How CNC machines are so precise?

#CNC machine, #CNC machining,
A semi-closed-loop system is a combination of a closed-loop system and an open-loop system.
Imagine a scenario where a delivery person constantly updates you on their specific location. You can instantly instruct them to turn left or right, accelerate or stay still. This kind of control system, where instructions are issued, executed, results are returned, and adjustments are made, is a closed-loop system. On the other hand, if a delivery person only informs you that they've started their journey to your house without disclosing their route or whereabouts, you lack complete control over their actions. This type of control system, where instructions are issued but no result feedback is received, is an open-loop system. Clearly, closed-loop systems are more precise and controllable. CNC machine tools use a closed-loop system from the controller to the servo motor, and then an open-loop system from the servo motor to the load.
The specific control system consists of several components:
• Human-Machine Interface: Typically a screen with buttons and indicator lights. The human-machine interface converts the operator's intentions into language the controller can understand and sends it to the controller.
• Controller: Responsible for logically processing instructions from the human-machine interface and sending commands to the driver (e.g., speed, position, etc.).
• Driver: Converts instructions from the controller into specific voltage and current to drive the servo motor.
• Servo Motor: Receives pulse current from the driver, rotates, and drives the rotation through ball bearings.
• Internal Encoder: The servo motor contains an encoder, primarily to provide feedback signals such as speed and position to the driver.
• Ball Bearings: Convert rotary motion into linear motion, driving the load to move at a specified speed to a designated position.
From the controller to the rotating servo motor, this forms a complete closed-loop system. From the motor's rotation to the load's movement is an open-loop system. In the entire control system, the most critical component is likely the grating encoder. Imagine a disk, part of it blocked, and part of it unblocked. A laser beam is directed at this disk, with a photosensitive element on the other side. If the laser passes through, the photosensitive element outputs 1; if the laser is blocked, it outputs 0. As the disk synchronously rotates with the servo motor, based on the output sequence of 010101..., we can determine the servo motor's position, speed, and other parameters. Clearly, if a circular ring is divided into two halves, we can only determine if the motor has rotated 180 degrees. If divided into quarters, we know which 90-degree section it's in. Modern servo motor encoders can divide a circle into thousands or even millions of parts. This allows us to precisely know the servo motor's position, speed, and other parameters.