JPH0418310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus, and more specifically, the present invention relates to an image forming apparatus that transfers an image on an image carrier carrying a developed image to an intermediate transfer member, and further reproduces the image on the intermediate transfer member onto another transfer material. The present invention relates to an image forming apparatus that performs transfer.

Conventionally, in image forming apparatuses such as transfer-type color electrophotographic apparatuses, which sequentially form color images using different toners on an image bearing member such as a photoreceptor drum, and multiple-transfer each color image onto a transfer material, various types of image forming apparatuses have been used. A method has been proposed.

These methods can be classified into two types: One is to wrap the transfer material around a transfer material support roller or transfer material support belt made of rubber, metal, plastic, film, etc., and apply a bias voltage to the back surface of the roller or belt. The toner image on the image carrier is sequentially transferred onto a transfer material multiple times to obtain a multicolor image.

The other method is to use an endlessly moving roller or belt as the intermediate transfer body, and transfer the toner image on the image carrier onto this intermediate transfer body several times in sequence, and then transfer the toner image onto this intermediate transfer body several times. The multicolor images are finally transferred all at once onto a transfer material.

The former method requires a means to wrap the transfer material around a transfer material support means and a means to prevent the transfer material from shifting during multiple transfer steps, such as a gripper that grips the tip of the transfer material, This requires extremely complicated means such as a suction device that suction-holds the transfer material on the transfer material support means.

On the other hand, the latter method does not require the above-mentioned transfer material holding device and can prevent positional deviations during multiple transfers with high precision.

However, in any of the above transfer devices, it is difficult to transfer the developed images on the image carrier onto the transfer material at a constant transfer rate. In particular, in multiple transfer of color images, if the transfer rate of each color toner is different, the color balance of the copied image changes and a good color image cannot be obtained.

Factors that change this transfer rate include differences in toner particle size distribution and tribocharge amount, or changes in electrostatic attraction force due to repeated transfer steps of the intermediate transfer member. In particular, in a method in which an intermediate transfer body is constructed by wrapping an insulating film around a cylinder with an opening, and a toner image is transferred by applying a corona discharge from inside the transfer body, the potential on the back surface of the film, which is the image carrier, fluctuates. Easy to do. Other factors include changes in the surface resistance of the intermediate transfer member, and charge accumulation with the same polarity as the toner polarity that occurs on the surface of the same intermediate transfer member.

In order to solve the above problem, as in US Pat. A known method is to detect a change in the transmittance of toner remaining on an electrode after being transferred to a transfer drum, and to control the bias voltage of the transfer drum in accordance with the detected signal.

However, this method requires a mechanism for providing electrodes on the photosensitive drum itself and applying a bias voltage, making the device configuration complicated. In addition, since residual toner corresponding to 5% to 30% of the toner amount during development is detected, there may be cases where the amount of toner to be detected is small and the S/N ratio of the detection signal is insufficient. It tends to become uneven on the electrode, which causes problems in detection accuracy.

Furthermore, it is known to detect the density on the paper after fixing and control the charge amount of the transfer charger so that the appropriate image density is obtained, as disclosed in Japanese Patent Application Laid-Open No. 57-85062. The density is not accurate because the toner is melted and smooth.

Furthermore, in a method in which a toner image on an image carrier is developed in multiple colors onto an intermediate image carrier, and then the multicolor toner image is transferred all at once to a transfer material, the transfer efficiency changes depending on the thickness of each color toner. , a problem arises in that good color balance cannot be achieved.

In view of the above-mentioned problems, an object of the present invention is to use a simple device configuration to detect the amount of toner actually transferred onto an intermediate transfer material with high precision, and to control the amount of toner transferred so as to be constant. The present invention provides a novel image forming apparatus that can obtain good images.

The present invention will be described in detail below using specific examples with reference to the drawings. FIG. 1 is an explanatory diagram of an example in which the transfer device of the present invention is applied to a color copying machine.

In FIG. 1, reference numeral 1 denotes an electrophotographic photosensitive drum having an insulating layer, a photoconductive layer, and a conductive substrate on its surface, which is rotatably supported by a shaft 2 and rotates in the direction of an arrow 3. An original placed on the original platen glass 4 in synchronization with the rotation of the drum 1 is illuminated by an illumination lamp 6 integrated with a first scanning mirror 5, and the reflected light is scanned by a second scanning mirror 7. . The first scanning mirror 5 and the second scanning mirror 7 move at a speed ratio of 1:1/2. The reflected light image of the original document passes through a lens 8 and a third mirror 9, is separated into colors by a color separation filter 10, and is imaged on the surface of the photosensitive drum 1 by an exposure section 11.

