JP2002258638A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the change in the rate of reduction magnification or the occurrence of a density difference in an image by reducing the speed difference between an image carrier and a transfer belt caused by electrostatic attracting force which works in between. SOLUTION: The image forming apparatus is provided with an image carrier driving means 2 which rotationally drives an image carrier 1 on which a toner image T is formed and is carried at constant speed, a belt drive means 5 which rotationally drives a transfer belt 4 which is spread over a plurality of roll members 3 (for example, 3a, 3b) and disposed oppositely to the image carrier 1, and a bias application means 6 which is provided at the rear side of the transfer belt 4 in the opposing part of the image carrier 1 and the transfer belt 4, and applies a transfer bias to a recording material K transported by the transfer belt 4. The image forming apparatus is further provided with a belt resistance discriminating means 7 which discriminates the resistance value of the transfer belt 4, and a speed control means 8 to control the rotational speed of the transfer belt 4 by the belt drive means 5 on the basis of the resistance value determined by the belt resistance discriminating means 7.

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 a copying machine or a printer, provided with an image carrier on which a toner image is formed. The present invention relates to an improvement of a so-called belt transfer type image forming apparatus for transferring a toner image on a carrier to a recording material conveyed by the transfer belt.

[0002]

2. Description of the Related Art Conventionally, as this type of image forming apparatus,
For example, JP-A-4-133080 and JP-A-5-32
No. 3800 is known. This image forming apparatus, as shown in FIG. 12, for example, transfers a transfer belt 102 composed of an endless belt stretched over a plurality of support rolls 101a and 101b to an image carrier such as a photosensitive drum on which a toner image T is formed. A transfer nip N is formed by contacting the image carrier 103 with the image carrier 103.
The transfer belt 102 is configured to rotate in the direction of an arrow A from a drive source 10a via a gear or the like.
4a is transmitted via the image carrier 103,
Alternatively, the drive from the single drive source 104b is transmitted to the support roll 101a or 101b via a gear or the like, so as to rotate together with the image carrier 103. Further, a transfer bias having a polarity opposite to the toner charge polarity of the toner image T is applied to the transfer belt 102 from a transfer bias power supply 105 via an electrode roll 106. Reference numeral 107 denotes a charger for uniformly charging the image carrier 103, and reference numeral 108 denotes a developing device for developing an electrostatic latent image formed by a laser beam (not shown) with toner.

In this image forming apparatus, the recording paper P is conveyed to the transfer nip N by the transfer belt 102, and the toner image T formed on the image carrier 103 is transferred to the recording nip N at the transfer nip N. The image is electrostatically transferred to the P side. The recording paper P after the completion of the transfer is separated from the transfer belt 102 and sent to a fixing device 109 disposed downstream thereof. Reference numeral 110 denotes a tray for storing the paper P, 1
Reference numeral 11 denotes a pair of rolls for transporting the paper P, and reference numeral 112 denotes a blade for cleaning the surface of the transfer belt.

[0004]

By the way, in such a belt-type transfer apparatus, a predetermined voltage is applied to the electrode roll 106 to form a transfer electric field in the transfer nip portion N, whereby the image carrier 103 is formed. The upper unfixed toner image T is electrostatically transferred onto the recording paper P. Here, since a transfer voltage is applied to the transfer nip N by applying a predetermined voltage to the electrode roll 106, the transfer belt 102 is moved toward the image carrier 103 by electrostatic attraction generated according to the transfer electric field. The phenomenon of electrostatic attraction occurs.
In particular, when the resistance value of the transfer belt 102 is high or the resistance value of the recording paper P is high, the voltage value applied to the electrode roll 106 also increases, so that it is necessary to increase the transfer electric field. In proportion to this, the electrostatic attraction force acting on the transfer belt 102 to the image carrier 103 also increases. Then, the transfer belt 102 is attracted to the image carrier 103 by a strong electrostatic attraction force, which causes a change in the rotation speed of the transfer belt 102.

Here, the transfer belt 102 is connected to the image carrier 10.
3 is driven by the same drive source 104a as
A slip phenomenon occurs between the support roller 101a or the support roller 101b and the transfer belt 102, and the image carrier 10
3 and the recording paper P, a speed difference occurs. On the other hand, the transfer belt 102 is driven by a driving source 104 b different from the image carrier 103.
, The speed of the drive system between the drive source 104b and the support rolls 101a and 101b is changed, and eventually a speed difference occurs between the image carrier 103 and the recording paper P. In any case, the transfer belt 10
If the electrostatic attraction force acting between the image bearing member 2 and the image carrier 103 becomes too large, a speed fluctuation occurs between the recording sheet P and the image carrier 103, so that an image on the recording sheet P This causes a change in the reduction ratio and a difference in density. In particular, when the transfer belt 102 is formed of an elastic material such as rubber, the adhesion to the image carrier 103 is improved, so that the reduction ratio of the image and the density difference significantly occur. .

As means for reducing such a speed difference generated between the image bearing rotating body and the transfer belt, Japanese Patent Laid-Open No.
There are techniques disclosed in JP-A-160765 and JP-A-10-48971. In both cases, a torque limiter is provided between the drive roll and the drive source of the transfer belt to reduce the variation in load torque applied to the drive system against the speed variation of the transfer belt generated between the transfer belt and the image carrier. The speed of the transfer belt is synchronized with the speed of the image bearing rotary member. Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 6-27829, the speed of the transfer belt is controlled to be constant by providing a marker for detecting the position of the transfer belt and a detecting means for detecting the marker on the transfer belt. There is a way to do it.

However, it has been found that the following problem occurs in the former technique using the torque limiter. That is, since the torque value of the torque limiter changes over time, the load torque cannot be kept constant, and the speed of the transfer belt fluctuates. In addition, since the torque limiter is a mechanical mechanism, it is deteriorated due to stress abrasion and the like. In addition to a change in image reduction ratio and a density difference, the recording paper cannot be conveyed, and a trouble such as a jam occurs. Further, since the range of the torque value of the torque limiter is specified, the effect is reduced if the torque value exceeds the specified torque value due to a change in the resistance value of the transfer belt with time, a galling of the drive system, a load change due to wear, and the like.

On the other hand, in the latter technique using a marker, the marker cannot be accurately detected due to a stain on the marker surface or the like, so that the same trouble as described above may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problem, and reduces a speed difference between an image carrier and a transfer belt caused by an electrostatic attraction force acting between the two. Another object of the present invention is to provide an image forming apparatus capable of providing a high-quality image by preventing occurrence of a density difference between images and images.

[0010]

SUMMARY OF THE INVENTION The inventor of the present invention has considered that a factor of generating electrostatic attraction force acting between an image carrier and a transfer belt is as follows.
The inventors have found that the resistance value of the transfer belt has a great influence, and have come up with the present invention. That is, the present invention
As shown in FIG. 1, an image carrier 1 on which a toner image T is formed and carried, an image carrier driving means 2 for rotating the image carrier 1 at a constant speed, and a plurality of roll members 3 (for example, 3a,
3b) a transfer belt 4 which is stretched over the image carrier 1 and arranged opposite to the image carrier 1, a belt driving means 5 for rotating the transfer belt 4 and a facing portion of the image carrier 1 and the transfer belt 4; The image carrier 1 is provided on a recording material K provided on the back side of the transfer belt 4 and conveyed by the transfer belt 4.
A belt resistance determining unit for determining a resistance value of the transfer belt in an image forming apparatus including a bias applying unit for applying a bias to transfer the toner image on the transfer belt;
And a speed control unit 8 for controlling a rotation speed of the transfer belt 4 by the belt driving unit 5 based on the resistance value determined by the belt resistance determination unit 7.

In such technical means, the image forming apparatus according to the present invention, of course, has a mode in which one image carrier 1 is arranged to face one transfer belt 4 as shown in FIG. The present invention is also applicable to a mode in which a plurality of image carriers 1 are arranged to face one transfer belt (a so-called tandem image forming apparatus). Further, the image carrier 1 may be appropriately selected such as a drum shape, a belt shape, or the like.

Further, regarding the belt resistance determining means 7,
As long as the resistance value of the transfer belt 4 can be determined, the determination method may be appropriately selected. And
As a specific mode of the belt resistance determining means 7, for example, a belt resistance measuring means for measuring the resistance value of the transfer belt 4 is provided, and the transfer belt 4 is measured based on the measured resistance value of the transfer belt 4. There is a method of determining the resistance value.

In the above-described embodiment, the position of the belt resistance measuring means may be appropriately selected from the positions. However, from the viewpoint of accurately obtaining the resistance value of the transfer belt 4 at the transfer position, the image position is determined. It is preferable that the transfer belt 4 is arranged so as to measure a resistance value of the transfer belt 4 at a portion where the support 1 and the transfer belt 4 are opposed to each other.

