EP0242841A1 - Process and device for adjusting the pressing force of a pressing beam on a guillotine-type cutter - Google Patents

Abstract

A method for adjusting the pressing force of the pressing bar of a chopping machine (1) provides that the width of the stack of material to be fed is measured and the pressing force (P) is automatically changed in the same direction with the width, starting from a preselected basic value. For this purpose, a corresponding device on the cutting table (10) has a stack width measuring device (13). A control or regulating circuit (15) influenced by the measurement result changes the pressing force (P) depending on the width. This leads to very precise cutting results.

Description

The invention relates to a method for adjusting the pressing force of the press beam of a plan cutting machine, on which stacks of material to be cut are cut with different formats, and to a device for carrying out this method on a plan cutting machine with a cutting table and press beam, the press force of which can be changed.

In the case of face cutting machines, the cutting result depends, among other things, on the pressing force that the press beam exerts on the material to be cut during the cutting process. Too high a pressing force will damage the material on the stack surface. If the pressing force is too low, the material to be cut can shift due to the forces exerted by the knife during cutting. The press force depends on the material properties; softer material to be cut usually requires a higher pressing force than harder material to be cut. The format of the stack must also be taken into account; larger cutting widths require a higher pressing force than smaller cutting widths.

For this reason, conventional face cutting machines have an adjusting device with which the operator can adjust the respective pressing force. However, satisfactory cutting results are often not achieved here, either because the operator's experience is inadequate or because there is not always a change in the pressing force if this were necessary. In particular when dividing a large-sized stack into ever smaller stacks, for example for labels, the pressing force would have to be readjusted at relatively short intervals. This is tedious and time consuming.

The invention has for its object to provide a method of the type described above, by means of which the cutting results can be improved.

This object is achieved according to the invention in that the width of the stack fed in each case is measured and the pressing force, based on a preselected base value, is automatically changed in the same direction with the width.

With this procedure, the operator only needs to select a material-specific base value, while the width-dependent change of the pressing force takes place automatically. The base value can be determined with high accuracy, for example by a test pressing or on the basis of stored empirical values j from previous work with the same material to be cut. The width is measured in direct connection with the actuation of the press beam. Failure due to inadequate operator estimation or inadvertently missed Readjustment of the pressing force does not occur. When dividing a large-format stack into smaller formats, no interruptions to readjust the pressing force are necessary because the changing of the pressing force takes place automatically. This results in considerable time savings. Since the pressing force is very precisely adapted to the actual requirements, there is a high, constant cutting accuracy over the entire width of the material to be cut. This in turn leads to a long knife service life and a longer service life of the cutting machine, which means cost savings.

It is particularly advantageous if the pressing force is changed depending on the width so that the surface pressure under the press beam remains approximately constant. This means that the pressing force - if necessary while maintaining a small basic pressure - decreases linearly with the width. In most cases, this simple dependency leads to optimal results.

In particular, the base value for a certain material to be cut can be preselected with a maximum width and, to determine the pressing force, the base value can be reduced approximately in the ratio of the measured width to the maximum width. Since the base value corresponds to the greatest pressing force, any inaccuracies in the choice of the base value for smaller widths have a fraction of their size.

In a preferred embodiment it is ensured that for a number of selectable basic values a characteristic curve, which has different characteristic values for different widths, each assigned to a pressing force, is stored, depending on the measured width a characteristic value of a selected characteristic is called up and the pressing force is derived from it. By using the characteristic curves, pressing force parameters can be called up immediately after the width measurement. No arithmetic operations are therefore necessary. In addition, these characteristic values can be selected machine-specifically, i.e. taking into account all transfer functions in the control or regulating circuit.

The latter can be achieved in a simple manner in that at least two characteristic values of each characteristic curve are determined in a learning mode by randomly changing an auxiliary value corresponding to the characteristic values until the desired pressing force is reached and the auxiliary value thus obtained is stored as a characteristic value -.

The desired pressing force can be read off a display, for example. The characteristic value stored in this way takes into account the special properties of the machine and its press force setting.

The remaining stored characteristic values can be calculated from the characteristic values determined in the learning mode. This is especially true if the characteristic is a straight line.

The pressing force is preferably regulated as a function of a guide variable that changes depending on the width. The feedback of the actual value during control results in particularly precise press force settings.

The characteristic values of the characteristic curve are expediently used as the reference variable. It is convenient that the width of the stack be measured near the cut line. This ensures that the width that is subsequently to be cut is taken into account as a measured value in the setting of the pressing force.

