What's 28byj48 stepper motor?

First of all, let's take a look at the origin of the name of the 28BYJ-48 stepper motor.

28: The effective maximum outer diameter of the stepper motor is 28 mm

B: indicates that it is a stepper motor

Y: means permanent magnet type

J: indicates that it is a deceleration type (reduction ratio 1:64)

48: indicates four phases and eight beats

In other words, 28BYJ-48 means a four-phase eight-beat permanent magnet deceleration stepper motor with an outer diameter of 28 mm. Is it a bit messy? Don't worry, let's watch it a little bit.

Let me talk about the concept of a "4-phase permanent magnet". The internal structure diagram of 28BYJ-48 is shown below. First look at the inner ring. There are 6 teeth on it, marked as 0-5. This is called the rotor. As the name suggests, it is to rotate. Each tooth of the rotor has permanent magnetism, which is a permanent magnet. It is the concept of "permanent magnet type". Looking at the outer ring again, this is the stator. It remains stationary. In fact, it is fixed to the motor housing. There are 8 teeth on it, and each tooth is wound with a coil winding. The windings on the two opposite teeth are connected in series, which means that the two opposite windings will always be turned on or off at the same time, thus forming 4 phases, which are marked as ABCD, this is the concept of "4-phase".

Now we analyze its working principle: Assume that the initial state of the motor is shown in Figure 9-4, rotating counterclockwise. At the beginning, the switch of the B-phase winding is closed, and the B-phase winding is turned on, then the current is turned on. Magnetism will be generated on the top and bottom two stator teeth, and the magnetism on these two stator teeth will generate the strongest attraction to the 0 and 3 teeth on the rotor, as shown in the figure. The No. 0 tooth of the rotor is at the top and the No. 3 tooth is at the bottom in a balanced state; at this time, we will find that the No. 1 tooth of the rotor and the upper right stator tooth, which is a winding of phase C, present a small angle. , No. 2 teeth and the right stator tooth, that is, the D-phase winding presents a slightly larger angle. Obviously, this included angle is twice the angle between No. 1 tooth and C winding. Similarly, the situation on the left is the same. of.

Next, we disconnect the B-phase winding and turn on the C-phase winding. It is obvious that the upper right stator tooth will have the greatest attraction to the rotor 1st tooth, while the lower-left stator tooth will have the rotor 4th tooth. , Produces the greatest attractive force. Under the action of this attractive force, the rotor's 1st and 4th teeth will be aligned to the upper right and lower left stator teeth to maintain balance. In this way, the rotor will turn over the initial state when the 1st tooth and The angle of the included angle of the C-phase winding.

Next, disconnect the C-phase winding and turn on the D-phase winding. The process is exactly the same as the above situation. Finally, the rotor 2 and 5 teeth will be aligned with the stator D-phase winding, and the rotor will rotate through the same angle as mentioned above.

Then it is obvious that when the phase A winding is turned on again, that is, after a BCDA four-beat operation is completed, the 0 and 3 teeth of the rotor will be aligned from the original to the upper and lower two stator teeth, but become aligned to the upper left and lower right. On the two stator teeth, that is, the rotor has rotated through an angle of the stator teeth. By analogy, another four beats, the rotor will turn another tooth angle, after 8 four beats, the rotor will make a complete revolution, and the angle that a single beat makes the rotor turn is easy to calculate, That is, 360 degrees/(8*4)=11.25 degrees, this value is called the step angle. The above-mentioned working mode is the single four-beat mode of the stepper motor-four-beat single-phase winding is energized.

Look back at the reduction ratio parameter in the motor parameter table-1:64, the rotor rotates 64 times, the final output shaft will make one revolution, that is, it takes 64×64=4096 beats before the output shaft makes one revolution. . 4096 beats rotate one circle, then the angle of one beat rotation-the step angle is 360/4096, look at the step angle parameter 5.625/64 in the table, and you know that these two values are equal, everything is Has been matched.

The basic control principle should be over here, but no matter which manufacturer produces the motor, as long as the model is 28BYJ-48, the nominal reduction ratio is 1:64. But actually? After disassembly and calculation, it is found that the true and accurate reduction ratio is not this value of 1:64, but 1:63.684! The method of obtaining this data is also very simple. Actually, count the number of teeth of each gear, and then multiply the reduction ratio of each level to get the result. The measured reduction ratio is (32/9)(22/11) )(26/9)(31/10)≈63.684, so that the actual error is 0.0049, which is about 0.5%, it will be half a turn after 100 revolutions.

Then according to the actual reduction ratio of 1:63.684, it can be concluded that the number of beats required for one revolution is 6463.684≈4076. But in fact, the error still exists, because the above calculation results are obtained by approximation. The actual error is about 0.000056, which is 0.56 per 10,000. It will be half a turn after 10,000 revolutions, which is negligible.

So why are there errors in the manufacturer's parameters? Don’t the manufacturers know? To explain this problem, we have to go back to practical applications. The most common purpose of a stepper motor is to control the target to rotate through a certain angle, usually within 360 degrees. The original design purpose of this 28BYJ-48 is to For controlling the fan blades of the air conditioner, the movement range of the fan blades will not exceed 180 degrees. Therefore, in this application, the manufacturer gives an approximate integer reduction ratio of 1:64 which is accurate enough, which is also reasonable.

By Melissa [email protected]