JPH10288879A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a color density and to obtain high reliability by detecting the concn. of a toner patch on a photoreceptor after passing through a transfer means prior to the formation of an image and changing the concn. of toner based on the detected result. SOLUTION: A bias having the polarity reverse to that of the toner is applied to a primary transfer roller 107 by a primary transfer power source 108, thereby transferring the developed yellow toner onto an intermediate transfer body 106 by the work of the electric field of the bias. An electrophotographic process part is provided with a patch sensor 122 being a toner concentration detecting means in the position where is nearer to the downstream side than the primary transfer roller 107 and faces the surface of the photoreceptor 101. The degree of development is adjusted by controlling the voltage of a developing power source 123 being a means for changing the density of the image based on the detected result, the potential on the photoreceptor 101 is controlled by a means 124 for changing exposure energy to adjust the degree of the development, and transfer efficiency is adjusted by controlling the voltage of the primary transfer power source 108.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for irradiating a toner patch formed on a latent image carrier with light, detecting light reflected from the toner patch, and controlling image forming conditions based on the result. Printer using electrophotography process,
The present invention relates to a color image forming apparatus such as a facsimile and a copying machine.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic process has been put to practical use by taking advantage of the advantages that relatively high resolution is relatively easy and that plain paper can be used. However, since the electrophotographic process uses powder and static electricity, it is difficult to keep the image density constant regardless of the temperature and humidity environment and durability. In particular, since a color image forming apparatus uses four types of toners, that is, a yellow toner, a cyan toner, a magenta toner (hereinafter, these toners are collectively referred to as color toners) and a black toner, it is extremely difficult to always stabilize the color density. It is.

Therefore, the following technology has been conventionally proposed.

(1) As described in JP-A-59-13264, the amount of the developer transferred from the image carrier to the intermediate transfer member is detected, and the transfer efficiency is changed based on the detection result. The image density has been stabilized by controlling the means for causing this to occur.

(2) As described in JP-A-5-165293, the amount of toner on a photoreceptor is detected by an image density detecting means arranged before transfer, and a charging potential and an exposure potential are determined according to the detected density. Is set to the second set value to stabilize the image density.

(3) As described in JP-A-7-319234, the image density is stabilized by controlling the transfer current value based on the ratio of the toner density on the photosensitive member and the toner concentration on the transfer material transporting material.

[0007]

However, in general, the intermediate transfer member is often black because the conductive treatment is performed by dispersing carbon in the resin. Therefore, the method described in the prior art (1) requires a black toner. It was difficult to detect the concentration. When a white intermediate transfer member is formed by using ITO or the like as the conductive material, it is difficult to detect the color toner density. In order to detect all toner concentrations, it is conceivable to separately apply the intermediate transfer member and form a toner patch at a predetermined position. However, the cost of the intermediate transfer member is increased, and the S / N is reduced due to the difference in transferability of the differently applied portions. ,
When the coating is performed by printing or the like, a step is formed, and as a result, the life of the cleaning blade for cleaning the intermediate transfer member may be shortened.

Further, the method described in (2) is effective in a system in which the transfer efficiency does not fluctuate because the toner density is detected before the transfer, but the transfer efficiency fluctuates depending on the toner color, charge amount, environment and the like. Therefore, the correspondence with the toner density on the transfer material was insufficient. Further, the position of the sensor is often located below the developing device, and there has been a problem that the toner spilled from the developing device adheres to the sensor during long-term use, and the S / N is reduced.

In the method described in (3), sensors are required at least at two places on the photoreceptor and the transfer material transporting material, so that there is a problem in cost and apparatus size. Further, when the amount of development (the amount of toner after development and before transfer) varies, there is a problem that the density on the transfer material varies.

The present invention has been made in view of such a problem, and an object of the present invention is to perform low-cost, space-saving, high-accuracy density detection regardless of the color of toner and to correct process variations. Accordingly, an object of the present invention is to provide a color image forming apparatus which stabilizes color density and has high reliability.

