JP2017116778A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of suppressing permeability fluctuations due to the density variation of a developer.SOLUTION: An image forming device includes: a stirring and conveyance member; and a toner concentration detection sensor. The stirring and conveyance member includes: a shaft member, a spiral member, and first and second paddles. The first and second paddles are mutually separated in a peripheral direction of the shaft member. The first paddle is arranged on the upstream side of a conveyance direction of a developer from the second paddle. The first paddle and the second paddle connect the spiral member of the upstream side and the spiral member of the downstream side, respectively. The spiral member includes a noncontiguous part interrupted in the continuation to a spiral direction between a downstream end part in the first paddle and an upstream side end part in the second paddle. When assuming that a height from the shaft member of the first paddle is taken as A, the height from the shaft member of the second paddle is taken as B, and the height from the shaft member of the spiral member is taken as C, the first paddle, the second paddle, and the spiral member satisfy B<A≤C and C/3≤B≤3C/4.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus.

  Conventionally, the toner concentration of the two-component developer circulating in the developing device in the image forming apparatus is calculated by detecting the magnetic permeability of the two-component developer including toner and carrier. The detection result of the magnetic permeability can be changed not only by the toner concentration but also by the bulk density fluctuation or fluidity change of the developer. For example, when an environmental change such as temperature and humidity occurs or when the process speed is switched, the magnetic permeability detection result changes.

  In this case, a technique is known in which the toner density fluctuation is suppressed by stabilizing the state of the developer in the detection region of the toner density detection sensor. For example, in the image forming apparatus disclosed in Patent Document 1, the stirring and conveying member that conveys the developer includes a spiral member, a first plate member, and a second plate member. The first plate-like member connects the spiral member on the upstream side in the developer transport direction and the spiral member on the downstream side in the developer transport direction. The second plate-like member extends from the upstream spiral member toward the downstream side, and is formed with a space between the second spiral member and the downstream spiral member. A portion of the spiral member facing the detection surface of the toner concentration detection sensor is cut away, and the first plate member and the second plate member are arranged to face the detection surface of the toner concentration detection sensor. Has been.

Japanese Patent Laying-Open No. 2015-108761

  In the image forming apparatus described above, the first plate-like member and the second plate-like member arranged at the position where the spiral member is cut out are agitated while appropriately retaining the developer. However, generally, in a high temperature and high humidity environment, when the stirring and conveying member rotates at a low speed due to the switching of the process speed, it is considered that the developer conveying property around the toner concentration detection sensor is lowered. . In this case, a phenomenon called packing in which the developer is clogged in the agitating and conveying unit may occur. In addition, when the developer transportability is high, the sensor output may fluctuate greatly before and after the process speed is switched due to a decrease in the staying developer. As described above, depending on external factors, it is difficult to suppress the state fluctuation of the developer, and there is a possibility that the magnetic permeability fluctuation is caused by the density change of the developer.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can suppress magnetic permeability fluctuations due to changes in developer density.

An image forming apparatus according to an aspect includes an agitating and conveying member that conveys a two-component developer including a non-magnetic toner and a magnetic carrier while stirring, and an agitating and conveying member that detects the toner concentration of the developer And a toner concentration detection sensor for detecting a magnetic permeability according to a mixing ratio of the nonmagnetic toner and the magnetic carrier contained in the developer. The agitating and conveying member includes a shaft member, a spiral member that extends in a spiral direction around the shaft member and conveys the developer in the axial direction of the shaft member, and a position facing the detection surface of the toner density detection sensor on the shaft member. A first paddle and a second paddle are formed and extend in the axial direction of the shaft member. The first paddle and the second paddle are separated from each other in the circumferential direction of the shaft member, and the first paddle is disposed upstream of the second paddle in the developer conveying direction. The first paddle and the second paddle respectively connect the upstream spiral member in the developer transport direction and the downstream spiral member in the developer transport direction. The spiral member is a discontinuous portion in which the continuity in the spiral direction is interrupted between the downstream end portion of the first paddle in the developer transport direction and the upstream end portion of the second paddle in the developer transport direction. Have When the height of the first paddle from the shaft member is A, the height of the second paddle from the shaft member is B, and the height of the spiral member from the shaft member is C, the first paddle, The two paddles and the helical member satisfy the following formula (1).
B <A ≦ C and C / 3 ≦ B ≦ 3C / 4 (1)

  In this image forming apparatus, the developer is transported from the upstream side to the downstream side in the transport direction by the rotation of the spiral member. Then, at the position of the detection surface of the toner concentration detection sensor, the developer is stirred and retained in the rotation direction by the first paddle and the second paddle. Further, a discontinuous portion in which continuity in the spiral direction is interrupted is formed between the downstream end portion of the first paddle and the upstream end portion of the second paddle. For this reason, at the position of the discontinuous portion, the conveyance of the developer in the conveyance direction is suppressed, and the developer tends to stay. Further, when the height B of the second paddle is smaller than the height A of the first paddle, the conveyance and retention of the developer are controlled. In particular, by setting C / 3 ≦ B, the developer stirred and retained by the second paddle can be secured, so that the transportability does not become too high. For this reason, even when the process speed varies, the output of the toner density detection sensor is unlikely to vary. In addition, by setting B ≦ 3C / 4, the developer does not stay excessively, moderate transportability is ensured, and packing is suppressed. Thereby, the magnetic permeability fluctuation | variation by the density change of a developer can be suppressed.

  Further, at the end of the first paddle on the downstream side in the developer conveyance direction, the developer is conveyed more on the outer peripheral side opposite to the shaft member side than on the base end side on the shaft member side. The structure extended to the downstream of the direction may be sufficient. When the end of the first paddle has such a shape, the developer can be suitably transported to the downstream side through the end of the first paddle, and the magnetic permeability fluctuation due to the density change of the developer is further suppressed. can do.

  Further, the center position of the detection surface of the toner density detection sensor in the direction along the axial direction of the shaft member may be substantially the same as the center position of the second paddle. According to this configuration, the accuracy of the toner concentration detection sensor can be improved.

  Further, in the first paddle, when the length along the axial direction of the shaft member at the end on the outer peripheral side opposite to the shaft member side is D, and the pitch length of the spiral member is E In addition, the first paddle and the spiral member may be configured to satisfy D ≦ 1.5E. According to this configuration, excessive stagnation of the developer is suppressed, and the fluidity of the developer in the region facing the detection surface of the toner concentration detection sensor can be stabilized.

  Moreover, the structure which is 120 rpm-500 rpm may be sufficient as the rotation speed of a stirring conveyance member. Further, the developer may have a fluidity of 4.5 sec / 50 g to 12.5 sec / 50 g. According to such a configuration, the developer can be retained and transported suitably.

  According to one form of the image forming apparatus, it is possible to suppress a change in magnetic permeability due to a change in density of the developer.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a developing unit in the image forming apparatus. It is a figure which shows the structure of the stirring conveyance member in the toner density detection sensor periphery of a developing unit. It is a figure which shows the structure of the stirring conveyance member in the toner density detection sensor periphery of a developing unit. It is a figure which shows the structure of the stirring conveyance member in the toner density detection sensor periphery of a developing unit. It is the figure which looked at the structure of the stirring conveyance member from the axial direction. It is a figure which shows the structure of the stirring conveyance member in the toner density detection sensor periphery of a developing unit. It is a graph which shows the relationship between the height of a 2nd paddle, and a sensor output difference. It is a graph which shows the relationship between the height and amplitude of a 2nd paddle. It is a graph which shows the relationship between the shape of the edge part of a 1st paddle, and the sensitivity fluctuation rate at the time of process speed fluctuation | variation. FIG. 6 is a diagram illustrating an example of a developer movement around a toner concentration detection sensor. It is a figure which shows the output waveform for 1 period of a toner density | concentration detection sensor when a stirring conveyance member rotates. 6 is a graph showing the relationship between the axial length on the outer peripheral side of the first paddle and the amplitude of the toner density detection sensor.

  Embodiments according to the present invention will be specifically described below with reference to the drawings. For convenience, the same reference numerals are given to substantially the same elements, and the description thereof may be omitted.

  First, a schematic configuration of the image forming apparatus according to the present embodiment will be described with reference to FIG. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment is an apparatus capable of forming a color image using, for example, magenta, yellow, cyan, and black. The image forming apparatus 1 includes a recording medium conveying unit 10 that conveys a sheet P, a developing unit 20 that develops an electrostatic latent image, a transfer unit 30 that secondarily transfers a toner image onto the sheet P, and an image on a peripheral surface. A photosensitive drum 40 that is an electrostatic latent image carrier to be formed and a fixing unit 50 that fixes the toner image onto the paper P are configured.

