A Novel Fish-Inspired Robot with a Double-Cam Mechanism
Round 1
Reviewer 1 Report
The paper describes a mechanism for modulating undulate motion based on the double-cam mechanism. It is a very interesting area of research because scientists are not able to design as efficient propulsion systems as real fish have.
The proposed topic of a novel fish inspired robot is a little bit exaggerated. There are a lot of similar fish-inspired robots, many of them tested in the open water reservoirs. That is why the title can be changed to refer to a novel double-cam mechanism instead of a novel fish-inspired robot.
The literature review is modest and a little out of date in connection to the new designed fish-inspired vehicles. There are many new designs that should be taken into consideration and the results achieved should be compared. Almost the same fish-inspired robot can be found in papers:
http://www.roboticsproceedings.org/rss12/p11.pdf
https://doi.org/10.3390/biomimetics5040046
So the novelty can be defined as the mechanism, not to the whole fish.
Line 73: “Currently, several bionic fish with single joints have been developed. In 2008…” Since that time many new fish-inspired robots were designed and tested. A good review can be found in the paper:
https://www.sciencedirect.com/science/article/pii/S0029801819308261?via%3Dihub
There are also some used definitions like “mechanical efficiency”. Let me propose the paper where efficiency is defined in many aspects:
https://iopscience.iop.org/article/10.1088/1748-3190/10/4/046013
Also, it is not practical to use the undulating propulsion system parameters in reference to selected parameters. It is much better to use dimensionless variables like for example the Strouhal number.
There is no information on how the crucian carp movement was identified and described? Also, haw the parameters in equation (1) were calculated. There is a paper where the calculation is presented using a genetic algorithm, but in this paper, there is no method presented nor the paper citation where that method can be found:
https://www.sciendo.com/article/10.2478/pomr-2020-0025
and as can be seen from the paper this is not an easy task. The description of how the parameters were calculated should be explained.
The fish was fabricated using 3D printing technology, but what kind of material was used? There are many materials used in 3D printing technology. Also, it could be desired to put detailed information on what kind of blushless DC motor was used. Is it rotate continuously or in the 0-180 degree range?
In the text, there are imprecise definitions like: “stable swimming”, “is similar to” “good flexibility”.
The flexibility can be measured, you can investigate the paper:
https://www.sciendo.com/article/10.2478/pomr-2020-0078
or if the material used is commonly used in industry, the parameters should also be available.
The experiments were provided for two types of double-cam mechanisms. How was the movement pattern was calculated for tail swinging frequency in the range 0-4Hz? In Fig.7 the characteristic grows to the square of swinging frequency. The range should be wider or recalculated in respect to The Strouhal number. This is because the Strouhal number is the best way to compare the real fish parameters to the artificial one. The shape of the characteristics has a similar shape as presented in the paper linked below, but please focus on the thrust characteristic as a function of frequency oscillation and then compare it to the results as a function of the Strouhal number.
https://www.mdpi.com/1996-1073/14/24/8418
Other similar designs worth comparing:
https://www.fujipress.jp/main/wp-content/themes/Fujipress/pdf_subscribed.php
Some minor suggestions:
in line 123 “l” should be written in italics.
In equations (1) and (2) there is an extra gap after sin: ?in___(…)
In equation 3 the Xc and Yc refer to the B point position? If yes it could be confusing with a description of point “C”…
The distance L is between point O and A as depicted in Fig. 1 or between O and B as described in the text?
The trigonometric function is used, but there is no description of where is the rectangular angle. In line 193 the expression is put without the explanation of what one of the variables refer to.
Author Response
Dear reviewer,
Thank you very much for your hard work. We have revised our manuscript carefully according to your comments. All the revisions in the new manuscript are highlighted in red.
We have made changes in the manuscript and reply as follows.
Comment: The proposed topic of a novel fish-inspired robot is a little bit exaggerated. There are a lot of similar fish-inspired robots, many of them tested in the open water reservoirs. That is why the title can be changed to refer to a novel double-cam mechanism instead of a novel fish-inspired robot.
