Patent Description:
Covers, like pavilions, or sheds, made of flexible sheets, like canvas sheets, are occasionally used to cover open spaces, for example playgrounds festival areas, and other areas of outdoor activity, in order to protect the open spaces from direct sunlight, or rain. Covers are also used to protect the content of structures, like greenhouses, from direct sunlight. <CIT> discloses a cover system for a greenhouse with a frame and a flexible sheet and represents the closest prior art. Assembly and disassembly of such covers is complicated and cumbersome.

In some occasions, there is a desire to temporarily retract the cover. For example, when there is a need to temporarily allow exposure of plants in a greenhouse to sunlight, and then deploy the cover again over the greenhouse in order to prevent further exposure of the plants to excess sunlight. Such practice of retraction and deployment of the currently available covers is also cumbersome and complicated.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this subject matter belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present subject matter, suitable methods and materials are described below. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

According to the present invention, there is provided a cover system comprising the features of claim <NUM>.

Embodiments are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the embodiments. In this regard, no attempt is made to show structural details in more detail than is necessary for a fundamental understanding, the description taken with the drawings making apparent to those skilled in the art how several forms may be embodied in practice.

Before explaining at least one embodiment in detail, it is to be understood that the subject matter is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The subject matter is capable of other embodiments or of being practiced or carried out in various ways. In discussion of the various figures described herein below, like numbers refer to like parts. The drawings are generally not to scale.

For clarity, non-essential elements were omitted from some of the drawings.

The present subject matter provides a cover system, optionally comprises several covers, that allows easy and rapid deployment and retraction of at least one cover. The cover is deployed over an open space, which optionally can contain plants, trees, flowers, vegetables, or animals, for example in greenhouses, as well as children in playgrounds and army or industry equipment such as in hangars.

The cover system comprises: at least one cover sheet having four edges; a plurality of flexible rafters, each of the rafters is slidably connected to at least one of two opposite edges of the four edges; and at least one roller provided on at least one of two other opposite edges of the four edges, wherein the roller is configured to rotate, and the cover sheet is configured to wrap around the roller and be released from the roller, depending on a direction of rotation of the roller. According to one embodiment, the cover sheet has a square shape. According to another embodiment, each of the rafters is slidably connected to at least one of two opposite longitudinal edges, and wherein the at least one roller is provided on at least one of two transverse edges.

Referring now to <FIG>, schematically illustrating, according to an exemplary embodiment, a cover system. According to one embodiment, the cover system <NUM> comprises: at least one cover sheet <NUM>-X (X refers to a number of an item in a plurality of items that are similar or identical) having two opposite longitudinal sides L and two opposite transverse sides T; a plurality of rafters <NUM>-X, wherein each longitudinal side L of the cover sheet <NUM>-X is movably connected to a rafter <NUM>-X; and at least one roller <NUM>, wherein at least one of the transverse sides <NUM>-T of a cover sheet <NUM>-X is connected to the roller <NUM>, and wherein the roller <NUM> is configured to rotate, and the cover sheet <NUM>-X is configured to wrap around the roller <NUM> and be released from the roller <NUM>, depending on the direction the roller <NUM> is rotated. The covers <NUM>-X are configured to move according to the arrow <NUM>-X.

Optionally or alternatively, the sheet can be moved and wrapped around an appropriate roller <NUM> that can be on either side of the cover <NUM>-X or only on one side. In case there are two rollers <NUM> operated on both sides of the cover, the cover <NUM>-X can be wrapped on each one according to the current needs. As an example, the cover <NUM>-<NUM> is shown in <FIG> in a state in which it is partially wrapped on the corresponding frontal roller <NUM> so that a portion of the surface is covered and a portion <NUM> is uncovered while the volume beneath this portion <NUM> is exposed to sunlight, rain or the like.

According to one embodiment, the cover system <NUM> further comprises at least one support <NUM>-X configured to support each of the rafters <NUM>-X. According to another embodiment, illustrated in <FIG>, the support <NUM>-X can be in a form of a pole that is configured to hold the rafters <NUM>-X in a predetermined height above a surface of an open space, for example above a sand on the beach, above a grass loan, above a paved surface, above an orchard or crops, and the like. According to yet another embodiment, the support <NUM>-X can be a part of a structure, for example a part of a roof of a greenhouse.

