Image forming apparatus

Abstract

To provide an image forming apparatus that can suitably collect a transfer residual toner that is not transferred and remains on an image carrier.SOLUTION: A control unit of an image forming apparatus causes a voltage application unit to apply collection voltage to a cleaning roller 242 during image formation, estimates the surface potential of a photoreceptor drum 21 on the basis of a current flowing between the photoreceptor drum 21 and the cleaning roller 242, which is detected by a current detection unit during the application of the collection voltage, and when the surface potential of the photoreceptor drum 21 is reduced, changes the rotation speed of and the collection voltage applied to the cleaning roller 242.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] In electrophotographic image forming devices such as copiers and printers, devices are widely used that supply toner to an electrostatic latent image formed on the outer peripheral surface of a photosensitive drum, which serves as an image carrier, and develop it to form a toner image that is later transferred to paper.In such image forming devices, it is necessary to collect transfer-residual toner that is not completely transferred from the photosensitive drum to a transfer material such as an intermediate transfer belt or paper and remains on the photosensitive drum so that the transfer-residual toner does not affect the formation of the next image.

[0003] The conventional image forming apparatus disclosed in Patent Document 1 includes a cleaning roller that removes foreign matter, such as residual toner, from the surface of the photosensitive drum after the toner image is transferred to paper. Furthermore, the image forming apparatus changes the cleaning voltage applied to the cleaning roller when the transfer voltage applied to the transfer roller is changed. This allows stable cleaning to be performed by following fluctuations in the surface potential of the photosensitive drum. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-331875 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional technology, when the cleaning voltage applied to the cleaning roller reaches its upper limit, the cleaning performance of the photosensitive drum surface cannot be maintained, and there is a risk of uncollected toner being generated, which may affect the next image formation and cause image defects.

[0006] The present invention has been made in consideration of the above points, and aims to provide an image forming apparatus that can suitably collect residual toner that has not been completely transferred and remains on an image carrier. [Means for solving the problem]

[0007] In order to solve the above problems, the image forming apparatus of the present invention includes an image carrier, a charging unit, an exposure unit, a developing unit, a transfer unit, a cleaning roller, a voltage application unit, a current detection unit, and a control unit. The image carrier has a photosensitive layer formed on its outer peripheral surface. The charging unit charges the outer peripheral surface of the image carrier to a predetermined surface potential. The exposure unit exposes the outer peripheral surface of the image carrier charged by the charging unit to light, thereby forming an electrostatic latent image by attenuating the charge. The developing unit supplies toner to the electrostatic latent image on the image carrier to form a toner image. The transfer unit transfers the toner image formed on the outer peripheral surface of the image carrier to a transfer target. The cleaning roller removes and collects deposits from the outer peripheral surface of the image carrier. The voltage application unit applies a predetermined voltage to the charging unit, the developing unit, the transfer unit, and the cleaning roller. The current detection unit detects the current flowing between the image carrier and the cleaning roller when the voltage application unit applies a collection voltage to the cleaning roller. The control unit controls the image carrier, the charging unit, the developing unit, the transfer unit, the cleaning roller, and the voltage application unit. During image formation, the control unit applies the recovery voltage to the cleaning roller using the voltage application unit, estimates the surface potential of the image carrier based on the current detected by the current detection unit when the recovery voltage is applied, and changes the recovery voltage and the rotation speed of the cleaning roller when the surface potential of the image carrier decreases. [Effects of the Invention]

[0008] According to the configuration of the present invention, by detecting a decrease in the surface potential of the image carrier, it is possible to recognize a decrease in the recovery performance for transfer residual toner that was not completely transferred and remains on the image carrier. Then, by changing the recovery voltage of the cleaning roller and the rotational speed of the cleaning roller, the difference in rotational speed of the cleaning roller relative to the image carrier can be changed, thereby improving the recovery performance for transfer residual toner on the image carrier. This makes it possible to efficiently recover transfer residual toner from the image carrier. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional front view of an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a block diagram showing the configuration of the image forming apparatus of FIG. 1. [Figure 3] 2 is a schematic cross-sectional front view of the periphery of an image forming unit of the image forming apparatus of FIG. 1. [Figure 4] 10 is a graph showing the relationship between the transfer current to the intermediate transfer belt and the amount of toner on the belt. [Figure 5] 10 is a graph showing the relationship between the amount of transfer residual toner on the photosensitive drum and the amount of uncollected toner. [Figure 6] 10 is a graph showing the relationship between the amount of transfer residual toner on the photosensitive drum and the cleaning level. [Figure 7] 10 is a graph showing the relationship between the recovery voltage of the cleaning roller and the amount of decrease in the surface potential of the photosensitive drum. [Figure 8] 10 is a graph showing the settable ranges of the transfer current and the collection current. [Figure 9] 9 is an explanatory diagram showing control for setting conditions outside the settable ranges of the transfer current and the recovery current within the ranges in the graph of FIG. 8. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following.

[0011] FIG. 1 is a schematic cross-sectional front view of an image forming apparatus 1 according to an embodiment. FIG. 2 is a block diagram showing the configuration of the image forming apparatus 1 shown in FIG. 1. FIG. 3 is a schematic cross-sectional front view of the periphery of an image forming unit 20 of the image forming apparatus 1 shown in FIG. 1. An example of the image forming apparatus 1 according to this embodiment is a tandem color printer that receives image data and a print command related to a print job from an external computer and transfers a toner image onto paper S using an intermediate transfer belt 31. The image forming apparatus 1 may also be a so-called multifunction device that has functions such as printing, scanning (image reading), and facsimile transmission.

