JP2020056947A - Developing device and image forming apparatus including the same - Google Patents

Abstract

To provide a developing device that can prevent the developing device from being increased in size in a direction orthogonal to a rotary shaft of a stirring and conveying member, while preventing an increase in stress to a developer, and an image forming apparatus including the same.SOLUTION: A first spiral 43 has a rotary shaft 43b that is rotatably supported in a developer container 22, a first spiral blade 43a that is formed on an outer peripheral surface of the rotary shaft 43b and conveys a developer in an axial direction by the rotation of the rotary shaft 43b, and a second spiral blade 43c that is formed on an outer peripheral surface of the rotary shaft 43b to overlap a formation area of the first spiral blade 43 in the axial direction, is wound opposite to the first spiral blade 43a, and has a radial height R2 smaller than that of the first spiral blade 43a. A toner concentration sensor 51 is arranged such that a detection surface 51a is opposite to an intersection 47 of the first spiral blade 43a and second spiral blade 43c at a position immediately below the rotary shaft 43b.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a developing device having a stirring and conveying member for stirring and conveying a developer and a toner density sensor for detecting toner density, and an image forming apparatus having the same.

  In an image forming apparatus, a latent image formed on an image carrier such as a photoreceptor is developed by a developing device and visualized as a toner image. As one of such developing devices, a two-component developing method using a two-component developer is adopted. In this type of developing device, a developer including a carrier and a toner is accommodated in a developing container, and a developing roller for supplying the developer to the image carrier is arranged, and the developer inside the developing container is stirred. A stirring and conveying member for conveying and supplying the developing roller is provided.

  In this developing device, toner is consumed by the developing operation. For this reason, in order to replenish the toner consumed by the development, it is necessary to measure the toner concentration in the developer using a toner concentration sensor disposed in the developing container.

  Here, in order to accurately measure the toner density, it is necessary to suppress the developer from staying on the detection surface of the toner density sensor. Therefore, a developing device in which a scraper for cleaning the detection surface of the toner concentration sensor is provided on the stirring and conveying member, and a developing device in which the toner concentration sensor is disposed obliquely downward with respect to the rotation axis of the stirring and conveying member, are known. I have.

  In a developing device equipped with a scraper on the stirring / conveying member, the scraper slides on the detection surface of the toner density sensor to clean the rotation when the stirring / conveying member rotates, thereby suppressing the accumulation of developer on the detection surface of the toner concentration sensor. can do. Further, in a developing device in which the toner concentration sensor is disposed obliquely downward with respect to the rotation axis of the stirring / conveying member, the detection surface of the toner concentration sensor is disposed inclined with respect to the horizontal plane. Stagnation of the developer can be suppressed.

  A developing device in which a scraper is provided on a stirring and conveying member is disclosed in, for example, Patent Document 1. A developing device in which a toner concentration sensor is disposed obliquely downward with respect to the rotation axis of the stirring and conveying member is disclosed in, for example, Patent Document 1. 2 is disclosed.

JP 2014-142677 A JP 2018-66860 A

  However, in a developing device in which a scraper is provided on the stirring / conveying member, there is a problem that the toner is rubbed against the detection surface by the scraper, so that stress on the developer is increased. Further, in a developing device in which the toner concentration sensor is arranged obliquely downward with respect to the rotation axis of the stirring and conveying member, there is a problem that the size of the development device increases in a direction perpendicular to the rotation axis.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to reduce a stress on a developer while suppressing a stress on a developer in a direction orthogonal to a rotation axis of a stirring and conveying member. An object of the present invention is to provide a developing device capable of suppressing an increase in the size of the developing device and an image forming apparatus including the developing device.

  In order to achieve the above object, a developing device according to a first configuration of the present invention includes a developing container that stores a developer containing a toner and a developing device that is provided in the developing container and carries the developer in the developing container on a surface. The image forming apparatus includes a developer carrier, a stirring and conveying member that stirs and conveys the developer in the developing container, and a toner concentration sensor having a detection surface for detecting a toner concentration in the developing container. The stirring / transporting member includes a rotating shaft rotatably supported in the developing container, a first spiral blade formed on the outer peripheral surface of the rotating shaft, and transporting the developer in the axial direction by the rotation of the rotating shaft. A second spiral blade formed on the outer peripheral surface of the rotating shaft so as to overlap the formation region of the first spiral blade, having a reverse winding with the first spiral blade, and having a smaller radial height than the first spiral blade. Have. The first spiral blade intersects with the second spiral blade at at least one place during one rotation of the rotation axis. The toner density sensor is disposed so that the detection surface is located immediately below the rotation axis and faces the intersection of the first spiral blade and the second spiral blade.

