Bending machine with automatic correction of the position of the sheet metal

Abstract

A rotary bending machine for rotary bending a bending section of an object comprises a control and a device for determining an actual distance of a bending point from a reference point of the rotary bending machine, wherein the control is configured to correct the control parameters for advancing the object based on a deviation between expected and actual distance of the bending point to the reference point.

Description

[0001] The invention relates to a bending machine for round bending, also called round rolling, of a sheet metal, in particular a bending machine according to the preamble of claim 1.

[0002] Bending machines with at least three rollers or cylinders for bending sheet metal or other bendable objects are known from the prior art. A sheet metal is mentioned below as a representative of other objects to be bent. A sheet metal can typically have a thickness of more than 3 mm and in particular more than 50 mm.

[0003] Typically, the sheet metal to be bent is fed into the bending machine from one side. The position of the rollers is adjusted for a bending process so that they exert a force on the sheet metal and bend it accordingly. At least one roller of such a bending machine is motor-driven, so that the driven roller feeds the sheet metal through the rollers of the bending machine. The sheet metal is continuously bent as it is conveyed through the appropriately adjusted rollers.

[0004] One challenge when bending a sheet metal is to precisely achieve the desired bending radius and to maintain the start and end points of the sheet metal section to be bent.

[0005] Bending machines with three or more rollers are known from the prior art, which have sensors for tracking or controlling parameters of the bending machine during a bending process. EP 477 752 describes a bending machine with sensors for determining the position of a respective roller so that the geometry of the rollers relative to one another can be determined and corrected. EP 1 644 140 describes a bending machine with sensors for determining the bending radius after a bending process so that the geometry of the rollers can be adjusted or corrected. WO2009 / 101649 describes a bending machine for round bending an elongated workpiece, which has sensors for determining a bending radius at a point on the workpiece that is close to the point on the workpiece currently to be bent.

[0006] Further bending machines are known from JP 2007 083 260 A and US 2017 / 333 968 A1.

[0007] To achieve a precise bend, in addition to maintaining the desired bending radius as accurately as possible, it is also necessary to maintain the length of the section of sheet metal to be bent, whereby the length of the section to be bent must be measured along the neutral fiber of the sheet metal.

[0008] The relative position of the rollers and the rotation of the driven roller are input into the bending machine's control system before the bending process. For bending machines with at least one motor-driven roller, the problem is how to feed the sheet metal precisely so that the actual length of the transported neutral axis of the sheet corresponds to the set length and the beginning and end of the section of sheet metal to be bent are reached as precisely as possible.

[0009] The conveying of the sheet metal through the bending machine is subject to errors, for example slippage between the driven roller and the sheet metal and the compression of the sheet metal on the inside of the radius due to bending, so that the length of the actually conveyed distance deviates from the set length of the conveyance in practice, even if the slippage and / or shortening on the inside of the radius of the sheet metal between the driven roller and the surface of the sheet metal as well as the geometric and material properties are taken into account when determining the control parameters to be entered.

[0010] This problem is solved by a bending machine according to claim 1 and a corresponding bending method.

[0011] The invention is described in more detail below with reference to an embodiment shown in the figures. Fig. 1 is a schematic representation of the rollers of a bending machine with four rollers and a sheet to be bent; Fig. 2 is a schematic representation of the position of the sheet in a starting position at the beginning of the bending process; Fig. 3 is a schematic representation of a position of the sheet for correcting the control parameters; Fig. 4 is a schematic representation of a position of the sheet with the first bending point resting on the top roller; Fig. 5 is a schematic representation of a position of the sheet for correcting the control parameters; Fig. 6 is a schematic representation of a position of the sheet with the bending process for a given bending section completed.

[0012] Fig. 1 shows schematically the rollers of a bending machine 1 with four rollers 3 - 6 for round rolling an originally planar sheet 2. The bending machine comprises an upper roller 3 and a lower roller 4 typically arranged vertically below it as well as a first side roller 5 and a second side roller 6. The holders of the rollers as well as drives and a control system are not shown.

