What is a Stepper Motor and how do they work?

A type of DC motor, stepper motors are employed in daily industrial and commercial applications because of their affordability, reliability, high torque at low speeds, and simple form for universal applications. More specifically, stepper motors are a type of brushless synchronous DC motor that does not rotate continuously until shut off. Instead, they are a kind of digital input-output device for precise starting and stopping. They are built so that the current passing through them hits coils that are quickly powered on and off, which allows the motor to turn through a fraction of a rotation at a time in ‘steps.’ They are built to divide one full rotation into many smaller part-rotations. These are used to direct the stepper motor to move through established degrees or angles of rotation.

Stepper motors can transfer extremely accurate movements to mechanical parts that require precision. These digitally-controlled motors are essential in open-loop motion-control positioning systems. They are typically seen in holding or positioning applications in which movement control is necessary. Stepper motors are often used in industrial and scientific applications including robotics, machine tools, pick and place machines, automated wire cutting and wire bonding machines, and precise fluid control devices.  

Normal brushed DC motors are constructed of a stator and rotor; the rotor moves and has no winding, brushes, or commutator, while the stator is composed of three or four phases of winding. Inside the stator, voltage is applied to terminals that causes a wire coil, also called the rotor, to rotate. The rotor acts as an electromagnet and it rotates quickly at the center of the motor. Both electrical contacts and a rotary electrical switch called a commutator permit the current to change directions quickly, allowing the rotor coil to spin in one direction as long as it is given sufficient voltage. The issue with these normal motors is that they spin until the power source is removed, making them less precise than stepper motors, which are discussed in further detail below.

Stepper motors consist of a fixed wire housing (the stator) placed around several ‘toothed’ electromagnets spinning at the center, and they convert a pulsing electrical current into single-step movements of this ‘toothed’ component around a central shaft. Every stepper motor pulse moves the rotor precisely a full turn; when the current switches between wire coils outside the motor, the rotary part can perform full or partial turns when necessary. It can also be made to pause at an exact spot when necessary. When compared to normal DC motors, stepper motors are able to rapidly locate themselves at a position and hold that position for as long as is necessary. As such, they are commonly used in precise applications like robotics and printing.

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