• 한국정밀공학회지
• /
• 제32권10호
• /
• pp.865-871
• /
• 2015

This study was conducted in order to develop a finger exoskeleton system using ionic polymer metal composites (IPMCs) as the actuator and sensor in a hybrid structure. To use the IPMC as an actuator producing large force, a first order transfer function was obtained using results from a block force for DC excitation that applied to two IPMCs of 20mm-width, 50mm-length, and 2.4mm thickness together. After which the validation of 200gf control with anti-windup PI controller was confirmed. A 5mm-width, 50mm-length, 0.6mm-thickness of IPMC was also modeled as a sensor for tip displacement. As a result, the IPMC sensor could been utilized as a trigger role for the actuator. Finally, an IPMC sensor and actuator were installed on the joint of a single DOF exoskeleton in the hybrid structure, and test for the control of 40gf of block force and predefined sequence of motion was performed.

• 대한기계학회논문집
• /
• 제17권9호
• /
• pp.2172-2180
• /
• 1993

Under general loadings, including body forces, crack-face tractions and thermal loading, the energy release rate equation for a two-dimensional cracked body is presented. Defining the virtual crack extension as the variation of the geometry, the equation is directly derived by a shape design sensitivity of the potential energy. Although the form of the derived energy release rate equation is different from other researchers's results, the three example show that the former is exactly the same as the latter. However, the final integral equation do not involve the derivative of the displacement on the crack surface and crack tip region, thereby improving the numerical accuracy in the computation of the energy relase rate. Moreover, as it was derived from the governing equation including non-linear elasticity without special assumptions, the energy release rate of a elasto-plastic fracture can be obtained and any numerical stress analysis method can be applied.

• 한국항공우주학회지
• /
• 제32권3호
• /
• pp.58-65
• /
• 2004

유한요소법을 이용하여 액체 로켓 엔진 터보 펌프 터빈의 천이 열전달 및 구조 해석이 수행되었다. 해석 모델은 3차원 8절점 등매개변수 솔리드 요소로 구성되었으며, 전체 모델의 1/80만이 해석되었다. 열 스파이크를 포함하는 시동 조건과 정상상태에서의 하중이 고려되었다. 블레이드 면 위의 열전달 계수는 상용 열유동 해석 프로그램인 Fluent를 이용하였다. 개발된 유한 요소 코드를 이용하여 시동 및 정상상태에서 천이 열전달 응답을 구하였다. 또한, 원심력과 열하중이 가해질 때, 최대 응력 및 슈라우드의 변위를 구하였다.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국제학술편); Seoul National University, Seoul; 20-22 Oct. 1993
• /
• pp.202-207
• /
• 1993

A theoretical and experimental study is presented for the force holding control of a miniature robotic ringer which is driven by a pair of piezoelectric unimorph cells. In the theoretical analysis, one finger is modeled as a flexible cantilever with a tactile force sensor at the tip and the mate of the finger is a solid beam supposed with sufficient stiffness. Further, the force sensor is modeled by a one-degree-of-freedom, mass-spring system and the output of sensor is then described by the sensor stiffness multiplied by the relative displacement. The problem investigated in this paper is that two typical holding tasks of the human finger are picked up and applied to the robotic finger. One is the work holding a stationary object with a prescribed, time-varying force and the other one is to keep the contacted force constant even if the object is in motion. The simple PID feedback control scheme is used to control the minute gripping force of order 0.01 Newton. It is shown both experimentally and theoretically that the artificial finger with the piezoelectric actuator works well in the minute force holding of the tiny object.

• 한국지반환경공학회 논문집
• /
• 제2권3호
• /
• pp.89-99
• /
• 2001

본 연구에서는 가장 널리 사용되고 있는 지반모델인 Modified Cam-Clay 모델을 이용하여 피에조콘 관입 및 소산시험의 수치해석을 수행하였다. Modified Cam-Clay 모델 및 관련 유한요소 식들을 피에조콘 관입의 대변형 현상을 고려하기 위하여 Updated Lagrangian frame에서 formulation 하였다. 유한요소 해석 결과 얻어진 콘 관입저항치, 간극수압 및 소산곡선을 양산지역 현장 시험결과와 비교 분석하였다. 수치해석 결과는 시험결과와 비교적 잘 부합하는 것으로 고찰되었으나 보다 현실에 근접한 simulation을 위하여 연속적인 깊은 관입의 적절한 수치해석적 modeling이 요구되는 것으로 고찰되었다.

