Painted in two seconds

SINTEF has calculated the spray trajectory and produced the robot control system for spray painting the figures. Photo: Rune Petter Ness

When 23 million miniature figures have to be decorated to an accuracy of 0.1 mm, nimble-fingered Chinese workers are not the answer.

By Jan Helstad and Anne Lise Aakervik

Next time you open a Kinder Egg, gobble up the chocolate and examine the figure hidden in the yellow plastic cylinder, spare a thought for China, where teams of workers sit and paint the tiny figures by hand. Thanks to good sight, fine brushes and steady hands, such micro-details as eyebrows and fingernails appear where they ought to be. Six months after the figures are sent from Europe they come back and can be popped into the eggs.
And it is just this time perspective that has got an Italian sub-supplier to the Kinder Egg manufacturer Ferrero to search for a manufacturing technique capable of cutting down production time. In a market that has to fight for people’s attention, the company wants the figures to reflect current events, and it wishes to produce shorter series that are adapted to the market. This means substituting automation for human hands.

Europe taking over
Two Italian companies currently produce the plastic pieces by injection moulding. Together with a company in Spain, another in the UK and one in Hungary, they will now be responsible for the whole production process. The decoration will be added using a robot production line in whose development SINTEF has played a major role. Given that we are talking about just over 23 million figures a year, the companies would not have been able to base production on manual labour, and SINTEF was asked to help to automate the process. Since the aim of the project was to bring manufacturing back to Europe, the companies received funding from the EU.

Multidisciplinary job
The process is very similar to what happens inside a standard ink-jet printer, in which a row of spray nozzles emit short pulses of ink while the paper moves forward. The pulses create tiny dots of colour as they hit the paper, and the combination of many dots creates an image. SINTEF was responsible for the mathematics and control technology. On the basis of a CAD description of the figures, the SINTEF scientists were able to calculate a spray trajectory or “timetable” for where each spray needed to be aimed, in which colour and for how many milliseconds, after the start of the process.
The research department has created a robot control system that steers and synchronizes the spray heads and the robot hand. With an accuracy of 0.1 mm each figure is positioned in front of the spray nozzle with the appropriate colour. Each figure is given two seconds to be finished, by which time 2400 tiny dots of colour have covered all the parts of the surface of the figure that need to be painted. With that, the hand-painting era is over, even for Kinder Egg figures.

Contact: Geir Horn,
SINTEF Electronics and Cybernetics,
Dept. of Automation
Tel: +47 93 05 93 35
Email: Geir.Horn@sintef.no