JP2008009034A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which can form high quality images on various transfer materials different in bending stress without scattering toner or making alignment errors when transferring. <P>SOLUTION: The distance is made variable between the top of the guide and the transferring position forming the path to carry the transfer material to the transferring position. For instance, the above distance is changed depending on the basis of weight of the transfer material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as an electrophotographic image forming apparatus.

  In an electrophotographic image forming apparatus, an image on an image carrier such as a photosensitive member or an intermediate transfer member is transferred to a transfer material such as paper to form an image on the transfer material. If the image is transferred or the device is downsized, the trailing edge of the transfer material will vibrate at the transfer position where the image is transferred. There is a problem.

  In Patent Documents 1 and 2, such problems are pointed out, and countermeasures against them are proposed.

  That is, in Patent Document 1, it is proposed to provide a guide member that loosely presses the transfer material at the guide portion that guides the transfer material to the transfer position.

In Patent Document 2, a guide member made of an elastic body is fixed to the front ends (ends on the downstream side in the transfer direction of the transfer material) of a pair of guide plates that guide the transfer material to the transfer position, and the free end of the guide member is bent at a predetermined angle. It has been proposed.
JP-A-61-188345 JP-A-8-76607

  The image quality degradation caused by the vibration at the trailing edge of the transfer material will be described with reference to FIGS.

  In FIG. 1, the transfer material P is transported by a registration roller 23 to a transfer position TR formed by a transfer roller 7 </ b> A that performs secondary transfer and a ground roller 61, and a toner image is transferred from the intermediate transfer body 6 to the transfer material P. Is transferred to.

  Reference numerals 30 and 31 denote a pair of guide plates for guiding the transfer material P between the registration roller 23 and the transfer position TR, and are made of a rigid sheet metal.

  When the rear end of the transfer material P moves away from the guide plates 30 and 31, the rear end of the transfer material jumps up and vibrates, and this vibration causes toner dust and transfer deviation. Toner dust is a phenomenon in which spots are formed in a non-image portion as shown in FIG. 2A, and transfer deviation is a phenomenon in which an image is shifted as shown in FIG. 2B. It has been found that such a phenomenon occurs when the transfer material P is thick paper due to the rigidity of the transfer material P being high, and an elastic guide member made of an elastic body is provided at the tip of the guide plate 30 so that the post-transfer material It is suppressed by suppressing the jumping of the edge, and an effect of suppressing toner dust and transfer deviation can be obtained.

  Patent Documents 1 and 2 both utilize the suppression effect of such elastic guide members, and these techniques can prevent a certain degree of image quality degradation, but have the following problems. It became clear.

  In recent years, as a result of higher performance of image forming apparatuses, that is, colorization, and diversification of fields of use for creating various documents other than office documents, measures such as Patent Documents 1 and 2 are not sufficient. As a result of the diversification of the types of transfer materials used, the width of change in the bending stress of the transfer materials used is widened, and transfer deviation and toner dust due to the transfer material jumping at the transfer position become problems and countermeasures are required. It is coming.

  An object of the present invention is to solve the problems in the prior art as described above with respect to image quality degradation occurring in a transfer portion.

The object is achieved by the following invention.
1.
An image carrier, contact-type transfer means for transferring a toner image on the image carrier to a transfer material, transport means for conveying a transfer material toward a transfer position formed by the contact-type transfer means, and the transfer position It has a pair of guide plates that form a transport path between the transport means, and the distance between the tip of the guide plate closer to the image carrier and the transfer position of the pair of guide plates is variable. An image forming apparatus.
2.
2. The image forming apparatus according to item 1, wherein the distance is changed by displacing the contact-type transfer unit in a transfer material conveyance direction.
3.
3. The image forming apparatus according to claim 1 or 2, wherein the distance is changed by displacing the guide plate closer to the image carrier in the transfer material conveyance direction.
4).
4. The image forming apparatus according to any one of 1 to 3, further comprising a control unit that controls the distance according to a bending stress of a transfer material.
5.
The image forming apparatus according to any one of claims 1 to 4, further comprising a control unit that controls the distance according to a thickness of a transfer material.
6).
6. The image forming apparatus according to any one of 1 to 5, wherein the contact-type transfer unit includes a transfer roller.
7).
7. The image according to any one of 1 to 6, wherein the guide plate closer to the image carrier has a base portion made of a rigid body and a tip portion made of an elastic body supported by the base portion. Forming equipment.
8).
5. The image forming apparatus according to 4 above, further comprising a user interface for inputting information on bending stress of the transfer material to the control unit.
9.
5. The image forming apparatus according to 4 above, further comprising a rigidity detection unit that detects a bending stress of the transfer material, wherein the control unit changes the distance based on an output of the rigidity detection unit.
10.
The image forming apparatus according to any one of 1 to 9, wherein the image carrier has a belt shape.
11.
11. The image forming apparatus according to any one of 1 to 10, wherein the image carrier is made of an intermediate transfer member.

  According to the present invention, since the distance between the transfer position formed by the transfer means and the guide plate for guiding the transfer material to the transfer position is made variable, even if various types of transfer materials having different bending stresses are used, The occurrence of toner dust is sufficiently suppressed, and it is possible to always form an image with high image quality.

  Hereinafter, the present invention will be described based on an embodiment of the present invention, but the present invention is not limited to the embodiment. In this specification, the guide plate and the front end of the guide plate are described as the rear end of the transfer material, but the downstream side in the transfer material transport direction is the front end, and the upstream side is the rear end.

  FIG. 3 shows a schematic configuration of the image forming apparatus according to the embodiment of the present invention.

  The image forming apparatus shown in FIG. 3 is a color image forming apparatus capable of forming a color image. The color image forming apparatus includes an image forming apparatus main body GH and an automatic document feeder JG installed on the image forming apparatus main body GH.

  The image forming apparatus main body GH includes four image forming units 10Y, 10M, 10C, and 10K, a control unit 100, a belt-like intermediate transfer body 6, a paper feed conveyance unit, and a fixing unit 24. A so-called tandem-type full-color image forming apparatus in which two image forming units 10Y, 10M, 10C, and 10K are arranged in parallel along the moving direction of the belt-shaped intermediate transfer body 6 that moves in the direction of arrow AA in the figure. It is.

  The image forming unit 10Y that forms a yellow image includes a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a first cleaning unit 8Y disposed around the photoreceptor 1Y. The image forming unit 10M that forms a magenta image includes the photoconductor 1M, the charging unit 2M, the exposure unit 3M, the developing unit 4M, and the first cleaning unit 8M as described above. The image forming unit 10C that forms a cyan image includes the photoconductor 1C, the charging unit 2C, the exposure unit 3C, the developing unit 4C, and the first cleaning unit 8C as described above. The image forming unit 10K that forms a black image includes the photoconductor 1K, the charging unit 2K, the exposure unit 3K, the developing unit 4K, and the first cleaning unit 8K as described above. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute an electrostatic latent image forming unit. 5Y, 5M, 5C, and 5K are toner containers containing yellow toner, magenta toner, cyan toner, and black toner, respectively, and these toner containers correspond to consumption in the developing units 4Y, 4M, 4C, and 4K. Toner is supplied.

  Each of the photoreceptors 1Y, 1M, 1C, and 1K is a negatively chargeable OPC photoreceptor in which an OPC photosensitive layer is formed on a metal drum. As the photoreceptors 1Y, 1M, 1C, and 1K, those other than the OPC photoreceptor such as an aSi photoreceptor can be used, and a positively charged photoreceptor can also be used. Each of the photoconductors 1Y, 1M, 1C, and 1K is provided with an encoder (not shown) that outputs a pulse for each rotation, and the control means 100 detects the output to thereby detect the photoconductor. The rotational speeds of 1Y, 1M, 1C, and 1K can be counted.

