JP2002116641A - Toner image transfer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a toner image transfer device that prevents a sudden transfer bias change resulting from a sudden temperature rise in an image forming device and therefore prevents a failure in transfer of a toner image to a recording sheet, even in the case where only a resistance of a transfer roll is measured and the magnitude of a transfer bias to be applied is controlled. SOLUTION: The toner image transfer device is composed of the transfer roll 31 which transfers a toner image from a photoreceptor drum 27 to the recording sheet P, a transfer bias power source which applies a transfer bias to the transfer roll 31, and a roll resistance monitor means which monitors a resistance of the transfer roll 31 as required. The toner image transfer device is also composed of a history holding means which stores the monitored resistance of the transfer roll 31, and an application bias determination means which controls the transfer bias power source based on the resistance of the transfer roll 31, monitored by the roll resistance monitor means most recently, and based on the previous resistance stored in the history holding means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, which transfers a toner image formed on an image carrier such as a photosensitive drum to an image receiving body such as a recording sheet. More particularly, the present invention relates to an improvement in a toner image transfer device that transfers a toner image while applying a transfer bias to a transfer roll disposed opposite to the image carrier.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a laser beam printer using an electrophotographic system, a toner image corresponding to image information is formed on a photosensitive drum and then transferred to a recording sheet. A recorded image is formed. For example, in a laser beam printer, first, the surface of the photosensitive drum is charged to a predetermined background potential, and then the surface of the photosensitive drum is exposed to a laser beam modulated by image information to form an electrostatic latent image. I have. Next, after developing the electrostatic latent image with toner to form a toner image as a visible image, the toner image is transferred to a recording sheet, and the recording sheet after the transfer of the toner image is heated and fixed by a fixing device. The recording image has been obtained with.

In the process of forming such a recorded image,
As a method of transferring the toner image to the recording sheet, a method of directly transferring the toner image from the photosensitive drum to the recording sheet, or a method of first transferring the toner image to an endless film-like intermediate transfer belt and then transferring the toner image to the recording sheet For example, a method of secondary transfer is used. Of these, the transfer method using an intermediate transfer belt is most suitable for forming a full-color image that requires superposition of toner images of a plurality of colors, and is used in a color copying machine or the like.

In any of the transfer methods, a transfer member such as a transfer roll is disposed at a position facing an image carrier such as a photosensitive drum or an intermediate transfer member with a recording sheet interposed therebetween. The toner image is electrostatically transferred to the surface of the recording sheet by applying a charge having a polarity opposite to that of the toner to the back surface of the recording sheet. For example, when the charge polarity of the toner is minus (-), a plus (+) transfer bias is applied to the transfer member disposed on the back surface of the recording sheet, and plus (+) charge is applied to the back surface of the recording sheet. Will be given.

Factors that affect the electrostatic transfer of toner images include environmental factors such as temperature and humidity. Generally, the resistance value of the transfer roll tends to increase in a low-temperature and low-humidity environment, and to decrease in a high-temperature and high-humidity environment. The same applies to the resistance value of the recording sheet. Therefore, if these influential factors fluctuate, even if a transfer bias of the same magnitude is applied, a sufficient transfer electric field cannot be generated between the image carrier and the recording sheet depending on these influential factors, The transfer efficiency is remarkably deteriorated.

For this reason, in the conventional image forming apparatus, the resistance value of the transfer roll should be measured at a predetermined timing after the main power of the apparatus is turned on, and the measured value should be applied to the transfer roll. There has been proposed one configured to determine an optimum transfer bias. Specifically, prior to the start of a print job corresponding to the user's print support, a constant current is supplied or a constant voltage is applied to the transfer roll, and a voltage value or a current value output at that time is changed. In addition to the measurement, the resistance value of the transfer roll is estimated from the measured value, and an optimum transfer bias is selected by referring to a transfer bias setting table stored in advance.

