It is electromagnetic and electro-dynamic equipment.A stepper motor is a brushless DC motor whose rotor rotates in discrete angular displacements when its stator windings are energized in a programmed manner.
1.Various reluctance motor (i) single stack (ii) multi stack
2.Permanent magnet motor (i) Claw pole motor
SINGLE STACK VARIABLE RELUCTANCE MOTOR:
SINGLE STACK VARIABLE RELUCTANCE MOTOR
The VR stepper motor is characterized by the fact that there is no permanent magnet either on the rotor or the stator. The construction of a 3-phase VR stepper motor is shown in figure.
The stator is made up of silicon steel stamping s with inward projected even or odd number of poles or teeth (usually the number of poles of stator is an even number). Each and every stator pole carries a field coil or exciting coil. In case of even number of poles the exciting coils of opposite poles are connected in series. The two coils are connected such that their MMF get added. The combination of two coils is known as phase winding.
The rotor is also made up of silicon steel stamping s with outward projected poles and it does not have any electrical winding. The number rotor poles should not be equal to the number of stator poles to have self starting capability and bi-directional rotation. The width of the rotor teeth should be equal to the width of stator teeth.
MULTI STACK VARIABLE RELUCTANCE MOTOR:
MULTISTEP VARIABLE RELUCTANCE MOTOR
These are used to obtain smaller step sizes, typically in the range of 2˚ to 15˚. Although three stacks are common a multi stack motor may employ as many as seven stacks. This type is known as the cascade type.
A multi stack variable reluctance stepper motor can be considered to be made up of “m” identical single stack VR motors with their rotors mounted on a single shaft. The stators and rotors have the same number of poles and therefore same pole pitch. For a “m” stack motor, the stator poles in all m stacks aligned, but the rotor are displaced by 1/m of the pole pitch angle from one another. All the stator pole windings in a given stack are excited simultaneously and forms one phase.
for more electrical machine design notes refer to the following Links:-