Patent Description:
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.

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 part of that board may be defective, which in turn may lead to a defective PCB. This situation is schematically shown in <FIG>, where three panels <NUM>, <NUM>, <NUM> are shown, each having a 4x1 array of boards A-D. While the left-most panel <NUM> is completely free from defects, the adjacent panel <NUM> has a defective board 2A, while the right-most panel <NUM> 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. For the 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 of ten 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 <NUM>% efficiency. Furthermore, if two or more boards are defective then additional measures must be taken.

A solution to the above problem is to pre-separate or "singulate" the individual boards 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, <CIT> describes a method in which individual boards are respectively positioned, but this only permits the sequential printing of one substrate at a time. <CIT> 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. <CIT> describes an alternative apparatus, in which all boards may be aligned simultaneously using a reference webbing, and then simultaneously printed. This solution works well, though will not be suitable if an incoming unprinted board is positioned too far from its correct position.

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 <CIT>. <FIG> schematically shows an example of such an assembly <NUM>, here including a <NUM> x <NUM> array of individual support "towers" <NUM>. Each tower <NUM> is topped with a support surface <NUM> upon which a workpiece (not shown) may be supported during a printing operation. Furthermore, each tower <NUM> 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 <CIT>, 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 ASM under the name "MASS", and provides a very fast and accurate printing solution. In an extension of the MASS methodology, <CIT> describes how such apparatus may be used to print a plurality of singulated substrates which are arranged at pitches in the transport direction that are smaller than the spacing of individual support towers. Furthermore, in a yet further extension of the MASS methodology, <CIT> describes how such apparatus may be used to print a plurality of singulated substrates which are arranged at pitches orthogonal to the transport direction that are smaller than the spacing of individual support towers.

<CIT> discloses an apparatus for printing singulated substrates, which uses a printing screen having a cavity portion formed therein.

<CIT> discloses an apparatus for printing singulated substrates, which uses a single X-Y positioning mechanism to move all substrates into physical alignment with a referencing plate.

<CIT> and <CIT> each disclose apparatus for printing singulated substrates, in which individual substrates are sequentially aligned.

However, a problem exists in that, even using the methodology as set out in <CIT> and <CIT>, there is a lower limit to the pitch of a singulated workpiece array printable - if the workpieces or pitch are so small that more than one workpiece overlies an upper support surface of a single support tower, the MASS system is not suitable.

The present invention seeks to overcome this problem and enable the use of a support tower tooling system, such as MASS, with all currently-used arrays of singulated workpieces. In particular, it is an aim of the present invention to provide apparatus and methodology to align singulated workpieces with an aperture pattern of a patterned printing screen while the workpieces are located inside a printing machine and prior to conducting a printing operation, using such a support tower tooling system. The present invention therefore enables printing of singulated workpieces housed in all standard carrier trays, such as "JEDEC" trays, using 'MASS-type' tooling.

In accordance with the present invention, this aim is achieved by providing each support tower with a plurality of support surfaces, each support surface of the plurality being arranged at a differential height profile in a pre-printing configuration, so that lifting of the or each support tower causes individual workpieces to be contacted from below in a staggered manner, so that they can be individually aligned.

In accordance with a first aspect of the present invention there is provided tooling for supporting workpieces during a printing operation, comprising:.

In accordance with a second aspect of the present invention there is provided a printing machine for printing workpieces at a printing location within the printing machine, comprising:.

In accordance with a third aspect of the present invention there is provided a method of aligning workpieces prior to a printing operation, comprising the steps of:.

Other specific aspects and features of the present invention are set out in the accompanying claims.

The invention will now be described with reference to the accompanying drawings (not to scale), in which:.

An alignment method in accordance with the present invention is schematically shown in <FIG>.

<FIG> show an initial stage of the method, in which a carrier <NUM>, such as a JEDEC tray, external to a printing machine (<NUM>, see <FIG>) is to be transported to a printing location by a transport system (not shown) of the printing machine <NUM>. As is well-known in the art, such a transport system may typically comprise a number of conveyors (not shown) which the carrier <NUM> may directly rest on, the conveyors configured to move, in a horizontal plane and in the X direction shown, a carrier <NUM> loaded with unprinted workpieces <NUM> from an input to the printing machine <NUM>, then to the printing location, and, following completion of a printing operation in which print medium such as solder paste is transferred onto an upper surface of the workpieces, to an output of the printing machine <NUM>. Although not shown in these figures, the carrier <NUM> may then be transported to other parts of a production line as required, for example to a placement machine, inspection machine or reflow oven. As will be understood by those skilled in the art, the printing machine <NUM>, including its transport system, is controlled by a control system running sophisticated software via suitably programmed processors, computers or the like.

