Method for calculating the thickness of a material strip when feeding the material strip into a processing area of ​​a machine tool

Abstract

The invention is a method for calculating the thickness of a material strip (5) when it is fed into a processing area of ​​a machine tool (1). The material strip (5) is clamped between two rotatable rollers (3, 4), their relative positions relative to one another in a clean original state with a "zero" roller spacing (reference relative positions) are detected, and their relative positions relative to one another in the intended feeding process (current relative positions) are measured. The difference between the current relative positions and the reference relative positions, which results in the thickness of the material strip (5) when the rollers are in a clean original state, is corrected according to the invention in the event of a change in the diameter of the rollers (3, 4) due to contamination. For this purpose, in the original state of the clean rollers (3, 4) in the reference feeding operation, the assigned reference rotation angle of the roller (3) is detected for at least one roller (3) at the detected reference feed length, so that the original feed length / rotation angle ratio for this roller (3) is known and its original diameter is also clearly defined. Any deviations from these parameters during the intended feeding operation are converted into changes in the diameter of at least one of the rollers (3) and taken into account when calculating the thickness of the material strip (5).The present invention solves the current problems in strip thickness using rollers.

Description

[Technical field]

[0001] The invention relates to a method for calculating the thickness of a material strip when the material strip is fed into a processing area of ​​a machine tool, a roller arrangement used to perform the method, a feed device including the roller arrangement, and a machine tool for performing the method equipped with a roller arrangement or a feed device according to the preamble of the dependent claims. [Background technology]

[0002] In the industrial stamping of products from strips of material, there are always applications where the precise thickness of the strip is important.

[0003] For example, when stamping coins, the thickness of the strip is used to estimate the weight of the coin - if the thickness is not correct, the coin will not be accepted.

[0004] In a motorized sheet punching process, sheets are assembled into packages. Small errors in strip thickness cause large variations in package height. To control this variation, the thickness is measured. Just before reaching the bundle height, it is decided based on the measurement whether the bundle height needs to be corrected. The choice is either to leave the package as it is, to add one sheet, or to subtract one sheet at the end.

[0005] A measurement of the strip thickness is always made before it is sent. Various systems and vendors exist for the measurement.

[0006] High-precision measuring systems are equipped with either a diamond tip or a laser head. If the strip is wide, the measurement is not just taken at one point, but the measuring head moves back and forth across the entire strip. The average value is then taken to calculate the thickness of the strip. If coated strips are used, diamond tips cannot be used as they would destroy the coating.

[0007] A less accurate system has rollers; a lower fixed roller and an upper movable roller connected to a ram. The upper roller is pressed against the strip with a defined force. The strip is then clamped between the two rollers. The rollers are moved relative to one another for calibration (zero). The sheet metal strip is then inserted and the distance the upper roll is lifted is calculated as the strip thickness. During a production run, the variation in strip thickness needs to be accounted for in order to accurately measure the package height.

[0008] In principle, measurements with rollers are extremely accurate. Unfortunately, however, rollers are subject to external factors such as dirt and the coating of the strip. When punching electrosheets, coated strips are often used. The coating is an insulating layer between the individual sheets. The better the insulation between the sheets, the better the magnetic field of the motor that is formed from them. It is therefore important in this case that the coating also remains intact. When measuring with rollers, it is normal for small particles of the strip coating to accumulate on the roller. The accumulation on the roller increases in thickness over time. As the accumulation of particles on the roller increases, the accuracy of the measurement decreases. To achieve a permanently accurate measurement, the rollers would need to be cleaned quite frequently, which is not done in practice. Summary of the Invention [Problem to be solved by the invention]

[0009] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to provide a technical solution which does not have the above-mentioned disadvantages of the prior art or which at least overcomes some of them.

[0010] This object is achieved according to the invention by the subject matter of the independent claims.

[0011] In accordance with these, a first embodiment of the invention is a method for calculating a thickness of a strip of material as it is fed into a processing area of ​​a machine tool, preferably an automatic punching machine. [Means for solving the problem]

[0012] To carry out the method, the roller arrangement is provided with two rollers which are parallel and can be moved towards or away from each other perpendicular to their axis of rotation, which rollers are designated according to the claims as first and second rollers. Advantageously, the rollers are movable relative to each other perpendicular to their axis of rotation and thus can be moved towards or away from each other. The term "roller" according to the claims also includes rollers of rotationally symmetric shape and other roller elements with a width greater or less than the width of the material strip to be fed.

[0013] Before the material strip is fed as intended into the processing area of ​​the machine tool and the thickness of the material strip is calculated, various reference parameters are calculated.

[0014] On the one hand, parallel rollers are positioned relative to each other such that the two rollers are in contact (distance "zero"), in which the relative position of the rollers relative to each other is defined as a reference relative position, which can be done, for example, in a roller arrangement including a fixed roller and a movable roller, by calculating the absolute position of the movable roller in the fixed system.

[0015] On the other hand, the two parallel rollers are spaced apart and arranged in such a way that a material strip is clamped between them, either the material strip that is to be fed into the processing area of ​​the machine tool as intended or the material strip that is to be used only for calculating the reference parameters.

