Delta RMC151 User Manual download pdf (Page 107)

3 Controller Features

3.5.8. Gain Scheduling

Gain scheduling is the process of dynamically changing the gains of an axis based on some

scheduling variable. The scheduling variable may be any measurable quantity in any RMC

For example, an axis may require different gains based on its position. In this case, the axis'

position is the scheduling variable. By defining the gains as a function of the axis's position,

the gain scheduling results in optimum control.

Gain Scheduling Using Curves

Gain scheduling can be implemented in the RMC by using curves and the curve

interpolation functions. Gain scheduling involves these steps:

1. Determine the gain values at several points

Tune the axis for several different values of the scheduling variable. For example, if

the scheduling variable is the axis position, you should tune the axis at the ends, and

perhaps one or more positions in the middle. Record the gains for each position.

2. Define the gain curve for each gain

Using the Curve Tool

and the gain values you recorded, create a curve for each gain.

The scheduling variable will be the x values of the curve, and the gain values will be

the y values. The curve interpolates between the points you entered, providing a

smooth gain scheduling function. Cubic curves will provide the smoothest transition

between gains, although linear curves will work as well. If you choose a cubic curve,

choose the Natural Velocity Endpoint Behavior. Constant curves are not recommended,

as they will cause undesirable discontinuities in the gain terms, especially the Feed

Forwards.

3. Continually apply the gain to the axis

Create a user program that uses the CRV_INTERP_Y

function to get the curve values

for the current scheduling variable value, and apply the values to the gains. The user

program must run continuously.

For example, the user program below will apply the gains and the output bias based

on the axis position. The expression can easily be expanded to handle multiple

axes.

To successfully use this program, make sure the RMC is in RUN mode. This can be

done by setting the RMC to start up in RUN mode in the Programming Properties,

on the RUN/PROGRAM page. Also, in the Programming Properties, on the Halts

tab, make sure the task this program is running on is set to halt. To start this user

program when the RMC starts up in RUN mode, use the _FirstScan tag on the

Program Triggers

3.5.9. Valve Linearization

Valve linearization refers to compensating for non-linear hydraulic valves.

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Delta RMC151 User Manual Page 107