Patent Publication Number: US-6219504-B1

Title: Process cartridge and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process cartridge, and an electrophotographic image forming apparatus capable of detachably mounting the process cartridge. 
     The electrophographic image forming apparatus forms an image on a recording medium electrophotographic image forming process, and comprises, for example, an electrophotographic copier, an electrophotographic printer (such as an LED (light-emitting diode) printer, a laser-beam printer or the like), an electrophotographic facsimile apparatus, or an electrophographic word processor. 
     The process cartridge includes developing means or cleaning means, and charging means and an electrophotographic photosensitive member, which are integrated to form the cartridge so as to be detachably mountable in the main body of the electrophotographic image forming apparatus, or includes at least one of developing means and cleaning means, and charging means and an electrophotographic photosensitive member which are integrated to form the cartridge so as to be detachably mountable in the main body of the electrophotographic image forming apparatus, or includes at least charging means and an electrophotographic photosensitive member which are integrated to form the cartridge so as to be detachably moutable in the main body of the electrophotographic image forming apparatus. 
     2. Description of the Related Art 
     In conventional electrophotographic image forming apparatuses for forming an image on a recording medium using an electrophotographic image forming process, a process cartridge method is adopted in which an electrophotographic photosensitive member and process means operating thereon are integrated to form a process cartridge so as to be detachably mountable in the main body of the image forming apparatus. According to this process cartridge method, maintenance of the apparatus can be performed by the user himself without calling a serviceman, resulting in great improvement in the operability of the apparatus. Hence, the process cartridge method is widely being used in image forming apparatuses. 
     The process cartridge includes a cleaning unit provided by integrating charging means, cleaning means and a photosensitive drum, and a developing unit provided by integrating developing means and toner to be supplied thereto. The cleaning unit and the developing unit are connected by a connecting member in order to constitute the process cartridge. 
     The developing unit also includes a toner frame for accommodating the toner to be supplied to the developing means, and a developing frame for supporting the developing means. The toner frame and the developing frame are integrally fixed according to ultrasonic welding or the like. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a process cartridge and an electrophotographic image forming apparatus which prevents deformation of a frame and the adverse influence on toner and respective process means due to heat by discharging heat accumulated at a surrounding portion of an electrophotographic photosensitive member and within the process cartridge. 
     According to one aspect of the present invention, a process cartridge detachably mountable in a main body of an image forming apparatus includes an electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, frames for supporting the electrophotographic photosensitive member and the charging means, first holes for taking in air, provided at one end portion of the frames in the longitudinal direction and opened at a portion near one end portion of the charging means in the longitudinal direction, and second holes for discharging air, provided at another end portion of the frames in the longitudinal direction and opened at a portion near another end portion of the charging means in the longitudinal direction. 
     According to another aspect of the present invention, a process cartridge detachably mountable in a main body of an image forming apparatus includes an electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, frames for supporting the electrophotographic photosensitive member and the charging means, first holes for taking in air, provided at one end portion of the frames in the longitudinal direction so as to cross the longitudinal direction of the charging means, and second holes for discharging air, provided at another end portion of the frames in the longitudinal direction so as to be parallel to the longitudinal direction of the charging means. 
     According to still another aspect of the present invention, a process cartridge detachably mountable in a main body of an image forming apparatus includes an electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, developing means for developing a latent image formed on the electrophotographic photosensitive member using toner, a cartridge frame obtained by disposing the charging means in a space between a frame for supporting the electrophotographic photosensitive member and the charging means and a frame for supporting the developing means, and connecting the two frames, first holes for taking in air into the space, provided at one end portion of the cartridge frame in the longitudinal direction, and second holes for discharging air from the space, provided at another end portion of the cartridge frame in the longitudinal direction. 