[0007]

However, when the resistance value of the transfer roll is directly measured and the transfer bias is determined only from the measurement result as described above, the resistance value of the transfer roll with respect to the change of the influencing factors described above. Is considered, but the change in the resistance value of the recording sheet is not taken into account. For example, if the print job immediately after turning on the main power is continuous printing on a large number of recording sheets, the temperature in the apparatus, which was relatively low when the main power was turned on, rises rapidly due to heat radiation of the fixing device. As a result, the temperature of the transfer roll tends to increase as the temperature in the apparatus increases. In a small printer or the like, since the transfer roll and the fixing device are relatively close to each other, such a temperature rise of the transfer roll is remarkable. For this reason, when the resistance value of the transfer roll is measured after the end of the first print job, the resistance value is extremely lower than when the main power is turned on, and the transfer bias of the transfer bias determined based only on this measured value is determined. The magnitude must be significantly lower than the transfer bias determined before the first print job.

On the other hand, even if the temperature in the image forming apparatus rises rapidly due to continuous printing, the image forming apparatus is used for printing because the room temperature or the like in the room where the apparatus is installed does not suddenly change. The temperature of the recording sheet itself and the amount of moisture absorption do not change much, and the temperature of the recording sheet already set in the apparatus changes only moderately. When a new recording sheet is supplied to the image forming apparatus, the supplied recording sheet is completely independent of the temperature inside the apparatus. That is, even when the resistance value of the transfer roll changes abruptly due to a change in the temperature inside the apparatus, it is considered that the resistance value itself of the recording sheet does not significantly change.

Therefore, if the transfer bias of the transfer roll is determined based only on the transfer roll resistance measured before the start of the print job, the magnitude of the transfer bias relative to the resistance of the recording sheet is reduced. There is a problem that a shortage may occur and transfer defects such as white spots may occur in the transferred image.

The present invention has been made in view of such a problem, and an object thereof is to control the magnitude of a transfer bias to be applied by measuring only the resistance value of a transfer roll. However, it is possible to provide a toner image transfer device capable of avoiding a sudden change in transfer bias due to a sudden rise in temperature in the image forming apparatus and avoiding poor transfer of a toner image to a recording sheet. It is in.

[0011]

That is, the present invention is used in an image forming apparatus for forming a recorded image by transferring a toner image formed on an image carrier to an image receiving body based on image information. A transfer roll that is disposed opposite to the image bearing member and transfers the toner image from the image bearing member to the image receiving member; and a transfer bias power supply that applies a transfer bias to the transfer roll. Roll resistance monitoring means for monitoring the resistance value of the transfer roll, if necessary, history holding means for storing the resistance value of the transfer roll which has been already monitored, and newly monitored by the roll resistance monitoring means. Determining an applied bias for controlling the transfer bias power supply based on both the resistance value of the transfer roll and the previous resistance value stored by the history holding unit. It is characterized in that a stage.

Also in the present invention, the roll resistance monitoring means monitors the resistance value of the transfer roll as required, and the applied bias determination means determines the magnitude of the transfer bias to be applied to the transfer roll based on the monitored value. This is no different from the prior art. However, a history holding unit is provided to store the resistance value of the transfer roll monitored in the past, and when the resistance value of the transfer roll is newly monitored, the new monitor resistance value is stored as the previously stored resistance value. , A new transfer bias to be applied to the transfer roll is determined based on these values.

When the transfer bias is determined on the basis of both the latest monitor resistance value and the previous monitor resistance value, the latest monitor resistance value rapidly changes with respect to the previous monitor resistance value. Even if it fluctuates, the transfer bias can be determined taking into account not only the former value but also the latter value, so the transfer bias fluctuates rapidly based only on the resistance value of the transfer roll. Can be avoided. For example, when only the resistance value of the transfer roll sharply decreases and the resistance value of the recording sheet does not change much, when the transfer bias is greatly reduced,
As described above, the transfer bias is insufficient with respect to the resistance value of the recording sheet, and the transfer failure is likely to occur. However, according to the present invention, the fluctuation width of the transfer bias can be automatically controlled by also referring to the previous monitor resistance value. Therefore, even when the resistance value of the transfer roll fluctuates rapidly, it is possible to prevent the transfer bias from becoming insufficient and to avoid the occurrence of transfer failure as much as possible.

