Device for performing measurement tasks on the surface of a printed sheet

Abstract

The invention relates to a device for performing measurement tasks on the surface of a printed sheet, comprising a sheet support surface for the full-surface placement of the printed sheet, a measuring device movable above the sheet support surface, and a control unit connected to the measuring device at least via data transmission, wherein the measuring device is movable in a stationary plane spaced apart from the sheet support surface, wherein the measuring device comprises a light source and an image sensor, wherein the light source and the image sensor are arranged such that a light beam emitted by the light source and reflected from the surface of the printed sheet resting on it strikes a light-sensitive area of ​​the image sensor, and wherein the control unit is configured such thatthat it determines both the luminous intensity of the light beam reflected from the surface of the printed sheet in relation to the luminous intensity of the light beam emitted by the light source, and the actual position of the reflected light beam on the light-sensitive surface of the image sensor in relation to a previously defined target position on the light-sensitive surface of the image sensor.

Description

[0001] The invention relates to a device for carrying out measuring tasks on a surface of a printed sheet according to the preamble of claim 1.

[0002] DE 10 2020 118 254 A1 discloses a control station of a sheet processing machine, comprising at least one measuring device and at least one support surface for inspecting a sheet, wherein the control station has at least one alignment device for aligning the sheet on the support surface.

[0003] DE 10 2017 200 869 A1 discloses a measuring table for a processing machine system, wherein the measuring table has a sheet depositing surface with at least one opening which is operatively connected to a vacuum generator, wherein the sheet depositing surface has so many openings that a sheet of maximum format can be fixed over its entire surface.

[0004] DE 102 11 070 A1 discloses a device for measuring a measurement object, comprising an optical sensor, wherein the optical sensor comprises an optical probe with a light source and a measuring lens for directing a light beam onto a measurement object and a receiver device for detecting a light beam reflected by the measurement object and generating a corresponding measurement signal; with a feed device for changing the distance between the optical sensor and the measurement object in a first coordinate direction depending on the measurement signal generated by the receiver device;and with an evaluation unit for determining the coordinates of the measuring point on the measuring object, wherein the receiver device has a position-sensitive receiver that generates an evaluable measuring signal within a measuring window, wherein the feed device adjusts the distance between the optical sensor and the measuring object such that the receiver of the receiver device receives the light beam reflected by the measuring object within the measuring window; and wherein the evaluation unit determines the coordinates of the measuring point on the measuring object from the position of the optical sensor and the measuring signal generated by the receiver device. In a preferred embodiment of this device, the transmission power of the light source is controllable as a function of the light intensity of the light beam reflected by the measuring object received by the receiver device.

[0005] From DE 197 58 260 A1 a device for measuring the distance from a surface with at least one light source, an optical system and at least one light receiver is known, wherein this device directs a first light beam or the like from a first direction onto a region of the surface and receives it again, wherein the optical system directs a second light beam or the like from a second direction onto substantially the same region of the surface and receives it again and wherein the device superimposes both received light beams or signals derived therefrom in at least one direction in reverse relation to one another.

[0006] EP 1 694 049 A1 discloses a measuring head for a color measuring device, comprising an illumination arrangement having at least one light source for illuminating a measurement object located in a measurement plane at an angle of incidence of substantially 45°, a pickup arrangement for capturing the measurement light remitted by the measurement object at an angle of reflection of substantially 0° relative to the normal to the measurement plane, a photoelectric receiver arrangement for converting the measurement light captured by the pickup arrangement into corresponding electrical signals, and a light reference arrangement provided with a deflection arrangement that can be inserted into the beam path between the illumination arrangement and the pickup arrangement and removed again, located at a relatively large distance from the measurement plane, which deflects at least part of the illumination light into the pickup arrangement when located in the beam path.wherein the deflection arrangement is designed as a prismatic or truncated pyramid-shaped or truncated cone-shaped, substantially transparent body with a reflective flat base surface, a scattering layer parallel thereto, and at least one lateral light entry surface inclined at 45° to the base surface, wherein the base surface is oriented perpendicular to the optical axis of the pick-up arrangement and the scattering layer faces the pick-up arrangement, and wherein the body is dimensioned such that, when in the beam path, the light coming from the illumination arrangement enters the body substantially perpendicularly through the at least one light entry surface and is reflected by the base surface into the scattering layer.

