EP0338944A1 - Method and device for controlling the resilience by bending of an elongated element such as a tube. - Google Patents

Abstract

The invention relates to the monitoring of the spring-back of a tube (7), or other deformable elongate element, on it being bent by wrapping around a forming component (1), with clamping of the tube (in 5) at a portion (7c) located in front of the bend to be formed. <??>After producing the bend (7a), the portion (7c) of the tube located in front of this bend remains clamped, while its portion (7b) located to the rear of the bend (7a) is released. The extent of the spring- back is determined by a detection means (13) which carries out a measurement or a referencing on the released portion (7b) of the tube located to the rear of the bend (7a). The detection of the spring-back is made on rotation of the tube (7) and of the forming component (1) about the axis (2) of the bend (7a) by detecting the instant when the portion (7b) reaches a predetermined position. <??>This process enables the bending of the tube (7) to be resumed after detecting the spring-back. <IMAGE>

Description

The present invention relates to a method for controlling the elastic return, during a bending operation of a deformable elongated element. The invention also relates to a device, associated with a bending tool, which is intended for the implementation of this control method. This invention applies more particularly, but not exclusively, to the control of the elastic return of the tubes, on automatic machines for bending the tubes.

The bending of the tubes, aimed at forming on these tubes bends characterized by their radius and their angle, is carried out by means of tools usually comprising: a forming roller rotating around an axis orthogonal to the initial direction of the tube to be bent, having at its periphery an annular groove and supporting, or forming by itself, a first jaw - a second jaw carried by a bending arm mounted rotating around the axis of the forming roller, the second jaw being movable on the arm and cooperating with the first jaw to grip and drive the tube to be bent - a strip parallel to the initial direction of the tube, located behind the jaws and intended to be applied laterally against the tube to be bent.

Thus, to produce an elbow on a part of the tube to be bent, this part is clamped between the two jaws and driven forward by the control of rotation of the bending arm, so as to wind in the groove of the forming roller, while that the strip, applied laterally against the tube behind the part being bent, avoids any unwanted deformation of the tube beyond the part to be bent, and ensures the reaction to bending forces.

The dimensional characteristics of the forming roller determine the radius of the bend thus formed on the tube, while the angle of rotation of the bending arm determines the angle of the bend. However, due to the phenomenon known as "elastic return", the final angle of the elbow is always less than the angle of the controlled rotation of the bending arm.

It follows from the above that, to bend a tube at a very precise angle value, it is necessary to have the bending arm describe a rotation at an angle equal to this value, increased by the elastic return. This supposes that one can know or determine the elastic return to take it into account. This elastic return can certainly be determined from theoretically, but it is also important to be able to control its real value in practice. There is such a need, in particular, when it comes to adjusting an automatic bending machine, before executing on the machine a series of all identical bends.

A known method for controlling the elastic return consists in detecting the extent of this elastic return on the bending machine, by means of mechanical probes. The implementation of this known method requires an opening of the jaws, releasing the tube in its part which has just been bent, the feelers coming into contact with the region of the tube situated in front of the bend formed.

The main drawback of the existing process, summarized above, lies in the fact that after detection of the elastic return, it is practically impossible to resume bending the tube, taking account of this elastic return, to bring the elbow exactly to the desired angle value. Indeed, the tube should be clamped again between the two previously opened jaws. However, it is impossible to pinch the tube again in a manner identical to the previous bending. This results in a marking of the tube by the jaws, which makes this tube unusable subsequently. Thus, the tube used to control the elastic return is a lost tube, which is difficult to accept in the case of expensive tubes due to their dimensions and / or their material.

Furthermore, the probes currently used for controlling the elastic return constitute on the bending machines additional bulky and annoying devices, located in the bending zone.

Also known, from document DD-A-109331 (East German patent), another method for controlling the elastic return of a tube in which, after execution of the elbow, the part of the tube situated in front of this elbow remains tight, while the part of said tube located behind the elbow is released, and in which a measurement or a location, determining the extent of the elastic return, is carried out on the part of said tube located behind the elbow.

Thus, after bending, the elastic return of the tube takes place freely, while this tube remains clamped between the jaws of the bending tool. The detection of the elastic return is made in the released part of the tube, located behind the elbow, away from the bending zone. The bending can then be resumed, taking into account the elastic return, without at any time interrupting the tightening of the tube in its part located in before the elbow therefore without marking the tube; the tube used for controlling the elastic return is therefore never lost, and therefore the principle of such a procedure proves to be advantageous.

