Image forming apparatus

Abstract

An image forming apparatus includes an image bearing member, an exposure device, a conductive member, a bias application unit, and a developing device having a developing roller and a toner supply roller. The bias application unit is configured to apply a bias to the toner supply roller, the developing roller, and the conductive member during image formation such that a first potential difference between the toner supply roller and the developing roller and a second potential difference between the conductive member and the developing roller cause normally charged toner to move from the toner supply roller and the conductive member, respectively, to the developing roller, and a third potential difference between the conductive member and the toner supply roller causes normally charged toner to move from the conductive member to the toner supply roller. The second potential difference is greater than the first potential difference and greater than the third potential difference.

Description

Technical Field

[0001] This disclosure relates to an image forming apparatus including a developing device, the developing device including a toner supply roller configured to supply toner only to a developing roller. Background Technology

[0002] The developing apparatus discussed in Japanese Patent Application Publication No. 2017-21278 includes: a developer container holding a developer comprising toner and a carrier; a developing roller carrying and conveying the toner to the developing position; and a toner supply roller carrying and conveying developer supplied from the developer circulation path and supplying toner only to the developing roller. This developing apparatus is equipped with a toner blocking member for blocking toner that separates from the developing roller and is not used for developing, floating in the space between the toner supply roller, the developing roller, and the walls of the developer container. This blocking member is arranged near the developing roller in the space between the magnetic roller, the developing roller, and the walls of the developer container, downstream of the developing roller, at a position where, as seen in the rotation direction of the toner supply roller, the developing roller is closest to the toner supply roller.

[0003] In the structure discussed in Japanese Patent Application Publication No. 2017-21278, during the image forming operation, a potential difference is formed between the toner supply roller and the developing roller. This potential difference allows normally charged toner to migrate from the toner supply roller to the developing roller, and the same potential is applied to the toner blocking member and the toner supply roller.

[0004] In the configuration discussed in Japanese Patent Application Publication No. 2017-21278, during image formation operation, toner that has separated from the developing roller but is not used for development and floats in the gap between the toner blocking member and the developing roller can be collected by an electric field. However, according to the configuration discussed in Japanese Patent Application Publication No. 2017-21278, during image formation operation, the same potential is applied to the toner blocking member and the toner supply roller, so that the toner floating in the gap between the toner blocking member and the toner supply roller cannot be collected by the electric field. Therefore, during image formation operation, a portion of the toner that has separated from the developing roller but is not used for development and floats in the space between the toner supply roller, the developing roller, and the wall of the developer container may be dispersed to the outside of the developing equipment by airflow. Summary of the Invention

[0005] This disclosure aims to provide an image forming apparatus including a developing device, the developing device including a toner supply roller configured to supply toner only to a developing roller, and the image forming apparatus being able to return toner that has been scattered on the portion of the developing roller facing the toner supply roller to a circulation path during an image forming operation.

[0006] According to an aspect of this disclosure, an image forming apparatus includes: an image carrier member; an exposure device configured to expose the image carrier member to form an electrostatic latent image on the image carrier member; and a developing device including a first chamber and a second chamber, a first delivery screw and a second delivery screw, a rotatable developing roller, and a rotatable toner supply roller, wherein the first chamber is configured to contain a developer containing a toner and a carrier, wherein the second chamber is separated from the first chamber by a partition wall and configured to form a circulation path for the developer between the second chamber and the first chamber, wherein the first delivery screw is disposed in the first chamber and configured to deliver the developer in a first direction, wherein the second delivery screw is disposed in the second chamber and configured to deliver the developer in a second direction opposite to the first direction, wherein the developing roller is disposed facing the image carrier member and configured to carry the toner and deliver the toner to a developing position, at which the electrostatic latent image formed on the image carrier member is developed, and wherein the toner supply roller is disposed facing the developing roller and configured to carry the toner. The toner supply roller carries and conveys the developer supplied from the first chamber, and supplies the toner only to the developing roller. At a position where the toner supply roller and the developing roller face each other, the rotation direction of the toner supply roller is opposite to that of the developing roller. A conductive member is arranged facing the toner supply roller and the developing roller, downstream of the developing position in the rotation direction of the developing roller and upstream of the position where the toner supply roller is positioned closest to the developing roller. A bias application unit is configured to apply a bias voltage to the toner supply roller during image formation operations. The developing roller and the conductive member are configured such that: i. a first potential difference is formed between the toner supply roller and the developing roller to allow normally charged toner to move from the toner supply roller to the developing roller; ii. a second potential difference is formed between the conductive member and the developing roller to allow normally charged toner to move from the conductive member to the developing roller; and iii. a third potential difference is formed between the conductive member and the toner supply roller to allow normally charged toner to move from the conductive member to the toner supply roller, wherein the second potential difference is greater than the first potential difference and greater than the third potential difference.

[0007] Further features of this disclosure will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0008] Figure 1 This is a cross-sectional view of the structure of an image forming apparatus according to a first exemplary embodiment.

[0009] Figure 2 This is a cross-sectional view of the construction of a developing apparatus according to a first exemplary embodiment.

[0010] Figure 3This is an enlarged cross-sectional view of the construction of a developing apparatus according to a first exemplary embodiment.

[0011] Figure 4 This is a schematic diagram of the waveform of the bias voltage applied to the developing roller, the magnetic roller, and the toner blocking member according to a first exemplary embodiment.

[0012] Figure 5 This is a schematic diagram showing the duty cycle of the bias waveform.

[0013] Figure 6 This is a schematic diagram of the waveform of the bias voltage applied to the developing roller, the magnetic roller, and the toner blocking member according to the second exemplary embodiment. Detailed Implementation

[0014] Exemplary embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, the following exemplary embodiments do not limit the present disclosure as defined in the claims, and not all combinations of features described in the first exemplary embodiment are necessary for the solutions of the present disclosure. The present disclosure can be implemented in various applications such as printers, various printing presses, copiers, fax machines, and multifunction devices.

