• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1026-1029
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• 2003

There are always some errors in force sensing of multi-axis force sensors that aggravate sensor performance. Error sources may be classified mainly in two groups. One is structural error due to inaccuracy of sensor body, and the other is error due to noise signals existing in the sensed information. This paper presents a brief review about the principle of multi-axis force sensors, and then a method that can reduce the effect of noise signals. The method is to read digital signals in computer instead of analog voltage signals. We can eliminate the bad effect of electromagnetic waves emitted from computer and of 60 Hz noise emitted from AC source by the proposed method. The proposed method is investigated through experimental demonstration. The experimental results show the proposed method improves the sensor performance significantly.

• The Journal of Korea Robotics Society
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• v.12 no.3
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• pp.356-364
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• 2017

This paper presents a force control based on the observer without taking any force or torque measurement from the robot which allows realizing more stable and robust human robot interaction for the developed multi-functional upper limb rehabilitation robot. The robot has four functional training modes which can be classified by the human robot interaction types: passive, active, assistive, and resistive mode. The proposed observer consists of internal disturbance observer and external force observer for distinctive performance evaluation. Since four training modes can be quantitatively identified as impedance variation, position-based impedance control with feedback and feedforward controller was applied to the assistive training mode. The results showed that the proposed sensorless observer estimated cleaner and more accurate force compared to the force sensor and the impedance controller embedded with the proposed observer completed the assistive training mode safely and properly.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.11
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• pp.2688-2695
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• 2000

In multi-axis force sensor, compliance matrices representing structural behaviour of internal sensor bodies play an important role in decoupled sensing and accuracy, Recently, error propagation through compliance matrices has been studied via approximation approach. However the upper bound of measured force error has not been known. In this paper, error propagation in force sensing is analysed in a unified way when both strain measurement error and compliance matrix error exist, and the upper bound of the measured force error is derived exactly(not approximately). The analysis is examined through a numerical example.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.1
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• pp.43-48
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• 2013

In this paper, magnetic buoyancy force on nonmagnetic solid object submerged in magnetic liquid was simulated and measured. For the evaluation of the force, a multi-physics approach of hydrostatic equilibrium considering magnetic body force as well as gravity is presented. The magnetic body force should be regarded as an additional forcing term in the momentum equation of hydrodynamics. It is also shown that the virtual air-gap based Kelvin's force formula is a useful method for the calculation of force distribution in the magnetic liquid. The experimental result which was performed by a load-cell measurement system agreed quantitatively well with the numerical one.

• Coupled systems mechanics
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• v.9 no.4
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• pp.311-323
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• 2020

This paper deals with the effect of the mode shapes on the dynamic response of a multi-storey frame subjected to moving train loads which are modelled as loads of constant intervals with constant velocity using the finite element method. The multi-storey frame is modelled as a number of Bernoulli-Euler beam elements. First, the first few modes of the multi-storey frame are determined. Then, the effects of force span length to beam length ratio and velocity on dynamic magnification factor (DMF) are evaluated via 3D velocity-force span length to beam length ratio-DMF graphics and its 2D projections. By using 3D and 2D graphics, the directions of critical speeds that force the structure under resonance conditions are determined. Last, the mode shapes related to these directions are determined by the time history and frequency response graphs. This study has been limited by the vibration of the frame in the vertical direction.

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.52-56
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• 2022

Single-grain (c-normal or c-parallel) and multi-grain YBCO superconductors were prepared by a melt growth process with/without seeding. The magnetic levitation force and trapped magnetic field at liquid N₂ temperature (77 K) of the YBCO superconductors were investigated. Samples for the levitation force measurement were zero-field cooled (ZFC) to 77 K, and samples for trapped field measurement were field-cooled (FC) using Nd magnets. As for the magnetic levitation force, the c-normal, single grain sample showed the largest value, whereas the multi-grain sample showed the lowest value. The trapped magnetic field of the c-normal and c-parallel single-grain samples was 4-5 times that of the multi-grain sample. In addition, as the external magnetic field (the number of magnets) increased, the both properties increased proportionally. These results were explained in terms of the orientation dependence of the levitation forces and the magnetic field trapping capability of the YBCO superconductor.

• Transactions of Materials Processing
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• v.14 no.8 s.80
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• pp.689-695
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• 2005

Multi-pass wet wire drawing process is used to produce fine wire in the industrial field. The production of fine wire through multi-pass wet wire drawing process with appropriate dies pass schedule would be impossible without understanding the relationship among many process parameters such as material properties, dies reduction, friction conditions, drawing speed etc However, in the industrial field, dies pass schedule of multi-pass wet wire drawing process has been executed by trial and error of experts. This study investigated the relationship among many process parameters quantitatively to obtain the important process information fur the appropriate pass schedule of multi-pass wet wire drawing process. Therefore, it is possible to predict the many important process parameters of multi-pass wet wire drawing process such as dies reduction, machine reduction, drawing force, backtension force, slip rate, slip velocity rate, power etc. The validity of the analyzed drawing force was verified by FE simulation and multi-pass wet wire drawing experiment. Also, pass redesign was performed based on the analyzed results, and the wire breakage between the original pass schedule and the redesigned pass schedule was compared through experiment.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.9
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• pp.126-134
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• 2003

This paper investigates the multi-pass wet wire drawing process considering the slip between the wire and the capstan. The production of fine wire through multi-pass wet wire drawing process would be impossible without backtension. The backtension is affected by many process parameters, such as slip, dies reduction, coiling number of wire at the capstan, machine reduction, characteristic of lubricant etc. Up to date, die design and dies pass schedule of multi-pass wet wire drawing process have been performed by trial and error of expert in the industrial field. In this study, an analysis program which can perform the analysis and considering the effect of slip at each capstan was developed. The effects of many important parameters (drawing force, backtension force, needed power, slip rate, slip velocity rate etc.) on multi-pass wet wire drawing process can be predicted by this developed program. It is possible to obtain the important basic data which can be used in the pass schedule of multi-pass wet wire drawing process by using this developed program.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.4
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• pp.1351-1372
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• 2022

A self-organizing multiple unmanned aerial vehicles (multi-UAVs) deployment based on virtual forces has a difficulty in ensuring the quality-of-experience (QoE) of users because of the difference between the assumed center for users in a hotspot and an actual center for users in the hotspot. This discrepancy is aggravated in a non-uniform and mobile user distribution. To address this problem, we propose a new density based virtual force (D-VF) multi-UAVs deployment algorithm which employs a mean opinion score (MOS) as a metric of QoE. Because MOS is based on signal-to-noise ratio (SNR), a sum of users' MOS is a good metric not only to secure a wide service area but to enhance the link quality between multi-UAVs and users. The proposed algorithm improves users' QoE by combining virtual forces with a random search force for the exploration of finding multi-UAVs' positions which maximize the sum of users' MOS. In simulation results, the proposed deployment algorithm shows the convergence of the multi-UAVs into the position of maximizing MOS. Therefore, the proposed algorithm outperforms the conventional virtual force-based deployment scheme in terms of QoE for non-uniform user distribution scenarios.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.539-542
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• 1996

The forces exerted on an object by the end-effectors of multi-manipulators are decomposed into the motion-inducing force and the internal force. Motion-inducing force effects the motion of an object and internal force can't effect it. The motion of an object can't track exactly the desired motion because of internal force component, therefore internal force component must be considered. In this paper using the resolved acceleration control method and the fact that internal force lies in the null space of jacobian matrix, we construct independently the position, motion-inducing force and internal force controller. Secondly we construct the robust controller to preserve the robustness with respect to the uncertainty of manipulator parameters.