Alignment systems and methods

Abstract

An alignment system 10 for aligning a plurality of singulated workpieces (32A-F, Fig.5A) received within a printing machine within a horizontal (X-Y) plane. The system comprises a plurality of towers 14 spaced apart in the horizontal plane. Each tower has a head 16 configured to support a respective singulated workpiece thereon in use. The system further comprises an actuation tool 22 which is movable within the horizontal plane; and an actuation means (24, 26, 28, Fig.3) operatively connected to the actuation tool for driving the actuation tool within the horizontal plane. Each tower is associated with a respective locking system 30A-F, each locking system being independently operable to place its associated tower in a tool-locking state in which at least the head of the respective tower is locked relative to the actuation tool so as to prevent relative movement between the respective head and the actuation tool in the horizontal (XY) plane. Advantageously the towers are also selectively lockable relative to a base 12 of the alignment system, so that successive towers may be aligned by the actuation tool in a stepwise manner.

Description

This invention relates to an alignment system for aligning a plurality of singulated workpieces, a printing machine comprising such an alignment system, and a method for aligning a plurality of singulated workpieces received within a printing machine. Background and Prior Art Industrial screen-printing machines typically apply a conductive print medium, such as solder paste or conductive ink, onto a planar workpiece, such as a circuit board, by applying the conductive print medium through a pattern of apertures in a printing screen (sometimes referred to as a foil or stencil) using an angled blade or squeegee. Where the area of the pattern is relatively small with respect to the area of the screen, it is possible to include more than one pattern within the screen, thus allowing more than one area of a board, or more than one board, to be printed simultaneously using the same screen. Alternatively, more than one relatively small screen may be used within the same printing machine to enable the more than one area of a board, or more than one board, to be printed simultaneously using respective screens. While such simultaneous printing may clearly be more efficient than sequential printing, there are problems associated with these techniques. i) Printing of more than one area of a board As noted above, it is possible to print a plurality or array of patterns onto respective areas of a single board or panel in a single print operation, to produce a plurality of printed circuit boards (PCBs) which may be subsequently physically separated. This technique is conceptually and technically simple - a panel with a plurality of boards is loaded into a printing machine, correctly aligned and then all the boards of the panel are printed simultaneously. However, with any circuit board there is a risk that at least partofthat board may be defective, which in turn may lead to a defective PCB. This situation is schematically shown in FIG. 1, where three panels 1, 2, 3 are shown, each having a 4x1 array of boards A-D. While the leftmost panel 1 is completely free from defects, the adjacent panel 2 has a defective board 2A, while the right-most panel 3 has a defective board 3B. It is inefficient to pre-check the circuit boards for defects and reject an entire panel if one board is found to be defective. It is also inefficient and problematic to print a pattern onto an identified defective board and reject the separated defective board subsequent to the printing process. One current solution to this problem is to identify defective boards before commencement of the printing operation, and sort the panels into separate batches having similar defects, for example a first batch which is defect-free, a second batch in which the left-most board is defective, a third batch in which the second-left board is defective and so on. A dedicated respective screen may then be used with each batch. For example, a screen having all four aperture patterns would be used for the first batch, while screens having only three aperture patterns would be used for each remaining batch. Forthe 4x1 array described here, this would result in the use of five different screens per panel to print on a side of the panel. Since each panel will typically be printed on both sides, this could lead to the use often different set-ups for a single panel type, rather than the optimal two (i.e. one for each side). In addition, the second to fifth batches will only be printing at 75% efficiency. Furthermore, if two or more boards are defective then additional measures must be taken. ii) Printing of more than one board A solution to the above problem is to pre-separate or "singulate" the individual boards or workpieces before the printing process. Here, any defective boards could be identified before printing and rejected immediately, so that only non-defective boards are printed. While this process is relatively efficient, it introduces complications. In particular, it is difficult both to support and to align individual relatively small boards for simultaneous (or sequential) printing. Various approaches have been developed to overcome these problems. For example, GB 2484373 A describes a method in which individual boards are respectively positioned, but this only permits the sequential printing of one substrate at a time. JP-2009-248551 describes a method in which the position of each board is checked individually, and each board is sequentially repositioned using a repositioning arm. While this technique permits all boards of a panel to be printed on simultaneously, additional apparatus (i.e. the positioning arm) is required, and moving the arm between workpieces is time-consuming. WO2014 / 166956 describes an alternative apparatus, sold by ASMPT under the name "TRS", in which each singulated workpiece is supported by an individual tower, and all workpieces may be physically aligned simultaneously using a reference webbing, and then simultaneously printed. The top of each tower is movable with respect to the base of the tower, so that during referencing, the top of the towers, with their associated workpieces, may move relative to the tower base. The top of each tower is resiliently biased towards a neutral home position in the horizontal (X-Y) plane, so that after printing the workpieces automatically return to their original positions. This solution works well, though will not be suitable if an incoming unprinted workpiece is positioned too far from its correct position. There is an additional problem that alignment accuracy may be compromised if edge features of the workpieces are of poor tolerance, i.e. its use of edge alignment will only produce results as good as the quality of the edges. A workpiece support assembly, capable of supporting and