[0016] The material strip clamped between the rollers advances a certain feed length while the rollers roll without slipping on the strip surface. The rollers rotate through a corresponding specific rotation angle, which includes a section of the circumference of the roller that corresponds to the feed length. The feed length may, but does not necessarily, correspond to a desired feed length for the intended feed of the material strip. This feed length is recorded as a reference feed length, and the corresponding rotation angle of the first roller is recorded as a first reference rotation angle. Alternatively or additionally, the ratio of the calculated feed length and the calculated rotation angle of the first roller can also be recorded as a first reference feed length / rotation angle ratio, which refers to the diameter of the roller at the reference state.

[0017] After the reference parameters have been obtained, if the material strip to be fed as intended into the processing area of ​​the machine tool has not yet been placed between the rollers for the calculation of the reference parameters, the material strip is placed between the rollers so that it runs perpendicular to the rotation axis of the rollers and the material strip is clamped between the rollers.

[0018] The material strip clamped between the rollers is fed into the processing area of ​​the machine tool by advancing it in a predetermined interval with the rollers rotating in intervals through a rotation angle corresponding to a feed length.

[0019] The relative positions of the rollers with respect to each other are detected every feed interval, which can be done, for example in a roller arrangement including one fixed roller and one movable roller, by measuring the absolute position of the movable roller in the fixed system.

[0020] Furthermore, for each feed interval the rotation angle of the first roller, the achieved feed length and / or the ratio of feed length to the rotation angle of the first roller are recorded.

[0021] If the feed length can always be kept exactly constant at a set value, for example when using a die-cutting machine with a pilot pin which is inserted into a pilot opening in the material strip at the end of the feed movement, then it is not necessary to calculate the current feed length for each feed interval, but instead the known set feed length can be used.

[0022] Next, for each feed interval, the currently detected feed length is compared to a reference feed length (unless a known, accurately maintained set feed length is used as described above), the currently recorded rotation angle of the first roller is compared to a first reference rotation angle, and / or the ratio of the currently detected feed length to the rotation angle of the first roller is compared to a first reference feed length / rotation angle ratio.

[0023] The thickness of the material strip is then calculated from the difference between the reference relative position and the currently calculated relative position of the rollers to each other, which corresponds to the distance between the two rollers if the diameter of the rollers is the same as the diameter when the reference relative position is detected.

[0024] If the currently detected feed length deviates from the reference feed length, the currently detected rotation angle of the first roller deviates from the first reference rotation angle and / or the ratio of the currently detected feed length and rotation angle of the first roller deviates from the first reference feed length / rotation angle ratio, the calculated feed length deviation, the calculated rotation angle deviation and / or the calculated feed length / rotation angle ratio deviation are converted into a possible deviation of the first roller diameter from the diameter of the first roller at the time of detection of the reference relative position according to the relationship between the roller diameter, the rotation angle and the feed length and are taken into account in calculating the thickness of the material strip.

[0025] This can be done, for example, by correcting the currently calculated relative positions of the rollers to take this diameter deviation into account when calculating the thickness of the material strip, or by correcting the thickness of the material strip calculated from the currently calculated relative positions of the rollers to take this diameter deviation into account.

[0026] The diameter of the first roller when the reference relative position is detected is obtained from the relationship between the roller diameter and the feed length, from the reference feed length and the first reference rotation angle, or from the ratio of the first reference feed length / rotation angle.

[0027] In other words, the invention relates to a method for calculating the thickness of a material strip when it is fed into the processing area of ​​a machine tool, in which the material strip is clamped between two rotatable rollers, the relative positions of the rollers relative to one another being detected in the original state with clean rollers and with a roller state of "zero" (reference relative position) and the relative positions of the rollers relative to one another being detected in the intended feed movement at each feed interval (current relative position). The difference between the current relative position and the reference relative position, which results in the thickness of the material strip when the rollers are in the original clean state, is corrected according to the invention in the event of a change in the diameter of the rollers due to contamination or the like. For this purpose, in the original state of the clean rollers, at the detected reference feed length, additionally for at least one roller, a reference rotation angle of the roller involved in the reference feed movement is detected in advance, so that the original feed length / rotation angle ratio for this roller is known and thus also its original diameter is clearly defined. If deviations from these parameters occur during the intended feed movement, they are converted into a change in the diameter of at least one roller and are taken into account when calculating the thickness of the material strip.

[0028] The invention makes it possible to solve the problems mentioned at the beginning for measuring strip thickness using rollers.

[0029] Preferably, any variation in the diameter of the second roller is taken into account when calculating the thickness of the material strip.

[0030] In a first preferred variant, this is done in the same way as for the first roller. When calculating the reference parameters, a second reference rotation angle and / or a second reference feed length / rotation angle ratio for the second roller are also recorded.

[0031] Then, for each feed interval, the rotation angle of the second roller is further compared with a second reference rotation angle and / or the feed length / rotation angle ratio of the second roller is compared with a second reference feed length / rotation angle ratio. If the currently detected rotation angle of the second roller deviates from the second reference rotation angle and / or the currently detected feed length / rotation angle ratio of the second roller deviates from the second reference feed length / rotation angle ratio, the calculated deviation of the rotation angle of the second roller and / or the calculated feed length / rotation angle ratio is converted into a possible deviation of the diameter of the second roller from the diameter of the second roller at the detection of the reference relative position due to the relationship between the diameter of the roller, the rotation angle and the feed length and is taken into account when calculating the thickness of the material strip.

