An optimization method for turning processing of eccentric shafts of RV reducers

Abstract

The present application relates to the technical field of eccentric shaft processing, and specifically to a turning processing optimization method for RV reducer eccentric shafts, the method comprising: real-time collection of vibration signals at the turning tool holder during the turning processing of the RV reducer eccentric shaft and framing, obtaining the severity of the maximum amplitude drop in each frame signal and the maximum fixed-frequency energy ratio of each frame signal; obtaining the first eigenvalue of each frame signal; constructing a signal sequence of each frame signal, calculating the slope of the fitting straight line of the first eigenvalues of all frame signals in the signal sequence of each frame signal, recorded as the change slope, obtaining the chatter threshold of each frame signal, combining 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 sequence number during the previous pass, to adjust the spindle speed. The present application achieves optimization of turning processing for RV reducer eccentric shafts by adjusting the spindle speed during turning processing.

Description

Technical Field

[0001] The present application relates to the technical field of eccentric shaft processing, and in particular to a turning processing optimization method for an eccentric shaft of an RV reducer. Background Art

[0002] Austempered ductile iron, commonly referred to as ADI (Austempered Ductile Iron), is commonly used in the manufacture of high-strength mechanical parts, such as the eccentric shaft of a rotary-vector (RV) reducer, due to its high strength and excellent wear resistance. RV reducers are key components in robot joints, and the machining quality of the eccentric shaft, one of their core components, is a crucial factor in determining the RV reducer's performance. Using ADI material in RV reducer eccentric shafts not only significantly enhances their load-bearing capacity and service life under high loads and complex stress environments, but also effectively reduces their weight, thereby reducing the robot's energy consumption and improving the joint's mobility and efficiency.

[0003] The turning accuracy of the RV reducer's eccentric shaft directly affects the RV reducer's transmission accuracy, assembly accuracy, and overall performance. High-precision turning of the eccentric shaft ensures the stable operation of the RV reducer under high loads and high-precision requirements, thereby guaranteeing efficient and reliable movement of the robot joints. However, turning chatter (self-excited vibrations between the tool and the workpiece caused by regenerative effects, etc.) can lead to noticeable vibration marks on the workpiece surface, increased roughness, tool deviation from the cutting path, and dimensional deviations, reducing machining accuracy. Eccentric shafts are more susceptible to chatter due to their complex structure, insufficient rigidity, and large variations in cutting forces, further reducing machining accuracy.

[0004] Publication No. CN110102787A discloses a variable spindle speed turning chatter suppression method based on amplitude modulation, which performs hammer modal tests and cutting force coefficient tests on the turning tool and workpiece respectively, obtains the tool tip displacement frequency response function and the cutting force coefficient of the workpiece, and periodically adjusts the spindle speed through amplitude modulation to suppress turning chatter. However, this method ignores the change in chatter frequency as the turning process proceeds, and the chatter suppression effect for the entire turning process is poor. At the same time, for workpieces made of ADI materials, their higher hardness and toughness make it easier for them to generate cutting force and cutting heat during the processing. Too frequent speed adjustments in the sinusoidal variable spindle speed method will lead to instability in cutting force and cutting heat, resulting in uneven distribution of cutting heat, which will cause thermal cracks or deformation on the workpiece surface, affecting the turning quality. Summary of the Invention

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

[0006] The present application discloses a turning optimization method for an eccentric shaft of an RV reducer, which adopts the following technical solutions:

[0007] One embodiment of the present application provides a turning optimization method for an eccentric shaft of an RV reducer, the method comprising the following steps:

[0008] Real-time acquisition of vibration signals from the tool holder during the turning process of the eccentric shaft of the RV reducer;

[0009] The vibration signal is divided into frames, and the severity of the maximum amplitude drop in each frame signal is obtained by analyzing the change in the amplitude of each frame signal in the time domain; each peak value of each frame signal in the frequency domain and the width of each peak value dropping to 3dB of the peak value are obtained, and the maximum fixed frequency energy ratio of each frame signal is obtained based on the peak values and the corresponding widths; the first eigenvalue of each frame signal is obtained by combining the severity and the maximum fixed frequency energy ratio;

[0010] Each frame signal and a preset number of consecutive frame signals before it are combined into each signal sequence, and the slope of the fitting straight line of the first eigenvalue of all frame signals in the signal sequence of each frame signal is calculated and recorded as the change slope of each frame signal. The vibration threshold of each frame signal is obtained by the maximum value of the change slope 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 sequence number during the previous tool pass; the second eigenvalue of each frame signal is obtained by 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 sequence number during the previous tool pass; and the spindle speed is adjusted according to the difference between the chatter threshold and the second eigenvalue.

