Contact Force/Motion Hybrid Control for a Hydraulic Legged Mobile Manipulator via a Force-Controlled Floating Base

Hydraulic legged mobile manipulators are favored because they provide high power density and a strong explosive force. Hydraulic mobile manipulators require contact force control to handle increasingly mobile interaction tasks. However, the highly nonlinear dynamics and model inaccuracy of multiple hydraulic joint systems increase the difficulty of force control. To overcome this problem, we propose an interaction force control strategy for a hydraulic legged mobile manipulator operating via a force-controlled floating base. The interaction task involving multiple subtasks, such as torso motion, contact force, operational end-free motion, and leg motion, is decomposed into motion and force-control subparts under positional constraints. These tasks are transformed into a quadratic programming optimization problem with multiple constraints, and the task priorities are adjusted by a weight matrix. The effectiveness of our control strategy is demonstrated through simulations and physical experiments. Under the proposed strategy, the hydraulic legged mobile manipulator maintains its advantage (performing large load operations) while controlling the appropriate contact force during interactive operations.