DE102023135201A1 - Method for outputting data from a programmable logic controller - Google Patents

Abstract

The invention relates to a method (10) for outputting data from a programmable logic controller, wherein data from variables of a real-time program executed on the controller, in particular one executed cyclically, are read by a server also executed on the controller and are sent to a client via a data connection in notifications of at least one notification type that correspond to a defined communication standard. Sending a message from the real-time program to the server via a messaging system triggers the reading of the data and its sending in a notification.

Description

The invention relates to a method for outputting data from a programmable logic controller (PLC).

Programmable logic controllers of the type in question are used to control technical devices, such as machines and/or systems. Modern programmable logic controllers are controlled similarly to other computers using programs executable on the programmable logic controller.

Programmable logic controllers must regularly be able to meet relatively stringent real-time requirements. Accordingly, real-time programs are executed on programmable logic controllers. In this context, real-time programs are understood to be programs capable of meeting the stringent real-time requirements placed on the operation of a PLC for controlling a machine and/or system.

This is made possible, in particular, by specific procedures for executing real-time programs. Furthermore, there are certain programming languages that have been specifically developed for programming programmable logic controllers and are designed to meet real-time requirements.

However, particularly with the increasing networking of programmable logic controllers with other information technology devices, there is also growing interest in enabling communication between the programmable logic controller and other information technology devices. These needs arise particularly in the context of Industry 4.0, but even simple cases in which, for example, a programmable logic controller is connected to an information technology device, such as a tablet computer, via a data connection for inspection or maintenance purposes can be challenging in terms of technical feasibility.

The reason for this is often that, although there are communication standards for data communication in industrial environments, the use of these communication standards regularly requires the execution of programs on programmable logic controllers whose capabilities for meeting real-time requirements are not sufficient, for example, to meet the hard real-time requirements placed on a real-time program for controlling a machine.

The invention is therefore based on the object of demonstrating a method for outputting data from a programmable logic controller which makes it possible to output the data in conformity with a specific communication standard and at the same time ensures that the execution of a real-time program is not impaired while fulfilling the real-time requirements placed on this program.

The object is achieved by a method having the features of claim 1. The features of the dependent claims relate to advantageous embodiments.

The method is used to output data from a programmable logic controller. Data from variables of a real-time program executed on the controller are read by a server also executed on the controller. The real-time program is processed cyclically. A real-time program is therefore understood to be a program that can be reliably executed by the programmable logic controller within a specified cycle time. For example, the real-time program can be a program written in one of the Standard EN 61131-3:2014-06 A program written in a defined programming language.

The data is then sent from the server to a client via a data connection in notifications of at least one notification type. The notification type defines, in particular, the selection of variables from which the data contained in a notification of the respective notification type is read.

The problem is solved in particular by sending a message from the real-time program to the server via a messaging system, which triggers the reading of the data and its sending in a notification.

Messaging systems enable different information technology entities to communicate with each other through the exchange of data packets, also known as telegrams or datagrams. These are usually used predominantly in distributed systems, i.e. when different computers connected via data lines guided programs should communicate with each other.

In the present case, such a messaging system is used to enable communication between two programs running on the same programmable logic controller, i.e., on the same computer. The messaging system can, in particular, be a message-passing system. In connection with the present invention, it has been found that this advantageously brings about a temporal decoupling of the executions of both programs, which has a particularly positive effect on maintaining the real-time capability of the real-time program.

Servers of the type in question, which serve to enable data communication via sent notifications according to a defined communication standard in an industrial environment, are typically not capable of meeting such stringent real-time requirements as the real-time programs of programmable logic controllers in question. It has been shown that, due to the temporal decoupling achieved by using the messaging system as a "trigger," it is nevertheless possible to use such a server to send notifications without compromising the real-time capability of the real-time program.

The real-time program is processed by the programmable logic controller with priority. This means, in particular, that other programs, such as the server, only have access to the computing time of the programmable logic controller that remains after the timely execution of the real-time program has been ensured.

The use of the messaging system allows for a single message to be sent at a specific point during the real-time program's execution. Afterward, the real-time program continues to execute. The server receiving the message can complete its tasks of reading the data and sending it in the notification within the available processing time, without affecting the further execution of the real-time program in a way that would lead to a delay in its execution.

