CN109877647A - A performance degradation evaluation system of machine tool servo axis based on built-in encoder - Google Patents
A performance degradation evaluation system of machine tool servo axis based on built-in encoder Download PDFInfo
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Abstract
本发明涉及一种基于内置编码器的机床伺服轴性能退化评估系统，包括：工况设定模块，用于控制设定被评估伺服轴的工作速度恒定；采集模块，与所述内置编码器连接，用于获取所述内置编码器输出的角位置增量信息；性能退化特征指标获取模块，用于对所述角位置增量信息进行转换处理，并获得被评估伺服轴的性能退化特征指标。与现有技术相比，本发明采用机床电机上用于运动反馈控制的编码器信息作为伺服轴性能评估的信息源，不仅能够降低测试成本，提高早期故障检测的灵敏度，还能摆脱精密设备传感器安装困难的局限性。
The invention relates to a system for evaluating the performance degradation of a machine tool servo axis based on a built-in encoder, comprising: a working condition setting module for controlling and setting the working speed of the evaluated servo axis to be constant; a collection module, which is connected with the built-in encoder , which is used to obtain the angular position increment information output by the built-in encoder; the performance degradation characteristic index acquisition module is used to convert the angular position increment information, and obtain the performance degradation characteristic index of the evaluated servo shaft. Compared with the prior art, the present invention uses the encoder information used for motion feedback control on the machine tool motor as the information source for the performance evaluation of the servo axis, which can not only reduce the test cost, improve the sensitivity of early fault detection, but also get rid of the precision equipment sensor. Installation difficult limitations.
Description
Technical field
The invention belongs to mechanical system health monitoring, fault diagnosis, the mechanical signal processing technology fields of Performance Evaluation, especially
It is to be related to a kind of lathe axis servomotor performance degradation assessment system based on built-in encoder.
Background technique
The performance of precision machine tool equipment servo axis components (such as motor, retarder, bearing, ball-screw) and assembly are logical
It is often all intact.However, during the military service of equipment, by the early defect influence on development of key components and parts, the fortune of equipment
Row precision and performance can gradually fail, and then influence processing quality and even result in the accidents such as scram.Carrying out status assessment is
The premise for implementing health control and maintenance to equipment is also to ensure that equipment is reliable, effective means of high-efficiency high-accuracy operation.So
And relative to commonly used equipment, the structure of the process units such as precise numerical control machine is extremely complex, and degradation filture also has diversity.
Therefore the vibration information of equipment is also more complicated, characterizes the characteristic information of the faint degeneration of axis servomotor moving component usually by complexity
Structural vibration and ambient noise information are flooded, so that the existing performance degradation assessment method based on vibrating with noise is difficult
Directly apply.In addition, being limited (such as spray coolant, limited body sky by harsh working environment for some precision equipments
Between, closing working environment etc.), be difficult that sensing unit additionally is installed.Under this background, there is an urgent need to a kind of significantly more efficient
Assessment technology is tested to improve the accuracy of lathe axis servomotor Performance Evaluation.
Summary of the invention
It is an object of the present invention to overcome the above-mentioned drawbacks of the prior art and provide one kind to be based on built-in coding
The lathe axis servomotor performance degradation assessment system of device.
The purpose of the present invention can be achieved through the following technical solutions:
A kind of lathe axis servomotor performance degradation assessment system based on built-in encoder, comprising:
Operating condition setting module, the operating rate for controlling the evaluated axis servomotor of setting are constant；
Acquisition module is connect with the built-in encoder, for obtaining the Angle Position increment of the built-in encoder output
Information；
Performance degradation characteristic index obtains module, for carrying out conversion process to the Angle Position increment information, and obtains
The performance degradation characteristic index of evaluated axis servomotor.
Further, the acquisition module includes a Count Board.
Further, the performance degradation characteristic index acquisition module includes:
Trend amount removal unit obtains discrete angular position for carrying out the removal of trend amount to the Angle Position increment information
Intelligence wave momentum sequence:
In formula, v0For the revolving speed of electric machine built-in encoder, n is the points of discrete series, v0N is trend amount,For angle
Positional increment information,For discrete angular position intelligence wave momentum sequence；
Fourier transform unit, for carrying out Fourier transformation processing to the discrete angular position intelligence wave momentum sequence,
Obtain corresponding instantaneous angular acceleration discrete series are as follows:
In formula, a (n) is instantaneous angular acceleration discrete series, and N is the length of discrete angular position sequence, and k is discrete frequency, C
It (k) is weight Fourier coefficient；
Wavelet transform unit is corresponded to for carrying out continuous wavelet transform to the instantaneous angular acceleration discrete series
Time-frequency domain expression-form:
In formula, ψ (t) is mother wavelet function, and x (t) is signal to be analyzed, and s is scale factor, and f is equivalent Fourier frequency,
T is time factor, and * expression takes conjugation；
Indicator calculating unit, for calculating the performance degradation characteristic index based on continuous wavelet transform:
In formula, WTIF is performance degradation characteristic index, B=[fmin, fmax] be selection integral frequency band.
