Speaker
Dr
Josep Virgili
(Naval Postgraduate School)
Description
This paper describes the design and the parameter identification procedure of a modular spacecraft robotic arm that combined with appropriate ancillary equipment (base-spacecraft, target and end-effector) provides an experimental set-up where control approaches and whole mission scenarios (e.g. servicing and debris removal) can be validated and demonstrated.
The originality of the here studied prototype robotic arm consists in its modularity. Each manipulator link contains its own power system, communications, harmonic drive motor with controller, torque sensor and a computing platform. The structure of the links has been manufactured using additive manufacturing allowing to quickly and inexpensively generate links of different lengths (with different mass and inertia properties). The manipulator links are modular and easy to re-arrange to meet the requirements of a particular experiments (number of links and length of these links).
A spacecraft equipped with a robotic arm is required to fulfill a wide range of missions (e.g servicing and debris removal) and few spacecraft with robotic arms have already been successfully flown. The dynamics of a space manipulator are substantially different from its terrestrial counterparts as the base-spacecraft is free to react to the manipulator motion. When the base-spacecraft mass and inertia are comparable to the manipulator's ones (i.e. as it is the case for small base-spacecraft) the base-spacecraft reaction can be significant and can not be safely omitted when modeling or treated as a small disturbance during control.
A substantial amount of theoretical and simulation work has been previously conducted by many researchers to tackle the operation and control of a space manipulator and its base-spacecraft. The difficulty to recreate the conditions of a space manipulator mounted on a small spacecraft on the ground limits the availability of validation experiments on control approaches and dynamical modeling.
A prototype modular robotic manipulator consisting of three links with three rotational degrees-of-freedom has been designed and integrated. Each link has a length of ~40 cm and has a mass of ~2 kg. This robotic manipulator is mounted onboard a ~10 kg Spacecraft Simulator that floats via air-pads over of a 4-by-4 meter granite monolith recreating in two dimensions the reduced gravity and quasi-friction-less environment of space. As it operates on a granite table the movement of both the manipulator and the base-spacecraft are restricted to two translational and one rotational degrees-of-freedom (planar movement). The base-spacecraft is equipped with eight cold-gas thruster and a reaction wheel and thus is able to control its position and attitude.
As the manipulator can be re-arranged in a different number of configurations, a method to quickly identify the manipulator parameters (mainly mass, inertia and the Denavit-Hartenberg parameters) will be presented. Finally, a few basic manipulator and base-spacecraft control capabilities of the experimental set-up are demonstrated.
| Applicant type | First author |
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Primary author
Dr
Josep Virgili
(Naval Postgraduate School)
Co-authors
Mr
Jerry Drew
(Naval Postgraduate School)
Prof.
Marcello Romano
(Naval Postgraduate School)
