DE29516465U1 - Stencil holder - Google Patents

Description

Stencil holder

The invention relates to a stencil holder for stencils made of metal foils, preferably for screen printing, in particular for applying adhesive for gluing electronic components to circuit boards or solder paste for reflow soldering electronic components to circuit boards, comprising a frame, at least two stencil holders arranged on the frame, releasably holding the stencil, and a stencil clamping device with which the stencil can be clamped in at least a first clamping direction.

Such stencil holders are known from the brochure "DEK MICRO-MOUNT - Advanced stencil clamping system" from DEK Precision Screen Division, 11 Albany Road, Granby Industrial Estate, Weymouth, Dorset DT 4 9TH, England. With these, for example, the stencil is fixed by the two stencil holders facing each other and clamped in the first clamping direction extending between the stencil holders.

However, with these known clamping devices, the template cannot be clamped evenly.

The invention is therefore based on the object of improving a stencil holder of the generic type in such a way that the stencil can be tensioned as evenly as possible.

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16 October 1995

This object is achieved according to the invention in a stencil holder of the type described at the outset in that the stencil has holding strips extending adjacent to a stencil area, that these holding strips extend at most over the respective length of an edge of the stencil area in the respective longitudinal direction of the same, that each holding strip can be releasably fixed to a stencil holder and that the stencil can be tensioned in a first tensioning direction and a second tensioning direction running transversely to the first by means of the stencil tensioning device engaging the stencil holders.

The advantage of the solution according to the invention is that the clamping forces can have an optimal effect on the stencil area and are not changed, in particular reduced, by holding strips that extend beyond the stencil area and are connected to one another in these areas that extend beyond it, and thus act unevenly on the stencil and in extreme cases lead to distortions.

In particular, another great advantage of the solution according to the invention with regard to the uniform tensioning of the template is that it can be tensioned in two transverse tensioning directions and thus

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in particular, the template area is tensioned in two mutually perpendicular tensioning directions, in contrast to the solution known from the prior art, in which tensioning only takes place in one tensioning direction.

In principle, it would be conceivable to make the template area and the holding strips from different materials and, for example, to connect the holding strips to the template area in some suitable way.

However, it is far more advantageous if the stencil area and the holding strips are made of a single piece of metal foil.

In the solution according to the invention, the template is expediently designed such that it has a rectangular template area and a total of four holding strips arranged opposite one another in pairs, wherein each pair of holding strips can be tensioned in a tensioning direction.

In principle, it would be possible to fix each holding strip to several template holders. However, it is particularly advantageous if each holding strip, especially as a whole, can be releasably fixed to a single template holder, so that each template holder as a whole applies the clamping force to the entire holding strip.

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A 52 980 &khgr;

16 October 1995

In order to releasably fix the holding strips to the template holders, it is preferably provided that each holding strip can be releasably fixed to the respective template holder by means of a positive locking. In contrast to a frictional locking, a positive locking is a much simpler solution and is more suitable for absorbing a clamping force than a frictional locking.

In the simplest case, it is provided that each holding strip can be releasably fixed to the respective template holder by a series of form-locking elements, whereby the form-locking elements are preferably arranged one after the other in the row at essentially uniform intervals.

No further details have been given yet regarding the fixation of the template in the respective template holder. For example, a force-locking clamp would be conceivable. However, it has proven to be particularly useful if the template is fixed in the template holder by means of a positive locking, since the clamping forces can be transferred to the template much better via a positive locking connection.

Such a positive connection can be achieved by all types of positive locking elements that are effective between the template holder and the holding web. In the simplest case, such positive locking elements comprise openings in the holding strips and holding elements that pass through the openings.

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With interchangeable templates, it has proven to be particularly advantageous if the template holder has a positioning device that works transversely to the clamping direction. With this positioning device, it is possible to position the template exactly transversely to the clamping direction and thus automatically achieve its exact position transversely to the clamping direction when a template is exchanged.

This is particularly useful in a clamping device according to the invention, in which the template can be clamped in two clamping devices running perpendicular to each other, since such a positioning device then automatically enables an exact determination of the location of the template in the plane formed by the template.

Such a positioning device can be designed in a variety of ways. For example, such a positioning device could be formed by optical marks. However, positioning the template with a positioning device is particularly simple and safe if it includes a fit.

The fit can be designed in a variety of ways; it can be formed by two spaced fitting surfaces between which a section of the template can be inserted.

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However, it is particularly useful if the fit is formed by a row of holes into which corresponding fitting fingers engage.

A particularly advantageous embodiment provides that the openings and the holding elements that pass through them are simultaneously designed as fits for the exact positioning of the template in the template holder.

With regard to the design of the template holders, no further details have been given in connection with the previous explanation of the individual embodiments. One advantageous embodiment provides that in each tensioning direction two opposing holding webs, which are mounted on the frame, form the template holders, whereby a holding strip can be fixed to each holding web.

Preferably, each retaining web is designed such that it has retaining elements that pass through openings in the retaining strip, wherein the openings are preferably arranged in the form of a row of holes on the retaining strip.

In order to fix the respective retaining strip to the respective retaining web in such a way that the retaining elements remain in engagement with the openings in the respective retaining strip, it is preferably provided that in a

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In the fixed position, each holding strip is held in place by a holding-down device on a fixing support surface of the respective holding web. This ensures that the holding strip does not lift off the fixing support surface of the respective holding web and thus the holding elements also come out of engagement with the openings.

It is particularly useful if the hold-down device in the fixing position grips the respective holding strip with its fingers in the areas between the holding elements designed as fixing pins in order to prevent the metal foil of the holding strip from buckling up in the areas between the fixing pins during tensioning, since buckling up in this way would also lead to the formation of wrinkles in the template.

Regarding the positioning of the template perpendicular to the plane in which it extends, no further details have been given. For example, it would be conceivable to carry out this positioning via the position of the retaining bars in this direction.

It has proven to be particularly advantageous, in particular in order to obtain a stable position of the stencil suitable for a screen printing process, if the stencil is supported by a support web between a stencil area and an engagement point of the holding web.

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It would be conceivable to use the support bar to act against the template. However, it is particularly advantageous if the holding bar, which can be moved in the clamping direction, places the template against the support bar when clamping.

For example, this is possible because the holding bar pulls the template against the support bar when it is clamped.

This can be achieved particularly advantageously by arranging and moving the stencil holders on a side opposite the stencil on a plane defined by the support webs. This also has the further advantage that the stencil holders do not interfere with the movement of a squeegee working on the stencil.

With regard to the arrangement of the support bars on the template holder, no further details were given in connection with the previous explanation of the individual embodiments.

A particularly advantageous embodiment provides that the stencil holder has an outer frame made of frame supports, in which a stencil field is arranged and that the stencil field is limited by four support webs which are connected to the frame via struts. In this solution, the outer frame thus makes it possible to position the stencil holder exactly at its

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outer circumference and in addition, the template is also positioned exactly relative to the outer frame by the support bars that form the template field and are firmly connected to the outer frame.

The positioning of the stencil using the support bars can be achieved particularly easily in that each of the support bars has a support surface onto which the holding strips of the stencil can be placed. This means that in this embodiment, the stencil with the holding strips rests on the support surfaces of the support bars, so that in particular the stencil area lies within the stencil field defined by the support bars, which is a great advantage in particular for a crease-free and preferably even tensioning of the stencil.

In order to be able to connect the holding strips to the holding webs in a simple manner, it is preferably provided that each holding strip extends beyond the respective support web to the respective holding web, so that the holding webs can engage the holding strips outside the template field delimited by the support webs.

With regard to the mobility of the retaining webs in the respective clamping directions, no further details have been given in connection with the previous description of the solution according to the invention. An advantageous embodiment looks like this:

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that of two holding webs effective in a clamping direction, at least one is movable in the direction of the respective clamping direction by means of the template clamping device. The other holding web can, for example, be held immovably on the frame in the clamping direction.

No further details have been given so far regarding the arrangement of the retaining bars that can be moved in the clamping direction. For example, it would be useful if the retaining bars were guided by any type of sliding guide.

It has proven to be particularly advantageous if the holding webs are mounted on a parallel guide that is effective in the respective clamping direction. This parallel guide could, for example, be designed as a lever guide. However, it is particularly advantageous if the parallel guide comprises two longitudinal guides that are parallel to one another.

The longitudinal guides are conveniently designed as guide rods on which guide bushes slide.

As an alternative to guide rods with guide bushes as longitudinal guides, which, for example, guide the retaining webs within their longitudinal extension, one solution provides for the retaining webs to be guided at the ends on longitudinal guides.

Preferably, longitudinal guides are provided between the two ends of each support web and the struts connected to the frame.

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which in particular offer the possibility of precisely guiding the respective retaining web in the direction of its longitudinal extension and thus transversely to the respective clamping direction.

Each such longitudinal guide is expediently formed by rolling elements running in a guide groove, whereby preferably the guide groove is arranged in the respective strut running at the end of the web and, for example, the rolling elements are held on the holding web.

All sliding guides can be designed in such a way that they allow movement in the respective clamping direction with play transversely to it. However, if the movement of the respective holding web is to be limited exclusively to the clamping direction, the respective sliding guide is preferably provided with as little play as possible.

With regard to the design of the template clamping device, no further details were given in connection with the previous description.

Thus, in an advantageous variant of the invention, the template clamping devices are formed by hydraulic or pneumatic clamping elements that are effective in the respective clamping direction and are each coupled to one another in such a way that the same forces act on the holding webs at the same time.

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In the simplest case, the clamping device in this solution comprises at least one clamping cylinder acting between the respective holding bar and the frame, with which the respective holding bar can be moved to clamp the templates.

In order to achieve an equal effect of all clamping cylinders and to clamp in each clamping direction simultaneously with the same clamping force in accordance with the invention, it is preferably provided that the clamping cylinders are connected in parallel and connected to a pressure line so that the same pressure builds up in each clamping cylinder and thus, with identical clamping cylinders, each clamping cylinder generates the same clamping force.

In principle, one clamping cylinder per retaining bar would be sufficient. In order to achieve the most even possible force on each retaining bar, two clamping cylinders arranged at a distance from each other and acting in parallel are advantageously provided between the respective retaining bar and the frame.

An advantageous embodiment of a clamping device according to the invention provides, as an alternative to the above-mentioned options, a tensioning cable which acts simultaneously on the two holding webs which are opposite one another and can be moved in the same tensioning direction and can be tensioned by a tensioning element. The tensioning cable is expediently an inelastic cable.

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Preferably, the tension cable has a loop that is effective between the frame and the respective retaining web, the size of which can be varied depending on the pulling effect on the tension cable. In particular, the tension cable is deflected via rollers to form the loop in order to avoid any clamping and thus the occurrence of uneven forces on the retaining webs.

A particularly advantageous embodiment, in which the template can be clamped in two clamping directions, provides that the clamping cable serves to clamp all four holding webs.

