Abstract:
The image forming apparatus of the present invention has: an image carrier to retain electrostatic latent images on its surface; a developing unit holding plural developing devices that can be exchanged by a rotatable revolver and supported rotatably by the main body of the image forming apparatus; a stepping motor that rotates the developing unit and moves a desired developing device to a developing position opposing to the image carrier; a locking mechanism that is capable of moving the revolver to the free unlocking position and the locking position to engage with the revolver for stopping the developing devices at the positions to exchange them; and an backstop gear that is movable to a first free position from the revolver and to a second position to engage with the revolver for preventing the developing unit to move in the direction reverse to the rotating direction by the stepping motor; and a backstop gear that moves to the second position when the stepping motor is shut off.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to image forming apparatuses such as electro-photographic apparatuses, printers and the like, and an image forming apparatus to get color developed images using a rotary type developing unit.  
           [0003]    2. Description of the Related Art  
           [0004]    In image forming apparatuses to get color images according to an electro-photographic system such as color copiers, printers and the like, for achieving the downsizing, an apparatus is developed, which forms latent images corresponding to yellow (Y), magenta (M), cyan (C) and black (BK) on a photosensitive drum by rotating the drum plural times and supplies toners in different colors to the drum from plural developing devices, visualizes the formed color images and obtains a full-color image by superposing the visualized toner images on a photosensitive drum or an intermediate transferring substance.  
           [0005]    Further, a revolver type developing unit is developed to supply toners in different colors to latent images formed on a photosensitive drum when the drum is rotated. This revolver type developing unit is equipped with 3 developing devices containing yellow (Y), magenta (M) and cyan (C) toners and further, a developing device for black (BK) toner added.  
           [0006]    For this revolver type developing unit, there are two methods available for removing developing devices from a revolver during the maintenance including a periodic inspection; one method is to pull out developing devices in the longitudinal direction from the opening of the front frame of the main body of an image forming apparatus after rotating the developing unit to a prescribed position and the other method is to take out developing devices in the direction vertical to the shaft of a revolver from the side frame of the main body of an image forming apparatus after rotating a developing unit to a prescribed position.  
           [0007]    In both methods, it is necessary to prevent a developing unit from rotating in the reverse direction for a malfunction when a developing unit is unbalanced when removing developing devices from a revolver. In Japanese Patent Application No. 11-316479, a device is disclosed to prevent the rotation of a developing unit in the reverse direction. This device prevents the rotation of a developing unit that is positioned using a stepping motor by engaging a plunger into a notch or prevents the reverse rotation of a developing unit by providing a one-way clutch to a central shaft of a developing unit. Thus, the reverse rotation of a developing unit when removing developing devices is prevented.  
           [0008]    However, in the above-mentioned conventional image forming apparatus, developing devices are removed by stopping a developing unit in the state with voltage or current applied to a stepping motor for driving the developing unit. Therefore, for example, even when a developing unit is blocked to rotate by a plunger or a one-way clutch, there is still the possibility for generating abnormal rotation for a malfunction of a stepping motor.  
           [0009]    Furthermore, the above-mentioned conventional image forming apparatus is in such a structure that a one-way clutch is installed to the central shaft of a developing unit and the one-way clutch is easily worn by the rotation of a developing unit, the clutch accuracy drops for its wear and tear and a certain play may be produced during the operation of the one-way clutch. Therefore, for example, when the central shaft of the developing unit rotates in conjunction with the rotation of a developer conveying auger of developing devices, a play is produced when the one-way clutch is operating, and when the developing unit rotates in the reverse direction even if only slightly, not only safety in the developing device removing work is impaired but also the developing devices can be damaged.  
           [0010]    Accordingly, a highly reliable image forming apparatus to obtain developed color images using a revolver type developing unit is desired, which is capable of surely preventing the counter-rotation of the developing unit in the removing work of developing devices from a revolver, securing safety during the maintenance and preventing the damage of developing devices held by the developing unit.  
         SUMMARY OF THE INVENTION  
         [0011]    An object of the present invention is to provide an image forming apparatus that is capable of preventing the counter-rotation of a developing unit when exchanging developing devices held by a revolver type developing unit, promoting safety of operator during the maintenance work, and assuring prevention of damage of developing devices or peripheral equipment.  