individually aligning a multiplicity of relatively small workpieces (commonly referred to as "singulated" workpieces) has been described in EP3693168A1. FIG. 2 schematically shows an example of such an assembly 4, here including a 2 x 4 array of individual support "towers" 5. Each tower 5 is topped with a support surface 6 upon which a workpiece (not shown) may be supported during a printing operation. Furthermore, each tower 5 is individually actuable to move in orthogonal directions X and Y, which would typically be in the horizontal plane, and also to rotate about an orthogonal Z axis, which would typically extend in the vertical direction to provide so-called theta correction. As described in EP3693168A1, such movement may be advantageously provided through the use of a parallel kinematic actuation system within each tower. Other arrays of greater or smaller dimension are of course possible. This system has been released by ASMPT under the name "MASS", and provides a very fast and accurate printing solution. While this may be considered the "gold-standard" of singulated systems, the use of individually actuable towers is technically complex, and furthermore requires a certain minimum pitch between towers so that they can relatively move without risk of collision, and accommodate the physical space needed for the hardware. The present invention seeks to overcome these drawbacks, and provide a method and apparatus for enabling fast and accurate alignment of singulated workpieces, which is unaffected by poor edge tolerances and capable of aligning workpieces within arrays of small pitches. In accordance with the present invention this aim is achieved by providing an actuation tool capable of selective engagement with individual tooling towers, the towers being selectively lockable relative to the actuation tool. Summary of the Invention In accordance with a first aspect of the present invention there is provided an alignment system for aligning a plurality of singulated workpieces received within a printing machine within a horizontal (X-Y) plane, comprising: a plurality of towers spaced apart in the horizontal plane, each tower having a head configured to support a respective singulated workpiece thereon in use; an actuation tool which is movable within the horizontal plane; an actuation means operatively connected to the actuation member for driving the actuation tool within the horizontal plane; and wherein each tower is associated with a respective locking system, each locking system being independently operable to place its associated tower in a tool-locking state in which at least the head of the respective tower is locked relative to the actuation tool so as to prevent relative movement between the respective head and the actuation tool in the horizontal (X-Y) plane. In accordance with a second aspect of the present invention there is provided a printing machine comprising the alignment system of the first aspect. In accordance with a third aspect of the present invention there is provided a method for aligning a plurality of singulated workpieces received within a printing machine within a horizontal (X-Y) plane, comprising the steps of: i) locating each singulated workpiece onto a head of a respective tower; ii) detecting the alignment of each of the singulated workpieces; iii) driving an actuator memberto until it aligns with the detected alignment of a first singulated workpiece; iv) locking the head upon which the first singulated workpiece is located to the actuator member so that relative movement between the said head and the actuator member is prevented; v) driving the actuator member to until it aligns with the detected alignment of another singulated workpiece; vi) locking the head upon which the another singulated workpiece is located to the actuator member so that relative movement between the said head and the actuator member is prevented; and vii) repeating steps v) to vi) until all of the plurality of singulated workpieces are aligned with the actuator member. Other specific aspects and features of the present invention are set out in the accompanying claims. Brief Description of the Drawings The invention will now be described with reference to the accompanying drawings (not to scale), in which: FIG. 1 schematically shows three panels, each holding four boards; FIG. 2 schematically shows a known multiple tower support system; FIG. 3 schematically shows, from above, an alignment system in accordance with a first embodiment of the present invention; FIG. 4 schematically shows, from the side, the alignment system of FIG. 3; FIGs. 5A-E schematically show, from above, stages in an alignment sequence in accordance with the present invention; FIGs. 6A-F schematically show, from above, stages in an alternative alignment sequence in accordance with the present invention; FIG. 7 schematically shows, in a sectional side view, an alignment system in accordance with a second embodiment of the present invention at a transport height; FIG. 8 schematically shows the alignment system of FIG. 7, in a sectional side view orthogonal to that of FIG. 7, at a printing height; FIG. 9 schematically shows, in a sectional side view, an alignment system in accordance with a third embodiment of the present invention, at a printing height; FIGs. 10A-C schematically show sections of a tower of the alignment system of FIG. 9 from various positions; and FIG. 11 schematically shows, from above, a spring suitable for use with the alignment system of FIGs. 9 and 10A-C. Detailed Description of the Preferred Embodiments of the Invention FIG. 3 schematically shows, from above, an alignment system 10 in accordance with a first embodiment of the present invention, while FIG. 4 schematically shows, from the side, the alignment system 10 of FIG. 3. This embodiment is described to introduce the general principles of the present invention, and for this reason only the key components are shown. The alignment system 10 comprises a base 12, which is configured to rest on a support table (sometimes referred to as a 'rising table' due to its ability to be lifted up and down parallel to the vertical Z axis shown) of a printing machine. A plurality of towers 14 stand on the base 12, so as to be aligned along there length parallel to the vertical Z axis. The number of towers 14 may be selected for the particular application - in the example shown there are twelve towers 14 in a 6x2 array, but the number is not so limited, and may theoretically be any number greater than one, in any size or configuration of array. In this embodiment, each tower 14 comprises a lower section 20 which is fixed to the base 12, and an upper portion 18 which may move horizontally, i.e. in the X-Y plane, relative to the respective lower portion 20. At the top of each upper portion 18 is a head 16, which is fixed relative to its respective upper portion 18. Each head 16 is adapted to support a respective singulated workpiece (not shown) thereon in use, and hence the alignment system 10 shown is suitable for printing twelve singulated workpieces at a time. Preferably but not essentially, each upper portion 18 is biased to a 'neutral' position in the horizontal (X-Y) plane with respect to its respective lower portion 20, so that it will return to that position when any horizontal displacing force is removed. This may be achieved by, for example, providing an internal spring mechanism or resiliently deformable member such as rubber between the upper and lower portions. An actuation tool 22, which in this embodiment comprises a planar, fenestrated plate member, is provided parallel to the horizontal X-Y plane and spaced from the base 12. The actuation tool 22 comprises a plurality of through-holes 23 through which respective towers 14 extend. The actuation tool 22 is movable within the horizontal X-Y plane, and as such may be supported by bearings (not shown), with its movement driven and controlled by three linear actuators 24, 26 and 28. Actuators 24 and 26 act as Y / 0 actuators: if the actuators 24, 26 are driven in the same direction by the same extent, then the actuation tool 22 will undergo translation parallel to the Y axis; if they are driven in opposite directions by the same extent then the actuation tool 22 will undergo a pure rotation in the 0 direction, i.e. about an axis parallel to the vertical Z axis. Driving of the actuators 24 and 26 to different extents will cause the actuation tool 22 to undergo a composite translation parallel to the Y axis and 0 rotation. Actuator 28 meanwhile is an X actuator, so that driving actuator 28 will cause the actuation tool 22 to translate linearly parallel to the X axis. Using the three actuators 24, 26 and 28 singly or in combination can therefore produce any desired translation and / or rotation within the horizontal plane within the extent limits of the actuators. It should be noted that the through-holes 23 are dimensioned so as to avoid collision with the towers 14 during any such movement. In practice this is not difficult, since any required movement of the actuation tool 22 is likely to be very small, e.g. translations of about 1 millimetre or less and rotations of <5 degrees. Each tower 14 is associated with a respective locking system, shown in FIG. 4 as comprising locks 30A-F. Each lock 30A-F is independently operable. As shown in FIG. 4, purely by way of example, the leftmost locks 30A and 30B have been moved into a configuration in which the heads 16 of their respective towers 14 are locked relative to the actuation tool 22 so as to prevent relative movement between the respective head 16 and the actuation tool 22. In this configuration, these two towers 14 are placed in a 'tool-locking state'. Locks 30C and 30D meanwhile are in a configuration in which the heads 16 of their associated towers 14 are locked relative to the base 12, and hence the support table, so as to prevent relative movement between the respective head 16 and the base 12 and support table. As shown, this is achieved by locking the upper section 18 of each tower 14 to the respective lower section 20. In this configuration, these two towers 14 are placed in a 'baselocking state'. Finally, locks 30E and 30F are in a configuration in which the heads 16 of their associated towers 14 are unlocked relative to the base 12, and hence the support table, so as to permit relative movement between the respective head 16 and the base 12 and support table. In this configuration, these two towers 14 are placed in an 'unlocking state'. All locking / unlocking operations are controlled by a control means (not shown), such as a computer, PC, processing means or the like located at or remote from the printing machine, as is well-known in the art per se. FIGs. 5A-E schematically show, from above, stages in an alignment sequence in accordance with the present invention, in which a 3x2 array of singulated workpieces 32A-F is transported into a printing machine within a carrier. The figures all show the singulated workpieces 32A-F when located at a printing position within the printing machine, overlying the alignment system 10 as described with reference to FIGs. 1 and 2, with the workpieces 32A-F supported on respective heads 16 of respective towers 14. For clarity, various items are omitted from these figures, in particular the base 12, as well as the carrier and a surround plate. These are shown in and described in relation to later FIGs. 7-9. The actuation tool 22 is shown with six dashed rectangles 33, which indicate ideal alignment targets for each respective workpiece 32A-F, e.g. when a workpiece 32A-F is correctly aligned relative to the actuation tool 22, that workpiece 32A-F will fit snugly within its respective alignment target 33. In FIG. 5A, all workpieces 32A-F are shown in their initial, unaligned positions. The lack of alignment is greatly exaggerated here for clarity - in practice the level of misalignment would be so low as to be hard or impossible to discern by human eye, but of sufficient magnitude to lead to unacceptable print qualities if not resolved. All of the towers 14 are in an unlocked state. Although omitted for clarity, each workpiece 32A-F is provided with a reference marking or fiducial. In the position shown, each workpiece's fiducials are detected, for example by using an overhead camera as is well-known in the art per se (and illustrated in an exemplary manner as 56 in FIG. 7), to ascertain the misalignment of each workpiece 32A-F. The alignment sequence can proceed as soon as the fiducials are captured - preferably all of the fiducials of all of the workpieces 32A-F are captured at this stage, but it is also possible, though not as efficient, to capture fiducials of each workpiece 32A-F immediately prior to its alignment as described below. As shown in FIG. 5B, a first workpiece 32A is then constrained relative to the base, i.e. its supporting tower 14 is placed in the base-locking state. With the workpiece 32A thus constrained (as denoted by the circle on workpiece 32A), the actuation tool 22 is moved, by appropriate control of the actuators 24, 26 and 28, so that it aligns with the workpiece 32A as shown, i.e. so that the workpiece 32A is aligned within its alignment target 33. Once workpiece 32A is so aligned, its tower 14 is placed in the tool-locking state, so that the head 16, and hence workpiece 32A, is constrained relative to the actuation tool 22. This process may then be repeated for each workpiece 32B-F. FIG. 5C shows workpiece 32B constrained relative to the base by placing its tower in the base-locking state, as denoted by the circle on workpiece 32B, and the actuation tool 22 moved so that workpiece 32B aligns with its alignment target 33. It is important to note that the workpiece 32A remains constrained relative to the actuation tool 22 throughout this step, and indeed remains so constrained until printing has occurred (see