Technical Knowledge

Stepper motor selection
Release Date : 2019-03-08 10:27:51

Stepper motor selection

 
Stepper motors are composed of three major elements: step angle (involving phase number), static torque, and current. Once the three major factors are determined, the model of the stepper motor is determined.


1, the choice of step angle

 
         The step angle of the motor depends on the accuracy of the load. The minimum resolution (equivalent) of the load is converted to the motor shaft, and the angle of each equivalent motor should be taken (including deceleration). The step angle of the motor should be equal to or less than this angle. At present, the step angle of stepping motors on the market generally ranges from 0.36 degrees/0.72 degrees (five-phase motors), 0.9 degrees/1.8 degrees (two-phase and four-phase motors), and 1.5 degrees/three degrees (three-phase motors).


2, the choice of static torque
 
        The dynamic torque of the stepper motor is difficult to determine at once. We often determine the static torque of the motor first. The static torque selection is based on the load on which the motor operates, and the load can be divided into inertial load and friction load. A single inertia load and a single friction load are not present. When starting directly (generally from low speed), both loads should be considered. When starting acceleration, the inertia load is mainly considered. When the constant speed is running, only the friction load is considered. Under normal circumstances, the static torque should be 2-3 times of the friction load. Once the static torque is selected, the base and length of the motor can be determined (the geometry).


3, the choice of current
 
        Motors with the same static torque have different operating characteristics due to different current parameters. The current of the motor (reference drive power and drive voltage) can be judged according to the torque frequency characteristic curve.



4, torque and power conversion
 

        Stepper motors are generally used in a wide range of speed control, their power is variable, generally only measured by torque, torque and power are converted as follows: P = Ω · M Ω = 2π · n / 60 P = 2πnM / 60, Where P is the power unit watt, Ω is the angular velocity per second, the unit is radians, n is the speed per minute, M is the torque unit is Newton·meter P=2πfM/400 (half-step operation) where f is the number of pulses per second ( Referred to as PPS).



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