MODELING AND CONTROL OF QUADRUPED ROBOT WITH FLEXIBLE LEGS

Abstract

Compliances in legged robots leads to several potential benefits such as accommodation of contact/impact forces, actuator size reduction due to lesser power requirement, realization of energy efficient robots, accomplishment of dynamieally stable gaits such as hopping, bounding, galloping etc. With a motivation to contribute further towards the enhancement of the versatility of flexible legged quadruped robots, work pertaining to the development of strategies for posture control, environment interaction force control and fault accommodation through reconfiguration has been carried out. In this thesis, quadruped robot leg has been modeled as a flexible leg by introducing a compliant element in the lower link of the leg. For realizing locomotion of the quadruped robot, a gait pattern has been implemented first. Robot locomotion through the implemented gait has been realized through simulation and experiments for both the rigid and flexible legged quadruped robot models. The implemented gait pattern facilitates the representation of the locomotion dynamics of the quadruped robot in a sagittal plane. Bond graph has been used as a tool for modeling of locomotion dynamics of robot. Use of compliant elements in the robot's legs can lead to increased posture disturbance i.e. body angular displacements viz. rolling, pitching etc. during locomotion. Posture control assumes even more significance when robot has to navigate through restricted space. In this work, a posture control strategy based on moving appendage device has been conceptualized. The efficacy of the conceived moving appendage based posture controller for controlling the pitching motion in flexible legged quadruped robot has been successfully demonstrated through simulation and experimental results. A legged robot during the course of its locomotion experiences impact forces from the ground and also it can be subjected to unknown external impact forces from the environment, at body or elsewhere. Impedance control strategy has been developed for achieving trajectory tracking along with the environment interaction force control. The efficacy of the strategy has been demonstrated through two case studies. First case deals with trajectory tracking and interaction force control at the robot leg tip (toe) and second case at the body center of gravity (CG) of a flexible legged robot. One of the main focuses of legged robotics research has been to develop solutions for applications demanding unmanned missions in inaccessible or hazardous sites. To improve the probability of mission success in such critical applications, the robots must be capable enough to autonomously detect the component failures and take corrective/preventive maintenance action in real time. In the thesis, fault accommodation strategy through reconfiguration for joint actuator faults in quadruped robots has been developed. Hardware redundancy is a prerequisite for the implementation of the strategy. In the work, posture controller has served as the redundant device necessary for fault accommodation. The fault accommodation strategy has been developed and implemented through simulation for both the rigid and flexible legged quadruped robot models.