JPH07256921A - Light quantity correction device of fluorescent head - Google Patents

Abstract

PURPOSE:To obtain a light quantity correction device of a fluorescent head, capable of adjusting a quantity of light for correcting the fluorescent head for a change in quantity of light with time or for adjusting a printing density. CONSTITUTION:A title device comprises a lighting control circuit 12 controlling the lighting of dots of a fluorescent head 11 per dot, a storage means 13 having a plurality of kinds of data tables 13a storing data for imparting a lighting time per dot to the lighting control circuit 12, and a selection means 14 selecting one of the two or more kinds of data tables 13a....

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent head light quantity correction device for correcting the light quantity of a fluorescent head used in an electrophotographic image forming apparatus or the like.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, an LED head or a fluorescent head is used as an exposure device.

FIG. 5 is a sectional view of a fluorescent head. A vacuum space is formed in the case 1 by the case 1 and the glass substrate 2. A cathode electrode (filament) 3 is provided in the vacuum space, and electrons e are emitted by applying a voltage thereto. Further, an anode electrode 4 is formed on the glass substrate 2. A phosphor 5 is formed on the anode electrode 4 located in the vacuum space, and when the electron e emitted from the cathode electrode 3 collides with the anode electrode 4, the phosphor 5 is excited to generate light. Then, it is emitted to the outside through the glass substrate 2.

FIG. 6 is a perspective view of the glass substrate 2 on which the anode electrode 4 and the phosphor 5 are formed. The phosphors 5 are arranged in a line, and each phosphor 5 forms a light emitting portion (photocell). Although each phosphor 5 is formed uniformly, the amount of light emitted from each phosphor 5 actually varies. That is,
There is a variation in the amount of light in each dot-based light emitting unit (hereinafter, simply referred to as a dot) that constitutes such a fluorescent head. Therefore, the variation in the light amount of the dots is corrected.

As the dot light amount correction in the fluorescent head, there are a method in which all the dots are lit at the same time for adjustment, and a method in which the dots are lit sequentially for each dot and the light amount is detected and adjusted. It can be said that the method of sequentially lighting is superior in terms of cost and accuracy reproducibility.

[0006]

However, in the exposure during actual image formation, particularly in the normal rotation developing type in which light is irradiated to a portion other than the character portion of the original,
It is rare that only one dot is lit, and most dots are lit at the same time. There is a difference between the light amount of each dot when many dots are lit and the light amount of each dot when detected in 1-dot units by the above method. This is for the following reason.

FIG. 7 schematically shows the flow of electrons e between the cathode electrode 3 side and the anode electrode 4 side. With respect to the potential on the cathode electrode 3 side, assuming that the central potential is V ₀ and the potentials at both ends are V ₁ and V ₂ , respectively, a large amount of current flows between the anode and the cathode when all dots are lit, and the potential of the cathode electrode 3 is Since it depends on the amount of current flowing at the center and at the ends, V ₀ <V ₁ and V ₂ . On the other hand, when one dot is lit, almost no current flows, so V ₀ ≈V ₁ , V ₂
Becomes Therefore, when many dots are turned on, the end portion becomes brighter than the center portion (center portion of the fluorescent head) of the cathode electrode 3. That is, if the correction data based on the light amount of each dot detected in the unit of one dot is used as it is, there is a problem that the end portion becomes bright when all dots are lit.

When a large amount of current flows in the end portion of the cathode electrode 3 in this way, the temperature of the cathode electrode at this end portion rises, and oxide scattering from this end portion increases,
It adheres to the phosphor 5 to reduce the luminous efficiency. That is, the end side becomes darker as the cumulative lighting time increases.

Further, the light quantity of the fluorescent head is adjusted to adjust the print density in image formation. Conventionally, the light quantity is changed by adjusting the drive potential of the fluorescent head, so that the drive potential is adjusted. A circuit is needed. Also, with this drive potential adjustment, it is difficult to adjust the light amount in dot units.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a fluorescent head light quantity correction device capable of correcting a change in the light quantity of the fluorescent head over time and adjusting the light quantity for print density adjustment.

[0011]

A first configuration stores a lighting control means for controlling lighting of individual dots of a fluorescent head and data for giving a lighting duty for each dot to the above lighting control means. It is characterized by comprising a storage means having a plurality of different data tables and a selection means for selecting one of the plurality of kinds of data tables.

In the second configuration, in the first configuration, as the plurality of types of data tables, at least a data table for initial use and a data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time. May be included.

In the third configuration, in the first configuration, as the plurality of types of data tables, at least a data table for initial use and a data table for print density adjustment may be included.

