National Instruments NI-Motion User Manual
Page 39
Chapter 3
Tuning Servo Systems
© National Instruments Corporation
3-11
Figure 3-8 describes how to use NI motion controllers with velocity
amplifiers.
Figure 3-8. NI Motion Controllers with Velocity Amplifiers Algorithm
You typically use velocity feedforward when using controllers with
velocity amplifiers. The uncompensated following error is directly
proportional to the specified velocity. You can reduce the following error
by applying velocity feedforward. Increasing the integral gain (Ki) also
reduces the following error during constant velocity, but at the expense of
increased following error during acceleration and deceleration and reduced
system stability.
Note
National Instruments does not recommend increasing Ki.
Velocity feedforward is rarely used when operating in PID mode with
torque block amplifiers. In this case, following error is typically much
smaller because it is proportional to the torque required rather than to the
velocity. When operating in PID mode with torque block amplifiers,
velocity feedforward is not required.