Press brake and press brake control method

Abstract

To provide a press brake that can shorten a processing time for bending a sheet metal.SOLUTION: A control device controls a table lifting mechanism so that an upper table is moved up at a first or higher stages, to unload a sheet metal W, in an unloading period of time for calculating a spring-back quantity of the sheet metal W after the sheet metal W is bent at a temporary bending angle. The control device determines whether the unloading of the sheet metal W has been completed, on the basis of an amount of change or a rate of change of an angle of a first flange Wff measured by a first angle sensor 21F or of an angle of a second flange Wrf measured by a second angle sensor 21R, at the latest stage in the first or higher stages, and at a time point at which the sheet metal W is bent at a predetermined angle before the sheet metal W is unloaded or at the last minute stage in the first or higher stages.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a press brake and a press brake control method.

Background Art

[0002] A press brake includes an upper table on which a punch is mounted and a lower table on which a die is mounted. The upper table is lowered onto the lower table to sandwich a sheet metal placed on the die between the punch and the die and bend it (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Even if a sheet metal is bent to a target bending angle by a press brake, the bending angle of the sheet metal bent by springback becomes wider than the target bending angle. Therefore, in order to bend the sheet metal to the target bending angle, it is necessary to bend the sheet metal at a bending angle narrower than the target bending angle in consideration of the springback amount.

[0005] As described above, in order to bend a sheet metal to a desired target bending angle by a press brake, a unloading operation for calculating the springback amount is required. The unloading period for calculating the springback amount is one of the additional times other than the time required to actually bend the sheet metal within a series of steps from the start to the completion of bending the sheet metal. Other additional times may be required within a series of steps. Such additional time within a series of steps for bending a sheet metal is a factor that lengthens the processing time consisting of the series of steps. It is desired to shorten the processing time when bending a sheet metal as much as possible.

Means for Solving the Problems

[0006] A first aspect of one or more embodiments includes an upper table for mounting a punch, a lower table for mounting a die, a table lifting mechanism for raising and lowering the upper table or the lower table, and when bending a sheet metal by sandwiching the sheet metal between the punch and the die and raising and lowering the upper table or the lower table by the table lifting mechanism, a first angle sensor for measuring an angle of a first flange on a front side of the sheet metal with respect to the punch and the die, and a second angle sensor for measuring an angle of a second flange on a rear side of the sheet metal with respect to the punch and the die, and a control device for calculating a bending angle of the sheet metal based on the angles of the first and second flanges measured by the first and second angle sensors and controlling the raising and lowering of the upper table or the lower table by the table lifting mechanism, wherein the control device controls the table lifting mechanism to lower the upper table or raise the lower table to bend the sheet metal to a predetermined angle, and then controls the table lifting mechanism to raise the upper table in one or more steps or lower the lower table in one or more steps to unload the sheet metal. When unloading the sheet metal, based on a change amount or a change rate of the angle of the first flange measured by the first angle sensor or the angle of the second flange measured by the second angle sensor between the latest step in the one or more steps and the time point when the sheet metal was bent to the predetermined angle before unloading the sheet metal or the step immediately before in the one or more steps, a press brake is provided for determining whether the unloading of the sheet metal is completed.

[0007] A second aspect of one or more embodiments includes an upper table on which a punch is mounted, a lower table on which a die is mounted, a table lifting mechanism for raising and lowering the upper table or the lower table, and when bending a sheet metal by sandwiching the sheet metal between the punch and the die and raising and lowering the upper table or the lower table by the table lifting mechanism, a first angle sensor that measures the angle of a first flange on the front side of the sheet metal with respect to the punch and the die, and a second angle sensor that measures the angle of a second flange on the rear side of the sheet metal with respect to the punch and the die. A control device that controls a press brake includes controlling the table lifting mechanism to lower the upper table or raise the lower table to bend the sheet metal to a predetermined angle, and then controlling the table lifting mechanism to raise the upper table in one or more steps or lower the lower table in one or more steps to unload the sheet metal. When unloading the sheet metal, based on the amount of change or the rate of change of the angle of the first flange measured by the first angle sensor or the angle of the second flange measured by the second angle sensor at the latest step in the one or more steps and the time point when the sheet metal was bent to the predetermined angle before unloading the sheet metal or the step immediately before in the one or more steps, a press brake control method is provided for determining whether the unloading of the sheet metal is completed.

Advantages of the Invention

[0008] According to the press brake and the press brake control method according to one or more embodiments, the processing time when bending a sheet metal can be shortened.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 6C

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

[0010] Hereinafter, a press brake and a press brake control method according to one or more embodiments will be described with reference to the accompanying drawings.

[0011] FIG. 1 shows the overall configuration of a press brake 100 according to one or more embodiments. As shown in FIG. 1, the press brake 100 includes an NC (Numerical Control) device 10 that functions as a control device for controlling the press brake 100. A machining program database 50 is connected to the NC device 10 via a network. The press brake 100 includes an upper table 1, a lower table 3, and left and right side plates 5R and 5L. An upper die holder 2 is attached to the upper table 1, and a lower die holder 4 is attached to the lower table 3.

[0012] The upper table 1 is configured to move up and down by hydraulic cylinders 6L and 6R provided on the left and right. The hydraulic cylinders 6L and 6R will be referred to as a table lifting mechanism 6. The table lifting mechanism 6 may include actuators other than the hydraulic cylinders 6L and 6R. The table lifting mechanism 6 lowers the upper table 1 so as to approach the lower table 3 or raises it so as to be separated from the lower table 3.

