Endless belt and method for applying a mask-shaped coating onto an endless belt

Abstract

The invention relates to a method for applying a mask-shaped coating onto an endless belt (2), wherein the coating is applied onto an outer surface of the endless belt (2) in the form of drops by means of a printer (3); first markings (6a) and second markings are applied onto the endless belt (2), a plurality of second markings (6b) being applied between two first markings (6a), and the first markings (6a) differing from the second markings (6b) in terms of shape; the first markings (6a) are detected by means of at least one optical sensor (4), in particular a camera, and are compared with at least one reference marking (7a), and the second markings (6b) are detected by means of a second sensor (5); a first clock pulse is generated from a chronological sequence of successive first markings (6a), and a second clock pulse (T2) is generated from a chronological sequence of successive second markings (6b); the first clock pulse (T1) and the second clock pulse (T2) are combined in order to form a control clock pulse (T3), and a pressure signal is generated as a function of the control clock pulse (T3); and drops of a coating material are ejected onto the outer surface of the endless belt (2) according to the pressure signal by means of the printer (3).

Description

[0001] ENDLESS TAPE AND A METHOD FOR APPLYING A MASK-SHAPED COATING TO AN ENDLESS TAPE

[0002] The invention relates to a method for applying a mask-shaped coating to an endless belt, wherein the coating is applied in droplet form to an outer surface of the endless belt by means of a printer.

[0003] Furthermore, the invention relates to an endless belt.

[0004] A method or device of the type mentioned above is known from EP1395443B 1. In the known solution, a mask-shaped coating is applied using a digital printing process, and in a further process step, a material is applied to the uncoated areas of the belt to create a textured surface by etching or depositing material. For printing, the belt passes under a printer that is stationary in the direction of its movement. However, in the known method, the continuous belt, which typically runs between two deflection rollers, can be stretched due to mechanical stress, or the speed of the continuous belt can change during the printing process. This can result in the printed image corresponding to the mask not being correctly transferred to the continuous belt.Another relevant method is known from EP3057785B 1.

[0005] It is an object of the invention to provide a method which is characterized by increased accuracy in the transfer of the mask onto the endless tape.

[0006] The aforementioned problem is solved according to the invention by a method of the type mentioned at the outset in that first markings and second markings are applied to the endless belt, wherein several of the second markings are placed between two first markings, and the first markings differ from the second markings in shape, wherein the first markings are detected by means of at least one optical sensor, in particular a camera, and compared with at least one reference marking, wherein the second markings are detected by means of a second sensor, wherein a first clock is generated from a temporal sequence of successive first markings and a second clock is generated from a temporal sequence of successive second markings, wherein the first clock and the second clock are combined to form a control clock, and wherein a pressure signal is generated depending on the control clock.wherein droplets of a coating material are ejected onto the outer surface of the continuous belt by means of the printer in accordance with the print signal.

[0007] The solution according to the invention allows for the simple implementation of a reliable incremental encoder for printer control, whereby the clock signal can be adjusted to the actual, current position of the continuous belt relative to the printer. Compared to known solutions, the solution according to the invention enables significantly improved correction of belt stretch or consideration of speed changes of the continuous belt rotating relative to the printer during the printing process. Lateral misalignment or lateral deviation of the continuous belt perpendicular to a direction of rotation can also be very reliably compensated for by the solution according to the invention. Thus, the invention ensures a correct and rapid transfer of the printed image onto the continuous belt, independent of interference.

[0008] In an advantageous embodiment of the invention, it may be provided that at least one measure of the conformity between the first marking and the reference marking is determined from the comparison between at least one of the first markings and the reference marking, and if the determined measure is above a threshold value, the first marking is classified as conforming to the reference marking.

[0009] The time interval between two consecutive first marks classified as corresponding to the reference mark can determine the first beat.

[0010] To determine whether the first markings correspond to the reference marking, a cross-correlation function can be formed between an image of one of the first markings captured by the sensor, in particular the camera, and a stored image of the reference marking.

[0011] Furthermore, a third marker can be positioned on the endless belt, differing from the first and second markers. This allows for the establishment of a defined zero point, where the time interval between two detection times of the third marker corresponds to one complete revolution of the endless belt. Advantageously, the first markers and / or the third marker are rotationally symmetrical.

[0012] The first markings are formed at least by at least two concentrically arranged similar geometric figures, in particular circles.

[0013] By comparing the first markings with the reference marking, a position of the first markings in relation to a transverse direction of the endless belt can be determined, whereby the position of the printer is changed according to a deviation of the first marking from a target position in the direction of the transverse direction of the endless belt.

[0014] The above-mentioned problem can also be solved according to the invention with an endless belt of the type mentioned at the outset by having first markings with a first, in particular constant, division on at least one surface viewed in a circumferential direction, wherein second markings with a second constant division are arranged between the first markings, wherein the second division is smaller than the first division.

[0015] According to an advantageous embodiment of the invention, the endless tape may have a third marking that defines a zero point and differs from the first and second markings.

[0016] To better understand the invention, it is explained in more detail with reference to the following figures.

[0017] They each show, in a highly simplified, schematic representation:

[0018] Fig. 1 shows a device for carrying out the method according to the invention.

