Collation machine

Abstract

A collation machine 1 has an upper supply 2 of upper elements 4 and a lower supply 6 of lower elements 8 whereby a controller 26 and transport apparatus 18 create a series of stacks by arranging upper

Description

The present invention relates to collation machines for aligning or collating sheets of material, and to methods of operating such a collation machines. Many products comprise a plurality of sheets overlayed on one another and secured together, for example by lamination. Some, or all, of the layers may comprise features that should be aligned with features on other layers of the final product. The features may include printing, electronic chips or components, or security features. The products may include credit cards, bank cards, ID cards or passport data pages, and the accurate alignment of the layers may be required to ensure functionality, for example RFID of NFC operation, to create visible security images, or to create machine readable features. In some processes, each sheet may comprise components for a plurality of products such as ID or credit cards and misalignment between sheets, particularly angular misalignment, prior to singulation of the products, for example by cutting, may result in poor quality, or nonfunctional end products. The present invention provides a collation machine comprising: an upper supply for holding a plurality of upper elements; a lower supply for holding a plurality of lower elements; transport apparatus for moving upper and lower elements; a controller; an alignment control location comprising an upper alignment sensor and a lower alignment sensor; wherein the controller can control the transport apparatus to create a series of stacks at the alignment control location by moving an upper element from the upper supply and a lower element from the lower supply to the alignment control location and arranging the upper element over the lower element based on control parameters; wherein the controller can use the upper alignment sensor and lower alignment sensor to determine the position of an upper target reference on the upper element and a lower target reference on the lower element and, based on the determined positions, determine an alignment difference between the upper and lower elements in the stack indicative of an offset between the upper and lower elements and produce an error signal based on the alignment difference. The provision of an alignment control location comprising an upper alignment sensor and a lower alignment sensor allows the controller to carry out an automated check to be made on the accuracy of the alignment between the upper element and lower element in the stack that has been created by the machine. The check may be made on each stack that is created, or only on some of the stacks. The controller then produces an error signal which is based upon the alignment difference, possibly in combination with alignment differences from previous stacks. As the creation of the stacks is controlled based on control parameters, there is an assumption that, once the parameters are set up correctly, the alignment between elements the stack should be remain as predetermined. However, it has been found that alignment checks are required as alignment drift can occur, for example due to material, print variation, component wear, or control errors. Alignment checks have previously been carried out manually, for example by piercing one or more holes through a stack to provide a visual check of the alignment. Such a manual check is time consuming and may not have been carried on every stack created. For example a check may have been carried out on one in every 10 to 20 stacks to save time. If any misalignment is identified during a visual check, an operator of the machine could then take steps to adjust operation of the machine to try to correct the misalignment. This could be by manually adjusting physical elements of the machine, or by making adjustments to an automated control system, for example by adjusting control parameters. As skilled operator may be able to see the alignment error and quickly identify the control parameter that should be updated, but the process could require a significant period of trial and error. The present invention therefore provides a way in which the alignment accuracy for a stack produced, possibly each stack produced, or a majority the stacks produced, can be automatically checked and an error signal produced. The error signal could be used for one or more of the following functions: • to provide an alert to a user, for example an alert that the alignment between the top and bottom sheets is outside, or is moving towards being outside, of a predetermined specification; • to provide advice to an operator, for example how to adjust operation of the machine to reduce any alignment error; • to stop the operation of the machine, for example is an error signal outside a threshold is detected; and • to automatically modify future operation of the machine as will be discussed in more detail below. This may allow a faster set up of a collation machine and / or an automatic adjustment to keep the stacks created by the collation machine aligned within a predetermine tolerance. The upper supply is a part of the collation machine in which upper elements are initially located prior to being incorporated into a stack. In operation the upper supply may be fixed to the collation machine so that the position of the upper supply remains constant relative the collation machine. The upper supply may comprise a removable component, for example a tray, magazine, or trolley which is removable from the collation machine so that upper elements can be loaded into the upper supply and the upper supply returned to the collation machine, for example into an upper supply location. The upper supply location may be in a pre-determined position relative the collation machine. The upper supply may comprise a wheeled trolley and / or an autonomous mobile robot onto which a plurality of upper elements can be loaded. The lower supply is a part of the collation machine in which lower elements are initially located prior to being incorporated into a stack. As with the upper supply, in operation the lower supply may be fixed to the collation machine so that the position of the lower supply remains constant relative the collation machine. The lower supply may comprise a removable component, for example a tray, magazine, or trolley which is removable from the collation machine so that lower elements can be loaded into the lower supply and the lower supply returned to the collation machine, for example into a lower supply location. The lower supply location may be in a pre-determined position relative the collation machine. The lower supply may comprise