In this way, it is possible to output data from the real-time program to a client in a defined communication protocol without the server required to use the communication protocol impairing the real-time capability of the real-time program.

The real-time program can be organized in function blocks. Function blocks are program organizational units. A real-time program organized in function blocks is, in particular, a program Standard EN 61131-3:2014-06 defined function block language, which is also referred to as FBS/C+.

The real-time program can have at least one function block containing variables that contain data to be read from the server and sent to the client via the notification. This allows for convenient handling of the functionality for sending notifications when creating the real-time program.

The real-time program can have a plurality of different function blocks, each containing variables containing data to be read by the server and sent to the client via a notification. The method can provide for the server to send notifications of different notification types to the client. In particular, each of the different function blocks is assigned a notification type such that when a notification of a specific notification type is sent, data is read from variables of the function block assigned to that specific notification type and sent with the notification.

The server can in particular be an OPC UA server. The client can in particular be an OPC UA client. The notification can in particular be an OPC UA event. The notification type can in particular be an OPC UA event type. OPC UA is a communication standard that is significantly widespread in industrial environments. Accordingly, the use of the OPC UA communication standard makes it possible to establish compatibility between the programmable logic controller on which the described method is executed and a large number of existing information technology entities or existing types of information technology entities. The entities can be entities from the hardware and/or software areas.

OPC UA events are a standardized OPC UA functionality for transmitting event messages. OPC UA events are data structures that, in addition to data specified in the standard that concerns certain basic information, can also contain data that can be defined within the scope of the described procedure. By defining this definable data, different OPC UA event types can be created. OPC UA events of different OPC UA event types differ accordingly, particularly based on the definitions of this definable data.

The method may provide for the server to access the variables of the real-time program via a data access layer of the real-time program. Such a data access layer is also referred to as a data access layer. The data access layer enables and/or simplifies the server's access to variables of the real-time program, which are, in particular, enabled for corresponding access by the server.

In particular, the method can provide that the server accesses the same physical memory area as the real-time program itself when accessing the variables of the real-time program. In this way, it is not necessary for the data from the variables to be transferred from the processing of the real-time program, for example by sending them in a message to the server and/or by writing copies of the data to a special memory area designated for shared use by the server and the real-time program. Instead, the server can read the data itself directly from the memory area of the real-time program. In this way, despite the temporal decoupling between the server and the real-time program, a high level of integration between the server and the real-time program still results with regard to their processing. This leads to a high level of efficiency overall.

The method may provide that the sending of the message from the real-time program to the server is triggered by setting a first variable of the real-time program to a specific value.

The variable can, in particular, be a Boolean variable. In this context, the method specifically provides that the sending of the message from the real-time program to the server is triggered by setting a first variable of the respective function block to a specific value.

Setting such a variable to a specific value when sending the message makes it easy to implement a "handshake" between the real-time program and the server. Setting a specific variable for the respective function block to a specific value makes it possible, in particular, to distinguish between different notification types and their associated function blocks when controlling this "handshake."

In connection with the present method, this distinction results in particular in the fact that the sending of a notification of a specific notification type according to the described method does not affect the sending of notifications of other notification types insofar as the sending of notifications of other notification types is not hindered by the triggered and still being processed sending of a notification of a specific notification type.

The method can provide that setting the first variable of the real-time program, in particular the first variable of the respective function block, to the specific value prevents the values of other variables of the real-time program that are to be read out for sending the respective notification from being changed. In other words, by setting the first variable, the variables from which data to be read out are to be sent with the notification from the server are no longer changed after the first variable has been set to the specific value.

Especially if the real-time program is executed with a higher priority, the server may read the data with a significant delay. This may even mean that, if the real-time program is executed cyclically, the server only reads the data in a later execution cycle of the real-time program than the execution cycle in which the message was sent and the first variable was set to the specified value.

By setting the variable to a specific value, it can be ensured that when the server reads additional variables from the real-time program or function block, they still have the same values or contain the same data as when the message was sent to the server. This ensures data integrity if, after the notification is triggered by sending the message to the server, a certain amount of time passes before the server reads the data from the real-time program.

