WO2024201153A1

WO2024201153A1 - Front-loading tensioning frame

Info

Publication number: WO2024201153A1
Application number: PCT/IB2024/051611
Authority: WO
Inventors: Graham Coleman-Hill
Original assignee: ASMPT SMT Singapore Pte Ltd
Current assignee: ASMPT SMT Singapore Pte Ltd
Priority date: 2023-03-25
Filing date: 2024-02-20
Publication date: 2024-10-03
Anticipated expiration: 2025-09-25
Also published as: GB202304392D0; EP4688437A1; TW202438328A; GB2628536A; CN120882566A; KR20250133369A

Abstract

A tensioning frame (30) for a printing screen (31) in which all movable parts are mechanically driven. In particular, such movable parts may include not only an engagement projection used for engaging with a printing screen (31), but also an abutment surface which presses down onto the upper surface of the printing screen (31) when loaded into the tensioning frame (30).

Description

Front-loading Tensioning Frame

This invention relates to a tensioning frame for tensioning a printing screen.

Background and Prior Art

Industrial screen-printing machines typically apply a conductive print medium, such as solder paste or conductive ink, onto a planar workpiece, such as a circuit board, by applying the conductive print medium through a pattern of apertures in a printing screen (sometimes referred to as a mask or stencil) using an angled blade or squeegee.

A printing screen is a substantially planar sheet which before use is cut to include apertures which define the pattern to be printed. In one common form it comprises a screen sheet formed of metal or plastics material, while in another common form comprises a mesh comprising a flexible, perforate sheet, for example a woven mesh of polypropylene or stainless steel strands. In both forms it is necessary to hold the printing screen under tension during a printing operation, and conventionally this is achieved by removably attaching the printing screen to a rectangular tensioning frame. There are various such tensioning frames and methods for providing engagement between a printing screen and a tensioning frame, with one well-known example being the VectorGuard (RTM) system, which is described in WO-2003093012-A1, WO-2005046994-A2, WO-2007091035-A1, WO-2009047012-A2 and GB-2526536-A. Other systems are described in, for example, US-5606911, US-5606912, US- 5941171, US-6038969, US-6067903, US-6289804, WO-2017164493-A1, WO-2017188555-A1, WO-2019103284-A1.

FIG. 1 schematically shows, in perspective view, the underside of a known VectorGuard tensioning frame 1, FIG. 2 schematically shows, in perspective view, a known printing screen 3 adapted for engagement with the VectorGuard tensioning frame 1 of FIG. 1, while FIG. 3 schematically shows a cross-section of a beam 2A of the VectorGuard tensioning frame in engagement with a printing screen 3. As can be seen from FIG. 1, the tensioning frame 1 is planar and defined by a plurality (here four) of elongate beams 2A-D which extend around the periphery of the tensioning frame 1, forming a rectangle, which in use may surround and tension a printing screen 3. The beams are identical in construction. Adjacent beams 2 are connected by corner pieces 4, one of which also includes a pneumatic port 13. Each beam includes a number of engagement surfaces 5, for engaging with a printing screen 3 in use. As can be seen in FIG. 1, the individual engagement surfaces 5 of each beam 2 are adjacent, and together form a composite engagement surface. With particular reference to FIG. 3, it can be seen that each beam (here beam 2A is shown) is hollow, comprising an elongate channel formed therein, the channel extending parallel to the length of the respective beam 2 and having an opening 6 at an engagement side (i.e. the underside) thereof, the engagement side of each beam 2 being co-planar and orientated parallel to the plane of the frame 1. The beam 2 is therefore approximately U-shaped in cross-section. Located within the channel is an engagement body 7 with three approximately radially-extending arms: a first arm 8 engages with a biasing member, here a spring 9, located between the arm 8 and an inner surface of the beam 2A; a second arm 10 which engages with a pneumatically inflatable tubing 11 located between the arm 10 and an inner surface of the beam 2A and which is connected to pneumatic port 13; and a third arm 12 carrying engagement surface 5. The engagement body 7 is mounted for rotation about a spindle 14 which is an integral part of the beam 2, with the rotation controlled by the inflation of tubing 11, acting against the bias of spring 9. The third arm 12 is sized so that the engagement surface 5 projects outwardly of the beam from the channel opening 6, during at least part of the engagement surface's range of travel during rotation of the engagement body. To tension a printing screen 3, the tubing 11 is first inflated to rotate the engagement body 7 clockwise as shown and thus move engagement surface 5 to the left as shown, and slightly retracted into the channel. A printing screen 3, which as shown in FIG. 2 has a patterned foil or mesh 15 and a supporting edging 16, which includes edging corner pieces 161, is then positioned proximate the underside of the frame 1. Pneumatic pressure is then released from tubing 11, which deflates, allowing the engagement body 7 to rotate anticlockwise as shown under the biasing force of spring 9, so that the engagement surface 5 moves to the right as shown, and slightly outwardly, to engage with a corresponding inclined profile of the edging 16, thus applying a tensioning force to the printing screen 3.