In this case, the tension cable is redirected via pulleys in the corner areas of the template holder.

In principle, such a tensioning cable has the advantage that it can be tensioned by pulling a clamping bolt using a mechanical tensioning element, for example a lever element or a clamping sleeve, and this tensile force remains constant for a long time, so that, particularly in a case in which the template is to be tensioned for a long time with the same clamping forces, such a tensioning cable is advantageous over hydraulic or pneumatic solutions due to its simplicity.

Furthermore, such a tension cable has the further advantage that it can be easily guided in any desired direction through the pulleys.

A 52 980 &khgr;
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No specific information has yet been given regarding the force applied by the clamping device to the retaining bars. For example, it would be possible to act on the retaining bar at two spaced-apart points using a clamping cable.

However, it is particularly advantageous, in particular to ensure easy movement of the holding bar and clamping of the same, if the template clamping device engages the center of the holding bars and preferably the holding bars are guided on both sides of the central force attack.

With regard to the manner in which the stencil is clamped in the two clamping directions running transversely to one another, a wide variety of solutions are conceivable. For example, an advantageous solution provides that the stencil holders have two opposing holding webs that are guided on the frame so that they can move exclusively in the direction of the first clamping direction, that the stencil clamping device has a clamping force source that acts on both holding webs simultaneously with the same clamping force, that the stencil holders have two opposing holding webs that are guided on the frame so that they can move exclusively in the direction of the second clamping direction, and that the stencil clamping device has a clamping force source that acts on both holding webs simultaneously with the same clamping force.

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The advantage of this solution is that during clamping, the exact guidance of the two holding bars exclusively in the first clamping direction and in the second clamping direction ensures a defined position of the templates fixed in the template holders in a direction transverse to the respective clamping direction and that, on the other hand, the simultaneous application of the same clamping force to each of the holding bars also results in uniform clamping of the template in the first clamping direction, so that the two holding bars move away from each other under the influence of the same clamping force.

In this case, the template is preferably fixed in its position relative to the frame by the two clamping directions running transversely to one another and the exclusive guidance of the holding webs in these clamping directions. Thus, the second clamping direction simultaneously fixes the template in the first clamping direction and the first clamping direction fixes the template in the second clamping direction, so that with such a design of the solution according to the invention, the template fixed to the template holder can necessarily be positioned exactly in both clamping directions.

A particularly advantageous embodiment of this solution provides that a single clamping force source acts on all retaining webs.

A 52 980 &khgr;

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As an alternative to this solution, another embodiment of the solution according to the invention provides that of two holding webs effective in the first clamping direction, one of the holding webs is firmly connected to the frame and the holding web opposite the fixed holding web is movable in the first clamping direction relative to the frame and that the holding webs effective in the second clamping direction are movable in the first clamping direction relative to the frame and at least one of the holding webs effective in the second clamping direction is movable in the second clamping direction relative to the frame. This solution assumes that the template can be sufficiently positioned by the holding web firmly connected to the frame, in which case the mobility of the holding webs effective in the second clamping direction in the first clamping direction is necessary in order to avoid creasing, whereby this mobility can be achieved by a guide play.

It is particularly advantageous in this embodiment if the retaining web, which is effective in the first tensioning direction and is movable in this direction, is also movable in the second tensioning direction relative to the frame in order to compensate for folds here too, whereby the mobility in the second tensioning direction can also be realized by means of a guide play.

A further embodiment of a solution according to the invention provides that of two in the first clamping direction

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effective holding webs, at least one of the holding webs is mounted so as to be movable relative to the frame in the first clamping direction, that both holding webs effective in the first clamping direction are mounted so as to be displaceable in the second clamping direction and that the holding webs effective in the second clamping direction are movable relative to the frame in the first clamping direction and at least one of the holding webs effective in the second clamping direction is movable relative to the frame in the second clamping direction.

In both of the above-described embodiments, it is conceivable to arrange one of the holding webs acting in the second clamping direction so that it is immovable in the second clamping direction and only to move the other holding web. It is particularly advantageous if both holding webs acting in the second clamping direction are mounted so that they can move relative to the frame, so that symmetrical clamping in the second direction can be achieved.

In connection with the solution that at least one of the holding webs effective in the first clamping direction is movable relative to the frame in the first clamping direction, an advantageous solution provides that one of the holding webs is mounted immovably on the frame in the first clamping direction in order to thus specify a fixed position for the template in the first clamping direction.

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However, it is also possible that both retaining webs effective in the first clamping direction are mounted so that they can move relative to the frame, in which case the position of the template can be detected preferably via a marking on the template.

The invention also relates to a stencil made of metal foil, preferably for screen printing.

If the stencil is to be tensioned in two essentially perpendicular tensioning directions, it has proven to be advantageous according to the invention if the stencil has holding strips extending adjacent to a stencil area, whereby these holding strips extend at most over the respective length of the stencil area, so that the tensioning forces can have an optimal effect on the stencil area and are not reduced by holding strips extending beyond the stencil area and connected to one another in this area extending beyond it, thus acting unevenly on the stencil and in extreme cases leading to distortions.

The template is expediently designed in such a way that it has a rectangular template area and a total of four holding strips arranged in pairs opposite one another.

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In principle, it would be conceivable to make the template area and the holding strips from different materials and, for example, to connect the holding strips to the template area in some suitable manner.

However, it is much more advantageous if the stencil area and the holding strips are made of a single piece of film.

In principle, the film can also be made of a wide variety of materials.

