Image forming device

Abstract

To prevent a variation in transfer load between transfer means of upper imaging means and transfer means of lower imaging means.SOLUTION: An image forming apparatus comprises: a transfer medium 1 that makes a circulation movement along a substantially horizontal direction; upper imaging means 2 (2a, 2b) in which image holding means 4 are arranged above and opposite to transfer means 5 with the transfer medium 1 therebetween; and lower imaging means 3 (3a, 3b) in which image holding means 4 are arranged below and opposite to transfer means 5 with the transfer medium 1 therebetween. Each transfer means 5 of the upper imaging means 2 and the lower imaging means 3 has a transfer member 6 that extends along a width direction intersecting the direction of movement of the transfer medium 1 and is in contact with the transfer medium 1, and pressing means 7 that presses the transfer member 6 toward the image holding means 4. The pressing means 7 selects a pressing force against the transfer member 6 for the upper imaging means 2 larger than that against the transfer member for the lower imaging means 3 in a direction to make uniform a pressing load of the transfer member 6 on the image holding means 4. The transfer member 6 for the upper imaging means 2 may be reduced in weight compared with the transfer member for the lower imaging means 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, image forming apparatuses of this type are already known, for example, as described in Patent Documents 1 to 4. Patent document 1 discloses an image forming apparatus including an intermediate transfer belt stretched horizontally by a tension roller, a chromatic image forming station with a photosensitive drum arranged opposite the upper flat surface of the intermediate transfer belt, and a black image forming station with a photosensitive drum arranged opposite the lower flat surface of the intermediate transfer belt. Patent document 2 discloses an image forming device that has an intermediate transfer belt that is approximately isosceles triangular in shape and has an upper inclined surface and a lower inclined surface, and two image forming units are arranged side by side on the upper inclined surface of this intermediate transfer belt, and two image forming units are arranged side by side on the lower inclined surface to form a four-color image. Patent document 3 discloses an image forming apparatus in which the image forming units are arranged in two or more transfer areas formed by dividing the transfer belt member with multiple tension members, in a manner in which the visible images formed by each of the multiple image forming units are transferred onto a transfer belt member, and the visible images transferred onto the transfer belt member are then transferred onto a recording medium. Patent document 4 discloses an image forming device in which a yellow image forming unit and a cyan image forming unit are arranged as a first image forming unit on the upper side of an intermediate transfer belt, and a magenta image forming unit and a black image forming unit are arranged as a second image forming unit on the lower side thereof, and further, one LED is arranged for each of the two image forming units of the first and second image forming units, and image light is switched and irradiated onto the photosensitive drums of the two image forming units in response to the two rotations of the intermediate transfer belt. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-108045 A (Embodiment of the Invention, Figure 1) [Patent Document 2] Japanese Patent Application Laid-Open No. 5-84972 (Example, Figure 8) [Patent Document 3] JP 2009-80325 A (Best Mode for Carrying Out the Invention, Figure 1) [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-246779 (Embodiment of the Invention, Figure 2) Summary of the Invention [Problem to be solved by the invention]

[0004] The technical problem that the present invention aims to solve is to provide an image forming apparatus that has both an upper image forming means having an image holding means above the transfer means with the transfer medium sandwiched therebetween, and a lower image forming means having an image holding means below the transfer means with the transfer medium sandwiched therebetween, and that suppresses variations in the transfer load of each transfer means of the upper image forming means and the lower image forming means. [Means for solving the problem]

[0005] The invention of claim 1 is an image forming apparatus comprising an upper image forming means in which an image holding means is arranged opposite to the upper side of a transfer means across a transfer medium moving in a predetermined direction, and a lower image forming means in which an image holding means is arranged opposite to the lower side of the transfer means across the transfer medium, wherein each transfer means of the upper image forming means and the lower image forming means has a transfer member that extends along a width direction intersecting the direction of movement of the transfer medium and contacts the transfer medium, and a pressing means that presses the transfer member toward the image holding means, and the pressing means selects a pressing force on the transfer member for the upper image forming means that is greater than that for the lower image forming means, in a direction that makes the pressing load of the transfer member on the image holding means equal.

[0006] The invention of claim 2 is an image forming apparatus according to claim 1, characterized in that the pressing means has a pressing spring that presses the transfer member, and the elastic restoring force of the pressing spring is adjusted. The invention of claim 3 is an image forming apparatus according to claim 2, characterized in that the spring constant of the pressure spring is made larger for the upper image forming means than for the lower image forming means. The invention of claim 4 is an image forming apparatus in which, in the image forming apparatus of claim 2, the pressure spring has a larger elastic deformation amount for the upper image forming means than for the lower image forming means. The invention of claim 5 is an image forming apparatus characterized in that, in the image forming apparatus of claim 1, the transfer member is held at a position away from a fulcrum relative to a transfer holding member that can swing around the fulcrum, and the pressing means includes the transfer holding member, a pressing holding member that is arranged to be able to swing around the fulcrum relative to the transfer holding member, and a pressing spring that is held elastically deformable between the transfer holding member and the pressing holding member. The invention of claim 6 is an image forming apparatus characterized in that, in the image forming apparatus of claim 5, when the distance from the fulcrum of the pressing and holding member to the holding position of the pressing spring is L1 and the distance from the fulcrum of the transfer and holding member to the holding position of the transfer member is L2, the value of L2 / L1 is larger for the upper image forming means than for the lower image forming means. The invention of claim 7 is an image forming apparatus characterized in that, in the image forming apparatus of claim 5, when the distance between the holding positions of the pressure spring held by the transfer holding member and the pressure holding member is D, the value of D is larger for the upper image forming means than for the lower image forming means. The invention according to claim 8 is the image forming apparatus according to claim 1, characterized in that the pressing means acts independently on each of the upper image forming means and the lower image forming means. The invention of claim 9 is an image forming apparatus according to claim 8, characterized in that the pressing means independently holds both ends of the transfer member in the longitudinal direction (corresponding to the width direction of the transfer medium). The invention of claim 10 is an image forming apparatus characterized in that, in the image forming apparatus of claim 1, the pressing means makes it possible to share all or part of the components used in at least one of the upper imaging means and at least one of the lower imaging means. The invention of claim 11 is an image forming apparatus characterized in that, in the image forming apparatus of claim 10, the pressing means makes it possible for all or part of the components used in at least one of the upper image forming means or the lower image forming means to be shared at both ends of the longitudinal direction of the transfer member (corresponding to the width direction of the transfer medium). The invention according to claim 12 is the image forming apparatus according to any one of claims 1 to 11, characterized in that the transfer member is a transfer roll made of a hollow pipe.

