JP2010175720A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that stably transfers a toner image so as to have high quality, by maintaining the constant speed of rotation of an elastic belt, which is elastically stretchable, whether for a short time or for a long period. <P>SOLUTION: According to the speed of rotation of a transfer conveyance belt 7, detected by a photointerrupter 38, a control section 110 modifies the stretched state of the transfer conveyance belt 7 as required by controlling a tension adjustment mechanism 40. The tension adjustment mechanism 40 is controlled so as to apply a different appropriate tension to the transfer conveyance belt 7, according to an environmental temperature and the degree of wear so that the speed of the conveyance of a recording material P in a transfer section T1 converges to a prescribed value. By controlling the tension of the transfer conveyance belt 7 using the tension adjustment mechanism 40 a constant speed difference between the peripheral speed of a drive roller 31 rotated at a constant speed and the speed of rotation of the transfer conveyance belt 7 is produced, and thereby, the speed of the transfer conveyance belt 7 is made to converge to a prescribed constant speed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that transfers a toner image onto a recording material carried on an elastic belt, and more particularly to control that suppresses the occurrence of defective transfer images due to wear of the elastic belt or environmental temperature changes.

  An image forming apparatus for transferring a toner image from an image carrier (photosensitive member or intermediate transfer member) to a recording material carried on an endless belt member has been put into practical use.

  When a toner image is transferred with the recording material supported on the belt member, if the belt member has a speed variation, the toner image is stretched and transferred to the recording material according to the speed variation state when passing through the transfer portion. . For this reason, a striped pattern perpendicular to the conveyance direction of the recording material appears in the transferred image, and the image quality deteriorates.

  Patent Document 1 discloses an image forming apparatus that sequentially transfers and superimposes toner images from a plurality of photosensitive members onto a recording material electrostatically attracted to an endless belt member. Here, the rotational speed pattern of the driving roller is determined for one rotation of the belt member so as to cancel the speed fluctuation pattern estimated in advance from the eccentric amount of the driving roller and the uneven thickness of the belt member.

  In Patent Document 2, the clock pattern formed on the inner peripheral surface of the intermediate transfer belt is read by an optical sensor to detect the speed fluctuation every moment, and the rotational speed of the driving roller is controlled so as to cancel the detected speed fluctuation. ing.

  Patent Document 3 discloses a recording material conveyance belt that sucks and conveys a recording material by stretching an elastic belt made of a rubber material in a tension state between a pair of support rotating bodies having a fixed inter-axis distance.

JP 2000-310897 A JP 2007-47842 A JP 2008-110875 A

  As shown in Patent Document 3, when a recording material is physically attracted to an elastic belt and passed through a toner image transfer portion, the recording material onto which the toner image has been transferred is easily imaged downstream of the transfer portion. It can be conveniently separated from the carrier. This is because it is not necessary to provide a neutralizing device, a separation claw, a curvature separation structure and the like for separation downstream of the transfer unit.

  Further, since the elastic belt stretched between the support rotating bodies with the fixed inter-axis distance itself generates tension, there is no need to provide a tension roller as shown in Patent Documents 1 and 2. The number of parts is small.

  However, it has been reported that an elastic belt that can be elastically stretched is distorted due to slippage with a support rotating body immediately after starting in an extremely cold region.

  In addition, when continuous operation is performed for a long time, the slip state with the driving roller and the expansion / contraction state along the surface of the driving roller change as the temperature of the elastic belt increases. For this reason, it has been reported that even if the rotational speed of the driving roller is constant, the conveyance speed of the recording material carried on the elastic belt is lowered and the transferred image length is gradually shortened.

  Therefore, as shown in Patent Document 2, there has been proposed control for detecting the rotational speed of the elastic belt and feeding it back to the driving roller.

  However, if the speed of the drive roller is changed, the stretched elastic belt expands and contracts and normal feedback cannot be obtained. As the feedback fluctuates, the rotation of the driving roller becomes unstable and the belt member undergoes a short-term speed fluctuation, and the quality of the transferred image is lowered.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of stably transferring a toner image with high quality by keeping the rotational speed of an elastic belt that can be elastically expanded and contracted constant in the short term and in the long term. It is said.

