Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-01-27
2001-02-27
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Transfer
C347S116000
Reexamination Certificate
active
06195524
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based on Patent Application No. HEI 11-019144 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus provided with a function for detecting a toner marker on a transfer member supporting a toner image transferred from a photosensitive member, and specifically relates to multi-color overlay position dislocation in a color image forming apparatus.
2. Description of the Related Art
In conventional color image forming apparatuses, the density difference between a transfer member and various color toner marks transferred onto the belt or drum-like transfer member is detected via a photosensor, and the positional dislocation of the toner marks is detected by the output of the photosensors.
In such conventional apparatuses, however, photosensors generally detect the density difference between the transfer member and toner marks created by each process for colors Y, M, C, K, the center position of the mark is determined from the photosensor output to infer the position of each mark, and the degree of dislocation if any of the position of marks of each color from a standard position is discriminated and the amount of such dislocation is corrected during image formation. Essentially, although determination of the image overlay condition is best when the images have been overlaid, it is necessary to determine the dislocation from a standard value for detection data individually because the photosensors cannot recognize each color toner mark when being overlaid. In this case, it becomes difficult to suppress the influence of error components during detection, e.g., detection timing and speed fluctuation of the transfer member during transfer, errors of detection timing relating to timing differences and the like. Furthermore, since such detection is accomplished based on the magnitude of the photosensor output, there is concern that sensor output may be reduced by soiling of the sensor and the like.
SUMMARY OF THE INVENTION
An object of the present invention is to eliminate the previously described disadvantages by providing an image forming apparatus capable of excellent detection of the position of a toner mark on a transfer member without being influenced by transfer member thickness variation or position oscillation, and having a toner mark detection function capable of higher precision detection by eliminating errors due to differences in measurement timing by directly detecting the overlay dislocation of a plurality of toner layer with the same timing.
These objects are attained by the image forming apparatus of the present invention comprising an image-bearing body, a transfer member for supporting a toner image transferred from the image-bearing body, and a detecting unit for detecting toner marks on the transfer member, wherein the detecting unit detects the distance from the detecting unit to the transfer member and detects the distance from the detecting unit to the toner mark, and is provided with a determining unit that determines the toner mark position from the difference in these two distances.
In this construction, detection error elements caused by transfer member thickness variation and transfer member position variation during detection are eliminated because the toner mark positions are detected from the difference in the detected distance from the detecting unit to the transfer member and the detected distance from the detecting unit to the toner mark. Furthermore, toner mark position dislocation can be detected with excellent precision when toner layers of a plurality of color toner marks are overlaid on the transfer member.
The detection unit of the image forming apparatus of the present invention attaining the aforesaid objects is provided with at least two position sensing devices arranged in a direction perpendicular to the transport direction of the transfer member, wherein one position sensing device detects the toner mark, and the other position sensing device detects the transfer member, and the detecting unit detects the thickness of the toner mark via the difference in the detection values of the two position sensing devices.
In this way measurement errors due to detection timing are eliminated.
The determining unit of the image forming apparatus of the present invention attaining the aforesaid objects compares the difference between the detection values of the two position sensing devices relative to overlaid toner marks of at least two colors to a first reference level and a second reference level, discerns an area having a different comparison result as toner mark color dislocation, and determines the amount of dislocation and the amount of correction from the continuous time of the area of different comparison results.
In this way the position dislocation in color image formation can be corrected.
The detecting unit of the image forming apparatus of the present invention attaining the aforesaid objects detects the thickness of the toner marks by the difference in the voltage values output from the two position sensing devices.
The detecting unit of the image forming apparatus of the present invention attaining the aforesaid objects is a sensor comprising at one photoemitter device and two photoreceptor devices.
In this way detection errors due to undulation of the transfer member coinciding with a time difference of the light emission control of the photoemitter device can be eliminated because the toner mark and the transfer member are detected at the same time using the light emitted from a single photoemitter device.
The detecting unit of the image forming apparatus of the present invention attaining the aforesaid objects is two sensors comprising one photoemitter device and one photoreceptor device.
REFERENCES:
patent: 4485982 (1984-12-01), St. John et al.
patent: 5510885 (1996-04-01), Mori et al.
patent: 5875380 (1999-02-01), Iwata et al.
patent: 6008826 (1999-12-01), Foote et al.
patent: 6101359 (2000-08-01), Tamura
patent: 6-253151 (1994-09-01), None
patent: 8-286458 (1996-11-01), None
Higashi Toshikazu
Takasu Akira
Brase Sandra
McDermott & Will & Emery
Minolta Co. , Ltd.
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