WO2007123394A1 - Stretcher for painting canvas - Google Patents

Abstract

The invention concerns a stretcher for cloth, consisting of a number of in crossection identical frame sections (1), featuring an assembly frame at the exterior that may or may not be attached, across which and on which mounting is completed of the stretched cloth (D). In order to create a stretcher, the ends of four frame sections are affixed together using collapsible corner links featuring sawtooth clamps, for which the corner structure provides. As a result, the corner is open to the outside, creating an opening that can be adjusted according to need. This allows the cloth that needs to be folded (30) into the corner to be mounted in a neat line to the back of the stretcher. The shape of the metal frame sections was chosen in such a way that, thanks to flexible parts (15) that follow the motion, the size of the stretching surface can be adjusted, i.e. enlarged or reduced, either manually or automatically to the size change of the canvas, which may be caused by changes in the moisture level of the fabric or by lack of tension after the cloth has been mounted.

Description

STRETCHER FOR PAINTING CANVAS

The invention concerns a stretcher for canvas, comprising a number of interlocking frame sections, with an assembly mechanism attached to the back of the frame sections, and provided with corner joints.

The invention also concerns a method for fabricating a stretcher for painting canvas and for tensioning the canvas.

The conventional and still generally used methods for fixing sagging canvas rely on a canvas tensioning frame, whereby the tips of the four wooden or partly metal frame sections are equipped with adjustable corner joints featuring fixing options, the sole purpose of which is to enlarge or reduce the total size of the frame itself. These methods all feature an adjustable structural form, whereby the individual frame sections are included either separately or in adjustable form in the corner joint. These types of methods are known from French Patent number 439638 (Vidal) and European Patent Number 0102922 (Staro), both of which systems, however, are limited to tightening a sagging cloth, whereas in fact the problems are caused to a large extent by a shrinking of the cloth; in addition to Dutch Patent Number 9202248 (Schotel), in which the pin structure is replaced with an adjustable metal corner joint. Moreover, a structure is defined in international patent application WO 94/25296 whereby the cloth is tightened over a board and clamped on the sides by means of holders. The holders are clamped as a frame around the board.

Specific disadvantages of all known systems mainly concern the structural weakness of the corner joints and the lack of options for fastening a cloth that has already been stretched, either in its entirety or partially, without needing to unfasten the frame construction and therefore affect the stability.

An additional drawback of loosening the corners in an existing stretcher structure, in order to either tighten or loosen the cloth, is that it is not always possible to use sufficient manual force, while it also cannot be estimated in advance how much manual force is needed, as a result of which irreversible damage may be caused to the fabric and its treatment. EPO 102922 entails a spring mechanism along the length of the assembled frame sections. The known systems provide for an adjustment method in which the longitudinal frame sections are solely adjustable in the comers and do not allow for a direct adjustment of the stretching surface.

Of all current systems, none allow for the possibility of neutralising part of the change in tension on the cloth, without any aid and using only flexibility, without the need for manual adjustment. The French patent application FR 2 837 136 entails a structure in which the edge on which the cloth is laid is pressed forward by means of springs. This, however, involves a high risk of damage to the cloth.

It is an object of the invention to provide for a stretcher structure that easily adjusts to changes in the tension of the stretched cloth.

The stretcher is characterised according to the invention in that the frame sections contain a hollow profile, featuring a flexible wall on the outside edge for support of the cloth, and a hinge line (S) for the flexible wall at the back of the profile.

When tensioning the cloth, the pressure will be brought to bear on the flexible wall which will follow the movement along the hinge line. Changes in tension of the cloth, whether an increase (stretching), or a decrease (sagging), will be partly compensation by an elastic movement of the flexible wall to the inside or outside.

The flexible wall of this structure and the hinge mechanism do, therefore, facilitate the absorption of this stretching or shrinking of the cloth both partially and across the entire frame.

This invention offers increased flexibility in relation to stretchers in which the entire frame is pressed outward from the corners. Local distortions can be accommodated. In a preferred embodiment, the stretcher contains adjustment elements for moving the flexible wall in a direction diagonally to an outer edge of the stretcher to enable hinging of the flexible wall along the hinge line.

