JP2001154513A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of applying the fine difference of the surface resistivity of a transfer carrying means such as a transfer belt to the control of a transfer current and performing the feedback control of the transfer current. SOLUTION: As a bias impression means to be in contact with the surface of the transfer belt 6, a roller 20 serving also as a cleaning roller for cleaning the surface of the transfer belt 6 is provided for applying a high voltage. The high voltage is applied from the roller 20 and a current flowing through the surface layer of the transfer belt 6 to a photosensitive body 3 is detected. Thus, the separate measurement of resistance as the entire transfer carrying means and the surface resistance is performed, the surface resistivity on a real machine is detected, the transfer current is set at an optimum value so as to be matched with the resistance value based on it and outputted and the transfer current is secularly controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and the like.

[0002]

2. Description of the Related Art In these image forming apparatuses, transfer current control conventionally used by the present applicant includes differential constant current control (a target current value is determined and the current value (current to a photosensitive drum)). Detect the feedback current to match
This is a control method that determines the output current from the high-voltage power supply, and is a control capable of coping with uneven resistance of the belt in one used belt. ). The difference constant current control will be described with reference to FIGS.

[0005] In the transfer / transport apparatus indicated by reference numeral 1 in FIG. 1, a belt unit 2 is detachably supported on a main body 1A. The belt unit 2 includes a pair of rollers 4 for transferring a developed image from the drum-shaped photoconductor 3 shown in FIG.
5, a transfer belt 6 wound around the transfer belt 5, a DC solenoid 8 for moving the transfer belt 6 toward and away from the photoconductor 3, a contact / separation lever 9, a bias roller 11 for applying a transfer bias to the transfer belt 6, and a transfer belt 6 And a contact plate 13 for removing the electric charges from the contact plate 13. A cleaning device 16 having a cleaning blade 16A for scraping off paper dust and the like from residual toner and transfer paper S adhered to the surface of the transfer belt 6 and a high voltage power supply 12 for applying a voltage to the bias roller 11 are provided in the main body shown in FIG. 1A.

The roller 5 has a gear 5b connected to a drive motor (not shown) as shown in FIGS. 1 and 2, and is driven to rotate. The transfer belt 6 can move in the transport direction of the transfer paper S (the direction of the arrow A in FIG. 3) at a position facing the photoconductor 3 following the rotation of the roller 5. As shown in FIG. 5, the transfer belt 6 has a two-layer structure. When the electric resistance measured by JIS K6911 is 100 V DC, the surface layer 6 b as a coating layer has a surface resistivity of the belt surface. 1X10 ⁹ Ω~1 × 10 ¹² Ω, the surface resistivity of the inner layer 6a is ^{1 × 10 7 Ω~1 × 10 9} Ω, and a volume resistivity of ^{5 × 10 8 Ω · cm~5 ×} 10 10 Ω ・ c
m.

The rollers 4 and 5 are rotatably supported by a support 7 as shown in FIGS. The support 7 can swing about the support shaft 5 a of the roller 5, which is located downstream of the transfer position with respect to the photoconductor 3, in the transfer paper conveyance direction indicated by the arrow A among the rollers 4 and 5. . The support 7 is operated by a DC solenoid 8 driven on the transfer position side of the transfer belt 6 by a signal from a control plate 8A. That is, the DC solenoid 8
, A contact / separation lever 9 is connected, and the contact / separation lever 9 moves the support 7 to move the transfer belt 6 toward and away from the photoconductor 3.

The control plate 8A is configured so that the leading end of the transfer paper S conveyed in a state where it is aligned with the leading end position of the image formed on the photoreceptor 3 by the registration roller 10 serving as a sheet conveying means is transferred to the photoreceptor 3. When approaching, a drive signal is issued to drive the DC solenoid 8. Accordingly, the driving of the solenoid 8 causes the support member 7 to approach the photosensitive drum 3 and the transfer belt 6 abuts on the photosensitive member 3, thereby transferring the transfer paper S at a position facing the photosensitive member 3. A nip portion B that can be conveyed while being in contact with 3 is formed.

