JP2010145815A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reliably prevent the occurrence of a shock line so that even when a thick recording medium is used, a shock received when the recording medium enters the fixing means is not directly transmitted to the transfer means, by regulating the magnitude relationship of forces in a tangential direction for holding a recording medium by a transfer means, an intermediate conveying means and a fixing means. <P>SOLUTION: An image forming apparatus includes: an image carrier on which a toner image is formed; the transfer means which transfers the toner image formed on the image carrier to the recording medium; the fixing means which fixes the toner image on the recording medium, while nipping and conveying the recording medium in a fixing nip portion; and the intermediate conveying means which is disposed between the transfer means and the fixing means and carries and conveys the recording medium. When the force in the tangential direction for holding the recording medium by the transfer means is denoted as [F<SB>1</SB>N], the force in the tangential direction for holding the recording medium by the intermediate conveying means is denoted as [F<SB>2</SB>N], and the force in the tangential direction for holding the recording medium by the fixing means is denoted as [F<SB>3</SB>N], F<SB>1</SB><F<SB>2</SB><F<SB>3</SB>is satisfied. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic printer, copying machine, or facsimile machine, a toner image formed on a photosensitive drum is transferred to a recording medium by a transfer roller, and the recording medium on which the toner image is transferred The toner image is fixed on the recording medium by passing through the fixing device, but the shock received when the recording medium enters the fixing device is transmitted to the photosensitive drum and the transfer roller via the recording medium. As a result, a streak-like shock line extending in a direction perpendicular to the recording medium conveyance direction is generated. Therefore, by curving the recording medium conveyance path from the transfer roller to the fixing device, the recording medium is bent (bent) to reduce or prevent the occurrence of shock lines (for example, patents). Reference 1).
JP 11-338290 A

  However, in the conventional image forming apparatus, depending on the thickness and rigidity of the recording medium, it is difficult to prevent the recording medium from being appropriately bent.

  The present invention solves the above-mentioned conventional problems, and uses a thick recording medium by defining the magnitude relationship of the tangential force with which the transfer means, intermediate conveying means and fixing means hold the recording medium. Even so, an object of the present invention is to provide an image forming apparatus capable of reliably preventing the occurrence of a shock line without the shock received when the recording medium enters the fixing unit being directly transmitted to the transfer unit. To do.

Therefore, in the image forming apparatus of the present invention, an image carrier on which a toner image is formed, transfer means for transferring the toner image formed on the image carrier to a recording medium, and the recording medium on the fixing nip. A fixing unit that fixes a toner image on the recording medium while being nipped and conveyed by a unit, and an intermediate conveyance unit that is disposed between the transfer unit and the fixing unit and carries and conveys the recording medium, The tangential force that the transfer means holds the recording medium is F ₁ [N], the tangential force that the intermediate conveying means holds the recording medium is F ₂ [N], and the fixing means is the recording medium. When the tangential force for holding the medium is F ₃ [N], F ₁ <F ₂ <F ₃ .

  According to the present invention, the image forming apparatus defines the magnitude relation of the tangential force with which the transfer unit, the intermediate conveyance unit, and the fixing unit hold the recording medium. As a result, even if a thick recording medium is used, the shock received when the recording medium enters the fixing unit is not directly transmitted to the transfer unit, and the occurrence of a shock line can be reliably prevented. it can.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a schematic diagram of the image forming apparatus according to the first embodiment of the present invention.

  In the figure, reference numeral 10 denotes an image forming apparatus, for example, an electrophotographic printer, a facsimile machine, a copying machine, a printer, a facsimile machine, and a multifunction machine having a function of a copying machine (MFP: Multi Function Printer). It may be a kind of image forming apparatus. In the present embodiment, the case where the image forming apparatus 10 is a so-called tandem color electrophotographic printer will be described.

  The image forming apparatus 10 includes an image forming unit 20, and the image forming unit 20 is arranged so as to be sequentially arranged in the transport direction (the left direction in the drawing) along the transport path of the recording medium 12. The toner images are transferred onto the recording medium 12 by toner image forming portions 21K, 21Y, 21M, and 21C corresponding to four colors of black, Y (yellow), M (magenta), and C (cyan), respectively, and Coulomb force. The transfer section 32 is provided. The toner image forming units 21K, 21Y, 21M, and 21C have the same configuration, and the colors of toners stored as developers are different. When the toner image forming units 21K, 21Y, 21M, and 21C are described in an integrated manner, the toner image forming unit 21 will be described. Each toner image forming unit 21 is mounted in the image forming apparatus 10 as a detachable independent unit, and forms an image on the recording medium 12 conveyed along the conveyance path.

