Turning optimization method for RV reducer eccentric shaft

Abstract

The invention relates to the technical field of eccentric shaft machining, in particular to a turning optimization method for an RV reducer eccentric shaft, and the method comprises the steps: collecting a vibration signal at a turning tool rest in real time in the turning process of the RV reducer eccentric shaft, and framing the vibration signal; acquiring the decreasing intensity of the maximum amplitude in each frame of signal and the maximum solid frequency energy ratio of each frame of signal; acquiring a first characteristic value of each frame of signal; constructing a signal sequence of each frame signal, calculating a slope of a fitting straight line of the first characteristic values of all frame signals in the signal sequence of each frame signal, recording the slope as a change slope, obtaining a flutter threshold value of each frame signal, and combining the change slope of each frame signal to obtain a flutter threshold value of each frame signal; and adjusting the rotating speed of the main shaft according to the difference of the first characteristic value between each frame of signal and the signal frame with the same sequence number during the previous feeding. By adjusting the rotating speed of the main shaft in the turning process, optimization for turning of the eccentric shaft of the RV speed reducer is achieved.

Description

Technical Field

[0001] This application relates to the technical field of eccentric shaft machining, and particularly relates to an optimization method for turning machining of an eccentric shaft for an RV reducer. Background Art

[0002] Ductile iron after austempering treatment, usually simply referred to as ADI (Austempered Ductile Iron), is commonly used to manufacture high-strength mechanical parts, such as the eccentric shaft of an RV (Rotary-Vector) reducer, due to its high strength and excellent wear resistance. The RV reducer is a key component at the robot joint, and the machining quality of the eccentric shaft, as one of its core components, is an important factor determining the operation effect of the RV reducer. The eccentric shaft of the RV reducer made of ADI material can not only significantly enhance its bearing capacity and service life under high load and complex stress environments, but also effectively reduce the weight of the eccentric shaft, thereby reducing the energy consumption of the robot and improving the motion flexibility and working efficiency of the robot joint.

[0003] The turning machining accuracy of the eccentric shaft of the RV reducer directly affects the transmission accuracy, assembly accuracy and overall performance of the RV reducer. High-precision turning machining of the eccentric shaft can ensure the stable operation of the RV reducer under high load and high-precision requirements, thereby ensuring the efficient and reliable motion of the robot joint. However, turning chatter (self-excited vibration caused by the regeneration effect between the tool and the workpiece) will cause obvious vibration marks on the workpiece surface, increased roughness, tool deviation from the cutting path and dimensional deviation, reducing the machining accuracy. Due to factors such as its complex structure, insufficient rigidity and large variation of cutting force, the eccentric shaft is more likely to appear chatter, further reducing the machining accuracy.

[0004] Publication No. CN110102787A discloses a method for suppressing turning chatter based on amplitude modulation, which respectively performs hammer impact modal tests and cutting force coefficient tests on the turning tool and the workpiece, obtains the tip displacement frequency response function and the cutting force coefficient of the workpiece, and periodically adjusts the spindle speed by means of amplitude modulation to suppress turning chatter. However, this method ignores the change of chatter frequency during the turning machining process, and the chatter suppression effect for the entire turning process is not good. At the same time, for workpieces made of ADI material, its high hardness and toughness make it more likely to generate cutting force and cutting heat during the machining process. The too frequent speed adjustment of the sine variable spindle speed method will lead to instability of the cutting force and cutting heat, resulting in uneven distribution of the cutting heat, thereby causing thermal cracks or deformation on the workpiece surface and affecting the turning machining quality. Summary of the Invention

[0005] In view of the above, it is necessary to provide an optimization method for turning the eccentric shaft of an RV reducer. Compared with the traditional optimization method for turning the eccentric shaft of an RV reducer, by adjusting the spindle speed during the turning process, the optimization of turning the eccentric shaft of an RV reducer is achieved.

