Rockwell Automation 1398-PDM-xxx IQ Master Version 3.2.4 for IA-2000 and IQ-5000 Positioning Drive Modules, IQ-55 - Manual (Page 414)

392 Application Examples • Vertical, Form, Fill and Seal
Publication 1398-PM601A-EN-P — October 2000
APPENDIXES
Vertical, Form, Fill and Seal
Description
Vertical form, fill, and seal (VFFS) machines are used in a variety of packaging applications. As the
name implies, the machine starts with film in a roll, forms the film into a tube, fills the tube with the cor-
rect amount of product, and seals the top and bottom of the package. The VFFS machine typically is
used in packaging of dry materials such as cereals, snack foods, kitty litter, and fertilizer. The product
itself is gravity fed into the tube, often by a precision scale which measures the proper amount of prod-
uct before the fill operation. The motion control system must feed the film the correct length for each
bag. If the film is pre-printed, registration is required to maintain the seal in the correct position relative
to the printing. On some machines, a second axis may be used to control the tension on the film. The
ULTRA Plus or IQ Positioning Drive Module provides the capabilities required for the film feed with
optional registration plus the film tension control. The ULTRA Plus or IQ combines the flexibility of a
programmable position controller with the reliability and low maintenance of brushless servo systems.
Advantages of a Servo System
•
The operator interface and programmability of the ULTRA Plus or IQ allows quick set-up and
change-over between different product lengths.
• Accurate, repeatable digital control produces quality parts with minimum scrap.
• The high speed interrupt input yields precise registration adjustment.
Design Considerations
Mechanics
The servo motor should be chosen based on the torque and speed required plus 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. If a gearbox is used, a low backlash type gear (using planetary technology)
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.
Accuracy
The accuracy of the system is determined by the mechanics of the system and the performance of the
position control. In order to achieve a given accuracy, the resolution of the position feedback should be
at least five times better than the desired accuracy. The tuning of the position and velocity control loops
also affect the accuracy of the system, as well as the time to settle into position after a move.
Operator Interface
The controller must provide the operator with the capability to easily and quickly change the setup of
the machine. The variables that can be changed are the product length, the move speed, the registration
distance and window (if used), the seal time or dwell between moves, and the gear ratio between the
pull belts and the feed rolls which control the tension. The operator should be able to change these vari-
ables while the machine is running to allow fine-tuning of the different parameters.
I/O Requirements
The VFFS control requires several I/O connections. The controller must output a signal to begin the seal
and cut operation, and must monitor an input indicating that the seal and cut operation is complete.
Additional I/O is required for stopping and starting the machine, and possibly for a jog mode to thread
the film into the machine.
Registration
Registration is required when the film is pre-printed so the bags are sealed and cut relative to the print-
ing on the film. An external registration sensor turns on when the registration mark is detected. In many
cases the registration mark is printed on the material in a position where no other printing or marks will
be detected by the registration sensor. Sometimes it is not possible to put the registration mark in a clear
lane, and other printing will be detected by the registration sensor. In this case the controller must estab-