JPH05107948A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a satisfactory image by means of transfer by optimally controlling transfer conditions for a toner image. CONSTITUTION:A pattern image of 16 density levels are formed on a photosensitive drum 1. The transfer efficiency of each density level is detected by detecting the toner density of the pattern image on the photosensitive drum 1 before transfer and the density of the residual toner after the transfer by means of optical sensors 31 and 32, respectively. A difference between the detected transfer efficiency of each density level and the transfer efficiency under the optimum transfer conditions is obtained. When an amount of toner charge is judged not to be a proper value based on that, the amount of toner charge before the transfer of the toner image is controlled by a pretransfer electrifier 39; when a transfer electric field is judged not to be a proper value, the transfer electric field by a transfer electrifier 7 is controlled. Therefore, the transfer conditions can be optimally controlled and a satisfactory image can be obtained by the transfer.

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,
Particularly, it relates to an image forming apparatus using electrophotography.

[0002]

2. Description of the Related Art Conventionally, copying machines using electrophotography as an image forming apparatus have been widespread, and in recent years, full-color copying machines have also started to spread.

FIG. 5 shows a conventional color image forming apparatus. In this image forming apparatus, the illumination lamp 9 and the light receiving element 10
And the original 11 is read while traveling and R, G, B
Convert to color electric signal. The electric signals of the three colors are converted into image signals of four colors of magenta, cyan, yellow and black by an image processing device (not shown). The surface of the photoconductor on the photosensitive drum 1 is cleaned in advance by the cleaner 5, and the influence of the latent image formed in the previous time is removed by the pre-exposure lamp 12 and the pre-electrifier 13.

After the photosensitive drum 1 is uniformly charged by the primary charger 6, a light source 2 such as a laser first irradiates the photosensitive drum 1 with light corresponding to a magenta image signal, so that the photosensitive drum 1 is exposed to magenta. A latent image is formed. This latent image is developed by the magenta developing unit 3M, and a magenta toner image is formed on the photosensitive drum 1.

On the other hand, the transfer paper 14 contained in the cassette
Are sent to the transfer drum 4 by the paper feed roller 15.
The transfer paper 14 is electrostatically attracted onto the transfer drum 4 by the attraction charger 16, and is conveyed to the image transfer portion facing the photosensitive drum 1 as the transfer drum 4 rotates, where the transfer charger 7 causes the photosensitive drum 1 to move. The upper magenta toner image is continuously transferred onto the transfer paper 14.

Subsequently, cyan, yellow, and black are similarly processed, and a cyan toner image, a yellow toner image, and a black toner image are sequentially formed on the photosensitive drum 1, and the cyan toner image, the yellow toner image, and the black toner image are formed. The images are transferred one after another onto the transfer paper 14 in a superposed manner, whereby a full-color image in which toner images of four colors are superposed on the transfer paper 14 is obtained. At this time, cyan, yellow,
The black developing devices 3C, 3Y, and 3B slide laterally in each case to be located at the developing position facing the photosensitive drum 1, and perform the respective development there.

After the transfer of the four color toner images on the transfer paper 14 is completed, the transfer paper 14 is separated from the transfer drum 4 by the separating claw 17.
Then, the sheet is sent to the fixing device 8 by the conveying belt 18, the image is fixed there, and then discharged to the sheet discharge tray 19.

[0008]

In such a color image forming apparatus, the transfer process has a great influence on the image. This transfer process is greatly affected by the amount of toner charge and the transfer electric field.

FIG. 6 shows a change in the residual toner concentration on the drum surface obtained by irradiating the drum surface of the photosensitive drum 1 after the toner image transfer with light and detecting the reflected light by the toner image density. It is a graph which shows about the case where the amount of electrification charge is changed. The transferred toner image has a toner density as shown by a straight line L in the figure on the drum surface of the photosensitive drum 1 after development and before transfer, and is finally transferred and output on the transfer paper 14. It increases with this in proportion to the concentration.

