This study introduces a novel tip-tilt-piston aligner based on aligned folded beam flexure. It was designed to enhance precision positioning by minimizing parasitic motion. Through finite element analysis, we compared this aligner with a traditional folded beam flexure-based mechanism, revealing a remarkable 135% increase in translational stiffness and superior rotational stiffness ratios. These advancements are expected to reduce parasitic motion arising from actuator misalignment and external disturbances, ultimately elevating positioning accuracy. The aligner’s suitability as a guiding device was affirmed and optimal actuator placement positions were determined. This research provides valuable insights into precision positioning mechanism design, underscoring the role of flexure geometry and precise actuator placement in minimizing parasitic motion for improved accuracy.
Directed energy deposition (DED) additive manufacturing technology enhances the functionality of existing or damaged parts by adding metallic materials to the surfaces. Blown-powder DED technology utilizes a focused, high-energy source to fuse the part’s surface with the supplied metal powder. Maintaining a constant stand-off distance (SOD), the distance between the deposition head and the workpiece, is a key factor in ensuring deposition quality, as variations in SOD will change the powder focus position and the laser spot size on the surface. Therefore, traditional additive manufacturing systems require CAD or pre-scanned surface data. In this study, we proposed auto-surface tracking technology. No workpiece CAD data or pre-scanned surface data are required, and in-situ measurement and feedback control can automatically consider the deposition height differences that cause a change in SOD when depositing the next layer. The accuracy of the SOD measurements and feedback control error was verified using a step height sample. The mean SOD measurement error was 4.7 ㎛ with a standard deviation of 42 ㎛ (reference SOD, 14 ㎜). The feasibility of the autosurface tracking technology was confirmed through the additive manufacturing processes of the gear and an actual blanking mold applied in the defense and industrial fields.
The fundamental flow models of metallic materials at room temperature, including the Ludwik, Hollomon, Swift and Voce models, were evaluated in terms of tensile test with an emphasis on the necking phenomena and post-necking behavior, to emphasize their limitation in satisfying tensile strength and Considère condition as well as the pre-necking and post-necking strain hardening. To resolve this limitation and enhance the applicability of the new proposed flow model to typical strain hardening materials, the Ludwik-Swift blended flow model is proposed after investigation into three blended flow models among the Ludwik, Voce and Swift models. Results revealed that there is no interpolation-based blended flow model of the fundamental flow models for the example flow curve exhibiting typical strain hardening but that the extrapolation-based combination of them can provide an engineering solution when the Ludwik and Swift models are blended. It was revealed that the reason for their good matching lies in the distinct difference in the strain hardening exponent, between the Ludwik and Swift models in the case of metallic materials with typical strain hardening.
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Novel finite element model of analyzing wall thickness during tube drawing considering raw tube’s thickness non-uniformity and die misalignment N. A. Razali, J. B. Byun, M. S. Joun International Journal of Material Forming.2024;[Epub] CrossRef
The collaboration of robots and humans sharing workspace, can increase productivity and reduce production costs. However, occupational accidents resulting in injuries can increase, by removing the physical safety around the robot, and allowing the human to enter the workspace of the robot. In preventing occupational accidents, studies on recognizing humans, by installing various sensors around the robot and responding to humans, have been proposed. Using the LiDAR (Light Detection and Ranging) sensor, a wider range can be measured simultaneously, which has advantages in that the LiDAR sensor is less impacted by the brightness of light, and so on. This paper proposes a simple and fast method to recognize humans, and estimate the path of humans using a single stationary 360° LiDAR sensor. The moving object is extracted from background using the occupied grid map method, from the data measured by the sensor. From the extracted data, a human recognition model is created using CNN machine learning method, and the hyper-parameters of the model are set, using a grid search method to increase accuracy. The path of recognized human is estimated and tracked by the extended Kalman filter.
The need for automated material handling inside the factory has been steadily increasing, especially due to implementation of intelligent manufacturing for better productivity and product quality. Automated material handling devices include logistics robots, automated guided vehicles, industrial robots, collaborative robots, and pick-and-place devices. This study focuses on the development of a low-cost logistics robot that works effectively within a simulated smart factory environment. A nominal PID controller is implemented to guide the robot to follow the line painted on the factory floor. The tracking error information is generated by four down-facing infrared sensors and is fed into the controller. The line-following performance is significantly improved with augmentation of a model-based friction compensator. Optimization of battery power depending on the remaining charge status enhances the reliability. All hardware/software development is supported by the Arduino platform. The step-by-step movement and performance of the logistics robot is verified inside the simulated smart factory environment that includes a robot arm, three conveyors, and two processing stations.
