Image forming apparatus

Abstract

To provide an image forming apparatus that is reduced in size and can prevent scattering of toner inside the apparatus.SOLUTION: An image forming apparatus, in a non-image forming period, performs control to vibrate a first filter 621 to generate a potential difference in a direction in which toner moves from a developing roller 44 to a photoreceptor drum 21, and rotates the developing roller 44 in a direction opposite to that in an image forming period and rotates the photoreceptor drum 21 in the same direction as that in the image forming period, and thereby recovers scattered toner falling from the first filter 621 and attached to an outer peripheral surface of the developing roller 44 by using a drum cleaning unit through the photoreceptor drum 21. In a stationary magnet 442 of the developing roller 44, the absolute value of the vertical magnetic force gradient of an opposite position 442c to a center part 621c of the first filter 621 is 4.0 mT / ° or less with respect to the direction of rotation of a developing sleeve 441.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In electrophotographic image forming apparatuses such as copiers and printers, a device that forms a toner image to be later transferred onto paper is widely used by supplying toner to an electrostatic latent image formed on the outer peripheral surface of an image carrier such as a photoreceptor drum and developing it. In order to continuously form a uniform image, the image forming apparatus conveys a developer containing toner accommodated in a developing container while stirring it inside the developing container.

[0003] In conventional image forming apparatuses, there has been a concern that toner scatters from the inside of the developing container to the outside, and the inside of the apparatus is contaminated by the scattered toner. An example of a conventional technique for solving such problems is disclosed in Patent Document 1.

[0004] The conventional image forming apparatus disclosed in Patent Document 1 includes a developing device that forms a toner image on an image carrier, a suction duct that sucks toner scattered from the developing device, a dust collecting filter provided in the suction duct, and a vibration device that vibrates the suction duct. Then, this image forming apparatus controls the vibration device based on the amount of scattered toner from the developing device. Thereby, toner scattering can be prevented.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the conventional image forming apparatus, since a suction duct is provided outside the developing device, there has been a problem that the apparatus becomes large-sized.

[0007] The present invention has been made in view of the above points, and aims to provide an image forming apparatus that can suppress toner scattering within the apparatus by having a miniaturized configuration. [Means for solving the problem]

[0008] To solve the above problems, the image forming apparatus of the present invention comprises an image carrier, a charging unit, a cleaning unit, a developing device, a voltage application unit, and a control unit. An electrostatic latent image is formed on the outer surface of the image carrier. The charging unit charges the outer surface of the image carrier. The cleaning unit cleans the outer surface of the image carrier. The developing device comprises a developing container, a developer transport member, and a developer carrier. The developing container contains a developer including toner to be supplied to the image carrier. The developer transport member is rotatably supported in the transport chamber of the developing container and transports and circulates the developer while agitating it. The developer carrier is rotatably supported in the developing container facing the image carrier and supplies the toner in the transport chamber to the image carrier. The voltage application unit applies a developing voltage to the developer carrier. The control unit controls the image carrier, the charging unit, the cleaning unit, the developing device, and the voltage application unit. The developing apparatus includes a toner collection mechanism having a duct, a filter, an exhaust fan, and a vibration generating unit. The duct is connected to the transport chamber, and air from the transport chamber flows through it. The filter is located at the connection point between the duct and the transport chamber, above the developer carrier, and collects the toner flowing from the transport chamber into the duct. The exhaust fan causes the air from the transport chamber to flow out through the duct. The vibration generating unit vibrates the filter. When not forming an image, the control unit vibrates the filter using the vibration generating unit, controls the charging unit and the voltage application unit so that a potential difference is generated in the direction in which the toner moves from the developer carrier to the image carrier, and rotates the developer carrier in the opposite direction to when forming an image, and rotates the image carrier in the same direction as when forming an image, thereby enabling a scattered toner collection mode in which scattered toner that has fallen from the filter and adhered to the outer surface of the developer carrier is collected by the cleaning unit via the image carrier. The developer carrier comprises a developing sleeve and a fixed magnet. The developing sleeve is a rotatable, hollow cylindrical shape that carries the developer on its outer surface. The fixed magnet is fixed non-rotatably inside the developing sleeve, and has multiple magnetic poles arranged along the circumferential direction of the developing sleeve.The fixed magnet has a vertical magnetic field gradient of 4.0 mT / ° or less at a position opposite the center of the filter with respect to the rotational direction of the developing sleeve. [Effects of the Invention]

[0009] According to the configuration of the present invention, a toner collection mechanism for sucking up and collecting scattered toner is formed within the developing apparatus, and the scattered toner collected by the filter can be recovered in the cleaning section via the developer carrier and the image carrier. Furthermore, with the above configuration of the fixing magnet of the developer carrier, scattered toner can be efficiently recovered via the image carrier. Therefore, the miniaturized configuration makes it possible to suppress toner scattering within the image forming apparatus. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional front view of an image forming apparatus according to one embodiment of the present invention. [Figure 2] Figure 1 is a block diagram showing the configuration of the image forming apparatus. [Figure 3] Figure 1 is a schematic cross-sectional front view of the area around the image forming section of the image forming apparatus. [Figure 4] Figure 3 is a vertical cross-sectional front view of the developing apparatus in the image forming section. [Figure 5] Figure 3 is a horizontal cross-sectional plan view of the developing apparatus in the image forming section. [Figure 6] Figure 3 is a vertical cross-sectional side view of the developing apparatus in the image forming section. [Figure 7] Figure 3 is a partially enlarged cross-sectional front view of the area around the image forming unit, and is an explanatory diagram of the scattered toner recovery mode. [Figure 8] Figure 4 is a graph showing the distribution of perpendicular magnetic force and the change in perpendicular magnetic force gradient in the circumferential direction of the developing roller of the developing apparatus. [Figure 9] This is a magnified view of a portion of the graph showing the distribution of perpendicular magnetic force and the change in perpendicular magnetic force gradient in the circumferential direction of the developing roller in Figure 8. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following.

