Digital copy machine allowing duplex copying in short time through novel recirculation timing

An image forming apparatus comprising:

• image reading means for reading out an original image and providing digital data corresponding to the density of each pixel in said original image,
• a memory for storing image data of said readout original image,
• image formation means for forming an image on a sheet according to image data read out from said memory,
• first input means for entering an image formation mode,
• second input means for entering the number of originals prior to initiation of image formation,
• detection means for detecting the size of a sheet used for image formation,
• first calculation means for calculating the number of sheets n (n.gtoreq.2) of a size detected by said detection means that can be circulated at one time by a sheet transportation mechanism,
• determination means for making determination of an image formation mode entered by said first input means,
• first control means for determining the optimum image formation sequence of image formation for all originals according to the number of originals entered by said second input means, the number of sheets n calculated by said first calculation means, and an image formation mode determined by said determination means,
• second calculation means for calculating all the differences between the time when image formation of the (2n-1)th page of an original image can be initiated before completion of the image formation of said all originals in the sequence determined by said first control means and the time when the n-th sheet is fed to said image formation position after the first sheet is provided at a normal timing,
• comparison means for comparing all the time differences calculated by said second calculation means, and
• second control means for delaying feeding of the first sheet according to a comparison result of said comparison means.

An image forming apparatus that allows image formation on a first face of a sheet and on a second face corresponding to the back surface of said sheet comprising:

• a reader to read an original image;
• a memory to store image data of a read out of said original image;
• an image former to form an image on a sheet fed to an image formation position according to image data read out from said memory;
• a circulation type sheet transporter having a transportation path that can accommodate n (n.gtoreq.2) sheets to refeed a sheet to the image formation position after an image has been formed on the first face to invert the face of the sheet to the opposite side;
• a determination unit to determine whether image data required for a first operation of sequential image formation onto the second face of said n sheets circulated through said sheet transporter is stored in said memory;
• and
• a controller to control initiating image formation onto the first face of said first sheet according to a determination result of said determination unit.

A method of forming an image on a first face and second face corresponding to a back surface of the first face, comprising the steps of:

• reading out an original image;
• storing image data of a read out original image into a memory;
• forming an image on a sheet fed to an image formation position according to image data read out from said memory;
• refeeding a sheet to the image formation position after conveying the sheet in sequential order through a transportation path that can accommodate n (n.gtoreq.2) sheets and inverting the face of the sheet to an opposite side;
• and
• initiating image formation onto the first face of the first sheet after image data required for forming an image onto the second face of said n sheets circulated through said sheet transporter has been stored in said memory when it is desired that image formation is to be carried out on both the first face and the second face of at least n sheets.

An image forming apparatus comprising:

• image reading means for reading an original image and providing digital data corresponding to the density of each pixel in said original image;
• a memory for storing image data of said read original image;
• image formation means for forming an image on a sheet according to said image data read out from said memory;
• a circulation type sheet transportation mechanism including a transportation path of a length that can accommodate n (n.gtoreq.2) sheets for inverting a sheet having an image formed on one side to the opposite side and refeeding the reversed sheet to an image formation position;
• and
• control means for controlling the feed timing of the first sheet so that the n-th sheet arrives at said image formation position after the point in time when image data has been stored of the original image of the (2n-1)th page can be initiated in order to set the number of sheets of the first circulation to n by said sheet transportation mechanism in duplex image formation using at least n sheets.