EP1120176A1 - Method for controlling the stroke of a press brake - Google Patents

Abstract

Method for adjusting the stroke of a press brake comprising a movable apron (1) supporting a punch (2), a fixed apron (3) supporting a die (4), means of displacement (5.5 ′) of the movable apron relative to the fixed apron, the said means of displacement resting on uprights (6,6 ') integral with the fixed apron, measurement rules (9,9') for measuring the displacement of the movable apron relative to at the uprights, at least one sensor (8, 8 ') measuring a physical parameter (p) varying with the force exerted by said punch on a sheet placed on said matrix, and an electronic control device (7) for the folding movement controlling the speed of said movement of movement between a top dead center and a bottom dead center (BDC), provided with a calculation means for correcting the value of said bottom dead center as a function of the measurement of said displacement and of said physical parameter . The difference in thickness between the actual thickness of the sheet and the set value (e) of the thickness of the sheet is measured by comparing the actual position of said displacement at which a predetermined variation Δp of said physical parameter occurs. (p) with the theoretical position of said displacement where this variation Δp should occur, and the electronic control device (7) calculates a correction of the bottom dead center taking into account said difference in thickness. <IMAGE>

Description

The present invention relates to a method for adjusting the stroke of a press brake comprising a movable deck supporting a punch, a fixed apron supporting a die, means for moving the movable deck relative to the fixed deck, the said means of movement based on fixed amounts of the fixed deck, measurement rules for measuring the displacement of the movable deck relative to at the uprights, at least one sensor measuring a parameter physics varying with the force exerted by said punch on a sheet placed on said matrix and a device folding movement control electronics controlling the speed of said movement of movement between a neutral point high and a bottom dead center and provided with a calculation means for correct the value of said bottom dead center according to the measurement of said displacement and of said physical parameter.

Applicant's patent CH 686119 describes a press brake of this type. When bending a sheet, the force undergone by the amounts of a press under the effect of the thrust of the jacks causes amounts to bend, which can result in frame deformation up to 1-2mm. This bending changes the depth of penetration of the punch into the die, this which creates an error in the bending angle obtained on the part to be to fold. In the adjustment process according to CH 686119, we determines, for example using pressure sensors, the force undergone by each of the amounts under the action of the means movement of the movable deck and we compare each of the values obtained with a predetermined diagram establishing the relationship between the force undergone by the respective amount and the bending of the upright, and the slide stroke is increased so as to compensate for bending errors due to press deformations, particularly due to bending amounts.

Another parameter likely to generate an error of the bending angle is the variability of the thickness of the sheet processed. One of the parameters is the nominal thickness of the sheet. introduced in the press brake control electronics during the initial stroke adjustment.

The actual thickness of the sheet must be measured in principle every time by the operator. Indeed, the sheet steel manufacturers supply sheets of which the actual thickness varies from up to up to 10% of the nominal thickness value. If a sheet nominal thickness of 2mm must for example be bent at 90 ° in a 12mm V-shaped opening, a variation in thickness of ± 10% will induce, if it is not corrected, a variation of the folding angle between 88 ° and 92 °.

The operator should therefore before each folding operation measure the actual thickness of the sheet it will process and enter this data into the control electronics of the press brake so that it corrects the stroke of the slide.

Experience shows that this preliminary measure is unfortunately often overlooked by operators, which causes the production of a certain number of parts including the folding angle is outside tolerance standards.

The purpose of the present invention is to provide a method of adjusting the stroke of a holding press brake account for variations in the actual thickness of the sheets processed, without requiring operator intervention.

To this end, the invention provides a method such as defined input, in which the difference between the thickness sheet metal and the set value of the thickness of the sheet is measured by the electronic control device of the press by comparing the actual position of the displacement, to which occurs a predetermined variation of a parameter physics varying with the force exerted by the punch on the sheet placed on the matrix, with the theoretical position of the displacement where this predetermined variation should occur produce, and in which the electronic device of command calculates a correction for the bottom dead center taking account for this difference in thickness.

Preferably, to detect more precisely said actual displacement position where the variation Δp, the speed of movement is reduced to a measurement acquisition speed (vam), lower than a predetermined folding speed (vl), when the punch is at a predetermined distance from the level theoretical plate pinching greater than the tolerance of thickness Δe for manufacturing said sheet, and the speed of movement increases to said speed of folding after detection of said predetermined variation Δp of said physical parameter (p).

According to a preferred embodiment of the invention, the movement of the movable platform takes place at approach speed from top dead center to a safety distance predetermined with respect to the theoretical level of pinching, that is to say the level reached by the deck during its lowering, where the sheet begins to be pinched between punch and matrix, distance where the speed is reduced to a speed of folding; the speed of movement of the deck is again reduced to a measurement acquisition speed, to a measurement acquisition distance, i.e. at a distance relative to this theoretical level of equal pinch or greater than the manufacturing thickness tolerance of the sheet metal; the speed is maintained at this acquisition speed of measurement over a displacement distance at least equal to double the measurement acquisition distance; the speed of displacement is then increased again up to speed folding. It is finally reduced and brought back to zero at approaching bottom dead center (or BDC, Bottom Dead Center).

