JP2013044956A - Two-component developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device capable of dealing with both of a fine gradation image and a higher density image with excellent performance by providing the control reference values of two thick and thin toner concentrations.SOLUTION: A developing device 25 includes a first developing tank 6 supplying a two-component developer 4 to a developing roller 3 supplying toner to a photoreceptor and a second developing tank 8 supplying the developer 4 to the first developing tank 6. When the toner is normal low concentration toner, the developer 4 is circulated between the first developing tank 6 and the second developing tank 8 through a first circulation port 23 and a second circulation port 24, as shown by arrows e, f, g, and h. When the toner is high concentration toner, the bulk of the developer 4 is increased by the increased toner amount, so that a partition plate 27 of a bulk absorption part 26 is opened and a detour for the developer 4 equivalent to the increased bulk is formed to pass the developer 4 through a third circulation port 28, to prevent a fin 22 of a stirring and conveying member 7 from being buried in the developer 4.

Description

  The present invention relates to a two-component developing device that can provide two types of density control reference values for toner density and can cope with both fine gradation images and higher density images with good performance.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses include a type using a one-component developer (toner) and a type using a two-component developer. Since the method using a single component developer is relatively easy to handle and control, a single component toner has been dominant as a developer.

  However, as demand for speeding up printing (hereinafter also referred to as printing) increases in recent years, non-magnetic toner (hereinafter simply referred to as toner) and magnetic carrier (hereinafter simply referred to as toner) are required for speeding up printing processing. Since a method using a two-component developer comprising a carrier) can cope better, various developing devices using a two-component developer have been proposed.

  Developers using a two-component developer are each provided with a stirring and conveying member that conveys the two-component developer while stirring and mixing in a developing tank divided into two chambers of the developing device. These two agitating and conveying members circulate in the developing tank divided into two chambers while agitating and conveying the two-component developer, and supply the two-component developer to the developing roller of the developing device.

  By the way, a development method using a two-component developer (hereinafter simply referred to as a developer) exhibits good development characteristics. However, in recent years, a finer gradation degree is required for an image formed by an electrophotographic image forming apparatus. High image quality has been demanded.

  In order to obtain an image with a high gradation, that is, to achieve delicate development, it can be dealt with by reducing the toner particles. For this reason, the reduction in the toner particle diameter is rapidly progressing. In addition, when the particle size of the toner is small, there is an advantage that less toner is consumed.

  Such a delicate development method using a toner having a small particle diameter provides very good results for the development of a document containing a high gradation image such as a photographic image. On the other hand, development of an image having no gradation, which is often solid-printed for each color, such as a poster, requires high-density development having a strong concealing power that is opposite to delicate.

  However, since the toner having a small particle size has a small concealment amount on the image, there is a drawback that it is difficult to develop a high density compared to the case of using a toner having a large particle size. As described above, it is difficult to achieve two types of images, a delicate low density image and a high density image without gradation, under the same development conditions.

  As a method for solving this problem, it is necessary to change the toner density depending on the image. That is, when creating a delicate photographic image, development is performed with a low toner concentration of the developer, and when the image is dark such as a poster, development is performed with a high toner concentration.

  As far as the adjustment of the toner density is concerned, various methods have been proposed. However, the purpose of adjusting the toner density is different for each purpose (see, for example, Patent Documents 1, 2, and 3).

  For example, Patent Document 1 shows a toner density adjustment method for adjusting the toner density in order to suppress carrier development. Japanese Patent Application Laid-Open No. 2004-228561 shows that the development bias voltage is changed in order to change the target image density according to the user's request instantaneously and easily.

  Further, in Patent Document 3, in order to output a specified image density from the start of printing after the change without changing complicated process elements in an image forming apparatus using a two-component development method, a change in toner density is specified. First, the image formation is disabled.

  Thereafter, the set toner density is changed to the designated density, the toner density detection output is compared with the set toner density changed to the designated density, and the toner density change process is performed so that the toner density detection output becomes the designated density. It shows that image formation is started after completion of the density changing process.

  By the way, in the two-component development method, generally, when a delicate image is required, the toner density of the developer is kept low, and a sufficient triboelectric charge is imparted to the toner to faithfully reproduce the electrostatic latent image on the photoreceptor. According to the development, a clear print image is formed on the photoconductor.

  In addition, when a high density image is required, the toner density of the developer is increased as much as possible to reduce the amount of frictional charge with the carrier, so that a large amount of toner can be involved in the development, and the high density on the photoreceptor. A printed image having a density is formed.

  FIG. 3A is a cross-sectional view of a developing device in a conventional general two-component developing system. FIG. 2B is a perspective view showing the inside of the developing tank by removing the upper casing (hereinafter referred to as a lid) of the developing tank of the developing device, and FIG. It is sectional drawing of the 2nd developing tank seen in.

  As shown in FIGS. 3A, 3B, and 3C, the developing device 1 includes a first agitating and circulating member 5 that supplies toner of the developer 4 to the photosensitive drum 2 via the developing roller 3. A developing tank 6 and a second developing tank 8 which is adjacent to the first developing tank 6 and has a stirring circulation member 7 therein.

  The first developing tank 6 and the second developing tank 8 are surrounded by a housing 9 at the lower and side portions, and provided with a stepped lid 11 and a flat lid 12 at the upper portion. Inside the housing 9 and the lids 11 and 12, the first developing tank 6 and the second developing tank 8 are partitioned by a partition wall 13.

  On the side of the developing roller 3 of the stepped lid 11, a developer regulating plate 14 that regulates the developer 4 so as not to leak to the outside is connected to the lid 11. A toner hopper 15 that replenishes toner to the second developing tank 8 is disposed above the second developing tank 8.

  The toner hopper 15 and the second developing tank 8 are connected by a toner supply path 16. The toner is replenished from the toner hopper 15 to the second developing tank 8 through the toner replenishment path 16 as indicated by an arrow a. A toner concentration sensor 17 that detects the concentration of toner in the second developing tank 8 is disposed on the side of the second developing tank 8.

  The agitation circulation member 5 includes a screw shaft 18 and fins 19 that are fixed to the screw shaft 18 and rotate. Similarly, the stirring circulation member 7 includes a screw shaft 21 and fins 22 that are fixed to the screw shaft 21 and rotate.

  The screw shafts 18 and 21 are axially supported at both ends 18a and 21a by bearings (not shown) provided on the side surfaces in the axial direction of the first developing tank 6 and the second developing tank 8, respectively. Further, both ends 3a of the shaft of the developing roller 3 are supported by a frame of an image forming apparatus main body (not shown).

  One end of each of the shaft ends 18a and 21a of the screw shafts 18 and 21 and one end of each of the shaft ends 3a of the developing roller 3 are, for example, a motor, a toothed pulley, or a toothed body of an image forming apparatus body (not shown). It is driven to rotate by engaging with a drive system including a belt, an idle gear, a drive gear, and the like.

  By this rotational drive, the developing roller 3 is rotationally driven in the counterclockwise direction indicated by arrow b in FIG. 3A, and the stirring circulation member 5 of the first developing tank 6 rotates in the counterclockwise direction indicated by arrow c. The agitating and circulating member 7 of the second developing tank 8 is driven to rotate in the counterclockwise direction indicated by the arrow d.

  By being driven to rotate in this way, the agitation circulation members 5 and 7 cooperate to cause the developer 4 to be indicated by arrows e, f, g, and h as shown in FIGS. 3 (b) and 3 (c). Then, the developer 4 is circulated through the first circulation port 23 and the second circulation port 24 formed in the partition wall 13 with stirring.

  An image forming apparatus (not shown) in which the developing device 1 is provided includes an operation panel including an input button (not shown) that allows the user to specify a desired image density from, for example, two types of image densities. A control device is provided for performing development processing in accordance with image density designation from the user.

  Although not specifically shown in the figure, the control device is centered on the CPU, and is connected to the CPU via a system bus (ROM) (read only memory), RAM (Random Access Memory), EEPROM (electrically erasable programmable ROM), toner supply path It has an open / close drive unit, a sensor drive monitoring unit, and the like.

  In such a general two-component developing type developing device, the toner concentration of the developer in the developing tank is set to a delicate image toner concentration. Here, it is assumed that high density image printing is designated by the user like poster printing.

  In this case, the CPU replenishes the second developing tank 8 with a larger amount of toner than usual by controlling the opening / closing device of the toner replenishment path 16. In the case of a normal toner concentration, the toner volume is 30% with respect to the carrier volume.

  If the amount of toner to be replenished for high-density image printing is doubled, for example, the volume of the developer 4 increases by “((0.3 × 2) /1.3) × 100 = 46”%. To do. Even in the case of 1.5 times the normal value, “((0.3 × 1.5) /1.3) × 100 = 34”% increases.

