This paper presents the detailed steps for design and development of a compliant legged fault tolerant quadruped robot where each leg has two links and two motorized revolute joints for locomotion. The body and upper links of legs are rigid whereas the lower link of each leg is compliant. Amble gait is demonstrated on the developed robot. Safety and reliability are the most critical issues for the quadruped robot. During the failure of any joint, performance of quadruped robot is affected. In this paper, locked joint failure is also discussed. Strategies for fault tolerant control of the quadruped are developed and experimentally validated. The developed robot can be used for various hardware-in-the-loop controller prototyping such as reconfiguration, fault tolerant control, and posture control, etc. pertaining to quadruped robots.
Quadruped robots are designed to work in remote or hazardous environments which are unreachable or harmful for humans. In these situations, reliability and adaptability are the most critical issues for the quadruped robot. During the failure of any actuator, the performance of quadruped robot is severely affected. The failure can lead to joint locking or free joint. In the case of free joint, leg joint loses actuator torque and also the capability to support the robot body on the ground. Leg joint also loses resistance to external load and acts as a free rotating hanging link. This article presents strategies for controlling a compliant legged quadruped robot in the presence of free swinging failure. The strategy is motivated by the natural crawling by infants and adapted crawling by persons with specific disabilities. Bond graph has been used for dynamic modeling of the system. The control strategy has been tested both through simulations and experiments conducted on a prototype quadruped robot.
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