Development and Evaluation of Energy-Saving Electro-Hydraulic Actuator

Round 1

Reviewer 1 Report

Dear Authors

This paper proposed a novel energy saving hydraulic system using switching control valves. The hydraulic system is based on EHA system and equipped with a switching valve block. The valve block includes seven ON/OFF valves and a hydraulic accumulator. The simulation results reveal that the system is able to save approximately 20% energy consumption compared with a traditional EHA. Experimental results are also presented to corroborate the theoretical contributions.

The paper deals with an interesting topic, although some minor and major observations must be addressed before a final decision can be taken.

1. For‘Table 1. Operating modes of the hydraulic system.’Please explain the working process of RURG What is the role of accumulator HA?
2. For‘Figure 4. (a) Reuse normal in mode; (b) Reuse normal in mode.’Please check whether the names of Figure (a)and Figure 4. (b) are the same.

Author Response

Dear Reviewer

The first of all, we would like to thank you so much for your valuable, useful comments and accommodations as well as positive acknowledgment on our manuscript. Based on these comments, the revised version has been improved remarkably. All changes in the new version have been marked by blue highlighted tool. We hope to meet with the approval from Reviewer. All the comments from the Reviewers have been responded point by point. Please find them in attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

The submission deals with a topic of interest. It is appreciated that numerical simulation is verified by real tests. Unfortunately, the paper has numerous weaknesses that drove me to reject it. The main reasons are:

Editorial level

E1 - It seems that the paper has not been verified prior submission. Some sentences have no verbs or there are double words.

E2 - The technical/scientific vocabulary is fuzzy or even incorrect (e.g. "recuperation" is used while in the domain we use "recovering" or "regeneration", "reliability" is used instead of "fidelity", e.g. what means "technology" used instead of "approaches" or even no word, "virtual modelling" instead of "virtual test", "slope of position" instead of "speed", "circle" instead of "cycle", etc…). The use of "power quadrant" should be preferred to compare the modes of operation in combination of the direction of motion. The use "Aiding load" or "opposite load" would also make the understanding clearer.

E3 - The English is very poor with numerous grammatical and spelling errors

E4 - In the first figures, the arrows are misleading as they either represent the actual direction (e.g. flow and force) or the sign convention (e.g. x).

E5 - The symbols sometimes change or are not even defined. Units are sometimes false (Nm instead of N/m).

E6 - It should be better to have dimensionless torque and speed factors, e.g. by introducing the pump displacement and e.g. the piston hydrostatic area.

E7 - Table 2 should be written for SI units

E8 - tstart and tend should be  mentioned in fig 10 as the limits of integration for eq 3 and 4

E9 - Table 5 should only mention the differences between switching strategies, otherwise it is impossible for the reader to clearly perceive them.

E10 - Figure 11 should show the name of the components defined in fig 10 to facilitate readability

E11 - The phase numbers have to be added on the figures to facilitate understanding

Scientific - Technical

S1 - The statements mentioned in the state of the art review are not justified

S2 - In the figures, the pump rotation should no be in both directions

S3 - It not clear how the phase change is detected by the controller

S4 - The use of proportional valves models has to be justified

S5 - It seems that the authors have not managed actively the introduction of fluid compressibility (only a single pipe), although the most compliant domain comes from the cylinder chambers.

S6 - The authors have to justify the use of a motor model as a source of speed.

S7- It seems that the mechanical efficiency of the pump is not considered, as well and the volumetric efficiency in the motor mode. This limits the accuracy of the conclusions.

S8 - Authors mentioned high power applications, while the motor power is only 1.5 kW.

S9 - The setting of the slider friction parameters has to be justified.

S10 - Since fig 12, the levels at end of the cycle should be identical to those at the beginning of the cycle to conclude correctly and with realism for repetitive cycles.

S11 - In figure 12, the max pump speed is not consistent with the data of the pump.

S12 - It is not sufficiently explained how the motor is controlled (open loop?) to produce the desired cycle

S13 - It is a pity that the investigations in the accumulator pressure and volume are conducted sequentially, the exploration should cover the entire possible domain, which is widely facilitated by the design explorer feature of the simulation SW.

S14 - The comparison of simulated and measured RF should be part of the analysis, prior the conclusion.

S15 - The RF should be measured and simulated at AC supply level, not only at pump shaft level

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Author Response

Dear Reviewer

The first of all, we would like to thank you so much for your valuable, useful comments and accommodations as well as positive acknowledgment on our manuscript. Based on these comments, the revised version has been improved remarkably. All changes in the new version have been marked by blue highlighted tool. We hope to meet with the approval from Reviewer. All the comments from the Reviewers have been responded point by point. Please find the attached file

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

It is appreciated that the authors placed a significant effort in response to the reviewer comments.