a wheeled trolley and I or an autonomous mobile robot onto which a plurality of lower elements can be loaded. The upper supply and lower supply may both comprise the same type of removable component. The stack created may comprise only the upper and lower elements, or may comprise one or more intermediate elements between the upper and lower elements. The upper elements and / or lower elements and / or intermediate elements may comprise single sheets of material, for example a plastic, paper, or card sheet, and may comprise printing or other features on at least one side thereof. The upper elements and / or lower elements may comprise a plurality of sheets of material, for example plastic, paper, or card sheets and may comprise printing or other features on at least one side thereof. The plurality of sheets of material may be laminated together so that they essentially behave as a single sheet. The plurality of sheets of material may be in the form of an intermediate stack. An intermediate stack is a plurality of sheets of material secured together in at least one tack location to form a sheet set. A tack location comprises a localised bond between elements of the stack to secure them together, effectively a local lamination. A tack may be formed though, for example heat sealing or ultrasonic welding. In an intermediate stack the plurality of sheets of material are secured together in at least one tack location, the at least one tack location may comprise no more than 20% of the surface area of each sheet, such that the remaining surface area of each sheet is not secured together. An intermediate stack may be secured together in at least four tack locations, or at least six tack locations. The, or each, tack location may be at or adjacent an edge of the stack of sheets, for example within 5cm of an edge of the stack of sheets. The intermediate stack may comprise a plurality of sheets which have substantially the same outer shape and size. For example, for a square or rectangular intermediate stack the plurality of sheets may be substantially square or rectangular. For a square or rectangular intermediate stack there may be a tack location at or adjacent at least one corner of the stack of sheets, or at or adjacent at each corner of the stack of sheets, for example within 5cm of a corner of the stack of sheets. The transport apparatus may comprise one or more grippers and / or one or more vacuum cups and / or one or more vacuum beds that can move relative to the machine, for example relative to a collation bed of the machine. The transport apparatus may comprise one or more pairs of grippers and / or one or more pairs of vacuum cups that together grip an element and move relative to the machine. Each gripper or vacuum cup in the pair may be movable independently so that the angular orientation of the element relative to the machine can be adjusted. Elements, such as sheets or intermediate stacks, may be combined and I or passed between grippers, or sets of grippers, as they are moved to the alignment control location. The controller may comprise a single controller, or a plurality of separate sub-controllers. The controller or sub-controllers may comprise one or more microprocessors. The controller may comprise a memory to store control parameters for controlling operation of the collation machine. The alignment control location may be any location of the collation machine, for example a location of the collation bed at which a stack is created. The upper alignment sensor and a lower alignment sensor may be any form of sensor capable of detecting, or capturing an image of, one or more features of an element, either while the element is stationary at the alignment control location, or as the element moves through the alignment control location. The upper alignment sensor and a lower alignment sensor may be arranged at a predetermined location relative to the alignment control location. The upper alignment sensor and a lower alignment sensor may comprise one or more optical sensors. The upper alignment sensor and a lower alignment sensor may comprise a print mark sensor capable of detecting a print mark on the element. The upper alignment sensor and a lower alignment sensor may comprise one or more print mark sensors. The upper alignment sensor and a lower alignment sensor may each comprise a first sensor for determining an offset in a first direction, and optionally a second sensor for determining an offset in a second direction and / or a third sensor for determining an angular offset. The upper alignment sensor and a lower alignment sensor may comprise an imaging sensor, such as a camera, capable of capturing a digital image or video of upper or lower element such that the image captured can be processed by the controller to identify the position of the target reference on the upper or lower element. The camera may capture a plurality of images of upper or lower element to facilitate the determination of a position, which can include an angular orientation. Since an image sensor captures an image of the element rather than detecting a feature a single camera may be used to allow the position of an element in a first direction, second direction and the orientation of the element. The collation machine is able to create a series of stacks at the alignment control location. Stacks can be created sequentially at the alignment control location. Once created, a stack is moved away from the alignment control location for further processing using the same, or another machine. The further processing may comprise creating one or more tacks to secure the elements of the stack together. This may create an intermediate stack which can be used as an upper or lower element in a collation machine, or which can be moved to another machine for further processing. Further processing may comprise, for example, 6 laminating elements of the stack together, cutting the stacks into singulated units, other operations, or combinations of such operations. For example, each stack may comprise a plurality of units, which may be arranged in a grid, for example credit card, ID3 card, or passport page sized units, for example ID1 or ID3. The control parameters may include distances and angles through which the upper and lower elements are moved by the transport apparatus from the upper supply and lower supply, or from a measured or detected position of the element, or of printing on a surface of the element. The control parameters may include distances through which transport apparatus coupled to the upper and lower elements is moved in order to move upper and lower elements from the upper supply and lower supply, or from a measured or detected position. As noted above, the transport apparatus may be coupled to the upper and lower elements in a variety of