Asset management shell (AAS) is an important concept of Industry 4.0. AAS essentially adds a digital model "shell" to physical equipment (so-called assets) to realize asset information exchange. AAS converts hardware devices into a service (service), which can be requested and provided through software. For example, requesting a CNC machine tool to "punch a hole in a certain position" is a service. Under the viewpoint of I4.0, the device will become a service provider (Service Provider). PLCs no longer perform parts of the production process, but provide production services with well-defined interfaces. It transforms the original production process completed by humans and machines into the data flow and control flow of the IT system, and the processing becomes a call of the software in the network. Moreover, these data streams and control streams conform to unified standards and have nothing to do with manufacturers. When all devices are added with standard-compliant AAS, the goal of "plug and production" can be realized.
Let's start with a simple scene
Here we give an example to illustrate, using the robotic arm to realize the loading and unloading of CNC machine tools, and use a PLC as the controller. After the I4.0 management shell has been implemented in both the CNC and the manipulator controller, the controller program can request the CNC management shell to process an aluminum shell (a kind of service) . Or request the robotic arm to take the raw material from the pallet of raw materials (a service) and place it on the CNC machine tool. When the CNC management shell sends a completion event, the robotic arm removes the processed aluminum shell (a service) . Place on finished trays. The whole process is shown in the figure below.
The above processing steps are:
- Take raw materials
- processing
- Take the finished product
This control method is a Master/Slave structure. If the traditional control technology is used, the controller is realized by a PLC or an industrial computer (if an HMI interface is required).
In the actual production process, details such as the machining CNC program, the movement of the robot, and the position recognition between the robot and the pallet are also required. These tasks can be done manually, such as manually importing CNC programs into industrial computers, processing quantities, and so on. It is also possible to use the upper layer MES software to remotely download various parameters. So the architecture becomes as follows:
This kind of master-slave architecture system is common in automatic systems. The production process control is completed in the controller, and the CNC and the robotic arm accept the service call from the master controller and provide status information to the master controller. The CNC and the robotic arm have their own programs, downloaded by the controller, or downloaded by other computers (such as CNC programming workstations).
If the CNC and the manipulator are equipped with AAS, the program of the controller has nothing to do with the manufacturer and model of the CNC and the manipulator. Because the AAS of each manufacturer's hardware products has the same model, a unified access protocol is adopted. At present, there are various protocols for CNC controllers and robotic arm controllers, and it takes a lot of time to get familiar with the manufacturer's proprietary protocols and parameters. It costs a lot of money to adapt the fieldbus interface card and API driver for the robot arm and CNC. This is the direct benefit that AAS brings to system integration.
To make a digression, on many occasions, the new technology of the automation system does not bring much direct value to the end user (CNC processing plant), but saves the development cost of system integration. Of course, the reduction of development cost will be transmitted to the final user. user.
Distributed AAS architecture
In addition to the master-slave architecture, AAS can also adopt a distributed control method. For example, the above CNC processing unit can be changed to the following method:
This process is distributed serially
1 Notify the robotic arm to take the raw material and install it on the CNC operation table.
2 The robotic arm notifies the CNC to start machining.
3 CNC notifies the robotic arm to take away the processed aluminum casing.
This structure becomes more complicated. The robot arm AAS needs to communicate with the CNC AAS. The Robot AAS informs the CNC AAS "Hey man, let's process it", when the CNC process is finished, the CNC AAS tells the Robot AAS "Old man, come and pick it up".
So, how to download the program in CNC and robotic arm? Obviously there are two ways:
1 The controller downloads the program to the robot arm, and the robot arm downloads to the CNC
2 Downloaded directly to the two AASs by the controller through AAS communication.
Obviously, the first method is relatively simple. The equipment manufacturer builds the AAS according to the characteristics of the equipment and the services provided, and then the upper layer software can control the equipment. It does not need to know the status of the equipment in the front and back processes, nor does it need to cooperate with the neighbors, just look at the meaning above. However, the distributed AAS network is also a common structure in the multi-unit coordinated production line. For example, different labels are attached to beverages on the canning line, and the docking between the automatic handling trolley and the production unit, etc. Distributed collaborative networks are easier to program and deploy devices.
Two communication methods of AAS
From this point of view, AAS has two communication methods:
Vertical communication : the communication protocol between the upper layer software and AAS, they can be OPC UA protocol, HTTP protocol and so on.
Horizontal communication: The communication protocol between AAS and AAS is called I4.0 language in Industry 4.0 Platform.
Where the AAS is deployed
AAS is the management shell of assets, and the so-called asset is a broad object. Can be anything of value to the business. Specifically, it can be a field device such as a PLC servo drive, a sensor, or it can be MES, ERP software, or the main controller in the device. In theory, each object can add an AAS.
In the process of building a digital manufacturing system, do we build an AAS for all physical equipment and software? Or build AAS selectively? There is a question of trade-off. Implementing an AAS requires additional computing power and increases initial engineering effort.
For example, the interior of a CNC machine tool may be composed of a Windows-based main controller, several PLCs, servo motors, sensors, and actuators. The control equipment PLC inside CNC does not need to implement AAS, but uses traditional field bus and control protocol to realize data communication. AAS needs to exchange data with internal assets through the traditional field control bus.
Of course, some components with AAS can be formed into a production unit during the engineering design process. Every device and component has an AAS.
