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 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 <NUM>×<NUM> 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. This technique does permit all boards of a panel to be printed in simultaneously, but the sequential repositioning is time-consuming and the positioning arm apparatus takes up useful space within the printing machine. <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.

<CIT> describes a workpiece support assembly having the precharacterising features of claim <NUM>. Similarly to <CIT>, a separate reference webbing is used to simultaneously align the supported workpieces.

The present invention seeks to overcome these problems and provide apparatus and methodology for printing a plurality of singulated workpieces, such as circuit boards, in a single printing operation. Advantageously, the present invention enables simultaneous alignment of the workpieces while maintaining high levels of flexibility in the printing process. The simultaneous vision alignment enabled by the present invention will maintain or increase alignment accuracy whilst increasing throughput. Furthermore, the proposed apparatus is compact, particularly being of relatively low height and may be retrofitted to existing printing machines. Other advantages include the ease of providing vacuum supply to clamp workpieces thereon, and the small number of moving parts.

In accordance with the present invention this aim is achieved by providing support towers for individual workpieces, each tower individually capable of adjusting the position and orientation of a workpiece supported thereon so that each workpiece may have a unique alignment position.

In accordance with a first aspect of the present invention there is provided a workpiece support assembly for supporting and aligning a plurality of singulated workpieces in a printing operation, the workpiece support assembly comprising an assembly body and a plurality of support members mounted on the assembly body which each support a workpiece in use, each support member comprising:.

In accordance with a second aspect of the present invention there is provided a printing machine comprising the workpiece support assembly of the first aspect.

In accordance with a third aspect of the present invention there is provided a method of printing a plurality of singulated workpieces, 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:.

A support member <NUM> according to a first embodiment of the present invention is schematically shown in <FIG>, in an exploded perspective view. A tooling module <NUM> for use with support member <NUM> is schematically shown in exploded perspective view in <FIG>. Support member <NUM>, with tooling module <NUM> attached is schematically shown in a perspective view in <FIG>. As can be seen in these figures, the support member <NUM> has a central axis parallel to the vertical in use, which in the art is generally referred to as the Z-axis. The support member <NUM> comprises two main sub-structures, a head unit <NUM> and a base <NUM>. The head unit <NUM>, which is located at the top of the support member <NUM> in use, is provided to support a workpiece thereon within an X-Y plane normal to the Z-axis, via a tooling module such as tooling module <NUM> shown in <FIG>, which may be connected to a tooling interface plate <NUM> at the top of the head unit <NUM>. The base <NUM> comprises a housing <NUM> which is preferably mounted on a table (see for example <FIG>) for reception into a printing machine (not shown), the table carrying a plurality of such support members in a parallel and spaced configuration, such that the support members cannot contact each other during operation. Each support member <NUM> of the plurality may support a respective singulated workpiece in use, as will be described in more detail subsequently. The support member <NUM> also comprises an actuation mechanism with a stator <NUM> and rotor <NUM>, which is selectively operative to translate the head unit <NUM> parallel to the X-Y plane and / or to rotate the head unit <NUM> about an axis orthogonal to that plane, i.e. parallel to the Z-axis in the so-called θ direction. The stator <NUM>, which is fixed to and within the base <NUM>, comprises a printed circuit board (PCB) with a plurality of drive units each in the form of a coil, provided thereon. Here, three drive units each comprising an independently operable linear motor coil <NUM> are mounted on the PCB, with their coil axes located parallel to the X-Y plane and having non-parallel axes, here being equally distributed about the Z-axis, i.e. at <NUM>° to each other.