[0011]

That is, the present invention provides a color image forming apparatus for solving the above-mentioned problems. (1) Exposure means for writing a latent image on a photoreceptor; Developing means for visualizing the toner, transfer means for electrostatically transferring the toner image visualized by the developing means onto the image carrier, and transfer of a predetermined toner patch density formed prior to image formation A density detecting means for detecting on the photoreceptor after the means, and a density changing means for changing a toner density on the photoreceptor after the transfer means based on a result of the density detecting means. .

(2) In (1), the density changing means is means for changing a bias applied to the developing means.

(3) In (1), the density changing means is means for changing exposure energy.

(4) In (1), the density changing means is means for changing a bias applied to the transfer means.

(5) Exposure means for writing a latent image on a photoreceptor, developing means for visualizing the latent image with black and color toners, and a toner image visualized by the developing means on an image carrier. Transfer means for electrostatically transferring, density detection means for detecting the density of a predetermined toner patch formed prior to image formation on the photoreceptor after passing through the transfer means, and based on the result of the density detection means And a density changing means for changing the toner density on the photoreceptor after the transfer means, wherein the bias applied to the transfer means when the toner patch passes through the transfer means has the same polarity bias (Vc) and reverse polarity as the toner. Bias (Vt).

(6) In (5), the bias when the toner patch passes through the transfer means is | Vc | <| Vt |
It is characterized by being.

(7) In (5), the density changing means is means for changing a bias applied to the developing means.

(8) In (5), the density changing means is means for changing the exposure energy of the exposure means.

(9) In (5), the density changing means is means for changing a bias applied to the transfer means.

[0020]

Embodiments of the present invention will be described below.

FIG. 1 is a main sectional view of an electrophotographic process section of an image forming apparatus according to an embodiment of the present invention.

First, the configuration of the electrophotographic process section and its operation during image formation will be described. The charging roller 102 charges the photoconductor 101 to a uniform certain potential (for example, -700 V) by the action of an electric field of a power supply (not shown). Exposure means 1
600 dpi (dot per
The laser beam having the resolution of (inch) is guided onto the photoreceptor 101 by the return mirror 104 to form an electrostatic latent image. Next, the yellow toner developing unit 105Y is brought into contact with the developing unit 105 of the one-component contact type which can be moved in the direction of the arrow in FIG.
The negatively charged yellow toner is reversely developed by the action of the electric field 23 and is visualized on the photoreceptor 101. The developed yellow toner is transferred onto the intermediate transfer member 106 by a primary transfer power source 108 by applying a bias having a polarity opposite to that of the toner to the primary transfer roller 107 by the action of the electric field. The transfer residual toner on the photoreceptor 101 is collected by a photoreceptor cleaner 109 which cleans the photoreceptor by bringing the blade into contact therewith, and then the photoreceptor potential is reset by a discharging lamp 110. The same operation is performed by synchronizing the position of the intermediate transfer member 106 and the light emission timing of the exposure unit 103 with a magenta toner developing unit 105M, a cyan toner developing unit 105C,
By repeating the process for the black toner developing device 105K, the toner of each color is superimposed on the intermediate transfer member 106 to form a full-color image. During this time, the secondary transfer roller 116 and the intermediate transfer member cleaner 119 are kept separated. On the other hand, a transfer material 113 such as paper or OHP is conveyed from a paper supply cassette 112 to a pair of registration rollers 114 by a paper supply means 111, and is synchronized with a drive roller 115 in synchronization with the full-color image on the intermediate transfer body 106 in FIG. The sheet is conveyed to a secondary transfer section formed by a secondary transfer roller 116 that can be separated and moved in the direction of the arrow. In the secondary transfer section, the transfer material 113
In synchronization with this, the secondary transfer roller 116 contacts the intermediate transfer body 106 to form and press the nip, and the voltage determined by the calculating means 121 for calculating the voltage obtained from the primary transfer power source 108 is 2 A full-color toner image is formed on the transfer material 113 by the constant voltage control of the next transfer power supply 117 by the action of the electric field. Thereafter, the transfer material 113 is fixed by the fixing unit 120 and discharged out of the apparatus.

In the electrophotographic process section, a patch sensor 122 as a toner density detecting means is further provided with a primary transfer roller 1.
07 is provided at a position facing the surface of the photoreceptor 101 downstream. As a means for changing the image density based on the detection result, the developing amount is adjusted by controlling the voltage of the developing power source 123, and the potential on the photosensitive member 101 is controlled by the exposure energy changing means 124. Various means are provided for adjusting the transfer efficiency by controlling the voltage of the primary transfer power supply 108 for adjusting the development amount.

FIG. 2 shows a configuration example of the patch sensor 122.

The patch sensor 122 includes a light emitting element 151, a light receiving element 152, a condenser lens 153, an imaging lens 154, and a holder 155. Light emitted from the light emitting element 151 is collected on the irradiation surface 156 by the condenser lens 153. The toner patch passes on the irradiation surface 156. Then, a so-called diffuse reflection component obtained by removing a specular reflection component from the light reflected by the irradiation surface 156 is formed by the imaging lens 154.
Through the light receiving element 152. In this way,
The reflectance of the irradiation surface 156 is measured.

The sequence from the creation of a patch for stabilizing the image density based on the density (reflectance) detected by the patch sensor 122 to the printing operation will be described below.

First, a plurality of solid pattern yellow color patches of about 1 cm square are formed on the photoreceptor 101, and the transfer efficiency is stepwise adjusted to a bias at which the transfer efficiency becomes approximately 0 to 80 to 100%, which is the transfer efficiency during normal printing. It passes through a primary transfer unit that is set in a specific manner. As an example, four color patches are created, and are respectively -200V, 400V, and 600V.
V and 800 V are output from the primary transfer power supply 108.

The yellow-color patch that has passed through the primary transfer section is measured for reflectance by the patch sensor 122 having the above-described configuration, and the bias (−200) when the transfer efficiency is substantially zero is obtained.
The yellow development amount (represented by the symbol My), for example, 0.5 mg / cm ² is detected from the reflectance of the toner that has passed through V). The transfer efficiency of yellow toner at each bias (symbol ηy) is determined based on the reflectance of the transfer residual toner passing at 400 V, 600 V, and 800 V and the detected development amount.
For example, 80%, 95%, and 90% can be detected, and a bias (600 V) having the highest transfer efficiency is selected at the time of image formation. When the transfer efficiency is substantially zero, the polarity of the bias (represented by the symbol Vc) is the same as that of the toner, and the polarity of the bias (represented by the symbol Vt) with the highest transfer efficiency is the opposite polarity to the toner. Vc is
Avoid creating toner of opposite polarity by charge injection | Vc
It is preferable that | <| Vt |. My × ηy (0.5
× 0.95), the amount of yellow toner adhering to the intermediate transfer member 106 (denoted by Dy) 0.475 mg /
cm ² can be calculated, and a predetermined range, for example, 0.
Judge whether it is in the range of 45 to 0.50 mg / cm ² . In this example, since the image is within the determined range, the operation for generating a patch of the next color is performed.
The amount of development My is adjusted by increasing or decreasing the bias of the power supply 123 for development, the patch is regenerated, and the process is repeated until Dy falls within or close to the predetermined range. The same effect can be obtained by increasing or decreasing the developing amount My by controlling one or both of the exposure power and the printing duty by the exposure energy adjusting means 124 and changing the contrast potential with the developing bias.

Similarly, patches are prepared for each of the magenta, cyan, and black toners, and the developing bias, the transfer bias, and the exposure energy are adjusted so that the amounts of adhesion Dm, Dc, and Dk on the intermediate transfer member 106 fall within a predetermined range. Control.