Further, in such a mode, from the viewpoint of obtaining the resistance value of the transfer belt 4 more accurately,
It is preferable that the belt resistance measuring unit measures the resistance value of the transfer belt 4 under the condition that the recording material K does not exist in the facing portion between the image carrier 1 and the transfer belt 4.

Similarly, from the viewpoint of more accurately obtaining the resistance value of the transfer belt, the belt resistance measuring means determines that the recording material K enters the opposing portion of the image carrier 1 and the transfer belt 4. It is preferable to measure the resistance value of the transfer belt 4 just before the transfer.

As another mode of the belt resistance determining means 7, for example, an environment information measuring means for measuring environmental information is provided, and the resistance value of the transfer belt 4 is determined based on the measured environmental information. Technique.

Further, as another mode of the belt resistance determining means 7, for example, a surface potential measuring means for measuring the surface potential of the transfer belt 4 is provided, and based on the measured surface potential of the transfer belt 4, A method of determining the resistance value of the transfer belt 4 can be used.

Further, as another mode of the belt resistance judging means 7, for example, a leak current measuring means for measuring a leak current flowing to the roll member 3 (3a or 3b) via the transfer belt 4 is provided. Then, there is a method of determining the resistance value of the transfer belt 4 based on the measured leakage current.

The above three aspects are all factors that cause the resistance value of the transfer belt 4 to vary, and the correlation between these factors and the resistance value of the transfer belt 4 indicates that the resistance of the transfer belt 4 is high. It is possible to determine the value.

The present invention is not limited to the above-described embodiment in which the speed of the transfer belt 4 is controlled based on the resistance value of the transfer belt 4, and the electrostatic attraction acting between the image carrier 1 and the transfer belt 4. A mode in which the speed of the transfer belt 4 is controlled based on the magnitude of the force is also an object. That is, as shown in FIG. 1, an image carrier 1 on which a toner image T is formed and carried, and an image carrier driving means 2 for rotating the image carrier 1 at a constant speed, as shown in FIG. , A plurality of roll members 3
(For example, 3a, 3b), a transfer belt 4 that is disposed to face the image carrier 1, a belt driving unit 5 that rotationally drives the transfer belt 4, the image carrier 1 and the transfer belt 4 And a bias applying means 6 which is provided on the back side of the transfer belt 4 at the opposite portion of the transfer belt 4 and applies a bias for transferring the toner image T on the image carrier 1 to the recording material K conveyed by the transfer belt 4. In the image forming apparatus provided with the image forming apparatus, an attraction force determining means 9 for determining an electrostatic attraction force acting between the image carrier 1 and the transfer belt 4, and an electrostatic attraction force determined by the attraction force determining means 9 Speed control means 8 for controlling the rotation speed of the transfer belt 4 by the belt driving means 5 based on the

In such technical means, if the attraction force discriminating means 9 is capable of discriminating the electrostatic attraction force acting between the image carrier 1 and the transfer belt 4, the measured electrostatic attraction force is determined. In addition to the type that makes a determination based on the force, factors that correlate with the electrostatic attraction force, for example, the image carrier 1 and the transfer belt 4
May be determined based on the electric field or charge density formed between the transfer belt 4 and the resistance value of the transfer belt 4 described above. The determination may be made based on the drive load (for example, drive current or the like) utilizing the fact that the drive load of the image carrier driving means 2 fluctuates with the fluctuation of the electrostatic attraction force.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a first embodiment of an image forming apparatus to which the present invention is applied. In the figure, reference numeral 10 denotes a photosensitive drum as an image carrier, which rotates in the direction of arrow A. Around the photosensitive drum 10, a charger 11 for uniformly charging the surface of the drum (photosensitive layer) is provided. An optical image corresponding to predetermined image information is exposed on the charged photosensitive drum 10 to form an electrostatic image. An image exposure device 12 for forming a latent image, a developing device 13 for supplying a developer to the surface of the photosensitive drum 1 to develop an electrostatic latent image into a toner image, and a belt type for transferring the toner image to a recording sheet P A transfer device 18, a cleaning device 14 for removing toner and the like remaining on the photosensitive drum 10 after transfer, and the like are provided.

Reference numeral 15 denotes a paper feed tray for stacking and storing the recording paper P, 15a denotes a feed roll for feeding the recording paper P one by one from the paper feed tray 15, and 16 denotes a recording roll fed from the paper feed tray 15. Transfer the paper P to the photosensitive drum 10
A registration roll that sends out the toner image at a predetermined timing between the transfer roller 18 and the transfer device 18;
2 shows a fixing device of a roll type for fixing the toner image on the roll.

