Design and Preliminary Evaluation of a Soft Finger Exoskeleton Controlled by Isometric Grip Force

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presented a design of a soft hand exoskeleton controlled by residual isometric grip force. Some preliminary tests were conducted to evaluate the performance of the proposed exoskeleton. Below are some comments and concerns from the reviewer:

1. The proposed exoskeleton was designed to assist the movement of the index finger. From this perspective, the phrase "soft hand exoskeleton" is inappropriate because the other fingers of a hand were not assisted. Maybe "soft finger exoskeleton" is better.

2. The exoskeleton overview in Figure 1(A) was unclear. The authors should use labels [like in Figure 1(B)] to show different components of the exoskeleton, e.g., the linear actuator and the force sensor. For example, what is the function of the red pulley connected to hand wrist? Also, what is the function of the rod connected to the thumb? Please clarify.

3. In Figure 1(A), it seems that the soft finger structure was connected to the index finger using a rubber band, which is quite unstable for rehabilitation applications. Please improve that.

4. In section 2.3 and Figure 3, the authors have mentioned that the force measured from the force sensor consists of 5 digits (digit 1 for the thumb force, digit 2 for the index force, etc.). However, it is not explained how the force sensor measures these forces (for example in section 2.1). The authors should provide more details about the force sensor, e.g., the model name of the sensor and how the sensor measures the forces from different fingers.

5. In section 2.4.3, thee authors are recommended to provide some figures to illustrate the experiment process of the grip lift hold process.

6. The literature study part could be further extended. Currently, in addition to the molding approach, there are also other studies using 3D printing technology to directly fabricate the compliant bending finger structure (see the references below). From this perspective, the authors are also recommended to mention those work in the Introduction section as important state of the art. Below are some related work on 3D-printed compliant bending finger structures:

"LARG: A Lightweight Robotic Gripper With 3-D Topology Optimized Adaptive Fingers". https://doi.org/10.1109/TMECH.2022.3170800

"3D printed, modularized rigid-flexible integrated soft finger actuators for anthropomorphic hands". https://doi.org/10.1016/j.sna.2020.112090

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper presents a hand exoskeleton that incorporated a linear actuator controlled compliant mechanism and a grip force control strategy. The results may be helpful in developing new stratigies for assisting stroked affected patient. The paper is well organized and the detail is suffient for audience who are interested in the device. Following are several of my own comments and questions.

1. Section 2.2 titled "fabrication and working principles of compliant mechanism". It seems only the fabrication process was described, there is a lack of description on the working principles.

2. In figure 1-a, I would suggest the authors use arrow head to point out which part is which like what is done in figure 1-b.

3. Could the author explain why the grip force is called "residual isometric".

Author Response

Please see attachment. 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors developed a hand exoskeleton utilizing a soft-compliant mechanism and a novel force control strategy in this work. They leveraged isometric grip force control of digits 3-5 to manipulate an index-thumb pinch grip. The study included a characterization of the exoskeleton's output impedance and force and an assessment of its intuitiveness during a grip-lift-move task with unimpaired individuals. Results indicated improved movement frequency by 30% and user preferences for greater force sensitivity and flexion force from digits 3-5 to drive index finger extension. The promising findings suggest the need for further investigation in neurologically impaired participants. The contributions of the work are novel and exciting and can be accepted with a few corrections, as suggested below.

1. The key features of the hand exoskeleton developed in this study, particularly its soft-compliant mechanism and novel force control strategy, should be highlighted at the end of the Introduction section.

2. There should be a more explicit explanation of the process and methodology for characterizing the compliant mechanism's output impedance and force. The mathematical formulations for the residual force control scheme should be briefly discussed.

3. More details are needed on how the strategy improved movement frequency on the grip-lift-move task by 30%, and what implications this improvement has. 

4. The information about the user preferences gathered from the unimpaired individuals regarding force sensitivity and operating mode should be more clear. 

5. What were the specific benefits and limitations identified for each operating mode of the exoskeleton, especially in the context of index finger movement (closing vs. opening)?

6. What further studies do the authors believe are pertinent to fully explore the potential of this force control strategy in neurologically impaired participants?

7. The figures in the paper, particularly Figure 6, seem to have line curves that may be difficult to interpret. Also in the case of Figure 7, the authors should mention the acceptance level of significance. Could the authors further clarify these figures based on selected statistical metrics? Moreover, need to improve the clarity of visual representations for better readability. 

At present, the organization, presentation, and figures of the work are poorly provided. This should be improved before acceptance.

Author Response

Please see attachment. 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have revised the manuscript according to my comments. Therefore, I agree to publish this paper in this journal.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed all the concerns raised by the reviewer, and the revised manuscript can now be accepted.