Each beam 2 includes a projection 17 located on the inner side, i.e. that side which faces the interior of the tensioning frame 1, which projects towards the printing screen 3 in use, i.e. downwardly as shown. The distal end of the projection 17 forms an abutment surface 18. When a printing screen 3 is located into the tensioning frame 1 and tension applied thereto by engagement of the engagement surfaces 5 and the edging 16, it can be seen that the rotary movement of the engagement surfaces 5 will cause the edging 16 to move both laterally away from the centre of the tensioning frame 1, thus increasing tension in the printing screen 3, and also slightly upwards towards the centre of the beams 2. This vertical movement causes the foil / mesh 15 to lift into contact with the abutment surface 18. It can be seen therefore that together, the abutment surfaces 18 of each beam 2 act as a bearing edge and define the plane of the tensioned foil / mesh 15 in use.

In practice, the VectorGuard tensioning frame is manufactured by forming each beam 2, and each engagement body 7, as metal extrusions. Each engagement body 7 may then be slid onto the spindle 14 from an end of the beam 2, and springs 9 and the tubing 11 a re also inserted at one end of the beam 2 and slid along to the intended position.

The VectorGuard system in particular provides simple, consistent and reliable operation, leading to its widespread uptake in the industry.

However, a problem exists with such known apparatus in that it is difficult to automate the loading of a printing screen into the tensioning frame and subsequently into a printing machine.

Referring again to FIGs. 1 to 3, to load a printing screen 3 into the tensioning frame 1, the tensioning frame 1 may be placed upside down on a flat surface such as a table. Pneumatic pressure is applied to the tensioning frame 2 to inflate tubing 11 and thus retract the arm 12 into the channel. A printing screen 3 may then be placed onto the underside of the tensioning frame 1 and the pneumatic pressure turned off. The arm 12 may then move under the action of spring 9 to engage with the edging 16 of the printing screen 3 and tension the screen. This also serves to centre the printing screen 3 relative to the tensioning frame 1. The loaded tensioning frame 1 may then be turned right side up, and the loaded frame placed into a printing machine for use in a printing operation. The loading of the tensioning frame 1 therefore requires two separate inversions of the frame, together with an intermediate screen positioning step, followed by a separate machine loading step.

To this end, the present applicant developed a new form of tensioning frame, compatible with VectorGuard printing screens, which permits cartridge-style side-loading of printing screens into the tensioning frame. In this way, the printing screen may be loaded, for example manually or by a robot such as an autonomous intelligent vehicle, into a tensioning frame, without removing the frame from a printing machine, greatly streamlining the loading processes. As set out in WO 2021/094962 Al, this was achieved by providing a side opening 19 in a tensioning frame 20 to receive a printing screen, as schematically shown in FIG. 4. Here, the printing screen 3 is shown extending through the side opening 19 provided in a front beam 21 of the tensioning frame 20 during its loading in a direction A.

While this modification sounds trivial, in fact it is surprisingly difficult to implement. This is because there are various parts of the tensioning mechanism which may obstruct the loading of the printing screen 3. As described in WO 2021/094962 Al, in order to enable such side-loading various components of the tensioning frame 20 are configured to move between engaged and loading positions, as schematically shown in FIGs. 5 and 6 respectively. In particular, it is necessary to move an engagement arm 22, which engages with the edging 16 of the printing screen 3 in use to apply a tensioning force thereto, and an abutment surface 23, which provides similar functionality to the abutment surface 18 shown in FIG. 3, i.e. providing a reliable tensioning plane for the foil 15 and blocking off the tensioning mechanism within the beam to prevent ingress of print medium (not shown) during a printing operation.

The tensioning frame 20 uses a pneumatic source to control operation. In particular, the engagement arm 22 is moved into the retracted position shown in FIG. 6 by pneumatically inflating a bladder 24 to push a shuttle 25 leftward as shown, which impels the engagement arm 22 into contact with a camming surface, which in turn causes the engagement arm 22 to rotate relative to the shuttle 25 and move upwardly, i.e. away from the vicinity of the printing screen 3. The abutment surface 23 meanwhile is moved vertically by a separate rotor 27, which is also pneumatically driven. In more detail, the abutment surface 23 is formed at the lower edge of a movable wall portion 28, and the movable wall portion 28 is drivable by the rotor 27 into a lowered configuration in which the abutment surface 23 contacts the foil 15, and a raised configuration in which it is positioned away from the vicinity of the printing screen 3.

That design is effective, however, for certain applications it is preferable to avoid pneumatic actuation. It is therefore an aim of the present invention to provide a tensioning frame which dispenses with pneumatic actuation, and instead implements a wholly mechanical actuation system. As a further aim, the tensioning frame may optionally be actuated manually, thus providing a particularly low-cost solution for customers. As an alternative, the frame may be actuated in an automated system, for example by an autonomous intelligent vehicle (AIV) or automated guided vehicle (AGV) equipped with a simple actuation tool. Advantageously, such a tensioning frame may also permit cartridgestyle side-loading of printing screens into the tensioning frame.

In accordance with the present invention this aim is achieved by providing a tensioning frame in which all movable parts are mechanically driven. In particular, such movable parts include not only an engagement projection used for engaging with a printing screen, but also an abutment surface which presses down onto the upper surface of the printing screen when loaded into the tensioning frame.