[0006] The optimization method for turning the eccentric shaft of an RV reducer in this application adopts the following technical solution: An embodiment of this application provides an optimization method for turning the eccentric shaft of an RV reducer. The method includes the following steps: Real-time collect the vibration signal at the tool rest of the turning tool during the turning process of the eccentric shaft of the RV reducer; Frame the vibration signal. By analyzing the change of the amplitude of each frame signal in the time domain, obtain the severity of the maximum amplitude drop within each frame signal; obtain each peak in the frequency domain of each frame signal and the width of the peak on both sides of each peak that drops to 3 dB of its peak. Through the peaks and their corresponding widths, obtain the maximum natural frequency energy ratio of each frame signal; combine the severity and the maximum natural frequency energy ratio to obtain the first eigenvalue of each frame signal; Form each signal sequence by combining each frame signal and the continuous preset number of frame signals before it. Calculate the slope of the fitting line of the first eigenvalues of all frame signals in the signal sequence of each frame signal, which is denoted as the change slope of each frame signal. Through the maximum value of the change slopes of all frame signals in the signal sequence of each frame signal, and the difference in the first eigenvalue between each frame signal in the signal sequence and the frame signal with the same serial number during the previous tool feed, obtain the chatter threshold of each frame signal; through the change slope of each frame signal and the difference in the first eigenvalue between each frame signal and the signal frame with the same serial number during the previous tool feed, obtain the second eigenvalue of each frame signal; adjust the spindle speed according to the difference between the chatter threshold and the second eigenvalue.

[0007] In one of the embodiments, the process of obtaining the severity is as follows: Statistically calculate the maximum value of the amplitude of each frame signal in the time domain, calculate the mean value and the dispersion of the amplitude of each frame signal in the time domain; statistically calculate the duration from the maximum value to the mean value of each frame signal; Take the opposite number of the duration as the exponent of the exponential function with the natural constant as the base; Calculate the difference between the maximum value and the mean value, and calculate the ratio of the difference to the dispersion; The severity is positively correlated with the ratio and the calculation result of the exponential function respectively.

[0008] In one of the embodiments, the severity is the product of the ratio and the calculation result of the exponential function.

[0009] In one embodiment, the process of obtaining the maximum fixed-frequency energy ratio is as follows: Statistically calculate the maximum peak value of each frame of signal in the frequency domain; Calculate the product of each peak value of each frame of signal and its corresponding width; Calculate the sum of the accumulations of the products of all peak values of each frame of signal; The maximum fixed-frequency energy ratio is the ratio of the product of the maximum peak values of each frame of signal to the sum of the accumulations.

[0010] In one embodiment, the first eigenvalue is the product of the severity and the maximum fixed-frequency energy ratio.

[0011] In one embodiment, the process of obtaining the flutter threshold is as follows: Denote the difference between each frame of signal and the first eigenvalue of the frame signal with the same serial number during the previous tool feed as the feature difference; Statistically calculate the maximum value among all the feature differences corresponding to all frame signals in the signal sequence of each frame of signal; Statistically calculate the highest value of the change slope of all frame signals in the signal sequence of each frame of signal; The flutter threshold is positively correlated with the maximum value and the highest value respectively.

[0012] In one embodiment, the flutter threshold is the product of the normalized value of the highest value and the maximum value.

[0013] In one embodiment, the second eigenvalue is the product of the normalized value of the change slope of each frame of signal and the feature difference corresponding to each frame of signal.

[0014] In one embodiment, the adjustment of the spindle speed includes: Calculate the normalized result of the difference between the second eigenvalue of the current frame signal and the flutter threshold, and take the product of the normalized result and the preset maximum spindle speed change amount as the spindle speed change amount of the adjacent next frame signal of the current frame signal; adjust the current spindle speed through the spindle speed change amount.

[0015] In one embodiment, the specific method of adjusting the current spindle speed through the spindle speed change amount is as follows: If the current spindle speed is greater than the preset spindle speed adjustment limit, take the difference between the current spindle speed and the spindle speed change amount of the adjacent next frame signal as the spindle speed of the adjacent next frame signal; otherwise, take the sum of the current spindle speed and the spindle speed change amount of the adjacent next frame signal as the spindle speed of the adjacent next frame signal.

