• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.1
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• pp.203-209
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• 2009

The purpose of this study is to develop a minimally constraint joint angle measurement system for the feedback control of FES (functional electrical stimulation) locomotion. Feedback control is desirable for the efficient FES locomotion, however, the simple on-off control schemes are mainly used in clinic because the currently available angle measurement systems are heavily constraint or cosmetically poor. We designed a new angle measurement system consisting of a magnet and magnetic sensors located below and above the ankle joint, respectively, in the rear side of ipsilateral leg. Two magnetic sensors are arranged so that the sensing axes are perpendicular each other. Multiple positions of sensors attachment on the shank part of the ankle joint model and also human ankle joint were selected and the accuracy of the measured angle at each position was investigated. The reference ankle joint angle was measured by potentiometer and motion capture system. The ankle joint angle was determined from the fitting curve of the reference angle and magnetic flux density relationship. The errors of the measured angle were calculated at each sensor position for the ankle range of motion (ROM) $-20{\sim}15$ degrees (dorsiflexion as positive) which covers the ankle ROM of both stroke patients and normal subjects during locomotion. The error was the smallest with the sensor at the position 1 which was the nearest position to the ankle joint. In case of human experiment, the RMS (root mean square) errors were $0.51{\pm}1.78(0.31{\sim}0.64)$ degrees and the maximum errors were $1.19{\pm}0.46(0.68{\sim}1.58)$ degrees. The proposed system is less constraint and cosmetically better than the existing angle measurement system because the wires are not needed.

• Journal of Korean Society for Geospatial Information Science
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• v.6 no.2 s.12
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• pp.21-34
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• 1998

SAR is an active imaging sensor emitting its own energy source and can be operated in all weather conditions. Thus SAR provides data which can not be obtained by an optical sensor. In this study, the potentials and problems of the techniques for DEM extraction from the SAR imagery were evaluated through theoretical researches and practical experiments. And then the accuracy was tested by RMS error between the digitized map contour and the results from this experiment. Here, two types of DEM extraction method were evaluated. One was an analytical photogrammetric technique, and the other was a SAR interferometric processing. From the experiment, we found that the photogrammetric technique is currently the most suitable method considering topographic conditions of Korea. In the SAR interferometry technique, we also conclude that the problems caused by decorrelations due to the temporal reasons and due to the scattering effects from vegetation should be solved.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1321-1329
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• 1993

Long time creep strength and life prediction of 1% Cr-Mo-V and 12% Cr rotor steel were performed by using round-bar type specimens under static load at 500-600.deg. C TTP (time temperature parameter), MCM (minimum commitment method) and ISM (initial strain method newly devised) as life prediction methods were investigated, and the results could be summarized as follows. (1) The minimum parameter of SEE (standard error) by TTP was proved as LMP (larson-miller parameter), and the minimum parameter of RMS (root mean squares), by data less than 10$^{3}$hrs was MHP (manson-haferd parameter). (2) The parameters of the minimum and the maximum strength values predicted in $10^{5}$hrs creep life of 1% Cr-Mo-V steel by TTP were LMP and MSP, respectively. In case of 12% Cr steel above $550^{\circ}C$ OSDP (orr-sherby-dorn parameter) was minimum and MSP (manson-succop parameter) was maximum, but below $550^{\circ}C$, the inverse phenomena was observed. On the other hand the creep strengths before $10^{3}hrs$ life by MCM were similar to those by TTP, but the strengths after $10^{3}hrs$ life were 10-25% lower than those by TTP. (3) Creep strengths by ISM were maximum 5% lower than those by TTP. Because $10^{5}hrs$ strengths were similar to those of the lower band by TTP, the ISM was safer than the TTP.

• Agricultural and Biosystems Engineering
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• v.6 no.2
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• pp.47-53
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• 2005

AMachine vision is a promising tool for the autonomous guidance of farm machinery. Conventional CCD camera for the machine vision needs a desktop PC to install a frame grabber, however, a web camera is ready to use when plugged in the USB port. A web camera with a notebook PC can replace existing camera system. Autonomous steering control system of this research was intended to be used for combine harvester. If the web camera can recognize cut/uncut edge of crop, which will be the reference for steering control, then the position of the machine can be determined in terms of lateral offset and heading angle. In this research, a white line was used as a cut/uncut edge of crop for steering control. Image processing algorithm including capturing image in the web camera was developed to determine the desired travel path. An experimental vehicle was constructed to evaluate the system performance. Since the vehicle adopted differential drive steering mechanism, it is steered by the difference of rotation speed between left and right wheels. According to the position of vehicle, the steering algorithm was developed as well. Evaluation tests showed that the experimental vehicle could travel within an RMS error of 0.8cm along the desired path at the ground speed of $9\sim41cm/s$. Even when the vehicle started with initial offsets or tilted heading angle, it could move quickly to track the desired path after traveling $1.52\sim3.5m$. For turning section, i.e., the curved path with curvature of 3 m, the vehicle completed its turning securely.

