Is the stepping motor and servo motors the same
The torque characteristics are different The output torque of the stepping motor decreases with the speed of the revolution, and falls sharply at high speed, so the maximum working speed is 300 ~ 600RPM. Ac servo motor for constant torque output, that is, at its rated speed (2000 RPM and 3000 RPM) of less than, can be rated output torque and constant power output above the rated speed for. Four, overload ability is different The step motor is generally not overloaded. Ac servo motor has the capability of overload. With the example of the 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 moment of inertia 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.
Low frequency characteristics In low speed, the step motor is prone to low frequency vibration. The vibration frequency is related to the load condition and drive performance, and the frequency of vibration 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 work in low speed, general damping technology should be adopted to overcome the low frequency vibration phenomenon, such as add damper on motor, or drive the segmentation technology, etc. Ac servo motors are very stable, even at low speeds. 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.
Different control accuracy 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 steps in the step of the motor. 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 rotating encoder on the back end of the 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 wiring and programming of a different step motor is much simpler than the servo. But the control accuracy of the servo is much higher than the step!
Performance difference Stepper motor control for the open loop control, start frequency is too high or too much load step easy appear lost or blocked, stops frequently occur high speed overshoot phenomenon, so as to ensure the control accuracy, should handle the ascending and descending speed problem. Ac servo drive system for closed-loop control, the actuator can be directly to the motor encoder feedback signal sampling, internal position loop and speed loop, general won't appear step motor lose step or overshoot phenomenon, more reliable control performance. Speed response performance is different It takes between 200 and 400 milliseconds for a step motor to accelerate from rest to a working speed (usually a few hundred revolutions per minute). Better acceleration performance of the ac servo system, a panasonic MSMA 400 w ac servo motor as an example, from static accelerated to the rated speed 3000 RPM it takes only a few milliseconds, can be used for quick start-stop control occasions.
