Abstract:
An image forming apparatus may include a moving unit configured to support a cartridge and to slide in a generally horizontal direction between multiple positions. For example, the positions may include a first position where the moving unit is located inside the main body and a second position where the moving unit is located outside the main body. Additionally or alternatively, the moving unit being may also move between the first position and a third position located below the first position. The moving unit may also be configured to electrically connect electrodes based on its movement.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation of and claims the benefit of priority from U.S. application Ser. No. 13/633,331 filed on Oct. 2, 2012, which is a continuation of Ser. No. 13/337,808, filed on Dec. 27, 2011, which issued as U.S. Pat. No. 8,306,452, entitled “Image Forming Apparatus and Photosensitive Unit,” which is a continuation of U.S. application Ser. No. 12/408,755, filed on Mar. 23, 2009, entitled “Image Forming Apparatus and Photosensitive Unit,” which issued as U.S. Pat. No. 8,107,853, and which claims priority to Japanese Patent Application No. 2008-77518 filed on Mar. 25, 2008. The contents of the above noted applications are hereby incorporated into the present application by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to an image forming apparatus such as a color laser printer and a photosensitive unit mounted on the image forming apparatus. 
       BACKGROUND 
       [0003]    For example, there is proposed a so-called color image forming apparatus, in which a photosensitive unit including a plurality of photosensitive members, chargers charging the photosensitive members, developing rollers feeding developing agents to the photosensitive members and cleaning brushes capturing foreign matter adhering to the photosensitive members in response to the colors of the developing agents, is detachably mounted. 
         [0004]    In the image forming apparatus, wire electrodes applying biases to discharge wires of the chargers, grid electrodes applying biases to grids of the chargers, developing roller electrodes applying biases to the developing rollers and cleaning electrodes applying biases to the cleaning brushes are provided on the same side surface of a drum unit as the photosensitive unit in response to the colors respectively. These electrodes come into contact with contacts individually provided on the main body of the image forming apparatus when the drum unit is mounted in the main body of the apparatus, to be fed with power from the main body of the apparatus. 
         [0005]    Among these electrodes, the wire electrodes and the cleaning electrodes are arranged on the same straight line extending along a direction for mounting or dismounting the photosensitive unit in or from the main body of the apparatus, while the grid electrodes and the developing roller electrodes are arranged on the same straight line extending along the direction for mounting or dismounting the photosensitive unit in or from the main body of the apparatus, to form a train parallel to a train of the wire electrodes and the cleaning electrodes at an interval. 
         [0006]    In the photosensitive unit, the intervals between the adjacent electrodes must be generally increased, in order to reliably bring the electrodes and the corresponding contacts provided on the main body of the apparatus into contact with one another and to prevent an electric leak between the electrodes. In particular, the interval between the train of the wire electrodes and the cleaning electrodes and the train of the grid electrodes and the developing roller electrodes must be increased. In this case, however, the degree of freedom in design may be reduced. 
       SUMMARY 
       [0007]    One aspect of the present invention may provide a photosensitive unit capable of improving the degree of freedom in design when a plurality of electrodes are so arranged as to form parallelly extending trains and an image forming apparatus with which the photosensitive unit is mounted. 
         [0008]    The same or different aspect of the present invention may provide an image forming apparatus including: a main body provided with an accommodation chamber partitioned by an inner side surface; a photosensitive unit, slidable between an accommodated position where the photosensitive unit is accommodated in the accommodation chamber and a drawn position where the photosensitive unit is drawn from the accommodation chamber, holding a plurality of photosensitive members parallelly arranged along the sliding direction of the photosensitive unit; a first electrode provided on a first outer side surface formed on the photosensitive unit to extend along the sliding direction while being opposed to the inner side surface in an orthogonal direction orthogonal to the sliding direction; a second electrode provided on a second outer side surface formed on the photosensitive unit to protrude toward the inner side surface beyond the first outer side surface in the orthogonal direction while extending in parallel with the first outer side surface; a third electrode provided on a first inner side surface formed on the inner side surface to extend along the sliding direction, to be opposed to the first electrode at an interval in the orthogonal direction as viewed from the sliding direction when the photosensitive unit is located between the accommodated position and the drawn position, and to come into contact with the second electrode along the orthogonal direction when the photosensitive unit is located on the accommodated position; and a fourth electrode provided on a second inner side surface formed on the inner side surface to extend in parallel with the first inner side surface and to protrude toward the photosensitive unit beyond the first inner side surface in the orthogonal direction, to be opposed in the orthogonal direction to a third outer side surface opposite to the second outer side surface with respect to the first outer side surface in the photosensitive unit when the photosensitive unit is located between the accommodated position and the drawn position, and to come into contact with the first electrode along the orthogonal direction when the photosensitive unit is located on the accommodated position. 
         [0009]    One or more aspects of the present invention provide a photosensitive unit slidably mounted in/dismounted from a main body of an image forming apparatus provided with an accommodation chamber partitioned by an inner side surface, including: a plurality of photosensitive members parallelly arranged along the sliding direction of the photosensitive unit, on which electrostatic latent images are formed; a plurality of first process members provided correspondingly to the plurality of photosensitive members, for visualizing the electrostatic latent images formed on the photosensitive members; a plurality of second process members provided correspondingly to the plurality of photosensitive members separately from the first process members, for visualizing the electrostatic latent images formed on the photosensitive members; a first electrode provided on a first outer side surface formed on the photosensitive unit to extend along the sliding direction while being opposed to the inner side surface in an orthogonal direction orthogonal to the sliding direction, and connected to an electrode of the main body thereby feeding power received from the electrode of the main body to the first process members; and a second electrode provided on a second outer side surface formed on the photosensitive unit to protrude toward the inner side surface beyond the first outer side surface in the orthogonal direction while extending in parallel with the first outer side surface, and connected to the electrode of the main body thereby feeding power received from the electrode of the main body to the second process members. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a right side sectional view showing illustrative aspects of a printer as an example of an image forming apparatus of one or more aspects of the present invention. 
           [0011]      FIG. 2  is a right side elevational view of the printer in a state where a drum unit is located at a drawn position. 
           [0012]      FIG. 3  is a perspective view of a principal part of the printer in the state shown in  FIG. 2  as viewed from above. 
           [0013]      FIG. 4  is a right side elevational view of the principal part of the printer in the state shown in  FIG. 2 . 
