Rockwell Automation 1746-QS,D17466.19 SYNCHRONIZED AXES MODULE - Manual (Page 23)

4–7
Publication 1746-6.19 March 1998
7. If moving a relatively large mass with a relatively small hydraulic
cylinder, first investigate the affect of:
a) Integrator Mode selection in the Command-mode word:
active always, for accel/decels, in position, or never.
b) Integrator Limit selection in the Config word:
20% for a typical hydraulic system, 80% for a difficult system.
Also, see step 6 for using
INTEGRAL GAIN to help minimize the
end-point position error.
For additional information on PID Gains, refer to that topic, below.
Adjusting Command-word Speed and Acceleration Values
Increase the SPEED and ACCELERATION command words gradually
while making long moves. Use Hydraulic Configurator to plot the
moves and look for following errors, overshoot, or oscillations.
Eventually, when the
SPEED and ACCELERATIONS are too high, the
moves will cause an error on the axis.
If an overdrive error occurs, there is not enough drive capacity to drive
the axis at the requested SPEED. Should this occur, reduce the SPEED.
If excess Following Error occurs, the appropriate FEEDFORWARD
configuration parameter must be adjusted for extend and retract moves.
If excess Following Error persists, ACCEL and DECEL ramps may be too
steep for your system response. You can reduce their values, or increase
the
ACCEL FEEDFORWARD term.
Also remember that you can specify either the time or the distance in
which the
ACCELERATION or DECELERATION must occur.
After correcting the problem of excess Following Error, keep moving the
axis back and forth with increasing
SPEED values until you reach desired
speed. Should the system seem a little sloppy, try increasing the
PROPORTIONAL GAIN until the axis moves with a steady state
FOLLOWING ERROR (as observed by axis plot) and stops at the end point
with minimum in-position error. Remember: the parameters are not
updated in the module until you issue the “P” command.
Adjusting Feedforward Parameters
In many hydraulic systems the feedforward parameters (EXTEND
FEEDFORWARD and RETRACT FEEDFORWARD) are the most
important parameters for position tracking during a move.
Use the auto Feedforward Adjust command “F” to minimize the
FOLLOWING ERROR . Refer to General Tuning Procedure, step 2.
For move information, refer to these parameters in the Help Topics.