Difference between revisions of "BaSyx / Documentation"
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= BaSyx Documentation=
= BaSyx Documentation =
Revision as of 11:34, 20 November 2018
This page provides an architecture overview for developers regarding the BaSyx open-source platform. The following subsequent pages provide in-depth information regarding specialized aspects:
BaSyx end-to-end communication BaSyx Virtual Automation Bus for End to end communication
BaSyx runtime environment / device interfaces
The BaSys 4.0 project defines the following main component types:
|Control component||Provides a conforming BaSys 4.0 service based interface that enables access to device capabilities.|
|Group component||Provides higher-level services that use services of other control and group components.|
|Gateway||Protocol gateway that bridges five BaSys communication primitives between protocols to enable end-to-end communication.|
|Asset Administration Shell||An Asset Administration Shell (AAS) is a digital object that represents a physical or non-physical entity. It stores all relevant data and provides access to operations through its sub models.|
|Asset Administration Shell sub models||Sub models are part of one Asset Administration Shells. They consist of (optionally nested) properties and operations. AAS sub model providers provide different kinds of data as AAS sub models.|
|Registry / Discovery||The registry/discovery component enables registration and lookup of Asset Administration Shells.|
|Strategy / Optimization||The Strategy/Optimization component calculates production plans and production schedules that define when, and on which machine a production step for a specific product will be executed.|
|Process control||The process control component executes the production plans that the Strategy/Optimization component did create.|
|Monitoring||The monitoring component enables the monitoring of the production process. It for example collects and aggregates data for analysis or pushes selected and aggregated data to a dashboard.|
The graphic below illustrates the components of a BaSys 4.0 production system. Components connect to a virtual end-to-end communication medium that in fact may be realized with different networks and protocols. Communication is via defined primitives that are mapped to each protocol in a specific manner. Gateways bridge between protocols and enable a virtual end-to-end communication.
Interfaces are well-defined interaction points in the BaSys 4.0 architecture. They enable the substitution of component implementations and the development of conforming implementations by 3rd parties. BaSys 4.0 components and BaSyx components define HTTP-REST interfaces on middleware and plant levels, as well as OPC-UA and native TCP BaSyx interfaces on device level.
BaSys 4.0 conforming components need to implement the interfaces shown in the above figure and the following table. The BaSyx platform provides a reference implementation for core components that are necessary to create and deploy an Industrie 4.0 solution.
|Component type||Necessary provided interfaces||Interface type|
|Control component||RTE Management, Service status, Service selection, Service invocation||OPC-UA, BaSyx native|
|Group component||RTE Management, Service status, Service selection, Service invocation||OPC-UA, BaSyx native|
|Gateway||Gateway||Any to any|
|Asset Administration Shell||AAS||HTTP-REST|
|Asset Administration Shell sub models||Sub model||HTTP-REST|
|Registry / Discovery||Discovery, Registry||HTTP-REST|
|Strategy / Optimization||---||HTTP-REST|
|Process Control||Process management, Process execution||HTTP-REST|
Strategy / optimization and Monitoring components are highly plant specific. These components use provided interfaces of other BaSys 4.0 components, but are not required to provide defined BaSys 4.0 interfaces.
Virtual Automation Bus
One challenge of Industrie 4.0 is to integrate heterogeneous devices with possibly different communication protocols into a complete system. BaSys 4.0 solves this problem by utilizing a Virtual Automation Bus (VAB). The VAB defines the following five primitives:
|Get||Retrieves an element|
|Set||Sets the value of an element|
|Create||Creates a new element|
|Delete||Deletes an existing element|
|Invoke||Invokes a method|
Each protocol may be mapped to the VAB by creating a mapping of this five primitives to its native communication techniques. As an example, in the world of HTTP the delete primitive may be mapped to a HTTP-Delete request. Communication between networks using different protocols is supported by gateways translating between the protocols.
The benefit of this approach is a reduced implementation effort to bridge different communication technologies. Instead of having to translate from every protocol to every protocol (NxM) it is possible to use the VAB primitives as intermediate and reduce the complexity (N+M).
We support three strategies for integrating devices with a BaSys 4.0 production architecture:
- Smart SPS/PLC are PLC controllers with sufficiently smart RTE that enable the development of BaSys 4.0 control components and conforming BaSys 4.0 interface implementation on the device.
- Smart Devices are devices that directly provide a BaSys 4.0 conforming interface. They implement the BaSys 4.0 interface implementation on the device, e.g. on an embedded microcontroller.
