Evaluation of electric powered wheelchairs and exposure to whole-body vibration

The detrimental results of whole-body vibration (WBV) and their effect on humans in the seated position have been documented. Although wheelchair users are subjected to WBV little research has been conducted to assess, or attempt to reduce them. Whole-body vibrations were measured in power and manual wheelchairs driving over a standard poured sidewalk surfaces and eight interlocking paver surfaces to determine if vibration transmitted to users differed between surfaces. A sensor for detecting ground forces and moments on power wheelchairs while driving was developed. Twenty-two individuals, twenty without a physical disability and two with a physical disability drove two power wheelchairs over an activities of daily living (ADL) course to evaluate effectiveness of suspension in power wheelchairs at attenuating vibration. The suspension elements of the two power wheelchairs were characterized and a spring-mass model was developed to determine the transfer function between the force input and the vibration measured at the seat. The results showed that there were differences in surfaces with some of the interlocking paver surfaces transmitting lower amounts of vibration to users. Ground reaction force and moment sensors (SMARTHUB and SMARTCASTER) were successfully developed, calibrated, and tested while driving over the ADL course. There were differences in the amount of vibration experienced by users for different suspension settings. The suspension model developed to predict the vibrations at the seat based on the input force, underestimated the accelerations at the seat. Alternative suspension models that would further reduce vibrations transmitted to users were also examined. Results showed that an additional suspension element below the seat could further reduce vibrations. Although suspension in power wheelchairs reduced the amount of whole-body vibration transmitted to users, they do not attenuate them enough to adequately reduce the possibility of secondary injuries, such as disc degeneration and low-back pain. Future research should focus on analysis of whole-body vibration experienced by power wheelchair users over longer periods of time and should be collected during everyday use. Additionally, alternative suspension designs that could reduce the amount of whole-body vibrations transmitted to users and maintain or increase power wheelchair performance should be developed and tested.