     According to yet another aspect of the present invention, an electrophotographic image forming apparatus, capable of detachably mounting a process cartridge, for forming an image on a recording medium includes (a) a process cartridge including an electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, frames for supporting the electrophotographic photosensitive member and the charging means, first holes for taking in air, provided at one end portion of the frames in the longitudinal direction and opened at a portion near one end portion of the charging means in the longitudinal direction, and second holes for discharging air, provided at another end portion of the frames in the longitudinal direction and opened at a portion near another end portion of the charging means in the longitudinal direction, (b) mounting means for detachably mounting the process cartridge, (c) intake holes, communicating with the first holes, provided at an outer frame of a main body of the image forming apparatus facing the first holes of the process cartridge, in a state in which the process cartridge is mounted in the main body of the image forming apparatus, (d) discharge means for discharging air within the main body of the image forming apparatus communicating with the second holes of the process cartridge to the outside of the apparatus, in a state in which the process cartridge is mounted in the main body of the image forming apparatus, and (e) conveyance means for conveying the recording medium. 
     According to yet a further aspect of the present invention, an electrophotographic image forming apparatus, capable of detachably mounting a process cartridge, for forming an image on a recording medium includes (a) a process cartridge including an electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, frames for supporting the electrophotographic photosensitive member and the charging means, first holes for taking in air, provided at one end portion of the frames in the longitudinal direction so as to cross the longitudinal direction of the charging means, and second holes for discharging air, provided at another end portion of the frames in the longitudinal direction so as to be parallel to the longitudinal direction of the charging means, (b) mounting means for detachably mounting the process cartridge, (c) intake holes, communicating with the first holes, provided at an outer frame of a main body of the image forming apparatus facing the first holes of the process cartridge, in a state in which the process cartridge is mounted in the main body of the image forming apparatus, (d) discharge means for discharging air within the main body of the image forming apparatus communicating with the second holes of the process cartridge to the outside of the apparatus, in a state in which the process cartridge is mounted in the main body of the image forming apparatus, and (e) conveyance means for conveying the recording medium. 
     According to still another aspect of the present invention, an electrophotographic image forming apparatus, capable of detachably mounting a process cartridge, for forming an image on a recording medium includes (a) a process cartridge including an electrophotographic photosensitive member, charging means for charging the electrophotographic photosensitive member, developing means for developing a latent image formed on the electrophotographic photosensitive member using toner, a cartridge frame obtained by disposing the charging means in a space between a frame for supporting the electrophotographic photosensitive member and the charging means and a frame for supporting the developing means, and connecting the two frames, first holes for taking in air into the space, provided at one end portion of the cartridge frame in the longitudinal direction, and second holes for discharging air from the space, provided at another end portion of the cartridge frame in the longitudinal direction, (b) intake holes, communicating with the first holes, provided at an outer frame of a main body of the image forming apparatus facing the first holes of the process cartridge, in a state in which the process cartridge is mounted in the main body of the image forming apparatus, (c) discharge means for discharging air within the main body of the image forming apparatus communicating with the second holes of the process cartridge to the outside of the apparatus, in a state in which the process cartridge is mounted in the main body of the image forming apparatus, and (d) conveyance means for conveying the recording medium. 
     The foregoing and other objects, advantages and features of the present invention will become more apparent from the following detailed description of the preferred embodiment taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side cross-sectional view illustrating an electrophotographic image forming apparatus according to an embodiment of the present invention; 
     FIG. 2 is a perspective view illustrating an external appearance of the apparatus shown in FIG. 1; 
     FIG. 3 is a side cross-sectional view illustrating a process cartridge shown in FIG. 1; 
     FIG. 4 is a schematic perspective view illustrating an external appearance of the process cartridge shown in FIG. 3; 
     FIG. 5 is a left side view of the process cartridge shown in FIG. 3; 
     FIG. 6 is a front view of the process cartridge shown in FIG. 3; 
     FIG. 7 is a horizontal cross-sectional view of the electrophotographic image forming apparatus shown in FIG. 1; 
     FIG. 8 is a diagram illustrating the positional relationship between left-side holes in the process cartridge shown in FIG.  3  and holes in the image forming apparatus; and 
     FIG. 9 is a diagram illustrating a manner in which air flows from within the process cartridge shown in FIG. 3 via a fan of the image forming apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will now be described with reference to the drawings. In the following description, the lateral direction of a process cartridge B indicates a direction of mounting/detaching the process cartridge B with respect a main body  14  of an apparatus, and coincides with the direction of conveying a recording medium. The longitudinal direction of the process cartridge B indicates a direction crossing (substantially orthogonal to) the direction of mounting/detaching the process cartridge B with respect to the main body  14  of the apparatus, and is crossing (substantially orthogonal to) the direction of conveying a recording medium. 
