Stepping motors, as an open-loop control system, are inherently linked with modern digital control technology. In current domestic digital control systems, the application of stepping motors is widespread. With the emergence of all-digital AC servo systems, AC servo motors are increasingly being used in digital control systems as well. To adapt to the trend of digital control development, most motion control systems use stepping motors or all-digital AC servo motors as actuator motors. This article compares the performance of the two.
One, Different control accuracy
Two-phase hybrid stepper motors typically have a step angle of 1.8° or 0.9°, while five-phase hybrid stepper motors usually have a step angle of 0.72° or 0.36°. Some high-performance stepper motors can achieve even smaller step angles through microstepping. SANYO DENKI's two-phase hybrid stepper motors offer a step angle selection of 1.8°, 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, and 0.036° via a dip switch, compatible with both two-phase and five-phase hybrid stepper motor step angles.
Control precision of the交流 servo motor is guaranteed by the rotating encoder at the rear end of the motor shaft. Taking the Yaskawa full digital AC servo motor as an example, for motors equipped with a standard 2000-line encoder, the pulse resolution is 360°/8000 = 0.045° due to the internal four-fold frequency technology in the driver. For motors with a 17-bit encoder, the driver completes one revolution of the motor for every 131072 pulses received, resulting in a pulse resolution of 360°/131072 = 0.0027466°, which is 1/655th of the pulse resolution of a stepper motor with a step angle of 1.8°.
Low Frequency Characteristics Vary
Stepper motors often exhibit low-frequency vibration at low speeds. The vibration frequency is related to the load conditions and the performance of the driver, and it is generally considered to be half the starting frequency of the motor when it is unloaded. This low-frequency vibration phenomenon, determined by the working principle of stepper motors, is highly detrimental to the normal operation of machinery. When stepper motors operate at low speeds, damping techniques should generally be employed to overcome the low-frequency vibration, such as adding a damper to the motor or using microstepping technology on the driver.
The AC servo motor operates extremely smoothly, even at low speeds without any vibration. The AC servo system features resonance suppression capabilities, covering the mechanical rigidity deficiencies, and internally possesses a frequency analysis function (FFT) to detect the mechanical resonance points, facilitating system adjustments.
