Patent Grant
10948845
Embodiments described herein relate generally to an image forming unit and an image forming apparatus.
In the related art, there are image forming apparatuses such as a multi-function peripheral (hereinafter, referred to as an “MFP”) and a printer. The image forming apparatus includes a developing device that develops a latent image on an image carrier. In recent years, in order to save energy, a developer containing a toner having a low melting point is used in a developing device in some cases.
In the image forming apparatus, the amount of developer transported in the developing device is reduced, which may affect an image.
In general, according to one embodiment, there is provided an image forming unit including: an image carrier; a charger; a latent image forming unit; a developing roller; and a regulating member. The charger charges the image carrier. The latent image forming unit forms a latent image on the image carrier. The developing roller is arranged to face the image carrier and develops the latent image with a developer including a carrier and a toner. The regulating member regulates a layer thickness of the developer of a surface of the developing roller. The regulating member extends in a direction approaching the developing roller. A magnetic force exerted by the developing roller at a tip end of the regulating member in an extending direction is 55 mT or less.
Hereinafter, an image forming unit and an image forming apparatus according to embodiments will be described with reference to the drawings. In each drawing, the same reference numerals are given to the same components. In each drawing, the dimension and shape of each member may be exaggerated or simplified for clarity.
As shown in
Hereinafter, a case where the image forming apparatus 1 is an MFP will be described as an example. The image forming apparatus 1 generates digital data (image file) by reading an image formed on a sheet-like recording medium (hereinafter, referred to as “sheet”) such as paper. The image forming apparatus 1 forms an image on a sheet using toner based on digital data.
The image forming apparatus 1 includes a display unit 110, an image reading unit 120, an image forming unit 130, and a sheet tray 140.
The display unit 110 operates as an output interface and displays characters and images. The display unit 110 operates as an input interface and receives an instruction from a user. For example, the display unit 110 is a touch panel type liquid crystal display.
For example, the image reading unit 120 is a color scanner. Color scanners include a CIS (Contact Image Sensor), a CCD (Charge Coupled Device), and the like. The image reading unit 120 reads an image formed on a sheet using a sensor and generates digital data.
The image forming unit 130 forms an image on a sheet using toner. The image forming unit 130 forms an image based on image data read by the image reading unit 120 or image data received from an external device. For example, an image formed on a sheet is an output image called a hard copy, printout, and the like.
The sheet tray 140 feeds a sheet to be used for image output to the image forming unit 130.
As shown in
The scanner unit reads an image formed on a sheet to be scanned. The scanner unit outputs the generated image data to the image processing unit. The image processing unit converts image data into a signal. The image processing unit controls the operation of the exposure unit 4 based on the signal.
The exposure unit 4 irradiates a photosensitive drum 12b of the image forming unit 12 with light. The exposure unit 4 includes an exposure light source such as a laser or an LED. The exposure unit 4 is a specific example of a latent image forming unit (latent image forming tool).
The image forming unit 12 forms an image using toner. The transfer roller 17 faces the photosensitive drum 12b. The transfer roller 17 transfers the image formed by the image forming unit 12 onto a sheet S. The paper feeding unit 20 feeds a sheet S. The fixing device 32 fixes the image transferred onto the sheet S to the sheet S by heating and pressing. The sheet S having the image formed thereon is discharged out of the apparatus from a sheet discharge unit (not shown).
A specific example of the image forming unit 12 of the image forming apparatus 1 of the embodiment will be described.
As shown in
As shown in
The photosensitive drum 12b is a specific example of an image carrier (image carrying unit). The photosensitive drum 12b includes a photoreceptor (photosensitive area) on the outer peripheral surface thereof. For example, the photoreceptor is an organic photo conductor (OPC).
The charger 12c charges the surface of the photosensitive drum 12b.
The cleaning member 12d removes a part of the toner attached to the photosensitive drum 12b.
The outline of the operation of the image forming unit 12 will be described.
The photosensitive drum 12b is charged by the charger 12c. The exposure unit 4 (refer to
As shown in
As shown in
The first mixer 61 and the second mixer 62 mix the developer in the container 60 and guide the developer to the developing roller 63.
The developing roller 63 carries the developer by a magnetic force. The developing roller 63 faces the photosensitive drum 12b. The developing roller 63 includes a magnet roller 67, and a developing sleeve 68. The magnet roller 67 includes a plurality of magnetic pole portions N1, S2, N3, N2, and S1. The rotation direction of the developing sleeve 68 is referred to as “rotation direction J1”. Reference numeral 63a denotes an axial portion of the developing roller 63. Reference numeral Cp denotes a central axis Cp of the developing roller 63. The direction of the central axis Cp is referred to as the “axial direction”.
