JP5989213B2 - Developing device and magnet roller - Google Patents

Description

  The present invention relates to a developing device in which a magnet roller is disposed in a non-rotating manner inside a developer carrier, and more specifically, uneven developer loading on the surface of the developer carrier located at a corner of the end in the longitudinal direction of the magnet roller. It relates to the structure to be relaxed.

  Widely used in image forming apparatuses in which a developing device carries a one-component developer or two-component developer containing toner on a rotating developer carrying member and develops an electrostatic image formed on the image carrying member into a toner image. It has been.

  In order to magnetically support the developer on the surface of a developer carrier (development sleeve) made of a nonmagnetic material, a magnet roller is disposed on the inside of the developer carrier so as not to rotate. In the magnet roller, the N magnetic pole and the S magnetic pole which are continuous in the longitudinal direction are arranged on the outer peripheral surface, and the magnetic flux passing through the non-magnetic developer carrier and communicating between the adjacent N magnetic pole and the S magnetic pole is The developer is magnetically supported on the surface of the developer carrier.

  Patent Document 1 discloses a method of manufacturing a magnet roller in which a magnet roller is formed by bonding and fixing a magnet piece having a fan-shaped cross section around a support shaft.

  By the way, as shown in FIG. 2, the magnet roller 29 is formed in a cylindrical shape as a whole so that the distance from the surface of the rotating cylindrical developing sleeve (developer carrier) 28 can be kept constant. For this reason, at the corner portion of the end surface in the longitudinal direction of the magnet roller 29, the magnetic flux wraps around the end surface toward the center, and more magnetic flux is generated than on the cylindrical surface inside the end portion. This is because the magnetic flux density is higher and the magnetic force is stronger at the edge portion of the magnetic pole surface of the permanent magnet than at the magnetic pole surface inside the edge.

  For this reason, more developer is locally carried on the surface of the developing sleeve 28 at a position corresponding to the end face in the longitudinal direction of the magnet roller 29 than on the peripheral surface located in the longitudinal center of the magnet roller 29. End up. As a result, in a portion where a large amount of developer is carried, the developer deteriorates due to the rubbing of the layer thickness regulating blade 30, or linear development unevenness occurs on the image surface (Patent Document 2).

  Therefore, in Patent Document 2, the end of the cylindrical magnet roller is chamfered in order to reduce the rise of magnetic force on the end surface in the longitudinal direction of the magnet roller. As shown in FIG. 7, the diameter of the end of the magnet roller 29 is gradually decreased toward the outside in the longitudinal direction, and the distance between the surface of the magnet roller 29 and the surface of the developer carrying member is gradually increased. As a result, the rising of the magnetic force at the end of the magnet roller 29 is offset.

Japanese Patent Laid-Open No. 1-115109 JP-A-10-91002

  As shown in FIG. 7, when the outer periphery of the end portion of the magnet roller 29 is finished to have a uniform diameter, uneven developer carrying on the surface of the developing sleeve 28 located at the end portion of the magnet roller 29 occurs unintentionally. Turned out to be. On the surface of the developing sleeve 28 located at the end of many magnetic poles (N magnetic pole in FIG. 7) on the outer peripheral surface of the magnet roller 29, it is observed that an increase in magnetic flux density remains and developer carrying unevenness is formed. It was. On the other hand, on the surface of the developing sleeve 28 located at the end of the small magnetic pole (S magnetic pole in FIG. 7) on the outer peripheral surface of the magnet roller 29, the magnetic flux density is lower than the surroundings, and uneven developer loading is formed. It was observed.

  If the developer carrying unevenness is unintentionally formed on the surface of the end portion of the developing sleeve 28, this effect may cause a difference in the development efficiency of the electrostatic image and may cause density unevenness in the output image. Further, there is a possibility that the developer is deteriorated by locally increasing the pressure along the layer thickness regulating blade 30.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device and a magnet roller that can reduce uneven developer carrying at a position corresponding to the end of a magnet member (magnet roller) on the peripheral surface of the developer carrying member.

  The developing device of the present invention is a developing device comprising a developer carrying member for carrying a developer and a magnet member disposed inside the developer carrying member, and the magnet member has a first outer surface. A first magnet part having a polarity and a second magnet part having an outer surface having a second polarity different from that of the first polarity in the circumferential direction; The ratio of the first magnet part occupied in the cross section orthogonal to the longitudinal direction of the magnet member is larger than the ratio of the second magnet part occupied in the cross section, and the longitudinal direction of the magnet member The ratio of the first magnet portion occupied in the cross section orthogonal to the end portion is smaller than the longitudinal center portion of the magnet member, and in the longitudinal end portion of the magnet member, Serial volume of the outer surface of the first magnet unit, the smaller than the longitudinal center portion of the first magnet portion, and wherein the.

  In the developing device of the present invention, if the magnetic member remains cylindrical, the magnetic flux density is higher than the magnetic pole having the other polarity, and the volume of the longitudinal end of the magnet member relative to the longitudinal central portion of the magnet member Reduce the ratio. That is, in comparison with the central portion, the end portion is made relatively small to reduce the magnetization. On the other hand, in the other magnetic pole, the magnetic flux density of the magnetic pole is lower than that of the one magnetic pole in the cylindrical shape. Approach the magnetic pole level. A magnet member having such an end appearance is used.

  By partially removing the magnetic material at the end with the volume set for each magnetic pole, the difference in magnetic flux density between the magnetic poles at the corners of the end is reduced. Thereby, the developer restraining force on the surface of the developer carrying member located at the end of the magnet member can be appropriately weakened for each magnetic pole.