[0007] The invention according to claim 13 comprises upper image forming means in which an image holding means is arranged above a transfer means across a transfer medium moving in a predetermined direction, and lower image forming means in which an image holding means is arranged below the transfer means across the transfer medium, each of the transfer means of the upper image forming means and the lower image forming means has a transfer member that extends along a width direction intersecting the moving direction of the transfer medium and comes into contact with the transfer medium, and a pressing means that presses the transfer member toward the image holding means, and the transfer member for the upper image forming means is lighter than that for the lower image forming means. The pressing means selects a pressing force against the transfer member for the upper image forming means greater than that for the lower image forming means in a direction in which the pressing load of the transfer member against the image holding means is equal. The image forming apparatus is characterized by the above.

[0008] The invention according to claim 14 is an image forming apparatus according to claim 13, wherein the transfer member is a transfer roll made of a hollow pipe, and the thickness of the hollow pipe for the upper image forming means is thinner than that for the lower image forming means. 。 [Effects of the Invention]

[0009] According to the invention of claim 1, in an image forming apparatus equipped with both an upper image forming means having an image holding means above the transfer means with the transfer medium sandwiched therebetween, and a lower image forming means having an image holding means below the transfer means with the transfer medium sandwiched therebetween, it is possible to suppress variations in the transfer load of each transfer means of the upper image forming means and the lower image forming means. According to the invention of claim 2, the pressing force against the transfer member can be easily adjusted by utilizing the elastic restoring force of the pressing spring. According to the invention of claim 3, attention is paid to the spring constant of the pressing spring, and the pressing force against the transfer member can be easily adjusted. According to the invention of claim 4, the pressing force against the transfer member can be easily adjusted by focusing on the amount of elastic deformation of the pressing spring. According to the invention of claim 5, it is possible to easily construct a pressing means that includes a functional element for holding the transfer member and is capable of adjusting the pressing force against the transfer member. According to the invention of claim 6, by performing the same rotation control on the same pressing spring and the same pressing and holding member, the pressing force by the pressing means can be changed between the upper image forming means and the lower image forming means. According to the invention of claim 7, by performing different rotation controls on the same pressing spring and the same pressing and holding member, the pressing force by the pressing means can be changed between the upper image forming means and the lower image forming means. According to the invention as defined in claim 8, when various combinations of upper and lower image forming means are realized, transfer means can be appropriately installed for each image forming means. According to the invention of claim 9, it is possible to provide a pressing means that can increase the degree of freedom in adjustment for assembly errors without using a transmission mechanism for transmitting pressure from the pressing mechanism on one end side to the other end side, compared to when both longitudinal ends of the transfer member are held in a non-independent manner. According to the invention as defined in claim 10, the pressing means can be shared for at least a part of the upper imaging means and the lower imaging means, thereby improving the operating accuracy of the pressing means and reducing costs. According to the invention of claim 11, the pressing means can be shared at both longitudinal ends of the transfer member for at least one of the upper image forming means or the lower image forming means, thereby improving the operating accuracy of the pressing means and reducing costs. According to the invention of claim 12, compared to when the transfer member is a transfer roll with a solid structure, it is possible to reduce the deflection in the center of the longitudinal direction caused by the weight of the transfer member, and it is possible to suppress the variation in the transfer load of the transfer means in the upper image forming means and the lower image forming means. According to the invention of claim 13, in an image forming apparatus equipped with both an upper imaging unit having an image holding unit above the transfer unit with the transfer medium sandwiched therebetween, and a lower imaging unit having an image holding unit below the transfer unit with the transfer medium sandwiched therebetween, it is possible to suppress variations in the transfer loads of the transfer units of the upper imaging unit and the lower imaging unit. In particular, this invention suppresses deflection of the transfer unit used in the upper imaging unit at the center in the longitudinal direction, and promotes application of a pressing load due to the weight of the transfer unit used in the lower imaging unit, compared to when the upper imaging unit and the lower imaging unit use transfer members of the same weight. Furthermore, in the present invention, the variation in the transfer load of each transfer means of the upper and lower image forming means can be further suppressed compared to when the same pressing means is used for the upper and lower image forming means. According to the invention of claim 14, compared to when transfer rolls made of the same hollow pipe are used as the transfer members of the upper and lower image forming means, it is possible to suppress deflection of the transfer member used in the upper image forming means at the center in the longitudinal direction, and to promote application of a pressure load due to the weight of the transfer member used in the lower image forming means. 。 [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1(a) is an explanatory diagram showing an outline of an embodiment of an image forming apparatus to which the present invention is applied, FIG. 1(b) is an explanatory diagram showing the main parts of the configuration of an upper image forming means, and FIG. 1(c) is an explanatory diagram showing the main parts of the configuration of a lower image forming means. [Figure 2](a) is an explanatory diagram showing an example of the configuration of the transfer means of the upper imaging means shown in Figure 1(b), (b) is an explanatory diagram showing an example of the configuration of the transfer means of the lower imaging means shown in Figure 1(c), (c) is an explanatory diagram showing another example of the configuration of the transfer means of the upper imaging means, and (d) is an explanatory diagram showing an example of the configuration of the transfer means of the lower imaging means. [Figure 3] 1 is an explanatory diagram showing the overall configuration of an image forming apparatus according to a first embodiment. [Figure 4] FIG. 10 is a perspective view illustrating the details of a pressing mechanism of a transfer device used in the upper image forming engine. [Figure 5] 5 is a view taken along the arrow V in FIG. 4. [Figure 6] FIG. 6 is an explanatory view similar to FIG. 5, showing details of a pressing mechanism of a transfer device used in a lower imaging engine. [Figure 7] 1A is an explanatory diagram showing a schematic view of a main part of a transfer device used in an upper image forming engine, and FIG. 1B is an explanatory diagram showing a schematic view of a main part of a transfer device used in a lower image forming engine. [Figure 8] (a) is an explanatory diagram showing the state of application of the pressure load on the transfer roll of the transfer device by the upper image creation engine, (b) is an explanatory diagram showing the state of application of the pressure load on the transfer roll of the transfer device by the lower image creation engine, and (c) is a graph showing the pressure load distribution on the transfer roll of the transfer device. [Figure 9] FIG. 10(a) is an explanatory diagram showing a schematic view of the main parts of a transfer device used in an upper image creation engine of an image forming apparatus according to a second embodiment, and FIG. 10(b) is an explanatory diagram showing a schematic view of the main parts of a transfer device used in a lower image creation engine of the same image forming apparatus. [Figure 10] FIG. 10(a) is an explanatory diagram showing a schematic view of the main parts of a transfer device used in an upper image creation engine of an image forming apparatus according to a third embodiment, and FIG. 10(b) is an explanatory diagram showing a schematic view of the main parts of a transfer device used in a lower image creation engine of the same image forming apparatus. [Figure 11] FIG. 10(a) is an explanatory diagram showing a schematic view of the main parts of a transfer device used in an upper image creation engine of an image forming apparatus according to embodiment 4, and FIG. 10(b) is an explanatory diagram showing a schematic view of the main parts of a transfer device used in a lower image creation engine of the same image forming apparatus. [Figure 12]FIG. 10(a) is an explanatory diagram showing a schematic view of the main parts of a transfer device used in an upper image creation engine of an image forming apparatus according to embodiment 5, and FIG. 10(b) is an explanatory diagram showing a schematic view of the main parts of a transfer device used in a lower image creation engine of the same image forming apparatus. [Figure 13] (a) is an explanatory diagram showing the main parts of a pressing mechanism that holds one end of a transfer device used in the upper image-forming engine of an image forming apparatus according to embodiment 6; (b) is an explanatory diagram showing the main parts of a pressing mechanism that holds the other end of a transfer device used in the upper image-forming engine of the same image forming apparatus; and (c) is an explanatory diagram showing the main parts of a pressing mechanism that holds one end of a transfer device used in the lower image-forming engine of the same image forming apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0011] Overview of the implementation form FIG. 1(a) is an explanatory diagram showing an outline of an embodiment of an image forming apparatus to which the present invention is applied. In the same figure, the image forming device comprises a transfer medium (in this example, an intermediate transfer medium is used) 1 that moves in a circular motion in an approximately horizontal direction, upper image forming means 2 (in this example, two are arranged side by side: specifically, 2a and 2b) with an image holding means 4 arranged opposite to the upper side of transfer means 5 across the transfer medium 1, and lower image forming means 3 (in this example, two are arranged side by side: specifically, 3a and 3b) with an image holding means 4 arranged opposite to the lower side of transfer means 5 across the transfer medium 1. As shown in Figures 1(b) and 1(c), each transfer means 5 of the upper image forming means 2 and the lower image forming means 3 has a transfer member 6 that extends along the width direction intersecting the movement direction of the transfer medium 1 and contacts the transfer medium 1, and a pressing means 7 that presses the transfer member 6 toward the image holding means 4, and the pressing means 7 selects a larger pressing force on the transfer member 6 for the upper image forming means 2 than for the lower image forming means 3 in a direction that makes the pressing load of the transfer member 6 on the image holding means 4 equal. In the image forming apparatus shown in FIG. 1(a), the image formed by the upper image forming means 2 and the lower image forming means 3 is transferred onto a transfer medium 1 (in this example, an intermediate transfer medium) and then transferred onto a recording medium 15 by a transfer device 16, but the present invention is not limited to this type of configuration.