However, due to the stress the foil is subjected to, it has proven advantageous if the foil is a metal foil.

With regard to the fixing of the holding strips to the holding webs, no further details have been given about the template so far. It has proven to be particularly advantageous if each holding strip has a row of holes for fixing it to the respective holding web, so that the fixing pins arranged on the holding webs can be brought into engagement with the individual holes in the row of holes.

Further features and advantages of the invention are the subject of the following description and the drawing of an embodiment.

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In the drawing show:

Fig. 1 is a plan view of a first embodiment of a stencil holder according to the invention;

Fig. 2 is an enlarged partial view of a longitudinal side of the stencil holder;

Fig. 3 is a section along line 3-3 in Fig. 2;

Fig. 4 is an enlarged sectional view taken along line 4-4 in Fig. 2 with the template holder holding the template;

Fig. 5 is a view similar to Fig. 4 with the template holder open;

Fig. 6 is a plan view of a template for the template holder;

Fig. 7 shows an enlarged section through a clamping element of the template holder.

Fig. 8 is a plan view similar to Fig. 1 of a second embodiment of a stencil holder according to the invention;

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Fig. 9 is an enlarged partial view similar to Fig. 2 of the second embodiment;

Fig. 10 is a section along line 10-10 in Fig. 9; Fig. 11 is a section along line 11-11 in Fig. 9;

Fig. 12 is a plan view similar to Fig. 8 of a third embodiment of a stencil holder according to the invention and

Fig. 13 is a plan view similar to Fig. 8 of a fourth embodiment of a stencil holder according to the invention.

A first embodiment of a stencil holder according to the invention, shown in Fig. 1, comprises a frame, designated as a whole by 10, which is formed by frame supports 12, 14, 16 and 18 forming four long sides of the frame. The frame 10 can be accommodated in the area of the frame supports 12 to 18, for example in a screen printing system, and can be positioned precisely in order to precisely position a stencil, designated as a whole by 20, for screen printing.

The template 20 lies in a template field 22 of the frame 10, which is limited by four support bars 24, 26, 28 and 30. The support bars 24 to 30 are in turn

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in continuation of the same up to the frame supports 12 to 18 stretchers 32, 34, 36, 38 are connected to these (Fig. 1 and 2).

As shown by way of example in the case of the support web 30 in Fig. 2 and 3, each of the support webs 24 to 30 comprises a support surface 40 on which lateral holding strips 44, 46, 48 and 50 of the template 20 can be placed in order to position the template 20 on a defined plane 52, wherein the plane 52 is defined by the support surfaces 40 of the support webs 24, 26, 28 and 30.

Each of the holding strips 44 to 50 (Fig. 6) further extends beyond the respective support web 24 to 30 up to a respective holding web 54, 56, 58, 60 to which the holding strip 44 can be fixed.

For this purpose, the respective holding strip 44 to 50 has a row of holes 64 (Fig. 6) running along an outer side edge 62, through which fixing pins 66 of a row of fixing pins 68 arranged on the respective holding web 54 to 60 reach through (Fig. 3, 4, 5). To the side of the row of holes 64, the respective holding strip 44 to 50 rests on a fixing support surface 70 of the respective holding web 54 to 60 and is held resting on the fixing support surface 70 by means of a hold-down device 72, with the fixing pins 66 protruding from the fixing support surface 70 and reaching through the respective row of holes 64 of the holding strip 44 to 50 resting on this fixing support surface 70.

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The hold-down device 72 preferably has a support strip 74 which extends parallel to the fixing support surface 70 and, as shown in Fig. 2, engages over the respective holding strip 44 to 60 in its areas between the fixing pins 66 with fingers 76. The hold-down device 72 also comprises a guide leg 78 which rests on a side 80 of the respective holding web 54 to 60 facing away from the respective support web 24 to 30 and is movable transversely, preferably perpendicularly to the fixing support surface 70 relative to the respective holding web 54 to 60 in order to move the support strip 74 towards or away from the fixing support surface 70 (Fig. 4, 5). Preferably, the hold-down device 72 is acted upon by a compression spring 82 acting on the support bar 74 in the direction of a position of the support bar 74 that releases the respective holding strip 44 to 50 (Fig. 5) and can be moved against the force of the compression spring 82 into a position in which the respective holding strip 44 to 50 rests on the fixing support surface 70 (Fig. 4) and can be secured in this position by clamping screws 84, whereby the clamping screws 84 pass through elongated holes 86 in the guide leg 78 and thus, together with the elongated holes 86, serve as a guide for the guide legs 78 on the respective holding web 54 to 60.

According to the invention, both the holding webs 54 to 60 with the respective hold-down devices 72 and the fixing pins 66 are arranged so that in the position fixing the holding strips 44 to 50 they are below a through an upper side 90 of the

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Stencil 20 must lie in the plane 92 defined in the area of the stencil field 22, so that a doctor blade running over the upper side 90 can move over both the hold-down device 72 and the fixing pins 66 without collision.

Each of the holding webs 54 to 60 is guided so as to be movable in only one clamping direction 98 or 100 by a parallel guide formed by two guide rods 94 and 96 parallel to the respective clamping direction 98, 100, whereby the clamping directions 98 and 100 run parallel to the plane 92 and are also perpendicular to one another. The holding webs 54 and 58 are only movable in the clamping direction 98 and the holding webs 56 and 60 are only movable in the clamping direction 100.

For example, the guide rods 94 and 96 are held on the support webs 24 to 30, but they can also be held additionally or alternatively on the frame supports 12 to 18.