ways and any suitable method can be used. Suitable methods include gripping the element between gripping elements, or using a vacuum cup. The position of an element may be detected prior to the transport apparatus being coupled to the elements, for example using an image capture device for example a camera to capture an image of the element. The captured image can be analysed to determine the portion and or orientation of one or more printed marks, or other target features, relative to the machine. The position of may be detected as an element is moved towards the alignment control, for example using an image capture device for example a camera to capture an image of the element, or by using a print mark detector which may require less processing than using an image sensor. The exact position of an element or its printing relative to the machine need not be detected by in a single operation. For example a position in a first direction may be determined by a first print mark sensor and later a position in a second direction perpendicular to the first might be determined by a different print sensor. The orientation may be determined based on a particular mark, or by determining the position in a first direction of two print marks which are spaced apart in a second direction perpendicular to the first direction. The position may be determined based on the position of printing on the element. In this way the collating machine is able to ensure that the upper element and lower element are stacked such that the printing on each element is aligned. The upper target reference and lower target reference may be any feature which can be identified from an image captured by the upper or lower camera so that the position of the element relative to the collation machine can be determined. The upper target reference 7 and lower target reference may comprise a printed mark, symbol, or image, or may comprise a physical feature of the element, for example an attached element, or an aperture or cutout. The upper target reference and lower target reference may allow an image captured by the upper or lower camera to be analysed to determine the orientation of the upper target reference and lower target reference relative to the collation machine. The alignment difference may comprise any relevant information that is indicative of an offset between the upper and lower elements which may be in any direction, or combination of directions and may be an angular offset. The offset between the upper and lower elements may be a difference between one or more of: a) a position in a first direction; b) a position in a second direction perpendicular to the first; c) an angular orientation of the elements. The error signal indicative of the alignment difference is created, and this may be used for a variety of purposes, for example to automatically generate an alert if the error signal is indicative of a problem, to automatically stop, or pause, the collation machine if the error signal is indicative of a serious problem. If the error signal is indicative of an error signal exceeding an error threshold, the controller may be configured to automatically alter one or more control parameters of the machine. The alteration of the one or more control parameters of the machine may be to reduce the alignment difference for future stacks. The error signal may be calculated based on an individual stack, of may be calculated based on a plurality of stacks. The plurality of stacks upon which the error signal is calculated may be randomly selected, or based on a predetermined pattern, for example every 5th or 10th stack produced. The plurality of stacks may be sequential stacks produced by the collation machine. Basing the error signal on a plurality of stacks helps to minimise the effect of random errors and can facilitate the detection of errors that might be caused by issues with the machine such as failing or faulty components. For example, random errors might be expected to produce an average zero error, but an issue with the collation machine may lead to a non-zero average error, or a gradually increasing non-zero error. The error signal may be calculated as a moving average, for example taking the average of an offset in the alignment in any direction or orientation for the most recent five stacks tested, or the most recent seven, ten, fifteen, or twenty stacks tested. The controller may be adapted to produce an alert signal if the alignment difference or the error signal exceeds an alert threshold, or a trend in the error signals that exceeds a threshold. The alert threshold for alignment difference may be set to identify a particularly badly aligned stack, for example by producing an audible or visual alert, by pausing the machine, or by shutting down the machine. The alert threshold may be set to indicate the presence of a systemic error, for example alignment drift, that might indicate a problem with the collation machine. There may be a plurality of alert thresholds for different aspects of the stack alignment or trends and I or different severities of issues. The collation machine may comprise a first sensor arranged at a pre-determined location on the machine for detecting a sensor feature of one of an upper element or lower element as it is moved to the alignment control location. The control parameters may comprise a distance in a first direction that the respective upper or lower element is moved after detection of the sensor feature by said first sensor. The alignment difference between the upper and lower elements may comprise an offset distance in the first direction, and the control parameter adjusted may be a distance in a first direction that the upper element or lower element is moved after detection of the sensor feature by the first sensor to reduce the alignment difference for subsequent stacks. The collation machine may further comprise a second sensor arranged at a pre-determined location on the machine for detecting a sensor feature of one of an upper element or lower element as it is moved to the alignment control location. The control parameters may comprise a distance in a second direction that the element is moved after detection of the sensor feature by the second sensor. The second direction may be perpendicular, or transverse, to the first direction. The alignment difference between the upper and lower elements may comprise an offset distance in the second direction and the control parameter adjusted may be the distance in the second direction that the upper element or lower element is moved after detection of the sensor feature by the second sensor. The invention extends to a method of operating a collation machine, the method comprising: providing a plurality of upper elements in an upper supply; providing a plurality of lower