How does a CNC machine work

A CNC machine utilizes a dedicated computer known as the Controller, which manages most of the functions and stores programs in its memory. Working in harmony with the Controller are two other components: the Programmable Logic Controller (PLC) and the Servo amplifier & motor. The PLC can be integrated into the CNC Controller or function as a separate unit, providing external support. The servo drive or amplifier supplies the necessary voltage to the servo motors, enabling the machine's axes to move as required. When a command is sent from the Controller, it goes directly to the Servo amplifier unit, which provides the required voltage for axis movement by rotating a servo mechanism linked to the machine axes. The PLC supplies the necessary voltage to energize output elements and actuators such as relays, solenoids, and contactors, enabling various operations like starting an induction motor, controlling coolant flow, automatic workpiece changing, and opening a door. These are miscellaneous functions typically controlled by a PLC.

To ensure the successful completion of the work, the CNC machine continuously monitors the process. Feedback mechanisms are employed, which involve the use of position and velocity feedback devices such as Linear Scales, Encoders, and Resolvers, along with the axis movement path or servo motor shaft. Additionally, sensors like proximity switches, limit switches, pressure switches, and float switches are utilized to monitor different conditions or states of the machine, such as checking if machine doors are closed or if coolant is active. Each operation performed by the CNC machine is continuously monitored, and the confirmed information is sent to the Controller through specific feedback devices. This is why the CNC system is referred to as a closed-loop system. The absence of feedback signals to the Controller generates various fault messages, depending on the type of missing feedback. The block diagram provided illustrates the structure of a CNC machining center.

Upon examining the block diagram, it becomes evident that the CNC Controller serves as the central control unit of the CNC system, working in conjunction with the PLC to carry out all operations. Miscellaneous command information is sent to the Controller through an Operator panel, Numeric keyboard, or Machine control panel. The Monitor displays real-time information about axis position, program details, and any fault messages. Commands for axis movement or spindle rotation are directly transmitted from the Controller to the Spindle & Axes Servo drives, and the servo drives generate the necessary voltages to rotate the Servo Motors. The axis servo motor rotates a Ball-screw, which is connected to the motor shaft via a Coupling, enabling the machine axis or bed to move to the desired position. Simultaneously, the servo motor relays the position and velocity information of the axis movement directly to the Controller and Servo amplifier. The spindle servo motor rotates the cutting tool at high speeds and removes material from the workpiece through a shearing process, achieved through relative movement of the axes. The PLC is responsible for handling input elements or sensors and output elements or actuators associated with auxiliary functions related to the machine. Input elements or sensors provide information about the physical state of a machine part, which is then transmitted as an electrical signal to the Controller through the PLC. Output elements or actuators are employed to modify the physical status of the machine or perform auxiliary functions under the control of the PLC.