Abstract:
The present disclosure provides a cardboard-based unit, structural elements comprising said unit and land-vehicles comprising said units and structural elements.

Description:
TECHNOLOGICAL FIELD AND BACKGROUND 
       [0001]    The present disclosure relates to units substantially or entirely made of cardboard that may be used as structural elements in structures and devices such as wheeled devices (e.g. bicycle or tricycle). 
         [0002]    WO11067742 discloses a human-powered land vehicle sufficiently rigid so as to transport a human rider. The vehicle is constructed from pulpably recyclable and shreddably recyclable materials. 
       GENERAL DESCRIPTION 
       [0003]    The present disclosure provides, by a first of its aspects, a structural unit made from or comprising cardboard as its major component. This means that cardboard constitutes typically at least about 60%, 65%, 70%, 75%, 80%, 85%, 90%, and at times even at least 95% of the total weight of the structure. The unit comprises, as will be illustrated below, low density cardboard layers. 
         [0004]    By a first aspect, the unit of this disclosure comprises reinforcing, elongated members that may be made of cardboard, e.g. may be cardboard cylinders or rods; or may be made of other light materials, such as wood or plastic. The elongated members are then wholly or partially enveloped by portions of the low density cardboard panel formed to be in tight association with said elongated members. Some other portions of the cardboard panel are associated with one another to define a multi-layer cardboard element. 
         [0005]    By a second aspect, the multi-layer cardboard unit comprises a high density cardboard layer. For example, two low density cardboard layers may sandwich a high density cardboard layer. A particular example is a 3-layer structure with two external layers of low density cardboard sandwiching a high density cardboard layer. 
         [0006]    A unit of this disclosure may also combine features of both aspects, namely comprising one or more such elongated members as well as a high density cardboard layer sandwiched between two low density cardboard layers. 
         [0007]    Said elongated members with the associated portions of the cardboard panel jointly form a core-envelope element. The core-envelope element may be situated at and define edges of a multi-layer planar unit. The core-envelope element has usually also a functional significance in reinforcing the structural rigidity in bend, compression and tension resistance disclosure, as will also be explained further below. The structure of the disclosure may constitute a part of a device, such as a wheeled device, e.g. parts of a bicycle or tricycle. 
         [0008]    The disclosure, thus provides, by the first aspect, a substantially planar, cardboard-based unit comprising (i) two or more layers of cardboard that are closely associated, typically adhered, with one another and that may be constituted by a formed low-density cardboard panel, and comprising (ii) two or more integral core-envelope elements, each comprising enveloping portions of the low density cardboard that are tightly associated with corresponding two or more elongated members. For example, the unit may be constituted from a formed cardboard panel that is wrapped about the elongated members, with portions of the panel facing one another are tightly associated with one another, e.g. by an adhesive. 
         [0009]    Provided, by the second aspect of this disclosure, is a unit comprising a high density cardboard panel sandwiched between two layers of low-density cardboard. 
         [0010]    The combination of one or more layers of a high density cardboard, particularly when tightly sandwiched between two layers of low-density cardboard as provided by the second aspect, provides for additional reinforcement, especially against compression or deformation in a direction normal to the plane of the cardboard layers, as compared to such a unit that has a similar layers&#39; structure but devoid of the high density cardboard layer. 
         [0011]    It should be noted that the structural unit may also comprise an external varnish or other coating layer. The reference made herein to a multi-layer structure excludes such layers and focuses on the structural elements of the unit. Thus, for example, a unit with a 3-layer cardboard structure may also comprise additional coating layers. 
         [0012]    Generally, the term “elongated” means that the element has a length dimension that is significantly more prominent than other measurements of the element. Such an element may generally have the structure similar to that of the elongated element disclosed in co-owned PCT application having the publication number WO2014/061012 (hereinafter: “the &#39;012 PCT application”). One or both of the panel portions embracing the elongated member (referred to therein as the “rectangular sub-structure”) is integral with panel portion that forms other parts of the structure. 
         [0013]    The term “cardboard panel” means a planar or substantially planar cardboard piece with a broad surface that is substantially thin as compared to its length and width. The cardboard panel may be a uniform cardboard piece but may also, for example, be made of two or more planar cardboard pieces glued or otherwise adhered together to form a larger cardboard panel that is formed into the unit&#39;s different elements. 
         [0014]    The term “formed” (or any of its linguistic variations) means to denote the act of giving form or shape to the cardboard panel, namely forming the panel into a final intended shape in the unit. Such forming comprises, for example, wrapping a portion of the panel over the elongated member to thereby obtain the core-envelope structure of the so-formed elongated element. Such forming may also comprise, in some embodiments, defining voids in said planar element. 
         [0015]    The term “integral” means that the panel portions that are used in the formation of the different elements are all portions of a single, formed panel. Thus, for example, in the case of a panel portion that is enveloping the elongated member, defining two skirts of the panel extending from an apex defined along the elongated member, at least one or both of the skirt portions of the panel extends into other portions of the panel that define one or more other elements of the unit. 
