Introduction
Recently, there have been two competing lines of thought in the field of industrial control. Some argue that PC can be effectively used for control, while others claim that PC is never suitable for factory environments. Today, these competitors easily accept the current status of PC machines being used for many industrial production controls, as one manufacturer after another has adopted PC control solutions in part of their production. Therefore, the traditional viewpoint that PC is merely an office machine, unsuitable for the dusty environment of factories, is also changing. Beckhoff is one of the pioneers of PC-based automation technology: as early as 1986, Beckhoff’s first PC control system was introduced. Today, Beckhoff has applied its proprietary technology accumulated over the years to industrial PCs. Beckhoff industrial PCs combined with TwinCAT automation software provide a high-performance control system for implementing PLC, NC, and CNC functions. Hans Beckhoff, the founder of Beckhoff, strongly advocates relying on PC control technology to drive the automation market. After developing the first DOS-based system in 1985, he never looked back. Software is the key to the operation of PC control systems, and in Beckhoff’s philosophy, adding hardware is considered counterproductive. Beckhoff’s success hinges on two key points: (1) All work is done by software on a single platform (2) Provide everything the customer needs, so they do not have to purchase other components elsewhere However, PC will not replace traditional control modes such as PLC because suppliers of PC-based industrial control solutions primarily develop software. No matter how important soft logic (control based on PC, commonly called ‘soft’ control or ‘soft’ logic) is, it only accounts for about 5% of the entire automation project, while approximately 50%~60% of the cost is in parts like I/O and motor drives, and industrial PCs may account for 10%~20%. Even if soft logic companies achieve great success, they still face integration issues. The manufacturing industry is well aware: they want to buy complete systems, not scattered individual components; buying PCs here, software packages there, and I/O buses elsewhere is undesirable. We often encounter situations where customers say they need an open system, but in the end, they typically buy all components from the same supplier. What they really need is assurance that they won’t be stuck due to equipment failures and can turn to another supplier when necessary (i.e., they need reliable, standard equipment). Furthermore, the Windows system may be a favorite among software workers, but it poses significant problems for factory floor control. Windows is too heavy for factory computers, requiring thousands of megabytes of disk space, and in industrial settings, it is preferable to have no moving parts, as they slow down computer response and introduce uncertainty. Therefore, if Windows is used for industrial control, it may require additional coprocessor boards, solid-state drives, enhanced real-time performance, or kernel modifications. However, modifying the Windows system in any way is no longer considered an open structure but rather a proprietary PC control system, with its own limitations and support standards. Therefore, it is generally believed that the new hope for PC control lies in the Windows CE operating system, which occupies very little space, has real-time performance, and has some open-source components. Many products based on WinCE are already available in the industrial sector.
Next, we will analyze the advantages and disadvantages of PC-based industrial control systems (PCBCS) compared to other control systems.
Since the emergence of industrial control systems in the mid-21st century, the degree of automation in industrial production has continuously improved. The types of instruments and devices used in industrial control environments have become increasingly varied and complex, leading to a growing importance of industrial control systems in overall industrial development. To adapt to the development of industrial production, modern industrial control systems have continually evolved and advanced alongside social production. Compared to analog instruments, PLCs, DCSs, and FCSs, the industrial control systems based on PC (suitable for industrial environments or general PCs) can process data and communicate more quickly and effectively, flexibly control various terminals in industrial control environments, and enable rapid communication between them. This allows the control system to closely integrate with higher-level management systems, facilitating production monitoring and management. More importantly, it is a fully developed system that is very conducive to product development, maintenance, and upgrades. Thus, it has gained widespread recognition in the field of industrial control, with related application areas rapidly expanding, becoming a new trend in industrial control.
Structure and Openness of PCBCS
The PCBCS control system mainly consists of three parts: PC; intelligent or non-intelligent I/O components; specific application software. The PC generally refers to an industrial PC, but sometimes it may also be a general PC, depending on the working environment. The PC is the core of the entire control system, capable of data processing, acquiring data information, issuing control signals, communicating with other PCs, and displaying operations. The I/O components generally refer to control terminals, data acquisition terminals, and their connections. These components are primarily used in field environments and are the peripheral structure of the entire control system, including not only ordinary I/O ports but also some intelligent terminals, and even small PLCs, controlling the entire automated production line. Specific application software installed on the PC directs and coordinates the entire control system to operate steadily and effectively, simplifying and modularizing hardware circuits, significantly reducing hardware costs, while the programming of application software becomes relatively complex.
