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ABSTRACT
Paper breaks are an efficiency robbing reality on all types of paper machines and
coaters. Reducing breaks has become more and more important with the increasing speed and operating complexities of today's paper and board machines.
Fully digital break recording technology, using the latest CCD cameras and digital image processing, is now offering papermakers new opportunities to find
and solve the many reasons causing breaks. These systems continuously monitor, in real-time, all of the critical locations from the wet end to the dry end of the paper machine and coater. When a break occurs the
system downloads the event into a permanent storage, making it possible to fully analyze what took place just before and after the break. This allows the papermaker to take the necessary corrective steps to prevent
the break from occurring again.
Taking advantage of the latest technological advancements in digital image processing, these systems are now able to offer high image resolution, high
reliability with minimal moving parts, and are able to provide automatic image analysis and alarming for holes, edge faults and sheet breaks.
These systems have now been proven on all types of paper machines, from the wet end to the dry end, ranging from slower board machines to the worlds fastest
machines producing LWC, fine paper, newsprint, tissue etc.
This paper discusses the latest available techniques in camera break recording technology, their applications, and the results that have been achieved to
date
INTRODUCTION
Although, many common causes for breaks have been solved with improved paper machine technology, the increase in machine speeds and widths together with
more complicated processes, are still causing far too many breaks in press sections, size presses, coaters, and even at the dry end of the machine. Also events taking place during reel turn-ups and in the winder can
be common and difficult to troubleshoot.
Breaks are typically classified as coming from either known or unknown sources. Breaks coming from known sources can usually be eliminated, but the unknown
ones can cause significant losses in machine operating speeds and efficiencies. For example, a paper machine producing 400 tons/day, with two breaks per day, lasting on average twenty (20) minutes each, causes over
one (1) million dollars in efficiency losses per year.
During the late eighties, some mills began experimenting with video cameras together with VCR recorders, to better see the event and thus solve the reason
for it. These systems although a step in the right direction, were not able to withstand the paper machine environment, were difficult to operate, had insufficient image resolution, and most importantly were
unreliable.
In the beginning of the nineties major advancements were made in CCD (charge coupled device) camera technology together with faster shutter speeds. This
improved image quality together with higher resolution "Super" VHS format VCR's. The results of such an improved break recording system were reported by a Mid-Western paper mill (1), and demonstrated the potential these systems offered in solving the reason for unknown breaks.
Such an automated analog (VCR based) event capturing system was installed on the UPM-Kymmene, Kaukas mill's off-machine coater in 1993. It helped the
coater achieve a major speed increase as reported by the mill at the 1994 Tappi Coating Conference (2).
BREAK RECORDING TECHNOLOGY
The extensive R&D over the last five years into digital image handling and its associated software, has resulted in a high resolution and an easy-to-use
technology able to rapidly and reliably solve the reasons for breaks. These systems also allow users an opportunity to prevent breaks before they happen, with their ability to continuously monitor all critical
locations, allowing the papermaker to take corrective actions before a break occurs.
In general these systems today have the following capabilities:
- Designed specifically for paper machine operating conditions
- Very high image resolution, exceeding 300,000 Pixels per image
- 60 images per second at 60 Hz line frequency
- Water & heat resistant camera enclosures to allow all required locations to be monitored
- PC, Windows™ based user interface to allow fast and easy viewing of all events
- Software that automatically stores & tags all events, plus allows for other user customized features
- Large break library
- Easy upgradability for additional cameras
- Ability to download & upload data from a millwide system
Figure 1 shows the general layout of a digital event capturing system. With this type of technology systems all components have to be matched to each other
to ensure that no weak links limit the overall performance of the system. Generally cameras on machines wider than 4 meters (150") are mounted in pairs (front side, back side) and almost always in press sections.
Figure 1: Automated digital break recording systems are designed to maximize the visibility and results on all
types of paper machines and coaters to prevent and eliminate breaks. Cameras are typically mounted in pairs,
front & back side, and the system is software controlled though a PC operator interface. The interface cabinet
houses all of the computer and image processing and storage components, and is typically located in an electrical room.
System Components
Cameras
Cameras form a critical part of an event capturing system. If they are not sensitive enough, nor designed to
withstand the paper machine operating conditions and suffer from rapid fiber & dirt build-up, the system cannot
offer the visibility of the event to solve its cause. The system has to be designed specifically to overcome these problems.
CCD based video camera technology has dramatically improved over the last 10 years and now offers high
sensitivity (below 0.1 lux, using high quality lenses), with very fast shutter speeds of up to 1/10000 of a second. The
fast shutter ensures minimal sheet travel and this improves the image sharpness as shown in the below table.