  According to the developing device of the first configuration of the present invention, the toner density sensor is disposed such that the detection surface is located immediately below the rotation axis. Thus, unlike the case where the toner concentration sensor is disposed obliquely downward with respect to the rotation axis of the stirring and conveying member, it is possible to suppress the developing device from increasing in the direction perpendicular to the rotation axis.

  Further, in the case where a stirring and conveying member in which the second spiral blade is formed so as to overlap the formation region of the first spiral blade in the axial direction is used, the rotation of the stirring and conveying member causes the intersection of the rotation direction of the rotating shaft with the rotation of the rotating shaft. The developer collects in a region near the downstream side. For this reason, as described above, by disposing the toner concentration sensor such that the detection surface faces the intersection of the first spiral blade and the second spiral blade, the first spiral blade is rotated by rotating the stirring and conveying member. When the intersection with the second spiral blade passes through the detection surface, the developer on the detection surface can be caused to flow by the pressure of the developer near the downstream side of the intersection. Accordingly, the developer can be prevented from staying on the detection surface, so that the accuracy of detecting the toner density by the toner density sensor can be improved. Further, since it is not necessary to provide a scraper for suppressing the developer from staying on the detection surface, it is possible to suppress an increase in stress on the developer.

FIG. 1 is a schematic diagram illustrating an overall configuration of an image forming apparatus 1 on which developing devices 2a to 2d according to a first embodiment of the present invention are mounted. Side sectional view showing the configuration of the developing device 2a according to the first embodiment of the present invention. Sectional plan view showing a stirring unit of the developing device 2a according to the first embodiment of the present invention. A partially enlarged view of a first spiral 43 which is a stirring and conveying member according to the first embodiment of the present invention as viewed from above. A partially enlarged view of a first spiral 43 which is a stirring and conveying member according to the first embodiment of the present invention as viewed from above. FIG. 10 is a cross-sectional view taken along a line 100-100 in FIG. 5, showing a structure around a first spiral 43. Partial enlarged view of the periphery of the large diameter portion 43d of the first spiral 43 according to the second embodiment of the present invention viewed from above. FIG. 8 is a cross-sectional view taken along the line 110-110 of FIG. 7, showing a structure around a first spiral 43; Partial enlarged view of the periphery of the large-diameter shaft portion 43e of the first spiral 43 of the third embodiment of the present invention as viewed from above. Partial enlarged view of the periphery of the large-diameter shaft portion 43e of the first spiral 43 of the modification of the third embodiment of the present invention, as viewed from above.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(1st Embodiment)
FIG. 1 is a schematic sectional view of an image forming apparatus 1 on which developing devices 2a to 2d according to a first embodiment of the present invention are mounted. Here, a tandem type color printer is shown. Photosensitive drums 11a, 11b, 11c and 11d each carrying a visible image (toner image) of each color are provided in the image forming apparatus 1, and each of the photosensitive drums 11a, 11b, 11c and 11d is charged with each of the steps of charging, exposure, development and transfer. , Magenta, yellow and black images are sequentially formed. Further, an intermediate transfer belt 17 that rotates clockwise in FIG. 1 is provided adjacent to each image forming unit including the photosensitive drums 11a to 11d.

  When image data is input from a host device such as a personal computer, first, the chargers 13a to 13d uniformly charge the surfaces of the photosensitive drums 11a to 11d. Next, the exposure device 12 irradiates light according to the image data, and forms an electrostatic latent image on each of the photosensitive drums 11a to 11d according to the image data. The developing devices 2a to 2d are filled with a predetermined amount of a two-component developer (hereinafter, also simply referred to as a developer) containing toners of cyan, magenta, yellow, and black by a toner container (not shown). The toner in the developer is supplied onto the photosensitive drums 11a to 11d by the developing devices 2a to 2d, and electrostatically adheres. As a result, a toner image corresponding to the electrostatic latent image formed by the exposure from the exposure device 12 is formed.

  Then, an electric field is applied at a predetermined transfer voltage between the primary transfer rollers 26a to 26d and the photoconductor drums 11a to 11d by the primary transfer rollers 26a to 26d, and cyan, magenta, yellow, and yellow on the photoconductor drums 11a to 11d are applied. The black toner image is primarily transferred onto the intermediate transfer belt 17. Toner and the like remaining on the surfaces of the photosensitive drums 11a to 11d after the primary transfer are removed by the cleaning devices 14a to 14d.