The ability and ease of the covers to deploy and retract is due to the structure of the rafters <NUM>-X and its connection to the cover sheet <NUM>-X.

Referring now to <FIG>, schematically illustrating, according to an exemplary embodiment, a rafter of the cover system. According to one embodiment, a rafter <NUM> comprises a tube <NUM>, a cable <NUM> threaded within the tube <NUM> and extending out of the tube <NUM>; and one, or two rails <NUM> flexibly attached to the tube <NUM>, wherein the rail <NUM> is configured to hold a cover sheet and allow the cover sheet to slide along the length of the rail <NUM> according to embodiments that are described hereinafter. The exemplary rafter <NUM> illustrated in <FIG> comprises two rails <NUM> attached to opposite sides of the tube <NUM>. However, the rafter <NUM> can comprise one rail <NUM> attached to the tube <NUM>. The cable can be any type of cable that is configured to withstand relatively high strength. The cable can be entwined or unite.

According to one embodiment, the rafter <NUM> further comprises one, or two connectors <NUM>, each connector <NUM> is configured to connect the rail <NUM> to the tube <NUM>. As can be seen in <FIG>, the connector <NUM> is attached to the rail <NUM> and the tube <NUM>, and resides between the rail <NUM> and the tube <NUM>. According to another embodiment, the connector <NUM> is narrow. According to yet another embodiment, the connector <NUM> allows bending of the rail <NUM> relative to the tube <NUM>.

As illustrated in <FIG>, the rail <NUM> comprises a hollow <NUM> along the entire length of the rail <NUM>, and a slot <NUM> along the entire length of the rail <NUM>. The slot <NUM> of the rail <NUM> is positioned distally from the tube <NUM> to which the rail <NUM> is attached. Thus, when the rafter <NUM> comprises two rails <NUM> attached to the tube <NUM>, the slots <NUM> of the two rails <NUM> are directed opposite one to the other.

The rail <NUM> can have a profile in any shape that is suitable for allowing the cover sheet to slide along the length of the rail <NUM> according to embodiments that are described hereinafter. The exemplary rail <NUM> illustrated in <FIG> has a round profile, and with the slot <NUM>, it has substantially a C-shape profile. However, this shape of profile is only exemplary and should not be considered as limiting the scope of the present subject matter. For example, the rail can have a rectangular profile having a slot <NUM>, a triangular profile having a slot <NUM>, and the like.

According to one embodiment, the rafter <NUM> is flexible. In other words, the tube <NUM> is flexible, the cable <NUM> is flexible, and the rail <NUM> is flexible. According to another embodiment, the connector <NUM> is flexible as well. In this way, the rafter can be wind into a compact structure.

Referring now to <FIG>, schematically illustrating, according to an exemplary embodiment, cover sheets connected to a rafter. The rafter <NUM> is shown to connect to two cover sheets <NUM>-<NUM> and <NUM>-<NUM> on both sides, which is a portion of the system <NUM> as shown in <FIG>, in an enlarged view. According to one embodiment, the cover sheet <NUM>-X is flexible, and is made of a flexible material, like canvas, nylon, fabric, net, and the like. According to another embodiment, a plurality of sliders <NUM> is attached to a longitudinal edge L of the cover sheet <NUM>-<NUM> and <NUM>-<NUM>. The sliders <NUM> are configured to be threaded in the hollow <NUM> of the rail <NUM>, and slide along the rail <NUM>. Thus, the slot <NUM> of the rail <NUM> allows connection of the sliders <NUM> to the cover sheets <NUM>-<NUM> and <NUM>-<NUM>, when the cover sheets pass through the slot <NUM>.

According to the aforementioned embodiment, the plurality of sliders <NUM> is directly attached to the longitudinal edge L of the cover sheet <NUM>. According to another embodiment, illustrated in <FIG>, the plurality of sliders <NUM> is attached to a longitudinal edge of a strip <NUM>, when an opposite longitudinal side of the strip <NUM> is attached to the longitudinal edge L of the cover sheet <NUM>. According to still another embodiment, the strip <NUM> is adhered to the longitudinal edge L of the cover sheets.

