1. Performance Comparison of Servo Motors and Stepper Motors Stepper motors, as an open-loop control system, are fundamentally linked to modern digital control technology. They 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 they 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 1.8° and 0.9°, while five-phase hybrid stepper motors typically have step angles of 0.72° and 0.36°. Some high-performance stepper motors also have even smaller step angles after microstepping. For example, the step angle of a two-phase hybrid stepper motor produced by SANYO DENKI can be set to 1.8°, 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, and 0.036° via a DIP switch, making it compatible with the step angles of both two-phase and five-phase hybrid stepper motors. The control accuracy of an AC servo motor is ensured by a rotary encoder at the rear of the motor shaft. Taking a SANYO all-digital AC servo motor as an example, for a motor with a standard 2000-line encoder, due to the quadruple frequency technology used in the driver, its pulse equivalent is 360°/8000 = 0.045°. For a motor with a 17-bit encoder, the motor rotates once for every 131072 pulses received by the driver, meaning its pulse equivalent is 360°/131072 = 0.0027466°, which is 1/655 of the pulse equivalent of a stepper motor with a step angle of 1.8°. II. Different Low-Frequency Characteristics 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 of the motor's no-load starting frequency. This low-frequency vibration, determined by the working principle of stepper motors, is very detrimental to the normal operation of the machine. When stepper motors operate at low speeds, damping techniques should generally be used to overcome low-frequency vibration, such as adding dampers to the motor or using microstepping technology in the driver. AC servo motors operate very smoothly and do not vibrate even at low speeds. AC servo systems have resonance suppression capabilities, which can cover insufficient mechanical rigidity, and the system has a frequency response time (FFT) function to detect mechanical resonance points, facilitating system adjustment. III. Different Torque-Frequency Characteristics The output torque of a stepper motor decreases as the speed increases, and drops sharply at higher speeds. Therefore, its maximum operating speed is generally between 300 and 600 RPM. AC servo motors provide constant torque output, meaning they output rated torque up to their rated speed (typically 2000 RPM or 3000 RPM), and constant power output above that speed. IV. Different Overload Capabilities Stepper motors generally lack overload capacity. AC servo motors have strong overload capacity. Taking the Sanyo AC servo system as an example, it has speed and torque overload capabilities. Its maximum torque is two to three times its rated torque, which can be used to overcome the inertial torque of inertial loads at startup. Because stepper motors lack this overload capacity, a larger torque motor is often selected to overcome this inertial torque during selection, while the machine does not need such a large torque during normal operation, resulting in wasted torque. V. Different Operating Performance Stepper motors use open-loop control. Excessive starting frequency or 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 use closed-loop control. The driver can directly sample the encoder feedback signal, forming internal position and speed loops. Generally, the missed steps or overshoot issues 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 their operating speed (typically several hundred revolutions per minute). AC servo systems have better acceleration performance. For example, a Sanyo 400W AC servo motor can accelerate from a standstill to its rated speed of 3000 RPM in just a few milliseconds, making it suitable for applications requiring rapid start and stop. In summary, AC servo systems are superior to stepper motors in many performance aspects. However, stepper motors are still frequently used as actuators in some less demanding applications. Therefore, in the design process of a control system, factors such as control requirements and cost must be comprehensively considered to select an appropriate control motor. 2. Servo Motor Selection Calculation Method Note three points: 1. Rotation speed: Based on the customer's actual requirements, motors with different rotation speeds can be selected for the same power. Generally, the lower the rotation speed, the cheaper the price. 2. Torque: Must meet actual needs, but does not need excessive margin like stepper motors. 3. Inertia: Select motors with different inertia based on site requirements. For example, the machine tool industry generally uses P1 series high-inertia servo motors.