Answer: Thank you for the valuable advice. We agree with you that the main contribution of this fish-inspired robot is using a double-cam mechanism and it is better to show the main character in the title of this paper. We have modified the title to “A novel fish-inspired robot with a double-cam mechanism”.
Comment: The literature review is modest and a little out of date in connection to the newly designed fish-inspired vehicles. Many new designs should be taken into consideration and the results achieved should be compared. Almost the same fish-inspired robot can be found in papers:
http://www.roboticsproceedings.org/rss12/p11.pdf
https://doi.org/10.3390/biomimetics5040046
So the novelty can be defined as the mechanism, not to the whole fish.
Answer: Thank you for your comment. You are right that fish-inspired robots are very widely researched and there are also many new fish-inspired robots developed in this field. We have added some new papers relative to our research topic in the revised manuscript, including the paper suggested by you.
Comment: Line 73: “Currently, several bionic fish with single joints have been developed. In 2008…” Since that time many new fish-inspired robots were designed and tested. A good review can be found in the paper:
https://www.sciencedirect.com/science/article/pii/S0029801819308261?via%3Dihub
So the novelty can be defined as the mechanism, not to the whole fish.
Answer: Thank you for your suggestion. As you said, we have read this good review paper and cited it in our manuscript. You got our main contribution very accurately and correctly, and the novelty in our work is the new mechanism rather than the whole fish robot.
Comment: There are also some used definitions like “mechanical efficiency”. Let me propose the paper where efficiency is defined in many aspects:
https://iopscience.iop.org/article/10.1088/1748-3190/10/4/046013
Also, it is not practical to use the undulating propulsion system parameters about selected parameters. It is much better to use dimensionless variables like for example the Strouhal number.
Answer: Thank you for your helpful comment. We read the paper provided by you and it is helpful for us to describe the efficiency of our fish-like robot. We agree with you that dimensionless variables are better to be used and we used the Strouhal number according to your comment in the revised manuscript.
Comment: There is no information on how the crucian carp movement was identified and described? Also, haw the parameters in equation (1) were calculated. There is a paper where the calculation is presented using a genetic algorithm, but in this paper, there is no method presented nor the paper citation where that method can be found:
https://www.sciendo.com/article/10.2478/pomr-2020-0025
and as can be seen from the paper this is not an easy task. The description of how the parameters were calculated should be explained.
Answer: Thank you for your good comment and question. It is necessary to obtain the undulatory motion data from real fish swimming to design the parameters of the double cam mechanism, which requires high-quality video. Unfortunately, our team can’t take it by ourselves. We found a video from Harvard University which shows perfect caringform swimming motion. We processed this video and extract the features of each frame. The fitting method is used to calculate the parameters in equation (1).
Comment: The fish was fabricated using 3D printing technology, but what kind of material was used? There are many materials used in 3D printing technology. Also, it could be desired to put detailed information on what kind of blushless DC motor was used. Is it rotate continuously or in the 0-180 degree range?
Answer: Thank you for your question. We have re indicated the information of materials and motors in the manuscript. The material of the fish head (including the head and the anterior part of the body) was UV curable resin and the tensile modulus is 1600mpa while the bending modulus is 1300mpa. We use Maxon DCX 32L motor with a GPX32A reducer and an Escon Module50/5 servo controller, and the information of motors is as follows:
|
Parameter |
Value |
|
Norminal voltage U/V |
24 |
|
Norminal speed n/rpm |
453 |
|
Norminal torque T/NM Norminal current I/A Reduction ratio |
0.57 2.87 5.3:1 |
Comment:In the text, there are imprecise definitions like: “stable swimming”, “is similar to” “good flexibility”.
The flexibility can be measured, you can investigate the paper:
https://www.sciendo.com/article/10.2478/pomr-2020-0078
or if the material used is commonly used in industry, the parameters should also be available.
