JP2001350392A - Printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printer which precisely reproduces positional relationship between a photoreceptor unit and an intermediate transfer unit. SOLUTION: In the printer, the central shaft 14a of a photoreceptor follower roll 14 of the photoreceptor unit 3 is situated almost at an intermediate position between the transfer rolls 21a and 21b of the intermediate transfer unit 6. Accordingly, a press contact force F1 applied from the intermediate transfer unit 6 to the photoreceptor unit 3 acts toward the center of the central shaft 14a perpendicularly to the insertion direction W of the photoreceptor unit 3. The units 3 and 6 are fixed by a locking member, which prevents both the units 3 and 6 from being rotated about the central shaft 14a. This firmly fixes the units 3 and 6 without altering the positional relationship between the units 3 and 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a printing apparatus which is set to transfer an image formed on a photoreceptor unit to a sheet via an intermediate transfer unit.

[0002]

2. Description of the Related Art In general, an electrophotographic image forming apparatus (copying machine, facsimile machine, printer, etc .; hereinafter simply referred to as a printer) is mainly composed of a photoconductor, a charger, an exposing device, a developing device, and a fixing device. Equipment. The charging device uniformly charges the surface of the photoconductor. The exposure device exposes a charged photoconductor surface according to image information to form an electrostatic latent image. The developing device develops the electrostatic latent image to generate a toner image.
The fixing device fixes the toner image on the sheet.

In this type of printer, a color printer capable of forming a color image using four color (yellow, magenta, cyan, and black) toners has been developed. This color printer includes a photosensitive member and an intermediate transfer member. Then, four toner images corresponding to the respective colors are generated on the photosensitive member, and these toner images are superimposed on the intermediate transfer member and transferred. As a result, a color toner image is formed on the intermediate transfer member. The toner image is set so as to be transferred and fixed on a sheet.

In such a color printer, the photosensitive member and the intermediate transfer member are consumable members. Therefore, it is necessary to remove it at a predetermined time and perform inspection and replacement (maintenance work). At this time, the photoconductor and the intermediate transfer body are inserted (re-inserted) into the printer, but if the photoconductor and the intermediate transfer body are correctly mounted and the positional relationship between them is not accurately reproduced, the image The formation cannot be performed well.

Therefore, conventionally, a photoreceptor / intermediate transfer member is unitized, and a positioning member is provided in the printer, so that accurate mounting of them can be realized.

[0006]

However, when the photosensitive member and the intermediate transfer member are formed in one unit, there are the following problems. That is, in this case, both the photosensitive member and the intermediate transfer member (entire unit) are replaced at the same time. However, since these service lives are different from each other, at the end of one service life, the other members that can still be used are discarded, and the use cost of the color printer increases. In addition, if the unit is replaced in accordance with the longer service life, it goes without saying that a good image cannot be formed.

On the other hand, when the photosensitive member and the intermediate transfer member are separately unitized, there is no economic problem at the time of replacement as described above. However, the positional relationship between the two units must be accurately reproduced. These consumables need to be replaced in large copiers / printers.
It is designed to be performed by servicemen who specialize in maintenance and inspection. However, in a small printer, it is necessary to replace it by the user himself. Therefore, when it is difficult to mount the unit, there is a problem that not only the image forming quality is deteriorated, but also in the worst case, the apparatus is broken down.

The present invention has been made to solve the above-mentioned conventional problems. An object of the present invention is to provide a printing apparatus capable of accurately reproducing a mutual positional relationship between a photoconductor unit and an intermediate transfer unit.

[0009]

In order to achieve the above object, a printing apparatus (printing apparatus) according to the present invention includes an image forming unit and an intermediate transfer unit which are arranged so as to be in contact with each other. A printing apparatus which is set to perform printing using the image transferred to the intermediate transfer unit after transferring the image formed on the forming unit to the intermediate transfer unit at a contact portion between the two units,
While one of the two units has a projection, the other unit has a locking piece having a locking groove, and the projection is inserted into the locking groove of the locking piece. The direction of the pressing force acting on the unit having the projection from the unit having the locking piece at the contact portion of the two units, and the direction of the projection with respect to the locking groove is set. The angle formed with the insertion direction is set to 90 degrees or less.

The printing apparatus has an image forming unit provided with an image forming body (photoreceptor and the like) and an intermediate transfer unit provided with an intermediate transferring body for temporarily holding an image of the image forming unit. are doing. The two units are brought into contact with each other to transfer the image on the image forming body to the intermediate transfer body, and to further print (transfer and fix) the image on the intermediate transfer body onto a sheet. . Such a printing apparatus can be suitably used, for example, when a plurality of images are generated using a plurality of image forming bodies and these images are to be printed on a sheet in a superimposed manner.