[0015] The same or equivalent parts shown in the accompanying drawings are given the same reference numerals and symbols and will not be described again.

[0016] The X-axis, Y-axis, and Z-axis are orthogonal to each other, with the Z-axis being basically parallel to the vertical direction, and the Y-axis and X-axis being basically parallel to the horizontal direction.

[0017] Structure of an image forming apparatus

[0018] Reference Figure 1 The image forming apparatus 1 according to a first exemplary embodiment of the present disclosure is described. Figure 1 This is a cross-sectional view of an image forming apparatus 1 according to a first exemplary embodiment of the present disclosure. The image forming apparatus 1 forms an image on a sheet P. In the first exemplary embodiment, the image forming apparatus 1 is a printer. The image forming apparatus 1 employs a series system and includes a feeding unit 10, a transport unit 20, an image forming unit 30, and an ejection unit 100.

[0019] The feeding unit 10 includes a box 11 that holds multiple sheets P. The sheets P are paper sheets or synthetic resin sheets. The feeding unit 10 feeds the sheets P from the box 11 to the conveying unit 20. The conveying unit 20 conveys the sheets P to the image forming unit 30. The image forming unit 30 forms an image on the sheets P. The conveying unit 20 conveys the sheet P with the image formed to the discharge unit 100. The discharge unit 100 discharges the sheets P to the outside of the image forming apparatus 1.

[0020] The image forming unit 30 includes an exposure unit 31, a unit 32a, a unit 32b, a unit 32c, a unit 32d, an intermediate transfer belt 33, a secondary transfer roller 34, and a fixing unit 35.

[0021] Exposure unit 31 illuminates each unit 32a to 32d with light based on image data to form an electrostatic latent image on each unit 32a to 32d.

[0022] Unit 32a forms a yellow toner image based on an electrostatic latent image. Unit 32b forms a magenta toner image based on an electrostatic latent image. Unit 32c forms a cyan toner image based on an electrostatic latent image. Unit 32d forms a black toner image based on an electrostatic latent image.

[0023] The intermediate transfer belt 33 rotates in the rotation direction R1. Four toner images are transferred from units 32a to 32d onto the outer surface of the intermediate transfer belt 33, thereby superimposing the four toner images to form an image. The secondary transfer roller 34 transfers the image formed on the outer surface of the intermediate transfer belt 33 onto the sheet P. The fixing unit 35 heats and presses the sheet P to fix the image onto the sheet P.

[0024] Each unit 32a to 32d includes a photosensitive drum 50 (image carrier), a charging device 51, a developing device 60, a primary transfer roller 53, an electrostatic eliminator 54, and a cleaner 55.

[0025] Multiple photosensitive drums 50 are arranged in the rotation direction R1 of the intermediate transfer belt 33, adjacent to the outer surface of the intermediate transfer belt 33. Multiple primary transfer rollers 53 are configured to correspond to the multiple photosensitive drums 50 and face the multiple photosensitive drums 50 across the intermediate transfer belt 33.

[0026] In each of the units 32a to 32d, the charging device 51, the developing device 60, the primary transfer roller 53, the static eliminator 54, and the cleaner 55 are arranged sequentially along the outer peripheral surface of the corresponding photosensitive drum 50.

[0027] The photosensitive drum 50 rotates in the rotation direction R2. The charging device 51 electrically charges the outer peripheral surface of the photosensitive drum 50. The outer peripheral surface of the photosensitive drum 50 is irradiated with light from the exposure device 31 to form an electrostatic latent image.

[0028] The developing apparatus 60 causes the toner to adhere to the electrostatic latent image formed on the outer peripheral surface of the photosensitive drum 50, thereby developing the electrostatic latent image and forming a toner image on the outer peripheral surface of the photosensitive drum 50. In other words, the photosensitive drum 50 carries the toner image.

[0029] The primary transfer roller 53 transfers the toner image carried by the photosensitive drum 50 to the outer surface of the intermediate transfer belt 33.

[0030] Static eliminator 54 eliminates static electricity from the outer peripheral surface of the photosensitive drum 50. Cleaner 55 removes residual toner images from the outer peripheral surface of the photosensitive drum 50.

[0031] In this exemplary embodiment, the image forming apparatus 1 is a printer, but it can be a copier, fax machine, or multifunction printer. A multifunction printer includes, for example, at least two of a copier, printer, fax machine, and scanner. The image forming apparatus 1 is a color printer, but it can be a monochrome printer.

[0032] Next, we will refer to Figure 2 and Figure 3 A developing apparatus 60 according to a first exemplary embodiment of the present disclosure is described. Figure 2 This is a cross-sectional view of a developing apparatus 60 according to a first exemplary embodiment of the present disclosure. Figure 3 Is Figure 2 An enlarged view of the toner blocking member 65 and its vicinity in a cross-section of the developing apparatus 60 shown in the figure.

[0033] like Figure 2 As shown, the developing apparatus 60 includes a housing 70 (developer container), a developer storage unit 80 (developer container), a magnetic roller 63 (toner supply roller), a developing roller 64 (toner carrier), a toner blocking member 65 (conductive member), and an adjusting blade 66.

[0034] The developer storage unit 80, magnetic roller 63, developing roller 64, toner blocking member 65, and adjusting blade 66 are disposed within the housing 70. The housing 70 includes a wall 71 and an opening 72.

[0035] The developer storage unit 80 stores a two-component developer (hereinafter simply referred to as developer) comprising a toner and a carrier. The developer storage unit 80 includes a first delivery chamber 81, a second delivery chamber 82, and a partition wall 83. The developer storage unit 80 is divided into the first delivery chamber 81 and the second delivery chamber 82 by the partition wall 83.

