Legged locomotion over irregular terrains: state of the art of human and robot performance

Abstract

Legged robotic technologies have moved out of the lab to operate in real environments, characterized by a wide variety of unpredictable irregularities and disturbances, all this in close proximity with humans. Demonstrating the ability of current robots to move robustly and reliably in these conditions is becoming essential to prove their safe operation. Here, we report an in-depth literature review aimed at verifying the existence of common or agreed protocols and metrics to test the performance of legged system in realistic environments. We primarily focused on three types of robotic technologies, i.e., hexapods, quadrupeds and bipeds. We also included a comprehensive overview on human locomotion studies, being it often considered the gold standard for performance, and one of the most important sources of bioinspiration for legged machines. We discovered that very few papers have rigorously studied robotic locomotion under irregular terrain conditions. On the contrary, numerous studies have addressed this problem on human gait, being nonetheless of highly heterogeneous nature in terms of experimental design. This lack of agreed methodology makes it challenging for the community to properly assess, compare and predict the performance of existing legged systems in real environments. On the one hand, this work provides a library of methods, metrics and experimental protocols, with a critical analysis on the limitations of the current approaches and future promising directions. On the other hand, it demonstrates the existence of an important lack of benchmarks in the literature, and the possibility of bridging different disciplines, e.g., the human and robotic, towards the definition of standardized procedures that will boost not only the scientific development of better bioinspired solutions, but also their market uptake.

Evolution, Design, and Future Trajectories on Bipedal Wheel-legged Robot: A Comprehensive Review

“…In contemporary research, dynamic and optimal control algorithms are key [90], [91], ensuring stability during various conditions such as mode transitions, balance adjustments, and shifts in the robot's center of mass [12], [85]. These factors are central to a robot's adaptability, resilience, and energy conservation [43], [92], [93]. Recent designs like the manipulator-armed attached on wheellegged robot [94], [95] and the agile hydraulic robot [96], [97], exemplify these state-of-the-art control and stability features.…”

“…Central to this progression is integrating predictive control, trajectory planning, and reinforcement learning, all contributing synergistically to optimize robotic performance [90], [91], [103], [104]. Furthermore, by factoring in the intricacies of diverse terrains and varied operational conditions, the practicality and versatility of these robots in real-world settings become increasingly evident [78], [80], [92], [93], [99], [136], [138], [183]- [185].…”

Design of Bionic Foot Inspired by the Anti-Slip Cushioning Mechanism of Yak Feet

“…Most importantly, the anti-slip performance depends largely on the structure of the foot, which plays a decisive role in the stable walking of the robot [9][10][11][12][13]. The development of bionics provides new research ideas for the foot design of robots and improving the locomotion of quadruped robots [14,15].…”

Stability and Safety Learning Methods for Legged Robots

“…The problem becomes even more difficult for multi-body mechanical structures, such as legged machines, where assimilation to linear dynamics is often at the expense of the reliability of the defined controller. The search for stability guarantees for this class of complex mechanical systems becomes an urgent challenge as legged robots are becoming increasingly popular [3,4]. They are expected to complement traditional wheeled machines due to their dexterity and ability to explore highly unstructured terrains with minimal invasiveness.…”