JP2006154006A - Image forming apparatus and method of setting transfer current value - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly set a transfer current value in accordance with a state change of a member constituting a transfer part. <P>SOLUTION: Before the start of image formation, a current is caused to flow to a primary transfer roll 15 with a first current value I1 by a primary transfer current source 61 while charging a photoreceptor drum 11 by a charging device 12, and a first voltage value V1 generated at this time is measured. Next, a current is caused to flow to the primary transfer roll 15 with a second current value I2 by the primary transfer current source 61, and a second voltage value V2 generated at this time is measured. In a transfer control part 70, the first current value I1, the first voltage value V1, the second current value I2, and the second voltage value V2 are used to perform primary regression analysis, and a system resistance T being an inclination and an offset potential A being an intercept are obtained. A transfer current value I is set on the basis of the system resistance R, and the lifetime of the photosensitive drum 11 is discriminated on the basis of the offset potential A. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile, and more particularly to an image forming apparatus using a contact transfer method.

2. Description of the Related Art Conventionally, an image forming apparatus is known that includes a photosensitive drum on which a toner image is formed and supported, and a transfer device that transfers the toner image on the photosensitive drum to a sheet. The photosensitive drum is charged by a charging device, an electrostatic latent image is formed by an exposure device, and then developed by a developing device to form a toner image. Further, as the transfer device, for example, a transfer device provided with a transfer roll that is pressed against the photosensitive drum and a bias power source that applies a transfer bias between the transfer roll and the photosensitive drum is used. In the transfer device, a transfer electric field is formed between the transfer roll and the photosensitive drum by applying a transfer bias between the photosensitive drum and the transfer roll. The toner image formed on the photosensitive drum is electrostatically transferred onto the sheet by the formed transfer electric field.
The contact transfer method using a contact transfer member such as a transfer roll can reduce the amount of ozone generated, which is a problem of the corona method that is a non-contact transfer method, and can suppress the blur of the transferred image. Has advantages.

  By the way, in the contact charging method described above, a transfer electric field is formed by applying a transfer bias to each member (transfer roll, photoconductor drum) constituting the transfer portion. For this reason, it is necessary to set the transfer bias in consideration of a change in resistance of each of these members over time or a change in resistance due to the environment. Here, for example, if the transfer bias is too small, the transfer electric field becomes too weak, and a transfer failure occurs due to insufficient transfer. On the other hand, if the transfer bias is too large, for example, the transfer electric field becomes too strong, and a discharge mark (image quality defect caused by a discharge occurring between the photosensitive drum and the paper and a missing toner image) or A transfer failure due to a transfer phenomenon (a phenomenon in which toner re-transfers from the paper side to the photosensitive drum side) occurs.

  As a conventional transfer bias setting method, during non-image formation, a constant current is applied to the transfer roll while the photosensitive drum is charged, and image formation is performed according to the detected voltage value obtained by detecting the voltage at this time. There is a technique for determining the transfer current of time (see Patent Document 1).

JP 2003-241444 A (page 3-4)

In the transfer current setting method described above, since the transfer current is supplied while the photosensitive drum is charged, the detection voltage value is determined by the voltage generated by supplying the transfer current and the photosensitive drum. The voltage generated by the charging potential is superimposed.
However, in the conventional setting method, since the transfer bias is set in a state where the charged potential of the photosensitive drum is ignored, there is a possibility that an excess or deficiency is caused with respect to a really necessary transfer bias, resulting in a transfer failure. It was. Specifically, for example, when the charged potential of the photosensitive drum is high, the detection voltage value is increased by being dragged to the charged potential, so that the transfer portion is considered to be in a high resistance state, and the transfer current is reduced. The value may be set low. However, when the resistance of the actual transfer portion is low, transfer shortage occurs. Conversely, when the charging potential of the photosensitive drum is low, the detection voltage value is lowered by being dragged to the charging potential, so that the transfer portion is considered to be in a low resistance state, and the transfer current value is set high. there is a possibility. However, when the resistance of the actual transfer portion is high, transfer failure due to discharge occurs.

Further, the charging potential of such a photosensitive drum varies depending on the film thickness of the photosensitive layer formed on the surface of the photosensitive drum. Usually, the film thickness of the photosensitive layer decreases as the number of image formation increases, and the charging potential gradually decreases.
Conventionally, the surface potential of the photosensitive drum is monitored by disposing the surface potential sensor or the like on the photosensitive drum to determine the life of the photosensitive drum. However, a surface potential sensor or the like must be provided. Therefore, there has been a problem that the apparatus configuration becomes large and complicated, and the cost increases.

The present invention has been made to solve such a technical problem, and an object of the present invention is to appropriately set a transfer current value corresponding to a change in state of a member constituting the transfer portion. It is in.
Another object is to determine the lifetime of an image carrier such as a photosensitive drum with a simple configuration.

  For this purpose, an image forming apparatus to which the present invention is applied includes an image carrier on which a toner image is carried, an image carrier that is directly or indirectly pressed against the image carrier and is supplied with a transfer current. A transfer member that transfers the toner image on the carrier to the transfer member, a voltage detection unit that detects a voltage applied to the image carrier and the transfer member, and a current flowing through the transfer member at a first current value Based on the first voltage value detected by the voltage detection means and the second voltage value detected by the voltage detection means when a current is passed through the transfer member at the second current value, the transfer operation is related. Setting means for setting transfer parameters.

Here, the transfer parameter set by the setting means may be a transfer current value supplied to the transfer member. In this case, the setting means obtains a voltage difference between the first voltage value and the second voltage value detected by the voltage detection means, and sets the transfer current value according to the voltage difference. Can do. In addition, the setting means includes a first system resistance obtained from the first voltage value detected by the voltage detection means and the first current value passed when the first voltage value is detected; The transfer current value is determined in accordance with the second system resistance obtained from the second voltage value measured by the voltage detection means and the second current value passed when the second voltage value is detected. It can be characterized by setting. Further, the setting means performs a primary regression analysis from the first current value, the first voltage value, the second current value, and the second voltage value, and the transfer current according to the slope obtained by the primary regression analysis. It can be characterized by setting a value.
Further, the transfer parameter set by the setting means can be characterized in that it is the magnitude of the charging bias with respect to the image carrier.

From another point of view, an image forming apparatus to which the present invention is applied includes an image carrier that carries a toner image, a transfer member that is directly or indirectly pressed against the image carrier, and a transfer member that transfers to the transfer member. Measured by a transfer power supply for supplying current, a voltage measurement unit for measuring a voltage generated between the image carrier and the charging member, and a voltage measurement unit when a current is passed through the transfer member at a first current value. A determination unit that determines the lifetime of the image carrier based on the first voltage value and the second voltage value measured by the voltage measurement unit when a current is passed through the transfer member at the second current value. Is included.
Here, the determination unit performs a primary regression analysis from a relationship between a plurality of voltages and a plurality of corresponding currents, and determines the lifetime of the image carrier based on an intercept obtained by the primary regression analysis. be able to. The image carrier may be a photoreceptor having a photosensitive layer on the surface, and the determination unit may estimate the film thickness of the photosensitive layer based on the intercept.

Further, from the category of methods, the present invention is a method for setting a transfer current value to be supplied to a transfer unit that transfers a toner image formed on an image carrier to a recording material by contact transfer. A step of passing a current at a current value of 1, a step of measuring a first voltage value generated in the transfer portion when a current is passed at a first current value, and a second current value of the transfer portion. A step of passing a current at a step, a step of measuring a second voltage value generated in the transfer portion when the current is passed at a second current value, a first current value, a first voltage value, Determining a transfer current value based on the second current value and the second voltage value.
Here, in the step of determining the transfer current value, a primary regression analysis is performed from the first current value, the first voltage value, the second current value, and the second voltage value, and the transfer current value is obtained by the primary regression analysis. The transfer current value is determined according to the inclination.

According to the present invention, since the state change caused by the image carrier side and the state change caused by the transfer side are distinguished from the relationship between the current and voltage flowing through the transfer portion, The transfer current value can be appropriately set corresponding to the state change.
In addition, according to the present invention, the life of the image carrier can be determined from the relationship between the current flowing through the transfer portion and the voltage.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described below in detail with reference to the accompanying drawings.
—Embodiment 1—
FIG. 1 shows a schematic configuration of an image forming apparatus according to the present embodiment. The image forming apparatus is configured to sequentially transfer each color component toner image formed on the photoconductive drum 11 and arranged on the photoconductive drum 11 so as to be rotatable in the direction of the arrow B and the photoconductive drum 11 arranged in the direction of the arrow A. An intermediate transfer belt 20 that is held by (primary transfer) is provided. The color image forming apparatus also includes a secondary transfer device 30 that collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 20 to the paper P, and fixes the secondary transferred image onto the paper P. The fixing device 50 is provided.

