• Title/Summary/Keyword: Rotational Speed

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A preliminary study on the surface finishing of a hard disk slider using magnetorheological (MR) fluid (자기유변유체를 이용한 하드디스크 슬라이더의 표면연마를 위한 기초연구)

  • Jung, B.S.;Jang, K..I.;Min, B..K.;Lee, S.J.;Seok, J.
    • Transactions of the Society of Information Storage Systems
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    • v.3 no.2
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    • pp.66-72
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    • 2007
  • Surface finishing using magnetorheological (MR) fluid is useful to finish small but not too small workpieces such as those in a few millimeter scale. However, due to the high surface hardness, this finishing process does not seem to be suit for applying to a hard disk slider. In this work, a preliminary study is performed on the finishing of the hard disk slider surface with a mixture of an MR fluid and diamond powder. During a wheel type MR finishing process, centrifugal force is found to be a major factor to cause a reduction in material remove rate (MRR), which is supported by a theoretical model. To facilitate this founding, the rotational speed of tool is confined to 500rpm while a rectilinear alternating motion with the mean speed, which is equivalent to the rotational speed, is additionally applied to the workpieces. As a consequence, MRR of about 2 times of the sole rotational case is obtained. This paper shows that MR finishing process can be used to polish a hard material in millimeter scale efficiently by controlling the speeds of the tool and the workpiece.

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Numerical Analysis on Changes in Flowrate of Draft Water and Power by Changing Design Parameters of a Long-Distance Water Circulation (저층수 흡입식 광역 순환장치의 설계변수에 따른 배출량 및 소비동력 변화 특성에 대한 수치 해석 연구)

  • Song, Dong-Keun;Hong, Won-Seok;Kim, Young-Cheol;Park, Myong-Ha
    • The KSFM Journal of Fluid Machinery
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    • v.13 no.1
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    • pp.23-28
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    • 2010
  • A draft tube which has impeller to elevate bottom water and spread it over surface of lake water, induces convective circulation of lake water, a Long-Distance Circulation (LDC). Circulation of lake water make stratified water mixed and enhance DO (Dissolved Oxygen) of bottom water. Circulation rate of water is determined by draft rate of the tube, which is dependent on design parameters of the draft tube system, i. e. dimension of impeller and diffuser, inclined angle of impeller, impeller shape, and rotational speed. In this study, change in draft rate and power consumption of circulation equipment was investigated numerically with changing impeller dimension, angle and rotational speed. It was found that flowrate of draft water was increased as the dimensions of draft tube and impeller, and rotational speed and inclined angle of impeller increased. The power consumption was also elevated with increasing parameter values, and final selection of parameter values was made to satisfy target flowrates and power consumption.

A Study on the Machining Accuracy according to Vibration and Unbalance Decrease in Rotational Speed Domains of High Precision Machine Tools (정밀 공작기계의 회전 영역별 진동 및 불평형량 감소에 따른 가공 정밀도 영향에 관한 연구)

  • Son, Deok-Soo;Kim, Sang-Hwa;Park, Il-Hwan
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.12 no.2
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    • pp.121-126
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    • 2013
  • Precision machine tools for high dignity cutting are needed for efforts to improve machining accuracy. However, there are many factors to improve machining accuracy. This study investigated how machining accuracy changes when variation and unbalance amount in rotational speed domain is decreased. Machining accuracy of initial machine tools depends on manufacturing and assembly of parts such as bearing. And then, vibration and noise vary with volume of unbalance amount when it is rotation, so it effects unbalance amount. Also vibration and noise increased by unbalance shorten spindle's life and it especially makes worse boring accuracy. Therefore, this study studied the change of roundness and cylindricity of workpiece when it decreases variation and unbalance in rotational speed domain.

