Patent Publication Number: US-8983339-B2

Title: Developing cartridge with shaft and tubular member and image forming apparatus having the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119 from Korean Patent Application No. 10-2011-0123728, filed on Nov. 24, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present general inventive concept relates to a developing cartridge and an image forming apparatus having the developing cartridge, and more particularly, to a developing cartridge which includes a charging unit using a tubular member and an image forming apparatus which has the developing cartridge. 
     2. Description of the Related Art 
     An image forming apparatus such as a printer, facsimile, copier, multifunction peripheral (MFP) and the like forms a prescribed image in a print medium using electrophotography. In general, such an image forming apparatus consists of charging, exposure, development, transfer of a developed image, and fixing processes so as to form an image on a print medium. In the charging process, a charging unit charges a photoconductive body to a prescribed electric potential. In the exposure process, a laser scanning unit scans the photoconductive body charged to the prescribed electric potential with a laser so as to form an electrostatic latent image corresponding to printing data on the photoconductive body. In the development process, a developing unit develops a toner image by supplying toner to the photoconductive body on which the electrostatic latent image is formed. In the transfer process, a transfer unit transfers the toner image formed on the photoconductive body to the printing data. In the fixing process, a fixing unit fixes the toner transferred to the printing data, thereby forming a prescribed image in the print medium. Thereafter, the print medium is discharged outside the image forming apparatus and the printing is completed. 
     A charging unit may be generally divided by using a non-contact charging system or contact charging system. A charging unit according to the non-contact charging system uses corona discharge typically. The charging unit using the corona discharge has the advantage of charging a photoconductive body uniformly, but leads to producing discharge products such as ozone. Therefore, a separate unit is required to dispose of the discharge products such as ozone, etc., and this addition of a separate unit results in increasing a size of the image forming apparatus and costs for manufacturing the same. 
     A charging unit using the contact charging system may be divided by using a conductive roller, a conductive brush, a film-shaped charging electrode or a tube-shaped structure, etc. 
     A charging unit employing the conductive roller needs a support device for the roller and the like, and has a complex construction. An elastic roller must be in close contact with a charge acceptor so that a stable minute gap is formed to charge the charge acceptor uniformly, and hence, the hardness of rubber must be comparatively low. Such rubber contains a comparatively large amount of process oil. Such a charging unit has a problem of affecting image quality adversely due to contamination of a surface of the charge acceptor, caused by the process oil. Further, a rubber roller should be in a higher dimensional accuracy, and this leads to increasing the manufacturing costs. 
     A charging unit employing the conductive brush is advantageous in uniform contact, as compared with the elastic roller. However, the conductive brush is manufactured at a high manufacturing cost and is likely to form brush marks that cause irregular charging adversely affecting the image. 
     A charging unit employing the film-shaped charging electrode vibrates due to frictional electrification because a working edge of the film-shaped charging electrode is in contact with the charge acceptor, whereby the charging potential is liable to be caused to become unstable. Furthermore, if foreign matters, such as toner and additives, adhere to the working edge of the film-like charging electrode, creeping discharge occurs to cause defective stripes of charges. A method to solve such a problem applies both a DC voltage and an AC voltage simultaneously to the film-shaped charging electrode. However, the AC voltage generates vibrations resonant with the frequency of the AC voltage and generates charging noise. 
     A charging unit employing the cylindrical (tube-shaped) structure has problems such as a slip phenomenon of a tubular member occurring due to a frictional force produced between the tubular member and an elastic member, and also a bias occurring due to an axial force resulting from the pressure difference between left and right when being driven for rotation. 
     SUMMARY OF THE INVENTION 
     The present general inventive concept relates to a developing cartridge and an image forming apparatus having the same. 
     Additional features and utilities of the present general inventive concept will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the general inventive concept. 