  Here, a charging device 12 for charging the photosensitive drum 11 to a predetermined potential is disposed around the photosensitive drum 11. Further, a laser exposure device 13 for writing an electrostatic latent image on the photosensitive drum 11 charged by the charging device 12 by exposure is provided downstream of the charging device 12 in the rotation direction of the photosensitive drum 11. Further, yellow (Y), magenta (M), cyan (C), and black (K) color component toners are accommodated on the downstream side in the rotation direction of the photosensitive drum 11 with respect to the laser exposure device 13 to accommodate the photosensitive member. A rotary developing device 14 is provided to which developing devices 14Y, 14M, 14C, and 14K that visualize the electrostatic latent image on the drum 11 with toner are rotatably mounted. A primary transfer roll 15 for transferring a toner image carried on the photosensitive drum 11 to the intermediate transfer belt 20 is provided downstream of the rotary developing device 14 in the rotation direction of the photosensitive drum 11 and further downstream. A drum cleaner 16 is provided on the side to remove the residue on the photosensitive drum 11 after the primary transfer. In the present embodiment, a negatively charged toner is used.

Further, the intermediate transfer belt 20 is stretched around a plurality of (four in the present embodiment) support rolls 21 to 24. Here, the support roll 21 is a drive roll for the intermediate transfer belt 20.
The support roll 22 is a metal idle roll used for positioning the intermediate transfer belt 20 and forming a flat primary transfer surface. Further, the support roll 23 is a correction roll (steering roll: disposed so as to be tiltable about one end in the axial direction as a fulcrum) that restricts meandering in a direction substantially orthogonal to the conveyance direction of the intermediate transfer belt 20. The support roll 24 is a backup roll of the secondary transfer device 30 described later. A belt cleaner 25 for removing residues on the intermediate transfer belt 20 after the secondary transfer is disposed at a position facing the intermediate transfer belt 20 with the drive roll 21 therebetween. The intermediate transfer belt 20 is made of a resin such as polyimide, polycarbonate, polyester, polypropylene, polyethylene terephthalate, acrylic, vinyl chloride or the like containing various amounts of carbon black as a conductive agent, and has a volume resistivity of 10 ^6. is formed so as to be ~10 ¹⁵ Ω · cm, the thickness is set to 0.1mm for example.

The secondary transfer device 30 includes a secondary transfer roll 31 disposed on the toner image carrying surface side of the intermediate transfer belt 20 and a backup serving as a counter electrode of the secondary transfer roll 31 disposed on the back surface side of the intermediate transfer belt 20. And a roll 24. Furthermore, a metal power supply roll 32 is disposed in contact with the backup roll 25. Here, the volume resistivity of the backup roll 24 is set in a range of 10 ³ to 10 ¹⁰ Ω · cm. The secondary transfer roll 25 uses, for example, foamed urethane rubber having carbon dispersed on the surface, and a roll coated with fluorine coating, and its volume resistivity is in the range of 10 ³ to 10 ¹⁰ Ω · cm. Set to
A belt cleaner 25 for removing residues on the intermediate transfer belt 20 after the secondary transfer is disposed at a portion facing the drive roll 21 with the intermediate transfer belt 20 interposed therebetween. Note that the secondary transfer roll 31 and the belt cleaner 25 are disposed so as to be able to come into contact with and separate from the intermediate transfer belt 20, and when a color (multiple color) image is formed, the toner image before the final color is secondary. These are separated from the intermediate transfer belt 20 until they pass through the transfer roll 31 and the belt cleaner 25.

  The paper transport system transports the paper tray 40 that stores the paper P, the pickup roll 41 that picks up and feeds the paper P accumulated in the paper tray 40 at a predetermined timing, and the paper P that is fed out by the pickup roll 41. A transport roll 42 is provided. Further, a registration roll (registration roll) 43 for feeding the paper P to the secondary transfer device 30 at a predetermined timing is disposed on the downstream side of the transport roll 42 in the paper transport direction. Further, a belt transport device 44 for transporting the paper P after the secondary transfer to the fixing device 50 is provided downstream of the secondary transfer device 30 in the paper transport direction.

  Further, the fixing device 50 includes a heating roll 51 having a heating source therein and rotatably arranged. In addition, the fixing device 50 includes a pressure roll 52 that is disposed in pressure contact with the heating roll 51 and rotates following the heating roll 51. Here, the heating roll 51 is controlled by a temperature adjusting unit (not shown) so that the surface temperature is within a predetermined temperature range.

  Next, an image forming process of the color image forming apparatus according to the present embodiment will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. First, the photosensitive drum 11 and the intermediate transfer belt 20 start to rotate. Then, the surface of the photosensitive drum 11 is charged to a predetermined potential by the charging device 12, and then an electrostatic latent image corresponding to the image is written by the laser exposure unit 13, and any of the corresponding developing units 14Y, 14M, 14C, and 14K is written. The electrostatic latent image is developed as a result. For example, if the electrostatic latent image written on the photosensitive drum 11 corresponds to yellow, the electrostatic latent image is developed by the yellow developing device 14Y containing yellow toner, and the photosensitive drum 11 is developed. A yellow toner image is formed on the top. The toner image formed on the photosensitive drum 11 is intermediated from the photosensitive drum 11 by the primary transfer bias applied to the primary transfer roll 15 at the primary transfer position where the photosensitive drum 11 and the intermediate transfer belt 20 are in contact with each other. Primary transfer is performed on the transfer belt 20. On the other hand, the toner remaining on the photosensitive drum 11 after the primary transfer is removed by the drum cleaner 16.

  Here, when forming a single color image, the toner image primary-transferred to the intermediate transfer belt 20 is immediately secondary-transferred to a sheet. When a color image is formed by superimposing a plurality of color toner images. In this case, the toner image formation on the photosensitive drum 11 and the primary transfer process of the toner image formed on the photosensitive drum 11 are repeated for the number of colors. For example, when a full color image is formed by superimposing four color toner images, yellow, magenta, cyan, and black toner images are sequentially formed on the photosensitive drum 11, and the toner images of these colors are sequentially transferred to the intermediate transfer belt. 20 is primarily transferred. On the other hand, the intermediate transfer belt 20 rotates with the same period as the photosensitive drum 11 while holding the primary transferred toner image, and a magenta, cyan, and black toner image is formed on the intermediate transfer belt 20 for each rotation. Is transferred and overlaid.

  The toner image primarily transferred to the intermediate transfer belt 20 in this manner is conveyed to the secondary transfer position as the intermediate transfer belt 20 rotates. On the other hand, the paper P is supplied to a secondary transfer position at a predetermined timing by a registration roll 43 (not shown), and the secondary transfer roll 31 nips the paper P against the intermediate transfer belt 20 (backup roll 24). Then, at the secondary transfer position, the toner image carried on the intermediate transfer belt 20 is caused by the action of the secondary transfer electric field formed between the secondary transfer roll 31 and the backup roll 24 which are the secondary transfer device 30. Electrostatic transfer (secondary transfer) is performed on the paper P. Thereafter, the paper P onto which the toner image has been transferred is conveyed to the fixing device 50, where the toner image on the paper P is heated and pressed and fixed, and is discharged to a paper discharge tray (not shown). On the other hand, the residual toner remaining on the intermediate transfer belt 20 that has passed the secondary transfer position is removed by the belt cleaner 25.

Next, a method for setting a primary transfer bias (primary transfer current), which is a feature of the present embodiment, will be described in detail.
FIG. 2 is a diagram for explaining a primary transfer system in the color image forming apparatus according to the present embodiment. In the present embodiment, the photosensitive drum 11 as an image carrier includes, for example, a base 11a made of cylindrical aluminum and an organic photosensitive layer 11b formed on the outer peripheral surface of the base 11a. Have. Further, the charging device 12 is disposed in pressure contact with the photosensitive drum 11 so as to be rotatable. The charging roller 12a is driven to rotate as the photosensitive drum 11 rotates, and a predetermined charging bias (this embodiment) is applied to the charging roll 12a. And a charging power source 12b for applying a negative polarity). Furthermore, the primary transfer roll 15 as a transfer member is configured, for example, by covering the outer periphery of a stainless steel conductive core with a rubber conductive foam elastic body. The resistance is appropriately adjusted by mixing a substance having ion conductivity (for example, NBR rubber) or a substance having electron conductivity (for example, carbon black) into the conductive foamed elastic body.