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Machine Speed
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Distance the image (sheet) moves at different shutter speeds
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1/10,000 1/4000 1/2000
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m/min ft/min
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mm inches mm inches mm inches
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400 1300
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0.67 0.026 1.7 0.07 3.3 0.13
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600 1950
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1.00 0.040 2.5 0.1 5.0 0.2
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800 2625
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1.33 0.052 3.3 0.13 6.7 0.26
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1000 3300
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1.66 0.065 4.2 0.16 8.3 0.33
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1200 3950
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2.00 0.079 5.0 0.2 10.0 0.4
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1400 4600
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2.33 0.092 5.8 0.23 11.7 0.46
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1600 5250
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2.66 0.105 6.7 0.26 13.3 0.52
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1800 5900
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3.00 0.118 7.5 0.3 15.0 0.6
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The image frequency of cameras is a function of the line frequency, which in North America is 60Hz, and with non
-interlacing (separates the odd and even fields in the image) this allows 60 images per second to be viewed, instead
of the NTSC broadcast standard 30 images/second. As the table below shows, the image frequency defines the distance the sheet travels during 1/60th of a second. For example at 1400 m/min (4600 ft/min) the sheet travels 38 cm
(15") between each image. The cameras therefore need to be properly located, allowing at least this much sheet in the machine direction to be visible.
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Machine Speed
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Distance sheet travels between two half images @ 60 Hz or 16.66 ms
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m/min ft/min
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centimeters inches
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400 1300
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11 4.3
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600 1950
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16 6.3
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800 2625
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22 8.7
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1000 3300
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27 10.6
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1200 3950
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33 13.0
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1400 4600
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38 15.0
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1600 5250
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44 17.3
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1800 5900
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50 19.7
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Figure 2 shows the camera capabilities available today. Special enclosures have been developed to enable the
cameras to withstand continuous operating temperatures of over 110°C (230°F). Various lens-cleaning techniques are used to ensure visibility is maintained.
Figure 2: The cameras form a critical part of an event monitoring system. They need to incorporate high
sensitivity, fast shutter speeds, zoom lenses together with waterproof & high temperature rated enclosures that
have effective lens cleaning capabilities. Also important is sufficient & right type of lighting, and a complete selection of mounting brackets.
Having the correct lighting is also very important. There must be enough lighting, and the right type, to ensure
maximum shutter speeds can be obtained and that no so called fade-in / fade-out problems occur as a result of the
light line frequency interfering with the camera image frequency. Also, a large selection of mounting brackets are
essential to allow for the best possible web viewing locations to be utilized and to ensure the cameras are not in the way of any routine machine maintenance.
Event Capturing
How and what type of methods are used for recording the events is just as critical as the cameras. The main
objective is to be able to record at the highest possible resolution.
Digitally storing the images has become desirable, but up until now all digital methods have had to rely on various
compression techniques to be able to store a sufficient amount of pictures. The image compression has resulted in a
major loss of image quality, and diminished the potential of the system to find the reason for the break. Also
potential reliability problems with hard drives and the large space requirements (several PCs required), have further complicated these systems.
Techniques that are now commonly used to maximize digital image quality are lossless "zip" type compression
(groups gray scale pixels minimizing their size), as well as advanced Motion JPEG type compression that is able to
compress the file size without any noticeable loss in image quality (does the compression in areas that show the same colors or tones).
Techniques are now available that keep the camera image history both in RAM and hard drive memory. This allows
both instantaneous access to the event following a break (no download time) as well as partial RAM based downloads when the system is, for example, triggered by a hole detector.
Operator interface and software
A critical factor to any break analysis system, is its user interface. It has to be simple to use, trouble free, and allow for complete viewing and break storage.
Figure 3: PC Windows® NT based operator interfaces offer a simple, fast and complete access to all events. It
allows operators to view any of the camera images in either quad or single image formats, and with the customized paper machine view rapidly know where each camera is located.
Figure 3 & 4 show examples of system page layout's that allow the operator to rapidly view all of the cameras in real
-time and to identify how the break took place. It also allows the operator to decide how many seconds before and
after a break is stored in the break bank, and with its "VCR type" controls, makes viewing the breaks simple.
Figure 4: Shows the break analysis page that rapidly advises the operator where the break took place using gray
-scale-image analysis. This identifies which camera saw a sheet change such as a hole or edge fault go by. Camera
synchronization is used to view the exact same spot in the sheet as it traveled past each of the earlier cameras,
allowing the operator to view the sheet for holes or other factors that caused the break further down the machine.
A further available feature is to analyze the changes that take place from one image to the next and in this way
rapidly locate a hole or other fault that has passed by the cameras.
Also available today is the ability of the system to scan all of the camera locations to show the exact same location
of the sheet where it broke further down the machine. This allows the operator to see, for example, what the sheet
looked like in the press section for holes, etc. that resulted in the break in the dry end (see figure 4).
Further analysis tools now available are multi-level, image enhanced zoom (see Figure 5) and region-of-interest that
allows the operator to analyze any specific camera area for changes both in real-time and after the event.
The software makes it easy to store the information following each break. Important for the operator is a rapid event
download so that the operator can view the break immediately after it occurred with all the cameras active, and at the
same time, store in the software and note the reason for it. It allows the user to rapidly analyze the most recent event and, for example, compare it with a previous one, which is similar, by just clicking on it.
