Performance comparison between servo motor and stepper motor - News - Global IC Trade Starts Here Free Join
Stepper motors are widely used in modern digital control systems as an open-loop control mechanism. However, with the development of all-digital AC servo systems, AC servo motors have become more common in such applications. To keep up with this trend, many motion control systems now use either stepping motors or fully digital AC servo motors as their primary actuators. Although both types share similar control methods—using pulse and direction signals—they differ significantly in performance and application scenarios. Here’s a detailed comparison between the two.
First, control precision varies greatly between the two. A typical two-phase hybrid stepper motor has a step angle of 1.8° or 0.9°, while a five-phase hybrid motor usually has a smaller step angle of 0.72° or 0.36°. Some high-performance stepper motors can even achieve smaller step angles through subdivision techniques. For example, SANYO DENKI's two-phase hybrid motor allows users to set step angles as small as 0.036° via a DIP switch, offering compatibility with both two-phase and five-phase configurations.
In contrast, AC servo motors rely on a rotary encoder at the motor shaft for precise positioning. A standard 2000-line encoder provides a pulse equivalent of 0.045° when using quadrature frequency technology. For a 17-bit encoder, the pulse equivalent is even finer at approximately 0.0027466°, which is about 1/655th of the pulse equivalent of a 1.8° step motor. This level of precision makes AC servo motors ideal for high-accuracy applications.
Second, low-speed performance differs significantly. Stepper motors tend to experience low-frequency vibration at slow speeds, which can affect system stability. This issue is often mitigated by adding dampers or using subdivision techniques. On the other hand, AC servo motors operate smoothly even at low speeds, thanks to built-in resonance suppression features and frequency analysis capabilities (FFT), making them more reliable in dynamic environments.
Third, torque characteristics vary. Stepper motors lose torque rapidly as speed increases, limiting their maximum operating speed to around 300–600 RPM. In contrast, AC servo motors maintain constant torque up to their rated speed (typically 2000–3000 RPM) and transition to constant power output beyond that. This makes them more suitable for high-speed, high-torque applications.
Fourth, overload capacity also sets them apart. Stepper motors typically lack overload capability, while AC servo motors can handle significant torque peaks—up to two to three times their rated torque. This allows them to overcome inertial loads during startup, reducing the need for oversized motors and improving energy efficiency.
Fifth, operational performance is another key factor. Stepper motors operate in an open-loop system, which means they may lose steps or stall if the load is too high or the speed is too fast. AC servo motors, however, use closed-loop control with feedback from the encoder, ensuring more accurate and stable operation under varying conditions.
Sixth, speed response time is a major advantage of AC servo systems. While a stepper motor may take 200–400 milliseconds to reach its working speed, an AC servo motor like Shanyang's 400W model can accelerate from 0 to 3000 RPM in just a few milliseconds. This rapid response makes them ideal for applications requiring quick start-stop cycles.
In summary, while AC servo motors offer superior performance in terms of precision, torque, and speed, stepper motors still have their place in cost-sensitive or less demanding applications. When designing a control system, it’s important to consider factors like performance requirements, budget, and application environment to choose the most suitable motor type.
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