Deformation model and experimental evaluation of a contractable and bendable wire-pulling mechanism with embedded soft tubes for a robotic tongue

Nobutsuna Endo

doi:10.1186/s40648-021-00193-6

Abstract

Few physical models of oral and laryngeal systems for human speech movement exist for computer or mechanical simulators. In particular, a robot tongue mechanism that fully reproduces the deformation motion of the human tongue is lacking. The human tongue is an aggregate of muscles that is devoid of a skeleton. It possesses only a small hyoid. A mechanism that can drive and control the deformation of a soft body, such as the human tongue, along multiple degrees of freedom has not been realized to date. To solve this problem, a wire-pulling mechanism with embedded soft tubes is proposed. Using this mechanism, a flexible tongue that can be deformed along multiple degrees of freedom without breaking the wire is achieved. A prototype planar mechanism with two degrees of freedom that is capable of contraction and bending was fabricated. A deformation model that assumes a piecewise constant curvature (PCC) was formulated. Deformation tests confirmed that the prototype is capable of contraction and bending movements that are consistent with those of the model. Variations in the error with respect to the hardness of the deformable part are discussed, and the limits of the deformation model based on the PCC assumption are presented.

Highlights

Motor functions in the human oral and laryngeal systems include speech, mastication, swallowing, and sucking
A linear trajectory in the configuration space and an arc-shaped trajectory in the task space are drawn in Fig. 8; these are similar to the deformation model
The error and relative error of the neutral arc length l tend to increase with decreasing wire length l1 when the plasticizer mixing ratio is between 10 and 50 wt%

Summary

Introduction

Motor functions in the human oral and laryngeal systems include speech, mastication, swallowing, and sucking. Analyzing the movements of the oral (pharynx, upper jaw, palate, tongue, lower jaw, teeth, and lips) and laryngeal (around the vocal folds and the epiglottis) systems is more complicated than analyzing the motion of the limbs, trunk, and head. An alternative approach for reproducing a physical model of oral and laryngeal systems is to use robots, such as Waseda Talker (WT) [1, 2], vocal [3], or mastication [4] robots. The WT series is limited to reproducing speech functions that are used to utter vowels and some consonants by vibrating the vocal cords and deforming the shape of the vocal tract in the oral cavity. The WT model is currently the best reproduction of the human oral and laryngeal systems

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Conclusion