[0012] In this embodiment, the upper and lower image forming means 2 and 3 are installed above and below the transfer medium 1. However, in this type of configuration, the effect of bending due to the weight of the long transfer member 6, which is a component of the transfer means 5, varies greatly in the longitudinal direction, making it difficult to set the same transfer load on the transfer member 6 using the same pressing means. In other words, the central portion of the transfer member 6 bends significantly, which makes it easy for poor image quality to occur. For example, in the upper image forming means 2, it is difficult to apply the transfer load near the center of the transfer member 6, making it easy for image mottle to occur, while in the lower image forming means 3, the central portion of the transfer member 6 is easily subjected to excessive load, making it easy for image retransfer to occur. Therefore, in this embodiment, first, the pressing means 7 (specifically, 7u and 7d) of the transfer means 5 are devised to improve the above-mentioned poor image quality. In this embodiment, the weight P0 of the transfer members 6 (specifically, 6u and 6d) should be taken into consideration, and adjustments should be made to equalize the pressing loads of the transfer members 6 used in the upper image forming means 2 and the lower image forming means 3. Specifically, the weight P0 of the transfer member 6u (6) of the upper image forming means 2 acts in the opposite direction to the transfer load, and the weight P0 of the transfer member 6d (6) of the lower image forming means 3 acts in the same direction as the transfer load, so the pressing forces P1 and P2 applied by the pressing means 7 to the transfer members 6 (6u and 6d) need to be selected so that P1 > P2 is satisfied. Here, "adjusting in a direction to make the pressure load by the transfer member 6 equal" not only means making the pressure load by the transfer member 6 equal, but also broadly includes situations in which the pressure load is adjusted toward equality, even if it is not equal.

[0013] In such technical means, the upper image forming means 2 and the lower image forming means 3 broadly include those having an image holding means 4 (photosensitive body, dielectric) and a transfer means 5, and the image forming method is not limited to the electrophotographic method but also includes other methods such as the ion irradiation method. Furthermore, the transfer medium 1 is not limited to an intermediate transfer medium, but also includes recording media such as paper. When the transfer medium 1 is a recording medium, a method is adopted in which the recording medium is conveyed by a recording medium conveying means (conveyor belt, etc.). Furthermore, the movement direction of the transfer medium 1 is not limited to the horizontal direction, but also includes directions inclined relative to the horizontal direction. Furthermore, the transfer means 5 is only required to include a transfer member 6 and a pressing means 7, and the transfer member 6 is assumed to be in contact with the transfer medium 1, but a configuration that allows contact and separation by a contact and separation mechanism is often adopted. Here, the contact and separation mechanism is not limited to a swinging type, but also includes a linear forward and backward mechanism. Furthermore, the transfer member 6 is typically assumed to be a rotatable roll member, but also includes forms other than roll members (tensioned belt members). Here, the roll member may be solid, but a hollow roll member is preferred from the viewpoints of reducing weight and increasing bending rigidity. Furthermore, the transfer method is typically an electrostatic transfer method, but is not limited to this and also includes a pressure transfer method. Furthermore, the pressing means 7 generally presses both longitudinal ends of the transfer member 6, but it is also possible to provide separate pressing mechanisms at both ends, or to provide a pressing mechanism at one end and press the other end via a link mechanism linked to the pressing mechanism.

[0014] Next, a typical or preferred embodiment of the image forming apparatus according to the present embodiment will be described. 2(a) and 2(b), a typical embodiment of the pressing means 7 is one having a pressing spring 10 that presses the transfer member 6 (6u, 6d) and adjusting the elastic restoring force of the pressing spring 10. Here, a compression spring is typically used as the pressing spring 10, but it goes without saying that a combination of a tension spring and a link arm may also be used. In addition, typical modes for adjusting the elastic restoring force of the pressure spring 10 include a mode in which the spring constant for the upper image forming means 2 is larger than that for the lower image forming means 3, and a mode in which the amount of elastic deformation (amount of compression if a compression spring is used) for the upper image forming means 2 is larger than that for the lower image forming means 3.

[0015] Furthermore, as a typical configuration example of the pressing means 7, for example, as shown in Figures 2(a) and (b), when the transfer member 6 is held at a position away from a fulcrum relative to a transfer holding member 8 that can swing around the fulcrum, the pressing means 7 may have the transfer holding member 8, a pressing holding member 9 that is arranged to be able to swing around the fulcrum relative to the transfer holding member 8, and a pressing spring 10 that is held between the transfer holding member 8 and the pressing holding member 9 so as to be elastically deformable. In this embodiment, for example, when the same pressing spring 10 is used as the pressing means 7, the pressing force of the pressing means 7 on the transfer member 6 can be adjusted by setting the distance from the fulcrum of the pressing and holding member 9 to the holding position of the pressing spring 10 as L1 (not shown in Figure 2), and the distance from the fulcrum of the pressing and holding member 9 to the holding position of the transfer member 6 as L2 (not shown in Figure 2), and making the value of L2 / L1 larger for the upper imaging means 2 than for the lower imaging means 3. Another method is to set the distance between the holding positions of the pressure spring 10 held by the transfer holding member 8 and the pressure holding member 9 as D (not shown in Figure 2), and make the value of D larger for the upper imaging means 2 than for the lower imaging means 3.

[0016] A preferred embodiment of the pressing means 7 is one that acts independently on each of the upper and lower image forming means 2 and 3. This embodiment is preferable in that it makes it possible to select an appropriate pressing means 7 for each of the image forming means when providing an image forming apparatus with various combinations of upper and lower image forming means 2 and 3. In this embodiment, when holding both ends of the transfer member 6 in the longitudinal direction (corresponding to the width direction of the transfer medium 1), it is possible to consider a configuration in which the pressing means 7 holding one end holds the other end via a linkage mechanism, but from the viewpoint of stably pressing both ends of the transfer member 6 in the longitudinal direction, a configuration in which both ends of the transfer member 6 in the longitudinal direction are held independently is preferred.

[0017] Furthermore, from the viewpoint of reducing the cost of the pressing means 7, it is preferable that the pressing means 7 be able to share all or some of the components used in at least one of the upper imaging means 2 and at least one of the lower imaging means 3. In this embodiment, it is preferable that the pressing means 7 be made such that all or part of the components used in at least one of the upper imaging means 2 or the lower imaging means 3 can be shared at both longitudinal ends of the transfer member 6.

[0018] In addition, in this embodiment, there is another aspect in which the transfer member 6 of the transfer means 5 is devised to improve the above-mentioned poor image quality. As shown in Figures 1(a) and 2(c)(d), this type of image forming apparatus comprises an upper image forming means 2 (e.g., 2a, 2b) in which an image holding means 4 is arranged opposite to the upper side of a transfer means 5 across a transfer medium 1 moving in a predetermined direction, and a lower image forming means 3 (e.g., 3a, 3b) in which an image holding means 4 is arranged opposite to the lower side of a transfer means 5 across the transfer medium 1, and each transfer means 5 of the upper image forming means 2 and the lower image forming means 3 has a transfer member 6 that extends along a width direction intersecting the moving direction of the transfer medium 1 and contacts the transfer medium 1, and a pressing means 7 that presses the transfer member 6 toward the image holding means 4, and the transfer member 6 for the upper image forming means 2 is lighter than that for the lower image forming means 3.

[0019] Here, compared to a mode in which the same weight is used for the transfer member 6 of the upper image forming means 2 and the lower image forming means 3, the deflection of the transfer member 6 at the longitudinal center is suppressed in the upper image forming means 2, and the influence of the weight P0u of the transfer member 6 acting in the opposite direction to the pressing force P1 by the pressing means 7 is reduced. In contrast, in the lower image forming means 3, the weight P0d of the transfer member 6 acting in the same direction as the pressing force P2 by the pressing means 7 effectively functions as part of the pressing load. As a measure to reduce the weight of the transfer member 6, for example, a hollow pipe may be used for the upper image forming means 2 and a solid roll for the lower image forming means 3, or both the upper and lower image forming means 2 and 3 may be transfer rolls made of hollow pipes, with the thickness of the hollow pipe for the upper image forming means 2 being thinner than that for the lower image forming means 3. In the latter embodiment, as shown in Figures 2(c) and 2(d), when the thickness of the transfer member 6u for the upper image forming means 2 is t1 and the thickness of the transfer member 6d for the lower image forming means 3 is t2, the relationship t2 > t1 may be satisfied. Furthermore, in addition to measures to reduce the weight of the transfer member 6, it is preferable to select a larger pressing force for the pressing means 7 on the transfer member 6 for the upper image forming means 2 than for the lower image forming means 3, in order to make the pressing load of the transfer member 6 on the image holding means 4 equal.

[0020] The present invention will be further described below based on the embodiments shown in the accompanying drawings. Embodiment 1 -Overall configuration of image forming device- FIG. 3 shows the overall configuration of the image forming apparatus according to the first embodiment. In the figure, the image forming device 20 has multiple (four in this example) image creation engines 30 that form images of multiple color components (for example, yellow, magenta, cyan, and black), and is provided with an intermediate transfer module 40 that temporarily transfers and holds the image formed by each image creation engine 30 before transferring it to a recording medium S such as paper. The image creation engines 30 are arranged around this intermediate transfer module 40, and a secondary transfer device 50 is provided in part of the intermediate transfer module 40 that transfers the image transferred to the transfer module onto the recording medium S. Furthermore, a fixing device 60 is provided downstream of the transfer area by the secondary transfer device 50 in the conveying direction of the recording medium S, so as to fix an unfixed image fixed to the recording medium S. The recording medium S with the fixed image is discharged to a discharge receiver not shown.