As shown in <FIG>, in this example carrier <NUM> is loaded with four unprinted, singulated workpieces <NUM>, labelled 11A-11D. These workpieces <NUM> may not be well-aligned within the carrier <NUM>, although it should be noted that the amount of misalignment shown in <FIG> is exaggerated for clarity. Each workpiece <NUM> is provided, in a fixed and preset location, with at least one workpiece fiducial <NUM>, a graphical symbol that can be easily recognised by an optical sensor.

The printing machine <NUM> comprises a tooling table <NUM>, which includes a tooling table upper surface <NUM>, this being flat and aligned in the horizontal (X, Y) plane as shown. The tooling table <NUM> is drivable in the vertical direction, i.e. both parallel and antiparallel to the Z axis as shown, by a drive mechanism (not shown). In particular, the tooling table <NUM> is at least drivable between a lowest position in which the tooling table upper surface <NUM> is at a height Z0 shown and a highest position in which the tooling table upper surface <NUM> is at a height ZP shown, which range includes intermediate heights ZA and ZB as shown. The height difference between ZB and ZA is greater than the thickness of a workpiece <NUM>.

Tooling <NUM> is mounted to the tooling table upper surface <NUM>, for vertical movement with the tooling table <NUM>. In the example shown, the tooling comprises two support towers <NUM>, <NUM>, projecting upwardly from an assembly unit <NUM>. The assembly unit <NUM> comprises control circuitry for controlling movement of the support towers <NUM>, <NUM>, as will be described in more detail below. These support towers <NUM>, <NUM> are both of the "MASS" type described previously, comprising respective bases <NUM>, <NUM> and heads <NUM>, <NUM> positioned vertically above the bases <NUM>, <NUM>. Each head <NUM>, <NUM> is relatively moveable with respect to its respective base <NUM>, <NUM> in a horizontal (X, Y) plane. Being MASS-type towers, each base <NUM>, <NUM> comprises an actuator (not shown) for driving the respective head in the horizontal plane relative to the base <NUM>, <NUM>, and in this embodiment the actuator is operative to drive the respective head <NUM>, <NUM> in orthogonal X and Y directions within the horizontal plane, and also to rotate the respective head <NUM>, <NUM> about a vertical axis parallel to the Z-axis shown. Advantageously, the actuators may be parallel kinematic actuators to provide such movement while remaining compact in size, as described in <CIT>. The support towers <NUM>, <NUM> are provided with vacuum connections, so that the respective heads <NUM>, <NUM> may be selectively supplied with an at least partial vacuum supplied by a separately provided vacuum pump (not shown) located elsewhere in the printing machine <NUM>. Each head <NUM>, <NUM> is fitted with first and second supports arranged in a linear array, with head <NUM> being provided with supports 21A, 21B, while head <NUM> is provided with supports 21C and 21D. Each support 21A-D has a respective support surface 22A-D at an upper end thereof, with each of these support surfaces being adapted to support a single respective workpiece 11A-D thereon. Each of the support surfaces 22A-D is provided with at least one opening (not shown) for selectively supplying an at least partial vacuum to a workpiece 11A-D when it is supported thereon, to anchor the workpiece to the respective supporting support surface. The vacuum supply to each opening is received from the respective head <NUM>, <NUM>. The opening may optionally comprise a gauze-type material. As a further alternative, the support surfaces 22A-D may optionally comprise sintered material through which vacuum may be supplied. For each support tower <NUM>, <NUM>, a first one of the support surfaces, i.e. support surfaces 22A and 22C, is relatively moveable with respect to the second one of the support surfaces, i.e. support surfaces 22B, 22D, only in a vertical direction (parallel to the Z-axis) in use. As shown, the first support surfaces 22A, 22C are located in a pre-printing configuration in which the first (22A, 22C) and second (22B, 22D) support surfaces are spaced in the vertical direction (parallel to the Z-axis), i.e. the first support surfaces 22A, 22C are vertically higher than the second support surfaces 22B, 22D by a distance ZB - ZA. The first support surfaces 22A, 22C may be moved downwards to a printing configuration (see <FIG>) in which they are substantially coplanar in the horizontal (X, Y) plane with the second support surfaces 22B, 22D. As can be more clearly seen from above in <FIG>, each support surface 22A-D has a shape and dimension selected to generally correspond with that of a workpiece <NUM>, so that it can provide adequate support therefor. For clarity, in all of the views from above, such as <FIG>, the support surfaces 22A-D are shown with dashed lines. Also for clarity, the surround plate (<NUM>, see <FIG>) which would be present within the printing machine <NUM>, has been omitted. Similarly, the surround plate <NUM> is omitted from all of the views from above, i.e. <FIG>.

