Abstract:
A swivel joint for pivotably coupling a tray to a support element of a seating implement. The swivel joint includes a tubular inner structure arranged substantially coaxially with and non-rotatably connectable to the support element, and a mounting structure at least partially surrounding the tubular inner structure in a radial direction. The mounting portion is pivotable relative to the tubular inner structure and rigidly coupled to the tray. The tubular inner structure includes at least one opening extending in the peripheral direction between two angular positions, and the mounting structure has at least one projection which projects in a radial direction and engages with the at least one opening of the tubular inner structure. The swivel joint provides additional structural integrity to compensate for loads on the tray and also provides a pivoting point to allow the tray to move easily between positions of use and non-use.

Description:
RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119 of German Utility Model Application No. DE 10 2010 054 435.3, filed Dec. 14, 2010, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The field of the disclosure generally relates to joints and linkage mechanisms for desks and other seating implements for pivotably supporting a desk tray. In particular, the disclosure relates to swivel joints designed and configured in a manner suitable for supporting increased loads on the desk tray. 
     BACKGROUND 
     U.S. Pat. No. 7,731,277 of Weber et al. discloses a seating implement with a base frame structure and a tray, wherein the tray is dimensioned to support a notebook computer or other objects and is mounted to a support element of the base frame structure by way of a swivel joint. To support increased loads (in comparison with a smaller writing desk), such as when a computer or other object rests on the tray, a portion of the support element to which the swivel joint is mounted extends substantially horizontally and at an angle of between about 35 degrees and 60 degrees relative to the main seat direction of the seating implement. Such a configuration allows the support element to extend a distance underneath the tray to provide additional support and structural integrity. In addition, when the tray is upwardly pivoted in a position of non-use, it is possible to comfortably get into and out of the seating implement. 
     The present inventors have identified a need for a low-maintenance and structurally sound swivel joint on a seating implement, where the swivel joint is configured to support increased loads. The present inventors have also identified a need for such a swivel joint that can be easily assembled with few and relatively inexpensive parts. In addition, the present inventors have identified a need for a support element mounted to the swivel joint in an orientation in which the support element extends substantially parallel to the main seat direction of the seating implement to reduce interference of the joint mechanism with a user occupying the seating implement. 
     SUMMARY 
     An apparatus is disclosed for improved seating implements having a joint, such as a swivel joint, for pivotably mounting a second article (such as a desk tray, tablet, or other structure of any size and shape, including a plate-shaped configuration) to a first article (such as a supporting structure having a tubular cross-section), where the swivel joint is configured for supporting increased loads due to, for example, the weight of the second article itself and loads supported by the second article. The first article may include support elements of any suitable cross-section and can be hollow or solid, as desired. In some embodiments, the swivel join may be fixed to and carried at a side or end edge of the second article. Alternatively, the joint may also be mounted to an inner or central portion of the second article. 
     In some embodiments, the joint comprises a tubular inner portion arranged substantially coaxially in relation to the first article and non-rotatably connectable thereto. The joint also includes an outer portion at least partially surrounding the tubular inner portion of the joint in the radial direction, where the outer portion is pivotable relative to the tubular inner portion of the joint between two end positions and may be fixedly connectable to the second article. The tubular inner portion and the outer portion each include at least one opening extending in the peripheral direction between two angular positions, and each also include at least one projection which projects in the radial direction inwardly and outwardly, respectively, and engages with the at least one opening of the tubular inner portion and the outer portion, respectively. 
     The pivotal movement of the joint occurs by the relative rotary movement between the tubular inner portion and the outer portion of the joint. In some embodiments, the pivotal angle of the joint ranges between about 60 degrees and 180 degrees. In other embodiments, the range is between about 75 degrees and about 150 degrees. In some embodiments, for optimized pivotal movement, the tubular inner portion comprises a substantially circular cross-section, which may surround the first article over its full periphery or over only part of its periphery. 
     The end positions of that pivotal movement may be predetermined by the boundaries of the at least one opening in the inner portion and outer portion, respectively, into which the at least one projection on the outer portion and inner portion, respectively, engages. The boundaries of the opening or openings may correspond in that respect substantially to the respective end positions of the second article. In some embodiments, the end positions of the swivel joint can manage without the involvement of additional fastening elements and without additional rotation-limiting elements. 