[0013] The upper die holder 2 is equipped with the punch Tp which is the upper die, and the lower die holder 4 is equipped with the die Td which is the lower die. In FIG. 1, a modular type is shown in which the upper die holder 2 is integrally attached over the entire length of the lower end of the upper table 1, but an intermediate plate type in which a plurality of intermediate plates for mounting the punch Tp are attached in the longitudinal direction of the lower end of the upper table 1 may also be used. The intermediate plate is also an upper die holder.

[0014] Mounting the punch Tp on the upper table 1 means mounting the punch Tp on the upper die holder 2 or the intermediate plate. Mounting the die Td on the lower table 3 means mounting the die Td on the lower die holder 4. Two or more punches Tp may be mounted side by side on the upper table 1, and two or more dies Td may be mounted side by side on the lower table 3.

[0015] On the back side of the lower table 3, a back gauge 40 is arranged. The back gauge 40 includes abutments 42a and 42b that move in the left - right direction along the back gauge carriage 41. Here, the number of abutments is set to two, namely, abutments 42a and 42b, but the number of abutments is not limited to two. The abutments 42a and 42b are configured to move also in the height direction and the front - rear direction.

[0016] Before the operator places the sheet metal W to be processed on the die Td and bends the sheet metal W by sandwiching it between the punch Tp and the die Td, the abutments 42a and 42b move to positions corresponding to the die Td. The operator places the sheet metal W on the die Td such that the end on the back side of the sheet metal W abuts against the abutments 42a and 42b. That is, the abutments 42a and 42b act to determine the front - rear position of the sheet metal W when the sheet metal W is placed on the die Td.

[0017] On the left side of the press brake 100, an operation pendant 7 having a display unit 71 and an operation unit 72 including a plurality of operation buttons is attached via an arm 7a. The operation pendant 7 is connected to the NC device 10. A foot switch 8 having an open foot switch 81 for raising the upper table 1 and a closed foot switch 82 for lowering the upper table 1 is connected to the NC device 10.

[0018] FIG. 2 shows a configuration example of the angle sensors provided in the press brake 100. Although not shown in FIG. 1, as shown in FIG. 2, the press brake 100 includes angle sensors 21F and 21R for measuring the angle of the sheet metal W when bending the sheet metal W. The angle sensor 21F is the first angle sensor, and the angle sensor 21R is the second angle sensor. The angle sensor 21F is disposed on the front side of the die Td, and the angle sensor 21R is disposed on the rear side of the die Td. The angle sensors 21F and 21R are so-called contact type angle sensors. In the example shown in FIG. 2, the angle sensors 21F and 21R are disposed close to the die Td. The angle sensors 21F and 21R may be disposed at positions separated from the die Td.

[0019] The angle sensors 21F and 21R are each configured to move up and down by sensor elevating mechanisms 22F and 22R. When it is necessary to measure the angle of the sheet metal W, the angle sensors 21F and 21R located below move upward by the sensor elevating mechanisms 22F and 22R according to the control by the NC device 10.

[0020] The angle sensors 21F and 21R have a main body portion 211 and a protruding portion 212 that can protrude and retract with respect to the main body portion 211. At the upper end portion of the protruding portion 212, a slightly protruding tip portion 213 is provided. In the state before starting the processing of bending the sheet metal W shown in FIG. 2, the protruding portions 212 of the angle sensors 21F and 21R are in the state where they do not protrude the most. FIG. 3 shows the angle of the sheet metal W detected by the angle sensors 21F and 21R. As shown in FIG. 3, when the punch Tp descends and the sheet metal W is bent, the protruding portion 212 protrudes upward as the sheet metal W is displaced upward.

[0021] As shown in FIG. 3, the angle sensor 21F measures the angle θf formed by the back surface of the front flange Wff, which is on the front side of the punch Tp and die Td of the sheet metal W, and the center line of the punch Tp and die Td indicated by the dashed line. The angle sensor 21R measures the angle θr formed by the back surface of the rear flange Wrf, which is on the rear side of the punch Tp and die Td of the sheet metal W, and the center line of the punch Tp and die Td. The front flange Wff is the first flange, and the rear flange Wrf is the second flange. As shown in FIG. 2, the angles θf and θr measured by the angle sensors 21F and 21R are input to the NC device 10. The NC device 10 calculates the bending angle θw of the sheet metal W shown in FIG. 3 by adding the angle θf and the angle θr.

[0022] The angle sensor for measuring the angle of the sheet metal W is not limited to a contact type angle sensor, and a laser type angle sensor may be used. When a laser type angle sensor is used as the angle sensor, the sensor elevating mechanisms 22F and 22R are not necessary, and the laser type angle sensors on the front side and the rear side are at fixed positions in the height direction. The laser type angle sensors on the front side and the rear side include a laser light emitting unit that irradiates linear laser light on the back surfaces of the front flange Wff and the rear flange Wrf, and an imaging unit that captures the irradiated linear laser light. The NC device 10 obtains the angles θf and θr based on the angle of the linear laser light in the captured image by the imaging unit and calculates the bending angle θw of the sheet metal W.

[0023] In the press brake 100 configured as described above, the NC device 10 controls the press brake 100 to bend the sheet metal W according to the machining program stored in the machining program database 50.