To determine the basic value for a specific material to be cut, one can proceed, for example, in such a way that a stack of a predetermined width is pressed with a defined pressing force, the compression path is measured, and the basic value, which increases with it, is derived from this. Such a test pressing can always be carried out when there is no empirical data for a specific product to be cut.

A device suitable for carrying out the method on a face-cutting machine with a cutting table and press beam, the pressing force of which can be changed, is characterized in that a stack width measuring device is arranged on the cutting table and that a control or regulating circuit is provided which is influenced by the measuring result and which adjusts the pressing force depending on the width changes. The arrangement of the measuring device on the cutting table ensures that the current width dimension is included in the pressing force setting. The control or regulating circuit is able to quickly adjust the pressing force thus imparted.

In particular, the measuring device should be located in the cutting table below the press beam. This gives the exact assignment of the press force to the stack width loaded by the press beam.

It is favorable that the measuring device in the cutting table has a number of sensors arranged across its width, each of which responds when covered by a stack, and that the control or regulating circuit changes the pressing force depending on the number of responsive sensors. With this arrangement, it does not matter whether the stack to be cut is on the left, right or in the middle of the cutting table.

Since each sensor marks a certain latitude,! the number of responsive sensors can be used for width measurement.

A wide variety of designs come for the sensors; NEN, in particular touch contacts, proximity initiators, diffuse sensors or the like.

The device expediently also comprises a characteristic curve memory, from which characteristic values for guiding the control or regulating circuit can be called up depending on the width. This results in a very simple construction of the control or regulating circuit.

In a preferred construction it is ensured that the pressure beam is loaded by a hydraulic piston-cylinder arrangement and the pressure supplied can be adjusted by means of a control valve which can be actuated as a function of a characteristic value called up. In particular, there is a control unit that is connected on the input side to a basic value setting device, the stack width measuring device, the characteristic curve memory and an actual value feedback, and on the output side to the control input of the control valve.

In this case, a programmer can also be connected to the control unit, in which basic values and, if appropriate, width values are stored. In this programmer, values of an earlier order can be stored so that they can be called up at the push of a button when a new order of the same type is carried out.

• Fig. 1 eine schematische Darstellung einer ersten Vorrichtung gemäß der Erfindung,
• Fig. 2 einen Schnitt durch den Preßbereich bei einem Stapel maximaler Breite,
• Fig. 3 einen Schnitt durch den Preßbereich bei einem Stapel geringerer Breite,
• Fig. 4 ein Kennlinienfeld und
• Fig. 5 eine schematische Darstellung einer zweiten Ausführungsform.

The invention is explained in more detail below with reference to preferred exemplary embodiments illustrated in the drawing. Show it:

• 1 is a schematic representation of a first device according to the invention,
• 2 shows a section through the pressing area in a stack of maximum width,
• 3 shows a section through the pressing area in a stack of smaller width,
• Fig. 4 is a characteristic field and
• Fig. 5 is a schematic representation of a second embodiment.

In Fig. 1, a face cutting machine 1 is schematically illustrated, the press beam 2 is movable up and down in stand guides 3. The drive is operated by a direction-reversible piston-cylinder arrangement 4, the working pressure chamber 5 of which can be supplied with pressure fluid via a line 6. The hydraulic fluid is conveyed from a container 8 by a pump 7. The hydraulic pressure is set with a control valve 9, which is designed, for example, as a proportional valve. Below the press beam 2 is a Cutting table 10, in which sensors 11 schematically indicated are accommodated in a row below the press beam 2. The number depends on the width of the cutting table and the desired accuracy of the width measurement.

The sensors are commercially available mechanical contacts (push-button contacts), proximity initiators, light barriers; or reflected light sensor, air nozzles with dynamic pressure meter or the like. As shown in FIGS. 2 and 3, stacks of material of different widths are cut on the face cutting machine 1. FIG. 2 shows a wide stack 12, FIG. 3 shows a stack 12a of smaller width. As a result, all 8 sensors are covered in FIG. 2, whereas only 3 sensors are covered in FIG. 3. The number N of sensors covered is therefore a measure of the width of the stack. The sensors 11 thus form a stack width measuring device 13. A width signal is output via the signal line, which is equal to the number N of the excited sensors 11.

