• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.1
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• pp.115-126
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• 1996

In the time optimal control problem, bang-bang control has been used becaese it is the theoretical time minimum solution. However, to improve tracking speed performance in the time optimal control, it is important to select a switching point accurately which makes the velocity zero near the target track. But it is not easy to select the swiching point accurately because of the damping coefficient variation and uncertainties of modeling an actual system. The Adaptive model following control(AMFC) is implemented to relieve the difficulty and inconvenience of this task. The AMFC and make the controlled plant follow as closely as possible to a desired reference model whose switching point can be calculated easily and accurately, assuring the error between the states of the reference model and those of the controlled plant appoaches zero. The hybrid control method composed of AMFC and PID is applied to a tracking actuator of the magneto optical disk drive(MODD) in random access devices to improve its slow tracking performance. According to the simulaion and experimental results, the average tracking time as small as 20ms is obtained for a 3.5 magneto-optical disk drive. The AMFC also can be applied for other random access devices to improve the average tracking performance.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.10 s.175
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• pp.174-185
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• 2005

This paper presents the design, fabrication, and testing results of a dual stage actuator system for a fine positioning of magnetic heads in magnetic disk drives. A novel rotary microactuator which is electrostatically driven and utilized as a secondary actuator was designed. The stator and rotor electrodes in the microactuator was revised to have the optimal shapes and hence produces much higher rotational torque compared with the conventional comb-shape electrodes. The microactuators were successfully fabricated using SoG(silicon on glass) processing technology, which is known as being cost-effective. The fabricated microactuator has the structural thickness of $45{\mu}m$ with the gap width of approximately $3{\mu}m$. The dynamic characteristic of microactuator/slider assembly was investigated, and its natural frequency and DC gain were measured to be 3.4kHz and 32nm/V, respectively. The microactuator/slider assembly was integrated into a HDD model V10 of Samsung Electronics Co. and a dual servo algorithm was tested to explore the tracking performance of dual stage actuator system where the LDV signals instead of magnetic head signals were used. Experimental results indicate that this system achieves the tracking accuracy of 30nm. This value corresponds to a track density of 85,000 track per inch(TPI), which is about 3 times greater than that of current hard disk drives.

• Transactions of the Society of Information Storage Systems
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• v.5 no.2
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• pp.96-101
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• 2009

In recent years, the demand for portable digital devices such as cellular phone, digital camera, and MP3 player has been largely increased. To meet the requirements of such portable applications the information storage devices with smaller size, higher capacity, and lower power consumption are needed. A small form factor (SFF) HDD using a load/unload (L/UL) system is one of the appropriate alternatives to satisfy these requirements. Due to complexity of L/UL process and mechanism, it is required to investigate for better understanding the effects of design parameters. Among the various design parameters, flexible cable and friction force on the L/UL ramp become important to the dynamic characteristics of L/UL process as the system is miniaturized. The program for L/UL simulation which considers the effect of flexible cable and L/UL ramp is needed. Unfortunately, there is hardly any commercial program for the L/UL simulation except the Computer Mechanics Laboratory (CML) air bearing design program and the CML L/UL simulation code. Furthermore, the design parameters such as flexible cable and the L/UL ramp are not considered in the CML L/UL simulation code. So we embody the L/UL simulation considering flexible cable and an L/UL ramp by using the ANSYS/LS-DYNA. In this thesis, the effects of flexible cable and friction force on the dynamic characteristics and the performances of the L/UL process are studied. Numerical simulation and related experiments are carried out and compared each other.

• Journal of Drive and Control
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• v.15 no.3
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• pp.14-20
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• 2018

Wet clutches in an automatic transmission enable the transmission of the engine power by the frictional torque experienced and noted between disk and plates. Since the clutch frictional torque considerably affects the shift quality of an automatic transmission as well as the durability of the machinery, its friction characteristics must be carefully examined to meet the design requirements. The SAE No. 2 friction test machine is a well-known standard to evaluate mainly the friction characteristics of plate clutches along with the required automatic transmission fluids. This paper reviews the experimental analysis of the wet clutch friction characteristics by using the exclusively developed clutch test machine which is capable of controlling the clutch test procedure, in accordance with the applicable test standard and processing of the experimental data automatically. As the clutch test machine is designed for the accommodation of dual clutches which is applied to the real transmission, it can evaluate not only the clutch friction characteristics, but also an actuation performance of a measured clutch piston. In respect to friction characteristics involving dynamic friction coefficients, the energy absorbed in a clutch disk and the recorded temperatures of clutch plates during braking actions and procedures are also investigated. Additionally, the change of friction coefficients by the use of the repeated clutch application is also observed with the endurance test functions of an accurately calibrated and dedicated clutch test machine.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.12
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• pp.5412-5419
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• 2011