[0012] As shown in Figures 1, 2 and 3, the image forming apparatus 1 includes a paper supply 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, a control unit 8 and a memory unit 9, which are provided in its main body 2.

[0013] The main body 2 is equipped with an operation panel 2c. The operation panel 2c is located, for example, at the top front of the main body 2 and includes a display unit 2d such as a liquid crystal display. The operation panel 2c displays on the display unit 2d images of screens related to settings such as the type and size of paper S to be used for printing, printing conditions such as enlargement / reduction, single-sided printing, double-sided printing, and combined printing, and input of execution commands, and receives these inputs directly from the user. Furthermore, the display unit 2d also serves as a notification unit that notifies the user of the status of the image forming apparatus 1, precautions, error messages, etc., by displaying them.

[0014] The paper supply unit 3 is located at the bottom of the main body 2. The paper supply unit 3 stores multiple sheets of paper S before printing, and separates and sends out the sheets S one by one 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 sent out from the paper supply unit 3 to the secondary transfer unit 33 and the fixing unit 6, and then ejects the paper S after fixing from the paper outlet 4a to the paper ejection unit 7. The exposure unit 5 is located at the top of the main body 2. The exposure unit 5 irradiates the image forming unit 20 with laser light controlled based on image data.

[0015] The image forming units 20 are disposed below the exposure unit 5 and above the intermediate transfer belt 31. The image forming units 20 include 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 otherwise specified.

[0016] The image forming unit 20 includes a photosensitive drum (image carrier) 21 that is supported so as to be rotatable in a predetermined direction (counterclockwise in FIGS. 1 and 3). The image forming unit 20 further includes a charging unit 22, a developing unit 23, and a drum cleaning unit (cleaning unit) 24 that are arranged around the photosensitive drum 21 along the direction of rotation of the photosensitive drum 21. A primary transfer unit 32 is arranged between the developing unit 23 and the drum cleaning unit 24.

[0017] The photosensitive drum 21 has a photosensitive layer formed on its outer circumferential surface. The charging unit 22 charges the outer circumferential surface of the photosensitive drum 21 to a predetermined surface potential. The exposure unit 5 exposes the outer circumferential surface of the photosensitive drum 21 charged by the charging unit 22 to light, and forms an electrostatic latent image of the original image on the outer circumferential surface of the photosensitive drum 21, with the charge attenuated. The developing unit 23 supplies toner to the electrostatic latent image on the outer circumferential surface of the photosensitive drum 21 to develop it and form a toner image. Each of the four image forming units 20 forms a toner image of a different color.

[0018] The drum cleaning unit 24 removes and collects toner and other deposits (transfer residual toner) remaining on the outer peripheral surface of the photosensitive drum 21 after the toner image has been primarily transferred onto the outer peripheral surface of the intermediate transfer belt 31. Note that any toner that cannot be completely collected by the drum cleaning unit 24 and remains on the outer peripheral surface of the photosensitive drum 21 is collected by the developing unit 23 after passing through the charging unit 22. In this way, the image forming unit 20 forms an image (toner image) that will later be transferred to the paper S.

[0019] The transfer unit 30 includes an intermediate transfer belt (transfer receiving body) 31, primary transfer units 32Y, 32C, 32M, and 32B, a secondary transfer unit 33, and a belt cleaning unit 34. The intermediate transfer belt 31 is disposed below the four image forming units 20 and above the paper supply unit 3. The intermediate transfer belt 31 is disposed opposite the four photosensitive drums 21. The intermediate transfer belt 31 is supported so as to be rotatable in a predetermined direction (clockwise in FIG. 1), and is an endless intermediate transfer body (transfer receiving body) onto which 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 disposed in a so-called tandem arrangement, lined up in a row from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 31.

[0020] Primary transfer units 32Y, 32C, 32M, and 32B are disposed below image forming units 20Y, 20C, 20M, and 20B of the respective colors, with intermediate transfer belt 31 sandwiched between them. Secondary transfer unit 33 is disposed upstream of fixing unit 6 in the paper conveying direction of paper conveying unit 4, and downstream of four image forming units 20Y, 20C, 20M, and 20B in the rotation direction of intermediate transfer belt 31. Belt cleaning unit 34 is disposed downstream of secondary transfer unit 33 in the rotation direction of intermediate transfer belt 31.

[0021] The primary transfer unit 32 transfers the toner image formed on the outer circumferential surface of the photosensitive drum 21 onto the outer circumferential surface of the intermediate transfer belt 31. In other words, the toner image is primarily transferred onto the outer circumferential surface of the intermediate transfer belt 31 at 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 successively superimposed and transferred onto the intermediate transfer belt 31 at a predetermined timing, thereby forming a color toner image on the outer circumferential surface of the intermediate transfer belt 31 in which toner images of four colors, yellow, cyan, magenta, and black, are superimposed.

[0022] The color toner image on the outer circumferential surface of intermediate transfer belt 31 is transferred to paper S, which has been synchronously fed by paper transport unit 4, at a secondary transfer nip formed in secondary transfer unit 33. Belt cleaning unit 34 removes and cleans toner and other adhering matter remaining on the outer circumferential surface of intermediate transfer belt 31 after secondary transfer. In this way, transfer unit 30 transfers (records) the toner image formed on the outer circumferential surface of photosensitive drum 21 onto paper S.

