JPH03260672A - Color image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Work 1 The present invention relates to a color image forming apparatus.

[&TO] At present, electrophotographic recording methods are often applied to image forming devices such as copying machines and computer output terminals. An image corresponding to a light signal emitted from a light emitting body such as a beam or an LED is written as an electrostatic latent image on an electrostatic latent image carrier, and after this electrostatic latent image is turned into a visible image by a developing device, this visible image is Generally, a recorded image is obtained by transferring the image to a transfer material and then fixing the transferred image to the transfer material, or the recorded image is a single color such as black.

However, when copying a manuscript containing color-coded calculated values or graphs, or a computer-generated color graphic screen, if the image is color-coded using two or more colors, the information contained in the image will be reproduced without deterioration, and the information contained in the image will be reproduced without deterioration. Therefore, image forming apparatuses that form color images using an electrophotographic recording method have been proposed.

This color image forming apparatus has a configuration as shown in FIG. 9, for example, and includes a photosensitive tram l as an electrostatic layer image carrier formed by coating a photoconductive layer on a conductive substrate. We are prepared. The photoconductor tram 1 is rotated in the direction of the arrow shown in the figure, uniformly charged by a charger 2, and exposed 3 based on a first image signal by a light emitting element such as a laser.
to form a first electrostatic latent image corresponding to the first image signal. Subsequently, this first electrostatic image is transferred to a first developing device 4a containing, for example, yellow toner corresponding to the first image signal.
to form a first visible image. Next, the photosensitive drum 1 on which the first visible image has been formed is uniformly charged again by the charger 2 without being cleaned by the cleaning device 8, and is converted into a second image signal by the same light source as described above. A second electrostatic latent image corresponding to the second image signal is formed by performing exposure 3 based on the second image signal. 2 developing device 4b to form a second visible image. Next, the photosensitive drum 1 on which the first and second visible images have been formed is removed by a cleaning device 8 as described above.
The charger 2 uniformly charges the photoreceptor tram 2 again without cleaning it, and the exposure 3 based on the third image signal is performed using the same light source as described above, so that the surface layer of the photoreceptor tram l is charged with the third image signal. A corresponding third electrostatic layer image is formed, and this third electrostatic latent image is developed by a third developer 4c containing, for example, cyan toner corresponding to the third image signal,
forming a third visible image; Finally, the visualized images on the photosensitive drum 1 are transferred all at once onto a transfer material 6 by a transfer charger 5, and fixed by a fixing device 7 to obtain a permanent image. Further, residual toner remaining after transfer on the photosensitive drum is removed by a cleaning device 8 having a function that operates only after image transfer.

The cleaning device 8 includes a cleaning blade 81 and a cleaning roller 83 supported by a support 85, and the support 85 is movable toward and away from the photoreceptor drum 1 by a cam 82, thus cleaning The blade 81 and roller 83 are connected to the cam 82
It is configured such that it can be moved to a position where it contacts the photoreceptor drum 1 and to a position where it is spaced apart from the photoreceptor drum 1. As described above, when the first and second visible images are formed, the cleaning blade 81 and the roller 83 are located away from the photoreceptor drum 1, and when the third visible image is formed and transferred to the transfer material 6 all at once, The cleaning plate 81 and the roller 83 come into contact with the photoreceptor drum 1 under the action of the cam 82 to clean the transfer residual toner.

The cleaned toner is transferred to the toner feed screen 84.
The toner is then sent to a waste toner container (not shown).