On the other hand, the photosensitive drum 1 is charged in advance by a lamp 13 and an AC charger 14, and then charged by a primary charger 15, after which the original image is subjected to slit exposure in the exposure section 11. At the same time as this exposure, static electricity is removed or reversely charged by a secondary charger 16 that generates an alternating current or a corona of opposite polarity to the primary corona, and then the entire surface is further exposed using a full surface exposure lamp 17. As a result, an electrostatic latent image corresponding to the original image is formed on the drum 1.

The electrostatic latent image formed on the photosensitive drum 1 as described above is then visualized by a developing device 18 using toner having a polarity opposite to that of the primary charge. This developer 1
8 is yellow 18 ₁ , magenta 18 ₂ , cyan 18
The developing device is composed of three developing devices ( _{No. 3)} , and each developing device designated in accordance with the color separation filter used for exposure works individually to obtain a toner image of the required color.

Next, the developed image formed on the photosensitive drum 1 is
At the position of the pre-transfer charger 19, charging with a polarity opposite to that of AC or primary charging is performed simultaneously with the uniform exposure of the lamp 20. A predetermined bias voltage is applied to the grid wire provided in the opening of the pre-transfer charger 19 for each color, and the surface of the photosensitive drum 1 is approximately
It is charged from 0V to a predetermined voltage.

The developed images on the photosensitive drum 1 are transferred to an image carrier supported on the surface of the transfer drum 22 by a first transfer corona discharger 22 ₁ in the transfer drum 22 which is rotatably supported by a shaft 21 which will be described in detail later. sheet 2
2 ₂ and are sequentially transferred to form a multicolor image.

After the transfer, the remaining toner on the surface of the photosensitive drum 1 is cleaned by a cleaning device 12 composed of an elastic blade, and the photosensitive drum 1 proceeds to the next color-based toner image forming cycle.

On the other hand, the first, second, and third color toner images transferred by the first transfer charger 22 ₁ are transferred to the AC charger 2 together with the image bearing sheet 22 ₂ .
Static electricity is removed each time by 2 ₃ and 22 ₄ . The chargers 22 ₃ and 22 ₄ face each other, and the phases of the AC voltages applied to the respective discharge wires differ by 180°, thereby enhancing the static elimination effect.

In the above process, if the AC chargers 22 ₃ and 22 ₄ do not remove static electricity or if the static electricity removal is weak, charges with the opposite polarity to the transfer charge are accumulated on the toner image supporting surface of the image bearing sheet 22 ₂ , and the transfer charge is As the number of times increases, the toner transfer rate decreases.

FIG. 2 shows a copy image area d (encircled by a broken line) transferred to the image bearing sheet 22 ₂ and a transmission density detection image area used to control the amount of toner transferred from the photosensitive drum 1 to the image bearing sheet 22 ₂ . a, b, c
FIG. The horizontal direction of the sheet 22 ₂ corresponds to the rotation axis direction, and the vertical direction corresponds to the circumferential direction.

Detection image areas a, b, and c are configured to correspond to yellow, magenta, and cyan monochrome developments, respectively. After the surface of the photosensitive drum 1 is charged to a uniform potential, the latent images on the photosensitive drum 1 corresponding to these detected image areas a, b, and c are placed at the positions of the secondary charger 16 in FIG. Blank exposure lamps 16a provided corresponding to image areas a, b, and c are controlled to blink. That is, when forming a detection image area in the shape of FIG. 2, a light shielding plate is provided between the plurality of lamps 16a arranged in the direction of the axis of the photosensitive drum, and the number of lamps in the direction of the drum axis is adjusted according to the developing device to be used. Control blinking.

The latent images on the photosensitive drum corresponding to the image areas a, b, and c are sequentially developed with yellow, magenta, and cyan color toners, and then sequentially transferred to form toner images for each color. Here, the detected image areas a, b, c
may be outside the copy image area d.

Reference numerals 33 ₁ to 33 ₃ in FIG. 1 are light source lamps that illuminate the detected image areas a, b, and c in FIG. has been done. Further, 34 ₁ to 34 ₃ facing this lamp 33 are light receiving members such as CdS or SBC that detect the transmitted light that has passed through the detection image areas _a , b, and _c . Correspondingly, three are also arranged in the axial direction of the transfer drum 22. When the light receivers 34 ₁ to 34 ₃ corresponding to the lamps 33 ₁ to 33 ₃ are used in a reflective manner, there is a gap between the light source and the light receiver to reflect the toner color to be transferred to the detection image areas a, b, and c. Providing complementary color filters makes it easier to obtain a good S/N ratio during detection. However, when the transmission method is used and the toner used is powder, as in the embodiment shown in Fig. 1, the transmitted light is easily scattered, so it is difficult to obtain a sufficient S/N ratio even without using a complementary color filter. can. The light receiving members 34 ₁ to 3
4 ₃ are image areas a, b, c that should be detected every time each color toner is transferred in order to detect the amount of toner after transfer.
When any one of the toners passes through the toner, a light source and a light receiver corresponding to a predetermined detection image area are activated to detect the amount of light transmitted through the toner.

