Mitsubishi Heavy Industries Technical Review Vol. 58 No. 1 (March 2021)
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Development of the World’s First Defective Flute Image
Inspection System for Corrugated Cardboard

SHUICHI TAKEMOTO*1HIDEKI MIZUTANI*2

MASAHIRO YAMADA*3

TAKASHI TOYOHARA*3

Mitsubishi Heavy Industries Machinery Systems, Ltd. (MHI-MS) has successfully developedand commercialized a new image inspection system for defective flutes in corrugated cardboard,utilizing image processing technologies for the first time in the world. We have become able todetect defective flute shaping stably and accurately by taking advantage of image processingtechnologies to meet the needs of customers who want to prevent defective flute cardboard during
production. The introduction of this inspection system reduces jamming of corrugated cardboards
with insufficient strength due to defective flute. Furthermore, there is no more need for recalls orproduction do-overs, which used to be caused by the mixing of defective corrugated cardboards
into later processes, which has significantly improved the corrugated cardboards productivity ofcorrugators. Currently, this new inspection system has received positive reviews from manycustomers as the world’s first breakthrough in the corrugated cardboard industry and has alreadybeen introduced and is operating smoothly in 9 customer plants Japan and overseas.

|1. Introduction
In the corrugated cardboard industry, there has been an increase in the number of orders for
multiple different types in small batches with quick delivery times. Meanwhile, with respect tocorrugators which produce corrugated cardboard, when corrugated cardboards with insufficientstrength are manufactured due to defective shaping of the wavy flutes, which is called thecorrugating medium, the corrugated cardboard could become bent on the stacker’s conveyer belt in
the final corrugator process. Subsequent sheets can get stuck and pile up, causing a paper jam
which could result in a machine shutdown requiring many hours for recovery. Furthermore, themixing of defective flute cardboard with insufficient strength in later production processes could
cause recalls and production do-overs, which significantly lowers the corrugator’s cardboard
productivity. Under such circumstances, there is significant customer demand to prevent the mixingof defective flute cardboard in the production line. To meet this need, MHI-MS has successfully
developed and commercialized the world’s first defective flute image inspection system that detects
defective flute shaping stably and accurately, utilizing image processing technologies.

|2. Defective flute shaping in the corrugator
In a corrugator, corrugated cardboard is manufactured in the corrugated cardboard
production process as shown in Figure 1, where the flutes in the corrugating medium are first
formed by the corrugating rolls in the single facer. Next, the flutes in the corrugating medium andthe liner are glued together by the pressing belt, which is how single-faced corrugated cardboards
are manufactured. In this process of manufacturing single-faced corrugated cardboards in the single
facer, defective flute could occur due to various different factors such as insufficient pressure by*1

Team Manager, Engineering Department, Printing & Packaging Machinery Headquarters, Mitsubishi Heavy Industries*2

Principal Engineer, Engineering Department, Printing & Packaging Machinery Headquarters, Mitsubishi Heavy Industries*3

Chief Staff Manager, CIS Department, ICT Solution Headquarters, Mitsubishi Heavy Industries, Ltd.

Machinery Systems, Ltd.
Machinery Systems, Ltd.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 1 (March 2021)2

the corrugating rolls at the time of flute shaping and gluing, inadequate heat or glue, etc. Figure 2
shows one example of defective flute shaping where the flutes in the corrugating medium arecrushed due to failure in gluing, causing irregularities in the flute height.

Figure 1

Corrugated cardboard production process in a corrugator

Figure 2

Example of defective flute shaping|3. Overview of defective flute image inspection system
3.1

Installation location

In order to carry out inspection by using a camera to capture images of the side of thesingle-faced corrugated cardboard that faces the corrugating medium after the corrugated cardboard
is completed, as shown in the installation location in Figure 3, a camera and light are installed on
the bridge just before the glue machine which comes after the single facers. When a defective fluteis detected, it will be automatically removed by the defect remover located before the stacker in thelater process by tracking the defect and its travel route. Furthermore, Figure 4 is an installation
drawing for the camera and light, depicting an example of a typical corrugator line which canmanufacture up to double wall. Figure 5 is a photograph of the actual machine.

