in each case one reference pattern in the group is uniquely
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assigned just one control pattern. For example, it is
additionally possible for the mutually uniquely associated
control and reference patterns also to be arranged adjacently
on the two-dimensional surface of the imagesetting medium. By
means of a unique association or an adjacent arrangement, an
optical comparison can be carried out simply, quickly and
conveniently if the control patterns (basic patterns) are
covered by test patterns to form combination patterns. In
particular, the comparison can be carried out by means of a
single measurement, a first part of the image field being
assigned to the combination pattern and a second part of the
image field being assigned to the reference pattern.
A further advantageous feature can be formed by the fact that
the number of reference patterns in the group and the
associated control patterns in the basic pattern can be
uneven. It is then possible for the test pattern to cover a
first part of the control patterns with a first sub-pattern,
to cover a second part of the control patterns with a second
sub-pattern and to cover a control pattern both by the first
sub-pattern and with the second sub-pattern. As a result, at
the location of the first sub-pattern, a first combination
pattern is then produced, at the location of the second sub-
pattern, a second combination pattern is produced and, at the
location of the control pattern covered by the first and
second sub-pattern, a third combination pattern is produced.
The first and the second sub-pattern can be selected in such a
way that the first combination pattern is then exactly
identical to the associated control pattern covered by it when
the second combination pattern differs from the associated
control pattern covered by the latter, anal that the second
combination pattern is then exactly identical to the
associated control pattern covered by it when the first
combination pattern differs from the associated control
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pattern covered by the latter. The third combination pattern
can coincide either with the first or with the second
combination pattern. In this way, it is possible to carry out
detection of the sign of the relative position between the
first and second imagesetting device. For these additional
features, it can also be true that the reference patterns from
the group, the control patterns and the test pattern are two-
dimensional, but are uniform or translation-invariant in one
of the two linearly independent directions.
It is particularly advantageous if the basic pattern exhibits
50o area coverage, so that relative position deviations lead
to small area coverage changes in the patterns starting from
50o area coverage. In this range, area coverage changes can be
determined easily and well.
In one advantageous embodiment, the basic pattern and/or the
control patterns, if the basic pattern comprises a group of
control patterns, has a regular sequence of a number of
exposed and of the same number of unexposed points in one
direction of its extent. In other words, a pattern can be a
line grid or a strip grid. The lines can be parallel to one
another and in particular can run at right angles to the
direction in which the relative position is to be determined.
Furthermore, it is also possible for each of the reference
patterns in the group of reference patterns to have a regular
sequence of exposed and unexposed points in one direction of
its extent, the sequences in one period in each case having a
first and a second number of exposed points and a third and a
fourth number of unexposed points. The directions of the
extents of the reference patterns in the group of reference
patterns can advantageously also be parallel to one another.
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It is particularly advantageous if the number of reference
patterns in the group of mutually different reference patterns
is uneven and if a reference pattern is assigned to the
relative intended position, a first part of the group of
reference patterns is assigned to relative positions which are
greater than the relative intended position, and a second part
of the group of reference patterns is assigned to relative
positions which are smaller than the relative intended
position. In a first embodiment, for one absolute value of the
relative position, the reference pattern from the first part
of the group can be identical to the reference pattern from
the second part of the group. In a second embodiment, for one
absolute value of the relative position, the reference pattern
from the first part of the group with respect to the reference
pattern from the second part of the group may exhibit mirror
symmetry with respect to an axis at right angles to the extent
of one of the reference patterns.
In a preferred embodiment of the method according to the
invention, the group of mutually different reference patterns
can be arranged on the imagesetting medium so as to be ordered
in accordance with the associated relative intended position.
Also optional is the imagesetting or labeling of the reference
patterns by means of a scale. Expressed in other words, the
assignment of a reference pattern to a relative position or
position deviation is also directly visible to the human eye.
An ordered arrangement therefore permits quick and simple
optical evaluation of the imagesetting result.
