Abstract:
An aspect of the present invention is an LED print head grounding structure including: an LED print head that emits exposure light; a conductive member that is adjacent to one end and another end of the LED print head; a conducting portion that puts the one end of the LED print head and one end of the conductive member into electric conduction; and a grounding portion that grounds the other end of the LED print head and another end of the conductive member.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2009-080186 filed Mar. 27, 2009. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an LED print head grounding structure and an image forming apparatus provided therewith. 
     2. Related Art 
     In the image forming apparatus provided with the LED print head, when the LED print head is grounded, it is necessary that ground terminals provided at both ends in a longitudinal direction of the LED print head be grounded while the electric conduction is established between the ground terminals and a main frame configuring the image forming apparatus. 
     SUMMARY 
     In accordance with an aspect of the invention, an LED print head grounding structure includes: an LED print head that emits exposure light; a conductive member that is adjacent to one end and another end of the LED print head; a conducting portion that puts the one end of the LED print head and one end of the conductive member into electric conduction (electrically connects the one end of the LED print head and one end of the conductive member); and a grounding portion that grounds the other end of the LED print head and another end of the conductive member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will be described in detail with reference to the following figures, wherein: 
         FIG. 1  is a front view schematically illustrating an image forming apparatus according to an exemplary embodiment of the invention; 
         FIG. 2  is a perspective view illustrating an arrangement of a toner cartridge in the image forming apparatus of the exemplary embodiment; 
         FIG. 3  is a partially enlarged perspective view explaining attachment and detachment of the toner cartridge in the image forming apparatus of the exemplary embodiment; 
         FIG. 4  is a development perspective view illustrating an image forming unit in the image forming apparatus of the exemplary embodiment; 
         FIG. 5  is a perspective view illustrating the image forming unit in the image forming apparatus of the exemplary embodiment; 
         FIG. 6  is a partially enlarged view of the image forming unit of  FIG. 5 ; 
         FIG. 7  is a front view illustrating a configuration of the image forming unit in the image forming apparatus of the exemplary embodiment; 
         FIG. 8  is a development perspective view explaining an assembly configuration of the image forming unit in the image forming apparatus of the exemplary embodiment; 
         FIG. 9  is a perspective view explaining an assembly configuration of the image forming unit in the image forming apparatus of the exemplary embodiment; 
         FIG. 10  is a side view illustrating a mounting mechanism of the toner cartridge in the image forming apparatus of the exemplary embodiment; 
         FIG. 11  is a side view illustrating the mounting mechanism of the toner cartridge in the image forming apparatus of the exemplary embodiment; 
         FIG. 12  is an explanatory view illustrating a configuration of electric conduction and ground of an LED print head in the image forming apparatus of the exemplary embodiment; 
         FIG. 13  is a front sectional view illustrating the imaging unit in the image forming apparatus of the exemplary embodiment; 
         FIG. 14  is a partially enlarged perspective view illustrating the image forming apparatus of the exemplary embodiment; 
         FIG. 15  is an explanatory view illustrating a configuration of electric conduction and ground of an LED print head in an image forming apparatus according to a modification of the invention; 
         FIG. 16  is a partially enlarged perspective view illustrating the image forming apparatus of the exemplary embodiment; 
         FIG. 17  is a development perspective view illustrating a photosensitive unit constituting the image forming apparatus of the exemplary embodiment; 
         FIG. 18  is a perspective view illustrating the photosensitive unit constituting the image forming apparatus of the exemplary embodiment; 
         FIG. 19  is a perspective view illustrating the LED print head constituting the image forming apparatus of the exemplary embodiment; and 
         FIG. 20  is an explanatory view illustrating a process for producing the image forming apparatus of the exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the invention will be described below. 
     (Entire Configuration) 
       FIG. 1  illustrates a printer  10  that is of an image forming apparatus. The printer  10  is a digital printer that forms a color image or a monochrome image. An image processing device (not illustrated in the drawings) is provided inside the printer  10 . The image processing device performs image processing to image data transmitted from a personal computer or the like. 
     As illustrated in  FIGS. 2 and 3 , toner cartridges  11 Y,  11 M,  11 C, and  11 K are attached to a side part inside the printer  10 . Yellow (Y) toner, magenta (M) toner, cyan (C) toner, and black (K) toner are respectively stored in the toner cartridges  11 Y,  11 M,  11 C, and  11 K. Cartridge accommodating portions  8 Y,  8 M,  8 C, and  8 K are formed, in the side part inside the printer  10 , according to dimensions of the toner cartridges  11 Y,  11 M,  11 C, and  11 K. The toner cartridges  11 Y,  11 M,  11 C, and  11 K are detachably accommodated in the cartridge accommodating portions  8 Y,  8 M,  8 C, and  8 K. Therefore, the toner cartridges  11 Y,  11 M,  11 C, and  11  are exchangeably (detachably) provided in a printer main body  10 J. In the following description, members corresponding to the yellow, magenta, cyan, and black colors are distinguished from one another by adding suffixes Y, M, C, and K. 
