Dual-Loop Control of Cable-Driven Snake-like Robots

Round 1

Reviewer 1 Report

Recommendations are listed on attachment

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper deals with cable-driven snake robots. In the abstract, the authors declare that the paper presents:

• Point A): The design of a snake robot with angle and force sensors
• Point B): The definition of a "simpler and more direct kinematic model"
• Point C): Dual loop control with force and position feedback

From the review point of view needs to be clarified which is the target of the paper. None of the points A, B, or C are presented and discussed widely from the scientific point of view.

The authors must define in a clear way which is the paper's objective and discuss their research using the appropriate references.

For the Point B:

The authors must clarify which is the reference scientific case to whom the statement "simpler and more direct kinematic model" refers.

point 1)

The references used in the paper do not represent the most up to date sources for the topics presented in the paper. The authors must rewrite the introduction considering all the up to date scientific papers.

point 2)

line 94: Figure 2 is cited for the presentation of "The detailed structure of the robot arm". However, figure 2 does not represent the robot's structure.

point 3)

line 100: The authors declare that three cables drive each link. The paper does not clarify the position of the cables on the links. The authors must describe the position and the usage of the three cables regarding the joint's degrees of freedom.

point 4)

line 112: Equation (1) does not have the complete modulo operator at the denominator

point 5)

lines 115 and 116: The vectors u_iy' and u_ix' are not clearly defined. Please define them clearly before using them.

point 6)

 line 147: The parameter "A" is not clearly defined in the text. The authors must define the parameter.

point 7)

lines 171-178: The Newton-Raphson method for solving non linear systems is well known. The authors must remove the explanation of the method from line 171 to line 178

point 8)

line 285: Correct the word "mechaical" to mechanical

point 9)

lines 420-426: The paper presents a trivial explanation of implementing a PD controller. The authors must remove this trivial explanation.

point 10)

Experimental results, from line 447:

The paper presents the results considering only the movent of the snake robot in the plane. No discussion is presented on the movement capabilities or performances when the system moves outside the plane.

The authors must introduce a discussion of more complex movements outside the plane.

point 11)

Experimental results, from line 447:

The paper presents the results on the basis of the inverse dynamic model presented in paragraph 4. There is no discussion on the effect or on the values of the Coulomb friction coefficient in equation 21, line 225.

The authors must discuss all the parameters used for obtaining the experimental results.

point 12)

Experimental results, from line 447:

The presented results regarding the dual loop controller refer to static responses. There are no discussions on the dynamic behaviour of the proposed controller, such as response time or bandwidth.

The authors must present and discuss the dynamic behaviour of the proposed controller.

point 13)

Experimental results, from line 447:

The dynamic motion test presented refers to very slow movements. The maximum amplitude of the joint angle is 50 degrees, executed in 15-17 seconds. In this condition, as discussed above in point 12, the controller works mainly in steady state conditions.

The authors must introduce results and discussion regarding the motion trajectory's dynamic behaviour, outlining the proposed controller's dynamic capabilities.

line 285: Correct the word  "mechaical" to mechanical

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This paper presents the dual-loop control of a snake type robot. The kinematics and dynamics are computed based on the robot geometry with standard robotic systems approaches. Obtained results shows the effect of dual loop control. Please improve the following issues:

- please report the control actions for the robotic system joints on separate figures.

- please provide an appendix or reference to an extended version of the system inverse dynamics

- why the open loop response is not so different from the closed-loop? please perform quantitative performance analysis using ISE or ITAE criteria.

- check spelling and grammar (e.a mechaical - mechanical) page 8 line 285.

- please explain the PD control loops better on fig.9 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The paper does not need modifications.