Electromechanical Actuator-Based Solution for a Scissor Lift
Round 1
Reviewer 1 Report
Hello,
I think your topic is interesting and the study is well-organized. However, there are some aspects that should be improved:
• You should clearly explain in the abstract and conclusions that the hydraulic system under investigation is not energy-efficient compared to the most advanced EHAs proposed in the technical literature. So, this aspects partially explains the huge energy savings being obtained.
• Lines 367-369 talk about raising and then lowering the platform. However, it looks like that the following plots in Fig. 13-17 are only about the lifting phase (i.e., positive velocity, positive power, …). This scenario is what you mention later on line 497. I suggest that you clarify this apparent contradiction and remove any potential cause of confusion.
• One of the advantages of these energy-efficient systems is their ability to recover energy. I think that not addressing this aspect in the paper is a bad decision. Instead of offering a comprehensive analysis of the proposed system under representative operating conditions, you limit your discussion to a limited scenario (lifting).
• I believe there is a missing critical analysis of the proposed EMA-based solution. You should at least mention that those systems might have issues such as permissible continuous power that might cause unfavorable sizing compared to EHAs, higher overall mass, or higher installed power.
• The quality of the plots should be improved (Fig. 4, 6, 7 etc.). They are blurry.
• The font of the equations should mimic the one of the text.
Author Response
Hello! Thank you for your comments and suggestions. The full response is in the attached PDF.
Best regards, Viacheslav.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The authors have shown some practical work, without scientific contribution, but with contribution to energy efficiency, which is also significant. The work should be presented more precizely, with necessary details, with better consideration of both systems, especially electrical drive. My comments are listed below:
1. Lines 10 an 11: Here, the main challenges with drivetrains in this regard were resolved with electric solutions along with hydraulic topologies for implements or working hydraulics. – Please, try to rephrase this sentence
2. Line 114: „frequency converter“ rather than „frequency inverter“
3. Line 126: and it is analysis - and it is analysed
4. Line 130 : Please find better expression for „out-looks“
5. All figures are with low resolution, hence they are not clear
6. Lines 148, 149: What do you mean by „two-phase DC Machine (2)“?
7. Line 150: speed
8. Table 1: what is name of the value V=3.8 cc/rev? Is it flow, or displacement? What is the difference between V and q?
9. Line 173: Is it a self excited DC motor? Is it DC motor with permanent magnets on the stator? Why do you choose DC motor instead of permanent magnet synchronous motor, or brushless DC motor, for example? You are talking about energy savings, therefore you should be better explain the choice of electrical drive.
10. What should figure 2 represent? What is the output for the given input?
11. Line 196: c1 is the hydraulic capacity of the line [m5/N]. – Are you sure that it is a proper unit?
12. Figure 5: if you use term „control voltage“, there must be something between the battery and the motor inputs. Also position and speed are not the same values, as it is drawn in the block diagram.
13. Line 231. Line 200, Line 202, etc: What is the meaning of [-]?
14. Height of the platform xp could be designated in the Fig. 1, for example.
15. Line 246 – „of“ is better choice than „for“
16. Line 271 – more details of te simulation should be given. How is the electrical and hydraulic part connected? Block diagram should be given with control signals and output values.
17. All measured values should be specified in the omitted block diagram, or in Fig. 3
18. Line 284 - Fig. 8
19. What is meant to be explained with the paragraph from line 283 to 286? This should be better performed.
20. Line 297 – parameter k is not precisely defined, as well as series, sample and cycle.
21. Block diagram in the Figure 12 is not correct! The authors should better explain the whole DC drive and in accordance to this present the proper block diagram. The essence is how the drive is controlled. If it has PI speed controller, the block diagram of controlled DC drive cannot be drawn like that.
22. The title of Figure 16 is not correct. The figure should be divided in part a and b
23. Lines 492, 493 – mechanical stress can be reduced with a proper control. The authors should better investigate electrical drive control.
24. The use of English must be improved.
The use of English must be improved, mainly because required verbs are omitted at many places in the text.
Author Response
Hello! Thank you for your comments and suggestions. The full response is in the attached PDF.
Best regards, Viacheslav.
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper shows very interesting and actual topic. Results of the investigations are very interesting, and they give good outlook for positive changes in trends of industrial equipment design. In my opinion, the article is well-prepared, and the topic fits into actuators scopes.
Before publication, in my opinion a few issues should be improved:
1) The readability of the charts should be improved, by for example moving the titles of the axes away from the chart area,
2) In my opinion, in the figures 6-9 it would be better to present the percentage difference between both systems, rather than just absolute difference.
I also have a few questions:
1) What is leakage coefficient (a - m3/Ns) - equation 1? What is the physical basis of these parameters? The unit seems to be a little bit strange.
2) xR (equation 2) is a discrete or continuous value? Maybe percentage?
3) What is "i" in the equation 7? There is no explanation there.
