Discussion Redesign of a hand pallet truck by integrating ergonomics analysis and quality function deployment.
M.Y. Rosnaha et al. AJE Vol.9 2009 1-17
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The seat height adjustment of the current seat was not in working order. This may have caused the drivers not able to accommodate their legs adequately. If the seat is
too low, the knee flexion angle becomes large and the weight of the trunk is transferred to the seat pan surface over a small area at the ischial tuberosities [7].
The large knee and hip angles soon become uncomfortable, and the spine is flexed as the pelvis rotates backwards. When the seat is too high, the feet do not reach the
floor, so the pressure on the back of the thighs becomes uncomfortable. Individuals tend to slide forward to the front of the seat. This allows the feet to be supported,
but the seat back is not used properly to support the back. The seat height should be adjustable so that the feet can rest firmly on the floor with minimal pressure beneath
the thighs.
Although only 15 respondents reported pain in their arm and hand, an armrest is important in providing support for the arm and in reducing fatigue to the arm,
shoulder and neck. A seat should allow for relaxation of the muscles not required for the task as well as for intermittent relaxation of those that are [19].
More than half of the drivers complained that the leg room is inadequate. Adequate leg room is essential for the operator to adopt a satisfactory posture. The
leg room was found to be constrained by the steering wheel. Drivers were observed to have difficulty sitting in the seat smoothly because of inadequate leg room
between the seat and steering wheel. The lateral leg room must give clearance for the thighs and knees [17]. For vertical leg room, in some circumstances will be
determined by the knee height of a tall user 95th percentile. A more relevant measurement would be to consider the thigh clearance above the highest seat height
position using the 95th percentile male popliteal height and thigh thickness. The knee clearance is determined by buttock-knee length 95th percentile male from the
back of a fixed seat. Forward leg room is rather more difficult to calculate.
According to the literature, a RULA score of 3 or more indicates that further investigation is needed and that change may be required. With the recommended
seat, the final score was reduced to 2 Tables 6 and 8. This indicates that the posture is acceptable if it is not maintained or repeated for long periods of time.
Therefore, from the simulation results, the recommended seat design is acceptable because it can help reduce drivers’ fatigue while driving, especially in
improving the posture of the arm and wrist and for the trunk and legs. A more comfortable seat will increase the performance of the bus drivers. However, though
the overall score for the posture has improved, the score was 4 for the neck position of the 95th percentile in both the current and recommended seat design, and this is
cause for concern. Further investigation must be conducted out to identify further the cause of this problem.