The said effect is achieved so that the sharp edges of the wings extending from the body of the joint clip penetrate a little into the surfaces of the elements so that the essential joint spots are created by very small grooves and the edges penetrated into them. No machining is needed for the elements. It's sufficient that the elements are made of wood based board and have the same width and thickness.

Traditionally wood based shelf units assembled of elements are made so that first a frame is built by using screw bolts. A thin board like hardboard is nailed onto the back side of the frame in order to prevent it from collapsing sideways. Into the side wall elements holes are bored for shelf retainer clips, onto which the shelves are lifted.

Nowadays great popularity has been achieved by an element shelf unit system consisting of side walls, which resemble a ladder. Side walls have borings into which the shelf retainer clips are installed for hanging up the shelves. The motion sideways has been prevented by screwing crossing steel bars onto the back side of the shelf unit.

The above mentioned shelf units have one common disadvantage: The shelf units always have to be equipped with some supporting member on the back side, like crossing steel bars or hardboard. The assembly of these shelf units is also slow and awkward. These elements also require lots of work in manufacturing, since the installation of joint devices require different borings and grooves.

The US patent A 4616571 presents a joining device, which resembles the present invention. This invention can be used for joining vertical shelf elements between long horizontal shelf elements. The joining device comprises a cubic solid body which has crossing grooves into which the elements are pressed. In the groove the elements are squeezed between the walls of the groove. The joint is kept together by the friction force between the walls and the elements. The functioning of the joint has been improved so that the joining device can be attached to the back wall of the shelf unit by a screw.

The patent application GB 2204931 presents a joining device, which resembles the former patent very much. Different modifications of the joining device have been designed for Joints, cross joints and corner joints. In this case too the elements are pressed into grooves where the surfaces of the elements are squeezed between the walls of the grooves. In addition to this screws have been installed in the walls so that by using them additional tightelling force is achieved in the joint.

The greatest disadvantage of the former joining devices is the fact that they don't take into consideration thickness variations caused by changes in humidity.

Because of this the elements may be too thin or too thick to be pressed into the grooves of the joining device. The plane surfaces of the groove walls stick to the plane surfaces of the elements poorly since the surfaces may be slippery, especially when the elements have been painted or coated with plastic.

The characteristic features of the present invention are as follows: The joint clip has a simple structure and it is fast and easy to use. When the joint clip is under load, it creates a torque so that the more it is loaded the more it tightens. No screws are needed in the use of the joint clip. Neither is any separate supporting structure needed on the back side of the shelf unit, which prevents it from collapsing sideways. The joint clip grips the element surface only by its sharp edges, so small variations can be allowed in the thickness of the elements. The height of the shelves can be freely adjusted. Also side walls located between shelves can be freely adjusted. In addition to the former the present invention has features, which are presented in patent claim 1.

The accompanying drawings illustrate the inventive joint clip in which: FIG. 1 illustrates a perspective picture of the joint clip.

FIG. 2 illustrates a perspective picture of the joint clip in fig. 1, where the joint clip has been pressed onto a T-joint formed by the elements.

FIG. 3 illustrates a cross section of the joint clip viewed from the front where the joint clip has been pressed onto a T-joint formed by the elements.

FIG. 4 illustrates a cross section of such a joint clip, which is made for joining shelf elements on the same level.

Figures 1 and 2 illustrate a perspective picture of one joint clip meant for Joints, in which the joint clip has been made of sheet metal by pressing. The structure of the joint clip consists of a flat body 2 and of six wings extending from the body perpendicularly so that the wings 4a,4b squeeze with their edges the shelf element 7 and the wall element 6 in a 45" angle and of the wings 3a,3b, which are perpendicular to the former wings and which squeeze the surfaces of the shelf element and of the slanting wings 5a,5b, which squeeze with one edge the outer

surface of the wall element at the level of the upper and lower surfaces of the shelf. Figure 3 illustrates a cross section of the joint clip viewed from the front so that the edges of the six wings, which have penetrated into the surfaces of the elements, have been marked with the spots A,B,C,D,E,F,G,H. Figure 4 illustrates a cross section of such a joint clip, which is meant for joining two opposite shelves on the same level. In this case the wings 5a,5b in figure 3 have been replaced by the mirror pictures of the wings 3a,4a,3b,4b and marked as the wings 3c,4c,3d,4d. Body 2 has been replaced with a new body 10. On the opposite side of shelf element 7 another shelf element 8 has been drawn.