     Embodiments of the general inventive concept include a developing cartridge having a photoconductive body, a charging unit which charges a surface of the photoconductive body, and a developing unit which forms a toner image by supplying toner to the surface of the photoconductive body according to an aspect of the present general inventive concept, the charging unit includes a shaft applying a charging voltage and having a central axis parallel to a rotating axis of the photoconductive body, a tubular member of conductive material surrounding the shaft, which is disposed to be in contact with the surface of the photoconductive body, a current carrying member which is disposed on an inner surface of the tubular member and applies an electric current to the shaft and the tubular member, and a damping member which is disposed between the shaft and the current carrying member, and the shaft may be characterized in that a middle portion is thicker than opposite side portions in a longitudinal direction along the central axis. 
     The shaft may be formed in a cylindrical shape and a diameter may increase with being close to the middle portion. 
     A protrusion of the middle portion of the shaft may be in the range of 0.14 mm-0.35 mm in a direction of the photoconductive body. 
     The shaft may consist of an injection molding. 
     The tubular member may consist of conductive nylon. 
     The current carrying member may have a surface resistance of less than 10 8 Ω. 
     The damping member may be an elastic member having elasticity. 
     The damping member may consist of a foam. 
     Embodiments of the general inventive concept may also include a developing cartridge usable in an image forming apparatus, the developing cartridge comprising: a tubular member; a shaft extending through the tubular member and to apply a charging voltage to be transferred to a photoconductive body in contact with the tubular member, the shaft including a protrusion at a middle portion thereof; a current carrying member disposed inside the tubular member and connected to the shaft to transfer the voltage of the shaft to the tubular member; and a damping member disposed between the shaft and the current carrying member such that the current carrying member contacts the tubular member at the area of the protrusion. 
     In an embodiment, the protrusion is formed by increasing a thickness of the shaft toward the middle portion thereof. 
     In an embodiment, the protrusion is formed by the shaft being convexly curved in a direction facing the photoconductive body. 
     In an embodiment, the protrusion is formed by a lower side of the middle portion of the shaft being thicker than opposite end portions thereof. 
     Embodiments of the general inventive concept may also include a developing cartridge usable in an image forming apparatus, the developing cartridge comprising: a tubular member; a shaft extending through the tubular member and to apply a charging voltage to be transferred to a photoconductive body in contact with the tubular member; a current carrying member disposed inside the tubular member and connected to the shaft to transfer the voltage of the shaft to the tubular member, the current carrying member being formed convexly such that a middle portion thereof is disposed more closely to the photoconductive body than opposite end portions thereof in a longitudinal direction parallel to a central axis of the shaft; and a damping member disposed between the shaft and the current carrying member. 
     Embodiments of the general inventive concept may also include a developing cartridge usable in an image forming apparatus, the developing cartridge comprising: a tubular member; a shaft extending through the tubular member and to apply a charging voltage to be transferred to a photoconductive body in contact with the tubular member; and a damping member connected to the shaft and extending in a longitudinal direction parallel with a central axis of the shaft, the damping member being formed convexly such that a middle portion thereof is disposed more closely to the photoconductive body than opposite end portions thereof. 
     In an embodiment, the shaft includes a protrusion at the middle portion thereof being in a range of about 0.14 mm-0.35 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other features and utilities of the present general inventive concept will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a schematic cross-sectional view of an image forming apparatus equipped with a developing cartridge according to an exemplary embodiment; 
         FIG. 2  is a schematic view of a charging unit according to the exemplary embodiment of  FIG. 1 ; 
         FIG. 3  is a schematic cross-sectional view of a charging unit according to the exemplary embodiment of  FIG. 1 ; 
         FIG. 4  is a schematic view of excitation between a charging tube and a current carrying member when a charging unit is equipped in an image forming apparatus; 
         FIG. 5  is a view of images having foggy defects of a tubular period when the excitation of  FIG. 4  occurs; 
         FIG. 6  is a schematic view of installation of a charging unit according to the exemplary embodiment of  FIG. 1 ; 
         FIG. 7  is a schematic cross-sectional view of a charging unit according to another exemplary embodiment; 
         FIG. 8  is a schematic view of installation of a charging unit according to the exemplary embodiment of  FIG. 7 ; 
         FIG. 9  is a schematic cross-sectional view of a charging unit according to yet another exemplary embodiment; 
         FIG. 10  is a schematic cross-sectional view of a charging unit according to still another exemplary embodiment; 
         FIG. 11  is a schematic cross-sectional view of a charging unit according to still another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the embodiments of the present general inventive concept, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present general inventive concept by referring to the figures. 
