SHAPE: Simultaneous Water Hydraulic Actuation and Position Estimation of a Sensorless Remote Actuator through a Thin and Long Flexible Tube
Robotics
Summary
The authors developed a way to control robot joints remotely using water-filled flexible tubes instead of sensors on the robot itself, which often fail in tough environments. They figured out how to send power and get position information back through the tubes by analyzing pressure changes and small amounts of trapped air. This method lets them accurately control the robot's position even when conditions change, without needing sensors on the robot side. Their experiments showed the system works reliably over long distances and varying loads, improving remote robot control in difficult settings.
Authors
Yuki Nakamura, Shuto Yoshimura, Tomoyuki Noda, Yoshihiro Nakata
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.