[0024] Figure 4 shows an example of the control operation by the NC device 10. In Figure 4, it shows a state where the additional time other than the time required to actually bend the sheet metal W, such as the unloading period for calculating the springback amount, is not shortened by the specific time-saving method executed by the press brake 100. In Figure 4, the horizontal axis represents time, and the vertical axis represents the position in the height direction of the tip of the punch Tp. In Figure 4, the state between the position R3 and the position F3 is shown in an enlarged state for easy understanding of the change in the position in the height direction of the tip of the punch Tp. The distance from the position R3 to the position F3 is about 0.1 mm to 0.2 mm. Also, the distance from the contact position described later to the position F3 is about 2 mm to 3 mm.

[0025] Assume that the target bending angle of the sheet metal W is, for example, 90 degrees. The NC device 10 controls the lifting of the upper table 1 to bend the sheet metal W to the target bending angle of 90 degrees as shown in Figure 4. When the NC device 10 starts to lower the upper table 1, the tip of the punch Tp contacts the sheet metal W. The NC device 10 stops the upper table 1 with the tip of the punch Tp located at the contact position in Figure 4, and separates the stoppers 42a and 42b from the sheet metal W.

[0026] During the temporary bending period after the tip of the punch Tp contacts the sheet metal W, the NC device 10 lowers the position of the tip of the punch Tp to the position T1 and temporarily stops it, and then further lowers it to the position T2. In Figure 4, the upper table 1 (punch Tp) is lowered in two steps, but the number of lowering steps is not limited to two.

[0027] The position T2 during the temporary bending period is a position for bending to a predetermined temporary bending angle wider than 90 degrees of the target bending angle. The NC device 10 controls the table lifting mechanism 6 to lower the upper table 1 by a first depth value for bending the sheet metal W to the temporary bending angle during the temporary bending period. The first depth value of the punch Tp for bending the sheet metal W to the temporary bending angle after the tip of the punch Tp contacts the sheet metal W has been obtained in advance based on the bending theory. The depth value is the amount of descent of the punch Tp when the reference is the contact position where the tip of the punch Tp contacts the sheet metal W. That is, the depth value indicates the position of the tip of the punch Tp in the height direction. Hereinafter, the depth value is abbreviated as the D value.

[0028] At the completion of the temporary bending operation, the NC device 10 calculates a first bending angle θw1 as the bending angle θw of the sheet metal W based on the angles θf and θr of the front flange Wff and the rear flange Wrf measured by the angle sensors 21F and 21R. The NC device 10 holds the first bending angle θw1 at the completion of the temporary bending operation of the sheet metal W.

[0029] When the sheet metal W is bent to the temporary bending angle, the NC device 10 shifts the press brake 100 to an unloading period for calculating the springback amount. During the unloading period, the NC device 10 controls the upper table 1 to be raised in multiple steps in order to unload the sheet metal W while maintaining the state where the punch Tp is in contact with the sheet metal W. Unloading means removing the load applied to the sheet metal W.

[0030] In FIG. 4, the NC device 10 raises the position of the tip of the punch Tp to position R1 and temporarily stops, and calculates the bending angle θw of the sheet metal W based on the angles θf and θr measured by the angle sensors 21F and 21R. Subsequently, the NC device 10 raises the position of the tip of the punch Tp to position R2 and temporarily stops, and calculates the bending angle θw of the sheet metal W. At this time, if the difference between the bending angle θw(R1) at position R1 and the bending angle θw(R2) at position R2 is within the threshold value, it means that the unloading of the sheet metal W is completed. FIG. 4 shows an example where, at position R2, the difference between the bending angle θw(R1) and the bending angle θw(R2) is not within the threshold value, and it is determined that the unloading of the sheet metal W is not completed.

[0031] In this way, in the multi-stage unloading of the sheet metal W during the unloading period, it is possible to determine whether the unloading of the sheet metal W is completed based on whether the difference between the bending angle θw of the sheet metal W at the position of the stage immediately before the tip of the punch Tp and the bending angle θw of the sheet metal W at the position of the latest stage is within the threshold value. This method of determining whether the unloading of the sheet metal W is completed based on the bending angle θw of the sheet metal W is a commonly used determination method in the past.

[0032] The NC device 10 raises the position of the tip of the punch Tp to position R3 and temporarily stops, and calculates the bending angle θw of the sheet metal W. If the difference between the bending angle θw(R2) at position R2 and the bending angle θw(R3) at position R3 is within the threshold value, the NC device 10 determines that the unloading of the sheet metal W is completed at position R3. Note that at which stage the NC device 10 determines that the unloading of the sheet metal W is completed varies depending on various conditions such as the distance from position T2 to position R1, the distance from position R1 to position R2, and the distance from position R2 to position R3.

[0033] During the unloading period, with the sheet metal W in the unloaded state, the NC device 10 calculates a second bending angle θw2 as the bending angle θw of the sheet metal W based on the angles θf and θr measured by the angle sensors 21F and 21R. Even if it is bent to the first bending angle θw1 during the pre-bending period, when the sheet metal W is unloaded during the unloading period, the bending angle expands due to springback. The second bending angle θw2 is the bending angle θw of the sheet metal W expanded by springback. The NC device 10 calculates the springback amount by subtracting the first bending angle θw1 from the second bending angle θw2.

