EP1772405B1 - Method for positioning plate-shaped products in a treatment machine - Google Patents

Abstract

The method involves calculating variations in a positioning distance of grasping units (31) of a conveyor (30) with respect to a reference position by measuring the position of a mark integrated to the grasping units, and associating the variations to respective grasping units. The variations are then integrated in an original process of a control unit (40) for positioning plate-shaped elements in the grasping units, where the control unit controls trajectory of an introducer (20).

Description

The present invention relates to a method of positioning plate elements in a processing machine.

Such machines are used in particular in the printing and packaging industry, for example for making cardboard boxes from plate elements such as pre-printed sheets. Removed from a stack located upstream of the machine, these sheets are taken in an introducer station by an introducer for positioning in gripper bars mounted at regular intervals on a train of endless chains subsequent. The latter makes it possible to take the sheets to the different subsequent processing stations of the machine. Typically, such stations are dedicated to the cutting of leaves, the ejection of cutting waste and the receipt in stack of these sheets.

In a timed run, the train of chains moves and stops periodically so that during each move, all the gripper bars engaged with a sheet are moved from one station to the adjacent downstream station. If one wishes to obtain a printing or a shaping of quality, the positioning of the sheets within the different successive stations is a primordial operation. In the case of cutting a printed sheet, it will be understood that the positioning of the sheet in the cutting station must be precise. Indeed, it should be ensured that the tools used for cutting, for example the form of cutting a platen press, are in perfect register with the impression that has been made beforehand on the sheet.

The patent CH 690'470 describes a device for ensuring the quality of the production of a packaging manufacturing press. To do this, this device comprises a camera for reading, on the one hand registration marks related to printing, and on the other hand a mark for locating the position of the cutting. These registration marks are arranged on the front waste of the sheet held by the clip bar. The cutting mark is made by means of a perforator integral with the cutting tools. This perforator provides a hole in the front waste of the sheet simultaneously with the cutting of the latter. Further downstream, another device makes it possible to mark the sheets identified as defective by the camera, namely those which have an off-tolerance offset between printing and cutting.

In the patent EP 448 943 , it is referred to clamp bars connected at their ends to the conveyor chains by so-called "floating" fastening systems. These attachment systems allow to stop and momentarily block each clamp bar in a rigorously determined position in each station, this thanks to a mechanical locking system and elastic floating between the clip bar and the chain train. By means of such a system, the plate element can be positioned very precisely, on the one hand at the moment of its introduction in the clamp bar, and on the other hand in each of the treatment stations in which it system can be used to keep the bar in perfect registry with the tools of this station.

However, such a system has the disadvantage of either not being applicable in all machines, or not being the most appropriate system that could be arranged in some type of machine, especially in machines working cardboard corrugated.

The patent EP 1'044'908 relates to a device and method for positioning plate elements in an introduction station. Starting from a tablet located in a starting rear position, this method consists in switching on means for fixing a plate element on the tablet, and then controlling actuators to enable its forward displacement as a function of the position of the plate element on the tablet. As a result, the front edge of the plate member is brought, stopped and released into a predetermined position in the clamps of the gripper bar of the transport device before the shelf has finally been returned to the starting position. In order to be able to move the tablet forward, if necessary laterally or obliquely, by an adequate quantity, optoelectronic means read the coordinates of the position of the plate element and calculate the displacement necessary to position it at best in the clip bar.

Although optimized to achieve the positioning of the plate element in the gripper bar according to its initial starting position, it has nonetheless been found clear discrepancies between printing and cutting performed on these elements in machines equipped with such devices. These shifts, both lateral and longitudinal, persisted despite the fact that the positioning of the plate elements were correctly calculated from the registration marks related to printing, properly read by the optoelectronic means.

The object of the present invention is to remedy, at least in part, the aforementioned drawbacks so as to improve the positioning of plate elements in gripping members. In particular, this goal aims to prevent any appearance of registration defect between the different operations performed on these elements in the subsequent stations of the machine.

To this end, the subject of the present invention is a method for positioning plate elements in a processing machine according to claim 1.

• La figure 1 est une représentation schématique d'une machine de traitement au sein de laquelle défilent des éléments en plaque transportés par des barres de pinces.
• La figure 2 est une vue schématique en plan du bord frontal d'un élément en plaque en déplacement en direction d'une barre de pinces en vue d'être saisi par cette dernière.

