Method and system for determining a position of a position of a transport belt

Abstract

The invention relates to a printing press for imprinting material. The printing press comprises a transport belt, an optical sensor and an evaluation unit. The transport belt is movable in a feed direction over a feeding distance. The transport belt comprises a plurality of sections along the feed direction over the feeding distance. The optical sensor is configured to capture in a sequential manner at least one image of each section of the plurality of sections of the transport belt. The evaluation unit is configured to determine or specify a position of the transport belt based on the images of the plurality of sections of the transport belt.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a printing press for printing on a material, in particular a fabric. Furthermore, the invention relates to a method for determining the position of a conveyor belt of a printing press. Furthermore, the invention relates to a method for operating a printing press, in particular for controlling or regulating a printing press. TECHNICAL BACKGROUND

[0002] In printing presses, such as digital textile printing presses, precise positioning of the material to be printed—such as fabric, paper, cardboard, plastic, wood, or metal—relative to the printing press's print head ensures a good print result. Even the smallest deviation can lead to an unusable print result.

[0003] For example, a fabric or other material to be printed can be applied or glued onto a conveyor belt, also called a printing belt. The conveyor belt can move relative to the print head. The print head, which is also movable, can apply a printing medium, for example a dye, to a section of the fabric in a desired pattern, while the conveyor belt and the fabric remain stationary relative to the print head. The print head can print on the same spot on the fabric multiple times, while the conveyor belt and the material to be printed remain stationary relative to the print head. To do this, the print head can be moved at least twice or even four times across the width of the conveyor belt. The conveyor belt can then be moved further, and the print head can apply the printing medium, for example in the form of a dye or ink, to another section of the fabric.If the conveyor belt and thus the fabric are not moved relative to the print head with an accuracy that corresponds to the print resolution, the printed pattern on the fabric may be interrupted or a printing error in the form of an offset or a line may be visible. The printing error can be an (unwanted) gap in the pattern or an (unwanted) overlap in the pattern. The printing error can also be a left-right offset in the pattern. A left-right offset can result in a wedge-shaped gap and / or a wedge-shaped overlap in the pattern. There may be a gap on one side (perpendicular to the feed direction) of the pattern and an overlap on the other side. The inaccuracy in the position of the conveyor belt in relation to the print head can result from out-of-roundness of the drive and / or idler rollers, bearing tolerances, thickness tolerances or material weaknesses of the conveyor belt, etc.

[0004] AT 509 764 B1 relates to a measuring device of a printing press for measuring the feed of a conveyor belt of the printing press. The measuring device comprises at least one position sensor that can be attached to the conveyor belt and is linearly movable, as well as a stationary reference device. The position of the position sensor relative to the stationary reference device is detected. The position sensor is designed as a measuring sensor.

[0005] US 2011 / 222882 A1 relates to an image forming apparatus comprising a transport belt for a recording medium suspended from a plurality of roller elements. An image is secondarily transferred from a first image carrier to a recording medium through an intermediate transfer body. An image is directly transferred from a second image carrier to the recording medium. The image forming apparatus further includes a pattern image acquisition unit that acquires a pattern image, which is ultimately transferred from the first image carrier and the second image carrier to the transport belt of the recording medium.The distance from a secondary transfer position to a scanning position and the distance from a direct transfer position to the scanning position in the rotational direction of the recording medium transport belt are each the natural multiple of the circumferential length of a roller element that causes a speed change of the recording medium transport belt among the plurality of roller elements.

[0006] US 2003 / 052957 A1 relates to an image forming apparatus comprising a drum, an optical scanning mechanism, a developing mechanism, an intermediate transfer member, motion detection mechanisms, and a controller. The optical scanning mechanism deflects a laser light beam to form a latent image on a photosensitive surface of the drum. The developing mechanism contains a plurality of different color toners and develops the latent image into a color toner image. The intermediate transfer member rotates synchronously with rotation of the drum and receives the color toner image multiple times to form thereon a composite color toner image containing multiple images of the different color toners superimposed on one another. The motion detection mechanisms detect the respective movements of the drum and the intermediate transfer belt.The control unit controls the respective rotations of the drum and the intermediate transfer belt based on the results of the respective detection by the plurality of motion detection mechanisms.

[0007] US 2009 / 079999 A1 relates to an image forming device that records an image on a transported recording medium. The device includes a transport unit that transports the recording medium and a recording unit that records the image on the recording medium. An encoder outputs an encoder signal with pulses corresponding to a position of the transport unit. A measuring unit measures a pulse period of the encoder signal, and the measured pulse period is stored by a storage unit. A detection unit detects the absence of pulses in the encoder signal based on the value measured by the measuring unit.A pulse generation unit generates a recording time pulse based on the pulse period when the pulse omission is not detected, and generates the recording time pulse based on the pulse period stored in the storage unit and measured before the pulse omission when the pulse omission is detected. SUMMARY OF THE INVENTION

[0008] The invention is based on the object of providing a printing press that enables the position of a conveyor belt of the printing press to be determined with high accuracy. Furthermore, the invention is based on the object of providing a printing press that enables the position of a conveyor belt of the printing press to be determined in a short time. Furthermore, the invention is based on the object of providing a printing press that enables the position of a conveyor belt of the printing press to be determined cost-effectively.

[0009] This object is achieved by the features described in the independent patent claims. Advantageous embodiments are specified in the dependent claims.

[0010] A printing press for printing on a material comprises a conveyor belt, an optical sensor, and an evaluation unit. The conveyor belt is movable in a feed direction over a feed path. The conveyor belt comprises a plurality of sections along the feed direction over the feed path. The optical sensor is configured to sequentially capture at least one image of each of the plurality of sections of the conveyor belt. The evaluation unit is configured to detect or determine a position of the conveyor belt based on the images of the plurality of sections of the conveyor belt.

[0011] The evaluation unit can check whether there is a deviation between the desired positioning and the actual positioning of the material to be printed. In particular, it can check the distance by which the desired positioning and the actual positioning differ from each other. The deviation can be periodic. For example, if a roller on the conveyor belt is out of round, a positioning deviation can occur periodically. With each revolution of the roller, a deviation can occur at the same rotational position of the roller (in cylindrical coordinates at the same circumferential angle φ). Likewise, positioning deviations can arise periodically due to unevenness or differences in the thickness of the conveyor belt. The positioning deviations can be compensated for and / or form a basis for future positioning.In particular, the positioning deviations can serve as a basis for (directly) subsequent positioning, for example, at the same points on the conveyor belt during the next revolution. The positioning deviations can also serve as a basis for correction values. Future positioning can be performed based on the correction values. The correction values ​​can be stored in a memory, for example, in the memory of a control device.

[0012] In general, the position of the conveyor belt can be an absolute position or a relative position. The relative position of the conveyor belt can refer to a reference element, such as a print head. Likewise, the relative position of the conveyor belt can refer to a target position of the conveyor belt. For example, the relative position of the conveyor belt can be a deviation between the actual position of the conveyor belt (actual position of the conveyor belt) and the desired position of the conveyor belt (target position of the conveyor belt).

[0013] The material to be printed can be a textile material, in particular a fabric. The material to be printed can be any printable material, in particular a material printable with ink.

[0014] The printing press can comprise a motor, in particular an electric motor. At least one roller of the printing press can be driven, in particular rotated, by the motor. The conveyor belt can rest on the at least one roller. The conveyor belt can be non-positively connected to the at least one roller. The conveyor belt can be moved by rotation of the at least one roller.

[0015] The printing press may include at least one second roller. The second roller may not be driven by the motor. The second roller may be mounted for free rotation. The second roller may be frictionally connected to the conveyor belt.

[0016] The conveyor belt can be tensioned and / or supported by the first roller and the second roller. If the first roller is driven by the motor, the conveyor belt is moved. The second roller can rotate as the conveyor belt moves.

[0017] The first and second rollers of the printing press can be driven by one motor or each by a motor.

[0018] The printing press may include a control device. The control device may control the movement of the conveyor belt, in particular the motor.

