JPH10186744A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of precisely performing a calibration for enhancing the quality of an image formed on a sheet. SOLUTION: The density of a device calibrating image formed on a sheet and the density of the ground of the sheet are read by a first and second optical sensors provided on a test pattern reading part 17, and the density of the device calibrating image read by the first optical sensor is corrected on the basis of the density of the ground of the sheet read by the second optical sensor, whereby a device calibrating correction data is provided. This is inputted to a control part 18, and on the basis of this data, an image processing part 11, a charging part 12, an exposing part 13, a developing part 14, a transfer part 15, and a fixing part 16 are controlled by the control part 18 so as to form an image B of a desired density on a sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image on a sheet.

[0002]

2. Description of the Related Art Conventionally, in the above-described image forming apparatus, calibration for improving image quality of an image formed on a sheet is performed. In particular, in an electrophotographic image forming apparatus in which an image is formed through a plurality of steps, various controls are performed for each step to improve the image quality of an image finally formed on a sheet. . For example, JP-A-3-
Japanese Patent Application Laid-Open No. 0887768 discloses a method of monitoring a developed image formed on a photoreceptor as an image carrier, controlling each process so that the developed image becomes a predetermined developed image, and calibrating the apparatus. A technique for improving image quality has been proposed, and Japanese Patent Application Laid-Open No. 4-193576 discloses an apparatus in which the toner density after transfer is monitored and each process is controlled so that the toner density becomes a predetermined toner density. A technique for improving the image quality of an image by performing calibration has been proposed.

[0003]

However, since these techniques control the process in the intermediate stage of image formation and calibrate the apparatus, the quality of the image actually obtained by the user, that is, the quality of the fixed image itself is reduced. There is no guarantee that the image quality will be increased, and there is a problem that an error easily occurs between the image quality of the image based on the process controlled in the intermediate stage and the image quality of the fixed image.

In order to solve this problem, Japanese Patent Laid-Open Publication No.
Japanese Patent Application Laid-Open No. 77060/1992 and Japanese Patent Application Laid-Open No. 4-366165 disclose a method in which a reference image is formed on a sheet using an image forming apparatus, and the reference image is read using an image reading apparatus provided in the image forming apparatus. A technique for calibrating the device by controlling the temperature has been proposed. According to this technique, since the apparatus can be calibrated by controlling the fixing process, which is the final process, the accuracy of image quality is improved. However, there is a problem that this can be realized by an image forming apparatus provided with an image reading device such as a copying machine, but cannot be realized by an image forming device not provided with an image reading device such as a printer.

Japanese Patent Application Laid-Open No. H05-055868 discloses an optical fiber which reads reflected light from a test pattern in which a color band is inserted between a start pattern and a stop pattern and forms the level of the reflected light. There is proposed a technique for controlling the apparatus so as to reduce the difference between the reference value and the reference value and improving the image quality. According to this technique, the image forming apparatus can be calibrated even in the case of an image forming apparatus such as a printer that does not include an image reading device.

In such an image forming apparatus provided with a test pattern reading device independently of the presence or absence of the image reading device, in order to perform high-precision image quality control, reflected light from the test pattern is read with high accuracy. It is necessary to set a standard concentration. Although the above publication does not suggest what is used as the reference density, it is conceivable to use the density of the background of the paper as the reference density. There are several factors that cause a reading error when the density of the ground of the sheet is set as the reference density. Fluctuations in the light amount of the light source illuminating the test pattern are also one of the factors.
When the method that uses the density of the paper ground as the reference density is adopted,
As a result of the fluctuation of the light amount of the light source, if the light amount of the light source is different between when reading the test pattern density and when reading the density on the ground of the paper, the intensity of the reflected light input to the light receiving element fluctuates,
The output of the test pattern reader becomes a value different from the original output, and a reading error occurs.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides an image forming apparatus capable of accurately performing calibration for improving the image quality of an image formed on a sheet even if the light amount of a light source illuminating a test pattern varies. The purpose is to provide.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an image forming apparatus for forming an image on paper,
The image forming apparatus has a device calibration mode for forming a device calibration image on paper, and operates in the device calibration mode to read the density of the device calibration image formed on the paper and the density of the ground of the paper, respectively. The first and second optical sensors for obtaining respective density data by using the density of the ground of the paper read by the second optical sensor as a reference density are formed on the paper read by the first optical sensor. A device correction data acquisition unit having a data correction unit that obtains predetermined device calibration data by correcting the density data of the device calibration image, and the device calibration data obtained by the device calibration data acquisition unit. And a device calibrating unit for calibrating the image forming apparatus so that an image having a desired density is formed on a sheet based on the image forming apparatus.

Here, the first and second optical sensors simultaneously read the density of the paper ground and the density of the device calibration image formed on the paper which is different from the density of the paper ground. It is preferable that they are arranged.

[0010]

Embodiments of the present invention will be described below. The present invention is also effective in an image forming apparatus of a type other than the electrophotographic type. However, in the present embodiment, an electrophotographic type is described as an example. FIG. 1 is a block diagram of an electrophotographic image forming apparatus according to an embodiment of the present invention.

The image forming apparatus 10 forms an apparatus calibration image on a sheet by the image forming apparatus 10 and determines the density of the background color of the sheet and the density of the apparatus calibration image formed on the sheet. The image forming apparatus 10 has a device calibration mode for reading and calibrating the device. The image forming apparatus 10 includes a test pattern reading unit 17 and a control unit 18 which operate in the device calibration mode, which will be described later.

An image signal A is input to an image processing unit 11 shown in FIG. 1, and the image processing unit 11 performs image processing according to the input image signal A. The charging unit 12
A photoreceptor drum (not shown) is uniformly charged. The exposing unit 13 irradiates the photosensitive drum charged by the charging unit 12 with exposure light based on the data processed by the image processing unit 11 to form an electrostatic latent image on the photosensitive drum.

The developing section 14 develops the electrostatic latent image by applying toner on the photosensitive drum, and forms a toner image on the photosensitive drum. The transfer unit 15 transfers the toner image to a sheet. The fixing unit 16 fixes the toner image transferred on the sheet by pressure and heat of a roller.

The test pattern reading section 17 includes first and second optical sensors for reading the density of the ground of the sheet and the density of the apparatus calibration image formed on the sheet in the apparatus calibration mode, and the first and second optical sensors. There is provided a device calibration data acquisition unit having a data correction unit for obtaining device calibration data generated based on the density of the ground of the sheet and the density of the image read by the second optical sensor.

The control section 18 controls the image processing section 1 based on the apparatus calibration data obtained by the apparatus calibration data acquisition means so that an output image B having a desired density is formed on a sheet.
1, charging section 12, exposure section 13, developing section 14, transfer section 1
5. Control each unit of the fixing unit 16. FIG. 2 is a plan view (a) and a side view (b) showing an outline of a test pattern reading unit used in the present embodiment.

The test pattern reading section 17 includes a fixing section 1
6 (see FIG. 1), and reads the density of the device calibration image formed on the fixed paper and the density of the ground of the paper. As shown in FIGS. 2A and 2B, the test pattern reading unit 17 includes a sheet 2 conveyed in the direction of arrow A.
0 and the first and second optical sensors 21 and 22 disposed substantially vertically above the reading position P, and the optical sensors 21 and 22.
2, a lens 23 for guiding the reflected light from the sheet and a light source 24 for illuminating the vicinity of the reading position P at an angle of 45 degrees from the front. When a color image is handled as described later, red (R), green (G), and blue (B)
In some cases, a required number of optical sensors or R, G, and B light sources having filters attached thereto may be provided. As the light source 24, a fluorescent lamp, a halogen lamp, a laser, an LED, or the like is employed. In particular, lasers, LEDs, and the like emit light of a specific wavelength, so that the generated light can be used directly without being cut by a color separation filter or the like, so that the efficiency is high and the power consumption of the test pattern reading unit 17 is reduced. Is achieved.

In this embodiment, the test pattern reading unit 1
Inexpensive LEDs are used for the light source 24 of the seventh embodiment. LE
D can secure a required amount of light in a required color, and is small in size, and does not require a heat radiation mechanism used in a halogen lamp or the like, thereby contributing to downsizing of the device.
In addition, the LED can easily perform high-speed pulse lighting by applying a pulse voltage, and can supply an instantaneous current to the LED that is larger than the steady-state current when the LED is continuously turned on. Can be improved. In addition, L by pulse lighting
The emission intensity of the ED is also stabilized. Recently, GaN has been used as a material.
Blue and green high-brightness LEDs using (gallium nitride) have been developed. By using these blue and green high-brightness LEDs together with the conventionally used red high-brightness LEDs, the LEDs can be used for full-color light emission can do. In the present embodiment, full-color light emission is performed using these LEDs, whereby the size and power consumption of the test pattern reading unit 17 are reduced.

On the other hand, photodiodes, CCDs and the like are used as the optical sensors 21 and 22. The manner in which the test pattern reading unit 17 reads the density of the device calibration image 25 and the density of the paper ground will be described with reference to FIG. FIG. 3 is a diagram illustrating a positional relationship between the optical sensor and the device calibration image on the paper as viewed from above the test pattern reading unit.

When the paper 20 having the device calibration images 25 of various densities formed on the paper 20 is conveyed in the direction of arrow A and reaches the vicinity of the reading position P, the paper 20 is disposed above the reading position P in the drawing. The density of the device calibration image 25 is read by the first optical sensor 21 along the reading line 21 a on the paper 20, and at the same time, the paper 20 is read by the second optical sensor 22.
The density of the ground of the paper 20 is read along the upper reading line 22a. Since the lens 23 is used in the optical system of the test pattern reading unit 17 as shown in FIG. 2B, the optical sensors 21 and 22 of the optical sensors 21 and 22 are used.
The relative positions sandwiching the center line CL between the two are the reading line 21 a of the device calibration image 25 and the reading line 22 of the ground of the paper 20.
Although the relationship is opposite to the relative position of “a”, the first optical sensor 21 is provided immediately above the region of the device calibration image 25 without using such an optical system, and Even if the second optical sensor 22 is provided directly above, there is no problem.

As described above, in this embodiment, since the density of the device calibration image 25 and the density of the ground of the paper 20 are simultaneously read by the respective optical sensors, the device calibration image density can be read regardless of the light amount fluctuation of the light source. Is constant, and the error in normalizing the test pattern density based on the density of the paper background can be reduced.

The density data read in this way is sent to a data correction section in the device calibration data acquisition means. The data correction unit corrects the device calibration data by correcting the density data of the device calibration image read by the first optical sensor using the ground density of the sheet read by the second optical sensor as a reference density. can get. The device calibration data obtained by the device calibration data acquisition unit is sent to the device calibration unit in the control unit 18, and the device calibration unit uses the image processing unit 11, the charging unit 12, and the exposure unit 1 based on the device calibration data.
3. Control each unit of the developing unit 14, the transfer unit 15, and the fixing unit 16.

FIG. 4 is a block diagram of an optical sensor output signal processing circuit provided in the device calibration data acquisition means in the test pattern reading section 17. As shown in FIG. 4, the signal processing circuit receives the density data of the device calibration image from the first optical sensor 21 and the density data of the ground of the paper from the second optical sensor 22, respectively. An A / D conversion start pulse and a clock pulse are input to the first and second A / D converters 26 and 27 for D / D conversion and the A / D converters 26 and 27, respectively. And a pulse generating circuit 28 for synchronizing. By this signal processing circuit, the output data from the first optical sensor 21 and the output data from the second optical sensor 22 are simultaneously A / D converted, and the converted digital data is simultaneously sent to the data correction unit.

The data correction unit generates device calibration data by correcting the density data of the device calibration image formed on the paper using the density of the ground of the paper as a reference density. The device calibration data is sent to the device calibration means to calibrate the image forming apparatus. FIG. 5 is a block diagram showing a modification of the signal processing circuit shown in FIG. As shown in FIG.
This signal processing circuit includes an A / D converter 26, a pulse generation circuit 28, and a division circuit 29. The density data of the device calibration image from the first optical sensor 21 is input to the numerator input unit 29a of the division circuit 29, and the paper from the second optical sensor 22 is input to the denominator input unit 29b of the division circuit 29. The density data of the ground is input. The division circuit 29
Based on the two input data, normalized data is calculated by the following equation.

Normalized data = (test pattern density) ÷
(Density of paper ground) The normalized data is sent to a data correction unit after A / D conversion. When the signal processing circuit having the configuration of FIG. 5 is used, since the density data of the device calibration image and the density data of the ground of the paper are divided and then A / D converted at once, the light source Even if the light amount fluctuation occurs, the influence on the calculation processing result is smaller than when the signal processing circuit having the configuration of FIG. 4 is used.

In the above embodiment, the case where the number of the first optical sensors for reading the density of the image for device calibration is one has been described.
However, the present invention is not limited to this. For example, when a full color image is formed using four color materials of Y (yellow), M (magenta), C (cyan), and K (black) as in a color printer By providing optical sensors for reading the density of the device calibration image for four colors of yellow, magenta, cyan, and black, it is possible to simultaneously read the test pattern density of each color, and a high-quality color image forming apparatus Can be configured.

In the above embodiment, an electrophotographic image forming apparatus has been described. However, the present invention can be applied to an image forming apparatus such as an ink jet system, a thermal transfer system, and a silver halide photographic system.

[0027]

As described above, according to the image forming apparatus of the present invention, the density of the apparatus calibration image and the density of the ground of the paper are read by the two optical sensors, and the image forming apparatus is capable of reading the paper. Since the calibration is performed according to the density of the ground, it is possible to obtain an image of a desired density that is calibrated with high accuracy. Further, when the two optical sensors are arranged at positions where the density of the ground of the paper and the density of the image for device calibration are simultaneously read,
Even if the amount of light from the light source that illuminates the paper fluctuates, or if the amount of light input to the optical sensor fluctuates due to vertical movement due to vibration during paper transport, the density data of the device calibration image and the paper ground Since the ratio with the density data does not change, calibration can be performed with high accuracy, and an image with a desired density calibrated with high accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electrophotographic image forming apparatus according to a first embodiment of the present invention.

FIGS. 2A and 2B are a plan view and a side view, respectively, showing an outline of a test pattern reading unit used in the present embodiment.

FIG. 3 is a diagram illustrating a positional relationship between an optical sensor and a device calibration image on a sheet as viewed from above a test pattern reading unit.

FIG. 4 is a block diagram of a signal processing circuit of an optical sensor output provided in a device calibration data acquisition unit in a test pattern reading unit 17;

FIG. 5 is a block diagram showing a modification of the signal processing circuit shown in FIG.

[Explanation of symbols]

 Reference Signs List 10 image forming apparatus 11 image processing unit 12 charging unit 13 exposure unit 14 developing unit 15 transfer unit 16 fixing unit 17 test pattern reading unit 18 control unit 20 paper 21, 22 optical sensor 23 lens 24 light source 25 device calibration image 26, 27 A / D converter 28 pulse generation circuit 29 division circuit

Claims (2)

[Claims] 1. An image forming apparatus for forming an image on a sheet, wherein the image forming apparatus has an apparatus calibration mode for forming an apparatus calibration image on a sheet, and operates in the apparatus calibration mode. A first and a second optical sensor that respectively obtain the density data by reading the density of the device calibration image and the density of the ground of the paper formed on the paper, and the ground of the paper read by the second optical sensor. A data correction unit for obtaining predetermined device calibration data by correcting the density data of the device calibration image formed on the paper read by the first optical sensor with the density as a reference density. The image forming apparatus is calibrated so that an image of a desired density is formed on paper based on the calibration data acquisition unit and the calibration data obtained by the calibration data acquisition unit. An image forming apparatus comprising the that device calibration means. 2. The apparatus according to claim 1, wherein the first and second optical sensors simultaneously read a density of the ground of the paper and a density of an apparatus calibration image formed on the paper that is different from the density of the ground of the paper. The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed at a position.