Control Techniques FM-3 Reference Manual page 29

Absolute Index
Figure 23: Absolute Index Example 1
In the example above, the current position is 1 rev. If this index is initiated, the motor will travel to a position of 5 revs no
matter where it is sitting before the move. From 3 revs, it will travel 2 revs to finish at 5 revs. If the absolute index to 5 revs
is initiated a second time immediately after the index, no motion will occur because the motor will already be at a position of
5 revs.
The direction of an Absolute Index is determined by the starting position and the absolute index position. If the starting
position for the above index is 9 revs, then the motor will rotate in the negative direction to end up at 5 revs. The figure below
shows this.
Figure 24: Absolute Index Example 2
Absolute indexes with Rotary Rollover enabled will take the shortest path to the position entered in the index position
parameter.
Note
Absolute indexes move to positions relative to where the machine was homed using the Home, or the DefineHome
destination.
Incremental Indexes
An incremental index will move the motor a specified distance in the + or - direction regardless of the starting position. The
direction of the incremental index motion is determined by the sign (+ or -) of the Index Distance parameter.
Incremental Index
Figure 25: Incremental Index Example
In the example above, the motor starts at 1 rev, travels a distance of 2 revs and stops at 3 revs. If the same index is initiated
a second time, the FM-3 module would move the motor another 2 revs to a position of 5 revs. If initiated a third time, the
motor would travel another 2 revs to a final position of 7 revs. The figure below shows this operation.
Absolute Index
Start Position = 1 Rev
Index Position = 5 Revs
Absolute Index
Start Position = 9 Revs
Index Position = 5 Revs
Incremental Index
Start Position = 1 Rev
Index Distance = 2 Revs
Operational Overview
15