below). Once aligned, the workpiece 32B is constrained relative to the actuation tool 22 by placing its tower in the tool-locking state. The process may then be repeated for each remaining workpiece 32C-F. FIG. 5D shows the situation once all workpieces 32A-F have been aligned and constrained relative to the actuation tool 22, and the actuation tool 22 moved to its printing position, in which all workpieces 32A-F are in their correct alignments for printing. With the workpieces 32A-F in this position, they may now be printed onto. FIG. 5E shows the position subsequent to printing. The locks of all towers 14 are controlled so that all towers 14 are placed in the unlocked state. The towers 14 are returned to their starting positions and placed in their unlocked states, either through biasing as described above, or through active alignment (i.e. sequentially placing each tower 14 in the tool-locking state and moving it to its initial position before placing it in the unlocked state). In this position the workpieces 32A-F may be returned to their carrier (not shown), and transported out of the printing machine. The process illustrated in FIGs. 5A-E may therefore be summarised in that each workpiece 32A-F is sequentially placed into its correct printing position relative to the actuation tool 22, and then the actuation tool 22 is moved, with all workpieces 32A-F, so that the workpieces are in their correct printing position relative to the base 12. FIGs. 6A-F schematically show, from above, stages in an alternative alignment sequence in accordance with the present invention, again in which a 3x2 array of singulated workpieces 32A-F is transported into a printing machine within a carrier. The views of FIGs. 6A-F are similarto those of FIGs. 5A-E, and similar reference numerals are retained for similar items. In FIG. 6A, all workpieces 32A-F are shown in their initial, unaligned positions. As in FIG. 5A, the lack of alignment is greatly exaggerated here for clarity. All of the towers 14 are in an unlocked state. In the position shown, each workpiece's fiducials are detected, for example by using an overhead camera as is well-known in the art per se, to ascertain the misalignment of each workpiece 32A-F. The alignment sequence can proceed as soon as the fiducials are captured - preferably all of the fiducials of all of the workpieces 32A-F are captured at this stage, but it is also possible, though not as efficient, to capture fiducials of each workpiece 32A-F immediately prior to its alignment as described below. A first workpiece 32A is then constrained relative to the base 12, i.e. its supporting tower 14 is placed in the base-locking state. As shown in FIG. 6B, with the workpiece 32A thus constrained, the actuation tool 22 is moved, by appropriate control of the actuators 24, 26 and 28, so that it aligns with the workpiece 32A as shown, i.e. so that the workpiece 32A is aligned within its alignment target 33. Once workpiece 32A is so aligned, its tower 14 is placed in the tool-locking state (as denoted by the circle on workpiece 32A), so that the head 16, and hence workpiece 32A, is constrained relative to the actuation tool 22. As shown in FIG. 6C, the actuation tool 22, and hence workpiece 32A, is then moved so that the workpiece 32A lies in its correct position relative to the base for printing. Its tower 14 is then placed in the base-locking state, so that its head 16, and hence workpiece 32A, is constrained relative to the base 12. The tower 14 supporting workpiece 32A remains in the base-locking state until printing is completed. The process may then be repeated for each remaining workpiece 32B-F. Therefore, a second workpiece 32B is then constrained relative to the base 12, i.e. its supporting tower 14 is placed in the base-locking state. As shown in FIG. 6D, the actuation tool 22 is moved, by appropriate control of the actuators 24, 26 and 28, so that it aligns with the workpiece 32B as shown, i.e. so that the workpiece 32B is aligned within its alignment target 33. Once workpiece 32B is so aligned, its tower 14 is placed in the tool-locking state (as denoted by the circle on workpiece 32B), so that the head 16, and hence workpiece 32A, is constrained relative to the actuation tool 22. The actuation tool 22, and hence workpiece 32B, is then moved so that the workpiece 32B lies in its correct position relative to the base for printing. Its tower 14 is then placed in the base-locking state, so that its head 16, and hence workpiece 32B, is constrained relative to the base 12. The tower 14 supporting workpiece 32B remains in the base-locking state until printing is completed. The process may then be repeated for each remaining workpiece 32C-F. FIG. 6E shows the situation once all workpieces 32A-F have been aligned and constrained relative to the base 12, and the actuation tool 22 moved to its printing position, in which all workpieces 32A-F are in their correct alignments for printing. With the workpieces 32A-F in this position, they may now be printed onto. FIG. 6F shows the position subsequent to printing. The locks of all towers 14 are controlled so that all towers 14 are placed in the unlocked state. The towers 14 are returned to their starting positions and placed in their unlocked states, either through biasing as described above, or through active alignment (i.e. sequentially placing each tower 14 in the tool-locking state and moving it to its initial position before placing it in the unlocked state). In this position the workpieces 32A-F may be returned to their carrier (not shown), and transported out of the printing machine. The process illustrated in FIGs. 6A-F may therefore be summarised in that each workpiece 32A-F is sequentially moved, by the actuation tool 22, into its correct printing position relative to the base 12. An alignment system 40 in accordance with a second embodiment of the present invention will now be described with reference to FIGs. 7 and 8, of which FIG. 7 schematically shows, in a sectional side view, of the alignment system 40 at a transport height, and FIG. 8 schematically shows the alignment system 40, in a sectional side view orthogonal to that of FIG. 7, at a printing height. As far as possible, similar reference numerals to those used in previous figures will be retained. As can be seen from FIGs. 7 and 8, the alignment system 40 is suitable for aligning eight singulated workpieces 32 which enter a printing machine, for example along an input conveyor (not shown) within a carrier 42 in a 4x2 array. The alignment system comprises eight towers 54, each associated with a respective workpiece 32 of the array, which are supported by a support frame 44 via respective couplers 52 (described in more detail below). The heads of the towers 54, i.e. the ends of the towers 54 at the upper extent thereof, form support surfaces for respective workpieces 32. Positioned below the towers 54 are a plurality of actuation tools in the form of alignment stages 46, here two alignment stages 46 are shown, so each alignment stage 46 lies below four towers 54. Each alignment stage 46 comprises an upper surface which is accurately drivable within the horizontal X-Y plane, capable of X-direction translation, Y-direction translation, theta rotation about an axis parallel to the vertical Z axis, and superpositions of these translations and rotations. Conveniently, the alignment stages 46 may for example comprise MASS towers as described above and in EP3693168A1. Both the support frame 44 and the alignment stages 46 are located on the support or rising table 48 of the printing machine such that they move vertically with the rising table 48. In particular, they move with the rising table 48 between a lower position, referred to as 'transport height' and shown in FIG. 7, and an upper position, known as 'printing height' and shown in FIG. 8. At transport height, the alignment system 40 lies wholly below the carrier 42, so that the carrier 42 may be transported into, or out of, the printing machine without colliding with the alignment system 40. At printing height, the towers 54 are brought into supporting engagement with respective workpieces 32 from below, so that the workpieces 32 are supported on respective heads of the towers 54, at a height level with an upper surface of a surround plate 50. As is well-known in the art per se, surround plates 50 are used to ensure that the squeegee (not shown) of the printing machine can travel across a screen or stencil (not shown) abutting against the upper surfaces of the workpieces 32 smoothly, without 'bouncing' into gaps between the workpieces 32. Ideally, the upper surfaces of the surround plate 50 and workpieces 32 form as close to a contiguous planar surface as possible. Also shown is a look-down optical camera 56 of the printing machine, suitable for detecting the alignment of workpieces 32 by detecting of associated fiducials or other optically-detectable markings. The camera 56 may be movably mounted on a gantry (not shown), so that it can be moved over each workpiece 32 in turn to detect its alignment. Each tower 54 is associated with a respective locking system in the form of a coupler 52, via which it is supported by the support frame 44. Each coupler 52 comprises an upper coupler part 53, which is permanently connected to the support frame 44, and a lower coupler part 55, which is permanently connected to the alignment stage 46. The upper and lower coupler parts 53, 55 are relatively displaceable in the horizontal plane, for example being connected via a bearing, so that the alignment stage 46 can move freely in the horizontal plane. Each of the upper and lower coupler parts 53, 55 is selectively couplable to its respective tower 54, for example electromagnetically or by applying vacuum thereto, so as to place the tower 54 in the tool-locking state (by coupling the lower coupler part 55 to the tower 54) or the base-locking state (by coupling the upper coupler part 53 to the tower 54). If neither the upper now lower coupler parts 53, 55 are so coupled, then the tower 54 is in an unlocked state. This alignment system 40 may thus be operated in a substantially identical manner to the alignment system 10 described above. FIG. 9 schematically shows, in a sectional side view, an alignment system 60 in accordance with a third embodiment of the present invention, at a printing height. The alignment system 60 of this embodiment has some similarities with the alignment system 40 of FIGs. 7 and 8, except that, while alignment system 40 used locking systems for each tower held by the base or supporting frame, in this embodiment each tower's locking system is an integrated part of the tower itself. As will be described in more detail below, one advantage of this implementation is the ability to compensate for deviations in planarity of the alignment stage. As far as possible, similar reference numerals to those used in previous figures will be retained. As shown, the alignment system 60 comprises a plurality, here two, of towers 64, designated as a left tower 64A and right tower 64B, supported by a support frame 44 via a respective sleeve insert 62 inserted into voids in the support frame 44. Each tower 64 comprises a head 66 at an upper end thereofconfigured to support a respective workpiece 32 thereon in use, with the towers 64 being laterally spaced so as to underlie the respective workpieces 32 when they are transported into the printing machine in a carrier 42. The towers 64 take the form of a balbis in section, with an upper body 86, which carries the head 66, and a lower body 88 arranged parallel thereto, separated by a relatively thin stem 70. The towers 64 are received loosely within respective sleeve inserts 62, and constrained within a predetermined range of movement relative to their respective sleeve inserts 62 in both in the vertical (Z) direction and horizontal (X-Y) directions by an inwardly-projecting flange 68 of each sleeve insert 62, which surrounds the stem 70 and is of smaller diameter than the upper and lower bodies 86, 88, and smaller vertical extent than the stem 70. The lower surface of upper body 86 includes a tower magnetic coupling 78 and a tower air bearing 80, each formed within the upper body and overlying the flange 68. The towers 64 overlie an actuation tool in the form of an alignment stage 46. The alignment stage 46 comprises an upper surface which is accurately drivable within the horizontal X-Y plane, capable of X-direction translation, Y-direction translation, theta rotation about an axis parallel to the vertical Z axis, and superpositions of these translations and rotations. Conveniently, the alignment stage 46 may for example comprise a MASS tower as described above and in EP3693168A1. Both the support frame 44 and the alignment stage 46 are located on the support or rising table 48 of the printing machine such that they move vertically with the rising table 48. In particular, they move with the rising table 48 between a lower 'transport height' and an upper 'printing height', shown in FIG. 9, at which the workpieces 32 are supported on respective heads of the towers 64, at a height level with an upper surface of a surround plate 50. While it is possible to form the rising table 48 to have a very flat upper surface, it is more problematic to ensure flatness of the upper surface of the alignment stage 46. To illustrate this, FIG. 9 includes a deviating surface 72 on top of the alignment stage 46 which illustrates, in a greatly exaggerated form, possible deviations from flatness / standard height of the alignment stage 46. However, this design of alignment system 60 may compensate for such deviations, which is an important benefit. This is achieved by providing an alignment foot 74 at the lower end of each tower 64, connected to the lower body 88 via a spring 76. Preferably, the spring 76 permits relative vertical movement of the engagement foot 74 