EP0530452B1 - Method for controlling or tube bending machine - Google Patents

Description

The invention relates to a method for controlling a pipe bending machine according to the preamble of claim 1 and a pipe bending machine for pressure bending a pipe according to the preamble of claim 6.

When bending pipes, the pipe is pressed laterally against a bending template using a clamping jaw, which is then rotated, the clamping jaw executing a pivoting movement. When turning the bending template, the tube is bent around the bending template. For thin pipe walls, small bending radii, large pipe diameters and sensitive pipe materials, pressure bending is used, with the unbent pipe section being pressed in the direction of the bending template by a pressing device during the bending process. Here, the pressing device is advanced at a speed that is somewhat greater than the speed of rotation of the bending template corresponds so that the tube is subjected to a slight compression in the longitudinal direction during the bending process. Of particular importance is the mutual coordination between the rotary movement of the bending template and the feed movement of the pressing device. If the pressing device is pushed too quickly or too slowly, cracks, corrugations or areas of different wall thickness can arise on the pipe.

From DE-C-23 04 838 a method and a pipe bending device are known, in which the feed movement of the pressing device is coordinated with the rotary movement of the bending template. For this purpose, transducers are provided which determine the peripheral speed and the upsetting speed from the bending angle of the bending template and from the upsetting path of the pressing device. In a comparison, the difference between the two speeds is formed and, depending on this difference, a servo valve is controlled, which is designed as a quantity control valve and changes the return quantity of the hydraulic drive of the pressing device. The measured variables that are evaluated are thus speeds and the control signal causes a change in the flow rate, namely the return flow rate of the hydraulic oil from the drive of the pressing device. Such a speed control has the disadvantage that an incorrect upsetting pressure which has arisen once is maintained over the entire tube bending process, even if the two speeds are subsequently kept in the correct mutual relationship. This means that errors currently occurring are not corrected by the control system. The feed rate of the pressing device is changed by the flow controller. However, such a flow rate control has the disadvantage that it is relatively sluggish and inaccurate and that the flow rate, which is predetermined by the control device, may not be temporarily reached because the resistance of the pressing device and the pipe are too great. In this case there is no subsequent correction and no "catching up".

The invention has for its object to provide a control method and a pipe bending machine, with which it is possible to achieve a high degree of uniformity of the bending process and the pressing during pressure bending, any deviations being made up for or compensated for immediately.

This object is achieved according to the invention with the features of patent claims 1 and 6.

In the control method according to the invention for a pipe bending machine, the position signals of the bending template and the pressing device are determined and processed to generate the actuating signal without the like from the position signals by integration or the like. Speed signals are formed. One of the two drives is used as a guide drive and the other of the drives as a tracking drive. As a result of the processing of the position signals, it can be achieved that a position signal of the bending template must correspond to a position signal of the pressing device during the entire bending process. The position signal pairs are thus permanently assigned to one another. In the event of a deviation, one will be found immediately Correction takes place so that deviations made earlier do not continue into the future. The control signal generated as a function of the position signals controls the delivery pressure of the tracked drive. This means that the delivery pressure is changed as a function of the control signal, this dependence preferably being linear. However, another regulation, for example a PID regulation, is also possible in order to compensate for deviations more quickly. Pressure control can be carried out simply and precisely, since controllable pressure regulators are available with the required accuracy.

The position signal of the bending template can be determined, for example, by a rotation angle sensor, which responds to the rotation of the bending template. The position signal of the pressing device is determined by a displacement sensor. When determining the position signal of the bending template, the diameter of the bending template and the diameter of the pipe to be bent must of course be taken into account, since the bending radius of the pipe axis in the bending area must be used for the position comparison. Therefore, the position signal of the bending template, which is used as the basis for the evaluation, only arises after the signal transmitter signal has been multiplied by a factor that corresponds to the mean bending radius.

If the position control were carried out in such a way that the two position signals were always the same, the pressing device would not exert any upsetting pressure on the pipe. For this reason, the control is carried out in such a way that the feed position over the largest part of the feed length or bending length the pressing device must take is slightly larger than the feed position or rotational position of the bending template. The rigidity of the tube prevents the press-on device from actually reaching its respective setpoint based on the guide signal derived from the rotation of the bending template. The difference between the actual value and the desired value of the position of the pressing device causes the upset pressure to be maintained, which is proportional to the size of the after-running of the pressing device forced by the pipe. The upsetting pressure is thus generated by dictating a position advance in relation to the bending template to the pressing device, which, however, is not achieved and which in turn maintains a certain form in the drive of the pressing device. In this way, the feed pressure or upsetting pressure is kept at a constant value. It is possible to change this value according to a predetermined program sequence during the bending process.

