The Difference Between AC Servo Motor And Stepper Motor

- Feb 28, 2019-

The difference between AC servo motor and stepper motor


To understand the difference between the two, we need to have a deeper understanding of each object. First understand the working principle, the working principle of the 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 in the set direction, and its rotation is operated 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 controlling the displacement; at the same time, the speed and acceleration of the motor rotation can be controlled by controlling the pulse frequency, thereby achieving the purpose of speed regulation.The rotor inside the servo motor is a permanent magnet, and the U/V/W three-phase electric motor controlled by the driver forms an electromagnetic field. The rotor rotates under the action of the magnetic field, and the encoder feedback signal from the motor is supplied to the driver. The driver according to the feedback value and The target values are compared to adjust the angle at which the rotor rotates.The accuracy of the servo motor is determined by the resolution of the encoder.

First, the stepping motor and the servo motor are controlled differently. The stepping motor controls the rotation angle by the number of control pulses. One pulse corresponds to one step angle, but there is no feedback signal, and the motor does not know where to go. The positional accuracy is not high enough.The servo motor also controls the number of pulses. Each time the servo motor rotates by one angle, a corresponding number of pulses will be emitted. At the same time, the driver will also receive the feedback signal, which is compared with the pulse received by the servo motor, so that the system will know that it has been sent. How many pulses are given to the servo motor and how many pulses are received at the same time, the rotation of the motor can be controlled very accurately, so that accurate positioning can be achieved, which can reach 0.001 mm.

Second, different overload capabilities Stepper motors generally do not have overload capability. The AC servo motor has a strong overload capability. Take the Pil magnetic AC servo system as an example, it has speed overload and torque overload capability.Its maximum torque is three times the front torque and can be used to overcome the moment of inertia of the inertia load at the moment of starting. Because there is no such overload capability for stepper motors, stepper motors cannot be used in some applications.

Third, the speed response performance is different. It takes 200 to 400ms for the stepper motor to accelerate from standstill to the working speed (generally several hundred revolutions per minute). The AC servo system has better acceleration performance. Taking the Pil magnetic AC servo motor as an example, it accelerates from standstill to its rated speed of 3000 r/min. In just a few ms, it can be used in control situations where fast start-stop and high position accuracy are required.

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