The population in agriculture in Japan has been decreasing more and more. Now only less than 3,700,000 farm households are supporting Japan's agriculture. The Japanese gigantic business and industrial sectors attract many young people from the countryside. Seventy percent of the total agricultural population in Japan are mostly elderly people older than 60. As a result, there is a shortage of labor during busy periods, such as the transplanting and harvesting time. Besides that, there are strong demands for alleviating the work hours and the work loads in connection with the improvement of the agricultural work environment and quality. To alleviate labor shortage, to raise labor productivity, to save cropping cost, and to meet the conditions for the improved work environment and quality, it is urgently necessary to review and improve Japan's current mechanized farming system. Of all the crops, rice has reached its highest degree of mechanization in Japan. In fact, more than 90% of the farm operations, from land preparations, planting to drying after harvest are all mechanized. The Japan's mechanized rice cropping system using widely spread intermediate size agricultural machinery, howeve, still requires significant degree of heavy work load especially in walking with a moving machine and feeding of materials such as seedlings and fertilizers to ridding type machinery. To solve those problems, shifting to the rice cropping system using large size machinery has been concerned. In Japan's vegetable cropping, processes such as harvesting, sorting and grading require heavy work load and time. Those processes will have to be properly mechanized to meet the conditions for the improved work environment and quality. A legislative measure has been taken to promote research and development for advanced hi-tech agricultural mechanization systems including automation and robotization of farm works for the agricultural sectors where the traditional mechanization has been accomplished. The agriculture in Japan now is declining, all the mechanization measures can only maintain the current situation. Automation and robotization in agriculture may be the answer to a breakthrough. Thus the quality of farming can be improved. Studies on automatized systems for agricultural machinery have included the position and loading control for cutting and threshing process of the head-feeding combine, the draft control for tractors, and automated steering control for farm vehicles such as tractors and rice planters. Most of previous research works on steering control systems for agricultural vehicles have been limited to the sensing method and algorithm for position of the vehicle. None of the problems related to the instability of the steering system has been investigated. Thus, automated steering system for articulated vehicles using modern control theory was investigated in this study. In order to develop an automatic steering control system of articulated vehicles, adaptability of the linear multi-variable control theory based on the state space approach to the steering control was studied. The numerical model study showed a strong possibility of application of linear multi-variable control theory to the automated steering system. The results obtained from the numerical experiment for the step-function response of the control system were reported. Since the actual control object is always associated with disturbances and parameter fluctuations, the effect of the constant disturbance and the white noise upon the control system was discussed in terms of the response characteristics and stability of the system. The entire process of determination of mechanical parameters ( moment of inertia of vehicle, cornering power of vehicle, etc. ) and control parameters ( gain vector, etc. ) using an experimental vehicle was discussed. Estimation algorithm applicable to the determination of
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