  A primary transfer current source 61 as a transfer power source capable of adjusting an output current value is connected to the primary transfer roll 15, while the photosensitive drum 11 is grounded. The primary transfer current source 61 supplies a positive primary transfer bias (primary transfer current) to the primary transfer roll 15 by performing constant current control. A primary transfer current flows from the primary transfer current source 61 through the primary transfer roll 15, the intermediate transfer belt 20, and the photosensitive drum 11, thereby forming a transfer electric field between the photosensitive drum 11 and the intermediate transfer belt 20. The toner image on the photosensitive drum 11 is transferred to an intermediate transfer belt 20 as a transfer target. Further, a primary transfer voltmeter 62 as a voltage detecting means or a voltage measuring unit is connected between the primary transfer current source 61 and the photosensitive drum 11. The primary transfer voltmeter 62 measures a voltage generated between the primary transfer current source 61 and the photosensitive drum 11. In this embodiment, a transfer control unit 70 is provided as a setting means for setting a primary transfer current value to be supplied from the primary transfer current source 61 based on the voltage measurement result by the primary transfer voltmeter 62.

  FIG. 3 is a functional block diagram of the transfer control unit 70 described above. The transfer control unit 70 includes a transfer current value setting unit 71 that sets a primary transfer current value output from the primary transfer current source 61 (hereinafter simply referred to as a transfer current value). The transfer control unit 70 also transfers the first voltage value V1 output from the primary transfer voltmeter 62 when the first current value I1 set by the transfer current value setting unit 71 is passed. A voltage difference ΔV = V2− from the second voltage value V2 output from the primary transfer voltmeter 62 when the second current value I2 (I2 ≠ I1) set by the current value setting unit 71 is supplied. A voltage difference calculator 72 for calculating V1 is provided. Furthermore, the transfer control unit 70 includes a correction value storage unit 73 that stores a table in which the voltage difference ΔV obtained by the voltage difference calculation unit 72 is associated with the correction value k for the basic transfer current value I0. Furthermore, the transfer control unit 70 reads the corresponding correction value k from the correction value storage unit 73 based on the voltage difference ΔV obtained by the voltage difference calculation unit 72, and corrects the correction value k with respect to the basic transfer current value I0. Is provided with a correction unit 74 that obtains the transfer current value I in consideration of the above and outputs it to the transfer current value setting unit 71.

  Next, a process for setting the transfer current value I in the present embodiment will be described with reference to FIG. The transfer current value I is set during non-image formation, for example, before starting a job. At that time, the charging device 12 charges the photosensitive drum 11 in the same manner as in normal image formation, and the developing device constituting the rotary developing device 14 is positioned at a position facing the photosensitive drum 11. A developing bias is applied to a certain developing device (for example, the yellow developing device 14Y) in the same manner as in normal image formation. Then, the transfer current value I is determined after the time for the output of the primary transfer current source 61 to stabilize has elapsed.

  In this process, first, the first current value I1 is set by the transfer current value setting unit 71, and the first current value I1 is supplied to the primary transfer roll 15 by the primary transfer current source 61 (step 101). Then, the first voltage value V1 is measured by the primary transfer voltmeter 62 in the state where the first current value I1 is passed (step 102). The first voltage value V1 measured by the primary transfer voltmeter 62 is output to the voltage difference calculator 72 and temporarily stored in a memory (not shown) provided in the voltage difference calculator 72.

Next, the transfer current value setting unit 71 sets the second current value I2, and the primary transfer current source 61 causes the second current value I2 to flow through the primary transfer roll 15 (step 103). Then, the second voltage value V2 is measured by the primary transfer voltmeter 62 in the state where the second current value I2 is passed (step 104). The second voltage value V <b> 2 measured by the primary transfer voltmeter 62 is output to the voltage difference calculation unit 72.
In this description, it is assumed that the second current value I2 is set to a value larger than the first current value I1.

In the voltage difference calculation unit 72, the difference between the second voltage value V2 outputted from the primary transfer voltmeter 62 and the first voltage value V1 already outputted from the primary transfer voltmeter 62 and stored in the memory is obtained. The voltage difference ΔV = V2−V1 is calculated (step 105) and output to the correction unit 74. The correction unit 74 reads the correction value k corresponding to the input voltage difference ΔV from the correction value storage unit 73 (step 106), calculates the transfer current value I = k × I0 to be passed (step 107), and Output to the transfer current value setting unit 71. Thereafter, the transfer current value setting unit 71 sets the set transfer current value I for the primary transfer current source 61 (step 108), and the process ends.
In step 102 and step 104 described above, the same position is removed from the roll surface of the primary transfer roll 15 and, for example, 30 output voltages are measured every 10 msec. Averaging is performed using the deleted value to obtain the first voltage value V1 or the second voltage value V2.

  Here, FIG. 5 shows an example of a table stored in the correction value storage unit 73 of the transfer control unit 70. In the present embodiment, a different correction value k is selected every 100 V in accordance with the voltage difference ΔV between the first transfer voltage value V1 and the second transfer voltage value V2.

As described above, in the present embodiment, when the first voltage value V1 obtained when the first current value I1 is passed and the second current value I2 different from the first current value I1 are passed. The correction value k is selected based on the voltage difference ΔV with respect to the second voltage value V2 obtained in the above, and the transfer current value I used in the actual image forming operation is determined.
This was obtained based on experiments conducted by the present inventors. Hereinafter, this reason will be described.

The inventor first combines the primary transfer roll 15 and the intermediate transfer belt 20 having different resistance values with respect to the same photosensitive drum 11, the current value supplied by the primary transfer current source 61, and the primary transfer at that time. The relationship with the voltage value measured by the voltmeter 62 was investigated.
FIG. 6 shows the IV characteristics obtained as a result of the experiment. As shown in FIG. 6, in the generally used primary transfer current value range (about 60 μA), the IV characteristic is
V = RI + A
And linear regression. Here, I is a current value, and V is a voltage value. R representing the inclination is the system resistance of the entire photosensitive drum 11 (photosensitive layer 11b), the intermediate transfer belt 20, and the primary transfer roll 15. The system resistance R includes not only the resistance of each of the photosensitive drum 11, the intermediate transfer belt 20, and the primary transfer roll 15, but also the contact resistance at the primary transfer nip (between the photosensitive drum 11 and the intermediate transfer belt 20, the intermediate transfer belt). 20-between primary transfer rolls 15) and the like. Further, A representing an intercept is an offset potential due to the initial charging potential of the photosensitive drum 11. The offset potential means the potential that the photosensitive drum 11 (photosensitive layer 11b) charged by the charging device 12 shows at the primary transfer site. Therefore, the slope R obtained from the linear regression of the IV characteristic represents the electrical resistance of the primary transfer unit (photosensitive drum 11, intermediate transfer belt 20, primary transfer roll 15), and intercept A represents the photosensitive drum 11 side. It can be said that the charging state is shown respectively.
Therefore, the change in the system resistance R can be determined as occurring due to the change in the state of the primary transfer portion, particularly the intermediate transfer belt 20 and the primary transfer roll. Further, it can be determined that the change in the offset potential A is mainly caused by the change in the state of the photosensitive drum 11 (particularly, the photosensitive layer 11b).

Next, the inventor combines the photosensitive drum 11 having a different thickness of the photosensitive layer 11b with respect to the same primary transfer roll 15 and intermediate transfer belt 20, and the current value passed by the primary transfer current source 61, Occasionally, the relationship with the voltage value measured by the primary transfer voltmeter 62 was investigated.
FIG. 7 shows the IV characteristics obtained as a result of the experiment. FIG. 7 shows that when only the film thickness of the photosensitive layer 11b is changed, the system resistance R is hardly changed (the inclination is hardly changed), while the offset potential A is changed. Specifically, the value of the offset potential A decreases as the photosensitive layer 11b becomes thinner. That is, it is understood that the offset potential A corresponds to a change in charging potential accompanying a change in film thickness of the photosensitive layer 11b. From FIG. 7, even if the thickness of the photosensitive layer 11 b of the photosensitive drum 11 changes, the system resistance R of the entire photosensitive drum 11 (photosensitive layer 11 b), intermediate transfer belt 20, and primary transfer roll 15 is almost the same. It is understood that it has no effect.

The present inventor further combines different primary transfer rolls 15 and intermediate transfer belts 20 with respect to the same photosensitive drum 11 in a low-temperature and low-humidity environment, and the current value passed by the primary transfer current source 61 and at that time The relationship with the voltage value measured by the primary transfer voltmeter 62 was investigated.
FIG. 8 shows the IV characteristics obtained as a result of the experiment. In a high-temperature and high-humidity environment, the resistance of the primary transfer roll 15 and the intermediate transfer belt 20 is reduced, so that the voltage generated when the primary transfer current is passed is reduced and the system resistance R is reduced. On the other hand, in a low-temperature and low-humidity environment, the resistance of the primary transfer roll 15 and the intermediate transfer belt 20 increases, so that the voltage generated when the primary transfer current flows is increased and the system resistance R is increased.

Here, as in a conventional image forming apparatus, a case where a constant current is passed by the primary transfer current source 61 and the transfer current value I is determined from the voltage measured by the primary transfer voltmeter 62 at that time is considered. Try. That is, in this case, the transfer current value is determined by the current value and voltage value at one point.
At this time, the measured voltage is caused by the system resistance R (mainly determined by the state of the primary transfer roll 15 and the intermediate transfer belt 20) and the offset potential A (mainly the photosensitive layer of the photosensitive drum 11) as described above. 11b is determined by the film thickness of 11b. However, when the apparent system resistance is obtained using the obtained voltage and the flowing current, an error is included by the offset potential A. For this reason, when the transfer current value is set based on this apparent system resistance, a deviation from the originally required transfer current value may occur, resulting in a transfer failure.

  On the other hand, in the present embodiment, a plurality of (two in the present embodiment) current values I1 and I2 are caused to flow by the primary transfer current source 61, and a plurality of current values I1 and I2 measured at that time are measured by the primary transfer voltmeter 62. A voltage difference ΔV is obtained from the voltage values V1 and V2. The magnitude of this voltage difference ΔV is proportional to the system resistance R. That is, by acquiring the voltage difference ΔV, it is possible to remove the influence of the offset potential A caused by the photosensitive drum 11 side. In the present embodiment, the corresponding correction value k is selected from the obtained voltage difference ΔV, and the basic transfer current value I0 is corrected with the obtained correction value k, thereby transferring the transfer current value I used during image formation. It was decided to decide. As a result, an accurate transfer current value I can be obtained, and good primary transfer can be performed.

Next, a specific example will be described.
First, three samples with different combinations of the photosensitive drum 11, the intermediate transfer belt 20, and the primary transfer roll 15 were prepared. These are designated as samples 1 to 3, respectively. Then, a first current value I1 = 20 μA and a second current value I2 = 30 μA were applied to each of samples 1 to 3, and the corresponding first voltage value V1 and second voltage value V2 were measured. The results are shown below. Moreover, the IV characteristic of these samples 1-3 is shown in FIG. In addition, in FIG. 9, the linear regression line calculated | required from the IV characteristic of the samples 1-3 is also illustrated for reference.
Sample 1: When I1 = 20 μA, V1 = 450V
When I2 = 30μA, V2 = 700V
ΔV = 700−450 = 250V
Sample 2: When I1 = 20 μA, V1 = 220V
When I2 = 30μA, V2 = 300V
ΔV = 300−220 = 80V
Sample 3: When I1 = 20 μA, V1 = 580V
When I2 = 30μA, V2 = 900V
ΔV = 900−580 = 320V
From FIG. 9, it is understood that the magnitude of the voltage difference ΔV corresponds to the slope, that is, the system resistance R. Specifically, the voltage difference ΔV increases as the system resistance R increases, and the voltage difference ΔV decreases as the system resistance R decreases.

When the voltage difference ΔV is large (when the system resistance R is large), it is necessary to set the transfer current value I to be smaller. On the other hand, when the voltage difference ΔV is small, the transfer current value I is increased accordingly. Must be set larger.
Therefore, in the present embodiment, the magnitude of the correction value k stored in the correction value storage unit 73 is set to A>B>C>D>E>F> G. In other words, the correction value k decreases as the voltage difference ΔV increases. As a result, the transfer current value I can be set to an appropriate magnitude.

  As described above, the resistance of the primary transfer roll 15 and the intermediate transfer belt 20 varies depending on the surrounding environment such as temperature and humidity. Therefore, it is preferable to set the transfer current value I in consideration of these temperatures and humidity. Therefore, for example, as shown by a one-dot chain line in FIG. 3, when the temperature sensor 81 and the humidity sensor 82 are attached in the color image forming apparatus and the correction unit 74 performs correction, the measurement results of these temperature and humidity are taken into account. It is preferable to perform correction.

  In the present embodiment, basically, the first current I1 and the second current I2 are always constant. Here, it is known that the preferable magnitude of the transfer current value I varies depending on the environment such as temperature and humidity. For example, a low value is preferable in a low temperature and low humidity environment, and a high value is high in a high temperature and high humidity environment. preferable. Therefore, when the temperature sensor 81 and the humidity sensor 82 are provided, first, the temperature and humidity are measured, and the transfer current value I is selected after selecting the first current I1 and the second current I2 suitable for the environmental conditions. It is preferable to start the setting process.

-Embodiment 2-
The present embodiment is substantially the same as the first embodiment, but the apparent system resistance R1 obtained from the first current value I1 and the corresponding first voltage value V1, and the second current value I2. The transfer current value I is set based on the apparent system resistance R2 obtained from the corresponding second voltage value V2. In addition, in this Embodiment, about the thing similar to Embodiment 1, the same code | symbol as Embodiment 1 is attached | subjected and the detailed description is abbreviate | omitted.

  FIG. 10 shows a functional block diagram of the transfer control unit 70 in the present embodiment. The basic configuration of the transfer control unit 70 is substantially the same as that described in the first embodiment, but instead of the voltage difference calculation unit 72, the current set by the transfer current value setting unit 71 and the current There is provided a system resistance calculation unit 75 for obtaining an apparent system resistance from the voltage output from the primary transfer voltmeter 62 when the voltage is applied.

Next, the setting process of the transfer current value I in the present embodiment will be described with reference to FIG.
In this process, first, the first current value I1 is set by the transfer current value setting unit 71, and the first current value I1 is caused to flow through the primary transfer roll 15 by the primary transfer current source 61 (step 201). Then, the first voltage value V1 is measured by the primary transfer voltmeter 62 in the state where the first current value I1 is passed (step 202). The first current value I1 set by the transfer current value setting unit 71 and the first voltage value V1 measured by the primary transfer voltmeter 62 are input to the system resistance calculation unit 75, and the first system resistance R1 = V1 / I1 is calculated (step 203). The obtained first system resistance R1 is temporarily stored in a memory (not shown) provided in the system resistance calculation unit 75.

Next, the transfer current value setting unit 71 sets the second current value I2, and the primary transfer current source 61 causes the second current value I2 to flow through the primary transfer roll 15 (step 204). Then, the second voltage value V2 is measured by the primary transfer voltmeter 62 in the state where the second current value I1 is passed (step 205). The second current value I2 set by the transfer current value setting unit 71 and the second voltage value V2 measured by the primary transfer voltmeter 62 are input to the system resistance calculation unit 75, and the second system resistance R2 = V2 / I2 is calculated (step 206). Then, the first system resistance R1 and the second system resistance R2 are output to the correction unit 74.
In this description, it is assumed that the second current value I2 is set to a value larger than the first current value I1.

The correction unit 74 first determines whether or not the first system resistance R1 is significantly larger than the second system resistance R2 (step 207). If the first system resistance R1 is significantly greater than the second system resistance R2, the corresponding correction value k is read from the correction value table 1 stored in the correction value storage unit 73 (step 208).
On the other hand, if the first system resistance R1 is not significantly larger than the second system resistance R2 in step 207, then the second system resistance R2 is significantly larger than the first system resistance R1. It is determined whether or not (step 209). If the second system resistance R2 is significantly larger than the first system resistance R1, the corresponding correction value k is read from the correction value table 2 stored in the correction value storage unit 73 (step 210).
On the other hand, in step 209, if the second system resistance R2 is not significantly larger than the first system resistance R1, in other words, the first system resistance R1 and the second system resistance R2 are substantially the same. If there is, the corresponding correction value k is read from the correction value table 3 stored in the correction value storage unit 73 (step 211).
The correction unit 74 calculates the transfer current value I = k × I0 to be passed (step 212) and outputs it to the transfer current value setting unit 71. Thereafter, the transfer current value setting unit 71 sets the set transfer current value I for the primary transfer current source 61 (step 213), and ends the process.

In the present embodiment, an appropriate correction table is selected from a plurality of correction value tables based on the obtained relative magnitude relationship between the first system resistance R1 and the second system resistance R2, and the transfer is performed. The current value is corrected. The reason for this will be described below.
As described above, in the present embodiment, the second current value I2 is set to a larger value than the first current value I1. For this reason, the fact that the first system resistance R1 is significantly larger than the second system resistance R2 means that the true system resistance R decreases as the current increases. On the other hand, the fact that the first system resistance R1 is significantly smaller than the second system resistance R2 means that the true system resistance R increases as the current increases. That is, in these, it is understood that the true system resistance R has a current dependency (the IV characteristic is non-linear). On the other hand, the fact that the first system resistance R1 is equal to the second system resistance R2 indicates that the true system resistance R has no current dependence (the IV characteristic is linear). .

