Diffractive Optical Element (DOE) composed of repetitive patterns is necessary for 3D measurement, or for converting a laser beam into several spots. In this study, DOEs were fabricated through a direct laser lithographic system of which it is easy to fabricate a pattern on the specimen at low cost and under relatively simple process conditions. A commonly used method in laser direct laser lithography is the thermochemical technique. In this way, a single-line can be produced. At this time, when the high power of the laser is used, the laser ablation phenomenon occurs, so that a dual-line can be produced. As a result, it is possible to fabricate a pattern quickly with the proposed process method. And especially, it can increase the effect in repetitive patterns production. To fabricate repetitive fine patterns using dual-line, hexagonal and tripleshaped patterns were fabricated, by using the writing speed and laser intensity appropriately. Optical performance evaluation was performed by comparing the diffracted image of the fabricated hexagonal repetitive patterns with the simulation result.
In this paper, the design and fabrication of the calf-link with knee joint torque sensor of a tandem-driven walking-assist robot is described. Tendon-driven walking-assist robots should be designed and constructed with a wire wheel and a torque sensor, as one body to reduce the weight of the calf link. The torque sensor consists of four plate sensing parts crossed 90° around the wire wheel. Structural analysis was performed to determine the size of the torque sensor sensing part, and a torque sensor was built by attaching a strain gauge to the sensing part. As a result of the characteristics test, the reproducibility error and the nonlinearity error of the manufactured torque sensor were less than 0.03% and 0.04%, respectively. As a result of the calibration, the reproducibility error and the nonlinearity error were less than 0.08%, respectively. Thus, it is considered that the knee joint torque sensor of the calf link can be attached to the tandem-driven walking-assist robot.
In this study, a super-twisting sliding mode controller with a non-linear disturbance observer for a ball-screw servo system was designed to obtain a precise motion and fast convergent control performance. Unknown dynamics of the servo system were approximated into pre-assumed diagonal constants for rapid controller design in the real industry to avoid expensive and time consuming experimental identification process. Moreover, uncertainties due to nonlinear friction, axis misalignment and dead zone were estimated by a nonlinear disturbance observer, which is combined with the designed super-twisting controller. The designed controller and observer systems were applied to the 2-axis ball screw servo system to verify the efficacy of the proposed control system via simulation and experiment.
This paper presents gain optimization for a controller of a 6- DOF underwater robot with tilting thrusters. PID control system with anti-windup technique is designed to stabilize the hovering motion of the robot. The controller comprises thrust vector decomposition to overcome nonlinearity of the thrust vector and also includes an algorithm to compensate for saturation of thrusters. A total of 24 control gains should be tuned in this controller, and gain optimization is performed according to four system errors using genetic algorithm. First, 18 PID control gains were optimized and then 6 gains were optimized to affect anti-windup. As a result, control gains optimized by the integral absolute error showed the best performance, and it is verified that tracking error in position and orientation of the robot were reduced by 29.38% compared with initial gains.
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Hovering control of an underwater robot with tilting thrusters using the decomposition and compensation method based on a redundant actuation model Jeongae Bak, Yecheol Moon, Jongwon Kim, Santhakumar Mohan, TaeWon Seo, Sangrok Jin Robotics and Autonomous Systems.2022; 150: 103995. CrossRef
Gain Optimization of Kinematic Control for Wire-driven Surgical Robot with Layered Joint Structure Considering Actuation Velocity Bound Sangrok Jin, Seokyoung Han Journal of Korea Robotics Society.2020; 15(3): 212. CrossRef
To identify the impeller types automatically for an overhead stirrer operation, a digitalization of the analog magnetic signal of the permanent magnet arrays was performed. The permanent magnets were installed into the impeller shaft in NS-SN array, and their magnetic fields were measured by a hall sensor while the impeller was mounted on the stirrer. Results of the experiments and finite element analysis showed that the number of peaks of magnetic field signal was observed corresponding to the number of magnets. Considering the consistency of the number and the magnitude of magnetic field peaks, it was found to be more advantageous to measure the magnetic field in the axial than in the radial direction of the impeller. For eliminating the influence of the noise included in the analog signal and connecting it with the micro-controller of the stirrer, the analog magnetic field signal was transformed to the digital-pulse-patterned signal through DC offset, amplification, absolute value, and the comparator circuit. Through these processes, the error in identifying the impeller type could be significantly reduced compared with directly using the magnitude of the analog magnetic signal.
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A Study on Contactless Identification of Impellers Using a Digital Hall Sensor Ho-Cheol Lee Journal of the Korean Society of Manufacturing Process Engineers.2021; 20(12): 71. CrossRef
Analysis of Effect of Stirring Process Conditions on Liquid Viscosity in an Overhead Stirrer Ho Cheol Lee, Gi Dae Kim Journal of the Korean Society for Precision Engineering.2020; 37(9): 659. CrossRef
This paper addresses the design of an integrated high torque DC motor. In this paper, a method to improve the torque according to the shape of the stator magnet and the rotor teeth of the DC motor is studied. During the course of design, the rotor and stator are designed to satisfy the required performance through FEM analysis by reflecting similar materials in design. As a result of satisfying the design result and requirements, the motor that is imported and operated in the future can be applied as a domestic developed product.
