Momentum dumping for space robots

Abstract

During the robotic capture of a target object on orbit, accidental contacts may happen. During contacts, momentum is transferred to the system, causing a drift of the space robot in the inertial space. When no remediation is taken, the arm might converge to singularity or workspace limit within seconds, compromising the capture operation. This article presents a method to control the end-effector while simultaneously extracting any accumulated momentum in the system to cancel the drift. A feature of the method is that external actuators are only used for the momentum extraction and not to counterbalance the manipulator control forces. The control is validated with experiments using a Hardware-In-the-Loop (HIL) robotic simulator composed of a 7DOF (Degrees Of Freedom) arm mounted on a 6DOF moving base.

Coordinated Control of Spacecraft's Attitude and End-Effector for Space Robots

“…Note that this energy decoupling does not hold when using ν e instead of ν ⊕ e . Further simplifications of (21) are done by considering that the Coriolis and centrifugal vector terms can be shown to be zero for the centroid equation, i.e., −C T bc ω b − C T ec ν ⊕ e = 0 (see Appendix of [4]). Then, (21) simplifies to…”

“…In the early control concepts, attention was given to the possibility of completely turning off the spacecraft's actuators, resulting in a system for which the arm is commanded to realize an end-effector task while the spacecraft is left freefloating [1], [2], [3]. The free-floating idea was recently extended in the sense that the spacecraft's actuators are not completely turned off, but they are (minimalistically) used to dump any accumulated linear and angular momenta from the system [4] and stabilize the center-of-mass (CoM) of the space robot [5], endowing the floating-base space robot with the capability to resist contact. Although the advantages of the free-floating control and its extensions are evident in terms of fuel consumption, some missions may still require attitude pointing of the spacecraft.…”

An Energy-Based Approach for the Multi-Rate Control of a Manipulator on an Actuated Base

“…4. Notice that S is the dynamic system represented by the left hand side of (1), C b is the controller at the base expressed in (16) and C m is the controller of the manipulator (15). The controller C b is represented by electrical elements with impedance Z cb and a dependent voltage source which represents the coupling term of the manipulator, i.e.…”

“…More recently, the transposed Jacobian free-floating strategy has been extended to the nonzero momentum case [14], adding a disturbance compensation term. In [15], the transposed Jacobian free-floating control is extended to stabilize the system even in presence of contacts. This is achieved using actuators only to damp any accumulated momentum in the system.…”

“…This is achieved using actuators only to damp any accumulated momentum in the system. None of the actuated-base strategies [7], [8], [9], [10], [15] addressed the problem of multi-rate control.…”