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Application of PMSM Sensorless Control System on Lower Limb Rehabilitation Robot

Lower limb rehabilitation robot driven by a motor was a typical rehabilitation-assistive device for Parkinson’s Disease (PD) patients with abnormal muscle tone in their lower limbs. This paper investigated the sliding mode observer design of permanent magnet synchronous motor applied to a lower limb rehabilitation robot. Sensorless control technology was proposed to estimate the rotor position and velocity of PMSM with estimated back-EMF. Then two control algorithms have been developed for the robot: one that implements an inertia load (active mode) and one that implements a speed reference (negative mode). In the active mode, the robot operates as a regular exercise bike with electromagnetic brake torque that captures and records the pedal force signals. In the negative mode, the robot operates at a user-selected speed (cadence) that is essential to achieve the desired motor performance. A simulation was conducted with results validating the effectiveness of the proposed control scheme in terms of stable cycle speed and observer performance.