Light detection device and sheet processing apparatus including the same

Abstract

An exemplary aspect of the present disclosure, there is provided a light detection device including a first detecting portion to detect fluorescence from a first detection position on a conveyor path along which a sheet is conveyed, a second detecting portion to detect afterglow from a second detection position on the conveyor path along which the sheet is conveyed, a lighting portion to apply excitation light over a range including the first detection position and not including the second detection position, a first reference member which includes fluorescent material that emits fluorescence by being excited by the lighting portion and which emits reference light toward the first detecting portion, a second reference member to emit reference light toward the second detecting portion when the sheet is present at the second detection position, the reference light not influencing a result of detection by the second detecting portion, and a correction controller to correct a result of detection by the first detecting portion based on the reference light detected by the first detecting portion and to correct a result of detection by the second detecting portion based on the reference light detected by the second detecting portion.

What is claimed is: 
     
         1 . A light detection device comprising:
 a first detecting portion to detect fluorescence from a first detection position on a conveyor path along which a sheet is conveyed;   a second detecting portion to detect afterglow from a second detection position on the conveyor path along which the sheet is conveyed;   a lighting portion to apply excitation light over a range including the first detection position and not including the second detection position;   a first reference member to emit reference light toward the first detecting portion, the first reference member including fluorescent material which emits fluorescence by being excited by the lighting portion;   a second reference member to emit reference light toward the second detecting portion when the sheet is present at the second detection position, the reference light not influencing a result of detection by the second detecting portion; and   a correction controller to correct a result of detection by the first detecting portion based on the reference light detected by the first detecting portion and to correct a result of detection by the second detecting portion based on the reference light detected by the second detecting portion.   
     
     
         2 . The light detection device according to  claim 1 , wherein the second reference member is disposed to be separated from the second detection position by a predetermined distance along an optical path, and emits diffuse reference light. 
     
     
         3 . The light detection device according to  claim 2 , wherein the second reference member includes fluorescent material which emits fluorescence by being excited by the lighting portion, and is disposed at a position which the light emitted from the lighting portion enters. 
     
     
         4 . The light detection device according to  claim 2 , further comprising:
 a light guide to receive the reference light emitted from the first reference member, and to guide the received reference light so that the received reference light enters the second reference member, wherein   the second reference member diffusely reflects the reference light entering through the light guide.   
     
     
         5 . The light detection device according to  claim 2 , further comprising:
 a light guide to receive the reference light emitted from the first reference member, and to guide the received reference light so that the received reference light enters the second reference member; and   a reflector to reflect incident light, wherein   the second reference member diffusely transmits the reference light entering through the light guide, and   the reflector reflects the reference light diffused by the second reference member and causes the reference light diffused by second reference member to enter the second detecting portion.   
     
     
         6 . The light detection device according to  claim 2 , wherein the predetermined distance is set based on a detected transmittance of the sheet and a detected intensity of light emitted by the second reference member. 
     
     
         7 . A sheet processing apparatus comprising:
 a conveyor path to convey a sheet;   a first detecting portion to detect fluorescence from a first detection position on the conveyor path along which the sheet is conveyed;   a second detecting portion to detect afterglow from a second detection position on the conveyor path along which the sheet is conveyed;   a lighting portion to apply excitation light over a range including the first detection position and not including the second detection position;   a first reference member to emit reference light toward the first detecting portion, the first reference member including fluorescent material which emits fluorescence by being excited by the lighting portion;   a second reference member to emit reference light toward the second detecting portion when the sheet is present at the second detection position, the reference light not influencing a result of detection by the second detecting portion;   a correction controller to correct a result of detection by the first detecting portion based on the reference light detected by the first detecting portion and to correct a result of detection by the second detecting portion based on the reference light detected by the second detecting portion;   a determination portion to determine whether or not the sheet contains each of fluorescent printed information and phosphorescent printed information, based on a fluorescent image detected by the first detecting portion and an afterglow image detected by the second detecting portion; and   a classification processor to determine a type of the sheet based on a result of the determination by the determination portion and to classify the sheet by type.   
     
     
         8 . The sheet processing apparatus according to  claim 7 , wherein the second reference member is disposed to be separated from the second detection position by a predetermined distance along an optical path, and emits diffuse reference light. 
     
     
         9 . The sheet processing apparatus according to  claim 8 , wherein the second reference member includes fluorescent material which emits fluorescence by being excited by the lighting portion, and is disposed at a position which the light emitted from the lighting portion enters. 
     
     
         10 . The sheet processing apparatus according to  claim 8 , further comprising:
 a light guide to receive the reference light emitted from the first reference member, and to guide the received reference light so that the received reference light enters the second reference member,   wherein the second reference member diffusely reflects the reference light entering through the light guide.   
     
     
         11 . The sheet processing apparatus according to  claim 8 , further comprising:
 a light guide to receive the reference light emitted from the first reference member, and to guide the received reference light so that the received reference light enters the second reference member; and   a reflector to reflect incident light, wherein   the second reference member diffusely transmits the reference light entering through the light guide, and   the reflector reflects the reference light diffused by the second reference member and causes the reference light diffused by the second reference member to enter the second detecting portion.   
     
     
         12 . The sheet processing apparatus according to  claim 8 , wherein the predetermined distance is set based on a detected transmittance of the sheet and a detected intensity of light emitted by the second reference member.