Abstract:
A conveyor belt cleaning apparatus with an elastomeric biasing means. Some given number of the apparatus are seated on a horizontal mount which spans the width of a conveyor belt. Each unit is hollow. This void is loaded with filler material. A metallic blade seat is integral with the elastomeric material and configured to accept a blade.

Description:
This is a continuation of prior application No. PCT/US98/27290, filed Dec. 22, 1998, which designates the United States of America, which in turn claims priority to U.S. Provisional Patent Application No. 60/068,642, filed Dec. 23, 1997, which we hereby incorporate herein by reference in their entirety. The entire disclosure of the prior application is considered as being part of the disclosure of the accompanying application, and is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates a cleaner apparatus for a conveyor belt to scrape material from the belt. 
     BACKGROUND OF THE INVENTION 
     The present invention is directed to providing a belt scraper which is relatively low in cost and simple in construction in comparison to many conventional belt scraper apparatuses. For example, one more complex belt scraper employs a closed parallelogram linkage of four links having an internal, inflatable diaphragm to bias the links and a belt scraper blade against the underside of a conveyor belt. Such a system is relatively complex in that it requires a source of compressed gas to inflate the diaphragm and protective flaps to deflect the scrap debris from clogging the parallelogram linkages. The parallelogram linkages comprise four pivotally connected, steel link members two of which are generally horizontal, and the other two of which are generally inclined to the vertical. As the belt wears the tip away, the diaphragm pushes the linkages to raise the blade tip to continue scraping pressure against the conveyor belt. It will be appreciated that wet material, dirt and clays or sands or gravel or other caustic materials being conveyed by the conveyor belt can deposit in or about the linkages and interfere with the operation of the linkages. Also, the initial cost of a particular linkage and the gas bag add to the cost and the maintenance problems associated with this particular system. 
     The present invention is also directed to providing a belt scraper that is usable with belts spliced with mechanical belt splices made of metal belt fasteners. These metal belt fasteners strike the belt scraper, unless a mechanism is provided to lower the belt scraper upon approach of the belt fasteners. The belt scraper&#39;s striking of the metal fasteners can damage the splice, gouge the scraper blade and vibrate the scraper blade and generate noise. There is a need for a more fastener-friendly belt scraper that allows downward travel of the scraper blades and a cushioning of the impacts between the belt scrapers and the metal belt fasteners. 
     Another form of belt scraper device, such as disclosed in U.S. Pat. No. 3,841,470, uses an elastomeric block of solid rubber or synthetic resin to mount the blade. The blade holder includes a vertical plate fixed to a vertical face of the block; and there is a mild elastic deformation of the resilient member to provide the biasing force. This system does not provide much cushioning because of its rigidity. Further, this system does not maintain the blade pressed against the belt with sufficient force with wear of the scraper blade so that frequent force adjustments are necessary. It is most desirable that blade pressure be maintained without frequent adjustments or other kinds of maintenance. 
     It will be appreciated that belt scrapers for conveyors are often exposed to ambient weather conditions which can be either very hot during summertime or very cold in wintertime. Preferably, the belt scraper functions adequately in very cold temperatures where ice and snow accumulations may be formed on the conveyor belts and scrapers in addition to the dirt, clay, sand, caustic materials, etc. that are always present. When exposed to high temperatures, the belt scraper materials and biasing force elements must not deteriorate and lose their effectiveness. 
     It has been found that the blade mounts and the blades of the scraper may experience a considerable amount of vibration over a particular time period and with a large amplitude of vibration caused by the blades impacting mechanical belt fasteners. It is desirable to reduce the duration and amplitude of the vibrations in an inexpensive manner. It is further desired to provide a scraper blade and mount that dampens the vibration of the blades, while in use, and thereby increases their life against failure due to fatigue of the materials used. 
     Also, there is a need for a scraper blade system for scraping the conveyor belt that allows the belt to be reversed in the opposite direction and still provide a scraping of the belt bottom surface. The scraper blade system should provide the requisite force or pressure between the scraping blade and the belt, even though the wear occurs, by shifting the blade upwardly to take up the wear and to maintain the scraping pressure to remove the debris from the belt. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a new and improved belt scraper apparatus having scraper blades each mounted on an elastomeric blade mount body having integral portions formed thereon for deflection to provide a cushioning of the blade and a spring biasing force to urge the blade tips against the belt surface being cleaned. Herein, this is achieved by an elastomeric blade mount body which is a block-shaped body having a flexible, central, elongated portion preferably including a pair of generally parallel legs or arms, which may be flexed as the scraper is forced against the belt with the legs trying to return to their original non-flexed positions as the scraper blade wears. 
