Stepper drivers are the programmable circuits attached to stepper motors. The driver may be pre-configured with a set group of commands or it may be manually adjusted to perform a wider range of functions. The purpose of this circuit is to control the function of the stepper motor, so the part is also known as a stepper motor controller.
Stepper motors operate by using windings to create electromagnetic force. As each winding is energized, the shaft of the motor turns towards the activated winding. By controlling the order in which the windings receive power, stepper drivers are able to control the speed and movement of the motor's shaft.
The programmable features of stepper drivers make a range of motor functions possible. Using a stepper drive, operators can make a motor shaft turn clockwise, counter-clockwise, or alternate the direction by changing the order in which the bindings are energized. The operator can increase or decrease the speed of rotation by cycling the power at a different rate.
Using a process called micro stepping, stepper drivers can even move a shaft a fraction of a step with each cycle. This process can benefit some applications because it results in a smoother overall operation of the motor with a greater degree of control. Micro stepping is described by the number of partial steps it produces, so an eight step micro stepping controller would produce eight steps for every one step of the motor. If the motor shaft turns 100 steps per revolution, the micro stepping driver used in the example would increase this number to 800 steps.
The typical stepper driver is an open-looped system that receives no feedback on the position of the shaft. As a result, it may miss steps on overload. The closed-loop systems use rotor position feedback to adjust the operation of the motor. This allows the closed-loop driver and stepper motor to perform the same functions as a servo with more torque. Closed-loop drivers are commonly used in cases where extreme attention to delicate and measured movement is required.
Both of these driver circuits can be built into the home workshop environment by people with a basic understanding of electronic theory. Due to the simple circuitry design, stepper drivers are popular among hobbyists who need an economical option for precision controlled movements of motorized models and robotics. The stepper motor system's lower price tag and ease of installation make it a common replacement for servo units in home workshop designs.