elements in a lower supply; sequentially creating a series of stacks at an alignment control location by moving an upper element from the upper supply and a lower element from the lower supply to the alignment control location and arranging the upper element over the lower element using transport apparatus based on control parameters of the machine; using an upper alignment sensor and lower alignment sensor at the alignment control location to determine the position of an upper target reference on the upper element and a lower target reference on the lower element and, based on the determined positions, calculating an alignment difference between the upper and lower elements in the stack indicative of an offset between the upper and lower elements and generating an error signal based on the alignment difference. The error signa may be used as described earlier. If the error single exceeds an error threshold, the method may include automatically altering one or more control parameters of the machine to reduce the alignment difference for future stacks. The collation machine may include a controller and the method may be controlled by said controller. The method may be carried out using a collation machine as described above. The invention extends to a method of creating final stacks using a collation machine, the collation machine comprising: providing a plurality of first elements in a first supply; providing a plurality of second elements in a second supply; sequentially creating a series of stacks at a first location by moving a first element from the first supply and a second element from the second supply to the first location and arranging the first element over the second element using transport apparatus; tacking the first element to the second element together in at least one tack location to create a final stack; wherein at least one of the first elements and second elements comprises an intermediate stack comprising at least two sheets tacked together in at least one tack location. The first location may be the alignment control location mentioned above, or a different location. The method may be combined with the method described above. The first supply may be an upper supply or an intermediate supply, and the second location may be a lower supply, or an intermediate supply. The transport apparatus may comprise a vacuum cup to lift the intermediate stack from the upper supply or lower supply. The vacuum cup may engage the intermediate sheet at or adjacent a tack location. This reduces, or avoids, bagging or sagging of the intermediate stack which may create handling difficulties. The vacuum cups may be preset and fixed in the appropriate position, or may be manually movable by an operator, or movable by the controller using suitable actuators based on operator instructions or automatically based on data relating to the intermediate stack. The method may further comprise the initial steps of: providing a plurality of initial first elements in a first supply; providing a plurality of initial second elements in a second supply; wherein each initial first element and initial second element comprises a sheet; sequentially creating a series of stacks at an alignment control location by moving an initial first element from the first supply and an initial second element from the second supply to the alignment control location and arranging the initial first element over the initial second element using the transport apparatus; tacking the initial first element to the initial second element together in at least one tack location to create an intermediate stack; and storing the intermediate stacks at an intermediate location; and moving the intermediate stacks to one of the first supply or second supply that is to be used to create the final stack. This provides the opportunity for a two-pass method of creating a final stack using one collation machine. In this way a single collation machine can be used to create an aligned stack comprising more sheets than would be otherwise possible by feeding individual sheets into each of the supplies. For example, a collation machine having an upper supply, a lower supply and two intermediate supplies could normally create an intermediate stack of four separate sheets and this could then be passed back into the collation machine and at least three elements can be added to the intermediate stack to create a stack that comprises seven sheets. The intermediate stacks may be moved to one of the first supply or second supply once the first supply or second supply has been emptied by operation of the machine creating intermediate stacks. Providing a plurality of first elements in a first supply may comprise fitting a first magazine filled with first elements into the first supply. Providing a plurality of second elements in a second supply may comprise fitting a second magazine filled with second elements into the second supply. The method may comprise fitting the respective magazine automatically, for example using an automated shuttle or trolley. The invention further extends to a collation machine comprising: a first supply for holding a plurality of first elements; a second supply for holding a plurality of second elements; transport apparatus for moving first and second elements; a controller; wherein the controller can control the transport apparatus to create a series of stacks at a first location by moving a first element from the first supply and a second element from the second supply to the alignment control location and arrange the first element over the second element; wherein at least one of the first elements and second elements comprises an intermediate stack comprising at least two sheets tacked together in at least one tack location and the transport apparatus comprises a vacuum cup to lift the intermediate stack from the first supply or second supply, the vacuum cup engaging the intermediate sheet at or adjacent a tack location. The vacuum cup may be movable to engage the intermediate stack at or adjacent a tack location. The vacuum cup may be automatically movable, for example under control of a controller of the collation machine. There may be more than one vacuum cup and more than one tack location and the vacuum cups may each engage the intermediate stack at, or adjacent to, a tack location. A vacuum cup may contact the tack location, or be adjacent thereto, for example within 2cm, within 1cm or within 0.5cm of the tack location. The first element and the second element may be secured together by tacking in at least one tack location to create a final stack. The at least one tack location used to create the final stack may be offset from the tack location of the intermediate stack. The collation machine may include a tacking apparatus for creating at least one tack