JP2011248127A - Development device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a development device capable of precisely controlling toner concentration by controlling fluctuation of the bulk density of a developer around a detection position of a toner concentration sensor even if the fluidity of the developer is reduced.SOLUTION: An agitating screw 43 has screw blades having a constant spiral pitch, and in a continuous region including the detection position of the toner concentration sensor 47, continuous in a conveyance direction, a space volume within one pitch of the screw blades is set to be smaller than that in the front and rear regions. The agitating screw 43 has a screw blades having a fixed thickness, and in the continuous region including the detection position of the toner concentration sensor 47, continuous in a conveyance direction, another screw blade having the same spiral pitch is disposed in a space between the screw blades having the contact spiral pitch.

Description

  The present invention relates to a developing device that controls the toner density by detecting the magnetic permeability of a developer including toner and a carrier, and more particularly to an arrangement structure of a toner density sensor that increases the detection accuracy of the toner density.

  2. Description of the Related Art Image forming apparatuses that develop an electrostatic image on an image carrier by causing a developer (two-component developer) including a toner and a carrier to be carried on a rotating developer carrier are widely used. In an image forming apparatus using a two-component developer, only the toner in the developer is consumed as the image is formed, so the ratio of the toner to the developer (toner concentration) is reduced. For this reason, during image formation, the developing device is replenished with toner sufficient to compensate for the decrease in toner density associated with image formation.

  Here, in a developing device using a two-component developer, the developer and the carrier are circulated while stirring in the developer container to frictionally charge the toner and the carrier, thereby giving the toner a predetermined charge amount. For this reason, when the toner concentration, which is the weight ratio of the toner to the developer, decreases, the chance of toner friction increases, the toner charge amount increases, the amount of toner adhering to the same electrostatic image decreases, and the image density decreases. . On the contrary, when the toner concentration of the developer increases, the chance of friction of the toner decreases and the charge amount of the toner decreases, the amount of toner adhering to the same electrostatic image increases, and the image density increases.

  For this reason, the developing device is provided with a toner concentration sensor that detects the magnetic permeability of the developer circulating in the developing container, continuously measures the toner concentration, and maintains the toner concentration within a predetermined range in real time. The toner replenishment amount is controlled.

  However, since the toner concentration sensor generates an output corresponding to the density of the carrier (magnetic material) located on the magnetic permeability detection surface, the output is not stable when the density of the developer located on the magnetic permeability detection surface changes. . When the developer pressure state changes on the magnetic permeability detection surface as the screw blades rotate and the bulk density of the developer changes, the output changes even if the toner concentration does not change. Detection accuracy decreases.

  Therefore, in the conventional developing device, the toner density sensor is arranged by selecting a position where the developer circulating in the developing container is compressed to some extent and the bulk density is stabilized (Patent Documents 1 and 2).

  Patent Document 1 discloses a developing device in which a developer is transported by screw blades and a first transport path and a second transport path that constitute a circulation path are vertically stacked in a developing container. Here, the toner density sensor is disposed at a position where the developer is pushed up and transferred to the first transport path on the downstream side of the second transport path disposed on the lower side. On the downstream side of the second conveyance path, the developer is clogged up to the ceiling and is in a pressurized state, and the developer gap generated with the rotation of the screw blade is quickly eliminated. For this reason, the bulk density of the developer adjacent to the magnetic permeability detection surface is relatively stable.

  Patent Document 2 discloses a developing device in which a developer is transported by screw blades and a first transport path and a second transport path that constitute a circulation path are arranged horizontally in the developing container. Here, an agitating blade having a reverse conveying direction is arranged in a part of the longitudinal direction of the screw blade to form an intentional retention portion of the developer, and a toner concentration sensor is arranged here. In the developer retaining portion, the developer is clogged up to the ceiling and is in a pressurized state, and the developer gap generated with the rotation of the screw blade is quickly eliminated. For this reason, the bulk density of the developer adjacent to the magnetic permeability detection surface is relatively stable.