[0013] In the embodiment described here, only the top roller 3 is motor-driven, with the direction of rotation of the top roller 3 being indicated by the arrow 3a. In alternative embodiments, more than one roller can be driven to convey the sheet 2 to be bent. The geometry of the rollers in relation to one another can be changed. The rollers can be arranged in such a way that, on the one hand, they exert a force on the sheet 2 to bend the sheet 2 and, on the other hand, the pressure force of the top roller 3 exerts a sufficiently large force on the sheet 2 so that, when the top roller 3 rotates, the sheet is conveyed in the transport direction 2a, in the figure shown, from right to left. The bottom roller 4 rotates in the direction of rotation 4a and the side rollers 5 and 6 each rotate accordingly.

[0014] The bending machine 1 further comprises a control system not shown in the figures, which controls, among other things, the geometric arrangement of the rollers relative to one another and the rotation of the driven roller.

[0015] In this embodiment, sheet metal 2 is to be bent using bending machine 1. The center of thickness 2b of sheet metal 2 is referred to here as the neutral fiber; also referred to in the literature as the zero line. When bending sheet metal 2 into a curve, the sheet material is compressed on the inside of the neutral fiber 2b and stretched on the outside of the neutral fiber 2b. The region of the neutral fiber 2b of a homogeneous sheet typically retains its original length, as it was before bending.

[0016] If a sheet metal is to be bent into a specific curve, the bending radius and the target rotation, among other things, are determined in the conventional way before the bending process begins. The target rotation is the distance of the sheet metal 2 along the neutral axis, which is to be conveyed by the motor-driven roller. It is known, for example, that the surface distance of the sheet metal 2 on the inside of the bend is reduced by bending into a smaller radius, since the sheet metal 2 is compressed there. The corresponding parameters of the bending machine for bending the sheet metal 2 into a round shape are entered into the control system of the bending machine accordingly. Based on the entered parameters, the machine determines, among other things, the rotation of the driven roller, which conveys the sheet metal through the rollers.

[0017] The sheet 2 can have a length and a width of several meters each and a thickness of several millimeters, in particular more than 3 millimeters and more than 50 millimeters.

[0018] In the embodiment described here, the originally planar sheet 2 is to be bent into a curve with a constant radius in the bending section between a first bending point x = 100 to the second bending point at x = 1000, wherein the sheet 2 is bent as it is conveyed through the rollers of the bending machine 1. A bending point is the start or end of a section of the sheet that is to be bent into the constant radius, wherein the bending point lies on the neutral axis. The section in the conveying direction 2a upstream of the first bending point at x1 = 100, i.e. the section x0 = 0 to x1 = 100, as well as the section downstream of the second bending point, here x2 = 1000 to x3 = 1100, are not bent in the embodiment described here.

[0019] In a further development of the machine, a further section to be bent can be added after the first bending section. Precise adherence to the start and end of the additional section to be bent is achieved by a similar procedure when conveying sheet metal 2.

[0020] In practice, it has been shown that the actual length of sheet fed by the driven roller deviates from the length set in the machine control system. This is caused by various effects, such as slippage between the driven roller and the sheet.

[0021] According to the present invention, the control of the bending machine is corrected during a bending operation so that the actual conveyed distance of the sheet has a small deviation between the length set in the machine parameters and the actual conveyed distance.

[0022] The bending machine 1 comprises a device, here an optical system, in particular with at least one camera 7, for determining the actual distance of a bending point from a reference point of the bending machine 1. The reference point of the bending machine is one that has a known distance from the roller, here the top roller 3, around which the bending is to take place. In one embodiment, the reference point can be the point on the top roller that rests on the sheet 2 and at which the top roller 3 thus applies the force to convey the sheet onto the sheet. The device is connected to the control system of the bending machine 1 and configured to detect a bending point or a marking that can be detected by the device 7. The camera 7 is connected to the control system of the bending machine. The control system is configured and configured to determine the distance of a bending point of the sheet 2 from a reference point.Based on the distance, the bending machine control determines the actual position of a bending point relative to a predetermined, i.e. a previously calculated and thus expected distance value.

