Design and Simulation of a Seven-Degree-of-Freedom Hydraulic Robot Arm
Round 1
Reviewer 1 Report
This submitted work proposed a hydraulic robotic arm targeting for rescue missions. The preliminary design is conducted, which is investigated and optimized under finite element analysis. Simulations and experiments were done to validate the performance of the proposed platform in different possible working scenarios. Overall, the manuscript needs extensive revision on the writing, and the main concern is about the novelty of the proposed platform since the design is basically a common robotic arm and this kind of applications have been widely researched on both design and control aspects. The authors need to provide thorough and in-depth description to improve this issue along with other comments below before it is suitable for acceptance.
The references for the background introduction should be conducted with more up-to-date works in the field, most of the cited works are from over 5-10 years ago.
A discussion should be provided at the end of the introduction section to describe the contributions of this work compared against previous development in the field to demonstrate the novelty of this work.
The dimensions should be added on each component in Fig. 1 or Fig. 2
Can the authors provide some discussion of the limitations observed during the validation process?
Extensive editing of English language required
Author Response
Comments 1: The references for the background introduction should be conducted with more up-to-date works in the field, most of the cited works are from over 5-10 years ago.
Response 1: Thank you for pointing this out. I agree with this comment. I have updated the references, removing most of the literature that is from over 5-10 years ago, and there are now 17 papers in the last 5 years of literature.
Comments 2: A discussion should be provided at the end of the introduction section to describe the contributions of this work compared against previous development in the field to demonstrate the novelty of this work.
Response 2: Thank you for pointing this out. I agree with this comment. To clarify the purpose of the work and the contribution of this paper, I rewrote the final section of the introduction.
Introduction：In this study, a seven-degree-of-freedom hydraulic robotic arm for emergency rescue is proposed. A model of the robotic arm is built, and in order to reduce the weight of the robotic arm, 7075 aluminum alloy is used as the main body material. Milling is then used to remove any excess material from the robotic arm while still maintaining the strength of the device and ensuring that it meets the load premise of the ideal weight. This study builds the dynamics model under the two working scenarios of excavation and heavy lifting, and explores the finite element statics under these two working scenarios in order to test the strength of the robotic arm in the actual operation. The accuracy of the results of the finite element analysis was then confirmed by conducting stress-strain testing on a robotic arm prototype.
Comments 3: The dimensions should be added on each component in Fig. 1 or Fig. 2
Response 3: Thank you for pointing this out. I agree with this comment. I redrew Figures 1 and 2, adding dimensions to each component.The newly drawn pictures can be seen in the attachment.
Comments 4: Can the authors provide some discussion of the limitations observed during the validation process?
Response 4: Thank you for pointing this out. I agree with this comment. The findings and limitations of this paper are discussed in the discussion section.
Discussion: Based on the aforementioned simulation and experimental findings, it is clear that the robotic arm used in this study, which was built using aluminum alloy 7075, has the advantages of low weight and high load. The mechanism of the research robotic arm is not, however, the best-designed structure. To further lower the weight of the robotic arm, topology optimization of the structure might be done. Stress-strain tests were performed to determine the robotic arm's strength, and the results show that while the finite element results are quite descriptive, the relative errors for points 1, 2, 6, 8, and 13 are relatively large. This suggests that the accuracy of the testing apparatus and the testing procedure can be further optimized.
Comments 5: Extensive editing of English language required
Response 5: Thank you for your valuable and thoughtful comments. We have carefully checked and improved the English writing in the revised manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors,
1. In case of one affiliation, no need for number "1" superscript in the beginning of line 4.
2. Use semicolon (;) between keywords.
3. Try to choose the keywords from the following list:
https://www.ieee.org/content/dam/ieee-org/ieee/web/org/pubs/ieee-taxonomy.pdf
4. Add a space before citations.
5. Check the format of the MDPI citations and correct the citations according to the MDPI standards.
6. Add a "Conclusion" section.
7. Add an "Abbreviations" section to the end of the paper.
Best Regards
Author Response
Comments 1: In case of one affiliation, no need for number "1" superscript in the beginning of line 4.
Response 1: Thank you for pointing this out. I agree with this comment. I've removed the "1" at the beginning of line 4 in the latest manuscript.