The need is growing for high-speed spindle because various equipment are becoming more precise, miniaturization and high speed with the development of industries. Air-lubricated dynamic bearings are widely used in the optical lithographic manufacturing of wafers to realize nearly zero friction for the motion of the stage. Air-lubricated dynamic bearing can be used in high-speed, high-precision spindle system and hard disk drive(HDD) because of its advantages such as low frictional loss, low heat generation, averaging effect leading better running accuracy. In the paper, numerical analysis is undertaken to calculate the performance of air-lubricated dynamic bearing with herringbone groove. The static performances of herringbone groove bearings which can be used to support the thrust load are calculated. Electrochemical micro machining($EC{\mu}M$) which is non-contact ultra precision machining method has been developed to fabricate the air-lubricated dynamic bearing and optimum parameters which are inter electrode gap size, concentration of electrolyte, machining time are simulated using numerical analysis program.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.261-261
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• 2016

플래시 메모리 (flash memory)는 DRAM(dynamic racdom access memory)이나 SRAM(static random access memory)에 비해 소자의 구조가 매우 단순하기 때문에 집적도가 높아서 기기의 소형화가 가능하다는 점과 제조비용이 낮다는 장점을 가지고 있다. 또한, 전원을 차단하면 정보가 사라지는 DRAM이나 SRAM과 달리 전원이 꺼지더라도 저장된 정보가 지워지지 않는다는 특징을 가지고 있어서 ROM(read only memory)과 정보의 입출력이 자유로운 RAM의 장점을 동시에 가지기 때문에 활용도가 크다. 또한, 속도가 빠르고 소비전력이 작아서 USB 드라이브, 디지털 TV, 디지털 캠코더, 디지털 카메라, 휴대전화, 개인용 휴대단말기, 게임기 및 MP3 플레이어 등에 널리 사용되고 있다. 특히, 낸드(NAND)형의 플래시 메모리는 고집적이 가능하며 하드디스크를 대체할 수 있어 고집적 음성이나 화상 등의 저장용으로 많이 쓰이며 일정량의 정보를 저장해두고 작업해야 하는 휴대형 기기에도 적합하며 가격도 노어(NOR)형에 비해 저렴하다는 장점을 가진다. 최근에는 smart watch, wearable device 등과 같은 차세대 디스플레이 소자에 대한 관심이 증가함에 따라 투명하고 유연한 메모리 소자에 대한 연구가 다양하게 진행되고 있으며 유리나 플라스틱과 같은 기판 위에서 투명한 플래시 메모리를 형성하는 기술에 대한 관심이 높아지고 있다. 전하트랩형 (charge trap type) 플래시 메모리는 플로팅 게이트형 플래시 메모리와는 다르게 정보를 절연막 층에 저장하므로 인접 셀간의 간섭이나 소자의 크기를 줄일 수 있기 때문에 투명하고 유연한 메모리 소자에 적용이 가능한 차세대 플래시 메모리로 기대되고 있다. 전하트랩형 플래시메모리는 정보를 저장하기 위하여 tunneling layer, trap layer, blocking layer의 3층으로 이루어진 게이트 절연막을 가진다. 전하트랩 플래시 메모리는 게이트 전압에 따라서 채널의 전자가 tunnel layer를 통해 trap layer에 주입되어 정보를 기억하게 되는데, trap layer에 주입된 전자가 다시 채널로 빠져나가는 charge loss 현상이 큰 문제점으로 지적된다. 따라서 tunnel layer의 막질향상을 위한 다양한 열처리 방법들이 제시되고 있으며, 기존의 CTA (conventional thermal annealing) 방식은 상대적으로 높은 온도와 긴 열처리 시간을 가지고, RTA (rapid thermal annealing) 방식은 매우 높은 열처리 온도를 필요로 하기 때문에 플라스틱, 유리와 같은 다양한 기판에 적용이 어렵다. 따라서 본 연구에서는 기존의 열처리 방식보다 에너지 전달 효율이 높고, 저온공정 및 열처리 시간을 단축시킬 수 있는 마이크로웨이브 열처리(microwave irradiation, MWI)를 도입하였다. Tunneling layer, trap layer, blocking layer를 가지는 MOS capacitor 구조의 전하트랩형 플래시 메모리를 제작하여 CTA, RTA, MWI 처리를 실시한 다음, 전기적 특성을 평가하였다. 그 결과, 마이크로웨이브 열처리를 실시한 메모리 소자는 CTA 처리한 소자와 거의 동등한 정도의 우수한 전기적인 특성을 나타내는 것을 확인하였다. 따라서, MWI를 이용하면 tunnel layer의 막질을 향상시킬 뿐만 아니라, thermal budget을 크게 줄일 수 있어 차세대 투명하고 유연한 메모리 소자 제작에 큰 기여를 할 것으로 예상한다.

