In the field of die and mold machining, determining appropriate cutting conditions is crucial. Factors such as tool geometry, machining path, work material characteristics, machining efficiency, and finishing accuracy must be taken into consideration. However, the current method of determining cutting conditions relies heavily on the intuition and experience of skilled engineers, and there is a need for a system to replace such knowledge. One of the critical factors affecting machining accuracy and efficiency is the tool overhang length, which is directly related to tool geometry. Unfortunately, there is no clear guideline for its determination. In a previous study, researchers developed a system to quickly derive cutting conditions using a data mining method and Random Forest Regression (RFR) applied to a tool catalog database. In this study, we constructed a new cutting condition compensation system based on the existing model, which accounts for the tool overhang length. The results of cutting experiments under high aspect ratio overhang lengths confirm that the correction coefficients proposed by the system are significant.

To achieve reliable logistics, the construction of transportation infrastructure is essential, and the safety guarantees of various types of poles are required as well. A cyclic bending loading test is commonly conducted to investigate the fatigue strength of lighting poles. In the actual service environment, the loading mode may be not only simple bending but also torsion or a mixture of both. In addition, the base plate of the lighting pole is strengthened by a rib weld, and it is essential to understand the cracking from the stress concentrated point at that section and to obtain the fatigue property data. In the present work, we designed and developed a fatigue testing system that can conduct cyclic loading using two hydraulic actuators in a desired loading mode to the actual lighting pole. The fatigue strength property investigation in an arbitrary loading mode was made possible by controlling the movement of the two hydraulic actuators. The effect of the shape of the strengthening ribs on the fatigue strength of the base of lighting poles was investigated using two different rib shapes, and it was confirmed that the U-shaped ribs had a better fatigue life than the triangular-shaped ribs.

This paper proposes the fluorescence response-based optical probing (FROP) method for the 3-dimensional measurement of precise products. Several 3-dimensional measurement methods exist, such as micro-coordinate measuring machines, confocal microscopy, and point autofocus microscopy. However, measuring precise products with small, smooth, and steep (3S) structures—such as die molds and optical lenses—remains challenging. In this study, we propose a new surface detection scheme that utilizes autofluorescence from the sample surface. Unlike reflected light, fluorescence is emitted over a wide angle. Therefore, the optical response from the surfaces of 3S structures can be obtained by exciting fluorescence at the measured surfaces. This paper first explained the principle of FROP. Next, the fundamental FROP signal was examined on surfaces tilted at different angles. The FROP successfully detected vertical and even overhanging surfaces, demonstrating its strong potential for 3-dimensional measurement. The principle of surface position determination was then verified through comparisons with conventional confocal microscopy for 2.5D measurements, and thickness measurement results were compared with micrometer results. These results revealed that the peak position of the differentiation signal in FROP coincided with the sample surface. Finally, a 3-dimensional 3S structure was measured. The results confirmed that vertical surfaces could be successfully measured using the FROP method, whereas conventional confocal microscopy could not measure them. Consequently, the performance of FROP for 3-dimensional measurement of precise products was validated.

Critical resolved shear stress (CRSS) is one of the most important parameters in the field of plasticity in metals, and the CRSS ratios between slip systems govern the plastic anisotropy, workability, and so on. Therefore, it is highly valuable to develop a system that can predict CRSS ratios with high accuracy in a short period of time. With the above background, Sato et al. (Transactions of JSME (in Japanese), (2023)) developed a system to predict CRSS ratios using distributions of strain and crystal orientation. However, the system requires much time to predict CRSS ratios. In this study, a new CRSS ratio prediction system with low computational cost has developed by devising a calculation method and introducing the covariance matrix adaptation evolution strategy (CMA-ES), a method of meta-heuristics. The validation of system was conducted by prediction of CRSS ratios in virtual hexagonal close-packed (HCP) materials from the strain distributions obtained by a crystal plasticity finite element method (CPFEM) and crystal orientation distributions. The validation results showed that the prediction of CRSS ratios for <a> slip systems was success and the accuracy was similar when information from all measurement points and when representative values for individual grains were used. The prediction accuracy was also the same level when the method introducing CMA-ES was employed. These results indicate that the developed system can predict CRSS ratios for <a> slip systems in HCP metals within seconds.