[0023] The fixing unit 6 is disposed above the secondary transfer unit 33. The fixing unit 6 fixes the toner image to the paper S by applying heat and pressure to the paper S onto which the toner image has been transferred.

[0024] The paper discharge section 7 is disposed above the transfer section 30. The paper S on which the toner image has been fixed and printing has been completed is transported to the paper discharge section 7. The paper discharge section 7 takes out the printed paper (printed matter) from above.

[0025] The control unit 8 includes a CPU, an image processing unit, and other electronic circuits and electronic components (none of which are shown). Based on control programs and data stored in the memory unit 9, the CPU controls the operation of each component provided in the image forming apparatus 1 to perform processing related to the functions of the image forming apparatus 1. The paper supply 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 print on the paper S in cooperation with each other.

[0026] The storage unit 9 is configured by combining a non-volatile storage device (not shown) such as a program ROM (Read Only Memory) or a data ROM, and a volatile storage device (not shown) such as a RAM (Random Access Memory).

[0027] As shown in FIG. 2, the image forming apparatus 1 further includes a voltage application unit 12 and a current detection unit 13.

[0028] 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 charge wire 221 and grid electrode 222 of the charging unit 22, the developing roller 234 of the developing unit 23, the cleaning roller 242 of the drum cleaning unit 24, and the primary transfer roller 321 and secondary transfer roller 331 of the transfer unit 30. The voltage application unit 12 applies a predetermined voltage to the charging unit 22, the developing unit 23, the cleaning roller 242, and the transfer unit 30.

[0029] Specifically, voltage application unit 12 applies a charging current to charge wire 221 and a charging voltage to grid electrode 222, applies a developing voltage (developing bias) to development roller 234, applies a recovery voltage (cleaning bias) to cleaning roller 242, and applies a transfer voltage (transfer current) to primary transfer roller 321 and secondary transfer roller 331. Control unit 8 controls the application timing, voltage value (current value), polarity, application time, etc. of the voltage (current) to each of charge wire 221, grid electrode 222, development roller 234, cleaning roller 242, primary transfer roller 321, and secondary transfer roller 331 via voltage application unit 12.

[0030] The current detection unit 13 detects the current (drum inflow current) flowing between the photosensitive drum 21 and the cleaning roller 242 when the voltage application unit 12 applies a recovery voltage to the cleaning roller 242. The control unit 8 receives information related to the current detected by the current detection unit 13 from the current detection unit 13.

[0031] Next, the configuration of the image forming unit 20 and its surroundings will be described with reference to Fig. 3. Note that since the image forming units 20 for each color have the same basic configuration, the identification symbols representing each color of the components and their explanations will be omitted unless there is a particular need to limit them.

[0032] The image forming unit 20 includes a photosensitive drum 21, a charging unit 22, a developing unit 23, and a drum cleaning unit 24.

[0033] The photosensitive drum 21 has a cylindrical shape that is rotatably supported with its central axis horizontal, and is rotated at a constant speed around the central axis by a drive unit (not shown). The photosensitive drum 21 has a photosensitive layer made of, for example, an organic photoconductor (OPC) on the outer surface of a drum tube made of metal such as aluminum. An electrostatic latent image is formed on the outer surface of the photosensitive drum 21.

[0034] The charging unit 22 is disposed opposite the outer peripheral surface of the photosensitive drum 21 at a predetermined distance. The charging unit 22 has a charge wire 221 and a grid electrode 222. The charge wire 221 is a linear electrode extending parallel to the axial direction of the photosensitive drum 21 and generates a corona discharge between the charge wire 221 and the photosensitive drum 21. The grid electrode 222 is a lattice-shaped electrode extending in the axial direction of the photosensitive drum 21 and is disposed between the charge wire 221 and the photosensitive drum 21. The charging unit 22 applies a predetermined charging current to the charge wire 221 to generate a corona discharge, and further applies a predetermined charging voltage to the grid electrode 222, thereby uniformly charging the outer peripheral surface (surface) of the photosensitive drum 21 to a predetermined surface potential.

[0035] The developing unit 23 is disposed downstream of the charging unit 22 in the rotation direction of the photosensitive drum 21. The developing unit 23 includes a developer container 231, an agitating paddle 232, a supply roller 233, and a developing roller 234.

[0036] The developing container 231 has an elongated shape extending along the axial direction of the photosensitive drum 21 (the depth direction of the paper in FIG. 3 ), and is disposed with its longitudinal direction horizontal. The developing container 231 has an opening 231a in a part facing the photosensitive drum 21. The developing container 231 contains non-magnetic single-component toner as a developer. That is, the developing container 231 contains toner to be supplied to the photosensitive drum 21.

[0037] The agitating paddle 232 is disposed in the upper part of the developing container 231, at a position separated from the opening 231a by the developing roller 234 and the supply roller 233. The agitating paddle 232 is supported by the developing container 231 so as to be rotatable about an axis extending parallel to the photosensitive drum 21. The agitating paddle 232 further has a flexible film portion extending in the radial direction. The agitating paddle 232 agitates the toner in the developing container 231 by rotating about its axis.