In an advantageous development of the method according to the
invention of determining the relative position of a first
imagesetting device with respect to a second imagesetting
device, if the imagesetting medium is accommodated in a
printing unit for the purpose of imagesetting, provision is
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made for the imagesetting medium on which an image has been
set by the first and second imagesetting device to be printed
off onto a printing material before the identification of
coincident area coverage, the identification being performed
on the printing material, and the ident~_fication of the
relative position associated with the identified reference
pattern from the group are performed. In addition to the
particularly convenient and simple possibility of being able
to perform measurements of the area of coverage on the
printing material and not on the imagesetting medium
accommodated in the printing unit, this development of the
method according to the invention also has the advantage that,
if appropriate, influences of the printing unit on the
intended position or relative intended position of the two
imagesetting beams or imagesetting devices can be taken into
account, since it is ultimately a question of the relative
position of a pixel or printed dot placed by the first
imagesetting device in relation to the position of a pixel or
printed dot placed by the second imagesetting device in t:he
image on the printing material.
The method according to the invention, its advantageous
embodiments or its advantageous developments avoid high
expenditure on labor and time, since processing of the
imagesetting medium, printing form material, outside the
printing form exposer or the printing unit, and examination
under a reader or aids, such as magnifying glasses, imaging
optics or the like and renewed loading of an imagesetting
medium are no longer necessary, as opposed to the prior art.
The method according to the invention of determining the
relative position or the relative position deviation of two
imagesetting devices can be developed further to a method of
correcting the position of a first imagesetting device with
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respect to a second imagesetting device, more accurately, to
correcting the position of the points of projection of a first
imagesetting device with respect to points of projection of a
second imagesetting device, by changing the relative position
of the first imagesetting device with respect to the second
imagesetting device from an actual position to an intended
position and/or by changing the timed triggering (of the
switching on and off). In this method according to the
invention for correcting the position of the points of
projection, the area coverages are determined by a measuring
device, for example a photodiode or a CCD array, by the
intensity of the light reflected from the combination patterns
and the reference patterns being detected and the measured
values being compared in a suitable processing unit. As a
result, the identification of combination patterns and
reference patterns is made possible in electronic form, so
that a signal for changing the relative position of the first
imagesetting device with respect to the second imagesetting
device and, consequently, also for changing the relative
position of the associated points of projection can be
generated. On the one hand, this signal can be in the form of
a display for a human, on the other hand, provision can also
be made for the relative position to be changed from an actual
position to an intended position by an actuator mechanism. As
an alternative to this, the timed triggering of the first
imagesetting device relative to the second imagesetting device
can take place later or earlier than in the uncorrected state.
The method according to the invention for correcting the
position of the points of projection can be implemented in the
following way in a device: a printing form exposer having at
least a first and a second imagesetting device, which can be
moved relative to the imagesetting medium and/or to one
another by means of a controlled actuator mechanism, has a
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control unit. The printing form exposer is distinguished by
the fact that the control unit comprises an electronic unit
with a memory unit, in which a computer program for correcting
the position of the first imagesetting device by means of the
controlled actuator mechanism and/or by means of changed timed
triggering is stored, the computer program having at least one
functional section in which steps from the method according to
the invention for correcting the position by means of the
actuator mechanism and/or the timed triggering are performed.
As an alternative to this, an implementation can also be
performed for a printing unit or a printing unit group: a
printing unit having a first and a second imagesetting device
or a printing unit group having a first printing unit, to
which a first imagesetting device is assigned, and having a
second printing unit, to which a second imagesetting dev~_ce is
assigned, it being possible for the imagesetting devices to be
moved relative to the imagesetting medium or to the
imagesetting media and/or to one another by means of a
controlled actuator mechanism, has a control unit. The
printing unit or the printing unit group is distinguished by
the fact that the control unit comprises an electronic unit
with a memory unit, in which a computer program for correcting
the position of the first imagesetting device by means of the
controlled actuator mechanism and/or changing the timed
triggering is stored, the computer program having at least one
functional section in which steps from the method according to
the invention for correcting the position by means of the
actuator mechanism and/or changing the timed triggering a.re
performed. A printing press according to the invention - be it
a web-fed or a sheet-fed printing press - in particular.a
planographic printing press, an offset printing press or the
like, has at least one printing unit according to the
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invention and/or at least one printing unit group according to
the invention.
