Design of Optical Free-Form Surface Milling Machine Based on Mechanical Shunt and Dynamic Analysis
Round 1
Reviewer 1 Report
One of the conclusions of the article refers to the capabilities of the gravity balance device to improve the characteristics of the milling machine in terms of the Z axis load and fluctuation. So, this gravity balance device should be described in more detail or specified how the mechanism is implemented in the virtual model.
In my opinion, the dynamic equations (exposed in 4.1) used by ADAMS to perform the model simulations, are entirely fundamental. In fact, all dynamic simulation programs are based on them. Therefore, they do not contribute to the argument development of the article. In this sense, it might be interesting to provide the type of solver (integrator) utilized and the corresponding parameters.
Component constraints of the model should be stated more precisely. Stiffness and damping contact parameters should also be provided, as they significantly influence the dynamical behaviour of the Z-axis milling machine.
It should be specified to which model the results of Fig. 5 correspond (Z-axis motor installed on roof/columns; gravity balance device working /not working). In Fig. 5(c), fluctuations in acceleration seem to respond to errors associated with numerical calculation, not to real variations.
I have not understood the meaning of the three-dimensional (X, Y and Z-direction) projection curve of Z-axis screw nut. I think it should be clarified, or at least stated what the results of the corresponding graphs imply.
Finally, the reason why the first natural frequency of milling machine affecting manufacturing precision is 68Hz, should be explained.
Author Response
Thank you very much for your comments on our manuscript entitled “Research on Dynamic Characteristics of Optical Free-form Surface Milling Machine Based on Multibody Dynamics”. These comments are all helpful to improve our manuscript. We have carefully considered your valuable comments and useful suggestions, and have made the corrections. Revised portions are marked in red in the paper. The corrections and responses to the comments are as follows:
Point 1: One of the conclusions of the article refers to the capabilities of the gravity balance device to improve the characteristics of the milling machine in terms of the Z axis load and fluctuation. So, this gravity balance device should be described in more detail or specified how the mechanism is implemented in the virtual model.
Response 1: According to your opinion, we have added a detailed description of the gravity balance device in the paper.
On page 2-3: The number of Z-axis column is four, which are installed on the four corners of the milling machine bottom plate. The top of the Z-axis column is connected to the milling machine roof. The milling machine bottom plate is installed on the milling machine base, the cradle workbench is installed on the center position of milling machine bottom plate, and the optical free-form surface component is installed on the cradle workbench through workpiece fixture. The upper surface of the milling machine bottom plate is provided with milling waste liquid collection tank, the bottom of the milling waste liquid collection tank is provided with waste liquid collection hole, and the milling waste liquid is discharged through the waste liquid collection hole. The Z-axis column and the slide carriage is connected by Z-axis guide rail slider. The Z-axis guide rail slider is installed on Z-axis guide rail slider mounting groove. The Z-axis screw and the slide carriage is connected by Z-axis screw nut. The two-dimensional main motion platform is installed on the center position of milling machine roof, the oil cylinder rod of the gravity balance device sequentially passes through the two-dimensional main motion platform and the milling machine roof to connect with the two-dimensional follow-up motion platform, and the two-dimensional follow-up motion platform is installed on the center position of slide carriage.
On page 4: The two-dimensional main motion platform is composed of the X-axis main motion platform and the Y-axis main motion platform, which can do the main motion in the XY plane. The number of X-axis, Y-axis guide rail slider and X-axis, Y-axis motor screw mechanism of the two-dimensional main motion platform are two respectively, and they are arranged symmetrically on both sides of the oil cylinder axis. The two-dimensional follow-up motion platform is composed of the X-axis follow-up motion platform and the Y-axis follow-up motion platform. The two-dimensional main motion platform drives the two-dimensional follow-up motion platform move in the XY plane. The number of X-axis, Y-axis guide rail slider of the two-dimensional follow-up motion platform are two respectively, and they are symmetrically arranged on both sides of the oil cylinder axis. Since the Z-axis slide carriage does not participate in the X-axis and Y-axis movement, the motion travels of the X-axis and Y-axis of the two-dimensional main motion platform are smaller than the X-axis and Y-axis motion travels of the milling machine respectively. Because of the installation of the X-axis motion mechanism of the milling machine is under the Y-axis motion mechanism, the X-axis motion travel of the two-dimensional main motion platform is smaller than the Y-axis motion travel.
Point 2: In my opinion, the dynamic equations (exposed in 4.1) used by ADAMS to perform the model simulations, are entirely fundamental. In fact, all dynamic simulation programs are based on them. Therefore, they do not contribute to the argument development of the article. In this sense, it might be interesting to provide the type of solver (integrator) utilized and the corresponding parameters.