[0016] This application has at least the following beneficial effects: This application monitors the vibration signal at the tool rest of the turning tool, captures in real time the minute displacements and acceleration changes of the tool caused by chatter, and analyzes the chatter degree during the machining process of the eccentric shaft of the RV reducer. There is no need to conduct hammer impact modal tests and cutting force coefficient tests on the turning tool and the workpiece, avoiding the complex process of judging the turning chatter degree through cutting force modeling. At the same time, based on the turning chatter analysis of the monitored vibration signal, it can effectively adapt to the continuously changing chatter frequencies during the turning process, thereby enhancing the chatter suppression effect for the entire turning process of the RV reducer eccentric shaft; Furthermore, the time-frequency analysis method is adopted to extract the energy change characteristics of the vibration signal caused by turning chatter and the frequency domain characteristics of the vibration signal when chatter occurs, reducing the influence of the complex structure of the eccentric shaft on the turning chatter analysis and improving the reliability and accuracy of judging the chatter degree during the turning process of the RV reducer eccentric shaft; Furthermore, by using the characteristic change trends of the vibration signals at the same feed position for different tool passes and the vibration signals at different feed positions for the same tool pass, a chatter threshold is set. While effectively suppressing chatter, it reduces the amplitude and frequency of the main shaft speed adjustment, avoiding thermal cracks or deformations on the surface of the ADI material caused by uneven distribution of cutting heat, and achieving optimization for the turning process of the RV reducer eccentric shaft. Description of the Drawings

[0017] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a flowchart of the steps of a turning process optimization method for an RV reducer eccentric shaft provided by this application; Figure 2 It is a schematic diagram of the acquisition process of the first eigenvalue; Figure 3 It is a schematic diagram of the acquisition process of the chatter threshold and the second eigenvalue; Figure 4 It is a flowchart of the adjustment of the main shaft speed. Detailed Embodiment

[0019] In the description of the embodiments of the present application, words such as "exemplary", "or", "for example" are used to indicate examples, illustrations or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplary", "or", "for example" is intended to present relevant concepts in a specific manner.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application. It should be understood that unless otherwise stated in this application, " / " means "or".

[0021] In addition, it should be noted that the terms "first" and "second" in this application are used to distinguish similar objects and are not used to describe a specific order or sequence.

[0022] The following specifically describes the specific solution of a turning processing optimization method for the eccentric shaft of an RV reducer provided by this application with reference to the accompanying drawings.

[0023] A turning processing optimization method for the eccentric shaft of an RV reducer provided by an embodiment of this application. Specifically, the following turning processing optimization method for the eccentric shaft of an RV reducer is provided. Please refer to Figure 1 , and the method includes the following steps: Step 1, collect the vibration signal at the tool rest during the turning process of the eccentric shaft of the RV reducer in real time.

[0024] The cutting tool is a key part during the turning process of the eccentric shaft of the RV reducer. The vibration condition at the cutting tool can directly reflect the turning chatter situation. By installing a vibration sensor at the tool rest, the vibration signal during the turning process of the eccentric shaft of the RV reducer is collected in real time to accurately capture the tiny displacement and acceleration changes of the tool caused by chatter, and analyze the current degree of turning chatter.

[0025] In this embodiment, the acquisition frequency of the vibration sensor is 10 kHz. The value of the acquisition frequency is preset by the user and can be set by the implementer himself. This application does not make special restrictions.

[0026] In this embodiment, the feed rate for the turning process of the eccentric shaft of the RV reducer is set to 100 mm / min, the turning length is set to 25 mm, the number of tool passes is set to 5 times, and the processing time for each tool pass is 15 s in total. The feed rate, turning length, number of tool passes, and processing time for each tool pass are all preset by the user. The implementer can set them according to the actual situation, and this application does not make special restrictions.

[0027] The complex structure of the eccentric shaft causes coupling between multiple modes. At different positions, the interaction between the cutting tool and the eccentric shaft will excite different modal vibrations, and the coupling of these modal vibrations will make the chatter phenomenon more complex. The structural design of the eccentric shaft results in different rigidities at different positions, which further exacerbates the intensity change of the regenerative cutting effect, causing different degrees of cutting force fluctuations and different chatter degrees at different turning positions.

[0028] In this application, the vibration signals collected during each tool feed are frame-processed to obtain each frame signal, and the area of the eccentric shaft where the tool corresponding to each frame signal is located is recorded, denoted as the machining area of each frame signal, so as to facilitate subsequent comparative analysis of the vibration signals in different machining areas, and thus more accurately judge the change of the chatter degree in different machining areas. According to the time sequence of the tool feed, each frame signal and its machining area are numbered.

[0029] In this embodiment, the length of each frame signal is 0.5 seconds, and the value of the length of each frame signal is preset artificially. The implementer can set it according to the actual situation, and this application does not make special restrictions.

[0030] To reduce the influence of spectral leakage and high-frequency noise generated by the high-speed operation of the lathe, this application performs windowing and filtering processing on each frame signal respectively.

[0031] In this embodiment, the window function used is the Hanning window, and a low-pass filter is used to perform filtering processing on each frame signal respectively. The cut-off frequency of the low-pass filter is 500Hz.

[0032] Step 2: Analyze the vibration signal in the time domain and frequency domain to extract the chatter characteristics during the turning process.

[0033] In the actual machining scenario, the machining environment of turning is usually relatively complex. The interaction between the turning tool and the eccentric shaft will generate complex vibration signals. To ensure the machining accuracy and stability, it is necessary to accurately monitor and analyze the vibration signals.

[0034] The structure of the eccentric shaft of the RV reducer makes it difficult to effectively extract the chatter characteristics from it using traditional signal analysis methods. On the one hand, the eccentric structure of the eccentric shaft causes the vibration signal to exhibit strong non-stationarity and complexity, resulting in the overall time-domain waveforms of two frame signals with relatively high and relatively low turning chatter degrees being relatively close, and it is difficult for traditional signal analysis methods to extract effective characteristics reflecting turning chatter. On the other hand, the multi-modal coupling caused by the complex structure of the eccentric shaft results in multiple natural frequencies, causing the chatter energy to be distributed in multiple frequency ranges.

[0035] Turning chatter, as a self-excited vibration phenomenon, when the cutting system enters the chatter state, the cutting force and the cutting system interact with each other to form a positive feedback mechanism, resulting in the rapid accumulation of vibration energy and a significant increase in the energy of the vibration signal within a local time period. In addition, when chatter occurs, the eccentric structure of the eccentric shaft of the RV reducer causes the cutting force between the tool and the eccentric shaft to change periodically. When the cutting force matches the natural frequency of the cutting system, the vibration energy will be further amplified. At the same time, the centrifugal force generated by the eccentric shaft will be superimposed on the cutting force during the cutting process to form a larger dynamic load, intensifying the vibration intensity during chatter and leading to a significant increase in the energy of the vibration signal within a short time in the corresponding frame.

[0036] (1) By analyzing the change of the amplitude of each frame signal in the time domain, the severity of the maximum amplitude decrease within each frame signal is obtained.

[0037] In the time domain, when strong chatter occurs, the energy of the vibration signal in the corresponding frame increases within a local time period, the amplitude of the vibration signal increases significantly, manifested as sharp pulses or mutations of the vibration signal, reflecting the rapid accumulation and release of energy caused by chatter during the turning process.

[0038] The greater the maximum value of the amplitude of the vibration signal in the corresponding frame compared to its mean value, and the shorter the time it takes to drop to the mean value, the more intense the release of the maximum transient energy within the vibration signal of the corresponding frame, indicating a higher degree of turning chatter.

[0039] Taking the vibration signal collected during any single pass as an example, to quantify the intensity of the maximum transient energy release within each frame signal, by analyzing the change of the amplitude of each frame signal in the time domain, the severity of the maximum amplitude decrease within each frame signal is obtained, and the expression is: ; where represents the severity of the maximum amplitude decrease within the i-th frame signal; represents the maximum value of the amplitude of the i-th frame signal in the time domain; and respectively represent the mean value and the dispersion of the amplitude of the i-th frame signal in the time domain; exp( ) represents the exponential function with the natural constant as the base; represents the duration for the i-th frame signal to drop from the maximum value to the mean value. Among them, the exponential function is used to normalize the duration value to the range of (0,1].

[0040] In this embodiment, the dispersion is the standard deviation. As other implementation manners, on the basis of being able to measure the uneven degree of the amplitude distribution, the implementer can adopt other existing technologies, such as variance, coefficient of variation, etc., and this application does not make special restrictions.

[0041] It should be noted that during the calculation of the severity, by introducing the dispersion degree, the following is used to quantify the significance degree of the sharp pulses in each frame of the signal relative to the overall fluctuation; the greater the severity, the greater the energy rapidly accumulated and released in the i-th frame of the signal, and the greater the degree of chatter in turning machining.

[0042] (2) Obtain each peak value in the frequency domain of each frame of the signal and the width of the decline to 3 dB of its peak value on both sides of each peak value. Through the above-mentioned each peak value and its corresponding width, obtain the maximum natural frequency energy ratio of each frame of the signal.