In this printing apparatus, one of the two units has a projection. Further, the other unit is provided with a locking piece having a locking groove. When these units are installed in the printing apparatus, the projections are inserted into the locking grooves of the locking pieces so that the two units can be connected.

In this printing apparatus, since both units are brought into contact with each other to transfer an image to the intermediate transfer member, a pressing force acts between the two units at the contact portion. Therefore, in order to prevent the displacement of the unit due to such a pressing force, in the present printing apparatus, the direction of the pressing force acting on the unit having the projection from the unit having the locking pieces,
The angle between the locking groove and the insertion direction of the projection is set to 90 degrees or less.

That is, the above two units, the contact portion,
By adjusting the formation positions of the locking pieces, the projections, and the like, the pressure contact force is set so as not to act in the direction opposite to the insertion direction of the projections (the direction in which both units are separated). As a result, the two units can be firmly fixed without shifting their positional relationship.

Usually, the image forming unit is mounted on the printing apparatus after the intermediate transfer unit. Further, when the unit having the projection is mounted after the unit having the locking piece, the connection between the two units can be performed smoothly. For this reason, in the present printing apparatus, it is preferable that the unit having the protruding portion be the image forming unit and the unit having the locking piece be the intermediate transfer unit.

The image forming unit of the printing apparatus includes an image forming belt as an image forming body for forming an image and a pair of rollers for stretching and rotating the image forming belt on a frame or the like. It can be configured by fixing. Similarly, the intermediate transfer unit can be configured by fixing an intermediate transfer belt as an intermediate transfer body for holding an image and a roller pair for stretching and rotating the intermediate transfer belt to a frame or the like. .

In this case, it is preferable to use the central axis of one of the rollers of the image forming unit as the projection. Preferably, the locking piece having the locking groove is formed on the frame of the intermediate transfer unit. In this case, the projections and the locking pieces can be easily formed. In the image forming unit, it is preferable to use a driven roller whose central axis does not rotate as a roller that uses the central axis as a protrusion (hereinafter, referred to as a fixed roller).

Further, in the above configuration, the intermediate transfer belt of the intermediate transfer unit is provided at the contact portion between the two units.
It is preferable that the setting is such that the image forming belt is pressed against the fixed roller of the image forming unit. In this configuration, the projection of the image forming unit, which is the connecting portion between the two units, is made adjacent to the contact portion between the units. Thereby, the contact portion can be stabilized, and the image transfer from the image forming belt to the intermediate transfer belt can be favorably performed.

In this configuration, it is preferable that a contact portion for pressing the intermediate transfer belt against the image forming belt is provided at a contact portion between the two units. As a result, the two belts can be reliably brought into contact with each other, so that the image transfer from the image forming belt to the intermediate transfer belt can be performed more favorably.

Further, the pressure contact portion can be constituted by a pair of pressure contact rollers for supporting the intermediate transfer belt with the contact portion of the two units interposed therebetween. In this case, it is preferable that the line connecting the two rollers in the pressure roller pair is substantially parallel to the insertion direction of the projection into the locking groove. With this configuration, the pressure contact can be performed without hindering the rotation of the intermediate transfer belt.

In this case, the substantially middle portion of the pair of pressure contact rollers is positioned at the same position as the protrusion (the contact portion of the unit) in the direction of insertion of the protrusion into the locking groove.
Alternatively, it is preferable to be located on the upstream side of the projection (the insertion opening side of the locking groove is the upstream side, and the deep side of the locking groove is the downstream side).

In this configuration, the intermediate transfer belt acts like a string whose ends are fixed to the pressure roller pair. Therefore, the direction of the pressing force from the intermediate transfer belt (the pressing force from the intermediate transfer unit) depends on the positional relationship between the intermediate portion of the pressing roller pair and the protrusion (contact portion) (in the direction in which the protrusion is inserted into the locking groove). Relationship along the position). That is,
When the intermediate portion of the pressure roller pair is located downstream of the protrusion (contact portion), a component that tends to move the protrusion to the upstream side (the direction opposite to the insertion direction of the protrusion) is added to the pressing force. Is not preferred.

On the other hand, when the intermediate portion of the pressure roller pair is located at the same position as the projection (contact portion) or at the upstream side as in the above configuration, the projection is moved to the upstream side. The component to be caused does not occur. Thereby, both units can be firmly fixed without displacing the mutual positional relationship.

Further, a pressure roller for supporting the intermediate transfer belt at a contact portion between the two units may be used as the pressure contact portion. In this case, it is preferable that the pressing roller be located at the same position as the protrusion (contact portion) or at the upstream side of the protrusion (contact portion) in the insertion direction of the protrusion.

