Solid scanning optical writing device, and light amount...

Details Solid scanning optical writing device, and light amount... Solid scanning optical writing device, and light amount...

2000-12-13

2003-01-21

Pham, Hai (Department: 2861)

Incremental printing of symbolic information

Light or beam marking apparatus or processes

Scan of light

C347S246000

Reexamination Certificate

active

06509922

ABSTRACT:

This application is based on application No. JP 11-354948 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved solid scanning optical writing device, as well as a light amount correction method and light amount measuring device therefor, which are used to write images (latent images) on a photoreceptor using a PLZT light shutter array or an LED array.
2. Description of the Related Art
Various optical writing devices that turn ON/OFF light for each pixel using a PLZI light shutter array or LED array have conventionally been proposed as a device to form images (latent images) on photosensitive paper using a silver halide photosensitive material, film or electrophotographic photoreceptor. For example, as shown in FIG.
12
(A), in the case of an optical writing head comprising many light shutter elements
31
a
and
31
b
aligned in alternating fashion in two rows in the main scanning direction, an image for one line is formed in the following manner.
First, the light shutter elements
31
a
of one row are controlled to turn ON/OFF based on the image data, and consequently, the light from the light source is turned ON/OFF. As a result, the surface of the photosensitive paper, etc. being conveyed is exposed and an image (latent image) is formed.
When the area of the photosensitive paper on which the image has been formed reaches the exposure position for the light shutter elements
31
b
of the other row, the light shutter elements
31
b
of the other row are controlled to turn ON/OFF based on the image data, whereupon the light from the light source is turned ON/OFF and an image is formed on the surface of the photosensitive paper. Through this operation, the intermittent image formed by the turning ON/OFF of the light shutter elements
31
a
and the intermittent image formed by the turning ON/OFF of the light shutter elements
31
b
are combined, and an image for one line is formed.
Incidentally, PLZT light shutter arrays and LED arrays cause line noise in the output image due to the variations in the amount of light passing through each optical element or the amount of light emitted. In order to eliminate this noise, the variations in the light amount are corrected by performing correction calculation based on information obtained through measurement of either the darkness of the output image or the amount of light from the light shutter array (shading).
Because it is relatively easy to reduce the cost and make the measuring device small in size, a method that directly measures the light amount from the light shutter array is preferred. However, it is not easy to accurately measure the light amount for each pixel when the pixel density is 400dpi, and to match the information to the image.
For example, in the case of the optical writing head shown in FIG.
12
(A), if the light amount is measured with all of the light shutter elements
31
a
and
31
b
of double-rows ON, i.e., illuminated (double-row illumination) in order to measure the light amount per pixel when the light shutter elements
31
a
and
31
b
of double-rows are ON, a light amount distribution waveform shown in FIG.
12
(B) is obtained. However, in order to identify the position (address) of each light shutter element
31
a
and
31
b
in such a light amount distribution waveform, an expensive device such as a linear scale in which absolute addresses are defined must be used. Alternatively, where an expensive device such as a linear scale is not used, the position of each light shutter element
31
a
and
31
b
is identified by measuring the light amount for each light shutter element when only either row is illuminated (single-row illumination) and obtaining a light amount distribution waveform shown in FIG.
12
(C). The light amount for each pixel when the light shutter elements
31
a
and
31
b
of double-rows are illuminated is calculated by means of such processing methods as adding the light amount values measured per row. However, since this state in which only a single-row is illuminated is different from the original state in which double-rows are illuminated, strictly speaking, errors will occur in the light amount value between when the light amount measurement is performed and when actual exposure is carried out, resulting in image unevenness.
When a light shutter array, etc. is used for an optical writing head in actuality, it is often used in combination with image forming lenses (selfoc lens arrays) due to such issues as efficiency in the use of light and the need to ensure the distance to the exposure surface. FIG.
12
(A) shows the positional relationship between a selfoc lens array and the light shutter elements
31
a
and
31
b
of a PLZT light shutter array. The selfoc lens array comprises multiple rod lenses
35
a
that are combined such that one lens is placed between two lenses lengthwise, and the output light from each light shutter element
31
a
and
31
b
is formed into an image on the exposure surface via their corresponding rod lenses
35
a.
In the construction described above, the factors that hinder the uniformity of exposure when all of the light shutter elements are illuminated include (i) errors in the alignment of the light shutter elements formed on the PLZT light shutter chips (processing errors), (ii) positioning errors when the multiple light shutter chips are mounted on a substrate comprising glass or other materials, (iii) optical performance errors for each rod lens
35
a
of the selfoc lens array (depth of focus, chromatic aberration, rod lens alignment accuracy, etc.), and (iv) errors in the geometrical positioning of the light shutter elements
31
and the rod lenses
35
a
(assembly errors). Among these types of errors, errors in the optical performance of each rod lens
35
a
are the most significant, and often comprise the main reason for variations in light amount.
These errors cause a phase difference between the light amount distribution waveform obtained when only the light shutter elements
31
a
of one row are illuminated (curve L
1
) and the light amount distribution waveform obtained when only the light shutter elements
31
b
of the other row are illuminated (curve L
2
). In the presence of such a phase difference, the amplitude of the light amount distribution waveform when the light shutter elements
31
a
and
31
b
of double-rows are illuminated (curve L
3
) increases, resulting in so-called oscillation. For comparison purposes, FIG.
13
(B) shows the light amount distribution waveforms in each case under ideal conditions in which there is no phase difference. In other words, even if the transmitted light amounts for each light shutter element
31
a
and
31
b
are adjusted such that they are all the same when the rows are separately illuminated, the oscillation itself that occurs when double-rows are illuminated cannot be reduced.
OBJECTS AND SUMMARY
The present invention was created in view of the situation described above. An object of the present invention is to provide an improved solid scanning optical writing device and light amount measuring device and driving method therefor. Another object of the present invention is to provide (i) a solid scanning optical writing device having an improved light amount adjustment function, and (ii) an improved light amount adjustment method in the above device, and more particularly, to provide a solid scanning optical writing device, light amount correction method and light amount measuring device therefor that can essentially accurately measure the output light amount for each optical element and perform high-quality light amount correction based on the measurement data.
In order to attain these and other objects, the solid scanning optical writing device according to one aspect of the present invention comprises a solid scanning optical writing device that controls the many optical elements aligned in an alternating fashion in two rows in the main scanning direction to turn them ON/OFF b

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