In order to enable the holding webs 54 to 60 to slide easily on the guide rods 94 and 96, the holding webs are guided precisely and easily via guide bushes 102, preferably designed as ball bushes, on the guide rods 94 and 96 designed as round rods. Due to the precisely defined displacement of the opposing holding webs 54 and 58 in the clamping direction 98 and the mutual

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With the support webs 56 and 60 opposite one another in the clamping direction 100, the template 20 is positioned exactly in the plane with a row of holes 64 and fixing pins 68 designed in the form of a fit, so that the openings 110 provided in this plane are positioned in a defined manner in the plane 92 when the template 20 is inserted with the rows of holes 64 in the respective rows of fixing pins 68.

To tension the template 20, the opposing holding webs 54 and 58 as well as 56 and 60 can be moved in the corresponding tensioning direction 98 or 100 by means of a common template tensioning device, which comprises a bearing block arranged on each of the holding webs 54 to 60 and a tensioning roller 114 arranged rotatably on the respective bearing block 112, as well as deflection blocks 116 arranged opposite the bearing blocks 112 on the frame supports 12, 14, 16 and 18 with two deflection rollers 118 and 120, between which a tensioning cable 122, formed in the simplest case by a steel cable, emerges in the form of a loop 124 and wraps around the tensioning roller 114. The tension cable 122 extends from a fixed end 126, each deflected by corner deflection rollers 128, mounted in corner deflection blocks 130, from one deflection block 116 to the next, whereby in the area of each deflection block 116 the loop 124 leading to the respective holding web 54 to 60 is formed. At its end 132 of the tension cable 122 opposite the end 126, the latter is tensioned by means of a tensioning element 134 shown in Fig. 7, which has a

■ t ■ ·· ·

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Has a clamping bolt 136 which has an external thread 138 which in turn engages in an internal thread 140 of a clamping sleeve 142 which in turn is rotatably mounted on the frame 10, for example on the frame support 14 (Fig. 7).

Furthermore, the clamping bolt 136 is non-rotatable, but is guided on the frame 10 so that it can be moved in the direction of its longitudinal axis 144, preferably in an opening 146 through the strut 34, so that it can be moved in the direction of its longitudinal axis 144 by turning the clamping sleeve 42 of the clamping bolt 136 in order to tension the tensioning cable 122 and thus generate the tensioning force acting in the respective tensioning direction 98 or 100 via each of the loops 124 and thus simultaneously tension the template 20 in the tensioning directions 98 and 100, whereby the holding strips 44 to 50 come to rest on the support surfaces 40 of the support webs 24 to 30 and thus the template 20 rests exactly on the plane 52 defined by the support surfaces 40 of the support webs 24 to 30, so that In addition to the exact positioning of the template in the clamping directions 98 and 100, an exact positioning perpendicular to these clamping directions 98 and 100 can be achieved.

The stencil is preferably designed such that it has a central stencil area 150 in which the openings 110 required for screen printing are arranged.

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are, and the holding strips 44, 46, 48 and 50 are connected to the side edges 154, 156, 158 and 160 of the template area 150 forming an edge of the template area 150, each of which extends a maximum of the length of the respective corresponding side edges 154, 156, 158, 160, so that the template 20 has corner cutouts and as a result the clamping effect in one clamping direction 98 and the clamping effect in the other clamping direction 100 is not reduced by the holding strips 44 to 50, but can unfold fully over the respective extent of the template area 150 in the respective clamping direction 98, 100 (Fig. 6).

In a second embodiment of a stencil holder according to the invention, those parts that are identical to those of the first embodiment are provided with the same reference numerals, so that with regard to the description of the same, reference can be made in full to the statements on the first embodiment.

In the second embodiment of the stencil holder according to the invention, shown in Fig. 8 and 9, clamping cylinders 172a,b, 174a,b, 176a,b and 178a,b arranged in pairs on the respective frame support 12, 14, 16, 18 with their cylinder housing 170 act between the frame supports 12, 14, 16 and 18 and the holding webs 54, 56, 58, 60, whereby a piston rod 180 of the cylinders 172, 174, 176, 178 is connected to the respective holding web 54, 56, 58, 60.

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A pressure connection 182 of each of the cylinders 172, 174, 176, 178 is connected to a pressure line 184 guided on the frame 10, whereby the pressure line 184 can be connected centrally via a pressure connection piece 186 to a pressure source 188, which constantly supplies a constant pressure, which leads to each of the clamping cylinders 172, 174, 176, 178 acting with the same force on the respective holding web 54, 56, 58, 60, since the pressure line 184 in the parallel-connected clamping cylinders 172, 174, 176, 178 builds up the same pressure in each case.

In contrast to the first embodiment, as shown in Fig. 9 and Fig. 11, each of the holding webs 54, 56, 58, 60 is provided at its two ends 190, 192 with a pair of rollers 194, 196 of two rollers 198, 200 arranged at a distance from one another, which, as shown in Fig. 9 and 11 using the example of the holding web 60, are guided in a groove 202, 204 of the webs 336, 32 assigned to the ends 190, 192. The grooves 202, 204 are dimensioned such that they guide the rollers 198, 200 exactly parallel to the respective clamping direction, in the case of Fig. 9 and 11 the clamping direction 100, so that the respective holding web 60 is also guided parallel to the clamping direction 100.