FIG. 10 shows another conventional color image forming apparatus. This color image forming apparatus also uses a static image forming apparatus, which is formed by uniformly coating a photoconductive layer on a conductive substrate, similar to the conventional apparatus described above.
A photoreceptor tram is provided as an image carrier. The photoreceptor drum 1 is rotated in the direction of the arrow shown in the figure, uniformly charged by a charger 2a, and exposed 3a based on the first image signal using the light emitting element as described above.
After forming a first electrostatic layer image corresponding to the image signal, the second electrostatic latent image is developed by a first developing device 4a containing, for example, yellow toner corresponding to the first image signal. 1 form a visible image. Subsequently, the photosensitive drum 1 on which the first visible image has been formed is uniformly charged by the charger 2b, and then exposure 3b is performed based on the second image signal, and the second visible image is formed on the photosensitive drum l as described above. A second electrostatic iMI image corresponding to the image signal of 2. Form a visible image. Furthermore, after the photosensitive drum 1 on which the first and second visible images have been formed is uniformly charged by the charger 2c, exposure 3C is performed based on the third image signal, and as described above, the photosensitive drum 1 is A third developing unit 4 forms a third electrostatic latent image corresponding to the third image signal, and transfers this third electrostatic latent image to a third developing unit 4 containing, for example, cyan toner corresponding to the third image signal.
c to form a third visible image. The visible images thus formed on the photosensitive drum 1 are transferred all at once onto a transfer material 6 by a transfer charger 5, and fixed by a fixing device 7 to obtain a permanent image. Further, the residual toner remaining after transfer on the photosensitive drum is removed by the cleaning device 8.

The device shown in FIG. 1O has the following features compared to the device shown in FIG.
The number of chargers and light-emitting elements used for exposure increases, and the device itself becomes larger and more complex, although the device shown in Fig. 9 forms images in multiple colors by multiple rotations of the photoreceptor tram l. On the other hand, the apparatus shown in FIG. 10 can form images of a plurality of colors at the same time in one rotation of the photosensitive drum 1, so it has the advantage of being able to obtain one color image at high speed.

The above explanation uses yellow, magenta, and cyan as examples, which are typical colors used in electrophotographic color image forming apparatuses. , blue (Bf2), or other colors may be used.

However, in the above conventional color image forming apparatus, there is a problem in that the previous color toner, which has already been developed on the photoreceptor drum, gets mixed into the developing device when the second color and subsequent colors are developed. This is particularly noticeable in devices that use a contact development method in which the photosensitive drum and the developing sleeve are in direct contact, because the developing sleeves for the second and subsequent colors mechanically strip off the previous color toner image. Therefore, conventionally, a non-contact developing method has been widely used in which the photosensitive drum and the developing sleeve do not come into direct contact with each other, and therefore, there is no mechanical stripping of toner.

However, in this non-contact development method, the developer sleeve does not mechanically strip the previous color toner from the previous color toner image, but instead, the developer sleeve does not mechanically strip the previous color toner from the previous color toner image; This causes a small amount of the previous color toner to get mixed into the developing sleeve.Although this mixed amount is small compared to the contact development method, it accumulates in the developing device as the number of times of development increases, and eventually Color mixing occurs to the extent that it greatly disturbs the image.In order to improve this problem, a solid latent image is formed outside the image forming area on the photoreceptor drum, and after the development of a predetermined color is completed, the solid latent image of each color is JP-A-61-77872 discloses a method in which the mixed color toner on the developing sleeve is removed by developing the image, that is, it is consumed by a solid latent image on the photoreceptor drum, and the toner is disposed of together with the remaining toner by a cleaning device. However, this method requires an image to be developed using newly mixed toner, and it also has the disadvantage of extremely high running costs since a large amount of toner is consumed each time the desired image is formed. Ta.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a color image forming apparatus that can reduce color mixing due to the mixing of toners of other colors to a level that does not cause any practical problems, and can also minimize wasteful consumption of associated toners. .

The above-mentioned object for performing the task is achieved by the color image forming apparatus according to the present invention. To summarize, the present invention provides a color image forming apparatus that forms a color image by arranging a plurality of developing devices containing developers of different colors around an image carrier, in which at least one developing device carries developer. Detecting the amount of developer from a developing device of another color mixed into the developer on the developer carrier, and removing the developer on the developer carrier when the detected amount of mixed developer reaches a predetermined value. This is a color image forming device with special features.

