Abstract
Faces of android robots are one of the most important interfaces to communicate with humans quickly and effectively, as they need to match the expressive capabilities of the human face, it is no wonder that they are complex mechanical systems containing inevitable non-linear and hysteresis elements derived from their non-rigid components. Identifying the input-output response properties of this complex system is necessary to design surface deformations accurately and precisely. However, to date, android faces have been used without careful system identification and thus remain black boxes. In this study, the static responses of three-dimensional displacements were investigated for 116 facial surface points against a discrete trapezoidal input provided to each actuator in the face of a child-type android robot Affetto. The results show that the response curves can be modeled with hysteretical sigmoid functions, and that the response properties of the face actuators, including sensitivity, hysteresis, and dyssynchrony, were quite different. The paper further proposes a design methodology for surface motion patterns based on the obtained response models. Design results thus obtained indicate that the proposed response properties enable us to predict the design results, and that the proposed design methodology can cancel the differences among the response curves of the actuators. The proposed identification and quantitative evaluation method can be applied to advanced android face studies instead of conventional qualitative evaluation methodologies.
Highlights
Robot faces are important information display devices that show several types of communication cues such as intention, attention, emotion, and demand, with the combined deformations of several facial parts
The names of the n-th deformation unit (DU) (n = 1, · · ·, 16) are listed in the figure; blue indicates the DUs without sensory feedback, and green indicates the DUs with sensory feedback; and the dotted loops indicate the approximate regions where the skin sheet and movable mechanical parts were connected for each DU
This complex spatial distribution of displacements suggests that the conventional descriptions of android robot faces, with the number, approximate positions, and representative directions of movable mechanical parts, as shown in Figure 2, is insufficient for precisely representing the system performance because the actual displacement distributions are so complicated that they cannot be estimated from the conventional descriptions
Summary
Robot faces are important information display devices that show several types of communication cues such as intention, attention, emotion, and demand, with the combined deformations of several facial parts. Identification of Android Robot Face shells to maintain a life-like shape and is connected to internal movable mechanical parts at several points. These movable parts are driven by an actuation system that moves the connection points, and their displacements are propagated on the skin around them according to both the stiffness distributions of the skin sheet and the friction conditions between the skin sheet and internal shells. The static and dynamic frictions between the skin sheet and shells cause motion hysteresis, and the frictions may change temporally depending on subtle fluctuations in the contact conditions between the skin sheet and shells
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