• The Journal of Korean Academy of Prosthodontics
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• v.38 no.1
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• pp.108-115
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• 2000

This study was designed to compare the effect of polishing on surface roughness of composite resin. We used Z100(3M) composite resin and placed the composite resin in the hole (4mm thick and 4mm in diameter) of vinyl plate and polymerized it under manufacturer's instructions. Samples were divided into 5 groups by polishing methods. Group 1 was control: resin was polymerized under glass plate, Group 2: resin was polymerized without any polishing procedure, Group 3: resin was polymerized with a polishing procedure of abrasive disc, Group 4: bonding agent was applyed in thin layer and polymerized on the polished polymerized resin surface. Group 5: resin was polymerized under transparent celluloid strip. The surface roughness of each specimen was measured with Sufacoder SEF-30D (Kosaka lab. Ltd) under 0.08mm cut off, 0.05mm/s stylus speed, ${\times}40$ horizontal magnification, ${\times}5000$ vertical magnification. The results were as follows : 1. Group 1 showed the most smooth surface in this study. 2. Group 3 showed more rough surface than Group 2. Considering the surface roughness, it would be better to make the shape completely before polymerize the resin. To finish and polish after the polymerization of resin makes less smooth surface. 3. When we use the transparent celluloid strip, minimum finishing procedures are recommended. Any polishing procedure could not recover the smooth resin surface of celluloid strip. 4. Application and polymerization of the thin layer of bonding agent on the polished surface showed the minimum surface smoothing effect.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.150-153
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• 1995

In this paper the attitude control system is developed for longitudinal motion of Foil-Catamaran in regular waves with all-movable foils which attached to fore and after part of the ship and verified the system by theoretical calculation and model-tests. The linearized equations of motion of the ship is employed to apply the linear control theories, the PID control and the LQR. The strip method was used to calculate hydrodynamic coefficients and wave exciting forces of the demi hull, and unsteady hydrodynamic forces of foils are considered by using the result of Wu(1972). About 40-60% of motions is reduced in experiments. The control system described in this paper is able to extended to 6-DOF motions or control in irregular wave with trivial modification. And it is applicable to hull shape development for better seakeeping performance and to determine the size and the position of hydrofoils for the attitude control.

• Smart Structures and Systems
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• v.6 no.2
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• pp.91-100
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• 2010

An experimental study was carried out to investigate the shape control of plates via embedded shape memory alloy (SMA) wires. An extensive body of literature proposes the use of SMA wires to actively modify the shape or stiffness of a structure; in most cases, however, the study focuses on modeling and little experimental data is available. In this work, a simple proof of concept specimen was built by attaching four prestrained SMA wires to one side of a carbon fiber laminate plate strip. The specimen was clamped at one end and tested in an environmental chamber, measuring the tip displacement and the SMA temperature. At heating, actuation of the SMA wires bends the plate; at cooling deformation is partially recovered. The specimen was actuated a few times between two fixed temperatures $T_c$ and $T_h$, whereas in the last actuation a temperature $T_f$ > $T_h$ was reached. Contrary to most model predictions, in the first actuation the transformation temperatures are significantly higher than in the following cycles, which are stable. Moreover, if the temperature $T_h$ is exceeded, two separate actuations occur during heating: the first follows the path of the stable cycles; the second, starting at $T_h$, is similar to the first cycle. An interpretation of the phenomenon is given using some differential scanning calorimeter (DSC) measurements. The observed behavior emphasizes the need to build a more comprehensive constitutive model able to include these effects.

• Journal of Mechanical Science and Technology
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• v.15 no.2
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• pp.225-231
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• 2001

A mathematical model for the analysis of roll gap phenomena in the strip temper rolling process is described. A new approach to solve the roll indentation and diverging problem in modeling of severe temper rolling cases is obtained by adopting the preliminary displacement principle of two contacted rough bodies to describe the friction behavior in the roll gap. The mechanical peculiarities of the temper rolling process, such as a high friction value with high roughness rolls and a non-circular contact arc, low reduction and non-negligible entry and exit elastic zones as well as central preliminary displacement zone etc., are all taken into account. The deformation of work rolls is calculated with the influence function method and an arbitrary contact are shape is permitted. The strip deformation is modeled by the slab method and the entry and exit elastic deformation zones are included. The preliminary displacement principle is used to determine the boundaries and to calculate the friction of the central preliminary displacement zone. The model is calibrated against the production mill data and installed in the setup computer of a temper rolling mill in POSCO. The validity and precision of the model have been proven through a comparison of the measured roll forces and the predicted ones.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.08a
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• pp.3-9
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• 1999

The recent technical trend in hot rolling of steel can be described as process and product technologies which have been progressed with modern mill equipment and computers. Precise gauge and width control can be achieved by up-to-date control methods such as AGC and AWC systems. Roll benders and various shape control systems enabled high quality flatness and crown control. Mills can produce higher tensile materials by new process based on process metallurgy. The use of high speed steel rolls and on line roll grinders make the schedule free rolling easier which results in cost saving. Process itself goes toward continuous and simple flow type which has lower operation. Endless rolling and strip casting are examples of the trend. Materials with higher tensile strength and various functions have been developed in last years to meet the customer's needs and this trend will continue.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.1808-1813
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• 2005

