Backward tumbling control for power-assisted wheelchair based on phase plane analysis

We propose a novel control strategy of backward tumbling for power-assisted wheelchair operated by moving the push rims. The power-assistance units of wheelchair amplify the torque applied to the push rims. Excessive amplified torque sometimes causes dangerous backward tumbling. This paper analyzes backward tumbling as the interaction between the position of center-of-mass on man-wheelchair system and its angular velocity on the phase-plane. However, center-of-mass(COM) of man-wheelchair system cannot be directly measured. Therefore, the proposed control method prevents dangerous backward tumbling by decreasing assistance-ratio based on both COM observer to estimate the position of the COM considering some uncertainties; and phase plane analysis using the estimated. We show the effectiveness of the proposed control method in some experiments.