Device and method for accurately cutting sheets for transformer cores without causing damage

Abstract

The present invention relates to a device for cutting transformer core sheets, comprising a reel for a metal coil, an infeed for the metal, a measuring wheel for measuring a displacement of the metal, a tool and punch for making V-notches and holes, a first and second knife for cutting at an angle of 45° and -45°, an outfeed for cut sheets, a sensor for determining a position of a V-notch and / or a hole, and a first acquisition card for the measuring wheel and a second for the sensor, wherein the first and second acquisition card are configured to acquire at least 10,000 data points per second, wherein the device comprises a programmable logic controller, configured to process the data points at least 100 times per second. The invention also relates to a method and a use.

Description

[0001] DEVICE AND METHOD FOR ACCURATELY CUTTING SHEETS FOR

[0002] TRANSFORMER CORES WITHOUT CAUSING DAMAGE

[0003] TECHNICAL DOMAIN

[0004] The invention relates to a device and a method for cutting sheets for transformer cores and a use of the device and / or method for cutting metal into sheets for transformer cores.

[0005] STATE OF THE ART

[0006] Devices and methods for cutting sheets for transformer cores are known from the prior art.

[0007] Such a device and method is described, for example, in DE 2506682. The device comprises a reel for unwinding a metal coil. The unwound metal is fed into the device and moved through the device in a longitudinal direction. This is done using feed rollers between which the unwound metal is clamped. The unwound metal is cut alternately at an angle of 45° and -45° with respect to the longitudinal direction using a knife. This forms a first end and a second end of a sheet for a transformer core.

[0008] Sheets for transformer cores must be cut with very high precision. With sheets that are too small, air gaps can form in the corners of the transformer core, which has a very negative impact on the transformer's operation. With overly large sheets, the sheets may curl up a bit, which can also create air gaps. Traditionally, a measuring wheel is used when cutting the unwound metal to determine a displacement of the unwound metal in the longitudinal direction and thus a position of the first end and the second end of the sheet. The grip between the measuring wheel and the metal varies from coil to coil, and with a device like in DE '682 it is necessary to perform a calibration of the measuring wheel at the start of each new coil, which is cumbersome. This still does not rule out that during the unwinding of the coil slippage between the measuring wheel and the unwound metal occurs. This introduces an undetected error that persists until the end of the coil. This error can even accumulate with further slippage.

[0009] Sheets for transformer cores must not have any damage to the corners, as this causes an irregular stacking of the sheets in the core, which also leads to air gaps, resulting in additional energy losses. The present invention aims to at least find a solution to some of the above- mentioned problems or disadvantages.

[0010] SUMMARY OF THE INVENTION

[0011] In a first aspect, the present invention relates to a device according to claim 1.

[0012] This device is particularly advantageous because the displacement of the unwound metal in the longitudinal direction can be determined very accurately. It is also not necessary to calibrate the measuring wheel at the start of a new coil. Because the device comprises a sensor for determining a V-notch and / or a punched hole, and because data points from the sensor are acquired at a very high frequency, it is possible to calculate the displacement of the unwound metal from these data points with great accuracy. Because data points from the measuring wheel are also acquired at a high frequency, the device can regularly compare the displacement measured with the wheel to the calculated displacement from the sensor's data points. In case of a discrepancy between the two, it is possible to automatically recalibrate the measuring wheel, for example, by means of a correction factor. This eliminates the need to first unwind part of a new coil to calibrate the measuring wheel, thereby avoiding time loss due to calibration. Nor will a temporary slippage between the measuring wheel and the unwound metal result in an accumulated error in determining the displacement of the unwound metal.

[0013] Preferred embodiments of the device are set out in claims 2-9.

[0014] A specific preferred embodiment concerns a device according to claim 2.

[0015] This preferred embodiment is particularly advantageous to ensure that the unwound metal remains flat between the measuring wheel and the infeed. After unwinding the metal from the coil, the metal may exhibit some waviness. This results in a vertical movement, causing the distance measured with the measuring wheel not to correspond with a distance entered by the infeed. By placing two lying blocks between the infeed and the measuring wheel, a fixed position in the height direction of the unwound metal is ensured in the second position. Because the third and fourth lying blocks are movable in the longitudinal direction, it is possible to place the unwound metal in the first position between the four lying blocks and then in the second position to press the lying blocks against the unwound metal. The funnel- shaped opening that was required for the infeed of the unwound metal is eliminated by this displacement in the longitudinal direction, preventing any waviness in the unwound metal between the measuring wheel and the infeed.

[0016] In a second aspect, the present invention relates to a method according to claim 10.

[0017] This method has the advantage, among others, of allowing a very precise measurement of the displacement of the unwound metal in the longitudinal direction without calibration. As a result, the sheets for the transformer cores can be cut very accurately. The regular comparison between the calculated displacements based on the sensor data points and the measuring wheel data points ensures that even with slippage between the unwound metal and the measuring wheel, no cumulative error occurs.

[0018] Preferred embodiments of the method are described in dependent claims 11-14.

[0019] In a third aspect, the present invention relates to a use according to claim 15.

[0020] This use results in very precise cutting of metal into sheets for transformer cores, even if the metal unwound from a coil is wavy or if there is variation in surface finish and thickness of the metal between different coils or on the same coil. Additionally advantageous is that a quick transition from a first coil to a second coil can be made because no calibration of the measuring wheel is needed at the start of a new coil.

[0021] DETAILED DESCRIPTION

[0022] Unless otherwise defined, all terms used in the description of the invention, including technical and scientific terms, have the meaning as commonly understood by a person skilled in the art to which the invention pertains. For a better understanding of the description of the invention, the following terms are explained explicitly.

