JP2008129109A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing a decrease of a quantity of two-component developer conveyed on the developing sleeve. <P>SOLUTION: The blade 41 regulates the thickness of two-component developer attracted to the developing sleeve 39 by using a gap G formed between the blade 41 and the developing sleeve 39. The blade 41 is disposed on a developer conveyance path R2 between a magnet N2 (an example of a first magnet) and a magnet S1 (an example of a second magnet) and closer to the magnet S1 than to the magnet N2. In the gap G, a distance d between the end face 71 of the blade 41 and the surface of the developing sleeve 39 decreases toward the downstream side of the developer conveyance path R2 from the upstream of it. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system for recording an image.

  One of the image recording techniques used in image forming apparatuses (for example, digital multifunction peripherals, copiers, and printers) is electrophotography. In electrophotography, the surface of the photosensitive drum is uniformly charged (charging step), and the photosensitive drum is irradiated with a light image corresponding to the image by an illumination optical system to form an electrostatic latent image on the photosensitive drum ( Exposure process), a process of forming a toner image on the photosensitive drum by attaching toner to the electrostatic latent image on the photosensitive drum (developing process), and a process of transferring the toner image on the photosensitive drum to recording paper (transfer process) And a step of fixing the transferred toner image on the recording paper (fixing step).

  In the developing process, the developer is conveyed to the photosensitive drum by the developing roller. There is a two-component developer as a developer used in the development process. The two-component developer includes a toner made of a nonmagnetic material and a carrier made of a magnetic material. In the method using a two-component developer, the toner and the carrier are agitated to electrostatically couple the toner to the carrier, and then the development is performed with the carrier attracted to the sleeve (developing sleeve) of the developing roller by the magnet of the developing roller. The two-component developer is conveyed to the photosensitive drum by rotating the sleeve. The toner bonded to the carrier is electrostatically attracted by the electrostatic latent image on the photosensitive drum. As a result, the toner is separated from the carrier, and a toner image is formed on the photosensitive drum.

When the transport amount of the two-component developer on the developing sleeve decreases, white spots occur in the image recorded on the recording paper. For this reason, the invention which improves the technique which conveys two-component developer with a developing roller is proposed (for example, refer patent document 1 and patent document 2).
JP 2003-107860 A JP 2004-93672 A

  An object of the present invention is to provide an image forming apparatus capable of preventing a decrease in the transport amount of the two-component developer on the developing sleeve.

  An aspect of the image forming apparatus according to the present invention is an image forming apparatus provided with a developing unit that develops an electrostatic latent image formed on a photosensitive drum using a two-component developer, and the developing unit is agitated. A transport roller for transporting the two-component developer, a developing sleeve, a first magnet for attracting the two-component developer transported by the transport roller to the developing sleeve, the first magnet, and the photosensitive drum side And a magnet roller having a second magnet whose magnetic pole directed toward the developing sleeve is different from the first magnet, and two-component development is performed by the first and second magnets. A developing roller for rotating the developing sleeve on which the agent is sucked to convey the two-component developer to the photosensitive drum, and a developer conveying path from the first magnet to the second magnet. Above The thickness of the two-component developer that is provided closer to the second magnet than the first magnet and is sucked to the developing sleeve using a gap formed between the developing sleeve and the first magnet. A distance between the end surface of the blade and the surface of the developing sleeve is reduced from the upstream side to the downstream side of the developer transport path in the gap. To do.

  Another aspect of the image forming apparatus according to the present invention is an image forming apparatus including a developing unit that develops an electrostatic latent image formed on a photosensitive drum using a two-component developer, the developing unit including: A conveying roller that conveys the agitated two-component developer, a developing sleeve, a first magnet that draws the two-component developer conveyed by the conveying roller to the developing sleeve, the first magnet, and the photosensitive drum And a magnet roller having a second magnet different from the first magnet, the magnetic pole being provided at an adjacent position on the side and directed toward the developing sleeve, and having two components by the first and second magnets A developing roller that rotates the developing sleeve on which the developer is sucked to convey the two-component developer to the photosensitive drum, and a developer conveyance path from the first magnet to the second magnet. Before The two-component developer attracted to the developing sleeve is provided at a position closer to the second magnet than to the first magnet, and uses a gap formed with the developing sleeve. A blade for regulating the thickness, wherein the first magnet and the second magnet have the same magnetic force.

