Device for controlling an inkjet printing machine to provide a variable distance between an inkjet print head and a substrate

Abstract

A device for controlling the printing operation in an inkjet printing machine includes at least one inkjet print head disposed at an adjustable distance from a substrate to be printed on. A device receives a print job and a bad sheet sensor has a trigger threshold. A machine control unit adjusts the distance between the inkjet print head and the substrate to be printed on as well as the trigger threshold of the bad sheet sensor before or after the printing operation as a function of a received print job.

Claims

1. A device for controlling a printing operation in an inkjet printing machine, the device comprising: at least one inkjet print head disposed at an adjustable distance from a substrate to be printed on; a bad sheet sensor having a trigger threshold; a device for receiving print job data; and a machine control unit adapting said distance between said inkjet print head and the substrate to be printed on and adapting said trigger threshold of said bad sheet sensor as a function of received print job data including inks being used before or during the printing operation.

2. The device according to claim 1, which further comprises a drive connected to said machine control unit for adjusting a height of said inkjet print head.

3. The device according to claim 1, wherein said machine control unit includes a memory for storing print jobs subdivided into various categories of different distances between said inkjet print head and the printing substrate.

4. The device according to claim 1, wherein said device for receiving a print job includes an input device for inputs made by an operator.

5. The device according to claim 4, wherein said input device is a touch screen.

6. The device according to claim 1, wherein said device for receiving a print job includes an interface with a pre-press device for transmitting print job data.

7. The device according to claim 1, wherein said machine control unit records an occurrence of bad sheets and displays a message on a screen when a threshold saved on said machine control unit is exceeded to propose a greater distance between said inkjet print head and the substrate.

8. The device according to claim 1, wherein said distance between said inkjet print head and the substrate as well as said trigger threshold of said bad sheet sensor before or during the printing operation are dependent on characteristics of the printing substrate.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The figure of the drawing is a diagrammatic, longitudinal-sectional view of an inkjet printing machine with a bad sheet sensor and a height-adjustable inkjet print head.

DETAILED DESCRIPTION OF THE INVENTION

(2) Referring now in detail to the single figure of the drawing, there is seen a sheet-fed printing machine 100 constructed as a digital printing machine. A respective sheet 1000 is fed-in by a feeder 1 in order to be transported through a printing unit 2 to a delivery 3, in a direction of transport T. Cylinders, namely transfer cylinders 5 and a jetting cylinder 10, are the major devices for transporting a respective sheet 1000. Multiple inkjet print heads 4 that are electrically height-adjustable are disposed at a short distance a above the jetting cylinder 10 in order to print on a sheet 1000 that is moved past by the jetting cylinder 10 at the short distance a. The jetting cylinder 10 may also be referred to as a printing cylinder.

(3) In the illustrated embodiment, the jetting cylinder 10 has three sheet-holding regions 11 which are separated from one another by respective gaps 12. Grippers 13 hold the sheets 1000 on the sheet-holding regions 11. Measurement scales 18, 19 are provided in the gaps 12.

(4) A machine control unit or controller 15 having a user interface and a memory 22 is provided to control the printing machine 100 and in particular the height-adjustable inkjet print heads 4. A drive 21 connected to the machine control unit 15 adjusts a height of the inkjet print head 4. As described above, a device for receiving a print job may include an input device, in particular a touch screen 16, for an operator to make inputs and therefore the device may be part of the machine control unit 15. However, a device for receiving a print job may also be an interface 20 with a pre-print department for transmitting print job data. A sensor system 14 is disposed upstream of the inkjet print heads 4 as viewed in the direction of transport T. The sensor system 14 continuously monitors the sheets 1000 and the measurement scales 18, 19 and is also referred to as a bad sheet sensor. The sensor system 14 is disposed in the path of sheet travel and is likewise connected to the machine control unit 15. The sensor system 14 may monitor the traveling of the sheets, in particular the printing material thickness d, i.e. how far the sheets 1000 protrude beyond the sheet-holding areas 11. In this way, creases, dog ears, folds, waves, and sheets 1000 that are held insufficiently or badly may be detected. A data communication link is provided between the sensor system 14 and the machine control unit 15, which also includes a sensor control unit. The sensor system 14 needs to be disposed sufficiently far upstream of the inkjet print heads 4 for a collision between a sheet 1000 and inkjet print heads 4 to be avoided even if a problem occurs at the trailing edge of the sheet, for instance by stopping the machine 100, lifting the inkjet print heads 4, or ejecting the defective sheet 1000 (not illustrated). An ejection drum 25 for ejecting defective sheets, e.g. sheets 1000 with an incomplete print, is disposed downstream of the jetting cylinder 10.

(5) The machine control unit 15 receives the data of a print job to be executed on the sheet-fed printing machine 100 by using a touch screen or a pre-print interface. In this process, the machine control unit 15 analyzes the print job in terms of print quality, characteristics of the printing substrate, and other properties to be able to calculate a suitable distance between the sheets 1000 and the inkjet print head 4. In addition, the machine control unit 15 calculates the trigger threshold of the sensor system 14 as a function of the characteristics of the print job. Aspects that are taken into consideration in particular include the thickness and stiffness of the printing material because these characteristics are important in describing the danger of waves, bent edges, and dog-eared corners of the sheet 1000. In addition, multiple categories for categorizing print jobs may be saved on the machine control unit 15. High-quality print jobs may, for instance, be assigned to a class requiring a comparatively short distance between the inkjet print head 4 and the sheet 1000 and a correspondingly low trigger threshold for the sensor system 14. A category of medium-quality print jobs uses a greater distance and a correspondingly higher trigger threshold for the sensor system 14. Low-quality print jobs may use an even greater distance and a higher trigger threshold in order further to reduce waste caused by bad sheets 1000, i.e. sheets that are problematic. The device of the invention may in principle be used in all inkjet printing machines in which the distance between the inkjet print head 4 and the print sheets 1000 may be adjusted by adjusting the height of either the inkjet print head 4 or the printing cylinder 10 and which include a bad sheet sensor.

(6) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:

(7) 1 feeder

(8) 2 printing unit

(9) 3 delivery

(10) 4 inkjet print head

(11) 5 transfer cylinder

(12) 10 printing cylinder (jetting cylinder)

(13) 11 sheet-holding area/sheet-supporting surface

(14) 12 gap

(15) 13 gripper

(16) 14 sensor system

(17) 15 machine control unit with sensor control

(18) 16 touch screen

(19) 18 measuring gauge (AS)

(20) 19 measuring gauge (BS)

(21) 20 interface

(22) 21 drive

(23) 22 memory

(24) 25 ejection drum

(25) 100 sheet-fed printing machine

(26) 1000 sheet

(27) a distance

(28) T direction of transport