Image forming apparatus

Abstract

An image forming apparatus includes a feeder unit configured to feed one or more sheets held in a sheet container, and a sheet sensor configured to detect whether or not there are any sheets in the sheet container. When a sheet is to be fed to an image-forming unit, the feeder unit preliminarily conveys the sheet in a sheet feeding direction by a predetermined distance from a held position in the sheet container so that a trailing end of the sheet passes a detecting position of the sheet sensor.

1 . An image forming apparatus comprising: 
 a sheet container configured to hold therein one or more sheets;    a feeder unit configured to feed the one or more sheets from the sheet container;    an image-forming unit configured to perform an image forming operation on the one or more sheets fed by the feeder unit;    a sheet sensor configured to detect whether or not the one or more sheets are present in the sheet container; and    a controller configured to control the image forming operation of the image-forming unit in accordance with a detection result of the sheet sensor,    wherein a detection position of the sheet sensor is a trailing end portion of sheet at a held position in the sheet container, and    wherein when one sheet of the one or more sheets is to be fed to the image-forming unit, the feeder unit preliminarily conveys the sheet in a sheet feeding direction by a predetermined distance from the held position in the sheet container so that a trailing end of the sheet passes the detecting position of the sheet sensor.    
     
     
         2 . The image forming apparatus according to  claim 1 , wherein when the feeder unit conveys a last sheet of the one or more sheets in the sheet feeding direction by the predetermined distance from the held position and the sheet sensor thus determines that the sheet container will become empty, the controller controls the image-forming unit so as to stop the image-forming unit from performing a subsequent image forming process that follows a current image forming process for forming a toner image used for forming an image on the last sheet.  
     
     
         3 . The image forming apparatus according to  claim 1 , wherein the feeder unit includes a feed roller configured to feed the one or more sheets held in the sheet container, and a separator configured to separate each sheet from the one or more sheets fed by the feed roller in a one-by-one fashion and to convey the separated sheet, 
 wherein, as viewed in the sheet feeding direction, if a distance between a leading end of the one or more sheets held in the sheet container and the separator is defined as D and a distance between the separator and the leading end of each sheet conveyed by the predetermined distance is defined as E, the detecting position of the sheet sensor is located closer towards the leading end of the one or more sheets held in the sheet container from a position distant from the trailing end of the one or more sheets held in the sheet container by D, but is located closer towards the trailing end from a position distant from the trailing end by (D+E).    
     
     
         4 . The image forming apparatus according to  claim 1 , further comprising a trailing-end regulation member provided in the sheet container and movable in the sheet feeding direction, the trailing-end regulation member regulating the position of the trailing end of the one or more sheets held in the sheet container in accordance with the size of the one or more sheets, 
 wherein the sheet sensor is provided in the trailing-end regulation member.    
     
     
         5 . The image forming apparatus according to  claim 1 , wherein the sheet sensor comprises a plurality of sheet detection sensors, and wherein the number of the sheet detection sensors provided corresponds to sizes of the one or more sheets that are containable in the sheet container.  
     
     
         6 . The image forming apparatus according to  claim 1 , wherein the detection result of the sheet sensor is sent to the controller wirelessly or by electromagnetic induction.  
     
     
         7 . An image forming apparatus comprising: 
 a first and second sheet containers each holding therein one or more sheets;    a first and second feeder units each configured to respectively feed the one or more sheets held in each of the first and second sheet containers;    an image-forming unit configured to perform an image forming operation on the one or more sheets fed by the first and second feeder units;    a sheet sensor configured to detect whether or not the one or more sheets are present in the first sheet container; and    a controller configured to control a sheet feeding process of the first and second feeder units in accordance with a detection result of the sheet sensor,    wherein a detection position of the sheet sensor is a trailing end portion of sheet at a held position in the sheet container,    wherein when one sheet of the one or more sheets in the first sheet container is to be fed to the image-forming unit, the first feeder unit preliminarily conveys the sheet in a sheet feeding direction by a predetermined distance from the held position in the first sheet container so that a trailing end of the sheet passes the detecting position of the sheet sensor, and    wherein when the first feeder unit conveys a last sheet of the one or more sheets in the first sheet container in the sheet feeding direction by the predetermined distance from the held position and the sheet sensor thus determines that the first sheet container will become empty, the controller controls the second feeder unit so as to switch from the first sheet container to the second sheet container.    
     
     
         8 . The image forming apparatus according to  claim 7 , further comprising trailing-end regulation members respectively provided in the first and second sheet containers and movable in the sheet feeding direction, each of the trailing-end regulation members regulating the position of the trailing end of the one or more sheets held in the corresponding sheet container in accordance with the size of the one or more sheets, 
 wherein the sheet sensor is provided in the trailing-end regulation member of the first sheet container.    
     
     
         9 . The image forming apparatus according to  claim 7 , wherein the first feeder unit includes a feed roller configured to feed the one or more sheets held in the first sheet container, and a separator configured to separate each sheet from the one or more sheets fed by the feed roller in a one-by-one fashion and to convey the separated sheet, 
 wherein, as viewed in the sheet feeding direction, if a distance between a leading end of the one or more sheets held in the first sheet container and the separator is defined as D and a distance between the separator and the leading end of each sheet conveyed by the predetermined distance is defined as E, the detecting position of the sheet sensor is located closer towards the leading end of the one or more sheets held in the first sheet container from a position distant from the trailing end of the one or more sheets held in the first sheet container by D, but is located closer towards the trailing end from a position distant from the trailing end by (D+E).