How to correctly choose between servo motors and stepper motors? What are the similarities in performance between servo motors and stepper motors? This article will provide you with some insights into the performance of servo motors and stepper motors:
As an open-loop control system, the stepper motor is fundamentally linked to modern digital control technology. Currently, stepper motors are widely used in digital control systems in China.
With the emergence of fully digital AC servo systems, AC servo motors are increasingly being used 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 their control methods, they differ significantly in performance and application scenarios:
1. Different control precision
① The step angle of a two-phase hybrid stepper motor is generally 1.8° or 0.9°, while the step angle of a five-phase hybrid stepper motor is generally 0.72° or 0.36°. Some high-performance stepper motors have even smaller step angles after microstepping.
② The control accuracy of the AC servo motor is guaranteed by the rotary encoder at the rear end of the motor shaft. For a motor with a 17-bit encoder, the motor rotates once for every 131,072 pulses received by the driver, which means its pulse equivalent is 360/131,072 = 0.0027466°, which is 1/655 of the pulse equivalent of a stepper motor with a step angle of 1.8°.
2. Different low-frequency characteristics
① 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 the stepper motor, is very detrimental to the normal operation of the machine. When the stepper motor is operating at low speed, damping technology should generally be used to overcome the low-frequency vibration, such as adding a damper to the motor or using microstepping technology in the driver.
② The AC servo motor operates very smoothly, without vibration even at low speeds. The AC servo system has resonance suppression capabilities, which can cover insufficient mechanical rigidity, and the system has internal frequency analysis capabilities to detect mechanical resonance points, facilitating system adjustment.
3. Different torque-frequency characteristics
① 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.
② AC servo motors have constant torque output, meaning they can output rated torque up to their rated speed (usually 2000 RPM or 3000 RPM) and constant power output above their rated speed.
