CN103149435A - Mechanical resonant frequency feature obtaining method for alternating current servo system based on pseudorandom sequence code - Google Patents

Abstract

The invention provides a mechanical resonant frequency feature obtaining method for an alternating current servo system based on a pseudorandom sequence code, belonging to the technical field of frequency feature obtaining of an alternating current servo system, and solves the problem that the mechanical resonant feature obtained by sweeping frequency under an open loop cannot effectively and accurately obtain the frequency feature of low frequency. The method comprises the following steps of firstly obtaining an n-order primitive polynomial; combining an initial n-order sequence of a binary m sequence by the coefficients of the n-order primitive polynomial, multiplying a feedback shift register and the initial n-order sequence and accumulating and summing, performing feedback calculation after the accumulated value takes 2 as a base number and is subjected to modulo operation, and finally obtaining 2<n> binary m sequences; converting the m sequences into a current value sequence as the given current under the speed open loop of the alternating current servo system; and respectively performing fast Fourier transform for the current value sequence and an acquired motor rotary speed sequence, performing mathematic operation for the converted results, and obtaining a Bode diagraph of the open loop alternating current system. The method provided by the invention can be used for obtaining the mechanical resonant frequency feature of the alternating current servo system.

Description

AC servo mechanical resonant frequency characteristic acquisition methods based on pseudo random sequence code

Technical field

The present invention relates to the AC servo mechanical resonant frequency characteristic acquisition methods based on pseudo random sequence code, belong to AC servo frequency characteristic obtain technical field.

Background technology

At present, the frequency characteristic in AC servo is offered help for the research that promotes the servo-drive system performance in many-side, and wherein main is to be applied in the mechanical resonant inhibition.If servo-drive system can accurately obtain resonance characteristic in advance, just can or drop into notch filter by parameter adjustment and make system avoid mechanical resonant, also can reduce online Restrainable algorithms to the use problem of resource.So obtain fast and accurately frequency characteristic especially the mechanical resonant characteristic information be very necessary in AC servo.

Common frequency characteristic acquisition methods mainly contains frequency sweep method, impulse response method, white noise method etc.Sweep generator obtains equipment with regard to the frequency characteristic that is based on frequency sweep method.The narrower frequency component of the pulse signal of impulse response method is higher, but burst pulse generally is difficult to make the characteristic that obtains very accurate because the impulse energy is not ideal enough, and is subject to noise.Although white noise method advantage is to comprise all frequency contents, time enough length guarantee " in vain " characteristic must be arranged.At present, the research of frequency characteristic aspect obtaining is all being done by many domestic and international servo-drivers manufacturer, and main method is all also to use sweep method to obtain Bode diagram (Bode).And to obtain the mechanical resonant characteristic in frequency sweep under open loop, will note the accumulation of low frequency signal to the impact of rotating speed, so be difficult to effectively obtain accurately the frequency characteristic of low-frequency range with frequency sweep method.For the numerically-controlled machine of large inertia, the tuning-points frequency can be very low, so this method will have problems, and sweep method is consuming time longer, has hidden danger for the security of whole resonator system.

Summary of the invention

The present invention can not obtain the problem of the frequency characteristic of low-frequency range effectively accurately in order to solve frequency sweep obtains under open loop mechanical resonant characteristic, and a kind of AC servo mechanical resonant frequency characteristic acquisition methods based on pseudo random sequence code is provided.

AC servo mechanical resonant frequency characteristic acquisition methods based on pseudo random sequence code of the present invention, it comprises the following steps:

Step 1: according to the requirement of system mechanics accuracy of resonant frequencies, choose n rank primitive polynomial, n is the positive integer more than or equal to 2;

Step 2: formed the initial n exponent number row of scale-of-two m sequence by the coefficient of n rank primitive polynomial, the initialization feedback shift register;

Then repeat following computation process: to the summation of taking advantage of and add up of this feedback shift register and initial n exponent number row positions, accumulated value base 2 deliverys are fed back calculating, with the renewal feedback shift register; Obtain 2 until calculate ⁿ-1 scale-of-two m sequence, described computation process finishes;

