Patent Publication Number: US-2022215318-A1

Title: Method and computer programme for discovering possible errors in a production process

Description:
The invention relates to a computer-supported method for discovering at least one possible error in a production process for producing a metal product in a metallurgical system. Moreover, the invention relates to a corresponding computer program. 
     Such methods and computer programs are basically known in the prior art, for example, from the technical article “Exploring due date reliability in production systems using data mining methods adapted from gene expression analysis,” by Prof. Dr. K. Windt and Prof. Dr. Marc-Thorsten Hutt, published in the CIRP Annals—Manufacturing Technology 60 (2011), pages 473-476, journal homepage: http://ees.elsevier.com/cirp/default.asp. This article describes various methods, such as data mining and enrichment analysis, for discovering errors, particularly with methods for producing steel strip. The known enrichment analysis first requires the formation of clusters of process parameter values in a parameter space of the process to be examined. The clusters are then respectively evaluated with respect to their influence on an assigned performance indicator for the production process, which in this case is a delay or lateness for example. This influence is measured in the form of an enrichment factor, also known as a Z-score value. With the aid of enrichment analysis, the clusters that have an especially high or especially low influence on the performance indicator, which is the delay or lateness for example, in the parameter space of the production process can be identified in this manner. In a subsequent step, those individual process parameters which have an especially high influence can then be extracted from the cluster. 
     These results of the enrichment analysis only enable limited discovery of causes, no understanding of assigned underlying mechanisms, and no derivation of patterns for the production process to be analyzed for the improvement thereof with respect to a predetermined performance indicator. 
     The object upon which the invention is based is the calculation and evaluation of determined Z-score values for discovering at least one possible error in a production process for creating a metal product such that said Z-score values enable a further reduction of production time and/or a further reduction in costs for machinery use in the production process for creating metal products by discovering the causes of errors. 
     This object is achieved by means of the method claimed in claim  1 . This is characterized by the following steps: 
     generating a modified cluster by removing from the cluster or adding to the cluster at least one process parameter value, repeated applying of the performance enrichment analysis to the modified cluster and the assigned performance indicator to determine a second Z-score value between the modified cluster and the assigned performance indicator, and determining a change between the first Z-score value and the second Z-score value as a measure of the influence of the parameter value removed from the cluster on the dependency between the performance indicator and the cluster and thus as an indicator of a possible error and the cause thereof. 
     The object is likewise achieved by means of the method claimed in claim  3 . This method differs from the method claimed in claim  1  only by virtue of the fact that the performance indicator mentioned in claim  1  is replaced by an external process parameter value in claim  3 , which likewise originates from the parameter space of the production process but not from the claimed cluster. 
     The Z-score values determined by the performance enrichment analysis or the determined Z-score value differences directly indicate the mechanistic causes of systematic errors and deviations with respect to performance indicators in the production process to be examined and thus enable the identification of new strategies in the troubleshooting and optimization of this process. 
     The performance enrichment analysis (PEA) combines cluster analyses and optional dimension reduction with known enrichment analyses and network analyses. Clusters in the parameter space are interlinked, via the enrichment of performance indicators in the clusters, with the level of the process performance. The enrichment of a performance indicator for a cluster in this case is determined via the statistical Z-score value as compared to a zero-inflated model of randomized performance indicators. Any known standard method can be used for the cluster analysis. According to the invention, the PEA is not only applied to an original cluster of process parameter values in a parameter space of the production process but also to a modified cluster. The modification of the original cluster is that at least one process parameter value from the parameter space is either removed from the cluster or added to the cluster. A change in the Z-score values can then be determined by means of the claimed additional applying of the PEA to the modified cluster. This change in the Z-score values is a measure of how strong a “signal,” i.e. the coupling, is between clusters and performance indicators or between clusters and external process parameter values and thus the predictability of the performance indicator or external process parameter value of an order (from its cluster affiliation). The change in Z-score values when omitting or adding the parameter value indicates how strongly the parameter is contributing to the signal. 
     The aforementioned object of the invention is also achieved by means of the method claimed in claim  3 . An external parameter value, which belongs to the parameter space of the production process but not to the cluster, takes on the role of the performance indicator here. In this case, the prediction probability of a parameter value from the clusters to the remaining parameters is measured. 
     Definition of Terms 
     In addition to errors in the classical sense, the term “error” as relates to the present description also refers to systemic incompatibilities, deficiencies, also insufficient system capacities for example, in the production process to be examined. 
     The term “metal product” as relates to the present description refers particularly to metal strips of all possible thicknesses, for example between 0.5 mm and 800 mm, pre-strip, hot strip, or cold strip, the latter being untreated or treated in a strip treatment system, e.g. coated with zinc, but also a metal melt, etc. The term metal means particularly steel. 
     The term “metallurgical system” as relates to the present invention can mean any type of system which is suitable for creating the metal product to be produced. For example, the metallurgical system may be a casting system for creating a cast strand from a metal melt, a pre-roll train for rolling the cast strand into a pre-strip, a finishing roll train for rolling the cast strand or the pre-strip into a hot strip, a cold-rolling system or a strip treatment system for treating, particularly finishing or coating, a metal strip that was cold-rolled beforehand, etc. 
     The term “production process” includes the term “manufacturing process.” 
     In the scope of the present invention, a performance indicator is a key indicator for describing the effectiveness and/or the efficiency of a production process in a metallurgical system. Examples: delay or lateness in reaching the production target, production quantity, unit of time, etc. 
     The grouping of individual process parameter values into a cluster within a parameter space can be done with any of the known standard methods for cluster formation. 
     Performance enrichment analysis: A variant of machine learning with interpretable internal representations for discovering the mechanisms behind systematic changes of performance indicators in industrial production and manufacturing processes. 
     Z-score: This is a statistical measure of the significance of a measured variable. A zero-inflated model is used to generate data comparable to real data. The same measured variable as in real data is determined using this zero-inflated model data. This process is repeated multiple times so that a mean value and a standard deviation can be determined for the measured variable obtained from the zero-inflated model data. The Z-score is the difference between the measured variable for the real data and the mean value from the zero-inflated model data, divided by the standard deviation. A Z-score of +3 indicates, for example, that the measured variable is three standard deviations higher than the mean value of the zero-inflated model data. 
     Zero-inflated model: In statistics, this is the representation of random data which can be used as a contrast to the real data (thus to determine the distinction). The zero-inflated model used in the PEA is a randomly mixed (i.e. randomized) distribution of the performance indicators over orders. The clusters of orders in the parameter space are retained. 
     The connection between clusters and performance indicators is destroyed by the randomization. A deviation between the real and the randomized data (measured by the Z-score) thus indicates a systematic connection between clusters and performance indicators. 
     Cluster: A cluster is a group of points or parameter values in a space, the parameter space in this case, wherein the points in the group have more similarity among each other than the average of points outside the group. In the methodologies of data analysis, there are various methods available for operationalization of this formal definition and determination of such clusters. The PEA makes use of such standard methods, since the PEA commences with identified clusters and determines the enrichment (i.e. the Z-score) of the performance indicators as relates to this cluster. 
     Table 1 as follows shows examples of parameters, the measured or default values of which can be grouped into clusters: 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Category 
                 Attributes 
                 Parameters 
               