  Accordingly, the difference in magnetic flux density between the N magnetic pole and the S magnetic pole at the end of the magnet member viewed on the surface of the developer carrying member can be reduced to reduce developer carrying unevenness.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a structure of the image development apparatus in a cross section perpendicular | vertical to a longitudinal direction. It is explanatory drawing of the structure of the image development apparatus in the cross section along a longitudinal direction. It is explanatory drawing of a structure of the conventional magnet roller. It is explanatory drawing of the boundary condition of a magnet roller. It is explanatory drawing of the magnetic flux density distribution of the longitudinal direction in the image development sleeve surface. It is explanatory drawing of a structure of the magnet roller of a comparative example. It is explanatory drawing of the magnetic flux which a permanent magnet generate | occur | produces. It is explanatory drawing of the effect which shortens a permanent magnet in the magnetization direction. It is explanatory drawing of the magnetic flux density distribution of the longitudinal direction in a N magnetic pole and a S magnetic pole. 2 is an explanatory diagram of a configuration of a magnet roller according to Embodiment 1. FIG. It is explanatory drawing of a structure of the magnet roller of Example 2. FIG. It is explanatory drawing of a structure of the magnet roller of Example 3. FIG. It is explanatory drawing of a structure of the magnet roller of Example 4. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, as long as the magnetic material having a volume different between the N magnetic pole and the S magnetic pole on the outer peripheral surface of the magnet roller is removed from the end portion, a part or all of the configuration of the embodiment is replaced with Another embodiment in which the configuration is replaced can also be implemented.

  Accordingly, the present invention can be carried out in a developing apparatus that uses a single component developer as well as a two component developer. The two-component developer developing device can be implemented not only in a vertical developing device in which the developing chamber and the stirring chamber are arranged up and down, but also in a horizontal developing device in which the developing chamber and the stirring chamber are arranged horizontally. Such a developing device can be implemented without distinction in a tandem type / 1 drum type, an intermediate transfer type / recording material conveyance type, and a sheet-fed 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 image development apparatus 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. 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 Pa, Pb, Pc, and Pd are arranged along an intermediate transfer belt 5. is there.

  The intermediate transfer belt 5 is suspended by rollers 61, 62, 63 and is movable in the direction of arrow R2. In the image forming portion Pa, a yellow toner image is formed on the photosensitive drum 1 a and transferred to the intermediate transfer belt 5. In the image forming portion Pb, a magenta toner image is formed on the photosensitive drum 1 b and transferred to the intermediate transfer belt 5. In the image forming portions Pc and Pd, a cyan toner image and a black toner image are formed on the photosensitive drums 1c and 1d, respectively, and transferred to the intermediate transfer belt 5.

  The four-color toner images transferred to the intermediate transfer belt 5 are conveyed to the secondary transfer portion T2 and secondarily transferred to the recording material S. The recording material S taken out from the recording material cassette 12 by the pickup roller 13 is separated one by one by the separation roller 11 and fed to the registration roller 14. The registration roller 14 sends the recording material S to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 5. The recording material S to which the toner image has been transferred is heated and pressurized by the fixing device 16 to fix the toner image on the surface, and then is discharged to the discharge tray 17.

  The image forming portions Pa, Pb, Pc, and Pd are substantially the same except that the toner colors used in the developing devices 4a, 4b, 4c, and 4d are different. Hereinafter, the image forming unit Pa will be described, and the image forming units Pb, Pc, and Pd will be described by replacing “a” at the end of the reference numerals attached to the components of the image forming unit Pa with “b”, “c”, and “d”. To do.

  In the image forming portion Pa, a corona charger 2a, an exposure device 3a, a developing device 4a, a primary transfer roller 6a, and a drum cleaning device 19a are arranged around the photosensitive drum 1a.

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

  The primary transfer roller 6 a presses the inner surface of the intermediate transfer belt 5 to form a toner image transfer portion between the photosensitive drum 1 a and the intermediate transfer belt 5. By applying a positive DC voltage to the primary transfer roller 6a, a negative toner image carried on the photosensitive drum 1a is primarily transferred to the intermediate transfer belt 5. The drum cleaning device 19a collects the transfer residual toner remaining on the photosensitive drum 1a by escaping from the transfer to the recording material S.

  Although the photosensitive drum 1a, which is a commonly used drum-shaped organic photosensitive member, is used as the image carrier, an inorganic photosensitive member such as an amorphous silicon photosensitive member may be used, and a belt-shaped photosensitive member is used. It is also possible. The charging method, developing method, transfer method, cleaning method, and fixing method are not limited to the above methods.

<Developing device>
FIG. 2 is an explanatory diagram of the configuration of the developing device in a cross section perpendicular to the longitudinal direction. FIG. 3 is an explanatory diagram of the configuration of the developing device in a cross section along the longitudinal direction.

  As shown in FIG. 2, the developing device 4a develops an electrostatic image on the photosensitive drum 1a by carrying a developer containing toner and carrier on the developing sleeve 28. The photosensitive drum 1a rotates in the arrow R1 direction at a process speed (peripheral speed) of 273 mm / sec. The developing device 4a uses a two-component developer obtained by mixing a nonmagnetic toner and a magnetic carrier as a developer.

  In the developing container 22, a developing chamber 23 that supplies a developer to the developing sleeve 28 and an agitating chamber 24 that collects the developer from the developing sleeve 28 are arranged vertically. A developing sleeve 28 is rotatably disposed in a region of the developing container 22 facing the photosensitive drum 1a.

  As shown in FIG. 3, the developing chamber 23 and the stirring chamber 24 configured by partitioning the developing container 22 by a partition wall 27 constitute a developer circulation path for transporting the developer while stirring. A stirring chamber 24 is disposed below the developing chamber 23, a developing screw 25 is rotatably provided in the developing chamber 23, and a stirring screw 26 is rotatably provided in the stirring chamber 24. The developing screw 25 and the agitating screw 26 convey the developer in the developing chamber 23 and the agitating chamber 24 in the opposite directions and circulate in the developing container 22. The partition wall 27 is provided with openings 27A and 27B that transfer the developer in the vertical direction at both ends in the longitudinal direction.

  As shown in FIG. 2, there is an opening 22A at a position corresponding to the developing region of the developing container 22 facing the photosensitive drum 1a, and the developing sleeve 28 is rotated so that the developing sleeve 28 is partially exposed in the direction of the photosensitive drum 1a. It is arranged to be possible. The developing sleeve 28 is made of a nonmagnetic material such as aluminum or stainless steel, and has a diameter of 20 mm, and the photosensitive drum 1a has a diameter of 80 mm. By setting the closest area between the developing sleeve 28 and the photosensitive drum 1a to a distance of about 300 .mu.m, the developer magnetic brush conveyed to the developing unit is set so that development can be performed in contact with the photosensitive drum 1a. Has been.

  In the developing region, the developing sleeve 28 moves in the forward direction and the moving direction of the surface of the photosensitive drum 1a, and the peripheral speed ratio is 1.75 times the photosensitive drum. This peripheral speed ratio is set between 0 and 3.0 times, and preferably between 0.5 and 2.0 times. The higher the peripheral speed ratio, the higher the development efficiency. However, if the peripheral speed ratio is too large, problems such as toner scattering and developer deterioration occur. Therefore, the peripheral speed ratio is preferably set within the above range.

  A magnet roller 29 having a plurality of magnetic poles N 1, S 1, N 2, S 2, N 3 arranged on the surface thereof is disposed non-rotatingly inside the developing sleeve 28 in order to constrain the developer to the non-magnetic developing sleeve 28. The development pole S2 is disposed to face the photosensitive drum 1 in the development unit. The magnetic pole S <b> 1 is disposed to face the regulation blade 30. The magnetic pole N2 is disposed between the magnetic poles S1 and S2. The magnetic poles N1 and N3 are disposed to face the developing chamber 23 and the stirring chamber 24, respectively. The magnetic flux density of each magnetic pole was 40 mT to 70 mT, but the S2 pole used for development was 100 mT.

  The developing sleeve 28 carries the developer by the magnetic field of the magnet roller 29 and rotates in the direction of arrow R 28, and the layer thickness of the developer is regulated by cutting off the magnetic brush by the regulating blade 30.

  The regulating blade 30 is made of a nonmagnetic material formed of plate-like aluminum or the like extending along the longitudinal axis of the developing sleeve 28, and is disposed upstream of the photosensitive drum 1a in the developing sleeve rotation direction. Yes. Both the developer toner and the carrier pass between the tip of the regulating blade 30 and the developing sleeve 28 and are sent to the developing region.

  By adjusting the gap (gap) between the regulating blade 30 and the surface of the developing sleeve 28, the amount of the developer magnetic brush carried on the developing sleeve 28 is regulated so that the amount of developer conveyed to the developing region is reduced. Adjusted.

  The gap between the regulating blade 30 and the developing sleeve 28 is set to 200 to 1000 μm, preferably 300 to 700 μm. Here, the developer coating amount per unit area on the developing sleeve 28 is regulated to 30 mg / cm 2 by the regulation blade 30 set to 500 μm.

  The developing sleeve 28 conveys the two-component developer whose layer thickness is regulated by the regulating blade 30 to the developing area facing the photosensitive drum 1a, and supplies the developer to the electrostatic image formed on the photosensitive drum 1a. Develop to toner image. In the developing unit, the magnetic brush of the two-component developer raised by the magnetic pole S2 of the magnet roller 29 rubs the surface of the photosensitive drum 1a.

  At this time, in order to improve the development efficiency, that is, the application rate of the toner to the electrostatic image, the power source D28 applies an oscillating voltage obtained by superimposing the AC voltage on the DC voltage Vdc to the developing sleeve 28 as a developing bias voltage. . Here, an AC voltage having a DC voltage Vdc of −500 V, a peak-to-peak voltage Vpp of 800 V, and a frequency f of 12 kHz is used. However, the DC voltage and AC voltage conditions are not limited thereto.

  In such a two-component magnetic brush development method, generally, when an AC voltage is applied, the development efficiency increases and the image becomes high quality, but conversely, a fogging image in which toner adheres to the white background portion of the image is generated. It becomes easy. For this reason, the fog image is prevented by providing the fog removal potential Vback between the DC voltage Vdc applied to the developing sleeve 28 and the charged potential (that is, the white background potential) of the photosensitive drum 1a.

<Conventional magnet roller>
FIG. 4 is an explanatory diagram of the configuration of a conventional magnet roller. FIG. 5 is an explanatory diagram of boundary conditions of the magnet roller. FIG. 6 is an explanatory diagram of the magnetic flux density distribution in the longitudinal direction on the surface of the developing sleeve.

  As shown in FIG. 4, the conventional magnet roller 129 is configured by radially attaching a plurality of magnet pieces 141 made of a magnetic material around a non-magnetic support shaft 140. The magnet roller 129 needs to obtain a substantially similar magnetic pole cross-section pattern regardless of the location in any part in the longitudinal direction. Therefore, the magnetizations of the plurality of magnetic pole magnet pieces 141 are adjusted so that the magnitude of the magnetic flux density does not change in the longitudinal direction of the support shaft 140.

  As shown in FIG. 5, when considering a magnetic field by cutting an arbitrary part of the magnet roller 129, magnetic lines of force (magnetic flux) formed in the surrounding space by the magnet roller 129 are formed in the circumferential direction of the magnet roller 129, and in the longitudinal direction. Is not formed. This is because the magnetization in the longitudinal direction is zero and no magnetic flux is formed because the magnetizations in the cross sections adjacent in the longitudinal direction are equal. In other words, when the cross-sectional configuration of the magnetic poles of the magnet roller 129 does not change in the direction of the support shaft 140, the periodic boundary condition can be applied to an arbitrary cross-section, and therefore the magnetic lines of force do not extend in the longitudinal direction of the magnet roller 129. This is because if the magnetic field lines extend in the longitudinal direction, the symmetry to which the periodic boundary condition can be applied is lost, and a contradiction occurs.

  Therefore, since the periodic boundary condition can be applied to most of the magnet roller 129 except for the end portion, the magnetic lines of force do not extend in the longitudinal direction of the magnet roller 129. However, since the periodic boundary condition cannot be applied to the end of the magnet roller 129, the above discussion does not hold.

  At the end portion of the magnet roller 129, magnetic lines of force that wrap around the end surface toward the center side toward the outside are additionally generated. At the end of the magnet roller 129, magnetic lines of force are formed not only in the circumferential direction of the magnet roller 129 but also in the longitudinal direction, so that the magnetic flux density is higher than in the inner part.

  As shown in FIG. 6, the magnetic flux density in the longitudinal direction on the surface of the developing sleeve was measured by moving a stellar meter (TM: FIG. 10) in the longitudinal direction along the surface of the developing sleeve. As a result, it was confirmed that the magnetic flux density was locally increased at the position in the longitudinal direction corresponding to the end of the magnet roller 129, and the magnetic characteristics were increased. Such a rise in magnetic characteristics is called an edge effect.