[0023] In this document, "a" and "the" refer to both the singular and the plural, unless the context presupposes otherwise. For example, "a segment" means one or more segments.

[0024] The terms "comprise," "comprising," "consist of," "consisting of," "provided with," "include," "including," "contain," "containing," are synonyms and are inclusive or open terms that indicate the presence of what follows, and which do not exclude or prevent the presence of other components, characteristics, elements, members, steps, as known from or disclosed in the prior art.

[0025] Quoting numeric intervals by the endpoints comprises all integers, fractions, and / or real numbers between the endpoints, including those endpoints.

[0026] In a first aspect, the invention relates to a device for cutting sheets for transformer cores.

[0027] The device comprises a reel for unwinding a metal coil. The metal is preferably a type of steel with high permeability for magnetic flux or high permeability, such as transformer steel. Preferably, the metal comprises an insulating layer on both sides. The reel preferably comprises a motor for rotating the reel. The device preferably comprises a pot, a guide, or another suitable means for unwinding the coil of metal in a loop. This is advantageous if variations in the displacement speed of the unwound metal occur in the device. These are accommodated by the metal coil.

[0028] The device comprises an infeed for feeding the unwound metal in a longitudinal direction from the coil into a further part of the device. By "lying," it is meant that a plane formed by the unwound metal extends in a longitudinal direction and a transverse direction, where the longitudinal direction and the transverse direction define a horizontal plane. The device extends in the longitudinal direction. Preferably, the infeed comprises two feed rollers. At least one of the two feed rollers is movable in a height direction, transverse to the longitudinal direction, for clamping the unwound metal between the two feed rollers. At least one of the two feed rollers is coupled to a drive motor. The drive motor is preferably an electric motor. Preferably, the two feed rollers are coupled to a drive motor. More preferably, the two feed rollers are coupled to the same drive motor. By clamping the unwound metal between the two feed rollers and driving at least one of the two feed rollers, the unwound metal can be moved through the device in the longitudinal direction. The two feed rollers are preferably coated with a rubber layer, a polyurethane layer, or another suitable protective layer. This is advantageous to avoid damage to the unwound metal and, more particularly, to the insulating layer on the unwound metal. Alternatively, the infeed comprises wheels or conveyor belts between which the unwound metal is clamped.

[0029] The device comprises a measuring wheel for measuring a displacement in the longitudinal direction of the unwound metal. The measuring wheel has a known diameter. The measuring wheel comprises a rotary encoder for determining a radial position of the measuring wheel. Preferably, the rotary encoder has an accuracy of 16 bits, which corresponds to 65536 pulses per revolution of the encoder. Because the diameter of the measuring wheel is known and because a radial position of the measuring wheel can be determined with high resolution, it can be calculated very accurately over what distance the unwound metal has been moved through the infeed in the longitudinal direction. This is important because, for example, slippage between the infeed and the unwound metal can occur, or because, for example, a displacement of the unwound metal depends on a pressure with which feed rollers, wheels, or conveyor belts of an infeed are pressed against the unwound metal, causing the unwound metal not to move over an expected distance. Preferably, the device comprises a counterwheel. The counterwheel is opposite the measuring wheel and is configured for pressing on an opposite side of the unwound metal.

[0030] The device comprises a tool for making V-notches. The tool comprises a V-shaped knife or two knives arranged in a V-shape. The tool is movable in the height direction. The tool is positioned at an edge of a passage for the unwound metal through the device. The tool is punched through the unwound metal using an actuator, creating a V-notch at an edge of the unwound metal. The tool is positioned after the infeed. Preferably, the device comprises a discharge belt under the tool for removing scrap. The scrap is, in this case, the V-shape cut from the edge of the unwound metal. The V-notch is advantageous for receiving a middle leg of a transformer core. The V-notch is therefore preferably applied in a top plate and a bottom plate of the transformer core. It will be apparent to one skilled in the art that if no top plates or bottom plates are cut on the device, the tool is not used or even does not need to be present.

[0031] The device comprises a punch for punching holes in the unwound metal. The punch is movable in the height direction. By pressing the punch through the unwound metal using an actuator, a hole is punched in the unwound metal. Preferably, two holes are punched in each sheet for the transformer core. The holes are advantageous for stacking the sheets of the transformer core on pins through the punched holes. This keeps the transformer core together and positions the sheets correctly relative to each other. The punch is positioned after the infeed. The punch is positioned before or after the tool for making V-notches in the unwound metal. It will be apparent to one skilled in the art that if the sheets of the transformer core are positioned on top of each other and held together in a different way, the punch does not need to be used or even does not need to be present.

[0032] The device comprises a first knife for cutting the unwound metal at an angle of 45° to the longitudinal direction. Preferably, the angle is 45° ± 0.25°, more preferably 45° ± 0.1°, even more preferably 45° ± 0.01°, and even more preferably 45° ± 0.001°. The device comprises a second knife for cutting the unwound metal at an angle of -45° to the longitudinal direction. Preferably, the angle is -45° ± 0.25°, more preferably -45° ± 0.1°, even more preferably -45° ± 0.01°, and even more preferably -45° ± 0.001°. The first knife and the second knife are movable in the height direction. The first knife and the second knife extend over the full width of the passage for the unwound metal. The width of the passage is in a transverse direction, transverse to the height direction and transverse to the longitudinal direction. The first knife and the second knife are each punched through the unwound metal using their own actuator, cutting the unwound metal. By cutting the unwound metal twice, a sheet for the transformer core is formed. The first knife is used for forming a first end of the sheet, and the second knife is used for forming a second end of the sheet. In specific cases, for example, for forming a pointed first and second end as in a middle leg of a transformer core, both the first knife and the second knife or the tool are used for forming the first end and the second end. The first knife and the second knife are positioned after the infeed. Preferably, the first knife and the second knife are placed after the tool and after the punch. Preferably, the device comprises a discharge belt under the first knife and under the second knife for removing scrap. The scrap is, for example, a piece of metal that is cut off when a pointed end is formed. The device comprises an outfeed for discharging cut metal sheets from the device. The outfeed preferably comprises a conveyor belt or lying transport rollers for discharging the cut metal sheets in the longitudinal direction. The cut metal sheets are the sheets for the transformer core.