  The transfer paper S to which the toner image is transferred is housed in a paper cassette 32 arranged at a lower part in the image forming apparatus 1, and the transfer paper S is supplied to a predetermined position via a paper feed roller 33a and a registration roller pair 33b. At a timing, the sheet is conveyed to a nip portion (secondary transfer nip portion) of the intermediate transfer belt 17 with the secondary transfer roller 34 provided adjacent to the intermediate transfer belt 17. The transfer paper S on which the toner image has been secondarily transferred is conveyed to the fixing unit 18. Toner and the like remaining on the surface of the intermediate transfer belt 17 after the secondary transfer are removed by the belt cleaning device 31.

  The transfer sheet S conveyed to the fixing unit 18 is heated and pressed to fix the toner image on the surface of the transfer sheet S, thereby forming a predetermined full-color image. The transfer sheet S on which the full-color image has been formed is discharged to the discharge tray 37 by the discharge roller pair 19 as it is (or after being distributed to the reversing conveyance path 40 by the branching section 39 and forming images on both sides).

  FIG. 2 is a side sectional view showing a configuration of the developing device 2a according to the first embodiment of the present invention. In the following description, the configuration and operation of the developing device 2a corresponding to the photosensitive drum 11a shown in FIG. 1 will be described. However, the configuration and operation of the developing devices 2b to 2d are the same as those of the developing device 2a. Is omitted.

  As shown in FIG. 2, the developing device 2a includes a developing roller 20, a magnetic roller (developer carrier) 21, a regulating blade 24, a stirring member 42, a developing container 22, and the like.

  The developing container 22 forms an outer shell of the developing device 2a, and is partitioned into a first transfer chamber 22c and a second transfer chamber 22d at a lower portion thereof by a partition portion 22b. In the first transfer chamber 22c and the second transfer chamber 22d, a developer including a carrier and a toner is stored. The developing container 22 rotatably holds the stirring member 42, the magnetic roller 21, and the developing roller 20. Further, the developing container 22 has an opening 22a for exposing the developing roller 20 toward the photosensitive drum 11a.

  The developing roller 20 faces the photoconductor drum 11a, and is disposed on the right side of the photoconductor drum 11a at a predetermined interval. The developing roller 20 forms a developing area D for supplying toner to the photosensitive drum 11a at a position facing the photosensitive drum 11a. The magnetic roller 21 is opposed to the developing roller 20 at a predetermined interval, and is disposed diagonally below and to the right of the developing roller 20. The magnetic roller 21 supplies toner to the developing roller 20 at a position facing the developing roller 20. The stirring member 42 is disposed substantially below the magnetic roller 21. Further, the regulating blade 24 is fixedly held on the developing container 22 at an obliquely lower left side of the magnetic roller 21.

  The stirring member 42 includes a first spiral 43 and a second spiral 44 for stirring and transporting the developer. The second spiral 44 is provided below the magnetic roller 21 in the second transfer chamber 22d, and the first spiral 43 is provided in the first transfer chamber 22c adjacent to the right of the second spiral 44. The first spiral 43 is an example of the “stirring / conveying member” of the present invention.

  The first and second spirals 43 and 44 stir the developer to charge the toner in the developer to a predetermined level. As a result, the toner is held on the carrier. Further, communicating portions (an upstream communicating portion 22e described later and a downstream communicating portion 22e and a downstream portion) are provided at both ends in a longitudinal direction (a direction perpendicular to the paper surface of FIG. 2) of the partition portion 22b that partitions the first transfer chamber 22c and the second transfer chamber 22d. When the first spiral 43 rotates, the charged developer is transported to the second spiral 44 from one of the communication portions provided in the partition 22b, and the developer is transferred to the first transport chamber. It circulates through 22c and the second transfer chamber 22d. Then, the developer is supplied from the second spiral 44 to the magnetic roller 21.

  The magnetic roller 21 includes a roller shaft 21a, a magnetic pole member M, and a non-magnetic sleeve 21b made of a non-magnetic material. The magnetic roller 21 carries the developer supplied by the stirring member 42, and transfers only the toner from the carried developer to the developing roller 20. Supply. The magnetic pole member M is formed by alternately arranging a plurality of magnets having different polarities at the outer peripheral portion formed in a fan-shaped cross section, and is fixed to the roller shaft 21a by bonding or the like. The roller shaft 21a is non-rotatably supported by the developing container 22 with a predetermined interval provided between the magnetic pole member M and the non-magnetic sleeve 21b within the non-magnetic sleeve 21b. The nonmagnetic sleeve 21b is rotated in the same direction as the developing roller 20 (clockwise direction in FIG. 2) by a drive mechanism including a motor and gears (not shown), and a bias 56 in which an AC voltage 56b is superimposed on a DC voltage 56a is applied. Is done. On the surface of the non-magnetic sleeve 21b, the charged developer is carried by forming a magnetic brush by the magnetic force of the magnetic pole member M, and the magnetic brush is adjusted to a predetermined height by the regulating blade 24.

