Rockwell Automation 1398-PDM-xxx IQ Master Version 3.2.4 for IA-2000 and IQ-5000 Positioning Drive Modules, IQ-55 - Manual (Page 187)

Closed Loop Control • Closed Loop Velocity Control 165
Publication 1398-PM601A-EN-P — October 2000
TUTORIAL
Closed Loop Velocity Control
The most common velocity controller structure is a Proportional plus Integral (PI) loop. The choice of
the proportional (PGAIN) and integral (IGAIN) gains for the desired response is made based on the
application requirements. Proportional gain is always used, and higher PGAIN values result in higher
velocity loop bandwidths. The integral gain provides stiffness to load torque disturbances and reduces
the steady-state velocity error to zero. However, integral gain does add phase shift to the velocity con-
troller and can result in a longer settling time. Therefore, a low or zero IGAIN is sometimes used in
point to point positioning applications requiring fast settling times, while a higher IGAIN is used in
applications requiring high stiffness and a predictable path. In practice, the velocity controller is usually
tuned using trial-and-error techniques with the motor coupled to the real or simulated load. The ULTRA
Plus or IQ-Series controller provides automatic tuning of the velocity and position loops which is ade-
quate for many applications. The manual tune mode applies a small signal step command to the loop,
and allows real-time adjustment of the gains while observing the response to optimize the tuning.