The coils <NUM> are controlled via control boards <NUM> located at the bottom of base <NUM>, which comprise a processor (not shown) connected for both power and communication with an external source (not shown). The rotor <NUM> comprises a magnet assembly which is driven by the coils <NUM> in use. As is generally known in the art, the arrangement of linear motor coils <NUM> enables the rotor <NUM> to be translated along the X or Y-axes, or in any combination of the two, by selectively operating the coils <NUM> to produce a suitable superposition of the electromotive forces generated thereby. Similarly, if all coils <NUM> are operated with equal power, the rotor <NUM> will be caused to rotate in the θ direction, i.e. parallel to the Z-axis. The rotor may also be simultaneously both translated and rotated by suitable control of the coils <NUM>. It should be noted that such control may in other embodiments (not shown) also be achieved by using more than three coils. The accuracy of any such movement is controlled by providing at least one suitable encoder <NUM>, here on the head unit <NUM>, on the upper surface of a coil <NUM>, which is associated with a graticule (not shown) on the underside of rotor <NUM>. In other embodiments, at least one encoder may be provided on the base <NUM>.

To facilitate relative movement of the rotor <NUM> and stator <NUM>, a bearing, for example an air bearing <NUM> (most clearly visible in <FIG>), is located between the base <NUM> and the head unit <NUM>. The rotor <NUM> engages the underside of the tooling interface plate <NUM> so that the tooling interface plate <NUM> moves with the rotor <NUM>. A second bearing, for example an air bearing <NUM>, is located between the rotor <NUM> and the tooling interface plate <NUM> while being supported by the base <NUM>, and acts to support the tooling interface plate <NUM> in a low-friction manner. In more detail, and as more clearly shown in <FIG>, lugs of the air bearing <NUM> are supported by respective posts <NUM> which project upwardly from the base <NUM>. It can be seen most clearly from <FIG> that the support member <NUM> is provided with a through-bore, extending substantially along the axis of the support member <NUM>. An aperture <NUM> in the tooling interface plate <NUM> connects with the through-bore at one end, while a further aperture is at the distal end. This through-bore provides a vacuum path through the support member <NUM>, as will be described in more detail below.

The support member <NUM> is "intelligent" in that it is also provided with its own processor (not shown), so that control of the actuation mechanism via the encoder is managed within the support member <NUM>.

The tooling interface plate <NUM> is adapted to engage with a tooling module <NUM>, most clearly shown in <FIG>, such that the tooling module <NUM> moves with the tooling interface plate <NUM>. Advantageously, the tooling module <NUM> is a bespoke apparatus specifically tailored to a particular form of workpiece to be carried by the tooling module. The tooling module can be replaced by alternative modules to allow carrying of other workpieces. In alternative embodiments (not shown), the tooling module <NUM> may be integrally formed with the support member, in which case the tooling interface plate <NUM> may be omitted.

The tooling module <NUM> comprises a raised tooling chuck <NUM>, on which a workpiece, such as a singulated workpiece <NUM> is supported in use. Preferably, the tooling chuck <NUM> is modular, so that it may be removed from the tooling module <NUM> or exchanged in a simple manner. In a preferred embodiment, the tooling chuck <NUM> is magnetically coupled with the tooling module <NUM>, which arrangement removes the need for physical attachment means such as screws. At the upper surface of tooling chuck <NUM> is a vacuum engagement opening <NUM>, which communicates with a vacuum channel <NUM> which extends downwardly from the tooling module <NUM>. In use, and as shown in <FIG>, the vacuum channel <NUM> extends through the vacuum path of the support member <NUM>. The distal end of the vacuum channel <NUM> acts as a port for connection to an external vacuum source. When connected and an at least partial vacuum is applied, the workpiece <NUM> is thereby secured onto the tooling chuck <NUM>. It should be noted that if the dimensions of the path through the support member <NUM> are sufficiently large, then the vacuum channel <NUM> may be formed as a rigid pipe, for example a metallic or rigid plastics material, which will not be deformed during movement of the head unit <NUM>. In an alternative embodiment, the vacuum channel <NUM> may be formed as a flexible tube, for example comprising a plastics material, which may be deformed during movement of the head unit <NUM> without suffering damage. In a yet further embodiment, the support member <NUM> may be provided with a vacuum channel permanently located within the path, and the tooling module is adapted to engage with the vacuum channel proximate the aperture <NUM>.