[0007] DE 101 11 245 A1 discloses a device for determining the deviation of the position of n points, where n is a natural number, from their n disjoint reference positions, comprising a source of electromagnetic radiation, an imaging optics, and a photosensitive detector, wherein the position information is converted into intensity information, wherein n signals are generated by the detector essentially simultaneously or in parallel, wherein each of the n signals is uniquely assigned to one of the n points.

[0008] DE 103 36 493 A1 discloses a device for determining surface properties, comprising at least one first radiation device with at least one first radiation source, which directs a predetermined radiation onto a measuring surface; with at least one first radiation detector device, which receives at least a portion of the radiation reflected and / or scattered by the measuring surface and outputs at least one measurement signal that is characteristic of the reflected and / or scattered radiation, wherein at least one second radiation device is provided, which directs at least partially directed radiation onto the measuring surface at a predetermined angle;and at least one second radiation detector device with a predetermined radiation detector surface, which at least partially receives the radiation originating from the second radiation device and reflected from the measuring surface and determines its position on the detector surface;

[0009] DE 195 33 808 A1 discloses a method for inspecting a printed product, in which signals are derived from a surface of the printed product to be inspected by means of an optoelectronic device, in that at least one light spot is generated on the surface of the printed product across the width of the printed product by means of at least one light source, and in that the intensity of the light reflected from the surface is determined by means of at least one electrical radiation detector, wherein in order to monitor the distance of the surface of the printed product from the optoelectronic device the intensities are continuously determined simultaneously at two different locations on unprinted areas of the surface of the printed product and wherein the ratio of the intensity values ​​is continuously formed.

[0010] The invention is based on the object of providing a device for carrying out measuring tasks on a surface of a printed sheet, wherein the associated measuring device is designed to be particularly small, light and cost-effective and is thus suitable for use in a system that can be moved over a sheet depositing surface, ie in a dynamic system.

[0011] The object is achieved according to the invention by the features of claim 1. The dependent claims relate to advantageous embodiments and / or further developments of the solution found.

[0012] The advantages achievable with the invention are, in particular, that the proposed measuring device of the apparatus for performing measuring tasks on a surface of a printed sheet is very compact and is capable of performing two measuring tasks virtually simultaneously using the same means, namely both calculating a degree of reflection and calculating a distance or a deviation from a target distance, in particular to the surface of the printed sheet or the sheet deposit area. Due to its dual function, the measuring device required to perform the measuring tasks in question can be implemented more cost-effectively and with less space requirements. The mass of the movable measuring device is also reduced, so that a drive for moving this measuring device can be designed with less power and thus more cost-effectively. Further advantages will become apparent from the following description.

[0013] An embodiment of the invention is illustrated in the drawings and is described in more detail below.

[0014] They show: Fig. 1 shows a first representation of a measuring table with a device for carrying out measuring tasks on a surface of a printed sheet; Fig. 2 a second representation of a measuring table with a device for carrying out measuring tasks on a surface of a printed sheet; Fig. 3 a representation of the measuring principle based on two measuring situations.