           [0014]      FIG. 5  is a front elevational view of the printer in the state shown in  FIG. 2 . 
           [0015]      FIG. 6  is a perspective view of the principal part of the printer in the state shown in  FIG. 2  as viewed from below. 
           [0016]      FIG. 7A  is a right side elevational view of the printer in a state where the drum unit is located between an accommodated position and the drawn position. 
           [0017]      FIG. 7B  is a partially fragmented sectional view of the printer taken along the line A-A in  FIG. 7A . 
           [0018]      FIG. 8  is a perspective view of the principal part of the printer in the state shown in  FIG. 7A  as viewed from above. 
           [0019]      FIG. 9  is a right side elevational view of the principal part of the printer in the state shown in  FIG. 7A . 
           [0020]      FIG. 10  is a front elevational view of the printer in the state shown in  FIG. 7A . 
           [0021]      FIG. 11A  is a right side elevational view of the printer in a state where the drum unit is located at the accommodated position. 
           [0022]      FIG. 11B  is a partially fragmented sectional view of the printer taken along the line B-B in  FIG. 11A . 
           [0023]      FIG. 12  is a perspective view of the principal part of the printer in the state shown in  FIG. 11A  as viewed from above. 
           [0024]      FIG. 13  is a right side elevational view of the principal part of the printer in the state shown in  FIG. 11A . 
           [0025]      FIG. 14  is a front elevational view of the printer in the state shown in  FIG. 11A . 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Embodiments of the present invention are now described with reference to the drawings. 
       First Embodiment 
     Overall Structure of Printer 
       [0027]      FIG. 1  is a right side sectional view showing illustrative aspects of a printer as an example of an image forming apparatus of one or more aspects of the present invention. Directions are mentioned with reference to illustrated arrows (this also applies to the remaining drawings). The right-and-left direction and the width direction are identical to each other. 
         [0028]    The printer  1  is a color printer. As show in  FIG. 1 , the printer  1  includes four photosensitive drums  3  having central axes extending in the width direction, which are arranged in line along the anteroposterior direction, as examples of photosensitive members in a main body casing  2  as an example of the main body of the image forming apparatus. The four photosensitive drums  3  are hereinafter classified into a photosensitive drum  3 K (black), a photosensitive drum  3 C (cyan), a photosensitive drum  3 M (magenta) and a photosensitive drum  3 Y (yellow), in response to the colors (black, cyan, magenta and yellow) of toner images (described later) formed on the photosensitive drums  3  respectively. A charger  4  such as a scorotron charger, for example, a developing roller  5  and a cleaning brush  6  are opposed to each photosensitive drum  3 . 
         [0029]    A scanner unit  7  is arranged above these photosensitive drums  3 , so that the surface of each photosensitive drum  3  is exposed to a laser beam (see the broken line in  FIG. 1 ) emitted from the scanner unit  7  based on image data after the same is uniformly charged by the charger  4 . Thus, an electrostatic latent image based on the image data is formed on the surface of each photosensitive drum  3 . Each electrostatic latent image is visualized by a toner (developing agent) carried on the developing roller  5  corresponding to each photosensitive drum  3 , and a toner image (developing agent image) is formed on the surface of the photosensitive drum  3 . At this time, a developing bias (described later) is applied to the developing roller  5 . 
         [0030]    Sheets P are accommodated in a sheet supply cassette  8  arranged on a lower portion in the main body casing  2 . Each sheet P accommodated in the sheet supply cassette  8  is transported to a transport belt  9  with various rollers provided in the vicinity of the front end portion of the sheet supply cassette  8 , while the direction thereof is changed rearward from the front side. The transport belt  9  is arranged between the photosensitive drums  3 K,  3 C,  3 M and  3 Y and four transfer rollers  10  provided in response to the four photosensitive drums  3  respectively and opposed to the corresponding photosensitive drums  3  from below. The toner images formed on the surfaces of the photosensitive drums  3  are successively transferred and overlaid one the other on the sheet P transported to the transport belt  9  with transfer biases applied to the transfer rollers  10 . 
         [0031]    The sheet P having the toner images of the four colors transferred thereto is transported to a fixing section  11 . The toner images transferred onto the sheet P are thermally fixed in the fixing section  11 . Thereafter the sheet P is ejected to a sheet ejecting tray  12  provided on an upper portion of the main body casing  2  with various rollers, while the direction thereof is changed frontward from the rear side. 
         [0032]    In such image formation, the cleaning brushes  6  capture foreign matter such as residual toners and sheet dust remaining on the photosensitive drums  3  after the transfer of the toner images onto the sheet P. 
       Drum Unit 
       [0033]    The printer  1  includes a drum unit  13  as an example of a photosensitive unit configured to be mounted in and dismounted from the main body casing  2  in a state integrally holding the aforementioned photosensitive drums  3 , the chargers  4 , the developing rollers  5  and the cleaning brushes  6 . 
         [0034]    The drum unit  13  is slid along the anteroposterior direction from the front side to be mounted in or dismounted from the main body casing  2 , and accommodated in an accommodation chamber  50  (described later) formed in the main body casing  2  when the drum unit  13  is mounted in the main body casing  2 . The position of the drum unit  13  accommodated in the accommodation chamber  50  is referred to as an accommodated position (see  FIGS. 11A to 14  described later). On the other hand, the position of the drum unit  13  shown in  FIGS. 2 to 6  is referred to as a drawn position, where the drum unit  13  is drawn from the accommodation chamber  50 . 
         [0035]    In the following description, the front side in the anteroposterior direction is regarded as the upstream side a direction in which the drum unit  13  is mounted with respect to the main casing  2  (hereinafter referred to as a mounting direction of the drum unit  13 ) while the rear side is regarded as the downstream side in the mounting direction of the drum unit  13 . While the drum unit  13  is slid along the anteroposterior direction when the same is mounted in or dismounted from the main body casing  2 , while an orthogonal direction orthogonal to this sliding direction is regarded as the width direction. 
         [0036]    As shown in  FIG. 1 , the drum unit  13  includes a boxy unit casing  14  having open upper and lower surfaces (see  FIGS. 3 and 6 ), and the unit casing  14  includes four subunits  15  correspondingly to the four photosensitive drums  3 . In the following description, the four subunits  15  are classified into subunits  15 K,  15 C,  15 M and  15 Y in response to the colors of the toners respectively, similarly to the photosensitive drums  3 . These subunits  15  are arranged in line along the anteroposterior direction in the main body casing  2 , similarly to the aforementioned four photosensitive drums  3 . More specifically, these subunits  15  are arranged in the order of the subunits  15 K,  15 C,  15 M and  15 Y from the rear side. 
