A voice coil motor is a simple and linear electromagnetic actuator. Since it has a non-contact force and very low stiffness, it is widely used for precision positioning devices including magnetic levitation systems. During magnetic levitation, high force of a voice coil motor is required to compensate for the weight of the device and ensure a fast dynamic response. In this paper, two types of voice coil motors were analyzed by their volumetric change. The change of the generated force according to the volumetric change was inspected by finite element simulation models. The enhancement of force was dependent on which type of the voice coil motor is used, which component is enlarged, and which direction is the voice coil motor expands in. Based on the analysis results, two voice coil motors were optimally designed for a magnetic levitation positioning device. As a result of the design, it was confirmed that different types of voice coil motor generate different forces even if they have the same volume. For the two types of voice coil motors, the force differed by up to 40%.

Since the first invention of triboelectric nanogenerators (TENGs) in 2012, many mechanical systems have been applied to operate TENGs, but mechanical contact losses such as friction and noise are still big obstacles for improving their output performance and sustainability. Here, we report on a magnet-assembled cam-based TENG (MC-TENG), which has enhanced output power and sustainability by utilizing the non-contact repulsive force between the magnets. We investigate the theoretical and experimental dynamic behaviors of MC-TENGs according to the effects of the contact modes, contact and separation times, and contact forces (i.e., pushing and repulsive forces). We suggest an optimized arrangement of magnets for the highest output performance, in which the charging time of the capacitor was 2.59 times faster than in a mechanical cam-based TENG (C-TENG). Finally, we design and demonstrate a MC-TENG-based windmill system to effectively harvest low-speed wind energy, ~4 m/s, which produces very low torque. Thus, it is expected that our frictionless MC-TENG system will provide a sustainable solution for effectively harvesting a broadband of wasted mechanical energies.

The main objective of this paper is to propose, design, and control a novel dual servo magnetic levitation stage which is precise and vacuum compatible. The dual servo mechanism, comprising a coarse stage and a fine stage, was applied to a magnetic levitation stage system for the first time. The dual servo stage achieves high precision and a long stroke at the same time. The fine stage, which comprises voice coil motors, achieves high-precision motion by overcoming the limit of the coarse stage, the form of which is a planar motor. The planar motor was mathematically modeled and analyzed with respect to the main design parameters, after which the fine stage was optimally designed to be driven by high force. Both stages including a common heat exchanger were manufactured, and the heat exchanger cools down the heat given off from the planar motor and voice coil motors. The position measuring system consisted of laser interferometers and capacitive sensors, and the integrated dual servo stage was controlled with a master–slave control scheme. The experimental results showed a precision of 10 nm, thus confirming the suitability of the developed magnetic levitation stage for a high-precision fabrication process such as wafer lithography.

In this paper, prior to the commercialization of a developed active steering bogie, we want to analyze steering performance experimentally according to steering angle level with the aim of obtaining steering performance data to derive practical design specifications for a steering system. In other words, the maximum steering performance can be obtained by controlling the steering angle at the 100% level of the target steering angle, but it is necessary to establish the practical control range in consideration of the steering system cost increase, size increase, and consumer steering performance requirements and commercialize. The steering control test using the active steering bogie was conducted in the section of the steep curve with a radius of curvature of R300, and steering performance such as bogie angle, wheel lateral force, and derailment coefficient were analyzed according to the steering angle level. As the steering angle level increased, the bogie indicated that it was aligned with the radial steering position, and steering performance such as wheel lateral force and derailment coefficient was improved. The steering control at 100% level of the target steering angle can achieve the highest performance of 83.6% reduction in wheel lateral force, but it can be reduced to about one-half of the conventional bogie at 25% level control and about one-third at 50% level. Considering cost rise by adopting the active steering system, this result can be used as a very important design indicator to compromise steering performance and cost rise issues in the design stage of the steering system from a viewpoint of commercialization. Therefore, it is expected that the results of the steering performance experiment according to the steering angle level in this paper will be used as very useful data for commercialization.

The strong aerodynamic drag under a railroad vehicle in motion causes the track ballast to fly up and around. The flying ballast can collide with the underside of the coach, damaging the electronics installed there. There are even cases wherein the aerodynamics of fast-moving train causes the gravel to hit the side of the coach and break the windows. Extensive and numerous studies are underway to reduce the damage caused by such phenomena. In this study, a “smart paint sensor” for impact monitoring was fabricated using piezoelectric nano powder and commercial paint for railroad vehicles, and the application of impact monitoring to railroad vehicles was analyzed. The process was simplified because the use of commercial paint eliminated the need to apply an additional layer of functionalized paint. Furthermore, the fact that the paint can be evenly sprayed on a large surface made it suitable for use on large and intricate objects such as a railroad vehicle bogie. Because railroad vehicles are exposed to thermal stress for a long period of time, a thermal fatigue test was conducted in order to figure out the stability of the polymer-based material, which is relatively vulnerable to temperature variations. The test results were used to analyze the impact sensitivity of the piezoelectric paint sensor. For the analysis, a full-size mock-up of the railroad vehicle bogie and an impact monitoring system with piezoelectric paint sensor were implemented in order to visualize the impact signals from differently shaped objects with large surfaces.