In such a technical means, the history holding means may be constituted so as to store only the immediately preceding monitor resistance value, or to store the detected resistance values of several past times. You may comprise. As an example of the former, assuming that a new detection resistance value is Xn and the stored one-time detection resistance value is Xn−1, the transfer bias is calculated using the following equations (1) and (2). The virtual resistance value X for reference can be calculated. Note that a and b in the equation are constants.

X = (aX _n-1 × bX _n ) ^-ab (1)

X = (aX _n−1 + bX _n ) / (a + b) (2)

As an example of the latter, the detected resistance value stored first is X1, and the detected resistance value stored mth is X
m, and when the new detection resistance value is Xn, the virtual resistance value X for referring to the transfer bias can be calculated using the following equation (3). Again, a in the equation is a constant, and m <n.

[0018] _{X = (a m X m +} a m + 1 X m + 1 + ... + a n X n) / (a m + a m + 1 + ...... + a n) ... (3)

When the transfer bias is determined based on both the latest detection resistance value and the previous detection resistance value,
Weighting of these two values can be performed freely. That is, the transfer bias may be determined with emphasis on the latest detected resistance value, or the transfer bias may be determined with emphasis on the previous transfer bias. The greater the weight of the previous transfer bias, the smaller the change width of the transfer bias, and the more slowly the transfer bias changes for each print job. More specifically, by changing the magnitude of the constant a or b in the above formula, it is possible to freely weight the latest detected resistance value and the previous detected resistance value.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a toner image transfer device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an example of a laser beam printer that transfers a toner image from a photosensitive drum to a recording sheet using the toner image transfer device of the present invention. In FIG. 1, reference numeral 20 denotes a printer main body. Inside the printer main body 20, an image processing unit 21 for performing predetermined image processing on image information input from the outside, and the image processing unit An image output unit 22 that outputs an image based on image information on which predetermined image processing has been performed by the image processing unit 21 is provided. The image processing unit 21 in the printer main body 20 is provided with a host computer such as a personal computer (not shown), image information sent via a communication line such as a telephone line or a LAN, or an image reading device (not shown). Read image information and the like are input.

An image output unit 22 in the printer body 20
The ROS 23 (R) performs image exposure based on image information on which predetermined image processing has been performed by the image processing unit 21.
The ROS 23 performs image exposure using a laser beam LB in accordance with image information.

In the ROS 23, a laser beam LB is emitted from a semiconductor laser (not shown) according to gradation data of image information. The laser beam LB emitted from the semiconductor laser is deflected and scanned by the rotary polygon mirror 24, and is scanned on the photosensitive drum 27 as an electrostatic latent image carrier via the reflection mirrors 25 and 26.

The ROS 23 causes the laser beam LB
As the photosensitive drum 27 to be scanned and exposed, for example,
A photoconductor using an organic photoconductive substance (OPC) is used, and the photoconductor drum 27 is driven to rotate at a predetermined speed in a direction indicated by an arrow by a driving unit (not shown). . After the surface of the photosensitive drum 27 is charged to a predetermined potential by a charging roll (not shown), an electrostatic latent image is formed by scanning and exposing the laser beam LB in accordance with image information. The electrostatic latent image formed on the photosensitive drum 27 is
To form a toner image.

The toner image formed on the photosensitive drum 27 is transferred onto a recording sheet as an image receiving body by a transfer roll 31 arranged so as to be in contact with the photosensitive drum 27, and the toner image is formed on the recording sheet. The recording sheet on which is transferred is separated from the photoreceptor drum 27 by being neutralized by a separation charger 33 composed of a needle electrode. An AC voltage or an AC voltage obtained by superimposing a DC voltage is applied to the separation charger 27 including the needle-shaped electrodes.
The recording sheet is fed by a feed roll 35 from a feed cassette 34 arranged at a lower portion in the printer body 20. The fed recording sheet is transported by the transport roll 3
6 and the resist roll 37 convey the photosensitive drum 27 to the surface thereof.

