GB2054467A - Engaging construction, engaged sheet, engagement projection, and engagement structure - Google Patents

Abstract

A construction for engaging a sheet to a body e.g. a stencil to a duplicator, which includes an engagement projection protruding from the body and a portion of the sheet formed with an engaging aperture. The engagement projection is formed of first and second columnar portions extending from the body so as to be substantially parallel to each other. A bridging portion joins the ends of these columnar portions remote from the body. The engaging aperture is formed as first and second holes adapted to receive the first and second columnar portions, respectively. An elongated slit opening joins these two holes. The part of the sheet adjacent to the slit opening is elastically deformed only when the bridging portion passes through the slit, and is substantially not plastically deformed.

Description

SPECIFICATION Engaging construction, engaged sheet, engagement projection, and engagement structure Background of the invention The present invention relates to a structure for detachably engaging a sheet to a body, and, more particularly, relates to a particular arrangement and construction of one or more sheet engagement projections and one or more corresponding sheet engaging apertures, in such a sheet engaging structure.

In the mechanical arts it is often required to mount detachably a sheet to a body. For example, it is often required, in the field of stencil utilization and printing, to detachably mount a stencil sheet onto a rotary press drum of a stencil printer. For such detachable mounting, it has already been practiced to provide an engagement means on the body, and openings or apertures on the sheet adapted to be engaged with said engagement means.

A number of such engagement structures have already been suggested and practiced.

A first such known engagement structure comprises one or a plurality of columnar projections which protrude substantially perpendicularly from the body to which the sheet is to be mounted, and parts of the sheet which are formed with holes whose shape corresponds to the cross sectional shape of the columnar portion or portions. The sheet is engaged to the body by the columnar projections being passed each through its corresponding hole in the sheet, so that the peripheries of the hole or holes engage with the outer surfaces of the corresponding columnar projection or projections.With such a structure for engagement of the sheet to the body, there is an advantage in ease of engagement of the sheet to the body, because, simply by placing the sheet over the columnar projections projecting from the body, the sheet is joined to the body, without any deformation needing to be produced in the portions of the sheet around the holes therein, and, accordingly, without reqiring very much force to mount the sheet to the body. Further, when the sheet is mounted to the body, it is impossible to move the sheet with respect to the body in any direction in the plane of the sheet, which is desirable.However, since the sheet is freely movable in the direction perpendicularto its surface, by the holes sliding axially along the columnar projections, the sheet is liable to become accidentally detached from the body, by the holes in the sheet accidentally sliding to the ends of the columnar portions and coming off them.

A second structure for engagement of a sheet to a body has been proposed, upon consideration of the above described disadvantages in the first structure, in which the ends of the columnar portions remote from the body are provided with heads whose cross section is greater than that of the main parts of said columnar portions. Since the holes in the sheet, in this second construction, are still of a shape and size approximately corresponding to the cross sections of these main parts of the columna portions, they do not easily fit over the heads of the columnar portions, and, in order to pass the sheet over the heads of the columnar portions, it is therefore necessary to push the sheet firmly towards the body.

Thereby, both elastic and also plastic deformation are caused in the portions of the sheet surrounding the holes, when the heads of the columnar portions are pushed through these holes. When these holes have been pushed over the heads of the columnar portions, the peripheries of these holes will retract to a certain extent to partly resume their original size and shape, and, therefore, it is quite difficult for the sheet accidentally to come off the columnar portions by these holes again being passed over the heads of the columnar portions.

Such a sheet engaging structure has an advantage over the first explained structure in that it is much less likely, therefore, that the sheet should accidentally come off from the columnar portions. However, it has some disadvantages: first, that it may not be very easy to engage the sheet to the body, snce it is necessary to both elastically and plastically deform the parts of the sheet surrounding the holes, which need to be pushed over the heads of the columnar portions, and the resistance of the material of the sheet against such deformation may well be rather great; and, second, that the strength of the sheet as a whole may be reduced by the plastic deformation of the parts of the sheet which surround the holes therein, as these holes are forced over the heads of the columnar portion.This may deteriorate the strength of the sheet as a whole, and, even if this does not occur, because it is unlikely that these portions of the sheet surrounding the holes therein will completely return to their original size and shape, they will probably not closely mate to the outer cross sectional shapes of the columnar portions, and, consequently, a certain amount of free play will probably remain between the sheet and the columnar portions in directions parallel to the sheet, thus causing the difficulty that the sheet is not positively anchored with respect to movement between it and the body, in directions parallel to the sheet.