       (1) Unit Casing 
       [0037]    As shown in  FIG. 6 , the unit casing  14  integrally includes a left wall  16 , a right wall  17 , a front-side wall  18  and a rear-side wall  19 . 
         [0038]    The left and right walls  16  and  17 , which are similar to each other, are in the form of plates elongated in the anteroposterior direction and thin in the width direction, and opposed to each other at an interval in the width direction (see also  FIG. 3 ). More specifically, the upper and lower edges of the left and right walls  16  and  17  extend along the anteroposterior direction, and most parts of the front edges extend obliquely upward on the front side while the rear edges are bent in the form of arcs swelling out frontward (see  FIG. 4 ). Notches  39  bent frontward are formed in the vicinity of the lower end portions of the rear edges of the left and right walls  16  and  17  respectively (see  FIG. 4 ). 
         [0039]    As shown in  FIG. 3 , the left and right walls  16  and  17  are integrally provided with flange portions  20  extending outward in the width direction continuously from the upper edges respectively. The flange portions  20  are in the form of vertically thin plates flatly extending along the anteroposterior direction. 
         [0040]    On the rear end portion of each of the left and right walls  16  and  17 , rollers  59  ( FIG. 13 ) are rotatably provided in the vicinity of the rear end portion of the corresponding flange portion  20 . 
         [0041]    In each of the left and right walls  16  and  17 , downwardly protruding convexes  21  are integrally provided on the front and rear ends of the lower end portion. When the drum unit  13  is dismounted from the main body casing  2  and placed on the floor, the convexes  21  come into contact with the floor. 
         [0042]    On the right side surface of the right wall  17 , a region below the flange portion  20  is divided into an upper right surface  22  as an example of a second outer side surface, a middle right surface  23  as an example of a first outer side surface and a lower right surface  24  as an example of a third outer side surface successively from the upper side. It is understood that the lower right surface  24  is opposite to the upper right surface  22  with respect to the middle right surface  23 . 
         [0043]    The upper, middle and lower right surfaces  22 ,  23  and  24  are elongated in the anteroposterior direction, extend along the anteroposterior and vertical directions, and are flat as viewed from both of the anteroposterior and vertical directions (in other words, not irregular in the width direction), as shown in  FIG. 5 . As to the vertical dimensions, the upper right surface  22  is slightly larger than the lower right surface  24 , and the middle right surface  23  is the smallest (see  FIG. 2 ). 
         [0044]    The middle right surface  23  is arranged leftward beyond the upper right surface  22 , and the lower right surface  24  is arranged leftward beyond the middle right surface  23 . In other words, the upper right surface  22  protrudes outward (rightward) beyond the middle right surface  23  in the width direction, while the middle right surface  23  protrudes rightward beyond the lower right surface  24 . Therefore, the right side surface of the right wall  17  is concaved stepwise leftward toward the lower side. 
         [0045]    The lower edge of the upper right surface  22  and the upper edge of the middle right surface  23  are coupled with each other by a first coupling surface  25  slightly extending rightward continuously from the upper edge of the middle right surface  23  and thereafter extending obliquely upward on the right side to be connected to the lower edge of the upper right surface  22 . The lower edge of the middle right surface  23  and the upper edge of the lower right surface  24  are coupled with each other by a second coupling surface  26  slightly extending rightward continuously from the upper edge of the lower right surface  24  and thereafter extending obliquely upward on the right side to be connected to the lower edge of the middle right surface  23 . 
         [0046]    As shown in  FIG. 3 , the lower right surface  24  is integrally provided with a rightwardly protruding rib  27 . The rib  27  includes a first rib  28  extending along the anteroposterior direction and eight second ribs  29  extending obliquely upward on the front side continuously from the upper edge of the first rib  28 . Most part of the right side surface of the rib  27  is flatly formed, similarly to the lower right surface  24 . However, the rear end portion of the right side surface of the first rib  28  is inclined obliquely rearward on the left side and continuous with the lower right surface  24 , to form an inclined surface  30 . In other words, the inclined surface  30  swells out rightward from the downstream side (rear side) toward the upstream side (front side) in the mounting direction (see thick arrow in  FIG. 3 ) of the drum unit  13  with respect to the main body casing  2 . A portion of the right side surface of the first rib  28  excluding the inclined surface  30  and the right side surfaces of the second ribs  29  are flush with one another. 
         [0047]    The eight second ribs  29  are arranged at intervals in the anteroposterior direction. The eight second ribs  29  are classified into second ribs  29 A,  29 B,  29 C,  29 D,  29 E,  29 F,  29 G and  29 H successively from the rear side. 
         [0048]    The second rib  29 A extends from a portion close to the inclined surface  30  of the first rib  28 , while the second rib  29 H extends from the front end portion of the first rib  28 . The second rib  29 B is closer to the second rib  29 C than the second rib  29 A, while the second rib  29 C is closer to the second rib  29 B than the second rib  29 D. The second rib  29 D is closer to the second rib  29 E than the second rib  29 C, while the second rib  29 E is closer to the second rib  29 D than the second rib  29 F. The second rib  29 F is closer to the second rib  29 G than the second rib  29 E, while the second rib  29 G is closer to the second rib  29 F than the second rib  29 H. 
         [0049]    More specifically, the intervals between the second ribs  29 B and  29 C, between the second ribs  29 D and  29 E and between the second ribs  29 F and  29 G are equal to one another. Further, the intervals between the second ribs  29 A and  29 B, between the second ribs  29 C and  29 D, between the second ribs  29 E and  29 F and between the second ribs  29 G and  29 H are equal to one another, and these intervals are wider than the interval between the second ribs  29 B and  29 C. 
         [0050]    As shown in  FIGS. 5 and 6 , the upper end of the right side surface (excluding the inclined surface  30 ) of the first rib  28  and the lower end of the right side surface of each second rib  29  are continuous with each other, and the upper end of the right side surface of each second rib  29  is continuous with the aforementioned second coupling surface  26  (more specifically, the portion extending obliquely upward on the right side) from below. 
