JPH05227396A - Picture recorder - Google Patents

Abstract

PURPOSE:To correct density unevenness caused in the picture recording device. CONSTITUTION:The picture recording device has a 1st mode and a 2nd mode. In the 1st mode, a pattern generating section 13 is started and prescribed picture data are fed to a picture output section 14 and a picture with a prescribed density is outputted over the entire face of recording paper. The picture is read by a picture read section 10 and picture data at a prescribed sampling position are stored in a picture data storage section 11. In the 2nd mode, usual picture recording is implemented and the picture data stored in the picture data storage section 11 are read synchronously with the picture recording operation of the picture data of the original read by the picture read section 10, fed to a density correction section 12, a density correction section 12 corrects the picture data inputted from the picture read section 10 with the picture data from the picture data storage section 11 and the result is fed to a picture output section 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording device,
In particular, it relates to an apparatus for correcting density unevenness on an image recorded in an electrophotographic laser beam printer or a copying machine.

[0002]

2. Description of the Related Art In a laser beam printer or a copying machine adopting an electrophotographic system, density unevenness may occur in a recorded image. One of the causes is the fluctuation of the charging potential of the photoconductor. To solve this, for example, as disclosed in Japanese Patent Laid-Open No. 63-205670, the charging potential of the photoconductor is measured by a surface potential sensor. Is measured, and the charging potential of the photoconductor is controlled based on the measured potential.

[0003]

However, there are various causes of density unevenness, and there is density unevenness that cannot be removed only by controlling the charging potential of the photoconductor as in the conventional case. For example, in an electrophotographic system, a cylindrical mirror or a reflecting mirror is used to form an electrostatic latent image on a photoconductor with a laser beam. However, when the surface accuracy of the cylindrical mirror is not good or the reflectance of the reflecting mirror is If the unevenness is not constant over the entire range, density unevenness occurs in the main scanning direction as shown in FIG. 4, for example.

Further, in order to rotate the photoconductor, it is general to transmit the rotation of the motor to the photoconductor via a drive gear. However, when the drive gear is eccentric, the rotation of the photoconductor is uneven. Occurs, and as a result, the amount of exposure changes,
The density unevenness called banding noise as shown in FIG.

Further, when there is an error in the assembling accuracy of the developing device and the photoconductor, and the gap between the roll of the developing device and the photoconductor is different at both ends in the main scanning direction, the density of the main scanning direction is changed. Density unevenness with grade occurs. For example,
As shown in FIG. 6A, the gap G at the terminal end in the main scanning direction
_{When 1} is smaller than the gap G _{2 at} the starting end portion in the main scanning direction, density unevenness occurs as shown in FIG.

It is obvious that the density unevenness caused by such a mechanical error cannot be solved by the conventional method as described above, and the mechanical unevenness of individual members such as optical members is exclusively. At present, efforts are being made to solve the problems by improving the precision and their assembling precision, but it is very difficult to eliminate these density unevenness easily and at low cost.

Therefore, the present invention is to solve the above-mentioned problems, and even if there are some errors in the parts or their assembly, it is possible to easily and inexpensively correct the density unevenness based on them. Therefore, it is an object of the present invention to provide an image recording apparatus capable of obtaining a high quality recorded image.

[0008]

In order to achieve the above-mentioned object, the image recording apparatus of the present invention has a structure as shown in FIG. 1 and has first and second modes. The first mode is a mode in which what kind of density unevenness is occurring in the image recording apparatus is measured and the state of the density unevenness is stored, and the first mode indicates from a user interface (UI) not shown. Then, the pattern generating section 13 is first activated, and predetermined image data is supplied to the image output section 14, whereby an image having a predetermined constant density is output over the entire surface of the recording paper.

This image is obtained when an optical member related to image reading and image recording or a member such as an electronic circuit for processing image data is formed with a predetermined accuracy and is assembled with a predetermined accuracy. Is an image having a uniform density, but if there is an error of a predetermined value or more in the accuracy of each member or their assembly accuracy as described above, the image has a density unevenness based on those errors.

Next, the operator sets the output image in the image reading section 10 to read the image. At this time, the image data at the predetermined sampling position among the image data read by the image reading unit 10 is stored in the image data storage unit 11. This sampling position can be appropriately set according to the user's application, preference, and the like.

