Press brake and press brake control method

Abstract

According to the present invention, a control device, during an unloading period for calculating the springback amount of sheet metal (W) that has been bent at a temporary bending angle, controls a table raising / lowering mechanism to raise an upper table in one or more stages, thereby unloading the sheet metal (W). In the most recent stage among the one or more stages and at the time when the sheet metal (W) that has yet to be unloaded is bent at a prescribed angle or in the immediately preceding stage among the one or more stages, the control device determines whether the unloading of the sheet metal (W) has been completed on the basis of the amount of change or the rate of change in the angle of a first flange (Wff) measured by a first angle sensor (21F) or the amount of change or the rate of change in the angle of a second flange (Wrf) measured by a second angle sensor (21R).

Description

Press brake and press brake control method

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

[0002] A press brake has an upper table on which a punch is attached and a lower table on which a die is attached, and the upper table is lowered onto the lower table, and the sheet metal placed on the die is sandwiched between the punch and the die and bent (see Patent Document 1).

[0003] Patent No. 4280332

[0004] Even if a sheet metal is bent to a target bending angle using a press brake, the bending angle of the bent sheet metal will be wider than the target bending angle due to springback. 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, taking into account the amount of springback.

[0005] Thus, in order to bend a sheet metal to a desired target bending angle using a press brake, an unloading operation is required to calculate the amount of springback. The unloading period for calculating the amount of springback is one of the additional times, other than the time required to actually bend the sheet metal, in the series of steps from the start of bending the sheet metal to the completion of bending. Other additional times may also be required in the series of steps. Such additional time in the series of steps for bending the sheet metal increases the processing time of the series of steps. It is desirable to shorten the processing time when bending sheet metal as much as possible.

[0006] A first aspect of one or more embodiments includes an upper table on which a punch is attached, a lower table on which a die is attached, 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 of the metal sheet on a front side of the punch and the die and a second angle sensor for measuring an angle of a second flange of the metal sheet on a rear side of the punch and the die when the upper table or the lower table is raised and lowered by the table lifting mechanism with the metal sheet sandwiched between the punch and the die, and a control device for controlling the raising and lowering of the upper table or the lower table by the table lifting mechanism. and a control device for controlling the table lifting mechanism to lower the upper table or raise the lower table, and when the control device controls the table lifting mechanism to raise the upper table in one or more stages or lower the lower table in one or more stages to unload the sheet metal, the control device determines whether unloading of the sheet metal is complete based on the amount or rate of change in 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 stage of the one or more stages and the point at which the sheet metal was bent to the predetermined angle before unloading the sheet metal or the immediately preceding stage of the one or more stages.

[0007] In a second aspect of one or more embodiments, a control device for controlling a press brake includes an upper table on which a punch is attached, a lower table on which a die is attached, 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 of the metal sheet on a front side of the punch and the die, and a second angle sensor for measuring an angle of a second flange of the metal sheet on a rear side of the punch and the die when the upper table or the lower table is raised and lowered by the table lifting mechanism with the metal sheet sandwiched between the punch and the die to bend the metal sheet, and a control device for controlling a press brake includes a control device for lowering the upper table or a control device for lifting the lower table. and a press brake control method for determining whether or not unloading of the sheet metal has been completed based on the amount or rate of change in 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 stage of the one or more stages and the point at which the sheet metal was bent to the predetermined angle before unloading the sheet metal or the latest stage of the one or more stages and the point at which the sheet metal was bent to the predetermined angle before unloading the sheet metal or the immediately preceding stage of the one or more stages.

