Rockwell Automation 1398-PDM-xxx IQ Master Version 3.2.4 for IA-2000 and IQ-5000 Positioning Drive Modules, IQ-55 - Manual (Page 385)

Application Examples • Feed-To-Length Application 363
Publication 1398-PM601A-EN-P — October 2000
APPENDIXES
WAIT I12 ON ;Wait for a product
V3=@I2P2-@I1P2-OFFSET2 ;Calculate correction move distance:
;product position - flight position - offset. The
;’@’symbol reads position variables in encoder counts
MOVD = -CTOU2 V3 ;Perform correction move (converted back to user
; units)
WAIT I12 OFF ;Make sure product has cleared the sensor
JUMP MAIN ;Continue the process
;
END
NOTE:The correction distance is calculated in encoder counts so the correction distance is still properly
calculated if the internal position counter rolls over between flight and product.
Feed-To-Length Application
Description
Feed-to-length operations are common in many different industries for a variety of manufacturing pro-
cesses. Examples of feed-to-length applications include discrete part cutting, forming, or punching,
plastic bag manufacturing, press feeds, thermoformers, and sheet metal shearing or forming. A set of
pinch or nip rollers is controlled by an Allen-BradleyULTRA Plus or IQ-Series Positioning Drive Mod-
ule and brushless servo motor. The rollers feed material the required length into the machine, and then
hold the material in position while the operation is in process. On pre-printed materials the ULTRA Plus
or IQ-Series controller positions the material relative to a reference or registration mark on the material.
Advantages of a Servo System
•
The operator interface capability of the controller allows quick set-up and change-over between
different product lengths.
• Advanced microprocessor control produces maximum accuracy and speed.
• Programmable motion controller provides flexible system for future enhancements.
Design Considerations
Mechanics
The servo motor is chosen based on the torque and speed required, and the reflected inertia of the
mechanics. Gear reduction through belts and pulleys or a gearbox can help reduce the system inertia
reflected to the motor. A low backlash gearbox should be used to maintain accuracy from the motor to
the pinch rollers. If timing belts and pulleys are used, HTD tooth profile belts are recommended.
The conversion from rotary to linear motion is accomplished through the pinch rollers. As the diameter
of the rollers changes, the inches per turn conversion changes by PI (3.14159) times the change in diam-
eter. Therefore, the rollers should be constructed of a material which will not change diameter signifi-
cantly with temperature or time. The effect of changing pinch roller diameter is more noticeable for
longer moves.
Slippage
Force is transmitted to the material by the friction of the pinch rollers. As the acceleration increases, the
rollers may slip on the material, resulting in short moves. The acceleration must be kept low enough to
prevent slippage between the rollers and the material. A second encoder can be added to a measuring
wheel on the material to verify the position and allow corrections for slip. The Allen-Bradley ULTRA
Plus or IQ-Series controller can generate an S curve motion profile to minimize discontinuities in the
velocity which reduces the chance of slippage. The S curve profile requires higher peak torques from
the motor and higher peak currents from the drive.