HK1116735A - Device for the optical measurement of a printed sheet and method for operating the device - Google Patents

Description

Method for operating an apparatus for optically measuring printed sheets

Technical Field

The invention relates to a method for operating an apparatus for optically measuring printed sheets, comprising a measuring table with a movable measuring head.

Background

In order to monitor the printing quality during the running printing process, the printed sheets are placed on a measuring table and are detected by their measuring heads. Over time, the optical system of the measuring head becomes soiled, so that frequent cleaning thereof is necessary. This cleaning is performed manually, which is associated with various drawbacks.

On the one hand, the measuring head is not damaged during cleaning, depending on the caution of the operator. For example, when the optical system is wiped out of order, there is a risk that the optical system is scratched.

On the other hand, the operator is distracted by the clean execution of the running printing process. It is desirable, however, for the printing process to be monitored by the operator without interruption, so that the operator immediately intervenes in the event of a malfunction and therefore the number of waste sheets remains limited.

A measuring station is described, for example, in EP 0064024B 1, in which the aforementioned problems are present.

Such a measuring table requires that a so-called test sheet is removed from the delivery of the printing press in order to be placed on the measuring table for measurement. The measurement performed by means of the measuring table next to the printing press is therefore carried out off-line.

Measuring devices are also known, by means of which the printing quality is monitored in-line within the printing press. DE 102004021600 a1, for example, describes an in-line measuring device which comprises a measuring beam along which a measuring head can be moved. The measuring beam can be open at the bottom or be provided with a see-through cover at the bottom.

In the case of a downwardly open construction, air is blown into the measuring beam, which air constitutes an air flow discharged from the open underside, which air flow prevents dirt from entering the measuring beam. But thorough cleaning cannot be achieved by this air flow.

In the case of a see-through lid, the lid is cleaned manually by means of a cleaning tool which is adapted to the shape of the lid in order to at least reduce the risk of the lid being scratched. However, this cleaning tool is disadvantageous not only in that damage cannot be completely avoided, but also in that the operator cannot focus his attention on the running printing process.

Disclosure of Invention

The object of the invention is to provide a method for operating a measuring device having a measuring table, wherein the method ensures thorough cleaning. The object of the invention is, in particular, to provide a method in which damage to the measuring head due to cleaning is virtually avoided. The object of the invention is, in particular, to provide a method in which the operator can focus his attention entirely on the monitoring of the running printing process. Furthermore, the object of the invention is to achieve an apparatus which is suitable for carrying out the method of the invention.

According to the invention, a method for operating an apparatus for optically measuring printed sheets is proposed, which apparatus comprises a measuring table with a movable measuring head, wherein the measuring head is fully or at least partially automatically cleaned by a cleaning device of the measuring table.

According to the invention, a device for optically measuring printed sheets and in particular for carrying out the above-described method is also proposed, comprising a measuring table with a movable measuring head, wherein the measuring table has a cleaning device for fully or at least partially automatically cleaning the measuring head.

Reproducible thoroughness of the cleaning is ensured by the method according to the invention and the device according to the invention. Furthermore, the avoidance of damage to the measuring head is no longer dependent on the skill of the operator, and in any case can be avoided. Furthermore, the cleaning of the measuring head no longer requires the attention of the operator, so that the operator can concentrate on monitoring the running printing process.

Advantageous further configurations of the invention are given in the further description, which is briefly described below.

The measuring table can comprise a cleaning region into which the measuring head is supported such that it can be moved and in which the cleaning device is arranged such that the measuring head can be moved and cleaned by the cleaning device. The cleaning region can be located on the platen of the measuring station next to a support region provided on the measuring station. For the measurement, the sheets are placed on the support area and fixed therein. But the cleaning area and the support area may also be identical to each other. The cleaning device in this case is formed by a cleaning sheet (reinigingsbogen) which is placed on the measuring table in place of the test sheet to be measured. The cleaning sheet can be made of a fabric, a nonwoven material or a foam material, for example, and is wetted through with a cleaning agent.

The measuring head is mounted so as to be movable relative to the cleaning device during cleaning thereof, so that the measuring head is moved relative to the cleaning device during cleaning thereof. This allows a stationary arrangement of the cleaning device and the omission of an additional drive device provided for cleaning. The cleaning takes advantage of the inherent movement of the measuring head and the presence of the drive for this movement.

The stationary cleaning device can be, for example, a cleaning roller which rotates about its stationary rotational axis during cleaning. Instead of the cleaning roller, a cleaning belt may be used. The cleaning belt can be endless and run around a deflecting roller which rotates about its positionally fixed axis of rotation during cleaning. Likewise, the cleaning tape can also be a finite tape which is wound from a supply reel onto a winding reel before or during the cleaning of the measuring head, wherein the axes of rotation of the two reels can be fixed in position during the cleaning.