However, document DD-A-109331 only proposes, for measuring or locating the elastic return of the tube, a device comprising a part provided with an angular scale, mounted on the released part of the tube, and an optical sighting system. mounted on the frame of the bending machine.

Such a device therefore forms a kind of external measuring instrument, and its implementation requires the addition of complementary elements on the machine and on the tube to be bent, which constitutes a first drawback.

In addition, the practical use of such an elastic return measurement device requires a double human intervention, on the one hand to carry out the aiming and reading of graduation by means of the optical system, and on the other hand to order corrective action on the machine based on the reading taken using the sighting system.

Thus, the use of this device requires significant time, and the process of determining the elastic return and of correction as a function of the value of this elastic return cannot be automated.

The aim of the present invention is to allow rapid and automatic measurement and correction of the elastic return, without the addition of external measurement elements, in particular on the tube, and also by eliminating human intervention such as aiming and reading a graduation, this by simple means and particularly suitable for bending machines with numerical control, currently very common, having means of calculation.

To this end, the invention relates to a method for controlling the elastic return, when bending an elongate deformable element such as a tube by winding this element around a forming member, with clamping of this element in a situated part. in front of an elbow to be formed, the method providing in known manner that after execution of the elbow, the part of the elongated element such as a tube situated in front of this elbow remains tight, while the part of said element situated in the rear of the elbow is released, and that a measurement or a marking, determining the extent of the elastic return, is carried out on the released part of said element located behind the elbow, and this method being characterized in that the detection of the elastic return is carried out, after release of the elongated element such as tube in its part situated behind the elbow, by making this element and the forming member describe a rotation around the axis of the elbow, and by detecting the instant when the part of said element situated behind the elbow reaches a determined position, as well as the angular position of the forming member at this instant; then knowing the angular position of the forming member, a simple calculation makes it possible to obtain the value of the elastic return, this calculation being carried out automatically.

The part of the elongated element such as a tube, situated behind the elbow, can in particular be released after the elbow has been executed by loosening the clamp holding said element and by spacing the strip applied laterally against this element during bending, in the case of a bending machine provided with a clamp and a strip.

Advantageously, the release of the part of the elongated element such as a tube, situated behind the elbow, is carried out only after the forming member has described a rotation in the opposite direction to that of the bending previously carried out, and of value equal to the theoretical elastic return angle, reduced by a small angular difference.

The device according to the invention associated with a bending tool, and intended for the implementation of the method defined above, comprises in known manner a detection means disposed behind the bending tool, and capable of detecting at minus a position of the part of the curved element situated behind the elbow, after release of this part, the detection means being provided for detecting the instant of passage of the part of the curved element, situated behind the elbow , in a determined position, this during the rotation of this element and of the forming member, the angular position of the forming member at the time of this detection providing an indication of the extent of the elastic return.

The detection means is, for example, a photoelectric cell detecting the instant when the part of the curved element located behind the elbow intersects a light ray during its rotation.

In a particular embodiment of the device which is the subject of the invention, the detection means is carried by the strip belonging to the bending tool, applied laterally against the elongated element such as a tube to be bent, this strip being spaced from said element and placed in a determined position, to release the part of the element under consideration located behind the elbow. Preferably, the detection means is carried by the rear end of the strip. The device thus has a minimal bulk, and it is located away from the bending zone; although carried by a movable member, namely the slide, this device occupies a fixed position, perfectly defined, when it intervenes to determine the extent of the elastic return of the tube, or other elongated element.

In any case, the invention will be better understood with the aid of the description which follows, with reference to the appended schematic drawing illustrating, by way of nonlimiting example, an embodiment of this method for controlling the return. elastic, when bending an elongated element.

Figures 1 to 5 of the drawing very schematically show the bending tool of a tube bending machine, and they illustrate the successive phases of a process for controlling the elastic return of a tube, in accordance with the present invention.

