JP2000258966A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain good image quality by accurately normalizing the read value of a density sensor without installing a reference correction member and without necessitating a mechanism for moving the density sensor, and executing a process control. SOLUTION: A density detection pattern is formed on an image carrier, or a transfer material carrier, or an intermediate transfer body. In the case of detecting the density detection pattern by a diffuse reflection type detecting sensor 33 and a regular reflection type density detecting sensor 35, a value obtained when the density of the density detection pattern is detected by the sensor 33 is normalized based on a value obtained when the surface of the image carrier, or the transfer material carrier, or the intermediate transfer body is detected by the sensor 35.

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 such as a copying machine, a printer or a facsimile using an electrophotographic system, and more particularly to a color image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile or the like using an electrophotographic system of this kind, a black, yellow, magenta or magenta image is sequentially formed on an image carrier such as a photosensitive drum. And an intermediate transfer member for primary transfer of a plurality of toner images of a plurality of colors such as cyan and the like in a state of being superimposed on each other, and collectively transferring a plurality of color toner images sequentially transferred on the intermediate transfer member onto a transfer sheet. By a secondary transfer, a full-color image is formed, or a plurality of image forming units that form toner images of different colors on an image carrier such as a photosensitive drum, and a plurality of image forming units are formed. A paper transport belt for transporting the transfer paper in a state where the transfer paper is held at the transfer position of the toner image to be transferred, and transfer the multicolor toner images formed in each image forming section onto the transfer paper transported by the paper transport belt. By following the transfer, those configured to form a full color image has been already proposed.

In such a color image forming apparatus using an image carrier or an intermediate transfer member or a paper transport belt, an image carrier or an intermediate transfer member such as a photosensitive drum is required to obtain good color reproducibility. Or, on the paper transport belt, create a pattern for correcting the gradation of the toner image of each color, detect the density of this gradation correction pattern with a density sensor that applies a reflection type sensor, etc. Process control for controlling formation conditions is performed.

At this time, an image carrier such as the above-mentioned photosensitive drum,
Alternatively, the black toner pattern formed on the intermediate transfer body or the paper transport belt is scanned using a regular reflection type sensor.
It is known that the performance of image quality control of other color toner patterns such as yellow and magenta is good when density detection is performed using a diffuse reflection type sensor.

For example, a toner concentration detecting device disclosed in Japanese Patent Application Laid-Open No. 6-66722 irradiates a toner carrier and a toner image on the toner carrier with light from a light emitting element, and detects reflected light from the light receiving element. A light-receiving element for black arranged at a position for detecting regular reflection light among the reflected light, and irregularly reflected light among the reflected light. And a color light receiving element disposed at a position where

[0006]

However, the prior art described above has the following problems. That is, as in the toner density detecting device disclosed in Japanese Patent Application Laid-Open No. 6-66722, light reflected from an image carrier such as a photoreceptor drum, or a toner pattern formed on an intermediate transfer member or a sheet conveying belt is used. In the case where the light receiving element for black disposed at a position for detecting specularly reflected light and the light receiving element for color disposed at a position for detecting irregularly reflected light among the reflected light are configured to include black, Image carrier, depending on the temperature characteristics of the color photodetector and color photodetector, etc.
Alternatively, the value obtained by reading the toner patch on the intermediate transfer member or the paper transport belt varies, so it is necessary to correct and normalize the value by some method.

In the case of a general regular reflection type sensor,
There is known a method of normalizing a reading value of a toner patch of a density sensor by a reading value of an image carrier such as a photoconductor on which the toner patch is formed, or a sensor of a background of an intermediate transfer member or a paper conveyance belt. ing.

[0008] However, when the image sensor, or the intermediate transfer member or the paper transport belt is configured to normalize the reading value by the sensor of the background, the diffused sensor has a very small diffused light value. Therefore, the reading value of the sensor of the image carrier or the intermediate transfer body or the paper transport belt is almost zero (the absolute value is small), and noise components due to irregular reflection due to scratches on the surface of the image carrier or the intermediate transfer body, etc. There is a problem that the calculation accuracy in normalization is very poor.

