JP2008145640A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing wasteful disposal of two-component developer by supplying a quantity of carrier according to the degree of deterioration of the component developer. <P>SOLUTION: The image forming apparatus forms a latent image on a photoreceptor drum (image carrier) 1 and develops the latent image by the use of two-component developer composed of toner and carrier. The image forming apparatus includes: a concentration decreasing means for decreasing the toner concentration of the two-component developer; and an ejecting means by which two-component developer in which the toner concentration has decreased by the concentration decreasing means is forcibly ejected onto the photoreceptor 1. In addition, the apparatus includes a detecting means for detecting the deterioration of the two-component developer in which the toner concentration has decreased. The apparatus controls the ejecting means based upon the detection result of the detecting means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that develops a latent image formed on an image carrier using a two-component developer composed of a toner and a carrier.

  Image forming apparatuses such as copiers, printers, and facsimiles that employ an electrophotographic system include an image carrier such as a photosensitive drum, a charging device that uniformly charges the image carrier, and image information on the charged image carrier. An exposure apparatus for forming a latent image by irradiating exposure light according to the above, a developing apparatus for developing a latent image formed on the image carrier using a developer to visualize it as a developer image, and an image carrier Transfer device for transferring the developer image on the recording material such as paper, cleaning device for removing the developer remaining on the image carrier after transferring the developer image, and transferring the image onto the recording material The image forming apparatus includes a fixing device that heats and pressurizes the developed developer image to fix it on the recording material.

  By the way, in a developing device using a two-component developer composed of toner and carrier as a developing method, the toner and carrier are agitated and frictionally charged, and then the developer is carried on a developer carrier such as a developing roller. The latent image formed on the image carrier is subjected to development. For this reason, the toner is consumed and decreased with the image forming operation, whereas the carrier is not consumed and remains as it is. Accordingly, the carrier is more frequently agitated than the toner, and as the durability progresses, the resin film (coat) on the surface of the carrier is peeled off and the internal metal core is exposed.

  As described above, when the metal core inside the carrier is exposed, the resistance value of the carrier decreases, the current flowing from the developer carrier to the image carrier increases, and the image quality deteriorates such as carrier pulling and image fogging. The problem occurs.

Therefore, a trickle development system has been proposed in which a carrier is mixed in a replenishment toner container, developer is gradually replenished from the replenishment toner container into the developing container, and development is performed while discharging the deteriorated developer (for example, patents). References 1 and 2). According to this trickle development method, a new two-component developer containing a carrier is supplied and a deteriorated developer is recovered, so that the deterioration of the carrier is suppressed and the development characteristics of the two-component developer in the developing container are constant. Therefore, it is possible to prevent the image quality from being deteriorated due to fluctuations in the development characteristics of the developer.
JP 2002-131987 Japanese Patent Laid-Open No. 11-202630

  However, in the trickle developing method, since the carrier is mixed in the replenishing toner container, the carrier can be put into the developing container only at the time of toner replenishment, and the toner can be used regardless of the degree of deterioration of the carrier. Since only the amount of carrier corresponding to the replenishment amount can be input, the amount of carrier corresponding to the deterioration degree of the two-component developer cannot be input, and the two-component developer is wasted. was there.

  The present invention has been made in view of the above problems, and its object is to prevent wasteful disposal of the two-component developer by supplying an amount of carrier corresponding to the degree of deterioration of the two-component developer. An object of the present invention is to provide an image forming apparatus capable of performing the above.

  In order to achieve the above object, an invention according to claim 1 is an image forming apparatus for forming a latent image on an image carrier and developing the latent image using a two-component developer comprising a toner and a carrier. A density reducing means for reducing the toner density of the two-component developer, and a discharging means for forcibly discharging the two-component developer whose toner density has been reduced by the density reducing means onto the image carrier are provided. And

  According to a second aspect of the present invention, in the first aspect of the present invention, there is provided a detecting means for detecting the deterioration of the two-component developer whose toner density is lowered, and the discharging means is controlled based on a detection result of the detecting means. It is characterized by doing.

According to a third aspect of the present invention, in the second aspect of the invention, the detection means is a means for detecting at least one of L ^* , a ^* , and b ^* of the two-component developer having a lowered toner density. It is characterized by that.

According to the present invention, the deterioration of the two-component developer whose toner density has been reduced by the density reduction means is detected by at least one of L ^* , a ^* , b ^* , and for example, the deterioration degree of the two-component developer has a set value. In the case of exceeding the two-component developer, the deteriorated two-component developer is forcibly discharged onto the image carrier by the discharge means, so that an amount of carrier corresponding to the degree of deterioration of the two-component developer can be replenished. It is possible to prevent wasteful disposal of the developer.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of a main part of an image forming apparatus according to the present invention. The illustrated image forming apparatus forms an image on a recording material such as a sheet supplied from a sheet feeding unit (not shown) by an electrophotographic method. The image forming unit includes a rotatable photosensitive drum 1 as an image carrier, a primary charger 2 disposed around the photosensitive drum 1, a developing device 3, a transfer roller 4 as a transfer unit, and a cleaning device 5. It has.

