Whether visiting friends, going shopping or participating in events outside the home: mobility is the prerequisite for a self-determined life. People who are mobile also do not need to be looked after or attended to. However, something as simple as leaving their home without assistance is a major hurdle for persons with disabilities. "Very few buildings with older residents have elevators," explains Prof. Bernhard Wolf of the Heinz Nixdorf Chair for Medical Electronics at TUM.
It quickly became clear to the scientists: A wheelchair must be developed that can climb stairs. It should also be agile and narrow. The researchers thus limited the chassis to one axis. In contrast to a two-axle wheelchair chassis, this wheelchair can move forward and backward and rotate around its own axis almost simultaneously. The wheelchair holds itself up according to the inverted pendulum principle. "Each small positional change is recognized and immediately compensated by the drive system," says Wolf.
The ability to navigate even narrow staircases
So how exactly does the new wheelchair conquer staircases? Previous concepts have utilized crawler chassis or castor configurations. "But those wheelchairs have to be monitored during the process," explains Wolf. In other words, another person has to be on hand to ensure that the chair does not topple over. In addition, such wheelchairs have a large turning circle – making them unsuitable for use on narrow staircases.
The scientists decided on a bionic concept for their new chair. Two "feet" that have a similar configuration to human legs – with an upper and lower leg – are attached to the wheelchair. If the chair’s ultrasonic sensors detect stairs in the path of travel, the wheelchair reverses itself with its back to the stairs until the two wheels have physical contact with the first stair. Then the "feet" are extended, and the wheelchair lifts itself up the step. Powered by an electric motor, the legs push the wheelchair to the next higher step. Meanwhile, a camera system monitors the “staircase topography” to ensures that the wheelchair is firmly on a step and not, for example, on the edge.
This technology also makes it possible to manage very narrow staircases – with the exception of spiral staircases. When the chair’s done ascending the stairs, it retracts its legs, and swings back into forward motion in drive mode. The wheelchair can thus also go down the stairs again.
Comprehensive mobility concept
Using a prototype, engineers were able to show that their principle works. The concept goes beyond the climbing of stairs, however. "We want to give people a truly viable mobility alternative with this wheelchair," says Wolf. The chair could also be used as a car seat in the future, for example – dispensing with the need to fold and stow the wheelchair prior to departure. It would also not be necessary for the user to be lifted from the car seat back into the wheelchair upon arrival. Since it has an internal drive, it is narrower than a standard wheelchair.
The potential industrial partners are still reluctant, however. "I think it is because the principle is technically a little complex – and of course, there are already standardized wheelchairs", says Wolf. He is convinced that the demand for the bionic wheelchair would definitely be high: although it costs more than a standard wheelchair, it offers its users the possibility to move around more freely.
Cooperation partners in the project are CoKeTT Zentrum at Kempten University (Prof. Petra Friedrich) and the Chair of Ergonomics at TUM (Professor Klaus Bengler).
Dipl.-Biol. Christian Scholze
Technical University of Munich
Heinz Nixdorf Chair for Medical Electronics