The human hand as a model

Mohsen Saadat has always been inventive and technically gifted: as a child, at the age of five, the Iranian invented his own toys out of necessity, building small cars out of wire - without any tools. A passion for technology that has never left the 75-year-old. He moved to Germany at the age of 19, studied engineering and taught as a professor. In 1991, he finally founded GMG - Gesellschaft für modulare Greifersysteme in Soest, North Rhine-Westphalia. As he reports, his aim was to combine scientific methods of advanced engineering with state-of-the-art manufacturing processes.

"Within just a few years, we have succeeded in developing lightweight and flexible gripper systems for robots and automation systems modelled on the human hand," says Saadat proudly. He has convinced numerous industries of the benefits of his technology. The grippers, which have up to six individually movable fingers and in some cases over 100 joints, are used to handle car wheels in the automotive industry, to hold up sacks in filling plants when filling them with bulk goods or to package sausage and cheese in the food industry.

problem:
One of the challenges in this maturing process was to find suitable bearings for the moving metal components of the gripper, such as the finger joints. This was no small task, as the components had to be true jacks-of-all-trades, including low-friction, abrasion-resistant, maintenance- and lubrication-free and easy to install.

The use of classic roller bearings was ruled out. "Roller bearings are suitable for permanent rotational movements, require the production of more precise fits, involve complex assembly and disassembly and lead to metallic noises". Very space-saving plain bearings were also required, as otherwise the compact design of the grippers could not be realised.

Solution:
Bearings made of high-performance plastics from igus® provided the solution. They are tribologically optimised, i.e. improved in terms of friction and wear. "We have been relying on plain bearings from igus® since 1991. It was therefore clear from the outset that the polymer bearings would also be used in the multifunctional long-arm gripper. There is virtually no alternative to these bearings for us in automation technology, where reciprocating movements are constantly taking place," says Saadat.

Another advantage is that the polymer bearings are lightweight, corrosion-free and maintenance-free compared to many classic metal bearings, as they enable dry operation without a single drop of lubricating oil thanks to the integrated solid lubricants. "This is a very important specification. Because we couldn't possibly expect our customers to have to lubricate the gripper regularly."

The iglidur® polymer bearings are designed robust in such a way that the bearings ideally outlast the life of the gripper by around 30 years. "An advantage for our multifunctional gripper, as maintenance costs are reduced and productivity increases significantly." A test in the igus® in-house laboratory, the largest test laboratory in the industry, also proves how wear-resistant the bearings are. Here, the polymer bearings competed against classic metal bearings. Both bearing types pivoted on a gas-nitrided St52 steel shaft - with a load of 30 MPa and a speed of 0.01 metres per second. "The gliding layer of the metal bearings was already worn out after 60,000 cycles," says Stefan Loockmann-Rittich, head of the iglidur® plain bearing business unit.

"The bearings of the iglidur® G series, on the other hand, showed almost no signs of wear even after 200,000 cycles. They are therefore ideally suited for reliable and maintenance-free use over many years." specification, which incidentally also applies to another bearing type that can be found in the multifunctional gripper from GMG: the linear bushings of the drylin® R series (RJM-01-16), which enable controlled and safe linear movement of the gripper linkage. "The igus® bearings convince us time and again, which is why we will continue to rely on the iglidur® polymers in the future," summarises Saadat.