Bipolar stepper motors are a type of alternating current (AC) stepping motor that use electromagnetic coils, energized on command, to turn a shaft. Using this system, the shaft can be turned in measured movements, and can also be reversed. Unlike unipolar stepper motors, the bipolar motor allows the flow of electric current to move in both directions, thus reducing the number of coils needed to accomplish the task.
The function of bipolar stepper motors is quite simple. The stepper motor driver sends a pulse of electric current through the coil of the motor. The coil is energized, becoming an electromagnet. This creates a reaction with the motor shaft, pulling the rotor towards the coil. The driver then energizes the next coil in the series and the process repeats itself.
One unique aspect of stepper motors is that the driver can also tell the motor to perform functions other than simply rotating in one direction. Stepper drivers can make bipolar stepper motors run forwards, backward, or alternate between two points. When paired with a stepper motor controller, the function of the driver can be controlled externally, allowing the operator to speed up or slow down the movement of the shaft as well.
In some cases, a special type of controller called a micro stepper is used in conjunction with a bipolar stepper motor and driver. The micro stepper allows an even greater amount of control as the individual steps of the motor are further divided into micro steps. For example, if an individual had an eight step motor and the micro stepper made 100 micro steps per step, the motor's shaft could be moved to 800 different points along its rotation, rather than just the eight original steps.
A unipolar stepper motor is less efficient than similarly sized bipolar stepper motors because the bipolar motor performs the same function using half the number of coils. It does this by incorporating a special bipolar stepper motor drive that transfers electricity across the individual coils in two directions. This dual polarity makes it possible to instantly stop or reverse the direction in which the shaft is rotating.
Stepper motors are used for a variety of applications in which controlled movements are desired. For example, they are often found in industrial welding equipment and precision cutting equipment. This type of equipment is particularly well suited to amateur robotics building because the stepper motor and driver is significantly less expensive than servo units.