  A broken line 4 ′ shown in FIG. 3 (c) indicates the position of the bulk of the developer 4 that is increased when the developer 4 is replenished with toner having a high density as described above relative to the normal toner density. As shown in FIG. 3 (c), the fins 22, which are approximately 2/3 of the length of the stirring and circulating member 7, are buried in the developer 4 having an increased volume.

  The fins 22 buried in the developer 4 simply transport the developer 4 between the fins 22 and 22 and lose the stirring function. In particular, the developer 4 protruding above the fins 22 remains in the same position and is not stirred or transported.

  That is, since the stirring function of the second developing tank 8 is lowered, the developer 4 having a toner density for forming a high density image designated by the user is transferred from the first developing tank 6 to the developing roller 3. It has a problem that it cannot be supplied. Although not shown, if the amount of the developer 4 is too small and only exists below the screw shaft 21, for example, the conveyance by the fins 22 will not be successful. Therefore, it is important that the developer 4 in the second developing tank 8 is adjusted to an appropriate amount (bulk) as shown in FIG.

JP 2007-316136 A JP 07-325438 A Japanese Patent Application Laid-Open No. 06-035323

  However, as described above, the technique of Patent Document 1 is a technique for adjusting the toner density in order to suppress carrier development, and is not a technique for adjusting the toner density in order to achieve the image density desired by the user. . Therefore, the solution to the above problem cannot be dealt with.

  The technique of Patent Document 2 is a technique for realizing an image density desired by the user. However, instead of increasing the toner density of the two-component developer in order to correspond to the image density desired by the user, the developing bias voltage is used. It is a technology that changes the above, and is not a technology involved in the above problem.

  Further, the technique of Patent Document 3 is a technique for outputting at a specified image density from the start of printing after the change without changing complicated process elements, but is a technique for setting a timing for output at a specified image density. There is no specific proposal for the toner density changing (adjusting) method itself.

  The present invention solves the above-mentioned conventional problems, and is a two-component that can cope with both fine gradation images and higher density images with good performance by providing control reference values for two types of toner density. An object is to provide a developing device.

  In order to solve the above-mentioned problems, a two-component developing device of the present invention is a two-component developing device using a two-component developer containing toner and a carrier, and stores the two-component developer and supplies the toner to a photoreceptor. The first developer tank, and the two-component developer fed from a first circulation port which is adjacent to the first developer tank and has a stirring circulation member therein and communicates with the first developer tank. A second developer tank that is fed from a second circulation port communicating with the first developer tank while being agitated by a stirring circulation member, and circulates the two-component developer between the first developer tank; A toner hopper that replenishes the toner to the second developing tank, and the target toner concentration of the toner in the second developing tank is changed from the first toner density to a second toner density that is higher than the first toner density. The toner is transferred from the toner hopper to the second developing tank. And a two-component developer bulk adjusting means for adjusting the volume of the two-component developer that is circulated while being stirred by the stirring and circulating member in the second developing tank when being replenished .

  In the present invention, the volume of the two-component developer in the stirring circulation path is maintained at a predetermined value regardless of whether the toner density is low or high, so that the replenishment toner can be always mixed well by the stirring member. Therefore, it is possible to control the toner density stably, and by this, it is possible to cope with both the fine gradation image and the higher density image with good performance by providing two kinds of density density control reference values. Play.

(a) is a perspective view showing the inside of the developing layer in the developing device according to Example 1 of the present invention, with the lid having a step, a flat lid, a developer regulating plate, a toner concentration sensor, etc. removed from the housing. b) is a sectional view of the second developing tank when (a) is viewed in the direction of arrow B. FIG. (a) is a cross-sectional view of the developing device according to the second embodiment, (b) is a view showing the inside of the developing tank by removing the upper housing (lid) of the first developing tank of the developing device, and the second developing tank The perspective view shown with a cover attached, (c) is a cross-sectional view of the second developing tank when (a) is viewed in the direction of arrow C. (a) is a sectional view of a developing device in a conventional general two-component developing system, (b) is a perspective view showing the inside of the developing tank by removing the upper casing (lid) of the developing tank of the developing device, (c ) Is a cross-sectional view of the second developing tank when (a) is viewed in the direction of arrow A. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the toner density setting means is, for example, an input button of the operation panel, a CPU of the control device, etc., the toner density detecting means is, for example, the toner density sensor 17, and the toner density control means is For example, it is a CPU of a control device, and the developer bulk adjusting means is, for example, the bulk absorbing section 26, electromagnets 31, 32, and the like.