[0032] This can be done, for example, by correcting the currently calculated relative positions of the rollers to calculate the thickness of the material strip taking into account this diameter deviation, or by correcting the thickness of the material strip calculated from the currently calculated relative positions of the rollers to take into account this diameter deviation.

[0033] The diameter of the second roller when the reference relative position is detected is calculated by the relationship between the diameter of the roller, the feed length from the reference feed length and the second reference rotation angle or is calculated from the ratio of the second reference feed length / rotation angle. In this way, a particularly accurate measurement of the strip thickness can be achieved.

[0034] In a second preferred variant, the diameter of the second roller is assumed to vary in the same way as the diameter of the first roller during the operating time.

[0035] If it is determined that the currently detected feed length deviates from the reference feed length, that the currently detected rotation angle of the first roller deviates from the first reference rotation angle and / or that the currently detected feed length / rotation angle ratio of the first roller deviates from the first reference feed length / rotation angle ratio, then the calculated feed length deviation, the calculated rotation angle deviation and / or the calculated feed length / rotation angle ratio deviation are recalculated according to the relationship between the roller diameters, the rotation angle and the feed length to a possible deviation in diameter of the first roller from the diameter of the first roller when the relative position is detected, and the diameter of the second roller is assumed to be the same as the deviation from the diameter of the second roller when the reference relative position is detected, and when calculating the thickness of the material strip not only the calculated deviation in diameter of the first roller is taken into account but also the assumed deviation in diameter of the second roller.

[0036] This can be done, for example, by correcting the currently calculated relative positions of the rollers to calculate the thickness of the material strip taking these diameter deviations into account, or by correcting the thickness of the material strip calculated from the currently calculated relative positions of the rollers to take these diameter deviations into account.

[0037] In this way, a relatively accurate strip thickness measurement can be achieved with less technical effort than in the first variant.

[0038] In a preferred embodiment of the method, the axis of rotation of one roller, preferably the claimed second roller, is stationary (fixed) and the axis of rotation of the other roller is movable or pivotable (movable) perpendicular to the axis of rotation and substantially perpendicular to the direction of movement of the material strip, which results in a relatively simple device used to perform the method.

[0039] In a further preferred embodiment of the method, at least one of the rollers is driven and both rollers cooperate to advance the material strip at regular intervals, so that the roller on which the measurement of the strip thickness is carried out is at the same time the feed roller of the strip feed device, in this way the required technical equipment can be kept as low as possible and a compact solution is made possible.

[0040] In yet another preferred embodiment of the method, the position of the outer surface of at least one roller facing away from the material strip is measured in order to detect the relative positions of the rollers with respect to each other and advantageously of at least the first roller as claimed in the claims, this outer surface being usually easily accessible so that a change in the diameter of the roller due to the deposit can be detected 1:1 as a change in the relative position of this outer surface of the roller.

[0041] In another preferred embodiment of the method, the position of a body connected to the bearing of at least one of the rollers, preferably the body connected to the bearing of the first roller, is measured in order to detect the relative positions of the rollers with respect to each other. The positions of such components can be calculated very reliably, so that a change in the radius of the roller due to deposits can be detected 1:1 as a change in the position of these components. The change in the diameter of the roller due to deposits is therefore twice as large as the change in the position of these components.

[0042] In the two aforementioned embodiments, it is advantageous to use one or more non-contact distance measuring sensors to measure the position of the outer surface of each roller facing away from the material strip or the position of the body connected to the bearing of each roller, preferably an eddy current sensor, a capacitive sensor or a laser measuring device, in particular a confocal laser measuring system. Such sensors are available at low cost and allow highly accurate position measurements.

[0043] In the two above mentioned embodiments, it is also advantageous that the position of the outer surface of each roller facing away from the material strip or the position of the body connected to the bearing of each roller is calculated at a number of points, preferably in the region of both ends of each roller, which makes it possible to calculate the position particularly accurately.

[0044] In yet another preferred embodiment of the method according to the invention, the material strip is provided with a pilot opening, the position of which is calculated each time in order to determine the feed length of the material strip, preferably by means of a line sensor, in this way making it possible to calculate the feed length with high precision.

[0045] It is further preferred that the method is used in a punch press, where the strip of material, the thickness of which is calculated, is fed to a machine for producing a stack of sheets, and the calculated thickness of the strip is used to determine the height of the stack. The advantages of the invention become particularly evident in such an application of the process.

[0046] A second embodiment of the invention is a roller arrangement for use in carrying out the method of the first embodiment of the invention.

[0047] The roller arrangement comprises at least a pair of rollers between which the material strip can be clamped, and a device for detecting the relative position of the rollers with respect to each other and the rotation angle of at least one of the rollers. The term "roller" according to the claims also includes rollers of rotationally symmetric shape and other roller elements with a width greater or less than the width of the material strip to be fed.

[0048] The implementation of the method of the present invention is greatly simplified with such a roller arrangement.

