JP4857022B2 - Image forming apparatus - Google Patents

Description

  The present invention has a plurality of rotatable image carriers, and a copier, printer, and the like that form images by sequentially transferring an image formed on the image carrier to a belt member or a transfer material carried on the belt member, The present invention relates to an image forming apparatus such as a facsimile.

  In recent years, in an image forming apparatus using an electrophotographic method, an intermediate transfer method using an intermediate transfer member as a photosensitive drum as an image carrier is increasing. For example, a toner image is formed on each of four photosensitive drums arranged corresponding to each color of yellow, magenta, cyan, and black, and the toner images are sequentially primary transferred to an intermediate transfer belt to form a color image. To do. The color image is transferred to a transfer material in a secondary transfer portion, and the toner image on the transfer material is fixed and discharged out of the apparatus (Patent Document 1).

  In such an image forming apparatus, a primary transfer roller is pressed against a plurality of photosensitive drums with an intermediate transfer belt interposed therebetween. The photosensitive drum and the intermediate transfer belt are driven and transmitted by the same drive source or different drive sources, and are rotated and run at a predetermined speed, respectively.

JP 2000-347519 A

  In the conventional image forming apparatus described above, even if the photosensitive member and the intermediate transfer belt are rotated and run with very high accuracy, they are shifted to the respective peripheral speeds at the nip portion (primary transfer portion) between the photosensitive member and the intermediate transfer belt. And image defects such as color misregistration and banding may occur. The causes were the outer diameter accuracy / freight accuracy of the photosensitive member, the unevenness of the thickness of the intermediate transfer belt, the outer diameter accuracy of the driving roller of the intermediate transfer member, the play and accuracy of the drive transmission means, and the like.

  Such image defects such as color misregistration have become a serious problem particularly in image forming apparatuses that require high image quality. In order to solve the above problem, it has been proposed that the photosensitive member is driven to the intermediate transfer belt. Thus, the peripheral speeds at the nip portion (primary transfer portion) between the photosensitive member and the intermediate transfer belt are made constant, and a high-quality image free from image defects such as color misregistration and banding is formed.

  However, in order to stably follow and rotate at the nip portion between the photoreceptor and the intermediate transfer belt where the toner is interposed, it is necessary to pressurize with a contact pressure several times that of a normal independent drive type. There is. For this reason, the stress applied to the primary transfer roller made of an elastic material such as rubber or foam urethane is large, and there is a problem that the durability of the primary transfer roller is inferior to that of the normal independent drive type. It was raised.

  SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus in which durability of a transfer roller is improved in an image forming apparatus in which an image carrier is driven to rotate by a belt member.

  Another object of the present invention is to provide an image forming apparatus capable of reducing running costs while forming a high-quality image.

Typical means of the present invention for solving the above problems has a plurality of rotatable image bearing member, the belt of each of the image formed on said image bearing member, respectively by applying the image bearing member and a transfer roller for sequentially transferred to the transfer material carried on the member or a belt member, the image bearing member in an image forming apparatus which is driven to rotate by the rotation of the belt member, the accumulation of the image carrier or the transfer roller includes a cumulative rotational speed detecting means for detecting the rotational speed, the pressure of the transfer roller for the previous SL plurality of image bearing members, the belt member pressure in the rotating direction most upstream of the transfer roller is the lowest of transcription downstream of the are set contact pressure is the highest of the roller, when the accumulated rotation number detecting means detects the replacement accumulated rotation number set, the transfer roller in the rotational direction most upstream side of the belt member on the display unit Characterized by a display prompting the replacement of the downstream side of the transfer roller.

According to the present invention, in the image carrier driven type image forming apparatus, the contact pressure of the transfer roller can be reduced on the upstream side, so that the total durability is improved by replacing a plurality of transfer rollers, and the image forming apparatus The running cost of the main body can be reduced. Further, by reducing the contact pressure of the upstream transfer roller, the stress on the image carrier is reduced, and the influence of pitch deviation due to eccentricity of the image carrier can be suppressed. Therefore, it is possible to provide an image forming apparatus that forms a high-quality image that is resistant to banding and color misregistration. Also, the cumulative number of rotations of the image carrier or the transfer roller is detected, and as a result, the exchange of the most upstream transfer roller and the most downstream transfer roller is promoted, thereby extending the total component life of the transfer roller. It is possible to suppress the early replacement period.

  Next, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

[Entire configuration of image forming apparatus]
First, the overall configuration of the image forming apparatus will be briefly described with reference to FIG. 1 together with the image forming operation. The image forming apparatus of this embodiment forms a color image by an electrophotographic method.

  In the image forming means, four image forming stations are arranged substantially horizontally, and image forming stations Ua, Ub, Uc, Ud for forming toner images of black, cyan, magenta, and yellow are arranged from the right in FIG. . Each image forming station has the same configuration except that the color of the toner is different. Therefore, in the following description, the symbols a, b, c, and d attached to the drawings are omitted unless otherwise specified.

  In each image forming station U, a primary charger 7, a developing device 3, and a drum cleaner 6 are arranged around a photosensitive drum 4 as an image carrier. A scanner unit 10 for irradiating a laser beam in accordance with an image signal is disposed above the photosensitive drum 4.

  Further, an intermediate transfer belt 56 as a belt member is rotatably provided so as to abut on each photoconductive drum 4, and a primary transfer roller 51 is provided at a position facing each photoconductive drum 4 across the intermediate transfer belt 56. It has been.

  The intermediate transfer belt 56 is wound around a driving roller 54, a driven roller 55, and a secondary transfer inner roller 52, and is rotated clockwise in FIG. The photosensitive drum 4 rotates following the rotation of the intermediate transfer belt 56.

  During image formation, the surface of the photosensitive drum 4 that rotates as the intermediate transfer belt 56 rotates is uniformly charged by the primary charger 2. The photosensitive drum 4 is irradiated with laser light corresponding to the image signal from the scanner unit 3 to form an electrostatic latent image, and the latent image is developed with toner by the developing device 4 to be visualized.

  The toner image is primarily transferred to the intermediate transfer belt 56 by applying a bias to the primary transfer roller 51. Then, yellow, magenta, cyan, and black toners formed by the image forming stations are superimposed on the intermediate transfer belt 56 and transferred to form a color image. This color image is secondarily transferred from the feeding cassette 12 to the transfer material S conveyed by the pickup roller 81 and the conveyance roller 82 by the bias application to the secondary transfer outer roller 53 in the secondary transfer portion, and recorded. .

  Then, the recording material onto which the toner image has been transferred is guided to the fixing device 14, where the toner image is fixed on the transfer material S by applying heat and pressure, and then discharged outside the apparatus.

  Here, the photosensitive drum 4 is held by a bearing having a small rotational resistance, such as a ball bearing, so that the photosensitive drum 4 is easily driven to rotate as the intermediate transfer belt 56 rotates. As shown in FIG. 2, the intermediate transfer belt 56 is driven by a driving roller 54 disposed immediately downstream of the photosensitive drum 4a. As described above, since the driving roller 54 is located immediately downstream of the photosensitive drum 4a, the intermediate transfer belt 56 is located on the tension side of the nip portion with the photosensitive drum 4, so that the positions of the photosensitive drum 4 and the intermediate transfer belt 56 are the same. There is a relationship, and image defects such as color misregistration and banding are less likely to occur.

  Further, the primary transfer roller 51 that is driven to rotate while being pressed against the intermediate transfer belt 56 is also held at both ends by a bearing having a low rotational resistance, such as a ball bearing. Therefore, unnecessary stress is not applied to the intermediate transfer belt 56, and the positional relationship between the photosensitive drum 4 and the intermediate transfer belt 56 is stabilized. The station pitch of each color (the distance between the primary transfer rollers 51 of each color) is slightly deviated due to component accuracy and the like, and therefore, each color is matched by adjusting the laser exposure timing by initial adjustment and regular adjustment. If this adjustment is made, the photosensitive drum 4 is driven with respect to the intermediate transfer belt 56, so that the toner image on the photosensitive drum 4 can be faithfully reproduced on the intermediate transfer belt 56. Therefore, by rotating only the motor that drives the drive roller 54 with high accuracy, it is possible to form a high-quality image free from image defects such as color misregistration and banding.

[Pressure force of transfer roller]
Next, the pressure applied to the primary transfer roller 51 will be described. FIG. 3 is an explanatory perspective view of the vicinity of the black photosensitive drum 4a. In FIG. 3, the rotating shaft 41 of the photosensitive drum 4 and the rotating shaft 60 of the primary transfer roller 51 are supported on the drum unit side plates 101 and 102 by ball bearing bearings 42 and 61. That is, the contact pressure of the primary transfer roller 51 against the photosensitive drum 4 with the intermediate transfer belt 56 interposed is managed by the intrusion amount. Note that the contact pressure in this embodiment is not a linear pressure or a surface pressure, but a total pressure that is a total pressure.

