Research on Optimal Control of Excavator Negative Control Swing System
Round 1
Reviewer 1 Report
Dear Authors,
in my opinion a major revision for this article is necessary. The key points of criticism are explained in the following.
The scientific methodology is regarding the claims of an academic paper insufficiently described. I expect more detailed explanations of made assumptions, boundaries and especially the chosen methods and procedures. Furthermore the used terminology does not match with the state-of-the-art, respectively important technical terms are missing. For example when describing the main valve, the term valve lap is somehow explained, but not used.
Relating to your control strategy, the basic formula of a P and a PI-controller is well explained, but the parameter settings of your coefficients are missing, respectively not comprehensible. Did you use a look up table for the single control of the swing drive? Figure 3 includes a switch for the main pump, but it is not mentioned in the strategy.
Regarding the mode switches of your control strategy, a state diagram should be used to visualize these modes and the conditions between them.
At paragraph 4, a simulation model is introduced, but related information is missing. For classifying the results of this paper, it is for example necessary to know whether the model is validated with measurements of a real excavator or it is only verified. Furthermore, there is a lack of further explanations. Why did you use a trapezoidal wave for the control signal?
What are the groups in figure 9? Did you use a working cycle for the simulation or did you use a specified movement. What is the effect of your control strategy regarding the energy efficiency compared to the original control strategy. This aspect is completely missing and in my understanding, one of the main aspects, you wanted to show in your paper.
I also missed a list of notations in your paper.
My assumption is, that you only missed showing the methodology, which you used for your work. But if I did not see this in the next version I will vote for reject.
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The following is not really about the academic content. It is, what I would do, to give it a more proper or accurate look. Compared to other paper, your figure are excellent.
The main point, which improves your schemes (figures 1,2,3,4,6), is to add some text marks, which values are measured or which signal is on the signal lines.
At figure 1, why the main pump gets an electrical signal in a conventional NFC-system? Figure 6, could you use omega for the rotational speed instead the w?
The only information that I get from figure 7 is, that you work with AMESim. Probably you show the hydraulic scheme for the whole excavator and a 3D view oft the excavator. Also, a visualization of the movement cycle of the excavator kinematic cloud generate more insight for your results.
For your plots with a time series (figures 8,9,10), I think would be better to make them wider and make one column of subplots. Why did you make such long titles for your graphs, give your sub figures an accurate caption and shorter titles for the graphs. Also, you can use notifications for the graph titles.
In figure 9a, what is the outlet pressure of the pilot value? (Now I see that this is your favorite writing error in all figures.)
Bring the caption under your figure and not on the top of the next page.
One remark to your introduction, in a crude way, the PRVs are an independent metering for the swing main valve.
Author Response
Dear Reviewer/Editor:
Thank you for your comments on our paper "Research on Optimal Control of Excavator Negative Control Swing System". Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the comments are as follows.
Point 1: The scientific methodology is regarding the claims of an academic paper insufficiently described. I expect more detailed explanations of made assumptions, boundaries and especially the chosen methods and procedures. Furthermore, the used terminology does not match with the state-of-the-art, respectively important technical terms are missing. For example, when describing the main valve, the term valve lap is somehow explained, but not used.
Response 1: â‘ Considering Reviewer’s suggestion, we have tried our best to add more detailed explanations of the chosen methods and procedures in the paper. The revised parts mainly include: a control flow chart (as shown in Figure 7) is added to explain the three control strategies and their switching conditions more clearly, and the basis for setting control parameters is added, as shown in line 135-136, line 140-143, line 147, line 150-151, line 166, line 191. â‘¡ In addition, we have revised some technical terms according to Reviewer’s comments, change “closed length” to “overlap” (as shown in line 178.), change “Human-Mechanical interaction” to “Human-machine interaction” (as shown in line 64.), change “value flow area” to “value opening” (as shown in line 52, line 68.), change “bypass pressure” to “negative feedback pressure” (as shown in line 78, line 105, line 107.), change “outlet pressure of joystick pilot value” to “joystick-pilot pressure” (as shown in line 107, line 131, line 213.)