[0049] In a preferred embodiment, the roller arrangement comprises at least a pair of rollers between which the material strip can be clamped and which can be rotated to advance the material strip at regular intervals. These are therefore so-called feed rollers. Furthermore, the roller arrangement comprises a device capable of detecting the relative position of the rollers with respect to one another and the rotation angle of at least one roller at each feed interval. With such a roller arrangement, carrying out the process according to the invention is significantly simplified, in particular in a stamping press.

[0050] Advantageously, the device for detecting the relative position of the rollers with respect to one another comprises: It is designed to measure the position of the outer surface of at least one of the feed rollers facing away from the material strip, or to measure the position of a body connected to a bearing of at least one of the rollers, which allows a relatively simple and reliable quantitative measurement of the change in diameter or radius of the roller due to deposits.

[0051] It is also preferred that the device for measuring the position of the outer surface of each roller facing away from the material strip and / or the position of the body connected to the bearing of each roller comprises one or more non-contact distance measuring sensors, in particular eddy current sensors, capacitive sensors or laser measuring devices, in particular confocal laser measuring systems, which are available at low cost and allow for highly accurate position measurements.

[0052] Preferably, the device for detecting the relative position of the rollers with respect to one another is designed so that the position of the outer surface of each roller facing away from the material strip and / or the position of the body connected to the bearing of each roller can be measured at several points, in particular in the region of both ends of each roller, which makes it possible to perform said position measurements particularly precisely.

[0053] A third embodiment of the present invention is a feeder including the roller arrangement of the second embodiment of the present invention.

[0054] A fourth embodiment of the present invention is a machine tool performing the method of the first embodiment of the present invention and including the roller arrangement of the second embodiment of the present invention or the feed apparatus of the third embodiment of the present invention.

[0055] The machine tool is preferably a stamping press equipped with a die for producing stacks of sheet metal.

[0056] The advantages of the present invention are particularly evident in such machine tools.

[0057] Further preferred embodiments of the invention are evident from the dependent claims and from the following description with reference to the drawings. [Brief description of the drawings]

[0058] [Figure 1] FIG. 1 is a front view of a stamping press for processing a strip of material. [Diagram 2] FIG. 1 is a longitudinal section through a roller arrangement for measuring strip thickness according to the prior art; [Diagram 3] 1 is a schematic diagram illustrating a preferred embodiment of the method of the present invention; [Figure 4] FIG. 2 is a side view of a first roller configuration of the present invention. [Diagram 5] FIG. 5 is a vertical cross-sectional view taken along line AA in FIG. 4. [Figure 6] FIG. 11 is a side view of a second roller configuration of the present invention. [Figure 7] FIG. 7 is a vertical cross-sectional view taken along line BB in FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] FIG. 1 is a front view of a stamping press that processes strips of material into stacks of electrosheets.

[0060] As can be seen, the punch press 1 has at its infeed side a feed device 2 with a roller arrangement including an upper feed roller 3 and a lower feed roller 4, by means of which a material strip (not shown) is fed in a strip running surface S into a processing area of ​​the punch press 1.

[0061] FIG. 2 shows a longitudinal section through the roller arrangement of the feeder, in which the thickness of the strip is measured according to the prior art technique mentioned at the beginning.

[0062] In the situation shown here, the material strip 5 is placed between the lower fixed roller 4 and the upper movable roller 3 of the feeder, whereby the upper roller 3 is pressed with a defined force onto the strip 5 so that the strip 5 is clamped between the two rollers 3, 4. The distance measuring sensors 6a, 6b are used to measure the position of the bearing journals 7a, 7b of the movable upper roller 3, i.e. to calibrate without the material strip 5 and the rollers 3, 4 in contact with each other and then with the material strip 5 placed between the rollers 3, 4, as shown in FIG. 2 hereof. The positions measured with the rollers 3, 4 in contact with each other thus embody the relative positions of the rollers 3, 4 with respect to each other in a state of "zero" strip thickness, and the positions measured with the material strip placed between the rollers 3, 4 embody the relative positions of the rollers 3, 4 with respect to each other in a state representing the current strip thickness. The difference between the measured positions, or the relative positions of the rollers 3, 4 with respect to one another, is measured as the thickness of the strip, which presents the problems mentioned at the beginning if the diameter of the rollers changes due to contamination.

[0063] FIG. 3 is a schematic diagram illustrating a preferred embodiment of the method according to the invention for calculating the thickness of a material strip 5 as said material strip 5 is fed into the processing area of ​​a machine tool.

[0064] To carry out said method, a roller arrangement is provided with two rollers 3, 4 which are parallel and can be moved towards and away from each other perpendicular to their rotation axes. The rotation axes of the rollers 3, 4 are Running horizontally, the rollers are arranged vertically one above the other, resulting in an upper roller 3 and a lower roller 4. The rollers 3, 4 have equal roller diameters.

[0065] Before the material strip is deliberately fed into the processing area of ​​the machine tool, shown in FIG. 3, and the thickness of the strip is measured, various reference parameters are measured.