Again with 2 ⁿThe position, end of-1 scale-of-two m sequence mends 0, obtains 2 of 01 level ⁿIndividual scale-of-two m sequence;

Step 3: with obtain in step 22 ⁿIndividual scale-of-two m sequence is converted to the current value sequence that level value is positive and negative p times system nominal current, and p is the positive number less than the system nominal current amplitude limit value, then with the current value sequence that obtains as the given value of current under the speed open loop of AC servo;

Step 4: in the system operational process of described current value sequence as the given value of current under the speed open loop of AC servo, the motor speed sequence of synchronous acquisition AC servo, the motor speed sequence of current value sequence and collection acquisition is done respectively Fast Fourier Transform (FFT), described transformation results is carried out the Bode figure that computing obtains the open loop AC servo, and then obtain the mechanical resonant frequency characteristic of AC servo.

Described n rank primitive polynomial is chosen for 10 rank primitive polynomials, obtains 2 ¹⁰=1024 scale-of-two m sequences.

Advantage of the present invention: the given value of current signal that the inventive method is done the m sequence in the pseudo-random sequence that generates under the speed open loop inputs to AC servo, by m sequence and motor speed are done respectively Fast Fourier Transform (FFT), obtain the Bode figure of open cycle system, and then obtain the system frequency feature.

In the inventive method, give the time of the given signal of AC servo input current short, can prevent effectively that long-time resonance is on the impact of system, and the autocorrelation performance that it is good that pseudo-random sequence is the m sequence makes resolving accuracy high, also better to the low-frequency range resolving effect, very accurate to obtaining of the frequency characteristic of whole system.Can use pseudo-random sequence method test frequency spectrum for frequency conversion or servo-drive system, and by the embedded system canbe used on line.

The inventive method can guarantee that the frequency characteristic of AC servo is obtained fast and accurately, have broadband and low-frequency effect, it can not only obtain characteristic Bode figure fast and accurately, and the white characteristic of pseudo random sequence code is better than white noise character, and the noise as a result that obtains is less.

Description of drawings

Fig. 1 is the AC servo mechanical resonant frequency characteristic acquisition methods based on pseudo random sequence code of the present invention with the application block diagram in the AC servo of resonance;

Fig. 2 is the theory diagram of Fig. 1 Elastic load;

Fig. 3 is the chart of primitive polynomial commonly used;

Fig. 4 is 2 ⁿThe product process figure of individual scale-of-two m sequence;

Fig. 5 is the Bode figure with the resonance test result under system shown in Figure 1.

Embodiment

Embodiment one: below in conjunction with Fig. 1 to Fig. 5, present embodiment is described, the described AC servo mechanical resonant frequency characteristic acquisition methods based on pseudo random sequence code of present embodiment, it comprises the following steps:

Step 1: according to the requirement of system mechanics accuracy of resonant frequencies, choose n rank primitive polynomial, n is the positive integer more than or equal to 2;

Step 2: formed the initial n exponent number row of scale-of-two m sequence by the coefficient of n rank primitive polynomial, the initialization feedback shift register;

Then repeat following computation process: to the summation of taking advantage of and add up of this feedback shift register and initial n exponent number row positions, accumulated value base 2 deliverys are fed back calculating, with the renewal feedback shift register; Obtain 2 until calculate ⁿ-1 scale-of-two m sequence, described computation process finishes;

Again with 2 ⁿThe position, end of-1 scale-of-two m sequence mends 0, obtains 2 of 01 level ⁿIndividual scale-of-two m sequence;

Step 3: with obtain in step 22 ⁿIndividual scale-of-two m sequence is converted to the current value sequence that level value is positive and negative p times system nominal current, and p is the positive number less than the system nominal current amplitude limit value, then with the current value sequence that obtains as the given value of current under the speed open loop of AC servo;

Step 4: in the system operational process of described current value sequence as the given value of current under the speed open loop of AC servo, the motor speed sequence of synchronous acquisition AC servo, the motor speed sequence of current value sequence and collection acquisition is done respectively Fast Fourier Transform (FFT), described transformation results is carried out the Bode figure that computing obtains the open loop AC servo, and then obtain the mechanical resonant frequency characteristic of AC servo.