[0021] <Intermediate transfer module> In this embodiment, the intermediate transfer module 40 has a belt-shaped intermediate transfer body 45 (corresponding to the transfer medium 1 in Figure 1) made of, for example, polyimide resin stretched across multiple (four in this example) tension rolls 41 to 44, and by driving and rotating the tension roll 41 as a drive roll, the intermediate transfer body 45 can be rotated in the direction of arrow A, and by using the tension roll 44 as a tension roll, the tension of the intermediate transfer body 45 can be adjusted. In this example, the intermediate transfer body 45 has a horizontal moving portion 45a extending substantially horizontally between the tension rolls 41 and 42, and an inclined moving portion 45b extending substantially obliquely between the tension rolls 41 and 43. Furthermore, an intermediate transfer body cleaning device 47 is installed at a location of the intermediate transfer body 45 facing the tension roll 42 to clean off any residue on the intermediate transfer body 45 .

[0022] <Imaging engine> In this embodiment, an electrophotographic imaging engine is used as the imaging engine 30. Specifically, the imaging engine 30 includes a drum-shaped photoconductor 33 (corresponding to the image holding means 4 in FIG. 1), a charging device (using, for example, a charging roll) 34 that charges the photoconductor 33 around the photoconductor 33, a latent image writing device (using, for example, an LED writing head) 35 that writes an electrostatic latent image on the charged photoconductor 33, a developing device 36 that develops the electrostatic latent image written on the photoconductor 33 with an image forming agent (toner in this example), a transfer device 37 (using, for example, a transfer roll: corresponding to the transfer means 5 in FIG. 1) that faces the photoconductor 33 across the intermediate transfer body 45 and primarily transfers the image formed on the photoconductor 33 to the intermediate transfer module 40, and a cleaning device 38 that cleans off residue on the photoconductor 33 after the primary transfer. Furthermore, a device using corona discharge (such as a corotron or scorotron) may be used as the charging device 34, an ion flow writing head may be used as the latent image writing device, or a laser exposure device may be used for each image creating engine 30 or in a shared form.

[0023] <Secondary transfer device> In this embodiment, the secondary transfer device 50 has a secondary transfer roll 51 disposed at a position of the intermediate transfer body 45 facing the tension roll 44, and conveys the recording medium S sandwiched between the secondary transfer roll 51 and the intermediate transfer body 45, while applying a predetermined secondary transfer electric field between the secondary transfer roll 51 and the opposing tension roll 44, thereby transferring the image held on the intermediate transfer body 45 to the recording medium S. Of course, instead of the secondary transfer roll 51, a secondary transfer belt in a form in which the transfer belt is stretched between a plurality of rolls may be used. <Fixing device> In addition, in this embodiment, the fixing device 60 includes a heat fixing member 61 whose surface is heated by a heat source not shown, and a pressure fixing member 62 that is pressed against the heat fixing member 61 and clamps and transports the recording medium S together with the heat fixing member 61. Here, the heat fixing member 61 and the pressure fixing member 62 may be selected from roll-shaped or belt-shaped members as appropriate, and the heat source is not limited to a heater but may be selected from other members as appropriate, such as those using an induction heating method, and the heat source may be used on the pressure fixing member 62 side.

[0024] -Imaging engine classification- In this example, the image creation engine 30 is classified into two upper image creation engines 31 (specifically, 31a and 31b: corresponding to the upper image creation means 2 in Figure 1) in which the photosensitive elements 33 are arranged opposite each other above the transfer device 37 across the horizontal movement portion 45a of the intermediate transfer body 45, and two lower image creation engines 32 (specifically, 32a and 32b: corresponding to the lower image creation means 3 in Figure 1) in which the photosensitive elements 33 are arranged opposite each other below the transfer device 37 across the inclined movement portion 45b of the intermediate transfer body 45. The transfer device 37 used in the upper imaging engine 31 and the lower imaging engine 32 will now be described.

[0025] -Transfer device for upper imaging engine- In this example, as shown in Figures 4 and 5, the transfer device 37 used in the upper image creation engine 31 extends along the width direction intersecting the movement direction of the belt-like intermediate transfer body 45, and is equipped with a transfer roll 100 (corresponding to the transfer member 6 in Figure 1) that contacts the back surface of the intermediate transfer body 45 and rotates together with the intermediate transfer body 45, and a pressing mechanism 110 that rotatably holds and presses both end shaft portions 101 of the transfer roll 100. <Transfer Roll> In this example, a primary transfer voltage of the opposite polarity to the toner is applied to the transfer roll 100, forming a primary transfer electric field between the transfer roll 100 and the photosensitive member 33, so that the toner image on the photosensitive member 33 is primarily transferred to the intermediate transfer member 45. The transfer roll 100 is made of a hollow pipe made of metal such as aluminum, SUS, or SUM.

[0026] <Pressing mechanism> In this example, the pressing mechanism 110 acts independently for each of the upper image forming engines 31 (31a, 31b), and further, holds both end shaft portions 101 of the transfer roll 100 independently. Here, the basic configuration of the pressing mechanism 110 is that when the transfer roll 100 is in use, it presses the transfer roll 100 against the photosensitive body 33 at pressing position A with a predetermined transfer load, and when the transfer device 37 is replaced, etc., it retracts the transfer roll 100 to the waiting position B. Specifically, the pressing mechanism 110 includes a transfer holding bracket 120 as a transfer holding member that is swingable about a rotating shaft 111 serving as a fulcrum and that holds the shaft portion 101 of the transfer roll 100 at a position away from the rotating shaft 111, a pressing holding arm 130 as a pressing holding member that is fixed to the rotating shaft 111 serving as a fulcrum and swings as the rotating shaft 111 rotates, a pressing spring 140 that is held elastically deformable between the transfer holding bracket 120 and the pressing holding arm 130, and a pressing motor 150 that rotates the rotating shaft 111 within a predetermined angle range and swings and rotates the pressing holding arm 130 so that the transfer roll 100 moves to a pressing position A where it is pressed against the photosensitive body 33 and to a retracted position B where it is retracted from the back surface of the intermediate transfer body 45.