According to a preferred embodiment of the present invention, the amount of toner of other colors mixed into the developing device is detected by a sensor that detects the toner concentration on the developing sleeve, and when the amount of mixed toner reaches a limit value that causes color mixing, the amount of toner mixed into the developing device is detected. is developed by a removing means]
Removed from the Norf. Therefore, toner with substantially no color mixture is always adhered to the developing sleeve, and it is possible to obtain a clear color image without deterioration in image quality due to color mixture of mixed toner. In addition, if toner is not substantially mixed into the developing sleeve, running costs can be reduced because there is no unnecessary consumption of toner.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic sectional view showing a first embodiment in which the present invention is applied to an electrophotographic color image forming apparatus. Similar to the color image forming apparatus shown in FIG. have A charger 2 that uniformly charges the photoreceptor drum 1 along the rotational direction of the photoreceptor drum l indicated by an arrow in the figure;
For example, an exposure means for performing exposure 3 based on image signals of each color using a light emitting element such as a laser to form an electrostatic layer image corresponding to the image signal of each color on the photoreceptor tram; A first developing device 4 includes a color toner corresponding to the first color electrostatic latent image and has a configuration described below.
a. Second and third developing units 4b and 4C, which have the same configuration as the first developing unit and contain color toners corresponding to the second and third color electrostatic latent images, respectively, are arranged; Further downstream of these, there is a transfer charger 5 for transferring each visible image on the photoreceptor drum 1 to a transfer material 6;
A cleaning device 8 is arranged to clean residual toner on the photoreceptor drum after the visible image has been transferred. Note that the visible image transferred to the transfer material 6 is fixed by a fixing device 7 as usual.

The cleaning device 8 includes a cleaning blade 81 and a cleaning roller 83 supported by a support 85, and the support 85 is movable toward and away from the photoreceptor drum l by a cam 82, thus cleaning The blade 81 and roller 83 are connected to the cam 82
It is configured such that it can be moved to a position where it contacts the photoreceptor drum 1 and to a position where it is spaced apart from the photoreceptor drum 1. That is, when forming the first and second visible images, the cam 82
is in the inoperative position, and the cleaning blade 81 and roller 83 are separated from the photoreceptor drum l. However, when the third visible image is formed and transferred all at once to the transfer material 6, the cam 8
2 rotates to the illustrated operating position, and the cleaning blade 81 and roller 83 come into contact with the photosensitive drum 1 to clean the residual toner. The cleaned toner is sent to a waste toner container (not shown) by an I/toner feed screw 84.

Each developing device 4a in the color image forming apparatus of this embodiment,
4b and 4c, as shown in FIG. 1, a developing sleeve 41 for conveying each color toner, and this developing sleeve 41
A regulating blade 42 regulates the layer thickness of the upper color toner, and prevents contamination of the color toner on the developing sleeve by other color toners upstream from the developing area that is the closest part between the photoreceptor drum l and the developing sleeve 41. A sensor 43 that detects the degree of
and an on-off controllable removal blade 44 for removing the toner thereon. Further, the color image forming apparatus of this embodiment determines the color mixture state on the developing sleeve 41 based on the output from the sensor 43, and turns on the removal blade 44 when necessary.
It is equipped with a control circuit 9 for OFF control.

Next, the operation of the color image forming apparatus having the above configuration will be explained.

When the color image forming apparatus is in operation, each developing sleeve is filled with toner images of other colors that have already been developed on the photosensitive drum, regardless of whether the developing sleeve is in contact with the photosensitive drum or not. A small amount of toner is mixed in. As mentioned above, as long as the amount of mixed toner of other colors is small, color mixing will not occur in the image during development and will not disturb the created image. However, as the number of times of development increases, mixed toner accumulates on the developing sleeve, eventually resulting in color mixing and disturbing the created image. Therefore, it is necessary to remove the toner on the developing sleeve before it disrupts the created image (actually, it may be just before).

In this embodiment, the degree of contamination is detected by the sensor 43 installed in each developing device, and the control circuit 9
determines the necessity of toner removal, activates (turns on) the regulating blade 44 to remove the toner on the developing sleeve when necessary, and controls the regulating blade 44 to be inactive (off) when not necessary. .

