Instrumentation & Measurement Magazine 23-4 - 19
without ever reaching it (because the accuracy of the perception of sound sources is limited). To address this problem, we
can also add a term that takes into account the accumulation of
the error over a time window (similar to a well-known proportional-integral feedback controller):
Ft = K p et + Ki e j (3)
j
We therefore carry out guidance tests using proportionalintegral feedback, and we observe a significant increase in
accuracy. Fig. 7 shows the path of user 2 under the same conditions as the test illustrated in Fig. 5 but with the feedback
turned on.
For this experienced blind roller skater, with PI-feedback,
the maximum speed was up to 12 km/h and the average error
was 0.5 m (maximum 1.3 m, σ = 0.43). Table 4 summarizes the
Fig. 4. A blind man walking along an elliptical path. The blue line is the
course to follow and dots represent the user position with color for velocity
(blind subject #1).
Fig. 6. Proportional Feedback illustration. Depending on the position of the
user with respect to the track, the sound source is moved out of the track, in
the opposite direction, by a distance Ke.
Fig. 5. Roller skating along an elliptical path (Blind subject #2).
Considering the positioning error et, we introduce a proportional feedback:
Ft = K p et (2)
and we move the source by Ft in the direction opposite to the
error from the theoretical position on the path (Fig. 6). The parameter Kp is the proportional feedback coefficient and can
be tuned empirically. In some cases, the user follows the path
June 2020
Fig. 7. Blind user practicing roller skating with a proportional-integral
feedback with Kp = 0.7 and Ki = 0.1 (Blind subject #2).
IEEE Instrumentation & Measurement Magazine 19
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