In order to obtain the correct compression of the stack 12 at the maximum width of FIG. 2, a pressing force P _{1 is} required. If the same material to be cut is cut into a smaller format and now has, for example, the width of FIG. 3, a smaller pressing force is necessary in order to obtain the same surface pressure as in FIG. 2. The pressing force P ₂ is approximately equal to 3/8 x P ₁ .

4 shows a family of characteristic curves, in which the pressing force P is illustrated over the number N of the excited sensors 11. On the left ordinate, basic values B are given, which are for a specific cutting machine are optimal if a certain material to be cut is available as a stack of maximum width (see FIG. 2). The characteristic curves run in a straight line up to a minimum pressing force C if only one sensor 11 is covered. From these it can be seen which pressing forces are necessary if any intermediate value of the width has been measured for a given material to be cut (with a certain basic value B and possibly an associated minimum value C). These intermediate values of the pressing force are set automatically if one of the characteristic curves 14 has previously been selected on the basis of the basic value B associated with the material.

For this purpose, a control circuit 15 is provided, which has a control unit 16. Its first input 17 is connected to a basic value setting device 18. This has a selector switch 19 with which a characteristic curve 14 can be selected, the base value B of which corresponds to the material to be cut to be treated. A second switch 20 is used to switch the width-dependent influencing on or off. A second connection 21 is connected to a non-volatile characteristic curve memory 22, in which characteristic curves, similar to characteristic curves 14 in FIG. 4, are stored. In this case, it is sufficient to store individual characteristic values for each characteristic, corresponding to the points X in FIG. 4, which are each assigned a specific width, represented by the number of responsive sensors. Another input 23 receives the width signals from line 14. An input 24 receives signals via a converter 25 which correspond to the actual value of the pressure in line 6 and thus to the pressing force P. An outlet 26 is connected to the control valve 9.

Furthermore, a programmer 27 can be present, which takes the place of the basic value setting device 18 if the same material to be cut has been treated in an earlier processing and the values set at that time have been stored in the programmer.

During operation, a basic value associated with the material to be cut is first input using the basic value setting device 18. This means that a specific characteristic curve corresponding to one of the characteristic curves 14 has been selected in the characteristic curve memory 22. Specific characteristic values X are called up from this characteristic curve as a function of the number N of responsive sensors 11. On the basis of these characteristic values, the control valve 9 sets a specific pressure in the line 6 and thus a specific pressing force P. By feedback of the actual value of the pressure at the inlet 24, a regulation results, in which the required pressing pressure P is set precisely. If the stack width changes because the original large format has been divided, the pressing force automatically adapts to the smaller width, so that the surface pressure remains approximately constant.

If another material to be cut is presented, a base value belonging to it can be selected with the help of the switch 19 and thus another characteristic curve in the memory 22. The method of operation along this characteristic curve is the same as the method of operation just described.

A display device 29 is connected to the input 24 via a converter 28, from which the pressure in the line 6 or the pressing force P can be read.

In a learning mode, the pressing force can also be changed with an auxiliary value transmitter 30. You can change the auxiliary value so far until the display device 29 or a desired pressing force. indicates a desired hydraulic pressure. If one then transfers this auxiliary value into the characteristic curve memory 22, one is certain that a characteristic value has been stored which corresponds exactly to a defined pressing force in the cutting machine in question. In this way, the maximum values (corresponding to the basic values B) and the minimum values C can be determined and stored for all characteristic curves which are to be entered in the memory 22, while the characteristic values 23 in between can be calculated by a computer contained in the control unit 16. This ensures that the same structure of the control circuit 15 can be used for cutting machines of various sizes and types. Before the first start-up, only the family of characteristic curves need to be stored, the exact course of which can be determined with the aid of the auxiliary value transmitter 30. In this way, all the transfer functions of an individual machine present in the control circuit 15 are taken into account. One obtains extremely well-adapted pressing forces.

It is understandable that the family of characteristics in the memory 22 only corresponds to the characteristics 14 of FIG. 4, because only electrical data are stored in the memory 22, which data must first be converted into the pressing force in the control circuit.

The setting of the basic value with the help of the switch 19 takes place on the basis of the experience gained in previous cutting processes or with the aid of a trial pressing, in which it is determined how far the stack 12 can be compressed when a defined pressing force is applied. In Fig. 2 it is illustrated, for example, that a path a has been covered from the first touch of the stack 12, which can be determined, for example, with the aid of a button, until the press beam 2 comes to a standstill. Large distances require a higher pressing force to hold the stack securely, smaller distances require a lower pressing force.