[0007] Of the rollers 4 and 5 described above, the roller 4 located on the photoconductor 3 side is configured as a driven roller with respect to the roller 5 on the driving side, and the surface shape of the roller 4 is shown in FIG. Thus, both ends 4a in the axial direction,
4a is formed in a tapered shape, and the transfer belt 6
It is designed to prevent bias. Although the roller 4 is a conductive roller made of metal or the like, it only supports the belt having the electric resistance as described above, and may not be electrically connected directly to other conductive members. Further, the roller 4 can be fed back to the high voltage power supply 12 like a contact plate 13 described later to be grounded.

The driving roller 5 has a function of increasing the gripping force on the transfer belt 6 at the time of driving.
A material such as chloroprene rubber or silicone rubber is selected. Also, a conductive roller can be used without using rubber for the roller 5. It is also possible to return the feedback current from the roller 5 to the high voltage power supply 12.

When the rollers 4 and 5 are grounded, a transfer control plate 14 described later is connected to the rollers 4 and 5. It is also possible to ground both rollers 4 and 5 at the same time and feed back the feedback current.

The bias roller 11 is provided on the downstream side of the roller 4 in the moving direction of the transfer belt 6 (left side in FIGS. 3 and 4) so as to contact the inside of the transfer belt 6. The bias roller 11 constitutes a contact electrode for applying a charge having a polarity opposite to the charge polarity of the toner on the photoconductor 3 to the transfer belt 6.
It is connected to the.

The contact plate 13 is arranged on the inner surface of the transfer belt 6 near the lower driven roller 4 which is not the transfer paper transfer surface, and injects electric charge to the transfer paper S upstream of the transfer nip as described later. Is suppressed. This contact plate 13
Is for detecting the current flowing on the transfer belt 6 as a feedback current, and the current supplied from the bias roller 11 is controlled by detecting this current. For this reason,
The contact plate 13 has a bias roller 11 according to the detected current.
A transfer control plate 14 for setting a current to be supplied to the transfer control plate 14 is connected to the high-voltage power supply 12.

In such a transfer / transport apparatus 1, as shown in FIG. 4, the support 7 moves the transfer belt 6 closer to the photoconductor 3 as the transfer paper S is fed out from the registration roller 10. And a width of 4 to 8 mm corresponding to the length of the transfer paper between the photosensitive member 3 and the transfer direction.
A nip portion B is formed.

On the other hand, in the case of an analog machine, the surface of the photoconductor 3 is charged to, for example, -800 V. As shown in FIG. 6, positively charged toner is electrostatically adsorbed on this surface. Move to the nip in the state. The photoreceptor 3 is disposed near the photoreceptor 3 before reaching the nip portion, and a pre-transfer neutralization lamp (PTL) for weakening the charge on the surface of the photoreceptor 3.
15 reduces the surface potential. In FIG. 6, the height of the charged charges is represented by the size of a circle, and the state in which the charged charges are reduced by the pre-transfer charge removing lamp 15 is shown smaller than the circle before the charge removal.

In the nip portion B shown in FIG.
The upper toner is transferred onto the transfer paper S by the transfer bias from the bias roller 11 located on the transfer belt 6 side. The transfer bias is applied from the high voltage power supply 12 in the range of -1.5 kV to -6.5 kV. The transfer bias is variably set as a result of the constant current control as described below. That is, in FIGS. 3 and 4, the current value output from the high-voltage power supply 12 is I _1, and the value when the feedback current value flowing from the contact plate 13 to the ground via the transfer belt 6 is I ₂ . If you do,

[Number 1] I ₁ -I ₂ = I _OUT (However, I _OUT: constant) controlling the value of I ₁ so that the relation is obtained. This is to stabilize the surface potential Vp on the transfer paper S and eliminate the change in transfer efficiency, regardless of changes in environmental conditions such as temperature and humidity and variations in the manufacturing quality of the transfer belt 6. It is.

That is, the current flowing to the photoconductor 3 through the transfer belt 6 and the transfer paper S is regarded as I _OUT , so that the surface resistance on the transfer paper S is reduced or increased by increasing the surface resistance. A change in the ease of current flow is prevented from affecting the separation performance and transfer performance of the transfer paper S. Current I _OUT is conveying speed 330 mm / sec, and good transfer can be obtained in the case of setting the I _OUT = 35uA ± 5 .mu.A in the effective bias roller length 310 mm.