[0012] Figure 1 is a schematic cross-sectional front view of an image forming apparatus 1 according to an embodiment. Figure 2 is a block diagram showing the configuration of the image forming apparatus 1 in Figure 1. Figure 3 is a schematic cross-sectional front view of the area around the image forming section 20 of the image forming apparatus 1 in Figure 1. An example of the image forming apparatus 1 in this embodiment is a tandem-type color printer that transfers a toner image to paper S using an intermediate transfer belt 31. The image forming apparatus 1 may be a so-called multifunction device equipped with functions such as printing, scanning (image reading), and facsimile transmission.

[0013] As shown in Figures 1, 2, and 3, the image forming apparatus 1 comprises a paper feeding unit 3, a paper transport unit 4, an exposure unit 5, an image forming unit 20, a transfer unit 30, a fixing unit 6, a paper discharge unit 7, and a control unit 8, all located on its main body 2.

[0014] The paper feed unit 3 is located at the bottom of the main body 2. The paper feed unit 3 holds multiple sheets of paper S before printing and separates and feeds out the paper S one sheet at a time during printing. The paper transport unit 4 extends vertically along the side wall of the main body 2. The paper transport unit 4 transports the paper S fed from the paper feed unit 3 to the secondary transfer unit 33 and the fixing unit 6, and then discharges the fixed paper S from the paper discharge port 4a to the paper discharge unit 7. The exposure unit 5 is located above the paper feed unit 3. The exposure unit 5 irradiates the image forming unit 20 with laser light controlled based on image data.

[0015] The image forming unit 20 is positioned above the exposure unit 5 and below the intermediate transfer belt 31. The image forming unit 20 includes an image forming unit 20Y for yellow, an image forming unit 20C for cyan, an image forming unit 20M for magenta, and an image forming unit 20B for black. These four image forming units 20 have the same basic configuration. Therefore, in the following description, the identification symbols "Y," "C," "M," and "B" representing each color may be omitted unless specifically required.

[0016] The image forming unit 20 includes a photosensitive drum (image carrier) 21 that is rotatably supported in a predetermined direction (clockwise in FIGS. 1 and 3). The image forming unit 20 further includes a charging unit 22, a developing device 40, and a drum cleaning unit (cleaning unit) 23 that are arranged along the rotation direction around the photosensitive drum 21. A primary transfer unit 32 is arranged between the developing device 40 and the drum cleaning unit 23.

[0017] The photosensitive drum 21 is formed in a cylindrical shape extending in the horizontal direction and has a photosensitive layer formed of, for example, an amorphous silicon photosensitive material on its outer peripheral surface. The charging unit 22 charges the surface (outer peripheral surface) of the photosensitive drum 21 to a predetermined potential. The exposure unit 5 exposes the outer peripheral surface of the photosensitive drum 21 charged by the charging unit 22 to form an electrostatic latent image of the document image on the outer peripheral surface of the photosensitive drum 21. The developing device 40 supplies toner to this electrostatic latent image for development to form a toner image. Each of the four image forming units 20 forms a toner image of a different color. The drum cleaning unit 23 removes and cleans the toner and the like remaining on the outer peripheral surface of the photosensitive drum 21 after the toner image is primarily transferred to the outer peripheral surface of the intermediate transfer belt 31. In this way, the image forming unit 20 forms an image (toner image) to be later transferred to the paper S.

[0018] The transfer unit 30 includes an intermediate transfer belt 31, primary transfer units 32Y, 32C, 32M, 32B, a secondary transfer unit 33, and a belt cleaning unit 34. The intermediate transfer belt 31 is arranged above the four image forming units 20. The intermediate transfer belt 31 is a endless intermediate transfer member that is rotatably supported in a predetermined direction (counterclockwise in FIG. 1), and the toner images formed by each of the four image forming units 20 are sequentially superimposed and primarily transferred. The four image forming units 20 are arranged in a so-called tandem method in a row from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 31.

[0019] The primary transfer units 32Y, 32C, 32M, and 32B are arranged above the image forming units 20Y, 20C, 20M, and 20B for each color, sandwiching the intermediate transfer belt 31. The secondary transfer unit 33 is located upstream of the fixing unit 6 with respect to the paper conveyance direction of the paper conveyance unit 4, and downstream of the four image forming units 20Y, 20C, 20M, and 20B with respect to the rotation direction of the intermediate transfer belt 31. The belt cleaning unit 34 is arranged downstream of the secondary transfer unit 33 with respect to the rotation direction of the intermediate transfer belt 31.

[0020] The primary transfer unit 32 transfers the toner image formed on the outer peripheral surface of the photoreceptor drum 21 to the intermediate transfer belt 31. In other words, the toner image is primarily transferred to the outer peripheral surface of the intermediate transfer belt 31 by the primary transfer units 32Y, 32C, 32M, and 32B for each color. Then, as the intermediate transfer belt 31 rotates, the toner images of the four image forming units 20 are continuously transferred and overlapped on the intermediate transfer belt 31 at a predetermined timing, whereby a color toner image in which toner images of yellow, cyan, magenta, and black are overlapped is formed on the outer peripheral surface of the intermediate transfer belt 31.

