Ayush kr.SrivastavaAyush kr.Srivastava

PrinciPle of stePPer motor

A stepper motor (or step motor) is a brushless DC electric motor that divides a full rotation into a number of equal steps.

A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements.

The shaft or spindle of a stepper motor rotates indiscrete step increments when electrical command pulses are applied to it in the proper sequence. The motors rotation has several direct relationships to these applied input pulses.

tYPes of stePPer motor

There are three basic type of stepper motor. They are as follows

Variable-reluctance motor Permanent magnet motor Hybrid motor

PERMANENT MAGNET AND HYBRID STEPPER MOTOR

WHEN TO USE A STEPPER MOTOR A stepper motor can be a good choice whenever

controlled movement is required .They can be used to advantage in applications where you need to control rotation angle, speed, position and synchronism. Because of inherent advantages listed previously, stepper motor have their place in many different applications.

STEPPER MOTOR CHARACTERISTICS

1. Stepper motors are constant power devices. 2. As motor speed increases, torque decreases. 3. Rotation in both directions .4. A holding torque at zero speed .5. Repetition of accurate motion .

TORQUE GENERATION

The torque produced by a stepper motor depends on several factor.

1. Step rate 2. The drive current in the winding 3. Drive designThe basic relationship which define the intensity of magnetic

flux is defined by: H = (N x i)/ l where: H = Magnetic flux intensity N = The number of winding turns l = Magnetic flux path length

THE ROTATING MAGNETIC FIELD

When a phase winding of a stepper motor is energized with current a magnetic flux is developed in the stator. The direction of this flux is determined by the “Right Hand Rule”

The magnetic flux path developed when phase is energized with winding current in the direction. The rotor then aligns itself so that the flux opposition is minimized. In this case the motor would rotate clockwise so that its south pole aligns with the north pole and its north pole is aligns with the south pole. To get motor rotate we can provide a sequence of energizing the stator winding in such a fashion that provides a rotating magnetizing flux field which the rotor follows due to magnetic attraction

ADvANTAGEs

1. Excellent response to starting/stopping/ reversing.

2. It is possible to achieve very low speed synchronous rotation with a load that is directly coupled to the shaft.

3.The motors response to digital input pulses provides open-loop control, making the motor simpler and less costly to control.

The motor has full torque at standstill (if the windings are energized)

DISADVANTAGES

1. Resonances can occur if not properly controlled.

2. Not easy to operate at extremely high speeds.

APPLICATIONS

Computer-controlled stepper motors are one of the most versatile forms of positioning systems. They are typically digitally controlled as part of an open loop system, and are simpler and more rugged than closed loop servo systems.

Industrial applications are in high speed pick and place equipment and multi-axis machine CNC machines often directly driving lead screws or ballscrews. In the field of lasers and optics they are frequently used in precision positioning equipment such as linear actuators, linear stages, rotation stages, goniometers, and mirror mounts. Other uses are in packaging machinery, and positioning of valve pilot stages for fluid control systems.

Commercially, stepper motors are used in floppy disk drives, flatbed scanners, computer printers, plotters, slot machines, and many more devices.

Some people looking for generators for homemade Wind Turbines found success in using stepper motors for generating power.