The shape of the speed - torque curve can change quite dramatically depending on the type of driver used.
The bipolar chopper type drivers which Ericsson Components produces will maximum the speed - torque performance from a given motor. Most motor manufacturers provide these speed - torque curves for their motors.
It is important to understand what driver type or drive method the motor manufacturer used in developing their curves as the torque vs. speed characteristics of an given motor can vary significantly depending on the drive method used.
There are two major advantages of a type 1 system over type 0. The steady state error at rest is 0 and it responds precisely in velocity to constant velocity input commands (position ramps).
The single-step response characteristics of a stepper motor is shown in figure 11.
When one step pulse is applied to a stepper motor the rotor behaves in a manner as defined by the above curve.
The step time t is the time it takes the motor shaft to rotate one step angle once the first step pulse is applied.
This step time is highly dependent on the ratio of torque to inertia (load) as well as the type of driver used.
Where:
V1 = Stator Terminal Voltage
I1 = Stator Current
R1 = Stator Effective Resistance
X1 = Stator Leakage Reactance
Z1 = Stator Impedance (R1 + jX1)
IX = Exciting Current (this is comprised of the core loss component = Ig, and a
magnetizing current = Ib)
E2 = Counter EMF (generated by the air gap flux)
The counter EMF (E2) is equal to the stator terminal voltage less the voltage drop
caused by the stator leakage impedance.
4 E2 = V1 - I1 (Z1)
E2 = V1 - I1 (R1 + j X1 )
In an analysis of an induction motor, the equivalent circuit can be simplified further by
omitting the shunt reaction value, gx. The core losses associated with this value can be
subtracted from the motor Power and Torque when the friction, windage and stray
losses are deducted. The simplified circuit for the stator then becomes: