Wheelchair impact response to ISO test pendulum and ISO standard curb

If a product is to be certified by a national or international organization, it must undergo and pass a series of standardized tests. Standards are required to establish minimum performance and durability criteria for wheelchairs. Standards benefit consumers, manufacturers, and third party providers. Testers have expressed concern over the difficulty of properly conducting the current impact test for wheelchair casters and footrests. An alternative method for impact testing of the casters and footrests may incorporate use of the handrim impact test pendulum. This paper derives the center of percussion and provides an accurate description of the pendulum, and presents experimental results of impact accelerations measured using a curb and pendulum. Linear regression analysis was used to develop equations relating impact resultant acceleration to pendulum angle for each test case (i.e., caster impact, front footrest impact, side footrest impact). ANOVA was also used to examine differences in impact resultant accelerations among the wheelchairs. Pendulum impact angle was significantly correlated with impact resultant acceleration for caster impact (r=0.58, p=0.0001), for front footrest impact (r=0.58, p=0.0004), and for footrest side impact (r=0.42, p=0.0114), The curb impact test yielded a mean for all the wheelchairs´ maximum resultant impact accelerations of 7.4±2.09 g for caster contact, and 16.2±5.68 g for footrest contact. The mean equivalent pendulum release angle (i.e., the approximate pendulum angle equivalent to the curb impact accelerations) mere 24.4±1.95 degrees for castor contact, 33.8±4.80 degrees for frontal footrest contact, and 39.3±3.05 degrees for side footrest contact. The authors´ results indicate that the standard deviation in maximal resultant acceleration is about 25% between trials for each wheelchair using the curb impact method, whereas the standard deviation is about 10% using the pendulum method. This indicates that the pendulum method may be more repeatable. Differences in impact strength between wheelchairs can be detected by the pendulum impact tests, which is an indication that these tests may be useful in evaluating wheelchair quality