         [0051]    On the right side surface of the right wall  17 , four electrode groups  31  are arranged correspondingly to the aforementioned four subunits  15 K,  15 C,  15 M and  15 Y respectively, as shown in  FIG. 3 . The four electrode groups  31  are classified into electrode groups  31 K,  31 C,  31 M and  31 Y successively from the rear side, correspondingly to the subunits  15 K,  15 C,  15 M and  15 Y respectively. 
         [0052]    Each electrode group  31  is constituted of four electrodes, i.e., a wire electrode  32 , a grid electrode  33 , a cleaning electrode  34  and a developing roller electrode  35 . The grid electrode  33  and the developing roller electrode  35  function as examples of a first electrode, while the wire electrode  32  and the cleaning electrode  34  function as examples of a second electrode. 
         [0053]    In each electrode group  31 , the wire electrode  32  and the cleaning electrode  34  are so disposed as to align with each other in the anteroposterior direction along the lower edge of the upper right surface  22 , as shown in  FIG. 4 . More specifically, the wire electrode  32  is disposed in front of the cleaning electrode  34  at an interval. The right side surfaces of the wire electrode  32  and the cleaning electrode  34  are generally flush with the upper right surface  22 , or slightly protrude rightward from the upper right surface  22  (see  FIG. 5 ). 
         [0054]    On the other hand, the grid electrode  33  and the developing roller electrode  35  are so disposed as to align with each other in the anteroposterior direction along the lower edge of the middle right surface  23 . More specifically, the developing roller electrode  35  is disposed in front of the grid electrode  33  at an interval. The right side surfaces of the grid electrode  33  and the developing roller electrode  35  are generally flush with the middle right surface  23 , or slightly protrude rightward from the middle right surface  23  (see  FIG. 5 ). 
         [0055]    The grid electrode  33  and the developing roller electrode  35  are adjacent to the upper end portions of the corresponding second ribs  29  respectively. In other words, in the electrode group  31 K, the grid electrode  33  is adjacent to the upper end portion of the second rib  29 A and the developing roller electrode  35  is adjacent to the upper end portion of the second rib  29 B. Similarly, in the electrode group  31 C, the grid electrode  33  is adjacent to the upper end portion of the second rib  29 C and the developing roller electrode  35  is adjacent to the upper end portion of the second rib  29 D. In the electrode group  31 M, the grid electrode  33  is adjacent to the upper end portion of the second rib  29 E, and the developing roller electrode  35  is adjacent to the upper end portion of the second rib  29 F. In the electrode group  31 Y, the grid electrode  33  is adjacent to the upper end portion of the second rib  29 G, and the developing roller electrode  35  is adjacent to the upper end portion of the second rib  29 H. 
         [0056]    As to the positions of the electrodes in each electrode group  31  in the anteroposterior direction, the grid electrode  33  is positioned between the wire electrode  32  and the cleaning electrode  34 , while the developing roller electrode  35  is positioned frontward beyond the wire electrode  32 . 
         [0057]    When the four electrode groups  31  are collectively observed, all wire electrodes  32  and cleaning electrodes  34  are arranged on the same straight line extending along the anteroposterior direction to form a train X on the upper right surface  22 , and alternately arranged in this train X. On the other hand, all grid electrodes  33  and developing roller electrodes  35  are arranged on the same straight line extending along the anteroposterior direction to form a train Y on the middle right surface  23 , and alternately arranged in this train Y. 
         [0058]    More specifically, all wire electrodes  32  and cleaning electrodes  34 , and, all grid electrodes  33  and developing roller electrodes  35 , are parallelly arranged at an interval in the vertical direction, so that the train X of the wire electrodes  32  and the cleaning electrodes  34  is arranged above and the train Y of the grid electrodes  33  and the developing roller electrodes  35  is arranged below. 
         [0059]    As shown in  FIGS. 3 and 6 , the front-side wall  18  is extended between the front edges of the left and right walls  16  and  17 , while the rear-sidewall  19  is extended between the rear edges of the left and right walls  16  and  17 . 
         [0060]    As shown in  FIG. 3 , a first handle  36  is provided at the center of the front-side wall  18  in the width direction, while a second handle  37  is provided at the center of the rear-side wall  19  in the width direction. 
         [0061]    The first handle  36  generally has an inverted U shape having two free end portions, which are supported on the front-side wall  18 . More specifically, a support shaft  38  extending in the width direction is inserted into the front-side wall  18 , and this support shaft  38  is inserted also into the two free end portions of the first handle  36 . Therefore, the first handle  36  is swingable on the support shaft  38  between an upright position (not shown) where the first handle  36  is uprighted along the front-side wall  18  and a tilted position (see  FIG. 3 ) tilted frontward from the front-side wall  18 . Both end portions of the support shaft  38  in the width direction protrude outward from the unit casing  14  in the width direction. 
         [0062]    The second handle  37  also generally has an inverted U shape having two free end portions, which are connected to the rear-side wall  19 . 
         [0063]    The first and second handles  36  and  37  are grasped when the drum unit  13  is mounted in or dismounted from the main body casing  2 . 
       (2) Subunit 
       [0064]    As shown in  FIG. 1 , each subunit  15  is a hollow body inclined obliquely upward on the front side with respect to a horizontal plane (including the anteroposterior and right-and-left directions), and has the aforementioned photosensitive drum  3 , the charger  4 , the developing roller  5 , the cleaning brush  6 , a toner accommodation chamber  40 , an agitator  41 , a feed roller  42  and a layer-thickness regulating blade  43  therein. 
         [0065]    The toner accommodation chamber  40 , generally forming the upper half of the subunit  15 , accommodates the toner of the color corresponding to each subunit  15 . The feed roller  42  is arranged under the toner accommodation chamber  40 , to come into contact with the developing roller  5  from above. 
         [0066]    The developing roller  5  is in contact with the photosensitive drum  3  from the front side. The developing roller electrode  35  (see  FIG. 3 ) of the corresponding electrode group  31  is connected to the developing roller  5 . In image formation, a developing roller contact  60  (see  FIG. 3 ), described later, provided in the main body casing  2  applies the developing bias to the developing roller  5  through the developing roller electrode  35 . 