While the speed of movement of the movable deck is reduced to the measurement acquisition speed, the system can perform a large number of measurement cycles of the physical parameter per unit of travel length and can therefore accurately detect the start of the variation of this parameter, as well as the precise position where the variation of the parameter exceeds a predetermined value, which means that the punch has come into contact with the sheet and is starting to pinch it.

Control electronics determine actual thickness sheet metal while the deck descends at reduced speed of measurement acquisition and recalculates the parameters of the folding operation, in particular a correction of the neutral point low (BDC).

The correction of the bottom dead center includes a correction level geometry due to the over- or under-thickness of the sheet metal. In addition, the thickness of the sheet is a parameter which largely determines the reaction force experienced by the press, in particular the uprights, during folding, and, consequently, the distortion of the press and the error of penetration of the resulting punch. From tests preliminary, we can establish an abacus or algorithm linking actual thickness and deformation of the press and correct the penetration error from the single measurement of the actual thickness.

It is however possible to measure during a folding operation both the actual thickness of the sheet when the pinch begins and the reaction force undergone by the press during the actual folding and proceed to the bottom dead center correction from these two measurements separate.

Two different parameters can be used to determine variations in sheet thickness and bending suffered by an amount.

If one chooses, to determine the variations sheet thickness, a physical parameter which is also representative of the geometric deformations of the press, this same parameter allows both to correct the variations in sheet thickness, by detecting a initial variation Δp of the parameter, and the deformation of the press, by measuring the maximum variation of the parameter in folding course.

Preferably, the force undergone by the amounts under the action of the means of moving the deck is determined during the folding operation by measuring the same parameter physical and compared with a diagram establishing the relation between force undergone by an amount and bending of said amount, and the slide stroke is also increased so that compensate for bending errors due to deformation of the press from this measurement, in addition to correcting errors due to variations in sheet thickness.

If the means of movement of the press brake include two hydraulic cylinders associated respectively with two amounts, the value of the physical parameter can be measured at the level of each amount and the electronic control can independently correct the stroke each cylinder to its bottom dead center, or recalculate a common correction value from these two measurement zones.

The physical parameter chosen can be the pressure hydraulic prevailing in the upper part of a cylinder.

The physical parameter can also be the constraint mechanical that a cylinder exerts on the movable deck.

The physical parameter can also be the distance between a point in the upper part and a point in the part low of the press frame.

The physical parameter can also be a constraint mechanical that undergoes part of the press frame.

Les figures 1a et 1b sont des vues schématiques illustrant l'effet d'une variation d'épaisseur d'une tôle sur le point de contact poinçon-tôle;

La figure 2 est une vue schématique de face d'une presse-plieuse munie d'un capteur de pression et d'une électronique de commande;

La figure 3 est un diagramme illustrant le déplacement du tablier au cours d'une opération de pliage selon l'invention.

Other features and advantages of the present invention will appear in the description below of an embodiment with reference to the accompanying figures, among which

Figures 1a and 1b are schematic views illustrating the effect of a variation in thickness of a sheet on the punch-sheet contact point;

Figure 2 is a schematic front view of a press brake fitted with a pressure sensor and control electronics;

Figure 3 is a diagram illustrating the movement of the deck during a folding operation according to the invention.

The figure shows that for a sheet whose thickness real e + Δe is greater than the nominal thickness e, the punch P comes into contact sooner than expected initial setting. If the bottom dead center is not corrected, occurrence upward, folding is excessive, as illustrated in Figure 1b showing that the actual folding results in an angle r greater than the theoretical angle t of a sheet nominal thickness, shown in dotted lines.

The press brake shown in Figure 2 has a movable deck 1 supporting a punch 2 and a fixed deck 3 supporting a matrix 4. The movement of the movable deck is carried out using two hydraulic cylinders 5, 5 ', mounted on two respective uprights 6, 6 ′ integral with the deck inferior. Two measurement rules 9 and 9 ', mounted on the movable deck 1, measure the displacement of the movable deck relative to the respective uprights 6 and 6 '. The folding movement is controlled by a device control electronics 7. Two pressure sensors 8 and 8 ' are mounted respectively on each of the cylinders so as to detect the pressure at the top of each of them. The electronic control device is arranged to process the signals a1 and a2 respectively from each pressure sensors and also process two signals b1 and b2 from the 9 and 9 'measurement rules and representative displacements of the movable deck relative to each of the uprights 6 and 6 '.