If this flexibility of the flexible walls proves insufficient for all circumstances, the preferred embodiment allows for adjustment, either by hand or automatically, of the position of a part or the entire length of the wall, without having to loosen the stretcher by means of the corner joints between the separate frame sections. Loosening will temporarily weaken the structure, whereby restoration of the interrupted tension on the cloth and the corner joint will not be possible in all cases. The flexibility of the wall will have a tensioning effect on the cloth.

The invention provides for a preferred embodiment of a stretcher structure in which the corner joint has an opening. This makes it possible to feed the excess fabric of the corner fold through this opening for mounting to the rear or interior of the framework.

All existing systems rely on the traditional method for mounting of the canvas in the corners, causing the cloth to be folded sideways along the edge or to the back, resulting in a lasting, visible and annoying accumulation of cloth.

Two patents, DE122640 and US3657796, are known to provide for the mounting of excess fabric in the corners, with measures to feed fabric through an open corner. These corners, however, do not close during or after fastening.

In the present system, the corner joint features an opening through which the cloth is folded to the inside along a neat line that is out of sight, and fastening is completed so as to prevent cloth from accumulating on the outside or rear of the framework, and whereby the open corner preferably closes during fastening by means of a sawtooth mechanism on the corner joint.

These, and further, aspects of this invention are described and illustrated below by means of drawings.

Herein

Figure 1 shows a stretcher according to the invention; Figure 2 shows a detail of the stretcher according to the invention;

Figures 3 thru 8 show details of a preferred embodiment of a stretcher according to the invention, whereby the stretcher includes an adjustment mechanism;

Figures 9 and 10 show a perspective view of a preferred embodiment of a stretcher according to the invention;

Figures 11 and 12 show a perspective and partial cross-section view of details of an embodiment of a stretcher according to the invention;

Figure 13 shows a cross-section view of a detail of an embodiment of a stretcher according to the invention; Figure 14 shows a further detail of an embodiment of a stretcher according to the invention;

Figure 15 shows a perspective and partial cross-section view of details of a further embodiment of a stretcher according to the invention;

Figure 16 shows a further embodiment of a detail of a stretcher according to the invention;

Figure 17 shows a further example of a detail of a stretcher according to the invention;

Figure 18 shows a further example of a stretcher according to a embodiment of the invention in which the corner joints contain flexible walls. Figures 19A and 19B are two known stretchers.

The figures are examples only, comparable components are in general indicated by means of the same number.

Figure 1 shows the complete frame, buttressed by intermediate sections and cross pattern as seen from the front without the cloth, in addition to the positions of details and diameters, which are described in other figures, with details A and B including as an example two different corner joints within the same framework.

Figure 2 shows a longitudinal section along the plane that runs across the x-x' line in Figure 1, in addition to showing a frame profile of the stretcher where the corner joint is located. The corner joint (6) is fitted into the rail chamber (3) next to the profile chamber (7) of the frame section (1), with the profile of the comer link (6) sliding across the rail wall (4) and through rail hole (5) into profile hole (3). The corner joint (6) has a tapped hole (10), and can by means of an adjusting screw (9) be fastened against the frame section (1) at any desired point within an area of several centimetres from the corner. In this process, the adjusting screw (9) serves as a lock by locking the corner joint (6) in the rail chamber (3). In this example, the frame section (1) is fitted with an assembly frame (2) and has a hollow profile with a flexible wall (15), which extends to an outer edge over which the cloth is laid. The profile is fitted with a hinge line S to the rear, whereby the rear is defined in relation to the visible section of a stretched cloth. The flexible wall 15 hinges along hinge line S and follows the changes in the tension of cloth D, thereby absorbing the sag and shrinkage in cloth D. In all figures, the possible movement of flexible wall 15 is indicated by means of a double arrow.

During tensioning, pressure is exerted on flexible wall 15 that will hinge inward somewhat around line S. When further tensioning the cloth, flexible wall 15 will move inward by hinging around hinge line S, when tension is released from the cloth, the flexible wall will move outward. Hereby, a simple structure enables compensation of changes in mounted cloth D.