In order to attempt to overcome the disadvantages of the above two outlined previous constructions, it has been proposed and practiced to provide an engaging structure for a sheet to a body, wherein the body is formed with columnar portions with heads, in a manner similar to that in the second above described arrangement, and the sheet is formed with openings which are rather like keyholes. That is to say, each of these openings has a large hole portion which is adapted easily to pass the head portion of one of the columnar portions, and a slot portion which is adapted to receive the main part of the columnar portion, and which, therefore, is narrower than the cross section of the head portion of that columnar portion.Thus, when the sheet with the openings described above is to be engaged to the body over the columnar portions thereof, first the heads of all the columnar portions are passed through the large holes abovementioned in the sheet, which can be done easily, and then the sheet is displaced as a whole in a direction parallel to its surface with respect to the body, so that the slot portions of the openings in the sheet are all engaged around the main parts of the columnar portions and closely coact thereto.

This structure has the advantage of not requiring any elastic or plastic deformation to be caused in the portions of the sheet surrounding the holes therein.

However, it has two disadvantages that: first, because it is necessary to displace the sheet in a direction parallel to itself with respect to the body when fitting the sheet to the body, the mounting operation of such a sheet to the body becomes rather cumbersome, especiaily when the whole construction of the body is such that the displacement of the sheet is not desirable; and, secondly, the sheet is not positively anchored to the body in all directions parallel to the sheet, but is free with respect to the body in the reverse direction to the abovementioned engagement direction in which it is slid to engage the main portions of the columnar portions into the slot portions of the openings in the sheet; in other words, it is possible for the sheet to be slid in the reverse direction to this first direction, with respect to the body, so that, in the worst case, the main parts of the columnar portions may come out of the slot portions of the openings in the sheet, and enter into the larger parts of the holes in the sheet, whereupon much free play will be present between the sheet and the body in the directions parallel to the sheet, and, further, the sheet may even accidentally come away from the body, by the heads of the columnar portions again passing back through the large holes in the sheet.

Summary of the invention In view of the various problems in the prior art as described above, an object of the present invention is to provide a structure for engaging a sheet to a body, wherein a retaining portion of a projection protruding from the body is allowed to pass through an opening of the sheet by temporarily widening it, but no part of the sheet is distorted, as by stretching, folding, or kinking, during this engaging process, so as to cause any substantial plastic deformation of the sheet, and wherein distortion of the sheet as it is engaged to the body is purely simple elastic bending deformation, which completely disappears when the sheet has been engaged to the body.

A further object of the present invention is to provide such a structure for engaging a sheet to a body as described above, in which the sheet may be engaged or disengaged from the body simply by applying force to approach it thereto or remove it therefrom, without any portion of the sheet being so deformed that it does not spring back substantially to its original unstressed condition after said engagement or disengagement, and without any portion of the sheet being damaged as it is engaged or disengaged to or from the body, which engaging construction nevertheless positively and securely engages the sheet to the body without any substantial play being available therebetween, especially in directions parallel to the plane of the sheet when the sheet is mounted to the body.

According to the present invention, such an object, and others, are attained by the provision of an engaging construction for engaging a sheet to a body, comprising a portion of the sheet formed with an engaging aperture, and an engagement projection protruding from the body; wherein the engagement projection comprises first and second columnar portions extending from the body so as to be substantially parallel to each other, and a bridging portion joining the ends of these columnar portions remote from the body; and wherein the engaging aperture is formed as first and secdnd holes which receive said first and second columnar portions, respectively, and an elongated slit opening joining these holes; the part of the sheet adjacent to the slit opening being elastically deformable.