Summary of the Invention

In accordance with a first aspect of the present invention there is provided a tensioning frame for tensioning a printing screen, the tensioning frame being substantially planar and of rectangular shape, the tensioning frame comprising a plurality of elongate beams connected end to end to define the rectangular shape, wherein each beam comprises: a beam body, a chamber formed in the beam body, an elongate shaft located in the chamber and extending within the beam body, the elongate shaft being mounted for rotation about its longitudinal axis, relative to the beam body, an engagement projection moveable between a retracted position and an engagement position, the engagement projection configured to engage with a printing screen in use and apply a tensioning force thereto directed parallel to the plane of the tensioning frame as it moves from the retracted position to the engagement position, and an abutment surface moveable between a raised position and a lowered position, the abutment surface configured to contact an upper surface of the printing screen in use and apply a force thereto directed normal to the plane of the tensioning frame as it moves from the raised position to the lowered position, wherein the elongate shaft, the engagement projection and the abutment surface are mechanically linked so that rotation of the elongate shaft in a first rotational direction relative to the beam body moves both the engagement projection to the engagement position and the abutment surface to the lowered position, and rotation of the elongate shaft in a second rotational direction opposite to the first rotational direction moves both the engagement projection to the retracted position and the abutment surface to the raised position.

In accordance with a second aspect of the present invention there is provided a tensioning frame for tensioning a printing screen, the tensioning frame being substantially planar and of rectangular shape, the tensioning frame comprising a plurality of elongate beams connected end to end to define the rectangular shape, wherein each beam comprises: a beam body, a chamber formed in the beam body, an elongate shaft located in the chamber and extending within the beam body, the elongate shaft being mounted for rotation about its longitudinal axis, relative to the beam body, an engagement projection moveable between a retracted position and an engagement position, the engagement projection configured to engage with a printing screen in use and apply a tensioning force thereto directed parallel to the plane of the tensioning frame as it moves from the retracted position to the engagement position, and wherein the elongate shaft and the engagement projection are mechanically linked so that rotation of the elongate shaft in a first rotational direction relative to the beam body moves the engagement projection to the engagement position, and rotation of the elongate shaft in a second rotational direction opposite to the first rotational direction moves the engagement projection to the retracted position, and wherein the tensioning frame comprises: a drive interface for receiving rotary drive from an external source and transferring the rotary drive to the elongate shaft to drive the elongate shaft in the first or second rotational directions.

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

Brief Description of the Drawings

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

FIG. 1 schematically shows, in perspective view, the underside of a known tensioning frame;

FIG. 2 schematically shows, in perspective view, a known printing screen;

FIG. 3 schematically shows a cross-section of a beam of the tensioning frame of FIG. 1 in engagement with a printing screen;

FIG. 4 schematically shows, in perspective view, a known tensioning frame in a part- loaded configuration;

FIGs. 5 and 6 schematically show, in sectional side view, the tensioning frame of FIG. 4 in engaged and unloaded configurations respectively;

FIGs. 7 to 9 schematically show, in perspective view from above, a tensioning frame in accordance with the present invention at various stages of a loading sequence;

FIGs. 10 and 11 schematically show, in perspective view from below, the tensioning frame of FIG. 7 at various stages of a loading sequence;

FIG. 12 schematically shows, in perspective view from above, a section of a beam of the tensioning frame of FIG. 9;

FIGs. 13 to 17 schematically show sectional side views of the beam of FIG. 12 as its tensioning mechanism transitions from a fully retracted configuration to a fully engaged configuration; FIGs. 18 and 19 schematically show, in perspective and sectional side views respectively, details of a manual actuation system for the tensioning frame of FIG. 7;

FIGs. 20 and 21 schematically show, in sectional side view, an alternative tensioning frame in retracted and engaged configurations respectively;

FIGs. 22 and 23 schematically show, in perspective view from above, a tensioning frame in accordance with a further embodiment of the present invention, having a modular construction;

FIG. 24 schematically shows, in perspective view from above, a detachable robot module; and

FIG. 25 schematically shows, in perspective view from above, a detachable pneumatic module.

Detailed Description of the Preferred Embodiments of the Invention

A tensioning frame 30 in accordance with a first embodiment of the present invention is schematically shown in FIGs. 7 to 19. A loading sequence for loading a printing screen 31, which as shown comprises a VectorGuard printing screen 31 having a central foil 32 surrounded by profiled edging 33, into the tensioning frame 30 is illustrated in FIGs. 7 to 9.

