• Journal of the Korean Society for Precision Engineering
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• v.26 no.6
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• pp.50-58
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• 2009

Micro laser fabrication techniques can potentially be used for the manufacture of microstructures on the thin flat surfaces with large diameter that are frequently used in semiconductor industries. However, the large size of wafers can cause the degraded machining accuracy of the surface because it can be tilted or distorted by geometric errors of machines or the holding fixtures, etc. To overcome these errors the off-line focusing error compensation method is proposed. By using confocal autofocus system, the focusing error profile of machined surface is measured along the pre-determined path and can be compensated at the next machining process by making the corrected motion trajectories. The experimental results for silicon wafers and invar flat surfaces show that the proposed method can compensate the focusing error within the level of below $6.9{\mu}m$ that is the depth of focus required for the laser micromachining process.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.132-138
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• 2006

A tape feeder is an important part to supply a micro chip such as 1005 and 0603 components in SMT process. Traditional sprocket wheel type feeder has several problems such as backlash and indexing errors, low compatibility and confidence. However, it is very difficult to solve such problems due to the inevitable fraction defectives of sprocket wheel. Thus, the object of this works is to develop a linear type high precision tape feeding system using cam-slider mechanism. The proposed cam-slider mechanism is composed of several links and a plate, pneumatic actuator is used to generate linear motion. The proposed mechanism has distinct advantages over the conventional mechanism. It has reduced feeding errors, long lift-cycle, and slim width. As a result, the developed tape feeder using cam-slider mechanism shows special characteristics far high precision feeding for chip-mounters.

• Journal of Advanced Navigation Technology
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• v.17 no.3
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• pp.354-360
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• 2013

A stereo vision analysis was performed for motion and depth control of unmanned vehicles. In stereo vision, the depth information in three-dimensional coordinates can be obtained by triangulation after identifying points between the stereo image. However, there are always triangulation errors due to several reasons. Such errors in the vision triangulation can be alleviated by careful arrangement of the camera position and orientation. In this paper, an approach to the determination of the optimal position and orientation of camera is presented for unmanned vehicles.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.2C
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• pp.262-271
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• 2004

There are channel errors when video data are transmitted between encoder and decoder. These channel errors would make decoded image incorrect, so it is very important to detect and recover channel errors. This paper proposes a method of error detection and recovery by hiding specific information into video bitstream using fragile watermark and checking it later. The proposed method requires no additional bits into compressed bitstream since it embeds a user-specific data pattern in the least significant bits of LEVELs in VLC codewords. The decoder can extract the information to check whether the received bitstream has an error or not. We also propose to use this method to embed essential data such as motion vectors that can be used for error recovery. The proposed method can detect corrupted MBs that usually escape the conventional syntax-based error detection scheme. This proposed method is quite simple and of low complexity. So the method can be applied to multimedia communication system in low bitrate wireless channel.

• Journal of Ocean Engineering and Technology
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• v.18 no.4 s.59
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• pp.33-39
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• 2004

This paper presents a hybrid underwater navigation system for unmanned underwater vehicles, using an additional range sonar, where the navigation system is based on inertial and Doppler velocity sensors. Conventional underwater navigation systems are generally based on an inertial measurement unit (IMU) and a Doppler velocity log (DVL), accompanying a magnetic compass and a depth sensor. Although the conventional navigation systems update the bias errors of inertial sensors and the scale effects of DVL, the estimated position slowly drifts as time passes. This paper proposes a measurement model that uses the range sonar to improve the performance of the IMU-DVL navigation system, for extended operation of underwater vehicles. The proposed navigation model includes the bias errors of IMU, the scale effects of VL, and the bias error of the range sonar. An extended Kalman filter was adopted to propagate the error covariance, to update the measurement errors, and to correct the state equation, when the external measurements are available. To illustrate the effectiveness of the hybrid navigation system, simulations were conducted with the 6-d.o.f. equations of motion of an AUV in lawn-mowing survey mode.

• Journal of Korean Physical Therapy Science
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• v.10 no.2
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• pp.62-72
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• 2003