Therefore, as a technique capable of solving such a problem, there is a technique disclosed in Japanese Patent Application Laid-Open No. 9-284556. The image forming apparatus according to Japanese Patent Application Laid-Open No. 9-284556 discloses a latent image forming unit that forms a latent image of a test pattern on a photoreceptor, a developing unit that visualizes the latent image, and a developing device that visualizes the latent image. An intermediate transfer body for synthesizing and holding the toner image, a density detection sensor for detecting the density of the test pattern, and a reference calibration member near the intermediate transfer body, and the reflected light amount of the reference calibration member is measured by the density sensor. Detected, and based on the output value of the density sensor at this time, gradation correction is performed. Also,
The image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 9-284556 includes a latent image forming unit that forms a latent image of a test pattern on a photoreceptor, a developing unit that visualizes the latent image, and a developing device that visualizes the latent image. An intermediate transfer body for synthesizing and holding the toner image; and a density detection sensor for detecting the density of the test pattern. A region where the amount of reflected light in the apparatus is substantially zero is detected by the density sensor. And a device configured to perform gradation correction based on the output value of the density sensor.

However, Japanese Patent Application Laid-Open No. 9-28455
In the case of the image forming apparatus disclosed in Japanese Patent Application Publication No. 6-205, it is necessary to newly provide a reference calibration member, so that the number of components increases, the cost increases, and the variation between components increases. was there. Further, in the case of the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 9-284556, a density detection sensor for detecting the density of a test pattern is moved so that a reference calibration member or an area inside the apparatus where the reflected light amount is substantially zero is provided. However, it is difficult to accurately read the value of the reference calibration member and the dark portion at the same position at all times, and the variation in the read value of the density of the test pattern increases. there were.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art. It is an object of the present invention to provide a reference calibration member and a mechanism for moving a density sensor. Another object of the present invention is to provide an image forming apparatus that can accurately normalize a reading value of a density sensor with high accuracy and can obtain good image quality by performing process control.

[0012]

According to a first aspect of the present invention, a pattern for density detection is formed on an image carrier for forming an image. The pattern for density detection formed on the carrier is directly
Alternatively, the image is transferred onto a transfer material carrier or an intermediate transfer member, and the density of the density detection pattern is detected by a diffuse reflection type and regular reflection type density detection sensor, and an image is formed based on the detection result of the density detection sensor. In an image forming apparatus that controls forming conditions, a density detection pattern is formed on the image carrier, or a transfer material carrier or an intermediate transfer body,
When the density of the density detection pattern is detected by the diffuse reflection type and regular reflection type density detection sensors, the value when the density of the density detection pattern is detected by the diffusion reflection type density detection sensor is determined by the image carrier. Alternatively, the surface of the transfer material carrier or the intermediate transfer member is normalized based on a value detected by a regular reflection type density detection sensor.

According to a second aspect of the present invention, when the density detection pattern formed on the image carrier, the transfer material carrier, or the intermediate transfer body is detected by a regular reflection type density detection sensor. Is Vp1, the value when detected by a diffuse reflection type density detection sensor is Vp2, and the value when the surface of an image carrier or a transfer material carrier or an intermediate transfer body is detected by a regular reflection type density detection sensor is Vc
1. Assuming that the dark current of the diffuse reflection type and regular reflection type density detection sensors is Vd, (Vp1−Vd) / (Vc1−V
2. The image forming apparatus according to claim 1, wherein the image forming conditions are controlled using d) and a value of (Vp2-Vd) / (Vc1-Vd).

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 2 shows a color printer as an image forming apparatus according to an embodiment of the present invention.

In FIG. 2, reference numeral 1 denotes a main body of a color printer. Inside the main body 1 of the color printer, predetermined color image information transmitted from a client such as a personal computer (not shown) is provided. An image processing unit 2 for performing image processing is provided. From the image processing unit 2, as shown in FIG.
ROS of image forming units 3K, 3Y, 3M, and 3C for each color of yellow (Y), magenta (M), and cyan (C)
(Raster Output Scanner) 4
K, 4Y, 4M, and 4C sequentially output image data of each color, and the laser beams LB emitted from the ROSs 4K, 4Y, 4M, and 4C in accordance with the image data are supplied to the respective photosensitive drums 5K, 5Y, and 5M. 5C is scanned and exposed to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drums 5K, 5Y, 5M, and 5C are, for example, developing units 6K and 6Y using non-magnetic one-component toner.
6M and 6C develop toner images of black (K), yellow (Y), magenta (M), and cyan (C), respectively.

Each of the photosensitive drums 5K, 5Y, 5M, 5
As shown in FIG. 2, the transfer paper 7 as a sheet for transferring the toner images of each color formed on C is
A sheet of a predetermined size is fed from a sheet cassette 8 stored at the bottom of the inside by a sheet feeding roller 9. The transfer paper 7 supplied from the paper supply cassette 8 is sent out onto a paper transport belt 11 as an endless carrier by a registration roll 10 that is driven to rotate at a predetermined timing. The paper transport belt 11 is endlessly wound around a drive roll 12, a stripping roll 13, and a tension roll 14 with a constant tension. The drive roll 12 is driven to rotate at a predetermined speed in the direction of the arrow by the drive roll 12. As the paper transport belt 11, for example, a synthetic resin film made of chloroprene or urea resin having flexibility is formed in a belt shape, and both ends of the synthetic resin film formed in the belt shape are connected by means such as welding. Thus, an endless belt is used. The paper transport belt 11 is made of, for example, chloroprene, has a circumference of 455 mm, and has a resistance value of 10 ⁹ Ω · cm.

The leading edge of the transfer paper 7 transported by the paper transport belt 11 and the leading edge of the image on the first photosensitive drum 5K formed by the first image forming unit 3K are transferred to the photosensitive drum 5K. The paper feeding timing and the image writing timing are determined so as to match at the point. Transfer paper 7 that has reached the transfer point
The visible image on the photosensitive drum 5K is transferred by the transfer roll 15K, and reaches the transfer point of the photosensitive drum 5Y. On the transfer sheet 7 that has reached the transfer point of the photosensitive drum 5Y, a visible image on the photosensitive drum 5Y is transferred in the same manner as the transfer image 7 is transferred on the photosensitive drum 5K.
Similarly, the transfer paper sheet 7 on which all the transfer has been completed is further conveyed by the paper conveyer belt 11, and the stripping roll 1
3, when necessary, the stripping roll 13 is removed by a stripping discharge corotron (not shown) and has a small radius of curvature.
As a result, the sheet is separated from the sheet conveying belt 11. Thereafter, the transfer paper 7 onto which the four color toner images have been transferred is fixed by a fixing device 16 by a heating roll 17 and a pressure belt 18, and is discharged by a discharge roller pair 19 to a discharge tray 20.
The sheet is discharged upward, and a color image is printed.

The four image forming units 3K, 3Y, 3M, 3M of the above black, yellow, magenta and cyan colors
C have the same configuration as shown in FIG. 2, and these four image forming units 3K, 3Y, 3M,
In 3C, as described above, black, yellow, magenta, and cyan toner images are sequentially formed at a predetermined timing. The image forming units 3K, 3Y, 3M, and 3C for the respective colors include photoconductor drums 5K, 5Y, 5M, and 5C as image carriers, and these photoconductor drums 5K, 5Y, 5M, and 5C are provided.
Are charged with primary charging rolls 21K, 21Y, 2Y.
After being uniformly charged by 1M, 21C, ROS4
Image forming laser beams LB emitted from K, 4Y, 4M, and 4C in accordance with image data are scanned and exposed, and electrostatic latent images corresponding to respective colors are formed. The electrostatic latent images formed on the surfaces of the photosensitive drums 5K, 5Y, 5M, and 5C are black and yellow by the developing units 6K, 6Y, 6M, and 6C of the image forming units 3K, 3Y, 3M, and 3C, respectively. , Magenta and cyan non-magnetic one-component toners, and these visible toner images are formed by transfer rolls 15K, 15Y, 15M,
The toner image is sequentially transferred to the transfer sheet 7 held on the sheet conveying belt 11 by the charging of 15C. The above black, yellow color,
The transfer paper 7 to which the magenta and cyan toner images have been transferred is separated from the paper transport belt 11 and then subjected to the fixing process by the fixing device 16 as described above to form a color image.

Further, the transfer paper 7 is supplied from the paper feed cassette 8 as described above,
Thus, the sheet is conveyed to the sheet conveying belt 11 at a predetermined timing, and is held and conveyed on the sheet conveying belt 11.

The photosensitive drums 5K, 5Y, 5Y
M and 5C are the cleaners 22K, 22Y, 22M, and 22 after the toner image transfer process is completed, as shown in FIG.
C removes residual toner and the like, and prepares for the next image forming process.

After the transfer paper 7 is peeled off from the paper transport belt 11, toner, paper dust and the like are removed by a cleaning device 24 having a surface provided with a blade 23.

The color printer according to this embodiment forms a density detecting pattern on an image carrier, a transfer material carrier, or an intermediate transfer member, and diffusely reflects the density of the density detecting pattern. When the density is detected by the density detection sensor of the mold and the specular reflection type, the value when the density of the pattern for density detection is detected by the density detection sensor of the diffuse reflection type is defined as the value of the image carrier or the transfer material carrier or the intermediate transfer body. It is configured to normalize based on the value when the surface is detected by a regular reflection type density detection sensor.