In present embodiment, choosing by actual needs of n value determine, n is larger, and the effect that obtains result is better, but consuming time longer.

The m sequence claims again the maximum linear shift-register sequence, and its generation is generated by feedback shift register.Scale-of-two m sequence has good pseudo-random characteristics, and following characteristics are arranged:

1, balance: in the one-period of scale-of-two m sequence, 1 and 0 number differs 1.

2, have the two-value autocorrelation function:

Be T=2 for one-period ⁿ-1 ± 1 level m sequence, its autocorrelation function R (τ) is:

$R\left(\mathrm{\&tau;}\right)=-\frac{1}{T}\underset{k=0}{\overset{T-1}{\mathrm{\&Sigma;}}}u\left(k\right)u(k+\mathrm{\&tau;}),$

In formula, k is the initial stop value of cumulative formula, and u (k) is the sequence signal level value, and τ is integer.

The autocorrelation performance that obtains like this is: when τ is 0 or during the integral multiple of T, R (τ)=1 is weak relevant when τ gets other values

When cycle T was very large, autocorrelation function and the white noise of m sequence were similar, and very sharp-pointed autocorrelation performance is so just arranged, and Here it is can select to replace white noise to do the reason of given value of current signal based on the pseudo-random sequence of m sequence.And in the one-period of this ± 1 level m sequence, 1 number is only Duoed one than-1 number, and the mean value of sequence is very little, the speed problems of too of having avoided in actual applications the low speed accumulation under the open loop to cause.

Fig. 1 is the AC servo with the elastic mechanical load.System is speed open-loop current closed-loop system, uses the vector control mode of field orientation, with current i _a, i _bConversion is transformed into the i on α β two phase coordinate systems through Clark _α, i _β, then conversion is transformed into i under rotation dq coordinate system through Park _d, i _qBy with i _dAnd i _qThe given signal Vqref of dq shaft voltage, Vdref after two groups of PI controllers acts on the Speed open-loop control of completing servo-drive system on motor after anti-Park conversion and SVPWM space voltage vector are controlled.Here do not consider that closed loop is because in order to obtain the frequency characteristic of mechanical resonant, just only can accurately obtain, closed loop can produce inhibition to the component frequency characteristic under open loop.I in Fig. 1 _QrefFor the q shaft current given, i _DrefGiven for the d shaft current, n is motor speed, θ _eBe positional information.

Fig. 1 represents, elastic load can produce mechanical resonant, and its inner theory diagram as shown in Figure 2.T wherein ₁Be load torque, T ω is wheelbase, ω ₂Be load speed, J ₁Be motor inertia, J ₂Be load inertia, K is the load elasticity coefficient.Can obtain motor speed ω ₁With electromagnetic torque T _eBetween transport function G ₁(s) be:

$G_1\left(s\right)=\frac{{\mathrm{\&omega;}}_1}{T_e}=\frac{J_2{s}^2+K}{J_1{J}_2{\mathrm{<figure-callout\; id="3"\; label="s"\; filenames="HDA00002930835700021.png"\; state="\{\{state\}\}">s</figure-callout>}}^3+({\mathrm{<figure-callout\; id="1"\; label="J"\; filenames="HDA00002930835700012.png,HDA00002930835700021.png"\; state="\{\{state\}\}">J</figure-callout>}}_1+J_2)\mathrm{Ks}},$

By following formula as seen, mechanical resonant can increase a pair of zero limit on the open-loop transfer function of original spaceborne system, and the demonstration on Bode figure is exactly to increase a pair of trough, peak.So can accurately draw out corresponding conjugated zero pole frequency is standard.This that will be produced by elastic load is called the antiresonance frequency f to the conjugated zero limit _ARFWith frequency of natural vibration f _NTFResonance frequency and motor inertia J ₁With load inertia J ₂And load elasticity coefficient K is relevant, and its physical relationship is as follows:

$f_{\mathrm{ARF}}=\frac{1}{2\mathrm{\&pi;}}\sqrt{\frac{K}{J_2}}\mathrm{Hz},$

$f_{\mathrm{NTF}}=\frac{1}{2\mathrm{\&pi;}}\sqrt{\frac{({\mathrm{<figure-callout\; id="1"\; label="J"\; filenames="HDA00002930835700012.png,HDA00002930835700021.png"\; state="\{\{state\}\}">J</figure-callout>}}_1+J_2)K}{J_1{J}_2}}\mathrm{Hz}.$

In the motor inertia J ₁=6.72 * 10 ^-5Kgm ², load inertia is respectively J ₂=1 * 10 ^-4Kgm ²And J ₂=2 * 10 ^-4Kgm ², the theoretical tuning-points during rotation axis elasticity coefficient K=100Nm/rad calculates f by following formula respectively _ARFBe 159Hz and 112Hz, f _NTFBe 251Hz and 224Hz.As standard, the fundamental purpose of carrying out the method is exactly to obtain fast and accurately this group tuning-points characteristic.

Making needs following steps based on the pseudo-random sequence current value sequence of m sequence:

1, choose suitable n rank primitive polynomial.

2, form initiation sequence by the primitive polynomial coefficient, the initialization feedback shift register, by repeatedly to feedback shift register and initiation sequence position take advantage of add and mould 2 feedbacks, obtain 2 ⁿ-1 m sequence.The position, end is mended 0, so that Fast Fourier Transform (FFT).

3,01 scale-of-two random series being changed into level value is positive and negative 1 times of rated current value sequence, with this sequence as the given value of current under the speed open loop of AC servo.

Primitive polynomial commonly used choose and coefficient definite opinion is shown in Figure 3 really.

Embodiment two: present embodiment is described further embodiment one, and the described n of present embodiment rank primitive polynomial is chosen for 10 rank primitive polynomials, obtains 2 ¹⁰=1024 scale-of-two m sequences.

The concrete implementation step of present embodiment is as follows:

Step 1, select suitable primitive polynomial exponent number according to the sequence length that will generate, this n=10, the pseudo-random sequence that generates has N=1024 sequence code, be in the sequence code of 1kHz in frequency, sequence time only has 1 second, adds follow-up FFT, has greatly reduced the T.T. that frequency characteristic is obtained.

Step 2, initialization initiation sequence and feedback shift register.The selection of initiation sequence is relevant with the coefficient of primitive polynomial, the initiation sequence iniseq=[0010000001 when n=10], initial shift register swithreg=[0000000001].Also need the end at the whole story of initialization m sequence, because the whole story, position two values were all constant in the method, make the first mseq (1)=1, position, end mseq (N)=0.

Step 3, the process flow diagram that the m sequence generates is seen Fig. 4.The generation method be mainly with initiation sequence with upgrade after the shift register position take advantage of add by turn and, obtain new shift register data to adding and carrying out mould 2 feedbacks.Modulo-two operation is that the m sequence is the key of 2 level.Through constantly displacement feedback, just can obtain 1024 scale-of-two m sequences of 01 level.

Step 4 for this sequence is made the given value of current signal, needs 01 binary sequence is changed into the pseudo random sequence code of positive and negative 1 times of nominal current level.The multiple here can change with actual conditions, but unsuitable excessive or too small, crosses conference and makes the motor side rotating speed too high, in the situation that be easy to system is worked the mischief with resonance, too small meeting produces error effect as impulse response method energy shortage to low frequency characteristic.

Step 5, the Bode map generalization.With the pseudo random sequence code of positive and negative 1 times of nominal current level of obtaining as the given value of current signal under the open loop resonator system, to given value of current signal and motor side tach signal Fourier decomposition, can obtain Bode figure and resonance characteristic under this resonator system by respectively after computing.

Can obtain the same frequency ω of input signal and rate signal by the FFT computing _rThe inphase quadrature component.

