Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a batch process monitoring alarm method based on information fusion, which can greatly improve the alarm accuracy of multi-directional principal component analysis in the application of the intermittent process monitoring process, and adopts the following technical scheme in order to achieve the aim:
the invention comprises the following steps:
1) model data collection
If an intermittent operation is provided with J measurement variables and K sampling points, each measurement batch can obtain a J multiplied by K matrix, and after the measurement steps of the I batch are repeated, the obtained data can be expressed as a three-dimensional matrixX(I.times.J.times.K), wherein the measured variables are temperature, speed, pressure, stroke, etc. state parameters that can be measured during the batch run.
2) Three-dimensional data expansion
Combining three-dimensional matrices
X(I multiplied by J multiplied by K) is expanded according to the collection batch direction, namely variables on each sampling point in an operation batch are arranged according to the time sequence to obtain a two-dimensional matrix
Explicit matrix
Column KJ, line I.
3) Two dimensional matrix normalization
Setting a two-dimensional matrix
The variable at any point in the variable is
The variable is normalized by subtracting the mean and dividing the variance, and the calculation formula of the normalization is as follows:
wherein:
is that
Mean of any column of the matrix, s
jkIs that
Variance of any column of the matrix
4) Multi-directional principal component analysis modeling
Standardizing the two-dimensional matrix of the last step
And (3) performing PCA decomposition to complete the modeling of the multi-directional principal component analysis method, wherein the PCA decomposition process is as follows:
S=trace(TTT/(I-1)); (3)
wherein: t is tiIs orthogonal principal component directionAmount, piThe load vector is orthogonal normalization, S is the trace of the covariance matrix of the principal element and represents the interpretation degree of each principal element to the process;
in the formula (2), X is decomposed to obtain a score matrix T (I multiplied by JK) and a load matrix P (JK multiplied by JK).
5) Selecting the number R of principal elements
Restated equation (2) to the form:
wherein: t isr(I×R)、Pr(JK multiplied by R) are respectively a score matrix and a load matrix after R principal elements are reserved, and E is a residual error matrix;
through the above transformation, the multi-way principal component analysis model decomposes the original data space into principal component space and residual space, and the principal component space variables are highly correlated and generally sufficient to describe the variability of the data.
The number of principal elements R can be generally set according to the experience of the user or by adopting the Broken-Stick criterion, the content of the Broken-Stick is to keep the principal element when the interpretation degree S (R) of the R-th principal element accounts for a percentage of the total contribution sum (S) of all principal elements which is more than G (R), and otherwise, the result is terminated, wherein the calculation formula of G (R) is as follows:
wherein: s (r) is the degree of interpretation of the r-th principal element, and sum (S) is the sum of the contributions of all principal elements.
6) Two indices of the model data, T2 and SPE, and corresponding 95% and 99.999% control limits were calculated
a) 95% control limit of T2:
FR,n-R,αrepresenting a F distribution with a degree of freedom R, n-R, alpha being 5%;
99.999% control of T2Limiting:
FR,n-R,αrepresenting a F distribution with a degree of freedom R, n-R, alpha is 0.001%;
b) 95% control limit for SPE:
C
αis a critical value at the normal distribution calibration level alpha of 5%, C
α=norminv(0.95,0,1);
99.999% control limit for SPE:
wherein theta isiAnd h0Is calculated as above, where α is 0.001%, Cα=norminv(0.99999,0,1)。
7) Index SPE and T2 for calculating two spaces of sample data
An index of the sample residual space, SPE, calculates equation (10), where I is the identity matrix,
SPE=EET=X(I-PrPr T)XT (10)
the index T2 of the sample pivot space calculates equation (11),
T2=Tr TSr -1Tr (11)
8) obtaining historical alarm confidence based on fuzzy threshold
Respectively taking the 99.999 percent and 95 percent statistical control limits of T2 and SPE as fuzzy upper and lower limits to construct a fuzzy membership function
Converting the alarm of which the statistic exceeds the control threshold into the alarm reliability,