This study evaluates the effects of forced chatter vibration on the shape of bamboo fibers for the production of 100% bamboo molds. Considering that fiber shape variation during end milling affects the mechanical properties of the molded product, we first determined the effect of bamboo cylinder shape on natural vibration through impact testing and finite element analysis. Based on these results and the temperature at the time of cutting, cutting conditions that do not resonate with the natural frequency were examined, and it was found that a ratio of approximately 4.5 between the natural frequency and intermittent cutting frequency was appropriate. Next, we investigated the effect of the relationship between the endmill's intermittent cutting frequency and the natural frequency of bamboo on fiber shape. The results showed that when the ratio of the endmill's intermittent cutting frequency to the bamboo's first- and second-order natural frequencies was an integer multiple, resonance increased the vibration of the bamboo cylinder, which decreased the average width of the extracted fibers and increased their standard deviation. It was also shown that the effect of third-order natural frequencies was small. Further investigation of the effect of height variation confirmed that at heights below 125 mm the vibration amplitude was sufficiently small to have no effect on the mean or standard deviation of the fiber widths.

Automotive torsional dampers are designed to absorb torque fluctuations generated by the engine and deliver a smoother torque to the components located toward the rear. During the torsion evaluation test of these dampers, torsional torque is repeatedly applied while the damper rotates. Given that torsional dampers consist of dead zone elements and multi-stage spring elements, achieving effective torque control can be challenging during these evaluations. In this study, we proposed a method to enhance the performance of the torque control system used in traditional torsional evaluation test machines. Our approach involves modifying the target torsional torque reference by adding a one-pulse signal. Then, the shape of this one-pulse signal is determined through Bayesian optimization. We validated the effectiveness of this proposed method through both simulations and an experiment conducted on actual equipment.

Various training techniques have been devised to capture motion data during real-time walking and provide feedback to trainees, allowing them to adjust their gait to align the measured gait parameters with target values. However, these methods may not suit all individuals owing to physical differences. To address this, in our previous research, we used a MC-DCNN to classify gait based on ideal and non-ideal features. Activation maximization was applied to generate target gaits; however, the method did not account for human walking dynamics, thereby sometimes resulting in unnatural gait patterns. Consequently, some generated data exhibited unnatural values for human gait. Additionally, the constructed model was based on experimental data from eight young males wearing age-simulation suits, raising concerns about its applicability to actual older adults. In this study, we addressed these limitations by collecting gait data from adults aged over 65 years, including 10 males (70.6±2.5 years) and 8 females (70.6±2.8 years), as well as younger adults, including 8 males (22.1±0.8 years) and 7 females (20.7±0.5 years). Based on this dataset, we utilized the structure of a generative adversarial network (GAN) and leveraged identity loss and cycle consistency loss from CycleGAN to generate target gaits. Additionally, the generator model was designed to reflect both the temporal features of gait and the dependencies between gait variables. Consequently, the proposed model successfully converted gaits frequently associated with stumbling into gaits rarely associated with stumbling, depending on the degree of gait instability.

Active control of flow separation on a bluff body model utilizing dielectric barrier discharge plasma actuators (DBD-PAs) was experimentally demonstrated at Re = 28,000. The model consisting of a flat side plate and a quarter cylinder with a radius of 84.5 mm was placed 200 mm downstream from the exit of the blowing-type wind tunnel and fixed at a yaw angle of 10 degrees relative to the main flow. In the conventional spanwise arrangement of exposed electrode utilizing a string-array-type plasma actuator consisting of six Cu wires coated with silicone rubber and exposed electrodes, the control effect significantly decreased as the distance from the separation point increases. Therefore, blowing-type and suction-type vortex generating plasma actuators (VG-PAs) with exposed electrodes arranged in the streamwise direction were prototyped by combining the string- array-type DBD-PAs, and the effects of suppressing flow separation were verified by generating blowing and suction jets. Both blowing-type and suction-type VG-PAs were effective in suppressing flow separation, with the blowing jet reducing the displacement thickness by 64% and the suction one reducing it by 85% compared to the no control case. Strain rate analysis of the Y-Z cross section revealed that the control effect of the suction-type VG-PA can be obtained over a wider range in the spanwise direction than that of the blowing type VG-PA.