In the fourth configuration, in the second or third configuration, the data table for the initial use is based on the light amount data when one dot is lit, and the center and both ends of the fluorescent head when all dots are lit. It may be determined in consideration of the light amount characteristic.

In the fifth configuration, in the second configuration, the data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time is based on the data table for the initial use time and corresponds to the cumulative lighting time. It may be determined in consideration of the degree of decrease in the amount of light at the center and both ends of the fluorescent head.

In the sixth configuration, in the third configuration, the data table for print density adjustment is a data table for initial use or a data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time. Based on this, the data for each dot may be defined as a value obtained by adding or subtracting a predetermined amount.

[0017]

According to the first configuration, since there are a plurality of types of data tables in which the data for giving the lighting duty for each dot to the above-mentioned lighting control means are stored, there is no need to rely on the driving potential adjusting means of the fluorescent head. The light amount of the fluorescent head can be adjusted, and this can be performed in dot units.

According to the second structure, since the correction data for the change in the light amount of the fluorescent head over time is included in one of the data tables, it is possible to deal with the change in the light amount over time of the fluorescent head in dot units.

According to the third configuration, since the correction data for the light amount adjustment for adjusting the print density is included as one of the data tables, the light amount adjustment for the print density of the fluorescent head can be performed in dot units. .

According to the fourth structure, the data table for the initial use is based on the light amount data when one dot is turned on.
Since it is determined in consideration of the light amount characteristics at the center and both ends of the fluorescent head when all dots are lit, even when all dots are lit, the correction method by the 1-dot lighting method with relatively low cost and high accuracy is used. It is possible to form a light emitting state in which the light amount is flat as a whole.

According to the fifth configuration, the data table for when the cumulative lighting time of the fluorescent head reaches the predetermined time is:
Based on the data table for the initial period of use, it is determined in consideration of the degree of decrease in the amount of light at the center and both ends of the fluorescent head according to the cumulative lighting time, so even if the cumulative lighting time of the fluorescent head increases, the overall It is possible to form a light emitting state in which the light amount is flat.

According to the sixth configuration, the data table for adjusting the print density is based on the data table for the initial use or the data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time. Since it is determined as a value obtained by adding or subtracting a predetermined amount to the data on dots, it is possible to raise or lower the total light amount while forming a light emitting state in which the light amount is flat as a whole.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments.

FIG. 1 is a block diagram showing the schematic arrangement of a light quantity correction device for a fluorescent head and its peripheral devices. Reference numeral 11 in the drawing denotes a fluorescent head, and the fluorescent head 11 is arranged with its dot line direction aligned with the longitudinal direction (main scanning direction) of the photoconductor 15.

The lighting control circuit 12 includes the fluorescent head 11 described above.
The lighting of the individual dots is controlled based on the image data from the image data supply circuit 16. Further, the lighting time of each dot is controlled based on the data given from the storage means 13 described later.

The storage means 13 has a plurality of types of data tables 13a ... In which data for giving the lighting time for each dot to the lighting control circuit 12 is stored.

FIG. 2 shows dot numbers and each data table 1.
It is the figure which showed the data content in 3a ... In this example, the correction amount is represented by 4-bit data. As the data tables 13a, a data table for initial use, a data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time, and a data table for print density adjustment are prepared.

The data table for the initial use is defined based on the light amount data when one dot is turned on, taking into consideration the light amount characteristics at the center and both ends of the fluorescent head 11 when all dots are turned on. This will be specifically described below. FIG. 3 shows light amount data of the fluorescent head 11 before correction. The horizontal axis corresponds to the dot line direction of the fluorescent head 11, and represents the number of dots from the left end. The vertical axis represents the light amount of each dot. To generate the light amount data, a method of sequentially lighting each dot and detecting and adjusting the light amount is used. Based on this light intensity data, the virtual line (b) in the figure
Make sure that the light intensity of each dot matches the reference line indicated by
Calculate the correction value. If this correction value is used as it is, the end portion of the fluorescent head 11 becomes bright as described in the conventional example. Therefore, as indicated by a virtual line (c) for the data of (b), For example, the correction value is changed so that the dot light amount at a portion is increased by, for example, 20 to 30% with respect to the dot light amount at both ends. As a result, it is possible to form a light emitting state in which the light amount is flat as a whole even when all dots are lit, as shown in FIG. 4, while using a relatively low cost and highly accurate correction method by the one dot lighting method. it can.