         [0067]    The toner accommodated in the toner accommodation chamber  40  is agitated by the agitator  41 , fed to the feed roller  42  by the own weight thereof, formed as a thin layer, carried by the developing roller  5  as hereinabove described, to contribute to visualization of the electrostatic latent image formed on the corresponding photosensitive drum  3 . The layer-thickness regulating blade  43  regulates the thin layer of the toner carried by the developing roller  5  to a prescribed thickness. 
         [0068]    The charger  4  is opposed to the photosensitive drum  3  at an interval at the back of the photosensitive drum  3  on the oblique upper side. The charger  4  includes a discharge wire  44  opposed to the photosensitive drum  3  at an interval and a grid  45  provided between the discharge wire  44  and the photosensitive drum  3 . 
         [0069]    The wire electrode  32  (see  FIG. 3 ) of the corresponding electrode group  31  is connected to the discharge wire  44 , while the grid electrode  33  (see  FIG. 3 ) is connected to the grid  45 . 
         [0070]    In the charger  4 , a wire contact  61  (see  FIG. 3 ), described later, provided in the main body casing  2  applies a discharge voltage to the discharge wire  44  through the wire electrode  32  in image formation, thereby corona-discharging the discharge wire  44 . At the same time, a grid contact  62  (see  FIG. 3 ), described later, provided in the main body casing  2 , applies a grid voltage to the grid  45  through the grid electrode  33  to control the amount of electric charge fed to the photosensitive drum  3 , whereby the surface of the photosensitive drum  3  is uniformly charged, as hereinabove described. 
         [0071]    The cleaning brush  6  is opposed to and in contact with the photosensitive drum  3  at the back of the photosensitive drum  3 . The cleaning electrode  34  (see  FIG. 3 ) of the corresponding electrode group  31  is connected to the cleaning brush  6 . In image formation, a cleaning contact  63  (see  FIG. 3 ), described later, provided in the main body casing  2  applies a cleaning bias to the cleaning brush  6  through the cleaning electrode  34 . The cleaning brush  6  captures the aforementioned foreign matter present on the photosensitive drum  3  with this cleaning bias. 
         [0072]    Each subunit  15  can be separated into a first subunit  46  as an example of a first process member and a second subunit  47  as an example of a second process member. The first subunit  46 , forming the upper portion of the subunit  15 , has the developing roller  5 , the toner accommodation chamber  40 , the agitator  41 , the feed roller  42  and the layer-thickness regulating blade  43 . The second subunit  47 , forming the lower portion of the subunit  15 , has the photosensitive drum  3 , the charger  4  and the cleaning brush  6 . As hereinabove described, the electrostatic latent image formed on the corresponding photosensitive drum  3  is visualized by the functions of the individual components in the subunit  15 . Therefore, it is understood that the first and second subunits  46  and  47  contribute to the visualization of the electrostatic latent image formed on the photosensitive drum  3  respectively, even if the subunit  15  is separated into a first subunit  46  and a second subunit  47 . 
         [0073]    In this case, in the first subunit  46 , the developing roller electrode  35  is connected to the developing roller contact  60  (see  FIG. 3 ), whereby power (developing bias) is fed from the developing roller contact  60  to the developing roller  5  through the developing roller electrode  35 . 
         [0074]    In the second subunit  47 , the wire electrode  32  is connected to the wire contact  61  (see  FIG. 3 ), whereby power is fed from the wire contact  61  to the discharge wire  44  through the wire electrode  32 . Further, the grid electrode  33  is connected to the grid contact  62  (see  FIG. 3 ), whereby power (grid voltage) is fed from the grid contact  62  to the grid  45  through the grid electrode  33 . The cleaning electrode  34  is connected to the cleaning contact  63  (see  FIG. 3 ), whereby power (cleaning bias) is fed from the cleaning contact  63  to the cleaning brush  6  through the cleaning electrode  34 . 
         [0075]    While the second subunit  47  is fixed to the unit casing  14 , the first subunit  46  may be rendered mountable in and dismountable from the unit casing  14 . 
       Main Body Casing 
       [0076]    As shown in  FIG. 1 , a front cover  51  is provided on a front wall  49  of the main body casing  2 . The lower end portion of the front cover  51  is supported by a hinge or the like on the front wall  49 . Therefore, the front cover  51  is swingable on the lower end portion between a closed position (see  FIG. 1 ) where the upper end portion thereof comes into contact with the upper wall of the main body casing  2  and an open position (not shown) where the upper end portion separates from the upper wall of the main body casing  2 .  FIGS. 2 to 14  omit illustration of the front cover  51 . 
         [0077]    When the front cover  51  is swung to the open position, a mounting port  52 , generally rectangular in front elevational view, formed on the front wall  49  is released to expose the aforementioned accommodation chamber  50  frontward, as shown in  FIG. 5 . On portions forming the right and left edges of the mounting port  52  in the front wall  49 , recesses  58  dented rearward are formed at the same positions in the vertical direction respectively. 
         [0078]    The main body casing  2  includes a pair of side walls  53  opposed to each other at an interval in the width direction to hold the accommodation chamber  50  therebetween.  FIG. 7B  shows the right side wall  53  (right wall  54 ) in the pair of side walls  53 . In the right wall  54 , a left surface  55  which is an example of an inner side surface partitions the right side of the accommodation chamber  50 . The aforementioned front wall  49  is extended between the front end portions of the pair of side walls  53  (see  FIG. 5 ). 
         [0079]    As shown in  FIG. 3 , a reference shaft  56  extending in the width direction is provided in the rear end portion (end portion on the downstream side in the mounting direction of the drum unit  13 ) of the accommodation chamber  50  in the main body casing  2 . The reference shaft  56  is extended between the pair of side walls  53 . 
         [0080]    In the pair of side walls  53 , guide rails  57  are provided at positions opposed to each other in the width direction respectively above the aforementioned recesses  58  (see  FIG. 5 ). The guide rails  57  are so formed as to extend along the anteroposterior direction on the inner side surfaces of the corresponding side walls  53  in the width direction. In the guide rails  57 , the corresponding flange portions  20  of the drum unit  13  are slidably received, while the rollers  59  (see  FIG. 8 ) of the drum unit  13  are rolled therein. Rollers  71  are rotatably provided on the upper sides of the front end portions of the guide rails  57 . 
