Case Study Redesign of a hand pallet truck by integrating ergonomics analysis and quality function deployment.

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 Isa Halim et al. AJE Vol.9 2009 109-121 116 adjustable fork also were introduced right

6. Ergonomics simulation models

In manufacturing workplaces, production workers use the HPT for pushing and pulling activities. These activities should be analyzed to ensure that the HPT and carried materials do not lead to injury to the workers. Before pushing-pulling activities were analyzed, the existing HPT was modeled using CAD that is available in CATIA Software Figure 4. A manikin was used to represent the actual worker; it was created based on the 50 th percentile of anthropometry dimensions of 56 workers Table 3. Inferential statistical analysis such as comparison tests, correlations, and regression analysis are not included in the paper because the study focused primarily on determining the requirements of workers when using an HPT and incorporating those requirements in the new HPT design. However, the effectiveness of the redesigned HPT was confirmed by comparing a set of results obtained using the manikin when simulating the existing HPT and the redesigned HPT. Table 2. New design specifications for the redesigned HPT Parts Dimension Forks 1325 mm L,160 mm W, 240 mm spread Additional Wheel 101.6 dia. x 51.8 mm Load supporter 950 mm H x 560 mm L x 30 mm W Table 3. Anthropometry data of workers Body parts Mean SD 5 th Percentile 50 th Percentile 95 th Percentile Stature 170.68 2.9301 165.86 170.68 175.50 Axilla height 127.5 1.0787 125.73 127.50 129.27 Bimalleolar breadth 8.34 0.5486 7.44 8.34 9.24 Crotch height standing 78.48 1.6948 75.69 78.48 81.27 Hip breadth standing 32.46 2.0799 29.04 32.46 35.89 Waist height omphalion 100.61 5.2766 91.93 100.61 109.29 Waist breadth 30.23 2.1148 26.75 30.23 33.71 Chest height standing 123.98 1.9678 120.75 123.98 127.22 Chest breadth 32.43 1.9527 29.22 32.43 35.64 Sleeve outseam 55.63 3.9523 49.12 55.63 62.13 Radiale-stylion length 26.21 2.1802 22.63 26.21 29.80 Acromion-radiale length 28.96 2.0268 25.63 28.96 32.30

7. Analysis of pushing-pulling activities

For both designs, the HPT and its cage along with a manikin were modeled under actual working conditions to simulate pushing-pulling activities. This Redesign of a hand pallet truck by integrating Ergonomics analysis and quality function deployment 117 simulation is useful to determine the effects of the existing HPT design when workers perform pushing and pulling activities. In CAD, the existing HPT design was transferred into an ergonomics analysis environment, and the manikin was positioned where actual workers perform the pushing and pulling activities. An ergonomics analysis tool, Push and Pull Analysis Snook and Ciriello, 1991 was utilized to estimate the forces required to push and pull the existing HPT. Input data such as pushing-pulling frequency and travel distance of HPT were considered. Observation indicated that, pushing time is 18.75 s per push, that travel distance is 15 m, and that the distance from the hand to the floor is 1 m. For both HPTs, the analysis determined that maximal forces were different when pushing and pulling Table 4. When pushing the existing HPT, the maximum acceptable initial force is 311.094 N, and the maximum acceptable sustained force is 167.20 N; when pulling the HPT, the maximum acceptable initial force is 291.308 N, and the maximum acceptable sustained force is 159.042 N Figure 5. Figure 4. Model of Hand Pallet Truck HPT Table 4. Comparison results of Pushing-Pulling Analysis between existing HPT and redesigned HPT Existing HPT Redesigned HPT Forces Push Pull Push Pull Maximum acceptable initial force 311.094 N 291.308 N 319.874 N 273.212 N Maximum acceptable sustained force 167.204 N 159.042 N 167.064 N 153.302 N Isa Halim et al. AJE Vol.9 2009 109-121 118 Figure 5. A manikin simulates the pushing and pulling activities using existing HPT Figure 6 . A manikin demonstrates the pushing and pulling activities using redesigned HPT When pushing the redesigned HPT, the maximum acceptable initial force is 319.874 N, and the maximum acceptable sustained force is 167.064 N; when pulling, the maximum acceptable initial force is 273.212 N, and the maximum acceptable sustained force is 153.302 N Figure 6

8. Discussion

This section discusses the findings of study. Based on the questionnaire survey, workers identified “easy to maneuver”, “stability of load”, and “able to carry various sizes of object” as the most important requirements for an HPT. Priorities were developed in the HoQ to determine which technical specifications must be considered in HPT design. Based on the technical relative importance and percentage importance, a designer should focus on the following specifications to redesign the HPT: “width of fork”, “size of load supporter”, “overall width”, and “wheel size wide”. These technical specifications were incorporated in the new design of HPT to accommodate workers’ requirements such as “able to carry various sizes of object”, “easy to maneuver” and “stability of load”. The existing HPT has been redesigned by considering all workers’ requirements as identified using QFD method. Both existing HPT and redesigned HPT were analyzed to determine their maximum acceptable initial force and maximum acceptable sustained force during pushing and pulling activities. Through this analysis, the workers can determine the limit of forces that they should exert to avoid having a significant chance of being injured or developing occupational injuries. The results of analysis showed that the existing and redesigned HPT have different force limits for pushing and pulling activities Section 7. To avoid the risk of injury, workers should respect those limits when performing pushing and pulling activities using either existing design or redesigned HPT. The force limits were not changes significantly by the redesign Table 4, but this finding is essential to minimize the stresses on the workers when handling the HPT and reduce the risk of occupational injuries.