A Study on Cutting Conditions and Finishing Machining of Si Material Using Laser Assisted Module (레이저 보조 모듈을 이용한 Si 소재의 절삭조건 및 보정가공에 관한 연구)

  • Young-Durk Park
    • Design & Manufacturing
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    • v.17 no.2
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    • pp.15-21
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    • 2023
  • In this study, a diamond turning machine and a laser-assisted machining module were utilized for the complex combined cutting of aspheric shapes and fine patterns on the surface of high-hardness brittle material, silicon. The analysis of material's form accuracy and corrective machining was conducted based on key factors such as laser output, rotational speed, feed rate, and cutting depth to achieve form accuracy below 1 ㎛ and surface roughness below 0.1 ㎛. The cutting condition and corrective machining methods were investigated to achieve the desired form accuracy and surface roughness. The rotational speed of the spindle and the linear feed rate of the diamond turning machine were varied in five stages for the cutting condition test. Surface roughness and form accuracy were measured using both a contact surface profilometer and a non-contact surface profilometer. The experimental results revealed a tendency of improved surface roughness with increased rotational speed of the workpiece, and the best surface roughness and form accuracy were observed at a feed rate of 5 mm/min. Furthermore, based on the cutting condition experiments, corrective machining was performed. The experimental results demonstrated an improvement in form accuracy from 0.94 ㎛ to 0.31 ㎛ and a significant reduction in the average value of the surface roughness curve from 0.234 ㎛ to 0.061 ㎛. This research serves as a foundation for future studies focusing on the machinability in relation to laser output parameters.

Control of Rotational Angular Speed using Magneto-rheological Fluid (자기유변유체를 이용한 회전 각속력 제어)

  • 신성철;정재성;김정훈;이종원
    • The Korean Journal of Rheology
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    • v.11 no.2
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    • pp.67-72
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    • 1999
  • A magneto-rheological(MR) fluid based rotary loading and braking device is developed. The loading and braking forces of the device are accurately adjustable by controlling the yield stress of MR fluid, so that the vibration control, the precision position control and the speed control of rotating machines equipped with the device can be achieved. As an engineering application, constant rotational speed regulation is conducted using the device manufactured in laboratory, introducing PI control action not only with varying torque due to gravitation, with initial angular speed, but also with constant external torque made by hand. To do this, first, mathematical model was obtained via experiments. And then, simulation was carried out, based on the experimentally identified model. Its result was confirmed through experiment. It is identified by simulation and experimental results that PI action leads to satisfactory control performance in both cases that varying torque due to gravitation, with initial angular speed, and constant external torque are applied.

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Low Speed Design of Rear Rotor in Contra-Rotating Axial Flow Pump

  • Cao, Linlin;Watanabe, Satoshi;Momosaki, Simpei;Imanishi, Toshiki;Furukawa, Akinori
    • International Journal of Fluid Machinery and Systems
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    • v.6 no.2
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    • pp.105-112
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    • 2013
  • The application of contra-rotating rotors for higher specific speed pump has been proposed in our studies, which is in principle effective for reducing the rotational speed and/or the pump size under the same specification of conventional axial flow pump. In the previous experiments of our prototype, the cavitation inception at the tip region of the rear rotor rather than that of the front rotor and the strong potential interaction from the suction surface of the rear rotor blade to the pressure surface of the front one were observed, indicating the possibility to further improve the pump performance by optimizing rotational speed combination between the two rotors. The present research aims at the design of rear rotor with lower rotational speed. Considering the fact that the incoming flow velocity defects at the tip region of the rear rotor, an integrated inflow model of 'forced vortex' and 'free vortex' is employed. The variation of maximum camber location from hub to tip as well as other related considerations are also taken into account for further performance improvement. The ideas cited above are separately or comprehensively applied in the design of three types of rear rotor, which are subsequently simulated in ANSYS CFX to evaluate the related pump performance and therefore the whole low speed design idea. Finally, the experimental validation is carried out on one type to offer further proofs for the availability of the whole design method.

Oil-Air Lubrication Characteristics of a High Speed Spindle System for Machine Tools(I) Effect of Oil Supply Rate, Rotational Spindle Speed and Spindle System Structure (공작기계용 고속주축계의 오일에어윤활특성에 관한 연구 (I) 공급유량, 주축회전수 및 주축계 구조의 영향)

  • 김석일;최대봉;박경호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.2
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    • pp.351-358
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    • 1993
  • Recently a high speed spindle system for machine tools has attracted considerable attention to reduce the machining time, to improve the machining accuracy, to perform the machining of light metals and hard materials and to unite the cutting and grinding processes. In this study, a high speed spindle system is developed by applying the oil-air lubrication method, angular contact ball bearings, injection nozzles with dual orifices and so on. And a lubrication experiment for evaluating the performance of the spindle system is carried out. Especially, in order to establish the lubrication conditions related to the development of a high speed spindle system, the effects of oil supply rate, rotational spindle speed and so on are studied and discussed on the bearing temperature rise, bearing temperature distribution and frictional torque. And the effect of spindle system structure on the bearing temperature distribution is investigated.