Brief description ofthe drawings The present invention will become more fully understood from the following description of some preferred embodiments thereof, which is to be taken in conjunction with the accompanying drawings. It should be clearly understood, however, that the description of the embodiments, and the drawings, are all of them provided purely for the purposes of illustration and exemplification only, and are in no way to be taken as limitative of the scope of the present invention.In the drawings: Figure 1 is a schematic plan view, showing the edge or mounting portion of a stencil sheet mounted over a rotary press drum with its apertures being engaged to projections provided on the rotary press drum, according to a first preferred embodiment of the present invention; Figure 2 is a cross sectional view through the stencil sheet and the rotary press drum shown in Figure 1, taken along the line II - II in Figure 1; Figure 3 is a side view of the sheet engagement projection incorporated in the sheet engagement construction shown in Figures 1 and 2; Figure 4 is a plan view of the sheet engagement projection shown in Figure 3, taken along the arrows IV in Figure 3; Figure 5 is a cross sectional view through the sheet engagement projection of Figure 3, taken along the line V - V in Figure 3;; Figure 6 is a plan view of a sheet engaging aperture in the stencil sheet shown in Figures 1 and 2, which is adapted to be engaged over the sheet engagement projection shown in Figures 1 - 5; Figure 7 is a cross sectional view similar to Figure 5, showing a preferred modification of the sheet engagement projection shown in Figures 3 - 5; Figures 8 and 9 are views similar to Figure 6, showing other preferred embodiments of the sheet with engaging aperture, adapted to be engaged with the sheet engagement projections shown in Figures 3 - 5 and 7; Figures 10, ii, and 12 are views similar to Figure 6, showing further three other preferred embodiments of the engaging aperture, which are adapted to be engaged with three corresponding engagement projections which are not shown in the drawings; and Figure 13 is a perspective view, illustrating a still further preferred embodiment of the sheet engagement projection, and a corresponding engaging aperture, according to the present invention.

Description of the preferred embodiments In the drawings, the reference numeral 1 denotes a rotary press drum, and 2 designates a stencil sheet which is to be mounted on the drum for use therewith for printing. As seen in Figure 2, on the upper surface of the drum 1 there is mounted a sheet mounting pad 3, from which protrude, substantially radially, a plurality of sheet engagement projections 4 and a plurality of secondary sheet engagement projections 5.

The said plurality of sheet engagement projections 4 correspond to a plurality of sheet engaging apertures 7 provided in the stencil sheet 2, and the secondary sheet engagement projections 5 correspond to a plurality of secondary sheet engaging apertures 8 provided in the stencil sheet 2. With regard to these two different types of sheet engagement system, the secondary sheet engagement system incorporating the secondary sheet engagement projections 5 and the secondary sheet engaging apertures 8 is a per se well known type of system, according to the first above described prior art, the secondary sheet engagement projections 5 being simple columns, extending substantially perpendicularly to the sheet mounting pad 3, and of circular cross section, while corresponding to these the secondary sheet engaging apertures 8 are substantially circular holes of substantially the same diameter.On the other hand, the sheet engagement projections 4 and the sheet engaging apertures 7 are of a particular novel sort, according to the present invention. All of the sheet engaging apertures 7 and 8 are provided in a reinforced portion 6 of the stencil sheet 2, which extends along the left hand edge thereof in Figure 1.

In Figures 3 and 4, the first embodiment of the sheet engagement projections 4 according to the present invention is shown in more detail. Each of these sheet engagement projections 4 is formed of two columnar portions 9 projecting from the sheet mounting pad 3, substantially parallel to each other, and a bridging portion 10 which extends between the ends of these columnar portions 9 remote from the sheet mounting pad 3. Thereby, as a whole, the sheet engagement projection 4 is substantially of a staple-like shape, projecting from the sheet mounw ing pad 3. This general shape is common to all of the six preferred embodiments for this sheet engagement projection 4 which will be described, according to the present invention.In this first preferred embodiment shown in Figures 3 and 4, the cross sectional shapes of both of the columnar portions 9 are circular, and, likewise, the cross sectional shape of the bridging portion 10 is circular, as may be seen in Figure 5.~Further, since, in this embodiment, it is desirable to engage the stencil sheet 2 to and keep it lying in contact with the sheet mounting pad 3, the two columnar portions are arranged to be of an equal length and both of them protrude perpendicularly from the surface of the sheet mounting pad 3, so that said bridging portion 10 runs parallel to said surface.