         [0016]    As noted, portions of the panel according to said first aspect are wrapped about two or more elongated members such that the panel comes into tight association with said members to thereby define said elongated, core-envelope elements. The elongated core-envelope element, formed through the association between the elongated member and the enveloping cardboard panel, may impart an increased rigidity, e.g. bend, tension and compression resistance to the cardboard structure, as compared to rigidity and said resistance of a similar cardboard structure that does not include such elongated core-envelope elements. Said elongated core-envelope element may define an edge of a planar multi-layer (e.g. bi-layer) cardboard unit. Typically, two such elongated core-envelope elements define edges of a substantially planar element that extends therebetween. 
         [0017]    The elongated members (which, as noted above, may be made of cardboard, wood or plastic) typically have a rounded shape, e.g. circular cross-section (although at times it may be oval, elliptical, etc.); and accordingly said elongated core-envelope elements are typically rounded, although they may be shaped by the use of appropriate dies into other shapes, e.g. to have a substantially rectangular external cross-sectional shape. 
         [0018]    The disclosure embodies some features, common with those of the &#39;012 PCT application as well as of another PCT application Serial No. PCT/IL2013/050823, the relevant contents of both incorporated herein by reference. 
         [0019]    The cardboard-based unit of the first aspect of this disclosure has a 3- or 4-point bending strength normal to said elongated core-envelope elements that is significantly larger than that of a cardboard structure devoid of such elongated core-envelope elements. The term “significantly larger” means that it is at least two, five and, at times, at least 10-fold larger than that of either the reinforcing members or the regular bi-layer cardboard structure, one without the elongated members. Some explanations and parameters concerning this bend resistance can be found in the &#39;012 PCT application, the contents of which, as noted above, is incorporated herein by reference for the relevant portions thereof. 
         [0020]    The “low density cardboard panel” denotes a cardboard panel comprising (i) at least one low-density layer made of paper, high density paper or cardboard (for ease of reference the term “paper”, will be used hereinafter to refer collectively to paper, high density paper or cardboard) arranged to define a plurality of cells or voids, e.g., formed by corrugated, fluted or otherwise loosely packed paper sheets or strips that define a plurality of voids therebetween, and comprising (ii) one or more liner cardboard sheets lined at one side or both sides of the low-density layers (namely sandwiching the low-density layer between them). Examples of such cardboard panels are such known as “corrugated cardboard”, which consists of a fluted or corrugated paper panel(s) or strip and one or two flat linerboards at one or both (i.e. sandwiching) sides of the fluted or corrugated paper; and may also be such referred to as “honeycomb cardboard”. Such materials are widely used in the manufacture of boxes and shipping containers. The corrugated or honeycomb cardboard panels may be single-walled or multi-walled cardboard panel. 
         [0021]    The term “high density cardboard” denotes a cardboard panel that is substantially uniform throughout its cross-section. A high density cardboard does not have a low-density layer of the kind described above. 
         [0022]    By one embodiment of the first aspect, the cardboard-based unit comprises two first elongated core-envelope elements that are parallel to one to the other, being formed with corresponding parallel elongated members. Such first elongated core-envelope elements define edges of a planar element that extends therebetween. The first elongated core-envelope elements are associated to corresponding first parallel elongated members. Said first elongated members may separate each between a central segment of the original cardboard panel and one of first or second flanking segments that flank the central segment; the flanking segments and the central segment, once a portion of the panel is wrapped over the elongated members, jointly form a two-layer element. 
         [0023]    According to one embodiment, one or more portions of a first face of the first flanking segment are attached to one or more portions (opposite in the formed structure) of the first face of the central segment. By another embodiment, one or more portions of the first face of the first flanking segment and one or more portions of the first face of the second flanking segment are both attached to corresponding portions of the first face of the central segment. According to this embodiment at least two parallel elongated members are associated with the first face of the panel. The structure is typically foamed such that opposite edges of the original panel, being the edges at the end of the flanking segments, are brought into proximity with one another. In this manner a closed loop structure (as can best be seen in a cross-section) is formed by the panel, with the first elongated core-envelope elements defining the extreme ends of such a loop. 
         [0024]    By another embodiment, rather than forming a closed loop structure, a cardboard panel is folded into a form generally resembling an “S” shape with oppositely oriented folds. In such a configuration, one or more portions of a first face of the first flanking segment is attached to corresponding one or more portions of the first face of the central segment; while one or more portions of the second face of the central segment is attached to corresponding one or more portions of the second face of the second flanking segment. In this configuration, the elongated members within the first parallel elongated core-envelope elements are associated one with the first face and the other with the second face of the panel. 
         [0025]    By one embodiment such a planar cardboard unit is substantially uniform with a complete cardboard multi-layer structure over the entire surface. In another embodiment, one or more voids are formed in this planar cardboard element, which may have decorative or functional significance, e.g. through cut-outs from the multi-layer cardboard element or through appropriately forming of the original cardboard panel. 
