JPH0990781A - Electrostatic copying device having transfer belt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic copying device in which the characteristic of a transfer belt can be controlled by controlling 'tension' by a simple easy mechanical addition by utilizing that the electric resistance value of a middle resistance transfer belt is changed by the presence/absence or duration of extended state, and further the extension ratio. SOLUTION: In an electrostatic copying device having an endless transfer belt 6 arranged adjacent to a photoreceptor 3 in order to transfer the toner image on the photoreceptor 3 to a transfer paper and formed of an elastic material, a driving roller 5 and driven roller 4 for endlessly laying the transfer belt 6 over them and driving it, an applying roller making contact with the transfer belt 6 to apply a prescribed transfer voltage thereto, the driven roller 4 is moved to change the distance with the driving roller 5, whereby the extension ratio of the transfer belt 6 is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer,
Regarding an image forming apparatus using an electrostatic transfer system such as a facsimile machine, especially a condition of leaving a belt or a mounting state which is a problem that occurs when a transfer belt is used as a means for transferring a toner image on a photoconductor onto a transfer paper. The present invention relates to an electrostatic copying apparatus capable of preventing a change in electrical resistance value caused by a change in the transfer resistance and a transfer failure caused by the change.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrostatic transfer system such as a copying machine, a printer, a facsimile machine, etc., a photoconductor which is uniformly charged in advance is subjected to an optical reflection such as reflected light of a document in a dark place. To form an electrostatic latent image by exposing it with various image information, and to develop the electrostatic latent image with toner from a developing device to transfer the toner image onto a transfer paper by a transfer device and then fix it. In this way, image formation is performed. By the way, as the transfer device, the surface of the photoconductor is directly opposed to the corona charger, and the transfer paper passing between the photoconductor and the photoconductor is electrostatically charged by applying a charge having a polarity opposite to that of the toner image by corona discharge. A corona transfer method that performs electro-transfer and a bias roller that is a transfer means are faced to the photoconductor through a transfer belt made of a medium resistance material, and a transfer bias is applied when the transfer paper is conveyed to the transfer position by the transfer belt. Then, a contact transfer method is known in which a toner image is transferred onto a transfer paper.

[0003]

The contact type transfer method in which a bias is applied to the belt using a transfer belt is as follows.
Compared with the above-mentioned conventional corona transfer method, there are advantages such as a smaller amount of ozone generation, a smaller power supply capacity, and a good separation / conveyance performance of transfer paper. However, in the contact type transfer method using the transfer belt, the transferability is likely to change due to the difference in the resistance value of the transfer belt. Especially when the resistance value of the whole belt or a part of the belt is low, white spots are generated due to the discharge between the transfer paper and the photoconductor, or too much current flows in the low resistance portion, so that the high voltage power supply (bias supply source) ), The predetermined transfer output cannot be obtained and the transfer failure is likely to occur. In particular, as a transfer belt that performs transfer using contact electrodes, a medium resistance region (10 ⁶ to 10 ¹²
Ω) is used, but it is difficult to make a belt having a resistance value in this region so that it has a uniform resistance value over the entire circumference, and variations in resistance value are within the circumference. If this occurs, the above-mentioned transfer failure is likely to occur. On the contrary, if the resistance value of the transfer belt becomes high locally, the response of the high voltage power supply will not be in time,
Similarly, transfer defects are likely to occur. As the transfer belt having the resistance value in the medium resistance region, a material having a small resistance change is selected, but the belt is still left standing (time, temperature and humidity), and attached (whether or not it is stretched,
The resistance tends to change due to the ambient temperature, and such a change causes a transfer failure.

The present invention utilizes the fact that the electric resistance value of the medium resistance transfer belt changes depending on the presence or absence of a stretched state, the duration, and the stretching rate, and the characteristic of the transfer belt is "mechanically applied" by a simple mechanical addition. It is an object of the present invention to provide an electrostatic copying apparatus that can be controlled by controlling ". In addition, the electric resistance value of the transfer belt, which changes depending on whether the transfer belt is extended or not, and the extension rate, is detected by the device side, and the tension of the transfer belt is changed based on the detection result, so that the electric voltage suitable for the device can be obtained. It also aims to obtain the resistance value.