  When the non-magnetic sleeve 21b rotates, the magnetic brush is carried and carried on the surface of the non-magnetic sleeve 21b by the magnetic pole member M. When the magnetic brush contacts the developing roller 20, only the toner of the magnetic brush is applied to the non-magnetic sleeve 21b. The toner is supplied to the developing roller 20 according to the bias 56.

  The developing roller 20 includes a fixed shaft 20a, a magnetic pole member 20b, and a cylindrical developing sleeve 20c made of a nonmagnetic metal material.

  The fixed shaft 20a is non-rotatably supported by the developing container 22. On the fixed shaft 20a, a developing sleeve 20c is rotatably held, and a magnetic pole member 20b made of a magnet is fixed at a position facing the magnetic roller 21 with a predetermined interval from the developing sleeve 20c, and is fixed by bonding or the like. You. The developing sleeve 20c is rotated in a direction indicated by an arrow in FIG. 2 (clockwise) by a drive mechanism including a motor and gears (not shown). Further, a developing bias 55 in which an AC voltage 55b is superimposed on a DC voltage 55a is applied to the developing sleeve 20c.

  When the developing sleeve 20c to which the developing bias 55 is applied rotates clockwise in FIG. 2, the developing sleeve 20c is held on the surface of the developing sleeve 20c by the potential difference between the developing bias potential and the potential of the exposed portion of the photosensitive drum 11a in the developing area D. The discharged toner flies to the photosensitive drum 11a. The flying toner sequentially adheres to the exposed portion on the photosensitive drum 11a rotating in the direction of arrow A (counterclockwise), and the electrostatic latent image on the photosensitive drum 11a is developed.

  Next, the stirring section of the developing device 2a will be described in detail with reference to FIG. FIG. 3 is a plan cross-sectional view (a cross-sectional view taken along the line XX ′ in FIG. 2) illustrating the stirring unit of the developing device 2a.

  As described above, the first transfer chamber 22c, the second transfer chamber 22d, and the partition 22b are formed in the developing container 22, and an upstream communication part (communication part) 22e and a downstream part are formed. A communication portion (communication portion) 22f, a developer supply port (toner supply port) 22g, a developer discharge port 22h, an upstream side wall 22i, and a downstream side wall 22j are formed. In the first transfer chamber 22c, the left side in FIG. 3 is the upstream side and the right side in FIG. 3 is the downstream side. In the second transfer chamber 22d, the right side in FIG. 3 is the upstream side, and the left side in FIG. And Therefore, the communication part and the wall part are called the upstream side and the downstream side with respect to the second transfer chamber 22d.

  The partition 22b extends in the longitudinal direction of the developing container 22, and partitions the first transfer chamber 22c and the second transfer chamber 22d in parallel. The right end in the longitudinal direction of the partition 22b forms an upstream communication portion 22e together with the inner wall of the upstream side wall 22i, while the left end in the longitudinal direction of the partition 22b is the inner wall of the downstream side wall 22j. Together with this, a downstream communication portion 22f is formed. The developer circulates in the developing container 22 by sequentially passing through the first transfer chamber 22c, the upstream communication section 22e, the second transfer chamber 22d, and the downstream communication section 22f.

  The developer supply port 22g is an opening for replenishing the developer container 22 with new toner and carrier from a developer supply container (not shown) provided at an upper portion of the developer container 22, and is provided in the first transfer chamber 22c. It is arranged on the upstream side (left side in FIG. 3).

  The developer discharge port 22h is an opening for discharging surplus developer in the first and second transfer chambers 22c and 22d due to replenishment of the developer, and is provided at a downstream side of the second transfer chamber 22d. The two transfer chambers 22d are provided continuously in the longitudinal direction.

  The first spiral 43 includes a rotating shaft 43b, first spiral blades 43a spirally formed at a constant pitch in the axial direction on the outer peripheral surface of the rotating shaft 43b, and a first spiral blade 43a on the outer peripheral surface of the rotating shaft 43b in the axial direction. The second spiral blade 43c has the same pitch as that of the spiral blade 43a and is wound in the opposite direction (opposite phase) to the first spiral blade 43a. The second spiral blade 43c is formed so as to overlap the formation region of the first spiral blade 43a in the axial direction. In addition, the first spiral blade 43a and the second spiral blade 43c extend to both ends in the longitudinal direction of the first transfer chamber 22c, and are provided so as to face the upstream and downstream communication portions 22e and 22f. The rotation shaft 43b is rotatably supported by the upstream side wall 22i and the downstream side wall 22j of the developing container 22. The first spiral blade 43a and the second spiral blade 43c are molded integrally with the rotating shaft 43b by a synthetic resin.

