Method and apparatus for measuring a position of webs or sheets

The position of the edges of a web or sheet is determined by using an optical system in conjunction with a photoelectric receiver. The location of the sheet or web edge can be measured accurately even if the edge has various anomalies. The optical system provides different images of the web or sheet edge in two directions.

FIELD OF THE INVENTION 
The present invention is directed generally to a method and apparatus for 
measuring a position of a web or sheet. More particularly, the present 
invention is directed to a method and apparatus for using a photoelectric 
measuring device to locate the edge of a web or a sheet. Most 
specifically, the present invention is directed to a method and apparatus 
for locating a position of an edge of a web or a sheet having edge 
anomalies. The web or sheet edge is supported between a light source and a 
photoelectric receiver which form a portion of an optical system. The 
light source uses an upper condenser to form an upper light beam bundle. 
This upper light beam bundle strikes the edge of the sheet or web. The 
portion of the light beam bundle not stopped by the web or sheet passes 
through a diaphragm opening and through a lower imaging lens. The edge of 
the web is clearly defined on the photoelectric receiver in a first or 
transverse imaging plane extending in the direction of a transverse axis 
extending perpendicular to the edge of the web. The edge of the web is 
represented in a diffused and blurred fashion in the direction of a second 
or longitudinal imaging plane extending in the longitudinal axis extending 
parallel with the edge of the web. 
DESCRIPTION OF THE PRIOR ART 
In the field of printing, it is very important to be able to precisely 
locate and measure the position of a web or sheet that will be printed, or 
that has been printed in a first printing couple and that will be 
subsequently printed in a second printing couple. Accurate registration of 
the printing requires that the location of the web or sheet be accurately 
measured. Such a measurement must be taken frequently and thus it is also 
important that the measuring apparatus be capable of being operable in an 
efficient and dependable manner. 
In the German Published, Non-Examined Patent Application No. DE-OS-22 02 
087, there is disclosed a measuring system for the photoelectric 
measurement of a position of sheet edge with respect to a reference line. 
This prior device uses light emanating from an illuminating device with 
this light being received by a photoelectric receiver. A video signal is 
generated with this video signal corresponding to the position of the edge 
of a sheet that has been inserted between the illuminating device and the 
receiver. The photoelectric receiving element that is used in this prior 
device consists of a plurality of individual photoelectric elements that 
are arranged adjacent each other and that are positioned on behind the 
other. 
A significant limitation of this prior art device is its inability to 
differentiate between the edge of the sheet or web and some type of 
anomaly on the edge. Even the smallest damage to the edge of the sheet or 
web, or the projection of a fiber beyond the sheet edge will result in a 
faulty measurement of the location of the edge of the sheet or web. Each 
such edge projection, edge tear or projecting fiber or thread will result 
in an incorrect measurement or determination of the position of the sheet 
or web edge since each of these edge anomalies can be sensed by the 
measuring apparatus. If each incorrect web edge sensing event results in a 
press shut down, it will be readily apparent that such a system cannot be 
used. 
A need exists for a method and for a suitable apparatus for use in 
determining the position of an edge of a web or sheet which will not be 
rendered ineffective by various edge anomalies. The method and apparatus 
for measuring a position of webs or sheets in accordance with the present 
invention provides such a device and is a significant improvement over the 
prior art. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method and apparatus 
for measuring a position of webs or sheets. 
Another object of the present invention is to provide a method and 
apparatus for using a photoelectric measuring device to locate the edge of 
a sheet or web. 
A further object of the present invention is to provide a method and 
apparatus for measuring the position of a sheet or web having web edge 
anomalies. 
Still another object of the present invention is to provide a method and 
apparatus for using a photoelectric receiver with a plurality of 
photoelectric elements to locate the edge of a sheet or web despite the 
existence of web edge anomalies such as small web segments or fibers 
extending beyond the edge of the web. 
