48 based on images of a bathroom that we visited during the field observation (Fig. 8). The hands and feet of the evaluators were reproduced in the virtual space, and these virtual models were linked to the evaluators’ actual hands and feet in the real space. In addition, we placed simplified prototypes of the washing machine, washtub, water and laundry items in the real space, as shown in Fig. 9. The two types of washing machines were installed in the MP environment of the same Vietnamese bathroom and were evaluated by three Vietnamese people (two men and one woman). These evaluators were immersed in the virtual bathroom including the physical prototypes and carried out the laundry process using the washing machines. First, they evaluated the fully automatic washing machine when carrying out the preliminary process of manual washing using the wash basin on the floor. Then, the fully automatic washing machine was replaced with the twin-tub washing machine, which involved manual washing in the wash basin attached to the top of the machine while standing. The average values of the three evaluators for each criterion are shown in Fig. 10. The total average for all the criteria was 4.8 for the fully automatic washing machine and was slightly higher at 5.0 for the twin-tub washing machine. However, the score for “easy” decreased from 6.7 for the fully automatic washing machine to 5.3 for the twin-tub washing machine. Switching between the washing, rinsing and wringing processes and the work of transferring the clothes from the washing tank to the hydroextractor (i.e., the wringing and spinning tank) were found to lower the scores of the evaluation criteria for the twin-tub washing machine, but not necessarily for the fully automatic washing machine. These manual processes also resulted in lower scores for “calm,” “pleasing,” “refreshing” and “relaxed.” In contrast, the score for “free” increased because the quantity of water and washing time could be easily adjusted with the twin-tub machine. “Delicate” was connected to many requirements for laundry and is the only criterion connected to the requirement of “doesn’t damage clothes.” This score increased because the newly designed twin-tub washing machine allows manual clothes washing while standing with increased stability. Because none of the scores fell below 4.0, which is the middle value for each criterion, changes in the laundry processes were not considered to have negatively impacted the selected satisfiers. Although the overall score slightly improved with use of the twin-tub washing machine, the evaluation results for some of the criteria, which were based on satisfiers, suggest that the design needs to be further improved. In particular, the functions and structure of the twin-tub washing machine need to be changed so that it makes transferring clothes from the washing tank to the wringing and spinning tank easier. A detailed design H. KOBAYASHI et al. Prototype of the washing machineFig. 9 Tangible prototypes in the MP environment. Fig. 10 Average scores of each criterion assigned by three Fig. 8 Virtual space of the MP environment. evaluators for two types of washing machines. Prototype of the toiletWashbasin, clothesand waterSandals
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