The sensor 43 is, for example, an LED, as shown in FIG.
A light emitting element 431 such as , a filter 432 that transmits only light of a wavelength corresponding to each color toner, and this filter 432
The color toner upstream of the development area on each development sleeve 41 receives the light from the light emitting element 431. The reflected light is separated by a color filter 432 corresponding to the color of the toner, and the intensity of the transmitted light is converted into an electrical signal by a photoelectric element 433.

For example, the first, second and third developing units 4a, 4b and 4C
When three color toners, yellow, magenta and cyan, are used in the third developer 4c containing cyan, other color toners from the previous color yellow and magenta toner images are mixed in each time an image is created, and the third developer To reduce the cyan density of toner adhering to the developing sleeve of the developing device. Therefore, the output voltage Vo from the sensor 43, which is disposed above the developing sleeve and includes a filter corresponding to cyan, also decreases as the degree of cyan decreases.

FIG. 3 shows the number of times of development and the output voltage of the sensor 43 when the number of times reached 11 in an experiment in which the same image was created multiple times. It shows which relationship. As is clear from the figure, the output voltage (■) decreases as the number of development cycles increases, that is, the amount of mixed toner increases.On the other hand, the output voltage at the limit of the concentration of mixed toner of other colors, where color mixing is seen in the image, is V8 in the figure. The voltage was as shown in .

Therefore, the output voltage from the sensor 43 is ■. The problem of color mixture can be solved by operating the removing blade 44 and bringing it into contact with the developing sleeve 41 to remove the toner on the developing sleeve only when the voltage has decreased to 2, which indicates the concentration limit of mixed toner of other colors. .

Therefore, in this embodiment, the control circuit 9 is provided with a comparison circuit 11 as shown in FIG.
The control circuit 9 having an algorithm as shown in FIG. 5 controls the removing blade 44 of each developing device to be turned on or off in accordance with the result of this comparison. That is, the comparison result from the comparison circuit 11 is ■. >V, the control circuit 9 determines that the color toner on each developing sleeve can reproduce the appropriate color corresponding to the image signal (there is no color mixture), and does not operate the removing blade 44 of the developing device. Therefore,
The normal image creation process continues. However, if the comparison result of the comparison circuit 11 is ■o≦■3, the control circuit 9
determines that the color toners on each developing sleeve are mixed and color reproduction corresponding to the image signal is not possible, and operates the removing blade 44 of the developing device to bring it into contact with the developing sleeve 41, thereby removing the mixed colors. Remove the developer. Then, after determining that there is no color mixture again, the process proceeds to the normal image forming process.

FIG. 6 shows the output voltage (■) from the sensor 43 with respect to the number of times of development when the control circuit 9 is activated. This shows the changes in From this figure, it can be clearly seen that the output voltage VD from the sensor 43 always shows a value higher than the voltage value ■8 that causes image disturbance, and that the color toner on the developing sleeve is always maintained in a state without color mixing. Ru.

(Thus, according to the apparatus of this embodiment, when the amount of previous color toner mixed into the color toner on the developing sleeve increases due to an increase in the number of times of development, etc., and reaches a limit value that causes color mixing, the developer is removed. Since the toner on the developing sleeve is removed by the plate 44, it is possible to always form a bright color image without any disturbance due to color mixing.Also, as long as toner of other colors does not accumulate to the extent that color mixing occurs, the developing Since the toner on the sleeve is not removed, there is also the advantage that the amount of wasted toner is reduced.

In the above embodiment, a filter 432 that transmits only light of a wavelength corresponding to each color toner is used in the sensor 43, but an element that emits white light is used as the light emitting element 431, and a photoelectric element 433 having panchromatic characteristics is used. if,
Don't use filters (but don't use them).

In the above embodiment, the first developing device 4a also has second and third developing devices.
The present invention, which has the above-mentioned features in the same manner as the developing device, can be applied, but there are cases where the developing property is non-contact, and the image shown in FIG. Since it is considered that there is no contamination of other color developers into the first developing device 4a in the forming apparatus or the like, the present invention may be applied only to the second and third developing devices 4b and 4C.