Figures 3 through 8 show longitudinal diameters of various shape variations of frame section (1), along the plane across the z-z' line in Figure 1 where the adjusting screw (18) is located, and shows a frame profile of the stretcher as in Figure 2, with the profile surface (13) as the exterior of the profile chamber (7), which is connected to corners (14), which, either once or several times, turns over and continues into a flexible wall (15), which ends in the guide corner (16), along which the cloth to be mounted first touches the profile before it is folded over to the back. Area (17) is the area the profile has available to vary the tension on the cloth through the flexibility of the form and hinging over hinge line S by bending inward, tilting, or extending flexible wall (15) and guide corner (16). These embodiments show preferred embodiments. The stretcher is fitted with an adjustment mechanism. An adjustment screw serves as the adjustment mechanism in this embodiment. Adjusting screw (18) can either push outward the flexible wall (15) and therefore the guide corner (16) or let it ease, thereby offsetting the excess tension/lack of tension of the cloth. This is possible in any given location, determined by what positioning is selected for these adjusting screws (18), as the tapped holes of positions (19) and (20) are equipped with screw thread, and their positions in the profile can be adjusted as desired, or due to the flexibility of wall (15) across the longitudinal direction of the frame section.

Figure 9 shows a cut-out corner fragment corresponding to the corner shown in detail A, which displays the back and inside of a framework structure in assembled form, with the cloth being pulled into a fold (30) through the corner chamber (11). The corner chamber is an aspect of a preferred embodiment.

Figure 10 shows a detail as in Figure 9, whereby fold (30) is assembled to an assembly frame by means of crease (29). This example concerns a wooden assembly frame.

Figure 11 shows an exploded, 3-D detail A from Figure 1 of a corner joint of the stretcher. The corner joint (6) slides into the rail chamber (3) of the frame section (1). The comer joint (6) has a tapped hole (10), and can by means of an adjusting screw (9) be fastened against the frame section (1) at any desired point within a range of several centimetres. In this process, the adjusting screw (9) serves as a lock by locking the corner joint (6) in the rail chamber (3). The corners of the two frame sections to be assembled have been mitred in a corner (28) larger than 45 degrees, as a result of which, during the assembly of the corner joint (6) with the frame sections fixed at a 90-degree angle, the latter do not completely connect on the outside of the corner, creating a corner chamber (11) on the exterior of the corner construction of the framework in this corner. The size of the opening can be determined by changing the angle (28), aligning it with the space needed to move the excess cloth out of view to the back or the interior, where its fastening can also be completed out of view. The exploded fragment of this figure shows where the assembly frame is affixed, and how the adjusting screw (18) hits the flexible wall (15) via the rail wall (4), and, through the rail hole (5) and tapped hole (19) and (20), and how, by turning this adjusting screw (18) inward and outward, the position of the flexible wall (15) can tilt vis-a-vis the rest of frame section (1), which allows the tension on the mounted cloth to be changed. When adjusting screw (18) is detached from flexible wall (15), this wall can, through comers (14) and hinge line (S), independently absorb small changes in tension in the cloth.

Figure 12 shows an exploded, 3 -dimensional detail B from Figure 1 of a comer of the stretcher. The comer joint (6) slides into the rail chamber (3) of the frame section (1). The comer joint (6) has a tapped hole (10), and can by means of an adjusting screw (9) be fastened against the frame section (1) at any desired point within a range of several centimetres. In this process, the adjusting screw (9) serves as a lock by locking the comer joint (6) in the rail chamber (3). A blocking plate (8) has been affixed to the comer joint (6) at a 45-degree angle whose position is equal to the tangent plane that would be created if the profile sections were to be assembled together at a 90-degree angle. Blocking plate (8) prevents the profile sections from touching each other, in addition to creating a comer chamber (11), which is almost equal to the thickness of the blocking plate (8). The size of the opening can be determined by means of a shift in the thickness of the blocking plate (8), which is equal to the space needed to lead the excess cloth through comer chamber (11) to the inside, where the user can complete its fastening out of view. The exploded fragment from this figure shows where the assembly frame (2) is affixed, and how the adjusting screw (18), passing the rail wall (4) and rail hole (5) enters through the tapped hole (19) and (20) and hits the flexible wall (15), and how, by turning this adjusting screw (18) inward or outward, the user can tilt the position of the flexible wall (15) vis-a-vis the rest of frame section (1), which allows the tension on the mounted cloth to be changed. When the adjusting screw (18) is detached from the flexible wall (15), it is possible for this wall to independently absorb minor tension changes thanks to the flexibility of the cloth.

