Analysis of the characteristics of built-in PLC and independent PLC

Programmable controllers are essential components in CNC devices due to their valuable features, such as a customizable control program, high flexibility, ease of programming using process-oriented languages, comprehensive functionality, convenient expansion, and flexible configuration. They also offer simple system setup, making installation and debugging straightforward. Their reliability makes them an indispensable part of modern CNC systems. There are two main types of PLCs used in CNC machines: built-in PLCs and stand-alone PLCs.

The built-in PLC has several key characteristics:

(1) Its performance is determined by the specifications of the associated CNC device. The hardware and software are designed as core functions of the CNC system, offering a compact structure and strong adaptability.

(2) It typically uses either a shared microprocessor with the CNC or a dedicated one. In the former case, the PLC utilizes the remaining processing power of the CNC’s microprocessor, resulting in fewer I/O points. In the latter case, it has its own independent microprocessor, which is ideal for complex sequence control and high-speed operations.

(3) It is installed in the same chassis as other CNC circuits and shares the same power supply and grounding system.

(4) The hardware can be integrated onto the same printed circuit board as the CNC circuits or added as a separate module.

(5) It does not have a separate I/O interface; instead, it uses the I/O interface provided by the CNC device itself.

(6) Built-in PLCs enhance the communication capabilities of the CNC system. They support advanced control functions like ladder logic editing and transmission, offering a cost-effective solution that improves the overall performance-to-price ratio.

On the other hand, stand-alone PLCs have their own set of advantages:

(1) They can be custom-purchased or developed based on specific control requirements of the CNC machine, offering greater flexibility.

(2) These PLCs come with their own I/O interface circuits, allowing them to connect with both the CNC device and the machine side through these interfaces. They often use a modular design, housed in a plug-in cage, enabling easy expansion or reduction of I/O points by adding or removing modules.

(3) Stand-alone PLCs allow for enhanced control functions, such as supporting additional axis controls beyond the standard CNC setup.

(4) While they provide more flexibility, their performance-to-price ratio is generally not as favorable as that of built-in PLCs.