[0033] According to a preferred embodiment, the device comprises a sensor for determining a position of a V-notch and / or a punched hole. It is clear that if the sensor determines the position of a V-notch, the device also comprises the tool, and if the sensor determines the position of the punched hole, the device also comprises the punch. The sensor is preferably an optical sensor, more preferably a fiber optic sensor, suitable for detecting an edge of the V-notch or the punched hole. The sensor is preferably placed in a fixed position in the transverse direction during use. The sensor is preferably placed in a fixed position in the longitudinal direction during use. By detecting a first edge and a second edge of the V-notch and / or a punch hole and because a theoretical position of the V-notch and the punch hole is known, an exact distance over which the unwound metal is moved through the device can be calculated.

[0034] The device comprises a first acquisition card for acquiring data from the measuring wheel. The first acquisition card is an electronic card communicatively connected to the measuring wheel. For example, the first acquisition card is suitable for counting pulses from a rotary encoder of the measuring wheel. By counting the pulses, an exact distance over which the unwound metal is moved through the device can be calculated. The first acquisition card is configured for acquiring at least 10,000 data points per second, preferably at least 100,000 data points per second, more preferably at least 250,000 data points per second, even more preferably at least 500,000 data points per second, and even more preferably at least 1,000,000 data points per second.

[0035] The device comprises a second acquisition card for acquiring data from the sensor. The second acquisition card is an electronic card communicatively connected to the sensor. For example, the second acquisition card is suitable for detecting transitions between metal and no metal using the sensor. The second acquisition card is configured for acquiring at least 10,000 data points per second, preferably at least 100,000 data points per second, more preferably at least 250,000 data points per second, even more preferably at least 500,000 data points per second, and even more preferably at least 1,000,000 data points per second. The device comprises a programmable logic controller (PLC). The programmable logic controller is preferably configured for controlling motors and actuators of the device. The programmable logic controller is configured for processing the data points from the sensor and the measuring wheel at least 100 times per second for calibrating the measuring wheel, preferably at least 250 times per second, more preferably at least 500 times per second, even more preferably at least 750 times per second, and even more preferably at least 1000 times per second. This can be done, for example, by comparing the calculated distance using the sensor with the calculated distance using the measuring wheel. In principle, these two distances should be identical. Slippage may occur at the measuring wheel, for example, because a coil with a different type of metal or metal with a different thickness is used, causing a consistently different distance to be determined. The distance calculated with the sensor does not have this problem, so if enough data points are acquired per second, this distance is correct. The distance calculated using the sensor can be used to calibrate the measuring wheel. If temporary slippage occurs, for example, due to a local deviation in thickness of the unwound metal or a local deviation in surface finish of the unwound metal, this can also be detected because there is a temporary deviation in calculated distance between the measuring wheel and the sensor. This information can be used to correct a measured displacement by the measuring wheel, preventing an error from accumulating. The measuring wheel remains necessary because the sensor can only determine the distance at V- notches or punched holes. The position of the V-notches and / or the punched holes must also be determined with great accuracy, so the measuring wheel remains necessary and is the primary element for determining the displacement in the longitudinal direction of the unwound metal.

[0036] At least 10,000 data points are necessary for sufficient accuracy. For example, if the unwound metal is moved at a speed of 4 m / s in the longitudinal direction, it is possible to determine an edge of a V-notch or a punched hole with an accuracy of 0.4 mm using the sensor. With at least 1,000,000 data points, this is already with an accuracy of 0.004 mm.

[0037] This embodiment is therefore particularly advantageous because the displacement of the unwound metal in the longitudinal direction can be determined very accurately. It is also not necessary to calibrate the measuring wheel at the start of a new coil. Because the device comprises a sensor for determining a V-notch and / or a punched hole, and because data points from the sensor are acquired at a very high frequency, it is possible to calculate the displacement of the unwound metal from these data points with great accuracy. Because data points from the measuring wheel are also acquired at a high frequency, the device can regularly compare the displacement measured with the wheel to the calculated displacement from the sensor's data points. In case of a discrepancy between the two, it is possible to automatically recalibrate the measuring wheel, for example, by means of a correction factor. As a result, it is not necessary to first unroll a portion of a new coil to calibrate the measuring wheel. This also prevents metal from being wasted by first unwinding part of the coil of metal unused. Nor will a temporary slippage between the measuring wheel and the unwound metal result in an accumulated error in determining the displacement of the unwound metal.

[0038] According to one embodiment, the first knife and the second knife are the same knife. The knife is movable by an actuator between a first position and a second position. In the first position, the knife is positioned for cutting the unwound metal at an angle of 45° to the longitudinal direction. Preferably, the angle is 45° ± 0.25°, more preferably 45° ± 0.1°, even more preferably 45° ± 0.01°, and even more preferably 45° ± 0.001°. In the second position, the knife is positioned for cutting the unwound metal at an angle of -45° to the longitudinal direction. Preferably, the angle is -45° ± 0.25°, more preferably -45° ± 0.1°, even more preferably -45° ± 0.01°, and even more preferably -45° ± 0.001°.