The plurality of magnetic pole portions N1, S2, N3, N2, and S1 are arranged in parallel around the axis of the axial portion 63a in the developing sleeve 68. The magnetic pole portions N1, S2, N3, N2, and S1 include magnets. The magnetic pole portions N1, N2, and N3 are N poles. The magnetic pole portions S1 and S2 are S poles. The magnetic pole portions N1, S2, N3, N2, and S1 are arranged in parallel in the rotation direction J1 in this order. The plurality of magnetic pole portions N1, S2, N3, N2, and S1 are fixed at fixed positions. The magnetic pole portion N1 is a developing main pole.
The magnetic pole portion N1 faces the photosensitive drum 12b. The magnetic pole portion N1 causes the developer carried on the surface of the developing roller 63 to approach the photosensitive drum 12b. The magnetic pole portion N1 is arranged adjacent to the magnetic pole portion S1 on the downstream side in the rotation direction J1. At least a part of the magnetic pole portion S1 is arranged at a position facing the layer regulating member 65. The magnetic pole portion S1 contributes regulation of the layer thickness of the developer by the layer regulating member 65. The magnetic pole portion N2 functions as a gripping pole to pump up the developer.
The developing sleeve 68 has a cylindrical shape that contains the axial portion 63a and the magnet roller 67. For example, the developing sleeve 68 is formed of a non-magnetic material such as aluminum or stainless steel. The developing sleeve 68 can be rotated around the axis by a drive source (not shown). The developing sleeve 68 rotates clockwise (rotation direction J1) in
The layer regulating member 65 regulates the layer thickness of the developer carried on the surface of the developing roller 63. The layer regulating member 65 is a specific example of a regulating member. The layer regulating member 65 extends in a direction approaching the developing roller 63. A tip end 65a of the layer regulating member 65 in the extending direction faces the outer peripheral surface of the developing roller 63 (refer to
The developer is attached in a layer on the surface (outer peripheral surface) of the developing sleeve 68 by the magnetic force of the magnetic pole portion N2. The developer is moved in the rotation direction J1 with the rotation of the developing sleeve 68 while being held on the surface of the developing sleeve 68 by the magnetic force of the magnet roller 67. The developer reaches the magnetic pole portion N1 after the layer thickness is adjusted by the layer regulating member 65 and the magnetic pole portion S1. Some of the toner included in the developer is moved from the developing roller 63 to the photosensitive drum 12b. The toner is attached to the electrostatic latent image on the surface of the photosensitive drum 12b to form a developed image on the surface of the photosensitive drum 12b. The developer reaches the magnetic pole portion N3 through the magnetic pole portion S2 with the rotation of the developing sleeve 68. Some of the developer is separated from the surface of the developing sleeve 68 and is recovered in the storage unit 66.
The auto-toner sensor 64 detects the toner concentration in the developer in the developing device 12a. The control unit (not shown) supplies toner from a toner cartridge (not shown) to the developing device 12a based on the detection signal from the auto-toner sensor 64. Thus, the control unit keeps the toner concentration of the developer within a certain range.
In the image forming apparatus, white stripes or white bands may be formed in the image formed on the sheet. The reason can be presumed as follows.
For example, the reference line S is parallel to a tangential direction perpendicular to the radial direction and the central axis direction of the developing roller 63 at the point (closest point) on the outer peripheral surface of the developing roller 63 closest to the measurement point (the corner portion 65a1 of the tip end 65a of the layer regulating member 65). The corner portion 65a1 of the tip end 65a of the layer regulating member 65 is a corner portion of the layer regulating member 65 on a rear surface 65b side (the surface on the upstream side in the rotation direction J1).
As shown in
In Test Example A (refer to
On the other hand, in Test Example B (refer to
Thus, in both Test Examples A and B, there is a possibility that white stripes and white bands may be formed in the image.
In the developing device 12a, the following countermeasures were taken against this problem.
At the tip end 65a of the layer regulating member 65 (specifically, the corner portion 65a1), the magnetic force exerted by the developing roller 63 is 55 mT or less. Since the magnetic force is 55 mT or less, the shearing force F′ (refer to
In the developing device 12a, when the magnetic force is too low, the pumping amount of the developer is reduced. However, when the magnetic force is 35 mT or more, a sufficient pumping amount of developer can be obtained. Therefore, normal image formation can be performed.
In the developing device 12a, as shown in
By setting the angle of the magnetic force line M3 to 10° or less, the direction of the magnetic force line becomes closer to the direction in which the gap between the layer regulating member 65 and the developing roller 63 is formed (developer passing direction), and thus the transport force for passing the developer through the gap can be increased. Therefore, the transporting amount of developer can be secured. Thus, the occurrence of white stripes or white bands described above can be prevented. For example, the angle of the magnetic force line can be determined by adjusting the reversal position of the magnetic force between the magnetic pole portions N2 and S1.
The angle of the magnetic force line may be −10° or more. That is, the angle of the magnetic force line may be −10° or more and 10° or less.
