• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2005.05a
• /
• pp.97-102
• /
• 2005

This paper presents feed rate optimizaton of a PMLSM driven feed-slide for mininum vibrations by smoothing velocity curve with finite jerk. First of all, the PMLSM was designed and made to reduce detent force. Next, a PMLSM driven feed-slide system was mathematically modeled as a 4-degree-of-freedom lumped parameter model. The key idea of our vibration minimization method is to find out the most appropriate smooth velocity curve with finite jerk. The validity of our proposed method has been verified by comparing computer simulation results of the feed-slide model with experimental ones.

• Membrane and Water Treatment
• /
• v.10 no.5
• /
• pp.387-394
• /
• 2019

Membrane distillation (MD) is one of the water treatment processes which involves the momentum, heat and mass transfer through channels and membrane. In this study, CFD modeling has been used to simulate the heat and mass transfer in the direct contact membrane distillation (DCMD). Also, the effect of operating parameters on the water flux is investigated. The result shows a good agreement with the experimental result. Results indicated that, while feed temperature is increasing in the feed side, water flux improves in the permeate side. Since higher velocity leads to the higher mixing and turbulence in the feed channel, water flux rises due to this increase in the feed velocity. Moreover, results revealed that temperature polarization coefficient is rising as flow rate (velocity) increases and it is decreasing while the feed temperature increases. Lastly, the thermal efficiency of direct contact membrane distillation is defined, and results confirm that thermal efficiency improves while feed temperature increases. Also, flow rate increment results in enhancement of thermal efficiency.

• 한국기계연구소 소보
• /
• s.18
• /
• pp.29-35
• /
• 1988

When low sliding velocities in the boundary lubrication range are operating, irregular movements frequently occur which are a result of the stick-slip phenomenon. Such slide motions are undesirable in precision machine tools, particularly with feed back systems used in numerical and adaptive control machine tools. Accordingly, this paper reports analytical and experimental studies in the stick-slip characteristic of machine tool feeding system. The main conclusions of this study are as follows; The tendency towards stick-slip effects may be reduced by; 1). Reducing the drop in friction coefficient in the Stribeck curve(on the rising part of the friction characteristic at higher sliding speeds, the system is stable all the time) 2). Reducing the transition velocity by the use of a higher viscosity lubricating oil. 3). Increasing the stiffness(Damping)and reducing normal load(Sliding mass) Therefore, the Critical velocity is decided from the above conclusions and in designing of machine tool, feed rates(sliding velocity)must be design the more than critical velocity.

• Membrane and Water Treatment
• /
• v.2 no.3
• /
• pp.159-173
• /
• 2011

The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22 ${\mu}m$. A mathematical model is proposed to evaluate the membrane mass transfer coefficient, thermal boundary layers' heat transfer coefficients, membrane / liquid interface temperatures and the temperature polarization coefficients. The mass transfer model was validated by the experimentally and fitted well with the combined Knudsen and molecular diffusion mechanism. The mass transfer coefficient increased with an increase in feed bulk temperature. The experimental parameters such as, feed temperature, 313 to 333 K, feed velocity, 0.8 to 1.8 m/s (turbulent flow region) were analyzed. The permeation fluxes increased with feed temperature and velocity. The effect of feed bulk temperature on the boundary layers' heat transfer coefficients was shown and fairly discussed. The temperature polarization coefficient increased with feed velocity and decreased with temperature. The values obtained were 0.56 to 0.82, indicating the effective heat transfer of the system. The fouling was observed during the 90 h experimental run in the application of natural ground water and seawater. The time dependent fouling resistance can be added in the total transport resistance.