         [0081]    As shown in  FIG. 5 , on the left surface  55  of the right wall  54 , a region below the corresponding guide rail  57  is divided into an upper left surface  69  as an example of a first inner side surface and a lower left surface  70  as an example of a second inner side surface successively from the upper side. The upper and lower left surfaces  69  and  70  are elongated in the anteroposterior direction, extend along the anteroposterior and vertical directions, and are flat as viewed from both of the anteroposterior and vertical directions (in other words, not irregular in the width direction). As to the vertical dimensions, the upper left surface  69  is smaller than the lower left surface  70 . The upper left surface  69  is arranged leftward beyond the portion where the guide rail  57  is arranged on the left surface  55 , while the lower left surface  70  is arranged leftward beyond the upper left surface  69 . In other words, the lower left surface  70  protrudes inward (leftward) beyond the upper left surface  69  in the width direction, while the upper left surface  69  protrudes inward beyond the portion where the guide rail  57  is arranged on the left surface  55 . Therefore, the left surface  55  protrudes stepwise leftward toward the lower side. 
         [0082]    The right wall  54  is provided with (stores) four developing roller contacts  60 , four wire contacts  61 , four grid contacts  62  and four cleaning contacts  63  correspondingly to the electrode groups  31  of the drum unit  13  respectively, as shown in  FIG. 3 . The wire contacts  61  and the cleaning contacts  63  function as examples of a third electrode, while the grid contacts  62  and the developing roller contacts  60  function as examples of a fourth electrode. The developing roller contacts  60 , the wire contacts  61  and the cleaning contacts  63  also function as examples of electrodes of the main body of the image forming apparatus. 
         [0083]    The developing roller contact  60 , the wire contact  61 , the grid contact  62  and the cleaning contact  63  are disposed to be opposed to the corresponding developing roller electrode  35 , corresponding wire electrode  32 , corresponding grid electrode  33  and cleaning electrode  34  of each electrode group  31  respectively in the width direction when the drum unit  13  is mounted in the main body casing  2 . 
         [0084]    More specifically, the wire contacts  61  and the cleaning contacts  63  are disposed on the upper left surface  69  (see  FIG. 5 ), and alternately arranged on the same straight line extending along the anteroposterior direction. On the other hand, the grid contacts  62  and the developing roller contacts  60  are provided on the lower left surface  70  (see  FIG. 5 ), and alternately arranged on the same straight line extending along the anteroposterior direction. In other words, the wire contacts  61  and the cleaning contacts  63 , and, the grid contacts  62  and the developing roller contacts  60 , are parallelly arranged at an interval from one another in the vertical direction. 
         [0085]    Each of the developing roller contacts  60 , the wire contacts  61 , the grid contacts  62  and the cleaning contacts  63  integrally includes a large-diametral head portion  64  provided on the outer side (right side) in the width direction and a small-diametral shaft portion  65  extending inward (leftward) in the width direction from the head portion  64 , as shown in each of the developing roller contact  60  and the wire contact  61  in  FIG. 7B . 
         [0086]    A plurality of contact holes  66  are formed on the left surface  55  of the right wall  54  in response to the number of the contacts, to project shaft portions  65  of the developing roller contacts  60 , the wire contacts  61 , the grid contacts  62  and the cleaning contacts  63  leftward (toward the accommodation chamber  50 ) from the left surface  55  respectively. The contact holes  66  corresponding to the wire contacts  61  and the cleaning contacts  63  are formed on the upper left surface  69 , while the contact holes  66  corresponding to the grid contacts  62  and the developing roller contacts  60  are formed on the lower left surface  70 . 
         [0087]    The right wall  54  stores springs  67  engaging with the head portions  64  of the developing roller contacts  60 , the wire contacts  61 , the grid contacts  62  and the cleaning contacts  63  and urging the head portions  64  leftward. Thus, the developing roller contacts  60 , the wire contacts  61 , the grid contacts  62  and the cleaning contacts  63  are regularly urged leftward by the springs  67 . Thus, while the shaft portions  65  of the contacts  60  to  63  protrude into the accommodation chamber  50  from the right wall  54  through the contact holes  66 , the head portions  64  cannot move leftward beyond the contact holes  66 , whereby the contacts  60  to  63  are kept in the state supported on the right wall  54  without displacement. 
       Mounting Drum Unit in Main Body Casing 
       [0088]    When the front cover  51  (see  FIG. 1 ) is swung to the open position, the accommodation chamber  50  is exposed from the mounting port  52  of the main body casing  2  (see  FIG. 5 ). Thereafter the first handle  36  of the drum unit  13  located at the drawn position (see also  FIGS. 2 to 6 ) is grasped to push the drum unit  13  rearward, thereby inserting the drum unit  13  into the accommodation chamber  50  rearward from the front side along the anteroposterior direction. 
         [0089]    In order to insert the drum unit  13  into the accommodation chamber  50 , the rollers  59  (see  FIG. 8 ) provided on the rear end portion of the drum unit  13  are rolled on the corresponding guide rails  57  in the accommodation chamber  50  while the flange portions  20  are slid on the rollers  71  of the corresponding guide rails  57 , as shown in  FIG. 3 . 
         [0090]    When the drum unit  13  is inserted into the accommodation chamber  50 , the rear end portion of the right side surface (the upper, middle and lower right surfaces  22 ,  23  and  24 ) of the unit casing  14  of the drum unit  13  starts to be opposed to the left surface  55  of the right wall  54  partitioning the right side of the accommodation chamber  50  in the width direction (see  FIG. 5 ). 
         [0091]    When the drum unit  13  is continuously inserted, the headmost developing roller contact  60  is opposed to the lower right surface  24  in the width direction, extends onto the inclined surface  30  of the first rib  28  of the lower right surface  24 , and moves rightward against the urging force of the corresponding spring  67  (see  FIG. 7B ), as shown in  FIGS. 4 and 5 . Then, the headmost wire contact  61  is opposed to the middle right surface  23  at an interval from the right side. More specifically, the wire contact  61  is opposed to the corresponding grid electrode  33  and the corresponding developing roller electrode  35  provided on the middle right surface  23  at an interval in the width direction, as viewed from the anteroposterior direction (see  FIG. 5 ). In other words, the headmost wire contact  61 , not in contact with the drum unit  13  at this time, is kept at the same width-directional position as that before the insertion of the drum unit  13  into the accommodation chamber  50 . 
