In this study, finite element analyses are conducted for the glass molding press of a large-diameter concave meniscus lens. As press molding may commence in a non-uniform temperature field, thermal-structure two-way coupling simulations are applied to the molding process to understand the sequential changes in the lens shape and temperature distribution. Three types of glass preform, namely, ball model, approximate curvature model, and near net model, are prepared to investigate the effects of preform shape on formability and internal stress. Preforms with a small clearance (shape difference) from the mold shape require less time for complete transfer; however, high internal stresses occur during cooling. The internal stress generated during cooling is thermal stress, caused by the internal temperature difference; it can be reduced by expanding the contact regions between the lens surfaces and molds. Moreover, to improve formability and reduce internal stress when forming using an approximate curvature model, the preform shape and heat input temperature conditions to the upper and lower molds are optimized. In both cases, although the internal stress is slightly higher during the molding process, the entire lens surface is in contact with the mold during cooling, thus resulting in a significant decrease in internal stress.

This research investigates unstable outer cylinder whirl in a double rotating cylinder system, with both co- and counter-rotation, in which the axis of the outer cylinder is supported elastically in the radial direction and the axis of the inner cylinder is fixed and not allowed to whirl. A fixed (no rotation and no whirl) outermost cylinder is optionally installed outside the outer cylinder. It is assumed that the two (three) cylinders stay parallel to each other so that the gaps between them are axially uniform. A theory to analyze the complex eigenvalues of the coupled system of the gap flow and the motion of the outer cylinder is presented. The gap flow model accounts for the effects of inertia, compressibility and turbulence, and is coupled with the outer cylinder motion. Experiments were carried out for cases both with and without the outermost cylinder. The theoretical and experimental results were generally in agreement with respect to the whirl frequency, damping ratio, and boundary of the unstable whirl for different combinations of rotational speeds. The damping ratio and the frequency of the whirl decreased as the sum of the rotational speeds of the two cylinders increased. The presence of the outermost cylinder increased the sensitivity of the rotational speed of the outer cylinder to the damping ratio and the boundary of whirl occurrence, and narrowed the stable range of the speed of the outer cylinder. Also, only in counter-rotation in the case with the outermost cylinder, the frequency decrease tended to depend exclusively on the rotational speed of the inner cylinder, and the effect of the outer cylinder speed was reduced.

Vibration problems often occur in development of rocket engine turbopump, and an axial vibration is one of these problems. Rocket turbopumps often use the balance piston mechanism (BP), which is a self-balancing system, to balance the large axial thrust derived from the high discharged pressure. Turbopump rotor with BP is movable in the axial direction and supported by fluid stiffness generated by the BP. Although BP has a stable characteristic statistically, it becomes dynamically unstable in some cases owing to the compressibility of the fluid in the BP chamber. The stability of the BP has been studied in analysis approaches, but the experimental approach has yet to be conducted. In this study, an experimental research is conducted to confirm the occurrence of self-excited oscillation, and the results are compared to one dimensional theoretical analyses. From the experimental results, the effect of the BP parameters on stability is revealed. Here, it is concluded that there is a contradictory relationship between the BP static and dynamic characteristics.

A modified perturbation method (Kato and Matsuda, 2021) is used to obtain the solution of the heat transfer problem of a radiating straight fin with constant thermal properties. The main procedure of the modified perturbation method (MPM) is: (1) A perturbation parameter ε is assumed to be included in the nonlinear term of the differential equation. The solution θ is expressed by θ = φ + θ_f, where θ_f is an initial approximation of the solution. (In this paper, θ_f is assumed to be a constant) (2) θ = φ + θ_f is substituted into the differential equation and the nonlinear term is split into linear and nonlinear terms. (3) ε which is not in the nonlinear term is replaced by a newly introduced parameter ε´. (4) An asymptotic expansion of φ in powers of ε is assumed for the solution of the differential equation, from which we obtain the perturbation solution of φ including ε and ε´. (5) ε´ in the perturbation solution of φ is replaced by ε. Then we obtain the perturbation solution of θ. The obtained solutions by MPM are found to be in good agreement with the numerical results by the finite difference method. The solutions are also compared with those by the conventional perturbation method (CPM). It is found that MPM can extend the applicable range of the small parameter ε (radiation-conduction parameter) drastically compared with that by CPM. The modifications of the perturbation method by splitting the nonlinear term help reduce the contribution of the nonlinear term, which drastically improve the convergence characteristics of the solution.

