Over centre fastener

Abstract

The over centre faster 10 includes a handle 14 with a first end being pivotably connected to a base plate 12. A guide frame 16 is pivotably connected 32 to the handle, the pivotable connection between the guide frame and the handle being between the first and second ends. A guide block 18 is slidable relative to the guide frame. A hook 20 comprises a hooked end 20a an a threaded straight section. Ab urging element 38 for biasing the hooked end toward the guide frame. The threaded straight section passes through a hole in the guide frame and is securable for linear movement with the guide block. Movement of the hooked end in the direction of the guide block is limited by a threadedly adjustable stop 36; and wherein the means for securing the threaded straight section of the hook for linear movement with 15 the guide block are rotatably fixed in relation to the guide block

Description

FIELD OF THE INVENTION The invention relates to over centre fasteners and methods of operating them, and more specifically to spring loaded over centre fasteners. BACKGROUND Over centre fasteners, also known as over centre latches, or toggle latches, are common in many industries and applications where a fast and easy securing method is required. One example particularly relevant to the present invention is the securing of the curtain element on curtain sided vehicles, trailers, containers, and the like. The side curtains on vehicles often experience slippage or deviation from their fixed positions due to factors such as uneven road surfaces during vehicle motion, vibrations generated by the high-speed turbulent airflow around the vehicle, or other external influences. Such forces frequently lead to the gradual displacement of the fastening apparatus over extended periods of vehicular operation. To overcome this, adjustable spring loaded over centre fasteners exist which allow the tension on a curtain to be adjusted. Such fasteners work by adjusting the preload on a spring acting on the hook, either with or without adjusting the height of the hook to adjust the tension on the curtain. Adjusting the fastener can require multiple tools, as described in detail below, and is somewhat cumbersome. Further, during use and due to external factors described above, the mechanism remains under tension, meaning that the spring remains in a state of compression. The continual movement between moving parts results in scratching, noise pollution, abrasion, and, in some cases, corrosion due to wear on the contact surfaces exceeding the depth of anti-corrosion protection. Wear also causes the latch to become difficult to use, resulting in a large amount of force being required to correctly operate it. This may result in the latch not being secured correctly, thereby creating a safety hazard. SUMMARY OF THE INVENTION A solution is therefore required which leads to a safer and more durable fastener, and also a fastener that is simpler and more efficient to adjust. To solve the problems identified above, there is provided, in a first aspect of the invention, a fastener as set forth in claim 1 of the appended claims. In a second aspect of the invention, there is provided a method as set forth in claim 10. In a third aspect of the invention, there is provided a method as set forth in claim 11 of the appended claims. Preferred features of the invention are set forth in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an isometric view of a spring loaded over centre fastener, and Figures 2 is a detail section view of the mechanism shown in figure 1. DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows an adjustable spring loaded over centre fastener 10 (hereinafter referred to as an over centre fastener) comprising a base plate 12, a handle 14, a guide frame 16, a guide block 18, and a hook 20. The basic operating principle of the present invention is the same as a typical over centre fastener and so will not be described in detail. The base plate 12 comprises a rear face suitable to be attached to a complimentary shaped mounting point or surface. The base plate 12 may be attached to the mounting point or surface by any means known in the art, such as screws, bolts, or rivets passing through holes in the base plate 12, or by welding or adhesive. It will be appreciated that the means for attaching the base plate 12 to the mounting point or surface will be chosen based on the forces expected for a given application. Projecting from the planar surface of the base plate 12 are two short arms 22, the arms 22 being spaced from each other sufficiently to allow a first end of the handle 14 to lie between them. Holes in the arms 22 and the first end of the handle 14 allow for a pin 28 to pivotably connect the two components, the handle 14 able to pivot relative to the base plate 12 about the pin 28. The handle 14 may be of any shape or length according to the intended use and force required to operate the fastener 10 and may feature an ergonomically shaped grip 30 at its second end. The guide frame 16 is generally the shape of a flat-bottomed U with each of its ends being pivotably connected to the handle at a point between the first end and the grip 30 via a second pin 32. The hook 20 has a hooked end 20a and a threaded straight section 20b. The threaded straight section passes through, but does not threadedly engage with, a hole in the flat bottom of the guide frame 16. To limit movement of the hook 20 in one axial direction (downwards in the figures), a threaded fastener, such as a nut 34, is provided in threaded engagement with the threaded straight section 20b of the hook 20. The axial end of the hook 20 opposite the hooked end 20a is connected for linear movement with, but remains rotationally independent of, the guide block 18. This may be achieved using a number of methods, such as (i) providing a thread in the guide block 18 for threadedly engaging the threaded straight section 20b of the hook 20, or (ii) providing a non-threaded hole in or below the guide block 18, and providing a second threaded fastener 36 of larger outside diameter than the hole, the second fastener 36 threadedly engaging the threaded straight section 20b of the hook 20. In embodiments where a second threaded fastener 36 is used, it must be prevented from rotating relative to the guide block 18. This realises the advantage of the invention, which is to allow (i) the adjustment of the spring preload, and (ii) the adjustment of the spring preload and the hook height, with