JP2005173243A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can form images on both surfaces of a recording body by two sets of toner image forming means and toner image conveying belts, eliminates the need for disposing a space of a length twice the maximum width of an intermediate transfer belt and can widen the degree of freedom of a layout. <P>SOLUTION: Among the angles formed by a first image receiving surface which is a stretching surface to receive the toner image from a first image forming unit 80 among a plurality of the stretching surfaces of a first intermediate transfer belt 21 for transferring the image to be formed on the first surface of the recording element P to the recording body and a second image receiving surface which is a stretching surface to receive a toner image from a second image forming unit 81 among the plurality of the stretching surfaces of a second intermediate transfer belt 31 for transferring the image to be formed on the second surface of the recording body P to the recording body, the angle α of the angles inclusive of the conveyance path where the recording body is conveyed toward a transfer position is so specified as to satisfy 0°<α≤90°. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus capable of forming an image on one side and the other side of a recording medium.

  Conventionally, the following methods are known as image forming apparatuses capable of forming images on both sides of a recording medium (hereinafter referred to as paper). The toner image formed and carried on the photosensitive member or intermediate transfer member is first transferred onto one side of the sheet conveyed to the transfer position and fixed by a fixing device. Thereafter, the sheet is reversed and conveyed again to the transfer unit, and another image formed by the toner formed and carried on the photosensitive member or the intermediate transfer member is transferred to the other surface of the sheet, and sent to the fixing device again to be fixed. In the image forming apparatus of such a system, the paper once having passed through the fixing has a strong tendency to curl, and is likely to cause a jam during the reverse conveyance of the paper. Furthermore, once the paper passes through the fixing device, it is deformed due to heat and the water content changes, so complicated control is required, such as changing the image formation conditions for the second time and the transfer conditions to the paper. It is. Further, heat is transferred from the paper once heated to an image forming member such as a photosensitive member or an intermediate transfer member, and the life and image quality of these members are adversely affected. In addition to the image quality, there are problems such as paper tapping sound generated when the paper is reversed, noise generated by the reverse switching mechanism, and energy consumption for fixing the paper twice.

  Therefore, the present applicant has proposed the method disclosed in Patent Document 1. According to this type of image forming apparatus, the images on both sides of the paper are fixed simultaneously at the same time, so it is possible to save energy, and it is possible to eliminate problems in controlling the transfer conditions, such as member life and control problems. It was. Furthermore, by eliminating the paper reversing process, the paper transportability is improved and the occurrence of jams can be reduced. However, the double-sided image formation according to the method of Patent Document 1 includes a step of transferring the image formed and carried on the first intermediate transfer belt to the second intermediate transfer belt. The problem remained.

  In the image forming apparatuses disclosed in Patent Document 2 and Patent Document 3, productivity of image formation can be improved. That is, the image forming apparatus is capable of forming an image on both sides of the paper without the step of transferring the image formed and carried on the first intermediate transfer belt to the second intermediate transfer belt and without the paper reversing step. These image forming apparatuses are image forming apparatuses provided with two sets of image units in which a toner image forming unit including a photosensitive member and an intermediate transfer belt are combined. A full color image is formed by each of the two image units and transferred to both sides of the paper. Since each image formed on one side and the other side of the sheet can be converted into a toner image in parallel, productivity can be improved.

Japanese Patent Laid-Open No. 2002-202638 (FIG. 8) JP 2000-352889 A (FIG. 1) Japanese Patent Laid-Open No. 11-38687 (FIG. 11)

However, the image forming apparatuses disclosed in Patent Document 2 and Patent Document 3 have the following problems. When four developing units are arranged side by side on one stretching surface of the intermediate transfer belt to form a full-color toner image, the stretching surface that receives images from the four developing units (hereinafter referred to as an image receiving surface) It becomes longer than the tension surface. The straight line having the maximum length in the region surrounded by the intermediate transfer belt is substantially parallel to the image receiving surface. Since the intermediate transfer belt occupies a large area in the image forming apparatus, the arrangement of the image receiving surfaces of the two intermediate transfer belts greatly affects the shape of the entire image forming apparatus.
The image forming apparatus of Patent Document 2 has a configuration in which two intermediate transfer belts are arranged so that the image receiving surfaces are arranged in the horizontal direction. This configuration requires twice the maximum width of the intermediate transfer belt as the width dimension of the image forming apparatus, and requires a large installation space. Furthermore, when transferring from the intermediate transfer belt to the paper, the paper is conveyed in the vertical direction at the transfer position between the two intermediate transfer belts, so the paper must be bent between the paper feeding device and the paper discharge unit. Therefore, there remains a problem in the transportability of thick paper.
On the other hand, in the image forming apparatus disclosed in Patent Document 3, the sheet conveyance path is straight in the horizontal direction, and the conveyance of thick sheets is taken into consideration. However, the image receiving surfaces of the two intermediate transfer belts are arranged in the height direction, and the height dimension of the image forming apparatus requires twice the maximum width of the intermediate transfer belt, and is very tall. An image forming apparatus having poor stability is obtained.
As described above, when the intermediate transfer belt is arranged so that the two image receiving surfaces are arranged, it is necessary to provide a space having a length in which the maximum widths of the two intermediate transfer belts are arranged in the image forming apparatus. It narrows.

  The present invention has been made in view of the above problems, and an object of the present invention is to form an image to be formed on one side and the other side of a sheet with two sets of toner image forming means, a toner image conveying belt, In the image forming apparatus capable of forming images on both sides of the sheet, it is not necessary to provide a space having a length in which the maximum widths of the two intermediate transfer belts are arranged, and the degree of freedom in layout can be increased. An image forming apparatus is provided.