The developing device of Test Example A (refer to
(First Paper Passing Test)
A paper passing test was performed using the developing devices of Test Examples A and B. As a toner, a toner with a softening temperature of 56° C. to 60° C. was used. Continuous paper passing was performed while setting the device internal temperature (the temperature in the developing device) to 45° C. and 50° C., respectively. The number of sheets of passed paper was set to 10 k. The presence or absence of white stripes or white bands in the image formed on the sheet (paper) was examined. The results are shown in Table 1. k means 1000. For example, 1 k sheets mean 1000 sheets. 10 k sheets mean 10000 sheets.
In Table 1, “◯” (Good) denotes that white stripes or white bands are not formed and a normal image is obtained. “Δ” (Fair) denotes that although white stripes or white bands are not formed in the image, soft caking (adhered matter) of the developer is formed on the rear surface 65b (refer to
As shown in Table 1, in Test Example A, at a device internal temperature of 45° C., the toner fixed to the layer regulating member was observed when the number of sheets was 7 k or more. When the number of sheets was 9 k or more, white stripes or white bands were formed in the image. At a device internal temperature of 50° C., when the number of sheets was 3 k or more, the toner adhesion to the layer regulating member was observed. When the number of sheets was 6 k or more, white stripes or white bands were formed in the image.
In Test Example B, at any of device internal temperatures of 45° C. and 50° C., the toner adhesion to the layer regulating member was not observed. In addition, white stripes or white bands were not formed in the image.
Thus, in Test Example B with a magnetic force of 45 mT compared to Test Example A with a magnetic force of 60 mT, even when the device internal temperature was low, white stripes or white bands were less likely to be formed in the image.
(Second Paper Passing Test)
A paper passing test was performed using the developing devices of Test Examples A and B. The number of sheets of passed paper was set to 150 k. The presence or absence of white stripes or white bands in the image formed on the sheet (paper) was examined. The device internal temperature (the temperature in the developing device) was 40° C. or less. The results are shown in Table 2.
In Table 2, “◯” (Good) denotes that the developer layer is uniform, and a normal image is obtained without forming white stripes or white bands. “Δ” (Fair) denotes that the image was normal but the transporting amount of the developer is low. “X” (Not Good) denotes that the transporting amount of developer is decreased and white stripes or white bands are formed.
As shown in Table 2, in Test Example A, when the number of sheets was 110 k or more, the image was normal, but the transporting amount of the developer was low. In Test Example B, when the number of sheets was 20 k or more, the transporting amount of the developer was decreased and white stripes or white bands were formed in the image.
As described above, in Test Example B, when the number of sheets of passed paper was increased, white stripes or white bands were likely to be formed in the image.
(Third Paper Passing Test)
As shown in
The developing device of Test Example C was provided for the same paper passing test as the first paper passing test. The results are shown in Table 3.
As shown in Table 3, in Test Example C, toner adhesion, white stripes, and white bands were not observed and a normal image was able to be formed.
(Fourth Paper Passing Test)
The developing device of Test Example C was provided for the same paper passing test as the second paper passing test. The results are shown in Table 4.
As shown in Table 4, in Test Example C, the transporting amount of the developer was not decreased, white stripes and white bands were not formed, and a normal image was able to be formed.
From the results, it was confirmed that by setting the angle of the magnetic force line to 1°, the transporting amount of the developer was secured, and the occurrence of white stripes and white bands could be prevented.
(Fifth Paper Passing Test)
A plurality of developing devices having different magnetic forces or magnetic force line angles from those in Test Examples A to C were prepared, and these devices were provided for the same paper passing test as the first and second paper passing tests. The results are shown in
As shown in
The image forming apparatus of the embodiment can form a monochrome image using a black monochromatic toner. The image forming apparatus of the embodiment may be applicable to a color image. If the image forming apparatus is applicable to a color image, the image forming apparatus of the embodiment includes a plurality of image forming units. For example, in the plurality of image forming units, toners of yellow (Y), magenta (M), cyan (C), and black (K) are respectively used.
According to at least one of the embodiments described above, since the magnetic force is set to 55 mT or less, the toner adhesion to the layer regulating member is less likely to occur. Thus, white stripes and white bands can be prevented from being formed in the image.
With respect to any figure or numerical range for a given characteristic, a figure or a parameter from one range may be combined with another figure or a parameter from a different range for the same characteristic to generate a numerical range.
Other than in the operating examples, if any, or where otherwise indicated, all numbers, values and/or expressions referring to parameters, measurements, conditions, etc., used in the specification and claims are to be understood as modified in all instances by the term “about.”
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4951091 | Nawata | Aug 1990 | A |
| 20090010683 | Morimoto | Jan 2009 | A1 |
| Number | Date | Country |
|---|---|---|
| 205210516 | May 2016 | CN |
