Abstract:
A wall structure ( 10 ) comprising concrete composite masonry blocks ( 12 ) supported and interconnected by elongate support beams ( 16 ) is disclosed. The blocks ( 12 ) are shaped to be stacked in vertically independent columns ( 14 ) and are held in place by the specially shaped, lightweight support beams ( 16 ) placed between the adjacent columns ( 14 ). The wall structure ( 10 ) may be adapted for use as a bearing or non-bearing wall.

Description:
RELATED APPLICATIONS 
   This application is a Continuation in Part of U.S. patent application Ser. No. 09/547,206 filed 12 Apr. 2000 now U.S. Pat. No. 6,374,552. 

   BACKGROUND OF THE INVENTION 
   The present invention is drawn to a mortarless wall structure that may be adapted for use in many applications. Specifically, the present invention is a mortarless wall structure that may be adapted for use as a skirting wall, as wainscoting, as a small retaining wall, as a pool wall, as a veneer or fascia, as a fence, and as a bearing or non-bearing wall, among others. 
   Mobile homes, trailer homes, and modular homes are residential structures that are not built on a foundation. As a result, in order to prevent shifting and sinking of these structures, and moreover to ensure the structure is level regardless of the ground&#39;s topography, they are placed on stilts or supports that protrude from the ground and elevate the structure thereabove. This causes a visible gap in some areas between the ground and the bottom of the structure. 
   Mobile home skirting efforts, until now, have resulted in a variety of products which are either prohibitively expensive, or unattractive and unable to withstand sustained exposure to nature&#39;s elements. Attempts that fall into the latter category include such easily breakable products as wooden cross-hatching and plastic or foam panels that imitate a stone or brick wall. Solutions that tend to be prohibitively expensive or difficult to install include large, custom-made, cement slabs having a decorative face, and the use of standard cinder blocks and mortar to build a wall around the bottom of the structure. Consequently, there is a need for a sturdy, inexpensive alternative for skirting a mobile home, which is easy to install. 
   Until now, where brick, stone, or concrete were used as veneer or fascia, for fencing, and as bearing- and non-bearing walls, these structures were typically permanent in nature. In addition, the erection of these structures typically required specialized knowledge and skills to achieve. In light of these shortcomings, there is an additional need for a wall structure that may be used as a veneer or fascia, as a fence, and as a bearing or non-bearing wall, that is easily assembled by an unskilled user and that may also be dismantled and rebuilt without damage to the constituent parts of the wall structure. 
   SUMMARY OF THE INVENTION 
   The present invention provides a composite masonry block and wall system to be used to skirt elevated structures. The block is shaped to be stacked in vertically independent columns, held in place by specially shaped, lightweight, synthetic beams placed between adjacent columns, and also by synthetic U-shaped lateral supports which open downwardly and are attached to the bottom of the elevated structure. 
   The blocks comprise a split front face, a rear face, top and bottom surfaces, and side surfaces. The side surfaces comprise grooves for receiving supporting portions of the synthetic beams. The top and bottom surfaces are preferably shaped so that when an upper block is stacked on a lower block, the lower surface of the upper block sits on the upper surface of the lower block and the two blocks are relatively coplanar and vertical. This configuration is most easily accomplished using blocks having flat top surfaces and flat bottom surfaces that are relatively perpendicular to the front and rear faces. It would also be possible to accomplish this vertical block-to-block relationship using top and bottom surfaces comprised of complementary angles and/or curves. 
   The synthetic beams are preferably a weather resistant metal or plastic, nylon or other synthetic, durable, inexpensive material, such as poly-vinyl chloride (PVC). The purpose of the beams is to keep the independent vertical columns from buckling when subjected to a force normal to the plane of the wall. The rigidity of the blocks provides enough support to prevent failure in other directions. This purpose may be accomplished using relatively thin beams having lateral extensions for being received by the grooves in the sides of the blocks. 
   Preferably, these beams provide little to no support in a vertical direction. They merely maintain the blocks in independent vertical columns. The columns are considered independent because, unlike conventional brick or stonewalls, one horizontal course of blocks is aligned with the adjacent upper and lower courses so that the blocks in each course are in line with the blocks above and below them, as opposed to being laterally offset. This results in the formation of vertical columns of blocks that can move up and down, due to forces exerted by the ever-shifting earth, without upsetting, or otherwise exerting forces on, adjacent columns of blocks. 
