Enhancing Variable Friction Tactile Display Using an Ultrasonic Travelling Wave

Abstract

In Variable Friction Tactile Displays, an ultrasonic standing wave can be used to reduce the friction coefficient between a user's finger sliding and a vibrating surface. However, by principle, the effect is limited by a saturation due to the contact mechanics, and very low friction levels require very high vibration amplitudes. Besides, to be effective, the user's finger has to move. We present a device which uses a travelling wave rather than a standing wave. We present a control that allows to realize such a travelling wave in a robust way, and thus can be implemented on various plane surfaces. We show experimentally that the force produced by the travelling wave has two superimposed contributions. The first one is equal to the friction reduction produced by a standing of the same vibration amplitude. The second produces a driving force in the opposite direction of the travelling wave. As a result, the modulation range of the tangential force on the finger can be extended to zero and even negative values. Moreover, the effect is dependant on the relative direction of exploration with regards to the travelling wave, which is perceivable and confirmed by a psycho-physical study.

2MoTac: Simulation of Button Click by Superposition of Two Ultrasonic Plate Waves

“…with A L and A B the vibration amplitude of each mode (peak-peak); if A B < 0, the phase shift is π/2. Hence, by combining the two vibration modes, the points at the top surface follow an elliptical motion, which is able to create a net lateral force, as described in [4]. By changing the ratio Λ = AL AB , the shape of the elliptical trajectory is modified, as described in Fig.…”

“…Due to the deformation shape for each mode, the ratio Λ is not constant over the top surface, and its value is specified in the middle of the plate. The speed and phase of the vibration of each mode are controlled independently, using the vector control method [4,5]. From the vector control method we can define:…”

Travelling Ultrasonic Wave Enhances Keyclick Sensation

“…For specific operating conditions, they can help to propel the finger if they move in the same direction as the finger pulp when they come in contact with it. This effect additionally decreases the equivalent friction coefficient compared with a pure stationary wave [3]. Conversely, a travelling wave decreases the the friction reduction when the direction is reversed.…”

SwitchPaD: Active Lateral Force Feedback over a Large Area Based on Switching Resonant Modes

“…In an effort to realize these benefits, a variety of interesting devices have been developed with the goal of providing active lateral force feedback. For instance, Gueorguiev et al [7] proposed a traveling-wave based device that could provide 100 mN active lateral force with a pressing force of 0.5 N. Since devices employing traveling waves typically operate off resonance, a bulky actuator was required to generate strong lateral forces for haptic rendering. Our group has developed a range of resonant devices that can provide active lateral force, including the ShiverPaD [8] and eShiver [9].…”