4) What is the difference in the mass of the overall construction for both lifting systems? I suppose that this type of scissor lift can move by its own wheels (to change position), and I suppose that this movement is generated by the electric motors, which utilize the energy from the battery. In such case, that mass difference will have an influence for amount of energy which will be used for movement, which is consequence will have an influence for number of cycles available. Maybe it would be better to add this parameter to final analysis.
Author Response
Hello! Thank you for your comments and suggestions. The full response is in the attached PDF.
Best regards, Viacheslav.
Author Response File: Author Response.pdf
Reviewer 4 Report
The authors analyze the energy savings potential of replacing the hydraulic actuation system of a scissor-lift with a purely electric system using an EMA. They formulate and validate a simple lumped parameter model of the hydraulic system using experimental data, then assess the savings potential of replacing the hydraulic system with a linear EMA. After this, they use these savings numbers to carry out a simple battery cycle analysis and cost analysis using real electricity figures.
The paper is pretty simple but all the analysis seems valid and correct. There are two issues I have with it. First is that the possibility of overrunning load recovery is not even mentioned until the second to last paragraph, which makes no sense in the context of a machine used exclusively for lifting and lowering. Even if it wasn’t modeled and discussed in the analysis (though that might add some good depth to the work) it should be addressed in the prior work sections, but doesn’t seem to be at all. At the very least expand the works cited to acknowledge the possibility.
Second, the EMA technology (ball screw, roller screw, lead screw, etc) being used does not appear to be discussed at all, beyond a simple mention of the EMA’s lead and voltage. It is also not clear what, if any, considerations have been made to account for losses in the mechanical transmission components. These considerations should be clarified, as the EMA used is central to the novelty of the work, and currently very little information is given on it.
Beyond that, a few specific points that need attention:
1. Figures throughout are often slightly warped or grainy, likely due to careless re-sizing. Most egregious is figure 15.
2. Similarly, the figures regarding raise / lower cycles seem to use an ideal battery. There are losses in this cycle and some of this power may not be accessible due to discharging limits to avoid damaging the battery. If these factors were accounted for they were not mentioned.
3. Several valves were omitted from the hydraulic model, then referenced later as a reason that the model behavior is different. It should be clarified which valves are being neglected (just reference which number in the diagram) to explain why neglecting them is valid.
4. There are a lot of minor wording and grammar issues throughout. A quick pass through should resolve most of them.
Overall, with correction of the above issues and deeper analysis regarding the first two points this paper is acceptable.
None.
Author Response
Hello! Thank you for your comments and suggestions. The full response is in the attached PDF.
Best regards, Viacheslav.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Dear authors, below is the list of my comments:
1. Lines 150 to 153 below Figure 1: „In Figure 1, the electric part of the system consists of a 48 V battery, DC motor (2), DC motor controller, and computational unit which is running at constant speed.“
Figure 1 presents only DC motor designated with 1, which is mechanically coupled with pump. There is no battery, no DC motor controller, nor „computational unit which is running at constant speed“. What did you mean with this last statement – because it has no sense? DC motor controller provides motor to operate in accordance with the reference speed. The reference speed is set manually by the operator of the lift, or automatically by some supervision system. What is happening in your case? Your system is operating with variable speed, i.e. with required reference speed which can be changed, otherwise your system will not have any need for speed and current controllers.
2. Lines 163 – 165: “currents and voltages of electric motor and battery” - between battery and motor is DC/DC power converter which enables variable voltage at the DC motor armature in order to provide reference speed which is required. Therefore, the battery voltage is constant and armature voltage is changing and measuring.
3. Lines 180-183: Can you please explain how did you connect Excel with Simulink? Why did you do that instead of use Hydraulics Toolbox in Matlab, where you can model your hydraulic circuit?
If you are using equations connected to the hydraulic system in Excel, I suppose that you are calculating torque at the shaft of the motor from measured hydraulics system data. Am I right?
4. Line 201 and 202: ωp is the angular speed of the motor [rad/s], calculated using the mechanical characteristic of the motor - Why do you calculating the speed, when you require reference speed from the lift and you have probably PI speed controller? If it is correctly tuned, the motor must run with the reference speed.
5. Can you explain how did you make dynamic model of hydraulic system using Excel? There is obviously divergence between experimental and modeled dynamics if you are observing the final part of the Figure 8, beside neglecting deviations during the start.
6. Figure 15 has designations of EMA and EHA curves, while there is explanation of curves in the text with EMA and CH designations. It should be corrected.
7. Line 499: each EMA requires one variable speed electric motor with one servo drive
This statement is wrong. It should be: each EMA requires one variable speed drive with servo motor, or simple: each EMA requires one servo drive.
8. There are two battery voltages mentioned in the paper: 24V and 48V. Which value is correct?
9. After reading the whole paper carefully, I can only conclude that the system presented in Fig. 1 has no controller and that the motor is running at constant speed, while the whole regulation in the system is performed with valves. But there is still open question about values that you are measuring and how do you use them in calculation.
