Changhyun Cho - Academia.edu (original) (raw)

Papers by Changhyun Cho

In this paper, we propose a 3D automated measuring system which measures the mandibular movements... more In this paper, we propose a 3D automated measuring system which measures the mandibular movements and the reference plane of the jaw movements. In diagnosis and treatment of the malocclusions, it is necessary to estimate the mandibular movements and the reference plane of the jaw movements. The proposed system is configured with double stereo-cameras, PC, two moving pattern plates(MPPs), two fixed pattern plates(FPPs) and one orbital marker. The virtual pattern plate is applied to calculate the homogeneous transformation matrices which describe the coordinates systems of the FPP and MPP with respect to the world coordinates system. To estimate the parameters of the hinge axis, the Euler's theorem is applied. The hinge axis points are intersections between the FPPs and the hinge axis. The coordinates of a hinge axis point with respect to the MPP coordinates system are set up to fixed value. And then, the paths of the jaw movement can be calculated by applying the homogeneous tran...

In this paper the problems of a force display device equipped with energy dissipative actuators s... more In this paper the problems of a force display device equipped with energy dissipative actuators such as a brake or a damper are discussed. This kind of problem can be investigated by considering a force manipulability ellipsoid (FME). The direction in which a Cartesian force can be generated on the FME in a typical 2-link manipulator with passive actuators is very limited compared to the manipulator equipped with motors. To overcome this problem a redundantly actuated passive 2link manipulator is proposed in this research. By adopting either direct drive or coupled wire drive, the region in which force display is possible can be extended.

Advances in environmental research, 2012

We demonstrated that reductive degradation of 2,4,6-Trinitrotoluene (TNT) and hexahydro-1,3,5-tri... more We demonstrated that reductive degradation of 2,4,6-Trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (Royal Demolition Explosive, RDX) can be enhanced by bio-reduced ironbearing soil minerals (IBSMs) using Shewanella putrefaciens CN32 (CN32). The degradation kinetic rate constant of TNT by bio-reduced magnetite was the highest (0.0039 h-1), followed by green rust (0.0022 h-1), goethite (0.0017 h-1), lepidocrocite (0.0016 h-1), and hematite (0.0006 h-1). The highest rate constant was obtained by bio-reduced lepidocrocite (0.1811 h-1) during RDX degradation, followed by magnetite (0.1700 h-1), green rust (0.0757 h-1), hematite (0.0495 h-1), and goethite (0.0394 h-1). Significant increase of Fe(II) was observed during the reductive degradation of TNT and RDX by bio-reduced IBSMs. X-ray diffraction and electron microscope analyses were conducted for identification of degradation mechanism of TNT and RDX in this study. 4-amino-dinitrotoluene were detected as products during TNT degradation,

The Journal of Korean Institute of Communications and Information Sciences, 2012

Our PC have been under constant threat of malicious codes and viruses today. As many new ways of ... more Our PC have been under constant threat of malicious codes and viruses today. As many new ways of cyber attacks are being developed, such as zero-day-attack, nobody's PC is guaranteed to be safe from the attacks. In case where a user uses the existing verification protocol on a unsecured PC, the user's verification information may well be threatened by sniffing or man-in-the-middle attack. Especially, deadly attacks like memory hacking would give hard time for users to even recognize any symptom of virus infection. Therefore, this paper designs secured QR-Login user verification protocol for smart devices that are ready to communicate with QR-Code and proposes a way to keep critical data safe when using the internet. This way, user would be able to safeguard his/her critical data even when under attack by unknown attacks and safely carry out extremely sensitive task, like financial trading, on the device.

International Journal of Precision Engineering and Manufacturing, 2012

This paper proposes a general expression of the energy method for an n-dofs and n-links gravity c... more This paper proposes a general expression of the energy method for an n-dofs and n-links gravity compensator in the basis of space mapping. Joint space and gravity compensator space are determined and a mapping between the two spaces is considered. The mapping matrix is determined by mechanical constraints between two spaces. Potential energy in the joint space (i.e., the manipulator mass) and potential energy in the gravity compensator space (i.e., springs) are derived in generic forms. The design equation is obtained by partial differentiation of the potential energy in the both spaces and spring coefficients are determined with the design equation. Example studies are conducted to evaluate the mapping method. The bevel gravity compensator and a three-link spatial manipulator with the bevel gravity compensator are investigated. For the three-link spatial manipulator, the bevel gravity compensator and one-dof gravity compensator are equipped for link 3 and link 1 and the parallel constraint is adopted between the base and link 2 to obtain complete gravity compensation for all poses of the manipulator. Experimental results on gravity compensation indicate that gravitational torques are effectively counterbalanced.

