Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1999-02-22
2001-03-27
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S248000
Reexamination Certificate
active
06208366
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light emitting diode (LED) head having a function of detecting positional displacement of a photosensitive member and an electrophotographic image forming apparatus employing the same, and more particularly to an LED head having a function of detecting positional displacement of a photosensitive member and an electrophotographic image forming apparatus employing the same which are suitable for use with an electrophotographic color printing apparatus.
2. Description of the Related Art
Conventionally, an LED head having a function of detecting positional displacement of a photosensitive member of the type mentioned employs, as disclosed in, for example, in Japanese Patent Laid-Open No. 9975/1992, a writing light source in the form of an array such as an LED array which is used also as a light source for detection of the position of a photosensitive member and uses a photodiode as a position detector for the photosensitive member.
FIG. 2
schematically shows a construction of such a conventional LED head as described above. Referring to
FIG. 2
, the LED head
1
shown includes a position detecting LED array
4
for emitting light to position detector
3
, a latent image forming LED array
5
for irradiating light upon a photosensitive belt
2
, and a single rod lens array
8
. Therefore, photosensitive belt
2
and position detector
3
must be disposed within a range of a focal length of the rod lens array
8
. Usually, the range of the focal length is 0.2 mm or less. Actually, since the photosensitive belt
2
has some thickness, a gap
9
between the photosensitive belt
2
and the position detector
3
is smaller than 0.2 mm. The photosensitive belt
2
and the position detector
3
disposed with such a small gap left therebetween are brought into contact with each other readily, for example, by thermal expansion of them by a temperature variation or an impact upon the apparatus by an operator. Such contact between them gives rise to formation of a defective image because toner powder on the photosensitive belt
2
is scattered to damage an image or the speed of movement of the photosensitive belt
2
is dropped to cause partial contraction of an image.
Thus, the conventional LED head having such a function of detecting positional displacement of a photosensitive member as described above is disadvantageous in that, as the photosensitive member and the position detector are brought into contact with each other by thermal expansion of the apparatus or by some other cause, a defective image is produced because toner powder on the photosensitive member is scattered to damage an image or the speed of movement of the photosensitive member is dropped to cause partial contraction of an image.
The reason is that, because the rod lens array of the LED head has an equal focal length between a portion thereof which is used for detection of the position of the photosensitive member and another portion thereof which is used to write a latent image and besides the range of the focal length of the rod lens array is narrow, the photosensitive member and the position detector must be disposed within the narrow range of the focal length.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical head which provides between a photosensitive member and a position detector a sufficient distance over which the photosensitive member and the position detector are not brought into contact with each other readily by thermal expansion of the apparatus or a like cause and an electrophotographic image forming apparatus which employs the optical head.
In order to attain the object described above, according to an aspect of the present invention, there is provided an optical head having a function of detecting positional displacement of a photosensitive member, comprising a latent image forming light emitting element array for irradiating light upon the photosensitive member to form an electrostatic latent image on the photosensitive member, a position detecting light emitting element array for irradiating light to be used for detection of the position of an end portion of the photosensitive member, a position detector for detecting the position of the end portion of the photosensitive member from the light emitted from the position detecting light emitting element array, and exposure position correction means for varying an electrostatic latent image formation position of the latent image forming light emitting array in response to the position of the end portion of the photosensitive member detected by the position detector, a rod lens array for the position detecting light emitting element array having a focal length longer than a focal length of a rod lens array for the latent image forming light emitting element array.
Preferably, the latent image forming light emitting element array and the position detecting light emitting element array are formed on a same board. Each of the latent image forming light emitting element array and the position detecting light emitting element array may be an LED array.
According to another aspect of the present invention, the optical head described above can be used suitably as exposure means for exposing the photosensitive member to light in an electrophotographic image forming apparatus. Preferably, the photosensitive member is in the form of a belt.
With the optical head and the photoelectric image forming apparatus, since the position detector and the photosensitive member are not brought into contact with each other even if, for example, thermal expansion of the apparatus by a temperature variation occurs or an impact by operation of an operator acts upon the apparatus, such an image defect that toner powder on the photosensitive member is scattered by inadvertent contact between the position detector and the photosensitive member to damage an image or the speed of movement of the photosensitive member is dropped to cause partial contraction of an image does not occur.
The reason is that, because the focal length of the position detecting rod lens array is longer than the focal length of the latent image forming rod lens array, a sufficient gap can be assured between the position detector and the photosensitive member, and consequently, inadvertent contact between the position detector and the photosensitive member does not occur.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference symbols.
REFERENCES:
patent: 61-138265 (1986-06-01), None
patent: 4-9975 (1992-01-01), None
patent: 4-16969 (1992-01-01), None
Le N.
NEC Corporation
Nguyen Lamson D.
Ostrolenk Faber Gerb & Soffen, LLP
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