It can be seen that the tensioning frame 30 is substantially planar, in the X-Y plane as shown, and of rectangular shape in the X-Y plane, with all dimensions being compatible with standard printing machines. It should be noted that the tensioning frame 30 is shown in the orientation in which it would be used within a printing machine (not shown), and the Z axis shown therefore extends vertically upwards with the X-Y plane being horizontal. The tensioning frame 30 comprises a plurality, here four, of elongate beams 34A-D. The frontmost beam 34A as shown includes an entry opening 35 dimensioned to receive the printing screen 31 laterally therethrough in a direction parallel to the plane of the tensioning frame 30, i.e. parallel to the X-Y plane. The printing screen 31 may therefore be loaded into the tensioning frame 30 in the style of a cartridge. The entry opening 35 as shown is open at its lowest extent, however it is equally possible to form the entry opening 35 as a slot within the beam 34A. FIG. 7 shows the printing screen 31 partially inserted into the tensioning frame 30. In order for the printing screen 31 to be received in this way, it is necessary to ensure that the internal tensioning mechanism (described in more detail below) of the tensioning frame 30 is moved to a retracted configuration so as not to obstruct the passage of the printing screen 31. The configuration of the tensioning mechanism is controlled through the operation of levers 36A, B provided at beam 34A, as will be described in more detail below. When the levers 36A, B are oriented vertically upwards as shown in FIG. 7, the tensioning mechanism is in its retracted configuration. Following loading of the printing screen 31 into the tensioning frame 30, the levers 36A, B may then be rotated down towards beam 34A, for example manually, to move the tensioning mechanism into an engagement configuration, in which the printing screen is gripped by the tensioning frame 30 and tensioning force applied thereto. FIG. 8 show the levers 36A, B partially lowered, while FIG. 9 shows the levers 36A, B fully lowered so that the tensioning mechanism is at its engagement configuration. It can be seen that in this configuration, the levers 36A, B are located entirely within respective recesses 37A, 37B within the thickness of the beam 34A, ensuring the profile of the tensioning frame 30 is unaffected. The levers 36A, B are retained within the recesses during normal use of the tensioning frame 30. They may be released to the vertical orientation shown in FIG. 7 by pressing a button 38 provided on beam 34A.

It can be seen that, due to the provision of levers 36A, B, the beam 34A is wider than the other three beams 34B-D. In alternative embodiments, described below, the levers and button may be provided in a separate, detachable module, adapted to fit onto beam 34A. In this case, the beams 34A-D may all have substantially similar dimensions.

To unload the printing screen 31, the process described above is reversed, i.e. the levers 36A, B are released by pushing button 38 then raised to the upstanding orientation to disengage the tensioning mechanism from the printing screen 31. The printing screen 31 may then be slid out from the tensioning frame 30, through the entry opening 35. In alternative embodiments (not shown), an additional entry opening may be provided in at least one other beam 34B-D, so that the printing screen 31 may be loaded, or unloaded, through a choice of entry opening. It should also be noted that with this configuration, it is also possible to load a printing screen 31 into the tensioning frame 30 similarly as to conventional VectorGuard frames, i.e. by placing the printing screen 31 directly into the tensioning frame 30, either by turning the tensioning frame 30 upside down and placing an inverted printing screen 31 on top, or by placing the printing screen 31 on a flat surface and placing the tensioning frame 30 on top of it. The levers 36A, B may then be actuated to engage the printing screen 31 as previously described.

FIGs. 10 and 11 schematically show the tensioning frame 30 at various stages of a loading sequence in perspective view from below. FIG. 10 shows the printing screen 31 at the same point as FIG. 7, while FIG. 11 shows the tensioning frame 30 following insertion of the printing screen 31, but before the levers 36A, B are actuated to move the tensioning mechanism into the engaged configuration. In FIG. 10 especially an engagement projection 39, which forms part of the tensioning mechanism, can be seen depending downwardly from the tensioning frame 30. Also visible are corner pieces 40, which connect the ends of individual beams 34A-D together.

FIG. 12 schematically shows, in perspective view from above, a section of a beam 34B of the tensioning frame 30, illustrating the tensioning mechanism located therein in its engaged configuration, and with a printing screen 31 inserted into the tensioning frame 30. The beam 34B has been illustrated by way of example only, and all of the beams 34A-D include like tensioning mechanisms.

The beam 34B comprises a beam body 41 which provides structural rigidity to the beam 34B; it may for example be formed from an extruded metal material such as steel, aluminium or well-known alternatives. The beam body 41 is hollow, having a chamber 42 formed therein, which is defined by a chamber wall 43. The chamber 42 houses an elongate shaft 44 located therein which extends within the beam body 41, and extends for substantially the length of the beam body 41, including, at its ends, respective corner pieces 40. The elongate shaft 44 is mounted for location about its longitudinal axis (i.e. parallel to the Y axis as shown), relative to the beam body 41. As can be seen in FIG. 12, at this section of the beam 34B, the elongate shaft 44 has a cross sectional shape substantially of a major segment of a circle, though with an inwardly extending slot 49 formed in the circumference of the major segment, and furthermore part of the chamber wall 43 adjacent to this part of the elongate shaft 44 is of arcuate shape, thus permitting guided rotation of the elongate shaft 44 about its longitudinal axis. The elongate shaft 44 therefore also includes a chord surface 51.