  The image forming apparatus according to the present invention includes an image carrier that carries a toner image, an elastic belt that can be elastically stretched and supported on a plurality of support rotating bodies in tension, and is carried on the elastic belt. And a voltage applying means for applying a voltage between the image carrier and the elastic belt so as to transfer the toner image to the recording material. And an adjustment mechanism capable of adjusting the tension of the rotating elastic belt, a detecting means for detecting the speed of the rotating elastic belt, and the speed of the rotating elastic belt so as to approach a predetermined value. Control means for controlling the adjusting mechanism in accordance with the output of the detecting means.

  In the image forming apparatus of the present invention, the adjusting mechanism operates to adjust the tension of the elastic belt according to the speed detection result of the elastic belt that can be elastically expanded and contracted. By changing the tension state of the elastic belt to change the wrapping state and the slip state with respect to the support rotating body, the rotational speed of the elastic belt is controlled toward a predetermined value associated with the driving speed.

  For this reason, at least in a short period, the driving speed of the elastic belt is not changed, so that the driving speed is not unstable or fluctuated by the feedback of the detection speed. By changing the tension state, the change in the driving load of the support rotator is suppressed, so that the driving speed is also stabilized.

  Therefore, it is possible to stably transfer the toner image with high quality by keeping the rotational speed of the elastic belt constant for both the short term and the long term.

  Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings. The present invention provides another embodiment in which a part or all of the configuration of the embodiment is replaced with the alternative configuration as long as the rotational speed is stabilized by controlling the tension of the elastic belt that can be elastically expanded and contracted. But it can be done.

  Therefore, it can also be implemented in a secondary transfer section of a tandem type in which a plurality of photoconductors are arranged along the intermediate transfer belt, or a one-drum type full color printer capable of switching the development color.

  In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

  In addition, about the general matter regarding the image forming apparatus shown by patent documents 1-3, illustration is abbreviate | omitted and the overlapping description is abbreviate | omitted.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of a configuration of the image forming apparatus according to the first embodiment.

  As shown in FIG. 1, the image forming apparatus 100 is a monochrome printer in which a black image forming unit PK is attached to a transfer conveyance belt 7.

  In the image forming unit PK, a black toner image is formed on the photosensitive drum 6 and is attracted to the transfer conveyance belt 7 and transferred to a recording material passing through the transfer unit T1. The recording material P onto which the toner image has been transferred is sent to the fixing device 11 and is heated and pressed to fix the toner image, and then discharged onto the stacking tray 20 through the discharge roller 19.

  Alternatively, after fixing, the sheet is fed to the lower switchback roller 18 to perform switchback processing, transferred to the conveying roller 17 in a reverse state, and fed again to the transfer unit T1 for duplex printing.

  The recording material P drawn from the recording material cassette 10 by the pickup roller 14 is separated one by one by the separating device 15 and sent to the registration roller 9. The registration roller 9 receives and waits for the recording material P in a stopped state, and sends the recording material P to the transfer portion T1 in synchronization with the toner image carried on the photosensitive drum 6.

  The image forming unit PK includes a charging device 1, an exposure device 2, a developing device 3, a transfer conveyance belt 7, and a cleaning device 5 around the photosensitive drum 6.

  The photosensitive drum 6 is configured by applying an organic photoconductor (OPC) having a negative charging property to the outer peripheral surface of an aluminum cylinder, and rotates in a direction indicated by an arrow R1 at a predetermined process speed.

  The charging device 1 applies an oscillating voltage obtained by superimposing an AC voltage on a DC voltage to the charging roller to rotate the photosensitive drum 6 to charge the surface of the photosensitive drum 6 to a uniform dark portion potential VD having a negative polarity. .

  The exposure apparatus 2 scans a scanning beam image data obtained by developing the image data with a rotating mirror, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 6. In the exposed portion of the photosensitive drum 6, the dark portion potential VD is discharged and the light portion potential VL is lowered.

