• Journal of the Korean Society for Precision Engineering
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• v.30 no.12
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• pp.1321-1325
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• 2013

In this paper, we proposed an air bearing stage with active magnetic preloads in vertical directions compensating motion errors and attenuating vibrations to improve dynamic characteristics. This preloaded design gives simpler configuration of the stage, and active control of preload can be used for compensating motion errors by feedforward method. To improve dynamic characteristics, vibration of the table is monitored by an accelerometer, and controlled by a DSP based digital controller with integrator and band pass filters for suppressing roll and pitch vibration modes. The modes were evaluated by measuring frequency response functions, and compared with compensated responses. This showed effective results for suppressing poorly damped regenerative vibration of air bearings.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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• pp.216-223
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• 2000

A robot arm with free joints has some advantages over conventional ones. A light weight and low power consumed arm can be made by a reduction of the number of joint actuators. And this arm can easily overcomes actuator failure due to unexpected accident. In general such underactuated arm does not have controllability because of the lack of joint actuators. The two-link arm with a free joint introduced in this paper is also uncontrollable in the sense of linear system theory. However, the linearized system sometimes can not represent the inherent dynamic behavior of the nonlinear system. In this paper the dynamic characteristics of the two-link arm with a free joint in view of global motion including damping and friction effect of the joints is investigated. In the case of considering only the damping effect, the controllable goal positions are confined to a specific trajectories. But in the case of considering the friction effect, the system can be controlled to arbitrary positions using the friction of the free joint as a holding brake. Also numerical example of position control is presented.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.7
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• pp.730-736
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• 2012

Latest, many researchers do research on wearable robot. The purpose of the researches is very diverse, it will improve efficiency in the industry, taken to replace the many workers in the military field and taken to assist bodily functions run out by aging. However, there is no clear Differentiated strategy depending on the purpose for design and control of the wearable robot. Although a common purpose is to drive the robot by the sensor signal (intent signals), the optimization about the mechanism and control studies must be done according to the user's physical ability and purpose. In this study, the study's first phase for the development of wearable robotic gait rehabilitation, gait characteristics were analyzed elders and hemiplegia patients using a 3D gait analysis system (VICON512). As a result, asymmetric gait characteristics of the hemiplegia patients were found compared with the normal elderly.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.2
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• pp.81-91
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• 1992

A control methodology for suppressing the elastodynamic responses of high-speed flexible linkage mechanisms is presented by adopting the concept of smart structures featuring piezoelectric films. The dynamic modeling of the proposed mechanism is accomplished by employing a finite element formulation which accounts for dynamic motion in both inertial and elastic coordinates. The dynamics of piezoelectric actuators and sensors bonded on the original flexible structure are developed for one-dimensional beam in conjunction with the modal analysis. The linear optimal controller which consists of a feedback control law and a Luenberger observer is employed. Numerical simulation is performed to evaluate the improvement of elastodynamic responses.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.297-300
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• 2002

In this study, the deformation of the free surface motion of a magnetic fluid for the change in electromagnetic force is discussed and carried out theoretically and experimentally on the basis of Rosensweig Ferrohydrodynamic Bernoulli Equation. While applied magnetic fields are induced by 4$\times$4 electromagnet located under the magnetic fluid, the surface of the magnetic fluid is formed the balance of surface force, gravity, pressure difference, magnetic normal pressure and magnetic body farce. In case, magnetic fluid in characteristics of fluid adjusted to the opposite direction of the gravity direction. thus, the device of a magnetic fluid proposed the surface actuator. The device of surface deformation as well comparison between numerical simulation and experiments as will be presented.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.11
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• pp.65-74
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• 2002

This paper examines the usefulness of a Brake Steer System (BSS), which uses differential brake forces for steering intervention in the context of Intelligent Transportation Systems (ITS). In order to help the car to turn, a yaw moment can be achieved by altering the left/right and front/rear brake distribution. This resulting yaw moment on the vehicle affects lateral position thereby providing a limited steering function. The steering function achieved through BSS can then be used to control lateral position in an unintended road departure system. A 8-DOF nonlinear vehicle model including STI tire model will be validated using the equations of motion of the vehicle. Then a controller will be developed. This controller, which will be a PID controller tuned by Ziegler-Nichols, will be designed to explore BSS feasibility by modifying the brake distribution through the control of the yaw rate of the vehicle.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.151-157
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• 2004

In this paper, we propose a simple control scheme, based on second order sliding modes, which guarantees a fast and precise container transfer and the swing suppression during the container movement, despite of model uncertainties and unmodeled dynamic actuators. In the actual case, the swing suppression is obtained by constraining the system motion on a suitable surface which involves both the desired path and the swing angle. Strictly speaking, the trolley velocity is modified on-line, on the actual swing angle, to obtain the suppression of the oscillations not only at the end of the transport but during transfer as well. Such controller has been tested on a laboratory-size model of the 3Dcrane, and some experimental results are reported.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.3
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• pp.83-91
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• 2000

During static walking of a quadruped walking robot, stability of the robot depends on whether the projection of the mass center is located within the supporting area that is varying with leg motion and formed by standing legs. In this paper, force margin instead of the mass center was used to determine stability and body-tilting method was used to enhance it. On-line control of body tilting was realized with simple reaction feedback based on force margin of the static walking model of the robot instead of complicated calculation. Model reference on-line control where the model searches stable pose for predefined force margin also gave good walking performance.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.155-160
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• 2001

The road simulator system can simulate the longitudinal, lateral, and vertical movement changed by road conditions and vehicle dynamic characteristics while driving. This system provides the durability evaluation of vehicle suspensions. The system consists of hydraulic actuators, link mechanism, and servo controller. The hydraulic actuators are specially manufactured using low friction seals to endure high speed movement. The link mechanism is designed in order to minimize the dynamic effect during motion and remove the interference between 3axes actuators. The servo controller is composed of sensors, sensor amplifiers - displacement transducers and load cells, and an industrial PC with DSP board which calculates the control algorithm to control hydraulic actuators. The test results are included to evaluate the performance of this simulator comparing vehicle driving test.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.566-569
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• 2000

This hybrid position/force control for the dynamic walking of the biped robot is performed in this paper. After the biped robot was modeled with 14 degrees of freedom of the multibody dynamics, the equations of motion are constructed using velocity transformation technique. Then the inverse dynamic analysis is performed for determining the driving torques and the ground reaction forces. From this analysis, obtains the maximum ground contact force at the moment of contacting which act on the rear of the sole of swing leg and the distribution curve of the ground reaction. Because these maximum force and distribution type acts an important role to the stability of the whole dynamic walking, they are reduced and distributed smoothly by means of the trajectory of the modified ground reaction force. This new trajectory is used to the reference input for more stable dynamic walking of the whole walking region.