[0066] First, the rollers 3, 4 are positioned relative to one another such that their outer surfaces 11a, 11b are in contact. In this state, the relative positions of the rollers 3, 4 relative to one another are calculated as a reference relative position. For this purpose, a non-contact distance measuring sensor 6 in the form of a laser measuring device is provided, with which the position of the outer surface 11a of the upper roller 3, facing away from the material strip 5, is calculated by measuring the distance between the sensor 6 and the outer surface 11a of the upper roller 3 along a straight line G running through the rotation axes of both rollers 3, 4. In this case, the rotation axis of the lower roller 4 and the sensor 6 are stationary (fixed), so that when this reference measurement is performed in the initial state when the rollers 3, 4 are clean, the distance to the outer surface 11a of the upper roller 3 measured with the sensor 6 represents the relative position of the rollers 3, 4 relative to one another at "zero" roller spacing.

[0067] On the other hand, the rollers 3, 4 are spaced apart from one another and a material strip 5 is arranged between them, such that the material strip 5 is clamped between the rollers 3, 4. In this case, this material strip 5 is the material strip 5 that is intended to be fed into the processing area of ​​the machine tool, although it is also possible to use a different material strip for calculating the reference parameters.

[0068] The material strip 5 clamped between the rollers 3, 4 advances a certain feed length L as the rollers 3, 4 roll without slipping on the surfaces 12a, 12b of the strip. The rollers 3, 4 rotate through a corresponding certain rotation angle Ro, Ru, which includes a section of the circumference of the rollers corresponding to the feed length L. This reference feed length then corresponds to the desired feed length L when the material strip is fed as intended. However, a different feed length can also be selected to calculate the reference parameters. This feed length L is recorded as the reference feed length and the corresponding rotation angle Ro of the upper roller 3 is recorded as the reference rotation angle.

[0069] After the reference relative positions of the rollers 3, 4 to one another at "zero" roller spacing as well as the reference feed length and the associated reference rotation angle have been calculated in the clean initial state of the rollers 3, 4, the material strip 5 clamped between the rollers 3, 4 is fed as intended into the processing area of ​​the machine tool by advancing it at intervals the desired feed length L. This situation is depicted in FIG.

[0070] When the material strip 5 advances at intervals, the rollers 3, 4 roll without slipping on the strip surface and accordingly rotate at intervals by rotation angles Ru, Ro corresponding to the feed length L when the material strip 5 advances at intervals.

[0071] During the feed pause between two feed intervals, the material strip 5 is punched out by a punching machine. Each time, the material strip 5 is provided with a pilot opening 9 by means of a fixed punching machine 8, which opening is used to calculate the current feed length L in the next feed interval. For this purpose, a line sensor 10 is provided, by means of which the position of the last pilot opening 9 is measured each time to determine the feed length L of the material strip 5. The feed length L corresponds to the distance between the known position of the pilot opening 9 when it is opened by the punching machine 8 and the position of the pilot opening 9 measured by the line sensor 10 after the material strip 5 has advanced.

[0072] Also, during the intended feed movement, the relative position of the rollers 3, 4 with respect to each other is detected at each feed interval using a sensor 12, as well as the rotation angle Ro of the upper roller 3. This is done via an angle encoder (not shown) on the shaft of the upper roller 3.

[0073] Thereafter, for each feed interval, the currently detected feed length L is compared with the reference feed length, and the currently detected rotation angle Ro of the upper roller 3 is compared with the reference rotation angle.

[0074] The thickness of the material strip is calculated from the difference between the reference relative position and the relative position of the rollers 3, 4 relative to each other calculated by the sensor 6 at the current time, or from the difference between the distance between the sensor 6 and the surface 11a of the upper roller 3 in the reference measurement and the distance between the sensor 6 and the surface 11a of the upper roller 3 in the current measurement, this difference corresponding to the distance between the two rollers 3, 4 and therefore the thickness of the strip if the current diameter of the rollers 3, 4 were assumed to be the same as their original, uncontaminated diameter when the reference parameters were recorded.

[0075] If the currently detected feed length L deviates from the reference feed length and / or if the currently detected rotation angle Ro of the upper roller 3 deviates from the reference rotation angle, it is assumed that the diameters of both rollers 3, 4 have changed in the same way for both rollers 3, 4 since the reference relative position was calculated.

[0076] In this case, the deviation in the calculated feed length and / or the deviation in the calculated rotation angle is converted into a possible deviation in the diameter of the upper roller 3 from the diameter when the reference relative position is detected, in particular an increase in diameter, depending on the relationship between the roller diameter, the rotation angle and the feed length, and the theoretical strip thickness calculated from the difference between the reference relative position and the relative position of the rollers 3, 4 currently calculated by the sensor 12 is corrected by the diameter deviation.

[0077] The diameter of the upper roller 3 when the reference relative position is detected is calculated by the relationship between the roller diameter, the feed length from the reference feed length, and the reference rotation angle. The diameter of the lower roller 4 was the same as the diameter of the upper roller 3 when the reference relative position was detected.

[0078] Furthermore, the lower roller 4 is assumed to have undergone the same diametric deviation, in particular an increase in diameter, and the theoretical strip thickness calculated from the difference between the reference relative position and the relative position of the rollers 3, 4 currently measured by the sensor 6 is corrected by half the diametric deviation of the upper roller 3, taking into account this assumed diametric deviation of the lower roller 4. This is because the lower fixed roller 4 is arranged below the material strip 5, and an increase in diameter of this roller 4 only affects half the position change of the upper roller 3.