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

[0009] FIG. 1 is a diagram illustrating the overall configuration of a press brake according to one or more embodiments. FIG. 2 is a diagram illustrating an example of the configuration of an angle sensor included in the press brake according to one or more embodiments. FIG. 3 is a diagram illustrating the angle of the sheet metal detected by the angle sensor shown in FIG. 2. FIG. 4 is an example of a control operation by an NC device included in the press brake according to one or more embodiments, illustrating a state in which additional time other than the time required to actually bend the sheet metal is not reduced by a unique time-reducing method implemented by the press brake according to one or more embodiments. FIG. 5 is a diagram illustrating an example of the position of the punch tip, the angles of the front flange and rear flange, and the actual measured values ​​of the bend angle of the sheet metal when the NC device controls the table lifting mechanism to lower and raise the upper table to bend the sheet metal. FIG. 6A is a conceptual diagram illustrating a state in which the bent sheet metal changes from a state tilted more toward the front side to a state tilted more toward the rear side due to unloading. FIG. 6B is a conceptual diagram illustrating a state in which the bent sheet metal changes from a state tilted more toward the rear side to a state tilted more toward the front side due to unloading. FIG. 6C is a conceptual diagram showing a state in which the bent sheet metal changes from a state in which it is tilted further rearward due to unloading to an increasingly tilted state further rearward. FIG. 7 is an example of a control operation by an NC device provided in a press brake according to one or more embodiments, showing a state in which additional time other than the time required to actually bend the sheet metal is reduced by a unique time-reducing method executed by the press brake according to one or more embodiments. FIG. 8 is a flowchart showing the operation of a press brake according to one or more embodiments and a press brake control method according to one or more embodiments. FIG. 9 is a flowchart showing specific processing of steps S3 and S8 of FIG. 8. FIG. 10 is a diagram showing a first preferred example of a control operation by an NC device provided in a press brake according to one or more embodiments. FIG. 11 is a diagram showing a second preferred example of a control operation by an NC device provided in a press brake according to one or more embodiments. FIG. 12 is a diagram showing a third preferred example of a control operation by an NC device provided in a press brake according to one or more embodiments.

[0010] DETAILED DESCRIPTION OF THE INVENTION One or more embodiments of a press brake and a press brake control method will now be described with reference to the accompanying drawings.

[0011] Figure 1 shows the overall configuration of a press brake 100 according to one or more embodiments. As shown in Figure 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 be raised and lowered by hydraulic cylinders 6L and 6R provided on the left and right sides. The hydraulic cylinders 6L and 6R are hereinafter 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 that it approaches the lower table 3, and raises it so that it moves away from the lower table 3.

[0013] A punch Tp, which is an upper die, is attached to the upper die holder 2, and a die Td, which is a lower die, is attached to the lower die holder 4. Fig. 1 shows a modular type in which the upper die holder 2 is integrally attached over the entire length of the lower end of the upper table 1, but it may also be an intermediate plate type in which multiple intermediate plates for attaching punches Tp are attached in the longitudinal direction of the lower end of the upper table 1. The intermediate plates are also upper die holders.

[0014] Mounting a punch Tp on the upper table 1 means mounting the punch Tp on the upper die holder 2 or the intermediate plate. Mounting a 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] A backgauge 40 is disposed on the rear side of the lower table 3. The backgauge 40 has abutments 42a and 42b that move left and right along a backgauge carriage 41. Here, there are two abutments, 42a and 42b, but the number of abutments is not limited to two. The abutments 42a and 42b are configured to move in the height direction and the front and rear directions as well.

[0016] The operator places the metal sheet W to be processed on the die Td, and before sandwiching and bending the metal sheet W between the punch Tp and the die Td, the butts 42a and 42b move to positions corresponding to the die Td. The operator places the metal sheet W on the die Td so that the rear end of the metal sheet W butts against the butts 42a and 42b. In other words, the butts 42a and 42b act to determine the position of the metal sheet W in the front-to-rear direction when the metal sheet W is placed on the die Td.

[0017] 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 to the left side of the press brake 100. The operation pendant 7 is connected to an NC device 10. A foot switch 8 having an open foot switch 81 for raising the upper table 1 and a close foot switch 82 for lowering the upper table 1 is connected to the NC device 10.

[0018] FIG. 2 shows an example of the configuration of angle sensors provided in the press brake 100. Although not shown in FIG. 1, as shown in FIG. 2, the press brake 100 is provided with angle sensors 21F and 21R that measure the angle of the metal sheet W when bending the metal sheet W. The angle sensor 21F is a first angle sensor, and the angle sensor 21R is a 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 also be disposed at positions spaced apart from the die Td.