  The developing device 3 charges the magnetic toner to a negative polarity and carries it on the developing sleeve, and rubs the photosensitive drum 6 with the magnetic brush of the magnetic toner formed on the developing sleeve. By applying an oscillating voltage in which an AC voltage is superimposed on a negative DC voltage to the developing sleeve, the magnetic toner adheres to the portion of the bright portion potential VL that is relatively positive with respect to the developing sleeve, and electrostatically The image is reversal developed.

  The cleaning device 5 brings a cleaning blade into contact with the photosensitive drum 6 to remove the transfer residual toner remaining on the surface of the photosensitive drum 6 that has passed through the transfer portion T1.

<Transfer section>
FIG. 2 is an explanatory diagram of the configuration of the transfer unit using the transfer conveyance belt.

  As shown in FIG. 2, the transfer conveyance belt 7 is an elastic belt that can be elastically expanded and contracted, and tension is applied to a driving roller 31 and a driven roller 32 that are examples of a supporting rotating body having a fixed inter-axis distance. It is supported in the state. The auxiliary roller 30 that rotatably supports the inner surface of the transfer conveyance belt 7 between the driving roller 31 and the driven roller 32 is also a part of a voltage application unit that applies a voltage to the transfer unit T1.

  Since an image forming apparatus with a low process speed has a small radius of the photosensitive drum, the curvature is easily separated from the photosensitive drum by the rigidity of the recording material. However, in an image forming apparatus with a high process speed, the radius of the photosensitive drum is large, so that it is difficult to separate the curvature due to the rigidity of the recording material, and jamming around the photosensitive drum is likely to occur downstream of the transfer portion. Therefore, in the image forming apparatus 100, the recording material P is electrostatically attracted to the transfer conveyance belt 7 and conveyed by using the transfer conveyance belt 7, and the recording material is wound around the photosensitive drum 6 downstream of the transfer portion T1. Adopting an indispensable structure.

  The transfer conveyance belt 7 rotates in a conveyance direction indicated by an arrow while being pressed against the photosensitive drum 6 in a section supported by the auxiliary roller 30 and the driven roller 32.

  The transfer conveyance belt 7 is made of a material having a resistance that allows a transfer current difference between an inner side and an outer side of the recording material to be within an allowable range, and is a power source that is an example of a voltage applying unit through an auxiliary roller 30 and a driven roller 32. A positive transfer voltage V1 is applied from D2.

  As a result, the recording material P fed by the registration roller 9 is electrostatically adsorbed and fixed to the transfer / conveying belt 7, and is conveyed to the transfer unit T <b> 1 as the transfer / conveying belt 7 rotates. Then, the transfer electric field formed between the transfer conveyance belt 7 and the photosensitive drum 6 causes the toner image, which is negatively charged and carried on the photosensitive drum 6, to the recording material P carried on the transfer conveyance belt 7. Transcribed.

  The drive roller 31 disposed on the downstream side in the conveyance direction of the recording material P is controlled so as to always rotate at a constant peripheral speed. The rotational speed of the drive roller 31 is detected by the rotary encoder 31a. The motor control circuit 31b adjusts the drive input of the drive roller 31 according to the pulse output of the rotary encoder 31a, and maintains the rotation speed of the drive roller 31 constant regardless of the load fluctuation of the drive roller 31.

  Accordingly, the transfer / conveying belt 7 has a constant rotation speed by maintaining a constant winding state, a constant thickness, a constant tension state, a constant expansion / contraction state, and a constant slip state with respect to the drive roller 31. The recording material P is conveyed at a constant rotational speed corresponding to the rotational speed of the driving roller 31, and a toner image without expansion / contraction or disturbance is transferred from the photosensitive drum 6.

  However, the thickness, tension state, expansion / contraction state of the transfer conveyance belt 7, the slip state of the transfer conveyance belt 7 with respect to the driving roller 31, and the winding state vary depending on various factors. For this reason, even if the driving roller 31 rotates at a constant rotational speed, the speed fluctuation may occur in the recording material that is carried on the transfer conveyance belt 7 and passes through the transfer portion T1. When a speed change occurs in the recording material when passing through the transfer portion T1, the toner image transferred to the recording material P expands or contracts and is disturbed in a stripe shape.

  The transfer conveyance belt 7 is held by a driving roller 31 that is rotationally driven in a predetermined direction. The transfer conveyance belt 7 is caused by a contact frictional force between the inner surface of the transfer conveyance belt 7 and the surface of the drive roller 31 when the drive roller 31 rotates. Is rotated in a predetermined direction. In such a configuration, slipping occurs with the drive roller 31 when the transfer conveyance belt 7 rotates.

  When the environment is high, the elastic property of the transfer / conveying belt 7 causes elongation, and the tension of the transfer / conveying belt 7 held by the driving roller 31 decreases. For this reason, slip increases and the difference between the speed at which the drive roller 31 rotates and the speed at which the transfer and transport belt 7 transports increases. When the environment is low, the transfer / conveying belt 7 is contracted, and the load on which the transfer / conveying belt 7 is wound around the driving roller 31 increases. Becomes smaller.

  The slip state between the transfer conveyance belt 7 and the drive roller 31 also changes depending on the wear state of the contact surface of the transfer conveyance belt 7 with the drive roller 31. The slip between the transfer conveyance belt 7 and the driving roller 31 also changes depending on other situations.

  For this reason, in the configuration in which a constant pressure is applied to the transfer / conveyance belt 7, the rotation speed of the transfer / conveyance belt 7 cannot be kept constant. It will have a big influence on.

  However, even if the rotational speed of the driving roller 31 is controlled, the rotational speed of the transfer conveyance belt 7 cannot be controlled well. Control for detecting the rotational speed of the transfer / conveying belt 7 and increasing / decreasing the rotational speed of the driving roller 31 is inappropriate for the transfer / conveying belt 7 that is an elastic belt that can be elastically expanded and contracted. The speed detected by the transfer / conveyance belt 7 and the time difference between the change in the rotation speed of the driving roller 31 and the change in the rotation speed of the transfer / conveyance belt 7 are also affected by the expansion / contraction of the transfer / conveyance belt 7. For this reason, appropriate feedback control cannot be performed, and the speed control of the transfer / conveyance belt 7 diverges, resulting in a large speed fluctuation.

  Therefore, in the image forming apparatus 100, the adjusting mechanism appropriately changes the expansion / contraction state of the transfer conveyance belt 7 according to the speed detected by the detection unit. The control means controls the adjustment mechanism to change the tension applied to the transfer conveyance belt 7. The tension adjusting mechanism 40 is used to apply different appropriate tensions to the transfer / conveying belt 7 according to various situations so that the conveying speed of the recording material P in the transfer unit T1 is constant. By controlling the tension of the transfer / conveyance belt 7 using the tension adjusting mechanism 40, the speed difference between the rotational speed of the transfer / conveyance belt 7 and the peripheral speed of the drive roller 31 is reproduced uniformly. By controlling the slip at the time of transmission that the driving roller 31 gives to the transfer conveyance belt 7, the speed of the transfer conveyance belt 7 is kept constant.

<Speed detector>
FIG. 3 is an explanatory diagram of a mechanism for detecting the speed of the rotating elastic belt.

  As shown in FIG. 3, a photo interrupter 38, which is an example of a detection unit, outputs a signal corresponding to the surface speed of the transfer conveyance belt 7. As a characteristic of the transfer / conveying belt 7 that is elastically expandable / contractable, the circumference may be extended in a durability or high temperature environment, or may be contracted in a low temperature environment. Further, since the surface state of the transfer conveyance belt 7 changes and the slip state with the driving roller 31 changes, the tension of the transfer conveyance belt 7 is appropriately controlled according to the speed parameter of the transfer conveyance belt 7 at that time. There is a need.

  The transfer / conveying belt 7 has a large number of cutouts 7a having a constant width at regular intervals. The photo interrupter 38 is disposed at a position where the end of the transfer conveyance belt 7 passes.