The above is the first mode, and when the operation and processing of this first mode are completed, the operator changes the mode from the first mode to the second mode, which is the mode for performing normal image recording. .. In the second mode, when a document is placed on the image reading unit 10 and image recording is instructed, the image reading unit 10 starts reading the image of the document and the image data obtained as a result of the reading is read. Is input to the density correction unit 12 and further supplied to the image output unit 14 for image recording. At this time, the image data is synchronized with the image recording operation of the image data of the document read by the image reading unit 10. The stored image data is read from the storage unit 11 and supplied to the density correction unit 12. And the density correction unit 1
In 2, the image data input from the image reading unit 10 is corrected by the image data from the image data storage unit 11 and supplied to the image output unit 14.

As a result, even if the image recording apparatus has various mechanical errors as described above, it is possible to eliminate density unevenness and obtain a high quality image.

[0013]

Embodiments will be described below with reference to the drawings.
In the following embodiments, the present invention is applied to an electrophotographic copying machine that performs pulse width modulation (PWM) on image data, drives a laser drive circuit by this PWM signal, and performs laser scanning exposure. I will explain an example,
The present invention is not limited to this embodiment, and it goes without saying that it can be similarly applied to various other image recording apparatuses. Further, in the following embodiments, a black-and-white copying machine will be described for easy understanding, but it goes without saying that it can be applied to a color copying machine.

FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, in which 20 is a PWM circuit, 21 is a latch circuit, and 2 is a circuit.
2 is a level converter, 23 is a D / A converter (hereinafter simply referred to as D / A
A), 24 is a comparator, 25 is a level converter, 26 is a reference oscillator (hereinafter referred to as OSC), 27 is a frequency divider, 28 is a triangular wave generation circuit, 30 is a counter, 31 is ROM, 32 is a coordinate counter. , 33 is RAM, 34 is an isolation circuit, 35 is a level converter, and 36 is D /
A and 37 are arithmetic circuits, and 38 is a variable resistor. In addition,
In FIG. 2, the same or similar components as those in FIG. 1 are designated by the same reference numerals.

Next, the operation when the first mode is instructed in the configuration of FIG. 2 will be described. The first mode is a mode in which what kind of density unevenness is occurring in the image recording apparatus is measured and the state of the density unevenness is stored, and the density of the predetermined density is maintained over the entire surface of the recording paper of a predetermined size. It is composed of a first step of recording an image and a second step of reading the image recorded in the first step and storing the density of the image. The first mode is
It may be provided as one of the self-diagnosis modes used exclusively by service personnel for various adjustments, or a button for instructing the mode is provided on the console panel so that the user can perform it when desired. You may do it.

When the first mode is instructed, as a first step, a mode signal indicating the first mode is supplied from the predetermined CPU (not shown) to the ROM 31 of the pattern generating section 13 to read it. Made possible. Further, the counter 30 is supplied with a clock generated from the OSC 26 and having a predetermined frequency by the frequency divider 27, and the density data stored in the ROM 31 is read by the count value. The same density data is read for all input addresses. Here, ROM3
Although the density data to be stored in 1 may be a value that can obtain an image with an arbitrary density, an image with a predetermined halftone, for example, a density of about 0.5 is obtained so that the density unevenness can be satisfactorily measured and stored by the operation described later. It is desirable to use concentration data that can be obtained.

The density data read from the ROM 31 is converted from TTL to ECL by the level converter 22 via the latch circuit 21, converted into an analog signal by the D / A 23, passed through the arithmetic circuit 37, and passed through the comparator 24. Is input to one of the input terminals. Comparator 24
The triangular wave generated from the triangular wave generation circuit 28 is input to the other input terminal of the, and a PWM signal is generated.
The triangular wave generating circuit 28 generates a triangular wave having a predetermined cycle based on the reference clock generated by the OSC 26.

