Stabilization of legged robots with compliant joints

This research focuses on stabilizing lightweight biped robots with flexible joints using bio-inspired reflex actions along with feedback control. With the objective of expanding the controllability of a dynamical system, we add independent reflex arcs that are triggered directly by the disturbance signals to feedback controllers. A 10 degree of freedom biped robot was prototyped using 3D printing techniques and control methodologies were developed to stabilize it. A hybrid analog-digital controller has been designed to improve the stability of the biped robot against sudden impact disturbances. In order to design the hybrid controller, a high-resolution dynamic model of the robot was developed in a physics-based simulation environment. A series of disturbance experiments were performed to characterize the robot attitude when the robot experiences the disturbances. A passive reflex action provided by a mass-spring pendulum was evaluated in the simulation environment.;A computationally-effective method to design open-loop gait patterns by specifying eight key-points during the gait has been developed and evaluated. Since the joint flexibility is a significant factor affecting the gait stability, joint flexibility was incorporated into the model with torsional springs at each joint. The stiffness and damping coefficients of the servo motor were characterized to model the joint as a torsional spring-damper component. The simulation method for the flexible joint in the physics-based simulator was discussed and demonstrated. The expected deflections of joints were estimated from equations of motion and added to the joint angles. The modified angle profiles were validated by comparing the robot's attitude data from sensors mounted on the robot to its model predictions. Subsequently, a Center-of-Mass Jacobian based motion planning was also implemented for a feedback controller design to stabilize the locomotion by tracking the Zero-Moment-Point and Center-of-Mass trajectories.;This dissertation focuses on the design and implementation of a hybrid controller into a biped robot, controllability improvements by the added reflex actions and gait trajectory planning along with feedback control for the biped robot with joint compliances. The outcomes lead to effective locomotion design methods for biped robots with compliant joints. The broader impacts of this research are on enhancing the safety, simulation of compliant joint in 3D robotics simulators and enabling the insertion of low-cost additive manufacturing methods into the production of robust robotic systems.