More particularly, these figures show a tool comprising a forming roller 1, mounted rotating around its axis 2 and having, at its periphery, a groove 3 at least partially annular. Around the axis 2 is also mounted rotating a bending arm 4, which carries a jaw 5 movable in the radial direction. The jaw 5 cooperates with a part 6 of the forming roller 1, located opposite, to clamp a bending tube 7 which is initially rectilinear, the initial axis of the tube 7 being indicated at 8.

The bending tool further comprises a strip 9, extending parallel to the axis 8 of the tube to be bent 7, and itself having a longitudinal groove 10. The strip 9 is movable transversely, as indicated by an arrow 11, to be able to be applied laterally against the tube 7, behind the part to be bent, or separated from the tube 7. In addition, this strip 9 can be moved longitudinally, therefore parallel to the axis 8, to accompany the tube 7 in its advance movement described during bending.

The bending tube 7 is held, behind its bending part, by means of a clamp 12 carried by a carriage not shown, movable in the direction of the axis 8. The movement of the carriage provided with the clamp 12 allows to bring, at the level of the tool previously described, the part of the tube 7 which must be bent.

To bend the tube 7, this tube 7 is clamped between the movable jaw 5 and the part 6 of the forming roller 1, the strip 9 is also applied against the tube 7, and the bending arm 4 d is rotated '' a certain angle A around axis 2, in the direction of arrow F, as shown in Figure 1 which indicates the stop position of the arm 4 at the end of bending.

During a process of controlling the elastic return of the tube 7, the tube 7 is first bent to a known value, by controlled rotation of the bending arm 4, according to the angle A, as described previously with reference to the figure 1.

Then, a rotation of the bending arm 4 is controlled around the axis 2, in the opposite direction to that of the arrow F and at an angle B, the value of which is equal to the theoretical angle of elastic return of the tube 7 , minus a small deviation E - see Figure 2.

Up to this stage, the tube 7 remains clamped by the clamp 12, and the strip 9 remains applied against this tube 7.

In the following phase, illustrated by FIG. 3, the clamp 12 is loosened and the carriage, carrying this clamp 2, is moved backwards. Then, the strip 9 is slightly separated from the tube 7, as shown in Figure 4. Simultaneously, the strip 9 can be moved back (in the case of a strip 9 movable also longitudinally), so as to be returned to a position of reference, perfectly defined.

At this stage, the bent tube 7 is entirely released in its part forming an elbow 7a, and also over its entire part 7b situated behind the elbow 7a. On the other hand, the tube 7 remains pinched between the jaw 5 and the part 6 of the forming roller 1, in its part 7c situated in front of its elbow 7a, the jaw 5 being at no time loose. The release of the elbow 7a from the tube 7 then allows it to complete its elastic return which was previously limited to the value of the angle B; this means that the direction of the part 7b of the tube 7, located behind the elbow 7a can deviate slightly from the axis 8.

The next phase involves a detection element, placed in a determined position behind the bending zone. In the example shown, the detection element is a photoelectric cell 13, carried by the rear end of the strip 9.

This last phase consists in rotating the forming roller 1 and the bending arm 4, in the same direction as during bending, therefore in the direction of the arrow F, the rotation of the arm 4 being accompanied by a rotation of the 'assembly of the bent tube 7 around the axis 2, without the elbow 7a of this tube 7 is deformed. The rotation is automatically stopped when the rear part 7b of the tube 7 cuts the light beam from the photoelectric cell 13, this part 7b then forming an angle C with the direction of the axis 8 - see FIG. 5.

At this time, the angular position of the forming roller 1 and the bending arm 4 is "read" automatically, by means of an encoder provided on the bending machine. It is understood that this angular position is a variable which depends on the position taken by the tube 7 after release of its elbow 7a, therefore a variable depending on the angular difference E defined above. Consequently, a calculation makes it possible to determine then, from the angular position of the forming roller 1, an indication of the effective value of the elastic return of the tube 7.

The main interest of the process lies in the fact that this real value of the elastic return is determined by keeping the tube 7 always tightened, at the same point, between the jaw 5 and the part 6 of the forming roller 1. It thus becomes possible to resume the same bend 7a, to bring it to the exact desired value: for this purpose, the strip 9 is again applied laterally against the tube 7, and the bending arm 4 is actuated again in the direction of bending, describing a rotation of an angle equal to the value, previously determined, of the elastic return.

The same process can be repeated iteratively until the desired bending angle is very precise.

