EP0775028B1 - Method and machine for bending workpieces - Google Patents

Abstract

PCT No. PCT/EP96/02531 Sec. 371 Date Feb. 7, 1997 Sec. 102(e) Date Feb. 7, 1997 PCT Filed Jun. 11, 1996 PCT Pub. No. WO96/41690 PCT Pub. Date Dec. 27, 1996As part of a process for bending workpieces (14), when the workpiece (14) is released from the upper die (8) and/or the lower die (10), the actual size of the bending angle ( beta ) is continually determined; from the actual size of the bending angle ( beta ) found, the change in it is determined and, as soon as the change in the actual size of the bending angle ( beta ) assumes a predetermined value, the actual size of the then existing bending angle ( beta ) is compared with the desired size. On a tooling machine for carrying out the method described, there are scanning elements (17,18) and a device (24) for determining the actual size of the bending angle ( beta ) that are parts of a device (19) for determining the change in the actual size of the bending angle ( beta ). The device (24) for determining the actual size of the bending angle ( beta ) is connected to a comparison device (32) for comparing the actual size of the bending angle ( beta ) to the desired size.

Description

The invention relates to a method for folding workpieces, especially of sheet metal, in which on the workpiece its application with a forming stamp and / or one cooperating forming die at least one workpiece leg at a bend angle against at least one other Workpiece leg bent and then the workpiece from that Forming stamp and / or is relieved of the forming die, wherein during the relief of the workpiece from the forming die and / or the actual size of the bending angle is determined by the forming die and after the at least approximately complete discharge of the workpiece from the forming die and / or from the forming die the actual size of the bending angle then present with a Target size is compared.

The invention further relates to a processing machine for Bending workpieces, especially sheet metal, after a Method of the type described, with a forming die and a interacting with this and relative in the machining direction to this can be moved in a controlled manner by means of a drive control Forming stamp and with at least two probe elements, which in the machining direction relative to the forming die and / or the forming die and are movable relative to one another and themselves in a measuring position on at least one of two a bending angle on the legs enclosing the folded workpiece support the bent workpiece, the relative position of the Probe elements is a measure of the actual size of the bending angle and the probe elements with a device for determining the actual size of the bending angle.

As is known, occurs when bending workpieces, in particular of sheet metal, in addition to the desired plastic also an undesirable elastic deformation of the workpieces. From the elastic Deformation results after the relief of the concerned Workpiece from the forming tool springs open during the process of the bending process created workpiece angle and associated with it an increase in the of the legs of the workpiece angle included bending angle. Bending workpieces with a defined bending angle of a predetermined target size this complicates.

In the context of a generic method known from DE-A-30 08 701 the phenomenon described is taken into account by that after a first operation with the workpiece unloaded the actual size of the created bending angle measured and with it Target size is compared. This comparison shows that the actual angle is greater than the target angle, so a corrective Work started after completion at relieved workpiece a new actual-target-size comparison for the bending angle is made. Corrective post-processing the beveled workpiece is subjected to the process until the desired machining result is achieved.

According to DE-A-30 08 701 a processing machine with the initially specified generic features used. The serves in the machining direction or existing distance in the direction of movement of the probe elements as the basis for the trigonometric calculation of the created bending angle.

EP-A-0 166 351 describes a method for folding sheet metal Materials, in the context of which a sheet to be processed by means of of a forming tool and initially under application deformed by the bending tool with the target bending angle becomes. After a complete relief of the sheet from the bending tool becomes the amount of travel or angle of the opposite the resilience occurred. The determined The amount of springback then forms the basis for the Selection of the parameters of a subsequent corrective processing step. The processing machine disclosed in EP-A-0 166 351 makes use of the method described of a probe element that during the machining process rests on the sheet to be formed and with a computer-aided Evaluation device is connected.

Other known processing machines for performing the generic Procedures use an inductive or an pneumatic measuring device. In both cases Forming tool relieves the workpiece after a bending process for two points of each workpiece leg whose distance from the opposite and a V-shaped groove delimiting cross section Flank determined on a forming die. The course of the Groove flanks of the forming die give the target size of the one to be created Bending angle before. By determining the distance between the measuring points on the workpiece legs from the assigned groove flank it is determined whether the workpiece legs are parallel to the groove flanks run and accordingly the desired target angle include, or whether the legs of the workpiece angle in turn are aligned at an angle to the groove flanks and consequently deviate from their target course. From the measured Distance values becomes the actual size of the previous one Bending process created bending angle determined.

Due to the prior art described above, neither process-related and device-related means, which would allow the actual size of the bending angle to be defined to be measured immediately when the folded workpiece his state relieved of the forming tool or one unloaded state very close to quasi load-free state reached. Such an optimization of the timing for the Determination of the actual size of the in the previous operation created bending angle comes for example in terms of achievable processing speed and / or with regard to Process security is of vital importance. Will the actual size of the bending angle on a folded workpiece to the earliest possible time, i.e. at the time when the folded workpiece is load-free or quasi load-free for the first time is determined, then any corrective action that may be required can be made Bending process also at the earliest possible time initiate. Unnecessarily extending the total processing time Periods of time within which the actual size is determined of the bending angle is waited for, although the folded workpiece is already load-free or quasi-load-free avoid.

The measurement of the actual size of the bending angle as soon as it is reached a load-free condition due to the folded workpiece after the forming process is known in the case of another Generic method enables the course the between the forming tool and the folded workpiece during of the relief stroke of the forming tool effective force above the The amount of the relief stroke is approximately determined. Out the then approximately known course of the between the forming tool and effective force during the folded workpiece of the relief stroke is that amount of the relief stroke determines at which the between the forming tool and the folded Workpiece effective force assumes the value zero for the first time and in which the folded workpiece accordingly reached state relieved by the forming tool. Furthermore is part of the previously known process based on Individual measurements of the approximate course of the actual size of the bending angle above the amount of the relief stroke of the forming tool certainly. Based on this course of the actual size of the bending angle The actual size is above the amount of the relief stroke of the bending angle, which determines the amount previously determined the relief stroke is assigned, in which the between Forming tool and folded workpiece effective force reached zero. The actual size of the bending angle obtained in this way on the load-free workpiece with the target size of the bending angle compared and the comparison result in the case of a Angle deviation as the basis for a subsequent corrective Machining process used.

Based on the last discussed state of the art present invention has for its object to provide a method which is a simplified determination of the deviation the actual size of the bending angle on a no-load or quasi load-free folded workpiece of the target size of the Bending angle at the earliest possible time or at a earliest possible time very close. In terms of device, the present invention aims to to create a processing machine by means of which the inventive Procedure can be carried out.

The process-related problem is solved according to the invention by that as part of a process of the above Art the actual size of the bending angle during the relief of the Workpiece from the forming die and / or from the forming die it is continuously determined that from the determined actual values of the Bending angle whose change is determined and that as soon as the certain change in the actual size of the bending angle a predetermined Assumes value, the actual size of the bending angle then present is compared with the target size. The value for the change in the actual size of the bending angle when it is reached the actual-target-size comparison is made, the value zero or a value that comes very close to this. Of the For the sake of simplicity, the process according to the invention is used as a parameter for the voltage or load status of the folded workpiece the development of that size, namely the actual size of the bending angle, based on its exact Dimensioning with a predetermined target size directed the folding process is. This also results in high accuracy the procedure according to the invention.

