Screen loading system and method

Abstract

A tension frame (22) for tensioning a printing screen (3) comprises a plurality of elongate beams (30A-30D) extending around a periphery of the printing screen (3) and defining the tension frame (22), wherein at least one of the beams (30A-30D) comprises an opening (32) dimensioned to admit the printing screen (3) therethrough in a transverse direction. Mechanisms for engaging the tension screen (22) and the printing screen (3) are described, as are apparatuses and methods that permit transverse loading of the printing screen (3).

Description

[0001] This application is a divisional application of application number 202080070521.8, filed on November 12, 2020, with the title “Screen loading system and method”. TECHNICAL FIELD

[0002] The present invention relates to a tensioning frame for tensioning a printing screen, a method of loading a printing screen into a tensioning frame, and a robot for loading a printing screen into a tensioning frame. BACKGROUND

[0003] Industrial screen printers typically use an inclined blade or squeegee to apply a conductive printing medium, such as solder paste or conductive ink, onto a planar workpiece, such as a circuit board, by applying the conductive printing medium through a hole pattern in a printing screen, sometimes referred to as a mask or stencil.

[0004] A printing screen is a substantially planar sheet that, prior to use, is cut to include holes that define a pattern to be printed. In one common form, the printing screen comprises a screen sheet formed of a metallic or plastic material, while in another common form, the printing screen comprises a screen that includes a flexible perforated sheet, for example, a woven mesh made of polypropylene or stainless steel strands. In both forms, the printing screen must be kept under tension during the printing operation, traditionally by removably attaching the printing screen to a rectangular tensioning frame. Various such tensioning frames exist, as well as methods for providing engagement between the printing screen and the tensioning frame, with one well-known example being the VectorGuard (RTM) system, described in WO-2003093012-A1, WO-2005046994-A2, WO-2007091035-A1, WO-2009047012-A2, and GB-2526536-A. Other systems are described, for example, in US-5606911, US-5606912, US-5941171, US-6038969, US-6067903, US-6289804, WO-2017164493-A1, WO-2017188555-A1, WO-2019103284-A1.

[0005] Figure 1 shows schematically a perspective view of the underside of a known VectorGuard tension frame 1, figure 2 shows schematically a perspective view of a known printing screen 3 adapted to engage with the VectorGuard tension frame 1 of figure 1, and figure 3 shows schematically a cross-section of a beam 2A of the VectorGuard tension frame in engagement with the printing screen 3. From figure 1 it can be seen that the tension frame 1 is planar and defined by a plurality of (four in the figure) elongate beams 2A to 2D extending around the periphery of the tension frame 1 thereby forming a rectangle which, in use, can enclose and tension a printing screen 3. The beams are identical in construction. Adjacent beams 2 are connected by a corner piece 4, one of which also comprises a pneumatic port 6. Each beam comprises a number of engagement surfaces 5 which, in use, are used to engage with the printing screen 3. From figure 1 it can be seen that the respective engagement surfaces 5 of each beam 2 are adjacent and together form a composite engagement surface. With particular reference to figure 3 it can be seen that each beam (beam 2A is shown in the figure) is hollow comprising an elongate channel formed therein which extends parallel to the length of the respective beam 2 and has an opening 6 in its engagement side (i.e. underside), the engagement sides of each beam 2 being coplanar and oriented parallel to the plane of the frame 1. The cross-section of the beam 2 is therefore generally U-shaped. Within the channel is located an engagement body 7 having three generally radially extending arms: a first arm 8 which is in engagement with a biasing member (a spring 9 in the figure) located between the arm 8 and the inner surface of the beam 2A, a second arm 10 which is in engagement with a pneumatic inflatable tube 11 located between the arm 10 and the inner surface of the beam 2A and connected to a pneumatic port 13, and a third arm 12 which carries the engagement surfaces 5. The engagement body 7 is mounted for rotation about a main shaft 14 which is an integral part of the beam 2, with the rotation being controlled by inflation of the tube 11 to thereby counteract the bias of the spring 9. The third arm 12 is sized such that the engagement surfaces 5 protrude from the channel opening 6 to the exterior of the beam over at least a portion of the travel range of the engagement surfaces during rotation of the engagement body. To tension the printing screen 3, the tube 11 is first inflated to rotate the engagement body 7 clockwise as shown, thereby moving the engagement surfaces 5 leftwards as shown and slightly retracting into the channel. The printing screen 3 with patterned foil or screen 15 and support surround 16 including surround corner piece 161 as shown in figure 2 is then positioned adjacent the underside of the frame 1. Thereafter, the pneumatic pressure is released from the deflated tube 11 thereby allowing the engagement body 7 to rotate anticlockwise as shown under the biasing force of the spring 9 to move the engagement surfaces 5 rightwards as shown and slightly outwards to engage with the corresponding angled profile of the surround 16 to thereby apply a tensioning force to the printing screen 3.

[0006] Each beam 2 comprises a protrusion 17 on the inner side (i.e. the side facing the interior of the tensioning frame 1), which, in use, protrudes towards the printing screen 3, i.e. downwards as shown. The distal end of the protrusion 17 forms an abutment surface 18. When the printing screen 3 is positioned into the tensioning frame 1 and tension is applied thereto by engagement of the engagement surface 5 and the engagement of the border 16, it can be seen that the rotational movement of the engagement surface 5 moves the border 16 laterally away from the centre of the tensioning frame 1, thereby increasing the tension in the printing screen 3, and also slightly upwards towards the centre of the beam 2. This vertical movement brings the foil or screen 15 into contact with the abutment surface 18. Thus, it can be seen that the abutment surfaces 18 of each beam 2 together act as a support edge and, in use, define the plane of the tensioned foil / screen 15.

[0007] In practice, the VectorGuard tensioning frame is manufactured by forming each beam 2 and each engagement body 7 as a metal extrusion. Each engagement body 7 can then be slid onto the spindle 14 from the end of the beam 2, and the spring 9 and tube 11 are also inserted into one end of the beam and slid into position.

[0008] In particular, the VectorGuard system provides simple, consistent and reliable operation, which has led to its widespread adoption in the industry.

[0009] However, problems exist with this known apparatus in that it is difficult to automatically load a printing screen into the tensioning frame and then automatically load the tensioning frame into the printing press.

[0010] To load a printing screen 3 into the tensioning frame 1, it is recommended that the tensioning frame 1 is inverted onto a flat surface such as a platform. Pneumatic pressure is applied to the tensioning frame 22 to inflate the tube 11, thereby causing the arms 12 to retract into the channels. The printing screen 3 can then be placed onto the underside of the tensioning frame 1 and the pneumatic pressure is turned off. The arms 12 can then move under the action of the springs 9 to engage with the border 16 of the printing screen 3 and tension the screen. This also helps to centre the printing screen 3 with respect to the tensioning frame 1. The loaded tensioning frame 1 can then be flipped in a right upward direction and the loaded frame placed into the printing press for printing operations. Thus, loading the tensioning frame 1 requires two separate flips of the frame, with an intermediate screen positioning step, followed by a separate machine loading step.

[0011] The present invention aims to provide a new form of tensioning frame, which can be compatible with the VectorGuard printing screen for example, which permits the printing screen to be loaded into the tensioning frame in a cartridge form from the side. In this way, the printing screen can be loaded into the tensioning frame, for example, by a robot such as an autonomous intelligent vehicle, without the need to remove the frame from the printing press, thereby greatly simplifying the loading process.

[0012] According to the present application, this is achieved by providing a side opening in the tensioning frame to receive the printing screen, and by moving parts of the tensioning frame between a loading position and a working position to facilitate such loading. SUMMARY

[0013] According to a first aspect of the present application, there is provided a tensioning frame for tensioning a printing screen, the tensioning frame comprising a plurality of elongate beams extending around a periphery of the tensioning frame and defining the tensioning frame, the tensioning frame being substantially planar, wherein at least one beam comprises an opening, the opening being sized to permit receipt of the printing screen therethrough.

[0014] According to a second aspect of the present application, there is provided a tensioning frame for tensioning a printing screen, the tensioning frame comprising a plurality of elongate beams extending around a periphery of the tensioning frame and defining the tensioning frame, the tensioning frame being substantially planar,

[0015] Each beam comprises:

[0016] an engagement body at least partially located within the beam, the engagement body carrying an engagement arm for engagement with the printing screen in use, the engagement body being movable relative to the beam along a range of travel in a plane perpendicular to the length of the beam; and

[0017] an actuator operably connected to the engagement body, the actuator for moving the engagement body, and hence the engagement arm, relative to the beam,

[0018] wherein the engagement arm is movably mounted to the respective engagement body.

[0019] According to a third aspect of the present application, there is provided a method of loading a printing screen into a tensioning frame, the method comprising the steps of:

[0020] i) providing a tensioning frame, and

[0021] ii) inserting the printing screen into the tensioning frame from a side of the tensioning frame.

[0022] According to a fourth aspect of the present application, there is provided a robot for loading a printing screen into a tensioning frame, the robot comprising:

[0023] a printing screen store for storing at least one printing screen, and

[0024] a transfer mechanism for transferring the printing screen laterally from the printing screen store into the tensioning frame.

[0025] Other specific aspects and features of the present application are set out in the accompanying claims. BRIEF DESCRIPTION OF DRAWINGS

[0026] The application will now be described with reference to the accompanying drawings (not drawn to scale) in which:

[0027] Figure 1 shows schematically a perspective view of the underside of a known tension frame;

[0028] Figure 2 shows schematically a perspective view of a known printing screen;

[0029] Figure 3 shows schematically a cross-section of a beam of the tension frame of Figure 1 in engagement with a printing screen;

[0030] Figures 4A-4J Figure 4 shows a perspective view of a loading sequence using a tension frame according to an embodiment of the application;

[0031] Figure 5 Figure 5 shows schematically a top perspective view of a tension frame according to an embodiment of the application;

[0032] Figure 6 Figure 6 shows schematically a perspective view of a tension frame according to an embodiment of the application in a partially loaded configuration and a loaded configuration; Figure 5

[0033] Figure 7 Figure 8 Figure 7 shows schematically a perspective view of a tension frame according to an embodiment of the application in a loaded configuration; Figure 5

[0034] Figure 9 Figure 8 shows schematically a perspective view of a loaded tension frame according to an embodiment of the application; Figure 8

[0035] Figure 10 Figure 9 shows schematically a cross-sectional view of a beam 30C taken along line B-B of Figure 8; Figure 5

[0036] Figure 11 Figure 10 shows schematically a cross-sectional view of a beam 30D;

[0037] Figure 12 Figure 11 shows schematically a cross-sectional view of a beam 30C taken along line C-C of Figure 8; Figure 5

[0038] Figure 13 Figure 12 shows schematically a cross-sectional view of a portion of a beam 30C;

[0039] Figures 14-16 Figure 13 shows schematically a side view of a beam 30C during a blade lowering motion;

[0040] Figure 17A Figure 14 shows schematically a top plan cross-sectional view and a side view of a tension frame according to an embodiment of the application; Figure 17B ​​​​​​​

[0041] Figure 18A and Figure 18B schematically illustrates a top plan view and a side view of the tensioning frame;

[0042] Figure 19 schematically illustrates a pneumatic control arrangement;

[0043] Figures 20-23 schematically illustrates cross-sectional views of the beam 30C at various stages of a printing screen loading sequence;

[0044] Figures 24-27 schematically illustrates cross-sectional views of the beam 30C at various stages of a printing screen unloading sequence; and

[0045] Figure 28 schematically illustrates a perspective view of a tensioning frame according to a further embodiment of the application.

[0046] BRIEF DESCRIPTION OF DRAWINGS:

[0047] 1 - Tensioning frame

[0048] 2A to 2D - Beam

[0049] 3 - Printing screen

[0050] 4 - Corner piece

[0051] 5 - Engagement surface

[0052] 6 - Passage opening

[0053] 7 - Engagement body

[0054] 8 - First arm

[0055] 9 - Spring

[0056] 10 - Second arm

[0057] 11 - Pneumatically inflatable conduit

[0058] 12 - Third arm

[0059] 13 - Pneumatic port

[0060] 14 - Spindle

[0061] 15 - Foil / screen

[0062] 16 - Hem

[0063] 17 - Protrusion

[0064] 18 - Abutment surface

[0065] 20 - Autonomous intelligent vehicle (AIV)