  When such an edge effect is present, the amount of developer spikes increases only on the surface of the developing sleeve at a position corresponding to the end of the magnet roller 129. If the amount of spikes of the developer increases, only that portion strongly contacts the photosensitive drum facing the developing sleeve, and in a remarkable case, the developer may damage the surface of the photosensitive drum.

  Even if the photosensitive drum is not damaged, an abrupt change in magnetic flux density such as the edge effect causes a sudden change in the amount of developer on the developing sleeve. It tends to be a defective image recognized as a difference.

  Further, as a result of the developer being easily transferred to the photosensitive drum, as shown in FIG. 1, there is a risk of affecting the drum cleaning device 19a, the secondary transfer roller 10, the fixing device 16 and the like existing downstream from the developing device 4a. There is also.

  The Teslameter (TM: FIG. 10) used for the measurement is a magnetic flux density measuring device using a Hall element. The Hall element is a magnetic sensor that outputs a voltage corresponding to the magnetic flux density using the Hall effect in which an electric field (Hall electric field) appears in a direction orthogonal to both the current and the magnetic field. Since the direction and magnitude of the electromotive force (Hall electric field) is uniquely determined if the direction and magnitude of the magnetic field generated by the magnet and the reference current are determined, the direction of the reference current and the electromotive force (Hall electric field) The magnitude and direction of the magnetic field orthogonal to the current and electric field can be measured from

<Comparative example>
FIG. 7 is an explanatory diagram of a configuration of a magnet roller of a comparative example. FIG. 8 is an explanatory diagram of magnetic flux generated by the permanent magnet. FIG. 9 is an explanatory view of the effect of shortening the permanent magnet in the magnetization direction. FIG. 10 is an explanatory diagram of the magnetic flux density distribution in the longitudinal direction of the N magnetic pole and the S magnetic pole.

  In Patent Document 1 (Japanese Patent Laid-Open No. 1-115109) and Patent Document 2 (Japanese Patent Laid-Open No. 10-91002), by increasing the outer diameter of both end portions of the magnet roller 29, the magnetic characteristics rise due to the edge effect. Is corrected.

  As shown in FIG. 7, the outer diameter of both end portions of the magnet roller 29 is configured to be smaller than the central portion so that flat magnetic characteristics without an edge effect can be obtained. Since the magnetic force of the magnet piece 41 changes corresponding to the increase or decrease of the volume of the magnet piece 41, the magnetic flux density can be reduced by changing the volume of the magnet piece 41. By gradually reducing the outer diameter of the magnet roller at both ends of the magnet roller 29, it is possible to correct the magnetic characteristics at both ends by the edge effect and reduce the rise of the magnetic characteristics.

  As shown in FIG. 8, when this point is described in detail, the magnetic flux density of a general permanent magnet is defined by the density of the magnetic flux line, and the magnetic flux line is expressed as a (vector-like) addition of the magnetic force line and the magnetization line. be able to. This corresponds to the fact that the magnetic flux density B can be expressed by the addition (B = H + μM) of the magnetic field H and the magnetization M (the magnetic field H multiplied by the permeability μ). FIG. 8 illustrates these relationships by taking a bar magnet as an example.

  Since the magnetic flux lines satisfy Gauss's law divB = 0 (magnetic flux conservation equation) regarding the magnetic flux as a property, there is no springing out or suction at all points (synonymous with the absence of magnetic charge). That is, when the magnetization M inside the permanent magnet changes, the external magnetization changes accordingly.

  Therefore, as shown in FIG. 9, when the length of the permanent magnet is changed to reduce the volume of the magnet, the magnetization M of the permanent magnet is also reduced, so that the magnetic flux lines outside the permanent magnet are also changed, and the magnetic flux density is reduced. Become. From the above, in the configuration in which the outer diameters at both ends of the magnet roller 29 are reduced, the volume of the magnet piece 41 is reduced at both ends, so that the magnetic flux density at the ends is reduced and the rise of magnetic properties due to the edge effect is reduced. The

  However, according to the study by the inventors, the following problems remain in such a comparative example. In the comparative example, as shown in FIG. 2, the outer diameter of the magnet roller 29 including five magnetic poles N1, S1, N2, S2, and N3 is uniformly uniform in the circumferential direction with respect to the magnet piece 41 of any magnetic pole. It is small. For this reason, it has been found that there are magnetic poles that do not become completely flat, such as the edge effect remaining depending on the magnetic poles, or conversely, it becomes too gentle.

  As shown in FIG. 10A, the magnetic flux density of the N magnetic pole and the S magnetic pole of the magnet roller 29 was measured along the surface of the developing sleeve 28 in the longitudinal direction using the Teslameter TM. As a result, it has been found that the characteristics of the change in the magnetic characteristics at both ends of the magnet roller 29 are roughly divided into two in the N magnetic pole and the S magnetic pole.

  As shown in FIG. 10B, the magnetic poles N <b> 1, N <b> 2, and N <b> 3 of the magnet roller 29 have a large rise in magnetic characteristics due to the edge effect at the corners of the end of the magnet roller 29. In the magnetic poles N1, N2, and N3, the magnetic characteristics once risen at both ends of the magnet roller 29, then suddenly changed to the opposite S magnetic pole on the outer side, and then the magnetic flux density converged to 0 as going outward. doing.

  On the other hand, as shown in FIG. 10C, the magnetic poles S <b> 1 and S <b> 2 of the magnet roller 29 have almost no rise in magnetic characteristics due to the edge effect at the corners of the end of the magnet roller 29. In some cases, on the contrary, the magnetic properties have been gently reduced. The magnetic poles S1 and S2 have the magnetic flux density converged to 0 as the S magnetic poles without changing to the N magnetic poles of the opposite polarities outside the both ends of the magnet roller 29.

