A decentralized approach for the aerial manipulator robust trajectory tracking

Yarai Elizabeth Tlatelpa-Osorio; Hugo Rodríguez-Cortés; J. Á. Acosta

doi:10.1371/journal.pone.0299223

Peer Review History

Original SubmissionNovember 2, 2023
28 Nov 2023 Decision Letter - Gang Wang, Editor PONE-D-23-34692A decentralized approach for the aerial manipulator robust trajectory tracking.PLOS ONE Dear Dr. Tlatelpa-Osorio, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Please submit your revised manuscript by Jan 12 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. 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Additional Editor Comments: Some minor revisions should be made based on the reviewers' suggestions before acceptance. [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: Yes Reviewer #2: Yes ******** 2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: Yes ****** 3. Have the authors made all data underlying the findings in their manuscript fully available? 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Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #1: Yes Reviewer #2: Yes ****** 5. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #1: This paper aims to propose a new control strategy for an unmanned aerial manipulator (UAM). First, an equivalent model is proposed to equate the 2-revolute links robotic manipulator model to the 1-revolute, 1-prismatic links robotic manipulator model. Then based on this equivalent model, this paper designs a distributed controller for UAW for tracking. After careful reading, I have the following concerns. 1. The background introduction of the article is very detailed, but it seems that it is not clearly stated in the contribution section of the article which problems existing in the above-mentioned existing work are solved by this paper. 2. The structure of the article is quite messy, and I didn't find any basis for such an equivalent transformation. I also found no description of how this equivalence method simplifies the stability analysis. 3. In the section describing the UAM dynamics model, it is written that this paper considers a robotic manipulator to have two revolute joints, but in the simulation section, it is stated that the proposed controller is designed considering a quadrotor with a manipulator composed of a revolute joint and a prismatic joint. 4. The description of the simulation scene settings in the simulation part of the paper is insufficient, and the figures of the simulation scenes do not show what the author wants to prove. 5. The writing format of this paper is very irregular, especially the references section. Reviewer #2: This article proposes a Decentralized Robust Control Strategy for unmanned aerial manipulators in the presence of external disturbances. The author proposes an equivalent dynamic model that facilitates analysis and can be used to analyze the complete properties of the system. Overall, this article has sufficient workload and also provides a complete analysis and simulation process. Here are my suggestions. 1.The paper fail to mention the differences and advantages and disadvantages between centralized and decentralized control, and why decentralized control strategies should be adopted. 2.The format of the paper still needs to be checked and modified. For example, in the last paragraph of the Introduction, the Roman numerals after the section cannot be displayed. 3.The images in the paper are very blurry, and I cannot see the parameters of UAV and other values in the last image clearly. ****** 6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #1: No Reviewer #2: No ******** [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". 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Revision 1
17 Jan 2024 Author Response Please see the document "Response to Reviewers", there the format is clearer. Thank you in advance. Reply to Rewiever #1 R1: This paper aims to propose a new control strategy for an unmanned aerial manipulator (UAM). First, an equivalent model is proposed to equate the 2-revolute links robotic manipulator model to the 1-revolute, 1-prismatic links robotic manipulator model. Then based on this equivalent model, this paper designs a distributed controller for UAM for tracking. } Comment. Thanks for the time you devoted to revise our work. R1: After careful reading, I have the following concerns. 1. The background introduction of the article is very detailed, but it seems that it is not clearly stated in the contribution section of the article which problems existing in the above-mentioned existing work are solved by this paper.} Response. Thanks for this comment, which made us realize we needed to clarify this contribution in the manuscript. We have rewritten part of the introduction section to highlight the problem with previous works and our contribution. We notice that in most works addressing the Aerial Manipulator control by the decentralized approach, the interaction between the two dynamic sub-systems, robot arm, and UAV, is not studied, just neglected or somehow compensated, either it is only assumed that the dynamic interaction between the manipulator and the aerial vehicle can be treated as exogenous disturbances acting on each sub-system or neglected. Thus, as far as we know, the only work theoretically treating the interaction is in previos works, but only at the kinematic level of the robot arm, which means that, in practice, the analysis is only valid for slow movements when the accelerations can be neglected. This interaction is essential as the UAV dynamics are a part of the robotic arm dynamics, and the Newton-Euler Recursive algorithm helped us clarify it. Thus, in our proposed contribution, we deeply analyze the interaction at a dynamic level, not just at the robot arm kinematics, as in \\cite{acosta2020accurate}. This study has two main new outcomes: 1) being able to demonstrate that the interaction between the two subsystems can be treated as exogenous perturbations by proposing a novel equivalent transformation that allows designing an estimator for the torques and forces of the interaction, and 2) the estimator paves the way to design a controller capable of tracking prescribed trajectories with exponential convergence, a robust property highly desirable in practice. We emphasize that this analysis is missing in the literature, normally avoided with assumptions such as slow motion, which are not practical because there may be external disturbances such as gusts of wind that cause high accelerations. Indeed, in the simulation section, we show good performance under unexpected external wind gusts, thanks to the in-the-loop estimator. 