In Figure 6 a shape for the sheet engaging aperture 7, which is formed in the reinforced apertured portion 6 of the stencil sheet 2, for engagement with the sheet engagement projection 4 shown in Figures 3, 4, and 5, is shown. Generally, this sheet engaging aperture 7 is formed as a pair of circular holes 11 through the reinforced apertured portion 6, together with a slit 12, whose opposite sides form lips 13 which abut each other, this slit 12 joining these two holes 11 approximately along the line between their centers. The diameter of the circular holes 11 is substantially the same as or slightly greater than the cross sectional diameter of the cylindrical columnar portions 9 of the sheet engagement projection 4.For each of the sheet engagement projections 4 shown in Figure 1, there is provided a corresponding one of these sheet engaging apertures 7, and these sheet engaging apertures 7 are arranged on the reinforced apertured portion 6 of the stencil sheet 2 in a corresponding layout to the arrangement of the sheet engagement projections 4 on the sheet mounting pad 3.

When the stencil sheet 2 formed with these sheet engaging apertures 7 is to be engaged to the rotary press drum 1,the reinforced apertured portion 6 of the stencil sheet 2 is laid over the sheet mounting pad 3, with the sheet engaging apertures 7 corresponding to the sheet engagement projections 4, and then each of these sheet engaging apertures 7 is pressed towards its corresponding sheet engagement projection 4, by the periphery of the sheet engaging aperture 7 being pressed towards the central axis of the rotary press drum 1.For the initial positioning of the sheet engaging apertures 7 as corresponding to their respective sheet engagement projections 4, the provision of the simple cylindrical columnar secondary sheet engaging projections 5 as corresponding with the simple circular hole shaped secondary sheet engaging apertures 8 is convenient, because it is possible to place the secondary circular sheet engaging apertures 8 over their respective corresponding secondary sheet engagement projections 5 without applying any substantial force thereto, in order to obtain initial location of the stencil sheet 2 with respect to the sheet mounting pad 3 of the rotary press drum 1.Further, it is convenient, for this initial engagement, for some of the secondary sheet engagement projectons 5 to be circumferentially displaced around the periphery of the rotary drum 1 from the plurality of sheet engagement projections 4. It is, further, helpful for this initial engagement for some of the secondary sheet engagement projections 5, also, to be in the same circumferential position around the rotary press drum 1, as are the sheet engagement projections 4.

This arrangement can be seen in Figures 1 and 2.

It should be noted that, for this pressing of the peripheries of the sheet engaging apertures 7 towards the central axis of the rotary press drum 1, it is particularly convenient for the sheet engagement projections 4, and their corresponding sheet engaging apertures 7, to be arranged along a straight line, because in this case the operator may simply pinch his thumb and forefinger, for example, together, and run them along this line, with the sheet engagement projections passing between them. This will very quickly and easily mount the stencil sheet 2 to the rotary press drum 1. A further useful modification of this arrangement is to angle one of the sheet engagement projections 4, and its corresponding sheet engaging aperture 7, somewhat out of said line, by an angle of about 45" or less.This narrow angle will not significantly deteriorate the above mentioned convenience of attachment, but will ensure thatthe stencil sheet 2 can only be mounted to the rotary press drum 1 with a particular side facing the drum, and cannot be fixed upside down.

As the peripheries of the sheet engaging apertures 7 are pressed towards the central axis of the rotary press drum 1, as explained above, the bridging portion 10 of each of the sheet engagement projections 4 will be pressed againstthe lips 13, which are on either side of the slit 12, as shown in Figure 3.

Accordingly, the lips 13 will be bent out of the plane of the stencil sheet 2, along lines generally shown in Figure 6 by 14, 15, and 16. This elastic deformation of the lips 13 of the reinforced apertured portion 6 of the stencil sheet 2 occurs, substantially entirely, in a non-stretching, non-compressing, non-folding, nonkinking fashion. That is to say, because this bending of the lips 13 only occurs in one direction, along the aforesaid lines 14, 15, and 16, no substantial plastic deformation of the lips 13 occurs.Therefore, when the bridging portion 10 of the sheet engagement projection 4 has been pushed past the lips 13, so that the sides of the slit 12 become disengaged from this bridging portion 10, then the lips 13 spring back together, so that the sides of the slit 12 again abut, and the reinforced apertured portion 6 of the stencil sheet 2 around the sheet engaging aperture 7 will, substantially, be in its original or undeformed condition, with the sheet engaging aperture 7 engaged over the sheet engagement projection 4.