[0027] The transfer holding bracket 120 has an approximately U-shaped receiving portion 121 that holds both end shaft portions 101 of the transfer roll 100 on the free rotation end side away from the rotation axis 111, and bearings 122 fixed to this receiving portion 121 rotatably hold both end shaft portions 101 of the transfer roll 100. The transfer roller 100 is provided with a holding portion 123 for holding down the bearing 122 at the receiving portion 121. Reference numeral 125 denotes an electrode for applying current to the transfer roller 100. The pressing and holding arm 130 swings in accordance with the rotational movement of the pressing motor 150 within a predetermined angle range, and moves between a first position A1 corresponding to the pressing position A of the transfer roll 100 and a second position B1 corresponding to the retracted position B of the transfer roll 100. Note that the first position A1 and the second position B1 can be adjusted by appropriately changing the rotational angle range of the pressing motor 150.

[0028] Furthermore, the pressure spring 140 is made up of a compressible coil spring, and a spring holder 131 that holds one end of the pressure spring 140 is provided on the free rotation end side of the pressure holding arm 130, and a spring holder (not shown) that holds the other end of the pressure spring 140 is provided on the transfer hold bracket 120 that faces this spring holder 131. Therefore, the pressure spring 140 is sandwiched between the pressure holding arm 130 and the transfer hold bracket 120, and when the pressure holding arm 130 rotates from the second position B1 to the first position A1 in a direction approaching the transfer hold bracket 120, the pressure spring 140 is compressively deformed, and then the elastic restoring force of the pressure spring 140 causes the transfer hold bracket 120 to move in a direction away from the pressure holding arm 130. Conversely, when the pressing holding arm 130 rotates from the first position A1 toward the second position B1 in a direction away from the transfer holding bracket 120, the pressing spring 140 is tensilely deformed, and then the elastic restoring force of the pressing spring 140 causes the transfer holding bracket 120 to move in a direction approaching the pressing holding arm 130.

[0029] Furthermore, in this example, a position detector 160 is provided which detects that the transfer roll 100 is located at the retracted position B. In this example, the position detector 160 is provided with a position detection shielding plate 161 on the free rotation end side of the pressing holding arm 130, and is configured so that when the pressing holding arm 130 is located at the second position B1 (the transfer roll 100 is located at the retracted position B), the light emitting unit 162 and the light receiving unit 163 are arranged opposite each other at positions sandwiching the shielding plate 161 provided on the pressing holding arm 130. For this reason, in this example, when the transfer roll 100 is located at the retracted position B, the position detector 160 is shielded by the shielding plate 161 of the pressing holding arm 130 which moves following the transfer roll 100, and thereby detects that the transfer roll 100 is located at the retracted position B. The pressing mechanism at the other end of the transfer roll 100 may be arranged symmetrically with the pressing mechanism 110 at one end, with a mirror surface.

[0030] -Transfer device for lower imaging engine- As shown in FIG. 6, the basic configuration of the transfer device 37 used in the lower image creation engine 32 is substantially the same as that of the transfer device 37 used in the upper image creation engine 31, and includes a transfer roll 100 and a pressing mechanism 110 (rotating shaft 111, transfer holding bracket 120, pressing holding arm 130, pressing spring 140, and pressing motor 150). Although the basic parts are the same, the layout of each part is different because the positional relationship with respect to the photosensitive element 33 is upside down.

[0031] -Differences in the configuration of the transfer device between the upper and lower imaging engines- As described above, the transfer device 37 of the upper image creation engine 31 and the transfer device 37 of the lower image creation engine 32 have essentially the same basic configuration as shown in Figures 7(a) and (b), but in order to adjust the elastic restoring force of the pressure spring 140, a configuration is adopted in which the spring constant for the upper image creation engine 31 is larger than that for the lower image creation engine 32. That is, if the spring constant of the pressure spring 140 for the upper image creation engine 31 is k1 and the spring constant of the pressure spring 140 for the lower image creation engine 32 is k2, then the pressure springs 140 should be selected so that k1>k2 is satisfied.

[0032] -Setting up the transfer device for the upper and lower imaging engines- In this embodiment, when the transfer roll 100 of the transfer device 37 in the upper image-making engine 31 and the lower image-making engine 32 is set to the pressing position A, the pressing holding arm 130 of each pressing mechanism 110 is rotated from the second position B1 to the first position A1 by the pressing motor 150, as shown in Figures 7(a) and 7(b). In this example, assuming that the amount of elastic deformation of the pressing spring 140 becomes x0 as the pressing holding arm 130 of each pressing mechanism 110 moves from the second position B1 to the first position A1, the pressing force P1 by the pressing mechanism 110 of the upper imaging engine 31 becomes k1×x0, and the pressing force P2 by the pressing mechanism 110 of the lower imaging engine 32 becomes k2×x0.

[0033] Here, since k1>k2, it is possible to obtain P1>P2. Thus, in this embodiment, as shown in Figures 8(a) and (b), in the upper imaging engine 31, the weight P0 of the transfer roll 100 acts in the opposite direction to the pressing force P1 by the pressing mechanism 110, but as shown in Figure 8(c), by increasing the pressing force P1 by the pressing mechanism 110, the target load Ps of the pressing load of the transfer roll 100 is given as P1-P0. Furthermore, in the lower imaging engine 32, the weight P0 of the transfer roll 100 acts in the same direction as the pressing force P1 by the pressing mechanism 110, so as shown in Figure 8(c), even if the pressing force P2 by the pressing mechanism 110 is smaller than the target load Ps, the target load Ps of the pressing load of the transfer roll 100 is given as P2 + P0. In this way, in the upper image forming engine 31 and the lower image forming engine 32, the pressing load of the transfer roll 100 can be adjusted taking into account the weight P0 of the transfer roll 100 itself. Furthermore, when replacing the transfer device 37, the pressing holding arm 130 of each pressing mechanism 110 is rotated from the first position A1 to the second position B1 by the pressing motor 150, and the transfer roll 100 is moved to the waiting position B.