As shown in <FIG>, <FIG>, the carrier <NUM> is transported to the printing location in which the unprinted workpieces 11A-D overlie respective support surfaces 22A-D. It can be seen from <FIG> that the workpieces 11A-D are all misaligned with their underlying support surfaces 22A-D. <FIG> more clearly shows the relative positioning of parts within the printing machine <NUM>. In the printing location, the carrier <NUM> is located beneath a surround plate <NUM>, which is rigidly fixed to vertically-drivable rails (not shown) within the printing machine <NUM>. As is well-known in the art, a surround plate is a flat plate with apertures formed therein to receive respective singulated workpieces <NUM>. The top surface of the surround plate <NUM> is arranged to be co-planar with the upper surfaces of the workpieces <NUM> during a printing operation, to prevent undue stress being placed on the workpieces <NUM> by the downward pressure applied by a squeegee (<NUM>, see <FIG>). Above the surround plate <NUM> is a printing screen or stencil <NUM> which is rigidly fixed within the printing machine <NUM> and patterned with apertures corresponding to the desired target print pattern for the workpieces <NUM>. During a printing operation, a squeegee (<NUM>, see <FIG>) runs across the top of the printing screen <NUM> to force print medium through the apertures and onto the workpieces <NUM>. In the pre-printing configuration shown, and in the tooling table upper surface <NUM> is at height Z0, there is sufficient space between the surround plate <NUM> and the printing screen <NUM> for a camera <NUM> of a camera system to be positioned. In this stage of the method, the camera <NUM> is positioned above each workpiece 11A-D in turn, to capture each respective workpiece fiducial <NUM> (see <FIG>). The camera <NUM> may for example by fitted to a movable gantry (not shown) or arm to move it across the carrier <NUM>. In alternative embodiments (not shown), it may be possible to use a camera system capable of capturing the workpiece fiducials <NUM> of more than one workpiece 11A-D simultaneously. In either case, data associated with the captured fiducials is passed to the control system and processed to determine the position of each workpiece 11A-D in the horizontal (X, Y) plane as well as its orientation about a vertical axis parallel to the Z-axis, which is referred to as its θ rotation. Following capture of all of the workpiece fiducials <NUM>, the camera <NUM> is moved to a retracted position horizontally spaced from the carrier <NUM>, so as not to interfere with subsequent movement of the tooling table <NUM>, as shown in <FIG>.

As shown from above in <FIG>, each support tower <NUM>, <NUM> is then independently driven (i.e. the heads <NUM>, <NUM> are independently driven with respect to their bases <NUM>, <NUM>) such that the respective underlying first support surfaces 22A, 22C are brought into alignment with their respective overlying workpieces 11A, 11C, using the workpiece positions determined in the previous step. It will be understood that the position of each support tower <NUM>, <NUM> can be accurately controlled and determined through the use of suitable encoders in each support tower <NUM>, <NUM>. It should also be understood that since the movement of the heads <NUM>, <NUM> is small, the resulting displacement of the heads <NUM>, <NUM> and supports 21A-D is not discernible in <FIG>.

As shown in <FIG>, once the first support surfaces 22A, 22C are aligned with workpieces 11A, 11C, the tooling table <NUM> is raised so that the first support surfaces 22A, 22C are brought into contact with the respective workpieces 11A, 11C and lift them out of engagement with the carrier <NUM>. This corresponds with lifting the tooling table upper surface <NUM> to height ZA as shown. An at least partial vacuum is supplied to the first support surfaces 22A, 22C to securely adhere the respective workpieces 11A, 11C thereto. The at least partial vacuum is applied until completion of the printing operation.

Then, as shown in <FIG>, each support tower <NUM>, <NUM> is then independently driven (i.e. the heads <NUM>, <NUM> are independently driven with respect to their bases <NUM>, <NUM>) such that the respective underlying second support surfaces 22B, 22D are brought into alignment with their respective overlying workpieces 11B, 11D, using the workpiece positions determined previously. Since the movement of the heads <NUM>, <NUM> is small, the resulting displacement of the heads <NUM>, <NUM> and supports 21A-D is not discernible in <FIG>.

