Mechanical characteristics and caregiver burden reduction of a non-electrical power-assist wheelchair using a spiral spring

This study investigates the effectiveness of a non-electrical mechanical power-assist mechanism in reducing caregiver pushing force during uphill wheelchair propulsion. Although manual wheelchairs are widely used due to their simple structure and low cost, caregivers are required to exert large forces when ascending slopes. While electronic power-assisted wheelchairs have been developed, their application is often limited by cost, weight, and maintenance requirements. To address these issues, a spiral spring–based mechanical power-assist mechanism that operates without electrical components is proposed. First, static equilibrium experiments were conducted on an inclined surface to characterize the assist force generated by the mechanism. The assist force was measured while varying the number of spring windings, and the relationship between winding number and assist force was quantitatively clarified. Next, dynamic propulsion experiments were performed on a slope using a manual wheelchair equipped with the assist mechanism. The pushing force applied by the caregiver was measured using three-axis force sensors mounted on the wheelchair grips under assisted and non-assisted conditions. The maximum pushing force and the root mean square (RMS) value were calculated to evaluate the mechanical load on the caregiver. The experimental results demonstrated that both the maximum pushing force and the RMS value were reduced by approximately 30–40% with the assist mechanism. These results indicate that the proposed non-electrical mechanical power-assist mechanism is effective in reducing caregiver load during uphill wheelchair propulsion.