5.6 Other Mobility Assistive Technology Approaches

the obstacle information has already been reduced to that available from a number of particular directions. In the case of some of the other technologies used to obtain information, such as the camera, the potentially available information is much more complex and decisions have to be made about how much of this information should be conveyed to the user. The tendency has generally been to focus on information about obstacle locations rather than to try to present an overview or more detailed information of the scene.

In the case of a technology cane, which obtains information from a number of different directions, a number of different information channels, which could be auditory, tactile or a combination, will generally be required. Several typical beam configurations along with the total number of information channels for each configuration are given in Table 5.2.

The number of information channels given in Table 5.2 then has to be mapped to a user interface consisting of a suitable mixture of audio and/or tactile modes. For example, for the configuration of System 2, three vibrating tactile buttons matched to the cane-bearer’s thumb, and two fingers might be appropriate. Alternatively, the downward and forward channels could be tactile and the upward channel audio. Providing both tactile and audio options for all channels could have a number of benefits, including making the device available to deafblind users. However, there may be additional costs and increased complexity. Decisions on the human– technology interface are usually based on a combination of the results of end-user trials, technical constraints and cost considerations.

5.6 Other Mobility Assistive Technology Approaches

Guide dogs, long canes and technology canes are all well-established assistive technology solutions for obstacle avoidance. As indicated in Section 5.3, a number of (electronic) travel aids have been developed, though many of them have not gone beyond the prototype stage. In this section, the range of other devices that have been developed is illustrated by three examples, the Polaron, which is a clear travel path indicator, the Miniguide, which provides supplementary information to support a primary travel aid and the vOICe system, which provides a ‘soundscape’ of a visual scene.

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5.6.1 Clear-path Indicators

The engineering response to a typical travel scene (Figure 5.3) has been to decompose the problem into a number of issues and then devise systems for these sub-problems. As discussed previously, the long cane is able to detect obstacles and identify a clear-path at lower leg height. However, other obstacles may well reach down to chest and head height as in the example of overhanging branches on trees in the environment. Laser and ultrasound technology canes are able to detect a clear-path at lower leg height and, depending on the beam configuration, at other heights too. Therefore, there is a need for assistive devices to supplement the long cane by providing information on obstacles at head and chest height. Such devices are usually termed clear-path indicators, as they are generally designed to simply indicate that the forward path at chest and head level is clear and negotiable.

The Polaron

The Polaron, manufactured by Nurion-Raycal, USA, is a clear-path indicator or an object detector that is available in a torch format or in a version that can be worn on a loose strap around the neck to be positioned at chest height. It is described here in its chest-mounted format. The echolocation principle of ultrasonic sound is used to detect whether the path is clear. In the chest-mounted format, the ultrasound transmitter and receiver are worn at chest level. The range for detection of obstacles can be set at 1.22 m, 2.44 m or 4.88 m (4, 8, or 16 ft) from the user. A sophisticated human–technology interface of audio and tactile cues is used to inform the user of obstacles in the forward path, as shown in Table 5.3.

The Polaron has sufficient tactile cues to be used by a deafblind person. The chest mounted location has the advantage of leaving the user’s hands free. This enables the Polaron to be used together with a long cane or guide dog (in one hand), while still allowing the user to carry shopping or other baggage in the other. However, this location has the drawback of being conspicuous. Similarly, a blind person who uses a manual wheelchair could use the Polaron to support independent mobility.

Wheelchair mounted clear-path indicators

Whilst the Polaron can be used with a manual wheelchair, powered wheelchairs need a dedicated device. There are two main reasons for this. Powered wheelchairs can travel two to three times as fast as a pedestrian can and therefore a faster

Table 5.3. Audio-tactile interface cues – Polaron

194 5 Mobility: An Overview

making it suitable for those who prefer tactile information, such as deafblind people. The system can be used in several different ways, for clear-path detection and navigation.

•Clear-path detection. When the intermittent sound from the forward path detector is heard, then the wheelchair should be turned slowly until the intermittent beeping sounds stops. The absence of an intermittent beeping indicates that the forward path is now clear.