In a variant of the invention is expedient Process in which the forming die and the forming die while relieving the workpiece relative to each other be moved while relieving the workpiece of the course the actual size of the bending angle depending on the amount or the duration of the relative movement of the forming die and the forming die recorded and the change from the recorded history the actual size of the bending angle per unit of the amount or the duration of the relative movement of the forming die and the forming die certainly. In this case it is illustrated the slope of the tangents on the graph of the actual size of the bending angle over the amount or duration of the relative movement of Forming stamp and forming die as parameters for the extent of the change the actual size of the bending angle during workpiece relief determined. If the slope takes the value zero, then means this is that the actual size of the bending angle continues with Relative movement of the forming punch and forming die no longer changes and that the folded workpiece accordingly has reached the no-load state and the actual-target-size comparison for the bend angle can be performed. Is in the sense of inventive method as a value for the change in the actual size the bending angle at which the actual-target-size comparison a value close to zero must be specified, this is the case synonymous with the specification of an almost zero Slope of the tangents on the graph of the actual size of the bending angle over the amount or duration of the relative movement of the stamp and forming die.

In development of a method according to the invention, in which the forming die and the forming die during the relief of the workpiece are moved relative to one another, that the relative movement of the forming die and the forming die ends becomes as soon as the certain during the relief of the workpiece Change the actual size of the bending angle to the specified one Assumes value. This measure ensures an increase in Process reliability to ensure that the folded workpiece also in his relieved of the forming tool or in his quasi load-free state between the forming die and the forming die becomes. Is it for the change of the actual size of the bending angle predetermined value at which the actual-target-size comparison is made to a value close to zero, so this is tantamount to saying that between the beveled Workpiece and the forming tool still have a minimal force which is the folded workpiece between the forming die and Forming die fixed in position, but without the size of the bending angle to exert a notable influence. Is used as a value which defines the time of the actual-target-size comparison, which If the value is zero, the folded workpiece is the same decisive time from the forming tool completely relieved. Since the determination of the completely load-free state of the folded Workpiece the occurrence of this condition is minimal in time lags behind and accordingly the relative movement of the forming stamp and forming die only after a minimal period of time Complete relief of the folded workpiece occurs ends, in this case there is between the folded Workpiece and the forming die as well as the forming die slight play, but which fixes the position of the folded Workpiece is not necessarily affected. In both Rather, it is basically guaranteed that the beveled Workpiece its position, which is when it is finished forming ingested and while it was being relieved of stamps and Forming die has not changed as soon as it is load-free or quasi-load-free state reached. This condition is particularly important against the background that the at the comparison of the actual size of the bending angle when the load is off or quasi load-free folded workpiece with the nominal size of the Bending angle determined deviation as a correction value if necessary is used for post-processing of the folded workpiece and the orientation of the workpiece in post-processing the forming tool with the alignment during the previous one Must match in order for the desired Machining result can be achieved. Will after a first Bending process determined by comparing actual and target sizes that the actual size of the created bending angle when relaxed or quasi load-free folded workpiece Target size exceeds a determined amount, so is based on the determined deviation for a subsequent corrective folding process a penetration depth of the forming die on the forming die, which determines the depth of penetration in the previous operation by an amount exceeds, which depends on the degree of deviation of the Actual size of the bending angle is determined from the target size.

The above device-related object is achieved according to the invention with a processing machine of the type specified at the outset solved, in the case of which the sensing elements and the device for Determination of the actual size of the bending angle of parts of a device to determine the change in the actual size of the bending angle and the device for determining the actual size of the bending angle the actual size when the workpiece is unloaded continuously determined and communicates with a comparison device for comparison a target size of the bending angle with the actual size of the bending angle, which is present when using the device in question certain change in the actual size of the bending angle a predetermined Assumes value. Due to the relative mobility of the forming tool and the stylus can be the stamp or the forming die after folding the workpiece from it move away while the probe elements on the workpiece surface or on at least one leg of the created workpiece angle issue. That with the relief of the folded workpiece connected springs of the workpiece legs and the associated associated change in the actual size of the bending angle requires a Relocation of the touch elements on the folded workpiece relative to each other in the machining direction. A change the relative position of the probe elements in the direction mentioned accordingly indicates a change in the actual size of the bending angle on the folded workpiece. Once the tactile elements no longer change their mutual position in the machining direction, the folded workpiece has its relief from the forming tool Condition reached in which is the actual size of the bending angle caused by the previous one Bending process actually reached the actual size of the bending angle corresponds. Is the amount of change in the relative position the touch elements in the machining direction are not the same, however but very close to zero, this indicates that the actual size of the Bending angles changed only minimally and accordingly one Has reached value that comes very close to the value that fully assigned to the load-free state of the folded workpiece is.

In both cases, the relative positions of the probe elements the actual sizes of the bending angle with the help of their determination provided device calculated. Based on the calculated The actual sizes of the bending angle can be changed determine with the device provided for this purpose. Surrendered the value for changing the actual size of the bending angle The comparison device becomes zero or a value very close to this activated, with the help of the actual size of the Bending angle when the change value reaches zero or this Change value very close to a defined value The target size of the bending angle to be created is compared. The key elements therefore supply the output data on the basis of which it is determined whether the actual size of the bending angle in the Changes in the course of a continued workpiece relief, or whether that state of the folded workpiece is reached at which is the actual-target-size comparison for the bending angle is. The probe elements accordingly form a mechanical one Part of the device according to the invention for determining the Change the actual size of the bending angle.

Another component of this device for determining the optimal Time of the actual-target-size comparison for the bending angle provides the device for determining the actual size of the Bending angles. With their help, those quantities are determined by comparing them in a comparison unit for the Is the size of the bending angle immediately the presence or absence a change in the actual size of the bending angle can be.

In an expedient development of the processing machine according to the invention it is provided that the device for determining the Actual size of the bending angle in the machining direction on the forming die includes guided slide, each with one the probe elements can be moved in the machining direction. The described configuration of machines according to the invention allows it, the device for determining the actual size of the bending angle with a sufficient distance from the workpiece to be machined to be arranged, in an area in which a sufficient Installation space is available. The position of the probe elements in this variant of the invention by the relative position of the in connection with the touch elements standing slider is displayed.

A highly accurate determination of the relative position of the probe elements and thus the provision of extremely exact starting data for the Determination of the value of any changes in the actual size of the bending angle is in a preferred embodiment of the invention Processing machine enables that At least device for determining the actual size of the bending angle one associated with one of the probe elements and with this light source displaceable in the machining direction, preferably a corresponding LED, and at least one with the other touch element in connection with this in Machining direction displaceable and assigned to the light source optical sensor, preferably a PSD (Position Sensitive Detector). In addition, the components described have the device according to the invention for determining the actual size of the bending angle requires only a small amount of space. Out of it there is the possibility of the entire device in the forming tool to integrate.