  As the charging means 2Y, 2M, 2C, and 2K, a corotron discharger or a scorotron discharger can be used, and a discharge wire type, a saw electrode type, or the like can be used.

  The exposure unit 3Y has a semiconductor laser as a light source, and performs dot exposure of the photoreceptor 1Y with a laser beam, and performs exposure based on yellow image data. Similarly, the exposure unit 3M exposes the photoconductor 1M based on the magenta image data, the exposure unit 3C exposes the photoconductor 1C based on the cyan image data, and the exposure unit 3K uses the black image data. To expose. As the exposure means 3Y, 3M, 3C, 3K, an exposure means other than a laser beam such as an LED array or a liquid crystal can be used, but those that perform dot exposure are preferable.

  The developing means 4Y, 4M, 4C, and 4K form openings with respect to the photoreceptors 1Y, 1M, 1C, and 1K, and are rotatable cylindrical developer carriers 46Y, 46M, 46C, and 46K, and the developer. And a plurality of stirring screws 47Y, 47M, 47C, 47K for supplying the developer after stirring to the developer carriers 46Y, 46M, 46C, 46K. The toner replenished from the toner containers 5Y, 5M, 5C, and 5K is supplied to the developer carriers 46Y, 46M, 46C, and 46K while being stirred by the stirring screws 47Y, 47M, 47C, and 47K.

  As the developer, either a two-component developer containing a toner and a carrier or a one-component developer containing a toner and not containing a carrier may be used.

  Further, the developing means 4Y, 4M, 4C, and 4K may be either a reversal developing type that attaches toner to an exposed portion or a regular developing type that attaches toner to an unexposed portion, a contact developing method or a non-contact developing method. Either of these may be used. As described above, any known developing means can be used as the developing means 4Y, 4M, 4C, and 4K, but a reversal developing type developing means using a two-component developer is preferable.

  The first cleaning means 8Y, 8M, 8C, 8K are rubber cleaning blades 88Y, 88M, 88C, 88K as first cleaning members formed long in the longitudinal direction of the photoreceptors 1Y, 1M, 1C, 1K. Each. When the photoreceptors 1Y, 1M, 1C, and 1K are rotated with the edge portions of the cleaning blades 88Y, 88M, 88C, and 88K being in contact with the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K, the photoreceptors 1Y, 1M, and 1K are rotated. The surfaces of 1C and 1K are rubbed to clean the toner.

The intermediate transfer member 6 as an image carrier is formed of a semiconductive endless belt having a resistance value of 10 ⁵ Ωcm to ^{10 10} Ωcm, and is stretched around a plurality of rollers including the earth roller 61 so as to be able to move around. It is supported and moves around by a signal from the control means 100 to a drive means (not shown) of the intermediate transfer member.

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is transferred in a state where transfer rollers 7Y, 7M, 7C, and 7K as primary transfer units are pressure-bonded to the circulating intermediate transfer body 6. By applying a transfer voltage having a polarity opposite to that of the toner to the rollers 7Y, 7M, 7C, and 7K to form a transfer electric field, the toner images are sequentially transferred onto the intermediate transfer body 6 and synthesized to form a color image. The

  The transfer rollers 7Y, 7M, 7C, and 7K are basically released from the pressure release by the pressure release means 71Y, 71M, 71C, and 71K except during image formation, and are separated from the intermediate transfer body 6 to form an image. Before the toner image reaches the intermediate transfer position, the toner image is pressed against the intermediate transfer member 6 by the pressing release means 71Y, 71M, 71C, 71K. The selection of these crimping or crimping release is changed and controlled by the output from the control means 100 to the crimping releasing means 71Y, 71M, 71C, 71K.