  In a situation where the driving roller 31 transmits driving force to the transfer / conveying belt 7 and the transfer / conveying belt 7 rotates in the recording material conveying direction, the cutouts 7a at the ends of the transfer / conveying belt 7 are successively photo-interrupters. Pass 38.

  The controller 110 detects the transmitted light at the notch 7a from the state where the light is shielded at the interval of the notch 7a as the transfer conveyance belt 7 rotates, and again determines the time until the light is shielded at the interval of the notch 7a. Measure and use as speed parameter. Thus, the surface speed of the transfer conveyance belt 7 is detected using the speed parameter of the notch 7 a provided in the transfer conveyance belt 7. The controller 110 can reduce the speed detection error of the transfer conveyance belt 7 to a necessary level by shortening the sampling time for detecting the output of the photo interrupter 38.

  The detecting means is not limited to the combination of the photo interrupter 38 and the notch 7a. Alternatively, a magnetic or optical incremental pattern may be written on the transfer / conveying belt 7 to detect the incremental pattern with a magnetic head or an optical head. The speed of the transfer conveyance belt 7 may be measured by irradiating a sound wave and detecting the reflected sound to evaluate the Doppler effect.

  Further, between the driven roller 32 and the auxiliary roller 30 acting as a flywheel, the rotational speed of the transfer conveyance belt 7 is not easily affected by uneven rotation of the driving roller 31 or operation of a tension adjusting mechanism 40 described later. Therefore, the most stable transfer can be performed by forming the transfer portion T1 by bringing the photosensitive drum 6 into contact with the driven roller 32 and the auxiliary roller 30. At the same time, the rotational speed of the transfer / conveying belt 7 is measured with the minimum disturbance caused by the driving roller 31 and the tension adjusting mechanism 40 by disposing the photo interrupter 38 between the driven roller 32 and the auxiliary roller 30. Can do.

  In other words, an auxiliary roller arranged to support the elastic belt between a pair of supporting rotating bodies is provided, and the image carrier is in contact with the elastic belt between one supporting rotating body and the auxiliary roller. The detecting means detects the speed of the elastic belt between the auxiliary roller and the image carrier.

  The pair of support rotators includes a driving roller that drives the elastic belt and a driven roller that is driven to rotate by the elastic belt, and the image carrier is an elastic belt between the driven roller and the auxiliary roller. Abut.

<Tension adjustment mechanism>
As shown in FIG. 2, the transfer conveyance belt 7 is stretched around a pair of support rotators having a fixed inter-axis distance, and the tension adjusting mechanism 40 is supported by the pair of support rotators to carry a recording material. This is a mechanism for pressing the recording material carrying surface of the transfer conveyance belt 7 with a rotatable roller on the opposite side.

  The image forming apparatus 100 includes, as an example of an adjustment mechanism, a tension adjustment mechanism 40 that can change the tension applied to the transfer conveyance belt 7 when the recording material P is sucked, held, and conveyed. The tension adjusting mechanism 40 can adjust the tension of the elastic belt by changing the pressing force against the transfer / conveyance belt 7 by a tensioner roller 33 as a tension increasing / decreasing member of the transfer / conveyance belt 7. The tension adjusting mechanism 40 is disposed below an exchange unit in which the driving roller 31, the driven roller 32, and the transfer conveyance belt 7 are assembled together.

  The tensioner roller 33 is rotatably attached to a tensioner roller bearing 34, and the tensioner roller bearing 34 is given a characteristic of being displaced in a direction in contact with the outer peripheral surface of the transfer conveyance belt 7 by a tensioner spring 35. .

  Due to the displacement of the tensioner roller bearing 34 due to the characteristics of the tensioner spring 35, the tensioner roller 33 presses the outer peripheral surface of the transfer conveyance belt 7 with a predetermined pressure, whereby a predetermined tension is applied to the transfer conveyance belt 7. The end of the tensioner spring 35 opposite to the tensioner roller bearing 34 is supported by a rack member 36 that moves the tensioner roller bearing 34. The rack member 36 moves up and down when the motor 37a drives the tensioner drive gear 37, and changes the contraction amount of the tensioner spring 35 attached to the tensioner roller bearing 34.