The method can, in particular, provide that a second variable of the real-time program is set to a specific value by the server when the notification is sent. The method can, in particular, provide that a second variable of the respective function block of the real-time program is set to a specific value by the server when the notification of the notification type assigned to the function block is sent.

By implementing this procedure, it is possible to complete the "handshake" between the server and the real-time program, as already described above. By setting the second variable to the specific value, the real-time program can be easily signaled that the triggered process of sending a notification has been completed. For the real-time program, this can mean that certain functionalities of the real-time program are executed depending on the value of the second variable, which should be executed depending on whether the notification has been sent.

For example, the method can provide that after the respective notification has been sent, the respective first and/or second variable is reset to a start value. In particular, the value of the second variable can be used as a trigger for the reset. In this way, a control of the "handshake" between the real-time program and the server can be implemented, which provides that after the notification has been triggered, the first variable is initially set to a specific value. This initially prevents the values of variables from which data to be sent in the notification is to be read from. After the notification has been sent and thus also after the data has been read from these variables, the corresponding second variable is set to a specific value. This value of the second variable is in turn used as a trigger to reset the first and second variables to their start values and thus enable a change to the values of the variables whose change was initially prevented. Furthermore, a renewed processing of the real-time program enables the notification to be sent again with the values of the variables updated in the meantime.

This makes it possible to create asynchrony between the cyclical execution of the real-time program and the timing of the server's notification sending. While the real-time program is executed cyclically while meeting strict real-time requirements, the frequency at which the server sends notifications can fluctuate, particularly depending on the resources available to the server.

The notifications can be generated from data read from the server using a mapping. The mapping specifically describes the relationships between the data types of the read variables of the real-time program and the data types of the respective notification type. The mapping can be based on an information model in which the assignment information required for the mapping is stored. If the notification types are OPC UA event types, the data types of the respective notification type are specifically the properties of the respective OPC UA event type.

The method can provide that the variables that are the subject of the mapping are variables of structured data types. Structured data types each contain a plurality of member variables of specific data types. The data types of the member variables can, in particular, be data types selected from a closed, standardized pool of possible data types.

The method can provide that in the information model underlying the mapping, only the assignment information of the structured data types required for the mapping is stored, i.e. the information as to which variable of the real-time program with a structured data type is to be assigned to which structured data type of the respective notification type.

In this case, the method can provide that the server, in particular via the data access layer, accesses variables of the real-time program that can be accessed by the server in order to obtain a type model of these variables that describes the data types of variables of the real-time program. The type model describes, in particular, which member variables of which data types are contained in the variables of structured data types.

The respective data types of the member variables of the structured data types to be assigned to one another can then be determined by means of a stored assignment table, which describes the relations of the data types of the real-time program contained in the closed standardized pool of possible data types on the one hand and the notification types on the other hand, and the type model, from which the data types of the member variables of the structured data types used in the real-time program are assigned to each other at runtime.

The real-time program and the server can run together on the programmable logic controller in the same runtime environment. Running the server in the same runtime environment as the real-time program provides performance benefits, especially when accessing data.

The transmission of notifications from the server to the client can be done according to a subscription model.

Data to be output from the programmable logic controller can in particular relate to measured values obtained by sensors through measurements in the physical world.

For example, the measured values can be measured values of at least one operating variable of an electric drive system. The at least one operating variable can, in particular, be one or more of the following operating variables: position, speed, acceleration, rotational speed, angular position, angular speed, angular acceleration, voltage, current, electrical power, mechanical power, torque, and/or temperature.

Further practical embodiments and advantages of the invention are described below in connection with the drawing.

1 shows a process diagram of an exemplary process.

The exemplary method 10 can provide in a first method step 12 that the server first loads an information model in which assignment information required for the mapping is stored.

In a further method step 14, the server can access the variables of the real-time program to create a type model that describes the data types of variables of the real-time program.

The method 10 may provide that in a further method step 16 the server connects to a messaging system and waits for messages that trigger the sending of a notification.

In a further method step 18, the method 10 may provide that the client subscribes to notifications from the server according to a subscription model.

In a further method step 20, the method 10 can provide that by setting a first variable of a function block of the real-time program to a specific value, the sending of a message from the real-time program to the server is triggered.