       FIG. 1  is a schematic cross-sectional view of an image forming apparatus equipped with a developing cartridge according to an exemplary embodiment. Such an image forming apparatus  1  may be various devices such as a printer, a facsimile, a copier, or a multifunction peripheral (MFP), which form a prescribed image on a print medium. Reference numeral  2  in  FIG. 1  indicates a progress path of the print medium. 
     A paper feeding unit  10  may store a print medium such as paper. The print medium is transferred along a progress path  2  by a plurality of progress rollers  11 . 
     A charging unit  100  may charge a surface of a photoconductive body  20  to a prescribed electric potential using a contact charging system. The charging unit  100  is described in detail below. 
     A laser scanning unit  30  may form an electrostatic latent image corresponding to the printing data on the surface of the photoconductive body  20  by scanning the surface of the photoconductive body  20  with a laser. 
     A developing unit  40  may form a toner image by providing toner to the surface of the photoconductive body  20  on which the electrostatic latent image is formed. The developing unit  40  may comprise a toner storage section  41 , a toner supply roller  42 , a developing roller  43 , and a restriction blade  44 . 
     The toner storage section  41  may store toner therein. The toner supply roller  42  supplies the developing roller  43  with the toner stored in the toner storage section  41 , and thus a toner layer is formed on the developing roller  43 . The restriction blade  44  makes the toner layer on the developing roller  43  uniform. The toner layer on the developing roller  43  moves onto the electrostatic latent image formed on the surface of the photoconductive body  20  as a result of the potential difference so as to form a toner image. 
     A transfer unit  50  may transfer the toner image formed on the surface of the photoconductive body  20  to the print medium. 
     A cleaning unit  60  may remove residual toner from the surface of the photoconductive body  20  after the transfer process. 
     A fixing unit  70  may fix the toner image transferred to the print medium. The print medium to which the toner image is fixed is discharged outside the image forming apparatus  1  by a plurality of progress rollers  11 . 
     A developing cartridge  80  may integrally comprise components such as the charging unit  100 , the photoconductive body  20  and the developing unit  40 . After the image forming apparatus  1  is used for a certain period of time, a user may remove a developing cartridge  80  and install a new developing cartridge in the image forming apparatus  1 . According to the present exemplary embodiment, there is the toner storage section  41  in the developing cartridge  80 , while according to other exemplary embodiments, there may not be the toner storage section  41  in the developing cartridge  80 . In other words, in an alternative, there may be a separate toner cartridge which stores toner and the separate toner cartridge may couple to the developing cartridge  80 . In this case, the user may replace the toner cartridge and the developing cartridge  80  separately and individually. 
     Referring to  FIGS. 2 to 6 , the charging unit  100  of the developing cartridge  80  according to the present exemplary embodiment is described in great detail.  FIG. 2  is a schematic view of the charging unit  100  according to the present exemplary embodiment,  FIG. 3  is a schematic cross-sectional view of the charging unit  100  according to the present exemplary embodiment,  FIG. 4  is a schematic view of excitation between a charging tube and a current carrying member when a charging unit is equipped in an image forming apparatus,  FIG. 5  is a view of images having foggy defects of a tubular period when occurring the excitation of  FIG. 4 , and  FIG. 6  is a schematic view of installation of the charging unit  100  according to the present exemplary embodiment. 
     The charging unit  100  comprises a shaft  110  applying a charging voltage so as to charge the surface of the photoconductive body  20  from an external power supply (not shown), a tubular member  120  surrounding the shaft  110 , which is disposed to be in contact with the surface of the photoconductive body  20 , a current carrying member  130  which is disposed on an inner surface of the tubular member  120 , and a damping member  140  which is disposed between the shaft  110  and the current carrying member  130 . 
     The shaft  110  has a central axis parallel to a rotating axis of the photoconductive body  20  and is formed in a cylindrical shape. The shaft  110  may have a size of φ6*252 mm. The shaft  110  may consist of an injection molding and be formed of a conductive metal material, and for example may be formed of 40% PET and glass fiber (G/F). The shaft  110  may be formed to have a diameter which increases while becoming closer to a middle portion  112 , and thus the middle portion  112  is thicker than opposite side portions  114  in a longitudinal direction along the central axis. A protrusion A of the middle portion of the shaft  110  may be in the range of 0.14 mm-0.35 mm in a direction of the photoconductive body  20 . 
     Below is a table showing the image output results according to the protrusion (thickness) by making 3D measurements of the middle portion  112  and the opposite side portions  114  of the shaft  110 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Protrusion of the middle 
                   
