EP0242841B1 - Process and device for adjusting the pressing force of a pressing beam on a guillotine-type cutter - Google Patents

Description

The invention relates to a method for adjusting the pressing force of the press beam of a face cutting machine according to the preamble of claim 1 and to an apparatus for performing this method according to the preamble of claim 8.

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.

From DE-B-10 93 774 a pressing force adjusting device is known, in which a plurality of scanning devices distributed over the entire knife length are provided in the area of the pressing beam in a straight row, each of which is arranged in the circuit of a lifting magnet. The solenoids control a pressure regulator that influences the pressure of the pressure beam. While the pressing pressure is automatically set according to the length of the material to be cut in this way, additional manipulations are necessary to adapt the pressing pressure to the material to be cut. The machine must therefore be set by means of a further, manually operated pressure regulator, or compression springs must be switched on or off. This leads to a rather complicated structure and to difficulties in linking the width-dependent pressure setting with the material-dependent pressure setting.

The invention has for its object to provide a method of the type described above, with the help of improved cutting results can be achieved quickly and accurately.

This object is achieved according to the invention in that for a number of selectable basic values which are dependent on the material to be cut, a characteristic curve, which has different characteristic values for different widths, each associated with a pressing force, is stored as data, depending on the measured width, a characteristic value of a selected characteristic curve retrieved and from this the pressing force is derived.

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 a high degree of accuracy, for example by a test pressing or on the basis of stored empirical values from previous work with the same cutting material. The width is measured in direct connection with the actuation of the press beam. Errors due to an insufficient estimate by the operator or an inadvertently missed readjustment of the pressing force do 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 saves a considerable amount of time. Since the pressing force is very precisely adapted to the actual requirements, there is a high level of cutting accuracy over the entire width of the material to be cut. This in turn leads to a long knife life and a longer service life of the cutting machine, that is to say a cost saving.

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 parameters can be machine-specific, can be selected taking into account all transfer functions in the control or regulating circuit. Since the characteristic values are only recorded as electrical data, simple storage results.

It is particularly favorable 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.

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 arbitrarily 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 certain material to be cut, one can proceed, for example, in such a way that a stack with 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, with a stack-width measuring device arranged on the cutting table, which has a row of sensors distributed over the width of the cutting table, each of which responds when covered by a stack , and with a control or regulating circuit influenced by the measurement result, which changes the pressing force depending on the width, is characterized by a characteristic curve memory from which, according to the choice of this characteristic, corresponding characteristic values for guiding the control or regulating circuit depending on the number of responsive sensors can be called up are.

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.

Furthermore, 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 identifies a certain latitude, the number of responsive sensors can be used for the latitude measurement.

Because a characteristic curve memory is used for the data, the control or regulating circuit is very simple.

A wide variety of constructions come into consideration for the sensors, in particular pushbuttons, change initiators, diffuse sensors or the like.

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.

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:

Fig. 1

1 shows a schematic representation of a first device according to the invention,

Fig. 2

a section through the pressing area with a stack of maximum width,

Fig. 3

a section through the pressing area in a stack of smaller width,

Fig. 4

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 (touch contacts), proximity initiators, light barriers or diffuse sensors, air nozzles with a dynamic pressure gauge 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 P₂ is approximately equal to 3/8 x P₁.

4 shows a family of characteristic curves, in which the pressing force P is illustrated over the number N of the excited sensors 11. Basic values B are given on the left ordinate, 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 width value has been measured for a given material to be cut (with a certain base 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 that 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 needs 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 test 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 bar 2 comes to a standstill. Long 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 . 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 (11)

1. Method for adjusting the pressing force (P) of the pressure bar (2) of a guillotine-type cutting machine on which stacks of material (12, 12a) with different formats are cut, in which the width of the stack (12, 12a) delivered at any given time is measured and the pressing force (P) is automatically altered in the same direction as the width and in which the pressing force (P) is moreover adjustable as a function of the material to be cut, characterised in that for each of a number of selectable base values (B) depending on the material to be cut, a characteristic (14) comprising different parameters for different widths each associated with a pressing force (P) is stored as data, a parameter of a selected characteristic is called up as a function of the measured width, and the pressing force (P) is derived therefrom.
2. Method according to claim 1, characterised in that the pressing force (P) is altered as a function of width in such a way that the contact pressure under the pressure bar (2) remains approximately constant.
3. Method according to claim 1 or 2, characterised in that the base value (B) is preselected for a certain material with maximum width, and to determine the pressing force (P) the base value is reduced approximately in the ratio of measured width to maximum width.
4. Method according to any of claims 1 to 3, characterised in that two or more parameters of each characteristic (14) are determined in a learning mode by randomly altering an ancillary value corresponding to the parameters until the desired pressing force (P) is reached, and storing the ancillary value obtained in this way as a parameter.
5. Method according to claim 4, characterised in that the other stored parameters are calculated from the parameters determined in the learning mode.
6. Method according to any of claims 1 to 5, characterised in that the pressing force (P) is regulated as a control variable as a function of the parameters of the characteristic (14).
7. Method according to any of claims 1 to 6, characterised in that to determine the base value for a certain material, a stack (12) with a given width is pressed with a predefined pressing force (P₁), the path of compression (a) is measured, and from the latter is derived the base value which increases with it.
8. Device for carrying out the method according to any of claims 1 to 7 on a guillotine-type cutting machine with cutting table (10) and pressure bar (2) of which the pressing force (P) is variable, with a stack width measuring device (13) mounted on the cutting table (10) and comprising a row of sensors (11) which are distributed over the width of the cutting table and in each case respond when covered by a stack (12, 12a), and with a control or regulating circuit which is influenced by the measurement result and which alters the pressing force (P) as a function of width, characterised by a characteristic memory (22) from which, after selection of a characteristic, parameters (23) corresponding to this characteristic can be called up for directing the control or regulating circuit (15) as a function of the number of sensors (11) responding.
9. Device according to claim 8, in which the pressure bar is loaded by a hydraulic piston and cylinder assembly, characterised in that the pressure delivered can be adjusted by means of a single regulating valve (9) which can be operated as a function of a parameter which has been called up.
10. Device according to claim 9, characterised by a control unit (16) which is connected on the input side to a base value adjuster (18), the stack width measuring device (13), the characteristic memory (22) and an actual value feedback means and on the output side to the set input of the regulating valve (9).
11. Device according to claim 10, characterised in that a programme generator (27) in which base values and, if occasion arises, width values are stored is also connected to the control unit (16).

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