• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.19-25
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• 1987

An optimal control procedure is presented for steering of an unmanned cart which has two motored wheels on its left and right side. Steering, running and stopping are enabled by controlling the motor speed independently. An optimal proportional-plus-integral control is employed to eliminate steady state error which is sustained by a simple proportional control for tracking a circular arc path. A simple and readily-implemented suboptimal control is also examined. The suboptimal control gives comparable performance and therefore provides an effective approach for industrial application of the unmanned cart. Effects of design parameters of unmanned cart such as forward velocity, wheel radius and position of sensor are investigated. It is shown that within the practicable values of the parameters the controlled performance improves rapidly with increase of those parameters then the improvement becomes negligible, which suggests base values over which the parameters should be taken.

• Journal of Biosystems Engineering
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• v.23 no.1
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• pp.83-90
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• 1998

In this paper the automatic system for dairy cattle has been desisted such as body temperature measuring unit, feed supplying unit and temperature control unit. Since e disease is strongly related to the body temperature of cattle, early detection of the abnormal temperature would prevent the severe problems which nay occur in dairy farms. An electronic component AD590J is used as temperature sensor for the system, The device is highly robust against the noise since the output signal is the current so it can be applied to a long distance sensing The resolution of signal is 0.1$^{\circ}C$ and the current is 10㎷ Also 12-bit A/D converter is desisted fir interfacing the sensor with a one-chip microprocessor. A temperature measuring experiment using the developed system has been done for measuring the temperature of human beings and the system was proven to be useful for measuring the body temperature of dairy cattle properly. A geared AC motor is used for the feed supplying unit The heater and fm are used as temperature control unit. The feed supplying unit and temperature control unit are well operating in the laboratory experiment.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.394-400
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• 2008

This paper presents an analytical method to investigate the stability of FDBs (fluid dynamic bearings) considering the tilting motion. The perturbed equations of motion are derived with respect to translational and tilting motion for the general rotor-bearing system with five degrees of freedom. The Reynolds equations and their perturbed equations are solved by using the FEM in order to calculate the pressure, load capacity, and the stiffness and damping coefficients. This research introduces the radius of gyration to the equations of notion in order to express the mass moment of interia with respect to the critical mass. Then the critical mass of FDBs is determined by solving the eigenvalue problem of the linear equations of motion. This research is numerically validated by comparing the stability chart of FDBs with the time response of the whirl radius obtained from the direct integration of the equations of motion. This research shows that the tilting motion is one of the major design considerations to determine the stability of rotating system. It also shows that the stability of FDBs considering only translation is overestimated in comparison with the stability of FDBs considering both translational and tilting motion.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.4
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• pp.301-307
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• 2013

MRU(motor reduction unit) for KTX is a assembled complex structure that is equipped with a lot of parts at the express train KTX and that is the core power source operating variable speeds. This study is recorded the dynamic characteristics analysis results tested by EMA which is done through the parts and assembly test, transient analysis and stoped train test in order to design the online monitoring system for KTX MRU. And the mode shapes result from critical vibration frequency explain the relation with variable speeds of express train over 250 km/hr. Also these variable speeds make variable operational frequencies at pinion, axle gear mesh frequency and normal bearing fault frequencies. As the specified speed can make resonance with natural frequencies of the MRU, for the train operating stability, this study also presents the MRU's critical speeds calculated by the each train speed.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.4
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• pp.14-19
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• 2010

In this paper, using interleaved power factor correction how to improve the inverter efficiency studied. Interleaved method can reduce the conduction losses and the inductor energy. Generally, critical conduction mode (CRM) boost PFC converter used low power level because of the high peak currents. if you use the interleaved mode, CRM PFC can be used medium or high power application. interleaved CRM PFC can reduce current ripple for higher system reliability and size of buck capacitor and EMI filter size. Interleaved CRM PFC that is installed in front of inverter can maintain the constant voltage regardless of the input voltage.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.8
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• pp.653-658
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• 2014