         [0026]    In accordance with one embodiment, the cardboard-based unit comprises one or more integral second elongated, core-envelope elements (formed by a portion of the cardboard panel that is wrapped about an elongated member oriented normal to said first elongated core-envelope elements. 
         [0027]    In accordance with some embodiments, the cardboard-based unit of this disclosure (of both the first and the second aspects) constitutes part of a wheeled device or a land vehicle, such as a bicycle or tricycle. 
         [0028]    Provided by a third aspect this disclosure is a vehicle, such as a tricycle or bicycle comprising a structural unit of the kind described herein. A particular example is a bicycle of the kind known as a “balance bike” or “run bike”, which is a training bicycle, intended primarily for children, having no pedals or drive chain, and where the rider (typically the child) propels itself by pushing the ground with his/her feet. In such a bicycle or tricycle the body may be a structural unit with the characteristics of that of this disclosure. Also, or alternatively, the front wheel steering frame may also be a structural unit with the characteristics of that of this disclosure. 
         [0029]    By one embodiment the fork assembly has a fork with the characteristics of a structural unit according to the first aspect, with or without an additional high density cardboard panel sandwiched between the two low density cardboard panels; and the body has the characteristics of a structural unit according to the second aspect. 
         [0030]    Provided by an embodiment of the invention is a bicycle that comprises (i) a body that extends between a front end and a rear end of the bicycle with a rear wheel that is fitted at the rear end of the body, namely at the end itself or close to it, and (ii) a fork assembly that is pivotally coupled to the body and having a front wheel that is rotationally fitted to said fork. The body and the fork assembly comprise each an element that has the characteristics of the units disclosed herein. The body and the fork assembly are typically constituted entirely out of cardboard and have the characteristics of said units. 
         [0031]    By one embodiment the body comprises a planar body element embodying the characteristics of the unit of the second aspect of this disclosure and the fork assembly comprising an element embodying the characteristics of the unit of the first aspect of this disclosure. 
         [0032]    An exemplary bicycle, e.g. a training bike, has the following characteristics: 
         [0033]    (i) a body that comprises two planar body elements, each defining a vertical plane and are, typically, minor images of one another and having both a front end and a rear end, the two body elements being attached to one another at their front end portion to define a front body block and diverge from one another towards the rear end to thereby define a body space between them; each of said elements embodying the characteristics of the unit of said second aspect; 
         [0034]    (ii) a rear wheel fitted within the body space and being rotationally coupled to the two panels at a rear end thereof by a horizontal axle that is received within co-axial bushings (typically, but not exclusively, made of plastic) fitted in said panels; 
         [0035]    (iii) a steering assembly comprising a planar fork member embodying the characteristics of the unit of the first aspects and formed by cut-outs to define (1) a fork portion with two stems defining between them a stem space, and (2) a panel opening in a mid-portion of the panel; 
         [0036]    (iv) a vertical pivot-accommodating receptacle formed within said front body block and accommodating a pivot that extends vertically through the panel opening between bushings (typically, but not exclusively, made of plastic) formed at opposite edges of said opening to hinge said fork to said body; and 
         [0037]    (v) a front wheel fitted within the stem space and being rotationally coupled to the two stems by a horizontal axle that is received within co-axial bushings fitted in said stems. 
       EMBODIMENTS 
       [0038]    Some exemplary embodiments are defined in the numbered paragraphs below. The description of these embodiments is not intended to derogate but rather to add onto the general description above and the detailed description that follows. 
         [0039]    1. A unit, comprising
       one or more substantially planar elements comprising two or more layers of low density cardboard that are closely associated with one another, particularly such that are constituted from a formed low density cardboard panel; and two or more integral core-envelope elements that comprises enveloping portions of the low density cardboard that are tightly associated with corresponding two or more elongated members.       
 
         [0041]    2. The unit of embodiment 1, wherein the cardboard layers in said planar elements are attached to one another at portions thereof. 
         [0042]    3. The unit of embodiment 1 or 2, wherein said elongated members have a rounded cross-section. 
         [0043]    4. The unit of embodiment 3, wherein said elongated members have a circular cross-section. 
         [0044]    5. The unit of any one of embodiments 1-4, wherein said elongated members are made of wood, cardboard or plastic. 
         [0045]    6. The unit of any one of embodiments 1-5, wherein said cardboard panel comprises (i) at least one low-density layer and (ii) one or more liner cardboard sheets lining at least one side of the at least one low-density layer. 
         [0046]    7. The unit of embodiment 6, wherein the low-density cardboard is corrugated cardboard or honeycomb cardboard. 
         [0047]    8. The unit of any one of the embodiments 1-7, wherein said elongated core-envelope elements impart an increased rigidity and bend resistance to the cardboard unit. 
         [0048]    9. The unit of any one of the embodiments 1-8, wherein said elongated core-envelope elements define edges thereof. 
