Basic Introduction of Stepper Motors

Stepper motors are brushless, synchronous electric motors that converts digital pulses into mechanical rotation. Due to their lower cost, high consistency, high torque at low speeds, and rugged construction, they are found in both industrial and commercial applications.

Every wave of a stepper motor is divided into a discrete number of steps. The motor is sent a pulse for each step. Typically a single rotation is 200 steps or 1. 8 degrees of rotation per step. Since a stepper motor can only take one step at a time, and each step is the same size, the motor's position can be controlled without feedback. Certainly, as the pulse frequency increases the discrete step mobility will change into constant rotation - with the speed directly proportional to the pulse frequency.

There are three basic types: variable reluctance, permanent magnet, and hybrid. Hybrid motors combine the best features of the other two types. They are constructed with toothed stator poles and a permanent magnet rotor. Standard hybrids have 200 rotor teeth and rotate at 1. 8 degrees per step. Because they exhibit high static torque, high dynamic torque and run at very high step rates, they are used in a wide variety of programs including: computer disk drives, printers/plotters, and machine tools, pick and place machines, computerized wire cutting and wire bonding machines.

Operating modes consist of Full, Half and Micro step. The step mode output of any stepping motor is dependent on the design of the driver.

Full Step: Standard hybrid stepping motors have 200 rotor teeth, or 200 full steps per emerging trend of the motor shaft which equals 1. 8 degrees per step. Normally, full step mode is achieved by energizing both windings while alternately reversing the current. One pulse from the driver is equivalent to one step.

Half Step: The step motor rotates at 400 steps per revolution. One then two windings are also consider energized, causing the rotor to rotate half the distance, or 0. 9 degrees. Half step mode will produce a simpler rotation than full step but the tradeoff is less torque. (Approx. a 30% reduction).

Micro step: Micro stepping drives are capable of separating one step into 256 'micro steps', providing 51, 200 steps per revolution or 0. 007degrees per step. Micro stepping is typically used in applications that require accurate positioning and smooth motion over a wide range of speeds. Again, enhanced motion control is traded off against torque.

For More Information: Stepper Motors