In order to achieve the above object, the invention of claim 1 includes at least one first toner image forming means for forming a first toner image which is a toner image of the first image formed on the first surface of the recording medium. Is stretched around two or more support members that are roller-shaped first support rollers, holds the first toner image formed by the first toner image forming means, and the first surface of the recording medium A first toner image conveying belt that conveys the first toner image to a first transfer position, and a first transfer for transferring the first toner image to the first surface of the recording medium at the first transfer position. Means, a second toner image forming means for forming a second toner image which is a toner image of a second image formed on the second surface of the recording medium, and at least one of which is a roller-shaped second support roller 2 The second toner formed on the second toner image forming unit and stretched on two or more supporting members. A second toner image conveying belt that holds the image and conveys the second toner image to a second transfer position on the second surface of the recording medium; and the second toner image is recorded at the second transfer position. Two points on the first toner image conveying belt on an imaginary plane orthogonal to the rotation axis of the first support roller in an image forming apparatus having a second transfer means for transferring to the second surface of the body 2 on the second toner image conveying belt on a virtual plane perpendicular to the rotation axis of the first support roller and a straight line including the first longest line segment that is the longest line segment among the line segments having both ends of Of the corners formed by the straight line including the second longest line segment, which is the longest line segment among the line segments having both ends as points, a conveyance path along which the recording body is conveyed toward the first transfer position The angle α of the included angle is
It is characterized by satisfying 0 ° <α ≦ 90 °.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, at least a part of the first toner image conveying belt and the second toner image conveying belt overlap each other in the vertical direction. It is.
According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the first toner image is supplied from the first toner image forming means on the stretched surface of the first toner image conveying belt. A second image receiving surface which is supplied with the second toner image from the second toner image forming unit, out of a stretched surface of the second toner image conveying belt, and the image receiving surface is substantially parallel to the first longest line segment; The second longest line segment is substantially parallel, and the first toner image forming unit and the second toner image forming unit have at least an image carrier, a cleaning unit, a charging unit, an exposure unit, and a developing unit. A toner image forming unit having a shape and drawn on a virtual surface perpendicular to the drive axis of the image carrier on the surface portion of the image carrier from the developing unit to the cleaning unit in the moving direction of the image carrier. Can be tangential A first tangent line in contact with the cleaning unit and a second tangent line in contact with the developing unit, and a line segment having both ends of the contact point where the first tangent line and the cleaning unit are in contact with the intersection point; Of the angles formed by the line segment having both ends of the contact point where the second tangent line and the developing means are in contact with the intersection, the angle α when the angle not including the image carrier is β is It is characterized by satisfying 0 ° <α <β−180 °.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the transfer position downstream in the recording agent conveyance direction of the first transfer position or the second transfer position is defined as a transfer end position. The first toner transport path, which is the transport path from the paper feeding means that feeds the recording medium to the transfer end position, is substantially horizontal, and the first toner is bordered by the first recording medium transport path. The image conveying belt and the second toner image conveying belt are arranged vertically.
According to a fifth aspect of the present invention, there is provided the image forming apparatus according to the fourth aspect, wherein the first toner image conveying belt is stretched so that the first longest line segment is in a horizontal direction, and the first toner image forming means is provided. Is arranged above the first toner image conveying belt.
According to a sixth aspect of the present invention, in the image forming apparatus of the first, second, third, fourth or fifth aspect, each of the first toner image forming means and the second toner image forming means is composed of two or more units. The two or more units are toner image forming units that handle toners of different colors.
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect of the present invention, an installation interval between the plurality of second toner image forming units that form the second toner image is set to a plurality of the plurality of second toner image forming units that form the first toner image. It is characterized by being narrower than the installation interval between the first toner image forming units.
According to an eighth aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, fifth, sixth or seventh aspect, the first transfer position and the second transfer position on the conveyance path of the recording body. A recording apparatus conveying means that includes a fixing device that fixes an unfixed image on the recording medium on the downstream side in the recording medium conveyance direction, and that conveys the recording medium while maintaining the surface of the recording medium flat. It is characterized in that it is provided in a second recording body transport path which is a transport path of the recording body from the transfer position and the second transfer position to the recording body receiving portion of the fixing device.
According to a ninth aspect of the present invention, in the image forming apparatus according to the fourth, fifth, sixth, seventh or eighth aspect of the present invention, the sheet feeding unit supplies the recording body in a substantially horizontal posture with respect to the first recording body conveyance path. Means are provided.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the conveyance path of the recording body constituted by the first recording body conveyance path and the second recording body conveyance path is substantially the same plane. It is characterized by comprising.
According to an eleventh aspect of the present invention, in the image forming apparatuses according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth and tenth aspects, the recording is performed from the first transfer position and the second transfer position. A registration aligning means for aligning the lateral side and the leading end side in the transport direction of the recording body is provided upstream of the body transport path.
According to a twelfth aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, or eleventh aspects, the first transfer position is more than the second transfer position. Also, the first transfer means is a transfer roller capable of applying a bias by contacting the first toner image transport belt.
According to a thirteenth aspect of the present invention, in the image forming apparatus according to the twelfth aspect, the second transfer unit is a transfer charger capable of applying a bias without contact with the second toner image conveying belt. It is.

  In the image forming apparatus according to any one of the first to thirteenth aspects, the angle α formed by the first longest line segment and the second longest line segment is within the range according to claim 1, and the first longest line segment is formed. Since the second longest line segment has an inclination, the width for installing the two toner image conveying belts is narrower than when the two toner image conveying belts are arranged in parallel at the maximum width.

  According to the first to thirteenth aspects of the present invention, there is no need to provide a space having a length in which the maximum widths of the two intermediate transfer belts are arranged in the image forming apparatus, and the flexibility of layout can be increased. effective.

Embodiment 1
Hereinafter, a first embodiment (hereinafter referred to as a first embodiment) in which the present invention is applied to an image forming apparatus will be described. FIG. 1 illustrates a full-color printer capable of duplex printing by an electrophotographic method as the image forming apparatus 100 according to the first embodiment.
In the image forming apparatus main body 100 shown in FIG. 1, the first image unit 20 is disposed at the upper part and the second image unit 30 is disposed at the lower part with the recording material conveyance path 43A as a boundary. The first image unit 20 includes a first intermediate transfer belt 21 that is a first toner image transport belt that moves endlessly in the direction of the arrow, and the second image unit 30 is a second toner image transport belt that moves endlessly in the direction of the arrow. An intermediate transfer belt 31 is provided. Four first image forming units 80Y, 80C, 80M, and 80K, which are first toner image forming units, are arranged on the upper tension surface of the first intermediate transfer belt 21. On the other hand, four image forming units 81Y, 81C, 81M, 81K, which are four second toner image forming units, are arranged on the upper stretched surface of the second intermediate transfer belt 31. Y, C, M, and K along the numbers of the first and second image forming units correspond to the colors of the toner to be handled. Y is yellow, C is cyan, M is magenta, and K is black. Means. Similarly, Y, C, M, and K are provided along the photosensitive member 1 provided in the first and second image forming units and rotating together with the first intermediate transfer belt 21 and the second intermediate transfer belt 31. The photoreceptors 1Y to 1K are arranged at the same interval in each image forming unit, and at least at the time of image formation, are in contact with a part of the stretched portion between the intermediate transfer belts 21 and 31, respectively. These contacting surfaces are referred to as a first image receiving surface F1 and a second image receiving surface F2, respectively, and their positional relationships are shown in FIG.

As shown in FIG. 2, a line connecting two points that is the maximum width of the first intermediate transfer belt 21 is a first longest line segment S1, and a line connecting two points that is the maximum width of the second intermediate transfer belt 31 is connected. Let the minute be the second longest line segment S2. Since the image receiving surface is the longest of the stretched surfaces of the intermediate transfer belt, the first image receiving surface F1 is substantially parallel to the first longest line segment S1, and the second image receiving surface F2 is substantially parallel to the second longest line segment S2. It is. Among the corners formed by the straight line L1 including the first longest line segment S1 and the straight line L2 including the second longest line segment S2, the transport path R along which the paper P as a recording body is transported toward the transfer position is included. Let α be the angle of the angle. The angle α is set to satisfy 0 ° <α ≦ 90 ° or less. A conventional image forming apparatus that can transfer images on both sides and has two image forming units has a first image receiving surface and a second image receiving surface arranged in parallel. That is, α = 180 °. Since the image receiving unit is provided with the image forming units, the image receiving unit needs to be long enough to be arranged, and is the longest stretched surface of the intermediate transfer unit. If the image receiving surfaces are arranged in parallel, a considerable arrangement space is required regardless of whether the image receiving surfaces are arranged horizontally or vertically.
Therefore, as shown in FIG. 2, the angle α is larger than 0 ° and not larger than 90 °, that is, by arranging the second image receiving surface obliquely with respect to the first image receiving surface, space saving can be achieved as compared with the conventional one. Can be planned.

  Further, a configuration is adopted in which at least a part of the horizontal projection surface of the first intermediate transfer belt 21 at the upper portion and the horizontal projection surface of the second intermediate transfer belt at the lower portion overlap each other. That is, the shape is such that the second intermediate transfer belt in the lower part is recessed below the first intermediate transfer belt in the upper part. By adopting such a configuration, a more compact layout is possible in the lateral direction.