Comments 2: Use semicolon (;) between keywords.
Comments 3: Try to choose the keywords from the following list.
Response 2&3: Thank you for pointing this out. I agree with this comment. In the latest manuscript, I used semicolons (;) between keywords and modified some of the keywords.
Keywords: Hydraulic robotic arm; Redundant manipulator; Manipulator dynamics simulation, Finite element analysis; Stress-strain experiments
Comments 4: Add a space before citations.
Response 4: Thank you for pointing this out. I agree with this comment. I've added a space before citations in the latest manuscript.
Comments 5: Check the format of the MDPI citations and correct the citations according to the MDPI standards.
Response 5: Thank you for pointing this out. I agree with this comment. I corrected the reference formatting according to MDPI formatting.
References：
- Takahashi, T.; Tadakuma, K.; Watanabe, M.; Takane, E.; Hookabe, N.; Kajiahara, H.; Yamasaki, T.; Konyo, M.; Tadokoro, S. Eversion Robotic Mechanism With Hydraulic Skeletonto Realize Steering Function. IEEE Robot. Autom. Lett. 2021, 6, 5413–5420, doi:10.1109/LRA.2021.3073653.
- Han, S.; Chon, S.; Kim, J.; Seo, J.; Shin, D.G.; Park, S.; Kim, J.T.; Kim, J.; Jin, M.; Cho, J. Snake Robot Gripper Module for Search and Rescue in Narrow Spaces. IEEE Robot. Autom. Lett. 2022, 7, 1667–1673, doi:10.1109/LRA.2022.3140812.
- Hagiwara, T.; Katou, Y. Trial Production of a Small Snake Type Robot That Can Be Mounted on a Disaster Rescue Robot. In Proceedings of the 2021 18th International Conference on Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology (ECTI-CON); IEEE: Chiang Mai, Thailand, May 19 2021; pp. 1104–1107.
……
Comments 6: Add a "Conclusion" section.
Response 6: Thank you for pointing this out. I agree with this comment. I made changes to the “Discussion” section and added a “Conclusion” section.
Conclusion: In this paper, we started from the structural design of the seven-degree-of-freedom redundant rescue hydraulic robotic arm, completed the 3D model assembly in Solidworks , and then completed the finite element static analysis and structural optimization design of the robotic arm according to the actual working conditions of the rescue robotic arm, which is lightweight and has high load and large working range. In ADAMS simulation software, a virtual prototype of the mechanical analysis of the rescue hydraulic robotic arm was built to simulate the two common working conditions of excavation and handling, and to analyze the force of the robotic arm, followed by finite element analysis of the key parts of the robotic arm. In order to verify the accuracy of the finite element static analysis method of the robotic arm in this paper, theoretical and practical research methods were used, and stress-strain experiments were conducted at important locations of the robotic arm according to the finite element analysis model, verifying the correctness of the finite element analysis method. In the future research, different advanced control strategies will be applied to the robotic arm to further validate its capacity.
Comments 7: Add an "Abbreviations" section to the end of the paper.
Response 7: Thank you for pointing this out. I agree with this comment. The "Abbreviations" section was added at the end of the article.
Abbreviations: SCARA----Selective Compliance Assembly Robot Arm; NSGA-II---- Nondominated sorting genetic algorithm II; 7-DOFs----- seven degrees of freedom; FEM----- Finite Element Method.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear authors,
The article deals with the issue of modelling, simulation analysis and experimental validation of a 7-DOF robot arm controlled through a hydraulic system.
The article is well-formed. The abstract and the conclusions are clear. Carrying out both simulations and test bench experiments is advantageous.
However, I have several questions and suggestions which should be addressed:
1. References: You provided a list of 33 references. However, there is not even a single reference from Actuators, while it is a journal you would like to publish in. You should better justify your subject as suitable for the journal.
2. Introduction: Singular citations of multiple references should be avoided (e.g. [1-10]).
3. Section 4.1: Grid independence analysis should be carried out. Parameters of the mesh accepted for further calculations should be provided (e.g. number of cells and nodes). Also, maybe some obtained maximum and average values of mesh quality parameters, like orthogonal quality, skewness or aspect ratio, could be added.
