METHOD AND DEVICE FOR DIVIDING A STACK OF SHEETS INTO REAMS AND FEEDING THE REAMS INTO A WRAPPING MACHINE

Abstract: A method and a device for dividing a stack of sheets into reams and feeding the reams into a wrapping machine are disclosed. The method comprises the steps of dividing one ream at a time out of the stack by a dividing means (4), feeding the ream into the wrapping machine by a feeding means (5), and compressing the stack before each dividing operation by a compressing means (13). Furthermore, the method comprises the steps of determining the height of the stack before the first dividing operation, as well as determining the thickness of a ream on the basis of this height and predetermined values of the number of sheets in the stack and the desired number of sheets in a ream.

Description: METHOD AND DEVICE FOR DIVIDING A STACK OF SHEETS INTO REAMS AND FEEDING THE REAMS INTO A WRAPPING MACHINE This invention relates to a method for dividing a stack of sheets into reams and feeding the reams into a wrapping machine, as well as to a device for implementing the method, as set forth in the preambles to appended claims 1 and 4. A paper-cutting machine produces stacks comprising several thousand sheets. These stacks are divided into bundles, so-called reams, of a certain number of sheets, for instance 125, 250 or 500 sheets. The reams are then wrapped in a so-called wrapping machine. US Patent Specification 4,861,227 discloses a device, in the following referred to as a ream feeder, for dividing a stack of sheets into reams and feeding the reams into a wrapping machine. This known ream feeder has a compressing means which compresses the stack before a ream is fed into the wrapping machine. The idea is to compress the uppermost sheets in the stack so as to reduce the variations in the number of sheets included in a ream. It goes without saying that the number of sheets in each ream that is divided out should be as close as possible to the given number, thereby to minimise the economic losses due to excessive tolerances resulting in a waste of several sheets per ream. The thickness of a ream depends on the type of sheets, including such para- meters as grammage, surface finishing and moisture con¬ tent. The thickness value may, for instance, be manually inputted or be retrieved from a stored table, the type of sheet involved being inputted. Despite the compression performed, the prior-art ream f eeder according to the US patent does not achieve t h e aimed-at accuracy and has to operate with tolerances o f several per cent, which is much too high. The reason for this is that the sheet thickness varies from one stack to another as a result of variations in the manu¬ facturing process. The prior-art ream feeder does not take such variations into account, but uses a theoretical value of the thickness of a sheet of a certain type for determining the ream thickness. Another disadvantage of the prior-art ream feeder is the many different sheet-thickness values that have to be processed, owing to the great number of different sheet types involved. The object of this invention is to provide a method and a device enabling a substantial enhancement of the accuracy and obviating the need of full information on the type of sheets. This object is achieved by a method and a device which are of the type stated by way of introduction and have the distinctive features recited in the characteris¬ ing clauses of appended claims 1 and 4, respectively. A preferred embodiment of the invention will now be described in more detail with reference to the accompany- ing drawing, which schematically illustrates this embodi¬ ment. Thus, the drawing shows a preferred embodiment of a device for dividing a stack 1 of sheets into reams and feeding the reams into a wrapping machine. A device of this type is generally referred to as a ream feeder. This ream feeder comprises a vertically adjustable platform 2, on which a pallet 3 with the stack 1 is placed. The plat¬ form 2 is shown in an elevated dividing position, as well as in an initial position (dash-dot lines). The ream feeder further comprises a dividing means 4 and a feed¬ ing means 5, which cooperate in order to divide reams out of the stack 1 and feed these reams into the wrapping machine. The dividing means 4 is reciprocatingly suspend¬ ed from a beam 6 and comprises a reciprocating knife 7, which is to penetrate between two sheets in the stack, thus separating a desired number of sheets (corresponding to a ream) uppermost in the stack 1 from the remaining sheets in the stack 1 and creating a gap between these two sheets. The feeding means 5 is reciprocatingly sus¬ pended from a beam 8, which in turn is connected to the dividing means 4. The feeding means 5 comprises L-shaped branches 9, each comprising a horizontal portion 10 and a vertical portion 11. For reasons of clarity, only part of the vertical portion 11 is shown in the drawing. The branches serve to transfer the divided-out reams to a conveyor 12, which conveys them to the wrapping machine (not shown). The ream feeder further comprises a compressing means 13 for compressing the stack 1 in the dividing position illustrated. The compressing means 13 has an abutment 14, which is shown when applied against the uppermost sheet in the stack 1, and a motor 15. The dividing means 4 includes a parallelogrammatic link-arm structure with four link arms: a front link arm 16, a rear link arm 17, an upper link arm 19 and a lower link arm 18, which are pivotally interconnected. The com- pressing means 13 is mounted on the front link arm 16, as is the knife 7. The vertical distance between the abut¬ ment 14 and the knife 7, which determines the thickness of the ream, is thus fixed, but may be adjusted with the aid of the motor 15. The abutment 14 exerts on the stack l a downwardly-directed force, the size of which depends on the position of a counterweight 20 along the upper link arm 19, the latter acting as a lever whose pivot centre coincides with the connection between it and the rear link arm 17. The ream feeder also has means for determining the height of the stack 1. In the preferred embodiment illu¬ strated, these means comprise a device 21 for measuring the height of the pallet, a transducer 22 indicating the vertical displacement of the platform and here illustrat- ed schematically in the form of a roller 23 with a pulse generator, and a wire 24 which travels over the roller and which at one end is fixed to the platform and at the other end has a weight. The pulse generator