[0079] The theoretical strip thickness calculated from the difference between the reference relative position and the relative position of the rollers 3, 4 currently calculated by the sensor 12 is therefore corrected by 1.5 times the deviation in diameter of the upper roller 3. This is explained by the following example and the drawings.

[0080] When calculating the reference parameters, 32 mm, which is the distance between the outer surface 11a of the upper roller 3 and the distance measuring sensor 6, was calculated as the reference relative position of the rollers 3, 4 with respect to each other (roller distance "zero"). Furthermore, the reference rotation angle of the upper roller 3 was set to 90 degrees, and the reference feed length was calculated to be 31.42 mm. From these values, and due to the relationship between the roller diameter, rotation angle, and feed length, it can be easily calculated that the diameter of the upper roller 3 was 40 mm at the time when the reference relative position was calculated.

[0081] Taking into account the feed interval during the intended feed operation, the current relative positions of the rollers 3 and 4 were calculated when the rotation angle Ro of the upper roller was 90 degrees, the feed length L was 31.49 mm, and the distance between the outer surface 11a of the upper roller 3 and the distance measuring sensor 6 was 32 mm.

[0082] Therefore, the currently calculated feed length L is 0.07 mm longer than the reference feed length, and the difference between the reference relative position and the currently calculated relative position of the rollers 3, 4 is 0.415 mm. This difference corresponds to the thickness of the strip when the diameters of the two rollers 3, 4 are the same at present as when the reference relative position was calculated (theoretical strip thickness).

[0083] However, due to the relationship between the roller diameter, rotation angle, and feed length, the actual roller diameter of the upper roller 3 is 40.1 mm, i.e., the diameter is 0.1 mm larger than in the reference state. Furthermore, it is assumed that the diameter of the lower roller 4 also changes by the same amount, i.e., it also becomes 0.1 mm larger.

[0084] In order to take these diameter deviations into account when calculating the thickness of the material strip 5, the diameter of the upper roller 3 is increased by 0.1 mm and for the lower roller half the expected diameter increase, i.e. 0.05 mm, is now subtracted from the theoretical strip thickness of 0.415 mm, resulting in an actual strip thickness corrected accordingly of 0.4 mm.

[0085] 4 and 5 show a roller arrangement of the invention for use in carrying out a further preferred embodiment of the method of the invention in a side view (FIG. 4) and a longitudinal cross-sectional view taken along line AA of FIG. 4 (FIG. 5).

[0086] The roller arrangement comprises two parallel rollers 3, 4, an upper roller 3 and a lower roller 4, between which a strip of material 5 is clamped. The rollers 3, 4 are identical, the lower roller 4 is mounted on a fixed structure 13 and the upper roller 3 is mounted on a rocker 14 so that it can pivot relative to the lower roller 4. The strip of material 5 is biased towards the lower roller 4 by gravity and the force of two springs 15, and is therefore clamped between the rollers 3, 4 with a constant compression force.

[0087] Rotation angle encoders 16a, 16b for monitoring the rotation angles of the rollers 3, 4 are arranged on the ends of the bearing shafts of the rollers 3, 4 in order to measure the rotation angles of the rollers 3, 4.

[0088] On the upper side of the rocker 14, directly above the axis of rotation of the upper roller 3, in the region of the end of the upper roller 3, two fixed distance measuring sensors 6a, 6b are arranged at a distance from the upper side 17 of the rocker 14, so that the distance between each sensor 6a, 6b and the upper side 17 of the rocker 14 can be measured along a straight line G passing through the axes of rotation of the rollers 3, 4 in order to measure the relative positions of the rollers 3, 4 with respect to one another.

[0089] Except for the offsets explained below, the calculation of the thickness of the material strip 5 with this roller arrangement is carried out in a similar manner to that explained with reference to FIG.

[0090] Since in this case both rollers 3, 4 have rotation angle encoders 16a, 16b, the diameter deviation of the lower roller 4 occurs here in the same way as for the upper roller 3. That is to say that separate reference rotation angles are recorded for both rollers 3, 4, and then separate current rotation angles are recorded for each feed interval, with the aid of which the diameter deviations of the rollers 3, 4 are calculated separately.

[0091] In order to detect the relative position of the rollers to each other using distance measuring sensors 6a, 6, not as in FIG. 3, the position of the outer surface 11a of the upper roller 3 facing away from the material strip 5 is measured, but the position of the upper side of the rocker 14, i.e. the position of the body connected to the bearing of the upper roller 3, the theoretical strip thickness calculated from the difference between the reference relative position of the upper roller 3 and the relative positions of the rollers 3, 4 measured at the moment by the sensors 6a, 6b, is corrected by half the calculated deviation in the diameter of the upper roller 3, since in this situation an increase in the diameter of this roller 3 only half influences the change in the position of the top of the rocker 14. The distances measured by the sensors 6a, 6b are averaged.

[0092] As already explained with respect to figure 3, to correct the theoretical strip thickness, only half the diametric deviation of the fixed lower roller 4 is used. In this case, it is therefore corrected with half the diametric deviation of the upper roller 3 and half the diametric deviation of the lower roller 4.

