Dynamic trot-walking with the hydraulic quadruped robot — HyQ: Analytical trajectory generation and active compliance control

Abstract

This paper presents a trajectory generator and an active compliance control scheme, unified in a framework to synthesize dynamic, feasible and compliant trot-walking locomotion cycles for a stiff-by-nature hydraulically actuated quadruped robot. At the outset, a CoP-based trajectory generator that is constructed using an analytical solution is implemented to obtain feasible and dynamically balanced motion references in a systematic manner. Initial conditions are uniquely determined for symmetrical motion patterns, enforcing that trajectories are seamlessly connected both in position, velocity and acceleration levels, regardless of the given support phase. The active compliance controller, used simultaneously, is responsible for sufficient joint position/force regulation. An admittance block is utilized to compute joint displacements that correspond to joint force errors. In addition to position feedback, these joint displacements are inserted to the position control loop as a secondary feedback term. In doing so, active compliance control is achieved, while the position/force trade-off is modulated via the virtual admittance parameters. Various trot-walking experiments are conducted with the proposed framework using HyQ, a ∼ 75kg hydraulically actuated quadruped robot. We present results of repetitive, continuous, and dynamically equilibrated trot-walking locomotion cycles, both on level surface and uneven surface walking experiments.

A Literature Review on Walking Strategies of Legged Robots

“…Bu çalışma, bacaklarda sadece bir eyleyicinin kullanıldığı oldukça basit bir tasarıma sahip dört bacaklı bir robotun yürüme, koşma, merdiven tırmanma gibi yüksek hareket kabiliyeti sergileyebileceğini göstermesi açısından ayaklı robotlar literatüründe önemli bir yere sahiptir. [153][154][155][156][157][158].…”

Online Planning for Autonomous Running Jumps Over Obstacles in High-Speed Quadrupeds

“…The constraints (23) and (24) are posed to avoid a foot tripping over the obstacle, (25) and (26) ensure that the robot's foot has achieved the desired lateral clearance at the completion of the jump. The constraints (27) and (29) are used to guarantee that the robot's shoulder position from the ground at the end of the stance phase is within the range of the leg's workspace, and the constants z and z are chosen from the leg's linkage design.…”

“…StarIETH [9] has displayed a wide array of gaits up to 0.7 m/s with the incorporation of series elastic actuation in its legs. The hydraulically actuated HyQ [21] has shown the capacity for high-power movements and is capable of terrain robust trot walking at 0.35 m/s [23]. The MIT Cheetah 1 [22] and Cheetah 2 [16] robots have shown the capabilities of electric DC motors to enable high-speed locomotion [12] up to 6 m/s.…”

Towards automatic discovery of agile gaits for quadrupedal robots

“…A third approach based on fuzzy control was capable of learning the leg touchdown angles and leg thrusts required to track the desired running height and velocity of a quadruped in only one stride [17]. A recently introduced robust walking trot controller which combines an analytic trajectory generator with active compliance control was implemented on the more complex and powerful quadruped HyQ [18].…”