     The preferred elastomeric body can be made relatively inexpensively by being formed as a one-piece block of elastomeric material. The particular opening therein is preferably I-shaped defining a pair of upper and lower horizontal legs attached to the pair of vertical legs at points that acts as flexure points. The preferred body acts as a parallelogram when deflected and acts as a cushion mounting for the scraper blade. The vertical legs may be bent and deformed substantially, e.g., in a range of 15°-40° with respect to the vertical; while the horizontal legs maintain the blade tip substantially perpendicular to the conveyor belt surface. The particular elastomeric blade mount body is relatively corrosion-resistant and a low maintenance item which needs neither to be greased nor, in the usual case, to be protected by flaps from dirt or other debris on the conveyor. 
     In the preferred embodiment of the invention, a filler material is inserted into and fills the opening while still allowing the legs or arms to deflect. The preferred filler material is a foamed material which fills the opening and seals the opening against the intrusion of dirt or other foreign materials. The preferred foamed material is a closed cell, rubber foam which dampens vibrations in the elastomeric body and thereby, decreases the fatiguing of the elastomeric body. Because the elastomeric body is filled and has little or no exposed metal, there is no corrosion and there is little dirt or ice build-up inside the cushion that could affect the deflection of the legs of the elastomeric body. 
     In accordance with the invention, the preferred elastomeric blade mount is made of and selected from various elastomeric materials to have the properties of a good fatigue life and a low compression set. The typical elastomerics have static compression sets in the range of about 20% to 40%; while the preferred elastomeric is a polyurethane having a lower static compression set of about 13%. This lower compression set material, while still providing good flexibility and cushion characteristics, serves to maintain a more constant pressure force between the blade surface and the conveyor belt, e.g., in the range of 10 to 20 lbs./inch 2 . The low compression set elastomeric material increases the time between adjustments of the belt cleaner apparatus to keep the pressure contact within the desired range for good cleaning of the conveyor belt. 
     In accordance with another aspect of the invention, the blade mounts are mounted vertically on a lower, adjustable support which can be moved up, relative to the belt, to force the spring legs or arms of the mount against the belt with a high pressure. When the belt is moving at its normal speed, the friction force of the belt on the scraper blade will bend the vertical legs through an angle, e.g., 15°-20° to the vertical. These bent legs bias the blade with a pressure force against the belt of a predetermined amount usually in the range of 10-20 lbs./inch 2  of blade. Even though the bent legs may be inclined at 20° to the vertical by the traveling belt, the blade itself on the horizontal upper leg of the parallelogram remains perpendicular to the conveyor belt. The conveyor belt may be reversed in its travel direction, and the scraper will still function effectively. 
     When the scraper blade is struck by the belt fasteners, the legs are bent farther back than their usual bent position, and the deflection forces the blade and blade mount downwardly, e.g., about 0.125 inch in the downward direction. The bending of the legs is an energy-absorbing action that reduces the likelihood of gouging or fracturing of the scraper blade edge and damage to the belt fastener splice. Thus, the elastomeric body and bendable legs act as a cushion for the scraper blade. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is diagrammatic view of the scraper blade apparatus constructed in accordance with the preferred embodiment of the invention; 
     FIG. 2A is an end view of the scraper blade apparatus with the blade mount undeflected; 
     FIG. 2B is a view of the blade mount of FIG. 2A deflected and in a normal scraping position; 
     FIG. 2C is a view of the blade mount of FIG. 2B when further bent and displaced downwardly by a belt fastener; 
     FIG. 3 is a front elevational view of several scraper blades and a support mount therefor; and 
     FIG. 4 is a side view of the support and blade mounts shown in FIG. 3; 
     FIG. 5 is a front elevational view of a scraper blade mount constructed in accordance with another embodiment of the invention; 
     FIG. 6 is a side view of the blade mount of FIG. 5; 
     FIG. 7 is an enlarged view of a scraper blade, blade mount of FIG. 6, and a support for the blade mount; and 
     FIG. 8 is a cross-sectional view of a blade mount and a double scraper blade in accordance with a still further embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in the drawings, for purposes of illustration, the invention is embodied in a belt cleaner apparatus  10  having a plurality of scraper blades  12  each having a blade tip  14  in scraping contact with an outer surface  16  of a conveyor belt  18 . In the illustrated embodiment of the invention as shown in FIG. 1, the belt scraper blades  12  are shown just rearward of a head pulley  20 . In other instances, the blades  12  may be positioned underneath the head pulley to push the belt directly against the head pulley  20 , and this would be called a “head cleaner”. Also, the present invention is applicable to cleaners located at various positions from those described herein. 