  Here, reference numeral 11 denotes a medium tray that accommodates recording media 12 such as printing paper in a stacked state. A sheet feeding unit 13 feeds the recording medium 12 one by one from the medium tray 11 and feeds the recording medium 12 one by one. The paper feed unit 13 separates the pickup roller 14 disposed so as to be pressed against the recording medium 12 raised to a certain height and the recording medium 12 fed out from the medium tray 11 by the pickup roller 14 one by one. A roller pair of a feed roller 15 and a retard roller 16 is provided.

  Reference numeral 17 denotes a medium transport unit for transporting the recording medium 12 fed out from the paper feed unit 13 one by one to the image forming unit 20. The medium transport unit 17 includes transport roller pairs 22 and 23 for transporting the recording medium 12.

  Each toner image forming unit 21 includes an OPC (Organic Photo-Conductor) drum 25 as an image carrier for carrying a toner image, and a charging roller for negatively charging the surface of the OPC drum 25. 26, a laser head 27 as an exposure means comprising an LED (Light Emitting Diode) array for forming an electrostatic latent image on the surface of the charged OPC drum 25, and development for forming a toner image on the electrostatic latent image by frictional charging. A roller 24 and a toner supply unit 28 that supplies toner to the developing roller 24 are provided.

  The transfer unit 32 functions as a transfer unit, and transports the recording medium 12, an endless belt 33, a drive roller 34 rotated by a driving unit (not shown) to drive the endless belt 33, and the drive roller 34. A tension roller 35 that stretches the endless belt 33 in a pair and a transfer roller 36 that is disposed so as to be in pressure contact with each OPC drum 25 so as to face each toner image forming portion 21.

  Further, a fixing unit 37 as a fixing unit fixes the toner image transferred onto the recording medium 12 to the recording medium 12 by heat and pressure. The fixing unit 37 includes a halogen lamp 41 serving as a heat source therein, and includes a roller pair including an upper roller 42 whose surface is formed of an elastic body and a lower roller 43 that is in pressure contact with the upper roller 42. As a result, the fixing unit 37 fixes the toner image on the recording medium 12 while nipping and conveying the recording medium 12 at the nip portion between the upper roller 42 and the lower roller 43, that is, the fixing nip portion.

  Reference numeral 44 denotes a discharge roller pair for discharging the recording medium 12 on which the toner image is fixed by the fixing unit 37. Reference numeral 45 denotes a stacker unit for stacking the discharged recording medium 12.

  Further, the image forming apparatus 10 according to the present exemplary embodiment includes an intermediate conveyance roller pair 46 as an intermediate conveyance unit for carrying and conveying the recording medium 12 in a conveyance path between the fixing unit 37 and the transfer unit 32.

  Next, the configuration of the intermediate conveyance roller pair 46 will be described in detail.

  FIG. 1 is a perspective view showing a configuration of an intermediate conveyance roller pair according to the first embodiment of the present invention.

  As shown in the figure, the intermediate conveyance roller pair 46 includes a first intermediate conveyance roller 51 disposed on the upper side and a second intermediate conveyance roller 52 disposed on the lower side. The first intermediate transport roller 51 is formed by coating the surface of a shaft made of stainless steel, that is, SUS, with a fluororesin. The surface of the coating is smoothly finished to convey the recording medium 12. The material of the coating may be other than fluororesin as long as it is difficult for unfixed toner to adhere to it.

The second intermediate transport roller 52 is formed by covering the surface of the shaft made of SUS with fluorine rubber in which tin oxide is distributed as a conductive material. Since both ends of the second intermediate transport roller 52 are supported by the bearing 54, the fluoro rubber is removed and the shaft is exposed, and the other portions are covered with the fluoro rubber. The part covered with the fluoro rubber, that is, the rubber part has a diameter larger than both ends by the thickness of the fluoro rubber. The surface of the rubber part is polished and smoothly formed to convey the recording medium 12. The volume resistivity of the rubber part is 10 ⁶ [Ωcm]. The shaft may be other than SUS as long as it is a metal material. Further, the rubber portion may be a material in which a conductive material such as carbon or pigment is distributed in a rubber material such as urethane rubber, and has a conductivity, and a volume resistivity is about 10 ² to 10 ⁸ [Ωcm]. Any other material may be used.

  Reference numeral 53 denotes a base plate for supporting the intermediate conveyance roller pair 46, and is fixed to the main body of the image forming apparatus 10. The bearing 54 is made of a non-conductive plastic such as polyacetal and has a good sliding property, and is fixed to the base plate 53. The second intermediate transport roller 52 is rotatably attached to the base plate 53 by supporting both ends thereof with bearings 54.