  In another aspect of the image forming apparatus according to the present invention, in the gap, the distance between the end surface of the blade and the surface of the developing sleeve is reduced from the upstream side to the downstream side of the developer conveying path. Can be.

  According to one aspect of the image forming apparatus according to the present invention, the blade is located closer to the second magnet than to the first magnet. For this reason, the two-component developer positioned in the gap between the blade and the developing sleeve is attracted to the second magnet rather than the first magnet. Accordingly, since the influence of the frictional force generated on the two-component developer in the gap can be reduced, it is possible to prevent a decrease in the transport amount of the two-component developer.

  In the image forming apparatus according to the aspect of the invention, in the gap, the distance between the end surface of the blade and the surface of the developing sleeve is decreased from the upstream side to the downstream side of the developer conveyance path. As a result, the physical resistance when the two-component developer is conveyed can be lowered, and from this point, the decrease in the conveyance amount of the two-component developer can be prevented.

  According to another aspect of the image forming apparatus according to the present invention, the blade is located closer to the second magnet than to the first magnet, and the magnitude of the magnetic force between the first magnet and the second magnet is further increased. Are the same. For this reason, the two-component developer positioned in the gap between the blade and the developing sleeve is attracted to the second magnet rather than the first magnet. Accordingly, since the influence of the frictional force generated on the two-component developer in the gap can be reduced, it is possible to prevent a decrease in the transport amount of the two-component developer.

  According to another aspect of the image forming apparatus according to the present invention, the magnetic force between the first magnet and the second magnet is provided by providing the blade at a position closer to the second magnet than to the first magnet. Even if the sizes of the two are the same, it is possible to prevent a decrease in the transport amount of the two-component developer. Therefore, an increase in the cost of the developing roller can be avoided.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 records an image on a recording sheet by using an electrophotographic method, and can be applied to a digital multifunction peripheral, a copy-only machine, a facsimile-only machine, and a printer-only machine.

  The image forming apparatus 1 includes a paper feed cassette 3, a photosensitive drum 5, a charger 7, an exposure device 9, a developing device 11, a transfer roller 13, a fixing device 15, a motor 17, a controller 19, and the like.

  Recording paper P is stored in the paper feed cassette 3. The recording paper P in the paper feed cassette 3 is fed out one by one by the pickup roller 21 to the paper transport path R1. The pickup roller 21 rotates with the torque from the motor 17 transmitted via a sheet feeding clutch (not shown). Torque from the motor 17 is also used to rotate the photosensitive drum 5 and the like. Therefore, the controller 19 controls the sheet feeding clutch to control the rotation timing of the pickup roller 21. The recording paper P fed out to the paper conveyance path R1 is recorded with an image by an electrophotography, which will be described below, and is discharged onto a paper discharge tray.

  A photoconductive film is formed on the surface of the photosensitive drum 5. Around the photosensitive drum 5, a charger 7, an exposure device 9, a developing device 11, a transfer roller 13, and the like are arranged.

  The charger 7 uniformly charges the photoconductive film formed on the surface of the photosensitive drum 5 by, for example, corona discharge.

  The exposure device 9 is an illumination optical system including an LED array, for example, and controls lighting of each LED of the LED array based on image data (this image data is the basis of an image recorded on the recording paper P). Then, the rotating photosensitive drum 5 is exposed in a uniformly charged state. As a result, the charge is removed from the surface of the photosensitive drum 5 where the light from the LED is irradiated, and an electrostatic latent image is formed on the surface of the photosensitive drum 5.

  The developing device 11 includes a stirring roller 31, a conveying roller 33, a developing roller 35, and a case 37 in which these rollers are disposed and a two-component developer is accommodated. The stirring roller 31 has a screw shape. The toner and the carrier are frictionally charged by rotating the stirring roller 31 and stirring the toner and the carrier constituting the two-component developer. As a result, the toner and the carrier are electrostatically coupled and conveyed to the developing roller 35 using the conveyance roller 33 called a paddle roller.

  The two-component developer conveyed to the developing roller 35 is attracted by the magnet N2 of the developing roller 35 and sucked to the developing sleeve 39 of the developing roller 35. When the two-component developer is conveyed to the photosensitive drum 5 in a state where the thickness of the two-component developer on the developing sleeve 39 is not uniform, the image quality of the image recorded on the recording paper P is deteriorated (for example, two-component developer). If the amount of developer transported is small, white spots occur in the image).