By forming a toner patch before printing and forming an image under the determined process conditions, the toner concentration on the intermediate transfer member 106 becomes stable regardless of the environment and durability, and the transfer It was confirmed that the concentration on the material was also stable.

FIG. 3 is a schematic sectional view of another embodiment of the image forming apparatus of the present invention. The difference from the above-described embodiment is that the transfer material 113 is wound around the dielectric drum 501 and the colors are superimposed on the transfer material.

First, the operation of the apparatus will be described. Transfer material 11
Reference numeral 3 denotes a power supply 503 for attracting a transfer material to a dielectric drum 501, which is a transfer material carrier, after being conveyed from a paper cassette 112 to a pair of registration rollers 114 by a paper supply unit 111.
Outputs a voltage obtained by superimposing an AC voltage on the corona charger 502 and is attracted by the electrostatic force. The charging roller 102 uniformly charges the photosensitive member 101 to a certain potential (for example, -700 V). 600 dpi (dot perinc) formed by the exposure means 103 which is a laser scanning optical system
h) The laser beam having the resolution of
And the electrostatic latent image (for example, −10)
0V) is formed. Next, the yellow developing device 10 of the one-component contact developing device 105
5Y is brought into contact, the other developing units are separated from each other, and the negatively-chargeable yellow toner is reversely developed by the action of the electric field of the developing power source 123, and is visualized on the photoreceptor 101. The visualized yellow toner is applied to a conductive blade 504 on a transfer material 113 adsorbed on a dielectric drum 501 such as polyvinylidene fluoride or polycarbonate, by applying a bias having a polarity opposite to that of the toner to a conductive blade 504 from a transfer power supply 505. It is transferred by the action of an electric field. The transfer residual toner on the photoreceptor 101 is collected by a photoreceptor cleaner 109 which cleans the photoreceptor by bringing the blade into contact therewith, and then the photoreceptor potential is reset by a discharging lamp 110. The same operation is performed for the magenta developing unit 105M, the cyan developing unit 105C, and the black developing unit 105K by synchronizing the position of the dielectric drum 501 with the light emission timing of the exposure unit 103, and thereby the transfer material adsorbed on the dielectric drum 501 is obtained. The full-color image is formed by superimposing the toner of each color on the surface 113. Transfer material 11 on which full-color image is formed
Reference numeral 3 denotes a dielectric drum 50 by the action of an AC superimposed electric field applied to the corona charger 506 from the power supply for discharging 507.
After the charge is removed and peeled off from the sheet No. 1, the sheet is conveyed by the transfer material conveying belt 508 and discharged by the fixing unit 120 after fixing to the outside of the apparatus.

In the electrophotographic process section, a patch sensor 122 is further provided as a toner density detecting means.
It is provided at a position downstream of the photoconductor 04 and facing the surface of the photoconductor 101. As a means for changing the image density based on the detection result, the developing amount is adjusted by controlling the voltage of the developing power source 123, and the potential on the photosensitive member 101 is controlled by the exposure energy changing means 124. Various means are provided for adjusting the development amount and adjusting the transfer efficiency by controlling the voltage of the transfer power supply 505.

The sequence from the creation of a patch for stabilizing the image density based on the density (reflectance) detected by the patch sensor 122 to the printing operation will be described below.

First, a plurality of solid pattern yellow color patches of about 1 cm square are formed on the photoreceptor 101, and the transfer efficiency is set to a bias at which the transfer efficiency becomes approximately 0 to 80 to 100%, which is the transfer efficiency during normal printing. It passes through a transfer section that has been set as a target. As an example, four color patches are created, and are respectively -500V, 600V, 800V,
A voltage of 1000 V is output from the transfer power supply 505.