When the image is transferred from the photoconductor 3, the transfer paper S is also charged at the same time. Therefore, the transfer paper S is electrostatically attracted to the transfer belt 6 and the transfer paper can be separated from the photoconductor 3 by the relationship between the true charge of the transfer belt 6 and the polarization charge generated on the transfer paper S side. . Then, the transfer paper S itself is promoted by a peeling operation based on the stiffness of the transfer paper S utilizing the curvature separation of the photoconductor 3.

However, in such electrostatic attraction, in the case of high humidity due to a change in environmental conditions, current easily flows through the transfer sheet S, so that the transfer sheet cannot be separated properly.
For this reason, since the resistance value of the surface layer 6b of the transfer belt 6 shown in FIG.
The transfer of the true charges to the transfer paper S in the above is delayed, and the bias roller 11 is positioned downstream of the nip portion B in the transfer paper transport direction. Thus, the transfer of the true charges from the transfer belt 6 to the transfer sheet S is delayed, and the electrostatic attraction between the transfer sheet S and the photoconductor 3 is avoided.

To delay the transfer of the true charges used in this case means that no charges are generated on the transfer sheet S upstream from the transfer sheet S to the nip portion on the photosensitive member 3 side. This prevents the transfer paper S from being wound around the photoconductor 3 and also prevents the transfer paper S from separating from the photoconductor 3 from being poorly separated.

Further, it is preferable that the transfer belt 6 be selected from those having a small resistance change due to an environmental change. As a conductive material for controlling the resistance, an appropriate amount of carbon or zinc oxide is added, and a rubber belt is used as an elastic belt. In the case where is used, it is desired to select a material having a low hygroscopicity and a stable resistance value, such as chloroprene rubber, EPDM rubber, silicone rubber, epichlorohydrin rubber and the like.

The current I _OUT flowing to the photosensitive member 3 side
Is not unique and can be reduced when the transport speed is low, and can be increased when the transport speed is high or when the pre-transfer neutralization lamp 15 is not used.

On the other hand, the transfer paper S passing through the nip B is
The transfer belt 6 is electrostatically attracted and conveyed in accordance with the movement of the transfer belt 6, and the roller 5 on the driving side separates the curvature. For this reason, the diameter of the roller 5 is set to 16 mm or less. further,
When such a roller 5 is used, an experimental result has been obtained that it is possible to separate ^high- quality 45K paper (rigidity 21 cm 3/100).

The transfer paper S separated from the transfer belt by the driving roller 5 is guided by a guide plate and is conveyed between a heating roller 17a and a pad roller 17b constituting the fixing unit 17. The fixing unit 17 heats and melts the toner on the transfer paper S and presses the toner on the transfer paper S to fix the toner on the transfer paper S.

When the transfer of the image onto the transfer sheet S and the separation of the transfer belt 6 are completed, the contact / separation lever 9 is released in response to the excitation of the DC solenoid 8 being released, and the support 7 is separated from the photosensitive member 3. Is done. Then, the surface is cleaned by the cleaning device 16.

The cleaning device 16 includes a cleaning blade 16A, and the toner transferred from the surface of the photoconductor 3 or scattered around the transfer belt 6 without being transferred by rubbing the transfer belt 6. The toner and the paper dust of the transfer paper S when the toner adheres are scraped off.

The transfer belt 6, which is rubbed by the cleaning blade 16A, has a low friction coefficient on its surface to prevent phenomena such as an increase in driving force due to an increase in rubbing resistance or the turning of the cleaning blade 16A. It is coated with a systemic resin material amount, for example, polyvinylidene fluoride, ethylene tetrafluoride, or the like. The toner or paper dust written from the surface of the transfer belt 6 is stored from the main body 1A into a waste toner collecting container (not shown) by the collecting screw 16B.

In the drawings described above, the application electrodes for detecting the surface resistance of the transfer belt 6 are omitted. As an example of the application electrode, a roller or the like in contact with the surface of the transfer belt 6 can be given. The transfer current control includes a simple constant current method, but the description is omitted.

