An experimental approach to work seat design: Development of a chair for industrial sewing.

For a work seat to be effective, its design characteristics must consider both body geometry and the specific postures required to perform a job. This investigation was performed to develop a general research methodology for designing task-specific, ergonomically-sound work seats. This methodology was used to develop specific design recommendations for chairs used in industrial sewing operations. The results of this investigation are presented as a series of three papers. The first paper investigated the desired work posture for industrial sewing operations. A fractional factorial experiment was used to evaluate seven set adjustment variables. Overall discomfort, localized discomfort, height reduction, and electromyography (EMG) were used to assess the significance of these variables. The preferred posture was a low sit-st and posture which maintained the thighs at an angle 15 degrees below the horizontal. The second paper investigated a prototype sewing chair with seat-pan and backrest design features to accommodate the low sit-st and posture. The seat-pan consisted of a pelvic support for the ischial tuberosities, and a thigh support to maintain the thighs at a 15-degree downward angle. The backrest consisted of a lumbar support and a thoracic support for the upper back during backward leaning. This chair was compared to a traditional sewing chair in three field experiments--user comfort, backrest usage, and general preference. These experiments found that the prototype chair was preferred to the traditional chair. The third paper developed an anthropometric procedure for determining design specifications for the size, contour and location of the seat-pan and backrest for the low sit-st and posture, and an evaluation procedure for selecting backrest design alternatives. A three-dimensional anthropometric device was used to measure the contour of the thigh and spine. EMG and subjective comfort were used to compare backrest alternatives. The study found that that ischial tuberosities were a good seat-design reference point for describing body geometry and quantifying body movements. EMG and body discomfort were related to backrest shape, but not backrest distance. Both measures suggested that the back should be supported by a thoracic support slanted 15 degrees behind the vertical.PhDIndustrial engineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/162152/1/8907177.pd