  The recording medium conveyance unit 10 accommodates a sheet P as a recording medium on which an image is finally formed, and conveys the sheet P onto the recording medium conveyance path. The paper P is stacked and accommodated in the cassette T. The recording medium transport unit 10 causes the paper P to reach the secondary transfer region R at the timing when the toner image transferred to the paper P reaches the secondary transfer region R.

  The developing unit 20 is provided for each color. In the present embodiment, four developing units 20 are provided corresponding to magenta, yellow, cyan, and black. At positions facing the developing units 20, toner tanks 5 corresponding to the respective developing units 20 are provided. The developing unit 20 develops the electrostatic latent image formed on the photosensitive drum 40 with the toner supplied from the corresponding toner tank 5 to generate a toner image. The toner tank 5 is filled with the corresponding color toner.

  The transfer unit 30 conveys the toner image formed by the developing unit 20 to the secondary transfer region R. In the secondary transfer region R, the toner image is secondarily transferred to the paper P. The transfer unit 30 includes a transfer belt 31, suspension rollers 31a, 31b, 31c, and 31d that suspend the transfer belt 31, a primary transfer roller 32 that sandwiches the transfer belt 31 together with the photosensitive drum 40, and a transfer belt together with the suspension roller 31d. And a secondary transfer roller 33 that sandwiches 31.

  The transfer belt 31 is an endless belt that circulates and moves by suspension rollers 31a, 31b, 31c, and 31d. The primary transfer roller 32 is provided so as to press the photosensitive drum 40 from the inner peripheral side of the transfer belt 31. The secondary transfer roller 33 is provided so as to press the suspension roller 31 d from the outer peripheral side of the transfer belt 31.

  The photosensitive drum 40 is provided for each color (for each developing unit 20). These photosensitive drums 40 are provided along the moving direction of the transfer belt 31. A developing unit 20, a charging roller 41, an exposure unit 42, and a cleaning unit 43 are provided on the periphery of the photosensitive drum 40.

  The charging roller 41 uniformly charges the surface of the photosensitive drum 40 to a predetermined potential. The exposure unit 42 exposes the surface of the photosensitive drum 40 charged by the charging roller 41 according to an image formed on the paper P. As a result, the potential of the exposed portion of the surface of the photosensitive drum 40 changes, and an electrostatic latent image is formed.

  The cleaning unit 43 collects the toner remaining on the photosensitive drum 40 after the toner image formed on the photosensitive drum 40 is primarily transferred to the transfer belt 31. The toner collected by the cleaning unit 43 is transferred as a waste toner to a waste toner collecting device by a screw or the like.

  The fixing unit 50 attaches and fixes the toner image secondarily transferred from the transfer belt 31 to the paper P on the paper P. The fixing unit 50 includes a heating roller 51 that heats the paper P and a pressure roller 52 that presses the heating roller 51. The heating roller 51 and the pressure roller 52 are formed in a cylindrical shape, and the heating roller 51 includes a heat source such as a halogen lamp inside. A fixing nip portion, which is a contact area, is provided between the heating roller 51 and the pressure roller 52, and the toner image is melted and fixed on the paper P by passing the paper P through the fixing nip portion.

  Further, the image forming apparatus 1 is provided with discharge rollers 61 and 62 for discharging the paper P on which the toner image is fixed by the fixing unit 50 to the outside of the apparatus.

  Next, an outline of the configuration of the developing unit 20 will be described with reference to FIGS. As shown in FIGS. 2 and 3, the developing unit 20 includes a developing roller 21, a conveying member 22, a stirring and conveying member 23, and a toner concentration detection sensor 28.

  The developer used in the developing unit 20 is a two-component developer including, for example, a nonmagnetic toner and a magnetic carrier. The fluidity of the developer (based on JIS Z 2502: 2012) is, for example, 4.5 sec / 50 g to 12.5 sec / 50 g. The developing roller 21 is adjusted so that the toner and the carrier have a desired mixing ratio, and further mixed and agitated to uniformly disperse the toner and carry a developer to which an optimum charge amount is applied. The developing roller 21 rotates and conveys the developer to a region facing the photosensitive drum 40. As a result, the nonmagnetic toner in the developer carried on the developing roller 21 moves to the electrostatic latent image formed on the peripheral surface of the photosensitive drum 40, and the electrostatic latent image is developed.

