JP4339276B2 - Developing device and image forming apparatus to which the developing device is applied - Google Patents

Description

  The present invention is applied to a developing device configured to form a toner image by supplying toner toward an electrostatic latent image formed on a peripheral surface of a photosensitive drum by an electrophotographic method, and the developing device. The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, a developing device applied to an image forming apparatus adopting an electrophotographic method is known. This developing device supplies toner as a developer toward the electrostatic latent image formed on the peripheral surface of the photosensitive drum based on the image data, and the toner image formed on the peripheral surface is photosensitive. The sheet is transferred onto a sheet that is a material to be transferred that has been conveyed from the sheet storage unit by rotation around the axis of the body drum. A fixing device is provided immediately downstream of the photosensitive drum, and the paper on which the toner image is transferred is subjected to a fixing process for fixing the toner image on the paper by heating with the fixing device, and then discharged to the outside. It has become so.

  The developing device includes a stirring unit that stirs a developer (a toner in the case of a one-component system, a mixture of a toner and a carrier in a two-component system), and a toner that is being stirred by the stirring unit. And a cylindrical developing sleeve for supplying the toner to the peripheral surface of the photosensitive drum. The toner supplied from a predetermined toner cartridge into the housing is stirred as it is in the case of a one-component system, and is mixed and stirred with a carrier loaded in advance in the case of a two-component system, and rotates around an axis. The toner is supplied to the peripheral surface of the photosensitive drum in a uniform state through the peripheral surface of the developing sleeve. A blade is provided at a position directly above the peripheral surface of the developing sleeve facing the peripheral surface of the photosensitive drum through a predetermined gap, and the toner on the peripheral surface of the developing sleeve is relatively rubbed off by the blade. It is designed not to be excessively supplied to the body drum.

Among such developing devices, the one described in Patent Document 1 is attracting attention. This developing device has a thin-walled edge portion in which the thickness dimension of the edge surface of the blade facing the developing sleeve is set to be thinner than that of the blade body, and the magnetic lines of force of the magnets provided in the blade and the developing sleeve, respectively. It is made to concentrate on the edge part. As a result, a strong magnetic flux having a high density is formed in the gap space between the blade and the developing sleeve, so that the toner conveyed toward the photosensitive drum by the developing sleeve through the gap space is affected by this strong magnetic flux. Due to the restraint caused by the above, a uniform pressure is applied in the longitudinal direction of the blade, and thereby, a special effect can be obtained that a uniform state without coarseness is obtained.
JP 2003-167426 A

  As described above, the developing device described in Patent Document 1 has an excellent advantage that the toner in a uniform state is supplied from the developing sleeve toward the photosensitive drum. This also increases the amount of toner that is pushed out from this portion to both ends of the developing sleeve. In order to prevent the extruded toner from leaking from the end portion of the developing sleeve, a magnetic seal member made of a magnetic material is usually provided at both end portions of the developing sleeve, and the magnetic seal member and the magnet in the developing sleeve are provided. The leakage of toner is prevented by the magnetic flux bridged between the two.

  Accordingly, the toner pushed out from the end of the blade is prevented from moving by the magnetic seal member, and as a result, the pushed toner stays on the circumferential surface of the developing sleeve between the blade and the magnetic seal member. There is a problem in that the toner is bulged with toner accumulated in the portion, so-called toner thickening occurs.

  The present invention has been made in order to solve the above-described problems, and provides a developing device capable of preventing the toner thickening phenomenon formed on the peripheral surface of the developing roller from occurring. It is aimed.

According to the first aspect of the present invention, a developing sleeve having a sleeve-side magnet installed therein that supplies toner to a latent image area on the peripheral surface of the photosensitive drum while rotating around an axis is mounted in a predetermined casing. In the developing device, a blade that adjusts the supply amount of the toner to the photosensitive drum, which is disposed opposite to the central portion of the peripheral surface of the developing sleeve via a gap of a predetermined dimension, and the blade has a substantially entire length in the longitudinal direction. Attached to the blade-side magnet, and the blade-side magnet is provided at both ends so that the magnetic force of the magnetic field lines formed around the blade-side magnet is stronger than the magnetic force of the magnetic field lines generated by the sleeve-side magnet . The height dimension is set lower than the height dimension of the central portion.

  According to such a configuration, by rotating the developing sleeve around the axis while the toner is loaded in the housing, the toner in the housing is guided to the circumferential surface of the developing sleeve and is directed toward the photosensitive drum. Conveyed and supplied to the latent image area on the circumferential surface of the photosensitive drum rotating around the axis with the conveyance amount adjusted by diving through the gap between the blade side magnet and the lower edge of the blade and the circumferential surface of the developing sleeve Thus, a toner image is formed. This toner image is transferred to a sheet that has been synchronously conveyed in accordance with the rotation of the photosensitive drum.

  The blade side magnet is set so that the height dimension of both end portions is lower than the height dimension of the central portion. As a result, the magnetic force is stronger at both end portions of the blade side magnet than the central portion. The magnetic flux formed by cooperation with the sleeve side magnet is stronger than the central portion between the sleeve and the peripheral surface of the sleeve, and the toner on the peripheral surface of the developing sleeve is absorbed by the strong magnetic flux. The movement to the end is prevented, and the occurrence of toner thickening formed by the toner staying at the end of the developing sleeve is effectively prevented.

Incidentally, a magnet is manufactured by placing a magnetic material in a strong magnetic field space, but the magnetic flux in the magnetic field space has the property of concentrating on a thin part of the magnetic material, so the height dimension of both ends is If the set blade-side magnets lower than the central portion is left in the magnetic field space, both end portions become strong magnet from the central portion to concentrate the magnetic flux at both ends of the nature and the blade-side magnet.

  According to a second aspect of the present invention, in the first aspect of the invention, the setting of the height dimension of both end portions of the blade side magnet is performed by a step portion having a uniform height lower than the central portion. It is what.

  According to this configuration, since the height of the stepped portion is uniform, a magnetic force having the same strength is formed over the entire area of the stepped portion.

  According to a third aspect of the present invention, in the first aspect of the invention, the height dimension of both end portions of the blade-side magnet is set by an inclined portion whose height gradually decreases from the central portion toward the end portion. It is characterized by being.

  According to such a configuration, since the inclined portion gradually decreases in height as it goes toward the end, the magnetic force gradually increases toward the end.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the developing sleeve has an arcuate shape that is oppositely disposed at both end portions thereof with a gap of a predetermined dimension from the peripheral surface thereof. A pair of magnetic members are provided.

  According to such a configuration, even if the toner is directed toward the end of the developing sleeve through the end where the height of the blade side magnet is set low, the bridge is bridged between the magnetic member and the sleeve side magnet. This restricts the lines of magnetic force, thereby effectively preventing the toner from leaking from the end of the developing sleeve.

  According to a fifth aspect of the present invention, an image is formed such that a toner image is formed by supplying toner to an electrostatic latent image formed on the peripheral surface of the photosensitive drum, and the toner image is transferred to a sheet. In the forming apparatus, the developing device according to any one of claims 1 to 4 is applied to form the toner image.

  According to such a configuration, since the developing device according to any one of claims 1 to 4 is applied to the image forming apparatus, the image forming device functions as the developing device according to any one of claims 1 to 4. The effect is enjoyed, and the occurrence of toner thickening at both ends of the developing sleeve is effectively prevented.

  According to the first aspect of the present invention, the blade side magnet is set such that the height dimension of both end portions is set lower than the height dimension of the central portion, whereby both end portions of the blade side magnet have a stronger magnetic force than the central portion. Therefore, the magnetic flux formed by the cooperation of the sleeve side magnet is stronger than the central portion between this portion and the peripheral surface of the developing sleeve, and the developing sleeve is blocked by this strong magnetic flux. It is possible to prevent the toner on the peripheral surface from moving to the end of the developing sleeve, and to effectively prevent the toner from being formed by the toner staying at the end of the developing sleeve.

  According to the second aspect of the present invention, the step portions formed at both end portions of the blade-side magnet have the same height, thereby forming a magnetic force having the same strength over the entire step portion. Therefore, the clearance between the circumferential surfaces of the developing sleeves corresponding to the stepped portions generally refuses the intrusion of the toner with the same magnetic force, thereby effectively restricting the toner from exceeding the stepped portions.

  According to the third aspect of the present invention, the inclined portions formed at both end portions of the blade-side magnet gradually decrease as the height dimension goes toward the end portion, whereby the magnetic force gradually increases toward the end portion. Therefore, even if the toner enters the gap corresponding to the inclined portion, it is possible to reliably prevent further movement of the toner by the strongest magnetic force at the tip of the inclined portion.

  According to the fourth aspect of the present invention, since the developing sleeve is provided with a pair of magnetic members having an arc shape disposed opposite to each other with a gap of a predetermined dimension from the circumferential surface at both ends, even if the blade Even if the toner passes toward the end of the developing sleeve through the end portion where the height dimension of the side magnet is set low, the toner is restricted by the magnetic lines of force bridged between the magnetic member and the sleeve side magnet. Can be effectively prevented from leaking from the end of the developing sleeve.

  According to the fifth aspect of the present invention, the image forming apparatus can enjoy the effects of the developing device according to any one of the first to fourth aspects.

  FIG. 1 is a front cross-sectional view illustrating an embodiment of a printer to which a developing device according to the present invention is applied. As shown in FIG. 1, a printer (image forming apparatus) 10 includes a sheet storage unit 12 that stores sheets P to be subjected to a printing process, and one sheet fed from a sheet bundle P1 stored in the sheet storage unit 12. The apparatus main body 11 includes an image forming unit 13 that performs image transfer processing on the paper P and a fixing unit 14 that performs fixing processing on the paper P on which transfer processing has been performed by the image forming unit 13. In addition, a paper discharge unit 15 for discharging the paper P subjected to the fixing process by the fixing unit 14 is provided on the top of the apparatus main body 11.