- BaSys 4.0 interface devices connect existing legacy devices with proprietary connectors to a BaSys 4.0 production system. Interface devices implement the BaSys 4.0 conforming interface towards the production system, and connect to the device using its native communication technology and protocol. Service invocation is therefore triggered, for example, by calling an OPC-UA operation, by setting an OPC-UA variable, or even by changing a Modbus value. The concrete communication protocol to the device depends on the device to be integrated.
BaSys 4.0 sub model types
Asset Administration Shells consist of sub models. Sub models contain (optionally nested) properties and operations. Every sub model conforms to a sub model type. Sub model types may be defined specifically for a sub model. This is usually the case when a sub model is specific to one environment, or to one plant. BaSys 4.0 also predefines sub model types for specific sub models. These sub model types are either recommendations or mandatory. Recommended sub model types are not mandatory to use, but they are considered good designs and are provided as guideline. Mandatory sub models need to be implemented in a conforming manner to ensure correct operation.
Currently, The BaSys 4.0 project defines three sub model types:
- Topology: This sub model type defines a common sub model structure for the topology information of plants, production lines, and aggregated devices.
- Capability: This sub model type defines a common sub model structure for the description of (device) capabilities. Capability definitions are required for the description of device provided capabilities, and of capabilities required for product production steps.
- Identification: Virtual and physical production assets may carry different identities. For example, the same asset may be known by different identities to different stakeholders. Identifies may be globally unique or only local identities, such as serial numbers.
BaSys 4.0 control and group components
The Device Layer of a Basys4.0 compliant production systems contains Control Components and Group Components, which reflect the new skill-based and hierarchical programming approach of such a system. A Control Component represents the lowest layer of the plant and directly connects to the controlled process via an Input/Output (IO) interface and a network interface to the Group Components on the next hierarchical layer. Group Components are typically not directly wired to the physical process under control. Instead, they serve as orchestrators for the Control Components and provide a network interface to the underlying Control Components and another network interface for the connection to other Group Components and the Basys4.0 compliant Middleware.
BaSys 4.0 control component
Control Components are typically programmed via standardized PLC programming paradigms. The two fundamentally different approaches are the cyclic execution model of Function Blocks (FB) of the IEC61131-3 and the event-based execution of FBs according to IEC61499. IEC61131-3 defines five languages for programming PLCs and its standardization was first published in December 1993 (the most recent standard was published in February 2013). 3S is for example implementing an IEC61131-3 development and runtime environment called CodeSys. The standardization of IEC61499 started after the standardization of IEC61131, by the same standardization group, which previously worked on IEC61131 with the main objectives of solving portability, configurability and interoperability for industrial control applications that IEC61131 does not solve. The most recent version of the IEC61499 standard was published in November 2012. The standardization group added events to the interface of the FBs and therefore changed the execution semantics. IEC61499 targets distributed industrial automation systems in contrast to IEC61131, which is focused on centralized systems. Eclipse 4diac is an open-source implementation of an IEC61499 compliant development and runtime environment.
A Basys4.0 Control Component's IO interface connects the device to the sensors and actuators of the process in the field level (see figure). These IOs are digital or analog signals which are treated differently by each device manufacturer. Therefore, porting an existing runtime environment to a new PLC usually includes the adaptation of the runtime to the IO interface of the device. The connection to the next hierarchical layer (the Group Components still on the Device Level, or the different components in the Basys4.0 Middleware) is achieved by a network interface. Here, BaSyx proposes to use standardized network protocols as http/Rest or OPC UA. However there exist plenty of different proprietary network protocols and fieldbusses in state-of-the-art production systems. Usually each of the big market players provide their own fieldbus which cannot interact out of the box with fieldbusses of other manufacturers. This lack of interoperability can be tackled using BaSyx, which provides the possibility to introduce gateways from any kind of protocol to the afore mentioned standardized protocols on which BaSyx usually operates.
Examples for control components could for example be vertical and horizontal axis' that provide the basic skill "go-to-position" or a gripper that offers the basic skill "grip". These separate skills are then advertised via the network interface to Group Components and the Middleware.
BaSys 4.0 group component
BaSys4.0 compliant Group Components significantly differ from Control Components because they do not have an IO interface to the process under control, but rather two network interfaces, one to the underlying Control Component(s) and one for connecting to other Group Components or the services in the BaSys4.0 Middleware. The function of such a component is not to directly interact with the process, but to coordinate and orchestrate the Control Components, which are then interacting with the process. Therefore, a Group Component combines the different basic skills into composed skills and advertises these composed skills via OPC UA to upper layer Group Components or the Middleware. An example composed skill of an orchestrating Group Component of the Pick&Place station would be "assemble", which combines the basic skills "go-to-position" and "grip" in the appropriate order such that it achieves the desired task of assembling a product.
|BaSyx project links: Project BaSyx main wiki page | What is BaSyx? | BaSyx Developer Documentation|