Rockwell Automation 1756-HYD02 ControlLogix Hydraulic Servo Module - Manual (Page 67)

Publication 1756-UM525A-EN-P - June 2003 67
Using the 1756-HYD02 Module Features Chapter 4
Position Gains: Differential Velocity Error is multiplied by the Position Gains: Differential to produce a component to the analog output
or Velocity Command that ultimately attempts to correct for the velocity error, creating a damping effect.
Thus, increasing the Position Gains: Differential results in smoother motion, enhanced acceleration, reduced
overshoot, and greater system stability. However, too much Position Gains: Differential leads to high
frequency instability and resonance effects.
Feedforward Gains:
Velocity Feedforward Gains: Velocity scales the current Command Velocity by the Feedforward Gains: Velocity and
adds it as an offset. Hence, the Feedforward Gains: Velocity allows the following error of the hydraulic
closed loop system to be reduced to nearly zero when running at a constant speed. This is important in
applications such as electronic gearing, position camming, and synchronization applications, where it is
necessary that the actual axis position not significantly lag behind the commanded position at any time.
The optimal value for Feedforward Gains: Velocity is 100%. However, you may need to adjust the value to
accommodate axes with non-linear characteristics and other application considerations.
Feedforward Gains:
Acceleration Feedforward Gains: Acceleration scales the current Command Acceleration by the Feedforward Gains:
Acceleration and adds it as an offset to the analog output generated by the position loop. With this done,
the position loops do not need to generate much of a contribution to the analog output, hence the Position
and/or Velocity Error values are significantly reduced.
When used in conjunction with the Feedforward Gains: Velocity, the Feedforward Gains: Acceleration
allows the following error of the hydraulic closed loop system during the acceleration and deceleration
phases of motion to be reduced to nearly zero. This is important in applications such as electronic gearing,
position camming, and synchronization applications, where it is necessary that the actual axis position not
significantly lag behind the commanded position at any time.
Remember, however, because the output is scaled in velocity, the Feedforward Gains:Acceleration
calibration is application-dependent.
Integrator Hold The integrator is always enabled. With this setting, the position loop temporarily disables the integrators
while the command position is changing. Point-to-point moves use this feature to minimize the integrator
wind-up during motion.
Manual Tune This button accesses the Gains tab of the Manual Tune dialog for online editing.
The Manual Tune button is disabled when RSLogix 5000 is in Wizard mode, and when you have not yet
saved or applied your offline edits to the other parameters in this table.
Feature: Definition: