Review Article
An overview of collaborative robotic manipulation in multi-robot systems

https://doi.org/10.1016/j.arcontrol.2020.02.002Get rights and content

Abstract

Robotic manipulation aims at combining the versatility and flexibility of mobile robot platforms with manipulation capabilities of robot manipulators. This survey paper comprehensively reviews the state-of-the-art development of collaborative robotic manipulation from the perspective of modelling, control and optimization. Then, the recent results in this field can be categorized into coordination of multiple fixed manipulators, mobile robots and mobile manipulators, respectively. A classification and comparison of various issues and promising approaches is given. Finally, a short discussion section is given to summarize existing research and to point out several future research directions.

Introduction

Robotic systems are going through tremendous changes and increasingly bringing significant socioeconomic impacts to human lives (Valavanis & Saridis, 2012). For example, industrial robots (especially robot manipulators) have been widely and successfully used in conventional production processes due to their high endurance, speed, and precision in structured industrial environments (Hu, Tay, & Wen, 2012). With the developments in robotic/network technologies and the requirements on efficiency and quality in production processes, collaborative manipulation of robot manipulators (either fixed or mobile) has attracted increasingly attention due to practical potential in various applications and theoretical challenges (Hvilshoj, Bogh, Nielsen, & Madsen, 2012). Take manufacturing and automotive applications for example, the assembling, transporting, painting, packaging, and welding usually require high flexibility and maneuverability in practice. Notice that most of these tasks involve large maneuverability and manipulability, and cannot be carried out by a single robot. Hence, the cooperation of multiple robot manipulators arises as an important technique for increasing efficiency and enhancing flexibility in industrial applications. In addition to the high task complexity that is impossible for a single robot to accomplish, some other motivations for developing the multi-robot systems are below (Fink, Ribeiro, & Kumar, 2012a): 1) distributed property, i.e., the task is inherently distributed; 2) more time/energy efficiency, i.e., multiple robots can complete missions faster with low operational costs; 3) less system requirements, i.e., building some resource-constrained robots is much easier than developing a single powerful robot; 4) strong robustness and adaptivity, i.e., the robots can increase robustness against robot failures and self-adapt to changes; and 5) high scalability and flexibility, i.e., large-scale robot systems can function well in the presence of many robots.

Multi-robot systems usually refer to a group of fixed/mobile robots with sensing, computation, communication, and actuation capabilities that enable them to accomplish certain tasks cooperatively in a distributed fashion.1 Applications for these systems, as depicted in Fig. 1, include assembly and painting of fixed manipulators, transportation and formation of mobile robots, and manipulation and 3D printing of mobile manipulators. Coordination of these multiple robots needs systematic methodologies to design and analyze cooperative strategies to control multi-robot systems. To further illustrate the mechanism behind the whole system, Fig. 2 shows an integrated multi-robot coordination framework. The robot physical space consists of a large number of robots, while the communication space describes the communication network among the robots. With the help of sensor and control networks, a decision maker in the distributed monitoring and control center can employ control algorithms and techniques to make decisions, and then influence the physical robots.

Due to the vast amount of literature, it would be challenging to exhaustively review existing results on collaborative robotic manipulation. Rather than the exhaustive review, this survey focuses on the characterization of the multi-robot coordination in terms of the robot functionalities and control challenges as illustrated in Fig. 3. We further categorize the existing works into coordination of the fixed manipulators, mobile robots, and mobile manipulators, according to the robot functionalities and controlled variables as follows.

  • Manipulator coordination: a team of fixed robot manipulators cooperatively complete certain tasks (e.g., consensus, synchronization) either in the configuration space or task space by using local interaction rules. Coordination only considers the control of robotic manipulators.

  • Mobile robot coordination: a team of mobile robots cooperatively complete certain tasks (e.g., rendezvous, formation, swarming, flocking, coverage control, surveillance, mapping) based on local interaction rules. Coordination needs to consider sensing and communication abilities.

  • Mobile manipulator coordination: mobile robot manipulators (manipulators mounted on a mobile robot platform) cooperatively complete certain tasks by using local interaction rules. Coordination is required to consider robotic manipulation as well as locomotion in the control.