     FIG. 1 is a diagram illustrating the configuration of an electrophotographic image forming apparatus (laser-beam printer) A according to the preferred embodiment. FIG. 2 is a perspective view illustrating an external appearance of the apparatus. FIGS. 3-7 are diagrams relating to the process cartridge B shown in FIG. 1; FIG. 3 is a side cross-sectional view of the process cartridge B; FIG. 4 is a schematic perspective view illustrating an external appearance of the process cartridge B; FIG. 5 is a right side view of the process cartridge B; FIG. 6 is a diagram illustrating the process cartridge B as seen from the front side; and FIG. 7 is a diagram schematically illustrating the flow of air in a state in which the process cartridge B is mounted in the main body  14  of the apparatus. 
     In the following description, the upper and lower surfaces of the process cartridge B indicate surfaces which are placed upward and downward, respectively, in a state in which the process cartridge B is mounted in the main body  14  of the apparatus. 
     Electrophotographic image forming apparatus A and process cartridge B 
     First, a description will be provided of the laser-beam printer A, serving as the electrophotographic image forming apparatus accoding to the preferred embodiment, with reference to FIGS. 1 and 2. FIG. 3 is a side cross-sectional view of the process cartridge B. 
     As shown in FIG. 1, the laser-beam printer A forms an image on a recording medium (such as recording paper, an OHP (overhead projector) sheet, a cloth or the like) according to an electrophotographic image forming process. A toner image is formed on a drum-shaped electrophotographic photosensitive member (hereinafter termed a “photosensitive drum”). More specifically, the photosensitive drum is charged by charging means, and then a latent image corresponding to image information is formed by projecting a laser beam corresponding to the image information onto the photosensitive drum from optical means. A toner image is formed by developing the latent image by developing means. In synchronization with the formation of the toner image, a recording medium  2  set within a sheet feeding cassette  3   a  is subjected to reversal conveyance by a pickup roller  3   b , pairs of conveying rollers  3   c  and  3   d , and a pair of registration rollers  3   e . Then, the toner image formed on the photosensitive drum incorporated ion the process cartridge B is transferred onto the recording medium  2  by applying a voltage to a transfer roller  4 , serving as transfer means. Then, the recording medium  2  having the toner image transferred thereto is conveyed to fixing means  5  by a conveying guide  3   f . The fixing means  5  includes a driving roller  5   c , and a fixing roller  5   b  incorporating a heater  5   a , and fixes the transferred toner image by applying heat and pressure to the recording medium  2 . The recording medium  2  is then conveyed by pairs of discharging rollers  3   g ,  3   h  and  3   i , and is discharged onto a discharging tray  6  via a reversal path  3   j . The discharging tray  6  is provided at an upper surface portion of the main body  14  of the image forming apparatus A. It is also possible to discharge the recording medium  2  by a pair of discharging rollers  3   m  by operating a swingable flapper  3   k , without passing through the reversal path  3   j . In the embodiment, the pickup roller  3   b , the pairs of conveying rollers  3   c  and  3   d , the pair of registration rollers  3   e , the conveying guide  3   f , the pairs of discharging rollers  3   g ,  3   h  and  3   i , and the pair of discharging rollers  3   m  constitute conveying means  3 . 
     As shown in FIGS. 3-7, in the process cartridge B, a photosensitive drum  7  having a photosensitive layer (not shown) is rotated, and the surface of the photosensitive drum  7  is uniformly charged by applying a voltage to a charging roller  8 , serving as charging means. Then, a laser beam corresponding to image information from an optical system  1  is projected onto the photosensitive drum  7  via an exposure aperture  1   e , to form a latent image. The latent image is developed by developing means  9  using toner. Namely, the charging roller  8  is provided in a state of contact with the photosensitive drum  7 , and charges the photosensitive drum  7 . The charging roller  8  is rotated by being driven by the photosensitive drum  7 . The developing means  9  supplies a region to be developed of the photosensitive drum  7  with toner, and develops the latent image formed on the photosensitive drum  7 . The optical system  1  includes a laser diode  1   a , a polygonal mirror  1   b , a lens  1   c  and a reflecting mirror  1   d.    