JP 2003-287950 A JP 2008-102492 A

  When the toner concentration sensor is disposed as shown in Patent Documents 1 and 2, if the developer becomes old or the fluidity of the developer decreases due to operation in a high temperature and high humidity environment, the toner concentration of the developer is reduced. It became clear that it became impossible to control with high accuracy.

  When the toner density sensor is placed at a position where the developer flow stagnate, the developer gap generated by the rotation of the screw blades, that is, the decrease in bulk density, can be compensated by relying on the developer flow due to the pressure difference. It is done. For this reason, when the flowability of the developer decreases, the generated decrease in the bulk density cannot be filled quickly, and the variation in the bulk density of the developer developer adjacent to the magnetic permeability detection surface increases. The output of the toner density sensor becomes unstable (see (c) of FIG. 10).

  SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device capable of controlling the toner density precisely by suppressing the fluctuation of the bulk density of the developer around the detection position of the toner density sensor even if the developer fluidity is lowered. It is said.

  The developing device of the present invention includes a developer carrying member, a conveyance path that constitutes a part of a circulation path that circulates the developer including toner and carrier along the developer carrying member while stirring the developer in the developing container, A conveyance member that conveys the developer in the conveyance path and a magnetic permeability detection surface are opposed to the envelope surface of the ridge line of the screw blade so that the conveyance speed equal to the longitudinal direction can be obtained by rotating with screw blades And a toner density sensor arranged in such a manner. And as for the said screw blade, the space volume per pitch of the said screw blade is smaller than the said space volume in the upstream about the predetermined range of the conveyance direction containing the said magnetic permeability detection surface.

  In the developing device of the present invention, the developer is transported so as to obtain a constant transport speed along the transport path, while the space volume in one pitch of the screw blades is reduced so that the developer without stagnation can be obtained. A pressurized state is formed. The screw blade conveys the developer while pressing it in the conveying direction at a position opposite to the magnetic permeability detection surface, so that the decrease in bulk density caused by the rotation of the screw blade does not depend on the fluidity of the developer. It will be made up quickly.

  Therefore, even if the developer becomes old or is operated in a high-temperature and high-humidity environment and the fluidity of the developer decreases, fluctuations in the bulk density of the developer around the detection position of the toner density sensor are suppressed. The toner density can be accurately detected and precisely controlled.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a structure of an image formation part. It is a perspective view of a developing device. It is explanatory drawing of the cross-sectional structure along the longitudinal direction of a developing device. It is explanatory drawing of a cross-sectional structure perpendicular | vertical to the longitudinal direction of a developing device. 2 is an explanatory diagram of a configuration of a developing device according to Embodiment 1. FIG. FIG. 10 is an explanatory diagram of a configuration of a developing device according to Embodiment 2. FIG. 10 is an explanatory diagram of a horizontal sectional configuration of a developing device according to Embodiment 3. FIG. 10 is an explanatory diagram of a cross-sectional configuration perpendicular to the longitudinal direction of the developing device of Example 3. FIG. 10 is an explanatory diagram of a developer conveyance state in the developing device of Example 4.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is another implementation in which part or all of the configuration of the embodiment is replaced with the alternative configuration as long as the spatial volume at one pitch of the screw blades in the toner density sensor facing region is smaller than the upstream side. It can also be implemented in the form.

  Therefore, not only the vertical type (FIG. 5) in which the first conveyance path and the second conveyance path are arranged above and below, but also a horizontal developing device (FIG. 9) in which the first conveyance path and the second conveyance path are arranged horizontally. . Such a developing apparatus can be implemented without distinction in a tandem type / 1 drum type, intermediate transfer type / direct transfer type image forming apparatus.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. The image forming apparatus can be used for various purposes such as a printer.

  In addition, about the general matter of the developing device shown by patent document 1, 2, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. FIG. 2 is an explanatory diagram of the configuration of the image forming unit.

  As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full-color printer in which yellow, magenta, cyan, and black image forming portions PY, PM, PC, and PK are arranged along an intermediate transfer belt 51. is there.

