Remote Torque Control of a Water-Driven Robot with Air-Hydraulic Servo Booster

Abstract

Water-hydraulic system is environmentally friendly technology, and its application to robot manipulators is eagerly awaited. However, they are still expensive compared to oil-hydraulic systems because of the technical problems related to fast sliding motions between the solid materials contacting each other with the very small gap in the pumps or valves. To avoid these difficulties, we proposed an alternative solution, which lead to a pump-less hydraulic system called AHSB. The system utilizes an air-hydraulic booster to control the low-to-middle range water pressure by pneumatic servo valves. In this paper, we analyze the water-hydraulic dynamics and develop a robust pressure-based joint torque controller using Sliding Mode Control. The controller is implemented on a single-axis robot arm for the remote torque control application, which is crucially important for future tele-operated field robots. The experiments under quasi-static condition demonstrates the first successful torque control results on the water-driven robot with 10 kg payload, which is connected with 20 meter-long hydraulic hoses.