• The Journal of the Acoustical Society of Korea
• /
• v.6 no.4
• /
• pp.5-11
• /
• 1987

In this paper, the measurement of SAW velocity on piezoelectric ceramic is studied. It can be done by using oscilloscope and pulse generator, and measure the velocity especially when feed-through is appeared. The propagating distance was exactly calculated considering that IDT responses are obtained by convolution theory, therefore the velocity was measured by the above simple method. As the results, the measurement velocity at room temperature was 3480 m/sec for $YZ-LiNbO_3$ single crystal and 2770 m/sec for a family of $PbTiO_3$ceramics with feed-through signal.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.60 no.5
• /
• pp.1011-1016
• /
• 2011

This paper presents a robust current controller for a surface-mounted permanent magnet synchronous motor(SPMSM) by using a PI observer. The decoupling PI(proportional-integral) controller combined with an additional feed-forward compensation has been used for the current controller. The classical feed-forward compensation using velocity information and system parameters is not expected to achieve a robust performance against parameter uncertainties. This paper has adopted a PI observer for the feed-forward compensation to cope with parameter uncertainties without using velocity information. A simple PI observer has been designed to compensate the disturbances that represent velocity coupled terms and parameter uncertainties. Experimental results as well as computer simulations with 630W SPMSM confirm that the proposed approach can deal with the effects of the disturbance and improve the control performance.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.12 no.5
• /
• pp.1043-1054
• /
• 1988

The optimum cutting condition of rake angle in turning was investigated in SM45C and SM20C. Results of experiments in SM45C and SM20C are as follow. Specific cutting resistance became higher as the depth of cutting, feed or cutting velocity decreases at same rake angle and resistance became low value at 20.deg.(SM45C), 10.deg.(SM20C). The optimum cutting condition for SM45C is depth of cutting 0.7mm, rake angle 30.deg., cutting velocity 200mm/min, feed 0.1mm/rev, and for SM20C is depth of cut 0.5mm, rake angle 10.deg., cutting velocity 150mm/min, feed 0.1mm/rev.The rake angle for good roughness is 15.deg for SM45C, and that for SM20C is 25.deg. The roughness is influenced by feed and it has the lowest value at 0.1mm/rev and the cutting condition is closely related with the change of cutting velocity and feed.

• Journal of the Korean Society for Precision Engineering
• /
• v.26 no.3
• /
• pp.25-31
• /
• 2009

Femto-second laser ablation with the various feed velocities of the Invar alloy and the micro surface milling for the processing condition were studied. We used a regenerative amplified Ti:sapphire laser with a 1kHz repetition rate, 184fs pulse duration time and 785nm wavelength. Femto-second laser pulse was irradiated on the Invar alloy with the air blowing at the condition of various laser peak powers and feed velocities. An ablation characteristic according to feed velocity of the Invar alloy was appeared as the non-linear type at different zone of energy fluence. The micro surface milling of the Invar alloy using a mapping method was investigated. The optimal condition of micro surface milling was laser peak power of 22.8mW, feed velocity of 1 mm/s, beam gap of $1{\mu}m$. With the optimal processing condition, the fine rectangular shape without burr and thermal damage was achieved. Using the femto-second laser system, it demonstrates excellent tool for micro surface milling of the Invar alloy without heat effects and poor edge.

• Journal of Advanced Marine Engineering and Technology
• /
• v.33 no.5
• /
• pp.713-720
• /
• 2009

Numerous applications of position controlling devices using servoing technique and transmission of energy through belt drives are practiced in the industry. Belt drive is a simple, lightweight, low cost power transmission system. Belt drives provide freedom to position the motor relative to the load and this phenomenon enables reduction of the robot arm inertia. It also facilitates quick response when employed in robotics. In this paper, precision positioning of a belt driven mechanism using a feed-forward compensator under maximum acceleration and velocity constraints is proposed. The proposed method plans the desired trajectory and modifies it to compensate delay dynamics and vibration. Being an offline method, the proposed method could be easily and effectively adopted to the existing systems without any modification of the hardware setup. The effectiveness of the proposed method is demonstrated through computer simulation and experimental results.

• The Transactions of the Korean Institute of Electrical Engineers B
• /
• v.54 no.8
• /
• pp.351-357
• /
• 2005

This paper presents vibration minimization of a PMLSM driven feed-slide by using optimized smooth velocity curve with finite jerk. First of all, the PMLSM was designed and made to reduce detent force. Next, a PMLSM driven feed-slide system was mathematically modeled as a 4-degree-of-freedom lumped parameter model. The key idea of our vibration minimization method is to find out the most appropriate smooth velocity(feedrate) curve with finite jerk. The validity of our proposed method has been verified by comparing computer simulation results of the feed-slide model with experimental ones.