[0034] Embodiment 2 9(a) and 9(b) are explanatory diagrams showing the main part of a transfer device of an image forming apparatus according to the second embodiment. In the same figure, the basic configuration of the transfer device 37 of the upper image creation engine 31 and the transfer device 37 of the lower image creation engine 32 is configured in approximately the same manner as in embodiment 1, but in order to adjust the elastic restoring force of the compression spring 140, instead of the method of adjusting the spring constant as in embodiment 1, for example, a compression spring 140 with the same spring constant is used, and the amount of elastic deformation of the compression spring 140 (the amount of compression in this example) is adjusted. In this example, in each pressing mechanism 110, the distance from the rotating shaft 111, which serves as the fulcrum of the pressing holding arm 130, to the holding position of the pressing spring 140 is a common L1c, and the distance from the rotating shaft 111, which serves as the fulcrum of the transfer holding bracket 120, to the holding position of the transfer roll 100 is a common L2c. If the elastic deformation amount (compression amount) δ of the pressing spring 140, which has the same spring constant, is δ1 (on the upper image creation engine 31 side) and δ2 (on the lower image creation engine 32 side), then it is sufficient to ensure that δ1>δ2 is satisfied. At this time, in the upper imaging engine 31, in order to increase the elastic deformation amount (compression amount) δ1 of the pressure spring 140, the movement angle of the pressure holding arm 130 from the second position B1 to the first position A1 can be made larger compared to the pressure spring 140 of the lower imaging engine 32. This makes it possible to satisfy the magnitude relationship between the pressing force P1 by the pressing mechanism 110 of the upper image creation engine 31 and the pressing force P2 by the pressing mechanism 110 of the lower image creation engine 32, P1>P2. In this way, in the upper image creation engine 31 and the lower image creation engine 32, by appropriately adjusting the magnitude of the pressing forces P1 and P2 taking into account the weight P0 of the transfer roll 100, it is possible to adjust the pressing load of the transfer roll 100 to be approximately equal.

[0035] Embodiment 3 10(a) and 10(b) are explanatory diagrams showing the main part of a transfer device of an image forming apparatus according to the third embodiment. In the figure, the basic configuration of the transfer device 37 of the upper imaging engine 31 and the transfer device 37 of the lower imaging engine 32 is configured in approximately the same manner as in embodiment 2, but unlike embodiment 2, for example, when the distance between the holding positions of the pressure spring 140 held by the transfer hold bracket 120 and the pressure hold arm 130 is defined as D, the value of D is made larger for the upper imaging engine 31 than for the lower imaging engine 32. In addition, in Fig. 10, the solid line position of the pressure hold arm 130 corresponds to the first position A1, and the position indicated by the two-dot chain line indicates the position where one end of the pressure spring 140 in its natural length is held. In other words, as shown in Figure 10(a), if the distance between the holding positions of the pressing springs 140 of the upper imaging engine 31 is D1 and the distance between the holding positions of the pressing springs 140 of the lower imaging engine 32 is D2, by satisfying the relationship D1>D2, when the transfer roll 100 is set to the pressing position A, it is possible to ensure a greater compression amount of the pressing spring 140 when the pressing holding arm 130 is moved to the first position A1 by using a pressing spring 140 with a larger distance D between the holding positions of the pressing springs 140 of their natural length (D=D1) than by using a pressing spring 140 with a smaller D (D=D2). Therefore, in this example as well, the magnitude relationship between the pressing force P1 by the pressing mechanism 110 of the upper image creation engine 31 and the pressing force P2 by the pressing mechanism 110 of the lower image creation engine 32 can satisfy P1>P2.

[0036] Fourth embodiment 11(a) and 11(b) are explanatory diagrams showing the main part of a transfer device of an image forming apparatus according to the fourth embodiment. In this example, the layout of the pressing mechanism 110 of the upper image forming engine 31 and the pressing mechanism 110 of the lower image forming engine 32 is changed to adjust the pressing forces P1 and P2 against the transfer roll 100. In this example, as shown in Figures 11(a) and (b), assuming that the distance from the rotation axis 111 serving as the fulcrum of the pressing holding arm 130 to the holding position of the pressing spring 140 is L1 (specifically, L11, L12), and the distance from the rotation axis 111 serving as the fulcrum of the transfer holding bracket 120 to the holding position of the transfer roll 100 is L2 (specifically, L21, L22), the pressing mechanism 110 of the upper imaging engine 31 and the lower imaging engine 32 is configured such that the value of L2 / L1 is larger for the upper imaging engine 31 than for the lower imaging engine 32. In this example, since "L11" of the upper imaging engine 31 is shorter than "L12" of the lower imaging engine 32, even if L21 ≒ L22, it is understood that the ratio of L2 / L1 is larger for the upper imaging engine 31 than for the lower imaging engine 32. In this case, the pressure forces P1 and P2 from the pressure spring 140 are obtained by multiplying the elastic restoring force associated with the compression amount of the pressure spring 140 by the ratio L2 / L1. Therefore, in this example as well, the magnitude relationship between the pressing force P1 by the pressing mechanism 110 of the upper image creation engine 31 and the pressing force P2 by the pressing mechanism 110 of the lower image creation engine 32 can satisfy P1>P2.

[0037] Embodiment 5 12(a) and 12(b) are explanatory diagrams showing the main part of a transfer device of an image forming apparatus according to the fifth embodiment. In this example, the configuration of the transfer roll 100 is changed between the upper image forming engine 31 and the lower image forming engine 32 to improve poor image quality. In the same figure, each transfer device 37 of the upper image creation engine 31 and the lower image creation engine 32 basically employs the same pressing mechanism 110, but differs from embodiments 1 to 4 in the configuration of the transfer roll 100. In this example, the transfer rolls 100 of the upper image forming engine 31 and the lower image forming engine 32 both use hollow pipes 102. However, if the wall thickness t of the hollow pipe 102 of the upper image forming engine 31 is t1 and the wall thickness t of the hollow pipe 102 of the lower image forming engine 32 is t2, the relationship t1 < t2 is satisfied. In this case, when these hollow pipes 102 are made of the same material, the hollow pipe 102 for the upper image forming engine 31 is lighter than the hollow pipe 102 for the lower image forming engine 32. Therefore, as shown in Fig. 12(a), in the upper image forming engine 31, the self-weight P0 of the transfer roll 100 is reduced, and accordingly, the amount of deflection at the longitudinal center of the transfer roll 100 due to the self-weight P0 is reduced. In addition, there is little concern that the pressing force P1 applied to the transfer roll 100 by the pressing mechanism 110 is excessively reduced by the self-weight P0 of the transfer roll 100. On the other hand, in the lower image forming engine 32, since a certain amount of the self-weight P0 of the transfer roll 100 is ensured, it effectively acts as a pressing load on the transfer roll 100 together with the pressing force P2 applied to the transfer roll 100 by the pressing mechanism 110. Therefore, compared with the case where transfer rolls of the same weight are used in the upper image forming engine 31 and the lower image forming engine 32, in the upper image forming engine 31, the amount of deflection at the longitudinal center of the transfer roll 100 is reduced, so that the distribution of the pressing load by the transfer roll 100 is likely to be uniform, and the difference in the distribution of the pressing load by the transfer roll 100 between the upper image forming engine 31 and the lower image forming engine 32 can be reduced. In addition, in the present embodiment, as shown in Embodiments 1 to 4, if the pressing forces P1 and P2 of the transfer roll 100 by the pressing mechanism 110 are adjusted, it is possible to more equally adjust the transfer load by the transfer roll 100 between the upper image forming engine 31 and the lower image forming engine 32.