However there are still important points to clarify and spelling/wording/grammar imperfections to correct.

See pdf file.

I wll however recommend a minor revision. Please note, that in the next review, I will be very attentive to the actions taken concerning the scientific comments.

Comments for author File: Comments.pdf

Author Response

Response to Comments from Reviewer

We would like to thank you so much for your valuable, useful comments and accommodations as well as positive acknowledgment on our manuscript. All changes in the new version have been marked by red highlighted tool. We hope to meet with the approval from Reviewer. All the comments from the Reviewers have been responded point by point as following

Comment #1

What means effective here?

Answer:

Thank you so much for your comment.

Title of the paper is changed:

Development and evaluation of energy-saving Electro-Hydraulic Actuator

Comment #2

Mistakes in typing, words,..

Answer:

Thank you so much for your comment.

Mistakes in typing, words,.. are modified as your recommends (in red color).

Comment #3

Justify “Value of ω_n is calculated by using equation 1 within v is the desired velocity and r_o is selected as 1 meter”

Answer:

Thank you so much for your comment.

It is revised as follows. Value of ω_n is calculated by using equation 1 within v is the desired velocity and value of K_V for each phase is shown in table 2.

Comment #4

Question and Comment: still no mention to the indirect efficiency when the pump operates as a motor. This is mandatory to be addressed in a regenerative system.

Answer:

Thank you so much for your comment.

It is revised as follows. When value of pressure p₂ is higher than that value of p₁, the hydraulic pump works as a motor. When the pump works in motor mode, the system recovers energy from external load. In this study, values of the mechanical and volumetric efficiencies of the pump in the motor mode vary in two intervals [0.7-0.9] and [0.6 0.9], respectively.

Comment #5

Question and Comment: As the model is done, the compressibility of the fluid volume in the cylinder is neglected. It is not sufficiently rigourous becauses it is generally the most important source of hydraulic compliance. At least this limit has to be mentioned and this choice has to be justified.

Answer:

Thank you so much for your comment.

It is revised as follows. Model of the hydraulic cylinder is built based on compressibility of fluid in the cylinder chambers, leakage, damping coefficient on end stops and deformation on end stops at which damping rate is fully effective. Model of HJ020 in AMESim is used for the cylinder and its parameters are described in table 8 [1,9].  

Comment #6

Question and Comment: No mention to the energy supplied to the motor. If the electronic drive is not able to recover energywhich is generally the case for some seconds of cycle, the energy consummed by the motor has to be calculated by integrating the absolute value op power, not the power.

Answer:

Thank you so much for your comment.

It is revised as follows.

Comment #7

Surprising model of the model. Torque and back emf would have been sufficient here (is there really a need to introduce mutual inductance if the control of the motor is not implemented in details?).

Not clear what eq 8 represents or how it is obtained.

There is no speed or torque limit in the model. This is not realistic. It has to be verified current and voltage are realistic.

Explain why a motor model available in AMESim has not been used and the authors have re-constructed the model from equations using a signal (not power view?

Answer:

Thank you so much for your comments.

It is revised as follows. In this study, a model using signal for both AC servo motor and its servo controller is re-constructed because the control of the motor is not implemented in details. Moreover, only speed response of the servomotor and its controller is studied so a simple block diagram of the motor model is used [30,31,32] as shown in Fig.11.

Speed or torque is limited in revised model.

Comment #8

In table 8,

• These values are not used in the model, while the motor parameters mentioned in the former paragraph do not appear in the table.
• How are the efficiencies entered (as a function of speed, pressure?)
• These values are not used in the model, while the motor parameters mentioned in the former paragraph do not appear in the table

Answer:

Thank you so much for your comments.

It is revised as follows.

Table. 8 Parameters of the system

No	Equipment	Parameters	Values	Unit
1	Hydraulic pump	Displacement (V)	1.6.10-6	m3/rad
		Volumetric efficiency in pump mode	as a function of speed end pressure	-
		Mechanical efficiency in pump mode
		Volumetric efficiency in motor mode	as a function of speed end pressure	-
		Mechanical efficiency in motor mode
		Moment of inertia	0.012	kg.m2
2	Hydraulic valve	Nominal flow rate	10-3	m3/s
		Sifting time	20	ms
3	Hydraulic cylinder	Bore diameter D	6.10-2	m
		Rod diameter d	4.5.10-3	m
		Max Stroke	0.3	m
		Dead volume at port 1 end	5.10-5	m3
		Dead volume at port 2 end	5.10-5	m3
		Leakage coefficient	10-7	m3/s/bar
4	Hydraulic accumulator	Pre-charge pressure	60.105	Pa
		Volume	6.10-3	m3
5	Slider	Mass	100	kg
		External load	30	kN
		Viscous friction coefficient	0.1	N/(m/s)
		Coulomb force	250	N
		Stiction force	800	N
6	Spring	Stiffness	12.104	N/m
7	Pipe	Diameter	12.8.10-3	m
		Bulk modulus	8.109	Pa
		Length	0.5 -1.5	m
8	Relief valve	Setting pressure	15	MPa