     Each of the scraper blades is mounted on an elastomeric blade mount having an elastomeric body  40  which is flexible and which is flexed upwardly against the belt by a support  64 . The support  64 , in the illustrated embodiment of the invention, is mounted between a pair of upstanding frames or rails  32  and extends across the conveyor belt in a transverse direction and comprises a pair of slidable slide blocks  34  (FIG.  4 ), which are movable vertically by an adjustable device such as a threaded adjustment screw  36 . Other forms of vertical adjustments may be used rather than the screw assembly as shown herein. 
     In accordance with the present invention, there is provided a new and improved belt scraper apparatus having a plurality of scraper blades  12 , each of which has an elastomeric body  40  having a flexible, elongated, central portion  39  which deflects to provide the spring biasing force to urge the blades  12  against the belt surfaces  16  with sufficient pressure to provide a good scraping action. In the preferred embodiment of the invention, the elastomeric body  40  is a block-shaped body having a central opening  41  being elongated in a vertical direction to provide a pair of generally parallel legs or arms  44  which may be flexed, as shown between the relaxed position of FIG.  2 A and the flexed state of the legs  44  shown in FIGS. 1,  2 B and  2 C. The elastomeric blade mount body  41  may be made inexpensively by being a block of elastomeric material which is cut to size. The preferred elastomeric body has a generally rectangular cross-section for its central portion  39  which is located between an upper end  44   a  and a bottom end  44   b , and located between opposed sides  44   c  and  44   d . A number of elastomeric bodies are disposed side-by-side to make a long, composite scraper blade. To this end, the end walls  44   e  of one elastomeric body may be butted against the adjacent endwall  44   f  of the an adjacent elastomeric body, as best seen in FIG.  3 . 
     The preferred elastomeric block-shaped bodies  40  are in the form of an elastomeric material, such as a silicon rubber or polyurethane, which is corrosion-resistant and is a low maintenance item because it does not need to be greased or protected by flaps as was the prior art devices from dirt or other debris being scraped from the conveyor. The preferred elastomeric bodies are one-piece, block-shaped bodies with smooth, vertical, outer walls  44   c  and  44   d  which do not readily retain material being scraped from the blades. The parallelogram vertical legs  44  will be vertical when the elastomeric body is allowed to relax (FIG. 2A) and to return to its original shape. In its preferred and illustrated form, the elastomeric body  4  has a central, I-shaped opening  41  with the elastomeric material surrounding the opening. Although the illustrated embodiment employs an opening in the elastomeric body and uses the resiliency of the elastomeric material to provide the self-energizing force to push the scraper blade tightly against the conveyor belt, it is possible to embed metal springs in the elastomeric body with the metal springs being deflected to provide the self-energizing force. That is, a low durometer, elastomeric body without a central opening can have metal, coiled springs with coiled flexure points at four corners of the body embedded therein to provide the parallelogram force and movement structure in a manner similar to that provided by the illustrated embodiment of the invention. 
