• 한국기계가공학회지
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• 제21권2호
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• pp.116-122
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• 2022

This study proposed a method of testing the stability when selecting gears to reduce the weight of a 3-DOF wrist mechanism for a pick-and-place 3-DOF parallel robot with an increased workspace by using an additional straight axis at its top. We performed SolidWorks^® modeling- and ANSYS^®-based structural analysis of a pinion gear, which is most vulnerable to the force from a 3-DOF wrist mechanism, to lighten the robot weight for performing various tasks. When the initial analysis results considerably differed from the theoretical values calculated in advance, we checked and identified the errors in the contact conditions or input values. Ultimately, it is believed that the methodology presented in this paper will help in mitigating errors during analysis and determine the accurate values for a lightweight 3-DOF wrist mechanism for a parallel robot with an expanded workspace.

• 제어로봇시스템학회논문지
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• 제15권10호
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• pp.1029-1038
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• 2009

This paper proposes a gain switching algorithm for joint position control of a hydraulic humanoid robot. Accurate position control of the lower body is one of the basic requirements for robust balance and walking control. Joint position control is more difficult for hydraulic robots than it is for electric robots because of an absence of reduction gear and better back-drivability of hydraulic joints. Backdrivability causes external forces and torques to have a large effect on the position of the joints. External ground reaction forces therefore prevent a simple proportional-derivative (PD) controller from realizing accurate and fast joint position control. We propose a state feedback controller for joint position control of the lower body, define three modes of state feedback gains, and switch the gains according to the Zero Moment Point (ZMP) and linear interpolation. Dynamic equations of hydraulic actuators were experimentally derived and applied to a robot simulator. Finally, the performance of the algorithm is evaluated with dynamic simulations.

• 한국항해학회지
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• 제20권3호
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• pp.1-11
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• 1996

The accuracy for determining fishing ground and for setting fishing gear location, and the repeatability of ship position vary depending on fishing methods. Especially, Loran-C has been served to give fisherman highly accurate ship's position, and a number of fishing vessel are equipped with it's receivers. In this paper, in order to evaluate the accuracy of Loran-C fix of Korean chain in Korean southeast coast, the authors examined and analyzed the data of the receiver of Loran-C(LC 90, Furuno) and GPS(AccNav $Sport^{TM}$, Eagle) measured automatically and continuously for 2 seconds at interval of 5minutes during 2hours from $11^{th}$ to $21^{st}$, July, 1996 at six observed points, that is, Pusan, Wolnae, Pangojin, Chongja, Kampo and Kuryongpo in Korean southeast coast. As the result obtained, Loran-C signals showed little fluctuation with good reprodutibility. Good stability of Loran-C signals was indicated by the small value of the standard deviation 0.064~0.094$\mu\textrm{s}$. Although determination of the observed position could not be completely accurate, the extent of the error was estimated smaller than 0.35 nautical mile.

• 한국생산제조학회지
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• 제24권6호
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• pp.675-681
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• 2015

When many holes on a plane are machined simultaneously, the positional precision and machining efficiency are very important. Multi-spindle heads are typical order making products of which the number of shafts and hole positions vary depending on the size or form of the product. For the automatic design of multi-spindle heads, the design modules for power transmission systems for drive, idle, and spindle shafts were developed, and a design technique the determining the optimum position and number of idle shafts according to gear positions was developed. In addition, for the precise determination of the multi-spindle head, the design methods for the guide planes of columns, and feed mechanisms were devised. In addition, the design modules for accurate clamping and automatic transportation mechanisms were developed. Finally, in order to simplify and standardize the design process, the design analysis and simulation verification modules are integrated.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.1598-1602
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• 2003

The parallel-type mechanism provides more accurate and stiff motion than the serial-type mechanism. However, in case of using the haptic device, the performance of the force reflection can be deteriorated due to the singular points existing in workspace. In this paper, we propose a redundantly actuated parallel 3-DOF haptic device, which is singularity-free in the workspace and has an improved force reflection capability. In addition, we propose a new force distribution algorithm, which can reflect force of both high and low resolution, using two sets of actuator with different size. Redundant actuators are attached to the base frame in order to minimize the inertia of the system. Moreover, a wire and gear reduction system is employed to achieve high force reflection along with soft feeling. We confirm the performance of the force reflection capability throughout simulation.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.29-33
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• 2003

