In this investigation, we propose a simple and effective lateral shearing interferometer based on a polarization grating. In the lateral shearing device, an incident beam is split into two beams by a polarization grating, and the returning beams can be laterally shifted after reflecting off a flat mirror and passing through the polarization grating again. These two beams are not only laterally shifted, but also their polarization states are orthogonal to each other as circular polarizations. With a single image obtained by a pixelated polarization CMOS camera, the proposed LSI can obtain the phase map corresponding to the x-sheared interferogram, and the other phase map can be calculated from another single image obtained by 90° rotation of the shearing device. Then, the original wavefront corresponding to the surface figure of the specimen can be reconstructed by wavefront reconstruction algorithms. In the experiments, various wavefronts generated by concave mirrors and a deformable mirror were measured and compared with those of a commercial Shack-Hartmann sensor.

Tool-center-point (TCP) calibration and geometric error identification procedures are proposed to improve the accuracy of a 6-axis manipulator with a tilting rotary table. The accuracy of a 6-axis manipulator is affected by the accuracy of TCP calibration. In general, TCP calibration of the 6-axis manipulator uses a conical fixture provided by the manufacturer. However, since a TCP cannot be accurately positioned to the tip of the conical fixture repeatedly, a large positional deviation occurs at the calibration depending on the worker proficiency. Thus, accuracies of TCP calibration and the 6-axis manipulator are reduced. In this paper, a 3-DOF measuring device, consisting of a nest with three dial gauges and a precision ball, is developed to calibrate the TCP and to improve the accuracy of the 6-axis manipulator. Then, geometric errors of a tilting rotary table are identified via double ball-bar measurements according to the ISO 10791-6 with TCP initial alignment using an extension fixture. Finally, proposed TCP calibration and geometric error identification procedures are validated experimentally, and they show improvements in positional accuracy by 55 and 90%, respectively.

The gear has a wide range of transmitted force as various gear ratios are possible using a combination of teeth. It can transmit power reliably and cause relatively little vibration and noise. For this reason, the application of reducers of electric vehicles is being expanded. Vibration noise generated from gears is propagated into the quiet interior of a vehicle, causing various claims. In most gear studies, transmission error has been pointed out as the main cause of vibration noise of gears. Transmission errors have various causes, including design factors, manufacturing factors, and assembly factors. In general, when predicting transmission error through finite element analysis, design factors play an important role without considering manufacturing factors or assembly factors. In this study, relationships among important design variables (gear module, compensation rate, load torque, and transmission error) in gear design were investigated using analytical and experimental methods. In addition, a method of predicting gear meshing stiffness through the predicted gear transmission error was proposed to obtain variation of meshing stiffness due to changes of gear design parameters.

An optimal design was developed for housing of a 50-ton hydraulic breaker. A four-factor, two-level design was created using the full factorial design, and it was confirmed that the safety factor, the response value, exhibited a curvature. As the curvature was confirmed, a higher-order experiment, a response surface analysis was performed. Based on the Minitab"s optimized prediction of the safety factor and weight, the actual analysis was performed using ANSYS Workbench, the finite element analysis program. As a result, the safety factor was 2.03 and the weight was 3222.2 kg, which was almost consistent with the Minitab’s prediction. The safety factor decreased from 2.33 to 2.03 compared to that in the initial model, but the optimization model can also be judged as being safe because the safety factor was set to 2.00. The weight was reduced by 119.1 kg, from 3341.3 to 3222.2 kg.

Ground drilling technology for drilling has an environment where the major parts are prone to damage due to high stress, torque, and harsh operating conditions that can occur in the rotary power transfer structure. Research for preventing this damage is very important, as it can be coupled with the nature of drilling operations that take a long time in operation, which can lead to enormous cost and time consumption. Previous work investigated the cause of damage by analyzing the working environment and breakage of drilling holes for connecting rods, and a power transfer component of directional mud motors used in ground drilling systems. The material properties by heat treatment conditions for applied materials were analyzed. Based on prior work, we evaluated whether the stress concentration part shown in the analysis results matched the actual damage occurring point by conducting a structural analysis of the connecting rod, a damaged part, using the finite element analysis. We also analyzed how to reduce the stress concentration phenomenon that occurs during the mud motor operation by conducting part shape and design changes between the connecting rod and key parts.

This paper presents an improved input shaping method to eliminate vibration during circular interpolation of a flexible 2-axis positioning system. Due to the time delay introduced by input shaping, simultaneous 2-axis positioning with circular interpolation results in a certain amount of errors from the intended track or trajectory. This study investigated the track errors associated with circular interpolation caused by input shaping for a flexible 2-axis positioning system. The following three strategies for reducing such errors were proposed: velocity reduction in circular interpolation, adjustment of the time delay between 2 axes commands, and employment of a velocity profile compensation function. Simulations were performed to discuss the pros and cons of the three proposed strategies. Experiments were also performed to validate the results. Simulation and experiments showed that the track errors due to input shaping can be sufficiently reduced by combined use of the proposed strategies.

Bone plates made of biodegradable polymers have been used to fix broken bones. 3D printers are used to produce the bone plates for fracture fixing in the industry. The dimensional accuracy of the product printed by a 3D printer is less than 80%. Fracture fixing plates with less than 80% dimensional accuracy cause problems during surgery. There is an urgent need to improve the dimensional accuracy of the product in the industry. In this paper, a methodology using machine learning was proposed to improve the dimensional accuracy. The proposed methodology was evaluated through case studies. The results predicted by the machine learning methodology proposed in this paper and the experimental results were compared through the experiment. After verification, results of the proposed prediction model and the experimental results were in good agreement with each other.

As the Paris Agreement on Climate Change came into effect in 2021, the Korean government set a target of 63.8 GW new renewable power generation until 2030 and announced “The 3020 Implementation Plan of Renewable Energy”, which was a policy to supply more than 95% of the new generation capacity as solar power and wind power. Continuous investment in new renewable energy will be required to reduce the greenhouse effect and to achieve sustainable growth. In particular, offshore wind power is advantageous for the construction of a large-scale power complex. This paper evaluates the suitability of the jacket-type substructure by analyzing the weather environment, marine environment, water depth survey, ground survey, and major equipment selection data. When the new offshore wind power complex is planned, it can be useful for selecting the suitable substructure and determining the turbine capacity to achieve good performance.

In this study, soft actuators comprising conductive fibers, flexible polymers, and shape memory alloys, which can be used as textile products, are introduced. Conductive fibers play an important role because they can be used as sensors in wearable devices. The conductive fiber introduced in this study is a form that can be combined with a polymer, and it comprises a form wrapped around a flexible polymer. When an electric current is applied to the shape memory alloy embedded in the polymer, macroscopic deformation occurs due to phase transformation from the Martensite to the Austenite phase. Conductive fibers used in soft actuators are affected by resistive heat generated by the shape memory alloy and bending deformation of the actuator. Accordingly, changes in the conduction properties of conductive fibers were observed due to bending deformation and temperature changes. We also fabricated soft actuators with different types of polymers and observed the differences. The soft actuator presented in this study is a one-piece combination of a conductor and an actuator using a textile-type conductor, and it is likely to be used in smart clothing applications.