               
                   
               
             
            
               
                 Order 
                 Type of product 
                 Steel grade, production 
               
               
                   
                   
                 capacity 
               
               
                   
                 Measurement 
                 Width, thickness 
               
               
                   
                 Steel casting sequences 
                 Suitable number of steel 
               
               
                   
                   
                 casting sequences 
               
               
                   
                 Weight 
                 Coil weight, coating weight 
               
               
                 Production process 
                 Production depth 
                 Number of production 
               
               
                   
                   
                 steps 
               
               
                   
                 Change of production 
                 Number of changes of 
               
               
                   
                 sites 
                 production site 
               
               
                   
                 Rework intensity 
                 Number of rework steps 
               
               
                   
                 Quality 
                 Surface quality, steel 
               
               
                   
                   
                 quality 
               
               
                   
                 Changes in assignments 
                 Number of changes in 
               
               
                   
                   
                 assignments of order and 
               
               
                   
                   
                 product 
               
               
                   
               
            
           
         
       
     
    
    
     According to a first exemplary embodiment, it is advantageous to define a threshold value for the change between the first and the second Z-score value. This applies to the method in which the Z-score value defines the dependency of the performance indicator from the cluster and applies to the alternatively claimed method in which the Z-score value defines the dependency of an external process parameter value as a function of the cluster. The threshold value for the change of the Z-score value is preferably set such that, when the change of the Z-score value exceeds the threshold value, the influence of the cluster on the performance indicator or on the external process parameter value is considered to be relevant. 
     According to a further exemplary embodiment, the dimension of the parameter space is advantageously reduced respectively before the applying of the PEA. There are various methods known in the prior art for doing this. Thus, it is known to eliminate highly correlated process parameters or to transform vectors of the process parameters within the scope of a principal component analysis (PCA) to main components. 
     Preferably, the plurality of dependencies discovered with the aid of the PEA is transitioned into a network, the nodes of which are process parameter values and performance indicators and the connections of which represent a significant enrichment, i.e. Z-score value, preferably above the defined threshold value. This results in a visualization of the results of a performed PEA in the form of a dependency network diagram. The combining of a first network diagram, which results from applying the PEA to the original cluster, and a second network diagram, which results from applying the PEA to the changed cluster, leads to an overall network of enrichment-based relationships between process parameter values in the cluster and performance indicators or at least one external process parameter. The connections between the nodes in this overall network indicate directly and promptly implementable suggestions for troubleshooting and process optimization. 
     In other words, the following is claimed according to the present invention: 
     A function f1 evaluates a given list of orders according to the previously described method. For each identified cluster in the parameter space and for each category of the performance indicator, a Z-score value is determined which measures the predictability of the performance indicator as relates to this cluster. The result of this function is then a list of clusters with their corresponding Z-score values. The result of the first function f1 is then supplied as an input variable of a second function. In addition, a further (future) order is supplied to this second function as an input variable. First, the cluster which can be assigned to this further order is determined. Then, based on the Z-score value of this cluster, there is a determination as to whether a prediction of the performance indicator is possible for this new order. If this is the case, the prediction is output. Otherwise, it is output that there is no prediction possible for this order.