Answer: Thank you for your suggestion. As you said our wording is not rigorous enough, we have explained it further in the revised manuscript. Regarding the question of “stable swimming”: The frequency and amplitude of fishtail swing can be viewed as constant values when the fish swimming speed does not change significantly after some time and we consider this state to be stable swimming. Regarding the question of “is similar to”: the swimming posture is similar to that of real fish such as the fish in the video above and the video which can be found in reference[18]. Regarding the question of “good flexibility”, we supplement the relevant data of the material. The tensile modulus is 1600mpa while the bending modulus is 1300mpa.
Comment: The experiments were provided for two types of double-cam mechanisms. How was the movement pattern was calculated for tail swinging frequency in the range 0-4Hz? In Fig.7 the characteristic grows to the square of swinging frequency. The range should be wider or recalculated in respect to The Strouhal number. This is because the Strouhal number is the best way to compare the real fish parameters to the artificial one. The shape of the characteristics has a similar shape as presented in the paper linked below, but please focus on the thrust characteristic as a function of frequency oscillation and then compare it to the results as a function of the Strouhal number.
https://www.mdpi.com/1996-1073/14/24/8418
Other similar designs worth comparing:
https://www.fujipress.jp/main/wp-content/themes/Fujipress/pdf_subscribed.php
Answer: Thank you for your question and suggestion. Our two movement patterns are achieved using different cam profiles. During the design, we designed two cam profiles (in section 2) according to the simulated motion curve of real fish and cycloid motion curve. According to the designed cam structure, both different movement patterns can be realized. According to your suggestion that adding the strouhal number can better compare the swimming efficiency of different swing patterns, we have supplemented the relevant icons. The results show that the strouhal number of the robot fish under the real fish motion is lower than under the cycloid motion law, which indicates that the robotic fish is more efficient under the real fish motion.
Some minor suggestions:
Comment:in line 123 “l” should be written in italics.
Answer: Thank you for your careful review of the article, we have corrected it.
Comment: In equations (1) and (2) there is an extra gap after sin:
Answer: Thank you for your careful review of the article, we have deleted the extra gap after sin:.
Comment: In equation 3 the Xc and Yc refer to the B point position? If yes it could be confusing with a description of point “C”
Answer: Thank you for your suggestion. Equation 3 refers to point C, point B is the swing trajectory of the fishtail under the action of the conjugate cam, and points C and D are the theoretical contours of the two conjugate cams.
Comment: The distance L is between point O and A as depicted in Fig. 1 or between O and B as described in the text?
Answer: Thank you very much for spotting this typo, L refers to the distance between O and C.
Comment: The trigonometric function is used, but there is no description of where is the rectangular angle. In line 193 the expression is put without the explanation of what one of the variables refers to.
Answer: Thank you for the reminder, we have corrected it in the manuscript, We have changed to , and lp is the length of the swinging part of the caudal fin.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Overall, the paper is well written and organized with a proper length. The topic is of interest for this journal publication of this work can be considered. My overall opinion of this paper is quite good, however, some content presented is not clear enough. The work has potential for publication but, I would suggest major revision as follow:
1/ In the introduction, it is suggested that the novel index of this paper should be explained in detail. And the introduction should be added to do a better job of explaining the existing methods and why they are or are not valuable. The authors reviewed and summarized some existing methods relating to their work. Nonetheless, they have not clearly highlighted what novelty they have proposed in the manuscript. The novelty of the manuscript should be highlighted more specifically in this part.
2/ Benefit of the proposed method is not clear. This should be clarified. The objective/problem statement needs to be explained. What are the novelties of the proposed method? what the research challenges/motivations of the paper are?
3/ Write the organization of the paper in the introduction part.
4/ There are some overlaps in the text in the paper (same phrases and sentences). It shouldn't be cut-and-paste. For example, lines 18-19 in the abstract and lines 374-375 in the conclusion have the same sentences. The authors should check all paper again.
5/ In section 3, a sub-section “Assumptions” should be added to make the problem clearer. All assumptions and physical constraints should be provided. How many degrees of freedom DOF is applied in the underwater vehicle system? The author can refer to the “Assumptions” section of the following paper: https://doi.org/10.3390/s20051329
6/ A detailed block diagram of the proposed approach should be added to clarify the design procedure and structure.