Although the toner colors to be handled are different, the configurations of the first image forming units 80Y, 80C, 80M, and 80K are the same. Therefore, the configuration of the first image forming unit 80 will be described with reference to FIG.
In FIG. 3, when the image forming apparatus 100 is operated, a cylindrical photosensitive member 1 that is rotatably supported by a drive source (not shown) so as to rotate in the direction of the arrow is installed. An image forming member such as a scorotron charger 3, an exposure device 4, a developing device 5, a cleaning device 2, and a light static elimination device Q as charging means according to an electrophotographic process, a potential sensor S 1, and an image sensor S2 is arranged.
The photoreceptor 1 is obtained by forming an organic photosensitive layer (OPC), which is a photoconductive substance, on an aluminum cylinder surface having a diameter of about 30 to 120 mm. A photoconductor on which an amorphous silicon (a-Si) layer is formed can also be used. A belt-like photoreceptor can also be employed. The cleaning device 2 includes a cleaning brush 2a, a cleaning blade 2b, and a recovery member 2c, and removes and recovers foreign matters such as toner remaining on the surface of the photoreceptor.

  The exposure device 4 scans the light corresponding to the image data for each color on the surface of each photoreceptor 1 that has been uniformly charged by the charging means, and forms an electrostatic latent image. The exposure apparatus 4 in the illustrated example is an exposure apparatus that includes an LED (light emitting diode) array and an imaging element as light emitting elements, but uses a laser light source, a polygon mirror, etc., and beam light modulated according to image data to be formed. It is also possible to adopt a laser scanning type exposure apparatus. In addition to the charger 3, a type that makes contact with the surface of the photoreceptor 1, such as a charging roller, can be used as the charging means.

The development at this time is a development system that employs a two-component developer composed of toner and carrier. The electrostatic latent image for each color formed on the surface of each photoconductor 1 by the exposure device 4 with respect to the negatively charged photoconductor 1 is a toner of a predetermined color having the same polarity (negative polarity) as the charged polarity of the photoconductor. Developed to become a visible image. So-called reversal development is performed.
The yellow (Y), cyan (C), magenta (M), and black (K) toners are detected by the magnetically permeable toner detecting means 5e when consumed by the developing device that handles each color. Then, toner of each color is supplied to each developing device 5 by a supply unit (not shown) from a toner cartridge 86 provided in the toner cartridge housing portion 85 inside the image forming apparatus 100.
As this supply means, a system using a known MONO pump can be adopted. According to this method, there are few restrictions on the installation location of the toner cartridge, which is advantageous for space allocation in the image forming apparatus. Further, since the toner can be replenished in a timely manner, it is not necessary to provide a large toner storage space in the developing device, and the developing device can be downsized.

  The developing device 5 is provided with screws 5c and 5d for stirring and conveying the toner and carrier. When the developing device 5 is mounted on the image forming apparatus 100, one end of the toner replenishing unit is connected to a part of the screw 5d. The toner is supplied to the developing roller 5a rotating in the direction of the arrow by the screw 5c, but the thickness of the toner layer on the surface of the developing roller 5a is regulated to a predetermined thickness by the blade 5b. The developing roller 5a is a cylinder made of stainless steel or aluminum, and is supported by the frame of the developing device 5 so as to be rotatable and a distance from the photosensitive member is properly secured, and a predetermined line of magnetic force is formed inside. Has a magnet. As the toner, a spherical or irregular toner obtained by a conventionally known method is used. The volume average particle diameter is 20 μm or less, preferably 10 μm or less and 4 μm or more. A carrier obtained by a conventionally known method is also used. The carrier has a volume average particle size of about 25 μm to 60 μm.

Since the second image forming units 81Y, 81M, 81C, and 81K used in the second image unit 30 have the same configuration, the second image forming unit 81 will be described with reference to FIG.
The second image forming unit 81 shown in FIG. 4 has the same constituent members as the first image forming unit 80, but the rotational direction of the photosensitive member 1 is different from that of FIG. However, they are mutually shaped with respect to the y-axis passing through the rotation axis 1a of the photoreceptor 1 indicated by an arrow in the drawing. This shape is an important matter although it is related to the arrangement of image forming members provided around the photoreceptor 1. In other words, consideration is given to a method of connecting a connecting portion with the image forming apparatus 100, for example, a connecting portion with a driving unit, an electrical connecting portion, a toner supplying portion, and a toner discharging portion. Thereby, the first image forming units 80Y, 80M, 80C, and 80K can be compatible with the second image forming units 81Y, 81M, 81C, 81K. Therefore, it is not necessary to manufacture the developing device, the cleaning device, and the parts individually for the first image forming unit and the second image forming unit, and the efficiency in manufacturing parts and managing parts is high, and the overall cost can be reduced. Peeled off.

Further, here, an LED is adopted as an exposure apparatus in consideration of improvement in image forming productivity and cost reduction. A laser scanning method using beam light is well known as an exposure apparatus, but the cost can be reduced if an LED is used when forming an image at high speed. When the LED is employed, if the exposure device is installed below the photoconductor, toner powder or dust may accumulate in the exposure unit and cause a problem. Considering such a situation, the arrangement of the devices around the photosensitive member is limited to the shape shown in FIGS.
There are the following two conditions that can be used in the first image unit 20 and the second image unit 30 in the form of an axial object with the first and second image forming units as the center of the y-axis. As a first condition, a peripheral surface where no member for image formation is provided around the photosensitive member 1 is secured, that is, a wide range in which the intermediate transfer belt can contact is secured. The second condition is that the arrangement angle between the first intermediate transfer belt 21 and the second intermediate transfer belt 31 is appropriate.

The first condition and the second condition will be described with reference to FIGS. In FIG. 3 or FIG. 4, among the tangents that can be drawn around the photosensitive member 1 on the peripheral surface where no member for image formation is arranged, the tangent that contacts the developing device 5 is also in contact with the cleaning device 2. Let T2 be the tangent. The first intermediate transfer belt 21 can be installed in the direction of the arrow A1 with respect to the tangent line T1, and the second intermediate transfer belt 31 can be installed in the direction of A2. That is, the A1 side is the developing device 5, and the A2 side is that the intermediate transfer belt can be installed in a range where the belt does not contact the cleaning device 2. The inclusion of the second image bearing belt 31 in FIG. 3 shows an intermediate transfer belt on which the target image forming unit can be arranged with respect to the y axis including the rotation axis 1 a of the photoreceptor 1. Here, an intersection point between the tangent line T1 and the tangent line T2 is defined as an intersection point I, a contact point between the tangent line T1 and the developing device 5 is defined as C1, and a contact point between the tangent line C2 and the cleaning device 2 is defined as C2. Of the angles around the intersection point I formed by the line segment connecting the contact point C1 and the intersection point I and the line segment connecting the contact point C2 and the intersection point I, the angle that does not include the photoconductor 1 is β. When the angle α and the angle β satisfy 0 ° <α <β−180 °, the image forming unit is installed so that the image receiving surface F1 is in the arrow A1 direction and the image receiving surface F2 is in the arrow A2 direction. can do.
If the image forming unit 80 is turned upside down with respect to an axis orthogonal to the y axis and used as the image forming unit 81, at least the developing device 5 is affected by the earth gravity. This is because the conditions such as toner agitation and toner replenishment to the developing roller 5a are different and must be optimized, making it impossible to share parts.

  As shown in FIG. 2, the angle α is set to be greater than 0 degree and 90 degrees or less as a positional relationship between the image receiving surface of the first image carrying belt 21 and the image receiving surface of the second image carrying belt 31. When the angle is preferably 30 to 75 degrees, the image forming unit can adopt the form shown in FIG. 3 for the first image carrying belt and the form shown in FIG. 4 for the second image carrying belt. In other words, as described above, it is possible to avoid an image forming unit that makes it impossible to share parts.

