-->PONE-D-25-68774-->-->Gravity Compensation for Leachate Grid Cleaning Robots in Waste-to-Energy Plants: A Modeling and Simulation Study-->-->PLOS One

Dear Dr. Cao,

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PLOS One

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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: Partly

Reviewer #2: Yes

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-->2. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #1: Yes

Reviewer #2: Yes

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-->3. 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

Reviewer #2: Yes

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-->4. 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

Reviewer #2: Yes

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-->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 manuscript addresses a relevant engineering problem with a technically sound methodology. While the work is limited to simulation, it provides a solid theoretical foundation for future physical implementation. The writing is clear and the results are promising. I recommend minor revision to address the concerns outlined in the following, particularly regarding validation limitations and parameter documentation.

1. Expand validation discussion:Clarify that results are simulation-only and discuss implications for real-world implementation.

2. Strengthen limitations section:Include discussion of factors that could affect real-world performance.

3. Clarify parameter sources: Provide more detail on how stiffness values and other parameters were determined.

4. Technical corrections:

- Remove duplicate phrase at line 334

- Verify units consistency in Tables 3 and 4

- Improve figure placement relative to in-text references

5. Expand future work: Given that this is simulation-only research, the future work section should more clearly outline the path to physical implementation.

Reviewer #2: The manuscript presents a feedforward static gravity-compensation method for a hydraulically driven, rail-mounted 5-DOF manipulator intended to clean clogged leachate grids in waste-to-energy plants. The authors derive closed-form expressions for gravity-induced joint torques for Joints 2 and 3, model torsional compliance using reducer stiffness values (JS12 and SEA7), compute gravity-induced joint deflections via Hooke’s law, and apply a pre-compensation angle to the control inputs. The approach is validated entirely in Adams multibody simulations using the authors’ robot geometry and mass parameters; reported results show dramatic reductions in positioning error (≈92–97% reduction), with residual errors within ±0.1 mm, meeting the stated 0.5 mm engineering requirement. The paper is interesting and it can be published if the authors address the following concerns:

The conclusions repeatedly imply readiness for field deployment but all results are from idealized Adams simulations. Real hydraulic systems exhibit backlash, leakage, nonlinear friction, hysteresis in reducers, valve dynamics, servo-valve deadband, and sensor quantization—none of which are modeled. The claim of ±0.1 mm repeatable accuracy in a hydraulic manipulator (long-reach, weak-rigid) without closed-loop correction is unrealistic unless proven on hardware. The limitation is acknowledged (briefly) but is not treated with sufficient caution in the conclusions. Provide explicit caveats and reduce overstated claims until experimental data exist.

Modeling reducer + transmission as a single linear torsional stiffness (k) ignores nonlinearities (stiffness varying with angle/load), hysteresis and preload, and gear mesh/backlash. For hydraulic drives, compliant behavior may include rate-dependent terms. The simulation forces precise calibration (calibration to <0.01 mm) to succeed—this suggests the method is brittle to parameter uncertainty. Authors must quantify sensitivity of compensation to ±X% errors in stiffness, mass, and geometry (sensitivity analysis).

The method is static feedforward; yet the robot moves (albeit slowly). The paper assumes motions are slow enough to ignore dynamic torques, but joint accelerations, fluid dynamics in hydraulic lines, and end-effector reaction forces during unclogging (drilling into clogged debris) will produce additional torques and deflections. The paper does not model reaction forces seen during real unclogging—these could overwhelm the compensation and cause misalignment. Simulate scenarios with representative reaction forces and with small dynamic perturbations to demonstrate robustness.

Tables list link masses and reducer stiffness numbers but do not explain how stiffness values were measured or obtained (manufacturer datasheets? bench tests?). The paper states "stiffness values from Table 2" but does not document measurement methodology or uncertainty bounds. If values are from datasheets, typical datasheet figures are nominal and temperature/load dependent; include measurement or cite data source and include uncertainty.

The simulation calibration step “iterative adjustment until the end-effector position error at the calibration pose is <0.01 mm” is not practical on real long-reach hydraulic robots facing environmental noise. The paper must detail the calibration algorithm (what was adjusted? joint offsets? stiffness?) and provide sensitivity to calibration errors.

The review cites several gravity compensation and robot error compensation works (refs 17–29), but it omits important threads: (a) model-based compensation combining static/dynamic terms and sensitivity analyses in compliant robots; (b) studies on hydraulic actuator control uncertainties, valve dynamics, and compliance in hydraulic transmissions; (c) practical industrial implementations of gravity compensation on long-reach manipulators (including work on space cranes / boom arms / excavator-type manipulators). The authors must position their contribution relative to those bodies and clarify novelty.

How were the reducer stiffness values in Table 2 obtained (manufacturer spec, bench test, analytical model)? Provide measurement method and uncertainty bounds.

Please provide a sensitivity analysis: how does the residual end-effector error change for ±5%, ±10%, ±20% perturbations in (a) reducer stiffness, (b) link mass/inertia, and (c) joint zero offsets? Include worst-case scenarios.

