Evaluation of the Perceptual Characteristics of a Force Induced by Asymmetric Vibrations

Abstract

This paper describes the perceptual characteristics of a sense of a force induced by asymmetric vibration using a vibration speaker-type non-grounded haptic interface. We confirm that the vibration speaker generates a perceived force that pulls or pushes a user's hand in a particular direction when an asymmetric amplitude signal that is generated by inverting a part of a sine wave is input. In this paper, to verify the system with respect to various factors of force perception caused by asymmetric vibration, we conducted six experiments and the following results were obtained. (1) The force vector can be controlled by reversing the asymmetric waves. (2) By investigating the physical characteristics of the vibration, asymmetric vibration was confirmed. (3) The presentation of vibration in the shear direction on the finger pad is effective. (4) The point of subjective equality of the perceived force can be controlled by up to 0.43 N by changing the amplitude voltage of the input signals. (5) The minimum stimulation time required for force perception is 66.7 ms. (6) When the vibration is continuously presented for 40 to 50 s, the perceived force decreases because of adaptation. Hence, we confirmed that we can control both the direction and magnitude of the reaction force by changing the input signal of the vibration speaker.

Effects of Asymmetric Vibration Frequency on Pulling Illusions

“…If A 1 or A 2 are especially different, the profile of the waveform approaches the sinusoidal wave. Sinusoidal vibration does not induce the illusion [9]. In this experiment, A 1 and A 2 were equivalent.…”

“…The pulling illusion is different from the kinesthetic illusion caused by vibrational stimulation of tendons [5] because the pulling illusion requires stimulation of the fingertips rather than the tendons. The pulling illusion is expected to be used in force display for wearable and mobile devices because it can be induced by a small nongrounded device [6][7][8][9][10]. Owing to this advantage, the pulling illusion has been applied to a pedestrian navigation system for the visually impaired [2,11].…”

“…Lately, to induce this illusion, voice-coil type vibrators have been used [6][7][8][9][10] because vibrators are inexpensive and easily available [16]. Although some of these previous studies have reported the effect of frequency [8,9], only the input signal to the vibrator has been controlled between frequency conditions, and the acceleration profiles that output from the vibrator were not controlled. Voice-coil-type vibrators have a resonant frequency because of the spring component [17]; the gain and phase between the input and the output change significantly near the resonant frequency.…”

Motion Guidance Using Translational Force and Torque Feedback by Induced Pulling Illusion

“…In other words, this device can apply forces in four directions, in which a forward or backward translational force and a clockwise (CW) or counterclockwise (CCW) torque, by combination of the force vectors. These directions are controlled using an asymmetric-amplitude signal with a two-cycle sine wave that is inverted for a half-cycle [10]. Each signal was amplified with an amplifier circuit using a power amplifier IC (Texas Instruments Inc., LM386) with a maximum output voltage of ±4.5 V. The frequency of the input signal was 75 Hz.…”

“…Based on this finding, Amemiya et al proposed a method of applying vibrations with asymmetric acceleration to induce the perception of force toward a single direction in the user's hand [9]. Furthermore, we previously proposed a method of inducing pulling illusion by using a small voice-coil-type vibrator [10]. In addition, we developed a holdable device that presents an illusory translational force and torque by combining the two force vectors [11].…”