Further advantages and advantageous embodiments and
developments of the invention will be illustrated by using the
following figures and their descriptions. In detail:
figure 1 shows a schematic representation of the structure of
a pattern as can be used in the method according to the
invention,
figure 2 shows an advantageous embodiment of the patterns used
and their arrangement for the method according to the
invention,
figure 3 shows combination patterns written one above another
for a first relative position of the first with respect to the
second imagesetting device an arranged patterns and reference
patterns of the advantageous embodiment according to figure 2,
figure 4 shows combination patterns written one above another
for a second relative position of the first with respect to
the second imagesetting device on arranged patterns and
reference patterns of the advantageous embodiment according to
figure 2, and
figure 5 shows a schematic plan view of a. printing press
having an embodiment of a printing unit according to the
invention with a first and second imagesetting device, whose
relative position is determined and corrected by the methods
according to the invention.
Figure 1 serves to exp7_ain the structure of a pattern as can
be used in the method according to the invention. A pattern 10
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comprises a number of pattern units 12. The pattern units 12
correspond to pixels or printed dots, expressed in another
way, a pattern unit 12 is an imagesetting point, which is
produced on the imagesetting medium at least by an
imagesetting beam or an imagesetting device. Adjacent pattern
units 12 have a spacing which corresponds to the spacing of
imagesetting points. In one advantageous embodiment of the
method according to the invention, patterns 10 are used which
are constructed by pattern units 12 lying on a regular and
rectangular grid. By way of example, in the sequence of part
images A, B and C of figure 1, patterns 10 are shown which are
constructed in square form from eight by eight pattern units
12. Patterns 10 can also have a considerably larger number of
pattern units 12, 112 by 112 pattern units 12 in the preferred
embodiment which is described by using figures 2 to 4. In part
A of figure 1, in order to simplify the representation, it is
shown that the pattern 10 is built up from square pattern
units 12 whose surface centers of gravity lie on a rectangular
grid. For the method according to the invention, the pattern
units 12 can be present in two states: a non-imaged and an
imaged state. The imaged state can be achieved either by
setting an image with a first imagesetting device or by
setting an image with a second imagesetting device. In part B
of figure 1, it is shown by way of example that the first,
second, fifth and sixth columns from the left of the pattern
have had an image set by the second imagesetting unit. The
pattern 10 then has imaged pattern units 14. Further setting
of an image of an already imaged pattern unit 14 leads to no
qualitative state change in the sense of the method according
to the invention. Expressed in other words, a pattern unit 14
already imaged by the second imagesetting device does not
change qualitatively, that is to say remains imaged as a
result of renewed imagesetting by the first imagesetting
device. We assume that the first imagesetting device sets the
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image in the second and the third column from the left of the
pattern 10. Part C of figure 1 then shows that the imaged
pattern units 14 in the second column, which had already been
imaged, have not experienced any qualitative change, while the
pattern units 12 in the third column have now become imaged
pattern units 14. Expressed in other words, part B of figure 1
shows an example of a basic pattern or control pattern, which
becomes the combination pattern shown in part C of figure 1 as
a result of overwriting in the second arid third columns of the
pattern 10.
If the first and the second imagesetting~ devices have a
relative intended position with respect to each other, then
when the surface of the imagesetting medium is scanned in the
method according to the invention, it is ensured that the
pattern units 14 written by the first imagesetting device
cover at least a subset of the pattern units 14 written by the
second imagesetting device (master). Expressed in other words,
combination pattern and basic pattern coincide; there is no
requirement for manipulation. On the other hand, if the first
and the second imagesetting device have a relative actual
position with respect to each other which differs from the
intended position, then when the surface of the imagesetting
medium is scanned in the method according to the invention,
there is at least one pattern unit 14 written by the first
imagesetting device which does not cover a pattern unit 14
written by the second imagesetting device (master). Expressed
in other words, combination pattern and basic pattern do not
coincide; there is a requirement for manipulation.
