Patent Description:
Industrial screen-printing machines typically apply a conductive print medium, such as solder paste, silver 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 mask, foil or stencil) using an angled blade or squeegee. The same machines may also be used to print certain non-conductive media, such as glue or other adhesive, onto workpieces.

To ensure high quality printing, it is necessary to support the workpiece so that the surface to be printed is parallel to the printing screen, generally horizontal, with the workpiece support being capable of withstanding the pressure placed upon it during the printing operation, especially by the downward pressure applied by the squeegee, while maintaining the correct alignment of the workpiece.

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.

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.

Typically, when printing singulated workpieces, a plurality of the workpieces will be located in a carrier, and the workpieces will be moved through the printing machine, and indeed between different machines along an assembly line, within the carrier. <FIG> schematically show, from above, the following basic steps which may be performed. In <FIG>, for simplicity a workpiece support assembly having a 1x4 tower array is shown.

Those skilled in the art will recognise that in order to function as intended, the individual towers of an array such as that shown in <FIG> must have a certain minimum spacing therebetween (i.e. the "pitch" of the array), so that each tower may move and / or rotate freely, without risk of collision with an adjacent tower in the array.

When using a carrier loaded with singulated substrates, such a system generally works well, however there are some problems and restrictions faced when using such apparatus. For example:.

The present invention seeks to overcome these restrictions in a cost-effective and robust manner.

In accordance with the present invention, this aim is achieved by providing a more flexible stopping arrangement, and thereby selectively controlling the position of carriers within the printing machine.

Hereafter, a workpiece support system comprising an array of at least two discrete support surfaces, each support surface for supporting a workpiece thereon in use, will be termed a "multiple support system". One example of a multiple support system is a "multiple tower support system", in which each support surface is located on a respective tower, such as described in <CIT> for example. Other types of multiple tower support system exist, for example those in which parallel kinematics actuation is not used, or indeed multiple tower support systems in which the individual towers are not capable of the movement within any or all of the X, Y and theta (θ) directions, and an example of such a system is described in <CIT> for example. However, other types of multiple support system are possible which do not comprise towers, including for example a simple table with an upper support surface, the upper support surface including an array of regions each dedicated to supporting a respective workpiece, such that each region constitutes a support surface. It should also be understood that each support surface need not be flat, but could for example be contoured so as to support non-planar workpieces, or have a plurality of pins extending therefrom to support the underside of workpieces which have features located on the underside thereof which cannot contact a support surface directly, such as placed electronics components, holes or vias.

As background art may also be mentioned:.

In accordance with a first aspect of the present invention there is provided a method for printing workpieces having a first pitch along a horizontal transport path using a printing machine, the printing machine comprising:.

In accordance with a second aspect of the present invention there is provided a computer program for controlling a printing machine to perform the method of the first aspect.

In accordance with a third aspect of the present invention there is provided a printing machine for printing workpieces having a first pitch along a horizontal transport path, comprising:.

In accordance with a fourth aspect of the present invention there is provided a method for aligning a workpiece for printing within a printing machine, the printing machine comprising:.

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 embodiment of the present invention is schematically shown with reference to <FIG>. These show the interior of a printing machine from above (<FIG>), and in a sectional side view along the section A-A (<FIG>), and are aligned so that stationary components, such as towers <NUM>, are shown at the same X-position and scale throughout the four figures.

<FIG> schematically shows, from above, a printing area within a printing machine. Rails <NUM> are provided within the machine which define a horizontal transport path therebetween. The rails <NUM> may conveniently be provided with respective conveyors (not shown) to convey articles, in this case a carrier <NUM>, along the transport path in the direction shown by the large arrow, which is generally denoted the X-direction in the art. Therefore, it is to be understood that the horizontal plane is equivalent to the X-Y plane as shown, while "Z" denotes the vertical direction. As will be recognised by those skilled in the art, rails <NUM> are usually relatively moveable in the Y direction, so that articles of differing widths may be carried therebetween. For clarity, the carrier <NUM> is shown transparently, so that the positioning of components underneath the carrier <NUM> can be seen. The carrier <NUM> shown in this embodiment includes eight workpiece receptacles <NUM>, in a four by two matrix. Hereafter, each line of two adjacent workpiece receptacles <NUM> which lie in the same X position will be referred to as "columns", so that here, four columns are shown, with, for convenience, the leftmost column referred to as the "first column", and the rightmost column as the "fourth column" for example. Each workpiece receptacle <NUM> is designed to carry a single singulated workpiece (not shown for clarity). In order to print a pattern <NUM> onto a workpiece, it is necessary to align a workpiece receptacle, and hence its received workpiece, above the support surface <NUM> (see <FIG>) of a tower <NUM> of tooling (a multiple tower support system) arranged below the horizontal transport path. The patterns <NUM> are formed in a stencil or screen (not shown) located above the horizontal transport path. As shown in <FIG>, in this embodiment four towers <NUM> are provided, in a two-by-two matrix.