[0093] 6 and 7 show a further roller arrangement of the invention for use in carrying out another preferred embodiment of the method of the invention, in a side view (FIG. 6) and a longitudinal cross-sectional view taken along line BB in FIG. 6 (FIG. 7).

[0094] This roller arrangement differs essentially from that shown in figures 4 and 5 in that the upper roller 3 is not pivotally mounted on a rocker but is vertically movable along a linear guide. The distance gauges 6a, 6b are not designed here to be non-contact but measure directly in the bearing housings 14a, 14b of the bearings of the upper roller 3.

[0095] In other respects, the technical concept here is similar to that shown in FIGS. 4 and 5, and elements of the same function are given the same reference numerals as in FIGS.

[0096] The method of the invention carried out with this roller arrangement corresponds to the process described with reference to FIGS.

[0097] Although preferred embodiments of the present invention have been described in this application, it should be expressly noted that the present invention is not limited thereto and may be embodied in other ways within the scope of the claims.

Claims

1. A method for calculating the thickness of a material strip (5) when said strip is fed into a processing area of ​​a machine tool (1), in particular a punch press (1), comprising: a) providing a roller arrangement comprising two rotatable rollers (3, 4), namely a first roller (3) and a second roller (4), the rotation axes (Z) of the two rollers (3, 4) being parallel and the rollers (3, 4) being mobile, in particular movable relative to each other perpendicularly to the rotation axis (Z); b) positioning the two rollers (3, 4) relative to each other so that they are in contact with each other, and detecting in this state the relative positions of the rollers (3, 4) relative to each other as a reference relative position; c) placing the material strip (5) between the rollers (3, 4) such that the longitudinal direction of the material strip (5) runs perpendicular to the axis of rotation (Z) of the rollers (3, 4) and the material strip (5) is clamped between the rollers (3, 4); d) advancing the material strip (5) clamped between the rollers (3, 4) by the rollers (3, 4) rolling without slipping on the surface (12a, 12b) of the strip over a specific feed length (L), the rollers (3, 4) rotating through a specific rotation angle corresponding to the specific feed length (L); e) detecting the feed length (L) calculated as a reference feed length and the rotation angle of the first roller (3) calculated as a first reference rotation angle, and / or detecting a ratio between the calculated feed length (L) and the calculated rotation angle of the first roller (3) as a first reference feed length / rotation angle ratio; after that, f) if not already carried out at time c), preparing and positioning the material strip (5) between the rollers (3, 4) for its intended delivery to the processing area of ​​the machine tool (1) in such a way that the longitudinal direction of the material strip (5) runs perpendicular to the axis of rotation (Z) of the rollers (3, 4) and the material strip (5) is clamped between the rollers (3, 4); g) advancing the material strip (5) clamped between the rollers (3, 4) at regular intervals by a feed length (L) each time, the rollers (3, 4) rotating at regular intervals by a rotation angle (Ro, Ru); h) detecting at each feed interval the relative position of the rollers (3, 4) relative to one another and the rotation angle (Ro) and the feed length (L) of the first roller (3) or detecting at each feed interval the relative position of the rollers (3, 4) relative to one another and the rotation angle (Ro) and the feed length (L) of the first roller (3) and the ratio of the rotation angle (Ro) of the first roller (3); i) for each feed interval, comparing the currently detected feed length (L) with the reference feed length, comparing the currently detected rotation angle (Ro) of the first roller (3) with the first reference rotation angle and / or comparing the currently detected ratio of the feed length (L) to the rotation angle (Ro) of the first roller (3) with the first reference feed length / rotation angle ratio; j) calculating, for each feed interval, the thickness (5) of the material strip from the difference between the reference relative position and the currently calculated relative position of the rollers (3, 4) relative to one another; In a method comprising: if the currently detected feed length (L) deviates from the reference feed length, the currently detected rotation angle (Ro) of the first roller (3) deviates from the first reference rotation angle and / or the ratio of the currently detected feed length (L) to the rotation angle (Ro) of the first roller (3) deviates from the first reference feed length / rotation angle ratio, the calculated feed length deviation, the calculated rotation angle deviation and / or the calculated feed length / rotation angle deviation are converted from their diameter at the time of detection of the reference relative position into deviations in the diameter of the first roller (3) according to the relationship between the diameter of the roller, the rotation angle and the feed length and are taken into account in the calculation of the thickness of the material strip (5); method.

2. In step e), a second reference rotation angle and / or a second reference feed length / rotation angle ratio is determined for the second roller (4) in the same way as for the first roller (3), at each feed interval, the rotation angle (Ru) of the second roller (4) is further compared with the second reference rotation angle and / or the ratio of the feed length (L) and the rotation angle (Ru) of the second roller (4) is compared with a second reference feed length / rotation angle ratio, and if the currently detected rotation angle (Ru) of the second roller (4) deviates from the second reference rotation angle and / or the currently detected ratio of the feed length (L) and the rotation angle (Ru) of the second roller (4) deviates from the second reference feed length / rotation angle ratio, the calculated deviation of the rotation angle of the second roller (4) and / or the calculated ratio of the feed length / rotation angle is converted from its diameter at the time of detection of the reference relative position into a deviation of the diameter of the second roller (4) according to the relationship between the diameter of the roller, the rotation angle and the feed length, and is taken into account when calculating the thickness of the material strip (5). The method of claim 1.

