A compact form dynamics controller for a high-DOF tetrapod-on-wheel robot with one manipulator via null space based convex optimization and compatible impedance controllers

Abstract

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.

Rolling based locomotion on rough terrain for a wheeled quadruped using centroidal dynamics

“…the contact unilateral limit, the friction cone and the actuated-joint limits. In [32], we have verified the optimization based torque controller using our wheel motion generator in this paper.…”

“…Therefore, the fulfillment of the contact constraints by the torque controller ensures the robot stability to resist external disturbances, including the unknown rough terrains, the external force, etc, shown in the complex simulated scenarios in Section 5. Furthermore, we also developed one optimization based torque controller in [32] which can handle the contact situation with inequality constraints, e.g. the contact unilateral limit, the friction cone and the actuated-joint limits.…”

“…In addition, we developed one optimization based torque controller in [32] to achieve several operational tasks which are achieved by respecting the contact constraints. The inequality constraints include the base orientation and position limits, the actuated-joint position and velocity limits, the unilateral contact constraint and the friction cone.…”

“…The inequality constraints include the base orientation and position limits, the actuated-joint position and velocity limits, the unilateral contact constraint and the friction cone. The torque controller in [32] is verified on our robot with one manipulator on its base using our wheel motion generator in this paper. In these works, the contact constraints always have the highest priority which ensure the robot stability while handling several activities.…”

Attitude control strategy for unmanned wheel-legged hybrid vehicles considering the contact of the wheels and ground

“…Therefore, it is essential to construct an efficient attitude control strategy for the proposed structure of UWLHVs. Du and Benamar 15 proposed a whole-body compliant torque controller based on one-dimensional null-space-based convex optimization and compatible null-space-based impedance controllers. Ni et al 16 designed an active-passive transformable suspension system and presented a novel posture control strategy to improve ride comfort.…”