The purpose of this study is to prove the efficacy of the Kaltenborn-Evjenth Orthopedic Manipulative Therapy and the Conventional Physical Therapy that influence changes in pain and range of motion when those therapies are applied to patients with temporomandibular pint movement restriction. The subjects of the study were 30 randomly selected patients who had been diagnosed with temporomandibular pint movement restriction and had endured pain for more than two weeks. These patients had visited one of three hospitals in Pyongchon 00 Hospital. The subjects were divided into two groups with 15 patients each. The Kaltenborn-Evjenth Orthopedic Manipulative Therapy was applied to one group and the Conventional Physical Therapy was applied to the other group, once a day for three days. Then, the pain perception degree was measured by using the Visual Analogue Scale(VAS) and a digital device(Absolute Digimatic) measured the range of motion for each group. The average and standard errors were calculated for each measured items and a paired t-test was used for identifying significance in the differences in the pain perception degree and the range of motion between the two groups according to therapy. The significant level was set as ${\alpha}=0.05$. The changes in the pain perception degree were statistically significant in both groups; however, the group that received Kaltenborn-Evjenth Orthopedic Manipulative Therapy(KE-Group) showed more significant changes in a decrease in the pain perception degree than did the group that received the Conventional Physical Therapy(CPT-Group). Both groups showed significant results regarding changes in the range of motion: however, the KE-Group showed more of a significant difference in the average of the range of motion than did the CPT-Group(p<0.001). Comparing the changes in the range of motion between the two groups, the KE-Group showed a significant result which means that the KE-Group had a higher therapy effect than did the CPT-Group(p<0.05). Based on the results of this study, we found that the Kaltenborn-Evjenth Orthopedic Manipulative Therapy decreased pain and increased the range of motion. With such findings, we expect that the Kartenborn-Evjenth Orthopedic Manipulative Therapy can be used as an effective treatment method for patients with tempomrnandibular pint movement restriction and that the treatment period can be reduced with this therapy as well.

• 제어로봇시스템학회:학술대회논문집
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• 1997.10a
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• pp.700-703
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• 1997

A robust controller for a 6 DOF magnetically levitated fine manipulator is presented. The proposed controller consists of following two parts : a model reference controller (MRC) and a H$_{\infty}$ controller (HIC). First, the MRC stabilizes the motion of the manipulator. Then, the motion of the manipulator follows that of the reference model. Second, the HIC minimizes errors generated from the MRC due to noise and disturbance since the HIC is a kind of robust controller. The experiments of position control and tracking control are carried out by use of the proposed controller under the conditions of free disturbances and forced disturbances. Also, the experiments using PID controller are carried out under the same conditions. The results from above two controllers are compared to investigate the control performances. As the results, it is observed that the proposed controller has similar position accuracy but better tracking performances comparing to the PID controller as well as good disturbance rejection effect due to the robust characteristics of the controller. In conclusion, it is verified that the proposed controller has the simple control structure, the good tracking performances and good disturbance rejection effect due to the robust characteristics of the controller..

• Journal of the Society of Naval Architects of Korea
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• v.35 no.2
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• pp.29-37
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• 1998

Linear equations of motion for submersibles are one of the rest important design parameters, which are used as a governing equation for the shape design and the controller design. But, the estimated maneuvering coefficients in equations of motion by using empirical formulae, theoretical calculations or model tests might have some errors. Therefore the maneuvering coefficients should be verified from sea trial test. In this study, parallel extended Kalman filter method, Nelder & Mead Simplex method and genetic algorithm were applied to the parameter identification of roll maneuvering coefficients based on sea trial data. As a result, it was verified that Nelder & Mead Simplex method gave the most satisfactory results for the mathmatical models and the sea trial data used in this study.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.2
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• pp.59-66
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• 2007

Voice coil actuator is used linear motion system that requires precision positioning control. In order to control precision positioning of voice coil actuator, relation model between duty ratio and moving displacement of voice coil actuator is needed. This paper present a duty ratio - displacement model in PWM control of voice coil actuator. Transfer function of voice coil actuator is obtained by combining voice coil motor's equation of motion with the equation of circuit and characteristic of voice coil motor. Consider to initial condition of velocity and current, transfer function is transformed mathematical model. The induced model can predict output displacement, velocity and current according to duty ratio and amplitude. The model is verified by experimental tests such as velocity and displacement response of voice coil motor. Simulated results have tracking errors of less than 10 percent of experimental results.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.1
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• pp.8-16
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• 2006

The communication through optical fiber is taking an important role of the expansion of communication network with excellent transmitting rate and quality. As the optical communication is introduced to the backbone network at first and becomes a general communication method of network, the demand of kernel parts of optical communication such as PLC(Planar Light Circuit), Coupler, and WDM(Wavelength Division Multiplexing) element increases. The alignment and the attachment technology are very important in the fabrication of optical elements. In this paper, the driving mechanism of ultra precision stage is studied with the aim of optimal design of stage. The travel and the resolution of stage are investigated. The hysteresis of the stage is generated because of PZT actuator. The hysteresis and the inverse hysteresis are modeled in X, Y, and Z-axis motion. The input data of desired displacement of the stage according to input voltage is obtained from the inverse hysteresis equation. In the result of experiments with the input data, the errors due to hysteresis are well compensated.