Point 2: Relating to your control strategy, the basic formula of a P and a PI-controller is well explained, but the parameter settings of your coefficients are missing, respectively not comprehensible. Did you use a look up table for the single control of the swing drive? Figure 3 includes a switch for the main pump, but it is not mentioned in the strategy.
Response 2: â‘ We have added instructions for setting these coefficients according to Reviewer’s comment, as follows. As shown in line 135, should be large enough to fully open the PRV with a small joystick-pilot pressure. As shown in line 140-143, according to the formula (3), the proportional control range between joystick-pilot pressure and motor speed can be adjusted by setting parameters and . As shown in line 150-151, according to experience, when the controlled object has a relatively small inertia, and can be between 1 and 10, and and can be between 0.1 and 1. As shown in line 191， can be obtained through multiple tests. â‘¡ we did not use a look up table for the single control of the swing drive, but set the parameters of P and I based on experience, and in the paper, try by tests, is set to 1, is set to 0.1, is set to 5, is set to 0.5. â‘¢ We are very sorry for not clearly explaining the pump switching rules, the original explanation is only a text description without a clear expression, and we have made corrections, in line 144-147.
Point 3: Regarding the mode switches of your control strategy, a state diagram should be used to visualize these modes and the conditions between them.
Response 3: It is really true as Reviewer suggested, we have added this part to the paper. As shown in Figure 7, the control flowchart can clearly explain the three control strategies and their switching conditions.
Point 4: At paragraph 4, a simulation model is introduced, but related information is missing. For classifying the results of this paper, it is for example necessary to know whether the model is validated with measurements of a real excavator or it is only verified. Furthermore, there is a lack of further explanations. Why did you use a trapezoidal wave for the control signal?
Response 4: â‘ We are very sorry for that we neglected to explain the model in detail. The basic parameters of structural parts, pumps, hydraulic cylinders, and swing motor are measured by excavator manufacturers. But the multi-way valve lacks internal structural parameters, however, we can get rough parameters (such as main value overlap) through the pressure-flow characteristic curve of the main valve. We have added a simple description in the paper, as shown in line 203-204 â‘¡ According to the feedback from excavator manufacturer, the operating habits of operators are not always good (that is rough and not soft), they always perform very fast operations when the excavator swings. In order to simulate the worst operating conditions more realistically, we use trapezoidal waves as the input signal of the system, we have added a simple explanation in line 212. In addition, not mentioned in the paper, the trapezoidal wave signal can make the original system rotate close to 180 degrees.
Point 5: What are the groups in figure 9? Did you use a working cycle for the simulation or did you use a specified movement. What is the effect of your control strategy regarding the energy efficiency compared to the original control strategy. This aspect is completely missing, and in my understanding, one of the main aspects, you wanted to show in your paper.
Response 5: â‘ We are sorry for not explaining the detailed meaning shown in Figure 9 (now it is Figure 10). Figure 9 shows the different joystick-pilot pressure and corresponding motor flow in a single-swing action under a certain excavator posture (a specified movement). If swing system adopts volumetric speed control strategy, a certain proportional relationship can be established between motor flow and joystick-pilot pressure, it can be seen in Figure 10 that it is a good proportional relationship. In addition, the proportional control range of six-way type main valve is narrow and uncertain, because it has a large dead zone in its neutral position and its proportional control range is also easily affected by load pressure, therefore, we think that the relationship between joystick-pilot pressure and motor flow of original system has no reference value, and we did not show it in the paper. â‘¡ Regarding the improvement of energy efficiency by the control strategy, the key is to limit the motor overflow loss, and the energy efficiency improvement of the control strategy is mainly shown in Figure 9 (previously, it is Figure 8). Figure 9 (now it is Figure 10) is only to show that the control strategy can make the motor flow and joystick-pilot pressure have a good proportional relationship, not the improvement of energy efficiency, and it is an advantage beyond energy efficiency improvement. We are very sorry for negligence to explain Figure 9 (Now it is Figure 10) in detail, and we have added related explanations in line 238-240.
Point 6: The main point, which improves your schemes (figures 1,2,3,4,6), is to add some text marks, which values are measured or which signal is on the signal lines.