Experimental Assessment with Wind Turbine Emulator of Variable-Speed Wind Power Generation System using Boost Chopper Circuit of Permanent Magnet Synchronous Generator

  • Tammaruckwattana, Sirichai;Ohyama, Kazuhiro;Yue, Chenxin
    • Journal of Power Electronics
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    • v.15 no.1
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    • pp.246-255
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    • 2015
  • This paper presents experimental results and its assessment of a variable-speed wind power generation system (VSWPGS) using permanent magnet synchronous generator (PMSG) and boost chopper circuit (BCC). Experimental results are obtained by a test bench with a wind turbine emulator (WTE). WTE reproduces the behaviors of a windmill by using servo motor drives. The mechanical torque references to drive the servo motor are calculated from the windmill wing profile, wind velocity, and windmill rotational speed. VSWPGS using PMSG and BCC has three speed control modes for the level of wind velocity to control the rotational speed of the wind turbine. The control mode for low wind velocity regulates an armature current of generator with BCC. The control mode for middle wind velocity regulates a DC link voltage with a vector-controlled inverter. The control mode for high wind velocity regulates a pitch angle of the wind turbine with a pitch angle control system. The hybrid of three control modes extends the variable-speed range. BCC simplifies the maintenance of VSWPGS while improving reliability. In addition, VSWPGS using PMSG and BCC saves cost compared with VSWPGS using a PWM converter.

Air Cooling Characteristics of a High Speed Spindle System for Machine Tools (공작기계용 고속주축계의 공기냉각특성에 관한 연구)

  • Choi, Dae-Bong;Kim, Suk-Il;Song, Ji-Bok
    • Journal of the Korean Society for Precision Engineering
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    • v.11 no.1
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    • pp.123-128
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    • 1994
  • A high speed spindle system for machine tools can be used to reduce the machining time, to improve the machining accuracy, to perform the machining of light metals and hard materials, and to unite the cutting and grinding processes. In this study, a high speed spindle system is developed by applying the oil-air lubrication method, angular contact ball bearings, injection nozzles with dual orifices, cooling jacket and so on. And an air cooling experiment for evaluating the performance of the spindle system is carried out. Especially, in ofder to establish the air cooling conditions related to the development of a high speed spindle system, the effects of cooling air pressure, oil supply rate, air supply rate and rotational spindle speed are studied and discussed on the bearing temperature rise and frictional torque. Also the effects of cooling air pressure, rotational spindle speed and spindle system structure is investigated on the bearing temperature distribution. The experiment on the test model reveals the usefulness of the air cooling method.

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Analysis of Red Pepper Calyx Cutting Using a Rotational Cutter (회전날을 이용한 홍고추의 꼭지 절단 경향 분석)

  • 이승규;송대빈;정의권
    • Journal of Biosystems Engineering
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    • v.28 no.3
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    • pp.209-216
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    • 2003
  • Red pepper calyx cutting devices using a impacting force by a rotational cutter were devised and tested to obtain the fundamental data for development of a calyx removal unit. Fresh red peppers with 80∼87%(w.b.) of initial moisture contents were used as experimental materials. Square and wire type of rotational cutters were used to cut the red pepper calyx and the fresh red peppers were fed into the device both manually and automatically. Three rotational speeds of 250, 500, 700rpm were selected for a square, and 1000, 1500, 1800rpm for a wire type cutter respectively. Four types of red pepper fixing unit were used in manual feeding. The cutting rate of the square type cutter was over 50% regardless the shape and specification of the cutter. For the wire type cutter, the copper wire and nylon chord could not be applied to cut the red pepper calyx because of the low cutting rate. But for the fine wire, the cutting rate was higher and the cutting mechanism was more steady than copper wire and nylon chord. The cutting rate of automatic feeding and wire type cutting unit was about 70% for all levels of the rotational speed. The cutting rate was highly related to the impacting point of red pepper in carrier box. To increase the cutting rate using the rotational cutter, a proper device and mechanism was required to keep the impacting point consistently.