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Min-max Control for Vibration Suppression of Mobile Manipulator with Active Suspension System
Dongil Choi 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.2
This paper introduces a method to control the vibration of mobile manipulator on the vertical direction. When the mobile manipulation moves on uneven road, the road disturbance affects the manipulation system. It is important to suppress the disturbance for the stability of manipulation system. The vibration damping control method of a simplified double inverted pendulum model is designed to suppress vertical disturbance. In the double inverted pendulum model, the system matrix contains parameter uncertainty due to the simplification of the model. To control this system, we use static output feedback with min-max control. By using the static output feedback with min-max control, the desired closed-loop stability can be achieved while effectively suppressing disturbance even in the presence of system uncertainty. We measure the actual road disturbance by using an accelerometer. In the simulation, we prove the measured ground disturbance is successfully suppressed by using our control method and demonstrated effectiveness of proposed control method through comparative simulations with LQR control.
Choi, Woojun,Hu, Guoxiang,Kwak, Kyuju,Kim, Minseok,Jiang, De-en,Choi, Jai-Pil,Lee, Dongil American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.51
<P>This paper describes the effects of doped metals on hydrogen evolution reaction (HER) electrocatalyzed by atomically controlled MAu<SUB>24</SUB> and M<SUB>2</SUB>Au<SUB>36</SUB> nanoclusters, where M = Pt and Pd. HER performances, such as onset potential (<I>E</I><SUB>onset</SUB>), catalytic current density, and turnover frequency (TOF), are comparatively examined with respect to the doped metals. Doping Pt or Pd into gold nanoclusters not only changes the electrochemical redox potentials of nanoclusters but also considerably improves the HER activities. <I>E</I><SUB>onset</SUB> is found to be controlled by the nanocluster’s reduction potential matching the reduction potential of H<SUP>+</SUP>. The higher catalytic current and TOF are observed with the doped nanoclusters in the order of PtAu<SUB>24</SUB> > PdAu<SUB>24</SUB> > Au<SUB>25</SUB>. The same trend is observed with the Au<SUB>38</SUB> group (Pt<SUB>2</SUB>Au<SUB>36</SUB> > Pd<SUB>2</SUB>Au<SUB>36</SUB>> Au<SUB>38</SUB>). Density functional theory calculations have revealed that the hydrogen adsorption free energy (Δ<I>G</I><SUB>H</SUB>) is significantly lowered by metal-doping in the order of Au<SUB>25</SUB> > PdAu<SUB>24</SUB> > PtAu<SUB>24</SUB> and Au<SUB>38</SUB> > Pd<SUB>2</SUB>Au<SUB>36</SUB> > Pt<SUB>2</SUB>Au<SUB>36</SUB>, indicating that hydrogen adsorption on the active site of nanocluster is thermodynamically favored by Pd-doping and further by Pt-doping. The doped metals, albeit buried in the core of the nanoclusters, have profound impact on their HER activities by altering their reduction potentials and hydrogen adsorption free energies.</P> [FIG OMISSION]</BR>
Higher order analysis of thin-walled beams with axially varying quadrilateral cross sections
Choi, In Seop,Jang, Gang-Won,Choi, Soomin,Shin, Dongil,Kim, Yoon Young Elsevier 2017 Computers & structures Vol.179 No.-
<P><B>Abstract</B></P> <P>A thin-walled beam finite element with a varying quadrilateral cross section is formulated based on a higher order beam theory. For the calculation of distortions, the beam frame approach, which models the cross section by using two-dimensional Euler beams, is used. Distortions induced by the Poisson’s effect and warpings are analytically derived. Three-dimensional displacements at an arbitrary point of a present beam element can be described by interpolating three-dimensional displacements at the end sections. Straight and curved thin-walled beams with varying cross sections are solved to show the validity of the proposed approach.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Coupled behavior of 1-D deformations due to a varying cross section is predicted. </LI> <LI> Distortions by the Poisson’s effect and corresponding warpings are considered. </LI> <LI> The effectiveness is verified by solving straight/twisted/curved beam problems. </LI> </UL> </P>