  As described above, in the case of the magnet roller 29 having different numbers of N magnetic poles and S magnetic poles on the outer peripheral surface, the magnetic roller 29 is divided into a magnetic pole having a large edge effect and a magnetic pole having almost no edge effect. For this reason, when the outer diameter is uniformly reduced between the N magnetic pole magnet piece 41 and the S magnetic pole magnet piece 41 of the magnet roller 29, the edge effect remains in the N magnetic pole, and conversely, the edge effect is removed in the S magnetic pole. Pass.

  As a result, when the surface of the rotating developing sleeve 28 passes through the end of the N magnetic pole, the magnetic flux density increases and the developer carrying force increases, and immediately after that, when passing through the end of the S magnetic pole, the magnetic flux density increases. As a result, the developer carrying force is insufficient. As a result, development unevenness, toner scattering, carrier transfer, and the like are likely to occur at the end of the magnet roller 29.

  The reason why such a problem occurs is that although the edge effect at both ends is different between the N magnetic pole and the S magnetic pole, the end diameter is changed uniformly regardless of the N magnetic pole and the S magnetic pole. Because it has been. For this reason, the configuration of the comparative example is still not sufficient as a countermeasure against the rise of magnetic characteristics due to the edge effect.

  Such a phenomenon may occur even when the number of N magnetic poles and S magnetic poles on the outer peripheral surface is different as in the comparative example. The same N magnetic poles are generated between a magnetic pole having a large magnetization and a magnetic pole having a small magnetization. It also occurs between a magnetic pole having a large magnetic pole length and a small magnetic pole occupying the outer peripheral surface.

  In any case, a magnet roller having a plurality of magnetic poles is divided into a magnetic pole having a relatively strong edge effect and a magnetic pole having little edge effect. In this case, if the outer diameters of both ends are uniformly reduced, the edge effect may remain, or conversely, the magnetic characteristics of the ends may not be flat depending on the magnetic pole. . Even if the state of the edge effect at both ends differs depending on the magnetic pole, if the diameter is changed uniformly regardless of the magnetic pole, the edge effect remains in the magnetic pole having a high edge effect. And if the swell of the magnetic properties at both ends remains or falls too gently, there are concerns about problems.

  In the case of a cylindrical shape, when the outer diameter of the end portion of the magnet roller is changed in accordance with the magnetic pole having a weak edge effect, the magnetic property due to the edge effect still remains in the magnetic pole having a strong edge effect. If the swell of the magnetic characteristics due to the edge effect remains, as described above, it causes density unevenness of the output image and developer deterioration.

  On the other hand, when the outer diameter of the end of the magnet roller is changed in accordance with the magnetic pole having a strong edge effect, the magnetic characteristics at both ends of the magnetic pole with a weak edge effect are excessively lowered. If the magnetic properties at both ends gently fall, the force of the developing sleeve 28 holding the developer becomes weak, and there is a concern that the developer is carried by the photosensitive drum 1a or the developer leaks in the direction of the end. is there. Further, since the coating amount of the developer is reduced only in that portion, there is a fear that the developability is lowered and the image density is lowered.

  Therefore, in the following embodiments, the degree of change in the volume of the magnetic material at both ends of the magnet roller 29 is changed according to the state of the edge effect at both ends of the N magnetic pole and the S magnetic pole.

<Example 1>
FIG. 11 is an explanatory diagram of a configuration of the magnet roller according to the first embodiment. As shown in FIG. 2, the magnet roller 29, which is an example of a magnetic member, is disposed inside the developing sleeve 28, which is an example of a developer carrier, and has a plurality of different magnetic poles in the circumferential direction of the magnet roller 29. The magnet roller 29 is configured by arranging magnet pieces for each of a plurality of magnetic poles around a support shaft 40 penetrating the center.

  As shown in FIG. 10, the polarity when the magnetic force converges toward 0 in the space outside the magnet roller 29 on the central axis of the developing sleeve 28 is the S pole, which is an example of the first polarity. . For this reason, as shown to (a) of FIG. 11, the south pole which is an example of the 2nd polarity which is different from the 1st polarity among several magnetic poles becomes the same polarity as the 1st polarity. The volume ratio of the end portion in the longitudinal direction of the magnet roller 29 with respect to the central portion in the longitudinal direction of the magnet roller 29 is smaller.

  Further, the magnet roller 29 has more N poles as an example of one polarity on the outer peripheral surface than the S poles as an example of the other polarity. For this reason, the volume ratio of the end portion in the longitudinal direction of the magnet roller 29 to the center portion in the longitudinal direction of the magnet roller 29 is smaller in the magnetic pole having the N pole on the outer peripheral surface than in the magnetic pole having the S polarity.

  The volume of the magnetic material set for each magnetic pole is partially at the end of the magnet roller 29 more than the intermediate portion so as to reduce the difference in increase in magnetic flux density for each magnetic pole at the corner of the end of the magnet roller 29. Has been removed. The fan-shaped region at the end of the magnet roller 29 corresponding to the N magnetic pole has a larger volume of the removed magnetic material than the fan-shaped region at the end of the magnet roller 29 corresponding to the small S magnetic pole on the outer peripheral surface of the magnet roller 29. .

  A support shaft 40 having a round shaft is provided at the center of the magnet roller 29 according to the first embodiment. As shown in FIG. 2, since the magnet roller 29 is composed of five magnetic poles, it corresponds to each magnetic pole to form five magnetic poles N1, S1, N2, S2, and N3 around the support shaft 40. The magnet piece 41 is bonded to the position to be used.

  Needless to say, the present invention can be applied even if the number of magnetic poles is not five, the number of magnet pieces is not five, or the magnet pieces are not bonded together.

  As the support shaft 40, stainless steel is used. However, the present invention is not limited to this, and any material having a certain degree of rigidity, such as a metal such as iron, may be used. Regarding the shape, the round shaft is used in the first embodiment, but other shapes may be used.

  The magnet piece 41 may be formed of a known magnet such as a resin magnet or a sintered magnet based on resin or rubber. In Example 1, the magnet roller 29 was configured by forming the resin magnet piece 41 in a shape in which a fan-shaped shape was extended, and these were bonded to the support shaft 40 radially with an adhesive or the like.

  Here, as shown in FIG. 4, when the cross-sectional shape of the magnet piece is formed in the same shape over the entire length (support shaft axis) direction from the intermediate part to both ends, the magnetic properties rise due to the edge effect at both ends. Resulting in.

