JP2005242179A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a good quality of image over a long period of time by executing transfer control according to a state of the surface of a toner image carrier such as an intermediate transfer belt. <P>SOLUTION: A toner image is transferred to the intermediate transfer belt 16 from a photoreceptor drum 12a-15a by a primary transfer roller 22a-22d. The toner image on the intermediate transfer belt is transferred on to recording paper by a secondary transfer roller 26, and a toner that remains on the intermediate transfer belt is removed by a fur brush 27. A state of the surface of the intermediate transfer belt is detected by a reflection type sensor 21, and according to the result of the detection, a controller regulates at least one of the fur brush bias voltage (cleaning bias voltage), the primary transfer bias voltage, and the secondary transfer bias voltage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine using an electrophotographic process, and more particularly to an image forming apparatus having an intermediate transfer member such as an intermediate transfer belt.

  In general, in an image forming apparatus, an electrostatic latent image formed on an electrostatic latent image carrier such as a photosensitive drum is developed with a developer (toner) to form a visible image (toner image). It is known that an image is formed by transferring a visible image on an intermediate transfer member to a recording sheet after being transferred onto an intermediate transfer member such as an intermediate transfer belt as an image carrier. In an image forming apparatus, the image quality changes depending on factors such as the environmental atmosphere and durability fluctuations.

  Therefore, in order to prevent changes in image quality due to environmental atmosphere and durability fluctuations, that is, in order to prevent a decrease in transfer efficiency, the electric resistance values of charged members such as belt materials and rollers and recording paper are measured. The transfer bias current and the like are controlled in accordance with a predicted evaluation value obtained by predicting and evaluating a measurement value obtained in advance or a result obtained by measuring a time-dependent change characteristic and humidity dependency in advance (Patent Literature). 1).

  Further, in order to prevent a decrease in transfer efficiency, a predetermined current is applied to the transfer means as an environmental detection transfer bias until the charged portion of the toner image carrier carries the transfer site. Some control the bias conditions of the image forming apparatus in accordance with the output voltage (see Patent Document 2).

Japanese Patent Laid-Open No. 3-223779 (pages 4 to 10, FIGS. 1 to 5) JP-A-6-175514 (pages 6 to 13, FIGS. 1 to 5)

  By the way, in an image forming apparatus using an intermediate transfer member such as an intermediate transfer belt, the surface state of the intermediate transfer member changes due to secular change, thereby changing characteristics such as a surface resistance value. When the surface state of the intermediate transfer member changes, the image quality when the visible image is transferred to the recording paper changes.

  However, as described above, in the conventional image forming apparatus, when measuring or predicting the electric resistance values of the charged member and the recording paper, when the resistance value is measured, the member in contact with the belt material is measured. Since it is easily influenced and depends on the contact state of the counter roller for measurement, the measurement accuracy may be lowered. Also, in the case of predictive evaluation, the usage status varies depending on individual machines (image forming apparatuses), such as different recording papers used by users and different amounts of toner used per sheet. The current situation is that only the average value can be predicted for deterioration. Furthermore, when the transfer bias control is performed based on the output voltage corresponding to the environmental detection transfer bias, if the transfer roller is disposed in the belt-like image carrier, the belt-like image carrier is stretched. Since many members such as the member to be contacted with the image carrier, it is difficult to measure the environmental detection transfer bias. Even in the case of a transfer unit using only a transfer roller, the voltage value obtained is small because the current value used for the measurement is weak, and there is a risk that the measurement will be inaccurate due to noise generated in the image forming apparatus. Not only that, but a separate measurement circuit is required, resulting in high costs. For this reason, the transfer conditions cannot be controlled to a good state according to the deterioration state of the image carrier such as an intermediate transfer member, and as a result, a good image cannot be obtained and an inappropriate voltage is applied. As a result, there is a problem that the life of the image carrier may be impaired.

  Accordingly, the present invention provides an image forming apparatus capable of obtaining a good image quality over a long period of time by performing transfer control and cleaning control in accordance with the surface state of the toner image carrier in view of the problems of the prior art. It is for the purpose.

  Therefore, in order to solve such problems, the present invention provides an image carrier on which a toner image is formed, a transfer unit that applies a transfer bias voltage to transfer the toner image from the image carrier to a recording medium, and a cleaning bias voltage. And a cleaning unit that cleans the image carrier, and a detection unit that detects a surface state of the image carrier and outputs a detection signal indicating the surface state, and according to the detection signal And a control means for adjusting at least one of the transfer bias voltage and the cleaning bias voltage.

