Rockwell Automation Publication 1756-AT017A-EN-P - January 2013
Position-based Output Control with the MAOC Instruction 7
Position Reference: Actual versus Command
The MAOC instruction provides the option to use the actual feedback or the
command position as the master reference for the output cam:
• For axes configured as Feedback Only, the command position is equal to
the actual position.
• For axes configured as Virtual, the actual position is equal to the command
position.
Typically, the actual position for an axis has more variability than the command
position. For axes that have the option for either position, use the command
position to reduce possible error.
Figure 3 shows an extremely exaggerated case of actual position variability.
Filtering occurs when the position reference uses the actual position. This
increases the difficulty in determining when outputs change state, as shown by
labels A and B. In the example below, the MAOC instruction is bi-directional. If
the position reference is actual, the output energizes in a potentially troubling
manner. Setting the position reference to the command position improves the
output signal and the accuracy of the MAOC instruction.
Figure 3 - Command versus Actual Position
CUP
Actual
Command
Command On Time
Actual On Time
A
B
Time
On
Position
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