  Thus, when the photosensitive drum 1 is rotationally driven in the arrow direction (clockwise) in FIG. 1 at a predetermined process speed, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential by the primary charger 2. The Next, when exposure light L such as laser light is irradiated on the surface of the photosensitive drum 1 from an exposure device (not shown), an electrostatic latent image is formed on the surface of the photosensitive drum 1. The electrostatic latent image is developed by the developing device 3 using a two-component developer and is visualized as a toner image. The two-component developer is composed of a toner and a carrier, and the carrier is coated with a resin film (coat) such as an acrylic polymer or a fluororesin polymer on the surface of a metal core made of a magnetic material such as iron, nickel, cobalt, or ferrite. ).

  On the other hand, a recording material is supplied from a paper feeding unit (not shown) to the transfer nip N between the photosensitive drum 1 and the transfer roller 4 at a predetermined timing synchronized with the toner image on the photosensitive drum 1. As a result, the toner image on the photosensitive drum 1 is transferred onto the recording material. Note that the developer remaining on the surface of the photosensitive drum 1 after the transfer of the toner image to the recording material is removed by the cleaning device 5, and the photosensitive drum 1 is prepared for the next image formation.

  The recording material onto which the toner image has been transferred is conveyed to a fixing device (not shown), heated and pressed by the fixing device to receive the toner image, and then discharged (not shown) provided outside the apparatus. The paper is discharged to the paper tray, and a series of image forming operations is completed.

  Next, the configuration and operation of the developing device 3 will be described with reference to FIG.

  FIG. 2 is a cross-sectional view of the developing device 3. The developing device 3 shown in FIG. 2 has a developing container 6 containing a two-component developer therein, and a new two-component developer for supplying the developing container 6 to the developing container 6. A replenishment toner container 7 is provided. Here, the replenishment toner container 7 is detachably attached to the developing container 6, and a replenishment roller 8 and a stirring member 9 are accommodated therein.

  The inside of the developing container 6 is divided into a developing chamber S1 and a toner stirring chamber S2 by a partition wall 10, and these developing chamber S1 and toner stirring chamber S2 are developed at both ends in the longitudinal direction of the partition wall 10 and developing. They communicate with each other by a communication passage (not shown) formed between the container 6 and the container 6.

  A developing roller 11 as a developer carrying member is rotatably provided in an opening facing the photosensitive drum 1 in the developing chamber S1, and the developing roller 11 is provided above the opening of the developing container 6. A developing blade 12 for regulating the layer thickness of the developer carried thereon is attached. Here, a minute gap (for example, 0.2 to 0.4 mm) is formed between the developing blade 12 and the developing roller 11. A permanent magnet (not shown) is fixed inside the developing roller 11.

  Further, stirring members 13 and 14 are rotatably accommodated in the developing chamber S1 and the toner stirring chamber S2 in the developing container 6, respectively.

  In the developing device 3 configured as described above, when the agitating members 13 and 14 are driven to rotate in the direction indicated by the arrows (clockwise) in the developing chamber S1 and the toner agitating chamber S2 in the developing container 6, respectively. The two-component developer in 6 circulates between the developing chamber S1 and the toner stirring chamber S2 while being agitated, and is applied to the surface of the developing roller 11 rotating in the direction of the arrow (counterclockwise) by the magnetic force of the internal permanent magnet. Supported. The layer thickness of the two-component developer carried on the surface of the developing roller 11 is regulated by the developing blade 12 by rotating together with the developing roller 11, and the toner in the two-component developer is moved in the direction indicated by the arrow (clockwise). The electrostatic latent image formed on the rotating photosensitive drum 1 is attracted in accordance with the amount of electric charge and used for development.

  Thus, when the image forming operation is repeated, the toner of the two-component developer contained in the developing container 6 of the developing device 3 is consumed and reduced, whereas the carrier is not consumed and remains as it is. For this reason, the carrier is agitated more frequently than the toner, and as the durability progresses, the resin film (coat) on the surface of the carrier is peeled off and the internal metal core is exposed, and the carrier deteriorates.

  Therefore, in this embodiment, a trickle development method is adopted in which the two-component developer is gradually replenished from the replenishment toner container 7 into the developing container 6 and at the same time the development is performed while discharging the deteriorated developer in the developing container 6. However, in this embodiment, an amount of carrier (actually a two-component developer) corresponding to the degree of deterioration of the two-component developer in the developing container 6 is supplied from the replenishing toner container 7 to the developing container 6. It is characterized by.

Specifically, the operation time of the developing device 3 is counted by the number of image formations, and when the number of image formations reaches a set number, density reduction means for reducing the toner concentration of the two-component developer in the development container 6; A discharge means for forcibly discharging the two-component developer whose toner density has been reduced by the density reduction means onto the photosensitive drum 1 is provided. Here, a detecting means for detecting the deterioration of the two-component developer having a lowered toner concentration is provided, and at least one of L ^* , a ^* , b ^* of the two-component developer having the lowered toner concentration is detected by the detecting means. The discharge means is controlled based on the detection result. Note that L ^* indicates lightness, and a ^* and b ^* indicate color.

  FIG. 3 shows a system configuration for carrying out the trickle developing method. In the image forming apparatus, the image forming unit 20 shown in FIG. 1, the control unit 30 for controlling the image forming unit 20, and the toner density are reduced. A detection unit 40 that detects deterioration of the two-component developer is provided.

The image forming unit 20 includes a charge control unit 21 that controls the voltage V ₀ applied to the primary charger 2 shown in FIG. 1 and a development control unit 22 that controls the development bias V _Bias applied to the developing roller 11. Is provided. Further, the detection unit 40 is provided with an L ^* value detection unit 41 for detecting L ^* (lightness) of the two-component developer whose toner density is lowered.

Further, the control unit 30 includes a sheet number setting unit 31 for setting the number of image formations as a parameter for determining the timing of lowering the toner density of the two-component developer in the developing container 6, and the actual number of image formations. a number calculating section 32 for calculating a toner forced discharge control unit 33 for driving and controlling the charging control unit 21 of the image forming unit 20, detected by the L ^* value detection unit 41 of the detector 40 the L ^* value Carrier deterioration determining unit 34 that determines carrier deterioration based on the carrier discharge, and carrier discharge for controlling the development control unit 22 of the image forming unit 20 when the carrier deterioration determining unit 34 determines that the carrier is deteriorated. A control unit 35 is provided. Here, the toner forced discharge control unit 33 constitutes a density reduction unit, and the carrier discharge control unit 35 constitutes a discharge unit.

  Next, the trickle developing method employed in the image forming apparatus according to the present invention will be described with reference to the flowchart shown in FIG.

The set number S ₁ is set by the number setting unit 31 shown in FIG. 3 (step S1). Here, the set number S ₁ is a parameter that determines the timing of lowering the toner density of the two-component developer, and is proportional to the operating time of the developing device 3 (that is, the degree of deterioration of the carrier).

During the image forming operation, the image forming number S is calculated (counted) by the number calculating unit 32 shown in FIG. 3, and when the number S reaches the set number S ₁ (when the determination result in step S2 is YES). The toner forced discharge control unit 33 shown in FIG. 3 controls the charge control unit 31 of the image forming unit 20 to set the applied voltage V ₀ to the primary charger 2 to 0 (V ₀ = 0) (step S3). In the present embodiment, the set number S ₁ is set to 10,000.

As described above, when the voltage V ₀ applied to the primary charger 2 is set to 0 (V ₀ = 0), the toner of the two-component developer including the positively charged toner and the magnetic carrier carried on the developing roller 11 is obtained. It is forcibly discharged to the photosensitive drum 1 (step S4), and the forced discharge of the photosensitive drum 1 of the toner is continued until the time Ta reaches the set time T ₁ (step S5). In this embodiment, the set time T ₁ is set to 120 sec, and a developing bias V _{Bias of} 250 V is applied to the developing roller 11 during toner discharge. Further, if the agitating members 13 and 14 are driven while the toner is being discharged, the two-component developer is circulated and the toner is discharged wastefully. Therefore, the agitating members 13 and 14 must be stopped while the toner is being discharged. Is desirable.

Thus, when the toner of the two-component developer carried on the developing roller 11 is forcibly discharged to the photosensitive drum 1 for the set time T ₁ (= 120 sec) (when the determination result in step S is YES) ), The toner concentration of the two-component developer is lowered, and then the L ^* value (lightness) of the two-component developer having the lowered toner concentration is detected by the L ^* value detector 41 shown in FIG. S6).

Here, the L ^* value indicates the degree of deterioration of the two-component developer (carrier), and the carrier deterioration determination unit 34 shown in FIG. 3 performs the two-component developer (carrier) based on the detected L ^* value. The degree of deterioration is determined (step S7). As a result of the determination, the L ^* value is the set value L ₁ ^*
If this is the case (when the determination result in step S7 is YES), the development control unit 22 is controlled by the carrier discharge control unit 35 shown in FIG. 3, and the development bias V _Bias applied to the development roller 11 is Controlled (step S8), the two-component developer carried on the developing roller 11 (a deteriorated two-component developer containing a large amount of deteriorated carrier) is forcibly discharged to the photosensitive drum 1.