  A primary transfer voltage is applied to the transfer rollers 7Y, 7M, 7C, and 7K from a power source that is a primary transfer output applying unit (not shown). As a control method of the primary transfer voltage applied to the primary transfer means, (1) a constant current method for setting a predetermined target current value and controlling the transfer current to be the target current value; (2) There is a constant voltage method in which a predetermined target voltage value is set and control is performed so that the transfer voltage becomes this target voltage value. In (1), the current value becomes the primary transfer output, and in (2), the voltage value becomes the primary transfer output. In this embodiment, the constant current control (1) is performed, and the current value is set as the primary transfer output. The control unit 100 controls the primary transfer output and the application timing, which are current values, for each of the transfer rollers 7Y, 7M, 7C, and 7K by a signal to the primary transfer output application unit. During normal image formation, the primary transfer output is set to 30 μA so that the transfer rate is approximately 100%.

  Reference numeral 7A denotes a transfer roller as transfer means for performing secondary transfer, and a transfer voltage having a polarity opposite to that of the toner image is applied to transfer the toner image from the intermediate transfer member to the transfer material P.

As the transfer rollers 7A, 7Y, 7M, 7C, and 7K, semiconductive rollers having a resistance value of 10 ⁵ Ωcm to ^{10 10} Ωcm are preferably used.

  The color toners remaining on the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K after the toner is primarily transferred to the intermediate transfer member 6 are respectively cleaned by the cleaning blades 88Y, 88M, 88C, and 88K as the first cleaning members. To be cleaned.

  The transfer material P accommodated in the paper feed cassette 20 of the paper feed transport unit is fed by the paper feed means 21 of the paper feed transport unit and passes through the paper feed rollers 22A, 22B, 22C, 22D, the registration rollers 23, and the like. The color image is conveyed to the secondary transfer means 7A and secondarily transferred onto the transfer material P at once. The transfer material P onto which the color image has been transferred is subjected to fixing processing by the fixing unit 24, is sandwiched between paper discharge rollers 25, and is placed on a paper discharge tray 26 outside the apparatus.

  On the other hand, after transferring the color image to the transfer material P by the transfer means 7A, the intermediate transfer body 6 from which the transfer material P has been separated is a rubber that is a second cleaning member formed long in the width direction of the intermediate transfer body 6. Cleaning is performed by the second cleaning means 8A having a cleaning blade 89A made of metal.

  4 shows a secondary transfer portion in the image forming apparatus shown in FIG.

  The transfer material P is transported by a registration roller 23 serving as transport means and transported to a transfer position TR formed by the transfer roller 7A and the earth roller 61. A voltage having a polarity opposite to that of the toner is applied to a transfer roller 7A as a transfer unit that performs secondary transfer, and the toner image is transferred from the intermediate transfer body 6 to the transfer material P. The transfer roller 7A is a contact-type transfer unit composed of a conductive transfer roller, and presses the transfer material P against the ground roller 6A to perform transfer.

  Reference numerals 30 and 31 denote a pair of guide plates for guiding the transfer material P between the registration roller 23 and the transfer position TR, and are made of a rigid sheet metal.

  Reference numerals 33 and 34 denote guide plates that form a transport path on the upstream side of the transport path formed by the guide plates 30 and 31.

  The relationship between the bending stress of the transfer material, the free length of the transfer material, and the thickness (basis weight) of the transfer material will be described with reference to FIG.

  As shown in FIG. 4, the free length L is the length of the rear end of the transfer material that extends rearward (upstream in the transport direction) from the transfer material restraint position, which is the transfer position TR. The length of the part that can move freely. The free length L is equal to the distance between the tip 30A of the guide plate 30 closer to the intermediate transfer body 6 and the transfer position TR of the pair of guide plates 30 and 31 that guide the transfer material P toward the transfer position TR. .

  In the following description, the free length L is also referred to as a distance L between the tip 30A of the guide plate 30 and the transfer position TR.