• 한국해양학회지
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• v.27 no.1
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• pp.19-34
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• 1992

Marine seismic refraction surveys have been carried out by Korea Institute of Geology, Mining and Materials(KIGAM) since 1984. The recording of refraction data was based on analog instrumentation. Therefore the resolution of refraction data was not good enough to distinguish many layers. The objective of the interpretation of seismic refraction data is the determination of intervals and critically refracted seismic wave propagation velocities through the layers beneath the sea floor. To determine intervals and velocities precisely, the resolution of refraction data should be enhanced. The intent of the study is to improve the quality of shallow marine refraction data by the digital technique using microcomputer- based acquisition and processing system. The system consists of an IBM AT microcomputer clone, an analog-digital(A/D) converter. A mass storage unit and a parallel processing board. The A/D converter has 12 bits of precision and 250 kHz of conversion rate. The magneto-optical disk drive is used for the mass storage of seismic refraction data. Shallow marine seismic refraction surveys have been carried out using the system at 6 locations off Ulsan and Pusan area. The refraction data were acquired by the radio sonobuoy. The refraction profiles have been produced by the laser printer with 300 dpi resolution after the basic computer processing. 5-9 layers were interpreted from digital refraction profiles, whereas 2-4 layers were interpreted from analog refraction profiles. the propagation velocities of sediments were interpreted as 1.6-2.1 km/sec. The propagation velocities of acoustic basement were interpreted as 2.4-2.7 km/sec off Ulsan area, 4.8 km/sec off Pusan area.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.33 no.3
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• pp.511-525
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• 2023

As awareness of personal data protection increases, various Full Disk Encryption (FDE)-based applications are being developed that real-time encryption or use virtual drive volumes to protect data on user's PC. FDE-based applications encrypt and protect the volume containing user's data. However, as disk encryption technology advances, some users are abusing FDE-based applications to encrypt evidence associated with criminal activities, which makes difficulties in digital forensic investigations. Thus, it is necessary to analyze the encryption process used in FDE-based applications and decrypt the encrypted data. In this paper, we analyze Cryptomator and Norton Ghost, which provide volume encryption and backup functions. We analyze the encrypted data structure and encryption process to classify the main data of each application and identify the encryption algorithm used for data decryption. The encryption algorithms of these applications are recently emergin gor customized encryption algorithms which are analyzed to decrypt data. User password is essential to generate a data encryption key used for decryption, and a password acquisition method is suggested using the function of each application. This supplemented the limitations of password investigation, and identifies user data by decrypting encrypted data based on the acquired password.

• Journal of Technology Innovation
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• v.19 no.1
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• pp.79-109
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• 2011

In his highly cited book, Innovator's Dilemma (1997), Christensen introduced a notion of disruptive technology that is based on the observations from disk-drive industry and used it as an explanatory variable through which new entrants outperform incumbents in the industry. In explaining his later observations of disruptive innovations in other industries, however, his early theory based on disruptive technology has been applied to all cases without careful distinction between the notions of technology and business model (Markides, 2006). Furthermore, it has been criticized that his model suffers from lack of enough explanatory power and other important factors that are necessary to fully explain the observed phenomena in various cases (Danneels, 2004). Motivated by the critics in literature, the current study carefully distinguishes between innovation of technology and innovation of business model in the process of disruptive innovation, and apply our framework to the case of internet shopping mall business. Our study yields two main results. First, the internet-related business model which Christensen argued as an example of disruptive innovation is accomplished through two distinctive and separable growth phases: a period of technology growth and a period of business model growth. Second, in the process of disruptive innovation, the notion of enabling technology plays an important bridging role that connects core technology and business model. Furthermore, we confirm that the success of business model innovation depends on the degree of maturity of the enabling technologies. In conclusion, Christensen's notion of disruptive innovation can be further detailed in terms of technology innovation and business model innovation, and if there exist enabling technologies, the chance of success of the business model is higher when the enabling technology is matured rather than when the core technology is merely acknowledged as a disruptive technology.