[0005]

In order to achieve the above-mentioned object, the invention of claim 1 is arranged in the vicinity of a photoconductor in order to transfer a toner image on the photoconductor onto a transfer paper, and is made of an elastic material. The configured endless transfer belt, a drive roller and a driven roller for stretching and driving the transfer belt in an endless manner, and an application roller for applying a predetermined transfer voltage to the transfer belt. In the electrostatic copying apparatus having a roller, the expansion ratio of the transfer belt is changed by moving the driven roller to change the distance between the driven roller and the driving roller. According to a second aspect of the present invention, the driven roller is moved to change the distance between the driven roller and the driving roller, thereby increasing the tension of the transfer belt during the image forming operation by the electrostatic copying apparatus, and during the non-image forming operation. It is characterized in that the tension of the transfer belt is reduced. According to a third aspect of the present invention, the electric resistance value of the transfer belt is controlled by moving the driven roller to change the distance between the driven roller and the driving roller.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 is a perspective view of an essential part of an example of an image forming unit to which the present invention is applied, FIG. 2 is a configuration diagram of a transfer belt supporting roller, and FIGS. 3 and 4 are operations of an image forming unit including a transfer belt. Explanatory drawing, FIG. 5 is a sectional view of the transfer belt, FIG.
FIG. 6 is a diagram showing a state of charges at a transfer position. In addition,
7 and 8 show the main configuration of the first embodiment of the present invention.
Shown in A transfer / conveyance apparatus indicated by reference numeral 1 in FIG. 1 includes a belt unit 2 including a transfer belt as a main body (unit frame body) 1A.
It is detachably supported. Belt unit 2
Is an endless transfer belt 6 wound around a pair of rollers 4 and 5 for transferring the developed image formed on the drum-shaped photoconductor 3 shown in FIG. 5
, A DC solenoid 8 and a contact / separation lever 9 for moving the transfer belt 6 rotating around the fulcrum as a fulcrum to and from the photoconductor 3, and a bias roller 11 for applying a transfer bias to the transfer belt 6.
And a contact plate 13 disposed on the inner surface of the transfer belt 6 for removing the electric charge of the transfer belt 6. Further, the cleaning device 16 having the cleaning blade 16A for scraping off the residual toner adhering to the surface of the transfer belt 6 and the paper waste of the transfer paper S, and the high voltage power supply 12 for applying the voltage to the bias roller 11 are It is provided on the main body 1A side shown in FIG.
One of the rollers 5, as shown in FIGS. 1 and 2, is a drive roller that has a gear 5b connected to a drive motor (not shown) and is rotationally driven. The transfer belt 6 is the roller 5
Driven by the rotation of, the sheet moves in the conveying direction of the transfer sheet S (direction of arrow A in FIG. 3) at a position facing the photoconductor 3. Transfer belt 6
Is a surface layer (a coating layer having a low friction coefficient) as shown in FIG.
The surface layer 6b has a surface resistivity of 1 × 10 ⁹ Ω to 1 when a DC100V is applied to the surface layer 6b, which has a two-layer structure including an inner layer 6a and an inner layer 6a. × 10 to ¹² Omega, the inner layer 6a has a surface resistivity of 1 × 10 ⁷ to 1 × 10 ⁹ Omega
And its volume resistivity is 5 × 10 ⁸ Ω · cm -5 ×
Each of them is set to 10 ¹⁰ Ω · cm.

The driven roller 4 and the driving roller 5 are rotatably supported by a support 7 as shown in FIGS. The support 7 is one of the rollers 4 and 5 shown in FIG.
In the transfer paper transport direction indicated by arrow A, the support shaft 5a of the drive roller 5 located on the downstream side of the transfer position with respect to the photoconductor 3 can be swung toward and away from the photoconductor as a fulcrum. There is. This support 7 is pressed by a DC solenoid 8 driven by a signal from the control plate 8A, or returned by its own weight or a spring force to bring the transfer belt 6 into contact with or separate from the surface of the photoconductor. Works like. That is, the contact / separation lever 9 is connected to the DC solenoid 8, and the contact / separation lever 9 moves the support 7 to bring the transfer belt 6 into contact with or separate from the photoconductor 3.

In the control plate 8A, the front end of the transfer sheet S conveyed in a state of being aligned with the front end position of the toner image formed on the photoconductor 3 by the registration roller 10 which is a paper conveying means is the photoconductor. When approaching 3, a drive signal is issued and D
The C solenoid 8 is driven. Therefore, this solenoid 8
Drive the support member 7 close to the photoconductor drum 3 and bring the transfer belt 6 into contact with the photoconductor member 3, so that the transfer paper S is brought into contact with the photoconductor member 3 at a position facing the photoconductor member 3. A nip portion B that can be conveyed is formed.

Of the rollers 4 and 5, the driven roller 4 located on the side of the photoconductor 3 is configured as a driven roller for the driving side roller 5, and is also a roller. As shown in FIG. 2, the surface shape of 4 is such that both ends 4a, 4a in the axial direction are formed in a tapered taper shape to prevent the transfer belt 6 from being offset. The driven roller 4 is a roller made of a conductive material such as metal, but only supports the transfer belt having a medium electric resistance value as described above, and is electrically different from the other. Is not directly connected to the conductive member of. As the roller 5 on the driving side, a material such as EPDM rubber, chloroprene rubber, or silicone rubber is selected because it is necessary to exert a function of enhancing gripping force with respect to the transfer belt 6 during driving.

The bias roller 11 is provided so as to contact the inside of the transfer belt 6 on the downstream side (left side in FIGS. 3 and 4) of the driven roller 4 in the moving direction of the transfer belt 6. The bias roller 11 constitutes a contact electrode for applying a charge having a polarity opposite to the charging polarity of the toner on the photoconductor 3 to the transfer belt 6, and is connected to the high voltage power supply 12. The contact plate 13 is arranged on the inner surface of the belt near the driven roller 4 on the lower side of the transfer belt 6 which is not the transfer sheet conveying surface, and the charge is injected into the transfer sheet S on the upstream side of the transfer nip portion. Is suppressed. Further, the contact plate 13 is for detecting the current flowing on the transfer belt 6 as a feedback current, and the supply current from the bias roller 11 is controlled by the detection of this feedback current. Therefore, the contact control plate 14 is connected to the contact plate 13 for setting and controlling the current supplied to the bias roller 11 according to the detected current. The transfer control plate 14 is connected to the high voltage power supply 12. Connected and control this.

In such a transfer / transport device 1, as shown in the transfer state of FIG. 4, the support 7 exposes the transfer belt 6 to the transfer belt 6 as the transfer paper S is fed from the registration roller 10. A dip portion B having a width of about 4 to 8 mm, which corresponds to the length along the transporting direction of the transfer sheet, is formed between the photoconductor 3 and the body 3 so as to approach the body 3. on the other hand,
The surface of the photoconductor 3 is charged to, for example, −800 V, and as shown in FIG. 6, the toner of positive charge is electrostatically adsorbed to this surface and is moved to the nip portion. Then, the photoconductor 3 receives the photoconductor 3 before reaching the nip portion.
The surface potential is lowered by a pre-transfer charge eliminating lamp (PTL) 15 which is arranged in the vicinity and weakens the charge on the surface of the photoconductor. In FIG. 6, the height of the charge is represented by the size of the circle, and the state in which the charge is reduced by the pre-transfer charge eliminating lamp 15 is shown smaller than the circle indicating before charge removal.

At the nip portion B shown in FIG.
The upper toner is a bias roller located on the transfer belt 6 side.
It is transferred onto the transfer paper S by the transfer bias from the printer 11. This transfer bias is applied from the high-voltage power supply 12 in the range of -1.5 KV to -6.5 KV, but the transfer bias is variably set as a result of the following constant current control. 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 side through the transfer belt 6 is detected is I ₂ . In such a case, the value of I ₁ is controlled so that the relationship of I ₁ −I ₂ = I _OUT (where I _OUT : constant) (1) is obtained between them. this is,
This is for stabilizing the surface potential V _P on the transfer paper S to eliminate the change in transfer efficiency regardless of changes in environmental conditions such as temperature and humidity and variations in manufacturing quality of the transfer belt 6. . That is, the current flowing to the photoconductor 3 side through the transfer belt 6 and the transfer paper S is regarded as I _OUT , and the current to the transfer belt 6 due to the surface resistance V _P on the transfer paper S being lowered or increased. It is configured to prevent a change in the ease of flow of the sheet from affecting the separation performance and the transfer performance of the transfer paper S. In the case of this embodiment, the current I _OUT flowing through the transfer belt 6 and the transfer paper S to the photoconductor 3 side is 330 mm /
sec, effective bias roller length 310 mm, I
Good transfer was obtained when _OUT was set to 35 μA ± 5 μA.

When the image transfer from the photoconductor 3 is performed, 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 sheet S utilizing the curvature separation of the photoconductor 3 is promoted by the peeling operation due to the waist strength of the transfer sheet S itself. However, in such electrostatic adsorption, due to changes in environmental conditions, when the humidity is high, a current easily flows through the transfer sheet S, so that the transfer sheet cannot be separated. Therefore, since the resistance value of the surface layer 6b of the transfer belt 6 shown in FIG. 5 is set to be slightly higher, the transfer of the true charge to the transfer paper S at the nip portion B is delayed, and further, Bias roller 11 to nip B
It is located on the downstream side of the transfer paper conveyance direction. As a result, the transfer of the true charge from the transfer belt 6 to the transfer sheet S is delayed, and the electrostatic attraction relationship between the transfer sheet S and the photoconductor 3 is avoided. Here, delaying the transfer of the true charge means that no charge is generated in the transfer paper S on the upstream side until the transfer paper S reaches the nip portion on the photoconductor 6 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, as the material of the transfer belt 6, it is preferable to select a material whose resistance change due to environmental changes is small, and as an electrically conductive material for controlling the resistance, carbon, zinc oxide or the like is added in an appropriate amount to form an elastic body. When a rubber belt is used as the belt, it is desired to select a material such as chloroprene rubber, EPDM rubber, silicone rubber, and epichlorohydrin rubber that has a low hygroscopic property and a stable resistance value. The value of the current I _OUT flowing to the side of the photoconductor 3 is not unique and can be reduced when the transport speed is slow, and conversely, when the transport speed is fast or the pre-transfer charge eliminating lamp 15 is used. If it is not used, it will be increased. On the other hand, the transfer paper S that has passed through the nip portion B is electrostatically adsorbed and conveyed in accordance with the movement of the transfer belt 6, and is transferred on the drive side.
Curvature separation at La 5 is performed. Therefore, the diameter of the roller 5 is set to 16 mm or less. Furthermore, such B - in the case of using La 5, experimental results have been obtained that it is possible to separate fine 45K paper (stiffness transverse 21 [cm ^3/100]).

Further, the transfer sheet S separated from the transfer belt at the outer peripheral position of the drive roller 5 is guided by a guide plate to form a heating roller 17a and a pad roller 1 which constitute the fixing section 17.
It is transported to and from 7b. In the fixing unit 17, the toner on the transfer paper S is heated and melted and pressed onto 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 moves in the retreating direction in response to the release of the excitation of the DC solenoid 8, and the support 7 moves from the photosensitive member 3. Be separated. Then, the cleaning device 16 cleans the surface. The cleaning device 16 is provided with a cleaning blade 16A, and by rubbing the transfer belt 6, the toner transferred from the surface of the photoconductor 3 or scattered around the transfer belt 6 without being transferred. The toner powder from the toner or the transfer paper S, which has been attached, is scraped off. The transfer belt 6 rubbed by the cleaning blade 16A has a low friction coefficient in order to prevent an increase in driving force due to an increase in rubbing resistance or a phenomenon such as the curling of the cleaning blade 16A. The surface is coated with a fluorine-based resin material such as polyvinylidene fluoride or ethylene tetrafluoride. The toner or paper dust scraped from the surface of the transfer belt 6 is stored in a waste toner recovery container (not shown) from the main body 1A by the recovery screw 16B.