  The conveying member 22 is rotatably arranged in the developing unit 20 and conveys the developer in a conveying direction H substantially parallel to the rotation axis of the developing roller 21 by a rotating operation. The conveying member 22 carries a predetermined amount of developer on the circumferential surface of the developing roller 21 that rotates in the forward direction with the conveying member 22. The conveying member 22 includes a shaft member 22a and a spiral member 22b formed on the peripheral surface of the shaft member 22a. The spiral member 22b has a spiral blade shape, and rotates the developer clockwise when viewed in the transport direction H, thereby transporting the developer from the upstream side to the downstream side in the transport direction H. The rotation speed of the conveying member 22 is, for example, 120 rpm to 500 rpm.

  The agitating / conveying member 23 is disposed in the developing unit 20 at a position farther from the developing roller 21 than the conveying member 22 so as to be able to rotate so as to face the conveying member 22 over substantially the entire length thereof. ing. The conveyance member 22 and the agitation conveyance member 23 are disposed in a space separated by the housing of the developing unit 20. These spaces communicate with each other on the upstream side in the developer transport direction H. The stirring and conveying member 23 includes a shaft member 24, and a spiral member 25, a first paddle 26, and a second paddle 27 formed on the peripheral surface of the shaft member 24. The agitating and conveying member 23 agitates the developer by a rotating operation and conveys the developer in a conveying direction G substantially parallel to the axial direction M of the shaft member 24. The transport direction G is a direction facing the transport direction H. The rotation speed of the agitation transport member 23 is, for example, 120 rpm to 500 rpm.

  The spiral member 25 extends in the spiral direction around the shaft member 24, and conveys the developer in the axial direction M of the shaft member 24. The spiral member 25 has a spiral blade shape, and includes a first transport unit 25 a that transports the developer in the transport direction G, and a second transport unit 25 b that transports the developer in the direction opposite to the transport direction G. The first transport unit 25 a rotates counterclockwise when viewed in the transport direction G, and transports the developer from the upstream side to the downstream side in the transport direction G. The second transport unit 25 b is formed at the end 24 b of the shaft member 24 on the downstream side in the transport direction G, and transports the developer in the direction opposite to the transport direction G. As a result, the developer is pushed up at the end 24 b without clogging, and the developer is transported from the agitation transport member 23 to the transport member 22.

  The first paddle 26 has a conveying force in the rotation direction N of the stirring and conveying member 23. The first paddle 26 has a substantially rectangular shape and is erected on the shaft member 24. The first paddle 26 extends along the axial direction M of the shaft member 24, for example, in S <b> 2 between two pitches of the spiral member 25. The first paddle 26 extends from the upstream spiral member 25 in the transport direction G to the downstream side in the transport direction G in the two pitches S2. A space L is formed between the first paddle 26 and the downstream spiral member 25. The first paddle 26 holds the developer in the rotational direction N without substantially conveying the developer in the axial direction M, and stirs it in the rotational direction N, and further downstream through the space L in the direction shown by the arrow J. The developer is caused to flow to the side (see FIG. 11).

  The second paddle 27 holds the developer and stirs it in the rotational direction N without substantially transporting the developer in the axial direction M. The second paddle 27 has a substantially rectangular shape and is erected on the shaft member 24. The second paddle 27 extends along the axial direction M of the shaft member 24 in one pitch S <b> 1 of the spiral member 25.

  The toner concentration detection sensor 28 detects the toner concentration of the developer conveyed by the agitating and conveying member 23 in order to detect the toner concentration of the developer. The toner concentration detection sensor 28 detects the magnetic permeability according to the mixing ratio of the nonmagnetic toner and the magnetic carrier contained in the developer. The toner concentration detection sensor 28 has a detection surface 29 that faces the developer conveyed by the agitation conveyance member 23. The first paddle 26 and the second paddle 27 rotate in a direction in which the detection surface 29 is scraped up (rotation direction N). The toner concentration detection sensor 28 is disposed at an angle of, for example, approximately 45 ° with respect to the horizontal plane so that the detection surface 29 faces the first paddle 26 and the second paddle 27.