[0011] In one embodiment, the intensity is obtained as follows:

[0012] Counting the maximum value of the amplitude of each frame signal in the time domain, calculating the mean and dispersion of the amplitude of each frame signal in the time domain; and counting the time length for each frame signal to drop from the maximum value to the mean value;

[0013] Taking the opposite of the duration as the exponent of an exponential function with a natural constant as the base;

[0014] Calculating a difference between the maximum value and the mean value, and calculating a ratio of the difference to the dispersion;

[0015] The intensity is positively correlated with the ratio and the calculation result of the exponential function respectively.

[0016] In one embodiment, the severity is the product of the ratio and a calculation result of the exponential function.

[0017] In one embodiment, the maximum fixed frequency energy ratio is obtained by:

[0018] Count the maximum peak value of each frame signal in the frequency domain;

[0019] Calculating the product of each peak value of each frame signal and the corresponding width;

[0020] Calculating the cumulative sum of the products of all peak values of each frame signal;

[0021] The maximum fixed frequency energy ratio is a ratio of the product of the maximum peak values of each frame signal to the accumulated sum.

[0022] In one embodiment, the first characteristic value is the product of the severity and the maximum fixed frequency energy ratio.

[0023] In one embodiment, the process of obtaining the chatter threshold is as follows:

[0024] The difference between the first characteristic value of each frame signal and the frame signal with the same sequence number during the previous pass is recorded as the characteristic difference;

[0025] Counting the maximum value of the characteristic difference values corresponding to all frame signals in the signal sequence of each frame signal;

[0026] Counting the maximum value of the change slope of all frame signals in the signal sequence of each frame signal;

[0027] The vibration threshold is positively correlated with the maximum value and the highest value respectively.

[0028] In one embodiment, the chatter threshold is a product of a normalized value of the highest value and the maximum value.

[0029] In one embodiment, the second characteristic value is the product of the normalized value of the change slope of each frame signal and the characteristic difference value corresponding to each frame signal.

[0030] In one embodiment, adjusting the spindle speed includes:

[0031] Calculate the normalized result of the difference between the second eigenvalue of the current frame signal and the vibration threshold, and use the product of the normalized result and the preset maximum spindle speed change as the spindle speed change of the next frame signal adjacent to the current frame signal; adjust the current spindle speed according to the spindle speed change.

[0032] In one embodiment, the current spindle speed is adjusted by the spindle speed change, specifically by:

[0033] 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 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 of the adjacent next frame signal is used as the spindle speed of the adjacent next frame signal.

[0034] This application has at least the following beneficial effects:

[0035] This application monitors the vibration signals at the turning tool holder to capture the minute tool displacements and acceleration changes caused by chatter in real time, analyzing the chatter level during the machining of the RV reducer's eccentric shaft. This eliminates the need for hammer modal testing and cutting force coefficient testing of the turning tool and workpiece, thus avoiding the complex process of determining the degree of turning chatter through cutting force modeling. Furthermore, turning chatter analysis based on monitoring vibration signals can effectively adapt to the constantly changing chatter frequency during the turning process, thereby improving the chatter suppression effect for the entire RV reducer's eccentric shaft turning process.

[0036] Furthermore, a time-frequency analysis method is used to extract the energy variation characteristics of the vibration signal caused by turning chatter, as well as the frequency domain characteristics of the vibration signal when chatter occurs. This reduces the influence of the complex structure of the eccentric shaft on the turning chatter analysis and improves the reliability and accuracy of judging the chatter degree during the turning process of the eccentric shaft of the RV reducer.