         [0049]    10. The unit of embodiment 9, wherein said edges have a rounded external cross-sectional shape. 
         [0050]    11. The unit of any one of embodiments 1-10, wherein two of said elongated core-envelope elements are parallel one to the other. 
         [0051]    12. The unit of embodiment 11, wherein the two parallel elongated core-envelope elements define edges of a substantially planar structural element that extends therebetween. 
         [0052]    13. The unit of any one of embodiments 1-12, wherein two flanking segments of a panel are folded over the elongated members and are associated with a central segment of the panel that is defined between said elongated members. 
         [0053]    14. The unit of embodiment 13, wherein one or more portions of one face of said first flanking segment are attached to one or more portions of the same face of said central segment. 
         [0054]    15. The unit of embodiment 13 or 14, wherein the panel has first and second faces and wherein the first face of the two flanking segment are attached to the first face of said central segment. 
         [0055]    16. The unit of embodiment 14 or 15, wherein the elongated members are associated with the same face of the panel. 
         [0056]    17. The unit of any one of embodiments 13-16, wherein
       the panel has first and second faces,   the first face of each of the flanking segments is associated with the first face of the central segment, and wherein   opposite edges of the panel, at the end of said flanking segments, are proximal to one another.       
 
         [0060]    18. The unit of embodiment 13 or 14, wherein
       one or more portions of a face of one flanking segment are attached to corresponding one or more portions on the same face of said central segment, and   one or more portions of said second flanking segment are attached to corresponding one or more portions of the opposite face of said central segment.       
 
         [0063]    19. The unit of embodiment 18, wherein
       one of the parallel elongated members is associated with one face of the panel, and   the other of the parallel elongated members is associated with the opposite face of the panel.       
 
         [0066]    20. The unit of any one of the embodiments 1-19, wherein said planar element comprises one or more voids. 
         [0067]    21. The unit of any one of embodiments 11-20, comprising one or more integral second core-envelope elements oriented normal to said parallel elongated core-envelope elements. 
         [0068]    22. The unit of any one of embodiment 1-21, comprising a high density cardboard panel sandwiched between two layers of low-density cardboard. 
         [0069]    23. A structural unit having a planar element that comprises a high density cardboard layer sandwiched between two layers of low-density cardboard. 
         [0070]    24. The unit of embodiment 23, wherein the two layers of low density cardboard that sandwich a high layer are formed from a single folded cardboard panel. 
         [0071]    25. The unit of embodiment 23 or 24, wherein each layer is adhered to a neighboring layer. 
         [0072]    26. The unit of any one of embodiments 23-25, being shaped according to structural requirements by cut-outs in the planar element. 
         [0073]    27. The unit of any one of embodiments 1-26, being part of a wheeled device. 
         [0074]    28. The unit of embodiment 27, wherein the wheeled device is a bicycle or tricycle. 
         [0075]    29. The unit of embodiment 27 or 28, having the following characteristics:
       being a fork of a bicycle or tricycle and configured for coupling with (i) a front wheel and (ii) one or more other parts of the bicycle or tricycle.       
 
         [0077]    30. The unit of embodiment 29, comprising a core-envelope element integral with said planar element and configured as a handlebar of the bicycle or tricycle. 
         [0078]    31. The unit of any one of embodiments 1-30, comprising at least one hollow elongated member. 
         [0079]    32. The unit of embodiment 31, wherein at least one of the hollow elongated members is cylindrical and accommodates an axle. 
         [0080]    33. A land vehicle comprising a structural unit as defined in any one of embodiments 1-32. 
         [0081]    34. The land vehicle of embodiment 33, being a bicycle or tricycle. 
         [0082]    35. The land vehicle of embodiment 34, being a balance bike. 
         [0083]    36. The land vehicle of embodiment 34 or 35, comprising a front-wheel steering unit having the characteristics of a unit of any one of embodiments 1-32. 
         [0084]    37. A bicycle comprising a body extending between a front end and a rear end, a fork pivotally coupled to the body, a front wheel fitted to said fork, and a rear wheel fitted at the rear of said body, the body and the fork assembly comprising each an element having the characteristics of the unit of any one of embodiments 1-32. 
         [0085]    38. The bicycle of embodiment 37, wherein
       the body comprises a planar body element embodying the characteristics of the unit of any one of embodiments 23-25; and   the fork assembly comprises an element embodying the characteristics of the unit of any one of embodiments 1-22. 39. A bicycle comprising:   a body extending between a front end and a rear end, a fork pivotally coupled to the body, a front wheel fitted to said fork and a rear wheel fitted at the rear of said body.   the body and the fork assembly comprising each an element having the characteristics of the unit of any one of embodiments 1-32.       
 
         [0090]    40. The bicycle of embodiment 39, wherein
       the body comprises a planar body element embodying the characteristics of the unit of any one of embodiments 23-25; and   the fork assembly comprising an element embodying the characteristics of the unit of any one of embodiments 1-22.       
