I. The Evolution of Automation Controllers: From Relays to PLC, PAC, and IPC
Until the late 1960s, large relays were the best choice for controlling automated machines. They were expensive, difficult to use, and challenging to troubleshoot. Then a new technology emerged that addressed all of these issues: the programmable logic controller (PLC). This allowed manufacturers to easily program smaller and cheaper controllers than the older, bulky relays. The rise of the PLC gave rise to other controllers, such as the programmable automation controller (PAC) and industrial personal computers (IPC).
Today, each of these different controllers is used for specific tasks. Many factors influence the decision of which controller to use in a project.
II. What are PLC, PAC, and IPC?
1. PLC
PLC (Programmable Logic Controllers) primarily focus on logic control and are used for controlling multiple points. PLC are used in single-unit devices such as entry-level dispensing machines, packaging machines, and production line controls. In terms of CPU power requirements, the computational workload is relatively low, and most designs are based on MCUs or ARM processors. When computing power is insufficient, a DSP is added, and when interfaces are limited, an FPGA is added. PLC performance relies on specialized hardware, and application execution is implemented using dedicated hardware chips. This non-universal nature of the hardware limits the system's functional potential and openness. Due to its dedicated operating system, its real-time performance, reliability, and functionality cannot compare to general-purpose real-time operating systems, resulting in the PLC's overall specialized and closed nature. Because PLC user application execution is implemented in hardware, most PLC on the market are dedicated to specific machines and lack much reusability. In 3C product line production, we've seen that after the product cycle is completed, the PLC is stored in the warehouse and decommissioned. Early PLC were notable for having I/O connections, and most even lacked network interfaces. As shown in the figure below, this makes them ideal for dedicated machines.
2. PAC
A PAC (Programmable Automation Controller) not only performs logic control but also focuses on motion control. By connecting motion units via various industrial bus interfaces, these products are designed for more complex industrial equipment, such as semiconductor equipment, high-speed printing equipment, and 3D printing equipment. In terms of CPU power requirements, these devices require more complex computations and floating-point operations, leading many high-end devices to utilize PAC designs. In terms of core computing architecture, products often utilize the x86 architecture due to its openness, while higher-performance products often utilize FPGAs. Compared to PLC, the PID control algorithm used is not optimized for the PLC hardware architecture. The complex algorithms required for real-world motion control require powerful floating-point processors and large amounts of memory, both of which the PAC platform can provide. Engineers must optimize control algorithms beyond simple PID control. This plays a significant role in industrial equipment reuse. The PAC's performance is based on its lightweight control engine, a standard, universal, and open real-time operating system, and high-performance computing hardware system design. Its openness and flexibility lay a solid foundation for future "software-defined production."
3. IPC
IPC (industrial personal computer) is often translated as "industrial control computer" (IP CAMERA is also a common abbreviation for IPC, but this is beyond the scope of this article). However, the term "industrial control computer" is inaccurate and should be considered an "industrial computer." It is widely applicable to computers used in non-home personal environments, such as all-in-one computers and heads-up displays in factories. PCs used for tasks that do not affect production can be suitable for IPC. However, in core factory control applications, these computers often cannot be used. They require higher reliability, stability, and electrical parameters. While they may appear somewhat similar in appearance, they differ significantly in terms of interface processing, physical wiring, and software requirements.
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III. What are the differences between PLC, PAC, and IPC?
Pros and Cons of PLC
PLC offer many advantages over previous technologies and are robust and reliable. However, they only have a microcontroller, resulting in limited logic capacity.
These limitations make them less suitable for complex applications requiring motion control. To implement motion control, additional modules must be added to the PLC. Alternatively, a hybrid system consisting of one or more PLC and an industrial PC can be used. Therefore, PLC are well suited for small automation projects that perform simple tasks.
Advantages and Disadvantages of PLC
IPC, also known as Industrial PCs, made their debut in the 1990s. They offered users the ability to run PLC-style applications on regular PC operating systems.
Initially, the first IPC faced challenges in harsh factory environments and had stability issues with their operating systems. However, the latest versions have addressed these issues and are now effectively utilized in larger applications. They can be used alone or in conjunction with one or more PLC. However, if in the 1990s it seemed that IPC were about to take over, it is now clear that PAC are leading the field.
Advantages of PAC
PAC offer the same advantages as hybrid systems, but without the added hardware. They have two or more microcontrollers installed and feature more complex logic systems than PLC. Therefore, they can operate in multiple areas, such as motion, discrete, and process control, using a single platform. They also offer better integration with SCADA[3], which enables them to manage complex industry-specific instructions.
IV. PLC, PAC, or IPC: How to Choose the Right Controller for Your Application
In terms of the implementation difficulty of PLC, PAC, and IPC, PLC implementation requires both hardware knowledge and deep expertise in industrial embedded software. Most PLC are typically implemented by embedded engineers. They cater to specific industry needs, and many local companies have domestically produced them. They come with closed application software programming and are widely used in specialized automation equipment.
IPC are currently the easiest to implement. However, if used in core equipment, subsequent debugging costs are very high. Most systems are Windows-based and come with no accompanying software.
Due to their openness and adaptability, PAC have relatively high implementation requirements. They require both hardware and BIOS, RTOS, industrial application software, and excellent project management skills to design PAC suitable for a wide range of industrial equipment. Their open application software programming is widely used in advanced manufacturing equipment, but currently, they are primarily imported. Choosing between PLC, PAC, and IPC involves many factors, including budget, scale, support, complexity, and future scalability.
In terms of applicability within a factory environment, IPC can be used for computing equipment when production won't be impacted, or when multiple equipment restarts are tolerated.
When production speed and quality may be affected, PLC or PAC should be used.
If the production line primarily relies on logic control, a PLC should be used.
In terms of automation level, PAC should be used for high-level automation and reliability applications (such as semiconductor production equipment and industrial printing presses).
A simpler approach is to consider the number of motor axes you need to control: for fewer than eight axes, a PLC is preferred, while for more than 16 axes, a PAC is preferred.
Although implementing multiple PLC simplifies maintenance with just one PAC, multiple PLC can be more complex. While PAC are simple to use and maintain, they require a high level of software proficiency from electrical engineers.
V. Summary
With the growing demand for automation in the manufacturing industry, PLC, PAC, and IPC each play an important role. PLC are suitable for simple control tasks, while PAC excel in highly complex and high-precision applications, particularly in motion control and high-end equipment. IPC offer advantages in computing power and flexibility, but are primarily used in auxiliary systems. In the future, with the advancement of smart manufacturing and digital transformation, PAC are likely to become the mainstream choice, while PLC and IPC will continue to demonstrate their respective strengths in specific scenarios.
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