Agricultural residues are the most abundant biomass and forage resources. Chopping is a precondition for either use, and reducing the shearing force has been considered as one of the most effective way to save energy. A smaller force can also permit more compact mechanical parts of chopping devices. In several cases, power consumption may be large, even when the shearing force is small, if the corresponding cutting velocity is high. Consequently, it is important to minimize both cutting force and power consumption simultaneously. This paper presents a practical approach to solve the multi-objective optimization problem for chopping processes of corn stalks. Applying the Taguchi design of experiments, a plan of 27 chopping tests was conducted. Based on the grey relational grade analysis and analysis of variance technique, optimum levels as well as the percentage contribution of such parameters were identified. Experimental results showed that the multi-response optimization problem in chopping corn stalks can be effectively addressed through the combination of Taguchi design and grey relational analysis. The results can be expanded for practical applications in design and operation of chopping machines for agricultural residues.

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This paper presented comparison results of two locomotion models: a pure-vibration driven and a vibro-impact driven system. In experiments, the friction force can be varied without changing the internal and the body masses. The mathematical models of the two systems were developed and experimentally verified. Using dimensionless models, the results can be expanded to other sizes in practice. The two models were compared in the following aspects: the progression rate, the motion direction and the dynamics response. The effect of friction as an important variable on the dynamic response of the two scaled models were examined and compared by means of bifurcation analysis and basin of attraction. It has been found that, the pure-vibration can provide forward motion better than the vibro-impact does. The highest progression rate of the vibro-impact was less than that of the pure-vibration system in the investigated ranges of input parameters. Besides, the pure-vibration always has period-1 motion, whereas the vibro-impact system has a rich and complex dynamic response, including period-1, period-2 as well as chaotic motions. The results obtained would be useful for design and operating the self-propelled locomotion systems.

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