  In addition, a movable bearing 55 is attached to a long hole formed in the base plate 53 above the bearing 54. The movable bearing 55 is made of non-conductive and slidable plastic such as polyacetal, and is movable only in the vertical direction. The first intermediate transport roller 51 is rotatably attached to the base plate 53 by supporting both ends thereof with movable bearings 55.

  The movable bearing 55 is urged in the vertical direction by a pressing spring 56 attached to the base plate 53. Therefore, the movable bearing 55 moves along the slot until the second intermediate conveyance roller 52 and the first intermediate conveyance roller 51 come into contact with each other.

  Further, the second intermediate transport roller 52 has a second gear 57 attached to one end thereof and is driven by a motor (not shown). A first gear 61 is attached to one end of the first intermediate conveyance roller 51 at a position where it meshes with the second gear 57, and the first intermediate conveyance roller 51 is also driven by the motor.

  One end of the first intermediate conveyance roller 51 is connected to a conductive first contact 62, and the first contact 62 is connected to a frame ground (not shown). Further, one end of the shaft made of metal of the second intermediate transport roller 52 is connected to a conductive second contact 63, and the second contact 63 can apply a voltage of +2 [KV] (not shown). It is connected to the. The voltage applied to the second intermediate transport roller 52 may be about +1 to +5 [KV], and a potential difference is generated between the paired first intermediate transport roller 51 and the second intermediate transport roller 52. It only has to be.

  Next, a method for measuring the holding force with which the intermediate conveying roller pair 46 holds the recording medium 12 in the tangential direction in the present embodiment will be described.

  FIG. 3 is a diagram for explaining a method for measuring the holding force of the intermediate conveyance roller pair in the first embodiment of the present invention, and FIG. 4 is a schematic diagram of the main part of the image forming apparatus in the first embodiment of the present invention. It is.

  In this case, the intermediate conveyance roller pair 46 is separated from the rollers that drive the first intermediate conveyance roller 51 and the second intermediate conveyance roller 52, and is in a state where no driving force is applied. As shown in FIG. 3, the measurement medium 64 is sandwiched between the first intermediate conveyance roller 51 and the second intermediate conveyance roller 52. Here, the measurement medium 64 is, for example, paper such as P paper 64 [gsm] manufactured by XEROX, and two holes are formed at the tip.

  Then, for example, one end of a line 65 made of a material that is difficult to stretch, such as a fishing line, is hooked in the hole, and the other end is hooked on a spring balance 66. In this state, as shown in FIG. 3, the measuring medium 64 is pulled in the transport direction via the spring balance 66, the maximum force value indicated by the spring balance 66 is measured, and the measured value is used as the intermediate transport roller pair. Reference numeral 46 denotes a holding force as a tangential force for holding the recording medium 12.

  Similarly, the holding force at which the transfer unit 32 and the fixing unit 37 as shown in FIG. 4 hold the recording medium 12 is measured. In this case, it is assumed that the transfer unit 32 and the fixing unit 37 are in a state where no driving force is applied to each roller.

Incidentally, the holding force of the transfer unit 32 measured in this manner and F _1, the holding force of the intermediate conveying roller pair 46 and F _2, the holding force of the fixing portion 37 and F _3.

  Next, the operation of the image forming apparatus 10 having the above configuration will be described. First, the operation of the entire image forming apparatus 10 will be described.

  As shown in FIG. 4, the medium tray 11 is detachably mounted in the main body of the image forming apparatus 10, and a recording medium 12 is stacked inside. Then, a motor (not shown) is driven to rotate the pickup roller 14 of the paper feeding unit 13. Then, the recording medium 12 fed out by the pickup roller 14 is conveyed to the nip position of the roller pair composed of the feed roller 15 and the retard roller 16 and separated one by one. Then, the recording medium 12 fed out one by one from the paper supply unit 13 is sent to the medium conveyance unit 17 and further sent to the image forming unit 20 by the conveyance roller pairs 22 and 23.

  In each toner image forming unit 21 of the image forming unit 20, the laser head 27 selectively irradiates the surface of the OPC drum 25, so that the electrostatic latent image is formed on the surface of the OPC drum 25 negatively charged by the charging roller 26. Form. The developing roller 24 develops the electrostatic latent image by attaching the toner supplied from the toner supply unit 28 to the surface of the OPC drum 25. As a result, a toner image is formed on the OPC drum 25.

