JP2002341675A - Image forming device and belt unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device constituted so that the cost of components of a both-side transfer device can be reduced in accordance with a user's demand. SOLUTION: The both-side transfer device is constituted so that intermediate transfer belts having different circumferential length may be interchanged between belt units 20a and 20b equipped with respective intermediate transfer belts. The belt units 20a and 20b are provided with several rollers for endlessly moving the intermediate transfer belts (not illustrated in figure) in a stretched state. The circumferential length of the intermediate transfer belt for the belt unit 20a is made to differ from that for the belt unit 20b. By having such the constitution, the user can select the intermediate transfer belt corresponding to the size of user's demand. Thus, the cost of the components of the both-side transfer means is reduced in accordance with the user's demand.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and the like.
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having double-sided transfer conveyance means for conveying a recording medium while transferring a visible image to both sides of a recording medium such as transfer paper.

[0002]

2. Description of the Related Art Conventionally, there has been known an image forming apparatus for forming a visible image on both sides of a recording medium such as a transfer sheet by using a so-called switchback system. This switchback method
A method in which a recording medium is passed through a transfer means and a fixing device to fix a visible image such as a toner image on only one surface thereof, and then the recording medium is reversed and returned to the transfer means and the fixing device again. .

However, this image forming apparatus has a disadvantage that a complicated switchback mechanism for reversing the recording medium once passed through the fixing device and returning it to the transfer means is required, resulting in an increase in cost. . In addition, the switchback of the recording medium makes it difficult to increase the speed of double-sided transfer, or causes heat to cause curl of the recording medium during the first fixing, thereby easily causing a jam at the time of switchback. There was also a problem.

In view of this, as a transfer means, a double-sided transfer means for conveying a recording medium while transferring a visible image to both sides of the recording medium is provided, and the recording medium is passed through the recording medium and then sent to a fixing device. An apparatus has been proposed in Japanese Patent Application Laid-Open No. Hei 1-209470. This image forming apparatus carries out double-sided transfer on a recording material by the following process. That is, first, a first visible image is formed on an image carrier such as a photosensitive drum, and the first visible image is statically transferred onto an intermediate transfer belt that moves endlessly while contacting the image carrier at a transfer position. Intermediate transfer is performed electrically. In parallel with this intermediate transfer, the second
The formation of a visible image is started, and the recording medium is sent to the above-described transfer position at an appropriate timing, and is sandwiched between the image carrier and the intermediate transfer belt. Then, while sandwiching the first visible image on the intermediate transfer belt, the recording body, and the second visible image on the image carrier in a sandwich at the transfer position, the second visible image is placed on the image carrier. Is transferred directly onto the recording medium. After the direct transfer, the recording medium is moved by two times with the endless movement of the intermediate transfer belt.
The sheet is conveyed to a secondary transfer position by the next transfer charger, where the first visible image on the intermediate transfer belt is
The next transfer is performed to complete the double-sided transfer.

The image forming apparatus has substantially the same configuration as that of the image forming apparatus disclosed in JP-A-1-209470, but an image forming apparatus having a reverse charging charger in place of the secondary transfer charger is also known. In this image forming apparatus, the first visible image before being re-sent to the transfer position is reversely charged. The second visible image and the oppositely charged first visible image are simultaneously transferred at the transfer position by moving them in opposite directions toward the recording medium.

According to these image forming apparatuses, double-sided transfer can be performed by the double-sided transfer unit without switching back the recording medium from the fixing device to the transfer unit.
Therefore, it is possible to eliminate a cost increase due to the provision of the switchback mechanism and a jam at the time of switchback.
In addition, it is possible to solve a situation in which the high speed of the double-sided transfer is prevented by the switchback.

[0007]

However, none of these image forming apparatuses can form an image having a size exceeding the circumference of the intermediate transfer belt on both sides of the recording medium. With such a size, the entire intermediate transfer cannot be completed before the front end of the first visible image is intermediate-transferred onto the intermediate transfer belt and re-sent to the transfer position. For this reason, it becomes impossible to synchronize the leading end of the first visible image and the leading end of the second visible image at the transfer position. Therefore, in order to enable image formation on recording media of a plurality of sizes, the peripheral length of the intermediate transfer belt must be set in accordance with the recording media of the maximum size. For example, in an image forming apparatus in which the maximum corresponding size of a recording medium is A3 size, it is necessary to set the peripheral length of the intermediate transfer belt to be equal to or longer than the vertical size of A3 size (about 420 mm).

However, in such a setting, for example, a user who uses only a recording medium of at most B4 size at a maximum is forced to use a larger intermediate transfer belt having a circumference equal to or longer than the vertical dimension of A3 size. As a result, there is a problem that extra component costs are forced.

This problem occurs in an image forming apparatus provided with an intermediate transfer belt as an intermediate transfer member of the double-side transfer means. However, the same problem may occur in an image forming apparatus including an intermediate transfer roller or the like that moves on an endless track or a device that conveys a recording medium while reciprocating near the transfer position.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of reducing the cost of parts of a double-sided transfer means according to a user's request, and an image forming apparatus having the same. It is to provide a belt unit to be used.

[0011]

In order to achieve the above object, the invention according to claim 1 comprises an image carrier for carrying a visible image,
A visible image forming means for forming a visible image on the image carrier; and transferring the first visible image intermediately transferred from the image carrier onto an intermediate transfer member onto one surface of a recording medium. A double-sided transfer means for transferring the second visible image from the image carrier to the other surface of the recording medium and holding and transporting the recording medium on the moving intermediate transfer body; The double-sided transfer means is configured so that the intermediate transfer members having different sizes can be exchanged. According to a second aspect of the present invention, in the image forming apparatus of the first aspect, a control unit for controlling the visible image forming unit and the double-sided transfer unit, and the control unit for acquiring size information of the intermediate transfer body Characterized in that information acquisition means for transmitting the information to the user is provided. According to a third aspect of the present invention, in the image forming apparatus of the second aspect, an identification unit for identifying a size of the intermediate transfer body mounted on the double-sided transfer unit is provided as the information acquisition unit. It is a feature. Claim 4
According to the invention, in the image forming apparatus according to any one of claims 1, 2 and 3, an intermediate transfer belt is used as the intermediate transfer member, the endless movement of the intermediate transfer belt for holding and transporting the recording material on its surface. Things. The invention of claim 5 is
5. The image forming apparatus according to claim 4, wherein the double-sided transfer unit is configured so that a belt unit including at least the intermediate transfer belt and a plurality of tension members that stretch the intermediate transfer belt is replaceable. Is what you do. Also,
According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect,
The double-sided transfer means is configured such that belts having different belt circumferential lengths and the same belt width can be exchanged as the intermediate transfer belts having different sizes. According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, a delivery unit for delivering a recording medium to the belt unit and a receiving unit for receiving a recording body from the belt unit are provided. A layout within the housing so that the space occupied by the belt unit located between the belt and the receiver in the housing of the image forming apparatus main body is the same regardless of the length of the intermediate transfer belt in the belt unit. Is set. According to an eighth aspect of the present invention, in the image forming apparatus of the seventh aspect, the positions of the members outside the belt unit are fixed regardless of the circumference of the intermediate transfer belt while maintaining these functions. In order to make it possible, a layout within the housing of the image forming apparatus main body is set. According to a ninth aspect of the present invention, there is provided the image forming apparatus according to the eighth aspect, wherein an auxiliary member for assisting a function of an external member provided outside the belt unit, or an assisted member for which the function is assisted by the external member. A member is provided in the belt unit, and the position of the auxiliary member or the assisted member in the image forming apparatus main body is the same among the plurality of belt units having different belt circumferential lengths. .
According to a tenth aspect of the present invention, there is provided the image forming apparatus according to the seventh, eighth or ninth aspect, wherein the belt unit is separated from the main body of the image forming apparatus to expose the recording medium transport path in the double-sided transfer unit. In addition, the above-mentioned double-sided transfer means is constituted. According to an eleventh aspect of the present invention, in the image forming apparatus of the tenth aspect, an openable and closable unit is provided in a housing of the image forming apparatus main body, and the belt unit is held by the openable and closable unit. The belt unit is moved toward and away from the image forming apparatus main body in accordance with opening and closing of the image forming apparatus. Also,
According to a twelfth aspect of the present invention, in the image forming apparatus of the eleventh aspect, an opening / closing door that swings about a rotation axis is used as the opening / closing section. Claim 1
According to a third aspect of the present invention, in the image forming apparatus according to the eleventh aspect, a belt cleaning unit for cleaning the image forming substance attached to the intermediate transfer belt is provided in the double-sided transfer unit.
As the opening / closing section, an opening / closing section which is opened and closed with respect to the image forming apparatus main body by moving in a horizontal direction is used. The invention of claim 14 is based on claim 7,
The image forming apparatus of any one of 8, 9, 10, 11, 12 and 13 is characterized in that an opening for projecting a part of the belt unit from the housing of the main body of the image forming apparatus is provided in the housing. Further, the invention of claim 15 is the invention of claim 5, 6, 7, 8, 9, 10, 11, 12, 13, or 14.
In the image forming apparatus of (1), if necessary, only a direct transfer of a visible image from the image carrier to the recording medium without the intermediate transfer belt is performed, and an image is formed only on one surface of the recording medium. It is characterized by doing. The invention according to claim 16 is based on claims 5, 6, 7, 8, 9, 10, 1
The image forming apparatus according to any one of 1, 12, 13, 14 and 15, further comprising a supply unit configured to supply the recording medium contained therein to the belt unit and to be detachably attached to a housing of the image forming apparatus main body. And the replacement of the belt unit can be performed from the same side of the housing. The invention of claim 17 is based on claims 5, 6, 7, 8, 9, 10, 11, 1
In the image forming apparatus of 2, 13, 14, 15, or 16, the belt unit having the intermediate transfer belt having a belt width smaller than the vertical size of the B4 size and a belt peripheral length equal to or larger than the vertical size of the A3 size is used. It is characterized by the following. The invention of claim 18 is based on claim 5,
6, 7, 8, 9, 10, 11, 12, 13, 14, 1
In the image forming apparatus according to any one of 5, 16 and 17, when two or more recording materials are continuously formed on both sides with an image having a half or less of the intermediate transfer belt circumferential length, the above-described image forming apparatus is used for at least two images. The method is characterized in that the first visible image is continuously formed on the image carrier, and then the second visible image is continuously formed. The invention of claim 19 is based on claim 5,
6, 7, 8, 9, 10, 11, 12, 13, 14, 1
In the image forming apparatus of any one of 5, 16, 17 or 18, when one side of an image having a half or less of the intermediate transfer belt circumferential length is continuously formed on two or more recording materials, at least every two images are formed. Wherein the first visible image is continuously formed on the image carrier. Claim 2
0 is an image forming apparatus according to claim 18 or 19, wherein one of the plurality of belt units is a belt width corresponding to a long side dimension of a fixed size recording medium as the intermediate transfer belt. And the interval required for continuously transporting the recording body toward the recording medium transport path of the double-sided transfer means is G, an integer of 2 or more is n, and the short side dimension of the recording body is When represented by Ly, each has a condition that satisfies the condition of “belt circumference> n × Ly + (n−1) × G”. According to a twenty-first aspect of the present invention, there is provided the image forming apparatus according to the twentieth aspect, further comprising an atypical recording body supply unit configured to supply the atypical recording body toward the recording medium transport path. It is. The invention according to claim 22 is the image forming apparatus according to claim 21, wherein another one of the belt units has a belt width corresponding to the long side dimension as the intermediate transfer belt, and When an integer of 1 or more is represented by m,
“Belt circumference> (n + m) × Ly + (n + m−1) ×
G ". The invention according to claim 23 is the invention according to claim 22.
In the image forming apparatus, the non-standard recording medium supply means uses a non-standard recording medium wound in a roll shape, and the non-standard recording medium is supplied in accordance with a length of an image to be intermediately transferred to the intermediate transfer belt. It has a cutting means for cutting the recording medium. The invention according to claim 24 is based on claims 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15. The image forming apparatus according to 15, 16, 17, 18, 19, 20, 21, 22, or 23, comprising a plurality of the image carriers, and transferring the visible image formed on each of the image carriers to the intermediate transfer belt. And intermediate transfer to form a superimposed image. According to a twenty-fifth aspect of the present invention, in the image forming apparatus of the twenty-fourth aspect, a plurality of the image carriers are arranged in line with each other. According to a twenty-sixth aspect of the present invention, in the image forming apparatus of the twenty-fifth aspect, each image is formed such that the visible images on the plurality of image carriers are superimposed and transferred while the recording medium is conveyed in the vertical direction. The carrier is arranged in a vertical direction. The invention of claim 27 is based on claims 1, 2, 3, 4, 5,
6, 7, 8, 9, 10, 11, 12, 13, 14, 1
5, 16, 17, 18, 19, 20, 21, 22, 2,
A receiving unit for receiving a control signal from a computer, and controlling the image carrier, the visible image forming unit, and the double-sided transferring unit based on a reception result of the receiving unit in the image forming apparatus of any one of 3, 24, 25, and 26; And control means for performing the control. The invention according to claim 28 is a belt unit including an intermediate transfer belt that intermediately transfers a visible image in a series of image forming processes, and a plurality of stretching members that stretch the intermediate transfer belt, Claims 5, 6, 7,
8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23, 24, 2
It is characterized by being used in the image forming apparatus of No. 5 or 26. The invention according to claim 29 is based on claim 28
A belt unit for use in the image forming apparatus according to claim 14, wherein the case unit covers at least a portion of the image forming apparatus that protrudes from the opening, and this is used as a part of a housing of the main body of the image forming apparatus. It is characterized by functioning. Also, the invention of claim 30 is based on claim 29.
In the above belt unit, the size information of the intermediate transfer belt inside the case member is added to the case member. In these inventions, by allowing the user to select an intermediate transfer member having a size that meets the requirement, it is possible to reduce the component cost of the double-sided transfer means according to the requirement of the user.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an electrophotographic printer (hereinafter, simply referred to as a printer) will be described as one embodiment of an image forming apparatus to which the present invention is applied. First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram of the present printer. In the figure, a printer 100 includes a process unit 6 in which a photosensitive drum 1 serving as an image carrier is incorporated at substantially the center in the vertical direction in the apparatus. The process unit 6 integrally incorporates the drum cleaning device 2, the static elimination device 3, the charging device 4, the developing device 5 and the like in addition to the photosensitive drum 1, and is to be replaced when the service life expires.