In the embodiment shown in Fig. 9, the respective retaining web 60 is guided transversely to the clamping direction 100 in that its ends 190, 192 are attached to the respectively facing

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Strut 36, 32 slides with its end surface 210, 212 on the surface 206, 208 facing the holding web 60. An even more precise guidance of the respective holding web 58 transversely to the clamping direction 98 is possible by the fact that a rolling element guide is effective between the ends 190, 192 of the respective holding web 60 and the struts 36, 32 of the frame 10,
via which the ends 190, 192 of the respective retaining web 60 are then supported on the end struts 32, 36 arranged at the respective ends.

The connection between the piston rod 180 of each of the clamping cylinders 172, 174, 176, 178 is made by a bore 220 arranged in the respective retaining web 58, which is an end-side, reduced-diameter section 222 of the
Piston rod 180 passes through, which is provided at its end with a radially projecting disk 226 which engages over an annular flange 224 in the respective retaining web and which allows the tensile force of the respective clamping cylinder 176 to act on the respective retaining web 58 via the annular flange 224.

To ensure particularly precise positioning of the retaining webs 54,
56, 58, 60 in the tensioned state of the template 20, an end stop in the form of two end stop elements 230 is preferably assigned to one of two pairs of opposing holding webs 54, 58 or 56, 60,
which allow to define a final position of the respective

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Holding web 54, 56 with a pulling effect on all holding webs 54, 56, 58, 60, so that the respective opposite holding web 58, 60 holds the template tensioned starting from these end positions due to the clamping cylinders 176, 178 acting on it, while the clamping cylinders 172, 176 hold the respective holding web 54, 56 against the stop pins 230. The stop elements 230 thus make it possible to position the template 20 with even greater precision than is possible with the longitudinal guides of the holding webs 54, 56, 58, 60.

In a variant of the second embodiment, it is also conceivable to guide the retaining webs 54, 56, 58, 60 not only parallel to the respective clamping direction 98, 100 in which they are effective, but also to provide that each pair of retaining webs 54, 58 or 56, 60 effective in one of the clamping directions 98 or 100 is at least limitedly movable in the other clamping direction 100 or 98. For this purpose, as shown in the example of the retaining web 60 in Fig. 9, the respective retaining web 60 is guided in that its ends 190, 192 are guided with play between the respective facing struts 36, 32, so that the end surfaces 210, 212 of the retaining web 60, after limited movement in the direction of the first tensioning direction 98, come to rest on the surfaces 206, 208 of the struts 36, 32 facing them, while the respective retaining web 60 in its

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clamping direction 100 and is also guided in this direction by the rollers 198, 200 located in the grooves 202, 204 so as to be movable relative to the frame 10.

With this variant of the second embodiment, it is no longer possible to position the stencil 20 precisely during clamping, but it is possible to position the clamping frame for the screen printing process precisely using the devices for moving the clamping frame by means of a marking on the stencil so that the openings 110 are in the desired position.

In a third embodiment of a stencil holder according to the invention, shown in Fig. 12, one of the holding webs 54, 56, 58, 60, for example the holding web 54, is fixed immovably to the frame 10 both in its effective clamping direction 98 and also transversely to this, i.e. parallel to the clamping direction 100.

The remaining retaining webs 56, 58, 60 are mounted so as to be movable both in their effective clamping direction, i.e. in the case of the retaining web 58 in the first clamping direction 98 and in the case of the retaining webs 56 and 60 in the direction of the clamping direction 100, but preferably also transversely to their effective clamping direction, i.e. in the case of the retaining web 58 in the clamping direction 100 and in the case of the retaining webs 56 and 60 in the clamping direction 98, wherein the retaining webs 56, 58, 60 are preferably guided with play in this direction, as described in connection with the variant of the second embodiment.

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Furthermore, the holding webs 56, 58, 60 can also be acted upon by the clamping cylinders 174, 176 and 178 in the manner described in order to clamp the template 20.

In the third embodiment according to Fig. 12, although the holding web 54 is held firmly on the webs 38 and 34, when the clamping cylinders 174, 176 and 178 are acted upon, the possibility of uniformly clamping the template in both clamping directions 98, 100 is given by the fact that the holding webs 56, 60 have the possibility of moving transversely to their effective clamping direction 100, i.e. in the clamping direction 98, between the webs 36 and 32 with play and thus compensate for a slight deformation of the template 20 clamped starting from the fixed holding web 54. In addition, the retaining web advantageously also has the possibility of moving with play transversely to its effective clamping direction 98, i.e. in the clamping direction 100, between the webs 38 and 34 in order to compensate for any transverse movements that may occur when the retaining webs 56, 60 are clamped with the clamping cylinders 174 and 178, i.e. movements in the direction of the clamping direction 100.

With regard to the description of the remaining features of the third embodiment, reference is made in full to the statements on the first and second embodiments.

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In a fourth embodiment, shown in Fig. 13, both the retaining web 54 and the retaining web 56 are no longer acted upon by a clamping cylinder, but are fixed in their effective clamping direction 98 or 100 between end stops 230 and 232 or 234 and 236.

The retaining webs 54 and 56 are mounted with play between the respective struts 38 and 34 or 32 and 36 transversely to their respective effective clamping direction, that is to say in the case of the retaining web 54 in the clamping direction 100 and in the case of the retaining web 58 in the clamping direction 98, the retaining webs 54 and 56 are preferably fixed in the same way as described in connection with the second embodiment, i.e. via grooves 202 and 204 in the corresponding webs 38 and 34 or 32 and 36 and the pairs of rollers 194, 196 arranged at the ends of the retaining webs 54 and 56.