Figure 13 shows a longitudinal section along the plane running through the y- y' line from Figure 1, from the point where the cross profile (21) connects to the frame profile (1 ). For this purpose, a cross-profile link (22) is placed in the selected location, with the side covering the rail hole (5) of frame section (1) and affixed to the frame profile using the self-tapping screws (12). Both of the raised assembly arms (23) and (24) of the cross-section link (22) are covered by the cross-section (21), after which they are affixed using adjusting screws (9), which lock into the screw thread of thread openings (25) on cross-section link (22), pressing on the wall between the rail chamber (3) and profile chamber (27), hereby fastening the cross-profile link to the cross profile (21).

Figure 14 shows an exploded, 3-D detail C from figure 1 of a corner construction of the stretcher, where the cross profile (21) connects with the frame profile (1). To this end, a cross-profile link (22) is placed longitudinally over the rail hole (5) and affixed using the self-tapping screws (12), through opening (26) in the cross-profile link (22), in the interior wall between rail chamber (3) and profile chamber (7) of the frame profile (1). The cross profile (21) is slid over both opened assembly arms (23) and (24) of the cross-profile link (22) and affixed using adjusting screws (9), which are locked into the screw thread of thread openings (25) on the cross-profile link (22), thereby affixing it to the rail chambers (3) of the cross profile (21).

These sections, their characteristics, and their individual placement within the framework, as shown in this example, enable the following functions:

Folding out four frame sections in order to set up the stretcher across which the cloth can be tightened is facilitated by fastening the frame section on which the corner link (6) should be assembled by tightening the adjusting screw (9), which clamps to the frame profile (1). Two adjoining, 90-degree frame sections can be assembled to the corner link (6) using the same method. The adjusting screws (18) along all sides facilitate the use of every type of cloth, including those that are not woven in a 90-degree angle, as this allows for the partial correction of distortion. If it proves necessary to manually correct for shrinkage, the tension can be controlled by adjusting the adjusting screws (18), regardless of the direction of the weave in the fabric. Potential aberrations in the desired 90-degree direction of the cloth to be mounted can be corrected by adjusting screws (18) and the resultant tilting of the wall (15). While mounting the cloth, users adjust the tension, after which, from the flexible corners (14) potential shrinkage can be automatically absorbed by the flexibility of the material the corner of which (14) will follow the motion, or by altering the adjusting screws used as needed. Figure 15 shows a further example of a detail of a stretcher according to the invention. In this case, flexible wall 151 is a hollow wall. Hinge line S is to the rear of the profile. The flexible wall can move elastically around hinge line S by means of adjusting mechanism 152, a pin in this example, which can be pushed into opening 153. The depth to which the pin is pressed determines the local deviation of the flexible wall. This allows for easy adjustment of the tension on the cloth. In Figure 15 use is made of a comer joint 66, which is made of a material that is preferably harder than the frame sections is fitted with sawteeth that can lock themselves into the frame sections with the primary function that during the mounting of the surplus canvas in the corner on the inside of the profile, the corner opening will close due to the barbed effect of the sawteeth when the tensioned canvas is fastened to the inside of the frame. Planes C and D, which are shown in cross-section, are the planes along the profile intended for gluing of the cloth. Figure 16 shows a further embodiment of a detail of a stretcher according to the invention. The flexible wall 161 can hinge around hinge line S. Adjusting screw 162 serves to determine the position of flexible wall 161 by means of assembly blocks (165) that can be placed on rails (166) as required. In this example, the cloth is clamped in clamp 163 by means of a clamping pin 164. Figure 17 shows a further embodiment. The stretcher is provided with a cloth chamber 171 closed off with a cap 172. The inside of cap 172 and chamber 173 are fitted with a fastening mechanism, sawteeth in this example. Closing of cap 173 clamps and tensions the cloth.

Figure 15 shows an embodiment in which the frame sections have angled sides which are connected to one another in the corners by means of corner joints 66.

