valimotor

  Stepper motor’s output torque is decreasing with the increasing of the speed, and it would drop dramatically when the speeds is higher, so its maximum operating speed is generally at 300 ~ 600RPM. AC servo motor has constant torque output, which can output rated torque in its rated speed (typically 2000RPM or 3000RPM). Above the rated speed, it is constant power output.

   Generally, stepper motors do not have overload capacity. However, ac servo motor has a strong overload. Take Sanyo AC servo system for example, It has the speed and torque overload abilities, its maximum torque is two to three times bigger than the rated torque .which can be used to overcome the inertia of the load moment of inertia at the start moment. Because there is no such overload for Stepper motor, you need to overcome this moment of inertia in the selection of induction motors.

  As a kind of open-loop control system, stepper motor is intrinsically linked with modern digital control technology. In the current domestic digital control system, stepper motor is widely used. With the appearance of all-digital AC servo systems, AC servo motor also are increasingly used in digital control systems. In order to meet the development trend of digital control, motion control systems mostly use digital stepper motors or AC servo motor as the implementation of the motor. Although the both are similar in the control (pulse train and direction signal), there are big differences in applications performance and occasions.

  AC servo system is superior to stepper motor in many performances. But stepper motors are used as the implementation motor in some less demanding situations. Therefore, control requirements ,costs and many other factors must be take into account in the control system design process.

Stepper motor is an open loop servo motion system actuator, it uses the pulse to control and send off the angular displacement. Compared with AC servo motor and DC servo motor, the outstanding advantages of stepper motor is low cost, moreover, it without any accumulation errors. However, the stepper motor has many deficiencies in operation aspect, such as low-frequency oscillation, noise, low distinguish rate etc. these defects have severely restricted the application scope of stepper motor. The running performance of stepper motor has close relationship with motor driver. The shortcomings of the stepper motor can be overcome by the improvements of drive technology.

Relative to the other drive, subdivided drive methods not only can reduce the step angle and improve the resolution shelter of stepper motor, but also can reduce or eliminate low-frequency vibration and make the motor run more smoothly. In summary, the effect control of sub-driven is the best.

Stepper motor’s control is open loop control; it is easy to emerge the phenomenon of stall and lose the load step when the start frequency is too high or the loaded is too bigger. Therefore, to ensure the accuracy of the control, you should solve the handle up and spin-down problem well. AC servo drive system is closed loop control, the motor driver can directly sampled the motor encoder feedback signal, Internal structure compose of the position loop and speed loop, so it  generally does not appear lost step or stepper motor overshoot phenomenon, the control performance is more reliable. The speed response performance between stepper and servo motor also are different, Stepper motor needs 200 ~ 400 ms accelerates from zero to operating speed (typically several hundred per minute, rpm). AC servo system has better acceleration performance.