Motor excitation sequence
Now that we know that a series of excitations will rotate the stepper motor, we will design the hardware to implement the required step sequence. A piece of hardware that can move a motor (or a combination of hardware and software) is called a motor drive.
It can be seen from Figure 4 how we can excite the windings of the two-phase motor to rotate the rotor of the motor. In the figure, the winding taps in the motor are labeled 1A, 1B, 2A and 2B, respectively. 1A and 1B are the two taps of the winding 1, and 2A and 2B are the two taps of the winding 2.
First, a positive voltage is applied to pins 1B and 2B, and 1A and 2A are grounded. Then, a positive voltage is applied to the legs 1B and 2A, and 1A and 2B are grounded. This process actually depends on the direction in which the wires are wound around the slots, assuming that the wires are wound in the same direction as described in the previous section. Going one by one, we get the excitation sequence summarized in Table 1, where "1" represents a positive voltage and "0" represents a ground.
There are two possible flows of current in the motor windings. Such motors are called bipolar motors and bipolar drive sequences. A bipolar motor is usually driven by a circuit called an H-bridge. Figure 5 shows the circuit that connects the two bridges of the H-bridge and the stepper motor. The H-bridge is connected to a fixed-voltage DC power supply through a resistor (the amplitude of which can be selected according to the requirements of the motor). Then, the circuit is connected to the two windings via four switches (labeled S1, S2, S3 and S4, respectively). Root tap. The distribution of this circuit looks a bit like a capital letter H, so it is called an H-bridge.
As can be seen from Table 1, to energize the motor, the first step is to set tap 2A to logic 0 and 2B to logic 1, so we can close switches S1 and S4 and open switches S2 and S3. Next, we need to set tap 2A to logic 1 and 2B to logic 0, so we can close S2 and S3 and disconnect S1 and S4. Similarly, in the third step we can close S2 and S3 and disconnect S1 and S4. In the fourth step, we can close S1 and S4 and disconnect S2 and S3.
The excitation method for winding 1 is no different, and a pair of H-bridges can be used to generate the desired excitation signal sequence. Table 2 shows the location of each step of the switch during the excitation process.
Although the drive of a single-pole motor is relatively simple to control, it is more complicated than a bipolar motor because it uses a center tap in the motor, and its price is usually more expensive than a bipolar motor. In addition, since the current only flows through half of the motor windings, the unipolar motor can only produce half of the magnetic field.
After knowing the construction principles of unipolar and bipolar motors, we can derive the relationship between the tap and the winding when we encounter a motor that does not have a tap or a data sheet. A motor with 4 taps is a two-phase bipolar motor. We can determine which two taps belong to the same winding by measuring the impedance between the wires. A motor with 6 taps may be a two-phase unipolar motor or a three-phase bipolar motor, as determined by measuring the impedance between the wires.
If you want to buy a fan motor, please pay attention to Cooling Fan Motor.
