JP2006126449A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure stable cleaning performance in an image forming apparatus where an intermediate transfer member (for example, intermediate transfer belt) is cleaned by using a rotator constituted by implanting a brush on its outer peripheral surface such as a brush roller. <P>SOLUTION: The image forming apparatus is equipped with an image forming part, and the intermediate transfer belt 4, the surface of which a toner image formed by the image forming part is primarily transferred to, and which secondarily transfers the toner image to paper continuously. It has a cleaning mechanism 30, which is equipped with a conductive brush roller 72 driven to be rotated while it abuts on the surface of the intermediate transfer belt, and a DC power source circuit 78 for applying bias voltage to the brush roller, and which electrically and mechanically removes the toner remaining on the intermediate transfer belt after secondary transfer. The cleaning condition of the cleaning mechanism is changed in accordance with the irregularities of the surface of the intermediate transfer belt. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer. In particular, the present invention relates to an image forming apparatus that primarily transfers a toner image formed by an image forming unit to an intermediate transfer member, and then performs secondary transfer onto a sheet.

  Conventionally, a tandem type color image forming apparatus in which four photosensitive drums are arranged along an intermediate transfer belt is known. In this apparatus, yellow, magenta, cyan, and black toner images are formed on the respective photosensitive drums, and these toner images are sequentially superimposed on an intermediate transfer belt to be primarily transferred to obtain a color toner image. Thereafter, the color toner image is secondarily transferred onto a sheet that passes between the intermediate transfer belt and a secondary transfer roller that is in pressure contact with the belt, thereby outputting a color image on the sheet.

  In such an image forming apparatus, as a method of removing toner remaining on the intermediate transfer belt after the secondary transfer, a blade cleaning method using a urethane rubber blade or a fur brush cleaning using a brush roller having a brush implanted on the outer peripheral surface A method is used. The blade cleaning method has been widely used because of its simple structure and low cost. However, in recent years, a polymerized toner that can reduce the particle size and spheroidize and thus stabilize the image quality has been replaced with a pulverized toner. Therefore, it has been studied to use brush cleaning instead of blade cleaning, which tends to cause cleaning failure in the case of polymerized toner.

  In Patent Document 1, an intermediate transfer belt is provided by providing an insulating roller so as to be able to contact with and separate from the intermediate transfer belt, and detecting the surface potential of the contact portion of the roller with the belt immediately after separating the roller. An image forming apparatus that detects an upper filming layer and removes the filming layer based on the detection result is disclosed. This apparatus is for detecting the presence or absence of a filming layer, and does not detect irregularities (on the filming layer) on the intermediate transfer belt.

Patent Document 2 discloses an image forming apparatus including a cleaning member for removing residual toner on the intermediate transfer belt and a rubbing member for polishing the surface of the intermediate transfer belt to remove the filming layer. Has been. The surface of the intermediate transfer belt is irradiated with light, and the operation of the rubbing member is controlled based on the amount of reflected regular reflection light and irregular reflection light. This apparatus is for removing the filming layer and does not control the operation of the cleaning member.
JP-A-6-295111 Japanese Patent Laid-Open No. 5-273893

  However, the brush cleaning method has a smaller mechanical force to remove the toner and foreign matter adhering to the intermediate transfer belt than the blade cleaning method, so the toner and foreign matter are formed on the intermediate transfer belt as a thin layer, that is, a filming layer. Easy to do. Since minute irregularities are formed by a brush on the filming layer, there is a possibility that minute toner enters the concave portion and a cleaning defect occurs, resulting in an image defect.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to ensure stable cleaning performance in an image forming apparatus that cleans an intermediate transfer body (for example, an intermediate transfer belt) using a rotating body in which a brush is implanted on an outer peripheral surface such as a brush roller. And

In order to achieve the above object, an image forming apparatus according to the present invention includes:
An image forming unit for forming a toner image;
An intermediate transfer body on which the toner image formed in the image forming unit is primarily transferred to the surface, and then the toner image is secondarily transferred to paper;
Toner remaining on the intermediate transfer member after the secondary transfer, comprising a conductive brush rotating member that is driven to rotate in contact with the surface of the intermediate transfer member, and a DC power supply circuit that applies a bias voltage to the rotating member. A cleaning mechanism that electrically and mechanically removes,
A detection unit for detecting the uneven state on the surface of the intermediate transfer member and outputting a detection signal corresponding to the state;
A controller for controlling the cleaning mechanism, which changes the cleaning condition of the cleaning mechanism in accordance with the detection signal of the detection unit;
It is characterized by providing.

