In addition to the motor body, the performance of the stepper motor is greatly affected by the driving method. The driving method of the stepping motor is divided into the full-step, the half-step, and the micro-step, etc. What do they mean? Here is the explanation for you:
Three basic drive modes for stepper motor drives: full-step, half-step, and micro-step.
FULL-STEP DRIVE
During the full-step drive, the stepper motor driver energizes the two coils of the two-phase stepper motor in a pulse/direction command. Each pulse of this drive mode causes the motor to move a basic step angle. The following figure shows the sequence of the motor stator current in the whole step drive mode:
Below is the current vector segmentation diagram:
Below is the I vs T diagram:
The current vector driven by the full-step divides a circle into four equal parts, and the current waveform is rough. With this driving method, the motor will shake at low speed and the noise will be large. However, the advantage of the full-step drive is that the hardware or software is relatively simple in design so that the drive manufacturing cost is easily controlled.
HALF-STEP DRIVE
In the case of single-phase excitation, the rotor stops at one position. After the driver receives the next pulse and gives two excitations at the same time, the rotor will move half a step angle and stop in the middle of the two adjacent full-step positions. In this cycle, the two-phase coil is single-phase and then double-phase excited, and the stepping motor will rotate at half a step angle of each pulse. Compared with the whole step method, the half-step method has the advantages of double the precision and less vibration at low-speed operation. The following figure is a schematic diagram of the motor stator current sequence in a half-step drive mode:
The half-step driving method is relatively more complicated than the full-step driving method. At the same time, both phases may need to be energized, and the energizing current should be √2/2 of the single-phase energizing current. Of course, it is also possible to directly pass a current equal to the single-phase current. As a result, the torque during the rotation of the motor is not constant, but it has the advantage of simplifying the driving circuit or software writing.
The driving phase sequence of the half-step driving method is as follows: BB’→BB’& A’A→A’A→B’B & A’A→B’B→B’B & AA’→AA’→ AA’& BB ‘. The motor is energized according to the above phase sequence, and the resulting current vector divides a circle into 8 parts.
Below is the current vector segmentation diagram:
Below is the I vs T diagram:
As can be seen from the above figure, the current waveform of the half-step drive is relatively smooth. Compared with the whole step drive, the motor’s step angle resolution is doubled, and the motor runs more smoothly and quietly.
MICRO-STEP DRIVE
Microstep drive is to gradually increase the current of each phase in a stepwise manner so that the force that attracts the rotor changes slowly. Each time the rotor is stationary at the equilibrium point of the force, the step angle is made n fine. This method can make the rotor run smoothly, so this method can be considered as one of the effective methods to reduce vibration at low speed. Comparing the following figure, we can see a certain law: the more subdivision, the more and more the current vector segmentation circle is dense.
Figure c is a segmentation diagram of the 4 subdivisions drive. In a sense, the whole step and the half step drive are also subdivision driven, and their relationship is like the relationship between square and rectangle.
The figure above shows the current diagram of 4 subdivisions. It can be seen from the figure that the current curve of each phase is more delicate than the current curve of the half-step drive, which is similar to a sine wave.
The subdivision drive method is an extremely effective way to reduce vibration, but there are the following points to note:
- The better the subdivision drive works at low speeds. If the input frequency is too fast, the subdivision waveform will not be able to get the desired current waveform, which will make the motor tracking accuracy worse.
- The more the number of subdivisions, in theory, the more obvious the effect of reducing vibration, but the actual effect to 8 subdivisions is not large. By actually testing the current waveforms and motor rotation angles of different subdivisions, we find that there is no difference in effect between 8 subdivisions and 16 subdivisions.
- Although the angle of the subdivision can be located, its accuracy is not high. Therefore, when positioning control, it is positioned by subdivided 2-phase or 1-phase conduction.
MOONS’ SR series two-phase DC stepper motor driver is a cost-effective subdivision driver based on PID current control algorithm. It also provides three driving modes: full-step, half-step, and micro-step, which is convenient for customers to choose their own applications.
