Converting machine
AssigneeBobst Lyon
InventorAbdelmalik Badreddine
Life of this patent
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Abstract
The invention relates to a method of aligning a plurality of printed motifs on a sheet (3) in a converting machine (10). An actual position (Pa_1) at a first sensor is defined as an initial reference position (P_ref1) for the sheet, and at least one displacement error (Δd2) is calculated and compared to a first threshold (T1). If the displacement error is lower than the first threshold, then the angular position (α) of a printing cylinder (42) in the second flexographic printing unit (16b) is adjusted. However, if the error is higher than the first threshold, then at least part of the of the displacement error (Δd_2) is corrected by modifying the speed (V) of a vacuum transfer unit located between the first printing unit and the second printing unit.
Claims13
A method of aligning a plurality of printed motifs on a sheet in a converting machine, the converting machine comprising a flexographic printing module having at least a first printing unit configured to print a first motif and a second printing unit configured to print a second motif, the first and second flexographic printing units being arranged in succession along a direction of transportation of the sheet, the converting machine further comprising a register correction system having a first sensor arranged in a first detection position at a distance upstream of the first printing unit and a second sensor arranged in a second detection position at a distance upstream of the second printing unit, the method comprising:
- detecting a passage of a front leading edge of the sheet with the first sensor,
- determining an actual position of the front leading edge at the first detection position from a detection time of the first sensor,
- defining the actual position as an initial reference position for the sheet,
- calculating a second reference position at a downstream-located second sensor position,
- detecting a passage of the front leading edge with the second sensor and determining an actual position of the front leading edge at the second sensor position from a detection time provided by the second sensor,
- calculating an individual displacement error at the second detection position by determining a difference between the detected actual position and the second reference position,
- comparing the individual displacement error to a first threshold,
- if the individual displacement error is lower than the first threshold, then providing an angular position correction to a printing cylinder in the second flexographic printing unit, and
- if the error is higher than the first threshold, then providing a first correction in the form of an angular position correction to the printing cylinder and a second correction to change the position of the sheet, said second correction is performed by modifying the transportation speed of a vacuum transfer unit located between the second sensor position and the second printing unit, and whereby the sum of the first and second corrections equal the individual displacement error.
A converting machine comprising:
- a flexographic printing module having at least a first printing unit configured to print a first motif on a sheet and a second printing unit configured to print a second motif on the sheet, the first and second flexographic printing units being arranged in succession along a direction of transportation of the sheet, and
- a register correction system, the register correction system comprising a first sensor arranged in a first detection position at a distance upstream of the first flexographic printing unit and a second sensor arranged in a second detection position at a distance upstream of the second flexographic printing unit, the register correction system being configured to perform a method of aligning a plurality of printed motifs on the sheet, the method comprising:
- detecting a passage of a front leading edge of the sheet with the first sensor,
- determining an actual position of the front leading edge at the first detection position from a detection time of the first sensor,
- defining the actual position as an initial reference position for the sheet,
- calculating a second reference position at a downstream-located second sensor position,
- detecting a passage of the front leading edge with the second sensor and determining an actual position of the front leading edge at the second sensor position from a detection time provided by the second sensor,
- calculating an individual displacement error at the second detection position by determining a difference between the detected actual position and the second reference position,
- comparing the individual displacement error to a first threshold,
- if the individual displacement error is lower than the first threshold, then providing an angular position correction to a printing cylinder in the second flexographic printing unit, and
- if the error is higher than the first threshold, then providing a first correction in the form of an angular position correction to the printing cylinder and a second correction to change the position of the sheet, said second correction is performed by modifying the transportation speed of a vacuum transfer unit located between the second sensor position and the second printing unit, and whereby the sum of the first and second corrections equal the individual displacement error.
Dependencies are inferred from the claim text.