  According to the present invention, even when the surface of the intermediate transfer body changes in surface unevenness due to the formation of the filming layer, the cleaning condition (for example, the number of rotations of the brush rotating body) is changed according to the surface unevenness. As a result, stable cleaning performance can be ensured.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings. In the following description, an example in which the present invention is applied to a tandem color printer will be described. However, in the present invention, the photosensitive drum and the intermediate transfer belt are opposed to each other, and each rotation of the intermediate transfer belt is performed on the photosensitive drum. It can also be applied to a so-called four-cycle color printer in which a yellow, magenta, cyan or black toner image formed in this way is transferred to an intermediate transfer belt and a full color image is formed by rotating the intermediate transfer belt four times. The present invention can also be applied to an image forming apparatus other than a printer. Note that in this specification, terms indicating directions (for example, “up”, “down”, “right”, “left”, and other terms including these terms) are used as appropriate, but in the drawings used for explanation These terms are only intended to indicate the direction of the present invention, and the present invention should not be construed to be limited to these terms.

  FIG. 1 shows a tandem type color printer 2 which is an embodiment of an image forming apparatus according to the present invention. The printer 2 includes an intermediate transfer belt 4 at substantially the center of the inside thereof. The intermediate transfer belt 4 is supported by the outer peripheral portions of the three rollers 6, 8, and 10 and is driven to rotate in a counterclockwise direction A in the drawing. The roller 6 is a tension roller that applies tension to the intermediate transfer belt 4. The roller 10 is drivingly connected to a driving source (not shown), and the rollers 6 and 8 are driven to rotate as the roller 10 rotates.

  Below the lower horizontal portion of the intermediate transfer belt 4, four image forming portions 12Y, 12M, 12C, and 12K respectively corresponding to yellow (Y), magenta (M), cyan (C), and black (K) colors. Are arranged side by side along the intermediate transfer belt 4.

  Each image forming unit 12 (12Y, 12M, 12C, 12K) has a photosensitive drum 14 (14Y, 14M, 14C, 14K) as an image carrier. Around each photosensitive drum 14, a charger 16 (16Y, 16M, 16C, 16K), an exposure device 18 (18Y, 18M, 18C, 18K), in order along the rotation direction (clockwise direction in the drawing), Primary transfer rollers 22 (22Y, 22M, 22C, 22K) facing the respective photosensitive drums 14 (14Y, 14M, 14C, 14K) with the developing device 20 (20Y, 20M, 20C, 20K) and the intermediate transfer belt 4 interposed therebetween. , And cleaning devices 24 (24Y, 24M, 24C, 24K) are respectively disposed. As each toner accommodated in the developing device 20, a polymerized toner is used. In this embodiment, it is assumed that the regular charging polarity of the toner is negative. In the present embodiment, the image forming units 12Y to 12K constitute an image forming unit.

  The primary transfer roller 22 is positioned immediately downstream of the photosensitive drum 14 with respect to the rotation direction A of the intermediate transfer belt 4, thereby pressing the intermediate transfer belt 4 toward the photosensitive drum so that the intermediate transfer belt 4 is moved to the photosensitive member. It is ensured that the toner is conveyed between the photosensitive drum and the primary transfer roller 22 in a state of being in close contact with the drum. A positive bias voltage is applied to each primary transfer roller 22.

A secondary transfer roller 26 is pressed against a portion of the intermediate transfer belt 4 supported by the roller 10. A positive bias voltage is applied to the secondary transfer roller 26.
A nip portion between the secondary transfer roller 26 and the intermediate transfer belt 4 forms a secondary transfer region 28.

  A cleaning mechanism 30 is provided on the left side of the intermediate transfer belt 4 for electrically and mechanically removing and collecting toner remaining on the intermediate transfer belt after the secondary transfer. The cleaning mechanism 30 will be described in detail later.