[0027]

In the above-described control method, the output current changes sequentially in accordance with the resistance of the transfer belt 6, so that the control is performed sequentially from the viewpoint of the belt resistance. The belt resistance is captured from the aspect of the volume resistance obtained by combining the surface resistance and the resistance of the rubber surface (that is, the entire belt resistance), and the transfer current is determined based on the value. However, there is a disadvantage that the surface resistivity, the volume resistivity, and the resistance of the rubber of the transfer belt 6 cannot be separated and the transfer current cannot be finely controlled. Further, as a problem in resistance measurement in the conventional transfer current control, the surface resistance is a surface resistance of each component, and is a resistance value before being mounted on an actual machine.

In a transfer current control system of an image forming apparatus, the resistance of a contact member (transfer belt or the like) has a large effect on image quality and transportability. Even when a transfer belt is used, the overall resistance of the belt, that is, the volume resistance has a large effect on image quality and transportability. Furthermore, it can be said that not only the resistance of the belt but also the resistance of the coat layer on the surface have a large effect on image quality and transportability. When the surface resistivity of the belt is high, an abnormal image tends to occur. In particular, a blank image occurs. Further, when the surface resistivity of the belt is low, it affects the transferability of the transfer paper. There is a problem that a jam or a nail attraction (a phenomenon that a nail is attached to an image due to the separation of the nail by the transfer paper) occurs.

Therefore, the present invention provides an image forming apparatus in which the surface resistivity of a transfer / conveying means such as a transfer belt is detected in a state of being mounted on an actual machine, and the value can be used for controlling a transfer current. The purpose is to:

Further, according to the present invention, a delicate difference in surface resistivity can be applied to the control of the transfer current more than the method of controlling the transfer current by detecting the entire resistance of the transfer means such as a transfer belt. It is an object of the present invention to provide an image forming apparatus capable of performing the above feedback control.

Another object of the present invention is to provide an image forming apparatus which does not require a new electrode for detecting surface resistance.

Still another object of the present invention is to provide an image forming apparatus which can use the separating means efficiently.

Still another object of the present invention is to provide an image forming apparatus capable of performing control in accordance with the environmental characteristics of the material coating the surface of the transfer / transporting means.

[0034]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier for carrying a toner image; An endless belt-shaped transfer / conveying means for transferring the toner image, a driving means for rotating and driving the transfer / conveying means, a cleaning means for cleaning the transfer / conveying means, a stretching means for stretching the transfer / conveying means, Transfer bias applying means for applying a transfer bias to the transfer conveying means,
In an image forming apparatus comprising: a bias applying unit that applies a bias to the transfer / conveying unit positioned on or near the surface of the transfer / conveying unit, comprising a current detecting unit for detecting a current flowing through the image carrier, A current flowing through the image carrier when a bias is applied from the bias applying means can be detected.

According to a second aspect of the present invention, in order to achieve the above object, a transfer bias applied from the bias applying means to the transfer / conveying means is a constant voltage.

According to a third aspect of the present invention, there is provided a transfer bias control means for determining and controlling the transfer bias based on a current value detected by the current detection means in order to achieve the above object. And

According to a fourth aspect of the present invention, in order to achieve the above object, the cleaning means also serves as the bias applying means, and the polarity of the applied bias is opposite to that of the toner.

According to a fifth aspect of the present invention, in order to achieve the above object, the bias applying means also serves as means for separating the sheet from the image carrier.

According to a sixth aspect of the present invention, in order to achieve the above object, the bias applying means is a charger.

According to a seventh aspect of the present invention, in order to achieve the above object, the bias applying means can apply at least two different applied biases, and the current detecting means can supply a current corresponding to each applied bias. At least two values are detected, and the transfer bias control means varies the transfer bias applied to the transfer / transport means in accordance with the detected values.

[0041]

Embodiments of the present invention will be described below with reference to the drawings. In the following, portions common to the related art are denoted by the same reference numerals, and redundant description is omitted.