Further, in the above embodiment, a blade is used to remove the mixed color toner on the developing sleeve, but the blade is not limited to any blade as long as it can appropriately remove the toner on the sleeve. For example, it goes without saying that fur brushes, rubber rollers, etc. that have been conventionally used in cleaning devices may be used.

Further, in the above embodiment, a case was described in which the present invention is applied to an image forming apparatus configured to form toner images of multiple colors on a photoreceptor drum and transfer them all at once onto a transfer material.
The present invention can also be applied to a multi-transfer type color image forming apparatus in which a toner image formed on a photosensitive drum is transferred to a transfer paper for each color, and this process is repeated multiple times to obtain a color image. Of course. In this case, the color toner of the toner image on the photoreceptor drum does not mix into the developing devices of other colors, but the Rh toner from the developing device may mix into the other developing devices. Particularly, when a plurality of developing devices are moved, for example, rotated, in order to downsize the main body of the apparatus, the above-mentioned scattering of toner becomes unavoidable. The present invention can also solve the problem of such scattered toner getting mixed into other developing devices and causing color mixing. Furthermore, the present invention can also be applied to color image forming apparatuses other than electrophotographic systems such as electrostatic recording systems.

Next, a second embodiment of the present invention will be described with reference to FIG. Note that the color image forming apparatus of this embodiment is also of an electrophotographic type and has a configuration similar to that of the apparatus of the first embodiment shown in FIG. 1, so corresponding parts are given the same reference numerals. The explanation will be omitted unless necessary.

In a second embodiment of the present invention shown in FIG. 7, each developing unit 4a,
The configuration is largely different from the first embodiment in that 4b and 4c have only a sensor 43 for detecting color mixture and do not have a removal blade. Therefore, this embodiment is based on the first
This embodiment employs a method for removing mixed toner of other colors, which is different from that of the embodiment.

Next, its operation will be explained. First, as in the first embodiment, the degree of contamination of toner of other colors on each developing sleeve 41 is detected by each sensor 43, and the detected voltage (2) and the contamination density limit V are determined by the comparison circuit of the control circuit 9. 11 (4th
(see figure). The result of this comparison is ■. ＞Vg
If so, as in the first embodiment, the control circuit 9 determines that it is possible to re-view the appropriate colors corresponding to each color signal, and the normal development process is executed. However, Vo≦■.

In this case, it is determined that the control circuit 9 is unable to reproduce appropriate colors corresponding to each color signal, and the comparison result is ■. >V
, a solid latent image is formed on the photoreceptor drum 1 by exposure 3 until it becomes solid, and each color is developed, and the developed solid image is not transferred to the transfer material 6, but a toner image formed by mixed color toner is created. The cleaning device 8 performs a process of removing the particles. At this time, the cleaning device 8 is always in operation.

In the apparatus of this embodiment as well, when the amount of previous color toner mixed into the color toner on the developing sleeve increases due to an increase in the number of times of development, etc., and reaches a limit value that causes color mixing, a solid latent image is formed and developed. Since this mixed color toner is removed by a cleaning device, a clear color image without any disturbance due to color mixing can always be formed.Also, unless toner of other colors accumulates to the extent that color mixing occurs, the edge replacement image will not be removed. Since the process of removing toner during formation and development is not performed, there is an advantage that the amount of wasted toner is reduced. Furthermore, this embodiment has the advantage that the structure of the developing device is simplified and the cost of the apparatus itself can be reduced.

In the second embodiment, when executing the process of removing mixed color toner, the bias applied between the photoreceptor drum and the developing sleeve is set higher than during normal development to increase the efficiency of toner removal. Enhancing is effective and desirable.

The sensor 43 in each of the above embodiments detects the state of toner color mixing at one point on the developing sleeve 41;
The color mixing state of the toner on the developing sleeve 41 is somewhat uneven depending on the size of the sleeve.
It is desirable to be able to detect the entire longitudinal direction of the sensor. The above-mentioned configuration can be realized, for example, by connecting a large number of sensors 43 in the longitudinal direction of the developing sleeve 41, but this increases the number of light emitting elements 431 and photoelectric elements 433, resulting in a considerable increase in cost. .

