Design and evaluation of a laboratory-based wheelchair castor testing protocol using community data

Abstract

Wheelchair castors fail frequently causing physical, social and economic consequences for wheelchair users. These failures occur in spite of established wheelchair test methods and regulations, suggesting that the existing tests may not be sufficient to screen poorly designed castors. An expert stakeholder group, convened by the International Society of Wheelchair Professionals (ISWP), noted castor failures as a high priority and recommended that a new castor testing system should be developed. In a previous study, the effect of shock exposure on castor durability was studied. The current paper extends the previous work and focuses on the development of a castor testing protocol based on shock, corrosion and abrasion exposure data collected in the community. The testing protocol was applied to 8 different castor models tested under four conditions: shock, corrosion + shock, abrasion + shock and abrasion + corrosion + shock. For each model, a total of n = 8 samples were evaluated across the four conditions. Results demonstrate that corrosion and abrasion reduced castor durability between 13% to 100% depending on the model. Importantly, the inclusion of corrosion and abrasion resulted in changes in the failure modes for 75% of the tested models and two-thirds of the altered failure modes are associated with increased risk of injury for wheelchair users. These results suggest that corrosion and abrasion present in the community reduce castor durability, thus supporting their inclusion in the castor testing protocol and potentially other wheelchair standards.

Rolling resistance of casters increases significantly after two years of simulated use

“…Casters undergo corrosion exposure in a salt fog chamber followed by shock and abrasion testing on turntable equipment with multiple bumps of varying heights. 21 One of the caster testing studies showed that testing affected the rolling of axle bearings and turning of stem bearings of casters, similar to what was observed in the community. 21 These observations combined with expert feedback from the International Society of Wheelchair Professionals (ISWP) Standards Working Group provided the motivation for specifically investigating the effect of environmental factors on RR in this study.…”

“…Accelerations due to road shocks were translated to durability test equipment with appropriate slat height. 21 Number of road shocks observed during the testing were extrapolated to two years of shock exposure since majority of casters fail within 2 years. Testing caster models with a combination of shocks, abrasion and corrosion reproduced real world caster failures.…”

“…Testing caster models with a combination of shocks, abrasion and corrosion reproduced real world caster failures. 21 For example, corrosion affected the rolling of bearings. With abrasion, worn-out tire tread and tire cracking failures were observed.…”

“…Caster wear was observed in a less-resourced setting and used as a standard to determine the grit of sandpaper best replicating wear to represent one year of use. 21 The standard simulates around two years of shock and abrasion exposures in the community. Due to limited caster availability and the extended time required for shock and abrasion testing, only one sample of each model was tested.…”

“…Exposure was limited to a preset order of environmental exposure with corrosion, shock and abrasion that are a subset of environmental factors and do not fully reproduce the environment experienced in the community although both methods were developed through iterative steps to assure external validity. 21 , 22 Separate evaluation of abrasion and shock may identify the individual contribution of caster surface abrasion and bearing damage on increased RR.…”