     The developing means  9  feeds toner within a toner receptable  11 A to a developing roller  9   c  by rotation of a toner feeding member  9   b . The developing roller  9   c  incorporating a fixed magnet  9   g  is rotated, a toner layer having triboelectrified charges is formed on the surface of the developing roller  9   c  by a developing blade  9   d , and the toner is supplied to the region to be developed of the photosensitive drum  7 . By transferring the toner onto the photosensitive drum  7  in accordance with the latent image, a visualized toner image is formed. The developing blade  9   d  regulates the amount of toner on the circumferential surface of the developing roller  9   c . Toner stirring members  9   e  and  9   f  for circulating the toner within a developing chamber are rotatably mounted near the developing roller  9   c.    
     After transferring the toner image formed on the photosensitive drum  7  onto the recording medium  2  by applying a voltage whose polarity is opposite to that of the toner image, toner particles remaining on the photosensitive drum  7  are removed by cleaning means. The cleaning means  10  scrapes off toner particles remaining on the photosensitive drum  7  by means of an elastic cleaning blade  10   a  provided so as to contact the photosensitive drum  7 , and collects the toner particles in a used-toner reservoir  10   b.    
     The process cartridge B includes a toner frame  11  including the toner receptable (toner accommodating unit)  11 A for accommodating toner, and a developing frame  12  for holding the developing means  9 , including the developing roller  9   c  and the like, which are connected to each other. The process cartridge B is obtained by also connecting a cleaning frame  13 , in which the photosensitive drum  7 , the cleaning means  10  including the cleaning blade  10   a  and the like, and the charging roller  8  are mounted, to the combined block of the toner frame  11  and the developing frame  12 . The process cartridge B is detachably mountable in the main body  14  of the apparatus by the operator. 
     An exposure aperture le for projecting light corresponding to image information onto the photosensitive drum  7 , and a transfer aperture  13   n  for causing the photosensitive drum  7  to face the recording medium  2  are provided in the process cartridge B. More specifically, the exposure aperture le is provided on the cleaning frame  13 , and the transfer aperture  13   n  is provided between the developing frame  12  and the cleaning frame  13 . 
     Next, a description will be provided of the configuration of the housing of the process cartridge B of the embodiment. 
     The process cartridge B of the embodiment is in the form of a cartridge whose housing obtained by connecting the toner frame  11  and the developing frame  12  to each other and rotatably connecting the cleaning frame  13  to the combined block of the toner frame  11  and the developing frame  12  incorporates the photosensitive drum  7 , the charging roller  8 , the developing means  9 , the cleaning means  10  and the like. The process cartridge B is detachably mounted in cartridge mounting means provided in the main body  14  of the apparatus. 
     Configuration of the housing of the process cartridge B 
     As described above, the process cartridge B of the embodiment has the housing obtained by connecting the toner frame  11 , the developing frame  12  and the cleaning frame  13 . The configuration of the housing will now be described. 
     As shown in FIG. 3, the toner feeding member  9   b  is rotatably mounted on the toner frame  11 . The developing roller  9   c  and the developing blade  9   d  are mounted on the developing frame  12 , and the stirring members  9   e  and  9   f  for circulating toner within the developing chamber are rotatably mounted near the developing roller  9   c . An antenna bar  9   h  is mounted substantially in parallel with the developing frame  9   c  so as to face the developing roller  9   c  in the longitudinal direction. A developing unit D, serving as an integrated second frame, is provided by welding the toner frame  11  and the developing frame  12  to each other (according to ultrasonic welding in the embodiment). 