  A predetermined number (one in this embodiment) of paper cassettes 121 is provided in the paper storage unit 12 so as to be detachable from the apparatus main body 11. A pickup roller 122 is provided at the upstream end (right side in FIG. 1) of the paper cassette 121 to feed out the paper P one by one from the paper bundle P1. The paper P fed out of the paper cassette 121 by driving the pickup roller 122 is supplied to the image forming unit 13 through the paper feed conveyance path 123 and the registration roller pair 124 provided at the downstream end of the paper feed conveyance path 123. It is supposed to be paper.

  The image forming unit 13 performs a transfer process on the paper P based on image information transmitted from a computer or the like, and is rotatable around a drum shaft 21 extending in the front-rear direction (direction perpendicular to the paper surface of FIG. 1). A charging roller 30, an exposure device 40, a developing device 50, a transfer roller 60, and a cleaning device 70 are arranged in a clockwise direction from a position immediately above the photosensitive drum 20 along the circumferential surface of the provided photosensitive drum 20. It is formed by being installed.

  The photosensitive drum 20 is for forming a toner image along the electrostatic latent image after forming an electrostatic latent image on the peripheral surface, and an amorphous silicon layer is laminated on the peripheral surface. It is suitable for forming these images. The photosensitive drum 20 is coaxially and integrally supported by a drum shaft 21 extending in the front-rear direction (a direction orthogonal to the paper surface of FIG. 1) at a substantially central portion of the apparatus main body 11, and is driven by driving means (not shown). The drum shaft 21 can rotate integrally with the drum shaft 21 by driving and rotating the drum shaft 21 in the clockwise direction.

  The charging roller 30 forms a uniform charge on the peripheral surface of the photosensitive drum 20 rotating in the clockwise direction around the drum core, and is driven while the peripheral surface is in contact with the peripheral surface of the photosensitive drum 20. Electric charges are applied to the photosensitive drum 20 while rotating. Instead of the charging roller 30, a corona discharge type that applies a charge to the peripheral surface of the photosensitive drum 20 by corona discharge from a wire may be employed.

  The exposure apparatus 40 irradiates the peripheral surface of the rotating photosensitive drum 20 with laser light to which intensity is applied based on image data transmitted from an external device such as a computer, and the laser light thereby is checked. The electrostatic latent image is formed on the peripheral surface by erasing the electric charge of the formed portion.

The developing device 50 supplies toner T, which is a developer, to the peripheral surface of the photosensitive drum 20 to attach the toner T to a portion of the peripheral surface where an electrostatic latent image is formed. A toner image is formed on the peripheral surface of the toner. In this embodiment, a so-called one-component system consisting only of toner T is used as the developer, but the present invention is a one-component system where the developer consists only of toner T. However, the developer may be a so-called two-component system in which the developer is composed of toner T and carrier.

Incidentally, the toner T is a fine powder having a particle diameter of 6 to 12 μm in which additives such as a colorant, a charge control agent and wax are dispersed in a binder resin. On the other hand, the carrier is magnetic particles having a particle size of 60 to 200 μm such as magnetite (Fe ₃ O ₄ ), and is used for charging the toner T. The toner T is a consumable that is appropriately supplied from the toner cartridge 59 to the developing device 50, whereas a predetermined amount of the carrier is loaded in the developing device 50 in advance, and is used without being consumed. In general, in this embodiment, no carrier is loaded in the developing device 50.

  The transfer roller 60 transfers a positively charged toner image formed on the peripheral surface of the photosensitive drum 20 to the paper P with respect to the paper P sent to a position immediately below the photosensitive drum 20. A negative charge having a polarity opposite to that of the toner image is applied to the paper P.

  Accordingly, the paper P that has passed the position immediately below the photosensitive drum 20 is pressed and held between the transfer roller 60 and the photosensitive drum 20, and the toner image on the circumferential surface of the photosensitive drum 20 that is positively charged is negatively charged. The sheet P is peeled off toward the surface of P, whereby the transfer process is performed on the sheet P.

  The cleaning device 70 is for removing and cleaning the toner T remaining on the peripheral surface of the photosensitive drum 20 after the transfer process. The peripheral surface of the photoconductive drum 20 cleaned by the cleaning device 70 goes to the charging roller 30 again for the next image forming process.

  The fixing unit 14 performs a fixing process by heating the toner image of the paper P that has been subjected to the transfer process by the image forming unit 13, and includes a heat roller 141 in which an energizing heating element such as a halogen lamp is mounted. A pressure roller 142 having a peripheral surface opposed to the lower portion of the heat roller 141 is provided. Then, the paper P after the transfer process is composed of a heat roller 141 that is driven to rotate clockwise around the roller center, and a pressure roller 142 that is driven to rotate counterclockwise around the roller center. By passing through the nip portion between them, heat from the heat roller 141 is obtained and the fixing process is performed. The paper P subjected to the fixing process is discharged to the paper discharge unit 15 through the paper discharge conveyance path 143.

  The paper discharge unit 15 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 151 for receiving the discharged paper P is formed at the bottom of the concave portion.

  FIG. 2 is a partially cut perspective view showing the first embodiment of the developing device 50, and FIG. 3 is a sectional view taken along the line AA. 2 and 3, the XX direction is referred to as the left-right direction, the YY direction is referred to as the front-rear direction, and in particular, the -X direction is referred to as the left, the + X direction is referred to as the right, the -Y direction is referred to as the front, and the + Y direction is referred to as the rear. . As shown in these drawings, the developing device 50 includes a first spiral feeder 51 that conveys toner replenished from the toner cartridge 59 toward the rear in a housing 58 having an irregular box shape. The second spiral feeder 52 that transports the toner delivered from the first spiral feeder 51 forward, and the toner T that is being transported by the second spiral feeder 52, and the peripheral surface of the photosensitive drum 20 And a developing sleeve 53 to be supplied to the latent image area.

  As shown in FIGS. 2 and 3, the housing 58 has an L shape when viewed from the −Y direction (FIG. 2), and the left side is inclined upward from a substantially central position in the left-right direction. The bottom plate 581 with the left end facing the photoconductive drum 20, the top plate 582 disposed on the top facing the bottom plate 581, and a pair of front and rear direction bridges between the bottom plate 581 and the front and rear ends of the top plate 582. Side plate 583 (the front side plate is indicated by a two-dot chain line in FIG. 2) and a toner receiving tray 584 installed between the pair of side plates 583.

  The top plate 582 is formed in a stepped shape with one step higher on the left side. The lower top plate 582a on the right side, the high top plate 582b on the left side, the left end edge of the lower top plate 582a, and the high top plate. It consists of a vertical top plate 582c installed between the right end edge of the plate 582b. A toner receiving port 582d for receiving toner from the toner cartridge 59 is provided at the front end of the lower top plate 582a. Further, between the left end edge of the high-top plate 582 b and the left end edge of the bottom plate 581, the toner T in the housing 58 is separated from the peripheral surface of the photosensitive drum 20 so as to face the peripheral surface of the photosensitive drum 20. A toner supply port 586 for supplying the toner is opened.

  The toner receiving tray 584 includes a first tray 584a that accommodates the first spiral feeder 51, a second tray 584b that accommodates the second spiral feeder 52, and a third tray 584c that is opposed to the developing sleeve 53 at the bottom. It has. The first to third trays 584a, 584b, 584c are each formed in an arc shape in front view so as to correspond to the corresponding first and second spiral feeders 51, 52 and the developing sleeve 53. Also, a right side wall 587 is provided at the right end of the first tray 584a, and this right side wall 587 is installed between the right ends of the bottom plate 581 and the lower top plate 582a, so that the right side in the housing 58 is closed. ing.

  The first spiral feeder 51 includes a first feeder shaft 511 penetrating between a pair of side plates 583 at a position immediately above the first tray 584a, and a first spiral concentrically fitted and fixed to the first feeder shaft 511. A fin 512 is provided. The first spiral fin 512 is formed in a spiral shape in a left-handed state, and the first feeder shaft 511 rotates clockwise in a front view so as to convey the toner T on the first tray 584a backward. It has become.

  The second spiral feeder 52 includes a second feeder shaft 521 penetrating between a pair of side plates 583 at a position directly above the second tray 584b, and a second spiral concentrically fitted and fixed to the second feeder shaft 521. The fin 522 is provided. The second spiral fin 522 is spirally formed in a right-handed state, and the second feeder shaft 521 rotates clockwise in front view so as to convey the toner T on the second tray 584b forward. It has become.

  A partition wall 585 is provided between the first and second trays 584a and 584b. A front circulation port 585a is opened at the front position of the partition wall 585, and a rear circulation port 585b is opened at the rear position. The toner T introduced from the toner cartridge 59 into the housing 58 via the toner receiving port 582d is first transported backward in the first tray 584a by the driving rotation of the first spiral feeder 51, and flows backward. It is carried into the second tray 584b through the opening 585b, conveyed forward in the second tray 584b by the driving rotation of the second spiral feeder 52, and thereafter circulated between the first and second trays 584a, 584b. However, a part is supplied to the developing sleeve 53.

  The developing sleeve 53 includes a sleeve shaft 531 penetrating between a pair of side plates 583 and a sleeve body 532 concentrically and integrally fitted to the sleeve shaft 531. The developing sleeve 53 is set at a position above the third tray 584c so that the circumferential surface of the sleeve main body 532 faces the circumferential surface of the photosensitive drum 20 through the toner supply port 586. By driving the driving means, the toner T rotates around the sleeve shaft 531 in the counterclockwise direction in FIG. 3, thereby causing the toner T fed onto the third tray 584 c to face the peripheral surface of the photosensitive drum 20. Yes.

  In the present invention, the toner T is properly supplied to the photoconductive drum 20 to the developing device 50 configured as described above, and the so-called toner is formed by staying at the end of the sleeve body 532. A toner thickening prevention structure 80 is attached to prevent thickening and to prevent leakage of the toner T from the end of the sleeve main body 532.