Figure 18 shows an improved embodiment. In this embodiment, corner joints 181 also contain a hollow profile with a flexible wall 184 and a hinge point S. Corner joints 181 are connected to the frame sections 181 by means of the clamping protrusions 182. In this example, the corner joints contain protrusions 182 that are inserted in corresponding cavities in frame sections 183. It is clear that similar male-female joints can be formed by a cavity in the corner joint 181 and a protrusion from the frame section 1. Frame sections 1 and corner joints 181 can be easily connected to one another. In this preferred embodiment, corner joint 181 contains a corner chamber in which the comer of the cloth can be folded without being visible from outside. Figure 18 also shows a double pin 186. The double pin makes it possible to fasten the cloth in a single movement, while also providing improved clamping between corner joints 181 and frame sections. Also, tongue 187 of double pin 186 closes of the visible part of corner chamber 185. The corner of the cloth is thus hidden from view.

Figures 19A and 19B show two known stretchers, whereby the stretcher shown in Figure 19A is known from WO 94/25296 and the stretcher shown in Figure 19B from FR 2 837 136.

In the stretcher shown in Figure 19A the cloth is tensioned and fastened in 191 by fasteners 192, which are clamped in chambers 191. Further tensioning or easing is difficult and only possible by manually pressing in or releasing the fasteners 192. The situations as sketched on the right-hand side do not provide any possibility for accommodating differences in tension. Depending on the materials used and structure it may be possible, although not disclosed, that some movement around point S is possible in the structure shown on the left-hand side. Such a movement, however, will pull the cloth over corner point Hl and possibly cause damage. The possible hinge point S is not at the back, but at the front of the profile.

Figure 19B shows a structure known from FR 2 837 136. In this structure, the stretcher contains a back part 193 and a front part 194.e Springs V are provided between the parts 193 and 194. These springs V ensure that the cloth is kept under tension. However, a change in tension will cause the cloth to be pulled over corner point H; more or less of the image can be seen, depending on the tension. Even worse is that the cloth is rubbed against the corner point each time that a change in tension occurs, the repeated forward and backward movement (e.g., due to fluctuations in temperature or humidity) will cause wear and tear in the corners and in the image. In the invention, the flexible edge moves outward and the cloth does not or hardly rubs over the corners; this rubbing effect is completely excluded when the cloth is glued to the side. The edges move inside or out, depending on whether the cloth shrinks or expands. It is noted that two other stretchers are known from DE 122640 and US

3657796.

In the stretcher known from DE 122640, the cloth is fed inward through the open corner and (kept) tensioned by means of an adjustment mechanism. This does not allow for the possibility for inside mounting whereby the opening in the comer closes itself.

Also the construction known from US 365779 clearly includes an open corner in which excess fabric can be mounted to the back of the canvas, which can lead to the undesirable accumulation of cloth on the back and whereby the open corner is fixed and does not close during fastening. This structure claims to realise a visually neat corner which is, however, not closed, as is the case in this invention due to the fact that the sawteeth provide for full closing of the corner during tensioning and mounting.

The invention also concerns a method for mounting canvas on a stretcher.

Obviously, the invention allows for numerous variations which are not limited to the examples given above.

The profile can, for example, be made of metal, but also of plastic, or a combination whereby, for example, the flexible wall can be made of thin metal or plastic while the rest of the frame section could be made of a different material.

The adjustment elements could be an adjusting screw or pin. The adjustment element can be adjusted by hand. The adjustment element can also be electronic, for example as a piezo-electric element or a hydraulic element with an electric drive.

The mounting mechanism could be a wooden mounting frame, as in Figures 2 thru 4, or a cloth clamping system as shown in Figures 15, 16 and 17.

The invention is also embodied in a frame section 1 or a corner joint 6, 66 or 131 for use in a stretcher according to the invention.

The invention is also embodied in a method whereby frame sections and corner joints are assembled to form a stretcher, a section of cloth is fastened by means of fastening materials, after which the adjustment mechanism is applied to move the flexible walls around hinge points S, resulting in the tensioning of the cloth. The excess cloth can subsequently be folded away in the corner chambers. The corner chambers can then be closed off so that they are hidden from sight.

The end result is a well mounted cloth and an attractive visual appearance. This system allows for easy retensioning of the cloth in the future.