  Subsequently, the toner image carried on the OPC drum 25 is transferred onto the recording medium 12 which is electrostatically attracted to the endless belt 33 and conveyed at the nip portion between the OPC drum 25 and the transfer roller 36, and is recorded on the recording medium. A negatively charged toner image is formed on the toner 12. The endless belt 33 is caused to travel when a drive unit (not shown) rotates the drive roller 34. In this case, the OPC drum 25 and the endless belt 33 of each toner image forming unit 21 are driven in synchronism with each other, and the toner images composed of the respective color toners are sequentially superimposed on the recording medium 12 electrostatically attracted to the endless belt 33. It is transferred together.

  Then, the recording medium 12 onto which the toner image is transferred by each toner image forming unit 21 of the image forming unit 20 passes through the intermediate conveyance roller pair 46 and is sent to the fixing unit 37. When the recording medium 12 is nipped and conveyed by the upper roller 42 and the lower roller 43 of the fixing unit 37, heat and pressure are applied to the toner image on the recording medium 12. As a result, the toner image is melted and fixed on the recording medium 12. Then, the recording medium 12 on which the toner image is fixed passes through the fixing unit 37 and is then discharged to the stacker unit 45 by the discharge roller pair 44.

  Next, the operation of the intermediate conveyance roller pair 46 will be described.

  As described above, the first intermediate transport roller 51 is grounded to the frame ground through the first contact 62, and the second intermediate transport roller 52 is supplied with a voltage of +2 [KV] from the power supply device through the second contact 63. Applied. Therefore, the flow of electrons flows from the first intermediate conveyance roller 51 to the second intermediate conveyance roller 52. Therefore, the negatively charged unfixed toner image formed on the recording medium 12 is drawn toward the recording medium 12 and does not adhere to the first intermediate conveyance roller 51. That is, the image forming apparatus 10 includes a toner adhesion preventing unit that applies a voltage to the intermediate conveyance roller pair 46. As a result, the recording medium 12 can be transported to the fixing unit 37 without affecting the toner image.

  Next, the state of the recording medium 12 when the leading end of the recording medium 12 enters the fixing unit 37 will be described. First, the state of the recording medium 12 in a comparative example that does not have the intermediate conveyance roller pair 46 will be described.

  FIG. 5 is a diagram showing a state of a thin recording medium in a comparative example, and FIG. 6 is a diagram showing a state of a thick recording medium in a comparative example.

  Here, a case where the intermediate conveyance roller pair 46 is not disposed between the transfer unit 32 and the fixing unit 37 as in the conventional image forming apparatus will be described.

  In the fixing unit 37, the toner image on the recording medium 12 is melted and fixed to the recording medium 12 by heat and pressure. Therefore, the upper roller 42 and the lower roller 43 are larger than the transfer unit 32 and the conveying roller pair. Pressure is being applied. That is, the upper roller 42 and the lower roller 43 are in pressure contact with each other with a larger pressure than the other roller pairs. Therefore, when the leading end of the recording medium 12 enters the fixing unit 37, the upper roller 42 and / or the lower roller 43 are pushed away against a large pressure. Stagnant.

  Here, when the recording medium 12 has a relatively thin thickness such as a paper thickness of 0.3 [mm] or less or a continuous amount of 300 [gsm] or less, as shown in FIG. When the leading edge of the medium 12 stagnates, it is pushed by the transfer unit 32 from the rear, so that a portion A is bent between the fixing unit 37 and the transfer unit 32. Therefore, even if the leading end of the recording medium 12 stagnates, the transfer unit 32 is not affected.

Here, the moving distance of the recording medium 12 immediately before the fixing unit 37 is s ₀ , the moving distance of the recording medium 12 in the transfer unit 32 is s _1, and the rotation amount of the OPC drum 25 is r. If the moving amount of the tip of the recording medium 12 is 0, 0≈s ₀ <s ₁ ≈r, and the moving distance of the recording medium 12 in the transfer unit 32 and the rotation amount of the OPC drum 25 are substantially equal. It can be seen that the toner image is normally transferred.

On the other hand, when the recording medium 12 has a relatively thick thickness such that the paper thickness is 0.3 [mm] or more or the continuous amount exceeds 300 [gsm], the rigidity of the recording medium 12 is high. 6, when the leading end of the recording medium 12 is stagnated, even if it is pushed by the transfer unit 32 from behind, the portion A is hardly bent between the fixing unit 37 and the transfer unit 32. Therefore, when the leading end of the recording medium 12 is stagnated, the recording medium 12 is stagnated at the transfer unit 32 at the same time. Even if the recording medium 12 is stagnated in the transfer unit 32, the OPC drum 25 rotates at the same speed as usual and continues to transfer the toner image to the recording medium 12. Therefore, the toner density only in the portion where the recording medium 12 stagnates. Becomes darker than other portions, and a shock line, which is a streaky line extending in a direction perpendicular to the conveyance direction of the recording medium 12, appears. In other words, 0≈s ₀ ≈s ₁ <r, and a difference occurs between the moving distance s ₁ of the recording medium 12 in the transfer unit 32 and the rotation amount r of the OPC drum 25, so that a shock line is generated.