An example of an inexpensive sensor capable of detecting the entire length of the developing sleeve 41 is shown in FIG. This sensor 45 includes a rotatable support shaft 451 and a sensor unit 45 that is movable in the direction of the arrow shown in the figure as the support shaft 451 rotates.
2, and is installed above and parallel to the developing sleeve 41. The sensor unit 452 includes a light emitting element 453 such as an LED, and a photoelectric element 454 such as a phototransistor that converts light reflected from the toner on the developing sleeve into an electrical signal such as a voltage. In the case of adopting the configuration of the first embodiment, the sensor unit 452 further includes a filter that transmits only light having a wavelength corresponding to each color toner.

The sensor 45 in the above-mentioned image formation has a shape (each time the elephant formation ends, the drive gear 455 rotates, the support shaft 451 rotates, and the sensor unit 452 is moved in the longitudinal direction).

During this movement, the sensor unit 452
The density of the upper color toner at various locations is sequentially detected as a voltage V0, and the control circuit 9 is made to judge the color mixing state of the toner on the developing sleeve, as in the above embodiment. And ■. ≦■
, if even one point exists, the process of removing the mixed color toner on the developing sleeve is performed in the same way as in the above embodiment.

This sensor 45 can detect the color mixture state on the developing sleeve more accurately than the sensor 43 shown in FIG. Furthermore, there is an advantage that the manufacturing cost of the device can be kept low because there is no need to use a large number of expensive light emitting elements and photoelectric elements.

In this example, the sensor unit 452 is moved in the longitudinal direction of the developing sleeve 41 using the support shaft 451, the drive gear 455, etc., or the sensor unit 452 is simply moved in the longitudinal direction of the developing sleeve 41. It goes without saying that any configuration can be used as long as it is possible, and for example, a combination of belts, chains, pulleys, gears, etc. may be used.

As described above, the color image forming apparatus according to the present invention uses a sensor to detect the mixing state of toner of other colors with respect to the toner of a color on the developer carrier of the developing device, and determines the magnitude of this sensor output. Since the system is configured to remove the mixed color toner on the developer carrier when the color reaches a predetermined value, the color mixture state can be detected very accurately, thus ensuring that the created image is not disturbed due to the mixing of other color toners. This has the effect that it can be prevented and clear color images can always be obtained. Further, since the mixed color toner on the developer carrier is removed only when necessary, the amount of wasted toner yellowing is considerably less than that of the conventional method.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing a first embodiment in which the present invention is applied to an electrophotographic color image forming apparatus of 11°. FIG. 2 is a schematic perspective view showing an example of a sensor used in the device of FIG. 1. FIG. 3 is a characteristic curve diagram showing changes in sensor output voltage when the number of times of development is increased. FIG. 4 is a circuit diagram showing an example of a comparator circuit used in the control circuit of the device shown in FIG. 1. FIG. 5 is a flowchart showing an example of an algorithm for controlling the control circuit of the device shown in FIG. FIG. 6 is a characteristic curve diagram showing changes in the sensor output voltage when the number of times of development is increased in the apparatus shown in FIG. FIG. 7 is a schematic sectional view showing a second embodiment of the present invention. FIG. 8 is an explanatory diagram showing another example of a sensor that can be used in the device of the present invention. FIG. 9 is a schematic sectional view showing an example of a conventional electrophotographic color image forming apparatus. FIG. 10 is a schematic sectional view showing another example of a conventional electrophotographic color image forming apparatus. a 4 b 4 c. 41. 2 43, 4 Photosensitive drum Charger First developer Second developer Third developer Developing sleeve regulating blade 45, sensor: Removal blade Cleaning device: Control circuit Figure 3 Development number development number v and Figure 4 45

Claims (1)

[Claims] 1) In a color image forming apparatus that forms a color image by disposing a plurality of developing devices around an image carrier, at least one
means for detecting the amount of developer mixed in from another developing device with respect to the developer on the developer carrier of one developing device; and when the detected mixed amount reaches a predetermined value, the developer on the developer carrier is detected. 1. A color image forming apparatus comprising: a means for removing an agent.