MEMS the word

Citation

Loughlin, C. (2004), "MEMS the word", Assembly Automation, Vol. 24 No. 1. https://doi.org/10.1108/aa.2004.03324aaa.001

MEMS the word

MEMS the word

Our theme for this issue is “Precision Assembly Technologies for Mini and Micro Products” and about half of our contributions are based on a selection of papers from IPAS 2003 (International Precision Assembly Seminar, Bad Hofgastein, Austria, 17-19 March 2003). These have been updated and in many cases extensively revised for this issue of Assembly Automation.

The area of technology covered in this issue is particularly interesting because everything is so different when you start talking about sub- millimetre sized components and nanometre positioning requirements.

If you consider a “normal” sized desktop robot that is perhaps capable of lifting 1 kg with 0.1 mm positioning accuracy, and then scale everything up so that it is capable of lifting 100 kg with 1mm accuracy, you will find that both robots can be pretty well identical in basic construction. It is just that the one has bigger cross-sections, sturdier bearings and gets a bit warmer.

However, if you scale everything down by the same degree the same technologies are simply not available, or at least not yet, but fortunately whole new ways of doing things become both possible and appropriate. For example in our paper by Hesselbach (refer pp. 49–57) flexure hinges measuring just 3 mm £ 0.15 mm are used instead of preloaded bearings to provide 1 degree of freedom movements. These bend in a pseudo-elastic manner and survive in excess of 1 million, 208 bends before failure, while providing 1 mm positioning accuracy. Try that with everything scaled up a hundred times and you will soon be left with two pieces of fatigued metal.

Along with these new opportunities also come difficulties associated with handling very small parts. All of a sudden gravity is shown to be the very weak force that it really is and in its place electrostatic, magnetic, surface tension and Van der Waals forces take control. These can help with the picking up of small parts, but can also make it very difficult to put them down again.

Why should we want to make things smaller than they currently are? We have not changed much in size over the years, and so if the keyboard on which I am typing suddenly shrunk to a tenth of its present size I could find it rather awkward to use. The attraction is not just that we can make existing devices smaller, although that is often very useful, but also that whole new potential applications can be opened up.

If you consider that the revolution in the semiconductor industry that has given us powerful computers that fit in our pockets, is basically concerned with moving electrons around at high speed and at low cost; then microassembly technologies are to mechanical parts and fluids what the semiconductor revolution has been to electrons.

Computers are all very well and useful, but if your heart needs a new valve then no amount of smart processing will fix the problem. What you need is the ability to move physical objects. And in the same way that electronics have shrunk from a room full of valves needing a small power station to a pocket calculator and a hearing aid battery; so Micro Electro Mechanical Systems (MEMS) have the potential to shrink the cumbersome peristaltic pumps of a bedside dialysis machine into an implantable device.

Clive Loughlin