• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.3
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• pp.337-342
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• 2011

Medical lift column controlling the vertical position while supporting heavy eccentric load should have the high fatigue strength as well as the extremely low structural deflection and vibration in order to maintain the positioning accuracy. The lift column driven by a induction motor is generally in a three-step sliding boom structure and exhibits the time-varying stress distribution according to the up-and-down motion. This study is concerned with the numerical prediction of the fatigue strength of the lift column subject to the time-varying stress caused by the up-and-down motion. The stress variation during a motion cycle is obtained by finite element analysis and the fatigue life is predicted making use of Palmgren-miner's rule and S-N curves. In order to secure the numerical analysis reliability, a 3-D FEM, model in which the detailed lift column structure and the fitting parts are fully considered, is generated and the interfaces between lift column and pads are treated by the contact condition.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.2
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• pp.61-71
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• 1999

This paper resents a novel cargo system adapted for a sea port subjected to severe time-varying tide. The proposed system can perform loading or unloading by using a sort of hydraulic elevator associated with real-tim position control. As a preliminary phase, a small-sized model of the cargo system is designed and constructed. The model consists of three principal components ; container palette transfer(CPT) car, platform with lifting columns and cargo ship. The platform activated by the electro-rheological(ER) valve-cylinder is actively controlled to track the position of the cargo ship subjected to be varied due to the time-varying tide and wave motion. Following the derivation of the dynamic model for the platform and cargo ship motions, an appropriate control scheme incorporating time sequence and PID(proportional-integral-derivative) controller is formulated and implemented. Both the simulated and the measured control results are presented to demonstrate the effectiveness of the proposed cargo system.