Design of a lightweight hydraulic actuating bipedal robot with an onboard power system

Abstract

This paper presents the development of a hydraulic actuating bipedal robot. We describe the overall robot development process, from the development of the hydraulic key components such as hydraulic actuators and valves to robot platforms. We set the goal of the developed robot to be a fully autonomous robot so that it can walk independently without supplying external energy. In order to develop a hydraulic actuating robot, systematic integration of several hydraulic components is essential. Therefore, in this paper, all hydraulic components are self-developed to have the performance required for the robot. Through this, a robot could be configured compact and light. The direct-drive valve with a low leakage flow rate is developed and applied to increase the robot's energy efficiency. This paper also describes how to control the developed hydraulic actuator and valve. Hydraulic actuators are challenging to model due to model uncertainty and nonlinearity. Therefore, control of hydraulic actuators has been considered a challenging task. To deal with the control complexity, we propose learning-based control, a powerful method to capture a complex model. We present the process of acquiring the suitable data points for the training and the method to train the inverse model from the data obtained. In addition, the controller is applied to the hydraulic actuator to verify the force control performance. Finally, the development of the hydraulic actuating bipedal robot platform 'LIGHT' is presented. LIGHT consists of a body and legs without arms and has a total of 13 degrees of freedom. LIGHT is characterized by its compact, lightweight, but high rigidity with height 150cm and weight 60kg. In order to minimize hydraulic hoses that are essential for hydraulic robots but harm the aesthetics, we design the robot with an internal pipe structure in which the hydraulic oil can be supplied to each joint through the internal pipe. We experimentally verified that the robot could walk independently without supplying external power by a mounting battery and an onboard hydraulic power unit.