  Next, the state of the recording medium 12 in the image forming apparatus 10 according to the present embodiment having the intermediate conveyance roller pair 46 will be described.

  FIG. 7 is a diagram showing the state of the recording medium in the first embodiment of the present invention. FIG. 8 is a diagram showing the relationship between the holding force of each part and the occurrence of a shock line in the first embodiment of the present invention. FIG. 9 is a schematic diagram of a main part of a modification of the image forming apparatus according to the first embodiment of the present invention.

  In the image forming apparatus 10 according to the present embodiment as well, as in the comparative example shown in FIG. 5, the recording medium 12 has a paper thickness of 0.3 [mm] or less or a continuous amount of 300 [gsm] or less. In the case where the thickness is relatively thin, even if the leading end of the recording medium 12 stagnates, the transfer portion 32 is not affected.

  On the other hand, when the recording medium 12 has a relatively thick thickness such that the paper thickness is 0.3 [mm] or more or the continuous amount exceeds 300 [gsm], as shown in FIG. Although the recording medium 12 stagnates for a moment at the moment when the leading end of 12 enters the fixing unit 37, the recording medium 12 is held by the intermediate conveying roller pair 46, so that the recording medium 12 is positioned upstream in the conveying direction of the recording medium 12. The effect on the transfer portion 32 is reduced.

  Further, since the intermediate conveyance roller pair 46 is driven, the force for pushing the leading end of the recording medium 12 into the fixing unit 37 is larger than that in the conventional image forming apparatus, and the stagnation time is also short. Further, the force for pushing the leading end of the recording medium 12 into the fixing unit 37 is the sum of the force for the transfer unit 32 to transport the recording medium 12 and the force for the intermediate transport roller pair 46 to transport the recording medium 12. Even with the recording medium 12 that is thicker and more rigid than the conventional image forming apparatus, it is possible to cause the portion B to bend.

Here, assuming that the moving distance of the recording medium 12 immediately before the intermediate conveying roller pair 46 is s ₂ , 0≈s ₀ <s ₂ <s ₁ ≈r, and the moving amount of the recording medium 12 in the transfer unit 32 is Since the rotation amount on the OPC drum 25 is substantially equal, the toner image is normally transferred.

In FIG. 8, when the recording medium 12 has a continuous quantity up to 500 [gsm] that can be easily purchased in the market, the image forming apparatus 10 according to the present embodiment holds the transfer unit 37. The state of occurrence of the shock line when the force F ₁ is fixed and the holding force F ₃ of the fixing unit 37 is changed is shown.

In FIG. 8, a circle mark indicates that a shock line has not occurred, a triangle mark indicates that a light shock line has occurred, and a cross mark clearly indicates that a shock line has occurred. From this result, when the holding force of the upstream roller pair in the conveyance direction of the recording medium 12 is F _front and the holding force of the downstream roller pair is F _rear , the ratio of the holding force of the roller pair is F _front. When the condition of ≧ 1/2 × F _rear is satisfied, it can be seen that if the continuous amount of the recording medium 12 is in the range of up to 500 [gsm], it is possible to form an image without generating a shock line.

However, when the holding force of the upstream roller pair is stronger than the holding force of the downstream roller pair, the force to push into the fixing unit 37 located on the downstream side cannot be obtained, so the condition of F _rear > F _front is satisfied. In addition, F _rear > F _front ≧ 1/2 × F _rear .

In the present embodiment, an intermediate conveyance roller pair 46 is disposed between the transfer unit 32 and the fixing unit 37, and when the relationship between each part is applied as the upstream side and the downstream side in the conveyance direction, F _{When 2} > F ₁ ≧ 1/2 × F ₂ and F ₃ > F ₂ ≧ 1/2 × F ₃ are satisfied, a shock line does not occur. Then, as a result of measuring the holding force of the transfer unit 32, the intermediate conveyance roller pair 46 and the fixing unit 37 by the method shown in FIG. 3, F ₁ = 7.5 [N], F ₂ = 15 [N], F ₃ = 30 [N]. Therefore, F ₂ > F ₁ ≧ ½ × F ₂ and F ₃ > F ₂ = ½ × F ₃ are satisfied, and image formation is possible without occurrence of shock lines.