When the system resistance R has a current dependency, it is necessary to set (correct) the transfer current value corresponding to the current dependency. If there is current dependency, the required correction method differs depending on whether the system resistance R increases or decreases with current. Further, even when the system resistance R does not have current dependency, the required correction method is different.
Therefore, in the present embodiment, the tendency of resistance fluctuation is confirmed from the first system resistance R1 and the second system resistance R2, and the transfer current value is corrected by a correction table corresponding thereto. As a result, the transfer current value I can be set to an appropriate magnitude.

-Third embodiment-
The present embodiment is substantially the same as the second embodiment, but a linear regression analysis is performed from the first current value and the corresponding first voltage value, and the second current value and the corresponding second voltage value. The system resistance R as the slope and the offset potential A as the intercept are obtained, and the transfer current value I is set based on the obtained system resistance R. In addition, in this Embodiment, about the thing similar to Embodiment 1, the same code | symbol as Embodiment 1 is attached | subjected and the detailed description is abbreviate | omitted.

  FIG. 12 is a block diagram of the transfer control unit 70 in the present embodiment. The basic configuration of the transfer control unit 70 is substantially the same as that described in the first embodiment. However, instead of the voltage difference calculation unit 72, a linear regression analysis is performed on the IV characteristic to perform system resistance R. A linear regression analysis unit 76 for obtaining the offset potential A is provided. Further, unlike the first embodiment, the transfer control unit 70 according to the present embodiment is not provided with the correction value storage unit 73.

Next, the setting process of the transfer current value I in the present embodiment will be described with reference to FIG.
In this process, first, the first current value I1 is set by the transfer current value setting unit 71, and the first current value I1 is caused to flow through the primary transfer roll 15 by the primary transfer current source 61 (step 301). Then, the first voltage value V1 is measured by the primary transfer voltmeter 62 in the state where the first current value I1 is passed (step 302). The first current value I1 set by the transfer current value setting unit 71 and the first voltage value V1 measured by the primary transfer voltmeter 62 are output to the primary regression analysis unit 76 and provided in the primary regression analysis unit 76. Temporarily stored in a stored memory (not shown).

Next, the second current value I2 is set by the transfer current value setting unit 71, and the second current value I2 is caused to flow through the primary transfer roll 15 by the primary transfer current source 61 (step 303). Then, the second voltage value V2 is measured by the primary transfer voltmeter 62 in the state where the second current value I2 is passed (step 304). The second current value I2 set by the transfer current value setting unit 71 and the second voltage value V2 measured by the primary transfer voltmeter 62 are output to the primary regression analysis unit 76.
In this description, it is assumed that the second current value I2 is set to a value larger than the first current value I1.

In the primary regression analysis unit 76, the first current value I1 and the first voltage value V1 read from a memory (not shown), the input second current value I2 and the second voltage value V2, and the like. Is used to perform a linear regression analysis. Then, the system resistance R that is the slope and the offset potential A that is the intercept are obtained by linear regression analysis (step 305) and output to the correction unit 74.
The correction unit 74 calculates a transfer current value I suitable for forming a transfer electric field according to the obtained system resistance R (step 306), and outputs it to the transfer current value setting unit 71. Thereafter, the transfer current value setting unit 71 sets the set transfer current value I for the primary transfer current source 61 (step 307), and the process ends.

  As described above, in the present embodiment, a linear regression analysis is performed using the first current value and the corresponding first voltage value, the second current value and the corresponding second voltage value, and the system resistance R and offset potential A were obtained. The transfer current value I is set based on the obtained system resistance R. Here, the system resistance R is obtained in a state where the influence of the charging potential of the photosensitive drum 11 is removed, and thus is very close to a true value. Therefore, the transfer current value I set based on the system resistance R can be set to an appropriate magnitude.

-Embodiment 4-
Although the present embodiment is substantially the same as the third embodiment, the transfer current value I is not set from the result of the linear regression analysis, but the adjustment of the charging potential of the photosensitive drum 11 or the photosensitive drum 11 is performed. The life is judged. In addition, in this Embodiment, about the thing similar to Embodiment 1, the same code | symbol as Embodiment 3 is attached | subjected and the detailed description is abbreviate | omitted.

  FIG. 14 shows a block diagram of the transfer control unit 70 in the present embodiment. The basic configuration of the transfer control unit 70 is substantially the same as that described in the third embodiment, but instead of the correction unit 74, the magnitude of the charging bias applied from the charging power source 12b to the charging roll 12a is set. A charge setting unit 77 is provided. The charge setting unit 77 also determines the life of the photosensitive drum 11 (photosensitive layer 11b), and when the life is reached, the information is output to the user interface (UI) 63. Yes. In the present embodiment, the transfer control unit 70 functions as a determination unit.

Next, a charging potential setting process in the present embodiment will be described with reference to FIG.
In this process, first, the charging bias is set to a predetermined reference value by the charging setting unit 77 (step 401). Next, the first current value I1 is set by the transfer current value setting unit 71, and the first current value I1 is passed through the primary transfer roll 15 by the primary transfer current source 61 (step 402). Then, the first voltage value V1 is measured by the primary transfer voltmeter 62 in the state where the first current value I1 is passed (step 403). The first current value I1 set by the transfer current value setting unit 71 and the first voltage value V1 measured by the primary transfer voltmeter 62 are output to the primary regression analysis unit 76 and provided in the primary regression analysis unit 76. Temporarily stored in a stored memory (not shown).

Next, the second current value I2 is set by the transfer current value setting unit 71, and the second current value I2 is caused to flow through the primary transfer roll 15 by the primary transfer current source 61 (step 404). Then, the second voltage value V2 is measured by the primary transfer voltmeter 62 in the state where the second current value I2 is passed (step 405). The second current value I2 set by the transfer current value setting unit 71 and the second voltage value V2 measured by the primary transfer voltmeter 62 are output to the primary regression analysis unit 76.
In this description, it is assumed that the second current value I2 is set to a value larger than the first current value I1.

In the primary regression analysis unit 76, the first current value I1 and the first voltage value V1 read from a memory (not shown), the input second current value I2 and the second voltage value V2, and the like. Is used to perform a linear regression analysis. Then, the system resistance R that is the slope and the offset potential A that is the intercept are obtained by linear regression analysis (step 406) and output to the charge setting unit 77.
The charging setting unit 77 determines whether or not the obtained offset potential A is equal to or lower than a predetermined threshold A0 (step 407). The threshold A0 will be described later. Here, when the offset potential A is larger than the threshold value A0, the charging setting unit 77 calculates a charging bias suitable for obtaining an appropriate charging potential according to the obtained offset potential A (step 408). The charged bias is set in the charging power source 12a (step 409), and the process is terminated. On the other hand, when the offset potential A is less than or equal to the threshold value A0, the charge setting unit 77 displays on the UI 63 that the life of the photosensitive drum 11 has been reached (step 410) and ends the process.

  As described with reference to FIG. 7, the offset potential A decreases as the thickness of the photosensitive layer 11 b of the photosensitive drum 11 decreases. Further, by repeating the image forming operation, the film thickness of the photosensitive layer 11b gradually decreases. There is a limit to the film thickness required for image formation. Therefore, in this embodiment, the offset potential A at a film thickness slightly before this limit is determined as the threshold A0.

As described above, in the present embodiment, a linear regression analysis is performed using the first current value and the corresponding first voltage value, the second current value and the corresponding second voltage value, and the system resistance R and offset potential A were obtained. In the present embodiment, a surface potential sensor for measuring the surface potential of the photosensitive drum 11 is not provided, but the potential of the photosensitive drum 11 can be obtained by adopting such a method.
Based on the obtained offset potential A, the charging bias applied to the charging roll 12a for charging the photosensitive drum 11 is set. Thereby, it is possible to accurately set the charging bias. In the present embodiment, the lifetime of the photosensitive drum 11 can be determined by predicting the film thickness of the photosensitive layer 11b of the photosensitive drum 11 based on the obtained offset potential A.

In the present embodiment, the charging bias applied to the charging roll 12a is adjusted based on the obtained offset potential A. However, the present invention is not limited to this. For example, the exposure amount by a laser exposure apparatus ( The intensity of the light beam) and the developing bias applied to each developing device 14Y, 14M, 14C, 14K may be adjusted.
In this embodiment, the charging bias applied to the photosensitive drum 11 from the offset potential A is set or the life of the photosensitive drum 11 is determined. Of course, the transfer current value I based on R may also be set.