[0021] The color toner image on the outer peripheral surface of the intermediate transfer belt 31 is transferred to the paper S that has been sent in synchronization by the paper conveyance unit 4 at the secondary transfer nip portion formed in the secondary transfer unit 33. The belt cleaning unit 34 removes and cleans the attachments such as toner remaining on the outer peripheral surface of the intermediate transfer belt 31 after secondary transfer. In this way, the transfer unit 30 transfers (records) the toner image formed on the outer peripheral surface of the photoreceptor drum 21 to the paper S.

[0022] The fixing unit 6 is arranged above the secondary transfer unit 33. The fixing unit 6 heats and presses the paper S onto which the toner image has been transferred to fix the toner image on the paper S.

[0023] The paper discharge unit 7 is arranged above the transfer unit 30. The paper S on which the toner image has been fixed and the printing is completed is conveyed to the paper discharge unit 7. The paper discharge unit 7 allows the printed paper (printed matter) to be taken out from above.

[0024] The control unit 8 includes a CPU, an image processing unit, a memory unit, and other electronic circuits and electronic components (none of which are shown). The CPU controls the operation of each component provided in the image forming apparatus 1 based on control programs and data stored in the memory unit, and performs processing related to the functions of the image forming apparatus 1. The paper feeding unit 3, paper transport unit 4, exposure unit 5, image forming unit 20, transfer unit 30, and fixing unit 6 each receive individual commands from the control unit 8 and perform printing on the paper S in conjunction with each other. The memory unit consists of a combination of non-volatile memory devices such as program ROM (Read Only Memory) and data ROM, and volatile memory devices such as RAM (Random Access Memory).

[0025] Furthermore, as shown in Figure 2, the image forming apparatus 1 further includes a voltage application unit 12 and a current detection unit 13.

[0026] The voltage application unit 12 includes, for example, a power supply unit and a control circuit (neither of which are shown). The voltage application unit 12 is electrically connected to the developing roller (developer carrier) 44 of the developing apparatus 40, which will be described later. The voltage application unit 12 applies a developing voltage to the developing roller 44. The control unit 8 controls the timing, voltage value, polarity, application time, etc., of applying the developing voltage to the developing roller 44 via the voltage application unit 12.

[0027] The current detection unit 13 detects the current flowing between the photoreceptor drum 21 and the developing roller 44 when a developing voltage is applied to the developing roller 44. The control unit 8 receives information related to the current detected by the current detection unit 13 from the current detection unit 13.

[0028] Next, the configuration of the developing apparatus 40 will be explained using Figures 4, 5, and 6 in addition to Figures 2 and 3. Figures 4, 5, and 6 are the vertical cross-sectional front view, horizontal cross-sectional plan view, and vertical cross-sectional side view of the developing apparatus 40 of the image forming unit 20 in Figure 3. Since the basic configuration of the developing apparatus 40 for each color is the same, the description of the identification symbols representing each color and the explanation of the components will be omitted. In this explanation, "axial direction" refers to the axial direction of rotation of the photosensitive drum 21, the first transport member 42, the second transport member 43, and the developing roller 44, which extend parallel to each other (the depth direction of the paper in Figures 3 and 4, and the left-right lateral direction in Figures 5 and 6).

[0029] The developing device 40 supplies toner to the outer surface of the photosensitive drum 21. The developing device 40 is detachable from, for example, the main body 2 of the image forming apparatus 1. The developing device 40 comprises a developing container 50, a first transport member (developer transport member) 42, a second transport member (developer transport member) 43, a developing roller (developer carrier) 44, and a regulating member 45.

[0030] The developing container 50 has an elongated shape that extends along the axial direction of the photoreceptor drum 21, and is positioned with its longitudinal direction horizontal. That is, the longitudinal direction of the developing container 50 is parallel to the axial direction of the photoreceptor drum 21. The developing container 50 contains a developer containing toner to be supplied to the photoreceptor drum 21, for example, a two-component developer containing toner and a magnetic carrier. The developer may be, for example, a magnetic one-component developer containing magnetic toner, or a non-magnetic one-component developer.

[0031] The developing container 50 includes a partition 51, a first transport chamber 52, a second transport chamber 53, a first connecting section 54, and a second connecting section 55.

[0032] The partition 51 is located in the lower part of the interior of the developing container 50. The partition 51 is positioned approximately in the center in a direction intersecting the longitudinal direction of the developing container 50 (the left-right lateral direction in Figure 4, and the up-down direction in Figure 5). The partition 51 is formed in a roughly plate shape that extends in the longitudinal and up-down directions of the developing container 50. The partition 51 divides the interior of the developing container 50 in a direction intersecting the longitudinal direction.

[0033] The first transport chamber 52 and the second transport chamber 53 are located inside the developing container 50. The first transport chamber 52 and the second transport chamber 53 are formed by dividing the inside of the developing container 50 with a partition 51. The first transport chamber 52 and the second transport chamber 53 are arranged in parallel at approximately the same height.

[0034] The second transport chamber 53 is located in the developing container 50, adjacent to and below the area where the developing roller 44 is located. The first transport chamber 52 is located in the developing container 50, further away from the developing roller 44 than the second transport chamber 53. The first transport chamber 52 is connected to a developer supply pipe (not shown), and developer is supplied through the developer supply pipe. In the first transport chamber 52, the developer is transported in a first direction f1 by the first transport member 42. In the second transport chamber 53, the developer is transported in a second direction f2, opposite to the first direction f1, by the second transport member 43.

[0035] The first connecting section 54 and the second connecting section 55 are positioned on the outer sides of both ends in the longitudinal direction of the partition section 51. The first connecting section 54 and the second connecting section 55 connect the first transport chamber 52 and the second transport chamber 53 in directions intersecting the longitudinal direction of the partition section 51 (the left and right lateral directions in Figure 4, and the up and down directions in Figure 5), that is, in the thickness direction of the partition section 51, which is roughly plate-shaped. In other words, the first connecting section 54 and the second connecting section 55 connect the first transport chamber 52 and the second transport chamber 53 at both ends in the longitudinal direction.

