• This motor called “stepper” due to its behavior, that it moves in steps. This 
   machine  can  be  classified  as  a  Reluctance  Motor  or  sometimes  as  a 
   Permanent Magnet Motor, and one of its types is the Hybrid Stepper Motor 
   due  to  the  mixing  between  the  usage  of  cores  of  reluctance  type  and   
   permanent magnet type in the construction of its rotor.
  • Hence, there are three types of this motor: The Variable Reluctance type, The 
   Permanent Magnet Type, and The Hybrid Type.
  • But as it is well known that both of the PMM and RM can move in steps 
   when their stator winding composed of salient poles and fed by DC voltage 
   through electronic switches.
  • So, what is new in this type of machines? 
     The main idea of manufacturing this type of motor, is the load requirements 
  in the following applications:
   1. Printers.
   2. Plotters.
   3. High-end office equipments.
   4. Hard disk drives.
   5. Medical equipments.
   6. Fax machines.
   7. Automotive.
   8. Robotics.
   9. And many more.
   Now you have to think about the common requirements of these equipments! It is 
   clear that they need a machine able to furnish the following:
   •  Ease to control rotation angle, speed, position and synchronism.
   •  A low power and low cost and small volume drives. 
 • An open loop control drives.
 • Accurate, precise, reliable and repeatability of movement drives.
 The above requirements lead to create the stepper motor. Hence, this motor is a 
 new technology (but not a new idea) machine. It has special characteristics to be 
 used in such applications.
 In order to study this machine, its construction and principle of operation must be 
 studied.
        The Construction of Stepper Motor
 As it mentioned before that there are three types of this motor:
 Variable Reluctance (VR) Motor:
 • It composed of a soft iron multi-toothed rotor 
  and salient wound stator.
 • When the stator windings are energized with 
  DC current the poles become magnetized.
 • Rotation  occurs  when  the  rotor  teeth  are 
  attracted to the energized stator poles.
           Multi-stack variable-reluctance motor