  In the present invention, the detecting means is an image density measuring means for outputting, as the detection signal, a light reception voltage value corresponding to the amount of reflected light reflected by the image carrier when the light applied to the image carrier is reflected. At least one of a first table in which a relationship between the light reception voltage value and the transfer bias voltage is defined and a second table in which a relationship between the light reception voltage value and the cleaning bias voltage is defined in the means are preset. Has been.

  In the present invention, for example, the transfer unit is a secondary transfer unit to which a secondary transfer bias voltage is applied as the transfer bias voltage, and the image carrier is an intermediate transfer belt on which each color toner image is transferred as the toner image. The image forming apparatus further includes a primary transfer unit that applies a primary transfer bias voltage and transfers the color toner images to the image carrier, and the control unit performs the first transfer according to the detection signal. At least one of the secondary transfer bias voltage, the secondary transfer bias voltage, and the cleaning bias voltage may be adjusted. At this time, the control means has a first table in which a relationship between the light reception voltage value and the primary transfer bias voltage is defined, and a first table in which a relationship between the light reception voltage value and the cleaning bias voltage is defined. At least one of the second table and the third table in which the relationship between the light reception voltage value and the secondary transfer bias voltage is defined in advance.

  As described above, the image forming apparatus of the present invention detects the surface state of the image carrier and adjusts at least one of the transfer bias voltage and the cleaning bias voltage according to the detection signal representing the surface state. Therefore, it is possible to perform transfer control and cleaning control according to changes in the surface state due to durability deterioration of the image carrier, and as a result, a good image can be obtained over a long period regardless of the surface deterioration of the image carrier. And a longer life can be achieved. Further, since the image density measuring means used for optimizing the characteristics of the output image of the image forming apparatus in recent years has been used as a means for detecting the surface state of the image carrier, it is satisfactory without adding any additional members. An image can be obtained.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, but are merely illustrative examples. Not too much.

  Referring to FIG. 1, FIG. 1 is a diagram schematically showing a color image forming apparatus showing an example of an image forming apparatus according to the present invention. The illustrated image forming apparatus 11 has each color (for example, magenta (M), cyan). (C), yellow (Y), and black (BK)) image forming units 12 to 15 are provided, and each of the image forming units 12 to 15 includes amorphous silicon (a-Si) photosensitive drums 12a to 15a. Is provided. Although not shown, the image forming units 12 to 15 are provided with a charger, an exposure unit, a developing device, a cleaning device, and the like around the photosensitive drums 12a to 15a, respectively.

  Image forming units 12 to 15 are sequentially arranged along the intermediate transfer belt 16 serving as an image carrier from the upstream side in the rotation direction of the intermediate transfer belt 16, and the intermediate transfer belt 16 includes a driving roller 17, a driven roller 18, and a backup roller. It is stretched around 19a to 19c and is driven to rotate in the direction indicated by the solid line arrow by the rotation of the drive roller 17. A reflective sensor 21 is disposed facing the intermediate transfer belt 16 so as to face the backup roller 19a positioned upstream of the drive roller 17 in the rotation direction of the intermediate transfer belt 16, and the reflective sensor 21 will be described later. Thus, the surface state of the intermediate transfer belt 16 is detected.

  When image formation is performed, the surfaces of the photosensitive drums 12a to 15a are uniformly charged, and the photosensitive drums 12a to 15a are exposed according to the document image data to form electrostatic latent images. Then, the electrostatic latent image is developed by a developing device (not shown), and each color toner image is formed on the photosensitive drums 12a to 15a (titanium oxide having a resistance value of 10Ω or less is added to each color toner as an external additive. As added). The primary transfer rollers 22a to 22d are opposed to the photosensitive drums 12a to 15a with the intermediate transfer belt 16 interposed therebetween, and the respective color toner images on the photosensitive drums 12a to 15a are intermediated by the primary transfer rollers 22a to 22d. A color toner image is formed on the intermediate transfer belt 16 by being sequentially transferred to the transfer belt 16 (primary transfer bias voltages are applied to the primary transfer rollers 22a to 22d during the primary transfer and primary transfer). Is done. The residual toner remaining on each of the photosensitive drums 12a to 15a is cleaned by a cleaning device.

