Legged robots offer superior terrain traversability compared to wheeled robots, making them a focus of extensive research. The performance of legged robots depends on their leg mechanisms. Among the various options, leg mechanisms utilizing link mechanism provide advantages in energy efficiency and load capability. However, the design of link leg mechanisms is nontrivial because the analytical design of the link mechanisms is challenging due to their nonlinear nature. Thus, our preliminary research developed a new design method for one-degree-of-freedom link leg mechanisms, one of the simplest link mechanisms, as a foundational step toward a comprehensive design method of link leg mechanisms. While this method could design functional link leg mechanisms, their performance was insufficient for properly walking because they were designed through single-objective optimization to maximize walking distance. In this study, we extend the method incorporating multi-objective optimization, Nondominated Sorting Genetic Algorithm II (NSGA-II). This approach includes two additional objectives: maximizing foot lift height and minimizing body rocking. We also refined the decoding technique to address the problem identified in our preliminary research. The improved method can design link leg mechanisms with the performance required for effective locomotion, and a fabricated link leg mechanism based on a resulting design demonstrates this capability in real-world environments.

Recent progress in aerospace technology has brought the creation of reusable space vehicles, thereby increasing demand for thermal protection systems (TPS). Fibrous insulating materials coated with high-emissivity materials are used in modern reusable space vehicles as insulation for suppressing radiant heat transfer. To realize radiative insulation with a high-emissivity layer, low-thermal-conductivity materials with sufficient thickness have been required, and considerations such as reduced brittleness and ease of handling have generally been secondary. Porous MgAl2O4 ceramics with 1–5 μm pores and grain clusters exhibit high reflectance and low emissivity in the 1–5 μm wavelength range because of their diffuse reflectance based on Mie theory. These properties are the suppression of heat input through low emissivity, which results in a space-saving in the thermal insulation layer. Porous MgAl2O4 ceramic coatings were formed on Ti–6Al–4V surfaces by low-temperature flame spraying to mitigate brittleness and were investigated in vacuum under radiant heating using an infrared lamp system. The spraying changed the microstructural shape and denser. However, these pores and grains of 1–5 μm, corresponding to the wavelength of radiation, remained. Infrared heating tests in vacuum confirmed that the coating restricted radiation transfer only at 1 mm thickness. Consequently, materials that combine low emissivity with high-temperature stability are considered essential for enhancing the flexibility, reliability, and performance of thermal control systems in next-generation aerospace applications.

A vibration energy harvester generates power by utilizing resonance. Stationary sine-wave excitation is a common method of evaluating vibration energy harvesters. However, environmental vibrations are often non-stationary. For example, human vibrations are often impulse vibrations with large instantaneous accelerations. In this study, we applied impulse vibrations to a piezoelectric vibration energy harvester (PVEH) and evaluated the input acceleration of the impulse vibrations, deflection, and output power waveforms. The PVEH was fabricated into a cantilever shape, and the resonance frequencies were varied by attaching different proof masses. Based on the results of the experiment and FEM analysis, it was observed that the pulse width of the input impulse vibration and the resonance frequency of the PVEH at which the maximum output power was obtained were inversely proportional. The conventional design method of matching the resonance frequency of a PVEH to the number of impulse vibrations per second results in challenges regarding the size and complexity of the device. However, the proposed method focuses on the acceleration waveform of impulse vibrations, making it effective even when the input vibrations are non-periodic. In addition, the proposed design method can generate high power with a small and simple structure. Therefore, it is promising for application in wearable devices.

The crack growth rate of stress corrosion cracking is influenced by residual stress; therefore, if the three-dimensional residual stress in welded pipes can be accurately evaluated, their remaining service life may be predicted. While welding simulations offer a means of assessing residual stress, but weld joining techniques are known to yield significant individual variations even under similar welding conditions. Consequently, a residual stress evaluation grounded in actual measurement data is essential. A non-destructive method for estimating three-dimensional residual stress distribution in situ employs X-ray Diffraction alongside eigenstrain theory. In this approach, the eigenstrain of the entire structure is derived through inverse analysis of measured surface elastic strain values, with three-dimensional residual stresses subsequently calculated by inputting these estimated eigenstrains into a finite element (FE) model. However, to estimate three-dimensional eigenstrains from two-dimensional surface data, it is necessary to appropriately reduce the number of unknown variables. Function approximation serves as an effective method for this reduction, though its optimization is required, as the accuracy of the estimation depends on the function's shape. Previous studies have typically relied on empirical methods to determine the shape of this function. This study first elucidates, through numerical analysis, the challenges associated with empirically defining the approximate function shape of eigenstrain. Subsequently, a novel method is proposed, approximating the eigenstrain by employing a superposition of Chebyshev polynomials and Gaussian functions and optimizing the function’s shape with relatively few parameters. The proposed method’s effectiveness is demonstrated via numerical analysis, aiming to establish an approach that eliminates reliance on empirical assumptions.

The Rules on Fitness-for-Service of the Japan Society of Mechanical Engineers (the rules on FFS) stipulates the limit load evaluation method based on the plastic collapse strength as one of the fracture evaluation methods for pipes with circumferential flaws. However, since the limit load evaluation method treats flaws as a decrease in thickness regardless of their location, the internal pressure acting on the flaw surface is not taken into consideration even when the flaws are on the inner surface of the pipe. The limit load evaluation method that takes into account the effect of the internal pressure acting on the flaw surface was derived, and the results were compared for plastic collapse loads with and without considering the internal pressure acting on the flaw surface. When the flaw was shallow and its angle was small, both plastic collapse loads were almost the same. However, when the flaw was deep and its angle was large, the plastic collapse load decreased due to the internal pressure acting on the flaw surface. Especially when the internal pressure was high, the impact was large. In the rules on FFS, the safety factor is taken into consideration in the evaluation of allowable stress, and the flaw depth is limited by a regulatory requirement when the flaw angle exceeds 60°. Due to this consideration and requirement, the impact of internal pressure acting on the flaw surface on collapse strength is negligible. If the flaw depth limitation is eliminated when the flaw angle exceeds 60° or when accurate fracture strength has to be evaluated such as in reliability evaluation, the plastic collapse evaluation formula that take into account the effect of pressure acting on the flaw surface should be employed.

