Design and Implementation of Bulk Feeders Using Voice Coil Motors
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript uses voice coil motors to design and implement a dual-axis bulk feeder and a quad-axis bulk feeder, to improve some problems existing in traditional bulk feeders.
1. The illustration is suggested to be improved to show detailed information.
2. The limitation and applicable scope of the proposed feeder should also be introduced.
3. Some quantitative conclusions are suggested to be provided.
Comments on the Quality of English LanguageThe language can be improved.
Author Response
Thank the reviewer for these comments. Some descriptions or modifications have been added to this revised paper.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe presented work concerns the use of vibration motors to control the operation of mass feeders. The introduction discusses the types of construction of the devices considered. In my opinion, there is no need to go back to the end of the eighteenth century in the introduction. The introduction is quite poor and does not contain much information showing the outline. The work does not discuss the method of controlling the device. There is no comparison of various parameters of their work, e.g. selection of the frequency and amplitude of vibrations on the speed of sorting elements, etc. This part of the work is the most poor.
Author Response
Thank the reviewer for these comments. Some descriptions or modifications have been added to this revised paper.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe paper is very interesting and provides very good results with a common practical real-life application.
However, there are some things that I would like to point out.
The explanations are often rather simple. eg.
- To use PWM control to generate a variable voltage to an electromagnetic actuator is a well-known fact (6)
- the actuator back EMF is proportional to the actuator speed (3)
- The movement is the integral of the acceleration force over mass (7)
These equations are just stated, but not used to design the actual excitation control system of the voice coils, which would be very interesting to see.
Equations (8) and (9) are not correct. As explained in Figure 8, the speed of the coil movements changes within the same cycle, to actually make the material move. Therefore, the movement in z and x axes will be periodic with w, but not perfectly sinusoidal. The real waveform will have a very high harmonic content and be more triangular shaped. The “bending” of the waveform is needed to get a wave movement of the material.
The authors should state which excitation waveforms they use. What are the reference waveforms for the coil current controls? Is there a closed-loop current control implemented? Is the used PWM frequency higher than the mechanical vibration frequency? What are the phase shifts between the coil excitations? These waveforms should be given for all cases shown in Figure 12, 13, 14 and 15.
I should be more analytical explained what force control is applied to control the moving speed of the feeding material.
Comments on the Quality of English LanguageThe English is very good, with only minor corrections needed.
Author Response
Thank the reviewer for these comments. Some descriptions or modifications have been added to this revised paper.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsThe technical details of the paper have been increased as requested. Thank you for that.
However, I have still some comments on some explanations given in the paper.
Eq (12) and (13) still seem not correct and are not properly explained. This is just the Fourier series of a square wave. According to these equations, the material moves back and forward in deltaX and deltaZ, but there is no absolute movement. Eq (12) and (13) are pure AC waveforms.
Thank you for including more details about the PWM excitation. However, the explanations in the paper are not clear. It seems you are using 2 PWM waveforms, one with 12Hz for the fundamental coil vibration and 20kHz for the voltage control. The different features of these 2 frequencies must be properly explained.
You mention that you use 60%,70%,80%,90% and 100% duty cycle. This just applies to the 20kHz voltage PWM frequency and results in an amplitude modulation of the 12Hz fundamental frequency. Is the PWM cycle of the fundamental frequency also changed?
Fig. 20a shows the waveform of the fundamental coil voltage waveform. What are the 2 shown waveforms? I assume that is of 2 coils. There is no phase shift between these coils. Thus the material should just vibrate, but there should be no movement. The same comment applies to Fig. 22a and d.
In Fig 21 there are phase shifts shown in the 20kHz signals which are not explained. Why are they there?
Author Response
Comment 1: Eq (12) and (13) still seem not correct and are not properly explained. This is just the Fourier series of a square wave. According to these equations, the material moves back and forward in deltaX and deltaZ, but there is no absolute movement. Eq (12) and (13) are pure AC waveforms.
Response 1: Thank you for your valuable feedback and insightful comments regarding Equations (12) and (13). In this study, we utilize voice coil actuators with different directions to create a tilted plane, as shown in Figure 8(a). This tilt causes horizontal movement of the material. In this revised paper, Equations (12)-(15) are rewritten to describe the motion of the proposed system.
Comment 2: Thank you for including more details about the PWM excitation. However, the explanations in the paper are not clear. It seems you are using 2 PWM waveforms, one with 12Hz for the fundamental coil vibration and 20kHz for the voltage control. The different features of these 2 frequencies must be properly explained.