     The mutual engagement between the at least one opening and the at least one projection provides a high degree of stability to the swivel joint. Depending on the selected materials and dimensions of the components, a joint configured in a manner as described in this disclosure is suitable for supporting high loads. In such configurations, the swivel joint may, on its own, support the second article and any loads resting thereon without reliance on the supporting element. 
     In some embodiments, the shape, size, number and arrangement of the at least one opening and the at least one projection correspond to one other. In such configuration, basically any shape, size, number, and arrangement may be possible. In other embodiments, the at least one opening can extend the entire thickness of the tubular inner portion, or can only be in the form of a recess in the inner portion. In yet other embodiments, the numbers of openings and projections may be different, with one or a plurality of projections potentially engaging with each opening. 
     In some embodiments, to provide added stability of the joint, the projections may contact the inner portion in the axial and rest against the inside edges of stops in the openings, or have minimal clearance. The openings may be of a substantially uniform shape and size in the peripheral direction so that a pure rotary movement may be achieved (without additional movement in the axial direction). 
     In one embodiment the outer portion of the joint has at least one shell-shaped, mounting portion which at least partially embraces the inner portion and on which is provided the at least one projection or the at least one opening. Such construction of the outer portion with at least one mounting portion permits simple assembly of the joint. The outer portion of the joint may have two or more mounting portions which enclose the inner portion substantially over its full periphery. In addition, the mounting portions also comprise a shell-shaped configuration to embrace the tubular inner portion and rotate relative thereto. 
     In another embodiment, the outer portion of the joint has at least one housing portion non-rotatably connectable to and partially embracing the at least one mounting portion which can be fixedly connected to the second article. Such an embodiment may provide for simple assembly of the joint and the housing portion may serve to encapsulate the joint and its movable parts to reduce possible access or tampering with the joint and to decrease a risk of injury. In some embodiments, to further simplify assembly, the at least one housing portion of the outer portion can be pushed on in the axial direction over the at least one shell-shaped mounting portion and can be fixed in the axial direction by a securing means. 
     In another embodiment, the outer portion of the joint can be connected to the second article in a positively locking relationship. The positively locking relationship between the second article and the joint allows for direct transmission of the loads from the second article into the structurally stable joint. In addition to the positively locking connection to the second article, the outer portion of the joint can also be connected to the second article in a force-locking relationship. 
     In another embodiment, the at least one projection is a separate component connected to the outer portion or the inner portion, respectively, of the joint. In such embodiments, the projection can be constructed or may comprise a strong and structurally sound material capable of bearing heavy loads, such as steel, and the outer portion or the inner portion may be made from a less expensive and/or lighter weight material. Alternatively, the at least one projection may form a unitary or integral component of the outer portion or the inner portion, respectively, of the joint. In such embodiments, the number of separate components is reduced and assembly methods may be simplified. 
     In another embodiment, the at least one projection is of a substantially strip-shaped configuration in the axial direction of the inner portion to bear over a large surface area against the inside edges of the opening or openings, thereby increasing stability of the joint. The strip-shaped projection may extend in the axial and radial directions of the tubular inner portion of the joint. 
     In another embodiment, the tubular inner portion of the joint is a separate component from and non-rotatably connectable to the first article. In other embodiments, the tubular inner portion of the joint forms a unitary or integral component of the first article. In such embodiments, the assembly process may be simplified, as the number of components to be fitted together is reduced, and the stability of the non-rotatable connection may be increased. In embodiments where the inner portion of the joint is integral with the first article, the at least one opening, or the at least one projection, or both may also be integral or form a unitary structure with or on the first article. 
     In one embodiment, the tray support element is integral with or formed as a unitary structure of the base frame structure of the seating implement of furniture. Such a configuration, may serve to simplify the assembly process and increase the overall stability of the seating implement. In addition, loads on the desk tray may be redistributed from the joint to the base frame structure by way of the support element. In another embodiment, a portion of the support element, to which the joint is mounted, extends substantially horizontally (plus or minus 10 degrees) and substantially parallel (plus or minus 15 degrees) relative to a main direction of use of the article of furniture. 