-Embodiment 5-
FIG. 16 is a diagram illustrating an outline of an image forming apparatus to which the present exemplary embodiment is applied. In this image forming apparatus, a plurality (four in this embodiment) of image forming units 110 (specifically 110K, 110Y, 110M) in which toner images of each color component are formed in the main body 100 by, for example, electrophotography. , 110C), an intermediate transfer belt 120 for sequentially transferring (primary transfer) each color component toner image formed by each image forming unit 110 is provided. The image forming apparatus also includes a secondary transfer device 130 that collectively transfers (secondary transfer) the superimposed image transferred to the intermediate transfer belt 120 to the paper P, and a fixing device that fixes the secondary transferred image on the paper P. 150.

  Here, the image forming unit 110 for each color component includes a photosensitive drum 111 and a charging device 112 that charges the photosensitive drum 111 to a predetermined potential. The image forming unit 110 also includes a laser exposure device 113 that writes an electrostatic latent image on the charged photosensitive drum 111, and a developing device 114 that develops the electrostatic latent image on the photosensitive drum 111 by storing each color component toner. Have. Further, the image forming unit 110 includes a primary transfer roll 115 that transfers a toner image carried on the photosensitive drum 111 to the intermediate transfer belt 120, and a drum cleaner 116 that removes residues on the photosensitive drum 111 after the primary transfer. It has.

  The developing device 114 employs a two-component developing method using a so-called two-component developer having a toner and a carrier (hereinafter referred to as a developer). In each developing device 114 according to the present embodiment, a new developer is supplied into the developing device 114 at a predetermined timing, and so-called trickle is discharged to the outside as a waste developer as a result of surplus developer. The method is adopted. Thereby, it is possible to remove the carrier that has deteriorated with long-term use, and to secure the developing performance. For this reason, a developer cartridge 117 (specifically, 117K, 117Y, 117M, and the like) for supplying each color developer to the image forming units 110K, 110Y, 110M, and 110C is provided above the image forming unit 110. 117C).

  The intermediate transfer belt 120 is stretched around a plurality of (six in this embodiment) support rolls 121 to 126. Here, the support roll 121 is a drive roll for the intermediate transfer belt 120. The support rolls 122, 123, 126 are used as driven rolls. The support roll 124 is a correction roll (steering roll: disposed so as to be tiltable with one end in the axial direction as a fulcrum) that restricts meandering in a direction substantially perpendicular to the conveyance direction of the intermediate transfer belt 120. The support roll 125 is a backup roll of the secondary transfer device 130 described later. A belt cleaner 127 for removing residues on the intermediate transfer belt 120 after the secondary transfer is disposed on the intermediate transfer belt 120 with the drive roll 121 interposed therebetween. The intermediate transfer belt 120 is made of a resin such as polyimide, polyamide, polyester, polypropylene, polyethylene terephthalate, or various rubbers containing a suitable amount of a conductive agent such as carbon black.

  The secondary transfer device 130 includes a secondary transfer roll 131 arranged in pressure contact with the toner image carrying surface side of the intermediate transfer belt 120 and a counter electrode of the secondary transfer roll 131 arranged on the back side of the intermediate transfer belt 120. And a backup roll 125. Further, in the secondary transfer device 130, a power supply roll 132 that applies a secondary transfer bias having the same polarity as the charging polarity of the toner to the backup roll 125 is disposed in contact therewith.

  In addition, the paper transport system includes a paper tray 140 that stores paper P as a sheet, a pickup roll 141 that picks up the paper P accumulated in the paper tray 140 at a predetermined timing, and transports it to the transport path 144. A transport roll 142 for transporting the fed paper P is provided. In addition, a registration roll (registration roll) 143 for sending the paper P to the secondary transfer device 130 at a predetermined timing is disposed downstream of the transport roll 142 in the paper transport direction. A belt conveyance device 171 for conveying the paper P after the secondary transfer to the fixing device 150 is provided in the conveyance path 144 on the downstream side in the paper conveyance direction from the secondary transfer device 130.

  Furthermore, the fixing device 150 includes a heating roll 151 having a heating source therein and rotatably arranged. Further, the fixing device 150 includes a pressure roll 152 that is disposed in pressure contact with the heating roll 151 and is driven to rotate by the heating roll 151. Here, the heating roll 151 is controlled to be within a predetermined temperature range by a temperature adjusting unit (not shown).

  A discharge path 145 for transporting the paper P toward the upper side is provided downstream of the fixing device 150 in the paper transport direction. A plurality of transport rolls 146 are disposed in the discharge path 145. A paper discharge tray 101 for discharging the image-formed paper P is provided on the downstream side of the discharge path 145 and at the top of the main body 100.

  In the present embodiment, a paper reversing conveyance mechanism 160 is provided that reverses the sheet P that has been fixed on one side by the fixing device 150 and returns it to the secondary transfer device 130 when the duplex mode is selected. The sheet reverse conveyance mechanism 160 is provided with a branch path 161 that branches downward with respect to the discharge path 145 from the fixing device 150. The branch path 161 further extends a reverse path 162 downward, and this A return path 163 returning from the reverse path 162 to the transport path 144 before the registration roll 143 is connected in communication. In addition, an appropriate number of transport rolls 164 are provided on these paths as necessary. Further, a gate 165 is provided on the exit side of the fixing device 150 to switch the conveyance direction of the paper P after fixing to the discharge path 145 or the branch path 161, and the branch point between the branch path 161 and the return path 163 is before and after inversion. A gate 166 for switching the transport direction of the paper P is provided. Further, a switchback roll 167 is attached to the reversing path 162 so as to be rotatable forward and backward.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. Image data output from an image reading device (IIT) (not shown), a personal computer (PC) (not shown), or the like is input to an image forming apparatus as shown in FIG. In the image forming apparatus, after predetermined image processing is performed by an image processing apparatus (IPS) (not shown), an image forming operation is performed by the image forming unit 110 and the like. In the image processing apparatus (IPS), the input reflectance data is subjected to predetermined image editing such as shading correction, positional deviation correction, brightness / color space conversion, gamma correction, frame deletion, color editing, and moving editing. Image processing is performed. The image data subjected to the image processing is converted into color material gradation data of four colors of yellow (Y), magenta (M), cyan (C), and black (K), and is output to the laser exposure unit 113. .

  In the laser exposure unit 113, for example, an exposure beam emitted from a semiconductor laser is applied to each of the photosensitive drums 111 of the image forming units 110K, 110Y, 110M, and 110C according to the input color material gradation data. . In the photosensitive drum 111 of the image forming units 110K, 110Y, 110M, and 110C, the surface is charged by the charging device 112, and then the surface is scanned and exposed by the laser exposure unit 113, whereby an electrostatic latent image is formed. The formed electrostatic latent image is converted into yellow (Y), magenta (M), cyan (C), and black (K) colors by the developing devices 114 of the image forming units 110K, 110Y, 110M, and 110C. Developed as a toner image.

  The toner images formed on the photosensitive drums 111 of the image forming units 110K, 110Y, 110M, and 110C are transferred onto the intermediate transfer belt 120 at the primary transfer portion where the photosensitive drums 111 and the intermediate transfer belt 120 are in contact with each other. Transcribed. More specifically, in the primary transfer portion, a primary transfer bias is applied to the base material of the intermediate transfer belt 120 by the primary transfer roll 115 to reverse the toner charging polarity, and the unfixed toner image is transferred to the intermediate transfer belt 120. Primary transfer is performed by sequentially superimposing on the surface. The unfixed toner image primarily transferred in this way is conveyed to the secondary transfer device 130 as the intermediate transfer belt 120 rotates.

  On the other hand, in the paper transport system, the pickup roll 141 rotates in synchronization with the image formation timing, and the paper P is supplied from the paper tray 140. The paper P supplied by the pickup roll 141 is transported along the transport path 144 by the transport roll 142 and reaches the secondary transfer device 130. Before reaching the secondary transfer device 130, the paper P is temporarily stopped by the registration roll 143, and the registration roll 143 rotates in accordance with the movement timing of the intermediate transfer belt 120 carrying the toner image as described above. The position of the paper P and the position of the toner image are aligned.

  In the secondary transfer device 130, the secondary transfer roll 131 is pressed against the backup roll 125 via the intermediate transfer belt 120. At this time, the sheet P conveyed at the same timing is sandwiched between the intermediate transfer belt 120 and the secondary transfer roll 131. At this time, when a secondary transfer bias (negative polarity in the present embodiment) having the same polarity as the charging polarity of the toner is applied to the power supply roll 132, a transfer electric field using the secondary transfer roll 131 as a counter electrode is formed. . The unfixed toner image carried on the intermediate transfer belt 120 is electrostatically transferred to the paper P at the secondary transfer position pressed by the secondary transfer roll 131 and the backup roll 125.

