Fault-tolerant gait design for quadruped robots with two locked legs using the GF set theory

Fault-tolerant gaits can give legged robots the ability to walk under fault conditions, and hence prolong the service life. However, for quadruped robots with two locked legs, fault-tolerant gaits can be rarely found. This paper proposes a novel fault-tolerant gait for quadruped robots with two locked legs using the GF set theory. First, a quadruped robot and eight stages of its fault-free static gait are introduced. Then, the GF set theory is applied to analyze the robot's mobility stage by stage, which takes the mobility loss caused by the two locked legs into account. By taking full advantage of the mobility, the fault-tolerant gait pattern and trajectory planning method are developed. Further, the omnidirectional locomotion capability, adaptability to rough terrains, energy consumption, speed and influences of locking angles of the fault-tolerant gait are addressed to show its performances. Finally, the fault-tolerant gait and its performances are validated by three simulations. The results show that the robot with the fault-tolerant gait can walk omnidirectionally and adapt to rough terrains while keeping the static stability margin positive.