As mentioned above, the plurality of sliders <NUM> is configured to be threaded in the hollow <NUM> of the rail <NUM>, and slide along the rail <NUM>. According to one embodiment, the plurality of sliders <NUM> is configured to freely slide along the rail <NUM>. According to another embodiment, a friction between a surface the slider <NUM> and an inner surface of the rail <NUM>, facing the hollow <NUM> is minimal, thus allowing smooth sliding of the slider <NUM> along the rail <NUM>. Such minimal friction between the surface of the slider <NUM> and the inner surface of the rail <NUM> can be achieved by making the slider <NUM> of a material having a low friction coefficient, or coating the surface of the slider <NUM> with a material having a low friction coefficient, or making the rail <NUM> of a material having a low friction coefficient, or coating the inner surface of the rail <NUM>, facing the hollow <NUM>, with a material having a low friction coefficient, or any combination thereof.

The attachment of the plurality of sliders <NUM> to the longitudinal edge L of the cover sheet <NUM>-X, according to the aforementioned embodiments, retains the flexibility of the longitudinal edge L of the cover sheet <NUM><NUM>-X. For example, when there is a gap between the sliders <NUM>, it is possible to bring the sliders <NUM> close one to another, while somewhat folding the longitudinal edge L of the cover sheet <NUM>-X in the gap between two adjacent sliders <NUM>. This allows, for example, shortening of the length of the cover sheet <NUM>-X to some extent. This embodiment is different, and advantageous, compared to prior art cover sheets. The edges, for example longitudinal edges, of prior art cover sheets are supported by rigid frames, or rigid beams, which render the edges of the prior art cover sheets rigidity.

According to one embodiment, the shape and size of the slider <NUM> corresponds to the shape and size of the hollow <NUM> of the rail <NUM>. For example, the rail <NUM> illustrated in <FIG> has a tube-like structure having a round profile. Accordingly, the slider <NUM> has a ball-like shape having a round profile and a size that fits the size of the hollow <NUM> of the rail <NUM>, in a manner that allows sliding of the slider <NUM> along the rail <NUM>, as described above. However, the embodiment illustrated in <FIG>, regarding the size and shape of the slider <NUM> should not be considered as limiting the scope of the present subject matter. The slider <NUM> can have any size and shape as long as it enables threading of the slider <NUM> into the hollow <NUM> of the rail <NUM>, and sliding of the slider <NUM> along the rail <NUM>.

According to one embodiment, the size of the slider <NUM> is smaller than the size of the slot <NUM> of the rail <NUM>. Thus, the slider <NUM> can be confined within the hollow <NUM>, and slide inside the hollow <NUM> of the rail <NUM> without being able to pass through the slot <NUM> and disconnect from the rail <NUM>. In other words, the plurality of sliders <NUM> are configured to maintain a connection between the cover sheet <NUM>-X and the rail <NUM>.

As illustrated in <FIG>, the cable <NUM> is prone to longitudinal forces, designated with double arrow <NUM>. These longitudinal forces <NUM> are applied on the cable <NUM> when the cable <NUM> is stretched between two opposite supports <NUM> (as shown in <FIG>). Thus, according to one embodiment, the cable <NUM> is configured to withstand longitudinal forces <NUM> applied to the cable <NUM>. As further illustrated in <FIG>, the cable <NUM> is prone to a first transverse force. An exemplary first transverse force is designated with a rightward arrow <NUM>. The first transverse force <NUM> is a pulling force applied by a first cover <NUM>-<NUM> that is connected to the rafter <NUM> according to embodiments described above. Similarly, the cable <NUM> is prone to a second transverse force. An exemplary second transverse force is designated with a leftward arrow <NUM>. The second transverse force <NUM> is also a pulling force applied by a second cover <NUM>-<NUM> that is connected to another side of the rafter <NUM> according to embodiments described above. It has to be mentioned that when only one cover sheet <NUM>-X is connected to the rafter <NUM>, then only one transverse force is applied on the cable <NUM>. Thus, according to another embodiment, the cable <NUM> is configured to withstand a first transverse force <NUM>, or a second transverse force <NUM>, or both a first transverse force <NUM> and a second transverse force <NUM>.