  Further, as shown in FIG. 7, when the outer diameters of both end portions of the N-pole magnet piece 41 and the S-pole magnet piece are made smaller than the middle portion, the magnetic characteristics due to the edge effect in the N-pole magnet piece 41 are obtained. The excitement will remain.

  Therefore, as shown in FIG. 10A, before changing the diameter at both ends, the magnetic flux density distribution in the longitudinal direction of each magnetic pole is measured, and the end of each magnetic pole is measured according to the measurement result. The outer diameter was designed.

  Of the five magnetic poles of the magnet roller 29 of the first embodiment, the three poles of the magnetic poles N1, N2, and N3 have a large edge effect, and the two poles of the magnetic poles S1 and S2 have a small edge effect. Therefore, the volume of the notch of the magnet piece 41 at each end of each of the magnetic poles N1, N2, and N3 is made larger than the volume of the notch at each end of each of the magnetic poles S1 and S2, so The magnetic characteristics are made flatter.

  As shown in FIG. 11 (a), the outer diameters of only the both ends of the magnet pieces 41 of the magnetic poles N1, N2, and N3 are made smaller than the intermediate portions, and the outer diameters of both ends of the magnet pieces 41 of the magnetic poles S1 and S2 are The configuration is not changed. As a result, the edge effect of the magnetic pole is greatly suppressed for the magnetic poles N1, N2, and N3 having a large edge effect, and the end magnetic characteristics are prevented from becoming too gentle for the magnetic poles S1 and S2 having a small edge effect. Thereby, a flat magnetic characteristic on the surface of the circumference of the developing sleeve 28 along the end of the magnet roller 29 was obtained without depending on the difference between the N magnetic pole and the S magnetic pole.

  In the case where there is a rise in magnetic characteristics due to the edge effect at any one of the magnetic poles S1 and S2, the outer diameter of the magnetic pole having the rise is reduced. Even in this case, if care is taken to make the outer diameter larger than that of the magnetic poles N1, N2, and N3, flat magnetic characteristics on the surface of the circumference of the developing sleeve 28 along the end of the magnet roller 29 can be obtained.

  The change in the outer diameter at both ends of the three poles of the magnetic poles N1, N2, and N3 is the same in the first embodiment, but the volume of the notch is set according to the size of the edge effect of the magnetic poles N1, N2, and N3. You can make them different. By setting the volume of the notches at both ends larger than the larger one according to the size of the edge effect, the entire edge effect can be reduced more effectively.

  For example, when the magnetization intensity of the magnetic pole N1 is larger than the magnetization intensity of the magnetic pole N2, the outer diameter of the magnetic pole N1 can be made smaller than the outer diameter of the magnetic pole N2. However, although there is a correlation between the strength of magnetization and the strength of the edge effect, it may be reversed due to the relationship between the half width and the adjacent pole, so the edge effect is measured as shown in FIG. Therefore, it is better to set each notch volume.

  As described above, in the magnet roller configuration in which the magnetic flux is not balanced between the N magnetic pole and the S magnetic pole on the outer peripheral surface due to the difference in the number of N magnetic poles and S magnetic poles on the outer peripheral surface, the edge effect for each magnetic pole can be made uniform. it can.

  By changing the notch amount of the magnet roller according to the degree of the edge effect of the magnetic pole, it is possible to prevent the edge effect from being excessively gentle while suppressing the edge effect at the end of all the magnetic poles. In all the magnetic poles, while suppressing the edge effect at the end, it also prevents the toner from becoming too gentle, thereby improving the state of the developer on the developing sleeve and maintaining a good image forming state. It becomes possible. It is possible to provide a developing device capable of maintaining a good image forming state.

  In the first embodiment, the material of the magnet piece 41 constituting the magnet roller 29 is a resin magnet, but a sintered ferrite magnet may be used. However, sintered ferrite magnets have the disadvantages that they are brittle and easily damaged, and are easily shrunk during sintering, and there is a limit to the magnet shape control.

  For this reason, in the configuration in which the edge effect of each magnetic pole is corrected by finely controlling the end shape of the magnet roller, it can be said that a resin magnet that can easily control the shape and volume of the notch is suitable.

  Moreover, in Example 1, although the magnet roller 29 was comprised by bonding together the several magnet piece 41, this invention can be implemented also when the magnet roller 29 is comprised integrally from the beginning. However, in the configuration in which the end shape of the magnet roller 29 is changed according to the degree of the edge effect for each magnetic pole, the configuration in which the magnet piece 41 is provided for each magnetic pole and bonded together is easier to process the shape and the volume of the notch There is an advantage that it is easy to control.

  If the support shaft 40 is made of a magnetic material, the magnetic flux density tends to hardly converge to 0 at the end of the magnet roller 29. This is because the magnetic support shaft 40 is magnetized and the support shaft 40 itself behaves like a magnet. Therefore, the support shaft 40 is preferably made of a non-magnetic material, and in the first embodiment, it is made of stainless steel.

<Example 2>
FIG. 12 is an explanatory diagram of the configuration of the magnet roller of the second embodiment. As shown in FIG. 11, in Example 1, the outer diameter of the magnet piece 41 was changed with a uniform thickness from both ends to a certain distance. On the other hand, in Example 2, as shown in FIG. 12, the outer diameter of the magnet piece 41 is changed in a tapered shape from both ends to a certain distance.

  Similarly to the first embodiment, the volume of the notch at both ends of the three-pole magnet piece 41 of the magnetic poles N1, N2, and N3 is defined as the volume of the notch at both ends of the two-pole magnet piece 41 of the magnetic poles S1 and S2. It is larger than the volume. Thereby, the influence of the edge effect of each magnetic pole at the end of the magnet roller 29 measured on the surface of the developing sleeve 28 can be made uniform, and unevenness in the developer carrying performance in the longitudinal direction and the circumferential direction of the developing sleeve 28 is eliminated. ing.

  Further, in the configuration in which the volume is reduced in a taper shape, the magnetic effect in the longitudinal direction of the developing sleeve is flattened in response to the fact that the edge effect at the end of the magnet roller 29 becomes more prominent toward the end. It is possible. Further, since the edge portion of the magnet roller 29 is gentle, it is possible to suppress damage during handling such as during manufacture.