[0019] The material to be printed can be arranged on the conveyor belt. The material to be printed can be (removably) connected to the conveyor belt by an electrostatic force, by mechanical fastening, by adhesive bonding, or by a thermoplastic layer of the conveyor belt. Preferably, the conveyor belt comprises a thermoplastic layer through which the material to be printed can be or is (removably) connected to the conveyor belt.

[0020] The optical sensor may be an electro-optical sensor. The optical sensor may convert light or a change in light into an electrical signal. The light may be ultraviolet light, visible light (to a human), and / or infrared light. The light may have a wavelength in a range from 100 nm to 1500 nm, preferably from 380 nm to 1000 nm, more preferably between 380 nm and 780 nm or between 800 nm and 900 nm. The optical sensor may be a camera or comprise a camera.

[0021] The optical sensor can have a distance from an edge of the conveyor belt of at least 10 cm, preferably at least 30 cm, more preferably at least 50 cm. The distance of the optical sensor from an edge of the conveyor belt can be at most 1.5 m, preferably at most 1.0 m, more preferably at most 0.8 m. The distance of the optical sensor from an edge of the conveyor belt is preferably between 0.1 m and 1.5 m, more preferably between 0.3 m and 1.0 m, more preferably between 0.6 m and 0.8 m. The edge of the conveyor belt can be an end of the conveyor belt perpendicular to the feed direction.

[0022] The optical sensor can have a distance from an edge of the conveyor belt of at least 5% of the width of the conveyor belt, preferably at least 15% of the width of the conveyor belt, more preferably at least 25% of the width of the conveyor belt. The distance of the optical sensor from an edge of the conveyor belt can be at most 80% of the width of the conveyor belt, preferably at most 55% of the width of the conveyor belt, more preferably at most 45% of the width of the conveyor belt, more preferably at most 32% of the width of the conveyor belt. The distance of the optical sensor from an edge of the conveyor belt is preferably between 5% and 80% of the width of the conveyor belt, more preferably between 15% and 55% of the width of the conveyor belt, more preferably between 32% and 45% of the width of the conveyor belt. The width of the conveyor belt can be a (total) extension of the conveyor belt perpendicular to the feed direction.

[0023] The conveyor belt may have a width of at least 0.5 m, preferably at least 1.0 m, more preferably at least 1.5 m. The width of the conveyor belt may be between 0.5 m and 7.0 m, preferably between 1.0 m and 6.0 m, more preferably between 1.5 m and 5.0 m, more preferably between 1.5 m and 4.0 m.

[0024] The optical sensor can be directed toward an edge region of the conveyor belt. The plurality of sections along the feed direction can be located in an edge region of the conveyor belt. An edge region can have a distance from the edge of the conveyor belt of less than 300 mm, preferably less than 150 mm, more preferably less than 50 mm, and more preferably at most 30 mm. The edge of the conveyor belt can be an end of the conveyor belt perpendicular to the feed direction.

[0025] In the direction of the feed direction, the optical sensor can have a distance from a print head of the printing press that is essentially (±10% or ±5%) a multiple of a feed step (also referred to as a movement step). A feed step can be a distance of movement of the conveyor belt in the direction of the feed direction between two printing steps. The material to be printed can be printed while the conveyor belt is not moving; then the conveyor belt can be moved in a feed step, and subsequently the material to be printed can be printed. Preferably, the material to be printed is not moved during the movement of the conveyor belt. The distance in the direction of the feed direction between the optical sensor and the print head can be at most 1 m, preferably at most 0.8 m, more preferably at most 0.6 m, more preferably at most 0.4 m, more preferably at most 0.2 m, more preferably at most 0.1 m.

[0026] The conveyor belt can be movable in exactly one feed direction. The feed path can be the entire length of the conveyor belt. Preferably, the feed path is equal to the circumference, in particular equal to the outer circumference, of the conveyor belt. The feed path can be longer than the entire length of the conveyor belt or the circumference of the conveyor belt.

[0027] The conveyor belt can be a continuous belt (endless belt). The feed distance can be at least 5 m, preferably at least 10 m, more preferably at least 20 m, more preferably at least 50 m, more preferably at least 100 m, more preferably at least 500 m, more preferably at least 1000 m, more preferably at least 2000 m. The feed distance can be at least a multiple of the length or circumference of the conveyor belt; preferably, the feed distance is at least twice, more preferably at least 5 times, more preferably at least 50 times, more preferably at least 100 times, more preferably at least 250 times, more preferably at least 500 times, as long as the length or circumference of the conveyor belt.

[0028] The conveyor belt may have a length or circumference of at least 1 m, preferably at least 2 m, more preferably at least 4 m, more preferably at least 5 m, more preferably at least 8 m.

[0029] The plurality of sections along the feed direction can be present over the entire feed path. The plurality of sections can be evenly or unevenly distributed.

[0030] The optical sensor can capture images over the entire length or circumference of the conveyor belt, especially in the direction of feed.

[0031] The printing press can be a textile printing press, in particular a digital textile printing press. The printing press can comprise a print head. The printing press can comprise at least two, preferably at least three, more preferably at least four, more preferably at least five, more preferably at least six, more preferably at least eight, and preferably at least twelve print heads. The print head or print heads can be provided for each color. The print head or print heads can be arranged in a print head carrier (carriage). The printing press can be an inkjet printing press.

[0032] The print head can be movable relative to the conveyor belt, in particular in a direction that is not parallel to the feed direction. The print head can be movable perpendicular to the feed direction (linearly). In particular, a print head carrier with the print head or print heads can be movable relative to the conveyor belt.

[0033] The print resolution of the printing press can be at least 500 dpi (dots per inch), preferably at least 700 dpi, more preferably at least 900 dpi, more preferably at least 1100 dpi, more preferably at least 1200 dpi. Particularly preferably, the printing press has a print resolution between 1100 dpi and 1300 dpi. The print resolution of the printing press can be substantially (± 10% or ± 5%) 1200 dpi.

[0034] The printing machine can be configured to determine a deviation between a desired position of the conveyor belt (target position of the conveyor belt) and an actual position of the conveyor belt (actual position of the conveyor belt) of less than 500 µm, preferably of less than 300 µm, more preferably of less than 150 µm, more preferably of less than 100 µm.

[0035] The evaluation unit can include a processor. The processor can determine the position of the conveyor belt based on the images of the plurality of sections of the conveyor belt. The evaluation unit can be (physically) integrated into the printing press.

[0036] Alternatively, the evaluation unit may not be (physically) integrated into the printing press. For example, the evaluation unit may be a computer that communicates with the printing press or not. The computer may not be (physically) integrated into the printing press.

[0037] The evaluation unit can be located at a location remote from the printing press. For example, the evaluation unit is a server. The server can be configured to determine the positions of conveyor belts of different printing presses. The different printing presses can be located at different locations.

[0038] The evaluation unit can communicate with the optical sensor.

[0039] In a typical printing process, a material to be printed can be placed on the conveyor belt. The conveyor belt can move the material to be printed under the print head. The print head can apply ink to the material to be printed. In particular, the print head is moved perpendicular to the direction of movement of the conveyor belt in order to apply ink at least in sections across substantially the entire width of the material to be printed. The material to be printed can then be moved by the conveyor belt in the direction of feed. The print head can again apply ink to the material at least in sections across substantially the entire width of the material to be printed. The steps of moving the conveyor belt and applying ink by the print head can be repeated.

[0040] The evaluation unit is configured to determine a deviation between an actual position and a target position of the conveyor belt on the basis of the images of the plurality of sections of the conveyor belt or on the basis of the determined position of the conveyor belt.

[0041] The printing press may include a control device. The control device may be configured to adjust the movement of the conveyor belt based on the deviation between the actual position and the target position of the conveyor belt.

[0042] For example, the evaluation unit can determine a curve of the deviations. A counter curve can be created for the deviation curve. The counter curve can be created by the evaluation unit. Alternatively or additionally, the counter curve can be created by a user. A counter curve created by the evaluation unit can also be changed or adapted by a user. The control device can adjust or carry out the movement of the conveyor belt based on the counter curve. Alternatively or additionally, the evaluation unit can determine counter values ​​for the deviation values. The deviation values ​​and the counter values ​​can be linked, for example in a table.