Further, the detailed process of the Fourier transform unit are as follows:
1) discrete angular position sequence is calculated using Fast Fourier Transform (FFT)Fourier coefficient
2) by the Fourier coefficient of acquisition multiplied by weight coefficient-(2 π fsn/N)2, obtain weight Fourier coefficient:
3) inverse fast Fourier transform is carried out to the weight Fourier coefficient, obtains the discrete sequence of instantaneous angular acceleration
Column.
Further, the mother wavelet function in the wavelet transform unit are as follows:
In formula, σ is decay factor, and f is the frequency of Morlet morther wavelet.
Further, the value of the performance degradation characteristic index is bigger, then axis servomotor performance degradation is more serious.
Compared with prior art, the present invention have with following the utility model has the advantages that
The present invention is using the encoder information on machine motor for motion feedback control as axis servomotor Performance Evaluation
Information source can not only reduce testing cost, improve the sensitivity of incipient fault detection, moreover it is possible to get rid of precision equipment sensor peace
Fill difficult limitation.In addition, the method for the present invention is directly assessed with built-in information, no testing cost.
Detailed description of the invention
Fig. 1 is the lathe X- axle construction figure tested in embodiment；
Fig. 2 is X- spindle motor encoder Angle Position increment information schematic diagram, and (2a) is tested for the first time, (2b) second of survey
Examination；
Fig. 3 is angle position information undulate quantity schematic diagram, and (3a) is tested for the first time, (3b) second of test；
Fig. 4 is that angle position information fluctuates spectrum diagram, and (4a) is tested for the first time, and (4b) is tested for the second time；
Fig. 5 is IAA schematic diagram, and (5a) is tested for the first time, (5b) second of test；
Fig. 6 is IAA spectrum diagram, and (6a) is tested for the first time, (6b) second of test；
Fig. 7 is WTIF schematic diagram, and (7a) is tested for the first time, (7b) second of test；
Fig. 8 is the flow diagram that the present invention assesses.
Specific embodiment
The present invention is described in detail with specific embodiment below in conjunction with the accompanying drawings.The present embodiment is with technical solution of the present invention
Premised on implemented, the detailed implementation method and specific operation process are given, but protection scope of the present invention is not limited to
Following embodiments.
The present invention realizes a kind of lathe axis servomotor performance degradation assessment system based on built-in encoder, including operating condition setting
Module, acquisition module and performance degradation characteristic index obtain module, wherein for controlling, setting is evaluated to be watched operating condition setting module
The operating rate for taking axis is constant；Acquisition module is connect with the built-in encoder, for obtaining the built-in encoder output
Angle Position increment information；Performance degradation characteristic index obtains module and is used to carry out conversion process to the Angle Position increment information,
And obtain the performance degradation characteristic index of evaluated axis servomotor.The acquisition module includes a Count Board (such as Heidenhain
IK220 Count Board).
As shown in figure 8, the present embodiment includes: the step of assessment using above-mentioned assessment system
Step 1: certain model turn-milling complex machining center axis servomotor (X- axis) is set by numerical control module, makes it in zero load
Under state, permanent operating condition is operated under the speed of 550mm/min, and wherein the structure of X- axis is as shown in Figure 1.
Step 2: with the angle of Heidenhain IK220 Count Board test axis servomotor (X- axis) electric machine built-in encoder output
Positional increment information, wherein sample frequency is 1000Hz.This experiment carries out during being on active service in machining center, completes two altogether
Secondary test, test interval is about 6 months twice.Fig. 2 is the Angle Position increasing for testing the X- spindle motor encoder of acquisition twice
Measure information.As figure shows, the information tested twice is all two straight lines, can hardly be reflected any with equipment performance degeneration phase
The information of pass.Positional increment information obtained is discrete digital signal, is denoted as
Step 3: trend amount is carried out to Angle Position increment information obtained, obtains angle position information undulate quantity.Remember angle
The trend amount of positional increment information is v0N, then discrete angular position intelligence wave momentum sequenceAre as follows:
In formula, v0For the revolving speed of electric machine built-in encoder；N is the points of discrete series.
The angle position information undulate quantity tested twice is as shown in figure 3, Fig. 4 is its spectrum information.It can by Fig. 3 and Fig. 4
Know, there are apparent cyclic swings for the angle position information tested twice, and its vibration frequency is equal to passing through for ball-screw ball
Frequency.But Cong Tuzhong is difficult to be further discovered that information relevant to equipment performance degeneration.In addition, the fluctuation of second of test
Amplitude has dropped instead, so if being only then extremely easy to happen erroneous judgement with the amplitude index of fluctuation information.
