STEPPER MOTORS: THE BASICS

Found in both industrial and commercial settings as a result of their affordability, reliability, durable construction, and high torque at low speeds, stepper motors are brushless synchronous electric motors that work by converting digital pulses into mechanical rotation. Every revolution of a stepper motor consists of a division of steps and the motor is sent a pulse for each step. A stepper motor’s position can be controlled without feedback because stepper motors are able to take only one step at a time and each step is the same size. When pulse frequency increases to a certain point the step movement will turn into continuous rotation with the speed directly related to the frequency of pulses.

There are a number of reasons to use a stepper motor: 1) open-loop control simplifies the motor and makes control less expensive; 2) the motor’s rotation angle is directly proportional to the input pulse; 3) you need precise positioning and reliable repetition of movement; 4) stepper motors have wide operational ranges because the speed is commensurate to the input pulses’ frequency; 5) they have excellent response times with regard to starting, stopping, and reversing; 6) good stepper motors are accurate within three to five percent of a step; 7) when the windings are energized stepper motors have full torque at complete standstill and, when the load is coupled, you can achieve remarkably low speed synchronous rotation; and 8) because stepper motors don’t have contact brushes, they have an exceptionally high mean time between failure.

The three types of basic stepper motors are variable reluctance, permanent magnet, and hybrid — hybrids combine the strengths of variable reluctance and permanent magnet engines. Hybrid stepper motors have toothed stator poles, a permanent magnet rotor,typically  two hundred rotor teeth, and most hybrid motors rotate at under two degrees each step. As a result of their high static and dynamic torque and their ability to run at quite high step rates, hybrid stepper motors are commonly used in a number of different applications including computer disk drives, printers, machine tools, and much more.

Hopefully this brief overview helped you to understand a little bit more about the operation of stepper motors, their characteristics, and some common applications where stepper motors are employed.