[0043] A deviation can be determined continuously by the evaluation unit and the movement of the conveyor belt can be adjusted by the control device.

[0044] The optical sensor can be arranged stationary on the printing press. The optical sensor can be arranged stationary relative to the printing press.

[0045] The optical sensor can be connected to the printing press, in particular, it can be permanently connected to the printing press or detachably connected to the printing press. The optical sensor can be integrated into the printing press. For example, the optical sensor can be connected to the printing press via a bracket or arm. The bracket or arm can be adjustable. This allows the optical sensor to be directed at a specific section of the conveyor belt, especially when the conveyor belt is not moving.

[0046] Alternatively, the optical sensor may not be connected to the printing press. The optical sensor may be held by a bracket or an arm. The bracket or arm may not be connected to the printing press. For example, the bracket or arm is connected to a rack, frame, or support. Likewise, the bracket or arm may be placed on the floor; preferably, the printing press is placed on the same floor. Even if the optical sensor is not connected to the printing press but is associated with the printing press, since the optical sensor is directed toward a portion of the conveyor belt, the optical sensor may be included in the printing press.

[0047] The optical sensor cannot change its position when the conveyor belt moves. Preferably, no component of the optical sensor changes its position when the conveyor belt moves. The optical sensor, in particular all components of the optical sensor, can be immobile or stationary when the conveyor belt moves.

[0048] The optical sensor cannot make contact with the conveyor belt. Preferably, no component of the optical sensor makes contact with the conveyor belt. The optical sensor can be arranged without contact with the conveyor belt.

[0049] The optical sensor can be a first optical sensor. The printing press can comprise a second optical sensor. The first optical sensor and the second optical sensor can be spaced apart from one another. Preferably, the first optical sensor and the second optical sensor are spaced apart from one another in a direction that is non-parallel, in particular perpendicular, to the feed direction. The first optical sensor and the second optical sensor can be spaced apart from one another in a plane parallel to a plane defined by the conveyor belt. Preferably, the first optical sensor and the second optical sensor are directed towards the opposite edges of the conveyor belt or are assigned to opposite edges of the conveyor belt.

[0050] In an advantageous embodiment, the first and second optical sensors are designed identically. "Identical" here means that the sensors are functionally similar, for example, they are each implemented by a camera.

[0051] The first optical sensor and the second optical sensor can have different distances from an edge of the conveyor belt, for example, from a respective nearest edge of the conveyor belt. For example, the first optical sensor can have a distance of between 0.1 m and 0.59 m from a first edge of the conveyor belt. The second optical sensor can have a distance of between 0.60 m and 1.2 m from a second edge of the conveyor belt. The distance can be perpendicular to the feed direction.

[0052] The first optical sensor can be positioned between 5% and 35% of the conveyor belt's width from a first edge of the conveyor belt. The second optical sensor can be positioned between 35% and 65% from a second edge of the conveyor belt. The first edge and the second edge can be opposite edges.

[0053] The first optical sensor can be positioned at the above-described distance from a first edge of the conveyor belt. The second optical sensor can be positioned at the above-described distance from a second edge of the conveyor belt. The first edge and the second edge can be opposite edges of the conveyor belt.

[0054] The first optical sensor can be directed toward a first edge region of the conveyor belt. The second optical sensor can be directed toward a second edge region of the conveyor belt. The first edge region and the second edge region can be opposite edge regions of the conveyor belt, in particular opposite edge regions of the conveyor belt in a direction perpendicular to the feed direction.

[0055] The printing press can comprise at least one third optical sensor. The third optical sensor can be spaced apart from the first and / or second optical sensor. Preferably, the third optical sensor is spaced apart from the first and / or second optical sensor in the feed direction. The third optical sensor can be directed toward the first or second edge region.

[0056] The first, second and / or third optical sensor may be any optical sensor disclosed herein.

[0057] The plurality of sections along the feed direction across the feed path may be a first plurality of sections along the feed direction across the feed path. The conveyor belt may comprise a second plurality of sections along the feed direction across the feed path. The first plurality of sections and the second plurality of sections may be spaced apart from one another. Preferably, the first plurality of sections and the second plurality of sections are spaced apart from one another in a direction that is not parallel to the feed direction. The first optical sensor may be configured to sequentially capture at least one image of each section of the first plurality of sections. The second optical sensor may be configured to sequentially capture at least one image of each section of the second plurality of sections.The evaluation unit can be configured to detect or determine the position of the conveyor belt based on the images of the first plurality of sections and the images of the second plurality of sections.

[0058] The first plurality of sections can be present in the first edge region of the conveyor belt. The second plurality of sections can be present in the second edge region of the conveyor belt. The second plurality of sections can be present over the entire feed path. The second plurality of sections can be evenly or unevenly distributed.

[0059] The evaluation unit can be configured to determine a first position of the conveyor belt based on the images of the first plurality of sections, and the evaluation unit can be configured to determine a second position of the conveyor belt based on the images of the second plurality of sections. The evaluation unit can be configured to determine a deviation between the first position and the second position of the conveyor belt.

[0060] For example, a conicity or deviation from a cylindrical shape of one of the rollers on which the conveyor belt rests can result in a positioning error. One side (perpendicular to the feed direction) of the conveyor belt may have moved further than the other side (perpendicular to the feed direction). The resulting positioning error can be detected by two optical sensors and determined in the evaluation unit.

[0061] The conveyor belt can be moved discontinuously or intermittently along the feed direction over the feed path. The conveyor belt can be moved stepwise along the feed direction over the feed path.

[0062] The printing press can be a step-and-repeat printing press. With a step-and-repeat printing press, the material to be printed can be printed while the conveyor belt is stationary, i.e., not moving. After printing, the material to be printed is transported along the conveyor belt in the direction of the feed direction. At the desired position, the conveyor stops (does not move further), and the material to be printed can continue to be printed.

[0063] The optical sensor may be configured to capture at least one image of each portion of the plurality of portions while the conveyor belt is moving and / or not moving.

[0064] The printing machine may include a print head. The conveyor belt may include a marking element. The sections of the plurality of sections of the conveyor belt may include or be sections of the marking element. The print head may be configured to apply a mark to the marking element. The print head may be arranged in a print head carrier.

[0065] The marking element may comprise or consist of a printable material. Preferably, the print head is configured to print on the marking element.

[0066] The marking element can have the same length or circumference as the conveyor belt. The marking element can be arranged on the conveyor belt over the entire length or circumference of the conveyor belt, in particular without interruption.

[0067] Preferably, the marking element is arranged on the conveyor belt in such a way that the optical sensor can capture images of the (entire) marking element, in particular when the conveyor belt is moved over its entire length.

[0068] The marking element can be arranged on the conveyor belt in an area in which a material to be printed can be positioned for printing by the print head. Preferably, no material to be printed is arranged on the conveyor belt when the marking element is arranged on the conveyor belt.

[0069] The marking that can be applied, in particular printed, to the marking element by the print head can be a regular marking. The marking can comprise lines.

[0070] In particular, the print head can apply at least two reference markings to the marking element, in particular while the conveyor belt is stationary or is not being moved. Between the at least two reference markings, the print head can apply at least one position marking, in particular while the conveyor belt is stationary or is not being moved. Between the application of the reference markings and the application of the position marking, the conveyor belt can move or be moved.

[0071] The optical sensor can capture images of the markings on the marking element. The evaluation unit can determine or detect the position of the conveyor belt based on the images. In particular, the evaluation unit can determine a distance (in the feed direction) between the position marking and the first reference marking. Alternatively or additionally, the evaluation unit can determine a distance (in the feed direction) between the position marking and the second reference marking. Based on the determined distance or distances, a position of the conveyor belt can be determined by the evaluation unit; in particular, a deviation from a target position to an actual position of the conveyor belt can be determined.

