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A stepper motor is a device for discrete motion, and it is inherently connected to modern digital control technology. In current domestic digital control systems, stepper motors are widely used. With the emergence of fully digital AC servo systems, AC servo motors are also being used more and more in digital control systems. To keep up with the development trends of digital control, stepping motors or fully digital AC servo motors are commonly used as actuator motors in motion control systems. Although the two share similar control methods (pulse trains and direction signals), there are significant differences in their performance and application areas. A comparison of their performance is now made. The control precision varies. The step angle of two-phase hybrid stepper motors is generally 3.6 degrees or 1.8 degrees, while that of five-phase hybrid stepper motors is usually 0.72 degrees or 0.36 degrees. There are also some high-performance stepper motors with a smaller step angle. For example, a stepper motor produced by SITONG for slow-speed wire cutting machines has a step angle of 0.09 degrees ； The three-phase hybrid stepper motors produced by the German company BERGER LAHR have a step angle that can be set to 1.8 degrees, 0.9 degrees, 0.72 degrees, 0.36 degrees, 0.18 degrees, 0.09 degrees, 0.072 degrees, and 0.036 degrees using a DIP switch; they are compatible with the step angles of both two-phase and five-phase hybrid stepper motors. The control accuracy of the AC servo motor is ensured by the rotary encoder at the rear end of the motor shaft. Taking the **fully digital AC servo motor as an example, for a motor equipped with a standard 2500-line encoder, thanks to the quadrupling technique used inside the driver, its pulse equivalent is 360 degrees/10000 = 0.036 degrees. For a motor equipped with a 17-bit encoder, the driver receives 217=131072 pulses per rotation of the motor; thus its pulse equivalent is 360 degrees/131072=9.89 seconds. It is 1/655 of the pulse equivalent of a stepper motor with a step angle of 1.8 degrees. Different low-frequency characteristics: Stepper motors are prone to low-frequency vibration at low speeds. The vibration frequency is related to the load conditions and the performance of the driver; it is generally considered to be half of the motor’s no-load starting frequency. This low-frequency vibration phenomenon, determined by the working principle of stepper motors, is very detrimental to the proper operation of the machine. When a stepper motor operates at low speeds, damping techniques are generally used to overcome low-frequency vibrations, such as installing dampers on the motor or using microstepping technology in the driver. AC servo motors operate very smoothly, with no vibration even at low speeds. AC servo systems have resonance suppression capabilities that can address insufficient mechanical stiffness, and they are equipped with a frequency analysis function (FFT) that allows the detection of the machine’s resonance points, facilitating system adjustment. The torque-frequency characteristics are different: The output torque of a stepper motor decreases as the speed increases, and this decrease becomes more significant at higher speeds; therefore, its maximum operating speed is generally between 300 and 600 RPM. AC servo motors provide constant torque output; that is, within their rated speed range (usually 2000 RPM or 3000 RPM), they can deliver the rated torque, while above the rated speed they offer constant power output. Different overload capacities: