JP2015227989A - Intermediate transfer unit and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent vibration phenomenon or change in speed of an intermediate transfer belt, to prevent color misregistration or color unevenness.SOLUTION: An intermediate transfer unit includes: image forming units 11K, 11Y, 11M, 11C; an intermediate transfer belt 12; and a secondary transfer roller 16. The intermediate transfer unit transfers a plurality of images on an intermediate transfer belt in a superimposed manner, and allows a recording sheet P to pass through a secondary transfer section S formed by the intermediate transfer belt and the secondary transfer roller, for transfer. The intermediate transfer unit includes: a tension sensor 21 arranged near the secondary transfer roller 16, to detect tension of the intermediate transfer belt; a tension control mechanism 22 which applies a frictional force in contact with the intermediate transfer belt, to control tension of the intermediate transfer belt; and a tension control apparatus 23 which controls the tension control mechanism, according to the change in tension of the intermediate transfer belt obtained from the tension sensor.

Description

  The present invention relates to an intermediate transfer unit in an electrophotographic laser printer, a copying machine, a facsimile, and the like, and an image forming apparatus including the intermediate transfer unit.

  In recent years, documents processed in offices and the like have been rapidly colored, and image forming apparatuses such as copying machines, printers, and facsimiles that handle these documents have also been rapidly colored. Currently, these color image forming apparatuses tend to be improved in image quality and speeded up with the improvement and speed of office processing in offices and the like. As a color image forming apparatus that can meet such a demand, for example, it has an image forming unit of each color of black (K), yellow (Y), magenta (M), and cyan (C) and is formed by each image forming unit. Various so-called tandem-type color image forming apparatuses that perform multiple transfer of images of different colors onto a transfer material or intermediate transfer member to be conveyed to form a color image have been proposed and commercialized.

  Examples of this type of tandem color image forming apparatus include the following. FIG. 8 is a schematic diagram showing a configuration of a conventional tandem type image forming apparatus. As shown in FIG. 8, the tandem type image forming apparatus 10 includes a black image forming unit 11K that forms a black (K) image and a yellow image forming unit 11Y that forms a yellow (Y) image. And a magenta color image forming unit 11M that forms a magenta (M) color image and a cyan color image forming unit 11C that forms a cyan (C) color image. These four image forming units 11K, 11Y, 11M, and 11C are horizontally arranged at a predetermined interval.

  Also, an intermediate transfer belt 12 as an annular transfer material carrier is disposed below the four image forming units 11K, 11Y, 11M, and 11C. The four image forming units 11K, 11Y, 11M, and 11C are provided with photosensitive drums 13K, 13Y, 13M, and 13C, and the surfaces of the photosensitive drums 13K, 13Y, 13M, and 13C are uniformly charged. Thereafter, an image forming laser beam is scanned and exposed according to image information to form an electrostatic latent image.

  The electrostatic latent images formed on the surfaces of the photosensitive drums 13K, 13Y, 13M, and 13C are respectively black, yellow, and yellow by developing units (not shown) of the image forming units 11K, 11Y, 11M, and 11C. A visible toner image is formed by developing with magenta and cyan toners. These visible toner images are pre-transfer charged by a pre-transfer charger (not shown) and then sequentially transferred onto the intermediate transfer belt 12. In FIG. 1, reference numeral 14 denotes a driving roller around which the intermediate transfer belt 12 is wound, and reference numeral 15 denotes a driven roller.

  The intermediate transfer belt 12 to which the toner images of the respective colors have been transferred is transferred to the recording paper P that is passed through at the position of the secondary transfer roller 16 to perform image formation. In particular, in the case of a color image forming apparatus including a transfer fixing unit that performs fixing simultaneously with the secondary transfer roller 16, it is necessary to perform transfer fixing while bringing the recording paper P and the intermediate transfer belt 12 into contact with each other at a relatively high pressure. is there. Therefore, when the recording paper P enters the transfer fixing unit, a braking force is generated to stop the belt running at the transfer fixing unit. Then, the belt tension increases rapidly, and the belt tension on the belt slack side decreases rapidly. As a result, shocking vibration is generated in the intermediate transfer belt 12, and this vibration propagates through the intermediate transfer belt 12 and is transmitted to the photosensitive drums 13K, 13Y, 13M, and 13C during image formation or primary transfer. It causes image degradation locally.

  Also, when the recording paper comes out from the transfer and fixing unit, a vibration phenomenon occurs due to the release of the braking force, which similarly causes image deterioration. For this reason, “color misregistration” that causes misregistration between the colors of each other, “color unevenness” that slightly changes the hue, or a very ugly striped pattern occurs in the background color. There is a problem of causing shock jitter (image deterioration in which uneven color or stripes occur). As described above, it is important to suppress the vibration phenomenon and the speed fluctuation of the image forming belt such as the photosensitive member including the intermediate transfer belt and the sheet conveying belt.

  In Patent Document 1, a portion other than the image formed on the surface of the intermediate transfer belt is pressed against the image forming surface of the intermediate transfer belt with a tension roller. This is because a spring provided in the translation direction of the tension roller absorbs vibration due to shocking tension fluctuations of the belt to reduce image deterioration.

  In Patent Document 2, the first and second tension rollers are movably supported on both sides of a transfer portion serving as a disturbance generation source based on the supply of the recording medium, and are in contact with the belt photoreceptor. Further, a position sensor for detecting the position of the tension roller is provided. Based on the detection of the position sensor, the speed servo control circuit controls the speed of the transfer backup roller so that the first tension roller is maintained at substantially the same position. A plurality of write heads are provided for forming latent images of each color on the belt photoconductor.

  In this image forming apparatus, when a recording medium is fed into a transfer nip formed between a transfer backup roller and a transfer pinch roller in a transfer portion, a braking force is generated to stop the belt photoreceptor from running. To do. Then, the belt tension on the belt tension side suddenly increases, and the belt tension on the belt slack side tends to decrease rapidly. When the belt tension on the belt tension side increases, the displacement of the second tension roller is suppressed. When the belt tension on the belt slack side decreases, the position sensor detects the displacement of the first tension roller, and the speed servo control circuit increases the rotational speed of the transfer backup roller to suppress the belt tension from decreasing. By maintaining the first tension roller in a fixed position in this way, image deterioration due to belt tension fluctuation is reduced.

  Furthermore, Patent Document 3 discloses a technique for preventing the belt member tension variation due to the load variation from being sufficiently absorbed when a sudden load variation has occurred in the belt device on which the belt member is driven. ing. That is, the contact member that contacts the belt member and applies tension is fixed so that the relative position in the apparatus is not displaced. Further, the belt member is configured to be deformable so that the tension of the belt member does not fluctuate. As a result, with a relatively simple configuration, without causing an increase in cost, weight, and size, a shock jitter does not occur on an image even if a sudden load fluctuation occurs in the apparatus.

  As described above, in a color image forming apparatus including a transfer fixing unit, it is important to suppress vibration and speed fluctuation phenomenon of an image forming belt such as a conveyance belt including an intermediate transfer belt. SUMMARY OF THE INVENTION An object of the present invention is to provide an intermediate transfer unit and an image forming apparatus that can suppress the occurrence of color shift and color unevenness by suppressing the vibration phenomenon and speed fluctuation of the intermediate transfer belt.

  An intermediate transfer unit according to the present invention includes a plurality of image forming units, an intermediate transfer belt, and a secondary transfer roller that forms a secondary transfer portion with the intermediate transfer belt, and is formed by the plurality of image forming units. In the intermediate transfer unit for transferring the plurality of images superimposed on the intermediate transfer belt, passing the recording medium through the secondary transfer portion and transferring the image on the intermediate transfer belt to the recording medium, the secondary transfer unit A tension sensor that is disposed in the vicinity of the transfer roller and detects the tension of the intermediate transfer belt; a tension control mechanism that controls the tension of the intermediate transfer belt by applying a frictional force in contact with the intermediate transfer belt; And a tension control device that controls the tension control mechanism based on a change in tension of the intermediate transfer belt obtained from the tension sensor.

  According to the present invention, the vibration phenomenon and speed fluctuation of the intermediate transfer belt can be suppressed, the occurrence of color misregistration and color unevenness can be prevented, and high image quality can be achieved.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. Schematic diagram illustrating the configuration of an image forming apparatus according to a second embodiment of the present invention. A graph showing the result of simulating the change in tension of the intermediate transfer belt when recording paper enters the transfer section Schematic diagram showing the configuration of an image forming apparatus according to a third embodiment of the present invention. 6 is a graph showing a change in speed of the surface of the intermediate transfer belt in the image forming apparatus according to the third embodiment of the present invention. The graph which shows an example of the measurement result of the speed fluctuation which generate | occur | produced in the intermediate transfer belt when the recording paper enters the transfer part to the secondary transfer part which transfers the image formed on the intermediate transfer belt to the recording paper Measurement results of rotation transfer characteristics from the drive motor of the intermediate transfer belt to the speed of the surface of the intermediate transfer belt Schematic diagram showing the configuration of a conventional tandem color image forming apparatus

  In the present invention, a tension control mechanism that controls the tension in the vicinity of the secondary transfer roller in accordance with a change in the tension of the intermediate transfer belt obtained from the tension sensor is in contact with the intermediate transfer belt and applies a relative friction force. Control the tension with. Further, a tension control device for controlling the tension control mechanism is provided.

  Thus, shock jitter due to transfer characteristic degradation when the toner image formed by the intermediate transfer unit is transferred from the intermediate transfer belt to a recording sheet as a recording medium can be prevented. In addition, it is possible to reduce the tension fluctuation caused by the entry of the recording paper that causes the tension fluctuation and the removal of the recording paper from the secondary transfer portion near the generation source. For this reason, it is possible to reduce the speed fluctuation transmitted to the primary transfer portion, and the image quality can be improved.

<Embodiment 1>
Hereinafter, an intermediate transfer unit and an image forming apparatus according to the embodiment will be described. FIG. 1 is a schematic diagram showing a configuration of an image forming apparatus according to Embodiment 1 of the present invention. The image forming apparatus 20 includes black (K), yellow (Y), magenta (M), and cyan (C) image forming units 11K, 11Y, 11M, and 11C as image forming apparatuses. Images of different colors formed by the image forming units 11K, 11Y, 11M, and 11C are transferred to the intermediate transfer belt 12, and the images are superimposed. In the same manner as the image forming apparatus 10 shown in FIG. 8 as a conventional example, the intermediate transfer belt 12 includes a driving roller 14, a driven roller 15, a secondary transfer roller 16, and a counter roller 17. These constitute an intermediate transfer belt unit.

  The image forming apparatus 20 includes a tension sensor 21 that detects the tension of the intermediate transfer belt 12. The tension sensor 21 is disposed in the vicinity of the secondary transfer roller 16. A tension control mechanism 22 capable of controlling the tension in the vicinity of the secondary transfer roller in accordance with the tension fluctuation obtained from the tension sensor 21 is disposed so as to contact the intermediate transfer belt 12 belt. Various known mechanisms can be employed as the tension control mechanism 22. The tension control mechanism 22 controls the tension by applying a relative frictional force to the intermediate transfer belt 12. A tension control device 23 for controlling the tension control mechanism 22 is also provided.

  The tension sensor 21 is installed as close as possible to the secondary transfer portion S composed of the intermediate transfer belt 12, the secondary transfer roller 16, and the opposing roller 17. As a result, it is possible to reliably and accurately measure the tension fluctuation occurring in the vicinity of the secondary transfer portion S, and to effectively control the tension of the intermediate transfer belt 12. The tension control device 23 calculates a control signal based on the tension value obtained from the tension sensor 21 so that the fluctuation of the intermediate transfer belt 12 is reduced, and drives the tension control mechanism 22 in accordance with this signal. Thereby, the fluctuation in the speed of the intermediate transfer belt 12 is reduced by suppressing the fluctuation in the tension of the intermediate transfer belt 12.

  Further, shock jitter due to transfer characteristic deterioration when the toner images formed by the image forming units 11K, 11Y, 11M, and 11C are transferred from the intermediate transfer belt 12 to the recording paper P that passes through the secondary transfer portion S is prevented. Can do. At the same time, fluctuations in tension due to the entry of the recording paper P and the removal of the recording paper P from the secondary transfer portion S are reduced in the vicinity of the fluctuation source. As a result, tension fluctuations propagated to the primary transfer portion constituted by the image forming units 11K, 11Y, 11M, and 11C and the intermediate transfer belt 12 are also reduced. Thereby, the speed fluctuation on the primary transfer surface can also be reduced. As a result, high image quality can be achieved.

  As described above, according to the image forming apparatus 20 according to the first embodiment, the tension sensor capable of detecting the tension of the intermediate transfer belt 12 is disposed in the vicinity of the secondary transfer roller 16, and the tension sensor obtained according to the tension fluctuation obtained from the tension sensor. Thus, the tension in the vicinity of the secondary transfer roller 16 is controlled. As a result, the image formed by the intermediate transfer unit not only prevents shock jitter due to transfer characteristic degradation occurring in the secondary transfer unit S, but also from the entry of the recording paper and the secondary transfer unit S that cause tension fluctuations. Fluctuations in tension due to missing recording paper can be reduced in the vicinity of the source. As a result, the speed fluctuation transmitted to the primary transfer portion can be reduced, and the image quality can be improved.

<Embodiment 2>
Next, an image forming apparatus according to Embodiment 2 of the present invention will be described. FIG. 2 is a schematic diagram showing a configuration of an image forming apparatus according to Embodiment 2 of the present invention. The image forming apparatus 30 according to the second embodiment has a contact roller 32 that contacts the intermediate transfer belt 12 as a tension control mechanism that applies tension to the intermediate transfer belt 12, and the belt transfer surface on the belt transfer surface according to the tension fluctuation by the tension sensor 21. The torque generator 31 can control the tension. The contact roller 32 is provided on the downstream side of the secondary transfer roller 16 in the intermediate transfer belt 12.

  The torque generator 31 can use a motor or an electromagnetic brake that can apply torque to the contact roller 32. The torque generating device 31 is controlled by the tension control device 23, and the contact roller 32 comes into contact with the intermediate transfer belt 12, whereby the tension fluctuation of the intermediate transfer belt 12 is suppressed. When the speed fluctuation of the intermediate transfer belt 12 is reduced, high image quality can be realized as a result. Further, by using a motor or an electromagnetic brake as the torque generator 31, control can be performed with a simple configuration and low cost without using a special control mechanism.

  As described above, in the image forming apparatus 30 according to the second embodiment, the tension control mechanism capable of controlling the tension of the belt transfer surface according to the tension variation by the tension sensor is in contact with the intermediate transfer belt and the roller of the roller. The structure which consists of a mechanism which can generate | occur | produce a torque in a rotation direction is provided. Thereby, it can install in the position which wants to suppress a tension | tensile_strength fluctuation | variation with a simple structure. Further, only using a motor or an electromagnetic brake for the torque generating mechanism enables torque control at a low cost without using a special control mechanism, leading to higher image quality.

<Embodiment 3>
Next, an image forming apparatus according to Embodiment 3 will be described. FIG. 3 is a graph showing the result of simulating the change in the tension of the intermediate transfer belt when the recording paper enters the transfer portion. This graph shows a result of simulating the state of tension fluctuation generated in the intermediate transfer belt 12 in the vicinity of the secondary transfer surface due to the force received when the recording paper enters the secondary transfer portion S. Of the two waveforms in FIG. 3, a waveform with a large tension variation (A in the diagram) indicates the tension variation at a position that is upstream of the secondary transfer roller. Similarly, a small waveform (same B) shows the tension fluctuation in the downstream portion of the secondary transfer roller.

  As a result, it can be understood that the tension fluctuation of the intermediate transfer belt 12 is generated with different magnitude and phase at the position of the intermediate transfer belt 12. The image forming apparatus 40 according to the third embodiment is provided with a plurality of tension control mechanisms in order to reduce the fluctuations corresponding to these tension fluctuations. FIG. 4 is a schematic diagram showing a configuration of an image forming apparatus according to Embodiment 3 of the present invention.

  A second tension sensor 24 is arranged on the downstream side of the secondary transfer roller 16 of the intermediate transfer belt 12 and a torque generator 31 and a contact roller 32 are arranged. The torque generator 31 and the contact roller 32, the second torque generator 33, and the second contact roller 34 constitute a tension control mechanism. In addition, a second torque generator 33 and a second contact roller 34 are disposed upstream of the secondary transfer roller 16. Thereby, different tension fluctuations occurring upstream and downstream of the secondary transfer roller 16 are reduced.

  Further, a tension roller 18 that maintains the tension of the intermediate transfer belt 12 is disposed downstream of the secondary transfer roller 16. In the image forming apparatus 40 according to the third embodiment, the tension control device 23 controls the torque generation device 31 and the second torque generation device 33 based on the tension sensor 21 and the second tension sensor 24. Therefore, the image forming apparatus 40 according to the third embodiment can efficiently reduce the tension fluctuation, reduce the speed fluctuation, and improve the image quality.

  In the image forming apparatus 40 according to the third embodiment, the case where the tension control device is not operated and the case where the tension control device is operated are compared. FIG. 5 is a graph showing changes in the speed of the surface of the intermediate transfer belt in the image forming apparatus according to Embodiment 3 of the present invention. It can be seen that when the tension control device is not operated (FIG. 5 (a)), the speed of the intermediate transfer belt 12, which has changed greatly, is reduced when the tension control device is operated (b). As described above, since the belt speed fluctuation is reduced, the toner transfer is improved and the image quality can be improved.

  As described above, the image forming apparatus 40 according to the third embodiment includes a roller that is in contact with the intermediate transfer belt and a plurality of mechanisms that can generate torque in the rotation direction of the roller. As a result, it is possible to efficiently and appropriately reduce the intermediate transfer belt 12 in which the tension fluctuation has occurred at the position where the tension has occurred, and to reduce image degradation.

<Embodiment 4>
Next, an image forming apparatus according to Embodiment 4 will be described. FIG. 6 shows an example of a measurement result of the speed fluctuation generated in the intermediate transfer belt when the recording paper enters the transfer portion to the secondary transfer portion that transfers the image formed on the intermediate transfer belt to the recording paper. It is a graph. This is an example of a measurement result of the speed fluctuation generated in the intermediate transfer belt due to the force received when the recording paper enters the secondary transfer portion S. The measurement result with the large fluctuation ((A) in the figure) is the speed fluctuation of the belt near the secondary transfer, and the measurement result with the small fluctuation (the same (b)) is the speed fluctuation of the belt on the primary transfer surface. As shown in the figure, the speed variation of the intermediate transfer belt 12 varies depending on the measurement position on the intermediate transfer belt, but the magnitude of the speed variation is substantially the same. .

  From the measurement so far, it can be seen that the cycle in which the speed fluctuation occurs depends greatly on the frequency of the primary resonance in the transfer characteristic in the rotation direction with respect to the “drive motor to the surface speed of the intermediate transfer belt” of the intermediate transfer belt 12. ing. FIG. 7 shows the measurement result of the rotation transmission characteristic with respect to the speed of the surface of the intermediate transfer belt from the drive motor of the intermediate transfer belt. Therefore, by controlling the tension with respect to the fluctuation component of the period that fluctuates most in FIG. 6, that is, the frequency of the primary resonance shown in FIG. Can be realized.