[0039] This embodiment is advantageous because only one knife is necessary, allowing the device to be more compact in the longitudinal direction.

[0040] According to a preferred embodiment, the device comprises four lying blocks at the measuring wheel for guiding the unwound metal. A first and a second lying block form a funnel-shaped opening, followed by a flat passage, for the unwound metal. A third and a fourth lying block are movable in the longitudinal direction from a first position to a second position. The four lying blocks extend in the transverse direction transverse to the longitudinal direction. In the first position, the funnel-shaped opening is present. The funnel-shaped opening lies in a cross-section in the longitudinal direction of the four lying blocks. A largest opening of the funnel-shaped opening is directed toward the reel, and a smallest opening of the funnel-shaped opening is directed toward the further part of the device. The funnel-shaped opening is part of the passage for the unwound metal and helps determine a position in the height direction of this passage. In the second position, the third and fourth lying blocks fill the funnel-shaped opening to form a flat passage for the unwound metal. It is clear that the third and fourth blocks are placed in the first and second blocks. This embodiment is particularly advantageous for ensuring that the unwound metal remains flat between the measuring wheel and the infeed. After unwinding the metal from the coil, the metal may exhibit some waviness. This results in a vertical movement, causing the distance measured with the measuring wheel not to correspond with a distance entered by the infeed. By placing two lying blocks between the infeed and the measuring wheel, a fixed position in the height direction of the unwound metal is ensured in the second position. Because the third block and the fourth block are movable in the longitudinal direction, it is possible to place the unwound metal between the four lying blocks in the first position and then move the lying blocks against the unwound metal in the second position. The funnel- shaped opening that was required for the infeed of the unwound metal is eliminated by this displacement in the longitudinal direction, preventing any waviness in the unwound metal between the measuring wheel and the infeed.

[0041] If the measuring wheel is placed in front of the funnel-shaped opening, then the third and fourth blocks preferably have a concave outer surface, where the concave outer surface is concentric with the measuring wheel and possibly a counterwheel in the second position. This is advantageous because it allows the third and fourth blocks to be positioned very close to the measuring wheel, allowing the flat passage for the unwound metal to extend to the measuring wheel.

[0042] According to a preferred embodiment, the infeed comprises guides for aligning the unwound metal in the transverse direction transverse to the longitudinal direction. If the infeed comprises two feed rollers, as previously described, the guides can be placed before the feed rollers, after the feed rollers, or both before and after the feed rollers. Preferably, at least guides are placed after the feed rollers. The guides extend in the longitudinal direction. A first guide is placed in the transverse direction on a first side of the passage for the unwound metal. A second guide is placed in the transverse direction on a second opposite side of the passage for the unwound metal. The unwound metal is thus guided by the two guides on two opposite edges. At least one guide comprises a spindle at two opposite ends for moving the guide in the transverse direction. Preferably, both guides comprise a spindle at two opposite ends. The spindle is preferably coupled to a drive motor. Preferably, both spindles of a guide are coupled to the same drive motor. The spindle is advantageous so that at least one guide can be moved in the transverse direction until the first guide presses against a first edge of the unwound metal and the second guide presses against a second opposite edge of the unwound metal. Two spindles at two opposite ends of the guide are advantageous because they allow the guide to better absorb torsional forces around an axis in the height direction, making the unwound metal more stable in the longitudinal direction. Preferably, the spindles are at most 30 cm below the passage for the unwound material, more preferably at most 25 cm, even more preferably at most 20 cm, and even more preferably at most 15 cm. This distance can be measured in a device in operation as a distance in the height direction between a bottom side of the unwound metal and a center point of the spindle. This limited distance is advantageous because it allows the guide to better absorb torsional forces around an axis in the longitudinal direction, making the unwound metal more stable in the transverse direction.

[0043] According to a preferred embodiment, the infeed comprises guides for aligning the unwound metal in the transverse direction transverse to the longitudinal direction. If the infeed comprises two feed rollers, as previously described, the guides can be placed before the feed rollers, after the feed rollers, or both before and after the feed rollers. Preferably, at least guides are placed after the feed rollers. The guides extend in the longitudinal direction. A first guide is placed in the transverse direction on a first side of the passage for the unwound metal. A second guide is placed in the transverse direction on a second opposite side of the passage for the unwound metal. The unwound metal is thus guided by the two guides on two opposite edges. The guides in this embodiment have a very similar construction and operation and the same purpose as in a previously described embodiment of the guides. These two embodiments can be advantageously combined.

[0044] At least one guide is movable in the transverse direction by a servomotor. The device comprises a means for measuring a motor torque of the servomotor. This is advantageous because the motor torque can be used to determine whether the at least one guide presses sufficiently against the edge of the unwound metal. If a too low motor torque is measured, the at least one guide presses insufficiently against the unwound metal, causing the unwound metal to be insufficiently guided and aligned, and if a too high motor torque is measured, the at least one guide presses too much against the unwound metal, which may cause the unwound metal to bulge in the transverse direction. This is particularly advantageous for automatically adjusting the position of the at least one guide, especially if a tolerance on a width of the unwound metal deviates from a nominal value for the width by cutting a wider coil of metal into multiple narrower coils of metal. This is additionally advantageous because in this way the width of the unwound material can also be measured. According to a preferred embodiment, the outfeed comprises lateral guide rollers for guiding the cut metal sheets in the longitudinal direction. A first series of lateral guide rollers are placed in the transverse direction on a first side of the passage for the unwound metal. The first series of lateral guide rollers comprises multiple rollers placed next to each other in the longitudinal direction. A second series of lateral guide rollers are placed in the transverse direction on a second opposite side of the passage for the unwound metal. The second series of lateral guide rollers comprises multiple rollers placed next to each other in the longitudinal direction. The unwound metal is thus guided by the first series and the second series on two opposite edges of the unwound metal. The lateral guide rollers are movable in the transverse direction transverse to the longitudinal direction. This means that the first series or the second series or the first and second series are movable in the transverse direction. The device comprises a control for moving the lateral guide rollers in the transverse direction.