As will be discussed in detail in the description of the preferred 
embodiments which is presented subsequently, the edge of the sheet or web 
whose position is to be detected is supported on an object holder above a 
diaphragm having an opening of a defined length and width. A light source 
and an upper light condenser are placed above the object holder. This 
upper light source and upper light condenser form a bundle of light rays. 
These light rays will pass through the diaphragm opening beneath the 
object holder and will be focused by a lower imaging lens. These focused 
light beams, in the form of a focused bar or beam of light, are received 
by a photoelectric device that has a length and a width which are less 
than that of the diaphragm opening. An edge of a web or sheet which is 
supported by the object holder is positioned in the path of the cylinder 
shaped upper light beam bundle. Only those light beams not striking the 
sheet or web will pass through the diaphragm opening and be focused on the 
photoelectric device. Minor edge anomalies will interfere with the passage 
of a portion of the beam of light but will not stop the passage of the 
entire beam. Thus, while the intensity of the focused light beam striking 
the photoelectric device may be slightly diminished by the presence of the 
web edge anomalies, it will still be substantially greater that the light 
received by that portion of the photoelectric device blocked by the sheet 
or web. Thus an accurate measurement of the location of the sheet or web 
will be obtained which will not be affected by these minor edge anomalies. 
The light image of the web will be made diffused and blurred in the 
longitudinal axis extending parallel to the edge of the web. The light 
image of the web will be made very sharp in the transverse axis 
perpendicular to the edge of the web. 
So long as the web or sheet edge anomalies are small in width with respect 
to the width of the opening in the diaphragm which underlies the object 
holder, the light in the light beam bundle will not be significantly 
reduced in strength. The portion of the light which passes through the 
diaphragm opening and is then focused by the imaging lens into the focused 
bar of light that strikes the photoelectric receiver will still be 
substantially greater in strength than the ambient light that may be 
received by the portion of the photoelectric device underlying the web or 
sheet. The photoelectric receiver is used to generate an analog video 
signal. The amplitude of the video signal from the portion of the 
photoelectric device not covered by the web is so much greater than the 
signal from the covered portion that the inclusion of edge anomalies on 
the edge of the web or sheet will not adversely affect the accuracy of the 
measurement of the position of the web or sheet provided by the device. 
Various anomalies at the edge of the sheet or web, such as paper fibers, 
ragged cut edges, edge tears and the like will not hamper the operation of 
the device. Even if the anomaly is greater in width that the width of the 
photoelectric receiver, it will not create an inaccuracy, so long as the 
width of the anomaly is not greater that the width of the diaphragm 
opening. While these anomalies will reduce the light intensity, they will 
not adversely affect the readings of the photoelectric receiver, as was 
the case with the prior art devices. The electronic evaluation device can 
still determine the exact position of the edge of the web or sheet in 
spite of the difference in light intensity resulting from the existence of 
web or sheet edge anomalies. 
Another particular advantage of the present invention is that it is 
possible, in accordance with the method of the invention, to evaluate not 
only an area of the edge corresponding to the width of the photoelectric 
receiver but to also evaluate an area of the edge of the web considerably 
greater that the width of the photoelectric receiver. The area of the web 
edge evaluated may be greater that the width of the photoelectric receiver 
by a factor of between, for example 50 and 1000. The measuring accuracy of 
the present invention is considerably increased by this. The various 
components used in the present invention are generally standard or 
conventional parts which are not particularly expensive. 
The method and apparatus for measuring a position of webs or sheets in 
accordance with the present invention overcomes the limitations of the 
prior art. It is substantial advance in the art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring initially to FIG. 1 and taken in conjunction with FIGS. 3 and 4, 
there may be seen a first preferred embodiment of a device for measuring 
the position of a web or sheet, generally at 1, in accordance with the 
present invention. Web or sheet 1 is provided with an edge 3 which extends 
as a generally straight line at least with in the limits of the measuring 
range of the subject invention. A photoelectric receiver, generally at 2, 
is positioned beneath the web or sheet 1, as seen in FIGS. 1 and 3-6, and 
is used to determine the location or position of the edge 3 of the sheet 
or web 1. The web or sheet 1 is essentially light-absorbent. In the 
remainder of the description of the preferred embodiment, web or sheet 1 
will be referred to as web 1. Web or sheet 1 is preferably a paper web or 
a paper sheet that is being used in a rotary printing press. However, it 
is to be understood that web 1 is not to be so limited and could be any 
other material in the shape of a web, sheet, or panel, such as sheet metal 
or foil. The designation of this web or sheet as web 1 hereinafter will be 
primarily for the sake of simplicity. 
As may be seen in FIG. 1, web 1 has an edge 3 that is not perfectly 
straight but rather has one or more edge anomalies 4. These edge anomalies 
4 can be in the form of small edge rips or tears or can be fibers or the 
like which extend beyond the edge 3 of the web 1. It will be understood 
that the edge anomaly 4 depicted in FIG. 1 is representative of a number 
of possible anomalies which may exist on the edge 3 of the web 1. 
The web 1, whose position is being delimited by the edge 3 having anomalies 
4, is placed into a bundle 6 of a light beams formed by an optical system 
7. This bundle 6 of light beams emanates form a light source 8 and impacts 
on the photoelectric receiver 2. The edge 3, or a shadow of the edge 3 of 
the web 1, is pictured on the photoelectric receiver 2 in an imaging plane 
11 by utilization of an optical component 9 or of a system of optical 
components in such a way that the image is clear in a transverse imaging 
scale in a transverse axis 12 extending perpendicularly to the edge 3 of 
the web 1, and is blurred and diffused in a longitudinal imaging scale in 
a longitudinal axis 13 extending parallel with the edge 3 of the web 1. 
The transverse imaging scale is not necessarily equal to the longitudinal 
image scale of the optical system 7. In a particularly advantageous 
manner, the transverse imaging scale can be one to one, and because in 
this, the conversion of measurements corresponding to the transverse 
imaging scale can be omitted. The edge 3 of the web 1 is evaluated over a 
selectable measuring width b3 which may be, for example, b3=0.5 mm to 10 
mm, and which can be defined by means of a diaphragm 19. This measuring 
width b3 of the edge 3 of the web 1 is imaged blurred or distorted in the 
imaging plane 11 in the direction of the longitudinal axis 13 by means of 
the optical device. 
A CCD (charge-coupled device) line sensor 2, that is generally known, can 
be employed as a photoelectric receiver 2 and is provided with a plurality 
of photoelectric elements. This CCD line sensor 2 can consist of, for 
example, 1728 measuring elements that are arranged in a line. These 
measuring elements have a size of 10 .mu.m.times.13 .mu.m, for example, 
and a center distance between two measuring elements is 10 .mu.m, i.e. 
there are 100 measuring elements in a millimeter. This results in a 
measuring length 12 of 17.28 mm of the described CCD line sensor 2. The 
usable working range can, of course, also be less that the measuring range 
12. In the subject embodiment the working range corresponds to the 
measuring length 12. 
By means of an electronic evaluation device, not specifically shown, the 
CCD line sensor 2 provides an analog video signal 14, which has an 
amplitude path corresponding to the position of the edge 3 of the web 1. 
In this way, as may be seen in FIG. 2, an amplitude A3 of the area of a 
length la2 of the CCD line sensor 2 covered by the web 1 can be minimal, 
for example, while the uncovered area of a length lu2 of the CCD line 
sensor 2 can provide an amplitude A1 corresponding to the intensity of an 
illumination device 16. This illumination device 16 is generally part of 
the optical system 7, referred to previously, and may be seen most clearly 
in FIGS. 3 and 4. 
If the edge 3 of the web 1 now has one or several anomalies 4 in the area 
of the measuring width b3, these web edge anomalies 4 are also represented 
correspondingly blurred in the imaging plane 11 in the direction of the 
longitudinal axis 13, and thus are represented on the CCD line sensor 2. 
