Abstract:
This device for positioning the sheets comprises a feed table with a drive for feeding the sheets. At least one front positioning stop stops the leading edges of the sheets. A register for the lateral position of the sheets. A device compares the lateral position to a reference position. A transverse drive for the sheets and a control applies the drive. The transverse drive comprises a transverse slide arranged between the stop and the feed table. A drive for the transverse slide is connected to the control. An attachment device jointly attaches the sheet to the transverse slide.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention refers to a device for positioning sheets into an introduction station of a processing machine, comprising a feed table with drive means for the sheets, at least one positioning front stop for stopping the leading edges of the sheets, means for registering the lateral position of the sheets, means for comparing the position to a reference position, means for transversely driving the sheets and control means for controlling the drive means dependent on the direction and the space between the registered lateral position of the sheet and the reference position and for stopping the sheet when the sheet meets with said reference position.  
         [0002]     In positioning devices usually used for machines that process paperboard, solid board, corrugated board sheets, such as converting presses comprising a plurality of stations, the positioning of the sheets must be very accurate in both a longitudinal direction and in a transverse direction at each station they cross. To this end, the sheets are regularly infed by a feeder towards the feed table, the sheets are shingled enabling their seizing by a gripper bar and their conveying towards the subsequent stations.  
         [0003]     Each sheet is usually aligned on the feed table first against front stops and then against lateral stops by means of advance rollers or plastic foils supporting downwards on the table. During processing of thin sheets, since the sheets are often injured when they reach the stops, they can thus generate a positioning error and their edges are marked.  
         [0004]     The problem arising with the sheet positioning is also especially delicate when the sheet is used in several operations, such as printing, folding lines creasing, and diecutting, since these operations must be carried out most exactly and each depends on the preceding operation. In spite of all precautions, errors or drifts in position of the processed portion with respect to the leading and lateral edges of the sheet caused, for example, from successive alignments at different locations of a sheet edge being not exactly rectilinear, or from systematic alignments at the same locations while leaving a mark. However, the diecutting of pre-printed elements does not permit of any positioning error in order to reach the desired quality of the manufactured product.  
         [0005]     U.S. Pat. No. 6,264,196 discloses that when the sheet reaches front stops mounted on a cylinder, it is seized by a gripper of a gripping device arranged on a carriage that is laterally held by two opposed compression springs. One of the springs is coaxial to a rod and is compressed between one end of the carriage and one rod shoulder. The end of the rod holds a pressure roller that is actuated against a cam section, located between two standby areas  41 ,  42 . When the sheet reaches the front stops, it is seized by the gripping device and the rod roller rests in the standby area of the cam. Once the grippers close, the pivoting cylinder drives the roller into a cam section while laterally moving the carriage and thus the sheet itself. When a detector registers the sheet edge, a brake is actuated to stop the carriage. The remaining travel of the rod is absorbed by the spring.  
         [0006]     In the above mentioned patent, the register position is not compared with a reference one for moving the sheet into one direction and with a distance corresponding to the space between the registered lateral position of the aligning mark and the reference position. No comparison is effectively carried out, and the original position of the sheet is not registered. One simply moves the sheet until its lateral edge reaches the desired position. The displacement applied by the cam remains the same and is not related to the registered error, since that error is unknown. One simply stops the carriage when the sheet edge is registered by a detector. However, the front stops are not fixed, but fixedly attached to the cylinder.  
         [0007]     U.S. Pat. No. 4,989,855 describes a positioning device wherein the stops are motorized in order to modify their position. That device comprises means for registering an aligning mark on the sheets to be aligned, comparing that mark with a reference position and adjusting the stops for correcting the sheet position. Such a device works like a common device and has the same risks, namely as far as the lateral aligning is concerned.  
         [0008]     EP 669,274 proposes an aligning device wherein the sheet to be aligned is actuated against the front lays, and the sheet is then laterally moved against side guides by means of a pull rod and a pad between which the sheet is seized. The sheet motion is stopped by side guides and the pull rod ends its motion sliding with respect to the flat element. Such a device is more particularly adapted for relatively rigid sheets such as corrugated ones.  
         [0009]     EP 1,044,908 describes a positioning device with no pad, comprising a movable shelf with temporary fastening means for the sheet to be aligned. On the one hand, the shelf is longitudinally moved by a back-and-forth motion and, on the other hand, by correction motions the shelf is moved about three vertical studs each fixedly attached to a carriage, a central carriage sliding into a longitudinal guide and two lateral carriages sliding into transverse guides. The correction motions of the shelf are produced by three linear motors controlled by opto-electronic registering means. The correction is carried out during the sheet conveying by the movable shelf, in order to drive the leading edge of the sheet in the grippers of a gripper bar in an accurate reference position, so that the temporary fastening means of the shelf can free the sheet and the shelf can be brought back to its original position for restarting with a new sheet. This device saves the time needed for sheet alignment, thus appreciably increasing the processing machine rate.  