[0045] This embodiment is advantageous for guiding the unwound metal and the cut sheets during discharge from the device. The unwound metal already has a considerable length at the outfeed viewed with respect to the reel. The lateral guide rollers are advantageous to prevent the unwound metal from moving in the transverse direction near the outfeed. This could potentially have a negative impact on the accuracy with which the unwound metal can be cut. This could also lead to damage during discharge as the unwound metal or the cut sheets hit a part of the device. Being movable in the transverse direction is advantageous because it allows the lateral guide rollers to be pressed against edges of the unwound metal or against edges of the cut metal sheets for optimal guidance during discharge. This embodiment, like a previously described embodiment for guides at the infeed, could be advantageously combined with a means for measuring a motor torque of a drive motor with which the lateral guide rollers are moved in the transverse direction.

[0046] The control is particularly advantageous for moving the lateral guide rollers away from the unwound metal or the cut sheets when a V-notch or a first end passes by. These are the points where the cut sheets or the unwound metal could hit the lateral guide rollers, which could lead to damage and later possibly to air gaps in the transformer core. Preferably, the device comprises a third series of lateral guide rollers on the first side and a fourth series of lateral guide rollers on the second side. By separating the first and third series and the second and fourth series in the longitudinal direction, it is almost always possible to guide the unwound metal or the cut sheets at the outfeed with a combination of the first and second series or a combination of the third and fourth series.

[0047] According to a preferred embodiment, the first knife and the second knife are movable in the transverse direction transverse to the longitudinal direction. The first knife is rotatable between a first position for cutting the unwound metal at an angle of 45° to the longitudinal direction and a second position for cutting the unwound metal at an angle of 90° to the longitudinal direction. Preferably, the angle in the first position is 45° ± 0.25°, more preferably 45° ± 0.1°, even more preferably 45° ± 0.01°, and even more preferably 45° ± 0.001°. Preferably, the angle in the second position is 90° ± 0.25°, more preferably 90° ± 0.1°, even more preferably 90° ± 0.01°, and even more preferably 90° ± 0.001°. Between the first knife and the second knife is a collection tray for collecting cut metal sheets.

[0048] This embodiment is advantageous for cutting very short sheets for transformer cores, and particularly for reactor cores. Such short sheets, for example, do not yet reach the outfeed when the sheets are completely cut from the unwound metal. As a result, the sheets would no longer be moved to the outfeed, stack up in the device, and eventually block and possibly damage the device. The short sheets would also be damaged themselves. By providing a collection tray between the first knife and the second knife, such short sheets can still be cut and collected on the device without blocking the device.

[0049] Such short sheets are usually also narrower in the transverse direction. Because the first knife and the second knife are movable in the transverse direction and the first knife and the second knife are angled relative to each other, the first knife and the second knife can be placed closer together in the longitudinal direction without moving the first knife and the second knife in the longitudinal direction. The first knife and the second knife are directed toward each other at an angle. By cutting the unwound metal closer to the mentioned angle with the first knife and the second knife, it is possible to cut shorter sheets from the unwound metal, provided the unwound metal is sufficiently narrow.

[0050] According to a preferred embodiment, the measuring wheel is nitrided and sharpened. Traditionally, measuring wheels are made of thermally hardened metal. Nitrided and sharpened metal is advantageous because nitriding causes less deformation and stress than thermal hardening, while the surface still becomes hard and wear-resistant. The measuring wheel retains a nice round shape without post- treatment. The surface is just as precise, and there is less chance of damaging the metal, particularly the insulating layer on the material, by nitriding instead of thermal hardening.

[0051] According to a preferred embodiment, the measuring wheel and the infeed are mounted separately. Preferably, the measuring wheel is mounted on its own frame. This embodiment is advantageous because vibrations from the infeeds, for example, vibrations caused by feed rollers in the infeed, are not transferred to the measuring wheel. These vibrations can cause distortions of the measuring wheel or can cause the measuring wheel to occasionally lose contact with the unwound metal, resulting in slippage. This leads to measurement errors. These measurement errors are avoided by the separate frame.

[0052] According to a preferred embodiment, the device comprises a gap at the first knife and / or the second knife. The gap may or may not be common to both knives. A discharge belt for removing scrap is placed under the gap. This embodiment is advantageous if, for example, a point needs to be cut at the first end or the second end of the sheet, leaving a piece of metal as scrap. This scrap is removed by the discharge belt, preventing it from accumulating. This is additionally advantageous for cutting the beginning of a new coil of metal into pieces. The beginning of a new coil of metal is often damaged, making it unusable and potentially causing air gaps in the transformer core.

[0053] In a second aspect, the invention relates to a method for cutting sheets for transformer cores.

