EP0650832B1 - Fabric stretching device - Google Patents

Abstract

In a device (10) for stretching a rectangular gauze material or similar fabric (12) in a printing frame (14), having tensioning devices (16) which are arranged on the sides of said printing frame and in which the fabric is fastened by means of a clamping mouth (18) in each case consisting of clamping jaws (32, 36), which are movable relative to one another and can be positioned one on the other under pressure on the closing path of a closing lever (50), and is subsequently tensioned in the pulling direction by a change in position of the clamping mouth units caused by a piston/cylinder unit for flow medium, a further closing path is disposed after the closing path determined by the closing lever (50), when the clamping jaws (32, 36) are moved together, said further closing path being controlled by a piston rod (72). Additionally, the piston rod (72) is to be part of the piston/cylinder unit for the pulling movement of the tensioning device (16). Assigned to the piston in the cylinder (20) are an open position of the clamping mouth (18) near to the clamping jaws (32, 36), a central position when the clamping jaws are closed, and an adjoining stroke path for the tensioning operation. <IMAGE>

Description

The invention relates to a device for clamping a piece of tissue according to the preamble of claim 1.

Such a device is described in CH-A-679 918 with the note that the production of printed circuit boards in the screen printing process requires a very high accuracy of the piece of fabric used in a screen printing stencil, which is why an extremely uniform clamping of the piece of fabric is required; uneven stress distributions create distortions in the piece of tissue, and stress peaks occurring therein can lead to an undesirable tearing process. According to CH-A-679 918, these disadvantages are to be made possible by a clamping jaw which can be closed by means of a mechanical lever system and which is connected to the free end of a piston rod of the cylinder / piston unit by a universal joint. The mechanical pressing together of an upper jaw by a closing lever on a lower jaw which is fixed in the pressing direction does not allow its individual application with a compressible force, ie it cannot be adapted to the respective circumstances when the piece of tissue is clamped.

Finally, DE-A-36 01 167 discloses an automatic silk tensioning device for tensioning silk on a silk screen printing frame. In a first stretching process, the silk is stretched on four sides using a clamp table and in a second stretching process using stretchers on the clamp table. From the underside of the stapled silk, a pressure frame is lifted onto a lifting table and pressed against the silk. Then an adhesive is applied to the frame and dried artificially. The excess silk surrounding the frame is then cut away, the frame covered with silk is removed and an empty frame is fed.

Knowing this state of the art, the inventor has set himself the goal of improving the device of the type mentioned at the outset while avoiding the identified defects and of making the adaptation of the pressing force on the clamping jaws controllable during the clamping process.

The teaching according to the independent claim leads to solving this problem; the sub-claims describe particularly favorable further training.

According to the invention, when the clamping jaws are brought together, a further closing path is arranged after the first closing path determined by the closing lever; the latter is controlled by a piston rod of the cylinder / piston unit, and the piston rod allows the cylinder to assume a first opening position of the clamping jaw close to the clamping jaws and, after a partial stroke, a middle position with the clamping jaws closed, and a subsequent stroke path on which the clamping process takes place . A piston disk is preferably assigned to the piston rod as a piston.

According to a further preferred feature of the invention, a short-stroke cylinder is provided, by means of which the respective clamping jaw can be arranged below the surface of the printing frame before the piece of tissue is inserted and can be closed after insertion, after which that short-stroke cylinder can be actuated to unlock a slide and the clamping jaw can be actuated above the surface is adjustable. The clamping jaw should also be held in this gripping position until a latching member for the short-stroke cylinder is released, the piston disc being able to be guided into the middle position over the partial stroke length.

The cylinder held at the end by a swivel bearing on the base or base profile is displaceably mounted on the other side in a pipe socket on which the piston rod is fixed with its end remote from the piston. In addition, the piston rod passes through an end plate of the cylinder, wherein the piston rod rests movably in its sealed through bore.

It has proven to be advantageous to link the pipe socket to a guide element and to pivotally connect it to a carriage carrying the clamping jaws; the latter should be mounted on a profile designed as a base element.

The guide element is advantageously a bracket, the legs of which overlap the two side surfaces of the profile and are connected to the slide by an axis of rotation. Parallel to the latter, the slide carries a pivot axis for a hood-like support member of the movable jaw.

