METHOD AND SYSTEM FOR DETERMINING A POSITION OF A POSITION OF A TRANSPORT BELT

Abstract

The invention relates to a printing machine for printing a material. The printing machine comprises a conveyor belt, an optical sensor and an evaluation unit. The conveyor belt is movable in a feed direction along a feed path. The conveyor belt comprises a plurality of portions along the feed direction over the feed path. The optical sensor is arranged to detect at least one image of each portion of the plurality of portions of the conveyor belt sequentially. The evaluation unit is arranged to identify or determine a position of the conveyor belt on the basis of the images of the plurality of portions of the conveyor belt.

Claims

1. A printing machine for printing a material, in particular a fabric, paper, cardboard, plastic, wood or metal, comprising: a conveyor belt, wherein the conveyor belt is movable in a feed direction over a feed path, wherein the conveyor belt comprises a plurality of portions along the feed direction over the feed path; an optical sensor, wherein the optical sensor is arranged to detect at least one image of each portion of the plurality of portions of the conveyor belt sequentially; and an evaluation unit which is arranged to determine a position of the conveyor belt based on the images of the plurality of portions of the conveyor belt, wherein the optical sensor comprises a first optical sensor and a second optical sensor 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.

2. The printing machine according to claim 1, wherein the optical sensor is arranged stationarily on the printing machine or is arranged stationarily relative to the printing machine.

3. The printing machine according to claim 1, wherein the first and second optical sensors are directed towards or associated with opposite edges of the conveyor belt.

4. The printing machine according to claim 3, wherein the plurality of portions along the feed direction over the feed path is a first plurality of portions along the feed direction over the feed path and the conveyor belt comprises a second plurality of portions along the feed direction 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, wherein the first optical sensor is arranged to detect at least one image of each portion of the first plurality of portions sequentially and the second optical sensor is arranged to detect at least one image of each portion of the second plurality of portions sequentially, and wherein the evaluation unit 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.

5. The printing machine according to claim 1, wherein the conveyor belt is movable along the feed direction over the feed path discontinuously, with interruptions or stepwise.

6. The printing machine according to claim 1, wherein the printing machine comprises a printing head and the conveyor belt comprises a marking element, wherein the portions of the plurality of portions of the conveyor belt comprise or are portions of the marking element, and wherein the printing head is arranged to apply a marking, in particular a regular marking, to the marking element.

7. The printing machine according to claim 6, wherein the marking element is removably applied to a surface of the conveyor belt.

8. The printing machine according to claim 6, wherein the marking element extends continuously over the feed path along the feed direction, and the marking element extends completely continuously along the feed direction on the conveyor belt.

9. The printing machine according to claim 6, wherein the evaluation unit is arranged to determine the position of the conveyor belt based on the marking of the marking element.

10. The printing machine according to claim 6, wherein the marking element is a first marking element and the conveyor belt comprises a second marking element, wherein the first marking element and the second marking element are spaced apart in a direction that is not parallel to the feed direction, and wherein the printing head is arranged to apply a marking to the first marking element and to the second marking element.

11. The printing machine according to claim 1, wherein the portions of the plurality of portions of the conveyor belt comprise or are portions of a surface of the conveyor belt.

12. The printing machine according to claim 1, wherein the optical sensor has a resolution of at least 400 dpi.

13. The printing machine according to claim 1, wherein the optical sensor comprises an illumination device, in particular a light-emitting diode or a laser diode, through which light with a wavelength of greater than 800 nm.

14. The printing machine according to claim 1, wherein a distance between a surface of the conveyor belt and the optical sensor is less than 20.0 mm.

15. A method for determining a position of a conveyor belt of a printing machine, comprising: moving the conveyor belt in a feed direction over a feed path, wherein the conveyor belt comprises a plurality of portions along the feed direction over the feed path; sequentially detecting at least one image of each portion of the plurality of portions of the conveyor belt by a first optical sensor and a second optical sensor 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; and determining the position of the conveyor belt based on the images of the plurality of portions of the conveyor belt.