  The adjustment mechanism is not limited to the tension adjustment mechanism 40. A roller, a friction plate, or the like that biases the inner surface of the transfer / conveyance belt 7 with a variable pressing force may be used. Instead of a tension mechanism for keeping the tension constant, any tension adjusting mechanism that can adjust the tension so that the speed is reproduced at a constant level may be used.

<Example 1>
4 is a perspective view of the transfer unit, FIG. 5 is an explanatory diagram of control for increasing the speed of the transfer conveyance belt, FIG. 6 is an explanatory diagram of control for decreasing the speed of the transfer conveyance belt, and FIG. It is a flowchart.

Transfer conveyance belt 7: thickness 600 μm, width 400 mm × circumference 360 mm
Drive roller 31: material stainless steel pipe, diameter 20 mm x length 410 mm
Follower roller 32: material stainless steel pipe, diameter 20 mm x length 410 mm
Photosensitive drum 6: diameter 80mm, process speed 300mm / sec
Distance between shafts of driving roller 31 and driven roller 32: 200 mm
Transfer voltage: 2000V
Tension adjustment range by the tension adjustment mechanism 40: 0.1 to 0.3 N
Speed adjustment range of transfer conveyance belt 7: -5% to + 5% of process speed

  As shown in FIG. 4, the tension adjusting mechanisms 40 are arranged at both ends of the tensioner roller 33 and operate in synchronization. The control means (110) controls the adjustment mechanism (40) according to the output of the detection means (38) so that the speed of the rotating elastic belt (7) approaches a predetermined value. The controller 110 controls the conveyance speed of the recording material P to an appropriate value by moving the tensioner roller 33 up and down to change the tension of the transfer conveyance belt 7.

  As shown in FIG. 5, the driving roller 31 rotates at a constant peripheral speed. When the rotation speed of the transfer conveyance belt 7 measured using the photo interrupter 38 decreases and falls within the allowable range, the tension adjusting mechanism 40 raises the tensioner roller 33 so that the rotation speed of the transfer conveyance belt 7 falls within the allowable range. The tension of the transfer / conveyance belt 7 is increased until the return.

  As shown in FIG. 6, when the rotation speed of the transfer conveyance belt 7 increases and exceeds the allowable range, the tension adjustment mechanism 40 lowers the tensioner roller 33 so that the rotation speed of the transfer conveyance belt 7 returns to the allowable range. Until this is done, the tension of the transfer / conveying belt 7 is reduced.

  As shown in FIG. 7 with reference to FIG. 2, the control unit 110 detects the speed index formed on the transfer conveyance belt 7 by the photo interrupter 38 and measures the surface speed at which the transfer conveyance belt 7 rotates. (S301).

  The control unit 110 compares the rotation speed calculated from the output of the photo interrupter 38 with a target value, and determines whether or not to perform adjustment of the tension adjustment mechanism 40 (S302). If the measured speed is different from the target value, the sampling time is shortened, the output of the photo interrupter 38 is taken in again, and the rotational speed of the transfer conveyance belt 7 is measured (S303). If the measured rotational speed satisfies the target value tolerance, the operation is terminated.

  However, when the measured rotation speed of the transfer / conveyance belt 7 is slower than the target value (slow in S303), it is necessary to increase the tension of the transfer / conveyance belt 7 as shown in FIG. This is because it is considered that the transmission force from the driving roller 31 to the transfer conveyance belt 7 is reduced due to the decrease in the tension of the transfer conveyance belt 7.

  The control unit 110 inputs a predetermined pulse to the motor 37 a to move the rack member 36 in a direction approaching the transfer conveyance belt 7 and abuts the tensioner roller 33 on the transfer conveyance belt 7 using a spring force. Let Thereby, the tension of the transfer conveyance belt 7 is increased and converged to the target rotational speed.