[0036] The first delivery chamber 81 includes a first delivery screw 811. The second delivery chamber 82 has a second delivery screw 812. The first delivery screw 811 rotates in the rotation direction R3 to deliver the developer while stirring it in the first delivery chamber 81. The second delivery screw 812 rotates in the same rotation direction R4 as R3 to deliver the developer while stirring it in the second delivery chamber 82. As a result, the developer is delivered while circulating between the first delivery chamber 81 and the second delivery chamber 82. That is, a circulation path for the developer is formed between the first delivery chamber 81 and the second delivery chamber 82.

[0037] The toner is charged by stirring with the first conveying screw 811 and the second conveying screw 812. In the first exemplary embodiment, the toner is a positively charged toner. That is, in the first exemplary embodiment, the normally charged toner is positively charged.

[0038] The second conveying screw 812 supplies developer to the magnetic roller 63.

[0039] A magnetic roller 63 is arranged inside the housing 70. The magnetic roller 63 carries developer on its surface.

[0040] The magnetic roller 63 faces the second conveying chamber 82 and is rotatably supported by the housing 70. The magnetic roller 63 includes a magnet 631 and a sleeve 632. The sleeve 632 is rotatable and cylindrical. The magnet 631 is fixedly arranged within the sleeve 632 and thus does not rotate. That is, the sleeve 632 rotates in the direction of rotation R5, while the magnet 631 remains stationary. The magnet 631 has five magnetic poles N1, S1, S2, N2, and S3. In the first exemplary embodiment, the magnetic flux densities of the five magnetic poles N1, S1, S2, N2, and S3 are 100 mT, 50 mT, 50 mT, 60 mT, and 60 mT (the peak value of the magnetic flux density Br in the normal direction of the magnetic roller 63), respectively.

[0041] The adjusting blade 66 is attached to the housing 70 along the longitudinal direction of the magnetic roller 63. As can be seen from the rotation direction R5 of the magnetic roller 63, the adjusting blade 66 is positioned upstream of the closest position P1 on the developing roller 64 relative to the magnetic roller 63 (the position on the developing roller 64 closest to the magnetic roller 63). A small gap is formed between the tip of the adjusting blade 66 and the magnetic roller 63.

[0042] The adjusting blade 66 is arranged to face the magnetic roller 63 and adjusts the thickness of the developer layer carried by the magnetic roller 63 (the amount of developer carried by the magnetic roller 63).

[0043] The developing roller 64 is arranged inside the housing 70 facing the magnetic roller 63. The developing roller 64 receives toner carried by the magnetic roller 63. The developing roller 64 carries the toner and delivers it to the position (developing position) where an electrostatic latent image is to be formed on the photosensitive drum 50. The developing roller 64 is rotatably supported by the housing 70. The developing roller 64 includes a magnet 641 and a sleeve 642. The sleeve 642 is rotatable and cylindrical. The magnet 641 is fixedly arranged inside the sleeve 642 and does not rotate. That is, the sleeve 642 rotates in the direction of rotation R6, while the magnet 641 remains stationary.

[0044] Magnet 641 has a magnetic pole S4. Magnetic roller 63 and developing roller 64 face each other, and at their facing position (closest position P1), there is a predetermined gap between them. In the first exemplary embodiment, the predetermined gap is 250 μm. The magnetic pole S4 of magnet 641 is opposite to the magnetic pole (N1 pole) that magnet 631 faces. In the first exemplary embodiment, pole S4 has a magnetic flux density of 50 mT (the peak value of the magnetic flux density Br in the normal direction of developing roller 64).

[0045] The magnetic roller 63 supplies toner only to the developing roller 64 by utilizing the electric field formed between the magnetic roller 63 and the developing roller 64 at the portion of the developing roller 64 facing the magnetic roller 63 (the closest position P1). At the portion of the developing roller 64 facing the magnetic roller 63, a small amount of carrier in the developer carried by the magnetic roller 63 may adhere to the developing roller 64. Even in this case, it is considered that the magnetic roller 63 supplies toner only from the developer carried by the magnetic roller 63 to the developing roller 64.

[0046] A DC voltage and an AC voltage are applied to the magnetic roller 63. The DC voltage and AC voltage are also applied to the developing roller 64. These voltages are applied to the magnetic roller 63 and the developing roller 64 from the developing bias power supply (bias application unit) via a bias control circuit. Due to the potential difference between the voltage applied to the magnetic roller 63 and the voltage applied to the developing roller 64, normally charged toner is supplied from the magnetic roller 63 to the developing roller 64. After development, the toner on the developing roller 64 is collected by the magnetic roller 63 due to the AC component of the potential difference between the voltage applied to the magnetic roller 63 and the voltage applied to the developing roller 64.

[0047] Figure 4 This is a waveform diagram of the bias voltage applied to the developing roller 64, the magnetic roller 63, and the toner blocking member 65 in the first exemplary embodiment. Figure 4 As shown, a developing bias is applied to the developing roller 64. The developing bias has an AC component that is superimposed on each other and a DC component of 70V (Vdc1 = 70V). The AC component has a frequency of 4kHz (f1 = 4kHz), a peak-to-peak voltage of 1.4kV (Vpp1 = 1.4kV), and a duty cycle of 40% (Dslv = 40%).

[0048] In a first exemplary embodiment, a developing bias voltage with a frequency of 10 kHz (f2 = 10 kHz), an inter-peak voltage of 1.75 kV (Vpp2 = 1.75 kV), and a duty cycle of 30% (Dmag = 30%) is applied to the magnetic roller 63. The developing bias voltage has a superimposed DC component of 340 V (Vdc2 = 340 V) and an AC component of a blank pulse waveform, wherein a blank period of 1.5 cycles is provided immediately after each positive (+) component ends.

