Towards dynamic alternating tripod trotting of a pony-sized hexapod robot for disaster rescuing based on multi-modal impedance control

Abstract

SUMMARYHexapod robots are well suited for disaster rescuing tasks due to their stability and load capability. However, most current hexapod robots still rely on static gaits that largely limit their locomotion speed. This paper introduces a hierarchical control strategy to realize a dynamic alternating tripod trotting gait for a hexapod robot based on multi-modal impedance control. At the low level, a position-based impedance controller is developed to realize an adjustable compliant behavior for each leg. At the high level, a new gait controller is developed to generate a stable alternating tripod trotting gait, in which a gait state machine, a leg compliance modulation strategy, and a close-looped body attitude stabilizer are imposed. As a result, the alternating tripod trotting of the hexapod robot can be synchronized as the running of a bipedal robot with stable body attitude. Moreover, this control strategy was verified by experiments on a newly designed pony-sized disaster rescuing robot, HexbotIV, which successfully achieved a dynamic trotting gait with ability to resist the disturbances of mildly uneven terrains. Our control strategy as well as the experimental study can be a valuable reference for other hexapod robots and thus paves a way to the practical deployment of disaster rescuing robots.

Mechanism, Actuation, Perception, and Control of Highly Dynamic Multilegged Robots: A Review

“…Pictured in Figure 8, both the Octopus [34] and Hexabot-IV [6] hexapod robots with high payloads were developed by Shanghai Jiao Tong University for daily maintenance Figure 6 The Lauron-V hexapod robot [30] and emergency relief of nuclear power plants. Compared to quadruped walking robots, hexapod robots can accept higher payloads and achieve greater stability, which facilitates operation and transportation in unstructured environments.…”

“…The maximum climbing slope is approximately 25°, and it can traverse obstacles with a height of up to 400 mm. The Hexabot-IV [6] is a hexapod walking robot intended to carry rescue equipment such as firefighting hose nozzles, electric drills, or manipulators. Its outline dimensions are about 1.1 m × 0.72 m × 1 m (length × width × height) in the standard standing position.…”

“…It is now widely acknowledged that robotic technologies at that time were far from sufficient for carrying out complex rescue operations [5]. Recently, supported by the National Basic Research Program of China (973 Program), a series of hexapod robots with parallel legs were developed by Shanghai Jiao Tong University (SJTU) for firefighting, transportation, and detection in disaster environments, such as nuclear accidents [6][7][8]. The payloads of these hexapod robots can reach up to 500 kg.…”

“…In fact, robustness and safety are the key considerations for legged robots in outdoor environments, easily outweighing agility and autonomy. In practice, it is very difficult for current legged robots to be used in real applications in outdoor environments [11]; actually, only a few legged robots take into account the requirements of a specific application, such as nuclear disaster relief (e.g., SJTU hexapod robots [6][7][8]) or inspection of gas and oil sites (e.g., ANYmal [3] and its previous version). In addition, the performances of legged robots are related to many factors, including their mechanisms and actuation, perception, and control methods.…”

Whole-Body Motion Planning for a Six-Legged Robot Walking on Rugged Terrain

“…The black balls in the figure correspond to rotational joints of the robot. In this simulation, the robot is commanded to walk across the rugged terrain patch along a given walking path using the alternating-tripod gait [7,[22][23][24].…”