S. Morikawa

Bio: S. Morikawa is an academic researcher from Shiga University. The author has an hindex of 1, co-authored 1 publications receiving 25 citations.

A 3-D Nonhomogeneous FE Model of Human Fingertip Based on MRI Measurements

Abstract: A 3-D nonhomogeneous finite-element (FE) dynamic model of a primate fingertip is developed in this paper based on magnetic resonance (MR) imaging measurements for better understanding the mechanism of human finger sensation. The geometries of a human fingertip are measured using an MR system, and a series of 2-D images is obtained. Utilizing a boundary tracking method, boundaries of the fingertip and distal phalanx are tracked from each image slice and a set of boundary nodes is generated to construct a 3-D tetrahedral mesh of the fingertip. The 3-D mesh is then utilized to formulate a nonhomogeneous FE dynamic model for simulating the fingertip behaviors. The constitutive model, which consists of elastic and viscous elements, is employed to govern the dynamic behaviors of individual tetrahedral FE. The FE model is further extended to deal with contact interaction between the fingertip and an external instrument. Differing with conventional fingertip models, the model presented in this paper is able to not only better represent internal and external geometries of a human fingertip but also take the tissue viscosity into consideration. Simulation and experiments are performed with both a human finger and a fingertip phantom under different indentation operations. We found that the Voigt model can simulate the force behaviors of a fingertip phantom but has difficulty to reproduce the force relaxation behavior of a human fingertip. We have therefore introduced a parallel five-parameter physical model to solve this problem.

Simulating the three-dimensional deformation of in vivo facial skin.

Abstract: Characterising the mechanical properties of human facial skin is a challenging but important endeavour with applications in biomedicine, surgery simulation, forensics, and animation. Many existing computer models of the face are not based on in vivo facial skin deformation data but rather on experiments using in vitro facial skin or other soft tissues. The facial skin of five volunteers was subjected to a rich set of deformations using a micro-robotic device. The force–displacement response was recorded for each deformation. All volunteers' facial skin exhibited a non-linear, anisotropic, and viscoelastic force–displacement response. We propose a finite element model that simulated the experimental deformations with error-of-fits ranging from 11% to 23%. The skin was represented by an Ogden strain energy function and a quasi-linear viscoelastic law. From non-linear optimisation procedures, we determined material parameters and in vivo pre-stresses for the central cheek area of five volunteers and five other facial points on one volunteer. Pre-stresses ranged from 15.9 kPa to 89.4 kPa.

Surface strain measurements of fingertip skin under shearing.

Abstract: The temporal evolution of surface strain, resulting from a combination of normal and tangential loading forces on the fingerpad, was calculated from high-resolution images. A customized robotic device loaded the fingertip with varying normal force, tangential direction and tangential speed. We observed strain waves that propagated from the periphery to the centre of the contact area. Consequently, different regions of the contact area were subject to varying degrees of compression, stretch and shear. The spatial distribution of both the strains and the strain energy densities depended on the stimulus direction. Additionally, the strains varied with the normal force level and were substantial, e.g. peak strains of 50% with a normal force of 5 N, i.e. at force levels well within the range of common dexterous manipulation tasks. While these observations were consistent with some theoretical predictions from contact mechanics, we also observed substantial deviations as expected given the complex geometry and mechanics of fingertips. Specifically, from in-depth analyses, we conclude that some of these deviations depend on local fingerprint patterns. Our data provide useful information for models of tactile afferent responses and background for the design of novel haptic interfaces.

Haptics as an Interaction Modality

Abstract: This chapter focuses on the biological and behavioral basics of the haptic modality. On one side, several concepts for describing interaction are presented in Sect. 2.2, and on the other side, the physiological and psychophysical bases of haptic perception are discussed in Sect. 2.1. The goal of this chapter is to provide a common basis to describe interactions and to convey a basic understanding of perception, and the description via psychophysical parameters. Both aspects are relevant to the formal description of the purpose of a haptic system and the derivation of requirements, which are further explained in Chap. 5. Several conclusions arising from the description of perception and interaction are given in Sect. 2.4.