  Thereafter, the sheet P on which the toner image is electrostatically transferred is peeled off from the intermediate transfer belt 120 and then conveyed to the fixing device 150 by the belt conveying device 171. The unfixed toner image on the paper P conveyed to the fixing device 150 is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 150. Thereafter, the paper P on which the fixed image is formed is directed toward the discharge path 156 by the gate 165, and the paper P is discharged to the paper discharge tray 101. On the other hand, after the transfer to the paper P is completed, the residual toner remaining on the intermediate transfer belt 120 is conveyed to a portion facing the belt cleaner 127 as the intermediate transfer belt 120 rotates, and is intermediated by the belt cleaner 127. It is removed from the transfer belt 120.

  Further, when forming images on both sides of the paper P, the leading edge of the paper P that has passed through the fixing device 150 enters the branch path 161 by the gate 165, and is conveyed to the reversing path 162 by the gate 166 after being transported through the branch path 161. enter in. In the reverse path 162, the paper P is once transported toward the back side by the switchback roll 167, and then temporarily stops at a timing immediately after the rear end of the paper P passes through the gate 166, and then switched back at a predetermined timing. By rotating the roll 167 in the reverse direction, it is conveyed in the reverse direction. At that time, the sheet P enters the return path 163 through the gate 166. The sheet P conveyed on the return path 163 is returned to the conveyance path 144 by the conveyance roll 164. At this time, the paper P is in a state where the front and back sides are reversed, unlike when the paper P was first in the transport path 144. This time, the unfixed toner image is electrostatically transferred onto the back surface of the paper P, fixed by the fixing device 150, and then discharged to the paper discharge tray 101 via the discharge path 145.

Here, FIG. 17A is a diagram for explaining the primary transfer system, and FIG. 17B is a diagram for explaining the secondary transfer system. Note that one primary transfer system will be described as an example, but the other three have the same configuration.
In FIG. 17A, the photosensitive drum 111 has a base material 111a made of, for example, cylindrical aluminum, and an organic photosensitive layer 111b formed on the outer peripheral surface of the base material 111a. . The charging device 112 is disposed in pressure contact with the photosensitive drum 111 so as to be rotatable. The charging roller 112a is driven to rotate as the photosensitive drum 111 rotates, and the charging roller 112a has a predetermined charging bias (this embodiment). In this embodiment, a charging power source 112b for applying negative polarity) is provided. Further, the primary transfer roll 115 is configured, for example, by covering the outer periphery of a conductive core material made of stainless steel with a conductive foam elastic body made of rubber. The resistance is appropriately adjusted by mixing a substance having ion conductivity (for example, NBR rubber) or a substance having electron conductivity (for example, carbon black) into the conductive foamed elastic body.

  A primary transfer current source 181 capable of adjusting the output current value is connected to the primary transfer roll 115, while the photosensitive drum 111 is grounded. The primary transfer current source 181 supplies positive primary transfer bias (primary transfer current) to the primary transfer roll 115 by performing constant current control. A primary transfer current flows from the primary transfer current source 181 through the primary transfer roll 115, the intermediate transfer belt 120, and the photosensitive drum 111, thereby forming a transfer electric field between the photosensitive drum 111 and the intermediate transfer belt 120. The toner image on the photosensitive drum 111 is transferred to the intermediate transfer belt 120. A primary transfer voltmeter 182 is connected between the primary transfer current source 181 and the photosensitive drum 111. The primary transfer voltmeter 182 measures a voltage generated between the primary transfer current source 181 and the photosensitive drum 111. In this embodiment, a transfer control unit 200 is provided that sets a primary transfer current value to be supplied from the primary transfer current source 181 based on the voltage measurement result by the primary transfer voltmeter 182.

  In the following description, the primary transfer current source 181 provided in the black image forming unit 110K is referred to as a K color current source 181K. The other colors are also referred to as Y color current source 181Y, M color current source 181M, and C color current source 181C, respectively. The primary transfer voltmeter 182 provided in the black image forming unit 110K is referred to as a K color voltmeter 182K. The other colors are also referred to as Y color voltmeter 182Y, M color voltmeter 182M, and C color voltmeter 182C, respectively.

  In FIG. 17B, the secondary transfer roll 131 is connected to a secondary transfer power supply 183 capable of adjusting the output current value, while the power supply roll 132 is grounded. The secondary transfer current source 183 supplies a positive secondary transfer bias (secondary transfer current) to the secondary transfer roll 131 by performing constant current control. Then, when a secondary transfer current flows from the secondary transfer current source 183 through the secondary transfer roll 131, the intermediate transfer belt 120, the backup roll 125, and the power supply roll 132, the sheet P (not shown) nipped from the intermediate transfer belt 120 A transfer electric field is formed between them, and the toner image on the intermediate transfer belt 120 is transferred onto the paper P. A secondary transfer voltmeter 184 is connected between the secondary transfer current source 183 and the power supply roll 132. The secondary transfer voltmeter 184 measures a voltage generated between the secondary transfer current source 183 and the power supply roll 132. In this embodiment, based on the voltage measurement result by the secondary transfer voltmeter 184, the secondary transfer current value supplied from the secondary transfer current source 183 in the transfer control unit 200 is similar to the primary transfer current value. It is set.

In the present embodiment, in the primary transfer system, the photosensitive drum 111 (111K, 111Y, 111M, 111C) functions as an image carrier and transfers a toner image to the intermediate transfer belt 120 which is a transfer target. At this time, the primary transfer roll 115 as a transfer member is indirectly disposed in pressure contact with the photosensitive drum 111 via the intermediate transfer belt 120. In the primary transfer system, the primary transfer current source 181 functions as a transfer power source, and the primary transfer voltmeter 182 functions as a voltage detection unit or a voltage measurement unit.
On the other hand, in the secondary transfer system, the intermediate transfer belt 120 functions as an image carrier and transfers a toner image onto a sheet P that is a transfer target. At this time, the secondary transfer roll 131 as a transfer member is placed in direct pressure contact with the intermediate transfer belt 120. In the secondary transfer system, the secondary transfer current source 183 functions as a transfer power source, and the secondary transfer voltmeter 184 functions as a voltage detection unit or a voltage measurement unit.

  FIG. 18 is a functional block diagram of the transfer control unit 200 described above. The transfer control unit 200 sets primary transfer current values output from the K color current source 181K, Y color current source 181Y, M color current source 181M, and C color current source 181C, and outputs from the secondary transfer current source 183. A transfer current value setting unit 201 that sets a secondary transfer current value is provided. Further, the transfer controller 200 outputs the first output from the primary transfer voltmeter 182 or the secondary transfer voltmeter 184 when the first current value I1 set by the transfer current value setting unit 201 is supplied. When the voltage value V1 and the second current value I2 (I2 ≠ I1) set by the transfer current value setting unit 201 are passed, the voltage is output from the primary transfer voltmeter 182 or the secondary transfer voltmeter 184. A voltage difference calculation unit 202 for calculating a voltage difference ΔV = V2−V1 with the second voltage value V2 is provided. Furthermore, the transfer control unit 200 includes a correction value storage unit 203 that stores a table in which the voltage difference ΔV obtained by the voltage difference calculation unit 202 is associated with the correction value k for the basic primary transfer current value Ia. The correction value storage unit 203 also stores a table in which the correction value j for the basic secondary transfer current value Ib is associated. Furthermore, the transfer control unit 200 reads the corresponding correction value k from the correction value storage unit 203 based on the voltage difference ΔV obtained by the voltage difference calculation unit 202, and corrects the correction value for the basic primary transfer current value Ia. A correction unit 204 is provided that calculates a primary transfer current value If (IfK, IfY, IfM, IfC) in consideration of k, and outputs it to the transfer current value setting unit 201. The correction unit 204 reads the corresponding correction value j from the correction value storage unit 203 based on the voltage difference ΔV obtained by the voltage difference calculation unit 202, and corrects the correction value k with respect to the basic secondary transfer current value Ib. Is obtained, and is output to the transfer current value setting unit 201.

  Next, the setting process of the primary transfer current value If and the secondary transfer current value Is in the present embodiment will be described with reference to the flowchart shown in FIG. In this process, the black primary transfer current value IfK, the yellow primary transfer current value IfY, the magenta primary transfer current value IfM, and the cyan primary transfer current value IfC are set for each color as the primary transfer current value If. It will be. This process is performed at the time of non-image formation, for example, before starting a job. At that time, the charging device 112 provided in each image forming unit 110 charges each photosensitive drum 111 in the same way as in normal image formation, and each developing device has the same as in normal image formation. A development bias is applied. This process is performed after a period of time during which the outputs of the primary transfer current source 181 and the secondary transfer current source 183 are stabilized.

  In this process, first, the primary transfer current value IfK is set in the black image forming unit 110K arranged on the most upstream side in the rotation direction of the intermediate transfer belt 120 (step 501), and then the yellow located downstream thereof. In the image forming unit 110Y, a primary transfer current value IfY is set (step 502). Then, the primary transfer current value IfM is set in the magenta image forming unit 110M further downstream (step 503), and then the primary transfer current value IfC is set in the cyan image forming unit 110C downstream thereof (step 503). Step 504). Then, after each primary transfer current value IfK, IfY, IfM, IfC is set, the secondary transfer current value Is is set (step 505), and a series of processes is completed.