7/ The parameters of the system used in all equations should be given in the paper.
8/ The presentation of the paper can be improved and the quality of some figures should be enhanced, i.e, Figures 2, 3, 4, 7, 8, and 9.
9/ The explanations and analysis of the results should be enriched to show the validity of the data. More discussions should be given to clearly demonstrate the limitations/validity of the obtained results, i.e, discuss more Figure 2.
10/ Detailed implementation information should be provided (hardware, software, configuration, settings). A detailed discussion of hardware and software applied to the mining vehicle should be mentioned. Provide specifications of the hardware and software used for simulation of the approach. Because there is not enough data on this paper, the research results on the core idea of this paper seem unreliable.
11/ More comparison results to other solutions are welcomed. It is highly expected the proposed approach is compared with the existing ones to demonstrate that it is novel and valid. The authors can demonstrate the comparison in the result section.
12/ It is better to show the simulation results by using the numerical program then compare them with the experiment results.
13/ Obviously, the performance of the underwater vehicle is affected by environmental disturbances such as wind, wave, and current. There is no result robustness under the disturbance. The author needs to give more detailed data references or results.
14/ Some items in section References refer to the middle of the last century. Is it possible to replace these items with the newer ones?
15/ English writing needs improving. The manuscript writing can be further polished with professional English. The manuscript can be thoroughly revised for grammar check. For example, in line 198, “Equation (8) and (9)” should be “Equations (8) and (9)”. The title of this paper “Novel” should be “novel” and so on. Please check all the paper.
Author Response
Dear reviewer,
Thank you very much for your hard work. We have revised our manuscript carefully according to your comments. All the revisions in the new manuscript are highlighted in red.
We have made changes in the manuscript and reply as follows.
Comment: In the introduction, it is suggested that the novel index of this paper should be explained in detail. And the introduction should be added to do a better job of explaining the existing methods and why they are or are not valuable. The authors reviewed and summarized some existing methods relating to their work. Nonetheless, they have not highlighted what novelty they have proposed in the manuscript. The novelty of the manuscript should be highlighted more specifically in this part.
Answer: Thank you for your suggestion. According to your suggestion that in the manuscript the novel index is not clear enough and have reworked the supplementary explanation, we have modified the title to “A novel fish-inspired robot with a double-cam mechanism”, and the novelty of the article is mainly reflected in the double cam structure. The conjugate cam mechanism is applied to the robotic fish while the motor just rotates continuously, and the different wave motions of the robotic fish can be realized under the condition that the motor has a constant speed. By setting the profile of the double cam mechanism, the robotic fish can be made to swim according to a specific movement form.
Comment: The benefit of the proposed method is not clear. This should be clarified. The objective/problem statement needs to be explained. What are the novelties of the proposed method? what the research challenges/motivations of the paper are?
Answer: Thank you for your question and suggestion. This paper proposes a design method of a single-joint bionic robotic fish based on a conjugate cam mechanism, which can realize a specific tail swing of the robotic fish under the uniform rotation of a single motor, which greatly reduces the requirements for the accuracy of the control system, and also improve the precision of the robot fish's motion. Furthermore, by changing the profile of the cam, various swinging postures can be imitated.
Comment: Write the organization of the paper in the introduction part.
Answer: Thank you for your suggestion. The organization of this article is as follows. In Section 2, the calculation method and process for designing the cam profile according to the pattern of motion are described. In Section 3, a kinetic analysis to solve for the required drive torque for the two motion patterns is given. In Section 4, the overall structure design and fabrication are described. Section 5 shows the experiments and results. In last, Conclusions of our work are shown.
Comment: There are some overlaps in the text in the paper (same phrases and sentences). It shouldn't be cut-and-paste. For example, lines 18-19 in the abstract and lines 374-375 in the conclusion have the same sentences. The authors should check all papers again.
