1. Field of the Invention:
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or the like, for forming an image by developing a latent image formed on a photoconductor drum with developer delivered from a developer unit. More particularly, the invention relates to an image forming apparatus wherein the scattering of developer falling through the clearance between the photoconductor drum and the developer unit is prevented.
2. Description of the Prior Art:
In an image forming apparatus such as an electrophotographic copying machine, printer, or the like, an electrostatic latent image is formed, as shown in FIG. 7, on a photoconductor drum 51 (rotating in the clockwise direction as shown by the arrow B in the drawing), the electrostatic latent image then being developed with developer delivered from a developer unit 60, after which the image formed on the photoconductor drum 51 is transferred to copy paper to form a copy image. The developer unit 60 is provided with a developing sleeve 61 (rotating in the counterclockwise direction as shown by the arrow A in the drawing), which is disposed in a housing 62 and in a location facing the photoconductor drum 51, the developing sleeve 61 having a magnetic brush formed thereon to carry developer to the photoconductor drum 51.
The housing 62 of the developer unit 60 is so disposed that a slight clearance is created with respect to the photoconductor drum 51. As a result, part of the developer being carried by the magnetic brush provided on the circumferential surface of the developing sleeve 61 may fall downward through the clearance between the photoconductor drum 51 and the housing 62 to be scattered in a copy paper conveyance path beneath the developer unit 60. The developer scattered in the copy paper conveyance path will adhere to the copy paper conveyed thereto and therefore stain the copy paper. If an image is transferred to the stained copy paper, the transferred image will come out blurred.
To prevent the above problem, a developer collecting member 80 for collecting the developer falling through the clearance between the photoconductor drum 51 and the housing 62 of the developer unit 60 is disposed beneath the position at which the photoconductor drum 51 faces the developer unit 60. Generally, the photoconductor drum 51 is rotatably supported between a pair of photoconductor drum supporting side plates 52, each having in the lower part thereof a supporting portion 52a so formed as to protrude toward the developer unit. The developer collecting member 80 is so mounted as to stretch between the supporting portions 52a of the photoconductor drum supporting side plates 52, each end thereof being secured to the corresponding supporting portion 52a with a screw 82 or the like. The developer falling from between the photoconductor drum 51 and the developer unit 60 is collected on the developer collecting member 80, thus preventing the developer from being scattered in the copy paper conveyance path beneath the developer collecting member 80.
Conventionally, the developer collecting member 80 is formed from sheet metal into such a shape as to prevent the collected developer from dropping. Since the developer collecting member 80 is formed from such sheet metal, when each end of the developer collecting member 80 is secured to the supporting portion 52a of the corresponding photoconductor drum supporting side plate 52 by a screw 82, the entire developer collecting member 80 may be twisted depending on the tightening condition of the screw 82. If the developer collecting member 80 is mounted in a twisted state, the pair of photoconductor drum supporting side plates 52 may be disaligned with each other, and the photoconductor drum 51 may not be properly supported between the photoconductor drum supporting side plates 52. If the photoconductor drum 51 is supported between the disaligned photoconductor drum supporting side plates 52, the photoconductor drum 51 may not be properly positioned with respect to the developer unit 60. If the photoconductor drum 51 is not properly positioned with respect to the developer unit 60, the electrostatic latent image on the photoconductor drum 51 will not be developed by the developer unit 60.
In recent years, there have been image forming apparatuses developed, that are capable of forming a multi-color image using developers of different colors such as black and red. Some of such image forming apparatuses comprise, as shown in FIG. 8, a main developer unit 60 for developing an electrostatic latent image on the photoconductor drum 51, for example, with a black developer, and a sub developer unit 70 for developing the latent image on the photoconductor drum 51, for example, with a red developer, the sub developer unit 70 being disposed above the main developer unit 60, both facing the photoconductor drum 51 (rotating in direction B). The main developer unit 60 and the sub developer unit 70 are respectively provided with developing sleeves (rotating in direction A) 61 and 71 disposed in respective housings 62 and 72 and facing the photoconductor drum 51, the housings 62 and 72 being swingable about respective fulcrums 63 and 73 to move the respective developing sleeves 61 and 71 close to and away from the photoconductor drum 51. When the developing sleeves 61 and 71 are moved close to the photoconductor drum 51 and positioned in the developing position, the developer units 60 and 70 develop the latent image on the photoconductor drum using the developing sleeves 61 and 71. On the other hand, in the receding position away from the photoconductor drum 51, the developer units 60 and 70 do not develop the latent image on the photoconductor drum 51, the developing sleeves 61 and 71 being inoperative.
In such image forming apparatuses, wherein the main developer unit 60 and the sub developer unit 70 are disposed one above the other, developer collecting members 81 and 81 are disposed, one beneath the position at which the main developer unit 60 faces the photoconductor drum 51 and the other beneath the position at which the sub developer unit 70 faces the photoconductor drum 51.
In the above case, it is necessary to position the developer collecting members 81 and 81 so that they do not interfere with the corresponding developer units 60 and 70 even when the developer units 60 and 70 are swung to the receding position away from the photoconductor drum 51. As a result, when the developer units 60 and 70 are positioned at the developing position close to the photoconductor drum 51, a large clearance is created between the developer collecting members 81 and 81 and the housings 62 and 72 of the respective developer units 60 and 70. If the clearance is enlarged between the housings 62 and 72 of the developer units 60 and 70 and the respective developer collecting members 81 and 81, the developer falling through the clearance between the photoconductor drum 51 and the developer units 60 and 70 will not be completely collected by the respective developer collecting members 81 and 81, resulting in the scattering of developer below the developer collecting members 81 and 81. Also, if the clearance is enlarged between the housings 62 and 72 of the developer units 60 and 70 and the respective developer collecting members 81 and 81, air may flow through the clearance and cause the developer collected on the developer collecting members 81 to fly around. Providing larger size developer collecting members 81 may be considered to prevent the developer from scattering therebelow, even when the developer units 60 and 70 are positioned in the receding position away from the photoconductor drum 51, but, since the clearance between the photoconductor drum 51 and the developer units 60 and 70 varies with the swinging motion of the developer units 60 and 70, it is not possible to completely prevent the developer from scattering downward with the provision of the developer collecting members 81 and 81.