The method is thus applicable to the initial adjustment of a machine for bending tubes, before the execution of a series of all identical bends, with the advantage that the first tube, used for focusing, is neither lost, or even marked by a loosening of the jaw 5 which would be followed by a tightening. This process can also be used to carry out a "sampling" check during the execution of a series of bends.

The implementation of the method can be done on automatic machines for bending tubes, new or existing, the addition of the detection element (cell 13) on an existing machine constituting only a very limited transformation, easily achievable .

In addition, the speed and automatism of the process make it possible, in certain cases, to apply this process not only for an initial adjustment of the machine but also for a control during the execution of each elbow. This is particularly the case for the bending of heterogeneous tubes, for example with differences in hardness, weld beads, a non-constant thickness or outside diameter.

It should be noted that it would not depart from the scope of the invention by replacing the photoelectric cell 13 by any equivalent detection means, such as a mechanical detector actuating an electrical contact, the detection means being associated with the strip 9 or independent of this strip. Furthermore, the invention is not necessarily linked to the presence of the clamp 12 and the carriage carrying this clamp, and it can also be applied to a bending machine without a carriage. Finally, the method of the invention is not limited to the bending of the tubes, and it also relates to any elongated element, such as a bar or profile, bent by similar means and also subject to the phenomenon of elastic return.

Claims (8)

1. Method for controlling the elastic return, when bending an elongate deformable element such as a tube (7) by winding this element around a forming member (1), with clamping of this element (at 5) in a part (7c) located in front of an elbow (7a) to be formed, this method providing that after execution of the elbow (7a), the part (7c) of the elongated element such as tube (7) located in front of this elbow (7a) remains tight, while the part (7b) of said element (7) located behind the elbow (7a) is released, and that a measurement or a location, determining the extent of the elastic return, is carried out on the released part (7b) of said element (7) located behind the elbow (7a), characterized in that the detection of the elastic return is carried out, after release of the elongated element such as tube (7) in its part (7b) located behind the elbow (7a), making this element (7) and the forming member (1) describe a rotation around the axis (2) of the elbow (7a), and detecting the instant when the part (7b) of said element (7) located behind the elbow (7a) reaches a determined position, as well as the angular position of the forming member (1) at this instant. 2. Method according to claim 1, characterized in that the part (7b) of the elongated element such as tube (7), located behind the elbow (7a), is released after execution of the elbow (7a) by loosening d 'a clamp (12) holding said element (7) and by spacing a strip (9) applied laterally against this element (7) during bending. 3. Method according to claim 1 or 2, characterized in that the release of the part (7b) of the elongated element such as tube (7), located behind the elbow (7a), is carried out only after the forming member (1) has described a rotation in the opposite direction to that of the bending previously carried out (F), and of value (B) equal to the theoretical angle of elastic return, reduced by a small angular deviation (E). 4. Method according to any one of claims 1 to 3, characterized in that, after determining the extent of the elastic return, the bending of the elongated element such as tube (7) is resumed taking into account the elastic return , without interrupting at any time the tightening of this element (7) in its part (7c) located in front of the elbow (7a). 5. Device for controlling the elastic return, during the bending of an elongated element such as a tube (7), for implementing the method according to any one of claims 1 to 4, this device being associated with a tool bending (1,4,5,9) and essentially comprising a means of detection (13) disposed behind the bending tool (1,4,5,9) and capable of detecting at least one position of the part (7b) of the curved element (7) located behind the elbow ( 7a), after release of this part (7b), characterized in that the detection means (13) is provided for detecting the instant of passage of the part (7b) of the curved element (7), located behind of the elbow (7a), in a determined position, this during the rotation of this element (7) and of the forming member (1), the angular position of the forming member (1) at the instant of this detection providing an indication of the extent of elastic return. 6. Device according to claim 5, characterized in that the detection means is a photoelectric cell (13), detecting the moment when the part (7b) of the curved element (7) located behind the elbow (7a) cuts a ray of light during its rotation. 7. Device according to claim 5 or 6, characterized in that the detection means (13) is carried by a strip (9) belonging to the bending tool, applied laterally against the elongated element such as tube (7) during the bending of this elongated element (7). 8. Device according to claim 7, characterized in that the detection means (13) is carried by the rear end of the strip (9).

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