Answer: Thank you for your suggestion. We have revised the content in the abstract as follows: “According to the experimental results, we can find that the swimming speed of the robotic fish is different under various wave motions. When other conditions are the same, the speed that the robot fish can achieve by imitating the swing motion of the real fish is 1.5 times that of the robot fish doing the cycloid motion.”
Comment: In section 3, a sub-section “Assumptions” should be added to make the problem clearer. All assumptions and physical constraints should be provided. How many degrees of freedom DOF is applied in the underwater vehicle system? The author can refer to the “Assumptions” section of the following paper: https://doi.org/10.3390/s20051329
Answer: Thank you for your suggestion. We gave the assumptions as follows: “It is very difficult to calculate the interaction forces that fluid acts on the irregular surface of the fish. Here we assume that the forces acting on the skin of the fish are equal to acting on the projected neutral surface of the robotic fish to make the theoretical problem to be simplified.” Besides, the degrees of freedom DOF is one in the underwater vehicle system.
Comment: A detailed block diagram of the proposed approach should be added to clarify the design procedure and structure.
Answer: Thank you for your suggestion. We added a detailed block diagram of the proposed approach as follows
Comment: The parameters of the system used in all equations should be given in the paper.
Answer: Thank you for your suggestion. We calculated the profile of the cam after a real fish, and we also provide the video source that can be found in [18]. In addition, in line 193 the expression, We have changed to , lp is the length of the swinging part of the caudal fin. Besides, In Equation(14), J is the moment of inertia of the tail; is the angular acceleration of the tail.
Comment: The presentation of the paper can be improved and the quality of some figures should be enhanced, i.e, Figures 2, 3, 4, 7, 8, and 9.
Answer: Thank you for your suggestion. we have repaired and improved all of the figures mentioned by you in the revised manuscript.
Comment: The explanations and analysis of the results should be enriched to show the validity of the data. More discussions should be given to demonstrate the limitations/validity of the obtained results, i.e, discuss more Figure 2.
Answer: Thank you for your suggestion, we have re-illustrated Figure 2 as follows: In Fig. 2 we show the theoretical profiles of the cams that achieve the two wave motions. The cams can rotate around the center of rotation. The robot fish is equipped with these two cams to realize the movement of real fish and cycloid movement.
Comment: Detailed implementation information should be provided (hardware, software, configuration, settings). A detailed discussion of hardware and software applied to the mining vehicle should be mentioned. Provide specifications of the hardware and software used for simulation of the approach. Because there is not enough data on this paper, the research results on the core idea of this paper seem unreliable.
Answer: Thank you for your suggestion. In the experiment, a camera is fixed and hung above a swimming pool (3.6mmÍ2mmÍ1mm), to record the video of the robotic fish passing through its field of view (as shown in Figure 6), and analyze the speed of the robotic fish. To drive the robotic fish, a brushless DC motor (Maxon DCX 32L motor with a GPX32A reducer and an Escon Module50/5 servo controller, parameters are shown in Table2.) is used. A lithium battery with 2000 mAh is used as the power source. To make the system compact and easily manipulated, an Arduino Nano board based on ATmega328 was selected as the lower controller, where Bluetooth and wireless communication modules were embedded to transmit the commands. And the specifications of the motor are as follows:
|
Parameter |
Value |
|
Norminal voltage U/V |
24 |
|
Normial speed n/rpm |
453 |
|
Normial torque T/NM Normial current I/A Reduction ratio |
0.57 2.87 5.3:1 |
Comment: More comparison results to other solutions are welcomed. It is highly expected the proposed approach is compared with the existing ones to demonstrate that it is novel and valid. The authors can demonstrate the comparison in the result section.
Answer: Thank you for your suggestion. Adding some comparisons as you mentioned can better reflect the characteristics of the robotic fish. However, the approach proposed in our work is different and the main contribution in this paper is to give a double-cam mechanism to imitate different swing motions for the fish-like robot, and as we knew there is no other research that shows a similar function. If we focus on one swing motion, maybe the swimming performance is not different between our design and others. Currently, we did not find sufficient data to do the comparison experiments and we hope in further work, this work can be done
Comment: It is better to show the simulation results by using the numerical program then compare them with the experiment results.