Response 2: Thank you so much for your suggestion, we have introduced the type of solver used by ADAMS and provided the type of solver (integrator) utilized and the corresponding parameters.
On page 8: The type of solver used by ADAMS software include linear solver (CALAHAN solver and HARWELL solver), nonlinear solver, DAE solver [(SI2: GSTIFF, WSTIFF and CONSTANT_BDF), (SI1: GSTIFF, WSTIFF and CONSTANT_BDF) and (I3: GSTIFF, WSTIFF, DSTIFF and CONSTANT_BDF)] and ODE solver (ABAM solver and RKF45 solver). The selection of the integrator and the setting of the solver have a great influence on the simulation speed and accuracy. In ADAMS, GSTIFF I3 and GSTIFF SI2 are the most widely used integrator, among them, the calculation accuracy of GSTIFF SI2 integrator is much higher than that of GSTIFF I3, but the calculation efficiency is lower, it is suitable for simulation calculation of this model, the accuracy of the solver is set to 1×10-5, the step size is 1×10-4.
Point 3: Component constraints of the model should be stated more precisely. Stiffness and damping contact parameters should also be provided, as they significantly influence the dynamical behaviour of the Z-axis milling machine.
Response 3: Indeed, the stiffness and damping parameters of the joint surface will significantly affect the dynamic characteristics of the milling machine. According to your opinion, we have added the stiffness and damping parameters used by ADAMS. Our future research plan will focus on the influence of the joint surface parameters on the milling machine dynamics.
On page 8: The contact stiffness between the Z-axis screw and the Z-axis screw nut is 3.1×108N/m, and the contact damping is 3.6×103N.s/m. The contact stiffness between the Z-axis lead screw and the Z-axis bearing is 4.4×108N/m, and the contact damping is 3.8×103N.s/m. The contact stiffness between the Z-axis guide rail and the Z-axis slider is 2.37×108N/m, and the contact damping is 4.3×103N.s/m. The contact stiffness between the Z-axis column and the milling machine bottom plate is 5.05×108N/m, and the contact damping is 1.91×104N.s/m. The contact stiffness between the milling machine bottom plate and the milling machine base is 8.08×109N/m, and the contact damping is 3.06×105N.s/m.
Point 4: It should be specified to which model the results of Fig. 5 correspond (Z-axis motor installed on roof/columns; gravity balance device working /not working). In Fig. 5(c), fluctuations in acceleration seem to respond to errors associated with numerical calculation, not to real variations.
Response 4: According to your advice, we have added a deterministic description of the model used in the simulation results, including the type of structural scheme used and the working state of the gravity balance device in the paper.
On page 8: the Z-axis motor is installed on the roof
On page 9: the gravity balance device is working and the flexible multibody model is used
On page 10: When the gravity balance device is working and the flexible multibody model is used.
Point 5: I have not understood the meaning of the three-dimensional (X, Y and Z-direction) projection curve of Z-axis screw nut. I think it should be clarified, or at least stated what the results of the corresponding graphs imply.
Response 5: According to your advice, we have added an explanation of the three-dimensional (X, Y and Z-direction) projection curve of Z-axis screw nut to clarify the specific meaning of its expression in the paper.
On page 10: The three dimensional projection curve of Z-axis screw nut indirectly indicates the dynamic characteristics of the Z-axis screw, it will affect the driving precision of the Z axis.
Point 6: Finally, the reason why the first natural frequency of milling machine affecting manufacturing precision is 68Hz, should be explained.
Response 6: Thank you again, the explanation has been added in the paper. Because the motion axes of the milling machine are installed on the internal frame, it also can be seen from the mode shapes that the first, second, fourth and ninth order vibration modes are the vibration of the milling machine external frame, and the other vibration modes are the vibration of the milling machine internal frame, so the first order mode of milling machine affecting manufacturing precision is the third order.
On page 14: Because the motion axes of the milling machine are installed on the internal frame
Reviewer 2 Report
Balancing equipment is indeed required in any precision machine tooling. What is the novelty in showing that your simulation work confirms this prior knowledge? Your rationale should clearly indicate your innovation for each reference you mention. What is new in your approach to use ADAMS? What was the freeform surface you implemented for the simulation work, what were the required dynamics of this surface? The most interesting research question is not asked, nor researched: what is the final result on the surface accuracy of the freeform you refer to? What are your insights and future work on the machine design starting from your work in this paper?
Author Response
Thank you very much for your comments on our manuscript entitled “Research on Dynamic Characteristics of Optical Free-form Surface Milling Machine Based on Multibody Dynamics”. These comments are all helpful to improve our manuscript. We have carefully considered your valuable comments and useful suggestions, and have made the corrections. Revised portions are marked in red in the paper. The corrections and responses to the comments are as follows:
Point 1: Balancing equipment is indeed required in any precision machine tooling. What is the novelty in showing that your simulation work confirms this prior knowledge?