  In the image forming unit PY, a yellow toner image is formed on the photosensitive drum 1Y and transferred to the intermediate transfer belt 51. In the image forming unit PM, a magenta toner image is formed on the photosensitive drum 1M, and transferred onto the yellow toner image on the intermediate transfer belt 51 in an overlapping manner. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 1C and 1K, respectively, and transferred onto the intermediate transfer belt 51.

  The four-color toner images transferred to the intermediate transfer belt 51 are conveyed to the secondary transfer portion T2 and secondarily transferred to the recording material P. The recording material P taken out from the recording material cassette 11 by the pickup roller 12 is separated one by one by the separation roller 13 and fed to the registration roller 14. The registration roller 14 sends the recording material to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 51. The recording material P to which the toner image has been transferred is heated and pressurized by the fixing device 7 to fix the toner image on the surface, and then is discharged outside the machine body.

  The image forming units PY, PM, PC, and PK are substantially the same except that the toner colors used in the developing devices 4Y, 4M, 4C, and 4K are different. Hereinafter, the image forming unit PY will be described, and the image forming units PM, PC, and PK will be described by replacing Y at the end of the reference numerals attached to the constituent members of the image forming unit PY with M, C, and K. To do.

  As shown in FIG. 2, the image forming unit PY includes a corona charger 2Y, an exposure device 3, a developing device 4Y, a primary transfer roller 5Y, and a drum cleaning device 6Y around the photosensitive drum 1Y.

  A photosensitive drum 1Y, which is an example of an image carrier, has a photosensitive layer having a negative polarity on the outer peripheral surface of an aluminum cylinder, and rotates in the direction of arrow R1 at a predetermined process speed. The corona charger 2Y charges the surface of the photosensitive drum 1Y to a uniform negative potential. The exposure device 3Y scans the laser beam with a rotating mirror and writes an electrostatic image of the image on the surface of the charged photosensitive drum 1Y. The developing device 4Y develops an electrostatic image using a developer containing toner and a carrier to form a toner image on the photosensitive drum 1Y.

  The primary transfer roller 5Y presses the inner surface of the intermediate transfer belt 51 to form a primary transfer portion T1 between the photosensitive drum 1Y and the intermediate transfer belt 51. By applying a positive DC voltage to the primary transfer roller 5Y, the negative toner image carried on the photosensitive drum 1Y is primarily transferred to the intermediate transfer belt 51. The drum cleaning device 6Y collects transfer residual toner remaining on the photosensitive drum 1Y by escaping from the transfer to the recording material P.

  The tandem type image forming apparatus has a disadvantage in terms of space and cost as compared with the one-drum type that sequentially develops each color toner image on one photosensitive drum, but can easily increase the image forming speed. There is a merit. For this reason, in recent years, there is a high need for speeding up full-color image forming apparatuses.

<Developing device>
FIG. 3 is a perspective view of the developing device. FIG. 4 is an explanatory diagram of a cross-sectional configuration along the longitudinal direction of the developing device. FIG. 5 is an explanatory diagram of a cross-sectional configuration perpendicular to the longitudinal direction of the developing device.

  As shown in FIG. 3, the developing device 4Y develops an electrostatic image on the photosensitive drum (1Y: FIG. 2) by supporting a developer containing toner and a carrier on a developing sleeve 44 which is an example of a developer carrier. . The developing device 4Y uses a two-component developer in which nonmagnetic toner particles (toner) and magnetic carrier particles (carrier) are mixed as a developer. When a two-component developer is used, the toner does not need to contain a magnetic material, so that the color tone is good in color image formation.

  As illustrated in FIG. 4, the developing container 41 includes a developing chamber 41 a that is an example of a first transport path and an agitation chamber 41 b that is an example of a second transport path arranged vertically. The agitating chamber 41b communicates with the developing chamber 41a at both ends in parallel with the developing chamber 41a. The developing screw 42, which is an example of a first conveying member, supplies the developer in the developing chamber 41a to the developing sleeve 44 while conveying the developer. The agitation screw 43, which is an example of a second conveyance member, conveys the developer in the agitation chamber 41b in the direction opposite to the development screw 42 and circulates the developer between the development chamber 41a.

