Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS - Manual (Page 34)

Positioning with Allen-Bradley PC
Chapter 4
4Ć10
RunĆSingleĆStep Moves
For run-single-step moves, axis synchronization is dependent upon the
axis response on each move. The same is true for continuous moves with
the next move in the opposite direction.
In both cases, the 1771-ES expander executes the next move
automatically as soon as the current move is done, without waiting for a
start signal. However, the time it takes for each move cannot be precisely
calculated because the following error has to close before the move is
done.
Auto Position Correction
The auto position correction feature may prevent an accumulation of
position error caused by occasional noise on the channel A and B inputs.
However, if the environment is excessively noisy, or if the cabling and
shielding is not proper, this feature causes the axis to jump or jerk. This
jump or jerk should indicate to you that a problem exists.
You enter the number of lines on the encoder and the feedback multiplier
into the parameter block. From this, the 1771-ES expander knows how
many feedback pulses it should receive each encoder revolution. The
module also receives a marker pulse each revolution.
Each time the 1771-ES expander receives a marker pulse, it checks the
value in the position register to see if it is an even multiple of the number
of feedback pulses per revolution. If the value is off, the 1771-ES
expander will automatically adjust it.
This feature corrects position errors caused by noise on the channel A and
B encoder feedback signals. However, the function of this feature
assumes a noise-free marker signal.
The marker signal does have some noise protection because the 1771-ES
expander only accepts a marker signal when the channel A and B signals
are high (unless you set the marker logic jumper to the not-gated
position).
To command axis motion, you must be able to specify axis position by
establishing an axis position scale, or coordinate system, for each axis.
Specifying Axis Position