Motion Planning with End-Effector Attitude Constraints for Free-Floating Space Robot

Paper number

IAC-21,A6,6,4,x64502

Author

Mr. Yongxing Tang, China, Northwestern Polytechnical University;National Key Laboratory of Aerospace Flight Dynamics

Coauthor

Prof. Zhanxia Zhu, China, National Key Laboratory of Aerospace Flight Dynamics,Northwestern Polytechnical University,Xi'an

Coauthor

Dr. Hongwen Zhang, China, School of Astronautics,Northwestern Polytechnical University

Year

2021

Abstract

For capturing of space debris with Free-Floating Space Robot(FFSR), in order to ensure the effective observation of the target by the hand-eye camera, the End-Effector(EE) attitude of FFSR is required to be maintained within a certain range when FFSR is moving toward the target. This type of problem is called Motion Planning with End-Effector Attitude Constraints(EE-AC-MP). For motion planning problem with task constraints, the existing methods are mainly aiming at the Implicit Equality Task Constraints(IETC) of the fixed-base manipulator. The existing methods can handle the more stringent IETC, but existing methods are aimed at path planning that only considers geometry. EE-AC-MP of FFSR needs to consider differential constraints directly. Besides, EE-AC-MP of FFSR needs to consider not only Implicit Inequality Task Constraints(IITC), but also Explicit Inequality Task Constraints(EITC). EITC means that the attitude of FFSR base is required to be maintained within a certain range.

Taking into account above problems, this paper proposes RRT For FFSR with EE-Attitude-Constraints(RRT-for-FFSR-with-EEAC). The key of RRT-for-FFSR-with-EEAC is that the local trajectories generated by local planners should respect IITC and EICT. RRT-for-FFSR-with-EEAC catains two types of local planners: local planner for ectending toward goal and local planner for ectending randomly, and we call them Local Planner for Random-Configuration-Guiding Constraint-Growth(LP-RC-GCG) and Local Planner for Goal-EE-Pose-Guiding Constraint-Growth(LP-GEE-GCG) respectively. Firstly, when designing LP-RC-GCG and LP-GEE-GCG, we propose Control-Based Local Planner Designing Method(CBLP-DM). CBLP-DM is an iterative process, and the action is generated by using the pseudo-inverse of Jacobian matrix to project error in each iteration. CBLP-DM can consider differential constraints directly and respect EITC. Then, considering that the degree-of-freedom(DOF) of the manipulator joint is less than the sum of DOF of FFSR’s configuration and the DOF of the EE attitude, we propose a principle named ‘Adjust Base Attitude/EE Attitude When Necessary’ for the action generation in each iteration of CBLP-DM. For each iteration of LP-GEE-GCG, only when the perturbation of the base attitude reaches a threshold, the base attitude is adjusted in the null-space of the Generalized-Jacobian-Matrix. For each iteration of LP-RC-GCG, only when the EE attitude reaches a threshold, the EE attitude is adjusted in the null-space of the Jacobian Matrix Related to State-Transition. With this principle, the problem of ‘the DOF of constraints and task is more than the DOF of the actuator can be alleviated, and IITC can be satisfied.

Abstract document

IAC-21,A6,6,4,x64502.brief.pdf

Manuscript document

IAC-21,A6,6,4,x64502.pdf (🔒 authorized access only).

To get the manuscript, please contact IAF Secretariat.