The transfer amount detection signal of each color toner detected by the light source and receiver is sequentially sent to the detection circuit 35 shown in FIG.
₁ to ₃ and control circuits 36 ₁ to _{36 3} , the high voltage power supply 37 of the first transfer charger 22 ₁ and the grid bias power supply 38 of the pre-transfer charger 19 are controlled. Then, the amount of toner transferred to the document image following the toner transfer in the detected image area is controlled to an appropriate value.

The above light source 33 ₁ , light receiving member 34 ₁ , detection circuit 3
5 ₁ and a control circuit 36 ₁ are used to control the transfer amount of one color toner.

In implementing the present invention, the power source 37,
Effects can also be obtained by controlling at least one power source without controlling all 38 at the same time.

The control circuits 36 ₁ to ₃ in the embodiment shown in FIG. 1 incorporate a standard voltage generation circuit and a comparison circuit, and compare the output signals of the detection circuits 35 ₁ to ₃ with the output signals of the standard voltage generation circuit. Then, according to the compared level difference, the voltage of the high-voltage power supply 37 of the first transfer charger 22 ₁ is controlled at a predetermined timing by the operation of the arithmetic control circuit and memory circuit built in the control circuits 36 _{1 to} 36 3 to obtain an appropriate voltage. Set the toner transfer amount.

Note that the amount of toner transferred increases within a certain range as the voltage applied to the first transfer charger 22 ₁ or the voltage applied to the grid of the pre-transfer charger 19 is increased. In the first illustrated device, when the toner has negative polarity, the voltage applied to the transfer charger ₂₂₁ is in the range of +5.0KV to +8.0KV, and the voltage applied to the pre-transfer charger 19 (the voltage applied to the discharge wire is The voltage applied to the grid (-6.0KV) is controlled in the range of 0V to -500V.

The above-mentioned transfer amount detection of each color toner is performed by blank exposure control prior to the actual exposure of the original image when copying is performed again after a pause for a certain period of time.
Sequence control in which latent images corresponding to detected image areas a, b, and c are formed on the photosensitive drum, developed and transferred, and transferred images of three color toners are formed in the detected image areas a, b, and c of the transfer drum. is accomplished. or
The copying interval may be controlled at an arbitrary copy interval by the operator selecting the transfer amount detection switch.

As an example of forming the above-mentioned detection image area, see Fig. 3a.
As shown in FIG. 3b, it can be formed outside the copy image area d, and can be set in the rotational axis direction of the image bearing sheet as shown in FIG. 3a, or in the circumferential direction of the sheet as shown in FIG. 3b. You may do so.

On the other hand, the transfer paper 25 in the cassette 24 is fed into the machine by the paper feed roller 26, and then transferred to the register roller 27.
The multicolor image formed on the image bearing sheet 22 ₂ is transferred all at once onto the transfer paper 25 by the corona discharge action of the second transfer charger 28 at the transfer position. At this time, if corona discharge is performed from the inside of the transfer drum 22 using the charger ₂₂₅ of the same polarity as the toner image (that is, the polarity opposite to the polarity of the second transfer charger 28) or an AC charger, it is possible to generate a thick layer of two or three colors. The toner layer can also be transferred to the transfer paper very efficiently.

The reason for this is that the charges on the back surface of the sheet 22 ₂ of the transfer drum 22 are eliminated by the corona discharge of the charger _{22 5} and the binding force of the toner on the surface of the transfer drum is favorably reduced. This is to assist the efficiency of retransfer by the second transfer charger 28 by charging the back surface with a charge of the same polarity as the toner image and repelling the toner on the surface of the sheet ₂₂₂ . In addition, the charger 22
Reference numeral ₅ serves as a counter electrode for drawing out the corona from the transfer charger 28, which increases the amount of discharge directed toward the toner image from the charger 28, contributing to the effect of increasing the retransfer efficiency.

Therefore, the toner in the lowest layer of the transfer drum 22 can be sufficiently transferred, and an image with good color balance can be obtained.

