At first glance, a floating-base robotic system is a kinematic chain, and its equations of motion are described by the inertia-coupled dynamics of its shape and movable base. However, the dynamics embody an additional structure due to the momentum evolution, which acts as a velocity constraint. In prior works of robot dynamics, matrix transformations of the dynamics revealed a block-diagonal inertia. However, the structure of the transformed matrix of Coriolis/Centrifugal (CC) terms was not examined, and is the primary contribution of this article. To this end, we simplify the CC terms from robot dynamics and derive the analogous terms from geometric mechanics. Using this interdisciplinary link, we derive a two-part structure of the CC matrix, in which each partition is iteratively computed using a self-evident velocity dependency. Through this CC matrix, we reveal a commutative property, the velocity dependencies of the skew-symmetry property, the invariance of the shape dynamics to the basis of momentum, and the curvature as a matrix operator. Finally, we show the application of the proposed CC matrix structure through controller design and locomotion analysis.

In this paper, we propose an operational space control formulation for a planar N-link underactuated manipulator (PAN–1)1with a passive first joint subject to actuator constraints (N ⩾ 3), covering both stabilization and tracking tasks. Such underactuated manipulators have an inherent first-order nonholonomic constraint, allowing us to project their dynamics to a space consistent with the nonholonomic constraint. Based on the constrained dynamics, we can design operational space controllers with respect to tasks assuming that all joints of the manipulator are active. Due to underactuation, we design a Quadratic Programming (QP) based controller to minimize the error between the desired torque commands and available motor torques in the null space of the constraint, as well as involve the constraint of motor outputs. The proposed control framework was demonstrated by stabilization and tracking tasks in simulations with both planar PA2and PA3manipulators. Furthermore, we verified the controller experimentally using a planar PA2robot.

In this paper, we propose three novel Hardware-in-the-loop simulation (HLS) methods for a fully-actuated orbital robot in the presence of external interactions using On-Ground Facility Manipulators (OGFM). In particular, a fixed-base and a vehicle-driven manipulator are considered in the analyses. The key idea is to describe the orbital robot's dynamics using the Lagrange-Poincaré(LP) equations, which reveal a block-diagonalized inertia. The resulting advantage is that noisy joint acceleration/torque measurements are avoided in the computation of the spacecraft motion due to manipulator interaction even while considering external forces. The proposed methods are a consequence of two facilitating theorems, which are proved herein. These theorems result in two actuation maps between the simulated orbital robot and the physical OGFM. The chief advantage of the proposed methods is physical consistency without level-set assumptions on the momentum map. We validate this through experiments on both types of OGFM in the presence of external forces. Finally, the effectiveness of our approach is validated through a HLS of a fully-actuated orbital robot while interacting with the environment.

When a space robot accidentally or voluntarily comes in contact with a target object, a workspace shift happens due to exchange of momentum between the objects. The problem of workspace adjustment is addressed herein. A novel controller is derived to simultaneously adjust the workspace and control the end-effector pose. The controller is based on a center-of-mass (CoM) regulation which fixes the workspace in the inertial space while leaving the base free to move, resulting in fuel efficiency. The control is validated on hardware using a robotic simulator composed of a seven degree-of-freedom (DOF) arm mounted on a 6DOF moving base.

In this paper we address the problem of controlling a robotic system mounted on an actuated floating base for space applications. In particular, we investigate the stability issues due to the low rate of the base control unit. We propose a passivity-based stabilizing controller based on the time domain passivity approach. The controller uses a variable damper regulated by a designed energy observer. The effectiveness of the proposed strategy is validated on a base-manipulator multibody simulation.

On-orbit servicing involves a new class of space missions in which a servicer spacecraft is launched into the orbit of a target spacecraft, the client. The servicer navigates to the client with the intention of manipulating it, using a robotic arm. Within this framework, this work presents a new robotic experimental facility which was recently built at the DLR to support the development and experimental validation of such orbital servicing robots. The facility allows reproducing a close-proximity scenario under realistic three-dimensional orbital dynamics conditions. Its salient features are described here, to include a fully actuated macro-micro system with multiple sensing capabilities, and analyses on its performance including the amount of space environment volume that can be simulated.