   The resulting wall of this system is surprisingly strong. It may even be used to provide support to the elevated structure. Once installed the elevated structure may be lowered onto the blocks. Alternatively, the blocks may merely serve as a skirt, which improves the aesthetics of the structure and keeps unwanted birds and animals from nesting or otherwise residing under the structure. In this embodiment, it is not necessary that the blocks make actual contact with the structure. 
   The use of the lateral support beams also obviates the need for mortar between the blocks. This mortarless system is advantageous over traditional brick and mortar walls for obvious reasons. First, fewer materials are required to build a wall. Second, one person can easily construct a wall at their leisure. There are no time constraints imposed by drying mortar. Third, the wall can be constructed regardless of weather conditions. Also, the loose block system can be constructed on any surface, including sand, gravel, dirt, or concrete. It is not necessary to pour a foundation. 
   The lateral support beams also allow the use of relatively thin blocks. These thin, wafer-like blocks are relatively lightweight, resulting in ease of handling and shipping, and a reduction in material costs. The blocks are preferably between 1 and 4 inches thick, more preferably on the order of 2½ inches thick. As they are generally between 6 and 12 inches in height, it would be difficult to use such a tall thin block to create a brick wall using mortar. The tall, thin blocks would have to be held in place somehow to allow the mortar to dry. However, tall thin blocks provide certain advantageous and the present invention provides a way of incorporating the advantageous of such a block. These advantageous include an increased front face surface area, resulting in a more attractive wall. The design also provides increased lateral support, ideal for use with such a beam system. 
   The loose block system also allows the wall to be disassembled and reassembled. This not only gives flexibility during initial construction, but also allows later renovations to be made easily and inexpensively. For instance, often it is desirable to vent wall structures such as skirting walls to prevent the buildup of moisture or condensation between the ground and the elevated structure. These vents can be easily installed into an existing wall, especially if they are of similar dimensions and configurations as the blocks. The blocks of a given column are simply removed and reinstalled, replacing one of the blocks with the vent. Other auxiliary items, such as an access door or lights, could be installed in a similar manner. 
   The wall design of the present invention also allows a wall corner to be constructed without supporting beams or mortar. Two walls are simply aligned to form a butt joint and fasteners such as appropriate plastic pegs or screws and plastic inserts are used to fasten one wall to the other. Alternatively, construction mastic, a type of adhesive, may be applied instead of or in combination with the screws. Again, ease of installation is greatly improved by the loose block, mortarless system of the present invention. 
   Another embodiment of the present invention is well suited for use as a veneer or as wainscoting. In this embodiment, the support beam also includes one or more leg structures that extend from the support beam toward a structure over which the wall structure will be applied as a veneer. The leg structure comprises a leg and a foot that are preferably arranged at right angles to one another and to the support beam, but which may be constructed at any appropriate angle. 
   A double-ended support beam is useful in adapting the wall structure of the present invention to the creation of a double-sided wall. In this embodiment of the present invention, two block engaging structures comprising a web and at least one flange extending therefrom are coupled together in a spaced apart relationship by a spacer or web. The respective block engaging structures engage the grooves between the side edges of adjacent block columns of respective wall faces to couple the wall faces together. 
   Another embodiment of the support beam of the present invention is useful in constructing walls having a single face. In this embodiment, the support beam comprises a block engaging structure that extends from a sold or hollow elongate post. The block engaging structure of this support beam preferably comprises a web having extending therefrom a pair of flanges that are constructed and arranged to engage the opposing grooves formed in the side surfaces of adjacent block columns in the wall face. The post portion of this support beam can be secured directly to a wall support structure such as a foundation, footing, ledge, or bracket. Where the post portion of the support beam is hollow, the support beam can be slipped over a structural member that is secured directly to a wall support structure such as a foundation, footing, ledge, or bracket. 