[0072] The print head can apply at least three reference markings to the marking element, preferably while the conveyor belt is stationary or is not being moved. Between the first and second reference markings, the print head can apply at least one first position marking, in particular while the conveyor belt is stationary or is not being moved. Additionally, the print head can apply a second position marking between the second and third reference markings, in particular while the conveyor belt is stationary or is not being moved. Between the application of the reference markings and the position markings, the conveyor belt can move or be moved.

[0073] The evaluation unit can determine a distance (in the feed direction) between the first position marking and the first reference marking and / or the second reference marking. Alternatively or additionally, the evaluation unit can determine a distance (in the feed direction) between the second position marking and the second and / or third reference marking. Based on the determined distance(s), a position of the conveyor belt can be determined by the evaluation unit; in particular, a deviation from a target position to an actual position of the conveyor belt can be determined.

[0074] The reference markings may be lines. Alternatively or additionally, the position marking(s) may be lines. The lines may be continuous lines or broken lines, in particular dotted lines.

[0075] The reference markings can be applied to the marking element by a first print head. The position marking or the position markings can be applied to the marking element by a second print head. The first print head and the second print head can be different print heads. The print heads can be arranged in a print head carrier.

[0076] The marking element can be removable or detachably applied to a surface of the conveyor belt.

[0077] The marking element can be glued to the conveyor belt. In particular, the conveyor belt comprises a thermoplastic or a thermoplastic layer. The marking element can be (removably) bonded to the thermoplastic or the thermoplastic layer. The conveyor belt can have no thermoplastic or thermoplastic layer if the marking element is applied to the conveyor belt. Preferably, the marking element is applied (directly) to a surface of the conveyor belt. A thermoplastic or a thermoplastic layer cannot be understood as a surface of the conveyor belt.

[0078] The marking element can extend continuously along the feed path along the feed direction. The marking element can extend completely continuously along the feed direction on the conveyor belt.

[0079] The evaluation unit can be configured to detect or determine the position of the conveyor belt based on the marking or markings of the marking element.

[0080] The marking element may be a first marking element. The conveyor belt may comprise a second marking element. The first marking element and the second marking element may be spaced apart from one another. Preferably, the first marking element and the second marking element are spaced apart from one another in a direction that is not parallel to the feed direction. The print head may be configured to apply a mark to the first marking element and to the second marking element. The first marking element and the second marking element may be spaced apart from one another in a direction that is perpendicular to the feed direction.

[0081] The second marking element may be any marking element disclosed herein.

[0082] The first marking element can be arranged on the conveyor belt such that the first optical sensor can capture images of the (entire) first marking element, in particular when the conveyor belt is moved over its entire length. The second marking element can be arranged on the conveyor belt such that the second optical sensor can capture images of the (entire) second marking element, in particular when the conveyor belt is moved over its entire length.

[0083] The at least two reference markings and the position marking can be applied to the second marking element in the same way as to the first marking element. The at least three reference markings and the two position markings can also be applied to the second marking element in the same way as to the first marking element.

[0084] Distances between markings of the second marking element can be determined by the evaluation unit in the same way as distances between markings of the first marking element.

[0085] Preferably, the evaluation unit determines a position of the conveyor belt based on the distances between reference markings and position markings of the first and second marking elements. Particularly preferably, the evaluation unit determines a deviation from a target position of the conveyor belt to an actual position of the conveyor belt based on the distances between reference markings and position markings of the first and second marking elements.

[0086] The portions of the plurality of portions of the conveyor belt may include or be portions of a surface of the conveyor belt.

[0087] The optical sensor can be configured to capture images (directly) from a surface of the conveyor belt. The sections of the plurality of sections can be (exclusively) surface sections of the conveyor belt.

[0088] The conveyor belt can include a printing area. If a material to be printed is positioned within the printing area, the material can be printed by the printing press. Material outside the printing area of ​​the conveyor belt cannot be printed by the printing press.

[0089] The optical sensor can be configured to capture images (directly) from a surface of the conveyor belt outside the printing area. The sections of the plurality of sections can be (exclusively) surface sections of the conveyor belt outside the printing area.

[0090] The conveyor belt may include an adhesive layer, such as a thermoplastic or thermoplastic layer, in sections. The material to be printed can be arranged or be arranged on the adhesive layer.

[0091] The optical sensor can be configured to capture images (directly) from a surface of the conveyor belt that does not have an adhesive layer. The portions of the plurality of portions can be (exclusively) surface portions of the conveyor belt that do not include an adhesive layer.

[0092] A material to be printed may be located on the conveyor belt if the optical sensor captures images of sections of the conveyor belt. Alternatively, no material to be printed may be located on the conveyor belt if the optical sensor captures images of sections of the conveyor belt.

[0093] The optical sensor can have a resolution (sensitivity) of at least 400 dpi (dots per inch). Preferably, the optical sensor has a resolution of at least 1000 dpi, more preferably at least 4000 dpi, more preferably at least 8000 dpi, more preferably at least 12000 dpi, more preferably at least 15000 dpi, more preferably at least 20000 dpi, more preferably at least 25000 dpi. The optical sensor can capture images of sections of the conveyor belt at the specified resolution. The optical sensor can have the resolution without smoothing, filtering, and / or acceleration. The optical sensor cannot perform any smoothing, filtering, and / or acceleration.

[0094] The resolution of the optical sensor can be at least 400 cpi (counts per inch). Preferably, the optical sensor has a resolution of at least 1000 cpi, more preferably at least 4000 cpi, more preferably at least 8000 cpi, more preferably at least 12000 cpi, more preferably at least 15000 cpi. The optical sensor can capture images of sections of the conveyor belt at the specified resolution.

[0095] The optical sensor can have a tracking speed of at least 10 ips (inches per second). Preferably, the optical sensor has a tracking speed of at least 25 ips, more preferably at least 50 ips, more preferably at least 100 ips, more preferably at least 200 ips, more preferably at least 300 ips, more preferably at least 350 ips, more preferably at least 400 ips. A high tracking speed allows for high measurement accuracy of the optical sensor at high conveyor belt speeds. The optical sensor can capture images of sections of the conveyor belt at the specified tracking speed.

[0096] The optical sensor can have a frame rate of at least 1000 fps (frames per second). Preferably, the optical sensor has a frame rate of at least 2000 fps, more preferably at least 4000 fps, more preferably at least 6000 fps, more preferably at least 8000 fps, more preferably at least 10000 fps, more preferably at least 11000 fps. The optical sensor can capture images of sections of the conveyor belt at the specified frame rate.

[0097] The optical sensor can be configured to detect or recognize a movement of a substrate, for example, the conveyor belt, of less than 100 µm, preferably less than 50 µm, more preferably less than 10 µm, more preferably less than 1.0 µm. The movement can be a movement of the substrate relative to the optical sensor.

[0098] The optical sensor can comprise an illumination device. The illumination device can emit light in the direction of the plurality of sections or onto the plurality of sections. The illumination device can be a light-emitting diode (LED). The illumination device can be a laser diode. The illumination device can emit light with a wavelength greater than 800 nm, more preferably greater than 825 nm, more preferably greater than 850 nm, in the direction of the plurality of sections. In particular, the illumination device can emit light with a wavelength between 800 nm and 900 nm, preferably between 825 nm and 850 nm, more preferably between 843 nm and 853 nm, in the direction of the plurality of sections. The illumination device can emit light with a wavelength between 380 nm and 800 nm in the direction of the plurality of sections.

[0099] The illumination device may comprise one or more light sources. The illumination device may comprise at least two light sources, in particular at least three light sources, wherein the light sources are configured to generate light with different wavelengths or different wavelength ranges. The (respective) light may be radiated in the direction of the plurality of sections or onto the plurality of sections.

[0100] The illumination device can be an RGB (red-green-blue) illumination device. The illumination device can comprise a light source for generating red light, a light source for generating green light, and / or a light source for generating blue light. Red light can be present in a wavelength range from 630 nm to 700 nm. Green light can be present in a wavelength range from 500 nm to 560 nm. Blue light can be present in a wavelength range from 450 nm to 475 nm.

[0101] In general, the lighting device can be configured to radiate light in a mixed color toward the plurality of sections or onto the plurality of sections. The mixed color can result from light from different light sources.