[0037] Furthermore, the vibration threshold is set by utilizing the vibration signals of different tool passes at the same feed position, as well as the characteristic change trend of the vibration signals of the same tool pass at different feed positions. This effectively suppresses the chatter while reducing the amplitude and frequency of the spindle speed adjustment, avoiding thermal cracks or deformation on the surface of the ADI material caused by uneven cutting heat distribution, and realizing optimization for the turning processing of the eccentric shaft of the RV reducer. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0039] Figure 1 A flowchart of the steps of a turning process optimization method for an eccentric shaft of an RV reducer provided in this application;

[0040] Figure 2 Schematic diagram of the process of obtaining the first eigenvalue;

[0041] Figure 3 Schematic diagram of the process of obtaining the chatter threshold and the second eigenvalue;

[0042] Figure 4 This is the flow chart for adjusting the spindle speed. DETAILED DESCRIPTION

[0043] In the description of the embodiments of this application, words such as "exemplary," "or," and "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary," "or," and "for example" is intended to present the relevant concepts in a concrete manner.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application relates. The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be understood that, unless otherwise indicated, " / " represents or.

[0045] It should also be noted that the terms "first" and "second" in this application are used to distinguish similar objects, rather than to describe a specific order or sequence.

[0046] The following describes in detail a specific solution for the turning optimization method for the eccentric shaft of the RV reducer provided in this application with reference to the accompanying drawings.

[0047] An embodiment of the present application provides a turning process optimization method for an RV reducer eccentric shaft. Specifically, the following turning process optimization method for an RV reducer eccentric shaft is provided. Figure 1 , the method comprises the following steps:

[0048] Step 1: Real-time acquisition of vibration signals at the turning tool holder during the turning process of the eccentric shaft of the RV reducer.

[0049] The turning tool is a critical component in the turning process of the RV reducer's eccentric shaft. The vibration of the turning tool directly reflects the condition of turning chatter. By installing a vibration sensor on the tool holder, the vibration signal during the turning process of the RV reducer's eccentric shaft is collected in real time. This accurately captures the tiny tool displacements and acceleration changes caused by chatter, and analyzes the current degree of turning chatter.

[0050] In this embodiment, the acquisition frequency of the vibration sensor is 10 kHz. The value of the acquisition frequency is preset manually and can be set by the implementer. This application does not impose any special restrictions.

[0051] In this embodiment, the feed speed of the eccentric shaft turning of the RV reducer is set to 100 mm / min, the turning length is set to 25 mm, the number of passes is set to 5 times, and the processing time for each pass is 15 seconds. The feed speed, turning length, number of passes and processing time for each pass are all preset manually. The implementer can set them according to actual conditions, and this application does not impose any special restrictions.

[0052] The complex structure of the eccentric shaft causes coupling between multiple modes. The interaction between the tool and the eccentric shaft at different locations excites different modal vibrations, and the coupling of these modal vibrations further complicates the chatter phenomenon. The eccentric shaft's structural design results in varying rigidity at different locations, exacerbating the intensity variations of the regenerative cutting effect. This results in varying degrees of cutting force fluctuation and varying chatter levels at different turning positions.

[0053] This application processes the vibration signals collected during each tool pass by framing them to generate individual frame signals. The corresponding eccentric shaft region of the tool is recorded as the processing region for each frame signal. This facilitates subsequent comparative analysis of vibration signals from different processing regions, allowing for more accurate determination of changes in chatter levels in these regions. Each frame signal and its corresponding processing region are numbered according to the chronological order of tool passes.

[0054] In this embodiment, the length of each frame signal is 0.5 seconds. The length of each frame signal is preset manually and can be set by the implementer according to actual conditions. This application does not impose any special restrictions.

[0055] In order to reduce the influence of spectrum leakage and high-frequency noise generated by the high-speed operation of the lathe, this application performs windowing and filtering on each frame signal.

[0056] In this embodiment, the window function used is a Hanning window, and a low-pass filter is used to filter each frame signal, and the cutoff frequency of the low-pass filter is 500 Hz.

[0057] Step 2: Extract the chatter characteristics during turning by analyzing the vibration signal in the time domain and frequency domain.

[0058] In real-world machining scenarios, turning environments are often complex. The interaction between the turning tool and the eccentric shaft generates complex vibration signals. To ensure machining accuracy and stability, these vibration signals must be precisely monitored and analyzed.

[0059] The eccentric shaft structure of the RV reducer makes it difficult to effectively extract chatter characteristics 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 the two frames of signals with high and low turning chatter levels being similar, making it difficult for traditional signal analysis methods to extract effective features reflecting turning chatter. On the other hand, the multimodal coupling caused by the complex structure of the eccentric shaft leads to the existence of multiple natural frequencies, causing the chatter energy to be distributed across multiple frequency ranges.

