Slip Modeling and Estimation for a Planetary Exploration Rover: Experimental Results from Mt. Etna

For wheeled mobile systems, the wheel odometry is an important source of information about the current motion of the vehicle. It is used e.g. in the context of pose estimation and self-localization of planetary rovers, which is a crucial part of the success of planetary exploration missions. Depending on the wheel-soil interaction properties, wheel odometry measurements are subject to inherent errors such as wheel slippage. In this paper, a parameter-based approach for whole-body slip modeling and calibration is applied to a four-wheeled lightweight rover system. Details on the method for slip parameter calibration as well as the system-specific implementation are given. Experimental results from a test campaign on Mt. Etna are presented, showing significant improvements of the resulting wheel odometry measurements. The results are validated during a long range drive of approx. 900 m and discussed w. r. t. the advantages but also limitations of the method within a space exploration scenario

The LRU Rover for Autonomous Planetary Exploration and its Success in the SpaceBotCamp Challenge

The task of planetary exploration poses many challenges for a robot system, from weight and size constraints to sensors and actuators suitable for extraterrestrial environment conditions. As there is a significant communication delay to other planets, the efficient operation of a robot system requires a high level of autonomy. In this work, we present the Light Weight Rover Unit (LRU), a small and agile rover prototype that we designed for the challenges of planetary exploration. Its locomotion system with individually steered wheels allows for high maneuverability in rough terrain and the application of stereo cameras as its main sensor ensures the applicability to space missions. We implemented software components for self-localization in GPS-denied environments, environment mapping, object search and localization and for the autonomous pickup and assembly of objects with its arm. Additional high-level mission control components facilitate both autonomous behavior and remote monitoring of the system state over a delayed communication link. We successfully demonstrated the autonomous capabilities of our LRU at the SpaceBotCamp challenge, a national robotics contest with focus on autonomous planetary exploration. A robot had to autonomously explore a moon-like rough-terrain environment, locate and collect two objects and assemble them after transport to a third object - which the LRU did on its first try, in half of the time and fully autonomous

Preliminary Results for the Multi-Robot, Multi-Partner, Multi-Mission, Planetary Exploration Analogue Campaign on Mount Etna

This paper was initially intended to report on the outcome of the twice postponed demonstration mission of the ARCHES project. Due to the global COVID pandemic, it has been postponed from 2020, then 2021, to 2022. Nevertheless, the development of our concepts and integration has progressed rapidly, and some of the preliminary results are worthwhile to share with the community to drive the dialog on robotics planetary exploration strategies. This paper includes an overview of the planned 4-week campaign, as well as the vision and relevance of the missiontowards the planned official space missions. Furthermore, the cooperative aspect of the robotic teams, the scientific motivation, the sub task achievements are summarised

Finally! Insights into the ARCHES Lunar Planetary Exploration Analogue Campaign on Etna in summer 2022

This paper summarises the first outcomes of the space demonstration mission of the ARCHES project which could have been performed this year from 13 june until 10 july on Italy’s Mt. Etna in Sicily. After the second postponement related to COVID from the initially for 2020 planed campaign, we are now very happy to report, that the whole campaign with more than 65 participants for four weeks has been successfully conduced. In this short overview paper, we will refer to all other publication here on IAC22. This paper includes an overview of the performed 4-week campaign and the achieved mission goals and first results but also share our findings on the organisational and planning aspects

Whole-Body Stability for a Humanoid Robot: Analysis, Control Design, and Experimental Evaluation

Future service robots have to be able to act compliantly in unstructured, dynamic environments and in the presence of humans residing in their workspace. Torque control methods such as the well-established impedance algorithms are suitable in this context. In order to provide mobility of the robotic system, it has to be equipped with legs or wheels. In case of nonholonomic wheeled platforms, position or velocity control methods are commonly applied. An admittance interface can be used to incorporate the kinematically controlled mobile platform to the torque controlled whole-body control framework. While the kinematic controller compensates the inertia and Coriolis/centrifugal couplings from the upper body to the moving base, inertia and Coriolis/centrifugal couplings from the base to the upper body remain in the system dynamics. Depending on the choice of control parameters, deteriorated performance or even a loss of stability of the overall system can be observed due to those remaining couplings. In this master’s thesis, the effects of inertia and Coriolis/centrifugal couplings on the overall system dynamics of impedance controlled robots with a kinematically controlled mobile platform are addressed. Initially, the general problem is analyzed using simple linear and nonlinear model systems. Building on the findings of that analysis, an approach for the compensation of the inertia and Coriolis/centrifugal couplings is presented and a proof of stability for the resulting system dynamics is given. Experiments with DLR’s humanoid robot Rollin’ Justin validate the approach

Whole-Body Impedance Control for a Planetary Rover with Robotic Arm: Theory, Control Design, and Experimental Validation