FIG. 7 is a diagram showing a main part of an embodiment of the image forming apparatus according to the present invention. FIG. 7 is a simplified version of the configuration of the apparatus shown in FIG. 1. Although the basic configuration is not the same as that of the apparatus shown in FIG. There is provided a roller 20 which also serves as a cleaning roller for cleaning the surface. The roller 20 removes the toner adhered to the surface coating layer of the transfer belt 6 by an electric force. Instead of cleaning the surface of the transfer belt 6 with a cleaning blade as in the related art,
It is possible to improve the cleaning property by cleaning with electric force. Further, the margin of the contact condition with the transfer belt 6 can be increased more than the blade, and the curl does not occur unlike the blade.

The roller 20 is for applying a high voltage for detecting the surface resistance of the transfer belt 6 and is in contact with the surface layer 6 b which is a coating layer of the transfer belt 6. Material is S
US or the like, but a sponge roller or the like may be used as long as it does not damage the surface layer 6b. Further, a transfer roller or the like may be used. When the surface resistance is detected by the roller 20,
The first time in the morning when the apparatus is turned on, the time when the process controller operates, the time when the job ends, and the like are good. When measuring the resistance of the entire transfer belt 6 at the time of operation of the process controller or at the end of a job, it is efficient to detect the surface resistance after detecting the overall resistance of the transfer belt 6. The power supply required for detecting the surface resistance by the roller 20 can be used in combination with a transfer power supply such as a high-voltage power supply 12 for applying a transfer bias as shown in the figure.

When a high voltage is applied from the roller 20, a current flows through the surface layer 6b of the transfer belt 6 to the photosensitive member 3. In order to detect the current, a control unit 21 including a current detection unit 22 and a calculation unit 23 is connected to the photoconductor 3 as shown in the figure. When the current flowing through the photoconductor 3 is detected, the drive roller 5, the driven roller 4, and the bias roller 11 for applying a transfer bias are grounded as shown. That is, the application electrode is the roller 20, the detection electrode is the photoreceptor 3, the driving roller 5, the driven roller 4, and the bias roller 1.
1 is configured as a ground electrode, and it is possible to configure a system for detecting the surface resistivity on an actual machine.

For example, a constant voltage is applied to the roller 20 while the transfer belt 6 and the photosensitive member 3 are grounded, and the current flowing through the surface layer 6b of the transfer belt 6 at that time is detected by the current flowing through the photosensitive member 3. I do. If the current flowing into the photoconductor 3 is large, it indicates that the resistance of the surface layer 6b of the transfer belt 6 is low, and if the current is small, it is high. A bias of about several KV may be applied to the roller 20.

The voltage applied from the roller 20 can be changed in several ways. That is, 100V, 500V,
The voltage can be changed to 1 KV, and the characteristics of each transfer belt 6 can be grasped by detecting the current value corresponding to each voltage. This means that the characteristics of the surface layer 6b can be grasped by detecting current values corresponding to different voltage values. That is, by checking whether or not the surface layer 6b has a voltage application dependency, it can be seen that when there is no dependency, the surface resistance changes due to the environment of the material of the surface layer 6b.
Also, when there is a voltage dependency, it can be seen that there is not much change in the environment of the resistance of the surface layer 6b.

Next, the case where the surface resistance of the transfer belt 6 is low and the case where it is high will be described. First, if the surface resistance is high,
When the rubber resistance is the same, a blank image is more likely to occur when the surface resistance is high. A blank image is generated by pre-transfer. If the surface resistance is high, the photosensitive member 3 and the transfer belt 6
Discharge is easily generated between the two, and a blank image easily occurs. Therefore, when the surface resistance of the transfer belt 6 is high, control is performed so that the transfer current is set low in order to reduce the transfer charge when transferring to paper. FIG. 9 shows the transfer belt 6.
This shows the presence or absence of a blank image due to the difference in surface resistance. As shown in FIG. 9, when the surface resistivity is high, control is performed to lower the transfer current in order to reduce the pre-discharge amount.

