Image forming apparatus

Abstract

An image forming apparatus includes a stacking unit having a stack tray, a conveyance unit, an image forming unit, a direct current (DC) brush motor, a drive unit, a detector, a first determiner, and a second determiner. An image forming unit forms an image on a sheet conveyed by the conveyance unit from the stack tray. The drive unit drives the DC brush motor to lift and lower the stack tray in a vertical direction. The detector detects a drive current flowing through a DC brush motor winding. The first determiner determines a DC brush motor rotor rotation amount based on the number of times an absolute value of a current value of the detected drive current changes from a value smaller than a threshold to a value greater than the threshold. The second determiner determines a residual amount of stack tray stacked sheets based on the determined rotation amount.

What is claimed is: 
     
         1 . An image forming apparatus comprising:
 a stacking unit including a stack tray on which a sheet is to be stacked;   a conveyance unit configured to convey the sheet stacked on the stack tray;   an image forming unit configured to form an image on the sheet conveyed by the conveyance unit;   a direct current (DC) brush motor configured to lift and lower the stack tray in a vertical direction;   a drive unit configured to drive the DC brush motor;   a first detector configured to detect a drive current flowing through a winding of the DC brush motor;   a first determiner configured to determine a rotation amount of a rotor of the DC brush motor based on the number of times an absolute value of a current value of the drive current detected by the first detector changes from a value smaller than a threshold to a value greater than the threshold; and   a second determiner configured to determine a residual amount of sheets stacked on the stack tray based on the rotation amount determined by the first determiner.   
     
     
         2 . The image forming apparatus according to  claim 1 , further comprising an extraction unit configured to extract a signal in a predetermined frequency band from the drive current detected by the first detector,
 wherein the first determiner determines the rotation amount based on the signal after processing by the extraction unit is performed.   
     
     
         3 . The image forming apparatus according to  claim 2 , wherein the extraction unit includes a band-pass filter. 
     
     
         4 . The image forming apparatus according to  claim 1 , wherein the absolute value is increased when electrical connection between a commutator and a brush of the DC brush motor is switched. 
     
     
         5 . The image forming apparatus according to  claim 1 , wherein the stacking unit and the DC brush motor are connected by a gear. 
     
     
         6 . The image forming apparatus according to  claim 5 , wherein the gear includes a plurality of gears. 
     
     
         7 . The image forming apparatus according to  claim 1 , further comprising a memory configured to store data indicating a relationship between the rotation amount of the DC brush motor and the residual amount of sheets stacked on the stack tray,
 wherein the second determiner determines the residual amount of sheets stacked on the stack tray based on the data stored in the memory and the rotation amount determined by the first determiner.   
     
     
         8 . The image forming apparatus according to  claim 1 , wherein the stack tray moves to a first position when the stacking unit is pulled out from the image forming apparatus. 
     
     
         9 . The image forming apparatus according to  claim 8 , wherein the first position is a bottom position of the stack tray. 
     
     
         10 . The image forming apparatus according to  claim 8 , wherein, when the stacking unit is inserted into the image forming apparatus, the driving unit drives the DC brush motor such that the stack tray moves from the first position to a second position. 
     
     
         11 . The image forming apparatus according to  claim 10 , wherein the second position is a position where an uppermost sheet stacked on the stack tray is fed. 
     
     
         12 . The image forming apparatus according to  claim 10 , wherein the second determiner determines the residual amount of sheets stacked on the stack tray based on the rotation amount of the DC brush motor while the drive unit drives the DC brush motor to move the stack tray from the first position to the second position. 
     
     
         13 . The image forming apparatus according to  claim 1 , further comprising a second detector configured to detect an uppermost sheet stacked on the stack tray,
 wherein, when the stacking unit is inserted into the image forming apparatus, the drive unit drives the DC brush motor until the uppermost sheet is detected by the second detector.   
     
     
         14 . The image forming apparatus according to  claim 13 , wherein the second determiner determines the residual amount of sheets stacked on the stack tray based on the rotation amount of the DC brush motor while the drive unit drives the DC brush motor. 
     
     
         15 . An image forming apparatus comprising:
 a stacking unit including a stack tray on which a sheet is to be stacked;   a conveyance unit configured to convey the sheet stacked on the stack tray;   an image forming unit configured to form an image on the sheet conveyed by the conveyance unit;   a DC brush motor configured to lift and lower the stack tray in a vertical direction;   a drive unit configured to drive the DC brush motor;   a detector configured to detect a drive current flowing through a winding of the DC brush motor;   a first determiner configured to determine a rotation amount of a rotor of the DC brash motor based on the number of times an absolute value of a current value of the drive current detected by the detector changes from a value greater than a threshold to a value smaller than the threshold; and   a second determiner configured to determine a residual amount of sheets stacked on the stack tray based on the rotation amount determined by the first determiner.