In the pipe bending machine according to the invention for pressure bending a pipe, position transmitters for determining the positions of the bending template and pressing device are connected to a control device in which the difference in position signals is formed and which, depending on this, controls a controllable pressure regulator for changing the delivery pressure of one of the two drives. Here, too, the control is such that the position of the pressing device must slightly exceed that of the bending template during the major part of the bending process, so that the pressure regulator is constantly commanded to be pressurized.

A certain difference, by which the position signals must differ, does not necessarily have to be predetermined, but a certain percentage of this difference can also be predetermined. It is only important that the control is carried out in such a way that a higher setpoint is specified for the position signal of the pressing device than for the position signal of the bending template corresponding to this position.

In the following an embodiment of the invention will be explained with reference to the drawings.

Fig. 1

eine schematische Darstellung einer Rohrbiegemaschine mit der erfindungsgemäßen Steuerung der Nachdrückvorrichtung und

Fig. 2

ein Diagramm zwischen dem Vorschubweg der Nachdrückvorrichtung und dem Rotationsweg des Rohres auf der Biegeschablone entsprechend der in einem Funktionsspeicher gespeicherten Beziehung.

Show it:

Fig. 1

is a schematic representation of a pipe bending machine with the control of the pressing device and

Fig. 2

a diagram between the feed path of the pressing device and the rotation path of the tube on the bending template according to the relationship stored in a function memory.

The pipe bending machine shown schematically in FIG. 1 has a bending template 10 rotatably mounted on a machine table (not shown). The bending template 10 arranged with the vertical axis of rotation 11 has essentially the shape of a cylindrical body, on the circumferential surface of which a bending groove 12 is formed, which takes up approximately half of the cross section of the tube 13 to be bent. A counter jaw 14 is attached to the bending template 10, with which a jaw 15 cooperates to jointly grip around the tube 13 and clamp it for the bending process. The clamping jaw 15 is attached to a pivot arm 16 which can be pivoted about an axis which is arranged coaxially with the axis of rotation 11 of the bending template 10. The clamping jaw 15 can be moved radially on this swivel arm 16 in order to clamp or release the tube.

The unbent section 13a of the tube 13 is supported by a pressing device 17. The pressing device has a slide 18 which can be moved in the direction of the double arrow 19 transversely to the tube section 13a. The carriage 18 carries a lower carriage 20 which can be moved in the longitudinal direction to the unbent pipe section 13a, i.e. in the direction of the double arrow 21, and a drive 22 for moving the lower carriage 20. The drive 22 is designed as a piston-cylinder unit which is fixed to the carriage 18 is arranged and the piston 23 engages the piston rod 24 on the lower slide 20 to move it. The cylinder of the drive 22 has a working chamber 25 and a return stroke chamber 26, which are separated by the piston 23.

A position transmitter 30 is also mounted on the slide 18 and cooperates with a position measuring bar 31 attached to the lower slide 20. In the present exemplary embodiment, the position measuring bar 31 is a toothed rack, which drives a pinion of the position transmitter 30 when the lower carriage 20 is moved longitudinally, in which pulses are generated, the number of which is a measure of the position of the lower carriage 20.

Another position transmitter 32 is arranged on the bending template 10. This position transmitter 32 has, for example, a rotation angle encoder that indicates the rotational position of the bending template 10. The bending template 10 is rotated by a hydraulic drive 33.

A slide rail 34 is attached to the lower slide 20 in the vicinity of the bending template 10 and presses against the tube 13 from the side facing away from the bending template and supports the unbent tube section 13a during the bending process. Furthermore, a thrust element 35 is attached to the lower slide 20, which engages on the rear part of the unbent pipe section 13a. The thrust element 35 can have a clamping jaw 36 in order to firmly clamp the pipe section 13a. It is designed so that it engages on the pipe without sliding.