[0019] The angle sensors 21F and 21R are configured to be raised and lowered by sensor lifting mechanisms 22F and 22R, respectively. When it is necessary to measure the angle of the metal sheet W, the angle sensors 21F and 21R located below are moved upward by the sensor lifting mechanisms 22F and 22R under the control of the NC device 10.

[0020] The angle sensors 21F and 21R each have a main body 211 and a protruding portion 212 that can be freely extended and retracted relative to the main body 211. A slightly protruding tip 213 is provided at the upper end of the protruding portion 212. In the state before the start of bending the metal sheet W shown in FIG. 2, the protruding portions 212 of the angle sensors 21F and 21R are in a state where they are least protruding. FIG. 3 shows the angles of the metal sheet W detected by the angle sensors 21F and 21R. As shown in FIG. 3, when the punch Tp descends and the metal sheet W is bent, the protruding portion 212 protrudes upward as the metal sheet W is displaced upward.

[0021] As shown in FIG. 3 , the angle sensor 21F measures the angle θf between the back surface of the front flange Wff of the sheet metal W, which is located forward of the punch Tp and the die Td, and the center line of the punch Tp and the die Td, as shown by the dashed line. The angle sensor 21R measures the angle θr between the back surface of the rear flange Wrf of the sheet metal W, which is located rearward of the punch Tp and the die Td, and the center line of the punch Tp and the 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 sensors that measure the angle of the metal sheet W are not limited to contact angle sensors and may be laser angle sensors. When laser angle sensors are used as angle sensors, the sensor lifting mechanisms 22F and 22R are not required, and the front and rear laser angle sensors are in fixed positions in the vertical direction. The front and rear laser angle sensors have a laser emission unit that irradiates a linear laser beam onto the rear surfaces of the front flange Wff and the rear flange Wrf, and an imaging unit that captures an image of the irradiated linear laser beam. The NC device 10 determines the angles θf and θr based on the angle of the linear laser beam in the image captured by the imaging unit, and calculates the bending angle θw of the metal sheet W.

[0023] In the press brake 100 configured as described above, the NC device 10 controls the press brake 100 to bend the metal plate W in accordance with the processing program stored in the processing program database 50.

[0024] FIG. 4 shows an example of the control operation by the NC device 10. FIG. 4 illustrates a state in which additional time, other than the time required to actually bend the sheet metal W, such as the unloading period for calculating the springback amount, has not been reduced by the unique time-reducing method executed by the press brake 100. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the height position of the tip of the punch Tp. In FIG. 4, the distance between positions R3 and F3 is enlarged to facilitate understanding of the change in the height position of the tip of the punch Tp. The distance from position R3 to position F3 is approximately 0.1 mm to 0.2 mm. The distance from the contact position (described later) to position F3 is approximately 2 mm to 3 mm.

[0025] The target bending angle of the metal sheet W is set to, for example, 90 degrees. The NC device 10 controls the elevation of the upper table 1 so as to bend the metal sheet W to the target bending angle of 90 degrees, as shown in FIG. 4. When the NC device 10 starts to lower the upper table 1, the tip of the punch Tp comes into contact with the metal sheet W. The NC device 10 stops the upper table 1 with the tip of the punch Tp positioned at the contact position shown in FIG. 4, and moves the abutments 42a and 42b away from the metal sheet W.

[0026] During the pre-bending period after the tip of the punch Tp comes into contact with the metal sheet W, the NC device 10 lowers the position of the tip of the punch Tp to position T1, stops it temporarily, and then lowers it further to position T2. ​​In Fig. 4, the upper table 1 (punch Tp) is lowered in two stages, but the number of stages of lowering is not limited to two.

[0027] Position T2 during the pre-bending period is a position for bending the sheet metal W to a predetermined pre-bending angle that is wider than the target bend angle of 90 degrees. During the pre-bending period, 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 pre-bending angle. The first depth value of the punch Tp for bending the sheet metal W to the pre-bending angle after the tip of the punch Tp contacts the sheet metal W is determined in advance based on bending theory. The depth value is the amount of descent of the punch Tp when the contact position where the tip of the punch Tp contacts the sheet metal W is used as the reference. In other words, the depth value indicates the height direction position of the tip of the punch Tp. Hereinafter, the depth value will be abbreviated as D value.