In the image forming apparatus 10 according to the present embodiment, no shock line is generated under the conditions of F ₂ > F ₁ ≧ 1/2 × F ₂ and F ₃ > F ₂ = 1/2 × F ₃ , but the upstream roller If the holding force of the pair does not exceed the holding force of the downstream roller pair, the recording medium 12 is pushed in, so that F ₃ > F ₂ > F ₁ is satisfied in the image forming apparatus 10 having the intermediate conveyance roller pair 46. If so, the shock line is reduced or no longer occurs.

  In the present embodiment, the case where the image carrier is the OPC drum 25 and the method of directly transferring the toner image to the recording medium 12 has been described. However, the method of transferring the toner image to the recording medium 12 is as follows. Any type may be used. For example, an endless belt 125 that is an intermediate transfer member may be used as an image carrier as in a modification shown in FIG. In this case, the toner image on the OPC drum 25 is first transferred onto the endless belt 125, and then the toner image on the endless belt 125 is transferred to the recording medium 12.

  As described above, in the present embodiment, even when a thick recording medium 12 having a paper thickness of about 0.3 [mm] or more or a continuous amount exceeding 300 [gsm] is used, the fixing unit Since the shock when the leading edge of the recording medium 12 enters 37 is not directly transmitted to the transfer section 32, the occurrence of a shock line can be prevented.

  Next, a second embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st Embodiment, the description is abbreviate | omitted by providing the same code | symbol. The description of the same operation and the same effect as those of the first embodiment is also omitted.

  FIG. 10 is a perspective view showing a main part of the intermediate conveyance roller pair in the second embodiment of the present invention.

  In the present embodiment, an optical paper thickness sensor (not shown) is disposed between the conveying roller pair 23 and the toner image forming unit 21K as means for detecting the thickness of the recording medium 12. Then, the thickness value of the recording medium 12 detected by the paper thickness sensor is transmitted to a control unit (not shown) of the image forming apparatus 10.

  As shown in FIG. 10, a cam 72 is disposed above the pressing spring 56 that biases the movable bearing 55 attached to the base plate 53 of the intermediate conveyance roller pair 46. The cam 72 includes a semicircular portion for pushing the seating surface of the pressing spring 56 and an L-shaped portion capable of lifting the first intermediate conveyance roller 51, and is driven by a motor capable of forward and reverse rotation (not shown). It rotates about the rotation axis 73 in the direction indicated by arrows a and b. Note that a indicates the forward rotation direction, and b indicates the reverse rotation direction. The control unit, motor, cam 72, and the like function as holding force adjusting means.

  Since the configuration of other points is the same as that of the first embodiment, description thereof is omitted.

  Next, the operation of the image forming apparatus 10 in the present embodiment will be described.

  FIG. 11 is a diagram showing the operation of the cam in the second embodiment of the present invention, and FIG. 12 is a diagram showing changes in the holding force of the intermediate conveyance roller pair in the second embodiment of the present invention.

  First, when the recording medium 12 fed out from the medium tray 11 reaches the paper thickness sensor, the paper thickness sensor detects the thickness of the recording medium 12 and transmits the detected value to the control unit. Then, the control unit drives the cam 72 by rotating the motor based on the detected thickness of the recording medium 12.

  Here, when the paper thickness of the recording medium 12 is thinner than 0.3 [mm], the control unit reverses the motor and rotates the cam 72 in the direction of the arrow b. As a result, the L-shaped portion of the cam 72 rises and lifts the shaft of the first intermediate conveyance roller 51, so that the state shown in FIG. 11C is obtained, and the first intermediate conveyance roller 51 and the second intermediate conveyance roller The roller 52 is completely separated.

When the paper thickness of the recording medium 12 is 0.3 [mm], the control unit does not operate the motor and does not rotate the cam 72. As a result, the cam 72 and the first intermediate conveyance roller 51 are in a state as shown in FIG. 11A, and the first intermediate conveyance roller 51 is pressed against the second intermediate conveyance roller 52 by the pressing spring 56. In this case, the holding force of the intermediate conveyance roller pair 46 is F _{2 min} .

  Furthermore, when the paper thickness of the recording medium 12 is greater than 0.3 [mm], the control unit rotates the motor in the forward direction and rotates the cam 72 in the direction of arrow a. As a result, the L-shaped portion of the cam 72 is lowered and the pressing spring 56 is pressed and contracted, so that the state shown in FIG. 11B is obtained, and the first intermediate transport roller 51 is moved to the second position by the pressing spring 56. The intermediate conveying roller 52 is pressed strongly.