When the stencil sheet 2 is engaged by these sheet engaging apertures 7 formed in the reinforced apertured portion 6 thereof over the sheet engagement projections 4, then the peripheries of the circular holes 11 engage closely to the outercircum- ferences of the columnar portions 9, and, accordingly, the stencil sheet 2 is positively engaged to the rotary press drum 1, with substantially no free movement of the stencil sheet 2 in its own plane being possible with respect to this rotary press drum 1. When the stencil sheet is in this position, engaged on the rotary press drum 1, then the lips 13 on either side of the slit 12, by their elasticity, oppose any force which tends to remove the stencil sheet 2 from the sheet engaging projections 4.As seen in Figure 3, the parts of the columnar portions 9 which extend from the sheet mounting pad 3 to the side of the bridging portion 10 which is closestto the sheet mounting pad 3 are relatively short. Thus, the stencil sheet 2 is firmly engaged in its position to the sheet mounting pad 3 on the rotary press drum land, substantially, cannot move with respect to the rotary press drum 1, either in any direction along the plane of the sheet, or perpendicularly to the plane of the sheet.

In Figure 7, there is shown a modification of the form of the sheet engagement projection 4 shown in Figures 3 - 5. This sheet engagement projection is formed with a pair of columnar portions 9 which are of circular cross section, as were the columnar portions 9 of the embodiment shown in Figures 3 - 5.

However, in this modification, the cross sectional shape of the bridging portion 10 is changed from the circular shape in such a manner that, while the upper side 10a in the drawing of the cross section of the bridging portion 10 is curved in approximately a circularshape,the lower side 10b is flattened.By this shape for the bridging portion 10, the mounting of the stencil sheet 2 onto the sheet engagement projection 4 is easy, because the upper part 10a of the circular cross section of the bridging portion 10 will smoothly and easily push apart the lip portions 13 of the stencil sheet 2, while, on the other hand, when the stencil sheet 2 is impelled away from the sheet mounting pad 3, the relatively flatly formed lower surface 10b of the cross section of the bridge portion 10 will have much more difficulty in bending aside the lips 13 of the reinforced apertured portion 6 of the stencil sheet 2, because this flattened portion 10b provides relatively little levering or wedging open action to open the slit 12.This is advantageous, because, once a stencil sheet has been mounted upon a rotary press drum, it is to be kept mounted upon this drum during use. After printing operations from this stencil sheet have been completed, this stencil sheet is certainly removed from the rotary press drum and discarded. Therefore, in normal use, it is relatively unlikely that any requirement should occur for a stencil sheet to be removed from a rotary press drum without being damaged. Accordingly, tight engagement of the stencil sheet to the rotary press drum is desirable, while, on the other hand, any added difficulty thereby caused in removing the stencil sheet from the rotary press drum without damaging it may usually be relatively unimportant for practical purposes.

In Figure 8 there is shown an alternative form for the sheet engagement aperture 7 formed in the reinforced apertured portion 6 of the stencil sheet 2, which makes mounting of the stencil sheet to the printing drum much easier. In this embodiment, the sides of the slit 12 do not abut each other, in their unstressed condition, but on the contrary are somewhat spaced apart. Thus between the lips 13 there is a certain gap. In this embodiment, the engagement of the sheet engaging aperture 7 over the sheet engagement projection 4 becomes much easier.

This, of course, increases the likelihood of the stencil sheet 2 coming off the sheet engagement projection 4 accidentally; however, in practice, even in this embodiment, this likelihood may be sufficiently small for practical purposes to cause no substantial problem.

In Figure 9, there is shown a further modification of the shape of the sheet engagement aperture 7. In this embodiment, which is, as is the embodiment of Figure 8, designed to be used with a sheet engagement projection which is essentially the same as that shown in Figures 3,4 and 5, the sides of the slit 12 are not formed as parallel straight lines, but are formed as arcuate lines. Thus, the width of the slit 12 varies along its length, and is least towards the middle of the slit 12, while it increases along with increase of distance away from the middle of the slit 12, so that, in fact, the ends of the slit 12 merge continuously and smoothly into the peripheries of the circular holes 11.In this case, smooth and correct engagement of the sheet engaging apertures 7 in the reinforced apertured portion 6 of the stencil sheet 2 over the sheet engagement projections 4 is even more positively assured, because of the smooth shape of these lips 12, which ensures that they will bend smoothly in an elastic fashion, without undergoing any local stretching or compression, so that, once the sheet engaging apertures 7 are engaged over the sheet engagement projection 4, the lips 13 will spring back elastically with no substantial plastic deformation of them having occurred, even at the ends of the slit 12 which meet the circular apertures 11, i.e., even at the points along the sides of the slit 12 which correspond to the sharp corners which are formed in the embodiment shown in Figures 6 and 8.

