The inertial properties (mass, center of gravity, and inertia tensor) of an object are fundamental and important input values. They have a significant effect on the accuracy of human motion simulation. Thus, an accurate identification method of inertial properties is crucial. All inertial properties of individual links modeled with multiple links cannot be identified from the link motion, interjoint torque, or external force data because they are redundant to the multibody dynamics model. Minimum dynamic parameters needed to represent the multibody dynamics model have been defined and identified. These dynamic parameters are obtained by combining the geometric parameters and inertial properties of the counterpart elements and are called the minimum set of inertial parameters (MSIP). A set of measured link motions and ground reaction forces are utilized in conventional identification methods. The MSIP for a sagittal plane can be identified from motions such as the walking motion of human bodies. However, it is difficult to perform three-dimensional identification, including planes beyond the sagittal plane. Therefore, a new method for identifying MSIP by expanding and applying free vibration measurements has been developed. With this method, highly accurate three-dimensional identification has been demonstrated using a mock-up model of the human body consisting of two links made of iron. However, the human body is complex and possesses flexibility due to muscles and organs, making it uncertain whether the developed method, which assumes a rigid body model, can be applied. In this study, appropriate identification procedures and conditions were examined to apply the developed method to the complex and multi-degree-of-freedom human body. The results demonstrated that valid identification of the MSIP can be obtained without exciting the body’s flexibility.

The commonly used screw propellers are known to suffer from issues such as sludge agitation and safety concerns for aquatic organisms. This has resulted in the exploration of biomimetic propulsion mechanisms. Previous research in bio-normative in-fluid propulsion systems has focused on mimicking the swimming patterns of organisms adapted to specific environments, including body and/or caudal fin (BCF) locomotion in fish for high Reynolds number (Re) regions and ciliary or wavelike motions in microorganisms for low Re regions. Thus, this study focused on the development of a flexible biomimetic propulsion mechanism inspired by the deformation movements of Euglena, aiming to create a propulsion system that achieves low environmental impact and universal adaptability. The objective was to enable advanced deformation and diverse motion patterns through the sliding motion of the pellicular strips on the cell surface, thereby replicating Euglena 's elastic and highly deformable movements to achieve multiple swimming modes. This technology can facilitate the realization of a versatile in-fluid propulsion mechanism that can emulate the swimming morphology of various organisms within a single system. To achieve this, we proposed a novel high-degree-of-freedom deformation mechanism using a composite sliding structure of porous polytetrafluoroethylene (PTFE) sheets driven by rectangular cross-section coil shape memory alloy (SMA) actuators (SMAAs). A prototype of the proposed mechanism was fabricated. Although the ultimate goal is to achieve three-dimensional motion, initial evaluations were conducted in two-dimensional motion for simplicity and foundational analysis. As a result, experiments were conducted to verify its effectiveness and evaluate its potential for reproducing EM and adapting to various swimming modes. The SMAA-loaded porous PTFE fibers exhibited S-shaped bending deformation owing to the sliding motion of multiple fibers, similar to the deformation principle of Euglena. Further experiments with different driving patterns indicated the possibility of locally controlling the deformation within the structure. Moreover, it was suggested that modifying the mechanism to increase the degree of freedom by ensuring a fixed distance between the porous PTFE fibers while facilitating sliding could enhance motion efficiency and adaptability, making it suitable for achieving various swimming modes, including those observed in both low- and high- Re regimes.