 
         [0093]    41. A bicycle, comprising:
       a body that comprises two planar body elements, each defining a vertical plane and are, typically, minor images of one another and having both a front end and a rear end, the two body elements being attached to one another at their front end portion to define a front body block and diverge from one another towards the rear end to thereby define a body space between them; each of said elements embodying the characteristics of the unit of any one of embodiments 23-25;   a rear wheel fitted within the body space and being rotationally coupled to the two panels at a rear end thereof by a horizontal axle that is received within co-axial bushings fitted in said panels;   a steering assembly comprising a planar fork member embodying the characteristics of the unit of any one of embodiments 1-22 and formed by cut-outs to define
           a fork portion with two sterns defining a between them a stem space, and   a panel opening in a mid-portion of the panel;   a vertical fork pivot-accommodating receptacle formed within said front body block and accommodating a pivot that extends vertically through the panel opening between bushings foamed at opposite edges of said opening to hinge said fork to said body; and   
           a front wheel fitted within the stem space and being rotationally coupled to the two stems by a horizontal axle that is received within co-axial bushings fitted in said stems.       
 
         [0101]    42. The bicycle of embodiment 41, wherein one or more of the bushings, typically all of them, are made of plastic. 
         [0102]    43. The bicycle of embodiment 42, being a training bike. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0103]    In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: 
           [0104]      FIG. 1A  is a schematic representation of the manner of production of a cardboard-based unit according to an embodiment of the disclosure. 
           [0105]      FIGS. 1B and 1C  show, respectively, a schematic perspective view and a view from above, of the so formed unit. 
           [0106]      FIGS. 2A  is a schematic representation of the manner of production of a cardboard-based unit according to another embodiment of the disclosure. 
           [0107]      FIGS. 2B and 2C  show, respectively, a schematic perspective view and a view from above, of the so formed unit. 
           [0108]      FIG. 3A  is a schematic illustration of the manner of production of a cardboard-based unit according to a further embodiment of the disclosure. 
           [0109]      FIG. 3B  shows a cardboard-based unit according to that embodiment. 
           [0110]      FIG. 3C  shows a side vies of the unit of  FIG. 3B . 
           [0111]      FIG. 4  shows a front view of a cardboard-based unit according to another embodiment of the disclosure, which similar on overall shape to that of  FIG. 3B , with some functional cut-outs. 
           [0112]      FIG. 5A  is a front view of a cardboard panel with marked segments to be cut-out prior to forming of the cardboard-based unit according to another embodiment of the disclosure. 
           [0113]      FIG. 5B  shows the panel of  FIG. 5A  with segments cut-out and after positioning of the elongated members. 
           [0114]      FIG. 5C  shows a front view of the cardboard-based unit formed from the panel of  FIG. 5B . 
           [0115]      FIGS. 6A-6B  are schematic representations showing a perspective view and front view, respectively, of a balance bike according to an embodiment of the invention. 
           [0116]      FIGS. 7A-7H  are schematic illustrations of steps in the manufacture of the body of a balance bike. 
           [0117]      FIGS. 8A-8H  are schematic illustrations of steps in the manufacture of the handlebar and fork assembly. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0118]    The disclosure will now be illustrated below with reference to a number of embodiments, schematically represented in the attached drawings. In the description below,  FIG. 1  (namely  1 A,  1 B and  1 C) relate to one embodiment, and each of  FIGS. 2 ,  3 ,  4  and  5  relate to different embodiments. The different components of these embodiments are each indicated by a three digit numeral, the first digit given according to the figure in which they appear (for example, in  FIG. 1  the numerals all begin with “1”; whereas in  FIGS. 2  with the numeral “2”); while the last two digits are specific for the component. In different figures like components are indicated by a three digit numeral having the same last two digits. By way of example, component  102  in  FIGS. 1A and 1B  is like (having similar function to) component  202  in  FIGS. 2A and 2B . Such like components may not be described each time and the reader is directed to look into the description of the corresponding component in other embodiments. 
         [0119]    It should be noted that for the purpose of illustration, some dimensions were drawn out of proportion. By way of example, in some figures a cardboard panel is shown, from which a cardboard-based unit is produced. The panel is shown to have a thickness that is out of proportion of the thickness of at least some of the actual panel to be used in accordance with the disclosure. The out of proportion thickness is for illustration purposes only as had it been drawn to proportion, it may have been more difficult to view it in the drawings. 
         [0120]    Reference is first being made to  FIG. 1A  showing a cardboard panel  100  associated with two elongated members  102 ,  104  positioned on corresponding parallel lines  106 ,  108 , on a first face  140  of panel  100 , equidistant from respective opposite edges  110 ,  112  (lines  106 , 108  are imaginary lines that do not exist in the actual panel). Elongated members  102 ,  104 , that are parallel to one another, separate between respective flanking portions  114 ,  116  and a central portion  118  of the panel. 
