Rockwell Automation 1771-QB Linear Pos. - Manual (Page 129)

Initializing and Tuning the Axes
Chapter 8
8Ć11
Example: Maximum Velocity Calculation
If you have a cylinder with a 2 inch bore (inside diameter) and a servo valve
rated for 10 gallons per minute, the maximum velocity is approximated as
follows:
Velocity = 4.9 x 10/2 2 = 12.25 ips
4. Use bits 5 and 6 of axis control word 1 (N45:131) to jog the axis back and
forth between the software travel limits until the maximum velocity
stabilizes in the status block.
Important: The maximum velocity predictions will vary slightly for moves at
different velocities due to non-linearities in the hydraulic system. If it is critical
that the module perform best at a particular velocity, that velocity should be
used to determine the optional analog calibration constants. Otherwise, it is
recommended that you use a moderately low velocity (10% of the maximum
velocity) for this purpose. Adjust this velocity in N45:27.
5. The maximum positive velocity (words N44:30 in the status block) is the
positive analog calibration constant. The maximum negative velocity
(words N44:32 in the status block) is the negative analog constant. Enter
these values into the parameter block (words N45:3, and N45:4).
Important: If the maximum velocity returned by the module is dramatically
different than your initial guess, check the analog output switches and the
analog range word.
Feedforward Gain
The feedforward gain can dramatically reduce the following error during a
move. The effectiveness of the feedforward gain is dependent on the accuracy
of the analog calibration constants, the linearity of the servo valve, and system
responsiveness.
You can usually achieve acceptable results by selecting a conservative
feedforward gain of 30%. For more precise velocity control, adjust the
feedforward gain as follows:
1. Start the hydraulic pump and check the pressure.