     Additional aspects and advantages will be apparent from the following detailed description of preferred embodiments, which proceeds with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a seating implement with a tray mounted by way of a joint, according to one embodiment. 
         FIG. 2  is a side view of the seating implement of  FIG. 1  with the tray in a position of use. 
         FIG. 3  is a side view of the seating implement of  FIG. 1  with the tray in an upwardly-folded position of non-use. 
         FIG. 4  is a cross-sectional view taken along section A-A of the joint in  FIG. 2 . 
         FIG. 5  is a cross-sectional view taken along section B-B of the joint in  FIG. 2 . 
         FIG. 6  is a cross-sectional view taken along section C-C of the joint in  FIG. 3 . 
         FIG. 7  is a perspective view of the seating implement of  FIG. 1  illustrating an exploded view of the joint. 
         FIG. 7A  is an enlarged view of the joint in  FIG. 7 . 
         FIG. 8  is a front view of a stack of a plurality of seating implements with their respective trays in an upwardly-folded position of non-use, according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to the drawings, this section describes particular embodiments and their detailed construction and operation. The embodiments described herein are set forth by way of illustration only and not limitation. The described features, structures, and characteristics may be combined in any suitable manner in one or more embodiments. In view of the disclosure herein, those skilled in the art will recognize that the various embodiments can be practiced without one or more of the specific details or with other methods, components, materials, or the like. For the sake of clarity and conciseness, certain aspects of components are presented without undue detail where such detail would be apparent to those skilled in the art in light of the teachings herein and/or where such detail would obfuscate an understanding of more pertinent aspects of the embodiments. 
     As one skilled in the art will appreciate in light of this disclosure, certain embodiments may be capable of achieving certain advantages, including some or all of the following: (1) providing a seating implement with a tray or tablet support by a joint mechanism, where the joint mechanism is capable of supporting increased loads on the tray or tablet; (2) providing a seating implement that can be stacked with other similar or identical seating implements; (3) providing a seating implement with a pivoting tray for affording increased space for getting into and out of the seating implement; and (4) providing a joint mechanism that can be easily assembled with few and inexpensive parts. 
     In the following description of the figures and any example embodiments, the system may be described and referred to as a seating implement, such as a desk or chair, having a rotatable tray. It should be understood that such use is merely one use for such a system and should not be considered as limiting. Other uses for such a system with the characteristics and features described herein may be possible, for example, the system may include furniture for lying down, such as a patient bed, where the furniture includes a rotatable tray or other similar structure. Still other uses not described herein may be possible. 
       FIGS. 1 and 2  illustrate various views of a chair with a side tray in its position of use;  FIG. 3  shows the chair with the tray in its upwardly pivoted position of non-use; and finally  FIG. 8  illustrates a plurality of such chairs in a stacked configuration with each of the trays in a pivoted position of non-use. 
     Referring now to  FIGS. 1-3 , the chair  100  includes a base frame structure  9  a seat  16 , a backrest  18 , and a hinged tablet or tray  20 . In some embodiments, the seat  16  and the backrest  18  may be formed as a single, continuous unit. The base frame structure  9  of the chair  100  further includes a left-hand side frame  10  with two chair legs, a right-hand side frame  12  with two chair legs and at least one transverse bearer  14  connecting the left-hand and right-hand side frames  10 ,  12  together and serving as a support for the seat  16 . According to one embodiment, the chair leg portions of the respective frames  10 ,  12  comprise a unitary, continuous structure. The left-hand and right-hand side frames  10 ,  12  may be configured, sized, and dimensioned in a corresponding fashion such that a plurality of chairs  100  can be stacked as illustrated in  FIG. 8 . The tray  20  may be sized and dimensioned to provide a workspace area as desired, while providing sufficient clearance for the user sitting in the chair  100  so the user does not feel constricted by the tray  20 . For example, in some embodiments, the tray  20  may have length and width dimensions of up to 500 mm by 600 mm. In other embodiments, dimensions of up to 450 mm by 600 mm. In yet other embodiments, the tray  20  may have a maximum length of about 560 mm, a maximum width of about 400 mm. In still other embodiments, the tray  20  may have a surface area of between 0.25 square meters and 0.3 square meters. According to another embodiment, the tray  20  comprises a substantially planar panel having dimensions in the range as previously described to support a laptop computer or other similar devices. 