So that the device for determining the change in the actual size of the bending angle can provide sufficiently accurate results previously the actual sizes of the bending angles by comparing them the changes that may occur are calculated exactly have been determined. This in turn presupposes that the relative positions of the tactile elements from which to compare Actual sizes of the bending angle are determined, if possible exactly the course of the legs of the bending angle on the folded Play workpiece. For this reason, must be defined for a Support of the feeler elements on the leg in question or on the relevant legs of the folded workpiece be taken care of. This requirement is within the meaning of the invention thereby taken into account that the probe elements in the measuring position transverse to that of a forming edge of the forming die and the Projecting the defined direction from the forming die and on both legs of the folded workpiece abut, the touch elements on one and the same Side of the named level with different distances from the forming edge on the legs of the folded workpiece support.

Tactile elements that are components of devices according to the invention to determine the change in the actual size of the bending angle can be used in different ways be designed. So are in the sense of the invention as disks or Disc segments trained sensing elements are provided as well Probe elements in the form of transverse to that of a forming edge of the Forming stamp and the processing direction defined level aligned probe rods. In particular as disks or disk segments Designed touch elements can be manufactured with little manufacturing effort produce. If you are thin enough, you can in the measuring position with a point-like touch on the folded workpiece and in recesses in the form of narrow slots on the forming die in the machining direction become.

A preferred embodiment of the processing machine according to the invention is characterized in that the touch elements transverse to that of a forming edge of the forming die and the machining direction defined plane can be deflected relative to each other are. Due to the described relative mobility of the Probe elements in the transverse direction of the plane mentioned can be Tactile elements with different courses of the two legs bring the folded workpiece to the system. If necessary the probe elements are able to move in the transverse direction said plane automatically relative to each other to position that both sensing elements on the relevant Leg or on the relevant legs of the folded Workpiece.

The relative transverse mobility of the probe elements in the transverse direction that of the forming edge of the forming die and the machining direction According to the invention, the defined level is on the one hand realizes that the probe elements relative to the plane mentioned relative are pivotable to each other. Additionally or alternatively the relative transverse mobility of the probe elements in the sense of the invention be caused by the fact that the probe elements are transverse to the mentioned plane are displaceable relative to each other.

Lay the probe elements while executing a relative movement in the transverse direction of a forming edge of the forming die and the machining direction defined plane on the workpiece leg (s) the result of the determination the actual size of the bending angle can be influenced. Indeed is the influence of the described relative transverse deflection of the Probe elements on the resulting actual size of the bending angle extremely low.

However, it is a highly accurate determination of the actual size of the bending angle strived for, this influence must nevertheless be taken into account. For this purpose, in the case of a preferred embodiment the processing machine according to the invention, in which the probe elements transverse to that of a forming edge of the forming die and the machining direction defined plane relative are deflectable to each other, as part of the device for determination a device to change the actual size of the bending angle provided to determine the relative transverse deflection of the probe elements, which in connection with an evaluation device stands, by means of which the relative transverse deflection of the probe elements taken into account when determining the actual size of the bending angle becomes.

An extremely exact determination of the relative transverse deflection of the In the case of a further variant of the invention, touch elements are used Processing machine with transverse to that of a forming edge of the forming die and the machining direction Plane deflectable relative to each other accomplished that the device for determining the relative Transverse deflection of the probe elements at least one with one of the sensing elements in connection with and transverse deflectable with this Light source, preferably a corresponding LED, as well at least one connected to the other probe element, with this transversely deflectable and associated with the light source optical sensor, preferably a corresponding PSD, having.

In terms of a constructive simplification of processing machines according to the invention, in the case of which the device for determination the actual size of the bending angle at least one with one of the Touch elements that can be moved in the machining direction and at least one with the other probe element in the same Has displaceable optical sensor, is (are) as Light source and as an optical sensor of the device for determination the relative transverse deflection of the probe elements with the Probe elements that can be moved in the machining direction or the corresponding optical sensor (s).

A largely automated workpiece processing allows one embodiment of the processing machine according to the invention, in the case of which the device for determining the change of Actual size of the bending angle in connection with the drive control stands, Is by means of the device for determining the change the actual size of the bending angle found that the by an elastic return movement of the legs of the folded Workpiece-related change in the actual size of the bending angle predetermined value, i.e. 0 or very close to 0 coming value, has been reached by means of the drive control that serves to relieve the folded workpiece Relative movement of forming stamp and forming die ended. Thereby it is ensured that the forming die and the forming die are relative remain motionless to each other as soon as the folded one Workpiece reaches its load-free or quasi-load-free state. In their then adopted position, form stamps fix and forming die the folded workpiece in the processing position. In addition, the actual size of the bending angle determines the no-load or quasi-no-load condition is assigned to the folded workpiece. This actual size of the Bending angle is compared with the specified target size, and the existing deviation may serve as the basis for an automatically initiated and carried out corrective Postprocessing.

It should generally be pointed out that the method according to the invention and the device according to the invention in principle both for workpiece processing using the embossing process as well suitable for workpiece processing by so-called "free bending" are.

Figur 1

die perspektivische Gesamtansicht einer ersten Ausführungsform einer hydraulischen Gesenkbiegepresse mit einer Vorrichtung zur Bestimmung der Änderung der Ist-Größe des Biegewinkels,

Figur 2a

eine Schnittdarstellung in der Draufsicht auf die Schnittebene II in Figur 1 bei in unterer Endlage befindlichem Umformstempel,

Figur 2b

eine Darstellung entsprechend Figur 2a bei von dem Umformwerkzeug entlastetem Werkstück nach dem Abkanten,

Figur 3

den grafischen Verlauf der Ist-Größe des Biegewinkels β in Abhängigkeit von dem Rückhubweg s des Umformstempels beim Abkanten des Werkstücks gemäß den Figuren 1 bis 2b,

Figur 4

eine Schnittdarstellung zu einer zweiten Ausführungsform einer Gesenkbiegepresse mit einer Vorrichtung zur Bestimmung der Änderung der Ist-Größe des Biegewinkels,

Figur 5

eine teilgeschnittene Seitenansicht im Bereich des Umformstempels der Gesenkbiegepresse gemäß Figur 4,

Figur 6a und Figur 6b

Prinzipskizzen zu der Funktionsweise der Vorrichtung zur Bestimmung der Änderung der Ist-Größe des Biegewinkels an der Gesenkbiegepresse gemäß den Figuren 4 und 5,

Figur 7a und Figur 7b

Prinzipsskizzen zu einer dritten Ausführungsform einer Gesenkbiegepresse mit einer Vorrichtung zur Bestimmung der Änderung der Ist-Größe des Biegewinkels,

Figur 8

eine Schnittdarstellung zu einer Gesenkbiegepresse gemäß den Figuren 7a und 7b,

Figur 9

eine Schnittdarstellung des Umformstempels in der Draufsicht auf die in Figur 8 senkrecht zu der Zeichenebene in Richtung der Linie IX-IX verlaufende Schnittfläche,

Figur 10

den Ausschnitt D gemäß Figur 9 in vergrößertem Maßstab und

Figur 11

eine vierte Ausführungsform einer hydraulischen Gesenkbiegepresse mit einer Vorrichtung zur Bestimmung der Änderung der Ist-Größe des Biegewinkels in der Draufsicht.