[0102] Each of the light sources may comprise or be an LED. Each of the light sources may comprise or be a laser diode.

[0103] The lighting device can be provided outside the optical sensor.

[0104] The lighting device can emit colorless light toward the plurality of sections. The light emitted toward the plurality of sections can be white light.

[0105] The distance between the surface of the conveyor belt and the optical sensor may be less than 20.0 mm. Preferably, the distance between the surface of the conveyor belt and the optical sensor is less than 15.0 mm, more preferably less than 10.0 mm, more preferably less than 7.0 mm, more preferably less than 5.0 mm, more preferably less than 3.0 mm.

[0106] The distance between the surface of the conveyor belt and the optical sensor may be at least 0.1 mm, preferably at least 0.5 mm, more preferably at least 1.0 mm.

[0107] In particular, the distance between the surface of the conveyor belt and the optical sensor is between 0.1 mm and 20 mm, preferably between 0.5 mm and 10 mm, more preferably between 1.0 mm and 3.0 mm.

[0108] A method for determining a position of a conveyor belt of a printing press comprises the steps of: moving the conveyor belt in a feed direction over a feed path, wherein the conveyor belt comprises a plurality of sections along the feed direction over the feed path; sequentially capturing at least one image of each section of the plurality of sections of the conveyor belt by an optical sensor; and determining the position of the conveyor belt based on the images of the plurality of sections of the conveyor belt.

[0109] The printing machine may be any printing machine disclosed herein.

[0110] A method for operating a printing press is disclosed. The printing press can be any printing press disclosed herein. The method comprises the steps of: moving a conveyor belt of the printing press in a feed direction over a feed path, wherein the conveyor belt comprises a plurality of sections along the feed direction over the feed path; sequentially capturing at least one image of each section of the plurality of sections of the conveyor belt using an optical sensor; determining a deviation between an actual position and a desired position of the conveyor belt based on the images of the plurality of sections of the conveyor belt; and adjusting the movement of the conveyor belt based on the deviation between the actual position and the desired position of the conveyor belt.

[0111] A printing press for printing on a material comprises a conveyor belt, an optical sensor, an evaluation unit, and a control device. The conveyor belt is movable in a feed direction over a feed path. The conveyor belt comprises a plurality of sections along the feed direction over the feed path. The optical sensor is configured to sequentially capture at least one image of each section of the plurality of sections of the conveyor belt. The evaluation unit is configured to determine a deviation between an actual position and a target position of the conveyor belt based on the images of the plurality of sections of the conveyor belt. The control device is configured to adapt the movement of the conveyor belt based on the deviation between the actual position and the target position of the conveyor belt.

[0112] The printing machine may be any printing machine disclosed herein. SHORT DESCRIPTION OF THE CHARACTERS

[0113] The invention and further embodiments and advantages of the invention are explained in more detail below with reference to figures, whereby the figures merely describe exemplary embodiments of the invention. Identical components in the figures are provided with the same reference numerals. The figures are not to be considered to scale; individual elements of the figures may be exaggeratedly large or oversimplified. Fig. 1 shows a printing machine 100; Fig. 2 shows an optical sensor 20a in one embodiment; and Fig. 3 shows an optical sensor 20b in a further embodiment.

[0114] Fig. 1shows a printing press 100 with a conveyor belt 10 in a perspective view. The printing press may include a print head 41. The print head 41 may be arranged in a print head carrier 40. The print head carrier 40 may include a plurality of print heads 41. The print head carrier 40 may include at least six print heads 41, in particular at least six print heads 41 per color.

[0115] A material to be printed, such as fabric, paper, cardboard, plastic, wood, or metal, can be applied to the conveyor belt 10. For this purpose, the conveyor belt 10 can comprise a thermoplastic or a thermoplastic layer to which the material to be printed can be releasably bonded. The conveyor belt 10 can move the material to be printed in a feed direction R. In particular, the conveyor belt 10 positions the material to be printed relative to the print head 41 or the print head carrier 40.

[0116] The print head 41 can be movable, in particular linearly movable. The print head 41 can be moved in a direction non-parallel, preferably perpendicular to the feed direction R. The print head 41 can be moved by the print head carrier 40. For this purpose, the print head carrier 40 can be moved so that the print head 41 arranged on or in the print head carrier 40 is moved.

[0117] The printing press 100 can have a first roller. Additionally, the printing press 100 can have a second roller. The conveyor belt 10 is preferably an endless belt or a continuous belt. The conveyor belt 10 can be wrapped around the first and second rollers and stretched between the rollers. Preferably, the conveyor belt 10 is frictionally connected to at least one of the rollers, preferably to the first roller and the second roller.

[0118] At least one of the rollers can function as a drive roller for the conveyor belt 10. The drive roller can be driven by a motor, for example, an electric motor. The motor can cause the drive roller to rotate. The rotation of the drive roller can move the conveyor belt 10. The other roller can be non-driven and preferably fulfills a supporting and / or holding function. Alternatively, the second roller can also be driven, in particular driven in the same way as the first roller.

[0119] In a typical printing process, the material to be printed can be applied to the conveyor belt 10. For this purpose, the material to be printed can, for example, be unwound from a roll on which the material to be printed is stored. The conveyor belt 10 is moved a predefined distance and the print head 41 prints a pattern onto the material to be printed. For this purpose, the print head 41 can be moved, in particular moved such that the entire width (direction perpendicular to the feed direction R) of the material to be printed is printable or is printed. The conveyor belt is then moved again a predefined distance in the direction of the feed direction R and the print head 41 prints the material to be printed. These steps (moving the conveyor belt 10 and printing the material to be printed) can be repeated many times to obtain a printed material.The printed material can be detached from the conveyor belt 10 at one end of the conveyor belt in the area of ​​a roller, for example, by detaching the printed material from the thermoplastic or thermoplastic layer of the conveyor belt 10. Finally, the printed material can be stored, for example, rolled up on a storage reel. Before storage, the printed material can be further processed. For example, the printed material can be dried or steamed.

[0120] Between two movement steps of the conveyor belt 10, wherein preferably the material to be printed is printed between the two movement steps, there can be a time period of less than 1.0 s, preferably less than 0.5 s, more preferably less than 250 ms.

[0121] The printhead carrier 40 can comprise multiple printheads 41. Each of the printheads 41 can apply a color to the material to be printed.

[0122] The printing press 100 comprises at least one first optical sensor 20a. The at least one sensor 20a can be arranged in a first holder 21a. The first optical sensor 20a can be held and / or positioned by the holder 21a. The holder 21a can be detachably or non-detachably connected to the printing press 100. The holder 21a can be an integral part of the printing press 100. By connecting the holder 21a of the first optical sensor 20a to the printing press 100, a user can easily align the optical sensor 20a relative to the conveyor belt 10.

[0123] Alternatively, the mount 21a may not be (directly) connected to the printing press 100. For example, the mount 21a may be arranged or placed on a floor next to the printing press 100. Likewise, the mount 21a may be connected to a support. The support is preferably not (directly) connected to the printing press 100. This allows the optical sensor 20a to be decoupled from any vibrations of the printing press 100.

[0124] The printing press may comprise a second optical sensor 25a. The second optical sensor 25a may be arranged in a second holder 26a. The second holder 26a may be configured identically to the first holder 21a. The second optical sensor 25a may be arranged opposite the first optical sensor 20a, in particular in a direction non-parallel or perpendicular to the feed direction R. The first optical sensor 20a and the second optical sensor 25a may have a substantially equal (±10% or ±5%) distance from the print head 41 in the feed direction R. A distance between the first sensor 20a and the second sensor 25a non-parallel or perpendicular to the feed direction R may be at least 0.5 m.

[0125] The first optical sensor 20a and / or the second optical sensor 25a may be a camera. The first optical sensor 20a and the second optical sensor 25a may be the same or different optical sensors.