securing the first element and the second element together. The tacking apparatus may include at least one intermediate tacking head for creating the at least one tack securing the elements of the intermediate stack together and at least one final tacking head for creating 5 the at least one tack securing the elements of the final stack together. The at least one final tacking head may be offset from the intermediate tacking head to create a tack at a offset location. The tacking apparatus may include at least one movable tacking head which can be moved 10 between an intermediate tacking position for creating the at least one tack securing the elements of the intermediate stack together and a final tacking position for creating the at least one tack securing the elements of the final stack together. The invention will now be described by way of example only with reference to the following figures in which: Figure 1 shows a schematic plan view of a collation machine; Figures 2a to 2g show a sequence of operation of the collation machine of Figure 1; Figures 3a and 3b show operation of the collation machine using an intermediate sheet; Figure 4 shows a side view of the alignment control location of the collation machine of Figure 1; Figures 5a to 5c show operation of the tacking station; and Figure 6 show a side view of an intermediate stack. Figure 1 shows a schematic plan view of a collation machine 1. The collation machine 1 comprises an upper, or first, supply 2 for holding a plurality of upper, or first, elements 4 and a lower, or second, supply 6 for holding a plurality of lower, or second, elements 8. In this example each upper element 4 in the upper supply 2 is a sheet comprising print marks 10 and an upper target feature 12, in this case the upper target feature 12 is a further printed mark, visible on a top surface 14 of the upper elements 4. The lower elements 8 have print marks 10’ and lower target features 12’ that are equivalent to those on the upper element 4, but they are visible on a bottom surface 16 of the lower elements 8. It should be noted that, although the print marks 10’ and lower target features 12’ are shown in dashed lines in this figure, they may not be visible from above. The collation machine 1 include transport apparatus 18 which comprise a plurality of grippers 20 and vacuum cups 22 for moving the upper and lower elements 4,8 across a collation bed 24 of the collation machine 1. The collation machine 1 includes a controller 26 for controlling operation of the collation machine 1 and includes a plurality of detectors 28, in this case print mark sensors. Operation of the collation machine 1 will be described in more detail with reference to later figures. The collation machine 1 further comprises an alignment control location 30 comprising an upper alignment sensor 32 and a lower alignment sensor 34. The controller 26 can control the transport apparatus 18 to create a series of stacks at the alignment control location 30 by moving an upper element 4 from the upper supply 2 and a lower element 8 from the lower supply 6 to the alignment control location 30 and arrange the upper element 4 over the lower element 8 based on control parameters. The control parameters may be stored in a memory 36 of the controller 26. The collation machine 1 may also comprise tacking apparatus 38 comprising a plurality of tack heads 40 for securing upper and lower elements 4,8 together at tack locations as will be described with reference to later Figures. For some or all of the stacks created, the controller 26 can use the upper alignment sensor 32 and lower alignment sensor 34, in this case the upper alignment sensor 32 and lower alignment sensor 34 each comprise a camera, to determine the position of the upper target reference 12 on the upper element 4 and a lower target reference 12’ on the lower element 8 and, based on the determined positions, calculate an alignment difference between the upper and lower elements 4,8 in the stack indicative of an offset between the upper and lower elements 4,8 and produce an error signal indicative of the alignment difference. Figures 2a to 2g show a sequence of operation of the collation machine 1 of Figure 1. In Figure 2a the vacuum cups 22 are activated and used to engage the top surface 14,14’ of an upper element 4 and a lower element 8 so that an edge 42 of each element can be raised by lifting the vacuum cups 22. Rasing an edge 42 in this way facilitates the engagement of some of the grippers 20, in this case supply grippers 44 to engage and grip the elements 4,8. In Figure 2b the vacuum cups 22 have been deactivated to release the elements 4,8 and the supply grippers 44 have moved the elements in a first direction 46, in this example across the collation bed 24. As the elements 4,8 are moved, some of the sensors 28, in this case first sensors 48, detect some of the print marks 22, in this case first print marks 50. There are two first print marks 50, two first grippers 44 and two first sensors 48, each print mark may be associated with one of the first grippers 44 and first sensors 48. The control parameters of the controller 26 comprise a distance that each of the grippers 48 move after the associated print mark 50 has been detected. This allows each of the elements 4,8 to be arranged in a predetermined position in the first direction 46 and in a predetermined orientation based upon the print marks 50. The process has been described in relation to the upper element 4 in which the sensors 48 are arranged above the upper element 4 to detect print marks on the top surface 14. An equivalent process occurs with the lower element 8, but the sensors 48 are arranged below the lower element 8 to detect print marks 50 on the bottom surface 16’ of the lower element 8. During operation of the collation machine 1 the upper and lower elements 4,8 do not move again in the first direction 46, only in a second direction 52 which is perpendicular to the first direction 46 and is directed along the collation bed 24. Figure 2c shows the collation machine 1 after collation grippers 54 have been engaged with the upper and lower elements 4,8 to hold the elements 4,8 securely. Once the collation grippers 54 are engaged the first grippers 44 are released. The collation grippers 54 may be grippers which pinch the element between grip parts, or may be, for example vacuum beds which use a vacuum to secure the element to a movable surface. Figure 2d shows the collation machine 1 once the upper element 4 and lower element 8 have been moved along the collation bed 24 in the second direction using the collation grippers 54. As the upper and lower elements 4,8 are moved in the second direction 52, second print marks 56 are detected by second print sensors 58 and the elements 4,8 pass over, or under the