Rockwell Automation 1398-PDM-xxx IQ Master Version 3.2.4 for IA-2000 and IQ-5000 Positioning Drive Modules, IQ-55 - Manual (Page 386)

364 Application Examples • Feed-To-Length Application
Publication 1398-PM601A-EN-P — October 2000
APPENDIXES
Accuracy
The accuracy of the system is determined by the mechanics of the system and the performance of the
position controller. To achieve a given accuracy, the resolution of the position feedback should be at
least five times better than the desired accuracy. Tuning of the position and velocity control loops also
affects the accuracy of the system, as well as the settling time for the system to be in position after a
move.
Interfacing
The ULTRA Plus or IQ-Series controller provides great flexibility as a programmable motion controller
for interfacing to the machine. The program illustrated in this application note provides a “cut” output
which turns on to indicate that the material is in position and the operation can begin. A “ready” input
indicates that the operation is complete and the controller can begin the next move. Another output is
programmed to turn on before the move is complete and can be used to initiate an action prior to the
material being in position. Some applications require the material to back away from the knife as the cut
is made. In these cases, a “continue” input is used to signal the controller to make the back-up move,
before the “ready” input starts the next forward move.
Registration
Registration is useful when an operation must be performed relative to a reference position or printed
mark on the material. An external registration sensor turns on when the registration mark is detected.
The ULTRA Plus or IQ controller records the position where the registration mark is detected, and at the
end of the move compares the distance moved past the registration mark to the desired registration dis-
tance. If the two distances are different, the correction is added to the next move. This technique works
well for correcting for stretch or printing variations which change gradually as the material is unrolled,
but it does not work well if the variation from one move to the next is significant. The accuracy of the
registration system is affected by the speed of the sensor used, resulting in an error that is a function of
the material speed when the registration mark is sensed. The registration sensor output is connected to
input 11 on the ULTRA Plus or IQ controller. Input 11 is the trigger for a hardware latch which latches
the position within 1.5 microseconds of the off to on transition of the sensor.