  Therefore, the thickness of the two-component developer sucked on the developing sleeve 39 is regulated by the blade 41 in the process of being conveyed to the photosensitive drum 5. This regulation is referred to as ear cutting, and thereby the thickness of the two-component developer on the developing sleeve 39 is made uniform. The blade 41 is fixed to the bracket 45 via the spacer 43, and the bracket 45 is fixed to the case 37.

  The toner contained in the two-component developer conveyed from the developing roller 35 to the photosensitive drum 5 is attracted by the electrostatic latent image formed on the photosensitive drum 5 and moves to the photosensitive drum 5. As a result, the electrostatic latent image on the photosensitive drum 5 is developed, and a toner image is formed on the photosensitive drum 5.

  The recording paper P conveyed along the paper conveyance path R 1 is nipped by the photosensitive drum 5 and the transfer roller 13. Since a bias voltage is applied to the transfer roller 13, the toner image on the photosensitive drum 5 is transferred onto the recording paper P. After the transfer, the photosensitive drum 5 is cleaned to remove the two-component developer remaining on the photosensitive drum 5, and image recording starting from the charging process is made possible again.

  The recording paper P to which the toner image is transferred moves along the paper transport path R1 and is sent to the fixing device 15. The fixing device 15 includes a heating roller 51 and a pressure roller 53. The heating roller 51 has a cylindrical shape, and a heater 55 made of, for example, a halogen lamp is disposed in the cylinder. A temperature sensor 57 such as a thermistor is disposed near the surface of the heating roller 51. The temperature measured by the temperature sensor 57 is sent to the controller 19. Based on this temperature data, the controller 19 controls the surface temperature of the heating roller 51 by switching the heater 55 on and off.

  The recording paper P is heated while being fed while being nipped by the heating roller 51 and the pressure roller 53. As a result, the toner forming the toner image is melted and fixed on the recording paper P. Thereafter, the recording paper P is sent to the paper discharge tray.

  Next, the developing roller 35 and the blade 41 will be described in detail. FIG. 2 is a diagram illustrating the positional relationship of the blade 41 with respect to the developing roller 35. The developing roller 35 includes a developing sleeve 39 and a magnet roller 61 disposed in the developing sleeve 39 coaxially therewith.

  The developing sleeve 39 is made of a nonmagnetic material such as aluminum. The developing sleeve 39 is rotated by torque from the motor 17 shown in FIG. On the other hand, the magnet roller 61 is fixed without rotating.

  The surface of the magnet roller 61 is made of a magnetic material. By selectively magnetizing the surface of the magnet roller 61, five magnets N2, S1, N1, S2, and S3 are formed on the surface. Instead of magnetizing, those magnets may be attached to the surface of the magnet roller 61.

  The magnet N2 (an example of a first magnet) is provided in the vicinity of the conveyance roller 33 with the north pole facing the developing sleeve 39. The two-component developer conveyed by the conveyance roller 33 is attracted to the developing sleeve 39 by the magnet N2. The magnet S1 (an example of a second magnet) is provided at a position adjacent to the magnet N2 and the photosensitive drum 5 side with the south pole facing the developing sleeve 39.

  The magnet N1 is provided next to the magnet S1 and in the vicinity of the photosensitive drum 5 with the north pole facing the developing sleeve 39. The magnet S2 is provided next to the magnet N1 with the south pole facing the developing sleeve 39 side. The magnet S3 is provided next to the magnet S2 with the south pole facing the developing sleeve 39 side.

The magnetic flux density of the magnet is, for example, as follows.
Magnet N2 ... 600G
Magnet S1 ... 600G
Magnet N1 ... 1000G
Magnet S2 ... 600G
Magnet S3 ... 300G

  The two-component developer conveyed from the conveyance roller 33 is placed on the rotating developing sleeve 39 and conveyed to the photosensitive drum 5. In order to prevent the two-component developer from falling from the developing sleeve 39 during the conveyance, the two-component developer is removed by using the magnetic field formed by the magnet N2 and the magnet S1 and the magnetic field formed by the magnet S1 and the magnet N1. Suck onto the developing sleeve 39. Reference numeral R <b> 2 indicates a conveyance path of the two-component developer from the conveyance roller 33 to the photosensitive drum 5 (hereinafter referred to as “developer conveyance path”).