As most clearly seen in <FIG>, each tower <NUM> is provided with a support surface <NUM> at an upper end thereof for engaging with a respective workpiece in use, with the support surfaces <NUM> being discrete and horizontally spaced. For clarity, the support surfaces <NUM> are shown as being flat, but in fact these may be contoured or profiled so as to support non-flat workpieces thereon in use. The towers <NUM> are provided on a tooling unit <NUM>, which in turn is mounted on a rising table <NUM>. The rising table <NUM> is vertically-movable between a lower, retracted position (shown in <FIG>) and an upper, extended position (not shown), with the vertical distance travelled being shown as "H" in <FIG>, in which the support surfaces <NUM> are brought up and into engagement with their overlying workpieces, to lift the workpieces away from the carrier <NUM>. In this extended position, a printing operation may be performed to print the engaged workpieces. The support surfaces <NUM> are of smaller horizontal dimension than their respective towers <NUM>, and are small enough to be able to project within a workpiece receptacle located directly above a respective tower <NUM> during raising of the rising table <NUM> to the extended position.

In a preferred embodiment, the support surfaces <NUM> of each tower <NUM> are moveable within the horizontal or X-Y plane, upon receipt of suitable control signals received via the tooling unit <NUM>. Yet more preferably, each support surface <NUM> is translatable both parallel to the horizontal path and orthogonally to the horizontal path within the horizontal or X-Y plane, and rotatable about a respective vertical or Z axis, similarly to the workpiece support assembly <NUM> shown in <FIG> and <FIG>.

As can be most clearly seen in <FIG>, the individual workpiece receptacles <NUM> have a relatively small pitch of length L in the X direction, while the towers <NUM> have a relatively large pitch in the X direction, and so it is impossible to locate all workpieces above respective support surfaces <NUM> at once. In accordance with the present invention, this problem is solved by enabling the carrier <NUM>, and hence any workpieces carried thereby, to be stopped in more than one location along the X direction. In the embodiment shown, a first physical stop <NUM> is provided proximate the rails to stop the carrier <NUM> at a first location along the horizontal path, in which workpieces carried in the second and fourth workpiece receptacle columns of the matrix directly overlie respective support surfaces <NUM>, as shown in <FIG>. The workpieces carried in the first and third workpiece receptacle columns of the matrix do not align with any support surfaces <NUM>, but do overlie the rising table <NUM>. In this position, the rising table <NUM> may be raised so that the support surfaces <NUM> engage with the workpieces in the second and fourth columns of the carrier <NUM>. Once engaged and lifted from the carrier <NUM>, the workpieces may be aligned by suitable movement of the support surfaces <NUM> in the X-Y plane, and then printed with respective print patterns <NUM>. The rising table <NUM> is then lowered back to the retracted position, so that printed workpieces are returned to their respective workpiece receptacles <NUM> in carrier <NUM>.

The carrier <NUM> is then transported to a second position which is a length L in the X direction, i.e. corresponding to the pitch of the workpiece receptacles <NUM>. The carrier <NUM> is stopped at this second position by a second physical stop <NUM>, so that it is stopped at the position shown in <FIG>. Although not clearly shown, both the first and second physical stops <NUM>, <NUM> are retractable, so that they can be moved in and out of the horizontal path, to selectively stop the carrier <NUM> at either the first or second position. Controllable physical stops are known in the art per se, and so need not be described further here, but typically comprises an arm, rod or other barrier which may be selectively pivoted or translated into and out of the horizontal path by means of an actuator controlled by a processor, computer or other control means.