16. A method for operating a printing machine, comprising: moving a conveyor belt of the printing machine in a feed direction over a feed path, wherein the conveyor belt comprises a plurality of portions along a feed direction over the feed path; sequentially detecting at least one image of each portion of the plurality of portions of the conveyor belt by a first optical sensor and a second optical sensor 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; determining a deviation between an actual position and a target position of the conveyor belt based on the images of the plurality of portions of the conveyor belt; and adjusting a movement of the conveyor belt based on the deviation between the actual position and the target position of the conveyor belt.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0111] In the following, the invention and/or further embodiments and advantages of the invention are explained in more detail with reference to figures, wherein the figures describe only embodiments of the invention. Identical components in the figures are provided with identical reference signs. The figures are not to be regarded as true to scale; individual elements of the figures may be exaggerated in size or simplified.

[0112] FIG. 1 shows a printing machine 100;

[0113] FIG. 2 shows an optical sensor 20a in one embodiment; and

[0114] FIG. 3 shows an optical sensor 20b in a further embodiment.

[0115] FIG. 1 shows a printing machine 100 with a conveyor belt 10 in a perspective view. The printing machine may comprise a printing head 41. The printing head 41 may be arranged in a printing head support 40. The printing head support 40 may comprise a plurality of printing heads 41. The printing head support 40 may comprise at least six printing heads 41, in particular at least six printing heads 41 per colour.

[0116] A material to be printed, for example a 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 adhered. 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 printing head 41 or to the printing head support 40.

[0117] The printing head 41 can be movable, in particular linearly movable. The printing head 41 can be moved in a non-parallel direction, preferably perpendicular to the feed direction R. The printing head 41 can be moved by the printing head support 40. For this purpose, the printing head support 40 can be moved so that the printing head 41 arranged on or in the printing head support 40 is moved.

[0118] The printing machine 100 can have a first roller. In addition, the printing machine 100 may have a second roller. The conveyor belt 10 is preferably an endless belt or a continuous belt. The conveyor belt 10 can be laid around the first and second rollers and tensioned between the rollers. Preferably, the conveyor belt 10 is non-positively connected to at least one of the rollers, preferably to the first roller and to the second roller.

[0119] At least one of the rollers can act 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 conveyor belt 10 can be moved by the rotation of the drive roller. The other roller can be non-driven and can preferably fulfil 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.

[0120] 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 unrolled from a roll on which the material to be printed is stored. The conveyor belt 10 is moved a predefined distance and the printing head 41 prints a pattern on the material to be printed. For this purpose, the printing head 41 can be moved, in particular moved in such a way that the entire width (direction perpendicular to the feed direction R) of the material to be printed can be printed 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 on the material to be printed. These steps (moving the conveyor belt 10 and printing the material to be printed) can be repeated many times in order to obtain a printed material. The printed material can be released from the conveyor belt 10 at one end of the conveyor belt in the area of a roller, for example by releasing the connection of the printed material from the thermoplastic or the thermoplastic layer of the conveyor belt 10. Finally, the printed material can be stored, for example rolled up on a storage roll. Before storage, the printed material can be treated further. For example, the printed material can be dried or vaporised.

[0121] A time period of less than 1.0 s, preferably less than 0.5 s, more preferably less than 250 ms, can lie between two movement steps of the conveyor belt 10, wherein the material to be printed is preferably printed between the two movement steps.

[0122] The printing head support 40 may comprise a plurality of printing heads 41. Each of the printing heads 41 can apply a colour to the material to be printed.

[0123] The printing machine 100 comprises at least one first optical sensor 20a. The at least one sensor 20a can be arranged in a first bracket 21a. The bracket 21a can be used to hold and/or position the first optical sensor 20a. The bracket 21a may be detachably or non-detachably connected to the printing machine 100. The bracket 21a can be an integral part of the printing machine 100. By connecting the mount 21a of the first optical sensor 20a to the printing machine 100, a user can easily align the optical sensor 20a relative to the conveyor belt 10.

[0124] Alternatively, the bracket 21a may not be (directly) connected to the printing machine 100. For example, the bracket 21a may be arranged or placed on a floor next to the printing machine 100. Similarly, the bracket 21a may be connected to a support. Preferably, the support is not (directly) connected to the printing machine 100. This allows the optical sensor 20a to be decoupled from any vibrations of the printing machine 100.

[0125] The printing machine may comprise a second optical sensor 25a. The second optical sensor 25a may be arranged in a second bracket 26a. The second bracket 26a may have the same design as the first bracket 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 (10% or 5%) equal distance to the printing 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.

[0126] 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.