Furthermore, the improved transfer rate facilitates cleaning of the surface of the image bearing sheet 22 ₂ in a later step. Immediately after the transfer paper 25 is transferred and charged by the transfer charger 28, the transfer paper 25 is charged by the AC charger 29.
5 Separation and charge removal is performed on the back side, and the transfer paper is separated from the transfer drum 22. And the conveyor belt 30
The sheet is then delivered to a heat roller fixing device 31 coated with silicone oil, where it is pressurized and heated, and then discharged onto a tray 32.

On the other hand, a cleaning device 23 using a fur brush that can freely approach and separate comes into contact with the surface of the image bearing sheet 22 ₂ of the transfer drum, and the residual toner on the sheet 22 ₂ is cleaned. A cleaning brush 22 ₆ that contacts the back surface of the sheet 22 ₂ is provided opposite the cleaning device 23 . This brush ₂₂₆ not only performs mechanical back-up when the cleaning device 23 operates, but also cleans the back surface of the image bearing sheet ₂₂₂ .

As described above, the color electrophotographic device shown in FIG. Transfer to.

In the illustrated embodiment, the transfer drum 22 of the transfer device has an image-bearing sheet 22 ₂ , such as an insulating resin film, as shown in a perspective view in FIG.
, a support member 22 ₁ that supports this film at its edge, and an end edge of this film 22 ₂ and support member 2
2 ₁ ( _the dotted portion in FIGS. 4 and 5). FIG. 5 shows an axial cross-sectional view of the transfer drum 22. As shown in FIG. The support member 22 ₁ has two cylindrical frame portions on both sides, and a connecting portion 22 that connects and unifies the two frame portions.
It has a. Note that if the image-bearing sheet 22 ₂ is sufficiently thick and maintains a mechanically cylindrical shape, the above-mentioned connecting portion becomes unnecessary.

Plastic films such as polyester, polypropylene, and triacetate are used as the insulating film for the above-mentioned image-bearing sheet.
The thickness is 25μ to 300μ, preferably around 100μ.

In addition, a surface resistance of 1 x 10 ⁸ Ω is required to prevent uneven transfer, toner scattering, and charge-up phenomena on the image bearing surface due to peeling discharge that tend to occur immediately after separation from the photosensitive drum during transfer.
resin with a relatively high resistance of 1×10 ¹² Ω, or
A better transferred image can be obtained by coating the image bearing surface of the high resistance film 22 ₂ with a photoconductive resin such as PVK or ZnO. The elastic member 22 ₈ interposed between the film 22 ₂ and the support member 22 ₇ is made of, for example, a low hardness rubber with a JIS hardness of 40 or less (urethane rubber, ethylene/propylene rubber, chloroprene rubber, NBR, natural rubber, silicone rubber, etc.). (low hardness) or rubber and plastic foams (foamed butyl rubber, foamed polyurethane, foamed polyethylene, foamed polystyrene, foamed vinyl chloride, etc.). The thickness of the elastic member 22 ₈ is 0.5
A range of about 5 mm to 5 mm is suitable.

FIG. 6 shows a sectional view of a color copying machine which is a modification of the apparatus shown in FIG. In the illustrated apparatus, as shown in FIG. 7, a detection image area e provided on the image bearing sheet 22 ₂ is developed with yellow, magenta, and cyan color toners superimposed. Then, the amount of toner in this image area e is detected by a light source 43 serving as a detection means and a light receiving member 44, and the amount of toner transferred onto the transfer material 25 is controlled.

Formation of the toner image in the detection image area e is substantially the same as in the case of FIG. 2, using a part of the blank exposure lamp 16a provided at the position of the secondary charger 16. By lighting the lamp 16a at a predetermined timing every time each color is developed, the photosensitive drum 1
A latent image is formed thereon, and each color toner that has developed this latent image forms a three-color toner image in the detection image area e.

In the apparatus shown in FIG. 6, the light receiving member 44 detects the amount of transmitted light when passing through the detection image area e, and detects the amount of toner after the three colors of toner have been transferred. The detection signal is sequentially transmitted to the detection circuit 45 and the control circuit 4 in the figure.
6, the second transfer charger 28 and the charger 22 ₅
high-voltage power supplies 47 and 48, and a grid bias power supply 49 for the charger ₂₂₁₀ that operates before transfer. Note that in carrying out the present invention, effects can be obtained even if at least one of the power supplies is controlled without controlling all of the power supplies 47, 48, and 49 described above.