[0066] 21 - printing press

[0067] 22 - tension frame

[0068] 23, 24, 24A - printing screen

[0069] 25 - printing space

[0070] 26 - hatchway

[0071] 27 - clamping rail

[0072] 28 - empty slot

[0073] 30A to 30D - beam

[0074] 31A to 31D - corner block

[0075] 32 - opening

[0076] 33 - blade

[0077] 34 - strip

[0078] 35 - engagement body

[0079] 36 - bridge

[0080] 37 - beam body

[0081] 38 - beam cover

[0082] 39 - engagement arm

[0083] 40 - pivot

[0084] 41 - torsion spring

[0085] 42 - compression spring

[0086] 43 - line

[0087] 44 - profiled edge

[0088] 45 - profiled section

[0089] 46 - leaf spring

[0090] 47 - engagement surface

[0091] 48 - abutment surface

[0092] 49 - motion conversion mechanism

[0093] 50 - gap

[0094] 51 - plate

[0095] 52 - drive pin

[0096] 53 - rotor

[0097] 54 - slot

[0098] 55 - first actuation member

[0099] 56 - second actuation member

[0100] 57 - hole

[0101] 58, 59 - pivot pin

[0102] 60 - aperture

[0103] 61, 62 - actuator aperture

[0104] 63 - locking pin

[0105] 64 - locking spring

[0106] 65 - first pneumatic port

[0107] 66A to 66D - pneumatic line

[0108] 67 - connection location

[0109] 68 - pneumatic line

[0110] 69 - pneumatic logic network

[0111] 70 - male protrusion

[0112] 71 - inclined surface

[0113] 80 - tensioning frame

[0114] 81A to 81D - beam

[0115] 161 - corner cover

[0116] 82 - second pneumatic port

[0117] 83 - coupling

[0118] 84 - piston

[0119] 85 - pneumatic source

[0120] 86 - control device

[0121] 87 - printer

[0122] 88 - transport mechanism

[0123] A - loading direction

[0124] R - rotation axis DETAILED DESCRIPTION

[0125] A. Exemplary loading and unloading of a printing press

[0126] Before describing the configuration of the tensioning frame according to the present application, reference will be made to Figures 4A-4J Describing an embodiment according to the present application, a printing press provides an exemplary loading / unloading sequence of a printing screen, Figures 4A-4J New functions achievable by such a tensioning frame are shown.

[0127] In Figure 4A , an autonomous intelligent vehicle (AIV) 20 approaches a printing press 21. The AIV 20 has storage means for carrying one or more tensioning frames, each of which can be selectively loaded with a printing screen, such as the printing screen shown in Fig. 2, which tensioning frame can comprise a tensioning frame according to the present application and described in more detail hereinafter, or another type of tensioning frame, such as the known VectorGuard frame previously described with reference to Figs. 1-3. In the specific example shown, the AIV 20 shown is loaded with a tensioning frame 22 according to the present application, which tensioning frame 22 is in this embodiment pre-loaded with a printing screen 23. Further, the AIV 20 is provided with a printing screen storage magazine for storing at least one printing screen. As shown, the AIV 20 carries four printing screens 24, which are not loaded into a tensioning frame. In addition, the AIV 20 further comprises a transfer mechanism, generally shown at 88, for transferring a printing screen 24 from the printing screen storage magazine laterally into a tensioning frame. The transfer mechanism can for example comprise a movable arm or tray which is able to push a printing screen laterally between its storage means and a tensioning frame. The AIV 20 is operable to rearrange or shuffle the tensioning frames and printing screens within its magazine, so that a selected tensioning frame or printing screen can be loaded into or received from the printing press. An AIV having such a shuffling mechanism for planar objects is well known in the art, and its operation need not be described in detail in this embodiment.

[0128] In Figure 4B , the AIV 20 is aligned with the printing press 21. In this position, the AIV 20 is able to load a tensioning frame or a printing screen into the printing press 21 for reception within a printing space 25 of the printing press 21. As shown, a hatch 26 of the printing press 21 is in an open position to provide external access to the printing space 25. It will be appreciated that other printing presses (not shown) can have other ways of providing such access.

[0129] In Figure 4C , the AIV 20 loads the tensioning frame 22, which already contains (for the sake of example only) the printing screen 23, into the printing press 21. The tensioning frame 22 is shown as fully loaded within the printing press 21, in a position in which it is supported by clamping rails 27. At this point, the magazine of the AIV 20 has an empty slot 28.

[0130] In Figure 4D which the printer 21 is loaded and operable after closing the hatch 26. Then, a printing operation can be started in which a workpiece (not shown) is printed using a printing medium through a hole pattern provided in the printing screen 23.

[0131] In Figures 4E-4H which, after completion of the printing operation, the AIV 20 unloads the printing screen 23 from the tensioning frame 22 into a storage slot within the AIV 20. In more detail, in Figure 4E which the AIV 20 is moved into alignment with the printer 21 and the bins of the AIV 20 are disturbed to provide an empty slot at the vertical height of the printing screen 23 within the printer 21. According to the present invention, the printing screen 23 is removed from the tensioning frame 22 through an opening (not explicitly shown) provided in the beam of the tensioning frame, while the tensioning frame 22 remains clamped within the printer 21. In Figure 4F which the printing screen 23 is shown almost completely removed from the tensioning frame 22, while Figure 4G the printing screen 23 is shown received inside the slot of the AIV 20. Then, as Figure 4H indicated, the bins of the AIV 20 are disturbed to move a new printing screen 24A to the same vertical height as the tensioning frame 22 clamped within the printer 21.

[0132] In Figure 41 which the AIV 20 loads the printing screen 24A into the tensioning frame 22 still clamped within the printer 21.

[0133] In Figure 4J which the AIV 20 can move away, with the printer 21 and its tensioning frame 22 fully loaded, and ready for a printing operation after closing the hatch 26.

[0134] To achieve this functionality, in one aspect the present invention provides a robot for loading a printing screen into a tensioning frame, the robot comprising: a printing screen storage bin for storing at least one printing screen; and a transfer mechanism for transferring a printing screen from the printing screen storage bin laterally into the tensioning frame. Such a robot, such as the AIV 20 described above, can comprise a frame storage device for storing a tensioning frame, wherein the transfer mechanism is adapted to transfer the tensioning frame into a printer. Advantageously, the robot can comprise an autonomous intelligent vehicle as shown in Figures 4A-4C and Figures 4E-4J However, in other embodiments such a robot can for example comprise a dedicated robot arm located in the vicinity of a printer having a built-in printing screen storage mechanism and optionally a built-in frame storage device.