In the present embodiment, the transfer device 18
A transfer belt 20 composed of an endless belt, and support rolls 21 for supporting the transfer belt 20 so as to rotate and run in the direction of arrow B in synchronization with the photosensitive drum 10 while the transfer belt 20 is stretched.
22, a bias power source 23 for supplying a transfer bias having a polarity opposite to the toner charging polarity of the transfer toner image to the transfer belt 20
The main part is composed of a power supply roll 24 for applying a transfer bias output from the bias power supply 23 to the transfer belt 20 and a cleaning blade 25 for removing toner and the like attached to the transfer belt 20.

The transfer belt 20 includes two support rolls 2
The transfer nip N is formed in such a manner that the transfer nip N is formed in a state where the transfer nip N is in contact with the photosensitive drum 10 in a state where the transfer nip N is stretched by the reference numerals 1 and 22.
At least the support roll 21 on the upstream side of the transfer nip portion N is disposed in a grounded state, and one of the two support rolls (the support roll 21 in the present embodiment) is a transfer roll. It is a drive roll for the belt 20.

The power supply roll 24 is connected to the photosensitive drum 10.
The transfer belt 20 is disposed between two support rolls 21 and 22 that support a surface that comes into contact with the transfer belt 20. The bias power supply 23 outputs a transfer bias having a bias waveform composed of a rectangular pulse.

A motor 30 serving as a drive source for driving the photosensitive drum 10 and a motor 31 serving as a drive source for driving the drive roll for rotating the transfer belt 20 and supporting the transfer belt 20 are provided. Each of the motors 30 and 31 includes a mechanism capable of outputting a rotation state of an encoder or the like, and the output is sent to the drive controller 70 as needed. The drive controller 70 includes the motor 3
0, a rotation circuit sent from the motor 31 is monitored, and a comparison circuit for comparing the rotation speeds of the two motors is provided.
Is controlling the rotation.

Further, a bias power supply 23 for applying a bias to the power supply roll 24 is controlled by a controller 19. An appropriate bias value is applied to the power supply roller 24 at an appropriate timing under the control of the controller 19. The voltage value applied to the power supply roll 24 is monitored by the controller 19, and the information (the resistance value of the transfer belt 20) is sent to the drive controller 70 described above.

In this embodiment, the photosensitive drum 10
In this case, use an organic photoreceptor whose outer diameter is 84 mm
The process speed was set to 350 mm / s. Transfer bell
For example, chloroprene rubber and carbon black
To give a volume resistivity of 5.1 × 10⁶Adjusted to Ω · cm
Thickness 0.5mm, width 340mm, belt circumference 262
mm surface of tube-shaped belt substrate (paper suction side)
, A fluororesin paint (carbon
The surface resistance is 7.9 × 10 by adding black. ⁸Ω
Prepared) Coated to a thickness of about 7μm to form a surface layer
What was used was used. For each of the above resistance values,
For robe (Mitsubishi Yuka Co., Ltd .: Hi Resta)
The measurement was performed under the condition that 500 V was applied for 10 seconds.

The support roll 21 has an outer diameter of 14 mm.
mm aluminum roll, supporting roll 22
Used was an aluminum roll having an outer diameter of 12 mm. The transfer belt 20 is supported by the support rolls 21 and 22 in an extended state, and is stretched only by the elasticity of the belt itself. At this time, the stretch length of the transfer belt is 27.
It was set to 0 mm. The amount of the transfer belt 20 biting into the photosensitive drum 10 at the transfer nip N was set to 0.5 mm. If the bite amount is 0.2 mm or less, the line image tends to be broken during transfer. The width of the transfer nip N (the width of the photosensitive drum 10 in the circumferential direction) was 10 mm.

The material and thickness of the transfer belt 20 are not particularly limited as long as the belt satisfies the required mechanical strength. For example, as for the material, in addition to the material of the transfer belt used in the present embodiment, a rubber material such as EPDM rubber, NBR rubber, silicon rubber, urethane rubber, or a synthetic material made of nylon, Teflon (registered trademark), or the like is used. A resin film or the like can be used. However, a rubber material is preferable from the viewpoint of simplifying the configuration of the drive system without slipping when the belt is driven. This transfer belt 20, as described above,
It is preferable that the volume resistivity is set in the range of 10 ⁵ to 10 ^13.5 Ω · cm and the surface resistance is set in the range of 10 ⁵ to 10 ^15.5 Ω. When the value exceeds the value, the transfer belt 20 is excessively charged, and it is necessary to provide a charge removing means for removing the charge.