         [0092]    When the drum unit  13  is further inserted, the headmost developing roller contact  60  relatively moves frontward with respect to the drum unit  13 , and slides with respect to the right side surface of the first rib  28  at this time. The portion of the right side surface of the first rib  28  excluding the inclined surface  30  is flatly formed as hereinabove described, whereby the developing roller contact  60  sliding with respect to the right side surface of the first rib  28  is kept at a constant width-directional position. Then, the grid contact  62  positioned at the back of the developing roller contact  60  is opposed to the lower right surface  24  in the width direction and extends onto the inclined surface  30  of the first rib  28  similarly to the developing roller contact  60 , and thereafter slides with respect to the right side surface of the first rib  28  while, the grid contact  62  is kept at a constant width-directional position. 
         [0093]    At this time, the headmost wire contact  61 , continuously opposed to the middle right surface  23  at an interval from the right side, relatively moves frontward with respect to the drum unit  13 . Then, the cleaning contact  63  positioned at the back of the wire contact  61  is opposed to the middle right surface  23  from the right side at an interval, similarly to the wire contact  61 . More specifically, the cleaning contact  63  is opposed to the corresponding grid electrode  33  and the corresponding developing roller electrode  35  provided on the middle right surface  23  at an interval in the width direction (see  FIG. 5 ). Therefore, the cleaning contact  63  is kept at the same width-directional position as that before the drum unit  13  is inserted into the accommodation chamber  50 . The cleaning contact  63 , continuously opposed to the middle right surface  23  from the right side at an interval, relatively moves frontward with respect to the drum unit  13 . 
         [0094]    As the insertion of the drum unit  13  progresses, the remaining developing roller contacts  60  and grid contacts  62  are successively opposed to the lower right surface  24  in the width direction, extend onto the inclined surface  30  of the first rib  28 , and thereafter slide with respect to the right side surface of the first rib  28  while the same are kept at constant width-directional positions, similarly to the above. Then, the remaining wire contacts  61  and cleaning contacts  63  are successively opposed to the middle right surface  23  from the right side at intervals, and thereafter relatively move frontward with respect to the drum unit  13  while maintaining this state. 
         [0095]    As the insertion of the drum unit  13  further progresses, each of the developing roller contacts  60  and the grid contacts  62  approaches a position where the first rib  28  is branched into the corresponding second rib  29 , as shown in  FIGS. 8 and 9 . In the drum unit  13 , the rollers  59  project rearward from the guide rails  57  and the flange portions  20  are displaced from the rollers  71  of the guide rails  57  at this time. 
         [0096]    Thus, the drum unit  13  moves obliquely downward on the rear side by the own weight thereof and the flange portions  20  thereof are placed on the guide rails  57 , as shown in  FIGS. 12 and 13 . At the same time, the notches  39  of the drum unit  13  come into contact with the reference shaft  56  of the accommodation chamber  50  from the front side to hold the same therebetween, while both end portions of the support shaft  38  of the drum unit  13  are fitted into the corresponding recesses  58  on the front wall  49  of the main body casing  2  respectively (see  FIG. 14 ). Thus, the drum unit  13  is arranged at the accommodated position, and completely mounted in the main body casing  2 . After the drum unit  13  is completely mounted in the main body casing  2 , the front cover  51  is swung to the closed position, to close the mounting port  52  of the main body casing  2  (see  FIG. 1 ). 
         [0097]    When the drum unit  13  is arranged at the accommodated position, each of the developing roller contacts  60 , the wire contacts  61 , the grid contacts  62  and the cleaning contacts  63  relatively moves obliquely upward on the front side with respect to the drum unit  13  moving obliquely downward on the rear side. 
         [0098]    When the drum unit  13  is arranged at the accommodated position, therefore, each of the developing roller contacts  60  and the grid contacts  62  is transferred to the second coupling surface  26  continuous with the right side surface of the corresponding second rib  29  after sliding with respect to the right side surface of this corresponding second rib  29 . At this time, each of the developing roller contacts  60  and the grid contacts  62  is guided rightward by the second coupling surface  26  (more specifically, a portion extending obliquely upward on the right side) against the urging force of the corresponding spring  67  (see  FIG. 11B ), thereafter reaches the middle right surface  23 , comes into contact with the corresponding one of the developing roller electrodes  35  and the grid electrodes  33  from the right side along the width direction, and is connected thereto (see also  FIGS. 11B and 14 ). 
         [0099]    When the drum unit  13  is arranged at the accommodated position, further, each of the wire contacts  61  and the cleaning contacts  63  is displaced from the state (see  FIGS. 7B and 10 ) opposed to the middle right surface  23  (the corresponding one of the grid electrodes  33  and the developing roller electrodes  35 ) from the right side at an interval, and received by the corresponding first coupling surface  25 . At this time, each of the wire contacts  61  and the cleaning contacts  63  is guided rightward by the first coupling surface  25  (more specifically, a portion extending obliquely upward on the right side) against the urging force of the corresponding spring  67  (see  FIG. 11B ), thereafter reaches the upper right surface  22 , comes into contact with the corresponding one of the wire electrodes  32  and the cleaning electrodes  34  from the right side along the width direction, and is connected thereto (see also  FIGS. 11B and 14 ). 
         [0100]    Thus, when the drum unit  13  is arranged at the accommodated position, each of the developing roller contacts  60 , the wire contacts  61 , the grid contacts  62  and the cleaning contacts  63  comes into contact with the corresponding one of the developing roller electrodes  35 , the wire electrodes  32 , the grid electrodes  33  and the cleaning electrodes  34  of the corresponding electrode groups  31  from the right side, and is connected thereto. 
         [0101]    In order to dismount the drum unit  13  located at the accommodated position from the main body casing  2 , the front cover  51  (see  FIG. 1 ) is swung to the open position to expose the drum unit  13  from the mounting port  52  of the main body casing  2  (see  FIG. 14 ), and the first handle  36  is grasped to draw the drum unit  13  frontward. 
         [0102]    Thus, the drum unit  13  having been located at the accommodated position is pulled obliquely upward on the front side as shown in  FIGS. 8 and 9 , through a procedure reverse to the aforementioned procedure of mounting the same. Then, each of the developing roller electrodes  35 , the wire electrodes  32 , the grid electrodes  33  and the cleaning electrodes  34  is displaced from the corresponding one of the developing roller contacts  60 , the wire contacts  61 , the grid contacts  62  and the cleaning contacts  63  obliquely upward on the front side, to be released from the connection with the corresponding contact. At this time, each of the wire contacts  61  and the cleaning contacts  63  is opposed to the middle right surface  23  from the right side at an interval, while each of the developing roller contacts  60  and the grid contacts  62  is in contact with the right side surface of the first rib  28  through the corresponding second rib  29  (see  FIGS. 7B and 10 ). 