[0038] The supply roller 233 is disposed in the lower part of the developing container 231, between the opening 231a and the stirring paddle 232. The supply roller 233 is disposed opposite the developing roller 234. The supply roller 233 is supported by the developing container 231 so as to be rotatable about an axis extending parallel to the photosensitive drum 21. The supply roller 233 carries toner to be supplied to the outer peripheral surface of the developing roller 234 in the region facing the developing roller 234. The supply roller 233 rotates in the same direction as the developing roller 234.

[0039] The developing roller 234 is disposed in an opening 231a of the developing container 231, and a portion of it is exposed from the developing container 231. The developing roller 234 is disposed opposite the photosensitive drum 21 and is in contact with the photosensitive drum 21. The developing roller 234 is supported by the developing container 231 so as to be rotatable about an axis extending parallel to the axis of the photosensitive drum 21. The developing roller 234 carries toner to be supplied to the outer circumferential surface of the photosensitive drum 21 in the region facing the photosensitive drum 21. The developing roller 234 rotates in the opposite direction to the photosensitive drum 21. The developing roller 234 supplies the toner in the developing container 231 to the outer circumferential surface of the photosensitive drum 21, and develops the electrostatic latent image to form a toner image.

[0040] The drum cleaning unit 24 is disposed downstream of the primary transfer unit 32 in the rotation direction of the photosensitive drum 21. The drum cleaning unit 24 includes a collection container 241 and a cleaning roller 242.

[0041] The collection container 241 has an elongated shape that extends along the axial direction of the photosensitive drum 21 (the depth direction of the paper in FIG. 3) and is disposed with its longitudinal direction horizontal. The collection container 241 contains adhering matter such as toner that has been removed and collected from the outer peripheral surface of the photosensitive drum 21 by the cleaning roller 242.

[0042] The cleaning roller 242 is partially exposed from the collection container 241 and is disposed opposite the photosensitive drum 21. The cleaning roller 242 is supported by the collection container 241 so as to be rotatable about an axis extending parallel to the axis of the photosensitive drum 21. The cleaning roller 242 is configured, for example, as a sponge roller having a predetermined cell diameter. The cleaning roller 242 contacts the outer peripheral surface of the photosensitive drum 21 with a predetermined pressure. A collection voltage is applied to the cleaning roller 242 by the voltage application unit 12 during image formation. The cleaning roller 242 removes and collects deposits, including toner, remaining on the outer peripheral surface of the photosensitive drum 21 after primary transfer.

[0043] The cleaning roller 242 collects the toner in the cells of the sponge. As the cumulative driving time of the drum cleaning unit 24 increases, the toner accumulates in the cells, making it difficult for the cleaning roller 242 to collect the residual toner after transfer. The performance of the cleaning roller 242 in collecting the residual toner after transfer can be improved by appropriately adjusting the collection voltage (cleaning bias) of the cleaning roller 242.

[0044] Next, the collection of residual toner by the cleaning roller 242 will be described in detail.

[0045] 4 is a graph showing the relationship between the transfer current to the intermediate transfer belt 31 and the amount of toner on the belt. In the graph shown in FIG. 4, the horizontal axis represents the transfer current applied to the primary transfer roller 321, and the vertical axis represents the amount of toner on the belt that has been primarily transferred from the photosensitive drum 21 to the intermediate transfer belt 31 relative to the transfer current. The amount of toner on the belt is estimated based on the toner density detected by a density detection unit (not shown) for the toner image transferred to the outer surface of the intermediate transfer belt 31. As shown by the curve in FIG. 4, it can be seen that the amount of toner on the belt increases as the transfer current increases.

[0046] 4 represents the amount of developing toner supplied from the developing unit 23 to the photosensitive drum 21 when forming a toner image. The amount of developing toner is predicted from the amount of toner on the belt of the toner image transferred to the outer peripheral surface of the intermediate transfer belt 31, using a prediction table (not shown) stored in advance in the storage unit 9, etc.

[0047] The amount of residual toner after transfer is calculated based on the difference between the amount of developed toner predicted using a prediction table, etc., and the amount of toner on the belt. The residual toner after transfer is toner that is supplied from the developing unit 23 to the photosensitive drum 21 and remains on the photosensitive drum 21 without being transferred to the outer peripheral surface of the intermediate transfer belt 31 during the primary transfer.

[0048] 4, the difference between the amount of developed toner represented by the dashed line and the amount of toner on the belt represented by the curved line is the amount of residual toner after transfer. In other words, the lower the transfer current, the greater the amount of residual toner after transfer, which may make it difficult for cleaning roller 242 to collect the residual toner after transfer.

[0049] Fig. 5 is a graph showing the relationship between the amount of transfer residual toner and the amount of uncollected toner on the photosensitive drum 21. In the graph shown in Fig. 5, the horizontal axis represents the amount of transfer residual toner of a reference image (not shown) remaining on the photosensitive drum 21, and the vertical axis represents the amount of uncollected toner of the reference image that was not completely collected by the cleaning roller 242 and the developing unit 23 and remained after one rotation of the photosensitive drum 21 and was transferred to the intermediate transfer belt 31, relative to the amount of transfer residual toner.

[0050] When checking the relationship between the amount of residual transferred toner and the amount of non-recovered toner, a reference image, which is a toner image, is formed on the photoreceptor drum 21. Then, by changing the transfer current, the amount of residual transferred toner remaining on the photoreceptor drum 21 after primary transfer of the reference image increases or decreases, and further, the amount of non-recovered toner increases or decreases.

[0051] FIG. 5 shows the results of measuring the amount of non-recovered toner with respect to the amount of residual transferred toner by changing the applied voltage (recovery voltage) of the cleaning roller 242 in a plurality of steps of Va, Vb, and Vc. As shown in FIG. 5, when the amount of residual transferred toner (horizontal axis) is small, the residual transferred toner is recovered by the cleaning roller 242 and the developing unit 23, so the amount of non-recovered toner (vertical axis) becomes 0. As the amount of residual transferred toner increases, the amount of non-recovered toner gradually increases and is depicted as a curve shown in FIG. 5.

[0052] The amount of recoverable toner with respect to the applied voltage (recovery voltage) of the cleaning roller 242 is measured based on the amount of non-recovered toner. More specifically, in FIG. 5, the amount of recoverable toner Ta with respect to the applied voltage Va of the cleaning roller 242, the amount of recoverable toner Tb with respect to the applied voltage Vb, and the amount of recoverable toner Tc with respect to the applied voltage Vc are each measured based on the amount of non-recovered toner. According to FIG. 5, the higher the applied voltage of the cleaning roller 242, that is, in the order of applied voltage Va < Vb < Vc, the larger the amount of residual transferred toner that can be recovered, that is, the amount of recoverable toner (Ta < Tb < Tc).

[0053] FIG. 6 is a graph showing the relationship between the amount of residual transferred toner on the photoreceptor drum 21 and the cleaning level. In the graph shown in FIG. 6, the horizontal axis is the amount of residual transferred toner remaining on the photoreceptor drum 21, and the vertical axis is the cleaning level with respect to the residual transferred toner. The cleaning level indicated by the vertical axis represents the degree of recovery of the residual transferred toner by the cleaning roller 242, and the level deteriorates as going upward. Also, "C / D" in FIG. 6 is the "rotation speed ratio" and is represented by "cleaning roller rotation speed (C) / photoreceptor drum rotation speed (D)".

[0054] 6 shows the results of evaluating the cleaning level for residual toner after transfer when the rotational speed ratio (C / D) between photosensitive drum 21 and cleaning roller 242 is changed in multiple stages: 1.0, 0.8, 0.6, and 0.4. As shown in FIG. 6, when the amount of residual toner after transfer (horizontal axis) is small, the residual toner is collected by cleaning roller 242, so the amount of uncollected toner is 0 and the cleaning level is good (bottom end of vertical axis). As the amount of residual toner after transfer increases, the amount of uncollected toner also gradually increases, and the cleaning level deteriorates, as depicted by the curve shown in FIG. 6.

[0055] Any toner not collected by the cleaning roller 242, even if only a small amount, results in a collection failure. In other words, any deterioration in the cleaning level from a good state (bottom end of the vertical axis) results in a collection failure. Therefore, for each rotational speed ratio (C / D), the settable range is when the cleaning level is good (bottom end of the vertical axis) and the transfer residual toner ranges from 0 to the maximum value.

[0056] In detail, in FIG. 6, when the rotational speed ratio (C / D) is 0.8, the amount of transfer residual toner that can be collected is approximately 1.0 g / m 2 When the rotational speed ratio (C / D) is 0.6, the amount of transfer residual toner that can be collected is approximately 1.7 g / m 2 6, the smaller the rotational speed ratio (C / D) between the photosensitive drum 21 and the cleaning roller 242, that is, in the order of rotational speed ratio (C / D) 1.0<0.8<0.6<0.4, the larger the amount of transfer residual toner that can be collected and the wider the settable range of the rotational speed ratio.

[0057] 7 is a graph showing the relationship between the collection voltage of the cleaning roller 242 and the amount of decrease in the surface potential of the photosensitive drum 21. In the graph shown in FIG. 7, the horizontal axis represents the collection voltage applied to the cleaning roller 242, and the vertical axis represents the amount of decrease in the surface potential of the photosensitive drum 21.

[0058] The photosensitive drum 21 is positively charged, and the cleaning roller 242 is negatively charged. As a result, as shown in Fig. 7, the greater the absolute value of the collection voltage of the cleaning roller 242, the greater the amount of decrease in the surface potential of the photosensitive drum 21. The control unit 8 estimates the surface potential of the photosensitive drum 21 based on the current flowing between the photosensitive drum 21 and the cleaning roller 242, which is detected by the current detection unit 13 when the collection voltage is applied.

[0059] 5, the higher the applied voltage (collection voltage) of cleaning roller 242, the greater the amount of transfer residual toner that can be collected, that is, the better the collection performance of transfer residual toner on photosensitive drum 21. However, when the collection voltage of cleaning roller 242 is increased, the amount of decrease in the surface potential of photosensitive drum 21 increases, as shown in FIG.

[0060] In the drum cleaning unit 24, an electric field is generated by the potential difference between the surface potential of the photosensitive drum 21 and the collection voltage applied to the cleaning roller 242, and the action of this electric field causes the transfer residual toner on the photosensitive drum 21 to move onto the cleaning roller 242 and be collected. If the amount of decrease in the surface potential of the photosensitive drum 21 increases, the potential difference between the surface potential of the photosensitive drum 21 and the collection voltage of the cleaning roller 242 decreases, which may cause a problem in which toner unintentionally adheres to the white portion (background portion, skin surface portion) of the recording paper. The range of the collection voltage to be applied to the cleaning roller 242 up to the maximum amount of decrease in the surface potential of the photosensitive drum 21 that does not cause such an image defect is the settable range.

[0061] 8 is a graph showing the settable ranges of the transfer current and the recovery current. In the graph shown in Fig. 8, the horizontal axis represents the transfer current [µA] applied to the primary transfer roller 321, and the vertical axis represents the recovery current [µA] applied to the cleaning roller 242.

[0062] 8, when the collection current of cleaning roller 242 is reduced, the collection performance of the residual toner on photosensitive drum 21 decreases, resulting in "collection failure." For this reason, a minimum value Cmin is set for the settable range of the collection current of cleaning roller 242. In FIG. 8, the minimum value Cmin of the collection current extends linearly in the horizontal direction, and collection failure occurs when the collection current is lower than the minimum value Cmin.

[0063] Furthermore, if the transfer current of the primary transfer roller 321 is reduced, the transfer performance of the toner image formed on the photosensitive drum 21 to the intermediate transfer belt 31 will decrease, resulting in transfer defects. For this reason, a minimum value Tmin within the settable range of the transfer current of the primary transfer roller 321 is determined. In Figure 8, the minimum value Tmin of the transfer current extends linearly in the vertical direction, and transfer defects will occur if the transfer current is lower than the minimum value Tmin.

[0064] Furthermore, increasing the collection current of cleaning roller 242 and the transfer current of primary transfer roller 321 causes charging defects on the photosensitive drum 21. For this reason, a maximum value TCmax within the settable range is determined for the collection current of cleaning roller 242 and the transfer current of primary transfer roller 321. In Figure 8, the maximum values ​​TCmax of the collection current and transfer current extend diagonally in a straight line, and charging defects occur when the combination of the collection current and transfer current is higher than the maximum value TCmax.

[0065] The hatched area shown in FIG. 8, which is surrounded by the three straight lines Cmin, Tmin, and TCmax thus determined, is the settable range of the transfer current and the recovery current.

[0066] As described above, during image formation, control unit 8 applies a collection voltage to cleaning roller 242 via voltage application unit 12. This makes it possible to remove and collect deposits (transfer residual toner) including toner remaining on the outer peripheral surface of photosensitive drum 21 after primary transfer. The higher the collection voltage applied to cleaning roller 242, the greater the amount of transfer residual toner that can be collected, improving the collection performance for transfer residual toner on photosensitive drum 21.

[0067] Meanwhile, when the collection voltage is applied, the control unit 8 estimates the surface potential of the photosensitive drum 21 based on the current (drum inflow current) flowing between the photosensitive drum 21 and the cleaning roller 242, detected by the current detection unit 13. This allows the control unit 8 to determine whether the surface potential of the photosensitive drum 21 will decrease. By detecting a decrease in the surface potential of the photosensitive drum 21, it is possible to recognize a decrease in the collection performance for transfer residual toner that was not completely transferred and remains on the photosensitive drum 21.

[0068] Then, based on the fact that the surface potential of the photosensitive drum 21 has decreased when the collection voltage is applied, the control unit 8 recognizes that the collection voltage is too high and exceeds the settable ranges of the transfer current and collection current shown in Fig. 8. In response to this, the control unit 8 executes control to adjust the collection conditions for the cleaning roller 242 for the transfer residual toner on the photosensitive drum 21. [Example]

[0069] Next, a description will be given of adjustment and evaluation of the recovery conditions for the cleaning roller 242 for the transfer residual toner on the photosensitive drum 21. Table 1 shows the control conditions of the image forming apparatus for this adjustment and the evaluation.

[0070] [Table 1]

[0071] As shown in Table 1, the control conditions are different between the image forming apparatus 1 of the embodiment of the present disclosure and the image forming apparatuses of Comparative Examples 1 and 2. The installation environment of each apparatus is a low-temperature, low-humidity environment. The "rotational speed ratio" is expressed as "cleaning roller rotational speed / photosensitive drum rotational speed." "Fogging" refers to a defect in which unintended toner adheres to the white area (background, skin) of the recording paper. Other conditions include a photosensitive drum having a photosensitive layer made of an organic photoconductor (OPC), a diameter of 24 mm, and a peripheral speed of 120 mm / s. The diameter of the cleaning roller is 11 mm. The transfer current is 5 μA.

[0072] Regarding Table 1, the image forming apparatus of Comparative Example 1 has a rotation speed ratio between the photosensitive drum and the cleaning roller of 0.8, a recovery current of 10 μA, and a current flowing into the drum of 50 μA. In Comparative Example 1, the high recovery current results in good recovery of the residual toner after transfer, but the charged state is poor, resulting in fogging.

[0073] In the image forming apparatus of Comparative Example 2, the rotational speed ratio between the photosensitive drum and the cleaning roller is 0.8, the recovery current is 5 μA, and the current flowing into the drum is 40 μA. In Comparative Example 2, the recovery current is lower than in Comparative Example 1, so the charging state is good and the occurrence of fogging can be suppressed, but the recovery of the residual toner after transfer is poor, resulting in unrecovered toner.

