The turning electric spindle is a new technology that integrates the machine tool spindle with the spindle motor, emerging in the CNC machine tool field. Alongside linear motor technology and high-speed tooling technology, it propels high-speed machining into a new era. The electric spindle is a set of components, including the electric spindle itself and its accessories: the electric spindle, high-frequency inverter, oil mist lubricator, cooling unit, built-in encoder, tool changing device, etc. The motor's rotor is directly used as the machine tool's spindle, with the spindle unit's housing serving as the motor base, thereby achieving integration of the motor and the machine tool spindle.

Currently, with the rapid development and improvement of electrical transmission technology (such as variable frequency speed regulation technology, motor vector control technology, etc.), the mechanical structure of the high-speed CNC machine tool's main drive system has been greatly simplified, and belt drives and gear drives have basically been eliminated. The machine tool spindle is directly driven by an internal motor, thus reducing the length of the machine tool's main drive chain to zero, achieving the "zero drive" of the machine tool. This drive structure, where the spindle motor and the machine tool spindle are combined into one, makes the spindle component relatively independent from the machine tool's drive system and overall structure, thus allowing it to be made into a "spindle unit," commonly known as an "electric spindle." As the electric spindle mainly uses AC high-frequency motors at present, it is also called a "high-frequency spindle." Due to the absence of intermediate transmission stages, it is sometimes referred to as a "direct drive spindle."