  The toner density detection result is confirmed by the output voltage from the toner density detection sensor 28. This output voltage has a periodic waveform shape as the stirring and conveying member 23 rotates even if the toner concentration is constant. This is because the developer is periodically and densely formed by the agitating and conveying member 23. When the developer is large and the magnetic permeability is high, the developer is in a dense state, and the output from the toner concentration detection sensor 28 is high. When the developer is low and the magnetic permeability is low, the developer is in a rough state, and the output from the toner concentration detection sensor 28 is low.

  Next, details of the configuration of the agitation transport member 23 around the toner concentration detection sensor 28 will be described with reference to FIGS. As shown in FIGS. 4 and 5, the first paddle 26 is arranged on the upstream side in the transport direction G with respect to the second paddle. That is, the first paddle 26 and the second paddle 27 are separated from each other in the circumferential direction of the shaft member 24. In the present embodiment, the first paddle 26 and the second paddle 27 are arranged at positions spaced apart from each other by approximately 180 ° in the circumferential direction of the shaft member 24. As a result, the upstream end portion 26 a of the first paddle 26 is disposed upstream of the upstream end portion 27 a of the second paddle 27 by approximately a half pitch of the spiral member 25.

  Further, the spiral member 25 is a discontinuous portion in which the continuity in the spiral direction is interrupted between the downstream end portion in the transport direction G of the first paddle 26 and the upstream end portion of the second paddle 27 in the transport direction G. 25c. In the illustrated example, the discontinuous portion 25 c is formed over the entire range from the upstream end portion 27 a of the second paddle 27 to the downstream side of the first paddle 26. That is, in this range, the spiral member 25 for approximately half a pitch is not formed. At the position where the non-continuous portion 25c is formed, the developer is hardly transported in the transport direction G. The upstream side end portion 26a of the first paddle 26 in the transport direction G and the upstream end portion 27a of the second paddle 27 in the transport direction and the downstream side of the first paddle 26 in the transport direction of the developer. A spiral member 25 is formed between the side end portion and the end portion 27b of the second paddle 27 on the downstream side in the developer transport direction (see FIG. 5).

  The first paddle 26 and the second paddle 27 are disposed so as to face the detection surface 29 of the toner concentration detection sensor 28. That is, the first paddle 26 and the second paddle 27 are arranged at a position overlapping the detection surface 29 of the toner concentration detection sensor 28 in the axial direction M of the shaft member 24. For example, as shown in FIG. 4, the center position 29 c of the detection surface 29 of the toner density detection sensor 28 in the direction along the axial direction M is substantially the same as the center position 27 c of the second paddle 27. Further, as shown in FIG. 5, in the direction along the axial direction M, the detection surface 29 of the toner density detection sensor 28 is upstream of the end portion 26 d of the first paddle 26, and the first paddle 26 It is included in the extended range. In the illustrated example, the detection surface 29 faces the downstream end of the first paddle 26 in the transport direction G.

6A to 6C schematically show the heights of the first paddle 26, the second paddle 27, and the spiral member 25 from the shaft member 24. FIG. As shown in FIG. 6, when the height from the outer peripheral surface of the shaft member 24 of the first paddle 26, the second paddle 27 and the spiral member 25 is A, B and C, respectively, the first paddle 26, The second paddle 27 and the spiral member 25 are formed so as to satisfy the following expression (1). In the present embodiment, the height A of the first paddle 26 from the shaft member 24 is substantially equal to the height C of the spiral member 25 from the shaft member 24. The height B of the second paddle 27 from the shaft member 24 is smaller than the height A of the first paddle 26 from the shaft member 24. As an example, the height A of the first paddle 26 is 5 mm, the height B of the second paddle 27 is 2.5 mm, and the height C of the spiral member 25 is 5 mm.
B <A ≦ C and C / 3 ≦ B ≦ 3C / 4 (1)

  An end 26d on the downstream side in the developer transport direction G in the first paddle 26 has an oblique shape (see FIG. 4). The end 26d of the first paddle 26 is located on the downstream side in the developer conveyance direction G on the outer peripheral side 26c opposite to the shaft member 24 side rather than on the base end side 26b on the shaft member 24 side. It extends to.