An engagement carriage 45 is partially located within the chamber 42. In this embodiment, the engagement carriage 45 has a two-part construction: the main section is formed by a leaf spring, for example made from sheet steel or the like, with the material and thicknesses selected for the required level of tensioning, with a second part, i.e. a movable wall portion 46, rigidly fixed to a first end of the leaf spring. The movable wall portion 46 is rigid, and may conveniently be formed from a steel or aluminium extrusion for example. The movable wall portion 46 is substantially planar, with its plane extending vertically (i.e. parallel to the Z axis shown) in use. An abutment surface 47 is formed at the lowermost extent of the movable wall portion 46 which, when the tensioning mechanism in the engaged configuration shown and the movable wall portion 46 is in a corresponding lowered position as shown, is configured to abut and press into the upper surface of foil 32, applying a force directed normal to the plane of the printing screen. The abutment surface 47 therefore extends over the bottom surface of the movable wall portion 46, substantially parallel to the X-Y plane in operation. Near the top of the movable wall portion 46 is a tongue 48 which projects outwardly therefrom towards the interior of the chamber 42. This is configured to be loosely received by the slot 49, such that rotation of the elongate shaft 44 causes movement of the slot 49 and hence movement of the tongue 48 and engagement carriage 45, as will be described in more detail below. The distal end of the leaf spring forms an engagement projection 39 which is configured to engage with a printing screen 31, in particular with a profiled edging 33 of the printing screen 31. As shown, the engagement projection 39 extends downwardly and outwardly (i.e. away from the centre of the tensioning frame 30) from the engagement carriage 45, at approximately 45° to the Z-axis in use. With the tensioning mechanism in the engaged configuration shown, and the engagement projection 39 in a corresponding engagement position, the engagement projection 39 engages with the edging 33 and applies a tensioning force to the printing screen 31 directed parallel to the plane of the tensioning frame, in the negative X direction as shown. The engagement projection 39 is therefore rigidly connected to the abutment surface 47 via the engagement carriage 45. The leaf spring of the engagement carriage 45 also includes a leaf spring guide section 50, which is located at the leftmost side of the engagement carriage 45 as shown, and is formed from a folded-over section of the leaf spring. This leaf spring guide section 50 is dimensioned to snugly fit within the chamber wall 43 of chamber 42, and acts to guide movement of the engagement carriage during movement of the tensioning mechanism. Due to the resilience of the leaf spring, the leaf spring guide section 50 may flex during this movement.

It can be seen therefore that the elongate shaft 44, the engagement projection 39 and the abutment surface 47 are mechanically linked. In this way, rotation of the elongate shaft 44 in a first rotational direction (i.e. clockwise as shown) relative to the beam body 41 moves both the engagement projection 39 to its engagement position and the abutment surface 47 to its lowered position, and rotation of the elongate shaft 44 in a second rotational direction opposite to the first rotational direction (i.e. anticlockwise or counterclockwise as shown) moves both the engagement projection 39 to a retracted position and the abutment surface 47 to a raised position.

FIGs. 13 to 17 schematically show sectional side views of the beam 34B of FIG. 12 as its tensioning mechanism transitions from a fully retracted configuration to a fully engaged configuration. In FIG. 13, the tensioning mechanism is fully retracted, achieved by rotating the elongate shaft 44 in the second rotational direction, i.e. anticlockwise / counterclockwise to its maximum extent, delimited by the movable wall portion 46 abutting against a chamber wall 43 at an upper region of the chamber 42. The movable wall portion 46 is thereby placed in its raised position, in fact the entire engagement carriage 45 is moved upwardly and rotated. This also causes the engagement projection 39 to move upwardly to its retracted position. It can be seen that with the movable wall portion 46 in the raised position and the engagement projection in the retracted position, the printing screen 31 can be inserted laterally into the tensioning frame 30 without risk of collision with any part of the engagement carriage 45. It can also be seen that in this retracted position, the engagement carriage 45 is adjacent the chord surface 51 of the elongate shaft 44.

FIGs. 14 to 16 show successive similar sectional side views of the beam 34B as its tensioning mechanism transitions from the retracted to the engaged configuration. This transition is effected by rotating the elongate shaft 44 in the first rotational direction, i.e. clockwise as shown. It can be seen that the engagement carriage 45, and hence the engagement projection 39 and movable wall portion 46, is driven around and downwardly towards the printing screen 31. In particular, the rotational movement of the engagement projection 39 is ideal for engaging with the profiled edging 33of the printing screen 31. In addition, it can be seen that the leaf spring guide section 50 ensures correct positioning of the engagement carriage 45 with respect to the leftmost side of the chamber 42 as shown.

In FIG. 17, the tensioning mechanism has reached the engaged configuration, in which the engagement projection 39 is in its engagement position and applies a tensioning force to the printing screen 31 in the negative X direction as shown, via the profiled edging 33. In addition, the abutment surface 47 contacts the upper surface of the foil 32 and presses downwardly into it, i.e. applying a downward force. This ensures a repeatably levelled surface for printing. The movable wall portion 46 is in its lowered position in which it at least partially closes the chamber 42, to prevent printing medium from fouling the tensioning mechanism. Although not clear from FIG. 17, in practice the edging 33 would be slightly rotated by the application of these tensioning and downward forces.

FIGs. 18 and 19 schematically show, in perspective and sectional side views respectively, details of a manual actuation system for the tensioning frame 30. These figures are made partly transparent, so that internal details of the tensioning frame 30 can be seen. FIG. 18 shows, in perspective view from above, part of beams 34A and 34D, with an intermediate corner piece 40. The elongate shaft 44 of each beam is visible running along the length of the beam. For beam 34D, it is also possible to see individual engagement carriages 45 aligned along the length of the elongate shaft 44. These individual engagement carriages 45 may be separated by struts 52, which may form part of the beam body 41, and serve to increase the strength and rigidity of the beam 34D, as is described in more detail in WO-A1-2021/038353. In this way, the beam body 41 comprises a plurality of chambers 42, spaced along the beam 34D, forming a series of pockets to receive respective engagement carriages 45. In alternative embodiments (not shown), spacers may be used to separate individual engagement carriages, or alternatively a single, long engagement carriage may be provided which extends approximately the length of the beam body 41. Each elongate shaft 44 includes a shaft end section 53 at each end thereof, of circular cross-section, with each shaft end section 53 being accommodated within a corner piece 40, the corner piece 40 retaining the elongate shafts 44 in the correct position relative to the beam bodies 41. Each shaft end section 53 comprises teeth 54, which mesh together so that rotating the elongate shaft 44 of one beam consequently causes the adjacent, meshing elongate shaft 44 of an adjacent beam to also rotate. Therefore, rotation of any elongate shaft 44 of the tensioning frame 30 will impel all other elongate shafts 44 to rotate, in the same direction with respect to the centre of the tensioning frame 30.