and lower body 88, but prevents any lateral, i.e. horizontal relative movement therebetween. This may be achieved by using a design of spring 76 as shown in FIG. 11 for example, which will be described in more detail below. The spring 76 biases the engagement foot 74 to a neutral position from which the engagement foot 74 may move vertically up or down relative to the lower body 88. In this neutral position, motion is not transferred between the alignment stage 46 and the tower 64 via the engagement foot 74. Each tower 64 comprises a respective locking system, with each locking system being independently operable to place its associated tower 64 in a tool locking state in which the head 66 of the respective tower 64 is locked relative to the alignment stage 46 so as to prevent relative movement between the respective head 66 and the alignment stage 46. An additional locking system is also provided, to selectively lock the tower 64 to the flange 68 and hence the frame 44. In more detail, each tower 64 comprises, at the lower surface of upper body 86, a tower magnetic coupling 78, arranged to lie adjacent the upper surface of the respective flange 68. The upper surface of flange 68 includes a tower air bearing 80 arranged to lie adjacent the lower surface of the upper body 86. These features are actuable to lock / unlock the tower 64 to the flange 68, and hence to the support frame 44. In addition, in this embodiment each tower 64 comprises, at the lower surface of engagement foot 74, a stage magnetic coupling 82 and a stage air bearing 84, arranged so that they may engage with the upper surface of the alignment stage 46, which is magnetically permeable, including the deviating surface 72. These features are actuable to lock / unlock the tower 64 to the alignment stage 46. It can be seen that each magnetic coupling 78, 82 is associated with a respective air bearing 80,84. The magnetic couplings 78,82 provide coupling force for locking, while application of air (positive air pressure) via the air bearings 80, 84 is used to overcome the magnetic coupling force, effectively unlocking the respective coupling. In this embodiment, the air bearing 84 provides a very small physical disconnect between the engagement foot 74 and the upper surface of the alignment stage 46 so that (horizontal) sliding can occur therebetween with minimal vertical / Z travel between connect and disconnect. It will be understood that the air bearing 84 may additionally or alternatively be used to provide locking, for example by reversing the airflow communicating with the air bearing and thus creating an at least partial vacuum. In alternative embodiments (not shown), there may be other forms of interface between the engagement foot 74 and the upper surface of the alignment stage 46. For example, the interface between engagement foot 74 and alignment stage 46 could alternatively be via one of the following: - A maintained gap with a physical connection / disconnection for locking; A physical connection, but low friction so that sliding can occur, e.g. using a conventional bearing or simply contacting low-friction surfaces, in conjunction with a separate locking mechanism (such as a vacuum / electromagnetic lock etc). To illustrate operation, in FIG. 9 the left tower 64A is shown in a stage-unlocked state, in which positive air pressure is applied to the stage air bearing 84 to decouple the stage magnetic coupling 82 from the alignment stage 46. The tower air bearing 80 has no air applied, and so the tower magnetic coupling 78 is magnetically coupled to the flange 68. As shown therefore, the left tower 64A is held stationary with respect to the flange 68 and frame 44, but is free to move relative to the alignment stage 46. It should be noted that if positive air pressure was supplied to the tower air bearing 80, then the left tower 64A would be decoupled from both the frame 44 and the alignment stage 46, and thus able to move relative to both. In FIG. 9 the right tower 64B is placed in a tool locking state; air supply to the stage air bearing 84 is turned off, so that the stage magnetic coupling 82 couples to the alignment stage 46. Deviations in flatness of the alignment stage 46 due to deviating surface 72 are compensated for by vertical movement of the engagement foot 88 via extension of the spring 76. It should be noted that the limited horizontal movement of the towers 64 relative to the sleeve inserts 62 also assists in compensating for flatness deviations of the alignment stage 46. The tower air bearing 80 has positive air pressure applied, and so the tower magnetic coupling 78 is magnetically decoupled to the flange 68. As shown therefore, the right tower 64B is held stationary with respect to the alignment stage 46, but is free to move relative to the flange 68 and frame 44. The air bearings 80, 84 may also be used to perform locking instead of, or in combination with, respective magnetic couplings 78, 82, by applying a negative pressure, i.e. an at least partial vacuum, thereto. FIGs. 10A-C schematically show sections of a tower 64 of the alignment system of FIG. 9 from various azimuthal positions about the vertical Z axis, providing more constructional details, in particular showing the pneumatic arrangement of the tower 64, with all airways for the tower 64 being provided via the tower's sleeve insert 62. FIG. 10A shows the vacuum pathway by which an at least partial vacuum may be supplied to the upper surface of the head 66, to releasably secure a workpiece (not shown) thereto. A vacuum source (not shown) is connected to a vertical channel 90 formed in a sidewall of the sleeve insert 62. The upper end of channel 90 communicates with a horizontal duct 92 formed in the flange 68, which in turn communicates with a suction cup 94 provided between the flange 68 and lower body 88. The suction cup 94 (and indeed the other suction cups 100 and 108 described below) is flexible, for example made from a rubber or plastics material, so that it does not prevent relative movement between the tower 64 and the flange 68 in the required movement range. The lower end of suction cup 94 communicates with a horizontal duct 96 formed in the lower body 88, which in turn communicates with a vertically-extending central channel 98 formed centrally in the tower 64, and extending from the lower body 88, through the stem 70 and through the upper body 86 to the upper surface of head 66. In this way, connecting the vacuum source to channel 90 creates an at least partial vacuum at the head 66. FIG, 10A also shows some features for supplying air to the stage air bearing 84, including a centrally arranged suction cup 100 in communication with a horizontal duct 102 formed in the engagement foot 74 leading to the stage air bearing 84. These features are explained in more detail with reference to FIG. IOC below. FIG. 10B shows the air pathway by which air is supplied to orfrom the tower air bearing 80. A vertical channel 104 