  The second spiral 44 includes a rotating shaft 44b, a first spiral blade 44a spirally formed at a constant pitch in the axial direction on the outer peripheral surface of the rotating shaft 44b, and a first spiral blade 44a on the outer peripheral surface of the rotating shaft 44b in the axial direction. The second spiral blade 44c has the same pitch as the spiral blade 44a and a second spiral blade 44c wound in the opposite direction (opposite phase) to the first spiral blade 44a. The second spiral blade 44c is formed so as to overlap with the formation region of the first spiral blade 44a in the axial direction. The first spiral blade 44a has the same pitch as that of the first spiral blade 43a of the first spiral 43, and has a reverse winding (opposite phase) to the first spiral blade 43a. Further, the first spiral blade 44a and the second spiral blade 44c have a length equal to or longer than the axial length of the magnetic roller 21, and are further provided to extend to a position facing the upstream communication portion 22e. The rotating shaft 44b is arranged in parallel with the rotating shaft 43b, and is rotatably supported by the upstream side wall 22i and the downstream side wall 22j of the developing container 22. In addition, the first spiral blade 44a and the second spiral blade 44c, as well as the restricting portion 52 and the discharge blade 53, are integrally provided on the rotating shaft 44b. Detailed configurations of the first spiral blades 43a and 44a and the second spiral blades 43c and 44c will be described later.

  The regulating portion 52 blocks the developer transported downstream in the second transport chamber 22d, and enables the developer that has reached a predetermined amount or more to be transported to the developer outlet 22h. It is. The restricting portion 52 is formed of a spiral blade having a reverse winding (opposite phase) to the first spiral blade 44a provided on the rotating shaft 44b, and is substantially equal to the outer diameter of the first spiral blade 44a and smaller than the pitch of the spiral blade 44a. Is set. The regulating portion 52 forms a predetermined gap between the inner wall portion of the developing container 22 such as the downstream side wall portion 22j and the outer peripheral portion of the regulating portion 52. Excess developer is discharged from this gap.

  The rotation shaft 44b extends into the developer outlet 22h. A discharge blade 53 is provided on the rotation shaft 44b in the developer discharge port 22h. The discharge blade 53 is formed of a spiral blade having the same winding direction as the first spiral blade 44a, but has a smaller pitch and a smaller outer periphery of the first spiral blade 44a. Accordingly, when the rotation shaft 44b rotates, the discharge blade 53 also rotates, and the surplus developer conveyed into the developer discharge port 22h over the regulating portion 52 is sent to the left side of FIG. Is to be discharged. In addition, the discharge blade 53, the regulating portion 52, the first spiral blade 44a, and the second spiral blade 44c are formed integrally with the rotating shaft 44b by a synthetic resin.

  Gears 61 to 64 are arranged on the outer wall of the developing container 22. The gears 61 and 62 are fixed to the rotating shaft 43b, the gear 64 is fixed to the rotating shaft 44b, and the gear 63 is rotatably held by the developing container 22 and meshes with the gears 62 and 64.

  According to the first spiral 43 having the above configuration, the first spiral blade 43a is provided on the outer peripheral surface of the rotating shaft 43b, and the first spiral blade 43a is moved in the first direction (see FIG. 3) by the rotation of the rotating shaft 43b. The developer is conveyed while stirring in the direction of arrow P). Further, on the outer peripheral surface of the rotating shaft 43b, the first spiral blade 43a is wound in reverse (opposite phase) between the pitches of the first spiral blade 43a (between the blades), and The second spiral blade 43c having a small diameter is also provided. The second spiral blade 43c causes the developer to convey in a second direction (the direction of arrow Q) opposite to the first direction by the rotation of the rotation shaft 43b.

  Further, according to the second spiral 44 having the above configuration, the first spiral blade 44a is provided on the outer peripheral surface of the rotating shaft 44b, and the first spiral blade 44a is moved in the first direction (see FIG. The developer is transported in the direction indicated by arrow Q in FIG. 3 while stirring. Further, on the outer peripheral surface of the rotating shaft 44b, the first spiral blade 44a is wound in reverse (opposite phase) between the pitches of the first spiral blade 44a (between the blades), and the first spiral blade 44a A second spiral blade 44c having a small diameter is also provided. The second spiral blade 44c causes the developer to convey the developer in a second direction (the direction of arrow P) opposite to the first direction by the rotation of the rotation shaft 44b.