  In the magnets S2 and S3, the magnetic poles having the same polarity are directed toward the developing sleeve 39, so that no magnetic field lines are formed between these magnets. Therefore, the two-component developer that is not used for development (that is, the carrier and the toner that is not used for development) is peeled off from the developing sleeve 39 and returned to the developing device 11 shown in FIG.

  A gap G formed between the blade 41 and the developing sleeve 39 is used to regulate the thickness of the two-component developer sucked on the developing sleeve 39. The position of the blade 41 will be described. A virtual straight line passing through the position of the magnet N2 and the center C of the magnet roller 61 is a straight line L1, a virtual straight line passing through the position of the magnet S1 and the center C is a straight line L2, and a virtual straight line passing through the position of the blade 41 and the center C is a straight line L3. . The angle formed by the straight line L1 and the straight line L2 is, for example, 60 °. A virtual straight line that bisects this angle is defined as a straight line L4.

  The angle formed by the straight lines L1 and L3 is 33 °, and the angle formed by the straight lines L2 and L3 is 27 °. When this is generalized, the blade 41 is a developer transport path R2 from the magnet N2 (an example of the first magnet) to the magnet S1 (an example of the second magnet), and the magnet S1 is more than the magnet N2. It is located near the top. The effect produced by this will be described.

  When the thickness of the two-component developer is regulated by the blade 41, a frictional force acts on the two-component developer. Since this frictional force acts in the direction opposite to the conveying direction of the two-component developer, the conveying amount of the two-component developer on the developing sleeve 39 may be reduced. In the present embodiment, the blade 41 is located closer to the magnet S1 than the magnet N2, and the magnets N2 and S1 have the same magnetic force (600G). For this reason, the two-component developer positioned in the gap G between the blade 41 and the developing sleeve 39 is attracted to the magnet S1 rather than the magnet N2. Therefore, since the influence of the frictional force can be reduced, the conveyance of the two-component developer on the developing sleeve 39 is stabilized, and thereby it is possible to prevent a decrease in the conveyance amount of the two-component developer.

  By adjusting the thickness of the spacer 43 provided between the blade 41 and the bracket 45, the optimum position of the blade 41 can be achieved in order to prevent a decrease in the transport amount of the two-component developer. The blade 41 is made of a nonmagnetic metal (for example, brass), the bracket 45 is made of a nonmagnetic metal (for example, stainless steel), and the spacer 43 is made of, for example, stainless steel.

  In the present embodiment, the magnitudes of the magnetic forces of the magnet N2 and the magnet S1 are the same (both magnets have a magnetic flux density of 600 G). However, if the magnetic force of the magnet S1 is made larger than the magnetic force of the magnet N2, the force with which the two-component developer is attracted by the magnet S1 increases. Therefore, even if the position of the blade 41 is not adjusted, the transport amount of the two-component developer It seems to be able to prevent the decrease.

  Since the magnet N2 has a role of attracting the two-component developer conveyed by the conveyance roller 33 to the developing sleeve 39, the magnetic force of the magnet N2 cannot be reduced. Therefore, the magnetic force of the magnet S1 must be further increased. However, since the magnet N2 has the above-mentioned role, it is necessary to make the magnetic force relatively large. In order to further increase the magnetic force of the magnet S1, a special material has to be adopted, which increases the cost of the developing roller 35. It becomes.

  In this embodiment, the blade 41 is provided at a position closer to the magnet S1 than to the magnet N2, thereby preventing a decrease in the transport amount of the two-component developer even when the magnets N2 and S1 have the same magnetic force. be able to.

  In order to prevent a decrease in the transport amount of the two-component developer on the developing sleeve 39, the image forming apparatus 1 according to the present embodiment also includes the following aspects.

(Aspect 1)
FIG. 3 is a diagram showing that the thickness of the two-component developer D is regulated by the blade 41. FIG. 4 is a diagram in which the two-component developer D is removed from FIG. The end surface 71 of the blade 41 facing the developing sleeve 39 is curved so as to approach the developing sleeve 39 from the upstream side to the downstream side of the developer transport path R2. In other words, in the gap G, the distance d between the end surface 71 of the blade 41 and the surface of the developing sleeve 39 is decreased from the upstream side to the downstream side of the developer transport path R2. This lowers the physical resistance when the two-component developer D is conveyed. Accordingly, it is possible to prevent a decrease in the transport amount of the two-component developer D.

  When the blade 41 is manufactured by punching, sagging occurs at each end face of the blade 41, and the blade 41 becomes curved. Therefore, even if the end surface 71 is not particularly processed into a curved shape, the end surface 71 where the sagging has occurred can be used as it is.