Response 2: Thank you for your feedback. This study does use two different frequencies. In Section 4 of this revised paper, we illustrate the functions and characteristics of the two frequencies to explain the proposed system design and control strategy. These are described as follows:
- Validation Results
In the system design, there are two key frequencies: the electrical vibration frequency and the PWM cycle frequency. The electrical vibration frequency is used to control the fundamental motion of the material on the platform. It can be viewed as the vibration frequency of the movement of the physical system. It is used to control the displacement of the material on the platform to ensure the effective movement and bounce of the material. The PWM cycle frequency is used to regulate the input voltage of the voice coil actuator to provide precise control. The change in the PWM duty cycle affects the speed of the voice coil actuator. Therefore, this variation in speed results in different amounts of displacement. The electrical vibration frequency and PWM cycle frequency used in the following experiments are 12Hz and 20kHz respectively.
Comment 3: You mention that you use 60%,70%,80%,90% and 100% duty cycle. This just applies to the 20kHz voltage PWM frequency and results in an amplitude modulation of the 12Hz fundamental frequency. Is the PWM cycle of the fundamental frequency also changed?
Response 3: Thank you for your comment. We maintain the electrical vibration frequency constant (12Hz) to ensure the consistency of the vibration of the material on the platform. However, we vary the PWM duty cycle (60%, 70%, 80%, 90%, and 100%) at the PWM cycle frequency (20kHz). The change in the PWM duty cycle affects the speed of the voice coil actuator movement. Therefore, this variation in speed leads to different material movement speeds, resulting in varying displacement amounts.
Comment 4: Fig. 20a shows the waveform of the fundamental coil voltage waveform. What are the 2 shown waveforms? I assume that is of 2 coils. There is no phase shift between these coils. Thus the material should just vibrate, but there should be no movement. The same comment applies to Fig. 22a and d.
Response 4: Thank you for your observation regarding the waveforms. Indeed, the two waveforms shown in Figure 20(a) and Figure 20(b) are results of two voice coils. Figure 20(a) and Figure 20(b) are the results of the vibration frequency (12Hz) and the PWM control waveform (20kHz) respectively. The voice coil has two wires through which PWM signals enter from different lines (positive terminal and negative terminal), resulting the voice coils in different directions. When the PWM signal enters through the positive terminal, the voice coil moves to z > 0 direction. When it enters through the negative terminal, the voice coil moves to z < 0 direction. Figure 20(b) shows the waveform from two voice coils. The first signal is extracted from the upper motor's positive terminal, and the second signal is extracted from the lower motor's negative terminal. These signals show the same PWM duty cycle.
Comment 5: In Fig 21 there are phase shifts shown in the 20kHz signals which are not explained. Why are they there?
Response 5: Thank you for your question. The waveform of different duty cycles (60%, 70%, 80%, 90%, and 100%) and the displacement and dispersion of the material under the duty cycle after one second of operation are shown in Figure 21. It shows that the same vibration frequency but different duty cycles result in different displacement amounts.
Author Response File: Author Response.pdf
Round 3
Reviewer 3 Report
Comments and Suggestions for AuthorsHello,
Thank you for the consideration of my comments in the revision of the paper.
The additional information about the coil excitation voltages helps the reader to understand the paper much better. Thank you for including the extra explanations.
Equations (12) to (15) are again completely modified, but I also doubt their correctness. Particularly the -1/2gt term in equation (13) and (15) does not make sense. The material is not falling down, but it stays approximately at the same height (except of a small part due to the tilt of the plate). I believe the reader may understand the operation of the vibration feeder without equations (13) to (15). I therefore suggest removing these equations, because in my opinion, they cause more confusion.
Comments on the Quality of English Language
The English quality is good as it is.
Author Response
Comment 1: Equations (12) to (15) are again completely modified, but I also doubt their correctness. Particularly the -1/2gt term in equation (13) and (15) does not make sense. The material is not falling down, but it stays approximately at the same height (except of a small part due to the tilt of the plate). I believe the reader may understand the operation of the vibration feeder without equations (13) to (15). I therefore suggest removing these equations, because in my opinion, they cause more confusion.
Response 1: Based on your suggestion, we have deleted Equations (12) to (15) in this revised paper. We sincerely appreciate your thorough review and valuable suggestions.
