Kinetostatics of a Snake Robot with Redundant Degrees of Freedom
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis paper proposes a kinetostatic approach based on matrix transformation and screw theory for analyzing and calculating the joint torques of a super redundant snake robot. This paper employs the proposed kinetostatic method to calculate the joint torques of a real super redundant snake robot and compares the calculation process of this method with the traditional static equilibrium method. The effectiveness of the proposed method is verified, and it has certain advantages in terms of computational efficiency. Despite the significant contributions made by this paper in the analysis and calculation of the kinetostatics of snake robots, the reviewer still has some confusion:
1. In the section (3.1), the author mentions that because there is a certain mathematical relationship between angular velocity and joint rotation angle, Equation (6) can be derived into Equation (7). However, in terms of expression, Equation (6) and Equation (7) appear to have the same form. This has caused confusion for the reviewer.
2. In the fifth chapter, the author mentions that the static equilibrium method requires solving the inverse of a matrix, which is more computationally expensive than solving the product of a matrix and a vector as required by the screw kinetostatics method. Therefore, the conclusion that "the computational cost of the static equilibrium method is much lower than that of the screw kinetostatics method" may cause confusion for the reviewer.
3. The titles of both the second and third chapters mention the snake robot, especially the title of the second chapter is "Structure of the super redundant snake robot". While the author chooses to use the phrase "a flexible robot" in the title of section (3.2) and the fourth chapter. Although the snake robot can be understood as a type of flexible robot, this mode of expression may cause some confusion for the reviewer.
Comments on the Quality of English LanguageEnglish is good for reading
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe work presented in this manuscript is about the study of kinetostatics of a snake robot with redundant degrees of freedom. The work can be considered for possible publication in this journal shall the following points be addressed.
(1) It is suggested to change the title from "Kinetostatics of a super redundant snake robot" to "Kinetostatics of a snake robot having redundant degrees of freedom". The use of "super redundant snake robot" means the sanke robot is "super redundant" which is not the same as the snake robot has super redundant degrees of freedom.
(2) The work is interesting and the approaches used were appropriate. However, the writing may need a bit of improvement to allow readers catching up the key points the author tried to deliver.
(3) Equations (8), (9), (11), (12) showed $i but were not clearly explained until way back in line 190 and equation (18). The sympols shall be explained directly and clearly the first time mentioned.
(4) Figure 4 may need much improvement to show the details for each joint.
(5) Each of the plots in Figure 5 is not clear. Graphical improvments are required.
(6) Figure 6 shows calculated results of joint torques. Does the title for each plot refers to specific joint? I mean does "Motion1" for the snake robot's 1st joint torque? Also, it is suggested that all the plots in this figure to have the same scale for vertical axis.
(7) Same confusion was observed for Figure 7. So what is the difference between the "calcuated" and "simulated" results in Figure 6, and Figure 7, respectively? What are the significances between the two?
(8) The work is interesting. However, the authors may need to clearly address the novelty in kinetostatics for the model snake robot. Are the method applied new to the research community? What is implication of the kinetostatics analysis to the snake robot's movement? Since the robot has redundant DOF, it will be more interesting to see results of its inverse kinematics rather than simply looking into its joint motor's torque.
Comments on the Quality of English Language
The quality of the use of English in this article is okay to understand. However, much improvement may be needed shall the manuscript is aimed at academic journal level.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis manuscript proposed a computational method based on a kinetostatic model for joint torque analysis of redundant robots. The approach itself is of interest to many roboticists. However, the insufficient verification and presentation significantly lower the quality of this paper. The comments are listed below.
1. As described at the end of Section 1 (lines 75 to 76), the authors should provide the experimental results using the prototype to reinforce the simulation analysis.
2. The reviewer could not completely understand the entire construction of the proposed method until reading Sections 5 and 6. I recommend providing a schematic figure that explains the structure of the method and computation procedure in Section 3.
3. It will be more effective to emphasize the differences by adding the computational structure and procedures of conventional methods along with the proposed method in the figure.
4. To support the conclusion, it is suggested to show the dynamic equations of motion of the model to be compared and explain which specific computations are simplified by the proposed method. Without this, it is unclear by what principle the computational cost is reduced.
5. The verification and analysis of the proposed method are insufficient. The simulation analysis was done only in specified conditions with a fixed trajectory, and its scope of feasibility is unclear. As the authors mentioned in Section 1, the reviewer guessed that the challenge of this study is to address the consideration of acceleration parameters by the kinetostatics method. As stated in the title, please show that this method can be applied to more agile movements of a snake robot.
i. At the very least, the calculated result and the ADAMS simulation results should be deeply analyzed in quantity by comparing them with overlapping graphs.
ii. Further analysis should be performed at different motion frequencies and waveform profiles, such as triangular or rectangular waves, and the scope of applicability of the method should be shown.
iii. The reviewer recommends showing the calculation results of the proposed method and conventional methods from previous studies and comparing them in terms of calculation cost and accuracy.
6. The explanation of the snake robot was insufficient, and the reviewer couldn’t fully understand its mechanical structure.
i. On line 79, it says "nine equal modules," but what does that refer to?
ii. What do “Robot” and “Segment” in Fig. 1 correspond? There is no explanation in the text. Which part corresponds to the snake robot? Which part is the head?
iii. It is hard to know the mechanical structure of the robot and its joint definitions only with Fig. 1. Also, the relationship between the left-top figure and the right-bottom figure in Fig. 4. Where the origin of the coordinate system is on the left-top figure?
7. The definition of S and $ in equations (8) and (9) appeared in equations (18)-(20), and it is too far from the original equations. Also, it may be hard to understand the equations in Section 3.1 without Fig. 4 and the contents at the beginning of Section 3.2. Please reorganize the structure of Section 3.
8. Minor comments: Numerous errors, mistakes, and typos are found in this manuscript. Please seriously re-read the entire paper several times and revise it.
- line 61: Zhao et al.
- The explanation in lines 93-97 is unclear. Kinematics and Kinetics are confused. Please explain it precisely.
- Equations (6) and (7) are overlapping. Probably (6) is incorrect.
- Should line 181 refer to Fig. 2?
- J in equation (24) is undefined.
- Table 4 is not explained in the text. What was it used for?
Comments on the Quality of English LanguageThe authors need to polish the English throughout entire the manuscript.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsAll my comments and questions have been implemented and answered. The manuscript is ready for publication in this journal.
Author Response
Thank you very much for your positive comments.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe overall structure and methodology of the research are now more precise thanks to some figures added by the authors. What still disappointed the reviewer is that no actual experiments were conducted. Is this method only applicable in a zero-gravity environment? If so, please state clearly in the paper. Also, such a calculation method should be better evaluated by implementing it in an actual machine using computational cost and accuracy to prove its effectiveness. If you do not conduct experiments, you should remove the last sentences in the introduction: "Finally, an experimental prototype system is built and used for gluing operations within narrow spaces. The experimental results indicate that robot can complete all flexible operations in narrow and complex space." Then, explain how reasonable results can be obtained without conducting experiments.
Comments on the Quality of English LanguageMinor errors are still remained.
Author Response
Please see the attached response.
Author Response File: Author Response.pdf