[0036] The first connecting section 54 connects the downstream end of the first transport chamber 52 in a first direction f1 with the upstream end of the second transport chamber 53 in a second direction f2. The developer is transported from the first transport chamber 52 side to the second transport chamber 53 side through the first connecting section 54. The second connecting section 55 connects the downstream end of the second transport chamber 53 in a second direction f2 with the upstream end of the first transport chamber 52 in a first direction f1. The developer is transported from the second transport chamber 53 side to the first transport chamber 52 side through the second connecting section 55.

[0037] The first transport member 42 is positioned within the first transport chamber 52. The second transport member 43 is positioned within the second transport chamber 53. The second transport member 43 extends parallel to and close to the developing roller 44. The first transport member 42 and the second transport member 43 are supported by the developing container 50 so as to be rotatable around an axis that extends horizontally parallel to the developing roller 44. The basic configuration of the first transport member 42 and the second transport member 43 is the same, with spiral blades provided on the outer circumference of a rotating shaft that extends along the longitudinal direction of the developing container 50.

[0038] The first transport member 42 transports the developer in a first direction f1, from the second communication section 55 side toward the first communication section 54 side, along the axis of rotation, while agitating it within the first transport chamber 52. The second transport member 43 transports the developer in a second direction f2, from the first communication section 54 side toward the second communication section 55 side, along the axis of rotation, while agitating it within the second transport chamber 53. In other words, the first transport member 42 and the second transport member transport the developer while agitating it in opposite directions, circulating it in a predetermined circulation direction.

[0039] The developing roller 44 is located within the developing container 50, above the second transport member 43, and is positioned opposite the photoreceptor drum 21. The developing roller 44 is supported in the developing container 50 so as to be rotatable around an axis that extends parallel to the axis of the photoreceptor drum 21. The developing roller 44 has, for example, a cylindrical developing sleeve 441 that rotates counterclockwise in Figures 3 and 4, and a fixed magnet 442 fixed non-rotatably within the developing sleeve (see Figure 4).

[0040] The developing roller 44 has a portion of its outer surface exposed from the developing container 50, facing and in close proximity to the photoreceptor drum 21. In the region facing the photoreceptor drum 21, the developing roller 44 carries toner on its outer surface to be supplied to the outer surface of the photoreceptor drum 21. The developing roller 44 carries toner from the second transport chamber 53 of the developing container 50 and supplies it to the photoreceptor drum 21. In other words, the developing roller 44 causes the toner from the second transport chamber 53 to adhere to the electrostatic latent image on the outer surface of the photoreceptor drum 21, forming a toner image.

[0041] The regulating member 45 is positioned upstream of the developing roller 44 in the rotational direction of the developing roller 44 in the area where the developing roller 44 and the photoreceptor drum 21 face each other. The regulating member 45 is positioned in close proximity to the developing roller 44, with a predetermined gap between its tip and the outer circumferential surface of the developing roller 44. The regulating member 45 extends over the entire axial area of ​​the developing roller 44. The regulating member 45 regulates the thickness of the developer (toner) layer carried on the outer circumferential surface of the developing roller 44, passing through the gap between the tip of the regulating member 45 and the outer circumferential surface of the developing roller 44.

[0042] The developer in the developing container 50 circulates between the first transport chamber 52 and the second transport chamber 53 in a predetermined circulation direction through the first and second transport members 42 and 43, passing through the first and second transport members 54 and 55. At this time, the toner in the developing container 50 is agitated and charged, and carried on the outer surface of the developing roller 44. The toner carried on the outer surface of the developing roller 44 has its layer thickness restricted by the regulating member 45, and then is carried to the area facing the developing roller 44 and the photoreceptor drum 21 by the rotation of the developing roller 44. When a predetermined developing voltage is applied to the developing roller 44, the potential difference between the potential of the developing roller 44 and the surface (outer surface) of the photoreceptor drum 21 causes the toner carried on the outer surface of the developing roller 44 to move to the outer surface of the photoreceptor drum 21 in the facing area. As a result, the electrostatic latent image on the outer surface of the photoreceptor drum 21 is developed by the toner.

[0043] Next, the more detailed configuration of the developing apparatus 40 will be explained using Figures 4, 5, and 6. Figures 4 and 6 include arrows indicating the airflow direction fd within the duct 61.

[0044] The developing device 40 includes a toner collection mechanism 60. The toner collection mechanism 60 includes a duct 61, a filter 62, an exhaust fan 63, and a vibration generating unit 64. The filter 62 includes a first filter 621 and a second filter 622.

[0045] The duct 61 is positioned adjacent to the second transport chamber 53. The duct 61 faces the photoreceptor drum 21 in a direction intersecting the longitudinal direction of the developing container 50 (the left-right lateral direction in Figure 4, and the depth direction of the paper in Figure 6), separated by the area where the developing rollers 44 are located inside the developing container 50. The duct 61 is connected to the second transport chamber 53 at its upstream end in the air flow direction. Air from inside the second transport chamber 53 flows through the duct 61. The duct 61 has an intake port 611 and an exhaust port 612.

[0046] The air intake port 611 is located at the connection point between the duct 61 and the second transport chamber 53, and is positioned above the developing roller 44. That is, the air intake port 611 is located at the upstream end of the duct 61 in the airflow direction. The air intake port 611 opens over the entire length of the second transport chamber 53. The air intake port 611 is formed, for example, in a rectangular shape extending in the length of the second transport chamber 53 and faces the developing roller 44. The air intake port 611 connects the inside of the second transport chamber 53 and the inside of the duct 61. Air in the second transport chamber 53 flows into the duct 61 through the air intake port 611.