That is, when the pressing roller is located downstream of the protrusion (contact portion), a component for moving the protrusion to the upstream side (opposite to the insertion direction of the protrusion) is added to the pressing force. Direction component), which is not preferable.
On the other hand, when the pressing roller is located at the same position as the protruding portion (contact portion) or on the upstream side as in the above configuration, a component for moving the protruding portion to the upstream side occurs. Absent. Thereby, both units can be firmly fixed without displacing the mutual positional relationship.

[0025]

[First Embodiment] A first embodiment of the present invention will be described. FIG. 2 is an explanatory diagram illustrating a configuration of the color printer (the present printer) according to the present embodiment. This printer forms a color image on predetermined recording paper (sheet) in accordance with image data transmitted from the outside. Then, as shown in FIG. 2, an optical unit 1, a developing unit 2, a photoconductor unit 3,
It has an intermediate transfer unit 6, a second cleaner unit 7, a fixing unit 8, a paper transport path L, a paper feed tray 9, and a paper discharge tray 10.

The photoreceptor unit (image forming unit) 3
It is located (mounted) almost in the center of the printer,
The photoconductor belt 13 includes a photoconductor driven roller 14, a photoconductor drive roller 15, a charger 4, and a first cleaner unit 5.

The photoreceptor belt 13 is an electrostatic latent image carrier of the printer having an endless belt shape. The rollers 14 and 15 stretch the photoconductor belt 13 and
It is driven to rotate in the direction. The charger 4 is a charger type charger for uniformly charging the surface of the photoreceptor belt 13 to a predetermined potential. The first cleaner unit 5 includes a photosensitive belt 13 after development and image transfer.
The toner remaining on the surface is removed and collected. The configuration of the photoconductor unit 3 will be described later in detail.

The optical unit 1 is a laser scanning unit (LSU) in the present printer, which includes a laser irradiation unit 11 and a reflection mirror 12. Then, the charged photosensitive belt 13 has a function of forming an electrostatic latent image corresponding to image data on its surface by exposing the charged photosensitive belt 13 with laser light. The image data handled by the printer corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y).
Therefore, the optical unit 1 is set so as to sequentially form four types of latent images corresponding to each color on the photoreceptor belt 13.

The developing section 2 develops the electrostatic latent image formed on the photosensitive belt 13 to generate a toner image.
As shown in FIG. 2, the developing unit 16 includes a developing unit 16 including developing units 16a to 16d, and a cam unit 17 including detaching cams 17a to 17d.

The developing units 16a to 16d are provided with the photosensitive belt 1
3 is provided so as to be capable of coming and going. Then, by contacting the photoreceptor belt 13, the latent images on the photoreceptor belt 13 are developed with K, C, M, and Y toners, respectively.
It has a function of generating a toner image on the photoreceptor belt 13.

The contact / disengagement cams 17a to 17d are connected to the developing device 16a.
To 16d to control the state of contact with the photoreceptor belt 13. That is, the detachment cams 17a to 17d
Selects one of the developing units 16 a to 16 d according to the color set for the latent image on the photoconductor belt 13 and makes the photoconductor belt 13 come into contact with it. The cam unit 17 is provided so as to rotate about the point K, which will be described later.

The intermediate transfer unit 6 disposed below the photosensitive unit 3 includes a transfer belt driving roller 18, a transfer belt tension roller 19, an intermediate transfer belt 20,
Transfer rollers 21a and 21b are provided. Roller 18
Reference numeral 19 denotes a device that stretches the intermediate transfer belt 20 and drives the intermediate transfer belt 20 to rotate in the direction of arrow B. Transfer rollers 21a and 21b
Is used to transfer the toner image on the photosensitive belt 13 to the intermediate transfer belt 2.
0 is transferred.

The intermediate transfer belt 20 is a photosensitive belt 13
This is an intermediate transfer member of the present printer, which is provided so as to come into contact with the intermediate transfer member. The color toner image (multicolor toner image) is temporarily held by sequentially superimposing and transferring the toner images of each color formed on the photoreceptor belt 13.

The toner remaining on the surface of the photoreceptor belt 13 without being transferred to the intermediate transfer belt 20 is removed and collected by the first cleaner unit 5 provided on the upper part of the photoreceptor unit 3. Have been. In addition,
The detailed configuration of the intermediate transfer unit 6 will be described later.