  When the distance between the photosensitive drum shaft and the primary transfer roller shaft in each image forming station is La, Lb, Lc, and Ld from the downstream side in the rotation direction of the intermediate transfer belt 56, the relationship between the distances is La <Lb <Lc. <Ld is configured. That is, the distance between the photosensitive drum shaft and the primary transfer roller shaft is the largest on the most upstream side in the rotation direction of the intermediate transfer belt 56 and decreases as it goes downstream.

  Therefore, the contact pressures of the photosensitive drums 4a, 4b, 4c, and 4d and the primary transfer rollers 51a, 51b, 51c, and 51d change depending on the difference in distance, and the contact pressures Pa, Pb, Pc, and Pd are Pa> Pb> Pc> Pd. That is, the contact pressure of the transfer rollers 51a, 51b, 51c, and 51d with respect to the four photosensitive drums 4a, 4b, 4c, and 4d is the contact pressure of the transfer roller 51d that is the most upstream in the rotation direction of the intermediate transfer belt 56. The lowest is set. Then, the contact pressure is set so as to increase sequentially as it goes downstream, and the contact pressure of the most downstream transfer roller 51a is set to be the highest.

  The contact pressure Pd of the primary transfer roller 51d that is the most upstream in the rotation direction of the intermediate transfer belt 56 is such that when one color of toner is deposited on the intermediate transfer belt 56, the intermediate transfer belt 56 and the photosensitive drum 4d do not slip. It is a setting. Similarly, the contact pressure Pa of the primary transfer roller 51a on the most downstream side in the rotation direction of the intermediate transfer belt 56 causes the intermediate transfer belt 56 and the photosensitive drum 4a to slide when four colors of toner are deposited on the intermediate transfer belt 56. There is no setting.

  Depending on the type of toner, the material of the drum surface layer, the material of the intermediate transfer belt 56, and the material and hardness of the primary transfer roller 51, the contact condition for causing the photosensitive drum 4 to follow the intermediate transfer belt 56 varies. As an example, in this embodiment, the photosensitive drum 4 is an OPC drum, the toner is a polyester polymer toner, the material of the intermediate transfer belt 56 is polyimide, the material of the primary transfer roller 51 is NBR (acrylonitrile butadiene rubber), and the hardness is Asker. It is 35 degrees in C. The contact pressures Pa, Pb, Pc, and Pd of the primary transfer rollers 51a, 51b, 51c, and 51d are Pd = 40N, Pc = 60N, Pb = 80N in order from the upstream side in the rotation direction of the intermediate transfer belt 56, respectively. Pa = 100N is set.

  The durability life of the primary transfer roller 51 is almost inversely proportional to the contact pressure P, and the life of 40N is about 2.5 times that of 100N. Therefore, conventionally, since the primary transfer rollers 51 of all the image forming stations are set to 100 N having a high contact pressure, the lifetime is short. However, in this embodiment, the most downstream primary transfer roller 51a, the most upstream primary transfer roller 51d, the second most downstream 51b, and the second most upstream 51c are interchanged (rotated) halfway. The life of parts is approximately 1.75 times that of conventional products. In other words, if the number of replacements of the conventional primary transfer roller 51 is 100K (100,000), for example, the rotation time is 87.5K, but the replacement to the new primary transfer roller 51 is 175K.

  (100K + 250K) / 2 = 175K

  100K: Life at the contact pressure of 100N of the most downstream photosensitive drum 4a

  250K: Life at the time of 40N contact pressure of the most upstream photosensitive drum 4d

  In particular, when the contact pressure of the primary transfer roller 51 on the upstream side is high, the influence of the eccentricity of the photosensitive drum 4 due to the pressure of the primary transfer roller 51 is cumulatively affected as it goes downstream, causing color misregistration. Etc. may be generated. However, in this embodiment, since the contact pressure is lower toward the upstream side, this accumulated error is small and the image is stable.

  In the above description, the rotation time and the replacement time for a new product are indicated by the number of recorded sheets for easy understanding. However, the number of sheets is an approximate value, and is actually determined by the cumulative number of rotations of the primary transfer roller 51 (or the photosensitive drum 4).