[0135] B. Exemplary tension frame structure

[0136] Figure 5 and Figure 6 schematically shows top and bottom perspective views of the tensioning frame 22 in an unloaded state, i.e. without a printing screen accommodated, and a perspective view of a printing screen 3 (only shown in Figure 5 ). The printing screen 3 is shown in this embodiment as a printing screen compatible with the VectorGuard as previously described, having a foil / screen 15 attached at its periphery by a border 16 comprising border corner pieces 161, as is well known in the art. The tensioning frame 22 is sized to accommodate a printing screen 3 of a specific size, which is generally standard in the art. The tensioning frame 22 is shown as having a rectangular shape, defined by four elongated beams 30A-D, each forming one side of the rectangle around the periphery of the tensioning frame 22. Adjacent beams are connected together via corner blocks 31A-D, for example using screws, an interference fit or other known alternatives. Throughout the detailed description, the use of a suffix A-D appended to a reference numeral means that the identified component is associated with a specific beam 30A-D or corner block 31A-D. It can be seen that, by this configuration, the tensioning frame 22 is essentially planar, as shown, extending in an X-Y plane which, in use, corresponds to a horizontal plane. The side of at least one of the beams 30A-D, in this embodiment only beam 30D, is provided with an opening 32, which is sized to permit the accommodation of a printing screen 3 therethrough in a direction parallel to the plane of the tensioning frame 22, as indicated by arrow A. In the embodiment shown, the opening 32 is provided as an open-sided recess formed in the beam 30D and adjacent corner blocks 31C, 31D. However, in alternative embodiments, the opening 32 can be closed on all sides, such that it takes the form of a slot or “letterbox” within the respective beam and corner blocks, for example by providing an optional strip 34 extending between the underside of the adjacent corner blocks, i.e. 31C and 31D as shown. Each beam 30A-D also comprises a blade 33, which is arranged adjacent to the inner side of the respective beam, i.e. at the side of the beam facing the inner region of the tensioning frame 22, in which, in use, the central region of the printing screen 3 is located (see Figure 8 ). As described in more detail below, each blade 33 is movable relative to its respective beam 30A-D along a range of travel in a direction perpendicular to the plane of the tensioning frame 22, i.e. along a vertical or Z-axis as shown. In accordance with Figure 6As can be seen, each beam 30A-D also comprises a plurality of engagement bodies 35, which are arranged linearly along the length of the respective beam. The plurality of engagement bodies 35 are spaced apart by bridges 36, as described in more detail below.

[0137] Figure 7 and Figure 8 a top perspective view of the tensioning frame 22 is schematically shown in a partially loaded configuration and a loaded configuration. Figure 5 a top perspective view of the tensioning frame 22 is schematically shown in a partially loaded configuration and a loaded configuration. Figure 7 a printed screen 3 is shown extending through the opening 36 during loading thereof in the direction A, whereas Figure 8 a printed screen 3 is shown fully received within the tensioning frame 22. From this figure, it can be seen that when the printed screen 3 is loaded in the tensioning frame 22, the printed screen 3 does not protrude beyond the coverage of the tensioning frame 22.

[0138] Figure 9 a bottom side of the loaded tensioning frame is schematically shown. Figure 8 a bottom side of the loaded tensioning frame is schematically shown.

[0139] Figure 10 a bottom side of the loaded tensioning frame is schematically shown. Figure 5Figure 4 is a cross-sectional view of beam 30C taken along line B-B. Like the other beams 30A, 30B, 30D, beam 30C has a two-piece construction that includes a main beam body 37 rigidly connected to a beam cover 38. Each of these parts can be formed of extruded metal such as steel, aluminum, or the like and connected together by screws, interference fit, or the like. Formed in the gap between beam body 37 and beam cover 38 is a void 50 that accommodates a motion conversion mechanism 49 for driving blade 33 as described in greater detail below. Beam body 37 is formed as a hollow channel that extends the length of beam 30C with the bottom of the beam body 37 having an open side or aperture 60. Within the channel is located an engagement body 35 that is sized so that engagement body 35 moves laterally within beam body 37 relative to beam 30C (i.e., along the horizontal X-axis and along a range of travel within a plane that is perpendicular to the length of beam 30C) so that engagement body 35 acts like a shuttle or piston. An end of an actuator (in this embodiment in the form of a pneumatic inflatable tube 43) adjacent the lateral outer edge of beam 30C is operatively connected to engagement body 35. Tube 43 extends the length of beam 30C and is pneumatically connected to adjacent corner blocks 31B, 31C. In fact, tube 43 need not be fixedly connected to engagement body 35 but can simply be positioned alongside the engagement body 35 so that tube 43 is in contact with the engagement body 35 over at least some of the range of travel of the engagement body 35 as described in greater detail below. The other end of engagement body 35 is operatively connected to a biasing device such as a compression spring 42 that biases engagement body 35 laterally outward (i.e., in the positive X-direction as shown toward tube 43). Compression spring 42 is also located within the channel of beam body 37. Engagement body 35 can be formed of a rigid material such as steel, aluminum, carbon fiber, or rigid plastic. A lower side of engagement arm 39 is movably mounted to engagement body 35 so that engagement arm 39 is movable relative to engagement body 35. In the illustrated embodiment, engagement arm 39 is pivotably mounted to engagement body 35 via a pivot 40 so that, as shown, engagement arm 39 can rotate relative to engagement body 35 about a pivot or Y-axis that is parallel to the length of beam 30C. Engagement arm 39 is biased toward an extended position in which it projects downward through the channel opening by a biasing device that in the illustrated embodiment comprises a torsion spring 41. The position of engagement arm 39 relative to engagement body 35 is controlled using a profiled edge 44 of beam 30C that in this embodiment is provided on the underside of beam cover 38 and takes the form of an inclined surface. If engagement body 35 is driven toward beam cover 37 (i.e., in the negative X-direction as shown), engagement arm 39 comes into contact with profiled edge 44 and rotates clockwise to a retracted position as shown. Engagement arm 39 carries an engagement surface 47 for engaging a printing screen when in use as described in greater detail below. As Figure 10As shown, the conduit 43 is fully inflated to maximize the drive of the engagement body 35 in the negative X direction. Against the bias of the torsion spring 41, the engagement arm 39 is fully moved into its retracted position by contact with the profiled edge 44, and in this retracted position the engagement arm 39 does not protrude through the hole 60 below the channel or beam cover 38. In this retracted position, a printing screen can be inserted into the tension frame 22 without risk of collision between the printing screen and the engagement arm 39. The underside of the beam 30C includes a profiled section 45, which in this case is formed as a protrusion extending outwardly in the negative X direction as shown. In this embodiment, a conformal surface including a leaf spring 46 is also provided adjacent to this profiled section 45, extending downwardly from the beam body 37. In use, this profiled section 45 and leaf spring 46 act to contact the hem of a printing screen, thereby helping to support the printing screen and ensure that the printing screen is centered within the tension frame 22, as described in more detail below.

[0140] In an alternative embodiment (not shown), the engagement arm 39 can be in translational motion relative to the engagement body 35, for example, slidable relative to the engagement body 35, for example, loosely held within a slot provided in the engagement body 35. In this case, the engagement arm 39 can be biased towards an extended position in which it protrudes downwardly through the channel hole 60 by an optional biasing means such as a compression spring. In this embodiment, the profiled edge 44 can act as a cam for lifting the engagement arm 39 upwardly relative to the engagement body 35 and into a retracted position, such cam mechanisms being readily understood per se.

[0141] It should be noted that the construction of the beams 30A, 30B is the same as that of the illustrated beam 30C. However, the construction of the beam 30D including the opening 36 is slightly different, and Figure 11 A corresponding cross-sectional view is shown schematically in Fig. 3B. In this figure, it can be seen that the beam 30D is narrower, with the lower surface of the beam body 37 being at the same level as the bottom of the channel, and unlike the beams 30A to 30C, there is neither a profiled section 45 nor a leaf spring 46. With this construction, there is no obstruction to the insertion of a printing screen through the opening 36 in the direction A (positive Y direction as shown).

[0142] Figure 12 A corresponding cross-sectional view is shown schematically in Fig. 3B. In this figure, it can be seen that the beam 30D is narrower, with the lower surface of the beam body 37 being at the same level as the bottom of the channel, and unlike the beams 30A to 30C, there is neither a profiled section 45 nor a leaf spring 46. With this construction, there is no obstruction to the insertion of a printing screen through the opening 36 in the direction A (positive Y direction as shown). Figure 5Figure 6 is a cross-sectional view of the beam 30C taken along the line C-C. This section coincides with the location of the bridge 36 between the two adjacent joint bodies 35 located in the middle. The bridge 36 is itself a protrusion of the beam cap 38. A plate 51 is inserted into the channel, the plate being planar and extending parallel to the X-Z plane, perpendicular to the length of the beam 30C. The plate is located between the adjacent joint bodies 35 and can act as a bearing between them. The bridge 36 and the plate 51 provide additional structural stiffness to the beam 30C and in particular help to prevent deformation of the channel or torsional deformation of the beam 30C. The plate 51 comprises a recess 52 which accommodates the pipe 43. It should be noted that the use of such a reinforcing bridge is further described in International Patent Application No. PCT / IB2020 / 057581.

[0143] Reference is now made to Figures 13-16 The operation of the blade 33 is described, wherein, Figure 13 A cross-sectional view of a portion of the beam 30C is shown schematically, while Figures 14-16 Sequential side views of the beam 30C during the blade lowering motion are shown schematically. First, reference is made to Figure 13for clarity, most of the beam 30C is hidden and only the details of the blade 33 and its associated motion conversion mechanism 49 are shown. The term "motion conversion" refers to the fact that the mechanism operates to convert motion in a first direction to motion in another, different direction. In fact, the motion conversion mechanism 49 described in the present embodiment converts linear motion along the length of the beam 30C to rotational motion, which is then converted to linear motion of the blade 33 in the vertical or Z-axis direction. The blade 33 shown in the present embodiment is in a working position in which the blade 33 is fully lowered relative to the beam 30C so that the blade 33 is in contact with the upper surface of the foil / screen 15 of the printing screen 3. The blade 33 is connected to a rotor 53 located within a void 50 by means of a drive pin 52. The drive pin 52 extends through a vertical slot 54 formed in the beam cover 38, thereby forming a slotted link mechanism, as described in more detail below. The rotor 53 shown takes the form of a planar disc which extends in a plane parallel to the blade 33 (i.e. the Y-Z plane shown) and is mounted to the beam body 37 so as to rotate about a rotation axis R which extends parallel to the X-axis (as shown). In use, the rotor 53 is rotated by means of first and second actuation members 55, 56 which engage opposite edges of the rotor 53. Each of the first and second actuation members 55, 56 comprises a drive rod which is linearly drivable along the length of the beam 30C (i.e. parallel to the Y-axis as shown) and is pivotably connected to the rotor 53. In more detail, the first actuation member 55 is pneumatically drivable along the length of the beam 30C, whilst the second actuation member 56 is mechanically connected to the first actuation member 55, for example via a parallelogram linkage (not shown). In this way, the first and second actuation members can be driven in opposite directions, which in turn causes the rotor 53 to rotate about the rotation axis R. The drive pin 52 is fixedly connected to the blade 33, for example via a screw thread, but loosely held within an oblong hole 57 (best seen in Figure 14 Figure 3) formed in the rotor 53. Figure 13Also shown is a locking mechanism, in this embodiment a locking pin 63 mounted between the beam cover 38 and the blade 33, which is operable to lock the blade 33 in the illustrated working position. As shown, the locking pin 63 passes through an opening in the beam cover 38 and is in contact with the rotor 53. By profiling the side of the rotor to form a cam surface, the locking pin 63 can then be moved into locking engagement with the blade 33 parallel to the illustrated X axis when the rotor 53 is in a predetermined rotational state. A locking spring 64, in this embodiment a compression spring, is arranged to bias the locking pin 63 to the right (i.e. in the positive X direction as illustrated), which will ensure that the locking pin disengages from the blade 33 when the direction of rotation of the rotor 53 is reversed. In practice, more than one locking mechanism can be required along the length of each beam 30A to 30D, depending on the size of the tension frame 22 for example.

[0144] In Figures 14-16 The blade 33 is shown partially transparent in order to make the position of the rotor 53 and the first and second actuating members 55 and 56 visible. Figure 14 The blade 33 is shown in its withdrawn position, in which it is in its vertically highest position so that it is spaced from the printing screen when in use. In this position, the drive pin 52 is at the top of the slot 54. The first actuating member 55, which is connected to the rotor 53 via a pivot pin 58 located within an oval actuator hole 61 of the rotor 53, is biased to the right, while the second actuating member 56, which is connected to the rotor 53 via a pivot pin 59 located within an oval actuator hole 62 of the rotor 53, is biased to the left.

[0145] Figure 15 An intermediate stage is shown in which the blade 33 is being driven downwards. The first actuating member 55 has been driven to the left, while the second actuating member 56 has been driven to the right, so that the rotor 53 is rotated anticlockwise as illustrated. As a result, the drive pin 52 and hence the blade 33 are moved downwards relative to the slot 54.

[0146] Figure 16 A final stage is shown in which the blade 33 is being driven downwards to its working position. The first actuating member 55 has been driven fully to the left, while the second actuating member 56 has been driven fully to the right, so that the rotor 53 is rotated anticlockwise further as illustrated. As a result, the drive pin 52 is moved down to the bottom of the slot 54, and the blade 33 is correspondingly moved to its lowest extent. Although Figure 16 Not shown in this figure, but in this position the locking pin 63 is engaged so that the blade 33 cannot be raised by applying an upwards force to the blade 33, but only by reversing the rotation of the rotor 53 by driving the first and second actuating members 55 and 56 in opposite directions (i.e. left and right respectively).

[0147] As mentioned above, the tubes 43 as well as the first and second actuation members 55, 56 are pneumatically operated. For this purpose, pneumatic ports have to be provided at the tension frame 22 and at the associated pneumatic paths through the tension frame 22.

[0148] Figure 17A and Figure 17B The pneumatic path arrangement for operating the tubes 43 is schematically shown. In more detail, Figure 17A and Figure 17B respectively a planar and a side view of the tension frame 22 are schematically shown, omitting features not relevant for the arrangement for the sake of clarity. The corner blocks 31A-D comprise convex protrusions 70 which are received within the respective adjacent beams 30A-D. The first pneumatic port 65 is provided on the corner block 31B for connection to an external pneumatic source (not shown). The first pneumatic port is directly connected to the pneumatic lines 66B, 66C leading to the beams 30B and 30C, respectively, which in turn are connected to the pneumatic lines 66A, 66D leading to the beams 30A and 30D, respectively. These pneumatic lines 66A-D are connected to form a closed loop which extends through all beams 30A-D and corner blocks 31A-D of the tension frame 22. The pneumatic lines 66A-D are connected to the tubes 43 at the connection locations 67. Thus, when a pneumatic pressure is applied via the first pneumatic port 65, the tubes 43 of each beam expand in unison. When the pneumatic supply is switched off, each tube 43 is retracted by the action of the respective compression spring 42.

[0149] Figure 18A and Figure 18B The pneumatic path arrangement for operating the blades 33 is schematically shown. Figure 18A and Figure 18BA plan view and a side view of the tensioning frame 22 are shown schematically, with features unrelated to the arrangement omitted for clarity. The corner block 31B is provided with a second pneumatic port 82 for connection to an external pneumatic source (not shown). This second pneumatic port is connected directly to a pneumatic line 68 via the intermediate corner blocks 31B, 31A, 31D, which extends around a substantial portion of the tensioning frame 22 (i.e. through the beams 30B, 30A and 30D). Each corner block 31A to 31D includes a union 83 which pneumatically connects the pneumatic line 68 to a respective piston 84 which is linearly movable parallel to the length of the adjacent beam 30A to 30D. Each piston 84 provides mechanical actuation to a respective first actuation member 55 to reversibly drive the respective first actuation member 55 along the length of its respective beam 30A to 30D within the void 50. When pneumatic pressure is applied via the second pneumatic port 82, each piston 84 of each beam is driven together. Similarly, when negative pressure or vacuum is applied via the second pneumatic port 82, each piston 84 of each beam is driven together in the opposite direction back. If the pneumatic supply to the second pneumatic port 82 is cut at any time, the first and second actuation members 55, 56 will remain in their current position, and if this current position is a position in which the blade 33 is lowered to its working position, this is assisted by the locking mechanism. In this way, the tensioning frame 22 can be held in a loaded state in which the blade 33 is lowered to its working position without the need to apply pneumatic pressure.

[0150] In an alternative embodiment (not shown), the pneumatic line 68 can form a closed loop around the entire tensioning frame 22 via the respective intermediate corner blocks 31A to 31D (i.e. the closed loop extends through all of the beams 30A to 30D). Alternatively or additionally, both the first and second actuation members can be pneumatically driven, for example with an additional piston at each corner block for driving the second actuation member and associated pneumatic line to drive both the first and second actuation members.

[0151] Figure 19An exemplary pneumatic control arrangement for the tensioning frame 22 is schematically shown. As shown, in use, the first pneumatic port 65 and the second pneumatic port 82 are pneumatically supplied by a pneumatic source 85 via a pneumatic logic network 69. The pneumatic logic network 69 is used to control the pneumatic flow through each of the pneumatic lines and paths 66A to 66D, 68. As described below, the pneumatic logic enables the sequencing of the two pneumatic flows to operate the tensioning frame 22 during the loading and unloading sequence of the printing screen. Additionally, advantageously, the operation of the pneumatic source 85 can be controlled by a control device 86 such as a computer, processor, etc. Advantageously, the pneumatic logic network 69, the pneumatic source 85, and the control device 86 can all be located within a printing press, typically shown as 87, to enable in-situ operation. In this case, the control device 86 can also control some or all of the printing operations of the printing press 87. Dedicated pneumatic lines for connection to each of the first pneumatic port 65 and the second pneumatic port 82 may be located within the printing press 87 and arranged to align with the tension frame 22 when loaded into the printing position within the printing press 87. If the loading operation is performed outside the printing press, the operator may, for example, directly connect and operate the pneumatic logic network and / or the pneumatic source.

[0152] In an alternative embodiment, at least a portion of the pneumatic logic network may be disposed inside the tension frame 22.

[0153] C. Exemplary loading sequence

[0154] Now refer to Figures 20-23 An exemplary loading sequence for loading the printing screen 3 into the tensioning frame 22 according to the invention is described, in conjunction with... Figure 10 Similarly, each accompanying figure schematically shows along Figure 5 The sectional view of beam 30C taken from line BB.

[0155] a) such as Figure 20 As shown, the loading sequence begins with the tension frame 22 in the pre-loaded position. In this pre-loaded position, the blade 33 is raised to its retracted position, and the conduit 43 expands in response to the bias of the compression spring, causing the engagement body 35 to move to its leftmost position as shown (i.e., towards the inner region of the tension frame 22). In this position, in response to the bias of the torsion spring 41, the profiled edge 44 pushes the engagement arm 39 into its retracted position. Through the tension frame 22 in this position, the printing screen 3 passes through the opening 32 (… Figure 20 (Not visible in the middle) Lateral insertion. For this step, the associated pneumatic supply to the tensioning frame 22 controlled by the pneumatic logic network 69 can be summarized as follows:

[0156] Pneumatic supply to first pneumatic port 65: Open

[0157] Pneumatic supply to second pneumatic port 82: closed

[0158] b) As shown, the blade 33 is lowered to its working position in which its abutment surface 48 is in contact with the foil / screen 15 of the printing screen 3. Although not visible in this figure, the locking mechanism is engaged to lock the blade 33 in this working position. For this step, the associated pneumatic supply to the tensioning frame 22 controlled by the pneumatic logic network 69 can be summarized as follows: Figure 21

[0159] Pneumatic supply to first pneumatic port 65: open

[0160] Pneumatic supply to second pneumatic port 82: open (positive pressure)

[0161] c) As shown, the conduit 43 starts to contract to push the compression spring 42 to the right, thus the engagement arm 39 starts to move towards its extended position. For this step, the associated pneumatic supply to the tensioning frame 22 controlled by the pneumatic logic network 69 can be summarized as follows: Figure 22

[0162] Pneumatic supply to first pneumatic port 65: closed

[0163] Pneumatic supply to second pneumatic port 82: closed

[0164] d) As shown, the conduit 43 is fully contracted to push the engagement body 35 fully to the right, thus enabling the engagement arm 39 to move to its extended position so that its abutment surface 47 is in contact with the inclined surface 71 of the border 16. The complementary angles of the abutment surface 47 and the inclined surface 71 ensure the engagement of the printing screen 3 with the tensioning frame 22. The border 16 is pushed to be in full contact with the leaf spring 46 of the profiled section 45 which is used to protrude the border 16 upwards. The printing screen 3 is now fully engaged and tensioned so that the printing operation can be performed. For this step, the associated pneumatic supply to the tensioning frame 22 controlled by the pneumatic logic network 69 can be summarized as follows: Figure 23

[0165] Pneumatic supply to first pneumatic port 65: closed

[0166] Pneumatic supply to second pneumatic port 82: closed

[0167] From the above, it should be understood that the printing screen 3 remains loaded and tensioned in the tensioning frame 22 without the need to maintain the pneumatic pressure of the tensioning frame 22. Thus, the loaded tensioning frame 22 can be easily stored, transported or loaded into a printing machine as needed.

[0168] ​​​It should be noted that, as mentioned above, although the tensioning frame 22 can be mounted from the side, this is not mandatory, and optionally, the printing screen 3 can be mounted in a manner similar to that of the existing VectorGuard type tensioning frame, that is, by placing the printing screen 3 on the underside of the tensioning frame 22 while simultaneously... Figure 20 The state shown is then followed by performing the same loading steps b) to d) as previously described, followed by flipping the loaded tension frame to achieve the state shown. Figure 23 The steps for the working orientation are shown. Alternatively, the printing screen can be placed on the surface, and then the tensioning frame can be placed on top of the printing screen 3, while in the working orientation, i.e., as shown... Figure 20 As shown, loading steps b) to d) are then performed in the same manner as the previously set loading steps. Conformal surfaces can facilitate these loading methods; for example, the shape of the leaf spring 46 assists in centering the printed screen when loaded in these ways. Those skilled in the art will also recognize that providing a connecting arm 39 movably mounted to the corresponding connecting body 35 facilitates these loading methods; since the printed screen 3 is inserted while the connecting body 35 is moved to its leftmost position by the expansion of the conduit 43, and in this position the connecting arm 39 is in its retracted position, it is ensured that the connecting arm 39 retracts during the loading of the printed screen 3. Therefore, any risk of the connecting arm getting stuck or being mispositioned relative to the printed screen binding 16 is eliminated. This benefit can be achieved in embodiments where no openings are provided on the sides of the tension frame to allow for lateral loading of the printed screen 3.

[0169] For end users, the ability to load the tension frame 22 in any of these ways greatly increases flexibility, for example, if the end user does not have permission to use the loading robot or AIV.

[0170] D. Exemplary unloading sequence

[0171] Now for reference Figures 24-27 An exemplary unloading sequence for unloading the printing screen 3 from the tension frame 22 according to the invention is described, in conjunction with... Figure 10 Similarly, each accompanying figure schematically shows along Figure 5 The sectional view of beam 30C taken from line BB.

[0172] e) such as Figure 24 As shown, while the engaging arm 39 continues to tension the printing screen 3, the locking mechanism (not shown) disengages and the blade 33 rises toward its retracted position. For this step, the associated pneumatic supply to the tensioning frame 22 controlled by the pneumatic logic network 69 can be summarized as follows:

[0173] Pneumatic supply to first pneumatic port 65: Off

[0174] Pneumatic supply to second pneumatic port 82: open (negative pressure)

[0175] f) As shown, the blade 33 is fully raised to its withdrawn position and the conduit 43 starts to expand, overcoming the bias of the compression spring 42, moving the engagement body 35 to the left. The engagement surface 47 is out of contact with the inclined surface 71, releasing the tension in the printing screen 3. For this step, the associated pneumatic supplies to the tensioning frame 22 controlled by the pneumatic logic network 69 can be summarized as follows: Figure 25

[0176] Pneumatic supply to first pneumatic port 65: open

[0177] Pneumatic supply to second pneumatic port 82: open (negative pressure)

[0178] g) As shown, the conduit 43 is almost fully expanded, the engagement body 35 is almost completely pushed to the left, and the engagement arm 39 starts to rotate towards its retracted position due to its action with the profiled edge 44. For this step, the associated pneumatic supplies to the tensioning frame 22 controlled by the pneumatic logic network 69 can be summarized as follows: Figure 26

[0179] Pneumatic supply to first pneumatic port 65: open

[0180] Pneumatic supply to second pneumatic port 82: closed

[0181] h) As shown, the conduit 43 is fully expanded, the engagement body 35 is completely pushed to the left, and the engagement arm 39 is completely in its retracted position. The printing screen 3 can now be removed via the opening 32. For this step, the associated pneumatic supplies to the tensioning frame 22 controlled by the pneumatic logic network 69 can be summarized as follows: Figure 27

[0182] Pneumatic supply to first pneumatic port 65: open

[0183] Pneumatic supply to second pneumatic port 82: closed

[0184] Figure 28 ​​​A perspective view of a tensioning frame 80 with partially offloaded printing screens 3 according to a further embodiment of the application is shown schematically. Similar to the previous embodiment, the tensioning frame 80 comprises four beams 81A to 81D, with beam 80D having an opening to permit the printing screens 3 to be loaded or unloaded through the opening. However, in this embodiment, a second opening is provided in beam 81B, so that the printing screens 3 can alternatively be loaded or unloaded through this second opening. This type of tensioning frame can permit the printing screens 3 to be loaded into the tensioning frame from a first side of the printing press using a robot such as an AIV, while the tensioning frame is in the printing press, and then unloaded from the tensioning frame 80 by a robot such as an AIV from an opposite side of the printing press. This type of arrangement can improve the speed of changeover of the printing screens, since a new printing screen can be loaded immediately after unloading of the previous printing screen. In addition, since the loading AIV only handles clean printing screens, it can remain clean, while the unloading AIV can remain as a dirty AIV or a handling AIV, handling only used printing screens.