  A paper feed cassette 34 is detachably disposed below the printer 2. The sheet (recording medium) S stacked and housed in the sheet feeding cassette 34 is the uppermost one by the rotation of the sheet feeding roller 36 disposed at a position facing the vicinity of the front end of the sheet S stacked in the sheet feeding cassette 34. Are sent one by one to the conveyance path 38.

  A conveyance path 38 passes from the paper feed cassette 34 through the nip portion of the timing roller pair 40, the secondary transfer region 28, the fixing device 42, and the nip portion of the paper discharge roller pair 44. It extends to the tray 46.

  Referring to FIG. 2, which is a control block diagram of the printer 2, a controller 48 that controls the entire printer 2 includes an image buffer 56 for storing RGB image data captured from an external terminal (for example, a personal computer), the image For example, an image processing unit 58 for performing various image processing on the data, for example, converting RGB image data into YMCK image data, a communication control unit 59 for communicating with an external terminal, and the like are connected.

  Further, the charging unit 60 (including each charger 16 and its power source), each exposure device 18, the developing unit 61 (including each developing device 20, its power source, drive source, etc.), and the fixing unit 62 (fixing device). 42, the power supply thereof, and the like), the transfer unit 64 (including each primary transfer roller 22, the secondary transfer roller 26, and a power source for applying a predetermined bias voltage to these rollers), the conveyance unit 66 (intermediate transfer). The driving roller 10 of the belt 4, a group of rollers positioned on the conveyance path 38 and their driving sources, etc.), the cleaning mechanism 30, and the like are operated by receiving a control signal from the controller 48.

  Next, a schematic operation of the printer 2 will be described.

  When a plurality of RGB image signals are transmitted from the external terminal to the communication control unit 59 of the printer 2, the image processing unit 58 creates digital image data color-converted into yellow, magenta, cyan, and black for each sheet. And stored in the image buffer 56. The controller 48 transmits a control signal to the exposure devices 18Y to 18K of the image forming units 12Y to 12K based on the color image data for each sheet stored in the image buffer 56, and the exposure devices 18Y to 18K Exposure is performed by irradiating the photosensitive drums 14Y to 14K with laser light. As a result, electrostatic latent images for the respective colors are formed on the surfaces of the respective photosensitive drums 14Y to 14K.

  The electrostatic latent images formed on the photosensitive drums 14Y to 14K are supplied with negative yellow, magenta, cyan, and black toners by the developing units 20Y to 20K, respectively, and are visualized to become toner images of the respective colors. . Then, the toner images of the respective colors are primarily transferred in a superimposed manner on the intermediate transfer belt 4 moving in the direction of arrow A by the action of the primary transfer rollers 22Y to 22K to which a positive bias voltage is applied.

  The superimposed toner image formed on the intermediate transfer belt 4 in this way reaches the secondary transfer area 28 as the intermediate transfer belt moves. In the secondary transfer region 28, the superimposed toner images are sent out from the paper feed cassette 34 to the conveyance path 38 by the action of the secondary transfer roller 26 to which a positive bias voltage is applied, and are fed by the timing roller pair 40. Secondary transfer is performed collectively on the supplied paper S. The toner remaining on the intermediate transfer belt 4 after the secondary transfer may be charged to the reverse polarity (positive) in addition to the toner having the normal charge polarity (negative). However, as described below, cleaning is performed. Collected by mechanism 30.

  The sheet S on which the superimposed toner image is formed in this way is then sent to the fixing device 42 where the toner image is fixed. Then, the paper S is discharged to the paper discharge tray 46 via the paper discharge roller pair 44.

  Referring mainly to FIG. 3, the cleaning mechanism 30 includes a collection unit 70 that collects toner. The collection unit 70 has a brush roller 72 as a brush rotating body, which is formed by implanting a conductive brush on the surface of the conductive roller and abuts a portion supported by the roller 8 of the intermediate transfer belt 4. The brush roller 72 is drivably coupled to a drive source (not shown) so as to move in opposite directions at the contact portion with the intermediate transfer belt 4. A conductive collection roller 74 is in contact with the brush roller 72. The collection roller 74 is drivably coupled to a drive source (not shown) so as to move in opposite directions at the contact portion with the brush roller 72. A conductive scraper 76 is in contact with the collection roller 74.