[0047] The exhaust port 612 is located, for example, at the back of the developing container 50. The exhaust port 612 is located at the downstream end of the duct 61 in the airflow direction. The air in the second transport chamber 53 is discharged from the duct 61 through the exhaust port 612. The duct 61 may also be connected at the exhaust port 612 to another exhaust path equipped with a fan inside the main body 2.

[0048] The exhaust fan 63 is connected to the exhaust port 612. When the exhaust fan 63 is driven, the air inside the second conveying chamber 53 is forcibly discharged to the outside through the duct 61. In other words, the exhaust fan 63 causes the air inside the second conveying chamber 53 to flow out to the outside via the duct 61.

[0049] The first filter 621 is positioned at the intake port 611, which is the connection point between the duct 61 and the second transport chamber 53. The first filter 621 has the same shape as the intake port 611 and is formed in a rectangular shape, for example, extending in the longitudinal direction of the second transport chamber 53. The first filter 621 covers the intake port 611. That is, the first filter 621 faces the developing roller 44. The first filter 621 is made of, for example, nonwoven fabric and collects toner contained in the air flowing from the second transport chamber 53 into the duct 61.

[0050] The second filter 622 is positioned downstream of the first filter 621 in the airflow direction within the duct 61. The second filter 622 has the same cross-sectional shape as the first filter 621 in the direction intersecting the airflow direction within the duct 61, and is formed, for example, in a rectangular shape extending in the longitudinal direction of the second transport chamber 53. The second filter 622 covers the airflow cross-section within the duct 61. The second filter 622 is made of, for example, nonwoven fabric and collects toner contained in the air that passes through the first filter 621 and flows through the duct 61.

[0051] [Table 1]

[0052] Table 1 shows an example of the performance of the first filter 621 and the second filter 622. When the upstream and downstream static pressures were measured with an airflow rate of 10 cm / s, the pressure loss for the first filter 621 was 0.42 mmAq, and for the second filter 622 it was 4.50 mmAq. Furthermore, for example, the collection efficiency for both 0.3 μm and 8 μm particles was higher for the second filter 622 than for the first filter 621.

[0053] With the configuration of the filter 62 described above, the first filter 621 can be configured to be less prone to clogging and not collect large amounts of toner in the second transport chamber 53. Furthermore, the second filter 622 can prevent toner from leaking outside the developing container 50.

[0054] The vibration generating unit 64 is positioned, for example, adjacent to the back of the developing container 50. The vibration generating unit 64 includes, for example, a vibration motor, a control board, and other electronic circuits and electronic components (none of which are shown). An excitation weight is attached to the output shaft of the vibration motor, with its center of gravity eccentrically offset from the rotation axis of the output shaft.

[0055] The vibration generating unit 64 is connected to the first filter 621. When the vibration motor is driven, the vibration generating unit 64 vibrates the first filter 621. By vibrating the first filter 621 with the vibration generating unit 64, toner collected by and adhering to the first filter 621 can be made to fall off. Therefore, the performance of the first filter 621 can be restored, and toner scattering within the image forming apparatus 1 can be continuously suppressed.

[0056] Furthermore, the control unit 8 of the image forming apparatus 1 can execute a scattered toner recovery mode in which the toner collected by the first filter 621 is recovered by the drum cleaning unit 23. Figure 7 is a partially enlarged cross-sectional front view of the area around the image forming unit 20 in Figure 3, and is an explanatory diagram of the scattered toner recovery mode.

[0057] In Figure 7, the rotation direction R11 of the photoreceptor drum 21 during image formation, the rotation direction R21 of the developing roller 44 during image formation, and the rotation direction R22 of the developing roller 44 during the toner scattering recovery mode are indicated by arrows. The rotation directions R21 and R22 of the developing roller 44 are opposite to each other. Also, for the sake of explanation, toner (in the shape of black circles) that has fallen from the first filter 621 is drawn below the first filter 621, on the outer surface of the developing roller 44, and on the outer surface of the photoreceptor drum 21 in Figure 7, but the actual toner is much smaller than the toner (in the shape of black circles) drawn in Figure 7.

[0058] In the scattered toner recovery mode, the control unit 8 vibrates the first filter 621 with the vibration generating unit 64 when not forming an image. Furthermore, the control unit 8 controls the charging unit 22 and the voltage application unit 12 so that a potential difference is generated in the direction in which the toner moves from the developing roller 44 to the photoreceptor drum 21, and rotates the developing roller 44 in the opposite direction to when image is formed (direction R22 in Figure 7), and rotates the photoreceptor drum 21 in the same direction as when image is formed (direction R11 in Figure 7). As a result, scattered toner that falls from the first filter 621 and adheres to the outer surface of the developing roller 44 is recovered by the drum cleaning unit 23 via the photoreceptor drum 21 in the scattered toner recovery mode. Note that in the scattered toner recovery mode, no transfer bias is applied in the primary transfer unit 32 to prevent toner adhering to the outer surface of the photoreceptor drum 21 from moving from the photoreceptor drum 21 to the intermediate transfer belt 31.

[0059] Furthermore, as shown in Figure 7, the developing roller 44 includes a developing sleeve 441 and a fixing magnet 442.

[0060] The developing sleeve 441 is a hollow cylindrical shape extending along the axial direction of the developing roller 44 and is rotatably supported in the developing container 50. The developing sleeve 441 carries developer on its outer surface.

[0061] The fixed magnet 442 is cylindrical in shape, extending along the axial direction of the developing roller 44, and is fixed non-rotatably inside the developing sleeve 441. The fixed magnet 442 extends along the axial direction across the entire length of the developing sleeve 441.