[0043] Furthermore, perform a fast Fourier transform on each frame of the signal respectively to obtain each frequency domain sequence; obtain each peak value in each frequency domain sequence, denoted as each natural frequency peak, which respectively represents the amplitude of the multi-order natural frequencies of the cutting system. Denote the width of the decline to 3 dB of the amplitude on both sides of each natural frequency peak as the natural frequency band of each natural frequency peak, which represents the spectral distribution range of different orders of natural frequencies. The fast Fourier transform is a well-known technology and will not be elaborated in this application.

[0044] To evaluate the energy concentration degree of the natural frequency peak, and further reflect the coupling degree between the cutting force and the cutting system and the degree of turning chatter, through each natural frequency peak and its natural frequency band in the frequency domain of each frame of the signal, obtain the maximum natural frequency energy ratio of each frame of the signal, and the expression is: ; represents the maximum natural frequency energy ratio of the i-th frame of the signal; represents the maximum natural frequency peak in the frequency domain sequence of the i-th frame of the signal; represents the natural frequency band of the maximum natural frequency peak in the frequency domain sequence of the i-th frame of the signal; represents the number of natural frequency peaks in the frequency domain sequence of the i-th frame of the signal; represents the k-th natural frequency peak in the frequency domain sequence of the i-th frame of the signal; represents the natural frequency band of the k-th natural frequency peak in the frequency domain sequence of the i-th frame of the signal. Among them, represents the energy concentration degree of the i-th frame of the signal near all natural frequencies.

[0045] It should be noted that when the maximum natural frequency peak and its natural frequency band increase significantly, the value of the calculated maximum natural frequency energy ratio is larger, indicating that more energy is concentrated near the natural frequency with the largest peak, meaning that the coupling degree between the cutting force and the cutting system is higher, and the degree of turning chatter generated is higher.

[0046] (3) Combine the above-mentioned severity and the maximum natural frequency energy ratio to obtain the first eigenvalue of each frame of the signal.

[0047] Further, by combining the severity of each frame signal with the maximum fixed-frequency energy ratio, the first eigenvalue of each frame signal is obtained. Specifically: the product of the severity of each frame signal and the maximum fixed-frequency energy ratio is used as the first eigenvalue of each frame signal. The fixed-frequency coupling characteristics of each frame signal are quantified by the first eigenvalue to evaluate the degree of turning chatter.

[0048] It should be noted that: on the one hand, the greater the severity, the greater the energy rapidly accumulated and released within each frame signal, and the greater the degree of chatter generated by fixed-frequency coupling during turning machining, and the greater the first eigenvalue calculated and obtained; on the other hand, when the cutting force is more strongly coupled with a certain fixed frequency of the cutting system, more energy is concentrated near this fixed frequency, resulting in stronger turning chatter, and the first eigenvalue of each frame signal is greater. The schematic diagram of the acquisition process of the first eigenvalue is as Figure 2 shown.

[0049] Step 3, adjust the spindle speed according to the extracted chatter characteristics.

[0050] Considering the characteristic that the eccentric shaft of the RV reducer made of ADI material is more likely to generate cutting heat during turning, for the traditional strategy of suppressing chatter by changing the spindle speed, the spindle speed changes too frequently, resulting in uneven distribution of cutting heat on the surface of the ADI material and affecting the quality of turning machining.

[0051] During the turning machining process of the eccentric shaft of the RV reducer, the periodic change of the cutting force acts on the workpiece and is further transmitted to the cutting system to change the force state of the cutting system, affecting the dynamic response of the cutting system, and thus causing slight fluctuations in the degree of turning chatter within a short period. If the change in the degree of chatter each time triggers the speed adjustment, it will lead to frequent changes in the spindle speed.

[0052] The excitation frequency of the cutting force on the cutting system increases with the increase of the spindle speed. When the excitation frequency of the cutting system is close to or equal to the natural frequency of the cutting system, resonance will occur, resulting in a relatively large degree of turning chatter.

