Imperfect register correcting method to be carried out on a multicolor image forming apparatus

Claim 1

An imperfect register correcting method to be applied to correcting the incorrect disposition and functions of the components of a multicolor image forming apparatus which forms a multicolor image by sequentially superposing color images formed by a plurality of image forming units thereof, causing imperfect register of the color images formed by the plurality of image forming units, said imperfect register correcting method comprising: a first imperfect register correcting cycle comprising steps of: forming images of specific register marks generated by pattern generators included in the image forming units by the image forming units on a recording sheet transporting means included in the multicolor image forming apparatus, obtaining register mark data by reading the images of the register marks by image sensors, calculating corrections for correcting skews of the plurality of image forming units on the basis of the differences of the register mark data representing the positions of the images of the register marks formed by the image forming units excluding one specified image forming unit among the plurality of image forming units from the register mark data representing the position of the image of the register mark formed by the specified image forming unit, and correcting the skews of the image forming units excluding the specified image forming unit on the basis of the calculated corrections; a second imperfect register correcting cycle comprising steps of: forming images of the specific register marks by the image forming units on the recording sheet transporting means, obtaining register mark data by reading the images of the register marks by the image sensors, calculating corrections for correcting the positions and functions of the image forming units on the basis of the difference of the register mark data representing the positions of the images of the register marks formed by the image forming units excluding the specified image forming unit among the plurality of image forming units from the register mark data representing the position of the image of the register mark formed by the specified image forming unit, and correcting the positions and functions of the image forming units in respect of dislocation with respect to the scanning direction, dislocation with respect to the feed direction, and error in scanning width; characterized in that the second imperfect register correcting cycle is carried out subsequent to the first imperfect register correcting cycle.