10. Then block diagram in Fig. 12 is questionable: what is happening with armature current. Is it measured, or estimated in the model?
11. Concerning my questions in the first review that you haven’t answered properly:
- Q: Height of the platform xp could be designated in the Fig. 1, for example.
A: Thank you for your comment. The full height of the platform is in datasheet.
Explanation: I intended to say that there is no xp designation in any figure. Maybe its proper place is in figure 3.
- Q: “Line 297 – parameter k is not precisely defined, as well as series, sample and cycle.”
A: Thank you for your comment. It is just a statistical formula for an accuracy evaluation.
Parameter k is a value of any variable. Exp means experimental, smod means simulated model.
Explanation: You gave me the answer which is not related to the question, but you have omitted from the revised paper expressions „series and samples“. Why?
The use of English is improved.
Author Response
Hello dear reviewer. Here you can find an attachment with respond to all your comments on round 2.
Author Response File: Author Response.pdf
Round 3
Reviewer 2 Report
Revision 3:
1. Line 12: Delete “It allowed”
2. Fig. 1: It should be 8 before Lowering valve, not 4
3. Fig. 1: At the place 2 (in blue color) it should be written: 2- DC/DC controlled voltage source converter, in Schematics it should be at the place 2 instead of “Control unit”, DC/DC controlled voltage source converter,
At the place 1 – 48V Battery and in the line 153 instead of “DC motor controller” - DC/DC controlled voltage source converter.
4. Line 152: 48V battery. You need DC/DC buck power converter (or chopper, or DC/DC controlled voltage source converter) to lower the voltage to 24V which requires your DC motor at it’s input. There is no other control of DC motor, except of tuning required voltage at the motor input. Considering lines 459 and 460, if you have 24V, you need DC/DC power converter to keep the voltage at that value, or maybe you have different batteries in EMA and EHA case?
5. How do you explain Fig. 8, part from 22 to 27s? Why do you have deviation between experimental and simulation results? Due to the influence of the omitted valves 6, 8 and 9?
6. Line 300, 301: „Figure 8 represents a pressure difference in the transient process that lasted less than 1.5s“ – I cannot see where is that 1.5s at the time diagram of 30s. Can you excatly designate that period (i.e. from 3s to 4.5s)?
7. Figure 8 should end at the instant when your red line drop to zero, at 27s, because the pressure is not reaching zero, but recording of measurement has stopped. The pressure must stay at the constant value to hold the platform at the requred hight. Holding of platform is performed with valves and the motor is stopped at t=22s, what can be seen in Fig. 9.
8. Where have you realized current and speed controller presented in Fig. 12? Which unit provides variable voltage to the motor in accordance to speed and current controller?
9. Lines 405, 406: You cannot say “The DC motor model gives a negative feedback to the current controller and speed controller”, but “The estimated value of current and speed from DC motor model are used as negative feedbacks for suitable controllers”, or similar.
10. What is happening at the end of time diagrams represented in Fig. 13 and Fig. 14, exactly from t=24s? Why do you have increase of current in experimental data and how can you have this value equal to zero after 1s in experimental data and at t=24s in simulated data, while you have to hold the cabin at some height? Your system must perform electrical braking: at the first instant the current will have sudden drop and after that it will start to increase in order to develop the motor torque equal to the load torque. Then you have to use mechanical brake to hold the cabin at required height with motor speed equal to zero, but with proper current and motor torque. Also, your simulation is not properly designed, with current equal to zero.
11. Also, consumed electrical power cannot drop to zero, for the same reason as the current cannot drop to zero. Mechanical power will drop to zero, but the total power used from the battery will be spent on barking resistor, transformed to power losses.
12. Fig. 16 cannot present consumed power, for the reason explained in previous comment. Additionally, the figure presents greater energy consumption in case B, which is EMA based solution, but you have written quite opposite. What is wrong, the text or the figure?
13. Now, we cannot trust any of other calculations of energy, because we don’t know what have you presented in power diagrams. Also, we cannot accept your analysis of energy consumption, as well as your calculations of energy savings. Either we cannot analyze „number of work cycles for one complete battery charge cycle“.
14. Lines 477, 488: Why have you considered lifting and lowering cycle? There are not solved all the issues in lifting and you are considering lowering, which is not analyzed in the paper? What is the purpose of that? Those are very approximate economic calculations and they cannot be accepted.
15. Sections 5.2, Chapter 6 and 7 have to be revised considering previous corrections in analysis. Sections 5.2 may be excluded, since it includes lowering, which is not analyzed in the paper and also it is not completed with the cost of EMA and EHA solutions.
Author Response
Hello dear reviewer. We have attached the responce in a PDF file. Thank you for your time and comments.
Author Response File: Author Response.pdf