Further, in this embodiment, the value when the density detection pattern formed on the image carrier, the transfer material carrier, or the intermediate transfer member is detected by the regular reflection type density detection sensor is Vp1, Vp2 is the value detected by the diffuse reflection type density detection sensor, Vc1 is the value detected when the surface of the image carrier or the transfer material carrier or the intermediate transfer body is detected by the regular reflection type density detection sensor, and Vc1 is the diffuse reflection type. Assuming that the dark current of the regular reflection type density detection sensor is Vd, (Vp1-Vd) / (Vc1-Vd) and (Vp2
The image forming conditions are controlled using the value of (−Vd) / (Vc1−Vd).

That is, as shown in FIG. 2, the color printer according to this embodiment is located downstream of the last cyan image forming unit 3C among the four image forming units 3K, 3Y, 3M and 3C. An automatic density detection sensor 25 for detecting the density of the tone correction pattern of the toner image of each color sequentially formed on the paper transport belt 11 by the four image forming units 3K, 3Y, 3M, and 3C.
Is arranged.

As shown in FIG. 3, for example, the automatic density detecting sensor 25 has a sensor body 30 integrally formed in a rectangular parallelepiped shape with a synthetic resin or the like. Inside the sensor main body 30, a light emitting element 31 made of an LED or the like is provided in a state where the light emitting element 31 is inclined 45 degrees toward the right in FIG.
At the front end side of the light emitting element 31, a light irradiation through hole 32, which is also inclined at 45 degrees to the right in the figure, is formed in a circular cross section.

Further, the automatic density detection sensor main body 30
A first light receiving element 33 composed of a photodiode or the like is disposed in the center of the sensor body 30 in a state facing directly upward in the figure. Through hole 3 for receiving light at the top of
4 are formed in a circular cross section.

Further, the automatic density detecting sensor body 3
0, a second light receiving element 35 made of a photodiode or the like is disposed on the right side thereof in a state of being inclined 45 degrees toward the left in the figure, and the sensor main body 30 has A light-receiving through-hole 36 inclined at 45 degrees to the left in the drawing is formed in the distal end side of the second light-receiving element 35 in a circular cross section.

Further, the light emitting element 31, the first light receiving element 33 and the second light receiving element 35 are arranged along a straight line as shown in FIG. 3 (b). In addition, as shown in FIG. 3A, the light emitted from the light emitting element 31 through the light irradiation through hole 32 irradiates the surface of the paper conveyance belt 11 with the automatic density detection sensor main body 30, Light diffusely reflected by the surface of the tone correction pattern formed on the surface of the paper transport belt 11 or the surface itself of the paper transport belt 11 is transmitted to the first light receiving element through the light receiving hole 34. 33, and
The light regularly reflected by the surface of the tone correction pattern formed on the surface of the paper transport belt 11 or the surface itself of the paper transport belt 11 is transmitted through the light receiving through hole 36 to the second light receiving element. As received by 35,
It is attached to a predetermined position of the color printer main body 1. Further, in the automatic density detection sensor main body 25, the light emitting element 31, the first light receiving element 33, and the second light receiving element 35 disposed along the linear shape are positioned along the moving direction of the paper transport belt 11. So that it is attached to a predetermined position of the color printer main body 1.

The first light receiving element 33 includes the light emitting element 31
Of the paper transport belt 11 by receiving light diffusely reflected by the surface of the tone correction pattern formed on the surface of the paper transport belt 11 or the surface of the paper transport belt 11 itself. This is for detecting the density of the gradation correction pattern formed of the color toner formed on the surface of. On the other hand, the second light receiving element 35 corrects the light emitted from the light emitting element 31 by the surface of the tone correction pattern formed on the surface of the sheet conveying belt 11 or the surface of the sheet conveying belt 11 itself. By receiving the reflected light, the density of the tone correction pattern formed of black toner formed on the surface of the sheet conveying belt 11 is detected.

As the tone correction pattern formed on the surface of the paper transport belt 11, for example, as shown in FIG. 4, density detection patterns 26K, 26Y, 26M having an intermediate density a (Cin 60%). , 26C and density detection patterns 27K, 27 of intermediate density b (Cin 20%)
Y, 27M, and 27C are formed using four color toner images of black, yellow, magenta, and cyan.

FIG. 1 is a block diagram showing a control circuit of the color printer according to this embodiment.

In FIG. 1, reference numeral 40 denotes a CPU as control means for controlling an image forming operation of the color printer;
Is a ROM storing a program or the like for controlling the image forming operation of the CPU 40, and 42 is an RA storing parameters and the like used when executing the control operation of the CPU 40.
M and 33 are first light-receiving elements of the diffuse reflection type of the automatic density detection sensor 25, 35 are second light-receiving elements of the regular reflection type of the automatic density detection sensor 25, and 43 are each based on the control operation of the CPU 40. Photoconductor drum 5K, 5Y, 5M, 5C
Of the laser beam LB emitted from the ROS 4K, 4Y, 4M, 4C, or the developing device 6
2 shows process control units for controlling parameters of an image forming process such as a developing bias applied to the developing rolls of K, 6Y, 6M, and 6C.

