Workers at a BMW assembly line have tested – and liked – an artificial thumb produced by 3D printing that helps reduce excess strain on the thumb joints.
For car manufacturing workers, the thumb is strained more than any other finger. Day in, day out it must bear heavy loads – literally.
Christin Hölzel, a PhD student from the Technische Universität München (TUM) had an idea: A support for the thumb that reduces strain on the joints. Assembly line workers at the BMW Group’s Munich plant gave their ‘thumbs up’ for the invention, which is now being deployed in a BMW pilot project.
Thumbs do four times the work of the other fingers during manual production. A good example is car assembly, where plug seals made of rubber are pressed into the floor pan with great force. They are used, among other things, to close drain holes for the paint coat.
Pressing on the plugs can lead to an overextension of the thumb joint. “Imagine the way a thumbnail is pressed into a wall with great force. The thumb bends in a backwards arch and the joints are overextended,” explains Veit Senner, who heads TUM’s research on sport equipment and materials.
Of course, pressing once is not a problem – but the workers at the BMW Group production line repeat this motion hundreds of times. “Over time, this can harm the joint,” says Senner.
Exoskeleton protects thumb joint
As part of her studies at TUM’s Chair of Ergonomics, Hölzel is working with the BMW Group to investigate how to reduce the strain induced by these kinds of work processes. She has developed a flexible, synthetic exoskeleton for the thumb to prevent overextension of the thumb joint.
For the workers to accept the ergonomic tool, it’s important that it doesn’t obstruct other work processes. The exoskeleton is therefore open at the thumb joints so the thumb can move freely. But on the inside, the synthetic material is built up in a thick layer. When the thumb is extended, reinforced elements make contact with each other and act a strong splint. That way, the force used to press on the plug is distributed along the entire thumb, all the way to the wrist.
Individually tailored, 3D-printed assembly aid
Since all human thumbs are unique, the so-called orthoses are individually adapted. The worker’s hand is scanned to measure the form and size, and the tailor-matched assembly aid is printed on a 3D printer. Assembly workers at the BMW Group plant in Munich have already tested – and liked – the artificial thumbs.
Next, Hölzel will use a computer model and simulation to put the finger on exactly how much the ergonomic aid reduces the load on the thumb joint, and whether it induces additional strain on other joints.