  Delivery openings 41d and 41e that allow the developer to pass in the vertical direction are provided at both ends in the longitudinal direction of the partition wall 41c. The developing screw 42 and the agitating screw 43 circulate the developing container 41 while agitating and conveying the developer. A toner concentration sensor 47 for detecting the toner concentration of the developer conveyed through the stirring chamber 41b is provided in the vicinity of the transfer portion 41e that transfers the developer from the stirring chamber 41b to the developing chamber 41a.

  As shown in FIG. 5, the developing sleeve 44 is rotatably disposed at a position facing the photosensitive drum 1Y in the developing container 41 containing the developer. A layer thickness regulating blade 46 is disposed upstream in the rotation direction of the developing area where the developing sleeve 44 faces the photosensitive drum 1, and regulates the thickness of the developer carried on the developing sleeve 44.

  The developing container 41 is partitioned into a developing chamber 41a and a stirring chamber 41b by a partition wall 41c provided horizontally, and a stirring chamber 41b is disposed below the developing chamber 41a. A developing screw 42 is rotatably provided in the developing chamber 41a, and a stirring screw 43 is rotatably provided in the stirring chamber 41b. The toner concentration sensor 47 detects the magnetic permeability of the developer conveyed through the stirring chamber 41 b at a position facing the ridge line of the screw blade of the stirring screw 43.

  Inside the developing sleeve 44, as shown in FIG. 9, a plurality of magnetic poles N1, S1, N3, N2, and S2 are arranged on the surface, and a magnet 45 supported non-rotatably is arranged. In the developer, the magnetic carrier is restrained by the magnetic flux formed between the magnetic poles of the magnet 45 and is carried on the surface of the developing sleeve 44, and the negatively charged toner is electrostatically charged on the surface of the positively charged carrier. To form a magnetic brush.

<Toner supply control>
As shown in FIG. 2, when the toner is consumed as the image is formed, the control unit 30 takes out the replenishing toner from the hopper 20Y and supplies it to the developing device 4Y according to the amount of toner consumed in the development. The control unit 30 performs so-called video count type toner replenishment control, calculates the amount of toner consumed for each image based on the image data used for exposure, and forms the next image. Replenishment toner that is calculated only at times is supplied to the developing device 4Y.

  However, with the video count method alone, errors in the toner replenishment amount may accumulate, and the toner weight ratio (toner concentration) in the developer may deviate from the appropriate range. For this reason, the toner density sensor 47 is provided in the developing device 4Y to actually measure the toner density. If the toner density falls within the proper range, the toner replenishment amount is increased by the video count method. If the toner density exceeds the proper range, the video count method is used. The amount of toner supply has been reduced.

  In addition, the control unit 30 controls the exposure device 3Y to form a predetermined electrostatic image on the photosensitive drum 1Y every time a predetermined number of images are formed, and develops the developing device 4Y to develop a color patch for measuring the toner development amount. Form. Then, the control unit 30 changes the induction target value of the toner density using the toner density sensor 47 so that the toner development amount becomes a predetermined value based on the measurement result of the color patch by the reflected light sensor 31. .

  The toner density sensor 47 detects the toner density of the developer in the developing device 4Y, and the control unit 30 controls the hopper 20Y so that the toner density in the developing device 4Y measured by the toner density sensor 47 becomes a desired toner density. To control.

  As a developer toner concentration detection method, several methods have been proposed so far, and a magnetic detection method has been widely used. In the magnetic detection system, a magnetic sensor is provided in the developing device, and the toner concentration of the developer is detected by detecting a change in magnetic permeability due to a difference in the toner concentration of the developer near the detection surface of the magnetic sensor. Since the magnetic sensor changes its output in response to the difference in magnetic flux density of the magnetic material, it can detect the density of the magnetic material on the detection surface of the magnetic sensor.

  Since the toner in the developer is non-magnetic but the carrier is a magnetic material, the magnetic sensor generates an output corresponding to the probability of the carrier in the developer. As a result, the toner density can be detected relatively from the output of the magnetic sensor.

  However, since the magnetic detection method directly detects the amount of carrier, not the amount of toner, not only when the toner concentration in the developer changes, but also when the bulk density of the developer changes. In addition, the output of the magnetic sensor changes. Therefore, in the vicinity of the detection surface of the magnetic sensor, it is necessary to compress the developer to some extent to reduce the change in the bulk density of the developer.

  For this reason, in Patent Document 1 (Japanese Patent Laid-Open No. 2003-287950), a toner sensor is detected by providing a magnetic sensor in a place where the developer is compressed to some extent as in the developer delivery section 41e of FIG. It was.

  Further, in Patent Document 2 (Japanese Patent Application Laid-Open No. 2008-102492), a short reverse spring is provided on the screw near the detection surface of the magnetic sensor so that the developer is pressed against the detection surface of the magnetic sensor.

  However, in Patent Document 1 in which a magnetic sensor is provided at an intermediate position between the developing screw 42 and the agitating screw 43 as in the developer delivery portion 41e shown in FIG. 4, there are cases where restrictions are placed on the arrangement of the magnetic sensor. Further, when the toner in the developing device 4Y is consumed and the developer surface becomes low, the developer delivery unit 41e weakens the developer compression and reduces the bulk density, thereby detecting the toner density. May fall off.

  Further, in Patent Document 2 in which a short ridge in the reverse direction is provided in the vicinity of the detection surface of the magnetic sensor, the developer stagnates in the portion where the short honey is provided. Agent clogging and developer aggregation are likely to occur. As a result, developer agitation failure or conveyance failure may occur, and image density unevenness or density fluctuation may occur.

  In the following embodiments, the detection surface of the toner concentration sensor is disposed at a position where the ridge line of the screw blade passes at a close distance, thereby forming a pressure state in the transport direction on the detection surface of the toner concentration sensor. By keeping the screw blades at a constant spiral pitch and maintaining a constant conveying speed for the developer, the space volume at one pitch of the screw blades is reduced to realize a developer pressure state without stagnation. Yes. For this reason, the decrease in the bulk density generated so as to follow the movement of the screw blades is quickly compensated in the transport direction without depending on the fluidity of the developer.

<Example 1>
FIG. 6 is an explanatory diagram of the configuration of the developing device according to the first embodiment. FIG. 6 is an enlarged view of the vicinity of the toner density sensor in the longitudinal section of FIG. In Example 1, the number of screws in the stirring screw near the detection surface of the toner concentration sensor is larger than in other portions.

  As shown in FIG. 4, the agitation chamber 41b, which is an example of a conveyance path, constitutes a part of a circulation path in the developing container that circulates the developer containing toner and carrier while stirring. The agitation screw 43, which is an example of a conveyance member, conveys the developer in the agitation chamber 41b so as to obtain a conveyance speed equal to the longitudinal direction by rotating with screw blades. However, the actual transport speed is not always strictly constant in the longitudinal direction because it is affected by the state of the developer, the branching of the circulation path, and the merge.

  As shown in FIG. 5, the toner concentration sensor 47 is disposed in the developing container 41 with the magnetic permeability detection surface facing the envelope surface of the ridge line of the screw blade that accompanies rotation.

  As shown in FIG. 6, in Example 1, the screw blades of the stirring screw 43 have a space volume per pitch of the screw blades per pitch on the upstream side in a predetermined range corresponding to the magnetic permeability detection surface. It is smaller than the space volume. Specifically, another screw blade formed at the same spiral pitch is arranged at an interval of the screw blade formed at a constant spiral pitch. Further, the toner concentration is at a position where the developer is lifted on the downstream side in the longitudinal direction of the stirring screw 43 and transferred to the developing chamber 41a which is an example of another conveying path in which the developing screw 42 which is an example of another conveying member is disposed. A sensor 47 is arranged.