Here, when the holding force of the transfer unit 32 is F _1a , the holding force of the fixing unit 37 is F _3a, and the maximum value of the thickness of the recording medium 12 usable in the image forming apparatus 10 is T _max , this embodiment In this embodiment, the control unit controls the holding force of the intermediate conveyance roller pair 46 as shown in FIG. 12 by rotating the cam 72 based on the thickness of the recording medium 12 detected by the paper thickness sensor.

  In the present embodiment, the example in which the holding force of the intermediate conveyance roller pair 46 is changed based on the thickness of the recording medium 12 detected by the paper thickness sensor has been described, but the thickness of the recording medium 12 is acquired. Any means may be used. For example, the thickness of the recording medium 12 used in the image forming apparatus 10 may be set in advance.

Further, the first intermediate conveyance roller 51 and the second intermediate conveyance roller 52 are separated from each other in advance, and before the leading end of the recording medium 12 passes through the intermediate conveyance roller pair 46 and reaches the fixing unit 37, the first intermediate conveyance roller 51 and the second intermediate conveyance roller 52 are separated from each other. The conveying roller 51 is brought into contact with the recording medium 12 so as to apply a holding force F _{2 min} , and the first intermediate conveying roller 51 is separated from the recording medium 12 after the leading end of the recording medium 12 has passed through the fixing unit 37. May be.

  Thus, in the present embodiment, the first intermediate conveyance roller 51 and the second intermediate conveyance roller 52 of the intermediate conveyance roller pair 46 can be separated from each other, so that the recording medium 12 has a paper thickness of 0.3 mm. In the case of thinner and frequently used ones, even if the first intermediate conveyance roller 51 and the second intermediate conveyance roller 52 are separated from each other and the driving of the intermediate conveyance roller pair 46 is stopped, image formation is performed. Therefore, the power consumption of the image forming apparatus 10 can be suppressed. When the recording medium 12 has a paper thickness of 0.3 mm or more, it is only necessary to apply a minimum holding force that does not generate a shock line, and the load on the motor can be reduced. is there. Therefore, the occurrence of a shock line can be prevented without consuming more power than necessary.

  Next, a third embodiment of the present invention will be described. In addition, about the thing which has the same structure as 1st and 2nd embodiment, the description is abbreviate | omitted by providing the same code | symbol. Also, the description of the same operations and effects as those of the first and second embodiments is omitted.

  FIG. 13 is a schematic diagram of a main part of an image forming apparatus according to the third embodiment of the present invention.

  In the figure, reference numeral 73 denotes a transfer unit as transfer means in the present embodiment, which includes an endless belt 74 that conveys the recording medium 12 and a drive roller 75 that is rotated by a drive unit (not shown) to drive the endless belt 74. . The drive roller 75 includes a shaft made of SUS, and the surface of the shaft is coated with a fluororesin in order to obtain friction with the endless belt 74. In addition, the material of the said shaft should just be an electroconductive material, and aluminum etc. may be sufficient as it. The drive roller 75 is connected to a power supply device capable of applying a voltage of +1 [KV] via a contact (not shown).

  Reference numeral 76 denotes an intermediate conveyance roller pair as intermediate conveyance means in the present embodiment, which includes a first intermediate conveyance roller 77 disposed on the upper side, shares a drive roller 75 with the transfer unit 73, and It functions as a second intermediate conveyance roller disposed on the side. The first intermediate transport roller 77 is the same as the second intermediate transport roller 52 in the first embodiment. The first intermediate transport roller 77 is electrically connected to the frame ground via a contact (not shown), and is connected to the drive roller 75 via a gear (not shown).

  Since the configuration of other points is the same as that of the first embodiment, description thereof is omitted.

  Next, the operation of the image forming apparatus 10 in the present embodiment will be described.

  First, the transfer unit 73 is driven to transfer the toner image to the recording medium 12. At this time, the drive unit rotates the drive roller 75, but the first intermediate transport roller 77 connected to the drive roller 75 by the gear is also rotated at the same time.

  When the recording medium 12 conveyed by the endless belt 74 passes between the OPC drum 25 and the transfer roller 36, the toner image is transferred. Then, after passing through the toner image forming unit 21 </ b> C, the recording medium 12 enters the intermediate conveyance roller pair 76 while being placed on the endless belt 74 and is conveyed to the fixing unit 37.

