Digital Twins for Discrete Manufacturing Lines: A Review

Round 1

Reviewer 1 Report

The paper claims to review digital twins (DTs) from the manufacturing perspective. However, the following important topics/concepts are left out, unfortunately.

What is a Digital Twin? What is the difference among a digital twin, digital model, digital shadow, and digital thread? Since all these technologies are researched nowadays and the terminologies are close, it is very important to present a clear idea of a twin, distinguishing from the others.

Also, what are the characteristics or functional requirements of a twin? what are the features one should be aware of while developing a twin? A very important question as well.

There is also an issue called effect of time latency/delay, being investigated by researchers. Since a digital twin must ensure a real-time dual communication flow (Physical - Cyber - Physical) and modern NCS suffers from delay (due to being wireless, using a lot of sensors, transmission/processing/queueing delay, etc.), effect of delay in systems like digital twins's has become an important research issue.

The submitted manuscript does not discuss these elaborately at all. The authors can think of creating a section describing the abovementioned issues related to digital twin (what it is, how it differs from other technologies, key features or functional requirements, etc.). Also, the authors can think of finding out the challenging issues like time latency and others in the final segment of the paper. The following papers can give a kick-start regarding these (https://doi.org/10.1016/j.aei.2020.101225, https://doi.org/10.1016/j.jii.2021.100242).

The figures are blurry and hard to see and comprehend. In most of the cases, the font size is also small. The authors must redo these. If the authors are using figures from other papers, then cite the corresponding source. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This is a review of DT's applications for the discrete manufacturing line. Authors have synthesized and analyzed the related studies. However, the content needs to be revised and improved according to the following suggestions:

1. Currently, Table 1 has four groups of DT applications, so they should be combined into three groups as presented in the content on page 3, lines 79 to 85.

2. Figure 2 should be explained clearly to show the application of DT for the discrete manufacturing line.

3. References should appear in the content in order from 1, 2, to the end. Check the accuracy of the citation: for example, page 8, Guo [14] but in the reference section it must be [15].

4. In Section 3, each application of DT such as Design and Improvement of a Discrete Manufacturing Line; Production Line Scheduling and Control; Fault Prediction and Maintenance of Critical Equipment should add a figure that shows the current structure of the system and how DT applies to the system. As well as how the technologies in Section 4 are applied to deploy DT to the current system.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper analyses the literature on the applications of DTs for discrete production lines.

The paper is well structured and correctly explained. The terminology is appropriate and suitable. The conclusion concludes the paper with the three main contributions of the paper.

Some refinements to the text could be made to simplify or shorten some rather long sentences, e.g. in the introduction one sentence stretches from line 10 to line 17. I leave it to the authors to decide whether this is feasible.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors responded positively to all the queries by the reviewer.

Reviewer 2 Report

The research content has been revised and improved. I agree with author's response as well as agree for publishing this paper in the Journal.