In this embodiment, rotational drive is directly imparted to the elongate shaft 44 of beam 34D by manual actuation of lever 36B, which in FIG. 18 is shown as fully lowered, so that it does not project above the upper surface of the tensioning frame 30. The lever 36B is mechanically connected to the elongate shaft 44 of beam 34D via a lever linkage 55 and a rotatable drive head 56. The lever linkage 55 is pivotably mounted to the lever 36B and the drive head 56 at respective ends thereof. The drive head 56 is mounted for rotation about the same axis as the elongate shaft 44 of beam 34D, and directly drives that elongate shaft 44 via a spindle (not clearly shown in FIG. 18) which rigidly connects the drive head 56 to that elongate shaft 44.

Also shown in FIG. 18 is button 38, which, when depressed, unlocks the levers 36A and 36B and pushes them up away from the plane of the tensioning frame 30, so as to permit manual grasping of the levers 36A, 36B. The associated mechanism is more clearly shown in FIG. 19. This figure shows the lever 36B only partially lowered. The button 38 is mounted for mechanical engagement with the base of a pivotable locking latch 57 which is biased by a locking biasing means such as an extension spring (not shown) into a locking position. The locking latch 57 has a hooked end, distal to its base, adapted to engage with a hook 58 provided at the free end of lever 36B and retain the lever 36B at its lowered position. The locking biasing means therefore acts to bias the locking latch 57 to rotate clockwise as shown, and in the locking position the hooked end of the locking latch 57 may engage with the hook 58. The lever 36B is provided with a separate lever biasing means (not shown) such as a compression spring, which biases the lever 36B towards its raised position. Depressing the button 38 causes the locking latch 57 to move against its bias and rotate counter or anticlockwise as shown, disengaging with the hook 58. The lever 36B is thereby released, and moves upwardly and away from the plane of the tensioning frame 30 due to its lever biasing means. The lever 36B may then be manually grasped and lifted further to its fully upright position (see FIG. 7 for example). Lifting of the lever 36B pushes the lever linkage 55 to the right as shown, which in turn rotates the drive head 56 clockwise as shown, causing the elongate shaft 44 of beam 34D to similarly rotate clockwise, and thus move the tensioning mechanism into the retracted configuration. When the lever 36B is pressed down into the lowered position again, the hook 59 reengages with the locking latch 57 to lock into the lowered position. During this movement, the elongate shaft 44 turns in the other direction, and the tensioning mechanism is moved into the engaged configuration. Operation of lever 36A is functionally identical to lever 36B, and since both levers 36A, 36B and all of the elongate shafts 44 of the tensioning frame 30 are mechanically linked, all of these parts move in concert.

In alternative embodiments, the drive head 56 may comprise teeth which mesh with those of the elongate shaft 44 of beam 34A, to directly drive that elongate shaft 44.

FIGs. 20 and 21 schematically show, in sectional side view, a beam of an alternative tensioning frame 60 in retracted and engaged configurations respectively. This embodiment is very similar to the first embodiment described above, with two main differences. Firstly, the engagement carriage 61 is integrally formed, including the engagement projection 62, movable wall portion 63 and abutment surface 64. Secondly, movement of the engagement carriage 61 is effected by using a cam feature 65 carried by the elongate shaft 66. The cam feature 65 comprises a cam surface which resembles a hook, and by comparing FIGs. 20 and 21 it can be seen that the shape of this hook, when rotated, drives the engagement carriage 61 into retracted and engaged positions very similarly to that of the previous embodiment. As previously, movement of the engagement carriage 61 is constrained by its abutment with interior chamber walls formed in the beam.

FIGs. 22 and 23 schematically show, in perspective view from above, a tensioning frame 70 in accordance with a further embodiment of the present invention, having a modular construction. In this embodiment, the basic tensioning frame 70 is provided without actuation means such as levers. If manual actuation, for example via levers, is a required option, then a detachable module 71 may be fitted to a beam 34A, which detachable module 71 comprises a manual actuator, such as a lever, and associated actuation mechanism as described with reference to FIGs. 18 and 19 for example. The detachable module 71 is adapted for modular, i.e. repeatably releasable, engagement with the tensioning frame 70. This may be realised by, for example, by providing each drive head in the detachable module 71 with a relatively short spindle (not visible) which protrudes from the side of the detachable module 71, and providing a drive interface 72 (see FIG. 23) on the outer lateral side of beam 34A which may receive the protruding spindle. When inserted into the drive interface 72, the spindle is operative to mechanically connect, e.g. meshingly engage, with an elongate shaft, such that rotation of the spindle, due to manual actuation of a lever, causes rotation of the elongate shaft. Advantageously, the detachable module 71 comprises a module interface (not visible) which may releasably connect to a beam interface 73 located on the outer lateral side of beam 34A, to hold the detachable module 71 to the tensioning frame 70 and ensure correct insertion of the spindle into the drive interface 72. An additional drive interface 72 may be provided in beam 34A, and in FIG. 23 two such drive interfaces are shown, associated with different respective elongate shafts 44. In alternative embodiments, the manual actuator could comprise other means than levers capable of rotatably driving the elongate shaft 44, such as knobs, buttons, sliders etc.

