William Ammer

Performance assessment of a pushrim-activated power-assisted wheelchair control system

Wheelchairs are an important form of mobility for people with disabilities. For many years, there have only been three wheelchair varieties: electric-powered wheelchairs, scooters and manual wheelchairs. Recently, wheelchairs have been developed that use a combination of human power and electric power. The human power is delivered by the arms through the pushrims while the electric power is delivered by a battery through two electric motors. The shared control system for a pushrim-activated power-assisted wheelchair (PAPAW) must account for the human behavior and the interaction with the device. The PAPAW uses a form of gain scheduling based upon events recorded from the pushrim torque. The control system significantly altered (p<0.05) selected variables from pushrim torque curves for manual wheelchair propulsion and PAPAW operation as desired. The peak torque was reduced by over 50%, and the time on the rim was nearly doubled with the PAPAW. The PAPAW provided intuitive control and was capable of significantly reducing the strain on the upper extremities commonly associated with secondary disabling conditions among manual wheelchair users.

A prototype power assist wheelchair that provides for obstacle detection and avoidance for those with visual impairments

BackgroundAlmost 10% of all individuals who are legally blind also have a mobility impairment. The majority of these individuals are dependent on others for mobility. The Smart Power Assistance Module (SPAM) for manual wheelchairs is being developed to provide independent mobility for this population.MethodsA prototype of the SPAM has been developed using Yamaha JWII power assist hubs, sonar and infrared rangefinders, and a microprocessor. The prototype limits the user to moving straight forward, straight backward, or turning in place, and increases the resistance of the wheels based on the proximity of obstacles. The result is haptic feedback to the user regarding the environment surrounding the wheelchair.ResultsThe prototype has been evaluated with four blindfolded able-bodied users and one individual who is blind but not mobility impaired. For all individuals, the prototype reduced the number of collisions on a simple navigation task.ConclusionThe prototype demonstrates the feasibility of providing navigation assistance to manual wheelchair users, but several shortcomings of the system were identified to be addressed in a second generation prototype.

Evaluation of selected sidewalk pavement surfaces for vibration experienced by users of manual and powered wheelchairs.

Abstract Background: Obstades such as bumps, curb descents, and uneven driving surfaces cause vibrations that affect the wheelchair, and in turn, the wheelchair user. Chronic exposure can cause low-back pain, disk degeneration, and other harmful effects. Little research has been conducted to assess the vibrations experienced by wheelchair users. Objective: The purpose of this study was to conduct an evaluation of the vibration exposure du ring electric-powered wheelchair driving and mechanical energy requirements for manual wheelchair propulsion over selected sidewalk surfaces. The goal was to determine the criteria for a wheelchair-pedestrian access route that does not require excessive propulsive work or expose wheelchair users to potentially harmful vibrations. Methods: Ten unimpaired individuals participated in this study. Six sidewalk surfaces were tested. Measured variables included power of the acceleration per octave, mechanical work to propel over surfaces, peak acceleration, and frequency at which peak acceleration occurs. Results: For both the manual and electric-powered wheelchair, at 1 m/s, significant differences were found in peak accelerations between the seat and footrest (P < 0.0001) and between the sidewalk surfaces (P = 0.004 ). The greatest risk for injury caused by shock and vibration exposure occurs at frequ encies near the natural frequency of seated humans (4-15 Hz). The values for work required to propel over the surfaces tested were not stat istically significantly different. Besides appearance and construction, the only distinguishing characteristic was surface roughness caused by the joints. Conclusion: When treating the poured concrete sidewalk as the standard, surfaces 2, 3, 5, and 6 compared most favorably in t erms of vibration exposure, whereas surface 4 produced mixed results. Surfaces 2, 3, 5, and 6 yielded results that were similar to the poured concrete sidewalk and could be considered acceptable for wheelchair users. in conclusion, surfaces other than the t raditional poured concrete can be used for pedestrian access routes without adding vibration exposure or reducing propulsion efficiency.

Seat & footrest vibrations in manual wheelchairs

Newer manual wheelchairs have incorporated suspension systems in the hopes of decreasing harmful shock and vibration transmission. This study examined differences in the shock and vibration transmitted to a manual wheelchair occupant with and without suspension caster forks and with and without rear suspension systems. Significant differences were found in the peak accelerations at the seat (p = 0.0004) and footrest (p = 0.0007) between the wheelchairs when using the OEM caster forks versus the suspension casters. The wheelchairs with suspension had significantly different frequencies at which the peak accelerations occurred for both the seat (p = 0.01) and footrest (p = 0.0001). The wheelchairs that had the suspension caster forks had lower total power per octave than the wheelchairs with the OEM caster forks. For the footrest vibrations, significant differences were found between the types of caster forks for all octaves except those associated with frequencies above 78.75 Hz. There were significant differences for wheelchairs with and without rear suspension for total power per octave of seat vibrations in the octaves between 7.81 Hz and 9.84 Hz (p = 0.01), and 12.40 Hz. and 15.63 Hz (p = 0.008). Suspension caster forks reduce the shock and vibration exposure to the user of a manual wheelchair. Rear suspension systems reduce some of the factors related to shock and vibration exposure, but they are not clearly superior to traditional designs.