JP2006195356A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect the toner concentration of developer even when an amount of the developer changes. <P>SOLUTION: A bypass path is formed by an opening 71 between a first developer storage section 41a and a second developer storage section 41b. The first developer storage section 41a recovers and supplies developer held on a developing sleeve 42. The second developer storage section 41a has an area B in which inner walls are formed at prescribed intervals and an area A, located downstream of the area B in the direction of developer conveyance, in which the intervals of the inner walls are narrower than those in the area B. The second developer storage section 41b incorporates a developer stir auger 46 that stirs and mixes toner with developer fed from the first developer storage section 41a and that feeds the developer to the first developer storage section 41a. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device or the like, and more particularly to a developing device or the like that develops an electrostatic latent image in an image forming apparatus using an electrophotographic system.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, for example, a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged, and the photosensitive drum is controlled based on image information. An electrostatic latent image is formed on the photosensitive drum by exposure with the exposed light. The electrostatic latent image is converted into a visible image (toner image) by a developing device, and the toner image is further transferred to a recording sheet and fixed to perform image formation.

  In a developing device used in such an image forming apparatus, a one-component developing method using a magnetic toner or a two-component developing method using a two-component developer in which a toner and a magnetic carrier are mixed is used. In a color image forming apparatus, since it is necessary to form a clear color image, a two-component developing method using a color toner not containing magnetic particles has become mainstream. In a developing device (two-component developing device) using this two-component developing system, a developer in which toner and a magnetic carrier are mixed is conveyed to a photosensitive drum by a developer carrier, and a developing electric field is applied to the photosensitive drum. By applying the developer while being applied, the charged toner is attached to the electrostatic latent image for development.

  In such a two-component developing device, since it is necessary to stabilize image quality, it is necessary to always perform development with a developer having a predetermined toner concentration (toner / magnetic carrier) and charge amount. Therefore, the developer after being subjected to the development of the electrostatic latent image is separated from the developer carrier while the developer carrier rotates once, and then a new developer is supplied immediately thereafter. The developer is replaced. At that time, an appropriate amount of new toner is supplied from the toner container to the developer released from the developer carrying member, and the developer and the newly supplied toner are sufficiently stirred and mixed by a mechanical stirring means. Done. Then, the refreshed developer is supplied again to the developer carrier. In order to optimize the developer toner concentration and sufficiently frictionally charge the toner in such a developer circulation cycle, the two-component developing device requires a mechanism for accurately detecting the toner concentration of the developer. Become.

Here, as a conventional technique for accurately detecting the toner concentration of the developer in the two-component developing device, the toner concentration detecting means is provided on the bottom surface in the developing tank, and the means for stirring and transporting the developer removes the developer with the toner concentration. There is a technique related to a developing device configured to be transported in the vicinity of the position where the detection unit is disposed (see, for example, Patent Document 1). This technology increases the amount of developer in the vicinity of the position where the toner density detecting means is disposed more than the amount of developer in other developer tanks, and is more accurate without being affected by changes in the developer amount in the developer tank. It is intended to detect the toner density.
In addition, a toner concentration detecting means is provided in a region where the pressure of the developer conveyed to the developer conveying path is partially increased, and the toner concentration is reduced in a state where the developer conveying speed is reduced and a large amount of developer is retained. There is a technique for detecting (see, for example, Patent Document 2).

JP-A-8-36297 (page 3-7) JP-A-6-308833 (page 4-6)

  By the way, the toner concentration of the developer is a mixing ratio of the toner in the developer and the magnetic carrier (toner / magnetic carrier). Changes in the amount of magnetic carrier are captured by, for example, changes in the magnetic permeability of the developer. For this reason, it is necessary to always supply a certain amount of developer to the sensor surface of the toner density detecting means. However, the developer volume varies depending on the toner concentration. Also, trickle mechanism (the carrier is mixed in the toner to be replenished and the magnetic carrier is supplied at the same time as the toner, while the developer is discharged and the deteriorated magnetic carrier is removed. The amount of developer in the developing device also fluctuates when using the technique for extending the length of the developing device. Therefore, as described in Patent Documents 1 and 2 and the like described above, the two-component developing device is configured so that a sufficient amount of developer is supplied in the vicinity of the toner concentration detecting unit.

  However, since the toner concentration detecting means captures the change in the amount of magnetic carrier in the developer per unit volume as described above, the developer supplied to the sensor surface of the toner concentration detecting means in detecting the toner concentration. It will also be affected by the pressure. That is, even if the developer has the same toner concentration, when the developer pressure is high, the distance between the magnetic carriers is close, so the amount of magnetic carrier in the developer per unit volume is apparently increased. The toner density is detected lower than actual. On the other hand, when the developer pressure is low, the toner density is detected to be higher than actual. As described above, in order to accurately detect the toner concentration in the two-component developing device, even when the amount of developer fluctuates, a constant amount of developer is always supplied to the sensor surface of the toner concentration detecting means. There is a problem that it is necessary to realize a mechanism in which the pressure of the developer is kept constant.

Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to accurately detect the toner concentration of the developer even when the amount of the developer fluctuates. There is to do.
Another object is to detect the toner density of the developer with high accuracy even in a developing device having a mechanism for supplying and discharging the developer including the carrier.

  For this purpose, the developing device of the present invention includes a developer carrying member that carries and rotates the developer, and a developer supply container that collects and supplies the developer carried on the developer carrying member. A first region in which the inner wall is formed at a predetermined interval, and a first region in which the interval between the inner walls is narrower than that in the first region. And a developer conveying member disposed therein, stirring and mixing of the toner with respect to the developer sent out from the developer supply container part, and delivery of the developer to the developer supply container part. Is provided with a developer circulation container portion performed by the developer conveying member, and an opening for short-circuiting the developer supply container portion and the developer circulation container portion.

  Here, the developing device of the present invention can be characterized in that it further includes a toner concentration detecting means disposed in the second region of the developer circulation container section. Further, the developer transport member disposed in the developer circulation container is formed in a spiral shape, and the rotation radius of the developer transport member in the second region is smaller than the rotation radius in the first region. It can also be characterized. Furthermore, the opening may be formed by notching a part of the upper part of the partition wall that separates the developer supply container part and the developer circulation container part. The opening is downstream in the developer transport direction in the developer circulation container, and is formed in the first region, or formed from the first region to the second region. It can also be characterized. In particular, the upstream end of the opening may be located 20 mm or more upstream from the upstream end of the second region.

Further, the developing device of the present invention includes a developer carrying member that carries and rotates the developer, a developer supply container that collects and supplies the developer carried on the developer carrying member, The developer conveying member is disposed on the developer supplying member, and the developer agitated and mixed with the developer fed from the developer supply container and the developer fed to the developer supply container are performed by the developer conveying member. A developer circulation container part in which a stepped portion narrowing the cross-sectional area is formed in the downstream part of the developer conveying direction, and a bypass for allowing the developer staying upstream of the step part in the developer circulation container part to flow out to the developer supply container part It is characterized by having a route.
Here, a toner density detecting unit disposed in a step portion of the developer circulation container portion may be further provided. In particular, the toner concentration detecting means may be arranged on the side surface of the developer circulation container portion.
Further, the apparatus further comprises developer supplying means for supplying a developer in which toner and magnetic carrier are mixed in the developer circulation container section, and developer discharging means for discharging the developer to the outside of the apparatus. It can also be.

Further, the present invention is regarded as an image forming apparatus, and the image forming apparatus of the present invention includes an image carrier on which an electrostatic latent image is formed and a developing unit that develops the electrostatic latent image formed on the image carrier. A developer carrying member that rotates while carrying the developer, a developer supply container unit that collects and supplies the developer carried on the developer carrier, and a developer transport unit; A member is disposed inside, and the developer agitating and mixing the toner with respect to the developer sent out from the developer supply container part and sending the developer to the developer supply container part are performed by the developer conveying member. A developer circulation container portion formed with a stepped portion that narrows the cross-sectional area in the downstream portion in the transport direction, and a bypass path through which the developer staying upstream of the stepped portion of the developer circulation container portion flows out to the developer supply container portion , The toner density placed in the step of the developer circulation container It is characterized by comprising a detecting means.
Here, the developer conveying member disposed in the developer circulation container portion is formed in a spiral shape, and the rotation radius of the developer conveying member at the step portion is larger than the rotation radius in the region upstream of the step portion. It can be set as the structure formed small.

  According to the present invention, the toner concentration and the toner charge amount in the developer can be controlled with high accuracy, and therefore, a clear and high-quality image with rich gradation can be formed.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus shown in FIG. 1 is an intermediate transfer type image forming apparatus generally called a tandem type, and a plurality of photosensitive units 1Y, 1M, 1C, 1K on which toner images of respective color components are formed by electrophotography. Each color electrostatic latent image formed on each of the photosensitive units 1Y, 1M, 1C, and 1K, exposure units 3Y, 3M, 3C, and 3K for writing the electrostatic latent images on the photosensitive units 1Y, 1M, 1C, and 1K Each of the color component toner images formed by the developing unit 4Y, 4M, 4C, 4K and the photosensitive units 1Y, 1M, 1C, 1K as developing devices for developing the toner is sequentially transferred (primary transfer) to the intermediate transfer belt 15. A primary transfer unit 10, a secondary transfer unit 20 that collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 15 to a sheet P that is a recording material (recording paper), and a secondary transferred image Fix on paper P And a fixing device 60. Moreover, it has the control part 40 which controls operation | movement of each apparatus (each part).

  In the image forming apparatus according to the present embodiment, each of the photosensitive units 1Y, 1M, 1C, and 1K includes a charger that charges the photosensitive drums 11 around the photosensitive drums 11 that rotate in the arrow A direction. A charging roll 12 as an example and a drum cleaner 17 as an example of a cleaning member for removing residual toner on the photosensitive drum 11 are provided. The photosensitive units 1Y, 1M, 1C, and 1K are substantially linear in order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side of the intermediate transfer belt 15. Is arranged. Then, the primary transfer roll 16 performs intermediate transfer so that the color component toner images formed on the photosensitive drums 11 of the respective photosensitive units 1Y, 1M, 1C, and 1K are transferred to the intermediate transfer belt 15 in the primary transfer unit 10. The belt 15 is disposed so as to come into contact with the photosensitive drum 11.

Further, an LED print head (LPH) 13 is disposed in each of the exposure units 3Y, 3M, 3C, 3K. The exposure units 3Y, 3M, 3C, and 3K are arranged corresponding to the photoreceptor units 1Y, 1M, 1C, and 1K, respectively, and the photosensitive drum 11 receives the light emitted from the LED print head (LPH) 13. An image is formed on the surface, and an electrostatic latent image is formed on the surface of the photosensitive drum 11.
Further, each of the developing unit 4Y, 4M, 4C, 4K is similarly arranged corresponding to each of the photosensitive units 1Y, 1M, 1C, 1K, and the electrostatic latent image formed on the photosensitive drum 11 is used. Are visualized with each color toner contained therein.

The intermediate transfer belt 15 as an intermediate transfer member is constituted by a film-like endless belt in which an appropriate amount of an antistatic agent such as carbon black is contained in a resin such as polyimide or polyamide. And the volume resistivity is formed so that it may become 10 < ⁶ > -10 < ¹⁴ > (omega | ohm) cm, The thickness is comprised by about 0.1 mm, for example. The intermediate transfer belt 15 is circulated and driven (rotated) at a predetermined speed in the direction B shown in FIG. 1 by various rolls. As these various rolls, a drive roll 31 that is driven by a motor (not shown) excellent in constant speed and rotates the intermediate transfer belt 15, and an intermediate that extends substantially linearly along the arrangement direction of the photosensitive drums 11. A support roll 32 that supports the transfer belt 15, a tension roll 33 that functions as a correction roll that applies a constant tension to the intermediate transfer belt 15 and prevents meandering of the intermediate transfer belt 15, and a backup provided in the secondary transfer unit 20. A cleaning backup roll 34 provided in a cleaning unit for scraping off residual toner on the roll 25 and the intermediate transfer belt 15 is provided.

As described above, the primary transfer unit 10 includes the primary transfer roll 16 as an example of a transfer unit that is disposed to face the photosensitive drum 11 with the intermediate transfer belt 15 interposed therebetween. The primary transfer roll 16 includes a shaft and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR, and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm. The primary transfer roll 16 is placed in pressure contact with the photosensitive drum 11 with the intermediate transfer belt 15 in between, and the primary transfer roll 16 has a voltage (with negative polarity; the same applies hereinafter) having a polarity opposite to that of the toner. (Primary transfer bias) is applied. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15 so as to form superimposed toner images on the intermediate transfer belt 15.

The secondary transfer unit 20 includes a secondary transfer roll 22 as an example of a transfer unit disposed on the toner image carrying surface side of the intermediate transfer belt 15 and a backup roll 25. The backup roll 25 is composed of a tube of EPDM and NBR blend rubber with carbon dispersed on the surface, and EPDM rubber on the inside. And it forms so that the surface resistivity may be 10 < ⁷ > -10 < ¹⁰ > (omega | ohm) / square, and hardness is set to 70 degrees (Asker C), for example. The backup roll 25 is disposed on the back side of the intermediate transfer belt 15 to form a counter electrode of the secondary transfer roll 22, and a metal power supply roll 26 to which a secondary transfer bias is stably applied is disposed in contact with the backup roll 25. ing.

On the other hand, the secondary transfer roll 22 includes a shaft and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR, and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm. The secondary transfer roll 22 is disposed in pressure contact with the backup roll 25 with the intermediate transfer belt 15 interposed therebetween. Further, the secondary transfer roll 22 is grounded, and a secondary transfer bias is formed between the secondary transfer roll 22 and the backup roll 25. The toner image is secondarily transferred onto the paper P conveyed to the transfer unit 20.

  Further, on the downstream side of the secondary transfer portion 20 of the intermediate transfer belt 15, an intermediate transfer belt that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15. A cleaner 35 is provided so as to be able to contact and separate. On the other hand, on the upstream side of the yellow photoreceptor unit 1Y, a reference sensor (home position sensor) 38 that generates a reference signal serving as a reference for taking the image formation timing in each of the photoreceptor units 1Y, 1M, 1C, and 1K. It is arranged. The reference sensor 38 recognizes a predetermined mark provided on the back side of the intermediate transfer belt 15 and generates a reference signal. In response to an instruction from the control unit 40 based on the recognition of the reference signal, each photoconductor unit 1Y. , 1M, 1C, 1K, each exposure unit 3Y, 3M, 3C, 3K, and each developing unit 4Y, 4M, 4C, 4K are configured to start image formation. Further, an image density sensor 39 for adjusting image quality is disposed on the downstream side of the black photoconductor unit 1K.

  In addition, in the image forming apparatus of the present embodiment, as a paper transport system, a paper tray 50 that stores the paper P, a pickup roll 51 that picks up and transports the paper P accumulated in the paper tray 50 at a predetermined timing, After the transfer roll 52 that transports the paper P fed by the pickup roll 51, the transport chute 53 that feeds the paper P transported by the transport roll 52 to the secondary transfer unit 20, and after the secondary transfer by the secondary transfer roll 22. A transport belt 55 that transports the transported paper P to the fixing device 60 while being sucked by a fan disposed therein, and a fixing entrance guide 56 that guides the paper P to the fixing device 60 are provided.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. In the image forming apparatus as shown in FIG. 1, image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is subjected to predetermined image processing by an image processing device (IPS) not shown. After the application, the image forming operation is executed by the photosensitive units 1Y, 1M, 1C, and 1K, the exposure units 3Y, 3M, 3C, and 3K, and the developing units 4Y, 4M, 4C, and 4K. In the image processing apparatus (IPS), the input reflectance data is subjected to predetermined image editing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, and moving editing. Image processing is performed. The image data that has been subjected to image processing is converted into color material gradation data of four colors Y, M, C, and K, and is output to the exposure units 3Y, 3M, 3C, and 3K.

The surface of each of the photosensitive drums 11 of the photosensitive units 1Y, 1M, 1C, and 1K is uniformly charged by the charging roll 12. In each of the exposure units 3Y, 3M, 3C, and 3K, exposure light is emitted from the LPH 13 to each of the photosensitive drums 11 in accordance with the input color material gradation data. That is, the LPH 13 includes a LPH driving unit, a light emitting diode array (LED array), and a Selfoc lens (registered trademark) array, and a signal controlled based on the color material gradation data is transmitted from the LPH driving unit to the LED. The LED array emits light based on a signal from the LPH drive unit, and forms an image on the surface of the photosensitive drum 11 by a SELFOC lens (registered trademark) array.
The surface of each of the photosensitive drums 11 of the photosensitive units 1Y, 1M, 1C, and 1K is exposed by the LPH 13 to form an electrostatic latent image. Thereafter, the formed electrostatic latent image is developed with each color toner of Y, M, C, K by each of the developing unit 4Y, 4M, 4C, 4K, and a toner image is formed.

  The toner images formed on the photosensitive drums 11 of the photosensitive units 1Y, 1M, 1C, and 1K are transferred onto the intermediate transfer belt 15 in the primary transfer unit 10 where the photosensitive drums 11 and the intermediate transfer belt 15 come into contact with each other. Is transcribed. More specifically, in the primary transfer portion 10, a voltage (primary transfer bias) having a polarity opposite to the toner charging polarity (minus polarity) is applied to the base material of the intermediate transfer belt 15 by the primary transfer roll 16, and the toner image. Are sequentially superimposed on the surface of the intermediate transfer belt 15 to perform primary transfer.

  After the toner images are sequentially primary transferred onto the surface of the intermediate transfer belt 15, the intermediate transfer belt 15 moves and the toner image is conveyed to the secondary transfer unit 20. When the toner image is transported to the secondary transfer unit 20, in the paper transport system, the pick-up roll 51 rotates in accordance with the timing at which the toner image is transported to the secondary transfer unit 20, and the paper of a predetermined size is transferred from the paper tray 50. P is supplied. The paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the secondary transfer unit 20 via the transport chute 53. Before reaching the secondary transfer unit 20, the paper P is temporarily stopped, and a registration roll (not shown) rotates in accordance with the movement timing of the intermediate transfer belt 15 on which the toner image is carried. And the position of the toner image are aligned.

  In the secondary transfer unit 20, the secondary transfer roll 22 is pressed against the backup roll 25 via the intermediate transfer belt 15. At this time, the sheet P conveyed at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 22. At this time, when a voltage (secondary transfer bias) having the same polarity as the toner charging polarity (negative polarity) is applied from the power supply roll 26, a transfer electric field is formed between the secondary transfer roll 22 and the backup roll 25. Is done. The unfixed toner image carried on the intermediate transfer belt 15 is collectively electrostatically transferred onto the paper P in the secondary transfer unit 20 pressed by the secondary transfer roll 22 and the backup roll 25. .

Thereafter, the sheet P on which the toner image has been electrostatically transferred is transported as it is while being peeled off from the intermediate transfer belt 15 by the secondary transfer roll 22, and transported downstream of the secondary transfer roll 22 in the sheet transport direction. It is conveyed to the belt 55. The transport belt 55 transports the paper P to the fixing device 60 while sucking the paper P in accordance with the optimal transport speed in the fixing device 60. The unfixed toner image on the paper P conveyed to the fixing device 60 is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 60. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge placement unit provided in a discharge unit of the image forming apparatus.
On the other hand, after the transfer onto the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and the cleaning backup roll 34 and the intermediate transfer belt cleaner 35 are transferred. Is removed from the intermediate transfer belt 15.

Subsequently, the developing unit 4Y, 4M, 4C, 4K used in the image forming apparatus of the present embodiment will be described in detail. Hereinafter, the developing unit 4Y that develops yellow (Y) toner will be described as an example, but the developing units 4M, 4C, and 4K are similarly configured, and magenta (M) toner, cyan (C) toner, and black, respectively. (K) Developing with toner to form M, C, and K toner images.
FIG. 2 is a schematic sectional view of the developing unit 4Y. As shown in FIG. 2, the developer unit 4Y includes a developer holding container for storing a developer, a support container 41 as a casing of the developer unit 4Y, a developer sleeve 42 as a developer carrier, and a developer as a developer sleeve. 42, a developing magnet 43 to be attracted to 42, a blade 44 for regulating the developer layer thickness (coating amount), a developer supplying auger 45 for circulating the developer in the longitudinal direction of the developer unit 4Y while stirring the developer, and a developer stirring auger 46, a toner supply path 47 for supplying toner to the support container 41 is provided.

The support container 41 has an opening toward the photosensitive drum 11, and a developer containing portion that contains a developer in which toner and a carrier that is magnetic particles are mixed is provided inside. The developer storage section includes a first developer storage section (developer supply container section) 41a and a second developer storage section (developer circulation container section) by a storage section wall 48 provided in the longitudinal direction of the developer unit 4Y. 41b.
A developer supply auger 45 is disposed in the first developer accommodating portion 41a, and a developer stirring auger 46 is disposed in the second developer accommodating portion 41b. The accommodating portion walls 48 are not provided at both ends in the longitudinal direction of the developing device unit 4Y, and the first developer accommodating portion 41a and the second developer accommodating portion 41b are connected at the both end portions, and the developer Are configured to circulate with each other.

The developing sleeve 42 is made of a nonmagnetic material such as aluminum or SUS, and is rotated in the direction of arrow C by a driving unit (not shown). A developing bias consisting of a DC voltage or a developing bias in which a DC voltage is superimposed on an AC voltage is applied to the developing sleeve 42 from a power source (not shown), and a developing electric field is formed between the developing sleeve 42 and the photosensitive drum 11.
A developing magnet 43 is included in the developing sleeve 42. The developing magnet 43 is provided with a developing pole N1 provided substantially opposite to the photosensitive drum 11, a trimming pole S1 provided substantially opposite to the blade 44 and restricting the amount of developer applied, and the developed developer. The same polarity arranged adjacent to each other in order from the upstream side in the rotation direction of the developing sleeve 42 in order to form a repulsive magnetic field for releasing the developer carried on the developing sleeve 42 and the transport pole S2 transported into the support container 41. A magnetic pole N2 (first repulsive magnetic pole) and a magnetic pole N3 (second repulsive magnetic pole) of (the same repulsive pole) are sequentially arranged in the circumferential direction.
The blade 44 is made of a non-magnetic material or a magnetic material, and regulates the layer thickness of the developer carried on the developing sleeve 42 to a constant amount in cooperation with the trimming pole S1 of the developing magnet 43. As a result, a predetermined amount of developer is uniformly carried on the developing sleeve 42 in the axial direction.

  In the developing sleeve 42 including the developing magnet 43, after the developer held in the first developer accommodating portion 41a is attracted to the developing sleeve 42 by the second repulsive magnetic pole N3, the amount of developer on the developing sleeve 42 is increased. The (application amount) is regulated to a predetermined amount by the trimming pole S1 and the blade 44. Then, the developer sleeve 42 is rotated to convey the developer to the photosensitive drum 11, and under the developing electric field, the developer is spiked by the developing pole N 1 and brought into contact with the photosensitive drum 11. The electrostatic latent image is developed. The developer that has been developed is transported into the support container 41 by the transport pole S2, and is separated from the developing sleeve 42 by the repulsive magnetic fields of the first repulsive magnetic pole N2 and the second repelling magnetic pole N3. Further, the developer separated from the developing sleeve 42 is collected in the first developer accommodating portion 41a.

  On the other hand, the developer supply auger 45 of the first developer accommodating portion 41a and the developer stirring auger 46 of the second developer accommodating portion 41b are each provided with a screw around the shaft. The developer supply auger 45 and the developer stirring auger 46 are rotated in opposite directions by driving means (not shown) to convey the toner and the carrier in opposite directions while stirring. Since the first developer accommodating portion 41a and the second developer accommodating portion 41b are connected at both ends of the developer unit 4Y, the developer flows into each other, and the developer supply auger 45 and the developer agitating auger 46 It is configured to circulate between the first developer accommodating portion 41a and the second developer accommodating portion 41b. Therefore, the developer separated from the developing sleeve 42 and collected in the first developer accommodating portion 41a is conveyed to the second developer accommodating portion 41b by the developer supply auger 45 and the developer agitating auger 46.

  In addition, the support container 41 is a toner that supplies toner to the second developer accommodating portion 41b at the upper portion of the second developer accommodating portion 41b and upstream in the developer conveying direction by the developer stirring auger 46. A supply path 47 is formed. The toner supply path 47 is connected to a toner container 5Y disposed above the developing unit 4Y. Then, yellow (Y) toner is stored in the toner container 5Y, and the toner is dropped from the toner container 5Y through the toner supply path 47, whereby the toner is supplied to the second developer accommodating portion 41b of the developing unit 4Y. ing. Each of the developer units 4M, 4C, and 4K includes a toner container 5M that stores magenta (M) toner, a toner container 5C that stores cyan (C) toner, and a toner that stores black (K) toner. The container 5K is connected via a toner supply path 47 to supply each color toner to the second developer accommodating portion 41b.

  When new toner is supplied to the developer from the toner container 5Y in the second developer accommodating portion 41b, the toner concentration is controlled to a predetermined range by the toner concentration detection sensor 49 (see FIG. 3 at a later stage). The toner supply amount is adjusted. The developer to which the toner has been newly supplied is sufficiently stirred and mixed by the developer stirring auger 46 with the toner and the magnetic carrier, and the first developer accommodating portion formed by the developer supplying auger 45 and the developer stirring auger 46. By the circulation between 41a and the second developer accommodating portion 41b, it is conveyed again to the first developer accommodating portion 41a. Then, from the first developer container 41a, the developer whose toner density is adjusted to a predetermined range and sufficiently charged to the toner is supplied to the developing sleeve. In this way, the developer is circulated.

  Here, in the developer unit 4Y of the present embodiment, the second developer accommodating portion 41b that accommodates the developer stirring auger 46 is the most downstream region in the developer transport direction by the developer stirring auger 46, The opening area (the area of the opening in the plane orthogonal to the developer stirring auger 46: the same applies hereinafter) in the upstream portion of the connection region with the first developer containing portion 41a is the same as that of the second developer containing portion 41b. It is formed narrower by a predetermined amount than the opening area of other regions. In addition, on the upstream side of the region where the opening area is narrow (it may have an overlapping portion with the region where the opening area is narrow), the first developer accommodating portion 41a and the second developer may be provided. An opening serving as a bypass path through which the developer in the second developer accommodating portion 41b flows out to the first developer accommodating portion 41a is formed in the accommodating portion wall 48 that separates the accommodating portion 41b. A toner concentration detection sensor 49 is disposed on the side surface portion of the inner wall of the first developer accommodating portion 41a in a region where the opening area is narrow.

FIG. 3 is a view showing the inside of the developing device unit 4Y in the most downstream region in the direction in which the developer is conveyed by the developer stirring auger 46. As shown in FIG. As shown in FIG. 3, the second developer accommodating portion 41b is the most downstream region in the developer conveying direction by the developer stirring auger 46, and is upstream of the connection region 41c with the first developer accommodating portion 41a. A step 70 is formed in a portion (region A: second region in the drawing), and the region A is a region upstream of the region A by the step 70 (region B: first region in the drawing). In contrast, the opening area is narrowed by a predetermined amount. That is, the interval between the accommodating portion wall 48 in the region A and the inner wall of the second developer accommodating portion 41b is narrower by a predetermined amount than the interval between the accommodating portion wall 48 in the region B and the inner wall of the second developer accommodating portion 41b. It is configured.
In addition, an opening 71 for allowing the developer in the second developer accommodating portion 41b to flow out to the first developer accommodating portion 41a is formed in the accommodating portion wall 48 in the most downstream region in the developer conveying direction of the region B. ing.

A toner concentration detection sensor 49 for detecting the toner concentration (toner / magnetic carrier) of the developer is disposed in the area A in which the opening area is narrow and formed on the inner wall of the first developer accommodating portion 41a. It is installed. As the toner concentration detection sensor 49, for example, a method of detecting a change in the magnetic permeability of the developer based on a change in the toner concentration is used.
Here, the toner concentration detection sensor 49 is disposed on the side surface portion of the inner wall of the first developer accommodating portion 41a. This is because when the toner concentration detection sensor 49 is disposed at the bottom of the first developer accommodating portion 41a, the developer moves slowly at the bottom due to the weight of the developer, and the developer is not easily conveyed. This is because the toner density of the developer being conveyed may not be detected accurately. On the other hand, the side surface portion of the first developer accommodating portion 41a is not greatly affected by the developer's own weight, and the developer is smoothly conveyed, so that the toner concentration of the conveyed developer is accurately set. Can be detected.

As described above, the step portion 70 is configured so that the space between the housing portion wall 48 in the region A and the inner wall of the second developer housing portion 41b is narrower than the space in the region B by a predetermined amount. Since the opening area in the plane orthogonal to 46 is set to be smaller than the opening area of the region B, when the developer agitating auger 46 transports the developer in the second developer accommodating portion 41b, the region The volume of the developer in A can be higher than the volume of the developer in region B. Therefore, even if the amount of the developer fluctuates by appropriately setting the step of the step portion 70 in accordance with the design size of the second developer accommodating portion 41b, the developer amount to be set, and the like, the region A In this case, it is possible to always maintain a state in which the entire sensor surface of the toner density detection sensor 49 disposed on the side surface in the second developer accommodating portion 41b is filled with the developer.
For this reason, a constant amount of developer can be maintained on the sensor surface of the toner density detection sensor 49 (that is, the amount that fills the entire surface of the sensor), so detection based on variations in the developer amount. The generation of errors can be suppressed.

  On the other hand, an opening 71 through which the developer in the second developer accommodating portion 41b flows out to the first developer accommodating portion 41a is formed in the accommodating portion wall 48 of the region B in the most downstream area in the developer transport direction. Yes. Therefore, when the amount of developer flowing from the region B into the region A increases and the developer stays in the boundary region between the region B and the region A, the developer is first developed from the opening 71. It can be made to flow out (bypass) to the medicine container 41a. As a result, the opening 71 functions to prevent the developer pressure in the region A from rising above a predetermined value.

  That is, when the amount of developer increases due to some influence (for example, if it is continuously used in a state where the toner concentration is reduced and the volume is reduced, the developer is replenished by the trickle mechanism described later, and the amount of developer increases. In addition, when the toner concentration increases from that state, the volume of the developer further increases at a time (however, in this case, the developer is gradually discharged by the trickle mechanism). (2) The developer conveyed along the developer accommodating portion 41b is not conveyed to the region A but is shortened by the opening 71 when the developer stays in front of the region A. 1 developer is transported to the side of the container 41a.

  Here, FIG. 4 is a diagram illustrating the function of the opening 71 to adjust the developer amount when the bulk of the developer in the region A increases. FIG. 4 shows a state in which the inside of the second developer accommodating portion 41b is viewed from the side. As shown in FIG. 4, the developer is conveyed with a predetermined bulk in the second developer accommodating portion 41b (region B), but in the region A, the accommodating portion wall 48 and the second developer accommodating portion 41b. The distance between the inner wall of the developer and the inner wall of the second developer container 41b in the region B is narrower than the distance between the inner wall and the inner wall of the second developer container 41b by a predetermined amount. More than B. In this case, if the bulk of the developer in the region A is about a predetermined height (the height indicated by the solid line in the figure), the developer pressure on the sensor surface 49a of the toner concentration detection sensor 49 is higher than expected. Must not. Further, the developer hardly stays at the entrance of the area A.

  However, when the toner concentration of the developer increases, for example, a trickle mechanism (mixing the carrier in the toner to be replenished in the developing device, while supplying the magnetic carrier simultaneously with the toner by the developer supplying means, The developer is discharged immediately by the developer discharging means and the deteriorated magnetic carrier is removed to extend the total life of the developer, and the developer is discharged immediately before the developer is discharged. In a case where the amount is increased, the bulkiness of the developer in the region A may exceed a predetermined height (the height indicated by the alternate long and short dash line in the figure). In this case, the developer stays at the entrance of the area A. Then, the developer staying from the opening 71 disposed on the upstream side of the region A (the developer in the shaded portion in the figure) flows out into the first developer accommodating portion 41a, and the inlet portion of the region A In this case, the stagnation of the developer in the region A is eliminated, and the bulk of the developer in the region A is suppressed from exceeding a predetermined height.

  Therefore, when the amount of developer in the second developer accommodating portion 41b increases due to the replenishment of toner in the second developer accommodating portion 41b, or when a trickle mechanism is used. Even when the amount of developer in the second developer accommodating portion 41b varies, the developer staying at the entrance of the region A is shortened by the opening 71 and conveyed to the first developer accommodating portion 41a. As a result, the bulkiness of the developer in the region A can be suppressed from exceeding a predetermined height. As a result, the developer pressure in the region A where the toner concentration detection sensor 49 is disposed is suppressed from being increased more than necessary.

As described above, the toner concentration detection sensor 49 can accurately detect the toner concentration by suppressing the developer pressure in the region A in which the toner concentration detection sensor 49 is disposed from being increased more than necessary. It becomes possible. That is, since the toner concentration detection sensor 49 captures a change in the amount of magnetic carrier in the developer per unit volume, in detecting the toner concentration, the pressure of the developer supplied to the sensor surface of the toner concentration detecting means is detected. It will also be affected. Specifically, even if the developer has the same toner concentration, when the developer pressure is high, the distance between the magnetic carriers is close, so the amount of magnetic carrier in the developer per unit volume is apparent. The toner density is detected to be lower than actual. On the other hand, when the developer pressure is low, the toner density is detected to be higher than actual. As described above, in the two-component developing device in which the amount of the developer varies, it is difficult to accurately detect the toner concentration even when the developer pressure on the sensor surface of the toner concentration detection sensor 49 varies. Become.
On the other hand, in the developer unit 4Y of the present embodiment, the toner concentration detection sensor 49 can always detect the toner concentration under a substantially constant developer pressure regardless of the amount of the developer. it can. Therefore, it is possible to detect the toner density with high accuracy without being affected not only by the influence of the fluctuation of the developer amount but also by the influence of the developer pressure as much as possible.

  In describing the developing unit 4Y of the present embodiment, as shown in FIG. 3, a configuration in which the opening 71 is on the upstream side of the region A and does not overlap with the region A is used. It was. However, in the opening portion 71, it is sufficient to perform the function of causing the developer staying in the boundary region between the region B and the region A to flow out to the first developer accommodating portion 41a. If the most upstream side end of the opening 71 is positioned upstream from the most upstream side end of the region A, the opening 71 can be formed so as to have an overlapping portion with the region A. is there. However, the distance between the uppermost stream end of the opening 71 and the uppermost stream end of the area A is set to 20 mm or more so that the developer staying in the boundary area between the area B and the area A can be effectively discharged. It is preferable to do this.

  The developer stirring auger 46 is pivotally supported at both ends in the longitudinal direction of the support container 41 and rotates. At this time, the effect of the rotational force received from the driving means (not shown) and the frictional resistance received from the developer. As a result, bow-shaped deflection occurs at the center with both shaft fulcrums as fixed points. Therefore, since it is necessary to prevent the rubbing between the developer stirring auger 46 and the housing portion wall 48 and the inner wall of the second developer housing portion 41b, the developer stirring auger 46, the housing portion wall 48, and the first wall are assumed in consideration of such bending. 2 It is necessary to provide a predetermined gap between the inner wall of the developer container 41b. Therefore, the screw diameter of the developer stirring auger 46 is preferably configured to be smaller in the region A where the space between the housing portion wall 48 and the inner wall of the second developer housing portion 41b is narrower than the region B. Thus, by configuring the screw diameter of the developer stirring auger 46 to be small in the region A, the conveying force of the developer stirring auger 46 in the region A is lower than that in the region B. It is also possible to carry out effectively.

As described above, in the developer units 4Y, 4M, 4C, and 4K according to the present embodiment, the container wall 48 and the second wall in the downstream area (area A) in the developer transport direction of the second developer container 41b. 2 The interval between the inner wall of the developer accommodating portion 41b and the inner wall of the second developer accommodating portion 41b in the region upstream of the region A (region B) is narrower by a predetermined amount. ing. In addition, an opening 71 for allowing the developer in the second developer accommodating portion 41b to flow out to the first developer accommodating portion 41a is formed in the accommodating portion wall 48 in the most downstream region in the developer conveying direction of the region B. ing. A toner concentration detection sensor 49 for detecting the toner concentration is disposed in a region A in which the opening area is narrowly formed and on the side surface of the inner wall of the first developer accommodating portion 41a. With such a configuration, even when the developer amount fluctuates, the toner concentration detection sensor 49 is always supplied with a substantially constant amount of developer, and is always under a substantially constant developer pressure. Therefore, the toner density can be detected with high accuracy. As a result, the toner concentration and the toner charge amount in the developer can be controlled with high accuracy, and thus a high-quality image that is clear and rich in gradation can be formed.
In particular, when a trickle mechanism is used in the developing device, the amount of developer in the developing device is likely to fluctuate, so the configuration of the present embodiment is effective for accurate detection of toner density.

  As an application example of the present invention, there is application to an image forming apparatus such as a copying machine, a printer, and a fax machine using an electrophotographic system.

1 is a schematic configuration diagram illustrating an image forming apparatus of the present invention. It is a schematic sectional drawing of a developing device unit. FIG. 5 is a diagram illustrating the inside of the developing unit in a most downstream region in a direction in which the developer is conveyed by the developer agitating auger. FIG. 10 is a diagram illustrating a function of adjusting the amount of developer by an opening when the volume of developer in a region A increases. It is a figure explaining the other arrangement position of an opening part.

Explanation of symbols

1Y, 1M, 1C, 1K ... photosensitive unit, 3Y, 3M, 3C, 3K ... exposure unit, 4Y, 4M, 4C, 4K ... developer unit, 5Y, 5M, 5C, 5K ... toner container, 11 ... photosensitive member Drum, 12 ... charging roll, 13 ... LED print head (LPH), 15 ... intermediate transfer belt, 16 ... primary transfer roll, 17 ... drum cleaner, 20 ... secondary transfer section, 41 ... support container, 41a ... first development Developer container 41b second developer container 41c connection region 42 developing sleeve 43 developing magnet 44 blade 45 developer auger 46 developer agitation 47 toner supply Road, 48, container wall, 49, toner concentration detection sensor, 70, stepped portion, 71, opening

Claims (12)

A developer carrier that carries and rotates the developer;
A developer supply container for collecting and supplying the developer carried on the developer carrying member;
A first region in which inner walls are formed at a predetermined interval, and a second region in which the inner wall is positioned downstream of the first region in the developer transport direction and the interval between the inner walls is narrower than the first region. And a developer conveying member disposed therein, and agitation and mixing of the toner with respect to the developer sent out from the developer supply container part and delivery of the developer to the developer supply container part And a developer circulation container portion which is performed by the developer transport member,
A developing device comprising: an opening for short-circuiting the developer supply container section and the developer circulation container section.   2. The developing device according to claim 1, further comprising a toner concentration detecting unit disposed in the second region of the developer circulation container.   The developer conveying member disposed in the developer circulation container is formed in a spiral shape, and the rotation radius of the developer conveying member in the second region is larger than the rotation radius in the first region. The developing device according to claim 1, wherein the developing device is formed smaller.   The developing device according to claim 1, wherein the opening is formed by notching a part of an upper portion of a partition wall that separates the developer supply container part and the developer circulation container part.   The opening is downstream in the developer transport direction in the developer circulation container, and is formed in the first region or straddles the second region from the first region. The developing device according to claim 1, wherein the developing device is formed.   The developing device according to claim 5, wherein the upstream end portion of the opening portion is located 20 mm or more upstream from the upstream end portion of the second region. A developer carrier that carries and rotates the developer;
A developer supply container for collecting and supplying the developer carried on the developer carrying member;
A developer conveying member is disposed inside, and the developer conveying member performs stirring and mixing of the toner with respect to the developer sent from the developer supply container and sending of the developer to the developer supply container. And a developer circulation container portion in which a stepped portion that narrows the cross-sectional area is formed in the downstream portion of the developer conveyance direction,
A developing device comprising: a bypass path for allowing the developer staying upstream of the stepped portion in the developer circulation container portion to flow out to the developer supply container portion.   8. The developing device according to claim 7, further comprising a toner concentration detecting unit disposed in the step portion of the developer circulation container.   9. The developing device according to claim 8, wherein the toner density detecting means is disposed on a side surface of the developer circulation container. Developer supplying means for supplying a developer in which toner and magnetic carrier are mixed in the developer circulation container section;
8. The developing device according to claim 7, further comprising developer discharging means for discharging the developer to the outside of the device. An image carrier on which an electrostatic latent image is formed;
Developing means for developing the electrostatic latent image formed on the image carrier,
The developing means includes
A developer carrier that carries and rotates the developer;
A developer supply container for collecting and supplying the developer carried on the developer carrying member;
A developer conveying member is disposed inside, and the developer conveying member performs stirring and mixing of the toner with respect to the developer delivered from the developer supply container and delivery of the developer to the developer supply container. And a developer circulation container portion in which a stepped portion that narrows the cross-sectional area is formed in the downstream portion of the developer conveyance direction,
A bypass path for allowing the developer accumulated on the upstream side of the stepped portion of the developer circulation container portion to flow out to the developer supply container portion;
An image forming apparatus comprising: a toner concentration detecting unit disposed in the step portion of the developer circulation container portion.   The developer transport member disposed in the developer circulation container portion is formed in a spiral shape, and the rotation radius of the developer transport member at the stepped portion is a rotation radius in a region upstream of the stepped portion. 12. The image forming apparatus according to claim 11, wherein the image forming apparatus is formed smaller than the image forming apparatus.

Images