In this way, the communication of devices with AAS is more flexible and more complex. The AAS of the upper layer can call the SubModule of the AAS of the lower layer.
Each AAS is both a service provider and a service requester.
I4.0 language
In the I4.0 point of view, the horizontal agreement is called I4.0 language, which conforms to the VDI/VDE 2193 standard. It is built on a message-based communication protocol (such as the MQTT protocol). in JSON format.
AASs communicate through messages.
Currently, the specification of the i4,0 language only has the MQTT protocol. The hierarchical structure of the network is shown in the figure below.
The I4.0 language is not compatible with OPCUA's SUB/PUB protocol. I don't know whether it is possible to use OPCUA's SUB/PUB protocol to transmit I4.0 language? MQTT-based protocols are not real-time. In the field of field control, it is a development direction to adopt OPC UA SUB/PUB protocol as the field control bus. But how to combine it with AAS level communication is worth studying.
Software Architecture of Administration Shell (AAS)
As I mentioned in the previous blog post, AAS can be divided into AAS As File, static parameter AAS, programmable AAS (proAAS) and dynamic AAS. AAS file is the AAS used in the engineering design process, while other AASs are embedded in the device.
Static AAS
Static AAS is relatively simple, and has a vertical protocol stack (AAS Stack) and an AAS model inside. This is similar to OPC UA. In fact, the AAS model can be built using the OPC UA information model and accessed using the OPC UA protocol.
Active AAS
The network protocol of active AAS is relatively complicated:
1 Able to access submodules of other AAS.
Active AAS nodes are both service providers and service requesters. From the point of view of OPCUA, they are both OPCUA server and OPCUA Client,
2 Ability to call other AAS services
3. Algorithm adjustments can be made according to service requests sent by other AASs.
This part of the function corresponds to the algorithm inside AAS, and these algorithms are not part of the equipment control program , but additional programs (they are part of the original main control equipment program, complete industrial optimization, scheduling and parameter configuration, etc.). Who will write this part of the software, the equipment provider, or the system integrator? What language is used to write it? These are all issues worthy of discussion.
Therefore, the program inside AAS is as follows.
AAS is divided into two parts, one is the static AAS model, and the other is the dynamic AAS, which responds to service requests.
For a more detailed breakdown, the software architecture of AAS is as follows.
more complex scenarios
The actual production scene is extremely complicated. Take the above CNC processing unit as an example. The actual scene also needs pallets of raw materials and products. The robotic arm needs to identify the workpiece through image recognition equipment or mutual interaction methods (such as RFID) where to put it. In order to interact with each other, the pallet needs to have an AAS shell. Furthermore, in order to grab the parts, information such as the geometric shape of the raw material is required, which requires the AAS (static AAS) of the raw material. If the raw material involves external procurement or internal rough processing, it also requires the technology of the classification number of the raw material Specification. Ideally, all equipment and materials involved in the production process would require a digital model (the so-called management shell).
All technical improvements are aimed at improving production efficiency, reducing production costs and improving product quality. If only the robotic arm and CNC are installed in the workshop, then the loading and unloading of pallets, handling, and external procurement of the supply chain. If these tasks still rely on manpower to complete, compared with the investment, the production efficiency will not be improved much. Therefore, enterprises are not willing to adopt digital technology to transform production lines.
In order to achieve AAS communication between suppliers, it is necessary to standardize terms, attributes, and indicators. This requires importing the Ecl@ss dictionary server.
consensus
Judging from the current development of I4.0, I4.0 does not develop more new IT technologies. The key is to establish various information models, and to establish and promote language standardization. The realization of technology is not difficult. The entire industry has reached a consensus that the realization of interconnection is the key to realizing the vision of I4.0. Standardization is a very arduous and lengthy process, because it takes a long time to find consensus, deal with conflicts of interest among competitors, and even international coordination. In the process of promotion, the phenomenon of "standard rigidity" will appear, and users will not adopt the standard until it is generally accepted. But when everyone stalls, waiting for everyone else to make progress, time is wasted.
Therefore, it is necessary to find a way to overcome the rigidity of standards, such as how to adopt part of the standardized content in the early stage of development, how to benefit the manufacturing industry locally. By taking advantage of standardization to develop new business models, developers get commercial benefits. These are questions for engineers and management to ponder. This is not only a technical issue, but also a social and business issue.
conclusion
Industry 4.0 management shell is a brand-new digital manufacturing method with a new concept. It is a vision map of future digital manufacturing proposed by German-based foreign institutions. The problems they want to solve are different from the problems we face, and the language and cultural background are also different. Therefore, we do not fully understand many concepts and concepts. Facing our current situation, there are many opportunities for innovation. There is no need to imitate others.
All the efforts of Industry 4.0 are aimed at realizing shorter innovation cycles, more personalized products, and more flexible production. It is often mentioned that the car offers a wide variety of colors and trim configurations. The production line needs to be adjusted frequently according to the products produced. If the production line is a dedicated production line set up for a single product. For example, only one color of Ford is produced. Industry 4.0 doesn't take much advantage. The introduction of artificial intelligence technology, the optimization of control algorithms, etc. should not be the problems to be solved by Industry 4.0. This is a question that is often misunderstood.
There are many deviations of understanding in the blog post I wrote. It is for your reference only and to discuss together.