The data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time is based on the data table for the initial period of use, and shows the degree of decrease in light quantity at the center and both ends of the fluorescent head according to the cumulative lighting time. It is set in consideration. That is, assuming that the light amount by the correction amount of the data table for the initial use is flat in the dot line direction, the dot line center is indicated by the virtual line (b) with respect to the virtual line (b) according to the accumulated time. By determining the correction value so that the dot light amount on both ends is larger than the dot light amount for the portion, a light emitting state in which the light amount is flat as a whole after the cumulative time has elapsed is formed. The degree of light reduction due to the cumulative lighting time can be experimentally obtained.

The data table for adjusting the print density is based on the data table for the initial use or the data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time, and a predetermined amount is added to the data for each dot. It is defined as a value obtained by adding or subtracting. That is, as the correction data in this case, a common value is added or subtracted through all the dots to the data table for initial use or the data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time. It is used as a correction value.

The selecting means 4 is for selecting one of a plurality of types of data tables 3a .... For example, the data table can be selected by generating an address for reading the data content stored in any of the data tables 3a .... Further, the selection of the data tables 3a ... Can be performed by the processing of the control unit in the image forming apparatus or the like. As the processing of the control unit, the measurement of the cumulative lighting time by the internal timer is compared with a preset cumulative lighting time value, and when the cumulative lighting time by the internal timer exceeds the set cumulative lighting time value. , The data table 3a prepared for use when the cumulative lighting time is exceeded is automatically switched.

Further, it can be selected by a user's key operation in an image forming apparatus or the like in which the light quantity correction device for the fluorescent head is used. That is, it is possible to raise or lower the total light amount of the fluorescent head while forming a light emitting state in which the light amount becomes flat as a whole by the operation of the user. Of course, the means for varying the drive potential to the fluorescent head 11 is unnecessary.

A data generating means for calculating and storing data for when the cumulative lighting time of the fluorescent head 11 reaches a predetermined time or data for adjusting print density based on the data in the data table for initial use. You may prepare. Since the data for when the cumulative lighting time reaches a predetermined time is a substantially quadratic curve, it is sufficient to have a calculation formula that outputs such a value, and for the data for print density adjustment, add / subtract Can be easily generated by.

[0034]

As described above, according to the present invention, based on the correction data based on the light amount of each dot when detected in a unit of one dot which is inexpensive and highly accurate, the end portion is bright when all dots are turned on. The problem of becoming can be solved. Further, the problem that the end side becomes darker due to the increase in the cumulative lighting time is also solved. Further, there is an effect that the light amount adjustment of the fluorescent head for adjusting the print density in the image formation does not need the drive potential adjusting circuit and the light amount can be adjusted in dot units.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a light quantity correction device for a fluorescent head.

FIG. 2 is an explanatory diagram showing contents of a data table in a storage unit.

FIG. 3 is a graph showing light amount data before correction.

FIG. 4 is a graph showing corrected light amount data.

FIG. 5 is a vertical sectional view of a fluorescent head.

FIG. 6 is a perspective view of a glass substrate on which an anode electrode and a phosphor are formed.

FIG. 7 is a schematic diagram showing a flow of electrons between a cathode electrode side and an anode electrode side.

[Explanation of symbols]

 11 Fluorescent Head 12 Lighting Control Circuit 13 Storage Section 13a Data Table 14 Selection Means 15 Photosensitive Member 16 Image Data Supply Circuit

Claims (6)

[Claims] 1. A lighting control means for controlling lighting of individual dots of a fluorescent head, and a storage means having a plurality of types of data tables storing data for giving a lighting duty for each dot to the lighting control means. And a light quantity correction device for a fluorescent head, comprising: a selection unit that selects one of a plurality of types of data tables. 2. The plurality of types of data tables include at least a data table for initial use and a data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time. The light amount correction device for a fluorescent head according to claim 1. 3. The light amount of the fluorescent head according to claim 1, wherein the plurality of types of data tables include at least a data table for initial use and a data table for print density adjustment. Correction device. 4. The data table for the initial use is defined based on the light amount data when one dot is turned on, considering light amount characteristics at the center and both ends of the fluorescent head when all dots are turned on. The light amount correction device for a fluorescent head according to claim 2 or 3. 5. The data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time is based on the data table for the initial period of use, and the light amount decreases at the center and both ends of the fluorescent head according to the cumulative lighting time. The light amount correction device for a fluorescent head according to claim 2, wherein the light amount correction device is determined in consideration of the degree. 6. The data table for print density adjustment is based on the data table for initial use or the data table for when the cumulative lighting time of the fluorescent head reaches a predetermined time, and the data for each dot is stored. The light quantity correction device for a fluorescent head according to claim 3, wherein the quantity is determined as a value obtained by adding or subtracting a fixed amount.