To distinguish, you must first understand the difference between the two.
Let me talk about how it works:
A 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 the "step angle") in a set direction, and its rotation is step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses 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, thereby achieving the purpose of speed regulation.
The rotor inside the servo motor is a permanent magnet. 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. At the same time, the encoder feedback signal from the motor is supplied to the driver. The driver according to the feedback value and target. The values ​​are compared to adjust the angle at which the rotor rotates. The accuracy of the servo motor is determined by the accuracy (number of lines) of the encoder.
Difference 1: Different ways of control
The stepping motor controls the rotation angle by the number of control pulses, and one pulse corresponds to one step angle. The servo motor controls the angle of rotation by controlling the length of the pulse time.
Difference 2: The required work equipment and workflow are different
The power supply required for the stepper motor (the required voltage is given by the drive parameters), a pulse generator (mostly now using the plate), a stepper motor, and a drive (the drive sets the step angle angle, as set The step angle is 0.45 °, at this time, give a pulse, the motor goes 0.45 °); its working process for the stepper motor generally requires two pulses: signal pulse and direction pulse. The power supply required for the servo motor is a switch (relay switch or relay board), a servo motor; its working process is a power connection switch, and then connected to the servo motor.
Difference 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 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.
Difference 4: Different moment frequency characteristics
The output torque of the stepper motor decreases as the speed increases, and it drops sharply at higher speeds, so the maximum operating speed is generally 300-600r/min.
The AC servo motor is a constant torque output, that is, it can output the rated torque within its rated speed (generally 2000 or 3000 r/min), and it is a constant power output above the rated speed.
Difference 5: Different overload capabilities
Stepper motors generally do not have overload capability.
The AC servo motor has a strong overload capability. Take the Panasonic AC servo system as an example, it has speed overload and torque overload capability. Its maximum torque is 3 times the front torque and can be used to overcome the moment of inertia of the inertia load at the moment of starting. (Because of the lack of such overload capability, stepper motors often need to select a motor with a large torque in order to overcome this moment of inertia, and the machine does not need such a large torque during normal operation. Torque waste phenomenon)
Difference 6: Different speed response performance
It takes 200 to 400 ms 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 Panasonic MSMA400W AC servo motor as an example, it accelerates from standstill to its rated speed of 3000 r/min. It only takes a few ms and can be used in control situations where fast start-stop is required.
To put it bluntly, the number of poles is large, the speed is slow, the angle of control, the power line pins are mostly stepper motors, and the power is often low. The high precision and high speed can be applied to the control of speed, position and torque. The power lines are all UVW three wires, usually servo motors. Moreover, the number of pole pairs is usually not more than 5, and the power is from tens of watts to tens of kilowatts.
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