• 한국정밀공학회지
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• 제27권8호
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• pp.48-53
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• 2010

5-axis CNC machining now is getting popular because it can deal with complex shapes such as impeller, turbine blade and propeller without additional equipment or process, proving a set of various tool orientations. CAM software related to 5-axis machining is being developed quickly so that users can take advantage of potential capacities of 5-axis machine tools. However, only a few researches can be found in the area of control strategy development for 5-axis machining. This paper proposes a 5-axis cross-coupling control system based on a novel tool orientation error model. The proposed tool orientation error model provides accurate information on the tool orientation error in real time, which in turn enables directly controlling the tool orientation accuracy. The proposed control system also employs a contour error model to calculate the contour error and reflect it in the control as well. The accuracy of the proposed tool orientation error model is verified and the performance of the 5-axis cross-coupling control system in terms of both contouring and tool orientation accuracy is evaluated through computer simulations compared with existing 5-axis control systems.

• 한국정밀공학회지
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• 제16권8호
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• pp.122-129
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• 1999

A 5-axis CNC machine tool is more useful compared with a 3-axis machine tool, because the position and the orientation of a tool tip can be controlled simultaneously. Unlike the 3-axis machine tool, the 5-axis machine tool has the volumetric position error and volumetric orientation error due to the quasi-static error of each machine tool joint which is a major source of machined part error. So, the generalized error synthesis model of the 5-axis CNC machine tool was developed to predict and to compensate for the volumetric position error and the volumetric orientation error. It was proposed that a compensation algorithm to correct simultaneously the volumetric position error and the volumetric orientation error of the 5-axis CNC machine by error inverse kinematic.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2002년도 추계학술대회 논문집
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• pp.24-29
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• 2002

In any rapid prototyping process, the layer by layer building process introduces an area error between the staircase and the surface line specified by the computer-aided design model. This affects the dimensional accuracy as well as the surface finish for different part build orientations. This paper describes a methodology for computing the area error for any orientation of the part built by the fused deposition modelling system. This technique can be applied to determine the best build orientation of the part, based on the minimum area error. This technique is verified by comparing the results with the experimental measurements of the area error of the parts built at different orientations.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1996년도 춘계학술대회 논문집
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• pp.483-487
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• 1996

We consider the estimation of the position and orientation of 6 DOF motion bed (Stewart platform) from the measured cylinder length. The solution of forward kinematics is not solved yet as a useful realtime application tool because of the complity of the equation with multiple solutiple solutions. Hence we suggest an algorithm for the estimation of forward kinematics solution using Luenberger observer withnonlinear error correction term. The Luenberger observer withlinear model shows that the estimation error does not go to zero in steadystate due to the linearization error of the dynamic model. Hence the linear observer is modified using nonlinear measurement error equation and we prove thd practical stability of the estimation error dynamics of the proposed observer using lyapunov function.

• Journal of Mechanical Science and Technology
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• 제16권6호
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• pp.799-809
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• 2002

In order to utilize a parallel mechanism as a machine tool component, it is important to estimate the errors of its end-effector due to the uncertainties in parts. This study proposes an error analysis for a new parallel device, a cubic parallel mechanism. For the parallel device, we consider two kinds of errors. One is a static error due to link stiffness and the other is a dynamic error due to clearances in the parts. In this study, we propose a stiffness model for the cubic parallel mechanism under the assumption that the link stiffness is a linear function of the link length. Also, from the fact that the errors of u-joints and spherical joints are changed with the direction of force acting on the link, they are regarded as a part of link errors, and then the error model is derived using forward kinematics. Lastly, both the error models are integrated into the total error, which is analyzed with a test example that the platform moves along a circular path. This analysis can be used in predicting the accuracy of other parallel devices.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 26-27 Oct. 1990
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• pp.1173-1177
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• 1990

Cerebellar Model Linear Associator Net(CMLAN), a kind of neuro-net based adaptive control function generator, was applied to the problem of direct inverse calibration of three and six d.o.f. POMA 560 robot. Since CMLAN autonomously maps and generalizes a desired system function via learning on the sampled input/output pair nodes, CMLAN allows no knowledge in system modeling and other error sources. The CMLAN based direct inverse calibration avoids the complex procedure of identifying various system parameters such as geometric(kinematic) or nongeometric(dynamic) ones and generates the corresponding desired compensated joint commands directly to each joint for given target commands in the world coordinate. The generated net outputs automatically handles the effect of unknown system parameters and dynamic error sources. On-line sequential learning on the prespecified sampled nodes requires only the measurement of the corresponding tool tip locations for three d.o.f. manipulator but location and orientation for six d.o.f. manipulator. The proposed calibration procedure can be applied to any robot.