It should be noted that the tooling module <NUM> shown is exemplary only, and may take a variety of shapes, profiles and sizes. In addition, the chuck may comprise a manifold, connected or connectable to the vacuum channel, for distributing the vacuum to various parts of the workpiece thereon. Furthermore, a vacuum sensing system may be provided, as is generally known in the art, to detect sub-optimal vacuum clamping of the workpiece.

<FIG> schematically shows from above an actuation mechanism <NUM> according to a second embodiment of the present invention. Similarly to the actuation mechanism of <FIG>, three individually operable drive units in the form of actuators <NUM> are used, which are linearly drivable along respective axes being equally distributed about the Z-axis, i.e. at <NUM>° to each other. The actuators <NUM> act on a generally triangular rotor <NUM>, with each acting on a surface <NUM> of the rotor orthogonal to the driving axis of the respective actuator <NUM>. Each actuator is free to move relative to the respective surface <NUM> within the X-Y plane. As with the embodiment of <FIG>, suitable operation of the three actuators <NUM> can cause the rotor <NUM> to translate, to rotate, or to both translate and rotate.

<FIG> schematically shows, in perspective view, a support apparatus <NUM> of a printing machine fitted with a workpiece support assembly in accordance with an embodiment of the present invention, having a 4x1 array of workpiece support members <NUM>, each of which is similar to that shown in <FIG>. For clarity, surrounding components of the printing machine have been omitted. Each support member <NUM> is shown as supporting a singulated workpiece <NUM>. The most forward-located singulated workpiece 35A is shown in <FIG> in a raised position for the purposes of illustration only - as will be described in more detail below, generally all workpieces <NUM> would be raised and lowered in concert. For convenience, <FIG> also shows a conventional co-ordinate system.

Each workpiece support member <NUM> is mounted an on assembly body, which as shown includes a table <NUM>, on which the support members <NUM> are supported and optionally attached, and a reference plate <NUM> which is attached on top of the table <NUM>, for example by screws. The reference plate <NUM> includes a central aperture which is configured to receive the array of support members <NUM>, so that the support members <NUM> extend through the aperture of the reference plate <NUM>. The support members <NUM> are attached, for example by screws, to the reference plate <NUM> at attachment points <NUM>. In this way, the table <NUM> ensures that each support member <NUM> is located at the correct height (i.e. the correct Z-axis position), while the reference plate <NUM> ensures that the support members <NUM> are correctly positioned in the X-Y plane. To achieve this X-Y positioning, it will be understood that the aperture of the reference plate <NUM> should closely conform to the external surfaces of the support member array when in the desired location. In alternative embodiments, the reference plate <NUM> could for example include more than one aperture, for example one aperture per support member <NUM>. The table <NUM> is supported by a two-part cradle structure <NUM>. The two parts of the cradle structure <NUM> may be moved relative to each other in the Y-direction, for example by suitable manual rotation of a worm gear, so that the width of the cradle structure <NUM> may be adjusted, for example to accommodate differently-sized tables <NUM>.

A pair of transport rails <NUM> is provided in the printing machine, which extend parallel to the X-axis. Each rail <NUM> comprises a conveyor belt or the like operative to transport workpieces <NUM> therebetween in the positive X direction as is generally known in the art. As will be more clearly shown in <FIG>, the workpieces <NUM> are located in a carrier <NUM> which is directly transported by the rails <NUM>. In more detail, the workpieces <NUM> are mounted on dowels (not visible in the figures) located within the carrier <NUM>. The rails <NUM> are carried by a pair of elongate "clatter bars" <NUM> which extend parallel to the Y-axis, via piston mechanisms <NUM>, which permit the rails <NUM> to be raised in the Z-direction relative to the clatter bars <NUM> when engaged by the underlying cradle structure <NUM>, as will be described in more detail below.