During the bending process, the straight tube is clamped between the clamping jaw 15 and the counter clamping jaw 14. Then the bending template 10 is rotated according to a predetermined program, whereby the tube is drawn around the bending template 10 and at the same time the straight tube section 13a is moved forward. During the bending process, the lower slide 20 is advanced parallel to the pipe section 13a by the hydraulic drive 22. This feed takes place in such a way that the tube 13 is pushed by the thrust element 35, the tube section 13a being compressed.

The signal from the position transmitter 32 is processed in a processing unit 40, in which the bending radius BR is stored, to form the first position signal PS1. The bending radius BR takes into account the radius of the bending template 10 and the diameter of the pipe to be bent. The bending radius is the radius by which the pipe center axis is bent and the position signal PS1 indicates the path that the pipe has traveled around the bending template 10 from the beginning of the bending process.

The second position signal PS2 corresponds to the output signal of the position transmitter 30. It corresponds to the path that the lower slide or the push element 35 has passed through from the start of the pipe bending process.

The two position signals PS1 and PS2 are fed to a control unit 41 and compared there with one another in a comparator COMP. The output signal of the comparator is compared with the signal stored in a functional memory FS and the difference signal between the functional signal stored in the functional memory FS and the output signal of the comparator COMP is processed together with a signal which is taken from a parameter memory PS. The parameter memory PS contains parameters which can be entered manually, such as a material parameter MP of the tube 13, a wall thickness parameter WSP of the tube 13, a diameter parameter DP of the tube 13 and a bending radius parameter BRP. The signal obtained in this way is amplified by an amplifier V and fed as a control signal SS to a pressure regulator 42, which regulates the delivery pressure in a pressure line 43 leading from a pressure source 44, for example a pump, to the working chamber 25 of the drive 22 to a value which Control signal SS is proportional.

The control of the pipe bending machine works as follows:
The drive 33 of the bending template is positively controlled, ie it works either at constant speed or according to a program running according to the angle of rotation of the bending template with varying speeds and possibly downtimes. Depending on the angle of rotation caused by the drive 33, the processing circuit 40, taking into account the bending radius BR, generates the position signal PS1, which indicates the path of rotation of the tube 13 around the bending template 10. The position signal PS1 forms the reference variable for the control device 41. It is fed to the function memory FS in order to call up the function values which are stored for the individual position values. The comparator COMP compares the position signals PS1 and PS2 with one another and delivers a difference signal to the functional memory FS. This difference signal is compared with the function value corresponding to the position signal PS1 and the resulting difference signal is processed in the parameter memory PS with the corresponding material parameters MP, DP, WSP and BRP in order to generate the control signal SS. This control signal SS sets a corresponding pressure on the pressure regulator 42, which is then applied to the piston 23 of the drive 22.

2 shows the relationship between the position signals PS2 and PS1. The 45 ° line, in which the position signals PS1 and PS2 are equal to one another, is shown in dashed lines. The curve 45 indicates the content of the functional memory FS for the individual position signals PS1 with respect to the 45 ° line.

) als Steuersignal gebildet. Anders ausgedrückt: Der Sollwert, den das Positionssignal PS2 an der druch PS1 bestimmten Stelle einnehmen müßte, wird gleich (PS1 + Δs) gemacht. Die Abweichung des Istsignals PS2 von diesem Sollsignal wird im Parameterspeicher PS mit den entsprechenden Parametern multipliziert und anschließend als Stellsignal SS ausgegeben. Wären die Positionssignale PS1 und PS2 einander gleich, dann würde somit ein dem Funktionssignal Δs entsprechendes Sollsignal erzeugt werden, das bewirkt, daß der Druckregler 42 in der Arbeitskammer 25 einen entsprechenden Vorschubdruck für die Nachdrückvorrichtung 17 erzeugt.The position signal PS1 forms the reference variable and the position signal PS2 takes on a value which depends on the feed resistance of the pipe. If the control were carried out in such a way that the values of PS1 and PS2 are equal to one another, then the curve would run along the 45 ° line shown in broken lines. In this case, the thrust element 35 and the clamping jaw 14 would each assume the same travel positions in relation to their initial position, but the pipe would not be pushed with pressure, so that no pressure bending would take place. In order for pressure bending to take place, curve 45 deviates from the 45 ° line. In the initial phase of the bending process, only the bending template 10 is initially rotated, while the drive 22 for the pressing device is initially not yet pressurized. Therefore, the curve 45 runs below the 45 ° line up to a value S 1 of the position signal PS1. After this initial phase, curve 45 runs over the 45 ° line. In the function memory FS, the difference (PS2 - PS1) is compared with the function signal Δs and the difference ( $\text{PS1 + Δs - PS2}$

