移动机器人在目前的应用中以单体独立工作为主，而单体受尺寸、负载和成本的限制，其功能和性能上受到制约，因此，移动机器人正朝着多机协作的方向发展。多机协作可以分为有机械连接和无机械连接两种，本文主要研究有机械连接的多机协作形式，多机之间通过机械连接可以扩展功能，提升负载能力。本文研究了蚂蚁搬运食物机制，提出了多机协作系统三要素设计体系：本体结构、信息融合和作业策略，面向不同搬运需求，设计了六自由度多机协作系统和三自由度多机协作系统，相应地提出了信息融合方法，并在控制上依次实现了轮式移动机器人运动控制器设计、稳定性控制以及多机协同作业策略。首先，通过李雅普诺夫第二方法，设计了具有输入饱和约束的运动控制器，解决了移动机器人在速度空间约束情况下的轨迹跟踪问题，并针对跟踪目标广义速度和朝向观测不准确的工况，在轨迹跟踪控制器中引入位置误差积分项，大幅减小了因观测误差而带来的轨迹跟踪误差。提出了单机系统倾翻稳定和横向滑移稳定的分析方法，指出重心控制是移动机器人稳定性控制的本质。在此基础上，优化了单机系统的越障策略，提出通过改变偏航角的方法降低机器人重心，提升越障性能。并在单机越障策略的基础上，优化得到多机越障策略，通过合理控制多机系统越障参数，使其越障能力得到大幅提升。同时，本文考虑了多机协同在故障模式下的稳定性，即多机系统中单体发生故障时，例如履带锁死或脱带，系统仍能保持稳定的条件，并建立了稳定性控制方法。在以上研究基础上，开展了多机协同作业策略研究，根据信息融合时信息获取权限的完备性，分别提出了中央控制策略和分布式控制策略。面向中央控制策略，提出了基于局部观测的自标定方法，使得机器人单元可以快速感知自身在多机系统中的相对坐标，进而通过全局速度规划完成多机协同作业；面向分布式控制策略，通过研究蚂蚁搬运食物的机制，提出了基于力感知的分布式控制策略，为机器人针对性的设计了导纳控制器，机器人单元之间无需任何显式通信，只需通过个体与负载之间的相互作用力即可实现协同搬运作业。最后，对所提出的中央控制策略和分布式控制策略开展了仿真和实验验证，结果表明：本文所提出的两种作业策略，均可保证多机系统的稳定协同作业，本文所提出的方法切实有效。
Mobile robots usually work individually in the current application background. The functionality and performance of a single robot are limited significantly by its size, payload capacity, and product cost. Therefore, the development of mobile robots is moving toward the direction of multi-robot cooperative systems. There are mainly two types of multi-robot cooperation: cooperation with mechanical connections and cooperation without mechanical connections. This work mainly studies multi-robot cooperation with mechanical connections. The mechanical connections of multiple robots can expand functionality and improve the load capacity of the multi-robot system.Inspired by the behavioral mechanisms of cooperative transport in ants, this work proposes a three-element design for the multi-robot cooperative system, including robot structure, information fusion, and operation strategy. A 6-DoF cooperative system and a 3-DoF cooperative system are designed to meet different transport requirements. To realize a stable operation of the multi-robot system, three hierarchical control problems are successfully solved, which are the motion controller design of the wheeled mobile robot, the stability analysis of the mobile robot, and the multi-robot cooperation strategy. In terms of Lyapunov's second method, a motion controller with input saturation constraints is designed, which solves the problem of trajectory tracking of mobile robots under the speed space constraints. On this basis, given an inaccurate observation of the reference target’s generalized velocity and orientation, a position error integral term is introduced into the trajectory tracking controller, which greatly reduces the trajectory tracking error caused by the observation error.The stability in overturning and lateral slippage of a single mobile robot is analyzed. Control of the gravity-center is regarded as the essence of stability control for a mobile robot. On this basis, the obstacle crossing strategy of a single robot is optimized by changing the climbing yaw angle for lowering the robot's gravity center. Furthermore, based on the single-robot obstacle-crossing strategy, a multi-robot obstacle-crossing strategy is proposed and optimized. By optimizing obstacle-crossing parameters of the multi-robot system, the obstacle-crossing ability is improved. Besides, this work studies the stability of multi-robot coordination in fault mode when a malfunction occurs in the multi-robot system, such as track lock or track broken. A tolerant control method is proposed to maintain the system stabilization.Based on the above two studies, two cooperation strategies of the multi-robot collaborative system are proposed, including the central control strategy and the distributed control strategy. A self-calibration method on local observation is proposed to make the robots quickly perceive the relative coordinates in the multi-robot system, and then the central control strategy of the multi-robot cooperation is achieved by global speed planning. For the distributed control strategy, imitating behavioral mechanisms of cooperative transport in ants, a force-perception based strategy is proposed, in which the admittance controller is designed. The cooperative transport can be realized through the force interaction between robots and payloads, without any explicit communications among the robots.Finally, simulations and experiments are performed to verify the proposed central control strategy and distributed control strategy. The results show that both of the two cooperation strategies can guarantee the stability and cooperative operation of multi-robot systems. The proposed methods in this work are feasible and effective.