The charging device 4 includes a photosensitive drum 1 which is rotated clockwise in the figure by driving means (not shown).
Is uniformly charged, for example, to a negative polarity. The surface of the photosensitive drum 1 uniformly charged in this way is exposed by an exposure device described later to carry an electrostatic latent image.

The developing device 5 develops the electrostatic latent image on the photosensitive drum 1 into a toner image with the toner on the developing roller exposed from the opening of the casing. The developed toner image is transferred to an intermediate transfer belt or transfer paper P by a belt unit described later.

The drum cleaning device 2 cleans the photosensitive drum 1 by removing the toner remaining on the photosensitive drum 1 after the transfer of the toner image.

The static eliminator 3 eliminates residual charges on the photosensitive drum 1 after cleaning. By this charge elimination, the surface of the photosensitive drum 1 is initialized and prepared for the next image formation.

An exposure apparatus 7 is provided on the right side of the process unit 6 having such a configuration in the drawing. This exposure device 7
Irradiates the photosensitive drum 1 with a laser beam L emitted based on image information from a writing position between the charging device 4 and the developing device 5.

Further, on the lower side of the process unit 6 in the figure, there is provided a sheet feeding means having a sheet feeding cassette 26 which can be detached from the housing 101 in the direction of arrow C in the figure. The sheet feeding means includes a sheet feeding roller 27 fixed to the printer main body and a pair of registration rollers 2 in addition to the sheet feeding cassette 26.
8 and so on. A plurality of transfer papers P as recording bodies are stored in the paper supply cassette 26.
The paper feed roller 27 is in contact with the uppermost transfer paper P.
When the paper feed roller 27 is rotated clockwise in the figure by a driving unit (not shown), the uppermost transfer paper P is sandwiched between the rollers of the registration roller pair 28. The registration roller pair 28 sends out the sandwiched transfer paper P toward a transfer nip described later at an appropriate timing.

Further, on the left side of the process unit 6 in the figure, a belt unit 20 for contacting the photosensitive drum 1 while moving the intermediate transfer belt 10 endlessly in the direction of the arrow in the figure.
a is provided. The belt unit 20a includes an intermediate transfer belt 10 as a recording material holding member, a driving roller 1
1, a driven roller 12, 13, 14, a transfer roller 15, a backing roller 16, and the like.

The driving roller 11 and the driven roller 1
2, 13, and 14 mean that the driving roller 11 is driven while tensioning the intermediate transfer belt 10 as a recording material holding belt.
Endless movement by the rotation drive of. The drive roller 11 is configured so that the winding angle of the intermediate transfer belt 10 is ensured to some extent and the driving force is reliably transmitted to the belt.

The intermediate transfer belt 10 forms a transfer nip by winding a portion not stretched around the driving roller 11 and the driven rollers 12, 13, and 14 around a part of the peripheral surface of the photosensitive drum 1. I have.

The transfer roller 15 is disposed so that the intermediate transfer belt 10 is sandwiched between the transfer roller 15 and the photosensitive drum 1 in the transfer nip. Then, for example, a positive transfer bias is applied to the back surface of the intermediate transfer belt 10,
A transfer electric field is formed between the photosensitive drum 1 and the transfer drum. In the transfer nip, the toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 10 by the influence of the transfer electric field and the nip pressure.
Alternatively, the image is transferred onto the transfer paper P sent into the nip by the registration roller pair 28. Note that, instead of the transfer roller 15, a transfer charger that faces the back surface of the intermediate transfer belt 10 via a predetermined gap may be provided.

The intermediate transfer belt 10 has a volume resistance value of 10 ⁷ to 10 ¹⁴ [Ω] from the viewpoint of ensuring good electrostatic transferability in the transfer nip.
cm].

The backing roller 16 is in contact with the back surface of the intermediate transfer belt 10 downstream of the transfer nip in the belt moving direction. At this contact position, the transfer charger 17 is disposed so as to face the front surface of the intermediate transfer belt 10 via a predetermined gap.

The transfer paper P on which the toner image on the photosensitive drum 1 has been transferred by the transfer nip is transferred to the intermediate transfer belt 1.
With the belt kept endless, it passes through a position facing the transfer charger 17 with the endless movement of the belt. At this time, the toner image on the intermediate transfer belt 10 is transferred to the belt contact surface under the influence of the electric charge generated by the transfer charger 17. By bringing the backing roller 16 into contact with the back surface of the intermediate transfer belt 10 at this opposing position, the undulation of the belt at the transfer position at the transfer charger 17 can be suppressed, and the disturbance of the image due to the undulation can be reduced. . Therefore, the backing roller 16 is
A plays a role as an auxiliary member for assisting the function of the transfer charger 17 outside.

The transfer paper P on which the toner image has been transferred as described above is conveyed to a belt stretching position by the driving roller 11. At this belt tension position, the leading end portion of the transfer paper P does not follow the intermediate transfer belt 10 that moves so as to draw an arc along the peripheral surface of the drive roller 11, but depends on its own waist strength. Peel off from the intermediate transfer belt 10. Then, the transfer paper P, which has not yet reached the belt tension position by the driving roller 11, continues to move with the intermediate transfer belt 10, and is pushed upward in the vertical direction by the rear end side portion.

Above the belt unit 20a, there is a fixing roller 30b having a heat source such as a heater therein, and a pressure roller 30a which abuts on the fixing roller 30 at a predetermined pressure and elastically deforms to form a fixing nip. A heating and fixing device 30 is provided. The transfer paper P peeled off from the intermediate transfer belt is sent into the heat fixing device 30. Then, the toner images on both sides thereof are fixed by being heated or pressurized by being sandwiched by the fixing nip, and then sent out to the discharge path 33.

After receiving the transfer paper P sent in the vertical direction from the heating and fixing device 30, the discharge path 33 changes the moving direction of the transfer paper P to a direction close to the horizontal direction, and then, toward the discharge device 34. Send out.

The discharge device 34 discharges the transfer paper P received from the discharge path 33 toward the upper surface of the printer housing. On this upper surface, a stack portion 40 is formed so as to be inclined upward in the discharge direction of the transfer paper P, and the transfer paper P discharged from the discharging device 34 is
Are sequentially stacked. In this manner, by using the upper surface of the printer housing as the stack unit 40, it is possible to reduce the size of the apparatus and save the installation space.

On the other hand, the intermediate transfer belt 10 which has transferred the transfer paper P to the heating and fixing device 30 at the belt stretching position by the driving roller 11 adheres residual toner not transferred to the transfer paper P to the front surface thereof. It may be done. If the intermediate transfer belt 10 with the residual toner adhered thereto is transported again to the transfer nip along with its endless movement, the toner image formed next will be disturbed by the residual toner or the transfer paper P will be disturbed. There is a risk of getting dirty.

Therefore, a belt cleaning device 50 is provided downstream of the belt tension position in the belt moving direction. This belt cleaning device 50
It has a scraping blade, a conveying screw, a contact / separation mechanism (not shown), and the like.

The scraping blade is made of a metal such as stainless steel and is formed in a thin plate shape.
Between the belt and the front side of the belt. Residual toner on the front surface of the intermediate transfer belt 10 is removed from the belt surface by the scraping blade abutting in this manner, and falls onto the transport screw. By arranging the belt cleaning device 50 so as to sandwich the intermediate transfer belt 10 between the scraping blade and the driven roller 14, the following becomes possible. That is, the driven roller 14 functioning as a belt stretching roller can also function as an auxiliary member that backs up the scraping blade.

The transport screw rotates while receiving the residual toner that has fallen from the scraping blade 52, thereby transporting the residual toner in the axial direction thereof and sending it to a collection unit (not shown).

The contact / separation mechanism causes the cleaning roller 51 to contact / separate from the intermediate transfer belt 10 by swinging the entire belt cleaning device 50 about the axis D by, for example, turning on / off a solenoid (not shown). When the first toner image, which will be described later, moves to the cleaning position instead of the residual toner due to the contact and separation,
The scraping blade is separated from the intermediate transfer belt 10. Thereby, it is possible to avoid a situation in which a first toner image described later is cleaned. By separating the intermediate transfer belt 10 from the intermediate transfer belt 10 when cleaning is unnecessary, the load on the drive source of the intermediate transfer belt 10 and the drive roller 11 can be reduced.