[0062] The fixed magnet 442 has multiple magnetic poles arranged along the circumferential direction of the developing sleeve 441. The fixed magnet 442 has multiple magnetic poles, for example, a pumping pole, a regulating pole, a developing pole, a transport pole, and a stripping pole (none of which are shown).

[0063] The pumping electrode is positioned in the region opposite the second transport chamber 53 (see Figure 4). The pumping electrode pumps the developer being transported within the second transport chamber 53 onto the outer surface of the developing sleeve 441. The pumping electrode may also be composed of magnetic poles common to the regulating electrode.

[0064] The regulating pole is positioned downstream of the pumping pole and opposite the regulating member 45 with respect to the rotational direction R21 during image formation of the developing sleeve 441. The regulating pole generates a peak magnetic force at the position opposite the regulating member 45. The magnetic force of the regulating pole and the regulating member 45 regulate the thickness of the developer layer supported on the outer surface of the developing sleeve 441.

[0065] The developing electrode is positioned downstream of the regulating electrode and in the region facing the photoreceptor drum 21 with respect to the rotation direction R21 during image formation of the developing sleeve 441. For example, the developing electrode generates a peak magnetic force in the region where the developing roller 44 and the photoreceptor drum 21 are closest. When a developing voltage is applied to the developing electrode, only the toner is ejected to the photoreceptor drum 21, developing the electrostatic latent image on the outer surface of the photoreceptor drum 21.

[0066] The transport electrode is positioned downstream of the developing electrode with respect to the rotation direction R21 of the developing sleeve 441 during image formation. The developer is carried on the outer surface of the developing sleeve 441 by the magnetic force of the transport electrode and is transported in the direction of rotation as the developing sleeve 441 rotates.

[0067] The peeling electrode is positioned downstream of the transport electrode and upstream of the pumping electrode with respect to the rotational direction R21 of the developing sleeve 441 during image formation. The developer that reaches the region opposite the peeling electrode peels off from the outer surface of the developing sleeve 411 and falls into the second transport chamber 53.

[0068] Figure 8 is a graph showing the distribution of perpendicular magnetic force and the change in perpendicular magnetic force gradient in the circumferential direction of the developing roller 44 of the developing apparatus 40 shown in Figure 4. Figure 9 is a magnified view of a portion of the graph showing the distribution of perpendicular magnetic force and the change in perpendicular magnetic force gradient in the circumferential direction of the developing roller 44 shown in Figure 8.

[0069] The horizontal axis in Figures 8 and 9 linearly represents the circumferential position on the developing roller 44 using the central angle. The position at angle 0° is approximately the developing electrode, which is the area where the developing roller 44 and the photoreceptor drum 21 face each other. The angle on the horizontal axis in Figures 8 and 9 increases along the rotational direction R21 of the developing sleeve 441 during image formation, starting from the developing electrode. Figure 9 is an enlarged view of the angle range from 40° to 120° in Figure 8.

[0070] The left vertical axis in Figures 8 and 9 represents the perpendicular magnetic force [mT], corresponding to the solid data lines in the figures. The perpendicular magnetic force is the magnetic force normal to the outer surface of the developing roller 44, and can be measured, for example, using a magnetic force measuring device. The right vertical axis in Figures 8 and 9 represents the perpendicular magnetic force gradient [mT / °], corresponding to the dashed data lines in the figures.

[0071] In this embodiment, a magnetic force measuring device (GAUSS METER Model GX-100, manufactured by Nippon Denji Sokki Co., Ltd.) was used, and the developing roller 44 was mounted on an angle adjustment jig and rotated in fixed increments while the vertical magnetic force was measured. When the measurement accuracy is very high, the vertical magnetic force gradient can be obtained by dividing the difference in vertical magnetic force measured at different angles by the difference in measurement angles. However, when the measurement accuracy is low, the vertical magnetic force gradient cannot be determined accurately. Therefore, in this embodiment, the vertical magnetic force was measured by changing the measurement angle in increments of 0.02°, and (the difference in vertical magnetic force at a 0.08° difference / 0.08°) was calculated as "gradient 1" at the midpoint within that 0.08° range. Then, the average gradient of the data (2° / 0.02° = 100 data points) in the 2° angle range of "gradient 1" was calculated as the vertical magnetic force gradient. An example of the calculation of the vertical magnetic force gradient is shown in Table 2.

[0072] [Table 2]

[0073] Table 2 shows, as an example, data for the angle range from 10.00° to 10.16° in Figure 8. In Table 2, for example, the gradient 1 (-5.00 mT / °) at an angle of 10.08° is obtained by dividing the difference (-0.40 mT) between the perpendicular magnetic force of 73.3 mT at an angle of 10.04° and the perpendicular magnetic force of 72.9 mT at an angle of 10.12° by 0.08°. Also, for example, the average gradient (-4.70 mT / °) at an angle of 10.08° is the average value of the data (100 data points) for gradient 1 in the 2° angle range from 9.08° to 11.08°, and is the "perpendicular magnetic force gradient".

[0074] Furthermore, the fixed magnet 442 has a vertical magnetic field gradient of 4.0 mT / ° or less at the position 442c (see Figures 4 and 7) opposite the central part 621c of the first filter 621, with respect to the rotational direction of the developing sleeve 441. In other words, the fixed magnet 442 has a vertical magnetic field gradient of -4.0 mT / ° or more and +4.0 mT / ° or less at the position 442c vertically below the central part 621c of the first filter 621, with respect to the rotational direction of the developing sleeve 441. [Examples]

[0075] Next, we will explain the evaluation of toner scattering within the image forming apparatus 1. In this evaluation, 100,000 images with a print density of 20% were printed on paper S, and toner scattering within the image forming apparatus 1 was confirmed. For this evaluation, the first 70,000 sheets were printed in a normal temperature and humidity environment (24°C / 40%), and the 70,001st to 100,000th sheets were printed in a high temperature and high humidity environment (28.5°C / 80%).