Optimizing stiffened panel structures used in ships and aircrafts are becoming increasingly important for reducing material costs while maintaining or enhancing structural strength. These structures require simultaneous optimization of continuous design variables (panel thicknesses) and discrete design variables (stiffener cross-sectional shapes), making gradient-based methods less applicable. Consequently, heuristic approaches such as Genetic Algorithms (GA) are often employed; however, GA typically imposes a high computational burden in large-scale optimization problems. To address this, the use of deep reinforcement learning (DRL) has been investigated for large-scale combinatorial optimization. Among DRL approaches, Double Deep Q-Network (DDQN) has been reported as effective, yet its application to structural optimization involving high computational demands from Finite Element Analysis (FEA) remains limited. To overcome such an environment, in this study, an optimization flow for structural optimization is considered, and states, actions, and rewards appropriately representing design variables, constraint conditions, and objective functions are discussed. In addition, this study also proposes incorporating an elite-preservation algorithm into DDQN to reduce the computational load of structural optimization. Experimental results show that the proposed method yields designs under various load conditions that are up to 6% lighter than those obtained using GA, with a computational time reduction of approximately 81%. These findings confirm the feasibility of efficient and effective optimization for stiffened panel structures and suggest potential benefits in cost reduction and performance enhancement in future structural designs.

Various devices have been developed in recent years to assist human jumping using plate springs, rubber tubes, and other means. Nevertheless, using products of many kinds is difficult because they generate jumping force with human ankles fixed. Cooperating with human users is favorable for enhancing both usability and jumping height. Some researchers have adopted this approach. Unfortunately, the jumping height remains insufficient. As described in this paper, we have developed devices of two types that emphasize cooperation with the human user: a rotational model and a linear model. The former, which is used for comparison purposes, provides floor reaction force using a rotational mechanism similarly to a human ankle joint. The latter provides normal force using the Scott–Russell mechanism, which moves in the vertical direction. Moreover, this mechanism enables the user to generate floor reaction force for a longer duration. Experimentation demonstrated that the jumping height with the linear model increased by approximately 0.8 – 35% (0.4 – 12.4 cm) compared to that without a device. Moreover, the duration generating the jumping force when using the linear model increased by approximately 34% compared to that obtained when using the rotational model.

In this study, we investigated the propagation and reflection behavior of thermal and elastic waves based on a dynamic thermoelastic equation coupled with a non-Fourier heat conduction equation for two-dimensional plate problems under plane stress condition. This paper focuses on numerical simulations of photoacoustic microscopy and reports the results of assuming circular defects near the surface of a two-dimensional plate to investigate the effects of differences in defect size and depth on the temperature and particle velocity along the plate surface and stress distribution in the plate. It was found that the presence of defects caused thermal and elastic waves to be reflected and synthesized, resulting in large oscillations in these distributions. In particular, it was observed that the temperature distribution was concentrated at the tip of the defect, and it was confirmed that the defect shape has a strong influence on the surface temperature distribution.

Table tennis, a sport that is played widely around the world, and even at the Olympics, is also a recreational sport enjoyed in diverse facilities that can accommodate table tennis tables. Table tennis ball rotation during the game is not well understood because the ball rotation is nearly invisible to observers and players. This study was conducted to elucidate table tennis ball behavior, such as its rotation, that a table tennis player senses through the table tennis racket with eyes, ears, and tactile sense. The rotational and translational motions of balls of various rotations launched from a table tennis machine were assessed using a high-speed camera. After balls with various rotations were made to collide with a racket fixed at 90 degrees to the ground, the racket strain was examined at eight points. A ball with no rotation was free-fallen; it collided with a racket fixed horizontally. Fast Fourier transform analysis was applied to the strain values of the ball impacting the racket tip and the racket center. The kinetic energy values of the ball before and after impact were compared. Findings indicated that the number of rotations of the ball decreased after the struck the racket. When a ball with rotation is struck with the racket, the vibration caused by the grip strain persists for a long time (0.2 s). When the ball has free-fallen in the racket center, the vibration is less than when it has free-fallen at the racket edge area. Players are thought to sense the ball rotation not only with their eyes and ears, but also as tactile information related to the vibration strength of the grip section. The racket vibration shapes differ when a ball strikes the racket center and when it hits the racket edge area. Specifically, less vibration is felt when the ball hits the racket center, thereby enabling the player to return the ball skillfully with high speed, power, high ball rotation, etc.