The yellow-color patch that has passed through the primary transfer section is measured for reflectance by the patch sensor 122 having the above-described configuration, and the bias (-500) when the transfer efficiency is substantially zero is obtained.
The yellow development amount (represented by the symbol My), for example, 0.5 mg / cm ² is detected from the reflectance of the toner that has passed through V). Also, based on the reflectance of the transfer residual toner that has passed through the transfer portion at 600 V, 800 V, and 1000 V and the detected development amount, the transfer efficiency of the yellow toner at each bias (represented by the symbol ηy), for example, 80%, 95%,
90% can be detected, and a bias (800 V) having the highest transfer efficiency is selected at the time of image formation. When the transfer efficiency is substantially zero, the polarity of the bias (represented by the symbol Vc) is the same as that of the toner, and the polarity of the bias (represented by the symbol Vt) with the highest transfer efficiency is the opposite polarity to the toner. Vc
Should not create toner of opposite polarity by charge injection |
It is preferable that Vc | <| Vt |. My × ηy (0.
5 × 0.95), the amount of yellow toner adhering to the dielectric drum 501 (denoted by Dy) 0.475 m
g / cm ² can be calculated, and it is determined whether it is within a predetermined range, for example, 0.45 to 0.50 mg / cm ² .
In this example, the operation enters the patch generation operation of the next color because it is within the predetermined range. However, when the Dy is not within the predetermined range, the developing amount My is adjusted by increasing or decreasing the bias of the developing power supply 123. Regenerate the patch and repeat until Dy is within or close to the defined range. Development amount M
The same effect can be obtained by increasing or decreasing y by controlling one or both of the exposure power and the printing duty by the exposure energy adjusting means 124 and changing the contrast potential with the developing bias.

Similarly, patches are prepared for the magenta, cyan, and black toners, and the developing bias, the transfer bias, and the exposure energy are adjusted so that the adhesion amounts Dm, Dc, and Dk on the dielectric drum 501 fall within a predetermined range. Control.

As described above, by forming a toner patch before printing and forming an image under the determined process conditions, the toner density on the dielectric drum 501 becomes stable regardless of the environment and durability. It was confirmed that the above concentration was also stable.

Next, a phenomenon that the toner once transferred to the intermediate transfer member or the transfer material on the dielectric drum is gradually returned to the photosensitive member while being in contact with the photosensitive member a plurality of times (hereinafter referred to as a reverse transfer phenomenon) is remarkable. A control method in a simple process will be described. This reverse transfer phenomenon is remarkable when the charge amount of the toner is low, the roughness of the intermediate transfer body / transfer material is rough, and their resistance values are low.

Therefore, in the process described above with reference to FIG. 3, the amount of reverse transfer, which is grasped in advance as shown in Table 1, is calculated by the following equation to obtain the final output toner on the transfer material. Adhesion amount (yellow toner adhesion amount,
The symbol Py) can be predicted.

Py = My × (ηy−15) × 1/100 = 0.5 × (95−15) × 1/100 = 0.40 mg / cm ²

[0042]

[Table 1]

Next, it is determined whether Py is within a predetermined range, for example, 0.35 to 0.40 mg / cm ² .
In this example, since it is within the defined range, the patch generation operation of the next color is started. However, if Py is not within the defined range, the development amount My is adjusted by increasing or decreasing the bias of the developing power supply 123. Then, the patch is regenerated, and the process is repeated until Py enters or falls close to the predetermined range. Development amount M
The same effect can be obtained by increasing or decreasing y by controlling one or both of the exposure power and the printing duty by the exposure energy adjusting means 124 and changing the contrast potential with the developing bias.

Similarly, patches are prepared for the magenta, cyan, and black toners to determine Pm, Dc, and Dk from the adhesion amounts Dm, Dc, and Dk on the dielectric drum 501 and the data shown in Table 1.
The developing bias, the transfer bias, and the exposure energy are controlled so that Pc and Pk fall within a predetermined range.

The data in Table 1 can be more accurately predicted by detecting and rewriting the temperature and humidity environment, the type of paper, and the amount of toner charge to thereby estimate the amount of toner on the transfer material.

As described above, it was confirmed that the toner density on the transfer material 113 was stable irrespective of the environment and durability by forming a toner patch before printing and forming an image under the determined process conditions.

