A caster-up test method for manual wheelchairs under worst-case conditions

This study validated the caster-up durability test specified in ISO 7176-30, originally developed to ensure the structural safety of wheelchairs designed for changing occupant posture. As caregiver-assisted caster-up maneuvers are common in standard manual wheelchairs, particularly in aging societies, the study examined the applicability of this test to such wheelchairs. A worst-case scenario, involving a downward vertical force applied to the push handles, was defined. A custom test apparatus capable of simulating both the ISO-defined method and the worst-case method was developed. Mechanical stress on the wheelchair frame was quantified using strain gauges. Results showed that the worst-case method induced approximately 1.3 times greater strain at specific locations on the back support pipe compared to the existing method, indicating a potential underestimation of stress in the current ISO test. Durability tests conducted on four commercial wheelchair models found that two passed and two failed under the worst-case method. While the test method itself appears generally valid, the criterion for allowable readjustments requires reconsideration. These findings suggest that incorporating the worst-case method into durability testing could enhance user safety, supporting reconsideration of certain ISO 7176-30 requirements.