Unknown Input Observer-Based Fixed-Time Trajectory Tracking Control for QUAV with Actuator Saturation and Faults

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this article, trajectory tracking control problem of a quadrotor unmanned aerial vehicle is investigated under external disturbances, inertia uncertainties, actuator faults, and input saturation. Fixed-time UIO is designed for disturbance estimation without the requirement of disturbance (or its derivative) upper bound. The topic is interesting and some significant results are presented. The detailed comments are

 

1.       Grammar and formatting can be checked carefully again throughout the paper to improve the presentation.

2.       Unlike to other works, input saturation refers to rotor speed saturation in this paper. The difference of rotor speed saturation and thrust or torque saturation can be further clarified?

3.       How to obtain the derivative of speed  in Equation 26?

4.       Why introduce a new state  in the process of observer design? Please explain it detailly.

5.       What are the advantages of proposed observers compared with other observers? The advantages should be emphasized in Conclusion.

Comments on the Quality of English Language

In this article, trajectory tracking control problem of a quadrotor unmanned aerial vehicle is investigated under external disturbances, inertia uncertainties, actuator faults, and input saturation. Fixed-time UIO is designed for disturbance estimation without the requirement of disturbance (or its derivative) upper bound. The topic is interesting and some significant results are presented. The detailed comments are

 

1.       Grammar and formatting can be checked carefully again throughout the paper to improve the presentation.

2.       Unlike to other works, input saturation refers to rotor speed saturation in this paper. The difference of rotor speed saturation and thrust or torque saturation can be further clarified?

3.       How to obtain the derivative of speed  in Equation 26?

4.       Why introduce a new state  in the process of observer design? Please explain it detailly.

5.       What are the advantages of proposed observers compared with other observers? The advantages should be emphasized in Conclusion.

Author Response

We would like to thank the reviewer for his feedback. Thank you also for the constructive comment which was useful to improve the quality of our paper. We have carefully considered all the comments in this revised version. The revised points are marked up with the yellow color in the manuscript. Please see the new version and our reply below for more details.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors

The rotational and translational movement are coupled in Quadrotor systems. On what basis you have decoupled and derived the control.

Atleast few experimental results are expected. How do you validate these kind of nonlinear control algorithms.

Introduction, abstract and conclusion may be improved with more technical contents. 

what is the maximum external wind load it can tackle. If you could give a variation from minimum to maximum for all these parameters of uncertainity then it will be nice supported with simulation results. 

The simulation and comparison part can be improved for writing and technicality

Comments on the Quality of English Language

The english writing may be improved in the entire manuscript

Author Response

We would like to thank the reviewer for his feedback. Thank you also for the constructive comment which was useful to improve the quality of our paper. We have carefully considered all the comments in this resubmitted version. The revised points are marked up with the blue color in the manuscript. Please see the new version and our reply below for more details.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

 

Please see my review on the manuscript titled ‘Unknown Input Observer-Based Fixed-time Trejectory Tracking Control for QUAV with Actuator Saturation and Faults’.

Title: appropriate, describes the manuscript’s content

 

Abstract: Results missing, please add outcome of this research specifically, not only in general description of applied methods.

 

Keywords: the keywords describe the manuscript, adequately.

The manuscript is structured unlike the usual required one: Introduction, Literature background, Methods, Results, Discussion. Instead the following main parts are for the main chapters, hence I add errors and questions to these part, if any arised.

Introduction: Primary literature is presented well here, the relevant definitions are presented here.

 

Mathematical Model and Problem Formulation:

Problem formulation is

LINE 217 instead of sig^p sign^p should be used.

Control schemes:

 

Simulation and Comparisons:

 

Conclusion: it is not detailed, and does not contain secondary literature. Please, add more.

 

Discussion: it is recommended to have one, please add it.

 

Reference list: The cited literatures are relevant and well-edited into the content.

 

Figures and tables:

Fig. 2 is very elegant and describes the method parts and order very well, however the font size should be bigger. Although, the article is going to be available online, and in its digital form zooming is an option, but in print, it is not good enough.

On the Fig. 3., the legend is almost unreadable: too small font size, similar case with the axis labels --- Please enlarge those!

Fig. 4 is okey.

Fig. 5 and 6. same as previous, but the inserted subfigures are even smaller, please find other way for their presentation e.g. enlargement and replacement

Same with Fig. 7, 8, 9, and 10. In addition, on Fig. 8, the actual curve cannot be seen since it is too lime green light.

Comments on the Quality of English Language

It has a good quality, only minor mispellings occur.

Author Response

We would like to thank the reviewer for his feedback. Thank you also for the constructive comment which was useful to improve the quality of our paper. We have carefully considered all the comments in this revised version. The revised points are marked up with the red color in the manuscript. Please see the new version and our reply below for more details.

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

This paper presents unknown input-observer based trajectory tracking control for the quadrotors which may be subject to external disturbances, inertia uncertainties, actuator faults, and input saturation. The control is decoupled into translational and rotational sub-systems and input-observed are designed for both. 

Some of the contributions/advantages include:

1. Fixed-time convergence of error

2. No prior knowledge of upper bound required

3. Using the saturation constraint over the rotor speed instead of thrust/torque. 

4. Figures presented are good/high quality

5. Simulations presented shows the efficacy of the designed controller

 

Concerns: 

3D trajectory plot is missing in the simulations, please include that if possible. 

 

 

Comments on the Quality of English Language

English language is fine, minor edits may be required. 

Author Response

We would like to thank the reviewer for his feedback. Thank you also for the constructive comment which was useful to improve the quality of our paper. We have carefully considered all the comments in this revised version. The revised points are marked up with the green color in the manuscript. Please see the new version and our reply below for more details.

Author Response File: Author Response.docx

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

I looked at the revised version and I am okay with the publication of the current paper.

Comments on the Quality of English Language

English quality is good, minor spell checks might be needed.