According to one embodiment, the rail <NUM> is configured to withstand a transverse force <NUM> or <NUM> applied by the cover sheet <NUM>-X connected to the rail <NUM> through the sliders <NUM>. The transverse forces <NUM> or <NUM> that is applied by the cover sheet <NUM>-X tend to pull the sliders <NUM> out of the rail <NUM> through the slot <NUM>. Thus, according to a preferred embodiment, the rail <NUM> is configured to withstand the transverse forces <NUM> and <NUM> and does not bend in a manner that widens the slot <NUM> and allows the sliders <NUM> to be pulled out of the rail <NUM> through the slot <NUM>, and thereby disconnect the cover sheet <NUM> from the rafter <NUM>. According to another embodiment, the rail <NUM> is configured to withstand a transverse force <NUM> or <NUM> in a certain degree. Accordingly, a rail <NUM> can be made of materials and designed in a manner that allows the rail <NUM> to withstand a certain degree of transverse forces <NUM> and/or <NUM>. Thus, different rails <NUM> can be designed to withstand different degrees of a transverse force <NUM> or <NUM>.

According to one embodiment, the cable <NUM> is made of a single strand. According to another embodiment, the cable <NUM> is made of a plurality of interwoven strands.

Referring now to <FIG>, schematically illustrating, according to an exemplary embodiment, a cross-sectional view of a rafter connected to a cover sheet. <FIG> illustrates an exemplary embodiment of the rafter <NUM> in which a tube <NUM> is connected to a rail <NUM> with a connector <NUM>. Inside the tube <NUM> there is a cable <NUM>. The rail <NUM> comprises a hollow <NUM> and a slot <NUM>. Inside the hollow <NUM> of the rail <NUM> there is a slider <NUM>. Since the hollow <NUM> is cylindrical, the slider <NUM> has a ball-like shape having a circular profile that corresponds to a circular profile of the hollow <NUM> of the rail <NUM>. All illustrated in <FIG> is a gap between the slider <NUM> and an inner surface of the rail <NUM>. This gap allows the slider <NUM> to freely slide along the rail <NUM>. Nevertheless, as described above there are additional embodiments in which the ability of the slider <NUM> to freely slide along the rail <NUM> is represented. In addition, since <FIG> illustrates a cross sectional view, only one of the plurality of sliders <NUM> that are illustrated in <FIG>, is shown.

Another embodiment that is illustrated in <FIG> is the size of the slider <NUM> that is larger than the size of the slot <NUM> of the rail <NUM>. Thus, when a transverse force <NUM> is applied on the slider <NUM> and tends to pull the slider <NUM> out of the rail <NUM> through the slot <NUM>, the slider <NUM> does not pass through the slot <NUM> and does not exit the rail <NUM>.

However, according to another embodiment, the rail <NUM> is configured to withstand a transverse force <NUM> and/or <NUM> and prevents exit of the slider <NUM> through the slot <NUM> up to a certain threshold level, and when the level of the transverse force <NUM> and/or <NUM> is higher than the threshold level, the rail <NUM> is configured to become flexible and allows widening of the slot <NUM> in an manner that allows the slider <NUM> to exit through the slot <NUM>. This embodiment allows, for example, disconnection of the cover sheet <NUM>-X from the rafter <NUM> by pulling the cover sheet <NUM>-X and thereby applying a transverse force <NUM> and/or <NUM> on the slider <NUM> that is higher than the threshold level that the rail is configured to withstand.

Still another embodiment that is illustrated in <FIG> is the connection of the slider <NUM> to the cover sheet. According to exemplary embodiment illustrated in <FIG>, the slider <NUM> is connected to strip <NUM>, when the strip <NUM> is connected to the cover sheet (the cover sheet is not shown in <FIG>), as illustrated in <FIG>. As can be seen in <FIG>, the strip <NUM> is attached to the slider <NUM> and passes through the slot <NUM> of the rail <NUM>. The strip <NUM> can be attached to the slider <NUM> by, for example, an adhering material, mechanical clamping, and the like.