The invention is explained in more detail below on the basis of schematic representations of exemplary embodiments. Show it:

Figure 1

the overall perspective view of a first embodiment of a hydraulic die bending press with a device for determining the change in the actual size of the bending angle,

Figure 2a

2 shows a sectional illustration in plan view of the sectional plane II in FIG. 1 with the forming die in the lower end position,

Figure 2b

2 shows a representation corresponding to FIG. 2a with the workpiece relieved of the forming tool after the folding,

Figure 3

the graph of the actual size of the bending angle β as a function of the return stroke s of the forming die when bending the workpiece according to FIGS. 1 to 2b,

Figure 4

1 shows a sectional illustration of a second embodiment of a die bending press with a device for determining the change in the actual size of the bending angle,

Figure 5

3 shows a partially sectioned side view in the area of the forming die of the press brake according to FIG. 4,

Figure 6a and Figure 6b

Principle sketches on the functioning of the device for determining the change in the actual size of the bending angle on the die bending press according to FIGS. 4 and 5,

Figure 7a and Figure 7b

Principle sketches for a third embodiment of a die bending press with a device for determining the change in the actual size of the bending angle,

Figure 8

7 shows a sectional illustration of a die bending press according to FIGS. 7a and 7b,

Figure 9

3 shows a sectional illustration of the forming die in a top view of the cutting surface running perpendicular to the drawing plane in the direction of the line IX-IX in FIG. 8,

Figure 10

the section D of Figure 9 on an enlarged scale and

Figure 11

a fourth embodiment of a hydraulic die bending press with a device for determining the change in the actual size of the bending angle in plan view.

A die bending press 1 shown in FIG. 1 comprises a machine frame with two stands 2, 3. Between stands 2, 3 is a top beam 4 in a illustrated by a double arrow 5 vertical machining direction can be raised and lowered. The upper beam 4 goes into a press beam at its lower end 6 over, which extends over the entire machine front. Hydraulic are used to raise and lower the upper beam 4 Press cylinder 7 which engage the press beam 6. In a undercut longitudinal groove of the press beam 6 is a strip-like Forming punch 8 in the form of a continuous bending punch held, which ends down in a forming edge 9. Of the Forming punch 8 acts with a forming die designed as a bending die 10 together. The latter is on a table 11 of the die bending press 1 is mounted and has the stamp 8 on it facing side a V-shaped groove 12.

In a control panel 13 are the drive control of the press brake 1 and other facilities for automated machine operation housed within the scope of which a workpiece 14, namely a sheet of metal is folded. In your starting position the sheet 14 is shown in Figure 1 with solid lines. In its folded condition, in which they are two one Bending angle β including workpiece legs 15, 16, the metal sheet 14 is indicated by dashed lines. In Figure 1 also hinted, are sensing elements 17, 18 one Device 19 for determining the change in the actual size of the bending angle β.

FIG. 2a shows the situation at the time of the folding process at which the forming die 8 is in a position in which the sheet metal legs 15, 16 enclose a bending angle β between them with an actual size that is the desired size, in the present case 90 °. The feeler elements 17, 18 are held on slides 22, 23, which are arranged concentrically to one another and are displaceably guided inside the forming die 8 in the machining direction 5 relative to one another and relative to the forming die 8. In their position according to FIG. 2a, the feeler elements 17, 18 are arranged at a mutual distance d ₁ in the machining direction 5. Transversely to the machining direction 5, the contact points of the sensing elements 17, 18 on the sheet metal legs 15, 16 are at a predetermined and known distance a. The slides 22, 23 are part of a device 24 for determining the actual size of the bending angle β.

If the forming die 8 is moved from the position shown in FIG. 2a in the processing direction 5 away from the metal sheet 14, then effective elastic restoring forces in the metal sheet 14 lead to the springing of the folded metal sheet 14 from its state shown in FIG. 2a to the state according to FIG. 2b . The actual size of the bending angle β enclosed by the sheet metal legs 15, 16 increases. The springing of the folded sheet metal plate 14 is associated with a change in the relative position of the feeler elements 17, 18 in the machining direction 5. While the feeler elements 17, 18 had a distance d ₁ in the machining direction 5 in the machining stage in accordance with FIG. 2a, they take this in accordance with FIG. 2b Direction a mutual distance d ₂ . During the relief of the sheet metal plate 14 from the state shown in FIG. 2a to the state according to FIG. 2b, the relative position of the probe elements 17, 18 in the machining direction 5 has changed by (d ₁ -d ₂ ). The horizontal distance a of the contact points between the sheet metal legs 15, 16 and the feeler elements 17, 18 has remained unchanged.

During the described relief of the metal sheet 14 from the forming die 8, the actual size of the bending angle β was continuously determined by means of the device 24 only indicated in FIGS. 2a and 2b. For this purpose, the device 24 for determining the actual size of the bending angle β includes, in addition to the slides 22, 23, a device 25 for determining the relative position of the slides 22, 23 in the machining direction 5. Because of the between the slides 22, 23 and the feeler elements 17 , 18 existing connection is determined by means of the device 25 with the relative position of the slide 22, 23 in the machining direction 5, the relative position of the probe elements 17, 18 in the direction mentioned. In the processing phase according to FIG. 2b, for example, this relative position is represented by the distance d ₂ . From the determined distance d ₂ and the invariable distance a transverse to the machining direction 5, the actual size of an angle γ is calculated by a computing unit 26 of the device 24 for determining the actual size of the bending angle β according to a trigonometric function.

Since in the application sketched in Figures 2a and 2b symmetrical relationships with respect to a dash-dotted line Axis of movement 27 of the probe elements 17, 18 in the machining direction 5 prevail, corresponds to the actual size of the particular one Angle γ of half the actual size of the bending angle β. Because of the symmetrical course of the workpiece legs 15, 16 with respect the axis of movement 27 would be required to calculate the actual size of the bending angle β in the manner described above only one contact point of each of the sensing elements 17, 18 with the workpiece 14, both contact points expediently on one and the same side of the forming edge 9 of the bending punch 8 are at different distances from the forming edge 9.

By means of a comparison unit 28 which are during the Relief of the metal sheet 14 from the forming die 8 and actual quantities determined continuously by the computing unit 26 of the bending angle β between the workpiece legs 15, 16 compared with each other. The difference between an actual size of the bending angle β and the one immediately preceding it calculated actual size determined.

The forming die 8 is based on that shown in FIG. 2b Position further in the machining direction 5 from the folded Sheet 14 moved away, the workpiece legs 15 open, 16 further, that is, the actual size of the workpiece legs 15, 16 included bending angle takes on a value that above the value of the actual size of the bending angle β according to FIG. 2b lies. The spread of the workpiece legs 15, 16 and thus associated enlargement of the actual size of the one enclosed by them Bending angle β ends as soon as the sheet is relieved 14 enters from the forming die 8. From the occurrence of this state of relief performs a further return stroke movement of the forming die 8 no longer increases the actual size of the the workpiece legs 15, 16 included bending angle β. The deviation of a determined by means of the comparison unit 28 Actual size of the bending angle β directly from this actual size the previously calculated actual size takes on the Value 0.

A deviation 0 of two successively calculated actual values of the bending angle β thus indicates the entry of the load-free one State of the sheet 14 and thus the presence of the actual Actual size of the one created with the relevant folding process Bending angle β.

