Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1997-12-18
2001-03-13
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S246000, C250S205000, C250S559030, C250S559050
Reexamination Certificate
active
06201559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for measuring the quantity of light emergent from a light shutter array made of PLZT or emitted from an LED array and an image forming apparatus which forms an image (electrostatic latent image) on a recording medium with such an optical tip array.
2. Description of Related Art
Conventionally, various kinds of optical write heads which turn on and off light for each pixel with use of a light shutter array made of PLZT or an LED array have been used to form images (electrostatic latent images) on a silver-salt print sheet or film or an electrophotographic photosensitive member. For formation of images without unevenness, such an optical write head needs to be subjected to measurement of the quantity of light outputted from each element and to correction in quantity of light according to the measurement result.
Japanese Patent Laid Open Publication No. 61-150286 has disclosed a method of measuring the quantity of light outputted from each element. According to this publication, while LEDs are turned on one by one in order in a main scanning direction, a light-quantity sensor which faces the LEDs at a specified distance therefrom is moved in the main scanning direction. In such a one-by-one lighting method, it is necessary to synchronize the turning-on/off of the LEDs with the movement of the sensor accurately, and minute control of the start position of the sensor is necessary. Accordingly, an encoder and an accurate shifting mechanism need to be provided. Also, from the result of measurement in this method, influence of light leaking from adjacent elements cannot be recognized, and in forming a thick image, a problem of unevenness is left unsolved.
Further, for formation of a multi-tone image, it is necessary to measure the output light-quantity characteristic of each element accurately. It is insufficient to measure the quantity of light outputted from each element only when it is on as disclosed by the method of Japanese Patent Laid Open Publication No. 61-150286.
Also, conventionally, an optical write head is fitted in a jig before it is employed in an image forming apparatus, and the quantity of light outputted from each element is measured with a light-quantity measuring device comprising a photosensor. Then, correction data are produced based on the results of the measurement. However, these correction data are effective only in the early time of the optical write head and are not useful when the output characteristic of each light element changes because of aging and/or a change in environmental conditions.
Meanwhile, Japanese Patent Laid Open Publication No. 6-347925 has suggested an image forming apparatus which is provided with three optical write heads so as to form an image at a high speed. For this type of apparatus, it is more important to measure the quantity of light outputted from each element and carry out correction at real time. However, this is left unachieved.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of measuring the quantity of light outputted from each element of an optical write head accurately in simple control and an optical write head which is subjected to measurement in this method.
It is another object of the present invention to provide a method of measuring the quantity of light outputted from each element of an optical write head accurately enough such that the optical write head can be used for formation of multi-tone images.
Another object of the present invention is to provide a full-color optical write head which is subjected to accurate measurement of the quantity of light of each color outputted therefrom in simple control.
Another object of the present invention is to provide an image forming apparatus wherein an optical write head employed therein can be subjected to measurement of the quantity of light outputted from each element without being detached from the apparatus so that the apparatus can produce light-quantity correction data at real time.
Further, another object of the present invention is to provide an image forming apparatus wherein a light-quantity sensor for measuring the quantity of light outputted from each element of an optical write head to make light-quantity correction data is also used to monitor the quantity of light outputted from the optical write head during actual image formation.
Furthermore, another object of the present invention is to provide an image forming apparatus which can measure the quantity of light outputted from each of a plurality of optical write heads employed therein with a simple mechanism and produce light-quantity correction data at real time so as to form quality images at all times.
In order to attain the objects above, according to the present invention, an optical write head which drives an array of optical elements extending in a main scanning direction individually in accordance with image data comprises control means which commands thin-out driving of the optical elements wherein adjacent elements are not driven at a time. In order to measure the quantity of light outputted from each of the optical elements, a light-quantity sensor with a light-receiving slit is moved in the main scanning direction with the light-receiving slit facing the array of optical elements while the optical elements are thin-out driven. Then, the quantity of light outputted from each of the optical elements is calculated from the output of the light-quantity sensor.
According to the present invention, because light-quantity measurement is carried out during thin-out driving of the optical elements, addressing of the optical elements and light-quantity measurement can be carried out merely by moving the light-quantity sensor at a constant speed. It is not necessary to synchronize the drive of the optical elements with the movement of the sensor, and the control is simple. Also, since adjacent optical elements are not driven at a time, by measuring the quantity of light outputted from an undriven element, the quantity of light leaking from an adjacent driven element and entering thereto can be recognized. Thus, the quantity of light actually outputted from each element can be calculated accurately, which is effective to solve the problem of density unevenness in forming a thick image.
If each optical element is driven at a specified frequency and a specified duty for the measurement so that a plurality of samplings from each element can be carried out, the address of each element can be recognized from the maximum value, and the maximum value is determined as the quantity of light outputted from the element. In this way, during one scan, the addresses of the optical elements can be recognized, and the quantities of light outputted therefrom can be measured accurately.
Further, toward a full-color type optical write head which drives optical elements individually while switching the light color at a high speed, the light-quantity measurement with respect each color is carried out while the optical elements is thin-out driven under conditions (duty, voltage, current, etc.) suitable for the light color. Thereby, accurate measurement can be carried out. In this case, the light color is switched at a lower speed during the light-quantity measurement than the speed during actual image formation so that the light of each color can be turned on and off a plurality of times while the light-quantity sensor is detecting the quantity of light outputted from each of the optical elements. Thereby, during one scan, the quantities of light of each color at different levels outputted from each element can be measured, and the output light-quantity characteristic of each element can be measured more accurately, which is effective for formation of multi-tone images.
Further, the present invention relates to a method of measuring the quantity of light emitted from an optical write device which drives an array of optical elements individually in accordance with image data, and the method com
Kamoda Yuji
Masuda Tomohiko
Matsubara Ken
Saito Itaru
Wada Kenichi
Le N.
McDermott, Will & Will
Minolta Co. , Ltd.
Pham Hai C.
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