  The bending stress of the transfer material rear end RP becomes higher as the transfer material is thicker, that is, as the basis weight is larger and as the free length L is shorter. 5, the bending stress is required to deform the transfer material P so that the base PB of the transfer material P is fixed and the tip of the free end PA is displaced by a certain distance, for example, 3 mm. The force F represents the strength of the transfer material. The higher the rigidity of the transfer material P, the higher the value, and the longer the width H of the transfer material, the higher the value.

  The deterioration of the image quality due to the jumping of the transfer material P in the transfer portion is one of the causes caused by the impact caused by the jumping, and this impact propagates to the transfer material P and the intermediate transfer body 6, so This causes the toner and the toner on the intermediate transfer body 6 to move and cause the image quality to deteriorate.

  In particular, when the intermediate transfer member 6 is a belt, it is considered that the belt vibrates due to the impact and disturbs the toner image.

  Further, since the intermediate transfer member 6 is semiconductive, the charge of the toner image leaks through the intermediate transfer member 6, so that the electrostatic attractive force that attracts the toner image to the intermediate transfer member 6 is attenuated, The toner particles forming the toner image are relatively easy to move on the intermediate transfer body 6. Therefore, when the intermediate transfer member 6 vibrates, the toner particles move and the toner image is easily disturbed.

  In order to sufficiently suppress the deterioration in image quality due to impact, it has been confirmed by an experiment in which an image is formed by changing the transfer condition that the bending stress F needs to be 0.15 N or less. It was confirmed that by setting the free length L to 40 mm or less, a good image can be formed up to a basis weight of 350 gsm, which is the upper limit of the thickness of the transfer material actually used.

  Further analysis of the image quality degradation caused by the transfer revealed that the image quality degradation caused by the transfer is caused by the transfer material P in the vicinity of the transfer position TR in addition to the impact. That is, when the transfer material P is exposed in the vicinity of the transfer position TR, a phenomenon occurs in which the transfer material P contacts the intermediate transfer body 6 in the previous stage of transfer, that is, upstream of the transfer position TR and disturbs the toner image. .

  Such ramping of the transfer material P occurs in the case of a transfer material with low rigidity, such as thin paper, or a transfer material with wave / curl.

  Therefore, in the case of a transfer material with low rigidity, it is necessary to reduce the free length L.

  As a result of such examination, it is possible to perform good transfer and form a high-quality image by changing the free length L according to the bending stress of the transfer material.

  FIG. 6 shows a detailed structure of an example of the transfer unit of the image forming apparatus according to the embodiment of the present invention.

  A guide plate 30 that forms a transfer material guide surface closer to the intermediate transfer body 6 is formed integrally with a rack 40, and the rack 40 moves in the transfer material conveyance direction as indicated by an arrow W1 by driving a pinion 41. . This movement changes the distance L between the tip 30A of the guide plate 30 and the transfer position TR.

  FIG. 7 shows an example of the transfer section of the image forming apparatus according to the embodiment of the present invention.

  The transfer roller 7A constituting the secondary transfer means is supported by the support frame 50. That is, the shaft of the transfer roller 7A is supported by the bearing 51. The bearing 51 is supported by the support frame 50 by the coil spring 52, and the transfer roller 7A is supported by the coil roller 52 at a predetermined pressure on the ground roller 61. Press contact with the transfer body 6.

  Since the support frame 50 is integrated with the rack 53 and moves in the transfer material conveyance direction as indicated by the arrow W2 by driving the pinion 54, the transfer position TR formed by the nip between the transfer roller 7A and the intermediate transfer body 6 is transferred. The distance L changes due to the movement of the roller 7A indicated by the arrow W2, and the distance L between the tip 30A of the guide plate 30 and the transfer position TR changes.

  The movement mechanism shown in FIGS. 6 and 7 changes the distance between the front end of the guide plate and the transfer position according to the bending stress of the transfer material, thereby reducing the image quality caused by the impact of the transfer material jumping up and the transfer material. Therefore, it is possible to prevent image quality degradation caused by the rampage.

