Vision ensures shampoo bottles are well groomed

High demands for reliable and flexible quality control in the packaging industry are met using powerful, multicamera vision systems.

High demands for reliable and flexible quality control in the packaging industry are met using powerful, multicamera vision systems.

The visual appeal of a mass-produced consumer item such as shampoo is critical.

The design and look of the bottle is an important factor in choosing to buy the product and for that reason the labels must be error-free and accurately placed on the bottle.

Wella's fastest shampoo production lines run at up to 70,000 bottles per work-shift and a 100% error-free process is required.

These are difficult quality control requirements to meet and they can only be achieved using a high-performance vision system.

In the past the Wella production site in Huenfeld carried out random inspections of their production lines.

The quality requirements increased with the introduction of ISO9002 certification, making it absolutely essential that there was 100% quality control of goods leaving the factory.

Prior to installing the Cognex Checkpoint system, the existing method of quality control gave unsatisfactory results - the print and position of the label being simply compared with a reference image.

On the production line, the position of the bottle changes and it was not possible to accurately compare the bottles and so rejects could get passed.

The first step is therefore to identify the exact position of the bottle; once this is done the inspected bottle can then be compared with the reference image.

For this inspection strategy to succeed the vision system must be able to operate with differing bottles and labels and at high production speeds; line changes have to be fast and the system must be able to easily adapt to different bottle types in the future.

Having sent out its requirement specifications, Wella received proposals from a number of different industrial machine vision suppliers.

Its own research showed that Cognex had a particularly good reputation for stability, accuracy and reliability.

The project team at Wella discovered that Cognex had extensive hardware and software knowhow and internationally have successfully installed over 150,000 vision systems.

The company's machine vision systems also offered an extensive library of proven vision software tools.

Following a presentation at the Cognex Germany office in Karlsruhe, Wella was satisfied that Cognex could meet their requirements.

At the beginning of 1999, the first trial was started using a Checkpoint vision system.

Using a robust and precisely calculated algorithm, the results quickly showed that the project was feasible.

This positive outcome and the ease of use of the system lead the production managers to mutually agree to introduce the Checkpoint vision system.

The system provided various interfaces ready for integration with other control units as well as for collection of statistical data, simplifying the process of system integration dramatically.

With an overall ease of use and application development vision tools the Checkpoint system has proven to be easily operated.

The machine operators were able to adapt the system to changing requirements.

The Checkpoint vision system has been integrated into production since the beginning of November 1999.

Bottles and labels, differing in colour and shape, are being inspected for seven characteristics and at speeds of up to 3 items per second.

The bottles running on a conveyor are inspected on the front, back and from above in the packing station.

The complete inspection process is carried out with three CCD cameras and takes less than 200ms.

This is where the highly effective PatMax vision software tools comes into effect.

The revolutionary patented software from Cognex differentiates itself quite clearly from other processes, which use binary and grey-scale correlation for image analysis.

The PatMax software instead converts the object to a geometric representation.

By doing this, it is able to locate an object regardless of its position, orientation or changes in its dimensions.

By simultaneously inspecting the outline and pattern of the object, lighting and contrast variations are eliminated.

By comparing the object with a reference image, a defect classifier enables robust object detection even when images show severe non-linear distortions.

It is therefore possible to accurately check the colour and shape of "fancy" lettering for errors.

The edge detection tool makes it possible to accurately locate bottles on a running conveyor - including bottles with an oval shape.

A slight rotation of the bottle is not a problem, as even rotations of less than 1 degree about the main axis are detected.

Similarly, the position of the label on the bottle can be accurately located up to a tenth of a millimetre.

At the first station, the Checkpoint vision system inspects the label on both sides evaluating two images from two cameras, one mounted in front of the bottle looking at the front label and one in the back looking at the back label.

At the same time the bottle cap is inspected for proper fit.

Additional inspection tasks like label inspection for wrinkles will be implemented in the future.

At the second station, three CCD cameras using the same vision system inspect the packaging of bottles in 6 or 12-packs.

In the final stages of quality control a statistical evaluation is taken Talking about his experiences, Frank Groeger, head of the Centre for Engineering, Development and Process Technology at Wella, says: "Integrating the vision system has been an extensive and valuable experience; we now plan to install additional systems in this plant as well as in others.

In a sense we have become our own system integrators as the vision application knowledge is all held within the organisation.

With its robust and precise algorithms, Checkpoint has shown that it is easy to use.

Its greatest advantage however is its flexibility and accuracy".

As a result, Wella have already installed a second vision system and plans to integrate up to six more in the near future.

Since the installation Wella now has 100% quality control and its certification can be extended further.

Reasons for complaints in the past have been eliminated.

Defective labels, which had previously not been detected in random quality checks, no longer appear.

Early detection of faulty labels has enabled Wella to take the necessary steps to rectify the problem quickly.

Accidentally using the wrong roll of labels is no longer a problem as the error is quickly detected.

As well as the significant increase in quality there have been lots of additional advantages, which were not expected at the outset.

Knowledge about the production process was built up, so that machinery could be pushed to the very limits without reducing production effectiveness.

This leads to a more robust production process and to a better use of machines.

Last but not least, the experiences from this line can be transferred to other production lines.

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