Compared with the original mission of the programmable logic controller (PLC), the automation controller has far more functions than replacing the relay. Now, the controller can integrate logic, motion, robotics, and communicate with other machines and management systems. Performance can range from simple devices to multi-core processors.
The difference between traditional PLC, programmable automation controller (PAC) and industrial control computer (IPC) is mainly related to processing power and performance, but the boundaries between them are gradually blurring. Due to compliance with the International Electro technical Commission (IEC) 61131-3 programming specification, the control software has achieved a certain degree of standardization. The powerful real-time operating system running in the background avoids the dependence on the Microsoft Windows operating system. Therefore, the term "IPC-based control" may be more accurate if it is changed to "Intel-based or AMD-based" and can reflect the powerful mainstream processors used.
Since current automation controllers can do more things besides logic processing, PLC may be an outdated term. Because all automation controllers are programmable, the "P" in PAC also seems to be redundant. The controller is basically a computer that can run multiple operating systems (real-time, Microsoft Windows and Linux) on the same processor. IPC can be used for control, data collection, and new tasks that are constantly emerging, such as edge computing.
The response time of traditional PLCI/O communication depends on network performance, number of nodes, communication volume, CPU performance and CPU load; the use of stricter integration and open IEC61131 technology design, centralized software management and decentralized program execution can improve performance .
Controller function considerations
In the same software environment and the same program, running on the same processor and coordinating the functions of all machines is becoming a popular trend. This requires the synchronization of machine functions and the use of a modular code structure to make an organized and cohesive approach possible. Nevertheless, some areas do not need so much integrated control, such as simple applications, there is no expansion plan. The complexity and performance requirements of the application determine the specifications of the controller. There are many factors to consider when choosing a controller. Depending on the application, you may need to consider the following considerations.
Logic
The basic demand for logic control is why we continue to call automation controllers PLC. PLC open is an organization responsible for maintaining and expanding the scope of the IEC61131-3 programming standard, and managing a large amount of knowledge, training and libraries. The organization's activities go far beyond the scope of logical control, including sports, security, OPC unified architecture (UA), XML, etc.
Multi-axis motion
According to different requirements such as application complexity and movement synchronization, the automation controller can control dozens or even hundreds of motion axes. With the development of Moore's Law and industry standards, independent motion or robot controllers with dedicated motion networks are no longer needed.
Cyber security
In North America, hard-wired network security is still the first choice. The network security facility and the equipment that controls the machine run on the same network, which has been proven to be an effective control function. The realization of network security can be realized from the redundant core on the control processor, to the separate safety controller, and then to the safety input/output (I/O) in the small system. Cybersecurity also extends to sports safety and robot functions, allowing machines to operate in a safe mode instead of shutting down directly, which can provide excellent operating efficiency.
Robot integration
The same automation controller can integrate multiple Delta robots, SCARA robots, articulated and gantry robots, and other machine functions. In addition, it is possible to perform motion functions in an IEC61131-3 compatible environment. Due to the built-in stacking algorithm to the assembly mode, the dedicated robot controller can continue to provide valuable functions.
Machine monitoring
Monitoring the operating conditions of machines is a key part of predicting maintenance schedules and reducing unplanned downtime. The controller can be combined with various existing sensors (such as temperature probes and accelerometers) to monitor the actual situation. Before a catastrophic failure occurs, machine monitoring also helps to detect anomalies. Energy monitoring can also be applied to the use of compressed air, the use of natural gas in heaters and dryers, and the use of water in the process.
Data processing
The automation controller can be a network, an OPCUA server and a client. They have the function of collecting Industrial Internet of Things (IIoT) data and can receive instructions from the cloud or terminal to optimize the process. Automation controllers usually send data to manufacturing execution system (MES), enterprise resource planning (ERP), overall equipment efficiency (OEE), trusted platform module (TPM), and product lifecycle management (PLM) software. In the IIoT environment, it is also very important to receive useful analysis data.
