Fabrication and Characterization of Pneumatic Unit Cell Actuators
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1 In the Introduction,
The authors mentioned that “The design of the haptic display offered control over the direction of the feedback but is limited by the lack of amalgamation of different actuations and is constrained by the design.”
Please explain more about the limitations of the previous works.
2 Figure 3b,
What does the ratio mean?
3 Figure 7,
There are no labels for the horizontal axis.
4 The authors mentioned that the application for this work is VR/AR haptic feedback, which is a kind of important topic for soft actuators and robotics. However, it is not clear how this application is linked with this work. The authors studied different inflation cases and got some data; however, it is not clear the requirements for these applications and why these data are promising. There are lots of soft actuators that can be largely deformed or be actuated with high frequency. What are the advantages of the design in this work?
Comments on the Quality of English LanguageThe quality of English language is good
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis article is focused on the development of a pneumatic unit cell actuator for use in haptic feedback. It is a very interesting field of science and technology. This work is oriented towards the production and investigation of the properties of such actuators. From the point of view of production, it is a relatively simple actuator, which the authors then investigate in terms of static properties as well as frequency properties. Application-wise, the results of this study can be applied, for example, in the development of devices for virtual reality, where haptic feedback is a suitable addition to the device's functions. This type of actuator belongs to the so-called soft actuators that could also be used in other areas. Therefore, I consider the article to be highly topical and this issue needs to be addressed.
In the beginning of the article, the authors document the need to solve this problem with references to similar studies.
The methods for the production of such types of actuators are also presented, as well as the results of dimensional measurement.
Static Pressure Condition - Free Deflection Measurement was realized in the next part of this work. Furthermore, Static Pressure Condition - Blocking Force Measurement is also presented. Then there is also Frequency Condition - Free Deflection Measurement.
The results bring favorable results and indicate the potential for application use of these types of actuators.
The article is well prepared, but some important information is missing, and I have summarized some tips for improvement in the comments.
If possible, please include these comments.
Comments:
In the entire article, the prefix of the pressure unit "KPa" is wrongly stated, where it should be "kPa".
Chapter 2.3 presents the results of dimensional measurement. What is indicated in the mean values of the measurement results? Is it the variance of the measured values or is it a random measurement error?
What is the measurement uncertainty then?
What is the repeatability of the production process of such actuators in several production batches?
You state that "The proposed fabrication process produces PUCs that are approximately 2% to 3% thicker than the target thickness." Is this not caused by a systematic measurement error by the measurement method used?
In chapter 3.2 Static Pressure Condition - Free Deflection Measurement, you present the measurement results: "The recorded data from the Exilim Ex-F1 camera were analyzed frame-by-frame to measure free deflection."
With what measurement uncertainty was this data obtained? How can they be trusted?
What is shown in the measurement results? Is it measurement variance?
Likewise, the inlet pressure has some measurement uncertainty. If you want to obtain reliable data, it is necessary to indicate the measurement uncertainty in all experimental data according to the applicable regulations for their determination.
In the case of Fig. 7, there are no displays where it would be clear what the hysteresis of this actuator is. This means how it behaves during loading and unloading. What is the hysteresis is interesting mainly for other applications where more accurate positioning will be needed.
In the section "Static Pressure Condition - Blocking Force Measurement" there are measurement results and it is also not clear what is stated in the measurement result.
Measurement uncertainties are also missing. It is not so clear whether the dispersion of the values is caused by the variability of the actuators or the uncertainty of the measurement using the used measurement method.
The force transducer used has a voltage output, and even when processing the voltage signal, measurement errors and uncertainties also enter the process.
Also in Fig. 8, it is not clear whether the measured values show any hysteresis. How is it when loading and unloading the sample?
In the chapter "Frequency Condition - Free Deflection Measurement", it is also necessary to specify the information about the measurement results.
What was the hysteresis in these measurements? Was it different from the static measurements?
Are the displayed experiment results measurements on one or more samples? How does this depend on the variability of sample sizes?
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis paper presented the design, fabrication and characterization of pneumatic unit cell actuators for improving the task performance in teleoperation applications. Overall, this paper provided a lot of design and experiment details, and has solid contribution. However, several issues should still be addressed to further improve the quality of this paper. Below are some comments for the authors to consider:
1. In section 3.2.1, 3.3.1 and 3.4.1, the authors supposed that the relationship between free deflection, blocking force and pressure are linear [see equation (1), (2) and (3)]. However, the authors only used data fitting method to get the equations without explaining the physical principles behind them. In my opinion, the authors should also perform physical or mechanical modeling to derive mathematical equations to describe these relationships. For example, why are these variables in linear relationship? Please clarify.
2. The authors are recommended to perform finite element analysis on the developed soft actuator to better demonstrate its actuation principle.
3. The authors claimed that the developed pneumatic unit cell can be used to generate static pressure and vibrotactile feedback for teleoperation tasks. However, no tele-manipulation task was presented in this paper to demonstrate the application of the pneumatic unit cell. From this perspective, the authors are recommended to show examples to help the readers better understand the application of the proposed actuator.
4. The literature study part could be further extended. Currently, there are also other studies developing compliant constant-force mechanism-based actuators to improve the haptic feedback in teleoperation applications (see the references below). From this point of view, the authors are also recommended to mention those work in the Introduction section as an important part of the state of the art. Below are some related work on compliant constant-force mechanism-based actuators:
"Safe Manipulation in Robotic Surgery Using Compliant Constant-Force Mechanism". https://doi.org/10.1109/TMRB.2023.3237924
"Automatic Optimization for Compliant Constant Force Mechanisms". https://doi.org/10.3390/act12020061
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have made a lot modifications. I think the work can be published.
Reviewer 3 Report
Comments and Suggestions for Authorsis good.