print sensors 58. The control parameters of the controller 26 comprise a distance that each of the collation grippers 54 move after the associated second print mark 56 has been detected. This allows each of the elements 4,8 to be arranged in a predetermined position in the second direction 52. The collation grippers 54 gripping each element may move the same distance in the second direction 52 so that the orientation of the element 4,8 does not change. In this example the control parameters are selected such that the upper element 4 is arranged over the lower element 8 such that the printing on the elements 4,8 overlie and are aligned so that the elements 4,8 form a stack 60. Figure 2e shows the collation machine 1 after transfer grippers 62 have gripped the stack 60 and moved it to the alignment control location 30. The collation grippers 54 are not released until the transfer grippers 62 have been engaged so that the elements 4,8 of the stack 60 cannot move in an uncontrolled manner. The alignment control location 30 comprises an upper camera 32 and a lower camera 34. The controller 26 uses the upper camera 32 and a lower camera 34 to capture an image of the stack 60 from above and below. The images are then analysed by the controller 26 to determine the position and orientation of the upper target feature 12 and lower target feature 12’ relative to the collation machine 1. Based on the determined positions of the upper target feature 12 and lower target feature 12’ the controller calculates an alignment difference between the upper and lower elements 4,8 in the stack 60 indicative of an offset between the upper and lower elements 4,8 and produces an error signal based of the alignment difference. Figure 2f shows the stack 60 once it has been moved to the tacking apparatus 38 by the transfer grippers 62. The tack heads 40 engage the stack 60 and create tacks between the upper and lower elements 4,8 in tack locations. The tacks created by the tack heads 40 may be, for example, heat welds or ultrasonic welds. It should be noted that there are four tack heads 40 in this example that are used to create four tacks in the stack 60. In other examples a mobile tack head 40 could be used to create a plurality of tacks. Figure 2g shows the stack 60 after it has been released from the transfer grippers 62. The tack locations 64 can be clearly seen at, or adjacent to, the corners of the stack 60. The tacked stack may be an intermediate stack 66 which will be passed back through a collation machine, for example the collation machine 1, to add further elements to the stack 60. The tacked stack may be a final stack 68 which is to be passed to a further machine (not shown) for further operations for example lamination and / or cutting. The steps of Figures 2a to 2g are repeated to create a plurality of stacks 60. If the error signal produced is indicative of an error above a threshold one or more of the control parameters may be automatically altered to reduce the error signal for subsequent stacks 60. For example, the error signal may be a moving average based on the present stack and the preceding four stacks. If the error signal is indicative of an error in a first direction that exceeds a threshold, for example 0.25 mm offset between the upper and lower elements 4,8 in the first direction, the controller 26 may automatically adjust one or more control parameters to reduce the error in subsequent stacks. Figures 3a and 3b show operation of a collation machine 101 which is similar to the collation machine 1 of Figure 1 and operation of the device is similar and like components will be referenced with similar reference numerals incremented by 100. For simplicity some of the components, in particular the transport apparatus, sensors and cameras are not shown in this Figure. This collation machine 101 includes an intermediate supply 70 comprising a plurality of intermediate elements 72. In this collation machine 101 the first, or upper, element 104 in the first, or upper, supply 102 is an intermediate stack 66, for example one created by the machine 1. It should be noted that collation machine 1 and collation machine 101 may be the same collation machine. The vacuum cups 122 associated with the first, or upper, supply 2 are arranged over tack locations 64 of the intermediate stack 66. This facilitates lifting of the intermediate stack 66 so that it can be engaged by first grippers 44 as described above. The vacuum cups 122 may be movable manually or automatically to be over, or adjacent, the tack locations 64. In use the collation machine 101 takes an element from each of the upper, lower, and intermediate stations 2,6,70 and arranges them in a stack 74 with an intermediate element 70 between the upper and lower elements 104,108. The process of aligning the elements 70,104,108 is the same as described above, with marks on the elements 70,104,108 being detected as they are moved. The collation machine 101 may include an alignment control location, but this is not shown in this Figure. Figure 3b shows the stack 74 arranged below the tack heads 140. In this case the tack heads 140 have been moved to avoid the previous tack locations 64 of the intermediate stack 66. The collation machine 101 may include a plurality of different tack heads 140 located in a various offset positions so that a suitable set of tack heads 140 are selected to avoid the tack locations 64 on intermediate stack 66. The tack heads 140 may be movable manually or automatically to avoid the tack locations 64 on intermediate stack 66. Figure 4 shows a cross section view of the alignment control location 30 with a stack 60 arranged thereon. The collation bed 24 includes slots 76 within which the transfer grippers 62 can move. The alignment control location 30 includes an upper camera 32 and a lower camera 34. The upper camera 32 is arranged to capture an image of a portion of the upper element 4 of the stack 60 including an upper target reference feature 12. The collation bed 24 includes an aperture 78 to allow the lower camera 34 to capture an image of a portion of the lower element 8 of the stack 60 including the lower target reference feature 12’. Figure 5a to 5c show a sequence of operation of tack heads 40. In Figure 5a the stack 60 is arranged below the tack heads 40 and held in place using transfer grippers 62. In Figure 5b the tack heads 40 engage the stack 60 and create tacks in the tack locations 64 to secure 5 the upper element 4 to the lower element 8 and create an intermediate stack 66. In Figure 5c the tack heads have moved away from the stack 60 and the transfer grippers 62 have released the intermediate stack 66. Figure 6 shows a view of an intermediate stack 66 in which there are four tack locations 64 10 securing the upper element 4 to the lower element 8.