[0053] This application sets the initial spindle speed to , and in this embodiment takes a value of 800 rmp. The cutting force usually changes with the change of the spindle speed. At a lower speed, the amplitude of the cutting force is smaller, resulting in a lower vibration amplitude of the cutting system. The occurrence of chatter requires the cutting force to reach a certain amplitude and excite the resonance of the cutting system. Therefore, at the initial stage of turning the eccentric shaft of the RV reducer, the lower initial speed is difficult to trigger the chatter condition. This application uses the characteristics of the first frame vibration signal collected during the first turning feed as the benchmark for low-degree turning chatter, calculates the chatter threshold for each frame, and while ensuring the suppression of the degree of turning chatter, reduces the adjustment range and frequency of the spindle speed. The specific process is as follows: (1)For each frame signal and the consecutive preset number of frame signals before it, form each signal sequence, and calculate the slope of the fitting line of the first eigenvalues of all frame signals in the signal sequence of each frame signal, which is denoted as the change slope of each frame signal.

[0054] For the vibration signals obtained for each feed, arrange each frame signal and the consecutive preset number of frame signals before it in time sequence to form the signal sequence of each frame signal.

[0055] In this embodiment, the value of the preset number is 10. The value of the preset number is preset manually, and the implementer can set it by himself / herself. This application does not make special restrictions. When the number of signal frames before each frame signal is less than 10, the linear interpolation method is used to fill the missing data. The linear interpolation method is a well-known technology and will not be elaborated in this application.

[0056] To obtain the chatter development characteristics near each frame signal during turning, obtain the fitting line of the first eigenvalues of all frame signals in the signal sequence of each frame signal, and calculate the slope of each fitting line, which is denoted as the change slope of each frame signal. Among them, the calculation of the slope is a well-known technology and will not be elaborated in this application.

[0057] In this embodiment, the least squares method is used to obtain the fitting line. The least squares method is a well-known technology and will not be elaborated in this application. As other implementation manners, on the basis of being able to obtain the fitting line, the implementer can adopt other existing technologies, such as the weighted least squares method, etc. This application does not make special restrictions.

[0058] (2)Obtain the chatter threshold of each frame signal through the maximum value of the change slopes of all frame signals in the signal sequence of each frame signal and the difference in the first eigenvalues between each frame signal in the signal sequence and the frame signal with the same serial number during the previous feed; obtain the second eigenvalue of each frame signal through the change slope of each frame signal and the difference in the first eigenvalues between each frame signal and the signal frame with the same serial number during its previous feed.

[0059] Obtain the chatter threshold of each frame signal through the distribution of the change slopes of all frame signals in the signal sequence of each frame signal and the difference in the first eigenvalues between each frame signal in the signal sequence and the frame signal with the same serial number during the previous feed. The expression is: ; In the formula, represents the chatter threshold of the i-th frame signal; calculate the difference between the first eigenvalues of the i-th frame signal and the frame signal with the same serial number during its previous feed, which is denoted as the characteristic difference; represents the maximum value of the said characteristic differences corresponding to all frame signals in the signal sequence of the i-th frame signal; norm( ) represents the arctangent normalization function, which is used to normalize to (0, 1); Represents the maximum value of the change slopes of all frame signals in the signal sequence of the i-th frame signal.

[0060] Further, the second eigenvalue of each frame signal is obtained through the change slope of each frame signal and the difference in the first eigenvalue between each frame signal and the frame signal with the same serial number during the previous tool feed. The expression is: ; Represents the second eigenvalue of the i-th frame signal; Represents the eigenvalue difference corresponding to the i-th frame signal; norm( ) represents the arctangent normalization function, which is used to normalize to (0, 1); Represents the change slope of the i-th frame signal. In this application, the spindle speed is adjusted only when the second eigenvalue of each frame signal exceeds its chatter threshold, so as to avoid frequent changes in the spindle speed caused by small fluctuations in the chatter degree during turning in a short period. The schematic diagram of the acquisition process of the chatter threshold and the second eigenvalue is as Figure 3 shown.

[0061] Taking the vibration signal characteristics collected during the initial turning as the benchmark for low-level turning chatter, the chatter threshold of each frame signal is calculated to ensure timely adjustment of the speed when the chatter is too large. At the same time, since the chatter threshold is calculated based on the maximum value of the eigenvalue difference and the maximum value of the change slope, the chatter threshold will be maintained at a relatively high level, avoiding uneven distribution of cutting heat on the surface of the ADI material caused by too frequent adjustment of the speed.

[0062] (3) Adjust the spindle speed through the difference between the chatter threshold and the second eigenvalue.

[0063] Turning chatter is caused by the interaction between the cutting force and the vibration of the cutting system. When the frequency of the cutting force is close to the natural frequency of the cutting system, resonance is likely to occur, resulting in chatter.

