Finite-Time Height Control of Quadrotor UAVs
Round 1
Reviewer 1 Report
The paper talks about a Finite-time height control of quadrotor UAVs which is a topic of great interest in the scientific community. Authors propose a closed loop height control method that estimate and compensate the unkoknown disturbances by use of ESO, twisting-controller and Sliding mode controller. Validation is made by means of Simulation.
Paper is well written and presented, howewer,in its current form I do not consider the contribution mature for publication before the following guidelines are developed
1)There is a repetition in the first three numbers of the bibliography.
2)Authors should discuss how parameters alfa, beta and k in the simulation experiments are choosen and possibly provide the results of some simulations with a different choice of these parameters.
3)It would be better, to improve readability, that the trends of the tracking errors were also shown in the graphs of the test results.
4)It is unclear whether the simulations were performed while keeping the quadrator in the same vertical position. If this is the case it would be interesting to show the altitude tracking performance when the quadrator performs maneuvers in which there are also lateral displacements.
5)Since the article talks about ADRC and ESO I suggest to include in the references these other two contributions which are very specific on the topic and would enrich the introduction section.
-1- "From PID to Active Disturbance Rejection Control", Han J., IEEE Transactions on Industrial Electronics 2009
-2- "Trajectory robust control of autonomous quadcopters based on model decoupling and disturbance estimation", Alonge et al,International Journal of Advanced Robotic Systems 2021
FInally, in my opinion, I suggest to accept the paper after a careful review of what is indicated.
The paper is well written in English, I suggest re-reading due to the presence of some typo.
Author Response
We would like to thank the reviewers for their careful assessments and constructive comments on our submission, particularly the time being spent. We take the reviewers’ view very seriously, and have made every possible effort in order to address the concerns raised by the reviewers and modify the paper according to his/her suggestions and comments. Furthermore, we have also corrected all the errors and typos.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper novelty and proposed solution benefit in scope to existed knowledge in UAV control should be clearly denoted.
The paper gives some simulation results, that need to be verified by the experimental tests.
The proposed method and obtained results should be compared with other methods existing in the literature.
The conclusion should be supported with countable main results.
"schema"
Author Response
We would like to thank the reviewers for their careful assessments and constructive comments on our submission, particularly the time being spent. We take the reviewers’ view very seriously, and have made every possible effort in order to address the concerns raised by the reviewers and modify the paper according to his/her suggestions and comments. Furthermore, we have also corrected all the errors and typos.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper proposes a dual closed-loop control solution with an estimator for compensating the disturbance in the height control of the quadrotor UAV type.
The paper presents the design methodology and demonstrates the viability of this solution through simulation.
It is recommended some improvements to be considered of the current version of the paper by addressing several problems such as:
line 85: There is uncommon to start chapter with a figure;
line 90: if possible a more distinctive symbol for external disturbance would be recommended to be used;
line 98: prior Lemma 1, a short motivation of its introduction is recommended;
Please confirm if eq. 22 is based on eq. 18 and the error vector from line 160 is derived as a product of composed functions?
line 108-109: statement seems unfinished "Assuming that the external disturbance ... in the formula is continuously differentiable and bounded.";
line 152: check if there is the expected statement "the error system of the height velocity" (is about system error?);
In eq. 29 please check the differentiating variable such that the expression to be consistent;
In fig. 2 would be indicated to have near the comparators the sign for each input;
line 211/248: after the relation of zd(t) the measurement unit would be better included in square brackets;
line 215-218/241-245: short introduction on how values for the mentioned parameters are selected is recommended to be introduced;
In the paper is mentioned the superiority of the proposed solution but that it is not illustrated in comparison with e.g. one of mentioned traditional approaches.
In Conclusions: remarks based on indices/numerical values would increase the value of the proposal. Eg. better response time, reduction in % of chattering, possible some robustness evaluation, etc.
Author Response
We would like to thank the reviewers for their careful assessments and constructive comments on our submission, particularly the time being spent. We take the reviewers’ view very seriously, and have made every possible effort in order to address the concerns raised by the reviewers and modify the paper according to his/her suggestions and comments. Furthermore, we have also corrected all the errors and typos.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thanks to the authors that answered all my concerns. The quality of the paper in its current form has been improved. There remains only a problem with equation 29 where there are question marks to fix.
Author Response
We hope this revised version is now suitable for publication in Applied Sciences.
Author Response File: Author Response.pdf
Reviewer 2 Report
1. Equation (29) displays with some typos "...e(?) d?
2. The conclusion still does not have the main results according to obtained control performance
3. The references should include not only linear methods but also nonlinear and robust, i.e. https://doi.org/10.1016/j.robot.2014.04.002
Author Response
We hope this revised version is now suitable for publication in Applied Sciences.
Author Response File: Author Response.pdf
Reviewer 3 Report
Some minor editing issues would be indicated, few of them being listed below.
In eq. 1 there is not clear why trigonometric functions are formatted as subscript;
lines 122/123/125/263: the updated notation for disturbance is not taken into account;
in eq. 29: the integration variable is not displayed correctly;
in line 230: instead of ß1 should be ßi?
the curves in fig. 10 seem too thick
In fig. 11 The labels at the bottom of the figures are partially cut ;
in line 310: "in this paper achieves a more desired result with instantaneous following features" but "the real response" does not overlap completely the "estimated" signal. Expressing the better performances by numerical values (eg. value of overshoot, transient response time, etc.), eventually tabulated, would be more concludent;
lines 325-326: "dual closed-loop control frame behaves better effects on zero overshoot and instantaneous following features", would be clearer to refer to a critically damped obtained response.
Author Response
We hope this revised version is now suitable for publication in Applied Sciences.
Author Response File: Author Response.pdf
