Multi-color electrophotographic printer having multiple image forming units for creating multiple toner images in registry

A multi-color electrophotographic apparatus comprising:

• a casing having an access cover;
• image-transferring means for transferring a multi-colored image to a recording sheet;
• and
• an image-forming assembly having a plurality of image-forming units, each unit including a photoconductor and a developer storing therein toner of a single color for forming a single color toner image on each photoconductor, said image-forming assembly being arranged to be movable between operative and inoperative positions, the operative position being such that each image-forming unit lies at an image-forming station with the photoconductor thereof in engagement with said image-transferring means to transfer the toner image formed thereon in registration with each other to said image-transferring means for forming the multi-colored image, the inoperative position being such that all the photoconductors of said image-forming assembly are out of engagement with said image transferring means for allowing said image-transferring means to be unloaded from said casing through the access cover, said image-transferring means includes a transfer belt for transferring at the image-forming station the toner image formed on each photoconductor thereto in registration with one another for forming thereon the multi-colored toner image, a first transfer roller bringing the transfer belt into engagement with each photoconductor lying at the image-forming station, a second transfer roller arranged to urge the transfer belt for forming a nip between the transfer belt and a third transfer roller provided in said casing through which a recording medium passes to transfer the multi-colored toner image formed on the transfer belt to the recording medium, a fourth roller arranged coaxially with the first transfer roller, said fourth roller having a smaller diameter than that of the first transfer roller to restrict a degree of engagement of the first transfer roller with each photoconductor through the transfer belt at the image-forming station, and a tension roller for providing tension to the transfer belt stretched to a given degree.

A transfer belt unit for use in a multi-color electrophotographic apparatus including an image-forming assembly having a plurality of image-forming units each including a photoconductor and a developer having toner of a single different color for forming a different color toner image on the photoconductor, and driving means for moving said image-forming assembly to displace said image-forming units, in sequence, to an image-forming station, and a transfer member unit comprising:

• a transfer belt for transferring at the image-forming station the toner image formed on each photoconductor thereto in registration with one another forming a multi-color toner image, a first transfer roller bringing the transfer belt into engagement with each photoconductor that is positioned at the image-forming station, a second transfer roller arranged to urge the transfer belt to form a nip between the transfer belt and transferring means of a multi-color electrophotographic apparatus through which a recording medium passes, to transfer the multi-color toner image formed on the transfer belt to the recording medium, a third roller arranged coaxially with the first transfer roller, said roller having a smaller diameter than that of the first transfer roller to restrict a degree of engagement of the first transfer roller with each photoconductor through the transfer belt at the image-forming station, and a tension roller for providing tension to the transfer belt for maintaining the transfer belt stretched to a given degree.