<Example 3>
FIG. 13 is an explanatory diagram of the configuration of the magnet roller of the third embodiment. As shown in FIG. 12, in Example 2, the volume of magnetic material set for each magnetic pole was partially removed at the end of the magnet roller 29. On the other hand, in Example 3, a volume of magnetic material set for each magnetic pole is added at the end of the magnet roller 29.

  Of the N and S magnetic poles, the few magnetic poles on the outer peripheral surface of the magnet roller 29 are S magnetic poles. In the fan-shaped region at the end of the magnet roller 29 corresponding to the S magnetic pole, the magnetic material is partially added and the outer diameter is larger than the central portion of the magnet roller 29.

  Regarding the magnetic poles S1 and S2, the drop in the magnetic properties at the end of the magnet roller 29 is particularly severe, so the volume of the end of the magnetic poles S1 and S2 is increased to strengthen the magnetization. As a result, the magnetic characteristics in one round of the end of the magnet roller 29 can be made flatter.

<Example 4>
FIG. 14 is an explanatory diagram of a configuration of the magnet roller according to the fourth embodiment. As shown in FIG. 12, in Example 2, the edge effect was reduced by cutting out the outer periphery of the end of the magnet roller 29 to shorten the length of the permanent magnet. On the other hand, in Example 4, as shown in FIG. 14, the edge effect was reduced by notching the center side of the end of the magnet roller 29 to shorten the length of the permanent magnet. For this reason, the volume on the center side of the magnet roller 29 at the end in the longitudinal direction of the magnet roller 29 is smaller than the center in the longitudinal direction of the magnet roller 29.

  As shown in FIG. 12, when the outer diameter of the magnet is changed to suppress the edge effect, it is found that a ripple-like sudden change in magnetic characteristics is likely to occur corresponding to the portion where the outer diameter changes. It was. The reason why the magnetic characteristics of the ripple shape abruptly change is that the lines of magnetic force (flux lines) tend to concentrate in the portion where the diameter changes as in the end portion. This is because the magnetic field lines (magnetic flux lines) begin to circulate not only in the circumferential direction but also in the longitudinal direction because the periodic boundary condition is not satisfied in the portion where the diameter changes.

  Furthermore, since the outer diameter portion of the magnet roller 29 close to the developing sleeve 28 is changed, the fact that the change in magnetic characteristics easily affects the magnetic flux density at the surface position of the developing sleeve 28 is also greatly related. .

  Since the developing sleeve 28 holds the developer on the surface of the developing sleeve 28, the magnetic characteristics of the surface position of the developing sleeve 28 among the magnetic fields formed by the magnet roller 29 are the most important. Therefore, in order to make the developer carrying performance uniform around the surface of the developing sleeve located at the end of the magnet roller 29, the density of the magnetic flux generated by the magnet roller 29 on the surface of the developing sleeve 28 is flattened. is necessary. However, when the outer diameter of the magnet roller 29 is changed, there is an edge portion whose diameter changes in a portion close to the surface position of the developing sleeve 28. Therefore, the magnetic field lines (flux lines) in the longitudinal direction wrap around and are affected. Will be affected. Therefore, a ripple-like sudden magnetic characteristic change is likely to occur corresponding to the portion where the diameter changes.

  Therefore, in Example 4, the central portion of the magnet piece 41 adjacent to the support shaft 40 is cut away to weaken the magnetization, while the outer periphery of the magnet roller 29 is finished to a cylindrical shape with a uniform diameter up to the end. The feature is that the volume is reduced not by cutting out the outer diameter portion of the magnet roller 29 but by cutting out the center side.

  As shown in FIG. 14, the magnet roller 29 is configured by disposing a magnet piece 41 having a sector cross section for each of a plurality of magnetic poles around a support shaft 40 penetrating the center. In the magnet piece 41, the magnetic material is removed at the central portion adjacent to the support shaft 40 on the end face in the longitudinal direction.

  Also in the fourth embodiment, the magnet piece 41 is notched at both ends of the magnet roller 29, thereby reducing the volume of the magnetic material, shortening the length of the magnet, and reducing the rise in magnetic characteristics due to the edge effect. Since the volume of the magnet piece 41 is reduced even if the inner portion of the magnet piece 41 is cut out instead of the outer diameter portion, the magnetic flux density outside the magnet piece 41 is reduced in the same manner as when the outer diameter portion is cut out. It is possible.

  Therefore, also in the configuration of the fourth embodiment, it is possible to reduce the rise of magnetic characteristics due to the edge effect that originally exists at both ends, and it is possible to obtain flat magnetic characteristics.

  Moreover, in Example 4, since the outer peripheral surface was a columnar shape having a uniform diameter, a sharp ripple-like change in magnetic characteristics as in the case of irregularly changing the outer diameter was not observed. Also in the fourth embodiment, there is a wraparound of magnetic lines of force (magnetic flux lines) in the axial direction of the support shaft 40 at the cutout portion inside the magnet piece 41. However, since the position where the wraparound exists is greatly separated from the surface of the developing sleeve 28, the influence is hardly exerted. For this reason, there is no sudden change in ripple-like magnetic characteristics as in the case of changing the outer diameter.

  In the fourth embodiment, only the magnetic poles N1, N2, and N3 having a strong edge effect are cut out, and the magnetic poles S1 and S2 having a weak edge effect are not cut out. Thereby, even if the edge effect is different for each magnetic pole, it is possible to obtain flatter magnetic characteristics.

<Reason for different edge effects between N and S magnetic poles>
By the way, as shown in FIGS. 10B and 10C, outside the both end portions of the magnet roller 29, the magnetic poles do not depend on the N magnetic pole and the S magnetic pole, and both gradually converge from the S magnetic pole to 0. ing. The reason why both the N magnetic pole and the S magnetic pole converge on the S magnetic pole is considered as follows.