The improvement of dimensional accuracy for forged part is one of major goals in cold forging industry. There are many problems in controlling the dimension only by the trial-and-error, especially for a precision forged gear. A FEM analysis has been used in developing the forging technology. However, FE techniques have to be reconfirmed for predicting accurately the dimension of forged part. In this study, the effects of elastic characteristics and temperature changes are investigated by the comparisons between experimental and FEA in cold forging. When FE models related with elastic characteristics are considered as reality, FE results could predict the part dimension within the range of 10 $\mu\textrm{m}$. And if temperature also is considered really, the predicted dimensions are well coincided with the experimental down to about 5$\mu\textrm{m}$.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.68-71
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• 2003

Heat treatment is one of the critical manufacturing processes that determine the quality of a product. This paper presents experimental and analytical results for the quench of a ring gear in stagnant oil. The goal of this study is to develop heat transfer predicting model in an overall analysis of the quenching process. Thermal conductivities which are dependant on temperatures and convection coefficients which are obtained by inverse method are used to develop the accurate heat transfer model. The results of heat transfer model have a good agreement with experimental results.

• 한국자동차공학회논문집
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• 제7권9호
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• pp.112-118
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• 1999

Shrinkage behavior was investigated to obtain more accurate dimensions of injected molding parts for free and restricted shrinkage conditions. various parameters for metal inserted injection process, such as thickness of resin, holding pressure and time, mo이 temperature and restriction condition of mold, were considered for the analysis of shrinkage phenomena. For numerical analysis, MOLDFLOW software was used to find the deterministic parameters of filling time, temperature, pressure and holding time. Also , experimental shrinkage effects were measured through actual injection molding process and the resin thickness was under controlled as 3 mm , 5 mm, and 7mm for the shapes of plastic gear made of Polymide(PA) and Polyxymethlene(POM). The main parameters of these injection processes were found to be holding pressure, holding time and mold temperature in the case of metal inserted molding.

• 한국자동차공학회논문집
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• 제5권5호
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• pp.73-85
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• 1997

An automatic transmission is an important element of automotive power systems that allows a driving convenience. Compared to a manual transmission, however, it has a few problems in efficiency, shift feel, and maintenance. To improve these, it is imperative to understand the dynamics of automatic transmissions. This paper develops a dynamically-correct model of an automatic transmission, using the bond graph method. The bond graph method is ideally suited for modeling power systems, because the method is based on generalized power variables. The bond graph method is capable of providing correct dynamic constraints and kinematic constraints, as well as the governing differential equations of motion. The bond graph method is applied to 1-4 in-gear ranges, as well as various upshifts and downshifts of an automatic transmission, which allows an accurate simulation of an automatic transmission. Conventional automatic transmission models have no dynamic constraint, which do not allow correct simulation studies.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.457-464
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• 2001

The aeroacoustic phenomena in the simple rectangular open cavity are well published by many researchers. But the geometry shapes of aircraft landing gear wells, weapon bays, etc. are more complicate than that of the simple retangular cavity. They are more similar to the cavity having cover-plates at adges, or Helmholtz resonator. Therefore, the effects of cover-plates existing on edges of rectangular open cavity are numerically investigated in this paper. The compressible Navier-Stokes equations are solved for two-dimensional cavities with laminar boundary layers upstream. The high-order and high-resolution numerical schemes are used for the evaluation of spatial derivatives and the time integration. Physically correct numerical boundary conditions and buffer zone techniques are implemented to produce time-accurate solutions in the whole computation domain. The computational domain is large enough to directly resolve a portion of the radiated acoustic field. Results show that the cover-plates existing on edges of cavity reduce the noise convected from cavity, make the frequency of noise become higher, and change the directivity pattern. So these results can be used in the design of a low noise cavity.