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Servo Motor Performance Comparison

Jul 17, 2017

Servo Motor Performance comparison

Performance comparison of ac servo motor and stepper motor:

Stepper motor is a kind of discrete motion device, which has an essential connection with modern digital control technology. In the current domestic digital control system, stepping motor is widely used. With the emergence of digital ac servo system, ac servo motor is increasingly used in digital control system. In order to adapt to the development trend of digital control, most of the motion control systems adopt stepper motor or full digital ac servo motor as the motor. Although the two are similar in control mode (pulse train and directional signal), there are significant differences in the performance and application situations. The performance of the two is compared.

The control accuracy is different

Two-phase hybrid stepper motor step Angle is 3.6 ° and 1.8 °, 5 phase hybrid stepping motors interval Angle is 0.72 ° and 0.36 ° in general. There are also some high performance stepping motors with smaller step angles. Such as cross company produces a kind of stepping motor for wire walking machine, where the step Angle is 0.09 °. BERGER LAHR company in Germany (BERGER LAHR) production of three-phase hybrid stepping motor where the step Angle can dial the code switch is set to 1.8 ° and 0.9 ° and 0.72 ° and 0.36 ° and 0.18 ° and 0.09 ° and 0.072 ° and 0.036 °, combine the two and five phase hybrid stepper motor step Angle.

The control accuracy of ac servo motor is guaranteed by rotary encoder on the back end of motor shaft. Panasonic digital ac servo motor, for example, in line with standard 2500 encoder of the motor, drive due to the internal used four frequency multiplication technology, the pulse equivalent to 360 ° / 10000 = 0.036 °. For with 17 encoder of the motor, drive each receive 217 = 131072 pulse motor turns a circle, namely the pulse equivalent to 360 ° / 131072 = 9.89 seconds. Interval Angle is 1.8 ° is 1/655 of the pulse equivalent of stepper motor.

The low frequency characteristics are different

The low frequency vibration occurs at low speed. The vibration frequency is related to the load condition and the drive performance, and the vibration frequency is generally considered to be half the frequency of the motor. The low-frequency vibrations, determined by the principle of stepping motor, are very bad for the normal operation of the machine. When the stepper motor is working at low speed, the damping technique should be used to overcome the low frequency vibration phenomena, such as adding a damper on the motor, or using subdivision technology on the drive.

Ac servo motor runs smoothly, even at low speed without vibration. Ac servo system has a resonance suppression function, can cover the mechanical rigidity, and internal system has the function of frequency resolution (FFT), can detect the mechanical resonance point, is advantageous for the system adjustment.

Three, the moment frequency characteristic is different

The output torque of the stepping motor decreases with the increase of the speed, and decreases sharply at high speed, so its maximum working speed is generally 300 ~ 600RPM. Ac servo motor is the constant torque output, that is, within its rated rotating speed (generally 2000RPM or 3000RPM), the rated torque can be output, and the constant power output is at the rated speed above.

Four, overload ability is different

Stepper motor is generally not overloaded. Ac servo motor has strong overload capacity. With the example of panasonic ac servo system, it has the capability of speed overload and torque overload. The maximum torque is three times the rated torque, which can be used to overcome the inertia moment of the inertia load. Stepper motor because there is no this kind of overload capacity, in order to overcome the inertia moment when selection, often need to select a larger torque of the motor, and the machine during the normal work and don't need that big torque, there is a moment of waste phenomenon.