Convolutional Self-encoding Fault Monitoring Method Based on Batch Imaging

A convolutional self-encoding fault monitoring method based on batch imaging comprising:

• image processing batch data, establishing a convolutional autoencoder (CAE) model and using a support vector machine method (OCSVM) for fault monitoring, the specific steps are as follows:
• A;
• offline modeling stage:
• 1) collection of historical data:
• intermittent production cyclically reciprocates according to a certain cycle, and batch products are obtained in batches after the end of a single cycle;
• data of K process variables at J times are collected in each batch to obtain a two-dimensional matrix X(K×J), where K is the number of process variables collected, J is the number of sampling points, and I batches constitute a typical three-dimensional data representation form of a batch process-X(I×K×J);
• 2) data normalization:
• maximum and minimum normalized data processing methods are used to eliminate the influence of dimensions between different process variables, and an actual data range of the process variables is converted into a data range of a gray image that meets computer processing between 0 and 1, a calculation formula is as follows:
• x
• ~
• =
• x
• -
• x
• min
• x
• max
• -
• x
• min
• (
• 1
• )
• the specific steps are:
• a) expand historical three-dimensional data X (I×K×J) into two-dimensional data X (IK×J) along a variable direction;
• b) calculate maximum and minimum values of each variable;
• c) normalize each variable;
• d) refold a two-dimensional array into a three-dimensional array;
• e) calculate an average of all training batches to obtain an average value of normal batch data at each time;
• 3) set CAE network parameters and input data into CAE for training;
• in CAE, several convolutional layers, pooling layers, and fully connected layers constitute a coding unit, fully connected layer, de-pooling layer and deconvolution layer constitute a decoding unit;
• loss function adopts a mean square error function, by minimizing the loss function, reconstructing the mean square error between data and input data, and using back propagation algorithm to adjust a weight of each layer to realize unsupervised learning of features;
• 4) design statistics and control limits:
• Introduce OCSVM to model features extracted by CAE, find an optimal solution of hyperplane, and obtain a statistical calculation formula;
• design monitoring statistics as t opposite of a distance to the hyperplane, denoted by D, which is shown in formula (2):
• D=−(w*·ϕ(x)+b*) (2)
• 0 is a control limit of the designed monitoring statistics;
• when D>0, a fault occurs, otherwise it is normal;
• B;
• online monitoring stage:
• 1) data collection:
• collect data of all variables at a current moment k to get Xnew,k(1×J);
• 2) data normalization:
• normalize according to the maximum and minimum values of each variable obtained offline;
• 3) batch filling:
• combine the normalized data at time k and time 1−k−1, and fill in data at time k+1−K that does not occur subsequently with average value of a corresponding time of normal batch obtained in offline phase;
• 4) feature extraction:
• a batch of filled data is input to an offline modeling and training network to extract features;
• 5) fault monitoring:
• substituting features extracted in previous step into formula (2), and calculating statistic D, if D>0, it is determined that there is a fault at the current moment, and corresponding measures are taken, otherwise it is a normal state and needs to continue to monitor production process until the end of batch.