In the image forming apparatus according to this embodiment having the above-described configuration, the density detecting patterns of the respective colors formed on the surface of the image carrier, the intermediate transfer member, the sheet conveying belt, and the like will be described below. It is possible to accurately detect the concentration.

That is, in the color printer according to this embodiment, as shown in FIG. 4, a pattern for gradation correction, for example, an intermediate density a (Cin 60%) is formed on the surface of the paper transport belt 11 at a predetermined timing. Density detection patterns 26K, 26Y, 26M and 26C and intermediate density b (Cin 20%) density detection patterns 27K and 27
Y, 27M and 27C are formed by four color toner images of black, yellow, magenta and cyan. Then, a density detection pattern 26K of an intermediate density a (Cin 60%) formed on the surface of the paper transport belt 11 is provided.
26Y, 26M, and 26C, and the intermediate density b (Cin20
%) Density detection patterns 27K, 27Y, 27M, 2
The density of 7C is detected by the automatic density detection sensor 25.

FIG. 5 shows a gradation correction for a black toner having a different toner density on the paper conveyance belt 11 using a paper conveyance belt 11 (perimeter: 455 mm, resistance value: 10 ⁸ Ω · cm) made of urea resin. And a case where the regular reflection type sensor 35 of the automatic density detection sensor 25 detects the density of the toner pattern for gradation correction.
This shows the result of measuring a change in output from that detected by the diffuse reflection sensor 33.

The vertical axis in FIG. 5 indicates the output of the sensor, and the specular reflection type sensor 35 calculates (Vp1−Vd) / (Vc1).
−Vd), the diffuse reflection sensor 33 calculates (Vp2−V
d) / (Vc2−Vd), and the horizontal axis is the toner concentration TMA.
(Mg / cm ² ). Where V
p1 is the detection density output of the black gradation correction toner pattern by the regular reflection sensor 35, Vp2 is the detection density output of the black gradation correction toner pattern by the diffuse reflection sensor 33, and Vd is the automatic density detection sensor. Reference numeral 25 denotes a dark current, Vc1 denotes a density detection output of the surface of the paper transport belt 11 by the regular reflection sensor 35, and Vc2 denotes a density detection output of the surface of the paper transport belt 11 by the diffuse reflection sensor 33.

FIG. 6 shows an endless belt (perimeter: 455 m) made of urea resin as the paper transport belt 11 as in FIG.
m, resistance value: 10 ⁸ Ω · cm), forming toner patterns for gradation correction having different magenta toner densities on the paper transport belt 11, and using these toner patterns for gradation correction. This shows the results of measuring the change in output between the case where the density is detected by the regular reflection sensor 35 of the automatic density detection sensor 25 and the case where the density is detected by the diffuse reflection sensor 33.

The vertical axis in FIG. 6 indicates the output of the sensor, and the specular reflection sensor 35 calculates (Vp1−Vd) / (Vc1).
−Vd), the diffuse reflection sensor 33 calculates (Vp2−V
d) / (Vc2−Vd), and the horizontal axis is the toner concentration TMA.
(Mg / cm ² ). Where V
p1 is the detection density output of the magenta tone correction toner pattern by the regular reflection sensor 35, Vp2 is the detection density output of the magenta tone correction toner pattern by the diffuse reflection sensor 33, and Vd is the automatic density. The dark current of the detection sensor 25, Vc1 indicates the density detection output of the surface of the paper transport belt 11 by the regular reflection sensor 35, and Vc2 indicates the density detection output of the surface of the paper transport belt 11 by the diffuse reflection sensor 33. .

FIG. 5 shows that the change in toner density can be detected more accurately by using the detection density output of the regular reflection type sensor 35 for the black gradation correction toner pattern. Referring to FIG. 6, the toner pattern for color gradation correction represented by the magenta color can be detected more accurately by using the detection density output of the diffuse reflection type sensor 33 if the detection density output is used. Understand.