[0038] ◎ Embodiment 6 Figs. 13(a) to (c) are explanatory views showing the main part of the transfer device of the image forming apparatus according to Embodiment 6. In the same figure, when assembling the pressing mechanisms 110 of the upper image creation engine 31 and the lower image creation engine 32, it goes without saying that, for example, the pressing mechanisms 110 that hold both ends of the transfer roll 100 of the upper image creation engine 31 and the pressing mechanisms 110 that hold both ends of the transfer roll 100 of the lower image creation engine 32 can be configured separately for the left and right, or separately for the top and bottom. However, in this embodiment, FIG. 13(a) shows a pressing mechanism 110 that holds and presses one end of the transfer roll 100 in the transfer device 37 of the upper imaging engine 31. Also, Figure 13(b) shows a pressing mechanism 110 that holds and presses the other end of the transfer roll 100 in the transfer device 37 of the upper image-forming engine 31, but in this embodiment, the parts that make up the pressing mechanism 110 (for example, all or part of the transfer holding bracket 120, the pressing holding arm 130, and the pressing spring 140) are used as shared parts, and the pressing mechanism 110 on one end side is arranged symmetrically in a mirror-like manner. Furthermore, Figure 13(c) shows a pressing mechanism 110 in the transfer device 37 of the lower image creation engine 32 that holds and presses one end of the transfer roll 100. In this embodiment, the components that make up the pressing mechanism 110 used in the upper image creation engine 31 (for example, all or part of the transfer holding bracket 120, pressing holding arm 130, and pressing spring 140) are used as shared components, and the pressing mechanism 110 on one end of the upper image creation engine 31 is arranged symmetrically in a mirror-like manner, upside down. In this way, in this example, when the upper imaging engine 31 and the lower imaging engine 32 are installed, the transfer device 37 is also installed. However, if many of the parts for the pressing mechanism 110 of the transfer device 37 are shared, it is possible to reduce the cost of installing the upper imaging engine 31 and the lower imaging engine 32. [Explanation of symbols]

[0039] 1...transfer medium, 2 (2a, 2b)...upper image forming means, 3 (3a, 3b)...lower image forming means, 4...image holding means, 5...transfer means, 6 (6u, 6d)...transfer member, 7 (7u, 7d)...pressing means, 8...transfer holding member, 9...pressing and holding member, 10...pressing spring, 15...recording medium, 16...transfer device

Claims

1. an upper image forming means disposed above the transfer means and facing the image holding means across a transfer medium moving in a predetermined direction; a lower image forming means, in which an image holding means is disposed below the transfer means across the transfer medium, Each transfer means of the upper image forming means and the lower image forming means has a transfer member that extends along a width direction intersecting a moving direction of the transfer medium and contacts the transfer medium, and a pressing means that presses the transfer member toward the image holding means, an image forming apparatus characterized in that the pressing means selects a pressing force against the transfer member for the upper image forming means that is greater than that for the lower image forming means, in a direction that makes the pressing load of the transfer member against the image holding means equal.

2. 2. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the pressing means has a pressing spring for pressing the transfer member, and the elastic restoring force of the pressing spring is adjusted.

3. 3. The image forming apparatus according to claim 2, 10. An image forming apparatus according to claim 9, wherein the spring constant of the pressure spring for the upper image forming means is greater than that for the lower image forming means.

4. 3. The image forming apparatus according to claim 2, 10. An image forming apparatus according to claim 9, wherein the pressure spring has a larger elastic deformation amount for the upper image forming means than for the lower image forming means.

5. 2. The image forming apparatus according to claim 1, the transfer member is held at a position away from a fulcrum by a transfer holding member that is swingable around the fulcrum, an image forming apparatus characterized in that the pressing means includes the transfer holding member, a pressing and holding member that is swingable about the fulcrum relative to the transfer holding member, and a pressing spring that is held elastically deformable between the transfer holding member and the pressing and holding member.

6. 6. The image forming apparatus according to claim 5, The distance from the fulcrum of the pressing and holding member to the holding position of the pressing spring is L1, When the distance from the fulcrum of the transfer holding member to the holding position of the transfer member is L2, An image forming apparatus characterized in that the value of L2 / L1 is larger for said upper image forming means than for said lower image forming means.

7. 6. The image forming apparatus according to claim 5, When the distance between the transfer holding member and the holding position of the pressure spring held by the pressure holding member is defined as D, the value of D is larger for the upper image forming means than for the lower image forming means.

8. 2. The image forming apparatus according to claim 1, 10. An image forming apparatus according to claim 9, wherein said pressing means acts independently on said upper image forming means and said lower image forming means.

9. 9. The image forming apparatus according to claim 8, The image forming apparatus is characterized in that the pressing means independently holds both longitudinal end portions of the transfer member.

10. 2. The image forming apparatus according to claim 1, An image forming apparatus characterized in that the pressing means can share all or part of components used in at least one of the upper image forming means and at least one of the lower image forming means.

11. 11. The image forming apparatus according to claim 10, An image forming apparatus characterized in that the pressing means makes it possible to share all or part of the components used in at least one of the upper image forming means or the lower image forming means at both longitudinal ends of the transfer member.

12. 12. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the transfer member is a transfer roll made of a hollow pipe.

13. an upper image forming means disposed above the transfer means and facing the image holding means across a transfer medium moving in a predetermined direction; a lower image forming means, in which an image holding means is disposed below the transfer means across the transfer medium, Each transfer means of the upper image forming means and the lower image forming means has a transfer member that extends along a width direction intersecting a moving direction of the transfer medium and contacts the transfer medium, and a pressing means that presses the transfer member toward the image holding means, The transfer member for the upper image forming means is made lighter than that for the lower image forming means, an image forming apparatus characterized in that the pressing means selects a pressing force against the transfer member for the upper image forming means that is greater than that for the lower image forming means, in a direction that makes the pressing load of the transfer member against the image holding means equal.

14. 14. The image forming apparatus according to claim 13, an image forming apparatus, wherein the transfer member is a transfer roll made of a hollow pipe, the wall thickness of the hollow pipe for the upper image forming means being thinner than that for the lower image forming means;

Images