  Thus, in the present embodiment, the intermediate conveyance roller pair 76 shares the drive roller 75 of the transfer unit 73 as the second intermediate conveyance roller of the intermediate conveyance roller pair 76. As a result, the feeding speed of the recording medium 12 at the transfer section 73 and the feeding speed of the intermediate conveyance roller pair 76 can be made the same, so that the recording medium 12 between the transfer section 73 and the intermediate conveyance roller pair 76 can be made. It is possible to prevent the occurrence of a shock line due to the transfer portion 73 being pulled by the upstream roller pair due to the difference in the feed speeds.

  Even when the temperature of the endless belt 74 and the drive roller 75 of the transfer unit 73 changes due to the temperature rise inside the image forming apparatus 10 and the feed speed of the recording medium 12 fluctuates, Since it is the same speed as the feeding speed, image formation can be performed with stable image quality for a long time.

  In the first to third embodiments, the example in which the image forming apparatus 10 is a printer has been described. However, the present invention can also be applied to an MFP, a facsimile machine, and a copying machine.

  In the first to third embodiments, the direct transfer method in which the toner image formed on the OPC drum 25 is directly transferred onto the recording medium 12 has been described. However, the transfer method is limited. Instead, for example, as in the modification shown in FIG. 9, the toner image formed on the OPC drum 25 is transferred onto the endless belt 125, and the toner image transferred onto the endless belt 125 is recorded on the recording medium. A secondary transfer method in which the toner image is transferred to the toner image 12 may be used.

  In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.

It is a perspective view which shows the structure of the intermediate conveyance roller pair in the 1st Embodiment of this invention. 1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present invention. It is a figure explaining the measuring method of the retention strength of the intermediate conveyance roller pair in the 1st Embodiment of this invention. 1 is a schematic view of a main part of an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the state of the thin recording medium in a comparative example. It is a figure which shows the state of the thick recording medium in a comparative example. It is a figure which shows the state of the recording medium in the 1st Embodiment of this invention. It is a figure which shows the relationship between the retention strength of each part and generation | occurrence | production of a shock line in the 1st Embodiment of this invention. It is the schematic of the principal part of the modification of the image forming apparatus in the 1st Embodiment of this invention. It is a perspective view which shows the principal part of the intermediate conveyance roller pair in the 2nd Embodiment of this invention. It is a figure which shows the operation | movement of the cam in the 2nd Embodiment of this invention. It is a figure which shows the change of the holding force of the intermediate conveyance roller pair in the 2nd Embodiment of this invention. It is the schematic of the principal part of the image forming apparatus in the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Recording medium 25 OPC drum 32, 73 Transfer part 33, 74, 125 Endless belt 37 Fixing part 46, 76 Intermediate conveyance roller pair 72 Cam

Claims (9)

An image carrier on which a toner image is formed;
Transfer means for transferring a toner image formed on the image carrier to a recording medium;
Fixing means for fixing the toner image on the recording medium while nipping and conveying the recording medium at a fixing nip portion;
An intermediate conveying means disposed between the transfer means and the fixing means for carrying and conveying the recording medium;
The tangential force that the transfer means holds the recording medium is F ₁ [N],
F ₂ [N] is a tangential force that the intermediate conveying means holds the recording medium,
When the tangential force that the fixing unit holds the recording medium is F ₃ [N],
F ₁ <F ₂ <F ₃
An image forming apparatus. The image carrier is an OPC drum;
The image forming apparatus according to claim 1, wherein the transfer unit directly transfers a toner image from the OPC drum to the recording medium. The image carrier is an endless belt;
The image forming apparatus according to claim 1, wherein the transfer unit transfers a toner image from the endless belt to the recording medium. The image forming apparatus according to claim 1, further comprising a toner adhesion preventing unit that applies a voltage to the intermediate conveying unit. The intermediate conveying means includes a conductive roller pair,
The image forming apparatus according to claim 4, wherein the toner adhesion preventing unit prevents the toner from adhering to the roller pair by applying a voltage to the conductive roller pair. The image forming apparatus according to claim 1, wherein the intermediate conveying unit includes a holding force adjusting unit that changes a tangential force F ₂ that holds the recording medium according to a thickness of the recording medium. When the thickness of the recording medium is greater than a predetermined value, the intermediate conveying means increases the tangential force F ₂ for holding the recording medium,
The image forming apparatus according to claim 6, wherein when the recording medium is thinner than a predetermined value, the intermediate conveying unit weakens a tangential force F ₂ for holding the recording medium. The image forming apparatus according to claim 6, wherein the intermediate transport unit sandwiches and transports the recording medium, and separates when the thickness of the recording medium is smaller than a predetermined value. The image forming apparatus according to claim 1, wherein the transfer unit and the intermediate conveyance unit share a member.

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