When the surface resistance is low, even if the resistance of the rubber surface is in a normal range, it is not possible to ensure the transportability. This tendency is particularly remarkable in a situation where the resistance is low such as in a high temperature and high humidity (H / H) environment. The transportability refers to a separation failure between the transfer belt 6 and the photoconductor 3, and when the paper is separated from the photoconductor 3, the paper is not adsorbed to the transfer belt 6 but is adsorbed to the photoconductor 3 side. This is the case where the nail is separated by the third claw. When separated by nails, nail attraction occurs as described above. Therefore, in a transfer belt having a low surface resistivity, it is indispensable to set and control the transfer bias to be high. FIG. 10 shows the difference between the surface resistivity and the transportability particularly in an H / H environment. When the surface resistance is low, control is performed to increase the transfer current.

FIG. 11 is a flowchart showing the process from the detection of the resistance to the output of the transfer current. In step 1, the bias (1
(00 V, 500 V or 1 KV), the current is detected and converted into a resistance (Step 2), the current change rate is calculated (Step 3), and it is determined whether the change rate is 0.5 or less (Step 2). 4). If the rate of change is 0.5 or less, the correction coefficient is set to 0.8 for low temperature and low humidity (L / L) and 1.3 for H / H environment (step 5). It is detected (step 6), and if it is an H / H environment, it is determined whether or not the resistance value (surface resistance value) obtained in step 2 is 10 ⁹ or less (step 7). Correction is made (step 8), otherwise correction is not made (step 10). In the L / L environment, it is determined whether or not the resistance value (surface resistance value) obtained in step 2 is 10 ¹¹ or less (step 9), and if not, no correction is made (step 10).
If not, the correction is performed using the above-mentioned correction value (step 11). In each case, a corresponding transfer current is output (step 19).

If the change rate is larger than 0.5 in step 4, the correction coefficient is set to 0. 0 for the L / L environment.
9. Set 1.1 for H / H environment (step 1
2) The environment is detected (step 13), and if it is a H / H environment, it is determined whether or not the resistance value (surface resistance value) obtained in step 2 is 10 ⁹ or less (step 14). Correction is performed using the correction value (step 15), and otherwise correction is not performed (step 17). In the L / L environment, it is determined whether or not the resistance value (surface resistance value) obtained in step 2 is 10 ¹¹ or less (step 16). If it is below, no correction is made (step 17). (Step 18). In each case, a corresponding transfer current is output (step 19).

That is, by controlling the transfer bias according to the difference in the surface resistance as described above, the range in which the surface resistivity can be used can be expanded as compared with the related art, and it is possible to achieve both the abnormal image and the transportability. Become. In the past, in order to achieve this balance, it was necessary to take measures by defining the resistivity of the transfer belt. Further, in order to solve these problems, the resistivity of the rubber surface of the transfer belt is set to 9%.
In this embodiment, the current is controlled by detecting the surface resistivity without defining the resistance of the transfer belt 6 to some extent. It is possible to expand. As shown in FIGS. 9 and 10, by correcting the transfer current even when the surface resistivity is abnormal (in the flowchart of FIG. 11, the transfer current correction coefficient is × 0.8 in the L / L environment).
× 1.3 times in the case of H / H environment. ), Can solve the above problems.

It is preferable that the bias applied by the roller 20 has a polarity opposite to that of the toner. Basically, the polarity of the bias applied by the roller 20 may be either. However, if the reverse characteristic of the toner is used, the surface of the transfer belt 6 can be cleaned when detecting the surface resistance. That is, in the cleaning mode, the surface resistance can be detected simultaneously with the cleaning of the surface of the transfer belt 6.

FIGS. 12 and 13 show examples of application of an applied bias. The example of FIG. 12 is a case where the applied voltage is changed, and the example of FIG. 7 is a case where the applied time is changed under a constant applied voltage. The uppermost row shows the operation timing of the DC solenoid 8 (see FIGS. 3 and 4) that comes into contact with and separates from the transfer belt 6, the middle row shows the timing of applying an applied bias to the roller 20, and the lower row shows the timing of the current flowing into the photoconductor 3. This shows the detection timing. FIG. 14 shows general current detection, and the current change rate is obtained by detecting the current values immediately after the application and immediately before the end of the application. This rate of change is obtained by subtracting the current value immediately after application from the current value after application for a certain period of time and dividing the value by the current value immediately after application.