Figures 10, 11, and 12 show various further possible forms for the sheet engaging apertures.

Each of these forms for the sheet engaging apertures is adapted to correspond to a different form for the sheet engagement projections, which are not illustrated, in any of these cases, because they can be readily be imagined by one skilled in the art, based upon the present disclosure. That is to say, in the modification shown in Figure 10, each of the holes for the columnar portions is formed, not as a circular hole, but as an elliptical hole whose major axis is substantially perpendicular to the slit joining the centers of the holes. Corresponding to this, the columnar portions are formed with elliptical cross sectional shapes.

The modification shown in Figure 11 has holes for the columnar portions which are formed as squares, two of whose sides are parallel to the slit joining the holes, while the other two sides of these squares are perpendicular to this slit. Of course, the sheet engagement projection corresponding to this configuration for the sheet engaging aperture has columnar portions which are of square cross sectional shapes with opposing faces.

In the modification of the sheet engaging aperture shown in Figure 12, each of the holes for the columnar portions is formed as a square, and each of the sides of each of these squares is inclined at an angle of 45 to the slit which extends along the line between the centers of the holes. Of course, corresponding to this form for the sheet engaging aper turn, the cross sectional shapes of the pair of columnar portions of the sheet engagement projection are squares, and these columnar portions have opposing longitudinal edges.

In Figure 13, a further embodiment for the sheet engagement projections 4, and for the corresponding sheet engaging apertures 7, is shown. Figure 13 is a perspective view, and the solid lines therein show the sheet engagement projection and the sheet engaging aperture in perspective, while the dotted lines are projection lines which show the correspondence therebetween. In this embodiment, the two columnar portions 18 and 19 of this sheet engagement projection 17 have different cross sectional shapes, unlike the case in the other shown embodiments. That is to say, a columnar portion 18 is formed with a square cross sectional shape, while a columnar portion 19 is formed with a circular cross sectional shape.Corresponding to this, the sheet engaging aperture 21 in the stencil sheet 2, which corresponds to the sheet engaging apertures 7 of the other embodiments, is formed as a square hole 22 and a circular hole 23 which are joined by a slit 24 with its two sides abutting and extending between the centers of these holes 21 and 23. The projection lines show the correspondence of these holes 21 and 23 to the columnar portions 18 and 19, respectively.

This particular configuration is advantageous because it ensures that it is impossible for the stencil sheet 2 to be fitted by mistake in an upside down position on the rotary press drum 1, because of the asymmetry between the columnar portions 18 and 19 and their corresponding holes 22 and 23. Further, since the bridging portion 20 of this sheet engagement projection 17, corresponding to the bridging portion 10 of the embodiment shown in Figures 3 - 5, is formed as having a substantially isosceles triangular cross section, with the apex of the triangle facing away from the rotary press drum which supports the columnar portions, it is facilitated to attach the stencil sheet 2 to the rotary press drum 1, by providing angled surfaces which force apart the lip portions formed at opposite sides of the slit 24 of the stencil sheet 2, as the stencil sheet 2 is pushed down towards the rotary press drum 1. The flattened under surface of the bridging portion 20, as in the embodiment shown in Figure 7, effectively guards against the accidental coming off of the stencil sheet 2 from the sheet engagement projection 17.

According to the above description, and the drawings, the present invention has been described in detail with reference to the fitting of a stencil sheet onto a rotary press drum. However, the present invention is not to be considered as limited to this particular application. In fact, the present invention is applicable to any case in which it is required to mount a sheet onto a body. Neither is it necessary that the sheet which is to be mounted to the body should necessarily have a reinforced portion in which the engaging apertures are formed, although this may be desirable in some embodiments.