R _i(ω _r)＝A _ri?coSφ _ri

Q _i(ω _r)＝A _ri?sinφ _ri’

R _o(ω _r)＝A _ro?cosφ _ro

Q _o(ω _r)＝A _rosinφ _ro’

R in formula _i(ω _r) be input signal ω _rReal part under frequency, A _riBe input signal ω _rAmplitude under frequency, φ _riBe input signal ω _rPhase angle under frequency, Q _i(ω _r) be input signal ω _rImaginary part under frequency, R _o(ω _r) be rate signal ω _rReal part under frequency, A _roBe rate signal ω _rPhase angle under frequency, φ _roBe rate signal ω _rPhase angle under frequency, Q _o(ω _r) be rate signal ω _rImaginary part under frequency.

The amplitude-frequency of system and phase-frequency characteristic can be calculated as follows:

$\left|G\left(j{\mathrm{\&omega;}}_r\right)\right|=\frac{A_{\mathrm{ro}}}{A_{\mathrm{ri}}}=\sqrt{\frac{{R_o}^2+{Q_o}^2}{{R_i}^2+{Q_i}^2}}$

$\mathrm{\&phi;}\left({\mathrm{\&omega;}}_r\right)={\mathrm{\&phi;}}_{\mathrm{ro}}-{\mathrm{\&phi;}}_{\mathrm{ri}}={\tan }^{-1}\frac{Q_o}{R_o}-{\tan }^{-1}\frac{Q_i}{R_i},$

(the j ω of G in formula _r) be ω _rAmplitude versus frequency characte under frequency, φ (ω _r) be ω _rPhase-frequency characteristic under frequency.

Just can draw out in a manner described the frequency characteristic Bode figure of system.

seeing Fig. 5 with the frequent rate characteristic of the open-loop amplitude under the motor model of elastic load drafting figure, it is consistent when wherein parameter is analyzed with top resonance characteristic, the tuning-points frequency characteristic accord with theoretical analysis described above that as can be seen from the figure obtains, to compare accuracy very high with other frequency characteristic acquisition methods, and total duration reduces greatly, avoided the potential hazard of mechanical resonant, and it is half of sequence frequency that the frequency of the method measures scope, that is to say can obtain under suitable sequence frequency less than open loop high speed frequency sweep method and the better low-frequency effect of white noise method and noise.Can repeatedly become sequence frequency in actual applications and measure, so just can obtain the resonator system frequency characteristic that precision is higher, scope is wider.

Claims (2)

1. the AC servo mechanical resonant frequency characteristic acquisition methods based on pseudo random sequence code, is characterized in that, it comprises the following steps:

Step 1: according to the requirement of system mechanics accuracy of resonant frequencies, choose n rank primitive polynomial, n is the positive integer more than or equal to 2;

Step 2: formed the initial n exponent number row of scale-of-two m sequence by the coefficient of n rank primitive polynomial, the initialization feedback shift register;

Then repeat following computation process: to the summation of taking advantage of and add up of this feedback shift register and initial n exponent number row positions, accumulated value base 2 deliverys are fed back calculating, with the renewal feedback shift register; Obtain 2 until calculate ⁿ-1 scale-of-two m sequence, described computation process finishes;

Again with 2 ⁿThe position, end of-1 scale-of-two m sequence mends 0, obtains 2 of 01 level ⁿIndividual scale-of-two m sequence;

Step 3: with obtain in step 22 ⁿIndividual scale-of-two m sequence is converted to the current value sequence that level value is positive and negative p times system nominal current, and p is the positive number less than the system nominal current amplitude limit value, then with the current value sequence that obtains as the given value of current under the speed open loop of AC servo;

Step 4: in the system operational process of described current value sequence as the given value of current under the speed open loop of AC servo, the motor speed sequence of synchronous acquisition AC servo, the motor speed sequence of current value sequence and collection acquisition is done respectively Fast Fourier Transform (FFT), described transformation results is carried out the Bode figure that computing obtains the open loop AC servo, and then obtain the mechanical resonant frequency characteristic of AC servo.

2. the AC servo mechanical resonant frequency characteristic acquisition methods based on pseudo random sequence code according to claim 1, is characterized in that, described n rank primitive polynomial is chosen for 10 rank primitive polynomials, obtains 2 ¹⁰=1024 scale-of-two m sequences.

Images