Image forming apparatus with paper thickness detection unit and image forming method of the same

Abstract

An image forming apparatus of an embodiment of the invention includes a paper feed cassette to contain a sheet on which an image is to be printed, a pair of conveyance rollers to nip and convey the sheet taken out from the paper feed cassette, a paper thickness detection unit that is provided downstream of the sheet conveyed by the pair of conveyance rollers and near a nip point between the pair of conveyance rollers, has a rotator brought into contact with the sheet, and detects a thickness of the sheet by a shift generated when the sheet contacts with the rotator, a register roller to align the sheet after the thickness of the sheet is detected by the paper thickness detection unit, and a print ejection mechanism that prints and fixes an image to the sheet passing through the register roller and then ejects it.

1 . An image forming apparatus with a paper thickness detection unit, comprising:
 a paper feed cassette to contain a sheet on which an image is to be printed;   a pair of conveyance rollers to nip and convey the sheet taken out from the paper feed cassette;   a paper thickness detection unit that is provided downstream of the sheet conveyed by the pair of conveyance rollers and near a nip point between the pair of conveyance rollers, has a rotator brought into contact with the sheet, and detects a thickness of the sheet by a shift generated when the sheet contacts with the rotator;   a register roller to align the sheet after the thickness of the sheet is detected by the paper thickness detection unit; and   a print ejection mechanism that prints and fixes an image to the sheet passing through the register roller and then ejects it.   
     
     
         2 . The apparatus according to  claim 1 , wherein the paper thickness detection unit detects a shift amount of the rotator as a voltage value and detects the paper thickness. 
     
     
         3 . The apparatus according to  claim 2 , wherein the paper thickness detection unit samples the voltage value to obtain an average value. 
     
     
         4 . The apparatus according to  claim 3 , wherein the paper thickness detection unit detects the paper thickness as a difference between a voltage when the sheet does not contact with the rotator and a voltage when the sheet contacts with the rotator. 
     
     
         5 . The apparatus according to  claim 4 , wherein a distance D from a nip point between the pair of conveyance rollers to a point where the rotator contacts with the sheet is within a range of about 0 mm to 10 mm. 
     
     
         6 . The apparatus according to  claim 5 , wherein a pressing load P at which the rotator contacts with the sheet is within a range of about 60 g to 140 g. 
     
     
         7 . The apparatus according to  claim 4 , wherein a fixing temperature of the image in the print ejection mechanism is changed according to the paper thickness detected in the paper thickness detection unit. 
     
     
         8 . An image forming apparatus with a paper thickness detection unit, comprising:
 a plurality of paper feed cassettes to contain sheets on which images are to be printed;   a conveyance drive roller and a conveyance driven roller that nip and convey the sheet taken out from one of the plurality of paper feed cassettes;   a first conveyance guide provided at a side of the conveyance drive roller and a second conveyance guide provided at a side of the conveyance driven roller, which have openings at portions where the conveyance drive roller and the conveyance driven roller contact with each other, and guide the sheet conveyed by these rollers,   a paper thickness detection unit that is provided downstream of the sheet conveyed by the conveyance drive roller and the conveyance driven roller and near a nip point between the conveyance drive roller and the conveyance driven roller, includes a rotator brought into contact with the first conveyance guide and the sheet at a specified pressing load, and detects a thickness of the sheet by a shift generated when the sheet contacts with the rotator;   a register roller to align the sheet after the thickness of the sheet is detected by the paper thickness detection unit; and   a print ejection mechanism that prints and fixes an image to the sheet passing through the register roller and then ejects it.   
     
     
         9 . The apparatus according to  claim 8 , wherein the paper thickness detection unit detects a shift amount of the rotator as a voltage value and detects the paper thickness. 
     
     
         10 . The apparatus according to  claim 9 , wherein the paper thickness detection unit samples the voltage value to obtain an average value. 
     
     
         11 . The apparatus according to  claim 10 , wherein the paper thickness detection unit detects the paper thickness as a difference between a voltage when the sheet does not contact with the rotator and a voltage when the sheet contacts with the rotator. 
     
     
         12 . The apparatus according to  claim 11 , wherein a distance D from a nip point between the pair of conveyance rollers to a point where the rotator contacts with the sheet is within a range of about 0 mm to 10 mm. 
     
     
         13 . The apparatus according to  claim 12 , wherein a pressing load P at which the rotator contacts with the sheet is within a range of about 60 g to 140 g. 
     
     
         14 . The apparatus according to  claim 11 , wherein a fixing temperature of the image in the print ejection mechanism is changed according to the paper thickness detected in the paper thickness detection unit. 
     
     
         15 . An image forming apparatus with a paper thickness detection unit, comprising:
 a plurality of paper feed cassettes to contain sheets on which images are to be printed;   a conveyance drive roller and a conveyance driven roller that nip and convey the sheet taken out from one of the plurality of paper feed cassettes;   a first conveyance guide provided at a side of the conveyance drive roller and a second conveyance guide provided at a side of the conveyance driven roller, which have openings at portions where the conveyance drive roller and the conveyance driven roller contact with each other, and guide the sheet conveyed by these rollers,   a paper thickness detection unit that is provided downstream of the sheet conveyed by the conveyance drive roller and the conveyance driven roller and near a nip point between the conveyance drive roller and the conveyance driven roller, includes a rotator brought into contact with the first conveyance guide and the sheet at a specified pressing load through an opening of the second conveyance guide, and detects a thickness of the sheet by a shift generated when the sheet contacts with the rotator;   a register roller to align the sheet after the thickness of the sheet is detected by the paper thickness detection unit; and   a print ejection mechanism that prints and fixes an image to the sheet passing through the register roller and then ejects it.   
     
     
         16 . The apparatus according to  claim 15 , wherein the paper thickness detection unit detects a shift amount of the rotator as a voltage value, samples the voltage value to obtain an average value, and detects the paper thickness. 
     
     
         17 . The apparatus according to  claim 16 , wherein the paper thickness detection unit detects the paper thickness as a difference between a voltage when the sheet does not contact with the rotator and a voltage when the sheet contacts with the rotator. 
     
     
         18 . The apparatus according to  claim 17 , wherein a fixing temperature of the image in the print ejection mechanism is changed according to the paper thickness detected in the paper thickness detection unit. 
     
     
         19 . An image forming method, comprising:
 taking out a sheet on which an image is to be printed from a paper feed cassette;   nipping and conveying the taken-out sheet by a pair of conveyance rollers;   detecting a thickness of the sheet by a shift generated when a rotator, which is provided downstream of the pair of conveyance rollers to nip and convey the sheet and near a nip point between the pair of conveyance rollers and is brought into contact with the sheet, contacts with the sheet;   aligning the sheet by a register roller after the thickness of the sheet is detected; and   ejecting the sheet after an image is printed and fixed to the sheet passing through the register roller.   
     
     
         20 . The method according to  claim 19 , wherein at the detecting of the thickness of the sheet, a shift amount of the rotator is detected as a voltage value, the voltage value is sampled to obtain an average value, and the paper thickness is detected.