  A DC power supply circuit 78 is connected to the scraper 76. The DC power supply circuit 78 includes constant current power supplies 80a and 80b, and a switching circuit 82 that is disposed between the constant current power supply and the scraper 76 and connects the scraper 76 to one of the constant current power supplies 80a and 80b. The constant current power supplies 80a and 80b output constant currents having different levels (for example, the constant current power supply 80a outputs a current Ia of 5 to 15 μA, and the constant current power supply 80b outputs a current Ib of 20 to 30 μA). . The anodes of the constant current DC power supplies 80a and 80b are grounded. The switching circuit 82 is configured to connect one cathode of the constant current power supplies 80 a and 80 b to the scraper 76 based on a control signal from the controller 48. When the intermediate transfer belt 4 starts to be used from a new state, the constant current power source 80a is connected to the scraper 76.

  On the upstream side of the collection unit 70 with respect to the moving direction A of the intermediate transfer belt 4, a conductive brush 84 in which a conductive brush is implanted on a conductive base is in contact with the belt portion between the rollers 6 and 8. Is arranged. The conductive brush 84 is grounded. Therefore, the controller 48 flows constant currents having different levels (hereinafter referred to as cleaning current) from the DC power supply circuit 78 through the scraper 76, the recovery roller 74, and the brush roller 72, and then passes through the intermediate transfer belt 4 and the conductive brush. 84.

  In the cleaning mechanism 30 having such a configuration, when a cleaning current flows as described above, an electric field from the intermediate transfer belt toward the conductive brush is generated between the conductive brush 84 and the intermediate transfer belt 4. Due to this electric field, the toner charged to the reverse polarity (positive) on the intermediate transfer belt 4 becomes the normal charged polarity (negative) when passing through the conductive brush 84 (in other words, the toner passing through the conductive brush 84 is not charged). Polarity is aligned.)

  On the other hand, in the collection unit 70, an electric field from the brush roller toward the intermediate transfer belt is generated between the brush roller 72 and the intermediate transfer belt 4. As a result, the toner having the normal charging polarity (negative) is collected from the intermediate transfer belt 4 because the toner is electrostatically attracted to the brush roller 72. The toner adsorbed on the brush roller 72 subsequently moves onto the collecting roller 74 and is scraped off from the collecting roller by the scraper 76.

  As shown in FIG. 1, a detection unit 86 for detecting an uneven state on the surface of the intermediate transfer belt is disposed immediately downstream of the image forming unit 12 </ b> K with respect to the rotation direction A of the intermediate transfer belt 4. As shown in FIG. 2, the detection signal of the detection unit 86 is output to the controller 48. The controller 48 controls the DC power supply circuit 78 in accordance with the detection signal from the detection unit 86, thereby changing the level of the cleaning current.

  Referring to FIG. 4, the detection unit 86 includes a light emitting element 88 that emits light at an acute angle with respect to the normal line of the outer peripheral surface of the intermediate transfer belt 4, and a regular reflection light detection element that receives light specularly reflected by the intermediate transfer belt. 90a and a diffusely reflected light detecting element 90b that receives light irregularly reflected by the intermediate transfer belt. The detection signals (detection voltages) of the detection elements 90a and 90b are output to the controller 48, respectively. FIG. 5 shows how the detection signals of the detection elements 90a and 90b change as the number of printed sheets increases. In a new state, the light emitted from the light emitting element 88 to the smooth intermediate transfer belt 4 enters only the specular reflection light detection element 90a. However, when the use is started, the brush roller 72 is placed on the intermediate transfer belt 4. A filming layer is formed due to the small rubbing force caused by, and irregularities due to the filming layer are formed on the intermediate transfer belt (the surface of the intermediate transfer belt 4 begins to become rough). As a result, as shown in FIG. 4A, a part of the light emitted from the light emitting element 88 enters the irregularly reflected light detecting element 90b. As the number of printed sheets increases, the surface of the intermediate transfer belt 4 becomes rougher, and the light from the light emitting element 88 is likely to be irregularly reflected on the surface of the intermediate transfer belt. As shown in FIGS. The detection value of the irregularly reflected light detection element 90b increases. The controller 48 controls the switching circuit 82 of the DC power supply circuit 78 so that, for example, a value d of (detection value of the regular reflection light detection element 90a) − (detection value of the irregular reflection light detection element 90b) is determined in advance. In the case of the above (set value in FIG. 5) or more (when the surface roughness is relatively small), the connection of the constant current DC power supply 80a to the scraper 76 is maintained (cleaning current Ia), and the output difference d becomes smaller than the set value. In this case (when the surface roughness is relatively large), the constant current DC power supply 80b is connected to the scraper 76, thereby increasing the level of the cleaning current (that is, the level of the constant current) (cleaning current Ib). . As a result, even if the number of printed sheets increases and the surface becomes rough, the toner that has entered the recesses on the intermediate transfer belt 4 can be sufficiently collected by the brush roller 72. Thus, according to this embodiment, stable cleaning performance can be ensured even when the number of printed sheets increases.