[0060] Turning chatter is a self-excited vibration phenomenon. When the cutting system enters the chatter state, the cutting force and the cutting system interact to form a positive feedback mechanism, which leads to the rapid accumulation of vibration energy and a significant increase in the vibration signal energy within a local time period. In addition, when chatter occurs, the eccentric structure of the eccentric shaft of the RV reducer causes periodic changes in the cutting force between the tool and the eccentric shaft. 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, forming a greater dynamic load, which will increase the intensity of the vibration during the chatter process and cause the energy of the vibration signal to increase significantly in the corresponding frame within a short period of time.

[0061] (1) By analyzing the changes in the amplitude of each frame signal in the time domain, the severity of the maximum amplitude drop in each frame signal is obtained.

[0062] In the time domain, when strong chatter occurs, the vibration signal of the corresponding frame increases in the local time period, and the amplitude of the vibration signal increases significantly, which manifests as sharp pulses or sudden changes in the vibration signal, reflecting the rapid accumulation and release of energy caused by chatter during the turning process.

[0063] The larger the maximum amplitude of the corresponding frame vibration signal is compared with 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 in the corresponding frame vibration signal is, indicating that the degree of turning chatter is high.

[0064] Taking the vibration signal collected during any tool pass as an example, in order to quantify the intensity of the maximum transient energy release in each frame signal, the amplitude change of each frame signal in the time domain is analyzed to obtain the severity of the maximum amplitude drop in each frame signal. The expression is:

[0065] Where, Indicates the severity of the maximum amplitude drop in the i-th frame signal; Represents the maximum value of the amplitude of the i-th frame signal in the time domain; 、 They represent the mean and dispersion of the amplitude of the i-th frame signal in the time domain respectively; exp( ) represents the exponential function with a natural constant as the base; represents the time duration for the i-th frame signal to drop from the maximum value to the mean value. The exponential function is used to normalize the value of the time duration to (0, 1].

[0066] In this embodiment, the dispersion is the standard deviation. As other implementation methods, on the basis of being able to measure the uneven distribution of amplitudes, the implementer may adopt other existing technologies, such as variance, coefficient of variation, etc., and this application does not impose any special restrictions.

[0067] It should be noted that: in the process of calculating the intensity, by introducing discreteness, using Quantify the significance of the sharp pulses in each frame signal relative to the overall fluctuation; the greater the severity, the greater the energy quickly accumulated and released in the i-th frame signal, and the greater the degree of chatter in the turning process.

[0068] (2) Obtain each peak value of each frame signal in the frequency domain and the width of each peak value on both sides of the peak value that drops to 3dB of the peak value, and obtain the maximum fixed frequency energy ratio of each frame signal through the peak values and the corresponding widths.

[0069] Furthermore, a fast Fourier transform is performed on each frame signal to obtain frequency domain sequences. Peak values within each frequency domain sequence are obtained and recorded as fixed-frequency peaks, representing the amplitudes of the multi-order natural frequencies of the cutting system. The width of each fixed-frequency peak, which drops by 3 dB on either side of the amplitude, is recorded as the fixed-frequency band of each fixed-frequency peak, representing the spectral distribution range of different-order fixed frequencies. Fast Fourier transforms are well-known techniques and will not be described in detail in this application.

[0070] To evaluate the energy concentration of the fixed-frequency peak, and thus reflect the degree of coupling between the cutting force and the cutting system, as well as the degree of turning chatter, the maximum fixed-frequency energy ratio of each frame signal is obtained by comparing the fixed-frequency peaks and fixed-frequency bands in the frequency domain of each frame signal. The expression is:

[0071] ; represents the maximum fixed frequency energy ratio of the i-th frame signal; Represents the maximum fixed frequency peak in the frequency domain sequence of the i-th frame signal; represents the fixed frequency band of the maximum fixed frequency peak in the frequency domain sequence of the i-th frame signal; represents the number of fixed frequency peaks in the frequency domain sequence of the i-th frame signal; Represents the kth fixed frequency peak in the frequency domain sequence of the i-th frame signal; represents the fixed frequency band of the kth fixed frequency peak in the frequency domain sequence of the i-th frame signal. Indicates the energy concentration of the i-th frame signal near all fixed frequencies.