The length of the first paddle 26 in the longitudinal direction (the length of the shaft member 24 in the axial direction M) is the same as or longer than the length of one pitch of the spiral member 25 and longer than the length of two pitches. short. In the present embodiment, the first paddle 26 connects the upstream spiral member 25 in the transport direction G and the downstream spiral member 25 by one pitch, and further, the downstream spiral member 25. Extends downstream. As shown in FIG. 7, when the length on the outer peripheral side 26c of the first paddle 26 is D in the direction along the axial direction of the shaft member 24, and the length of one pitch of the spiral member 25 is E. The first paddle 26 and the spiral member 25 are formed so as to satisfy the formula (2). As an example, the length E of one pitch of the spiral member 25 is about 20 mm, and the length D of the outer peripheral side 26c of the first paddle 26 is about 24 mm. In the present embodiment, since the first paddle 26 straddles the upstream spiral member 25 and the downstream spiral member 25 in the transport direction G, the length D is equal to or greater than the length E. .
D ≦ 1.5E (2)

  The length of the second paddle 27 in the longitudinal direction (the length of the shaft member 24 in the axial direction M) is substantially equal to the length E of one pitch of the spiral member 25. That is, the second paddle 27 connects the spiral member 25 on the upstream side in the developer transport direction G and the spiral member 25 on the downstream side in the developer transport direction G in one pitch S1.

  As described above, in the image forming apparatus 1 according to the present embodiment, the developer is transported from the upstream side in the transport direction G to the downstream side by the rotation of the spiral member 25. Then, at the position of the detection surface 29 of the toner concentration detection sensor 28, the developer is stirred and retained in the rotation direction N by the first paddle 26 and the second paddle 27. Further, a discontinuous portion 25 c in which continuity in the spiral direction is interrupted is formed in the spiral member 25 between the downstream end portion of the first paddle 26 and the upstream end portion of the second paddle 27. For this reason, at the position of the discontinuous portion 25c, the conveyance of the developer in the conveyance direction G is suppressed, and the developer tends to stay. Further, since the height B of the second paddle 27 from the shaft member 24 is smaller than the height A of the first paddle 26 from the shaft member 24, the conveyance and retention of the developer are controlled.

  FIG. 8 is a graph showing the relationship between the height B of the second paddle and the sensor output difference. The sensor output difference is a difference when the process speed is changed between full speed and half speed (output value at half speed−output value at full speed). In this embodiment, the target is that the fluctuation of the toner density detection sensor 28 is within 0.5% when the process speed is full speed and half speed. In this case, for example, when the toner density detection sensor 28 has a sensitivity of 0.3 V / 1%, the sensor output difference is 0.15 V or less. As shown in FIG. 8, when the height B of the second paddle 27 is smaller than C / 3, the sensor output difference is large. This is because the amount of the developer stirred and retained by the second paddle 27 becomes small and the amount of the developer conveyed in the conveyance direction G increases, so that the process speed dependency in the sensor output becomes high. On the other hand, when the height B of the second paddle 27 is set to C / 3 or more, the process speed dependency in the sensor output can be reduced. This is because the developer stirred and retained by the second paddle 27 can be secured, and the transportability does not become too high. Therefore, by setting the height B of the second paddle 27 to C / 3 or more, even when the process speed varies, the output of the toner density detection sensor 28 is unlikely to vary.

  FIG. 9 is a graph showing the relationship between the height of the second paddle 27 from the shaft member 24 and the amplitude of the output waveform in the toner concentration detection sensor 28. As shown in FIG. 9, when the height B of the second paddle 27 is greater than 3C / 4, the amplitude of the output waveform drops sharply. That is, the fluctuation of the sensor output by the toner density detection sensor 28 is small. This is because, as the height of the second paddle 27 increases, the developer transportability decreases, and the developer staying in the first paddle 26 and the second paddle 27 becomes excessive. Thus, if the staying developer becomes excessive, packing tends to occur. On the other hand, when the height B of the second paddle 27 is 3C / 4 or less, a constant amplitude is obtained, and it can be seen that the developer does not stay excessively and that packing is difficult to occur. Therefore, by forming the first paddle 26, the second paddle 27, and the spiral member 25 so as to satisfy the formula (1), the dependence on the process speed is low, and a stable residence performance is provided. it can. Thereby, the magnetic permeability fluctuation | variation by the density change of a developer can be suppressed.