[0015] Fig. 1 and Fig. 2 each show, in a perspective view, an example and in a simplified manner, a measuring table which interacts with a sheet-fed printing press, this measuring table having a device 01 for carrying out measuring tasks on a surface of a printed sheet which is preferably coated with a printing fluid, e.g. with a printing ink or with an ink or with a varnish. This device 01 in turn has a sheet depositing surface 02 for the full-surface placement of the printed sheet and a measuring device 04 arranged above the sheet depositing surface 02, preferably at a distance from the surface of the printed sheet being deposited thereon and a digital, in particular programmable, control unit 06 which is at least data-technically connected to the measuring device 04, this measuring device 04 being movable in a stationary plane 18 parallel to the sheet depositing surface 02, at least along a single straight line, i.e. at least bidirectionally in the longitudinal direction of the measuring table.Two opposite directions of travel of the measuring device 04 are shown in the . Fig. 2 is shown by way of example and indicated by a double arrow. In an advantageous embodiment, the measuring device 04 is designed to be bidirectionally movable along two mutually orthogonal straight lines in a stationary plane 18 parallel to the sheet depositing surface 02, i.e. the measuring device 04 is movable in an x-direction and in a y-direction. Furthermore, it can be provided that the measuring device 04, in addition to its mobility in the plane 18, is also designed to be bidirectionally movable in a straight line perpendicular to the plane 18, i.e., in the z-direction, and to be fixable at a selectable height position above the sheet depositing surface 02.

[0016] The sheet support surface 02 preferably has a plurality of openings 11, each with a small cross-sectional area compared to the format of the printed sheet, e.g., at least one hundred times smaller. These openings 11 are each pneumatically connected to a suction device 03 that generates a barometric vacuum, with which a printed sheet resting fully on the sheet support surface 02 can be secured there and held in place while the measuring tasks are being carried out. With expanded functionality, the measuring table can also be designed, for example, as a control station for the sheet-fed printing press that interacts with it, or used as such.

[0017] The measuring device 04 has at least one light source 07 and one image sensor 08, wherein the light source 07 and the image sensor 08 are arranged such that a light beam emitted by the light source 07 and reflected on the surface of the printed sheet lying on the sheet depositing surface 02 strikes a light-sensitive surface of the image sensor 08 ( Fig. 3). The light source 07 and the image sensor 08 are advantageously arranged together in the same housing 09 of the measuring device 04. The light source 07 is designed, for example, as a laser or an LED. The image sensor 08 is designed, for example, as a line image sensor or as an area image sensor.

[0018] It is now proposed to design the control unit 06 in such a way that it determines both a luminous intensity of the light beam reflected from the surface of the printed sheet lying on the sheet depositing surface 02 in relation to the luminous intensity of the light beam emitted by the light source 07 and an impact position of the reflected light beam on the light-sensitive surface of the image sensor 08 forming an actual position in relation to a previously defined target position on the light-sensitive surface of the image sensor 08. This measuring principle clarifies the Fig. 3, where the Fig. Figure 3 shows two different measurement situations M1 and M2. The first measurement situation M1 is shown in solid lines, whereas the second measurement situation M2 is shown in dashed lines.

[0019] In both measuring situations M1; M2, the light source 07 arranged in the measuring device 04 emits a light beam and directs this light beam onto the surface of the printed sheet resting on the sheet support surface 02. This light beam is at least partially reflected on the surface of the printed sheet resting on the sheet support surface 02 according to the principle "angle of incidence equals angle of reflection", with the reflected light beam then striking the light-sensitive surface of the image sensor 08, which is also arranged in the measuring device 04. The image sensor 08 is designed such that its measurement signal can be represented as a spatially resolved intensity profile 12; 17 in both measuring situations M1; M2. As shown in the Fig. 3, an aperture 13 or a lens 14 or an objective 14 can be arranged in the beam path between the light source 07 emitting a light beam and the surface of the printed sheet resting on the sheet support surface 02 in order to collimate the light beam emitted by the light source 07. Likewise, a lens 16 can be arranged in the beam path between the surface of the printed sheet resting on the sheet support surface 02 and the light-sensitive surface of the image sensor 08 in order to image the light beam reflected by the printed sheet as a light spot with a very small cross-sectional area on the light-sensitive surface of the image sensor 08.

