Search

For the problem of autonomous and safe landing on irregularly shaped asteroids, a real-time collision-free trajectory optimization method based on deep neural networks (DNNs) is proposed. First, in order to overcome the difficulty of solving the optimal trajectories by indirect methods caused by anti-collision path constraints and the difficulty of establishing the mapping relationship between states and initial costates by DNNs, a two-stage anti-collision trajectory optimization model is constructed, which can provide the initial costates for trajectory optimization under anti-collision constraints of each stage through the approximate analytical solution of costates. It can efficiently generate a large number of optimal trajectory samples. Second, a region division strategy is proposed for further reducing the time-consuming of DNN training. Then, the path constraints are slightly relaxed to avoid the optimal trajectories predicted by DNNs from violating the anti-collision constraints. The proposed method is applied to the scenarios of landing on asteroids 101955 Bennu and 433 Eros. The simulation results indicate that this method can estimate the initial costates efficiently and accurately, and can plan the optimal trajectories of anti-collision landing in real time. [ABSTRACT FROM AUTHOR]

In this article, we address the task of cooperative path following control of multiple autonomous quadcopters in the presence of unknown external disturbances. Under the assumption that the communications among the vehicles are bidirectional and continuous, a synchronized path following strategy is proposed that regulates the speed of each vehicle along its path to reach consensus in relative position. Moreover, collision-free transient paths from the vehicle initial positions to a group of suitable selected positions along the desired paths are designed. Building on the backstepping technique, the proposed path following controller for each individual vehicle drives the quadcopter toward, and to stay within an arbitrarily small neighborhood of its corresponding desired path, achieving global uniformly ultimately boundedness. In addition, the devised controller guarantees that the actuations are bounded with respect to the position error. The controller is also made robust to external constant or slowly time-varying disturbances by the introduction of dynamic estimators for the disturbances. A projection operator is used to ensure that the estimates remain within the prescribed bounds and are sufficiently smooth to be backstepped. In order to validate the effectiveness and performance of the proposed methodology, we present and analyze both simulation and experimental results. [ABSTRACT FROM AUTHOR]

Abstract: The stability of autonomous vehicle platoons with limits on acceleration and deceleration is determined. If the leading-vehicle acceleration remains within the limits, all vehicles in the platoon remain within the limits when the relative-velocity feedback coefficient is equal to the headway time constant . Furthermore, if the sensitivity , no collisions occur. String stability for small perturbations is assumed and the initial condition is taken as the equilibrium state. Other values of and that give stability with no collisions are found from simulations. For vehicles with non-negligible mechanical response, simulations indicate that the acceleration-feedback-control gain might have to be dynamically adjusted to obtain optimal performance as the response time changes with engine speed. Stability is demonstrated for some perturbations that cause initial acceleration or deceleration greater than the limits, yet do not cause collisions. [Copyright &y& Elsevier]

Tower crane scheduling is a classic conundrum. It is further complicated to prevent collisions and reduce idle transportation time among multiple overlapping tower cranes. Unlike previous research attempts, this study aims to provide an optimal solution to this multiple crane service scheduling problem (MCSSP). Firstly, the MCSSP was translated to a Mixed Integer Linear Programming (MILP) model. Then, the model was optimized by 1) distributing the lifting requests in overlapping areas to the proper tower cranes; 2) selecting the appropriate supply location to serve each lifting request; and 3) arranging the lifting sequences of each tower crane to complete the requests. Compared with previous methods, the proposed MILP model (solved using Gurobi™) can result in the saving of 6.54%–18.07% of total operation costs meanwhile achieving the non-collision goal. The findings of this research can be deployed in optimizing efficiency and safety in the real-life scheduling of multiple overlapping tower cranes. • An MILP model is formulated to optimize the service schedules of multiple tower cranes. • The operation safety and transportation efficiency are both considered in this model. • The schedules can be rearranged by optimizing lifting sequences, requests distributions and selection of material storages. • This model can possibly spend extra limited operation cost to prevent all the collision and ensure the operation safety. [ABSTRACT FROM AUTHOR]

Many solutions about the teleoperation of unmanned robotic excavators have been studied continuously. However, if excavators that are remotely controlled were employed, the probability of an accident would be higher. For this reason, there have been many ways proposed to attempt to reduce accidents in these dangerous situations. In this paper, a novel methodology will be introduced with a focus on the multiple excavators themselves. The proposed method details how one excavator can be generated or expressed as an obstacle in the Configuration-Space (C-space) with respect to another excavator's side for collision avoidance each other. This method is based on kinematics information which is measurable and given. Therefore, this method can be used or applied independently by using widely used pose sensors and wireless communication devices. The phase of mathematical derivation about obstacle sets is described in detail. The results are shown in accompanying figures and tables for demonstrating that the proposed method detected the proximity and found the collision-free zone accurately. The proposed system can be powerful when applied to a teleoperation system, where it would be particularly useful and helpful to the operator. [ABSTRACT FROM AUTHOR]