Optical scanning apparatus, optical writing apparatus, and image forming apparatus

Abstract

F-theta lenses, included in scanning lens systems, are arranged on a main scanning plane facing an optical deflector and substantially linearly symmetrically on the main scanning plane with reference to a rotational center of the optical deflector. Each f-theta lens has a no-power portion in the main scanning direction. Synchronization-detecting light passes through the no-power portion of the f-theta lens, thus enabling reduction in color shift due to temperature variation in an image forming apparatus without increasing the cost and complexity in controlling color shift.

What is claimed is: 
     
       1. An optical scanning apparatus comprising:
 2n (where n≧1) light sources, each light source including m (where m≧1) light emitting units; 
 a plurality of synchronization detecting unit units that receives m×n receive light beams from the light sources, scans a scanning surface by the light beams emitted by 2n light sources, and determines a write timing for writing to the scanning surface, the light beams being substantially symmetrical with respect to a sub-scanning cross-section that includes a rotational axis of an optical deflector; 
 an optical deflector that deflects the light beams from the light sources; and  
 a first scanning lens system and a second scanning lens system arranged on either side of the optical deflector and causing m that cause the light beams to perform imaging on the respective scanning surfaces photosensitive members, the first scanning lens system including at least a first scanning lens and the second scanning lens system including at least a second scanning lens, wherein
 synchronization detection by the plurality of synchronization detecting unit is performed at one end of each scan line units are configured to perform synchronization detection, and 
 the first scanning lens is a scanning lens that the light beams deflected by the deflector first enter in the first scanning lens system and the second scanning lens system is a scanning lens that the light beams deflected by the deflector first enter in the second scanning lens system, the first scanning lens and the second scanning lens are arranged substantially symmetrically with reference to a line in a main scanning direction orthogonal to the that passes through a rotational axis of the optical deflector and is substantially parallel to a longitudinal direction of the first and second scanning lenses, and 
 the first and second scanning lens system systems includes include a no-power portion in the main scanning direction, and the light beams guided to the plurality of synchronization detecting unit units pass through the no-power portion. 
 
 
     
     
       2. The optical scanning apparatus according to  claim 1 , wherein a magnitude of a spot position shift of the synchronization-detecting light in the main scanning direction on an imaging surface or its equivalent due to temperature variation detected by the plurality of synchronization detecting unit units is 5 μm/° C. or less. 
     
     
       3. The optical scanning apparatus according to  claim 1 , wherein an inter-surface deviation of a surface tilt of the optical deflector is kept to 200 seconds or less. 
     
     
       4. The optical scanning apparatus according to  claim 1 , wherein a synchronization optical system systems of the plurality of synchronization detecting unit units that converges the converge synchronization-detecting light into a light-receiving unit corrects units correct the effect of a surface tilt of the optical deflector. 
     
     
       5. The optical scanning apparatus according to  claim 1 , wherein from among a first set of scanning lenses L 1 , L 2 , and so on up to q (where j=1, 2, 3 . . . ) forming the first scanning lens system in the sequence of the nearest to the farthest from the optical deflector on one side of the optical deflector and a second set of scanning lenses L′ 1 , L′ 2 , and so on up to Lj (where j=1, 2, 3, . . . ), any pair of scanning lenses Lj and Lj have an identical geometry. 
     
     
       6. An image forming apparatus comprising:
 an exposing unit; 
 a developing unit; 
 a transfer unit; 
 a fixing unit; and  
 the optical scanning apparatus according to  claim 1 . 
 
     
     
       7. The optical scanning apparatus according to  claim 1 , wherein the first scanning lens system and the second scanning lens system are arranged facing each other on either side of the optical deflector. 
     
     
       8. An optical scanning apparatus, comprising:
 2n (where n≧1) light sources, each light source including m (where m≧1) light emitting units; 
 a plurality of synchronization detecting unit units that receives m×n receive light beams from the light sources, scans a scanning surface by the light beams emitted by 2n light sources, and determines a write timing for writing to the scanning surface, the light beams being substantially symmetrical with respect to a sub-scanning cross-section that includes a rotational axis of an optical deflector; and 
 an optical deflector that deflects the light beams from the light sources; and  
 a first scanning lens system and a second scanning lens system arranged on either side of the optical deflector and causing m that cause the light beams to perform imaging on the respective scanning surfaces photosensitive members, the first scanning lens system including at least a first scanning lens and the second scanning lens system including at least a second scanning lens, wherein
 synchronization detection by the plurality of synchronization detecting unit is performed at one end of each scan line units are configured to perform synchronization detection, 
 the first scanning lens system is a scanning lens that the light beams deflected by the deflector first enter in the first scanning lens system and the second scanning lens system is a scanning lens that the light beams deflected by the deflector first enter in the second scanning lens system, the first scanning lens and the second scanning lens are arranged substantially symmetrically with reference to a line in a main scanning direction orthogonal to the that passes through a rotational axis of the optical deflector and is substantially parallel to a longitudinal direction of the first and second scanning lenses, and 
 the synchronization-detecting synchronization detecting units are configured to receive the light does beams such that the light beams do not pass through the scanning lens system first and second scanning lenses. 
 