  In order to reduce the physical resistance when transporting the two-component developer D, the end surface 71 is polished so that the ten-point average roughness Rz of the end surface 71 is 2 μm or less (in this embodiment, about 1 μm).

(Aspect 2)
The surface of the developing sleeve 39 is roughened (for example, sandblasting) so that the ten-point average roughness Rz of the surface of the developing sleeve 39 is about 10 μm. As a result, the conveying force of the developing sleeve 39 is increased to prevent a decrease in the conveying amount of the two-component developer D.

(Aspect 3)
The tip of the bracket 45 is cut by a predetermined length L (for example, 2.5 mm), and the space S defined by the bracket 45 and the blade 41 is widened. This reduces the physical resistance when transporting the two-component developer D, and prevents a decrease in the transport amount of the two-component developer D. In addition, since the magnetic force generated in the bracket 45 can be reduced by cutting the tip, it is possible to prevent a decrease in the transport amount of the two-component developer D from this point.

1 is a diagram schematically illustrating an image forming apparatus according to an embodiment. In the image forming apparatus according to the present embodiment, it is a diagram showing the positional relationship of the blade with respect to the developing roller. In the image forming apparatus according to the present embodiment, it is a diagram showing that the thickness of the two-component developer is regulated by a blade. FIG. 4 is a diagram in which a two-component developer is removed from FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 3 ... Paper feed cassette, 5 ... Photosensitive drum, 7 ... Charger, 9 ... Exposure device, 11 ... Developing device, 13 ... Transfer roller 15 ... Fixer, 17 ... Motor, 19 ... Controller, 21 ... Pickup roller, 31 ... Agitating roller, 33 ... Conveying roller, 35 ... Developing roller, 37. ..39, developing sleeve, 41 ... blade, 43 ... spacer, 45 ... bracket, 51 ... heating roller, 53 ... pressure roller, 55 ... heater, 57 ... temperature sensor, 61 ... magnet roller, 71 ... blade end face, P ... recording paper, R1 ... paper transport path, N1, N2, S1, S2, S3 ... magnet , R2 ... developer transport path, G ... blade and development path L1, L2, L3, L4 ... virtual straight line, C ... center of magnet roller, d ... distance between blade end face and developing sleeve surface, L · ..Length of cutting bracket end, S ... space

Claims (3)

An image forming apparatus including a developing unit that develops an electrostatic latent image formed on a photosensitive drum using a two-component developer,
The developer is
A transport roller for transporting the stirred two-component developer;
A developing sleeve and a first magnet that draws the two-component developer conveyed by the conveying roller to the developing sleeve and a position adjacent to the first magnet on the photosensitive drum side and to the developing sleeve side A magnet roller having a second magnet whose directed magnetic pole is different from the first magnet, and rotating the developing sleeve on which the two-component developer is sucked by the first and second magnets. A developing roller for conveying a two-component developer to the photosensitive drum;
A developer transport path from above the first magnet to the second magnet, provided closer to the second magnet than to the first magnet; A blade that regulates the thickness of the two-component developer sucked onto the developing sleeve using a gap formed between the two,
In the gap, the distance between the end surface of the blade and the surface of the developing sleeve is reduced from the upstream side to the downstream side of the developer transport path. An image forming apparatus including a developing unit that develops an electrostatic latent image formed on a photosensitive drum using a two-component developer,
The developer is
A transport roller for transporting the stirred two-component developer;
A developing sleeve and a first magnet that draws the two-component developer conveyed by the conveying roller to the developing sleeve and a position adjacent to the first magnet on the photosensitive drum side and to the developing sleeve side A magnet roller having a second magnet whose directed magnetic pole is different from the first magnet, and rotating the developing sleeve on which the two-component developer is sucked by the first and second magnets. A developing roller for conveying a two-component developer to the photosensitive drum;
A developer transport path from above the first magnet to the second magnet, provided closer to the second magnet than to the first magnet; A blade that regulates the thickness of the two-component developer sucked onto the developing sleeve using a gap formed between the two,
The image forming apparatus, wherein the first magnet and the second magnet have the same magnetic force. 3. The image forming apparatus according to claim 2, wherein a distance between an end surface of the blade and the surface of the developing sleeve in the gap is reduced from the upstream side to the downstream side of the developer transport path. .

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