Performance Comparison of Servo Motors and Stepper Motors
As an open-loop control system, the motor has an essential connection with modern digital control technology. In the current domestic digital control system, stepper motors are widely used. With the emergence of all-digital AC servo systems, AC servo motors are increasingly used in digital control systems. In order to adapt to the development trend of digital control, stepper motors or all-digital AC servo motors are mostly used as executive motors in motion control systems. Although the two are similar in control mode (pulse train and direction signal), there are big differences in performance and application occasions.
1. Different control precision
2. Different low frequency characteristics
Stepper motors are prone to low-frequency vibrations at low speeds. The vibration frequency is related to the load condition and the performance of the driver. It is generally believed that the vibration frequency is half of the no-load take-off frequency of the motor. This low-frequency vibration phenomenon determined by the working principle of the stepping motor is very unfavorable 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 driver, etc.
The AC servo motor runs very smoothly and does not vibrate even at low speeds. The AC servo system has a resonance suppression function, which can cover the lack of rigidity of the machine, and the system has a frequency analysis function (FFT) inside the system, which can detect the resonance point of the machine and facilitate system adjustment.
3. The moment-frequency characteristics are different
The output torque of the stepper motor decreases with the increase of the speed, and it will drop sharply at a higher speed, so its maximum working speed is generally 300-600RPM. The AC servo motor has a constant torque output, that is, it can output a rated torque within its rated speed (generally 2000RPM or 3000RPM), and it is a constant power output above the rated speed.
4. Different overload capacity
Stepper motors generally do not have overload capability. AC servo motor has strong overload capacity. Take Sanyo AC servo system as an example, it has speed overload and torque overload capabilities. Its maximum torque is two to three times the rated torque, which can be used to overcome the moment of inertia of the inertial load at the moment of starting. Because the stepper motor does not have this kind of overload capacity, in order to overcome this moment of inertia when selecting a model, it is often necessary to select a motor with a larger torque, and the machine does not need such a large torque during normal operation, so the torque appears. The phenomenon of waste.
5. Different operating performance
The control of the stepping motor is an open-loop control. If the starting frequency is too high or the load is too large, step loss or stalling will easily occur. When the speed is too high, overshooting will easily occur when the speed is too high. Therefore, in order to ensure its control accuracy, it should be handled properly. Ascent and deceleration issues. The AC servo drive system is closed-loop control. The drive can directly sample the feedback signal of the motor encoder, and the internal position loop and speed loop are formed. Generally, there will be no step loss or overshoot of the stepping motor, and the control performance is more reliable.
6. Different speed response performance
It takes 200-400 milliseconds for a stepper motor to accelerate from a standstill to a working speed (generally several hundred revolutions per minute). The acceleration performance of the AC servo system is good. Taking Sanyang 400W AC servo motor as an example, it only takes a few milliseconds to accelerate from static to its rated speed of 3000RPM, which can be used in control occasions that require fast start and stop.
To sum up, the AC servo system is superior to the stepper motor in many aspects of performance. But in some less demanding occasions, stepper motors are often used as executive motors. Therefore, in the design process of the control system, various factors such as control requirements and cost should be considered comprehensively, and an appropriate control motor should be selected.
Taiye Machinery was founded in 2005, the company is located in the beautiful Zhejiang, China，Taiye machine provide a full set of professional extrusion die equipment and extrusion dies, We have an aluminum extrusion die factory and a professional extrusion die equipment company in China. Our machine tools product include machining center, CNC lathe, wire cut EDM machine, EDM machine, Vacuum Furnace, etc.