• 대한기계학회논문집A
• /
• 제24권4호
• /
• pp.955-962
• /
• 2000

Scanning Probe Microscope (SPM) such as Scanning Tunneling Microscope (STM) and Atomic Force Microscope (AFM) was shown to be the powerful tool for nano-scale characterization of a fracture surface . AFM was used to study cross sectional profiles and dimensions of fatigue striations in 2017-T351 aluminum alloy. Their widths (SW) and heights (SH) were measured from the cross sectional profiles of three-dimension AFM images. The following results that will be helpful to understand the fatigue crack growth mechanism were obtained. (1) Coincidence of the crack growth rate with the striation width was found down to the growth rate of 10-5 mm/cycle. (2) The relation of SH=0.085(SW)1.2 was obtained. (3) The ratio of the striation height to its width SH/SW did not depend on the stress intensity factor range K and the stress ratio R. (4) Not only the SW but also the SH changed linearly with the crack tip opening displacement (CTOD) when plotted in log-log scale. From these results, the applicability of the AFM to nano-fractography is discussed.

• 대한기계학회논문집
• /
• 제14권1호
• /
• pp.103-111
• /
• 1990

본 연구에서는 성장하는 균열선단에서 열림변위의 임계증분에 대한 균열성장 조건에 기본을 두고 계산된 파단하중을 실험결과와 비교하여 균열성장저항을 특성 지 을수 있는 새로운 재료상수를 제안한 것이다.

• 대한기계학회논문집A
• /
• 제26권3호
• /
• pp.528-536
• /
• 2002

As one step for the safety performance of LNG storage tank, the change in fracture toughness within the X-grooved weld heat-affected zone (HAZ) of newly developed 9% Ni steel, which was submerged arc (SA)-welded, was investigated. Both crack initiation fracture toughness and crack arrest fracture toughness were evaluated by the crack tip opening displacement (CTOD) tests and compact crack arrest (CCA) tests. As the evaluated region approached the fusion line, each test result shorted different tendency, that is, crack initiation toughness decreased while crack arrest toughness increased. The results were discussed through the observation of the microstructural change.

• 한국정밀공학회지
• /
• 제29권1호
• /
• pp.64-71
• /
• 2012

In this paper, a parallel manipulator is comprised of two sliders and four links. Sliders execute a linear reciprocating motion depending on parallel guides and make the connected links rotate. A couple of links connected by sliders do coupling motion. The end-effector called a link tip has orientation angle. Through the kinematics analysis of this manipulator, we found displacement, velocity and acceleration using direct and inverse kinematics. We used equations that derived from this analysis and determined five constraint conditions. These conditions had much to do with rotation states of links, the relative relation of link length and coupling motion state. To verify those, we suggest a new algorithm regarding constraint conditions of a manipulator. With the result which performed the algorithm, we found out that operation range of coupled links was limited by relative relation of link length and that manipulator was not able to carry out a series of link motion, in case of being the link vertical between two parallel guides.

• Archives of Plastic Surgery
• /
• 제34권6호
• /
• pp.785-791
• /
• 2007

Purpose: Paraffin has been used to augment depressed nasal contour for many years by illegally. Reported complications of nasal paraffinoma were skin thinning, displacement of nasal profile, redness, chronic inflammation and malignant change to skin cancer. The current authors report results of the secondary rhinoplasty after excision of nasal paraffinoma. Methods: Through the open rhinoplasty incision, paraffinoma was removed under direct vision. Saline irrigation and meticulous hemostasis were performed. Simultaneously, the secondary depressed nasal deformity was corrected with autogenous dermofat graft harvested from inferior gluteal fold. The dermofat was fixed to the nasofrontal area with bolster suture, and the interdormal area of the tip. Results: A total of 13 patients underwent secondary augmentation with autogenous dermofat graft after removal of paraffinoma from 2000 to 2004. The mean follow-up period was 15 months. There were no postoperative complications. All patients were satisfied with their surgical results. However, there were 10 to 20 percent resorption of the grafted dermofat. Conclusion: It is suggest that autogenous dermofat be one of good materials for the correction of the secondary deformity after removal of nasal paraffinoma. In addition, autogenous dermofat graft presented easy harvesting and manipulation for transfer, high survival rate by firm fixation to the recipient site and stable surgical results.