Compared to previous control systems like DCSs and FCSs, PCBCS is a fully open control system in all aspects. Other control systems, such as PLCs, DCSs, etc., although superior in overall performance and system integration, lack openness, have a limited number of interfaces, and are relatively expensive, with product upgrades and modifications constrained. The recently emerging FCS has an open bus protocol, but still faces the coexistence of multiple field buses, making it difficult for any one bus protocol to completely replace others. This has caused significant inconvenience in product development and maintenance. In contrast, PCBCS does not have these issues, allowing anyone to develop their own application software based on existing system software, greatly increasing the freedom of software programming without the need for a specific protocol to constrain it. The components used in the system are also completely open, meaning users are no longer required to select components that adhere to a specific protocol or a proprietary company; they can choose better-performing and more reasonably priced products for system design and maintenance based on a common standard, greatly reducing development and maintenance costs.
Advantages of PCBCS Control Systems
1. Significantly Reduced System Costs With the rapid development of large-scale integrated circuits, since the mid-1990s, the rapid advancement of computer technology has greatly enhanced the performance of microcomputers while their prices have become very low. Compared to microprocessors and PLCs, PCs offer tremendous cost-effectiveness. Moreover, compared to PLCs, DCSs, and FCSs, the PCBCS control system is unmatched in data processing speed and massive storage capabilities. Investments in related signal acquisition and processing boards, power supplies, racks, cabinets, wiring, etc., will also be significantly reduced. The low cost and high speed of PCs, along with their ease of operation based on application software and user-friendly interfaces, are far superior to those of control devices like PLCs. Similarly, using serial buses, devices from different field buses can easily connect to the PC, processing through application software, eliminating the complex wiring between previous devices and greatly reducing equipment costs. For simple devices that lack intelligence and digitalization, they can also be directly connected to the PC, communicating with the PC using analog signals (via processing boards).
2. Very Fast Processing and Communication Speeds, Large Information Storage PCs have high processing speeds, reliable operating platforms, massive storage, networking, and intelligence. When performing data processing (such as analog calculations), the computational speed of PCs is usually more than a hundred times that of PLCs and DCSs. Additionally, PCs have very large storage capacities, making it very convenient to access system-related data. In terms of data communication, with the development of network technology, the high-speed processing capabilities of PCs are now quite mature. The communication technology of PCs is very fast, whether it is communication between PCs or between PCs and I/O components. If the communication lines are overloaded, multiple PCs can be used for segmented control, and then network communication can occur between the various PCs. This greatly ensures the stability of the entire system. Problematic parts can also be quickly isolated from the system.
3. Easy Integration of Process Control, Batch Control, and Motion Control Production automation requires the entire control system to be highly integrated to ensure the coordinated operation of the entire production system. PCs can collect and process a large number of analog, digital, pulse, and switch signals through specially designed multi-channel input-output boards. With the high-speed processing capabilities of PCs, they can rapidly perform process control for a production line, motion control for a specific actuator, and batch control and logical control for multiple components on-site. Based on high-speed processors, massive memory, multi-threaded processing, and high-speed communication, PC control is more advantageous when managing relatively large systems. It can better integrate all related systems, offering superior coordination and faster processing speeds.
4. Simple System Design, Debugging, and Maintenance, Quick and Convenient Access to Upper-Level Information Because PCBCS is an open system, engineers can design the entire control system faster and better based on existing technologies and knowledge. Due to the user-friendly interface of PCs, simple interfaces, and good component universality, debugging and maintenance of the entire system are also very straightforward. Furthermore, because of the PC, accessing information within the system is very convenient, and communication with other upper-level systems is also very simple, making relevant information readily understandable.
5. Good Portability of System Software Although PCBCS significantly saves costs on hardware, software programming has become relatively challenging. However, the portability of the system software for PCBCS is good; software programming becomes challenging only when starting a new project. If there are other related software references or upgrades based on existing software, programming will become very simple, allowing for easy development of new or upgraded software. Based on existing PCBCS systems, software development is no longer a problem.