  The magnet piece 41 of the N magnetic pole is configured such that the outer peripheral surface (the surface on the side close to the developing sleeve 28) is an N magnetic pole, so that the inner side in contact with the support shaft 40 is an S magnetic pole. This is because there is no single-pole permanent magnet. Similarly, the magnet piece 41 having an S magnetic pole on the outer peripheral surface is an N magnetic pole on the inner side. Then, the wraparound in the longitudinal direction of the magnetic force lines (magnetic flux lines) at the end of the magnet roller 29 is mainly caused by extending from the magnetic pole on the outer peripheral surface toward the inner magnetic pole.

  Here, considering the magnetic characteristics at the end of the magnet roller 29, the magnetic characteristics immediately outside the end of the magnet roller 29 converge to either the N magnetic pole or the S magnetic pole. At this time, the convergence is determined by the balance of the magnetic poles on the inner surface of the magnet piece 41 in contact with the support shaft 40 of the magnet roller 29.

  The reason is that the magnetic lines of force (magnetic flux lines) extend from the magnetic poles on the outer peripheral surface of the magnet piece 41 relatively in the circumferential direction, whereas the magnetic lines of force (magnetic fluxes) extend from the magnetic poles inside the magnet piece 41 in the axial direction of the support shaft. This is because the line) extends. This is because the magnetic pole balance on the inner surface of the magnet piece 41 is effective in determining the magnetic characteristics on the outer side in the support shaft direction.

  From this point of view, looking at the comparative example of FIG. 7, the magnet roller 29 is composed of a total of 5 poles, 3 N poles and 2 S poles. The S magnetic pole of the pole is 3 poles, and the N magnetic pole opposite to the S magnetic pole is 2 poles. Therefore, on the inner side surface of the magnet piece 41, the S magnetic pole is in a state of winning as a balance.

  Accordingly, it is considered that the magnetic roller 29 converges from the S magnetic pole to 0 without depending on the N magnetic pole and the S magnetic pole on the outer side in the axial direction of the support shaft.

  As described above, when the magnetic roller 29 converges from the S magnetic pole to 0 outside the support shaft axial direction, the magnetic line of force (magnetic flux line) wraps around the end of the magnet piece 41 in the axial direction of the support shaft 40. Outside, it converges to the S magnetic pole regardless of the polarity of the magnetic pole.

  For this reason, when the outer peripheral surface is an N magnetic pole, the magnetic lines of force (magnetic flux lines) tend to extend between different poles, and the edge effect is relatively strong. On the other hand, when the outer peripheral surface is an S magnetic pole, the magnetic lines of force (magnetic flux lines) are not easily stretched between the same poles, the edge effect tends to be relatively weak, and in some cases, it falls gently.

  As described above, in a configuration including a plurality of magnetic poles, the magnetic field is largely divided into two, that is, a magnetic pole having a relatively strong edge effect and a magnetic pole having little edge effect. These phenomena occur because each magnetic pole of the magnet roller does not depend on its polarity and eventually converges to one of the polarities outside the magnet roller portion of the magnet roller in the axial direction of the support shaft. Yes.

  If the polarity converging on the outside in the axial direction of the magnet roller is called the convergence polarity, a magnetic pole having a polarity different from the convergence polarity tends to have a strong edge effect, and a magnetic pole having the same polarity as the convergence polarity has a weak edge effect.

  The converging polarity is determined by the magnetic pole balance on the inner surface of the magnet roller, and converges to the polarity of the magnetic pole that is well balanced. Actually, by measuring the magnetic flux density at the outer position of the end of the magnet roller with a teslameter, it is possible to know the polarity that easily converges.

  Since the present invention is directed to a mag roller having a magnet arranged around an axis, the polarity is determined by measuring a magnetic field in a circumferential direction perpendicular to the axis among magnetic fields generated by the magnet. In this case, when the direction of the magnetic field is away from the axis, it is an S magnetic pole, and when it is directed toward the axis, it is an N magnetic pole.

1a, 1b, 1c, 1d Photosensitive drums 3a, 3b, 3c, 3d Exposure devices 4a, 4b, 4c, 4d Developing device 22 Developing container, 23 Developing chamber, 24 Stirring chamber 25 Developing screw, 26 Stirring screw 28 Developing sleeve, 29 Magnet roller 40 Support shaft, 41 Magnet piece

Claims (4)

A developer carrying member carrying the developer;
In a developing device comprising a magnet member disposed inside the developer carrier,
The magnet member includes a first magnet portion having an outer surface having a first polarity and a second magnet portion having an outer surface having a second polarity different from the first polarity in the circumferential direction. ,
In the central portion of the magnet member in the longitudinal direction, the proportion of the first magnet portion occupied in the cross section perpendicular to the longitudinal direction of the magnet member is greater than the proportion of the second magnet portion occupied in the cross section. big,
The ratio of the first magnet portion occupied in the cross section perpendicular to the longitudinal direction of the magnet member is smaller at the end portion than at the longitudinal center portion of the magnet member, and at the longitudinal end portion of the magnet member. The volume on the outer surface side of the first magnet part is smaller than the center part in the longitudinal direction of the first magnet part.
A developing device. The volume on the outer surface side of the first magnet part is reduced so that the proportion of the first magnet part occupied in the cross section perpendicular to the longitudinal direction of the magnet member decreases toward the end in the longitudinal direction. It is configured to become smaller toward the end in the longitudinal direction,
The developing device according to claim 1. In a magnet roller provided with a first magnet part having an outer surface having a first polarity and a second magnet part having an outer surface having a second polarity different from the first polarity in the circumferential direction,
In the central portion of the magnet roller in the longitudinal direction, the proportion of the first magnet portion occupied in the cross section orthogonal to the longitudinal direction of the magnet roller is greater than the proportion of the second magnet portion occupied in the cross section. big,
The ratio of the first magnet portion occupied in the cross section perpendicular to the longitudinal direction of the magnet member is smaller at the end portion than at the longitudinal center portion of the magnet member, and at the longitudinal end portion of the magnet member. The volume on the outer surface side of the first magnet part is smaller than the center part in the longitudinal direction of the first magnet part.
A magnet roller characterized by that. The volume on the outer surface side of the first magnet part is reduced so that the proportion of the first magnet part occupied in the cross section perpendicular to the longitudinal direction of the magnet member decreases toward the end in the longitudinal direction. It is configured to become smaller toward the end in the longitudinal direction,
The magnet roller according to claim 3.

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