The invention will be better understood from the study of an embodiment taken in no way limiting and illustrated by the appended figures in which:

• The figure 1 is a schematic representation of a processing machine in which scroll plate elements carried by clamp bars.
• The figure 2 is a schematic plan view of the front edge of a plate member moving in the direction of a clip bar for gripping by the latter.

In order to avoid any confusion in the description which follows, the terms upstream and downstream will be defined with reference to the direction of movement of the plate elements, as illustrated by the arrow D in the figures. These elements move from upstream to downstream, generally following the main axis X of the machine, in a movement clocked by periodic stops. Also, it will be specified that the longitudinal and lateral adjectives are defined with respect to this main axis X.

The figure 1 shows a schematic overview of a processing machine 1 in which the method of the present invention can be applied. This machine comprises a series of processing stations, among which there will typically be an introduction station 2 followed by a cutting station 3, a waste ejection station 4 and a receiving station 5. The number and kind of treatment stations which may vary according to the complexity of the shaping operations to be performed on plate elements 10.

In the introduction station 2, the latter are arranged in a stack 11, which is supported in particular against a gauge 6 also acting as a front stop for these elements. Thanks to the gap left at the bottom of the gauge 6, these elements can be removed one by one from the bottom of a stack 11 by means of an introducer 20. This device will allow to introduce each of them in an organ for gripping 31 of a conveyor 30, as best seen in the figure 2 . This conveyor generally consists of a chain train 32, between which chains are arranged a plurality of clamp bars, each acting as a gripping member 30 for the plate member 10.

The chain train 32 moves and stops periodically so that during a movement, each gripper 31 has moved from one station to the adjacent downstream station. The position of the stops of the gripping members is dictated by a movement of the chain train a constant distance. This distance corresponds to the theoretical pitch of these organs on the train of chains. Treatment stations 2, 3, 4 and 5 are fixed and spaced apart by this same step so that at each stop, the gripping members 31 stop in tracking with the tools of these stations.

With reference to the figure 2 , it represents, in a schematic view from above, a downstream portion of a plate member 10 moving in the direction of a bar clamp by the introducer 20. Such introducer may, for example, consist of A sucker plate 21. This suction pad sucks the plate member from the bottom of the stack 11, slide it under the dipstick 6 and bring it into a determined position engaged with the grippers. the grasping organ 31. The trajectory of the introducer 20 depends on the initial position of the plate member 10 at the bottom of the stack. This position is detected by first sensors 7 located directly downstream of the gauge 6 ( figure 1 ). Preferably, there will be a pair of these sensors above the plane of passage of the plate elements and another below. Thanks to this arrangement, it becomes possible to read printed marks 12 ( figure 2 ) allowing the identification of an impression made either on the front or the back of the plate element. Such marking marks are generally affixed on its front part, namely on the frontal waste useful for the gripping of the plate element by the gripping member.

As soon as the initial position of the plate element has been detected by said first sensors 7, it is immediately transmitted to a control unit 40 for calculating the trajectory of the introducer 20. Knowing the theoretical position of stopping the gripping member 31 in the insertion station, the control unit is then able to calculate the values of the displacement parameters (lateral, longitudinal or transverse) of the introducer, so that this the last can correctly bring the plate element that it carries in the gripping member according to its initial starting position. These calculations are carried out according to an original process, which also allows the control unit 40 to control the introducer 20.

Led by the gripping member in the cutting station 3, the plate member will then be cut into a die corresponding to the desired shape, for example to obtain a plurality of boxes of a given form. In this station, or in one or more subsequent stations, can also be performed other operations such as creasing fold lines, embossing some surfaces and / or the removal of patterns from metallized strips for example. In order to obtain a product of good quality, it is necessary, on the one hand, that all these operations are carried out in perfect registration with each other, and on the other hand that this marking is also in register with the printing in the case where the treated plate elements were previously printed.

Despite the implementation of said original positioning process, it has nonetheless been found registering offsets between these operations and the existing printing on the plate elements. It has also been noted that this untimely problem usually arises when dealing with chain trains of a certain age or having suffered shocks as a result of jamming for example. The explanation of these misregistration results from the following.

The distance separating two consecutive gripping members 31, in this case two adjacent gripper bars, should be constant and equal for all the gripping members of the conveyor. This is particularly the case when the chain train is new or the machine in which it is mounted is new. However, for various reasons this distance can either vary over time or vary abruptly according to various events. This variation may also be irregular so as to have different differences between the gripping members. After examining all the causes involved, it was found that the wear, shocks or excessive temperature variations of the carrier caused such variations. However, these variations have never been taken into account until now, since they are not suitable for identifying the operations performed on the plate elements.