This has the result that, in the area of the anomalies 4, a beam path of 
the light beam bundle 6 is changed and, depending on the size of the 
anomaly 4, a corresponding change in the intensity of the illumination 
device 16 acting on the CCD line sensor 2 is generated. In this way, an 
amplitude A2 of the video signal 14 corresponding to the width of the 
anomaly 4 is created. The strength of this amplitude A2 lies between the 
amplitude A3 in the covered state of the CCD line sensor 2 and the 
amplitude A1 in the completely uncovered state of the CCD line sensor 2, 
as long as the anomaly 4 does not occupy the entire measuring width b3. It 
is now possible, by means of a suitable known electronic device, to 
determine the position of the edge 3 of the web 1 from this stepped video 
signal 14. While the amplitude of the video signal A2 will be less than 
the amplitude of the video signal A1, it will still be greater that the 
amplitude A3. Only if the width of the anomaly 4 were greater than the 
measuring width b3 would the amplitude A2 approach, or be reduced to the 
level of the amplitude A3. So long as video signal amplitude A2 remains 
greater than amplitude A3, the position of the edge 3 of the web 1 can be 
accurately determined even if the edge 3 is rendered less than straight by 
the occurrence of the edge anomalies 4. 
The foregoing discussion provides an overview of the apparatus for 
accomplishing the method of determining the position of web 1 in 
accordance with the present invention. The following discussion will now 
deal in greater detail with the structure of the apparatus in accordance 
with the subject invention. 
A first preferred embodiment of the apparatus for executing the method in 
accordance with the invention, as may by seen most clearly in FIGS. 3 and 
4, essentially consists, for example, of an illumination device 16, and 
object holder 17, and IR filter 18, a diaphragm 19, an imaging lens 21 and 
a photoelectric receiver, for example a CCD line sensor 2. These elements 
16, 17, 18, 19, 21 and 2 are all arranged along an optical axis 20 which 
is depicted as being generally vertical but need not be. The illumination 
device 16 essentially consists of an infrared (IR) light source 23 and a 
condenser 24. The IR light source 23 radiates diffuse light rays 26. A 
main plane 25 of the condenser 24 is located at a distance a23 which is 
2.times.f24 with respect to the IR light source, 23, which corresponds to 
twice the focal length f24, for example f24=20 mm of the condenser 24. In 
the depicted first preferred embodiment a non-spherical lens is used as 
the condenser 24. The condenser 24 can also consist of several lenses, for 
example a combination of a concave-convex lens and one or several 
non-spherical lenses. 
The condenser 24 focuses the light rays 26 at a distance a19=2.times.f24, 
at which distance the diaphragm 19 is situated. The imaging lens 21 is 
located after the diaphragm 19 and has a first focal length fq21, for 
example fq21=10 mm, in a transverse axis extending perpendicularly in 
respect to the edge 3 of the web 1, and a second focal length fl21 in a 
longitudinal axis 13 extending parallel with the edge 3 of the web 1. The 
object holder 17, which supports the web 1, is disposed between the 
condenser 24 and the imaging lens 21 in such a way that the edge 3 of the 
web 1 to be measured lies at an object width g30 with respect to the main 
plane 30 of the imaging lens 21. The imaging plane 11 of the CCD line 
sensor 2 is disposed at an image width b30 with respect to the main plane 
30 of the imaging lens 21. The imaging plane 11 of the CCD line sensor 2 
is disposed at an image width b30 with respect to the main plane 30 of the 
imaging lens 21. To obtain a clear image, the reciprocal value of the 
focal length fq21 must result in the sum of the reciprocal values of the 
object width g30 and the image width b30, i.e. 1/fq21=1/g30+1/b30. 