In this study, a vibration analysis method is presented based on the substructure elimination method for a Bernoulli-Euler beam. Vibration analysis using modal analysis is effective for reducing the degrees of freedom and enables the analysis of a beam on which actuators and sensors are installed. When mechanical impedances are installed at the boundaries or the beam is coupled to other structures, a free-free beam is employed for conventional modal analysis using continuous functions. However, conventional modal analysis provides inaccurate simulation results when the coupled mechanical impedances considering the characteristic impedances of the beam are large. To address this issue, the modal analysis of a beam using the substructure elimination method was proposed in this study. Because the substructure elimination method for beams was only briefly reported on by the first author, several problems currently exist. To solve these problems, a substructure elimination method is proposed using a simply supported beam in addition to a guided-guided beam. Additionally, a new formulation method based on constraint conditions was proposed as a versatile method for setting arbitrary boundary conditions. The appropriate length, line density, and bending stiffness of the elimination regions, and the highest order of the eigenmode, were determined through simulations. The effectiveness of the proposed method was then verified by comparing the simulation results of the proposed method and exact solutions obtained using the boundary conditions. Based on a comparison with the simulation results of conventional modal analysis using a free-free beam, the precision of the proposed method is significantly higher than that of conventional modal analysis.

In excavation by hydraulic excavators, automation of excavation is effective in reducing the burden on operators and improving work efficiency. This paper focuses on automatic control of the weight of excavated soil. To control the weight of excavated soil, a soil dynamic model is required. However, the interaction between soil and bucket is complex and computationally expensive, making it unsuitable for real-time control. In this paper, we propose a dynamic model of excavation based on the experimental data of the weight of excavated soil and the workload done by the bucket. In addition, a differential equation that expresses the relationship between the data is derived. Based on the proposed model, a control method is also proposed to achieve the reference weight of excavated soil by changing the dragging length, assuming that the power done by the bucket during excavation is equivalent to the swept volume. Furthermore, we evaluate the effectiveness of the proposed method by excavating under several soil conditions using the proposed method.

Conventional remote operation of excavators is less efficient than direct operation. To address this, we have developed a semi-autonomous control system that combines autonomy (a dynamical system with an attractor) and human action (admittance control), and proposed discrete task selection within the dynamical system. In this paper, we propose a semi-autonomous leader-follower excavation system that achieves continuous task trajectory deformation in a nonlinear dynamical system with an attractor and separates task selection from trajectory deformation. The attractor is designed in a virtual space and transformed into the bucket’s state via coordinate transformation to change only the digging position without altering the loading position. Trajectory deformation is estimated by an Extended Kalman Filter based on human operational input and set dynamic characteristics, with task selection operations frequency-separated from the deformation. We implemented and verified the proposed method using a prototype excavation robot.

As a method for cleaning the nozzle of clinical analyzers with high cleaning efficiency, ultrasonic cleaning was selected because the cleaning mechanism can be miniaturized and its effect on dispensing accuracy is negligible. As for nozzle cleaning, it is necessary to meet two requirements: (i) suppress the wetting range of the nozzle inserted in the chamber of the ultrasonic cleaner and (ii) generate cavitation at a depth of a few millimeters from the liquid surface. To meet those requirements, a new ultrasonic cleaner with an L-shaped cleaning head for high-efficiency cleaning of the nozzle is proposed. The cleaning head is composed of two vibration plates at its tip to concentrate the sound pressure in the cleaning area, and the shape of the head enables the vibration phase of the ultrasonic-irradiation surfaces of the plates to be reversed with a single bolt-clamped Langevin-type ultrasonic transducer (BLT). The BLT with the proposed cleaning head has three resonant frequencies: that of the BLT, f_BLT, that of the lower plate, f_L-P, and that of the upper plate, f_U-P. At f_BLT, the BLT expands and contracts in the longitudinal direction. At f_L-P and f_U-P, deformation of each vibration plate is large. By setting the resonance frequencies in increasing order of magnitude, i.e., f_L-P, f_BLT, and f_U-P, it is possible to reverse the phases of the two vibration plates by driving the BLT at f_BLT. It was experimentally confirmed that the sound pressure can be concentrated in the cleaning area of the cleaning head by driving the BLT at f_BLT.