   These and other objectives and advantages of the invention will appear more fully from the following description, made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views. And, although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention, which may be embodied in other specific structure. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an elevated structure skirted with the wall structure of the present invention; 
       FIG. 2  is a perspective view of a block of the present invention; 
       FIG. 3  is a perspective view of a support beam of the present invention; 
       FIG. 4  is a side elevational view of a column of the present invention taken generally along lines  4 — 4  of  FIG. 1 ; 
       FIG. 5  is a plan view, taken generally along lines  5 — 5  of  FIG. 1 , of two adjacent blocks of the present invention abutted and held by a support beam; 
       FIG. 6  is a plan view of two blocks abutted with a support beam installed using an alternative configuration; 
       FIG. 7  is a plan view of two blocks being pressed together and resiliently deforming a support beam; 
       FIG. 8  is a plan view of two blocks abutted with an alternative embodiment of a support beam; 
       FIG. 9  is a plan view of two blocks abutted with another alternative embodiment of a support beam; 
       FIG. 10  is a plan view of a corner of the wall structure of the present invention; 
       FIG. 11  is a plan view of a two abutting blocks with another alternative embodiment of a support beam coupling the blocks to an existing structure; 
       FIG. 12  is a plan view of a two abutting blocks with another alternative embodiment of a support beam coupling the blocks to an existing structure; 
       FIG. 13  is a plan view of a two abutting blocks with another alternative embodiment of a support beam coupling the blocks to an existing structure; 
       FIG. 14  is a plan view of a double-sided free standing wall structure wherein the respective sides of the wall structure are coupled together by a double ended support beam; and, 
       FIG. 15  is a plan view of a freestanding wall structure in which the support beam is formed integral to a post. 
   

   DETAILED DESCRIPTION 
   Referring now to the drawings and first to  FIGS. 1–4 , there is shown a wall structure  10  comprised of a plurality of blocks  12  forming columns  14  partially spaced apart and held in place by vertically oriented, lateral support beams  16 . Downward opening brackets  18  attached to the bottom of the structure being skirted, are placed over the top block  12  of selected columns  14  to help prevent wall  10  from tipping rearwardly or forwardly. As used herein, the term “forward” means away from the center of the elevated structure and the term “rearward” means toward the center of the elevated structure. 
   Attention is now directed to the individual components of wall system  10 .  FIG. 2  depicts a preferred embodiment of block  12 . It can be seen that block  12  generally comprises a front face  20 , a rear face  22 , a top surface  24 , a bottom surface  26  and side surfaces  28   a  and  28   b . Block  12  is preferably made of a dry composite masonry material, which hardens quickly when compressed in a mold. It is envisioned that other materials could be used, such as concrete, fiberglass, ceramics, hard plastics, or dense foam. The present invention would also be achieved if blocks  12  were formed of wood, preferably treated wood. Though the general shape of the blocks is more important to achieve the present invention than the material used, it has been found that the aforementioned preferred dry composite masonry material provides the most desirable combination of strength, appearance, economy, and ease of manufacturing. 
   Front face  20  is forwardly spaced from rear face  22  by a predetermined distance herein defining the depth  30  of block  12 . As shown in  FIG. 2 , it is envisioned that front face  20  is formed using a splitting process, thereby forming an attractive, roughened face. This, however, is not necessary to carry out the spirit of the invention. Front face  20  could alternatively be molded, pressed, carved, etched, painted, or otherwise formed in any manner. Preferably, depth  30  is relatively constant throughout the extents of block  12 , excepting the variations caused by the splitting process and also excepting splitting recesses or other interruptions in the split look of front face  20 . Splitting recesses  21  are preferably formed in front face  20  to provide an area for splitting block  10  along a straight line. 
   Top surface  24  is separated from bottom surface  26  by a distance defining the height  32  of block  12 . When blocks  12  are arranged vertically to form a column  14 , bottom surface  26  of any block  12  other than the bottom block of a column, rests on the top surface  24  of the block below. It is therefore preferred that top surface  24  and bottom surface  26  are so shaped to facilitate a stacking relationship between two blocks  12  that results in an upper block  12  resting vertically on a vertically oriented lower block  12 . This relationship is most easily achieved by making top surface  24  and bottom surface  26  flat and relatively perpendicular to rear face  22  and/or front face  26 , as shown in the Figures. Alternatively, it is envisioned that top and bottom surfaces  24  and  26  be comprised of complementary angles which are not perpendicular to rear face  22  and/or front face  26 , but result in the vertical relationship between upper and lower blocks  12 , described above. It is also envisioned that this relationship be achieved through the use of concave and convex surfaces or using tongue and groove configurations. 