The paper feed tray 9 is a tray for storing sheets (recording paper) used for printing, and is provided on the outer wall of the printer. The paper discharge tray 10 provided at the top of the printer is a tray on which printed sheets are placed. The printer also includes a sheet in the paper feed tray 9 and an intermediate transfer unit 6.
A paper transport path L for feeding the paper to the paper discharge tray 10 via the printer and the fixing unit 8 is provided. Further, a pickup roller 22, a registration roller 23, a sheet transfer roller 24, a fixing unit 8, and a transport roller 25 are arranged near the trays 9 and 10 and the sheet transport path L.

The transport roller 25 facilitates sheet transport.
It is a small roller for assisting, and a plurality of rollers are provided along the paper transport path L. Pickup roller 22
Reference numeral denotes an intake roller provided at the rear end of the paper feed tray 9 and supplies sheets from the paper feed tray 9 to the paper transport path L one by one.

A pre-registration detection switch (not shown) is provided between the pickup roller 22 and the registration roller 23. The pre-registration detection switch detects that a sheet being conveyed toward the paper conveyance path L has passed a predetermined position, and outputs a prescribed detection signal.

The registration roller 23 temporarily holds the sheet being conveyed along the sheet conveyance path L. Then, it has a function to convey the sheet to the sheet transfer roller 24 with good timing in accordance with the rotation of the intermediate transfer belt 20 so that the multicolor toner image on the intermediate transfer belt 20 can be transferred onto the sheet satisfactorily.

That is, the registration roller 23 conveys the sheet such that the leading end of the multicolor toner image on the intermediate transfer belt 20 is pressed against the leading end of the printing range of the sheet based on the detection signal output from the pre-registration detection switch. Is set to

The sheet transfer roller 24 is set to rotate while sandwiching the sheet together with the intermediate transfer belt 20. Then, the multicolor toner image on the intermediate transfer belt 20 is transferred to a sheet using the power of a high-voltage power supply (not shown).

The toner remaining on the surface of the intermediate transfer belt 20 without being transferred to the sheet is transferred to the intermediate transfer unit 6.
Is set so as to be removed and collected by the second cleaner unit 7 provided on the side of the. Note that this second
The cleaner unit 7 is provided so as to be detachable from the intermediate transfer unit 6 (the intermediate transfer belt 20).

The fixing unit 8 includes a heat roller 31, a driving roller 32, and a driven roller 33. The heat roller 31 and the driven roller 33 rotate with the sheet interposed therebetween by the driving force of the driving roller 32. Further, the heat roller 31 is set to have a predetermined fixing temperature, and the multicolor toner image transferred to the sheet is melted and pressed by thermocompression bonding of the sheet together with the driven roller 33, and the heat roller 31 is pressed against the sheet. It has the function of heat fixing.

The sheet after fixing the multicolor toner image is
The sheet is conveyed along the sheet conveying path L by the conveying rollers 25, passes through the rear side of the contact / disengagement cams 17a to 17d, and is turned upside down (with the multicolor toner image facing downward).
It is discharged above zero.

Next, the detailed structure of the photosensitive unit 3 and the intermediate transfer unit 6 will be described. FIG.
FIG. 3 is an explanatory diagram showing the configuration of units 3 and 6 in detail.
As shown in this figure, the photoconductor unit 3 and the intermediate transfer unit 6 include a portion of the photoconductor belt 13 that is stretched around the photoconductor driven roller 14 and the intermediate transfer belt 20.
Are arranged so as to abut on the contact portion P.

That is, both units 3 and 6 are arranged such that the intermediate transfer belt 20 presses the photosensitive belt 13 against the photosensitive follower roller 14 at the contact portion P. The printer is set so that the toner image of each color formed on the photoreceptor belt 13 is transferred to the intermediate transfer belt 20 at the contact portion P. In this contact portion P, both units 3
A pressing force described later acts between the six.

As shown in FIG. 3, the photosensitive unit 3
The above-described charger 4, first cleaner unit 5, photosensitive member driven roller 14, photosensitive member driving roller 15, tension roller 42 and auxiliary roller 43 are connected to frame 41.
It is a configuration fixed to. Also, the photoconductor unit 3
The rollers 14, 15, 42, and 43 are rotatably supported on the frame 41.

The tension roller 42 is a roller 14.1
This is for keeping the tension (tension) of the photoreceptor belt 13 stretched around 5 at a constant value. The auxiliary roller 43 is for smoothing the rotation of the photoreceptor belt 13.

The photoconductor driving roller 15 is set so as to rotate together with the rotating shaft 15a by the driving force of a motor (not shown), and to rotate the photoconductor belt 13 in the direction A. On the other hand, the photosensitive member driven roller 14
With 3, the rotation is made about the central axis 14a. As a result, the photoconductor belt 13 rotates smoothly without slipping in accordance with the rotation of the photoconductor drive roller 15.