[0049] Reference Figure 5 The diagram illustrates the duty cycle of the bias waveform. Duty cycle Dslv indicates the duty cycle on the time axis as the toner is dispersed from the developing roller 64 to the photosensitive drum 50 side (the side with the same polarity as the toner). Duty cycle Dmag indicates the duty cycle on the time axis as the toner is dispersed from the magnetic roller 63 to the developing roller 64 side (the side with the same polarity as the toner).

[0050] For example, if a normally charged toner is used, and the positive potential is on the top, and assuming... Figure 5 The upward and downward directions represent positive and negative potentials, respectively. The duty cycle Dp can then be expressed as Dp = {a / (a+b)} × 100, where a is the time the electric field is applied to cause the toner to scatter, and b is the time the electric field is applied to remove the toner. In other words, the duty cycle Dp can be expressed as the percentage of time a positive potential is applied relative to the total applied time.

[0051] If a negatively charged toner is used, the duty cycle is expressed as DP = {b / (a+b)} × 100.

[0052] As described above, since the toner used in the first exemplary embodiment is a positively charged toner, the toner is moved from the magnetic roller 63 to the developing roller 64 by setting the value of Vdc1 to be greater than the value of Vdc2. In the first exemplary embodiment, phase alignment is performed such that the time when the positive (+) component of the bias is applied to the developing roller 64 matches the time when the negative (-) component of the bias is applied to the magnetic roller 63. If an alternating current component is included, this periodically reverses the magnitude relationship between the potentials of the developing roller 64 and the magnetic roller 63, thereby producing the effect of collecting the toner on the developing roller 64 by the magnetic roller 63 after the developing process. On the other hand, this configuration, in which the toner is transferred between the developing roller 64 and the magnetic roller 63 by the developing bias as described above, allows the toner to float.

[0053] Accordingly, during the image forming operation (i.e., during the startup of the developing apparatus 60), the rotation of the magnetic roller 63 and the developing roller 64 causes toner to scatter and float from the magnetic roller 63, the developing roller 64, and the portions of the developing roller 64 facing the magnetic roller 63. The floating toner floats in the space S between the magnetic roller 63 and the developing roller 64 and the wall 71 of the housing 70.

[0054] like Figure 4 As shown, in the first exemplary embodiment, during the negative (-) component of the bias voltage applied to the developing roller 64, the AC component of the bias voltage applied to the magnetic roller 63 is substantially stopped. This is to prevent leakage (discharge) from occurring due to an increase in the potential difference between the developing roller 64 and the magnetic roller 63.

[0055] Generally, airflow is generated in the space S between the magnetic roller 63, the developing roller 64, and the wall 71 of the housing 70 by the rotation of the magnetic roller 63 and the developing roller 64. Therefore, the pressure inside the housing 70 becomes higher than the pressure outside the housing 70. This generates an airflow that moves air from the inside to the outside of the housing 70. As a result, in space S, toner not used for development is separated from the developing roller 64 by the magnetic brush, and the toner separated from the developing roller 64 may float and disperse along the airflow to the outside of the developing apparatus 60 through the opening in the housing 70. In particular, if the circumferential speed of the photosensitive drum 50 is equal to or higher than a predetermined circumferential speed (e.g., equal to or higher than 180 mm / s), the airflow velocity becomes higher. As a result, toner significantly disperses from the magnetic roller 63, the developing roller 64, and the portion of the developing roller 64 facing the magnetic roller 63.

[0056] As a countermeasure against this phenomenon, in the first exemplary embodiment, the toner blocking member 65 is arranged downstream of the closest position P1 where the developing roller 64 and the magnetic roller 63 are closest to each other, as seen in the rotation direction of the magnetic roller 63, essentially facing both the developing roller 64 and the magnetic roller 63. The toner blocking member 65 is arranged downstream of the position where the developing roller 64 develops the electrostatic latent image formed on the photosensitive drum 50, as seen in the rotation direction of the developing roller 64, and upstream of the closest position P1 where the developing roller 64 and the magnetic roller 63 are closest to each other, as seen in the rotation direction of the developing roller 64. The toner blocking member 65 is arranged closer to the developing roller 64 than the magnetic roller 63. That is, the toner blocking member 65 is arranged in the space S between the magnetic roller 63, the developing roller 64, and the wall portion 71, such that the shortest distance between the toner blocking member 65 and the developing roller 64 is shorter than the shortest distance between the toner blocking member 65 and the magnetic roller 63.

[0057] The toner blocking member 65 is preferably formed in a cylindrical or columnar shape. Compared to a cuboid shape with edges, a cylindrical or columnar toner blocking member 65 can be precisely manufactured with minimal surface warping. In a first exemplary embodiment, the toner blocking member 65 is formed in a columnar shape. The toner blocking member 65 is supported by a housing 70. The toner blocking member 65 is a weakly magnetic or non-magnetic metallic member. If the toner blocking member 65 is weakly magnetic, it is preferably made of austenitic stainless steel. The toner blocking member 65 is a conductive member made of a conductive material. For example, the diameter of the toner blocking member 65 is equal to or greater than 4 mm.

[0058] like Figure 3 As shown, the distance d1 (shortest distance) between the toner blocking member 65 and the developing roller 64 is preferably equal to or less than a predetermined size. In the first exemplary embodiment, the distance d1 between the toner blocking member 65 and the developing roller 64 is equal to or less than 0.3 mm. The distance d2 (shortest distance) between the toner blocking member 65 and the magnetic roller 63 is also preferably equal to or less than a predetermined size.

[0059] In the first exemplary embodiment, the distance d2 between the toner blocking member 65 and the magnetic roller 63 is equal to or less than 2 mm. The magnetic roller 63 carries developer including a carrier; therefore, setting the distance d2 to approximately equal to the maximum magnetic brush length of the portion of the magnetic roller 63 facing the toner blocking member 65 enhances the toner blocking effect. If the distance d2 is 1.0 mm or more longer than the maximum magnetic brush length, the toner blocking effect is weakened. On the other hand, if the distance d2 is 1.0 mm or more shorter than the maximum magnetic brush length, developer may remain on the facing portion.