[0034] If the springback amount based on the difference between the second bending angle θw2 and the first bending angle θw1 is obtained during the unloading period, the NC device 10 shifts the press brake 100 to the drawing-in period. The NC device 10 calculates a second D value considering the springback amount for bending the sheet metal W to the target bending angle. Simply put, if the springback amount is, for example, 2 degrees, it is conceivable to lower the upper table 1 by the amount of descent that can bend the sheet metal W at a bending angle of 88 degrees with the target bending angle set to 88 degrees. However, since the springback amount generally varies depending on the target bending angle, if the springback amount obtained during the unloading period is used as it is to set the target bending angle, it may not reach 90 degrees of the target bending angle.

[0035] Therefore, instead of using the springback amount obtained during the unloading period as it is, it is better for the NC device 10 to correct the springback amount obtained during the unloading period and then calculate a second D value for bending the sheet metal W to the set target bending angle.

[0036] During the pressing period, the NC device 10 controls the table lifting mechanism 6 to lower the upper table 1 in multiple steps by dividing the second D value into a plurality of parts, each time by the second D value. In FIG. 4, the NC device 10 lowers the tip position of the punch Tp from position R3 to position F1 and temporarily stops to calculate the bending angle θw of the sheet metal W. Subsequently, the NC device 10 lowers the tip position of the punch Tp to position F2 considering the bending angle at position F1 and temporarily stops to calculate the bending angle θw of the sheet metal W. Further, the NC device 10 lowers the tip position of the punch Tp to position F3 where the final bending angle of the sheet metal W becomes 90 degrees, which is the target bending angle, considering the bending angle at position F2.

[0037] Here, the pressing operation during the pressing period is divided into three steps, but it may be one step, two steps, or four or more steps. The number of steps of the pressing operation is not limited.

[0038] Once the sheet metal W is bent to the target bending angle, the NC device 10 shifts the press brake 100 to the final angle measurement period. The NC device 10 unloads the sheet metal W while maintaining the state where the punch Tp is in contact with the sheet metal W, and calculates the final bending angle θw of the sheet metal W based on the angles θf and θr measured by the angle sensors 21F and 21R.

[0039] In FIG. 4, the NC device 10 raises the tip position of the punch Tp to position L1 and temporarily stops to calculate the bending angle θw of the sheet metal W. Subsequently, the NC device 10 raises the tip position of the punch Tp to position L2 and temporarily stops to calculate the bending angle θw of the sheet metal W. Similar to the unloading during the unloading period, if the difference between the bending angle θw(L2) at position L2 and the bending angle θw(L1) at position L1 is within the threshold value, it means that the unloading of the sheet metal W is completed. If the difference between the bending angle θw(L2) at position L2 and the bending angle θw(L1) at position L1 is within the threshold value, the NC device 10 determines that the unloading of the sheet metal W is completed at position L2.

[0040] In the state where the sheet metal W is unloaded, the NC device 10 calculates the final bending angle θw of the sheet metal W. Subsequently, the NC device 10 controls the table lifting mechanism 6 to raise the upper table 1.

[0041] Next, in the control operation by the NC device 10 shown in FIG. 4, a specific time shortening method executed by the press brake 100 for shortening additional time such as the unloading period for calculating the springback amount will be described. FIG. 5 shows the position of the tip of the punch Tp, the angles θf and θr of the front flange Wff and the rear flange Wrf, and the measured values of the bending angle θw of the sheet metal W when the NC device 10 controls the table lifting mechanism 6 to lower and raise the upper table 1 in the same manner as in FIG. 4. The thick solid line indicates the position of the tip of the punch Tp, the thin solid line indicates the bending angle θw, the one-dot chain line indicates the angle θf, and the broken line indicates the angle θr. However, the position in the height direction of the waveform indicating the bending angle θw of the sheet metal W is shifted to be located between the angle θf and the angle θr for easy understanding that it is obtained from the angle θf and the angle θr. The bending angle θw is the angle obtained by adding the angle θf and the angle θr.

[0042] In FIG. 5, at the position R1 during the unloading period, the angle θf of the sheet metal W is larger than the angle θr. However, at the position R2, the angle θr becomes larger than the angle θf, and the magnitude relationship between the angle θf and the angle θr is reversed. Thus, the fact that the angle θf or θr of the sheet metal W fluctuates greatly means that the unloading is actually already completed at the time of the position R2. Let the angles θf and θr at the immediately preceding stage during the unloading period be the angles θf(n - 1) and θr(n - 1) respectively. Let the angles θf and θr at the latest stage during the unloading period be the angles θf(n) and θr(n) respectively.

[0043] If the NC device 10 satisfies at least one of a first condition that the absolute value of the angular difference between the angle θf and the angle θf(n - 1) exceeds a predetermined magnitude, and a second condition that the absolute value of the angular difference between the angle θr(n) and the angle θr(n - 1) exceeds a predetermined magnitude, it can be determined that the unloading of the sheet metal W is completed. Whether the first condition is satisfied or not, and whether the second condition is satisfied or not can be determined as follows.