If there is no change in the relative position of the sensing elements 17, 18 in Machining direction 5 and thus no change in the actual size of the Bending angle β more, so the comparison unit 28 Signal sent to a drive controller 29, based on this the latter stops a machine drive 30 of the press brake 1. As a result, the forming die 8 remains in relation to the forming die 10 in the machining direction 5 approximately in the position, which he had achieved as from the comparison unit 28 for the Deviation of two successive actual sizes of the bending angle β the value zero has been calculated for the first time. In this operating state, in which the sheet 14 is just its load-free Has reached state, are forming punch 8 and forming die 10 of the sheet 14 arranged immediately adjacent. Consequently is the metal sheet 14 from the forming stamp 8 and the cooperating forming die 10 in its current Fixed location.

As an alternative to the process sequence described above the signal for stopping the machine drive 30 already be given to the drive control 29 as soon as the means the comparison unit 28 calculated deviation between two successive Actual sizes of the bending angle β do not have the value 0 but takes a value close to 0. In this case, the metal sheet 14 a quasi when the machine drive 30 is stopped no-load condition reached.

The computing unit 26 described above for calculating the Actual sizes of the bending angle β as well as the downstream one Comparison unit 28 for comparing successively calculated Actual sizes of the bending angle β are part of a central computer 31. With its help, using the computing unit 26 determines the actual size of the bending angle β, which the Reaching the load-free or quasi-load-free state of the Sheet 14 is assigned. This actual actual size of the Bending angle β created in the folding process is then with the target size of the bending angle β, ie with that size compared with which the bending angle β is to be produced. To a comparison device 32 serves for this purpose for comparison an actual size of the bending angle β with a target size, wherein it the comparison device 32 is also a part of the Central computer 31 acts.

The deviation determined on the basis of the actual-target-size comparison the actual actual size of the created bending angle β from the The target size is used by the central computer 31, the machine drive 30 via the drive control 29 machining parameters for a subsequent corrective folding operation to specify. The central computer 31 has access to stored Values for example to identify the material and / or the thickness of the metal sheet 14. Is used for the deviation of the Actual size of the bending angle β with relieved or quasi load-free Sheet 14 of the target size of the bending angle β a certain The central computer 31 calculates the value under Consideration of the thickness and / or material of the sheet 14 based on the deviation, the required depth of penetration of the forming die 8 on the die 10, via which the forming die 8 in the subsequent corrective machining operation must drive into the forming die 10, so as a result of the corrective folding process, a bending angle β with the desired one Target size is created. In a first approximation, for a stamp penetration depth is given for the correcting folding process be in which the sheet 14 in the lower end position of the forming die 8 has a bending angle β with an actual size which is smaller by the previously determined angular deviation is the specified target size.

The criteria according to which in the central computer 31 the signal the drive control 29 for stopping the machine drive 30 is activated, are shown in Figure 3.

The course of the actual size of the Bending angle β over the path s determines which of the forming dies 8 covered during the relief of the sheet 14. Subsequently is by means of the central computer 31 for each actual size of the Bending angle β is the slope of the tangent t on the graph of the Bending angle β determined over the amount s. Takes the slope of the Tangents t have the value 0 or a value very close to 0 Value and accordingly the tangent t runs according to FIG. 3 horizontally or approximately horizontally, this indicates that the one calculated by means of the comparison unit 28 Deviation of two successively determined actual values of the Bending angle β is 0 or very close to the value 0. This in turn is synonymous with the entry of the no-load or quasi load-free state of the sheet 14 and thus marked the time or that amount of the return stroke movement of the forming die 8, in which from the central computer 31 via the Drive control 29 to stop the machine drive 30 and then a corrective folding process if necessary is to be initiated.

In the case of a die bending press 101, as shown in FIGS. 4 5 and 5, a sheet 114 is made to cooperate a forming die 108 and a forming die 110 below Formation of two workpiece legs enclosing a bending angle β 115, 116 folded. Just like the feeler elements 17, 18 the die bending press 1 according to FIGS. 1 to 3 are also Probe elements 117, 118 of the die bending press 101 in the forming die 108 integrated. Unlike the probe elements 17, 18 of the Die bending press 1 are the feeler elements 117, 118 of the die bending press 101 not designed as probe rods but as probe disks. The sensing elements are in guide slots 133, 134 117, 118 on the forming die 108 relative to this as well as relative guided to each other. The guidance of the tactile elements 117, 118 in a machining direction 105 serve sliders 122, 123, on which the sensing elements 117, 118 by means of pivot axes 135, 136 are articulated. Because of their given The feeler elements 117, 118 are pivotable transversely to the from a forming edge 109 of the forming die 108 and the machining direction 105 defined plane can be deflected relative to one another. The described deflectability of the feeler elements 117, 118 enables their self-centering in cases where a Axis 127 of the movement of the probe elements 117, 118 in the machining direction 105 unlike in the example shown, not with the bisector of the bending angle β between the workpiece legs 115, 116 coincides.

In addition to the management function already described above the sliders 122, 123 the task, the push buttons 117, 118 against falling out of into the forming edge 109 of the punch Secure 108 opening guide slots 133, 134.

The downward formation of the guide slots 133, 134 the forming die 108 has a special meaning. So allowed it the mentioned feature, the touch elements 117, 118 to immediately to lead to the forming edge 109 of the forming die 108. Accordingly, the touch elements 117, 118 also bring to work piece legs, which start out from the forming edge 109 only over a short leg length extend. The touch elements 117, 118 according to FIGS. 4 and 5 thus allow the determination of the actual size of the bending angle β or the determination of the change in the actual size of the bending angle β also in applications in which workpieces with very short Thighs are folded.

Since the probe elements 117, 118 are formed as thin platelets are and accordingly the guide slots 133, 134 only one have small width in the direction of the forming edge 109 the forming edge 109 in the area of the guide slots 133, 134 only interrupted over a short length and that with the Forming stamp 108 achievable processing result in its quality not affected.

Structure and method of operation of a die press 101 Device 119 for determining the change in the actual size of a bending angle β result from the figures 6a and 6b.

Components of the device 119 for determining the change in The actual size of the bending angle β is, on the one hand, that of FIGS. 4 and 5 previously described push buttons 117, 118 and the other a device 124 associated with the latter for determination the actual size of the bending angle β. The latter sits down again together from those shown in Figures 4 and 5 in detail and in FIGS. 6a and 6b for the sake of simplifying the illustration only indicated sliders 122, 123, one Device 125 for determining the relative position of the slide 122, 123 or the touch elements 117, 118 in the machining direction 105, a device 137 for determining the relative transverse deflection of the probe elements 117, 118 transverse to that of the forming edge 109 of the forming die 108 and the machining direction 105 Level, an evaluation device 138 for consideration a possible relative transverse deflection of the probe elements 117, 118 transversely to the level mentioned and a computing unit 126 for the calculation the actual size of the bending angle β. The device 124 for determining the actual size of the bending angle β is related with a comparison unit 128 for determining any deviations between successively determined actual values of the Bending angle β and with a device for comparing one Actual size of the bending angle β with a target size. The comparison unit Finally, 128 is coupled to a drive control 129 and this in turn with a machine drive 130 the die bending press 101. The functions of the evaluation device 138, the computing unit 126 and the comparison unit 128 taken from a central computer 131.