[0064] At the initial stage of turning the eccentric shaft of the RV reducer, the workpiece has not been cut and its stiffness is relatively high. As turning progresses, the workpiece material is removed, and the cross-sectional area of the remaining part decreases, resulting in a decrease in stiffness, which directly causes a change in the natural frequency of the cutting system.

[0065] Further, the spindle speed change amount of the adjacent next frame signal of the current frame signal is obtained through the difference between the chatter threshold and the second eigenvalue of the current frame signal, which is used to determine the adjustment amplitude of the current spindle speed. The expression is: ; Represents the spindle speed change amount of the (i + 1)-th frame signal; N represents the preset maximum spindle speed change amount; norm( ) represents the arctangent normalization function, which is used to Normalize to (0, 1); Denote the second eigenvalue of the i-th frame signal; Denote the chatter threshold of the i-th frame signal.

[0066] The specific method for adjusting the current spindle speed is as follows: If the current spindle speed is greater than the preset spindle speed adjustment limit, the difference between the current spindle speed and the spindle speed change amount of the adjacent next frame signal is used as the spindle speed of the adjacent next frame signal; otherwise, the sum of the current spindle speed and the spindle speed change amount of the adjacent next frame signal is used as the spindle speed of the adjacent next frame signal. The adjustment flow chart of the spindle speed is as shown in Figure 4 shown.

[0067] In this embodiment, to prevent the spindle speed from being too high or too low, the value of the spindle speed adjustment limit is set to 1000 rmp.

[0068] In summary, this application monitors the vibration signal at the tool rest of the lathe tool, captures in real time the minute displacement and acceleration changes of the tool caused by chatter, analyzes the chatter degree during the machining process of the eccentric shaft of the RV reducer, and does not require hammering modal testing and cutting force coefficient testing for the lathe tool and the workpiece, avoiding the complex process of judging the turning chatter degree through cutting force modeling. At the same time, based on the turning chatter analysis of the monitored vibration signal, it can effectively adapt to the continuously changing chatter frequency during the turning process, thereby improving the chatter suppression effect for the entire turning process of the eccentric shaft of the RV reducer; Furthermore, by using the time-frequency analysis method, the energy change characteristics of the vibration signal caused by turning chatter and the frequency domain characteristics of the vibration signal during chatter are extracted, reducing the influence of the complex structure of the eccentric shaft on the turning chatter analysis and improving the reliability and accuracy of judging the chatter degree during the turning process of the eccentric shaft of the RV reducer; Furthermore, by using the characteristic change trends of the vibration signals at the same feed position for different tool passes and the vibration signals at different feed positions for the same tool pass, the chatter threshold is set. While effectively suppressing chatter, it reduces the amplitude and frequency of spindle speed adjustment, avoiding thermal cracks or deformation on the surface of the ADI material caused by uneven distribution of cutting heat, and realizing the optimization for the turning process of the eccentric shaft of the RV reducer.

[0069] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to embodiments of the present disclosure. In this regard, each block in the flowchart or block diagram may represent a module, a segment of a program, or a part of code, which contains one or more executable instructions for implementing the specified logical function. In some alternative implementations, the functions noted in the blocks may occur in a different order than noted in the accompanying drawings. For example, two consecutive blocks may actually be executed substantially in parallel, or they may sometimes be executed in reverse order, depending on the functions involved. In the descriptions corresponding to the flowcharts and block diagrams in the accompanying drawings, the operations or steps corresponding to different blocks may also occur in a different order than disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps may actually be executed substantially in parallel, or they may sometimes be executed in reverse order, depending on the functions involved. Each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented by a dedicated hardware-based system that performs the specified functions or actions, or can be implemented by a combination of dedicated hardware and computer instructions.

[0070] For those skilled in the art, it is obvious that the present application is not limited to the details of the above-described exemplary embodiments, and without departing from the basic characteristics of the present application, the present application can be implemented in other specific forms. Therefore, in any regard, the above-described embodiments of the present application should be considered exemplary and non-limiting.