Step 4: discrete angular position sequence is calculated using Fast Fourier Transform (FFT) (FFT)Fourier coefficient
In formula, N is the length of discrete angular position sequence；
K is discrete frequency.
Step 5: the Fourier coefficient that step 4 is obtained is multiplied by weight coefficient-(2 π fsn/N)2, obtain weight Fourier
Coefficient
In formula, fsFor sample frequency.
Step 6: inverse fast Fourier transform (IFFT) is carried out to weight Fourier coefficient, obtains instantaneous angular acceleration
(Instantaneous Angular Acceleration, IAA) discrete series are as follows:
In formula, N indicates the length of discrete angular position sequence.
Fig. 5 is that resulting IAA information is calculated with the Angle Position fluctuation information tested twice, and Fig. 6 is its spectrogram.Relatively
In Angle Position fluctuation information, IAA can more reflect the motion information of system X- axis.As shown in Figure 5, comparison is tested twice, in lead screw
Later half time stroke, the IAA amplitude of second test significantly increases.In addition, as shown in fig. 6, subtracting in the frequency spectrum tested twice
The meshing frequency and each axis of fast device gears at different levels turn the clear display of frequency.With the increase of active time, caused by being influenced because of abrasion etc.
Performance degradation be mainly manifested between 300Hz-500Hz.
Step 7: selection is used for the mother wavelet function of continuous wavelet transform.Believe to the performance degradation feature in IAA signal
When breath is detected, morther wavelet is using Morlet small echo shown in formula (5):
Wherein: σ --- decay factor；
The frequency of f---Morlet morther wavelet.
This method uses Morlet small echo, similar with equipment fault, is more conducive to the extraction of failure.
Step 8: using formula (6) to IAA signal make continuous wavelet transform (Continue Wavelet Transform,
CWT), the time-frequency domain expression-form of signal is obtained:
Wherein: ψ (t) --- selected morther wavelet；
X (t) --- signal to be analyzed；
S--- scale factor；
F--- is equivalent Fourier frequency；
T--- time factor；
* --- expression takes conjugation；
T ' --- when shifter factor.
Step 9: when performance degradation occurs for equipment, new characteristic frequency can be generated, by selecting different integral frequency bands
The index is calculated, can effectively identify degeneration.This method calculates the performance degradation spy based on continuous wavelet transform using formula (7)
It is as follows to levy index (Wavelet Transform Integrated Feature, WTIF)
Wherein, Wψ(s, t) is the continuous wavelet transform of signal, B=[fmin, fmax] be selection integral frequency band.
Select 300-500Hz in the present embodiment to integrate frequency band.Fig. 7 is the WTIF index for testing IAA twice, by scheming
(7a) it is found that in the state that X-shaft transmission system is in relative healths, the WTIF index of IAA signal is in whole service section
It is at relatively low level.But with the increase of active time, the abrasion of X-axis is on the rise.Such as second of figure (7b)
Test is as it can be seen that its WTIF index was all dramatically increased 40-88 seconds and 100-117 seconds, to nearly 65 seconds and 110 seconds or so amplitude
Reach local peaking.Test explanation, the method that this patent proposes can preferably reflect the performance degradation of equipment.
The preferred embodiment of the present invention has been described in detail above.It should be appreciated that those skilled in the art without
It needs creative work according to the present invention can conceive and makes many modifications and variations.Therefore, all technologies in the art
Personnel are available by logical analysis, reasoning, or a limited experiment on the basis of existing technology under this invention's idea
Technical solution, all should be within the scope of protection determined by the claims.
Claims (6)
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN110595751A (en) * | 2019-09-19 | 2019-12-20 | 华东理工大学 | Wavelet reconstruction method of early fault characteristics guided by Gini index and its application |
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| CN104819841A (en) * | 2015-05-05 | 2015-08-05 | 西安交通大学 | Built-in-coding-information-based single sensing flexible angle-domain averaging method |
| CN108106841A (en) * | 2017-12-21 | 2018-06-01 | 西安交通大学 | Epicyclic gearbox intelligent failure diagnosis method based on built-in encoder signal |
| CN208254802U (en) * | 2018-06-28 | 2018-12-18 | 山东大学 | Wind power gear speed increase box fault diagnostic test platform based on multi-feature fusion |
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| EP0612591A1 (en) * | 1993-02-24 | 1994-08-31 | Fanuc Robotics North America, Inc. | Motorized rotary joint and method of constructing a modular robot utilizing same |
| JPH09233873A (en) * | 1996-02-29 | 1997-09-05 | Oki Electric Ind Co Ltd | Dc servo motor controller |
| CN102501141A (en) * | 2011-10-28 | 2012-06-20 | 西安交通大学 | Numerical control machine main shaft site dynamic balance method based on built-in sensor |
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