  In Example 1, the rotation speed of the developing screw 42 and the stirring screw 43 is 370 rpm, the screw diameter is φ27.6 mm, and the inner diameter of the stirring chamber 41b is φ30 mm. One pitch of the screw blades is 30 mm, the thickness of the screw blade is 0.6 mm at the tip portion, 6.2 mm at the root portion, and the screw shaft diameter is φ8 mm.

  In the first exemplary embodiment, a toner concentration sensor 47 is provided in the stirring chamber 41b of the transfer portion 41e that lifts and transfers the developer from the stirring chamber 41b to the developing chamber 41a. In the arrangement region of the toner density sensor 47, two screw blades having the same amount of advance (lead) per rotation of the stirring screw 43 are provided in parallel. By using two screw blades for the agitation screw 43, the space volume of the agitation chamber 41b in the vicinity of the toner concentration sensor 47 is set to about 50% without reducing the developer conveyance speed. By setting the space volume in the vicinity of the toner density sensor 47 to 50%, the developer transported using a large volume up to the vicinity of the toner density sensor 47 is 50 in the transport direction at the same transport speed in the vicinity of the toner density sensor 47. % Volume. As a result, the bulk density of the developer located on the detection surface of the toner density sensor 47 can be increased.

  In Example 1, when the ridge line of the screw blade of the stirring screw 43 passes the detection surface of the toner density sensor 47, the output value of the toner density sensor 47 varies (see FIG. 10B). However, at other screw blade intervals, the developer is compressed in the transport direction and the output value of the toner density sensor 47 is stabilized, so that the measurement accuracy of the toner density can be increased.

  According to the first embodiment, in the region where the screw blades of the stirring screw 43 are formed in two strips, the developer compression amount is increased without decreasing the speed at which the developer is conveyed, regardless of the location in the developer circulation path. be able to. For this reason, it becomes possible to expand the degree of freedom of the place where the toner density sensor 47 is installed, and there is a possibility that the developing device 4Y can be further downsized.

  Further, even when the developer is disposed in the vicinity of the delivery section of the developer, since the compression speed in the developer transport direction can be increased in the area where the screw blades are formed in two strips, the toner is consumed and the developer is reduced. Even in this case, the toner density can be measured more accurately.

  In addition, since the toner concentration can be accurately measured regardless of the amount of the developer in the developing device 4Y, the allowable range of temperature and humidity in which the toner concentration can be kept optimal is widened. Development defects such as density unevenness caused by changes in the amount and fluidity of the developer in the developing device 4Y can be reduced.

<Example 2>
FIG. 7 is an explanatory diagram of a configuration of the developing device according to the second embodiment. FIG. 7 is an enlarged view of the vicinity of the toner density sensor in the longitudinal section of FIG. As shown in FIG. 7, since the basic configuration of the developing device 4Y is the same as that of the first embodiment, the same components as those of the first embodiment are denoted by the same reference numerals as those in FIG.

  In the second embodiment, the screw shaft diameter of the screw blade is larger in the predetermined range where the toner concentration sensor 47 is disposed than on the upstream side of the predetermined range. By increasing the shaft diameter of the stirring screw 43 in the vicinity of the detection surface of the toner concentration sensor as compared with the front and rear portions, the space volume occupying one pitch of the screw blades is set small. The feature of the second embodiment is that the shaft diameter in the vicinity of the toner density sensor 47 of the stirring screw 43 is thicker than the surrounding portion.

  Specifically, the shaft diameter of the stirring screw 43 is 8 mm, whereas the shaft diameter in the vicinity of the toner concentration sensor 47 is 18 mm. As a result, the space volume can be reduced by about 35%, and the developer conveyed using a large volume to the vicinity of the toner density sensor 47 is compressed to 65% at the same conveyance speed in the vicinity of the toner density sensor 47. As a result, the bulk density of the developer can be increased.