   Side surfaces  28   a  and  28   b , as shown in  FIG. 2 , are preferably somewhat perpendicular to rear face  22  and/or front face  20  and preferably comprise a groove  34  for receiving a portion of beam  16 , shown in  FIG. 3 . Alternatively, it is envisioned that one side surface  28   a  or  28   b  have a groove and the other side surface have a tongue configured to mate with the groove, thereby obviating the need for beams  16 . However, in order to maintain the vertically independent characteristics of columns  14 , the use of beams  16  is preferred. 
   Beams  16 , shown in  FIG. 3 , preferably comprise a spine or web  36  and at least one rib  38 . Preferably, there are two pairs of ribs  38   a  and  38   b . This configuration of two pairs of ribs  38   a  and  38   b  attached to each other by web  36  forms somewhat of an I-beam configuration. It is preferred that one set of ribs  38   a  are resiliently deformable and even more preferred that they comprise flanges  40  to assist in guiding them into grooves  34 . A biased, resiliently deformable rib  38   a  places an even force on groove  34  and prevents movement and misalignment between blocks  12  of a given column  14 . 
   The distance between rib  38   a  and  38   b  is herein defined as the span  42  of the rib. The span  42  should either be as great as the distance between the groove  34  and the rear face  22 , or, in the case of the resiliently deformable rib  38 , should be able to achieve this distance through deformation when installed into the groove  34  of a block  12 . 
   Beams  16  may or may not be attached at their upper ends to the structure being skirted, at or near its bottom. Attaching beams  16  thusly provides support to the independent columns  14 , preventing them from leaning or falling forwardly or rearwardly. Beams  16  also act to align the blocks  12  of a given column  14 , ensuring that the blocks maintain a somewhat coplanar relationship. 
     FIGS. 6–9  show a variety of envisioned beam constructions and arrangements.  FIG. 6  shows a preferred arrangement of the preferred beam construction shown in  FIGS. 3 and 5 . It can be seen that preferably, beam  16  is placed in the opposing grooves  34  of adjacent blocks  12  so that resiliently deformable ribs  38   a  having flanges  40  are rearward of ribs  38   b . Doing so utilizes the forces exerted by the bias of ribs  38   a  to press the forward edges of opposing sides  28   a  and  28   b  together so that no gap is seen from the front of the wall. Arrows  41  represent these forces.  FIG. 7  shows how flanges  40  act to guide block  12  into beam  16  and also to assist in increasing span  42 . 
     FIG. 8  shows an alternative embodiment of beam  16  having two ribs  38   b  but only one resiliently deformable rib  38   a .  FIG. 9  shows yet another embodiment of a beam  16  comprising one pair of opposed ribs  38   b  such that the support beam  16  is essentially an elongate spline. 
   It is envisioned that brackets  18  be used in conjunction with beams  16  to provide stability to wall  10 . Referring now to  FIG. 4 , it can be seen that brackets  18  comprise a front wall  44  having a top edge  45  and a bottom edge  47 , a rear wall  46  rearwardly spaced apart from front wall  44 , and a top wall  48  joining top edge  45  of front wall  44  and rear wall  46 . Front wall  44  and rear wall  46  define a downward opening  50  into which the top surface  24  of the top block  12  of a column  14  may be inserted. In operation, bracket  18  is attached to the underside of a structure to be skirted and positioned so that the top block  12  of a column  14  is inserted into opening  50  and so that the bracket is located near the middle of the block  12 . It may be desired to make rear wall  46  of a greater vertical dimension that front wall  44  to provide additional support. It may also be desired to provide a bracket  18  with a rear wall  46 , which extends in a lateral direction further than front wall  44 . Furthermore, it is envisioned that brackets  50  could be a variety of lengths. For instance, brackets  50  could be as short as one inch or as long as the entire wall. 