Automatic configuration
Previously, replacing new components (such as drives) had to manually determine and load the correct firmware version for the device. Now, the automation controller can automatically read the equipment and remind the technician to make necessary adjustments without manual intervention.
Communication ability
Today, even low-cost controllers have one or more Ethernet communication ports to communicate with HMI, management systems, programming, and other non-time-critical tasks. For the controller, it is already very common to support a certain type of industrial Ethernet protocol, such as EtherNet/IP, EtherCAT, Powerlink, Profinet, etc., in order to form a deterministic network. Unfortunately, there is currently no universally recognized industrial Ethernet standard that can provide high-speed, deterministic communications suitable for machine control.However, the development of Time Sensitive Networks (TSN) has brought great expectations. TSN, together with OPCUA and OPCUA Pub-Sub (Pub-Sub), will bring more certainty to the IEEE802 series of Ethernet standards. The Industrial Internet Alliance has set up a test bed for it, and many industrial automation suppliers have participated in it to prove the feasibility of TSN in machine-to-machine communication.TSN is very important, mainly because in order for IIoT to work, it is necessary to realize the interoperability of communication between different control platforms in the factory, enterprise, and on the cloud. If a serial interface is needed, it should be specifically defined, because serial communication is currently less used.
Installation form
The following are the 3 most common types of installation of automation controllers.
1) IP20, cabinet installation: This is a commonly used installation form for traditional PLCs. There is a separate HMI, usually using integral, backplane/rail installation I/O, or remote installation I/O modules.
2) IP65/67/69K sealing, base or front panel installation: This form integrates HMI and controller, and adopts rocker type installation, which can give full play to the ergonomic advantages of the device, so it has become more and more popular.In addition to control, this form can also integrate PC functions to run various Microsoft Windows applications, such as HMI, although the trend of Web-based HMI is becoming more and more obvious. Compared with similar controllers, base-mounted controllers are often more expensive than panel-mounted, require stainless steel baffles, and higher sealing requirements.
3) IP20, cabinet type industrial computer, with independent HMI: Just like an integrated form, this form can also be used as a controller with a real-time operating system, various computer operating systems and network services. The controller can be independent, and the industrial computer is dedicated to non-control tasks such as edge, fog or cloud computing. History libraries, serialization, and visual inspection are also common applications.Advanced automation suppliers can provide users with a range of PLC products that meet different needs, for example, from micro PLCs with fixed I/O, to mid-range PLCs, to modular PLC systems that can handle thousands of I/Os.
Scalability
Although the software development environment is usually related to hardware (ultra-small, micro, medium, and large PLCs), it is also possible to work in a hardware-independent development environment. This means that the project can be programmed first, and then the control hardware can be selected or changed. This flexibility can be extended to motor and drive types. The low-end stepper or inverter can share the same program with the high-end servo. When a series of devices are designed to allow the reuse of key software elements, scalability requirements are particularly critical.
CPU performance
There are many types from low-end to multi-core processors to choose from, but their performance will overlap with each other. Therefore, it is recommended to cooperate with the technical support and sales engineer team of the technology provider to choose the best cost-effective solution for the expected application requirements, because they know their products better.Ideally, the processor should be expandable so that the control software can be compatible with all products on the controller product line. Automation technology suppliers will prepare sufficient inventory of important components to ensure product availability and provide migration services for alternatives.In addition, it is necessary to determine whether silent operation is required, and the expected ambient temperature for installing the controller. Other cooling options include fans, air conditioners, radiators, and water cooling.
RAM
Solid-state memory has become very popular in automation controllers, removable media (such as C-Fast cards), and permanently installed applications that are more cost-sensitive. The advantage of removable memory is that it can be easily replaced, it is convenient to make and store backups, and it is easy to expand the memory capacity.
However, you need to be careful when using industrial memory cards and make sure that the media meets the specifications required by the application. Different storage types have different service life, which depends on the read and write cycle. This is also a topic that needs to be discussed with automation suppliers.