1. Field of the Invention
The present invention relates to a multi-pass image forming apparatus and an image forming method using the same. More particularly, the present invention relates to a multi-pass image forming apparatus and an image forming method using the same, which can select a print mode in consideration of print speed and image quality.
2. Description of the Related Art
In a conventional image forming apparatus a digital image signal is received that corresponds to a desired image. An electrostatic latent image is then formed on a photosensitive medium by an exposing unit such as a laser scanning unit (LSU). The electrostatic latent image is then developed using a toner to form a toner image. The toner image is then transferred onto a recording medium. The toner image is then fixed onto the recording medium with high temperature and high pressure, thereby forming the desired image.
This image forming apparatus is typically classified as either a wet type image forming apparatuses or a dry type image forming apparatuses, according to the state of the toner and carrier. A wet type image forming apparatus is further classified as either an image forming apparatus having a one-component developer or an image forming apparatus having a two-component developer.
While the one-component developer supplies only the toner to form an image, the two-component developer supplies the carrier mixed with the toner to form an image. In the one-component developer, the toner is supplied to a photosensitive medium to form the toner image. The toner remaining on the surface of the photosensitive medium is then removed by a cleaning device such as cleaning blade and collected by a collecting device so that the toner can be reused.
Meanwhile, in the two-component developer, the carrier is not supplied to the photosensitive medium and collected. Instead, only the toner is supplied to the photosensitive medium to form the toner image. The toner remaining on the surface of the photosensitive medium is removed by a cleaning blade and collected by a collecting device so that the toner can be reused.
A multi-color image forming apparatus generally requires yellow (Y), magenta (M), cyan (C), and black (K) toners. Accordingly, the multi-color image forming apparatus requires four developers for adhering respective color toners to an electrostatic latent image. A development bias for adhering the toner to the photosensitive medium and a supplying bias for supplying the toner to a developing roller are applied to each of the developers. The development bias and supplying bias are high voltages of several hundreds or several thousands of volts.
Either a single-pass printing, which requires four exposure units and four photosensitive media or a multi-pass printing, which requires a single exposure unit and a photosensitive medium, may be employed in printing a multi-color image.
A single-pass multi-color image forming apparatus is mainly used in a high-speed multi-color image forming apparatus because it allows high-speed printing for both a monochromic image and a multi-color image. However, since the four exposure units and four photosensitive media are required, it is difficult to minimize a size of the apparatus and therefore has high manufacturing costs.
A multi-pass multi-color image forming apparatus includes a single photosensitive medium and a single exposure unit. In this apparatus, by repeatedly performing the exposing, developing, and transferring processes for each color so as to overlap each color on an intermediate transfer medium, a color toner image is formed on the intermediate transfer medium and then the color toner image is transferred and fixed onto a sheet of paper (S).
The multi-pass multi-color image forming apparatus requires a longer printing time for a multi-color image than that of the single-pass image forming apparatus. Also, it is difficult to perform color registration.
Accordingly, there is a need for an improved multi-color image forming apparatus that can select a print mode in consideration of print speed and image quality.