     In accordance with another important aspect of the invention, each of the elastomeric bodies  40  is provided with a filler material  50  which is disposed within the opening  41  to fill the same to close the opening to the intrusion of dirt, ice or other debris which could fill it or accumulate within the block body and eventually affect the performance thereof. The preferred filler material  50  is also a dampening material or means which serves to reduce substantially the duration of any vibrations and to lower the amplitude of any vibrations occurring when the blades are vibrated, such as when in contact with belt fasteners or other devices on the belt. Preferably, the dampening material serves somewhat in a manner of a dampening dashpot or the like for the blades  14  and the bodies  40 . A particularly good material is a foamed polymeric material, such as a low density, closed cell foam. The preferred foamed material is a closed cell rubber foam of 4-5 lbs./cu. ft. density, such as EMR#450 closed cell matallocene rubber available from Sentinel Company, located at Hyannis, Mass., United States of America. Thus, it will be understood that the foamed material  50  prevents accumulation of ice, dirt or other like from filling the hole  41 ; the foamed material does not interfere with the bending or deflection of the legs  44 ; and the foamed material serves as a dampening agent to increase the fatigue life of the elastomeric body. 
     In accordance with another important aspect of the invention, the shape of the preferred opening  41  includes an enlarged circular corner  52  at each of the four corners of the opening  41  to decrease the cross-sectional thickness of the block at the upper and lower ends of the legs to form reduced cross-sectional flexure joint sections  54 . These sections  54  act as flexure points to centralize or locate the bending so as to form four legs to define a parallelogram with the upper, block portion  56  being an upper parallel leg, and the lower, block portion  58  being a lower, horizontal parallel leg. The corners also define opposite ends for the vertical legs  44  which are the vertical legs of the parallelogram. 
     The parallelogram is preferred in that it tends to maintain the blade  14  at the same scraping angle to the belt as the blade wears away. Herein, the blade angle is 90° (see FIGS.  2 B and  2 C), i.e., perpendicular to the belt surface  16  even though the blade mount is bent between the relaxed FIG. 1 position and the deflected position of FIG.  2 B. Also, as the blades wear after considerable amount of scraping, the flexed legs  44  tend to push the scraper blade to maintain its same angular position with respect to the belt. The blade  14  could be positioned at a scraping angle other than the illustrated 90°, and the blade mount body  40  will maintain this angle as the blade tip wears. With the opening  41  in the illustrated elastomeric body, the legs  44  are equal in thickness and length and are deflected through equal angles. For example, in FIG. 2B, both of the legs  44  are illustrated as being bent at an angle A, which is a theoretical 20° to the vertical. When the belt fastener hits the blade, it exerts sufficient force to bend the legs  44  further, such as to the illustrated A′ angle, which is at a theoretical 28°, with the blade tip and the cushion being displaced downward about 0.125 inch due to the projecting downward thickness of the belt fastener on the underside of the conveyor belt. This 20° angle and this 28° angle are given by way of example only, and they were attained by forcing the blade tips upwardly against the belt and exerting on the blade tips  14  an upward normal force of 40 to 50 lbs. while the belt is stationary. Then, when the belt is running, the belt cleaner blade assumes the deflected position of 20° (shown in FIG. 2B) and exerts the desired scraping pressure. Herein, the scraping pressure is kept within a predetermined range to provide a good scraping action. In this illustrated example of the invention, a good scraping contact across the top of the blade surface with the belt is maintained with a scraping pressure in the range of 10 lbs. to 60 lbs. per square inch. The illustrated blade  14  is a metal blade that is about 6 inches in length and about 0.25 inch in width providing about 1.5 square inches of contact surface with the belt. If the blade  14  were made of urethane rather than metal, it would have about a 1.00 inch width and 6 square inches of surface contact. 
     When the blades  14  are all substantially vertically aligned perpendicular to the belt surface  16 , it has been found that the scraper blades  14  work very well in both the forward or reverse travel directions of the conveyor belt. This is unlike many of the prior art constructions wherein the blades as well as the mounts were disposed at a considerable angle to the vertical. 
     By way of example only, the illustrated elastomeric body is a rectangular block of polyurethane, preferably a polyether urethane having a low compression set and good fatigue life. The preferred MD140 polyether urethane has a static compression set below 15%, such as about 13%, which is in contrast to the usual static compression sets of 20% to 40%. In the example given herein, about 40-50 lbs. of vertical force is applied constantly to the elastomeric body. If the elastomeric body had a compression set of 40%, the support would have to be adjusted much more frequently to maintain the desired pressure between the blade tip and the belt, as explained above, than would the preferred material having a static compression set of only 13%. The above-identified MD140 polyether urethane also has a good fatigue life and a hardness of about 86 on the A scale. 