[0185] The above-described embodiments are merely exemplary and other possibilities and alternatives within the scope of the application will be apparent to those skilled in the art.

[0186] For example, while the above-described embodiments use an AIV to load and unload the printing screens, other forms of robot such as a fixed robot arm can also be used.

[0187] In the above-described embodiments, the locking mechanism comprises a locking pin which is driven directly into engagement and out of engagement with the blade 33 by the cam surface of the rotor 53. However, the locking mechanism can be implemented in several different ways, as will be appreciated by those skilled in the art, such as using a dedicated actuation mechanism to move the locking pin 63 into locking engagement with the blade 33, or by using a spring-loaded bearing, etc. As a further alternative, the locking mechanism can comprise a latching mechanism. With this arrangement, as will be appreciated by those skilled in the art, rotation of the rotor 53 in the first rotational direction through a certain angle of rotation causes the locking mechanism to latch into the locked position. To unlock the locking mechanism, the rotor 53 is then driven in the same (i.e. first) rotational direction through a small angle, causing the locking mechanism to unlatch, thus allowing the blade 33 to be raised to its withdrawn position when the rotor 53 is subsequently rotated in the opposite rotational direction.

[0188] With this latching mechanism, the alternative drive arrangement of the first and second actuation members 55 and 56 and the rotor 53 can be used. In particular, the above shown embodiment uses a simple piston 84 that is driven back by selectively applying positive and negative pneumatic pressure to the second pneumatic port 82 and the first and second actuation members 55 and 56. However, if a latching locking mechanism is employed, the simple piston 84 can be replaced by a spring return piston that only needs to be driven from its original position (in which the blade 33 is in its retracted position) by applying positive pneumatic pressure to the second pneumatic port 82 to drive the spring return piston and the first and second actuation members 55 and 56 and the rotor 53 to achieve latching and unlatching. Once unlatched, the pneumatic logic network 69 can switch the pneumatic supply to off, allowing the spring return to return the piston, the first and second actuation members 55 and 56 and the rotor 53 to their original position.

[0189] In the above described embodiments, the actuator for moving the engagement body as well as the first and second actuation members are all pneumatic, other forms of actuation can equally be used, in particular electrical actuation using an electric actuator such as a rotary or linear electric motor can be used for one or both of the two components. If electrical actuation is used, the previously described pneumatic logic can be replaced by suitably programmed electronic logic as is known per se in the art.

[0190] Further, if pneumatic actuation is used for moving the engagement body, other pneumatic actuators such as pneumatic pistons or cylinders can be used.

[0191] Although the above described motion conversion mechanism uses a slotted link mechanism, other forms of motion conversion mechanisms can equally be used such as for example a Geneva or Swiss mechanism. A mechanically simple variant can use a rack and pinion mechanism in which the rack replaces the actuation members that move linearly along the length of each beam and the pinion replaces the above described rotor.

[0192] While the tensioning frame described herein has been illustrated with respect to the loading of a known VectorGuard type printing screen, the tensioning frame according to the present application can equally be used with or readily adapted for use with other printing screens including a border profile or structure arranged to interact with the engagement mechanism.

Claims

1. A tensioning frame for tensioning a printing screen, the tensioning frame comprising a plurality of elongate beams extending around a periphery of the tensioning frame and defining the tensioning frame, the tensioning frame being substantially planar, wherein, At least one of the beams includes an opening sized to permit receipt of a printing screen therethrough; Each beam includes a blade movable relative to the beam along a range of travel in a direction normal to the plane of the tensioning frame between a retracted position in which the blade is spaced from the printing screen in use and a working position in which the blade is in contact with the printing screen in use. The opening is sized to receive the printing screen therethrough in a direction parallel to the plane of the tensioning frame.

2. The tensioning frame of claim 1, wherein, Each beam includes:

3. The tensioning frame of claim 1, wherein, a joining body at least partially located within the beam, the joining body carrying an engagement surface for engagement with a printing screen in use, the joining body being movable relative to the beam along a range of travel in a plane normal to the length of the beam; and an actuator operatively connected to the joining body for moving the joining body and the engagement surface relative to the beam. The actuator includes one of a pneumatic actuator, a pneumatic piston and an electric actuator.

4. The tensioning frame of claim 3, wherein, The plurality of beams define an interior region of the tensioning frame, a central region of a printing screen being located in the interior region in use, and the actuator is operable to move the joining body in a direction towards the interior region.

5. The tensioning frame of claim 3, wherein, 6. The tensioning frame of claim 5, including biasing means for urging the joining body in a direction away from the interior region. Each engagement surface is formed on a respective engagement arm, the engagement arm being movably mounted to the respective joining body, the engagement arm being movable relative to the joining body between a retracted position which permits full insertion of a printing screen into the tensioning frame in use and an extended position in which the engagement surface is contactable with a printing screen in use.

7. The tensioning frame of claim 3, wherein, The engagement arm is pivotably or slidably mounted to the respective joining body.

8. The tensioning frame of claim 7, wherein, The engagement arm is biased to the extended position.

9. The tensioning frame of claim 7, wherein, Each beam includes a profiled section for urging an edge of the printing screen towards the beam in use.

10. The tensioning frame of claim 1, wherein, The profiled section includes a spring.

11. The tensioning frame of claim 10, wherein, Each beam includes:

12. The tensioning frame of claim 1, wherein, a respective actuating member movable along the length of the respective beam, and a respective motion conversion mechanism operable to convert motion of the respective actuating member to motion normal to the plane of the tensioning frame and arranged such that motion of each blade in use is driven by the respective actuating member via the respective motion conversion mechanism. Each respective actuating member is pneumatically or mechanically driven.

13. The tensioning frame of claim 12, wherein, Each respective motion conversion mechanism includes a slotted link mechanism or a Geneva mechanism.

14. The tensioning frame of claim 12, wherein, 15. The tensioning frame of any one of claims 1 to 14, including a lock for locking the blade in the working position. The lock includes a retractable lock pin.

16. The tensioning frame of claim 15, wherein, ​

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