Response 6: We have made correction according to Reviewer’s suggestion, and the plots have better expression effects on control strategies.
Point 7: At figure 1, why the main pump gets an electrical signal in a conventional NFC-system? Figure 6, could you use omega for the rotational speed instead the w?
Response 7: â‘ In our region, large and medium-sized excavators mostly use electric proportional variable pumps instead of hydraulic control variable pumps. This so-called conventional NFC system can transmit the electrical signal of main valve bypass pressure to the electric proportional valve that can adjust pump displacement, thereby adjusting the flow of electric proportional pump. However, due to the constraints of cost and technical level, hydraulic controlled main valves are still used by excavators. Therefore, despite the use of electric proportional pumps, excavators still have energy-saving and stability problems in human-machine interaction. In short, the technical scheme shown in the paper is only an improvement on main valve pilot control circuit. And it’s more appropriate to change the word “conventional” to the word “original” â‘¡ Furthermore, we have changed the “w” to “ω” according to Reviewer’s comment.
Point 8: The only information that I get from figure 7 is, that you work with AMESim. Probably you show the hydraulic scheme for the whole excavator and a 3D view of the excavator. Also, a visualization of the movement cycle of the excavator kinematic cloud generate more insight for your results.
Response 8: Reviewer's suggestions are very good, but the Figure is shown to provide readers with an excavator simulation model that can be used for reference. In addition, this study only analyzes the single-swing motion and the swing-stick compound motion, two motions are simple and not typical work cycles, just showing the model does not affect the understanding of the full text, therefore, we think that we can only show the simulation model. In particular, Reviewer’s suggestion is very instructive for our follow-up research.
Point 9: For your plots with a time series (figures 8,9,10), I think would be better to make them wider and make one column of subplots. Why did you make such long titles for your graphs, give your sub figures an accurate caption and shorter titles for the graphs. Also, you can use notifications for the graph titles.
Response 9: According to Reviewer’s comments and suggestion, we have made the three pilots wider and modified the titles of all subplots. When we made these plots, we only considered marking what each curve represents, and ignored the title length of the plots and sub-plots. By dealing with these issues raised by Reviewer, the visual effect of the plots has really improved, as shown in figures 9,10,11.
Point 10: In figure 9a, what is the outlet pressure of the pilot value? (Now I see that this is your favorite writing error in all figures.)
Response 10: We have changed the “outlet pressure of the pilot value” to “joystick-pilot pressure” according to Reviewer’s comment.
Point 11: Bring the caption under your figure and not on the top of the next page.
Response 11: We are very sorry for our carelessness, and we have made correction according to Reviewer’s suggestion.
Point 12: One remark to your introduction, in a crude way, the PRVs are an independent metering for the swing main valve.
Response 12: We have made correction according to Reviewer’s suggestion, as shown in line 67.
Special thanks to you for your good comments.
We tried our best to improve the paper and made some changes, and these changes will not influence the content and framework of the paper. We appreciate for your warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article is interesting but there were found in the text minor failures. They do not have a significant impact on the value of the article but in my opinion they can be improved before printing. My remarkes are listed bellow.
1 - The text uses references to figures without spaces, eg Figure1.
2 - The variables in the equations are without units and not all are described, e.g. uv11, up1, up2, uv2. I propose to insert these variables in the text, e.g. control signal of main pump up1.
3 - In Figures 5 and 8 the captions are transferred to the second page. They should be together with the drawings.
4 - In Figure 7, the authors have included very small elements that will be completely invisible after printing. I suggest that you replace them with simplified block modules, eg Main Pump, Main Value without filling them with details.
Author Response
Dear Reviewer/Editor:
Thank you for your comments on our paper "Research on Optimal Control of Excavator Negative Control Swing System". Those comments are all valuable and very helpful for revising and improving our paper. We have studied comments carefully and have made correction. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the comments are as follows.
Point 1: The text uses references to figures without spaces, e.g. Figure1.