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Smart Design of Rotor and Permanent Magnet considering Torque and Torque Ripple of Interior Permanent Magnet Synchronous Motor of Electric Vehicle Seong-Hwan Bang, Si-Mok Park, Min-Gi Chu, Ji-Hun Song, Dong-Ryul Lee Journal of the Korean Society for Precision Engineering.2021; 38(8): 605. CrossRef
Effect of Thermal Conductivity of Coil Insulator Material on the Temperature Variation of High Voltage Motor Jaehyun Park, Seung Ho Paek, Hyun Woo Lee, Heesung Park Journal of the Korean Society for Precision Engineering.2020; 37(5): 355. CrossRef
The purpose of this study was to investigate the flow characteristics and cooling performance for the heavy turbine blade with different shapes. Research was focused on the numerical study on forced convective heat transfer coefficients for three different blades with base, tip, and hole. Thus, selected local locations for various temperature distributions were shown in the flow domain. Final temperature on the local surface of blades was compared with three different blades. According to the results of velocity and temperature distributions in the fluid domain, the blade with holes had the best convective cooling performance with higher 13-16% average heat transfer coefficient than the other two blades. Apparent vortex at the tip of tip and hole blade caused the stable temperature drop. According to the calculations of local convective heat transfer coefficient between blade surface and atmosphere in the blade, approximately 18% of heat transfer coefficient at hole was higher than the base blade and 7% at hole blade was higher than the base blade. Lowest cooling performance existed at the center position of all three blades.
The purpose of this study was to develop a selective patterning process with functional nanoparticles, using the selective hydrophobic treatment which can give surface energy differences. It is important to selectively pattern the nanoparticles in solution, to the desired site in a variety of fields such as transparent electrodes, displays, and bio-sensors. Selective hydrophobic treatment can reduce the additional post processes such as cleaning to remove particles unwanted position, which is a drawback of the existing solution process. Various patterns with sub-micron size that can’t be achieved with other solution processes could be fabricated by nanoimprint lithography, selective surface treatment, and a solution coating process. The transparent conductive electrode (TCE) using silver mesh patterns on the flexible substrate created from our study showed 24 Ω of sheet resistance and more than 82% transmittance. To verify the possibility of nano-patterning of various materials, quantum dot (QD) was also patterned by selectively filling. Selective surface treatment technology has significantly improved the filling process of nanoparticles into fine patterns less than 1 μm wide.
Generally, press molds have thermal and mechanical impact wear during usage. To improve the life of the mold, enhancement of mechanical properties such as abrasion resistance and shockproof capability is required. To solve this, we propose the multi-layered cladding process of functional materials with different mixing ratios. AISI-D2 material, known as cold die steel, was used as base material and AISI-M4 and -H13 powders were used for surface cladding on the base metal for high resistance wear and shockproof capability. Four cases of specimens were prepared to compare mechanical properties after tests. Through this study, a specimen multiple cladded with mixing M4 and H13 powders for middle layer and M4 powder only for top layer showed 80% improvement in shockproof capability. We posit that this method based on multi-layer cladding with a combination of functional metal powders increased mold life.
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Hybrid Mechanical Surface Treatment Technology via UNSM and Burnishing for Realizing High Surface Hardness Yeong-Wook Gil, Sang-Hu Park Journal of the Korean Society of Manufacturing Process Engineers.2023; 22(10): 10. CrossRef
A Study on the Method and Application of Shaft Repair using Directed Energy Deposition Process Yoon Sun Lee, Min Kyu Lee, Ji Hyun Sung, Myeong Pyo Hong, Yong Son, Seouk An, Oe Cheol Jeong, Ho Jin Lee Journal of the Korean Society of Manufacturing Process Engineers.2021; 20(9): 1. CrossRef
Effect of Post-Heat Treatment on the AISI M4 Layer Deposited by Directed Energy Deposition Gyeong Yun Baek, Gwang Yong Shin, Ki Yong Lee, Do Sik Shim Metals.2020; 10(6): 703. CrossRef
Despite the importance of the usage stage in life cycle assessment (LCA), there is a lack of comprehensive studies on the usage stage modeling. Based on the literature review, this paper establishes a general framework of the usage stage modeling by redefining existing models and proposing new models. The proposed computational framework can provide the overview of the current research as well as lead researchers and practitioners to consider proper modeling techniques. The framework includes the representative usage scenario method, usage context modeling, and time series usage modeling. Also, future research directions are suggested with the proposed computational framework.
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