[0028] Upon completion of the pre-bending operation, the NC device 10 calculates a first bending angle θw1 as the bending angle θw of the metal sheet 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 upon completion of the pre-bending operation of the metal sheet W.

[0029] Once the metal sheet W has been bent to the provisional bending angle, the NC device 10 transitions the press brake 100 to an unloading period for calculating the amount of springback. During the unloading period, the NC device 10 controls the upper table 1 to be raised in succession in multiple stages so as to unload the metal sheet W while maintaining the punch Tp in contact with the metal sheet W. Unloading refers to removing the load applied to the metal sheet W.

[0030] In Fig. 4, the NC device 10 raises the tip of the punch Tp to position R1 and stops it temporarily, and calculates the bending angle θw of the metal sheet W based on the angles θf and θr measured by the angle sensors 21F and 21R. Next, the NC device 10 raises the tip of the punch Tp to position R2 and stops it temporarily, and calculates the bending angle θw of the metal sheet 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 a threshold value, it is determined that the unloading of the metal sheet W is complete. Fig. 4 shows an example in which the difference between the bending angle θw(R1) and the bending angle θw(R2) at position R2 is not within the threshold value, and it is determined that the unloading of the metal sheet W is not complete.

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

[0032] The NC device 10 raises the position of the tip of the punch Tp to position R3, stops it temporarily, and calculates the bending angle θw of the metal sheet W. If the difference between the bending angle θw(R2) at position R2 and the bending angle θw(R3) at position R3 is within a threshold value, the NC device 10 determines that unloading of the metal sheet W is complete at position R3. Note that the number of stages at which the NC device 10 determines that unloading of the metal sheet W is complete 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] With the metal sheet W unloaded during the unloading period, the NC device 10 calculates a second bending angle θw2 as the bending angle θw of the metal sheet W based on the angles θf and θr measured by the angle sensors 21F and 21R. Even if the metal sheet W is bent to the first bending angle θw1 during the pre-bending period, when the metal sheet W is unloaded during the unloading period, the bending angle widens due to springback. The second bending angle θw2 is the bending angle θw of the metal sheet W widened due to springback. The NC device 10 calculates the amount of springback by subtracting the first bending angle θw1 from the second bending angle θw2.

[0034] If a 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 transitions the press brake 100 to the push-in period. The NC device 10 calculates a second D value that takes into account the springback amount required to bend the metal sheet W to the target bending angle. Simply put, if the springback amount is, for example, 2 degrees, the target bending angle can be set to 88 degrees, and the upper table 1 can be lowered by the amount sufficient to bend the metal sheet W to an 88-degree bending angle. However, because the amount of springback generally varies depending on the target bending angle, setting the target bending angle using the springback amount obtained during the unloading period may not result in a target bending angle of 90 degrees.

[0035] Therefore, rather than using the springback amount obtained during the unloading period as is, the NC device 10 should 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 run-in period, the NC device 10 divides the second D value into multiple parts and controls the table lifting mechanism 6 to sequentially lower the upper table 1 by the second D value in multiple stages. In Fig. 4, the NC device 10 lowers the tip of the punch Tp from position R3 to position F1, stops it temporarily, and calculates the bending angle θw of the sheet metal W. Next, taking into account the bending angle at position F1, the NC device 10 lowers the tip of the punch Tp to position F2, stops it temporarily, and calculates the bending angle θw of the sheet metal W. Furthermore, taking into account the bending angle at position F2, the NC device 10 lowers the tip of the punch Tp to position F3, where the final bending angle of the sheet metal W is the target bending angle of 90 degrees.

[0037] Here, the driving-up operation in the driving-up period is performed in three stages, but it may be performed in one stage, two stages, or four or more stages. The stages of the driving-up operation are not limited.