The straight line La is the toner density remaining on the surface of the photosensitive drum 1 after the transfer of the toner image indicated by the straight line L, and since the transfer is almost 100% in the low density portion of the toner image, Although the residual toner density is zero, the residual toner increases as the density of the toner image increases.

On the other hand, the straight line Lb is the residual toner density on the drum surface when the toner charge amount of the toner image of the straight line L is high, and the mirroring power of the toner with respect to the drum surface is high, so that the transfer efficiency is 100%. The point (point P at which the residual toner density becomes zero) is shifted to the lower density side than that of the straight line La. On the high-density side, the toner is superposed on the photosensitive drum 1 in many layers, so that the influence of the mirror image power is relatively small.
It does not differ much from the case of a. The straight line Lc is, on the contrary, the residual toner concentration when the amount of toner charge is low.

FIG. 7 is a graph showing a change in the residual toner density on the drum surface after the toner image transfer due to the toner image density when the transfer electric field is changed. Straight line Ld is straight line L
The residual toner density when the toner image is transferred with a lower transfer electric field than that of the straight line La. When the transfer electric field is lowered, the transfer efficiency is lowered as a whole, and the residual toner increases. On the contrary, the straight line Le is the residual toner concentration when the transfer electric field is increased.

As described above, since the transfer efficiency changes in a complicated manner due to the fluctuation of the toner charge amount before the toner image transfer and the fluctuation of the transfer electric field at the time of transfer, it is sufficient to detect the transfer efficiency at a single density. It is impossible to control the transfer properly. For this reason, in the past, image quality was likely to deteriorate due to insufficient transfer control in an image obtained on a recording material by transfer.

In view of the above situation, an object of the present invention is to form a toner image on an image carrier and transfer it to a recording material by applying a transfer electric field to obtain an image on the recording material. At this time, by forming a test image of a plurality of density levels on the image carrier and detecting the transfer efficiency at the plurality of density levels, the transfer condition of the toner image is optimally controlled, and a good image can be transferred. It is to provide an image forming apparatus capable of obtaining the above.

[0015]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier, image forming means for forming a toner image on the image carrier, and a toner image formed on the image carrier on a recording material by applying a transfer electric field. In an image forming apparatus provided with a transfer means for transferring, while forming a test image of a plurality of density levels consisting of a toner image on the image carrier,
Toner image transfer efficiency detection means is provided to detect the transfer efficiency of the test image at a plurality of density levels, and further toner image transfer condition control means is provided to detect the transfer efficiency of the test image at a plurality of density levels. The image forming apparatus is characterized in that a transfer condition of a toner image formed on the image carrier is controlled based on a detection result. The transfer condition is one or both of the pre-transfer toner charge amount of the toner image formed on the image carrier and the transfer electric field applied thereto.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the essential parts of an embodiment of the image forming apparatus of the present invention. In this embodiment, a test pattern having a plurality of density levels is created as a test image on the image carrier, and the transfer efficiency of the pattern image at the plurality of density levels is detected to form the pattern on the image carrier. A major feature is that the transfer condition of the toner image is controlled. For this reason, the image forming apparatus is provided with a toner image transfer efficiency detection unit and a transfer condition control unit. The other points of this embodiment are basically the same as those of the conventional image forming apparatus described with reference to FIG. 5, and the primary charger 6, the pre-electrifier 13, the pre-exposure lamp are arranged around the photosensitive drum 1. 12, cleaner 5 and lateral slide type developing devices 3M, 3C, 3Y,
3B, and a light source 2 which is a laser in this embodiment.
An image is formed by a similar image forming process including the transfer drum 4 and the like. Since the details are as described above, the description is omitted.