   Brackets  18  prevent rearward or forward movement of column  14  and also work in conjunction with beams  16  to prevent those columns  14  without brackets  18  from tipping over rearwardly or forwardly. As it is envisioned that beams  16  may or may not be attached to the structure, brackets  18  may be solely responsible for preventing wall  10  from tipping over. Brackets  18  can be of any suitable material, preferably synthetic, more preferably poly-vinyl chloride (PVC) or other durable plastic. It may be advantageous to make brackets  18  and beams  16  out of similar material. 
     FIG. 10  shows a preferred corner configuration using the blocks  12  of the present invention. The design of block  12  lends itself to the formation of corners without the need for mortar, corner braces, or other supports. Two blocks  12   a  and  12   b  are simply aligned to form a corner butt joint  51 . Preferably block  12   b  is broken along its splitting recess  21  to form a new split face  52  which roughly matches split front face  20  of block  12   a . Holes  54  are drilled through blocks  12   a  and  12   b  so that fastener  56  may be inserted. Fastener  56  may be any suitable fastener, preferably a screw or peg. Preferably such as appropriate plastic pegs or screws and plastic inserts are used to fasten one wall to the other. Alternatively, glue, preferably construction mastic  58 , may be applied instead of or, more preferably, in combination with fasteners  56 . 
     FIGS. 11–15  illustrate additional embodiments of the present invention.  FIG. 11  illustrates a support beam  16  having a pair of leg structures  59  that are constructed and arranged to secure a wall comprising columns  14  of blocks  12  to an existing support structure  62 . The support structure may be a building or any other type of structure that may require a wall structure  10  according to the present invention. Legs or leg portions  60  of the leg structures  59  extend rearwardly from the support beam  16  and are preferably secured to ribs  38 B thereof. The leg structures  59  may also be formed as part of the web  36  of the support beam  16 . Each leg or leg portion  60  has a foot  64 , which extends laterally therefrom to provide a point of connection for the support beam  16  to the existing structure  62 . Nails, screws, or other appropriate fasteners  66  are driven through the feet  64  of the support beam  16  and into the sheathing  68  of the wall of the existing structure  62 . The sheathing  68  of the typical wall is typically supported by a plurality of horizontal girts  70 . Once the support beam  16  has been secured to the existing structure  16 , blocks  12  are stacked between respective support beams  16  as illustrated in  FIG. 11  such that ribs  38 A of the support beam  16  are inserted into the grooves  34  in the sides of the blocks  12 . Note that the number, construction, and arrangement of flanges  38 A and  38 B may vary as described above in conjunction with  FIGS. 5–9   
   In order to prevent the inflow of water into the wall structure  10 , it may be desirable to apply a bead of a waterproof material  90  such as a mastic or a caulk along the top surface  24  of the blocks  12 . The bead of waterproof material  90  forms a seal between the upper surface  24  of the lower block  12  upon which the bead has been placed and the lower surface  26  of the block  12  immediately above the lower block. 
   Legs or leg portions  60  of support beam  16  preferably extend rearwardly from flanges  38 B in a perpendicular relationship thereto. Similarly, it is preferred that the feet  64  of the support beam  16  extend laterally perpendicular to the legs  60 . The perpendicular relationship of the feet and legs to the remainder of the support beam  16  is the preferred embodiment thereof, it must be kept in mind that the purpose of the legs  60  and feet  64  is to provide and offset for the block wall  10  from the wall of the existing structure  62 . This offset allows a block wall  10  to be secured over uneven surfaces such as the steel siding  72  illustrated in  FIG. 11 . As can be seen, legs or leg portions  60  of support beam  16  are sufficiently long such that the support beam  16  clears ridge  73  of the steel siding  72 . As can be appreciated, steel siding  72  typically presents a plurality of vertically flat attachment surfaces. Where a wall structure  10  is to be applied to a wall of an existing structure  62  that is not vertically smooth, furring strips or blocking may be fastened to the wall of the existing structure  62  as needed. As support beams  16  provide no vertical support for the blocks  12 , the blocks must be provided with some sort of foundation. Examples of suitable foundation include a concrete pad or footing that is sunk into the ground, and a cantilever ledge or bracket which is securely affixed to the wall of the existing structure. 
