Dynamic analysis of auger driller during luffing motion by bond graph

To investigate the inherent complex dynamic characteristics of luffing mechanism of auger driller, the rigid body motion of structures and the dynamic behavior of the drive system should be studied in an integrated model. The working principle and structural characteristics of the luffing mechanism is firstly analyzed, then the bond graph model of revolute joint, cylinder and boom are proposed based multi-body theory, and the bond graph model of hydraulic system is also constructed. Through the analysis of the dynamic characteristics and interaction rules of each sub model, the transmission path of power flow is described. Coupling the boom structure and hydraulic actuator, the complete bond graph model of luffing mechafnism have been developed in a unified way. The total governing equations of the system have been derived from the model. Numerical results of chamber pressure of luffing cylinder implies to the good accuracy of the bond graph study, while comparing with experimental results. Meanwhile, the effects of the installation position parameters of the joints on system response have been studied through simulation, which provides a theoretical basis for improving the dynamic performance of the luffing mechanism

Synthesizing Robust Walking Gaits via Discrete-Time Barrier Functions with Application to Multi-Contact Exoskeleton Locomotion

Successfully achieving bipedal locomotion remains challenging due to real-world factors such as model uncertainty, random disturbances, and imperfect state estimation. In this work, we propose the use of discrete-time barrier functions to certify hybrid forward invariance of reduced step-to-step dynamics. The size of these invariant sets can then be used as a metric for locomotive robustness. We demonstrate an application of this metric towards synthesizing robust nominal walking gaits using a simulation-in-the-loop approach. This procedure produces reference motions with step-to-step dynamics that are maximally forward-invariant with respect to the reduced representation of choice. The results demonstrate robust locomotion for both flat-foot walking and multi-contact walking on the Atalante lower-body exoskeleton