The aim of this study is to propose a new modified optimality criteria method for non-positive definiteness in multi-objective density-based topology optimization problems. Our proposed modified optimality criteria method is a density update method that was developed by incorporating the concept of Newton’s method into the conventional optimality criteria method. Topology optimization for strain energy minimization and von Mises stress minimization problems were performed separately, and actual experiments revealed the characteristics of each. Each optimization problem setting has its individual advantages: strain energy minimization is computationally stable, whereas von Mises stress minimization obtains a higher-strength structure. Therefore, in this study, to take advantage of both, we performed multi-objective optimization using the modified optimality criteria method. Since updating was not possible with the previously proposed modified optimality criteria method in multi-objective optimization problems, we propose incorporating mapping to enable it to be updated. As a numerical example problem, topology optimization was performed on the MBB beam model and gripper model for a robotic arm using the conventional optimality criteria method and our proposed mapping–based modified optimality criteria method to compare the update methods. Numerical example of the MBB beam model demonstrate that the mapping–based modified optimality criteria method is independent of the move-limit and can be updated. The mapping–based modified optimality criteria method also has a small number of arbitrary parameter settings that can cause problems for engineers because the weighting factor in the optimality criteria method is set in each element. Numerical example of the gripper model are used here to investigate the speed of updating the mapping–based modified optimality criteria method and guidelines for setting the appropriate weight coefficients of performance function to create a design.

CVT chains are widely used in vehicles because the slip between parts is small, which enables efficient power transmission. However, the intermittent motion of CVT chain pins entering and leaving the pulleys causes undesirable vibration in the whole chain, and affects the basic performance of the CVT. Therefore, it is important to investigate the influence of the geometrical specifications of the chain on this vibratory motion. This study focused on the pin-pulley slip length when the pins enter and leave the pulleys, and a mathematical model for the power loss of a CVT chain was developed. The validity of this model was verified and confirmed experimentally. In addition, the influence of the shape of chain components on power loss was also investigated. In particular, the influence of the position of the contact point between the pins and pulleys on power loss was investigated both theoretically and experimentally, and geometric parameters were optimized. As a result, the model formulated in this paper can be used to investigate measures for reducing CVT power loss.

Human faces are mechanical systems that display emotional and linguistic information with motions of the deformable facial tissues. Since each facial action forms a different stress-strain field that characterizes the differentiated facial appearance, a detailed analysis of strain distributions for each facial action will contribute to analytical and synthetical studies on human faces. This study evaluated strain distributions of 44 facial actions of a Japanese adult male based on the three-dimensional displacements of 125 tracking markers attached to the facial surface. We investigated how much the facial skin surface is stretched and compressed in each facial region based on the evaluated area strains produced by each facial action. Then, we visualized the strain distributions and surface undulation to analyze the complexity of the deformations on a face. The results show that the positive and negative surface strains intermingled on a face even in simple facial actions, potentially reflecting the complex facial structure under the facial skin layers, where several tissues with different material properties, e.g., adipose tissues and retaining ligaments, are distributed heterogeneously. These results are beneficial for artificial face designers as a design target and evidence to consider the effective skin structure and locations of actuators for artificial faces.

In human motion capture systems, reflective markers attached to the body have been widely used to track motion using optical cameras. However, when the speed of motion increases, because the brightness and angle of view of the camera are limited, and the markers often fall off, particularly of detailed body parts such as fingers in full-body movements, other parts of the body (palms) have been investigated. This study attempted to acquire finger movements during a high-speed throwing task without attaching markers using automatic image recognition technology based on deep learning (DeepLabCut) and verified its accuracy compared to conventional methods. As a result, the absolute distance between the 3D coordinates obtained from the two motion capture systems was an average of 15.5 to 29.4 mm depending on tracked points, and the correlation coefficients between them ranged from 0.932 to 0.999. Therefore, the shapes of the time-series profiles of the 3D coordinates obtained from the two motion- capture systems were similar. These results suggest that motion measurement using markerless motion capture is possible in environments where conventional motion capture systems are difficult to use.