Approximately half of all traffic fatalities involve pedestrians and cyclists, and exceeding the speed limit is one of the most serious factors causing fatal accidents. The use of an Intelligent Speed Assistance system (ISA) is being considered to reduce the number of traffic accidents caused by exceeding the speed limit. ISAs indicate the speed limit information to drivers or perform a control intervention to avoid exceeding the speed limit. The purpose of this study was to investigate the effects of compliance with the speed limit on reducing the number of vehicle-cyclist collisions, by using a near-miss incident database. This study sought to estimate the effects of an ISA, which provides control interventions to ensure that travel speeds do not exceed the speed limit. In the database, we extracted near-miss incident data that cyclists initiated a road-crossing from blind intersections with speed limits of 30 km/h (i.e., 956 cases), and defined a safety margin as the axis of the effect of accident prevention. Subsequently, the effect of compliance with the speed limit by the ISA on ensuring the safety margin under hazardous events caused by exceeding the speed limit was analyzed. The limitations of the effect of compliance with the speed limit by the ISA were also assessed. The data analysis revealed the following. Of the 956 cases, 129 cases (13 %) showed insufficient safety margins due to exceeding the speed limit. The frequency with which the use of the ISA can be effective in ensuring safety was not high. However, of the 129 cases, 100 cases (78 %) showed that the use of the ISA led to an adequate safety margin; the use of the ISA increased the time available for accident prevention by an average of 0.74 s. The results of this data analysis can contribute to the discussion on the social implementation of ISAs.

A method for detecting misfires in internal combustion engines using information from the ignition coil's discharge has been developed. A dual discharge concept has been adopted, in which a sub-discharge for detecting misfires is carried out during the expansion stroke following the main-discharge for ignition. The peak value of the primary voltage of the ignition coil and the discharge duration have been selected as discharge feature values for determining misfires. Verification results using a single-cylinder engine confirmed that high misfire detection accuracy can be obtained by optimising the timing of the sub-discharge and the dwell period.

Various testing methods for adhesive strength are prescribed in JIS but no testing method is indicated under no singular stress field. Usually, strength of materials should be considered for plane specimens where uniform stress distributions can be expected. However, in the case of adhesive strength evaluation, all bonded specimens exhibit a singular stress field, the intensity of which (ISSF) varies depending on the adhesive layer geometry. This is the reason why the adhesive strength varies depending on the adhesive layer geometry. In this paper, therefore, a protruding butt joint is proposed to obtain a constant interface stress distribution. Then, the essential adhesive strength is clarified under uniform interface stress without localized stress concentrations. Unlike standard butt joints, where strength is significantly affected by adhesive layer thickness h, it was found that the adhesive strength in the proposed joint remains constant at critical stress σ_B = 47.7 MPa, regardless of h. It is also found that in JIS butt joints, the border at h=0.1 mm allows a distinction between fracture due to internal stress and fracture due to a singular stress field. In the case of failure due to a singular stress field, by calculating the region (process zone) where the average stress is the original strength of the butt joint, σ_B = 47.7 MPa, it is thought that failure will occur at a position r_B = 14.7 μm from the adhesive end. This is almost equal to the fracture origin of a rectangular column butt joint reported in a previous study, and can be said to be a reliable evaluation method.