         [0121]    In order to form a cardboard-based unit according to an embodiment of the disclosure, panel  100  is folded along lines  106 ,  108 , as represented by arrows  106 A,  108 A such that portions thereof  120 ,  122  along and flanking lines  106 ,  108  wrap around and envelope tightly the elongated members  102 ,  104 , such that in the eventually formed unit, as seen in  FIGS. 1B and 1C , portions  114 ,  116  are tightly associated at their first face, e.g. through use of adhesive, with the first face of portion  118 . 
         [0122]    In the formed unit shown in  FIGS. 1B and 1C , two elements can be identified: two parallel, elongated, core-envelope elements  130 ,  132  that define edges of the unit with a planar bi-layer element  134  extending therebetween. Also, in this embodiment, panel edges  110 ,  112  are brought into close proximity with one another. In this way, the formed cardboard panel defines a closed loop configuration about the two elongated members. 
         [0123]    The elongated members  102 ,  104  in this embodiment and those described below have a circular cross-section. In some embodiments they may have other round cross-sections, e.g. elliptical, oval. 
         [0124]    The elongated, core-envelope elements  130 , 132 , as also the other elongated, core-envelope elements in the embodiments described below, have rounded edges which are a result of the forming process. However, through the use of appropriate dies or molds, the edges may be press-formed to have other forms, e.g. rectangular. The cardboard panel may, by one embodiment, be a corrugated or honeycomb cardboard panel. However, the disclosure is not limited to cardboard panels of this type. 
         [0125]    Reference is now being made to  FIGS. 2A-2C  which illustrates a unit according to another embodiment ( FIGS. 2B and 2C ) and the manner of forming such a unit ( FIG. 2A ). As distinct from the embodiments of  FIGS. 1A-1C , according to those of  FIGS. 2A-2C  the cardboard panel is formed into a shape resembling an “S”, rather than a closed loop. 
         [0126]    In describing the embodiments of  FIGS. 2A-2C , in order to facilitate description, reference will be made to two opposite faces of the panel designated as a first face  240  and a second opposite face  242 . 
         [0127]    As can be seen in  FIG. 2A , elongated member  202  is associated with first face  240  (positioned along line  206  parallel to edge  210 ) and elongated member  204  (parallel to elongated member  202 ) is associated with the second face  242  (positioned along line  208  parallel to edge  212 ). 
         [0128]    As illustrated in  FIG. 2A , lines  206 ,  208  define three portions of substantially the same widths, including two flanking portions  214 ,  216 , and a central portion  218 . The panel  200  is formed by folding it along line  206  in the direction represented by arrow  206 A and in the opposite direction along line  208  in the direction represented by arrow  208 A. Eventually the so-formed cardboard-based unit, seen in  FIGS. 2B-2C  has two parallel, elongated, core-envelope elements  230 ,  232  at opposite ends of an overall substantially planar 3-layer element  234 . 
         [0129]    In the two embodiments of  FIGS. 1A-2C , as previously described, parallel elongated members  102 ,  104  and  202 ,  204  (corresponding to elongated core-envelope elements  130 ,  132  and  230 ,  232 ) extend the entire length of the original cardboard panel and hence along the entire length of the formed cardboard-based unit. However, in some embodiments, such members may extend only the partial length, typically the majority of the length of the panel. According to another embodiment, rather than a single elongated member in said elongated, core-envelope element, two or more elongated members, arranged along the same axis, may be comprised within the elongated elements. In other words, the elongated member, in this case, is defined by a number of individual segments that may all be of the same or a different length. Such segments may be positioned such that an end of one is position adjacent an end of another; or such segments may, at times, be spaced apart from one another. The different segments may be made of the same or a different material. While such segments will typically have the same cross-sectional shapes, they may, at times, have different cross-sectional shapes. 
         [0130]    Another cardboard-based unit and the manner in which it is formed are shown in  FIGS. 3A-3C , which has a somewhat more complex design than that of the preceding illustrated embodiments. 
         [0131]    Turning now to  FIG. 3A , a cardboard panel  300  and three elongated members  302 ,  304 ,  350  can be seen. Elongated members  302 ,  304  are situated parallel to one another and to edges  310 ,  312 , along lines  306 ,  308 ; and elongated member  350  is positioned parallel to edge  358 , namely, oriented normal to elongated members  302 ,  304 . Cardboard panel  300  is cut along lines  306 B,  308 B which extend parallel to edge  358  from respective edges  310 ,  312  to respective lines  306 ,  308 . 
         [0132]    The flanking portions  314 ,  316  defined between lines  306 ,  308  and respective cuts  306 B,  308 B are folded in the direction of arrows  306 A,  308 A, in a similar manner to that described with respect to  FIG. 1A , to eventually form, in the unit shown in  FIG. 3B , a vertical structure  370  with a bi-layer element defined between two parallel, elongated core-envelope elements  330 ,  332  at the edges thereof. The top portion  354  of the cardboard panel, defined between lines  352  and edge  358 , is then folded along line  352  and over elongated member  350  in the direction of arrow  352 A to form a transverse elongated, core-envelope element  372 . As can best be seen in  FIG. 3C , the cardboard panel portion extending down from element  372  is integral with the central portion of the panel in structure  370 . 
