How Step Motors Work

Identification

Step motors, or stepper motors, are electric motors used in a number of applications. Business machines, computer peripherals, robotics and motion control technology all make use of stepper motions within their designs. The device is made up of a rotor and electromagnets. The rotor itself is a magnetic shaft that rotates inside a series of electromagnets. The electromagnets are actually coils of wire lined up in a step fashion around the rotor. The rotor rotates by means of electrical pulses sent out by the wires. Each coil of wire makes up a phase in the rotor's rotation. As such, motor types are described in terms of their number of phases, as in three-phase, four-phase and five-phase motors. Three components are involved in the step motor process--an indexer, a driver and a user interface. Its overall purpose is to convert electrical current into mechanical energy.

Function

Through the user interface, step motors are controlled by the indexer. The indexer is a microprocessor device that generates step pulses and directional signals to the driver. The driver delivers energy to the motor's windings using the signal commands it receives from the indexer. The rotor's surface is magnetized, which causes a current to be generated each time it passes a wire coil. As the rotor rotates, electrical current alternates from one coil to the next, causing a constant current and voltage to run through the device. These coils are positioned at measured degree intervals from one another, which is what keeps the rotor moving. The number of degree intervals between each coil will depend on the type of application being used. The device is able to generate a high torque at low speeds and is relatively inexpensive to make; however, higher speeds result in a lower torque capacity.

Types

Step motors come in three basic designs--permanent magnet, variable reluctance and hybrid. The permanent magnet design is the most basic, using a magnetized rotor and coils. Coils are arranged in 45- or 90-degree intervals. These are mainly used in business machines. Variable reluctance motors use a non-magnetized rotor, so the overall rotational movement is smoother. Pole sets replace the coiled wire arrangements with each set positioned at 15-degree intervals. Variable reluctance designs are used in applications like micro slide devices where high torque powers are not needed. Hybrid motors combine characteristics from both the variable reluctance and permanent magnet designs. They're made up of magnetized rotors that sit inside multi-toothed pole sets. The multi-toothed design can accommodate degree intervals of anywhere from 0.09 to 3.6 degrees per each step interval. Hybrid designs are capable of running at high speeds and high torque power. They're most commonly used in industrial applications, like lathe machines.

Resources

• How Stepper Motors Work