Although the present invention has been described using the two systems (intermediate transfer system and transfer drum system), the present invention is not limited to these embodiments. As long as the detection is performed, the present invention can be applied to, for example, a tandem type or a color image forming apparatus of a color superimposition type on a photosensitive member.

[0048]

According to the first or fifth aspect of the present invention, the density of the toner patch on the photoreceptor can be detected regardless of the color of the toner. In addition, by detecting the density on the photoreceptor after transfer, a density close to the density on the transfer material, which is the final output, can be detected, and the toner patch density can be detected with high accuracy. , Stable color density can be secured.

According to the second or seventh aspect of the present invention, the toner density on the transfer material can be kept constant by increasing or decreasing the amount of development by means for changing the bias applied to the developing means.

According to the third or eighth aspect of the present invention, the toner density on the transfer material can be kept constant by increasing or decreasing the amount of development by means for changing the exposure energy.

According to the fourth or ninth aspect of the present invention, the toner density on the transfer material can be kept constant by increasing or decreasing the transfer efficiency by means for changing the bias applied to the transfer means.

According to the sixth aspect of the present invention, the bias when the transfer efficiency is substantially zero and the bias when the transfer efficiency is maximum are optimized, so that the toner density on the transfer material can be kept constant.

The effect is as follows.

[Brief description of the drawings]

FIG. 1 is a main cross-sectional view of an electrophotographic process unit of a color image forming apparatus using an intermediate transfer member according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a patch sensor.

FIG. 3 is a main cross-sectional view of an electrophotographic process unit of a color image forming apparatus using a transfer drum according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Photoreceptor 103 Exposure means 104 Folding mirror 105Y Yellow developing device 105M Magenta developing device 105C Cyan developing device 105K Black developing device 106 Intermediate transfer member 107 Primary transfer roller 108 Primary transfer power supply 122 Sensor means 123 Development power supply 124 Exposure energy Changing means 151 Light emitting element 152 Light receiving element 153 Condensing lens 154 Imaging lens 155 Holder 156 Irradiation surface

Claims (9)

[Claims] An exposure means for writing a latent image on a photoreceptor;
Developing means for visualizing the latent image with black and color toners; transfer means for electrostatically transferring the toner image visualized by the developing means onto an image carrier; and a transfer means formed prior to image formation. Density detection means for detecting the density of a predetermined toner patch on the photoreceptor after passing through the transfer means; and based on the result of the density detection means, the toner density on the photoreceptor after the transfer means. A color image forming apparatus comprising a density changing unit for changing the density. 2. A color image forming apparatus according to claim 1, wherein said density changing means is means for changing a bias applied to said developing means. 3. The color image forming apparatus according to claim 1, wherein said density changing means is means for changing exposure energy of said exposure means. 4. A color image forming apparatus according to claim 1, wherein said density changing means is means for changing a bias applied to said transfer means. 5. Exposure means for writing a latent image on a photoreceptor,
Developing means for visualizing the latent image with black and color toners; transfer means for electrostatically transferring the toner image visualized by the developing means onto an image carrier; and a transfer means formed prior to image formation. Density detection means for detecting the density of a predetermined toner patch on the photoreceptor after passing through the transfer means; and based on the result of the density detection means, the toner density on the photoreceptor after the transfer means. And a bias applied to the transfer unit when the toner patch passes through the transfer unit is a bias having the same polarity (Vc) and a reverse bias (Vt) as the toner. Color image forming apparatus. 6. A color image forming apparatus according to claim 5, wherein a bias when said toner patch passes through said transfer means is | Vc | <| Vt |. 7. A color image forming apparatus according to claim 5, wherein said density changing means is means for changing a bias applied to said developing means. 8. A color image forming apparatus according to claim 5, wherein said density changing means is means for changing exposure energy of said exposure means. 9. A color image forming apparatus according to claim 5, wherein said density changing means is means for changing a bias applied to said transfer means.