Roll-to-Roll printing process has become a great issue as a breakthrough for low cost and mass production of electronic devices such as organic thin film transistor, and etc. To print the electronic devices, multi-layer printing is essential, and high precision register control is required for this process. Unlike stop-and-repeat printing process, it is impossible to control the register in a static state since the roll-to-roll process is a continuous system. Therefore, the behavior of web such as polyethylene terephthalate (PET) and polyimide (PI) by the tensile and thermal stress generated in the roll-to-roll process as well as motor control of driven rolls has to be considered for a high precision register control. In this study, the correlation between curing temperature and thermal deformation of PET web is analyzed. Finally, it is verified experimentally that the temperature disturbance generates the more serious register error under the higher curing temperature.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.357-360
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• 2002

Nowadays, the improvement and development of Multi-media, information and communication technology are rapidly processed. And many products, for example, digital camera, digital camcorder, and PDA, are used for them. They need large data storage capacity and small size, light storage system. Due to that, many studies and researches in data storage system have been carried out. Especially, micro drive system was presented by IBM.(1) However, its system is expensive and uneasy to be portable. In ODD technologies, 1 inch drive system is not yet or in processing status.(2) If to be possible and to be come up, it is cheap than HDD system and easy to transfer information. In this paper, a miniaturized actuator(about linch) is designed and tested for ODD system. Specially, it is adapted for NFR(Near-field Recoding) system using SIL(Solid Immersion Lens). It is the dual-servo actuator which consists of a coarse actuator and fine actuator. Its actuating force generation method is VCM(Voice Ceil Motor). The fine actuator has 4-wire suspensions and bobbin wrapped by coil and includes focusing motion as well as tracking motion. The coarse actuator has an actuating coil and V-grooved guide mechanism. Also, the characteristics of the designed actuator is estimated by sine-swept mode and LDV(Laser Doppler Vibro-meter).

• Journal of the Korean Society for Precision Engineering
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• v.19 no.2
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• pp.203-212
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• 2002

Active magnetic hearings allow much high surface speed than conventional ball bearings and therefore greatly suitable for high speed cutting. This paper describes a design and test of an active magnetic bearing system with 16-pole radial magnets. The spindle is originally designed for a CNC lathe and driven by outer motor with 5.5 kW power and maximum speed 10,000 rpm. Considering static load condition and geometric restrictions, radial magnet is designed 16-pole type for smaller outer diameter of the spindle system. Dynamic system characteristics such as natural frequency, critical speed, stiffness, damping and system stabilities are simulated with a rigid rotor model including direct feedback controller. The designed spindle system is realized with digital PIDD controller to compensate phase lag of PWM amplifier and magnet coils. With levitation and step response experiment the control system characteristics are tested, and the spindle is rotated up to 10,000 rpm stab1y.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.12
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• pp.1049-1054
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• 2015

Nowadays, there are many researches involving structural actuators, which have adjustable stiffness; they are also called variable stiffness actuators (VSA). The VSAs can adjust the characteristics of actuators for various functions and human-machine safety. This paper describes the design and analysis of two types of VSAs. To adjust stiffness, the actuators are controlled by a principle of lever ratio mechanism, by changing a pivot position or a spring position in the structure with springs. To make the principle workable, the designs are simplified by using a ball screw system with a motor. Each structure shows different static properties with variable rates of stiffness. We have also shown the experimental verification of the dynamic performance of the two types of VSAs. This research can be applied to various industrial fields, where humans work in conjunction with robots.

• Tribology and Lubricants
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• v.12 no.4
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• pp.28-34
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• 1996

The lubrication characteristics of high-speed ball bearings have been investigated empirically using 45mm bore split inner ring ball bearings employed in small industrial gas turbine engines with oil-jet lubrication method. For the close structural simulation, experiments carried out with bearing mounting supports of real engines, such as bearing housings and oil nozzle assemblies with squeeze film dampers. Thus the results of tests can be directly applied to the design and the development of gas turbine engines. Testing was done by varying operating speeds, axial load on bearings, and lubricant flow rates. During testing, the temperature of bearing at outer-ring face, the power consumption of the driving motor, and the rotating resistance of the bearing were measured. From this study, the representative factors for lubrication characteristics at high speed was found, and the most important one was not operating speed but axial load up to 1.95 million dmN speed and 2969 N axial load. Furthermore, the detailed variation of the rotational resistance of the bearing could be visualized by measuring the change of the radial load under the bearing supports. The rotational resistance consists of the frictional resistance and the bearing-cavity oil resistance.