  In the following drawings of the first and second embodiments of the present invention, the same components as those shown in FIG. 3 are assigned the same reference numerals as those in FIG. 3 in order to clearly show the difference from the conventional configuration. Only the components directly related to the invention are given numbers different from those in FIG. In addition to the configuration of the conventional control device, the control device that controls the developing devices according to the first and second embodiments includes a partition plate opening / closing drive unit, a magnet on / off drive unit, and the like.

  FIG. 1A is a perspective view showing the inside of the developing layer of the developing device according to the first embodiment, with a stepped lid, a flat lid, a developer regulating plate, a toner concentration sensor, and the like removed from the housing. FIG. 5B is a cross-sectional view of the second developing tank when FIG. 5A is viewed in the direction of arrow B.

  As shown in FIGS. 1A and 1B, the developing device 25 of this example supplies the developer 4 to the developing roller 3 that supplies toner to a photosensitive drum (not shown), as shown in FIG. The first developing tank 6 and the second developing tank 8 for supplying the stirred developer 4 to the first developing tank 6 are provided.

  In a normal printing mode, that is, a printing mode for printing a fine image, as shown in FIG. 1B, the fins 22 of the stirring circulation member 7 of the second developing tank 8 are connected to the first circulation port 23 and the first circulation port 23, respectively. Between the two circulation ports 24, a portion of about ½ or more is exposed above the developer 4.

  As a result, the developer 4 fed into the second developing tank 8 from the first circulation port 23 is sufficiently agitated before being sent from the second circulation port 24 to the first developing tank 6. Then, the toner adheres to the carrier at a predetermined concentration, and the developer 4 having an appropriate toner concentration is supplied to the developing roller 3.

  Here, it is assumed that high density image printing such as poster printing is designated by the user. As shown in FIG. 1A, the developing device 25 of the present example is provided with a bulk absorbing portion 26 provided outside the first developing tank 6 with respect to the first circulation port 23.

  The bulk absorbing portion 26 is partitioned from the first developing tank 6 by an openable / closable partition plate 27 just outside the first circulation port 23. The bulk absorbing portion 26 has a third circulation port 28 that communicates with the second developing tank 8.

  The bulk absorbing section 26 replenishes toner increased for high-density image printing from the toner replenishment path 16 to the second developer tank 8, and the developer 4 in the agitating and conveying path of the second developer tank 8. When the bulk increases, the partition plate 27 is opened to form a detour for the developer 4 fed from the first developer tank 6 to the second developer tank 8.

  Due to the bypass formed by the bulk absorbing portion 26, the developer 4 in the first developing tank 6 passes through the bypass from the third circulation port 28 of the bulk absorbing portion 26 as indicated by an arrow i. To the developing tank 8. The developer 4 having an increased bulk is absorbed in the detour by an amount corresponding to the increased bulk by passing through the detour.

  Thus, the developer 4 conveyed while being stirred between the first circulation port 23 and the second circulation port 24 of the second developing tank 8 is shown by a broken line 4 'in FIG. Thus, the fins 22 are exposed above the developer 4 as shown in FIG. 1B without increasing in the agitation conveyance path, so that the developer 4 is conveyed while being properly agitated by the agitation circulation member 7. Is done.

  FIG. 2A is a cross-sectional view of the developing device 30 according to the second embodiment, and FIG. 2B shows the inside of the developing tank by removing the upper housing (lid) of the first developing tank of the developing device. FIG. 3 is a perspective view showing the second developing tank with a lid attached. FIG. 2C is a cross-sectional view of the second developing tank as viewed in the direction of arrow C in FIG.

  2A shows an example in which the magnet 31 (32), which is a feature of this example, is arranged inside the lid 12 of the second developing tank 8, and in FIGS. 2B and 2C, An example in which the magnets 31 and 32 are arranged outside the lid 12 of the second developing tank 8 is shown.

  These magnets 31 and 32 are electromagnets, respectively, and generate a predetermined magnetic force as required by current control from a control unit (not shown). Here, it is assumed that high density image printing such as poster printing is designated by the user.

  The control unit supplies the toner increased for high-density image printing to the second developing tank 8 from the toner replenishing path 16, and the volume of the developer 4 in the stirring and conveying path of the second developing tank 8 is increased. When it increases, the magnets 31 and 32 are energized while referring to the output of the toner density sensor 17.

  As a result, as shown in FIG. 2 (a) or 2 (c), the developer 4 below the magnet 31 is adsorbed as developer 4-1 as shown by the arrow j, and below the magnet 32. The developer 4 is adsorbed as developer 4-2 as indicated by an arrow k. The developer 4 having increased bulk is made into magnets 31 and 32 by the increased volume.

