• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.621-625
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• 2005

This paper presents a new hybrid serial-parallel robot(HSPR), which has six degrees of freedom driven by ball screw linear actuators and motored joints. This hybrid robot design presents a compromise between high rigidity of fully parallel manipulators and extended workspace of serial manipulators. The hybrid robot has a large, singularity-free workspace and high stiffness. Therefore, the presented kinematic structure of the hybrid robot is particularly suitable for multi-tasking machining processes such as milling, drilling, deburring and grinding. In addition to the machining processes, the hybrid robot can be used for welding, fixturing, material handling and so on. The study on design of the hybrid robot is performed. A kinematic analysis and mechanism description of the hybrid robot with six-controlled degree of freedom is presented. In the virtual design works by DADS, workspace and force analysis are discussed. A numerical model is treated to demonstrate our analysis and to determine the range of permissible extension of the struts. Also, we determine some important design parameters for the hybrid robot.

• Journal of Magnetics
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• 제1권2호
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• pp.75-81
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• 1996

Study on the HDDr Characteristics of Nd16Fe76-xB8Zrx (x=0-2.0) Alloys and the Magnetic Properties of the HDDR Materials Nd16Fe76-xB8Zrx (where x=0-2.0) have been studied to see the effect of Zr addition on HDDR characteristics. A particular emphasis was place upon the anisotropy of the HDDR material. Anisotropy of the HDDR powder material has been evaluated by comparing the remanence values of the aligned sample measured along the aligning direction and the direction perpendicular to it. The HDDR characteristics of the alloys were investigated by means of DAT and TPA. Magnetic chracterisation of the HDDR processed materials was performed using a VSM and a TMA. The magnetic domain structure of the HDDR materials was examined by means of polarised microscope using a solid HDDR processed material. It has veen found that small addition (0.1 at %) of Zr to Nd-Fe-B-type alloy retards thedisproportionatio kinetics of the hydrogenated material. Desorption characteristic of the disproportionated materials has been found not to be affected significantly by the Zr addition. The Zr addition has been found to facilitate size of the powder. As the particle size decreases, the intrinsic coercivity decreases radically, and this is explained in terms of structural damage and/or oxidation caused during mechanical milling. It has also been found that the degree of alignment representing the anisotropic character of the HDDR powder is enhanced with decreasing particle size. Alloys with compositions based on

• 한국분말재료학회지
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• 제19권4호
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• pp.259-263
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• 2012

Dependence of the freeze-drying process condition on microstructure of porous W and pore formation mechanism were studied. Camphene slurries with $WO_3$ contents of 10 vol% were prepared by milling at $50^{\circ}C$ with a small amount of dispersant. Freezing of a slurry was done in Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at $800^{\circ}C$ for 30 min, and sintered in the furnace at $900^{\circ}C$ for 1 h. After heat treatment in hydrogen atmosphere, $WO_3$ powders were completely converted to metallic W without any reaction phases. The sintered samples showed large pores with the size of about $70{\mu}m$ which were aligned parallel to the camphene growth direction. Also, the internal wall of large pores and near bottom part of specimen had relatively small pores with dendritic structure due to the growth of camphene dendrite depending on the degree of nucleation and powder rearrangement in the slurry.

• 한국세라믹학회지
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• 제32권9호
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• pp.1047-1055
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• 1995

Mn-Zn ferrite granules were formed by a spray-drying method of the slurry containing different kinds and concentrations of binders at various temperatures. The slurry was made by conventional ceramic processing method, that is, by mixing Fe2O3, MnO, ZnO powders (52 : 24 : 24 mol%), calcining and milling. Typical shape of the spray dried granules was spherical. The compaction behavior of these granules was dependent on the spray-drying temperature and the kind and concentration of binders. At lower pressure the granules were displaced and at higher pressure the granules were deformed and fractured to fill pores among the granules. The optimum concentration of the binder was 0.5wt%. The granules containing 0.5wt% PVA 205 were deformed and fractured well and the green density was higher than others. At higher concentrations of the binder the granules were deformed rather than fractured, therefore the green density was lowered because of the remaining unfilled pores. The decomposition temperature and the heat released were increased with increasing the concentration of the binders. The compaction response of the granules containing PVA 205 was more efficient than those containing PVA 217 and PVA 117. Green density was not dependent on the degree of hydrolysis of the binders. The compaction response of the granules spray-dried at 15$0^{\circ}C$ was most efficient.

