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Stepper Motors : A Motor for CNC Equipment

Computer Numerical Control (CNC) equipment are machines that are typically used in manufacturing. CNC stands for ‘computer numerical control’ and machines that use this technology rely on computers to control tools like lathes, routers, grinders, and mills. Precise movement is required to ensure accuracy and reliability, and this is one of the reasons why stepper motors are preferred for CNC equipment. A stepper motor is an electromechanical device that performs mechanical movements by converting electrical pulses. The most preferred types of stepper motors are – linear stepper motors, geared stepper motors, PM stepper motors etc.

Digital pulses cause stepper motors to activate instead of consistently applying voltage to them. While traditional electric motors rotate continuously, stepper motors step or rotate in angular increments that are fixed. Hence, stepper motors are typically used for applications that require precise position control. When arranged in a stepper motor, driver, and controller system design, the stepper motor is assumed to perform digital instructions. Stepper motors lack feedback to continuously control a position, making them considered as an open-loop system.

Stepper motors are made up of the rotor and stator laminations, shaft, copper and lead wires, bearings, magnets, front and end covers, and washers. The shaft is usually made of stainless steel, and the rotor and stator laminations are typically made of silicon steel, which is preferred for higher electrical resistivity. Magnets for stepper motors come in various types like Nd-Fe-B bonded, ferrite sintered, and ferrite plastic to meet different construction needs. The bearings may vary in size, and the housing materials may be made of heat-resistant metals like aluminum.

Stepper motors are primarily used for motion control, whether rotational or linear. For rotational motion, digital pulses must be received in correct sequence to make the shaft rotate in discrete steps. The pulse or step signal can be produced by timing logic, microprocessors, a relay closure, or toggle switch. Digital pulses enable shaft revolutions. Every revolution needs a specific number of pulses, in which a pulse is equivalent to a rotary step or increment. This means that a step is only a portion of a complete rotation.

 
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