Claims

1. An optimization method for turning processing of the eccentric shaft of an RV reducer, characterized in that The method includes the following steps: Collect vibration signals at the tool rest of the turning tool in real time during the turning process of the eccentric shaft of the RV reducer; Frame the vibration signals. By analyzing the change of the amplitude of each frame signal in the time domain, obtain the severity of the maximum amplitude drop within each frame signal; obtain each peak value of each frame signal in the frequency domain and the width of the drop to 3 dB of its peak value on both sides of each peak value. Through the respective peak values and the corresponding widths, obtain the maximum natural frequency energy ratio of each frame signal; combine the severity and the maximum natural frequency energy ratio to obtain the first eigenvalue of each frame signal; Form each signal sequence by combining each frame signal and a preset number of consecutive frames of signals before it. Calculate the slope of the fitting line of the first eigenvalues of all frame signals in the signal sequence of each frame signal, denoted as the change slope of each frame signal. Through the maximum value of the change slopes of all frame signals in the signal sequence of each frame signal, and the difference in the first eigenvalues between each frame signal in the signal sequence and the frame signal with the same serial number during the previous tool feed, obtain the chatter threshold of each frame signal; through the change slope of each frame signal and the difference in the first eigenvalues between each frame signal and the signal frame with the same serial number during the previous tool feed, obtain the second eigenvalue of each frame signal; adjust the spindle speed according to the difference between the chatter threshold and the second eigenvalue.

2. The turning process optimization method for the eccentric shaft of an RV reducer according to claim 1, characterized in that The process of obtaining the severity is as follows: Statistically calculate the maximum value of the amplitude of each frame signal in the time domain, calculate the mean value and the dispersion of the amplitude of each frame signal in the time domain; statistically calculate the duration from the maximum value to the mean value of each frame signal; Take the opposite number of the duration as the exponent of the exponential function with the natural constant as the base; Calculate the difference between the maximum value and the mean value, and calculate the ratio of the difference to the dispersion; The severity is positively correlated with the ratio and the calculation result of the exponential function respectively.

3. The turning process optimization method for the eccentric shaft of an RV reducer according to claim 2, characterized in that, The severity is the product of the ratio and the calculation result of the exponential function.

4. The turning process optimization method for the eccentric shaft of an RV reducer according to claim 1, characterized in that, The process of obtaining the maximum natural frequency energy ratio is as follows: Statistically calculate the maximum peak value of each frame signal in the frequency domain; Calculate the product of each peak value of each frame signal and its corresponding width; Calculate the sum of the accumulations of the products of all peak values of each frame signal; The maximum natural frequency energy ratio is the ratio of the product of the maximum peak value of each frame signal to the sum of the accumulations.

5. The turning process optimization method for the eccentric shaft of an RV reducer according to claim 1, characterized in that, The first eigenvalue is the product of the severity and the maximum natural frequency energy ratio.

6. The turning process optimization method for the eccentric shaft of an RV reducer according to claim 1, characterized in that The process of obtaining the chatter threshold is as follows: Denote the difference in the first eigenvalues between each frame signal and the frame signal with the same serial number during the previous tool feed as the characteristic difference; Statistically calculate the maximum value among the characteristic differences corresponding to all frame signals in the signal sequence of each frame signal; Statistically calculate the highest value of the change slopes of all frame signals in the signal sequence of each frame signal; The chatter threshold is positively correlated with the maximum value and the highest value respectively.

7. The turning process optimization method for the eccentric shaft of an RV reducer according to claim 6, wherein The chatter threshold is the product of the normalized value of the highest value and the maximum value.

8. The turning process optimization method for the eccentric shaft of an RV reducer according to claim 6, characterized in that The second eigenvalue is the product of the normalized value of the change slope of each frame signal and the characteristic difference corresponding to each frame signal.

9. The turning process optimization method for the eccentric shaft of an RV reducer according to claim 1, characterized in that The adjustment of the spindle speed includes: Calculate the normalized result of the difference between the second eigenvalue of the current frame signal and the flutter threshold, and use the product of the normalized result and the preset maximum spindle speed change amount as the spindle speed change amount of the adjacent next frame signal of the current frame signal; adjust the current spindle speed by the spindle speed change amount.

10. The turning process optimization method for the eccentric shaft of an RV reducer according to claim 9, characterized in that, The method of adjusting the current spindle speed by the spindle speed change amount is specifically as follows: If the current spindle speed is greater than the preset spindle speed adjustment limit, use the difference between the current spindle speed and the spindle speed change amount of the adjacent next frame signal as the spindle speed of the adjacent next frame signal; otherwise, use the sum of the current spindle speed and the spindle speed change amount of the adjacent next frame signal as the spindle speed of the adjacent next frame signal.

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