[0060] The maximum magnetic brush length here refers to the maximum vertical distance from the surface of the magnetic roller 63 to the tip of the magnetic brush at the portion of the magnetic roller 63 facing the toner blocking member 65. Since the developing roller 64 is only coated with toner, the distance d2 between the toner blocking member 65 and the magnetic roller 63 can be further shortened, or more precisely, preferably shortened, to enhance the effect of blocking the toner.

[0061] Simply placing the toner blocking member 65 in the space S between the magnetic roller 63, the developing roller 64, and the wall 71 is insufficient to completely block the flow of toner, allowing it to leak from the gaps and scatter outside the developing apparatus 60. Furthermore, toner may adhere to the toner blocking member 65 and drip down, affecting image quality. Specifically, if the toner blocking member 65 is positioned above the magnetic roller 63 when viewed vertically, toner may drip onto the magnetic roller 63, potentially causing a higher toner concentration at the point of droplet application. Therefore, image density may increase after the magnetic roller 63 rotates.

[0062] Therefore, in the first exemplary embodiment, when the magnetic roller 63 and the developing roller 64 are driven, a DC potential Vdc3 is applied to the toner blocking member 65, which has the same polarity as the normally charged toner and is greater in absolute value than the potentials of the developing roller 64 and the magnetic roller 63.

[0063] In other words, during the image forming operation, a potential difference (first potential difference) is formed between the magnetic roller 63 and the developing roller 64, causing normally charged toner to move from the magnetic roller 63 to the developing roller 64. Furthermore, during the image forming operation, a potential difference (second potential difference) is formed between the toner blocking member 65 and the developing roller 64, causing normally charged toner to move from the toner blocking member 65 to the developing roller 64. Additionally, during the image forming operation, a potential difference (third potential difference) is formed between the toner blocking member 65 and the magnetic roller 63, causing normally charged toner to move from the toner blocking member 65 to the magnetic roller 63. The second potential difference is greater than both the first and third potential differences. In this manner, the bias application unit applies a bias voltage to the magnetic roller 63, the developing roller 64, and the toner blocking member 65 to form the first, second, and third potential differences between them.

[0064] As described above, the potential difference between the toner blocking member 65 and the developing roller 64 makes it possible to press the toner from the toner blocking member 65 toward the developing roller 64.

[0065] The above-described structure also allows the toner to be pressed from the toner blocking member 65 to the magnetic roller 63 due to the potential difference between the toner blocking member 65 and the magnetic roller 63.

[0066] As a result, the toner floating in the gap between the toner blocking member 65 and the developing roller 64 is collected by the developing roller 64, while the toner floating in the gap between the toner blocking member 65 and the magnetic roller 63 is collected by the magnetic roller 63. This exemplary embodiment can prevent the toner floating in the space S between the magnetic roller 63, the developing roller 64, and the wall 71 from scattering to the outside of the housing 70, and can also prevent the toner from adhering to the surface of the toner blocking member 65 and dripping therefrom.

[0067] In the first exemplary embodiment, the applied voltage Vdc3 applied to the toner blocking member 65 is set to 800V (Vdc3 = 800V).

[0068] The applied voltage Vdc3 to the toner blocking member 65 is made greater than the DC component of the bias voltage applied to the developing roller 64 (Vdc1 = 70V) and the DC component of the bias voltage applied to the magnetic roller 63 (Vdc2 = 350V). This achieves the aforementioned advantageous effect.

[0069] Furthermore, in the first exemplary embodiment, the applied voltage (Vdc3 = 800V) to the toner blocking member 65 is set to be less than the maximum value of the positive (+) component of the bias voltage applied to the developing roller 64 (Vpp1(max) = 910V), which has an AC component and a DC component that are superimposed on each other. That is, the absolute value of the potential of the DC component of the bias voltage applied to the toner blocking member 65 is set to be less than the absolute value of the peak potential on the side of the AC component of the bias voltage applied to the developing roller 64 that is of the same polarity as the normally charged toner.

[0070] In the first exemplary embodiment, the applied voltage (Vdc3 = 800V) to the toner blocking member 65 is set to be less than the maximum value of the positive (+) component of the bias voltage applied to the magnetic roller 63 (Vpp2(max) = 1565V), which has superimposed AC and DC components. That is, the absolute value of the DC component potential of the bias voltage applied to the toner blocking member 65 is set to be less than the absolute value of the peak potential on the side of the AC component of the bias voltage applied to the magnetic roller 63 that is of the same polarity as the normally charged toner.

[0071] The above settings are made for two reasons described below. One reason is to suppress leakage caused by an excessive potential difference between the toner blocking member 65 and the developing roller 64 due to the AC component of the bias voltage applied to the developing roller 64, and to suppress leakage caused by an excessive potential difference between the toner blocking member 65 and the magnetic roller 63 due to the AC component of the bias voltage applied to the magnetic roller 63.