Figure 2 shows an advantageous embodiment of the patterns used
and their arrangement for the method according to the
invention. Figure 2 has a left-hand and a right-hand part, the
right-hand part being an enlargement of a detail from the
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left-hand part. In this advantageous embodiment, as
illustrated in the left-hand part, the method according to the
invention is based on fifteen reference patterns 16 and
fifteen control patterns (basic patterns 18). In the method
according to the invention, images of reference patterns 16
and basic patterns 18 are set by the second imagesetting
device, the master. Each reference pattern 16 is assigned a
control pattern 18, so that fifteen blocks exist. A scale 20
is provided, of which an image is likewise set, said scale
labeling the fifteen blocks and visualizing the unique
assignment of each reference pattern 16 to a relative
position. This procedure is advantageous in particular for the
measurement or checking of a printing material pulled off from
the imagesetting medium. In this embodiment, the patterns have
112 by 112 pattern un~_ts 12. As viewed from area center of
gravity to area center. of gravity, adjacent pattern units 12
have a spacing of 10 um. The patterns correspond to a grid of
60 lines per centimeter with addressing of 1000 lines per
centimeter.
In this embodiment, the reference patterns 16 differ from one
another in such a way that, as a result of the area coverage
of the combination patterns produced by overwriting the
.control patterns (basic patterns 18) by means of a test
pattern, spacing changes of 5 um can be made visible or
measurable. The blocks comprise reference patterns 16 and
basic patterns 18 which are formed by line grids, which are
uniform in the direction at right angles to the direction in
which the relative position is to be determined. The line grid
for the basic pattern 18, that is to say all the control
patterns, is constructed regularly: it has columns of imaged
and non-imaged pattern units 12. Figure 2 shows that, as
viewed from left to right, alternately eight columns have an
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image set and eight columns have no image set. The basic
pattern therefore exhibits 50% area coverage.
The reference patterns 16 are to be classified here into a
first, upper part here and a second, lower part here, and a
central reference pattern for the intended position 22. The
central reference pattern for the intended position 22, as
viewed from left to right, has alternately eight columns with
an image set and eight columns with no image set, that is to
say, like the basic pattern 18, exhibits an area coverage of
500. This central reference pattern 22 is assigned to the
relative position 0 um, more accurately a deviation 0 um from
the relative intended position, as can also be seen from the
scale 20. In the first, upper part here, reference patterns 16
are arranged in an ordered fashion, are assigned the relative
positions -5.0 um, -10.0 um, -15.0 um, -20.0 um, -25.0 urn, -
30.0 um and -35.0 Vim, and are reproduced in the scale 20.. From
adjacent reference pattern to reference pattern, the area
coverage (tonal value) increases in steps of 3.1250 as far as
71.8750 for -35.0 um. This increase in area coverage is
achieved as follows.
If the reference pattern 16 for a specific relative position
is considered, then the reference pattern 16 for the relative
position of the next step, that is to say the specific
relative position minus 5.0 um, differs in the fact that a
further column of pattern units 12 also has an image set by
the second imagesetting device. The arranged sequence,
starting from the central reference pattern 16 with 500 area
coverage, is formed as follows in the advantageous embodiment
shown in figure 2 by means of the variation in a 4-column
periodicity: for 0 um, eight with an image set, eight with no
image set, eight with an image set, eight with no image set;
for -5.0 um, eight with an image set, eight with no image set,
CA 02415612 2003-O1-06
nine with an image set, seven with no image set; -10.0 um,
nine with an image set, seven with no image set, nine with an
image set, seven with no image set; -15"0 Vim, nine with an
image set, seven with no image set, ten with an image set, six
with no image set; -20.0 um, ten with an image set, six with
no image set, ten with an image set, six with no image set; -
25.0 um, ten with an image set, six with no image set, eleven
with an image set, five with no image set; -30.0 um, eleven
with an image set, five with no image set, eleven with an
image set, five with no image set; and -35.0 um, eleven with
an image set, five with no image set, twelve with an image
set, four with no image set. As a result of the four-column
periodicity, in which only a proportion of the area coverage
of the reference patterns 16 is changed by 3.125% from one
relative position to the next relative position, it is
possible to make a relative position deviation which is finer
or smaller than the spacing of the pattern units 12
detectable, in particular here, half of the spacing of
adjacent pattern units 12; the measured variable is the
integral area coverage of the combination pattern, which is
compared with the integral area coverage of the reference
patterns 16.
The reference patterns in the second, lower part here are
arranged in order and are assigned to the relative positions
5.0 um, 10.0 um, 15.0 um, 20.0 um, 25.0 um, 30.0 ~m and 35.0
pm, as also reproduced in the scale 20. In this advantageous
embodiment, the two reference patterns 16 which are assigned
to two relative positions whose absolute value coincides are
the same and follow the four-column periodicity listed in more
detail above for the first part.