[0020] The two measuring situations M1; M2 differ in their respective distance of the surface of the printed sheet resting on the sheet support surface 02 to a reference height H, i.e. in the two measuring situations M1; M2 the distance of the surface of the printed sheet resting on the sheet support surface 02 to the reference height H has different values. The reference height H is determined by the fixed arrangement of the plane 18 to the sheet support surface 02 in the first measuring situation M1. In the second measuring situation M2 the distance of the surface of the printed sheet resting on the sheet support surface 02 to the reference height H has a value that differs from the reference height H and, in this case, is greater in magnitude. Thus, in the second measuring situation M2 there is a height difference h to the reference height H determined in the first measuring situation M1.This height difference h results in the light beam reflected from the surface of the printed sheet resting on the sheet support surface 02 being imaged on the light-sensitive surface of the image sensor 08 at an impact position which is different from that in the first measurement situation M1 and possibly also generating an intensity profile 17 which is different from that in the first intensity profile 12. As can be seen from the . Fig.3, the intensity profile 17 belonging to the second measurement situation M2 is shifted relative to a position of the intensity profile 12 belonging to the first measurement situation M1, i.e. it is formed at a different location on the light-sensitive surface of the image sensor 08. In this example, the first measurement situation M1 is to serve as the reference. Thus, the position at which the reflected light beam strikes the light-sensitive surface of the image sensor 08 in the first measurement situation M1 is considered a target position previously defined with reference to this light-sensitive surface of the image sensor 08. The position of this target position is stored as a value in the control unit 06, for example in the form of coordinates.The control unit 06 is now preferably designed such that it determines a measure for a distance a between the impact position of the reflected light beam on the light-sensitive surface of the image sensor 08 in the second measuring situation M2 and the target position previously defined with reference to this light-sensitive surface of the image sensor 08.Since the arrangement of the light source 07 and the image sensor 08 in the measuring device 04 remains unchanged in the two measuring situations M1; M2, the control unit 06 can be designed in such a way that it calculates a measure for the height difference h and, if necessary, also a measure for the sum of the reference height H and the height difference h from a reflection angle α of the light beam reflected from the surface of the supporting printed sheet, which is determined by the arrangement of the light source 07 and the image sensor 08, and the measure for the distance a between the impact position of the reflected light beam on the light-sensitive surface of the image sensor 08 in the second measuring situation M2 and the target position on the light-sensitive surface of the image sensor 08 determined in the first measuring situation M1 with reference to the printed sheet. The reflection angle α of the light beam reflected from the surface of the supporting printed sheet is, for example,an angle of 60° is specified. If the measuring device 04 is moved over the sheet support surface 02, a height profile of the surface of the printed sheet resting on the sheet support surface 02, or if necessary, only of the sheet support surface 02, can be created in the manner described above. In the latter case, the planarity or surface roughness of the sheet support surface 02, for example, can be determined or checked in the manner described.

[0021] In addition, it can preferably be provided that the control unit 06 is designed such that it calculates a reflectance of the surface of the printed sheet, which is coated, for example, with the printing fluid, from the ratio of the luminous intensity of the light beam reflected by the surface of the printed sheet resting on the sheet support surface 02 to the luminous intensity of the light beam emitted by the light source 07. Since the term gloss is understood to mean that a surface reflects light completely or partially in a specular manner, the calculated reflectance helps to assign a gloss level to the surface measured in the manner described above. Gloss levels are often described and differentiated from one another using terms such as dull matt, matte, semi-matt, semi-gloss, glossy, or high-gloss. In the printing industry, gloss levels are determined based on the European standard EN ISO 2813 as amended.from June 1999, entitled: Determination of the reflectometer value of coatings (except metallic coatings), usually determined at a measuring angle, i.e. reflection angle α of 60°. Typically, a reflectometer value and thus a gloss level in the range between 0 and 7 is referred to as dull matt, a gloss level in the range between 8 and 17 as matt, a gloss level in the range between 18 and 29 as semi-matt, a gloss level in the range between 30 and 59 as semi-gloss, a gloss level in the range between 60 and 89 as glossy, and a gloss level in the range between 90 and a maximum of 100 as high gloss. List of reference symbols 01 Device for carrying out measuring tasks 02 Sheet storage area 03 Suction device 04 Measuring device 05 - 06 Control unit 07 Light source 08 Image sensor 09 Housing 10 - 11 Opening 12 first intensity profile 13 aperture 14 lens; objective 15 - 16 lens 17 second intensity profile 18 Level a distance h height difference H Reference height M1 first measurement situation M2 second measurement situation α reflection angle