[0072] The second reason is as follows. The above-described setting reverses the magnitude relationship between the voltage applied to the toner blocking member 65 and the voltage applied to the developing roller 64 and the magnetic roller 63 for a certain period of time, thereby promoting the separation of toner from the toner blocking member 65. In the first exemplary embodiment, the voltage Vdc3 applied to the toner blocking member 65 is more preferably set to be less than the maximum value Vpp1(max) of the positive (+) component of the bias voltage applied to the developing roller 64 and the maximum value Vpp2(max) of the positive (+) component of the bias voltage applied to the magnetic roller 63. On the other hand, in order to obtain the effect of promoting the separation of toner from the toner blocking member 65, the voltage Vdc3 applied to the toner blocking member 65 is set to be less than the maximum value Vpp1(max) of the positive (+) component of the bias voltage applied to the developing roller 64, or is set to be less than the maximum value Vpp2(max) of the positive (+) component of the bias voltage applied to the magnetic roller 63. Applying any of these settings will produce the corresponding effect. When using a negatively charged toner, a similar effect can be obtained by setting the absolute value of the voltage Vdc3 applied to the toner blocking member 65 to be less than the maximum value Vpp1(max) of the absolute value of the negative (-) component of the bias voltage applied to the developing roller 64 and the maximum value Vpp2(max) of the absolute value of the negative (-) component of the bias voltage applied to the magnetic roller 63. In terms of absolute value, similar advantageous effects can be obtained when using a negatively charged toner.

[0073] Discharge (leakage) will be described here. If the applied voltage Vdc3 to the toner blocking member 65 is further increased, the potential difference between the DC component Vdc1 of the bias applied to the developing roller 64 and the DC component Vdc2 of the bias applied to the magnetic roller 63 can be further increased, thereby enhancing the toner blocking effect. However, an excessively large potential difference between the two may cause leakage. In the event of leakage, the bias may be disturbed. Interference with the bias may result in defective images.

[0074] As described above, in the first exemplary embodiment, the normally charged toner is a positively charged toner. Therefore, in the first exemplary embodiment, the DC component Vdc2 of the bias voltage applied to the magnetic roller 63 is set to be greater than the DC component Vdc1 of the bias voltage applied to the developing roller 64. Furthermore, the applied voltage Vdc3 to the toner blocking member 65 is set to be greater than the DC component Vdc2 of the bias voltage applied to the magnetic roller 63. That is, the following relationship is established: "the absolute value of the DC component Vdc1 of the bias voltage applied to the developing roller 64" < "the absolute value of the DC component Vdc2 of the bias voltage applied to the magnetic roller 63" < "the absolute value of the applied voltage Vdc3 to the toner blocking member 65". However, the DC component Vdc1 of the bias voltage applied to the developing roller 64, the DC component Vdc2 of the bias voltage applied to the magnetic roller 63, and the applied voltage Vdc3 to the toner blocking member 65 are the same polarity as the normally charged toner.

[0075] As described above, in the first exemplary embodiment, the applied voltage Vdc3 to the toner blocking member 65 is set to be relatively large, such that the potential difference between the developing roller 64 and the toner blocking member 65 may be particularly large.

[0076] Therefore, in the first exemplary embodiment, an insulating layer is provided on the surface of the toner blocking member 65. Insulating the surface of the toner blocking member 65 can suppress leakage. As long as the insulating layer is made of an insulating material, it has the effect of suppressing leakage. When using a normally charged toner, an insulating layer material that may have a positive (+) polarity (the same polarity as the toner) is selected so that the toner cannot adhere to the surface of the insulating layer, because like polarities tend to repel each other. Therefore, in the first exemplary embodiment, a polyimide tube that easily takes on a positive (+) polarity is used, and an insulating layer is formed on the surface of the toner blocking member 65 by utilizing the heat shrinkage of the polyimide tube. When using a negatively charged toner, a perfluoroalkane (PFA) (fluoropolymer) tube or the like that that easily takes on a negative (-) polarity is preferably used.

[0077] A separate high-voltage power supply unit (other power supply) can be provided to apply the applied voltage Vdc3 to the toner blocking member 65. However, if the applied voltage is generated by the bias applied to the developing roller 64 or the magnetic roller 63, a separate high-voltage power supply unit (other power supply) is not necessarily required. For example, a dual-voltage rectifier circuit can be used to allow an output DC bias voltage that is substantially equal to the peak-to-peak value of the AC component of the input bias voltage. In the first exemplary embodiment, the AC component of the peak-to-peak voltage of 1.4 kV (Vpp1 = 1.4 kV) is applied to the developing roller 64, while the AC component of the peak-to-peak voltage of 1.75 kV (Vpp2 = 1.75 kV) is applied to the magnetic roller 63.

[0078] Accordingly, the applied voltage (Vdc3 = 800V) to the toner blocking member 65 can be generated by a dual-voltage rectifier circuit using either the peak-to-peak voltages Vpp1 and Vpp2. If the required voltage cannot be obtained by the dual-voltage rectifier circuit due to the small peak-to-peak value of the AC component of the input bias or the large voltage drop caused by resistance, etc., a peak hold circuit or the like can be used.

[0079] One advantage of generating the applied voltage Vdc3 to the toner blocking member 65 from the bias voltage applied to the developing roller 64 or the magnetic roller 63 is that it eliminates the need for a separate high-voltage power supply unit. Another advantage is as follows: If a high-voltage power supply unit is provided independently of the developing roller 64 and the magnetic roller 63, there are situations where the applied voltage Vdc3 is not applied to the toner blocking member 65 (=0V) due to a malfunction of the high-voltage power supply unit. In this case, the potential relationship between the developing roller 64 and the magnetic roller 63 may be reversed, potentially causing toner to move to the toner blocking member 65. Furthermore, if a high-voltage power supply unit is provided independently of the developing roller 64 and the magnetic roller 63, and the applied voltage Vdc3 is not applied to the toner blocking member 65 (=0V) due to a malfunction of the high-voltage power supply unit, the potential difference from the developing roller 64 and the magnetic roller 63 may become unnecessarily large. In the first exemplary embodiment, the maximum value of the voltage applied to the magnetic roller 63 is greater than the maximum value of the voltage applied to the developing roller 64, and the potential difference between the magnetic roller 63 and the toner blocking member 65 is 1565V, which may lead to leakage.