Figure 5: Shows how any specific area on the image can be zoomed into. Using image enhancement routines, the
pixel resolution is optimized during the zooming process to enhance the clarity of the image.
CAMERA LOCATIONS
Cameras that have been designed for high temperature applications, together with sufficient cleaning technology
and lights, can be located in all sections of a paper machine and coater (see Figure 6 for details).
The trim squirts application has been found very useful to ensure that build-up, wear and plugging is not effecting
their operation. In the press section the most common locations are the pick-up, center roll and last press. All open
draws should be monitored. It has been found that viewing the sheet in the first dryer section is also important
particularly useful with unfelted uno-runs. Coaters and size presses are always camera equipped due to their
typically high break frequency. Calenders and the reel, for turn-ups, can also be problem areas. Winders can be
equipped, as well as other off machine operations with the most important one being off-machine coaters.
Figure 6: The cameras with waterproof and high temperature rating, can be located in all break sensitive
locations. The most common ones are the trim squirts, press section, first dryer section, coater, size press, calender and reel.
RESULTS
To date event monitoring systems have provided papermakers an effective new tool to reduce breaks. With a
sufficient number of cameras correctly placed, a nearly complete picture of what happened can be achieved.
The reduction in breaks, with previously unknown causes, has ranged from 20% to over 80%. The amount of
reduction has been found to be a function of several variables such as: type of break, similarity of breaks, number of
cameras, camera locations, and user capabilities. Going over these variables, it is clear that if the reason for the break
is very unusual, finding it can be difficult thus reducing the result. If on the other hand most of the breaks are a result of the same cause, this commonly results in a large reduction in breaks.
The number of cameras and their locations is fundamental to ensure that no break occurs in a location that has not
been equipped with a camera. The cameras when equipped with a quick disconnect, can be rapidly moved from one location to another, ensuring that the best locations are utilized based on the production conditions.
Figure 7: Shows a typical 500 t/d newsprint machine payback based on a one break per day reduction. Event
monitoring systems have been found to result in a 20% to over 80% reduction in breaks, with this result being a
function of many variables such as: type of break, similarity of breaks, number of cameras, camera locations, and
user capabilities. Obviously the higher the breaks to start off with, the larger the break reduction opportunity and payback.
Figure 7 shows the potential return on investment of less than three (3) months, based on a 35% reduction in
unknown breaks on a 500 t/d machine. The typical lost production time is 15 minutes, but in some machines it can be significantly longer, particularly to achieve the required sheet quality.
A somewhat secondary benefit reported by the users, has been the ability of the system to allow the operators to
conclude whether or not the break is speed related. In the past, without finding the reason for the break, the machine
was often slowed down in hopes this would eliminate the problem. However, with the ability to view the breaks is
slow motion and to better understand how it was created, it can be concluded by production that machine speed is not the cause of the break. If this is known, production rates can be maintained or even increased.
A further result has been the ability of the system to allow preventive measures to be taken prior to the break
occurring. With good picture quality and a sufficient number of cameras, problems occurring from trim squirts, felts,
sheet flutter, sheet tension, vibration, coating, condensation and in general, any type of visual problem can be seen and corrected before a break, or other operational problem takes place.
CONCLUSIONS
Minimizing all sources of paper machine breaks has a major effect on increasing paper machine and coater operating
efficiencies and production rates. Camera, recording and software technology has now been developed to a point where effective and reliable event capturing is possible.
Automated and digital technology has been found to reduce breaks by 20% to over 80%.
In summary, automated break recording systems are today able to:
- Automatically & in real-time, monitor & record all critical locations on the paper machine, coater, winder, etc.
- Using easy to operate PC Windows® based software, allows the operators to fully view & manipulate all of the image information.
- Allow environmentally enclosed, high resolution cameras to be placed in all of the critical locations, such as
the wire & press section, dryer hood, coater, size press, calender, winder, etc.
- Provide a permanent record of each event that can be easily viewed, printed, tagged and compared to other breaks.
- Allow operators to be given early warning of a change, such as trim build-up, sheet flutter, release angle.
- Interfaced to millwide systems for complete reporting.
With a typical payback of less than six (6) months, it is expected that in the next five years the use of this technology
will grow rapidly to ensure maximum paper machine efficiency, production and paper quality is maintained.
REFERENCES
1. Dewitte, Jesse A, et al, "Video surveillance troubleshooting at LSPI ", Tappi Journal, Vol 78, No. 8, August 1995.
2. KORPELA, Markku S., "Mill Experiences at Kymmene-Kaukas", TAPPI 1994 Coating Conference, San Diego, CA., Proceedings page 310.
3. RUDT, Robert J., et al, "System for Monitoring a Continuous Manufacturing Process", United States Patent, No.
5,717,456 (issued Feb. 10,'98) & No. 5,821,990 (issued Oct. 13,'98), assignee Champion International Corporation, Stanford, Connecticut.
January, 2002
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