               
               
                   
                 portion in the direction of the 
               
               
                   
                 photoconductive body (mm) 
                 Image output 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Shaft 1 
                 0.0076 
                 Images having foggy defects 
               
               
                   
                   
                 of a tubular period 
               
               
                 Shaft 2 
                 0.1358 
                 Satisfactory 
               
               
                 Shaft 3 
                 0.2010 
                 Satisfactory 
               
               
                 Shaft 4 
                 0.3478 
                 Satisfactory 
               
               
                   
               
            
           
         
       
     
     As shown in the above table, if the protrusion of the middle portion of the shaft  110  is formed in the range as described above, no foggy defect is formed in portions of images at the time of the tubular period. 
     The tubular member  120  has a hollow shape, which has a hollow interior. The tubular member  120  may have a size of φ8.5*241 mm. The tubular member  120  may be formed of nylon and conductive additives such as carbon black, an ionic conductor and the like. As the photoconductive body  20  rotates, the tubular member  120  also rotates by a frictional force produced between the tubular member  120  and the photoconductive body  20 . 
     The current carrying member  130  is connected to the shaft  110  and is in contact with the inner surface of the tubular member  120 . The current carrying member  130  may be formed in a shape of a thin film. The current carrying member  130  may have a size of 1.1t*6 mm*226 mm. The current carrying member  130  is preferable to have a surface resistance of 10 8 Ω. The current carrying member  130  may be formed of flexible and conductive materials, and conductive UHMW-PE may be employed. A length of the current carrying member  130  is formed to be longer than that of the damping member  140  so that the damping member  140  may not be in direct contact with the inner surface of the tubular member  120 . The charging voltage applied to the shaft  110  may be transferred to the tubular member  120  through the current carrying member  130 . 
     The damping member  140  applies pressure to the tubular member  120  and the current carrying member  130  towards the photoconductive body  20 . It is possible for the photoconductive body  20  and the tubular member  120  to be in stable contact with each other with the aid of the damping member  140 . To this end, the damping member  140  may be formed of an elastic member which has elasticity as foam, and may be, for example, formed of a sponge with #711G of BOW employed therein. 
     The materials and shapes of the shaft  110 , the tubular member  120 , the current carrying member  130  and the damping member  140  as described above are simply exemplified, and it should be understood that the above materials and shapes may be variable. 
     The charging voltage applied to the shaft  110  is transferred to the tubular member  120  through the current carrying member  130 , and thus a discharge is produced in a wedge-shaped minute gap between an outer surface of the tubular member  120  and the photoconductive body  20 . The photoconductive body  20  is a non-conductor of electricity, but due to such a discharge, a surface potential may be formed on the surface of the photoconductive body  20 . The charging voltage applied to the shaft  110  may be an AC voltage, a DC voltage or a mixture of the AC voltage and the DC voltage. Such a charging voltage can be easily understood by those skilled in the art, and thus a detailed explanation is omitted. 
     By the above described discharge, the charging unit  100  may generate noise, and in particular if the charging voltage is applied in the form of the AC voltage, the noise can be loud. In order to reduce such noise, the charging unit  100  of the developing cartridge  80  according to the present exemplary embodiment does not use a charging roller but the hollow tubular member  120 . This is because the tubular member  120  is more flexible than the charging roller, and therefore the noise generated by the discharge can be reduced. 
     Further, since a part of low molecular weight materials which constitute the charging roller spreads to a photoconductive body, a charging unit using the charging roller may contaminate the photoconductive body. The contaminated photoconductive body causes deterioration in image quality. The spread accelerates further as a contact force increases between the charging roller and the photoconductive body. The charging unit  100  according to the present exemplary embodiment uses the hollow tubular member  120 , not the charging roller, and thus the mass of the tubular member  120  is considerably less than that of the charging roller. Accordingly, the contact force decreases between the photoconductive body  20  and the tubular member  120 , and this can prevent the spread of low molecular weight materials. 
