Instrumentation & Measurement Magazine 23-4 - 18

Experiment 1
A blind user is equipped
with the device. We ask him
to walk slowly and let himself be guided by the system
along an elliptical track. The
results are given in Fig. 4
(walking, user 1). The user
follows the track with very
good accuracy: the average
deviation from the ideal route
is emean ~17 cm (max 53 cm,
σ = 0.12). Such a precision can
typically allow a narrow path
to be followed. In this experiment, the average speed of
1.8 km/h corresponds to a
slow walking.

Fig. 2. Message exchanges between software modules.

◗◗ Then, a blind person wears the device and the guidance
starts (i.e., by pressing the guidance button) at any location close enough to the recorded track. The device directs
the user to the nearest point on the track and starts the
guidance.
The device usually requires very little training, and the user
can follow the sound almost immediately. Nevertheless, training allows the user to increase his/her performance and move
faster. For testing purposes, we recorded a large elliptic track
on a 30 m x 25 m gym. In the experiments described next, we
measure, at any time, the user's position and the distance to
the path to be followed, denoted by et. For m measurements,
we compute the averaged error over a path:
	

emean =

 et
m

	(1)

Experiment 2
A blind roller-skater is equipped with the device. We ask him
to let himself be guided by the system and try to gain speed, if
possible. The results are shown in Fig. 5. The user has been able
to reach an average speed of 8.3 km/h with peak speed at 11
km/h. In these conditions, the average error increases to 0.66
m (max 2.27 m, σ = 0.45), but this remains reasonable for practical use. The user describes the experience as quite comfortable.

Experiment 3
We believe that in the preceding experiment, the user did not
have enough time to locate the sound accurately, which could
explain the increase in error. To address this problem, we introduce a new type of feedback.

Fig. 3. The complete system. (a) The helmet with GNSS antenna and the head-tracker and , the processing unit in a blue case with the D-GNSS receiver in green
(typically placed in a small backpack). (b) The device worn by a blind roller-skater. Two UWB antennas are also visible.
18	

IEEE Instrumentation & Measurement Magazine	

June 2020



Instrumentation & Measurement Magazine 23-4

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