         [0010]     EP 1,151,833 discloses a closely related device, in which a sheet gripping device is connected to the movable shelf by at least one link comprising a plurality of levers forming a parallelogram that can be put out of shape about an horizontal swiveling axis in order to impede the arrival of a component of horizontal strength issued from the opening levers of the temporary fastening grippers of one sheet edge on the shelf.  
         [0011]     Both of the above mentioned devices are very efficient in their positioning accuracy as the rate increasing of said positioned sheets are concerned. The alternative of an uninterrupted positioning of the conveyed sheet effectively enables saving the time needed for a common alignment. However, the resulting productivity increase requires a huge investment. The cost increase between a common registering system and an uninterrupted positioning device like the ones described in EP 1,044,908 and EP 1,151,833 is appreciable and economically justified only for some kind of machines.  
         [0012]     EP 1,308,406 discloses a device for registering a lateral edge of a sheet in an introduction station. One compares the registered position of one lateral edge of the sheet with the desired position, and produces a correction signal that generates an adjusting signal transmitted to an adjusting member for moving the lateral edge to the desired position. This operates directly on the conveyed sheet with respect to the measured space between the registered position and the desired position. On the other hand, this document includes no detail about how to perform the method.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention has an aim to, at least partly obviate, the usual drawbacks of common sheet aligning devices, without considerably increased cost of the processing machine to which the sheets positioning device is related.  
         [0014]     To this end, the present invention relates to a sheet positioning device into an introduction station of a processing machine. This device for positioning the sheets comprises a feed table with a drive for feeding the sheets. At least one front positioning stop stops the leading edges of the sheets. A register registers for the lateral position of the sheets. A device compares the registered lateral position to a reference position. A transverse drive drives the sheets and a control applies the drive. The transverse drive comprises a transverse slide arranged between the stop and the feed table. The drive for the transverse slide is connected to the control. An attachment device jointly attaches the sheet to the transverse slide.  
         [0015]     The main advantage of the present invention that it joins two aligning methods. To align the sheet leading edge, as with common positioning devices, it uses front lays against which the sheet is conveyed by the feed table, since the method of positioning the leading edges of the sheets is reliable, simple and has no appreciable drawback. Said front lays can be fixed or adjustable. For lateral alignment, sheets driving means are controlled by opto-electronic means, without using side guides that have drawbacks, i.e. especially when processing flexible sheets. Since the lateral alignment is achieved, as for common positioning systems, after the leading edge of the sheet is aligned by the front lays, the single movement applied to the sheet for laterally aligning it is a rectilinear motion. This produces appreciable simplification in the mechanical design or the electronic control, with respect to a movable device according to three vertical axis, like for abovementioned devices. Another important advantage of the present invention is that the lateral alignment enables sheet displacement in both directions, whereas a mechanical positioning allows only to pull or to push, while moving the sheet in only one direction.  
         [0016]     Whereas devices for a single mechanical positioning only can align the sheets depending on the sheet edge, the device according to the invention can achieve the positioning according to a printed aligning mark. It enables preventing errors between the print of the sheets printed in reels and their edges sectionally diecut by the reel, while using the print and not the diecut sheet edge as a reference and the angle of the leading edge of the sheet to be aligned can vary by several degrees with respect to the perpendicular axis.  
         [0017]     Further features and advantages of this invention will become evident from the reading of the following description and from the enclosed drawings illustrating, schematically and by way of example, an embodiment of the device for positioning according to the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a perspective view illustrating the method of positioning of the invention;  
         [0019]      FIG. 2  is a transverse elevation view of the positioning device;  
         [0020]      FIG. 3  is a sectional view according to the line III-III of  FIG. 2 ;  
         [0021]      FIG. 4  is a sectional view according to the line IV-IV of  FIG. 2 ;  
         [0022]      FIG. 5  is the same view as  FIG. 2 , illustrating an alternative;  
         [0023]      FIG. 6  is a sectional view according to the line VI-VI of  FIG. 5 ;  
         [0024]      FIG. 7  is a sectional and partially enlarged view of the detail in the ring VII of  FIG. 5 ;  
         [0025]      FIG. 8  is a data-processing diagram of the control device of the method of positioning. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]     A method of positioning according to the invention is illustrated in FIGS.  1  to  8 . The sheet  1  to be aligned is conveyed by a feed table T of a sheets processing machine, such as a die cutting press, or a printing machine, wherein the sheet that just went through a printing or die cutting operation must be accurately positioned with a view to a subsequent operation on it, to ensure a same reference position of the sheet for successive operations, so that the print or die cutting position, for example, is not shifted with respect to the preceding die cutting or printing operation.  
         [0027]     To this end, after the first operation is performed on the sheet, the sheet  1  is conveyed in the direction of arrow F by the feed table T against a plurality of front lays  2 , whose position could be adjustable. In this example, this operation is preferably carried out by at least one pressure roller  3 , controlled by a cam or a pneumatic cylinder (not shown), pressing the sheet  1  against a transverse slide  4 , arranged in the feed direction between the feed table T and the front lays  2 . The pressure roller  3  could alternatively be a gripping device, namely a suction pipe arranged on the transverse slide and connected to a suction supply. A photoelectric cell or a camera  5  is adapted to register a lateral edge of the sheet  1  or, preferably, to register an aligning mark, which has a position that is typically the one of the printing or die cutting of said sheet  1  and to compare that position to a reference one. The cell  5  is connected to an input of a control station  6 , which has one output connected to an actuator, namely a linear motor  7  for driving the transverse slide  4  with respect to the space between the measured lateral position of the sheet and the reference position. The control station  6  produces a supply current of a linear motor  7  dependent upon the direction in which the linear motor  7  moves to bring the edge of the sheet  1  into the reference position.  