[0072] It should be noted that when the maximum fixed-frequency peak and its fixed-frequency band increase significantly, the larger the value of the calculated maximum fixed-frequency energy ratio is, indicating that the energy is more concentrated near the fixed frequency with the largest peak, which means that the degree of coupling between the cutting force and the cutting system is higher, and the degree of turning chatter generated is higher.

[0073] (3) Combining the intensity and the maximum fixed frequency energy ratio, obtain the first eigenvalue of each frame signal.

[0074] Furthermore, the intensity of each frame signal and the maximum fixed-frequency energy ratio are combined to obtain a first eigenvalue for each frame signal. Specifically, the product of the intensity of each frame signal and the maximum fixed-frequency energy ratio is used as the first eigenvalue for each frame signal. The fixed-frequency coupling characteristics of each frame signal are quantified using the first eigenvalue to assess the degree of turning chatter.

[0075] It should be noted that: on the one hand, the greater the intensity, the greater the energy rapidly accumulated and released in each frame signal, the greater the degree of chatter generated by the fixed-frequency coupling in the turning process, and the larger the first eigenvalue obtained by calculation; on the other hand, the stronger the coupling between the cutting force and a certain fixed-frequency of the cutting system, the more energy is concentrated near the fixed-frequency, the stronger the turning chatter generated, and the larger the first eigenvalue of each frame signal. The flowchart of obtaining the first eigenvalue is shown in the figure below. Figure 2 shown.

[0076] Step 3: Adjust the spindle speed based on the extracted vibration characteristics.

[0077] Considering that the eccentric shaft of the RV reducer of ADI material is more likely to generate cutting heat during the turning process, the traditional strategy of varying the spindle speed to suppress chatter changes the spindle speed too frequently, resulting in uneven cutting heat distribution on the surface of the ADI material, affecting the turning quality.

[0078] During the turning process of an eccentric shaft with an RV reducer, the periodic changes in cutting force act on the workpiece and are further transmitted to the cutting system, changing the force state of the cutting system and affecting the dynamic response of the cutting system. This in turn causes small fluctuations in the degree of turning chatter within a short period of time. If each change in chatter triggers a speed adjustment, the spindle speed will fluctuate frequently.

[0079] 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 large degree of turning chatter.

[0080] This application sets the initial spindle speed to In this embodiment The value is 800rmp. The cutting force usually changes with 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 stimulate the resonance of the cutting system. Therefore, in the early stage of RV reducer eccentric shaft turning, the lower initial speed It is difficult to trigger the chatter condition. This application uses the vibration signal characteristics of the first frame collected during the first turning pass as the benchmark for low-level turning chatter, calculates the chatter threshold for each frame, and reduces the adjustment amplitude and frequency of the spindle speed while ensuring the suppression of the turning chatter level. The specific process is as follows:

[0081] (1) Each frame signal and its previous preset number of consecutive frame signals are combined into a signal sequence, and the slope of the fitting straight line of the first eigenvalues of all frame signals in the signal sequence of each frame signal is calculated and recorded as the change slope of each frame signal.

[0082] For the vibration signal obtained from each tool pass, each frame signal and the previous preset number of frame signals are arranged in time sequence to form a signal sequence of each frame signal.

[0083] In this embodiment, the value of the preset number is 10. The value of the preset number is preset manually and can be set by the implementer. This application does not impose any special restrictions. When the number of signal frames before each frame signal is less than 10, linear interpolation is used to fill the missing data. Linear interpolation is a well-known technology and will not be described in detail in this application.

[0084] To capture the chatter development characteristics of turning near each frame signal, a fitted line is obtained for the first eigenvalue of all frame signals in the signal sequence of each frame signal. The slope of each fitted line is calculated and recorded as the slope of change for each frame signal. The calculation of the slope is well known and will not be further described in this application.

[0085] In this embodiment, the least squares method is used to obtain the fitting straight line. The least squares method is a well-known technology and will not be described in detail in this application. As other implementation methods, on the basis of being able to obtain the fitting straight line, the implementer may adopt other existing technologies, such as the weighted least squares method, etc., and this application does not impose any special restrictions.

