APPARATUS FOR TENSIONING AND CLAMPING MATERIAL

This invention relates to apparatus for tensioning and clamping material. The invention may be especially useful for tensioning canvas material over stretcher frames.

In the art world, canvas material has for centuries been stretched over wooden frames. The wooden frames have mitred corner joints and expanding wedges. The expanding wedges are located at the corner joints and they act to wedge the corner joints apart. This causes the frame to increase in size and thereby stretch a canvas which has already been secured to the frame. The expanding wedges are tapped into their corner joints until the frame has expanded sufficiently to provide the required tension on the canvas. The process is laborious and old fashioned.

It is an aim of the present invention to provide apparatus for tensioning and clamping material, which apparatus can be used in a variety of different types of applications, and which apparatus is an improvement on the above mentioned apparatus traditionally used in the art world.

Accordingly, in one non-limiting embodiment of the present invention there is provided apparatus for tensioning and clamping material, which apparatus comprises a first part and a second part: the first part being for forming a fixed point over which the material is tensioned and clamped; the

second part being for moving over the first part firstly to tension the material and secondly to clamp the tensioned material to the first part; the first part comprising a fixed portion over which the material passes; the second part comprising a first jaw, a second jaw, hinge means for allowing the first and second jaws to open and close about the fixed portion of the first part, and tightening means for tightening the first and second jaws over the fixed portion of the first part, the first jaw having a concave portion which is able to slide over the fixed portion of the first part, the second jaw having a concave portion which is able to slide over the fixed portion of the first part; and the fixed portion of the first part, the concave portion of the first jaw and the concave portion of the second jaw being such that they form a tensioning and clamping arrangement for the material, and the tensioning and clamping arrangement being such that it comprises gripping formations.

The apparatus of the present invention is easy to use. More specifically, the second part is loosely tightened about the first part, with the material to be stretched extending between the first and the second parts. With an appropriate degree of tightness between the first and the second parts, the second part can be rotated backwards and forward with respect to the first part to enable the material to be pushed and pulled through the first and the second parts and thereby to be tensioned. When the required degree of tension in the material has been achieved, then the second part can be permanently tightened to the first part, and the material will then

remain in its tensioned condition. The apparatus of the present invention can advantageously be formed as an integral part of a frame, in which case the frame may be a picture frame or a frame used for a variety of other purposes. Alternatively, the apparatus of the present invention may be made as a separate item for fixing to a frame, in which case the frame can again be a picture frame or a frame used for a variety of other purposes.

Preferably, the apparatus is one in which the gripping formations are on the fixed portion of the first part. However, if desired, the gripping formations may be on one or both of the concave portions of the first and second jaws. Alternatively, the gripping formations may be partially on the fixed portion of the first part and partly on one of the concave portions of the first and second jaws.

Preferably, the apparatus is one in which the gripping formations are teeth which project in the direction of tensioning movement of the second part over the first part. Other gripping formations may be employed, so that, for example, the gripping formations may be dimples or knurls.

Preferably, the fixed portion is part circular in cross section. Other shapes for the fixed portion may however be employed.

The apparatus of the invention may be one in which the first part includes a body portion for forming a frame over which the material is tensioned, or for being fixed to a frame over which the material is tensioned.

The hinge means may be a pivot pin extending through apertures in end portions of the first and second jaws. Other types of hinge means may be employed.

The tightening means is preferably a screw tightening means. Other type of tightening means may however be employed.

When the tightening means is a screw tightening means, then the screw tightening means preferably comprises a screw having a threaded portion for enabling the first and second jaws to be tightened progressively over the first and second convex portions of the first part. Preferably, the screw has a head with a bore for receiving an Allen key. Alternatively, or in addition, the screw may have a head with flat sides for receiving a spanner.

The present invention also extends to a frame when comprising the apparatus of the invention. The frame may include a plurality of the pieces of the apparatus disposed around the frame. The frame may be a picture frame, a billboard frame, or any other suitable and appropriate type of frame.