may alterna¬ tively be connected to a drive mechanism for elevating and lowering the platform 2. The device 21 for measur¬ ing the height of the pallet has a reciprocating arm 26, at whose end is arranged a vertically adjustable trans¬ ducer 27 comprising a microswitch and a photosensor. The means for determining the height of the stack 1 further includes a microswitch 28, which indicates when the dividing position has been attained. A control unit (not shown) is arranged for determin¬ ing the thickness of a ream and controlling the ream feeder. This control unit is of conventional type, such as a PLC (Programmable Logic Controller). A preferred mode of implementation of the inventive method is described below. The platform 2 is placed in an initial position indicated by the pulse generator 23. A pallet 3 with a stack 1 of sheets is then placed on the platform 2. The vertical position of the platform 2 may now need to be adjusted. Then, the arm 26 of the device 21 for measur¬ ing the height of the pallet is advanced until its end touches the stack 1. The transducer 27 is lowered until it comes into contact with the upper side of the pallet 3, which is indicated by the microswitch arranged at the end of the transducer 27. The length of the distance that the transducer has been lowered is inputted into the con¬ trol unit, which on the basis of this length and previous knowledge of the position of the arm 26 in relation to the platform 2 is able to determine the height of the pallet 3. If the pallet does not project beyond the stack 1, the photosensor indicates the transition between the paper of the sheets and the wood of the pallet 3, and this indication is used in the same manner as that of the microswitch. Subsequently, the platform 2 is elevated to a position in which the uppermost sheet in the stack 1 is located at a distance from the underside of the abutment 14. This is indicated by a transducer (not shown). In this position, the abutment 14 is set in the correct position in relation to the edge 29 of the stack. Then, the abutment 14 is lowered by disengaging the link-arm structure, which thus pivots freely about two points of connection on a line I-I extending through the rear link arm 17. Since the part of the structure to the left of the line I-I in the Figure is heavier than the part to the right, the abutment 14 is lowered until the rear portion 30 of the lower link arm 18 is applied against the switch 28 in an end position. This lowering movement is braked by a damper 31. The switching of the switch 28 results in another elevation of the platform 2. During this elevation, the uppermost sheet in the stack 1 comes to be applied against the abutment 14, and the compres- sion of the stack 1 begins. The compression continues until the upwardly-directed force acting on the abutment 14 just exceeds the downwardly- irected force exerted by the abutment. When this occurs, the abutment 14 leaves the end position, and the switch is immediately reset, which entails an interruption of the elevation of the platform 2. The platform 2 has now reached the dividing position. The total elevation has been registered by the pulse counter 23. On the basis of this value, the height of the pallet 3 determined previously, and the distance between the upper side of the platform 2 when in the ini¬ tial position and the underside of the abutment 14 when in the end position, the control unit is able to deter¬ mine the height of the stack 1 according to the formula hs = al-a2-hp (1) wherein hs is the height of the stack, al is the distance between the upper side of the platform 2 and the under¬ side of the abutment 14, a2 is the total elevation men- tioned above, i.e. the distance between the initial posi¬ tion and the dividing position, and hp is the height of the pallet 3. The number of sheets in the stack and the desired number of sheets in each ream, which are known before¬ hand, are in advance inputted into the control unit. On the basis of these values and the value hs, the control unit can determine the thickness of a ream, which is set as the vertical distance between the knife 7 and the underside of the abutment 14 by operating the motor 15, such that the abutment 14 is elevated or lowered with the aid of a connecting and setting unit 32. The measuring operation described above considerably enhances the accuracy of the process. Thus, the number of sheets in each ream only varies by HK 1-2, or at worst 3, sheets per ream. In a ream comprising 500 sheets, this corresponds to +_ 0.6% at the most, which is to be compar- ed with the variations in the order of several per cent of the prior-art device. In tests where the method according to the invention was implemented in a device according to the invention, the "negative" variation could even be eliminated, such that the desired number of sheets in a ream could be chosen (via the ream thickness) to be 501 when the nomi¬ nal and guaranteed number was 500. The number of sheets in the divided-out reams varied between 501 and 504. The method and the device according to the invention yield very little waste, as compared with the prior art. Thus, the invention enables considerable cost savings. The high degree of accuracy is partly due to the suspension of the abutment 14 (and of the knife 7) from the link-arm structure, using the lever principle in order to achieve a suitable compression force. This results in mechanically rigid and direct control of the elevation of the platform, as well as in the high precision of the distance al, which would not be possible with the compressing means of the above-mentioned US- 4,861,227, in which the abutment is "suspended" from a gas cylinder. Basically, a ream is divided out in the following way. In the dividing position, the knife 7 is advanced, such as to penetrate somewhat (a few mm) between two sheets. The abutment 14 is raised, and the knife 7 is further inserted and at the same time lifts the uppermost ream to form a gap. The branches are advanced, introduced into the gap and further advanced, so as to transfer the ream to the conveyor 12, which in turn conveys the ream to the wrapping machine. Although a preferred embodiment of the invention has been described above, it is understood that many modifi¬ cations of the method as well as of the device are con¬ ceivable within the scope of the invention as defined in appended claims 1 and 4. For instance, the height of the stack can be measured in many different ways, and the means for performing this measurement may be of different design.

