Digital copier including means for erasing digital image data over a given area, especially suitable for preventing jamming of paper

Claim 2

A digital copier for transferring an image formed on a photoconductive element by digitally processing a document image and fixing the image on a paper sheet, the digital copier comprising: image reading means for converting the document image into a multi-level density signal by a photoelectric conversion device; converting means for converting the multi-level density signal from said image reading means into digital image data; storing means for storing the digital image data from said converting means; image forming means for reading the digital image data out of said storing means to form an image based on the image data on the photoconductive element; transferring means for transferring the image formed by said image forming means to the paper sheet being transported; erasing means for erasing the digital image data over a predetermined area in a subscanning direction; and a counter providing a numerical value indicating a number of black pixels in a predetermined range included in the digital image data along a leading edge of the document, the digital image data being erased by the erasing means when the number of black pixels counted is greater than a predetermined value.

Claim 3

A copier as claimed in claim 1, wherein the area where the digital image data is to be erased by said erasing means is controlled on the basis of a count outputted by said counter.

Claim 4

A copier as claimed in claim 1, wherein the area where the digital image data is to be erased by said erasing means is controlled on the basis of a count outputted by said counter and entered conditions particular to the paper sheet.

Claim 5

A digital copier for transferring an image formed on a photoconductive element by digitally processing a document image and fixing the image on a paper sheet, the digital copier comprising: image reading means for converting the document image into a multi-level density signal by a photoelectric conversion device; converting means for converting the multi-level density signal from said image reading means into digital image data; storing means for storing the digital image data from said converting means; image forming means for reading the digital image data out of said storing means to form an image based on the image data on the photoconductive element; transferring means for transferring the image formed by said image forming means to the paper sheet being transported; erasing means for erasing the digital image data over a predetermined area in a subscanning direction; image reversing means for inverting polarity of the digital image data; and counting means for counting black pixels in a predetermined range included in the digital image data along a leading edge of the document, the digital image data being erased by the erasing means when the number of black pixels counted is less than a predetermined value.

Claim 6

A digital copier for transferring an image formed on a photoconductive element by digitally processing a document image and fixing the image on a paper sheet, the digital copier comprising: image reading means for converting the document image into a multi-level density signal by a photoelectric conversion device; converting means for converting the multi-level density signal from said image reading means into digital image data; storing means for storing the digital image data from said converting means; image forming means for reading the digital image data out of said storing means to form an image based on the image data on the photoconductive element; transferring means for transferring the image formed by said image forming means to the paper sheet being transported; erasing means for erasing the digital image data over a predetermined area in a subscanning direction; image reversing means for inverting polarity of the digital image data; and counting means for counting black pixels in a predetermined range included in the digital image data along a leading edge of the document, the digital image data being erased by the erasing means when the number of black pixels counted is less than a predetermined value.

Claim 7

A copier as claimed in claim 4, wherein the area where the image area is to be erased by said erasing means is controlled on the basis of a count representative of a number of the black pixels and outputted by said counting means in association with image reversal processing which is executed by said image reversing means.

Claim 8

A copier as claimed in claim 5, wherein said counting means counts the black pixels when the digital image data is written to said storing means, erasure of the digital image data by said erasing means being executed when the digital image data is read out of said storing means.

Claim 9

A digital copier for transferring an image formed on a photoconductive element by digitally processing a document image and fixing the image on a paper sheet, the digital copier comprising: image reading means for converting the document image into a multi-level density signal by a photoelectric conversion device; converting means for converting the multi-level density signal from said image reading means into digital image data; storing means for storing the digital image data from said converting means; image forming means for reading the digital image data out of said storing means to form an image based on the image data on the photoconductive element; transferring means for transferring the image formed by said image forming means to the paper sheet being transported; erasing means for erasing the digital image data over a predetermined area in a subscanning direction; image reversing means for inverting polarity of the digital image data; and counting means, (1) in the event of no image reversal, for counting black pixels in a predetermined range included in the digital image data along a leading edge of the document, the digital image data being erased by the erasing means when the number of black pixels counted is greater than a predetermined value, and (2) in the event of image reversal, for counting white pixels in a predetermined range included in the digital image data along a leading edge of the document, the digital image data being erased by the erasing means when the number of white pixels counted is greater than a predetermined value.

