Inertial navigation technology originally designed for precise guidance of missiles is widely used in weapon systems. Guided missiles have become supersonic and high maneuverability with advancement of science and technology. Antivibration performance against high vibration and shock energy is accordingly required. Sensors of an Inertial Navigation System (INS) have a high sensitivity. Conversion coefficients for acceleration values and bias errors in signals must be minimized. A vibration isolator is generally applied to protect INS by attenuating the vibration and shock energy transmitted from dynamic disturbances. The stiffness and damping are changed using highly damped materials such as elastomers that must be protected from disturbances. A vibration isolator is widely used in various fields. However, it is important to understand characteristics of a vibration isolator composed of elastomer because it has nonlinearities such as hyperelasticity and viscoelastic as well as damping characteristics. In this study, a COTS vibration isolator suitable for INS was selected through theoretical approach. Response characteristics of the system in a vibration and shock environment were analyzed through FEM analysis and vibration and shock test. In addition, through repeated excitation test, reproducibility and structural stability were confirmed when the vibration isolator was installed in the system.

This paper proposes a new rotary welding torch with a ball-jointed mechanical seal structure that simultaneously realizes the enclosure of CO₂ gas, the energization of welding current, and the insulation for system protection. In order to effectively compare the operation mechanism of the proposed device with the conventional rotary welding torch, a schematic technique is introduced to clearly visualize the operation and connection structure of the model. The kinematic state and constraint degrees of freedom of the tool are clearly shown, and it is easy to distinguish between the two designs that use different component parts and connection structures but result in the same final motion. In addition, the four dynamic characteristics of a rotary torch operating at 20 Hz (driving torque, vibration reaction force, natural frequency, and inertial mismatch) were analyzed to demonstrate superior performance to conventional products. The welding test showed that the tool normally operated even in a harsh welding environment, verifying its applicability in the field.

This study deals with the structural integrity of a co-axial octocopter cargo drone. Most unstable states in progress of various flight missions of the cargo drone are considered to be derived from take-off and landing operations. In order to evaluate the structural integrity of these states, three-dimensional FE (finite element) simulation using whole frame assembled with structural members and components is performed, and then the effective stress level and deflection degree are investigated. Also, topology optimization is adopted to improve the locally concentrated stress and large deflection around front and rear sections of the motor-support side member. From topology optimization, it is ensured that the shape and location of plate support have to be modified for improving the stress level and the deflection degree. Based on the optimized and modified feature, FE simulation is re-performed. Consequently, it is confirmed that the effective stress and the deflection are reduced to about 26.67% and 19.15% around the side member, respectively.

This study performed high-frequency heat treatment experiments and simulations of the park gear of an automobile transmission. The heating temperature and hardening depth were measured during high-frequency heat treatment. Moreover, by applying the resonance RCL circuit, the current value of the coil during high-frequency heat treatment, the electromagnetic and heat transfer material properties dependent on the temperature, and the phase transformation function were all applied to the simulation. In the high-frequency heat treatment experiment, the heating temperature was 977.4℃ and the 1st direction hardening depth was 1.5 mm, the 2nd direction hardening depth was 3 mm, and the 3rd direction hardening depth was 2.5 mm, and the reliability was verified by comparing the simulation heating temperature of 1,097℃ and the 1st direction predicted hardening depth of 1.6 mm, the 2nd direction predicted hardening depth of 2.8 mm, and the 3rd direction predicted hardening depth of 2.7 mm. The error rate of the heating temperature results was 12.2% whereas that of the hardening depth results was 7.1%.

This paper proposed the simulation model of the servo system with three-stage reducer and presented the result of frequency analysis of the servo system considering backlash ratios and motor input voltage. By virtue of this work, we realized that if the motor input voltage of the system was large, the influence of each stage backlash ratio could be minimized or removed. Besides, we also found that if the motor input voltage was small, this created an optimal backlash ratio combination which could maximize the anti-resonance and resonance frequency of the servo system. This paper could be useful for determining each stage backlash ratio in designing a three-stage geared servo system with fast response.

Precision positioning stages are devices for precisely positioning objects according to required degrees of freedom and performance. Precision positioning stages are classified into serial and parallel mechanisms. Except for specific applications, the parallel mechanism is preferred. In serial mechanism, dynamic characteristics such as resonant frequency are clearly different from axis to axis and the first resonance frequency is distinctly low compared to the second. These make the control performance different for each axis and incurs limitation in control. In this study, the first and second resonant frequencies in a serial 2-DOF precision positioning stage were increased while maintaining their approximal value. Compliance analysis for the stage was performed by applying the matrix based method. A new concept of resonant frequency isotropy (RFI) was introduced and design optimization was performed in which first and second resonant frequencies almost coincided. This optimization allowed for the design of a serial 2-DOF precision positioning stage with enhanced first resonance frequency by 50.8% and RFI by 80.2% compared to the initial design. This paper is expected to increase the use of precision positioning stages based on serial mechanism and apply the concept of RFI to the positioning stages with more than 2-DOF.

This paper investigated the influence of the backlash ratio on frequency response characteristic in servo systems with twostage gear reducer, according to the change of magnitude of motor input voltage. The backlash ratio is defined as the ratio of the first gear stage backlash magnitude in relation to total backlash magnitude. This paper presents that the maximum anti-resonance and resonance frequency of the system can take place at the maximum backlash ratio if the motor input voltage of the system is large. On the other hand, if the motor input voltage is small, the maximum anti-resonance and resonance frequency of the system will occur at an arbitrary backlash ratio. In order to develop the geared servo system with fast response, it is effective to increase the maximum allowable motor input voltage and to reduce the magnitude of backlash on the second gear reduction stage.

Most of passive implants belong to medical device are consist of metallic and nonmetallic materials. According to the sort of components, it makes more influence into the human body. In this study, we performed induced-RF (Induced-Radio Frequency) heating evaluation which is part of MRI (Magnetic Resonance Imaging) compatibility and safety test and in-vivo pyrogen test with lumbar stand-alone cage. RF from 3T MRI coil was radiated on medical device, and provided heat nearby stand-alone cage. Thermal change detected areas are distinguished by metallic and nonmetallic part. As followed detection areas, febrility was shown and metallic part was slightly higher than control area, nonmetallic part. Furthermore, stand-alone cage was performed in accordance with in-vivo pyrogen test, and solution injected rabbits had no fever for test period. Through physically and biologically evaluated stand-alone cage, exothemic reaction was observed and we predicted the effect when it would be inserted in patient.