The research works carried out in this paper deal with the control of a fast double-steering off-road mobile robot. Such kind of robots requires very high stable and accurate controllers because their mobility is particularly influenced by wheel-ground interactions. Hence, the vehicle dynamics should be incorporated in the control circuit to take into account these issues, which is developed based on the road geometry parameters and the slippage-friction conditions at the wheel-ground contacts. Relying on this dynamic model, we present in this paper the design and application of a constrained Model Predictive Control (MPC). It is based on the minimization of a cost function (optimizing the devi-
This paper proposes a new wheel motion generator to track the centroidal motion of one quadrupedon-wheel robot which has the ability to cross various rough terrains with the model based wholebody torque control. The generator is used to track the whole-robot centroidal motion reference. Firstly, the wheel contact model and the whole-body inverse kinematics model are derived using spatial vectors. The wheel motion is extracted out mathematically depending on the base and the legged motions, which serves as the kinematics model. Then the wheel motion generator is developed by combining both the kinematics model and the robot centroidal momentum/dynamics model. The models are decomposed into three components relating to the base motion, the legged motion and the wheel motion. The adaptive wheel motion references are derived in a detailed mathematical way and several algorithms are developed for the model decompositions. Finally, the robot is simulated to be driven on various rough terrains using the operational space control framework mixed with our proposed compatible prioritized impedance controller. The required torque for multiple tasks is generated by the feed-forward and feedback controllers while fulfilling the contact constraints.
This paper develops a compact form dynamics controller to generate multi-compliant behaviors for a new designed Tetrapod-on-wheel robot with one manipulator. The wholebody compliant torque controller is stated through one null space based convex optimization and compatible null space based impedance controllers. Different with fixed contact points of conventional quadruped robots, the kinematic wheel contact constraints are derived for our legged-on-wheel robot, which serves as the basis for each task reference extraction and each compliance controller. The compact relationships between task references and optimization control variables are extracted using null space based inverse dynamics, which is used to build the cost function in the operational space and/or in the joint space. The whole-body control frame is developed and several null space based feed-back impedance controllers are integrated into the compact relationships to allow the robot to achieve compliance and compensate the model impreciseness, especially the wheel contact model. Then the detailed algorithm is presented whose output combines the feed-forward and feedback torque. The validation of our approach is performed via advanced numerical simulations for a virtual legged-on-wheel robot with one manipulator.Keywords Compact-form dynamics controller • Tetrapod-on-wheel robot • Null space • Convex Optimization • Compatible Impedance Control • Wheel Contact Model
IntroductionConventional wheel robots have great performance and potential on continuous terrain with high speed and less energy consuming, but easily stuck on rough terrain with steep obstacles.
This paper develops a more general dynamics controller to generate whole-body behaviors for a quadrupedon-wheel robot. To track the quadruped centroidal motion, the wheeled motion is achieved by combining the wheel contact constraints and the centroidal momentum/dynamics model. The dynamics controller is based on a new hybrid hierarchical and prioritized weighted optimization framework. We propose one concept of a recursively updated dynamics model and this model enables to integrate the new prioritized weighted scheme in the hierarchical framework. In contrast with the conventional weighted scheme, we propose to use null-space projections among its sub-tasks. Then the prioritized impedance controller is proposed and integrated in our dynamics model, which enables to influence the hierarchical and prioritized weighted tasks in a decoupled way. The task accelerations in the two schemes are extracted with quadratic forms depending on the actuated torque and the prioritized impedance force using null-space based inverse dynamics. The inequality constraints are modified to ensure the compatibility with the hybrid convex optimization. This dynamics controller is more general and its algorithm is given completely which enables our robot to track the centroidal motion on rough terrain and handle other missions in three simulation scenarios.
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