An electrical unit E1 and a control unit E2 are arranged between the paper feed cassette 26 and the exposure device 7 in the vertical direction in the printer housing, and these devices are electrically controlled by these components. You.

Further, a fan F1 is provided in the upper right corner of the printer housing in the figure, and a fan F2 is provided on the left side of the belt unit 20a in the figure. The internal air is forcibly exhausted by these fans, and the excessive increase in the internal temperature is suppressed.

The printer 100 transfers a toner image to both sides of the transfer paper P as follows. That is, first, when an image information signal sent from a personal computer (not shown) or the like is received, the rotation driving of the photosensitive drum 1 is started, and the surface thereof is uniformly charged to a negative polarity by the charging device 4. Then, the exposure device 7 is drive-controlled based on the image information signal. The laser light L emitted from the exposure device by this drive control is scanned by a polygon mirror 7 rotated and driven by a motor, irradiates the photosensitive drum 1 via a mirror 7b, an fθ lens 7c, etc. Form a latent image.

The first electrostatic latent image is reversal-developed by a developing device 5 using a toner of negative polarity, and becomes a first toner image as a visible image on the photosensitive drum 1.
Moves to the transfer nip with the rotation of. At this time, the transfer paper P has not yet been sent to the transfer nip, and the first toner image is intermediately transferred onto the intermediate transfer belt 10 instead of the transfer paper P. Then, it moves endlessly with the intermediate transfer belt 10 and enters the cleaning position by the cleaning device 50. At this time, the cleaning device 50
Is in a state separated from the intermediate transfer belt 10.
Therefore, the first toner image returns to the transfer nip again without being cleaned by the cleaning device 50.

During the endless movement of the first toner image in this way, the next exposure step and development step are started, and a second toner image as a second visible image is formed on the photosensitive drum 1. Is done. Further, the pair of registration rollers 2
The transfer paper P is sent to the transfer roller 8 and the registration roller pair 28
The first surface (the lower surface in the figure) of the transfer paper P is sent out at a timing at which it can be superimposed on the first toner image returning to the transfer nip.

The second toner image is formed on the photosensitive drum 1 at such a timing that the second toner image exactly overlaps the second surface (upper surface in the drawing) of the transfer paper P sent to the transfer nip. Therefore, in the transfer nip where the first toner image has returned again, the first toner image on the intermediate transfer belt 10, the transfer paper P, and the second toner image on the photosensitive drum 1 are sandwiched. . Then, the second toner image is transferred to the second surface of the transfer paper P under the influence of the transfer electric field and the nip pressure formed by the transfer roller 15. At this time, the electrostatic force attracted to the intermediate transfer belt 10 acts on the first toner image located between the intermediate transfer belt 10 and the first surface of the transfer paper P by the transfer electric field. Therefore, the first toner image is in contact with the first surface of the transfer paper P, but has not yet been transferred there. The printer 1
In the case of 00, the transfer paper P is held on the intermediate transfer belt 10 by the natural charge of the belt of the opposite polarity to the charge carried on the transfer paper P by using an intermediate transfer belt having an electrically medium resistance as the intermediate transfer belt 10. ing. Therefore, the transfer sheet P can be held without applying a bias for holding the transfer sheet to the intermediate transfer belt 10.

The transfer paper P that has exited the transfer nip carries the second toner image on the second surface, and transfers the first toner image on the intermediate transfer belt 10.
With the toner image in contact with the first surface, the toner image moves together with the intermediate transfer belt 10. Then, the transfer charger 1
7, the first toner image that has only been in contact with the first surface up to that point is electrostatically secondary-transferred. At this time, the second surface of the transfer paper P and the transfer charger 17
A predetermined gap is held between the second and third toner images, so that the second toner image does not reversely transfer to the transfer charger 17 due to the contact with the transfer charger 17.

The portion of the intermediate transfer belt 10 which has sent out the transfer paper P toward the heat fixing device 30 reaches the cleaning position with its endless movement. However, before reaching, the belt cleaning device 50 that has been separated from the intermediate transfer belt 10 is swung, and the cleaning roller 51 and the intermediate transfer belt 10 come into contact with each other.
By this contact, residual toner adhered to the intermediate transfer belt 10 is cleaned.

According to the double-sided transfer, an image is formed on both sides of the transfer sheet P without switching back the transfer sheet P to a belt unit 20a as a transfer device or a heating and fixing device 30 described later. Therefore, it is possible to solve problems such as an increase in cost, a jam, and a hindrance to speeding up of transfer due to switchback of the transfer paper P.

As described above, since the belt unit 20a performs the double-side transfer process together with the transfer charger 17 and the belt cleaning device 50, it functions as a part of the double-side transfer means.

The transfer charger 17 is stopped when the first toner image passes through the position facing the backing roller 16 alone, not together with the transfer paper P or the second toner image. Controlled.

The first toner image is formed on the photosensitive drum 1 so as to be a normal image instead of a mirror image. This is for the following reason. That is, in the case of direct transfer from the drum to the transfer paper P, a mirror image is formed on the drum 1 of the photoconductor, and when this is directly transferred to the transfer paper P, a normal image is obtained. On the other hand, in the indirect transfer from the drum to the belt to the transfer paper P, when a mirror image is formed on the photosensitive drum 1, the mirror image is formed on the first surface of the transfer paper P. It goes without saying that the second toner image directly transferred to the transfer paper P is formed on the photosensitive drum 1 as a mirror image as usual.

Further, the transfer charger 17 is provided not on the downstream side of the transfer nip as shown in FIG. 1 but on the upstream side of the transfer nip. May be injected with a reverse charge. This is because double-sided simultaneous transfer can be performed by injecting reverse charges. Specifically, if the first toner image before returning to the transfer nip is reversely charged by injecting a reverse charge, the second nip image is transferred from the surface of the photosensitive drum 1 to the second surface of the transfer paper P at the transfer nip. It can be moved electrically. On the other hand, the reversely charged first toner image can be electrostatically moved from the intermediate transfer belt 10 to the first surface of the transfer paper P.

The above is the double-sided transfer process. When a toner image is formed on only one side of the transfer paper P, the single-sided transfer process described below is performed. That is, first, similarly to the case of the double-sided transfer, the surface of the photosensitive drum 1 is uniformly charged to a negative polarity, and then a laser beam L based on the image information signal is irradiated toward the surface, whereby An electrostatic latent image serving as a mirror image is formed on the photosensitive drum 1. Then, the toner image is reversely developed by the developing device 5 to be a toner image.

On the other hand, in parallel with the formation of the electrostatic latent image, the paper feed roller 27 is driven and the transfer paper P is sent out from a paper feed cassette (not shown), and is sandwiched between the registration roller pairs 28. The registration roller pair 28 sends out the transfer paper P toward the transfer nip at a timing when the transfer paper P can be superimposed on the toner image on the photosensitive drum 1.

The toner image on the photosensitive drum 1 superposed on the transfer paper P at the transfer nip is transferred to the second surface of the transfer paper P under the influence of the transfer electric field and the nip pressure.

The transfer paper P that has exited the transfer nip passes through a position facing the transfer charger 17 with the toner image carried on the second surface. However, this transfer charger 17
Is for the secondary transfer of the first toner image from the intermediate transfer belt 10 to the first surface of the transfer paper P. For this reason, even if the transfer sheet P carrying the toner image only on the second surface passes directly below the transfer sheet P, the transfer sheet P is not driven.

After passing through the position facing the transfer charger 17, the transfer paper P sent to the heat fixing device 30 is fixed to the toner image on the second surface thereof, and then is discharged.
Sent to Then, the sheet is stacked on the stack unit 40 via the discharge device 34 with the second surface thereof facing down (face down). In such a stack, even if originals of several pages are output in order from one page, the output originals can be stacked in page order in a state where the second side is sequentially viewed when the pages are turned. .

In the single-sided transfer process, the primary transfer and the secondary transfer of the first toner image can be omitted.

FIG. 2 is an enlarged view showing a part of the belt unit 20a and the photosensitive drum 1. As shown in FIG. In the figure, the driven roller 12, the transfer roller 15, and the photosensitive drum 1, which are located on the upstream side of the transfer nip in the belt moving direction, have diameters of 16 [mm], 10 [mm], 30 respectively.
[Mm] is used.

The coordinates of the central axis of the photosensitive drum 1 are (0,
0), the driven roller 12 having a diameter of 16 [mm]
It is arranged in parallel with the photosensitive drum 1 so that its central axis is located at coordinates (-22.1, -8.2). The transfer roller 15 having a diameter of 10 [mm] is disposed in parallel with the photosensitive drum 1 so that the center axis thereof is located at the coordinates (-20.0, 13.2).

The central axis of the photosensitive drum 1 and the driven roller 1
The line segment connecting the center axis 2 and the horizontal axis X forms an angle θ of 20 ° with the horizontal line X. Photoreceptor drum 1 of belt unit 20
Is determined as follows. That is, the driven roller 12 when the photosensitive drum 1 is not present
The position is set so that the photosensitive drum 1 can be cut into the belt portion bridging between the transfer roller 15 and the transfer roller 15 with a cut-in amount K of 0.54 [mm].

In the belt unit 20a, the belt portion bridging between the driven roller 12 and the transfer roller 15 adjacent to each other is positively urged by these two rollers and wound around the photosensitive drum 1. Will be attached. In the present embodiment, the intermediate transfer belt 10 is wound around a length of about 1/10 of the circumference of the photosensitive drum 1 to form a transfer nip having a width of about 8.7 [mm]. Will be formed. When such a transfer nip is formed,
Compared to a case where the photosensitive drum 1 and the intermediate transfer belt 10 are in point contact with each other at the transfer position, the two are more reliably brought into contact with each other. .

Regarding the driven roller 12 and the transfer roller 15 which contribute to the formation of the transfer nip, the material, cross-sectional structure, and the like of the intermediate transfer belt 10 are controlled so that the amount of deflection due to the tension force is suppressed to 0.1 mm or less. It is desirable to set the length, diameter, and the like. Specifically, the roller length L (the length of the portion receiving the load from the belt) [mm] and the cross section are set so that the deflection amount y [mm], which is a solution of the following equation 1, is suppressed to 0.1 or less. Structure (Second moment of area I [mm
⁴ )) is desirable. In addition, the necessary longitudinal elastic modulus E [kg / mm ³ ] and the weight per unit length [kg
/ Mm] may be selected. This is because the meandering of the intermediate transfer belt 10 at the transfer nip due to the bending of the driven roller 12 and the transfer roller 15 can be suppressed by suppressing the amount of deflection y to 0.1 [mm] or less.

Y =-(5WL ⁴ ) / (384EI)

Incidentally, regarding the second moment of area I,
The roller outer diameter D1 and the roller inner diameter D2 can be obtained by applying the following equation (2).

[Number 2] ^{I = π (D1 4 -D2 4} ) / 64

In the present embodiment, a solid stainless steel roller is used as the transfer roller having a diameter of 10 [mm], so that the deflection amount y is suppressed to 0.1 [mm] or less. In addition, a stretching roller 1 having a diameter of 16 [mm]
As No. 2, by using a stainless steel roller without a hollow, the amount of deflection y is suppressed to 0.1 [mm] or less. By grounding the tension roller 12, the tension roller 12 caused by friction with the intermediate transfer belt 10 is formed.
To avoid charging. Further, the transfer roller 1
Although a transfer bias of 7 kV or less is applied to 5, the distance L1 between the transfer roller 15 and the stretching roller 12 is set to 5 mm or more to avoid discharge between the two rollers. I am trying to do it. More specifically, the distance L1 is set to 7 [mm].