As shown in <FIG>, once the second support surfaces 22B, 22D are aligned with workpieces 11B, 11D, the tooling table <NUM> is further raised so that the second support surfaces 22B, 22D are brought into contact with the respective workpieces 11B, 11D and lift them out of engagement with the carrier <NUM>. This corresponds with lifting the tooling table upper surface <NUM> to height ZB as shown. An at least partial vacuum is supplied to the second support surfaces 22B, 22D to securely adhere the respective workpieces 11B, 11D thereto. The at least partial vacuum is applied until completion of the printing operation. During this lifting, the first support surfaces 22A, 22C are caused to remain at a constant absolute height, rather than moving up with the tooling table <NUM>, so that they move relatively closer to the second support surfaces 22B, 22D as these lift, until all the support surfaces 22A-D are substantially coplanar in the horizontal plane, at which point the first support surfaces 22A, 22C are in a printing configuration. There are various ways in which the first support surfaces 22A, 22C may be caused to move to the printing configuration. For example, each of the first support surfaces 22A, 22C may be driveable between its printing and pre-printing configurations. This could be achieved by providing a Z-axis actuator within each of the first supports 21A, 21C or support towers, particularly within the respective head <NUM>, <NUM>, operative to drive the respective first support surface 22A, 22C downwards relative to the respective second surfaces 22B, 22D. However, a simpler solution is to constrain each of the first support surfaces 22A, 22C from rising further up with the tooling table <NUM> once the tooling table upper surface <NUM> passes height ZA. This may be achieved for example by resiliently biasing each of the first support surfaces 22A, 22C to the pre-printing configuration (i.e. to its maximum vertical height), for example by connecting each of the first support surfaces 22A, 22C to its respective head <NUM>, <NUM> via a compression spring (not shown). A projection (not shown) may be provided at each first support surface 22A, 22C for abutting with an external limiting member (not explicitly shown) such that lifting of the first support surface 22A, 22C is prevented during lifting of the support tower <NUM>, <NUM> when the projection abuts with the external limiting member. In a preferred embodiment, the limiting member may comprise at least part of the surround plate <NUM>, i.e. either a member provided on the surround plate specifically for abutting with the projection, or the projection is dimensioned to abut with a 'normal' surround plate itself, which does not include any additional member provided for this purpose.

Then, as shown in <FIG>, each support tower <NUM>, <NUM> is then independently driven (i.e. the heads <NUM>, <NUM> are independently driven with respect to their bases <NUM>, <NUM>) such that all of the support surfaces 22A-D with their respective supported workpieces 11A-D are brought into the correct alignment, i.e. into alignment with the aperture pattern of the printing screen (<NUM>, see <FIG>). Since the movement of the heads <NUM>, <NUM> is small, the resulting displacement of the heads <NUM>, <NUM> is not discernible in <FIG>.

At the conclusion of this previous step, the alignment method is completed. It is now possible to print onto all of the workpieces 11A-D in a single print operation. As shown in <FIG>, once all of the workpieces 11A-D are correctly aligned, the tooling table <NUM> is further raised to its print height, at which the tooling table upper surface <NUM> is at height ZP. This lifting of the tooling table <NUM> causes both the carrier <NUM> and the surround plate <NUM> to also be lifted, as is well-known in the art. When the tooling table <NUM> is fully lifted to the print height, the workpieces 11A-D and the surround plate <NUM> are pressed against the underside of the printing screen <NUM>, with the upper sides of the workpieces 11A-D co-planar with the upper surface of the surround plate <NUM>. Since the surround plate <NUM> lifts with the tooling table <NUM>, the first support surfaces 22A, 22C will remain in their printing configuration throughout the lifting. Camera <NUM> is shown in a retracted position in which it does not interfere with the lifting of the tooling table <NUM>. Once the tooling table <NUM> is lifted to its print height, a squeegee <NUM> may be drawn across the upper surface of the printing screen <NUM> to impel printing medium through the apertures of the printing screen <NUM> and onto the workpieces 11A-D, as is well-known in the art per se.

Following completion of the printing operation, the tooling table <NUM> is lowered so that the tooling table upper surface <NUM> returns to height Z0, and the printed workpieces are returned to the carrier <NUM>. This position is shown from the side in <FIG>.

The transport system may then transport the loaded carrier <NUM> along the positive X direction shown, to the printing machine output, and hence on to other modules of a production line as required.

The above-described example shows a simple embodiment of the present invention, however the invention is not limited to that specific embodiment. In particular, there is great flexibility in the possible arrangements both of the support towers and of support surfaces on the support towers.