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

[0039] 4, the NC device 10 raises the tip of the punch Tp to position L1, stops it temporarily, and calculates the bending angle θw of the metal sheet W. Next, the NC device 10 raises the tip of the punch Tp to position L2, stops it temporarily, and calculates the bending angle θw of the metal sheet W. As with 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 a threshold value, it is determined that the unloading of the metal sheet W is complete. If the difference between the bending angle θw (L2) at position L2 and the bending angle θw (L1) at position L1 is within a threshold value, the NC device 10 determines that the unloading of the metal sheet W is complete at position L2.

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

[0041] Next, a unique time-saving method executed by the press brake 100 to shorten additional time, such as the unloading period for calculating the amount of springback, during the control operation by the NC device 10 shown in FIG. 4 will be described. FIG. 5 shows the actual measured values ​​of the tip position of the punch Tp, the angles θf and θr of the front flange Wff and rear flange Wrf, and 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 as in FIG. 4 . The thick solid line indicates the tip position of the punch Tp, the thin solid line indicates the bending angle θw, the dotted line indicates the angle θf, and the dashed line indicates the angle θr. However, the height direction position of the waveform indicating the bending angle θw of the sheet metal W is shifted to be located between the angles θf and θr to make it easier to understand that the bending angle θw is obtained from the angles θf and θr. The bending angle θw is the sum of the angles θf and θr.

[0042] In Figure 5, at position R1 during the unloading period, the angle θf of the metal sheet W is larger than the angle θr. However, at position R2, the angle θr is larger than the angle θf, and the magnitude relationship between the angles θf and θr is reversed. In this way, the fact that the angle θf or θr of the metal sheet W fluctuates significantly means that unloading has actually already been completed at position R2. The angles θf and θr at the immediately previous stage during the unloading period are defined as angles θf(n-1) and θr(n-1), respectively. The angles θf and θr at the most recent stage during the unloading period are defined as angles θf(n) and θr(n), respectively.

[0043] The NC device 10 can determine that unloading of the metal sheet W is complete when at least one of a first condition that the absolute value of the angle 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 angle difference between the angle θr(n) and the angle θr(n-1) exceeds a predetermined magnitude is satisfied. Whether the first condition or the second condition is satisfied can be determined as follows.

[0044] The NC device 10 determines that unloading of the metal sheet W is complete when formula (1) or formula (2) is satisfied. 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 ​​for the angle difference. At one stage in the unloading period, the NC device 10 may determine that unloading of the metal sheet W is complete when both formulas (1) and (2) are satisfied. Formula (1) is a first determination formula using the angle difference between the angle θf(n) and the angle θf(n-1), and formula (2) is a second determination formula using the angle 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 unloading of the metal sheet W is complete using equations (3) to (6) instead of equation (1) or (2). Equation (3) represents the ratio Ratioθf between the angle θf(n) and the angle θf(n-1), and equation (4) represents the ratio Ratioθr between the angle θr(n) and the angle θr(n-1). The NC device 10 can determine that unloading of the metal sheet W is complete if at least one of a third condition, in which the absolute value obtained by subtracting the ratio Ratioθf from 1 exceeds a third threshold value Ratioθfth, and a fourth condition, in which the absolute value obtained by subtracting the ratio Ratioθr from 1 exceeds a fourth threshold value Ratioθrth, is satisfied. The third threshold value Ratioθfth and the fourth threshold value Ratioθrth may be the same value or different values. The third threshold value Ratioθfth and the fourth threshold value Ratioθrth are threshold values ​​for the ratio of the changed angle (angle change ratio). The NC device 10 may determine that the unloading of the metal plate W is completed when both of the formulas (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] Equations (3) and (5) are third criterion formulas using the ratio between the angle θf(n) and the angle θf(n-1). Equations (4) and (6) are fourth criterion formulas using the ratio between the angle θr(n) and the angle θr(n-1).