  As described above, in the image forming apparatus according to the fourth embodiment, the tension control for the belt tension fluctuation control mechanism controls the fluctuation of the primary resonance frequency of the rotation transmission characteristic in the intermediate transfer belt drive system. As a result, it is possible to reduce the fluctuation component that contributes most to the fluctuation in the speed of the transfer belt that occurs when the recording paper enters or leaves, and it is possible to significantly reduce image deterioration.

<Other embodiments>
As the tension sensor 21, one that can be detected without contact can be employed. The following can be adopted as the tension sensor 21. That is, it is possible to employ a device that analyzes the tension from the vibration frequency of the string using a microphone or the like using the string vibration of the intermediate transfer belt 12 that changes depending on the tension. In addition, a contact-type pressure sensor is provided on the back surface of the intermediate transfer belt 12, and the tension can be measured from the string vibration frequency of the belt obtained from the pressure fluctuation, similarly to the microphone.

  In addition to this, an optical displacement sensor that can measure the gap between the sensor and the belt is provided near the intermediate transfer belt 12, and the tension is measured from the fluctuation frequency of the gap. It can be selected according to. In particular, when the sensor is of a non-contact type, there is no stress on the intermediate transfer belt 12 due to friction compared to the contact type, so that the durability of the intermediate transfer belt 12 can be maintained and deterioration can be prevented. Further, it is possible to detect a variation in tension without being affected by an increase in driving energy due to an increase in the rotational load of the belt, and it is possible to achieve durability and energy saving of the driving motor.

  As described above, if the tension sensor is detected without contact with the belt, there will be no belt deterioration due to contact friction, etc., and there will be no increase in drive energy due to an increase in belt rotation load, resulting in durability and energy saving of the drive motor. Can do.

11K, 11Y, 11M, 11C: image forming unit 12: intermediate transfer belts 13K, 13Y, 13M, 13C: photosensitive drum 14: drive roller 15: driven roller 16: secondary transfer roller 17: counter roller 18: tension roller 20 : Image forming device 21: Tension sensor 22: Tension control mechanism 23: Tension control device 24: Second tension sensor 30: Image forming device 31: Torque generator (tension control mechanism)
32: Contact roller (tension control mechanism)
33: Second torque generator (tension control mechanism)
34: Second contact roller (tension control mechanism)
40: Image forming apparatus P: Recording paper S: Secondary transfer section

Japanese Patent Application Laid-Open No. 2005-33884, JP-A-5-224572 Japanese Patent No. 5084240

Claims (6)

A plurality of image forming units, an intermediate transfer belt, and a secondary transfer roller that constitutes a secondary transfer unit with the intermediate transfer belt, and a plurality of images formed by the plurality of image forming units are transferred to the intermediate transfer belt In an intermediate transfer unit that transfers the image on the intermediate transfer belt onto the recording medium by passing the recording medium through the secondary transfer portion and transferring the image onto the recording medium.
A tension sensor disposed in the vicinity of the secondary transfer roller for detecting the tension of the intermediate transfer belt;
A tension control mechanism that controls the tension of the intermediate transfer belt by applying a frictional force in contact with the intermediate transfer belt;
A tension control device that controls the tension control mechanism based on a change in tension of the intermediate transfer belt obtained from the tension sensor;
An intermediate transfer unit characterized by comprising:   The intermediate transfer according to claim 1, wherein the tension control mechanism includes a contact roller rotating in contact with the intermediate transfer belt and a torque generation mechanism that generates torque in a rotation direction of the contact roller. unit.   The intermediate transfer unit according to claim 1, wherein a plurality of tension control mechanisms are provided.   4. The tension control device according to any one of claims 1 to 3, wherein the tension control device performs control corresponding to a change in a primary resonance frequency of a rotation transmission characteristic in a drive system of the intermediate transfer belt. Intermediate transfer unit.   The intermediate transfer unit according to any one of claims 1 to 4, wherein the tension sensor detects tension without contacting the intermediate transfer belt.   An image forming apparatus comprising: the intermediate transfer unit according to any one of claims 1 to 5; and an image forming apparatus that forms an image on the intermediate transfer belt.