Increasing Bending Performance of Soft Actuator by Silicon Rubbers of Multiple Hardness

Round 1

Reviewer 1 Report

The article deals with an interesting topic "Increasing bending performance of soft actuator by silicon rubbers of multiple hardness".
Despite its general qualities, it contains several weak parts that need to be redone.
1. The Disign and fabrication chapter presents the actuator design, but there is no more detailed description of the geometry, as well as a dimensional description of one segment of the actuator wall.
2. It is necessary to justify why the authors decided to implement the actuator with the given geometric specifications (wall thickness, rounding angle, distance and overall regularity of the wall).  

3. In the FEM analysis section, it is necessary to add the material characteristics entering the calculation. Although the authors stated that they used silicone rubber as the material, they did not state the exact values of the material constants and whether they considered the nonlinearities of the material or used a linear model. In which category was the material considered? hyperelastically? Linear Elastically? And what about the mathematical model?

4. Regarding the problem of local inflation, has the numerical model been verified for this undesirable condition?

Author Response

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Reviewer 2 Report

An interesting piece of work.  The authors attempted to study the effect of the different materials with hardness used is C-strain restricting part, ballonet and bottom part.  In my opinion Shore harness does not provide the complete picture of the materials.  Do the authors consider Young's modulus?

Further, there is a cross effect of the materials properties towards the 3 parts of the actuators.  However, the current study only study the material effects one at a time.  In my opinion a design of experiment using for example Taguchi method will be more appropriate to see the effect of the materials properties towards the bending angle and force.

Author Response

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Reviewer 3 Report

The serviceable application of flexible pneumatic actuators depends from their characteristics. The activity presented goes in this direction. In any case, one important point is to test the behavior of flexible actuator in the time. I suggest to move in this direction in future work.

Author Response

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Reviewer 4 Report

This paper is interesting and instructive to other researchers. Before publishing, I have some comments.

1. The authors should emphasize the importance of using pneumatic systems. There are many actuating methods, like hydraulic or electro-hydraulic methods. They should mention these kinds of methods.

Kellaris, N., Gopaluni Venkata, V., Smith, G. M., Mitchell, S. K., & Keplinger, C. (2018). Peano-HASEL actuators: Muscle-mimetic, electrohydraulic transducers that linearly contract on activation. Science Robotics, 3(14), eaar3276.

Mao, Zebing, Takeshi Iizuka, and Shingo Maeda. "Bidirectional electrohydrodynamic pump with high symmetrical performance and its application to a tube actuator." Sensors and Actuators A: Physical 332 (2021): 113168.

2. For various hardness, they should mention why variable hardness is necessary, like what kind of problem they must combat?

3. Again, there are many papers about the variable stiffness of soft robots, using particles, beads, or fibers. They should consider this point, especially the difference between stiffness and hardness. Here, I list some papers, which might be useful for you.

Chen, Y., Li, Y., Li, Y., & Wang, Y. (2017, July). Stiffening of soft robotic actuators—Jamming approaches. In 2017 IEEE International Conference on Real-time Computing and Robotics (RCAR) (pp. 17-21). IEEE.

Brown, E., Rodenberg, N., Amend, J., Mozeika, A., Steltz, E., Zakin, M. R., ... & Jaeger, H. M. (2010). Universal robotic gripper based on the jamming of granular material. Proceedings of the National Academy of Sciences, 107(44), 18809-18814.

Mao, Z., Kuroki, M., Otsuka, Y., & Maeda, S. (2020). Contraction waves in self-oscillating polymer gels. Extreme Mechanics Letters, 39, 100830.

4. It would be better to show the schematic of pneumatic systems in the figure.3

5. In figure.4, why choose this angle as a bending angle, whose centroid is changing when the actuator is driven.

6. Compared with the finger without multi-hardness, what is the advantage of your proposed soft finger?

Author Response

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Round 2

Reviewer 2 Report

Overall the revised manuscript is generally acceptable for publication.  However, I like to point out that the plots in Figures 8 are poorly constructed. Further, it is always the mistake by many researchers to joint the data points for experimental data.  Instead you only curve fit experimental data.  Please provide a better version of Figure 8 in the final submission for print.  I don't need to review this again.

Author Response

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Reviewer 4 Report

This paper is significantly improved. 

Please draw the schematic (principal figure) for the pneumatic system instead of the optical images. 

Author Response

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Author Response File: Author Response.pdf