Next, the characteristic configuration of the printer 100 will be described. 1, the left side of the printer 100 in FIG. 1 corresponds to the front. An operation panel 60 including a liquid crystal display, operation keys, and the like is provided in an upper housing 100 portion on the front side.
Various information is input to a control device E2 (not shown) by a key operation on the operation keys.

The housing 10 below the operation panel 60
The front surface is an opening / closing door 61 that swings around a rotation axis H. The belt unit 20a and the cleaning device 50 are supported by the opening / closing door 61, and are configured to swing with the opening and closing thereof. Therefore, when the opening / closing door 61 is opened in the direction of the arrow B in the figure, as shown in FIG. Then, of the paper transport path in the housing 101, the path between the two units is exposed. Further, the cleaning device 50 located near the registration roller pair 28 is largely separated from the registration roller pair 28, and the path before and after the registration roller pair 28 is also exposed. With these exposures, the entire paper transport path in the housing 101 is exposed, so that the jam processing can be easily performed. The belt unit 20a supports a unit including an intermediate transfer belt and the like inside the cover member 21, and is configured to be detachable from the opening / closing door 61 in a direction indicated by an arrow in FIG. However, the attachment and detachment of the belt unit 20a can be performed only from the back side of the door 61. Therefore, the belt unit 20a can be attached and detached only when the door 61 is opened with respect to the printer main body 100.

FIG. 4 is a perspective view showing the printer with the opening / closing door 61 opened. In the figure, a lever 64 is provided on a side surface of the opening / closing door 61, and by operating the lever 64, the opening / closing operation of the opening / closing door 61 is locked / unlocked.

In FIG. 1 described above, the cover member 21 of the belt unit 20a functions as a part of the opening / closing door 61 (therefore, the housing 101).
When the belt unit 20a is removed from the opening / closing door 61, as shown in FIG.
2 are formed. That is, the opening / closing door 61 has the opening 62, and the cover member 21 of the belt unit 20a functions as a lid for closing the opening.

In the printer 100, a belt unit having an intermediate transfer belt 10 having a longer circumference can be attached to and detached from the opening / closing door 61 instead of the belt unit 20a. Hereinafter, the belt unit having the intermediate transfer belt 10 having a long circumference is referred to as a large belt unit 20b.
What is called 0a is referred to as a small belt unit 20a.

FIG. 5 is a schematic configuration diagram showing the printer 100 with the large belt unit 20b mounted. In the figure, a large belt unit 20b includes a driving roller 11, a driven roller 12, and a driving roller 11 similar to the small belt unit 20a.
3, 14, a transfer roller 15, and a backing roller 16. The intermediate transfer belt 10 having a longer circumference than the small belt unit 20a is also provided. Further, in order to stretch the intermediate transfer belt 10 having a longer peripheral length, one additional driven roller is provided compared to the small belt unit 20a (the driven roller 18).

As described above, the printer 100 capable of replacing the small belt unit 20a and the large belt unit 20b can be used.
, The small belt unit 20a for the user
, It is possible to reduce the time required for both-side transfer. Specifically, when performing double-sided transfer using the intermediate transfer belt 10 that moves endlessly as the intermediate transfer member, the leading end of the first toner image is synchronized with the leading end of the second toner image as described above. To During the period from the start of the intermediate transfer of the first toner image to the start of the direct transfer of the second toner image, the belt always rotates once and the respective ends of both toner images are synchronized at the transfer nip. Intermediate transfer belt 10
The time required for one rotation depends on the circumference. Therefore, if the intermediate transfer belt 10 having a longer circumference than necessary is provided in the double-sided transfer means, the user can extend the double-sided transfer time more than necessary. Become. Therefore, an intermediate transfer belt 10 having a length corresponding to the user's own requirements is provided to the user.
By selecting the small belt unit 20a to which is attached, it is possible to shorten the double-side transfer time.

As shown in FIG. 1, the small belt unit 20 a exposes the side surface of the case member 21 through the opening (62) of the door 61 so that the front surface of the door 61 is flat. . On the other hand, in the large belt unit 20b including the intermediate transfer belt 10 having a longer circumference, the case member 21 is mounted so as to protrude partly from the opening of the door 61 as shown in FIG. . As described above, the intermediate transfer belt 1 is
By setting the stretched shape of the large belt unit 20
The space occupied by b in the housing 101 can be the same as the space occupied by the small belt unit 20a.

The printer 100 realizes the following layout by making the spaces the same as described above. That is, the layout is such that the belt unit can be replaced without moving the process unit 6, the heat fixing device 30, the cleaning device 50 as the receiving unit, the registration roller pair 28 as the delivery unit, and the like.

Further, in this printer, as shown in FIG. 1, the work of attaching and detaching the sheet feeding cassette 26 as the supply means and the work of replacing the belt unit can be performed from the same side of the housing 101. In such a configuration, the work of attaching and detaching the paper cassette 26 and the work of replacing the belt unit are performed by:
The access can be performed to the housing 101 from the same direction, and it is not necessary to secure a space around the access housing 101 separately for both operations. Therefore, space can be saved.

The backing roller 16 is provided with a transfer charger 17.
Functions as an auxiliary member for assisting the transfer function of. Also,
The transfer roller 15 functions as an assisted member that assists the transfer function on the photosensitive drum 1. In addition, the driven roller 14
Functions as an auxiliary member that assists the cleaning function of the cleaning device 50. Regarding these, it is desirable to dispose them so as to be positioned at the same position in the housing 101 regardless of the belt unit. Regarding the small belt unit 20a and the large belt unit 20b,
Transfer charger 17, cleaning device 50, respectively
This is because it is possible to reliably obtain the functional assistance for the photoconductor 1 and the functional assistance received from the photosensitive drum 1.

A reflection type photo sensor (hereinafter, referred to as a P sensor) 63 is mounted on the lower surface of the operation panel 60. The P sensor 63 includes a light-emitting element (not shown) that irradiates light toward the lower side of the operation panel 60.
And a light receiving element (not shown) that receives light from below the panel toward the panel.

As shown in FIG. 1, the small belt unit 2
Reference numeral 0a is attached to the printer main body so that the case member 61 does not protrude from the surface of the door 61. In such mounting, the light emitted from the light emitting element of the P sensor 63 reaches the printer installation surface relatively far away from the sensor without any light blocking. Then, the light is diffusely reflected here and its intensity is attenuated to a level not detected by the light receiving element. Therefore, when the small belt unit 20a is mounted on the door 61, the light receiving element of the P sensor 63 does not receive light from the light emitting element.

On the other hand, as shown in FIG. 5, the large belt unit 20 b makes the case member 21 protrude greatly from the opening (62) of the opening / closing door 61. P at this protruding part
A reflecting mirror (not shown) is attached at a position facing the sensor 63, and light emitted from the light emitting element of the P sensor 63 is reflected by the reflecting mirror and received by the light receiving element. The light receiving element outputs an electric signal having a value corresponding to the amount of received light to the control device E2.

When the value of the electric signal from the P sensor 63 exceeds a predetermined value, the control device E2 recognizes that the large belt unit 20b is attached to the door 61. On the other hand, if it is less than the predetermined value, it is recognized that the small belt unit 20a is attached. Therefore, in the printer 100, the P sensor 63, the case member 21, the reflecting mirror, and the like constitute an identification unit for identifying the size of the intermediate transfer belt 10. The P sensor 63
The size of the intermediate transfer belt 10 may not be automatically identified by using, but may be manually identified by a key operation on the operation panel 60.

In the small belt unit 20a and the large belt unit 20b, circumferential information indicating the circumferential length of the intermediate transfer belt 10 is attached to the case member 21 by a method such as embossing, printing, or sticking a seal. This perimeter information is attached to a position that is easily visible to the user,
The circumference of the intermediate transfer belt 10 can be easily identified by the user.

The intermediate transfer belts 10 of the small belt unit 20a and the large belt unit 20b have the same belt width, and the belt width is A4 size vertical dimension (about 2
97 mm). The intermediate transfer belt 10 has a circumference of 310 [mm], which is slightly longer than the A4 size lateral dimension (about 210 mm) in the small belt unit 20a. On the other hand, in the large belt unit 20b, the peripheral length is set to 500 [mm], which is slightly longer than the A3 size vertical dimension (about 420 mm).

The small belt unit 20a is
When mounted on the main body, the A4 size or B5 size image or the like has a vertical dimension that does not fit within the circumference of the intermediate transfer belt 10. When the image cannot be accommodated, the printer 100 forms the entire image by rotating the image by 90 ° so that the vertical direction of the image is accommodated in the belt width direction. Then, the intermediate transfer is performed on the intermediate transfer belt 10.

For an image whose vertical dimension falls within the peripheral length of the intermediate transfer belt 10, such as a postcard size, the image is intermediately transferred onto the intermediate transfer belt 10 such that the vertical direction is accommodated in the belt length direction. By performing the intermediate transfer of the image in this manner, an image of A4 size or less can be formed on both sides of the corresponding transfer paper P.

Further, all the images exceeding the A4 size and the A3 size or less are directly transferred onto the transfer paper P without intermediate transfer onto the intermediate transfer belt 10 even if a double-side transfer command is issued. It has become. In such a configuration, an image exceeding the A4 size and not more than the A3 size can be formed on the transfer paper P, though only on one side.

Therefore, when the small belt unit 20a is mounted, an image of A4 size or smaller is formed on both sides of the transfer paper P, and an image larger than A4 size and smaller than A3 size is formed on one side of the transfer paper P. can do.

On the other hand, in the state where the large belt unit 20b is mounted, even if the image is larger than A4 size and smaller than A3 size, the vertical direction can be accommodated in the belt length direction. Therefore, the printer 100 can intermediately transfer the image formed so that the vertical direction is accommodated in the belt length direction onto the intermediate transfer belt 10 and form both sides on the transfer paper P. Further, in this state, when an instruction to form both sides of an image of A4 size or smaller is issued, the image forming process is performed as follows. That is, first, the first toner image is continuously formed on the photosensitive drum 1 for every two images, and these are continuously and intermediately transferred onto the intermediate transfer belt 10. Even if continuous intermediate transfer is performed as described above, before the first first toner image is re-conveyed to the transfer nip with the endless movement of the intermediate transfer belt 10, the intermediate transfer of the second first toner image is performed. Can be finished. When the formation of the second first toner image is completed, the photosensitive drum 1
, A second toner image is continuously formed. Then, while continuously transferring the two transfer papers P to the transfer nip, the transfer papers P are subjected to double-side transfer. In such a configuration,
Each time an image is formed on both sides of two sheets of transfer paper, the drive amount of the intermediate transfer belt is reduced by one turn, so that the time for forming a double-sided image can be shortened.

