38s Video Tell You The Differences Between Stepper Motors And Servo Motors

This video will tell you what are the differences between servo motors and stepper motors with sound in 38s, which will help you to choose the right motor drives for your CNC machine. Pay attention to the sound in the video, don’t mute it.
Stepper motor is an actuator that converts electrical pulses into angular displacement. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (called "step angle") in the set direction, and its rotation runs step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses, so as to achieve the purpose of accurate positioning; at the same time, the speed and acceleration of the motor rotation can be controlled by controlling the pulse frequency, so as to achieve the purpose of speed regulation.
The rotor inside the servo motor is a permanent magnet. The U/V/W three-phase electricity controlled by the driver forms an electromagnetic field. The rotor rotates under the action of this magnetic field. At the same time, the encoder of the motor feeds back the signal to the driver, and the driver compares the target with the feedback value. The values ​​are compared, and the angle of rotation of the rotor is adjusted. The accuracy of the servo motor is determined by the accuracy of the encoder (number of lines).
1. Different control methods
The stepper motor controls the rotation angle by controlling the number of pulses, one pulse corresponds to a step angle. The servo motor controls the rotation angle by controlling the length of the pulse time.
2. The required work equipment and work flow are different
The power supply required by the stepper motor, a pulse generator, a stepper motor, and a driver (the driver sets the step angle angle, such as setting The step angle is 0.45°, at this time, give a pulse, the motor will go 0.45°); its working process is that the stepper motor generally needs two pulses: signal pulse and direction pulse. The power supply required by the servo motor is a switch (relay switch or relay card) and a servo motor; its work flow is a power connection switch and then the servo motor.
3. 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 drive. It is generally considered 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 stepper motor is very unfavorable to the normal operation of the machine. When the stepper motor is working 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 there is no vibration 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 internal frequency analysis function (FFT) of the system can detect the resonance point of the machine, which is convenient for system adjustment.
4. Different torque-frequency characteristics
The output torque of a stepper motor decreases with the increase of the speed, and will drop sharply at a higher speed, so its maximum working speed is generally 300~600r/min.
The AC servo motor has a constant torque output, that is, it can output a rated torque within its rated speed (generally 2000 or 3000r/min), and it is a constant power output above the rated speed.
5. Different overload capacity
Stepper motors generally do not have overload capacity.
AC servo motors have strong overload capacity. Take the Panasonic AC servo system as an example, it has speed overload and torque overload capabilities. Its maximum torque is 3 times the nominal torque, which can be used to overcome the moment of inertia of the inertial load at the moment of starting.
6. Different speed response performance
It takes 200-400ms 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 better. Take the Panasonic MSMA400W AC servo motor as an example, it accelerates from a standstill to its rated speed of 3000r/min. It only takes a few ms and can be used for control occasions requiring fast start and stop.
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