The Effect of Spool Displacement Control to the Flow Rate in the Piezoelectric Stack-Based Valve System Subjected to High Operating Temperature
Round 1
Reviewer 1 Report
In this paper it’s presented the precise control of a spool displacement which is significant to achieve advanced performance of a hydraulic valve system driven by the piezoelectric stack actuator.
Please define Vp in the eq. (1)
In eq. (17) the integral term it is “integral from 0 to t”, where 0 it’s the term (in time) which define the last stationary regime.
I suggest increasing the number of paper published in last five years included in references.
Please make a comparison between "Simulation and Experiment".
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Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
The authors studied the spool control of a direct drive valve actuated by an amplified piezo-stack. This valve configuration was already presented by the authors. In this paper, the control of the spool is performed at high temperature using a standard PID controller. Simulations and experimental results are compared. These are my comments:
The literature review is poor at the moment. Many other papers can be cited regarding the piezostack actuation of hydraulic valves.
The authors should better explain what was done in their previous papers, and what is new in this paper.
In typical hydraulics applications, the maximum oil temperature is 60 °C. What is the meaning of carrying out this analysis at 100 °C? What are the real applications of this?
Many assumptions are not justified, such as: damping coefficient of the piezo stack actuator, discharge coefficient (why 0.611 precisely?), Jet angle, damping coefficient of the spool.
In the model, the formula of the effective mass (???) of the piezostack must be justified.
Please, better explain the utility of employing the simulations in this work.
Please, show the hydraulic circuit of the experimental apparatus.
How do you measure the actual temperature of the stack? Does it reach 100 C?
The step response of fig. 9 shows a large overshoot. Can you justify this? Is it open loop?
The results presented do not have practical importance. These valves must be tested at different and high frequencies, at least up to 100-500 Hz. Please, report the results at high frequencies.
Please, show the Bode Plot of the closed loop control at the different temperatures.
At high frequencies, high current is generated by the amplifier because of the high capacitance of the piezo stack. This is the real problem. The authors should evaluate the current generated and its effects on the piezostack performance.
The trends of Fig. 14 must be explained.
What is the real innovation of this work? The PID control is a regular one, and the authors already performed analysis with the heating chamber. Please state this in the introduction and conclusions.
The flow rate seems very low for a pressure drop of 70 bar.
English and overall presentation must be improved.
Author Response
Please refer to the attached file.
Author Response File: Author Response.pdf
Reviewer 3 Report
I have a few questions / comments / suggestions.
- Figure 2 shows the schematic for the mechanical part while figure 3 shows the schematic for the fluid part. I suggest to provide more information on how the two parts interact with one another.
- Maybe I am not familiar with fluid modeling, the deviation of Eq (15) is not clear to me. Which fundamental governing equations did the authors start? Also in Eq (13) and (14), F_x = - F_t - F_s, the split into steady and transient may need some explanation.
- Eq (16) is the governing equation of the overall system including mechanical part and fluid part. But the equation only involves the primary / state variable x_s and its derivatives. I hope the authors can clarify the system order and the state variables, since the authors also study the dynamical performance, and explain why no variable associated with the fluid sub-system does not appear in the overall governing equation (Eq 16). The authors discussed temperature range (20C to 100C) in the article. Was thermal expansion considered in the model?
- How is Eq (16) solved numerically, say ODE45 in MATLAB? What are the initial conditions of the state variables and the mathematical expression of the input V_p(t)
- Figure 9 shows the step responses of the system both numerically and experimentally, I was wondering why the numerical solution does not exhibit over-shoot as experimental data, which is not consistent with the typical dynamic behavior. It seems to me that the system contains no effective damping.
- Figure 14 shows the pressure drop of the system at two selected temperatures. But the model does not depend on temperature. Would the author explain why? Also the authors may want to briefly describe / recall how the pressure drop is computed from data of displacements, or just measured from sensors experimentally.
- In Eq (17), the authors proposed to use PID and values of k_p, k_i and k_d were computed for two temperatures. Did the authors analyze data at intermediate temperatures, like the operating temperature at 90 C.
Author Response
Please refer to the attached file.
Author Response File: Author Response.pdf
Reviewer 4 Report
The manuscript, Tracking Control of a Spool Displacement in a Hydraulic Valve System Driven by Piezoelectric Stack Actuator: Simulation and Experiment. The methods are explained with formulation and consistent test . The paper is well structrured and clearly presented. Nevertheless, I have some suggestions for further improvements: 1 - The authors should better put their results in relation to what has been achieved in literature. This is not really clear in the manuscript. 2- The paper lacks a more complete review of the state of the art. The problem presented has certainly been addressed in the existing literature, particularly PSA, and the reviewer wonders whether or not previous contributions have considered the same approach taken in the current paper. This is not clear enough in the current text. This is important and the reviewer wonders whether or not previous contributions have considered the same approach as the one taken in this document The manuscript needs a thorough and comprehensive review. 3- Authors should reconsider what is the main novelty of their work and why it is relevant to this community. This should be made clear in the manuscript. 4 - Apart from the application, and the interesting study presented, I have the feeling that only well-known classical methods are used. I would like the authors to comment on this. 5 - The authors should reconsider what is the main novelty of their work and why it is relevant to this community. I would like the authors to comment on this too. 6- What is the challenges of this work? 7 - The formulation is ok, but equations (15) and (16) need some explanation. 8 - In "An Experimental Apparatus, the block-diagram presented in Figure 8 should be commented on further. This is relevant. 9 - What is the reason for using a PID controller in your application? 10 - I suggest a revision of the titles of Figures 4 and 5. 11 - I also suggest a moderate review of English.Author Response
Please refer to the attached file.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
the revised paper is accepted in the present form
Author Response
Authors’ Reply to Reviewer #2
Review Comments:
The revised paper is accepted in the present form, but English and style should be checked.
Answer:
English has been carefully checked throughout the manuscript in terms of the grammar, spelling and typos.
In addition, the style has been modified to adapt the journal Actuators.
Thank you very much for your time and effort.
Prof. Seung-Bok Choi on the behalf of all authors.