     A main frame  13   b  and a lid  13   a  of the cleaning frame  13  are welded to each other, to provide a receptacle, serving as the used-toner reservoir  10   b . The photosensitive drum  7  is rotatably supported on portions protruded from both sides of the main frame  13   b  in the longitudinal direction toward the developing means  9 . A hanging wall  21  is provided on the main frame  13   b  toward the photosensitive drum  7 . A cleaning plate  10   c  is fixed on the hanging wall  21 . An elastic cleaning blade  10   a  fixed on the cleaning plate  10   c  is in presssure contact with the photosensitive drum  7 . A scooping sheet fixed on the main frame  13   b  contacts the photosensitive drum  7  at a position below the elastic cleaning blade  10   a , so that the used-toner reservoir  10   b  of the cleaning frame  13  is sealed tightly. Namely, the front side, facing the developing means  9 , of the used-toner reservoir  10   b  of the cleaning frame  13 , is opened. 
     A frame wall  12   a  having a rib is provided at a portion of the developing frame  12  facing the cleaning frame  13 , and a plate  9   d   1 , on which the developing blade  9   d  is fixed, is fixed on the frame wall  12   a.    
     Arm portions  19  provided at both sides of the developing frame  12  in the longitudinal direction protrude in recesses provided at both sides of the cleaning frame  13  in the longitudinal direction. The developing frame  12  is rotatably connected to the cleaning frame  13  by means of a connection pin  20  threaded through the arm portions  19 . Alternatively, projections protruding in the longitudinal direction may be provided at the respective distal ends of the arm portions, and connection members (not shown) may be provided so as to grasp the projections. Compression springs  22   a  are inserted between the roots of the respective arm portions  19  and the main frame  13   b , in order to provide a moment to press the photosensitive drum  7  and the developing roller  9   c  around the connection pin  20 . 
     According to the above-described configuration, a cylindrical space S which is long in the longitudinal direction and has a cross section surrounded by an upper wall  13   b   1  of the main frame  13   b , the hanging wall  21 , the cleaning plate  10   c  and the elastic cleaning blade  10   a  of the cleaning frame  13 , the photosensitive drum  7 , the developing roller  9   c , the developing blade  9   d , the plate  9   d   1  and the frame wall  12   a , and whose end portions in the longitudinal direction are provided by overlap of two side walls of the developing frame  12  within two side walls of the cleaning frame  13 . 
     Process-cartridge mounting means 
     As shown in FIGS. 4 and 5, positioning bosses  13   f  protrude toward the outside in the longitudinal direction on the axis of the photsensitive drum  7  at both sides of the process cartridge B in the longitudinal direction. A posture determining rib  13   g  is provided behind each of the positioning bosses  13   f  in the mounting direction of the process cartridge B. A posture determining rib  13   h  is also provided above each of the positioning bosses  13   f.    
     In FIG. 1 , when an opening/closing member  35  is raised around a hinge  35   a , a cartridge mounting space within the main body  14  of the image forming apparatus can be seen. As shown in FIG. 8, groove-shaped guide rails  16   a  and  16   b  are provided at each of two inner walls of the process cartridge B in the longitudinal direction in this space. The process cartridge B is inserted in a direction X while the positioning bosses  13   f  and the positioning ribs  13   g  are guided by the guide rails  16   a , and the positioning bosses  13   h  are guided by the guide rails  16   b . The position of the process cartridge B is determined by fitting of the positioning bosses  13   f  into positioning grooves  16   c  provided at the respective ends of the guide rails  16   a . The process cartridge B receives a moment for rotating around the positioning bosses  13   f  due to the difference in the primary moment of the process cartridge B before and behind the positioning bosses  13   f . As a result, a contact portion  13   c  of the process cartridge B contacts a contact member  18  of the main body  14  of the apparatus, to determine the posture of the process cartridge B. 
     Configuration of the cleaning unit 
     The cleaning frame  13  of a cleaning unit C includes two frames, i.e., a cleaning frame lid  13   a  which covers the used-toner reservoir  10   b  and includes the contact portion  13   c  for contacting the main body  14  of the apparatus, and a cleaning main frame  13   b  having other cleaning means. These two frames are connected to each other according to ultrasonic welding or the like. 
