Bipolar Stepper MotorPublished on 24/2/2012 and last updated on 30/7/2018
Stepper motors are available in three basic configurations:Please Rate this Article
- Universal Stepper Motor- A universal stepper motor can be connected as a bipolar or a uni-polar stepper motor.
- Uni-polar Stepper Motor- A Uni-polar stepper motor can be used as uni-polar or a bipolar stepper motor.
- Bipolar stepper Motor- A bipolar stepper motor can only be used as a bipolar.
Bipolar Stepper BasicsA bipolar stepper motor has one winding per stator phase. A two phase bipolar stepper motor will have 4 leads. In a bipolar stepper we don’t have a common lead like in a uni-polar stepper motor. Hence, there is no natural reversal of current direction through the winding. A bipolar stepper motor has easy wiring arrangement but its operation is little complex. In order to drive a bipolar stepper, we need a driver IC with an internal H bridge circuit. This is because, in order to reverse the polarity of stator poles, the current needs to be reversed. This can only be done through a H bridge.
There are two other reasons to use an H Bridge IC
- The current draw by a stepper motor is quite high. The micro-controller pin can only provide up to 15 mA at maximum. The stepper needs current which is around ten times this value. An external driver IC is capable of handling such high currents.
- Another reason why H Bridge is used is because the stator coils are nothing but inductor. When coil current changes direction a spike is generated. A normal micro-controller pin cannot tolerate such high spikes without damaging itself. Hence to protect micro-controller pins, H bridge is necessary.
Interfacing to Micro-Controller4 micro-controller pins are required to control the motor. We need to provide the L293D with 5 V supply as well as the voltage at which the motor needs to operate. Since we will be using both the drivers of the IC, we will assert the enable pin for both of them.
Interfacing DiagramThere are three different ways in which we can drive the bipolar stepper motor-
- Only one of the phase winding is energized at a time. That is, either AB or CD is energized. Of course the coils will be energized in such a way that we get correct polarity. But only one phase is energized. This type of stepping will give less holding torque because only one phase is energized.
- In this method, both the phases are activated at the same time. The rotor will align itself between two poles. This arrangement will give higher holding torque than the previous method.
- The third method is used for half stepping. This method is used generally to improve the stepping angle. Here, in step 1 only 1 phase is ON, then in step 2, 2 phases are ON, then again only one phase is ON and the sequence continues.