The printer 100 is configured to perform only one-side transfer by direct transfer from the photosensitive drum 1 to transfer paper P without transferring all images on both sides as needed. This “as needed” is, for example, the following case. That is, first, a case where the one-sided transfer mode is selected by operating the operation panel 60 shown in FIG. Second, there is a case where the long side direction of the image size does not fit in the belt width or the belt circumference of the intermediate transfer belt 10, but the short side direction fits in the belt width. This corresponds to a case where a print command for an image exceeding the A4 size and not exceeding the A3 size is received with the small belt unit 20a mounted as described above. If the short side direction of the image falls within the belt width, the long side direction can be dealt with by making the intermediate transfer belt 10 rotate one or more times. However, if the toner image from the photosensitive drum 1 is intermediately transferred onto the intermediate transfer belt 10 while the intermediate transfer belt 10 is rotated one or more rounds, the vicinity of the front end of the toner image on the belt is overlapped with the vicinity of the rear end. Intermediate transfer of a toner image exceeding the belt circumference is impossible. Then, the transfer paper P
Only one-sided transfer by direct transfer to the surface is performed.
In such a configuration, if the long side direction of the image size does not fit in the belt width or the belt peripheral length of the intermediate transfer belt 10, but the short side direction fits in the belt width, it is formed on one surface of the transfer paper P. Can be.

Even when the large belt unit 20b is set and a continuous print command for only one side of two or more sheets of transfer paper P is issued, the photosensitive drum 1 is set for every two images. The first toner image is formed continuously.

FIG. 6 is a schematic diagram showing the intermediate transfer belt 10 of the small belt unit 20a together with the transfer paper P held thereon. In this figure, the endless intermediate transfer belt 10 is shown in a band shape. The transfer paper P shown in the figure is of A4 size, and has a long side dimension Lx and a short side dimension Ly of 297 and 210 [mm], respectively, and is conveyed with its long side positioned in the belt width direction. Is done. The belt width BW of the intermediate transfer belt 10 is set to 320 [mm], which is slightly longer than the long side dimension Lx, so that such conveyance is possible. Further, the belt circumferential length BL1 is set to 230 [mm] slightly longer than the short side dimension Ly (210 mm). The circumferential length is set in consideration of a margin of about 10 [mm] before and after the A4 size transfer paper P.

On the other hand, as described above, the large belt unit 2
The width of the intermediate transfer belt 10b is the same as that of the small belt unit 20a, and has a belt circumferential length corresponding to the A3 size vertical dimension (long side dimension). The circumference is theoretically A4 size short side dimension Ly (210 mm) × A3 size lateral dimension as shown in FIG.
Second, a dimension (BL2) that allows for a margin H of 10 [mm] before and after the transfer paper P is sufficient. That is, the large belt unit 2
0b, the circumference of the intermediate transfer belt 10 is 440
By setting [mm], intermediate transfer of an A4 size image can be performed. However, if the intermediate transfer belt 10 having such a configuration is used to continuously print the A4 size transfer paper P, the intermediate transfer belt 10
It is assumed that two A4 size images have been transferred intermediately. Then, as shown in FIG. 8, it becomes impossible to provide a margin between the two images. In order to secondary-transfer the two images thus intermediate-transferred to the two transfer papers P without margins, the respective transfer papers P need to be continuously passed without any interval. It is possible. This is because the sheet passing timing of each transfer sheet P is realized by detecting the leading end thereof. Between the two transfer sheets P, the pair of registration rollers 28 sandwiching the transfer sheet P
After the drive is temporarily stopped, an interval G is required to allow the timing for superimposing the transfer paper P on the toner image on the intermediate transfer belt 10 to be measured. Therefore, the printer 100
In FIG. 9, as shown in FIG.
b, the circumference BL2 of the intermediate transfer belt 10 is set to 500 [m
m]. This circumference BL2 of 500 [mm]
Is a dimension obtained by further adding a gap G (60 mm) between the transfer papers P to 440 [mm] which is a multiple of the short side dimension. The interval G (60 mm) is a dimension required for continuously transporting the transfer paper P as a recording medium toward the intermediate transfer nip. In such a large belt unit 20b, after two A4 size images, which are half the A3 size, are intermediate-transferred onto the intermediate transfer belt 10, each of them is reliably secondary-transferred onto transfer paper P which is continuously passed. Can be.

The example in which the intermediate transfer belt 10 having a belt width corresponding to the long side dimension Lx of the A4 size is provided as the small belt unit 20a and the large belt unit 20b has been described. However, the belt width may be made to correspond to the long side dimension Lx in a recording medium of another fixed size. For example, it may be made to correspond to the long side dimension of another A system size (A1, A2, A3, etc.). In addition to the standard size, in addition to the B size (B0, B1, B2, B3,
B4, B5), postcard size, US letter size (standard size: 8.5 x 11 inches, double size: 11 x
17 inches). In order to continuously transfer two or more images to a recording medium of a fixed size having the short side dimension Ly, the peripheral length of the intermediate transfer belt 10 is set so as to satisfy the following condition (3). Just set it. It goes without saying that the intermediate transfer belt 10 of the large belt unit 20b also satisfies this condition.

## EQU3 ## Belt circumference BL2> n × Ly + (n-1) × G where n is an integer of 2 or more (corresponding to the number of continuous sheets passed) G: interval between recording media

As shown in FIG. 10, the printer 100 is used by being connected to a personal computer 200. The printer 100 receives not only an image information signal but also a command signal for changing various image forming conditions. Is configured. Therefore, various image forming conditions can be changed by remote control of the personal computer 200 even from a place away from the printer 100.

As shown in FIG. 11, the case member 21 of the large belt unit 20a is connected to the opening (6
If it is made to protrude greatly from 2), the user tends to open and close the door by putting his hand on this protruding portion. However, in the printer 100, a mechanism such as a handle that is easily gripped by a hand is not provided at a portion of the case member 21 protruding from the opening. All such mechanisms are provided on the non-projecting portion of the case member 21.

By the way, in the structure shown in FIG. 3, when the opening / closing door 61 is opened by rotation about the rotation axis H,
As shown in the drawing, the belt cleaning device 50 is set to a sideways posture. In the belt cleaning device 50, collected toner cleaned from the intermediate transfer belt 10 is stored. For this reason, it is necessary to provide a reliable sealing mechanism for the toner leakage in the belt cleaning device 50 so that the collected toner does not leak to the outside of the apparatus even when the belt cleaning device is turned sideways. Therefore, the opening / closing mechanism of the opening / closing door 61 may be configured as in the first modified example device shown in FIG. In the first modified example device 100A, the opening / closing door 61 is configured to be opened and closed with respect to the printer main body by sliding horizontally on a rail 102 fixed to the printer main body. With this configuration, even if the opening / closing door 61 serving as the opening / closing unit is opened with respect to the printer main body, the belt cleaning device 50 does not fall down. Therefore, it is possible to avoid the leakage of the collected toner due to the overturn, and to simplify the seal mechanism for suppressing the toner leakage.

FIG. 13 is a schematic configuration diagram showing a second modification 100B. This modified example apparatus 100B includes four process units 6Y, M, C, and BK, and four corresponding exposure apparatuses 7Y, M, C, and BK. The belt units 20a and 20b are provided with four transfer rollers 15Y, M, C and BK, respectively. In addition, two paper cassettes 26 and a roll paper supply device 70 disposed below the two paper cassettes 26 are provided.

The above process units 6Y, M, C, BK
Are for forming Y (yellow), M (magenta), C (cyan), and BK (black) toner images, respectively, and have substantially the same configuration except that the color of the toner used is different. The process unit 6Y for yellow will be described as an example. As shown in FIG.
A charging device 4Y, a developing device 5Y and the like are provided. The charging device 4Y uniformly charges the surface of the photoconductor drum 1Y rotated clockwise in the figure by a driving unit (not shown). The photosensitive drum 1 uniformly charged in this way
The surface of Y is exposed by the exposure device 7Y, and carries an electrostatic latent image for Y. This Y electrostatic latent image is developed into a Y toner image by a developing device 5Y using Y toner.
Then, the intermediate transfer is performed on the intermediate transfer belt 10 of the intermediate transfer unit. On the other hand, the drum cleaning device 2Y
The toner remaining on the photosensitive drum 1Y after the transfer of the Y toner image is removed. Further, the charge removing device 3Y removes the charge remaining on the photosensitive drum 1Y after cleaning. By this charge elimination, the surface of the photoconductor drum 1Y is initialized and prepared for the next image formation. Other process units 6M, C, BK
In the same manner, the M, C, and K toner images are formed on the photosensitive drum in the same manner, and are superimposed on the intermediate transfer bell 10 in order and then intermediately transferred. In this embodiment, each photosensitive drum is exposed by a dedicated exposure device (7Y, M, C, BK). However, each photosensitive drum may be exposed by one exposure device. .

As described above, the intermediate transfer units 20a and 20b have the four transfer rollers 7Y, M, C and BK. These are for transferring toner images from the Y, M, C, and BK photosensitive drums to the intermediate transfer belt, respectively, and are provided between the Y, M, C, and BK photosensitive drums.
Transfer nip is formed. In each transfer nip, a transfer roller to which an intermediate transfer bias is applied from a power supply (not shown) is in contact with the back surface of the belt, thereby forming a transfer electric field.
The intermediate transfer belt 10 is moved endlessly in a counterclockwise direction in the drawing. Then, in each transfer nip, Y, M, C,
The BK toner images are sequentially superimposed and transferred intermediately. By the transfer of the superposition, a first toner image is formed on the intermediate transfer belt 10 by superimposing the four colors. The first toner image is collectively and secondarily transferred onto the first surface of the transfer paper P when passing through a position facing the transfer charger 17 with the endless movement of the belt. White transfer paper P
Is transferred to a full-color image. Meanwhile, the first
Prior to the batch secondary transfer to the surface, each process unit 6
In Y, M, C, and BK, the formation of the respective color toner images for the second toner image is started. The registration roller pair 28 sends out the transfer paper P toward the belt unit at a timing when the transfer paper P can be superimposed on the first toner image. Then, the toner images of the respective colors formed by the respective process units are superimposed and transferred on the second surface of the transfer paper P. By the transfer of the superposition, a full-color image is also formed on the second surface of the transfer paper P.

Near the right end in the figure inside the main body, Y, M,
Toner containers TY, TC, T for storing C, BK toner
M and TK are provided, from which toner is supplied to the corresponding developing devices.

In the second modified example apparatus 100B having the above configuration, a full-color image can be formed on both sides of the transfer paper P by a so-called tandem method. The tandem system is a system in which each single-color toner image for superposition is formed by a dedicated image carrier (photosensitive drum or the like). In addition to the tandem system, there is also a division system in which a full-color image is formed using only one image carrier. More specifically, four developing devices for Y, M, C, and BK toner images are arranged at positions facing one image carrier, and electrostatic latent images for Y, M, C, and BK are provided on this image carrier. Latent images are sequentially formed. Then, these are developed by corresponding developing devices to obtain Y, M, C, and BK toner images, and are sequentially superimposed on an intermediate transfer belt to perform intermediate transfer. In this division method, it is necessary to rotate the intermediate transfer belt at least four times to obtain a four-color superimposed toner image thereon, so that it takes a long time to form a full-color image. On the other hand, in the second modified example of the tandem system, the respective color toner images are formed in parallel by the respective process units 6Y, M, C, and BK, so that the full-color image can be obtained only by rotating the intermediate transfer belt 10 once. Can be formed. Therefore,
The formation speed of a full-color image can be greatly reduced as compared with the division method.

