Stepper motor is the executing parts and encoder is the feedback system. Encoder is used with stepper motor and PLC controls them. PLC sends the pulse command to the stepper driver. The driver supplies the current to stepper motor and make it run. And encoder will feedback the current position information to PLC. PLC will compare the feedback value with the target value and make adjustment of the rotter. DC motor with encoder is an important part in the open loop system.