Adaptive control of intelligent walker guided human-walker systems

Intelligent walkers (i-walkers) need to have precise torque generation to sustain safe human-walker motion. Utilizing a recently developed control oriented system model that involves the physical-human walker interaction (pHWI) based on the user gait dynamics and characteristics, this paper studies an adaptive control scheme design for high precision trajectory tracking of the i-walker robust to user gait dynamics, body pose and weight. The proposed control scheme involves a backstepping based kinematic controller to generate reference i-walker velocities that match the pre-defined i-walker trajectories. These desired velocities are tracked applying the torques generated by an adaptive sliding mode control (SMC) scheme that is robust to unknown torque disturbance arising from friction forces, center of gravity displacement and load changes due to pHWI. The proposed SMC scheme design contains a feedback linearization unit based on the computed torque control law, and is fed by the wheel velocity estimates generated by a system-dynamics based sliding mode observer. The designed adaptive control scheme is simulated for the users with symmetric and asymmetric gait patterns.