This invention relates to a tensioning system, and in particular to a tensioning system for use with a polytunnel structure and operable to allow adjustment of the tensioning of the ropes, straps or the like used to anchor a cover of the polytunnel structure in position.

One form of polytunnel structure in common use takes the form of a series of cover support member, typically of arcuate form and usually mounted to the upper ends of legs such that the cover support members are supported above the ground at a desired height. A cover material, for example of a suitable flexible plastics material sheet is supported upon the cover support members, the cover material adopting a profile similar in shape to the shapes of the cover support members. Typically, the cover support members are of arcuate form and result in the cover material adopting a substantially part cylindrical form. Straps, ropes or the like are used to anchor the cover material in position. The ropes, straps or the like extend over the cover material and are anchored to parts of the support structure of the polytunnel structure. By way of example, they may be attached to anchor points in the form of hooks or hoops associated with the legs. The ropes, straps or the like typically extend in a zig-zag fashion along the length of the polytunnel. The ropes, straps or the like are tensioned to tension the cover material.

In some polytunnel structures there is a desire to be able to roll up parts of the cover material, for example to increase ventilation to the interior of the polytunnel structure. As, in the event of rain or high winds, there may be a wish to return the cover material to its original position in order to provide protection to crops within the polytunnel against damage, there may be a need to roll up and unroll parts of the cover material on a regular basis, for example in some circumstances it may be desired to undertaken adjustments several times a day.

Before rolling up or unrolling of the cover material can be undertaken, there is usually a need to release the tension in the ropes, straps or the like used to anchor the cover material in position as the tension in the ropes, straps or the like may prevent such rolling up or unrolling operations from being undertaken. Releasing the ropes, straps or the like to reduce the tension therein is a time consuming operation, leading to the operation of adjusting the level of ventilation being a time consuming, labour intensive, complex task. Accordingly, the level of ventilation may, in practise, not be adjusted as often as is desirable, simply to save time.

It is an object of the invention to provide a tensioning system which simplifies the task of adjusting the tension in the straps, ropes or the like, and so simplifies the task of rolling up or unrolling the cover material, allowing ventilation adjustments to be made in a shorter period of time and in a manner requiring less man power.

According to the present invention there is provided a tensioning system for use with a polytunnel structure, the tensioning system comprising a tensioning member extending along the length of at least part of the polytunnel structure, the tensioning member being rotatable about its axis, the tensioning member including, at intervals along its length, anchor points to which ropes, straps or the like can be secured.

In use, with the ropes, straps or the like anchored to the anchor points, rotation of the tensioning member in one rotary direction will result in winding of the ropes, straps or the like around the tensioning member, increasing the tension in the ropes, straps or the like. Rotation of the tensioning member in the opposite direction releases or reduces the tension. It will be appreciated that a single operation of rotating the tensioning member adjusts the strap or rope tension along the full length of the polytunnel structure in a single operation.

Conveniently, the ropes, straps or the like associated with two adjacent polytunnel structures are anchored to the anchor points of a single tensioning member. Accordingly, the tension of the ropes, straps or the like associated with both polytunnel structures can be adjusted in a single operation. Preferably, the tensioning member is adapted to allow it to be driven for rotation by an electrically powered motor. Alternatively a hand operated crank or the like may be provided to aid manual rotation of the tensioning member.

Where the polytunnel structure is of the type including a rainwater collection gutter, the tensioning member is preferably supported for rotation within the gutter. By way of example, it may be supported by brackets secured to the gutter and/or to legs supporting the gutter.

The invention also relates to a polytunnel structure including such a tensioning system, the system being operable to adjust the tension of anchor ropes, straps or the like used to anchor a cover material sheet in position. A second, adjacent polytunnel structure may be provided, the tensioning system simultaneously adjusting the tension of the ropes, straps or the like associated with both structures.

According to another aspect of the invention there is provided a method of adjusting the tension an anchor rope, strap or the like comprising providing a tensioning system as set out hereinbefore, and rotating the tensioning member thereof to adjust the tension in the rope, strap or the like.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic representation illustrating a tensioning system in accordance with an embodiment of the invention employed in a polytunnel structure;

Figure 2 is a view to an enlarged scale illustrating part of the system of Figure 1; and

Figure 3 is a plan view illustrating part of the system of Figure 1. The accompanying drawings illustrate part of two adjacent polytunnel structures 10, 10'. Each polytunnel structure 10, 10' comprises a series of cover support members 12, each of which is of arcuate form and is supported, at its ends upon legs 14. Each leg 14 includes, at its upper end, a U-shaped section defining limbs over which end parts of the cover support members 12 are fitted to secure the cover support members 12 in position. A cover material 16 extends over the cover support members 12 of each polytunnel structure 10, 10'.