  The recording paper P is conveyed to the secondary transfer position in synchronization with the formation of the color toner image on the intermediate transfer belt 16 from a paper feeding device (not shown). A secondary transfer roller 26 is disposed at the secondary transfer position. The secondary transfer roller 26 is opposed to the driving roller 17 with the intermediate transfer belt 16 interposed therebetween, and the color on the intermediate transfer belt 16 at the secondary transfer position. After the toner image is transferred to the recording paper P by the secondary transfer roller 26 (in the case of secondary transfer, a secondary transfer bias voltage is applied to the secondary transfer roller 26), the recording paper P is fixed to the fixing unit ( The color toner image on the recording paper P is fixed and discharged to a paper discharge tray (not shown).

  After the secondary transfer, the intermediate transfer belt 16 is cleaned as described later by a cleaning unit (for example, a fur brush) 27 facing the driven roller 18 and the intermediate transfer belt 16 therebetween. At the time of cleaning, a cleaning bias voltage is applied to the fur brush 27.

  As the image is formed, the surface state of the intermediate transfer belt 16 deteriorates and the surface resistance value, surface roughness, and the like change. The deterioration of the surface state varies depending on the image pattern (printing rate) to be formed. That is, it varies depending on the degree of adhesion of the external additive contained in the toner to the intermediate transfer belt 16. The image quality when the visible image (toner image) is transferred onto the recording paper and the cleaning characteristics of the intermediate transfer belt 16 by the cleaning unit 27 vary depending on the surface state of the intermediate transfer belt 16.

  In order to prevent such a change in image quality, the cleaning bias voltage, the primary transfer bias voltage, and the secondary transfer bias voltage are controlled according to the surface state of the intermediate transfer belt 16 as described later.

  Referring also to FIG. 2, the reflective sensor 21 includes a light emitting unit 21 a and a light receiving unit 21 b, and light having a predetermined light amount (light emission amount) is intermediately transferred from the light emitting unit 21 a without performing image formation. The belt 16 is irradiated, and the reflected light from the intermediate transfer belt 16 is received by the light receiving unit 21b. The light receiving unit outputs a voltage signal indicating a voltage value (light receiving voltage value) corresponding to the amount of reflected light, and this voltage signal is given to the controller 31. The controller 31 controls the cleaning bias voltage, the primary transfer bias voltage, and the secondary transfer bias voltage according to the voltage signal. In this embodiment, the reflective sensor 21 is a sensor for detecting the image density of the toner image formed on the intermediate transfer belt 16 or a registration correction sensor used for correcting the positional deviation of the toner images of the respective colors. Also serves as.

  Now, when the intermediate transfer belt 16 is in an initial state (for example, a state where printing has never been performed), the surface state of the intermediate transfer belt 16 is measured. At this time, the amount of light emitted from the light emitting unit is adjusted so that the light receiving voltage value in the light receiving unit becomes a predetermined light receiving voltage value (for example, 4 volts). When the light reception voltage is a predetermined light reception voltage value, the cleaning bias voltage, the primary transfer bias voltage, and the secondary transfer bias voltage are respectively set to a predetermined cleaning bias voltage (for example, 1.0 kV) and a predetermined primary transfer bias. The voltage (for example, the primary transfer bias corresponding to BK was set to 1.2 kV) and a predetermined secondary transfer bias voltage (for example, 1.4 kV) were set.

  After setting as described above, the surface state of the intermediate transfer belt 16 is measured by the reflective sensor 21 as described above for every predetermined number of printed sheets (for example, 1000 sheets). Assuming that the surface resistivity is an index as a surface state, when a PC belt is used as the intermediate transfer belt 16, the received light voltage value is lowered and the surface resistivity is lowered as shown in FIG. I understand. On the other hand, when a rubber + coat (PTFE) belt is used as the intermediate transfer belt 16, it can be seen that, as shown in FIG. 3B, the received light voltage value increases and the surface resistivity decreases.

  Here, if a PC belt is used as the intermediate transfer belt 16, the controller 31 has a cleaning bias table (third table) and a primary transfer bias shown in FIGS. 4A to 4C, respectively. A table (first table) and a secondary transfer bias table (second table) are set. These tables show the cleaning bias voltage value, the primary transfer bias voltage value, and the secondary transfer bias voltage value for obtaining the optimum image quality according to the surface resistivity (that is, the light reception voltage value) of the intermediate transfer belt 16. Therefore, a table for obtaining an optimum image quality is obtained in advance by experiments.