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Path Planning and Trajectory Tracking for Automatic Guided Vehicles Yongwei Tang, Jun Zhou, Huijuan Hao, Fengqi Hao, Haigang Xu, Rahim Khan Computational Intelligence and Neuroscience.2022; 2022: 1. CrossRef
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By patterning finely with a laser with a thickness of 100 μm or less such as ABS and forming an electronic circuit through plating, a high-density flexible PCB applicable to wearable and mobile devices can be realized. ABS films with a thickness of 60, 90, and 120 μm were prepared, and a crater measuring 100 μm or less was formed by irradiating a fiber laser with a wavelength of 1064 nm with a single pulse. The size of the craters is affected by the intensity of laser irradiation and the thickness of the film, and the heat dissipation layer reduces the change in size caused by the difference in the thickness of the film. For films with a thickness of 60 μm, it has been found that small craters of more than 10% can be obtained due to the heat dissipation layer. Thermal analysis showed in the ABS film without the heat dissipation layer, the maximum temperature increased to 373oC, but decreased to 261℃ in the ABS film with the heat dissipation layer. With a decrease in the thickness of the film, the heat dissipation layer further reduces the pattern by laser irradiation.
This study aims to investigate the fatigue life of T-Type fillet welded joints for excavators subjected to bending loads, and also to verify the predicted fatigue life of the welded part using the effective notch stress method. Moreover, this study aims to determine an optimal toe angle of the T-Type fillet welded structure. In this context, the fatigue lives of T-Type fillet welded specimens (SM490A) were measured and the effective notch stress method for predicting the fatigue life of the T-Type fillet welded structure was verified by comparing with the FAT-225 curve of IIW (International Institute of Welding) as was suggested for the current types of welded structures. Considering simultaneously the scattering factor of the welded structure, the stress condition at the toe part higher than the root part, and the stress minimization condition of the toe part, the optimum toe angle at the T-Type fillet welding was identified at 30°. Likewise, the maximum stress (310.5 MPa) when the toe angle was 30° was about 14% less than the maximum stress (354.0 MPa) at 45°, and the fatigue life was improved by about 30%.
The purpose of this study was to develop an efficient mold heating technology by an embedded heating unit. To localize the heating effect in the mold core and prevent heat transfer to surrounding mold plates, the core module with embedded heating unit was assembled to a mold plate in a detachable manner. The detachable core module was then separated from the mold plate when the mold was opened, and thus could be rapidly heated by the embedded heater. The heated core contacted with the mold plate when the mold was closed, and could be cooled by heat conduction to the mold plate of which thermal inertia was much larger than that of the core module. To verify thermal efficiency of the proposed structure, heat transfer simulation was performed with an experimental validation. Mold filling simulation was also performed to investigate the effect of mold heating on improving flow characteristics through a thin and narrow channel. Injection molding experiments were also conducted by adopting the proposed embedded heating module.
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A Study on Conformal Heating of Curved Mold Using CNT Film Heater Seo-Hyeon Oh, Eun-Ji Jeon, Hyeon-Min Lee, Yeong-Bae Ko, Keun Park Journal of the Korean Society for Precision Engineering.2022; 39(7): 469. CrossRef
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It is possible to produce irregular structures quickly and accurately using rapid prototyping technology. However, there are still some obstacles in fabricating large-scale structures. In order to overcome these technical hitches, equipment has been developed for manufacturing irregular structures using EPS, making it an easy process. Conventional laser cutting systems can produce undesirable slopes in the structure when cutting EPS due to the divergence of the laser beam, resulting in step differences in the overall shape. Therefore, the objective of this study was to reduce the divergence of the laser beam using a concave lens and to find the optimal cutting conditions of the EPS through cutting experiments. As a result of the study, it was confirmed that the collimated beam cutting system can reduce the cutting slopes compared to the focused beam cutting system. In addition, experimental equations for depth of cut with cutting speed and laser intensity were derived.
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Optimal slope cutting algorithm for EPS free-form formwork manufacturing Harim Kim, Heejae Ahn, Chanwoo Kim, Dongyoun Lee, Taehoon Kim, Yeonho Ko, Hunhee Cho Automation in Construction.2022; 143: 104527. CrossRef
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Manufacturing Automation System of Freeform Concrete Formwork Using S-LOM Method Joonhyeok Sim, Hakmin Kim, Kyunwoo Park, Chanwoo Kim, Daehie Hong Journal of the Korean Society for Precision Engineering.2020; 37(1): 43. CrossRef
This paper proposes a 3D localization method for an outdoor mobile robot. This method assesses the 3D position including the altitude information, which is impossible in the existing 2D localization method. In this method, the 3D position of the robot is predicted using an encoder and an inclination sensor. The predicted position is fused with the position information obtained from the DGPS and the digital compass using extended kalman filter to evaluate the 3D position of the robot. The experimental results showed that the proposed method can effectively evaluate the 3D position of the robot in a sloping environment. Moreover, this method was found to be more effective than the conventional 2D localization method even in the evaluation of the plane position where altitude information is unnecessary.