[0076] Furthermore, in this evaluation, the scattered toner recovery mode was executed every 4,000 printed pages. More specifically, every 4,000 printed pages, the vibration generating unit 64 was activated to reverse the rotation of the developing roller 44, with the developing voltage set to 150V and the surface potential of the photoreceptor drum 21 set to 20V.

[0077] Table 3 shows the magnetic pole arrangement of the fixed magnet 442. As shown in Table 3, in this evaluation, we prepared image forming apparatus 1 of the embodiment of the present invention and image forming apparatuses of Comparative Examples 1 and 2, each with a different magnetic pole arrangement of the fixed magnet 442.

[0078] [Table 3]

[0079] In Figure 9, the vertical magnetic field gradient of the fixed magnet 442 is greater than +4.0 mT / ° in range A from angle 52.14° to 68.32°, greater than or equal to -4.0 mT / ° and less than or equal to +4.0 mT / ° in range B from angle 68.34° to 91.34°, and less than -4.0 mT / ° in range C from angle 91.36° to 100.56°.

[0080] Regarding Table 3, in the image forming apparatus 1 of the example, the vertical magnetic field gradient of the fixed magnet 442 at the position 442c facing the central part 621c of the first filter 621 is between -4.0 mT / ° and +4.0 mT / ° (range B in Figure 9). In the image forming apparatus of Comparative Example 1, the vertical magnetic field gradient of the fixed magnet 442 at the position 442c facing the central part 621c of the first filter 621 is greater than +4.0 mT / ° (range A in Figure 9). In the image forming apparatus of Comparative Example 2, the vertical magnetic field gradient of the fixed magnet 442 at the position 442c facing the central part 621c of the first filter 621 is less than -4.0 mT / ° (range C in Figure 9). The evaluation results are shown in Table 4.

[0081] [Table 4]

[0082] Regarding Table 4, the toner scattering status inside the image forming apparatus was checked visually. The criteria for "toner scattering confirmation" were as follows: "○" if no toner scattering was confirmed and the inside of the apparatus was kept clean, and "×" if toner scattering was confirmed and the inside of the apparatus was contaminated with scattered toner.

[0083] Table 4 shows that in Comparative Examples 1 and 2, toner scattering occurs within the image forming apparatus in a high-temperature, high-humidity environment. In contrast, in the image forming apparatus 1 of the embodiment of the present invention, toner scattering does not occur within the apparatus in both a normal temperature, normal humidity environment and a high-temperature, high-humidity environment.

[0084] In this way, according to the configuration of this embodiment, a toner collection mechanism 60 for sucking up and collecting scattered toner is formed inside the developing device 40, and the scattered toner collected by the filter 62 can be recovered by the drum cleaning unit 23 via the developing roller 44 and the photoreceptor drum 21.

[0085] In high-temperature, high-humidity environments, the amount of toner charge tends to decrease, and the amount of toner scattered tends to increase. Also, when the vertical magnetic field gradient of the fixed magnet 442 at the position 442c facing the central part 621c of the first filter 621 is greater than +4.0 mT / ° (range A in Figure 9) and less than -4.0 mT / ° (range C in Figure 9), the magnetic brushes of the developer formed on the outer surface of the developing roller 44 facing the first filter 621 will be tilted, for example, in the circumferential direction of the developing roller 44. There is no gap between the tilted magnetic brushes.

[0086] In the image forming apparatuses of Comparative Examples 1 and 2, toner that falls from the first filter 621 and adheres to the outer surface of the developing roller 44 falls onto the tilted magnetic brush. As a result, the toner cannot be taken into the gaps between the magnetic brushes, causing a large amount of toner to scatter, and it is believed that the inside of the apparatus was contaminated with scattered toner.

[0087] Therefore, according to the configuration of this embodiment, the absolute value of the vertical magnetic field gradient of the fixed magnet 442 at the position 442c facing the central part 621c of the first filter 621 is 4.0 mT / ° or less (-4.0 mT / ° or more, +4.0 mT / ° or less) (range B in Figure 9). In this case, the magnetic brushes of the developer formed on the outer surface of the developing roller 44 facing the first filter 621 are in an upright position normal to the surface of the outer surface of the developing roller 44. Gaps are created between the upright magnetic brushes.

[0088] In the image forming apparatus 1 of this embodiment, scattered toner that falls from the first filter 621 and adheres to the outer surface of the developing roller 44 falls onto the upright magnetic brush. This allows the scattered toner to be taken into the gaps between the magnetic brushes, thereby suppressing toner scattering. In other words, the image forming apparatus 1 of this embodiment is capable of adhering a large amount of scattered toner that falls from the first filter 621 to the outer surface of the developing roller 44, and efficiently recovering it via the photoreceptor drum 21. Therefore, the miniaturized configuration makes it possible to suppress toner scattering within the image forming apparatus 1.

[0089] Furthermore, it is preferable that the absolute value of the vertical magnetic force gradient of the fixed magnet 422 at the position facing the entire area of ​​the first filter 621 with respect to the rotation direction of the developing sleeve 441 is 4.0 mT / ° or less. With this configuration, the magnetic brushes of the developer can be kept upright over a wide area of ​​the outer surface of the developing roller 44 facing the first filter 621. This makes it possible to enhance the effect of capturing scattered toner that has fallen from the first filter 621 into the gaps between the magnetic brushes. Therefore, scattered toner can be recovered efficiently.

