• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.3
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• pp.235-242
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• 2009

This paper presents vehicle road test of a semi-active suspension system equipped with continuously controllable magnetorheological(MR) dampers. As a first step, front and rear MR dampers are designed and manufactured based on the optimized damping force levels and mechanical dimensions required for a commercial middle-sized passenger vehicle. After experimentally evaluating dynamic characteristics of the MR dampers, the test vehicle is prepared for road test by integrating current suppliers, real-time data acquisition system and numerous sensors such as accelerometer and gyroscope. Subsequently, the manufactured four MR dampers(two for front parts and two for rear parts) are incorporated with the test vehicle and a skyhook control algorithm is formulated and realized in the data acquisition system. In order to emphasize practical aspect of the proposed MR suspension system, road tests are undertaken on proving grounds: bump and paved roads. The control responses are evaluated in both time and frequency domains by activating the MR dampers.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.1
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• pp.17-23
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• 2009

This paper proposes a new type of MR(magnetorheological) fluid based suspension system and applies it to military vehicle for vibration control. The suspension system consists of gas spring and MR damper. The nonlinear behavior of spring characteristics is evaluated with respect to the wheel travel and damping force model due to viscosity and yield stress of MR fluid is derived. Subsequently, a military vehicle of 6WD is adopted for the integration of the MR suspension system and its nonlinear dynamic model is established by considering vertical, pitch and roll motion. Then, a sky-hook controller associated with semi-active actuating condition is designed to reduce the imposed vibration. In order to demonstrate the effectiveness of the proposed MR suspension system, computer simulation is undertaken showing vibration control performance such as roll angle and pitch angle evaluated under bump and random road profiles.

• Transactions of the Society of Information Storage Systems
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• v.1 no.2
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• pp.182-187
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• 2005

A large area micro mirror is an optical element that functions as changing an optical path by reflection in integrated optical system. We fabricated the large area silicon mirror by anisotropic etching using MEMS for implementation of integrated optical pickup. In this work, we report the optimum conditions to better fabricate and design, greatly improve mirror surface quality. To obtain mirror surface of $45^{\circ},\;9.74^{\circ}$ off-axis silicon wafer from (100) plane was used in etching condition of $80^{\circ}C$ with 40wt.% KOH solution. After wet etching, polishing process by MR fluid was applied to mirror surface for reduction of roughness. In the next step, after polymer coating on the polished Si wafer, the Si mirror was fabricated by UV curing using a trapezoid bar-type way structure. Finally, we obtained peak to valley roughness about 50 nm in large area of $mm^2$ and it is applicable to optical pickup using blu-ray wavelength as well as infrared wavelength.

• 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.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.1
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• pp.54-61
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• 2014

This paper proposes a driver supportive device with haptic cue function which can transmit optimal gear shifting timing to a driver without requiring the driver's visual attention. Its performance is evaluated under vehicle model considering automotive engine, transmission and vehicle body. In order to achieve this goal, a torque feedback device is devised and manufactured by adopting the MR (magnetorheological) fluid and clutch mechanism. The manufactured MR clutch is then integrated with the accelerator pedal to construct the proposed haptic cue device. A virtual vehicle emulating a four-cylinder four-stroke engine, manual transmission system of a passenger vehicle and vehicle body is constructed and communicated with the manufactured haptic cue device. Control performances including torque tracking and fuel efficiency are experimentally evaluated via a simple feed-forward control algorithm.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.1
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• pp.92-99
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• 2014

An aspherical lens, which resolves several problems with a spherical lens,typically serves asa key part of an optical system. Generally, an aspherical lens is fabricated using a diamond turning machine or by mean of injection molding. However, residual stress and/or tool marks can arise when using a commercial fabricating method such as DTM or injection molding. A polishing process, thus, is commonly used to obtain a high-precision aspherical lens. In this study, a polishing method using MR fluid was applied to minimize several problems, in this case residual stress and the creation of tool marks, during the cutting process. The MR polishing system was developed to polish aspherical lenses. A series of experiments were performed to obtain a very fine surface roughness. PMMA (the lens material for molding) was used as a workpiece, and the gap size, magnetic field intensity, wheel speed and feed rate were selected as the parameters in this study. Finally, a very fine surface roughness of Ra=2.12nm was obtained after MR polishing.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.5
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• pp.85-90
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• 2017

Mica-glass ceramics has features such as micro-sized crystals, high strength, chemical resistance, semitransparent optical properties, etc. Due to its superior material properties, mica glass ceramics have increasing applications in dental and medical components, insulation boards, chemical devices, etc. In many applications, especially for dental and medical components, ultra-precise polishing is required. However, it is known to be a very difficult-to-grind material because of its high hardness and brittle properties. Thus, in this study, a newly developed ultra-precise polishing method is applied to obtain nano-level surface roughness of the mica glass ceramics using magnetorheological (MR) fluids and nano abrasives. Nano-sized ceria particles were used for the polishing of the mica glass ceramics. A series of experiments were performed under various polishing conditions, and the results were analyzed. A very fine surface roughness of Ra=6.127 nm could be obtained.