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 variable control programs, excellent flexibility, ease of programming using process-oriented languages, robust 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 programmable controllers used in CNC machine tools: built-in PLCs and stand-alone PLCs.

The built-in PLC has several distinct characteristics:

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

(2) It can either use a shared microprocessor with the CNC or have a dedicated one. In the former case, it utilizes the residual processing power of the CNC’s microprocessor, resulting in fewer I/O points. In the latter case, it uses an independent microprocessor, which is suitable for complex sequence programs and high-speed motion control.

(3) It is housed in the same chassis as other CNC circuits and shares the same power supply and ground connection.

(4) The hardware circuit may be fabricated on the same printed circuit board as other CNC components or designed as an additional board.

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

(6) The built-in PLC enhances the communication capabilities of the CNC system directly. It supports ladder editing, advanced control functions, and offers a cost-effective solution, improving the overall performance-to-price ratio of the CNC system.

On the other hand, stand-alone PLCs also have unique advantages:

(1) They can be purchased or developed flexibly based on the specific control requirements of the CNC machine tools.

(2) These PLCs come with their own I/O interface circuits. The connections between the PLC and the CNC device, as well as between the PLC and the machine side, are managed through these interfaces. Stand-alone PLCs typically have a modular structure, installed in a plug-in cabinet, allowing for flexible I/O point configuration via the addition or removal of modules or boards.

(3) They allow for expanded control functions, enabling the addition of two or more axes for more complex operations.

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