Briefly describe the three performance differences between servo motor and stepper motor
As an open-loop control system, stepper motors are intrinsically linked to modern digital control technology. In the current domestic digital control system, the application of stepper motors is very extensive. With the advent of all-digital AC servo systems, AC servo motors are increasingly being used in digital control systems. In order to adapt to the development trend of digital control, stepping motor or all-digital AC servo motor is mostly used as the execution motor in the motion control system.
Although the two are similar in control mode (burst and direction signals), there are large differences in performance and application. Kunma Electromechanical has been focusing on the electromechanical industry for many years. It has rich experience in the selection and maintenance of industrial control products. Now we compare the performance of the two.
Different control accuracy
The step angle of the two-phase hybrid stepping motor is generally 1.8° and 0.9°, and the step angle of the five-phase hybrid stepping motor is generally 0.72° and 0.36°. There are also some high performance stepper motors that have smaller step angles after subdivision. The two-phase hybrid stepping motor produced by SANYODENKI can be set to 1.8°, 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, 0.036° through the DIP switch. Compatible with the step angle of two-phase and five-phase hybrid stepping motors.
The control accuracy of the AC servo motor is guaranteed by the rotary encoder at the rear of the motor shaft. Taking Sanyo's all-digital AC servo motor as an example, for a motor with a standard 2000-line encoder, the pulse equivalent is 360°/8000=0.045° due to the quadruple frequency technology inside the driver. For a motor with a 17-bit encoder, the drive receives one revolution of 131072 pulse motors, ie its pulse equivalent 360°/131072=0.0027466°, which is the pulse equivalent of a stepper motor with a step angle of 1.8°. /655.
Different low frequency characteristics
Stepper motors are prone to low frequency vibration at low speeds. The vibration frequency is related to the load condition and the performance of the driver. It is generally considered that the vibration frequency is half of the take-off frequency of the motor no-load. This low frequency vibration phenomenon, which is determined by the working principle of the stepper motor, is very detrimental to the normal operation of the machine. When the stepper motor works at low speed, damping technology should generally be used to overcome the low frequency vibration phenomenon, such as adding a damper to the motor or using subdivision technology on the drive. The AC servo motor runs very smoothly, and vibration does not occur even at low speeds. The AC servo system has a resonance suppression function, which can cover the rigidity of the machine, and has a frequency analysis function (FFT) inside the system, which can detect the resonance point of the machine and facilitate system adjustment.
Different moment frequency characteristics
The output torque of the stepping motor decreases as the speed increases, and it drops sharply at higher speeds, so the maximum operating speed is generally 300-600 RPM. The AC servo motor is a constant torque output, that is, it can output the rated torque within its rated speed (generally 2000RPM or 3000RPM), and it is a constant power output above the rated speed.
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