4. Equation (8) is incorrect. The factor 1/2 applies to all three expressions.
5. Experimental setup: locations of all measurement points presented in Table 5 should be marked on the arm view.
6. Result of experiments (1): The maximum measured stress in the experiments is below 10 MPa (point 9). However, the results of simulations indicate significantly higher values at some points. Can you justify if the measurement points were appropriately arranged?
7. Results of experiments (2): You declare that the difference between the simulated value and the experimentally measured stress value is not large. However, the low absolute error rate is due to the small stress values. In contrast, the relative error between the simulation and the experimental values is even several hundred per cent (e.g. points 1, 2, 6, 8, 13). Can you comment on these results?
Regards,
Author Response
Comments 1: References: You provided a list of 33 references. However, there is not even a single reference from Actuators, while it is a journal you would like to publish in. You should better justify your subject as suitable for the journal.
Response 1: Thank you for pointing this out. I agree with this comment. I've updated the references in the manuscript to include 4 references from actuators.
Comments 2: Introduction: Singular citations of multiple references should be avoided (e.g. [1-10]).
Response 2: Thank you for pointing this out. I agree with this comment. In the revised manuscript, I made changes to that section.
Introduction: Over the past decades, different types of rescue robots have been developed, such as snake-shaped SAR robots [1–3], bionic crawling SAR robots [4,5], wheel-footed robots with enhanced obstacle-crossing capabilities [6–8], aircraft-based rescue robots [9,10], rope-assisted climbing robots for applications in mountainous environments [11], and de-formable robots for water rescue [12].
Comments 3: Section 4.1: Grid independence analysis should be carried out. Parameters of the mesh accepted for further calculations should be provided (e.g. number of cells and nodes). Also, maybe some obtained maximum and average values of mesh quality parameters, like orthogonal quality, skewness or aspect ratio, could be added.
Response 3: Thank you for pointing this out. I agree with this comment. In the revised manuscript, I performed a mesh independence analysis, as in Figure 30; and provided mesh parameters for each component, as in Table 4. Figure 10 and table 4 can be seen in the attachment.
Comments 4: Equation (8) is incorrect. The factor 1/2 applies to all three expressions.
Response 4: Thank you for pointing this out. I agree with this comment. This is a small oversight, and the formulas used in the processing of the experimental data are all correct.
Comments 5: Experimental setup: locations of all measurement points presented in Table 5 should be marked on the arm view.
Response 5: Thank you for pointing this out. I agree with this comment. All measurement points were labelled on the robotic arm as shown in Figure 35. Figure 35 can be seen in the attachment.
Comments 6: Result of experiments (1): The maximum measured stress in the experiments is below 10 MPa (point 9). However, the results of simulations indicate significantly higher values at some points. Can you justify if the measurement points were appropriately arranged.
Response 6: Thank you for pointing this out. I agree with this comment. In the experimental process, we will adjust the machinery to its almost unstressed posture, at this time for the patch of strain gauges, and then zero the strain gauge channel, and then hang a heavy object on the end of the mechanical arm, adjusted to the stressed posture, recorded the hydraulic cylinder stroke, to be stable strain gauge readings for the numerical record, repeat the above process at the same point, remove the deviation from the value of the larger, and then take the average value. However, in practice, there is no precise measurement of the unstressed attitude of the robotic arm, so there will be a deviation between the experimental and theoretical values, which is difficult to be eliminated by repeating the experiment many times. Therefore, when arranging experiments, we try to measure different points on different parts as much as possible to observe the force on the robotic arm.
Comments 7: Results of experiments (2): You declare that the difference between the simulated value and the experimentally measured stress value is not large. However, the low absolute error rate is due to the small stress values. In contrast, the relative error between the simulation and the experimental values is even several hundred per cent (e.g. points 1, 2, 6, 8, 13). Can you comment on these results?
Response 7: Thank you for pointing this out. I agree with this comment. As mentioned above, the experimental process, there will be a certain deviation between the theoretical value and the experimental value, in the case of small force, due to its own base is small, its reflection to the theoretical value and the actual value of the ratio will be larger.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thanks for addressing the comments.
Reviewer 3 Report
Dear Authors,
You made most of the suggested amendments.
In my opinion, the article may be published.
Regards,