  In the second embodiment, it is possible to reduce the space volume occupied by one pitch of the screw blades while minimizing the shortening of the toner density detection time without changing the developer conveyance speed. Therefore, it is possible to increase the bulk density of the developer and stabilize the output of the toner concentration sensor 47 while keeping the amount of the staying developer to a minimum.

<Comparative example>
(1) As a method for reducing the space volume occupied by one pitch of the stirring screw 43, a method of providing a paddle between the pitches of the stirring screw 43 is also conceivable. However, when the paddle is provided, as in Patent Document 2, the bulk density of the developer changes before and after the paddle, so that the output value of the toner density sensor 47 varies due to the paddle, and the measurement accuracy of the toner density is increased. Not good.

  (2) As another method of reducing the space volume occupied by one pitch of the stirring screw 43, a method of reducing the helical pitch of the screw blades of the stirring screw 43 in the vicinity of the toner concentration sensor 47 is also conceivable. However, if the pitch of the stirring screw 43 is reduced, the developer conveying speed is also reduced. Therefore, the developer is likely to stay immediately after the pitch of the stirring screw 43 is reduced. As a result, as in Patent Document 2, the possibility of developer deterioration and clogging increases.

  (3) As another method of reducing the space volume occupied by one pitch of the stirring screw 43, there is a method of increasing the thickness of the spiral auger of the stirring screw 43. Certainly, according to the method of increasing the thickness of the spiral auger of the stirring screw 43, it is possible to compress the developer without reducing the conveying speed. However, since the stirring screw 43 rotates, the time to face the spiral auger becomes longer as the thickness of the spiral auger of the stirring screw 43 is increased with respect to the detection surface of the toner concentration sensor 47. And while the spiral auger of the stirring screw 43 is facing the detection surface of the toner concentration sensor 47, the accurate toner concentration cannot be measured, so the detection time for detecting the toner concentration is shortened. . As a result, the toner density detection accuracy deteriorates.

<Example 3>
FIG. 8 is an explanatory diagram of a horizontal sectional configuration of the developing device according to the third embodiment. FIG. 9 is an explanatory diagram of a cross-sectional configuration perpendicular to the longitudinal direction of the developing device of Example 3.

  In the first and second embodiments, the developing chamber 41a in which the developing screw 42 is arranged and the stirring chamber 41b in which the stirring screw 43 is arranged are arranged vertically, but the arrangement is not limited to the upper and lower arrangement.

  As shown in FIG. 9 with reference to FIG. 8, the developing device 4Y of Example 3 includes a developing container 41 in which a developing chamber 41a and an agitating chamber 41b are horizontally arranged to circulate the developer. The developing container 41 is partitioned into a developing chamber 41a and a stirring chamber 41b by a partition wall 41c extending in the vertical direction. A developing screw 42 is disposed in the developing chamber 41a, and a stirring screw 43 is disposed in the stirring chamber 41b. At both ends in the longitudinal direction of the partition wall 41c, delivery portions 41d and 41e that allow the developer to pass horizontally between the developing chamber 41a and the stirring chamber 41b are provided.

  The developing screw 42 and the stirring screw 43 convey the developer while stirring and circulate the inside of the developing container 41 horizontally. A developing sleeve 44 is rotatably disposed at a position of the developing container 41 facing the photosensitive drum (1: FIG. 1).

  In the developing device 4Y of the third embodiment, as in the first embodiment, the stirring screw 43 in the vicinity of the detection surface of the toner density sensor 47 can have a larger number of screw blades than the other portions. As a result, the bulk density of the developer located on the detection surface of the toner density sensor 47 can be increased, and the output of the toner density sensor 47 can be stabilized.

  Also in the developing device 4Y of the third embodiment, as in the second embodiment, the stirring screw 43 in the vicinity of the detection surface of the toner concentration sensor 47 can have a larger screw shaft diameter than other portions. As a result, the bulk density of the developer located on the detection surface of the toner density sensor 47 can be increased, and the output of the toner density sensor 47 can be stabilized.