         [0028]     FIGS.  2  to  4  illustrate the device for positioning the sheets into an introduction station of a processing machine. That device comprises in its center a transverse support  8  fixedly attached to the frame  9  of the processing machine which extends to both ends of the transverse support  8 . The support has in its center a linear motor  7 , which includes a U-shaped magnet rail  10  that is fastened by screws  11  to the transverse support  8 . A reel  12 , positioned into the magnet rail  10  of the linear motor  7 , is fastened to a movable section  13  of the linear motor  7  by screws  16 . The reel  12  is connected to an output of the control station  6  ( FIG. 1 ). The movable section  13  acts like a transverse slide. It is connected to the transverse support  8  by two carriages  14   a,    14   b  arranged on both sides of the linear motor  10 ,  12 . Each carriage  14   a,    14   b  is coupled to two parallel guiding slides  15   a,    15   b  ( FIG. 3 ). The upper surface of the transverse slide, comprised of the movable section  13 , is fixedly attached to an aluminum section  17  covered with a material having a high friction coefficient such as polyurethane, or which presents a roughened surface.  
         [0029]     The positioning device also comprises a transverse profile  18  fixedly attached to two vertical slides  19   a,    19   b,  mounted in two vertical guides  20   a,    20   b  fixedly attached to the frame  9 . The bottom of each vertical slide  19   a,    19   b  is pressed by a spring  21   a,    21   b  against a roller  22   a,    22   b,  assembled swiveling at the end of an arm of a swing  23   a,    23   b  rotatable in its center on the frame  9 . Another roller, of which only the roller  24   a  is shown on  FIG. 4 , is assembled swiveling at the other arm end of each swing  23   a,    23   b.  The rollers of the swings  23   a,    23   b  are pressed against two related cams, of which only the cam  25   a  is shown on  FIG. 4 , are fixedly attached to a control shaft  26  kinematically linked to the drive mechanism (not shown) of the processing machine for the sheets  1 .  
         [0030]     Two pairs of pressure rollers  27   a,    27   b  are freely swiveling about their pair axis perpendicular to the transverse section  18 , i.e. parallel to the advance direction F of the sheet  1  and fixedly attached to two supports  28   a,  respectively  28   b.  Each support  28   a,    28   b  comprise two adjusting units  29   a,    29   b,    30   a,    30   b  to adjust the height, respectively the lateral position of each support  28   a,    28   b.    
         [0031]     Each turn about the control shaft  26  is related to a working cycle of the positioning device during which the cams  25   a,    25   b  are pivoting the swings  23   a,    23   b,  driving thus the rollers  27   a,    27   b  downwards against the aluminum section  17 , seizing the sheet  1  between said section  17  and the rollers  27   a,    27   b  after the sheet is supported against the front lays  2 . The register cell  5  registers the position of the lateral edge of the sheet  1  or of an aligning mark on the sheet and sends the value as well as the direction of the measured space to the control station  6 . The latter sends an electric current to the reel  12  of the linear motor for moving the transverse slide  13 , forming the movable part of the linear motor, in the desired direction until the position registered by the register cell refers about the lateral position of the sheet  1  as being related to the reference position.  
         [0032]     The operation of lateral displacement of the sheet  1  by the linear motor is achieved in synchronism with the rotation of the control shaft  26 , so that when the correction is over, the cams  25   a,    25   b,  connected to the control shaft  26 , are swiveling the swings  23   a,    23   b  ( FIG. 4 ) in the anticlockwise direction, while raising the slides  19   a,    19   b  and the rollers  27   a,    27   b.  The sheet  1  is thus free and the cycle can re-start with a new sheet  1 . The means used for stripping the positioned sheet comprise a common gripper bar. The latter is not shown as it is not mentioned in the present invention and is of no use for its understanding.  
         [0033]     According to the alternative of the device illustrated on FIGS.  5  to  7 , instead of joining the transverse section  18  to vertical slides  19   a,    19   b,  that alternative comprises a transverse section  31  fixedly attached by its both ends to the frame  9 . Each pair of pressure rollers or shoes  27   a,    27   b  is then fixedly attached to the rod of a cylinder  32   a,    32   b,  as well as to two guide rods  33   a,    33   b,  arranged sliding inside the cylinder  32   a,    32   b,  so that the rollers or shoes  27   a,    27   b  are applied against the sheet  1  supporting on the movable section  13  of the linear motor at the time of its lateral alignment by means of the cylinders  32   a,    32   b.  Such an alternative is more advantageous than the embodiment illustrated by  FIG. 2 , since it is less expensive.  
         [0034]     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.