Future planetary rovers will gain the ability to manipulate their environment in addition to the maneuverability of current systems. For dedicated contact interaction, Cartesian impedance control is a well-established approach from numerous terrestrial applications. In this paper we will present a whole-body Cartesian impedance controller for a planetary rover equipped with a robotic arm. In contrast to classical terrestrial whole-body controllers, the issue of proper wheel force distribution will be addressed within the control framework. A global optimization solves this redundancy in the over-actuation of the mobile base while additionally handling the kinematic redundancy in the serial kinematic sub-chain of the robot. The approach is experimentally validated on the DLR Lightweight Rover Unit. It can be used for versatile manipulation in rough terrain such as encountered in planetary exploration or terrestrial search-and-rescue scenarios

Investigating the Influence of Haptic Feedback in Rover Navigation with Communication Delay

Safe navigation on rough terrain in the presence of unforeseen obstacles is an indispensable element of many robotic applications. In such conditions, autonomous navigation is often not a viable option within certain safety margins. Yet, a human-in-the-loop can also be arduous to include in the system, especially in scenarios where a communication delay is present. Haptic force feedback has been shown to provide benefits in rover navigation, also when confronted with higher communication delays. Therefore, in this paper we present the results of a user study comparing various performance metrics when controlling a rover with a car-like interface with and without fictitious force feedback, both with no communication delay and with a delay of 800 ms. The results indicate that with force feedback the navigation is slower, but task performance in the proximity of obstacles is improved

Datasets of Long Range Navigation Experiments in a Moon Analogue Environment on Mount Etna

Long range navigation capabilities are crucial to increase the level of autonomy for robotic planetary exploration missions. As the opportunities to collect data on the surfaces of other planets are both very limited and expensive, space analogue sites on Earth play an important role to develop and test robotic systems. We provide and present two datasets captured with our Lightweight Rover Unit (LRU) at a planetary surface analogue test site on Mt. Etna, Sicily, Italy. In distinction to many other robot navigation datasets, we were able to capture datasets in an environment that is in terms of its visual and terramechanical properties close to the character of surfaces of rocky planets, hence making our data valuable for the development of visual-inertial navigation systems for planetary and unstructured GPS-denied outdoor environments. We make both of our datasets publicly available and free to download for other researchers to use them to test, improve and evaluate their navigation methods. We provide raw data in the form of ROS bagfiles containing gray-scale images, dense depth images, sensor readings from an Inertial Measurement Unit (IMU) and wheel odometry estimates. In addition, the data contains ground truth for the rover trajectory obtained via differential GPS (DGPS) to allow an evaluation of robot localization methods. The datasets were recorded during experiments, in which our rover traversed paths of approximately 1 km in length each. This makes them useful for testing pose estimation methods over long ranges

Passive Hierarchical Impedance Control via Energy Tanks

Modern robotic systems with a large number of actuated degrees of freedom can be utilized to perform several tasks at the same time while following a given order of priority. The most frequently used method is to apply null space projections to realize such a strict hierarchy, where lower-priority tasks are executed as long as they do not interfere with any higher-priority objectives. However, introducing null space projectors inevitably destroys the beneficial and safety-relevant feature of passivity. Here, two controllers are proposed to restore the passivity: one with local energy tanks on each hierarchy level and one with a global tank for the entire system. The formal proofs of passivity show that no energy is generated by these controllers. Once the tanks are empty, passivity is still guaranteed at the cost of some control performance. Simulations and experiments on a torque-controlled robot validate the approaches and predestine them for the usage in safety-relevant applications

Whole-body impedance control of wheeled mobile manipulators: Stability analysis and experiments on the humanoid robot Rollin' Justin

Humanoid service robots in domestic environments have to interact with humans and their surroundings in a safe and reliable way. One way to manage that is to equip the robotic systems with force-torque sensors to realize a physically compliant whole-body behavior via impedance control. To provide mobility, such robots often have wheeled platforms. The main advantage is that no balancing effort has to be made compared to legged humanoids. However, the nonholonomy of most wheeled systems prohibits the direct implementation of impedance control due to kinematic rolling constraints that must be taken into account in modeling and control. In this paper we design a whole-body impedance controller for such a robot, which employs an admittance interface to the kinematically controlled mobile platform. The upper body impedance control law, the platform admittance interface, and the compensation of dynamic couplings between both subsystems yield a passive closed loop. The convergence of the state to an invariant set is shown. To prove asymptotic stability in the case of redundancy, priority-based approaches can be employed. In principle, the presented approach is the extension of the well-known and established impedance controller to mobile robots. Experimental validations are performed on the humanoid robot Rollin’ Justin. The method is suitable for compliant manipulation tasks with low-dimensional planning in the task space