The lower edges of the cover material 16 are wound around respective rollers 18. It will be appreciated that rotation of the rollers 18 results in the cover material 16 being rolled up on to the rollers 18, or unrolled from the rollers 18, depending upon the direction of rotation, and that accordingly the level of ventilation provided to the interior of the polytunnel structure can be adjusted.

The U-shaped sections of the legs 14 together support a rainwater gutter member 20 positioned to collect rainwater draining from the cover material 16, in use, carrying the collected rainwater to an end of the polytunnel structure or other convenient location, for example for collection and subsequent use for irrigation of crops growing within the polytunnel structure.

In accordance with the invention, located within the gutter defined by the gutter member 20 is an elongate tensioning member 22 in the forms of a steel tube, rod or bar of, for example, circular cross section. It will be appreciated, that other materials and other shapes of material may be used without departing from the scope of the invention. The tensioning member 22 is secured in position by brackets 24 which extend over the tensioning member 22 and which are anchored by suitable threaded fasteners to the legs 14. Whilst this represents one manner in which the tensioning member 22 may be secured and supported in position, it will be appreciated that other securing techniques may be used. The primary requirement of the securing technique used is that the tensioning member 22 may be rotated about its axis, in use. Located at intervals along the length of the tensioning member 22 are anchor points in the form of hooks 26 or the like to which anchoring ropes or straps 28 that extend over the cover material 16 of the polytunnel structures 10, 10' may be secured.

In use, during assembly of the polytunnel structures, the anchor ropes, straps or the like 28 of both of the polytunnel structures 10, 10' are attached to or wound around the hooks 26 in a manner similar to that typically used when attaching the ropes, straps or the like to anchor points fixed to the legs of a polytunnel structure, the ropes, straps or the like taking on a zig zagged formation. Tensioning of the ropes or straps 28, and hence of the cover material 16, is achieved by rotating the tensioning member 14 about its axis. Such rotation results in parts of the ropes, straps or the like 28 becoming wound around the tensioning member 14.

When it is desired to adjust the level of ventilation in the polytunnel structures 10, 10', the tensioning member 14 is rotated in the reverse direction, unwinding at least some of the rope or strap material therefrom, and so reducing the tension in the ropes, straps or the like, and in the cover material 16. Once the tension in the ropes, straps or the like 28 has been released to a desired degree sufficient to allow rotation of the rollers 18, the rollers 18 can be rotated to roll up or unroll the cover material 16 to adjust the level of ventilation to the desired degree. Once rotation of the rollers 18 has been completed, the tensioning member 14 is rotated to wind parts of the ropes, straps or the like 28 onto the tensioning member 14, tensioning the ropes, straps or the like 28 to the desired degree. The tensioning of the ropes, straps or the like 28 serves to secure the cover material 16 in position, tensioning the cover material 16, and also to secure the rollers 18 against movement, avoiding undesired rotation thereof and so ensuring that the level of ventilation is maintained at the desired level.

It will be appreciated that the use of the invention is advantageous in that the operation to adjust the tensioning of the ropes, straps or the like 28 can be undertaken simply and quickly, in a labour efficient manner. If desired, rotation of the tensioning member 14 may be undertaken in a motorised fashion for example using an electrically powered motor and gearbox to drive the tensioning member for rotation. Alternatively, a hand operated crank or the like may be fitted to the tensioning member to aid rotation thereof. The invention allows the tensioning of the ropes, straps or the like of two adjacent structures to be adjusted in a single operation, further simplifying the operation of adjusting the ventilation of the polytunnel structures. It will be appreciated, however, that if desired only the anchor ropes, straps or the like of a single polytunnel structure may be secured to the tensioning member.

Along the opposite edges of the polytunnel structures 10, 10', the ropes, strap or the like 28 may be anchored to anchor points associated with the legs 14 or other parts of the polytunnel structure in substantially the usual fashion. Where a number of polytunnel structures are arranged side-by-side, it will be appreciated that the tensioning system of the invention need only be provided adjacent alternate rows of legs of the structures in order for the entire arrangement to benefit from the invention.

Although described herein in relation to adjusting the level of ventilation, the tensioning system may also be used when completely deskinning a polytunnel structure, if desired.

Whilst one embodiment of the invention is described herein, it will be appreciated that a wide range of modifications and alterations may be made to the tensioning system without departing from the scope of the invention as defined by the appended claims.