A servo motor is an engine that controls the operation of mechanical components in a servo system. It is an indirect variable speed device that supports the motor. Today, we will understand the biggest difference between servo motor and stepper motor. Only with a deep understanding of servo motor and stepper motor, can we better choose the industrial environment suitable for different working conditions. Now let's talk about the servo motor and stepper motor what are the biggest differences?
First to understand the internal structure of servo motor and stepping motor:
1. Different low-frequency characteristics
Stepper motor is prone to low frequency vibration at low speed. The vibration frequency is related to the load condition and driving performance. It is generally considered that the vibration frequency is half of the take-off frequency of the motor at no load. This low-frequency vibration phenomenon is determined by the working principle of the stepper motor, which is very adverse to the normal operation of the machine. Stepper motor running at low speed, generally should use damping technology, such as in the motor with a damper, or in the drive with a shock absorber, to overcome the low-frequency vibration phenomenon.
Ac servo motor runs very smoothly, no vibration at low speed. The system has resonance suppression function, which can solve the problem of insufficient mechanical stiffness. At the same time, the system also has frequency resolution function (FFT), through which the resonance point of the machine can be detected, which is easy to adjust the system.
2, different overload capacity
Stepper motors generally have no overload capacity. Ac servo motor with strong overload capacity. As an example, the Panasonic AC servo system has the characteristics of speed overload and torque overload. Its maximum torque is three times the rated torque, which can be used to overcome the torque generated by the inertial load at startup. Stepping motor because there is no such overload capacity, in order to overcome this inertia moment when selecting the motor, often need to choose a larger torque, and in normal operation, the motor does not need so large torque, there will be a waste of torque phenomenon.
3, different speed response performance
It takes 200 to 400 milliseconds for a stepper motor to accelerate from rest to working speed (typically a few hundred revolutions per minute). Taking Panasonic MSMA 400 W AC servo motor as an example, the AC servo system accelerates from rest to the rated speed of 3000 RPM in just a few milliseconds, which can be used in control situations requiring fast start and stop.
4, different operating performance
The control of stepper motor adopts open-loop control, which is easy to lose step or block when the starting frequency is too high or the load is too large, and it is easy to overshoot when the speed is too high. Therefore, the problem of rising and falling speed should be handled well to ensure the control accuracy of the motor. In the AC servo drive system, the closed-loop control can directly collect the feedback signal of the motor encoder, and form the position ring and speed ring inside, generally there will be no stepping or overshoot phenomenon of the stepper motor, and the control performance is more reliable.
5, different control accuracy
The step Angle of two-phase hybrid stepper motor is generally 3.6°, 1.8°; The step Angle of five-phase hybrid stepping motor is generally 0.72° and 0.36°. There are also some high-performance stepper motors with smaller step angles. The step Angle can be set to 1.8°, 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, 0.036° and 0.036°, and is compatible with the step Angle produced by Sito.
The rotary encoder at the back of the motor shaft ensures the control accuracy of the AC servo motor. For Panasonic full digital AC servo motor, the pulse equivalent of the motor with 2500 wire standard encoder is 360°/10000=0.036° due to the quadruple frequency technology used in the driver. For a motor with a 17-bit encoder, each drive receives 217=131072 pulse motor rotations, that is, its pulse equivalent is 360°/131072=9.89 seconds. That is, 1/655 step Angle of 1.8° stepper motor pulse equivalent.
Through the above analysis, we find that the AC servo system is superior to the stepper motor in many aspects. However, stepper motor is often used as the executive motor in some occasions with low requirements. Therefore, in the design of industrial control system, the control requirements, costs and other factors should be considered comprehensively to choose the appropriate servo control system.