[0080] Therefore, in the first exemplary embodiment, the bias voltage to be applied to the toner blocking member 65 is generated from the bias voltage applied to the magnetic roller 63 by a dual-voltage rectifier circuit. From the advantages described above, it is preferable not to use different power supplies, but to use the same power supply to generate both the bias voltage applied to the magnetic roller 63 and the bias voltage applied to the toner blocking member 65. However, it is clear that the disclosure according to the first exemplary embodiment can be similarly applied to variations in which the power supply for generating the bias voltage to be applied to the magnetic roller 63 and the power supply for generating the bias voltage to be applied to the toner blocking member 65 are different.

[0081] In the first exemplary embodiment, as described above, the toner blocking member 65 is arranged in the space S between the magnetic roller 63 and the developing roller 64 and the wall portion 71, which is located downstream of the closest position P1 where the developing roller 64 and the magnetic roller 63 are closest to each other, as seen in the rotational direction of the magnetic roller 63.

[0082] The toner blocking member 65 is arranged downstream of the position where the developing roller 64 develops the electrostatic latent image formed on the photosensitive drum 50, as seen in the rotation direction of the developing roller 64, and upstream of the closest position P1 where the developing roller 64 and the magnetic roller 63 are closest to each other, as seen in the rotation direction of the developing roller 64.

[0083] Due to the potential difference between the toner blocking member 65 and the developing roller 64, toner is pressed from the toner blocking member 65 towards the developing roller 64. Furthermore, due to the potential difference between the toner blocking member 65 and the magnetic roller 63, toner is pressed from the toner blocking member 65 towards the magnetic roller 63. As a result, toner floating in the gap between the toner blocking member 65 and the developing roller 64 is collected by the developing roller 64, while toner floating in the gap between the toner blocking member 65 and the magnetic roller 63 is collected by the magnetic roller 63. This exemplary embodiment prevents toner floating in the space S between the magnetic roller 63 and the developing roller 64, and between the wall 71 inside the housing 70, from being carried by the airflow and scattered outside the housing 70.

[0084] In the first exemplary embodiment, as an example, only the DC component of the bias voltage is applied to the toner blocking member 65. Conversely, the second exemplary embodiment differs from the first exemplary embodiment in that a bias voltage consisting of a superposition of the DC and AC components is applied to the toner blocking member 65. In the second exemplary embodiment, only the differences from the first exemplary embodiment will be described. Other components and operations are similar to those in the first exemplary embodiment, and therefore detailed descriptions thereof will be omitted.

[0085] Applying a DC bias to the toner blocking member 65 enhances the toner-blocking effect through the electric field between the toner blocking member 65 and the magnetic roller 63, as well as through the electric field between the toner blocking member 65 and the developing roller 64. However, because the potential relationship between the biases changes over time, new floating toner may be generated. Furthermore, an excessively large potential difference between them increases concerns about leakage.

[0086] Therefore, in the second exemplary embodiment, a bias voltage is applied to the toner blocking member 65, the AC component of which is the same as the AC component of the developing roller 64, the AC component having a frequency of 4 kHz (f1 = 4 kHz), an inter-peak voltage of 1.4 kV (Vpp1 = 1.4 kV) and a duty cycle of 40% (Dslv = 40%), and the DC component of which is 800 V (Vdc3 = 800 V), which is different from the DC component of the developing roller 64.

[0087] A bias voltage is applied to the toner blocking member 65, causing the normally charged toner to receive a force acting in the direction of the developing roller 64, while at least the potential relationship between the developing roller 64 and the toner blocking member 65 remains unchanged. Furthermore, the potential difference between the developing roller 64 and the toner blocking member 65 does not become excessive, thereby suppressing leakage.

[0088] In the second exemplary embodiment, the AC component of the bias voltage applied to the toner blocking member 65 is the same as the AC component of the bias voltage applied to the developing roller 64. Alternatively, the AC component of the bias voltage applied to the toner blocking member 65 may be the same as the AC component of the bias voltage applied to the magnetic roller 63. In this case, the normally charged toner is continuously subjected to force in the direction of the magnetic roller 63, while at least the potential relationship between the magnetic roller 63 and the toner blocking member 65 remains unchanged. Furthermore, the potential difference between the magnetic roller 63 and the toner blocking member 65 does not become excessive, thereby suppressing leakage.

[0089] However, among the DC components of the bias voltage applied to the toner blocking member 65, the DC components of the bias voltage applied to the developing roller 64, and the DC components of the bias voltage applied to the magnetic roller 63, the absolute value of the DC component of the bias voltage applied to the toner blocking member 65 is set to the maximum.

[0090] Therefore, between the minimum bias voltage Vpp1(min) applied to the developing roller 64 and the minimum bias voltage Vpp2(min) applied to the magnetic roller 63, there is a greater concern that leakage may occur in the gap between the toner blocking member 65 and the developing roller 64, which has a smaller value. Therefore, it is more preferable that the AC component of the bias voltage applied to the toner blocking member 65 is the same as the AC component of the bias voltage applied to the developing roller 64.

[0091] Other exemplary embodiments

[0092] This disclosure is not limited to the exemplary embodiments described above, and various modifications (including organic combinations of exemplary embodiments) can be made based on the key points of this disclosure, and such modifications are not excluded from the scope of this disclosure.

[0093] The exemplary embodiments described above have been taken as an example using an image forming apparatus employing an intermediate transfer belt 33, as follows: Figure 1 As shown in the figure. However, the construction of the image forming apparatus is not limited thereto. This disclosure also applies to image forming apparatuses configured to transfer an image onto a sheet P that is in direct contact with the photosensitive drum 50.