As shown in <FIG>, at this second location along the horizontal path, workpieces carried in the first and third workpiece receptacle columns of the matrix directly overlie respective support surfaces <NUM>. The previously-printed workpieces carried in the second and fourth workpiece receptacle columns of the matrix do not align with any support surfaces <NUM>, but do overlie the rising table <NUM>. In this position, the rising table <NUM> may be raised so that the support surfaces <NUM> engage with the workpieces in the first and third columns of the carrier <NUM>. Once engaged and lifted from the carrier <NUM>, the workpieces may be aligned by suitable movement of the support surfaces <NUM> in the X-Y plane, and then printed with respective print patterns <NUM>. The rising table <NUM> is then lowered back to the retracted position, so that the recently printed workpieces are returned to their respective workpiece receptacles <NUM> in carrier <NUM>. The carrier <NUM>, with its completely printed workpieces, may then be transported out of the printing machine along the horizontal transport path in the X-direction.

The concept may be extended to allow efficient printing of carriers having workpiece receptacles at yet smaller pitches. For example, if a carrier having a six-by-two array of workpiece receptacles was used, and the pitch between workpiece receptacles was a third of the pitch between support surfaces, then all workpieces of the carrier could be printed in three print operations. In this case, preferably by printing columns three and six first, then moving the carrier forward by one pitch and printing columns two and five, then moving the carrier forward another one pitch and printing columns one and four.

Another embodiment of the present invention is schematically shown with reference to <FIG>. The method described here enables a plurality of workpieces W, which are not retained within a carrier, to be printed in a single printing operation. <FIG> shows the interior of a printing machine from above, while <FIG> shows this in a sectional side view along the line B-B. Many components shown are similar to those previously described, and so need not be described at length here. Rails <NUM> define a horizontal transport path therebetween for carrierless workpieces W, with four workpieces W being shown. With such a configuration, the workpieces W are directly supported by, and conveyed along, rails <NUM>. This naturally restricts the workpieces W to enter the printing machine one at a time, and so for this embodiment a tooling unit <NUM> is provided which carries a plurality of towers <NUM> in a four-by-one matrix, with each tower <NUM> having a support surface <NUM> at an upper end thereof, the support surfaces being dimensioned and profiled as necessary to adequately support a workpiece W thereon. The tooling unit <NUM> is mounted onto rising table <NUM>.

In order to improve printing efficiency, it is possible, in accordance with the present invention, to print four separate singulated workpieces W with a printing pattern <NUM> in a single printing operation. This benefit is enabled by providing four separate physical stop elements <NUM> along the horizontal transport path, each selectively operable to stop a respective workpiece W directly above a respective support surface <NUM>. The physical stop elements <NUM> are operated under control of a control system (not shown), such as a computer, processor or the like.

The tooling (i.e. tooling unit <NUM>, towers <NUM> and support surfaces <NUM>) and rising table <NUM> operate in an identical manner as in the previously-described embodiment. When the rising table <NUM> is raised to its extended position, each support surface <NUM> engages with its respective overlying workpiece W and lifts it away from the rails <NUM>. Following any alignment of the workpiece W, for example by movement of the support surface <NUM> in the X-Y plane, the workpieces are printed in a single print operation, and then may be returned to the rails <NUM> by lowering of the rising table <NUM> back to the retracted position.

Since the physical stop elements <NUM> are selectively operable, workpieces W can be prevented from stopping above support surfaces <NUM> of damaged or non-functional towers <NUM>, for example, but instead stopped above an adjacent, fully functional, support surface <NUM>.

Another embodiment of the present invention is schematically shown with reference to <FIG>. This is quite similar to that shown in <FIG>, however here, rather than the workpieces W being directly supported by rails, they are placed in carriers, with all the workpieces of a plurality of carriers being printable in a single printing operation.