There are many requirements, issues and complexities that engineering design problems must take into account, and these engineering items are often treated as constraints in optimization problems. The constraint optimization problems (COPs) are the most popular type of problems, therefore, optimization algorithms for the COPs have been attracted more and more attention. Particle swarm optimization is one of the most popular algorithms for solving the COPs due to the simplicity and efficient convergence performance, and various types of PSO are actively developed in recent years. However, despite the popularity, they still have limitations in terms of search efficiency. Notably, it takes a lot of calculation costs to obtain the optimal solution on the boundary of constraints or the complicated feasible area. To overcome the difficulties, this paper presents a novel particle swarm optimization algorithm named independent 2-group particle swarm optimization (I2GPSO). I2GPSO is based on the following ideas - a constraint handling method, a novel structure of particles and a novel local search operator. The constraint handling method uses the existing penalty function method. The structure of particles defines two particle groups that have original roles, efficiently enabling PSO to search globally and locally. The local search operator is introduced into one group and enables particles to search near the boundary of constraints efficiently or candidates of the optimal solution. These novel approaches effectively reinforce the optimization efficiency of the PSO algorithm. The optimization capability and character of I2GPSO is illustrated in 11 benchmark problems. The results are compared with other state-of-the-art PSOs, and it is shown that the proposed algorithm possesses competitive search efficiency.

We expect that gait will be useful information for detecting wandering and managing the health of elderly people utilizing a monitoring support robot. However, some kind of sensor is needed to extract pedestrian gait features. In this paper, we proposed a privacy-aware method of extracting gait features from pedestrians’ feet only. This paper describes methods for detecting frames in which heel-strike and toe-off events occurred in foot video, and for extracting the heel contact position in the image. Firstly, dynamic regions were extracted utilizing edge detection and optical flow, and then clustering was used to extract pedestrians’ feet regions. Subsequently, the acceleration field was estimated using optical flow, the acceleration was decomposed into tangential and radial components, and the radial component acceleration was used to detect heel-strike frame. Next, we extracted static regions in the pedestrians’ feet region by utilizing edge detection, optical flow, clustered foot regions, and motion characteristics during gait, and finally performed toe-off frame detection. The heel contact position in the image was extracted by using Otsu’s binarization and static region. We conducted gait experiments with several camera direction conditions and applied it to the system. The RMSE of the estimated and true values for heel-strike and toe-off frame detection were within about one frame in all conditions, and the F-measure was above 80 % in all conditions. The F-measure for heel contact position detection also exceeded 80 % in all conditions.

Tensegrity structures are lightweight structures, often deployable, consisting of axial members (rods and cables). One of their design problems is to determine the minimum member mass to support an external force under the buckling and yielding conditions. In the previous work, the deformation of the structure is not considered, and the equilibrium position is assumed to be known in advance. However, when the structure is subjected to an asymmetric force, for example, the equilibrium position is not obvious and is typically unknown. As a more realistic problem setting, this study discusses a minimal mass design considering the deformation by an asymmetric external force. The self-equilibrated configuration is chosen as the initial configuration for the optimization. The internal force at this configuration is called the prestress, and is often utilized to improve structural stability and stiffness. The problem setting in this paper also allows us to introduce the prestress in the design. Mechanical formulae considering the deformation without the prestress are first derived. A minimal mass design problem allowing the deformation can be formulated by using these formulae. The problem is a nonlinear problem with many variables, and requires proper initial estimates. The paper also addresses this issue by employing dynamical simulation. The prestress can be introduced by modifying the member force calculation in the above formulae. Numerical examples are conducted to show the efficiency of the proposed method.

The damping performance of a rolling-ball damper was examined experimentally and numerically. The damper consists of multiple rolling balls on a circular track attached to the main vibration body. Since, unlike mass-spring-tuned mass dampers, it does not use a spring, it is far superior in durability. Moreover, the cover of the damper ensures that the rolling balls will not jump out from the track. However, determining the combination of parameters that maximize performance remains challenging. In this study, we used a novel evolutionary algorithm and the discrete element method. In terms of convergence and calculation time, we compared the particle swarm optimization (PSO) and cuckoo search algorithms and chose PSO as the evolutionary algorithm. To verify the validity of the numerical method, an experimental apparatus that acts as an equivalent horizontal single-degree-of-freedom system was used. The main vibration body is excited sinusoidally at the support using a motor and a slider-crank mechanism. Steel balls were used as rolling balls. The displacement of the support and the main vibration body was measured using two laser displacement sensors. The numerical results were compared with the experimental results for the relationship between amplitude and frequency to verify the validity of the numerical method.