Further, as shown in FIG. 2, since the recording material conveyance path R can be secured almost horizontally and linearly above the image receiving surface F2, the conveyance and reliability of the sheet are excellent, and the entire image forming apparatus is well organized. Become.
In particular, the first image carrying belt is stretched horizontally and flatly, and the second intermediate transfer belt is stretched long and inclined in the vertical direction. The space in the height direction of the intermediate transfer belt is increased. However, as shown in FIGS. 3 and 4, the image forming unit has a vertical dimension with respect to the horizontal dimension by ensuring a wide range in which the image forming unit can contact the intermediate transfer belt. Is a short configuration. For this reason, in the second image unit, the image forming unit is disposed obliquely in the vertical direction with respect to the first image unit in which the image forming unit is disposed substantially horizontally. In addition, the interval between the image forming units can be set short, and the space in the height direction of the second image unit can be saved. As a result, the degree of freedom in the layout in the height direction is increased, so that the recording medium conveyance path can be set to an ideal height considering operability, a paper feeding device, and a post-processing device (not shown). .

In addition, since the paper feeding devices having almost the same height as that occupied by the second intermediate transfer belt can be installed side by side, it is possible to install a paper feeding device capable of storing a large amount of paper. In addition, the sheet feeding surface on the upper surface of the sheet feeding device and the recording medium conveying path can be made substantially the same height, and the sheet feeding / conveying reliability can be ensured.
As described above, the image forming units 80 and 81 have many common points due to the arrangement of the image forming apparatus around the photosensitive member and the arrangement of the intermediate transfer belt, that is, the realization of the second condition. But it is very advantageous.

Next, the intermediate transfer belt will be described. The first intermediate transfer belt 21 as the first toner image conveying belt is supported by a plurality of rollers 23, 24, 25, 26 (two), 27, 28, 29 and travels in the direction of the arrow. The first image forming units 80Y to 80K are provided below the photoreceptors 1Y, 1C, 1M, and 1K. The first intermediate transfer belt 21 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. Further, a primary transfer roller 22 is provided on the inner peripheral portion of the first intermediate transfer belt 21 so as to face the respective photoreceptors 1Y, 1C, 1M, and 1K.
A cleaning device 20 </ b> A is provided on the outer periphery of the first intermediate transfer belt 21 at a position facing the roller 23. The cleaning device 20 </ b> A wipes away unnecessary toner remaining on the surface of the first intermediate transfer belt 21 and foreign matters such as paper dust.
Members related to the first intermediate transfer belt 21 are integrally configured as the first image unit 20, and can be attached to and detached from the image forming apparatus 100.

On the other hand, the second intermediate transfer belt 31 as the second toner image conveying belt is supported by a plurality of rollers 33, 34, 35, 36 (two), 37, 38 and travels in the direction of the arrow. The second image forming units 81Y to 81K are provided in contact with the photoreceptors 1Y, 1C, 1M, and 1K. The second intermediate transfer belt 31 is endless, and is stretched and arranged so that a part of each photoconductor after the developing process comes into contact. A primary transfer roller 32 is provided on the inner peripheral portion of the second intermediate transfer belt 31 so as to face the photoreceptors 1Y, 1C, 1M, and 1K.
A cleaning device 30 </ b> A is provided on the outer periphery of the second intermediate transfer belt 31 at a position facing the roller 33. The cleaning device 30 </ b> A wipes off unnecessary toner remaining on the surface of the intermediate transfer belt 31 and foreign matters such as paper dust.
Members related to the second intermediate transfer belt 31 are integrally configured as the second image unit 30 and can be attached to and detached from the image forming apparatus 100.

The intermediate transfer belts 21 and 31 are belts having, for example, a resin film or rubber having a base thickness of 50 to 600 μm as a base. The toner image carried by each photoconductor 1 has a resistance value that enables electrostatic transfer onto the belt surface by a bias applied to the primary transfer rollers 22 and 32. As an example of such a belt, carbon is dispersed in polyamide, and the volume resistance value thereof is adjusted to a resistance of about 10 ⁶ to 10 ¹² Ωcm. Belt detent ribs for stabilizing the running of the belt are provided on one side or both ends of the belt.

As the primary transfer rollers 22 and 32, the surface of a metal roller serving as a core metal is coated with a conductive rubber material, and the core metal part to which a bias is applied from a power source (not shown) is raised. Here, as for the conductive rubber material, carbon is dispersed in urethane rubber, and the resistance is adjusted to a volume resistance of about 10 ⁵ Ωcm.

  By the way, the above-described image forming apparatus is of a type in which both the first image and the second image formed on the recording medium are carried on the first and second intermediate transfer belts to perform secondary transfer. As an image forming apparatus for forming an image on both sides of a recording medium, there is a configuration as described in FIG. 1 of JP-A-2003-57905. In this method, both sides of the image are simultaneously formed by intermediate transfer and direct transfer by passing a recording medium between the intermediate transfer belt and the developing unit. Such a configuration saves space because there is only one intermediate transfer belt. However, since direct transfer from the photoconductor cannot change transfer conditions depending on the recording medium, image formation corresponding to a plurality of types of recording bodies cannot be performed. On the other hand, if both sides are configured to use intermediate transfer, the intermediate transfer belt can change the transfer conditions depending on the surface characteristics of the recording medium. Can do.

  The image forming apparatus 100 can perform monochrome recording using only black toner. In such a case, there are photosensitive members that are not used. Therefore, not only the unused photoreceptors 1Y, 1C, 1M or the developing device 5 are operated, but also a mechanism for keeping these unused photoreceptors and the image carrying belt 21 or 31 in a non-contact state is provided. An internal frame (not shown) that supports the roller 26 and the primary transfer roller 22 is provided, and is supported so as to be rotatable about a certain point. Then, by rotating in a direction away from the photosensitive member, only the photosensitive member 1K comes into contact with the image carrying belt 21 or 31, and an image forming process is executed to create a monochrome image using black toner. This is advantageous in terms of improving the life of the photoreceptor.

Further, a first secondary transfer roller 46 is provided on the outer periphery of the first intermediate transfer belt 21 in the vicinity of the support roller 28. The secondary transfer roller 46 is made of a metal roller serving as a core metal and is coated with conductive rubber, and a bias is applied to the core metal part from a power source (not shown). Carbon is dispersed in the conductive rubber, and the volume resistance is adjusted to about 10 ⁷ Ωcm. By applying a bias to the first secondary transfer roller 46 while passing the paper P between the first intermediate transfer belt 21 and the secondary transfer roller 46, an image formed by the toner carried by the first image carrying belt 21 is formed. It is transferred to the paper P.

  A transfer charger 47 serving as a second secondary transfer unit is provided on the outer periphery of the second intermediate transfer belt 31 and in the vicinity of the support roller 34. The transfer charger 47 is a known type, and a thin wire of tungsten or gold is used as a discharge electrode, held by a casing, and a transfer current is applied to the discharge electrode from a power source (not shown). By applying a transfer current while passing the paper P between the second intermediate transfer belt 31 and the transfer charger 47, an image by the toner carried by the second image carrying belt 31 is transferred to the paper P. The polarity of the transfer current applied to the transfer roller 46 and the transfer charger 47 is a positive polarity opposite to the polarity of the toner.