     As illustrated in  FIGS. 1 ,  4 ,  5 , and  7 , four image forming units  12 Y,  12 M,  12 C, and  12 K corresponding to Y, M, C, and K developers are arranged in the center of inside the printer  10 . The developer is such that non-magnetic toner and a magnetic carrier are mixed together. 
     A transfer unit  14  is provided above the image forming units  12 Y,  12 M,  12 C, and  12 K. An imaging unit (image formation unit)  15  includes the image forming units  12 Y,  12 M,  12 C, and  12 K and the transfer unit  14 . 
     The transfer unit  14  includes an intermediate transfer belt  16 , first transfer rollers  18 Y,  18 M,  18 C, and  18 K, and a second transfer roller  20 . The intermediate transfer belt  16  is an example of an intermediate transfer member. The first transfer rollers  18 Y,  18 M,  18 C, and  18 K that are of four first transfer members are arranged inside the intermediate transfer belt  16  to multiply transfer toner images of the image forming units  12 Y,  12 M,  12 C, and  12 K to the intermediate transfer belt  16 . The second transfer roller  20  transfers the toner images superimposed on the intermediate transfer belt  16  to a recording sheet P. 
     The intermediate transfer belt  16  is entrained around a driving roller  26  and a tension roller  22  with a constant tension, and the intermediate transfer belt  16  is circularly driven in a direction (counterclockwise) of an arrow X of  FIG. 1 . The driving roller  26  is driven by a motor (not illustrated in the drawings) and is disposed to face the second transfer roller  20 . 
     The first transfer rollers  18 Y,  18 M,  18 C, and  18 K are disposed to face photosensitive members  28  which will be described later ( 28 Y,  28 M,  28 C, and  28 K) of the image forming units  12 Y,  12 M,  12 C, and  12 K respectively with sandwiching the intermediate transfer belt  16  therebetween. 
     A transfer bias voltage having a polarity (for example, positive polarity in the exemplary embodiment) which is opposite a toner polarity is applied to the first transfer rollers  18 Y,  18 M,  18 C,  18 K. A transfer bias voltage having the polarity opposite the toner polarity is also applied to the second transfer roller  20 . 
     At an outer circumferential surface of the intermediate transfer belt  16  in a position where the tension roller  22  is provided, a cleaning device  30  is provided. The cleaning device  30  includes a cleaning brush  32  and a cleaning blade  34  to remove residual toner or sheet dust on the intermediate transfer belt  16  by the cleaning brush  32  and the cleaning blade  34 . 
     In the printer  10 , a control unit  36  that controls driving of each portion of the printer  10  is provided near a side face on the side opposite a path for transporting the recording sheet P. 
     A sheet feeding cassette  46  in which the recording sheets P are stored is disposed below the image forming unit  12 . A sheet transporting passage  50  through which the recording sheet P is transported is provided upwardly from an end part of the sheet feeding cassette  46  in the vertical direction. 
     A sheet feeding roller  48 , a pair of sheet separating and transporting rollers  52 , and sheet leading-end registration rollers  54  are provided in the sheet transporting passage  50 . The sheet feeding roller  48  delivers the recording sheet P from the sheet feeding cassette  46 . The pair of sheet separating and transporting rollers  52  feeds the recording sheet P one by one. The sheet leading-end registration rollers  54  matches arrival of the image on the intermediate transfer belt  16  and arrival of the recording sheet P such that the image is transferred to the recording sheet. The sheet feeding roller  48  sequentially delivers the recording sheet P from the sheet feeding cassette  46 , and the recording sheet P is tentatively transported to a second transfer position of the intermediate transfer belt  16  by the sheet leading-end registration roller  54 , which intermittently rotates, through the sheet transporting passage  50 . 
