We all know that the controller of the CNC shaped sponge cutting machine uses a CNC cutting system to manage operations—specifically, it controls the entire device via a programmable controller—enabling the machine to precisely cut out a wide variety of shapes.

　　Sponge Cutting Machine Controller Chassis

　　A Programmable Logic Controller (PLC) has two key operational aspects: input/output information transformation and reliable physical implementation. The transformation of input/output information is primarily achieved through programs stored in the PLC's memory. These programs include both system-level programs—also known as monitoring programs or CNC operating systems—and user-defined programs. System programs provide users with an editing and execution platform for their custom programs, while also handling essential common tasks such as self-checks, I/O refreshes, and communication with peripherals, host computers, or even other PLCs. On the other hand, user programs are designed by the end user according to specific control requirements. In essence, the type of control desired directly determines the nature of the corresponding user program.

　　Reliable physical implementation is primarily achieved through input (I, INPUT) and output (O, OUTPUT) circuits. Each input or output point is equipped with its own dedicated I or O circuit. Moreover, multiple such circuits are always integrated into a single module (or enclosure), which is then combined with other modules to form the PLC's complete I/O system (circuitry). Although these modules are quite numerous—accounting for most of the PLC's overall volume—they remain compact due to their highly integrated design. As a result, the PLC itself doesn’t end up being particularly large.

　　The input circuit continuously monitors the (connected, ON) or (disconnected, OFF) status of the input point and temporarily stores this state in its input latch (which may also be referred to by other names). Each input point has a corresponding input latch.

　　The output circuit includes an output latch (which may also go by other names). It has two states—high and low potentials—and can be latched. Additionally, it features a corresponding physical circuit that transmits these high- or low-potential states to the output points. Each output point is equipped with its own dedicated output latch.

　　The input latches and output latches here are actually the registers of the PLC’s I/O circuitry. They exchange information with the PLC’s memory via the PLC’s I/O bus, facilitated by the system program running on the PLC.

　　Reading the information from the input register into the PLC's memory is called "input refresh." The PLC's memory includes a specially designated mapping area dedicated to storing input information. Each corresponding bit in this area is referred to as an input relay, also known as a soft contact or the process-image input register. When these bits are set to 1, it indicates that the contact is closed; when set to 0, it means the contact is open. Since their state is determined by the input refresh process, they accurately reflect the current status of the input points.

　　The output latch also corresponds to the output mapping area in the PLC memory. Each output latch has an associated memory bit, known as the output relay, output coil, or process-image output register. Through the PLC I/O bus and the running system program, the status of the output relay is mapped to the corresponding output latch. This mapping process is also referred to as output refresh.

　　A PLC not only has input circuits capable of receiving switch signals, but sometimes it also includes input circuits designed to handle analog signals. However, the latter first require analog-to-digital conversion before the converted data can be stored in the PLC’s corresponding memory unit.

　　To generate analog output, an analog output circuit (referred to as an analog output module or unit) must be equipped. This circuit performs digital-to-analog conversion on the contents of the corresponding memory unit in the PLC, thereby producing the output signal.

　　In this way, the program the user needs to write is simply a transformation—from the memory area associated with PLC inputs to the memory area associated with outputs. This is essentially a data and logic-processing task. Given the PLC’s robust instruction set, it’s entirely feasible to develop a program that meets this requirement.