[0086] (2) The chatter threshold of each frame signal is obtained by the maximum value of the change slope 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 sequence number during the previous tool pass; the second eigenvalue of each frame signal is obtained by 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 sequence number during the previous tool pass.

[0087] The chatter threshold of each frame signal is obtained by the distribution of the change slope 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 sequence number during the previous tool pass. The expression is:

[0088] Where, represents the chatter threshold of the i-th frame signal; calculate the difference between the first eigenvalue of each frame signal and the frame signal with the same sequence number during the previous pass, and record it as the characteristic difference; represents the maximum value of the characteristic difference values corresponding to all frame signals in the signal sequence of the i-th frame signal; norm() represents the arc tangent normalization function, which is used to convert Normalize to (0,1); Indicates the highest value of the change slope of all frame signals in the signal sequence of the i-th frame signal.

[0089] Furthermore, the second eigenvalue of each frame signal is obtained by 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 sequence number during the previous pass. The expression is:

[0090] ; represents the second eigenvalue of the i-th frame signal; represents the characteristic difference corresponding to the i-th frame signal; norm() represents the arctangent normalization function, which is used to convert Normalize to (0,1); Indicates the slope of the change of the i-th frame signal. This application adjusts the spindle speed only when the second eigenvalue of each frame signal exceeds its chatter threshold, so as to avoid frequent changes in the spindle speed due to small fluctuations in the degree of turning chatter in a short period of time. The flowchart for obtaining the chatter threshold and the second eigenvalue is shown in the figure. Figure 3 shown.

[0091] Using the vibration signal characteristics collected during initial turning as a benchmark for low-level turning chatter, the chatter threshold is calculated for each frame, ensuring timely adjustment of the rotational speed when chatter becomes excessive. Furthermore, because the chatter threshold is calculated based on the maximum characteristic difference and the maximum slope of change, it is maintained at a relatively high level, preventing uneven heat distribution on the ADI material surface caused by overly frequent rotational speed adjustments.

[0092] (3) Adjusting the spindle speed according to the difference between the chatter threshold and the second characteristic value.

[0093] 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, it is easy to cause resonance, resulting in chatter.

[0094] In the early stages of turning the eccentric shaft of an RV reducer, the workpiece has not yet been cut and its rigidity 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 rigidity, which directly leads to a change in the natural frequency of the cutting system.

[0095] Furthermore, the spindle speed change of the next frame signal adjacent to the current frame signal is obtained by the difference between the chatter threshold value of the current frame signal and the second eigenvalue, which is used to determine the adjustment amplitude of the current spindle speed. The expression is:

[0096] ; represents the spindle speed change of the i+1 frame signal; N represents the preset maximum spindle speed change; norm() represents the arc tangent normalization function, which is used to convert Normalize to (0,1); represents the second eigenvalue of the i-th frame signal; Indicates the chatter threshold of the i-th frame signal.

[0097] 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 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 of the adjacent next frame signal is used as the spindle speed of the adjacent next frame signal. The spindle speed adjustment flow chart is shown in FIG. Figure 4 shown.

[0098] In this embodiment, in order to prevent the spindle speed from being too high or too low, the spindle speed adjustment limit is set to 1000 rpm.

[0099] In summary, this application monitors the vibration signal at the turning tool holder to capture in real time the minute tool displacements and acceleration changes caused by chatter, and analyzes the chatter level during the machining of the RV reducer's eccentric shaft. This eliminates the need for hammer modal testing and cutting force coefficient testing of the turning tool and workpiece, thus avoiding the complex process of determining the degree of turning chatter through cutting force modeling. Furthermore, turning chatter analysis based on monitoring vibration signals can effectively adapt to the constantly changing chatter frequency during the turning process, thereby improving the chatter suppression effect for the entire RV reducer's eccentric shaft turning process.

[0100] Furthermore, a time-frequency analysis method is used to extract the energy variation characteristics of the vibration signal caused by turning chatter, as well as the frequency domain characteristics of the vibration signal when chatter occurs. This reduces the influence of the complex structure of the eccentric shaft on the turning chatter analysis and improves the reliability and accuracy of judging the chatter degree during the turning process of the eccentric shaft of the RV reducer.