[0127] The first optical sensor 20a and/or the second optical sensor 25a detects a plurality of images of portions of the conveyor belt 10 along the feed path in the feed direction R. On the basis of the images, the position of the conveyor belt 10 is determined or identified by an evaluation unit 60. In particular, on the basis of the images, evaluation unit 60 can determine or identify whether there is a deviation between a target position of conveyor belt 10 and an actual position of 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 optical sensor 20a, 25a, can receive image data from the first and/or second optical sensor 20a, 25a and evaluate the image data.

[0128] For example, it may 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 printing 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 of 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). On the basis of 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.

[0129] If a deviation between the target position and the actual position of the conveyor belt 10 is determined by the evaluation unit 60, the movement of the conveyor belt 10 can be changed in such a way that a deviation, in particular a future deviation, is reduced.

[0130] For example, a deviation between the target position and the actual position of the conveyor belt 10 of +100 m can be determined by the evaluation unit 60. A positive deviation can represent that the conveyor belt 10 has been moved further than it should be moved. The deviation can also be 100 m. A negative deviation can represent that the conveyor belt 10 was not moved far enough. A deviation in the millimetre range, in particular in the single-digit millimetre range, can also be determined by the evaluation unit 60.

[0131] For the conveyor belt 10, a large number of deviations between the target position and the actual position of the conveyor belt 10 can be determined. Preferably, the conveyor belt 10 is moved stepwise 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 detect images of a plurality of portions along the feed path. The steps of the (planned or desired) stepwise movement may be at least 100 mm, wherein the steps may have a different size, in particular the sizes of the steps need not be constant.

[0132] On the basis of the images, the position of the conveyor belt 10 (actual position of the conveyor belt 10) can be determined, in particular 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) in order to determine a deviation.

[0133] 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.

[0134] A respective step of the movement can be correlated with the conveyor belt 10. A step can be assigned to a position or a location of the conveyor belt 10. At the same time, a deviation can be assigned to a position or a location of the conveyor belt. Positions or locations can be defined along the conveyor belt 10 starting from a starting point over the entire length or over the entire circumference of the conveyor belt 10. The locations or positions can be unique in the feed direction. A position of the conveyor belt 10 can be uniquely determined by the locations or positions.

[0135] For example, the conveyor belt 10 may have a slightly lower thickness at one location than at another location. This can result in a recurring or repeating deviation when the conveyor belt 10 is moved several times over 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 changed in the future when moving over this location or position on the basis of the known position deviation.

[0136] Alternatively or additionally, a respective step of the movement of the conveyor belt 10 may 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 roller that is not driven.

[0137] For example, the roller may have a slightly smaller radius at one location than at another location. The roller may be (slightly) out of round or conical. This can result in a recurring or repeating deviation when the roller is rotated several times over its entire circumference. By knowing a deviation between the actual position and the target position at a position of the roller, the movement of the conveyor belt 10 (for example caused by a rotation of the roller) can be changed in the future when moving over that position on the basis of the known position deviation.

[0138] Preferred values of the deviation, 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 modified or corrected distance, of the movement of the conveyor belt can be determined for the values of the deviation (in each case). This can be done by the evaluation unit. The conveyor belt can be moved on the basis of the distance of the movement, in particular the corrected distance, or the distance of the movement, in particular the corrected distance.

[0139] The distance of the movement can be controlled or regulated by a control device 70 of the printing machine. The control device 70 can comprise the evaluation unit 60. The control device 70 can be integrated in the printing machine 100. The control device 70 can be arranged outside the printing machine 100. The control device 70 can be in communication with the printing machine 100 (indicated by the double arrow in FIG. 1).

[0140] At least one marking element 50 may be applied to the conveyor belt 10. The marking element 50 can be detachably applied to the conveyor belt 10, for example by 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.

[0141] During a movement of the conveyor belt 10 or after a movement of the conveyor belt 10, the marking element 50 can be printed by the printing head 41. In doing so, the printing head 41 can apply the reference markings described above and the position marking or the position markings to the marking element 50. The conveyor belt 10 may or may not move when the marking element 50 is printed.

[0142] In the (positive) direction of the feed direction R of the conveyor belt 10, the optical sensor 20a may be spaced apart from the printing head 41. The optical sensor 20a can be arranged after the printing head 41 or before the printing head 41 in the feed direction R.