[0054] The method comprises the steps of: unwinding metal from a coil,

[0055] - feeding the unwound metal in a longitudinal direction to a first knife, wherein during feeding, a displacement of the unwound metal in the longitudinal direction is measured using a measuring wheel, making a V-notch in the unwound metal using a tool and / or punching a hole in the unwound metal using a punch, cutting the unwound metal with the first knife at an angle of 45° to the longitudinal direction to form a first end of the sheet of the transformer core, cutting the unwound metal with a second knife at an angle of -45° to the longitudinal direction to form a second end of the sheet of the transformer core, opposite the first end, discharging the sheet. The metal is preferably unwound in a loop from the coil. The metal is preferably a type of steel with high permeability for magnetic flux or high permeability, such as transformer steel. Preferably, the metal comprises an insulating layer on both sides.

[0056] Preferably, the unwound metal is cut with the first knife at an angle of preferably 45° ± 0.25° to the longitudinal direction, more preferably 45° ± 0.1°, even more preferably 45° ± 0.01°, and even more preferably 45° ± 0.001°.

[0057] The V-notch is advantageous for receiving a middle leg of a transformer core. The V-notch is therefore preferably applied in a top plate and a bottom plate of the transformer core. It will be apparent to one skilled in the art that if no top plates or bottom plates are cut, no V-notch needs to be made.

[0058] The punched hole is advantageous for stacking the sheets of the transformer core on pins through the punched holes. This keeps the transformer core together and positions the sheets correctly relative to each other. It will be apparent to one skilled in the art that if the sheets of the transformer core are positioned and held together in another way, no holes need to be punched.

[0059] Preferably, the unwound metal is cut with the second knife at an angle of preferably -45° ± 0.25° to the longitudinal direction, more preferably -45° ± 0.1°, even more preferably -45° ± 0.01°, and even more preferably -45° ± 0.001°.

[0060] Preferably, the discharged sheets are automatically stacked.

[0061] According to a preferred embodiment, a sensor is used to determine the position of the V-notch and / or the hole in at least 1 in 100 sheets. It is clear that if the sensor determines the position of a V-notch, a V-notch is also made during the execution of the method, and if the sensor determines the position of the punched hole, a hole is also punched during the execution of the method. Preferably, the position of the V-notch and / or the hole is determined in at least 1 in 50 sheets, more preferably in at least 1 in 25 sheets, even more preferably in 1 in 10 sheets, and even more preferably in every sheet. During the determination of the position of the notch and / or the hole, at least 10,000 data points per second are acquired from the sensor and at least 10,000 data points per second from the measuring wheel. Preferably, at least 100,000 data points per second are acquired from the sensor, more preferably at least 250,000 data points per second, even more preferably at least 500,000 data points per second, and even more preferably at least 1,000,000 data points per second. Preferably, at least 100,000 data points per second are acquired from the measuring wheel, more preferably at least 250,000 data points per second, even more preferably at least 500,000 data points per second, and even more preferably at least 1,000,000 data points per second. The data points from the sensor and the data points from the measuring wheel are processed at least 100 times per second, preferably at least 250 times per second, more preferably at least 500 times per second, even more preferably at least 750 times per second, and even more preferably at least 1000 times per second. The data points are preferably processed in a programmable logic controller.

[0062] A displacement of the unwound metal is calculated from both the data points of the sensor and the measuring wheel. The sensor is preferably an optical sensor, more preferably a fiber optic sensor, suitable for detecting an edge of the V-notch or the punched hole. By detecting a first edge and a second edge of the V-notch and / or a punch hole and because a theoretical position of the V-notch and the punch hole is known, a distance over which the unwound metal is moved through the device can be calculated. The calculated distances are compared. In principle, these two distances should be identical. Slippage may occur at the measuring wheel, for example, because a coil with a different type of metal or metal with a different thickness is used, causing a consistently different distance to be determined. The distance calculated with the sensor does not have this problem, so if enough data points are acquired per second, this distance is correct. In case of discrepancies, a correction factor for the measuring wheel is determined. The correction factor is then applied when measuring the displacement of the unwound metal using the measuring wheel.

[0063] If temporary slippage occurs, for example, due to a local deviation in thickness of the unwound metal or a local deviation in surface finish of the unwound metal, this can also be detected because there is a temporary deviation in calculated distance between the measuring wheel and the sensor. This information can be used to correct a measured displacement by the measuring wheel, preventing an error from accumulating. The measuring wheel remains necessary because the sensor can only determine the distance at V-notches or punched holes. The position of the V-notches and / or the punched holes must also be determined with great accuracy, so the measuring wheel remains necessary and is the primary element for determining the displacement in the longitudinal direction of the unwound metal. This embodiment has the advantage, among other things, that a very accurate measurement of the displacement of the unwound metal in the longitudinal direction is possible without calibration. As a result, the sheets for the transformer cores can be cut very accurately. The regular comparison between the calculated displacements based on the sensor data points and the measuring wheel data points ensures that even with slippage between the unwound metal and the measuring wheel, no cumulative error occurs.

[0064] According to a preferred embodiment, lateral guide rollers are pressed against the edges of the sheet during discharge. The lateral guide rollers are automatically pressed against the sheet after the first end of the sheet has passed the lateral guide rollers. The lateral guide rollers are automatically removed from the sheet at the V-notch. The lateral guide rollers are automatically pressed against the sheet when the V-notch has passed the lateral guide rollers.

[0065] This embodiment is advantageous for guiding the unwound metal and the sheets during discharge. The lateral guide rollers are advantageous to prevent the unwound metal from moving in the transverse direction during discharge. This could potentially have a negative impact on the accuracy with which the unwound metal can be cut. This could also lead to damage during discharge as the unwound metal or the sheets could hit something.

[0066] This embodiment is particularly advantageous to prevent the sheets from being damaged at a V-notch or a first end. These are the points where the sheets or the unwound metal could hit the lateral guide rollers, which could lead to damage and later possibly an air gap in the transformer core. By pressing the lateral guide rollers against the sheet only after the first end has passed and by temporarily removing the lateral guide rollers at a V-notch, this is avoided.