A surround plate <NUM> is provided in the printing machine in a plane parallel to the X-Y plane shown, which is used to eliminate or at least reduce print medium smearing on the upper side of the stencil, and to protect the stencil from "coining" between the workpieces. The surround plate is mechanically adjustable (the adjustment mechanism is not shown for clarity) in the Z-direction to enable the relative heights of the multiple workpieces <NUM> against the height of the surround plate <NUM> to be optimised. The surround plate <NUM> comprises a plurality of apertures corresponding in size and position to the array of support members <NUM>, and is located above the array and in registration thereto. In the preferred embodiment, the upper surface of the surround plate <NUM> is located at the printing height of the workpieces <NUM>, so that, following lifting of the workpieces <NUM> to their print positions (described in more detail below), the upper surfaces of both the workpieces <NUM> and the surround plate <NUM> are almost co-planar (typically the surround plate <NUM> may be fractionally lower than the upper surface of the workpieces <NUM>) to facilitate the printing process.

A pneumatic and electrical distribution box <NUM> is provided on the table <NUM>, for distributing pneumatic and electrical power, and communications signals, such as electrical control signals, to the support members <NUM> via associated lines (not shown for clarity). In particular, the pneumatic connection is operative to selectively apply an at least partial vacuum to the vacuum channel <NUM> and thus hold the respective workpiece <NUM> onto the support member <NUM>, while the electrical lines are operative to supply electrical power to the actuation mechanism of each support member <NUM>. The electrical and pneumatic supplies are controlled by a processor (not shown), for example a processor located within the printing machine, or an external processing means such as a laptop, PC or the like.

A lifting mechanism <NUM> is provided within the printing machine to raise the singulated workpieces <NUM> into a printing position. The lifting mechanism <NUM> comprises an actuator, which may for example by electrically or pneumatically driven, and operative to lift the cradle structure <NUM>, and hence also lift the rails <NUM>, which overlie the cradle structure <NUM>, table <NUM>, distribution box <NUM>, reference plate <NUM>, carrier <NUM>, support members <NUM> and any overlying workpieces <NUM>.

<FIG> schematically shows the lifting table of <FIG> with the surround plate <NUM> omitted for clarity. Here it can be seen that the workpieces <NUM> are located within carrier <NUM>, which engages with rails <NUM>. At the printing location, i.e. above the table <NUM>, the carrier <NUM> is clamped by an edge clamp or "snugger" <NUM>. This acts to fix the carrier <NUM> at the correct position in the Y-direction, as is known in the art. Carrier <NUM> includes a pattern of apertures which are sized so as to support respective workpieces <NUM> proximate the peripheries thereof, but to allow the workpieces <NUM> to move relative to the carrier parallel to the X-Y plane, in particular when the respective support member's actuation mechanism is driven.

<FIG> schematically shows the lifting table of <FIG> with the carrier <NUM> omitted for clarity. Here, pneumatic and electrical connectors <NUM> can be seen, which provide power from the distribution box <NUM> to the respective support members <NUM>. For clarity, the entirety of the connectors <NUM> are not shown. Also visible in <FIG> is a physical stop <NUM> which, as is known in the art, is a vertically drivable post which, when in a raised configuration, limits the movement of carrier <NUM> along the X-direction when driven by rails <NUM>. Following printing, the physical stop <NUM> is lowered so that carrier <NUM> can be transported away from the printing position.

<FIG> schematically show, from above, stages in a printing process in accordance with the present invention, using the apparatus of <FIG>. It should be noted that for clarity, many components, including in particular the surround plate <NUM> (see <FIG>), have been omitted.

<FIG> shows an initial product setup stage. A camera <NUM>, preferably a moving camera, is used to scan the positions of the support members <NUM> at their "home" or neutral position, by imaging fiducials <NUM> provided on the support members, with the arrow showing a typical direction of scan. Typically, tooling modules <NUM> (see <FIG>) are fitted to each support member <NUM> after this scanning stage. Alternatively, the support members may have tooling modules fitted prior to scanning, in which case the fiducials <NUM> may be located on the tooling modules. Similar fiducials will also be scanned on the stencil (not shown) to be used, either by the same camera <NUM> or by a dedicated camera (not shown), in which latter case the scanning of the support members and stencil may be performed simultaneously or near simultaneously. Once the relative positions of the support members and stencil are determined, a gross alignment of the stencil to the support members <NUM> is performed, typically by moving the stencil, as is known in the art. Alternatively or additionally, the position of the support assembly or table <NUM> may be adjusted.

