The difference between stepper motor and servo motor
Release time:
2023-04-03
Stepper motor as an open-loop control system, and modern digital control technology has an essential link. In the current domestic digital control system, stepper motor is widely used. With the emergence of all-digital AC servo systems, servo motors are increasingly used in digital control systems. In order to adapt to the development trend of digital control, the motion control system mostly uses stepper motor or digital AC servo motor as the executive motor. Although the two are similar in control mode (pulse and direction signal), there are big differences in performance and application. Now the use of stepper motor and servo motor performance for a comparison.
1. stepper motors and servo motors have different low-frequency characteristics (anti-resonance)
Stepping system is a lack of inherent resonance point, SR series stepper drive automatically calculate the resonance point, and in order to adjust the control algorithm, so as to achieve the purpose of suppressing resonance, greatly improve the stability of the intermediate frequency, making the high-speed when there is a greater torque output, more excellent high-speed performance.
The servo motor runs very smoothly and does not vibrate even at low speeds. The AC servo system has a resonance suppression function, which can make up for the lack of mechanical rigidity, and the system has a frequency resolution function (FFT), which can detect the mechanical resonance point and facilitate system adjustment.
2. working principle
These two kinds of motors are very different in principle. Stepper motors are open-loop control elements that convert electrical pulse signals into angular displacement or linear displacement. Check the working principle of stepper motors.
The servo is mainly positioned by pulses. The servo motor itself has the function of sending out pulses. Therefore, the servo motor will send out a corresponding number of pulses every time it rotates at an angle. In this way, it forms an echo or closed loop with the pulses received by the servo motor. In this way, the system will know how many pulses have been sent and how many pulses have been received back, thus accurately controlling the rotation of the motor and realizing accurate positioning.
3. cost
Stepper motors have advantages in cost performance. To achieve the same function, the price of servo motors is greater than that of stepper motors with the same power; the advantages of high response, high speed and high precision of servo motors determine the high price of products, which is inevitable.
4. running performance
Stepper motors are generally open-loop control, and out-of-step or locked-rotor phenomenon will occur when the starting frequency is too high or the load is too large. Therefore, it is necessary to deal with the speed problem or increase the encoder closed-loop control to see what is closed-loop stepping motor. The servo motor adopts closed-loop control, which is easier to control and does not have out-of-step phenomenon.
5. speed and overload capacity
Stepper motors are prone to low-frequency vibration when running at low speed, so when the stepper motor works at low speed, it is usually necessary to use damping technology to overcome low-frequency vibration, such as adding dampers to the motor or using subdivision technology on the driver, etc. The servo motor does not have this phenomenon, and its closed-loop control characteristics determine its excellent performance when running at high speed. The torque frequency characteristics of the two are different, and the rated speed of the general servo motor is greater than that of the stepper motor. The output torque of the stepper motor will decrease with the increase of the speed, while the servo motor is a constant torque output, so the stepper motor generally has no overload capacity, while the AC servo motor has a strong overload capacity.
In summary, there are big differences between stepper motors and servo motors in terms of working principle, overload capacity, operating performance and cost. However, both have their own advantages. If users want to make a choice, they need to combine their own actual needs and application scenarios.
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