Control of a hydraulically-actuated quadruped robot leg

Abstract

This paper is focussed on the modelling and control of a hydraulically-driven biologically-inspired robotic leg. The study is part of a larger project aiming at the development of an autonomous quadruped robot (hyQ) for outdoor operations. The leg has two hydraulically-actuated degrees of freedom (DOF), the hip and knee joints. The actuation system is composed of proportional valves and asymmetric cylinders. After a brief description of the prototype leg, the paper shows the development of a comprehensive model of the leg where critical parameters have been experimentally identified. Subsequently the leg control design is presented. The core of this work is the experimental assessment of the pros and cons of single-input single-output (SISO) vs. multiple-input multiple-output (MIMO) and linear vs. nonlinear control algorithms in this application (the leg is a coupled multivariable system driven by nonlinear actuators). The control schemes developed are a conventional PID (linear SISO), a Linear Quadratic Regulator (LQR) controller (linear MIMO) and a Feedback Linearisation (FL) controller (nonlinear MIMO).LQR performs well at low frequency but its behaviour worsens at higher frequencies. FL produces the fastest response in simulation, but when implemented is sensitive to parameters uncertainty and needs to be properly modified to achieve equally good performance also in the practical implementation.

THREE DEGREE OF FREEDOM LEG DESIGN FOR QUADRUPED ROBOTS AND FRACTIONAL ORDER PID (PIλDμ) BASED CONTROL

“…In this section, the fractional order Proportional-Integral-Derivative (FOPID) (Tepljakov,2019) controller and the classical PID are designed to comparative consider for the linear model of the robot leg are presented. PID controller is commonly preferred in experimental and simulation studies about singleleg of quadruped robots (Focchi et al, 2010). PIλDµ controller; in addition to the classical PID parameters, it is an advanced PID controller variant which includes the fractional derivative order (λ) and the fractional integral order (µ) parameters.…”

Stiffness and damping scheduling for legged locomotion

“…In this section we explore actively changing leg stiffness during the swing/stance phases of each leg and changing environments using LLR. Stiffnessbased controllers have been developed in robotics contexts [19], [20], some using learning approaches [21], [22], [23].…”

A Hydraulic-and-electric Robot Arm for Mobile Manufacturing

“…Compared to electric actuation, hydraulic actuation has higher power density together with high force and torque to make the robotic system smaller and faster [1]. In recent years, hydraulic actuating joints (HAJ) is wildly used in hydraulic robot system [2], variable geometry truss [3], legged robot [4], robot hand [5], etc. Most of robotic hydraulic actuators are longitudinal hydraulic cylinder which may limit the output angle of robotic rotation joint.…”