• 한국재료학회지
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• 제28권2호
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• pp.82-88
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• 2018

Stable slurries of YSZ in aqueous suspension with added polymer dispersants, namely, poly-methacrylic acid ammonium salt (PMMA), poly-acrylic acid (PAA) and poly-acrylic-co-maleic acid (PAMA), were mixed with the monomolecular dispersants citric acid and oxalic acid. The dispersion properties of the suspension were investigated using PSA, viscosity, sedimentation, and FT-IR. The polymer dispersants and monomolecular dispersants were attached to the YSZ surface by the carboxylic group, as shown by the FTIR results. A stabilized aqueous suspension was obtained when the polymer dispersant and citric acid were mixed and compared to the use of citric acid alone as a dispersant agent. When the polymer dispersant and citric acid were mixed and milled through attrition milling, there was a smaller particle size compared to when the polymer dispersant alone was used as a dispersant agent. This study determined that the particle size of the mixed dispersant was affected by the properties of the monomolecular dispersant and that the stability of the suspension was affected by the polymer dispersant. However, when slurries of YSZ were mixed with oxalic acid, the particle bridging behavior was the result of the high degree of viscosity and the small sedimentation height.

• 전기학회논문지
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• 제66권11호
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• pp.1600-1604
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• 2017

Mo-Cu alloys have been widely used for heat sink materials, vacuum technology, automobile and many other applications due to their excellent physical and electronic properties. Especially, Mo-Cu composites with 5~20 wt% copper are widely used for the heavy duty service contacts due to their excellent properties like low coefficient of thermal expansion, wear resistance, high temperature strength and prominent electrical and thermal conductivity. In most of the applications, high dense Mo-Cu materials with homogeneous microstructure are required for high performance, which has led in turn to attempts to prepare ultra-fine and well-dispersed Mo-Cu powders in different ways, such as spray drying and reduction process, electroless plating technique, mechanical alloying process and gelatification-reduction process. However, most of these methods were accomplished at high temperature (typically degree), resulting in undesirable growth of large Cu phases; furthermore, these methods usually require complicated experimental facilities and procedure. In this study, Mo-Cu alloying were prepared by planetary ball milling (PBM) and spark plasma sintering (SPS) and the effect of Cu with contents of 5~20 wt% on the microstructure and properties of Mo-Cu alloy has been investigated.

• 한국분말재료학회지
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• 제25권5호
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• pp.402-407
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• 2018

Molybdenum silicide has gained interest for high temperature structural applications. However, poor fracture toughness at room temperatures and low creep resistance at elevated temperatures have hindered its practical applications. This study uses a novel powder metallurgical approach applied to uniformly mixed molybdenum silicide-based composites with silicon carbide. The degree of powder mixing with different ball milling time is also demonstrated by Voronoi diagrams. Core-shell composite powder with Mo nanoparticles as the shell and ${\beta}-SiC$ as the core is prepared via chemical vapor transport. Using this prepared core-shell composite powder, the molybdenum silicide-based composites with uniformly dispersed ${\beta}-SiC$ are fabricated using pressureless sintering. The relative density of the specimens sintered at $1500^{\circ}C$ for 10 h is 97.1%, which is similar to pressure sintering owing to improved sinterability using Mo nanoparticles.

• 대한치과기공학회지
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• 제41권2호
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• pp.81-86
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• 2019

Purpose: The purpose of the present study was to compare the internal fit of two different temporary restorations fabricated by dental CAD/CAM system and to evaluate clinical effectiveness. Methods: Composite resin tooth of the maxillary first molar was prepared as occlusal reduction(2.0mm), axial reduction(1mm offset), vertical angle(6 degree) and chamfer margin for a temporary crown and duplicated epoxy die was fabricated. The epoxy dies were used to fabricate provisional restorations by CAD/CAM milling technique or 3D-printing technique. The inner data from all crowns were superimposed on the master die file in the 'best-fit alignment' method using 3D analysis software. Statistical analysis was performed using a Wilcoxon's rank sum test for differences between groups. Results: It showed that the internal RMS(Root Mean Square) values of the additive group were significantly larger than those of other group. No significant differences in internal discrepancies were observed in the temporary crowns among the 2 groups with different manufacturing method. Conclusion: All the groups had the internal fit within the clinical acceptable range (< $50{\mu}m$). The continuous research in the future to be applied clinically for the adaptation of additive manufacturing technique are needed.