<FIG> shows workpieces <NUM> entering the printing machine on carrier <NUM> (which for clarity is shown transparently), being driven by the rails <NUM> (see <FIG>). The workpieces <NUM> are each provided with workpiece fiducials <NUM>.

In <FIG>, once the carrier <NUM> is in printing position, as controlled by the physical stop <NUM> (see <FIG>), the workpieces <NUM> are lifted from the carrier <NUM> by raising the lifting mechanism <NUM> (see <FIG>) and hence the table <NUM> and support members <NUM> into contact with the undersides of the workpieces <NUM>. A vacuum or partial vacuum is applied to the support members <NUM> to clamp the workpieces <NUM> onto their respective chucks <NUM> (see <FIG> for example) of support members <NUM>. With the workpieces <NUM> lifted to a "vision height", which could be equal to, higher or lower than their printing height depending on the camera set-up, the camera <NUM> scans all workpiece fiducials <NUM>. The arrows show a suitable direction of scan.

In <FIG>, the support members <NUM> are aligned, based on the positions of the fiducials <NUM> determined in the previous step, by suitable operation of the respective support member actuation mechanisms. For example only, the left-most workpiece is shown as being repositioned in the Y-direction, the next workpiece is shown as being repositioned in the X-direction, the third workpiece is shown as being repositioned in θ about an axis parallel to the Z-axis, and the fourth workpiece is shown as being repositioned in a superposition of X, Y and θ movements. The alignment is controlled by the processor using the encoder provided on the head unit or base of each support member <NUM>. The support members <NUM> may be aligned either sequentially or simultaneously. Assuming the movement of the support members can be accurately controlled, no further scanning is required. However, in alternative embodiments a further scan, post-alignment, may be performed to confirm correct alignment and instigate an alignment correction process if required. Following alignment, the workpieces are moved to their printing height, and in-line with the surround plate <NUM> (see <FIG>).

<FIG> schematically shows a printing process, in which a stencil <NUM>, supported within a frame <NUM>, is engaged by a squeegee <NUM> to push print medium such as solder paste through the stencil aperture pattern and onto the workpieces. The arrow shows the direction of squeegee movement.

Following printing, the workpieces <NUM> may then be returned to their transport height in which they engage the carrier <NUM>, while the support members <NUM> lower out of the path of the carrier <NUM>. They may be returned to their home or neutral positions before or during this lowering. Vacuum will be retained until the workpiece is returned to its home position and returned gently to the dowels within the carrier <NUM>. In other words, when "transport height" is reached the vacuum clamping will be switched off.

<FIG> schematically shows the carrier <NUM> and workpieces <NUM> leaving the printing machine.

The embodiments described in respect of <FIG> all use a 4x1 array of support members. However, the present invention is equally applicable to other size arrays of two or more support members, e.g. 2x1 or 1x2, 2x2, 3x2, 2x3, 3x3 etc. By way of example, <FIG> schematically shows, in perspective view, the lifting table of <FIG> fitted with a workpiece support assembly in accordance with an alternative embodiment of the present invention, having a 4x2 array of workpiece support modules. This embodiment is very similar to that shown in <FIG>, and so need not be described in great detail. For clarity, it should be noted that the clatter bars are omitted from <FIG>.

In this embodiment, the workpiece support assembly comprises two rows of four support members <NUM>. Naturally, a surround plate <NUM> now includes eight apertures which overlie the respective support members <NUM>. The carrier (not visible in <FIG>) will also be adapted to carry eight workpieces in two rows of four. It can be seen that rails <NUM> have been moved further apart than shown in In order to provide the required pneumatic and electrical power to the support members, two distribution boxes <NUM>, 58A are provided, one for each row of support members <NUM>. Conveniently, with this arrangement, when it is desired to change the printing machine set-up from a <NUM>×<NUM> array (as in <FIG>) to a 4x2 array, it is necessary merely to add an additional distribution box 58A. Of course, the distribution box 58A may optionally be permanently provided on the table <NUM>, so that different support assembly configurations may be implemented with the minimum of effort.