• 한국산업융합학회 논문집
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• 제17권3호
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• pp.84-92
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• 2014

In this paper, a novel 5-axis hybrid-kinematic machine tool is introduced and the research results on accuracy improvement of the prototype machine tool are presented. The 5-axis hybrid machine tool is made up of a 3-DOF parallel manipulator and a 2-DOF serial one connected in series. The machine tool maintains high ratio of stiffness to mass due to the parallel structure and high orientation capability due to the serial-type wrist. In order to acquire high accuracy, the methodology of measuring the output shafts by additional sensors instead of using encoder outputs at the motor shafts is proposed. In the kinematic view point, the hybrid manipulator reduces to a serial one, if the passive joints in the U-P serial chain at the center of the parallel manipulator are directly measured by additional sensors. Using the method of successive screw displacements, the kinematic error model is derived. Since a ball-bar is less expensive than a full position measurement device and sufficiently accurate for calibration, the kinematic calibration method of using a ball-bar is presented. The effectiveness of the calibration method has been verified through the simulations. Finally, the calibration experiment shows that the position accuracy of the prototype machine tool has been improved from 153 to $86{\mu}m$.

• 전자공학회논문지B
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• 제31B권11호
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• pp.53-62
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• 1994

본 논문에서는 湖光立體視法(Photometric Stereo Method : PSM)을 적용하여 3차원 물체의 표면 방향정보를 추정할 때 조명원이 이상적인 평행광이 아닌 범용 조명환경인데서 기인한 표면 방향추정 오차의 해석 방법을 제시하였다. 제시한 방법에서는 원반 형태의 조사 대상 면을 포함한 조명환경에 대한 구체적인 모델링과 오차분포에 대한 직접적인 시뮬레이션을 통하여 오차해석을 하도록 하였다. 범용조명원은 beam angle을 갖는 점광원으로 가정하고, 조사 대상면에서의 밝기분포는 분산값이 변하는 가우스함수 형태로 모델링하였다. 설정된 조명 모델에서 분산을 여러값으로 변화시켜서 이에따라 PSM에서 나타나는 오차분포를 얻기 위한 목적으로, 임의의 세 방향으로 위치한 조사 대상면의 평균 밝기값을 계산하여 고정된 조명원의 위치벡터를 얻는 시뮬레이션 알고리듬을 제시하였다. PSM과 제안된 조명원의 위치추정 알고리듬 사이에는 상사관계(analogy)가 성립하기 때문에, PSM 적용시 비이상적인 조명모델에 의해 나타나는 물체표면방향 추정오차는 제시한 조명원 위치추정 시뮬레이션으로부터 직접적으로 구할 수 있다. 또한 설정된 조사대상면 모델과 같은 원방형태의 계측기구를 제작하여 임의의 방향벡터를 제공하도록 하고, 이를 측정과 시뮬레이션에 사용함으로써 오차해석과 보정을 체계적으로 수행할 수 있도록 하였다. 제시한 방법에 따라 방향 벡터를 제공하도록 하고, 이를 측정과 시뮬레이션에 사용함으로써 오차해석과 보정을 체계적으로 수행할 수 있도록 하였다. 제시한 방법에 따라 방향 벡터값들의 조합을 공간상에서 다양하게 변화시키면서, PSM에서 나타나는 방향추정 오차분포를 구하는 컴퓨터 시뮬레이션을 수행하였다. 시뮬레이션과 같은 방법으로 실측에 의한 방향추정 오차를 구하고 시뮬레이션에서 얻은 결과와 비교 검토하였다. 그 결과, 실제 측정실험에서 얻은 복합적인 오차중 상당부분은 비이상적인 범용조명원 모델로부터 기인한 것임을 확인할 수 있었다.

• 한국산학기술학회논문지
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• 제14권8호
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• pp.3625-3630
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• 2013

도어 모듈은 모듈화의 대표적인 예로 여러 부품들은 모듈형태로 완성하여 완성차 업체의 원가절감 및 조립시간 단축, 품질 향상 등에 큰 기여를 이루었다. 주요 부품중의 하나인 Door carrier plate는 주로 steel을 이용한 press 성형이 주였으나 최근에는 PP-LFT(유리 장섬유 강화PP)를 사용한 사출 공법을 적용함으로써 형상자유도를 높혀 모듈에 부착되는 많은 종류의 부품들을 통합할 수 있게 되었으며 중량 절감을 이룰 수 있게 되었다. 하지만 사출 성형시 제품의 형상 및 gate위치 설정의 한계성과, LFT의 특성에 의하여 변형이 비교적 심해 일반적으로 시사출 진행 후 보상 가공을 진행하여 조립성을 개선한다. 이러한 사후 수정 공정은 금형의 품질 저하 및 생산원가 상승의 주요인이다. 부분적으로 사출 CAE를 적용하여 warpage정도를 예측하나 그 신뢰성 확보에 어려움을 겪고 있다. 따라서 LFT를 사용하는 Door carrier plate에 대한 해석 신뢰성을 확보할 수 있는 기법으로 hyper-mesh에서 1차 mesh작업 후 moldlfow 자체 tool을 이용하여 mesh의 두께 구현성을 높혔으며, fiber orientation해석을 위하여 ARD-RSC model을 적용하였다.