[0090] The control unit 8 then executes a scattered toner recovery mode after a predetermined number of printed pages. For example, in the image forming apparatus 1 of the above embodiment, the control unit 8 executed the scattered toner recovery mode every 4,000 printed pages. With this configuration, scattered toner collected by the filter 62 can be periodically recovered by the drum cleaning unit 23 via the developing roller 44 and the photoreceptor drum 21. Therefore, it is possible to improve the effect of suppressing toner scattering within the image forming apparatus 1.

[0091] Furthermore, the developer used to form the toner image is a two-component developer containing a magnetic carrier and toner. It is known that toner scattering from the developing container 50 is likely to occur with two-component developers. Therefore, by executing the above-mentioned scattered toner recovery mode in the image forming apparatus 1 using a two-component developer, it becomes possible to suppress toner scattering within the image forming apparatus 1 even more effectively.

[0092] Furthermore, the photoreceptor drum 21 has a photosensitive layer formed of amorphous silicon photoreceptor on its outer surface. The photosensitive layer formed of amorphous silicon photoreceptor is known to have a high dielectric constant and a low toner charge. A low toner charge makes it easier for toner to scatter from the developing container 50. Therefore, by executing the above-mentioned scattered toner recovery mode in the image forming apparatus 1 using the photoreceptor drum 21 having amorphous silicon photoreceptor, it becomes possible to suppress toner scattering within the image forming apparatus 1 even more effectively.

[0093] Although embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and various modifications can be made to implement the invention without departing from the spirit of the invention.

[0094] For example, in the above embodiment, the image forming apparatus 1 is a so-called tandem-type color printing image forming apparatus that sequentially superimposes images of multiple colors, but it is not limited to such a model. The image forming apparatus may be a color printing image forming apparatus that is not of the tandem type, or a monochrome printing image forming apparatus. [Industrial applicability]

[0095] The present invention can be used in developing apparatuses and image forming apparatuses. [Explanation of symbols]

[0096] 1. Image forming apparatus 8 Control Unit 12 Voltage application section 13 Current detection unit 20 Image forming unit 21. Photosensitive drum (image carrier) 22 Charged part 23. Drum Cleaning Department (Cleaning Department) 30 Transfer section 31 Intermediate transfer belt 40 Developing equipment 42. First transport member (developer transport member) 43. Second transport member (developer transport member) 44. Developing roller (developer carrier) 45 Regulating members 50 developing containers 60 Toner collection mechanism 61 Duct 62 filters 63 Exhaust fan 64 Vibration generating part 441 Developing Sleeves 442 Fixed Magnet 442c Opposing position 611 Air intake 612 Exhaust port 621 First filter 621c central part 622 Second filter

Claims

1. An image carrier on which an electrostatic latent image is formed on its outer surface, A charging unit for charging the outer surface of the image carrier, A cleaning unit for cleaning the outer surface of the image carrier, A developing apparatus comprising: a developing container for containing a developer containing toner to be supplied to the image carrier; a developer transport member rotatably supported within the transport chamber of the developing container for transporting and circulating the developer while agitating it; and a developer carrier rotatably supported in the developing container opposite the image carrier for supplying the toner in the transport chamber to the image carrier; A voltage application unit for applying a developing voltage to the developer carrier, A control unit that controls the image carrier, the charging unit, the cleaning unit, the developing device, and the voltage application unit, The developing apparatus is A duct connected to the transport chamber through which air from the transport chamber flows, A filter is provided at the connection point between the duct and the transport chamber, positioned above the developer carrier, to collect the toner flowing from the transport chamber into the duct, An exhaust fan that discharges the air inside the transport chamber to the outside via the duct, A vibration generating unit that vibrates the aforementioned filter, Equipped with a toner collection mechanism, The control unit, when not forming an image, vibrates the filter with the vibration generating unit and controls the charging unit and the voltage application unit so that a potential difference is generated in the direction in which the toner moves from the developer carrier to the image carrier. It also rotates the developer carrier in the opposite direction to that during image formation and rotates the image carrier in the same direction as during image formation, thereby enabling a scattered toner recovery mode in which scattered toner that has fallen from the filter and adhered to the outer surface of the developer carrier is recovered by the cleaning unit via the image carrier. The developer carrier is A rotatable, hollow cylindrical developing sleeve that carries the developer on its outer surface, A fixed magnet is fixed inside the developing sleeve so as not to rotate, and has multiple magnetic poles arranged along the circumferential direction of the developing sleeve. It has, The image forming apparatus is characterized in that the fixed magnet has a vertical magnetic field gradient of 4.0 mT / ° or less at a position opposite the center of the filter with respect to the rotation direction of the developing sleeve.

2. The image forming apparatus according to claim 1, characterized in that the fixed magnet has a vertical magnetic field gradient of 4.0 mT / ° or less at a position facing the entire area of ​​the filter with respect to the rotation direction of the developing sleeve.

3. The image forming apparatus according to claim 1, characterized in that the control unit executes the scattered toner recovery mode every predetermined number of printed sheets.

4. The image forming apparatus according to claim 1, characterized in that the developer is a two-component developer comprising a magnetic carrier and the toner.

5. The image forming apparatus according to claim 1, characterized in that the image carrier has a photosensitive layer formed of an amorphous silicon photoreceptor on its outer surface.

6. The aforementioned filter is A first filter covers an air intake opening that extends across the entire length of the transport chamber and connects the transport chamber with the duct, A second filter is positioned downstream of the first filter in the airflow direction within the duct and covers the airflow cross-section within the duct, An image forming apparatus according to any one of claims 1 to 5, characterized by including the following:

Images