  The detection unit 86 outputs the detection value of the specular reflection light detection element 90a and the detection value of the irregular reflection light detection element 90b to the controller 48 as detection signals, but instead the detection unit 86 (regular reflection light You may comprise so that the detection element 90a)-(diffuse reflected light detection element 90b) may be output directly. The controller 48 uses a method other than the comparison between the value of (detected value of the specularly reflected light detecting element 90a) − (detected value of the irregularly reflected light detecting element 90b) and a predetermined value, for example, the (regularly reflected light detecting element 90a). Of the cleaning current) / (detection value of the irregular reflection light detection element 90b) and a predetermined value may be used to change the level of the cleaning current.

  Further, since the constant current DC power supply 80a or 80b is used as a power supply for generating the cleaning current, even if the resistance rises due to adhesion of toner to the brush roller 72, the collection roller 74, or the conductive brush 84, etc. Thus, a certain amount of current can be passed, and this can suppress a decrease in recovery efficiency.

  Referring to FIG. 6, when the level of the cleaning current is increased from the beginning (cleaning current Ib), the intermediate transfer belt 4 is excessively charged and the charged state is not in contact with the portion where the brush roller 72 contacts. Image noise (so-called sweep unevenness) may occur due to the difference. Therefore, it is difficult to set the cleaning current level higher from the beginning, and it is necessary to set it to Ia smaller than the cleaning current Ib. On the other hand, when the number of printed sheets is increased and the filming layer is sufficiently formed, the charging state of the intermediate transfer belt 4 changes (at this time, cleaning failure occurs with the cleaning current Ia), and image noise occurs. Since the level of the cleaning current is higher than that when the filming layer is not sufficiently formed, even if the level of the cleaning current is increased from Ia to Ib after the filming layer is sufficiently formed, the image noise Does not occur.

  The above description relates to an embodiment of the present invention, and the present invention is not limited to this and can be variously modified. For example, in the above embodiment, the controller 48 performs constant current control of the DC power supply circuit 78, but instead, the controller 48 may perform constant voltage control of the DC power supply circuit. In this case, as the number of printed sheets increases, the level of the constant voltage increases (as a result, the cleaning current also increases). In the case of constant voltage control, if the resistance increases due to toner adhesion to the brush roller 72, the collection roller 74, or the conductive brush 84, the cleaning current decreases, but by setting the initial level of the constant voltage to a certain extent, A necessary level of cleaning current (a necessary level of electric field strength between the intermediate transfer belt 4 and the brush roller 72 and electric field strength between the intermediate transfer belt and the conductive brush 84) can be ensured. Instead of increasing the level of constant current or constant voltage, the controller 48 controls the drive source of the brush roller 72 to increase the number of rotations of the brush roller (for example, from an initial value of 200 rpm to 250 rpm). Thus, after entering the filming layer, the toner that has entered the recesses on the surface of the intermediate transfer belt 4 (the filming layer) may be collected. Such a change in the cleaning conditions of the cleaning mechanism affects the image if it is performed during image formation (for example, if the rotational speed of the brush roller 72 is increased during image formation, the rotational speed of the intermediate transfer belt 4 in contact with the roller). This can be done during non-imaging. After changing the cleaning condition, the controller 48 forms a patch image on the intermediate transfer belt 4 and obtains the image density by using the detection unit 86 or another image density sensor, so that the image forming condition (for example, development) The developing bias of the container 20 is appropriately changed so that a desired image density can be obtained.