[0067] According to a preferred embodiment, guides press against opposing edges of the unwound metal during the infeed of the unwound metal. At least one guide is pressed against a first edge of the unwound metal using a servomotor. A motor torque of the servomotor is measured. If a predetermined first value of the motor torque is exceeded, the at least one guide is removed from the first edge of the unwound metal. If a predetermined second value of the motor torque is not reached, the at least one guide is moved to the first edge of the unwound metal. Preferably, a second guide is also pressed against a second opposite edge of the unwound metal. Measuring the motor torque is advantageous to determine whether the at least one guide presses sufficiently against the edge of the unwound metal. If a too low motor torque is measured, below the predetermined first value, the at least one guide presses insufficiently against the unwound metal, causing the unwound metal to be insufficiently guided and aligned, and if a too high motor torque is measured, above the predetermined second value, the at least one guide presses too much against the unwound metal, causing the unwound metal to bulge in the transverse direction. This is particularly advantageous for automatically adjusting the position of the at least one guide, especially if the unwound metal has a different tolerance due to cutting a wider coil of metal into multiple narrower coils of metal.

[0068] According to a preferred embodiment, when unwinding a new coil of metal, a first piece of the coil is cut off and discarded as scrap by repeatedly cutting the unwound metal with either the first knife or the second knife. The unwound metal is moved at most 5 cm between each cut, preferably at most 4 cm, more preferably at most 3 cm, even more preferably at most 2 cm, and even more preferably at most 1 cm. The cut piece falls under the first knife or the second knife and is removed as scrap by a conveyor belt.

[0069] This embodiment is advantageous for cutting the beginning of a new coil of metal into pieces. The beginning of a new coil of metal is often damaged, making it unusable and potentially causing air gaps in the transformer core. The beginning of the new coil could also be cut off in one go using the first knife and the second knife. In that case, it is not possible to let the cut-off beginning fall as a single piece of scrap under the first knife or second knife and remove it as scrap. The cut-off beginning would have to be removed manually, requiring the device for cutting sheets for transformer cores to be stopped and posing an unnecessary risk to an operator by coming near the first and / or the second knife. It would also be possible to provide a greater distance between the first knife and the second knife, but this means that the mentioned device would be unnecessarily longer for normal operation. Moreover, the length of the metal that needs to be cut off at the beginning of a new coil is not always the same. So even with a greater distance between the first knife and the second knife, it is possible that the cut-off piece would be too large, and manual intervention would still be needed. All these disadvantages are avoided in this embodiment. According to a preferred embodiment, the method comprises the additional step of guiding the unwound metal between four lying blocks. The four lying blocks extend in a transverse direction transverse to the longitudinal direction. A third and a fourth lying block are moved in the longitudinal direction to a first position. A first and a second lying block form a funnel-shaped opening followed by a flat passage for feeding metal from a new coil in the first position seen in the longitudinal direction from the coil. The third and fourth lying blocks are then moved to a second position. The third and fourth lying blocks fill the funnel-shaped opening to a flat passage for the unwound metal in the second position seen in the longitudinal direction.

[0070] This preferred embodiment is particularly advantageous for ensuring that the unwound metal always remains flat against the measuring wheel. After unwinding the metal from the coil, the metal may exhibit some waviness. This results in vertical movement, causing the distance measured with the measuring wheel not to match a displacement of the unwound metal. By moving the third and fourth lying blocks in the longitudinal direction, it is possible to place the unwound metal between the four lying blocks in the first position and then move the lying blocks against the unwound metal in the second position. The funnel-shaped opening needed for feeding the unwound metal is eliminated by this movement in the longitudinal direction, preventing waviness in the unwound metal.

[0071] One skilled in the art will appreciate that a method according to the second aspect is preferably performed using a device according to the first aspect and that a device according to the first aspect is preferably configured for performing a method according to the second aspect. Each feature described in this document, both above and below, can therefore relate to any of the three aspects of the present invention.

[0072] In a third aspect, the invention relates to the use of a device according to the first aspect and / or a method according to the second aspect for cutting metal into sheets for transformer cores.

[0073] This use results in very precise cutting of metal into sheets for transformer cores, even if the metal unwound from a coil is wavy or if there is variation in surface finish and thickness of the metal between different coils or on the same coil. Additionally advantageous is that a quick transition from a first coil to a second coil can be made because no calibration of the measuring wheel is needed at the start of a new coil.

Claims

CLAIMS1. Device for cutting sheets for transformer cores, comprising a powered reel for unwinding a metal coil, an infeed for feeding the unwound metal in a longitudinal direction from the coil into a further part of the device, a measuring wheel for measuring a displacement in the longitudinal direction of the unwound metal, a tool for making V-notches in the unwound metal, a punch for punching holes in the unwound metal, a first knife for cutting the unwound metal at an angle of 45° with the longitudinal direction, a second knife for cutting the unwound metal at an angle of -45° with the longitudinal direction, and an outfeed for discharging cut metal sheets from the device, characterized in that the device comprises a sensor for determining a position of a V-notch and / or a punched hole in the unwound metal, wherein the device comprises a first acquisition card for acquiring data from the measuring wheel, wherein the device comprises a second acquisition card for acquiring data from the sensor, wherein the first acquisition card and the second acquisition card are configured to acquire at least 10,000 data points per second, wherein the device comprises a programmable logic controller, and wherein the programmable logic controller is configured to process the data points from the sensor and the measuring wheel at least 100 times per second for calibrating the measuring wheel.