As an example, <FIG> schematically show, from above and in side view respectively, tooling <NUM> suitable for use in printing a batch of six workpieces 111A-F arranged in a carrier <NUM> in a 3x2 matrix array. This may be achieved by using three support towers <NUM>, <NUM>, <NUM>, each of which is MASS-type as previously described, mounted on an assembly unit <NUM>. The respective heads <NUM>, <NUM>, <NUM> of each support tower <NUM>, <NUM>, <NUM> each carry first and second support surfaces arranged in a linear array to underlie respective workpieces 111A-F in use, the first support surfaces 122A, 122C, 122E being at a greater height in the pre-printing configuration than the second support surfaces 122B, 122D, 122F. The operation of the tooling <NUM> is identical to that set out previously.

<FIG> schematically shows, in perspective view, tooling <NUM>, which includes eight MASS-type support towers 145A-H, arranged in a 4x2 array on an assembly unit <NUM>. The head of each support tower 145A-H carries four support surfaces 142A-D, arranged in a 2x2 square matrix array. Of these support surfaces, 142A-C may be considered "first support surfaces" which, similarly to first support surfaces 22A, 22C of the first-described embodiment, are relatively moveable with respect to the support surface 142D (i.e. a "second support surface") in a vertical direction in use between a printing configuration in which the first and second support surfaces are substantially coplanar in the horizontal plane, and a pre-printing configuration in which the first and second support surfaces are spaced in the vertical direction. In their pre-printing configurations shown, the support surfaces 142A-D are all spaced in the vertical direction, with support surface 142A being highest, followed by 142B, then 142C, with support surface 142D being the lowest support surface on the support tower. The tooling <NUM> is operated very similarly to that previously described. Overlying workpieces (not shown) are aligned as follows:.

Following alignment, the workpieces may be printed by:.

As noted previously, <CIT> describes how MASS-type tooling may be used to print a plurality of singulated substrates which are arranged at pitches in the transport direction that are smaller than the spacing of individual support towers, while <CIT> describes how such apparatus may be used to print a plurality of singulated substrates which are arranged at pitches orthogonal to the transport direction that are smaller than the spacing of individual support towers. Essentially both of these approaches implement a two-stage process, in which workpieces located at non-adjacent rows or columns of a carrier array are printed in a first print operation, while workpieces located at interspaced rows or columns of the carrier array are subsequently printed in a second print operation.

Such methodologies are entirely compatible with that of the present invention. By way of example, <FIG> schematically show, from above, sequential steps in a method for aligning twenty-seven workpieces <NUM> arranged in a carrier <NUM> in a 9x3 matrix array (an example being a JEDEC <NUM> 9x3 tray), using tooling <NUM> comprising three support towers <NUM>, <NUM>, <NUM> mounted on an assembly unit <NUM>. For convenience, the columns of workpieces are labelled as "<NUM>" to "<NUM>" above each column. Each support tower <NUM>, <NUM>, <NUM> includes a head which carries three support surfaces <NUM> arranged in a linear array, the support surfaces each corresponding to the dimension of a workpiece <NUM>, and spaced by a pitch equal to the pitch of adjacent workpieces <NUM> in a column (i.e. the distance in the Y direction between each workpiece aligned in the X direction) in the carrier <NUM>. Of these, support surface 222A may be considered a "first support surface" which, similarly to the first support surfaces 22A, 22C of the first-described embodiment, are relatively moveable with respect to the support surface 222B (i.e. a "second support surface") and to additional support surface 222C in a vertical direction in use between a printing configuration in which the support surfaces are substantially coplanar in the horizontal plane, and a pre-printing configuration in which the support surfaces are spaced in the vertical direction. In their pre-printing configurations shown, the support surfaces 222A-C are all spaced in the vertical direction, with support surface 222A being highest, followed by 222B, with support surface 222C being the lowest support surface on the support tower. The tooling <NUM> may be operated very similarly to that previously described, and so this aspect will not be described in depth again. It can be seen that the pitch between adjacent columns of workpieces <NUM> (i.e. the distance in the X direction between each column of three workpieces aligned in the Y direction) in the carrier <NUM> is smaller than the pitch between adjacent support towers <NUM>, <NUM>, <NUM>.

In the step shown in <FIG>, the carrier <NUM> with its unprinted and unaligned workpieces <NUM> is shown prior to being transported to the printing location overlying the tooling <NUM>.

