Our obst-entsteiner and its design

Many years ago, when Tina and I were younger, we had camping holidays in Europe.  On one of our visits to Germany we saw and bought a little kitchen gadget called an obst-entsteiner; the box still has the price (19.40 DM, as this was before the Euro became currency).  What does it do?  It removes stones from fruit, such as plums and cherries. Here it is:
Today we stripped one of our plum trees of fruit, and needed to remove the stones from 1500 grams of Mirabelle plums, ready to make jam.  (Mirabelle plums are very scarce in the UK, but they make the most delicious jam.)  However, these plums are very small - between 1 and 2 cm in diameter, the size of a large cherry.  So the stone remover came into use, for the first time in ages.

In operation, one must place the fruit in one of the two cup-rings, press the orange plunger and a prodder hits the fruit and pushes the stone through and out of the hole at the bottom.  Even for our small plums, we used the larger prodder (on the left in the picture) which has four blades to slice the fruit and a central recess between the blades to force the stone away.  Very simple - but if the fruit isn't ripe, then the stone comes away with some flesh attached.  So today's work saw repeated hits of the plunger, and quality control working with a small knife to remove the last bits of fruit flesh.  It took about 20-25 minutes.

Somebody, somewhere, designed this tool.  Someone chose the dimensions of the various parts to make it as versatile as possible, and imposed some constraints on their design.  Consider: the cup-rings must hold assorted sizes of fruit and the sizes of stones that go with them.  So the size of the cup and the hole are parameters to think about.  Double those parameters for the two sides of the machine, and make a compromise between them so that the two prodders cover sufficient range of fruit sizes for most customers.  Four parameters, several constraints, and an efficient design.  Maybe the designer didn't stop to write down these aspects of the engineering, but they were there somewhere. 

And good design engineering like this is part of the operational research universe.


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