It is desirable that the transfer belt 20 has a low friction surface layer from the viewpoint of preventing the transfer belt 20 from being stained by toner adhesion on the belt surface during long-term use. This low friction surface layer not only prevents toner from adhering, but also bends when passing through the support roll and prevents the cleaning blade 2 from being bent.
4 is made of a material that is unlikely to cause peeling or cracking due to the rubbing by No. 4. Specifically, in addition to the fluorine of the low friction surface layer in the above-described test, it can be formed of silicon, nylon, high-density polyethylene, or the like. The thickness of the low friction surface layer is not particularly limited as long as it does not impair the original function of the transfer belt. The method of forming the low-friction surface layer is not particularly limited, and is arbitrary. For example, in addition to the above-described spray coating method, an electrostatic coating method, a dip coating method, a roll coating method, and a two-layer forming method. A film method or the like can be applied.

Further, the plurality of support rolls for stretching the transfer belt 20 are not limited to two rolls.
A larger number may be used. Further, among the plurality of support rolls, the outer diameter of the support roll (support roll 22 in the present embodiment) which is disposed at a position where the recording paper after transfer from the transfer belt is separated may be such that the recording paper is peeled off. It is necessary that the transfer belt 20 be separated from the transfer belt by itself without the need for a peeling unit, and that the transfer belt 20 be stretched smoothly without wrinkles or slack. For example, the outer diameter of the support roll 22 in the present embodiment is slightly different depending on the elongation percentage when the transfer belt 20 is stretched.
What is necessary is just to set in the range of 10-13 mm.

Next, an image forming process in the image forming apparatus according to the present embodiment will be described. First, after the photosensitive layer of the rotating photosensitive drum 10 is uniformly charged by the charger 11, the light reflected from the original is converged on the charged surface by the image exposure device 12 from an optical image or an image-modulated laser beam. An optical image is irradiated to form an electrostatic latent image. Subsequently, toner is supplied from the developing device 13 and adheres only to the electrostatic latent image on the photosensitive drum 10 to form a toner image T. In this example, the photosensitive drum 1
0 is uniformly charged to a negative polarity to form an electrostatic latent image for reversal development, and then developed with a negatively charged toner, so that a negatively charged toner image T is formed. Has become.

Subsequently, in accordance with the timing of forming the toner image T, recording papers P of a predetermined size and type are fed out one by one from a paper feed tray 15 by a feed roll 15 a, and the timing is adjusted by a registration roll 16. Then, it is sent out toward the transfer nip N. Immediately before the leading edge of the first recording sheet P passes through the transfer nip portion N, based on an instruction from the controller 19, a predetermined voltage (V0) or a predetermined current (I
0) is applied. Here, for example, when the current (I0) is applied, the applied voltage (V0) is
Will occur. Then, the controller 19 detects the resistance value (R0) of the transfer nip N based on the result (see FIG. 3).

The information on the resistance value (R0) of the transfer nip N obtained by the controller 19 is
Is sent to the drive controller 70. The drive controller 70 determines the resistance value of the transfer belt 20 from the obtained resistance value (R0) of the transfer nip portion N (see FIG. 4), and from the result, the photosensitive drum 10 and the transfer belt 20
Is determined (see FIG. 5). As a result, immediately before the recording paper P reaches the transfer nip portion N, the current resistance value (R0) of the transfer nip portion N (that is, the electrostatic attraction force acting between the photosensitive drum 10 and the transfer belt 20) becomes the most. The suitable speed of the transfer belt 20 is determined, and the drive controller 7
From 0, a speed signal is sent to the motor 31. Motor 3
Numeral 1 drives the transfer belt 20 at an appropriate speed based on the transmitted signal.

As a result, the recording paper P conveyed on the transfer belt 20 is fed into the transfer nip N facing the photosensitive drum 10 and then electrostatically attracted to the surface of the transfer belt 20 while being electrostatically attracted to the surface of the transfer belt 20. The toner image T is electrostatically transferred from the photosensitive drum 10 in the transfer nip N at an appropriate speed. The recording paper P on which the toner image T is transferred is transferred to a transfer belt 20 supported by a support roll 22.
After being separated from the transfer belt 20 and peeled off at the portion, the toner image T is fed into the fixing device 17, where the toner image T is fixed, and finally discharged out of the device. Thus, an image is formed.

