Stepper motor


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This presentation is on stepper motor and its basic principle and uses

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Stepper motor

  1. 1. PrinciPle of stePPer motor 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. The sequence of the applied pulses is directly related to the direction of motor shafts rotation. The speed of the motor shafts rotation is directly related to the frequency of the input pulses and the length of rotation is directly related to the number of input pulses applied.
  2. 2. tYPes of stePPer motor     There are three basic type of stepper motor. They are as follows Variable-reluctance motor Permanent magnet motor Hybrid motor
  3. 3. PermAnent mAGnet AnD HYBriD stePPer motor
  4. 4. 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.
  5. 5. STEPPER MOTOR CHARACTERISTICS 1. 2. 3. 4. Stepper motors are constant power devices. As motor speed increases, torque decreases. Steppers exhibit more vibration than other motor types, as the discrete step tends to snap the rotor from one position to another. This vibration can become very bad at some speeds and can cause the motor to lose torque.
  6. 6. 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 design The 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
  7. 7. SIZE AND POWER In addition to being classified by their step angle stepper motors are also classified according to frame sizes which correspond to the diameter of the body of the motor. For instance a size 11 stepper motor has a body diameter of approximately 1.1 inches. Likewise a size 23 stepper motor has a body diameter of 2.3 inches (58 mm), etc. The body length may however, vary from motor to motor within the same frame size classification. As a general rule the available torque output from a motor of a particular frame size will increase with increased body length. Power levels for IC-driven stepper motors typically range from below a watt for very small motors up to 10 –20 watts for larger motors. The maximum power dissipation level or thermal limits of the motor are seldom clearly stated in the motor manufacturers data. To determine this we must apply the relationship PÊ=V ´ÊI.
  8. 8. 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
  12. 12. 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)
  13. 13. dIsAdvAntAges 1. Resonances can occur if not properly controlled. 2. Not easy to operate at extremely high speeds
  14. 14. 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.