Referring now to <FIG>, schematically illustrating, according to an exemplary embodiment, a cover system comprising three cover sheets connected through two rafters. <FIG> illustrates a first cover sheet <NUM>-<NUM> connected to a first rafter <NUM>-<NUM>; a second cover sheet <NUM>-<NUM> connected in one side to the first rafter <NUM>-<NUM>, while in an opposite side, the second cover sheet <NUM>-<NUM> is connected to a second rafter <NUM>-<NUM>; and a third cover sheet <NUM>-<NUM> also connected to the second rafter <NUM>-<NUM>, according to embodiments described above. Thus, the three cover sheets <NUM>-X that are connected by the two rafters <NUM>-X together form a cover system <NUM> that is configured to cover an open space, crops, or items, as described herein before.

<FIG> also illustrates an enlarged view of a part at an edge of the second rafter <NUM>-<NUM> and parts of the second cover sheet <NUM>-<NUM> and third cover sheet <NUM>-<NUM> that are connected to the second rafter <NUM>-<NUM>, according to some exemplary embodiments. The enlarged view illustrates the tube <NUM>, a cable <NUM> inside the tube <NUM> that also protrudes out of the tube <NUM>, a first rail <NUM>-<NUM> attached to one side of the tube <NUM>, and a second rail <NUM>-<NUM> attached to another side of the tube <NUM>. In the first rail <NUM>-<NUM> there is a plurality of second sliders <NUM>-<NUM> attached to the second cover sheet <NUM>-<NUM> through a second strip <NUM>-<NUM>. Similarly, in the second rail <NUM>-<NUM> there is a plurality of third sliders <NUM>-<NUM> attached to the third cover sheet <NUM>-<NUM> through a third strip <NUM>-<NUM>.

Also illustrated in <FIG> are two opposite longitudinal forces <NUM>-<NUM> and <NUM>-<NUM> that can be applied on the cover sheets <NUM>-<NUM>. When, for example, a first longitudinal force <NUM>-<NUM> is applied on the second cover sheet <NUM>-<NUM>, the second cover sheet <NUM>-<NUM> can be pulled in the same direction of the puling force so that the cover sheet <NUM>-<NUM> can wind around the roller <NUM>.

One of the advantages of the cover system <NUM> of the present subject matter is the flexibility of the cover sheets <NUM>-X and the flexibility of the rafters <NUM>-X. For example, the cover sheets <NUM>-X and rafters <NUM>-X can be shipped in spools. This is advantageous particularly due to the large number of components, as well as their large sizes, that occasionally have to be shipped. Another advantage is the easy installation and handling of the cover system <NUM>.

Returning now to <FIG>, illustrating an exemplary embodiment of the cover system <NUM>. The cover system <NUM> comprises a first rafter <NUM>-<NUM>, a second rafter <NUM>-<NUM>, a third rafter <NUM>-<NUM> and a fourth rafter <NUM>-<NUM>. The first rafter <NUM>-<NUM> is stretched over a first raw of supports, in a form of poles designated <NUM>-<NUM>; the second rafter <NUM>-<NUM> is stretched over a second raw of supports <NUM>-<NUM>; the third rafter <NUM>-<NUM> is stretched over a third war of supports <NUM>-<NUM>; and the fourth rafter <NUM>-<NUM> is stretched over a fourth raw of supports <NUM>-<NUM>.

The first rafter <NUM>-<NUM> is connected to one cover sheet <NUM>-<NUM>, and the fourth rafter <NUM>-<NUM> is connected to one cover sheet <NUM>-<NUM>. On the other hand, the second rafter <NUM>-<NUM> is connected to two cover sheets <NUM>-<NUM> and <NUM>-<NUM>, and the third rafter <NUM>-<NUM> is also connected to two cover sheets <NUM>-<NUM> and <NUM>-<NUM>. Thus, according to one embodiment, the rafter <NUM>-<NUM>, as an example, can comprise one rail on an appropriate side, and as a result, rafter <NUM>-<NUM> is configured to connect to one cover sheet <NUM>-<NUM>. According to another embodiment, the rafter <NUM>-<NUM>, as an example, can comprise two rails, each on one side of the rafter, and as a result, rafter <NUM> is configured to be connected between two cover sheets <NUM>-<NUM> and <NUM>-<NUM>.

