Collision Avoidance with Limited Field of View Sensing: A Velocity Obstacle Approach

Collision avoidance, in particular between robots, is an important component for autonomous robots. It is a necessary component in numerous applications such as human-robot interaction, automotive or unmanned aerial vehicles. While many collision avoidance algorithms take into account actuation constraints, only a few consider sensing limitations. In this paper, we present a reciprocal collision avoidance algorithm based on the velocity obstacle approach that guarantees collision-free maneuvers even when the robots are only capable to sense their environment within a limited Field Of View (FOV). We also present the challenges associated to sensors with limited FOV, show the conditions under which maneuvering can be safely done, and the modifications that a velocity obstacle approach requires to satisfy such conditions. We provide simulations and real robot experiments to validate our approach.

Enabling Large-Scale Collective Systems in Outdoor Aerial Robotics

Severin Leven

For many real-life applications such as monitoring, mapping, search-and-rescue or ad-hoc communication networks, fleets of flying robots are expected to out-perform existing solutions. Robots can join forces to cover larger areas in less time, act as efficient communication relays and overcome difficult terrain more easily than ground-based robots. Compared to a single robot, the main advantages of collective systems are robustness, parallelism, flexibility, and the fact that they enable tasks that could not be solved by a single robot. While a multitude of theoretical models for collective operation have already been developed and tested in simulation, they have rarely been validated with physical robots yet. Transition to reality has so far been inhibited because of strong limitations in scalability. Indeed, the cost, safety risk, and number of operators associated with a collective aerial system increase proportionally with the number of robots. Substituting such systems for single robots is therefore unattractive or even impracticable. In previous experimental approaches, a maximum of five physical robots were operated simultaneously in outdoor scenarios, assisted by human backup pilots on the ground. In contrast, most theoretical models rely on a minimum of ten robots to obtain interesting swarm effects. With respect to this discrepancy, we consider here ten robots to be a large-scale system in aerial robotics. In order to scale real collective aerial systems to at least ten robots, we suggest the following paradigm: flying robots must be low-cost, inherently safe, deal with mid-air collisions and require minimal supervision from an operator on the ground, such that the entire system warrants similar cost as well as similarly safe and easy deployment as a single, classical flying robot. Moreover, this would make swarms of flying robots as accessible as wheeled robots that have already been used successfully in larger collective systems. The above criteria can best be addressed with a global, systematic approach on all major design levels, which are the robot's airframe, low-level control, collective supervision and control as well as mid-air collision avoidance. On each level, we identified the bottlenecks related to scaling and developed methods for compliant robot design. Based on a systematic analysis of airframe configurations, a flying-wing is proposed that is made of low-cost, safe and durable foam material and can be deployed everywhere by hand-launch. A model for the dimensioning of such an airframe is presented. For low-level control, a novel minimalist control strategy is proposed, implemented on an inexpensive, custom-made autopilot and validated in field tests. In order to enable robots for collective operation, we suggest to use WiFi communication links and embedded Linux-computers onto which swarm designers can download distributed controllers for collective behaviors directly from their computer simulation. Furthermore, the idea is put forward to enable collective supervision through an operator interface with the modality for direct group-control. Implemented and field-proven, these solutions can serve as guidelines for other developers. Finally, the problem that robots may collide with each other during collective operation has been addressed with a model assessing the collision risk and a distributed strategy for mid-air collision avoidance, validated on real robots. Applying the proposed methodology allowed us to demonstrate the world's first collective system composed of ten autonomous flying robots in outdoor experiments with several different collective behaviors. Robots are low-cost (about 1/10 the cost of commercially available robots), inherently safe (kinetic energy of a medium-sized bird) and can be configured, deployed and supervised by a single operator on the ground. This represents a significant step for the scaling of flying collective systems with respect to the state of the art as well as an unprecedented operator-to-robot ratio.

EPFL2011

Are Autonomous Mobile Robots Able to Take Over Construction? A Review

Hadi Ardiny, Francesco Mondada, Stefan John Witwicki

Although construction has been known as a highly complex application field for autonomous robotic systems, recent advances in this field offer great hope for using robotic capabilities to develop automated construction. Today, space research agencies seek to build infrastructures without human intervention, and construction companies look to robots with the potential to improve construction quality, efficiency, and safety, not to mention flexibility in architectural design. However, unlike production robots used, for instance, in automotive industries, autonomous robots should be designed with special consideration for challenges such as the complexity of the cluttered and dynamic working space, human-robot interactions and inaccuracy in positioning due to the nature of mobile systems and the lack of affordable and precise self-positioning solutions. This paper briefly reviews state-ofthe-art research into automated construction by autonomous mobile robots. We address and classify the relevant studies in terms of applications, materials, and robotic systems. We also identify ongoing challenges and discuss about future robotic requirements for automated construction.

2015

Control of Contact Tasks in Autonomous and Human-Robot Collaborative Scenarios: A Dynamical System Approach

Walid Amanhoud

Robotic systems are more and more present in our daily life. Robots became indeed more economical, easy to program, safe and collaborative in their interaction with humans, versatile in performing different tasks and adaptive towards changes in the environment. Despite the recent advances in robotics, developingfully autonomous robots to achieve complex industrial or daily-life tasks is still very challenging. The human, due to his superior perception, understanding and reasoning skills, especially in uncertain environment, needs to be in the loop. Therefore, the ability of robots to collaborate with humans is of great interest inthe robotics community. Human-Robot Collaboration usually implies robots that share the control of the tasks with humans, providing adjustable autonomy level and mutual adaptation. A field that can particularly benefits from such collaboration is assistive robotics surgery. The introduction of shared autonomyin surgical tasks has several advantages. In particular, it can provide higher accuracy, flexibility, control and efficiency during the operation, over longer time periods, relieve the surgeon during repetitive tasks and reduce his mental workload. However, it is not very clear how to best use shared control to assist asurgeon during the operation. As part of a research project (the "Surgical project"), in this thesis we would like to propose solutions to that problem by building a teleoperated shared control architecture for a laparoscopic surgery scenario. While laparoscopic surgery usually involves one surgeon and two humanassistants to perform the surgery, the project aims to replace the assistants by two partially teleoperated robotic systems. The target shared control architecture would explore various strategies to ensure safety for both the patient and the surgeon, provide accuracy and stability in motion and force control of the toolsattached to the robots, reduce the mental workload of the surgeon and adapt the level of assistance based on well-identified criteria.The first year was mainly devoted to the control of motion and force for contact tasks which is of great importance in the context of the project. Robot force control is traditionally achieved either explicitly through hybrid position/force control or implicitly using impedance control. We propose an approach leveraging theproperties of dynamical systems (DS) for immediate re-planning and robustness to real-time perturbations by exploiting local modulation of the DS. Dynamical systems has been widely used as a tool to represent and generate motion in robotics application. Here the idea is to propose a DS formulation to generatecontact force in addition to motion. First implementation and experiments to evaluate the effectiveness of the strategy were conducted in practice with a 7-DOF robotic arm (KUKA LWR IV+).So far we focused on contact tasks that were performed autonomously by one or two robots. Future work will improve and use the proposed DS approach to consider contact tasks in shared control scenarios where one human and one or two robots need to collaborate to successfully achieve the tasks. Because of the nature of the surgical project we will use teleoperation systems to introduce the human in the loop. The developed teleoperated shared control architecture will be evaluated on laparoscopic surgery related tasks.