  Since the second spiral blades 43c and 44c are located radially inward of the outer ends (tips) of the first spiral blades 43a and 44a, the second spiral blades 43c and 44c are rotated by the second spiral blades 43c and 44c. The conveying action in the direction 2 occurs for a part of the developer existing near the rotation shafts 43b and 44b. Therefore, the transfer action in the first direction by the first spiral blades 43a and 44a is hardly hindered.

  As described above, by using the second spiral blades 43c, 44c, a transport action (second direction) opposite to the developer transport direction (first direction) by the first spiral blades 43a, 44a is generated. As a result, convection of the developer occurs between the pitches of the first spiral blades 43a, 44a, and the developer between the first spiral blades 43a, 44a hardly hinders the developer conveying action of the first spiral blades 43a, 44a. Is promoted. Accordingly, the new toner and the carrier supplied from the developer supply port 22g are rapidly and effectively stirred with the two-component developer in the first transport chamber 22c and the second transport chamber 22d, and the first transport chamber is provided. 22c, it is possible to effectively prevent the developer transport speed in the second transport chamber 22d from decreasing.

  The height (radial height R2, see FIG. 5) from the rotating shafts 43b, 44b to the tips of the second spiral blades 43c, 44c is from the rotating shafts 43b, 44b to the tips of the first spiral blades 43a, 44a. When the height is smaller than 1/4 of the height (radial height R1, see FIG. 5), the convection of the developer cannot be sufficiently generated between the pitches of the first spiral blades 43a and 44a, and the stirring effect is not obtained. May decrease. On the other hand, when R2 is larger than の of R1, the transport force in the second direction by the second spiral blades 43c and 44c becomes too large, and the first spiral blades 43a and 44a move in the first direction. In some cases, the transfer operation is hindered.

  Therefore, it is preferable that the radial height R2 of the second spiral blades 43c and 44c is not less than ４ and not more than の of the radial height R1 of the first spiral blades 43a and 44a. Thus, it is possible to effectively prevent a decrease in the transport speed while causing convection of the developer between the pitches of the first spiral blades 43a and 44a.

  Hereinafter, a detailed configuration of the first spiral blade 43a and the second spiral blade 43c of the first spiral 43 arranged in the first transfer chamber 22c will be described with reference to FIGS. Since the first spiral blade 44a and the second spiral blade 44c of the first spiral 44 arranged in the second transfer chamber 22d have the same configuration, the description is omitted here.

  As shown in FIGS. 4 and 5, the first spiral blade 43a and the second spiral blade 43c that constitute the first spiral 43 have a trapezoidal cross-sectional shape that crosses the length direction of each spiral blade. The first spiral blade 43a and the second spiral blade 43c are formed so as to intersect at two intersections 47 separated by 180 ° during one rotation of the rotation shaft 43b. The radial height R2 of the second spiral blade 43c is lower than the radial height R1 of the first spiral blade 43a. In the present embodiment, the radial height R1 of the first spiral blade 43a and the radial height R2 of the second spiral blade 43c are constant.

  The rotating shaft 43b of the first spiral 43 has a diameter of about 8 mm, the first spiral blade 43a has a diameter of about 16 mm (the radial height R1 is about 4 mm), and is formed at a pitch of about 20 mm in the axial direction. Have been. The second spiral blade 43c has a diameter of about 12 mm (the radial height R2 is about 2 mm), and is formed at a pitch of about 20 mm in the axial direction.

  In the first spiral 43, since the first spiral blade 43a and the second spiral blade 43c are formed, when the first spiral 43 rotates, the downstream side of the intersection 47 with respect to the rotation direction of the rotation shaft 43b (see FIG. 5). The developer gathers in an area W near (lower side) and the pressure of the developer increases.

  As shown in FIG. 3, in the first transfer chamber 22c, a toner density sensor 51 is disposed adjacent to the upstream side of the upstream communication portion 22e in the developer transfer direction (the direction of the arrow P). . In FIG. 3, since the toner density sensor 51 is located on the back side of the first spiral 43, the toner density sensor 51 is indicated by a broken line.

  As the toner density sensor 51, a magnetic permeability sensor that detects the magnetic permeability of the developer in the developing container 22 is used. When the magnetic permeability of the developer is detected by the toner density sensor 51, a voltage value corresponding to the detection result is output to a control unit (not shown). The toner density is determined from the output value.

  The output value of the toner density sensor 51 changes according to the toner density. The higher the toner density, the higher the ratio of the toner to the magnetic carrier, and the lower the output value because the ratio of the toner that does not pass magnetism increases. On the other hand, the lower the toner concentration, the lower the ratio of the toner to the carrier, and the higher the ratio of the carrier that transmits magnetism, so that the output value increases.

