Rockwell Automation 1756-HYD02 ControlLogix Hydraulic Servo Module - Manual (Page 66)

66 Publication 1756-UM525A-EN-P - June 2003
Chapter 4 Using the 1756-HYD02 Module Features
The table below lists the configurable features available on the Gains tab.
Feature: Definition:
Position Gains: Proportional Position gain is used with position error to correct an axis’ position. The proportional gain specifies the
amount of correction (velocity command) that the controller applies for each unit of position error. You must
determine how much position error is expected while an axis runs at a specific speed.
To produce a component of the Velocity Command that ultimately attempts to correct for the position error,
multiply the Position Gains:Proportional by the Position Error.
• Too little Position Gains:Proportional results in excessively compliant, or mushy, axis behavior.
• Too large a Position Gains:Proportional, on the other hand, can result in axis oscillation due to loop
instability.
To set the gain manually, you must first set the velocity output scaling factor in the Output tab of this dialog.
If you know the desired position loop gain in inches per minute per mil or millimeters per minute per mil, use
the following formula to calculate the corresponding P gain:
Position Gains:Proportional = 16.667 * Desired Loop Gain (IPM/mil)
If you know the desired gain bandwidth of the position loop in Hertz, use the following formula to calculate
the corresponding P gain:
Position Gains:Proportional = Bandwidth (Hertz) x 6.28
The typical value for the Position Gains:Proportional is ~100 Sec-
1
.
Position Gains: Integral The Integral (i.e., summation) of Position Error is multiplied by the Position Gains: Integral, or Pos I Gain, to
produce a component to the Velocity Command that ultimately attempts to correct for the position error.
Position Gains: Integral improves the steady-state positioning performance of the system. Increasing the
integral gain generally increases the ultimate positioning accuracy of the system. Excessive integral gain,
however, results in system instability.
In certain cases, Position Gains: Integral control is disabled. One such case is when the analog output to the
axis’ drive is saturated. Continuing integral control behavior in this case would only exacerbate the
situation. When the Integrator Hold parameter is set to Enabled, the axis loop automatically disables the
integrator during commanded motion.
The Position Gains: Integral is also disabled when the axis’ actual position is within the deadband
compensation window of the target position. This keeps the axis from hunting when valves with overlapped
spools are used.
While the Position Gains: Integral is typically established by the automatic axis loop tuning procedure (in the
Tuning tab of this dialog), its value may also be set manually. Before doing this, the Velocity Scaling factor
for the axis must be established for the drive system. Once this is done, the Position Gains: Integral can be
computed based on the current or computed value for the Position Gains:Proportional using the
following formula:
Position Gains: Integral =.025 X 0.001 s/ms X (Position Gains:Proportional)
2
Assuming a Position Gains:Proportional value of 100 Sec-
1
this results in a Position Gains: Integral value of
0.25 1/ms-s