Development of Evaluation Function for Openability of Opening Diameter of Aluminum Beverage Bottles and Its Application to Optimum Design

The present paper proposes an evaluation function of openability considering the transition of gripping postures, i.e. two-finger gripping and three-finger gripping, so as to evaluate opening ease of aluminum beverage bottles and to specify the rigorous dimension of the cap diameter that is best suited for consumers' satisfaction. First, we have investigated effects of cap diameter on the gripping postures. It is found that subjects tend to shift the gripping posture from two-finger gripping (gripping with thumb and first finger) to threefinger gripping (gripping with thumb, first, and second finger) with increase of the opening diameter. An evaluation function is defined as a ratio between maximum torques that consumers can apply and a required torque for opening. In addition, the cap diameter is the only design variable, and the thumb length, which associates with the transition of the gripping postures and a maximum gripping force, is selected as a state variable in order to take individual differences into consideration. Moreover, an evaluation function is formulated considering the transition of the gripping postures of consumers. The function is composed by using the data obtained from measurement of the maximum gripping force, the maximum torque, and the thumb length, and then the function is optimized. The result of optimization has shown that the optimum opening diameter is obtained at 28.0 mm in case of the subjects. © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved