Delta RMC151 - Manual (Page 194)

RMC70/150 and RMCTools User Manual
Switching feedback for an axis is useful in certain testing applications, or for using
several transducers to provide the desired resolution over the range of the feedback.
For details, see Switching Feedback using Custom Feedback.
• Feedback linearization
Feedback linearization refers to either "straightening" the output of a transducer to
make up for its nonlinearity, or calculating the measurement of some point that is
geometrically related to the transducer measurement, such as calculating the end of a
swing arm based on the position of the cylinder that moves the swing arm.
Feedback linearization can de done using curves or a mathematical formula. For details,
see Feedback Linearization using Curves and Feedback Linearization using Mathematical
Formula.
• Redundant feedback
If one of multiple feedback devices fails, the system can continue operating without
interruption.
For details, see Redundant Feedback using Custom Feedback.
How It Works
Axes defined with custom feedback do not have an assigned physical feedback. Rather,
they have an _Axis[].CustomCounts register (_Axis[].SecCustomCounts for secondary
inputs) that can be written to. You must create a user program that continuously
calculates the feedback value and assigns it to this register.
The _Axis[].CustomCounts or _Axis[].SecCustomCounts value will have the Scale and
Offset applied to it, and the result then appears in the Actual feedback register for that
axis, whether it be Actual Position, Actual Velocity, Actual Pressure, Actual Force or Actual
Acceleration. Typically, the Scale and Offset are left at their default values of 1 and 0,
which means that the Custom Counts value remains unchanged and the value you want
as the feedback can be directly written to the _Axis[].CustomCounts or
_Axis[].SecCustomCounts register.
Limitations
Custom feedback has the following implications:
• The RMC must always be in RUN mode
• One task will be continuously running the user program that is performing the custom
feedback calculations. You must make sure this program always runs, as described
below.
• Auto-tuning cannot be used, since auto-tuning requires that the RMC be in PROGRAM
mode. Auto-tuning may be used for other axes in the RMC, but the custom feedback
axes can not be operating while auto-tuning other axes.
• Rotary axes are not supported by custom feedback.
Setting Up and Using Custom Feedback
Planning Number of Axes
Applications making use of custom feedback usually require the use of extra reference
axes. This may result in exceeding the total number of axes available, particularly in the
RMC70 series, which is limited to four axes.
For example, consider a single-axis position feedback linearization application utilizing
custom feedback. Without custom feedback, a single-axis position application uses one
axis in the RMC. However, the custom feedback will require two axes: the control axis,
which will use custom feedback, and a reference axis, which will use the physical input
from the position transducer.
Make sure to carefully determine the axis usage so that it does not exceed the number of
axes available. The RMC70 series supports 4 total axes and the RMC150 supports 16 total
axes. A reference axis is counted as one axis.
174 Delta Computer Systems, Inc.