  As described above, in this example, the developer 4 conveyed while being stirred between the first circulation port 23 and the second circulation port 24 of the second developing tank 8 is equivalent to the increased amount of toner. The excess developer 4 having increased bulk is attracted by the magnet 31 or 32 and temporarily retracted.

  As a result, the developer 4 in the agitating / conveying path of the second developing tank 8 is replenished with the increased amount of toner without increasing in the agitating / conveying path as indicated by the broken line 4 'in FIG. In the same state as before, the bulk of the developer 4 is kept substantially constant.

  Accordingly, in this case as well, the fins 22 are exposed above the developer 4 as shown in FIG. 2C, so that the developer 4 is conveyed while being properly stirred by the stirring circulation member 7.

Although several embodiments of the present invention have been described, the present invention is included in the invention described in the claims and the equivalents thereof. Hereinafter, the invention described in the scope of claims of the present application will be appended.
[Appendix 1]

In a two-component developing device using a two-component developer containing toner and carrier,
A first developing tank that contains the two-component developer and supplies the toner to a photoreceptor;
The two-component developer fed from a first circulation port provided with an agitation circulation member adjacent to the inside of the first development tank and communicating with the first development tank is agitated by the agitation circulation member while the agitation circulation member is stirred. A second developer tank that is sent out from a second circulation port that communicates with the first developer tank and circulates the two-component developer between the first developer tank;
A toner hopper for replenishing the toner to the second developing tank;
The target toner concentration of the toner in the second developing tank is changed from the first toner density to a second toner density that is higher than the first toner density, and the toner is supplied from the toner hopper to the second developing tank. A developer bulk adjusting means for adjusting the volume of the two-component developer that is circulated while being stirred by the stirring and circulating member in the second developing tank,
A two-component developing device comprising:
[Appendix 2]

The developer bulk adjusting means is provided on the outer side of the first developer tank by an openable partition plate rather than the first circulation port, and is connected to the second developer tank. The two-component developing device according to appendix 1, wherein the two-component developing device is a bulk absorbing portion having a mouth.
[Appendix 3]

  The developer bulk adjusting means includes the first circulation port and the second circulation above the moving path of the two-component developer that is circulated while being stirred by the stirring circulation member of the second developer tank. The two-component developing device according to supplementary note 1, wherein the two-component developing device is a magnet provided between the mouth and the magnet.

  The present invention can be used in a two-component developing device that can provide both high-concentration images and higher-density images with good performance by providing two types of density control reference values.

DESCRIPTION OF SYMBOLS 1 Developing apparatus 2 Photosensitive drum 3 Developing roller 4 Two-component developer (developer)
DESCRIPTION OF SYMBOLS 5 Stirring circulation member 6 1st developing tank 7 Stirring circulation member 8 2nd developing tank 9 Housing | casing 11 Lid with level | step difference 12 Flat lid | cover 13 Partition 14 Developer control board 15 Toner hopper 16 Toner replenishment path 17 Toner density sensor 18, 21 Screw shaft 18a, 21a Shaft ends 19, 22 Fin 23 First circulation port 24 Second circulation port 25 Developing device 26 Bulk absorber 27 Partition plate 28 Third circulation port 30 Developing device 31, 32 Magnet

Claims (3)

In a two-component developing device using a two-component developer containing toner and carrier,
A first developing tank that contains the two-component developer and supplies the toner to a photoreceptor;
The two-component developer fed from a first circulation port which has a stirring circulation member adjacent to the first developing tank and communicates with the first developing tank is stirred by the stirring circulation member. A second developer tank that is sent out from a second circulation port communicating with the first developer tank and circulates the two-component developer between the first developer tank;
A toner hopper for replenishing the toner to the second developing tank;
The target toner concentration of the toner in the second developing tank is changed from the first toner density to a second toner density that is higher than the first toner density, and the toner is supplied from the toner hopper to the second developing tank. A developer bulk adjusting means for adjusting the volume of the two-component developer circulated while being stirred by the stirring and circulating member in the second developing tank when
A two-component developing device comprising:   The developer bulk adjusting means is provided on the outer side of the first developer tank by an openable partition plate rather than the first circulation port, and is connected to the second developer tank. 2. The two-component developing device according to claim 1, wherein the two-component developing device has a mouth.   The developer bulk adjusting means includes the first circulation port and the second circulation above a moving path of the two-component developer that is circulated while being stirred by the stirring circulation member of the second developing tank. The two-component developing device according to claim 1, wherein the two-component developing device is a magnet provided between the mouth.