  In FIG. 4A, the symbol ▲ represents the cleaning bias voltage value for each received light voltage value, and the cleaning bias voltage value is a maximum bias value that can be cleaned (indicated by symbol A) and a minimum bias voltage value that can be cleaned. (Indicated by symbol B). Similarly, in FIG. 4B, the symbol ▲ represents the primary transfer bias voltage value for each received light voltage value, and this primary transfer bias voltage value is indicated by the maximum bias value (denoted by C) that can be primary transferred. ) And the minimum bias voltage value (indicated by reference sign D) that can be transferred primarily. Further, in FIG. 4C, the ▲ mark represents the secondary transfer bias voltage value for each light reception voltage value, and this secondary transfer bias voltage value is the maximum bias value (denoted by E) that can be secondary transferred. And a minimum bias voltage value (indicated by symbol F) that can be subjected to secondary transfer.

  When a predetermined number of sheets are printed, the controller 31 looks at the light reception voltage value output from the light receiving unit 21b (at this time, the controller 31 stops image formation), and according to this light reception voltage value, the cleaning bias voltage value, The primary transfer bias voltage value and the secondary transfer bias voltage value are adjusted. For example, when the received light voltage value decreases to 3 V, the controller 31 changes the cleaning bias voltage value from 1.0 kV to 0.9 kV, and the primary transfer bias voltage value from 1.2 kV to 0.9 kV (here, 1 corresponding to BK). The secondary transfer bias voltage value is adjusted from 1.4 kV to 1.2 kV.

  In this way, when the cleaning bias voltage, the primary transfer bias voltage, and the secondary transfer bias voltage are adjusted in accordance with changes in the surface condition such as the surface resistivity of the intermediate transfer belt 16, there is almost no change in image quality. Even if the surface resistivity of the intermediate transfer belt 16 changes, it is possible to maintain good image quality over a long period of time, and as a result, it is possible to extend the life of the image forming apparatus. Since the surface state of the intermediate transfer belt 16 varies greatly depending on the image pattern (printing pattern), the surface state of the intermediate transfer belt 16 is measured and each bias voltage value is controlled. Image quality control can be performed.

  In the above-described example, an example in which the cleaning bias voltage, the primary transfer bias voltage, and the secondary transfer bias voltage are adjusted according to changes in the surface state such as the surface resistivity of the intermediate transfer belt 16 has been described. Even if at least one of the cleaning bias voltage, the primary transfer bias voltage, and the secondary transfer bias voltage is adjusted according to the change in the surface state such as the surface resistivity of 16, the image quality can be improved over a long period of time. It was confirmed that it could be maintained well.

  When a rubber + coat (PTEF) belt is used as the intermediate transfer belt 16, the controller 31 has a cleaning bias table, a primary transfer bias table, and a secondary transfer shown in FIGS. 5A to 5C, respectively. A transfer bias table is set. In FIG. 5A, a symbol ▲ represents a cleaning bias voltage value with respect to each light reception voltage value. The cleaning bias voltage value is a maximum bias value that can be cleaned (indicated by symbol G) and a minimum bias voltage value that can be cleaned. (Indicated by the symbol H). Similarly, in FIG. 5B, the symbol ▲ represents the primary transfer bias voltage value for each received light voltage value, and this primary transfer bias voltage value is indicated by the maximum bias value (reference numeral I) that can be primary transferred. ) And the minimum bias voltage value (denoted by the symbol J) that can be primarily transferred. In FIG. 5 (c), the symbol ▲ represents the secondary transfer bias voltage value for each received light voltage value, and this secondary transfer bias voltage value is the maximum bias value (indicated by symbol K) that can be secondary transferred. And a minimum bias voltage value (indicated by a symbol L) that can be subjected to secondary transfer.

  As described above, according to the material of the intermediate transfer belt 16, a light receiving voltage value (that is, a surface resistivity of the intermediate transfer belt 16), a cleaning bias voltage, a primary transfer bias voltage, and a secondary voltage that can obtain good image quality in advance. If the relationship with the transfer bias voltage is defined in the table, a good image quality can be obtained over a long period of time with any intermediate transfer belt 16 made of any material.