The PWM signal generated by the comparator 24 is converted from ECL to TTL by the level converter 25 and supplied to the laser beam drive circuit (not shown in FIG. 2).
Image recording is performed. And this image, when the accuracy of all members including optical members such as the cylindrical mirror of the image output unit is within the defined error range, and the assembly accuracy thereof is also within the defined error range. Is an image of a given density that is almost uniform over the entire surface of a paper of a given size, but if the surface accuracy of the cylindrical mirror in the image output section is not good or the reflectance of the reflecting mirror is over the entire surface of the reflecting mirror. If the density is not constant over a range, density unevenness as shown in FIG. 4 occurs, and if the gear that drives the photoconductor is eccentric, the density unevenness as shown in FIG. If the gap between and is not constant over the main scanning direction, density unevenness as shown in FIG. 6B will occur.

Although the level converter 22 is not an essential constituent element of the present invention, it is provided for high-speed processing of PWM signal generation in the comparator 24 and density correction in the arithmetic circuit 37 described later. There is something. This also applies to the level converter 35. Further, the level converter 25 is provided for a laser beam drive circuit operating in TTL.

The above is the first stage of the first mode,
At this first stage, the isolation circuit 34 of the image data storage unit 11 is opened by a predetermined CPU (not shown), so the density data read from the RAM 31 and passed through the latch circuit 21 is RAM3
3 or level converter 35 is not supplied. At this time, the D / A 36 is made inoperative by a predetermined CPU (not shown), and therefore no signal is input to the minus (-) input of the arithmetic circuit 37.
The signal from the D / A 23 is passed through the arithmetic circuit 37.

When the first stage is completed, the predetermined CPU
The OM 31 is notified of a predetermined mode signal, its operation is stopped, the isolation circuit 34 is stopped, and the RAM 33 is made writable. At this time, the laser beam drive circuit is made inoperative.

In this state, when the image obtained in the above-described first step is placed on the image reading unit (not shown) and a reading instruction is given, the density data output from the image reading unit is latch circuit 21. To the data terminal of the RAM 33 via the isolation circuit 34. At this time, R
Since the AM 33 is writable, when the address is given from the coordinate counter 32, the inputted density data is written at the address. That is, in the configuration shown in FIG. 2, the density data read based on the coordinate data given to the coordinate counter 32 is sampled and written in the RAM 33, but the coordinates given to the coordinate counter 32 are generally the density. Since the unevenness is most likely to occur in both the main scanning direction and the sub-scanning direction, it goes without saying that it may be fixedly set in advance in a grid pattern with a predetermined pitch as shown in FIG. 3A. It is desirable that a service person or a user can arbitrarily set the UI according to the density unevenness occurrence state. That is, for example, when there is no density unevenness in the sub-scanning direction as shown in FIG. 4 and density unevenness occurs only in the main scanning direction, the sampling position is only in the main scanning direction as shown in FIG. 3B. You can set it, and see Fig. 5
When there is no density unevenness in the main scanning direction but only in the sub-scanning direction as shown in FIG. 3, the sampling position may be set only in the main scanning direction as shown in FIG. 3C. Is. The coordinate counter 32 is an OS
Coordinates are counted by a clock generated by C26 and divided by a frequency divider 27 into a predetermined frequency.

Whichever method is adopted, the set sampling position is stored in a predetermined memory, read by a predetermined CPU and given to the coordinate counter 32, whereby it is recorded in the above-mentioned first step. The density data at a predetermined sampling position of the image is written in the RAM 33. It is obvious that this density data has information of density unevenness uniquely occurring in the copying machine.

The above is the second stage of the first mode, which completes the operation of the first mode.

When the above first mode is completed, the service person or the user changes the mode to the second mode. The second mode is a mode for copying a normal original image, and when the second mode is instructed, a predetermined CPU
Notifies the ROM 31 of a mode signal indicating non-operation, and RA
The M33 is set to the readable state and the isolation circuit 34 is set to the stopped state.

In this state, the document is placed on the image reading section, and the document image is read when the start of copying is instructed. The density data of this image is once latched by the latch circuit 21, The level is converted by the level converter 22, converted into an analog signal by the D / A 23, and input to the plus (+) input terminal of the arithmetic circuit 37. At this time, coordinate data is given to the coordinate counter 32 from a predetermined CPU, and when the count value of the coordinate counter 32 matches the given coordinate data, the count value is given to the RAM 33 as a read address. , The density data written at the address is read from the RAM 33. The coordinate data given to the coordinate counter 32 is the same as the coordinate data given when the density data is written in the RAM 33 in the second stage of the above-mentioned first mode, and the coordinate count in the coordinate counter 32 is the image. As a matter of course, it is performed in synchronization with the image recording in the output unit.