     FIG. 12  illustrates a support beam  16  having two pairs of flanges  38 A and  38 B separated by a web  36  and only a single leg structure  59  comprising a leg  60  portion and foot  64 . The embodiment of  FIG. 12  is particularly useful when an obstruction such as ridge  73  of steel siding  72  would prevent one of the leg structures  59  illustrated in  FIG. 11  from securely contacting the wall of the structure  62 . Fasteners  66  are sufficient to provide the requisite lateral support for the wall structure  10 . The support beam  16  having only a single leg structure  59  may be rotated end-for-end depending on the offset location of an obstruction such as ridge  73 . 
   Preferably the support beam  16  of the present invention will be extruded or molded from a material such as a plastic, a fiber reinforced resin, or a metal such as aluminum. In addition to forming embodiments of support beams  16  having the respective profiles of the support beams illustrated in  FIG. 12 , it is possible that one leg structure  59  could be removed from a support beam  16  such as the support beam  16  of  FIG. 11  having two leg structures  59 , thereby resulting in the support beam embodiment illustrated in  FIG. 12 . However, where a single leg structure  59  would be sufficient to provide the needed lateral support for a wall structure  10 , it would be more economical to manufacture support  16  having only a single leg structure  59 . 
     FIG. 13  illustrates a support beam  16  that is constructed and arranged to provide lateral support to a wall structure  10  as described in conjunction with  FIGS. 11 and 12 . The main difference here being that the support beam  16  of  FIG. 13  has a pair of flanges  38 A and only a single flange  38 B extending from the web  36 . Leg structure  59  extends rearwardly from the flange  38 B preferably in a perpendicular relation thereto. While it is preferred that the leg or portion  60  and foot  64  be arranged at right angles to each other and to the flange  38 B of the support beam  16 , these structures may be arranged at any angle to one another provided, of course, that there is a sufficient offset from the wall of the existing structure  62  to allow installation of the blocks  12  of the wall structure  10  and that the foot  64  of leg structure  59  may be securely fastened to a supporting structure  62 . 
     FIG. 14  illustrates a double-ended support beam  80 , which is useful for constructing a dual wall structure  10  having a front face  74  and a rear face  76 . The space  78  between the front and rear faces  74 ,  76  of the dual wall structure  10  of  FIG. 14  may remain hollow or may be filled. As can be seen from  FIG. 14  each end of the double ended support beam  80  comprises a support beam or block engagement structure having a cross-sectional profile similar to the support beam  16  illustrated in  FIG. 5 . As depicted, the support beams or block engagement structures are arranged back-to-back in a spaced apart relation and connected by a spacer web  82 . Spacer web  82  is connected to the base pair of ribs  38 B of each of the support beam portions in a perpendicular fashion. In this manner, support beam  80  couples the dual walls of the wall structure  10  to provide mutual lateral support. Further support can be had by backfilling the space  78  between the front and rear sides of the dual wall structure  10  with gravel, earth, sand, concrete, or an insulating material  79 . It will be appreciated that a cap  81  may be placed over the top of the dual wall structure  10  of  FIG. 14  to prevent the ingress of water and nuisance animals. It will also be appreciated that such a cap  81  may be secured to the dual wall structure by known technologies and techniques, if desired. See, for example, the use of adhesive material depicted in  FIG. 11 . 
     FIG. 15  illustrates a single sided wall structure  10  comprising columns  14  of blocks  12  supported by a post-like support beam  84 . Support beam  84  comprises a post  85  having extending therefrom a web  36 . A pair of ribs  38 A extends laterally from the web  36  in the same manner as the ribs of support beams  16  described in conjunction with  FIG. 3 . As installed, post  85  is preferably rigidly seated in a footing or foundation set into the ground below the wall structure  10 . As can be appreciated, blocks  12  are stacked between respective post support beams  84  as described above. The posts  85  of the post-support beam  84  preferably have a hollow cross section. However, post  85  may also be a solid in cross section or may have a reinforcing structure such as a pipe or a rod received therein. An alternate embodiment for the post to support beam  84  involves securely seating a plurality of rods or members in footings or a foundation beneath the wall structure  10  and sliding the post beam  84  of the type illustrated in  FIG. 15  thereover. Blocks  12  would then be disposed between respective pairs of post support beams  84  as described above. 
   The foregoing is considered as illustrative only of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.