A Dummy's Guide to Assistive Navigation Devices

Mobility assistive devices can roughly be categorized into two types: walkers and wheelchairs. Walkers are used by persons who can walk with some assistance. They are meant to give physical support and improve equilibrium. From a practical point of view, walkers imply a highly collaborative profile: if the walker tries to move in a different way than the user or he/she is not expecting it, a fall could happen. Most works on walkers focus, consequently, on kinematics and balance and force calculation. Wheelchairs, however, are meant for persons who can not move on their own and, hence, require a less collaborative profile in a physical sense. Most works on wheelchairs used to focus on navigation.

In fact, robot navigation only requires human intervention to pinpoint a goal, as any mobile robot can nowadays do all the rest. However, persons like to take part in these tasks and, indeed, it seems beneficial to give them a good share of control to avoid loss of residual capabilities and/or improve the rehabilitation process. This work focuses on this second kind of devices.

Assisted wheelchair navigation is not a new idea. As soon as platform navigation was solved in robotics and power wheelchairs were affordable, researchers had the idea of combining robotics and chairs into assistive wheelchairs, that had some say in what persons did with them. SENARIO, VAHM, Wheelesley, SIAMO, Rolland, Navchair, Smartchair or Spherik are all wheelchairs based on autonomous navigation systems.

Unfortunately, research found some resistance in real testing. Users with disabilities were only available in large numbers in hospitals and associations and these places had extensive regulations to state the limits of trials, including Ethical Committees. Doctors are required to control tests at all times and evaluation of experiment results was far from simple.

Indeed, most work on assistive navigation devices is still in the research stage, but there are some companies that manufacture such products. KIPR, for example, has designed a controller that can be attached to conventional power wheelchairs in its Tin Man series. Applied AI Systems manufactures TAO-7, mostly to researchers, though, for approximately 38000 USD. Active Media Robotics has also announced development of its IEW for a similar price: 37000 USD. Smile Rehab, Ltd manufactures simpler models, Smart Wheelchair and Smart Box, for 14000 and 5000 USD, respectively. Smart Box is just an add-on to a wheelchair, like Wheelchair Pathfinder, from Nurion Industries, also for 4500 USD.

All commercial and research systems present differences, but they also share some common features: a set of sensors to perceive the environment, a HCI controller, one or more CPUs and a control software to decide what to do at a given circumstances. Or, like R. P. Brennan said:

Those parts of the system that you can hit
with a hammer are called hardware;
those program instructions that you can
only curse at are called software.

This section basically goes through this common ground to state the different choices that robotic wheelchairs may offer. We separately cover the hardware and software modifications required in a conventional wheelchair to achieve an autonomous assistive device in the following sections.


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