Fig. 4 describes a block diagram to facilitate the understanding of this classification, representing several elementary fixed manipulators, mobile robots, and combination of them.

In response to this classification, this paper reviews various distributed control and coordination technologies that enable the robots to achieve team-level and global tasks efficiently by using local interaction rules. Specifically, we firstly formulate a general distributed coordination problem and further discuss distinctions of robots’ collective behaviors in terms of robot tasks and control objectives. We then review recent results on coordination of fixed manipulators, mobile robots, and mobile manipulators, respectively, focusing on robot modeling, control, design, and optimization. A classification and comparison of various issues and promising approaches is carried out.

The organization of this paper is given as follows. In Section 2, preliminaries on graph theory and communication network description are firstly presented. Then, the general distributed coordination problem with respect to various collective behaviors is provided. From 3 Coordination of robot manipulators, 4 Coordination of mobile robots, 5 Coordination of mobile manipulators, the existing results on coordination of fixed manipulators, mobile robots, and mobile manipulators are reviewed, respectively. Finally, we conclude the paper with a short discussion on future research directions.

Section snippets

Graph theory

Let G = {V,E} represent a graph and V  ∈  {1, 2, ⋅⋅⋅, N} denote the set of vertices. The set of edges is denoted as EV×V. Every robot is represented by a node in the graph. An edge is an ordered pair (j,i)E if node j can be directly supplied with information from node i. We assume (i,i)E. Ni = {jV(j,i)E} denotes the neighborhood set of vertex i. An undirected graph is connected if there exists an undirected path between any two nodes. A digraph G contains a directed spanning tree if

Kinematic and dynamic models of robotic manipulators

Consider a team of N robotic manipulators with the Euler-Lagrange (EL) dynamics described by Feng, Hu, Ren, Dixon, and Mei (2018)Mi(qi)q¨i+Ci(qi,q˙i)q˙i+Gi(qi)+fi(q˙i)=τi+di,where qiRn is the vector of generalized coordinates, Mi(qi)  ∈  Rn×n is the inertia matrix, Ci(qi,q˙i)q˙i  ∈  Rn is the vector of Coriolis and centrifugal torques, Gi(qi)Rn is the vector of gravitational torque, fi(q˙i)Rn represents the unknown unmodelled dynamics (or frictions), τi Rn is the control input, and diRn is

Coordination of mobile robots

In Section 3, many different control strategies using only measurable information (e.g., the relative displacements) have been proposed such that synchronization/consensus of multiple fixed robotic manipulators can be achieved. In contrast, for the coordination of a group of mobile robots, only the relative distances of neighbors are employed to achieve the system-level coordination, e.g., rendezvous, formation, swarming/flocking, connectivity preservation, and obstacle avoidance.

One objective

Dynamic models of mobile manipulators

Consider a group of N mobile manipulators. When taking the constraints of mobile robot platforms into account, the EL dynamics can be described by:Mi(qi)q¨i+Ci(qi,q˙i)q˙i+Gi(qi)+fi(q˙i)+di=τi+JiThi,Mi(qi)=[MbiMbmiMmbiMmi],Ci(qi,q˙i)=[CbiCbmiCmbiCmi],Gi(qi)=[GbiGmi],fi(q˙i)=[fbifmi],di=[dbidmi],τi=[τbiτmi],Ji=[Ai0JbiJmi],hi=[hbihei], where qi=[qbi,qmi]TRn denotes the vector of generalized coordinates with qbiRnb representing the generalized coordinates for the robot bases, and qmiRnm

Conclusions and open research issues

As an emerging field of research in robotics, collaborative robotic manipulation has been recently attracting more and more attention. This paper presented a brief technical review on collaborative robotic manipulation. The classification on coordination of fixed robot manipulators, mobile robots, and mobile manipulators was presented. Many existing issues and a variety of approaches were outlined for collaborative robotic manipulation. Some open problems and current research activities were

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    The work is supported by the National Research Foundation of Singapore (M4061925.048), Delta-NTU Corporate Lab Program with the project reference of Delta-NTU CORP-SMA-RP8.

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