Abstract:
In an image forming apparatus, a first developing device is held by a rockable first holder, and a second developing device is held by a slidable second holder. The first or second developing device can be opposed, alternatively, to an image carrier by sliding the second holder. Thus, developing agents stored individually in the first and second developing devices can be alternatively supplied by use of a simple arrangement.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an image forming apparatus serving as, for example, an electronic copying apparatus, and more specifically to an image forming apparatus provided with a plurality of developing devices and constructed so that a latent image is developed through alternative use of the developing devices. 
     BACKGROUND OF THE INVENTION 
     Generally, an electronic copying apparatus has a developing device within its housing. A developing agent is supplied from the developing device to an electrostatic latent image formed on a photosensitive drum, and the latent image is thereby developed. However, electronic copying apparatuses provided with a plurality of developing devices have recently been developed. In copying apparatuses of this type, the developing devices are opposed, alternatively, to a photosensitive drum, and supply the drum with developing agents of different colors for multicolor developing. 
     These prior art copying apparatuses, however, require a sophisticated selecting mechanism for alternatively opposing the developing devices to the photosensitive drum, resulting in increased size and higher cost. 
     SUMMARY OF THE INVENTION 
     The present invention has been contrived in consideration of these circumstances, and is intended to provide an multi-color image forming apparatus in which a plurality of developing devices can be opposed alternatively to an image carrier without requiring a complicated selecting mechanism. 
     In order to achieve the above object, there is provided an image forming apparatus in which a first developing device is held by a rockable first holder, and a second developing device is held by a slidable second holder. The first or second developing device can be opposed, alternatively, to an image carrier by sliding the second holder. Thus, developing agents stored individually in the first and second developing devices can be alternatively supplied by use of a simple arrangement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to 11 show a first embodiment of an image forming apparatus according to the present invention, in which: 
     FIG. 1 is a side view schematically of an electronic copying apparatus; 
     FIG. 2 is a vertical, sectional view of a developing device; 
     FIG. 3 is a perspective view of a magnet roller; 
     FIG. 4 is a perspective view of a mixer; 
     FIG. 5 is a perspective view of the electronic copying apparatus; 
     FIGS. 6 and 7 are a perspective view and a side view, respectively, schematically illustrating the manner in which, the developing devices are inserted; 
     FIG. 8 is a perspective view of first and second holders; 
     FIG. 9 is a perspective view illustrating the operation of the holders; 
     FIG. 10 is a side view of the electronic copying apparatus in which the second developing device is opposed to the photosensitive drum; 
     FIG. 11 is a side view of the electronic copying apparatus in which the first developing device is opposed to the photosensitive drum; and 
     FIGS. 12 and 13 are side views schematically illustrating a second embodiment of the image forming apparatus of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of an electronic copying apparatus according to the present invention and as applied to an electronic copying apparatus will now be described in detail with reference to the accompanying drawings of FIGS. 1 to 11. 
     In FIG. 1, numeral 1 designates the housing of the electronic copying apparatus. A photosensitive drum 2, as an image carrier, is disposed in the central portion of the housing 1 so as to be rotatable in the clockwise direction. The photosensitive drum 2 is surrounded by a main charger 3, two developing devices 4a and 4b, a transfer charger 5, a separation charger 6, and a cleaning unit 7, which are arranged successively in the rotating direction of the drum 2. A sheet cassette 8 is removably attached to the lower portion of the right-hand side of the housing 1. The sheet cassette 8 is designed so as to deliver paper sheets P one at a time. Each delivered sheet P is fed along a transport path 9 inside the housing 1. Aligning rollers 10, the transfer and separation chargers 5 and 6, a guide plate 11, a fixing unit 12, and exit rollers 13 are arranged successively in the feeding direction of the paper sheet P along the transport path 9. A receiving tray 14 is attached to the lower portion of the left-hand side of the housing 1. 
     An original table 1a is mounted for reciprocal movement on the top of the housing 1. An optical system 15 is provided under the original table 1a. The optical system 15 includes a lamp 16, and a lens 18. The image of an original put on the original table 1a is projected onto the photosensitive drum 2 by the optical system 15. A cooling fan 20 is disposed over the fixing unit 12 inside the housing 1, so that air in the housing 1 can be exhausted. 
     Each of the developing devices 4a and 4b is constructed as shown in FIG. 2. In FIG. 2, numeral 21 designates a flat developing vessel. A developing chamber 22 of substantially a rectangular shape, and a toner chamber 23, as a developing agent resupply section, are formed integrally with and adjacent to each other in the developing vessel 21. The developing chamber 22 contains a magnet roller 24 (see FIG. 3), a scraper 25, and a mixer 26 (see FIG. 4). The magnet roller 24, which consists of a sleeve 27 and permanent magnets 28 fixedly arranged therein, serves to carry a toner 29 from the developing chamber 22 to the photosensitive drum 2. The scraper 25 serves to scrape off the toner 29 which remains on the sleeve 27 without having been used in the developing process on the photosensitive drum 2. The removed toner 29 is stirred by the mixer 26 to prevent massing. An auxiliary chamber 30 is provided between the upper portions of the developing chamber 22 and the toner chamber 23 so as to connect the same. A resupply roller 31 is disposed in the auxiliary chamber 30 so that the toner 29 in the toner chamber 23 is fed into the developing chamber 22 at a fixed rate as the resupply roller 31 rotates. 