Journal of Institute of Control, Robotics and Systems, 2010

This paper presents a gravity compensator for the manipulator of a service robot. The manipulator... more This paper presents a gravity compensator for the manipulator of a service robot. The manipulator of a service robot is operated with low velocity for the safety reason in most cases. In this situation gravitational torques generated by the mass of links are often much greater than dynamic torques for motion. A gravity compensator can counterbalance the gravitational torques, thereby enabling to utilize relatively low power motors. In this paper the gravity compensation for the roll-pitch rotation is considered which is often used for the shoulder joints of the manipulator of a service robot or humanoid robot. A gimbals is implemented and two 1-dof gravity compensators are equipped at the base. One compensates the gravitational torque at the roll joint and another provides the compensational torque for the gimbals. Various analyses showed that the proposed compensator can counterbalance the gravitational torques of 87% at the pitch joint and 50% at the roll joint. It is verified from dynamic simulations that the proposed compensator effectively counterbalances the gravitational torques.

International Journal of Control Automation and Systems, Jul 1, 2004

In displaying a virtual wall using a passive haptic device equipped with passive actuators such a... more In displaying a virtual wall using a passive haptic device equipped with passive actuators such as electric brakes, unsmooth motion frequently occurs. This undesirable behavior is attributed to time delay due to slowness in the virtual environment update and force approximation due to the inability of a brake to generate torque in arbitrary directions. In this paper a new control scheme called direct control is proposed to achieve smooth display on the wall-following task with a passive haptic device. In direct control, brakes are controlled so that the normal component of a resultant force at the end-effector vanishes, based on the force analysis at the end-effector of the passive haptic device using the passive FME (Force Manipulability Ellipsoid). Various experiments have been conducted to verify the validity of the direct control scheme with a 2-link passive haptic system.

2011 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2011

ABSTRACT

International Journal of Control, Automation and Systems, 2012

This paper presents robotic manipulators that employ the bevel gravity compensator. The bevel gra... more This paper presents robotic manipulators that employ the bevel gravity compensator. The bevel gravity compensator can counterbalance a 2-dof rotation comprised of two 1-dof gravity compensators and a bevel differential. Each 1-dof gravity compensator is equipped at the rotating bevel gear, respectively. Analyses of the energy and torque for a 1-link and 2-dof manipulator indicate that the proposed gravity compensator performs static balancing completely. Multi-link and spatial manipulator applications are discussed in this paper. In these applications, mechanical constraints are adopted to achieve complete gravity compensation, since the pose of the distal link with respect to the inertial frame varies with alterations of the pose of the proximal link. Energy analyses reveal that the proposed manipulators employing bevel gravity compensators can completely achieve static balancing. The simulation results show that the gravitational torques can be effectively counterbalanced in regards to the proposed manipulators.

Ari Juels proposed yoking-proof protocol for authenticating multiple tags using RFID system. Then... more Ari Juels proposed yoking-proof protocol for authenticating multiple tags using RFID system. Then, one-time yoking-proof protocol, which is a lightweight version using minimalist MACs was proposed. However, Ari Juels's protocol is vulnerable to replay attack during the handshake process for authentication between tags. Some solutions have been proposed for making up for the vulnerability but those also had some weaknesses in some ways. In this study, a protocol has been proposed for making up for the vulnerability of one-time yoking-proof protocol while allowing multiple authentications instead of one, depending on the tag capacity.

Secure QR-Pay system based on QR-code by expressing dimensional can pay things between User and S... more Secure QR-Pay system based on QR-code by expressing dimensional can pay things between User and Shop while Offline. A shop shows payment information by expressing QR-code to display window. A user shots a situation by using mobile Device attached a camera. If a user confirms payment information and ask an approval, the payment system can be settled by itself. It's a very easy system. For this process, payment gateway(PG) helps calculate process in connection with payment. This system we proposed provides non- repudiation and confidentiality of payment information. Also, it offers mutual Authentication between user and shop to use public certificate.

Proceedings 2003 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 2003) (Cat. No.03CH37453)

In this paper, a new design of a 6DOF haptic master is presented, and the architectural parameter... more In this paper, a new design of a 6DOF haptic master is presented, and the architectural parameters are discussed in consideration of the kinematic characteristics. This device was intended to teleoperate a mobile manipulator, which requires planar 3 DOF motion for navigation of the vehicle and full 6 DOF motion for manipulation. The proposed haptic master is composed of two parallel mechanisms, and each mechanism offers 3DOF independently. The spatial mechanism, which extends the workspace into 3D, is attached on the planar mechanism for vehicle operation. Since low inertia is vital to back drivability and transparency of the haptic device, all actuators are placed on the base and thus some forces for haptic feedback are transmitted by the tendon-driven mechanism. This paper presents the kinematic analysis of the haptic master with respect to the workspace and the performance indices related to the Jacobian. The actual system was constructed with the architectural parameters determined on the basis of the analysis.