According to one embodiment, the degree of retraction of one cover sheet is independent of the degree of retraction of other cover sheets of the cover system. For example, referring now to <FIG>, the first cover sheet <NUM>-<NUM> can be fully retracted, while the second cover sheet <NUM>-<NUM> and the third cover sheet <NUM>-<NUM> are fully extended. Another example is that the first cover sheet <NUM>-<NUM> and the second cover sheet <NUM>-<NUM> can be partially extended, while the third cover sheet <NUM>-<NUM> is fully retracted. This is to illustrate the flexibility of usage of the cover system <NUM> of the present subject matter.

According to one embodiment, the direction of movement of one cover sheet along the rafter or rafters, to which the cover sheet is connected, is independent of the direction of movement of other cover sheets of the cover system, along the rafters, to which the other cover sheets are connected. The directions of movements of the cover sheets and rafters are illustrated in <FIG> with double-headed arrows <NUM>-X. Each cover sheet <NUM>-X can move in directions <NUM> independently of the other cover sheets.

Referring now to <FIG>, schematically illustrating, according to an exemplary embodiment, a cover sheet comprising a plurality of different parts. In the aforementioned embodiments, the cover sheet <NUM> was regarded as uniform in its entirety, for example in terms of transparency. However, according to another embodiment, the cover sheet <NUM> can comprise a plurality of sub-cover sheets <NUM>-X that are attached one to the other along the length of the cover sheet <NUM>. According to yet another embodiment, the sub-cover sheets <NUM>-X are different in their transparency. For example, <FIG> illustrates two sub-cover sheets of the cover sheet <NUM> - a first sub-cover sheet <NUM>-<NUM> and a second sub-cover sheet <NUM>-<NUM>. As will be understood hereinafter, this cover sheet <NUM> can comprise additional sub-cover sheets <NUM>-X that are not seen in <FIG>. For example, the first sub-cover sheet <NUM>-<NUM> can be opaque and prevents passage of light through it, and the second sub-cover sheet <NUM>-<NUM> can be transparent and allows passage of light through the second sub-cover sheet <NUM>-<NUM>.

In addition, <FIG> illustrates a first roller <NUM>-<NUM> attached to one side of the cover sheet <NUM>, and a second roller <NUM>-<NUM> attached to an opposite side of the cover sheet <NUM>. Simultaneous rolling of the first roller <NUM>-<NUM> and the second roller <NUM>-<NUM>, in the same direction and velocity causes changing of the sub-cover sheet <NUM> that is practically used for covering. Thus, the exemplary cover sheet <NUM> that is illustrated in <FIG> can comprise additional sub-cover sheets <NUM> that are wrapped around the rollers <NUM>-X. For example, as illustrated in <FIG>, the first sub-cover sheet <NUM>-<NUM> that is opaque is practically used for covering. When there is a desire to allow light to pass through the cover sheet <NUM>, the first roller <NUM>-<NUM> and the second roller <NUM>-<NUM> can simultaneously roll clockwise in the same speed. As a result, the first sub-cover sheet <NUM>-<NUM> is wrapped around the first roller <NUM>-<NUM>, and the second sub-cover sheet <NUM>-<NUM>, that is transparent, is released from the second roller <NUM>-<NUM> and practically used for covering, thus allowing passage of light through the cover sheet <NUM>.

It should be mentioned that the embodiments illustrated in <FIG> are possible due to the structure of the cover system <NUM> of the present subject matter, namely the rafters <NUM>-X and the embodiments of connection of the cover sheet <NUM> with the rafter enables the aforementioned ability to change the type of sub-cover sheet <NUM>-X that is practically used for covering.

According to one embodiment, the roller <NUM> is manually operated. According to another embodiment, the roller <NUM> is operated by a rotor.

It is appreciated that certain features of the subject matter, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the subject matter, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub combination.

Claim 1:
A cover system (<NUM>) comprising:
at least one cover sheet (<NUM>-X) having four edges;
a plurality of flexible rafters (<NUM>-X), each of the rafters is slidably connected to at least one of two opposite edges of the four edges; and
at least one roller (<NUM>) provided on at least one of two other opposite edges of the four edges, wherein the roller (<NUM>) is configured to rotate, and the cover sheet (<NUM>-X) is configured to wrap around the roller (<NUM>) and be released from the roller (<NUM>), depending on a direction of rotation of the roller (<NUM>).