Claims

1. A collation machine comprising:an upper supply for holding a plurality of upper elements;a lower supply for holding a plurality of lower elements;transport apparatus for moving upper and lower elements;a controller;an alignment control location comprising an upper alignment sensor and a lower alignment sensor;wherein the controller can control the transport apparatus to create a series of stacks at the alignment control location by moving an upper element from the upper supply and a lower element from the lower supply to the alignment control location and arrange the upper element over the lower element based on control parameters;wherein the controller can use the upper alignment sensor and lower alignment sensor to determine the position of an upper target reference on the upper element and a lower target reference on the lower element and, based on the determined positions, determine an alignment difference between the upper and lower elements in the stack indicative of an offset between the upper and lower elements and produce an error signal based on of the alignment difference.

2. A collation machine as claimed in claim 1, in which, if the error signal exceeds an error threshold, the controller can automatically alter one or more control parameters of the machine to reduce an alignment difference for subsequent stacks created by the collation machine.

3. A collation machine as claimed in claim 1 or claim 2, in which the error signal is calculated based on a plurality of stacks.

4. A collation machine as claimed in claim 3, in which the error signal is calculated based on a plurality of sequential stacks.

5. A collation machine as claimed in claim 3 or claim 4, in which the error signal is a moving average.

6. A collation machine as claimed in any preceding claim, in which the controller can produce an alert signal if the error signal exceeds an alert threshold.

7. A collation machine as claimed in any preceding claim, in which the collation machine further comprises a first sensor arranged at a pre-determined location on the machine for detecting a sensor feature of one of an upper element or lower element as it is moved to the alignment control location, and the control parameters comprise a distance in a first direction that the respective upper or lower element is moved after detection of the sensor feature by said first sensor;wherein the alignment difference between the upper and lower elements comprises an offset distance in the first direction and the control parameter adjusted is the distance in a first direction that the upper element or lower element is moved after detection of the sensor feature by the first sensor.

8. A collation machine as claimed in claim 7, in which the collation machine further comprises a second sensor arranged at a pre-determined location on the machine for detecting a sensor feature of one of an upper element or lower element as it is moved to the alignment control location, and the control parameters comprise a distance in a second direction that the element is moved after detection of the sensor feature by said second sensor, the second direction being perpendicular to the first direction;wherein the alignment difference between the upper and lower elements comprises an offset distance in the second direction and the control parameter adjusted is the distance in the second direction that the upper element or lower element is moved after detection of the sensor feature by the second sensor.

