What types of motors used in CNC machines

Computerized Numerical Control (CNC) Machines have been historically and primarily developed to achieve accurate and precise positioning of tool and work-piece in relation to each other. This whole positioning system is simply based on the coordinates of the machine work space or envelop. In order to achieve these coordinates for the positioning or movement of the tool and / or machine table (or work-piece), a CNC machine provide commands to the various electrical drives through various CNC codes and data supplied by the operator in the form a part-program. Thus, the accuracy and precision of these CNC machines and hence the performance of the CNC machines is primarily dependent on the accurate and precise movement of the tool and/or machine table (or work-piece) generated by these electrical drives and associated mechanisms. These movements of tool or work-piece takes place along some axis of the CNC machine and thus the various electrical drives affecting these movements are referred as axes drives. For axes drives, the CNC machines mainly use two types of motors viz. Stepper Motors and Servo Motors. Each of these classes of motors has several variants and each have their advantages and disadvantages. Servomotors are not a specific class of motor although the term servomotor is often used to refer to a motor suitable for use in closed-loop control systems that require feedback mechanisms. A stepper motor is a pulse-driven motor that changes the angular position of the rotor in steps and is widely used in low cost, open loop position control systems that require no feedback mechanisms. This study provides an understanding of the technology and operations of stepper motors that shall assist in their selection and possibly advancement to further improve the performance of CNC machines.