Cooperative Target Enclosing and Tracking Control with Obstacles Avoidance for Multiple Nonholonomic Mobile Robots
Round 1
Reviewer 1 Report
ID: applsci-1581058-peer-review-v1
Title: Cooperative Target Enclosing and Tracking Control with Obstacle Avoidance for Multiple Nonholonomic Mobile Robots
The focus of the paper is on the investigation of the cooperative control problem for a group of autonomous mobile robots. The robots are required collaboratively enclosing and tracking a stationary or moving target in a circular formation. Authors proposed a distributed coupling controller scheme consisted of target encircling, phase positioning, spacing assignment and avoiding obstacles.
The topic may be interest of UAV and robotics researchers as it may have applications in modern robotic applications. However, I have some comments about content of the paper. Please see the following comments:
- My main issue with this paper is that some terms have not defined properly. For example, “avoiding obstacles” and “collision” are not defined in this paper. Please provide a rigid definition of them.
-Another major issue with this paper is its theorem. I do not think their proofs are important enough to be in the body of the paper. Can authors please move them to the appendix of the paper?
-As I know, a single entity optimizes the operation of the multiple robots in centralized control. However, the decisions are taken locally and negotiations can take place, or may take place, as the different robots usually have different goals in decentralized control. I do not see a discussion about it in the paper.
Can authors please add this description to the paper (either in Section 1 or 3 where the controller design is explained) and see if their manuscript is close to any of these designs.
-The use of English is not good, and consequently the paper requires a proofread. Let me give some examples. Never use etc. at the end of a series that begins with for example, e.g., such as, and the like, because these terms make etc. redundant: they already imply that the writer could offer other examples.
Page 1: applications, such as vehicles or fleets escorting and patrolling [1,2], space and ground exploration [3,4], autonomous search and rescue [5,6], cooperative pursuit and surveillance [7,8], environment monitoring and sampling [9,10], etc.
-I would like to see a list of more possible applications after references 1-10 in the first paragraph of the paper. Robotic warehousing can be briefly added to the list with following citations, which also studied collision-free robot movements. [a] Optimization of an automated storage and retrieval systems by swarm intelligence, Procedia Engineering, vol. 100, pp. 1309-1318 [b] A cross-entropy method for optimising robotic automated storage and retrieval systems, International Journal of Production Research, vol. 56, no. 19 pp. 6450-6472
-Other errors:
Page 4: Figure 1.For this reason --> Figure 1. For this reason
Page 4: we consider to move --> we consider moving
Page 5: where it also express --> where it also expresses
Page 6: Proof of Theorem 1. Denote --> Proof. Denote
Page 7: Proof of Theorem 2. Let --> Proof. Let
Page 9: shown in Figure 3-5 --> shown in Figures 3-5
…
Page 12: shown in Figure 7-9 --> shown in Figures 7-9
Page 13: a evenly distributed circular --> an evenly distributed circular
Page 15: speeds of the three robot --> speeds of three robots
The paper benefits from a proofread.
Author Response
Question1: My main issue with this paper is that some terms have not defined properly. For example, “avoiding obstacles” and “collision” are not defined in this paper. Please provide a rigid definition of them.
Answer: Thank you for your valuable comments. In this paper, we add strict definitions or explanations for some terms in Section 1. For example, “For the former, cooperative circumnavigation is that a group of autonomous robots circumnavigate the stationary or moving target with prescribed radius, circular velocity, and inter-robot angular spacing [17].” (the first sentence of the third paragraph); “However, the problem of collision avoidance between agents was only considered, ignoring the fact that there may be other obstacles in the actual environment.” (the last sentence of the third paragraph); “For the latter, cooperative following generally address some specific missions that do not need to rotate around the goal for energy saving or some practical purposes …” (the first sentence of the fourth paragraph); “In addition, the obstacles avoidance problem of circular formation that includes adjacent agents and surrounding obstacles is rarely considered.”(the second sentence of the fifth paragraph); …
Question2: Another major issue with this paper is its theorem. I do not think their proofs are important enough to be in the body of the paper. Can authors please move them to the appendix of the paper?
Answer: Thank you for your valuable comments. I don't think these proofs need to be placed at the appendix of the paper. When a theorem is proposed, it will be followed by the proof of the theorem, which can help readers understand each component of the reasoning process more clearly, especially for the analysis of the stability of the proposed control law. In addition, to some complex theorem proofs, they will be considered to move them to the appendix of the paper. The proof of the two theorems proposed in this paper is simple and clear, which is more convenient for readers to clearly understand a complete proof process of the convergence of the control objectives.
Question3: As I know, a single entity optimizes the operation of the multiple robots in centralized control. However, the decisions are taken locally and negotiations can take place, or may take place, as the different robots usually have different goals in decentralized control. I do not see a discussion about it in the paper. Can authors please add this description to the paper (either in Section 1 or 3 where the controller design is explained) and see if their manuscript is close to any of these designs.