The density data read from the RAM 33 is converted from TTL to ECL by the level converter 35, and D /
When the density data of the original image converted into an analog signal by A36 and input to the minus (-) input terminal of the arithmetic circuit 37 is D _O and the density data read from the RAM 33 is D _N , (D _O − D _N ) is calculated. It is obvious that density unevenness is corrected by this. For example, if density unevenness occurs in the image output unit for some reason and a certain standard density is copied at a higher density at the coordinate position, the density data read from the RAM 33 is read. D _N
Is larger than the standard value, and thus the level of the output signal of the arithmetic circuit 37 is smaller than the standard value.
Since this is copied at a density higher than this value in the image output unit, the density at the coordinate position of the copied image eventually becomes the standard density. Of course, in the case of other density unevenness as well, the density unevenness is similarly corrected. The variable resistor 38 is provided so as to be able to adjust the degree of density unevenness correction, and a serviceman or a user can appropriately select the density unevenness in the copying machine or the user's preference. It is designed to be adjustable.

Although one embodiment of the present invention has been described above, the paper size of the image output in the first stage of the first mode described above and the coordinate counter 32 in the second mode.
The following is a supplementary note on the coordinate data given to the. First, the paper size can be the maximum size that can be copied by the copying machine, and A4 and B5 can be used.
It is also possible to carry out for each paper size such as. And
In the former case, when copying a document image, it is sufficient to provide the coordinate counter 32 with coordinate data only within the range of the document size based on the document size detected by the image reading unit, and in the latter case. The density data for each paper size is written in the RAM 33, but the density data for the same size as the original size detected by the image reading unit may be read.

Although one embodiment of the present invention has been described above, it will be apparent to those skilled in the art that the present invention is not limited to the above embodiment and various modifications can be made.

[0030]

As is apparent from the above description, according to the present invention, the following effects can be obtained.

Since it is possible to correct reproducible density unevenness that is likely to occur on a recorded image, high-quality image recording can be performed.

Since the initial variations of the components such as the laser scanning optical system of the image reading unit or the image output unit, the photoconductor, and the developing device can be corrected, the tolerance of these components can be relaxed. It is possible to provide a low-cost image recording device.

By periodically activating the first mode and measuring the concentration, it is possible to compensate for the deterioration of the component parts due to the change with time, so that the frequency of maintenance work can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of the present invention.

FIG. 2 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 3 is a diagram showing an example of density data sampling positions in a first mode.

FIG. 4 is a diagram showing an example of density unevenness.

FIG. 5 is a diagram showing an example of density unevenness.

FIG. 6 is a diagram showing a cause of density unevenness and an example thereof.

[Explanation of symbols]

10 ... Image reading unit, 11 ... Image data storage unit, 12 ... Density correction unit, 13 ... Pattern generation unit, 14 ... Image output unit,
20 ... PWM circuit, 21 ... Latch circuit, 22 ... Level converter, 23 ... D / A converter, 24 ... Comparator, 25
... Level converter, 26 ... Reference oscillator, 27 ... Divider, 2
8 ... Triangle wave generating circuit, 30 ... Counter, 31 ... ROM,
32 ... Coordinate counter, 33 ... RAM, 34 ... Isolation circuit, 35 ... Level converter, 36 ... D / A converter, 37 ... Arithmetic circuit, 38 ... Variable resistor.

Claims (2)

[Claims] 1. A first mode in which an image having a predetermined constant density is recorded over the entire surface of a sheet and image data at a predetermined sampling position is stored when the image is read, and an image of an original is read. A second mode in which the image data stored in the first mode is read in synchronization with the recording of the image of the read original when image recording is performed, and the image data of the image of the original is corrected by the read image data. An image recording apparatus comprising: 2. A sampling position of an image having a predetermined constant density in the first mode is set at a predetermined interval in a main scanning direction and / or a sub scanning direction of image recording. The image recording device described.