  In the above embodiment, the constant current level can be changed in two stages, but it may be changed in three or more stages. The same applies when changing the level of the constant voltage or the number of rotations of the brush roller.

  Further, the cleaning mechanism is not limited to the above-described embodiment. For example, a pair of brush rollers to be brought into contact with the intermediate transfer belt is provided, and an electric field having a different direction is generated between each brush roller and the intermediate transfer belt. You may make it remove the toner of the reverse polarity to the toner which has regular charge polarity.

  In addition, the detection unit for detecting the uneven state on the surface of the intermediate transfer belt is not limited to the above configuration that acquires the light amount of the light regularly reflected by the intermediate transfer belt and the light irregularly reflected with respect to the incident light. For example, the detection unit may be configured to receive total scattered light, and the controller may be configured to measure the root mean square roughness based on the ratio between the total scattered light and the total light amount.

  The intermediate transfer member is not limited to a belt shape (intermediate transfer belt 4), and the brush rotating member is not limited to a roller shape (brush roller 72).

  As described above, the present invention can be applied not only to a tandem color image forming apparatus but also to a four-cycle color image forming apparatus (in this case, a photosensitive drum and a developing unit, a charger, etc. disposed around the photosensitive drum). And an image forming unit that primarily transfers the toner image to the intermediate transfer belt). In this case, the brush roller that contacts the intermediate transfer belt during cleaning needs to be separated from the intermediate transfer belt during image formation.

1 is a configuration diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a control block diagram of the image forming apparatus in FIG. 1. The enlarged view of the cleaning mechanism of FIG. The figure for demonstrating the detection method by the detection part of FIG. The graph which shows the relationship between the number of printed sheets and the output voltage output from each detection element of the detection part of FIG. The figure for demonstrating that the level of the cleaning current which generate | occur | produces an image noise, and the cleaning current which a cleaning defect generate | occur | produces becomes high as the number of printed sheets increases.

Explanation of symbols

2 Printer (image forming device)
4 Intermediate transfer belt (intermediate transfer member)
12Y to 12K Image forming unit (image forming unit)
30 Cleaning Mechanism 72 Brush Roller (Brush Rotating Body)
78 DC power supply circuit 80a, 80b Constant current power supply 86 Detection unit 90a Regular reflection light detection element (first detection element)
90b Diffuse reflected light detection element (second detection element)

Claims (5)

An image forming unit for forming a toner image;
An intermediate transfer body on which the toner image formed in the image forming unit is primarily transferred to the surface, and then the toner image is secondarily transferred to paper;
Toner remaining on the intermediate transfer member after the secondary transfer, comprising a conductive brush rotating member that is driven to rotate in contact with the surface of the intermediate transfer member, and a DC power supply circuit that applies a bias voltage to the rotating member. A cleaning mechanism that electrically and mechanically removes,
A detection unit for detecting the uneven state on the surface of the intermediate transfer member and outputting a detection signal corresponding to the state;
A controller for controlling the cleaning mechanism, which changes the cleaning condition of the cleaning mechanism in accordance with the detection signal of the detection unit;
An image forming apparatus.   The detection unit includes a light emitting element that emits light to the surface of the intermediate transfer member, a first detection element that receives light regularly reflected on the surface of the intermediate transfer member, and a second light that receives light irregularly reflected on the surface of the intermediate transfer member. The image forming apparatus according to claim 1, further comprising a detection element.   2. The image forming apparatus according to claim 1, wherein the controller performs constant current control of the DC power supply circuit and changes the level of the constant current as a cleaning condition in accordance with a detection signal of the detection unit.   The image forming apparatus according to claim 1, wherein the controller performs constant voltage control of the DC power supply circuit and changes the level of the constant voltage as a cleaning condition in accordance with a detection signal of the detection unit. The image forming apparatus according to claim 1, wherein the controller changes the number of rotations of the brush rotating body as a cleaning condition in accordance with a detection signal of the detection unit.

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