Friction Reduction through Ultrasonic Vibration Part 1: Modelling Intermittent Contact

Abstract

Ultrasonic vibration is employed to modify the friction of a finger pad in way that induces haptic sensations. A combination of intermittent contact and squeeze film levitation has been previously proposed as the most probable mechanism. In this paper, in order to understand the underlying principles that govern friction modulation by intermittent contact, numerical models based on finite element (FE) analysis and also a spring-Coulombic slider are developed. The physical input parameters for the FE model are optimized by measuring the contact phase shift between a finger pad and a vibrating plate. The spring-slider model assists in the interpretation of the FE model and leads to the identification of a dimensionless group that allows the calculated coefficient of friction to be approximately superimposed onto an exponential function of the dimensionless group. Thus, it is possible to rationalize the computed relative reduction in friction being (i) dependent on the vibrational amplitude, frequency, and the intrinsic coefficient of friction of the device, and the reciprocal of the exploration velocity, and (ii) independent of the applied normal force, and the shear and extensional elastic moduli of the finger skin provided that intermittent contact is sufficiently well developed. Experimental validation of the modelling using real and artificial fingertips will be reported in part 2 of this work, which supports the current modelling.

Why pens have rubbery grips

“…The illusion of a ridge (33) may be created by rapidly increasing friction during the exploration by a finger as a result of decreasing the amplitude of vibration or increasing the electrostatic field (3). The strength and stability of this effect are dependent on the contrast in friction that can be induced, which has critical implications for power requirements (34,35).…”

Evaluation of a friction reduction based haptic surface at high frequency

“…When a user's fingertip touches a vibrating plate, the skin of the pulp bounces, and this phenomenon has been reported in the literature [9], [11]. This phenomenon alone doesn't explain the friction reduction.…”

“…The squeeze film effect theory [7] calculates the overpressure due to the nonlinear compression of the air in the gap between the finger pulp and the surface while the reduction of the contact area can also explain the friction reduction. In [9], the active lubrication theory considers the fingertip as an elastic body, and takes into account the difference between the static and the dynamic friction coefficient. Since Vezzoli and al didn't investigate the model at frequency higher than 100kHz we explore the models result above 200kHz.…”

“…1 Frédéric Giraud, Michel Amberg, and Betty Lemaire-Semail are with Univ. Lille, Centrale Lille, Arts et Métiers Paris Tech, HEI, EA 2697 -L2EP -Laboratoire dElectrotechnique et dElectronique de Puissance, F-59000 Lille, France frederic.giraud@univ-lille1.fr 2 Tomohiro Hara and Masaya Takasaki are with the Department of Mechanical Engineering, Saitama University, Shimo-Okubo 255, Sakuraku, Saitama 338-8570, Japan vibration wavelength, smaller actuators and also smaller vibration amplitude [9]. In [10] surface acoustic waves at 15MHz have been used with vibration in the range of the nanometer to create a friction reduction.…”

Travelling Ultrasonic Wave Enhances Keyclick Sensation

“…Users detected more easily the falling friction than the rising friction and reported to feel it as a convincing keyclick sensation. The proposed method relies on sudden changes in the impedance of the finger [13], which are provoked by the influence of the ultrasonic lubrication [19,16] on the compression of the fingerpad. Lateral motion of the finger is generally necessary to the occurrence of friction modulation by ultrasonic lubrication.…”