As shown in FIG. 3, the intermediate transfer unit 6 includes a transfer belt driving roller 18, a transfer belt tension roller 19, an intermediate transfer belt 20, and transfer rollers 21a and 21b fixed to a frame 51. Configuration. The rollers 18, 19, 21 a, 21 b of the intermediate transfer unit 6 are rotatably supported on the frame 51.

Transfer Roller (Pressing Contact Part; Pressing Roller Pair) 21
Reference numeral a · 21b is a metal (for example, stainless steel) roller having a diameter of 8 to 10 mm. At substantially equal positions before and after the contact portion P on the inside (back side) of the intermediate transfer belt 20,
They are provided at intervals of 10 to 60 mm. Also,
To the transfer rollers 21a and 21b, a high voltage having a polarity (positive) opposite to the charging polarity (negative) of the toner image is applied from a high voltage power supply 53. The high voltage is used to transfer the toner image on the photosensitive belt 13 to the intermediate transfer belt 20.

The intermediate transfer belt 20 is an endless belt made of a polycarbonate film having a thickness of 100 μm, and includes a transfer belt driving roller 18, a transfer belt tension roller 19, and transfer rollers 21a and 21b.
Stretched (supported) by.

The transfer belt driving roller 18 rotates together with the rotating shaft 18a by the driving force of a motor (not shown).
The intermediate transfer belt 20 is set to be driven to rotate in the B direction. On the other hand, the transfer belt tension roller 19
Rotates about the central axis 19a together with the intermediate transfer belt 20. Thus, the intermediate transfer belt 20 rotates smoothly without slipping according to the rotation of the transfer belt driving roller 18.

The intermediate transfer belt 20 includes a transfer belt tension roller 19 and transfer rollers 21a and 21.
The predetermined transfer tension is given by b. Due to this tension, the intermediate transfer belt 20 moves the belt 1
At a contact portion P of 3.20, the photoconductor belt 13 (the center of the photoconductor driven roller 14) is 100 to 300
The contact force is g.

Next, the connection state between the photosensitive unit 3 and the intermediate transfer unit 6 will be described. As mentioned above,
The photoreceptor unit 3 and the intermediate transfer unit 6 make contact with the photoreceptor belt 13 and the intermediate transfer belt 20 at the contact portion P (the intermediate transfer belt 20 is contacted with the photoreceptor driven roller 14 by the photoreceptor belt Is pressed).

FIG. 4 is an explanatory diagram showing the intermediate transfer unit 6 detached from the printer. As shown in this figure, a locking piece 5 having a U-shaped locking groove (recess) H is provided on the side of the frame 51 in the intermediate transfer unit 6.
2 are provided. Then, as shown in FIG. 3, the locking piece 52 is provided so as to lock the locking groove H on the central shaft (projection) 14 a of the photosensitive member driven roller 14.

The locking groove H in the locking piece 52 is formed of side walls h1 and h2, which are parallel to each other and have the same length, and a semicircular bottom h formed at the end of the side walls h1 and h2. Have. In addition, the side walls h1 and h2
a and 21b extend in a direction parallel to a line connecting the two. Further, the distance between the side walls h1 and h2 (the width of the locking groove H).
Is set to substantially the same length as the thickness of the central axis 14a. Further, the bottom portion h of the locking groove H has the same shape (radius) as the outer periphery of the central shaft 14a so as to be able to adhere to the central shaft 14a without any gap.

The locking piece 52 is provided such that when the central shaft 14a is locked in the locking groove H, the center of the central shaft 14a is disposed substantially at the center of the transfer rollers 21a and 21b. ing. Therefore, the contact portion P between the photoreceptor belt 13 and the intermediate transfer belt 20 is transferred to the transfer rollers 21a and 21b.
Is located approximately in the middle. The position of the center on the central axis 14a is the side wall h1 · h
2 is a position along the extending direction, that is, a position along the insertion direction of the photoconductor unit 3. The direction of insertion of the photoconductor unit 3 is the same as that of the transfer rollers 21a and 21b.
Is a direction parallel to the line connecting.

Further, the intermediate transfer belt 20 between the transfer rollers 21a and 21b acts in the same manner as a string whose ends are fixed to the transfer rollers 21a and 21b. Therefore, as shown in FIG. 1, the pressing contact force F1 (the pressing contact force F1 acting on the photoconductor unit 3 from the intermediate transfer unit 6) caused by the tension of the intermediate transfer belt 20 causes the transfer rollers 21a and 21b to contact the transfer roller 21a and 21b at the contact portion P. It works toward the central axis 14a of the photoreceptor driven roller 14 from a direction perpendicular to the connecting straight line.