           [0012]    According to a preferred embodiment of the present invention, there is provided an image forming apparatus comprising: an image carrier for holding electrostatic latent images on the surface; a developing unit that has plural developing devices that can be exchanged by a rotatable holding unit and supported rotatably by the main body of the image forming apparatus; a driving source for moving a desired developing device by rotating the developing unit to a developing position opposite to the image carrier; a locking mechanism that is movable to an unlocking position of the holding unit and a locking position to engage with the holding unit for stopping at a position to exchange the developing devices and to a locking position when the driving source is shut off; and a backstop member that is movable to the first free position with the revolver and the second position to engage with the holding unit in order to prevent the rotation of the developing unit in the direction reverse to the rotating direction by the driving source, and to the second position when the driving source is shut off.  
           [0013]    Further, according to the preferred embodiment of the present invention, there is provided an image forming apparatus comprising: an image carrier for holding electrostatic latent images on the surface; a developing unit equipped with plural developing devices that can be exchanged by a rotatable revolver and supported rotatably by the main body of the image forming apparatus; a stepping motor for moving a desired developing device by rotating the developing unit to a developing position opposite to the image carrier; a locking mechanism that is movable to an unlocking position with the revolver and a locking position to engage with the revolver for stopping at a position to exchange the developing devices and to a locking position when the stepping motor is shut off; and a backstop gear that is movable to the first free position with the revolver and the second position to engage with the revolver in order to prevent the rotation of the developing unit in the direction reverse to the rotating direction by the stepping motor and to the second position when the stepping motor is shut off. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a schematic diagram showing the structure of an image forming unit in a preferred embodiment of the present invention;  
         [0015]    [0015]FIG. 2 is a diagram for explaining a developing unit and a locking mechanism in the unlocked state with the developing unit viewed from the developing device side in the embodiment of the present invention;  
         [0016]    [0016]FIG. 3 is a diagram for explaining the developing unit and the locking mechanism in the locked state with the developing unit viewed from the developing device side in the embodiment of the present invention;  
         [0017]    [0017]FIG. 4 is a diagram for explaining the developing unit and the locking mechanism in the unlocked state with the developing unit viewed from the revolver side;  
         [0018]    [0018]FIG. 5 is a partly perspective diagram showing the developing unit in the state with developing devices removed in the embodiment of the present invention;  
         [0019]    [0019]FIG. 6 is a partly perspective diagram showing the developing unit with developing devices removed and a main body guide;  
         [0020]    [0020]FIG. 7 is a perspective view showing the locking mechanism and a backstop gear in the embodiment of the present invention;  
         [0021]    [0021]FIG. 8 is an explanatory diagram showing a toggle panel in the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    A preferred embodiment of the present invention will be explained in detail referring to the attached drawings. FIG. 1 is a schematic diagram showing the structure of an image forming unit  10  of an image forming apparatus such as a color printer and the like in the embodiment of the present invention. Around a photosensitive drum  11  that is an image carrier of the image forming unit  10 , there are provided a charger  12  to uniformly charge the photosensitive drum  11  sequentially with the rotation of the photosensitive drum  11  in the arrow direction s, a laser writing unit  13  that is a latent image forming unit for forming latent images on the charged photosensitive drum  11 , first through third developing devices  16 - 18  containing three color toners; yellow (Y), magenta (M) and cyan (C), a rotary type developing unit  20  that rotates in the arrow direction t centering around a shaft  20   b , an intermediate transfer device  21  equipped with an intermediate transfer belt  21   a  that rotates in the arrow direction u, a cleaner  22 , and a charge elimination lamp  23 .  
         [0023]    Below the image forming unit  10 , there are a paper supply cassette  24  for housing recording paper (not illustrated), an aligning roller pair  27  to synchronize the leading edge of a recording paper to the leading edge of a toner image transferred on the intermediate transfer belt  21   a  along a conveying path  26  of recording paper taken out of the paper supply cassette  24 , a secondary transfer roller pair  28  for transferring a toner image secondarily on the intermediate transfer belt  21   a  on a recording paper, and a fixing roller pair  30  for fixing a toner image on a recording paper. The laser wiring unit  13  forms an electrostatic latent image on the photosensitive drum  11  by applying a laser beam corresponding to a writing signal of each color according to image information input from an external computer terminal, etc.  