The diagram in Figure 3 illustrates the process according to the invention. It shows the speed of descent v of the deck mobile and at the same time shows the variation in pressure hydraulic p measured at a pressure sensor 8 or 8 '. The descent is carried out initially at a speed high approach v1 until reaching a distance predetermined from the level where the punch comes from theoretically pinch the sheet, called safety distance ds. AT at this time, the speed is decreased to a speed of folding vp, imposed by the composition and nominal thickness sheet metal as well as the characteristics of the bending desired, bending angle and tool profile. This speed can typically be of the order of 10mm / s. If we designate the nominal thickness of the sheet by e, the tolerance on the thickness by Δe, the real thickness of the sheet will be included in the range e ± Δe. When the punch is found at a distance, called measurement acquisition distance, dam, theoretical pinch level, slightly higher than Δe, the descent speed is reduced to a speed acquisition of measurement, vam, which is of the order of the 10th of the folding speed vp, typically 1mm / s.

During the entire descent, the pressure sensors 8 and 8 'measure the hydraulic pressure p at each of the cylinders 5 and 5 'and the control device 7 records it and Trafficking. The pressure variation is shown (in arbitrary units) on the diagram in Figure 3. The reduction of the speed v of descent, of the speed approach v1 at the folding speed vp, is accompanied by a slight concomitant pressure increase dpl. The value of the pressure reached then, during the descent phase at the bending speed and before coming into contact with the sheet, is considered as a reference value pr. of this parameter. A pressure measurement cycle of the sensor assembly + electronic control device lasts approximately 10 ms: from so while the deck goes down at a folding speed vp of the order of 10mm / s, a pressure measurement is performed every 0.1mm; when the descent speed is reduced to the measurement acquisition speed vam, a measurement pressure is applied every 0.01mm. The device is therefore able to determine very precisely the moment when the pressure p increases again by an amount Δp, representative of the contact of the punch with the face top of the sheet. You can choose a value of Δp from around 1 bar. This contact can occur at any point between the representative points of sheets of thickness e + Δe and e-Δe respectively. The comparison of entry level in contact with level theoretical pinch determines the difference between thickness real and nominal value of the sheet and the control device 7 immediately recalculates a bottom dead center.

After contact, the pressure measured at the level of a sensor 8, 8 'increases according to an S curve up to reach pp value, bending pressure, often from around 300 bars, beyond which it varies little. The difference in value pp-pr determines the deformation of amounts and other parts of the press. The device control electronics 7 compare the value of pp or (pp-pr) with an algorithm specific to this press brake, stored in memory, establishing the relationship between this value and deformation of the fixed parts of the press, conditioning an error of penetration of the punch dy. The punch stroke can then be automatically corrected by consequence: the position of the bottom dead center of the slide (BDC) is thus increased by the value dy at the level of each upright, so as to create an independent folding movement of the press.

Once the level of the actual point of contact punch with the sheet is acquired, the descent of the apron mobile can be continued at the folding speed, the value de dy which can be calculated and used for a correction of BDC while folding takes place at speed vp.

In the diagram in Figure 3, the descent speed of the apron re-accelerates from the vam value to the vp value after having traveled a distance 2 Δe at speed vam. The distance on which the deck descends at vam speed can also be programmed to a slightly higher value, for example 2xdam. The acceleration could also be programmed to intervene as soon as the variation Δp is detected. Those skilled in the art will readily understand that the movement of the apron described above can be programmed according to many variants without departing from the scope of the invention: the variation of the speed between points ds and dam can be programmed differently. Speed can by example go directly from fast approach speed v1 at the slow speed of acquisition of measurement vam without being maintained at an intermediate constant value vp. In others terms, in this case, ds = dam.

Hydraulic oil pressure at the top of the cylinders is a parameter representative of all the phenomena and easy to measure with known sensors. It presents plus the advantage of being able to be correlated with both the entry of the punch into contact with the sheet and with the maximum deformation of the press brake during operation In progress.

However, those skilled in the art will readily understand that other measurable physical parameters may represent all or part of the process. During the descent of movable deck, before coming into contact with the sheet, the apron and punch are suspended and exert due to their weight a force directed downward on the frame of the hurry. At the time of contact with the sheet, the resulting from the forces changes direction due to the force of reaction.

• la contrainte mécanique qu'un vérin exerce sur le tablier mobile peut être mesurée à l'aide de jauges de contrainte. Cette contrainte présente un saut de valeur lorsque le poinçon entre en contact avec la tôle, qui se traduit par une variation mesurable de quelques mV, pour atteindre ensuite une valeur maximale, de l'ordre du Volt, qui peut être corrélée à la déformation de la presse.
• La distance entre un élément de la partie haute et un élément de la partie basse du cadre de la presse peut être mesurée par des capteurs électromécaniques, en soi connus, capables de détecter des variations de distance de l'ordre du um. Le début de la variation du signal électrique est représentatif de l'entrée en contact du poinçon avec la tôle.
• On peut également mesurer par jauges de contrainte, la contrainte mécanique que subit une partie du cadre, plutôt que de mesurer la contrainte mécanique entre vérins et tablier mobile.