The printer body 20 is provided with a manual feed tray 38 on the right side surface. The manual feed tray 38 is rotated clockwise to a substantially horizontal position and stopped, whereby the manual feed tray 38 is stopped. From, O
Transfer media of different materials and sizes, such as HP sheets and postcards, can also be fed through the feed roller 39 having a large diameter.

As described above, the recording sheet on which the toner image has been transferred from the photosensitive drum 27 is discharged from the surface of the photosensitive drum 27 by being discharged by the separation charger 33 composed of a needle-like electrode. Thereafter, the sheet is transported to the fixing device 40. The recording sheet conveyed to the fixing device 40 is
After the toner image is fixed on the recording sheet by heat and pressure by the heating roll 40a and the pressure roll 40b, the toner image is discharged by a discharge roll 42 onto a discharge tray 43 provided at an upper portion of the printer main body 20. The image forming process ends.

When images are printed on both sides of the recording sheet, the recording sheet on which the image is printed on one side is not discharged onto the discharge tray 43 as it is, but the discharge roll 42 is rotated in the reverse direction to form a plurality of sheets. The recording sheet is guided to a double-sided unit 47 provided with a transport roll 46, and is again transported to the transfer position of the photosensitive drum 27 in a state where the recording sheet is turned upside down.

FIG. 2 is a block diagram showing the configuration of a transfer section for transferring the toner image T from the photosensitive drum 27 to the recording sheet P. The photosensitive drum 27 with the recording sheet P interposed therebetween
The transfer roller 31 is formed by covering the periphery of the metal shaft 10 with urethane foam rubber 11 and impregnating the foam urethane rubber 11 with an ionic conductive agent. A voltage is applied and a predetermined current is supplied. Accordingly, when a transfer bias having a polarity opposite to that of the toner image T is applied to the transfer roll 31 to apply a charge to the back surface of the recording sheet P, a transfer electric field is formed between the recording sheet P and the photosensitive drum 27. Then, the toner image T held on the photosensitive drum 27 is electrostatically transferred to the recording sheet P.

In order to always transfer the toner image T onto the recording sheet P satisfactorily with a constant transfer efficiency, the transfer roll 3
It is necessary to form a transfer electric field having a certain strength between the transfer roller 31 and the photosensitive drum 27.
Resistance value greatly varies depending on the environment. For example, the resistance value of a high-temperature and high-humidity environment (28 ° C., 85% RH environment) and
(0 ° C., 15% RH environment) shows a fluctuation of about 10 ⁶ to 10 ¹⁰ Ω. As described above, when the resistance value of the transfer roll 31 changes under a constant transfer bias, the transfer electric field strength also changes, which affects the transfer efficiency of the toner image T.

In the printer of this embodiment, in order to always obtain a good transfer toner image irrespective of such a change in the resistance value of the transfer roll 31, the print job is not started when the main power of the printer is turned on or when the print job is started. In the meantime,
A constant voltage is applied to the transfer roll 31 from the transfer bias power supply 12, and an output current value between the transfer roll 31 and the photosensitive drum 27 is measured by the ammeter 13, and the measured value is referred to. The resistance value of the transfer roll 31 at that time is monitored (hereinafter, such a procedure for monitoring the resistance value of the transfer roll 31 is referred to as “transfer roll resistance monitor”). That is, the ammeter 13 corresponds to the roll resistance monitoring means in the present invention. Here, the resistance value of the transfer roll 31 is monitored by applying a constant voltage to the transfer roll 31, but a constant current is applied to the transfer roll 31, and the output voltage value at that time is applied. Is measured, the transfer roll 31
May be configured to monitor the resistance value.