It is also within the scope of the developments of the invention that the hood-like support member as a swivel body with parallel side walls - flanking the pipe socket - connects to the swivel axis of the slide and holds the jaw from above with a front edge parallel to the swivel axis. In addition, the hinge point for the pipe socket on the other side of the axis of rotation on the stirrup leg should be opposite a hinge point for a handlebar rod, which is articulated on the other side of its swivel body.

According to a further preferred feature of the invention, a hinge pin is connected as a hinge between the handlebar and swivel body - via a bolt rotatably mounted therein - with a rocker arm, the other end of which offers an elongated hole to a hinge axis of the bracket.

The hinge axis for the swing arm is guided according to the invention by the bracket leg about its hinge point for the handlebar.

The special assignment of the bracket and the swivel body slid over it to the slide, with their axes and the articulation points, creates one for the strand-like connecting elements connecting them - handlebar and swing arm Relative movement of the jaws that can be precisely controlled by mechanics and fluid.

It has proven to be particularly favorable to make the profile guiding the carriage liftable by means of a lifting cylinder which is mounted below the profile adjacent to the printing frame. In addition, a locking member is to be arranged in the vicinity of the lifting cylinder, which engages in the carriage in the front end position holding it. According to the invention, the clamping jaw can also lie in an end position of the slide above a plane determined by the frame.

Fig. 1:

die Draufsicht auf eine Vorrichtung zum Aufspannen von Siebmaterial für das Siebdruckverfahren mit vier Gruppen von Spanneinrichtungen;

Fig. 2:

die gegenüber Fig. 1 vergrößerte Frontansicht einer Spanneinrichtung;

Fig. 3:

die Seitenansicht zu Fig. 2;

Fig. 4:

ein geschlossenes Klemmaul der Spanneinrichtung in gegenüber Fig. 3 vergrößerter Seitenansicht;

Fig. 5:

das Klemmaul der Fig. 4 in geöffneter Stellung;

Fig. 6:

das Klemmaul der Fig. 4, 5 in zwei verschiedenen Stellungen;

Fig. 7:

eine teilweise geschnittene Frontansicht von Teilen der Fig. 4, 5;

Fig. 8:

den Schnitt durch eine Gelenkstelle der Spanneinrichtung;

Fig. 9:

den Schnitt durch einen Teil eines Zylinders der Spanneinrichtung;

Fig. 10:

die teilweise Seitenansicht eines Details der Fig. 4;

Fig. 11:

den gegenüber Fig. 10 verkleinerten Längsschnitt durch den gesamten Zylinder mit unterschiedlichen Positionen einer Kolbenscheibe;

Fig. 12:

ein vergrößertes Detail aus Fig. 1 in geschnitten skizzierter Wiedergabe.

Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments and from the drawing; this shows in

Fig. 1:

the top view of a device for clamping screen material for the screen printing process with four groups of clamping devices;

Fig. 2:

the enlarged front view of Figure 1 of a clamping device.

Fig. 3:

the side view of Fig. 2;

Fig. 4:

a closed clamping mouth of the clamping device in an enlarged side view compared to FIG. 3;

Fig. 5:

the clamping jaw of Figure 4 in the open position.

Fig. 6:

the clamping jaw of Figures 4, 5 in two different positions.

Fig. 7:

a partially sectioned front view of parts of Figures 4, 5;

Fig. 8:

the section through an articulation point of the clamping device;

Fig. 9:

the section through part of a cylinder of the clamping device;

Fig. 10:

the partial side view of a detail of Fig. 4;

Fig. 11:

the reduced compared to Figure 10 longitudinal section through the entire cylinder with different positions of a piston disc.

Fig. 12:

an enlarged detail of Fig. 1 in a cut representation sketched.

A device 10 for clamping a rectangular piece of fabric or a web 12 of preferably gauze-like screen material for use in the screen printing process has - along the four sides of a printing frame 14 - a plurality of clamping elements or tensioning devices 16. These each grip a section of the web 12 in its edge region with a clamping jaw 18 (FIGS. 2, 3) and tension the web 12, which is then fixed all around, by adjusting a pulling cylinder 20 in the pulling direction x. In Fig. 3, the web 12 rests on the surface 13 of the frame 14 and is pulled down from its outer edge to the clamping jaw 18 in its closed position at an angle of approximately 6 °.

In Fig. 1 is at 15 from line 15 _a with max. 10 bar of compressed air-fed control unit, from which three control lines 15 _b to 15 _d originate.

The tensioning device 16 has, on a base rail 22 as a base element, a channel-like wedge profile 24 that opens downwards towards it and has a sliding surface 25 that is inclined at an angle w, over which — above a central longitudinal slot 26 of length a of the wedge profile 24 — a slide 28 can be moved stores. From the end face of the wedge profile 24, a stop tongue 30 rises, between which and the frame 14 runs and an adjustable holding bracket 31 according to FIG. 3, which can be locked by a transverse pin 31a. On the side facing away from the frame 14 of the stop tongue 30, a short-stroke cylinder 27 is attached to the channel-like wedge profile 24, said cylinder being on the base rail 22 supports and which is explained in more detail with respect to FIG. 12.

Transversely to the longitudinal axis M of the clamping device 16, a lower clamping jaw 32, which projects on both sides and is designed as a channel profile, is cast on the slide 28, and a strip 34 made of elastic material is held in the channel space which opens upwards. In an upper jaw 36 there are two parallel elastic round profiles 37 which are also elastic.

4 shows in particular that the upper jaw 36 is a profile strip which is fixed to a downward-pointing pressure edge of a cross-sectionally triple-angled apron 38; the latter is firmly connected to a hood-like swivel body 40 of a U-like cross section, which opens downwards and through which a swivel axis 42 of the slide 28 passes.

On the slide 28, parallel to the swivel axis 42 and at a distance b of about 65 mm from it, an axis of rotation 44 is provided as a guide element - which can be moved within the support member or swivel body 40 - and has legs 47 penetrated by it parallel to it the side surfaces 23 of the spline 24 are movable. A hand or closing lever 50 protrudes from the upper yoke web 48 connecting the bow legs 47 and can be moved in a central longitudinal recess 39 of the apron 38 between the open position of the clamping jaws 32, 36 and their closed position.

At a distance e of 40 mm here, a pipe socket 54 is articulated on the stirrup legs 47 by means of a pair of aligned hinge bolts 52 and can be moved in a longitudinal recess 29 of the slide 28 (FIGS. 5, 6).

According to FIG. 4, a straight line G2 runs through the axis of rotation 44 and a further point of articulation 56 at an angle t of approximately 135 ° to the connecting line G1 of the axis of rotation 44 and the hinge pin 52. - On the leg 47, a two-piece handlebar rod 57 is mounted, which on the outside of the swivel body 40 connects this with a hinge pin 58 at the other end. At 60, a coil spring around an axial telescopic part of the length-adjustable handlebar rod 57 is indicated; the coil spring 60 can be provided at the foot of the handlebar rod 57 (Fig. 1, 5) or near its upper end (Fig. 4, 6).

Approximately in the middle between the axis of rotation 44 and the hinge point 56 - and laterally offset by a dimension n of approximately 18 mm - there is also a hinge pin 62 on the leg 47 of the bracket 46, which bolt moves into an elongated hole 63 within the swivel body 40 Swing arm 64 reaches.

The path of the individual parts 40, 46, 57, 64 from the open position of the clamping jaws 32, 36 indicated by the broken line about the pivot axis 42 and axis of rotation 44 into the closed position can be seen in FIG. 6. The hinge pin 52 generates a circular contour K1 about the axis of rotation 44 on its way, the hinge point 56 a circular contour K2. These paths K1, K2 result in a circular contour K3 as the movement path of the articulation pin 58.

The upper end of the rocker 64 is designed according to FIG. 8 as a round end pin 65, which is encompassed by a helical spring 60, and is rotatably attached to the articulated pin 58 of the handlebar rod 57. This hinge pin 58 is seated in a bearing pin 66 of diameter f of approximately 16 mm, which in turn is surrounded by a sleeve 68 which is welded on the inside to the roof part 38d of the apron 38. This sleeve 68 offers on the downward part of its circumference a guide slot 69 for that end bolt 65. In one embodiment, not shown, an axle eye in the head of the handlebar rod 57 is of a pin-like shape of the bearing pin 66 enforced and connected in this way to the depository.

The pipe socket 54, which is closed at the end with a plate 55 and - as mentioned - attached to the bracket 46 by means of articulated bolts 52, receives the head end of the pull cylinder 20 mentioned at the beginning. In another embodiment, a diametrical yoke rod is provided instead of the end plate 55.

In the end plate 55 of the pipe socket 54 with a diameter d1 of here 58 mm, the threaded end 71 of a piston rod 72 is screwed in the longitudinal axis A of the pipe socket 54 through the central through bore 74 of an end wall 75 of the pull cylinder 20 in its interior 76 - a diameter d2 of 50 mm - protrudes and is connected at its other end to an axially displaceable disk-like piston 78 therein. Sealing O-rings are identified at 79.

The tube wall 80 of the pull cylinder 20 is seated with its end distal to its end wall 75 sealed at an end plug 82 which is articulated at 84 to a rear flange 86 projecting from the base rail 22.

5 is open, the piston disk 78 is in the open position indicated in FIG. 11 at I near the end wall 75 and at a distance of the stroke h from its right-hand end position III in FIG. 11. The stroke h of the piston disk 78 measures approximately 150 mm in the embodiment shown. The angle q described when the piston disk 78 is transferred from the central position II into the opening position I described above from the articulation point 56 is approximately 56 ° (FIG. 6).

The clamping jaw 18 can be opened by manual actuation of the closing or hand lever 50, but is normally carried out pneumatically, in that fluid enters the pull cylinder 20 and acts on the piston disc 78. The piston disc 78 is from any position of the Stroke h moved to the central position II in the open position I.

In this process, the carriage 28 is also brought into the front position and fixed, a locking pin 90 guided in a U-profile 91 being pushed by a spring 60 _a along an inclined surface 92 of a link block 93 into the provided recess 94.

Since the link block 93 - preferably made of plastic - is fixed on the underside of the carriage 28, the latter is held in the described gripping position until the catch pin 90 is released from the catch recess 94. A movable pawl - not shown here - can also serve as the locking element.

When inserting the web 12 into the open jaw 18, the upper edge of the strip 34 made of elastic material is about 2 to 3 mm below the surface 13 of the pressure frame 14. After inserting the web 12, the jaws 32, 36 of the jaw 18 with the Closing or hand lever 50 placed on top of one another and prestressed until the position shown in FIG. 4 is reached. The hinge pins 62 of the pair of the rocker 64 are seated on their respective elongated hole bases and lie behind the associated handlebar rod 57 by the amount n of lateral displacement mentioned.

This prestressing process described can also be carried out pneumatically, in that fluid is applied to the piston disk 78 via the prechamber or the pressure chamber 88 and is pushed from the open position I shown in FIG. 11 into the central position II over a partial stroke length h1 of approximately 50 mm.

Before the actual tensioning process, the short-stroke cylinder 27 fastened to the wedge profile 24 is controlled via a line 97 indicated in FIG. 3 in such a way that the link block 93 is lifted out of the locking position and releases the slide 28 so that it can be guided in the pulling direction x.

The clamping jaw 18 also rises by the stroke of the short-stroke cylinder 27 and holds the web 12 for the tensioning process approximately 8 to 10 mm above the surface 13 of the frame 14 in front. This distance from the frame 14 serves above all to avoid injuries to the web 12 when Clamping process.

For the tensioning process, the pre-chamber 88 delimited by the end wall 75 and the piston disk 78 is acted upon by pneumatic fluid via a line indicated only in FIG. 3 at 95, thereby generating an adaptable pneumatic closing force on the clamping jaw 18, in addition to the mechanical closing force.

The distance i of FIG. 11 relative to the partial stroke length h1 to the full stroke length h determines the possible clamping path of the tensioning device 16 - but usually the full stroke length h is not used at all.

After the tensioning process, the clamping jaw 18 is lowered into the position described for FIG. 3, so that the web 12 rests on the frame 14 for gluing.

In FIG. 11, an indentation on the inner surface of the rear plug 82 of a further exemplary embodiment is merely indicated above the longitudinal axis A at 98. The piston rod nut 73 holding that piston disk 78 is immersed in this recess 98 in the end position III, whereby the stroke length is extended by the depth dimension k of the recess 98.

By introducing fluid into a rear chamber 89 with variable volume between the piston disk 78 and the end plug 82 via a further line 96 (FIG. 3), the piston disk 78 can be pressed against the pulling direction x in addition to the mechanical return, in order to clamp the jaw 18 to open.

