A lateral dynamics of a wheelchair: identification and analysis of tire parameters

From theory to practice: Monitoring mechanical power output during wheelchair field and court sports using inertial measurement units

An important performance determinant in wheelchair sports is the power exchanged between the athlete-wheelchair combination and the environment, in short, mechanical power. Inertial measurement units (IMUs) might be used to estimate the exchanged mechanical power during wheelchair sports practice. However, to validly apply IMUs for mechanical power assessment in wheelchair sports, a well-founded and unambiguous theoretical framework is required that follows the dynamics of manual wheelchair propulsion. Therefore, this research has two goals. First, to present a theoretical framework that supports the use of IMUs to estimate power output via power balance equations. Second, to demonstrate the use of the IMU-based power estimates during wheelchair propulsion based on experimental data. Mechanical power during straight-line wheelchair propulsion on a treadmill was estimated using a wheel mounted IMU and was subsequently compared to optical motion capture data serving as a reference. IMU-based power was calculated from rolling resistance (estimated from drag tests) and change in kinetic energy (estimated using wheelchair velocity and wheelchair acceleration). The results reveal no significant difference between reference power values and the proposed IMU-based power (1.8% mean difference, N.S.). As the estimated rolling resistance shows a 0.9-1.7% underestimation, over time, IMU-based power will be slightly underestimated as well. To conclude, the theoretical framework and the resulting IMU model seems to provide acceptable estimates of mechanical power during straight-line wheelchair propulsion in wheelchair (sports) practice, and it is an important first step towards feasible power estimations in all wheelchair sports situations.

Contrary to basic kinematic modelling, during tight turns, wheelchairs can slide sideways by non-negligible magnitudes: Collision risks may be increased

Small spaces make collision-free turns difficult for wheelchair users. Contrary to basic kinematic wheelchair modelling and not considered previously by engineers; when wheelchairs turn in small spaces, could lateral drift (sideways slipping) increase the risk of collisions with surrounding structures such as walls and doorways? An improved kinematic understanding can inform building design and therapeutic involvement with wheelchair use. Wheelchair lateral drift is investigated. Two experiments with assisted wheelchair use are reported. Weights represented wheelchair occupants. First, lateral drift was measured by motion capture (VICON): turns (n = 225) made by the experimenter, for six radii of curvature (0-613 mm) and four total-masses (81-142 kg). Second, lateral drift was measured by ruler: turns (n = 105) made by experienced wheelchair assistants (n = 22), for three radii of curvature (0, 306, and 800 mm), and self-selected maximum comfortable weights. Lateral drift away from centre of curvature occurred for all radii of curvature greater than 0 mm, and a maximum median lateral drift of 27 mm/rad occurred for 142 kg total mass with 459 mm radius of curvature. Lateral drift increased with mass (r² = 0.68 for 358 mm radius of curvature). During tight turns, lateral drift magnitude and direction is such that it can increase risks of collisions with surrounding structures.

Modeling manual wheelchair propulsion cost during straight and curvilinear trajectories

Minimizing the effort to propel a manual wheelchair is important to all users in order to optimize the efficiency of maneuvering throughout the day. Assessing the propulsion cost of wheelchairs as a mechanical system is a key aspect of understanding the influences of wheelchair design and configuration. The objective of this study was to model the relationships between inertial and energy-loss parameters to the mechanical propulsion cost across different wheelchair configurations during straight and curvilinear trajectories. Inertial parameters of an occupied wheelchair and energy loss parameters of drive wheels and casters were entered into regression models representing three different maneuvers. A wheelchair-propelling robot was used to measure propulsion cost. General linear models showed strong relationships (R² > 0.84) between the system-level costs of propulsion and the selected predictor variables representing sources of energy loss and inertial influences. System energy loss parameters were significant predictors in all three maneuvers. Yaw inertia was also a significant predictor during zero-radius turns. The results indicate that simple energy loss measurements can predict system-level performance, and inertial influences are mostly overshadowed by the increased resistive losses caused by added mass, though weight distribution can mitigate some of this added cost.

Measurement of rolling resistance and scrub torque of manual wheelchair drive wheels and casters

The effort needed to maneuver a manual wheelchair is a function of the occupied wheelchair's inertia and energy loss. The primary source of energy loss is due to the resistance of the drive wheels and casters on the ground. Specifically, manual wheelchairs have two major sources of frictional energy loss: rolling resistance and scrub torque. The objective of this study was to develop and validate component-level test methods to evaluate the energy loss properties of drive wheels and casters on different surfaces and with different applied loads. Rolling resistance is measured using a weighted coast-down cart and scrub torque is calculated by measuring the force required to rotate a plate that is loaded onto the tire's surface. Each test method was iterated and then applied to a cohort of drive wheels and casters. Both test methods demonstrated acceptable repeatability and the ability to distinguish energy loss parameters between common wheelchair components. The results show that caster and drive wheel energy losses can vary significantly across surfaces and with increased load on the casters. However, the findings also illuminate complex relationships between rolling resistance and scrub torque performance that embody a tradeoff in performance as applied to mobility during everyday life.