Here, the setting method itself of each primary transfer current value IfK, IfY, IfM, IfC is basically the same as that described in the first embodiment. However, in the present embodiment, for example, when setting the primary transfer current value IfY of the yellow image forming unit 110Y, it is set to be slightly larger than the primary transfer current value IfK of the previously set black image forming unit. ing. The same applies to the other image forming units, and the primary transfer current value has a relationship of IfK <IfY <IfM <IfC.
The method for setting the secondary transfer current value Is is basically the same as that described in the first embodiment. However, in the present embodiment, the secondary transfer current value Is is set in consideration of the information of the primary transfer current values IfK, IfY, IfM, and IfC that have already been obtained.

In the case of a tandem type image forming apparatus, if the primary transfer current values are set differently in each image forming unit 110, the toner that has been transferred to the intermediate transfer belt 120 due to insufficient transfer in the downstream image forming unit. There is a risk of reverse transfer to another image forming unit. In contrast, in the present embodiment, since the primary transfer current value is set while referring to the primary transfer current value in the image forming unit on the upstream side of itself, occurrence of such a problem is prevented. be able to.
Further, in the case of an intermediate transfer type image forming apparatus, if the primary transfer current value If and the secondary transfer current value Is are set without relevance, there is a possibility that a transfer failure may occur during the secondary transfer. is there. In contrast, in the present embodiment, since the secondary transfer current value is set while referring to the primary transfer current value, it is possible to prevent the occurrence of such a problem.

  In the first to fifth embodiments, the image forming apparatus using the intermediate transfer belt 20 (120) has been described as an example. However, the present invention is not limited to this, and the image forming apparatus does not have an intermediate transfer member. Can also be applied. Further, the present invention can be applied to an image forming apparatus using a transfer belt instead of the transfer roll.

1 is a diagram illustrating an image forming apparatus to which Embodiments 1 to 4 are applied. It is a figure for demonstrating the structure of a primary transfer system. FIG. 3 is a functional block diagram of a transfer control unit according to the first embodiment. 5 is a flowchart showing a transfer current value setting process in the first embodiment. It is a figure which shows an example of the table stored in a correction value storage part. FIG. 6 is a diagram illustrating IV characteristics when various primary transfer rolls and intermediate transfer belts are combined with the same photosensitive drum. FIG. 6 is a diagram showing IV characteristics when a photosensitive drum having a different photosensitive layer thickness is combined with the same primary transfer roll and intermediate transfer belt. FIG. 5 is a diagram showing IV characteristics when various primary transfer rolls and intermediate transfer belts are combined with the same photosensitive drum in a low temperature and low humidity environment. It is a figure which shows the IV characteristic obtained by experiment. 6 is a functional block diagram of a transfer control unit in Embodiment 2. FIG. 10 is a flowchart illustrating a transfer current value setting process according to the second embodiment. FIG. 10 is a functional block diagram of a transfer control unit according to Embodiment 3. 10 is a flowchart illustrating a transfer current value setting process according to the third embodiment. FIG. 10 is a functional block diagram of a transfer control unit in a fourth embodiment. 10 is a flowchart illustrating a process for setting a charging bias and determining a life of a photosensitive drum in the fourth embodiment. FIG. 10 is a diagram illustrating an image forming apparatus to which Embodiment 5 is applied. (a) is a diagram showing a primary transfer system, and (b) is a diagram showing a secondary transfer system. FIG. 10 is a functional block diagram of a transfer control unit in a fifth embodiment. 10 is a flowchart showing a transfer current value setting process in the fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Photosensitive drum, 11a ... Base material, 11b ... Photosensitive layer, 12 ... Charging device, 12a ... Charging roll, 12b ... Charging power source, 15 ... Primary transfer roll, 20 ... Intermediate transfer belt, 24 ... Backup roll, 30 ... Secondary transfer device 31 ... Secondary transfer roll 32 ... Power feeding roll 50 ... Fixing device 61 ... Primary transfer current source 62 ... Primary transfer voltmeter 63 ... UI 70 ... Transfer controller 71 ... Transfer current Value setting unit 72 ... Voltage difference calculation unit 73 ... Correction value storage unit 74 ... Correction unit 75 ... System resistance calculation unit 76 ... Primary regression analysis unit 77 ... Charge setting unit 81 ... Temperature sensor 82 ... Humidity sensor, 110 (110K, 110Y, 110M, 110C) ... image forming unit, 111 ... photosensitive drum, 111a ... substrate, 111b ... photosensitive layer, 112 ... charging device, 112a ... charge roll, 11 b: Charging power source, 115 ... Primary transfer roll, 120 ... Intermediate transfer belt, 125 ... Backup roll, 130 ... Secondary transfer device, 131 ... Secondary transfer roll, 132 ... Feeding roll, 150 ... Fixing device, 181 ... Primary transfer Current source 182 ... Primary transfer voltmeter, 183 ... Secondary transfer current source, 184 ... Secondary transfer voltmeter, 200 ... Transfer control unit, 201 ... Transfer current value setting unit, 202 ... Voltage difference calculation unit, 203 ... Correction Value storage unit, 204 ... correction unit, I1 ... first current value, I2 ... second current value, V1 ... first voltage value, V2 ... second voltage value, R1 ... first system resistance, R2 ... second system resistance, R ... system resistance, A ... offset potential

Claims (11)

An image carrier on which a toner image is carried;
A transfer member that is directly or indirectly pressed against the image carrier and that transfers a toner image on the image carrier to a transfer body by supplying a transfer current;
Voltage detecting means for detecting a voltage applied to the image carrier and the transfer member;
The first voltage value detected by the voltage detection means when a current is passed through the transfer member at a first current value and the voltage when a current is passed through the transfer member at a second current value. An image forming apparatus including: a setting unit that sets a transfer parameter related to a transfer operation based on a second voltage value detected by the detection unit.   The image forming apparatus according to claim 1, wherein the transfer parameter set by the setting unit is a transfer current value supplied to the transfer member.   The setting unit obtains a voltage difference between the first voltage value and the second voltage value detected by the voltage detection unit, and sets the transfer current value according to the voltage difference. The image forming apparatus according to claim 2.   The setting means includes a first system resistance obtained from a first voltage value detected by the voltage detection means and a first current value passed when the first voltage value is detected; The second system resistance obtained from the second voltage value measured by the voltage detection means and the second current value passed when the second voltage value is detected, The image forming apparatus according to claim 2, wherein a transfer current value is set.   The setting means performs a linear regression analysis from the first current value, the first voltage value, the second current value, and the second voltage value, and has a slope obtained by the primary regression analysis. 3. The image forming apparatus according to claim 2, wherein the transfer current value is set accordingly.   The image forming apparatus according to claim 1, wherein the transfer parameter set by the setting unit is a magnitude of a charging bias with respect to the image carrier. An image carrier on which a toner image is carried;
A transfer member that is directly or indirectly pressed against the image carrier;
A transfer power supply for supplying a transfer current to the transfer member;
A voltage measuring unit for measuring a voltage generated between the image carrier and the charging member;
The first voltage value measured by the voltage measuring unit when a current is passed through the transfer member at a first current value and the voltage when a current is passed through the transfer member at a second current value. An image forming apparatus including: a determination unit configured to determine a lifetime of the image carrier based on a second voltage value measured by the measurement unit;   The determination unit performs a primary regression analysis from the relationship between the plurality of voltages and the corresponding plurality of currents, and determines the lifetime of the image carrier based on an intercept obtained by the primary regression analysis. The image forming apparatus according to claim 7. The image carrier comprises a photoreceptor having a photosensitive layer on the surface,
The image forming apparatus according to claim 8, wherein the determination unit estimates a film thickness of the photosensitive layer based on the intercept. A method for setting a transfer current value to be supplied to a transfer unit that transfers a toner image formed on an image carrier to a recording material by contact transfer,
Passing a current at a first current value through the transfer section;
Measuring a first voltage value generated in the transfer portion when a current is passed at the first current value;
Passing a current at a second current value through the transfer portion;
Measuring a second voltage value generated in the transfer portion when a current is passed at the second current value;
Determining a transfer current value based on the first current value, the first voltage value, the second current value, and the second voltage value. In the step of determining the transfer current value,
A first regression analysis is performed from the first current value, the first voltage value, the second current value, and the second voltage value, and the transfer current is determined according to the slope obtained by the first regression analysis. The transfer current value setting method according to claim 10, wherein the value is determined.

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