Ultrasonic sensors give additional mobility to visually impaired

UltraCane is an electronic mobility aid that uses ultrasound to warn uses of obstacles ahead and at head height. Originally developed as a concept at the University of Leeds in around 2004, but subsequently adapted and now marketed by Yorkshire company Sound Foresight Technology. But designing for the blind and VI community is no easy task, as Dr Paul Clark, director of Sound Foresight, explains. "It's a subtle and interesting nut to crack, helping blind and VI people. Some people have created aids that use an acoustic sense, but the problem with that is that if you're blind or VI, your primary sense becomes your hearing. So the absolute last thing you want is anything that impedes your ability to comprehend your surroundings or adds another sound signal that you need to concentrate on." For this reason, the UltraCane is instead equipped with a dual-range, narrowbeam ultrasound system that provides a 100% hazard protection envelope in front of and, uniquely, forward of the head and chest of the user. Two ultrasound transducers provide range data on the closest potential hazards, such as plants, people, road signs, and overhanging branches. This makes the UltraCane equally practical on the street as in interior spaces. The range data is delivered to the user by two small, button-shaped tactile vibrators mounted in the moulded handle of the UltraCane. Says Dr Clark: "We've found that if we give tactile feedback, people swiftly start to build up a spatial map of their surroundings. You're sweeping your arm around and you're picking up objects as your arm reaches certain orientations. So people quickly learn the skill of building up a map of what's around them." The question of how best to present this tactile feedback was addressed in a similar way to that employed on car parking sensors. Thus, users receive a tactile cadence – essentially a buzz in the hand – that increases in intensity the closer they get to something. The use of two sensors, with one angled upwards to protect the chest and head area, means that users receive advanced warning that you're about to hit something. This means that they are able can stop and feel around with your hand to recognise any potential hazard. Just how important this can be is made clear by Dr Clark. "if you look at the hazards in a modern high street: low hanging tree branches; For Sale signs hanging over the pavement; coach wing mirrors that hang over the pavement; advertising hoardings that start as monopoles and flare out – blind people walk into all of these things, which and that's not pleasant for anybody." Just how effective this technology is was demonstrated on the BBC programme 'Miracles of Nature', when Dan Smith, who is completely blind was shown riding a bike through a woodland pathway using ultrasound to detect trees and other obstacles whilst cycling. This 'UltraBike' uses the same ultrasound technology that is incorporated into the UltraCane and features components of the UltraCane in its design. A number of other design issues have had to be addressed in the development of the modern UltraCane. One of these centred on the sensitivity of the receivers themselves . This was achieved despite the fact that ultrasonic transducers are very variable in manufacture. Says Dr Clark: "They have different resonant frequencies, for instance, so we have a clever way of dealing with that automatically to allow consistency from product to product. Because we obviously wanted to ensure that every UltraCane had the same, good sensitivity going out the factory door. If you measure them, if you get a big batch of typical transducers with a sensor frequency of around 40kHz – you might get around a 10kHz spread. They're very peaky, so if you go a little way away from its natural resonant frequency, you'll find that performance drops off quite dramatically. We attended to that with an automatic detection and feedback system." Another factor that had to be addressed was the question of ruggedness and reliability. This issue of 'manufacturing for reliability' was attended to by addressing unit feedback from the field. Or, as Dr Clark puts it: "We went out, gave it to people and found out how they broke it. It's a fundamental rule of life that anything that's handled by a person has a really rough life – especially if you're blind or VI. It's going to get knocked into things, so these things have to be rugged." Safety, of course, is another key factor in the design. Thus, the low battery warning comes into effect when there is still an hour's battery life left to reduce the risk of the user being stranded. Equally, it is fitted with a simple, thumb-operated battery cover and deliberately uses non-rechargeable batteries to ensure that users can easily purchase replacements. Dr Clark estimates the potential market for the UltraCane in the millions, but concedes that it is still relatively early days. However, he is positive about the future, saying: "The thing that keeps me going is the feedback from the owners… Look at some of the testimonials like 'It's given me back my dignity' and 'People don't believe I'm blind'. You couldn't pay for that kind of PR."