Claim 10

A digital copier for transferring an image formed on a photoconductive element by digitally processing a document image and fixing the image on a paper sheet, the digital copier comprising: image reading means for converting the document image into a multi-level density signal by a photoelectric conversion device; converting means for converting the multi-level density signal from said image reading means into digital image data; storing means for storing the digital image data from said converting means; image forming means for reading the digital image data out of said storing means to form an image based on the image data on the photoconductive element; transferring means for transferring the image formed by said image forming means to the paper sheet being transported; erasing means for erasing the digital image data over a predetermined area in a subscanning direction; image reversing means for inverting polarity of the digital image data; and counting means, (1) in the event of no image reversal, for counting black pixels in a predetermined range included in the digital image data along a leading edge of the document, the digital image data being erased by the erasing means when the number of black pixels counted is greater than a predetermined value, and (2) in the event of image reversal, for counting white pixels in a predetermined range included in the digital image data along a leading edge of the document, the digital image data being erased by the erasing means when the number of white pixels counted is greater than a predetermined value.

Claim 11

A copier as claimed in claim 7, wherein the area where the digital image data is to be erased by said erasing means is controlled on the basis of counts representative of a number of black pixels and a number of white pixels and output by said counting means in association with polarity inversions of the image executed by said image reversing means.

Claim 12

A digital copier for transferring an image formed on a photoconductive element by digitally processing a document image and fixing the image on a paper sheet, the digital copier comprising: image reading means for converting the document image into a multi-level density signal by a photoelectric conversion device; converting means for converting the multi-level density signal from said image reading means into digital image data; storing means for storing the digital image data from said converting means; image forming means for reading the digital image data out of said storing means to form an image based on the image data; erasing means for erasing the digital image data over a predetermined area in a subscanning direction when said image forming means forms an image; shifting means for shifting the digital image data in position in the subscanning direction when the digital image data is read out of said storing means; shift setting means for setting an amount of shift by which the image data is to be shifted by said shifting means; and transferring means for transferring the image formed by said image forming means to the paper sheet being transported; an amount of erasure by which the digital image data is to be erased in a leading edge portion of the image by said erasing means being varied on the basis of the amount of shift of the digital image data determined by said shift setting means.

Claim 13

A digital copier for transferring an image formed on a photoconductive element by digitally processing a document image and fixing the image on a paper sheet, the digital copier comprising: image reading means for converting the document image into a multi-level density signal by a photoelectric conversion device; converting means for converting the multi-level density signal from said image reading means into digital image data; storing means for storing the digital image data from said converting means; image forming means for reading the digital image data out of said storing means to form an image based on the image data; erasing means for erasing the digital image data over a predetermined area in a subscanning direction when said image forming means forms an image; shifting means for shifting the digital image data in position in the subscanning direction when the digital image data is read out of said storing means; shift setting means for setting an amount of shift by which the image data is to be shifted by said shifting means; and transferring means for transferring the image formed by said image forming means to the paper sheet being transported; an amount of erasure by which the digital image data is to be erased in a leading edge portion of the image by said erasing means being varied on the basis of the amount of shift of the digital image data determined by said shift setting means.

Claim 14

A copier as claimed in claim 9, wherein when the digital image data is shifted in an advancing direction with respect to image transfer, the amount of erasure by said erasing means is confined to a predetermined range so that the digital image data is controlled in a retarding direction than the paper sheet; when a value produced by subtracting the amount of shift from the amount of erasure is greater than zero, the amount of erasure is controlled on the basis of said value while, when said value is smaller than zero, the amount of erasure is determined to be zero.