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Servo Motor Control Precision
Oct 19, 2017

Servo Motor control precision

AC servo motor and stepper motor performance comparison:

Stepper motor is a discrete motion device, it and modern digital control technology has an essential link. In the current domestic digital control system, the application of stepper motor is very extensive. With the advent of all-digital AC servo systems, AC servo motors are also increasingly being used in digital control systems. In order to meet the development trend of digital control, most of the motion control system using stepper motor or all-digital AC servo motor as the implementation of the motor. Although both are similar in control mode (burst and direction signals), there are significant differences in performance and application. Now compare the performance of the two.

First, the control accuracy is different

Two-phase hybrid stepper motor step angle is generally 3.6 °, 1.8 °, five-phase hybrid stepper motor step angle is generally 0.72 °, 0.36 °. There are also some high-performance stepper motors with smaller step angles. Such as the four-way company for the use of stepper motor stepper motor, the step angle of 0.09 °; Germany 100 lattice company (BERGER LAHR) production of three-phase hybrid stepper motor its step angle through DIP switch is set to 1.8 °, 0.9 °, 0.72 °, 0.36 °, 0.18 °, 0.09 °, 0.072 °, 0.036 °, compatible with the two-phase and five-phase hybrid stepper motor step angle.

The accuracy of the AC servo motor is guaranteed by the rotary encoder at the rear of the motor shaft. To Panasonic all-digital AC servo motor, for example, with a standard 2500-wire encoder motor, because the drive internal use of the quadruple frequency technology, the pulse equivalent of 360 ° / 10000 = 0.036 °. For motors with 17-bit encoders, the driver receives 217 = 131072 pulse motors for one turn, ie, the pulse equivalent is 360 ° / 131072 = 9.89 seconds. Is 1/655 of the pulse equivalent of the stepper motor with step angle of 1.8 °.

Second, low-frequency characteristics of different

Stepper motor at low speed prone to low frequency vibration phenomenon. The vibration frequency is related to the load condition and the drive performance. It is generally believed that the vibration frequency is half of the motor no-load take-off frequency. This low-frequency vibration phenomenon, which is determined by the working principle of the stepper motor, is very unfavorable to the normal operation of the machine. When the stepper motor is operating at low speed, damping technology should generally be used to overcome the low frequency vibration phenomenon, such as in the motor plus damper, or drive on the use of sub-technology.

AC servo motor running very smoothly, even at low speed will not appear when the vibration phenomenon. AC servo system with resonance suppression function, can cover the lack of mechanical rigidity, and the system has a frequency resolution function (FFT), can detect the mechanical resonance point, easy to adjust the system.

Third, the frequency characteristics of different

The output torque of the stepper motor decreases as the speed increases and decreases drastically at higher speeds, so the maximum operating speed is typically between 300 and 600 RPM. AC servo motor for constant torque output, that is, its rated speed (usually 2000RPM or 3000RPM) within, can output the rated torque, above the rated speed for the constant power output.