The other two retaining webs 58 and 60 are mounted in the manner already described and can be acted upon by clamping cylinders 176 and 178 in the respective effective clamping direction 98 and 100, respectively.

In addition, the holding webs 58 and 60 are also arranged to be movable with play between the respective webs 34 and 38 or 32 transversely to their effective clamping direction, that is, in the case of the holding web 58 in the clamping direction 100 and in the case of the holding web 60 in the clamping direction 98.

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When pressure is applied to the clamping cylinders 176 and 177, the corresponding holding webs 58 and 60 act in the respective clamping direction 98 and 100, respectively, and at the same time all holding webs 54, 56, 58 and 60 have the possibility of being displaced transversely to the effective clamping direction between the corresponding webs to such an extent that the template 20 can be clamped evenly in both clamping directions 98, 100.

With regard to the description of the remaining features of the fourth embodiment, reference is made in full to the statements on the first and second embodiments.

Claims (1)

■ CLAIMS 1. Stencil holder for stencils made of metal foils, preferably for screen printing, comprising a frame, at least two stencil holders arranged on the frame and releasably holding the stencil, and a stencil clamping device, with which the stencil can be clamped in at least a first clamping direction, characterized in that the stencil (20) has holding strips (44, 46, 48, 50) extending adjacent to a stencil area (150), that these holding strips (44, 46, 48, 50) extend maximum over the respective length of an edge (154, 156, 158, 160) of the stencil area (150) in the respective longitudinal direction thereof, that each holding strip (44, 46, 48, 50) is attached to a respective stencil holder (54, 56, 58, 60) and that the template (20) can be clamped in a first clamping direction (98) and a second clamping direction (100) running transversely to the first by means of the template clamping device engaging the template holders (54, 56, 58, 60). 2. Stencil holder according to claim 1, characterized in that the stencil area (150) and the holding strips (44, 46, 48, 50) are made of a one-piece metal foil. A 52 980 &khgr; 16 October 1995 - 36 - 3. Template holder according to claim 1 or 2, characterized in that it has a rectangular template area (150) and a total of four holding strips (44, 48; 46, 50) lying opposite one another in pairs. 4. Stencil holder according to one of the preceding claims, characterized in that each holding strip (44, 46, 48, 50) can be releasably fixed to a single stencil holder (54, 56, 58, 60). 5. Template holder according to one of the preceding claims, characterized in that each holding strip (44, 46, 48, 50) can be releasably fixed to the respective template holder (54, 56, 58, 60) by means of a positive connection. 6. Stencil holder according to one of the preceding claims, characterized in that the stencil is fixed in the stencil holder through openings (64) in the holding strips (44, 46, 48, 50) and holding elements (68) passing through the openings (64). 7. Template holder according to one of the preceding claims, characterized in that each template holder (54, 56, 58, 60) has a positioning device (64, 68) acting transversely to the clamping direction (98, 100). A 52 980 x x-239 16 October 1995 - 37 - 8. Template holder according to claim 7, characterized in that the positioning device comprises a fitting (64, 68). 9. Template holder according to claim 8, characterized in that the fit is formed by a row of holes (64) in which corresponding fitting fingers (68) engage. 10. Template holder according to one of the preceding claims, characterized in that in each clamping direction (98, 100) two opposing holding webs (56, 60; 54, 58), which are mounted on the frame (10), form the template holders. 11. Stencil holder according to claim 10, characterized in that each holding web (54, 56, 58, 60) has openings (64) in the holding strip (44, 46, 48, 50) through which holding elements (68) pass. 12. Template holder according to one of claims 10 or 11, characterized in that in a position fixed to the respective holding web (54, 56, 58, 60), each holding strip (44, 46, 48, 50) is held resting on a fixing support surface (70) of the respective holding web (54, 56, 58, 60) by means of a hold-down device (72). A 52 980 x x-239 16 October 1995 - 38 - 13. Template holder according to claim 12, characterized in that the hold-down device (72) in the fixing position engages with fingers (76) over the respective holding strip (44, 46, 48, 50) in areas between the holding elements (68) designed as fixing pins (66). 14. Template holder according to one of the preceding claims, characterized in that the template (20) is supported between a template area (150) and an engagement of the holding web (54, 56, 58, 60) by a support web (24, 26, 28, 30). 15. Template holder according to claim 14, characterized in that the holding web (54, 56, 58, 60) pulls the template (20) against the support web (24, 26, 28, 30) when clamped. 16. Stencil holder according to one of claims 14 or 15, characterized in that the stencil receptacles (54, 56, 58, 60) are arranged on a side opposite the stencil (20) of a plane (52) defined by the support webs (24, 26, 28, 30). 17. Template holder according to one of claims 14 to 16, characterized in that it has an outer frame (10) formed from frame supports (12, 14, 16,18) in which a template field (22) A 52 980 &khgr; 16- October 1995 - 39 - is arranged and that the template field (22) is limited by four support webs (24, 26, 28, 30) which are connected to the outer frame (10) via struts (32, 34, 36, 38). 18. Template holder according to one of claims 14 to 17, characterized in that each of the support webs (24, 26, 28, 30) has a support surface (40) on which the holding strips (44, 46, 48, 50) of the template (20) can be placed. 19. Stencil holder according to one of claims 14 to 18, characterized in that each holding strip (44, 46, 48, 50) extends beyond the respective support web (24, 26, 28, 30) to the respective holding web (54, 56, 58, 60). 20. Template holder according to one of the preceding claims, characterized in that of two holding webs (54, 56, 58, 60) effective in a clamping direction (98, 100), at least one is movable in the direction of the clamping direction (98, 100) by means of the template clamping device. 