Answer: Thank you for your valuable comments. The architecture of the traditional multi-robot system can be divided into centralized and decentralized. The centralized architecture uses a host computer as the central decision-making unit to monitor the movement of the group and release control commands to coordinate the movement of each robot. Centralized control is very effective for single or a small number of robots, which can enable each robot to obtain global information and the optimal solution through the planning methods. However, the disadvantage is that any failure of the central decision-making unit may lead to the failure of the whole system. In addition, the centralized method cannot be scaled well. As the number of robots in the formation increases, it leads to huge communication overhead, and the processing speed of the main control unit is required to be high, so communication is also a bottleneck problem. In distributed control, there is no main control unit, and the authority of each robot is equal. Each robot has autonomous decision-making and the ability to exchange information with the rest of the robots. The advantage of the decentralized architecture is that it has good robustness and scalability for the failure of a single robot or the interruption of communication. At present, most of the cooperative control problems of multi-robot systems mainly use distributed control methods, so this paper does not discuss these two control methods too much.
In this paper, we adopt a decentralized control method, so that each robot can communicate with each other without relying on the main control unit for centralized control. And the controller we designed can arbitrarily increase or decrease the number of robots without causing problems such as system failure. The proposed controller is to control multiple non-holonomic robots to cooperatively enclose and track a static or moving target. Each robot can sense the states of the target and nearby robots, and then adjust its position.
To address the three issues raised in Section 2, we present the detailed controller design process in Section 3. The distributed coupling controller scheme consisted of target encircling, phase positioning and spacing assignment as well as avoiding obstacles. In addition, we give detailed design methods and theorem proofs for three parts.
Question 4: The use of English is not good, and consequently the paper requires a proofread. Let me give some examples. Never use etc. at the end of a series that begins with for example, e.g., such as, and the like, because these terms make etc. redundant: they already imply that the writer could offer other examples.
Page 1: applications, such as vehicles or fleets escorting and patrolling [1,2], space and ground exploration [3,4], autonomous search and rescue [5,6], cooperative pursuit and surveillance [7,8], environment monitoring and sampling [9,10], etc.
Answer: Thank you for your valuable comments. We have re-edited this article several times to correct various errors.
Question 5: I would like to see a list of more possible applications after references 1-10 in the first paragraph of the paper. Robotic warehousing can be briefly added to the list with following citations, which also studied collision-free robot movements. [a] Optimization of an automated storage and retrieval systems by swarm intelligence, Procedia Engineering, vol. 100, pp. 1309-1318 [b] A cross-entropy method for optimizing robotic automated storage and retrieval systems, International Journal of Production Research, vol. 56, no. 19 pp. 6450-6472.
Answer: Thank you for your valuable comments. We had access to the references you provided, mainly for automated storage and retrieval systems, which may be somewhat different from the multi-robot cooperative control in this paper. However, we have reconsidered multi-robot cooperative object transportation in robotic warehousing. Please refer to [1,2] in the References section at the end of this article.
Question 6: Other errors:
Page 4: Figure 1.For this reason --> Figure 1. For this reason
Page 4: we consider to move --> we consider moving
Page 5: where it also express --> where it also expresses
Page 6: Proof of Theorem 1. Denote --> Proof. Denote
Page 7: Proof of Theorem 2. Let --> Proof. Let
Page 9: shown in Figure 3-5 --> shown in Figures 3-5
…
Page 12: shown in Figure 7-9 --> shown in Figures 7-9
Page 13: a evenly distributed circular --> an evenly distributed circular
Page 15: speeds of the three robot --> speeds of three robots
The paper benefits from a proofread.
Answer: Thank you for your valuable comments. We have re-edited this article several times to correct various errors.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
- it is necessary to divide the introduction section into the introduction itself and the section and with related works. in the section with works, consider more formally the advantages and disadvantages of existing methods
- add links to newer studies (2019 аnd younge)
- it is necessary to add a comparison with analogues.
- it is necessary to justify the shape of the field for the experiments
Author Response
Question 1: it is necessary to divide the introduction section into the introduction itself and the section and with related works. in the section with works, consider more formally the advantages and disadvantages of existing methods.
Answer: Thank you for your valuable comments. We have greatly revised the introduction, which has been divided the introduction into two parts: introduction itself (first two paragraphs of the introduction) and with related works (the rest of the introduction). In the third paragraph, we compare the advantages and disadvantages of the cooperative circumnavigation control methods in these cited literature. In the fourth paragraph, we also compare the advantages and disadvantages of the cooperative following control methods. In addition, in the fifth paragraph, the disadvantages of these methods are summarized in detail, and the main contributions of the work are provided to solve these problems.
Question 2: add links to newer studies (2019 and younger)
Answer: Thank you for your valuable comments. We added some newer studies (2019 and younger), such as [1,2, 13-16, 17] in the references section of the article.
Question 3: it is necessary to add a comparison with analogues.
Answer: Thank you for your valuable comments. In the introduction, we summarize the advantages and disadvantages of the existing control algorithms, and put forward our own improvements. In the fifth paragraph of the introduction, we added a comparison with analogues.
Question 4: it is necessary to justify the shape of the field for the experiments
Answer: Thank you for your valuable comments. Limited to the requirements of the experimental site, we choose the underground parking lot for conducting experiments. The experimental site is wide and the shape of the field for the experiments is a rectangle, which can meet the experimental test environment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
I have read the paper once more, with focus on highlighted paragraphs. Authors could not resolve all issues I have mentioned in the previous revision, but the paper has a significant improvement in the current revision.
As such, I believe that the paper can be accepted as it is.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