Next, the first aspect of the present invention will be described with reference to FIGS.
An example of the form will be specifically described. The characteristic configuration of the present embodiment is that the driven roller 4 is configured to be movable in a direction orthogonal to its axial direction and the distance between the driven roller 4 and the drive roller 5 is changed, thereby changing the extension rate of the transfer belt. That is the point. That is, the driven roller 4 shown in FIG. 7 is supported by the bracket 25 that rotatably supports both shaft end portions of the driven roller 4, and is in the arrow direction A (to the drive roller 5) orthogonal to the axial direction of the driven roller 4. It is possible to move in and out). And the bracket 25 is at the center 1
Drive motor with worm gear at a point via the link mechanism 24.
A roller (DC motor) 23 moves the roller 4 in the direction of the arrow. That is, the worm 23a integrated with the output shaft of the motor 23 is meshed with the worm wheel 23b rotatably supported by the body 7 and the like, and the eccentric position 23c of the worm wheel 23b constitutes the link mechanism 24. Is pivotally supported on the bracket 25 by a link. With this configuration, the bracket 25 can be moved forward and backward (approach / separated) from the drive roller 5 by a desired distance by the forward and reverse rotations of the motor. The current detection means 27 detects the load torque applied to the drive motor 23 at this time from the torque converter 21 as a current value, and the control unit 30 determines the tension (resistance value) of the transfer belt based on the detected data. can do. In this example,
Only when the image forming operation of the image forming unit is performed, the driven roller 4 is separated from the drive roller 5 by a necessary distance to secure the tension (expansion rate = resistance value) necessary for the transfer, and when the non-image is formed, the tension is reduced to reduce the tension. The characteristic is that the durability (electrical characteristics) of the device is prevented from decreasing. Another characteristic is that the tension (resistance value) of the transfer belt is detected in real time by the above method, and the position of the driven roller 4 is finely adjusted so that the tension has an optimum value.

FIG. 8 is a schematic view showing the operation of the driven roller, and shows a state in which a transfer belt having a natural inner peripheral length of 300 mm is stretched by about 4% by being stretched by two rollers 4 and 5. ing. The thickness of the transfer belt at this time is 0.5 mm
Then, the inner peripheral length is about 312 mm. 0% extension
→ To reduce to 4%, follow the drive roller 5
The position of la 4 is about +6 mm on the right side in FIG. 8 (separation direction)
You can move it to. The amount of movement is determined by the rotation direction and the number of rotations of the motor 23, and can be controlled by the controller.

Next, <graph 1> in FIG. 9 shows the relationship between the expansion rate of the transfer belt 6 and the electric resistance value of the transfer belt. The characteristics of the transfer belt 6 increase as the expansion rate increases. , Indicates that the electric resistance value decreases. Assuming that the portion indicated by the arrow B is in the range of the appropriate electric resistance value, the range of the stretch rate of the belt (1 to 1) corresponding to the range of the electric resistance value is
If the driven roller 4 is moved to any position within 4%), an appropriate electric resistance value can be obtained. Further, the electrical characteristics of the transfer belt of the medium resistance material vary greatly depending on the material. For example, chloroprene rubber or EPDM mixed with a carbon conductive material exhibits the characteristics as shown in <graph 1> above. The rubber material of rubber type exhibits the characteristics shown in <graph 2>, which is completely opposite to the case of <graph 1>. Therefore, it is necessary to know the characteristics of the transfer belt material to be used in advance.

Next, <Graph 3> shows the change over time in the tension of the transfer belt. For example, if the transfer belt with a natural inner circumference of 300 mm is stretched by 4% and left to stand for a long time (about one week) with the inner circumference of about 312 mm, stress relaxation occurs, and the tension is lower than the initial value (10). It goes down to about 60%. At this time, the electric resistance value of the transfer belt also changes in the increasing direction as shown in Graph 4. As a result, the natural inner circumference is extended to about 305 mm by leaving it for a long time,
The expansion rate is 2.4%. In the present invention, as in the above example, the roller 4 of FIG.
Can be fixed to the right side (the direction away from the drive roller 5) by a predetermined distance (for example, 6 mm), but it is expanded to 4% only during the copying operation and lowered to 0.1% during the standby ( It is considered that the stress relief is reduced by approaching it by approaching the drive roller 5) and that it is easier to put it into practical use (the portion indicated by the dotted line roller in FIG. 8 is in the standby state.) As described above, only during the copy operation. Increase the tension to a predetermined level,
If the tension is relaxed during the rest, it is possible to reduce the tension change (stress relaxation) of the elastic belt 6 as much as possible, and it is possible to maintain the grip force during traveling for a long period of time. It is possible to suppress the change over time in the electric resistance value due to the stress relaxation peculiar to the elastic body transfer belt. According to the first embodiment, the resistance value of the belt can be detected from the torque of the motor even if there is a difference in the characteristics of the belt due to the difference in the materials as shown in Graphs 1 and 2 of FIG. Therefore, the optimum belt resistance value can always be secured.