         [0133]    Turning now to  FIG. 4 , showing a cardboard-based unit according to another embodiment of the disclosure, having the overall shape as that shown in  FIGS. 3B and 3C . As can be seen, the unit in  FIG. 4  differs from that of  FIG. 3B  by having two cut-outs voids  476 ,  478  that may be cut-out after forming the unit of  FIG. 3B . The unit may serve as a front element of a tricycle in which cut-out  478  accommodates a front wheel of a tricycle, the wheel received through axle holders embedded in the bottom part of element  470  (not shown in this Fig. but will be illustrated further below); while cut-out  478  is articulated to the rear part of a tricycle via a vertical axle receptacle embedded in element  470  (not shown but will be illustrated in  FIGS. 5B and 5C ). 
         [0134]    In some distinction from unit of  FIG. 4 , the cutouts may also be pre-formed in the panel. This is illustrated in  FIG. 5 . The cardboard panel  500  seen in  FIG. 5A  has an overall rectangular shape, but several pieces thereof, drawn as shadows, are cut out to yield the pre-formed panel shown in  FIG. 5B . 
         [0135]    Similar as in the case of  FIG. 3A , elongated members  502 ,  504  are positioned along parallel, vertical lines  506 ,  508  and another elongated member  550  is positioned along line  552  normal to lines  506 ,  508 . Short axle receptacles  580 ,  582  are placed close to the bottom end of portions  518 A,  518 B, defined at the two sides of the cut-out  578 , which are typically hollow plastic tube segments for receiving respective ends of the axles of the front wheel of a tricycle. Also placed at the cardboard&#39;s first face are two vertical segments  584 ,  586 , which may be also hollow plastic tubes, and serve for articulation to the main body of a tricycle. The pre-formed panel is then folded about the elongated member in the direction represented by arrows  506 A,  508 A and  552 A and then, after adhering opposite cardboard faces to one another, the cardboard-based unit shown in  FIG. 5C  is formed. 
         [0136]    Shown in  FIGS. 6A-6B  is a balance bike  600  having body  602 , fork and handlebar and fork assembly  604 , seat  606 , and front and rear wheels  608 ,  610 . The primary material out of which the balance bike  600  is cardboard; main exception include the wheels and some elements to be described below that include the axles, the elongated members, the bushings and the pins. 
         [0137]    As can further be seen in  FIGS. 6A-6B , body  602  is composed of two planar body elements  612 ,  614  that define each a vertical plane, and are essentially mirror images of one another. Elements  612 ,  614  are attached to one another at the front end portion  616  to define a front body block  617  and diverge towards the rear end  618  defining between them a body space  620 , which widens towards the rear end. 
         [0138]    As will further be explained, embedded in front body block  617  is a set of co-axial bushings (not seen in  FIGS. 6A-6B  but will be described below and illustrated in other Figs.) which accommodate a fork pivot (also to be described below) that provides for rotational engagement between the fork assembly  604  and body  602 , permitting a child rider holding handlebar  622  to steer the front wheel  608 . Fitted within the body space  620  is a stem  624  of seat  606 , which is held in position by pins  626  that cross between the two body elements  612 ,  614  and through stem  624 . Wheels  608 ,  610  are rotationally coupled to respective fork  605  and rear end  618  of body  602 , through respective axles  628 ,  630 . 
         [0139]    The manner in which the body, as well as the fork assembly, is constructed and hence also their constituents will now be described with reference to  FIGS. 7A-7H  and  8 A- 8 H. 
         [0140]      FIGS. 7A-7H  illustrate the manner of construction of body  602 , of which  FIGS. 7A-7G  illustrate steps for constructing one of body elements  612 ,  614 . At a first step, a cardboard panel  700  having a general rectangular shape is provided and a groove  702  is formed at about the midline  704  (represented by a dotted line) to thereby define two portions (A) of substantially the same dimensions. The cardboard panel may, for example, be corrugated or honeycombed cardboard, e.g. of 10-14 mm, 11-13 mm or at times 12 mm thickness. 
         [0141]    A high density cardboard panel  706 , typically a 600 g/m 2  cardboard sheet, having the same dimensions as portions A, shown in  FIG. 7B , is provided and a thin layer of glue is spread on both of its faces. Panel  706  is then integrated with panel  700 , which is folded about the midline  704 , to embrace and tightly associate through adherence to panel  706 , as seen in  FIG. 7C . This thus brings to the formation of the three-layered structure  710  with two external layers  708 A,  708 B of low density cardboard, e.g. corrugated or honeycombed, and an internal layer of high density cardboard. This three-layered structure is rigid and has load-bearing characteristics of a unit of the second aspect. 