That is, in the present printer, the pressing force F1 is applied to the center shaft 14a of the photosensitive member driven roller 14 with respect to the center axis 14a.
The center axis 14a is set so as to press against the side wall h1 perpendicularly to the insertion direction W of the photoconductor unit 3 (the direction in which the two side walls h1 extend in the locking groove H).

The unit 3.6 is fixed to the printer by a lock member (not shown) for preventing the entire unit 3.6 from rotating about the central shaft 14a. Next, attachment and detachment of the units 3 and 6 will be described. When checking or replacing each unit in this printer, as shown in FIG.
The cam unit 17 is rotated outward about a point. As a result, each unit can be removed from the printer in the order of the developing unit 16, the photoconductor unit 3, and the intermediate transfer unit 6.

When each unit is to be mounted again on the printer, the cam unit 17 is similarly rotated.
Then, first, the intermediate transfer unit 6 is mounted on the printer. Then, as shown in FIG. 6, the photoconductor unit 3 is attached to the printer such that the center shaft 14a is locked in the locking groove H of the locking piece 52 in the intermediate transfer unit 6. Thereafter, the developing unit 16 is mounted.

As described above, in the present printer, the center shaft 14 of the photosensitive member driven roller 14 in the photosensitive member unit 3 is used.
a is set so as to be disposed substantially in the middle of the transfer rollers 21a and 21b. Therefore, the contact portion P between the photoreceptor belt 13 and the intermediate transfer belt 20 is
a.21b is located substantially in the middle.

For this reason, the pressing force F1 (see FIG. 1) acting on the photosensitive unit 3 from the intermediate transfer unit 6 is
Is set to work so as to press the center axis 14a against the side wall h1 in the direction in which the two side walls h1 extend, that is, perpendicular to the insertion direction W of the photoconductor unit 3.

The unit 3.6 is fixed to the printer by a lock member (not shown) for preventing the entire unit 3.6 from rotating about the central axis 14a. Thus, in the present printer, the units 3 and 6 can be firmly fixed without shifting the positional relationship between the units.

That is, when the photoconductor unit 3 and the intermediate transfer unit 6 are fixed to the printer, the center axis 1
When the transfer roller 4a is located on the transfer roller 21a side (downstream in the insertion direction W) from the center of the transfer rollers 21a and 21b, the contact portion P between the photoreceptor belt 13 and the intermediate transfer belt 20 also
It is located on the transfer roller 21a side.

As described above, the transfer roller 21a
The intermediate transfer belt 20 between the transfer rollers 21b
Acts like a string with the end fixed to 21b. For this reason, when the contact portion P is located on the transfer roller 21a side, the direction of the pressing force (the pressing force acting on the photoconductor unit 3 from the intermediate transfer unit 6) due to the tension of the intermediate transfer belt 20 and The angle between the photoconductor unit 3 and the insertion direction W is greater than 90 degrees. Therefore, the pressing force against the photoconductor unit 3 is a component in a direction opposite to the insertion direction W of the photoconductor unit 3 (a component in a direction in which the photoconductor unit 3 is removed; And the units 3 and 6 cannot be stably fixed.

On the other hand, as in the present printer, the central shaft 14
When a is disposed at an intermediate portion between the transfer rollers 21a and 21b, a contact portion P between the photoreceptor belt 13 and the intermediate transfer belt 20 is also located at an intermediate portion between the transfer rollers 21a and 21b. Therefore, the angle between the pressing force F1 (see FIG. 1) acting on the photoconductor unit 3 from the intermediate transfer unit 6 and the insertion direction W of the photoconductor unit 3 is 90 degrees. For this reason, since the pressing force F1 does not have a component in the direction in which the photoconductor unit 3 is removed, the units 3.6 can be firmly fixed without displacing the mutual positional relationship.

The center shaft 14a is connected to the transfer roller 21a.
When the transfer roller 21b is disposed on the transfer roller 21b side (upstream side in the insertion direction W) from the center of the transfer roller 21b, the contact portion P between the photosensitive belt 13 and the intermediate transfer belt 20 is also
Located on the side. Therefore, the angle between the pressing force acting on the photoconductor unit 3 from the intermediate transfer unit 6 and the insertion direction W of the photoconductor unit 3 is smaller than 90 degrees.

For this reason, the pressing force against the photoconductor unit 3 is a component in the same direction as the insertion direction W of the photoconductor unit 3 (a component that presses the center shaft 14a against the bottom h of the locking groove H).
Will have. Therefore, similarly to the case where the center shaft 14a is arranged at the center of the transfer rollers 21a and 21b, the units 3 and 6 can be firmly fixed without shifting the positional relationship between them.

Accordingly, in the present printer, when the center shaft 14a of the photosensitive member driven roller 14 of the photosensitive unit 3 is locked in the locking groove H, the center of the center shaft 14a is substantially intermediate between the transfer rollers 21a and 21b. It can be said that it is preferable to provide the locking piece 52 of the intermediate transfer unit 6 so as to be disposed on the transfer roller 21b side (upstream side in the insertion direction W) from the portion or substantially the intermediate portion. That is,
In this printer, the pressing force acting on the photoconductor unit 3 from the intermediate transfer unit 6 and the insertion direction W of the photoconductor unit 3
So that the angle formed by the locking pieces 52 is 90 degrees or less.
It is preferable to adjust the installation position of (or the center axis 14a).

[Embodiment 2] A second embodiment of the present invention will be described. In the present embodiment, members having the same functions as the members described in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The color printer according to the present embodiment (this printer) is different from the color printer shown in the first embodiment in that the driven rollers 61a and 61b are used instead of the transfer rollers 21a and 21b as shown in FIG. 61b. Furthermore, this printer has both units 3
6, a press-contact transfer roller (press-contact portion; press-contact portion) for pressing the intermediate transfer belt 20 against the photosensitive belt 13.
The intermediate transfer unit 6 has a pressing roller 62.

The driven rollers 61 a and 61 b assist the rotation of the intermediate transfer belt 20. The pressure transfer roller 62 has a conductive elastic material (for example, EPD) on its surface.
M, urethane foam, etc.) and a roller having a diameter of 8 to 10 mm, and is provided at the center of the driven rollers 61a and 61b inside (back side) of the intermediate transfer belt 20, as shown in FIG.

A high voltage of a polarity (positive) opposite to the charging polarity (negative) of the toner image is applied to the pressure transfer roller 62 from a high voltage power supply 54. The high voltage is used to transfer the toner image on the photosensitive belt 13 to the intermediate transfer belt 20.

As shown in FIG. 7, the pressure transfer roller 62 is perpendicular to the insertion direction W of the intermediate transfer unit 6 from the back side (inside) of the intermediate transfer belt 20 at the center of the driven rollers 61a and 61b. Direction, 500-10
It is set so as to give a pressing force F2 of 00 g.

That is, in the present printer, the pressing force F2 acting on the photoreceptor unit 3 from the intermediate transfer unit 6 is applied by the pressing transfer roller 62. The pressure contact force F2 is controlled by the driven rollers 61a and 61a.
1b, the insertion direction W of the intermediate transfer unit 6
And it is set to work in the direction perpendicular to.

Further, in this printer, the first embodiment
Similarly to the color printer shown in FIG.
The center shaft 14a of the photosensitive member driven roller 14 is disposed at a substantially intermediate portion between the driven rollers 61a and 61b. Therefore, the above-described pressing force F2 acts from the direction perpendicular to the insertion direction W of the photoconductor unit 3 toward the central axis 14a of the photoconductor driven roller 14. That is, in this printer, the pressing force F2 is
The center axis 14a is perpendicular to the insertion direction W of the photoconductor unit 3 with respect to the center axis 14a of the photoconductor driven roller 14.
1 (see FIG. 4).

The unit 3.6 is fixed to the printer by a lock member (not shown) for preventing the entire unit 3.6 from rotating about the central shaft 14a. Thus, in the present printer, the units 3 and 6 can be firmly fixed without shifting the positional relationship between the units.

That is, as shown in FIGS. 8 and 9,
If the pressure transfer roller 62 is located on the driven roller 61a side (downstream of the insertion direction W in the photoconductor unit 3; L side of the line segment X) from the center of the driven rollers 61a and 61b, the photoconductor unit It can be said that it is difficult to stably fix 3. Note that the line segment X in these figures
Is a central axis 1 perpendicular to the insertion direction W of the photoconductor unit 3.
This is a line segment passing through the center of 4a.

That is, as shown in FIG. 8, even when the pressing force F2 of the pressing transfer roller 62 is directed toward the center of the center shaft 14a, the pressing transfer roller 62 is located on the L side of the line segment X. The angle θ between the insertion direction W of the photoconductor unit 3 and the pressing force F2 becomes larger than 90 degrees. Therefore, the pressing force F2 is a component F2a in the direction opposite to the insertion direction W of the photoconductor unit 3 (a component in a direction in which the photoconductor unit 3 is removed;
A component that separates the central shaft 14a from the bottom h (see FIG. 4) of the locking groove H is provided, and the photoconductor unit 3 cannot be stably fixed.