As an arithmetic means for calculating the current change rate, an arithmetic device such as a general microcomputer may be used. FIG. 15 is a block diagram of a configuration in which a microcomputer 31 is arranged between the operation unit 30 and the current detection unit 22 of the image forming apparatus. Of course, other calculation means may be used. The correction coefficient for the environment described above may be determined in advance and stored, for example, in the ROM of the microcomputer 31. FIG. 1
In FIG. 5, the roller 20 is generally shown as bias applying means.

In FIGS. 9 and 10, the column "when transfer current is corrected" indicates a case where the correction is made by the above-described correction. The transfer current is omitted because it differs for each model.

Although an example in which the bias applying means is a transfer belt cleaning means has been described above, it is also possible to use the bias applying means as a means for separating transfer paper from the transfer belt 6.

Further, FIGS. 16, 17 and 18 show the case where the bias applying means is a charger (CG), and also shows an example of the arrangement of the charger. The charger 32 may be disposed anywhere near the position where the paper is separated from the transfer belt 6. With the separation charger, there is no need to provide a bias applying unit that is in contact with the surface of the transfer belt 6 like the roller 20 that also serves as the cleaning roller as described above. 16, 17, and 18, illustration of an applied power supply for supplying a bias to the charger 32 is omitted.

In the present invention and the above-described embodiment, the transfer belt may be in a rotating state or a stationary state at the time of detecting the current value.

[0059]

As described above, the image forming apparatus of the present invention has current detecting means for detecting a current flowing through the image carrier, and is provided when a bias is applied from the bias applying means to the transfer / transporting means. Since the current flowing through the image carrier can be detected, the resistance of the transfer conveyance means such as the transfer belt can be measured on the actual machine, and can be combined with the transfer belt resistance measured before combining with the actual machine as in the past. In this way, it is possible to separately measure the resistance of the entire transfer conveyance means and its surface resistance, and by detecting the surface resistivity on the actual machine, the transfer current is adjusted to match the resistance based on the resistance. It is possible to set and output the optimum value, and also to grasp the change with time of the surface resistivity of the transfer / transporting means, so that the transfer current can be controlled with time.

According to the image forming apparatus of the present invention, as described above, the transfer bias applied to the transfer belt from the bias applying means is a constant voltage. There is an effect that the resistance can be measured by the same principle as described above.

As described above, the image forming apparatus of the third aspect has the transfer bias control means for determining and controlling the transfer bias based on the current value detected by the current detection means. In addition to the method of controlling the transfer current by detecting the resistance of the entire transfer conveyance means, the subtle difference in surface resistivity can be applied to the control of the transfer current, and the effect that the feedback control of the transfer current becomes possible. is there.

According to the image forming apparatus of the present invention, as described above, the cleaning means also serves as the bias applying means, and the polarity of the applied bias is opposite to that of the toner.
In addition to the above-mentioned common effects, there is no need to provide a new electrode or the like for detecting the surface resistance, and it is not only efficient to use the cleaning roller in combination, but also to apply the opposite polarity to the toner to form the belt. There is an effect that cleaning and detection of surface resistance can be performed simultaneously.

In the image forming apparatus according to the fifth aspect, as described above, the bias applying means also serves as means for separating the sheet from the image carrier, and according to the sixth aspect, the bias applying means is a charger. There is an effect that, by installing them near the belt, in addition to the above-mentioned common effects, the separating means and the charger can be used efficiently.

According to the image forming apparatus of the present invention, as described above, the bias applying means can apply at least two or more different applied biases, and the current detecting means sets at least the current value corresponding to each applied bias. Two or more are detected, and the transfer bias applied to the transfer / conveying means by the transfer bias control means is changed in accordance with the detected values. Therefore, in addition to the above-described common effects, the surface of the transfer / conveying means is coated. Control according to the characteristics of the material is possible, and there is an effect that it is possible to control whether the material exhibits characteristics that cause environmental fluctuation or not.

[Brief description of the drawings]

FIG. 1 is a perspective view of an example of a transfer conveyance device used in an image forming apparatus.

FIG. 2 is a plan view illustrating a basic configuration of the transfer / conveyance device of FIG. 1;

FIG. 3 is an image forming apparatus using the transfer conveyance device of FIG. 1;
FIG. 3 is a conceptual diagram showing a configuration in a state before a transfer operation.