  FIG. 8 is a block diagram of a control system for changing the distance between the transfer position and the guide plate tip according to the bending stress of the transfer material.

  Reference numeral 60 denotes a calculation control unit that performs control of the entire control system and calculation of the distance between the transfer position / guide plate tip, and 61 denotes a user interface. The type, size, etc. of the transfer material input from the operation unit or external device Is input to the arithmetic control unit 60.

  Information input from the user interface 61 includes size information such as A4 size and B4 size, information on the direction of the transfer material that indicates whether the transport direction is the short side or the transport direction is the long side, and the transfer material There is information on paper thickness such as basis weight. In the transfer material transfer, the factor affecting the toner dust and transfer deviation in the transfer part is the bending stress of the transfer material as described above, but the bending stress mainly depends on the rigidity of the transfer material, In addition to rigidity, the size of the transfer material is also an influencing factor. In other words, even if the transfer material has the same rigidity, the width (transfer material length in the direction orthogonal to the conveyance direction) is different, so that the bending stress changes and there is a strong tendency to cause an impact or a runaway caused by the jumping up. Changes.

  Reference numeral 62 denotes a humidity sensor. Since the rigidity of the transfer material varies depending on the humidity, the calculation control unit 60 calculates the output of the humidity sensor 62 in calculating the distance L.

  Reference numeral 63 denotes a front / back surface information output unit that outputs information indicating whether an image is formed on the front surface or the back surface of the transfer material.

  In the back side image forming step in double-sided image formation, a transfer material that has been heated by passing through the fixing device and reduced in water content is sent to the transfer position. Therefore, in the back side image formation, the rigidity of the transfer material is increased, and thus the calculation control unit 60 includes the information from the front and back side information output unit 43 in the calculation of the distance L.

  A storage unit 64 stores a correspondence table in which the distance L is associated with the bending stress of the transfer material. Table 1 shows an example of such a correspondence table, which is a correspondence table of basis weight versus distance L of the transfer material.

  Reference numeral 65 denotes driving means such as a motor for driving the pinion 41 in FIG. 5 or the pinion 54 in FIG. 6 according to a control signal from the arithmetic control unit 60.

  The calculation control unit 60 and the storage unit 64 constitute a control unit that controls the distance L. The calculation control unit 60 is based on information from the user interface 61, the humidity sensor 62, and the front / back surface information output unit 63. Referring to the correspondence table, the distance L is calculated and determined, and based on the determined distance L, the driving means 65 is controlled to change the distance L between the tip 30A of the guide plate 30 and the transfer position TR.

  FIG. 9 shows still another example of the embodiment of the present invention.

  In this example, the guide plate closer to the intermediate transfer body 6 of the pair of guide plates is constituted by a base portion 30B made of a rigid body such as a sheet metal and a tip end portion 30C made of an elastic body.

  The tip 30C is made of a resin film such as PET (polyethylene terephthalate) or PE (polyethylene), and is subjected to a conductive treatment in order to prevent frictional charging.

  The distal end portion 30C has an action of suppressing the jumping of the transfer material P, and thus toner dust and transfer deviation are prevented more satisfactorily. In this example, the distance L between the guide plate tip 30A and the transfer position TR is the distance between the tip 30A of the tip 30C and the transfer position TR as shown in the figure.

  10 and 11 show still another example of the embodiment of the present invention.

  In the image forming apparatus shown in FIG. 3, the rigidity detecting means shown in FIG. 10 is installed in a conveyance path where the transfer material P is strongly bent, for example, at a position indicated by B.

  The rigidity detecting means 70 includes a pressure contact portion 71 that contacts the transfer material, a compression spring 72, and a piezoelectric element 73.

  The pressure contact portion 71 is pressed by the spring 72 and faces the conveyance path. When the transfer material P passes through the conveyance path, the pressure contact portion 71 is pressed and displaced by the transfer material, and the pressing force by the transfer material P is detected by the piezoelectric element 73. The The pressure detected by the piezoelectric element 73 represents the bending stress of the transfer material P.