[0048] The NC device 10 may determine whether unloading of the metal sheet W is complete using equation (8) when equation (7) is satisfied, and may determine whether unloading of the metal sheet W is complete using equation (10) when equation (9) is satisfied. Equations (8) and (10) are equations for determining whether unloading of the metal sheet W is complete based on the angular difference between the angle θf of the front flange Wff and the angle θr of the rear flange Wrf. The NC device 10 can determine that unloading of the metal sheet W is complete if a fifth condition is satisfied, in which the value obtained by subtracting the angle θr(n) from the angle θf(n) is less than a fifth threshold value Δθfr, or a sixth condition is satisfied, in which the value obtained by subtracting the angle θf(n) from the angle θr(n) is less than a 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] Equations (7) to (10) are fifth judgment equations that use 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 unloading of the metal sheet W is complete using equations (11) to (13). The bending angle θw at the immediately preceding stage in the unloading period is defined as bending angle θw(n-1), and the bending angle θw at the latest stage in the unloading period is defined as bending angle θw(n). The value obtained by subtracting the ratio of angle θr(n-1) to bending angle θw(n-1) from the ratio of angle θf(n-1) to bending angle θw(n-1) is defined as Ratioθ(n-1). The value obtained by subtracting the ratio of angle θrn to bending angle θwn from the ratio of angle θfn to bending angle θwn is defined as Ratioθn. The NC device 10 can determine that unloading of the metal sheet W is complete if a seventh condition is satisfied, in which the absolute value of the difference between value Ratioθ(n-1) and value Ratioθn exceeds a 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 sixth judgment equations that use the ratio of the angle θf(n-1) to the bending angle θw(n-1), the ratio of the angle θr(n-1) to the bending angle θw(n-1), the ratio of the angle θf(n) to the bending angle θw, and the ratio of the angle θr(n) to the bending angle θw.

[0054] 6A and 6B, the metal sheet W shown by the two-dot chain line is an exaggerated representation of the position of the metal sheet W at the immediately preceding stage in the unloading period, and the metal sheet W shown by the solid line is an exaggerated representation of the position of the metal sheet W at the most recent stage in the unloading period. The magnitude relationship between the angle θf and the angle θr is reversed as in the example at position R2 in Fig. 5 in many cases when the bent metal sheet W changes from a state inclined more toward the front to a state inclined more toward the rear, or from a state inclined more toward the rear to a state inclined more toward the front, as in Fig. 6A or 6B.

[0055] 6A and 6B show examples in which the metal sheet W changes from a state inclined more toward the front to a state inclined more toward the rear, or vice versa. In contrast, as shown in an exaggerated manner in FIG. 6C , there are cases in which the metal sheet W changes from a state inclined more toward the front or rear so that the inclination further increases. In particular, if there is a large difference between the length of the front flange Wff and the length of the rear flange Wrf, the inclination may increase due to the difference in weight of the flanges. FIG. 6C shows a case in which the length of the rear flange Wrf is longer than the length of the front flange Wff, and the inclination of the metal sheet W increases further toward the rear from a state inclined more toward the rear.

[0056] As can be seen from the bending angle θw of the metal sheet W shown by the thin solid line at positions R2 and R3 in Figure 5, there is almost no change in the bending angle θw between positions R2 and R3. This proves that unloading of the metal sheet W has already been completed at position R2. According to a conventional method of determining whether unloading of the metal sheet W has been completed based on the bending angle θw of the metal sheet W, since there is a predetermined difference between the bending angle θw(R1) and the bending angle θw(R2) as shown in Figure 5, it is determined that unloading of the metal sheet W has not been completed at position R2.

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

[0058] Furthermore, in Figure 5, at position F2, which is the final stage of the penetration period, angle θf is larger than angle θr. However, at position L1 of the final angle measurement period, angle θr is larger than angle θf, and the magnitude relationship between angle θf and angle θr is reversed. Therefore, since angle θf or θr fluctuates greatly at position L1 of the final angle measurement period, this means that unloading has actually already been completed at the point of position L1. During the final angle measurement period, as with the unloading period, the NC device 10 can determine whether unloading of the metal sheet W has been completed using at least one of the first to sixth determination formulas.

[0059] However, if the angle θf and the angle θr at position L1 of the final angle measurement period are the angles θf(n) and θr(n) of the latest stage, the angle θf and the angle θr at position F2 (position F3 in Figure 4), which is the final stage of the driving period, become the angles θf(n-1) and θr(n-1) of the immediately previous stage.