Ground reaction force (GRF) analysis is critical to evaluate gait and running performances. However, installing force plates on the ground surface is costly, and their transportation is challenging owing to weight constraints and restricted measurement areas. This study proposes the method by Extended Kalman filter (EKF) to estimate the three-axis force components in the GRF, utilizing vertical force data from insole sensors, angular velocity, and acceleration data from inertial measurement units (IMUs). Shear forces were calculated using the acceleration in global coordinates, with the equivalent mass calculated by the vertical force and acceleration. The force components were then compensated for sensitivity and interference using a matrix. Moreover, the method was extended to include the center of pressure and unit position vector. The experimental protocol comprised two phases: calibration and measurement, conducted on force plates installed on the ground surface. The error compensation for force components was based on actual gait motion data and the results were compared with the force plates' outputs. The findings confirmed the effectiveness of this method. This method will be expanded to include motion measurements during long-distance walking and outdoor environments.

Tapping inspections of structures are commonly performed manually by technicians. However, in the case of nuclear structures and other hazardous environments, maintaining a safe distance from the inspection target is preferable. Additionally, there is a growing demand for automated inspection methods. This study proposes a novel remote tapping inspection method that eliminates the need for close proximity to the object. Our approach employs a String-Shoot Impactor, a device inspired by a string shooter toy, which propels a looped string into the air using rollers. By attaching a 4 mm diameter stainless steel ball to the string, we enable remote tapping of inspection targets. In this study, remote tapping tests were conducted from a distance of 2 meters, and the impact sounds were analyzed using frequency spectrum mapping. The results successfully distinguished defect areas from intact regions in a concrete specimen with a 300 mm diameter void defect. To further extend the inspection range, a high-speed String-Shoot Impactor was developed. The previous device, driven by a speed control motor with a maximum rotation speed of 1400 rpm, achieved a maximum launch velocity of 9.2 m/s. By replacing this motor with a brushless motor capable of 4000 rpm, the launch velocity was increased to 26 m/s, enabling an inspection distance of up to 3 meters. Additionally, the impactor was redesigned with three rollers, improving string retrieval performance and stabilizing the launching mechanism. Mounting the impactor on a tripod allowed smooth adjustment of the impact point, enhancing usability. The results demonstrate that this method enables remote tapping inspections from distances of several centimeters to several meters and can be applied in various orientations, from horizontal to vertical. Furthermore, by integrating the device into a suspended inspection setup, it becomes possible to inspect structures that are difficult to access from the ground.

Preventing falls is crucial for the elderly, and as an initial step, accurately quantifying their current balance abilities is essential. In this regard, the Center of Pressure (COP) has gained attention. This study proposes a novel mechanical model to accurately reproduce the human COP. If the proposed model can reproduce the human COP with high accuracy, it would enable the quantitative representation of human balance motion characteristics using model parameters. In this study, we first measured the time series of COP in a standing position from six subjects and constructed the Probability Density Function (PDF) of human COP. To reproduce this PDF, we propose a mechanical model that considers the human body as an inverted pendulum and the human foot as a triangular rigid body supported by viscoelastic material. The model control involves PD control incorporating randomness and dead-band effects. As a result, the proposed model successfully reproduced the characteristics, such as unimodal-peak and bimodal-peak patterns, observed in the human PDF by adjusting the control parameters. Specifically, the reproduction accuracy, which represents the agreement between the human and model PDFs, was over 87%, with an average of 96%. Moreover, we investigated the effect of model parameters on the PDF shape and clarified that increasing the effects of the PD control gain led to the emergence of unimodal-peak characteristics, whereas decreasing the gains resulted in bimodal-peak characteristics. Based on these results, we confirm that our proposed model can effectively parameterize human balancing behavior as observed in the PDF of COP.

This paper discusses a trajectory tracking control problem for the development of autonomous vehicles. The reference trajectory is generated by a kinematic model which is nonholonomically constrained not to skid at the rear drive wheels. A nonlinear dynamical controller to follow the trajectory is proposed by applying backstepping (BS) method, together with Dynamic Surface Control (DSC) to solve the so called “problem of explosion of terms in the BS method”. Ultimate boundedness of the closed-loop system is investigated. Finally, simulation results illustrate the effectiveness of the proposed controller.

This study addresses the challenge of reducing variability in permeability measurements for the vacuum-assisted resin transfer molding (VaRTM) process, which is essential for accurately evaluating resin impregnation behavior. Initial evaluations were conducted at two different institutions, comparing permeability in both the 0° and 90° fiber directions of carbon fiber plain-woven fabric to identify key challenges contributing to variability. The comparison revealed significant differences in permeability results due to inconsistencies in experimental settings and measurement methods. Based on these findings, improvements were proposed, including temperature control, adjustment of resin impregnation levels, and standardization of VaRTM settings and measurement methods. These improvements were then applied to the 0° direction under the minimum nesting condition. Results showed that the improved methodology significantly reduced variability, with differences between bottom and area measurements being less than 10%, and an average variability of 17%. This approach effectively minimizes variability in permeability measurements, enhancing the reliability of the VaRTM process.