On the other hand, the photosensitive drum 10 after the transfer is cleaned by the cleaning device 14. Further, regarding the transfer belt 20 in the transfer device 18, the recording paper P
Is separated by the cleaning blade 25. By performing the cleaning of the transfer belt 20, it is possible to prevent a situation in which the back surface of the recording paper P that is attracted to the transfer belt 20 at the next transfer time is stained by the toner remaining on and adhered to the transfer belt 20. .

In the present embodiment, the resistance value of the transfer belt 20 which affects the electrostatic attraction force acting between the photosensitive drum 10 and the transfer belt 20 is monitored, and the driving speed of the transfer belt 20 is adjusted based on the monitored value. By controlling, the transfer belt 2
Since the speed of the photosensitive drum 10 and the speed of the photosensitive drum 10 are made substantially the same, it is possible to prevent expansion and contraction of the transferred toner image T and occurrence of a density difference. Further, since scattering of toner induced by a decrease in transfer efficiency caused by a density difference can be reduced, dirt inside the image forming apparatus can be prevented, and cleaning members such as the cleaning device 14 and the cleaning blade 25 can be used. Can be extended, and the ease of maintenance and reliability can be increased.

Embodiment 2 This embodiment is substantially the same as Embodiment 1, except that the measurement timing of the resistance value of the transfer belt 20 is different from Embodiment 1. Note that among the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the detailed description thereof will be given here. Description is omitted.

In the image forming apparatus according to this embodiment, after the image forming operation is started, the rear end of the first recording sheet P has passed through the transfer nip N, and the leading end of the second recording sheet has After the leading end portion of the non-sheet passing portion of the transfer belt 20, which becomes the non-sheet passing portion until reaching the transfer nip portion N, reaches the transfer nip portion N, a bias power is supplied at a predetermined timing based on an instruction from the controller 19. 23, a predetermined voltage (V0) or a predetermined current (I0) is applied.
1) will occur. The controller 19 detects the resistance value (R1) of the transfer nip N based on the result (see FIG. 3). Since the resistance value of the transfer belt 20 shows a slight change even during the image forming cycle, the resistance value (R0) of the transfer nip portion detected almost before the first recording sheet P is inserted into the transfer nip portion N is equal to the resistance value (R0). May of course show different values.

The resistance value (R) of the transfer nip N, which is the non-sheet passing portion of the transfer belt 20, obtained by the controller 19.
The information of 1) is transmitted from the controller 19 to the drive controller 7.
0 will be sent. The drive controller 70 determines the resistance value of the transfer belt 20 from the obtained resistance value (R1) of the transfer nip N from the relationship shown in FIG. 4, and further determines the speed ratio between the photosensitive drum 10 and the transfer belt 20 from the result. (See FIG. 5). As a result, the speed of the transfer belt 20 is determined immediately before the recording paper P reaches the transfer nip N, and a speed signal is sent from the drive controller 70 to the motor 31. The motor 31 drives the transfer belt 20 at an appropriate speed based on the transmitted signal. These operations are always performed between recording sheets.

In the image forming apparatus according to the present embodiment, since the driving speed of the transfer belt 20 is set for each recording sheet P, the resistance of the transfer belt 20 changes during image formation. The speed of the transfer belt 20 and the speed of the photosensitive drum 10 can be made substantially the same even when the electrostatic attraction force acting between the photosensitive drum 10 and the transfer belt 20 changes with the The expansion and contraction of the image T and the occurrence of a density difference can be prevented.

Third Embodiment FIG. 6 shows an image forming apparatus according to a third embodiment of the present invention. Note that among the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the detailed description thereof will be given here. Description is omitted.

Generally, since the transfer belt 20 is made of a resin material or a rubber material having elasticity, its resistance value changes due to moisture absorption and is affected by the atmospheric humidity of the transfer belt 20. Therefore, a humidity detecting device 40 for detecting the atmospheric humidity of the transfer belt 20 is disposed near the transfer belt 20.

