JPH04207257A - Image reader - Google Patents

Abstract

PURPOSE:To speed up copying processing without degrading the stability of image quality by correcting the output of an image sensor at the time of original scanning with the output value of the image sensor at the time of scanning a reference plate before original scanning as a reference. CONSTITUTION:The white reference plate 47 is scanned by a scanning means 41 and after the output of the CCD sensor 44 is subjected to A/D conversion, the output is stored as a reference value by a correcting means 49 into a memory 50. The correcting means calculates D=-log(D/W) from the reference value W and the output 0 at the time of reading the original 45 and transfers the same to an image processor 51. The fluctuation in the light emission quantity of a fluorescent lamp 42 is corrected by this processing, by which the degradation in image quality is prevented. The timing for scanning the white reference plate 47 is controlled by a control means 54 in accordance with the control information of the memory 52 and the output of a counter 53 for the number of copies. The scanning of the reference plate 47 is substantially not executed when the relative light emission quantity of the fluorescent lamp 42 is nearly constant. The effective correction is executed in this way without lowering the copying processing speed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading device used in an image forming apparatus such as a copying machine using electrophotographic technology.

Conventional technology In a general color copying machine that uses electrophotographic technology, an image reading device reads a document placed on a platen glass, and this image information is separated into multiple basic colors to produce color-separated image information. (1) Expose the surface of the photoreceptor drum uniformly charged with light corresponding to one of the above to form an electrostatic latent image, and develop this electrostatic latent image with toner of a color corresponding to the basic color; By transferring this toner image onto a sheet of paper held by a transfer drum and performing these steps for all basic colors, a desired color image is obtained.

An image reading device that reads an original placed on a platen glass is equipped with a lamp that illuminates the original, and multiple mirrors and lenses that guide light reflected from the original surface to an image sensor such as a CCD sensor. Ru. An incandescent lamp (incandescent light bulb) such as a halogen lamp may be used as a lamp for illuminating the document, but a fluorescent lamp may be used because it can emit light efficiently with relatively low power. A fluorescent lamp is a type of discharge lamp that converts the strong ultraviolet rays of mercury emitted by low-pressure mercury discharge into light in other wavelength ranges using a phosphor coated on the inner wall of the discharge tube.

The glass tube of a fluorescent lamp is filled with several tens of mg of mercury and an inert gas mainly consisting of argon (Ar) gas. At each end of the tube are tungsten coil electrodes coated with an electron-emitting material such as barium oxide.

Since the emission characteristics of such fluorescent lamps vary depending on the temperature of the tube wall, A is a color image reading device using a T1 fluorescent lamp. The lamp is equipped with a heater and a cooling fan, and the heater and fan are appropriately driven so that the tube wall temperature of the fluorescent lamp reaches a predetermined temperature (for example, 43° C.), thereby stabilizing the amount of light emitted from the fluorescent lamp. That's what I do. However, depending on the surrounding environment (temperature environment) in which such a copying machine is used, the behavior of the fluorescent lamp from the initial state to the stable state is not constant (in general, the amount of light emitted by the fluorescent lamp decreases in a high temperature environment). The amount of light emitted by a fluorescent lamp tends to relatively increase in a low temperature environment.This relative change in the amount of light emitted by a fluorescent lamp occurs when copying This appears as a change in density, making it impossible to provide images with stable image quality.

For this reason, we have taken the following measures.

That is, a white reference plate is placed near the platen glass on which the original is placed, the reference plate is scanned immediately before scanning the original, and the output value of the image sensor when the reference plate is scanned is stored in memory as a reference value. By correcting the output value of the image sensor during document scanning based on the reference value stored in the memory, density fluctuations after copy processing are prevented from occurring even if the amount of light emitted from the fluorescent lamp changes.

Problems to be Solved by the Invention As mentioned above, conventionally, the scanning of the white reference plate to obtain the reference value used to prevent density fluctuations was performed every time immediately before scanning the original. There was a problem that the speed of reading processing was slow. In particular, free registration mode (a mode that automatically recognizes the orientation of the original and performs the copying process no matter where the original is placed on the platen glass) and image shift mode (a mode that automatically recognizes the orientation of the original and performs the copying process no matter where the original is placed or placed on the platen glass) In some modes (such as a mode that copies only a specified area), the original image may be read at a position relatively far from the white reference plate. The distance traveled to scan the plate is long, significantly slowing down the copying process.

The present invention has been made in view of these points, and it is an object of the present invention to increase the copying processing speed (image reading processing speed) without reducing image quality stability.

Means for Solving the Problems In order to solve the above-mentioned problems, an image reading device as shown below is provided.

A white reference plate is placed near the platen glass on which the original is placed, the reference plate is scanned before the original is scanned, the output value of the image sensor when scanning the reference plate is used as a reference value, and based on the reference value. The image sensor is configured to correct the output value of the image sensor during document scanning.

A means for detecting the lighting time of a lamp for document illumination is provided, and the relationship between the lighting time of the lamp and the amount of light emitted is actually measured in advance and stored and retained as control data, and the control data and the lighting time are measured in advance and stored as control data. Based on the lighting time of the lamp by the detection means, the amount of variation in the amount of light emitted by the lamp from the previous scan of the reference plate is recognized, and the amount of variation is set in advance by lighting the lamp for the next image reading. only when it is expected to exceed the value
The reference plate is configured to scan the reference plate.

According to the present invention, the relationship between the lighting time of a lamp for document illumination and the amount of light emitted by the lamp is actually measured in advance and stored as control data, and the relationship between the lighting time of the lamp for document illumination and the amount of light emitted from the lamp is measured in advance and stored as control data. detecting the total lighting time and recognizing the amount of variation in the amount of light emitted by the lamp from the control data and the total lighting time of the lamp;
The reference plate is scanned only when the amount of variation is expected to exceed a preset value due to lighting of the lamp for the next image reading. That is, at the initial stage of lamp lighting, the amount of light emitted from the lamp generally fluctuates widely, so it exceeds the preset value. As the lighting time increases and the lamp approaches a stable state, fluctuations in the amount of lamp light emission become relatively small.
There may be cases where the predetermined value is not exceeded, and in such cases, scanning of the reference plate will be performed intermittently. In this way, the reference plate is scanned intermittently according to the characteristics of the lamp, compared to the conventional method in which the reference plate was scanned every time immediately before scanning the document. , the copy processing speed (image reading speed) can be increased. The setting value regarding the amount of variation in the amount of light emitted from the lamp needs to be selected to a value that does not affect density variation during copying processing and is useful for improving processing speed. For example, =5%.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

First, with reference to FIG. 3, the overall configuration of a color copying machine that can employ a color image reading device to which the present invention is applied will be described. In the figure, 1 is a photoreceptor drum, and around the photoreceptor drum L there is an exposure device 3 consisting of a charger 2, a laser oscillator (not shown), a polygon mirror 3a1 and other mirrors 3b, etc. Charger 4
A transfer drum 4 including a, 4b, 4c, etc., a cleaning device 5, a static eliminator (not shown), etc. are arranged in this order. 6 is a rotary multicolor developing device, and this developing device 6 is provided downstream of the exposure position by the exposure device 3 and upstream of the transfer drum 4.

A color image reading device 7 to which the present invention is applied is provided at the top of the full-color copying machine.

The details will be described later. The image of the document placed on the platen glass 8 is read by the color image reading device 7, this image information is separated into a plurality of basic colors to form color separated image information, and exposure is performed based on this color separated image information. The device 3 is driven and the photosensitive drum 1 is exposed by irradiation with laser light.

Reference numeral 10.11 denotes a paper cassette containing a plurality of sheets of paper, and the sheets are carried out one by one from the paper cassette 10 or 11 and supplied to the transfer drum 4 by a paper conveyance device 12 comprising a plurality of conveyance rollers and the like. 13 is a paper peeling finger; 14 is a vacuum type paper conveying device; 15 is a fixing device; and 16, 17, 18, and 19 are toner boxes containing toner for each color.

The developing device 6 has four developing units corresponding to yellow, magenta, yellow, and black)21.22.23.24
These four developing units 21, 22, 2
3.24 is a pair of supporting members 25 that are rotatably provided, and each developing roll 26 is evenly arranged and supported with each developing roll 26 facing outward. Developing units 21, 22, 23.2
Reference numeral 4 denotes a magnetic brush type developing device, in which two augers 27 and 28 for stirring the toner are provided.

One side of the support member 25 also serves as a gear, and is rotationally driven by a motor 29 to connect the developing units 21, 22, 23, .
24 developing rolls 26 are selectively brought close to the photosensitive drum 1.

Therefore, the surface of the photosensitive drum 1 is charged in a negative manner by the charger 2, and the platen glass 8 is charged by the color image reading device 7.
The image of the document placed thereon is read, and the exposure device 3 forms an electrostatic latent image based on color-separated image information.

In the developing device 6, the motor 29 is driven, and the developing unit 21 containing toner of a color corresponding to the color separation image information is rotated and positioned so as to face the photosensitive drum 1. The formed electrostatic latent image is converted into a toner image by a corresponding developing unit 21. on the other hand,
A sheet of paper on which an image is to be formed is taken out from the paper cassette 10 or 11, conveyed by a sheet conveying device 12, and electrostatically attracted to the transfer drum 4 by corona discharge from the charger 4a. The transfer drum 4 is rotated in synchronization with the rotation of the photoreceptor drum 1, and the toner image on the photoreceptor drum 1 is transferred to the transfer charger 4.
The image is transferred to the paper by corona discharge caused by b.

After the photosensitive drum 1 undergoes processing such as being cleaned and neutralized by a cleaning device 5, a static eliminator, etc., it is uniformly charged again, and an electrostatic latent image is formed based on other color separation image information. At this time, in the developing group W6, the developing unit 22 corresponding to this color separation image information is connected to the photosensitive drum 1.
The image is developed in the same manner as above. This toner image is superimposed and transferred onto the paper carrying the previous toner image in the transfer section.

Such a process is carried out for each color separation image information,
A color image is formed on the paper. This paper has charger 4
After the adsorption force is weakened by corona discharge caused by c, it is separated from the transfer drum 4 by the fingers 13. The separated paper is transported by the paper transport device 14 and placed in the fixing bag @
After being thermally fixed by step 15, the image is discharged onto a tray 20 provided outside the full color copying machine. In addition, if it is necessary to replenish toner in the developing unit I6.17, 1.
8. Toner conveying pipe 3 with an auger inside from 19
1.32 as appropriate.

The configuration of the color image reading device 7 will be described below with reference to FIG.

41 is a scanning means, and the scanning means 41 is a fluorescent lab 42,
A self-hook lens 43 and a CCD sensor 44 are each integrally attached to a movable frame, and a driving means 46 is provided below a platen glass 8 on which a document 45 is placed.
It is designed to be moved from side to side by being driven by.

A white reference plate 47 is provided at one end of the platen glass 8 and is used to detect variations in the amount of light emitted from the fluorescent lamps 42. The illumination light from the fluorescent lamp 42 illuminates the original 4.
5 or the surface of the white reference plate 47, and is guided to the CCD sensor 44 by the self-hock lens 43, and the output of the CCD sensor 44 is sent to the A/D converter 4.
8, the signal is A/D converted and input to the correction means 49.

In the correction means 49, a predetermined calculation is performed based on the reference value stored in the memory 5o, and its output is sent to the exposure device 3 via the image processing device 51.

When the white reference 47 is scanned by the scanning means 4, C
After the output of the CD sensor 44 is A/D converted, it is stored in the memory 50 as a reference value by the correction means 49. Then, when the original 45 is scanned by the scanning means 41, the output of the CCD sensor 44 is A/D converted, and then corrected by the following calculations in the correction means 49. passed to.

That is, assuming that the output value to be passed to the image processing device 51 is D, the reference value in the memory 50 is W, and the output when reading the original 45 is O, the calculation D=-1og- is performed. By performing such calculations, fluctuations in the amount of light emitted from the fluorescent lamp 42 are corrected, so that fluctuations in the amount of light emitted from the lamp do not affect the image quality after copy processing.

However, scanning the white reference plate 47 every time before scanning the original 45 is done in a special mode such as the free registration mode or the image shift mode, as described above, when multiple copying processes are performed continuously. In order to significantly reduce the productivity when carrying out the above, the timing of scanning the white reference plate 47 by the scanning means 41 is controlled by the control means 54 based on the control data stored in the memory 52 and the output of the copy number counter 53. I try to control it.

The control data stored in the memory 52 is for the fluorescent lamp 4.
This is data obtained by actually measuring the relationship between the lighting time and the amount of light emitted from No. 2. FIGS. 2(A) and 2(B) are diagrams showing an example of data actually measured by the inventors of the present application, in which the horizontal axis represents the number of copies and the vertical axis represents the number of copies made using the fluorescent lamp 42.
It shows the relative light emission amount when the lamp light emission amount at the time of initial lighting is set to "100". This data was taken using an A3 size original, with its enlargement ratio set to 100%, and after giving the image reading device sufficient rest. In the figure, a represents data under a low temperature environment (10°C), and b represents data under a high temperature environment (28°C). In this embodiment, data a in a low-temperature environment where the lamp relative luminescence amount fluctuates greatly is employed as control data.

The control means 54 uses this control data and the copy number counter 5.
Only when the relative light intensity of the lamp is expected to exceed =5% if the next copy is made from the output of 3, the original 45
The driving means 46 is controlled so that the white reference plate 47 is scanned immediately before the white reference plate 47 is scanned. That is, based on the output value of the copy number counter 53, the fluctuation range of the lamp light emission amount is determined for the 7th copy, the 9th copy, the 15th copy, the 17th copy to the 55th copy, and the 57th copy to the 99th copy. The white reference plate 47 is not scanned because it is within the range of 15% and is not expected to exceed 5% in the next copy.

According to this embodiment, when the total lighting time of the fluorescent lamp 42 is relatively short, the white reference plate 47 is scanned almost every time, and the white reference plate 47 is gradually scanned every other sheet or every few sheets. The reference plate 47 is scanned, and the fluorescent lamp 42
If the relative luminescence of
The white reference plate 47 is hardly scanned. As a result, effective correction can be performed without reducing copy processing speed.

In addition to the above-described configuration, a means 55 for detecting the ambient temperature of this copying machine is provided, and a plurality of control data corresponding to various temperature environments are obtained in advance by actual measurement. ) and (B) are stored in the memory 52, and based on the output value of the temperature detection means 55, control data corresponding to the temperature environment closest to the output value is selected, By driving the drive means 46 based on this control data, it becomes possible to perform control in accordance with the actual temperature environment, and it is possible to further improve copy productivity.

In addition, in the item "Means to solve the problem",
It is explained that the scanning timing of the white reference plate is controlled based on the control data obtained by actually measuring the relationship between the amount of light emitted by the lamp and the lighting time of the lamp, and the output of the means for detecting the lighting time of the lamp, and in the above embodiment. is the control data that actually measured the relationship between the relative light amount of the lamp and the number of copies, and the copy number counter 53.
Although it has been explained that the scanning timing of the white reference plate 47 is controlled based on the output of , there is no real difference between them.

Effects of the Invention Since the present invention is constructed as described in detail above, it has the effect that it is possible to improve the processing speed while minimizing deterioration in image quality due to fluctuations in the amount of light emitted from the illumination lamp.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 (A) and (B) are diagrams showing an example of control data in an embodiment of the present invention, and Fig. 3 is a diagram of a full-color copying machine to which the present invention is applied. FIG. 3 is a diagram showing the overall configuration. 8... Platen glass, 41... Scanning means, 42... Fluorescent lamp, 44... CCD sensor, 45... Original, 47... White reference plate, 49... Correction means, 50 ...Memory (reference value), 52...Memory (control data), 53...Copy number counter, 54...Control means. Applicant: Fuji Xerox Co., Ltd. Agent: Patent Attorney Akira Matsumoto

Claims (1)

[Claims] 1. A white reference plate is placed near the platen glass on which the original is placed, the reference plate is scanned before scanning the original, and the output value of the image sensor when scanning the reference plate is used as a reference. In an image reading device that corrects the output value of an image sensor when scanning a document based on the reference value, the image reading device is provided with means for detecting the lighting time of a lamp for illuminating the document, and the lighting time of the lamp is The relationship between time and light emission amount is actually measured in advance and held as control data, and from the control data and the lighting time of the lamp by the lighting time detection means, the light emission amount of the lamp is calculated from the time when the reference plate was scanned last time. The reference plate is scanned only when the amount of variation is recognized and the amount of variation is expected to exceed a preset value by lighting a lamp for the next image reading. An image reading device characterized by: 2. Holding a plurality of the control data according to various temperature environments, providing a temperature detection means, selecting one of the plurality of control data based on the output temperature by the temperature detection means, and controlling the selected control data. The image reading device according to claim 1, wherein the reference plate is scanned according to data.