With knowledge of the method according to the invention, it is
clear to those skilled in the art that an increase in the
CA 02415612 2003-O1-06
sensitivity or a reduction in the size of the step width of
relative positions can be achieved by increasing the grid
frequency of the lines in the group of the reference patterns
16 and the control patterns 18 (basic patterns), expressed in
other words the spacing of the pattern units 12. For example,
therefore, four strips with an image set and four with no
image set. The patterns then correspond to a grid of 120 lines
per centimeter with addressing of 1000 lines per centimeter.
Furthermore, it is clear that, in the method according to the
invention, a refinement in the step width of relative
positions with a specific spacing of the pattern units 12 can
be achieved by means of a different number of strips in the
periodicity of the strip sequence; for example, by means of a
six-strip periodicity of the reference patterns 16 which,. in a
manner analogous to that described above for the four-strip
periodicity, in each case in permutation broadens the strips
with an image set, an ordered sequence of reference patterns
16 can be produced, which make it possible to visualize or
make measurable relative position deviations of one third of
the spacing of adjacent pattern units 12. For 2n-strip
periodicities broadened in permutation, it is generally true
that 1/n of the spacing of adjacent pattern units becomes
measurable, n being a natural number greater than or equal to
two.
By using figures 3 and 4, an explanation is to be given as to
how, by covering the control patterns (basic patterns) with a
test pattern, which produces combination patterns, relative
positions of the first imagesetting device with respect to the
second imagesetting device become measurable: in the event of
different relative positions between the two imagesetting
devices, different combination patterns are produced, whose
area coverage is determined (measured) and compared with the
area coverage of the reference patterns.
CA 02415612 2003-O1-06
In this advantageous embodiment, the test pattern has the
following property: the seven control patterns which are
assigned to the reference patterns 16 of the first, upper part
are overwritten by a test pattern of 112 by 112 pattern units
by means of the first imagesetting device, which has a two-
strip periodicity having four exposed and twelve unexposed
columns. The central control pattern which is assigned to the
reference pattern for the intended position is overwritten by
a test pattern of 112 by 112 pattern units having a two-strip
periodicity of eight exposed and eight unexposed columns. The
seven control patterns which are assigned to the reference
patterns 16 of the second, lower part, are overwritten by a
test pattern of 112 by I12 pattern units by means of the first
imagesetting device, which has a periodicity with four
unexposed, four exposed and eight unexposed columns, that is
to say has a two-strip periodicity which is offset by four
columns as compared with the test pattern over the first,
upper part.
The test pattern is written by the first imagesetting devices
in such a way that the pixels (pattern units) are driven as
though the relative position of the first with respect to the
second imagesetting devices were the intended position.
Expressed in other words, if the relative actual position,
that is to say the actual spacing between the two imagesetting
devices, is the relative intended position, that is to say the
intended spacing, then an image of a specific pattern element
of the test pattern (specific column, specific row) is set at
a time at which the projection of the imagesetting beam of the
first imagesetting device comes to lie at that coordinate
point on the surface of the imagesetting medium at which the
setting of an image of the pattern unit of the control pattern
(basic pattern) has been carried out at a different, preceding
CA 02415612 2003-O1-06
time in the same specific column and the same specific row.
The control patterns are therefore located in a region of the
surface of the imagesetting medium which can be swept over
both by the first and by the second imagesetting device or the
projections of their imagesetting beams, so that test patterns
can be written over the control patterns to produce
combination patterns. As those skilled in the art can quickly
imagine, firstly for the case of synchronous movement of the
two imagesetting devices, if there is a fixed spacing, this
overlapping region is reached by the first imagesetting device
when the latter comes at a later time into a region which has
previously been written by the second imagesetting device, or
secondly, an overlapping region can be defined by overlapping
amplitudes of the individual movements of the imagesetting
devices for the case of mutually independent movements of the
two imagesetting devices, that is to say a variable spacing
when there is a suitable actuator mechanism during the
imagesetting.