In the image forming apparatus according to the present embodiment, the transfer belt 20 is provided at a predetermined time interval from the start of the image forming operation.
Is detected, and the detected humidity (H0) is sent to the drive controller 70. Drive controller 70
Determines the resistance value of the transfer belt 20 from the obtained atmosphere humidity (H0) of the transfer belt 20 from the relationship of FIG.
Further, the speed ratio between the photosensitive drum 10 and the transfer belt 20 is determined from the result according to FIG. As a result, the recording paper P
The driving speed of the transfer belt 20 is also determined in real time while the
From 0, a speed signal is sent to the motor 31. Motor 3
Reference numeral 1 drives the transfer belt 20 at an appropriate speed based on the transmitted signal.

Fourth Embodiment FIG. 8 shows an image forming apparatus according to a fourth embodiment of the present invention. Note that among the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the detailed description thereof will be given here. Description is omitted.

In FIG. 8, a surface potential detecting device 50 is disposed downstream of the transfer nip N so as to face the transfer belt 20.

In the image forming apparatus according to the present embodiment, a predetermined voltage (V2) or a predetermined current (I2) immediately after the first recording sheet P reaches the transfer nip portion N after the image forming operation is started. Is applied. For example, when the current (I2) is applied, the transfer belt 20 is charged with the charge (Q0) from the current (I2) applied to the power supply roll 24. At this time, since the bias is applied before the leading end of the recording paper P, the transfer belt 20 in front of the leading end of the recording paper P is not affected by the resistance of the recording paper P and is determined only by the resistance value of the transfer belt 20. Thus, a charged portion is formed. Thereafter, when the recording paper P reaches the transfer nip N, a transfer bias value determined at a specified timing is applied to the power supply roll 24.

Thereafter, the transfer belt 20 before the recording paper P
Moves to a position facing the surface potential detecting device 50, and its surface potential (Vs) is detected. The obtained surface potential data (Vs) of the transfer belt 20 is sent to the drive controller 70, and the drive controller 70 calculates the transfer belt 2 from the obtained surface potential (Vs) based on the relationship shown in FIG.
The resistance value of the photosensitive drum 10 is determined from the result.
The speed ratio of the transfer belt 20 is determined according to FIG.
As a result, the speed of the transfer belt 20 is determined, and a speed signal is sent from the drive controller 70 to the motor 31.
The motor 31 drives the transfer belt 20 at an appropriate speed based on the transmitted signal. Since this operation is always performed before the leading edge of the recording paper P, the speed of the transfer belt 20 can be controlled with high accuracy.

Fifth Embodiment FIG. 10 shows an image forming apparatus according to a fifth embodiment of the present invention. Note that among the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the detailed description thereof will be given here. Description is omitted.

In FIG. 10, a current detecting device 60 for detecting a leakage current flowing through the transfer belt 20 is disposed on the support roll 21.

In the image forming apparatus according to the present embodiment, a predetermined voltage (V2) or a predetermined current (I2) immediately before the first recording sheet P reaches the transfer nip portion N after the image forming operation is started. Is applied. For example, when the current (I2) is applied, the transfer belt 20 is charged with the charge (Q0) by the current (I2) applied to the power supply roll 24.
The charge amount at this time is determined by the resistance value of the transfer belt 20.

Thereafter, when the charged transfer belt 20 comes into contact with the grounded support roll 21 on the upstream side of the transfer nip N, the electric charge accumulated in the transfer belt 20 flows to the ground, and the current is detected by the current detecting device. 60 will be detected. The data of the inflow current amount (Ir) detected by the current detection device 60 is sent to the drive controller 70.

The drive controller 70 determines the transfer belt 2 based on the relationship shown in FIG.
The resistance value of the photosensitive drum 10 is determined from the result.
The speed ratio of the transfer belt 20 is determined according to FIG.
As a result, the speed of the transfer belt 20 is determined, and a speed signal is sent from the drive controller 70 to the motor 31.
The motor 31 drives the transfer belt 20 at an appropriate speed based on the transmitted signal. Since this operation is always performed before the leading edge of the recording paper P, the speed of the transfer belt 20 can be controlled with high accuracy.

[0056]

As described above, according to the present invention,
Since the speed of the transfer belt is controlled according to the resistance value of the transfer belt, the speed difference between the image carrier and the transfer belt caused by the electrostatic attraction force is reduced, and the change in the reduction ratio is reduced. And the density difference between images can be prevented.
A high-quality image can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an image forming apparatus according to the present invention.

FIG. 2 is a schematic explanatory diagram of Embodiments 1 and 2 of the image forming apparatus to which the present invention is applied.

FIG. 3 is a graph illustrating a relationship between a supply roll applied voltage and a transfer nip resistance value.