[0023] In the embodiment described here, the first bending point 2c at x1 = 100 is applied on the narrow side of the sheet 2 as an optical marking which can be detected by the optical system, in the present embodiment by the camera 7. An optical marking can, for example, be applied in a color contrast to the sheet, for example as a colored symbol or as a line of predefined width perpendicular to the neutral fiber 2b.

[0024] The process steps of a bending process according to the invention are described in more detail below.

[0025] As a first step, see Fig. 2 , the sheet metal 2 to be bent is inserted into the bending machine 1 so that the sheet metal 2 is in the starting position for an upcoming bending process. The bending machine stores this position as a reference position for the subsequent conveying of the sheet metal 2. The corresponding position of the top roller 3 can be stored as "0". The reference edge x0 = 0 of the sheet metal lies at the point of the driven top roller 3 at which the sheet metal 2 is bent into the curve during the round bending process.

[0026] Starting from the starting position, the sheet metal 2 is conveyed in direction 2a by a predetermined distance due to the rotation of the driven roller 3. The control system of the bending machine 1 controls the rotation of the driven roller such that the sheet metal is conveyed by a distance that is shorter than the distance to the first bending point, but large enough that the marking of the bending point reaches the area captured by the camera 7 and the actual conveyed distance can be determined. In one embodiment, this distance is the distance until the first bending point touches the top roller minus a predefined distance, the expected distance, for example, 1 / 5 of the diameter of the top roller 3.

[0027] The length of the predefined distance is the expected distance of a bending point (2c, 2d) from a reference point of the bending machine, here the point of contact of the sheet 2 with the top roller 3, wherein the expected distance is selected such that the next expected bending point 2c, 2d or its marking is reliably detected by the camera 7 and thus the actual distance of the bending point 2c, 2d from the point of contact with the top roller 3 can be determined.

[0028] In practice, it has been found that, while the calculated control parameters are precisely adhered to during the conveying of sheet metal 2, the sheet metal 2 is not actually conveyed precisely, for example, due to slippage between the driven upper roller 3 and the sheet metal 2. The actual position of the sheet metal 2 in the bending machine 1 thus deviates from the previously calculated and expected position, or the actual distance of a bending point 2c, 2d after conveying deviates from the correspondingly expected distance.

[0029] To correct the position of sheet 2 in the control system with regard to the conveyance of the sheet, it is first conveyed as far as, see Figur 3 that the marked bending point 2c has an expected distance 9 from the contact point with the top roller 3. The predefined and expected distance 9 is typically located in the conveying direction 2a just before the contact point of the sheet with the top roller 3, at which the sheet is actually bent. The expected distance can, for example, be 1 / 5 of the diameter of the top roller 3.

[0030] Fig. 3 shows a position of the sheet metal in the bending machine 1 after the sheet metal 2 has been conveyed according to the originally entered control parameters until the next bending point in the conveying direction 2a, or the marking of the bending point, here 2c, is detected by the camera 7. The bending machine 1 has thus conveyed the sheet metal 2 according to the entered distance, i.e., the distance to the next bending point 2c minus the predetermined distance 9. In the following numerical example, this predetermined distance 9 has a length of 50.

[0031] The control system of the bending machine 2 receives the captured images from the camera, evaluates them and determines the actual position of the bending point 2c, i.e. the distance of the bending point from the reference point, and thus the deviation of the actually conveyed sheet length from the previously calculated and expected length.

[0032] The sectional view of the rollers, right in Fig. 3 , shows the distance 9 calculated in the control system and thus expected, i.e. the distance 9 of the bending point 2c expected according to the control parameters, as well as the actual position of the sheet 2, i.e. the actual distance 10 of the bending point 2c from the contact point 8 of the sheet 2 with the top roller 3, whereby the actual distance 10 of the bending point 2c of the sheet deviates from the expected distance 9.

[0033] In an exemplary embodiment, the first bending point is x1=100 from the left edge of the sheet. The calculated and thus expected distance 9 of the bending point is 50 from the contact point 8 of the top roller 3 with the sheet 2, i.e., the sheet 2 was conveyed by the distance (x1 - 50) = 100 - 50 from the top roller 3 according to the control parameters. The bending point 2c should therefore be expected to have a distance of 50 from the contact point 8 with the top roller 3.