Journal of hazardous materials, Jan 21, 2015

Abatement of fluorinated compounds (FCs) used in semiconductor and display industries has receive... more Abatement of fluorinated compounds (FCs) used in semiconductor and display industries has received an attention due to the increasingly stricter regulation on their emission. We have developed a 2.45GHz microwave plasma torch with reverse vortex reactor (RVR). In order to design a reverse vortex plasma reactor, we calculated a volume fraction and temperature distribution of discharge gas and waste gas in RVR by ANSYS CFX of computational fluid dynamics (CFD) simulation code. Abatement experiments have been performed with respect to SF6, NF3 by varying plasma power and N2 flow rates, and FCs concentration. Detailed experiments were conducted on the abatement of NF3 and SF6 in terms of destruction and removal efficiency (DRE) using Fourier transform infrared (FTIR). The DRE of 99.9% for NF3 was achieved without an additive gas at the N2 flow rate of 150 liter per minute (L/min) by applying a microwave power of 6kW with RVR. Also, a DRE of SF6 was 99.99% at the N2 flow rate of 60 L/min...

Proceedings 2001 ICRA. IEEE International Conference on Robotics and Automation (Cat. No.01CH37164)

Stroke accounts for over 2,000,000 people who have chronic acute arm impairments. Currently the r... more Stroke accounts for over 2,000,000 people who have chronic acute arm impairments. Currently the rehabilitation process for stroke involves a physical therapist manually moving the patient's arm, with no quantitative measurements for improvement. This problem extends to the fact that there are few technological devices available to assist in the rehabilitation process, even though it is largely mechanical by nature. Those devices that are available are often large, do not offer a full range of arm motion, are not portable, and not available to most physical therapists for clinical use. The robotic exoskeleton arm is designed to fix most of these problems. It will be lightweight, give the patient full degrees of freedom in movement, and will give the patient more options in physical therapy. It will have sensors attached to the arm that will give the therapist quantitative feedback on the patients recovery, which should mean a speedier and more complete rehabilitation. In order to help the physical therapist, a virtual environment will conduct the 2 patient through exercises in a game-like fashion. This should not only make the rehabilitation process more effective and interesting, but also allow for variety in the type of the exercises as the patient improves, i.e., increased productivity of the rehabilitation.

2003 IEEE International Conference on Robotics and Automation (Cat. No.03CH37422)

This paper presents design of a 6 DOF haptic master which is based on a combination of a planar 3... more This paper presents design of a 6 DOF haptic master which is based on a combination of a planar 3 DOF parallel mechanism and a spatial 3 DOF parallel mechanism. Since low inertia is vital to backdrivability and transparency of the haptic device, all actuators are placed on the base and thus some forces for haptic feedback are transmitted by tendon-driven mechanism. This device was intended to teleoperate a mobile manipulator, which requires planar 3 DOF motion for navigation of the vehicle and full 6 DOF motion for manipulation. Therefore, the proposed device is designed to have two modes of a planar task and a 3D task which are switchable without any change in hardware. This feature provides efficient actuation and reduces computational burden since only 3 actuators are involved in the case of a planar task. The paper deals with a detailed description of the proposed haptic master and Jacobian analysis. Some applications are given to verify the validity of this device.

11th Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2003. HAPTICS 2003. Proceedings.

Passive haptic devices have better stability than active ones, but usually have limited capabilit... more Passive haptic devices have better stability than active ones, but usually have limited capability of haptic display. In this paper a 2-link passive haptic device equipped with electric brakes is discussed. Since passive devices cannot generate forces in all directions, determination of the region available for force reflection is important to their design and operation. This analysis can be done by a socalled force manipulability ellipsoid (FME). In some haptic applications, the endpoint of a device is required to move along a certain trajectory (e.g., the surface of a virtual wall) and haptic display plays a role of path guide. Performance of path guidance is also investigated in this research. Finally, guideline for the design of more efficient passive haptic devices is briefly discussed.

2003 Symposium on VLSI Technology. Digest of Technical Papers (IEEE Cat. No.03CH37407)

90 nm DRAM technology and beyond requires the robust memory cell capacitor structure in order to ... more 90 nm DRAM technology and beyond requires the robust memory cell capacitor structure in order to increase cell capacitance for high performance and low power applications. Thus, the cell technology must have the feature of high capacitance of memory cell capacitor while maintaining its mechanical stability. To accomplish these purposes, we develop the multi-stack storage node structure whose enlarged bottom size of OCS(One Cylindrical Storage node) can give much better mechanical stability of the capacitor than that of the conventional capacitor. Using Al 2 O 3 /HfO 2 dielectric material together with this structure can give high cell capacitance 30fF/cell and low leakage current less than 1fA/cell.

Spondylodiscitis is very rare complication caused by Klebsiella pneumoniae. Among those, few case... more Spondylodiscitis is very rare complication caused by Klebsiella pneumoniae. Among those, few cases of spondylodiscitis concomitant with epidural abscess due to Klebsiella pneumoniae have been reported. We present a case of lumbar pyogenic spondylodiscitis with epidural abscess caused by Klebsiella pneumoniae that successfully treated with administration of cefotaxime, surgical drainage and intermittent closed continuous saline irrigation.