Variable stiffness locomotion with guaranteed stability for quadruped robots traversing uneven terrains

Abstract

Quadruped robots are widely applied in real-world environments where they have to face the challenges of walking on unknown rough terrains. This paper presents a control pipeline that generates robust and compliant legged locomotion for torque-controlled quadruped robots on uneven terrains. The Cartesian motion planner is designed to be reactive to unexpected early and late contacts using the estimated contact forces. Moreover, we present a novel scheme of optimal stiffness modulation that aims to coordinate desired compliance and tracking performance. It optimizes joint stiffness and contact forces coordinately in a quadratic programming (QP) formulation, where the constraints of non-slipping contacts and torque limits are imposed as well. In addition, the issue of stability under variable stiffness control is solved by imposing a tank-based passivity constraint explicitly. We finally validate the proposed control pipeline on our quadruped robot CENTAURO in experiments on uneven terrains and, through comparative tests, demonstrate the improvements of the variable stiffness locomotion.

Multi-constraint spatial coupling for the body joint quadruped robot and the CPG control method on rough terrain

“…By assuming a uniform distribution of the mass of each legged component, it is possible to determine the corresponding coordinate positions of the COG at the coxa, femur, tibia, and foot-end via the robot's single-leg joint coordinate system and their relevant root joint coordinate systems. According to equation (2), get the coordinate positions of each component, where CD p ii , CE p ii , CF p ii , and CL p ii is the coordinate position of the coxa, femur, tibia, and foot-end, respectively, the formulas as follows:…”

“…Quadrupedal bionic robots embody the advantages of flexibility, mobility, environmental adaptability, efficient energy utilization, and oversized loads in quadrupedal mammalian locomotion [1]. However, when the robot moves in a complex environment, it needs to face various harsh road conditions, such as uneven ground, muddy and slippery, full of gravel, continuous steep slopes, and soft soil, which extensively test and challenge the integrated motion performance of the quadrupedal robot [2]. In this process, the robot has to both climb over different obstacles and constantly adjust its position to adapt to the drastic changes of the terrain, and the dynamic change of the robot can cause its center of gravity (COG) to project outside the area of foothold, which can lead to unstable or even overturn [3].…”

The Limb Kinetics of Goat Walking on the Slope with Different Angles

“…The legged robot has received much attention in the past few years because of its excellent performance in complex environments [ 1 , 2 , 3 ]. Improvement of stability and gait control of the legged robot is an important research issue; quadruped robots have better mechanical load capability and stability than biped robots.…”