FIG. 4 is a conceptual diagram during the transfer.

FIG. 5 is an enlarged cross-sectional partial view of a transfer belt used in the transfer conveyance device of FIG. 1;

6 is an enlarged view conceptually showing a state during transfer in an image forming apparatus using the transfer / conveyance device of FIG. 1;

FIG. 7 is a diagram showing a main part of an embodiment of the image forming apparatus according to the present invention.

FIG. 8 is an enlarged sectional view of a main part of the embodiment of FIG. 7;

FIG. 9 is a graph showing the presence or absence of a blank image due to a difference in surface resistance of a transfer belt.

FIG. 10 is a graph showing the presence or absence of a blank image due to a difference in surface resistivity and transportability in an H / H environment.

FIG. 11 is a flowchart illustrating a process from detection of resistance to output of a transfer current in the image forming apparatus according to the embodiment of the invention.

FIG. 12 is a graph showing an example of application of an applied bias in an embodiment of the image forming apparatus according to the present invention.

FIG. 13 is a graph illustrating another example of application of an applied bias in an embodiment of the image forming apparatus according to the present invention.

FIG. 14 is a graph illustrating application of an applied bias and general current detection in an embodiment of the image forming apparatus according to the present invention.

FIG. 15 is a block diagram illustrating a configuration of a calculation unit that calculates a current change rate in an embodiment of the image forming apparatus according to the present invention.

FIG. 16 is a conceptual diagram illustrating a configuration in a case where a bias applying unit is a charger in an embodiment of the image forming apparatus according to the present invention.

FIG. 17 is a conceptual diagram illustrating another configuration when the bias applying unit is a charger in one embodiment of the image forming apparatus according to the present invention.

FIG. 18 is a conceptual diagram showing still another configuration in a case where the bias applying unit is a charger in one embodiment of the image forming apparatus according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transfer conveyance device 1A main body 2 belt unit 3 photoreceptor 4, 5 roller 6 transfer belt 6a inner layer 6b surface layer 7 support 8 DC solenoid 8A control plate 9 contact / separation lever 10 resist roller 11 bias roller 12 high voltage power supply 13 contact plate Reference Signs List 14 transfer control plate 15 pre-transfer static elimination lamp (PTL) 16 cleaning device 16A cleaning blade 16B collection screw 17 fixing unit 17a heating roller 17b pad roller 20 roller 21 control unit 22 current detection unit 23 calculation unit 30 operation unit 31 microcomputer 32 charger S Transfer paper B Nip

Claims (7)

[Claims] 1. An image carrier for carrying a toner image, an endless belt-shaped transfer / conveying means for transferring the toner image on the image carrier to a carried sheet, and a driving means for rotating the transfer / conveying means Cleaning means for cleaning the transfer / conveying means; stretching means for stretching the transfer / conveyance means; transfer bias applying means for applying a transfer bias to the transfer / conveyance means; and a surface or near the surface of the transfer / conveyance means And a bias applying means for applying a bias to the transfer / conveying means, wherein a current detecting means for detecting a current flowing through the image carrier is provided, and a bias is applied from the bias applying means. Wherein the current flowing through the image carrier can be detected. 2. The image forming apparatus according to claim 1, wherein a transfer bias applied from said bias applying unit to said transfer and conveying unit is a constant voltage. 3. The image forming apparatus according to claim 1, further comprising a transfer bias control unit that determines and controls the transfer bias based on a current value detected by the current detection unit. 4. An image forming apparatus according to claim 1, wherein said cleaning means also functions as said bias applying means, and the polarity of the applied bias is opposite to that of the toner. 5. An image forming apparatus according to claim 1, wherein said bias applying means also functions as means for separating said sheet from said image carrier. 6. An image forming apparatus according to claim 1, wherein said bias applying means is a charger. 7. The bias applying means can apply at least two or more different applied biases, and the current detecting means detects at least two or more current values corresponding to each applied bias, and according to the detected value. 6. The image forming apparatus according to claim 3, wherein said transfer bias control means varies a transfer bias applied to said transfer / conveyance means.