  Here, in the present embodiment, as shown in FIGS. 4 and 6, the toner density sensor 51 causes the detection surface 51 a for detecting the toner density to be horizontal at a position directly below the rotation shaft 43 b of the first spiral 43. Are located. Further, as shown in FIG. 4, the toner density sensor 51 is disposed such that the detection surface 51a faces the intersection 47. That is, the toner density sensor 51 is disposed at a position where the detection surface 51 a overlaps the intersection 47 in the axial direction of the first spiral 43.

  In the present embodiment, as described above, the toner density sensor 51 is disposed such that the detection surface 51a is located directly below the rotation shaft 43b. Thus, unlike the case where the toner density sensor 51 is disposed obliquely downward with respect to the rotation axis 43b of the first spiral 43, the developing devices 2a to 2d are arranged in a direction perpendicular to the rotation axis 43b (the left-right direction in FIG. 6). The increase can be suppressed.

  When the first spiral 43 in which the second spiral blade 43c is formed so as to overlap the formation region of the first spiral blade 43a in the axial direction is used, the rotation of the rotation shaft 43b is caused by the rotation of the first spiral 43. The developer gathers in a region W near the downstream side of the intersection 47 in the direction. For this reason, by arranging the toner density sensor 51 so that the detection surface 51a faces the intersection 47 as described above, when the intersection 47 passes through the detection surface 51a due to the rotation of the first spiral 43, The developer on the detection surface 51a can be caused to flow by the pressure of the developer near the downstream side of the intersection 47. Thus, the developer can be prevented from staying on the detection surface 51a, so that the accuracy of toner concentration detection by the toner concentration sensor 51 can be improved. Further, since it is not necessary to provide a scraper for suppressing the developer from staying on the detection surface 51a, it is possible to suppress an increase in stress on the developer.

(2nd Embodiment)
In the developing devices 2a to 2d according to the second embodiment of the present invention, as shown in FIGS. 7 and 8, the developer transfer of the second spiral blade 43c from the intersection 47 of the second spiral blade 43c facing the detection surface 51a. In a predetermined range on the upstream side in the direction (the right side in FIG. 7), a radial height that is larger than the radial height R2 of the other portion of the second spiral blade 43c and equal to or less than the radial height R1 of the first spiral blade 43a. A large-diameter portion 43d having a thickness is formed. The large diameter portion 43d is provided only at the intersection 47 facing the detection surface 51a (that is, only at one location). Here, the large diameter portion 43d is formed so as to have a radial height of about 3 mm.

  Other structures of the second embodiment are the same as those of the first embodiment.

  In the present embodiment, as described above, the second spiral blade 43c is located in a predetermined range on the upstream side of the second spiral blade 43c in the developer transport direction from the intersection 47 of the second spiral blade 43c facing the detection surface 51a. A large-diameter portion 43d having a radial height higher than the radial height R2 of the other portion and not more than the radial height R1 of the first spiral blade 43a is formed. Accordingly, when the intersection 47 passes through the detection surface 51a due to the rotation of the first spiral 43, the pressure of the developer near the downstream side of the intersection 47 can be further increased. Can be further suppressed.

  Other effects of the second embodiment are similar to those of the first embodiment.

(Third embodiment)
In the developing devices 2a to 2d according to the third embodiment of the present invention, as shown in FIG. 9, the area of the rotating shaft 43b facing the detection surface 51a has a larger diameter than the other parts of the rotating shaft 43b. A radial shaft portion 43e is formed. Here, the large diameter shaft portion 43e is formed to have a diameter of about 10 mm. The large-diameter shaft portion 43e is formed to have an axial length substantially equal to the diameter of the detection surface 51a.

  In the case where the large-diameter shaft portion 43e is provided, the developer conveying force of the second spiral blade 43c is reduced. Therefore, as shown in FIG. 10, an area of the second spiral blade 43c facing the detection surface 51a ( In the area where the large-diameter shaft portion 43e is formed, the radial height of the second spiral blade 43c is set to be larger than the radial height R2 of the other portion and equal to or less than the radial height R1 of the first spiral blade 43a. You may provide the large diameter part 43d which has. In this case, the large diameter portion 43d is formed about twice as large in the axial direction as the large diameter portion 43d of the second embodiment.

  The large-diameter shaft portion 43e needs to be formed so as not to protrude radially outward from the outer end portion (tip) of the second spiral blade 43c. Therefore, when the diameter of the large-diameter shaft portion 43e is set to be about 12 mm or more (the radial height R2 of the second spiral blade 43c) or more, as shown in FIG. What is necessary is just to provide so that it may project radially outward rather than the radial shaft part 43e.