Figure 3 relates in schematic form to combination patterns
written one over another for a first relative position,
differing from the intended position, of the first with
respect to the second imagesetting device on arranged patterns
and reference patterns of the advantageous embodiment
according to figure 2. Figure 3 has a left-hand and a right-
hand part, the right-hand part being an enlarged detail of the
left-hand part. In the left-hand part, the fifteen reference
patterns 16 and the scale 20 which have already appeared in
figure 2 are shown. The fifteen control patterns (basic
patterns) 18 from figure 2 have now been covered by the test
pattern, as described in more detail above, which has been
written by the first imagesetting device whose relative
position with respect to the second imagesetting device
(master) is to be determined, so that fifteen combination
CA 02415612 2003-O1-06
patterns 24 have been produced. There therefore exist fifteen
blocks each having a reference pattern 16 and a combination
pattern 24 for an associated relative position. Since, in this
example of figure 3, the first relative position of the
imagesetting devices with respect to each other differs from
the relative intended position, when the first imagesetting
device is driven to write the pixels (pattern units) as though
the relative position of the first with respect to the second
imagesetting device were the intended position, the test
pattern is offset with respect to the position of the control
patterns (basic patterns) 18 on the imagesetting medium by the
first relative position (deviation of the first position from
the intended position).
In the example of figure 3, the results for the first position
are the following combination patterns 24: a first subset of
the combination patterns 210 remains unchanged, since the
first imagesetting device has set an image only of pattern
units of which an image has already been set by the second
imagesetting device. As illustrated by using figure l, the
result is no qualitative change in the pattern units as a
result of renewed imagesetting. A second subset of the
combination patterns 212, on the other hand, now has a changed
two-strip periodicity: ten exposed and six unexposed strips.
In the right-hand part of figure 3, an enlargement of a detail
of the blocks of reference pattern 16 and combination pattern
24 for the relative positions 15.0 um, 20.0 ~zm and 25.0 um, in
addition to the scale 20, is shown. By means of optical
determination or measurement of the area coverage, it is shown
that the area coverage of a first identified combination
pattern 26 agrees with the area coverage of a reference
pattern 28 (ten exposed, six unexposed, ten exposed, six
unexposed), so that it can be concluded or a signal can be
generated within an electronic or information-technical
CA 02415612 2003-O1-06
processing unit that the reference pattern 28 corresponds with
the first identified combination pattern 26. An identification
of the reference pattern 28 has taken place and, on the basis
of the unique assignment to the relative position (deviation),
the latter is determined. In the example of figure 3, this is
the relative position 20.0 um. By means of the specified
method, for example in this advantageous embodiment, it is
therefore possible to determine both the magnitude and the
direction of the deviation.
Figure 4 describes combination patterns written above one
another schematically for a second relative position,
deviating from the intended position, of the first with
respect to the second imagesetting device on arranged patterns
and reference patterns of the advantageous embodiment
according to figure 2. Figure 4 has a left-hand and a right-
hand part, the right-hand part being an enlarged detail of the
left-hand part. In the left-hand part, the fifteen reference
patterns 16 and the scale 20 which have already appeared in
figure 2 are shown. The fifteen control patterns (basic
patterns) 18 from figure 2 have now been covered by the test
pattern, as described in more detail above, which has been
written by the first imagesetting device whose relative
position with respect to the second imagesetting device
(master) is to be determined, so that fifteen combination
patterns 24, which differ from those for the first position
according to figure 3, have been produced. Since, in this
example of figure 4, the second relative position of the
imagesetting devices with respect to each other differs from
the relative intended position, if the first imagesetting
device is driven to write the pixels (pattern units) as though
the relative position of the first with respect to the second
imagesetting devices were the intended position, the test
pattern is offset with respect to the position of the control
CA 02415612 2003-O1-06
patterns (basic patterns) 18 on the imagesetting medium by the
first relative position (deviation of the first position from
the intended position).