     In some embodiments, the seat  16  and the backrest  18  may comprise separate structures coupled or connected together by a supporting structure in an angular relationship as desired to provide a comfortable and/or ergonomic seating position. In other embodiments, the frames  10 ,  12  may each comprise two or more independent structures coupled or otherwise joined together by way of suitable longitudinal and transverse bearers to form the frames  10 ,  12 . 
     As is understood by one having ordinary skill in the art, the chair  100  and all of its components may be constructed from any suitable materials as desired. For example, the base frame structure  9  may be constructed from metal or metal alloys, such as steel, and the seat  16 , backrest  18 , and tray  20  may be constructed from plastic or wood. In some embodiments, the seat  16  and/or backrest  18  may include a fabric or cushioned covering to provide additional comfort. In other embodiments, the chair  100  and its components may be constructed from other materials, which may depend on various factors such as weight, cost, durability, and availability of materials. 
     The chair  100  further includes a support element  22  coupled to the base frame structure  9  for supporting the tray  20 . In one embodiment, the support element  22  is an elongated tubular structure, but may comprise other cross-sectional shapes, for example a square shaped bar. The support element  22  may be coupled to the base frame structure  9 , for example, it may be attached or welded to the right-hand side frame  12  or one of the transverse bearers  14 , or it may be formed as a continuous, single structure in conjunction with either of the side frames  10 ,  12  or the transverse bearer  14 . For convenience, the support element  22  is described in relation to the right-hand side frame  12 , but it should be understood that this adopted convention is not meant to be limiting and that the same concept applies to embodiments where the support element  22  is positioned near the left-hand side frame  10 . 
     The support element  22  has an elongated first portion which extends in a plane substantially parallel to the plane of the right-hand side frame  12  on the side remote from the seat inclined forwardly and upwardly from the latter. An upper end  23  of that elongated first portion determines the height of the tray  20  in its position of use (see  FIGS. 1 and 2 ). The height of the tray  20  may be increased by lengthening the elongated first portion to change the position of the upper end  23 . The support element  22  further includes a second portion (extending within joint mechanism  26 ) joining, either directly or by way of intermediate connectors, the first portion along the upper end  23 . The second portion of the support element  22  extends in a substantially horizontal plane (plus or minus 10 degrees) and substantially parallel (plus or minus 15 degrees) relative to the main seating direction of the chair  100  (right/left direction in  FIGS. 2 and 3 ). 
     The tray  20  is mounted by means of a joint mechanism  26  to the horizontal second portion of the support element  22  in such a way that the tray  20  is pivotable about an axis substantially parallel to that second portion of the support element  22  between a horizontal position of use (see  FIGS. 1 and 2 ) and an upwardly pivoted position of non-use (see  FIGS. 3 and 8 ). The pivot axis of the tray  20  extends substantially parallel to the main seating direction of the chair  100  and laterally relative to the chair  100 , such that when the tray  20  is in the upwardly-pivoted position of non-use, the chair  100  affords a user a sufficiently large and comfortable way of getting into and out of the chair  100 . 
     The pivotal angle afforded by the joint  26  is greater than 90 degrees and, in some embodiments, may be between about 110 degrees to 135 degrees to allow the tray  20  to be held in its upwardly-pivoted position of non-use solely by its own weight. In other embodiments, the pivotal angle may be different, such as between than 135 degrees and 180 degrees. In such configurations, the tray  20  is not oriented exactly vertically in its position of non-use (see  FIGS. 6 and 8 ) to provide for a plurality of such chairs  100  to be stacked. In other embodiments, the pivotal angle may be exactly 90 degrees, but such configurations will inhibit the stackability of the chairs  100  because the upright orientation of the tray  20  will not be conducive to stacking. The range of optimum pivotal angles of the tray  20  may depend on the dimensions of the tray  20  and the stacking spacing of the chairs. 