<FIG> schematically shows, in perspective view, a workpiece support assembly <NUM> in accordance with an alternative embodiment of the present invention, while <FIG> schematically shows, in perspective view, a composite control board for use with the workpiece support assembly of <FIG>. In the previously-described embodiments, each support member was provided with its own respective and individual control board for controlling the actuation mechanism of that support member. Such an arrangement is advantageous in that, for example, if a control board fails, then it may be easily replaced. However, for some applications, it may be preferable to make use of support members which are located closer together, i.e. they have a higher packing density. The workpiece support assembly <NUM> includes a plurality, here eight, support members <NUM>, which are relatively closely packed. Each support member is retained on a common assembly unit <NUM>. In this embodiment, rather than providing each support member with its own control board, a single, common or composite control board <NUM> (see <FIG>) is provided in the common assembly unit <NUM>, directly below the support members <NUM>. The composite control board <NUM> includes separate processor circuitry <NUM> for each respective support member <NUM>, and which is operable to control the actuation mechanism within each support member <NUM>. It may be seen that the support members <NUM> are somewhat shorter than those shown in the previous embodiments, since they no longer include dedicated control boards. Otherwise, the operation of the workpiece support assembly <NUM> is similar to that described with reference to the preceding embodiments.

Other forms of parallel kinematic actuation mechanism may be used within each support member. <FIG> for example schematically shows a hexapod-type actuation mechanism <NUM> (also known as a Stewart or Stewart-Gough platform). Here, a stator <NUM> is shown as being connected to a rotor <NUM> via a plurality of discrete drive units in the form of linearly actuable pistons <NUM>, as is generally known in the art. By individually controlling the extension of each piston <NUM>, the X, Y and θ position of the rotor <NUM> may be fully controlled relative to the stator <NUM>.

<FIG> schematically shows, from above, an actuation mechanism in accordance with a further embodiment. Here, an array of four drive units, each comprising a coil 95A-D, is provided on a base <NUM>. The coil 95A-D of each drive unit is wound about a respective winding axis, the winding axes being parallel to each other and orthogonal to the plane in which the head unit (not shown) moves in use. With such an arrangement, at least two of the drive units (here coils 95A and 95C) may be spaced in a first direction parallel to the plane, and at least two of the drive units (here coils 95B and 95C) spaced in a second direction parallel to the plane, the first and second directions being orthogonal. In this configuration, full translational and rotational control of the head unit is possible. A control board <NUM> is shown located at the centre of the drive unit array, which is connected to each coil 95A-D and operable to control the coils.

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 actuation mechanism may comprise alternative forms of parallel kinematic systems.

Claim 1:
A workpiece support assembly for supporting and aligning a plurality of singulated workpieces (<NUM>) in a printing operation, the workpiece support assembly comprising an assembly body (<NUM>, <NUM>) and a plurality of support members (<NUM>) mounted on the assembly body (<NUM>, <NUM>) which each support a workpiece (<NUM>) in use, each support member (<NUM>) comprising:
a base (<NUM>) mounted on the assembly body (<NUM>, <NUM>), and
a head unit (<NUM>) for supporting a workpiece (<NUM>) thereon,
characterised in that each support member (<NUM>) further comprises an actuation mechanism for moving the head unit (<NUM>) relative to the base (<NUM>),
wherein the actuation mechanism comprises a parallel kinematic system having at least three drive units (<NUM>, <NUM>, <NUM>, 95A-D) each directly acting on the head unit (<NUM>), such that the actuation mechanism is selectively operative to move the head unit (<NUM>) relative to the base (<NUM>) to cause a translation of the head unit (<NUM>) parallel to a plane, a rotation of the head unit (<NUM>) about an axis orthogonal to that plane, or a combination of said translation and said rotation.