Claims

Claims:

1 ) Stretcher for canvas, comprising a number of interlocking frame sections ( 1 ), with a mounting mechanism (2, 164, 172) attached to the back of the frame sections, provided with corner joints (6, 66, 181), characterized in that the frame sections contain a hollow profile, which profile is fitted on the outside with a flexible wall (15, 151, 161) for support of the canvas and in that the profile has a hinge line (S) at the back of the profile.

2) Stretcher according to claim 1 , characterised in that the stretcher is provided with adjustment elements (18, 152, 162) for moving the flexible wall in a direction diagonally to an outer edge of the stretcher to enable hinging of the flexible wall along the hinge line (S).

3) Stretcher according to claim 1 , characterised in that the stretcher is provided with adjustment elements (18) for moving the entire hollow profile in a direction diagonally to the outer edge of the stretcher.

4) Stretcher according to any one of the preceding claims, characterised in that the stretcher contains corner joints (181) which contain a hollow profile (181), featuring a flexible wall (184) for support of the cloth and a hinge line (S) at the back of the profile. 5) Stretcher according to claim 4, characterised in that the corner joints contain a corner chamber (185).

6) Stretcher according to claim 4 or 5, characterised in that the stretcher is fitted with a double pin (186) that extends over the corner.

7) Stretcher according to claim 5 and 6, characterised in that that the double pin (186) is fitted with a tongue (187) for the visual closing of the corner chamber.

8) Stretcher according to claim 1 , characterises that the stretcher contains four corner joints (66) placed at right angles for the assembly of the frame sections, whereby the corner joints are fitted with sawteeth (99) for a continuous tight close of the open corner joint through which the canvas was fed for mounting. 9) Stretcher according to any one of the preceding claims, characterised in that the stretcher contains a corner joint (6) with an adjusting screw (9) in a tapped hole (10) of the corner joint (6), which is slidable and fitted into a rail chamber (3) for fastening and thus for assembly of the corners. 10) Stretcher according to any one of the preceding claims, characterised in that the outer part of two frame sections to be assembled together is mitred, whereby the stretcher contains a blocking plate (88) to prevent both parts from touching during assembly of the corner joints (6, 66) at right angles, constructed in such a manner that a corner chamber (11) is formed in this corner on the outside of the frame.

11) Stretcher according to any one of the preceding claims, characterised in that the outer part of two frame sections to be assembled together is mitred, in an angle exceeding 45 degrees each, wherein during the assembly of the 90-degree corner link (6) with the frame sections, these do not fully connect on the outside of the corner, as a result of which a corner chamber (11) is created in this corner on the outside of the corner.

12) Stretcher according to claims 10 or 11, characterised in that the corner chamber (11) is variable in size, and is thereby adjustable to the area needed to complete assembly on the cloth out of view, thereby creating a sharp corner line.

13) Stretcher according to claims 10, 11 or 12, characterised in that the mounted cloth, on the interior of the stretcher, can be mounted through corner chamber (11) without the need to permanently, visibly fold over the excess cloth in the corner, or folding it in two along the outer edges of the stretcher. 14) Stretcher according to any one of the preceding claims characterised in that the profile contains several frame sections which are slidable, mechanically adjustable or controllable. 15) Stretcher according to any one of the preceding claims characterised in that the profile has surfaces on which the mounted cloth can be glued. 16) Stretcher according to any one of the preceding claims, mounted with cloth or canvas. 17) Stretcher according to any one of the preceding claims, characterised in that the frame contains cross sections (21), which are fitted within the framework of the stretcher, either as X-bracing or not.. 18) Stretcher according to any one of the preceding claims, characterised in that the back of the profile includes a cloth chamber (171) fitted with a door (172) whereby the door and the cloth chamber are fitted with corresponding cloth fastening materials. 19) Corner joint (6, 66, 181) for use in a stretcher according to any one of the claims 4 to 9.

20) Frame section (1) for use in a stretcher according to any one of preceding claims. 21) Method whereby the frame sections ( 1 ) and corner joints (6, 66, 181 ) are assembled to form a stretcher, a cloth (D) is fastened to the frame sections by means of mounting element and subsequently moved by means of adjustment elements (18, 152, 162) and flexible walls (15, 151, 161) of the frame section (1) around hinge line S on the back of the frame section for the tensioning of the cloth (D).

22) Method according to claim 21 whereby excess cloth in the corners is folded away in the corner chambers.