     Disposed in the toner chamber 23, moreover, is a film 33, as a feed mechanism, one end of which is fixed to the upper edge of the inner wall of the toner chamber 23 on the side of the auxiliary chamber 30, and the other end of which is wound around a shaft 32, as take-up means, provided opposite the auxiliary chamber 30 at the developing vessel 21. The toner 29 is placed on the film 33. As the film 33 is taken up by the rotating shaft 32, therefore, the toner 29 on the film 33 is lifted up and transported into the auxiliary chamber 30. 
     The opening through which the toner 29 is resupplied is formed in that portion of the developing vessel which corresponds to the top face of the toner chamber 23. A lid 23a is attached to the top portion of the developing vessel 21 so that the opening can be opened and closed as required. An ultrasonic sensor 34 is attached to the inside of the lid 23a. The ultrasonic sensor 34 detects the presence of the toner 29 in the toner chamber 23. The sensor 34 is adapted to rotate the shaft 32 when it is not in contact with the toner 29, and to deliver a signal for stopping the rotation of the shaft 32 when touched by the toner 29. 
     As shown in FIGS. 7 to 9, the first and second developing devices 4a and 4b are removably held by first and second holders 41 and 42, respectively, which are arranged vertically. The first holder 41 on the upper side is rockably supported on pivot means 43, while the second holder 42, on the lower side, is slidably supported by slider means 44. The first and second developing devices 4a and 4b are removably loaded into the housing 1, as indicated by arrows in FIG. 6. As the second developing device 4b is slid, the first holder 41 is rocked, so that the first and second developing devices 4a and 4b can be opposed, alternatively, to the photosensitive drum 2. 
     In a state such that the second developing device 4b is not in the second holder 42 or that the former is partially drawn out from the latter (or in a second non-developing position), the first holder 41 rocks downward (in the counterclockwise direction of FIG. 9) around the pivot means 43, and abuts against stopper means 45 to be held thereby in position. Thus held in the abutting position, the first holder 41 leads the first developing device 4a into the developing position. Meanwhile, when the second developing device 4b is inserted into the innermost part of the second holder 42 and carried on the slider means 44, the first holder 41 is forced upward. As a result, the first developing device 4a is moved from the developing position into the first nondeveloping position, and the second developing device 4b is brought into the developing position in its place. 
     In forming an image in the electronic copying apparatus constructed in this manner, the original on the original table 1a is scanned with a light beam applied by the optical system 15, and the light reflected from the original is projected onto the photosensitive drum 2 through the the lens 18, forming an electrostatic latent image on the drum 2. The electrostatic latent image is supplied with a toner 29a or 29b from either the first or second developing device 4a or 4b, and is thereby developed into a visible image. When the first and second developing devices 4a and 4b are in the positions indicated by the line in FIG. 10, the second developing device 4b is held in the developing position, where it supplies the toner 29b. If the second developing device 4b is slidingly drawn out to the position shown in FIG. 11, the first developing device 4a rocks around the pivot means 43, and it stops when its lowered end abuts against the stopper means 45. Thus, the first developing device 4a is located in the developing position where it faces the photosensitive drum 2 and supplies the toner 29a thereto. When the second developing device 4b is thereafter inserted into the second holder, the first developing device 4a is rocked upward to allow the second developing device 4b to face the photosensitive drum 2 again. 
     Meanwhile, the developed image is transferred to the paper sheet P from the sheet cassette 8 by the transfer charger 5. Thereafter, the paper sheet P is separated from the photosensitive drum 2 by the separation charger 6, and then fed along the guide plate 11 to the fixing unit 12. After the image is fixed by the fixing unit 12, the paper sheet P is discharged into the receiving tray 14 by the exit rollers 13. 
     According to this embodiment, as described above, the first or second developing device 4a or 4b can be alternatively located to face the photosensitive drum 2 in the developing position by sliding the lower or second developing device 4b. It is, therefore, possible to alternatively supply the toner 29a or 29b from the first or second developing device 4a or 4b without need of a complicated selecting mechanism. 
     It is to be understood that the present invention is not limited to the above described embodiment, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention. In the above embodiment, for example, the upper or first holder 41 is described as being supported rockably, and the lower or second holder 42 as being slidably supported by the slider means 44. Alternatively, however, a first holder 50 on the upper side may be slidably supported by slider means 51, with the second holder 52 on a lower side rockable around pivot means 53, as in a second embodiment shown in FIGS. 12 and 13. In this case, the second holder 52 is urged to rock upward by a spring 54. (Numeral 55 designates members equivalent to the stopper means 45 of the first embodiment.) 
     According to the second embodiment constructed in this manner, the first or second developing device 4a or 4b can be located, alternatively, in the developing position by sliding the upper or first developing device 4a, thus providing the same effect as in the first embodiment.