Stepper Motors are used in open loop control systems. The stepper motor rotates at fixed steps for every change in the driver signal. The typical step size of stepper motors is in range of 0.9 and 1.8 degrees. There are few types of stepper motors available such as bipolar permanent magnet stepper motor and unipolar permanent magnet stepper motor. Stepper motors are operated by applying current pulses of a specific frequency to the inputs of the motors. Stepper motors are capable of driving a 2.2-kw load with stepping rates from 1000 to 20,000 per second in angular increments from 180 degree down to 0.75 degree. The stepper motors are permanent magnet two-phase 12 V DC.
Stepping motors are another type of motor that is used in robots. It have a narrower range of torque output than servo motors and are more suitable for the cylindrical coordinate and gantry robots where the torque requirements are more uniform over the range of arm movement. Stepping motors move in response to pulses sent by the controller, each pulsing causing a small amount of motor movement, called a step. Because the controller counts and sends the appropriate number of steps to each motor, there is no need for an encoder to provide motor position information back to the controller. Controllers for stepping motor robots are simpler than for servo motors, resulting in reduced cost and controller complexity.