• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.405-413
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• 2006

In general mechanical servo systems, friction deteriorates the performance of controllers by its nonlinear characteristics. Especially, friction phenomenon causes steady-state tracking errors and limit cycles in position and velocity control systems, even though gains of controllers are tuned well in linear system model. Even if sensor is used higher accuracy level, it is difficult to improve tracking performance of the position to the same level with a general control method such as PID type. Therefore, many friction models were proposed and compensation methods have been researched actively. In this paper, we consider that the variation of mover's mass is various by loading and unloading. The normal force variation occurs by it an other parameters. Therefore, the proposed control system is composed of main position controller and a friction compensator. A parameter estimator for a nonlinear friction model is designed by adaptive control law and adaptive backstepping control method.

• Journal of Navigation and Port Research
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• v.31 no.1 s.117
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• pp.55-64
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• 2007

In general mechanical servo systems, friction deteriorates the performance of controllers by its nonlinear characteristics. Especially, friction phenomenon causes steady-state tracking errors and limit cycles in position and velocity control systems, even though gains of controllers are tuned well in linear system model. Even if sensor is used higher accuracy level, it is difficult to improve tracking performance of the position to the same level with a general control method such as PID type. Therefore, many friction models were proposed and compensation methods have been researched actively. In this paper, we consider that the variation of mover's mass is various by loading and unloading. The normal force variation occurs by it and other parameters. Therefore, the proposed control system is composed of main position controller and a friction compensator. A parameter estimator for a nonlinear friction model is designed by adaptive control law and adaptive backstepping control method.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.5
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• pp.416-422
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• 2001

The BLDC(Brushless DC) Motor is characterized by linear torque to current and speed to voltage. It has low acoustic noise and fast dynamic response. Moreover, it has high power density with high proportion of torque to inertia in spite of small size drive. However, when armature current is commutated, the current ripple is generated by the motor inductance components in stator windings and back-EMF. This current ripple caused to torque ripple. Therefore, it is difficult to apply the BLDC motor to a precision servo drive system. In this paper, a new current control algorithm using fourier series coefficients is proposed. This proposed algorithm can minimize torque ripple due to the phase current commutation of BLDC motor. Simulation and Experimental results prove the effectiveness at the Proposed algorithm through comparison with the conventional unipolar PWM method.

• Journal of Electrical Engineering and Technology
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• v.9 no.2
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• pp.514-522
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• 2014

A new type of high precision electromagnetic suspension (EMS) which can support heavy tray along long stroke rail is proposed in this paper. Compared with the conventional EMS, the suggested moving-core typed EMS has the levitation electromagnets (EMs) on the fixed rail. This scheme has high load capability caused by iron-core and enables simple tray structure. Also it does not have precision degradation caused by heat generation from EMs, which is a drawback of conventional EMS. With these merits, the proposed EMS can be an optimal contactless linear bearing in next generation flat panel display (FPD) manufacturing process if the ability of long stroke movement is proved. So a special Section Switching Algorithm (SSA) is derived from the resultant force and moment equations of the levitated tray which enables long stroke movement of the tray. In order to verify the feasibility of the suggested SSA, a simple test-setup of the EMS with 2 Section-changes is made up and servo-controlled in the simulation and experiment. The simulation shows the perfect changeover the EMs, and the experiment shows overall control performance of under ${\pm}40{\mu}m$ gap deviations. These results reveal that the newly suggested contactless linear bearing can simultaneously achieve high load capability and precision gap control as well as long stroke.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.9
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• pp.72-80
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• 2009

When the magnet wheel rotates over a conducting plate, it generates the traction torque as well as the repulsive force on the conducting plate. Partially-cut traction torque results in the linear force into the tangential direction. To cut the traction torque, the concept of magnetic shield is introduced. The direction change of the linear force is realized varying the shielded area of magnetic field. That is, the tangential direction of non-shielded open area becomes the direction of the linear thrust force. Specially a shape of permanent magnets composing the magnet wheel leads to various pattern of magnetic forces. So, to enlarge the resulting force density and compensate its servo property a few simulations are performed under various conditions such as repeated pattern, pole number, radial width of permanent magnets, including shape of open area. The theoretical model of the magnet wheel is derived using air-gap field analysis of linear induction motor, compared with test result and the sensitivity analysis for its parameter change is performed using common tool; MAXWELL. Using two-axial wheel set-up, the tracking motion is tested for a copper plate with its normal motion constrained and its result is given. In conclusion, it is estimated that the magnet wheel using partial shield can be applied to a noncontact conveyance of the conducting plate.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.287-290
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• 2005