In this image forming apparatus, as shown in FIG. 1, a transfer charger 7 is provided on the back side of the transfer drum 4 facing the photosensitive drum 2 as in the conventional case.
A voltage is applied to the transfer charger 7 by a high-voltage power supply 36 connected to the transfer charger 7 to generate a transfer electric field, and the transfer electric field is applied to a transfer material such as a transfer paper carried on the transfer drum 4. The toner image formed on the drum 1 is transferred onto a transfer material. The high voltage power supply 36 is a controllable constant voltage high voltage power supply.

According to this embodiment, the optical sensor 31 is provided on the outer surface of the photosensitive drum 1 between the developing device 3M and the transfer drum 4.
However, similarly, an optical sensor 32 is installed at a position between the cleaner 5 and the transfer drum 4, and these optical sensors 31,
Reference numeral 32 constitutes the transfer efficiency detecting means for the toner image. The optical sensors 31 and 32 are RAs that store the detection results.
R connected to M (random access memory) 33
The AM 33 is connected to the CPU (central processing unit) 34.

Further, an optical sensor 31 on the outer surface of the photosensitive drum 1
A pre-transfer charger 39 is installed between the transfer drum 4 and the transfer drum 4 to adjust the toner charge amount before transfer of the toner image formed on the photosensitive drum 1. The charger 39 is connected to a controllable constant-voltage high-voltage power supply 35. According to the present embodiment, the control target of the toner image transfer condition control means, that is, the transfer condition is the pre-transfer toner charge amount of the toner image and the transfer electric field applied when the toner image is transferred. Accordingly, by connecting the high-voltage power supply 35 to which the pre-transfer charger 39 is connected and the high-voltage power supply 36 to which the transfer charger 7 is connected to the CPU 34, the above-mentioned toner image transfer condition control means is configured. There is.

As described above, the pre-transfer toner charge amount of the toner image and the transfer electric field are controlled in the transfer condition control mode. First, a 16-level print signal (this is 10 _H , 20 _H , ..., F0 _H , FF _H (M
ax is FF _H ), and 1 is set on the photosensitive drum 1.
A latent image of a 6-gradation pattern image is formed and developed to form a 16-gradation pattern image of a toner image on the photosensitive drum 1. Then, the optical sensor 31 detects the toner reflection densities in the image portion of each density level of the pattern image, and the detected densities A ₁ , A ₂ , ..., A ₁₆ are stored in the RAM 33. Next, the pattern image is transferred onto the transfer drum 4, and the toner reflection densities 16B ₁ , B ₂ , ..., B ₁₆ of the residual toner in the image portion of each density level remaining on the photosensitive drum 1 at that time are optically determined. It is read by the sensor 32 and stored in the RAM 33.

[0021] Then CPU34 is transferred at each concentration level of 16 gradation pattern images efficiency _{T 1 = (A 1 -B 1} ) / A 1, T 2 = (A 2 -B 2) / A 2, ·· - to determine the _{T 16 = (a 16 -B 16} ) / a 16.

Next, the transfer efficiency T at each density level
_1, T _2, ···, transcription under optimum transfer conditions are stored in the T ₁₂ to a pre-CPU34 efficiency _{T S1, T S2, ···,} T
_S16 the difference between _{E 1 = T 1 -T S1,} E 2 = T 2 -T S2, ···, and E ₁ = T _{1 6} -T _S16 seek. The results are shown in FIGS. 2 and 3.

In FIG. 2, a curve Ga shows the case where the amount of charged electric charge of the toner before the transfer of the pattern image is higher than the optimum value, the transfer efficiency is smaller than that under the optimum condition, and the difference in the transfer efficiency is the density. It becomes smaller as the level increases. On the contrary, when the curve Gb becomes lower, the transfer efficiency becomes larger than that under the optimum condition, and the difference in the transfer efficiency also becomes smaller as the concentration level increases. In FIG. 3, a curve Gc shows a case where the transfer electric field is smaller than the optimum value, the transfer efficiency is smaller than that under the optimum condition, and the difference in the transfer efficiency becomes larger as the concentration level increases, and the curve Gd shows the transfer. It shows a case where the electric field is larger than the optimum value, the transfer efficiency is larger than that under the optimum condition, and the difference in the transfer efficiency becomes larger as the concentration level increases.