3. if the currently detected feed length (L) deviates from the reference feed length, the currently detected rotation angle (Ro) of the first roller (3) deviates from the first reference rotation angle and / or the ratio of the currently detected feed length (L) to the rotation angle (Ro) of the first roller (3) deviates from the first reference feed length / rotation angle ratio, the calculated feed length deviation, the calculated rotation angle deviation and / or the calculated feed length / rotation angle ratio deviation are converted into a diameter deviation of the first roller (3) from its diameter at the time of detection of the reference relative position by a relationship between the roller diameter, the rotation angle and the feed length, and the roller diameter of the second roller (4) is assumed to have the same deviation from its diameter at the time of detection of the reference relative position, and the assumed deviation is taken into account when calculating the thickness of the material strip (5), The method of claim 1.

4. 4. The method according to claim 1, wherein the axis of rotation (Z) of one of the rollers (3, 4), in particular the second roller (4), is stationary and the axis of rotation (Z) of the other roller (3) is movable perpendicularly to the axis of rotation (Z) and perpendicularly to the advancing direction of the material strip (5).

5. Method according to any one of the preceding claims, wherein at least one of the rollers (3, 4) is driven, causing the two rollers (3, 4) to feed the material strip (5).

6. The method according to any one of claims 1 to 5, wherein the position of an outer surface (11a) of at least one of the rollers (3, 4) facing away from the material strip (5) is calculated in order to detect the relative positions of the rollers (3, 4) with respect to one another, in particular the relative position of the first roller (3).

7. 7. The method according to claim 1, wherein, in order to detect the relative positions of the rollers (3, 4) with respect to one another, the position of a body (14; 14a, 14b) connected to a bearing of at least one of the rollers (3, 4), in particular a body (14; 14a, 14b) connected to a bearing of the first roller (3) is calculated.

8. 8. The method according to claim 6 or 7, wherein one or more non-contact distance measuring sensors (6; 6a, 6b), in particular eddy current sensors, capacitive sensors or laser measuring devices, in particular confocal laser measuring systems, are used to measure the position of the outer surface (11a) of each roller (3) facing away from the material strip (5) and / or the position of the body (14; 14a, 14b) connected to a bearing of each roller (3).

9. 9. The method according to claim 6, wherein the measurement of the position of the outer surface (11a) of each roller (3) facing away from the material strip (5) and / or the position of the body (14; 14a, 14b) connected to the bearing of each roller (3) is performed at several points, in particular in the region of both ends of each roller (3).

10. 10. The method according to claim 1, wherein the material strip (5) is provided with a pilot opening (9), the position of which is measured each time, in particular via a line sensor (10), in order to determine the feed length (L) of the material strip (5).

11. The method according to any one of claims 1 to 10, wherein the material strip (5) with calculated thickness is fed to a punching press (1) with a machine for producing a stack of sheet metal, and the height of the stack is measured using the calculated thickness of the sheet metal.

12. A machine tool for carrying out a method according to any one of claims 1 to 11 and including a roller arrangement, the roller arrangement comprising at least one pair of rollers (3, 4) capable of clamping a material strip (5) between both rollers, the material strip being advanced at regular intervals by rotating the rollers (3, 4) at regular intervals, and including a device (6; 6a, 6b) for detecting, at each feed interval, the relative position of the rollers (3, 4) with respect to each other and the rotation angle (Ro, Ru) of at least one of the rollers (3, 4).

13. 13. The machine tool according to claim 12, wherein the device (6; 6a, 6b) for detecting the relative position of the rollers (3, 4) with respect to one another is designed to measure the position of the outer surface (11a) of at least one of the feed rollers (3, 4) facing away from the material strip (5).

14. 14. Machine tool according to claim 12 or 13, wherein the device (6; 6a, 6b) for detecting the relative position of the rollers (3, 4) with respect to one another is designed to measure the position of a body (14; 14a, 14b) connected to a bearing of at least one of the rollers (3).

15. 15. The machine tool according to claim 12, wherein the device (6; 6a, 6b) for detecting the relative position of the rollers (3, 4) with respect to one another and for measuring the position of an outer surface (11a) of each roller (3) facing away from the material strip (5) and / or the position of the body (14; 14a, 14b) connected to a bearing of each roller (3) comprises one or more non-contact distance measuring sensors (6; 6a, 6b), in particular an eddy current sensor, a capacitive sensor or a laser measuring device, in particular a confocal laser measuring system.

16. 16. The machine tool according to claim 12, wherein the device (6; 6a, 6b) for detecting the relative position of the rollers (3, 4) with respect to one another is designed to enable measurement of the position of the outer surface (11a) of each roller (3) facing away from the material strip (5) and / or the position of the body (14; 14a, 14b) connected to a bearing of each roller (3) at several points, in particular in the region of both ends of each roller (3).

17. The machine tool according to any one of claims 12 to 16, wherein the machine tool is a stamping press (1) including a machine for producing stacks of sheets.

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