Hiroshima Prefecture is noted for its shelled oysters. To preserve their freshness as long as possible, a parameter design was carried out on the process conditions from shelling to delivery. The amount of triphenylformazan(TF) produced was used as an index of freshness. TF production mass(PM) was assumed to decrease exponentially from an initial value P₀ according to the number of days of storage(M), by the formula P_M = P₀e^(β-γ)M, where β is a coefficient of freshness preservation effect and γ is a freshness degradation constant. The input-output relation y=β×M=γ×M－ln(P₀/P_M) was used,with days of storage as a signal factor and the shelling quality as a noise factor. There were eight control factors, such as temperature, salt, casing, etc. The factors were assigned to an L₁₈ orthogonal array and an experiment was carried out. The gain of the existing and comparative conditions was reproduced fairly well in the confirmation experiment. There appears, however, to be a need for further study of the setting of the noise factor, the precision of measurement of the TF production mass, and the input-output relation.

The purpose of this paper is to study approaches and means relating to the social loss concept propounded in quality engineering, in order to introduce this concept into a corporation and make it well known. Process improvement (feedback control) by online quality engineering had proven inadequate, so this case study returned to parameter design, attempted to optimize toothpaste tube bonding conditions, and then applied online quality engineering. When 3 million tubes are produced annually, the improvement effect is about 100 million yen. Performing a loss calculation for each step, taking this step before volume production begins, and implementing remedies to tube bonding failures that have actually occurred in the field were made explicit to the company. As a result, an educational effect was observed from the bottom level of production personnel through the middle management level. The findings suggest that management has an important role to play in not stopping at simple problem solving and in avoiding the pitfall of partial optimization in technology development.