[0101] Furthermore, the vibration threshold is set by utilizing the vibration signals of different tool passes at the same feed position, as well as the characteristic change trend of the vibration signals of the same tool pass at different feed positions. This effectively suppresses the chatter while reducing the amplitude and frequency of the spindle speed adjustment, avoiding thermal cracks or deformation on the surface of the ADI material caused by uneven cutting heat distribution, and realizing optimization for the turning processing of the eccentric shaft of the RV reducer.

[0102] The flowcharts and block diagrams in the accompanying drawings show the possible implementation architectures, functions and operations of the systems, methods and computer program products according to the embodiments of the present disclosure. In this regard, each box in the flowchart or block diagram can represent a module, program segment or part of the code, and the module, program segment or part of the code contains one or more executable instructions for implementing the specified logical functions. In some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, which can depend 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 boxes can also occur in an order different from that disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, which can depend on the functions involved. Each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented by a dedicated hardware-based system that performs the specified function or action, or may be implemented by a combination of dedicated hardware and computer instructions.

[0103] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and that the present application can be implemented in other specific forms without departing from the basic characteristics of the present application. Therefore, from all perspectives, the above embodiments of the present application should be regarded as exemplary and non-restrictive.

Claims

1. A turning optimization method for RV reducer eccentric shaft, characterized in that: The method comprises the following steps: Real-time acquisition of vibration signals from the tool holder during the turning process of the eccentric shaft of the RV reducer; The vibration signal is divided into frames, and the severity of the maximum amplitude drop in each frame signal is obtained by analyzing the change in the amplitude of each frame signal in the time domain; each peak value of each frame signal in the frequency domain and the width of each peak value dropping to 3dB of the peak value are obtained, and the maximum fixed frequency energy ratio of each frame signal is obtained based on the peak values and the corresponding widths; the first eigenvalue of each frame signal is obtained by combining the severity and the maximum fixed frequency energy ratio; Each frame signal and a preset number of consecutive frame signals before it are combined into each signal sequence, and the slope of the fitting straight line of the first eigenvalue of all frame signals in the signal sequence of each frame signal is calculated and recorded as the change slope of each frame signal. The vibration threshold of each frame signal is obtained by the maximum value of the change slope 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 sequence number during the previous tool pass; the second eigenvalue of each frame signal is obtained by 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 sequence number during the previous tool pass; and the spindle speed is adjusted according to the difference between the chatter threshold and the second eigenvalue.

2. The turning optimization method for the eccentric shaft of the RV reducer according to claim 1, characterized in that: The process of obtaining the intensity is as follows: Counting the maximum value of the amplitude of each frame signal in the time domain, calculating the mean and dispersion of the amplitude of each frame signal in the time domain; and counting the time length for each frame signal to drop from the maximum value to the mean value; Taking the opposite of the duration as the exponent of an exponential function with a natural constant as the base; Calculating a difference between the maximum value and the mean value, and calculating a ratio of the difference to the dispersion; The intensity is positively correlated with the ratio and the calculation result of the exponential function respectively.

3. The turning optimization method for the eccentric shaft of the 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 optimization method for the eccentric shaft of the RV reducer according to claim 1, characterized in that: The process of obtaining the maximum fixed frequency energy ratio is as follows: Count the maximum peak value of each frame signal in the frequency domain; Calculating the product of each peak value of each frame signal and the corresponding width; Calculating the cumulative sum of the products of all peak values of each frame signal; The maximum fixed frequency energy ratio is a ratio of the product of the maximum peak values of each frame signal to the accumulated sum.

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

6. The turning optimization method for the eccentric shaft of the RV reducer according to claim 1, characterized in that: The process of obtaining the chatter threshold is as follows: The difference between the first characteristic value of each frame signal and the frame signal with the same sequence number during the previous pass is recorded as the characteristic difference; Counting the maximum value of the characteristic difference values corresponding to all frame signals in the signal sequence of each frame signal; Counting the maximum value of the change slope of all frame signals in the signal sequence of each frame signal; The vibration threshold is positively correlated with the maximum value and the highest value respectively.

7. The turning optimization method for the eccentric shaft of the RV reducer according to claim 6, characterized in that: The chatter threshold is a product of a normalized value of the highest value and the maximum value.

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

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

10. The turning optimization method for the eccentric shaft of the RV reducer according to claim 9, characterized in that: The specific method of adjusting the current spindle speed by the spindle speed change 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 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 of the adjacent next frame signal is used as the spindle speed of the adjacent next frame signal.

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