In this paper, we present the finger tip tactile sensor which can detect contact normal force as well as slip. The developed sensor is made of two different materials, such as polyvinylidene fluoride(PVDF) that is known as piezoelectric polymer and pressure variable resistor ink. In order to detect slip to surface of object, a PVDF strip is arranged along the normal direction in the robot finger tip and the thumb tip. The surface electrode of the PVDF strip is fabricated using silk-screening technique with silver paste. Also a thin flexible force sensor is fabricated in the form of a matrix using pressure variable resistor ink in order to sense the static force. The developed tactile sensor is physically flexible and it can be deformed three-dimensionally to any shape so that it can be placed on anywhere on the curved surface. In addition, we developed a tactile sensing system by miniaturizing the charge amplifier, in order to amplify the small signal from the sensor, and the fast signal processing unit. The sensor system is evaluated experimentally and its effectiveness is validated.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.4
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• pp.719-741
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• 1997

This study was undertaken to compare by Atomic Force Microscope the effects of various finishing and polishing instruments on surface roughness of filling and veneering composite resins. Seven composite resins were studied : Silux Plus (3M Dental Products, U.S.A.), Charisma (Heraeus Kulzer, Germany), Prisma THP (L.D.Caulk, Dentsply, U.S.A.), Photoclearfil (Kuraray, Japan), Cesead (Kuraray, Japan), Thermoresin LC (GC, Japan), Artglass (Heraeus Kulzer, Germany). Samples were placed and polymerized in holes (2mm thick and 8.5mm in diameter) machined in Teflon mold under glass plate, ensuring excess of material and moulded to shape with polyester matrix strip. Except control group (Polyester matrix strip), all experimental groups were finished and polishied under manufacturer's instructions. The finishing and polishing procedure were : carbide bur (E.T carbide set 4159, Komet, Germany), diamond bur (composite resin polishing bur set, GC, Japan), aluminum-oxide disc (Sof-Lex Pop-On, 3M Dental Products, U.S.A.), diamond-particle disc (Dia-Finish, Renfert Germany), white stone bur & rubber point( composite finishing kit, EDENTA, Swiss), respectively. Each specimens were evaluated for the surface roughness with Atomic Force Microscope (AutoProbe CP, Park Scientific Instruments, U.S.A.) under contact mode and constant height mode. The results as follows : 1. Except Thermoresin LC, all experimental composite resin groups showed more rougher than control group after finishing and polishing(p<0.1). 2. A surface as smooth as control group was obtained by $Al_{2}O_{3}$ disc all filling composite resin groups except Charisma and all veneering composite resin groups except Thermoresin LC(p<0.05). 3. In case of Thermoresin LC, there were no statistically significant differences before and after finishing and polishing(p>0.1). 4. Carbide bur, diamond bur showed rough surfaces in all composite resin groups, so these were inappropriate for the final polishing instruments.

• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.847-858
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• 2001

This paper considers the control model identification and H(sub)$\infty$ controller design for a tandem cold mill (TCM). In order to improve the performance of the existing automatic gauge control (AGC) system based on the Taylor linearized model of the TCM, a new mathematical model that can complement the Taylor linearized model is constructed by using the N4SID algorithm based on subspace method and the least squares algorithm based on ARX model. It is shown that the identified model had dynamic characteristics of the TCM than the existing Taylor linearized model. The H(sub)$\infty$ controller is designed to have robust stability to the system parameters variation, disturbance attenuation and robust tracking capability to the set-up value of strip thickness. The H(sub)$\infty$ servo problem is formulated and it is solved by using LMI (linear matrix inequality) techniques. Simulation results demonstrate the usefulness and applicability of the proposed H(sub)$\infty$ controller.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1937-1941
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• 2004

We present lateral actuated piezoelectric actuator using U-shaped PZT strip and lever structure for the RF switch application. In the previous study of RF switch, they used horizontal contact switch fabricated by thin film metals. However, thin film metals could not generate large contact force due to low stiffness. In this work, we suggest lateral contact switch which makes large contact force by increasing stiffness. In addition, we use PZT actuator for the high force actuation. Generally actuator using thin film PZT moves to the vertical direction due to the neutral axis shift. Therefore we need lateral motion generation mechanism based on the thin film PZT actuator. In order to increase lateral motion of thin film PZT actuator, we use U-shaped PZT actuator using residual stress control. Also, thin film PZT actuator can generate very small lateral motion of 120${\times}$10$^{-6}$ ${\mu}{\textrm}{m}$/V for d$_{31}$ mode, thus we suggest lever structure to increase stroke amplification. From the experimental study, fabricated PZT actuator shows maximum lateral displacement of 1 ${\mu}{\textrm}{m}$, and break down voltage of the thin film PZT actuator is above 16V.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.11
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• pp.66-72
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• 2008

During the plate and foil cold rolling process, considerable values of the force of material pressure on the tool occur. These pressures cause the elastic deformation of the roll, thus changing the shape of the deformation legion. Rolled copper foils should be characterized by a good quality and light dimensional tolerances. Because of automation that is commonly implemented in flat product rolling mills, these products should meet the requirements of tightened tolerances, particularly strip thickness, and feature the greatest possible flatness. The shape of the roll gap is influenced by the elastic deformation of rolls parts of the rolling process affecter of the pressure force. However, to control roll deformation should be difficult. Because the foil thickness is very thin and the permissible deviations in the thickness of foil are small. In this paper, FE-simulation of roll deformation in thin foil cold roiling process is presented.