CNC servo system is the executive body of CNC milling machine. It is the hub of connecting CNC system and machine tool. It is an automatic control system for controlling the position and speed of moving parts of milling machine (such as table, tool holder and so on). In general, the servo system is called a servo axis for feed motion control. Servo shaft with a linear axis (such as table, knife, etc.) and rotary shaft (such as CNC rotary table, etc.). The servo axis is to perform positioning and feed functions, involving position and speed control. CNC milling machine spindle only involves speed control, mainly to achieve spindle speed and torque output. When the spindle has position control (such as spindle positioning and other axis interpolation), the spindle is called the servo spindle, also known as the Cs axis.
In order to enable the moving parts to reach the position specified by the machining instructions quickly, accurately and stably, the servo system has open-loop, closed-loop and semi-closed-loop types depending on the presence or absence of position detection and feedback, and position feedback.
Open loop servo system is suitable for stepping servo system without position and speed detection. The CNC system will position command interpolation to get the pulse output to the stepper driver, signal processing and power amplifier driving machine stepper motor driven ball screw feed movement, the pulse number determines the moving distance of the worktable, pulse frequency determines the feed speed of working table. Because there is no position and speed detection, so the CNC milling machine worktable can not get the actual moving distance and speed, position accuracy by step angle, screw precision stepper motor and mechanical transmission, gap stiffness and other factors influence, position precision is relatively low, but the stability of open loop servo system is better.