1. Field of the Invention
The present invention relates to a method for controlling the concentration of a developer in a developing reservoir of a wet printer and an apparatus therefor. More particularly, this invention is directed to a method for controlling the concentration of a developer in a developing reservoir of a wet printer to maintain the concentration of the developer, in which a toner mixes with a liquid carrier element, within a predetermined range, and to an apparatus for supplying the developer of the wet printer.
2. Description of the Related Art
Referring to FIG. 1 showing a typical wet printer, a resetting apparatus 15, laser scanning units 16, developing units 30, a drying unit 18 and a transferring unit 20 are arranged and spaced apart from each other by a predetermined distance, adjacent to a circulation path of a photosensitive belt 14 circulated by three rollers 11, 12 and 13.
In the process of printing, the laser scanning units 16 scan light beams over a predetermined region of the photosensitive belt 14, which is circulated via the resetting apparatus 15. An electrostatic latent image is formed on the photosensitive belt 14 by the scanned light, and the electrostatic latent image is developed by a developer supplied from each developing unit 30. A color image is formed on the photosensitive belt 14 by the laser scanning units 16 which scan light beams of various colors and the developing units 30 which develop the scanned image with the developer corresponding to the color information of the light beam. Most of the liquid carrier element which is supplied to the photosensitive belt 14 from the developing unit 30, but not used, is returned into the developing unit 30.
The photosensitive belt 14 moves through the drying unit 18, which rotates partially in contact with the photosensitive belt 14. The drying unit 18 removes the liquid carrier element remaining on the photosensitive belt 14. The color image formed on the photosensitive belt 14 by a toner is then primarily transferred to a transfer roller 21, according to continuous movement of the photosensitive belt 14. Then, the image formed on the transfer roller 21 is secondarily transferred onto a sheet of paper 23 proceeding forward according to rotation of the transfer roller 21 and a pressure roller 22 which contact each other.
The developing process will be described with reference to FIG. 2 in more detail. The developing unit 30 includes a spray 33 for spraying a developer 32 stored in a developing reservoir 31, two squeeze rollers 34 and 35 for separating a liquid carrier element 32a which has not been used to form an image, and plates 36 and 37 for collecting the carrier element 32a flowing from the squeeze rollers 34 and 35 back into the developing reservoir 31. Reference numeral 38 indicates back-up rollers.
In the developing process, a toner 32b, of the developer 32 supplied onto the photosensitive belt 14 by the spray 33, attaches onto the electrostatic latent image of the photosensitive belt 14 by electrical attraction. Meanwhile, the liquid carrier element 32a of the developer 32 supplied onto the photosensitive belt 14 is mostly collected into the developing reservoir 31 as it passes through the two squeeze rollers 34 and 35.
Since the toner 32b is consumed during the above developing process, while the liquid carrier element 32a is not, the concentration of the developer 32 with respect to the toner 32b in the developing reservoir 31 is diluted. Thus, in order to appropriately maintain developing conditions, so that the concentration of the toner is maintained within a predetermined range, the toner 32b must be periodically supplied into the developing reservoir 31 to replenish the amount of the consumed toner. In the conventional art, a concentration measuring apparatus for controlling the concentration of the developer 32 in the developing reservoir 31 is installed in the printer, so that the structure of the printer is more complicated.