the need for fewer tools. The second threaded fastener may be prevented from rotating relative to the guide block by providing a recess in the guide block of complimentary shape to the fastener. Alternatively, projections may be provided that prevent rotation in that the guide block comprises protrusions positioned radially closer to the axis of the hook 20 than the longest radial distance to which the second threaded fastener 36 extends. Any other means known in the art for preventing rotation may be used, such as on or more insertable grub screws, spring pins, cotter pins or the like. It will be appreciated that although a second fastener 36 can be a conventional sixsided nut, it is appropriate to use any multi-sided threaded fastener. Alternatively, any single sided fastener capable of preventing itself rotating can be used. For example, a rivet nut could be installed in the hole in a guide block of appropriate thickness. The guide block 18 has slots 40 complimentary to the size of the sides of the guide frame 16 in order to allow the guide block 18 to move linearly in the axial direction of the threaded straight section 20b of the hook 20. The slots 40 also serve the purpose of preventing the guide block 18 from rotating relative to the guide frame 16. A typical guide block in the prior art is manufactured from a metal such as steel. To reduce wear on the guide frame 16, the guide block may be made from a plastics material, or indeed any material having a hardness less than the material of the guide frame 16. Alternatively, the guide block 18 could be made from any material but be coated with a material having less hardness than the material of the guide frame 16, the coating being either completely covering the guide block 18 or only coating the sections that will contact the guide frame 16. To reduce costs, the coating may only be applied to the sections of the guide block 18 designed to come into contact with the guide frame 16, i.e., the slots 40. A spring 38 is situated between the guide block 18 and the guide frame 16 and surrounds the threaded straight portion 20b of the hook 20. The spring serves to bias the hooked end 20a of the hook 20 toward to the guide frame 16, and therefore also biases the threaded fastener 34 into contact with the guide frame 16. In use, the handle 14 is pivoted about the base plate 12 in order to raise the guide frame 16 and thus the hook 20. A part of the article to be secured is then engaged with the hooked end 20a. The grip 30 is then forced by a user to pivot the handle 14 generally downward until the over centre fastener 10 is secure. The act of securing the fastener 10 moves the hook 20 in a downwards direction, thereby tensioning the article. For many reasons, it may be desired or required that the spring preload is adjusted, either at the same time as or without also adjusting the position of the hook 20. Adjusting the spring preload and hook position simultaneously requires the adjustment of the threaded fastener 34 acting to limit downward movement of the hook 20. A conventional over centre fastener requires using a wrench to secure the second fastener 36 to prevent it from rotating relative to the hook 20, and then using another wrench to turn the top threaded fastener 34 to complete the operation. Such an operations requires two hands as well as two tools. The present invention simplifies this process by allowing direct adjustment of the top threaded fastener 34 with just one wrench. This is facilitated by the guide block 18 ensuring that the lower fixing means are not able to rotate. Adjusting the spring preload without changing the hook position is accomplished by raising the guide block 18, and therefore the compressing the spring 38, independent of the hook. To do this using a conventional over centre fastener, it is required to use a wrench to secure a lower nut, and then rotate the hook relative to the lower nut. The present invention eliminates the need for a wrench and allows for direct adjustment of the spring tension by manually rotating the hook 20. This turns a two-handed job that requires one tool, into a one-handed job that requires no tools. This is made possible because, as the hook 20 rotates, the threaded fastener 34 rotates at the same rate and in the same direction, i.e., the threaded fastener 34 does not rotate relative to the hook 20. To improve reliability, the threaded fastener 34 may have low strength locking means such as a nylon insert to prevent unwanted relative rotation. The lower fixing means are not able to rotate relative to the guide block 18, thereby performing the function of the wrench in the prior art method. Therefore, with the rotation of the hook 20, the guide block 18 preloads the spring 38. It will be appreciated that the above description relates to several embodiments of the invention. Where alternatives have been proposed, they may be combined in any combination that is technically feasible. It will also be understood that not all possible alternatives have been disclosed. For example, the description above indicates that in some embodiments, the threaded fastening 34 which acts as a stop has a nylon insert to ensure the fastening 34 rotates with the hook 20 when the hook 20 is turned. It is clear that a nylon lined fastening is not required and that the purpose of limiting rotation may be accomplished using a standard threaded fastener, with or without a washer 42, a bearing, a low friction surface or surface finish; the purpose being to ensure the friction between the fastening 34 and the surface immediately below it is less than the friction caused by the threaded engagement between the fastening 34 and the hook 20. Other inconsequential modifications may, for example, include using a guide frame of a different shape. The purpose of the guide frame 16 is to provide a surface for slidable interaction between the guide block 18 and the guide frame 16, and also to provide a surface against which the fastening 34 can act as a stop for movement of the hook 20. Further, although a hook 20 is shown in the figures, and therefore described above, it will be appreciated that any attachment member known in the art may be used. For example, rather than having a hooked end 20a, the attachment member may have a looped end of any shape for accepting fastening means from the article to be secured. Similarly, there may be provided a radial hole towards the top of the straight section that can accept fastening means from the article to be secured.

