Modeling, analysis and optimization of a scissors linkage seat suspension

Under-the-seat scissors linkage suspensions have been in use for the off-road and construction vehicle market for many years. The off-road environment requires that the suspension be rugged while providing comfort to a seat occupant over a rough terrain. Since different operators can use the equipment at different times, the seat suspension must be adjustable for both the height and weight of the seat occupant. This study utilizes static and dynamic mathematical modeling to develop an optimal geometric and damping configuration for a recently developed scissors seat suspension. The proposed design allows for the suspension to be adjusted in order to change the seat height without substantially affecting its load-deflection characteristics. Since the height adjust travel is included within the scissors linkage stroke, the best configuration of internal components to provide this feature is not intuitive. Therefore, a suspension model was optimized until a satisfactory configuration with essentially constant load-deflection characteristics across the range of height and weight adjustments was achieved. The dynamic response optimization using a 4-DOF human surrogate-suspension model shows that for the given vibrational input, a non-linear damping function that increases slightly as it moves away from the static equilibrium position transmitted the least acceleration to the operator.