The integrated ergonomics analysis and QFD method Methods

Isa Halim et al. AJE Vol.9 2009 109-121 114 “stability of load”, and “able to carry various sizes of object” as the critically desirable requirements. Workers’ requirements for the new HPT design were compiled in the customers’ requirements section of the QFD House of Quality HoQ Figure 2. Table 1. Workers’ requirements to improve the existing HPT Score Features Workers’ requirements 1 2 3 4 5 Relative importance Light 6 5 6 5 8 3.13 Structure Stable while maneuvering 1 3 15 11 3.20 Having front wheels 3 10 9 7 1 2.77 Having rear wheels 2 6 11 10 1 3.07 Wheels Easy to maneuver 1 9 13 7 3.83 Comfort handle height 3 9 8 7 3 2.93 Comfort handle size 4 9 8 7 2 2.80 Handle Comfort handle position 5 7 9 9 0 2.73 Security of carried object 1 15 8 6 3.60 Security system Stability of load 1 2 8 13 6 3.70 Able to carry various sizes of object 1 3 9 9 8 3.67 Fork Suitable size of fork 2 6 12 6 4 3.13 Rating Score: 1- Unnecessary, 2- Less needed, 3-Needed, 4-Desirable, 5-Critically Desirable Redesign of a hand pallet truck by integrating Ergonomics analysis and quality function deployment 115 Figure 2. House of Quality HoQ for HPT improvement Development of the HoQ starts by capturing the workers’ requirements. Once all the workers’ requirements have been obtained, the relative importance of assigned by each worker is calculated by weighting each score by the number of worker who assigned it. The summed score for each row is then divided by the total number of workers involved in the survey. For example, to calculate the relative importance for the workers’ requirements “light”: 1 x 6 + 2 x 5 + 3 x 6 + 4 x 5 + 5 x 8 = 94. Hence, the relative importance = 94 30 number of workers = 3.13 Table 1. A relationship matrix is determined by mapping the strength of the relationship between workers’ inputs and the design features using the scores of 9, 3, 1 or 0 depending whether they were strong, medium, weak or none. The correlations among the design features were calculated to determine how well the design features are connected e.g., strongly positive strong, strong, negative or strongly negative. Competitive analysis was not conducted because the study focused only on what needs to be improved. This information is obtained through technical relative importance, i.e., the sum of the product of each workers’ relative importance and each strength relationship. As an example, to obtain the technical relative importance for technical specification “size of load supporter” Figure 2: 3.70 x 9 + 3.67 x 9 + 3.13 x 3 + 3.83 x 3 + 3.60 x 9 = 119.61 ≈ 120. High technical relative importance and percentage importance represent criteria that merit serious consideration. Hence, technical specifications such as “width of fork”, “size of load supporter”, “overall width”, and “wheel size wide” should be given highest priority because they obtained high technical relative importance and percentage importance. Therefore, a wider and adjustable fork, with load supporter, and appropriate design of wheels should be the main features of the redesigned HPT. A further requirement is that, minimizing structure weight is meaningful to ensure that the workers exert the least possible amount of force when moving the HPT. In the redesigned HPT Figure 3; Table 2, the fork is designed to be adjustable and longer to stabilize the HPT as well as to ease lifting and carrying the load. Installation of a pair of wheels one each at the left-rear and right-rear of the HPT is effective to reduce the required force and increase stability. A load supporter was also included in the new HPT design to minimize the tendency of the cage and load to slip off the HPT during load transfer. Figure 3. Redesigned HPT is equipped with load supporter and rear wheels left, wider and