Rockwell Automation 1771-QB Linear Pos. - Manual (Page 128)

Initializing and Tuning the Axes
Chapter 8
8Ć10
Each axis needs to be tuned to allow for its specific mechanical and electrical
characteristics. If you change system variables, such as hydraulic pressure,
cylinder size or servo valve characteristics, you may need to re-tune your axis as
well. Remember that every time you change parameters in the parameter block,
you should reset the axis using bit 9 of the axis control word 1 (N45:131).
Analog Calibration Constants
It is important that the positive and negative analog calibration constants be
optimized first. These are critical constants, since the PID and feedforward
gains use them to correct for directional differences in system performance.
Follow these steps to adjust the analog calibration constants:
1. Start the hydraulic pump and check the system pressure. Apply power to
the I/O chassis and the axis.
ATTENTION: To guard against possible injury: Keep all personnel
clear of the axis. Have a competent person standing by to disconnect
axis power and stop the flow of hydraulic fluid if necessary.
2. If you have previously tuned the axis, you can leave the PID and
feedforward gains unchanged. Otherwise initialize the loop parameters as
follows:
Proportional gain: Kp = 0.0100 ips/mil
Integral gain: K
I
= 0.0100 (ips/s)/mil
Derivative gain: K
D
= 0
Feedforward gain K
F
= 0
Gain break speed = 0 ips
Gain factor = 0
Integral term limit = 10%
PID band = 0.500
Deadband = 0
Maximum PID error = 1.000 in
Excess following error = 1.000 in
3. Initialize both analog calibration constants to the maximum velocity
possible for the servo cylinder selection. For hydraulic systems with
cylinders with circular cross sections, the maximum velocity can be
approximated using the following formula:
Velocity = 4.9 Q/B 2 (inches per second)
where: Q = flow rate in gallons per minute
B = bore of cylinder in inches
Axis Tuning