When the carrier and / or the gripping members have undergone some normal wear, the elements which make a tendency to deviate more and more from original machining or construction tolerances. Most often, a chain train will tend to lengthen thereby causing a variation of the initial pitch of the clip bars. However, such defects do not occur only in the longitudinal direction but can also occur transversely or across the main axis X of the machine. Shocks, stresses or strong jolts can result in stretching of the links of the chain train or undetectable displacements of one or more gripper bars.

Since the positioning defects of the gripping members 31 within the conveyor 30 may be independent of each other, it is appropriate to associate with each of these members the corresponding variations of its positioning defect with respect to its reference position. initial.

With the object of the present invention, it becomes possible to take these variations into account in the control unit 40 which controls the introducer 20, and thus to correct systematic errors and to improve the positioning of the elements. in plate in each of the gripping members.

The first main step of the resulting positioning method consists in calculating, for each of the gripping members 31, variations of distance in the positioning of these members within the various treatment stations 2, 3, 4, 5. variations are determined with respect to a reference position known in coordinates in a Cartesian system for example. To do this, the position of at least one mark 33 secured to the gripping member will be measured, as illustrated in FIG. figure 2 . This measurement could be easily performed using at least a second sensor 8, as shown in FIG. figure 1 .

By comparing this measurement with the reference position, the distance variation of the positioning will be determined. The latter can be quantified by at least one value, preferably by a pair of georeferenced values in said Cartesian coordinate system. In such a case, the reference position would be advantageously defined in the same system by original values taken by default.

According to the preferred embodiment, the calculations of said variations are made during an initial phase preceding the processing of the plate elements 10. This initial phase can typically take place during the initialization of the machine during its adjustment for example. During this initial phase, it is expected that the conveyor 30 performs a complete revolution in the machine, so that all the gripping elements 31 can scroll under the second sensor or sensors 8. Thus, the determination of the distance variation of the positioning of each of the gripping members is performed only once. However, it may be advisable to carry out several redundant measurements so that the measured position of the gripping members results from an average of more than one measurement performed on the same reference mark 33. Such a result could be obtained by rotating the carrier 30 more than one turn during the initial phase.

According to the intended embodiment, these measurements are made during the scrolling of the gripping members and not at the stop of the latter. This choice is simply the result of a lack of space within the machine to be able to arrange the second sensors 8 above the gripping member when it is stationary in the station concerned.

When the measurements are thus made "on the fly", it is also planned to take into account several additional parameters such as speed and acceleration, positive or negative, the scroll member 31 at the time of measurement. These values make it possible in particular to take into account the inertia of the gripping members and the resulting elastic deformations. Modifying somewhat the value of the measurement compared to what it should be if it had been done at rest, these additional parameters are preferably integrated in the calculations of the distance variations of the positioning of the gripping members 31 in the cutting station 3.

The second main step of the method of the present invention consists in associating said calculated variations with each of the corresponding gripping members. This association can for example be done by memorizing the values of these variations in distance in correlation with a system for locating the gripping members. Such a tracking system for the purpose of identifying and distinguishing each of the gripping members with respect to each other. This system can be of relative or absolute type. In the case of a relative system, it is sufficient to know the number of gripping members 31 of the conveyor 30 and to assign an incremental numbering to these members, starting with the first gripping member detected by the second sensor 8. in the case of an absolute system, each gripping member will be identified by a permanent identification number which will be its own. This second solution therefore requires the identification of each of these organs, which is advantageously not necessary in the first tracking system. By means of one or the other of these systems, it is possible to allocate and memorize in the control unit 40 at least one variation in distance to each of the gripping members.

The third main step of said method aims at integrating the positioning distance variations of the gripping members into the original process of the unit. 40 to improve the positioning of the plate members 10 in the gripping members. This integration allows a first exploitation of the calculated variations, or even an exploitation of corresponding corrective values, which must be taken into account in order to compensate for the positioning defects noted on each of the gripping members. Thanks to this, the control unit will be able to modify the positioning coordinates, initially determined by means of the first sensors 7, that the introducer 20 will have to reach at the end of each of its runs.

In the last step, the method of the present invention may further comprise controlling each of the positioning of the plate members by measuring the relative positions of at least two shaping marks. This control can be achieved by means of a third sensor 9, preferably at least one pair of sensors 9 arranged on either side of the plane of passage of the plate elements 10, downstream of the cutting station 3.

