Collaborative control of the knee-wheeled wheel-legged robot: Considering actuators characteristics

The potential of knee-wheeled wheel-legged robots (KW-WLRs) might be underestimated within the domain of wheel-legged robots (WLRs). When transitioning into legged motion mode, KW-WLRs exhibit passability comparable to traditional legged mobile robots on rough terrain. However, this comes at the cost of reduced flexibility due to the larger inertia of legs, when carrying a redundant knee-wheel. To address this challenge, a wheel-leg cooperation strategy is proposed, that leverages the redundant knee-wheel to enhance legs motion. Analyzing the characteristics of hydraulic actuators for the legs and a permanent magnet synchronous motor (PMSM) for the wheel in our KW-WLR mechanism, we design a delayed nonlinear model predictive controller (DNMPC) to collaboratively control the wheel-leg system. Simulation results demonstrate that our proposed wheel-leg collaborative strategy and controller, which consider the actuators’ characteristics, improve toe-end tracking performance across diverse working conditions and enhance the overall KW-WLR’s locomotion skill.