         [0024]    The first through third developing devices  16 - 18  have first through third developing rollers  16   a - 18   a  and conveying augers  16   c - 18   c  for supplying yellow (Y), magenta (M) and cyan (C) toners in developer containers  16   b - 18   b  to developing rollers  16   a - 18   a , respectively as shown in FIG. 2.  
         [0025]    The developing unit  20  is rotated in the arrow direction t when a stepping motor  41  drive a revolver following gear  40  provided to a revolver  31  that is a holding device. The developing unit  20  holds the first-third developing devices  16 - 18  by installing both ends of shafts (not illustrated) of developing rollers  16   a - 18   a  of the first through third developing devices  16 - 18  to a positioning unit  31   a  that is formed on the revolver  31  through bearings.  
         [0026]    As shown in FIG. 5, a developer fixing member  32  is mounted rotatably to the positioning unit  31   a  of the revolver  31  and when the developing devices  16 - 18  are removed, the positioning unit  31   a  is opened by removing a screw  32   a  and rotating the developing unit fixing member  32  in the arrow direction w. Further, when the developing devices  16 - 18  are mounted, after rotating the developer fixing member  32  in the reverse direction to the arrow direction w, the developing devices  16 - 18  are fixed to the revolver  31  by fixing the positioning unit  31   a  with a screw.  
         [0027]    As shown in FIG. 6, a guide  33  is formed on the revolver  31 . This guide  33  is a developing device installing guide that is a guide member to guide the developing devices  16 - 18  to the main body guide  10   b  provided to the frame  10   a  of the image forming apparatus by sliding them in the direction vertical to the shaft  20   b  of the developing unit  20  when the developing devices  16 - 18  are attached or detached.  
         [0028]    Next, the locking mechanism and the backstop will be described in detail. The locking mechanism  37  has a locking lever  37   b  that is a supporting member attached rotatably to a fixing member  36  at a supporting point  37   a  as shown in FIG. 7. The lock lever  37   b  supports a lock claw  37   d  made of polyoxy methylene (POM) that is a locking member at a supporting shaft  37   c . When the locking claw  37   d  is at the locking position by the rotation of the locking lever  37   b , it runs against a revolver locking claw  31   b  that is a locked portion formed on the revolver  31  and stops the revolver  31  at a position for exchanging the developing devices  16   a - 18   a . Further, the locking claw  37   d  deflects by about 5° in the arrow direction x in the free state when compared with the revolver locking claw  31   b.    
         [0029]    The locking lever  37   b  is biased to the unlock position shown in FIG. 2 always by a toggle spring  36   a  attached to the fixing member  36  shown in FIG. 8. When the locking lever  37   b  is rotated in the arrow direction q, it is biased in the arrow direction q by the biasing force of the toggle spring  36   a . The stationary side  39   a  of the toggle spring  36   a  is attached to a stationary member  36  and the moving side  39   b  is attached to the locking lever  37   b . The toggle spring  36   a  has actions to compress the locking lever  37   b  in the arrow direction q when its moving side  39   a  moves to above a line X that is connecting the supporting point of the locking lever  37   b  and the stationary side  39   a  of the toggle spring  36   a  and compresses the locking lever  37   b  in the arrow direction r when the moving side  39   b  moves to below the line X.  
         [0030]    Accordingly, when the locking lever  37   b  is turned to the arrow q side as shown by the dotted line, the toggle spring  36   a  compresses the locking lever  37   b  to the state turned to the arrow q side. On the other hand, when the locking lever  37   b  is turned to the arrow direction r side as shown by the one-dot chain line, the toggle spring  36   a  compresses the locking lever  37   b  to the state turned to the arrow r side.  
         [0031]    Further, a backstop gear  38  that is a backstop member having a built-in one-way clutch  38   a  is mounted to the support shaft  37   c  of the locking lever  37   b . As a result, the backstop gear  38  cannot turn in the arrow direction y shown in FIG. 7. Further, the support shaft  37   c  coaxially supports the locking claw  37   d  and the backstop gear  38 . When the locking claw  37   d  is at the lock position by the rotation of the locking lever  37   d , the backstop gear  38  engages with a revolver following gear  40  formed on the revolver  31 . Thus, the backstop gear  38  prevents the developing unit  20  from rotating in the reverse direction to the arrow direction t. Further, the backstop gear  38  moves to a first position wherein it does not interfere with the revolver following gear  40  by the rotation of the locking lever  37   d  when the locking claw  37   d  is at the unlock position.  
