parameter adjust？

parabolic velocity

when I choose the "parabolic velocity "to adjust the PID, what is the mean of the step size and step time?if i want to make the motor reach

perfect performance,how do i choose the step size and step time?

It will be hard to determine what "Perfect performance" for your motor is. Instead, you should define some criteria (design goals) you want to meet for your particular system, such as a certain bandwidth (e.g., 25 Hz), following error band (e.g., less than 10 cts for the most difficult move), rise time, overshoot, etc.

A good starting point is to choose a parabolic move similar to the most difficult move your system will actually have to make. That is, if your machine will have to make a parabolic move with a 10000 count move size in .5 seconds, you should select these as your move parameters when tuning. If your motor achieves the following error you desire with these move parameters, then it will be able to handle easier moves as well.

Please refer to the Practical Servo Loop Tuning Guidelines post for how to tune the motor with the Parabolic Move.