1) Stepper motors were available from many days in the technical field will those got commercialized in early 1960's when the transistor fabrication techniques made available.
2) This types are motors capable of switching large DC currents in the motor windings and this feature of switched winding current gives the stepping motor its unique 'Digital machine' properties which is an important aspect when compared to the other digital system.
3) The sudden growth of digital electronics throughout the 1970's assured the stepping motors future and today there a worldwide interest in its manufacturing and applications.
4) Recently more efforts and research has been made in development of more improved stepper motor in size, speed, accuracy and resolution.
5) We can be able to see in future the wider use of the steeper motors in control systems.
6) A stepper Motor is basically an electromagnetic transducer or an incremental actuator which converts digital input pulses or range in to output shaft in motion'
7) The main property or speciality of stepper motor is its ability to covert or translate switched excitation changes in to precisely defined increments of output shaft positions.
Let's start with the important definitions and the parameters related to the stepper motors:
This is the maximum starting torque that can be applied to the shaft of an unexcited motor without causing it to rotate continuously. This is present in the permanent magnet motor and in hybrid motors but it is not available in VR (Variable resistance) type stepper motor.
This can be stated as the maximum static torque which can be apply to the shaft of an excited motor without causing it to rotate continuously.
Critical Torque or pullout torque:
This is an angular displacement of the rotor in degrees corresponding each input pulse.
This is an maximum load torque for which motor responds to each input pulse without missing any input step; this is also called as pull in torque.
Synchronous stepping rate:
It is the maximum step rate at which motor can rotate without missing a step; it is possible to stop, start or reverse the motor at its speed.
1) It is an maximum stepping rate at which a rotor can rotate unidirectionally.
2) It is higher that synchronous stepping rate
3) It is not possible to stop, start or reverse the motor at this step rate without missing a pulse