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:

Figure 1 is a side view of apparatus for tensioning and clamping material;

Figure 2 is a view like Figure 1 but shows a second part in a closed position on a first part;

Figure 3 shows a first tensioning movement of the apparatus as " shown in Figure 2;

Figure 4 shows a second tensioning movement of the apparatus shown in Figure 2;

Figure 5 shows the apparatus of Figures 1 - 4 forming part of a picture frame;

Figure 6 is a section through the entire picture frame which is shown partially in Figure 5;

Figure 7 is a rear perspective view of the picture frame shown in Figures 5 and 6;

Figure 8 is a rear perspective view of a known traditional method of stretching material over a picture frame;

Figure 9 is a section like Figure 6 but shows the apparatus of the invention as applied to a frame forming part of a billboard; and

Figure 10 is a perspective view like Figure 7 but shows the billboard of Figure 9.

Referring to Figures 1 - 4, there is shown apparatus 2 for clamping and tensioning material 4. The apparatus 2 comprises a first part 6 and a second part 8. The first part 6 is for forming a fixed point over which the material 4 is tensioned and clamped. The second part 8 is for being moved over the first part 6 in the manner illustrated in Figures 2, 3 and 4. This movement is a backwards and forwards rotational movement of the second part 8 over the first part 6 and it is firstly to tension the material 4 and secondly to clamp the tensioned material 4 to the first part 6.

The first part 6 comprises a fixed portion 10 which has a part tubular toothed surface 12. The material 4 passes over this toothed surface 12.

The second part 8 comprises a first jaw 18, a second jaw 20 and a hinge means 22 for allowing the first and second jaws 18, 20 to open and close about the fixed portion 10 of the first part 6. The second part 8 is also

provided with tightening means 24 for tightening the first and second jaws 18, 20 over the first and second convex portions 10, 14 of the first part 6.

The first jaw 18 has a concave portion 26. The concave portion 26 has a smooth surface 28. As can be seen from Figures 1, 2, 3 and 4, the concave portion 26 is able to slide over the toothed surface 12 of the fixed portion 10 of the first part 6.

The second jaw 20 has a concave portion 30 which has a smooth surface 32. The concave portion 30 is also able to slide over the toothed surface 12 of the fixed portion 10 of the first part 6.

Figure 1 shows the second part 8 with the first and second jaws 18, 20 open, and with the material 4 having been passed between the first and second parts 6, 8 as shown. Figure 2 shows the first and second jaws 18, 20 tightened to an extent sufficient to enable the material 4 to be gripped for tensioning. Figure 3 shows a first rotational movement in the direction of arrow 34. With this rotational movement, a point 36 on the concave portion 26 pushes on the material 4 for tensioning purposes. Also, a point 38 on the concave portion 30 pulls on the material 4 for tensioning purposes. In Figure 3, it will be seen that the point 36 pulls the material 4 by pushing down on the material 4.

In order to effect further tightening of the material 4 from the position of the apparatus 2 shown in Figure 3, the second part 8 is rotated in the direction of the arrow 40 to the position shown in Figure 4. As can be seen from the position shown in Figure 4, further stretching and tensioning of the material 4 has taken place. In Figure 4, the point 38 has acted to pull the

material 4. In both Figures 3 and 4, pulling of the material 4 can be assisted by pulling or gripping with tools such for example as pliers at a free edge 42 of the material 4.

As shown in Figures 1 - 4, the part-tubular toothed surface 12 has teeth 14 which project in the direction of tensioning movement of the second part 8 over the first part 6. The teeth 14 and the smooth surfaces 28, 32 of the concave portions 26, 30 respectively form a tensioning and clamping arrangement for the material 4.

The first part 6 includes a body portion 44. The body portion 44 may form a frame over which the material 4 is tensioned. Alternatively, the body portion 44 may be for being fixed to a frame over which the material 4 is tensioned. An edge 46 of the body portion 44 is curved as shown for enabling the easy passage of the material 4 over the edge 46.

The hinge means 22 comprises a pivot pin 48 which extends through apertures in end portions 50, 52 of the first and second jaws 18, 20 respectively.