     As shown in FIG. 5, a plurality of threaded holes  13   d  are provided at sides E of the cleaning frame  13  so as to be threaded through the cleaning frame  13  at positions where the photosensitive drum  7  contacts the charging roller  8 . The cross-sectional positions of threaded holes  13   d  coincide with the contact portion between the charging roller  8  and the photosensitive drum  7  shown in FIG. 3, so that external air can easily flow into the contact portion between the charging roller  8  and the photosensitive drum  7 . In addition to the threaded holes  13   d , two threaded holes  13   d   1  threaded above the charging roller  8  are also provided at the sides E. The threaded holes  13   d   1  are present above the threaded holes  13   d . As shown in FIG. 7, intake holes  14   a  capable of introducing external air are provided in the main body  14  of the apparatus at positions facing the threaded holes  13   d . The intake holes  14   a  are provided in a wall  14   d , serving as a frame enclosing the main body  14  of the apparatus. Although schematically illustrated in FIG. 7, the positions of the intake holes are shifted from the positions of the threaded holes  13   d  so that external light does not directly enter the process cartridge B. As shown in FIG. 3, a space surrounded by the cleaning plate  10   c  and the developing blade plate  9   d   1  within the process cartridge B operates as a wind tunnel, so that air flows along the photosensitive drum  7  and the charging roller  8 . 
     A plurality of threaded holes  13   e  are also provided at a front surface G (see FIG. 9) orthogonal with respect to a side F of the cleaning frame  13  opposite to the side E in the longitudinal direction, and an exhaust fan  14   b  is provided at an opening threaded through the main body  14  of the image forming apparatus so as to face the threaded holes  13   e , in order to exhaust the heat around the charging roller  8  within the cleaning frame  13 . 
     As shown in FIG. 7, in addition to the above-described means for ventilating air in the process cartridge B, an intake fan  14   c  for introducing external air into the main body  14  of the image forming apparatus is provided at a portion upstream from the exhaust fan  14   b  in the conveying direction of the recording medium  2 . The air taken in by the intake fan  14   c  is divided into an air flow “a” flowing along the left side of the process cartridge B as seen from the mounting direction of the process cartridge B in the cartridge mounting space, and an air flow “b” passing through a space at a right portion of the process cartridge B. These air flows “a” and “b” thereafter join a sucked flow by the discharge fan  14   b . The air flows “a” and “b” passing through the left and right spaces along the process cartridge B then pass through a space between the optical case of the optical system  1  and the process cartridge B (see FIG.  1 ). 
     The above-described front surface G side has a negative pressure because the exhaust fun  14   b  sucks the air near the front surface G. External air is taken in from the intake holes  14   a  of the main body  14  of the apparatus, enters the process cartridge B passing through the threaded holes  13   d , flows along the charging roller  8  while carrying ozone, leaves the process cartridge B after passing through the threaded holes  13   e , and is exhausted t.o the outside of the main body  14  of the apparatus by the exhaust fan  14   b.    
     According to the above-described configuration, air flows near the electrophotographic photosensitive member and the charging means, to discharge heat accumulated near the electrophotographic photosensitive member and within the process cartridge, and to prevent deformation of the frames and the adverse influence of the heat on toner and the respective process means. 
     Although in the embodiment, a roller electrode has been illustrated as charging means, a contact-type electrode, such as a brush roller, a blade, a brush or the like, may also be used as charging means. Since such an electrode contacts the photosensitive member, the contact portion operates as a guide for an air flow, thereby allowing a smooth air flow and improving the exhaust effect within the cartridge. 
     It is considered to be most preferable to provide holes for taking in and exhausting an air flow at positions corresponding to a contact portion between the charging means and the photosensitive member. However, it is possible to obtain a sufficient exhaust effect even if the positions of the holes do not coincide with the contact portion between the charging means and the photosensitive member as in the embodiment. The effects of the invention may also be achieved not only when the positions of the intake holes coincide with the contact portion, but also when only the positions of the exhaust holes coincide with the contact portion, when the positions of both the intake and exhaust holes coincide with the contact portion, or when the positions of both the intake and exhaust holes do not coincide with the contact portion. 
     The individual components shown in outline in the drawings are all well known in the process cartridge and image forming apparatus arts and their specific construction and operation are not critical to the operation or the best mode for carrying out the invention. 
     While the present invention has been described with respect to what is considered to be the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, the present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.