is formed in the sleeve insert 62, to which an air / vacuum supply (not shown) may be connected which communicates with the lower end of the channel 104. The upper end of channel 104 communicates with a horizontal duct 106 formed in the flange 68, communicating in turn with the tower air bearing 80. FIG. IOC shows the air pathway by which air is supplied to or from the stage air bearing 84. A vertical channel 110 is formed in the sleeve insert 62, to which an air / vacuum supply (not shown) may be connected which communicates with the lower end of the channel 110. The upper end of channel 110 communicates with a horizontal duct 112 formed in the flange 68, communicating in turn with a suction cup 108 which extends vertically down into the lower body 88. The lower end of suction cup 108 communicates with a horizontal duct 114, which communicates in turn with the suction cup 100, which extends between the lower body 88 and the engagement foot 74. The lower end of suction cup 100 communicates with a horizontal duct 102 formed in the engagement foot 74, which communicates in turn with the stage air bearing 84. Conveniently, all of the above-described channels and ducts may be formed by drilling into the material of the tower 64, flange 68 and / or sleeve insert 62, and then blocking ends of the ducts or channels with bungs if required. As specific examples, bungs 120 are shown blocking the ducts 102 and the duct 92 at their radially-outermost ends, these ducts conveniently being formed by radially drilling into the engagement foot 74 and sleeve insert 62 / flange 68 respectively. Duct 114 is similarly blocked. This provides a cost-effective method of manufacture, as compared with integrally forming ducts and channels within solid material bodies. In FIGs. 10B and IOC it is also possible to see the stage magnetic coupling 82, which may conveniently comprise a simple permanent magnet. Such a permanent magnet may also be used as the tower magnetic coupling 78 (see FIG. 9). Although difficult to discern in FIGs. 10A-C, the spring 76 is located between the lower body 88 and engagement foot 74. FIG. 11 schematically shows, from above, a spring 76 suitable for use with the alignment system of FIGs. 9 and 10A-C. Spring 76 is formed from a thin, flat, circular disc, for example from a metal material, with various portions cut-out from the disc. The removal of these portions leaves a circular rim 122 from which three fingers 124 project radially inwardly at equidistantly spaced locations 126. Each finger 124 is curved, and extends parallel to the rim 122. In the example shown, there are three fingers 124, with each finger subtending slightly under a third of the rim 122's circumference. A central portion 128 of each finger 124 is cut out, leaving two thin, parallel arms 130 to constitute the majority of the length of each finger 124. This increases the flexibility of each finger 124 parallel to the Z (vertical) direction in use, i.e. normal to the plane of the paper, but constrains movement of the finger 124 relative to the rim 122 within the horizontal X-Y plane, i.e. within the plane of the paper. Each finger 124 is provided with an outer mounting hole 132 at the end nearest to location 126, and an inner mounting hole 134 at the distal end. These mounting holes 132, 134 are used to connect the spring 76 to the lower body 88 and engagement foot 74 (see FIGs. 9 to 10C). The engagement foot 74 and lower body 88 are therefore constrained in the horizontal X-Y plane, but free to relatively move and tilt parallel to the vertical Z axis. The alignment system 60 of FIGs. 9 to 11 may be operated as follows: i) Initially, each tower 64 is locked to the frame 44 by tower magnetic couplings 78 and optionally by applying negative pressure to tower air bearings 80, while coupling to the respective alignment stage 46 via stage magnetic couplings 82. ii) To release any potential preload due to this contemporaneous locking / coupling, the tower air bearings 80 are activated, allowing the towers 64 to move relative to the frame 44. iii) With all the towers 64 in this state, workpiece fiducials can be captured. iv) An alignment process similar to those described with reference to either FIGs. 5A-E or 6A-F may then be performed. Whichever process is adopted: - Locking of a tower 64 to the frame 44 is achieved by deactivating the respective tower air bearing 80; - The respective stage air bearing 84 is then activated to decouple the tower 64 from the alignment stage 46; - All towers 64 may then adopt this decoupled state; and - Towers 64 performing workpiece alignment are re-coupled to the alignment stage 46 and unlocked from the frame 44 by reactivating the respective tower air bearing 80. The above-described embodiments are exemplary only, and other possibilities and alternatives within the scope of the invention will be apparent to those skilled in the art. For example, the head of each tower may be movable vertically with respect to the base. In this case, the alignment system may comprise a plurality of vertical actuators, each vertical actuator being configured to move a respective head vertically with respect to its respective base. This may for example be achieved by adding an additional lock within each tower, so that each can translate independently. A suitable design, in which an air bearing is used, when activated, to permit vertical movement and, when deactivated, to act as a lock, is described for example in GB2216231.7. As described therein, when the air bearing of each tower is activated, it may 'float' upwardly until abutting the surround plate, which acts as a reference, at which point the air bearing may be deactivated, locking the tower into the correct vertical position. As an alternative, an active vertical control system, such as a ball spline or similar alternatives, could be provided within the stem of each tower. Reference numerals used: 1, 2, 3 - Panels 1A-D, 2A-D, 3A-D - Boards 4 - Workpiece support assembly 5 - Support towers 6 - Support surfaces 10, 40, 60 - Alignment system 12 - Base 14, 54, 64 - Towers 16, 66 - Heads 18 - Upper section 20 - Lower section 22 - Actuation tool 23 - Through-holes 24, 26 - Y / 0 Actuators 28 - X Actuator 30A-F - Locks 32, 32A-F - Workpieces 33 - Workpiece alignment targets 42 - Carrier 44 - Support frame 46 - Alignment stages 48 - Rising table 50 - Surround plate 52 - Coupler 53 - Upper coupler part 55 - Lower coupler part 56 - Camera 62 - Sleeve insert 64A - Left tower 64B - Right tower 68 - Flange 70 - Stem 72 - Deviating surface 74 - Engagement foot 76 - Spring 78 - Tower magnetic coupling 80 - Tower air bearing 82 - Stage magnetic coupling 84 - Stage air bearing 86 - Upper body 88 - Lower body 90, 104,110 - Channels 92, 96,102,106,112,114 - Ducts 5 94,100,108 - Suction cups 98 - Central channel 120 - Bung 122 - Rim 124 - Fingers 10 126 - Locations 128 - Central portion 130 - Arms 132 - Outer mounting holes 134 - Inner mounting holes 15

