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Planetary RObots Deployed for Assembly and Construction Tasks

Periodic Reporting for period 1 - PRO-ACT (Planetary RObots Deployed for Assembly and Construction Tasks)

Reporting period: 2019-02-01 to 2021-04-30

In-Situ Resource Utilisation (ISRU) enables sustainability in space exploration through the harnessing of resources that are available in space in order to create products and services for robotic exploration, human exploration, and for commercial purposes. The European Space Agency is preparing a mission to demonstrate the feasibility of ISRU on the Moon which requires designing a payload that performs excavation, beneficiation and hydrogen reduction of regolith ore producing a few grams of water. The installation, construction and operation of such plants will require advancement in the field of autonomous robotics. Towards this objective, the PRO-ACT project aims to demonstrate a novel approach of deploying multiple robots to work towards achieving common goals by (i) cooperative goal decomposition (ii) cooperative mission planning and execution (iii) cooperative manipulation for transport and assembly of the aforementioned ISRU Pilot Plant and its supporting infrastructure that will be of strategic value for proposed future lunar unmanned and manned exploration missions.

PRO-ACT highlights the logical and physical cooperation between several robots. The main focus is on 1) multi-robot system architecture 2) task allocation by mutual negotiation 3) cooperative planning and task execution 4) Cooperative Simultaneous Localization and Mapping (CSLAM) and 5) Cooperative Manipulation 6) robot hardware adaptations.

PRO-ACT uses outcomes of previous EU Horizon2020 Space Robotics Technologies projects implementing robotic building blocks (ESROCOS, ERGO, INFUSE, I3DS, HOTDOCK). The modified robot hardware integrated with software components is aimed to demonstrate cooperative mission scenarios in a lunar testbed area of DFKI Space Exploration Hall such as (i) transport of objects from the lander (ii) deployment of a folded gantry (iii) assembly of ISRU modules and outdoor cooperative mapping.
The following section presents the results of the final demonstration which were validated during the final demonstration test campaign executed remotely across 4 locations (DFKI, PIAP-Space, AVS, LAAS-CNRS).

Cooperative Mapping: This cooperative mapping demo involved both robots at different locations connected by a common network for the multi-agent task planned to schedule and issue goals to each other for cooperative exploration and mapping. The agents were able to receive and plan traverses for their respective mapping goals correctly and plan traverses in the allocated area using the Rover Guidance (RG). The local/rover DEMs (Digital Elevation Models) and global DEMs (merged) for each robot were generated and provided representative maps of the test areas.

Grading and Tool exchange: For the tool exchange task, initial tests consisted of commanding the robot arm to defined pre-docking poses of the HOTDOCK interface of the gripper and shovel. Following this, the robot arm motion planner was used to command the arm to the tool interfaces pre-docking poses and perform a straight line trajectory for the docking phase. The HOTDOCK interface was commanded to lock/unlock via the Veles control center automatically using a state machine which matched the goal when within range of the alignment sensors. The grading operation was validated first via teleoperation to adjust the height of the grader blade and check its interaction with the sandy surface. The next step was to perform the grading test using RG (Rover Guidance) with waypoints, perception and localisation which was verified successfully.

Cooperative Manipulation for unloading, transport & assembling modules: The cooperative manipulation demonstration consisted in having the two robots, Mantis and Veles, using their arms to manipulate an object while their mobile bases were static. The grasping capability on the Veles manipulator was demonstrated by grasping a box (with a marker) and a handle, and moving it between predefined positions. On the Mantis a similar approach was used, but the 5 Dof manipulator with limited workspace reachability, required that the mockup with the handle be positioned within the accessible workspace via repeated trials. The physical cooperative manipulation scenario had to be further adapted for the demo as the Mantis and Veles couldn’t be tested in the same location due to COVID-19. The test was moved to a different setup which consisted of 2 fixed robot manipulators with external perturbations added manually to simulate one of the manipulators to be on a mobile base. Numerous pick and place tasks could be successfully run on the LAAS setup, showing the ability of CM2P to plan motions for a closed kinematic chain, and the ability of CM2C to control the execution of the arms motions in presence of perturbations. A virtual cooperative manipulation demo focused on the synchronous planning and motion control for executing each robot’s task, to detect the marker on an object, approach the object and grasp it virtually (grasping was demonstrated independently) and finally move it to another location.

Gantry deployment & control: The initial scenario of the ganty deployment over uneven terrain was planned using the Veles assisting the deployment by pulling one of the legs with a constant force and velocity, while the Mantis would be anchoring one of the legs. The CM2C (Cooperative Motion Controller) would coordinate this by commanding the Gantry’s motion for this deployment together with the RWAs. Due to the updated scope of the demo where robots couldn’t be co-located due to COVID-19 travel constraints, validation of this setup was performed remotely to check the commanding of the deployment and reception of the telemetry from the client interface over a virtual network. The gantry was successfully deployed and reached the deployed-secured state with the desired velocity, and then retracted back to the retracted-secured state on the flat terrain.
In the scope of planetary robotics, most applications focus on single robots designed for specific missions to operate independently. The future idea of deploying multiple robots cooperating to a common goal remains in the domain of terrestrial research and in some industrial applications (Ex. Automated warehouses). Applying this concept to planetary robotics has significant benefits in proving enhanced capability, redundancy, larger area coverage and combined capabilities for roving, manipulation and sensing. The final goal is for robots to both logically and physically collaborate closely to achieve complex and dynamic goals that are challenging for independent robots.

PRO-ACT demonstrated the successful logical cooperation among robots that work together closely to execute tasks synchronously such as cooperative mapping together. In terms of physical collaboration, some aspects of the final demonstration shows that robots can work closely on manipulating on the same object for the tasks such as assembly and transport of large objects. The re-use of the space robotics building blocks to develop these integrated robotic systems is another significant achievement.

This applied domain of research demonstrates that future space exploration missions can include multiple cooperative and collaborative robots, and advances the research in this domain for terrestrial applications.
Animated view of the Mantis and Veles collaboratively moving an object
Mantis and Veles cooperatively exploring and mapping their environments simultaneously
Mantis grasping the ISRU mockup using one of its arms while walking on 5 legs
2 Panda robotic arms manipulating a grasped object in a closed kinematic chain
Veles mobile robot grading the surface autonomously
Mobile Gantry in unfolded or deployed state with cable driven actuators