     A fixing device  60  is provided above the second transfer roller  20 . The fixing device  60  includes a heating roller  62  which is heated and a pressurizing roller  64  which is pressed against the heating roller  62 . The recording sheet P to which the color toner images are transferred by the second transfer roller  20  is fixed in a press-contact portion between the heating roller  62  and the pressurizing roller  64  by the heat and pressure. Then a sheet discharge rollers  66  discharge the recording sheet P onto a discharge portion  68  which is disposed at an upper portion of the printer  10 . The sheet discharge rollers  66  are of an example of a discharge device provided on the downstream side in the transporting direction of the recording sheet P. The cleaning device  30  removes the residual toner and sheet dust from the surface of the intermediate transfer belt  16  after the toner image second transfer process is performed. 
     (Image Forming Unit) 
     The image forming unit will be described below. The image forming unit  12 M will be described by way of example. Because the other image forming units  12 Y,  12 C, and  12 K corresponding to the respective colors have the same configurations as the image forming unit  12 M, so the description is omitted. The suffix M is omitted in the components of the image forming unit  12 M. 
     As illustrated in  FIGS. 1 and 4  to  9 , the image forming unit  12  includes a photosensitive unit  23  and a development unit  70  provided below the photosensitive unit  23 . 
     A photosensitive member  28  which is driven to rotate in a direction (clockwise) of an arrow A is provided in the photosensitive unit  23 . A charging roller  72 , an LED print head  73 , an erase lamp  74 , and a cleaning portion  76  are provided around the photosensitive member  28 . The charging roller  72  that is of an example of a charging device evenly charges the photosensitive member  28  while being in contact with the surface of the photosensitive member  28 . The LED print head  73  irradiates the surface of the photosensitive member  28  with exposure light. The erase lamp  74  that is of an example of an erasing-charge device irradiates the surface of the photosensitive member  28  with light to erase charge after the transfer. The cleaning portion  76  cleans the surface of the photosensitive member  28  after the erasing of charge. 
     The charging roller  72 , the LED print head  73 , the development unit  70 , the erase lamp  74 , and the cleaning portion  76  are disposed in this order from the upstream side toward the downstream side in the rotating direction of the photosensitive member  28  while facing the surface of the photosensitive member  28 . 
     In the outer circumferential surface of the charging roller  72 , a cleaning roller  79  is rotatably provided at a side opposite the photosensitive member  28  to remove the toner and the like adhering to the surface of the charging roller  72 . The charging roller  72  is connected to an energizing portion (not illustrated in the drawings), and energized when forming of the image, thereby charging the surface of the photosensitive member  28 . 
     The development unit  70  develops an electrostatic latent image formed on the photosensitive member  28  by the exposure light with the corresponding color developer (toner). The development unit  70  includes a development chamber  82  and a stirring and conveying chamber  84 . The stirring and conveying chamber  84  is provided below the development chamber  82  and stirs (mixes) the developer supplied from the toner cartridge  11  to convey the developer to the development chamber  82 . 
     As illustrated in  FIG. 7 , in the stirring and conveying chamber  84 , it is partitioned into two stirring passages, that is, a first stirring passage  84 A and a second stirring passage  84 B by a partition wall  93  vertically provided from a bottom surface. An opened first connection port (not illustrated in the drawings) and an opened second connection port (not illustrated in the drawings) are formed at positions of both ends of the partition wall  93 , and the first stirring passage  84 A and the second stirring passage  84 B are communicated with each other by the first connection port and the second connection port. A top surface of the second stirring passage  84 B is opened and communicated with the development chamber  82 . 
     A projection  90  (see  FIGS. 10 and 11 ) is formed at one end of the first stirring passage  84 A so as to be projected outward further than an end face of the second stirring passage  84 B. An opening through which the toner is supplied from the toner cartridge  11  is formed in a top surface of the projection  90 . 
     A first stirring and conveying member  91  is disposed in the first stirring passage  84 A. Similarly, a second stirring and conveying member  92  is disposed in the second stirring passage  84 B. 
     The first and second stirring and conveying members  91  and  92  are driven by a driving unit including a motor (not illustrated in the drawings) and a gear (not illustrated in the drawings). By the rotation of the first stirring and conveying member  91  in a direction of an arrow C and the rotation of the second stirring and conveying member  92  in a direction of an arrow D (the directions of the arrows C and D differ from each other), the developer in the stirring and conveying chamber  84  is mixed with the supplied toner, conveyed in the first stirring passage  84 A and second stirring passage  84 B while stirred and mixed, and circulated between the first stirring passage  84 A and the second stirring passage  84 B. 
     As illustrated in  FIG. 7 , the development chamber  82  is communicated with the second stirring passage  84 B. A development roller  78  is provided in the development chamber  82 , and the development roller  78  is rotated in the direction (counterclockwise) of the arrow B about a longitudinal direction of the photosensitive member  28  as an axis direction. A thin-layer forming roller  97  that is of a layer regulating member is also provided in the development chamber  82 . Alignment portions  78 G are formed at both ends of the development roller  78 . The Alignment portions  78 G abut on the surface (circumferential surface) of the photosensitive member  28  to align the photosensitive member  28  and the development roller  78  (that is, to set a gap therebetween). 
     The thin-layer forming roller  97  is disposed on the upstream side of the photosensitive member  28  in the rotating direction of the development roller  78  while having a gap with the outer circumferential surface of the development roller  78 . The thin-layer forming roller  97  regulates (controls) an amount of developer passing on the development roller  78  to form a developer layer (thin layer) having a predetermined thickness on the development roller  78 . 
     The development roller  78  is disposed to face the outer circumferential surface of the photosensitive member  28  with an opening (not illustrated in the drawings) formed in the development chamber  82  therebetween. The development roller  78  is configured to include a magnet roller  78 B and a development sleeve  78 A. The magnet roller  78 B that is of a magnetic-field generating portion is fixed to the development chamber  82 . The development sleeve  78 A that is of a cylindrical rotating body is formed into a hollow cylindrical shape, and the development sleeve  78 A is provided rotatably around the outer portion of the magnet roller  78 B. A bias voltage is applied between the development roller  78  and the photosensitive member  28  to form an electric field, thereby moving the toner in the developer toward the latent image on the photosensitive member  28  during the development. 
     (Structure of Imaging Unit) 
     A housing structure of the imaging unit  15  will mainly be described. In the following description, in a case where it is easer to explain of the housing structure by adding of suffixes Y, M, C, and K, the suffixes are added, and in a case where it is not necessary to add the suffixes when explaining, the suffixes are omitted. 
     As described above, the imaging unit  15  is configured to include the image forming unit  12  and the transfer unit  14  located above the image forming unit  12  (see  FIGS. 4 and 5 ). A housing of the image forming unit  12  is configured to include a lower housing (a development housing)  102  constituting the development unit  70  and an intermediate housing (a photosensitive body and LED print head housing)  104  constituting the photosensitive unit  23 . A housing of the imaging unit  15  is configured to include an upper housing (a transfer housing)  106  constituting the transfer unit  14 , the intermediate housings  104 Y,  104 M,  104 C, and  104 K, and lower housings  102 Y,  102 M,  102 C, and  102 K. The photosensitive members  28 Y,  28 M,  28 C, and  28 K are positioned (aligned) with the intermediate housings  104 Y,  104 M,  104 C, and  104 K, respectively. The upper housing  106 , the intermediate housings  104 Y,  104 M,  104 C, and  104 K, and the lower housings  102 Y,  102 M,  102 C, and  102 K are made of a non-conductive material (resin). 
     The upper housing  106  includes a front surface portion  110  and a rear surface portion  112 . The front surface portion  110  and rear surface portion  112  are formed on both end sides in a width direction of the intermediate transfer belt  16 . Through holes  116 Y,  116 M,  116 C, and  116 K are formed in the front surface portion  110 . Support shafts  29 Y,  29 M,  29 C, and  29 K of the photosensitive members  28 Y,  28 M,  28 C, and  28 K in the image forming units  12 Y,  12 M,  12 C, and  12 K pierce the through holes  116 Y,  116 M,  116 C, and  116 K. 
     A high-voltage power supply board  200  is provided on the top of the upper housing  106  to supply the bias voltage to the development units  70 Y,  70 M,  70 C, and  70 K. A power feeding wire  118 YMC and a power feeding wire  118 K are provided in the front surface portion  110  of the upper housing  106 . The power feeding wire  118 YMC is electrically connected to the high-voltage power supply board  200  to feed the electric power to each of the development units  70 Y,  70 M, and  70 C. The power feeding wire  118 K is electrically connected to the high-voltage power supply board  200  to feed the electric power to the development unit  70 K. Conduction plates  120 Y,  120 M,  120 C, and  120 K are disposed in the front surface portion  110 . The conduction plates  120 Y,  120 M,  120 C, and  120 K are respectively extended downward from upper positions of the development units  70 Y,  70 M,  70 C, and  70 K. The conduction plates  120 Y,  120 M, and  120 C are electrically connected to the power feeding wire  118 YMC, and the conduction plate  120 K is electrically connected to the power feeding wire  118 K. 
     Hook portions  122 Y,  122 M,  122 C, and  122 K (also see  FIG. 14 ) are formed in lower end positions of the conduction plates  120 Y,  120 M,  120 C, and  120 K. Helical tension springs  124 Y,  124 M,  124 C, and  124 K are provided in the imaging unit  15 . The helical tension springs  124 Y,  124 M,  124 C, and  124 K are latched in the ends of the support shafts  77 Y,  77 M,  77 C, and  77 K of the development rollers  78 Y,  78 M,  78 C, and  78 K and the hook portions  122 Y,  122 M,  122 C, and  122 K. 
     When the upper ends of the helical tension springs  124 Y,  124 M,  124 C, and  124 K are latched in the hook portions  122 Y,  122 M,  122 C, and  122 K, the transfer unit  14 , the photosensitive unit  23 , and the development unit  70  are assembled to form the imaging unit  15 . Further, the lower ends of the conduction plates  120 Y,  120 M,  120 C, and  120 K and the upper ends of the helical tension springs  124 Y,  124 M,  124 C, and  124 K are put into electric conduction, whereby the helical tension spring  124  forms a power feeding path. 
     In  FIGS. 14 and 15 , the hook portions  122 Y,  122 M,  122 C, and  122 K and the helical tension springs  124 Y,  124 M,  124 C, and  124 K are provided on the front surface side of the imaging unit  15 . However, the hook portions  122 Y,  122 M,  122 C, and  122 K and the helical tension springs  124 Y,  124 M,  124 C, and  124 K are also provided on the rear surface side of the imaging unit  15 . 
     As illustrated in  FIGS. 8 and 9 , the support shaft  77  of the development roller  78  has a conductive property, and both ends of the support shaft  77  are each supported by a round hole  131  of a development roller support plate  130  constituting the development unit  70 . The development roller  78  and the hook  122  receive a tensile force (urging force) while being coupled by the helical tension spring  124 , thereby aligning respectively the development rollers  78 Y,  78 M,  78 C, and  78 K of the image forming units  12 Y,  12 M,  12 C, and  12 K with respect to the imaging unit  15 . 
     A temporarily-jointing latch structure  132  is formed by the development roller support plates  130  and the intermediate housing  104 . That is, a latching opening  134  is formed in the intermediate housing  104 , and an overhang plate  136  is formed in the development roller support plate  130 . The overhang plate  136  is latched in the opening  134 . The overhang plate  136  includes an overhang upper part  138  and an overhang lower part  140 . The overhang upper part  138  is gradually overhung toward the outside in the longitudinal direction of the support shaft of the development roller  78  from a top portion to a bottom portion. The overhang lower part  140  is continuously connected to the lower end of the overhang upper part  138  and extended downward from a position inside the overhang upper part  138  in the longitudinal direction of the support shaft. Accordingly, a step  142  is formed at a boundary between the overhang upper part  138  and the overhang lower part  140 . Coupling shafts  105  ( 105 R and  105 L) are provided at both ends in the longitudinal direction in the intermediate housing  104 . Coupling holes  108  ( 108 R and  108 L) are formed at both ends in the longitudinal direction in the lower housing  102 . The coupling shafts  105  are fitted in the coupling holes  108 . 
     (LED Print head and Grounding Structure thereof) 
     The LED print head  73  and the grounding (grounding) structure of the LED print head  73  will be described below. As illustrated in  FIGS. 12 to 19 , in the image forming unit  12 , the LED print head  73  (hereinafter referred to as LPH  73 ) is provided in parallel with the photosensitive member  28 . LPH  73  is supported by the intermediate housing  104 . 
     As illustrated in  FIG. 19 , the LPH  73  has a long and narrow shape, a ground terminal  146 L is provided in one longitudinal end portion  144 L of a board  144  of the LPH  73 , and a ground terminal  146 R is provided in another longitudinal end portion  144 R of the board  144 . The one longitudinal end portion  144 L is adjacent to one end (support-shaft one end portion  29 L which will be described later) of the support shaft  29 , and the other longitudinal end portion  144 R is adjacent to another end (support-shaft another end portion  29 R which will be described later) of the support shaft  29  (see  FIG. 12  and the like). 
     A support portion  150  is formed in the intermediate housing  104  to rotatably support the support shaft  29  (an example of a long member) of the photosensitive member  28  (see  FIGS. 12 and 14 ). At one end side of the support shaft  29 , a through hole  151  is formed in the support portion  150 , and the support shaft  29  pierces the through hole  151 . An insertion hole  107 L is formed in the upper housing  106 , and the support-shaft one end portion  29 L projected from the through hole  151  is inserted in the insertion hole  107 L. Accordingly, the support-shaft one end portion  29 L is projected toward the outside of the upper housing  106 . 
     As illustrated in  FIGS. 12 and 14 , in the imaging unit  15 , a plate spring member  156 L is provided as a connection terminal ngrounde support-shaft one end portion  29 L, and the plate spring member  156 L has a substantial L-shape as viewed from the front. A one end portion  157 E of the plate spring member  156 L has a shape such that it presses the ground terminal  146 L while abutting on the ground terminal  146 L. Another end portion  157 F of the plate spring member  156 L is extended to the neighborhood of the support-shaft one end portion  29 L of the photosensitive member  28  and exposed to the outside of the intermediate housing  104 . 
     A conduction portion  158  is provided in the imaging unit  15  to establish the conduction state between the support-shaft one end portion  29 L of the photosensitive member  28  and the other end portion  157 F of the plate spring member  156 L. As illustrated in  FIGS. 12 to 14 , the conduction portion  158  is configured to be a plate spring member  160  having a substantial U-shape. At this point, for example, the plate spring member  160  is shaped such that one end portion  160 E abuts on the support-shaft one end portion  29 L of the photosensitive member  28  so as to press the support-shaft one end portion  29 L from the axial direction, and another end portion  160 F abuts on the other end portion  157 F of the plate spring member  156 L so as to press the other end portion  157 F. The plate spring member  160  is engaged in the upper housing  106  by a bolt  162  between the one end portion  160 E and the other end portion  160 F. 
     As illustrated in  FIG. 15 , the conduction portion  158  may be configured to include a conductive helical compression spring  170 , a conductive helical compression spring  172 , a conduction member  173 , and a cap member  174 . The helical compression spring  170  urges the other end portion  157 F while abutting on the other end portion  157 F that is the upper end portion of the plate spring member  156 L. The helical compression spring  172  urges the support-shaft one end portion  29 L while abutting on the support-shaft one end portion  29 L from the axial direction. The conduction member  173  is connected to the helical compression springs  170  and  172  to put the helical compression springs  170  and  172  into electric conduction. The cap member  174  presses an end portion of the helical compression spring  172  on the side opposite from the support shaft  29  and an end portion of the helical compression spring  170  on the side opposite from the plate spring member  156 L. 
     Irrespective of the configuration of the conduction portion  158 , the support-shaft one end portion  29 L of the photosensitive member  28  and the ground terminal  146 L provided in the longitudinal one end portion  144 L of the board  144  of LPH  73  are put into electric conduction by the conduction portion  158 . 
     As illustrated in  FIGS. 12 and 16 , the through hole  151  is formed in the support portion  150  on the other end side of the support shaft  29  of the photosensitive member  28 , and the support shaft  29  pierces the through hole  151 . An insertion hole  107 R is formed in the upper housing  106 , and the support-shaft other end portion  29 R projected from the through hole  151  is inserted in the insertion hole  107 R. Accordingly, the support-shaft other end portion  29 R is projected toward the outside of the upper housing  106 . A gear  180  which the torque is transmitted is provided on the other end side of the support shaft  29 . 
     In the imaging unit  15 , a plate spring member  156 R is provided as a connection terminal ngrounde support-shaft other end portion  29 R, and the plate spring member  156 R has a substantial L-shape as viewed from the front. One end portion  187 E of the plate spring member  156 R is shaped so as to press the ground terminal  146 R while abutting on the ground terminal  146 R. An end portion  187 F of the plate spring member  156 R is shaped so as to extend to the neighborhood of the support-shaft other end portion  29 R of the photosensitive member  28  and be exposed to the outside of the intermediate housing  104 . 
     In the plate spring member  156 R, an engage portion  188  which is engaged in the LPH  73  is formed in the center of the plate spring member along the longitudinal direction of the LPH  73 . The end portion of the LPH  73  is pressed against an inner wall of the intermediate housing  104  and aligned such that it is sandwiched between the latch portion  188  of the plate spring member  156 R and the other end portion  187 F of the plate spring member  156 R. 
     As illustrated in  FIG. 16 , a wire-spring shape spring ground  190  and a plate ground  192  are provided in the imaging unit  15 . The spring ground  190  urges the support-shaft other end portion  29 R so as to press the support-shaft other end portion  29 R from the axial direction. An upper end portion of the plate ground  192  is connected to the spring ground  190 . The plate ground  192  is formed into a plate-spring shape, and the plate ground  192  includes a bent portion  194  that abuts on the other end portion  187 F of the plate spring member  156 R to press the other end portion  187 F. The spring ground  190  is connected to an apparatus ground (not illustrated in the drawings) which is general of the printer  10 . 
     Accordingly, in the exemplary embodiment, not only the ground terminal  146 L provided in the longitudinal one end portion  144 L of the LPH  73  but also the ground terminal  146 R provided in the longitudinal other end portion  144 R of the LPH  73  are grounded. 
     In  FIGS. 12 and 17 , although the horizontal positions (left and right) of the ground terminals  146 L and  146 R took inverted, this is generated by a difference in illustrated angle, so that it is not conflicted. 
     An image forming process of the printer  10  will be described below. 
     As illustrated in  FIG. 1 , the image data to which the image processing device (not illustrated in the drawings) performs the image processing is converted into pieces of gradation data of yellow (Y), magenta (M), cyan (C), and black (K) colors. The exposure light is emitted according to each gradation data to perform scanning exposure to each photosensitive member  28 , thereby forming the electrostatic latent images. 
     As illustrated in  FIG. 1 , the development unit  70  develops the electrostatic latent image formed on the photosensitive member  28 , and each electrostatic latent image is visualized as the yellow (Y), magenta (M), cyan (C), and black (K) toner images (developer images). The respective toner images sequentially formed on the photosensitive members  28  of the image forming units  12 Y,  12 M,  12 C, and  12 K are multiply transferred onto the intermediate transfer belt  16  by the four first transfer rollers  18 Y,  18 M,  18 C, and  18 K. 
     The yellow (Y), magenta (M), cyan (C), and black (K) toner images multiply transferred onto the intermediate transfer belt  16  are second transferred onto the transported recording sheet P by the second transfer roller  20 . The fixing device  60  fixes the yellow (Y), magenta (M), cyan (C), and black (K) toner images onto the recording sheet P, and the recording sheet P is discharged to the discharge tray  68 . 
     After the toner image transfer process, the cleaning portion  76  removes the residual toner and sheet dust from the surface of the photosensitive member  28 . The cleaning device  30  removes the residual toner and sheet dust from the surface of the intermediate transfer belt  16 . 
     An operation and effect of the exemplary embodiment will be described below. 
     In manufacturing the imaging unit  15 , lifetimes of main components such as the photosensitive members  28 Y,  28 M,  28 C, and  28 K and the development units  70 Y,  70 M,  70 C,  70 K are substantially matched with a lifetime of the main body of the printer  10  such that periodic component replacement is eliminated. For example, specifications are determined such that the main components and image forming apparatus main body reach the lifetimes (run down) when printing is performed with 50000 sheets. It is configured that components are replaceable on the assumption that the component needs to be non-periodic repaired (for example, in a case where the component is mistakenly damaged). 
     The imaging unit  15  is assembled in a procedure of  FIG. 20  using the components whose specifications are determined in the above-described manner. That is, the photosensitive unit  23  except for the support shaft  29  of the photosensitive member  28  and the development unit  70  are coupled by the coupling shaft  105  (that is,  105 R and  105 L) and the coupling hole  108  (that is,  108 R and  108 L) and thereafter, tentatively jointed by using the latch structure  132 . The transfer unit  14  is assembled in the image forming unit  12  from above, the support shaft  29  of the photosensitive member  28  is inserted in the photosensitive member  28 , the through holes  151  of the intermediate housing  104 , and the through holes  116  of the upper housing  106 . After the imaging unit  15  is assembled, it is assembled to a sheet feeding unit. 
     In assembling the imaging unit  15 , the helical tension springs  124 Y,  124 M,  124 C, and  124 K are latched in the support shafts  77 Y,  77 M,  77 C, and  77 K of the development rollers  78 Y,  78 M,  78 C, and  78 K and the hooks  122 Y,  122 M,  122 C, and  122 K. As a result, the imaging unit  15  in which the photosensitive unit  23  is sandwiched between the development unit  70  and the transfer unit  14  by the urging force of the helical tension springs  124  is formed, further, the development rollers  78 Y,  78 M,  78 C, and  78 K are aligned with respect to the photosensitive members  28 Y,  28 M,  28 C, and  28 K at the same time as the development units  70 Y,  70 M,  70 C, and  70 K are retained by the upper housing  106 . Accordingly, the imaging unit  15  having the extremely good assembly productivity and the simple structure are assembled. The apparatus structure is simplified because the helical tension spring  124  is used as an elastic body. 
     The support shaft  29  of each of the photosensitive members pierces the upper housing  106 . Therefore, positional accuracy between the photosensitive members  28  and the upper housing  106  is maintained in the good state to improve pitch accuracy between the photosensitive members. 
     The helical tension spring  124  urges the development unit  70  toward the transfer unit  14 , whereby the development roller  78  is rotatably supported by the intermediate housing  104  supporting the photosensitive member  28 . Accordingly, relative positional relationship between the photosensitive member  28  and the development roller  78  is determined with high accuracy. 
     The helical compression spring  124  puts the conductive plate  210  and the support shaft  77  of the development roller  78  into electric conduction. Therefore, because the helical compression spring  124  forms the power feeding path, it is not necessary to additionally provide a power feeding member. 
     When assembling the imaging unit  15 , the conduction portion  158  is fixed to the upper housing  106  by the bolt  162 , and the longitudinal other end portion  144 R of the board  144  of the LPH  73  is grounded to the apparatus ground through the plate spring member  156 R, the plate ground  192 , and the spring ground  190 . The longitudinal one end portion  144 L of the board  144  of the LPH  73  and the support shaft  29  of the photosensitive member  28  are put into electric conduction by the conduction portion  158 , and the spring ground  190  abuts on the support-shaft other end portion  29 R of the photosensitive member  28 . Therefore, the longitudinal one end portion  144 L of the board  144  of the LPH  73  is also grounded. Accordingly, both the longitudinal end portions of the board  144  of the LPH  73  can be grounded without drawing the long ground wire. 
     The longitudinal one end portion  144 L of the board  144  of the LPH  73  is grounded such that the longitudinal one end portion  144 L and the support shaft  29  of the photosensitive member  28 , which is the long member located closest to the longitudinal one end portion  144 L of the board  144  of the LPH  73 , are put into electric conduction by the conduction portion  158 . Accordingly, both the longitudinal end portions of the board  144  of the LPH  73  have the simple ground structures. 
     Even if the intermediate housing  104  retaining the LPH  73  is made of an insulating material such as resin, the board  144  of the LPH  73  is easily grounded. 
     The plate spring member  156 R urges the LPH  73  toward the longitudinal other end portion  144 R of the LPH  73 , and the longitudinal other end portion  144 R of the LPH  73  abuts on the inner wall of the intermediate housing  104 . Accordingly, the LPH  73  in the longitudinal direction is aligned with respect to the intermediate housing  104  by the urging force of the plate spring member  156 R. 
     The conduction portion  158  is fixed to the upper housing  106  by the bolt  162 , the plate spring member  160  (or the helical compression spring  170 ) urges (presses) the support shaft  29  of the photosensitive member  28  toward the support-shaft other end portion  29 R, and the plate spring member  160  (or the helical compression spring  172 ) urges (presses) the intermediate housing  104  toward the longitudinal other end portion  144 R of the LPH  73  via the plate spring member  156 L. Therefore, the position of the intermediate housing  104  in the longitudinal direction (the position of the LPH in the longitudinal direction or the position of the photosensitive body in the longitudinal direction) is aligned with respect to the upper housing  106 . That is, LPH  73  in the longitudinal direction is aligned with respect to the intermediate housing  104 , and the intermediate housing  104  in the longitudinal direction is aligned with respect to the upper housing  106 , thereby aligning the LPH  73  in the longitudinal direction with respect to the upper housing  106 . Each of four LPHs is aligned with the single upper housing, and the relative position therebetween in the longitudinal direction is substantially kept constant. Therefore, the color images are hardly deviated from one another, and the assembly productivity of the imaging unit  15  is improved. 
     The alignment and grounding are simultaneously performed only by assembling the conduction portion  158  in the imaging unit  15 , so that the assembly productivity of the imaging unit  15  is improved. 
     The reliability is enhanced from the viewpoint of strength when the conduction portion  158  is configured to include the helical compression springs  170  and  172  and the cap member  174 . 
     In the exemplary embodiment, the longitudinal one end portion  144 L of the board  144  of the LPH  73  and the support-shaft one end portion  29 L of the photosensitive member  28  are put into electric conduction by the conduction portion  158 , and the support-shaft other end portion  29 R of the photosensitive member  28  is grounded, thereby the both the longitudinal end portions of LPH  73  are grounded. Alternatively, a conductive long member is provided for reinforcement or the like, and the LPH  73  may be grounded using the long member. That is, the long member is provided in parallel with the LPH  73 , the longitudinal one end portion  144 L of the board  144  of the LPH  73  and the longitudinal end portion of the long member are put into electric conduction, and the longitudinal other end portion of the long member is grounded. In such a configuration, the similar operation and effect are obtained. 
     Although the exemplary embodiment of the invention is described above, the exemplary embodiment is only by way of example, and various modifications can be made without departing from the scope of the invention. Obviously the scope of the invention is not limited to the exemplary embodiment.