Claims

1. An alignment system for aligning a plurality of singulated workpieces received within a printing machine within a horizontal (X-Y) plane, comprising:a plurality of towers spaced apart in the horizontal plane, each tower having a head configured to support a respective singulated workpiece thereon in use;an actuation tool which is movable within the horizontal plane;an actuation means operatively connected to the actuation member for driving the actuation tool within the horizontal plane; andwherein each tower is associated with a respective locking system, each locking system being independently operable to place its associated tower in a tool-locking state in which at least the head of the respective tower is locked relative to the actuation tool so as to prevent relative movement between the respective head and the actuation tool in the horizontal (X-Y) plane.

2. The alignment system of claim 1, comprising a base configured to rest on a support table of the printing machine; andwherein each locking system is independently operable to place its associated tower in a base-locking state in which at least the head of the respective tower is locked relative to the base, and hence the support table, so as to prevent relative movement between the respective head and the base and support table in the horizontal (X-Y) plane.

3. The alignment system of claim 2, wherein each head is biased to a neutral position within the horizontal (X-Y) plane with respect to the base.

4. The alignment system of any preceding claim, wherein the actuation means is operable to drive the actuation tool with at least a component of motion from the group consisting of: linearly parallel to a horizontal X axis, linearly parallel to a horizontal Y axis orthogonal to the X axis, and about a vertical axis of rotation orthogonal to both the X and Y axes.

5. The alignment system of any of claims 2 to 4, wherein the base comprises a framewhich supports the plurality of towers, and the actuation tool comprises a stage supported by the support table, which may engage with a lower section of each tower.

6. The alignment system of claim 5, wherein the lower section of each tower comprises a foot which is movable vertically with respect to its respective head, the foot being configured to engage with the stage.

7. The alignment system of any of claims 1 to 4, wherein the actuation tool comprises a member with a plurality of through-holes through which respective towers extend.

8. The alignment system of any of claims 2 to 7, wherein each locking system comprises a pneumatic locking system which, when in the tool locking state applies a vacuum or reduced pressure between the tower and the actuation tool to lock the tower relative to the actuation tool, and, when in the base locking state applies a vacuum or reduced pressure between the tower and the base to lock the tower relative to the base.

9. The alignment system of claim 8, wherein the pneumatic locking system comprises an air bearing.

10. The alignment system of any preceding claim, wherein each locking system comprises a magnet for coupling the respective tower to the actuation tool.

11. The alignment system of any of claims 2 to 10, wherein each locking system comprises a magnet for coupling the respective tower to the base.

12. The alignment system of any of claims 2 to 11, wherein the head of each tower is movable vertically with respect to the base, and the alignment system comprises a plurality of vertical actuators, each vertical actuator configured to move a respective head vertically with respect to its respective base.

13. The alignment system of any preceding claim, comprising a control systemconfigured to operate the actuation means and the locking systems in dependence of detected alignments of the plurality of singulated workpieces.

14. A printing machine comprising the alignment system of any preceding claim.

15. A method for aligning a plurality of singulated workpieces received within a printing machine within a horizontal (X-Y) plane, comprising the steps of:i) locating each singulated workpiece onto a head of a respective tower;ii) detecting the alignment of each of the singulated workpieces;iii) driving an actuator memberto until it aligns with the detected alignment of a first singulated workpiece;iv) locking the head upon which the first singulated workpiece is located to the actuator member so that relative movement between the said head and the actuator member is prevented;v) driving the actuator member to until it aligns with the detected alignment of another singulated workpiece;vi) locking the head upon which the another singulated workpiece is located to the actuator member so that relative movement between the said head and the actuator member is prevented; andvii) repeating steps v) to vi) until all of the plurality of singulated workpieces are aligned with the actuator member.

16. The method of claim 15, wherein in step iii) the head on which the first singulated workpiece is located is locked relative to the printing machine, and in step v) the head on which the another singulated workpiece is located is locked relative to the printing machine.

17. The method of either of claims 15 and 16, wherein step ii) comprises optically detecting visible features of the singulated workpieces.

18. The method of any of claims 15 to 17, wherein the printing machine comprises the alignment system of any of claims 1 to 13.

19. A method of printing onto a plurality of singulated workpieces, comprising the steps of aligning the plurality of singulated workpieces using the method of any of claims 15 to 18, and, subsequent to step vii), printing onto the aligned singulated workpieces.Application No: GB2406465.1Examiner:Marc CollinsClaims searched: 1-19Date of search: 7 November 2024Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1,4, 7-10 and 14-19 at least WO 2014 / 166956 Al (DTGINT. GMBH) See whole document especially page 21, line 15 to page 22, line 13; page 25, lines 17-22 and figures. A - GB 2623976 A (ASMPT SMT SINGAPORE PTE LTD.) A - GB 2559982 A (ASMPT SMT SINGAPORE PTE LTD.) A - GB 2619961 A (ASM ASSEMBLY SYSTEMS SINGAPORE PTE LTD.) A - GB 2596517 A (ASM ASSEMBLY SYSTEMS SINGAPORE PTE LTD.) A - GB 2580347 A (ASM ASSEMBLY SYSTEMS SINGAPORE PTE LTD.)Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:www.gov.uk / ipoInternational Classification:Subclass Subgroup Valid From B41F 0015 / 18 01 / 01 / 2006 B41F 0015 / 26 01 / 01 / 2006 HO IL 0021 / 68 01 / 01 / 2006 H05K 0003 / 00 01 / 01 / 2006 H05K 0003 / 12 01 / 01 / 2006www.gov.uk / ipo

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