Accordingly, although the present invention has been shown and described in terms of some preferred embodiments thereof, and in language more or less specific with regard to structural features thereof, and with reference to the illustrative drawings, it should be understood that in any particular embodiment of the present invention various changes, modifications, and omissions of the form and the detail thereof can be made by a person skilled in the art, without departing from the essential scope of the invention. Therefore it is expressly desired that the scope of the present invention should be uniquely delimited by the legitimate and valid scope of the appended claims, which follow, and not by any of the perhaps purely fortuitous details of the shown embodiments, or of the drawings.

Claims (45)

1. An engaging construction for engaging a sheet to a body, comprising a portion of the sheet formed with an engaging aperture, and an engagement projection protruding from the body; wherein the engagement projection comprises first and second columnar portions extending from the body so as to be substantially parallel to each other, and a bridging portion joining the ends of these columnar portions remote from the body; and wherein the engaging aperture is formed as first and second holes which receive said first and second columnar portions, respectively, and an elongaged slit opening joining these holes; the part of the sheet adjacent to the slit opening being elastically deformable.

2. An engaging construction according to claim 1, wherein the cross sections of the first columnar portion, the second columnar portion, and the bridging portion are all circular.

3. An engaging construction according to claim 1 or 2, wherein the sides of the slit are formed as straight lines which, when the part of the sheet adjacent to the slit which is elastically deformable is in its unstressed free condition, abut each other, with the slit having no substantial width.

4. An engaging construction according to claim 1 or 2, wherein the sides of the slit are straight lines which, when the part of the sheet adjacent to the slit which is elastically deformable is in its unstressed free condition, are separated by a certain substantial gap.

5. An engaging construction according to claim 1 or 2, wherein the sides of the slit are formed as curved lines, which are closesttogethere at their central portions, and whose ends join smoothly to the sides of the first and second holes with no substantial corner being formed at their junction therewith.

6. An engaging construction according to claim 1, wherein the cross sections of the first and second columnar portions are circular, and wherein the cross section of the bridiging portion is substantially circular on its side remote from the body, and is flattened on its side nearest to the body.

7. An engaging construction according to claim 1, wherein the cross sections of the first and second columnar portions are ellipses.

8. An engaging construction according to claim 1,wherein the cross sections of the first and second columnar portions are squares each of which has two sides perpendicular to the plane containing the central axes of the columnar portions.

9. An engaging construction according to claim 1,wherein the cross sections of the first and second columnar portions are squares whose sides are at angles of approximately 45 to the plane containing the central axes of the columnar portions.

10. An engaging construction according to claim 1, wherein the cross sections of the first and second columnar portions are asymmetrical with respect to each other.

11. An engaging construction according to claim 10, wherein the cross section of the first columnar portion is a square, and the cross section of the second columnar portion is a circle.

12. An engaging contruction for engaging a sheet to a body, comprising a portion of the sheet formed with a plurality of engaging apertures, and a plurality of corresponding engagement projections protruding from the body; wherein each of the engaging projections comprises first and second columnar portions extending from the body so as to be substantially parallel to each other, and a bridging portion joining the ends of these columnar portions remote from the body; and wherein each of the engaging apertures is formed as a first and a second hole which receive the corresponding said first and second columnar portions, respectively, and an elongated slit opening joining these holes; the part of the sheet adjacent to each of the slit openings being elastically deformable.

13. An engagement construction according to claim 12, wherein the engagement projections are arranged along a first straight line on the body, and the engaging apertures are arranged along a second straight line on the sheet.

14. An engaging construction according to claim 13, wherein the bridging portions are arranged substantially parallel to the first straight line, and the slit openings are arranged substantially parallel to the second straight line.

15. An engaging construction according to claim 13, wherein all except one of the bridging portions are arranged substantially parallel to the first straight line, all except one of the slit openings are arranged substantially parallel to the second straight line, and said one bridging portion and said one slit opening are angled to said first and second straight lines, respectively, by an angle of not more than about 45 .

16. An engaging construction according to claim 13, 14, or 15, wherein the portion of the sheet is further formed with a plurality of locating apertures, and further comprising a plurality of locating rod shaped projections which protrude from the body and which correspond to the locating apertures when the sheet engaging apertures are engaged over the sheet engagement projections.