         [0142]    At a next step structure  710  is shaped to the intended body shape to achieve the desired form, as shown in  FIG. 7D . Then, as represented in  FIG. 7E , the edges of the structure, other than edge  712  which is defined by fold  704 , are then layered with a cardboard or paper strip  714 . 
         [0143]    A horizontal bore  716  is then formed at one end that will become the rear end of the body, and a vertical groove  718  having two peripheral wide portions  720 A,  720 B linked by a narrow portion  722  is formed at the other end, as seen in  FIG. 7F . Then, as seen in  FIG. 7G , two plastic bushings  724 A,  724 B are fitted into portions  720 A and  720 B, respectively. 
         [0144]    Another of elements  612 ,  614 , which is a mirror image to the first element is then prepared by identical steps and the two are attached tom one another at their front end portion to form body  602  with a front body block  617 , with a bore  725  that is defined by bushings  724 A and  724 B, as seen in  FIG. 7H . Two plastic bushings  726 ,  728  are then fitted into openings  716 ; these plastic bushings being intended to receive axle  630  of rear wheel  610 . At the next step (not shown) two lateral openings are formed in each of elements  612 ,  614  to accommodate seat holding pins  626 ,  628 . 
         [0145]    Reference is now being made to  FIGS. 8A-8H  illustrating the manner of production and the structure of the fork assembly  604 . 
         [0146]    These depressions define a central segment  830  and two flanking segments  832 ,  834 . Also formed are two short longitudinal grooves  806 ,  808  at about midline  810  of the panel; and two lateral grooves at the bottom end of the panel crossing depressions  802 ,  804 , having central segments  812 A,  814 A and lateral segments  812 B,  814 B. 
         [0147]    As can be seen in  FIG. 8B , longitudinal members that are constituted by rods  816 ,  818  are fitted into depressions  802  and  804 , respectively, the rods spanning the entire length of the grooves and having, respective, top portions  816 A and  816 B that project out of the top edge of the panel. Rods  816 ,  818  are typically, but not exclusively, made of wood, cardboard or plastic but may also be made of metal and many other materials. As can also be seen, bushing  820  is fitted at the bottom end of groove  806  and bushing  822  is fitted into groove  808 . Furthermore, bushings  824  and  826  are fitted into the two central groove segments  812 A and  814 A, respectively. Rods  816 ,  818  and bushings  820 ,  822 ,  824  and  826  are typically secured in position through the use of an adhesive. 
         [0148]    At the next step, seen in  FIG. 8C , a high density cardboard panel, which may have similar characteristics to the high density cardboard described above with regard to the body, is then formed to have the shape matching that of the panel&#39;s central segment  830 . The high density cardboard panel is then attached to the central segment  830 , typically through application of an adhesive. 
         [0149]    The two lateral segments  832 ,  834  are then folded in the direction of arrows X 1  and X 2  to form the structure  840 , seen in  FIG. 8D , in which the lateral edges of segments  832 ,  834  are associated with one another at the midline  810  to thereby define a three-layered structure with external low density cardboard layers. As can also be seen, after such folding, groove segments  812 A,  813 B jointly define a bore  842 ; a mirror-image opening, of course, also exists at the other end (not seen in this Figure). 
         [0150]    At the next step, rectangular section  848  is cut out from a mid-portion of structure  840  to define an opening  848 A and an elongated section  850  with a curved upper end is cut from a bottom portion of structure  840  to define a wheel space  850 A, to thereby form the fork unit  605 , seen in  FIG. 8E . 
         [0151]    Visible in  FIG. 8E  is also bore  846 , defined by bushing  826  which is revealed by the cut out of portion  848  and is coaxial with bore  842 . Cut out of portion  850  reveals bore  854  defined by bushing  822  which is coaxial with bore  852  defined by groove  806  (which accommodates at its bottom portion bushing  820 ). Bushings  824  and  826  within bores  842  and  846 , respectively, are intended to accommodate pivot  630 . Bushings  820  and  822  within respective bores  852  and  854  are intended to accommodate axle  856 , as seen in  FIG. 8 , to thereby couple the body and the fork in a pivotal manner to enable for steering, as described above. 
         [0152]    Handlebar  622  is seen in  FIG. 8G  and includes a cardboard cylinder  858  formed with three bores  860 ,  862 ,  864 , the latter accommodating pin  866 . The bore and the pin are positioned and dimensioned such that bores  860  and  862  can accommodate projections  816 A and  818 A of rods  816  and  818 , respectively, while the pin fits into bore  852 . The length of pin  866  is such that once inserted into bore  852 , it will fit into the space above bushing  820 . By combining the handlebar with the fork, assembly  604  is formed, seen in  FIG. 8H . 
         [0153]    By inserting body block  617  into opening  848 A and then inserting pivot  630  through bore  852  to pass through the bore  725  in body block  617 , the body  602  becomes pivotally coupled to assembly  604 . The front wheel  608  may then be fitted into the wheel space  850 A and rotationally coupled to the fork through axle  630 .