  Therefore, in the present embodiment, as shown in FIG. 3, a reflection plate 4af is attached to the photosensitive drum 4a as the cumulative rotational speed detecting means, and the rotational speed of the photosensitive drum 4a is counted by the optical sensor unit 110. ing.

  Then, when the cumulative rotational speed detection means detects the preset cumulative rotational speed, a message prompting the rotation of the primary transfer roller 51 is displayed on the display section on the operation section. Then, after reaching the same rotational speed after the rotation, when the cumulative rotational speed detecting means detects the preset cumulative rotational speed, a message prompting the replacement of the primary transfer roller 51 with a new one is displayed on the display unit. It is composed.

  Thereby, it is possible to easily know the replacement time of the primary transfer roller 51 or the replacement time of a new one.

  In the present embodiment, an example in which the contact pressure P of the primary transfer roller 51 is managed by the amount of the primary transfer roller 51 entering the photosensitive drum 4 has been described. However, as shown in FIG. 4, the contact pressure may be managed by the pressure spring 51s. This is because the same compression spring 51s is used for the pressure contact of the primary transfer roller 51 to each photosensitive drum 4 via the intermediate transfer belt 56, and the contact pressure of each primary transfer roller 51 is adjusted by adjusting the compression amount of the spring 51s. P is managed. In this way, the compression amount of the spring 51s can be adjusted more easily than when the distance between the rotation shaft of the photosensitive drum 4 and the rotation shaft of the primary transfer roller 51 is adjusted. Becomes easy.

  In the above-described embodiment, an image forming apparatus that primarily transfers the toner image formed on the photosensitive drum 4 to the intermediate transfer belt 56 that is a belt member and secondarily transfers the primary toner image to the transfer material S that is conveyed. Illustrated. However, the belt member of the present invention may be a transfer material conveyance belt that conveys the transfer material S by electrostatic adsorption or the like. In other words, a transfer material conveyance belt is rotatably arranged facing the plurality of photosensitive drums, and a transfer roller is brought into pressure contact with each photosensitive drum via the transfer material conveyance belt. Then, the toner images formed on the photosensitive drums are sequentially transferred to a transfer material conveyed by electrostatic attraction or the like to the transfer material conveyance belt to form an image. By setting the contact pressure of the transfer roller in such an image forming apparatus in the same manner as in the above-described embodiment, it is possible to extend the life of the transfer roller.

1 is a cross-sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a perspective explanatory view of a photosensitive drum and a primary transfer roller of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is an explanatory diagram of a contact pressure between the photosensitive drum and the primary transfer roller of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is an explanatory diagram for setting a contact pressure between a photosensitive drum and a primary transfer roller of an image forming apparatus according to another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS S ... Transfer material U ... Image forming station 3 ... Developing device 4 ... Photoconductor drum 4af ... Reflector 6 ... Drum cleaner 7 ... Primary charger
12 ... Feed cassette
14… Fixing device
41 Rotating shaft
42, 61… Ball bearings
51… Primary transfer roller
51s… Pressure spring
52… Roller in secondary transfer
53… Secondary transfer outer roller
54… Drive roller
55… driven roller
56… Intermediate transfer belt
60… rotating shaft
82… Conveying roller
101,102 ... drum unit side plate
110… Optical sensor unit

Claims (2)

A plurality of rotatable image bearing member are sequentially transferred to each of the transfer material carrying the image formed by applying the image bearing member to each of the image carrier to the belt member or a belt member transfer roller In the image forming apparatus in which the image carrier rotates following the rotation of the belt member ,
A cumulative rotational speed detecting means for detecting the cumulative rotational speed of the image carrier or the transfer roller;
The pressure of the transfer roller for the previous SL plurality of image bearing members, the belt member pressure in the rotating direction most upstream of the transfer roller is the lowest of which the contact pressure of the most downstream of the transfer roller is set highest, the When the cumulative rotational speed set by the cumulative rotational speed detection means is detected, the display unit displays a message prompting replacement of the transfer roller on the most upstream side in the rotational direction of the belt member and the transfer roller on the downstream side. An image forming apparatus. The image forming apparatus according to claim 1, wherein when the accumulated rotation number detecting means detects the replacement accumulated rotation number set, and wherein to Rukoto a display prompting the replacement of the transfer roller on the display unit Image forming apparatus.

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