<Example 4>
FIG. 10 is an explanatory diagram of a developer transport state in the developing device according to the fourth embodiment. In the developing device of Example 4, the same configuration as that of Example 1 is arranged at an intermediate position in the longitudinal direction of the stirring screw. 10, (a) is a cross section in the longitudinal direction of the screw blade, and (b) is an explanatory view of the output of the toner density sensor.

  As shown in FIG. 10A, in the fourth embodiment, a toner concentration sensor 47 is disposed at an intermediate position in the longitudinal direction of a stirring screw 43 that is an example of a conveying member. The space volume per pitch of the screw blades is equal between the upstream side and the downstream side of the predetermined range with two screw blades. A toner concentration sensor 47 is installed in the middle of the stirring chamber 41b, and two screw blades of the stirring screw 43 are disposed at a position opposite to the toner concentration sensor 47 so that the space volume per pitch is 50% or less.

  As shown in FIG. 10B, in Example 4A, the output of the toner density sensor 47 is more stable than in the case where the screw blades are not doubled (B). For this reason, the detection accuracy of the toner density is increased, and the toner density can be precisely controlled.

  In the developing device of Example 4, there is no need to provide a portion for slowing the developer conveyance speed in the stirring chamber 41b in order to accurately measure the toner concentration as in Patent Document 2. For this reason, it is possible to suppress problems caused by the retention of the developer.

<Example 5>
As color image forming apparatuses, two types of image forming apparatuses are mainly known. The first is a one-drum type in which a developing device for a plurality of colors is provided around one photosensitive member, and toner of each color is supplied from each developing device to an electrostatic latent image on the photosensitive member to form a composite toner image. The color image forming apparatus. The other is that a plurality of photoconductors are arranged adjacent to each other, and each photoconductor has a developing device, each of which forms a single color toner image and forms a composite toner image on a recording material or an intermediate transfer body. A tandem type color image forming apparatus is formed.

  In Examples 1 to 4, the embodiments in the developing device 4Y mounted in the tandem type color image forming apparatus have been described. However, the developing device of the present invention can also be implemented by a one-drum type color image forming apparatus.

1Y, 1M, 1C, 1K Photosensitive drums 4Y, 4M, 4C, 4K Developing devices 5Y, 5M, 5C, 5K Primary transfer rollers 20Y, 20M, 20C, 20K Hopper 41 Developing container 41a Developing chamber (first transport path)
41b Stir chamber (second transport path)
42 Development screw (1st conveying material)
43 Stirring screw (second transporter)
44 Development sleeve (developer carrier)
45 Regulating blade (Developer regulating member)
47 Toner concentration sensor 48 Magnet sheet (magnetic force generating member)

Claims (5)

A developer carrier;
A conveyance path that constitutes a part of a circulation path that circulates the developer including toner and carrier along the developer carrier while stirring in a developer container;
A transport member that transports the developer in the transport path so as to obtain a transport speed equal to the longitudinal direction by rotating with screw blades;
A toner concentration sensor arranged with a magnetic permeability detecting surface facing the envelope surface of the ridgeline of the screw blade,
The developing device according to claim 1, wherein a space volume per pitch of the screw blades is smaller than a space volume upstream of the screw blades in a predetermined range in the transport direction including the magnetic permeability detection surface.   2. The developing device according to claim 1, wherein in the predetermined range, another screw blade formed at the same spiral pitch is arranged at an interval of the screw blade formed at a constant spiral pitch. .   3. The developing device according to claim 1, wherein the screw shaft diameter of the screw blade is larger than the upstream side in the predetermined range. The predetermined range is set at an intermediate position in the longitudinal direction of the conveying member;
4. The developing device according to claim 1, wherein a space volume per pitch of the screw blades is equal between the upstream side and the downstream side of the predetermined range. 5.   4. The predetermined range is set at a position where the developer is lifted on the downstream side in the longitudinal direction of the conveying member and transferred to another conveying path where another conveying member is arranged. The developing device according to any one of the above.

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