Of the above electric circuits, the control circuit 46 has a built-in standard voltage generation circuit and a comparison circuit, and the detection circuit 4
The output signal of No. 5 is compared with the output signal of the standard voltage generation circuit. Then, according to the compared level difference, the high-voltage current of the high-voltage power supply 47 of the second transfer charger 28 is controlled at a predetermined timing by the operation of the arithmetic control circuit and the memory circuit built in the control circuit 46 to ensure proper toner transfer. The amount is adjusted so that the amount is transferred to the transfer material.

The amount or range of toner retransfer increases as the voltage applied to the second transfer charger 28, the charger ₂₂₅ , or the voltage applied to the grid of the charger ₂₂₁₀ increases. In the second illustrated device, when the toner has negative polarity, the voltage applied to the second transfer charger 28 is in the range of +5.0KV to +8.0KV, and the voltage applied to the charger ₂₂₅ is in the range of -5.0KV to -.
The voltage applied to the grid of the charger 22 ₁₀ (the voltage applied to the discharge wire is -6.0 KV) is controlled in the range of 0V to -500V.

The above-mentioned toner transfer amount detection is performed by blank exposure control prior to exposure of the original image when a copy operation is performed after a pause for a certain period of time, and a latent image corresponding to the detected image area e is formed on the photosensitive drum, which is then developed and transferred. Sequence control is performed to form a transferred image of three colors of toner in the detected image area e of the transfer drum. Alternatively, the operator can control the copying interval at any desired copying interval by selecting the retransfer amount detection switch.

Further, the retransfer amount detection control described above may be performed in combination with the control of the first transfer charger 22 ₁ shown in the first figure. In this case, in addition to the detected image area shown in FIG. 2, an image area corresponding to the detected image area e shown in FIG. 7 may be provided.

FIG. 8 is a sectional view of a digital color image forming apparatus in which the present invention is applied, in which an insulating drum 40 having an insulating layer and a conductive substrate on its surface is used in place of the photosensitive drum 1 of FIG. On this insulating drum 40, an electrostatic image corresponding to the above color separation is formed by a multi-stylus head 41. The residual toner on this insulating drum is removed by cleaning device 1.
2, residual charges are removed by an AC static eliminator 42, and the remaining charges are removed in preparation for the next step.

As an example of the use of the apparatus shown in FIG. 8, it is used for computer recording, facsimile recording, etc., and the stylus head 41 is driven by a control circuit (not shown) to form a latent image on the insulating drum 40. In addition, in the same figure, the members with the same numbers as in Figure 1 are as follows:
It is assumed that the device has the same functions as the device shown in FIG.

According to the present invention, the transfer amount of each color toner formed on an image bearing member such as a photosensitive drum or an insulating drum is determined by detecting the amount of developer actually transferred to an intermediate transfer member such as an image bearing sheet. Since the corrected toner image is finally transferred to a transfer material, an image with good color balance can be obtained even if the transfer efficiency fluctuates due to toner deterioration or environmental changes.

Of course, it is also applicable to an image forming apparatus using monochromatic toner, and in this case, images with stable density can be obtained at all times.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a copying apparatus to which a transfer device according to the present invention is applied, FIGS. 2, 3a and 3b are explanatory diagrams showing a detected image area, and FIG. 4 is a perspective view of a transfer drum. , FIG. 5 is a partial sectional view of the transfer drum, FIG. 6 is a sectional view showing another embodiment of the present invention, FIG. 7 is an explanatory diagram showing the detected image area of the device shown in FIG. 6, and FIG. FIG. 3 is a sectional view showing another embodiment of the present invention. In the figure, 1 and 40 are a photosensitive drum and an insulating drum, respectively, which are image carriers, 18 is a developing device, 22 ₁ is a first transfer corona discharger, 22 ₂ is an intermediate carrier, which is an image carrier sheet, and 33 ₁ to 33 ₃ is the light source, 34 ₁
~34 ₃ indicates a light receiving member.

Claims (1)

[Scope of Claims] 1. An image carrier, a means for forming a developed image on the image carrier, a first transfer means for transferring the developed image to the intermediate image carrier, and an image carrier for forming the developed image on the intermediate image carrier. a second transfer means for transferring a developer onto a transfer material, a detection means for detecting the amount of developer on the intermediate image carrier; An image forming apparatus comprising: means for changing transfer efficiency during transfer by the first transfer means. 2. The first transfer means is a transfer charging means,
The image forming apparatus according to claim 1, wherein the means for changing the transfer efficiency is the transfer charging means. 3. The method according to claim 1 or 2, wherein the means for changing the transfer efficiency is a discharge means for applying a discharge to the image carrier after the developed image is formed and before the image is transferred by the first transfer means. Image forming device.