  FIG. 4 is a perspective view showing an embodiment of the toner thickening prevention structure 80 for explaining the toner thickening prevention structure 80. 5 is an explanatory view in plan view of the toner thickening prevention structure 80 shown in FIG. 4, FIG. 6 is an explanatory view in side view of the toner thickening prevention structure 80, and FIG. It is explanatory drawing of the front view of the prevention structure. 4 to 7 are the same as those shown in FIG. 2 (X is the left-right direction (-X: leftward, + X rightward), Y is the front-rear direction (-Y: forward, + Y). : Back)). Hereinafter, the toner thickness preventing structure 80 will be described with reference to FIGS. 4 to 7 with reference to FIGS.

  First, as shown in FIG. 4, the toner thickening prevention structure 80 includes a blade 81 extending in the front-rear direction that is suspended from the left edge of the high-level top plate 582 b of the housing 58 (FIG. 2) toward the peripheral surface of the sleeve body 532. And a pair of front and rear magnetic members 82 disposed opposite to the front and rear edges of the sleeve main body 532 at the right position of the sleeve main body 532, and a blade side magnet 83 stacked on the right side of the blade 81. It is configured.

  The blade 81 rotates with respect to the latent image region 22 on the peripheral surface of the photosensitive drum 20 by rotating the developing sleeve 53 about the sleeve shaft 531 (region where an electrostatic latent image between two-dot chain lines shown in FIG. 4 is formed). The amount of toner T supplied in this way is regulated so as not to be oversupplied, and is provided so as to substantially traverse the sleeve body 532 above the sleeve body 532.

  In the embodiment, the blade 81 has a gap dimension (gap B (see FIG. 6)) between the lower edge and the peripheral surface of the sleeve body 532 set to 0.1 mm to 0.5 mm. Such a range is set when the gap B is less than 0.1 mm, the gap is too narrow and the toner T cannot be properly supplied to the peripheral surface of the photoconductive drum 20. If the gap B exceeds 0.5 mm, the toner T is excessively supplied to the photosensitive drum 20, and the latent image area of the photosensitive drum 20 is not formed. This is because a toner image that is too dark at 22 is formed.

  In the present embodiment, the blade 81 has a vertical dimension set to approximately 25 mm in accordance with local conditions. However, the present invention is not limited to the blade 81 having a vertical dimension of approximately 25 mm. It may be set as appropriate according to the situation such as the design conditions.

  The thickness t (FIG. 5) of the blade 81 is set to 2.0 mm in the present embodiment, but is not limited to 2.0 mm, and is 2.0 mm depending on the situation. Or less than 2.0 mm.

  In the present invention, a magnetic material is used as the blade 81. A magnetic material is used for the blade 81 so that the magnetic lines of force from the blade-side magnet 83 attached to the blade 81 and the sleeve-side magnet 533 (FIG. 6) housed in the sleeve body 532 are guided to the blade 81. As a result, the magnetic head is guided to the magnetic drum by the magnetic force lines formed in cooperation with the toner T to which the electric charge is applied in the gap between the leading edge of the blade 81 and the peripheral surface of the sleeve main body 532, and the toner T is transferred to the photosensitive drum 20. This is to prevent the toner from becoming thick due to toner depositing on the end of the sleeve main body 532 in cooperation with the blade side magnet 83.

  The magnetic member 82 is for preventing the toner T from moving from the central peripheral surface of the sleeve main body 532 toward the end until the toner T reaches the blade 81 in the housing 58. It is formed in an arc shape having a central angle of curvature set to about 180 ° when viewed. As shown in FIG. 7, the magnetic member 82 has an upper end that is in contact with and fixed to the right surface of the blade 81, and a lower end that is opposed to the third tray 584 c of the housing 58, whereby the sleeve body A separated state with respect to 532 is ensured.

  According to such a magnetic member 82, a magnetic brush is formed between the magnetic member 82 and the sleeve-side magnet 533 provided in the sleeve main body 532, and the magnetic brush restricts the movement of the toner T. The toner T is effectively prevented from moving from the peripheral surface of the sleeve main body 532 toward the end thereof.

  Such a magnetic member 82 has a curvature inner diameter dimension set to be larger by 0.1 mm to 0.5 mm than an outer diameter dimension of the sleeve main body 532. Such a range is set when the difference in the inside diameter of the curvature of the magnetic member 82 is less than 0.1 mm, the gap is too narrow and the peripheral surface of the sleeve body 532 is in sliding contact with the inner surface of the magnetic member 82. On the other hand, if the dimensional difference between the curvature inner diameters exceeds 0.5 mm, the toner T cannot be reliably prevented from leaking by the magnetic brush.