[0143] The portions of the conveyor belt 10 from which the optical sensor 20 detects images may comprise the marking element 50 (in portions). The portions may be fully portions of the marking element 50. The optical sensor 20a may be (fully) directed towards the marking element 50. The images of the optical sensor 20a may comprise the reference markings and/or the

[0144] position marking(s). On the basis of 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.

[0145] 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 that is essentially constant (10% or 5%) across the width of the conveyor belt 10. The width can be orientated 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. The deviation can increase or decrease (in portions) 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 direction of the width, the deviation can be positive at one location and negative at another location. If the deviation is positive, there may be a gap in the pattern and if the deviation is negative, there may be an overlap of portions of the pattern.

[0146] 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 for 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, there may be a gap 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 can be detected.

[0147] 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. If, for example, 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 in the pattern on one side and a gap in the pattern on the opposite side. The deviation on the opposite side of the transport belt 10 can thus be essentially halved (10% or 5%).

[0148] The printing machine 100 may include a washing unit 80. The washing unit 80 may be arranged to wash a portion of the conveyor belt 10. In particular, the washing unit 80 can wash or remove colour on the conveyor belt 10, in particular colour from the printing head 41 on the conveyor belt 10.

[0149] The washing unit 80 may be formed in a lower area of the printing machine 100. Lower may refer to the direction of gravity.

[0150] The conveyor belt 10 may be placed around at least two rollers. The conveyor belt 10 may comprise a portion located above a plane defined by the axes of rotation of the rollers. The conveyor belt 10 can comprise a portion that is located below the plane defined by the axes of rotation of the rollers. The portions can be temporarily above or below the plane. When the conveyor belt 10 is moved, a portion can be moved from above the plane to below the plane or a portion below the plane can be moved to above the plane. The surface of the conveyor belt can run parallel in portions.

[0151] The washing unit 80 can be arranged in the printing machine 100 in such a way that the portion of the conveyor belt 10 that is located below the axes of rotation of the rollers can be washed by the washing unit 80, at least in portions.

[0152] If a marking element 50 is arranged on the conveyor belt 10, the marking element 50 can be provided with a marking by the printing head 41 in a portion which is located above the plane defined by the axes of rotation of the rollers. If the conveyor belt 10 with the marking element 50 is moved further so that the printed portion of the marking element 50 is below the plane defined by the axes of rotation of the rollers, the marking on the marking element 50 can be removed by the washing unit 80. The portion of the marking element 50 can be moved when the conveyor belt 10 is moved so that the portion is above the plane defined by the axes of rotation of the rollers. The portion of the marking element 50 can again be provided with a marking by the printing head 41.

[0153] A marking of the marking element 50 may be removable or washable by the washing unit 80. This allows portions of the marking element 50 to be provided with the markings multiple times. The optical sensor 20a can detect images of the marked portion of the marking element 50 in each case.

[0154] The conveyor belt 10 can comprise a first marking element 50 and a second marking element 55. Generally, each of the marking elements may be any marking element disclosed herein.

[0155] A first optical sensor 20a may be associated with the first marking element 50. A second optical sensor 25a may be associated with the second marking element 55.

[0156] The first optical sensor 20a may be directed towards the first marking element 50. The first optical sensor 20a can detect images of markings, in particular reference and/or position markings, on the first marking element 50. The first optical sensor 20a can be directed towards the first marking element 50. The second optical sensor 25a can detect images of markings, in particular reference and/or position markings, on the second marking element 55.

[0157] The printing head 41 can apply, preferably print, markings, in particular reference and/or position markings, on the first marking element 50 and on the second marking element 55. It is preferred that the printing 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 can be applied to the second marking element 55 without the conveyor belt moving.

[0158] FIG. 2 shows an enlarged section of the printing machine 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 bracket 21a.

[0159] The conveyor belt 10 may comprise a first portion 11 having a layer. The layer may comprise a thermoplastic or the layer may be a thermoplastic layer. The conveyor belt 10 may include a second portion 12 that does not have the layer. The first portion 11 of the conveyor belt 10 may be a portion that can be reached by the printing head 41, i.e. a material to be printed on the conveyor belt 10 can be printed in this portion 11 by the printing head 41. The second portion 12 of the conveyor belt 10 can be a portion that cannot be reached by the printing head 41, i.e. a material to be printed on the conveyor belt 10 in the second portion 12 cannot be printed on by the printing head 41.

