A Formation Control and Obstacle Avoidance Method for Multiple Unmanned Surface Vehicles
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this paper, the authors propose a collision avoidance method considering the combination of artificial potential field and virtual structure method, adopting a leader-follower formation structure for application in unmanned surface vehicles (USV).
The paper presents an interesting proposal and contributes to the field of knowledge on the application of motion control in unmanned systems. Considering the results presented, some corrections to the paper should be considered before publication.
1- The figures with the results in section 5 could be grouped together. I recommend grouping 3 figures on the same line, this formatting makes it easier to visualize the results;
2- A graph with the variation in travel speed must be included in section 5. The travel time from point A to point B and the variation in speed is important for future comparisons with other methodologies. It is also important to determine whether there is a speed limit for the proposed method.
3- The authors only considered static obstacles in the simulations. However, it is important and relevant to analyze moving obstacles. I recommend including an analysis of the reliability of the proposal for obstacles that may be moving.
4- After the corrections, the abstract and the conclusions must be rewritten.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe paper deals with formation control and obstacle avoidance method for multiple unmanned surface vehicles. The topic is clearly emerging and fully in the scope of the journal and of the special issue "Autonomous Marine Vehicle Operations". The structure and concept of the paper are clear and the language quality is appropriate for a journal. However, there are few issues to be mentioned:
1) I am not sure that USV environment is more complex than for UAV and UGV, this sentence should be justified in deeper detail.
2) I would annotate axis in all Figures (see e.g. Fig. 11)
3) May be different zoom in horizontal axis could be done in Fig. 5. in order to see the important details.
4) Please check "Fres", I guess this is a typo and it should be "Frep".
5) Also please doublecheck equation (9) if it is written properly.
6) May be the model of the leader and follower is quite simplified. There could be more advanced constraints on how to change heading, velocity etc, namely based on real dynamics, different mass and other aspects of real USV. More detailed comments on that issue will be appreciated.
7) I would add more comments on future research visions to Conclusion section. For example, it could be mentioned some experiments in real-world environment are foreseen and how to deal with disturbances in physical environment.
8) Please add units to all tables wherever relevant.
9) More references to authors previous works would be nice in order to track the research baseline.
10) How complicated will be the change to other types of obstacles and areas than "cirle-like".
11) I would increase also the overall number of references as this is a journal paper.
12) Finally, I would revise also the English, there are some minor typos, see e.g. "regrarded".
Clearly, there are also many positive aspect like: nicely elaborated state-of-the-art in Introduction, clear description of main formation control methods in Section 3, precise description of algorithm, high quality references (lots of impact journals) etc.
Despite above mentioned comments, I think the paper could be updated and revised again.
The English quality is OK for the journal, only minor final edit is required.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsYour paper does not highlight your contribution over the vast options of formation strategies using APF and VS found in literature for autonomous vehicles.
Your simplified model of the USV can be the same as an UAV or a UGV, you han an interesting oportunity if consider the perturbations of the environment in the control law design.
Please make a thorough literature review in order to identify your contribution
Comments on the Quality of English Languageminor typesetting revision is required
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors made the requested corrections and clarifications, submitting a new version that can be accepted for publication.
Author Response
We appreciate the time and effort that you dedicated to providing feedback on our manuscript and are grateful for the insightful comments on and valuable improvements to our paper. Thank you for your nice comments on our manuscript.
Reviewer 3 Report
Comments and Suggestions for AuthorsThis version of the paper is worth to be published. The authors must make another experiment without the saturation in the control law (original PF formation controller) in order to determine the benefits they claim the saturation will provide. Other suggestions include:
Improve writing, you are repeating words in a single paragraph, such as method.
Line 268 change i in the parenthesis with j
Line 288 Im(.) does not stands for imaginary part?
It is not clear the definition of the group in simulation what do you mean with the 3 evenly spaced USVs on each side? That makes a 9-vehicle group? Because simulation results and figure 8 only show 6 elements.
I suggest including position error graphs to determine in a quantitative way if the vehicles maintain formation, because in figures 9 and 10 it can only be inferred qualitatively.
Include a comparison with the same experiment without the velocity saturation, in order to assess the benefits of your proposal.
What happens if the group does not start in final formation?
Comments on the Quality of English LanguageMinor grammar editing is required
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