• Journal of Biosystems Engineering
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• v.25 no.6
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• pp.457-462
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• 2000

Boom sprayers have been known by their excellency in field efficiency worker’s safety and pest control efficacy. The boom sprayer in Korea that was developed for paddy field is not suitable for upland field of which shape is irregular and inclination is steep, due to heavy chemical tank long boom width and manual on-off control of spraying. The goal of the study was to develope a boom control system that could control boom angles of left and right boom automatically and independently corresponding to local field slope. The prime mover was selected as a cultivating tractor. Main results of this study were as follows. 1. Ultrasonic sensor whose response time was 0.1s and response angle was within $\pm$20$^{\circ}$was selected to measure distance. Voltage output of the sensor(X, Volt) had a highly significant linear relationship with the vertical distance between the sensor and ground surface(Y, mm) as follows; Y=0.0036X-0.437 2. Left and right section of the boom could be folded up by a position control device(on-off control) which could control the left and right boom independently corresponding to local slope by equalizing distances between the sensor and boom at the center and left/right boom. Most reliable DB(dead band) was experimentally selected to be 75$\Omega$(6cm). 3. At traveling velocity of 0.3~0.5m/s RMS of error between desired and achieved height was less than 4.5cm The developed boom angle controller and boom linkage system were evaluated to be successful in achieving the height control accuracy target of $\pm$10cm.

• International Journal of Aeronautical and Space Sciences
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• v.16 no.3
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• pp.380-393
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• 2015

This study presents how we can evaluate stereo camera systems for the structural deformation monitoring. A stereo camera system, consisting of a set of stereo cameras and reflective markers attached on the structure, is introduced for the measurement and the stereo pattern recognition (SPR) method is utilized for the full-field structural deformation estimation. Performance of this measurement system depends on many parameters including types and specifications of the cameras, locations and orientations of them, and sizes and positions of markers; it is difficult to experimentally identify the effects of each parameter on the measurement performance. In this study, a simulation framework for evaluating performance of the stereo camera systems with various parameters has been developed. The maximum normalized root-mean-square (RMS) error is defined as a representative index of stereo camera system performance. A plate structure is chosen for an introductory example. Its several modal harmonic vibrations are generated and estimated in the simulation framework. Two cases of simulations are conducted to see the effects of camera locations and the resolutions of the cameras. An experimental validation is carried out for a few selected cases from the simulations. Using the simultaneous laser displacement sensor (LDS) measurements as the reference, the measurement errors are obtained and compared with the simulations.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.11
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• pp.1009-1017
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• 2010

As rotating machines play an important role in industrial applications such as aeronautical, naval and automotive industries, many researchers have developed various condition monitoring system and fault diagnosis system by applying various techniques such as signal processing and pattern recognition. Recently, fault diagnosis systems using artificial neural network have been proposed. For effective fault diagnosis, this paper used MLP(multi-layer perceptron) network which is widely used in pattern classification. Since using obtained signals without preprocessing as inputs of neural network can decrease performance of fault classification, it is very important to extract significant features of captured signals and to apply suitable features into diagnosis system according to the kinds of obtained signals. Therefore, this paper proposes the decision method of the proper feature vectors about each fault signal for neural-network-based fault diagnosis system. We applied LPC coefficients, maximum magnitudes of each spectral section in FFT and RMS(root mean square) and variance of wavelet coefficients as feature vectors and selected appropriate feature vectors as comparing error ratios of fault diagnosis for sound, vibration and current fault signals. From experiment results, LPC coefficients and maximum magnitudes of each spectral section showed 100 % diagnosis ratios for each fault and the method using wavelet coefficients had noise-robust characteristic.

• Journal of the Korean Society of Radiology
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• v.8 no.1
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• pp.19-26
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• 2014

This paper suggests techniques to enhance coding time which is a problem in traditional fractal compression and to improve fidelity of reconstructed images by determining fractal coefficient through adaptive selection of block approximation formula. First, to reduce coding time, we construct a linear list of domain blocks of which characteristics is given by their luminance and variance and then we control block searching time according to the first permissible threshold value. Next, when employing three-level block partition, if a range block of minimum partition level cannot find a domain block which has a satisfying approximation error, we choose new approximation coefficients using a non-linear approximation of luminance term. This boosts the fidelity. Our experiment employing the above methods shows enhancement in the coding time more than two times over traditional coding methods and shows improvement in PSNR value by about 1-3dB at the same compression rate.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.248-255
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• 2009

After several damages by PWSCC were found in the world, USNRC and PNNL(Pacific Northwest National Laboratory) started the research on PWSCC under the project name of PINC. The aim of the project was 1) to fabricate representative NDE mock-ups with flaws to simulate PWSCCs, 2) to identify and quantitatively assess NDE methods for accurately detecting, sizing and characterizing PWSCCs, 3) to document the range of locations and morphologies of PWSCCs and 4) to incorporate results with other results of ongoing PWSCC research programs, as appropriate. Korea nuclear industries have also been participating in the project. Thermally and mechanically cracked-four mockups were prepared and phased array and manual ultrasonic testing(UT) techniques were applied. The results and lessons learned from the preliminary RRT are summarized as follows: 1) Korea RRT teams performed the RRT successfully. 2) Crack detection probability of the participating organizations was an average 87%, 80% and 80% respectively. 3) RMS error of the crack sizing showed comparatively good results. 4) The lessons learned may be helpful to perform the PINC RRT and PSI /ISI in Korea in the future.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.5
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• pp.363-371
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• 2020

The parameters of the modified BM and JONSWAP spectra are estimated using spectral data set off Namhangjin, located in the east coast of Korea, collected during high wave events. The parameters of the modified BM spectrum were estimated to be 1.04 and 0.27, which were similar to the conventional values of 1.098 and 0.30, but showed significant differences in statistical terms. On the other hand, the peak enhancement factor of JONSWAP spectrum was estimated to be 1.4, which was substantially small compared to the conventional value of 3.3. The RMSE differences from the fitted results of the two spectra were small, approximately 0.2. In the frequency range greater than the peak frequency, however, the spectral energy density showed relatively mild decrease with increase of the frequency, compared to the standard forms of the modified BM and JONSWAP spectra.