Then, based on the monitored resistance value, the applied bias determination means 14 determines the transfer bias having the optimum magnitude to be used in the subsequent print job, and
This value is set in the transfer bias power supply 12, and the transfer of the toner image T from the photosensitive drum 27 to the recording sheet P is performed with this transfer bias. The applied bias determining means 14 is an MCU (Microprogram Control).
The transfer table for setting an optimum transfer bias voltage according to the resistance value of the transfer roll 31 is stored in advance in the built-in ROM. Therefore,
The applied bias determination means 14 monitors the resistance value of the transfer roll 31 from the measured current value, and refers to a transfer table in the ROM based on the monitored resistance value, thereby transferring the transfer data having the optimum size at that time. Deriving bias.
If the output current value is measured by the ammeter 13, it is considered that the resistance value of the transfer roll 31 is monitored.
The transfer table stored in the ROM is not actually created based on the relationship between the resistance value of the transfer roll 31 and the transfer bias, and is configured to directly derive the transfer bias from the measured output current value.

On the other hand, the transfer roll 31 and the photosensitive drum 27
And the intensity of the transfer electric field formed between the transfer rolls 31
Of the recording sheet P passing between the transfer roll 31 and the photosensitive drum 27, the change is not only affected by the variation in the resistance value of the recording sheet P. The resistance value of the recording sheet P is greatly affected by the moisture content, and the resistance value of the recording sheet P changes when the temperature or humidity in the room where the printer is installed fluctuates. However, the transfer roll 31
Is easily affected by temperature and humidity fluctuations. In the printer of this embodiment, the resistance value of the transfer roll 31 is monitored during a print job or the like. The effect on the That is, originally, the correction of the transfer bias based on the change in the resistance value of the transfer roll 31 should be effective for the change in the resistance value of the recording sheet P.

However, in the case where continuous printing is performed immediately after the main power of the printer is turned on, the internal temperature, which has been cooled down to about room temperature, rapidly rises due to the heat radiation of the fixing device 40. With this, the transfer roll 3
The temperature of 1 also rises sharply. In particular, in the case of a small-sized printer, the fixing device 40 and the transfer roll 31 are close to each other in the apparatus, and the temperature of the transfer roll 31 is significantly increased accordingly. FIG. 3 shows the result of measuring the in-machine temperature in a state where continuous printing is performed after the main power is turned on. The solid line (lower graph) shows the result measured near the transfer roll 31 and the broken line ( The upper graph shows the result measured at the upper part of the print unit 48 including the photosensitive drum 27 and the developing roll 30. As is apparent from this result, when continuous printing is started immediately after the main power is turned on, the temperature of the transfer roll 31 which was about room temperature rises about 10 ° C. after about 30 minutes. Therefore, immediately after the end of the first continuous print job, the transfer roll 31
When the resistance value of the transfer roller 31 is monitored, the resistance value of the transfer roll 31 rapidly decreases. When the magnitude of the transfer bias is determined based only on the monitored resistance value of the transfer roll 31, The job will use an extremely small transfer bias for the first print job. On the other hand, even when the internal temperature rises rapidly, the temperature and humidity of the recording sheet P do not change significantly from the time when the main power is turned on. The temperature fluctuation in the sheet P is far apart. For this reason, the latest transfer roll 31 monitored between print jobs
When the transfer bias is changed based only on the resistance value of
As a result, the magnitude of the transfer bias becomes insufficient with respect to the resistance value of the recording sheet, resulting in occurrence of transfer failure such as transfer omission. In the graph of FIG. 3, there is a time zone in which the temperature is sharply reduced. This is because the cover of the printer was opened due to the jam of the recording sheet. The rise and then a gradual decrease are due to the printer being stopped by the end of the print job.