         [0032]    Next, the color image forming process by the image forming unit  10  will be explained. In this image forming unit  10 , a full-color image is formed by superposing yellow (Y), magenta (M) and cyan (C) toner images in this order. When the image forming process is started, a developing roller  16   a  of the yellow (Y) developing device  16   a  of the developing unit  20  is arranged at the developing position opposite to the photosensitive drum  11 .  
         [0033]    When the image forming process is started, the photosensitive drum  11  rotates in the arrow direction s and is uniformly charged by the charger  12 , and the laser-writing unit  13  applies a laser beam according to a yellow image signal. Thus, a yellow electrostatic latent image is formed on the photosensitive drum  11 . This yellow (Y) toner is electrostatically supplied to the developing roller  16   a  when reaches the developing unit  20  and a yellow (Y) toner image is formed.  
         [0034]    Then, when the toner image formed on the photosensitive drum  11  reaches a position to contact the intermediate transfer belt  21  that is turned in the arrow direction u, the yellow toner image is electrostatically transferred primarily on the intermediate transfer belt  21  by the transfer bias from the primary transfer roller  40   a . After the primary transfer, the photosensitive drum  11  is cleaned and the cleaner  22  removes residual toner and the charge elimination lamp  23  removes the charge on the surface.  
         [0035]    Thereafter, in the similar manner as the yellow toner image forming process, the magenta and cyan toner image forming processes are repeated on the photosensitive drum  11  and further, the yellow (Y), magenta (M) and cyan (C) toner images are intermediately transferred sequentially on the intermediate transfer belt  21   a  from the photosensitive drum  11  and a color toner image with 3 color toners superposed is formed on the intermediate transfer belt  21   a . During these processes, the developing unit  20  is rotated in the arrow direction t by the stepping motor and the developing rollers  16   a - 18   a  corresponding to toner image colors formed on the photosensitive drum  11  is arranged opposing to the photosensitive drum  11 .  
         [0036]    The yellow (Y), magenta (M) and cyan (C) color toner images that are superposed on the intermediate transfer belt  21   a  are transferred in a lump on a recording paper that is taken out in the arrow direction v from the paper supply cassette  24  and conveyed to the secondary transfer roller pair  28  in synchronous with the color toner images. A full-color image is thus completed on a recording paper P.  
         [0037]    While the image forming process is repeated as described above, the exchange maintenance of the developing devices  16 - 18  is executed when a prescribed number of image forming sheets is reached or a prescribed time elapsed. When starting the exchange maintenance, operator should first pull out the power cord of the main body of the image forming apparatus to prevent the abnormal rotation of the developing unit  20  for a malfunction, etc. of the stepping motor  41  and make the drive of the developing unit  20  free and rotatable manually. Then, open the side cover of the main body of the image forming apparatus, rotate the locking lever  37   b  fixed in the unlock position shown in FIG. 2 in the arrow direction q. Thus, the locking lever  37   b  is released from the unlock state, compressed by the toggle spring  36   a  in the arrow direction q and moves to the lock position shown in FIG. 3.  
         [0038]    When the developing unit  20  is manually rotated in the arrow direction t and the position to exchange the developing devices  16 - 18  is reached under this state, the revolver locking claw  31  runs against the locking claw  37   d  of the locking lever  37   b  and the developing unit  20  stops at the position to exchange the developing devices  16 - 18 . As this time, the backstop gear  38  engages the revolver following gear  40  and prevents the developing unit  20  from rotating in the reverse direction to the arrow direction t.  
         [0039]    Then, operator should open a developer fixing member  32  in the arrow direction w by removing a screw  32   a , pull out the developing devices  16 - 18  in the direction vertical to the shaft  20   b  of the developing unit  20  from the positioning unit  31   a , slide a developing device mounting guide  33  in the arrow direction z along the developing devices mounting guide  33  shown in FIG. 3 and take out from the main body of the image forming apparatus along the main body guide  10   b . Then, load new developing devices  16 - 18  in the main body of the image forming apparatus along the main body guide  10   b  and the developing device mounting guide  33 , and after mounting the shafts of the developing rollers  16   a - 18   a  to the positioning unit  31   a  of the revolver  31 , fix the developing device fixing member  32  to the positioning unit  31   a  with a screw and fix it to the revolver  31 .  