  On the right side of the image forming apparatus 100, a paper feeding device 40 that accommodates paper P is provided. Paper feed device (tray) 40a storing a large amount of paper in a plurality of stages, for example, the upper stage, and three stages of paper feed cassettes 40b, 40c, and 40d below each can be pulled out to the right side (operation side) with respect to the paper surface. It is arranged. Different types of paper P are stored in the paper feed tray 40a and the paper feed cassettes 40b, 40c, and 40d, respectively. Among these, the uppermost sheet is selectively fed and separated by the corresponding sheet feeding / separating means 41A to 41D, and only one sheet is reliably transferred to the recording medium conveying path 43B or 43A by the plurality of conveying roller pairs 42B. Sent.

  A pair of registration rollers 45 are provided in the recording material conveyance path 43A in order to take a feeding timing for feeding the paper P to the secondary transfer position which is the first and second transfer positions. Further, a lateral registration correction mechanism 44 for setting the position perpendicular to the sheet conveyance direction to a normal position is provided in the recording medium conveyance path 43A. The lateral registration correction mechanism 44 includes the following. The sheet P is composed of a pair of reference guides and skew rollers (not shown), and the sheet P is slid and conveyed so that the edge of the sheet in the horizontal direction is pressed against the reference guide. Then, the paper is aligned at a predetermined position. The reference guide is moved and arranged at a predetermined position depending on the size of the paper. Note that the lateral registration correction mechanism 44 may be a jogger system that includes a regulating member that presses both sides of a sheet for a short time and a plurality of times from both lateral directions of the sheet with respect to the sheet conveyance direction to align the sheet at a predetermined position. Good.

The sheet P is conveyed from the registration roller pair 45 toward a transfer area that is a first transfer position constituted by the first intermediate transfer belt 21 and the secondary transfer roller 46. Thereafter, the sheet is transported toward a transfer area which is a second transfer position constituted by the second intermediate transfer belt 31 and the transfer charger 47.
Note that the recording medium conveyance path 43C having the conveyance roller pair 42C can be supplied with a sheet from another sheet feeding device 300 that can be installed upstream in the conveyance direction. The upper sheet feed surface of the sheet feed tray 40a is arranged so that the uppermost sheet in the sheet feed tray 40a is fed and then conveyed substantially horizontally without being bent. Therefore, even thick paper and highly rigid paperboard can be reliably fed. In addition, it is convenient to adopt an air paper feed made up of a vacuum mechanism so that the paper feed tray 40a can reliably feed papers having various characteristics. Although not shown, a sensor for detecting a sheet is provided at a key point of the recording material conveyance path, and serves as a trigger for various signals based on the presence of the sheet.

A recording medium for conveying the sheet P that has passed the second transfer position on the extension of the recording medium conveyance path 43A to the fixing nip of the fixing device 60 provided downstream in the conveyance direction of the sheet P while maintaining a planar state. The transfer means 50 is provided. The recording medium transport means 50 includes rollers 52, 53, 54, 55, and 56 that support a transport belt 51 that moves endlessly in the direction of the arrow. On the outside of the conveyor belt 51, a cleaning device 50A facing the roller 55, a suction charger 57 for sucking the paper P facing the roller 56, and a static elimination / separation charger 58 facing the roller 57 are disposed. I have.
The conveyance belt 51 that moves together with the paper P while being in contact with the unfixed toner image is negatively charged by the suction charger 57 with the same polarity as the polarity of the toner. As the conveyance belt 51, a metal belt, a polyimide belt, a polyamide belt, or the like can be employed. The surface is provided with releasability from the toner and has a chargeable resistance value. The traveling speed of the belt 51 is matched with the traveling speed of the paper P in the fixing device.
By providing this conveyance belt 51, it is possible to prevent image disturbance due to a difference in speed between the speed at which the paper P passes through the fixing device 60 and the speed at which the paper P passes through the transfer position. The following can be raised as image disturbance due to the difference in speed. When the paper P is long in the transport direction, when the fixing of the leading edge of the paper starts while a part of the paper P is in the transfer position, the paper P is pulled and transferred when the fixing speed is faster than the transfer speed. The resulting image will be stretched. In addition, since the leading edge of the paper P is stopped for a short time when it is sandwiched between the fixing rollers in the fixing device 60, the transfer may overlap if the paper is strong and difficult to bend.

  A fixing device 60 having a heating unit is provided on the downstream side of the recording material transport unit 50 in the paper transport direction. A type having a heater inside the roller, a belt fixing device that runs a heated belt, a fixing device that employs induction heating as a heating method, and the like can be employed. In order to make the color and glossiness of the images on both sides of the paper the same, the material, hardness, surface properties, etc. of the fixing roller and fixing belt are made equal. Further, the fixing condition is controlled by a full-color and monochrome image, or single-sided or double-sided, or is controlled by a control unit (not shown) so as to obtain an optimal fixing condition according to the type of paper. A cooling roller pair 70 having a cooling function is provided in the conveyance path after fixing in order to cool the sheet after fixing and stabilize the unstable toner state at an early stage. As the cooling roller pair 70, a heat pipe structure roller having a heat radiating portion can be adopted. The cooled sheet is discharged and stacked by a discharge roller pair 71 on a discharge stack unit 75 provided on the left side of the image forming apparatus 100. The discharge stacking unit employs a mechanism in which a receiving member moves up and down according to a stack level by an elevator mechanism (not shown) so that a large amount of sheets can be stacked. It is also possible to pass the paper through the paper discharge stack unit 75 and transport the paper toward another post-processing apparatus. As another post-processing apparatus, an apparatus for bookbinding such as drilling, cutting, folding, and binding can be connected.

  The toner cartridges 86Y, 86C, 86M, and 86K for each color in which unused toner is stored are detachably stored in the space 85. A toner conveying means (not shown) supplies toner to each developing device as necessary. In the configuration of this embodiment, the toner cartridge is common to the image forming units arranged vertically, but can be separated. The toner cartridge 86K for black toner that is highly consumed can have a particularly large capacity. This storage space 85 is on the back side when viewed from the operation direction on the upper surface of the image forming apparatus, and a plane portion is secured on the front side of the upper surface of the image forming apparatus, so that it can be used as a work table.

The operation provided on the upper surface of the image forming apparatus 100, the display unit 90 is provided with a keyboard or the like, and conditions for image formation can be input, the state of the apparatus is displayed on the display unit, and the operator and Information exchange with the image forming apparatus 100 is facilitated. The waste toner storage portion 87 provided inside the image forming apparatus 100 is connected to the image forming unit cleaning device 2, the image carrier belt cleaning devices 20 </ b> A and 30 </ b> A, and the conveyance belt 51 cleaning device 50 </ b> A. Then, foreign substances such as waste toner and paper dust sent from these are collected and stored in a lump. Since these cleaning devices (2, 20A, 20B, 50A) are not equipped with a large-capacity waste toner storage section, the cleaning device can be reduced in size, and the waste toner disposal operability is also good. A full sensor (not shown) is used to issue a warning such as toner disposal in the waste toner storage unit 87 or container replacement.
Further, in the electrical / control device 95 provided inside the image forming apparatus 100, various power supplies, control boards, and the like are protected and housed in a sheet metal frame.
The inside of the image forming apparatus becomes hot due to heat from the fixing device 60 or heat generated from the electrical device. However, as a countermeasure against this, a fan F is provided to prevent deterioration of the function due to heat of the internal members. The fan F is coupled to the heat radiating portion of the cooling roller pair 70 to ensure the cooling effect of the cooling roller pair 70.
In FIG. 1, reference numeral 200 denotes a document reading device, and 300 denotes a paper feeding device that can be additionally installed.