         [0103]    Then, the drum unit  13  is drawn out frontward along the anteroposterior direction. Thus, each of the wire contacts  61  and the cleaning contacts  63  relatively moves rearward with respect to the drum unit  13  while keeping the state opposed to the middle right surface  23  from the right side at an interval (see  FIGS. 7B and 10 ). On the other hand, each of the developing roller contacts  60  and the grid contacts  62  also relatively moves rearward with respect to the drum unit  13 , and slides with respect to the right side surface of the first rib  28  while the same is kept at the constant width-directional position (see  FIGS. 7B and 10 ). 
         [0104]    When the drum unit  13  is drawn out until all developing roller contacts  60  and grid contacts  62  separate from the first rib  28 , the drum unit  13  is arranged at the drawn position (see  FIGS. 2 to 6 ). Thus, the drum unit  13  can be dismounted from the main body casing  2 . 
       Operation and Effect 
       [0105]    (1) As hereinabove described, the grid electrodes  33  and the developing roller electrodes  35  are provided on the middle right surface  23  while the wire electrodes  32  and the cleaning electrodes  34  are provided on the upper right surface  22  on the right side surface of the unit casing  14  in the drum unit  13  slidable between the accommodated position and the drawn position with respect to the accommodation chamber  50  of the main body casing  2  of the printer  1 . 
         [0106]    While the middle right surface  23  and the upper right surface  22  are opposed to the left surface  55  of the right wall  54  defining the accommodation chamber  50  in the main body casing  2  in the orthogonal direction (width direction) orthogonal to the sliding direction (anteroposterior direction) of the drum unit  13  and extend along the anteroposterior direction in parallel with each other, the upper right surface  22  protrudes toward the left surface  55  (rightward) beyond the middle right surface  23  (see  FIG. 7B ). 
         [0107]    On the other hand, the left surface  55  is provided with the upper left surface  69  extending along the anteroposterior direction and the lower left surface  70  protruding toward the drum unit  13  (leftward) beyond the upper left surface  69  (see  FIG. 7B ). The upper left surface  69  is provided with the wire contacts  61  and the cleaning contacts  63 , while the lower left surface  70  is provided with the grid contacts  62  and the developing roller contacts  60 . 
         [0108]    In this printer  1 , the wire contacts  61 , the cleaning contacts  63 , the grid contacts  62  and the developing roller contacts  60  can come into contact with and feed power to the corresponding ones of the wire electrodes  32 , the cleaning electrodes  34 , the grid electrodes  33  and the developing roller electrodes  35  respectively when the drum unit  13  is located at the accommodated position, as shown in  FIGS. 11A to 14 . 
         [0109]    When the drum unit  13  is located between the accommodated position and the drawn position, on the other hand, the wire contacts  61  and the cleaning contacts  63  are opposed to the grid electrodes  33  and the developing roller electrodes  35  at intervals in the width direction as viewed from the anteroposterior direction, while the grid contacts  62  and the developing roller contacts  60  are opposed to the lower right surface  24  of the drum unit  13  in the width direction, as shown in  FIGS. 7B and 10 . Thus, the wire electrodes  32 , the cleaning electrodes  34 , the grid electrodes  33  and the developing roller electrodes  35  can be prevented from unnecessary contact with the wire contacts  61 , the cleaning contacts  63 , the grid contacts  62  and the developing roller contacts  60  when the drum unit  13  is located between the accommodated position and the drawn position. 
         [0110]    The upper right surface  22  protrudes rightward beyond the middle right surface  23  in the drum unit  13 , whereby the grid electrodes  33  and the developing roller electrodes  35  provided on the middle right surface  23 , and, the wire electrodes  32  and the cleaning electrodes  34  provided on the upper right surface  22 , can be separated from one another in the width direction. Thus, the train X of the wire electrodes  32  and the cleaning electrodes  34 , and, the train Y of the grid electrodes  33  and the developing roller electrodes  35 , can be so arranged that the interval (vertical interval) therebetween is narrowed as viewed from the width direction while the trains X and Y are insulated from each other (the insulation distance is maintained), as shown in  FIGS. 4 and 6 . 
         [0111]    (2) When the drum unit  13  moves between the accommodated position and the drawn position, the lower right surface  24  (more strictly, the right side surface of the first rib  28  provided on the lower right surface  24 ) flatly formed in the width direction maintains the grid contacts  62  and the developing contacts  60 , slidably coming into contact with the lower right surface  24 , at the constant width-directional positions (see  FIGS. 7B and 10 ). When the drum unit  13  moves between the accommodated position and the drawn position, therefore, the grid contacts  62  and the developing roller contacts  60  can be prevented from inhibiting movement of the drum unit  13  by unexpectedly moving in the width direction and interfering with the drum unit  13 . 
       Second Embodiment 
       [0112]    While each subunit  15  can be separated into the first and second subunits  46  and  47  in the drum unit  13  according to the aforementioned embodiment as shown in  FIG. 1 , the first and second subunits  46  and  47  may alternatively be integrally formed. In this case, consumable parts such as the toner accommodated in the toner accommodation chamber  40  and the developing roller  5  in the first subunit  46  and the photosensitive drum  3  in the second subunit  47  can be simultaneously exchanged by exchanging the subunit  15 . 
         [0113]    While the above embodiment has been described with reference to the so-called direct transfer color laser printer  1  directly transferring the toner image from each photosensitive drum  3  to the sheet P, one or more aspects of the present invention is not restricted to this but may alternatively as apply to an intermediate transfer color laser printer temporarily transferring toner images of respective colors from the photosensitive drums  3  to an intermediate transfer body and thereafter collectively transferring the same to the sheet P. 
         [0114]    The embodiments described above are illustrative and explanatory of the invention. The foregoing disclosure is not intended to be precisely followed to limit the present invention. In light of the foregoing description, various modifications and alterations may be made by embodying the invention. The embodiments are selected and described for explaining the essentials and practical application schemes of the present invention which allow those skilled in the art to utilize the present invention in various embodiments and various alterations suitable for anticipated specific use. The scope of the present invention is to be defined by the appended claims and their equivalents.