2. The structure of the article is quite messy, and I didn't find any basis for such an equivalent transformation. I also found no description of how this equivalence method simplifies the stability analysis. Response. Thanks for your comments. The content is reorganized, and some of the section’s names have been modified as follows. Section: UAM dynamic model. Subsection: Quadrotor dynamic model. Subsection: Robotic manipulator dynamic model. Section: Decentralized robust control strategy. Subsection: Quadrotor exogeneous disturbances estimator. Subsection: Quadrotor position and attitude control. Subsection:Robot arm controller based on the equivalent model. Subsection: UAM closed loop dynamics. Subsection: Stability analysis. Section: Numerical simulations. In the beginning of Section Decentralized robust control strategy, we have added the following paragraph: The control design is divided into two control loops: the inner loop is a state feedback controller that customizes the robotic manipulator effects on the aerial vehicle as an exogenous disturbance (C4D), generating a decentralized UAM dynamic model. In contrast, the outer control loop uses the decentralized model and independently applies control strategies for the quadrotor and robotic arm. We first present the C4D state feedback and then the estimator of the quadrotor exogeneous moments and forces (EQEMF). We have re-state a phrase to better clarify the difference between the two closed-loop systems, from: The UAM closed-loop dynamics (10)–(12) with the controller (13)–(15) results into: ' The UAM dynamics (10)–(12) with the inner loop controller RC4D (13)–(15) results in ... ' In regards of the comment about the stability analysis simplification we can say that the proposed coordinate transformation reveals the exogenous nature of the interaction forces in the equivalent dynamics, and therefore enables the design of the estimator and the subsequent stability analysis. 3. In the section describing the UAM dynamics model, it is written that this paper considers a robotic manipulator to have two revolute joints, but in the simulation section, it is stated that the proposed controller is designed considering a quadrotor with a manipulator composed of a revolute joint and a prismatic joint. Response. We thank this reviewer for this comment; after re-reading it, we agree that the explanation is unclear. One of the main contributions of this work is that we re-formulate the two revolute joints manipulator (1R2R) by a prismatic and a revolute joints (1R1P). Then, we design the control strategy for the 1R1P manipulator. Therefore, using the diffeomorphism transformation of Definition 1 in the simulations section, we can ‘mathematically translate’ the designed control strategy on the 1R2R joint manipulator for its implementation. Although this step might seem straightforward, it has been included for clarity of presentation. 4. The description of the simulation scene settings in the simulation part of the paper is insufficient, and the figures of the simulation scenes do not show what the author wants to prove. Response. Thanks for the comments, now we added more information about the simulation scenario as well as an improvement on the figures presented. 5. The writing format of this paper is very irregular, especially the references section. Response. Thank you. We have carried out a complete revision of the manuscript to improve the reading. Reply to Reviewer #2 This article proposes a Decentralized Robust Control Strategy for unmanned aerial manipulators in the presence of external disturbances. The author proposes an equivalent dynamic model that facilitates analysis and can be used to analyze the complete properties of the system. Overall, this article has sufficient workload and also provides a complete analysis and simulation process. Comment. Thank you for the time you devoted to reviewing our work and for highlighting the key points and the overall workload assessment.\\\\ Here are my suggestions. 1.The paper fail to mention the differences and advantages and disadvantages between centralized and decentralized control, and why decentralized control strategies should be adopted. Response. Thanks for your comment. In the introduction section, we have pointed out a reference that highlights the characteristics of the centralized and decentralized approaches. There is no crucial reason to follow one method or the other; however, the decentralized approach fits better with the attributes of the proposed disturbance estimator. 2.The format of the paper still needs to be checked and modified. For example, in the last paragraph of the Introduction, the Roman numerals after the section cannot be displayed. Response. Thanks for this observation, We carried out a complete revision of the manuscript and attended the problems with the format. 3.The images in the paper are very blurry, and I cannot see the parameters of UAV and other values in the last image clearly. Response. We changed the last image and added two tables, one with the physical parameters and other with the controller gains. Also, the quality of the images containing the error dynamics time evolution were revised. Attachments Attachment Submitted filename: Response to Reviewers.pdf* https://doi.org/10.1371/journal.pone.0299223.r002
6 Feb 2024 Decision Letter - Gang Wang, Editor A decentralized approach for the aerial manipulator robust trajectory tracking. PONE-D-23-34692R1 Dear Dr. Tlatelpa-Osorio, We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication. An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org. If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. Kind regards, Gang Wang Academic Editor PLOS ONE Additional Editor Comments (optional): The reviewers' remaining concerns have been resolved and the revised paper is recommended for acceptance. Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation. Reviewer #1: All comments have been addressed ******** 2. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: Yes ****** 3. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes ****** 4. Have the authors made all data underlying the findings in their manuscript fully available? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #1: Yes ****** 5. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #1: Yes ****** 6. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #1: The authors carefully revised the manuscript in accordance with the reviewers' comments. The paper describes the innovations clearly, the theoretical derivation is adequate and the simulation data are sufficient. ****** 7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #1: No ******** https://doi.org/10.1371/journal.pone.0299223.r003
Formally Accepted
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