Forced discharge of the photosensitive drum 1 of the two-component developer is continued until time Tb reaches the set time T ₂ (step S9, S10). In this embodiment, the developing bias V _Bias applied to the developing roller 11 and the application time (two-component developer discharge time) T ₂ are set to the values shown in Table 1 according to the detected L * value. Is set. Further, if the agitating members 13 and 14 are driven while the two-component developer is being discharged, the two-component developer on the developing roller 11 circulates, which is not preferable for detecting the L ^* value (deterioration). It is desirable to stop the stirring members 13 and 14 during discharge.

表１より明らかなように、Ｌ^＊ 値が大きくなるほどキャリアのコートが剥がれてキャリアの劣化が激しく、二成分現像剤をより多く排出させる必要があるため、Ｌ^＊ 値の増加と共に現像バイアスＶ_Biasと印加時間Ｔ₂ が大きく設定されている。

As is clear from Table 1, the larger the L ^* value, the more the carrier coat is peeled off and the deterioration of the carrier becomes more severe, and it is necessary to discharge more two-component developer. Therefore, as the L ^* value increases, the developing bias V _Bias increases. And the application time T ₂ is set large.

  Thus, when the two-component developer deteriorated as described above is discharged from the developing roller 11 to the photosensitive drum 1, if the two-component developer in the developing container 6 decreases, the replenishing roller of the replenishing toner container 7. 8 and the agitating member 9 are driven to supply a new two-component developer from the replenishment toner container 7 to the developing container 6, and the deteriorated two-component developer is replaced with a new two-component developer. The development characteristics of the two-component developer are kept constant.

On the other hand, if the result of determination is that the L ^* value is less than the set value L ₁ ^* (if the determination result in step S7 is NO), the two-component developer is not discharged onto the photosensitive drum 1, and The process ends (step S7 → step S10).

As described above, in this embodiment, when the image forming number S reaches the set number S ₁ , the toner of the two-component developer on the developing roller 11 is discharged to the photosensitive drum 1 and the toner of the two-component developer. to reduce the concentration to detect the deterioration degree of the carrier by detecting the L ^* value of the two-component developer having the toner density decreases, to determine the deterioration of the carrier by the detected L ^* value, L ^* value is a set value Since the two-component developer on the developing roller 11 is discharged to the photosensitive drum 1 only when the carrier is more than L ₁ ^{* and} the deterioration of the carrier is proceeding, an amount corresponding to the degree of deterioration of the two-component developer is obtained. The carrier can be replenished, and the two-component developer is not wasted and is very economical.

In the present embodiment, L ^* (brightness) is detected as a parameter for determining the deterioration degree of the two-component developer (carrier). However, two-component development is performed by detecting a ^* and b ^* (color). You may make it determine the deterioration degree of an agent (carrier).

1 is a schematic configuration diagram of a main part of an image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view of the developing device of the image forming apparatus according to the present invention. 1 is a block diagram showing a system configuration for carrying out a trickle development method employed in an image forming apparatus according to the present invention. 6 is a flowchart showing a trickle developing method employed in the image forming apparatus according to the present invention.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Primary charger 3 Developing device 4 Transfer roller 5 Cleaning device 6 Developing container 7 Supply toner container 8 Supply roller 9 Stirring member 10 Partition wall 11 Developing roller (developer carrier)
11a Permanent magnet 12 Developing blade 13, 14 Stirring member 20 Image forming unit 21 Charging control unit 22 Development control unit 30 Control unit 31 Number setting unit 32 Number calculation unit 33 Toner forced discharge control unit 34 Carrier deterioration determination unit 35 Carrier discharge control unit 40 detector 41 L ^* value detector L exposure light N transfer nip S1 developing chamber S2 toner stirring chamber

Claims (3)

In an image forming apparatus that forms a latent image on an image carrier and develops the latent image using a two-component developer composed of a toner and a carrier.
Concentration reducing means for reducing the toner concentration of the two-component developer, and discharge means for forcibly discharging the two-component developer whose toner concentration has been reduced by the density reduction means onto the image carrier are provided. An image forming apparatus.   The image forming apparatus according to claim 1, further comprising: a detecting unit that detects deterioration of the two-component developer having a lowered toner density, and the discharge unit is controlled based on a detection result of the detecting unit. The image forming apparatus according to claim 2, wherein the detecting unit is a unit that detects at least one of L ^* , a ^* , and b ^* of the two-component developer having a lowered toner density.

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