Claims (14)

1. Device for stretching a piece of fabric (12), in particular a rectangular gauze material, on a print frame (14) with stretching means arranged at the sides thereof, in which the piece of fabric (12) is fixed by means of respective clamping jaws (18) consisting of jaws (32, 36) which can move relative to one another and can be placed one on top of the other under locking pressure during the closing stroke of a closing lever (50) and is then stretched in the pulling direction (x) by a change of position of the clamping jaw units caused by a cylinder/piston unit (20, 78) for flow medium, characterised in that, when the jaws (32, 36) are brought together, a further closing stroke follows the first closing stroke defined by the closing lever (50), wherein the further closing stroke is controlled by a piston rod (72) of the cylinder/piston unit (20, 78) and, in the cylinder (20), the piston rod (72) can assume a first open position (I) of the clamping jaws (18) close to the jaws (32, 36) and, after part of the stroke length (h₁), a central position (II) when the jaws (32, 36) are closed and can execute a subsequent stroke (stroke length i) for the stretching process.
2. Device according to claim 1, characterised by a short-stroke cylinder (27) by means of which the respective clamping jaws (18) are arranged below the surface (13) of the upstream print flame (14) prior to the insertion of the piece of fabric (12) and can be closed following the insertion thereof, after which the short-stroke cylinder (27) can be actuated and the clamping jaws (18) can be adjusted above the surface (13) in order to unlock a slide (28).
3. Device according to claim 1, characterised by a piston (78) on the piston rod (72), the latter being part of the cylinder/piston unit (20, 78) for the pulling movement of a stretching means (16).
4. Device according to one of claims 1 to 3, characterised in that the clamping jaws (18) are held in the gripping position until the release of a locking member (90) for the slide (28) or the short-stroke cylinder (27), wherein the piston (78) can be brought into the central position (II) over part of the stroke length (h₁).
5. Device according to one of claims 1 to 4, characterised in that the cylinder (20) ending at one end in a bar-shaped base element (22, 24) is displaceably mounted at the other end in a connecting sleeve (54) in which the piston rod (72) is fixed via its end (71) remote from the piston (78), the piston rod (72) optionally traversing an end wall (75) of the cylinder (20) and the piston rod (72) being movably mounted in the sealed through bore (74).
6. Device according to at least one of claims 1 to 5, characterised in that the connecting sleeve (54) is hinged on to a guide element (46) and the latter is pivotably connected to a slide (28) which carries the jaws (32, 36) and is mounted to move in the pulling direction (x) on a profile (24) forming the base element.
7. Device according to one of claims 1 to 6, characterised by a guide element in the form of a bow (46), the arms (47) of which embrace the two sides (23) of the profile and are connected to the slide (28) by means of an axis of rotation (44).
8. Device according to one of claims 1 to 7, characterised in that the bow (46) is arranged within a hood-shaped supporting member for the movable jaw (36) serving as a tilting body (40) and is connected to the latter on either side by means of two toggle links (57, 64) which are hinged on the bow (46) at a distance (n) from one another.
9. Device according to at least one of claims 1 to 8, characterised in that the slide (28) is provided parallel to the axis of rotation (44) for the bow (46) with a pivot axis (42) for the hood-shaped supporting member or the tilting body (40) of the movable jaw (36).
10. Device according to at least one of claims 1 to 9, characterised in that a wrist pin (58) forming a joint between one of the toggle links (57) and the tilting body (40) is connected to a rocker arm (64) forming another toggle link, the other end of which provides an elongated hole (63) for a hinge axis (62) of the bow (46).
11. Device according to claim 8 or claim 10, characterised in that the hinge axis (62) for the rocker arm (64) is arranged so that it can be guided by the arm (47) of the bow (46) about its hinge point (56) for the toggle link (57) formed by a guide rod.
12. Device according to at least one of claims 1 to 11, characterised in that the tilting body (40) flanks the connecting sleeve (54) via parallel side walls, is hinged on to the slide (28) by means of the pivot axis (42) and holds the jaw (36) by means of a front edge parallel to the pivot axis (42).
13. Device according to at least one of claims 1 to 12, characterised in that, firstly, the hinge point (52) which connects the connecting sleeve (54) to the arm (47) of the bow and, secondly, a hinge point (56) for the guide rod (57) hinged on to the tilting body (40) at the other end also provided on the arm (47) of the bow are arranged on opposite sides of the axis of rotation (44).
14. Device according to at least one of claims 1 to 13, characterised in that the profile (24) guiding the slide (28) is arranged so that it can be lifted by a short-stroke cylinder (27) arranged below the profile (24) adjacent to the print frame (14), a locking member (90) optionally being associated with the short-stroke cylinder (27) and fixedly engaging the latter in an end position of the slide (28).

Images