For the determination of the change in the actual size of the bending angle β there are two different cases. On the one hand - as in figure 6a - the movement axis 127 of the probe elements 117, 118 in the machining direction 105 with a bisector 139 of the Bending angle β coincide. On the other hand, the course of the The axis of movement 127 deviate from the course of the bisector 139. The latter case is outlined in Figure 6b.

Due to the symmetrical design of the circular discs Probe elements 117, 118 with respect to the bisector 139 of the bending angle β lie the center MR of the probe element 118 and the center Mr of the probe element 117 in the measuring position located probe elements 117, 118 always on the bisector 139. The probe element 118 has a radius R, the probe element 117 a radius r. The workpiece legs 115, 116 of the folded sheet 114 are tangent to the feeler elements 117, 118.

With the device 125 for determining the relative position of the Probe elements 117, 118 in processing direction 105 become independent of the mutual course of the movement axis 127, that is: the machining direction 105, and the bisector 139 always in the processing direction 105, that is, in the direction of Axis of movement 127 existing distance of the centers Mr and MR Probe elements 117, 118 determined. This distance is in the figures 6a and 6b denoted by Δx. For the distance between the centers Mr and MR of the probe elements 117, 118 in the direction of the bisector 139 is correspondingly the symbol D in FIGS. 6a and 6b chosen.

Due to known mathematical relationships: sin β 2nd = R - r D <=> β = 2 arc sin R - r D

After the radii r and R of the probe elements 117, 118 are known, their difference (R - r) can be easily calculated. The size D corresponds to the size Δx in the application according to FIG. 6a. The size Δx is measured by means of the device 125. The actual size of the bending angle β is accordingly obtained when the movement axis 127 of the probe elements 117, 118 or the machining direction 105 coincide with the bisector 139 as follows: β = 2 arc sin R - r Δx

If the course of the movement axis 127 or the machining direction 105 deviates from the course of the bisector 139, as is sketched in FIG. 6b, then when calculating the actual size of the bending angle β, a relative transverse deflection Δy of the sensing elements 117, 118 is transverse to the plane defined by the forming edge 109 of the forming die 108 and the machining direction 105. The quantity Δy is measured by means of the device 137 for determining the relative transverse deflection of the probe elements 117, 118. The following then applies: D 2nd = (Δx) 2nd + (Δy) 2nd

The bending angle β in the event of a deviation of the courses of the movement axis 127 or the machining direction 105 and the bisector 139 according to FIG. 6b accordingly results as follows: β = 2 arc sin R - r (Δx) 2nd + (Δy) 2nd

Also in the case according to FIG. 6b, the size Δx is Device 125 for determining the relative position of the feeler elements 117, 118 in the machining direction 105 or in the direction of the movement axis 127 determined. The evaluation device 138 takes into account that in addition to a relative position Δx also a relative Transverse deflection Δy is included in the calculation of the bending angle β got to. Finally, the arithmetic unit 126 delivers as shown in FIG 6a the actual size of the bending angle β.

Each two consecutive of the continuously determined actual values of the bending angle β are determined using the comparison unit 128 checked for an existing deviation. Takes this deviation the value 0 or a value close to 0, this indicates that the folded sheet 114 in the course of the discharge of the forming die 108 their load-free or their quasi-load-free State and the bending angle β its within the scope of the previous one Folding process has actually reached actual size. If this is ascertained, a drive controller 129 takes care of it transmitted signal for stopping the machine drive 130. The when the load-free or quasi-load-free state occurs the folded sheet 114 existing size of the Bending angle β is in the comparison device 132 with the predetermined Target size for the bending angle β compared. Is that Actual size of the one created during the previous folding process Bending angle β above the target size, so by the Central computer 131 in that described above for Figures 1 to 3 Way parameters for a subsequent corrective Defined folding process and post-processing via the drive control 129 and the machine drive controlled thereby 130 initiated and carried out.

Figures 7a to 10 relate to a die bending press 201 a device 219 for determining the change in the actual variable of a bending angle β which cooperates on a metal sheet 214 a forming die 208 and a forming die 210 with Workpiece legs 215, 216 has been created. The device 219 for determining the change in the actual size of the bending angle β includes probe elements 217, 218, which along a movement axis 227 in a machining direction 205 relative to the forming stamp 208 with a forming edge 209 and displaceable relative to each other are. In addition, the probe elements 217, 218 are transverse to that of the forming edge 209 of the forming die 208 and the machining direction 205 defined plane can be deflected relative to each other. Unlike the feeler elements 117, 118 according to FIGS. 4 6b to 6b are not in the form of circular disks but from circular disc segments. In accordance with the key elements 117, 118 are the key elements 217, 218 formed as a thin plate. The vastness of a common Guide slot 233 for the probe elements 217, 218 on the forming stamp 208 can therefore be small in the direction of the forming edge 209 being held.

The actual size of the bending angle is determined by means of a device 224 β determined. The device 224 for determining the actual size of the Bending angle β is part of the device 219 for determining the Change the actual size of the bending angle β and includes two Pushbuttons 217, 218 carrying slides 222, 223, a device 225 for determining the relative position of the slides 222, 223 or the feeler elements 217, 218 in the machining direction 205, a Device 237 for determining the relative transverse deflection of the Probe elements 217, 218 transverse to that of the machining direction 205 or the axis of movement 227 and the forming edge 209 Level, an evaluation device 238 for taking into account a any transverse deflection of the probe elements 217, 218 transverse to the mentioned level and a computing unit 226 for calculating the Actual size of the bending angle β. Device 224 is coupled with a comparison unit 228, by means of which the Difference between two successively determined actual quantities of the Bending angle β is calculated and also a component the device 219 for determining the change in the actual size of the Bending angle β forms. The comparison unit 228 is in turn with a drive control 229 for a machine drive 230 in Connection. In a comparison device 232, the means the device 224 determines the actual size of the bending angle β Entry of the load-free or quasi-load-free state of the Sheet 214 with a target size specified for the bending angle β compared. The evaluation device 238, the computing unit 226, the comparison unit 228 and the comparison device 232 are combined in a central computer 231.

The operation of the press brake shown in Figures 7a to 10 corresponds to the mode of operation of the embodiment Figures 4 to 6b. Accordingly, on a press brake, as shown in Figures 7a to 10, in the Determining the change in the actual size of the bending angle β is taken into account, whether and if so to what extent the course of a Bisector 239 of the bending angle β from the course of the machining direction 205 or the movement axis 227 of the the bisector 239 symmetrical probe elements 217, 218 deviates.

The usual case is sketched in FIG. 7a, in which the bisector of the angle 239 of the bending angle β on the folded sheet 214 with the movement axis 227 of the probe elements 217, 218 and thus coincides with the machining direction 205. Here are the conditions with solid lines in the lower end position forming stamp for the relevant operation 208 shown. The chamfered ones are indicated with dashed lines Sheet 214 and the probe elements 217, 218 when the from the stamping stamp 208 relieved state of the sheet 214.