Claims

[1] Device (01) for carrying out measuring tasks on a surface of a printed sheet, comprising a sheet depositing surface (02) for the full-surface placement of the printed sheet and a measuring device (04) movable above the sheet depositing surface (02) and a control unit (06) connected to the measuring device (04) at least for data purposes, wherein the measuring device (04) is movable in a stationary plane (18) spaced from the sheet depositing surface (02), wherein the measuring device (04) has a light source (07) and an image sensor (08), wherein the light source (07) and the image sensor (08) are arranged such that a light beam emitted by the light source (07) and reflected on the surface of the printed sheet lying thereon strikes a light-sensitive surface of the image sensor (08), wherein the control unit (06) is designed such thatthat it determines both a luminous intensity of the light beam reflected from the surface of the supporting printed sheet in relation to the luminous intensity of the light beam emitted by the light source (07) and an impact position of the reflected light beam on the light-sensitive surface of the image sensor (08), forming an actual position, in relation to a previously defined target position on the light-sensitive surface of the image sensor (08), wherein the control unit (06) is designed such that it determines a measure for a distance (a) between the impact position of the reflected light beam on the light-sensitive surface of the image sensor (08) and the previously defined target position on the light-sensitive surface of the image sensor (08), , characterized bythat the control unit (06) is designed such that, in a second measuring situation (M2), it calculates a measure for a height difference (h) related to a reference height (H) from a reflection angle (α) of the light beam reflected from the surface of the supporting printed sheet and the measure for the distance (a) between the impact position of the reflected light beam on the light-sensitive surface of the image sensor (08) and the previously defined target position on the light-sensitive surface of the image sensor (08) with respect to the printed sheet, wherein the reference height (H) is defined by a distance, given in a first measuring situation (M1), between the stationary plane (18) and the sheet depositing surface (02), and that the control unit (06) is also designed such thatthat in the second measuring situation (M2) it calculates a degree of reflection of the surface of the printed sheet from the ratio of the luminous intensity of the reflected light beam to the luminous intensity of the light beam emitted by the light source (07). [2] Device (01) according to claim 1, characterized by that the light source (07) and the image sensor (08) are arranged together in a housing (09) of the measuring device (04). [3] Device (01) according to claim 1 or 2, characterized by that the light source (07) is designed as a laser or as an LED. [4] Device (01) according to claim 1 or 2 or 3, characterized by that the image sensor (08) is designed as a line image sensor or as an area image sensor. [5] Device (01) according to claim 1 or 2 or 3 or 4, characterized byin that the sheet depositing surface (02) has a plurality of openings (11), said openings (11) being connected to a suction device (03) with which a printed sheet resting on the sheet depositing surface (02) can be fixed and is fixed during the execution of the measuring tasks. [6] Device (01) according to claim 1 or 2 or 3 or 4 or 5, characterized by that an aperture (13) or a lens (14) or an objective (14) is arranged in the beam path between the light source (07) emitting a light beam and the surface of the printed sheet lying thereon. [7] Device (01) according to claim 1 or 2 or 3 or 4 or 5 or 6, characterized by that a lens (16) is arranged in the beam path between the surface of the printed sheet lying on it and the light-sensitive surface of the image sensor (08). [8] Device (01) according to claim 1 or 2 or 3 or 4 or 5 or 6 or 7, characterized bythat the measuring device (04) is designed to be movable bidirectionally in the fixed plane (18) spaced from the sheet depositing surface (02) at least along a single straight line or along two mutually orthogonal straight lines. [9] Device (01) according to claim 8, characterized by that the measuring device (04), in addition to its mobility in the plane (18), is designed to be bidirectionally movable along a straight line perpendicular to the plane (18) and to be fixable at a selectable height position above the sheet depositing surface (02). [10] Device (01) according to claim 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9, characterized by that the angle of reflection (α) of the light beam reflected from the surface of the printed sheet is set at 60°.

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