Next, an operation during single-sided recording in which the image forming apparatus 100 forms a full-color image on one side of the paper P will be described.
There are basically two types of single-sided recording methods that can be selected. One of the two types is a method in which an image carried on the first intermediate transfer belt 21 is directly transferred to one side of a sheet, and the other method is an image carried on the second intermediate transfer belt 31 on a sheet. This is a method of transferring directly to one side. Here, due to the configuration of the image forming apparatus 100, when the image carried on the first intermediate transfer belt 21 is directly transferred to one side of the paper, the image is formed on the upper surface of the paper. On the other hand, when the image carried on the second intermediate transfer belt 31 is directly transferred to one side of the paper, the image is formed on the lower surface of the paper. In the case where the data to be recorded is a plurality of pages, it is convenient to control the image forming order so that the pages are aligned on the paper discharge stack unit 75. A method will be described in which an image is carried on the first intermediate transfer belt 21 and then transferred onto a sheet so that the image order is recorded in order from the image data of the last page and the page order is aligned.

When the image forming apparatus 100 is operated, the photoreceptors 1Y, 1C, 1M, and 1K in the first intermediate transfer belt 21 and the first image forming units 80Y to 80K rotate. At the same time, the second intermediate transfer belt 31 rotates, but the photoreceptors 1Y, 1C, 1M, and 1K in the second image forming units 81Y to 81K are separated from the second intermediate transfer belt 31 and are not rotated. First, image formation by the image forming unit 80Y is started. By the operation of the exposure device 4 composed of an LED (light emitting diode) array and an imaging element, light corresponding to image data for yellow emitted from the LED is irradiated onto the surface of the photoreceptor 1Y uniformly charged by the charging device 3. Thus, an electrostatic latent image is formed.
This electrostatic latent image is developed with yellow toner by the developing roller 5a, becomes a visible image, and is electrostatically transferred onto the first intermediate transfer belt 21 that moves in synchronization with the photoreceptor 1Y by the transfer action of the primary transfer roller 22. Primary transfer. Such latent image formation, development, and primary transfer operations are sequentially performed in the same manner on the photosensitive members 1C, 1M, and 1K.
Thereafter, yellow, cyan, magenta, and black toner images are carried on the first intermediate transfer belt 21 as sequentially overlapping full-color toner images and are moved in the direction of the arrow together with the first intermediate transfer belt 21. .

  At the same time, the paper P used for recording is fed out from the paper feed tray 40a or the paper feed cassettes 40b to 40d in the paper feed device 40 by one of the paper feed / separation means 41A to 41D for its supply. And it is conveyed by the conveyance roller pair 42B and 42C to the recording medium conveyance path 43C. Before the leading edge of the sheet is not picked up by the registration roller pair 45, the lateral registration correction mechanism 44 is slid and conveyed so as to press against the reference guide in the lateral direction with respect to the conveyance direction of the sheet, and the lateral alignment of the sheet is adjusted. I can take off. The sheet is temporarily stopped by the registration roller pair 45, and is conveyed again to the transfer region at a timing so that the position with the image on the first intermediate transfer belt 21 becomes normal.

  The full-color toner image on the first intermediate transfer belt 21 is transferred to the upper surface of the paper P conveyed in synchronization with the first intermediate transfer belt 21 by receiving a transfer action by the secondary transfer roller 46. The bias applied to the secondary transfer roller 46 has a positive polarity opposite to the charging polarity of the toner. After the transfer, the surface of the first intermediate transfer belt 21 is cleaned by the belt cleaning device 20A. Further, foreign matters such as toner remaining on the surfaces of the photoreceptors 1Y, 1C, 1M, and 1K in the first image forming units 80Y to 80K that have finished the primary transfer are removed by the cleaning brush 2a and the cleaning blade 2b of the cleaning device 2. Made. The surface of each photoconductor is neutralized by a residual potential by the static eliminator Q to prepare for the next image formation / transfer process. The removed foreign matter such as toner is sent to the collecting unit 87 by the collecting unit 2c. Sensors S1 and S2 detect whether the surface potential after exposure on the surface of the photoconductor and the concentration of toner attached to the surface of the photoconductor after the development process are appropriate, and appropriately set image forming conditions. Information is sent to a control means (not shown) for control.

The sheet P on which the toner image that has been superposed on the first intermediate transfer belt 21 is transferred is transported toward the fixing device 60 by the transport belt 51 of the transport device 50. In order to ensure that the paper P can be transported together with the transport belt 51, the surface of the transport belt 51 is charged in advance by a paper suction charger 57. The neutralization / separation charger 58 operates so that the paper P is separated from the transport belt 51 and is reliably sent to the fixing device 60.
The toners of the respective colors superimposed on the paper P are subjected to the fixing action by the heat of the fixing device 60, and are melted and mixed to completely form a color image. Since toner is contained only on one side (upper surface) of the paper, less heat energy is required for fixing compared to double-sided recording having toner on both sides. A control means (not shown) optimally controls the power used by the fixing device according to the image. Until the fixed toner is completely fixed on the paper, it is rubbed by a guide member or the like on the conveyance path, and an image is lost or distorted. In order to prevent this problem, the cooling roller pair 70, which is a cooling means, operates to cool the toner and the paper. Thereafter, the paper is discharged by the paper discharge roller 71 onto the paper discharge stack 75 with the image surface facing upward. In the paper discharge stack section 75, the image forming order is programmed so that the recorded matter of the young pages is stacked so as to be sequentially stacked on top, so the page order is aligned. Since the paper discharge stack unit 75 is lowered as the number of discharged paper sheets increases, the paper sheets can be stacked in an orderly and reliable manner, and the page order is not disturbed. Instead of directly stacking the recorded paper on the paper discharge stack section 75, a punching process can be performed, or the paper can be conveyed to a post-processing device such as a sorter, a collator, a binding device, or a folding device.

  In another method of forming an image on one side of the paper P, image formation is not performed in the first image forming units 80Y to 80K, and image formation is performed in order from image data of young pages for page alignment. Different points. However, since it is basically the same as the single-sided recording process described above, details are omitted.

Next, the operation at the time of duplex recording in which images are formed on both sides of the paper P will be described. When a start signal is input to the image forming apparatus, an image for each color that is sequentially formed by the first image forming units 80Y, 80C, 80M, and 80K described in the single-sided recording operation is sequentially applied to the first intermediate transfer belt 21. Next transfer. Substantially in parallel with the step of supporting the first image, the images for the respective colors sequentially formed by the second image forming units 81Y, 81C, 81M, 81K are sequentially primary-transferred to the second intermediate transfer belt 31, and the second The process of carrying as an image is performed. As shown in FIG. 1, the interval between the second image forming units in the belt conveyance direction is set closer than the interval between the first image forming units. Thus, in order for the first image and the second image to coincide with each other at the front end in the sheet conveyance direction, the formation of the second image is started after the start of the formation of the first image. Since the sheet is stopped and retransmitted by the registration roller pair 45, the sheet is fed in consideration of the time and aligned by the lateral registration correction mechanism 44. The registration roller pair 45 transports the sheet to a first transfer station, which is a first transfer position constituted by the transfer roller 46 as the first secondary transfer means and the first intermediate transfer belt 21 at a timing. A positive transfer current is applied to the transfer roller 46, and the image is transferred from the first intermediate transfer belt to one side (upper surface in the figure) of the paper P.
Thus, the sheet P having an image on one side is continuously sent to the second transfer station which is the second transfer position where the transfer charger 47 as the second secondary transfer means is provided by the transfer operation of the transfer roller 46. Then, by applying a positive polarity transfer current to the charger, the full-color second image previously carried on the second intermediate transfer belt 31 is transferred to the lower surface of the paper P at a time.