During the relief of the metal sheet 214 from the forming die 208 after the folding process takes the actual size of the sheet metal legs 215, 216 included bending angle β to. In order to connected is a change in the relative position of the probe elements 217, 218 in the manner already described above. At The feeler elements 217, 218 change their relative position guided on a guide pin 240 which on the forming stamp 208th is fixed in position and overlapping elongated holes 241, 242 the slide 222, 223 engages.

Are the movement axis 227 of the probe elements 217, 218 in the machining direction 205 and the bisector 239 of the bending angle β congruent, so the determination is made during the Relief of the sheet 214 adjusting the actual sizes of the bending angle β analogous to the method described above for FIG. 6a based on the measured distances of the centers Mr and MR of the probe elements 217, 218 in the machining direction 205 and the difference between the known radii r and R of the probe elements 217, 218. The distance change occurs with each measurement dx of the centers Mr and MR determined, which are opposite to the previous one Measurement has stopped. By adding the changes in distance the respective distance between the centers Mr and MR results of the probe elements based on a distance output value.

If the courses of the movement axis 227 of the probe elements 217 218 or the machining direction 205 and the bisector 239 of the bending angle β from one another, as indicated in FIG. 7b is, so the determination of itself in the course of Relief of the metal sheet 214 from the forming stamp 208 one after the other actual values of the bending angle β in addition to the value dx takes into account a value dy which changes the relative transverse deflection of the probe elements 217, 218 transverse to the defined by the forming edge 209 and the machining direction 205 Represents level. It should be borne in mind that the value of dy according to Figure 7b does not match the amount of change the relative transverse deflection of the centers MR and Mr of the probe elements 217, 218, but that a geometric connection between the value dy and the amount of change in the relative lateral deflection of the centers MR and Mr, for example can be described by a ray set. Starting from one Initial value for the relative transverse deflection of the centers MR and Mr results from adding the specific changes dy the relative transverse deflection assigned to the respective measurement time of the centers MR and Mr. How the actual sizes of the bending angle β from the relative transverse deflection determined in each case and from the in the distance between the centers Mr and MR in the machining direction 205 is above 6b has already been explained in detail. The calculation the relative transverse deflection and the distance between the centers Mr and MR in processing direction 205 are carried out as is the determination the actual values of the bending angle β by means of the central computer 231 or its computing unit 226 and / or its evaluation device 238.

Also in the case of the die bending press 201 according to FIGS. 7a to 10 becomes the relative movement between the forming die 208 and the forming die 210 ends as soon as the load-free or quasi-load-free State of the sheet 214 occurs. The at this time The actual size of the bending angle β becomes the target size compared. A deviation determined in this way serves as Basis for the specification of application parameters for a subsequent one corrective folding process by the central computer 231 automated including the drive control 229 is initiated and carried out. The workpiece machining described including checking the processing result is repeated automatically until the actual created actual size of the bending angle β with the given Target size matches.

Like those shown in FIGS. 7a and 7b only hinted at Devices 225, 237 for determining the relative position the probe elements 217, 218 in the machining direction 205 or Determination of the relative transverse deflection of the probe elements 217, 218 are procured in detail, is just like the technically concrete Training other in Figures 7a and 7b in basic structure of components shown in Figures 8 to 10 remove.

The forming stamp 208 is, as shown in FIGS. 8 to 10, trained several times angled and takes inside the correspondingly designed slide 222, 223. This are rigid at their lower end with the circular disk segments trained probe elements 217, 218 connected. The forming stamp 208 is used to fold U-shaped bent parts.

Due to the described design of the guide for the slide 222, 223 on the guide pin 240, the slide 222, 223 together with the feeler elements 217, 218 attached to it in addition to a translational relative movement in the machining direction 205 perform a swivel movement transversely to it.

The device 225 for determining the relative position of the slide 222, 223 or the probe elements 217, 218 in the machining direction 205 includes a light source in the form of an LED 243 on the slide 223 and an optical sensor in the form of LED 243 a PSD (Position Sensitive Detector) 244 on the slider 222. The light from the LED 243 is struck by a pinhole 245 an active area 246 of the PSD. That on the active surface 246 of the PSD 244 incident light generates a photo stream by means of of which the above-mentioned change in relative position dx of the slide 222, 223 and the relative position by means of the relative position change the slide 222, 223 and thus the feeler elements 217, 218 in the machining direction 205 can be determined. The LED 243 as well the PSD 244 also function as components of the device 237 for determining the relative transverse deflection of the probe elements 217, 218 transverse to that of the forming edge 209 and the Machining direction 205 defined level. They serve for Determination of the change dy in the relative transverse deflection of the probe elements 217, 218.

Finally, a die bending press 301 is shown in FIG. 11. which on a forming die 308 above a forming die 310 a total of three in the longitudinal direction of the forming die distributed pairs of probe elements 317, 318, by means of which bending angle measurements are taken at three points on the forming tool can be carried out. To determine the change the actual size of a created bending angle and for control of the die bending press 301, devices such as those used 1 to 10 are described above. You can For example, tactile elements are used that are different in pairs are designed.

Claims (16)