     It will be appreciated that the conveyor belts are often run twenty-four (24) hours a day and seven (7) days a week at high speeds such as 650 ft./min. This results in quite frequent impacts by the belt fastener and/or other material on the belt against the scraper blade  14  causing vibrations in the elastomeric blade mont body  40 . The filler material  50  serves to dampen these vibrations and thereby increases the fatigue life for the elastomeric material. Likewise, the filler material is also being subjected to these vibrations. The elastomeric body and filler act as a cushion and to limit the amount of deflection and to decrease the frequency of the vibrations. The dampening by the filler material serves to reduce the hysteresis effect and heat buildup in the elastomeric body. 
     Another possible elastomeric material is a silicone rubber having a shore A durometer in the range of 90 to 95. Silicon rubber is able to deflect readily over a large temperature range of about −200° F. to about 500° F.; and hence, it will work well in hot climates as well as cold climates. Another alternative elastomeric material is black rubber, which may also be used for the elastomeric body  40 . The above-described, elastomeric materials for the body  40  behave like a rubber or a rubber-like material. The elastomeric material could be a rubber, a urethane or other plastic material that is sufficiently flexible and resilient to perform the functions for the mounting of scraper  12  to perform as described herein. 
     In the embodiment shown in FIG. 1, the elastomeric body includes a lower securing attachment or plate  60  of metal bonded or otherwise secured to the elastomeric body. To mount the blade  12  on the elastomeric body  40 , a blade attachment may be molded, in situ, in the upper end of the elastomeric body, as best seen in FIGS. 5-7. More specifically, a pair of angle-shaped plates  61  and  62  is molded, in situ, within the elastomeric block  40  at the upper end of the body to provide the blade attachment device. A slot  65  (FIG. 6) is defined between the steel plates  61  and  62  to receive a scraper blade  12   a  (FIG. 7) therein. A bolt  25  extends through apertures  63  in the elastomeric body  40  in the upstanding webs of the metal angles  61  and  62  and through a hole in the blade disposed in the slot  65  with a nut threaded on the bolt to secure the blade to the elastomeric body. In another embodiment for the blade attachment, as shown in FIG. 8, a T-shaped, blade holder  68  has a lower, horizontal web  69  which is integrally molded, in situ, within the elastomeric body  40 . A nut  26  and bolt  25  secure two blades, viz, a blade  76  and a blade  78  to an upstanding flange  71  of the T-shaped bracket. 
     Referring now to FIGS. 5-7, the lower securing attachment includes the plate  60  and a pair of bolts  79  with heads  80  of the bolts molded, in situ, in the elastomeric body  40  with threaded shanks  81  of the bolts extending down below the elastomeric body. Nuts  82  (FIG. 7) are threaded on the bolt shanks  81  to secure the blade mount and blade to the support  64 . 
     The illustrated block body  40  has a height of about 4.13 inches and a thickness of about 1.65 inches. The illustrated block body extends about 6-8 inches in length. As shown in FIG. 2, while the opening  41  in the block body  40  may have various shapes and forms from that illustrated, the preferred shape is generally described as a I-shaped, which has a central portion of about ¾ inch between interior wall surfaces  63  and  64 , which define the vertical sides of the opening  41 . The illustrated height of the opening  41  is about 2.5 inches in height. The half of a cylindrically-shaped openings  52 , which define the four flexure points  54 , are about ¼ inch in radius defining a height of about ½ inch and a lateral extent of about a ¼ inch. The openings  52  and the vertical walls  63  and  64  are joined at curved areas  71  to eliminate sharp corners, where stresses could concentrate and cause a cracking of the elastomeric body and/or filler material therein. Manifestly, the particular dimensions or shapes of the openings and of the block bodies themselves, which need not be rectangular, may be varied substantially and still fall within the purview of the present invention. 