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Unscented Kalman Filter Based 3D Localization of Outdoor Mobile Robots Woo Seok Lee, Min Ho Choi, Jong Hwan Lim Journal of the Korean Society for Precision Engineering.2020; 37(5): 331. CrossRef
The guided ultrasonic wave has the advantage of diagnosis on a wide area within in a short time due to the long distance propagation characteristic. However, there are many difficulties in signal analysis due to the mode conversions in the reflection from the defect and boundaries. In the use of guided waves for structure monitoring, it is necessary to understand the relation between the propagation mode and the mode of variation according to the shape of the defect. In this study, the characteristics of induced ultrasonic mode conversion is analyzed in taper defects formed from the surface of an aluminum plate. The defect depths of the plate thickness are 20, 50, and 80% and the characteristics of the reflection and transmission modes are analyzed on various defect widths, depending on the angle of change of the tapered shape. The A0 and S0 modes were selected as the excitation mode of the guided waves, the transmission and reflection coefficient amplitudes are analyzed. It is confirmed that the wavelength of the excitation mode having a large influence on the amplitude of the transmission and reflection signals generated by the taper defects depend on the shape of the defect.
A guided missile is a weapon system used in the interception of a ballistic missile using kinetic energy of a kill vehicle. The DACS (Divert and Attitude Control System) is a quick reaction propulsion system and subsystem of a kill vehicle that provides control over positions of a kill vehicle. The DACS allows for the interception of its target with greater accuracy and reliability. A Kill vehicle needs to move at high speed in a bid to intercept a ballistic missile after detecting a target. Thus, the weight reduction design of DACs system is required. The DACS operates under high temperature and pressure environment. In this study, one-way FSI (Fluid and Structure Interaction) analysis were conducted for various types of weight reduction valve model to validate its robustness. Through this process, we suggest an optimized weight reduction valve model
The precision-guided projectile is a weapon system for precision attacks, and the cannon-launched projectile is guided by a control device. The electrical actuator system is a subsystem of the control device, and the whole projectile undergoes high axial and lateral impact force for 1 to 10mseconds. In this study, a charpy, and a tensile impact analysis were conducted, using specimens made in the materials of SUS630 and Al7075-T6 to understand fracture mechanics and impact property, such as energy change rate. The impact analysis and gas-gun impact test were conducted, to validate the optimized housing model.
Gerotor oil pumps are widely used for the lubrication oil of an engine and the hydraulic source of an automatic transmission. Recently, improvements for the purposes of fuel efficiency and noise reduction have come to the forefront of the automobile industry, and it has become necessary to study the design of gerotors and ports. In this study, an expanded cardioid curve was developed, and an equation for a tooth profile with an expanded cardioid lobe shape has been suggested to reduce pump noise. The design was created using an automatic program; the program generated inner and outer rotor profiles and calculated performance parameters. Also, in order to decrease irregularity, CFD analyses were performed according to groove shapes in the exhaust port. Results showed the noise of the improved oil pump (the suggested gerotor [expanded cardioid] + the proposed port) was 5.44% lower than the existing oil pump (the existing gerotor [2-ellipse] + basic port).
FEM (Finite Element Method)-based numerical analysis model, which is known as CAE (Computer Aided Engineering) technology, has been adopted for the visual/mechanical analysis of machining process. The essential models for the FEM analytical model are the plasticity model of workpieces, friction model, and wear rate model. Usually, the outputs of the FEM analytical model are the cutting force, the cutting temperature, and chip formation. Based on these outputs, the machining performance can be virtually evaluated without experiments. Nowadays, there are emerging machining technologies, such as cryogenic assisted machining and CFRP machining. Therefore, FEM technique can be one of the good candidate to virtually evaluate emerging developed machining technologies.
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Post-machining Deformation Analysis for Virtual Machining of Thin Aluminium Alloy Parts Soo-Hyun Park, Eunseok Nam, Myeong Gu Gang, Byung-Kwon Min International Journal of Precision Engineering and Manufacturing.2019; 20(4): 687. CrossRef
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