2. The device according to claim 1, characterized in that the device comprises four lying blocks at the measuring wheel for guiding the unwound metal, wherein a first and a second lying block form a funnel-shaped opening, followed by a flat passage, for the unwound metal, wherein a third and a fourth lying block are movable in the longitudinal direction from a first position to a second position, wherein the four lying blocks extend in a transverse direction transverse to the longitudinal direction, wherein in the first position the funnel-shaped opening is present and wherein in the second position the third and fourth lying block fill the funnel-shaped opening to a flat passage for the unwound metal.

3. The device according to claim 1 or 2, characterized in that the infeed comprises guides for aligning the unwound metal in a transverse direction transverse to the longitudinal direction, wherein the guides extend in the longitudinal direction, and wherein at least one guide comprises a spindle at two opposite ends for moving the guide in the transverse direction.

4. The device according to any of the preceding claims 1-3, characterized in that the infeed comprises guides for aligning the unwound metal in a transverse direction transverse to the longitudinal direction, wherein the guides extend in the longitudinal direction, wherein at least one guide is movable in the transverse direction by a servomotor, and wherein the device comprises a means for measuring a motor torque of the servomotor.

5. The device according to any of the preceding claims 1-4, characterized in that the outfeed comprises lateral guide rollers for guiding in the longitudinal direction of the cut metal sheets, wherein the lateral guide rollers are movable in a transverse direction transverse to the longitudinal direction and wherein the device comprises a control for moving the lateral guide rollers in the transverse direction.

6. The device according to any of the preceding claims 1-5, characterized in that the first knife and the second knife are movable in a transverse direction transverse to the longitudinal direction, wherein the first knife is rotatable between a first position for cutting the unwound metal at an angle of 45° ± 5° with the longitudinal direction and a second position for cutting the unwound metal at an angle of 90° ± 5° with the longitudinal direction, and wherein between the first knife and the second knife there is a collection tray for collecting cut metal sheets.

7. The device according to any of the preceding claims 1-6, characterized in that the measuring wheel is nitrided and sharpened.

8. The device according to any of the preceding claims 1-7, characterized in that the measuring wheel and the infeed are mounted on separate frames.

9. The device according to any of the preceding claims 1-8, characterized in that the device comprises a gap at the first knife and / or the second knife, wherein a conveyor belt for removing scrap is placed under the gap.

10. Method for cutting sheets for transformer cores comprising the steps of: unwinding metal from a coil;- feeding the unwound metal in a longitudinal direction to a first knife, wherein during feeding a displacement of the unwound metal in the longitudinal direction is measured using a measuring wheel; making a V-notch in the unwound metal using a tool and / or punching a hole in the unwound metal using a punch; cutting the unwound metal with the first knife at an angle of 45° with the longitudinal direction to form a first end of the sheet of the transformer core; cutting the unwound metal with a second knife at an angle of -45° with the longitudinal direction to form a second end of the sheet of the transformer core, opposite the first end; discharging the sheet; characterized in that using a sensor, a position of the V-notch and / or the hole is determined in at least 1 out of 100 sheets, wherein during the determination of the position of the notch and / or the hole at least 10,000 data points per second from the sensor and at least 10,000 data points per second from the measuring wheel are acquired, wherein the data points from the sensor and the data points from the measuring wheel are processed at least 100 times per second, wherein a displacement of the unwound metal is calculated from both the data points of the sensor and the measuring wheel, wherein the calculated displacements are compared, wherein in case of deviations a correction factor for the measuring wheel is determined, after which the correction factor is applied when measuring the displacement of the unwound metal using the measuring wheel.

11. The method according to claim 10, characterized in that during the discharge of the sheet lateral guide rollers are pressed against edges of the sheet, wherein the lateral guide rollers are automatically pressed against the sheet after the first end of the sheet has passed the lateral guide rollers, wherein the lateral guide rollers are automatically removed from the sheet at the V-notch, and wherein the lateral guide rollers are automatically pressed against the sheet when the V-notch has passed the lateral guide rollers.

12. The method according to claim 10 or 11, characterized in that during the feeding of the unwound metal, guides press against opposite edges of the unwound metal, wherein at least one guide is pressed against a first edge of the unwound metal using a servomotor, wherein a motor torque of theservomotor is measured, wherein when exceeding a predetermined first value of the motor torque the at least one guide is removed from the first edge of the unwound metal and wherein when falling below a predetermined second value of the motor torque the at least one guide is moved to the first edge of the unwound metal.

13. The method according to claim 10, 11, or 12, characterized in that during the unwinding of a new coil of metal a first piece of the coil is cut off and discarded as scrap by repeatedly cutting the unwound metal using either the first knife or the second knife, wherein the unwound metal is moved at most 5 cm between each cut, wherein the cut piece falls under the first knife or the second knife and is removed as scrap by a conveyor belt.

14. The method according to any of claims 10-13, characterized in that the method comprises the additional step of guiding the unwound metal between four lying blocks, wherein the four lying blocks extend in a transverse direction transverse to the longitudinal direction, wherein a third and a fourth lying block are moved in the longitudinal direction to a first position, wherein a first and a second lying block in the first position seen in the longitudinal direction from the coil form a funnel-shaped opening followed by a flat passage for the feeding of metal from a new coil in, after which the third and fourth lying block are moved to a second position, wherein the third and fourth lying block in the second position fill the funnel-shaped opening to a flat passage for the unwound metal, seen in the longitudinal direction.

15. Use of a device according to any of claims 1-9 and / or a method according to any of claims 10-14 for cutting metal into sheets for transformer cores.