[0126] The first optical sensor 20a and / or the second optical sensor 25a captures a plurality of images of sections of the conveyor belt 10 along the feed path in the feed direction R. Based on the images, the position of the conveyor belt 10 is determined or ascertained by an evaluation unit 60. In particular, based on the images, the evaluation unit 60 can determine or ascertain whether there is a deviation between a target position of the conveyor belt 10 and an actual position of the conveyor belt 10. If necessary, the evaluation unit 60 can determine how large the deviation between the target position and the actual position of the conveyor belt 10 is. For this purpose, the evaluation unit 60, which is in communication (indicated by the double arrow in Fig. 1 ) with the first and / or second optical sensor 20a, 25a, receive image data from the first and / or second optical sensor 20a, 25a and evaluate the image data.

[0127] For example, it can be provided that the conveyor belt 10, in particular the material to be printed on the conveyor belt 10, is moved by a distance of at least 50 mm relative to the print head 41 in the feed direction R (target position of the conveyor belt 10). Preferably, the conveyor belt 10, in particular the material to be printed on the conveyor belt 10, is moved by a distance of at least 100 mm, more preferably at least 200 mm, more preferably at least 300 mm. The conveyor belt 10, in particular the material to be printed on the conveyor belt 10, can be moved by a distance between 50 mm and 1000 mm, preferably between 50 mm and 500 mm, more preferably between 100 mm and 450 mm, more preferably between 200 mm and 400 mm. By evaluating the images of the first and / or second optical sensor 20a, 25a, it is possible to determine the distance by which the conveyor belt 10 was actually moved (actual position of the conveyor belt 10).Based on the deviation between the target position and the actual position of the conveyor belt 10, the evaluation unit 60 can determine a change in the movement of the conveyor belt 10, preferably for a future movement of the conveyor belt 10.

[0128] If the evaluation unit 60 determines a deviation between the target position and the actual position of the conveyor belt 10, the movement of the conveyor belt 10 can be changed such that a deviation, in particular a future deviation, is reduced.

[0129] For example, the evaluation unit 60 can determine a deviation of +100 µm between the target position and the actual position of the conveyor belt 10. A positive deviation can represent that the conveyor belt 10 was moved further than it should have been. Likewise, the deviation can be -100 µm. A negative deviation can represent that the conveyor belt 10 was not moved far enough. Even a deviation in the millimeter range, particularly in the single-digit millimeter range, can be determined or detected by the evaluation unit 60.

[0130] For the conveyor belt 10, a plurality of deviations between the target position and the actual position of the conveyor belt 10 can be determined. The conveyor belt 10 is preferably moved step by step over a feed path that is at least 5 times, preferably at least 50 times, more preferably at least 100 times, more preferably at least 250 times, more preferably at least 500 times as large as the length or circumference of the conveyor belt 10. For the conveyor belt 10, at least 100, preferably at least 1000, more preferably at least 5000, more preferably at least 7000 deviations between the target position and the actual position of the conveyor belt 10 can be determined. The first and / or second optical sensor 20a, 25a can capture images of a plurality of sections along the feed path.The steps of the (planned or desired) stepwise movement may be at least 100 mm, whereby the steps may have a different size, in particular the sizes of the steps do not have to be constant.

[0131] Based on the images, the position of the conveyor belt 10 (actual position of the conveyor belt 10) can be determined, especially after each movement step. The actual position of the conveyor belt 10 can be compared with the size of the steps (target position of the conveyor belt 10) to determine any deviation.

[0132] The deviation can be determined for a plurality of steps, for example for at least 100 steps, preferably for at least 500 steps, more preferably for at least 1000 steps.

[0133] Each step of the movement can be correlated with the conveyor belt 10. A step can be assigned to a position or location on the conveyor belt 10. Likewise, a deviation can be assigned to a position or location on the conveyor belt. Along the conveyor belt 10, positions or locations can be defined starting from a starting point over the entire length or the entire circumference of the conveyor belt 10. The locations or positions can be unique in the feed direction. The location or positions can be used to uniquely determine the position of the conveyor belt 10.

[0134] For example, the conveyor belt 10 may be slightly thinner at one location than at another. This may result in a recurring or repeating deviation if the conveyor belt 10 is moved multiple times across its entire length. By knowing a deviation between the actual position and the target position at a location or position of the conveyor belt 10, the movement of the conveyor belt 10 can be modified in the future when moving across this location or position based on the known position deviation.

[0135] Alternatively or additionally, a respective step of the movement of the conveyor belt 10 can be correlated with a position of a roller. The position can be a circumferential angle of the roller. A respective step of the movement of the conveyor belt 10 can be correlated with a position of a first roller and a second roller. A roller can be a drive roller or a non-driven roller.

[0136] For example, the roller may have a slightly smaller radius at one location than at another. The roller may be (slightly) out of round or conical. This can result in a recurring or repeating deviation if the roller is rotated multiple times across its entire circumference. By knowing a deviation between the actual position and the target position at a particular position of the roller, the movement of the conveyor belt 10 (e.g., caused by a rotation of the roller) can be modified in the future during a movement across this position based on the known position deviation.

[0137] Preferably, deviation values, preferably correlated or linked to the position or location of the conveyor belt 10 and / or correlated or linked to the position of the roller, are collected in a table. A distance, in particular a changed or corrected distance, of the movement of the conveyor belt can be determined for each deviation value. This can be done by the evaluation unit. The movement of the conveyor belt can be based on the, in particular corrected, distance of the movement or can still be based on the, in particular corrected, distance of the movement.

[0138] The distance of the movement can be controlled or regulated by a control device 70 of the printing press. The control device 70 can comprise the evaluation unit 60. The control device 70 can be integrated in the printing press 100. The control device 70 can be arranged outside the printing press 100. The control device 70 can be in communication with the printing press 100 (indicated by the double arrow in Fig. 1 ) stand.

[0139] At least one marking element 50 can be applied to the conveyor belt 10. The marking element 50 can be releasably applied to the conveyor belt 10, for example, by adhesive bonding. The marking element 50 can extend over the entire length or the entire circumference of the conveyor belt 10, in particular in the feed direction R. The marking element 50 can be printable.

[0140] During or after a movement of the conveyor belt 10, the marking element 50 can be printed by the print head 41. The print head 41 can apply the above-described reference markings and the position marking(s) to the marking element 50. The conveyor belt 10 can move or not move while the marking element 50 is being printed.

[0141] In the (positive) direction of the feed direction R of the conveyor belt 10, the optical sensor 20a can be spaced apart from the print head 41. The optical sensor 20a can be arranged downstream of the print head 41 or upstream of the print head 41 in the feed direction R.

[0142] The sections of the conveyor belt 10 from which the optical sensor 20 captures images can encompass the marking element 50 (in sections). The sections can be entirely sections of the marking element 50. The optical sensor 20a can be directed (entirely) at the marking element 50.

[0143] The images from the optical sensor 20a can include the reference markings and / or the position marking(s). Based on the reference markings and the position marking(s), the evaluation unit can determine a deviation between the target position of the conveyor belt 10 and the actual position of the conveyor belt 10.

[0144] In general, a deviation between the target position and the actual position of the conveyor belt 10 can comprise a deviation in the feed direction R, which is essentially (±10% or ±5%) constant across the width of the conveyor belt 10. The width can be oriented perpendicular to the feed direction R. Alternatively or additionally, the deviation between the target position and the actual position of the conveyor belt 10, which is not constant across the width of the conveyor belt 10, can increase or decrease (section by section) in the direction of the width of the conveyor belt 10. The deviation can be positive and / or negative in the direction of the width of the conveyor belt 10. In the width direction, the deviation can be positive in one place and negative in another place. A positive deviation can mean a gap in the pattern, and a negative deviation can mean an overlap of sections of the pattern.

[0145] The deviation in the feed direction R, which is essentially constant (±10% or ±5%) across the width of the conveyor belt 10, can be compensated by changing the movement of the conveyor belt 10. For example, if the deviation between the actual position of the conveyor belt 10 and the target position of the conveyor belt 10 is positive, a gap may exist in the printed pattern. The target position can be adjusted, for example, by reducing the movement step of the conveyor belt 10, so that the deviation becomes smaller or even (within the measurement tolerance) no deviation is detectable.