•Finding a landmark. In this case the beeping signal is used as a homing signal so that the user keeps the intermittent beeping signal in front of the wheelchair and homes in on a desired destination landmark.

•Straight travel. In this mode the side beam is used. The wheelchair is positioned to within 30 cm of a wall or a hallway so that the side beam issues a constant and continuous tone. Forward travel that maintains this side beam tone means that the wheelchair is travelling parallel to the wall. When the side beam tone stops, an open doorway or a corridor intersection has been reached.

5.6.2 Obstacle and Object Location Detectors

There is a clear, though sometimes subtle, difference between obstacle avoidance and object location. The primary mobility aids, such as the guide dog and the long cane, provide obstacle avoidance information. However, there are differences between this task and the object location task, where the user actually wants to make contact with an object. This could include detecting the end of a queue, the start of a sales counter or the location of lift doors, the waste paper bin or a desk chair. The use of a long cane is probably inappropriate and, in addition, could be damaged in some circumstances, for example, by closing lift doors. To gain a specification for a suitable assistive technology system, the CAT model checklist is completed and shown in Table 5.4.

This results in a specification for a small lightweight hand-held device that could be used to explore and interrogate the surroundings of the user or find objects in the user’s immediate vicinity. The obvious analogy is a small torch whose light beam is used to illuminate the immediate surroundings of a sighted user.

Miniguide

The Miniguide (GDP 2006) is an assistive technology solution that meets many of the requirements of this specification. It is a small hand-held, torch-like device with dimensions of 80 mm long, 38 mm wide, and 23 mm thick. It uses the echolocation principle with ultrasonics to detect objects within the range of its beam. It is essentially a support device to be used in conjunction with a primary mobility technology, such as the long cane or a guide dog. But, it can also be used to interrogate the spatial layout of the local space around a user who might, for example, be trying to find the position of one particular item.

Table 5.4. CAT model checklist – specification for obstacle/object detection

Attribute – context

The first Miniguide was introduced to the market in 2000 and this model is illustrated in Figure 5.16a. This model was superseded in 2005 by a new realisation of the Miniguide concept that used an injection-moulded case, as shown in Figure 5.16b.

The description that follows is based on the User Guide for the new 2005 Miniguide model (GDP 2006). The Miniguide is battery powered and has four basic beam ranges for object detection: 0.5 m, 1 m, 2 m and 4 m. The torch-like body has a depressible ON/OFF switch and an ear plug socket at the back for an audio

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Figure 5.16a,b. Miniguide: a Miniguide circa 2000; b Miniguide circa 2005 (photographs reproduced by kind permission of GDP Research, Australia)

sound feedback signal. However, the Miniguide is basically tactile in that the torch vibrates at a speed that decreases with increasing distance of the object from the device. Slow vibrations indicate that the object detected is at the limit of the Miniguide beam range setting. A rapid vibration rate indicates that the object detected is very close to the Miniguide and no vibration indicates that there is no object within the range field of the beam. This tactile modality is suitable for visually impaired, blind and deafblind users.

However, the use of the earplug socket to obtain an audio-sound feedback signal creates an additional, or an alternative sensory information channel. Thus, the Miniguide can be configured to supply (1) only tactile feedback, (2) both tactile and audio feedback or (3) only audio feedback. The use of a single earphone allows the user to perceive the ambient background environmental noises, which provide important locational information to blind people, as well as receiving aural information from the Miniguide.

The Miniguide will be silent if it cannot detect an object in its current beam range setting. If an object is detected then an audio-feedback tone is produced. Two different types of audio tones are available:

1.“Chirp” audio tones. This is the default audio-tone for the Miniguide. The rate of “chirp” tones heard is the aural equivalent of the rate of vibration of the small motor within the Miniguide. A high “chirp” rate indicates that the object detected is close to the device.

2.Sweep audio tones. For the sweep audio setting, a continuous tone is produced, where the pitch indicates the closeness of the object detected to the Miniguide. The higher the pitch of the sweep audio tone, the closer the object detected is to the device. With practice, this variation in pitch can provide the user with some spatial awareness of their immediate environment. For example, the presence of a doorway with a wall on both sides would be indicated by the following sequence: high (wall), low (doorway), high (wall) in the audio sweep signal.