  The storage means 64 stores a correspondence table of the protrusion amount of the deformation restricting member corresponding to the output of the piezoelectric element 73, and the arithmetic control unit 60 is stored in the storage means 64 based on the output of the rigidity detection means 70. The distance L is determined with reference to the correspondence table, and the driving means 65 is controlled to set the distance L between the guide plate tip 30A and the transfer position TR.

  Table 2 shows the results of image formation experiments in which the image forming apparatus shown in FIG. 3 was used and the transfer speed of the transfer material was 220 mm / sec and black image formation was continuously performed.

  As the guide plate, the one shown in FIG. 9, that is, the tip provided with an elastic guide member made of a PET film having a thickness of 50 μm was used.

  Table 2 shows the evaluation results of the image quality in the comparative example in which the distance L between the transfer position and the guide plate tip is constant and in the example in which the distance L is controlled according to the thickness (basis weight) of the transfer material. .

  In Table 2, ◯ indicates that there is no toner dust and a good image is formed, Δ indicates that toner dust is slightly generated, and × indicates that clear toner dust is generated.

  As is clear from Table 2, in the comparative example, a deterioration in image quality was observed on thick paper with high rigidity, but in the examples, good images were formed on papers of all basis weights.

It is a figure which shows the transfer part structure in the conventional image forming apparatus. It is a figure which shows the example of image quality fall. 1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a secondary transfer unit in the image forming apparatus illustrated in FIG. 2. It is a figure for demonstrating the bending stress of a transcription | transfer material. FIG. 2 is a diagram illustrating a detailed structure of an example of a transfer unit of the image forming apparatus according to the embodiment of the present invention. 1 illustrates an example of a transfer unit of an image forming apparatus according to an embodiment of the present invention. It is a block diagram of a control system that changes the distance between the transfer position and the guide plate tip according to the bending stress of the transfer material. Still another example of the embodiment of the present invention will be described. It is a figure which shows a rigidity detection means. FIG. 10 is a block diagram of a control system of the embodiment shown in FIG. 9.

Explanation of symbols

6 Intermediate transfer body 7A Secondary transfer means 23 Registration roller 30, 31, 33, 34 Guide plate 60 Calculation control unit 70 Rigidity detection means TR Transfer position

Claims (11)

An image carrier, contact-type transfer means for transferring a toner image on the image carrier to a transfer material, transport means for conveying a transfer material toward a transfer position formed by the contact-type transfer means, and the transfer position It has a pair of guide plates that form a transport path between the transport means, and the distance between the tip of the guide plate closer to the image carrier and the transfer position of the pair of guide plates is variable. An image forming apparatus. The image forming apparatus according to claim 1, wherein the distance is changed by displacing the contact-type transfer unit in a transfer material conveyance direction. 3. The image forming apparatus according to claim 1, wherein the distance is changed by displacing the guide plate closer to the image carrier in a transfer material conveyance direction. The image forming apparatus according to claim 1, further comprising a control unit configured to control the distance according to a bending stress of the transfer material. The image forming apparatus according to claim 1, further comprising a control unit that controls the distance according to a thickness of a transfer material. 6. The image forming apparatus according to claim 1, wherein the contact-type transfer unit includes a transfer roller. 7. The guide plate according to claim 1, wherein the guide plate closer to the image carrier has a rigid base and a tip supported by the base and made of an elastic body. Image forming apparatus. The image forming apparatus according to claim 4, further comprising a user interface for inputting information on a bending stress of the transfer material to the control unit. The image forming apparatus according to claim 4, further comprising a rigidity detection unit that detects a bending stress of the transfer material, wherein the control unit changes the distance based on an output of the rigidity detection unit. The image forming apparatus according to claim 1, wherein the image carrier has a belt shape. The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer member.

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