In a further method step 22, the method 10 can provide that by receiving the message sent in method step 20, the server receives the information as to which function block the notification type of the notification, the sending of which is triggered by the receipt of the message, is assigned.

In a further method step 24, the method 10 may provide that the server generates a mapping using the information model from method step 12 and the type model from method step 14 and, if applicable, a predefined mapping table for the mapping of the data types of member variables of structured data types, and reads data from variables of the function block identified in method step 22.

In a further method step 26, the method 10 may provide that the server generates and sends a notification using the mapping and the read data.

The method 10 may provide in a further method step 28 that the client receives the notification.

The method 10 can provide in a further method step 30 that the server signals to the real-time program that the notification has been sent by setting a second variable of the function block of the real-time program to a specific value.

The features of the invention disclosed in the present description, the drawings, and the claims may be essential, both individually and in any combination, for the realization of the invention in its various embodiments. The invention is not limited to the described embodiments. It may be varied within the scope of the claims and taking into account the knowledge of the competent person skilled in the art.

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QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Standard EN 61131-3:2014-06 [0009, 0018]

Claims (15)

Method (10) for outputting data from a programmable logic controller, wherein data from variables of a real-time program executed on the controller and in particular cyclically processed are read out by a server also executed on the controller and are sent to a client via a data connection in notifications of at least one notification type which correspond to a defined communication standard, characterized in that the reading out of the data and the sending thereof in a notification are triggered by the sending of a message from the real-time program via a messaging system to the server. Procedure (10) according to Claim 1 , characterized in that the real-time program is organized in function blocks and has at least one function block containing variables containing data to be read by the server and sent to the client by means of the notification. Procedure (10) according to Claim 1 or 2 , characterized in that the real-time program has a plurality of different function blocks, each of which contains variables which contain data to be read out by the server and sent to the client by means of a notification, and the server sends notifications of different notification types to the client, wherein each of the different function blocks is assigned a notification type in such a way that when a notification of a specific notification type is sent, data is read out from variables of the function block assigned to this specific notification type and sent with the notification. Method (10) according to one of the preceding claims, characterized in that the server is an OPC UA server, the client is an OPC UA client, the notification is an OPC UA event and/or the notification type is an OPC UA event type. Method (10) according to one of the preceding claims, characterized in that the server accesses the variables of the real-time program via a data access layer of the real-time program. Method (10) according to one of the preceding claims, characterized in that when accessing the variables of the real-time program, the server accesses the same physical memory area as the real-time program itself. Method (10) according to one of the preceding claims, characterized in that the sending of the message from the real-time program to the server is triggered by setting a first variable of the real-time program, in particular a first variable of the respective function block of the real-time program, to a specific value. Procedure (10) according to Claim 7 , characterized in that setting the first variable of the real-time program to the specific value prevents the changing of the values of further variables of the real-time program to be read out for sending the respective notification, in particular further variables of the respective function block. Method (10) according to one of the preceding claims, characterized in that a second variable of the real-time program, in particular a second variable of the respective function block of the real-time program, is set to a specific value by the server when the notification is sent. Method (10) according to one of the preceding claims, characterized in that after the respective notification has been sent, the first and/or the second variable are reset to a starting value, wherein in particular the value of the second variable is used as a trigger for the reset. Method (10) according to one of the preceding claims, characterized in that the notifications are generated from data read from the server by means of a mapping, wherein the mapping describes the relations between the data types of the read variables of the real-time program and the data types of the respective notification type. Method (10) according to one of the preceding claims, characterized in that the real-time program and the server on the programmable logic controller are executed together in the same runtime environment. Method (10) according to one of the preceding claims, characterized in that data to be output from the programmable logic controller relate to measured values which have been obtained by means of sensors through measurements in the physical world. Method (10) according to one of the preceding claims, characterized in that the measured values are measured values of at least one operating variable of an electric drive system. Method (10) according to one of the preceding claims, characterized in that the at least one operating variable is one or a plurality of the operating variables position, speed, acceleration, rotational speed, angular position, angular speed, angular acceleration, voltage, current, electrical power, mechanical power, torque, and/or temperature.

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