[0074] In contrast, in the image forming apparatus 1 according to the embodiment of the present disclosure, the rotational speed ratio between the photosensitive drum 21 and the cleaning roller 242 is 0.6, the recovery current is 5 μA, and the current flowing into the drum is 40 μA. In the embodiment, the recovery current is lower than in Comparative Example 1, and the rotational speed ratio between the photosensitive drum 21 and the cleaning roller 242 is lower than in Comparative Example 2. As a result, in the embodiment, both the charging state and the recovery of the residual toner after transfer are good, and the occurrence of both fogging and unrecovered toner can be suppressed.

[0075] Fig. 9 is an explanatory diagram showing control for setting conditions outside the settable ranges of the transfer current and recovery current within the range in the graph showing the settable ranges of the transfer current and recovery current in Fig. 8. In the graph shown in Fig. 9, the horizontal axis represents the transfer current [μA] applied to the primary transfer roller 321, and the vertical axis represents the recovery current [μA] applied to the cleaning roller 242.

[0076] Condition C1 in Fig. 9 corresponds to the control condition of Comparative Example 1 in Table 1. As shown in Fig. 9, under condition C1 corresponding to Comparative Example 1 in Table 1, poor charging (fogging) occurs.

[0077] Condition C2 in Fig. 9 corresponds to the control condition of Comparative Example 2 in Table 1. As shown in Fig. 9, under condition C2 corresponding to Comparative Example 2 in Table 1, collection failure (uncollected toner) occurs.

[0078] In contrast, in the embodiment of the present disclosure, the recovery current is lowered compared to Comparative Example 1 (Condition C1) to be approximately the same as Comparative Example 2 (Condition C2), and the rotational speed ratio of the cleaning roller 242 to the photosensitive drum 21 is reduced from 0.8 to 0.6 compared to Comparative Example 2 (see Table 1), i.e., the difference in rotational speed between the cleaning roller 242 and the photosensitive drum 21 is increased. This reduces the minimum value Cmin of the recovery current, as shown in FIG. 9, and broadens the settable range for the recovery current downward. As a result, the recovery conditions for the cleaning roller 242 can be kept within the settable range.

[0079] As described above, when the surface potential of the photosensitive drum 21 decreases, the control unit 8 changes the collection voltage applied to the cleaning roller 242 and the rotation speed of the cleaning roller 242. By changing the collection voltage of the cleaning roller 242 and the rotation speed of the cleaning roller 242, the difference in rotation speed of the cleaning roller 242 with respect to the photosensitive drum 21 can be changed, thereby improving the collection performance of the transfer residual toner on the photosensitive drum 21. This makes it possible to preferably collect the transfer residual toner on the photosensitive drum 21.

[0080] In detail, when the surface potential of the photosensitive drum 21 decreases, the control unit 8 reduces the recovery voltage applied to the cleaning roller 242 and increases the difference in rotational speed of the cleaning roller 242 relative to the photosensitive drum 21 (decreases the rotational speed ratio).

[0081] According to this configuration, by lowering the collection voltage, it is possible to suppress the occurrence of charging failure (fogging). On the other hand, lowering the collection voltage may result in collection failure (uncollected toner). However, by increasing the difference in rotational speed of the cleaning roller 242 relative to the photosensitive drum 21, it is possible to keep the collection conditions for the cleaning roller 242 within a settable range. This makes it possible to appropriately collect the transfer residual toner on the photosensitive drum 21.

[0082] The drum inflow current includes not only the current flowing from the cleaning roller 242 to the photosensitive drum 21 but also the transfer current. If the transfer current is large, there is a risk that the minute current flowing from the cleaning roller 242 to the photosensitive drum 21 cannot be accurately detected.

[0083] For this reason, when detecting the current (drum inflow current) flowing between the photosensitive drum 21 and cleaning roller 242 during application of the recovery voltage to the cleaning roller 242, if it is difficult to distinguish it from the transfer current, the control unit 8 turns off the application of the transfer voltage to the primary transfer roller 321. That is, the control unit 8 applies the recovery voltage to the cleaning roller 242 in a state in which the voltage application unit 12 is not applying the transfer voltage to the transfer unit 30, and estimates the surface potential of the photosensitive drum 21 based on the current (drum inflow current) flowing between the photosensitive drum 21 and cleaning roller 242 detected by the current detection unit 13.

[0084] This configuration makes it possible to suppress the influence of the transfer voltage (transfer current) on the detection result by the current detection unit 13 when the recovery voltage is applied. This makes it possible to appropriately determine the timing at which the surface potential of the photosensitive drum 21 decreases. Therefore, the recovery voltage and rotation speed of the cleaning roller 242 can be changed at an appropriate timing in conjunction with the decrease in the surface potential of the photosensitive drum 21.

[0085] In addition, the control unit 8 changes the recovery voltage and rotation speed of the cleaning roller 242 depending on the magnitude of the current (drum inflow current) flowing between the photosensitive drum 21 and the cleaning roller 242, which is detected by the current detection unit 13 when the surface potential of the photosensitive drum 21 decreases.

[0086] For example, if the collection voltage of the cleaning roller 242 is too high, there is a risk of poor charging, so the control unit 8 lowers the collection voltage of the cleaning roller 242 that is too high to an appropriate voltage value depending on the magnitude of the current flowing into the drum. Lowering the collection voltage of the cleaning roller 242 correspondingly reduces the collection performance of the residual toner on the photosensitive drum 21. For this reason, the control unit 8 reduces the rotational speed ratio of the cleaning roller 242 to the photosensitive drum 21, thereby performing control to improve the collection performance of the residual toner.