representing a 99.999% probability statistical control limit for SPE or T2,
a 95% probability statistical control limit representing SPE or T2;
respectively substituting the upper and lower limits of the two statistics in the SPE, the T2 and the step 6) calculated in the step 7) into a function
Obtaining two alarm reliability sequences B
spe{b
spe(1),b
spe(2)……b
spe(t)},B
T2{b
T2(1),b
T2(2)……b
T2(t), wherein t is the sampling time;
9) computing combining weights based on alarm confidence
Firstly, an alarm reliability sequence B is calculatedspe(t){bspe(1),bspe(2)……bspe(K) The combining weights of
(a) When t is 1, since there is no relevant alarm information before t is 1, the global alarm reliability when t is 1 is the alarm reliability b at the first time0:1(NA)=bspe(1);
(b) When t is 2, the global alarm reliability is weighted and fused by the global alarm reliability at the time when t is 1 and the alarm reliability at the time when t is 2, and the global alarm reliability b at the time when t is 2 is obtained0:2(NA), calculated as shown in formula:
b0:2(NA)=α2b0:1(NA)+β2bspe(2) (13)
wherein alpha is20.5 denotes the pair b0:1Linear weighted value of (NA), beta2The weighted value of the alarm reliability at the current moment is expressed as 0.5;
(c) when t is more than or equal to 3, the global alarm reliability carries out weighted fusion by using the global alarm reliability of the first two moments and the alarm reliability of the current moment,
b0:t(NA)=αt b0:t-1(NA)+βtbspe(t) (14)
wherein the weight coefficient alphatWeight factor, beta, representing the global confidence of the last momenttIs a weighted value of the alarm reliability at the current moment, and the weighted value satisfy the relation alphat=1-βt. The formula is as follows (15) - (16)
Wherein Supt (b)i) The support degree of the alarm reliability is represented, and the calculation method is as follows:
(i) when t is more than or equal to 3, the alarm reliability b at the time t can be obtainedspeAnd global alarm evidence b at t-1 and t-20:t-1And b0:t-2Calculate b0:t-1And b0:t-2The distance between every two adopts an Euclidean distance formula:
then b0:t-1And b0:t-2The similarity between the alarm reliability degrees is determined,
Sim(b0:t-1,b0:t-2)=1-dst(b0:t-1,b0:t-2) (18)
obtained in the same way, Sim (b)0:t-2,bspe),Sim(b0:t-1,bspe)
(ii) Calculation of bspeAnd b0:t-1And b0:t-2The support degree of each alarm reliability relative to the other two alarm reliabilities, so that each evidenceThe degrees of support (19) to (21) are shown in the formulas:
Supt(bt)=Sim(b0:t-1,bspe)+Sim(b0:t-2,bspe) (19)
Supt(b0:t-1)=Sim(b0:t-1,bspe)+Sim(b0:t-2,b0:t-1) (20)
Supt(b0:t-2)=Sim(b0:t-1,b0:t-2)+Sim(b0:t-2,bspe) (21)
in the same way, the sequence B of the available alarm credibilityT2Combining weights of
10) Alarm decision based on global alarm reliability
When b is0:tAnd (NA) is more than or equal to 0.5, monitoring and alarming.
Compared with the prior art, the invention has the beneficial effects that: the method integrates the monitoring information of the historical moment and the current moment to make alarm decision, improves the accuracy of the process monitoring fault diagnosis result, and provides a new practical method for process monitoring without process prior knowledge.
Detailed Description
The invention is further described with reference to the following drawings and specific embodiments:
injection molding is a typical batch process, one batch of which mainly comprises four stages of injection, pressure holding, plasticizing and cooling, specifically, in an injection section, a high pressure of a hydraulic cylinder pushes a screw forward to push molten plastic in a machine barrel to a mold cavity, when the mold cavity is completely or nearly filled, the process is switched to a pressure holding stage, in which the high pressure continues to fill a small amount of material into the mold cavity to supplement material shrinkage due to cooling and solidification; when the gate cools and the material in the mold cavity is no longer affected by the injection nozzle, the hold pressure stage ends. The screw is rotated and retracted to push a sufficient amount of molten plastic to the front of the screw. The screw retreats while the volume calculation is started. After the head melt reaches a certain injection quantity, the screw stops moving back and rotating, and the process state of the time is called a plasticizing stage. And (4) when the pressure maintaining section is finished and the plasticizing process is carried out, simultaneously carrying out the cooling section until the material in the die reaches the hardness capable of being ejected, and finishing the cooling section.