21. Template holder according to one of the preceding claims, characterized in that the movable holding webs (54, 56, 58, 60) are guided by a sliding guide (94, 96, 102). A 52 980 x x-239 16 October 1995 - 40 - 22. Template holder according to claim 21, characterized in that the holding webs (54, 56, 58, 60) are mounted on a parallel guide (94, 96, 102) effective in the respective clamping direction (98, 100). 23. Template holder according to one of the preceding claims, characterized in that the template clamping device has clamping elements that are effective in the respective clamping direction (98, 100), which are each coupled to one another in such a way that the same clamping forces act on the holding webs (54, 56, 58, 60) at the same time. 24. Template holder according to one of the preceding claims, characterized in that the template clamping device comprises at least one clamping cylinder (172, 174, 176, 178) acting between the respective holding web (54, 56, 58, 60) and the frame (10). 25. Template holder according to claim 24, characterized in that the clamping cylinders (172, 174, 176, 178) are connected in parallel and are connected to a pressure line (184). 26. Template holder according to claim 25, characterized in that two parallel-acting clamping cylinders (172a, b, 174a, b, 176a, b, 178a, b) are provided between the respective holding web (54, 56, 58, 60) and the frame (10). A 52 980 x x-239 16 October 1995 - 41 - 27. Stencil holder according to claim 26, characterized in that the clamping cylinders (172, 174, 176, 178) are constantly subjected to a medium under pressure when the stencil (20) is tensioned. 28. Template holder according to one of claims 1 to 23, characterized in that the clamping device comprises a clamping cable (122) and a clamping element (134). 29. Template holder according to claim 28, characterized in that the tension cable (122) forms a loop (124) effective between the frame (10) and the respective holding web (54, 56, 58, 60). 30. Stencil holder according to one of the preceding claims, characterized in that the stencil holders have two opposing holding webs (54, 58) which are guided on the frame (10) so as to be displaceable exclusively in the direction of the first clamping direction (98), that the stencil clamping device has a clamping force source (122, 134) which acts on both holding webs (54, 58) simultaneously with the same clamping force, that the stencil holders have two opposing holding webs (56, 60) which are guided on the frame (10) so as to be displaceable exclusively in the direction of the second clamping direction (100), and that the stencil clamping device has a clamping force source (122, 134) which acts on the two holding webs (56, 60) simultaneously with the same clamping force. A 52 980 x x-239 16 October 1995 - 42 - 31. Template holder according to claim 30, characterized in that a single clamping force source (122, 134) acts on all holding webs (54, 56, 58, 60). 32. Template holder according to one of claims 1 to 29, characterized in that of two holding webs (54, 58) effective in the first clamping direction (98), one of the holding webs (54) is firmly connected to the frame (10), and the holding web (58) opposite the fixed holding web (54) is movable in the first clamping direction (98) relative to the frame (10), and that the holding webs (56, 60) effective in the second clamping direction (100) are movable in the first clamping direction (98) relative to the frame (10), and at least one of the holding webs (56, 60) effective in the second clamping direction (100) is movable in the second clamping direction (100) relative to the frame (10). 33. Template holder according to claim 32, characterized in that the holding web (58) which is effective in the first clamping direction (98) and is movable in this direction is also movable in the second clamping direction (100) relative to the frame (10). 34. Template holder according to one of claims 1 to 29, characterized in that of two holding webs (54, 58) effective in the first clamping direction (98), at least A 52 980 x x-239 16 October 1995 - 43 - one of the holding webs (58) is mounted so as to be movable in the first clamping direction (98) relative to the frame (10), that both holding webs (54, 58) acting in the first clamping direction are displaceable in the second clamping direction and that the holding webs (56, 60) acting in the second clamping direction (100) are movable in the first clamping direction (98) relative to the frame (10) and at least one of the holding webs (56, 60) acting in the second clamping direction (100) is movable in the second clamping direction (100) relative to the frame (10). 35. Template holder according to one of claims 32 to 34, characterized in that both holding webs (56, 60) effective in the second clamping direction (100) are mounted so as to be movable relative to the frame (10). 36. Template holder according to claim 34 or 35, characterized in that one of the holding webs (54) is mounted immovably on the frame (10) in the first clamping direction (98). 37. Template holder according to claim 34 or 35, characterized in that both holding webs (54, 58) effective in the first clamping direction (98) are mounted so as to be movable relative to the frame (10). ♦♦ » * « % Wi A 52 980 &khgr;
x-239 16 October 1995 - 44 - 38. Template for a template holder, in particular according to one of the preceding claims, characterized in that the template (20) has holding strips (44, 46, 48, 50) extending adjacent to a template area (150) and that these holding strips (44, 46, 48, 50) extend at most over the respective length of an edge (154, 156, 158, 160) of the template area (150) in the respective longitudinal direction thereof. 39. Template according to claim 38, characterized in that it has a rectangular template area (150) and a total of four holding strips (44, 48; 46, 50) lying opposite one another in pairs. 40. Template according to claim 38 or 39, characterized in that the template area (150) and the holding strips (44, 46, 48, 50) are made of a one-piece film. 41. Stencil according to one of claims 38 to 40, characterized in that the foil is a metal foil. 42. Template according to one of claims 38 to 41, characterized in that each holding strip (44, 46, 48, 50) has a row of holes (69) for fixing it to the respective holding web (54, 56, 58, 60).