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Ch06-I044963.fm Page 26 Tuesday, July 25, 2006 11:50 AM
Ch06-I044963.fm
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Acceleration Sensor
S2 S1
Rotor
Servo Motor

Haptic Force Generator
(a)
Figure 2: Experimental device for haptic illusion (size: 80 x 225 x 88 mm, weight: 0.386 kg). (a)
Overall view; (b) Haptic force generator

This equation indicates that the method based on Eqn. 8 requires measurement of the angular
acceleration Qx(= 4>) °f the rod.
DEVICE FOR HAPTIC ILLUSION

Figure 2 shows an experimental device for haptic illusion of rod length. The device consists of
a haptic force generator consisting of a gyroscope, as shown in Figure 2(b). and two three-axial
acceleration sensors of the piezo-resistance type (H560, Hitachi Metals, Ltd.) to detect the angular
acceleration fi_ Y- The haptic force generator consists of a gyroscope and a precession controller.
The DC motor rotates the rotor of the gyroscope at high speed. The precession controller consists
of a servo motor and a pulse width modulation circuit to control the servo motor. The precession
of the gyroscope is applied by the servo motor. By grasping the part of the haptic force generator
and wielding it around the X-axis, the gyro-moment is produced around the X-axis.
An experiment was performed in order to distinguish differences in superficial moment of iner-
tia. The subjects were able to easily discriminate changes in the superficial moment of inertia
produced by the device. However, subjects were not able to perceive changes in the superficial
moment of inertia as a change in the haptic illusion of rod length. A great deal of time is required
in order to correlate a change in the superficial moment of inertia and a change in the haptic
illusion of rod length because the perceived length is affected by the complicated shape of the
device.
CONCLUSIONS

This paper described the development of a haptic force generator using a gyroscope as a non-
installing and non-equipping device. It was shown theoretically that the haptic force generator was
able to superficially vary the moment of inertia of a rod. A device for haptic illusion of rod length
was developed based on this theory. Good agreement between the analytical and experimental
results indicates that the haptic force generator provides one of the essential functions of the
virtual cane.

REFERENCES

Funakubo H. and Hatsuyama Y. (1995). Assistive Technology, Sangyo-Tosho.
Turvey M.T. (1996). Dynamic touch. American Psychologist 51:11, 1134-1152.
Chan T.C. (1994). Haptic perception of partial-rod lengths with the rod held stationary or
wielded. Perception and Psychophysics 55:5, 551—561.