Hyun Chan Lee

A neuro-controller for synchronization of two motion axes

The coordinated and synchronized control of the motion of multiple axes is a challenging problem in motion control fields. In most multiaxis applications, controllers are usually designed for each of the motion axes, which results in a collection of decoupled single input and single output systems. For coordinated motion, however, decoupling sometimes causes damage to the overall performance objective. Therefore, a better way to control multiaxis systems is to introduce intelligent control actions in the controller so that the coordination objective of the desired motion is maintained. A method for achieving the synchronization of two motion axes using a neural network is described. We introduce a new cost function for better synchronization performance. Also, we derive a learning law to adjust the weights of the neural network, based on the gradient algorithm. The derived learning law guarantees good synchronization performance of two motion axes. Simulation and experimental results demonstrate the usefulness of the proposed scheme to synchronize the motion of multiple axes.

Real-time compensation of two-dimensional contour error in CNC machine tools

A real-time contour error compensation (RTCEC) system to improve contouring performance in CNC machine tools is proposed. The RTCEC system evaluates the contour error and modifies the reference position commands based on the computed contour error. Since the proposed compensation scheme can be executed on an external computer, it can be used in conventional CNC machine tools without modifying the interpolation and control algorithms of the CNC system. The compensation system, which introduces a new method for calculating the contour error in real-time without modifying the existing interpolation algorithm, has been implemented by integrating a PC with the existing CNC in a machining center. Experimental results on linear, circular and spiral contours demonstrate the performance of the proposed system.

Comparison of CuO-MOx (M=Ce, Zn, Cr and Zr) catalysts in various water-gas shift reactions

The water-gas shift (WGS) reaction in the temperature range of 100–350 °C for various feed compositions simulating forward, reverse and real WGS conditions was studied for a series of coprecipitated mixed metal oxide catalysts of 30 wt% of CuO and 70 wt% of metal oxide (CeO2, ZnO, Cr2O3, and ZrO2) as well as for a commercial WGS catalyst (ICI 83-3). The catalysts were characterized using BET, XRD, H2-TPR and N2O dissociation studies. Among the tested catalysts, CuO-Cr2O3 showed the best activity in the forward WGS, while the commercial catalyst was the best catalyst in the real and reverse WGS reactions. The effect of Cu content in the catalyst was also studied and, in the case of the real WGS, 50 wt% CuO-Cr2O3 was more active than 30 wt% CuO-Cr2O3. H2 and CO2 were found to inhibit the forward WGS, decreasing the reaction rate substantially, particularly at temperatures below 200 °C. The inhibition effect varied depending on the tested catalyst and increased with increasing H2 or CO2 concentration. As the inhibition effect was reversible, the competitive adsorption of H2 or CO2 on the active sites has been suggested to be responsible for the effect. The high activity of the commercial catalyst in the H2 rich real WGS could be described by the difference in the H2 inhibition between the catalysts. An easily reducible copper species was found in CuO-Cr2O3 and could be attributed to the high activity in the forward WGS. Keywords:Mixed Metal Oxide Catalysts, Water Gas Shift Reaction, H2 Inhibition, CO2 Inhibition, Copper Chromate Catalyst

Temperature oscillations in methanol partial oxidation reactor for the production of hydrogen

Methanol partial oxidation (POX) is a well-known reforming reaction for the production of hydrogen from methanol. Since POX is relatively fast and highly exothermic, this reforming method will be efficient for the fast startup and load-following operation. However, POX generates hot spots around catalyst and even oscillations in the reactor temperature. These should be relieved for longer operations of the reactor without catalyst degradations. For this, temperature oscillations in a POX reactor are investigated experimentally. Various patterns of temperature oscillations according to feed flow rates of reactants and reactor temperatures are obtained. The bifurcation phenomena from regular oscillations to chaotic oscillations are found as the methanol flow rate increases. These experimental results can be used for theoretical analyses of oscillations and for designing safe reforming reactors.

Wiener model and extremum seeking control for a CO preferential oxidation reactor with CuO-CeO 2 catalyst

To whom correspondence should be addressed. E-mail: jtlee@knu.ac.kr Equally contributed authors. †The material in this paper was partially presented at the 9 International Symposium on Advanced Control of Chemical Processes, June 7-10, 2015, Whistler, Canada. Copyright by The Korean Institute of Chemical Engineers. RETRACTED ARTICLE: Wiener model and extremum seeking control for a CO preferential oxidation reactor with CuO-CeO2 catalyst

Dynamics study for oscillatory temperature in methanol partial oxidation

Methanol partial oxidation (POX) is highly exothermic. The reaction temperature in a reactor can increase fast when the reaction starts. So, it is needed to know the temperature dynamics for a stable operation of reactor. As the POX occurs in the coated-aluminum reactor, it has been reported that the reactor temperature shows various patterns. There are temperature patterns such that the reaction temperatures have rapid increase, regular oscillation, chaotic oscillation or constant value. In this paper, operating conditions showing such reactor temperature patterns in methanol partial oxidation are investigated experimentally.