SHEET-FED PRINTING PRESS WITH A SENSOR SYSTEM AND METHODS FOR CALIBRATING AND FOR ALIGNING THE SENSOR SYSTEM

Abstract

A sheet-fed printing press includes a printing cylinder and a high-precision sensor system for monitoring a sheet run in the area of the printing cylinder. At least one gage, which is mounted on the printing cylinder, can be detected by the sensor system. It is particularly advantageous if the sensor system is configured to be self-calibrating. A method for calibrating a sensor system and a method for aligning a sensor system are also provided.

Claims

1. A sheet-fed printing press, comprising: a sheet run area for guiding a sheet run in a sheet transport direction; a printing cylinder having two end faces; at least one gage being mounted on said printing cylinder; and a sensor system for monitoring the sheet run in a vicinity of said printing cylinder and for detecting said at least one gage, said sensor system being disposed in said sheet run area, said sensor system including a light curtain having a multiplicity of laser beams, and said sensor system including a transmitter and a receiver; said transmitter being disposed at one of said end faces and said receiver being disposed at another of said end faces of said printing cylinder defining a viewing direction of said sensor system at right angles to said sheet transport direction.

2. The sheet-fed printing press according to claim 1, wherein said sensor system is self-calibrating.

3. The sheet-fed printing press according to claim 1, wherein said at least one gage images different sheet heights over an angle of rotation.

4. The sheet-fed printing press according to claim 1, wherein said printing cylinder includes a channel, and said at least one gage is mounted in said channel or next to said channel.

5. The sheet-fed printing press according to claim 1, wherein said printing cylinder has two sides, said at least one gage includes at least two gages, at least one of said gages is disposed on one side and at least one other of said gages is disposed on the other side of said printing cylinder.

6. The sheet-fed printing press according to claim 5, wherein said at least two gages are disposed with a mutual angular offset on said printing cylinder.

7. A method for calibration of a sensor system for monitoring a sheet run in a vicinity of a printing cylinder of a sheet-fed printing press, the method comprising the following steps: attaching at least one gage to the printing cylinder; using the sensor system to detect the at least one gage during rotation of the printing cylinder and to provide a measurement result; storing a desired value in a sensor controller and assigning a certain desired value as a measured value to a specific angle of rotation in the sensor controller; comparing the measurement result with the stored desired value; and if necessary, performing a correction of the sensor system for the calibration by storing the measured value as a threshold value for monitoring the sheet run in the sensor controller upon a deviation of the measured value from the desired value.

8. The method for calibrating according to claim 7, which further comprises taking manufacturing tolerances of the at least one gage into account in the calibrating and using the manufacturing tolerances for codetermining the desired value.

9. A method for aligning a sensor system for monitoring a sheet run of sheets of different thickness in a vicinity of a printing cylinder of a sheet-fed printing press, the method comprising the following steps: providing a printing cylinder having two sides; attaching at least one gage supplying measured values on one of the sides and attaching at least one other gage supplying measured values on another of the sides of the printing cylinder; using the sensor system to detect the at least two gages; providing the sensor system with a transmitter, a receiver and a light curtain with a multiplicity of laser beams; placing the transmitter on one side and placing the receiver on the other side of the printing cylinder; adjusting the sensor system independently on the one side of the printing cylinder having the transmitter and on the other side of the printing cylinder having the receiver for a parallel position of the sensor system; storing a threshold value in a machine controller; and comparing the measured values of the gages and making a correction of the position of the transmitter and the receiver or displaying a warning, upon exceeding the threshold value stored in the machine controller.

10. The method for aligning according to claim 9, which further comprises taking manufacturing tolerances of the gages into account when aligning for aligning the sensor system parallel to the printing cylinder.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0030] FIGS. 1A and 1B are diagrammatic, front-elevational views illustrating a process for aligning a sensor system;

[0031] FIG. 1C is a fragmentary, cross-sectional view showing gages for the alignment;

[0032] FIG. 2A is a fragmentary, cross-sectional view showing the use of gages for a permanent calibration of the sensor system;

[0033] FIGS. 2B and 2C are diagrams showing continuous and discontinuous curves of a sheet thickness plotted against an angle of rotation;

[0034] FIG. 3 shows the sensor system with only one gage; and

[0035] FIG. 4 is a longitudinal-sectional view showing a digital sheet-fed printing press with a sensor system for monitoring a sheet run.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Referring now to the figures of the drawings in detail and first, particularly, to FIG. 4 thereof, there is seen a sheet-fed printing press 100, which is constructed as a digital printing press. A respective sheet 1000 is transported from a feeder 1 in a transport direction T through a printing mechanism 2 to a delivery 3. The transport of a respective sheet 1000 is in this case primarily accomplished by using cylinders, namely transfer cylinders 5 and a printing cylinder 10. Located above the printing cylinder 10 at a distance a from the printing cylinder 10 are inkjet heads 4, which print a sheet 1000 passing by the printing cylinder 10 at a short distance. The printing cylinder 10 is therefore also designated as a jetting cylinder. A drive 6 is provided for the printing mechanism 2.

[0037] In the embodiment shown, the printing cylinder 10 has three sheet retaining regions 11, which are each separated from one another by a respective channel 12. The sheets 1000 are held on the sheet retaining regions 11 by using grippers 13. Gages 18, 19 are provided in the channels 12.