[0044] When the NC device 10 satisfies equation (1) or equation (2), it determines that the unloading of the sheet metal W is completed. The first threshold value Δθfth and the second threshold value Δθrth may be the same value or different values. The first threshold value Δθfth and the second threshold value Δθrth are threshold values of the angular difference. In one stage during the unloading period, the NC device 10 may determine that the unloading of the sheet metal W is completed when both equation (1) and equation (2) are satisfied. Equation (1) is a first determination formula using the angular difference between the angle θf(n) and the angle θf(n - 1), and equation (2) is a second determination formula using the angular difference between the angle θr(n) and the angle θr(n - 1). |θf(n)-θf(n - 1)|>Δθfth …(1) |θr(n)-θr(n - 1)|>Δθrth …(2)

[0045] The NC device 10 may determine whether the unloading of the sheet metal W is completed by using expressions (3) to (6) instead of expression (1) or expression (2). Expression (3) represents the ratio Ratioθf between the angle θf(n) and the angle θf(n - 1), and expression (4) represents the ratio Ratioθr between the angle θr(n) and the angle θr(n - 1). The NC device 10 can determine that the unloading of the sheet metal W is completed if at least one of the following conditions is met: the third condition that the absolute value obtained by subtracting Ratioθf from 1 exceeds the third threshold Ratioθfth; and the fourth condition that the absolute value obtained by subtracting Ratioθr from 1 exceeds the fourth threshold Ratioθrth. The third threshold Ratioθfth and the fourth threshold Ratioθrth may be the same value or different values. The third threshold Ratioθfth and the fourth threshold Ratioθrth are thresholds for the ratio of the changed angles (angle change ratio). The NC device 10 may also determine that the unloading of the sheet metal W is completed when both expressions (5) and (6) are satisfied.

[0046] θf(n) / θf(n - 1)=Ratioθf …(3) θr(n) / θr(n - 1)=Ratioθr …(4) |1 - Ratioθf|>Ratioθfth …(5) |1 - Ratioθr|>Ratioθrth …(6)

[0047] Expressions (3) and (5) are the third determination expressions using the ratio between the angle θf(n) and the angle θf(n - 1). Expressions (4) and (6) are the fourth determination expressions using the ratio between the angle θr(n) and the angle θr(n - 1).

[0048] When the NC device 10 satisfies formula (7), it may determine whether the unloading of the sheet metal W is completed using formula (8), and when it satisfies formula (9), it may determine whether the unloading of the sheet metal W is completed using formula (10). Formulas (8) and (10) are formulas for determining whether the unloading of the sheet metal W is completed based on the angle difference between the angle θf of the front flange Wff and the angle θr of the rear flange Wrf. The NC device 10 may determine that the unloading of the sheet metal W is completed if it satisfies the fifth condition that the value obtained by subtracting the angle θr(n) from the angle θf(n) is less than the fifth threshold value Δθfr, or if it satisfies the sixth condition that the value obtained by subtracting the angle θf(n) from the angle θr(n) is less than the fifth threshold value Δθfr. The fifth threshold value Δθfr is a threshold value for the angle difference.

[0049] θf(n - 1)>θr(n - 1) …(7) θf(n)-θr(n)<Δθfr …(8) θf(n - 1)<θr(n - 1) …(9) θr(n)-θf(n)<Δθfr …(10)

[0050] Formulas (7) to (10) are the fifth determination formulas using the magnitude relationship between the angle θf(n - 1) and the angle θr(n - 1) and the angle difference between the angle θf(n) and the angle θr(n).

[0051] Furthermore, the NC device 10 may determine whether the unloading of the sheet metal W is completed using formulas (11) to (13). Let the bending angle θw at the immediately preceding stage during the unloading period be the bending angle θw(n - 1), and the bending angle θw at the latest stage during the unloading period be the bending angle θw(n). Let the value obtained by subtracting the ratio of the angle θr(n - 1) to the bending angle θw(n - 1) from the ratio of the angle θf(n - 1) to the bending angle θw(n - 1) be Ratioθ(n - 1). Let the value obtained by subtracting the ratio of the angle θrn to the bending angle θwn from the ratio of the angle θfn to the bending angle θwn be Ratioθn. The NC device 10 may determine that the unloading of the sheet metal W is completed if it satisfies the seventh condition that the absolute value of the difference between the value Ratioθ(n - 1) and the value Ratioθn exceeds the sixth threshold value ΔRatioθ. The sixth threshold value ΔRatioθ is a threshold value for the angle change ratio.

[0052] {θf(n - 1) / θw(n - 1)} - {θr(n - 1) / θw(n - 1)} = Ratioθ(n - 1) …(11) (θfn / θwn) - (θrn / θwn) = Ratioθn …(12) |Ratioθ(n - 1) - Ratioθn| > ΔRatioθ …(13)

[0053] Equations (11) to (13) are the sixth determination expressions using the ratios of the angle θf(n - 1) to the bending angle θw(n - 1), the angle θr(n - 1) to the bending angle θw(n - 1), the angle θf(n) to the bending angle θw, and the angle θr(n) to the bending angle θw.

[0054] In FIGS. 6A and 6B, the sheet metal W indicated by the two-dot chain line shows the position of the sheet metal W at the stage immediately before the unloading period, and the sheet metal W indicated by the solid line shows the position of the sheet metal W at the latest stage during the unloading period, each exaggeratedly shown. As in the example at the position R2 in FIG. 5, the magnitude relationship between the angle θf and the angle θr is reversed when the bent sheet metal W changes from a state tilted more on the front side to a state tilted more on the rear side or vice versa, as shown in FIG. 6A or FIG. 6B.

[0055] FIGS. 6A and 6B show examples where the sheet metal W changes from a state tilted more on the front side to a state tilted more on the rear side or vice versa. Different from these, as exaggeratedly shown in FIG. 6C, there may be a case where the sheet metal W changes such that the tilt further increases from a state tilted more on the front side or the rear side. In particular, when there is a large difference between the length of the front flange Wff and the length of the rear flange Wrf, the tilt may increase due to the difference in the weight of the flanges. FIG. 6C shows a case where the length of the rear flange Wrf is longer than the length of the front flange Wff and the tilt of the sheet metal W further increases to the rear side from a state tilted more on the rear side.