The relative movement between the cleaning device and the measuring head during cleaning can be caused in one case by the displacement movement of the measuring head and by a simultaneous movement of the cleaning device and in the other case only by the movement of the cleaning device. The first-mentioned case is given, for example, in the case of the already mentioned configuration in which the cleaning device is designed as a cleaning roller, the relative movement resulting from the superposition of the displacement movement of the measuring head and the rotational movement of the cleaning roller. In this case, the cleaning device is designed as an air blowing nozzle which blows dirt out of the measuring head and which is arranged in the cleaning region. The relative movement between the measuring head and the blowing nozzle is caused only by the displacement movement of the measuring head, which can be displaced above the blowing nozzle in such a way that the air blast directed from below toward the measuring head sweeps successively over the section of the measuring head to be cleaned.

The contactless cleaning of the measuring head can be carried out not only by means of a blowing nozzle, but instead also by means of an ultrasonic transmitter arranged in the cleaning region.

The measuring table can be designed as a two-coordinate measuring table with an imaginary x-axis and an imaginary y-axis, wherein the measuring head can be moved along the x-axis into the cleaning region and can be mounted so as to be movable along the y-axis relative to the cleaning device during cleaning thereof. The measuring head is thus moved along the x-axis of the measuring table into the cleaning region and, during cleaning, is moved along the y-axis of the measuring table relative to the cleaning device. The x-axis and the y-axis lie in the plane of the platen of the measuring table and are essentially-when small inclinations of the platen that may exist are ignored-horizontal axes.

Of course, the measuring table can have an imaginary z-axis, along which the measuring head is mounted so as to be movable, in addition to the x-axis and the y-axis, which are oriented perpendicularly to one another. The z-axis is substantially a vertical axis and the movement of the measuring head along the z-axis can be used, for example, to press the measuring table towards or away from the cleaning device. The movement of the measuring head along the z-axis can also be used to adjust the measuring head to the distance required for the measurement relative to the sheet to be measured.

It is also conceivable that the movement of the measuring head relative to the cleaning device in the cleaning region is generated by a superposition of a movement of the measuring head along the x-axis and a simultaneous movement of the measuring head along the y-axis. The movement resulting from the superposition may be, for example, a zigzag or zigzag-shaped movement, by means of which the measuring head is guided over the already mentioned cleaning sheet. The movement resulting from the superposition may also be a spiral movement, by means of which the measuring head is guided over the blowing nozzle, so that dirt is forced by the blowing air from the center of the surface to be cleaned of the measuring head to its edge.

The cleaning device can be designed as a remover for removing dirt from the measuring head. In this case, it is conceivable that dirt is removed from the measuring head by means of the cleaning device by a movement of the measuring head relative to the cleaning device. In the case of a cleaning device in the form of a remover, the measuring head is contacted by the cleaning device during removal, wherein the removal of the contaminants can take place wettably and/or dryly.

In the case of the previously mentioned cleaning sheets which are designed to be wetted through with a cleaning agent, the measuring head is cleaned, i.e. washed, damp, for example by means of a cleaning device.

The first washing of the measuring head or its optical system and the subsequent dry-cleaning of the measuring head and the optical system can be carried out, for example, with a clean sheet having a wet section wetted with a cleaning agent and a dry section not wetted with a cleaning agent.

The cleaning, i.e. the dust removal, of the measuring head, which is carried out only dry, can be carried out, for example, with the aid of the already mentioned cleaning roller, if it is configured in the form of a fleece roller with a high dust removal effect.

The measuring head can be a Scanning Densitometer (Scanning-Densitometer) or a colorimetric measuring device, for example a colorimeter or spectrometer, and the measurement of the measuring head can be carried out either inside a test strip which is printed specifically on the printed sheet for this purpose or inside the actual printed image of the printed sheet (printed image inspection).

Drawings

Further structurally and functionally advantageous developments of the invention result from the following description of the embodiments and the associated drawings.

FIG. 1: a measuring station 1 is shown.

Detailed Description

The single figure shows a measuring table 1 on which a sheet 6 to be measured in terms of its printing quality is placed, the so-called test sheet. The measuring station 1 comprises a measuring beam 2 which is movable along a rail 3 in the x-direction x. The measuring beam 2 comprises a measuring head 4 which is movable in the y-direction y along a rail 5 arranged on the measuring beam 2. Furthermore, an axis 10 is provided on the measuring beam 2, along which the measuring head 4 can be moved in a direction perpendicular to the drawing plane of the drawing, i.e. toward the printed sheet 6 or away from the printed sheet 6. The drive for driving the displacement movement of the measuring beam 2 and the measuring head 4 is controlled by an electronic control device 11, but is not shown for the sake of clarity.

