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.