Once hot forgings for automotive parts such as wheel bearing flange to which cyclic asymmetric bending stress is continuously applied are produced, it is necessary to control their microstructure to obtain superior mechanical properties. It is however hard to control the microstructure uniformly because the strength is reduced as coarsening of ferrite grains. To investigate the microstructural alteration according to process variables during hot working, the variation of the ferrite grain size was studied by utilizing of the computer aided servo-hydraulic Gleeble tester which is hot deformation behavior reproduction equipment. In addition, the effect of the ferrite grain size of raw material on the austenite grain behavior of hot forgings was also examined. The rolling contact fatigue resistance of the induction hardened SAE 1055 steel was compared with the occasion of the same condition of SAE52100 bearing steel. As a result, it was confirmed that the ferrite grain sizes of the forgings depend on the heating temperature and cooling start temperature during hot forging and cooling processes. The induction hardened SAE1055 steel showed a superior rolling contact fatigue resistance to the induction hardened SAE52100 steel. The reason is that SAE1055 steel is freer from the material defect such as segregation than the comparative steel.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.5 s.170
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• pp.103-112
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• 2005

This paper presents one-axis high precision scanning system and illustrates the design of modified $X-Y-{\theta}$ stage as a tracker using VCM and commercialized air bearings for it. The scanning system for 100nm resolution is composed of the 3-axis stage and one axis long stroke linear motor stage as a follower. In this study a previous proposed and presented structure of VCM for the fine stage is modified. The tracker has 3 DOF($X-Y-{\theta}$ motions by four VCM actuators which are located on the same plane. So 4 actuating forces are suggested and designed to create least pitch and roll motions. This article will show about the design especially about optimal design. The design focus of this fine stage is to have high acceleration to accomplish high throughput. The optimal design of maximizing acceleration is performed in restrained size. The most sensitive constraint of this optimal design is heat dissipation of coil. There are 5 design variables. Because the relationship between design variables and system parameters are quite complicated, it is very difficult to set design variables manually. Due to it, computer based optimal design procedure using MATLAB is used. Then, this paper also describes the procedures of selecting design variables for the optimal design and a mathematical formulation of the optimization problem. Based on the solution of the optimization problem, the final design of the stage is also presented. The results can be verified by MAXWELL. The designed stage has the acceleration of about 5 $m/s^{2}$ with 40kg total mass including wafer chuck and interferometer mirror. And the temperature of coil is increased $50^{\circ}C$. In addition, the tracker is controlled by high precision controller system with HP interferometer for it and linear scaler for the follower. At that time, the scanning system has high precision resolution about 5nm and scanning resolution about 40nm in 25mm/s constant speed

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.11 s.104
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• pp.1276-1286
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• 2005

In this paper, the dual stage interaction between the coarse actuator and the fine actuator of an optical disk drive is studied, and the new control method to enhance the track pull-in performance using fine actuator control is proposed. First, the dynamic analysis for the dual stage and the experiments to find the each actuator dynamics are performed. From the experiments, some physical parameters of the actuators were derived, then, some simulations are performed to find the interaction effect of the fine actuator during seek motion. Second, the center servo which suppresses the vibration of fine actuator during seek motion is designed and evaluated. And the fine actuator control to reduce the relative velocity between the target track and beam spot is proposed. From simulations, we show that fine actuator control which has same frequency and same phase of the disturbance is effective to reduce the relative velocity, and this result leads to track pull-in enhancement. Hence, the proposed control method is good approach to improve the track pull-in performance. Finally, the realization of the proposed method and some comments of it are briefly discussed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.399-402
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• 2004

In the optical drive system, adopting the optical flying-type head (OFH) flying on a removable plastic disk, the flying stability of the small OFH should be carefully considered to ensure the reliability for first surface recording. Additional micro actuators for focus servo are discussed for better interface of optical flying head on thin cover layered plastic disk to eliminate focus error due to the non-uniformity of cover layer thickness and the tolerance of lens assembly. This study gives two simulation results on the flying stability of the OFH. One is the dependence of the flying height and pitch angle variations on the wavelength and amplitude of disk waviness. The other is the flying stability of the slider and suspension system during the dynamic load/unload (U/UL) process.

• Journal of Advanced Navigation Technology
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• v.8 no.2
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• pp.105-111
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• 2004

This paper describes the design of navigation system for an unmanned target drone which is operated by Korean army as for anti-air gun shooting training. Current target drone is operated by pilot control of on-board servo motor via remote control system. Automatic flight control system for the target drone greatly reduces work load of ground pilot and can increase application area of the drone. Most UAVs being operated nowdays use high-priced sensors as AHRS and IMU to measure the attitude, but those are costly. This paper introduces the development of low-cost automatic flight control system with low-cost sensors. The integrated automatic flight control system has been developed by integrating combining power module, switching module, monitoring module and RC receiver as an one module. The performance of navigation for low cost unmanned aerial vehicle, unmanned target drone as our test bed in this paper is verified by both Hardware in the loop simulation(HILS) to test performance of GPS as GPS output frequency high and results of flight test.