  Further, at the end 26d on the downstream side in the developer transport direction in the first paddle 26, the outer peripheral side, which is the opposite side to the shaft member 24 side, is closer to the base end side, which is the shaft member 24 side. It extends downstream in the developer transport direction G. FIG. 10 is a graph showing the sensitivity fluctuation rate when the process speed fluctuates depending on the shape of the end portion 26 d of the first paddle 26. The horizontal axis in FIG. 10 indicates the shape of the end portion 26d. For example, the term “perpendicular to the end surface” refers to the case where the downstream end in the developer conveying direction G at the end portion 26 d is substantially the same on the base end side 26 b and the outer peripheral side 26 c, that is, extends perpendicular to the shaft member 24. Shows the case. On the right side of the end surface perpendicularly, when the end portion 26d extends to the downstream side in the developer conveying direction G on the outer peripheral side 26c longer than the base end side 26b, that is, the developer is more than the shaft member 24. The case where it inclines in the downstream of the conveyance direction G is shown. On the left side of the end surface perpendicular to the left side, when the end portion 26d extends to the downstream side in the developer conveying direction G on the base end side 26b longer than the outer peripheral side 26c, that is, the developer is more than the shaft member 24. The case where it inclines to the upstream of the conveyance direction G is shown. The vertical axis in FIG. 10 shows the sensitivity fluctuation rate when the process speed fluctuates. The sensitivity fluctuation rate at the time of process speed fluctuation is the fluctuation rate of the control voltage necessary for controlling the toner density with a constant voltage output from the toner density detection sensor 28 when the process speed condition changes.

  As shown in FIG. 10, in the end portion 26d of the first paddle 26, if the extension of the developer in the downstream direction G is longer on the outer peripheral side 26c than on the base end side 26b, the process speed fluctuations The sensitivity fluctuation rate at the time is low. That is, since the end portion 26d of the first paddle 26 has such a shape, the space L is formed from the end portion 26d of the first paddle 26 in the direction indicated by the arrow J as shown in FIG. Through the developer. As described above, it is possible to further suppress the magnetic permeability variation due to the change in the developer density due to the process speed variation.

  Further, in the direction along the axial direction M of the shaft member 24, the center position of the detection surface 29 of the toner concentration detection sensor 28 is substantially the same as the center position of the second paddle 27. FIG. 12 shows an example of an output waveform for one cycle of the toner concentration detection sensor 28 when the stirring and conveying member 23 in the present embodiment rotates. In FIG. 12, the horizontal axis represents time, and the vertical axis represents the output of the toner density detection sensor 28. In this waveform, the waveform when the first paddle 26 passes the toner concentration detection sensor 28 is the position P1, and the waveform when the second paddle 27 passes the toner concentration detection sensor 28 is the position P2. When the second paddle 27 passes the detection surface 29, the retention of the developer is promoted by the second paddle. Further, when the first paddle 26 passes through the detection surface 29, the developer is held together with the passage while retaining the developer. As described above, since the developer stirred and retained by the first paddle 26 and the second paddle 27 passes through the position facing the detection surface 29, the accuracy of the toner density detection sensor 28 can be improved.

  The length D on the outer peripheral side of the first paddle 26 and the pitch length E of the spiral member 25 are configured to satisfy D ≦ 1.5E. FIG. 13 is a graph showing the relationship between the length in the axial direction M on the outer peripheral side 26 c of the first paddle 26 and the amplitude of the toner density detection sensor 28. As shown in FIG. 13, when the length D on the outer peripheral side of the first paddle 26 is longer than 1.5 times the pitch of the spiral member 25, the amplitude of the sensor output is drastically reduced. This is because the developer conveyed to the downstream side through the space L decreases as the space L becomes smaller. In this case, packing is likely to occur due to excessive developer remaining in the region facing the detection surface 29. The sensor output is also reduced when the length of the first paddle 26 is less than one pitch of the spiral member 25. This is because the downstream end of the first paddle 26 does not face the detection surface 29. That is, the developer stirred and retained by the first paddle 26 is difficult to be detected by the toner concentration detection sensor 28. As described above, the first paddle 26 and the spiral member 25 are formed so as to satisfy the expression (2), so that the fluidity of the developer is stabilized and the amplitude of the output of the toner concentration detection sensor 28 is stabilized. .

  The preferred embodiments of the present embodiment have been described above. However, the present invention is not limited to the above-described embodiments. The present invention is not limited to the gist described in each claim and can be modified or applied to others. It may be what you did.