The embodiment of FIG. 5 differs from that of FIG. 1 only in a different application of force to the press beam 2. The control valve 9 acts on a one-sided loadable piston-cylinder arrangement 105, which is connected to the press beam 2 via mechanical transmission members 31 is. These parts are returned to the rest position by a return spring 32 while relieving pressure. A force transducer 33, for example a strain gauge, is provided in the transmission members, from which an actual value signal of the pressing force is sent to the control unit 16 via the line 34. The remaining function corresponds to that of FIG. 1.

The learning mode can be carried out automatically by automatically actuating a specific pressing force from the auxiliary power generator 30 and, when the desired value is reached, the auxiliary value is automatically transferred to the memory 22 as a characteristic value. The transfer to the next adjustment is then also automatic. Such a learning mode only takes a few minutes.

The basic value is entered in the setting device 18 in coded form. Instead of the illustrated width measuring device 13, other known measuring devices could also be used, for example mechanical or optical devices which measure the distance between the stack sides.

Claims (17)

1. A method for adjusting the pressing force of the press beam of a chopping machine, on which stacks of material to be cut are cut with different formats, characterized in that the width of the stack (12) fed in each case is measured and the pressing force (P), starting from a preselected basic value ( B) is automatically changed in the same direction with the width. 2. The method according to claim 1, characterized in _that the pressing force is changed depending on the width so that the surface pressure under the press beam remains approximately constant. 3. The method according to claim 1 or 2, characterized in that the base value (8) is preselected for a certain material to be cut with the maximum width and for determining the pressing force (P) the base value is reduced approximately in the ratio of the measured width to the maximum width. 4. The method according to any one of claims 1 to 3, characterized in that for a number of selectable basic values (B) each have a characteristic curve which has different characteristic values for different widths, each associated with a pressing force (P), depending on the a characteristic value of a selected characteristic curve is obtained and the pressing force (P) is derived therefrom. 5. The method according to claim 4, characterized in that at least two characteristic values of each characteristic curve are determined in a learning mode in that an auxiliary value corresponding to the characteristic values is arbitrarily changed until the desired pressing force is reached, and the auxiliary value thus obtained is stored as a characteristic value. i 6. The method according to claim 5, characterized in that the remaining stored characteristic values are calculated from the characteristic values determined in the learning mode. 7. The method according to any one of claims 1 to 6, characterized in that the pressing force (P) is regulated in dependence on a guide variable that changes depending on the width. 8. The method according to claim 7, characterized in that the characteristic values of the characteristic curve serve as the reference variable. 9. The method according to any one of claims 1 to 8, characterized in that the width of the stack is measured in the vicinity of the cutting line. 10. The method according to any one of claims 1 to 9, characterized in that to determine the base value (B) for a certain material to be cut a stack (12) with a predetermined width with a defined pressing force (P ₁ ) pressed, the compression path (a) measured and from this the base value that increases with it is derived. 11. A device for performing the method according to one of claims 1 to 10 on a chopping machine with a cutting table and press beam, the pressing force of which can be changed, characterized in that a stack width measuring device (13) is arranged on the cutting table (10) and that one of the measurement result influenced control or regulating circuit (15) is provided, which changes the pressing force (P) depending on the width. 12. The apparatus according to claim 11, characterized in that the measuring device (13) is in the cutting table (10) below the press beam (2). 13. The apparatus according to claim 11 or 12, characterized in that the measuring device (13) in the cutting table (10) has a number of sensors (11) distributed over its width, each responding when covered by a stack (12) and that Control or regulating circuit (15) changes the pressing force (P) depending on the number of responsive sensors (11). 14. Device according to one of claims 11 to 13, characterized by a characteristic curve memory (22) from which characteristic values (23) for guiding the control or regulating circuit (15) can be called up depending on the width. 15. Device according to one of claims 11 to 14, characterized in that the pressure beam (2) by a hydraulic piston-cylinder arrangement (5; 15) and the pressure supplied by means of a control valve (9) is adjustable, which is dependent can be actuated by a retrieved characteristic value. 16. The apparatus according to claim 15, characterized by a control device (16), the input side with a base value setting device (18), the stack width measuring device (13), the characteristic curve memory (22) and an actual value feedback and the output side with the Control input of the control valve (9) is connected. 17. The apparatus according to claim 16, characterized in that a program generator (27) is also connected to the control unit (16), in which base values and optionally width values are stored.

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