In the subsequent step shown in <FIG>, the carrier <NUM> with its unprinted and unaligned workpieces <NUM> is shown having been transported to the printing location, so that workpieces <NUM> in its rightmost column "<NUM>" overlie the respective support surfaces 222A-C of support tower <NUM>, while workpieces <NUM> in column "<NUM>" overlie the respective support surfaces 222A-C of support tower <NUM>, and workpieces <NUM> in column "<NUM>" overlie the respective support surfaces 222A-C of support tower <NUM>. Once in this position, the workpieces in those columns are aligned as previously described, and are then printed as previously described.

In the subsequent step shown in <FIG>, the carrier <NUM> with its unprinted and unaligned workpieces <NUM> is shown having been transported by one pitch in the X direction, so that workpieces <NUM> in its second rightmost column "<NUM>" overlie the respective support surfaces 222A-C of support tower <NUM>, while workpieces <NUM> in column "<NUM>" overlie the respective support surfaces 222A-C of support tower <NUM>, and workpieces <NUM> in column "<NUM>" overlie the respective support surfaces 222A-C of support tower <NUM>. Once in this position, the workpieces in those columns are aligned as previously described, and are then printed as previously described.

In the subsequent step shown in <FIG>, the carrier <NUM> with its unprinted and unaligned workpieces <NUM> is shown having been transported by one pitch in the X direction, so that workpieces <NUM> in its third rightmost column "<NUM>" overlie the respective support surfaces 222A-C of support tower <NUM>, while workpieces <NUM> in column "<NUM>" overlie the respective support surfaces 222A-C of support tower <NUM>, and workpieces <NUM> in column "<NUM>" overlie the respective support surfaces 222A-C of support tower <NUM>. Once in this position, the workpieces in those columns are aligned as previously described, and are then printed as previously described.

Finally, as shown in <FIG>, the carrier <NUM>, in which all workpieces have been aligned and printed, is transported away from the printing location in the X direction, and on to other modules of a production line as required.

A further embodiment of the present invention is schematically shown, in a side view, in <FIG>. The arrangement shown is very similar to that shown in <FIG>, except that as shown, a referencing plate <NUM> is provided parallel to and vertically above the surround plate <NUM>. Referencing plates are used in some configurations of certain printing machines to actively align singulated workpieces if a MASS-type tooling is not used. An exemplary referencing system which uses two adjacent referencing plates is for example fully described in <CIT>, which describes aligning workpieces by sliding, in the horizontal plane, at least one of the referencing plates to contact edges of the singulated workpieces and impel them into correct alignment. In the embodiment shown in <FIG>, the limiting member comprises at least part of the referencing plate <NUM>, i.e. either a member provided on the referencing plate specifically for abutting with the projection, or the projection is dimensioned to abut with a 'normal' referencing plate itself, which does not include any additional member provided for this purpose. As will be understood by those skilled in the art, such referencing plates are retracted from the printing location before commencement of a printing operation.

Claim 1:
Tooling (<NUM>, <NUM>, <NUM>, <NUM>) for supporting workpieces (<NUM>, 11A-D, <NUM>) during a printing operation, comprising:
a support tower (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, 145A-H, <NUM>, <NUM>, <NUM>) comprising a base (<NUM>, <NUM>) and a head (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), the head (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) being positioned vertically above the base (<NUM>, <NUM>) in use, the head (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) being relatively moveable with respect to the base (<NUM>, <NUM>) in a horizontal plane in use,
the head (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) having first (22A, 22C, 122A, 122C, 122E, 222A, 222B) and second (22B, 22D, 122B, 122D, 122F, 222C) support surfaces located at an upper end thereof, each of the first (22A, 22C, 122A, 122C, 122E, 222A, 222B) and second (22B, 22D, 122B, 122D, 122F, 222C) support surfaces being adapted to support a respective workpiece (<NUM>, 11A-D) thereon,
wherein the first support surface (22A, 22C, 122A, 122C, 122E, 222A, 222B) is relatively moveable with respect to the second support surface (22B, 22D, 122B, 122D, 122F, 222C) in a vertical direction in use between a printing configuration in which the first (22A, 22C, 122A, 122C, 122E, 222A, 222B) and second (22B, 22D, 122B, 122D, 122F, 222C) support surfaces are substantially coplanar in the horizontal plane, and a pre-printing configuration in which the first (22A, 22C, 122A, 122C, 122E, 222A, 222B) and second support surfaces (22B, 22D, 122B, 122D, 122F, 222C) are spaced in the vertical direction.