  For example, in the above embodiment, only the first paddle 26 and the second paddle 27 are disposed at positions facing the detection surface, but the present invention is not limited to this. For example, in addition to the first paddle 26 and the second paddle 27, a paddle may be further added.

  Further, although the first paddle 26 and the second paddle 27 are erected on the shaft member 24 at a position approximately 180 ° apart from each other in the circumferential direction of the shaft member 24, the present invention is not limited thereto. For example, the position where the first paddle 26 and the second paddle 27 are erected on the shaft member 24 may be a position apart from each other by an angle other than approximately 180 ° in the circumferential direction of the shaft member 24. As described above, when one paddle is further added in addition to the first paddle 26 and the second paddle 27, the paddles may be arranged at intervals of 120 ° in the circumferential direction.

  Moreover, although the example in which the discontinuous portion 25c is formed from the upstream side of the second paddle 27 to the entire downstream side of the first paddle 26 is shown, it is not limited thereto. For example, a spiral member may be partially formed in the range from the upstream side of the second paddle 27 to the downstream side of the first paddle 26.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 23 ... Agitation conveyance member, 24 ... Shaft member, 25 ... Spiral member, 25c ... Discontinuous part, 26 ... 1st paddle, 26b ... Base end side, 26c ... Outer peripheral side, 26d ... End part 27 ... second paddle, 27c ... center position, 28 ... toner density detection sensor, 29 ... detection surface, 29c ... center position, A ... first paddle height, B ... second paddle height, C ... spiral Height of D-shaped member, D: length of first paddle, E: pitch of spiral member, M: axial direction, N: transport direction, L: space, S1: between 1 pitch, S2: between 2 pitches.

Claims (6)

An agitating and conveying member for conveying the two-component developer containing the non-magnetic toner and the magnetic carrier while stirring;
In order to detect the toner concentration of the developer, a toner concentration detection that detects a magnetic permeability according to a mixing ratio of the non-magnetic toner and the magnetic carrier contained in the developer conveyed by the stirring and conveying member. An image forming apparatus comprising: a sensor;
The stirring and conveying member is
A shaft member;
A spiral member extending in a spiral direction around the shaft member and transporting the developer in the axial direction of the shaft member;
The shaft member has a first paddle and a second paddle that are formed at a position facing the detection surface of the toner concentration detection sensor and extend in the axial direction of the shaft member,
The first paddle and the second paddle are separated from each other in the circumferential direction of the shaft member,
The first paddle is disposed upstream of the second paddle in the developer transport direction,
The first paddle and the second paddle connect the spiral member on the upstream side in the developer transport direction and the spiral member on the downstream side in the developer transport direction, respectively.
The spiral member is continuous in the spiral direction between a downstream end portion in the developer transport direction of the first paddle and an upstream end portion of the second paddle in the developer transport direction. With discontinuous discontinuities,
When the height from the shaft member in the first paddle is A, the height from the shaft member of the second paddle is B, and the height from the shaft member of the spiral member is C, The image forming apparatus, wherein the first paddle, the second paddle, and the spiral member satisfy the following formula (1).
B <A ≦ C and C / 3 ≦ B ≦ 3C / 4 (1)   At the end of the first paddle on the downstream side in the transport direction of the developer, the outer peripheral side that is opposite to the shaft member side is closer to the development side than the base end side that is the shaft member side. The image forming apparatus according to claim 1, wherein the image forming apparatus extends downstream in the conveyance direction of the agent.   3. The image forming apparatus according to claim 1, wherein a center position of the detection surface of the toner density detection sensor is substantially the same as a center position of the second paddle in a direction along an axial direction of the shaft member. . In the first paddle, the length along the axial direction of the shaft member at the end on the outer peripheral side opposite to the shaft member side is defined as D, and the pitch length of the spiral member is defined as E. The image forming apparatus according to any one of claims 1 to 3, wherein the first paddle and the spiral member satisfy the formula (2).
D ≦ 1.5E (2)   5. The image forming apparatus according to claim 1, wherein the rotation speed of the stirring and conveying member is 120 rpm to 500 rpm.   The image forming apparatus according to claim 1, wherein the developer has a fluidity of 4.5 sec / 50 g to 12.5 sec / 50 g.