[0034] The actual distance 10 of the bending point 2c from the contact point 8 of the sheet metal 2 with the top roller 3 is determined by the distance determination device based on an image from camera 7. For this purpose, camera 7 of the device captures the marking of the bending point 2c and supplies the corresponding data to the control system. Based on this data, the control system determines that the actual distance of the bending point from the contact point with the top roller 3 is, for example, 48. Based on the determined actual value, the control system corrects the parameter for the subsequent conveying so that the further conveying of the sheet metal is based on the corrected control parameters. Since in this numerical example the actual distance of the bending point 2c is not 50, as expected, but actually 48, as determined by the camera, the value of the distance already conveyed in the bending machine control system is adjusted accordingly to 52.

[0035] It should be noted that further conveying of sheet 2, for example, conveying the sheet until the bending point 2c is in contact with the top roller 3, is also subject to errors. However, the incorrectly conveyed distance is shorter than without the above-described control parameter correction, so the error in conveying the sheet is reduced and the bending point of the sheet is maintained more precisely.

[0036] In a further developed embodiment, the control determines the slip during the conveying of the sheet 2 from the calculated conveying distance and the determined deviation and takes this into account when calculating the further conveying of the sheet 2 in order to further minimize a deviation during the conveying of the sheet 2.

[0037] Fig. 4 shows the position of sheet metal 2 in bending machine 1 after the sheet metal has been conveyed according to the corrected control parameters until the bending point 2c is at the point of contact with the top roller 3. As sheet metal 2 is further conveyed, the rollers of bending machine 1 cause sheet metal 2 to be rounded. For this purpose, the sheet metal is further conveyed by the driven roller, here the top roller 3, according to the entered control parameters.

[0038] Fig. 5 shows schematically the rollers of the sheet metal bending machine 1 and the sheet metal 2. According to the entered control parameters, the sheet metal 2 is to be bent in the section x1 = 100 to x2 = 1000, whereby the sheet metal 2 is again conveyed to an expected distance 9.

[0039] As described above with regard to the actual position of the sheet 2 and the first bending point 2c, the sheet 2 was conveyed over a distance which is the length of the bending section minus an expected distance 9, so that the next bending point 2d also has an expected distance 9 from the contact point 8 of the sheet with the top roller 3. The expected distance 9 can be individual for a distance, but such that a bending point 2c, 2d or a marking thereof lies within the area detectable by a camera 7. Thus, the expected distance for the second conveying can be smaller than the expected distance as a percentage of the conveyed distance.In one embodiment, the slip between the sheet 2 and the driven top roller 3 can be determined based on previous conveying operations of the sheet and thus the value of an expected distance of an upcoming conveying operation can be calculated from the deviation between the expected and actual distance, so that the deviation from the expected distance becomes smaller.

[0040] The actual position of sheet metal 2 can also deviate from the expected position in the vertical direction during bending, typically when the actual properties of sheet metal 2 deviate from the expected / assumed properties. Accordingly, the actual position of the bending point 2c, 2d or its marking also deviates from an expected position in the vertical direction. In this case, the determined position of the bending point is projected onto the expected sheet metal shape, whereby the projection is defined by the shortest path to the expected sheet metal shape and is thus perpendicular to the expected sheet metal shape. If the projection of a bending point in the direction of the neutral fiber lies outside the sheet metal, i.e. the sheet metal is too short, the neutral fiber is extrapolated accordingly for the calculation of the distance 9.

[0041] The actual distance 10 of the sheet 2 from the contact point with the top roller, and thus the actual length already conveyed, is determined by the camera 7 as soon as the sheet has been conveyed the distance to the expected distance 9. Based on the determined actual distance 9, at least the value of the distance of the bending point 2d from the contact point with the top roller 3 stored in the bending machine 1 is corrected by the determined deviation from the expected distance value.