FIG. 23 shows the tensioning frame 70 without the detachable module 71 attached thereto, so that the drive interfaces 72 and beam interface 73 are visible. It can be seen that since the drive interfaces 72 are accessible, actuation of the tensioning frame 70 may be controlled not through manually actuated levers, but by insertion of respective rotary drives 74 from an external source, such as an AIV or AGV (not shown). The received rotary drives 74 may be actuated, i.e. rotated, by the AGV / AIV to transfer rotational drive from the rotary drives 74 to respective elongate shafts 44 to effect rotation thereof.

FIG. 24 schematically shows, in perspective view from above, a detachable robot module 75 for modular, i.e. repeatably releasable, engagement with a tensioning frame similar to tensioning frame 70 shown in FIG. 23. The detachable robot module 75 is optimised for actuation by a robot such as an AIV or AGV, allowing dedicated tooling (such as rotary drives 74 shown) carried by the AGV / AIV to engage with one or more robot interfaces 80 and hence to rotatably drive spindles 76 (for example similar to the spindles described above with reference to detachable module 71) protruding from the back of the detachable robot module 75 and hence the elongate shafts 44 via the drive interface 72. The detachable robot module 75 could attach to the tensioning frame 70 similarly to the detachable module 71.

FIG. 25 schematically shows, in perspective view from above, a detachable pneumatic module 77 for modular, i.e. repeatably releasable, engagement with a tensioning frame similar to tensioning frame 70 shown in FIG. 23. The detachable pneumatic module 77 includes a pneumatic port 78 on the front for receiving a pressurised air supply from an external source (not shown). The pneumatic port 78 supplies air to a pneumatic actuator arranged to rotatably drive spindles 76 (for example similar to the spindles described above with reference to detachable module 71) protruding from the back of the detachable pneumatic module 77 and hence the elongate shafts 44 via the drive interface 72. As shown, the pneumatic actuator could comprise cylinders 79 to directly act on spindles 76, though various types of pneumatic actuator could be used, including bladders, pistons etc. This arrangement may be preferred for some installations where, for example, pneumatic sources are available but the full automation solution offered by AGVs / AIVs is not appropriate.

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 modular systems described above with reference to FIGs. 22 to 25 need not include all functionality of the tensioning frames described in FIGs. 7-21. In particular, any or all of the lateral opening, abutment surface and movable wall portion could be omitted from the tensioning frame, such that the frame functions more similarly to a conventionally- loaded frame. In such a frame the abutment surface could for example be provided at the lower end of a fixed wall of the beams, as is known from the conventional VectorGuard frames. Reference numerals used:

I - Tensioning frame

2, 2A-D - Beams

3 - Printing screen

4 - Corner pieces

5 - Engagement surfaces

6 - Opening

7 - Engagement body

8 - First arm

9 - Spring

10 - Second arm

II - Inflatable tubing

12 - Third arm

13 - Pneumatic port

14 - Spindle

15 - Foil / mesh

16 - Edging

161 - Edging corner pieces

17 - Projection

18 - Abutment surface

19 - Side opening

20 - Tensioning frame

21 - Front beam

22 - Engagement arm

23 - Abutment surface

24 - Bladder

25 - Shuttle

26 - Camming surface

27 - Rotor

28 - Movable wall portion 30 - Tensioning frame

31 - Printing screen

32 - Foil

33 - Edging

34A-D - Beams

35 - Entry opening

36A, B - Levers

37A, B - Recesses

38 - Button

39 - Engagement projection

40 - Corner pieces

41 - Beam body

42 - Chamber

43 - Chamber wall

44 - Elongate shaft

45 - Engagement carriage

46 - Movable wall portion

47 - Abutment surface

48 - Tongue

49 - Slot

50 - Leaf spring guide section

51 - Chord surface

52 - Struts

53 - Shaft end section

54 - Teeth

55 - Lever linkage

56 - Drive head

57 - Locking latch

58 - Hook

60 - Tensioning frame

61 - Engagement carriage

62 - Engagement projection 63 - Movable wall portion

64 - Abutment surface

65 - Cam feature

66 - Elongate shaft

70 - Tensioning frame

71 - Detachable module

72 - Drive interface

73 - Beam interface

74 - Rotary drives

75 - Detachable robot module

76 - Spindles

77 - Detachable pneumatic module

78 - Pneumatic port

79 - Pneumatic cylinder

80 - Robot interfaces

Claims

1. A tensioning frame for tensioning a printing screen, the tensioning frame being substantially planar and of rectangular shape, the tensioning frame comprising a plurality of elongate beams connected end to end to define the rectangular shape, wherein each beam comprises: a beam body, a chamber formed in the beam body, an elongate shaft located in the chamber and extending within the beam body, the elongate shaft being mounted for rotation about its longitudinal axis, relative to the beam body, an engagement projection moveable between a retracted position and an engagement position, the engagement projection configured to engage with a printing screen in use and apply a tensioning force thereto directed parallel to the plane of the tensioning frame as it moves from the retracted position to the engagement position, and an abutment surface moveable between a raised position and a lowered position, the abutment surface configured to contact an upper surface of the printing screen in use and apply a force thereto directed normal to the plane of the tensioning frame as it moves from the raised position to the lowered position, wherein the elongate shaft, the engagement projection and the abutment surface are mechanically linked so that rotation of the elongate shaft in a first rotational direction relative to the beam body moves both the engagement projection to the engagement position and the abutment surface to the lowered position, and rotation of the elongate shaft in a second rotational direction opposite to the first rotational direction moves both the engagement projection to the retracted position and the abutment surface to the raised position.

2. The tensioning frame of claim 1, wherein a beam of the plurality of beams comprises an entry opening dimensioned to receive a printing screen therethrough in a direction parallel to the plane of the tensioning frame.

3. The tensioning frame of claim 2, wherein movement of the abutment surface to the raised position and the engagement projection to the retracted position causes the abutment surface and the engagement projection to move away from the entry opening so as to permit a printing screen to be fully inserted into the tensioning frame through the entry opening.

4. The tensioning frame of claim 1, wherein the abutment surface is formed on a movable wall portion, and in the lowered position the movable wall portion at least partially closes the chamber.

5. The tensioning frame of claim 4, wherein the movable wall portion comprises a tongue that is received within a slot formed in the elongate shaft.

6. The tensioning frame of claim 1, wherein the engagement projection is carried by an engagement carriage at least partially located within the chamber.

7. The tensioning frame of claim 6, wherein the engagement carriage comprises a leaf spring.

8. The tensioning frame of claim 6, wherein the engagement projection is rigidly connected to the abutment surface via the engagement carriage.

9. The tensioning frame of claim 6, wherein the engagement carriage is integrally formed with the abutment surface.

10. The tensioning frame of claim 6, wherein the elongate shaft comprises a cam surface for driving the engagement carriage.

11. The tensioning frame of claim 6, wherein movement of the engagement carriage, and hence the engagement projection, is constrained by the juxtaposition of the engagement carriage and at least one chamber wall defining the chamber.

12. The tensioning frame of claim 1, comprising a lever mechanically connected to an elongate shaft, such that the elongate shaft may be rotated by manual actuation of the lever.

13. The tensioning frame of claim 12, wherein the elongate shaft of each beam is mechanically connected to the lever, such that each elongate shaft may be rotated by manual actuation of the lever.

14. The tensioning frame of claim 1, wherein an elongate beam comprises a beam interface for releasably connecting a detachable module thereto.

15. The tensioning frame of claim 14, comprising the detachable module, the detachable module comprising a module interface for releasably connecting to the beam interface.

16. The tensioning frame of claim 15, wherein the detachable module comprises a lever, and wherein connection of the beam interface and the module interface mechanically connects the lever to an elongate shaft, such that the elongate shaft may be rotated by manual actuation of the lever.

17. The tensioning frame of claim 1, comprising a drive interface for receiving a rotary drive from an external source and transferring rotational drive to an elongate shaft to effect rotation thereof.

18. The tensioning frame of claim 1, wherein the elongate shafts of each beam are mechanically connected such that the elongate shafts rotate in concert.

19. A tensioning frame for tensioning a printing screen, the tensioning frame being substantially planar and of rectangular shape, the tensioning frame comprising a plurality of elongate beams connected end to end to define the rectangular shape, wherein each beam comprises: a beam body, a chamber formed in the beam body, an elongate shaft located in the chamber and extending within the beam body, the elongate shaft being mounted for rotation about its longitudinal axis, relative to the beam body, an engagement projection moveable between a retracted position and an engagement position, the engagement projection configured to engage with a printing screen in use and apply a tensioning force thereto directed parallel to the plane of the tensioning frame as it moves from the retracted position to the engagement position, and wherein the elongate shaft and the engagement projection are mechanically linked so that rotation of the elongate shaft in a first rotational direction relative to the beam body moves the engagement projection to the engagement position, and rotation of the elongate shaft in a second rotational direction opposite to the first rotational direction moves the engagement projection to the retracted position, and wherein the tensioning frame comprises: a drive interface for receiving rotary drive from an external source and transferring the rotary drive to the elongate shaft to drive the elongate shaft in the first or second rotational directions.

20. The tensioning frame of claim 19, wherein the external source comprises a module, and the tensioning frame comprises a module interface for releasably and repeatably attaching the module thereto such that the rotary drive engages with the drive interface.

21. A tensioning frame system comprising the tensioning frame of claim 20 and the module.

22. The tensioning frame system of claim 21, wherein the module comprises a manual actuator.

23. The tensioning frame system of claim 21, wherein the module comprises a pneumatic actuator.

24. The tensioning frame system of claim 21, wherein the module comprises an interface for engaging with a robot and receiving rotary drive therefrom.