Claims: CLAIMS 1. A method for dividing a stack of sheets into reams and feeding the reams into a wrapping machine, wherein one ream at a time is divided out of the stack by a dividing means and fed into the wrapping machine by a feeding means, and the stack of sheets is compressed before each dividing operation by a compressing means, c h a r a c t e r i s e d by the steps of determining the height of the compressed stack before the first dividing operation; and determining the thickness of a ream on the basis of said height and predetermined values of the num¬ ber of sheets in the stack and the desired number of sheets in a ream. 2. A method as set forth in claim 1, wherein the stack is initially placed on a vertically adjustable platform, c h a r a c t e r i s e d by the determination of the height of the stack comprising elevating the plat- form from an initial position to a dividing position, in which the uppermost sheet in the stack is so applied against an abutment forming part of the compressing means that the abutment exerts on this sheet a force resulting in a compression of the stack; and determining said height according to a formula hs = al-a2, wherein hs is the height of the stack, al is the distance between the upper side of the platform when in the initial position and the abutment surface applied against the uppermost sheet in the stack, and a2 is the distance between the initial position and the dividing position. 3. A method as set forth in claim 2, c h a r a c ¬ t e r i s e d by the elevation of the platform from the initial position to the dividing position comprising ele¬ vating the platform to a position immediately below the dividing position, the uppermost sheet in the stack being then located at a distance from the abutment; then lower¬ ing the abutment from a rest p ' osition to an end position in which it closes a switch; again elevating the platform in response to the closing of the switch in order to bring the uppermost sheet in the stack into application against the abutment; continuing to elevate the platform until an upwardly-directed force exerted by the sheet on the abutment cancels out the force exerted by the abut¬ ment, so that the abutment is just removed from the end position, which in turn breaks the switch; and interrupt¬ ing the elevation of the platform in response to the breaking of the switch, the dividing position having been attained. 4. A device for dividing a stack of sheets into reams and feeding the reams into a wrapping machine, com¬ prising a vertically adjustable platform for receiving the stack of sheets, a dividing and feeding means for dividing out one ream at a time of the stack and feeding it into a wrapping machine, and a compressing means for compressing the stack, c h a r a c t e r i s e d in that there are provided means for determining the height of the stack as well as means for determining the thickness of a ream on the basis of the height of the stack and predetermined values of the number of sheets in the stack and the desired number of sheets in a ream, said means for determining the height of the stack being adapted to do this when the stack is compressed by the compressing means. 5. A device as set forth in claim 4, c h a r a c ¬ t e r i s e d in that the platform is adapted to be ele¬ vated from an initial position, in which the stack is uncompressed, to a dividing position, in which the stack is compressed, an abutment forming part of the compress¬ ing means having a surface which is applied against the uppermost sheet in the stack and exerting a force on the stack which results in said compression, that said means for determining the height of the stack comprise means for determining the distance between the initial position and the dividing position, said means for determining the height of the stack doing this according to a formula hs = al-a2, wherein hs is the height of the stack, al is the distance between the upper side of the platform when in the initial position and said abutment surface when in the dividing position, and a2 is the distance between these positions. 6. A device as set forth in claim 4, wherein the stack is placed on a pallet arranged on the platform, c h a r a c t e r i s e d in that the means for determin- ing the height of the stack comprise means for determin¬ ing the height of the pallet, said means for determining the height of the stack doing this according to a formula hs = al-a2-hp, wherein hs is the height of the stack, al is the distance between the upper side of the platform when in the initial position and said abutment surface when in the dividing position, a2 is the distance between the initial position and the dividing position, and hp is the height of the pallet. 7. A device as set forth in any one of claims 4-6, c h a r a c t e r i s e d in that the dividing means com¬ prises a parallelogrammatic link-arm structure having four link arms which are movably interconnected, the abutment being arranged on one of the link arms. 8. A device as set forth in any one of claims 4-7, c h a r a c t e r i s e d in that the dividing means com¬ prises a reciprocating knife adapted to penetrate between two sheets in the stack, thus separating a desired number of sheets uppermost in the stack from the remaining sheets.

Inventors: NISSEN ALF PETER, NISSEN, ALF, PETER
Applicants: NISSEN ALF PETER, NISSEN, ALF, PETER
Application year: 1995
Main classification: B65H3
IPC codes: B65H3