Line head and image forming apparatus incorporating the same

Abstract

At least one light emission array includes a plurality of light emitting elements arrayed in a first direction. Each of the light emitting elements is an organic electroluminescence element. A monitor quantitatively monitors a light emitting state of at least one of the light emitting elements to obtain a monitored amount. A comparator compares the monitored amount and a reference amount. A controller performs a constant current control with respect to at least one of the light emitting elements in accordance with a result of the comparison performed by the comparator.

1 . A line head, comprising: 
 at least one light emission array including a plurality of light emitting elements arrayed in a first direction, each of which is an organic electroluminescence element;    a monitor, which quantitatively monitors a light emitting state of at least one of the light emitting elements to obtain a monitored amount;    a comparator, which compares the monitored amount and a reference amount; and    a controller, which performs a constant current control with respect to at least one of the light emitting elements in accordance with a result of the comparison performed by the comparator.    
   
   
       2 . The line head as set forth in  claim 1 , wherein the monitor monitors a drive voltage of the at least one of the light emitting elements.  
   
   
       3 . The line head as set forth in  claim 2 , wherein the reference amount is a value of the drive voltage.  
   
   
       4 . The line head as set forth in  claim 1 , wherein the constant current control is performed in a feed back control manner.  
   
   
       5 . The line head as set forth in  claim 1 , wherein the monitor monitors an emitted light amount of the at least one of the light emitting elements.  
   
   
       6 . The line head as set forth in  claim 1 , wherein the constant current control is performed with respect to each of the light emitting elements.  
   
   
       7 . The line head as set forth in  claim 1 , wherein the light emitting elements are divided into a plurality of groups, and the constant current control is performed with respect to each of the groups.  
   
   
       8 . The line head as set forth in  claim 1 , wherein the constant current control is simultaneously performed with respect to the respective light emitting elements.  
   
   
       9 . The line head as set forth in  claim 1 , wherein the constant current control is performed by increasing a drive current for the at least one of the light emitting elements, every time when the result of the comparison indicates that an emitted light amount of the at least one of the light emitting elements becomes lower than a threshold value.  
   
   
       10 . The line head as set forth in  claim 1 , wherein a plurality of light emission arrays are arranged in a second direction which is perpendicular to the first direction.  
   
   
       11 . An image forming apparatus, comprising: 
 an image carrier, having a photoconductive surface;    the line head as set forth in  claim 1 , which emits light to form an electrostatic latent image on the photoconductive surface; and    a developing device, which supplies developer onto the photoconductive surface to make the electrostatic latent image visible.    
   
   
       12 . A line head, comprising: 
 at least one light emission array including a plurality of light emitting elements arrayed in a first direction, each of which is an organic electroluminescence element;    a counter, which counts an amount indicative of a used state of at least one of the light emitting elements; and    a controller, which performs a constant voltage control with respect to at least one of the light emitting elements in accordance with the amount counted by the counter.    
   
   
       13 . The line head as set forth in  claim 12 , wherein the counter counts a cumulative operating time period of the at least one of the light emitting elements.  
   
   
       14 . The line head as set forth in  claim 12 , wherein the counter counts the number of a recording medium on which an image formed by the line head is recorded.  
   
   
       15 . The line head as set forth in  claim 12 , wherein the counter counts the number of formation of a dot array having a predetermined pattern.  
   
   
       16 . The line head as set forth in  claim 12 , wherein the constant current control is performed with respect to each of the light emitting elements.  
   
   
       17 . The line head as set forth in  claim 12 , wherein the light emitting elements are divided into a plurality of groups, and the constant current control is performed with respect to each of the groups.  
   
   
       18 . The line head as set forth in  claim 12 , wherein the constant current control is simultaneously performed with respect to the respective light emitting elements by applying same voltage.  
   
   
       19 . The line head as set forth in  claim 12 , wherein each of the light emitting elements is driven by a field effect transistor, and a condenser is connected between a gate electrode and a drain electrode of the field effect transistor.  
   
   
       20 . The line head as set forth in  claim 12 , wherein the constant current control is performed by increasing a drive voltage for the at least one of the light emitting elements, every time when the result of the comparison indicates that an emitted light amount of the at least one of the light emitting elements becomes lower than a threshold value.  
   
   
       21 . The line head as set forth in  claim 12 , wherein a plurality of light emission arrays are arranged in a second direction which is perpendicular to the first direction.  
   
   
       22 . An image forming apparatus, comprising: 
 an image carrier, having a photoconductive surface;    the line head as set forth in  claim 12 , which emits light to form an electrostatic latent image on the photoconductive surface; and    a developing device, which supplies developer onto the photoconductive surface to make the electrostatic latent image visible.    
   
   
       23 . A line head, comprising: 
 at least one light emission array including a plurality of light emitting elements arrayed in a first direction, each of which is an organic electroluminescence element;    a monitor, which quantitatively monitors a light emitting state of at least one of the light emitting elements to obtain a monitored amount; and    a controller, which performs a constant voltage control with respect to at least one of the light emitting elements in accordance with the monitored amount.    
   
   
       24 . The line head as set forth in  claim 23 , wherein the monitor monitors a drive current of the at least one of the light emitting elements.  
   
   
       25 . The line head as set forth in  claim 23 , wherein the monitored amount is input to the controller in a feed back control manner.  
   
   
       26 . The line head as set forth in  claim 23 , wherein the monitor monitors an emitted light amount of the at least one of the light emitting elements.  
   
   
       27 . The line head as set forth in  claim 23 , wherein the constant current control is performed with respect to each of the light emitting elements.  
   
   
       28 . The line head as set forth in  claim 23 , wherein the light emitting elements are divided into a plurality of groups, and the constant current control is performed with respect to each of the groups.  
   
   
       29 . The line head as set forth in  claim 23 , wherein the constant current control is simultaneously performed with respect to the respective light emitting elements by applying same voltage.  
   
   
       30 . The line head as set forth in  claim 23 , wherein each of the light emitting elements is driven by a field effect transistor, and a condenser is connected between a gate electrode and a drain electrode of the field effect transistor.  
   
   
       31 . The line head as set forth in  claim 23 , wherein the constant current control is performed by increasing a drive voltage for the at least one of the light emitting elements, every time when the result of the comparison indicates that an emitted light amount of the at least one of the light emitting elements becomes lower than a threshold value.  
   
   
       32 . The line head as set forth in  claim 23 , wherein a plurality of light emission arrays are arranged in a second direction which is perpendicular to the first direction.  
   
   
       33 . An image forming apparatus, comprising: 
 an image carrier, having a photoconductive surface;    the line head as set forth in  claim 12 , which emits light to form an electrostatic latent image on the photoconductive surface; and    a developing device, which supplies developer onto the photoconductive surface to make the electrostatic latent image visible.