) formed as a control signal. In other words, the setpoint that the position signal PS2 should have at the position determined by PS1 is made equal (PS1 + Δs). The deviation of the actual signal PS2 from this target signal is multiplied in the parameter memory PS by the corresponding parameters and then output as an actuating signal SS. If the position signals PS1 and PS2 were equal to one another, then a desired signal corresponding to the function signal Δs would be generated, which causes the pressure regulator 42 in the working chamber 25 to generate a corresponding feed pressure for the pressing device 17.

The curve 45 of Fig. 2 shows that in different phases of the bending process, that is, in different Different function signal Δs are generated in areas of the first position signal PS1. These different areas of the position signal PS1 are the areas 0-S₁, S₁-S₂, S₂-S₃, S₃-S₄ and S₄-S _E. S _E is the end position at which the bending process is ended. The values Δs, that is to say the target deviations of the position signal PS2 from the position signal PS1, are stored in the function memory FS as a function of the position signal PS1, for example in a read-only memory or as a function curve or as a cam disk.

In general, it is also possible to store a constant Δs in the functional memory, so that with the same position data PS1 and PS2, the piston 23 is always acted on by a constant pressure which presses the unbent pipe section 13a in the direction of the bending template.

Claims (7)

1. A method for controlling a pipe bending machine comprising a rotatable bending template (10) and a clamping jaw (15) for pressing a pipe (13) against said bending template (10), as well as a pushing device (17) capable of being advanced by a hydraulic drive (22) and engaging the unbent portion (13a) of said pipe, wherein a first measured value is obtained from the rotation of said bending template (10) and a second measured value is obtained from the advance of said pushing device (17), and an actuation signal (SS) for controlling the drive (33, 22) of one of said bending template (10) and said pushing device (17) is obtained from the difference between the said two measured values,
   characterised in
   that the measured values processed are the position signals (PS1, PS2) of said bending template (10) and said pushing device (17) and that said actuation signal (SS) changes the supply pressure of the controlled drive (22, 23) in dependence on position signals (PS1, PS2).
2. The method of claim 1, characterised in that said actuation signal (SS) is generated such that it tends to cause a lead of the drive (22) of said pushing device (17) over the drive (33) of said bending template (10).
3. The method of claim 1, characterised in that one of said two drives (22, 33) is positively controlled and the position signal (PS1) corresponding to said drive is used as the reference input for the controlled drive (22), and that the processing of the position signals (PS1, PS2) is done with varying parameters in dependence on the position signal (PS1) forming said reference input.
4. The method of claim 1, characterised in that a target position of said pushing device (17) is kept smaller than the actual position of said bending template (10) until the position signal of said bending template (10) has reached a predetermined value (S₁), and is then controlled to take a value that is greater than the actual position (PS1) of said bending template (10).
5. The method of claim 1, characterised in that the processing of said position signals (PS1, PS2) is variable in dependence on settable parameters of said pipe (13) or said bending template (10).
6. A pipe bending machine for pressure bending a pipe (13), comprising a bending template (10) rotatable by a first drive (33) and a clamping jaw (15) pressing a pipe (13) against said bending template (10), a pushing device (17) driven by a hydraulic second drive (22) and engaging the unbent portion (13a) of said pipe, position sensors (32, 30) for detecting the positions of said bending template (10) and said pushing device (17), and a control means (41) changing the drive (22) of said pushing device (17) or that of said bending template (10) in dependence on measured values obtained from the position signals (PS1, PS2),
   characterised in
   that said control unit (41) calculates the difference between said position signals (PS1, PS2) and controls a pressure controller (42) in dependence thereon to change the supply pressure of one of said two drives (33, 22).
7. The pipe bending machine of claim 6, characterised in that said drive (33) of said bending template (10) is positively controlled and the position signal (PS1) of said bending template (10) forms a reference input for the drive (22) of said pushing device (17) and that said control means (41) includes a function memory (FS), different regions of positions of said bending template (10) being associated to different function values (Δs) that are read out when said regions are reached and are used to generate said actuation signal (SS) for said pressure controller (42).

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