When the tandem system is adopted,
It is desirable that the photosensitive drums be arranged on a straight line as shown in FIG. This is for the following reason.
That is, as shown in FIG. 15, in the tandem system, each photosensitive drum can be arranged around the belt unit instead of being aligned. However, in such an arrangement, when the belt unit having the intermediate transfer belt 10 is separated from the printer main body, it is necessary to simultaneously separate any of the photosensitive drums. For example, when the belt unit is moved to the left in the drawing to be separated from the printer main body, it is necessary to simultaneously separate the photosensitive drum 1BK for black, which complicates the configuration for separation. On the other hand, as shown in FIG. 13, if the photosensitive drums 1Y, 1M, 1C, and 1K are arranged on a straight line, a free space is formed on the side of the belt opposite to the one on which the photosensitive drums are arranged. be able to. If the belt units 20a and 20b are moved toward the free space and separated from the printer main body, it is not necessary to separate the photosensitive drums at the same time, and the configuration for separation can be simplified.

Further, each photosensitive drum 1Y, M, C, BK
Is desirably set to the vertical direction, and the toner image of each color is transferred onto the transfer paper P while transporting the transfer paper P in the vertical direction. This is for the following reason.

That is, each photosensitive drum 1Y, M, C, BK
As shown in FIG. 16, the respective drums may be arranged horizontally above the belt unit in the vertical direction. However, in such an arrangement, a free space in which the photosensitive drum is not arranged is provided below the intermediate transfer belt 10, and it is necessary to move the belt unit downward to separate it from the printer body. is there. Since the downward direction is the base of the printer main body, such separation is extremely difficult, and it becomes necessary to lift the printer main body.

Further, as shown in FIG. 17, the photosensitive drums 1Y, 1M, 1C, and 1K can be disposed horizontally below the belt unit in the vertical direction. In this arrangement, a free space in which the photosensitive drums 1Y, 1M, 1C, and 1K are not disposed is provided above the intermediate transfer belt 10, and the belt unit is moved upward to be separated from the printer main body. Become. Such separation can be easily realized. However, in order to arrange the respective photosensitive drums 1Y, 1M, 1C, and 1K in the horizontal direction, the intermediate transfer belt 10 must be stretched so as to be largely spread in the horizontal direction as shown in the figure. It makes the belt unit largely bulky in the horizontal direction. On the other hand, as shown in the drawing, the paper feed cassette 26 for storing the transfer paper P is configured to horizontally store the transfer paper P in a lying state from the viewpoint of easiness of the paper discharge mechanism. General. The paper feed cassette 26 is also greatly bulky in the horizontal direction. If the belt unit and the sheet cassette 26 which are bulky in the horizontal direction are arranged side by side in the horizontal direction, the plane area of the printer body becomes extremely large. In order to avoid such an increase in the plane area, the two may be arranged so as to overlap in the vertical direction as shown in the figure. However, in such an arrangement, it is necessary to send the transfer paper P from the paper feed cassette 26 to the belt unit while reversing the transfer paper P, which complicates the transfer path of the transfer paper P. Further, in order to make the heat fixing device 30 receive the transfer paper P from the belt unit as short as possible, it is necessary to arrange the heat fixing device 30 beside the belt unit as shown in the figure. As a result, the heat fixing device 3
0 is provided near the center in the vertical direction of the printer main body, and the heat therefrom stays in the main body. Furthermore,
If the heat fixing device 30 is provided in the upper part of the printer main body in order to avoid such heat stagnation, the paper transport path is further complicated.

Therefore, each photosensitive drum 1Y, M, C, B
K is arranged in the vertical direction as shown in FIG. In such an arrangement, a free space without a drum can be provided on the side of the intermediate transfer belt 10. Therefore, the belt unit can be easily separated from the main body by operating the belt unit from the side of the main body. Paper cassette 2
The toner image can be transferred onto the transfer paper P while transferring the transfer paper P fed from the printer 6 in the vertical direction without reversing the transfer paper P, so that the paper transport path is not complicated. . Further, the transfer paper P from the belt unit
Can be disposed on the upper portion of the printer body as it is. For this reason, it is possible to avoid the heat retention and the complicated paper transport path for disposing the heat fixing device 30 from the center in the vertical direction to the upper portion.

In FIG. 13 shown above, the second modified example device 100B is a device in which a roll paper RP having an A4 size short side dimension Ly and an indefinite length is transferred to the belt units 20a, 20b.
0b is provided. Roll paper supply device 7 as non-standard recording material supply means
0 is a tension roller 71, two feed rollers 72
Pair, 74, a cutting device 73 disposed between both feed roller pairs
And so on. When the leading end of the roll paper RP is sandwiched between the pair of feed rollers 73 on the lower side in the figure and the lower end of the roll paper RP abuts on the tension roller 71, a predetermined tension is applied to the drawn portion. When the lower feed roller pair 73 in the figure is driven, the leading end side of the roll paper RP passes through the upper feed roller pair 74 in the figure and is pinched by the transport roller pair 29 disposed between the two paper feed cassettes 26. Further, the sheet is conveyed toward the registration roller pair 28 by the driving of the conveyance roller pair 29. Second Modified Example Device 10
OB is provided with the roll paper supply device 70 having such a configuration, so that it is possible to form an image on both sides even on an irregular recording medium.

FIG. 18 is a schematic diagram showing the intermediate transfer belt 10 of the small belt unit 20a of the second modification 100B together with the A4-size transfer paper P held by the belt. In the figure, the intermediate transfer belt 10 has a width BW
Is 320 corresponding to the long side dimension Lx (297 mm) of the A4 size transfer paper P, similarly to the printer 100 of the embodiment.
[Mm]. On the other hand, the circumference BL3 is A4
The size is such that continuous secondary transfer can be reliably performed on three transfer sheets P of the same size. Specifically, in order to satisfy the condition of Equation 3, “3 (corresponding to n) × 210 +
(3-1) × 60 = 750 ”, which is larger than 770 [m
m]. This is a dimension in which the margin of 10 [mm] is further taken into account at the both ends in the length direction in addition to the condition of the above equation (3). With this intermediate transfer belt 10, it is possible to realize secondary transfer for one A3 size sheet or secondary transfer for three A4 size sheets per rotation. Further, for an image of an irregular size, the width is equal to or less than the short side dimension Lx,
And 750 whose length is slightly larger than the short side dimension Ly.
[Mm] or less can be accommodated.

FIG. 19 is a schematic diagram showing the intermediate transfer belt 10 of the large belt unit 20b of the second modification 100B together with the A4 size transfer paper P held by the intermediate transfer belt. In the figure, the intermediate transfer belt 10 has a length of 320 [mm] corresponding to the long side dimension Lx, similarly to the small belt unit 20a. On the other hand, the circumference BL
4 is a continuous 2 for P4 sheets of A4 size transfer paper.
The dimensions are such that the next transfer can be performed. Specifically, “4 (corresponding to n) ×
210+ (4-1) × 60 = 1020 ”,
It is 1040 [mm]. This is a dimension in which the margin of 10 [mm] is further taken into account at the both ends in the length direction in addition to the condition of the above equation (3). In such an intermediate transfer belt 10,
Per transfer, secondary transfer of two A3 size sheets, A
Secondary transfer for four sheets of four sizes can be realized. In addition, an image of an irregular size can correspond to an image having a width of not more than the short side dimension Lx and a length of not more than 1020 [mm] slightly longer than the short side dimension Ly. Therefore, an image of an irregular size larger in length than the small belt unit 20a can be transferred on both sides. This makes it possible to reliably realize the secondary transfer of the fixed-size images of a larger number than the small belt unit 20a and the secondary transfer of the larger non-standard-size images.

It goes without saying that the above-mentioned sizes other than A4 can be applied as the standard size.
In order to reliably realize the secondary transfer of a larger number of standard size images and the secondary transfer of a larger non-standard size image than the small belt unit 20a to the larger large belt unit 20b, the following is required. What is necessary is just to satisfy the condition shown by Formula 4.

## EQU4 ## Belt circumference BL4> (n + m) × Ly + (n +
m-1) × G where n <m

In the second modified example apparatus 100B, an apparatus for storing roll paper RB and having a cutting device 73, which is a cutting means for the roll paper RB, is used as an atypical recording medium supply means. With such a configuration, the roll paper RB serving as the recording medium can be cut freely according to the length of the non-standard size image. Therefore, it is possible to avoid a situation where it is necessary to set a non-standard size sheet corresponding to the replaced unit due to the replacement between the small belt unit 20a and the large belt unit 20b.

The printers to which the present invention is applied have been described. However, the scope of the present invention is not limited to these printers, and various modifications are possible.

For example, instead of rotating the intermediate transfer belt 10 on which the first toner image has been transferred one turn and re-transporting the intermediate transfer belt 10 to the transfer nip, the intermediate transfer belt 10 is reversed and re-transported to the transfer nip. Is also good. However,
In the case of such a configuration, it is desirable to provide a contact / separation mechanism for contacting / separating the photosensitive drum 1 (image carrier) and the intermediate transfer belt 10 (recording member holding member).

The image carrier may be a belt type such as a photoreceptor belt, instead of a drum type such as the photoreceptor drum 1.

The intermediate transfer belt 1 is used as an intermediate transfer member.
Instead of a belt type such as 0, an intermediate transfer drum drum or an intermediate transfer roller may be used.

The latent image forming means which is a part of the image forming means is not a laser type exposure apparatus 7 but an LED.
Light exposure means may be used.

The present invention is applicable not only to a digital printer as described in each embodiment but also to an analog image forming apparatus using analog exposure. Of course, it goes without saying that the image forming apparatus is not limited to a printer, but may be a copying machine or a facsimile.