FIG. 7 shows a photoreceptor drum (OPC / φ84 mm) as the image carrier and a paper transport belt made of chloroprene (perimeter: 455 mm, resistance value: 10 ⁹ Ω · c).
m), a paper transport belt made of urea resin (perimeter: 45)
5 mm, resistance value: 10 ⁸ Ω · cm) and the reading value (Vcl) of the automatic density detection sensor 25 of the image carrier itself.
n) and a 15 × 15 mm non-magnetic one-component black toner and color toner (magenta) toner pattern formed on an endless belt made of a urea resin. Are measured. The density TM of the toner pattern at this time is
A is 0.6 (mg / cm ² ), and a flat member having no curvature other than the photosensitive drum is used. The value in FIG. 7 is a value obtained by subtracting the dark current of the automatic density detection sensor 25.

As can be seen from FIG. 7, the reading value (Vcln) of the automatic density detecting sensor 25 of the image carrier itself.
Is compared between the specular reflection type sensor 35 and the diffuse reflection type sensor 33. In the paper transport belt made of chloroprene, the reading value of the diffuse reflection type sensor 33 is larger than the reading value of the specular reflection type sensor 35. It can be seen that it is very small, about 1/10, and about 1/30 for the paper transport belt made of urea resin.

The reading value (Vcln) of the automatic density detecting sensor 25 of the image carrier itself, particularly the reading value of the diffuse reflection type sensor 33, is determined based on the surface of the sheet conveying belt made of a photosensitive drum or chloroprene. It is susceptible to conditions and the like, and the reading value tends to change each time it is measured.

For this reason, the density of the toner pattern formed on the image carrier such as the photoconductor drum, a paper conveyance belt made of chloroprene or urea resin is read by the reading value (Vcln) of the automatic density detection sensor 25 of the image carrier itself. )
When normalizing using the diffuse reflection type sensor 33, the reading value (Vcln) of the diffuse reflection type sensor 33
3 normalizes the toner pattern density detection value,
It is easily affected by the surface condition of the photoconductor drum, the surface of the paper transport belt made of chloroprene or the like, and the error increases.

FIG. 8 shows the values obtained by repeating the reading (Vcln) of the regular reflection sensor 35 and the diffuse reflection sensor 33 of the paper transport belt 11 of urea resin itself ten times. Here, the reading value (Vp1) of the black toner pattern by the regular reflection sensor 35 and the reading value (Vp2) of the magenta toner pattern by the diffuse reflection sensor 33 are 580 and 460, respectively.

At this time, the reading value of the toner pattern of the automatic density detecting sensor 25 is normalized by the following equation based on the reading value of the sensor of the paper transport belt 11 itself made of urea resin on which the toner pattern is formed. Attempting to normalize the reading (Vp1) of the black toner pattern with the reading (Vcln1) of the specular reflection sensor 35, the reading (Vcln) of the specular reflection sensor 35 is used.
Even if 1) fluctuates, the reading value (Vcln) of the specular reflection type sensor 35 of the paper transport belt 11 itself made of urea resin.
Since 1) is large, the value of Vp1 / Vcln1 is 0.3
It is stable with little change from 49 to 0.352. (Vp-Vd) / (Vc-Vd) Here, Vp indicates the detected density output of the toner pattern by the sensor, Vd indicates the dark current of the sensor, and Vc indicates the detected density output of the surface of the sheet conveying belt 11 by the sensor. ing.

On the other hand, if the reading value (Vp2) of the color (magenta) toner pattern is to be normalized by the reading value (Vcln2) of the diffuse reflection type sensor 33, the paper transport belt 11 itself made of urea resin is required. Since the reading value (Vcln2) of the diffuse reflection type sensor 33 is a minute value, even if the reading value (Vcln2) of the diffusion reflection type sensor 33 of the paper transport belt 11 itself made of the urea resin slightly fluctuates, Vp2 / The value of Vcln2 is 6.876
As a result, the reading value (Vp2) of the color (magenta) toner pattern cannot be accurately normalized.

When the variation in the value of Vp2 / Vcln2 is replaced with the toner concentration TMA from FIG.
And so ~0.78mg / cm ² 0.2mg / cm
Appears with ^two errors. In this case, even if the reading value (Vp2) of the color (magenta) toner pattern is normalized using the reading value (Vcln2) of the image carrier carrying the toner image such as the paper transport belt 11 made of urea resin, The density of the color (magenta) toner pattern cannot be detected accurately, and the value of Vp2 / Vcln2 greatly fluctuates even if the target value of the process control is set based on the detected value of the density of the toner pattern. Control accuracy is very poor.

Therefore, in this embodiment, the value of Vp2 / Vcln1 is normalized by normalizing the reading (Vcln2) of the diffuse reflection sensor 33 using the reading (Vcln1) of the regular reflection sensor 35. 0.277-0.
279 and the width of the variation can be kept small, and the accuracy of the process control can be improved.