[0056] As can be seen from the bending angle θw of the sheet metal W indicated by the thin solid line at positions R2 and R3 in FIG. 5, the bending angle θw hardly changes between positions R2 and R3. This is evidence that the unloading of the sheet metal W has already been completed at position R2. According to the conventional method for determining whether the unloading of the sheet metal W based on the bending angle θw of the sheet metal W has been completed, as shown in FIG. 5, since there is a predetermined difference between the bending angle θw(R1) and the bending angle θw(R2), it is determined that the unloading of the sheet metal W has not been completed at position R2.

[0057] In contrast, according to a new method for determining whether the unloading of the sheet metal W has been completed by using at least one of the first to sixth determination formulas executed by the press brake 100, it can be determined that the unloading of the sheet metal W has been completed at position R2. That is, by using the new determination method executed by the press brake 100, it is not necessary to provide the stage of position R3 in the unloading period shown in FIG. 4.

[0058] Furthermore, in FIG. 5, at position F2, which is the last stage of the pressing-in period, the angle θf is larger than the angle θr. However, at position L1 in the final angle measurement period, the angle θr becomes larger than the angle θf, and the magnitude relationship between the angle θf and the angle θr is reversed. Therefore, since the angle θf or θr fluctuates greatly at position L1 in the final angle measurement period, it means that the unloading has actually been completed at the time of position L1. The NC device 10 can also determine whether the unloading of the sheet metal W has been completed by using at least one of the first to sixth determination formulas during the final angle measurement period, similar to the unloading period.

[0059] However, when the angles θf and θr at position L1 in the final angle measurement period are the angles θf(n) and θr(n) of the latest stage, the angles θf and θr at position F2 (position F3 in FIG. 4), which is the last stage of the pressing-in period, are the angles θf(n - 1) and θr(n - 1) of the previous stage.

[0060] As can be seen from the bending angle θw of the sheet metal W at the positions L1 and L2 in FIG. 5, the bending angle θw hardly changes between the positions L1 and L2. This is evidence that the unloading of the sheet metal W has already been completed at the position L1. According to the conventional method for determining whether the unloading of the sheet metal W based on the bending angle θw of the sheet metal W has been completed, as shown in FIG. 5, there is a large difference between the bending angle θw at the position F2 and the bending angle θw at the position L1. Therefore, it is determined that the unloading of the sheet metal W has not been completed at the position L1.

[0061] In contrast, according to the new determination method executed by the press brake 100, it can be determined that the unloading of the sheet metal W has been completed at the position L1. That is, if the new determination method executed by the press brake 100 is used, it is not necessary to provide the stage of the position L2 in the final angle measurement period shown in FIG. 4.

[0062] As described above, when the new determination method executed by the press brake 100 is used, it is not necessary to provide the stage of the position R3 in the unloading period and the stage of the position L2 in the final angle measurement period shown in FIG. 4. Therefore, the NC device 10 may execute a control operation that does not include the positions R3 and L2 as shown in FIG. 7. As is clear from comparing FIG. 4 and FIG. 7, when the new determination method executed by the press brake 100 is used, the unloading period required to calculate the springback amount can be shortened, and the final angle measurement period required to calculate the final bending angle θw of the sheet metal W can be shortened.

[0063] In the example shown in FIG. 7, although the unloading of the sheet metal W is completed at position R2 during the unloading period, it is possible that the unloading of the sheet metal W is determined to be completed at position R1, which is the first stage during the unloading period. When the NC device 10 determines that the unloading of the sheet metal W is completed using at least one of the first to sixth determination formulas at position T2, which is the last stage during the pre-bending period, and position R1, which is the first stage during the unloading period, it shifts to the pressing-in period without providing the stage of position R2. In this case, the angles θf and θr at position R1 during the unloading period are the angles θf(n) and θr(n) of the latest stage, and the angles θf and θr at position T2, which is the last stage of the pre-bending period, are the angles θf(n - 1) and θr(n - 1) of the previous stage.

[0064] When using the new determination method executed by the press brake 100, within a series of processes for bending the sheet metal W, the unloading period, which is additional time other than the time required to actually bend the sheet metal W, for calculating the springback amount, and the final angle measurement period for calculating the final bending angle θw of the sheet metal W can be shortened. By using the new determination method executed by the press brake 100, it can be expected to shorten the time by several hundred milliseconds during the unloading period. It can also be expected to shorten the time during the final angle measurement period. According to the press brake 100, the processing time for bending the sheet metal W can be shortened.

[0065] Note that it is not essential to provide the final angle measurement period to calculate the final bending angle θw of the sheet metal W, and it may be omitted. In this case, only the unloading period can be shortened. If the final angle measurement period is provided, the operator does not need to measure, for example, using a digital bending angle meter whether the sheet metal W is actually bent to the target bending angle.

[0066] Using the flowcharts shown in FIGS. 8 and 9, the operation of the press brake 100 and the press brake control method executed by the press brake 100 will be described. In FIG. 8, when the bending process is started, the NC device 10 controls the table lifting mechanism 6 to lower the upper table 1 by a first D value so as to bend the sheet metal W to a predetermined temporary bending angle wider than the target bending angle at step S1. The NC device 10 calculates the first bending angle θw1 of the sheet metal W at step S2.