As described above, in the printer and the modified examples of the embodiment, the key operation on the operation panel 60 as the information acquisition means and the size information of the intermediate transfer belt 10 are acquired by the P sensor 60 as the information acquisition means. . Then, the acquired information is sent to the control device E2 as a control means to be recognized. In such a configuration, the control device E2 can appropriately control the driving of the exposure device 7 as the visible image forming device and the double-side transfer device (belt unit and the like) according to the size of the intermediate transfer belt 10. Further, a P sensor 63 is provided as the information acquisition unit, which serves as an identification unit that automatically identifies the size of the intermediate transfer belt 10 attached to the belt unit that forms a part of the double-sided transfer unit. In such a configuration, the size of the intermediate transfer belt 10 is identified by the P sensor 63, so that it is not necessary to input the size information of the belt to the information acquiring unit every time the belt unit is replaced with a belt unit having a different size. Can be. Further, as the intermediate transfer member, an intermediate transfer belt that transports the transfer paper P, which is a recording material, while holding it on the surface thereof while moving endlessly is used. In such a configuration, since the intermediate transfer member uses an intermediate transfer belt whose endless track shape can be freely set by excellent flexibility,
The degree of freedom in layout in the printer body can be improved. Further, by allowing the user to select a belt unit on which the intermediate transfer belt 10 having a length suitable for the user's request is mounted, the time for both-side transfer can be reduced. Further, a belt unit composed of the intermediate transfer belt 10 and rollers serving as a plurality of stretching members for stretching the intermediate transfer belt 10 is replaceable. In such a configuration, the intermediate transfer belt 10 can be integrally replaced as a belt unit together with the plurality of rollers as the tension members.
For this reason, the work of separating the intermediate transfer belt 10 from the plurality of tension members can be omitted, and the exchange workability can be improved. Further, the intermediate transfer belts 10 having different sizes from each other are provided.
The belts having different belt circumferential lengths and having the same belt width BW can be replaced. Although the belt circumferential lengths are different from each other, the intermediate transfer belts 10 having the same belt width BW can be exchanged. With such a configuration, it is possible to avoid a situation in which the photosensitive drum 1 serving as an image carrier must be replaced with one corresponding to the belt width BW when the intermediate transfer belt 10 is replaced. The layout in the housing 101 is set as follows. That is, the length of the housing 1
The layout occupies the same space regardless of the length of the intermediate transfer belt 10 in the belt unit. The belt unit length is a belt unit portion located between the registration roller pair 28 serving as a delivery unit and the heat fixing device 30 serving as a receiving unit. With this configuration, the transfer paper P can be automatically conveyed to the belt unit from the pair of registration rollers 28 to the heating and fixing device 30 via the belt unit. Further, regardless of the length of the intermediate transfer belt 10, the housing of the belt unit 1
Since the space occupied in the area 01 is the same, the belt unit can be replaced without moving the registration roller pair 28 and the heat fixing device 30. These operations for moving can be omitted, and the unit replacement workability can be improved. Although members outside the belt unit are provided in the double-sided transfer means, these members are maintained in the housing 101 so that their positions can be fixed regardless of the circumference of the intermediate transfer belt 10 while maintaining these functions. Layout is set. The members outside the belt unit in the double-sided transfer means include the cleaning device 50 and the transfer charger 1.
7 and the like. In such a configuration, the registration roller pair 28
It is possible to replace not only the heat and fixing device 30 but also the belt unit without moving each member outside the belt unit, thereby further improving the unit replacement workability.
In addition, the backing roller 16 and the driven roller 14
In addition, for the transfer roller 15 as an auxiliary member, etc., a plurality of belt units having different belt circumferential lengths are provided between a plurality of belt units.
The layout settings are set so that the positions in the area are the same. In such a configuration, regardless of the length of the intermediate transfer belt 10, the auxiliary member and the assisted member are used for the outer member whose function is assisted by the auxiliary member in the unit and the outer member assisting the function of the assisted member. It can work reliably. Further, the paper transport path in the double-sided transfer means is exposed by separating the belt unit from the printer main body. In such a configuration, the jam of the transfer paper P in the paper transport path can be easily removed by exposing the paper transport path by separating the belt unit from the printer main body. Further, an opening / closing door 61, which is an opening / closing unit that can be opened / closed, is provided in the housing 101, and the belt unit is held by the opening / closing door 61, and is moved toward and away from the printer main body as the belt unit is opened and closed. In this configuration, by opening and closing the opening and closing door 61 simultaneously with the contact and separation of the belt unit, it is possible to expose not only the paper transport path in the double-sided transfer means but also the surrounding paper transport path. Therefore, it is possible to remove the jam in the paper transport path in the double-sided transfer unit and remove the jam in the surrounding paper transport path by the same operation, and it is possible to improve the jam removal operability. In addition, an opening / closing door 61 that swings around a rotation axis H is used as the opening / closing section. In such a configuration, the opening / closing door 61 serving as the opening / closing portion is not a lid-like member separated from the housing 101 but swings around the rotation axis H. Therefore, it is not necessary to hold or hold the opening / closing unit in the hand after the opening operation or perform a work such as temporary placement. Further, a cleaning device 50 for cleaning toner, which is an image forming substance, attached to the intermediate transfer belt 10 is provided. Therefore, the intermediate transfer belt 1
It is possible to avoid such a situation that the toner image on the photosensitive drum 1 is disturbed or the transfer paper P is stained by the adhesion of the residual toner on the transfer drum P.

The operation of holding the opening / closing unit in the hand after the opening operation or temporarily placing the opening / closing unit in the first modification 100B can be omitted. Further, in the first modified example device 100B, an opening / closing unit that is opened / closed with respect to the printer body by horizontal movement is used. In such a configuration, the belt cleaning device 5
By avoiding leakage of the collected toner due to the overturning of 0, the sealing mechanism for suppressing toner leakage of the belt cleaning device 50 can be simplified.

Further, in the printer and the modified examples of the embodiment, an opening 62 for projecting a part of the belt unit is provided in the housing 101. This makes it possible to mount the large belt unit 20b, which is a relatively large unit that cannot be accommodated in the housing 101, of the plurality of belt units to the printer body.
Specifically, by providing the opening 62, a portion of the large belt unit 20 b that cannot be accommodated is removed from the housing 101 by the opening 6.
It is possible to mount it by protruding it outside through 2. Therefore, the size of the apparatus can be reduced and the cost can be reduced by adjusting the size of the housing 101 to the small belt unit 20a which is the smallest belt unit.
Further, if necessary, only the direct transfer of the toner image from the photosensitive drum 10 to the transfer paper P without the intermediate transfer belt 10 is performed, so that an image is formed only on the first surface of the transfer paper P. ing. With such a configuration, even an image that exceeds the circumference of the intermediate transfer belt 10 can be formed on the first surface of the transfer paper P. Further, a paper feed cassette 26 serving as a supply unit detachable from the housing 101 is provided,
The attachment / detachment work for the printer body and the belt unit exchange work can be performed from the same side (front) of the housing 101. In such a configuration, the sheet cassette 2
6 and the belt unit replacement operation can be performed by accessing the housing 101 from the same direction. Therefore, it is not necessary to separately secure a space around the access housing 101 for both operations, and space can be saved. Further, one (large belt unit 20b) of the plurality of belt units has a belt width BW smaller than the vertical dimension of the B4 size and A
An intermediate transfer belt 10 having a belt peripheral length equal to or greater than three vertical dimensions is provided. In such a configuration, an image can be formed on all the transfer sheets P of A3 size or less using the intermediate transfer belt 10 having a belt width BW shorter than the B4 size vertical dimension. When the large belt unit 20b is used, the following image formation is performed as needed. That is, when images are continuously formed on both sides of two or more transfer papers P, the first toner image is continuously formed on the photosensitive drum 1 for at least two images, and then the second toner is formed. An image is formed continuously. In such a configuration, an image is continuously formed on both surfaces of two or more transfer papers P, so that at least two or more first toner images are continuously and intermediately transferred to the intermediate transfer belt 10 for each rotation. . Then, the second transfer paper P
While the second toner image is continuously transferred directly to the surfaces, the first toner image previously intermediately transferred can be secondarily transferred to each first surface. As a result, the number of rotations of the intermediate transfer belt 10 can be reduced, and the both-side transfer time can be shortened. Also, in the case where images are continuously formed on two or more transfer papers P on one side, the first toner image is continuously formed on the photosensitive drum 1 for at least two images. I have. With this configuration, even when performing single-sided printing on only the first surface on two or more transfer sheets P, the number of rotations of the intermediate transfer belt 10 can be reduced to shorten the transfer time. Further, the intermediate transfer belt 10 of the large belt unit 20b has a belt width BW corresponding to the long side dimension Lx of the fixed size transfer paper P, and is referred to as “belt circumference> n × Ly + (n−1) × G”. Those that satisfy the conditions are provided. In the large belt unit 20b, after two or more images having a half size of the standard-size transfer paper P are continuously transferred onto the intermediate transfer belt 10 continuously, each of the images is reliably transferred onto the transfer paper P continuously fed. Secondary transfer.

Further, the printer of the second modified example apparatus 100B is provided with a roll paper supply device 70 as an irregular recording material supply means for supplying the irregular recording material roll paper RP toward the belt unit. . In such a configuration,
Images can be formed on both sides of the roll paper RP, which is a non-standard recording medium. Further, for the larger large belt unit 20b, the intermediate transfer belt 10 has a belt width BW corresponding to the long side dimension Lx, and
The one satisfying the above condition (4) is provided. With this configuration, it is possible to reliably realize the secondary transfer of the fixed-size images of a larger number than the small belt unit 20a and the secondary transfer of the larger non-standard-size images. Also,
Roll paper RP, which is a recording material wound in a roll shape, is used as the irregular-shaped recording material supply means.
A roll paper supply device 70 having a cutting device 73 for cutting according to the length of the image to be intermediately transferred to 0 is used. With such a configuration, it is possible to avoid a situation in which a non-standard size sheet corresponding to the unit after replacement has to be set due to the replacement between the small belt unit 20a and the large belt unit 20b. . Also, a tandem system is used in which a plurality of photosensitive drums are provided, and toner images of different colors formed on the respective photosensitive drums are superimposed on the intermediate transfer belt 10 and intermediately transferred to form a full-color image. In such a configuration, the formation speed of the full-color image can be greatly reduced as compared with the division system in which only one photosensitive drum is provided to form a full-color image. Also, a plurality of photosensitive drums are arranged in a straight line with each other. In such a configuration, a free space is formed on the side of the belt unit opposite to the side on which the photosensitive drum is disposed. As a result, it is possible to avoid a situation where the photosensitive drum needs to be separated at the same time as the belt unit, thereby simplifying the configuration for separation.
Further, the photosensitive drums are arranged in the vertical direction so that the toner images on the plurality of photosensitive drums are respectively transferred while being superposed while the transfer paper P is transported in the vertical direction. In such a configuration, the belt unit contact / separation (contact / separation with respect to the main body) caused by arranging the photosensitive drums in the horizontal direction is deteriorated, the paper transport path is complicated, and the heat fixing device 30 is disposed in the center of the housing. Heat stagnation can be avoided.

Further, in the printer and the modified examples of the embodiment, an I / O connector (not shown) as a receiving means for receiving a control signal from the personal computer 200 is provided. Further, a control device E2 for controlling the photosensitive drum 1 and the like based on the reception result is also provided. With such a configuration, it is possible to form an image or change image forming conditions based on a control signal from the personal computer 200. Therefore, an image can be obtained by issuing a print command by remote control of the personal computer 200 even from a place remote from the printer main body.

In the belt unit of the embodiment and each of the modified examples, the intermediate transfer belt having a size corresponding to the user's request is provided to the printer main body, so that the double-side transfer unit can be operated in accordance with the user's request. Parts cost can be reduced. Also, the opening 62 of the housing 101
A cover 21 is provided as a case member for covering a portion protruding from the cover 21 and functions as a part of a housing 101 of the printer main body. In such a configuration, the cover member 21 is
By functioning as a part of the housing 101, the amount of material of the housing 101 can be reduced and cost can be reduced. Further, the cover member 21 is provided with circumference information as size information of the intermediate transfer belt 10 inside the cover member 21. With such a configuration, the user can visually recognize the circumference information, and can easily identify the size of the photosensitive drum 10.

[0118]

According to any one of the first to thirty aspects of the present invention, the cost of parts of the double-sided transfer means can be reduced according to a user's request.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a printer according to an embodiment.

FIG. 2 is an enlarged configuration diagram showing a part of a small belt unit and the photosensitive drum 1 of the printer.

FIG. 3 is a partial configuration diagram illustrating a partial configuration of the printer with an opening / closing door opened.

FIG. 4 is a perspective view showing the printer in a state where an opening / closing door is opened.

FIG. 5 is a schematic configuration diagram illustrating the printer with a large belt unit mounted thereon.

FIG. 6 is a schematic diagram showing an intermediate transfer belt of the small belt unit together with A4-size transfer paper held by the intermediate transfer belt.

FIG. 7 shows an example of an intermediate transfer belt,
FIG. 3 is a schematic diagram showing three sizes of transfer paper.

FIG. 8 is a schematic diagram showing an intermediate transfer belt of the same example and two A4 size transfer papers held by the intermediate transfer belt.

FIG. 9 is a schematic diagram illustrating an intermediate transfer belt of a large belt unit of the printer according to the embodiment, together with two A4 size transfer sheets held by the intermediate transfer belt.

