A spool of pre-printed material with a registration mark is fed through a single color printing station. The web is driven by a prime mover at various speeds depending on the type of product. The logo must be printed and aligned with the registration mark on the pre-printed material. The printing pitch on the spool of pre-printed material can be various sizes, depending on production requirements, while the diameter of the print drum is fixed.
The EMAX 1-1/2 axis controller is chosen for this master/slave electronic cam application. An encoder is connected to the web feed roller to provide a master web speed/position reference. A servo motor is coupled to the printing and backup drums via a precision gearbox.
A touch-screen display is selected as a simple operator interface, and a high speed registration sensor is mounted above the web to sense the registration mark.
An application program is developed with the Emerald Motion Language (EML) PC software for the EMAX controller that has the following sequence:
- When a new spool of pre-printed material is loaded into the machine the web starts moving with the print head stationary but clear of the web. The EMAX, using the registration sensor measures the pitch of the pre-printed material.
- An electronic cam is then calculated to have the servo motor match web line speed when the print head is engaged with the web and then advance or retard when the print head is free. The advance or retard amount compensates for the difference in the circumference of the print cylinder and the pitch of the printing.
- The print head motion starts at the proper angle to print the logo on the web during the speed match portion of the printing cycle. Once the print head is free of the web the motor slows down or speeds up as necessary to print the logo on the next pitch of the web.
- The operator programs a positional watch window in which to expect the registration mark. If the mark occurs in the window the motion profile is retarded or advanced to compensate for slight pitch to pitch printing variations. If the mark is not found for several printing pitches an alarm is sounded to alert the operator of the problem.
ADDITIONAL APPLICATION FEATURES
- Automatic teach and learn of the pre-printed material pitch
- Operator adjustment:
- Number of registration marks missed before alarm
- Distance between registration mark and logo
- Width of the registration mark watch window
- Keypad/display for startup, operator messages and diagnostics
- High speed sensor registration
- Operator warning for loss of material or pre-printed registration marks
OTHER INDUSTRY APPLICATIONS:
- Web perforation
- Multi-color printing
- Labeling machine