Assessment of the ISO impact damping test for wheelchair cushions

The International Organization for Standardization (ISO) has published a test method that characterizes the ability of a wheelchair cushion to reduce impact loading. The objectives of this project were to improve the methodology described in the ISO standard, determine the repeatability of the accelerations resulting from the ISO test method and assess the test method's ability to distinguish the impact damping performance of different cushion designs. A small cohort of cushion was identified to reflect different material constructions and included flat elastic foam, flat viscoelastic foam, Roho High Profile, and Cloud. The ISO test method was deployed after changes to the equipment were made to better insure repeatable placement of the indenter onto the cushion. Three operators tested different cushions over two days. Acceleration of the indenter was collected and used to calculate acceleration magnitudes during indenter impact and rebound. The results of a Gage Repeatability & Reproducibility analysis indicated high reliability over operators and test days. Analysis of initial impact acceleration indicated that the test could distinguish between the different cushion designs. Ratios of successive impacts and rebounds were calculated and analyzed. Both showed high repeatability and could distinguish all cushion pairs except one. Assessment of this and previously collected data led to the suggestion that the ratio of impact accelerations should be reported rather than the rebound accelerations. In summary, with some slight but significant changes to the test rig, the ISO Impact Damping test method is a reliable means to characterize acceleration responses of wheelchair cushions.