Rockwell-automation 1771-QB Linear Pos. Manual de usuario descargar pdf (Pagina 128)

Initializing and Tuning the Axes

Chapter 8

810

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

= 0.0100 (ips/s)/mil

Derivative gain: K

= 0

Feedforward gain K

= 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

(inches per second)

where: Q = flow rate in gallons per minute

B = bore of cylinder in inches

Axis Tuning

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Rockwell-automation 1771-QB Linear Pos. Manual de usuario Pagina 128

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