     Hereinafter, it is described how the charging unit  100  of the developing cartridge  80  according to the present exemplary embodiment is equipped in an image forming apparatus. 
     As illustrated in  FIGS. 4 and 5 , when a charging unit is installed in an image forming apparatus, pressure is applied to opposite end portions of the charging unit in an arrow direction to provide a charge contact with a photoconductive body. If the pressure is applied to the opposite end portions, as illustrated in  FIG. 4 , the opposite end portions of the charging unit plays a role as a fulcrum of a lever, and thus a middle portion of the charging unit is bent toward an upper side. Due to such a curve, an excitation occurs in portions between a charging unit and a photoconductive body, and this leads to an unstable contact. As illustrated in  FIG. 5 , the excitation occurring between the charging unit and the photoconductive body results in foggy defects formed in portions of an image at the time of a tubular period. 
     As illustrated in  FIG. 6 , since a thickness of the middle portion  112  of the shaft  110  is greater than that of the opposite end portions  114 , the middle portion  112  of the charging unit  100  according to the present exemplary embodiment is not excited from the photoconductive body  20  even though the opposite end portions are pressed by the pressure (in an arrow direction) applied to the opposite end portions of the charging unit  100  when the charging unit  100  is installed. Since the pressure is applied continuously to the opposite end portions of the charging unit  100  in the direction illustrated by arrows for charge contact with the photoconductive body  20 , the opposite end portions are also not excited from the photoconductive body  20 . Therefore, the charging unit  100  is in a uniform contact with the photoconductive body  20 , and thus a uniform image can be obtained without faulty images. 
     Hereinafter, a charging unit according to another exemplary embodiment is described as follows: 
       FIG. 7  is a schematic cross-sectional view of a charging unit according to another exemplary embodiment and  FIG. 8  is a schematic view of installation of the charging unit according to the exemplary embodiment of  FIG. 7 . 
     The charging unit  200  according to the present exemplary embodiment is similar to the charging unit  100  according to the previously described exemplary embodiment. For example, a tubular member  220 , a current carrying member  230  and a damping member  240  of the charging unit  200  are identical to those of the above described charging unit  100 . Therefore, the components of the charging unit  200  are not explained again. 
     As illustrated in  FIG. 7 , a shaft  210  is formed windingly so that a middle portion  212  is disposed more closely to the photoconductive body  20  than opposite end portions  214  in a longitudinal direction along a central axis of the photoconductive body  20 . In other words, the shaft  210  is formed to be convexly curved in a direction of facing the photoconductive body  20 . 
     A protrusion (A) of the middle portion  212  of the shaft  210  is preferable to be in the range of 0.14 mm-0.35 mm in a direction of the photoconductive body  20  as described in the above exemplary embodiment. 
     Hereinafter, an installation of the charging unit  200  according to the present exemplary embodiment is described as follows: As illustrated in  FIG. 8 , if the charging unit  200  is installed in an image forming apparatus, as described in the previous exemplary embodiment, pressure is applied to opposite end portions of the charging unit  200  in a direction of arrows. By the pressure applied to the opposite end portions, the opposite end portions  214  are pressed toward the direction of the photoconductive body  20 , and thus the curve of the shaft  210  is straightened and a uniform contact is secured between the charging unit  200  and the photoconductive body  20 . Therefore, as described in the previous exemplary embodiment, due to the uniform contact with the photoconductive body  20 , the charging unit  200  can provide uniform images without fogging or other problems. 
     Hereinafter, a charging unit according to yet exemplary embodiment is described as follows: 
       FIG. 9  is a schematic cross-sectional view of a charging unit according to another exemplary embodiment. 
     The charging unit  300  according to the exemplary embodiment of  FIG. 9  is similar to the charging unit  100  according to the previously described exemplary embodiment. For example, a tubular member  320 , a current carrying member  330  and a damping member  340  of the charging unit  300  are identical to those of the above described charging unit  200 . Therefore, the components of the charging unit  300  will not be repeated again below in order to ensure brevity and conciseness of this application. 
