1. Field of the Invention
The present invention relates to a copier, facsimile apparatus, printer or similar image forming apparatus and, more particularly, to a rotary developing device included in an image forming apparatus and of the type effecting development after causing a plurality of developing sections to revolve around a rotary shaft until one of them reaches a developing position where it faces an image carrier.
2. Discussion of the Background
There has been known a full-color copier or similar full-color image forming apparatus of the type exposing an image carrier to color-separated light images to thereby form corresponding latent images, developing each latent image by toner of complementary color, and transferring the resulting toner images to a paper one above the other. There has also been known a multicolor image forming apparatus of the type exposing an image carrier to images to be reproduced in respective colors, developing the resulting latent images by developers of respective colors to thereby produce corresponding toner images, and transferring the toner images to a paper one above the other. This kind of image forming apparatus needs a plurality of developing sections each being assigned to a particular color. However, when the developing sections are implemented as independent units and arranged around the image carrier, the overall dimensions of the apparatus increase.
In light of the above, a rotary developing device having a plurality of developing sections constructed into a single revolver has been developed. The developing device, or revolver, is located in the vicinity of an image carrier and is revolved to sequentially bring the developing sections to a developing position where they face the image carrier. Each developing section located at the developing section develops a latent image formed on the image carrier by toner of particular color. In a revolver disclosed in Japanese Patent Laid-Open Publication No. 60-233668 (Document 1), for example, a hollow toner supply member is disposed in each developing section to extend in the lengthwise direction. The supply member is formed with a toner outlet in the peripheral wall thereof. Such supply members each store toner to be supplied to the respective developing section. Fresh toner storing portions, independent of the developing sections, are each connected to one of the supply members by a flexible tube. A screw or similar flexible conveyor member is disposed in the toner storing portion and tube in order to convey the toner from the respective toner storing section to the associated developing section. Japanese Patent Laid-Open Publication No. 63-153258 (Document 2) teaches a revolver having developing sections each storing toner of a particular color. In this revolver, a hopper is positioned in the vicinity of a developer carrier disposed in each developing section. When the revolver revolves, a predetermined amount of developer is introduced into the hopper.
However, the revolver proposed in Document 1 nee d s drive means for driving the conveying member for conveying the toner from the fresh toner storing portion to the associated developing section, complicating the construction and increasing the cost. Moreover, the mechanical force of the conveying member constantly acts on the toner being fed from the storing section to the developing section, accelerating the deterioration of the toner. The revolver of Document 2 has a drawback that the overall dimensions increase when a great amount of toner is stored in each developing section beforehand. Another drawback is that when the toner is irregularly distributed in the axial direction of the developer carrier due to the repeated operation of the developing section, the revolution cannot level the amount of toner alone. As a result, an image with irregular density is apt to occur despite that a sufficient amount of toner is present in the hopper.
To eliminate the above problems, a revolver having hoppers at, for example, one end of respective developing units has been proposed. Toner containers, each storing toner of a particular color, are removably mounted to and communicated to the respective hoppers. The toner in each container is replenished into the associated hopper by the revolution of the revolver. The supply of toner from the hopper to the associated developing section and the collection of excessive toner from the latter to the former are implemented by a screw or similar conveying means. This kind of revolver can replenish fresh toner from container into the associated hopper without resorting to a mechanical conveying mechanism. Further, the toner is not directly stored in the developing section, but it is stored in the hopper and container. Hence, the developing section and, therefore, the entire revolver is miniature.
Japanese Patent Laid-Open Publication Nos. 62-15572 and 62-251772 each disclose a revolver having a hopper at the end of each developing section. In this revolver, a screw or similar conveying means, as well as other members, is driven by common drive means without the intermediary of the flexible tube or similar long conveyance path, thereby conveying toner from the hopper to the associated developing section. This successfully stabilizes the amount of toner in the axial direction and, therefore, on the developer carrier, and reduces the sectional occupancy ratio of the revolver relative to the image carrier.
To make the hoppers and fresh toner containers miniature and store a great amount of toner in each of them, it is preferable that the containers mounted to the hoppers be provided with a generally circular contour concentric with the center of rotation of the revolver, as seen in the lengthwise direction of the developing sections. However, this kind of approach has a problem that only the toner passing over the portion where the container is connected to the hopper is replenished into the hopper during the revolution of the revolver. This is also true when the amount of toner remaining in the container is small. In this condition, the toner is apt to partly remain in the container without being consumed.
A current trend in the imaging art is toward a photoconductive element and a developing device, among others, implemented as units which can be replaced by the user. There has been developed a revolver replaceable as a developing unit, as taught in Japanese Patent Laid-Open Publication No. 63-78170 by way of example. However, handling this kind of revolver storing toner as a unit brings about various problems. For example, in the event of transport, the developing unit is heavy and contaminates, when broken, the surrounding by causing the toner to fly about. In addition, the toner is apt to smear the user's hands and cloths in the event of replacement of the developing unit.