To do this, it is intended to affix at least one cutting mark 13 on the front waste of the plate member, preferably not far from the printed mark 12. Preferably, according to the method of the present invention, the cutting marks 13 are made by incision of the plate member. One or more incisions, as illustrated in the figure 2 , can be obtained by means of knives specially dedicated for this purpose. These incisions reveal on the plate element a simple cutting net and are performed at the same time as the cutting operation in the corresponding station. Advantageously, this method of producing very fine cutting marks 13 generates no waste, unlike the cutting marks made up to now by perforation.

The cutting marks 13 and the printed marks 12 constitute shaping marks which can be read, by the same sensor 9, through a read window at a given instant. When they are matched with each other, these marks make it possible to appreciate the quality of the shaping of each plate element. The use of at least two of these sensors 9 also makes it possible to detect any parallelism defect, for example between the printing and cutting operations.

In the case where one of the third sensors 9 has detected such a defect or too large a gap between two different shaping marks, the defective plate element could for example be discarded in a downstream station specifically provided for this purpose. Such a station (not shown on the figure 1 ) would eject the defective plate elements according to a known operation, identical to that of the receiving station 5. However, this does not exclude the alternative to manually remove the defective elements, after their receipt.

Advantageously, the method of the present invention also makes it possible to collect data for statistical purposes. The information relating to the measurements of the positioning variations of the gripping members as well as the out-of-tolerance deviations and / or the measurements of the relative positions of the two shaping marks 12, 13 may for example be recorded in a computer file for a second time. exploitation of these data.

Advantageously, this method makes it possible to increase the longevity of the conveyor 30. In fact, although the strength of a used train of chains generally remains amply sufficient, the lengthening of some of its parts periodically necessitates its replacement in its entirety for to be able to maintain and guarantee a quality production. However, by taking into account possible variations of the pitch of the gripper bars, the life of such a string of chains can be extended, without prejudice to the quality of shaped plate elements.

Another advantage of the present invention lies in the fact that this method makes it possible to replace the mechanisms of the prior art aimed at locking the gripping members held to the conveyor by floating fastening systems. As a result, it becomes possible to dispense with such relatively complicated and expensive mechanisms, which moreover should equip all the gripping members.

Finally, it will be mentioned that the measured values relating to the positioning variations of the gripping members 31 may result from longitudinal, lateral or transverse positioning defects. A defect corresponding to a cross positioning of the gripping members could result from a different elongation of one chain relative to the other, or even from abnormal wear of the drive members of one of the two chains. In such a case, the plate elements adopt a flag position which, thanks to the object of the present invention, can be perfectly compensated during the positioning of these elements in the gripping members.

Claims (9)

1. Method of positioning thin flat objects (10) within a processing machine (1) comprising an inserter (20) for positioning these thin flat objects (10) in a plurality of gripper members (31) belonging to a conveyor (30) which draws them discontinuously through successive stations (3, 4, 5), the said inserter (20) being controlled by a controller (40) following a primary procedure, which method is characterized in that it consists in calculating, for each of the gripper members (31), variations in the positioning distance of these gripper members (31) relative to a reference position, assigning these variations to the respective gripper members (31), and incorporating these variations into the primary procedure of the controller (40) in order to improve the positioning of the thin flat objects (10) in the gripper members (31).
2. Method according to Claim 1, characterized in that the calculations of the said variations are performed by measuring the position of at least one reference point (33) fixed to each gripper member (31) and comparing this measured position with the said reference position.
3. Method according to Claim 1, characterized in that the calculations of the said variations are performed in the course of an initial phase before the said thin flat objects (10) are processed. '
4. Method according to Claim 2, characterized in that the measured position is the result of an average of several readings of the position of the said reference point (33) of a given gripper member (31).
5. Method according to Claim 2, characterized in that the said readings are taken while the gripper members (31) are in motion.
6. Method according to Claim 5, characterized in that speed and acceleration values for the said motion of the gripper members (31) produce additional parameters which are incorporated into the calculations of the said distance variations.
7. Method according to Claim 1, characterized in that the said assigning of the distance variations to the gripper members (31) is done by storing these variations correlated to a reference system of the gripper members (31).
8. Method according to Claim 7, characterized in that the said reference system of the gripper members (31) is a relative system that is a function of the number of gripper members (31) of the said conveyor (30).
9. Method according to Claim 1, characterized in that the said positioning of the thin flat objects (10) is checked as a final step by measuring the relative positions of at least two production marks (12, 13), at least one of which is made by an incision in the thin flat object (10) in a previous station (3)

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