[0067] At step S3, the NC device 10 controls the table lifting mechanism 6 to raise the upper table 1 until the unloading of the sheet metal W is completed. The NC device 10 calculates the second bending angle θ2 of the sheet metal W at step S4. The NC device 10 calculates the springback amount based on the difference between the second bending angle θw2 and the first bending angle θw1 at step S5. The NC device 10 calculates the second D value of the upper table 1 for bending the sheet metal W to the target bending angle in consideration of the springback amount at step S6.

[0068] At step S7, the NC device 10 controls the table lifting mechanism 6 to lower the upper table 1 in one or more stages based on the second D value to bend the sheet metal W to the target bending angle. At step S8, the NC device 10 controls the table lifting mechanism 6 to raise the upper table 1 until the unloading of the sheet metal W is completed. The NC device 10 calculates the final bending angle of the sheet metal W at step S9. The NC device 10 raises the upper table 1 at step S10 to end the bending process.

[0069] FIG. 9 shows the specific processes of steps S3 and S8. Here, the case of using the first determination formula, formula (1), or the second determination formula, formula (2), is taken as an example. Step S3 consists of steps S31 and S32, and step S8 consists of steps S81 and S82. The NC device 10 controls the table lifting mechanism 6 to raise the upper table 1 by one step at step S31 or S81 following step S2 or S7 in FIG. 8. The NC device 10 determines whether or not to satisfy formula (1) or formula (2) at step S32 or S82. If formula (1) or formula (2) is not satisfied (NO), the NC device 10 repeats steps S31 or S81 and steps S32 or S82. If formula (1) or formula (2) is satisfied (YES), the NC device 10 transfers the process to step S4 or S9 in FIG. 8.

[0070] As described above, the press brake 100 unloads the sheet metal W during the unloading period for calculating the springback amount of the sheet metal W bent at the temporary bending angle following the temporary bending period of bending the sheet metal W to a predetermined temporary bending angle wider than the target bending angle, and during the final angle measurement period for calculating the final bending angle of the sheet metal W following the pressing period of bending the sheet metal W to the target bending angle. At this time, the NC device 10 may determine whether or not the unloading of the sheet metal W is completed based on the change amount or change rate of the angle of the front flange Wff measured by the angle sensor 21F or the angle of the rear flange Wrf measured by the angle sensor 21R between the latest stage in one or more stages and the time when the sheet metal W was bent to a predetermined angle before unloading the sheet metal W or the immediately preceding stage in one or more stages.

[0071] When performing the control operation as shown in FIG. 7, the NC device 10 preferably controls the table lifting mechanism 6 as shown in FIGS. 10 to 12.

[0072] In FIG. 10, let the rising amount of the upper table 1 from the position T2 of the tip of the punch Tp at the end of the temporary bending period to the position R1, which is the stage immediately before the position R2 where the unloading of the sheet metal W is completed, be UR1. Let the rising amount of the upper table 1 from the position F3 of the tip of the punch Tp at the end of the pressing-in period, which is the rising amount of the upper table 1 at the beginning of the final angle measurement period, to the position L1 be UL1. As a first example, it is preferable to set the rising amount UR1 to the rising amount UL1. If the rising amount for raising the upper table 1 for unloading until the stage immediately before the unloading of the sheet metal W is completed during the unloading period is set to the rising amount of the upper table 1 at the beginning of the final angle measurement period, the time required for unloading during the final angle measurement period can be shortened.

[0073] FIG. 10 shows an example in which the final angle measurement period is in two stages at positions L1 and L2. However, similar to FIG. 7, the final angle measurement period may be in one stage at position L1. The first example can be used when the unloading period has at least two stages.

[0074] In FIG. 11, let the rising amount of the upper table 1 from the position T2 of the tip of the punch Tp at the end of the temporary bending period to the position R2 where the unloading of the sheet metal W is completed be UR2. As a second example, it is preferable to set the rising amount k×UR2, which is obtained by multiplying the rising amount UR2 by a predetermined coefficient k less than 1, to the rising amount UL1. If the rising amount for raising the upper table 1 for unloading until the stage where the unloading of the sheet metal W is completed during the unloading period is set to the rising amount of the upper table 1 at the beginning of the final angle measurement period after reducing it by a predetermined ratio, the time required for unloading during the final angle measurement period can be shortened.

[0075] FIG. 11 shows an example in which the final angle measurement period is in two stages at positions L1 and L2. However, similar to FIG. 7, the final angle measurement period may be in one stage at position L1.

[0076] As shown in FIG. 12, as a third example, the ascending amount UR2 may be set to the ascending amount UL1. If the ascending amount for raising the upper table 1 for unloading until the stage where the unloading of the sheet metal W in the unloading period is completed is set to the ascending amount of the first upper table 1 in the final angle measurement period, the time required for unloading in the final angle measurement period can be shortened. FIG. 12 shows an example where the final angle measurement period is one stage at position L1, but it may be two or more stages.

[0077] As in the first to third examples above, based on the ascending amount of the upper table 1 until the stage immediately before the unloading of the sheet metal W in the unloading period is completed, or until the stage where the unloading of the sheet metal W is completed, the ascending amount of the first stage of the upper table 1 in the final angle measurement period may be set. By doing so, it is possible to obtain both the effect of shortening the processing time by adopting the new determination method for determining whether or not the unloading of the sheet metal W described above is completed and the effect of shortening the processing time by adopting the first to third examples.