Answer: Thanks a lot for your suggestion. We agree with you. The numerical simulations are useful to guild the experiments to some extent because in many cases the physical system is difficult to be fabricated and costs much. However, in our work, the valuable simulation is difficult to be done because it is very difficult to obtain the accurate value of practical conditions such as the accurate shape and flexibility of the skin of the robot. We hope to evaluate the performance of the proposed system with the physical experiment and the experimental results can be believed to prove the efficiency of the proposed method.
Comment: Obviously, the performance of the underwater vehicle is affected by environmental disturbances such as wind, wave, and current. There is no result robustness under the disturbance. The author needs to give more detailed data references or results.
Answer: Thanks for your suggestion. You are correct that all these factors such as wind, waves, and so on will affect the performance of the proposed robot. In this work, we just consider an ideal environment, and the experiment is also conducted in our lab. In the future, we will discuss the robustness of the proposed robot under some disturbance.
Comment: Some items in section References refer to the middle of the last century. Is it possible to replace these items with the newer ones?
Answer: Thank you for your valuable suggestion. We added some new papers in the revised manuscript from Ref [16] to Ref [21], including the paper provided by you. Thank you very much again.
Comment: English writing needs improving. The manuscript writing can be further polished with professional English. The manuscript can be thoroughly revised for grammar check. For example, in line 198, “Equation (8) and (9)” should be “Equations (8) and (9)”. The title of this paper “Novel” should be “novel” and so on. Please check all the papers.
Answer: Thank you very much for your suggestion. We have revised all writing problems you mentioned in the new manuscript.
Author Response File: Author Response.pdf
Reviewer 3 Report
The article is very relevant subject and written in high level.However, there are some points that need to be corrected, so I recommend a Minor revision of the article.
The title of the article completely corresponds to it.
Comments:
- The article does not understand where the authors get data on the actual movement of fish. (wherever this data is available, the source must be indicated).
- The experimental setup, how the data was captured, and the equipment with what accuracy are not properly described.
- Most charts are of poor quality, they need to be reworked.
Author Response
Dear reviewer,
Thank you very much for your hard work. We have revised our manuscript carefully according to your comments. All the revisions in the new manuscript are highlighted in red.
We have made changes in the manuscript and reply as follows.
Comment: The article does not understand where the authors get data on the actual movement of fish. (wherever this data is available, the source must be indicated).
Answer: Thank you for your suggestion. We have added the source of the video in the manuscript [18]. We processed the data of video and capture the motion features of the fish, which is used in our work.
Comment: The experimental setup, how the data was captured, and the equipment with what accuracy are not properly described.
Answer: Thank you for your comment. In the experiment, a camera is fixed and hung above a swimming pool (3.6mmÍ2mmÍ1mm), to record the video of the robotic fish passing through its field of view (as shown in Figure 6), and analyze the speed of the robotic fish. To drive the robotic fish, a brushless DC motor (Maxon DCX 32L motor with a GPX32A reducer and an Escon Module50/5 servo controller, parameters are shown in Table2.) is used. A lithium battery with 2000 mAh is used as the power source. To make the system compact and easily manipulated, an Arduino Nano board based on ATmega328 was selected as the lower controller, where Bluetooth and wireless communication modules were embedded to transmit the commands. And the specifications of the motor are as follows:
|
Parameter |
Value |
|
Norminal voltage U/V |
24 |
|
Normial speed n/rpm |
453 |
|
Normial torque T/NM Normial current I/A Reduction ratio |
0.57 2.87 5.3:1 |
Comment: Most charts are of poor quality, they need to be reworked.
Answer: Thank you for your suggestion. we have repaired and improved Figure 2, 3, 4, 7, 8 and 9 in the revised manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
In a general way, most of my comments were answered by the authors. The manuscript now is acceptable for publishing.