[0019] It should be noted by way of introduction that in the differently described embodiments, identical parts are provided with the same reference numerals or component designations, whereby the disclosures contained in the entire description can be applied analogously to identical parts with the same reference numerals or component designations. Furthermore, the positional indications chosen in the description, such as top, bottom, side, etc., refer to the figure directly described and illustrated, and these positional indications are to be applied analogously to the new position if the position is changed. According to Fig. 1, a device 1 according to the invention for applying a mask-shaped coating to an endless belt 2 has a digital printer 3. The printer 3 serves to eject a coating material in droplet form onto an outer surface of the endless belt 2.

[0020] In the illustrated embodiment, the device 1 has a first optical sensor 4 in the form of a camera for detecting first markings 6a which are applied in a periodic sequence on or in the endless belt 2.

[0021] The sensor 4 is connected to a controller 8, for example, a suitably programmed microprocessor or signal processor. The controller 8 is configured to compare an image of the first markings 6a generated by the sensor 4 with an image of a reference marking 7a. The image of the reference marking 7a can be stored in a memory 8a connected to the controller 8. If a comparison of an image of the first marking 6a generated by the sensor 4 with the reference marking 7a reveals sufficient similarity, the first marking 6a is classified as corresponding to the reference marking 7a. To facilitate a comparison of the first markings 6a with the reference marking 7a, the first markings 6a can be rotationally symmetric. For example, the first markings 6a can be formed by at least two concentrically arranged identical geometric figures, in particular circles.

[0022] By comparing at least one of the first markers 6a with the reference marker 7a, at least one measure of the correspondence between the first marker 6a and the reference marker 7a is determined. If the determined measure exceeds a threshold, the first marker 6a is classified as corresponding to the reference marker 7a. For example, to determine the correspondence between the first markers 6a and the reference marker 7a, a cross-correlation function CCF (Eq. 1) can be used between a captured image Ii of one of the first markers 6a and the image I. o the reference marker 7a will be formed.

[0023] KKF(Ax, Ay) = ZZ I0(i,j).Ii(i+Ax, j+ Ay) (1)

[0024] Image The images II and I to be compared oThe images can be superimposed by shifting them in the x and y directions, and the maximum of the cross-correlation function can be found. Using a normalized cross-correlation function, a threshold can be easily defined, above which sufficient agreement between images Ii and I is indicated. oThis threshold value can be greater than zero and less than 1 in the case of a normalized cross-correlation function. From Equation 1, for example, a displacement of the endless belt 2 in the x-direction perpendicular to the y-direction of rotation of the endless belt 2 can be detected and corrected from the position of the maximum of the cross-correlation function. The x-coordinate of the maximum corresponds to the displacement of the endless belt 2 in the transverse direction. By comparing the first markings 6a with the reference marking 7a, the position of the first markings 6a with respect to a transverse direction of the endless belt 2 can thus be determined, and the position of the printer 3 can be changed according to a deviation of the first marking 6a from a target position in the direction of the transverse direction of the endless belt 2.

[0025] The position of printer 3 is changed according to the deviation of mark 6a from a target position in the transverse direction of the continuous belt 2. Printer 3 can be moved in the transverse direction of the continuous belt 1 by means of an actuator 9. The actuator 9, for example a spindle drive, can be connected to its own control unit 10, which is configured to adjust the actuator 9 according to the determined deviation of the position of mark 6a in the x-direction.

[0026] The direction of movement of the printer is indicated by a double arrow in Fig. 1. The printer 3 can be moved on a frame 11. For this purpose, the printer 3 can, for example, be arranged on a plate or table that is slidably mounted to profiles overlapping the endless belt 2 in the transverse direction. The endless belt 2 can run under the printer 3 or the frame 11 between two rollers 12 and 13, one of which can serve as a drive roller and the other as a deflection roller. The direction of movement of the endless belt 2 is indicated by an arrow.

[0027] A first clock signal TI is generated from the time interval between successive first markings 6a. Several second markings 6b are positioned between two first markings 6a. The first markings 6a differ from the second markings 6b in shape. As mentioned above, the first markings 6a are preferably rotationally symmetrical. The second markings 6b are, for example, designed as lines or as strip-shaped magnetized areas. The second markings 6b are detected by a second sensor 5. The detection of the first markings 6a and second markings 6b is independent of each other, with the first clock signal TI and the second clock signal T2 being determined by the time interval between the detection of two first markings 6a and the time interval between two second markings, respectively.Recording the first markings 6a is more time-consuming and slower than recording the second markings 6b.

[0028] The control unit 8 combines the first clock cycle TI and the second clock cycle T2 into a control clock cycle T3. The control clock cycle T3 can be configured to meet the condition that the number of second clock cycles T2 between any two first clock cycles TI corresponds to the number of second markers 6b between any two first markers 6a. That is, if the endless belt accelerates, the time interval between two second markers 6b decreases. In this case, the control clock cycle would be increased, with the increase occurring such that the predetermined number of second clock cycles 6b fulfills the aforementioned condition. This allows for very rapid responses to belt stretches 2 or changes in speed. Geometric or temporal changes in the distance between two markers 6a and 6b, caused by belt stretches or speed changes, can thus be accounted for with high accuracy.