 
     
     
       9. The optical scanning apparatus according to  claim 8 , wherein the first scanning lens system and the second scanning lens system are arranged facing each other on either side of the optical deflector. 
     
     
       10. An optical scanning apparatus, comprising:
 2n (where n≧1) light sources, each light source including m (where m≧1) light emitting units; 
 a plurality of synchronization detecting unit units that receives m×n receive light beams from the light sources, scans a scanning surface by the light beams emitted by 2n light sources, and determines a write timing for writing to the scanning surface, the light beams being substantially symmetrical with respect to a sub-scanning cross-section that includes a rotational axis of an optical deflector; and 
 an optical deflector that deflects the light beams from the light sources; and  
 a first scanning lens system and a second scanning lens system arranged on either side of the optical deflector and causing m that cause the light beams to perform imaging on the respective scanning surfaces photosensitive members, the first scanning lens system including at least a first scanning lens and the second scanning lens system including at least a second scanning lens, wherein
 synchronization detection by the plurality of synchronization detecting unit is performed at one end of each scan line units are configured to perform synchronization detection, 
 the first scanning lens is a scanning lens that the light beams deflected by the deflector first enter in the first scanning lens system and the second scanning lens system is a scanning lens that the light beams deflected by the deflector first enter in the second scanning lens system, the first scanning lens and the second scanning lens are arranged substantially symmetrically with reference to a line in a main scanning direction orthogonal to the that passes through a rotational axis of the optical deflector and is substantially parallel to a longitudinal direction of the first and second scanning lenses, and 
 an opening is provided in each of the first and second scanning lens system systems, and the synchronization-detecting synchronization detecting light passes through the opening. 
 
 
     
     
       11. The optical scanning apparatus according to  claim 10 , wherein the first scanning lens system and the second scanning lens system are arranged facing each other on either side of the optical deflector. 
     
     
       12. An optical writing apparatus comprising:
 a plurality of optical scanning apparatuses, each optical scanning apparatus including,
 2n (where n≧1) light sources, each light source including m (where m≧1) light emitting units; 
 a plurality of synchronization detecting unit units that receives m×n receive light beams from the light sources, scans a scanning surface by the light beams emitted by 2n light sources, and determines a write timing for writing to the scanning surface, the light beams being substantially symmetrical with respect to a sub-scanning cross-section that includes a rotational axis of an optical deflector; and 
 an optical deflector that deflects the light beams from the light sources; and  
 a first scanning lens system and a second scanning lens system arranged facing each other on either side of optical deflector and causing m that cause the light beams to perform imaging on the respective scanning surfaces photosensitive members, the first scanning lens system including at least a first scanning lens and the second scanning lens system including at least a second scanning lens,  
 wherein synchronization detection by the plurality of synchronization detecting unit is performed at one end of each scan line units are configured to perform synchronization detection, and 
 the first scanning lens is a scanning lens that the light beams deflected by the deflector first enter in the first scanning lens system and the second scanning lens system is a scanning lens that the light beams deflected by the deflector first enter in the second scanning lens system, the first scanning lens and the second scanning lens are arranged substantially symmetrically with reference to a line in a main scanning direction orthogonal to the that passes through a rotational axis of the optical deflector and is substantially parallel to a longitudinal direction of the first and second scanning lenses, 
 
 wherein synchronization-detecting synchronization detecting light of only one optical scanning apparatus is detected, and write timings of the other optical scanning apparatuses is are electrically estimated based on detection signals of detected synchronization-detecting synchronization detecting light. 
 
     
     
       13. The optical writing apparatus according to  claim 12 , wherein the optical deflectors of the optical scanning apparatuses have a common rotational axis. 
     
     
       14. The optical writing apparatus according to  claim 12 , wherein the light beams from the plurality of levels are incident on the same phase plane of the optical deflector at different incidence angles in the main scanning direction. 
     
     
       15. The optical writing apparatus according to  claim 12 , wherein the synchronization optical system includes systems include a synchronization mirror that guides the light beam towards the plurality of synchronization detecting unit units, and the synchronization mirror mirrors and the plurality of synchronization detecting unit units are coupled within the sub-scanning cross-section. 
     
     
       16. The optical writing apparatus according to  claim 12 , wherein the light beams from the a plurality of levels incident on the a same phase plane of the optical deflector are deflected in a main scanning direction by different reflecting points in the main scanning direction. 
     
     
       17. An image forming apparatus comprising;
 an exposing unit;   a developing unit;   a transfer unit;   a fixing unit; and   the optical scanning apparatus according to claim 8.   
     
     
       18. An image forming apparatus comprising;
 an exposing unit;   a developing unit;   a transfer unit;   a fixing unit; and   the optical scanning apparatus according to claim 10.