Adaptive Nonsingular Fast Terminal Sliding Mode Control of Aerial Manipulation Based on Nonlinear Disturbance Observer
Round 1
Reviewer 1 Report
The paper has proposed a new control aerial manipulation consisting of a quadrotor UAV and with a two degree of freedom manipulator. To achieve better control performance, based on an established dynamic model of the manipulation, a new controller was designed, which combined the adaptive controller and the nonsingular fast terminal sliding mode controller. The paper name the new controller as adaptive nonsingular fast terminal sliding mode controller. Furthermore, to compensate the external disturbance and internal model error, a nonlinear disturbance observer was introduced to optimize the control method. Finally, the control method was simulated to prove the method is efficient.However, there are still some problems that need to be solved before it is considered for publication.
Firstly, there are still some grammatical mistakes in the manuscript, such as, in page 1, ABSTRACT, “this paper presents a aerial manipulation”, the article ‘a’ should be ‘an’ , and words in “two degree of freedom” should be connected with ‘-’ to make it one word. In page 1, INTRODUCTION, “the coupling among them” should be “the coupling between them”. Please check the manuscript carefully further especially the usage of articles and prepositions.
Secondly, the expression and explanation of the formulas can be optimized further to make it more accurate and clearer. For example, in page 4, the vector ‘q’ is introduced in formula (6) and (7) where the vector ‘q’ was first mentioned in the paper, thus the explanation of the vector is necessary to make it easier for the readers to read, especially the first time. Please check the formulas in the manuscript to make it more convenient for the readers to read and comprehend the mathematical derivation process.
Furthermore, the figures in the manuscript could be improved to make it easier for the readers to comprehend what the figures convey. In page 8, though figure 2 has already express the block diagram of the controller which is designed in the paper clearly, the wordy block in the figure makes it harder to read, maybe abbreviations or some other expressions can be introduced to make the figure more intuitive. Besides, the quadrotor UAV with a mechanical arm in figure 1 seems more likely to be hand-painted, which could be replaced with more professional ones.
As for the part of simulation, the figures that directly show the research results are of great importance, cause readability of these figures can influence the judgement of the readers who may skim the paper. In my humble opinion, there is at least one point that can be improved. Since there will be performance comparison among different control algorithms, it is understandable to distinguish the curves in the figures from each other with different colors and abbreviations of different algorithms. However, there is nothing written before or after the figures to explain the specific meaning of each abbreviation, which conspicuously lower the readability of the figures. Please intentionally explain the abbreviations, authors may explain with brackets like “adaptive nonsingular fast terminal sliding mode control (ANFTSMC)”.
In the part of conclusion, the authors made a complete summary of the works done for the paper with concise words. But generally speaking, the conclusion of an academic paper is not suggested to include the summary only, the authors are suggested to include afterthought of the work in the paper and envisage the possible research that maybe conducted in the future.
Author Response
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Reviewer 2 Report
The paper is devoted to the problem of the trajectory tracking control of aerial manipulation. The manipulation system consists of a quadrotor unmanned aerial vehicle and a two degree of freedom manipulator. The adaptive nonsingular fast terminal sliding mode controller has been designed. Besides, a composite control rate based on the nonlinear disturbance observer and the adaptive nonsingular fast terminal sliding mode have been designed to compensate the external disturbance and the internal modeling error of the system. The simulation results show the effectiveness of the control method.
The paper is useful for specialists but should be rewritten and improved significantly since many formulas and variables are introduced without any explanations. As a result, the paper is difficult for understanding.
Some remarks.
Formula (25) should be explained.
What is \tau in (25)?
Why the occurrence of the acceleration signal must be avoided?
Formula (27) imposes a restriction on the function g(.), this should be discussed.
The assumption df/dt=0 on line 226 should be discussed; this results in the approximate nature of the solution.
Line 229: what is v?
The influence of \lanbda in (41) on the results should be commented.
The derivative in (43) should be checked; it must contain \lanbda.
Line 294: what are the normal numbers?
Line 316: incorrect sentence.
And many others.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The main part of the reviewer comments has been taken into account except two ones.
1. Reviewer hoped that formula (27) will be explained since it imposes a restriction on the function g(.). But authors repeated the sentence about the angular acceleration signal and did not introduce any explanations. Reviewer thinks that some explanation and discussion are necessary.
2. Explanation of the assumption df/dt=0 has been done by authors. But the approximate nature of the solution should be discussed; an error should be estimated (if it is possible).
Author Response
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