How does the compensation perform if joint stiffness is nonlinear (e.g., k(τ) varying with torque) or when backlash exists? Provide simulation or analytical results for a simple backlash and for a nonlinear stiffness curve.

The simulation assumes frictionless revolute joints except torsional springs at J2/J3. Why is joint friction neglected? Please quantify the expected friction torques and show their impact.

The calibration procedure achieving <0.01 mm at P0—what parameters were adjusted? How many iterations were required? How sensitive is the calibrated solution to small temperature drift (you claim ±5% stiffness change over 0–60°C)?

Reaction forces during unclogging: what is the expected force/torque profile at the end-effector when penetrating compacted debris? Have you measured/estimated this? Please simulate several reaction-force profiles and show whether the compensation still maintains alignment within 0.5 mm.

Hydraulic dynamics: how do actuator dynamics (fluid compressibility, valve dynamics, deadband) influence the effectiveness of a static feedforward compensation? If the hydraulic servo introduces phase lag or compliance, is pre-compensation still valid? Provide modeling or justification.

Did you account for base compliance and rail mounting flex? The mobile base and rail coupling could introduce additional compliance—how are those effects modeled or mitigated?

Please provide the Adams model or an export (or at least the full kinematic/dynamic parameter tables) so reviewers can reproduce simulations.

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Reviewer #1: No

Reviewer #2: No

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-->PONE-D-25-68774R1-->-->Gravity Compensation for Leachate Grid Cleaning Robots in Waste-to-Energy Plants: A Modeling and Simulation Study-->-->PLOS One

Dear Dr. Cao,

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  May 03 2026 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.

Please include the following items when submitting your revised manuscript:-->

• A letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

-->If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Shamshad Alam, PhD

Academic Editor

PLOS One

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If the reviewer comments include a recommendation to cite specific previously published works, please review and evaluate these publications to determine whether they are relevant and should be cited. There is no requirement to cite these works unless the editor has indicated otherwise.

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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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: (No Response)

Reviewer #2: (No Response)

**********

-->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: (No Response)

Reviewer #2: (No Response)

**********

-->3. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #1: (No Response)

Reviewer #2: (No Response)

**********

-->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: (No Response)

Reviewer #2: (No Response)

**********

-->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: (No Response)

Reviewer #2: (No Response)

**********

-->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: I have carefully reviewed the revised manuscript. The authors have made comprehensive and detailed revisions in response to the previous review comments. Below is a summary of the review comments:

Overall Recommendation: Minor Revisions

The authors provided a comprehensive and detailed response to all review comments, significantly improving the scientific rigor and transparency of the manuscript.

Minor Issues Remaining

Data Availability Statement: It is recommended to explicitly state the method of data access (e.g., providing Adams model files as supplementary material).

Completeness of Sensitivity Analysis: It is necessary to confirm that the results of Section 4.2 are complete.

Figure 7 Caption: The phrasing is slightly awkward and needs adjustment.

Reviewer #2: (No Response)

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-->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.

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Reviewer #1: No

Reviewer #2: No

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[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". If this link does not appear, there are no attachment files.]

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NAAS will assess whether your figures meet our technical requirements by comparing each figure against our figure specifications.

-->

Gravity Compensation for Leachate Grid Cleaning Robots in Waste-to-Energy Plants: A Modeling and Simulation Study

PONE-D-25-68774R2

Dear Dr. Cao,

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.

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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,

Shamshad Alam, PhD

Academic Editor

PLOS One

Additional Editor Comments (optional):

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: I have carefully reviewed the revised manuscript. The authors have fully resolved all three minor issues from the previous round and made significant additional improvements to the manuscript.

Overall Recommendation: Accept

There are seven points of Significant Improvements in the New Version:

1. Expanded Literature Review: Added systematic reviews of compliant robot compensation, hydraulic system control, and long-arm manipulator applications (References [21]-[31]).

2. Static Assumption Validation: Quantitative proof provided (inertial torque <0.1% of gravitational torque).

3. Base/Rail Flexibility Analysis: FEA analysis proves that the maximum additional deformation is <0.02 mm.

4. Joint Friction Quantification: Estimated end-effector displacement caused by friction is 0.06–0.50 mm.

5. Dynamic Perturbation Simulation (New Section 4.3):

Scenario A: Dynamic perturbations have negligible impact (<5%).

Scenario B: Under a 200 N step load, the error remains below 0.2 mm.

6. Calibration Sensitivity: Even with a calibration residual of ±0.10 mm, the maximum error is below 0.15 mm.

7. Temperature Drift: A ±5% stiffness variation results in approximately 0.12 mm of error.

However, I suggest several Minor Corrections in the following:

1. Remove duplicate sentences in the Abstract.

2. Rename the title of Section 4.1 to avoid repetition.

3. Unify "slot" and "crevice" terminology.

Conclusion

The manuscript demonstrates scientific rigor and academic integrity, meeting all PLOS ONE publication criteria. It is recommended to Accept.

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-->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.

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Reviewer #1: No

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