<FIG> shows the interior of a printing machine from above, while <FIG> shows this in a sectional side view along the line C-C. Many components shown are similar to those previously described, and so need not be described at length here. Rails <NUM> define a horizontal transport path therebetween for carriers <NUM>, with two carriers <NUM> being shown. Within each carrier <NUM>, two singulated workpieces W may be carried, here shown in a one-by-two array. Other configurations are possible, for example each carrier <NUM> may be adapted to carry a plurality of workpieces in a non-linear array, such as two-by-two. While as shown, a tooling unit <NUM> is provided which carries a plurality of towers <NUM> in a four-by-one matrix, with each tower <NUM> having a support surface <NUM> at an upper end thereof, the support surfaces being dimensioned and profiled as necessary to adequately support a workpiece W thereon, other configurations of tooling are possible, if, for example, each carrier <NUM> carries workpieces W in a non-linear array. The tooling unit <NUM> is mounted onto rising table <NUM>. With such a configuration, the carriers <NUM> are directly supported by, and conveyed along, rails <NUM>, with carriers <NUM> able to enter the printing machine one at a time.

In order to improve printing efficiency, it is possible, in accordance with the present invention, to print the four separate singulated workpieces W carried by the two carriers <NUM> with a printing pattern <NUM> in a single printing operation. This benefit is enabled by providing two separate physical stop elements <NUM> along the horizontal transport path, each selectively operable to stop a respective carrier <NUM> so that each of its workpieces W stop directly above a respective support surface <NUM>. The physical stop elements <NUM> are operated under control of a control system (not shown), such as a computer, processor or the like.

This embodiment may also be combined with the embodiment shown in <FIG>, so that more than one carrier <NUM> may be introduced into the printing area above the rising table <NUM>, each carrier <NUM> carrying workpieces W at a smaller pitch than the pitch between support surfaces <NUM>. In this case, additional stop elements would be required so that each carrier <NUM> could be stopped at a distance forward along the horizontal transport path equal to one workpiece pitch. Alternate columns of all carriers <NUM> would be printed in a single print operation, with the remaining columns printed in a second print operation.

Another embodiment of the present invention is schematically shown with reference to <FIG>. Here the arrangement is generally similar to that shown in <FIG>, with carrierless workpieces W supported and conveyed directly by rails <NUM>. In this case however, the workpieces W are relatively large, so that each may directly overlie first and second adjacent support surfaces 43A, 43B of tooling of a multiple tower support system. The printing patterns <NUM> shown are correspondingly large.

In order to improve printing efficiency, it is possible, in accordance with the present invention, to print two separate singulated workpieces W with a printing pattern <NUM> in a single printing operation. This benefit is enabled by providing two separate physical stop elements <NUM> along the horizontal transport path, each selectively operable to stop a respective workpiece W directly above first and second support surfaces 43A, 43B. The physical stop elements <NUM> are operated under control of a control system (not shown), such as a computer, processor or the like.

The tooling (i.e. tooling unit <NUM>, towers <NUM> and support surfaces 43A, 43B located at upper ends of respective towers <NUM>) and rising table <NUM> operate in an identical manner as in the previously-described embodiments. When the rising table <NUM> is raised to its extended position, each support surface <NUM> engages with its respective overlying workpiece W and lifts it away from the rails <NUM>. In this embodiment, alignment of the workpieces W is then performed, by moving the first and second support surfaces 43A, 43B while engaged with the overlying workpiece W. In particular, alignment is performed through coordinated movement of the support surfaces 43A, 43B in the horizontal or X-Y plane. This is particularly beneficial when using support surfaces 43A, 43B which are translatable both parallel to the horizontal path and orthogonally to the horizontal path within the horizontal plane, and rotatable about a respective vertical or Z axis. The workpieces W may then be printed in a single print operation, de-aligned (i.e. returned to the positions at which they arrived above the rising table <NUM>) if necessary and then returned to the rails <NUM> by lowering of the rising table <NUM> back to the retracted position.

Since the physical stop elements <NUM> are selectively operable, workpieces W can be prevented from stopping above support surfaces 43A, 43B of damaged or non-functional towers <NUM>, for example, but instead stopped above alternative fully functional, support surfaces 43A, 43B.