[0042] As mentioned above, the slip between top roller 3 and sheet 2, which can be determined from the determined deviation, can be taken into account for conveying sheet 2.

[0043] Subsequently, the sheet 2 is conveyed further in the same direction 2a based on the corrected value until the entire section to be bent is bent, i.e. the bending point 2d is in contact with the top roller 3, see Fig. 6 .

[0044] In this way, the beginning and end of the section of sheet 2 to be bent into a specified radius, i.e. from x1 = 100 to x2 = 1000, were more precisely maintained. List of reference symbols

[0045] 1Bending machine 2Sheet metal 2aTransport direction of the sheet metal 2bNeutral fiber of the sheet metal 2cFirst bending point of the sheet metal 2dSecond bending point of the sheet metal 3Top roller 3aArrow 4Bottom roller 5First side roller 6Second side roller 7Camera of a device for determining the distance between a bending point of the sheet metal and a reference point of the bending machine 8Contact point of sheet metal 2 with top roller 3, reference point 9Expected distance of the bending point to the contact point of top roller 3 with sheet metal 2 / reference point 10Actual distance of the bending point to the reference point

Claims

1. Round bending machine (1) for round bending a bending portion of an object (2) comprising - at least three rollers (3 - 6), one of the rollers being motor-driven, and - a control system for controlling the drive of the motor-driven roller (3) of the round bending machine (1) and - a device (7) for determining an actual distance of a bending point (2c, 2d) of the object (2) to a reference point of the round bending machine (1), the distance being determined along the neutral fiber (2b) of the object (2), and - the control system being configured to correct the control of the motor-driven roller (3) on the basis of the actual distance the device (7) for determining the actual distance of a bending point (2c, 2d) of the object (2) comprising a system for optically determining the bending point (2c, 2d), characterized in that the device for optically determining the bending point (2c, 2d) is configured to detect an optical marking on the object (2) and to determine the actual distance to the reference point of the round bending machine (1).

2. Round bending machine (1) according to claim 1, wherein it is configured to convey the object (2) to an expected distance of a bending point (2c, 2d) from the reference point, to determine the actual distance of the bending point (2c, 2d) from the reference point, and to correct parameters of the control system on the basis of the difference between the expected and actually determined distance.

3. Round bending machine (1) according to claim 2, wherein it is further configured to convey the object (2) until it reaches the bending portion on the basis of corrected parameters of the control system.

4. Round bending machine (1) according to any of the preceding claims, wherein the control system is configured to determine the slippage during the conveying of the object (2) on the basis of the difference between the expected and actual distance.

5. Round bending machine (1) according to claim 4, wherein the control system is configured to take the slippage into account when determining further conveyance of the object 2.

6. Round bending machine (1) according to any of the preceding claims, wherein the object is a metal sheet.

7. Round bending machine (1) according to claim 6, wherein the metal sheet has a thickness of more than 3 mm and in particular more than 50 mm.

8. Method for round bending a bending portion of an object (2) with a round bending machine (1), comprising the steps of: - conveying the object (2) to an expected distance of a bending point (2c, 2d) of the object (2) from a reference point (8) of the bending machine (1), and - determining the actual distance of the bending point (2c) from the reference point (8) of the bending machine (1) with a device (7) for determining the actual distance of the bending point (2c) of the object (2) from the reference point (8) of the bending machine (1), and - changing at least one control parameter of the bending machine (1) on the basis of the difference between the expected and the determined actual distance of the bending point (2c, 2d) from the reference point (8), and - further conveying the object (2) until it reaches the entire length of the bending portion on the basis of the at least one changed control parameter wherein the device (7) for determining the actual distance of a bending point (2c, 2d) of the object (2) comprises a system for optically determining the bending point (2c, 2d), and wherein the device for optically determining the bending point (2c, 2d) is configured to detect an optical marking on the object (2) and to determine the actual distance to the reference point of the round bending machine (1).

9. Method according to claim 8, wherein determining the actual distance of the bending point (2c, 2d) from the reference point (8) comprises optically capturing a marking of the bending point with a camera (7), and the camera (7) transmits data to a control system of the bending machine.

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