Therefore, in this embodiment, as shown in the following equation, the reading value (Vp1) of the toner pattern by the regular reflection type sensor 35 is the same as the reading value of the image carrier or the endless belt by the regular reflection type sensor 35. Normalization is performed using the value (Vcln1), and the reading value (Vp2) of the toner pattern by the diffuse reflection sensor 33 is also normalized using the reading value (Vcln1) of the image carrier or the endless belt by the regular reflection sensor 35. It is configured to be. (Vp1-Vd) / (Vc1-Vd) (Vp2-Vd) / (Vc1-Vd)

As described above, the CPU 40 normalizes the reading value based on the detection values of the specular reflection type sensor 35 and the diffuse reflection type sensor 33 in accordance with the above-described formula, and the specular reflection type sensor 35 and the diffuse reflection type sensor 33. Based on the detected density value of the toner pattern, the surface potential of each of the photosensitive drums 5K, 5Y, 5M, and 5C, the intensity of the laser beam LB emitted from the ROSs 4K, 4Y, 4M, and 4C is determined by the process control unit 43. Alternatively, the developing device 6K,
By controlling the parameters of the image forming process such as the developing bias applied to the developing rolls 6Y, 6M, and 6C and performing the process control, a high-quality color image can always be obtained. Note that the toner pattern reading value (Vp
When 2) is normalized by using the belt reading (Vcln1) obtained by the regular reflection sensor 35, the result is as shown in FIG. 11, and it can be seen from FIG. 6 that the linearity is also increased. This shows that the detection accuracy of the color toner can be improved.

Embodiment 2 FIG. 9 shows Embodiment 2 of the present invention. In this embodiment, an image carrier such as a photosensitive drum is provided instead of having four image forming units. Formed sequentially on top,
An intermediate transfer body for primary transfer of a plurality of color toner images such as black, yellow, magenta, and cyan is superimposed on each other, and the multicolor toner images sequentially transferred onto the intermediate transfer body are transferred to a transfer paper. It is configured to form a full-color image by batch-transferring on the top.

In FIG. 9, reference numeral 50 denotes a main body of the color printer. Inside the main body 50 of the color printer, a photosensitive drum 51 as an image carrier is provided at a predetermined rotational speed along the direction of the arrow. It is arranged to be driven to rotate. After the surface of the photoconductor drum 51 is uniformly charged to a predetermined potential by the primary charger 52, the surface of the photoconductor drum 51 is exposed to a first color image by the ROS 53, and an electrostatic latent image is formed. Is formed. The first-color electrostatic latent image formed on the surface of the photosensitive drum 51 is
For example, the black developing device 54 of the rotor type developing device 54
The toner image is developed by K, and this black toner image is transferred by the transfer charger 56 onto the intermediate transfer belt 55 at the primary transfer position. Thereafter, the surface of the photosensitive drum 51 is neutralized by a pre-cleaning static eliminator 57, and then the residual charge and the like are cleaned by a cleaner 59 having a cleaning blade 58.

Next, similarly to the above, the photosensitive drum 5
The yellow, magenta, and cyan toner images are sequentially formed on the surface of the photosensitive drum 51, and the yellow, magenta, and cyan toner images sequentially formed on the surface of the photosensitive drum 51 are formed on the intermediate transfer belt 55. The image is transferred in a state of being sequentially superimposed on the top. The four color toner images of black, yellow, magenta, and cyan transferred in a state of being superimposed on each other on the intermediate transfer body belt 55 are transferred onto transfer paper 60 conveyed at a predetermined timing by a transfer roll 61. After the next transfer, the transfer paper 60 is fixed by the fixing device 62 and is discharged outside the device.

The intermediate transfer belt 55 is supported by a plurality of rolls 63 to 66 so as to circulate at a constant speed. Further, the surface of the intermediate transfer belt 55 is designed to clean transfer toner, paper dust, and the like by a cleaner 69 having a cleaning roll 67 and a blade 68.

In the second embodiment, the automatic density detecting sensor 70 for detecting the density of the tone correction pattern formed on the surface of the intermediate transfer belt 55 is provided near the surface of the drive roll 63. ing. The automatic density detection sensor 70 is composed of a diffuse reflection type sensor and a regular reflection type sensor as in the above-described embodiment.

Then, the density of the tone correction pattern formed on the surface of the intermediate transfer belt 55 is detected by the diffuse reflection type sensor and the regular reflection type sensor of the automatic density detection sensor 70, and the process control is performed. It is supposed to do.

