Enhanced Trajectory Tracking via Disturbance-Observer-Based Modified Sliding Mode Control
Round 1
Reviewer 1 Report
The authors introduced enhanced trajectory tracking technique based on a sliding mode control (SMC) with a PID sliding surface and a saturation function-based ESO. The work is interesting and the following points are recommended to better improve it.
(1) The authors should better clarify the novelty of the work compared with previous works [27,30-34,35-37, 38].
(2) It is better to describe why employing a nominal model of the control system is a difficult job.
(3) It is better to state additional specific potential applications of the presented technique.
(4) Comparisons with related works, mentioned in (1) above, should be presented. What are the execution time and complexity of computations required for the proposed technique.
(5) It is better to use a second form for system dynamics f in Eq.(74), i.e. more complex than {5 xdot}.
(6) The estimated perturbation and actual perturbations in the system can be plotted in different simulation cases.
(7) Please define all terms in (77-78).
(8) What is the possible future work for this study?
Author Response
Thank you very much for your comments. It helped us to improve the quality of our work.
Author Response File: 
Author Response.docx
Reviewer 2 Report
In this study, a sliding mode control (SMC) with a pro-13 partial-integral-derivative (PID) sliding surface is designed and integrated with an extended state observer (ESO) based on saturation function-14. The article is well-written and well-organized. Although I am unfamiliar with this field, it is intuitive that the logic and experiment of this article are correct.
Here are my concerns:
1. Are many formulas necessary? The formulas and their symbols may require more explanation.
2. The sentence that leads to the formula should be ":" instead of "; ". , the full text has this problem; please check carefully.
3. Adding a large illustration to describe the method used in the article and the problem to be solved is suggested, which can improve the article's readability.
4. The experiment's curves are very smooth; is this in line with the actual situation?
Author Response
Thank you very much for your comments. It helped us to improve the quality of our work.
Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript discusses an enhancement for trajectory tracking. The added value is the sliding mode control and the improvements are shown in the simulations. In terms of scientific content, the discussed topic is valuable and worth studying. The way authors handle the topic is clear except in Section 2. Section 2 is just the mathematical formulations that are hard to follow and disturb the reader's attention. Section 2 has to be rewritten with explanations and an idea flow diagram. In terms of structure, the paper is well-prepared and easy to follow. The introduction point out the added value of the study.
Some other comments:
The legends of the Figures are missing for Figures 1 and 2. What do the blue and red lines represent what do they mean? These should be re-checked.
The quality of the English language is good. The structure is well prepared and the manuscript is well written.
Author Response
Thank you very much for your comments. It helped us to improve the quality of our work.
Author Response File: Author Response.docx
Reviewer 4 Report
See the attached file.
Comments for author File: 
Comments.pdf
Author Response
Thank you very much for your comments. It helped us to improve the quality of our work.
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
I am satisfied with the improvements.
The language level is convenient for a scientific paper.
Reviewer 4 Report
This paper can be accepted.
