Bipolar stepper motors use electromagnetic coils to rotate a shaft, allowing for measured motions and reversals. They require fewer coils than unipolar motors and can be controlled externally with a stepper motor controller or micro stepper. They are used in industrial equipment and amateur robotics construction.
Bipolar stepper motors are a type of alternating current (AC) stepper motor that uses command-excited electromagnetic coils to rotate a shaft. Using this system, the shaft can be rotated in measured motions and can also be reversed. Unlike unipolar stepper motors, the bipolar motor allows electric current to flow in both directions, thus reducing the number of coils needed to do the job.
The function of bipolar stepper motors is quite simple. The stepper motor driver sends a pulse of electric current through the motor coil. The coil is energized, becoming an electromagnet. This creates a reaction with the motor shaft, pulling the rotor towards the spool. The driver then energizes the next coil in the series and the process repeats.
A unique aspect of stepper motors is that the driver can also tell the motor to perform functions other than just rotating in one direction. Stepper drivers can operate bipolar stepper motors in forward, reverse or alternating two points. When paired with a stepper motor controller, the driver function can be controlled externally, allowing the operator to speed up or slow down the shaft motion 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 for even greater control as individual motor steps are further subdivided into micro steps. For example, if an individual had an eight-step motor and the microstep went 100 microsteps per step, the motor shaft could be moved to 800 different points along its rotation, rather than just the original eight 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 through individual coils in two directions. This double polarity makes it possible to instantly stop or reverse the direction of rotation of the shaft.
Stepper motors are used for a variety of applications where controlled motion is desired. For example, they are often found in industrial welding equipment and precision cutting equipment. This type of equipment is particularly suited to amateur robotics construction because the stepper motor and driver are significantly less expensive than the servo units.
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