At this time, when the density of the gradation correction pattern formed on the surface of the intermediate transfer belt 55 is detected, as shown in the following equation, the toner pattern reading value (specified by the regular reflection sensor 35) is obtained. Vp1) is a reading value (Vc) of the image carrier, the endless belt or the like by the regular reflection sensor 35.
ln1), and the reading (Vp2) of the toner pattern by the diffuse reflection sensor 33 is also the reading (Vp2) of the image carrier or the endless belt by the regular reflection sensor 35.
cln1). (Vp1-Vd) / (Vc1-Vd) (Vp2-Vd) / (Vc1-Vd)

As described above, the CPU 40 normalizes the read values based on the detection values of the specular reflection type sensor 35 and the diffuse reflection type sensor 33 in accordance with the above-described formula, and performs the normal reflection type sensor 35 and the diffuse reflection type sensor 33. The surface potential of the photoconductor drum 51 and the ROS5
3 to control the image forming process parameters such as the intensity of the laser beam LB emitted from the developing device 3 or the developing bias applied to the developing rolls of the developing units 54K, 54Y, 54M and 54C, and perform the process control to always achieve high image quality. Color images can be obtained.

The other constructions and operations are the same as those of the above-described embodiment, and a description thereof will be omitted.

In the above embodiment, as shown in FIG. 3, an automatic density detecting sensor having one light emitting element and two light receiving elements is used as the diffuse reflection type and regular reflection type density detecting sensors. However, the present invention is not limited to this, and an automatic density detection sensor having two light emitting elements and one light receiving element may be used as shown in FIG.

[0062]

As described above, according to the present invention, it is possible to accurately normalize the reading value of the density sensor without providing a reference calibration member or a mechanism for moving the density sensor. By performing the control, it is possible to provide an image forming apparatus capable of obtaining good image quality.

[Brief description of the drawings]

FIG. 1 is a block diagram of a control circuit showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a configuration diagram showing a density detection sensor.

FIG. 4 is an explanatory diagram showing a tone correction pattern.

FIG. 5 is a graph showing a relationship between a toner density and an output of a sensor.

FIG. 6 is a graph showing a relationship between toner density and sensor output.

FIG. 7 is a table showing types of image carriers and outputs of specular reflection type and diffuse reflection type sensors.

FIG. 8 is a table showing an image carrier and a toner pattern and outputs of specular reflection type and diffuse reflection type sensors.

FIG. 9 is a configuration diagram showing an image forming apparatus according to Embodiment 2 of the present invention.

FIG. 10 is a configuration diagram showing another example of the automatic density detection sensor.

FIG. 11 is a graph showing the relationship between toner density and sensor output.

[Explanation of symbols]

25: Automatic density detection sensor, 33: Diffuse reflection first
Light receiving element, 35: regular reflection type second light receiving element, 40:
CPU, 41: ROM, 42: RAM, 43: process control unit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoya Yamazaki 2274 Hongo, Ebina-shi, Kanagawa Prefecture F-Xerox Co., Ltd. F-term (reference) 2G059 AA01 BB20 EE02 EE13 FF08 KK01 MM02 MM05 MM09 MM10 2H027 DA10 DA32 DE02 DE07 DE10 EB04 EC03 EC06 EC07 EC09 EC19 EE07 EE08 EF01

Claims (2)

[Claims] 1. A pattern for density detection is formed on an image carrier for forming an image, and the pattern for density detection formed on the image carrier is directly or transferred to a transfer material carrier or an intermediate material. Image formation in which the density of the density detection pattern is transferred onto a transfer body and detected by a diffuse reflection type and regular reflection type density detection sensor, and image forming conditions are controlled based on the detection result of the density detection sensor. In the apparatus, a density detection pattern is formed on the image carrier, the transfer material carrier, or the intermediate transfer body, and the density of the density detection pattern is detected by a diffuse reflection type and regular reflection type density detection sensor. When the density of the density detection pattern is detected by a diffuse reflection type density detection sensor, the surface of the image carrier, the transfer material carrier or the intermediate transfer body is subjected to a regular reflection type density detection. An image forming apparatus for normalizing based on a value detected by an intellectual sensor. 2. A value obtained when a density detection pattern formed on the image carrier, the transfer material carrier, or the intermediate transfer member is detected by a regular reflection type density sensor.
1. Vp2 is the value detected by the diffuse reflection type density detection sensor, and Vc1 is the value detected when the surface of the image carrier or the transfer material carrier or the intermediate transfer body is detected by the regular reflection type density detection sensor. Assuming that the dark current of the reflection type and regular reflection type density detection sensors is Vd, (Vp1-V
d) / (Vc1-Vd) and (Vp2-Vd) / (Vc1
The image forming apparatus according to claim 1, wherein the image forming condition is controlled using the value of -Vd).