Will PC-based systems inevitably replace PLCs ? When applied to packaging production lines, what different roles do they play? Let's hear the opinions of three experts.
For a long time, PLCs have been a mainstay in the field of industrial automation control, providing highly reliable control applications for a wide variety of automated control equipment. This is primarily because they offer safe, reliable, and relatively complete solutions for automation control applications, perfectly suited to the current automation needs of industrial enterprises.
With the advent of the PC and Internet era, industrial PCs or PC-based controllers have emerged as highly competitive technologies. They seamlessly integrate into network-based information systems, possessing fundamental characteristics such as high performance, low cost, system openness, and a large talent pool. Consequently, PC-based controllers have experienced rapid growth and strong vitality since their inception. Some argue that PC-based controllers will replace traditional PLCs, but this requires addressing reliability and programming issues. In recent years, these problems have been largely resolved, and PC-based controllers have become comparable to PLCs in both appearance and reliability. Furthermore, the introduction and widespread adoption of the IEC 61131-3 programming language standard have paved the way for the rapid development of PC-based controllers. Thus, PC-based controllers combine the advantages of both PCs and traditional PLCs, allowing for seamless integration into network-based information systems.
So, will PC-based systems inevitably replace PLCs? When applied to packaging production lines, what different roles do they play? Let's hear the opinions of three experts.
Dong Jixin, Industry Sales Manager, B&R Industrial Automation
In the field of automatic control, PLC technology and PC-based technology are currently the most representative control technologies, but their technological origins and developments differ significantly.
PLCs (Programmable Logic Controllers) originated in the early 1970s. The earliest PLCs appeared as replacements for relay systems, primarily performing simple sequential control functions. However, upon their emergence, PLCs quickly demonstrated their vitality due to their high reliability, small size, and intuitive programming, becoming a "star" in the field of automatic control.
PC-based is a control system based on PC technology. The earliest PC-based control systems were centered around an industrial computer, expanded with dedicated boards featuring PCI interfaces. Leveraging advancements in IT technology, PC-based systems offer advantages in computing power, storage, networking, and software openness.
As can be seen from the above description, PLCs and PC-based systems differ significantly in their technical characteristics. PLCs are characterized by their small size, low power consumption, and strong anti-interference capabilities; they also boast high reliability, with a mean time between failures (MTBF) reaching 500,000 or even 1 million hours; they offer simple and intuitive programming modes (such as ladder diagrams); and they have an internal real-time clock. PC-based systems, on the other hand, offer high computing power; they feature open standard system platforms and PCI interfaces; they utilize sophisticated and low-cost display technologies; and they possess rich networking capabilities. However, their system reliability is slightly lower; for example, the MTBF of a high-performance IPC is approximately 50,000 hours. Furthermore, while PC-based systems have powerful CPUs, their multi-tasking operating systems are not real-time, so their program cycles are actually slower than those of high-performance PLCs.
These differences determine the different roles that PLCs and PC-based systems play in packaging machinery. PLCs typically operate at the lower levels of the equipment, providing reliable, real-time control, including I/O and motion control. PC-based systems, on the other hand, usually operate at the operational level, handling data acquisition, storage, and human-machine interface display. Currently, the development level of packaging machinery in China lags significantly behind leading international manufacturers. Few companies possess the design and production capabilities for highly automated and large-scale complete packaging machinery systems. Simple, low-automation, stand-alone equipment constitutes the majority, thus primarily using PLCs as controllers.
With the rapid development of packaging technology in China, future packaging equipment controllers should be able to integrate the technological advantages of both PLCs and PC-based systems. Indeed, modern control technology development shows this trend, with B&R's B&R 2005 series PCC controllers being a prime example. For instance, it's difficult to definitively classify the CP382 as either a PLC or a PC-based system; perhaps calling it a PC-based PLC would be more accurate.
In terms of computing power, the CP382 uses an Intel PIII 500 processor, boasting superior computing capabilities, including floating-point arithmetic. For networking, the CP382 features three aPCI slots, providing robust networking capabilities and compatibility with popular fieldbus technologies. It also comes standard with Ethernet, USB, and RS232 interfaces. For storage, it uses a CompactFlash card; 4GB CompactFlash cards are now widely available and more than sufficient for applications in the packaging machinery industry. Regarding the operating system, B&R uses the Runtime qualitative time-sharing multitasking operating system, combining multitasking and real-time features. For control software programming, it supports six programming languages, including ANSI C and Basic high-level languages.
This controller, which integrates PLC and PC-based technologies, has significant technological advantages and is bound to become the mainstream controller for future packaging machinery automation.
Xu Changrong, General Manager of Business Division, Beijing Hollysys System Engineering Co., Ltd.
While both PLCs and PC-based systems can be used for packaging equipment automation, their focuses differ. PLCs are better suited for equipment control, while PC-based systems are more used for monitoring equipment operating status. Compared to PC-based systems, PLCs offer advantages such as flexible configuration, smaller size, adaptability to harsh environments, stronger anti-interference capabilities, and higher reliability, but they are slightly inferior in terms of software functionality and system openness. Of course, with the continuous development of computer and control technologies, both PLCs and PC-based systems are absorbing each other's advantages to adapt to more application scenarios. From what I understand, PLCs are used far more extensively in packaging equipment than PC-based systems.