Response 1: Yes, precision machine tooling needs to set balancing equipment to reduce the impact of gravity on machining precision. However, after reading a lot of literature in this area, there is no research on the impact of gravity balance device on machine tool dynamics. This paper establishes a virtual prototype of the optical free-form surface milling machine, based on the model, the influence of the gravity balance device on the Z-axis dynamics of the milling machine was studied from a quantitative and qualitative perspective. At last, it was concluded that the gravity balance device can significantly improve the efficiency of the milling machine and suppress the fluctuation of the Z-axis load.
Point 2: Your rationale should clearly indicate your innovation for each reference you mention. What is new in your approach to use ADAMS?
Response 2: Thank you for your suggestion. The previous literature only established the rigid multibody dynamics model or the flexible multibody dynamics model when using the ADAMS for dynamic simulation. In the paper, the rigid multibody dynamics model and the flexible multibody dynamics model are both established, and the dynamic simulation research on the optical free-form surface milling machine is carried out according to comparison method. The results show that the simulation results of the rigid multibody dynamics model and the flexible multibody dynamics model are numerically consistent. We add the type of solver and parameters used in model.
Point 3: What was the freeform surface you implemented for the simulation work, what were the required dynamics of this surface?
Response 3: The optical free-form surface described in the paper is a precision optical element used in the optical system. This kind of part requires machining equipment with excellent dynamic performance. The obtained dynamic performance information of the optical free-form surface milling machine provides a theoretical reference for the selection of manufacturing process parameters, and at the same time provides data for the design of Z-axis components and control system.
Point 4: The most interesting research question is not asked, nor researched: what is the final result on the surface accuracy of the freeform you refer to?
Response 4: Thank you very much for your academic directional guidance. This kind of optical surface requires nano-scale roughness and ten-nano-scale profile. Precision milling has a great influence on the surface and sub-surface quality of optical free-form surface, and its machining effect will directly determine the efficiency and feasibility of subsequent machining such as grinding and polishing. Our future research plan will focus on the influence of machining parameters on the surface integrity of optical free-form surface during milling, such as the study of milling chatter mechanism, and the influence of the milling machine dynamics on the machining quality of optical free-form surface.
Point 5: What are your insights and future work on the machine design starting from your work in this paper?
Response 5: Finally, thank you again. I think that dynamic design combined with static design has become an inevitable trend in the development of modern machine tool design. Because the characteristic parameters of the joint surface have a significant impact on the performance of the machine tool, the research on the identification technology of the joint surface parameters has become very important. Input the joint surface parameters to the virtual prototype for performance information, and compare with the data obtained from the physical prototype experiment to determine the accuracy of the virtual prototype model.
Reviewer 3 Report
Please read and do all changes in the attached file, they are mandatory
Comments for author File: 
Comments.pdf
Author Response
Thank you very much for your comments on our manuscript entitled “Research on Dynamic Characteristics of Optical Free-form Surface Milling Machine Based on Multibody Dynamics”. These comments are all helpful to improve our manuscript. We have carefully considered your valuable comments and useful suggestions, and have made the corrections. Revised portions are marked in red in the paper. The corrections and responses to the comments are as follows:
Point 1: I do not like this kind of title ... research ... please give the real contribution in the title: what did you propose or what did you find out?
Response 1: Thank you for your suggestion, the title has changed to “Design of Optical Free-form Surface Milling Machine Based on Mechanical Shunt and Dynamic Analysis”, this title can better present the work and contribution of the paper.
Point 2: This wrong: Most of the existing machine tools are cantilever structures many are bridge type. Machines are divided into one-loop or two.loop structures se the book Machine Tools for high performance machines (springer). Cantilever is only the ram or vertical bar into which is located the spindle.
Response 2: Thank you for your correction, the wrong part has been deleted. I have read this book (Machine Tools for high performance machines) from beginning to end carefully, this is a very good material for machine tools.
Point 3: I do not see how you dealt forgetting some key sources. In machine tools since the works in the 80s by Machine Tools Task force, the proposal were many.
Response 3: Thank you for your remind, i am very interested in "key sources" and "Machine Tools Task force", but I don't know their meaning well, I hope to learn from you.
Point 4: Your approach is very good, a pity you did not include the works of leading groups in machine tools, For instance: Methodology for the design of a thermal distortion compensation for large machine tools based in state-space representation with Kalman filter, International Journal of Machine Tools and Manufacture 75:100 - 108 75 and A method for thermal characterization and modeling of large gantry-type machine tools, The International Journal of Advanced Manufacturing Technology 62 (9), 875-886 in both cases the results were real and interesting. I have read ref 5 and 6 not see many links....please replace by good ones.
