stepper motor accelration problem

Hi all,
I am developing stepper motor control board in the devicenet network using TI Dsp controller and National Motor driver rated with 3
amps continuous current. When i am testing my application in the position mode by giving some parameters like target position ,target velocity,target acceleration and target deceleration ,my 2 phase stepper motor is spinning with some constant velocity,even when i am changing the velocity in my timer period register in order to achieve the target accleration,it was rotating with constant velocity.I am able to see the changes in the period register value,but even then it was not able to accelerate,what could be the reason,please help me to achieve my motor to the target acceleration.The profile i am using was trapezoidal with the microstepping mode,and the motor specs are 2 phase and with max 3 amp current can carry.I am driving only 2 amp to the motor coils where chopping is done in the driver using some sense resistors.
Do i need to drive 3 amps instead of 2 amps to the coil for the motor with 3 amps max current,why because my motor was not able to achieve the target acceleration.What will happen if i drive 2 amp current to the coil ,even my motor withstands for 3amps current,Does the motor does not accelerate.Please give me your suggestions regarding the problem,i am able to see the changes in the Period register value .
Regards, Sudheervemana.
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sudheervemana wrote:

1. You may be going too fast - how many steps are there? Stepper motor may work only 1-2 revs per second reliably after that, it could start missing steps. 2. Are you quenching the back e.m.f. adequately? 3. Better off with AC motor control for this kind of thing where you want to control velocity and acceleration.
J
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