[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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The design of machinery for food processing requires the assessment of the respective safety and hygiene risks. Hygiene risks are very different from other safety risks. They are more associated with the ability of machines to be freed from product debris and micro-organisms, and thus preventing product contamination, rather than from the dangers of moving parts or electrical hazards to the operator. For the latter hazards, the identification is usually implemented by using the checklists, whose representative one is Table A.1 in the Annex A of ISO14121-1:2007. However, for hygiene hazards, any checklist suitable for the designers of food process machinery available. In this paper, a checklist is in deference ISO14159 constructed, being based on the answers of questionnaire to survey hygiene risks against the food process machine makers and users in reference to ISO14159.

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A system which has logical loop(s) was not generally solved in terms of the arithmetic operators of Boolean algebra. It appears infinite circulation of the unknown variables in the process of solving simultaneous Boolean equations. An exact method has been proposed for solving this problem in reliability analysis, but it was effective only in a restricted analysis condition. In the present paper, a generalized procedure is proposed for systems with logical loop(s). The proof of the solution for simultaneous Boolean equations is given in a simplified formulation. Discussions are made for time-dependent behavior of system operation to fundamental loop structures. It is shown the relation between operating condition of a loop structure and indefinite constants appeared in the solution of simultaneous Boolean equations. With this relation, it becomes possible to accurately evaluate the reliability of logical loops by the aid of algebraic solution of Boolean equations. Detailed explanation of this analysis procedure is given for an example system.

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