17. An engaging construction according to claim 16, wherein at least some of the locating projections are located along the first line.

18. An engaging construction according to claim 16, wherein at least some of the locating projections are located not on the first line.

19. An engaging construction according to claim 17, wherein at least some of the locating projections are located not on the first line.

20. An engagement projection for engaging a sheet to a body, comprising first and second columnar portions extending from the body so as to be substantially parallel to each other and a bridging portion joining the ends of these columnar portions remote from the body.

21. An engagement projection according to claim 20, wherein the cross sections of the first columnar portion, the second columnar portion, and the bridging portion are all circular.

22. An engaging projection according to claim 20, wherein the cross sections of the first and second columnar portions are circular, and wherein the cross section of the bridging portion is substantially circular on its side remote from the body, and is flattened on its side nearest the body.

23. An engagement projection according to claim 20, wherein the cross sections of the first and second columnar portions are asymmetric to each other.

24. An engagement projection according to claim 23, wherein the cross section of the first columnar portion is a square, and the cross section of the second columnar portion is a circle.

25. An engaging structure for engaging a sheet to a body, comprising a plurality of engagement projections protruding from the body, each of which comprises first and second columnar portions which extend from the body so as to be substantially parallel to each other, and a bridging portion joining the ends of these columnar portions remote from the body.

26. An engaging structure according to claim 25, wherein the engagement projections are arranged along a straight line on the body.

27. An engaging structure according to claim 25 or 26, further comprising a plurality of rod shaped locating projections which protrude from the body.

28. A sheet formed with an engaging aperture which has the shape of first and second holes and an elongated slit opening joining these holes, the part of the sheet adjacent to the slit opening being elastically deformable.

29. A sheet according to claim 28, wherein the first and second holes are circular.

30. A sheet according to claim 28, wherein the sides of the slit are formed as straight lines which, when the part of the sheet adjacent to the slit is in its unstressed free condition, abut each other, with the slit having no substantial width.

31. A sheet according to claim 28, wherein the sides of the slit are formed as straight lines which, when the part of the slit adjacent to the slit is in its unstressed free condition, are separated bv a certain substantial gap.

32. A sheet according to claim 28, wherein the sides of the slit are formed as curved lines, which are closest together at their central portions, and whose ends join smoothly to the sides of the first and second holes with no substantial corner being formed at their junctions therewith.

33. A sheet according to claim 28, wherein the first and second holes are ellipses.

34. A sheet according to claim 28, wherein the first and second holes are squares each of which has two sides perpendicular to the line joining their centers.

35. A sheet according to claim 28, wherein the first and second holes are squares whose sides are at angles of approximately 45 to the line joining their centers.

36. A sheet according to claim 28, wherein the first and second holes are asymmetrical to each other.

37. A sheet according to claim 36, wherein the first hole is a square, and the second hole is a circle.

38. A sheet formed with a plurality of engaging apertures, each of which has the shape of first and second holes and an elongated slit opening joining these holes, the parts of the sheet adjacent to each of the slit openings being elastically deformable.

39. A sheet according to claim 38, wherein the engaging apertures are arranged along a straight line.

40. A sheet according to claim 39, wherein the slit openings are arranged substantially parallel to said straight line.

41. A sheet according to claim 39, wherein all except one of the slit openings are arranged substantially parallel to said straight line, and said one slit opening is angled to said straight line by an angle of not more than about 45 .

42. A sheet according to claim 39, 40, or 41, further formed with a plurality of locating apertures.

43. A construction substantially as hereinbefore described, and as illustrated in, Figures 1 to 6, or Figure 7, or Figure 8 or Figure 9, or Figure 10, or Figure 11, or Figure 12, or Figure 13 ofthe accompanying drawings.

44. An engagement projection substantially as hereinbefore described, and as illustrated in, Figures 1 to 6, or Figure 7, or Figure 8, or Figure 9, or Figure 10, or Figure 11, or Figure 12, or Figure 13 of the accompanying drawings.

45. A sheet substantially as hereinbefore described, and as illustrated in, Figures 1 to 6, or Figure 7, or Figure 8, or Figure 9, or Figure 10, or Figure 11, or Figure 12, or Figure 13 of the accompanying drawings.