This paper deals with an advanced version of eMDVA (embedded Mass Dynamic Vibration Absorber), which is a passive multi-modal damping device that was proposed by the authors. The eMDVA consists of a mass embedded in a viscoelastic material, and the mass can vibrate freely in all directions. The authors showed in their former works that the eMDVA consisting of a single mass sphere embedded in a spherical or elliptical viscoelastic material with a constrained outer shape is valid for multiple vibration control target frequencies. Considering practical use, the authors are developing another configuration of the eMDVA where many masses are dispersed and embedded in a sheet-like viscoelastic material. While the original eMDVA utilizes the multi-directional vibrations of the embedded mass as a multi-modal dynamic vibration absorber, the sheet-like configuration achieves multi-modal vibration damping by using different sizes of masses. In this work, we take up an eMDVA in which a mass sphere is embedded in a cuboid viscoelastic material, assuming a partial element of the sheet-like eMDVA and the influence of the external shape of the viscoelastic material on the vibration of the embedded mass is investigated using finite element analysis. It is shown that the peak frequencies of the frequency response function (corresponding to natural frequencies of the embedded masses) can be adjusted by changing the diameter of the mass sphere and the thickness of the viscoelastic material, and this means the sheet-like eMDVA can be designed by the size of the embedded mass sphere. The numerical and experimental results are described in this paper, including the configuration of multiple masses embedded in the viscoelastic material side by side. In addition, a series of excitation tests are conducted using a plate-like structure, a 1:10 scale model of a railway vehicle’s underframe, and the multi-modal vibration reduction effect by the eMDVA has been confirmed.

This paper proposes a simple passive device with an adjustment mechanism for spring constant and damping coefficient to realize a dynamic vibration absorber (DVA) that can be used for various vibration control target frequencies. The proposed device consists of a coil spring and an air spring with an auxiliary reservoir and orifice. The active coil of the device's coil spring can be varied to adjust the spring constant. The main tank and reservoir tank are separated by an "orifice disk" with several orifices of different diameters, and the damping coefficient can be changed by selecting one of these orifices. A numerical model was constructed to design the spring constant and damping coefficient, and a DVA equipped with the proposed adjustment mechanism was developed. The results of stand-alone vibration tests showed that the changing trend of vibration response property agreed well with the numerical results, and the proposed adjustment mechanism worked well. Then, vibration control tests were conducted by mounting a dynamic vibration absorber on a plate-like structure that simulates the underframe of a railroad car at approximately 1/10 scale. As a result, a significant vibration reduction was successfully achieved for the bending mode of elastic vibration, and the usefulness of the proposed spring constant and damping coefficient adjustment mechanism was confirmed by adjusting the optimum spring constant and damping coefficient values, which varied at each measurement point.

Helical springs are used for many mechanisms. Rectangular wire helical springs are used in machines that require large spring loads, such as press machines, die machines, injection molding machines, construction machines, and load testing machines. Design formulas for the rectangular wire helical springs were given by Liesecke. However, pitch angle of the helical spring is neglected in his formulas, and they are inconvenient because we have to read factors used in the formulas from graphs. And, Shimizu et al. derived a theoretical equation, but there are still differences between values calculated by the equations and the FEM analysis results although a trend is consistent. And, the practical design equations are desired to be simple. Therefore, in this paper, simple practical design equations of the spring constant and the maximum shear stress are derived by using a fractional expression to FEM results by focusing on that the displacement and the stress generated in the helical spring are mainly caused by a tortional moment to the spring wire. Errors of the spring constant equations to the FEM results are less than 3 percents and errors of the maximum shear stress equation to the FEM results are less than 3.5 percents. Therefore, these equations are very useful for the practical design of the rectangular wire helical springs.