Papers by Author: Sang Sik Lee

Abstract: Si-Mn spring steel (JIS SUP 9) is primarily employed in the construction of coil springs, particularly those used in soil cultivators deployed in harsh environments. This is due to its specific properties, which allow it to resist permanent deformation, and also provide rapid and effective vibration relief. Si-Mn spring steel (JIS SUP 9) for use in such projects is normally subjected to oil quenching and heat treatment, in order to strengthen its resistance to both impact and fatigue. Unfortunately, oil quenching is associated with environmental issues, most notably pollution and the contamination of wastewater with oil. Therefore, the objective of this study was to describe an alternative aqua quenching for use with this heat treatment. However, aqua quenching has traditionally conferred a lower tensile laod than does oil quenching. This problem of lesser tensile load was solved by properly controlling the density and temperature of the aqua quenching liquid, as well as careful mixing. As a result, it has proven possible to achieve results with aqua similar to those conferred by oil quenching, with regard to chemical components, tensile load, and surface hardness. The tensile load results achieved by oil quenching were 13,145 Pa and 17,177 Pa, and the tensile loads achieved with aqua quenching were 15,392 Pa, 16,804 Pa, 17,923 Pa, and 18,668 Pa. Therefore, the results of our experiments demonstrated the appropriacy and efficacy of this aqua quenching technique as a component of heat treatment for Si-Mn spring steel (JIS SUP 9).

Abstract: The objective of this study was to develop a portable, wireless surface EMG of a noninvasive type. The limitations of the existing system include its large size and the necessity of a wire. Therefore, this study focused on the development of a portable and wireless type of EMG. The developed EMG, which has 10 channels, is composed of an electrode for the measurement of the EMG signal, a preamplifier for initial processing, a second amplifier, an A/D converter, and a Bluetooth module for wireless communication. The communication of the developed EMG used a UART (Universal Asynchronous serial Receiver and Transmitter) and Bluetooth protocols. The rate of serial communication was set to 723kbps. This system is able to obtain 2,000 Hz in each channel. The data transfer success rate of the developed EMG is 100%.

Abstract: The objective of this study was to develop an Ethernet-based telemedical blood pressure monitor. Although telemedical applications utilizing a variety of media are currently available, present systems do not provide remote signals with regard to integrated vital information, including blood pressure and pulse rate. In addition, the existing systems are largely embedded-structure, single-access, single-process models. Thus, we developed an Ethernet-based blood pressure monitor which includes a client/server structure, and is a real-time multi-access and multi-process system. The client for the developed system uses the Microsoft Comm Control in Microsoft Visual Basic and ODBC to connect Microsoft Chart Control with DB for a user interface. The server is programmed with the J2SE development platform, in a multi-thread structure. The system is capable of receiving data simultaneously. A TCP/IP socket was used for the Ethernet connection. The JDBC was applied to connect with the database for the saving, searching, and sampling of the data. The data transfer failure rate of the developed system was determined to be less than 0.05%.

Abstract: In golf, it is crucial that unintended shots, such as slices, be minimized. However, it has proven rather difficult to improve golf performance via investigations of the causes of slicing, as this particular phenomenon is induced by a cooperative effect by each segment of the body, rather than by a single postural anomaly. Thus, the objective of this study was to isolate and characterize the factors causing slicing, and to present possibilities for the improvement of golf performance via the minimization of the number of slices executed, using a three dimensional motion capture system, combined with multiple regression analysis, artificial neural network, and fuzzy logic techniques. This study obtained some interesting results, such as the following: (1) We isolated 9 slice-inducing factors, using a stepwise method. (2) Our artificial neural network (ANN) accurately separated 'slice' from 'normal' shots (classification rate: 100%). (3)We could present the possibility of reducing the number of slice using the fuzzy logic. We expect that our data might be eventually used to improve golf performance.

Abstract: The purpose of this study is to calculate the length and velocity change of gastrocnemius and soleus muscle-tendon complex (MTC) for diagnosis and estimation of the rehabilitation procedure of the patient from non-invasive 3D markers. The previous method measuring the length of MTC has been dependant on the regression equation based on the rotation angle in the sagittal plane. However, in view of the fact that movement analysis is based on the human body having a variety of structure, the measurement using merely rotation angle and regression equation which not based on each subject shank and foot length might not be accurate. In order to overcome these limitations, the length change of MTC is calculated, employing 3D MTC model accompanied with the trajectory data of markers attached anatomical landmarks, each subject measurements and femur condyle radius. Basically, more accurate length change could be acquired through the 3D trajectory data of markers in comparing with 2D data based on the rotation angle. As our study, the difference of the gastrocnemius length change between 3D marker trajectory based method and the method using a 2-D angle was approximately 4% (2cm) at maximum contraction and 1% (0.5cm) at maximum relaxation. Similarly, the difference in terms of the soleus was approximately 0.7% (0.3cm) at maximum contraction and 0.5% (0.2cm) at maximum relaxation.

Abstract: Equinus gait, defined as walking on one forefoot or both forefeet, has long been considered an undesirable characteristic in patients with a variety of neuromuscular disorders. In the equinus gait, the heel contact pattern is changed according to the severity, because an excessive ankle plantar flexion instigates rearfoot lifting in patients. However, no biomechanical severity index exists to evaluate the rehabilitation procedure of equinus gait. Therefore, we developed an SIEG (Severity Index of Equinus Gait) for nondestructive evaluation of the equinus gait and to validate the index with regard to 11 kinematic and kinetic factors of gait analysis. In this study, the 3-D heel contact pattern was considered for the development of a severity index. In order to verify the result, we compared the developed severity index values with ankle joint kinematic and kinetic factors in 3 test groups. As a result, the average SIEG values ranged between 10.45 (Normal group) and 26.61 (Severe group) and the highest correlation with regard to the 3 groups was shown in the developed severity index. Additionally, we also presented a fuzzy model using Takagi-Sugeno-Kang(TSK) logic with regard to the 12 factors in order to more accurately classify equinus gait.

Abstract: Currently available foot pressure sensors (FPS), which usually include a capacitive sensor and a piezoresistive sensor, tend to exhibit characteristically slow response times. Therefore, we used PZT (lead zirconate-titanate) ceramic in this study, as it responds more quickly than the currently-used materials. We have developed an algorithm which can be applied to the PZT ceramic-based measurement of foot pressure. This algorithm was also verified in experiments. In this study, we fabricated the electronic circuits and a sensor on the basis of the newly-developed algorithm, and then verified the algorithm experimentally.