• 한국식품영양과학회지
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• 제41권12호
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• pp.1785-1791
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• 2012

본 연구에서는 전분원료의 종류, 쌀의 도정도, 누룩의 종류를 달리하여 담근 막걸리의 품질 특성을 조사하였다. 밀가루는 쌀보다 조지방과 조단백 함량이 높았으며 수분함량은 낮았고, pH 및 총산함량은 쌀과 밀가루로 담근 막걸리 간에 차이가 없었다. 쌀과 밀가루로 담근 막걸리의 주된 유기산은 각각 lactic acid와 succinic acid였으며, 총 유기산 함량은 각각 4.0~5.6 mg/mL와 3.5 mg/mL로 쌀로 담근 막걸리의 유기산 함량이 더 많았다. 쌀과 밀가루로 담근 막걸리의 주된 유리당은 glucose였으며, 쌀과 밀가루로 담근 막걸리의 총 유리당 함량은 각각 76.41~54.53 mg/mL와 67.75 mg/mL로 쌀로 담근 막걸리의 유리당 함량이 더 많았다. 색도는 쌀 품종별로는 차이가 없었으며, 밀가루로 담근 막걸리의 b 값은 양의 값으로 황색이 진했다. 관능평가 결과, 쌀로 담근 막걸리가 밀가루로 담근 막걸리보다 기호도 점수가 더 높았다. 쌀의 도정도가 증가함에 따라 수분, 조지방, 조단백질, acetic acid의 함량은 감소하나, pH, 총산, 유리당, 색도에 있어서는 유의적인 차이가 없었다. 쌀의 도정도는 과실향을 제외한 기호도 점수에 유의적인 차이를 나타내지 않았다. 전통누룩과 개량누룩으로 담근 막걸리의 pH는 각각 4.29~4.65와 4.20~4.23으로 전통누룩으로 만든 막걸리의 pH가 더 높았으며, 총 유기산 함량도 전통누룩으로 담근 막걸리(3.5~6.3 mg/mL)가 개량누룩으로 담근 막걸리(2.3~4.3 mg/mL)보다 높았다. 총 유리당 함량은 개량누룩으로 담근 막걸리(59.44~73.34 mg/mL)가 전통누룩으로 담근 막걸리(56.45~59.75 mg/mL)보다 많았다. 색도는 전통누룩으로 담근 막걸리가 개량누룩으로 담근 막걸리보다 L, a, b 값이 높았으며, 관능적 기호도 점수는 개량누룩으로 담근 막걸리가 더 높았다. 본 연구 결과, 쌀로 담근 막걸리가 밀가루로 만든 막걸리에 비해 품질이 우수한 것으로 보이나, 쌀의 품종에 의한 품질 차이는 없었다. 쌀의 도정도에 따른 막걸리의 품질은 향미의 관능적 특성 외에는 영향을 미치지 않았으며, 도정을 많이 할수록 막걸리의 향미가 좋아졌다. 누룩 종류에 따른 막걸리의 품질 특성 분석 결과, 전통 누룩에 비해 개량누룩으로 담근 막걸리의 관능적 특성이 더 좋았다. 위 결과를 종합해 볼 때, 도정도가 높은 쌀을 전분질 원료로 하고 개량누룩을 사용하여 막걸리를 담근다면 품질이 우수한 막걸리를 제조할 수 있을 것이다.

• 한국산학기술학회논문지
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• 제19권8호
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• pp.176-182
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• 2018

심미 치과보철물의 가장 중요한 요인 중의 하나는 치아의 색상이다. 지르코니아는 디자인, 밀링, 착색, 건조, 소결과정을 거치는데, 이때의 지르코니아 착색제의 건조 정도가 색조에 어떠한 영향을 미치는지 알아보고자 한다. 실험을 위해 캐드캠을 이용하여 지르코니아 블록별(L block(LAZOR), Z block(Zircos-E block posterior), A block(AlphaZ))로 각 15개씩 총 45개의 원형 시편을 제작하였다. 그다음 지르코니아 시편을 화학적 착색제를 이용하여 미건조(0sec), 중간건조(10sec), 완전건조(10min)의 온도유지시간(Temperature dwelling time)을 부여하여 오븐에서 건조한 후 제조회사 지시대로 지르코니아 시편을 소결하였다. 분광광도계를 이용하여 색조를 측정하였다. 치과용 지르코니아 시편의 건조유지시간에 따라 색조의 변화를 비교 분석하기 위해 One-way ANOVA를 시행하고, 사후검정으로 Tukey test를 실시하였다. 지르코니아 $L^*$값은 L, A 시편과 $a^*$값은 A 시편, $b^*$값은 Z 시편의 건조 정도에 따라 통계적으로 차이가 없으나 (p>0.05), $L^*$값은 Z 시편과 $a^*$값은 L, Z 시편, $b^*$값은 L, A 시편이 건조 정도에 따라 통계적으로 차이가 있었다(p<0.05). 결론적으로 착색제의 건조유지시간이 길수록 지르코니아 명도를 밝게 하고, 법랑질의 광학적 특성을 증가시킨다.