     As illustrated in  FIG. 9 , a lower side of a middle portion  312  of a shaft  310 , which is close to the photoconductive body  20 , is formed to be thicker than opposite end portions  314 , and a protrusion (A) of the middle portion  312  of the shaft  310  is preferable to be in the range of 0.14 mm-0.35 mm in a direction of the photoconductive body  20  as described in the above exemplary embodiment. Herein, an upper side of the middle portion  312  is formed evenly and collinearly with respect to the opposite end portions  314 . In case that the charging unit  300  is installed in an image forming apparatus to provide a contact charge, as described in the above exemplary embodiment, since pressure is applied to opposite end portions in a direction of facing a photoconductive body, no inconvenience is caused in making a uniform contact between the charging unit  300  and the photoconductive body  20  although the upper side of the shaft  310  is not formed convexly. Since a thickness of the middle portion  312  is not necessarily greater than the opposite end portions  314  in the upper side of the shaft  310  of the charging unit  300  according to the exemplary embodiment, manufacturing efficiency of the shaft  310  increases. 
     Hereinafter, a charging unit according to yet another exemplary embodiment is described as follows: 
       FIG. 10  is a schematic cross-sectional view of a charging unit according to another exemplary embodiment. 
     The charging unit  400  according to this exemplary embodiment is similar to the charging unit  100  according to the above described previous exemplary embodiment. For example, a tubular member  420  and a damping member  440  of the charging unit  400  are the same as those of the above described charging unit  100 . Therefore, the components of the charging unit  400  will not be repeated again below in order to ensure brevity and conciseness of this application. 
     Upper and lower sides of a middle portion  412  and opposite end portions  414  are formed evenly and collinearly with respect to one another in a shaft  410 . 
     A current carrying member  430  is formed convexly so that a middle portion  432  may be disposed more closely to a photoconductive body than opposite end portions  434  in a longitudinal direction parallel to a central axis of the shaft  410 . 
     A protrusion (A) of the middle portion  432  of the current carrying member  430  is preferable to be in the range of 0.14 mm-0.35 mm in a direction of the photoconductive body  20  in the same manner of the middle portion of the shaft as described in the above exemplary embodiment. Therefore, the charging unit  400  according to this exemplary embodiment can achieve the same effect as the charging unit in which the middle portion of the above described shaft is thick without forming the shaft  410  to be convex. 
     Hereinafter, a charging unit according to still another exemplary embodiment is described as follows: 
       FIG. 11  is a schematic cross-sectional view of a charging unit according to still another exemplary embodiment. 
     The charging unit  500  according to the exemplary embodiment of  FIG. 11  is similar to the charging unit  100  according to the above described exemplary embodiment. For example, a tubular member  520  and a current carrying member  530  of the charging unit  500  are identical to those of the above described charging unit  100 . Therefore, the components of the charging unit  500  will not be repeated again below in order to ensure brevity and conciseness of this application. 
     Upper and lower sides of a middle portion  512  and opposite end portions  514  are formed evenly and collinearly with respect to one another in a shaft  510 . 
     A damping member  540  is formed convexly so that a middle portion  542  may be disposed more closely to the photoconductive body  20  than opposite end portions  544  in a longitudinal direction parallel to a central axis of the shaft  510 . 
     A protrusion (A) of the middle portion  542  of the damping member  540  is preferable to be in the range of 0.14 mm-0.35 mm in a direction of the photoconductive body  20  in the same manner of the middle portion of the shaft as described in the previous exemplary embodiment. Therefore, the charging unit  500  according to the exemplary embodiment can achieve the same effect as the charging unit in which the middle portion of the above described shaft is thick without forming the shaft  510  to be convex. 
     Although a few embodiments of the present general inventive concept have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the general inventive concept, the scope of which is defined in the appended claims and their equivalents.