We propose a state estimation-based fail-safe control framework for water-hydraulic robots driven by Air-Hydraulic Servo Booster (AHSB) to ensure its safe operation. A Kalman Filter estimates the most likely internal states such as water pressures and joint angles, by taking advantage of redundancy of the sensors installed to AHSB. Then, based on the covariance, the system detects and isolates failures such as sensor disconnection, friction fluctuation, and sudden external force. Experimental results demonstrate the effectiveness of the method, wherein, a robotic arm can continue the position tracking task even if a pressure sensor is completely broken.
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