FIG. 10 is an exemplary perspective view showing the printer and a personal computer connected to the printer.

FIG. 11 is a perspective view showing the printer with the large belt unit attached.

FIG. 12 is a partial configuration diagram showing a partial configuration of a first modified example device of the printer.

FIG. 13 is a schematic configuration diagram showing another second modified example device.

FIG. 14 is an enlarged configuration diagram illustrating a process unit for yellow in the second modified example apparatus.

FIG. 15 is a configuration diagram illustrating an example of a tandem system in which each photosensitive drum is disposed around a belt unit.

FIG. 16 is a configuration diagram showing an example of a tandem system in which each photosensitive drum is arranged in a horizontal direction above a belt unit.

FIG. 17 is a configuration diagram showing an example of a tandem system in which each photosensitive drum is disposed horizontally below a belt unit.

FIG. 18 shows an example of the intermediate transfer belt of the small belt unit of the apparatus of the second modified example, in which A4 size transfer paper P
FIG.

FIG. 19 shows an intermediate transfer belt of the large belt unit of the second modified example, and A4 size transfer paper P held by the intermediate transfer belt.
FIG.

FIG. 20 is a schematic diagram illustrating an image formed by intermediate transfer using the large belt unit.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 photoconductor drum (image carrier) 2 drum cleaning device 3 static elimination device 4 charging device 5 developing device 6 process unit 7 exposure device 10 intermediate transfer belt 11 drive roller (stretch member) 12, 13, 14, 18 driven roller ( Tension member) 15 transfer roller 16 backing roller 17 transfer charger 20 belt unit 21a small belt unit 21b large belt unit 26 paper cassette (supply means) 27 paper feed roller 28 registration roller pair (transfer section) 30 heat fixing device ( Receiving member) 30a Pressure roller 30b Fixing roller 33 Discharge path 34 Discharge device 40 Stack unit 50 Belt cleaning device 60 Operation panel 61 Opening / closing door 62 Opening 63 P sensor 70 Roll paper supply device (non-standard recording material supply means) 73 Cutting Equipment (cutting means) 100A First Modified Example Device 100B Second Modified Example Device 101 Housing D-axis E1 Electrical equipment E2 Control device (control means and receiving means) F1, F2 Fan H Rotation axis P Transfer paper (recording body) Lx Long side dimension Ly Short side dimension RP Roll paper (non-standard size recording medium)

Continued on the front page F-term (reference) 2H027 DA27 DE02 DE07 DE10 EB04 ED16 ED24 EE07 EF09 EJ15 FA13 HB05 HB16 2H028 BA06 BA07 BA16 BB04 BC01 2H030 AA06 AA07 AB02 AD05 AD17 BB42 BB46 BB56 2H071 BA23A BA29 DA22 DA32 EA04 EA18 2H200 FA12 FA19 GA02 GA12 GA23 GA33 GA47 GB25 GB36 GB44 HA02 HB12 HB22 JA02 JB06 JB13 JB39 JB40 JB42 JB50 JC03 JC09 JC10 JC12 JC20 LA03 LA08 LA13 LA24 LA38 LA40 LB13 LB17 PB

Claims (30)

[Claims] An image carrier for carrying a visible image, a visible image forming means for forming a visible image on the image carrier, and a first image bearing member intermediately transferred from the image carrier onto an intermediate transfer member. While transferring the visual image to one surface of the recording body, the second visible image is transferred from the image carrier to the other surface of the recording body, and the recording body is held on the moving intermediate transfer body. An image forming apparatus comprising: a double-side transfer unit for transferring the intermediate transfer member having a different size; 2. An image forming apparatus according to claim 1, wherein said control means controls said visible image forming means and double-side transfer means.
An image forming apparatus, comprising: an information acquisition unit that acquires the size information of the intermediate transfer body and transmits the information to the control unit. 3. An image forming apparatus according to claim 2, wherein an identification means for identifying a size of said intermediate transfer member mounted on said double-sided transfer means is provided as said information acquisition means. Forming equipment. 4. The image forming apparatus according to claim 1, wherein an intermediate transfer belt is used as the intermediate transfer member, the endless movement of the intermediate transfer belt for holding and transporting the recording material on its surface. Image forming apparatus. 5. The image forming apparatus according to claim 4, wherein the double-sided transfer means is configured such that a belt unit including at least the intermediate transfer belt and a plurality of stretching members for stretching the intermediate transfer belt is replaceable. An image forming apparatus comprising: 6. The image forming apparatus according to claim 5, wherein the two-sided transfer means is configured such that belts having different belt circumferences and the same belt width can be exchanged as the intermediate transfer belts having different sizes. An image forming apparatus comprising: 7. An image forming apparatus according to claim 6, further comprising: a transfer section for transferring a recording medium to said belt unit; and a receiving section for receiving a recording medium from said belt unit. The layout in the housing is set so that the space occupied by the belt unit portion located in the housing of the image forming apparatus main body is the same regardless of the length of the intermediate transfer belt in the belt unit. An image forming apparatus comprising: 8. The image forming apparatus according to claim 7, wherein the positions of the members outside the belt unit can be fixed while maintaining these functions regardless of the circumference of the intermediate transfer belt. An image forming apparatus, wherein a layout in a housing of an image forming apparatus main body is set. 9. An image forming apparatus according to claim 8, wherein an auxiliary member for assisting the function of an external member provided outside said belt unit, or an assisted member for which the external member assists the function, is provided on said belt unit. An image forming apparatus, wherein the position of the auxiliary member or the assisted member in the image forming apparatus main body is the same among a plurality of belt units having different belt circumferential lengths in the unit. 10. The image forming apparatus according to claim 7, 8 or 9, wherein the belt unit is separated from the image forming apparatus main body so that the recording material conveying path in the double-side transfer unit is exposed. An image forming apparatus comprising a transfer unit. 11. The image forming apparatus according to claim 10, wherein
An openable and closable unit is provided on the housing of the image forming apparatus main body, the belt unit is held by the openable and closable unit, and the belt unit is moved toward and away from the image forming apparatus main body with the opening and closing of the open and close unit An image forming apparatus comprising: 12. An image forming apparatus according to claim 11, wherein an opening / closing door swinging around a rotation axis is used as said opening / closing section. 13. An image forming apparatus according to claim 11, wherein a belt cleaning means for cleaning an image forming substance adhered to said intermediate transfer belt is provided in said double-sided transfer means, and said opening / closing unit is used to form an image by horizontal movement. An image forming apparatus using a device that opens and closes with respect to an apparatus main body. 14. An image forming apparatus according to claim 7, 8, 9, 10, 11, 12, or 13, wherein an opening for projecting a part of the belt unit from a housing of the main body of the image forming apparatus is provided.
An image forming apparatus provided in the housing. 15. The method of claim 5, 6, 7, 8, 9, 10, 1.
In the image forming apparatus of any one of 1, 12, 13 and 14, only the direct transfer of the visible image from the image carrier to the recording medium without the intermediate transfer belt is performed as necessary. An image forming apparatus for forming an image only on a surface of the image forming apparatus. 16. The method of claim 5, 6, 7, 8, 9, 10, 1.
The image forming apparatus according to any one of 1, 12, 13, 14 and 15, further comprising a supply unit configured to supply the recording medium contained therein to the belt unit and to be detachably attached to a housing of the image forming apparatus main body. An image forming apparatus, wherein an operation of attaching and detaching the belt unit and an operation of replacing the belt unit can be performed from the same side surface of the housing. 17. The method of claim 5, 6, 7, 8, 9, 10, 1.
In the image forming apparatus of any one of 1, 12, 13, 14, 15 and 16, the belt width is smaller than the vertical size of B4 size and A
An image forming apparatus using the belt unit having the intermediate transfer belt having a belt peripheral length of three or more vertical dimensions. 18. The method of claim 5, 6, 7, 8, 9, 10, 1.
In the case of the image forming apparatus of 1, 12, 13, 14, 15, 16 or 17, when two or more recording materials are continuously formed on both sides with an image having a half or less of the intermediate transfer belt circumferential length, An image forming apparatus, wherein the first visible image is continuously formed on the image carrier for every at least two images, and then the second visible image is continuously formed. 19. The method of claim 5, 6, 7, 8, 9, 10, 1.
1, 12, 13, 14, 15, 16, 17, or 18 in which an image having a half or less of the intermediate transfer belt circumference is continuously formed on two or more recording materials on one side. Wherein the first visible image is continuously formed on the image carrier for at least two images. 20. The image forming apparatus according to claim 18, wherein one of the plurality of belt units is a belt width corresponding to a long side dimension of a fixed-size recording medium as the intermediate transfer belt. And the interval required for continuously transporting the recording body toward the recording medium transport path of the double-sided transfer means is G, an integer of 2 or more is n, and the short side dimension of the recording body is An image forming apparatus characterized by having a condition satisfying a condition of “belt circumference> n × Ly + (n−1) × G” when each is expressed by Ly. 21. The image forming apparatus according to claim 20, further comprising an irregular-shaped recording medium supply means for supplying the irregular-shaped recording medium toward the recording medium transport path. 22. The image forming apparatus according to claim 21, wherein another one of the belt units has a belt width corresponding to the long side dimension as the intermediate transfer belt, and
When an integer of 1 or more is represented by m, “belt circumference> (n
+ M) × Ly + (n + m−1) × G ”. 23. An image forming apparatus according to claim 22, wherein said non-standard recording medium supply means uses a non-standard recording medium wound in a roll shape and is intermediate-transferred to said intermediate transfer belt. An image forming apparatus comprising cutting means for cutting the recording body according to the length of an image. 24. The method of claim 5, 6, 7, 8, 9, 10, 1.
1, 12, 13, 14, 15, 16, 17, 18, 1
An image forming apparatus according to any one of 9, 20, 21, 22, and 23, comprising a plurality of the image carriers, and superimposing a visible image formed on each of the image carriers on the intermediate transfer belt for intermediate transfer. An image forming apparatus for forming a superimposed image. 25. The image forming apparatus according to claim 24, wherein a plurality of said image carriers are arranged in a straight line with each other. 26. The image forming apparatus according to claim 25, wherein the visible images on the plurality of image carriers are transferred while being superimposed while transferring the recording body in the vertical direction.
An image forming apparatus wherein each image carrier is arranged in a vertical direction. 27. The method of claim 1, 2, 3, 4, 5, 6, 7,
8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23, 24, 2
5 or 26, in the image forming apparatus, receiving means for receiving a control signal from a computer, and control means for controlling the image carrier, the visible image forming means, and the two-sided transferring means based on the result of the receiving means. An image forming apparatus comprising: 28. A belt unit comprising: an intermediate transfer belt for intermediately transferring a visible image in a series of image forming processes; and a plurality of stretching members for stretching the intermediate transfer belt. 6, 7, 8, 9, 10, 11, 12, 13, 1
4, 15, 16, 17, 18, 19, 20, 21, 2,
A belt unit used in the image forming apparatus of 2, 23, 24, 25 or 26. 29. The belt unit according to claim 28, wherein:
The image forming apparatus according to claim 14, further comprising a case member that covers at least a portion of the image forming apparatus that protrudes from the opening, and that functions as a part of a housing of the image forming apparatus main body. Belt unit. 30. The belt unit according to claim 29,
A belt unit, wherein size information of the intermediate transfer belt inside the case member is added to the case member.