Response 4: I have read these two literatures carefully, it is really interesting, i also read a lot of literatures on the thermal characteristics of machine tools, acccording to your suggestion, the ref 5 and 6 have been replaced. The thermal deformation of the machine tool has a significant impact on the machining precision, nest, our future research plan will also focus on the thermal characteristics of milling machine.
Point 5: Free-form surface machining was very studied in the 90s, and 2000s by Salgado, Lamikiz, Lazoglu and others. Your state of the art is poor. You could think about how to monitor forces, position and other ideas in those works. https://doi.org/10.1016/j. mechatronics. 2005. 09. 001. You can develop your own ideas and please follow this.
Response 5: Thank you very much for your academic directional guidance. The literature you shared is very good, the author presents a data acquisition system that can simultaneously records cutting forces and cutting tool position of complex parts,the proposed method has been applied adopting several examples, it is very interesting and inspires me a lot. Later, i will read more literatures in this area, and strives to obtain the most advanced academic results.
Point 6: Please include a picture of the machine...is this a real one or a study about one. In the line of being a design, the key is the state of the art. Please rewrite it.
Response 6: Finally, thank you again. As a machine tool researcher and also a mechanical engineer engaged in machine tool development for many years, improving the performances and machining precision of machine tools is my mission, this milling machine is new and has obtained intellectual property rights (Patent No.: ZL 2020 1 0008995. 1). Using scientific methods to develop machine tools is a new trend in machine tool design, the development process of machine tool should first perform virtual design to obtain the performances data of the machine tool, the data can provide supports for the optimization design of the machine tool structure and process parameters, soon we will build a real milling machine to verify the performances of the machine tool.
Round 2
Reviewer 1 Report
In my opinion, now the explanation about the operation of the gravity balance device mechanism is very extensive, but somewhat cumbersome. What should be clearer is only how it has been implemented in the ADAMS model (not in the real machine). Have all of its parts been modeled, the XY-moving-plate included in the ADAMS model? or just the corresponding vertical force between the roof and the z-axis carriage has been applied?
Author Response
Thank you very much again for your comments on our manuscript entitled “Research on Dynamic Characteristics of Optical Free-form Surface Milling Machine Based on Multibody Dynamics”. The responses to the comments are as follows:
Point 1: In my opinion, now the explanation about the operation of the gravity balance device mechanism is very extensive, but somewhat cumbersome. What should be clearer is only how it has been implemented in the ADAMS model (not in the real machine). Have all of its parts been modeled, the XY-moving-plate included in the ADAMS model?
Response 1: Yes, all parts of the milling machine are modeled in ADAMS, the XY-moving-plate and the gravity balance device are also included in the model, but the model is simplified, the simplified contents are as follows: omit the X, Y-axis servo motors, delete the smaller holes and corners in the parts, and delete some small grooves, these deleted features have negligible influence on the results of simulation. The virtual model established in ADAMS is consistent with the real milling machine and can reflect the actual working status.
Point 2: or just the corresponding vertical force between the roof and the z-axis carriage has been applied?
Response 2: The vertical force in the ADAMS model is applied to the rod of the balance cylinder upwards, the vertical force is the sum of the gravity of slide carriage, X-axis motion mechanism, Y-axis motion mechanism, headstock, and spindle.
Reviewer 2 Report
I refer to my earlier comments which have been addressed answering the review report, but not in text.
Author Response
Thank you very much again for your comments on our manuscript entitled “Design of Optical Free-form Surface Milling Machine Based on Mechanical Shunt and Dynamic Analysis”. The responses to the comments are as follows:
Point 1: I refer to my earlier comments which have been addressed answering the review report, but not in text.
Response 1: We have carefully responded to your earlier comments on our manuscript point by point， if you have any suggestions for our manuscript, we will do our best to revise our manuscript sincerely.
Reviewer 3 Report
Check all the references, take them from editorial databases.
ELIMINATE REF 25. iT IS UNACCEPTABLE..IT IS ABOUT ROCKS.
Author Response
Thank you very much again for your comments on our manuscript entitled “Design of Optical Free-form Surface Milling Machine Based on Mechanical Shunt and Dynamic Analysis”. The responses to the comments are as follows:
Point 1: Check all the references, take them from editorial databases.
Response 1: According to your suggestion, all the references have been modified according to the format required by the journal.
Point 2: ELIMINATE REF 25. iT IS UNACCEPTABLE..IT IS ABOUT ROCKS.
Response 2: According to your suggestion, reference 25 has been deleted.