FIG. 4 is a graph showing a relationship between a transfer nip portion resistance value and a transfer belt resistance value.

FIG. 5 is a graph showing a relationship between a transfer belt resistance value and a peripheral speed ratio between the transfer belt and the photosensitive member.

FIG. 6 is a schematic explanatory view of an image forming apparatus according to a third embodiment of the present invention;

FIG. 7 is a graph showing a relationship between transfer belt atmosphere humidity and transfer belt resistance.

FIG. 8 is a schematic explanatory diagram of Embodiment 4 of an image forming apparatus to which the present invention has been applied.

FIG. 9 is a graph showing a relationship between a transfer belt surface potential and a transfer belt resistance value.

FIG. 10 is a schematic explanatory diagram of Embodiment 5 of an image forming apparatus to which the present invention has been applied.

FIG. 11 is a graph showing a relationship between a leakage current value and a transfer belt resistance value.

FIG. 12 is a schematic explanatory view of a conventional belt transfer type image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Image carrier drive means, 3 ... Roll member, 4 ... Transfer belt, 5 ... Belt drive means, 6 ... Bias applying means, 7 ... Belt resistance discriminating means, 8 ... Speed control means, 9 ... Adsorption force discriminating means, K ... Recording material, T ... Toner image

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA01 DA14 DC04 DE05 DE07 DE09 EC06 ED02 ED24 EE01 EE03 EE07 EF12 2H200 GA16 GA23 GA34 GB25 HA02 HB12 HB22 JA02 JA29 JA30 JB07 JB45 JB46 JB49 JB50 LA19 LA27 MA13 LC04 MA04 PA06 PA11 PA22 PA29 PA30 PB08 PB28

Claims (9)

[Claims] 1. An image carrier on which a toner image is formed and carried; an image carrier driving means for driving the image carrier to rotate at a constant speed; A transfer belt disposed, a belt driving unit that rotationally drives the transfer belt, and a recording material that is provided on a back surface side of the transfer belt at a portion facing the image bearing member and the transfer belt, and is conveyed by the transfer belt. An image forming apparatus comprising: a bias application unit configured to apply a bias for transferring a toner image on the image carrier; a belt resistance determination unit configured to determine a resistance value of the transfer belt; and a belt resistance determination unit configured to determine the resistance value of the transfer belt. An image forming apparatus comprising: a speed control unit configured to control a rotation speed of the transfer belt by the belt driving unit based on the determined resistance value. 2. The image forming apparatus according to claim 1, wherein the belt resistance determining unit includes a belt resistance measuring unit that measures a resistance value of the transfer belt. 3. The image forming apparatus according to claim 2, wherein the belt resistance measuring unit measures a resistance value of the transfer belt at a portion where the image carrier and the transfer belt face each other. Image forming device. 4. The image forming apparatus according to claim 3, wherein the belt resistance measuring unit detects the transfer belt under a condition that the recording material does not exist at a portion where the image bearing member and the transfer belt face each other. An image forming apparatus for measuring a resistance value. 5. The image forming apparatus according to claim 3, wherein the belt resistance measuring unit is configured to detect the transfer belt at a timing immediately before the recording material enters a portion where the image carrier and the transfer belt face each other. An image forming apparatus for measuring a resistance value of the image forming apparatus. 6. The image forming apparatus according to claim 1, wherein said belt resistance determining means includes environmental information measuring means for measuring environmental information. 7. The image forming apparatus according to claim 1, wherein the belt resistance determining unit includes a surface potential measuring unit that measures a surface potential of the transfer belt. 8. The image forming apparatus according to claim 1, wherein the belt resistance determination unit includes a leakage current measurement unit configured to measure a leakage current flowing to the roll member via the transfer belt. Characteristic image forming apparatus. 9. An image carrier on which a toner image is formed and carried; an image carrier driving means for rotating the image carrier at a constant speed; and an image carrier which is stretched over a plurality of roll members and faces the image carrier. A transfer belt disposed, a belt driving unit that rotationally drives the transfer belt, and a recording material that is provided on a back surface side of the transfer belt at a portion facing the image bearing member and the transfer belt, and is conveyed by the transfer belt. An image forming apparatus comprising: a bias applying unit configured to apply a bias for transferring a toner image on the image carrier; and an attraction force for determining an electrostatic attraction force acting between the image carrier and the transfer belt. Determining means for controlling the rotation speed of the transfer belt by the belt driving means based on the electrostatic attraction force determined by the attraction force determining means. Image forming apparatus.