[0146] The deviation in the feed direction R, which is not constant across the width of the conveyor belt 10, can be compensated for by changing the movement of the conveyor belt 10. For example, if a deviation (within the measurement tolerance) cannot be detected on one side of the conveyor belt 10 and the deviation on the opposite side of the conveyor belt is positive, the movement of the conveyor belt 10 can be changed so that there is a negative deviation on one side of the conveyor belt 10 and a positive deviation on the opposite side of the conveyor belt 10. The amounts of the negative and positive deviations can be essentially the same (±10% or ±5%). In other words, the movement of the conveyor belt 10 can be changed so that there is an overlap of the pattern on one side and a gap in the pattern on the opposite side.The deviation on the opposite side of the conveyor belt 10 can thereby be essentially halved (±10% or ±5%).

[0147] The printing press 100 may include a washing unit 80. The washing unit 80 may be configured to wash a portion of the conveyor belt 10. In particular, the washing unit 80 may wash off or remove ink on the conveyor belt 10, in particular ink from the print head 41 on the conveyor belt 10.

[0148] The washing unit 80 can be formed in a lower region of the printing press 100. "Lower" can refer to the direction of gravity.

[0149] The conveyor belt 10 can be wrapped around at least two rollers. The conveyor belt 10 can comprise a section located above a plane defined by the rotation axes of the rollers. The conveyor belt 10 can comprise a section located below the plane defined by the rotation axes of the rollers. The sections can temporarily lie above or below the plane. When the conveyor belt 10 is moved, a section can be moved from above the plane to below the plane, or a section below the plane can be moved above the plane. The surface of the conveyor belt can run parallel in sections.

[0150] The washing unit 80 can be arranged in the printing press 100 such that the section of the conveyor belt 10 which is located below the rotation axes of the rollers can be washed at least in sections by the washing unit 80.

[0151] If a marking element 50 is arranged on the conveyor belt 10, the marking element 50 can be provided with a mark by the print head 41 in a section that is located above the plane defined by the rotation axes of the rollers. If the conveyor belt 10 with the marking element 50 is moved further so that the printed section of the marking element 50 is located below the plane defined by the rotation axes of the rollers, the mark on the marking element 50 can be removed by the washing unit 80. The section of the marking element 50 can be moved when the conveyor belt 10 is moved so that the section is located above the plane defined by the rotation axes of the rollers. The section of the marking element 50 can be provided with a mark again by the print head 41.

[0152] A marking on the marking element 50 can be removable or washable by the washing mechanism 80. This allows sections of the marking element 50 to be provided with a marking multiple times. The optical sensor 20a can capture images of each marked section of the marking element 50.

[0153] The conveyor belt 10 may include a first marking element 50 and a second marking element 55. Generally, each of the marking elements may be any marking element disclosed herein.

[0154] A first optical sensor 20a can be assigned to the first marking element 50. A second optical sensor 25a can be assigned to the second marking element 55.

[0155] The first optical sensor 20a can be directed at the first marking element 50. The first optical sensor 20a can capture images of markings, in particular reference and / or position markings, on the first marking element 50. The first optical sensor 20a can be directed at the first marking element 50. The second optical sensor 25a can capture images of markings, in particular reference and / or position markings, on the second marking element 55.

[0156] The print head 41 can apply, preferably print, markings, in particular reference and / or position markings, to the first marking element 50 and the second marking element 55. It is preferred that the print head 41 applies markings to the first marking element 50 and the second marking element 55 while the conveyor belt 10 is not moving. In particular, at least one marking can be applied to the first marking element 50 and at least one marking to the second marking element 55 without the conveyor belt moving.

[0157] Fig. 2 shows an enlarged section of the printing press 100 with a view of a first optical sensor 20a. The marking element 50 is applied to the conveyor belt 10. The optical sensor 20a can be held by a holder 21a.

[0158] The conveyor belt 10 can comprise a first section 11 which has a layer. The layer can comprise a thermoplastic or the layer can be a thermoplastic layer. The conveyor belt 10 can comprise a second section 12 which does not have the layer. The first section 11 of the conveyor belt 10 can be a section which is accessible by the print head 41, i.e. a material to be printed on the conveyor belt 10 in this section 11 can be printed by the print head 41. The second section 12 of the conveyor belt 10 can be a section which is not accessible by the print head 41, i.e. a material to be printed on the conveyor belt 10 in the second section 12 cannot be printed by the print head 41.

[0159] The marking element 50 can be arranged on the section 11, in particular arranged completely. A connection between the marking element 50 and the conveyor belt 10 can be established or reinforced by a layer in the first section 11.

[0160] No material to be printed can be arranged on the conveyor belt 10 when the marking element 50 is arranged on the conveyor belt 10. In particular, the optical sensor 20a cannot capture images of sections of the conveyor belt 10 when a material to be printed is arranged on the conveyor belt. The optical sensor 20a can capture images of sections of the conveyor belt 10 when no material to be printed is arranged on the conveyor belt. The optical sensor 20a can also capture images of sections of the conveyor belt 10 when a material to be printed is arranged on the conveyor belt 10.

[0161] For example, the optical sensor 20a can capture images of sections of the conveyor belt 10 without any material to be printed being arranged on the conveyor belt 10. Based on the images, the positions of the conveyor belt 10 can be determined by the evaluation unit 60, in particular for a plurality of movement steps of the conveyor belt 10. Preferably, the evaluation unit 60 determines deviations from target positions and actual positions of the conveyor belt 10. Based on the positions of the conveyor belt 10 and / or the deviations, the movement steps can be adjusted such that deviations between actual positions and target positions of the conveyor belt 10 are at least partially reduced.

[0162] If a material to be printed is arranged on the conveyor belt 10, the conveyor belt 10 can be moved according to the adjusted movement steps. Between or during the movement steps, the material to be printed can be printed, for example, by the print head 41. When printing on the material to be printed, the marking element 50 can be arranged off the conveyor belt 10.

[0163] Alternatively, the material to be printed can be arranged on the conveyor belt 10 when the marking element 50 is arranged on the conveyor belt 10. The material to be printed is preferably arranged in the first section 11. The marking element 50 can be arranged on the first section 11 and / or on the second section 12.

[0164] Fig. 3shows an enlarged section of the printing press 100 with a view of a first optical sensor 20b in a further embodiment. The optical sensor 20b can be held by a holder 21b. A second optical sensor can be provided (not shown in Fig. 3 shown). The second optical sensor may be (substantially) the same or analogous to the first optical sensor.

[0165] The optical sensor 20b can be directed toward the second section 12 of the conveyor belt 10. Alternatively, the optical sensor 20b can be directed toward the first section 11 of the conveyor belt 10. No marking element 50 can be arranged on the conveyor belt 10 if the optical sensor 20b captures images of sections of the conveyor belt 10. In particular, the sections of the conveyor belt 10 from which the optical sensor 20b captures images can be a (direct) surface of the conveyor belt 10.

[0166] Preferably, a material to be printed is arranged on the conveyor belt 10 when the optical sensor 20b captures images of sections of the conveyor belt 10. This allows deviations between actual and target positions of the conveyor belt 10 to be determined during operation, so that dynamic changes can also be detected. Alternatively or additionally, the optical sensor 20b can capture images of sections of the conveyor belt 10 when no material to be printed is arranged on the conveyor belt 10.

[0167] If images of sections of the conveyor belt 10 are captured and a position of the conveyor belt 10 is determined while the material to be printed is arranged on the conveyor belt 10 (and is being printed), the movement of the conveyor belt 10 can be controlled based on the determined positions.

[0168] A continuous determination of positions of the conveyor belt 10 or of deviations between actual positions and target positions of the conveyor belt 10 can be provided. The continuous determination can extend over a period of at least 1 hour, preferably at least 3 hours, more preferably at least 5 hours, more preferably at least 15 hours, more preferably at least 30 hours or 50 hours, in particular continuously. The optical sensor 20b can be configured to determine position data of the conveyor belt 10. For this purpose, the optical sensor 20b can comprise an evaluation unit. The evaluation unit of the optical sensor 20b can be any evaluation unit 60 disclosed herein.