[0087] According to this configuration, the magnitude of the collection voltage and rotation speed of the cleaning roller 242 can be set in accordance with the degree of decrease in the surface potential of the photosensitive drum 21. Furthermore, the collection voltage and rotation speed of the cleaning roller 242 can be changed in stages in accordance with the degree of decrease in the surface potential of the photosensitive drum 21. In other words, when the surface potential of the photosensitive drum 21 decreases, it becomes possible to adjust the collection conditions for the cleaning roller 242 for the transfer residual toner in accordance with the states of the photosensitive drum 21 and the cleaning roller 242.

[0088] Furthermore, if the collection performance of the residual toner from transfer is significantly reduced, it will not be possible to address this issue by changing the collection voltage and rotation speed of the cleaning roller 242. Therefore, the control unit 8 may notify the user via the display unit 2d of information urging the replacement of the cleaning roller 242 when both the changed collection voltage and rotation speed of the cleaning roller 242 reach predetermined upper or lower limits.

[0089] This configuration allows the user to prevent uncollected toner from occurring on the photosensitive drum 21. Therefore, in the image forming apparatus 1, it is possible to suppress the occurrence of image defects caused by uncollected toner, and the user can continuously obtain printed materials on which high-quality images have been formed.

[0090] In addition, in the case of an apparatus in which the cleaning roller 242 is configured as an integral part of the drum cleaning unit 24 or the image forming unit 20 and cannot be replaced separately, replacement of the drum cleaning unit 24 or the image forming unit 20 may be encouraged when replacing the cleaning roller 242.

[0091] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and various modifications can be made without departing from the spirit of the invention.

[0092] For example, in the above embodiment, the image forming apparatus 1 is configured to include an intermediate transfer belt 31 onto which toner images formed in the four image forming units 20 are sequentially transferred and superimposed, but the present invention is not limited to such an apparatus. The present invention is also applicable to an image forming apparatus that includes, for example, a conveyor belt that conveys paper onto which a toner image is transferred from a photosensitive drum.

[0093] In the above embodiment, the image forming apparatus 1 is a so-called tandem type image forming apparatus for color printing, but is not limited to this type of model. The image forming apparatus may be a color printing image forming apparatus of other types than the tandem type as long as it is a model equipped with an intermediate transfer belt. [Industrial Applicability]

[0094] The present invention can be used in an image forming apparatus. [Explanation of symbols]

[0095] 1. Image forming device 2 Main unit 2d Display section (notification section) 5 Exposure section 6 Fixing section 8 Control Unit 9 Memory section 12 Voltage application section 13 Current detection unit 20 Image forming unit 21 Photosensitive drum (image carrier) 22 Charging section 23 Development section 24 Drum Cleaning Section 30 Transfer unit 31 Intermediate transfer belt (transfer receiving material) 32 Primary transfer unit 33 Secondary transfer unit 242 Cleaning Roller 321 Primary transfer roller S paper

Claims

1. an image carrier having a photosensitive layer formed on an outer peripheral surface thereof; a charging section for charging an outer peripheral surface of the image carrier to a predetermined surface potential; an exposure unit that exposes the outer peripheral surface of the image carrier charged by the charging unit to light and forms an electrostatic latent image by attenuating the charge; a developing unit that supplies toner to the electrostatic latent image on the image carrier to form a toner image; a transfer section that transfers the toner image formed on the outer peripheral surface of the image carrier to a transfer target; a cleaning roller that removes and collects deposits on the outer peripheral surface of the image carrier; a voltage application unit that applies a predetermined voltage to the charging unit, the developing unit, the transfer unit, and the cleaning roller; a current detection unit that detects a current flowing between the image carrier and the cleaning roller when the voltage application unit applies a recovery voltage to the cleaning roller; a control unit that controls the image carrier, the charging unit, the developing unit, the transfer unit, the cleaning roller, and the voltage application unit; Equipped with The control unit is During image formation, the voltage application unit applies the recovery voltage to the cleaning roller, a surface potential of the image carrier is estimated based on the current detected by the current detection unit when the recovery voltage is applied; When the surface potential of the image carrier is decreased, the recovery voltage and the rotation speed of the cleaning roller are changed.

1. An image forming apparatus comprising:

2. 2 . The image forming apparatus according to claim 1 , wherein the control unit reduces the recovery voltage and increases a rotational speed difference between the cleaning roller and the image carrier when the surface potential of the image carrier decreases.

3. 2. The image forming apparatus according to claim 1, wherein the control unit applies the recovery voltage to the cleaning roller in a state in which the voltage application unit is not applying a transfer voltage to the transfer unit, and estimates the surface potential of the image carrier based on the current detected by the current detection unit.

4. 2. The image forming apparatus according to claim 1, wherein the control unit changes the magnitude of the recovery voltage and the rotation speed depending on the magnitude of the current detected by the current detection unit when the surface potential of the image carrier decreases.

5. a notification unit that notifies a state of the image forming apparatus; 2. The image forming apparatus according to claim 1, wherein the control unit notifies the notification unit of information encouraging replacement of the cleaning roller when both the changed recovery voltage and the changed rotation speed reach a predetermined upper limit or lower limit.

Images