The injection molding process is continuously repeated to obtain stable and consistent products, and by taking the injection molding process as an example, the multivariate statistical monitoring method based on the alarm reliability comprises the following steps of:
(1) model data collection
If an intermittent operation is provided with J measurement variables and K sampling points, each measurement batch can obtain a J multiplied by K matrix, and after the measurement steps of the I batch are repeated, the obtained data can be expressed as a three-dimensional matrixX(I.times.JXK). In order to ensure that the detection data covers a working range of a long enough time, the value of a data batch I used for modeling in general industry is more than 100, and the measurement variables are state parameters which can be measured in the batch operation process such as temperature, speed, pressure, stroke and the like; based on the process time, the speed of process change and whether the model load is in a reasonable range, the number of sampling points K is generally less than 1000.
In this embodiment, the variables available for measuring the operating process of the variable laboratory injection molding machine are 8: the opening degree of a pressure valve, the opening degree of a flow valve, an injection stroke, an injection speed, an injection pressure and the temperature of a machine barrel (3 sections), 100 is taken for an operation batch I, and a sampling point K reserved for each batch is 488.
(2) Three-dimensional data expansion
See alsoFIG. 2, shows a three-dimensional matrix
XExpanding according to the collection batch direction, namely arranging the variables on each sampling point in an operation batch according to the time sequence to obtain a two-dimensional matrix
Matrix array
Is line I, column KJ;
(3) two dimensional matrix normalization
Setting a two-dimensional matrix
The variable at any point in the variable is
The variable is normalized by subtracting the mean and dividing the variance, and the calculation formula of the normalization is as follows:
wherein:
is that
Mean of any column of the matrix, s
jkIs that
The variance of any column of the matrix is,
the standardization processing of the step is equivalent to extracting the average running track of one operation in the intermittent process, and highlights normal random fluctuation among different operation batches in the intermittent process.
(4) MPCA modeling
The MPCA modeling is a method of firstly expanding a three-dimensional matrix into a large two-dimensional matrix and then performing conventional PCA decomposition, the step of performing PCA decomposition on the two-dimensional matrix X (I multiplied by JK) subjected to the normalization processing in the previous step comprises the following decomposition process:
S=trace(TTT/(I-1)); (3)
wherein: t is tiBeing orthogonal principal component vectors, piFor an orthogonally normalized load vector, S is the trace of the covariance matrix of the principal elements, representing the magnitude of the interpretation of the process by each principal element.
The formula (2) X is decomposed to obtain a score matrix T (I multiplied by JK) and a load matrix P (JK multiplied by JK).
(5) Selecting the number of principal elements
Generally, the first few principal elements generally contain most of the variance information of the gap process, and the other principal elements may mainly contain noise information, so equation (2) can be restated as follows:
wherein: t isr(I×R)、Pr(JK multiplied by R) are respectively a score matrix and a load matrix after R principal elements are reserved, and E is a residual error matrix;
with the above transformation, the MPCA model decomposes the original data space into a principal component space and a residual space, the principal component space variables being highly correlated, generally sufficient to describe the variability of the data.
The number of principal elements R can be generally set according to the experience of the user or by adopting the Broken-Stick criterion, the content of the Broken-Stick is to keep the principal element when the interpretation degree S (R) of the R-th principal element accounts for a percentage of the total contribution sum (S) of all principal elements which is more than G (R), and otherwise, the result is terminated, wherein the calculation formula of G (R) is as follows:
wherein: s (R) is the interpretation degree of the R-th principal element, and sum (S) is the sum of all the principal elements, in this embodiment, the number of the principal elements R is selected to be 3, and the interpretation degree for the process is 86.73.
(6) Calculating model statistical control limits
a) 95% control limit of T2:
FR,n-R,αrepresenting a F distribution with a degree of freedom R, n-R, alpha is 5%.
99.999% control Limit for T2:
FR,n-R,αrepresenting a F distribution with a degree of freedom R, n-R, alpha is 0.001%.