         [0040]    Then, move the locking lever  37   b  once in the reverse direction to the arrow direction q and after removing the locking claw  37   d  from the revolver locking claw  31 , and return the locking lever  37   b  to the locking position by rotating it in the arrow direction q again by the elastic force of the toggle spring  36   a . The freed locking claw  37   d  deflects once by about 5° in the arrow direction x. Therefore, even when returned to the lock position, the locking claw  37   d  does not interfere with the revolver-locking claw  31  and the developing unit  20  can be turned manually.  
         [0041]    When the developing unit  20  is rotated manually in the arrow direction t under this state, the locking claw  37   d  runs against the revolver locking claw  31  and the developing unit  20  is stopped at the position to exchange next developing devices  16 - 18 . Hereafter, in the similar manner as described above, exchange next color developing devices  16 - 18 .  
         [0042]    While exchanging the developing devices  16 - 18 , the developing unit  20  is firmly fixed at the exchange position by the locking claw  37   d  attached to the locking lever shaft  37   b  and the backstop gear  38 . That is, the rotation of the developing unit  20  in the arrow direction t is blocked by the locking claw  37   d  that is running against the revolver-locking claw  31 . On the other hand, the backstop gear  38  that is engaging with the revolver following gear  40  blocks the rotation of the developing unit  20  in the reverse direction to the arrow direction t. Furthermore, when the developing unit  20  tries to rotate in the direction reverse to the arrow direction t, a force to inroad into the revolver following gear  40  side acts on the backstop gear  38  for its effect of arrangement and despite of the back stop gear  38  being compressed only in the arrow direction q by the toggle spring  36   a , the reverse rotation of the developing unit  20  can be surely prevented without the possibility of disengagement of the backstop gear  38  and the revolver following gear  40 .  
         [0043]    When the developing devices  16 - 18  in three colors of yellow (Y), magenta (M) and cyan (C) are thus exchanged completely, the image forming process can be executed when the locking lever  37   b  is depressed in the direction reverse to the arrow direction q, the locking lever  37   b  is fixed at the unlock position by the toggle spring  36   a , the side cover is closed, a power cord of the main body of the image forming apparatus is connected, and the power is turned on.  
         [0044]    According to the above-mentioned embodiment, when the developing unit  20  is manually rotated in the state with the locking lever  37   b  rotated and the locking claw  37   d  moved to the lock position in exchanging the developing devices  16 - 18 , the reverse rotation of the developing unit  20  is prevented easily and surely and the developing unit  20  can be fixed at the exchange position of the developing devices  16 - 18  surely. Accordingly, in the maintenance to exchange the developing devices  16 - 18 , the operator&#39;s safety is secured and the damage of the developing devices or their peripheral equipment caused by the reverse rotation of the developing unit  20  can be prevented. Further, the power source of the stepping motor  41  is shut off in the exchange maintenance of the developing devices  16 - 18 . Therefore, the developing unit  20  does not cause the abnormal rotation for the malfunction of the stepping motor and the further safety is obtained.  
         [0045]    Furthermore, there is no possibility for deterioration of the one-way clutch  38   a  provided to the backstop gear  38  for wear, its clutching accuracy can be maintained satisfactorily and the reverse rotation of the developing unit  20  can be prevented at a high accuracy. Further, as the developing device mounting guide  33  is formed on the revolver  31 , the old developing devices  16 - 18  until reaching the main body guide  10   b  can be easily taken out and the contamination of the peripheral portions in taking out the developing devices can be reduced.  
         [0046]    Further, the present invention is not limited to the embodiment described above and various changes may be made without departing from the spirit and scope thereof. For example, toner colors in the developing devices held in the developing unit are not limited and further, one developing device containing black toner may be added and four developing devices may be provided. In addition, the image forming apparatus can be in any construction and for example, a developing device containing black toner may be arranged around the image carrier separately from the developing unit.  
         [0047]    As described above in detail, according to the present invention, the developing unit can be stopped at the position for exchanging the developing devices easily and certainly by manually rotating the developing unit after shutting off a driving source with the locking mechanism shifted from the unlock position to the lock position and also the reverse rotation of the developing unit can be prevented by the backstop member that is interlocking with the locking mechanism. Accordingly, in the exchange maintenance of the developing devices, the operator&#39; safety can be secured and damage of the developing devices or peripheral equipment can be prevented certainly. In addition, the further safety is assured without causing the abnormal rotation of the developing unit for the erroneous operation of the driving source.