How does a robotic arm in a manufacturing facility repeat the exact same movements over and over?
How does an automated milling machine move with such precision?
It's all because of the stepper motor
What's special about the stepper motor is that it can control the angular position of the rotor?
Without a closed feedback loop it is a simple accurate and open-loop system
Let's first understand how the variable reluctance type of stepper motor works which is the simplest one?
Later on we will move to a highly accurate and commonly used motor type
This motor has six stator teeth and can be energized with three separate DC. Power sources
The Rotor is made of a stack of steel laminations
It has a different number of teeth than the rotor for in this case
This is done. Intentionally, so that only one pair of rotor teeth is aligned with the stator at a time
You can explain how the stepper motor works by yourself
If you [de-energize] coil a and Energize B
It becomes clear that the rotor will rotate as shown
from the geometry it is clear that the one step size is 30 degrees to
[get] the next step the energized coil B and energized [C] after
[that] coil A becomes energized again in short the rotor moves to the position with the least reluctance the
[step] size of this motor is 30 degrees. You can improve the accuracy to 15 degrees with a small trick
When coil a is energized the rotor is in this position? We know that when coil B?
Is energized it moves 30 degrees?
What happens when coils A and B are energized together?
The rotor will come to a position between these two cases
Or it will move 15 degrees
after this [de-energized] A
then after reaching B
Energized C as well this kind of operation is known as half stepping
The motor we have been discussing is called a variable reluctance motor
The most versatile and commonly used stepper motor is the hybrid motor type
Let's explore the functioning of a typical 1.8. Degree. Step size hybrid motor
The Hybrid Motor has an actually magnetized rotor with toothed steel caps
So one end of the rotor becomes the North pole and the [other] end becomes a south pole
The accuracy of this motor lies in the clever arrangement of the rotor and [stator] teeth let's understand it first
The rotor has 50 teeth to understand the stator teeth arrangement first assume that the stator has 50 teeth as well
However the stator actually has two fewer teeth than the rotor
So we are left with 48 teeth
Let's arrange the 48 teeth into [four] group pairs as shown
Now let's realign these groups the green set moves so that it is half aligned with the rotor
The teeth of the yellow group are completely unaligned with the rotor teeth
The blue group is half aligned with the rotor the [red] group remains in place in
Short the red set is completely aligned with the rotor while the yellow set is unaligned
The other two sets are half aligned
Please remember that the rotor and facing you acts like the south pole
The stator coils are connected as shown
They are two independent coil sets
When set a is energized the stator forms a magnetized pattern as shown?
one pair of stator pulls acts as the North pole and the other as the south pole as
The opposite poles attract, they will be aligned the same polarity poles will be unaligned
When the coil B. Is energized observe, what happens to the rotor?
It has to rotate by a small angle in order to align with the new North Pole it
Is clear [that] this angle is [1/4] of the angular pitch?
in other words the rotor moves by 1.8 degrees
Next set a is energized with the opposite polarity again the rotor moves by 1.8. Degrees
This process is repeated and a highly accurate motion is achieved by the motor
The step Angle Resolution can be further improved by half-stepping
It is interesting to note that the north end cap teeth are placed in between the south end teeth
This way the alignment of the opposite polarity poles are guaranteed again
So this is how a hybrid stepper motor works
They are ideal for applications where precise movements and simple control are desired at
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