  Further, as shown in FIG. 6, such a magnetic member 82 has an inner end slightly in the front-rear direction of the sleeve main body 532 (the left-right direction of the paper surface in FIG. 6) and the end of the sleeve-side magnet 533. The installation position is set so as to overlap. In the present embodiment, the overlap amount m is set to 0.5 mm, but is not limited to 0.5 mm, and the overlap amount can be appropriately set according to the situation. The amount of overlap m is set because the magnetic brush from the sleeve-side magnet 533 is straightly formed in the radial direction of the sleeve-side magnet 533, so that the action of the magnetic force of the magnetic brush is maximized. This is to effectively restrict the movement of T toward the end of the sleeve body 532.

  Further, the magnetic member 82 has a front-rear width dimension C set to 5 mm to 10 mm. Such a range is set as the front-rear width dimension C. When the front-rear width dimension of the magnetic member 82 is less than 5 mm, the toner movement restriction force of the magnetic brush becomes weak because the width dimension is too small. While the toner T on the peripheral surface of the main body 532 cannot be sufficiently restricted from moving to the end portion of the sleeve main body 532, when the front-rear width dimension of the magnetic member 82 exceeds 10 mm, the toner movement restricting force of the magnetic brush is reduced. This is because there is no need to make the length more than 10 mm because it does not improve so much.

  The blade-side magnet 83 appropriately supplies the toner T on the circumferential surface of the sleeve body 532 in cooperation with the sleeve-side magnet 533 and the blade 81 made of a magnetic material that are mounted in the sleeve body 532 without moving. 4 to prevent the toner thickening from forming on the peripheral surface of the end portion of the sleeve body 532. As shown in FIG. 4, a pair of blades on the upstream side (right surface side) of the blade 81 is provided. The magnetic member 82 is fixed in a laminated state. The blade-side magnet 83 has a plate-like magnet body 831 formed by being set to be long in the front-rear direction, and a vertical dimension projecting in opposite directions from both ends of the magnet body 831. 831 and a step portion 832 that forms a step lower than that of 831.

  In the present embodiment, the magnet body 831 has a vertical dimension of 10 mm and a thickness dimension of 1.5 mm. In the present invention, the magnet body 831 has a vertical dimension of 10 mm. In addition, the thickness dimension is not limited to 1.5 mm, and an optimum value is appropriately set according to the situation.

  The step portion 832 is formed in a state where both end portions of the blade-side magnet 83 are cut out by a predetermined dimension from above. In this embodiment, the stepped portion 832 has a vertical dimension set to 4 mm and a protruding amount from the magnet body 831 set to 7 mm. The thickness dimension is set to 1.5 mm which is the same as that of the magnet body 831. The present invention is not limited to the vertical dimension, the protruding amount, and the thickness dimension of the stepped portion 832 being 4 mm, 7 mm, and 1.5 mm, respectively, and optimal values are appropriately set according to the situation. .

  In the present invention, the blade-side magnet 83 configured as described above is attached to the blade 81, so that the toner T on the circumferential surface of the sleeve body 532 can be appropriately supplied to the circumferential surface of the photosensitive drum 20. In addition, toner thickening can be prevented from being formed on the peripheral surface of the end portion of the sleeve main body 532.

  8A and 8B are enlarged explanatory views for explaining the operation of the toner thickening prevention structure 80. FIG. 8A is a cross-sectional view taken along line BB of FIG. 4, and FIG. 8B is a cross-sectional view taken along line CC of FIG. It is line sectional drawing. In addition, the direction display by X in FIG. 8 is the same as in FIG. 2 (−X: left, + X right). In FIG. 8, the size of the gap between the sleeve body 532 and the magnetic member 82 and the magnetic member side magnet 83 is exaggerated.

  First, in the present embodiment, as shown in FIGS. 8A and 8B, the sleeve-side magnet 533 that is housed in the sleeve body 532 in a non-moving state has a plurality of units that have a fan shape in a front view. Magnets (upper right first unit magnet 533a and upper left second unit magnet 533b are shown in FIG. 8) are integrated and formed in a cylindrical shape. The boundary position between the first unit magnet 533 a and the second unit magnet 533 b on the peripheral surface of the sleeve side magnet 533 is formed immediately below the blade side magnet 83. The first unit magnet 533a is set to the S pole on the circumferential surface side, and the second unit magnet 533b is set to the N pole on the circumferential surface side, while the blade side magnet 83 has the S side at the bottom. It is set to the pole.

  In the state where the sleeve side magnet 533 and the blade side magnet 83 are arranged and set in this way, the strength of the magnetic field lines that are bridged between the south pole of the first unit magnet 533a and the north pole of the second unit magnet 533b is increased. And the strength of the magnetic force of the magnetic field lines bridged between the S pole of the magnet body 831 of the blade-side magnet 83 and the N pole via the blade 81 are set to be the same, so that the circumferential surface of the sleeve body 532 In the portion corresponding to the magnet main body 831 of the blade side magnet 83, the magnetic field lines of the sleeve side magnet 533 and the magnetic field lines of the magnet main body 831 on the blade side magnet 83 side substantially antagonized, as shown in FIG. It is in a state.

  Accordingly, the toner T on the peripheral surface of the sleeve main body 532 is appropriately supplied toward the photosensitive drum 20 by being guided by the antagonistic magnetic lines of force by rotation around the center of the sleeve main body 532. become.

