There are two types of electric motors used in CNC technology: DC and AC motors. DC motors operate on Direct Current and AC motors on Alternating Current. The speed of a DC motor is controlled by varying the voltage of the incoming DC electricity. The speed of AC motors is controlled by varying the frequency of the incoming three-phase AC electricity. The torque of AC motors is proportional to the applied current. (4)
Steppers motors are a very common type of AC motor used in CNC machines. As the name implies, these motors rotate in steps, with one step per pulse of alternating current. Each step in movement is very small and there can be as many as 50,000 microsteps per revolution. (13)
If the torque applied to the stepper is within the motor’s limits, it can be very accurate. However, if the torque exceeds the motors capacity, the motor can “slip” and the desired position will not be reached. For this reason, open loop systems can become inaccurate. In a closed loop system, this “slip” can be adjusted for. If a stepper (or any other type of motor) is used in a closed loop system they are often referred to as servomotors. (3)
