Michael J. Dvorznak

Braking electric-powered wheelchairs: Effect of braking method, seatbelt, and legrests

OBJECTIVE To examine the influence of three electric-powered wheelchair braking conditions and four wheelchair seating conditions on electric-powered wheelchair motion and Hybrid II test dummy motion. This study provides quantitative information related to assessing the safety of electric-powered wheelchair driving. DESIGN Rehabilitation engineering comparison and ANSI/ RESNA standards testing. Convenience sample of eight different electric-powered wheelchairs. Within-chair comparisons were conducted. INTERVENTION Electric-powered wheelchairs were compared under three braking scenarios (joystick release, joystick reverse, power-off) and four seating conditions (seatbelt and legrests, seatbelt and no legrests, no seatbelt but legrests, no seatbelt and no legrests). SETTING A rehabilitation engineering center. MAIN OUTCOME MEASURES The braking distance, braking time, and braking accelerations for electric-powered wheelchairs during three braking scenarios; trunk motion, head motion, and trunk angular acceleration during three braking scenarios and four seating conditions; and number of falls from the wheelchairs for three braking scenarios and four seating conditions. RESULTS Significant differences (p < .05) were found in braking distance, braking time, and braking acceleration when comparing the joystick release and joystick reverse scenarios with the power-off scenario. The mean braking distance was shortest with the power-off braking scenario (.89m), whereas it was longest when the joystick was released (1.66m). Significant differences (p < .05) in head displacement and trunk angular displacement were observed among braking conditions and between seating conditions. There were also significant differences (p = .0011) among braking conditions for maximum trunk angular acceleration. The Hybrid II test dummy fell from the wheelchairs with highest frequency when there were no legrests and no seatbelt used. CONCLUSION The results of this study indicate that use of a seatbelt when driving an electric-powered wheelchair reduces the risk of falling from a wheelchair. Furthermore, the use of legrests can reduce the risk of injury to the wheelchair driver. This study shows that the most abrupt braking occurs when deactivating the power switch.

Kinematic comparison of Hybrid II test dummy to wheelchair user

Hybrid test dummies provide a safe alternative to human subjects when investigating mechanisms of wheelchair tips and falls. The data that researchers acquire from these test dummies are more useful if the test dummy represents the population being studied. The goal of this study was to measure the validity of a 50th percentile Hybrid II test dummy (HTD) as an accurate representation of a wheelchair user. A test pilot with T8 paraplegia due to traumatic spinal cord injury served as a basis for validation. Simple modifications were made to the HTD to approximate the trunk stability characteristics of a person with a spinal cord injury. An HTD, a modified HTD, and a human test pilot were seated in an electric-powered wheelchair and several braking tests performed. The standard HTD underestimated the kinematics when compared to the test pilot. The modified HTD had less trunk stability than the standard HTD during all braking methods. The modified HTD and wheelchair test pilot had similar trunk stability characteristics during kill switch and joystick full-reverse braking conditions. The modified HTD is a satisfactory representation of a wheelchair user with a spinal cord injury; however, the modified test dummy underestimates the trunk dynamics during the less extreme joystick release braking. Work should continue on the development of a low-speed, low-impact test dummy that emulates the wheelchair user population.

Kinematic analysis for determination of bioequivalence of a modified Hybrid III test dummy and a wheelchair user.

We investigated whether a modified 50th-percentile Hybrid III test dummy (HTD) (First Technology Safety Systems, Plymouth, MI) would have motion similar to a wheelchair test pilot (TP) with T8 paraplegia. Test cases were seated in a Quickie P100 electrically powered wheelchair (Sunrise Medical, Inc., Phoenix, AZ) driven at three speeds (0.8, 1.4, and 2.0 m/s). Three braking conditions-joystick release, joystick full reverse, and emergency power-off-were used to stop the wheelchair. The subsequent upper-body motion was recorded for the creation of kinematic exposure profiles of the wheelchair riders. The maximum concentration (Cmax) and area under the trunk angular displacement, velocity, and acceleration curves (AUC0-Cmax) were calculated. Assessments of average, individual, and population bioequivalence were conducted after data were subjected to natural logarithmic transforms. Only the Cmax of the trunk angular acceleration of the HTD and TP was average bioequivalent (0.82-1.04). Both Cmax and AUC0-Cmax measures for all kinematic exposures between the TP and HTD were individual and population bioequivalent (95% upper-confidence bound < 0, linearized bioequivalence criteria). This indicates that the HTD is a suitable surrogate for a wheelchair user in low-speed, low-impact wheelchair studies.

Displacement between seating surface and test dummy during transitions with a variable configuration wheelchair

Stand-up and reclining wheelchairs are important for providing pressure relief, blood flow, and function. This study examined the shear displacement between a test dummy and wheelchair seat. The results showed that shear displacement was present, but lower than previous reports.