  On the other hand, when the measured rotation speed of the transfer conveyance belt 7 is faster than the target value (fast in S303), it is necessary to reduce the tension of the transfer conveyance belt 7 as shown in FIG. This is because it is considered that the transfer conveyance belt 7 is held in the direction in which the transfer conveyance belt 7 is wound around the drive roller 31 as the transfer conveyance belt 7 is reduced or cured, and the transmission force is increased.

  The control unit 110 inputs a predetermined pulse to the motor 37a, thereby moving the rack member 36 in a direction away from the transfer conveyance belt 7 and reducing the pressing force of the tensioner roller 33 to reach the target rotational speed. Converge.

  As described above, in the first exemplary embodiment, in the image forming apparatus 100 using the transfer / conveyance belt 7, the surface speed of the transfer / conveyance belt 7 during rotation is measured with respect to the expansion / contraction of the belt due to environmental temperature and belt deterioration. To adjust the tension. As a result, the conveyance speed of the recording material can be kept constant by changing the tension applied to the transfer conveyance belt 7 while keeping the speed of the drive roller 31 constant, and stable image formation is possible. It is.

<Example 2>
FIG. 8 is an explanatory diagram of the configuration of the image forming apparatus according to the second embodiment.

  The second embodiment is an embodiment in an image forming apparatus 200 of a tandem intermediate transfer system that includes cyan, magenta, yellow, and black image forming portions PY, PM, PC, and PK.

  The transfer transfer belt 7 and the tension adjusting mechanism 40 similar to those of the first embodiment are disposed in the secondary transfer portion T2 that transfers the toner image from the intermediate transfer belt 16 to the recording material P.

It is explanatory drawing of a structure of the image forming apparatus of 1st Embodiment. It is explanatory drawing of a structure of the transfer part using a transfer conveyance belt. It is explanatory drawing of the mechanism which detects the speed of the elastic body belt to rotate. It is a perspective view of a transfer part. It is explanatory drawing of the control which raises the speed of a transfer conveyance belt. It is explanatory drawing of the control which reduces the speed of a transfer conveyance belt. 3 is a flowchart of control according to the first embodiment. FIG. 6 is an explanatory diagram of a configuration of an image forming apparatus according to a second embodiment.

DESCRIPTION OF SYMBOLS 1 Charging device 2 Exposure device 3 Development device 5 Cleaning device 6 Photosensitive drum 7 Elastic belt (transfer conveyance belt)
9 Registration Roller 10 Recording Material Cassette 11 Fixing Device 30 Auxiliary Rollers 31, 32 Supporting Rotating Body (Drive Roller, Driven Roller)
33 Tensioner roller 34 Tensioner roller bearing 35 Tensioner spring 36 Rack member 37 Tensioner drive gear 38 Detection means (photo interrupter)
P Recording material

Claims (5)

An image carrier for carrying a toner image;
An elastically stretchable elastic belt that is supported by being stretched over a plurality of support rotating bodies;
In an image forming apparatus, comprising: a voltage applying unit that applies a voltage between the image carrier and the elastic belt so as to transfer a toner image to a recording material carried on the elastic belt.
An adjustment mechanism capable of adjusting the tension of the rotating elastic belt;
Detecting means for detecting the speed of the rotating elastic belt;
An image forming apparatus comprising: a control unit that controls the adjustment mechanism in accordance with an output of the detection unit so that a speed of the rotating elastic belt approaches a predetermined value.   The image forming apparatus according to claim 1, wherein the elastic belt is stretched between a pair of support rotating bodies having a fixed inter-axis distance.   The adjusting mechanism is a mechanism that presses the recording material carrying surface of the elastic belt with a rotatable roller on the opposite side supported by the pair of supporting rotating bodies and carrying the recording material. Item 3. The image forming apparatus according to Item 2. An auxiliary roller for supporting an inner surface of the elastic belt between the pair of support rotating bodies;
The image carrier is in contact with the elastic belt between one supporting rotating body and the auxiliary roller,
The image forming apparatus according to claim 3, wherein the detection unit detects a speed of the elastic belt between the auxiliary roller and the image carrier.   The image forming apparatus according to claim 4, wherein the one supporting rotating body and the auxiliary roller rotate following the rotating elastic belt.

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