[0169] The optical sensor 20b may include a digital signal processor (DSP). The optical sensor 20b may be configured to detect a position change based on images captured by the optical sensor 20b. Preferably, the digital signal processor of the optical sensor 20b is configured to detect a position change based on images captured by the optical sensor 20b. The position change may be a position change of the conveyor belt 10.

[0170] The optical sensor 20b, in particular the digital signal processor of the optical sensor 20b, can be configured to determine, based on the images captured by the optical sensor 20b, a position change in a first direction and / or a position change in a second direction that is non-parallel to the first direction, in particular that is perpendicular to the first direction. The first direction can be the feed direction R.

[0171] A microcontroller of the optical sensor 20b can receive the data of the position change(s). The microcontroller can convert the data of the position change(s) into a USB signal or an RF signal. The converted data can be transmitted to the evaluation unit 60 or a control device 70.

[0172] The optical sensor 20b may include a lens. The lens may be a magnifying lens. LIST OF REFERENCE SYMBOLS

[0173] 10Conveyor belt 11Section 12Section 20aOptical sensor 20boPtical sensor 21aBracket 21bBracket 25aOptical sensor 26Bracket 40Print head carrier 41Print head 50Marking element 55Marking element 60Evaluation unit 70Control unit 80Wash-up unit 100Printing machine RFeed direction

Claims

1. A printing machine (100) for printing on a material, in particular a fabric, paper, cardboard, plastic, wood or metal, comprising: - a conveyor belt (10), wherein the conveyor belt (10) is movable in a feed direction (R) over a feed path, wherein the conveyor belt (10) comprises a plurality of portions along the feed direction (R) over the feed path; - an optical sensor (20a, 20b, 25a), wherein the optical sensor (20a, 20b, 25a) is arranged to detect at least one image of each portion of the plurality of portions of the conveyor belt (10) sequentially; - an evaluation unit (60) which is arranged to determine a position of the conveyor belt (10) based on the images of the plurality of portions of the conveyor belt (10); and a printing head (40) which is arranged to print on the material on the conveyor belt; wherein the optical sensor (20a, 20b, 25a) comprises a first optical sensor (20a, 20b) and a second optical sensor (25a) which are formed in a same way and are spaced apart from each other in a direction which is not parallel to the feed direction (R), and wherein the conveyor belt (10) is arranged to transport the material to be printed on, under the printing head (40).

2. The printing machine (100) according to claim 1, wherein the optical sensor (20a, 20b, 25a) is arranged stationarily on the printing machine (100) or is arranged stationarily relative to the printing machine (100), in particular, the optical sensor (20, 20b, 25a) is connected to the printing machine (100) or is not connected to the printing machine (100), and / or wherein the first and second optical sensors (20a, 20b, 25a) are directed towards or associated with opposite edges of the conveyor belt (10).

3. The printing machine (100) according to claim 2, wherein the plurality of portions along the feed direction (R) over the feed path is a first plurality of portions along the feed direction (R) over the feed path and the conveyor belt (10) comprises a second plurality of portions along the feed direction (R) over the feed path, wherein the first plurality of portions and the second plurality of portions are spaced apart from each other in the direction that is not parallel to the feed direction (R), wherein the first optical sensor (20a, 20b) is arranged to detect at least one image of each portion of the first plurality of portions sequentially and the second optical sensor (25a) is arranged to detect at least one image of each portion of the second plurality of portions sequentially, and wherein the evaluation unit (60) is arranged to determine the position of the conveyor belt based on the images of the first plurality of portions and the second plurality of portions.

4. The printing machine (100) according to any one of the preceding claims, wherein the conveyor belt (10) is movable along the feed direction (R) over the feed path discontinuously, with interruptions and / or stepwise.

5. The printing machine (100) according to any one of the preceding claims, wherein the printing machine (100) comprises a further printing head (41) and the conveyor belt (10) comprises a marking element (50, 55), wherein the portions of the plurality of portions of the conveyor belt (10) comprise or are portions of the marking element (50, 55), and wherein the further printing head (41) is arranged to apply a marking, in particular a regular marking, to the marking element (50, 55).

6. The printing machine (100) according to claim 5, wherein the marking element (50, 55) is removably applied to a surface of the conveyor belt (10).

7. The printing machine (100) according to claim 5 or 6, wherein the marking element (50, 55) extends continuously over the feed path along the feed direction (R), in particular wherein the marking element (50, 55) extends completely continuously along the feed direction (R) on the conveyor belt (10).

8. The printing machine (100) according to any one of claims 5 to 7, wherein the evaluation unit (60) is arranged to determine the position of the conveyor belt (10) based on the marking of the marking element (50, 55).

9. The printing machine (100) according to any one of claims 5 to 8, wherein the marking element (50, 55) is a first marking element (50) and the conveyor belt (10) comprises a second marking element (55), wherein the first marking element (50) and the second marking element (55) are spaced apart in a direction that is not parallel to the feed direction (R), and wherein the further printing head (41) is arranged to apply a marking to the first marking element (50) and to the second marking element (55).

10. The printing machine (100) according to any one of claims 1 to 4, wherein the portions of the plurality of portions of the conveyor belt (10) comprise or are portions of a surface of the conveyor belt (10).

11. The printing machine (100) according to any one of the preceding claims 1, wherein the optical sensor (20a, 20b, 25a) has a resolution of at least 400 dpi, preferably at least 1000 dpi, more preferably at least 4000 dpi, more preferably at least 8000 dpi, more preferably at least 12000 dpi, more preferably at least 15000 dpi, more preferably at least 20000 dpi, more preferably at least 25000 dpi.

12. The printing machine (100) according to any one of the preceding claims, wherein the optical sensor (20a, 20b, 25a) comprises an illumination device, in particular a light-emitting diode or a laser diode, through which rays of light with a wavelength of greater than 800 nm, preferably of between 800 nm and 900 nm, can be emitted in the direction of the plurality of portions.

13. The printing machine (100) according to any one of the preceding claims, wherein a distance between a surface of the conveyor belt (10) and the optical sensor (20a, 20b, 25a) is less than 20.0 mm, preferably less than 15.0 mm, more preferably less than 10.0 mm, more preferably less than 7.0 mm, more preferably less than 5.0 mm, more preferably less than 3.0 mm.

14. A method for determining a position of a conveyor belt (10) of a printing machine (100), comprising the following steps: - moving the conveyor belt (10) in a feed direction (R) over a feed path, wherein the conveyor belt (10) comprises a plurality of portions along the feed direction (R) over the feed path, wherein the conveyor belt (10) transports the material to be printed on, under a printing head (40) on the printing machine, wherein the printing head (40) is arranged to print on the material on the conveyor belt; - sequentially detecting at least one image of each portion of the plurality of portions of the conveyor belt (10) by a first optical sensor (20a, 20b) and a second optical sensor (25a) which are formed in a same way and which are spaced apart from each other in a direction which is not parallel to the feed direction (R); and - determining the position of the conveyor belt (10) based on the images of the plurality of portions of the conveyor belt (10).

15. A method for operating a printing machine (100), particularly for controlling or regulating a printing machine (100), comprising the following steps: - moving a conveyor belt (10) of the printing machine (100) in a feed direction (R) over a feed path, wherein the conveyor belt (10) comprises a plurality of portions along a feed direction (R) over the feed path, wherein the conveyor belt (10) transports the material to be printed on, under a printing head (40), wherein the printing head is arranged to print on the material on the conveyor belt (10); - sequentially detecting at least one image of each portion of the plurality of portions of the conveyor belt (10) by a first optical sensor (20a, 20b) and a second optical sensor (25a) which are formed in a same way and which are spaced apart from each other in a direction which is not parallel to the feed direction (R); - determining a deviation between an actual position and a target position of the conveyor belt (10) based on the images of the plurality of portions of the conveyor belt (10); and - adjusting the movement of the conveyor belt (10) based on the deviation between the actual position and the target position of the conveyor belt (10).

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