Figure 3

Installation location

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 1 (March 2021)
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Figure 4

Machine installation

Figure 5

Photograph of actual machine

3.2

System configuration

As shown in the configuration diagram in Figure 6, this inspection system consists ofvarious components in addition to the camera and light, such as the control panel in which theimage processing device is stored and a defect-image display screen for the operator’s use installedin the stacker area. When any defect is detected, an alarm lamp informs operators in different
locations by activating an alarm light and buzzer, and the image captured of the defect appears
instantly on the defect-image display screen situated in the stacker area. Furthermore, when adefect is detected, the detection signal is sent instantly to the corrugator production management
system, which tracks the position of the defective flute and removes it as soon as it reaches to thedefect remover.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 1 (March 2021)
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System configuration|4. Features of defective flute image inspection system
4.1

Stable and highly-accurate inspection with image processing

As shown in the measurement principle chart in Figure 7, the basic principle of the system isto detect irregularities in the flute height due to defective flute shaping based on variations in thewidth (length) of the bright section and the dark section in the image data of the light-dark portion
generated by illuminating a single-faced corrugated cardboard with linear lighting at an angle. The
borders between the bright and dark bands in individual flutes are identified throughblack-and-white edge extraction by image processing and thus the distance between the edges ismeasured. Consequently, if the measurements are outside of the acceptable range with reference tothe nominal value, the flute section is determined as defective. Meanwhile, with regard to thenominal value used for determining defects, the system stores basic parameters and the acceptable
range for each thickness type of corrugated cardboard with a different flute height (A, B, C and E).
However, even when the thickness type is the same, there are still some variations in themeasurements depending on the type of paper. Therefore, the acceptable range needs to be setwide, which has been an issue in high-accuracy inspection. As shown in Figure 8, we conductedauto-tuning where the maximum and minimum values in the acceptable range corresponding to thenominal value are automatically adjusted to the optimal level depending on the extent of variationsin the flute measurements at the time of changing paper type. The system learns through thisauto-tuning and has become capable of highly-accurate and stable inspection.

Mitsubishi Heavy Industries Technical Review Vol. 58 No. 1 (March 2021)
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Figure 7

Measurement principle

Figure 8 Concept of nominal value auto-tuning

4.2

Visualization of flute defects

Since customers have a need to clarify the cause of defects through visualizing the conditionsof flute defects to make use of in the maintenance of the machine and in taking preventive steps, wedeveloped an additional feature to display images of defects on a screen, taking advantage of thefact that this inspection system utilizes image processing. Firstly, as shown in Figure 9, when
detecting a flute defect, the operator is able to identify where and what kind of defect has occurred
instantly by displaying the image of the defective flute on the defect-image display screen in realtime and highlighting the location where the flute defect is detected. Furthermore, as shown in
Figure 10, images of other flute defects that have occurred in the past are also stored in the history
log. Images of a defect on a certain date could be retrieved from the defect history log and shown ata later date. Therefore, even when a defect couldn’t be examined immediately during operation, it
is still possible to review the type of defect and its location later and utilize the information forrecurrence prevention by reflecting the information in machine maintenance.

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Figure 9Real-time defect-image display

Figure 10 Past defect-images log|5. Example of actual flute defects
Figure 11 shows some typical defects actually detected at customer plants. Images of defects
detected are on the left side, while those on the right side are the defective flutes after removal.
Defective flutes caused by faulty machine settings in the individual conditions were detected.

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Figure 11

Sample of Aactual defects detected|6. Conclusion
This defective flute image inspection system is capable of detecting defective flute shaping
stably with high accuracy by utilizing image processing technologies. However, since making our
first delivery of this system, we have worked on not only boosting its performance, but also various
other improvements, such as adding new features and enhancing operability. These efforts havebeen based on a significant amount of user feedback and input from our customers, which has led
to the system’s high-quality finished product.
The customers who installed this inspection system have highly evaluated it, as paper
jamming caused by corrugated cardboards with insufficient strength due to defective flute has been
reduced and there is no more need for recalls or production do-overs, which used to be caused by
the mixing of defective corrugated cardboards into later processes, and this has significantly
improved the sheet productivity of corrugators. We have also received many enquiries about
potential orders for this machine as the industry’s first ground-breaking inspection system. It has
already been installed and is operating smoothly in 9 customer plants Japan and overseas. In thefuture, we will continue to develop new products suiting the needs of customers in corrugatedMitsubishi Heavy Industries Technical Review Vol. 58 No. 1 (March 2021)
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cardboard production.

References(1)

Introduction of Mitsubishi Heavy Industries Camera-Type Defective Flute Detector for Single Faced
Cardboard, Japan Corrugated Case Association, Corrugated Cardboard Seminar 2017, Proceedings p.45～47