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Stepper motor (Part 2)

In the first part of the video we had the chance to see the working principle of the permanent magnet stepper motor, as well as the variable reluctance stepper motor.

Now we will focus on the working principle of another type of stepper motor. This is the most commonly used stepper motor type today which combines the features of a permanent magnet stepper motor with those of a variable reluctance stepper motor. We are talking about of the Hybrid stepper motor.

The hybrid stepper motor has a magnetized rotor with toothed steel caps made of soft iron.
These two steel caps are magnetize so that one end of the rotor becomes the North pole and the other end becomes the South pole. As we can see, the teeth of the two rotors are unaligned.

In this example we can notice that the rotor has 50 teeth, each coil of the stator has some of them facing the rotor, for a total number of 48 teeth, but only in one pair of opposing coils the teeth are facing the teeth of the rotor. The other pairs are offset by one quarter, one half, and three quarter of the pitch of the teeth.

The stator magnetic field switches 45 degrees within one step, while the rotor rotates only for 1.8 degree. That’s becouse in the south pole of the magnet , the stator teeth in the north pole are attracted, while they are 90 degree offset. On the other hand, the teeth in the south pole of the stator are in the exact position that allows them to be rejected.
At the same time, in the north side of the magnet, the exact opposite is happening to stabilize the rotor.

More than 10 years in industrial supplies have led JAES to become a qualified partner for some of the most important industrial automation companies, providing its technical support over a wide range of stepper motor types, installed in many robotic arms.
There are three commonly used excitation modes for stepper motors, called: Full step, Half step and Micro stepping.

Let’s consider the example of the permanet magnet stepper motor seen in the first part of this video.
This type of stepper motor require the Full step drive mode, that’s becouse the rotor needs four steps in order to complete a 360 degree rotation. The full step mode provides high torque, since all the coils are always energized at any time.

In Half mode step sequence you get a step angle, which is half to the angle during the full mode. So the resolution is already increased to the double. This is possible by deenergize a coil. In this way you can get no constant torque.

The Microstepping is the most common method to control stepper motors nowadays.
In this mode you can get smooth motion of the rotor, less stress to the parts and a significant improvement in accuracy. That’s becouse the coils are provided with a voltage similar to the form of sine wave.
Unfortunately in microstepping the torque is decreased about 30 percent.

All these properties of the stepper motor make it suitable to be widely used in industrial automation. The stepper motors are in fact used for driving the robotic arms along the assembly lines, and they are present inside motorized refractor telescope, 3d printers, camera lenses, in computer hard disks, even in gimbal stabilizers.

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