Leveraging over a decade of experience in industrial control product development and a strong technological foundation, Hollysys has developed a new generation of small, integrated PLC product, HOLLiAS-LECG3. This product has been successfully applied in various packaging equipment, including the DXD automatic packaging machine and noodle packaging machines. The DXD fully automatic packaging machine, controlled by the G3 PLC, integrates feeding, bag making, filling, sealing, and cutting processes. It features photoelectric tracking, PLC control, and stepless speed regulation with deviation correction functions. It offers precise measurement, meets industry standards, and boasts stable performance, convenient operation, and high efficiency. The electrical control system of the DXD fully automatic packaging machine consists of a Human-Machine Interface (HMI), a bag-pulling control system, a bag-making control system, a paper feeding control system, a photoelectric control system, and a feeding and metering control system. This system is characterized by its advanced technology, economy, practicality, reliability, and flexibility. It not only improves the safety and economy of packaging equipment but also greatly enhances system flexibility, providing flexible solutions for different customer needs.
With the increasing demand for automation in packaging equipment, more and more packaging equipment manufacturers are considering equipping their equipment with advanced automation products to improve the technological content of their products and enhance their market competitiveness. Personally, I believe that in general-purpose equipment, users tend to prefer using a PLC plus HMI approach to control packaging equipment. In some equipment with special requirements, some users may also use a PC-based automation solution, or a PLC plus PC-based solution. In short, considering factors such as product reliability, stability, flexibility, and cost-effectiveness, PLCs have a broader application prospect than PC-based solutions in the field of packaging equipment automation.
Zhang Chunlin, Business Development Manager for Filling and Packaging Industry, OEM Management Department, Automation and Drives Group, Siemens (China) Co., Ltd.
1. What is the biggest difference between PLC and PC-based systems? What are their respective advantages?
PLC, also known as Programmable Logic Controller, is traditionally used in relatively simple industrial control applications such as logic control, sequential control, and time-based control. It boasts advantages such as small size, simple and practical programming, and convenient and flexible installation. Disadvantages include slow processing speed, limited expandability, and inconsistencies in programming languages among different manufacturers.
With the development of PC-based industrial computers (compared to ordinary computers, they have advantages such as dustproof, vibration-proof, electromagnetic interference-resistant, and high and low temperature resistant), PC-based automation systems, composed of industrial PCs, I/O and monitoring devices, and control networks, are gradually becoming another way to realize industrial automation. PC-based automation systems originate from PCs and can be fully integrated into information systems in the network era. They have advantages such as high performance, low price, system openness, abundant talent, and application foundation.
2. What roles do they play in the application of packaging equipment?
For general packaging equipment, such as bag forming/filling/sealing machines, beverage filling machines, etc., logic, sequence, and timing control are mainly used. Siemens' S7-200 and S7-300 series PLCs are widely used in this type of packaging machine.
In situations requiring not only logical, sequential, and timing controls, but also powerful computing, data processing, and process control, PLCs often fall short. For example, a food processing and packaging production line capable of producing hundreds of products needs extensive recipe storage and retrieval. Ordinary PLCs, limited by their memory, struggle to handle this task. In such applications, SIEMENS' PC-based industrial automation control system, WinAC, is a highly suitable product. With appropriate secondary development, it can also achieve dynamic display of equipment operating status; real-time display of electrical and process parameters; real-time curve display; historical curve display; a large dynamic standard database; and provide annual, monthly, daily, and randomly printed reports.
3. What is the current status of PLC and PC-based applications in domestic packaging equipment?
Currently, PLC-based control systems still dominate, which is related to the overall level of packaging machinery. At present, the domestic packaging machinery industry is characterized by a prevalence of stand-alone machine automation, with fewer entire packaging lines being networked, and even fewer being networked for the entire factory or company. With economic development and the widespread adoption of MES and ERP systems, PC-based control systems will be increasingly used.
4. Regarding packaging equipment, please share your views on the future development prospects of PLC and PC-based systems.
PLCs are currently widely used in industrial control due to their high stability and reliability. Combining the advantages of both PLCs and PCs, they are more in line with the trends of the networked and information age. Therefore, it seems that as the requirements for industrial control and information management increase, PLCs will indeed gradually lose some market share. However, we should also recognize that PLC manufacturers have already begun to continuously improve and expand the functionality of PLCs by utilizing the latest software and hardware achievements in the IT industry. The emergence of fieldbuses, communication, and network interfaces on PLCs means that individual PLCs are no longer isolated. PLCs will continue to develop towards open control systems, giving modern PLCs a new meaning. In practical applications, PLCs and IPCs are often combined, with the PLC at the lower level and the IPC at the higher level. Technically, PLCs are gradually adopting some IT technologies, and IPCs are also converging with some characteristics of PLCs. PLC and PC-based control systems will present a situation of both integration and competition.