  Other structures of the third embodiment are the same as those of the first embodiment.

  In the present embodiment, as described above, the large-diameter shaft portion 43e having a larger diameter than other portions of the rotation shaft 43b is formed in the region of the rotation shaft 43b facing the detection surface 51a. Accordingly, when the intersection 47 passes through the detection surface 51a due to the rotation of the first spiral 43, the pressure of the developer near the downstream side of the intersection 47 can be further increased. Can be further suppressed.

  Further, as described above, the area of the second spiral blade 43c facing the detection surface 51a is larger than the radial height R2 of the other part of the second spiral blade 43c and the diameter of the first spiral blade 43a. A large-diameter portion 43d having a radial height equal to or less than the directional height R1 may be formed. With such a configuration, the large diameter portion 43d of the second spiral blade 43c can be easily projected radially outward from the large diameter shaft portion 43e of the rotating shaft 43b, and therefore, the developer of the second spiral blade 43c The transfer force can be easily secured.

  Other effects of the third embodiment are the same as those of the first embodiment.

  It should be understood that the embodiments disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description of the embodiments, and includes all modifications within the scope and meaning equivalent to the terms of the claims.

  INDUSTRIAL APPLICABILITY The present invention can be used for a developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile, a multifunction machine using the electrophotographic method, and an image forming apparatus including the same.

  Further, the developing device of the present invention is limited to the developing devices 2a to 2d having the developer supply port 22g and the developer discharge port 22h, and having the magnetic roller 21 and the developing roller 20, as shown in FIG. However, the present invention can be applied to various developing devices.

  Further, in the above-described embodiment, the example in which the first spiral 43 arranged in the first transfer chamber 22c is used as the stirring and conveying member has been described. However, the present invention is not limited to this, and the second conveying chamber 22d may be used as the stirring and conveying member. A toner density sensor 51 may be provided in the second transfer chamber 22d using the second spiral 44 arranged.

  Further, in the above-described embodiment, an example in which the first spiral blade 43a and the second spiral blade 43c are formed at the same pitch has been described. However, the present invention is not limited to this, and the first spiral blade 43a and the second spiral blade 43c may be formed. The pitches may be different from each other.

1 Image Forming Apparatus 2a-2d Developing Device 21 Magnetic Roller (Developer Carrier)
22 Developing container 43 First spiral (stirring / conveying member)
43a First spiral blade 43b Rotary shaft 43c Second spiral blade 43d Large diameter portion 43e Large diameter shaft portion 47 Intersection 51 Toner density sensor 51a Detection surfaces R1, R2 Radial height

Claims (6)

A developing container containing a developer containing toner,
A developer carrying member that is provided in the developing container and carries the developer in the developing container on a surface thereof;
A stirring and conveying member for stirring and conveying the developer in the developing container,
A toner concentration sensor having a detection surface for detecting the toner concentration in the developing container,
With
A rotating shaft rotatably supported in the developing container, a first spiral blade formed on an outer peripheral surface of the rotating shaft, and configured to transport the developer in the axial direction by rotation of the rotating shaft; Formed on the outer peripheral surface of the rotating shaft so as to overlap with the formation region of the first spiral blade in the axial direction, and wound in a reverse direction to the first spiral blade and having a smaller radial height than the first spiral blade. A second spiral blade having
The first spiral blade intersects with the second spiral blade at at least one place during one rotation of the rotation shaft,
The developing device according to claim 1, wherein the toner density sensor is arranged so that the detection surface faces an intersection of the first spiral blade and the second spiral blade at a position immediately below the rotation axis.   In a predetermined range on the upstream side of the second spiral blade in the developer transport direction from the intersection point of the second spiral blade facing the detection surface, the height of the second spiral blade is higher than the radial height of another portion of the second spiral blade. 2. The developing device according to claim 1, wherein a large-diameter portion having a large diameter and a radial height equal to or less than a radial height of the first spiral blade is formed.   The developing device according to claim 1, wherein a large-diameter shaft portion having a larger diameter than other portions of the rotation shaft is formed in a region of the rotation shaft facing the detection surface. .   In a region of the second spiral blade facing the detection surface, a radial height that is larger than a radial height of another portion of the second spiral blade and equal to or less than a radial height of the first spiral blade. The developing device according to claim 3, wherein a large diameter portion having a thickness is formed.   The developing device according to claim 1, wherein the developer is a two-component developer including a carrier and the toner.   An image forming apparatus comprising the developing device according to claim 1.

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