The paper P on which the full color toner images are transferred on both sides in this way is transported to the fixing device 60 by the transport belt 51. The surface of the transport belt 51 is charged with the same negative polarity as the polarity of the toner by the suction charger. The unfixed toner on the lower surface of the paper is prevented from transferring to the belt. An alternating current is applied to the charge removal / separation charger 58, and the sheet is separated from the belt 51 and transferred to the fixing device 60. The toner image on both sides of the sheet is melted and mixed by the fixing process by heat of the fixing device 60. The sheet subsequently passes through the cooling roller pair and is discharged onto the discharge stack unit 75 by the discharge roller 71.
When double-sided recording is performed on a plurality of pages of paper, the image forming order is controlled so that the image of the young page becomes the bottom surface and is stacked on the paper discharge stack unit 75. As a result, when the paper is taken out from the paper discharge stack 75 and the top and bottom surfaces are reversed, the recorded matter is one page in order from the top, the second page on the back, the third page on the second sheet, and the fourth page on the back. Such control of image forming sequence and control such as increasing the power input to the fixing device compared to the one-side recording are executed by a control means (not shown).

  As for the single-sided recording and the double-sided recording operation, the example in which full-color recording is executed has been described, but monochrome recording using only black toner is also possible. When the need for maintenance or parts replacement arises, an exterior cover (not shown) is opened to perform maintenance. At this time, it is convenient to unitize the members constituting the image forming units 80 and 81 shown in FIGS. 3 and 4 and replace them as process cartridges. The form of the process cartridge is such that the image forming members excluding the intermediate transfer belts 21, 31 and the primary transfer roller 22, the exposure device 4 and the like from the configuration shown in FIGS. To fit inside. Further, this can be realized by appropriately providing a guide part and a handle for attaching and detaching the image forming apparatus 100.

As described above, according to the first embodiment, among the tension surfaces of the first intermediate transfer belt 21 and the second intermediate transfer belt 31, the first light receiving surface F1 and the second light receiving surface F2 that are the longest in the transport direction. Are arranged so as to be inclined rather than in parallel, it is not necessary to provide a space having a length in which the maximum widths of the two intermediate transfer belts are arranged, and the flexibility of layout can be increased.
Further, since the second image unit 30 is arranged below the first image unit 20 arranged substantially horizontally, space saving in the lateral direction can be achieved.
In addition, by setting the angle α formed by the first image receiving surface F1 and the second image receiving surface F2 within the range of the transferable area of the photosensitive member of an image forming unit of one form, the first image forming unit 80Y. , M, C, and K and the second image forming units 81Y, 81M, 81C, and 81K can be shared, and even when a plurality of developing units are used, they can be installed to save space. .
In addition, the first image unit 20 is installed on the upper side, the second image unit 30 is installed on the lower side, and the conveyance path 43 </ b> A that is the movement path of the sheet P is made substantially horizontal so that the sheet P is conveyed therebetween. Thus, the number of paper jams in the transport path can be reduced.
Further, by installing the first image unit above the conveyance path 43A in the horizontal direction, the dimension in the height direction at a position higher than the conveyance path can be suppressed.
In addition, since the installation interval of the second image forming units can be set narrow, the degree of freedom in the layout in the height direction is increased, and the recording material transport path can be set to a height that facilitates paper jam processing and the like. Can be improved.
In addition, by providing the recording material transport belt 51 that receives the transfer of the toner image and transports the paper P carrying the unfixed toner image, the image of the unfixed toner image on the paper surface can be prevented from being disturbed. it can.
Further, since the paper P can be supplied from the paper supply / supply surface that is substantially the same height as the recording material conveyance path 43A, the rigid paper P can also be supplied in the conveyance path. Further, by setting the conveyance path to be followed in the process of feeding the paper P, transferring the image, fixing, and discharging the sheet to be substantially the same plane, it becomes a straight conveyance path, and it is not necessary to bend the paper P. Therefore, image formation is possible even if the rigidity of the paper P is strong, and a wide range of types and characteristics of the paper P can be dealt with.
In addition, since the registration roller pair is provided on the upstream side in the transport direction from the transfer position, a good image without positional deviation can be obtained.
In addition, by setting the transfer position of the first image upstream of the transfer position of the second image, the transfer position can be shifted and the transfer conditions can be changed, so that the surface characteristics of the first surface and the second surface are different. Even if the paper P is used, good images can be obtained on both sides.

[Embodiment 2]
Next, instead of the configuration in which the first image forming unit 80 and the second image forming unit 81 are each four image forming units, a second embodiment (hereinafter referred to as “two image forming units”) is adopted. Embodiment 2) will be described. FIG. 5 shows a full-color printer capable of duplex printing by the electrophotographic method as the image forming apparatus 110 according to the second embodiment. The second embodiment is different from the first embodiment only in that two image forming units are used in place of the four image forming units in the first embodiment, and the description of other configurations is omitted.

  FIG. 6 is a schematic configuration diagram of the first image forming unit 180 used in the second embodiment. The difference from the first image forming unit 80 of the first embodiment is that the first image forming unit 80 has one developing device 5, whereas the first image forming unit 180 has two developing devices 105. Has been. That is, the configuration is such that a two-color toner image is formed with one photoconductor, and full-color printing is possible with two image forming units. Such a configuration in which two toner images are formed by one photoconductor is known in Japanese Patent Application Laid-Open No. 2003-167410.

Here, the operation of the first image unit 120 to which the first image forming unit 180 is applied will be described. Since operations other than the second image unit and the transfer process are the same as those in the first embodiment, a description thereof will be omitted.
First, an electrostatic latent image corresponding to yellow is formed on the photoreceptor 101YC of the first image forming unit 180YC, and developed on the surface facing the developing device 105Y. Then, the image is transferred to the first intermediate transfer belt 121. Thereafter, the yellow toner image carried on the first intermediate transfer belt 121 moves to the transfer position of the first image forming unit 180MK, and the magenta toner image developed by the developing device 105M is transferred in an overlapping manner.
The toner image obtained by superimposing the yellow toner image and the magenta toner image moves in the transport direction as it is, passes through the first transfer position, and moves to the transfer position of the first image forming unit 180YC. During this time, the first image forming unit 180YC removes the yellow toner remaining on the photoreceptor 101YC, and this time, the developing device 105C forms a cyan toner image. Then, the cyan toner image is superimposed and transferred onto the toner image in which yellow and magenta are superimposed. Thereafter, the black toner image is also transferred and superimposed by the first image forming unit 180MK, and a full-color toner image in which four colors are superimposed on the first surface of the paper P is transferred at the first transfer position. A similar operation is performed in the second image unit 130, and double-sided color printing is performed.

  As described above, by disposing two developing devices around one photoconductor, the number of photoconductors which are large members in the image forming unit can be halved. As a result, the length in the transport direction of each of the first and second image receiving surfaces can be shortened, the freedom of layout can be expanded both in the height direction and in the lateral direction, and space saving can be achieved. .

  In the first and second embodiments, an image forming unit using a photoconductor as a toner image forming unit is described. However, the present invention is not limited to this. The invention of claim 1 of the present application can be applied as long as it has two mechanisms for forming a toner image and carrying the toner image on a toner image conveying belt and forming an image on both sides of the recording medium. As the toner image forming means, for example, the present invention can be applied to a toner direct injection type powder image forming apparatus.

1 is a schematic configuration diagram of a copier according to a first embodiment. Explanatory drawing of angle (alpha) which two image receiving surfaces form. FIG. 3 is a diagram in which the developing unit used in Embodiment 1 is used as a first image unit. FIG. 3 is a diagram in which the developing unit used in Embodiment 1 is used as a second image unit. FIG. 3 is a schematic configuration diagram of a copier according to a second embodiment. FIG. 6 is a schematic configuration diagram of a developing unit used in Embodiment 2.