Les variations du paramètre physique choisi peuvent être mesurées en un seul point de la presse. Si elles sont mesurées en deux endroits différents, par exemple au niveau de deux montants latéraux, les valeurs mesurées et les corrections de point mort bas qu'elles déterminent peuvent être appliquées indépendamment au niveau des deux montants ou moyennées pour appliquer une correction globale.By way of nonlimiting examples of measurable parameters, there may be mentioned:

• the mechanical stress that a cylinder exerts on the movable deck can be measured using strain gauges. This constraint presents a jump in value when the punch comes into contact with the sheet, which results in a measurable variation of a few mV, to then reach a maximum value, of the order of Volt, which can be correlated with the deformation of the press.
• The distance between an element in the upper part and an element in the lower part of the press frame can be measured by electromechanical sensors, known per se, capable of detecting variations in distance of the order of µm. The start of the variation of the electrical signal is representative of the entry into contact of the punch with the sheet.
• It is also possible to measure, by strain gauges, the mechanical stress which a part of the frame undergoes, rather than measuring the mechanical stress between jacks and movable bulkhead.

Variations in the selected physical parameter can be measured at a single point on the press. If they are measured in two different places, for example at the level of two lateral uprights, the measured values and the low dead center corrections which they determine can be applied independently at the level of the two uprights or averaged to apply an overall correction.

Claims (10)

Method for adjusting the stroke of a press brake comprising a movable apron (1) supporting a punch (2), a fixed deck (3) supporting a matrix (4), means for displacement (5.5 ') of the movable deck relative to the deck fixed, the so-called means of movement based on uprights (6,6 ') integral with the fixed bulkhead, rules for measure (9.9 ') for measuring the displacement of the movable deck relative to the uprights, at least one sensor (8, 8 ') measuring a physical parameter (p) varying with the force exerted by said punch on a sheet placed on said die, and a electronic folding control device (7) the speed of the movement of movement between a neutral point high and a bottom dead center (BDC), provided with a calculation means to correct the value of said bottom dead center as a function of the measurement of said displacement and of said physical parameter, characterized in that the difference in thickness between the actual thickness of the sheet and a set value (e) of the thickness of the sheet is measured by comparing the position real of said displacement at which a variation occurs predetermined Δp of said physical parameter (p) with the theoretical position of said displacement where this variation Δp should occur, and that said electronic device command (7) calculates a correction for the bottom dead center in taking into account said difference in thickness. Method according to claim 1, characterized in that that the speed of movement is reduced to one measurement acquisition speed (vam), less than one predetermined bending speed (v1), when the punch is at a predetermined distance from the theoretical pinch level of the sheet greater than the thickness tolerance Δe of manufacturing of said sheet, and that the speed of movement of displacement increases to said folding speed after detection of said predetermined variation Δp of said physical parameter (p). A method according to claim 1 or claim 2, characterized in that said movement takes place at a approach speed (v1) from top dead center to a predetermined safety distance (ds) of the punch (2) by compared to the theoretical pinch level, where the speed is reduced to a folding speed (vp), that the speed is at again reduced to a measurement acquisition speed (vam), to a measurement acquisition distance (dam) of the punch by compared to said theoretical level of equal pinch or greater than the thickness tolerance Δe of the manufacture of said sheet and maintained at said acquisition speed of measure (vam) over a distance substantially equal to at least at double of said measurement acquisition distance (dam), and that the speed is then increased again until said folding speed (vp). Method according to claim 3, characterized in that that said measurement acquisition speed (vam) is approximately 1/10 of the folding speed (vp). Method according to any one of claims 1 to 4, characterized in that said physical parameter is chosen among the parameters representative of a deformation press geometry. Method according to any one of claims 1 to 5, characterized in that the electronic device for command (7) compares the measured values of said parameter physics (p) with a predetermined algorithm establishing the relationship between said physical parameter and the deformation of fixed parts of the press and corrects the bottom dead center in taking into account said deformation. Method according to any one of claims 1 to 6 of a press brake whose means of movement have two hydraulic cylinders associated respectively with two uprights, characterized in that said physical parameter is the hydraulic pressure measured at the top a jack. Method according to any one of claims 1 to 6, characterized in that said physical parameter is the mechanical stress that a cylinder exerts on the movable deck measured at this level by a strain gauge. Method according to any one of claims 1 to 6, characterized in that said physical parameter is a mechanical stress that part of the frame undergoes press measured at said part using a gauge of constraint. Method according to any one of claims 1 to 6, characterized in that said physical parameter is the distance between a point in the upper part and a point in the lower part of the press frame.

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