In the example of fig. 4, the result for the second position
is the following combination patterns 24: a third subset of
the combination patterns 218 now has a changed two-strip
periodicity: nine exposed and seven unexposed strips. A fourth
subset of the combination patterns 220, on the other hand,
remains unchanged, since the first imagesetting device sets
images only of pattern units of which images have already been
set by the second imagesetting device. As illustrated by using
figure 1, the result is no qualitative change in the pattern
units as a result of renewed imagesetting. In the right-hand
part of figure 4, an enlargement of a detail of the blocks of
reference pattern 16 and combination pattern 24 is now shown
for the relative positions -15.0 Vim, -10.0 um and -5.0 Vim,
together with the scale 20. By means of optical determination
or measurement of the area coverage, it is shown that the area
coverage of a second identified combination pattern 214
coincides with the area coverage of a reference pattern 216
(nine exposed, seven unexposed, nine exposed, seven
unexposed), so that it can be concluded or a signal can be
generated within an electronic or information-technical
processing unit that the reference pattern 216 corresponds
with the second identified combination pattern 214. An
identification of the reference pattern 216 has taken place
and, on the basis of the unique assignment to the relative
position (deviation), the latter is determined. In the example
of figure 4, this is the relative position -10.0 um. By means
of the method specified, for example in this advantageous
embodiment, it is therefore possible to determine both the
magnitude and the direction of the deviation, in this case of
figure 4, opposite to that of figure 3.
CA 02415612 2003-O1-06
Figure 5 is a schematic plan view of a printing press having
an embodiment of a printing unit according to the invention
with a first and a second imagesetting device, whose relative
position is determined and corrected by the methods according
to the invention. Provided within a printing press 50 is a
printing unit 52, in which an imagesetting medium 54 can be
written on or have an image set (direct imaging printing unit
or on-press imagesetting). A first imagesetting device 56 and
a second imagesetting device 58 are assigned to the
imagesetting medium 54 and have a relative position 510 with
respect to each other. Translation 514 of the first
imagesetting device 56 and translation 516 of the second
imagesetting device 58 are in each case symbolized by a double
arrow. Expressed in other words, the first and the second
imagesetting device 56, 58 can be moved both relative to the
surface of the imagesetting medium and also with respect to
each other in this embodiment. In order to produce these
movements, the printing unit 52 according to the invention
comprises a linear drive 516 with a suitable actuator
mechanism 518 for the first and the second imagesetting device
56, 58. The actuator mechanism 518 is linked to a control unit
520. The control unit 520 has a memory unit 522 in which a
computer program is stored which has at least one section in
which method steps relating to the position correction, which
comprises the steps of the method according to the invention
for determining the relative position of the first with
respect to the second imagesetting device 56, 58, are
executed. As an alternative to a computer program in a memory
unit 522, it is also possible to provide an electronic circuit
which can carry out the same logical operations.
The imagesetting medium 54 can be rotated about an axis of
rotation 524, for which purpose a suitable drive, not shown
CA 02415612 2003-O1-06
here, is provided. As a result of the rotation about the axis
of rotation 524 and the translations 512, 514 substantially
parallel to the axis of rotation 524, all the coordinate
points at which images are to be set on the surface of the
imagesetting medium 54 can be reached by at least one of the
two imagesetting devices 56, 58. With the aid of a measuring
device 526, which is translated along the travel path 528 by a
drive not shown here, indicated by the double arrow 530, the
area coverages of various patterns written by the imagesetting
devices, for example directly on the imagesetting medium or on
a printing material onto which the written image has been
printed off in the printing unit 52, can be determined. The
measuring device 530 is linked to the control unit 520, so
that the information obtained about the relative actual
position can be processed for the position correction, be it
via the controlled actuator mechanism, via a change in the
timed triggering or via both of these measures.
CA 02415612 2003-O1-06
LIST OF DESIGNATIONS
Pattern
12 Pattern unit
14 Set image of a pattern unit
16 Reference pattern
18 Basic pattern
Scale
22 Reference pattern for intended position
24 Combination pattern
26 First identified combination pattern
28 Reference pattern of the first actual position
210 First subset of combination patterns
212 Second subset of combination patterns
214 Second identified combination pattern
216 Reference pattern of the second actual position
218 Third subset of combination patterns
220 Fourth subset of combination patterns
50 Printing press
52 Printing unit
54 Imagesetting medium
5& First imagesetting device
58 Second imagesetting device
510 Relative position
512 Translation of the first imagesetting device
514 Translation of the second imagesetting device
516 Linear drive
518 Actuator mechanism
520 Control unit
522 Memory unit
524 Axis of rotation of the imagesetting medium
526 Measuring device
528 Travel path of the measuring device
530 Translation of the measuring device