The measuring head 4 has an optical system sensitive to soiling and is used for measuring the light density or the color of a test strip 7 printed on the printed image 8 or on the printed sheet 6 next to it.

The cleaning area arranged next to the sheet 6 is formed by a cleaning device 9. The cleaning device 9 is a soft, elastically yielding and smokable strip of textile or nonwoven material (Vliesstoff), which is moistened with a cleaning agent.

The illustrated system works as follows: if a sensor, not shown in the drawing, for detecting contamination of the optical system of the measuring head 4 signals to the control device 9 that the degree of contamination exceeds a certain threshold value, the control device 9 signals to the operator of the printing press equipped with the measuring station 1, for example by means of a red warning light, so that the operator can call up on the control device 9 a cleaning program for washing the measuring head 4. It is also possible for the control device 9 to automatically initiate the cleaning program in response to the sensor signal.

In both cases, the measuring beam 2 and the measuring head 4 are moved along the rails 3, 5 to a position in which the measuring head 4 is directly above the cleaning device 9, depending on the cleaning procedure. In a subsequent process step, the measuring head 4 is lowered along the axis 10 until it abuts against the cleaning device 9.

Subsequently, the measuring head 4 is moved back and forth along the rail 5 from one end to the other end of the cleaning device 9 a plurality of times, wherein the optical system of the measuring head 4 is wiped and cleaned by the cleaning device 9. The measuring beam 2 is moved in the x direction x at a minimum feed speed, so that the measuring head 4 describes a meandering or sinusoidal wave on the cleaning device 9.

By the material properties of the cleaning device 9 and the movement pattern of the measuring head 4, it is ensured that dirt can be transferred from the measuring head 4 to the cleaning device 9 and cannot be transferred back from the latter to the former.

In a final method step, the measuring head 4 is lifted again along the axis 10 from the cleaning device 9 and is then moved in the x-direction x and y-direction y into its position required for measuring the printed sheets 6.

In the cleaning process, a short waiting time can be taken into account between the end of cleaning and the beginning of the measurement of the printed sheet 6, during which time the remaining cleaning agent evaporates from the optical system. After this waiting time has elapsed, the control device 11 starts the measuring process or signals the operator via a green ready light, so that the operator can now start the measuring process by pressing a button.

Likewise, different cleaning programs can be stored in the control device 11, from which the desired cleaning program is selected and used depending on the current degree of soiling of the measuring head 4.

The cleaning device 9 may be a disposable item and be replaced by a new cleaning device 9 after cleaning has been performed.

Reference number table

1 measuring table

2 measuring beam

3 track

4 measuring head

5 track

6 printed sheets

7 test strip

8 printing images

9 cleaning device

10 axes

11 control device

x x direction

y y direction

Claims (10)

1. Method for operating an apparatus for optically measuring printed sheets (6), comprising a measuring table (1) with a movable measuring head (4), characterized in that: the measuring head (4) is cleaned fully automatically or at least partially automatically by a cleaning device (9) of the measuring table (1).

2. The method of claim 1, wherein: the measuring head (4) is moved into a cleaning region and cleaned in the cleaning region by a cleaning device (9).

3. The method of claim 2, wherein: when the measuring head (4) is cleaned, the measuring head is moved relative to the cleaning device (9).

4. The method of claim 3, wherein: the movement of the measuring head (4) into the cleaning region takes place along the x-axis (x) of the measuring table (1) of the device; during cleaning, the measuring head (4) is moved relative to the cleaning device (9) along the y-axis (y) of the measuring table (1).

5. The method according to claim 3 or 4, characterized in that: by means of the movement of the measuring head (4) relative to the cleaning device (9), dirt is removed from the measuring head (4) by the cleaning device.

6. Device for optically measuring printed sheets, in particular for carrying out the method according to one of claims 1 to 5, comprising a measuring table (1) with a movable measuring head (4), characterized in that: the measuring table (1) has a cleaning device (9) for fully or at least partially automatically cleaning the measuring head (4).

7. The apparatus of claim 6, wherein: the measuring table (1) comprises a cleaning region into which the measuring head (4) is mounted so as to be movable and in which a cleaning device (9) is arranged.

8. The apparatus of claim 6 or 7, wherein: the measuring head (4) is mounted so as to be movable relative to the cleaning device (9) during cleaning thereof.

9. The apparatus of claim 8, wherein: the measuring table (1) is designed as a two-coordinate measuring table with an x-axis (x) and a y-axis (y); the measuring head (4) can be moved along an x-axis (x) into a cleaning region and is mounted so as to be movable along a y-axis (y) relative to a cleaning device (9) during cleaning thereof.

10. The apparatus of any one of claims 6 to 9, wherein: the cleaning device (9) is designed as a remover for removing dirt from the measuring head (4).