Design, Modelling, and Control of Continuum Arms with Pneumatic Artificial Muscles: A Review

Round 1

Reviewer 1 Report

Title: Design, Modeling and Control of Soft Continuum Arms with Pneumatic Artificial Muscles: A Review

The presented work reviews pneumatic actuators that are used in robotic arms. The paper first introduced McKibben actuators and then reviewed several different designs and types of robotic arms that actuated with the use of pneumatic actuators. Then the paper provided reviewed some of the works for modeling and control of soft robots. Despite the topics and the subjects being interesting, the authors did not provide a requirement for a good review paper such as a comprehensive foundation on each topic, the current state of knowledge, and the gaps in existing studies for potential future research. Many sections are very short and did not bring enough information and references as it is expected in a review paper. It looks like the authors did not go through the details of each of the reviewed works in the paper and either some of the cited works are not described correctly. Therefore, the authors should consider a major review to publish their work as a review paper.

1.       Both in the abstract and conclusion the authors emphasize that their review presents a

highlighting of the soft arms’ flexibility, adaptability, and safety. However, they only discussed them in brief paragraphs in the Introduction using a few references (one citation for each). So I do not believe this can be considered as the highlights for this review work!

2.       Both in the abstract and conclusion the authors claim that the paper highlights the gap between theoretical potential and practical utilization of soft robots. But the authors never discussed what are exactly these gaps and limitations that are still available and need more research specifically in the design, modeling, and control of soft arms.

3.       The title for section 2.2 should be changed to “Bioinspired arms”.

4.       Mazzolai et al. [32] did not use soft pneumatic actuators in this work. They use cables for actuation and different configurations of the arm, they only used suction cups to establish the attachment and adhesion of the arm to the objects.

5.       Section 3 started well by introducing two kinematic analysis categories, forward and inverse. But it is not clear how the cited works that are in this section used this approach. More details on the procedure for implementing the kinematic models need to be discussed.

6.       Line 271: Figure 10 presents an example of inverse kinematic modeling. The figure quality is low and the figure did not give any helpful information to the reader. The figure needs to be revised.

7.       In line 295, the authors mentioned several other models. Why they did not provide any more details about each of these models if they are already used in other works?

8.       Considering the 2 previous comments, table 1 needs to be expanded by adding a comparison of more works for a review.

9.       Section 3.2 should be rearranged and rewritten since: first in line 31; Three commonly used methods for modeling the dynamics of soft robots are the Lagrangian formulation, the Ogden model, and the Cosserat rod theory. Then in line 367: The Lagrangian formulation accounts for the system-level dynamics, while the Ogden model captures the material-level behavior… So these models are different and they can not be compared like it is mentioned at the first of this section!

10.   Line 321: Ogden model is one of the hyperelastic material models. They are several other hyperelasticity models such as Mooney-Rivlin, Yeoh, Neo–Hookean, …. Did the authors check other works that used these models?

11.   Considering the 2 previous comments, table 2 needs to be modified.

12.   In many parts of this paper, the authors just mention the name of the method or model without providing enough description that how the cited reference is developed or used it. For example in section 4.1 what is the Koopman model or how Thuruthel [75] demonstrate the feasibility of their controller?

13.   Figure 12 quality is not good, also more descriptions need to be provided in the figure caption (or adding more text in the figure itself) to clarify what information the authors are trying to provide to the reader by presenting this figure.

The paper needs to be edited well for publishing since it contains grammar mistakes!

Author Response

The information about our answers contains in this file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents the current state reached in the construction of soft robots actuated with pneumatic muscles.

Regrettably the novelty of the paper is questionable. The paper presents just the current state of research in this field, the most useful information for the readers being only the bibliographic references. Overall, the novelty of this work is quite limited, and it simply reports some examples of robots whose construction uses pneumatic muscles. In order to be published the article should include  a more extended analysis of the state of art (> 20 pages).

The presentation method is good and in accordance with generally accepted standards in that area.

The researched bibliographic material is recent and the paper presents the latest achievements in this field.

The authors may consider the following comments for revising the paper.

-          Figures 3 and 7 should contain text written with larger characters.

-          Lines 221-223, 294, 392-394: character size.

-          The phenomena of hysteresis and compliance are not sufficiently explained.

Minor editing of English language required

Author Response

The information about our answers contains in this file.

Author Response File: Author Response.pdf

Reviewer 3 Report

In relation to the analyzed draft, I have the following remarks:

1. there is a discrepancy between the title and the content of the article. This discrepancy is important due to the review nature of the article. Thus, the field of "soft robotics" is very broad and includes a wide variety of robots. In my opinion, the title is correct in relation to the main content of the article, but inside it the term "soft robotics" should be replaced by the term "robots with pneumatic artificial muscle". In fact, the review mainly refers to this type of robots.

2. there are some fundamental mistakes in the article. An example: in line 37 it is stated that robots have "infinite degrees of freedom" which is not consistent with robotics in the sense that in robotics the number of actuators must be equal to the number of degrees of mobility.

3. various kinematic and control analysis methods are mentioned, but it is only descriptive, without presenting equations and especially without a comparative analysis. Which method is recommended in a certain situation and which other method lends itself to be used in another situation. I think that additional clarifications are necessary in a review article.

Author Response

The information about our answers contains in this file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Improve figure 13 quality

Minor editing is required to improve the language