6. Easy Integration of Control, Human-Machine Interface, and Programming Functions Due to the good human-machine interface of PCs, various related information is displayed sequentially during the control process, making it easy for operators to manage the entire system and complete control tasks. This eliminates adverse factors in control and accomplishes control objectives. Furthermore, operators can perform real-time programming, achieving functions that other systems cannot complete.
Disadvantages of PCBCS Control Systems First, the application of PCs in industrial environments is limited. Industrial field environments are relatively harsh, with temperature, humidity, dust, electromagnetic interference, and many adverse factors limiting the on-site application of PCs. However, existing industrial-grade PCs have very high stability and can meet most on-site requirements. Moreover, most existing PCBCSs avoid direct application of PCs on-site, instead using intelligent lower-level machines like PLCs or other intelligent devices, controlling the entire system via rapid communication from outside the field. In this mode, the various intelligent devices communicate independently of the PC, allowing for immediate isolation of faulty modules, ensuring system stability, and avoiding direct application of PCs on-site. Second, the stability of PCs themselves has not yet reached perfection. Although the performance of PCs has greatly improved and stability has significantly enhanced, the PCs used in PCBCSs require extremely high stability, which is a crucial factor limiting the application of PCs in control systems. However, based on the low cost of PCs, we can use one or two PCs as backup machines in the system, synchronously working with the current machine. Once the current main machine fails, the backup machine can immediately detect and take over, ensuring the normal operation of the system. Furthermore, communication lines may become saturated. Although PCs can quickly process large amounts of data, if a large amount of data is transmitted through one or several serial buses, communication performance will significantly decrease. Possible solutions include using multiple PCs for information acquisition and processing, with high-speed communication via Ethernet between the PCs. While this increases system complexity, it greatly reduces system response time. Simple or non-repetitive signals on-site can also be processed using embedded systems to ensure timely responses to critical signals.
From the above, it can be seen that PCBCSs have significant advantages in performance and cost as the main body of control systems. However, they have shortcomings in bottom-level control. In contrast, DCSs and FCSs are instrument-based control systems that exhibit significant superiority in bottom-level control. They connect various detection and control devices through field buses, linking a vast number of sensors, actuators, loop regulators, and other instruments from different manufacturers and standards through a set or several sets of network lines, enabling data exchange. This not only reduces system costs but also improves project progress and system reliability, making it an indispensable supplement to PCBCSs.
Moreover, in today’s era, the global level of network informatization is very high, and computer application technology is widespread. Every enterprise and company’s normal operations increasingly rely on computer internet systems. This widespread application of computer networks has significantly enhanced work efficiency; however, the openness of the internet poses significant risks to information security across various industries. How to control internal system resources, protect existing data, and prevent virus intrusions is a concern for all industries. Among these, network security for industrial control systems is of utmost importance. To avoid network intrusions and establish a secure and efficient internet platform to protect enterprise resources and data security, antivirus software and firewalls have emerged in networks. Network firewalls serve as a security barrier between internal and external networks, as well as between professional and shared networks, strictly processing network information transmitted through common lines, preventing many internal network users from being attacked by unauthorized personnel and restricting unreasonable and illegal operations by users, effectively preventing many malicious attacks or damages from hackers on ordinary users and enterprise computer systems. However, with the continuous improvement of hacker technology, the protective effect of firewalls has proven insufficient, particularly in the software aspect. Therefore, throughout the developmental process, hardware firewalls have played a crucial role. For example, embedded hardware offers relatively high processing speeds, efficient throughput, and stable operation in high-traffic working environments.
Summary PC-based control systems are generally recognized to have the following advantages: low cost of PCs, strong data processing capabilities, ease of installation and use of systems and software, short development cycles for application projects, good human-machine interaction, convenient network communication, advanced diagnostic capabilities, better software transparency, and low maintenance costs for the system. For example, information during the production process can be transmitted from one place to another via software rather than hardware, and data can be collected into Excel, allowing for easy classification, averaging, etc., thus better understanding the use of tools and machine anomalies.
In the actual development of PC control systems, several issues are primarily considered:
1. Is the Windows system stable enough (can it ensure continuous operation without crashing)?
2. Can the Windows system guarantee real-time response (except for WinCE, all are non-real-time systems, and extending real-time capabilities will increase costs)?
3. Network communication requires high real-time performance, and network transmission must be deterministic.
4. Data security, and how to ensure network security after industrial sites are connected.
Source: 【CSDN Community】 Blog by Lu Huadong
