User Manual
Appendix D
GFK-1742F
Jan 2020
Tuning Digital and Analog Servo Systems
429
Tuning the Position Loop
The very first step in adjusting the tuning for the position loop is to insure that the velocity
loop is stable and has response suitable to the application. Refer to the previous section for
methods of setting the velocity loop.
Preliminary Position Loop Settings for Tuning Session.
1.
If using Standard Mode control loop settings, set the User Unit and Counts
configuration to values appropriate to the mechanical configuration for the axis. See
the discussion and examples in Chapter 4 for details.
2.
Set the Velocity at 10 Volt value as described in Chapter 4.
3.
Set the Integrator Mode select
ion to “OFF”.
4.
Set the Feed Forward % to zero.
5.
Set the Position Error Limit to near maximum value. The maximum is 60,000 (User
Units / Counts).
Setting the Position Loop Gain
The position control loop is primarily a “PI” (Proportional, Integral) algorithm
with optional
Feed Forward. Begin tuning the position loop by setting the proportional gain (Pos Loop TC)
to provide a stable response with sufficient gain (bandwidth) to meet the motion profile
requirements. Setting the Integrator Mode to “OFF” as describ
ed in the previous section
creates a proportional-only control loop. There are two suggested methods of setting the
proportional gain (Pos Loop TC).
Position Loop Proportional Gain Method 1
Calculating the position loop proportional gain assumes that the mechanical design of the
machine will have sufficient bandwidth to remain stable and that any resonant frequencies
are higher than the bandwidth required by the motion profile.
Terminology
A large mismatch between the load and motor inertia can cause a RESONANCE in the
system. Resonance is oscillatory behavior caused by mechanical limitations and
aggravated by gearing backlash or torsion windup of mechanical members like
couplings or shafts. Resonance is eliminated by improving the mechanics, reducing
load/motor inertia mismatch or reducing servo gains (reduce performance).
BANDWIDTH is a figure of merit used to compare control system or mechanical
performance. As the frequency of command increases, the system response will begin
to lag. The bandwidth is defined as the frequency range over which system response
(gain) is at least 70% (-3 decibels) of the desired command.