User`s manual

D-12 Motion Mate™ DSM314 for Series 90™-30 PLCs User's Manual – January 2001 GFK-1742A
D
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 the configuration chapter for details.
2. Set the Velocity at 10 Volt value as described in the configuration chapter.
3. Set the Integrator Mode selection 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. We 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. By setting the Integrator Mode to “OFF” as requested in the previous section, we
create 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.
High Bandwidth
•
Allows the servo to more accurately reproduce the desired motion
•
Allows accurate following of sharp corners in motion paths and high machine cycle
rates