[0060] As can be seen from the bending angle θw of the metal sheet W at positions L1 and L2 in Figure 5, there is almost no change in the bending angle θw between positions L1 and L2. This proves that unloading of the metal sheet W has already been completed at position L1. According to a conventional method of determining whether unloading of the metal sheet W has been completed based on the bending angle θw of the metal sheet W, since there is a large difference between the bending angle θw at position F2 and the bending angle θw at position L1 as shown in Figure 5, it is determined that unloading of the metal sheet W has not been completed at position L1.

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

[0062] As described above, when the new determination method executed by the press brake 100 is used, there is no need to provide the stage at position R3 in the unloading period and the stage at position L2 in the final angle measurement period shown in Figure 4. Therefore, the NC device 10 can execute a control operation that does not include positions R3 and L2, as shown in Figure 7. As is clear from a comparison of Figures 4 and 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 for calculating the final bend angle θw of the metal sheet W can be shortened.

[0063] In the example shown in Figure 7, unloading of the metal sheet W is completed at position R2 during the unloading period, but it may be determined that unloading of the metal sheet W is completed at position R1, which is the first stage of the unloading period. If the NC device 10 determines that unloading of the metal sheet W is completed using at least one of the first to sixth determination equations at position T2, which is the final stage of the pre-bending period, and position R1, which is the first stage of the unloading period, the NC device 10 transitions to the push-in period without providing a stage at 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 final stage of the pre-bending period, are the angles θf(n-1) and θr(n-1) of the immediately preceding stage.

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

[0065] Note that providing the final angle measurement period to calculate the final bending angle θw of the metal sheet W is not essential and 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 metal sheet W is actually bent to the target bending angle.

[0066] The operation of the press brake 100 and a press brake control method executed by the press brake 100 will be described using the flowcharts shown in Figures 8 and 9. In Figure 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 in step S1 so as to bend the metal sheet W to a predetermined temporary bending angle that is wider than the target bending angle. In step S2, the NC device 10 calculates a first bending angle θw1 of the metal sheet W.

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

[0068] In 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 and bend the metal sheet W to the target bending angle. In step S8, the NC device 10 controls the table lifting mechanism 6 to raise the upper table 1 until unloading of the metal sheet W is complete. In step S9, the NC device 10 calculates the final bending angle of the metal sheet W. In step S10, the NC device 10 raises the upper table 1 to complete the bending process.

[0069] FIG. 9 shows the specific processing of steps S3 and S8. Here, an example is shown in which the first judgment formula (1) or the second judgment formula (2) is used. Step S3 consists of steps S31 and S32, and step S8 consists of steps S81 and S82. Following step S2 or S7 in FIG. 8 , the NC unit 10 controls the table lifting mechanism 6 to raise the upper table 1 by one step in step S31 or S81. In step S32 or S82, the NC unit 10 determines whether formula (1) or formula (2) is satisfied. If formula (1) or formula (2) is not satisfied (NO), the NC unit 10 repeats step S31 or S81 and step S32 or S82. If formula (1) or formula (2) is satisfied (YES), the NC unit 10 proceeds to step S4 or S9 in FIG. 8 .

[0070] As described above, the press brake 100 unloads the metal sheet W during an unloading period for calculating the amount of springback of the metal sheet W bent to the provisional bend angle, which follows a pre-bending period in which the metal sheet W is bent to a predetermined pre-bend angle wider than the target bend angle, and a final angle measurement period for calculating the final bend angle of the metal sheet W, which follows a push-in period in which the metal sheet W is bent to the target bend angle. At this time, the NC device 10 may determine whether unloading of the metal sheet W is complete based on the amount or rate of change in 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 point in time when the metal sheet W was bent to the predetermined angle before unloading the metal sheet W or the stage immediately preceding that stage in one or more stages.

