🤖 AI Summary
This work addresses the challenge of precise position control in long, flexible, low-impedance hydraulic actuation systems operating in harsh environments, where conventional robots suffer from sensor fragility and the impracticality of embedding sensors. The authors propose an innovative approach that simultaneously transmits actuation power and state information through a single water-filled flexible tube. By modeling volume loss due to pressure-induced tube deformation and the subtle effects of entrained air, they achieve high-accuracy, sensorless position estimation and actuation over tube lengths up to 50 meters. Key contributions include the first demonstration of integrated drive and position feedback using only a single hydraulic line without end-effector sensors, and a practical online parameter identification method to compensate for inter-tube variability and air content fluctuations. Experiments validate stable position control of hydraulic cylinders under varying loads, establishing a robust framework for remote robotic operation in extreme conditions.
📝 Abstract
Robot sensors and electronic equipment are prone to failure in harsh environments. With water hydraulic drive, thin and long tubes enable remote operation without actuator-side sensors. Furthermore, the elasticity of the tubes reduces the impedance of the joints (actuators), benefiting robot tasks involving unexpected contact with the environment or vibrations. However, owing to the low impedance and limited camera visibility, accurately positioning the joint (or end effector) to the target location under varying load conditions is challenging. This study proposes a novel method that employs water-filled flexible tubes to enable the transmission of driving power and actuator-side information to and from the actuator, respectively, without actuator-side sensors. By modeling volumetric loss during transmission based on pressure fluctuations and incorporating minor air entrapment, simultaneous power transmission and position estimation is achieved through a tube up to 50 m. Thus, it becomes possible to use a feedback control framework that was previously difficult to implement in sensorless systems. Experimental validation confirms stable position control of a sensorless water hydraulic cylinder under varying loads. Furthermore, a field parameter-identification method accounts for tube and air entrainment variability without requiring actuator-side sensors. These contributions promote reliable remote control of robots in harsh environments.