How to select stepper motor and servo motor?
How to select servo motor and stepper motor correctly?
It depends on specific application situation, and to put it in a simple way: Nature of load (for example, vertical load or horizontal load), requirements of torque, inertia, speed, accuracy and acceleration and deceleration, requirements of upper control (such as requirements of port interface and communication), whether major controlling mode is position, torque or speed mode, whether power supply is direct or alternating current power supply, or battery powered, and voltage scope. Based on this, we can determine models of motor and supporting drives or controllers.
Stepper motor system or servo motor system?
In fact, what motor system to use depends in specific situation and they have their own characteristics.
|Parameter||Stepper motor system||Servo motor system|
|Torque scope||Medium and small torque (generally below 20nm)||Small, medium and large, full range|
|Speed scope||Low (generally below 2000rpm, and big torquemotor is less than 1000rpm)||High (reach to 5000rpm), direct current servomotor can reach to 10,000~20,000rmp|
|Controlling method||Mainly position control||Diversified and intelligent controlling method,position/speed/torque method|
|Smoothness||Have vibrations n low speed (but it can be remarkablyimproved by using subdivided drives)||Good, smooth operation|
|Accuracy||Generally lower, but higher for subdivided drives||High (depend on resolution of feedback devices)|
|Frequency and torque characteristics||In high speed, torque will drop fast||Good torque nature and hard feature|
|Overload characteristic||Out of step when overload||3~10times of overload (short time)|
|Feedback mode||Most are open-loop control and can also connect encoder||Prevent from out of step, closed-loop,feedback of encoder|
|Encoder type||Photoelectric rotary encoder||(Increment/absolute value), rotating transformer|
|Resistance to shock||Good||General (rotating transformer can endure vibration)|
|Temperature rising||General||Relatively good|
|Maintainability||Basically can be free from maintenance||Relatively good|
How to match with stepper motor driver?
According to current of motor, drivers which are bigger or equal to the current can be used. If low vibration or high precision is needed, subdivided drivers can be selected. For big torque motor, we should use high voltage drivers as far as possible to obtain favorable high speed performance.
Differences between 2-phase and 5-phase stepper motors, how to select?
2-phase motor has a low cost, but its vibration is larger in low speed and torque drops fast in high speed. While 5-phase motor has small vibration and favorable high speed performance, and its speed is as much as 30~50% higher than that of 2-phase motor, and moreover, it can replace servo motor on some occasions.
When to select direct current servo system and its differences with alternating current servo?
Direct current servo motor can be divided into brush and brushless motors.
Brush motor has a low cost, simple structure, big starting torque, wide speed range and easy control and it requires to be maintained which is convenient (change carbon brush), generates electromagnetic interference and has requirements on environment. Therefore, it can be used in general industries and private use which are sensitive to cost.
Brushless motor has a small volume, light weight, big capacity, fast response, high speed, small inertia, smooth shifting and stable torque. Its control is complicated and easy to realize intelligence. Moreover, its electronic commutation is flexible and can choose square wave commutation or sine wave commutation. Motor can be free from maintenance, and it has a high efficiency, low operating temperature, small electromagnetic radiation and long service life, and it can be applied in various environments.
Alternating servo motor is also brushless motor, and it can be divided into synchronous and asynchronous motor. At present, motion control generally adopts synchronous motor since its power range is large and can realize large power. Moreover, it has big inertia and a low maximum rotational speed, and its speed will drop rapidly with increase of power. Therefore, it is suitable for low speed smooth operation.