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

[0072] 10 , the amount of lift of the upper table 1 from position T2 of the tip of the punch Tp at the end of the pre-bending period to position R1, which is the stage just before position R2 where unloading of the metal sheet W is complete, is designated as UR1. The initial amount of lift of the upper table 1 in the final angle measurement period, which is the amount of lift from position F3 of the tip of the punch Tp to position L1 at the end of the push-in period, is designated as UL1. As a first example, it is preferable to set the amount of lift UR1 to the amount of lift UL1. If the amount of lift by which the upper table 1 is lifted for unloading up to the stage just before unloading of the metal sheet W is complete during the unloading period is set as the initial amount of lift of the upper table 1 in the final angle measurement period, the time required for unloading in the final angle measurement period can be shortened.

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

[0074] 11 , the amount of lift of the upper table 1 from position T2 of the tip of the punch Tp at the end of the pre-bending period to position R2 where unloading of the metal sheet W is complete is set as UR2. As a second example, it is preferable to set the amount of lift UL1 to k × UR2, which is obtained by multiplying the amount of lift UR2 by a predetermined coefficient k less than 1. If the amount of lift by which the upper table 1 is lifted for unloading until unloading of the metal sheet W is complete during the unloading period is reduced by a predetermined percentage and set as the initial amount of lift of the upper table 1 in the final angle measurement period, the time required for unloading in the final angle measurement period can be shortened.

[0075] FIG. 11 shows an example in which the final angle measurement period has two stages, positions L1 and L2, but similar to FIG. 7, there is a possibility that the final angle measurement period will have one stage, position L1.

[0076] As a third example, as shown in Figure 12, the lift amount UR2 may be set to the lift amount UL1. If the lift amount by which the upper table 1 is raised for unloading until the unloading of the metal sheet W is completed during the unloading period is set to the initial lift amount of the upper table 1 during the final angle measurement period, the time required for unloading during the final angle measurement period can be shortened. While Figure 12 shows an example in which the final angle measurement period is one stage, position L1, it is possible for the final angle measurement period to be two or more stages.

[0077] As in the first to third examples above, it is advisable to set the amount of lift of the upper table 1 in the first stage during the final angle measurement period based on the amount of lift of the upper table 1 up to the stage immediately before the unloading of the metal sheet W is completed during the unloading period, or up to the stage at which the unloading of the metal sheet W is completed. In this way, it is possible to obtain the effects of both shortening the processing time by adopting the above-mentioned new determination method for determining whether the unloading of the metal sheet W is completed, and shortening the processing time by adopting the first to third examples.

[0078] The present invention is not limited to the one or more embodiments described above, and various modifications are possible without departing from the spirit and scope of the present invention. In the one or more 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 that is fixed in position. However, it is also possible for the upper table 1 to be a fixed table and the lower table 3 to be a slide table. In this case, the table lifting mechanism 6 lifts and lowers the lower table 3. The rise and fall of the upper table 1 can be read as the rise and fall of the lower table 3, respectively, and the first and second amounts of fall of the upper table 1 can be read as the first and second amounts of rise of the lower table 3.

[0079] In one or more embodiments, the position where the punch Tp is lowered toward the die Td and the pressure applied to the metal sheet W reaches a specified pressure as a reference position is defined as the value D. When the upper table 1 is a fixed table and the lower table 3 is a sliding table, the position where the die Td is raised toward the punch Tp and the pressure applied to the metal sheet W reaches a specified pressure as a reference position is defined as the value D.

[0080] This application claims priority based on Japanese Patent Application No. 2024-001220, filed with the Japan Patent Office on January 9, 2024, the entire disclosure of which is incorporated herein by reference.

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, and when bending a sheet metal by sandwiching it 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, 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, 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, when determining whether the unloading of the sheet metal is completed 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 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.

2. The press brake according to claim 1, wherein the control device determines whether the unloading of the sheet metal is completed based on a change amount or a 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 following 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 in which the control device bends the sheet metal to the target bending angle, the control device determines whether the 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. The press brake according to claim 1 or 2.

4. A control device for controlling a press brake comprising 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 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. When 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, the control device determines whether the 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 in which the control device bends the sheet metal to a predetermined temporary bending angle wider than the target bending angle, the control device determines whether the 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. The press brake control method according to claim 4.

6. The press brake control method according to claim 4 or 5, wherein the control device determines whether the unloading of the sheet metal is completed based on a change amount or a change rate of the angle of the first flange or the angle of the second flange in 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.

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