The joint clip is used so that the shelf element is held perpendicularly against the wall element and at the same time the joint clip is pressed onto the joint.When the joint clip is pressed all the way down, the joint is ready and when clips are pressed on all joints onto their front and back sides the shelf unit is ready.

The functioning mechanism of the joint clip is based on its three different ways of functioning at the same time. The first one attaches the clip on the wall element so that it can carry the load of the shelf; the second one attaches the clip on the shelf and at the same time the elements to each other; the third one creates a torque in the clip so that it prevents the shelf unit from collapsing sideways.

The functioning of joint clip 1 can be seen in figure 3. First the clip is pressed onto wall element 6. The wings 4a,4b and 5a,5b are located in body 2 so that their sharp edges E,F,G,H penetrate a little into the surfaces of the wall element.

The tension force, which occurs between the middle edges G,H and the side edges E,F resists the pressing as well as the friction force, which occurs when the edges penetrate into the surfaces of the elements. The amount of the resisting force is adjusted so that the clip can be pressed by hand onto the joint so that its edges penetrate into the surfaces of the elements about 2 - 5% of their thickness depending on the element material. When the edges penetrate into the wall element surfaces, they form a very small joint carrying the shelf. The joint is formed by the edges surrounding the element and by the grooves formed by the edges. In spite of the small size of the joining spots the joint is very firm and it can carry loads, which are over ten times more than the force parallel to the wings, which is used for pressing the clip onto the joint. This results from the fact that the clip is loaded in vertical direction so that the load is split horizontally along the length of the edge at the depth of its penetration.

In connection with loading the shelf there exists another force supporting the shelf, which is created by a torque caused by the load. The load lies on the edges A,B, from which the torque is transferred through point F to the other side of the wall element to the edges G,H. The transferring of the torque from one side to

another causes such an effect that the more the shelf is loaded the tighter the clip will be in the element. As a result of this the clip can always carry the load of the shelf until the clip or the shelf breaks.

The shelf element can be joined to the wall element so that after the clip has been pressed on the side wall element, the shelf element is pressed into the clip and at the same time the elements are squeezed together. The shelf is placed between the edges A,B and C,D correspondingly as before. The edges and their grooves form a joint, which attaches the clip on the shelf element and at the same time the elements to each other. When the shelf is loaded a torque is formed in the gripping edges so that an increased load improves the attachment. As a result of loading, the shelf bends down in the middle and correspondingly the end parts start to rise up. A torque from edge A starts to lift edge D of wing 3a. As a result the torque between the edges A and D resists loading and tightens the joint correspondingly. The same torque prevents the shelf from bending.

The force that prevents the shelf unit from collapsing sideways is in fact the same force as the above torque, which prevents the shelf from bending. For instance, if wall element 6 is pushed to the left from its top part, a torque is created between the edges A and B, but in this case the torque prevents the motion sideways. The combined effect of all the clips in the shelf unit makes it strong against forces sideways and consequently no separate supporters are needed on the back side of the shelf unit.

Figure 4 illustrates a modification of the inventive joint clip 1, where its contruction has been changed so that the new joint clip 9 is able to joint the two opposite shelf elements 7,8, which are on the same level. In the new structure wing 5a has been replaced with the mirror picture of the wings 3a,4a and correspondingly wing 5b with the mirror picture of the wings 3b,4b. The new parts have been marked in figure 4 with the wings 3c,4c,3d,4d. The joining mechanism of clip 9 functions in the same way as clip 1 in such cases, where the opposite shelves have a relatively small load, which is different on both sides. A partly different functioning appears in such a case, where the opposite shelves have rather heavy and equal loads. The loads cause torques between the edges A,D, and J,K that resist the bending of the shelf as in clip 1, but in this case the torques tend to take apart the upper edges E and R from the surfaces of the wall element. As a result the lower edges F and M are squeezed more onto the surfaces of the wall element causing additional tightening. The squeezing is made possible so that the holes L make the structure of the joint clip a little elastic.

The invention is not restricted to the text and drawings presented above, but it can be changed in accordance with the enclosed patent claims. The invention doesn't have to relate to a shelf unit,as shown above, but it can be modified to fit such supporting and frame structures, where the cross section of the element is square in shape or for instance in a smaller scale toy assembly kits.