1. Method for bending workpieces (14, 114, 214), in particular metal plates, in which at least one workpiece flank (15, 16; 115, 116; 215, 216) is bent at an angle of bend (β) towards at least one other workpiece flank (15, 16; 115, 116; 215, 216) of the workpiece (14, 114, 214) by acting on the workpiece with a forming punch (8, 108, 208, 308) and/or a forming die (10, 110, 210, 310) co-operating with the punch, and the workpiece (14, 114, 214) is subsequently relieved of pressure from the forming punch (8, 108, 208, 308) and/or from the forming die (10, 110, 210, 310), wherein the actual size of the angle of bend (β) is determined while the workpiece (14, 114, 214) is relieved of pressure from the forming punch (8, 108, 208, 308) and/or from the forming die (10, 110, 210, 310) and, after the workpiece (14, 114, 214) has been at least approximately completely relieved of pressure from the forming punch (8, 108, 208, 308) and/or from the forming die (10, 110, 210, 310), the actual size of the angle of bend (β) then obtained is compared with a desired size, characterised in that the actual size of the angle of bend (β) is continuously determined while the workpiece (14, 114, 214) is relieved of pressure from the forming punch (8, 108, 208, 308) and/or from the forming die (10, 110, 210, 310), that the change in the determined actual sizes of the angle of bend (β) is established from these sizes, and in that, as soon as the determined change in the actual size of the angle of bend (β) assumes a predetermined value, the actual size of the angle of bend (β) then obtained is compared with the desired size.
2. Method according to claim 1, wherein the forming punch (8, 108, 208, 308) and the forming die (10, 110, 210, 310) are moved relative to one another while the workpiece (14, 114, 214) is relieved of pressure, characterised in that the trend of the actual size of the angle of bend (β) is recorded as a function of the magnitude or of the duration of the relative movement of the forming punch (8, 108, 208, 308) and the forming die (10, 110, 210, 310) while the workpiece (14, 114, 214) is relieved of pressure, and the change in the actual size of the angle of bend (β) per unit of magnitude or duration of the relative movement of the forming punch (8, 108, 208, 308) and the forming die (10, 110, 210, 310) is determined from the recorded trend.
3. Method according to any one of the preceding claims, wherein the forming punch (8, 108, 208, 308) and the forming die (10, 110, 210, 310) are moved relative to one another while the workpiece (14, 114, 214) is relieved of pressure, characterized in that the relative movement of the forming punch (8, 108, 208, 308) and the forming die (10, 110, 210, 310) is terminated as soon as the determined change in the actual size of the angle of bend (β) assumes the predetermined value while the workpiece (14, 114, 214) is relieved of pressure.
4. Working machine for bending workpieces (14, 114, 214), in particular metal plates, according to a method as claimed in any one of the preceding claims, having a forming die (10, 110, 210, 310) and a forming punch (8, 108, 208, 308) which co-operates with the die and which can be moved in a controlled manner in a working direction (5, 105, 205) relative to the die by means of a drive control unit (29, 129, 229), and having at least two sensing elements (17, 18; 117, 118; 217, 218; 317, 318) which can be moved in the working direction (5, 105, 205) relative to the forming punch (8, 108, 208, 308) and/or the forming die (10, 110, 210, 310) and relative to one another and are supported in a measuring position at least at one of two flanks (15, 16; 115, 116; 215, 216) of the bent workpiece (14, 114, 214) which form an angle of bend (β) of the bent workpiece (14, 114, 214), wherein the relative position of the sensing elements (17, 18; 117, 118; 217, 218; 317, 318) is a measure of the actual size of the angle of bend (β), and the sensing elements (17, 18; 117, 118; 217, 218; 317, 318) are connected to a device (24, 124, 224) for determining the actual size of the angle of bend (β), characterised in that the sensing elements (17, 18; 117, 118; 217, 218; 317, 318) and the device (24, 124, 224) for determining the actual size of the angle of bend (β) are parts of a device (19, 119, 219) for determining the change in the actual size of the angle of bend (β), and that the device (24, 124, 224) for determining the actual size of the angle of bend (β) continuously determines the actual size while the workpiece (14, 114, 214) is relieved of pressure and is connected to a comparator device (32, 132, 232) for comparing a desired size of the angle of bend (β) with the actual size of the angle of bend (β) which is obtained when the change in the actual size of the angle of bend (β) determined by means of the said device (19, 119, 219) assumes a predetermined value.
5. Working machine according to claim 4, characterised in that the device (24, 124, 224) for determining the actual size of the angle of bend (β) comprises slides (22, 23; 122, 123; 222, 223) which are guided in the working direction (5, 105, 205) at the forming punch (8, 108, 208, 308) and each of which can be displaced in the working direction (5, 105, 205) with one of the sensing elements (17, 18; 117, 118; 217, 218; 317, 318).
6. Working machine according to claim 4 or 5, characterised in that the device (24, 124, 224) for determining the actual size of the angle of bend (β) comprises at least one light source, which is connected to one of the sensing elements (17, 18; 117, 118; 217, 218; 317, 318), can be displaced in the working direction (5, 105, 205) with this one element and is preferably a corresponding LED (243), and at least one optical sensor, which is connected to the other sensing element (17, 18; 117, 118; 217, 218; 317, 318), can be displaced in the working direction (5, 105, 205) with this other element, is associated with the light source and is preferably a PSD (Position Sensitive Detector) (244).
7. Working machine according to any one of claims 4 to 6, having two sensing elements (17, 18; 117, 118; 217, 218; 317, 318), characterised in that in the measuring position the sensing elements (17, 18; 117, 118; 217, 218; 317, 318) project from the forming punch (8, 108, 208, 308) transversely to the plane defined by a forming edge (9, 109, 209) of the forming punch (8, 108, 208) and the working direction (5, 105, 205) and each bear against both flanks (15, 16, 115, 116, 215, 216) of the bent workpiece (14, 114, 214), wherein the sensing elements (17, 18; 117, 118; 217, 218; 317, 318) are supported at the flanks (15, 16, 115, 116, 215, 216) of the bent workpiece (14, 114, 214) on the same side of the said plane at varying distances from the forming edge (9, 109, 209).
8. Working machine according to any one of claims 4 to 7, characterised in that the sensing elements (117, 118; 217, 218; 317, 318) are constructed as discs or disc segments.
9. Working machine according to any one of claims 4 to 8, characterised in that the sensing elements (17, 18) are constructed as sensing rods which are directed transversely to the plane defined by a forming edge (9) of the forming punch (8) and the working direction (5).
10. Working machine according to any one of claims 4 to 9, characterised in that the sensing elements (17, 18; 117, 118; 217, 218; 317, 318) can be deflected relative to one another transversely to the plane defined by a forming edge (9, 109, 209) of the forming punch (8, 108, 208, 308) and the working direction (5, 105, 205).
11. Working machine according to any one of claims 4 to 10, characterised in that the sensing elements (117, 118; 217, 218) can be pivoted relative to one another transversely to the plane defined by the forming edge (109, 209) of the forming punch (108, 208) and the working direction (105, 205).
12. Working machine according to any one of claims 4 to 11, characterised in that the sensing elements (17, 18) can be displaced relative to one another transversely to the plane defined by the forming edge (9) of the forming punch (8) and the working direction (5).
13. Working machine according to any one of claims 4 to 12, wherein the sensing elements (117, 118; 217, 218; 317, 318) can be deflected relative to one another transversely to the plane defined by a forming edge (109, 209) of the forming punch (108, 208, 308) and the working direction (105, 205), characterised in that a device (137, 237) for determining the relative transverse deflection of the sensing elements (117, 118; 217, 218; 317, 318) is provided as part of the device (119, 219) for determining the change in the actual size of the angle of bend (β), which device (137, 237) is connected to an evaluation unit (138, 238) by means of which the relative transverse deflection of the sensing elements (117, 118; 217, 218; 317, 318) is taken into account when determining the actual size of the angle of bend (β).
14. Working machine according to any one of claims 4 to 13, wherein the sensing elements (117, 118; 217, 218; 317, 318) can be deflected relative to one another transversely to the plane defined by a forming edge (109, 209) of the forming punch (108, 208, 308) and the working direction (105, 205), characterised in that the device (137, 237) for determining the relative transverse deflection of the sensing elements (117, 118; 217, 218; 317, 318) comprises at least one light source, which is connected to one of the sensing elements (117, 118; 217, 218; 317, 318), can be deflected transversely with the latter and is preferably a corresponding LED (243), and at least one optical sensor, which is connected to the other sensing element (117, 118; 217, 218; 317, 318), can be deflected transversely with the latter, is associated with the light source and is preferably a corresponding PSD (244).
15. Working machine according to any one of claims 4 to 14, wherein the device (124, 224) for determining the actual size of the angle of bend (β) comprises at least one light source, which can be displaced in the working direction with one of the sensing elements (117, 118; 217, 218), and at least one optical sensor, which can be displaced in the same direction with the other sensing element (117, 118; 217, 218), characterised in that the light source(s) which can be displaced in the working direction (105, 205) with the sensing elements (117, 118; 217, 218) and the corresponding optical sensor(s) are provided as the light source and as the optical sensor of the device (137, 237) for determining the relative transverse deflection of the sensing elements (117, 118; 217, 218).
16. Working machine according to one of claims 4 to 15, characterised in that the device (19, 119, 219) for determining the change in the actual size of the angle of bend (β) is connected to the drive control unit (29, 129, 229).

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