 

Comment #9

In figure 12a

For all these figures, it is sill not a repetitive cycle as the final values do not correspond to the initial ones.

Answer:

Thank you so much for your comments.

It is revised as follows. Response of speed of the motor with the servo controller in EHA mode respect to multi-step input is shown in Fig.12a. To finish a cycle, speed of the motor is staring from zero and finishing also at zero speed after 12^th second.

Fig.12a Pump speed response in EHA mode

Comment #10

In figure 12b

Is it realistic (no speed limit in the motor model)? This impacts the conclusions.

Answer:

Thank you so much for your comments.

It is revised as follows.

For both EHA and NRS strategies, flow outlet of the cylinder goes directly to the tank without any throttling control during returning phases. Therefore, value of speed for EHA or NRS strategy is so high at the beginning of FR phase when compared with that value for PS strategy.

Comment #11

In figure 14.c

There is not consideration to the reducer efficiency in back driving mode. The conclusions are optimistic.

Here it is implicitly assumed that the power electronics can recover all power coming from the motor. This is to be explained and justified given the design of the electronic drive. It has also to be mentioned that the energy losses in the electronic drive are neglected.

Answer:

Thank you so much for your comments.

It is revised as follows.

It can be observed that energy is always supplied from the motor. In which, that energy is used to charge the accumulator in RT phase while that energy is use to overcome external load and push the cylinder out during FF and SF phases. On the other hand, the motor still supplies energy during recovery phases and the recovery energy is stored in the accumulator instead of electronics drive as a traditional energy recovery EHA system. Moreover, it has also to be mentioned that the energy losses in the electronic drive are neglected and efficiencies of the pump are included.

Comment #12

Figure 15

Still a 2 times 1D (volume, then pressure) optimization, instead of a globel 2D optimization (volume and pressure at same time)

Answer:

Thank you so much for your valuable suggestion

It is revised as follows.

For partial recovery applications, energy recovery factor of the system versus pre-charge pressure and volume of the accumulator is described in Fig.15. In which, the setting value of the relief valve in the hydraulic circuit is 200 bar and that value is not increased because it depends on type of the pump. It is revealed that the RF varies and it reaches the high value about 0.6 when pre-charge pressure of the accumulator is 60 bar. This values are reduced when the pre-charge pressure is too high or that is too low. When it is set too low, the slider goes so fast. When the pre-charge pressure is increased the operating pressure of the system is increased and reaches setting pressure of the relief valve. Moreover, when volume of the accumulator increases, the recovery factor is also increased and vice versa. It is observed that the effect of the pre-charge pressure to the energy recovery factor is higher than the effect of the volume.  

Fig.15. Energy recovery factor versus accumulator volume under the various pressure of the accumulator

 

Comment #13

Figure 18c and 19.a

This is not a repetitive cycle

Answer:

Thank you so much for your useful comments.

It is revised as follows.

It is observed that, at the end of first cycle, pressure of the accumulator of the ending is higher than that of the beginning as shown in figure 18.c because recovery energy in returning phases is stored in the accumulator. Beside, speed of the pump at the beginning and the ending is different as shown in figure 19.a because the system charges the accumulator in a second for first cycle. Therefore, only position of the cylinder is repetitive cycle instead of any system parameter such as pressure of the accumulator or speed of the pump. For overcoming this phenomena, a charging accumulator strategy or a power management for total cycle should be added in next study. 

Comment #14

Figure 20.a

How do you measure the supply energy?

Answer:

Thank you so much for your comments.

It is revised as follows.

Supplying energy is calculated by indirectly measured torque and speed of the motor.

Comment #15

Figure 20.b

This validates the model for the proposed strategy, but not the model used for the EHA strategy (not tested) as it lacks of realism.

Answer:

Thank you so much for your comments.

It is revised as follows. For this system, only PS strategy is able to recover energy by using the accumulator.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The authors have considered the review with care and modified the submission according to the suggestions and needs for more detailed or justified explanations. I am pleased with most of the actions and answers.

This has motivated my decision to propose "Accept".