  On the other hand, since the step part 832 whose vertical dimension is shorter than the magnet body 831 is provided at the end part of the blade side magnet 83, the step part of the blade side magnet 83 is shown in FIG. The magnetic flux density of the magnetic field lines bridged between the S pole and the N pole in 832 is increased, whereby the magnetic force of the magnetic field lines formed around the magnet body 831 is greater than the first unit magnet 533a and the second unit magnet 533b. The magnetic field lines of the stepped portion 832 are stronger than the magnetic field lines bridged between the magnetic field lines and push the magnetic field lines of the sleeve-side magnet 533 downward. A strong exclusion force acts.

  Accordingly, the toner T that has reached the blade-side magnet 83 due to the counterclockwise rotation of the sleeve main body 532 is restricted from moving toward the end of the sleeve main body 532 by the strong displacement force. The toner T is prevented from accumulating on the inner side of the magnetic member 82, and the occurrence of toner fat due to the volume is prevented.

  As described above in detail, the developing device 50 according to the present invention includes the sleeve-side magnet 533 that supplies the toner T to the latent image region 22 on the peripheral surface of the photosensitive drum 20 while rotating around the sleeve shaft 531. The developing sleeve 53 is mounted in a predetermined casing, and the supply amount of the toner T, which is disposed opposite to the central portion of the peripheral surface of the developing sleeve 53, to the photosensitive drum 20 through a gap of a predetermined dimension. And a blade-side magnet 83 attached to the blade 81 over substantially the entire length in the longitudinal direction. The blade-side magnet 83 has a height dimension at both ends that is higher than a height dimension at the center. It is set low.

  According to such a configuration, by rotating the developing sleeve 53 about the axial center in a state where the toner T is loaded in the housing, the toner T in the housing is guided to the peripheral surface of the developing sleeve 53 and the photosensitive drum 20. , And is rotated around the drum shaft 21 in a state where the conveyance amount is adjusted by diving through the gap between the lower edge of the blade side magnet 83 and the blade 81 and the peripheral surface of the developing sleeve 53. The toner T image is formed by being supplied to the latent image region 22 on the circumferential surface of the drum 20. This toner T image is transferred onto the paper that has been conveyed in synchronization with the rotation of the photosensitive drum 20.

  The blade-side magnet 83 is set such that the height dimension of both end portions is set lower than the height dimension of the central portion, whereby the both end portions of the blade-side magnet 83 are stronger in magnetic force than the central portion. The magnetic flux formed by the cooperation with the sleeve-side magnet 533 is stronger than the central portion between the peripheral surface of the developing sleeve 53 and the peripheral surface of the developing sleeve 53. The toner T is prevented from moving to the end portion of the developing sleeve 53, and the toner thickening formed by the toner T staying at the end portion of the developing sleeve 53 can be effectively prevented.

Incidentally, a magnet is manufactured by placing a magnetic material in a strong magnetic field space, but the magnetic flux in the magnetic field space has the property of concentrating on a thin part of the magnetic material, so the height dimension of both ends is If the blade-side magnet 83 set lower than the central portion is left in the magnetic field space, the magnetic flux naturally concentrates at both ends of the blade-side magnet, thereby obtaining a magnet whose both ends are stronger than the central portion.

  In the above embodiment, since the stepped portion 832 having the same height and the height set lower than the magnet body 831 at the central portion is provided at both end portions of the blade side magnet 83, the stepped portion. The strength of the magnetic force formed between 832 and the sleeve main body 532 is the same over the entire stepped portion 832, and the toner T that has entered the lower portion of the magnet main body 831 is the same within the range of the stepped portion 832. The movement toward the end of the sleeve main body 532 is restricted by the force, whereby the toner T can be effectively restricted from exceeding the stepped portion 832.

  Further, since the developing sleeve 53 is provided with a pair of magnetic members 82 having an arc shape disposed opposite to both ends with a gap of a predetermined dimension from the peripheral surface thereof, even if the height of the blade-side magnet 83 is increased. Even if the toner T passes through the end portion whose size is set low and approaches the end portion of the developing sleeve 53, the toner T is restricted by the magnetic lines of force bridged between the magnetic member 82 and the sleeve side magnet 533, and thereby the toner T Can be effectively prevented from leaking from the end of the developing sleeve 53.

  Then, by adopting the developing device 50 to which the toner thickening prevention structure 80 is applied to the printer 10, the printer 10 enjoys the function and effect provided by the developing device 50, and the developing sleeve. Therefore, it is possible to effectively prevent image defects due to the occurrence of toner thickening at both ends of the toner, and it is possible to always perform clean print output without contamination.

  The present invention is not limited to the above embodiment, and includes the following contents.

  (1) In the above embodiment, the printer 10 is described as an example of the image forming apparatus to which the developing device 50 is applied. However, the present invention is limited to the image forming apparatus being the printer 10. Instead, it may be a copying machine, a facsimile machine, or a scanner that reads image information and sends it to a computer.