     The blade  12   c  disclosed in FIG. 8 is a double scraper blade  12   c  having a pair of opposed metal blades  76  and  78 , each with a tungsten carbide insert plate  76   a  and  78   a . The tungsten carbide inserts are very hard, wear-resistant plates which are seated in pockets in the metal blades  76  and  78 . The blades  76  and  78  are preferably about one inch in height and about six inches in length. It is thought that use of two-spaced blades  76  and  78  with a urethane spacer  79  therebetween may space the blades to straddle a depression in the middle of the metal belt fasteners thereby keeping a scraper blade edge from dipping into the depression. In the FIG. 8 embodiment, a pair of metal blades of tool steel or the like are secured to an upstanding, T-shaped blade holder  78  having a lower horizontal web  69  and upstanding flange  71  of the blade holder by a nut  26  and bolt  25 . A spacer block  79  of urethane, rubber or other elastomeric material may be secured by the nut  26  and bolt  25  to the blade holder. 
     The illustrated and described foamed, dampening material  50  is foamed within the opening  41  to completely fill the opening including the enlarged openings  52  at the four corners. However, a separate, preformed foamed sheet, which only substantially fills the body and does not fill all of the openings  52 , could be used. The preformed foam strip should keep out ice and dirt or other materials that could interfere with the bending of the elastomeric body. It has been found preferable that the foam body foamed in the opening  41  serves best to perform the dampening functions to reduce the amplitude and/or frequency of the vibrations of the scraper blade. 
     Turning now to FIG. 4, the illustrated clamp block  34  is adjusted vertically by the adjustment device  36 . The preferred and illustrated adjustment device  36  comprises a lower angle  90  which is secured by the rut and bolt fastener  92  to the parallel leg brace  32  on opposite sides of the conveyor belt. A horizontal leg  93  of the angle  90  is threaded and the adjustment device includes a pair of adjustment screws  94  at opposite sides of the conveyor belt which can be turned within the threaded leg  93  of the angle to push against a lower side  95  of a slide block  34 . The slide block  34  is slidably mounted on a leg  32  for vertical movement. 
     The slide blocks  34  are guided for vertical sliding along a vertical side  32   a  of the frame rail  32  by pairs of threaded screws  97  having the threaded shanks  99  extending through a vertical, central slot  100  (FIG. 3) in the upstanding frame rail  32 . When the screws  97  are loosened, the shanks of the screws slide in the slot  100  and guide the block  34  for travel vertically. The adjustment screws  94  are turned to push guide blocks  34  to raise the elastomeric body  40  and to push the scraper blade  12  tightly against the underside of the belt surface  16  with the desired force. Herein, the preferred blade pressure is in the range of about 10-60 lbs./inch 2  of blade surface, which, for a 6″ blade, and this is generated using a vertical force of 15-90 lbs. for the metal blade that is about 0.25 inch thick. 
     Herein, the blades are pushed vertically against the underside of the belt initially with a force higher than the 15-90 lbs. of force per blade; and this higher force is reduced when the conveyor belt  18  starts to travel and deflects the blade mount body  40  to about 20° or so, which is the normal scraping angle for the blade mount while the conveyor belt is traveling. 
     The illustrated support assembly  30  has the illustrated guide blocks  34  and includes a central cylindrical member or pipe  105 , which extends transversely across the belt. As best seen in FIG. 1, the pipe  105  has welded thereto the angle iron  64  with the upper leg of the angle iron being abutted against the top of the pipe  105 ; and with the other vertical leg  63  of the angle iron  64  being welded to a vertical side of the pipe  105 . 
     The pipe  105  is releasably clamped to the sliding blocks  34  at its opposite ends where it is supported by the respective vertical frame rails  32 . In this instance, the pipe  105  is mounted within a circular opening  34   c  in the sliding blocks, and the sliding blocks are each provided with an upper, split portion  34   a  and a lower split portion  34   b  which have an opening or space  34   c  between their respective facing surfaces. The portions  34   a  and  34   b  may be moved and forced against one another to clamp the pipe  105  by a threaded bolt  110 , which has an upper head abutting the top surface of the portion  34   a  and a nut  111  abutting the bottom surface of the portion  34   b . By tightening the nut  111  on the bolt  110 , the portions  34   a  and  34   b  may be squeezed toward each other to clamp tightly about the pipe  105 . It will be appreciated that the pipe  105  can be turned or rotated within the opening so as to assure that the position of the scraper blade  14  is in the desired position, which in this instance, is perpendicular to the belt surface  16 . The adjustable guide blocks also allow removal of the cleaner from the conveyor for blade replacement. 
     Although the invention has been described with various preferred embodiments, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention which is defined in the appended claims.