       FIGS. 4 through 6  illustrate cross sectional views of a swivel joint  26  and  FIGS. 7 and 7A  illustrate enlarged view of the joint  26  for pivotably supporting the tray  20 . With reference to  FIGS. 4 through 7A , the joint  26  has a tubular inner portion  30  and may be made of metal, such as steel, which is non-rotatably connectable, for example welded or screwed, or otherwise engaged around the support element  22 . A pair of openings  32  are provided along the inner portion  30  and may be in the form of window-like through orifices which are of a substantially rectangular configuration and are arranged one behind the other in the axial direction of the inner portion  30 . 
     In some embodiments, the inner portion  30  may be formed as a continuous structure of the support element  22 . In such embodiments, the openings  32  may be provided directly on the support element  22 . 
     The joint  26  further has an outer portion embracing the inner portion  30  and the support element  22 . That outer portion may be rotatable relative to the inner portion  30  of the joint  26  and thus relative to the support element  22 . In other embodiments, the tray  20  can be fixed in positively locking relationship and non-rotatable with respect to the outer portion of the joint  26 . 
     The outer portion of the joint  26  includes two shell-shaped mounting portions  34 ,  36  which may be made from a plastic or other lightweight material. The two mounting portions  34 ,  36  may be of substantially the same shape with respect to each other to reduce the production costs for the joint  26 . To increase stability, the mounting portions  34 ,  36  may each include numerous stiffening ribs  35  on an outside surface facing away from the inner portion  30  (see  FIG. 7A ). 
     The two mounting portions  34 ,  36  of the outer portion together embrace the inner portion  30  over at least a portion of its periphery, but may also embrace the full periphery of the inner portion  30 . In addition, mutually facing ends of the two mounting portions  34 ,  36  may be provided with or formed with complementary latching and/or clamping devices (for example pins and bores or noses and openings) to allow for the mounting portions  34 ,  36  to be fixedly assembled about the inner portion  30  in a preliminary assembly step. 
     The inside surface of the mounting portions  34 ,  36 , the surface facing toward the inner portion  30 , is of a corresponding shape to the external shape of the inner portion  30  to provide the embracing relationship previously described. In addition, the material of the mounting portions  34 ,  36  may be selected to provide a sufficiently low coefficient of sliding friction between the inner portion  30  and the mounting portions  34 ,  36  so that the tray  20  can be easily pivoted by the user with minimal effort, but not so low that the tray  20  will move too easily and disrupt the stability of the tray  20 . For example, the inner portion  30  may be made of steel and the mounting portions  34 ,  36  may be made of a synthetic material (e.g. PTFE, PA, PP, PE, etc.) with an addition of about 5% to 15% by weight percent of talcum, such that the coefficient of sliding friction ranges between 0.25 and 0.35. In other embodiments, the materials for the inner portion  30  and the mounting portions  34 ,  36  may be different than those described such that the coefficient of sliding friction is about 0.4. 
     The outer portion of the joint  26  further includes a housing portion  40  that may be made from metal, such as steel, and embracing the two mounting portions  34 ,  36  over the full periphery thereof. The mounting portions  34 ,  36  with their reinforcing ribs  35  and the housing portion  40  are such that the housing portion  40  embraces the two mounting portions  34 ,  36  substantially in positively locking relationship and thus non-rotatably connects thereto. As an additional securing means in the axial direction, provided on both mounting portions  34 ,  36  are two respective securing pins  42 , which in the assembled condition of the joint  26 , respectively project between two adjacent reinforcing ribs  35  of the respective mounting portion  34 ,  36 . 
     The mounting portions  34 ,  36  may include two elongate openings provided in succession in the axial direction of the inner portion  30 . Fitted, such as by a press fit, into those openings are two strip-shaped projections  38 . The projections  38  may be made from metal, such as steel, and are arranged in a corresponding fashion to the openings  32  in the inner portion  30 . The projections  38  are also of a length corresponding to the inside dimensions of the openings  32  in the inner portion  30  in the axial direction. The projections  38  may be formed as a unitary structure in relation to the mounting portions  34 ,  36  or may be formed as separate components and thereafter welded or otherwise attached. 
     It should be understood that while in the described example embodiments the openings  32  are provided on the inner portion  30  and the strip-shaped projections  38  are fitted into the mounting portions  34 ,  36  of the outer portion, in other embodiments, the projections  38  may be provided on the inner portion  30  and the corresponding openings  32  may be provided on the outer portion of the joint  26  and engaged in a similar fashion as previously described. 