Explanation of symbols

1 Photoconductor (Y, C, M, K after the number in the color of the toner to be handled)
2 Cleaning device
2a cleaning blade 2b cleaning brush 2c waste toner collecting means 3 charging charger 4 exposure device 5 developing device 5a developing roller 5b regulating blade 5c, 5d stirring means 5e toner sensor 20 first image unit 20a first intermediate transfer belt cleaning device 21 first 1 Intermediate transfer belt 22 Primary transfer roller
DESCRIPTION OF SYMBOLS 23 Belt support roller 24 Drive roller 26 Image-receiving surface maintenance roller 27 Tension roller 28 Transfer opposing roller 29 Bending roller 30 Second image carrier unit 30a Cleaning device for second image carrier belt 31 Second image carrier belt 32 Second image carrier Unit primary transfer roller 33 Cleaning backing roller 34 Drive / transfer facing roller 36 Image-receiving surface maintaining roller 37 Tension roller 40 Paper feed device 40a Upper paper feed device 40b, c, d Paper feed cassette 41A, B, C, D Feeding / separating means 42A, B, C pair of conveying rollers 43A, B, C recording medium conveying path 44 lateral registration correction mechanism 45 registration roller pair 46 secondary transfer roller 47 transfer charger 50 recording medium transporting means 50a cleaning for conveying belt Device 51 Conveying belt 52 Receiving roller 54 Releasing charger opposite roller 55 cleaning the backing roller 57 attracting charger 58 neutralization, separation charger 60 fixing device 70 cooling rollers 71 discharge roller pair
75 Paper discharge stack 80 First image forming unit (attached Y, C, M, K indicating the color to be handled behind)
81 Second image forming unit (attached Y, C, M, K indicating the color to be handled behind)
84 Toner cartridge housing 85 Toner cartridge (Y, C, M, K indicating the color to be handled behind)
87 Waste toner recovery unit 90 Operation / display unit (unit)
DESCRIPTION OF SYMBOLS 95 Electrical equipment / control apparatus 96 Fan 100 Image forming apparatus 200 Image reading apparatus 300 Paper feeder which can be additionally installed A1, A2 An arrow indicating a direction in which the intermediate transfer belt can be installed
Y Yellow C Cyan M Magenta K Black Q Static neutralizer

Claims (13)

First toner image forming means for forming a first toner image, which is a toner image of the first image formed on the first surface of the recording medium;
At least one is stretched over two or more support members which are first support rollers in the shape of a roller, holds the first toner image formed by the first toner image forming means, and A first toner image conveying belt that conveys the first toner image onto the surface to a first transfer position;
First transfer means for transferring the first toner image to the first surface of the recording medium at the first transfer position;
Second toner image forming means for forming a second toner image, which is a toner image of the second image formed on the second surface of the recording medium;
At least one is stretched around two or more support members which are second support rollers in the shape of a roller, holds the second toner image formed by the second toner image forming means, and A second toner image conveying belt that conveys the second toner image to the surface to a second transfer position;
An image forming apparatus including: a second transfer unit configured to transfer the second toner image to the second surface of the recording body at the second transfer position;
A straight line including a first longest line segment which is the longest line segment among two line segments having two ends on the first toner image conveying belt on a virtual plane orthogonal to the rotation axis of the first support roller; ,
Among the corners formed on the virtual plane by the straight line including the second longest line segment that is the longest line segment among the line segments having two ends on the second toner image conveying belt as both ends, the recording medium Is an angle α including a conveyance path along which the image is conveyed toward the first transfer position,
0 ° <α ≦ 90 °
An image forming apparatus characterized by satisfying the above. The image forming apparatus according to claim 1.
An image forming apparatus, wherein at least a part of the first toner image transport belt and the second toner image transport belt overlap each other in the vertical direction. The image forming apparatus according to claim 1.
The first image receiving surface that receives the supply of the first toner image from the first toner image forming unit and the first longest line segment of the stretched surface of the first toner image conveying belt are substantially parallel,
The second image receiving surface that receives the supply of the second toner image from the second toner image forming unit and the second longest line segment of the stretched surface of the second toner image conveying belt are substantially parallel to each other,
The first toner image forming unit and the second toner image forming unit are toner image forming units having the same shape and having at least an image carrier, a cleaning unit, a charging unit, an exposing unit, and a developing unit,
On a virtual plane perpendicular to the drive axis of the image carrier,
Of the tangent lines that can be drawn on the surface portion of the image carrier from the developing means to the cleaning means in the moving direction of the image carrier surface, the first tangential line that contacts the cleaning means and the first tangential line that contacts the developing means. At the intersection of two tangents,
The contact point between the first tangent line and the cleaning unit and a line segment having the intersection point as both ends, the contact point between the second tangent line and the developing unit and the line segment having the intersection point as both ends are formed. When the angle of the angle that does not include the image carrier is β, the angle α is 0 ° <α <β−180 °.
An image forming apparatus characterized by satisfying the above. The image forming apparatus according to claim 1, 2 or 3.
Of the first transfer position or the second transfer position, the transfer position on the downstream side in the recording material conveyance direction is set as the transfer end position,
The first recording medium conveyance path, which is the conveyance path from the paper feeding means for feeding the recording medium to the transfer end position, is made substantially horizontal,
An image forming apparatus, wherein the first toner image conveying belt and the second toner image conveying belt are arranged vertically with the first recording material conveying path as a boundary. The image forming apparatus according to claim 4.
The first toner image conveying belt is stretched so that the first longest line segment is in a horizontal direction, and the first toner image forming means is disposed above the first toner image conveying belt. Image forming apparatus. The image forming apparatus according to claim 1, 2, 3, 4, or 5.
The first toner image forming unit and the second toner image forming unit are each composed of two or more units, and each of the two or more units is a toner image forming unit that handles toner of different colors. An image forming apparatus. The image forming apparatus according to claim 6.
An installation interval between the plurality of second toner image forming units that form the second toner image is as follows.
An image forming apparatus characterized in that it is narrower than the interval between the plurality of first toner image forming units that form the first toner image. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6 or 7.
A fixing device for fixing an unfixed image on the recording medium downstream of the first transfer position and the second transfer position in the recording medium conveyance direction on the recording medium conveyance path;
A recording medium conveying means for conveying the recording medium while maintaining the surface of the recording medium in a planar shape is provided on the recording medium from the first transfer position and the second transfer position to the recording medium receiving portion of the fixing device. An image forming apparatus provided in a second recording material conveyance path which is a conveyance path. The image forming apparatus according to claim 4, 5, 6, 7 or 8.
An image forming apparatus comprising: the paper feeding unit that feeds the recording body in a substantially horizontal posture with respect to the first recording body conveyance path. The image forming apparatus according to claim 9.
An image forming apparatus, wherein the recording medium conveyance path constituted by the first recording medium conveyance path and the second recording medium conveyance path is configured to be substantially in the same plane. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10.
Image formation comprising registration aligning means for aligning the lateral side and the leading end side in the conveyance direction of the recording medium upstream of the recording medium conveyance path from the first transfer position and the second transfer position. apparatus. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11.
The first transfer position is located upstream of the second transfer position in the recording material conveyance direction, and the first transfer unit is in contact with the first toner image conveyance belt and is capable of applying a bias. An image forming apparatus. The image forming apparatus according to claim 12.
The image forming apparatus, wherein the second transfer unit is a transfer charger capable of applying a bias without contact with the second toner image conveying belt.

Images