Claims

1. An over centre fastener for securing an article, the over centre fastener comprising:5 a base plate (12) for fixing to a surface;a handle (14) having opposite ends, one end being pivotably connected to the base plate (12);a guide frame (16) pivotably connected to the handle (14), the pivotable connection (32) between the guide frame (16) and the handle (14) being between the opposite ends io of the handle (14);a guide block (18) slidable relative to the guide frame (16);an attachment member (20) comprising a first end (20A) for attaching to the article to be secured, and a threaded straight section (20B); andan urging element (38) for biasing the first end (20A) of the attachment member 15 (20) toward the guide frame (14);wherein the threaded straight section (20B) passes through a hole in the guide frame (16) and is secured for linear movement with the guide block (18); andwherein movement of the first end (20A) of the attachment member (20) in the direction of the guide block (18) is limited by a threadedly adjustable stop (34);2 0 characterised in that the means securing the threaded straight section of the attachment member (20) for linear movement with the guide block (18) are rotationally fixed in relation to the guide block (18).

2. The over centre fastener of claim 1, wherein the means for securing the 25 threaded straight section of the attachment member for linear movement with the guide block are threads integral to the guide block (18).

3. The over centre fastener of claim 1, wherein the means for securing the threaded straight section of the attachment member for movement with the guide block 3 0 i s a threaded fastener (3 6).

4. The over centre fastener of claim 3, wherein the threaded fastener (36) is a multiple sided threaded fastener.35 5. The over centre fastener of claim 4, wherein the guide block (18)comprises a recess of a shape complimentary of the threaded fastener, thereby preventing rotation of said threaded fastener (36) relative to the guide block (14).

6. The over centre fastener of claim 4, wherein the guide block comprises4 0 protrusions positioned radially closer to the axis of the attachment member than the longest radial distance to which the threaded fastener (36) extends.

7. The over centre fastener of any proceeding claim, wherein the guide block(18) comprises, at its surfaces in contact with the guide frame (14), a material of lower hardness than the material of the guide frame (14).5 8. The over centre fastener of claim 7, wherein the material of lowerhardness than the material of the guide frame is a plastics material.

9. The over centre fastener of any preceding claim, wherein the guide block (18) is made from a material of lower hardness than the hardness of the guide frame (14).io10. The over centre fastener of claim 9, wherein the guide block (18) is made from a plastics material.

11. A method for adjusting the spring preload on an over centre fastener 15 according to claim 1, the method consisting of rotating the attachment member in relationto the guide block.

12. A method of adjusting, simultaneously, the spring preload and the distance which the attachment member protrudes from the guide frame on an over centre 2 0 fastener of claim 1, the method consisting of rotating a threadedly adjustable stop in relation to the attachment member.

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