A plane-parallel glass plate 17, as seen in FIGS. 3 and 4, is provided as 
the object holder 17. The diaphragm 19 has a diaphragm opening 27 of a 
width of b27 and a length of l27. This diaphragm 19, and the filter 18, 
for example an IR filter, are disposed in front of or before in the 
direction of travel of the light beam, the imaging lens 21. The measuring 
width b3 at the edge 3 of the web 1 is determined by the projected length 
l17 of the diaphragm opening 27 of the diaphragm 19 with respect to the 
CCD line sensor 2. In the first preferred embodiment, the imaging lens 21 
is embodied in the form of a cylindrical lens 21 which is arranged in 
light rays 28 at the object width g30=2.times.fq21 in respect to the glass 
plate 17 in such a way that its plane side 29 lies parallel with the glass 
plate 17 and its longitudinal axis 31 is parallel with the edge 3 of the 
web 1 to be measured. In place of an imaging lens 21 it is also possible 
to employ a lens system consisting of several lenses. 
The CCD line sensor 2 is located in the imaging plane 11 perpendicularly to 
the edge 3 of the web 1 to be measured and thus generally parallel to the 
plane of web 1, and is after, in the direction of travel of the light 
beam, or behind the cylindrical lens 21 at the image width 
b30=2.times.fq21, i.e. again at twice the focal length fq21 of the 
cylindrical lens 21. In this way there is a transverse imaging scale of 
one to one in this first preferred embodiment. 
The edge 3 of the web 1 to be measured is placed parallel with the 
longitudinal axis 31 of the cylindrical lens 21 and is moved into the 
light rays 6 on the plane-parallel glass plate 17, so that it is located 
at the object width g30. A portion of the light rays 6 striking the edge 3 
of web 1 are deflected by web edge 3 to form light rays 28 and are passed 
on in a diffused manner. The light rays 28 emanating form the edge 3 to be 
measured impinge on the diaphragm opening 27. Only the portion of the 
light rays 28 impinging on the diaphragm opening 27 passes through the 
diaphragm 19 and strikes the cylindrical lens 21. The width b27, for 
example b27=0.1 mm to 2 mm, and the length l27, for example l27=0.2 mm to 
10 mm, of the diaphragm opening 27 are respectively less than a width b21, 
b21=9 mm, and a length l21, for example l21=18 mm, of the cylindrical lens 
21. The light rays 28 and thus the edge 3 of the web 1 to be measured are 
imaged clearly, but mirror-reversed, in the direction of the transverse 
axis 12 on the CCD line sensor 2 through the cylindrical lens 21. The 
diffuse light rays 28 impinging on the cylindrical lens 21 are deflected 
in the direction of the longitudinal axes 13 or 31 in such a way, that a 
diffused, blurred image of the edge 3 is generated on the CCD line sensor 
2. If the edge 3 of the web 1 to be measured has anomalies 4 located in 
the range of the CCD line sensor 2, these anomalies 4 are imaged exactly 
and mirror-reversed in the direction of the transverse axis 12 of the 
cylindrical lens 21, but diffused along the longitudinal axes 13 or 31 of 
the cylindrical axis 21. Thus only a portion of the light rays imaging the 
anomalies 4 strikes the CCD line sensor 2 along the longitudinal axis 13. 
Simultaneously a portion of the "free " light rays not affected by the 
anomalies 4 also strikes the CCD line sensor 2. An area of reduced 
intensity is thereby created on the CCD line sensor because of the 
anomalies 4, and this area of reduced intensity causes a previously 
described, stepped video signal, which is evaluated by an electronic 
device. 
A second preferred embodiment of an apparatus for executing the method of 
the present invention, as may be seen in FIGS. 5 and 6, essentially again 
comprises the illumination device 16, the object holder 17, the filter 18, 
a diaphragm 32, an imaging lens 33 and the photoelectric receiver, for 
example a CCD line sensor 2. These elements 16, 17, 18, 32, 33 and 2 are 
arranged along an optical axis 20, corresponding to the first device. 
The diaphragm 32 is disposed at a distance a32=2.times.f24 with respect to 
the main plane 25 of the condenser 24. The diaphragm 32 has a slit-like 
diaphragm opening 34 of a length l34, for example l34=0.2 mm to 10 mm, and 
a width b34, for example b34=0.1 mm to 2 mm. The length l34 extends 
parallel with edge 3 of the web 1 to be measured. 