Based on such a viewpoint, in the printer of the present embodiment, the magnitude of the transfer bias is determined in consideration of the history of the change in the resistance value of the transfer roll 31, and the transfer bias is determined by the resistance of the transfer roll 31. This prevents the value from fluctuating greatly due to a sudden change in the value. Specifically, a non-volatile memory 15 (corresponding to the history holding means of the present invention) for storing the resistance value of the transfer roll 31 used when reading the transfer bias from the transfer table is provided, and the transfer bias is determined next time. In this case, a new transfer bias is determined with reference to the stored resistance value. FIG. 4 is a conceptual diagram showing a method for determining such a transfer bias. For example, immediately after the main power of the printer is turned on, the transfer roll resistance is monitored, the transfer bias is determined from the monitor resistance value, and the first print job is performed using the determined transfer bias. It is stored in the nonvolatile memory 15. And
If the transfer roll resistance monitor is performed before the next print job, the correction monitor value is calculated by considering both the monitor resistance value at that time and the previous monitor resistance value stored in the nonvolatile memory 15. Then, the optimum transfer bias is read from the transfer table using the correction monitor value.
The determined correction monitor value is stored in the nonvolatile memory 15 as the monitor value at that time. Thereafter, every time the transfer roll resistance monitoring is performed, the correction monitor value is determined in the same procedure, and the optimum transfer bias is read from the transfer table.

The correction monitor value is determined by the following equation. X = (aX _n-1 + bX _n ) / (a + b) where X _n is the monitor resistance value of the transfer roll 31 newly monitored by the roll resistance monitoring means 13, X
_n-1 is the previous monitor resistance value stored in the history holding means, and a and b are constants for weighting the new monitor resistance value and the previous monitor resistance value. If it is desired to suppress a change in the magnitude of the transfer bias due to a change in the monitor resistance value, b> a, and if it is important to reflect the latest monitor resistance value on the transfer bais, conversely, b <A. In this embodiment, emphasis is placed on the previous monitor value stored in the history holding means, and a = 10 and b =
A correction monitor value is calculated as 1, and the transfer bias is read from the correction monitor value.

FIG. 5 shows constants a = 0, a = 1, a = 5, a
10 is a graph showing the results of examining the fluctuation of the correction monitor value after turning on the printer power for each value of = 10. The horizontal axis indicates the number of prints after the power is turned on, and the vertical axis indicates the correction monitor value. a = 0 means that no correction is performed on the monitor resistance value, and the monitor value in this case shows a fluctuation substantially similar to the temperature fluctuation of the transfer roll shown in FIG.
Further, it is understood that as the value of the constant a increases, the fluctuation of the correction monitor value becomes gentler without being dragged by the temperature fluctuation of the transfer roll.

Therefore, if the correction monitor value is determined while taking the previous monitor value into consideration as in the present embodiment, the temperature of the transfer roll 31 itself similarly increases with the rapid change of the internal temperature. Even if the correction monitor value changes, it is possible to prevent the correction monitor value itself from suddenly changing. This can prevent the transfer bias from changing only by the temperature change of the transfer roll 31 irrespective of the temperature change of the recording sheet P and the water content change. Is determined, and it is possible to prevent the transfer efficiency of the toner image from decreasing.

The determination of the transfer bias using the correction monitor value as in this embodiment can be said to be effective when the state of the temperature change of the transfer roll 31 and the state of the temperature change of the recording sheet P do not match. . Therefore, if the main power supply of the printer is O
When the temperature of both the transfer roll 31 and the recording sheet P has dropped to about room temperature after the FF has been performed for a long time, it is not necessary to correct the monitor resistance value as in the present embodiment. Therefore, when the main power is turned off, it is preferable to clear the previous monitor resistance value of the transfer roll 31 stored in the nonvolatile memory 15.

