Fingertip Recovery Time Depending on Viscoelasticity
The aim of this paper is to investigate the recovery time of human-fingertip’s mechanical properties after indentations cycles. To determine the influencing parameters, three indentation velocities, five recovery times and three subjects were tested. Duri
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Abstract. The aim of this paper is to investigate the recovery time of human-fingertip’s mechanical properties after indentations cycles. To determine the influencing parameters, three indentation velocities, five recovery times and three subjects were tested. During each experiment, the fingertip of participant was driven against a flat surface, while indentation displacement and velocity were controlled. The results show not only the indentation forces values increase depending on the indentation velocity increment, but also they decrease depending on the number of cycles. While the fingertip recovery depends on the time, but not on the indentation velocity. Finally the recovery time was determined: in 5 min the fingertip restored 99.6 % of the initial mechanical properties. Keywords: Recovery time · Viscoelasticity effect cal properties · Indentation pulp cycles
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Introduction
The investigation of the mechanisms of the human tactile perception represents an important topic in haptic research. Everyday, the human fingerpad plays an important role in the perception of physical environment to explore surfaces and textures, to grasp and to manipulate objects. Based on this concept and, since tactile sensitivity depends on the tissue strain and hence on the contact area, it is important to characterize the mechanical properties of the human fingertip, when it comes in contact with an object. Several studies have demonstrated that dynamic loading stimulation is affected by the mechanical response of the fingertip, from different points of view. For example, many works focused on the relationship between the mechanical stimuli imposed on fingertip skin and the tactile sensory response of mechanoreceptors [1–4]. Furthermore, from a biomechanics viewpoint, Gulati and Srinivasan [5] applied, with indenters of various shapes and sizes, sinusoidal displacement to the fingerpad. The recorded dynamic force response was measured and it revealed a non-linear dependence of the force on displacement, frequency and contact area. Serina et al. [6] modeled the response of fingerpad, during the tapping task, in a range of frequencies from 0.25 Hz to 3 Hz. Moreover, since the human fingertip has a complex structure [7,8] and it is also considered a non-homogeneous, anisotropic and non linear c Springer International Publishing Switzerland 2016 F. Bello et al. (Eds.): EuroHaptics 2016, Part I, LNCS 9774, pp. 33–44, 2016. DOI: 10.1007/978-3-319-42321-0 4
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material [9], several studies showed that the human fingertip should be modeled as a structural viscoelastic material [10] based on three main reasons: (i) the force response is only a function of the depth of indentation and the transient response is dependent on the velocity; (ii) the fingertip stress relaxation is evidenced by a decrease from a peak force value to a steady state value and (iii) the hysteresis graph of the human fingertip, subjects to several dynamic loads, indicates that the energy is being dissipated [11–14]. This viscoelasticity infl
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