After R is 3 and n is 100, the above formula is substituted, TsqCL95 is 8.3447 and TsqCL999 is 30.4307;
b) 95% control limit for SPE:
Cαis a critical value at the normal distribution calibration level alpha of 5%, Cα=norminv(0.95,0,1)=1.6449。
99.999% control limit for SPE:
wherein theta isiAnd h0Is calculated as above, where α is 0.001%, Cα=norminv(0.99999,0,1)=4.2649。
(7) Computing statistics of two spaces of sample data
SPE=EET=X(I-PrPr T)XT (10)
T2=Tr TSr -1Tr (11)。
(8) Obtaining historical alarm confidence based on fuzzy threshold
Obtaining two alarm reliability sequences B of a residual error space and a principal component space by using formulas (10) to (11)
spe{b
spe(1),b
spe(2)……b
spe(t)},B
T2{b
T2(1),b
T2(2)……b
T2(t), t is the sampling time, and the fuzzy membership function thereof
See figure 1.
(9) Separately calculating combining weights based on alarm confidence
Firstly, an alarm reliability sequence B is calculatedspe(t){bspe(1),bspe(2)……bspe(K) The combining weight of the { right } is greater than the first;
(a) when t is 1, since there is no relevant alarm information before t is 1, the global alarm reliability when t is 1 is the alarm reliability b at the first time0:1(NA)=bspe(1)
(b) When t is 2, the global alarm reliability is weighted and fused by the global alarm reliability at the time when t is 1 and the alarm reliability at the time when t is 2, and the global alarm reliability b at the time when t is 2 is obtained0:2(NA), calculated as shown in formula:
b0:2(NA)=α2b0:1(NA)+β2bspe(2) (12)
wherein alpha is20.5 denotes the pair b0:1Linearity of (NA)Weighted value, beta2The weighted value of the alarm reliability at the current moment is expressed as 0.5;
(c) when t is more than or equal to 3, the global alarm reliability carries out weighted fusion by using the global alarm reliability of the first two moments and the alarm reliability of the current moment,
b0:t(NA)=αt b0:t-1(NA)+βtbspe(t) (13)
wherein the weight coefficient alphatWeight factor, beta, representing the global confidence of the last momenttThe weighted value of the alarm reliability at the current moment is calculated by the following method:
(i) when t is more than or equal to 3, the alarm reliability b at the time t can be obtainedspeAnd global alarm evidence b at t-1 and t-20:t-1And b0:t-2Calculate b0:t-1And b0:t-2The distance between every two adopts an Euclidean distance formula:
then b0:t-1And b0:t-2The similarity between the alarm reliability degrees is determined,
Sim(b0:t-1,b0:t-2)=1-dst(b0:t-1,b0:t-2) (15)
obtained in the same way, Sim (b)0:t-2,bspe),Sim(b0:t-1,bspe)
(ii) Calculation of bspeAnd b0:t-1And b0:t-2The support of each alarm confidence level relative to the other two alarm confidence levels, so the support of each evidence is shown by the equations (16) - (18):
Supt(bspe)=Sim(b0:t-1,bspe)+Sim(b0:t-2,bspe) (16)
Supt(b0:t-1)=Sim(b0:t-1,bspe)+Sim(b0:t-2,b0:t-1) (17)
Supt(b0:t-2)=Sim(b0:t-1,b0:t-2)+Sim(b0:t-2,bspe) (18)
(iii) on the basis of the steps, the support degree of each alarm reliability relative to other two alarm reliability is obtained, and finally, a dynamically updated weight factor beta is obtainedtThe following formula (19);
αt=1-βt
similarly, a principal component spatial belief sequence B can be computedT2{bT2(1),bT2(2)……bT2(t) } alarm confidence combining weights.
(10) Alarm decision based on global alarm reliability
When b is0:tAnd (NA) is more than or equal to 0.5, monitoring and alarming.
The results of this example are as follows, see FIG. 3:
according to the invention, the alarm reliability of the historical moment and the current moment is integrated to carry out alarm decision, so that the accuracy and effectiveness of the process monitoring fault diagnosis result are improved.
It should be understood that the present invention is not limited to the injection molding process of the above-described embodiments, and that equivalent modifications or substitutions can be made by those skilled in the art without departing from the spirit of the present invention, and are intended to be included within the scope of the appended claims.