Therefore, the image forming apparatus compares the absolute value of the transfer efficiency E ₃ when the input signal level is 30 _H with the absolute value of E ₁₂ when the input signal level is C 0 _H , and if | E ₃ |> | E ₁₂ | In order to control the pre-transfer toner charge amount of the toner image formed on the photosensitive drum 1 by determining that the toner charge amount is out of the optimum value, the power source 35 of the pre-transfer charger 39 is controlled.
If | E ₃ | ≦ | E ₁₂ |, it is determined that the transfer electric field is out of the optimum value, and the power supply 36 of the transfer charger 7 is controlled to control the transfer electric field of the toner image. Decide that.

Next, the sum ΣE = E ₁ + E ₂ ... + E ₁₂ of the transfer efficiency difference E is calculated, the control amount is determined according to the amount of ΣE, and the control amount on the photosensitive drum 1 is determined. The toner charge amount control before transfer or the transfer electric field control is performed on the toner image formed on.

As described above, in this embodiment, a test pattern of a plurality of density levels formed of a toner image is used as a test image, the transfer efficiency at each density level is detected, and the toner image before transfer is detected based on the detected transfer efficiency. Since the toner charge amount and the transfer electric field are controlled, it is possible to optimally control the transfer conditions of the toner charge amount before transfer and the transfer electric field to obtain a good image by transfer.

FIG. 4 is a block diagram showing the essential parts of another embodiment of the image forming apparatus of the present invention. In the present embodiment, in the image forming apparatus of FIG. 1, instead of providing the optical sensor 32 at a position between the cleaner 5 on the outer surface of the photosensitive drum 1 and the transfer drum 4, as shown in FIG. A major feature is that the optical sensor 38 is provided at a position on the outer surface of the transfer drum 4 downstream in the direction from the transfer charger 7.

In the present embodiment, the above-mentioned optical sensor 38 forms the image on the photosensitive drum 1 and transfers it onto the transfer drum 4, or carries the transfer paper on the transfer drum 4 and transfers it onto the transfer paper. Toner reflection density (toner density after transfer) C ₁ , C ₂ , ..., C of a 16-gradation pattern image
Detect ₁₆

The photosensitive drum A ₁ toner reflection density (toner density before the transfer) detected 1 by the optical sensor 31 of the formed 16 gradation pattern images onto, A _2, ···, as A _16, transfer efficiency T _1, T _2, ···, the _{T 16, T 1 = C 1} / a 1, T 2 = C 2 / a 2, ···, obtained as _{T 12 = C 12 / a 12} .

After that, the control may be performed in the same manner as in the previous embodiment. Also in this embodiment, similarly to the previous embodiment, it is possible to optimally control the transfer condition of the toner image and obtain a good image.

Still another embodiment of the image forming apparatus of the present invention will be described. In the above embodiments, the transfer efficiency of the pattern image of 16 gradations was measured over all 16 density levels, but in this embodiment, two density levels, for example, 30 _H and C0 _H at the signal level are measured. Only the transfer efficiencies T ₃ and T _{12 at the} concentration level are measured.

Therefore, the input signal of the print pattern to the laser 2 of the signal source is only the signal levels 30 _H and C0 _H , and the difference E from the optimum value of the transfer efficiency at each calculated density level is E _3. And E ₁₂ only. In this case, the control amount is obtained from the sum E ₃ + E ₁₂ of E ₃ and E ₁₂ . By doing so, the amount of toner consumed in the transfer condition control mode can be saved.

After obtaining the control amount, the control may be performed in the same manner as in the previous embodiment. Also in this embodiment, similarly to the previous embodiment, it is possible to optimally control the transfer condition of the toner image and obtain a good image.