The imaging lens 33 is a spherical lens 33. Spherical lenses 33 have 
so-called aberrations which has the result that a focal length f33, for 
example f33=10 mm, is exact only along the optical axis 20. Outside of 
this range, a focal length f33' diverges from this exact value and the 
focal length f33' is concentrically reduced toward the outside, starting 
at the optical axis 20. It is also possible to utilize a lens system 
consisting of several lenses in place of an imaging lens 33. 
The object holder 17 in this second preferred embodiment is disposed 
between the condenser 24 and the spherical lens 33 in such a way that the 
edge 3 of the web 1 to be measured is placed at an object width g37 with 
respect to a main plane 37 of the spherical lens 33. The image plane 11 of 
the CCD line sensor 2 is disposed at a distance with respect to the main 
plane 37 of the spherical lens 33 corresponding to an image width b37. To 
obtain a clear image, the reciprocal value of the focal length f33 must 
result in the sum of the reciprocal values of the object width g37 and the 
image width b37, i.e. 1/f33=1/g37+1/b37. The spherical lens 33 is disposed 
at the object width g37, which, for example, corresponds to twice the 
focal length f33, from the object holder 17. The CCD line sensor 2 is 
located in the image plane 11 behind the spherical lens 33 at the image 
width b37, for example b37=2.times.f33, wherein a transverse image scale 
of one to one again results in this second preferred embodiment of the 
method and apparatus for measuring a position of webs or sheets in 
accordance with the present invention. 
The edge 3 of the web 1 to be measured, or whose position is to be 
determined, in placed into the light rays 6 of the illumination device 16 
by being supported on the object holder 17. A portion of the light beam 6 
striking the edge 3 of web 1 is deflected as light rays 36 and these light 
rays 36 are passed on in a diffused manner. The light rays 36 emanating at 
the edge 3 to be measured pass through the diaphragm opening 34. The 
portion of the light rays 36 penetrating the diaphragm opening 34 strikes 
the spherical lens 33. The light rays 36 in the immediate vicinity of the 
optical axis 20 are clearly represented by the spherical lens 33 on the 
CCD line sensor 2 in a mirror-reversed manner. In the direction of the 
transverse axis 12, the light rays 36 are restricted to a narrow area 
around the optical axis 20 by the slit-shaped diaphragm 32, while parallel 
with the edge 3, i.e. in the direction of the longitudinal axis 13, the 
light rays also penetrate the spherical lens 33 in the areas remote from 
the optical axis 20. The focal length f33' is shortened in these area, so 
that a diffused, blurred image of the edge 3 is created in the direction 
of the longitudinal axis 13. 
If the edge 3 of the web 1 to be measured has anomalies 4 located in the 
range of the CCD line sensor 2, these anomalies 4 are imaged exactly and 
mirror-reversed perpendicularly with respect to the edge 3, but are imaged 
diffused and blurred parallel to the edge 3. Thus a portion of the light 
rays imaging the anomalies 4 strikes the CCD line sensor 2 parallel with 
the edge 3, while simultaneously a portion of the "free" light rays not 
affected by the anomalies also strikes the CCD line sensor 2. Because of 
this engagement of the light rays 36 with the CCD sensor 2, an area of 
reduced intensity is created on the CCD line sensor 2 because of the 
anomalies 4. This is converted into the stepped video signal that is 
depicted in FIG. 2 and which can then be evaluated by a suitable 
electronic device to provide an accurate measurement of the location of 
the edge 3 of the web 1, even if the web is not uniform or straight 
because of the existence of edge anomalies. 
While preferred embodiments of a method and apparatus for measuring a 
position of webs or sheets in accordance with the present invention have 
been set forth fully and completely hereinabove, it will be apparent to 
one of skill in the art that a number of changes in, for example, the type 
of printing press with which this apparatus is used, the means for 
transporting the webs or sheets, the width of the webs or sheets and the 
like could be made without departing from the true spirit and scope of the 
present invention which is accordingly to be limited only by the following 
claims.