[0029] Subsequently, a printing signal is generated depending on the control clock T3, whereby droplets of a coating material are ejected onto the outer surface of the continuous belt 2 by the printer 3 according to the signal. The printing signal can be generated according to a predefined scheme that takes into account the number of pulses of the control clock T3 since the last printing signal. Furthermore, the printing signal can be edge-triggered. A very precise incremental encoder is implemented using sensors 4 and 5 and markers 6a and 6b.

[0030] To generate a defined zero, one of the first markers 6a on the continuous tape 2 can be replaced by a third marker 6c, which differs from the first markers 6a and the second markers 6b. The third marker 6c can be designed similarly to the first markers. In Fig. 1, the third marker has a point in the center in addition to the two concentric circles. The third marker 6c differs in shape from each of the first markers 6a and each of the second markers 6b. The detection of the third marker 6c can also be carried out by comparison with a stored reference marker 7b, analogous to determining the correspondence between the markers 6a and the reference marker 7a.

[0031] The markings 6a, 6b, 6c can be applied to a surface of the continuous belt 2 by means of a force-fit connection. For example, the markings 6a, 6b, 6c can be created by applying paint to the continuous belt 2 or by bonding a carrier material of the markings 6a, 6b, 6c to the continuous belt 2. Alternatively, the markings 6a, 6b, 6c can also be produced by other methods, such as material removal, in particular using a laser, or by etching, embossing, or forming sections of the continuous belt 2. The markings 6b are particularly preferably created by magnetization. Furthermore, the markings 6a, 6b, 6c are each arranged at an edge of the continuous belt 2 parallel to a side edge and outside the printed area.

[0032] Finally, for the sake of clarity, it should be noted that, for a better understanding of the structure, some elements have been shown not to scale and / or enlarged and / or reduced in size.

[0033] Reference numeral list

[0034] device

[0035] Endless tape

[0036] Printer

[0037] sensor

[0038] a) First mark b) Second mark c) Third mark a) Reference mark b) Reference mark

[0039] Control a storage

[0040] Actuator 0 Control 1 Frame 2 Roller 3 Roller

Claims

P a t e n t a n s p r ü c h e 1. A method for applying a mask-shaped coating to an endless belt (2), wherein the coating is applied in droplet form to an outer surface of the endless belt (2) by means of a printer (3), characterized in that first markings (6a) and second markings are applied to the endless belt (2), wherein several of the second markings (6b) are placed between two first markings (6a), and the first markings (6a) differ in shape from the second markings (6b), wherein the first markings (6a) are detected by means of at least one optical sensor (4), in particular a camera, and compared with at least one reference marking (7a), wherein the second markings (6b) are detected by means of a second sensor (5).wherein a first clock (T2) is generated from a temporal sequence of successive first markings (6a) and a second clock (T2) is generated from a temporal sequence of successive second markings (6b), wherein the first clock (T1) and the second clock (T2) are combined to form a control clock (T3), wherein a pressure signal is generated depending on the control clock (T3), and wherein drops of a coating material are ejected onto the outer surface of the endless belt (2) by means of the printer (3) according to the pressure signal.

2. Method according to claim 1, characterized in that at least one measure of the conformity of the first mark (6a) and the reference mark (7a) is determined from the comparison between at least one of the first marks (6a) and the reference mark (7a), and if the determined measure is above a threshold value, the first mark (6a) is classified as conforming to the reference mark (7a).

3. Method according to claim 1 or 2, characterized in that the time interval between two successive first markings (6a) corresponding to the reference marking (7a) determines the first clock cycle (TI).

4. Method according to one of claims 1 to 3, characterized in that, to determine whether the first markings (6a) correspond to the reference marking (7a), a cross-correlation function is used between a sensor (4), in particular the camera, captured image of one of the first markings (6a) and a stored image of the reference marking (7a) is formed.

5. Method according to one of claims 1 to 4, characterized in that a third marking (6c) is arranged at a position on the endless belt (2), which differs in shape from the first markings (6a) and second markings (6b).

6. Method according to one of claims 1 to 5, characterized in that the first markings (6a) are rotationally symmetrical.

7. Method according to one of claims 1 to 6, characterized in that the first markings (6a) are formed by at least two concentrically arranged similar geometric figures, in particular circles.

8. Method according to one of claims 1 to 8, characterized in that a position of the first markings (6a) in relation to a transverse direction of the continuous belt (2) is determined from a comparison of the first markings (6a) with the reference marking (7a), wherein the position of the printer (3) is changed according to a deviation of the first marking (6a) from a target position in the direction of the transverse direction of the continuous belt (2).

9. Endless strip (2), characterized in that it has first markings (6a) with a first, in particular constant, division on at least one surface viewed in a circumferential direction, wherein second markings (6b) with a second constant division are arranged between the first markings (6a), wherein the second division is smaller than the first division.

10. Endless tape according to claim 9, characterized in that it has a third marking (6c) which defines a zero point and differs from the first markings (6a) and the second markings (6b).

Images