     In the assembled condition of the joint  26 , those strip-shaped projections  38  on the second mounting portion  36  engage into the openings  32  in the tubular inner portion  30  (see  FIGS. 5 and 6 ). The pivotal travel of the outer portion relative to the inner portion  30  of the joint  26  is defined by the strip-shaped projections  38  abutting in the peripheral direction against the inside edges of stops  39  of the openings  32  in the inner portion  30 . In the illustrated embodiment, the pivotal angle is about 125 degrees, wherein the one end position for the position of use of the tray  20  is almost horizontal. 
     In the illustrated embodiments, the angular positions of the boundaries of the openings  32  in the inner portion  30  of the joint  26  substantially correspond to the desired angular positions of the position of use and the position of non-use of the tray  20 . In other embodiments, the openings  32  may be provided with a displacement in relation to those aforementioned angular positions. 
     The housing portion  40  of the outer portion of the joint  26  is of a generally U-shaped cross-sectional configuration, wherein an outwardly disposed limb  41  (see  FIG. 5 ) is of greater length than an inwardly disposed limb  43  (see  FIG. 5 ). Provided at the end of the outward limb  41  is an inwardly-directed external flange  44  which engages into a corresponding recess  21  in the outer edge of the tray  20  (see  FIG. 7A ). Provided at the end of the inward limb  43  is an outwardly-directed internal flange  46  which has a plurality of bores for receiving screws  48 . 
     While in the foregoing embodiments the two shell-shaped mounting portions  34 ,  36  and the housing  40  are described as separate components, in one embodiment, an exterior portion of the mounting portions  34 ,  36  may form the housing  40  once the mounting portions  34 ,  36  are connected to one another so that the joint  26  does not include a separate housing  40 , but the housing  40  is integrally formed as part of the mounting portions  34 ,  36 . In other embodiments, there may only be one mounting portion or there may be more than two shell-shaped mounting portions  34 ,  36 . 
     In operation, the tray  20  is received in positively locking relationship between the external flange  44 , the outer limb  41 , and the internal flange  46  of the housing portion  40  and fixed by the fixing screws  48  to the internal flange  46  of the housing portion  40 . The tray  20  is thus secured non-rotatably to the housing portion  40  and accordingly to the outer portion of the joint  26 . In such a configuration, the tray  20  can be rotated jointly with the outer portion of the joint  26  about the tubular inner portion  30 , with the range of pivotal movement being defined by the openings  32  and the projections  38 . The rotational limitation by the mutual engagement of openings  32  and projections  38  provides a highly stable joint  26  suitable for carrying heavy loads. This stability is accomplished with relatively few components and is of a simple and low-maintenance structure. 
     With reference to  FIG. 7A , the following describes a process for assembling the joint  26  with the functionality and characteristics described previously. First, the tubular inner portion  30  with the openings  32  is pushed onto the horizontal portion of the support element  22  and welded or otherwise rigidly attached thereto in the desired rotational position of the openings  32 . Thereafter, the two shell-shaped mounting portions  34 ,  36  are fitted laterally onto the inner portion  30  and pressed together. The mounting portions  34 ,  36  may be fixedly pre-assembled to the inner portion  30 , such as by the previously described latching and/or clamping means. 
     Next, the housing portion  40  is then pushed in the axial direction over the two mounting portions  34 ,  36 . The inwardly projecting external flange  44  of the housing portion  40  is guided only just above the mounting portion  34  so that the securing pins  42  are beneath the mounting portions  34 ,  36  to provide for axial movement. 
     Once the housing portion  40  has been positioned at its desired axial position over the mounting portions  34 ,  36 , the housing portion  40  is moved upwardly so that the securing pins  42  engage into intermediate spaces between adjacent reinforcing ribs  35  of the mounting portions  34 ,  36  and thus fix the housing portion  40  relative to the mounting portions  34 ,  36 . 
     Finally, the tray  20  may be inserted between the external flange  44  and the internal flange  46  of the housing portion  40  and fixed to the swivel joint  26  by means of the fixing screws  48 . Construction of the remainder portion of the chair  100  is not described in detail herein, but it may be constructed using assembly methods common in the industry. 
     It will be obvious to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.