Tag: stepper motor

Stepper motor is to receive the pulse current to achieve speed, position and direction of control. The number of pulses determines the position of the stepper motor, the pulse rate determines the motor speed and pulse direction determines the steering of motor. The control mode of most stepper motor is using PLC to send pulses to the driver and then drive motor to operate. Pulse mode has been around for several decades, and for some applications requiring high frequency, the pulse type can no longer meet the requirements, and it needs to be controlled by the bus type.

Stepper motor is an actuator that transforms the digital pulse signal into angular displacement. Namely, when stepper drive receives a pulse signal, it drives the stepper motor to rotate at a fixed angle (i.e. step angle) in the set direction. Stepper motor is a main executive component in the modern digital control system, and has a very wide range of applications because of the following advantages:

• Precise position control, as confirm the shaft rotation angle in accordance with the number of input pulses.
• Wide speed range, because the speed is proportional to the pulse frequency.
• Excellent starting and stopping as well as reverse response.
• Able to synchronously rotate at an extremely low speed just directly connecting the load to the motor shaft.
• Long service life. Unlike DC motors, stepper motors don’t need to adjust phase position by the brush and commutator, thus reducing the friction and increasing the service life.

Stepper motor is an open loop control element that transforms the electrical pulse signal into angular displacement or linear displacement. When a pulse signal is added to the motor, and the motor turns a step angle. The existence of this linear relationship, and stepper motor with only periodic error and no accumulated error, makes it widely used in various fields. This article describes the application of stepper motor in electronic clocks, industrial robot and packaging machine.

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.

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.

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.

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.