Recording sheet curl correcting mechanism and recording sheet curl correcting method

Abstract

A recording sheet curl correcting mechanism corrects curl produced in a recording sheet and for use in an image forming apparatus in that heat of a heat source is transferred to the recording sheet when images are printed while the recording sheet being conveyed. The correcting mechanism includes a curl correcting unit capable of bending the recording sheet in a direction opposite to that of curl produced on the recording sheet, and the curl correcting unit is arranged downstream the heat source in a feeding direction of the recording sheet ranging from a feed side toward a discharge side as well as arranged at a position where after heat due to the heat source during printing remains in the recording sheet.

1 . A recording sheet curl correcting mechanism for correcting curl produced in a recording sheet and for use in an image forming apparatus in that heat of a heat source is transferred to the recording sheet when images are printed while the recording sheet being conveyed, the correcting mechanism comprising curl correcting means capable of bending the recording sheet in a direction opposite to that of curl produced on the recording sheet,
 wherein the curl correcting means is arranged downstream the heat source in a feeding direction of the recording sheet ranging from a feed side toward a discharge side as well as arranged at a position where after heat due to the heat source during printing remains in the recording sheet.   
     
     
         2 . The mechanism according to  claim 1 , wherein the curl correcting means is movable so as to abut to or separate from the recording sheet. 
     
     
         3 . The mechanism according to  claim 1 , wherein the curl correcting means changes the degree of the bending the recording sheet in accordance with environmental conditions during the printing. 
     
     
         4 . The mechanism according to  claim 1 , wherein the curl correcting means changes the degree of the bending the recording sheet in accordance with the material of the recording sheet. 
     
     
         5 . The mechanism according to  claim 1 , wherein the curl correcting means changes the degree of the bending the recording sheet in accordance with the conveying speed of the recording sheet. 
     
     
         6 . The mechanism according to  claim 1 , wherein when the recording sheet is cylindrically wound roll paper, the curl correcting means changes the degree of the bending the recording sheet in accordance with the outer diameter of the roll paper. 
     
     
         7 . An image forming apparatus comprising:
 a conveying roller for conveying a recording sheet;   a thermal head having a heating element; and   a platen arranged to oppose the thermal head for pinching the recording sheet between the platen and the thermal head during printing images on the recording sheet,   wherein the image forming apparatus prints images by driving the heating element with turning on electricity while the recording sheet pinched between the thermal head and the platen being conveyed by the rotation of the conveying roller, and the image forming apparatus includes curl correcting means capable of bending the recording sheet in a direction opposite to that of curl produced on the recording sheet, and   wherein the curl correcting means is arranged downstream the heat source in a feeding direction of the recording sheet ranging from a feed side toward a discharge side as well as arranged at a position where after heat due to the heat source during printing remains in the recording sheet.   
     
     
         8 . A recording sheet curl correcting method for correcting curl produced in a recording sheet used in an image forming apparatus in that heat of a heat source is transferred to the recording sheet when images are printed while the recording sheet being conveyed, the method comprising the step of bending the recording sheet in a direction opposite of that of the curl in a state of the recording sheet being positioned downstream the heat source in a feeding direction of the recording sheet ranging from a feeding side toward a discharge side as well as in a state of after heat due to the heat source during printing remaining in the recording sheet. 
     
     
         9 . The method according to  claim 8 , further comprising the step of adjusting the correction of curl produced in the recording sheet by changing the degree of the bending the recording sheet. 
     
     
         10 . A recording sheet curl correcting method of a recording sheet used in an image forming apparatus that includes a conveying roller for conveying a recording sheet, a thermal head for sequentially transferring a plurality of inks on an ink ribbon onto the recording sheet by driving a heating element with turning on electricity, and a platen arranged to oppose the thermal head for pinching the ink ribbon and the recording sheet between the platen and the thermal head during the transferring each ink, the image forming apparatus being for printing images by sequentially transferring each ink while the recording sheet pinched between the thermal head and the platen being conveyed by the rotation of the conveying roller, the method comprising the step of bending the recording sheet in a direction opposite of that of curl after the final ink is transferred onto the recording sheet from the ink ribbon and in a state in that the recording sheet is positioned downstream a heat source in a feeding direction of the recording sheet ranging from a feeding side toward a discharge side as well as in a state of after heat due to the heat source during printing remaining in the recording sheet. 
     
     
         11 . A recording sheet curl correcting mechanism for correcting curl produced in a recording sheet and for use in an image forming apparatus in that heat of a heat source is transferred to the recording sheet when images are printed while the recording sheet being conveyed, the correcting mechanism comprising a curl correcting unit capable of bending the recording sheet in a direction opposite to that of curl produced on the recording sheet,
 wherein the curl correcting unit is arranged downstream the heat source in a feeding direction of the recording sheet ranging from a feed side toward a discharge side as well as arranged at a position where after heat due to the heat source during printing remains in the recording sheet.   
     
     
         12 . An image forming apparatus comprising:
 a conveying roller for conveying a recording sheet;   a thermal head having a heating element; and   a platen arranged to oppose the thermal head for pinching the recording sheet between the platen and the thermal head during printing images on the recording sheet,   wherein the image forming apparatus prints images by driving the heating element with turning on electricity while the recording sheet pinched between the thermal head and the platen being conveyed by the rotation of the conveying roller, and the image forming apparatus includes a curl correcting unit capable of bending the recording sheet in a direction opposite to that of curl produced on the recording sheet, and   wherein the curl correcting unit is arranged downstream the heat source in a feeding direction of the recording sheet ranging from a feed side toward a discharge side as well as arranged at a position where after heat due to the heat source during printing remains in the recording sheet.