Electric spindle is a new technology in the field of CNC machine tools that combines spindle and spindle motor. It, together with linear motor technology and high-speed cutting tool technology, has pushed high-speed machining into a new era. Electric spindle is a set of components, including the electric spindle itself and its accessories: electric spindle, high-frequency frequency converter, oil mist lubricator, cooling device, built-in encoder, tool changer, etc. The transmission structure of "combining the spindle motor with the spindle of the machine tool" makes the spindle components relatively independent of the transmission system and the overall structure of the machine tool, so it can be made into a "spindle unit", commonly known as "electric spindle", which has the characteristics of high speed, high precision and low noise. The structure of the inner ring with a lock is more suitable for spray lubrication. The rotor of the motor is directly used as the spindle of the machine tool, and the housing of the spindle unit is the motor base, which cooperates with other components to achieve the integration of the motor and the machine tool spindle.

With the rapid development and improvement of electric transmission technology (frequency conversion speed regulation technology, motor vector control technology, etc.). ）The mechanical structure of the main transmission system of high-speed CNC machine tools has been greatly simplified, and belt pulley transmission and gear transmission have been basically eliminated. The spindle of the machine tool is directly driven by a built-in motor, thereby shortening the length of the main transmission chain of the machine tool to zero and achieving "zero transmission" of the machine tool. The transmission structure of the spindle motor and the machine tool spindle is integrated into one, making the spindle components relatively independent of the transmission system and overall structure of the machine tool. Therefore, it can be made into a "spindle unit", commonly known as "electric spindle" or "electric spindle". At present, electric spindles mainly use AC high-frequency motors, so they are also known as "high-frequency spindles". Because there is no intermediate transmission link, it is sometimes called "DirectDriveSpindle".

In CNC machine tools, the electric spindle usually adopts the method of variable frequency speed regulation. There are currently three main control methods: ordinary variable frequency drive control, vector control drive control, and direct torque control.

Conventional frequency conversion is a scalar drive control, characterized by constant torque drive and output power proportional to speed. The dynamic performance of ordinary variable frequency control is not ideal, the control performance is poor at low speeds, the output power is not stable enough, and it does not have C-axis function. But the price is cheap, the structure is simple, and it is generally used for grinding machines and ordinary high-speed milling machines.

Vector control technology imitates the control method of DC motors, using rotor magnetic field orientation and vector transformation to achieve driving and control, with good dynamic performance. The vector control driver has a large torque value in the initial start-up stage, and the electric spindle itself has a simple structure and low inertia, so the start-up acceleration is large. After start-up, it can instantly reach the allowable maximum speed. This type of driver has two types: open-loop and closed-loop. The latter can achieve position and velocity feedback, not only with better dynamic performance, but also with C-axis functionality; However, the former has poor dynamic performance and does not have C-axis functionality, but its price is relatively cheap.

Direct torque control is a new high-performance AC speed regulation technology developed after vector control technology. Its control concept is novel, the system structure is simple and clear, and it is more suitable for driving high-speed electric spindles, which can better meet the dynamic and static characteristics requirements of high-speed electric spindles, wide speed range, and high-speed instantaneous shutdown. It has become a popular technology in the field of AC transmission.