1. Field of the Invention
The present invention relates to a developing device and an image forming apparatus with the same, and, more particularly, to delivery of developer in a developing device, and an image forming apparatus with the same.
2. Description of the Related Art
Of conventional electro-photographic image forming apparatuses such as, e.g., copiers, facsimiles, printers, or multi-functional print devices, or the like, the most widely used examples of developer include, e.g., a binary developing type, which uses a binary developer composed of toner and magnetic carriers, and a hybrid developing type, in which a binary developer composed of nonmagnetic toner and magnetic carrier is used, in both of which types the charged toner is carried by a developing roller, and is applied to an electrostatic latent image so as to develop the electrostatic latent image.
In such binary developing type image forming apparatus, for example, after an outer circumferential surface of a photosensitive drum (i.e. latent image carrier) is uniformly charged, the photosensitive drum is subjected to an exposure process using, e.g., a laser scanning unit, etc., to form an electrostatic latent image thereon representative of an image to be recorded. The toner, magnetized via a carrier and adhering to an outer circumferential surface of a developing sleeve (i.e. developer retainer) of a developing device, is supplied to the photosensitive drum via the rotation of the developing sleeve, to develop the electrostatic latent image. The resulting toner image is transferred, and is fixed by heat and/or pressure, to a recording medium, such as for example, a sheet of paper, thus completing the recording of the image.
An example of the developing device included in the above-described image forming apparatus is disclosed in Japanese Patent Laid-Open Publication No. JP-H06-051634 to Shintaro et al. (“Shintaro”).
Shintaro discloses a developing device that includes a developing roller installed to oppose an electrostatic latent image retainer, on which an electrostatic latent image is formed as charge potential differences. The developing roller is provided in the housing of the developing device, in which the binary developer composed of nonmagnetic toner and magnetic carrier is stored, and receives an amount of the developer magnetically adhering on the surface of the developing roller such that a magnetic brush is formed. The disclosed developing device further includes a developer regulating member to regulate the amount of the developer adhering to the developing roller, a first agitating chamber having a first auger to convey the developer along the rotational axis direction of the developing roller, and a second agitating chamber separated vertically from the first agitating chamber by a partition so as to be located below the first agitating chamber, the second agitating chamber having a second auger.
In a developing device having the above-described configuration, the developer moves upward from the second agitating chamber to the first agitating chamber via operation of the first and second augers, and then, is supplied from the first agitating chamber to the developing roller. The extraneous remaining developer after development is conveyed from the developing roller back to the second agitating chamber. This circulation of the developer may prevent possible deterioration of the developer, which can result from the developer remaining stationary in the first agitating chamber.
However, since the developer in the second agitating chamber is pushed upward to the first agitating chamber through a passage defined in a corner of the second agitating chamber, the developer in the passage may be subjected to a high pressure, causing deterioration of the developer.
Another example of the developing device is disclosed in Japanese Patent Laid-Open Publication No. JP 2002-014527 to Akihiro et al. (“Akihiro”). Akihiro discloses a developing device that includes a developing roller installed to oppose an electrostatic latent image retainer, and to which developer magnetically adheres, a first agitator disposed near the developing roller to agitate and convey the developer, a second agitator, which is installed below the first agitator, and which is adapted to receive the developer at a downstream end of the first agitator in a developer conveyance direction so as to agitate and supply the developer to the developing roller, and a developer elevator, which is installed at the center of vertical direction between the first agitator and the second agitator, and which is adapted to receive the developer at a downstream end of the second agitator in the developer conveyance direction so as to supply the developer to the second agitator.
The above-described developing device of Akihiro may have the effect of preventing deterioration of the developer due to the high pressure applied to the developer resulting in developing devices such as the above-described example of Shintaro by allowing the developer elevator to carry the developer magnetically adhered to the outer circumferential surface thereof to supply the developer directly from the first agitator to the second agitator. However, this necessitates a seal to prevent leakage of the developer from the developer elevator.
The developer elevator requires a complex magnet arrangement to allow the first agitator to have the developer to adhere thereto and the second agitator to release the developer, and also requires a sleeve to encase the magnet, and to form the outer circumferential surface, adding complexity and cost in manufacturing.