The tightening means 24 is a screw tightening means which comprises a screw 54 having a threaded portion 56 for enabling the first and the second jaws 18, 20 to be tightened progressively over the first and ^" second convex portions 10, 14 of the first part 6. The screw 54 has a head 58. A bore 60 extends through the head 58 and into the screw 54 as shown. The bore 60 receives a tightening tool in the form of an Allen key 64. When the material 4 has been sufficiently tightened, then the Allen key 64 can be screwed in a little more in order to tighten the second part 8 firmly with

respect to the first part 6 and thereby permanently to clamp the tensioned material 4 in position.

Referring now to Figures 5, 6 and 7, the apparatus 2 is shown as forming an integral part of a frame 66 of a painting. For this purpose, the body portion 44 has been produced to form part of the entire frame 66. This can best be appreciated from Figure 5 wherein it can be seen that the body portion 44 as shown in Figures 1 - 4 has been extended into a lower portion 68 and a strengthening flange 70. The lower portion 68 is provided with a curved edge 72 over which the material 4 stretches. It will be seen that the first part 6 and the second part 8 of the apparatus 2 are formed on the rear part of the frame 26. The free edge 42 of the material 4 is thus on the rear side of the frame 66. As can best be seen from Figure 6, arrows 74 indicate the front of the painting and in particular the front surface of the material 4, which is a canvas having a painting on it.

The apparatus 2 can easily be moulded from appropriate materials including aluminium and sufficiently rigid plastics materials.

The frame 66 shown in Figures 5, 6 and 7 of the present invention may be contrasted with a known frame 76 as shown in Figure 8. The frame 76 has corner mitred joints 78. These joints 78 are expanded by frame" expanding wedges 80. Canvas material 82 is secured in position on a rear face 84 of the frame 76 by means of staples 86. With the canvas material 82 appropriately stapled in position by the staples 86, tensioning is effected by tapping the wedges 80 further into their corners as shown. This method

of tensioning is old fashioned, laborious and considerably less accurate than the method afforded by the apparatus 2 of the present invention.

Figures 9 and 10 show an embodiment of the apparatus 2 as applied to a billboard. Figure 9 may be compared with Figure 6 and Figure 10 may be compared with Figure 7. Instead of the picture frame 66, Figures 9 and 10 show a billboard 88. The billboard 88 has a frame 90 which includes the apparatus 2. The apparatus 2 is covered by a hinged cladding part 92 which extends along each side of the frame 90 and which is hinged to the frame 90 by a hinge pin 94. In Figure 9 and 10, the material 4 may be an appropriate material for a billboard 88. The front of the billboard 88 and therefore the front of the material 4 is shown by arrows 96 in Figure 9. Figure 10 is a perspective view of the billboard 8 from the rear, with one of the hinged cladding parts 92 being opened in order to show the apparatus 2.

It is to be appreciated that the embodiments of the invention described above with reference to the accompanying drawings have been given by way of example only and that modifications may be effected. Thus, for example, first and second parts 6, 8 may be shaped differently to those shown. The apparatus 2 may be produced in a wide variety of materials, allowing for modern production methods which are much in advance of production of wooden frames of the type shown in Figure 8. The material 4 may be any suitable and appropriate material for the type of frame over which it is tensioned and clamped. Other types of tightening means 24 to the illustrated screw may be employed. The head 58 of the screw 54 may have flat sides for receiving a spanner as an alternative or in addition to the

provision of the bore 60 for the Allen key 64. In addition to tensioning picture canvases and billboard materials, the apparatus of the present invention may be used for tensioning material in the form of swimming pool covers, covers for lorries, or trailers of lorries, and covers over frames in order to form temporary shelters or temporary living accommodation. The material may be in sheet form as in the case of stretcher frames, billboards and shelter covering. Alternatively, the material may be in strip or belt form, as may be required for tightening straps or belts securing goods to lorries. When the material is used in strip form, then the strips can be of any suitable and appropriate widths.