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The difference between the servo motor and stepper motor

Date:2014-1-17 11:13:14 Hits:
Stepping motor and AC servo motor performance comparison
Stepping motor is a kind of discrete movement of the device, it and modern digital control technology has essential relation. In the current domestic digital control system, the application of the stepping motor is very extensive. With the advent of full digital AC servo system, AC servo motor is more and more applied in the digital control system. In order to adapt to the trend of the development of digital control, motion control system mostly adopts the step motor or the full digital AC servo motor as the actuator motor. Although the two are similar in the control mode (pulse and direction signal), but there is a big difference in performance and application situation. The performance of the two comparison.
A control accuracy, different
Two phase hybrid stepping motor step angle is 3.6 °, 1.8 °, five phase hybrid stepping motor step angle is 0.72 °, 0.36 °. There are some high performance stepper motor step angle smaller. As a Stone Company for the production of LSWEDM machine stepper motor, and the step angle is 0.09 °; Germany bergerlahr company (BERGER LAHR) three-phase hybrid step motor step angle into the production by dial switch is set to 1.8 °, 0.9 °, 0.72 °, 0.36 °, 0.18 °, 0.09 °, 0.072 °, 0.036 °, compatible with the step angle two-phase and five phase hybrid stepping motor.
AC servo motor control precision is ensured by the motor shaft end of the rotary encoder. To Panasonic full digital AC servo motor as an example, the motor with the standard 2500 line encoder, because the drive adopts four octave technique, the pulse equivalent to 360 ° /10000=0.036 °. The 17 encoder of the motor, drive each received 217=131072 pulse motor rotates a circle, the pulse equivalent to 360 ° /131072=9.89 seconds. Is the step angle is 1.8 ° stepper motor pulse equivalent to 1/655.
Two, the low frequency characteristics of different
Stepper motor is seen in low frequency vibration phenomenon at low speed. The vibration frequency and load condition and drive performance, generally thought that the vibration frequency for no-load off half the frequency of the. Low frequency vibration phenomenon is decided by the working principle of this by a stepping motor for the normal operation of the machine is very bad. When the stepping motor at low speed, the general should be to overcome the phenomenon of low frequency vibration with damping technology, such as with dampers in the motor, or drive on the subdivision technology etc..
AC servo motor running smoothly, even in low speed does not appear the phenomenon of vibration. AC servo system with the resonance suppression, can cover mechanical rigidity, and internal system has the function of frequency analysis (FFT), which can detect mechanical gongzhendian, convenient for system adjustment.
Three, the torque frequency characteristics of different
The output torque of the stepping motor with the speed increased, and at higher speeds will drop sharply, so the maximum operating speed is generally in the 300 ~ 600RPM. AC servo motor for constant torque output, namely in the rated speed (usually 2000RPM or 3000RPM) within, can output the rated torque, over the rated speed for constant power output.
Four, overload capacity
Stepper motor is not generally the overload capacity. AC servo motor has strong ability of overload. To Panasonic AC servo system as an example, it has the speed and torque overload overload capacity. The maximum torque is three times of the rated torque, can be used to overcome the inertia load in a moment of inertia starting moment. Stepping motor because without the overload capacity, in the selection in order to overcome this kind of moment of inertia, often need to select large torque motor, and the machine during normal operation and does not need to be so large torque moment, appeared the phenomenon of waste.
Five, the performance is different
The step motor control for open loop control, start frequency is too high or too much load lost or blocking the phenomenon of step turn off high speed, prone to overshoot phenomenon, so as to ensure the control accuracy, should handle raising, lowering speed problem. AC servo drive system for closed loop control, the driver can directly on the motor encoder feedback signal sampling, the internal structure of position loop and speed loop, general won't appear the step motor lose step or overshoot phenomenon, more reliable control performance.
Six, speed response performance of different
Stepper motor to accelerate from a standstill to speed (generally every minute of hundreds of RPM) needs 200 ~ 400 ms. AC servo system with good performance speedup, to Panasonic MSMA 400W AC servo motor as an example, to accelerate from a standstill to the rated speed 3000RPM just a few milliseconds, can be used to quickly and the control requirement stop occasion.
In summary, the AC servo system in many performance is better than the stepper motor. But in some of the requirements is not high also often use the occasion of stepping motor for actuating motor. Therefore, comprehensive consideration of the control requirements, cost factors in process control system design, selection of appropriate control motor.
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