  (2) In the above embodiment, the stepped portion 832 having a constant height is provided at both end portions of the blade-side magnet 83, but instead of the stepped portion 832, the vertical dimension extends from the magnet body 831 to the tip. You may provide the inclination part which decreases gradually as it goes. In the case where such an inclined portion is provided, the magnetic force formed by the inclined portion gradually increases toward the end portion, so that even if the toner T enters the area of the inclined portion, it is most at the tip of the inclined portion. Further movement of the toner T can be reliably prevented by the strong magnetic force.

  (3) In the above embodiment, the south pole of the blade side magnet 83 and the south pole of the first unit magnet 533a are arranged opposite to each other on the upstream side of the blade side magnet 83. The S pole of the blade-side magnet 83 and the S pole of the first unit magnet 533a are not limited to be disposed on the upstream side of 83, and the N poles may be disposed to face each other. You may arrange mutually.

  (4) In the above-described embodiment, a two-part separation type in which the toner T is replenished to the developing device 50 from the toner cartridge 59 that is detachably mounted is applied. The cartridge 59 is not limited to such a separation type, and may be a so-called developing unit in which the toner cartridge 59 is integrated with the housing 58 of the developing device 50 from the beginning. In the case of such a developing unit, the toner out is eliminated by replacing the old and new developing units.

1 is an explanatory front sectional view showing an embodiment of a printer to which a developing device according to the present invention is applied. FIG. 3 is a partially cut perspective view showing the first embodiment of the developing device. It is the sectional view on the AA line of FIG. FIG. 6 is a perspective view illustrating an embodiment of a toner thickening prevention structure. FIG. 5 is an explanatory view in plan view of the toner thickening prevention structure shown in FIG. 4. FIG. 5 is a side view of the toner thickening prevention structure shown in FIG. 4. FIG. 5 is a front view of the toner thickening prevention structure shown in FIG. 4. 5A and 5B are explanatory views for explaining the operation of the toner thickening prevention structure, in which FIG. 4A is a cross-sectional view taken along the line BB in FIG. 4, and FIG. 4B is a cross-sectional view taken along the line CC in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Printer (image forming apparatus) 11 Apparatus main body 12 Paper storage part 121 Paper cassette 122 Pickup roller 123 Paper feed conveyance path 124 Registration roller pair 13 Image forming part 14 Fixing part 141 Heat roller 142 Pressure roller 143 Paper discharge conveyance path 15 Ejection Paper unit 151 Paper discharge tray 20 Photosensitive drum 21 Drum shaft 22 Latent image area 30 Charging roller 40 Exposure device 50 Development device 51 Spiral feeder 511 Feeder shaft 512 Spiral fin 52 Spiral feeder 521 Feeder shaft 522 Spiral fin 53 Development sleeve 531 Sleeve shaft 532 Sleeve body 533 Sleeve side magnet 533a Unit magnet 533b Unit magnet 58 Case 581 Bottom plate 582 Top plate 582a Low top plate 582b High top plate 582c Vertical top plate 582d Toner receiving Outlet 583 Side plate 584 Toner receiving tray 584a First tray 584b Second tray 584c Third tray 585 Partition wall 585a Front distribution port 585b Rear distribution port 586 Toner supply port 587 Right side wall 59 Toner cartridge 60 Transfer roller 70 Cleaning device 80 Prevention structure 81 Blade 82 Magnetic member 83 Blade side magnet 831 Magnet body 832 Stepped portion B Gap C Front / rear width P Paper P1 Paper bundle T Toner

Claims (5)

In a developing device in which a developing sleeve having a sleeve-side magnet mounted therein is mounted in a predetermined housing for supplying toner to a latent image area on the peripheral surface of the photosensitive drum while rotating around an axis.
A blade that adjusts the supply amount of toner to the photosensitive drum disposed opposite to the central portion of the peripheral surface of the developing sleeve via a gap of a predetermined dimension;
A blade-side magnet attached to the blade over substantially the entire length in the longitudinal direction,
The blade side magnet has a height dimension at both ends lower than that of the central part so that the magnetic force of the magnetic field lines formed around the blade side magnet is stronger than the magnetic force of the magnetic field lines generated by the sleeve side magnet. A developing device that is set.   2. The developing device according to claim 1, wherein the height dimension of both end portions of the blade-side magnet is set by a step portion having a uniform height lower than the center portion.   2. The developing device according to claim 1, wherein the height dimension of both end portions of the blade side magnet is set by an inclined portion whose height gradually decreases from the central portion toward the end portion.   4. The developing sleeve according to claim 1, wherein a pair of magnetic members exhibiting an arc shape are provided on both ends of the developing sleeve so as to face each other with a gap of a predetermined dimension from the peripheral surface thereof. The developing device according to 1. In an image forming apparatus configured to form a toner image by supplying toner to an electrostatic latent image formed on the peripheral surface of the photosensitive drum, and to transfer the toner image to a sheet of paper,
An image forming apparatus, wherein the developing device according to claim 1 is applied to form the toner image.

Images