[0160] The marking element 50 can be arranged on the portion 11, in particular arranged completely. A layer in the first portion 11 can be used to create or reinforce a connection between the marking element 50 and the conveyor belt 10.

[0161] 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 detect images of portions of the conveyor belt 10 when a material to be printed is arranged on the conveyor belt. The optical sensor 20a can detect images of portions of the conveyor belt 10 when no material to be printed is arranged on the conveyor belt. The optical sensor 20a can also detect images of portions of the conveyor belt 10 when a material to be printed is arranged on the conveyor belt 10.

[0162] For example, the optical sensor 20a can detect images of portions of the conveyor belt 10 without a material to be printed being arranged on the conveyor belt 10. On the basis of the images, 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. Preferred, deviations from target positions and actual positions of the conveyor belt 10 are determined by the evaluation unit 60. On the basis of the positions of the conveyor belt 10 and/or the deviations, the movement steps can be adjusted in such a way that deviations between actual positions and target positions of the conveyor belt 10 are at least partially reduced.

[0163] If a material to be printed is arranged on the conveyor belt 10, the conveyor belt 10 can be moved according to the adapted movement steps. Between or during the movement steps, the material to be printed can be printed on, for example by the printing head 41. When printing on the material to be printed on, the marking element 50 may not be arranged on the conveyor belt 10.

[0164] 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 portion 11. The marking element 50 may be arranged on the first portion 11 and/or on the second portion 12.

[0165] FIG. 3 shows an enlarged section of the printing machine 100 with a view of a first optical sensor 20b in a further embodiment. The optical sensor 20b may be held by a bracket 21b. A second optical sensor may be provided (not shown in FIG. 3). The second optical sensor may be (substantially) the same or analogue to the first optical sensor.

[0166] The optical sensor 20b may be directed towards the second portion 12 of the conveyor belt 10. Alternatively, the optical sensor 20b may be directed towards the first portion 11 of the conveyor belt 10. No marking element 50 can be arranged on the conveyor belt 10 when the optical sensor 20b detects images of portions of the conveyor belt 10. In particular, the portions of the conveyor belt 10 from which the optical sensor 20b captures images can be a (direct) surface of the conveyor belt 10.

[0167] Preferably, a material to be printed is arranged on the conveyor belt 10 when the optical sensor 20b detects images of portions of the conveyor belt 10. This allows deviations between actual positions 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 detect images of portions of the conveyor belt 10 when no material to be printed is arranged on the conveyor belt 10.

[0168] If images of portions of the conveyor belt 10 are detected and a position of the conveyor belt 10 is determined while the material to be printed is arranged on the conveyor belt 10 (and being printed), the movement of the conveyor belt 10 can be regulated on the basis of the determined positions.

[0169] A permanent 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 h, preferably at least 3 h, more preferably at least 5 h, more preferably at least 15 h, more preferably at least 30 h or 50 h, in particular continuously. The optical sensor 20b can be arranged 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.

[0170] The optical sensor 20b may comprise a digital signal processor (DSP). The optical sensor 20b may be arranged to determine a change in position on the basis of images detected by the optical sensor 20b. Preferably, the digital signal processor of the optical sensor 20b is arranged to determine a position change on the basis of images detected by the optical sensor 20b. The change in position can be a change in position of the conveyor belt 10.

[0171] The optical sensor 20b, in particular the digital signal processor of the optical sensor 20b, can be arranged to determine a position change in a first direction and/or a position change in a second direction, which is not parallel to the first direction, in particular which is perpendicular to the first direction, on the basis of the images detected by the optical sensor 20b. The first direction can be the feed direction R.

[0172] A microcontroller of the optical sensor 20b may 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.

[0173] The optical sensor 20b may comprise a lens. The lens may be a magnifying lens.

LIST OF REFERENCE NUMERALS

[0174] 10 Conveyor belt [0175] 11 Portion [0176] 12 Portion [0177] 20a Optical sensor [0178] 20b Optical sensor [0179] 21a Bracket [0180] 21b Bracket [0181] 25a Optical sensor [0182] 26 Bracket [0183] 40 Printing head support [0184] 41 Printing head [0185] 50 Marking element [0186] 55 Marking element [0187] 60 Evaluation unit [0188] 70 Control device [0189] 80 Washing unit [0190] 100 Printing machine [0191] R Feed direction