[0094] While this disclosure has been described with reference to exemplary embodiments, it should be understood that this disclosure is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be interpreted in the broadest possible sense to include all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus, comprising: Image-carrying components; An exposure device configured to expose an image carrier to form an electrostatic latent image on the image carrier; A developing apparatus, comprising a first chamber and a second chamber, a first conveying screw and a second conveying screw, a rotatable developing roller, and a rotatable toner supply roller. The first chamber is configured to contain a developer containing toner and a carrier. The second chamber is separated from the first chamber by a partition wall and is configured to form a developer circulation path between the second chamber and the first chamber. The first delivery screw is arranged in the first chamber and configured to deliver developer along a first direction. The second delivery screw is arranged in the second chamber and configured to deliver the developer in a second direction opposite to the first direction. The developing roller is arranged to face the image carrier member and is configured to carry and deliver toner to the developing position, where the electrostatic latent image formed on the image carrier member is developed. The toner supply roller is arranged to face the developing roller and is configured to carry and transport the developing agent supplied from the first chamber, and to supply the toner only to the developing roller. At the position where the toner supply roller and the developing roller face each other, the rotation direction of the toner supply roller is opposite to the rotation direction of the developing roller. A conductive roller, arranged facing the toner supply roller and the developing roller, is positioned downstream of the developing position in the direction of rotation of the developing roller and upstream of the position where the toner supply roller is positioned closest to the developing roller; and A bias application unit is configured to apply a bias voltage to a toner supply roller, a developing roller, and a conductive roller during an image forming operation, such that: i. a first potential difference is formed between the toner supply roller and the developing roller to move normally charged toner from the toner supply roller to the developing roller; ii. a second potential difference is formed between the conductive roller and the developing roller to move normally charged toner from the conductive roller to the developing roller; and iii. a third potential difference is formed between the conductive roller and the toner supply roller to move normally charged toner from the conductive roller to the toner supply roller. The absolute value of the second potential difference is greater than the absolute value of the first potential difference and also greater than the absolute value of the third potential difference. The shortest distance between the developing roller and the conductive roller is equal to or less than 0.3 mm.

2. The image forming apparatus according to claim 1, in, A bias voltage with superimposed DC and AC components is applied to the toner supply roller. In this process, a bias voltage consisting of superimposed DC and AC components is applied to the developing roller, and In this process, a bias voltage with superimposed DC and AC components is applied to the conductive roller.

3. The image forming apparatus according to claim 2, in, The polarity of the DC component of the bias voltage applied to the toner supply roller, the DC component of the bias voltage applied to the developing roller, and the DC component of the bias voltage applied to the conductive roller are the same as the polarity of the normally charged toner. The absolute value of the DC component of the bias voltage applied to the conductive roller is greater than the absolute value of the DC component of the bias voltage applied to the toner supply roller, and is also greater than the absolute value of the DC component of the bias voltage applied to the developing roller.

4. The image forming apparatus according to claim 2 or 3, wherein, The AC component of the bias voltage applied to the conductive roller is the same as the AC component of the bias voltage applied to the toner supply roller.

5. The image forming apparatus according to claim 2 or 3, wherein, The AC component of the bias voltage applied to the conductive roller is the same as the AC component of the bias voltage applied to the developing roller.

6. The image forming apparatus according to claim 1, in, A bias voltage with superimposed DC and AC components is applied to the toner supply roller. In this process, a bias voltage consisting of superimposed DC and AC components is applied to the developing roller, and In this process, a bias voltage with only a DC component is applied to the conductive roller.

7. The image forming apparatus according to claim 6, in, The polarity of the DC component of the bias voltage applied to the toner supply roller, the polarity of the DC component of the bias voltage applied to the developing roller, and the polarity of the DC component of the bias voltage applied to the conductive roller are the same as the polarity of normally charged toner, and The absolute value of the DC component of the bias voltage applied to the conductive roller is greater than the absolute value of the DC component of the bias voltage applied to the toner supply roller, and is also greater than the absolute value of the DC component of the bias voltage applied to the developing roller.

8. The image forming apparatus according to claim 6 or 7, wherein, The absolute value of the DC component of the bias voltage applied to the conductive roller is less than the absolute value of the peak potential of the AC component of the bias voltage applied to the toner supply roller, which is on the same polarity side as the normally charged toner.

9. The image forming apparatus according to claim 6 or 7, wherein, The absolute value of the DC component potential of the bias voltage applied to the conductive roller is less than the absolute value of the peak potential of the AC component of the bias voltage applied to the developing roller, which is on the same polarity side as the normally charged toner.

10. The image forming apparatus according to claim 1, wherein, They share the following power supplies: a power supply configured to supply power for applying bias voltage to the toner supply roller via the bias voltage application unit during image forming operation; and a power supply configured to supply power for applying bias voltage to the conductive roller via the bias voltage application unit during image forming operation.

11. The image forming apparatus according to claim 1, wherein, They share the following power supplies: a power supply configured to supply power for applying bias voltage to the developing roller through the bias voltage application unit during image forming operation; and a power supply configured to supply power for applying bias voltage to the conductive roller through the bias voltage application unit during image forming operation.

12. The image forming apparatus according to claim 1, in, The toner supply roller includes a first magnet having a plurality of magnetic poles, the plurality of magnetic poles including the first magnetic pole, wherein the first magnet is fixedly arranged to not rotate within the toner supply roller, and The developing roller includes a second magnet having a second magnetic pole as a second magnetic pole, the second magnetic pole being arranged to face the first magnetic pole and having a different polarity from the first magnetic pole, wherein the second magnet is fixedly arranged to not rotate within the developing roller.

13. The image forming apparatus according to claim 1, in, The shortest distance between the developing roller and the conductive roller is shorter than the shortest distance between the toner supply roller and the conductive roller.

14. The image forming apparatus according to claim 1, in, The shortest distance between the toner supply roller and the conductive roller is equal to or less than 2 mm.

15. The image forming apparatus according to claim 1, wherein, The diameter of the conductive roller is equal to or less than 4 mm.

16. The image forming apparatus according to claim 1, wherein, The surface of the conductive roller is insulated.

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