[0038] A machine controller 15 with an operator interface and a memory is provided for driving the printing press 100. Located upstream of the inkjet heads 4 when viewed in the transport direction T is a sensor system 14, which is used for permanent monitoring of the sheets 1000 and the gages 18, 19. To this end, the sensor system 14 is disposed in the sheet run. The sheet run, in particular the printing substrate thickness d, can be monitored, i.e. how far the sheets 1000 project beyond the sheet retaining regions 11. Kinks, dog's ears, folded, corrugated, incompletely or poorly retained sheets 1000 can thus be identified. The sensor system 14 is connected in a data transmitting manner to the machine controller 15, which also includes a sensor controller.

[0039] The sensor system 14 must be disposed sufficiently upstream of the inkjet heads 4 so that even if there is a defect on the rear sheet edge, a collision of sheets 1000 and inkjet heads 4 can still be avoided, e.g. by stopping the machine 100, raising the inkjet heads 4 or discharging the defective sheet 1000 (not shown).

[0040] Located downstream of the jetting cylinder 10 is a discharge drum 25, through the use of which defective sheets, i.e. incompletely printed sheets 1000, can be discharged.

[0041] The method for aligning a sensor system 14 can be understood from FIGS. 1A and 1B. The sensor system 14 includes a light curtain 21 having a multiplicity of laser beams for monitoring the sheet run in the area of the printing cylinder 10. As a result of using a light curtain instead of a single light beam, the sheet run of sheets of different thickness can be monitored. The sensor system 14 also has a transmitter 16 and a receiver 17. The transmitter 16 is positioned on one side of the printing cylinder 10 and the receiver 17 is positioned on the other side of the printing cylinder 10. The transmitter and the receiver can be accommodated by a retaining clip 20. The retaining clip 20 of the sensor system 14 is accommodated by a machine frame of the printing press 100 which is not shown in detail and can be adjusted relative to the machine frame. The gages 18, 19 are provided in the channel 12 of the printing cylinder 10. The gage 18 is positioned on the drive-side end of the channel 12 and the gage 19 is positioned on the operator-side end of the channel 12. As can be seen clearly from the highly-exaggerated view of FIG. 1A, the sensor system 14 is not aligned parallel to the axis 10.1 and to the lateral surface 10.2 of the printing cylinder 10. An alignment of the sensor system 14 can now be made by lowering the sensor system 14 more severely on the operator side than on the drive side. That is, the sensor system 14 is lowered until the same value is measured on the two gages 18, 19. To this end, the gages 18, 19 are disposed with an angular offset θ with respect to one another, as shown in FIG. 1C. The result of this alignment method is shown in FIG. 1B. The sensor system 14 is now aligned parallel to the lateral surface and to the axis of the printing cylinder 10.

[0042] If two gages 18, 19 are provided, an increasing inclination of the sensor system 14 during operation can be identified and this can be corrected by the machine controller 15 or at least displayed to the machine operator.

[0043] If only one gage 18 is provided, as is seen in FIG. 3, an inclination cannot be detected.

[0044] A further alignment of the sensor system 14 can be necessary if the distance of the sensor system 14 from the lateral surface of the printing cylinder 10 is not correct. Then no correct monitoring of the sheet run can be made by the sensor system 14. In order to carry out an alignment of the sensor system 14 in this case, the distance of the sensor system 14 from the printing cylinder 10 is corrected until the measured values of the sensor system 14 recorded for at least one gage 18, 19 correspond to the desired values stored in a controller 15.

[0045] The structure of the sheet-fed printing press in the area of the gages and the method for calibrating the sensor system 14 can be seen from FIGS. 2A to 2C. The gages 18, 19 are mounted in a channel 12 of the printing cylinder 10 and connected thereto. Gages 18, 19 can also be provided in each channel 12 of the printing cylinder 10. In this case, one gage 18 is disposed at one end of the channel 12 and the other gage 19 is disposed at the other end of the channel 12, that is, one gage 18 is positioned on the drive side and one gage 19 is positioned on the operating side. In addition, the gages 18, 19 are disposed offset with respect to one another in the channel with an angular offset θ. The upper edge of a respective gage 18, 19 thereby forms a curve. Through the use of this curve a certain sheet height h is assigned to a specific machine angle or angle of rotation cp. As can be seen from the diagram of FIG. 2B, for example, by using the curve of the gage 18, 19 a sheet thickness h 0.3 mm is assigned to an angle of rotation φ0.3 mm and a sheet thickness h 0.6 mm is assigned to an angle of rotation φ0.6 mm. Each angle of rotation φ is in turn assigned a desired value in the controller 15 which is used as a threshold value for monitoring the sheet run. If a measured value different from the desired value is obtained in the measurement of the gages 18, 19 during rotation of the printing cylinder 10, the new measured value is stored as a threshold value in the controller 15 whereby a calibration of the sensor system 14 is accomplished.

[0046] The curve of the gages 18, 19 can alternatively also be discontinuous and composed of steps, as shown in FIG. 2C.

[0047] Advantageously common gages 18, 19 can be provided for aligning and calibrating. The gages 18, 19 can have partial surfaces for this purpose which are recorded by the sensor system 14 during the aligning or calibrating.