Response 1: We are very sorry for our incorrect writing, and we have re-written this part according to Reviewer’s comments. All modifications are located in line 76, line 80, line 102, line 111, line 152, line 169, line 178, line 182, line 189, line 191, line 195, line 204, line 211, line 214, line 220, line 225, line 227, line 231, line 244, line 247, line 248, line 254.
Point 2: The variables in the equations are without units and not all are described, e.g. uv11, up1, up2, uv2. I propose to insert these variables in the text, e.g. control signal of main pump up1.
Response 2: We have made correction according to reviewer’s suggestion, and all modifications are located in line 133, line 134, line 137, line 145, line 148, line 164, line 167, line 188.
Point 3: In Figures 5 and 8 the captions are transferred to the second page. They should be together with the drawings.
Response 3: We are very sorry for our carelessness. We have dealt with this problem after revising the text of the paper.
Point 4: In Figure 7, the authors have included very small elements that will be completely invisible after printing. I suggest that you replace them with simplified block modules, e.g. Main Pump, Main Value without filling them with details
Response 4: Reviewer's suggestion is very important, but we want to provide a complete excavator simulation model to give readers reference. Therefore, as shown in figure 8, we arranged the modules in the original model more compactly to make it clearer.
Special thanks to you for your good comments.
We tried our best to improve the paper and made some changes to more clearly explain the core content of this paper, and these changes will not influence the content and framework of the paper. We appreciate for your warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Dear Authors,
I am fine with your changes.
There are only some things I would like to see in the paper.
First you missed the Units for the controller parameters.
My second point for the values of the parameters, please write it clearly in the text that the parameter range is experimental determined.
Could you add some text marks like "single swing action", "compound swing action", "swing acceleration" and so on in your flow chart? Maybe you write all output signals (uCPRV, upump, uOPRV), in every state.
My last point is about the detail level of your simulation model. Is the model validate, yes or no? Maybe you add a phrase like "The simulation model is created with measurements from the manufacturer and validated to these measurements" or "The simulation model is created with data of the manufacture, but not validate for all operating points. With this model we made a proof of our control concept.".
It is delightful to see how the comments are respected!
Author Response
Dear Reviewer/Editor:
Thank you for your comments on our paper "Research on Optimal Control of Excavator Negative Control Swing System". Those comments are all valuable and very helpful for improving our paper. We have studied comments carefully and have made correction. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the comments are as follows.
Point 1: First you missed the Units for the controller parameters. My second point for the values of the parameters, please write it clearly in the text that the parameter range is experimental determined.
Response 1: â‘ We have made correction according to Reviewer’s comment, and we have added these Units to the paper, as shown in line 135, line 139, line 150, line 164, line 192. â‘¡ We have added related explanations about the parameter range in the paper according to Reviewer’s comments, as shown in line 150-151, line 165.
Point 2: Could you add some text marks like "single swing action", "compound swing action", "swing acceleration" and so on in your flow chart? Maybe you write all output signals (uCPRV, upump, uOPRV), in every state.
Response 2: It is really true as Reviewer suggested, we have added some texts to the control flow chart, which can express the control strategy of this article more clearly, as shown in Figure 7. In addition, we added an explanation in the paper, as shown in line 199-120.
Point 3: My last point is about the detail level of your simulation model. Is the model validate, yes or no? Maybe you add a phrase like "The simulation model is created with measurements from the manufacturer and validated to these measurements" or "The simulation model is created with data of the manufacture, but not validate for all operating points. With this model we made a proof of our control concept.".
Response 3: Reviewer’s suggestion is very good, and we have made correction, the revised part is as follows: In order to investigate the feasibility and correctness of the proposed technical scheme and control strategies, as shown in Figure 8, a simulation model of 37-ton excavator is established with data of manufacture, but not validate for its all operating points. The swing motion of excavator is simulated with the model, and the original and optimized system performance are compared and analyzed, thus verifying the control concept of this paper. (As shown in line 204-208).
Special thanks to you for your good comments.
We tried our best to improve the paper according to Reviewer’s comment, and hope that the correction will meet with approval. We appreciate for your warm work and recognition of our research work, all the comments on this paper are very helpful to improve the paper, once again, thank you very much for your comments and suggestions.
Author Response File: Author Response.pdf