  In the above example, the example in which the intermediate transfer belt 16 is an image carrier has been described. However, for example, the photosensitive drum may be an image carrier, and in this case, the surface state of the photosensitive drum is detected. Then, the bias voltage applied to the fur brush used when cleaning the photosensitive drum is adjusted according to the detection result, and the bias voltage of the transfer roller for transferring the toner image from the photosensitive drum is adjusted. Become.

  Since the surface state of the image carrier is detected and at least one of the transfer bias voltage and the cleaning bias voltage is adjusted according to a detection signal representing the surface state, transfer control according to the surface state of the image carrier As a result of obtaining good image quality over a long period of time regardless of the surface deterioration of the image carrier, it is possible to extend the life of an image forming apparatus such as a copying machine, a printer, or a facsimile machine. Applicable.

1 is a diagram schematically showing Embodiment 1 of an image forming apparatus according to the present invention. FIG. 2 is a block diagram for explaining control in the image forming apparatus shown in FIG. 1. It is a figure which shows the relationship between the surface resistivity and light reception voltage value in the material of an intermediate transfer belt, (a) is a figure which shows the relationship between the surface resistivity and light reception voltage value when an intermediate transfer belt is PC rubber, (B) is a diagram showing the relationship between the surface resistivity and the received light voltage value when the intermediate transfer belt is a rubber + coat (PTEF) belt. FIG. 4 is a diagram illustrating a table when the intermediate transfer belt is PC rubber, where (a) illustrates a table that defines a relationship between a cleaning bias voltage and a light reception voltage value, and (b) illustrates a primary transfer bias voltage and light reception. FIG. 5C is a diagram illustrating a table that defines the relationship between voltage values, and FIG. 5C is a diagram illustrating a table that defines the relationship between secondary transfer bias voltage and light reception voltage value. FIG. 4 is a diagram showing a table when the intermediate transfer belt is a rubber + coat (PTEF) belt, where (a) shows a table defining the relationship between the cleaning bias voltage and the received light voltage value, and (b) shows the primary. FIG. 5C is a diagram illustrating a table that defines the relationship between the transfer bias voltage and the light reception voltage value, and FIG. 6C is a diagram illustrating a table that defines the relationship between the secondary transfer bias voltage and the light reception voltage value.

Explanation of symbols

11 Image forming apparatus 12-15 Image forming unit 16 Intermediate transfer belt 21 Reflective sensors 22a-22d Primary transfer roller 26 Secondary transfer roller 27 Cleaning unit (fur brush)
31 controller

Claims (5)

An image carrier on which a toner image is formed; a transfer unit that applies a transfer bias voltage to transfer the toner image from the image carrier to a recording medium; and a cleaning unit that applies a cleaning bias voltage to clean the image carrier. In an image forming apparatus having
Detecting means for detecting a surface state of the image carrier and outputting a detection signal representing the surface state;
An image forming apparatus comprising: a control unit that adjusts at least one of the transfer bias voltage and the cleaning bias voltage in accordance with the detection signal. The detection means is an image density measurement means for outputting a light reception voltage value corresponding to the amount of reflected light reflected by the image carrier as the light applied to the image carrier as the detection signal.
The control means includes at least one of a first table in which a relationship between the light reception voltage value and the transfer bias voltage is defined and a second table in which a relationship between the light reception voltage value and the cleaning bias voltage is defined. The image forming apparatus according to claim 1, wherein the image forming apparatus is preset. The image carrier is an intermediate transfer belt on which each color toner image is primarily transferred as the toner image,
The image forming apparatus according to claim 1, wherein the transfer unit is a secondary transfer unit to which a secondary transfer bias voltage is applied as the transfer bias voltage. Primary transfer bias voltage is applied, and primary transfer means for transferring the color toner images to the image carrier,
4. The control unit according to claim 3, wherein the control unit adjusts at least one of the primary transfer bias voltage, the secondary transfer bias voltage, and the cleaning bias voltage in accordance with the detection signal. Image forming apparatus. The detection means is an image density measurement means for outputting a light reception voltage value corresponding to the amount of reflected light reflected by the image carrier as the light applied to the image carrier as the detection signal.
A first table defining a relationship between the light reception voltage value and the primary transfer bias voltage; a second table defining a relationship between the light reception voltage value and the cleaning bias voltage; The image forming apparatus according to claim 4, wherein at least one of the third tables in which a relationship between the light reception voltage value and the secondary transfer bias voltage is defined is set in advance.

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