Tag: stepper motor

Stepper motors is used in open-loop control, thus it is simple, low cost and can be widely used. However, the open-loop control of the stepper motor cannot avoid the inherent disadvantages of the stepper motor itself, that is, resonance, oscillation, step loss and difficult to achieve high speed. Correspondingly, the closed-loop control of stepper motor can make up these shortcomings, and have the advantages of open-loop drive and brushless DC servo motor.

Stepper motors are now widely used in the industrial areas, but from time to time some problems with stepper motors occurs as follows. Aimed to these problems, there are some troubleshooting for your reference.

1. How to control the direction of stepper motor?
2. When stepper motor generates vibration and noise, how to do it?
3. Why the stepper motor doesn’t rotate or move back and forth after it is powered?
4. Why the torque of stepper motor is decreasing with the rise in rotational velocity?
5. Why stepper motor can run normally at low velocity, but can’t start at certain higher velocity with some noise of whistler?
6. How to prevent the power interference of stepper motor?

Stepper motor is an open-loop control motor which transforms electric pulse signal into angular displacement or linear displacement.  However, there are some errors occuring between the actual angle stepper motor rotates and the theoretical step distance. There are some certain errors from one step to any other step, but the step number of each cycle of the stepper motor is the same. In the case of no step loss, the step error is not accumulated for a long time.
How to prevent step loss with stepper motor as the above mentioned? First of all, we need to know why stepper motor losses step?

1. The rotor acceleration is slower than the rotating magnetic field of the stepper motor.
2. The average speed of the rotor is higher than the average rotating speed of the stator magnetic field.
3. The load inertia of stepper motor is large.
4. The stepper motor produces the resonance.

Stepper motor is an actuator transforming electric pulse into angular displacement. Popularly, when receiving a pulse signal, the stepper motor will rotate a fixed angle (namely"stepping angle") according to the direction set for the stepper motor. The angular displacement volume can be controlled by controlling the pulse number to achieve the purpose of positioning accurately. In the meantime, the rotational velocity and acceleration of motor can be controlled by controlling the pulse frequency to achieve the purpose of speed control.

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.

Unipolar and bipolar driver architectures are most commonly used for stepper motors.
Unipolar stepper motor indicates the stepper motor with 2 coils and 5 or 6 lines. That is, one tap is increased in the middle of one coil. 5 lines can be seen as 6 ones. The two intermediate line of two coils can be connected. For there is tap in the middle of one coil, the current can flow towards different direction along the half way in one coil, but half of the motor coil is just used.
Bipolar stepper motor indicates the stepper motor with 2 coils and 4 lines. The current can flow in forward and reverse direction in two coils, so called bipolarity.

One of the most significant advantages of stepper motor is that it can be controlled accurately in open loop system because the rotor position can be determined only by tracking the input step pulse, but overheating problem occurs easily in stepper motor, so how to solve this problem if such condition occurs?

In the specific occasion, when the terminal load is stable, the action is simple and the motor basically runs at low speed, it is appropriate to choose the stepper motor with low cost and easily controlling. However, when terminal load fluctuation range is large, action is simple and the motor basically runs at low speed, if still choosing the stepper motor, a series of troubles are coming. In fact, in such situation, servo motor should be chosen, as the comprehensive cost will decline considering many factors.

For stepper motor specification, the operating temperature range for stepper motor should be 0～50℃ while humidity should be 20%～90%RH, and storage temperature should be -20～70℃ while humidity should be 15%～95%RH.