However, even if the main power supply is turned off, if the transfer roll 31 is turned on again before the transfer roll 31 is completely cooled, the temperature between the transfer roll 31 and the temperature of the recording sheet P may be reduced. Therefore, the monitor resistance value of the transfer roll 31 needs to be corrected. Therefore, even when the main power is turned off,
It is preferable that the monitor resistance value of the previous transfer roll 31 stored in the nonvolatile memory 15 be cleared only when it is determined that the temperature in the printer has dropped below the predetermined temperature. Whether or not the temperature in the printer has dropped to a predetermined temperature or less may be determined by, for example, providing a dedicated temperature sensor in the printer. The temperature at which the surface temperature of the heating roll 40a of the fixing device 40 is measured is determined. Using sensors,
When the surface temperature of the heating roll 40a falls below a certain level, the content of the nonvolatile memory 15 may be cleared.

After the last print job is completed, if a predetermined time or more has elapsed while the main power supply is kept ON, and the transfer of the toner image has never been performed during that time, the temperature change of the transfer roll 31 may occur. Is stabilized, and it is considered that the same change as the temperature change of the recording sheet P occurs. Therefore, it is not necessary to correct the monitor resistance value of the transfer roll 31.
Even in such a case, the contents of the nonvolatile memory 15 can be cleared.

[0041]

As described above, according to the toner image transfer apparatus of the present invention, the history holding means is provided, the resistance value of the transfer roll monitored in the past is stored, and the transfer roll is newly added. When the resistance value is monitored, both the new monitor resistance value and the stored previous monitor resistance value are referred to, and a new transfer bias to be applied to the transfer roll is determined based on these values. Therefore, even when only the resistance value of the transfer roll is measured to control the magnitude of the transfer bias to be applied, even if the transfer bias is sharply increased due to a sudden temperature rise in the image forming apparatus, etc. Fluctuations can be avoided, and defective transfer of the toner image to the recording sheet can be avoided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a laser beam printer to which the present invention has been applied.

FIG. 2 is a block diagram illustrating a configuration of a toner image transfer device of the present invention.

FIG. 3 is a graph showing a temperature rise of a transfer roll immediately after turning on a printer main power.

FIG. 4 is a conceptual diagram illustrating a method of correcting a monitor resistance value of a transfer roll according to the present invention.

FIG. 5 is a graph showing a change in monitor resistance value of a transfer roll corrected by the present invention.

[Explanation of symbols]

27: photosensitive drum, 31: transfer roll, P: recording sheet, T: toner image body

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA01 DA11 DA38 DE01 EA03 EA15 EC06 EC09 EE08 EF17 EH03 JC03 ZA01 2H032 AA05 BA23 CA02 CA12

Claims (5)

[Claims] 1. A toner image transfer apparatus used in an image forming apparatus for forming a recorded image by transferring a toner image formed on an image carrier to an image receiving body based on image information, A transfer roll that is disposed opposite to the image carrier and transfers the toner image from the image carrier to the image receiver; a transfer bias power supply that applies a transfer bias to the transfer roll; Roll resistance monitoring means for monitoring the resistance value, history holding means for storing the resistance value of the transfer roll already monitored, and resistance value of the transfer roll newly monitored by the roll resistance monitoring means and the history holding And a bias applying means for controlling the transfer bias power supply based on both the previous resistance value stored by the means. Image transfer device. 2. The toner image transfer device according to claim 1, wherein the contents stored in said history holding means are cleared when the main power supply of said image forming apparatus is turned off. 3. The storage device according to claim 1, wherein when the main power of the image forming apparatus is turned off and the temperature in the image forming apparatus becomes lower than a predetermined temperature, the stored contents of the history holding unit are cleared. 3. The toner image transfer device according to item 2. 4. When the transfer of the next toner image is not performed until a predetermined time has passed since the last transfer of the toner image to the image receiving member, the stored contents of the history holding means are cleared. The toner image transfer device according to claim 1, wherein: 5. The monitor resistance value of the transfer roll newly monitored by the roll resistance monitor means is X _n , and the previous monitor resistance value stored in the history holding means is X _n-1.
X = (aX _n-1 + bX _n ) / (a + b) [a, b:
The toner image transfer device according to claim 1, wherein the applied bias determination means controls the transfer bias power supply based on the correction monitor value X determined by the following equation: