Method and apparatus for creating color copies of an original by an electrostatic charging process

DETAILED DESCRIPTION It is an object of the present invention to furnish a method and arrangement wherein it is possible to create color copies by the above-described electrostatic charging system and wherein exact superposition, that is the superposition in exact registry of a first, second and third color component image, can be achieved.
The former is achieved by providing at least three electrostatic recording systems each followed by a developing station, each being used for the recording of one color component image.
The reproduction carrier is transported past the three recording stations and the color component image created at each station is superimposed on the previously recorded color components images by control of the electrodes.
In recording colored pictures the different color component images created images created at each of the recording stations must be superimposed exactly one on the other since otherwise color fringes and other color errors appear and also, because the resolution of the picture suffers if the color component images are incorrectly superimposed upon each other.
Both horizontal and vertical displacement of the rasters created by the electrodes at the different recording stations can appear because of the relatively great distances between the individual stations, the variations in position of the reproduction carrier caused by tolerances in the transport means, and expansion or shrinkage of the reproduction carrier caused by the developing and fixeing processes.
It should be noted that herein the horizontal direction is considered the direction in which the lines of electrodes extend and in which the original is scanned, while the vertical direction is the transport direction of the reproduction carrier.
The problem of the exact registry between the first, second and third color component image is solved by affixing a mark onto the reproduction carrier, preferably at the first recording station.
The mark is affixed outside of the field which will determine the copy, that is outside of the raster created by the first, second and third color component image