【正文】 ic servo system using evolution strategies MY Kim, CO Lee Abstract This paper deals with an experimental optimization problem of the controller gains for an electrohydraulic position control system through evolution strategies (ESs)based method. The optimal controller gains for the control system are obtained by maximizing ?tness function designed specially to evaluate the system performance. In this paper, for an electrohydraulic position control system which would represent a hydraulic mill stand for the rollgap control in plate hotrollings, the time delay controller (TDC) is designed, and three control parameters of this controller are directly optimized through a series of experiments using this method. It is shown that the nearoptimal value of the controller gains is obtained in about 5th generation, which corresponds to approximately 150 experiments. The optimal controller gains are experimentally con?rmed by inspecting the ?tness function topologies that represent system performance in the gain spaces. It is found that there are some local optimums on a ?tness function topology so that the optimization of the three control parameters of a TDC by ma nual tuning could be a task of great dif?culty. The optimized results via the ES coincide with the maximum peak point in opologies. It is also shown that the proposed method is an ef?cient scheme giving economy of time and labor in optimizing the controller gains of ?uid power systems experimentally. Keywords: Controller gain optimization。 Evolution strategies。 Automatic controller gain search。 Purshouse, 2020。 Jeon, Lee, amp。 Hyun amp。 Choi, Lee, amp。 Watton, 1989): the pressure?ow characteristics of valve, the saturation of valve and cylinder, the leakage ?ow characteristics of valve and cylinder with variation of supply pressure, the friction characteristic in cylinder, the variation of viscosity and pressibility of working ?uid with the temperature, the ?ow characteristic due to the shape of pipeline, and most importantly, the variation of the system gains with the supply pressure and the load pressure. Therefore, when these ?uid power systems are controlled, the controller gains are adjusted on the foundation of expert’s intuitive knowledge about the system and the tuning experience of the controller gains in general. It needs very excessive experiments through trial and error. But though some controller gains are obtained, it is hard to say that the results are the best gain set at a given situation. For the automatic adjustment of the controller gains in ?uid power systems, the research to application of a fuzzy gain adapter (FGA) has been performed (Jeon, 1997。 Schwefel, 1981。 Schwefel, 1994, 1996). When an appropriate ?tness function representing potential solutions is given as survivability of candidates, the tuning problem of controller gains can be considered as an optimization problem, so that an optimal controller gain set is searched in the region of gain spaces speci?ed by operator. A major advantage is that much experience on the gaintuning for the control system is not required, and the least information for the system is just required. Especially, in cases that a real experimental system is directly used for evaluating candidates, ESs are more suitable than other evolution algorithms due to its own characteristic called selfadaptation. In this study, a time delay controller (TDC) is designed as a controller for position control of an electrohydraulic servo system. The controller designed to have 2nd order error dynamics has three controller gains implicitly. By using an ES as optimization algorithms, the optimal controller gain set in the speci?ed gain spaces is determined through online experiments. For the veri?cation of the obtained results, the ?tness function topologies in the gain spaces experimentally are made out, and analyzed. Finally, the experimental results searched through ESs are shown to coincide with the optimal peak point that has best ?tness value on the speci?ed gain spaces. 2. Hydraulic servo system . Electrohydraulic position control system is the schematic diagram of the electrohydraulic position control system used in this study. This system is a test rig for the rollgap control of hydraulic mill stand, which was made for the improvement of thickness control performance in plate hotrolling processes (Gizburg, 1984。 Park, 1997). The rig simulat