9. A collation machine as claimed in any preceding claim, in which the upper alignment sensor and a lower alignment sensor each comprise a camera.

10. A method of operating a collation machine, the method comprising:providing a plurality of upper elements in an upper supply;providing a plurality of lower elements in a lower supply;sequentially creating a series of stacks at an alignment control location by moving an upper element from the upper supply and a lower element from the lower supply to the alignment control location and arranging the upper element over the lower element using transport apparatus based on control parameters of the machine;using an upper alignment sensor and lower alignment sensor at the alignment control location to determine the position of an upper target reference on the upper element and a lower target reference on the lower element and, based on the determined positions, calculating an alignment difference between the upper and lower elements in the stack indicative of an offset between the upper and lower elements; and21 producing an error signal based on of the alignment difference.

11. A method as claimed in claim 10, in which if the error signal exceeds an error threshold, the method comprises automatically altering one or more control parameters of the machine to reduce the alignment difference for future stacks.

12. A method as claimed in claim 11, in which the collation machine includes a controller and the method is controlled by the controller.

13. A method as claimed in claim 10 or claim 11, in which the method is carried out using a collation machine as claimed in any of claims 1 to 9.

14. A method of creating final stacks using a collation machine, the collation machine comprising:providing a plurality of upper elements in an upper supply;providing a plurality of lower elements in a lower supply;sequentially creating a series of stacks at a first location by moving an upper element from the upper supply and a lower element from the lower supply to the first location and arranging the upper element over the lower element using transport apparatus;tacking the upper element to the lower element together in at least one tack location to create a final stack;wherein at least one of the upper elements and lower elements comprises an intermediate stack comprising at least two sheets tacked together in at least one tack location.

15. A method as claimed in claim 14, in which the intermediate stack comprises at least two sheets tacked together in at least four tack locations at or adjacent edges of the sheets.

16. A method as claimed in claim 14 or claim 15, in which the transport apparatus comprises a vacuum cup to lift the intermediate stack from the upper supply or lower supply, the vacuum cup engaging the intermediate sheet at or adjacent a tack location.

17. A method as claimed in any of claims 14 to 16, in which the method further comprises the initial steps of:providing a plurality of initial upper elements in an upper supply;providing a plurality of initial lower elements in a lower supply;wherein each initial upper element and initial lower element comprises a sheet;sequentially creating a series of stacks at an alignment control location by moving an initial upper element from the upper supply and an initial lower element from the lower supply to the alignment control location and arranging the initial upper element over the initial lower element using the transport apparatus;tacking the initial upper element to the initial lower element together in at least one tack location to create an intermediate stack; andstoring the intermediate stacks at an intermediate location; andmoving the intermediate stacks to one of the upper supply or lower supply that is to be used to create the final stack.

18. A method as claimed in claim 17, in which the intermediate stacks are moved to one of the upper supply or lower supply once the upper supply or lower supply has been emptied by operation of the machine.

19. A method as claimed in claim 16 or claim 17, in which providing a plurality of upper elements in an upper supply comprises fitting an upper magazine filled with upper elements into the upper supply, and providing a plurality of lower elements in a lower supply comprises fitting a lower magazine filled with lower elements into the lower supply, and the method may comprise fitting the respective magazine automatically.

20. A method as claimed in any of claims 14 to 19, in which the method further comprises creating a tack in a tack location offset from the at least one tack location of the intermediate stack.

21. A collation machine comprising:an upper supply for holding a plurality of upper elements;a lower supply for holding a plurality of lower elements;transport apparatus for moving upper and lower elements;a controller;wherein the controller can control the transport apparatus to create a series of stacks at a first location by moving an upper element from the upper supply and a lower element from the lower supply to the alignment control location and arrange the upper element over the lower element;wherein at least one of the upper elements and lower elements comprises an intermediate stack comprising at least two sheets tacked together in at least one tack location and the transport apparatus comprises a vacuum cap to lift the intermediate stackfrom the upper supply or lower supply, the vacuum cup engaging the intermediate stack at or adjacent a tack location.

22. A collation machine as claimed in claim 21, in which the vacuum cup is movable to 5 engage the intermediate stack at or adjacent a tack location.

23. A collation machine as claimed in claim 22, in which the vacuum cup is automatically movable to engage the intermediate stack at or adjacent a tack location.10 24. A collation machine as claimed in any of claims 21 to 23, in which the collationmachine further comprises tacking apparatus which can be controlled to create a tack in the final stack which is offset from the at least one tack in the intermediate stack.

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