Characteristics of Stepper Motors

The main  characteristic of stepper  motors is torque  versus stepping or  pulse  rate. It give the  variation  of torque as a function of pulse rate ( Pulse  per second).

                                          Figure  Torque pulse  rate  characteristics  of a stepper  motors

When  increase in  pulse  rate or stepping  rate the  has less time to drive the  load from one position to next  hence the driving  torque  is decreased as shown in figure.

Torque pulse  rate characteristics  can be divided  into two  curves one is pull  in torque characteristics which shown  the maximum  pulse  rate at  which  motor  can start  synchronize  stop  or reverse for different values of load torque and another  one is pull out torque  characteristics which  shown  the maximum  pulse  rate at  which the  motor can  run for  different values  of load  torque  if motor is  already synchronized but  it cannot be  started  stopped  or reversed on that  particular input  pulse  rate.

These two  characteristics  are shown  in  figure  the characteristics  between  pull in  torque  and zero  pulse  rate  vertical line is  called the  start range  between  pull in torque  characteristics  and pull  out torque  stepping rate  gives the slew range. In the slew range the load follows the pulse rate or stepping rate  up to  pull out  torque characteristic. Beyond  a certain pulse  rate the  rotor con not follow  the command and  would  begin to miss pulses. Slew  range is  useful  for speed  control  and it is not suitable for positioning  control.