<FIG> schematically shows how the first and second support surfaces 43A, 43B may be used to co-operatively align an overlying workpiece W. The top part of <FIG> shows, from above, a workpiece W (made transparent for clarity) in a first orientation, supported at each end thereof by respective support surfaces 43A and 43B. The geometric centre of workpiece W is shown as <NUM>, while the geometric centres of support surfaces 43A and 43B are shown at <NUM> and <NUM> respectively. The lower part of <FIG> shows, again from above, the positioning of workpiece W and support surfaces 43A, 43B if the workpiece W is caused to rotate by an angle θ about a vertical or Z axis passing through its centre <NUM>, in an anticlockwise direction as shown. It is important that each support surface 43A, 43B cannot move relative to the overlying workpiece W, since to do so may cause damage to the workpiece W or any features present on its underside. The dashed lines show how the relative positions of the workpiece W and support surfaces 43A, 43B change with this rotation. It can be seen that the support surfaces 43A, 43B can be used to effect this rotation if the following conditions are met:.

The required movements of support surfaces 43A and 43B are possible using a "multiple tower support system", such as that described in <CIT> for example. While <FIG> only shows a rotation of workpiece W, it is of course also possible to cause a translation of workpiece W in the X-Y plane, by moving first and second support surfaces 43A and 43B an identical distance (i.e. moving in tandem) in the required direction of translation. Moreover, a combined rotation and translation of workpiece W is possible by superposing such movements.

While the embodiment described in <FIG> uses adjacent support surfaces 43A and 43B which are spaced in the X direction, i.e. along the horizontal transport path, to enable cooperative alignment, similar alignment is possible if the adjacent support surfaces are instead spaced in the Y direction, i.e. orthogonal to the horizontal transport path. Such an arrangement is useful where the workpieces are relatively long in the Y direction so as to span the two adjacent support surfaces.

In an alternative embodiment, the workpieces to be printed could be carried within a carrier.

It should be noted that the concept of aligning workpieces by placing them on two spatially-separated support surfaces, as generally described with reference to <FIG> and <FIG> need not require the workpieces to be stopped at respective first and second locations within the printing machine. For example, a single two-tower tooling could be used to align a single, relatively large, workpiece.

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, while the above-described embodiments use physical stop elements, it is equally possible to use a transport control system comprising a conveyor control operable to control the operation of the conveyor to bring a workpiece to a stop at a selected location above the rising table. In such a case, the transport control system may for example comprise a sensor associated with each of the first and second locations to sense the presence of a workpiece on the conveyor upstream of the respective location and pass a signal indicative of such presence to the conveyor control. In this way, full and flexible control of the workpieces and their stopping locations is enabled.

Claim 1:
A method for printing workpieces (W) having a first pitch along a horizontal transport path using a printing machine, the printing machine comprising:
a rising table (<NUM>, <NUM>, <NUM>, <NUM>) being vertically movable between a lower, retracted position and an upper, extended position, and
tooling (<NUM>, <NUM>, <NUM>, <NUM>) fitted to the rising table (<NUM>, <NUM>, <NUM>, <NUM>) to be carried therewith, the tooling (<NUM>, <NUM>, <NUM>, <NUM>) comprising a plurality of discrete and horizontally spaced support surfaces (<NUM>, <NUM>, <NUM>, 43A, 43B),
the arrangement being such that in use workpieces (W) are conveyed into and through the printing machine along the horizontal transport path, which is vertically above the tooling (<NUM>, <NUM>, <NUM>, <NUM>) when the rising table (<NUM>, <NUM>, <NUM>, <NUM>) is in the retracted position, and a support surface (<NUM>, <NUM>, <NUM>, 43A, 43B) may be brought into engagement with a workpiece (W) by raising the rising table (<NUM>, <NUM>, <NUM>, <NUM>) toward the extended position, to enable a printing operation to be performed to print the engaged workpiece (W),
the method comprising transporting a plurality of workpieces (W) to be printed into the printing machine along the horizontal transport path,
wherein the plurality of support surfaces are spaced along the horizontal transport path at a second pitch which is greater than the first pitch, and
the transport is controlled such that each workpiece (W) of the plurality of workpieces (W) is stopped at respective first and second locations within the printing machine, the first and second locations being spaced along the horizontal transport path and each being located directly above the rising table (<NUM>, <NUM>, <NUM>, <NUM>) when in its retracted position, with at least one of the first and second locations being directly located above a support surface (<NUM>, <NUM>, <NUM>, 43A, 43B) of the tooling (<NUM>, <NUM>, <NUM>, <NUM>).