[0078] The present invention is not limited to one or more of the embodiments described above, and various modifications can be made without departing from the gist of the present invention. In one or more of the embodiments described above, the upper table 1 is a slide table that can be raised and lowered, and the lower table 3 is a fixed table with a fixed position. However, it is also possible to make the upper table 1 a fixed table and the lower table 3 a slide table. In this case, the table lifting mechanism 6 raises and lowers the lower table 3. The raising and lowering of the upper table 1 are respectively read as the lowering and raising of the lower table 3, and the first lowering amount and the second lowering amount of the upper table 1 are read as the first raising amount and the second raising amount of the lower table 3.

[0079] In one or more embodiments, with reference to the position where the pressure applied to the sheet metal W becomes a specified pressure by lowering the punch Tp toward the die Td until the punch Tp contacts the sheet metal W, the amount of descent when the punch Tp is lowered beyond the reference position is defined as the D value. When the upper table 1 is the fixed table and the lower table 3 is the slide table, the amount of ascent when the die Td is raised beyond the reference position may be defined as the D value, with reference to the position where the pressure applied to the sheet metal W becomes a specified pressure by raising the die Td toward the punch Tp until the die Td contacts the sheet metal W.

Explanation of Signs

[0080] 1 Upper table 2 Upper die holder 3 Lower table 4 Lower die holder 5L, 5R Side plates 6 Table lifting mechanism 6L, 6R Hydraulic cylinders (table lifting mechanism) 7 Operating pendant 8 Foot switch 10 NC device 21F Angle sensor (first angle sensor) 21R Angle sensor (second angle sensor) 22F, 22R Sensor lifting mechanism 40 Back gauge 41 Back gauge carriage 42a, 42b Stops 100 Press brake Td Die Tp Punch W Sheet metal Wff Front flange (first flange) Wrf Rear flange (second flange)

Claims

1. an upper table for mounting a punch, a lower table for mounting a die, a table lifting mechanism for raising and lowering the upper table or the lower table, a first angle sensor for measuring an angle of a first flange on a front side of the sheet metal with respect to the punch and the die when the sheet metal is bent by raising and lowering the upper table or the lower table by the table lifting mechanism with the sheet metal sandwiched between the punch and the die, and a second angle sensor for measuring an angle of a second flange on a rear side of the sheet metal with respect to the punch and the die, a control device that calculates a bending angle of the sheet metal based on the angles of the first and second flanges measured by the first and second angle sensors and controls raising and lowering of the upper table or the lower table by the table lifting mechanism, comprising the control device controls the table lifting mechanism to lower the upper table or raise the lower table to bend the sheet metal to a predetermined angle, and then controls the table lifting mechanism to raise the upper table in one or more steps or lower the lower table in one or more steps to unload the sheet metal, determines whether unloading of the sheet metal is completed based on a change amount or change rate of the angle of the first flange measured by the first angle sensor or the angle of the second flange measured by the second angle sensor between the latest step in the one or more steps and a time point when the sheet metal was bent to the predetermined angle before unloading the sheet metal or the step immediately before in the one or more steps a press brake.

2. The press brake according to claim 1, wherein the control device determines whether unloading of the sheet metal is completed based on a change amount or change rate of the angle of the first flange or the angle of the second flange during an unloading period for calculating a springback amount of the sheet metal bent to the temporary bending angle, which follows a temporary bending period in which the sheet metal is bent to a predetermined temporary bending angle wider than a target bending angle.

3. In the final angle measurement period for calculating the final bending angle of the sheet metal, which follows the pressing period during which the control device bends the sheet metal to the target bending angle, the press brake according to claim 1 or 2 determines whether unloading of the sheet metal is completed based on the amount of change or the rate of change of the angle of the first flange or the angle of the second flange.

4. A control device for controlling a press brake, the press brake comprising: an upper table on which a punch is mounted; a lower table on which a die is mounted; a table lifting mechanism for raising and lowering the upper table or the lower table; a first angle sensor for measuring the angle of a first flange on the front side of the sheet metal with respect to the punch and the die when bending the sheet metal by raising and lowering the upper table or the lower table by the table lifting mechanism with the sheet metal sandwiched between the punch and the die; and a second angle sensor for measuring the angle of a second flange on the rear side of the sheet metal with respect to the punch and the die. After controlling the table lifting mechanism to lower the upper table or raise the lower table to bend the sheet metal to a predetermined angle, when unloading the sheet metal by controlling the table lifting mechanism to raise the upper table in one or more steps or lower the lower table in one or more steps, it is determined whether unloading of the sheet metal is completed based on the amount of change or the rate of change of the angle of the first flange measured by the first angle sensor or the angle of the second flange measured by the second angle sensor between the latest step in the one or more steps and the time when the sheet metal was bent to the predetermined angle before unloading the sheet metal or the step immediately before in the one or more steps. Press brake control method.

5. In the unloading period for calculating the springback amount of the sheet metal bent to the temporary bending angle, which follows the temporary bending period during which the control device bends the sheet metal to a predetermined temporary bending angle wider than the target bending angle, the press brake control method according to claim 4 determines whether unloading of the sheet metal is completed based on the amount of change or the rate of change of the angle of the first flange or the angle of the second flange.

6. The press brake control method according to claim 4 or 5, wherein the control device determines whether or not unloading of the sheet metal is completed based on a change amount or a change rate of an angle of the first flange or an angle of the second flange during a final angle measurement period for calculating a final bending angle of the sheet metal, which follows a pressing period for bending the sheet metal to a target bending angle.

Images