A stepper motor is a discrete motion device, fundamentally linked to modern digital control technology. Stepper motors are widely used in current domestic digital control systems. With the emergence of fully digital AC servo systems, AC servo motors are increasingly being applied in digital control systems. To adapt to the development trend of digital control, most motion control systems use stepper motors or fully digital AC servo motors as actuators. Although both are similar in control methods (pulse trains and direction signals), there are significant differences in their performance and application scenarios. A comparison of their performance is presented below. I. Different Control Accuracy Two-phase hybrid stepper motors typically have step angles of 3.6° and 1.8°, while five-phase hybrid stepper motors typically have step angles of 0.72° and 0.36°. Some high-performance stepper motors also have smaller step angles, such as a stepper motor for wire EDM machines produced by Beijing Hollysys Motor Technology Co., Ltd. (formerly Sitong Motor), with a step angle of 0.09°. Three-phase hybrid stepper motors can have their step angles set via DIP switches to 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, 0.036°, etc., compatible with the step angles of two-phase and five-phase hybrid stepper motors. The control accuracy of AC servo motors is ensured by a rotary encoder at the rear end of the motor shaft. Taking a certain imported brand motor as an example, a motor with a standard 2500-line encoder has a pulse equivalent of 360°/10000 = 0.036° due to the use of quadruple frequency technology in the driver. However, for a motor with a 17-bit encoder, the motor rotates once for every 2^17 = 131072 pulses received by the driver, meaning its pulse equivalent is 360°/131072 = 9.89 seconds. This is 1/655 of the pulse equivalent of a stepper motor with a step angle of 1.8°. Secondly, the low-frequency characteristics differ . Stepper motors are prone to low-frequency vibration at low speeds. The vibration frequency is related to the load and driver performance, and is generally considered to be half the motor's no-load starting frequency. This low-frequency vibration, determined by the working principle of the stepper motor, is very detrimental to the normal operation of the machine. When a stepper motor operates at low speeds, damping technology should generally be used to overcome low-frequency vibration, such as adding a damper to the motor or using microstepping technology in the driver. AC servo motors operate very smoothly, without vibration even at low speeds. AC servo systems have resonance suppression capabilities, covering insufficient mechanical rigidity, and internal frequency analysis (FFT) functionality to detect mechanical resonance points, facilitating system adjustments. III. Different Torque-Frequency Characteristics Stepper motors' output torque decreases with increasing speed, dropping sharply at higher speeds, thus their maximum operating speed is generally 300-600 RPM. AC servo motors provide constant torque output, meaning they output rated torque up to their rated speed (typically 2000 or 3000 RPM), and constant power output above the rated speed. IV. Different Overload Capabilities Stepper motors generally lack overload capability. AC servo motors have strong overload capability. Taking the Senchuang AC servo system as an example, it has speed overload and torque overload capabilities. Its maximum torque is three times the rated torque, which can be used to overcome the inertial torque of inertial loads at startup. Because stepper motors lack overload capacity, a larger torque motor is often selected to overcome this inertial torque during selection. However, the machine does not need such a large torque during normal operation, resulting in wasted torque. V. Different Operating Performance Stepper motor control is open-loop control. Excessive starting frequency or heavy load can easily lead to missed steps or stalling. Excessive stopping speed can cause overshoot. Therefore, to ensure control accuracy, acceleration and deceleration must be carefully managed. AC servo drive systems are closed-loop control. The driver can directly sample the encoder feedback signal, forming internal position and speed loops. Generally, the missed steps or overshoot of stepper motors are not present, resulting in more reliable control performance. VI. Different Speed ​​Response Performance Stepper motors require 200-400 milliseconds to accelerate from a standstill to operating speed (typically several hundred revolutions per minute). AC servo systems have better acceleration performance. For example, a 400W AC servo motor from a certain brand can accelerate from a standstill to its rated speed of 3000 RPM in just a few milliseconds, making it suitable for control applications requiring rapid start and stop. In summary, AC servo systems outperform stepper motors in many aspects. However, stepper motors are often used as actuators in less demanding applications. Therefore, the design of a control system must comprehensively consider factors such as control requirements and cost to select an appropriate control motor.