In each of the above embodiments, one photosensitive drum 1 is provided with four color developing devices 3M, 3C, 3Y, 3B and 1.
A full-color image forming apparatus in which two transfer drums 4 are combined has been described as an example, but the present invention is not limited to this.
Two photosensitive drums are provided, and developing devices 3M to 3
It is also applicable to a full-color image forming apparatus of the type in which one of B is combined and one common transfer belt is provided instead of the transfer drum 4. In this case, in order to be the same as in the embodiment of FIG. 4, it is necessary to provide one optical sensor for each photosensitive drum, which is similar to the optical sensor 31 for detecting the toner density of the test patch on the photosensitive drum 4. .. However, in order to detect the toner density of the test patch transferred onto the transfer belt, one optical sensor may be provided downstream of the transfer position from each photosensitive drum. If only one is provided to detect the toner density of the test patch, the number of optical sensors similar to the optical sensor 38 can be saved.

Further, the image forming apparatus is not limited to the one for color, and can be similarly applied to a monochrome image forming apparatus. Further, the image forming apparatus is not limited to the digital exposure type using the laser as the light source 2, but may be the analog exposure type. In this case, a 16-gradation standard plate may be provided in the non-image area of the document table, and this may be subjected to analog exposure and development to form a 16-gradation pattern image on the photosensitive drum 1.

[0036]

As described above, in the image forming apparatus of the present invention, a test image having a plurality of density levels composed of a toner image is formed on the image bearing member, and the toner image transfer efficiency detecting means is provided. The transfer efficiency of the test image at a plurality of density levels is detected, and a transfer condition control unit for the toner image is further provided, and based on the detection result of the transfer efficiency of the test image at a plurality of density levels, Since the transfer conditions such as the pre-transfer toner charge amount and the transfer electric field of the toner image formed on the toner image are controlled, the transfer condition of the toner image can be optimally controlled to obtain a good image by transfer.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a main part of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a graph showing a difference between a transfer efficiency at each density level of a pattern image having a plurality of density levels formed on a photosensitive drum of the image forming apparatus of FIG. 1 and a transfer efficiency under the optimum transfer condition. It is a graph shown about the case where is changed.

FIG. 3 is a graph showing the difference in transfer efficiency when the transfer electric field is changed.

FIG. 4 is a configuration diagram showing a main part of another embodiment of the image forming apparatus of the invention.

FIG. 5 is a configuration diagram showing a conventional image forming apparatus.

6 is a graph showing a change in residual toner density on the surface of the photosensitive drum after transfer of the toner image formed on the photosensitive drum of the image forming apparatus of FIG. 5 depending on the toner image density when the toner charge amount is changed.

FIG. 7 is a graph showing a change in the residual toner concentration on the surface of the photosensitive drum after the toner image is transferred, which is caused by changing the transfer electric field.

[Explanation of symbols]

 1 Photosensitive Drum 2 Light Source 4 Transfer Drum 7 Transfer Charger 31, 32, 38 Optical Sensor 33 RAM 34 CPU 35, 36 High Voltage Power Supply 39 Pre-transfer Charger

Front page continuation (72) Inventor Nobuatsu Sasuma 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yasushi Miura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (2)

[Claims] 1. An image carrier, an image forming means for forming a toner image on the image carrier, and a toner image formed on the image carrier by transferring a transfer electric field onto a recording material. In an image forming apparatus including a transfer unit, a test image having a plurality of density levels composed of a toner image is created on the image carrier, and a transfer efficiency detection unit for the toner image is provided to detect a plurality of the test images. The transfer efficiency at the density level is detected, and a transfer condition control unit for the toner image is further provided. Based on the detection result of the transfer efficiency at the plurality of density levels of the test image, the toner image formed on the image carrier is detected. An image forming apparatus in which transfer conditions are controlled. 2. The image forming apparatus according to claim 1, wherein the transfer condition is one or both of a pre-transfer toner charge amount of a toner image formed on the image carrier and a transfer electric field applied thereto.