A Self-Adaptive-Coefficient-Double-Power Sliding Mode Control Method for Lower Limb Rehabilitation Exoskeleton Robot

Round 1

Reviewer 1 Report

Thank you for the involvement in the review process of this novelty paper. The study of control strategies for rehabilitation exoskeleton robots need to be expanded and this article give a very interesting contribution. state of the art are well investigated and the theory well esplained. The review kindly suggests to publish the paper as it is.  

Author Response

Thank you for your recognition and comments on this manuscript.

Reviewer 2 Report

This manuscript discussed a self-adaptive-coefficient double-power sliding mode control method in order to overcome the difficulty of tracking the robot trajectory. The topic is of interest for this journal, it is the opinion of this reviewer that the manuscript can be considered acceptable for publication after minor revision. Some comments below are provided to the authors as suggestions for strengthening the manuscript.

 

1. In Figure 9, it is not clear what are differences the movements states. Please clarify.
2. The wearable experiment was conducted based on selected healthy testers, however, it is not clear how robust it is to deal with different conditions (multi-joint movement, and external perturbations) while using the lower limb rehabilitation exoskeleton robot. Please clarify.

Author Response

Thank you for your constructive suggestions. They are of great help to improve the quality of the manuscript. We provide a point-by-point response to your comments as follows. Please see the attachment.

Author Response File: Author Response.docx

Reviewer 3 Report

The paper presents a method for the control of a lower limb exoskeleton which aims to improve the robot behaviour. The authors propose an approach that combines an estimated dynamic model with a sliding mode control.

 

The introduction is ample and defines in a clear way the state-of-the-art in control strategies used for lower limb exoskeletons. As the paper title suggests that the robotic device is used for rehabilitation, a paragraph or two with the specific challenges of these patients and the targeted disabilities would be desirable.

 

Some works that refer to the first treatment stage for patients with severe impairments (bed-ridden), could be mentioned here:

 

Pisla, D.; Nadas, I.; Tucan, P.; Albert, S.; Carbone, G.; Antal, T.; Banica, A.; Gherman, B. Development of a Control System and Functional Validation of a Parallel Robot for Lower Limb Rehabilitation. Actuators 2021, 10, 277.

Vaida, C.; Birlescu, I.; Pisla, A.; Ulinici, I.; Tarnita, D.; Carbone, G.; Pisla, D. Systematic Design of a Parallel Robotic System for Lower Limb Rehabilitation. IEEE Access 2020, 8, 34522–34537.

 

In Section 2, Please describe a bit more in detail the construction of the exoskeleton. As I can see from the figure it has also embedded solution to adapt to different patients anthropometric characteristics. It would be interesting to have data regarding the link lengths span.

 

A question here related to the calculation of the centre of mass for the exoskeleton segments. How did you compute the parameters for the terms in eq. 2?

 

Please improve the quality of figure 3 to make it more readable.

 

It is not very clear for me what motion was performed in Section 4.2 for the simulation. Please explain it. Also, the figures seem to have low quality (just because exporting issues) and as the data is important they should be exported at higher quality.

 

The experimental results seem to validate the mathematical models and are important for the control system validation. Figures 10-13 show an excellent behaviour for the control system.

 

In figure 14, there seem to be a periodic error for the left and right knee which should be explained. The error is proportional with the motion amplitude? Or why do you have that variation?

 

On the overall I consider this a solid contribution for the journal.

 

Language:

Throughout the paper, please tray to refrain in using complex phrase construction which are very hard to read. Just a few examples:

Line 20: is designed to achieve adaptively adjust the compensation

Lines 30-31: The emergence of lower limb rehabilitation exoskeleton robots, …, a large number of clinical applications have shown that lower limb rehabilitation exoskeleton robots can play good auxiliary roles for patients with different degrees of injury.

Lines 39-40: And these robots are vulnerable to environmental factors, including the patient and the ground, during the control process.

 

Line 43: the proper term for PID (as it is also used in reference 7, and generally accepted in that way) is Proportional-Integral-Derivative

 

Please revise the title of Section 2, line 89

Author Response

Thank you for your constructive suggestions. They are of great help to improve the quality of the manuscript. We provide a point-by-point response to your comments as follows. Please see the attachment.

Author Response File: Author Response.docx