Next, a second embodiment of the present invention will be described with reference to FIG.
0 and FIG. 11 and FIG. Note that FIG.
The same reference numerals are given to the same portions as. In this embodiment, a high voltage power source 12 applies an application roller (transfer bias roller) 11
A constant voltage is applied to the transfer belt 6, and the current of the applied roller 11 in the state where the transfer belt 6 is in contact with the photoconductor is detected by the current detection means 27, and the control unit 30 is based on this detected value. The roller 4 is moved until the electric resistance value of is equal to an appropriate value. This form example is different from the form example described above in that the driven roller is always separated from the drive roller to provide tension in order to obtain the required resistance, and the resistance value is required because the transfer belt is depressed. Even if the tension deviates from the range, the tension is not increased, but the tension is further increased to control the position of the driven roller 4 to be separated from the drive roller 5 so that the electric resistance value of the belt falls within the required range. Is. Further, as a matter of course, a method of applying a constant voltage to the applied roller 11 and a method of applying a constant current to the applied roller 11 to measure the electromotive force are also applicable. According to the second embodiment described above, the optimum belt resistance value is always ensured by flexibly responding to the difference in the belt characteristics caused by the difference in the materials as shown in Graphs 1 and 2 of FIG. be able to. The belt resistance measuring method according to the second embodiment may be used to secure the proper position of the driven roller 4 during transfer, while the belt may be relaxed during non-image formation.

[0021]

In the first embodiment of the present invention, the tension is increased to a predetermined strength only during the copying operation to secure the required belt resistance value, and the tension is relaxed during the other standby. The change in tension (stress relaxation) of the transfer belt, which is an elastic belt, can be reduced as much as possible, and not only can the belt gripping force of the rollers during running be maintained for a long time, but also the stress relaxation unique to the elastic transfer belt. It is possible to suppress the change over time in the electrical resistance value that comes from the body.
In the second embodiment, the actual resistance value of the transfer belt is measured from the current or the voltage flowing in the transfer bias roller, and the driven roller 4 is moved based on the measured value. Since it is possible to control the change in the electric resistance value due to the change in the tension of the transfer belt to a certain constant value, it is possible to cope with the difference in the characteristics due to the difference in the material as shown in Graph 1 or 2 without any problem. it can.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of an example of an image forming unit to which the present invention is applied.

FIG. 2 is a configuration diagram of a support roller and the like of a transfer belt.

FIG. 3 is an operation explanatory diagram of an image forming unit including a transfer belt.

FIG. 4 is an operation explanatory diagram of an image forming unit including a transfer belt.

FIG. 5 is a sectional view of a transfer belt.

FIG. 6 is a diagram showing a state of electric charges at a transfer position.

FIG. 7 is an explanatory diagram of a main part configuration of a first embodiment of the present invention.

FIG. 8 is an operation explanatory diagram of the example of FIG. 7.

FIG. 9 is a diagram showing characteristics of a transfer belt.

FIG. 10 is an explanatory diagram of a configuration of a second example of the present invention.

11 is an operation explanatory diagram of the example of FIG.

FIG. 12 is an operation explanatory diagram of the example of FIG. 10;

[Explanation of symbols]

1 transfer / transport device, 2 belt unit, 3 photoconductor,
4 driven roller, 5 driving roller, 6 transfer belt, 8
DC solenoid, 9 contact and separation lever, 11 bias roller, 12 high voltage power supply, 13 contact plate, 16 cleaning device, 23 drive motor, 24 link mechanism, 25
Bracket, 27 current detection means, 30 control section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Ishii 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (3)

[Claims] 1. An endless transfer belt, which is disposed in proximity to the photoconductor and is made of an elastic material, for transferring a toner image on the photoconductor onto a transfer sheet, and the transfer belt is stretched endlessly. Drive roller for installing and driving
In an electrostatic copying apparatus having a roller and a driven roller, and an application roller that contacts the transfer belt and applies a predetermined transfer voltage, the driven roller is moved to move between the driven roller and the drive roller. An electrostatic copying apparatus having a transfer belt, wherein the expansion rate of the transfer belt is changed by changing the distance. 2. The tension of the transfer belt is increased during an image forming operation by the electrostatic copying apparatus by moving the driven roller to change the distance between the driven roller and the transfer roller, and the transfer belt is moved during a non-image forming operation. An electrostatic copying apparatus having a transfer belt according to claim 1, wherein the tension of the belt is reduced. 3. The electric resistance value of the transfer belt is controlled by moving the driven roller to change the distance between the driven roller and the driving roller. An electrostatic copying apparatus having a transfer belt.