A Robust Controller for Upper Limb Rehabilitation Exoskeleton

Round 1

Reviewer 1 Report

First of all I would like to congratulate the authors for the design of a portable exoskeleton. It is a magnificent initiative to bring this rehabilitation technology closer to people with stroke who live far away from rehabilitation centers (this aspect should be commented in the introduction). 
On the other hand, I have not found the weight of the exoskeleton. This is important, for example, one of the disadvantages of the use of portable exoskeletons in the workplace is the weight of the exoskeleton.
What are the limitations of your study and how should your portable exoskeleton be improved? This information may be useful for future research projects. 

Author Response

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Reviewer 2 Report

The paper is well written and clear.  The derivations of the controller are clear.

Another reference is H. Krebs of MIT

The paper presents an interesting controller.  However, there are some serious holes in the paper.  First, it is only simulation and no experiment.  That is OK for a preliminary work if the model is accurate.  What is lacking in the model is of the human.  The only model of the human is the mass and inertia.  There is no muscle activity or motion of the human on the robot.  This is a critical issue in rehabilitation.  The robot should try to correct only adverse motions.  Any motion that is desirable by the human should be allowed by the robot.  Their controller does not allow for this.  Doing the simulation of the controller with a human model such as OpenSim should be done.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The revision is slightly better than the first paper.  There are some minor issues well as major issues.

In figure 12, there seems to be a missing phrase in the caption:

CAD view showing the upper limb rehabilitation exoskeleton for.

For what?

There are still significant issues.

The powered degrees of freedom are:  Abduction/adduction of the humerus, Flexion/extension of the humerus, and flexion/extension of the elbow.  It should be noted that above approximately 90 degrees of adduction, the primary motion is of the scapula and not the humerus.  This is a limitation of the design.

What motors will be used?  Are they in the simulation model?

Cables can have high friction.  Is this accounted for in the model?

A strong suggestion was to look at more background such as Krebs, et al.  Manus system and other.  This was ignored.

While passive therapy is done, there are still forces and torques from the subject that are not accounted for.  Ligaments, tendons, and passive muscles exert loads that must be overcome.  These must be in your simulations.

Any human therapist, doing passive stretching of the patient will also try to get the patient to do active motions in the correct manor.  A purely position robot is limiting in this way.  Most research now is in robots that account for and do therapy on active muscles.  This is the goal to the therapy – to get the patient moving on their own.  This could be added to your system.

Critiques given by reviewers must be addressed in the paper as well as in the responses.

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The point of referencing Krebs was not so much to cite them as the methods of the control.  They, and other, sense the effort of the subject and gets out of the way if the subject is moving on their own.  The system is not an unbeatable position control, but a torque and position control system.  This is essentially what the human therapist does as well.  The proposed systems that you are working on could do this as well if there was torque sensing and control in addition to the position control.  This would make the system much more useful and acceptable in clinical use.  It would be worth a discussion of the future use in the paper.

Author Response

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Author Response File: Author Response.pdf