As shown in FIG. 9, even when the angle θ between the pressing force F2 of the pressing transfer roller 62 and the insertion direction W of the photosensitive unit 3 is 90 degrees, the pressing transfer roller 62 Is positioned on the L side, the pressing force F2 causes the photosensitive member unit 3 to apply a component force F2b toward the center of the central axis 14a and a component force F2c opposite to the insertion direction W of the photosensitive member unit 3. Works. For this reason, it is impossible to stably fix the photoconductor unit 3.

On the other hand, in this printer, the pressure contact transfer roller 62 is located at the center of the driven rollers 61a and 61b, and furthermore, the angle θ between the pressure contact force F2 of the pressure contact transfer roller 62 and the insertion direction W of the photosensitive member unit 3. Is 90 degrees. Therefore, no force is applied to the photoconductor unit 3 in the direction opposite to the insertion direction W, so that the units 3 and 6 can be firmly fixed without displacing the mutual positional relationship.

As shown in FIGS. 10 and 11,
If the pressure transfer roller 62 is located on the driven roller 61b side (upstream in the insertion direction W of the photosensitive unit 3; R side of the line segment X) from the center of the driven rollers 61a and 61b, the unit 3. 6 can be firmly fixed without shifting their positional relationship.

That is, as shown in FIG. 10, when the pressing force F2 of the pressing transfer roller 62 is directed toward the center of the central shaft 14a and the pressing transfer roller 62 is located on the R side of the line X. The angle θ between the insertion direction W of the photoconductor unit 3 and the pressing force F2 becomes smaller than 90 degrees. Therefore, the pressing force F2 has a component F2d (a component that presses the center shaft 14a against the bottom h of the locking groove H) in the same direction as the insertion direction W of the photoconductor unit 3. Therefore, the center axis 14a
The photoconductor unit 3 can be stably fixed in the same manner as when the photoconductor unit 3 is disposed at the center of the transfer rollers 21a and 21b.

As shown in FIG. 11, the pressing force F2 of the pressing transfer roller 62 and the insertion direction W of the photosensitive unit 3
Is 90 degrees and the pressure transfer roller 62 is positioned on the R side of the line segment X, the pressure force F2 causes the photosensitive member unit 3 to move toward the center of the central axis 14a. A force F2b and a component force F2e in the same direction as the insertion direction W of the photoconductor unit 3 act. Therefore, similarly to the case shown in FIG. 10, the photoconductor unit 3 can be stably fixed.

As described above, in the present printer, the installation position of the pressure transfer roller 62 (the position along the insertion direction W of the photoconductor unit 3) is set at the position corresponding to the center of the center shaft 14a. It can be said that the center or the driven roller 61b side from the center (the upstream side in the insertion direction W in the photoconductor unit 3; the R side of the line segment X) is preferable.

In the first and second embodiments, the engaging portion 52
Is provided in the intermediate transfer unit 6, and the central shaft 14 a of the photoconductor unit 3 is inserted into the groove H of the engaging portion 52. However, the present invention is not limited to this, and the engaging portion 52 may be provided in the photoconductor unit 3, and the center shaft 19 a of the intermediate transfer unit 6 may be inserted into the groove H of the engaging portion 52.

In the first and second embodiments, the intermediate transfer unit 6 is mounted first and the photosensitive unit 3 is mounted later in the printing apparatus. However, the present invention is not limited thereto, and the photoconductor unit 3 may be mounted first, and the intermediate transfer unit 6 may be mounted later. Further, it is preferable that the engagement unit 52 is provided on the unit to be mounted first, and the center axis of the roller in the unit to be mounted later is set to be mounted on the engagement unit 52.

In the first and second embodiments, the pressing force F1
The direction of F2 and the insertion direction W of the photoconductor unit 3 are
It works in the same plane. However, the present invention is not limited to this. Even when the directions of the pressing forces F1 and F2 and the insertion direction W of the photoconductor unit 3 are not in the same plane,
If the angle between them is 90 degrees or less, the unit 3.6
Can be fixed stably.

Further, a conductive elastic material (for example, EPDM, urethane foam, etc.) may be provided on the surfaces of the transfer rollers 21a and 21b.

Further, the printing apparatus of the present invention includes an image forming unit and an intermediate transfer unit arranged so as to be in contact with each other, and transfers an image formed on the image forming unit to the intermediate transfer unit at a contact portion between the two units. And a printing device that is set to perform printing using the image transferred to the intermediate transfer unit, wherein one of the two units has a protrusion while the other unit has a protrusion. Is provided with a locking piece having a locking groove, and is configured to connect both units by inserting a projection into the locking groove of the locking piece. The pressing force acting on the unit having the projection from the unit having the locking piece is prevented from having a component opposite to the direction in which the projection is inserted into the locking groove. A configuration in which the projections and the locking piece is arranged, and can be expressed.

Further, the printing apparatus of the present invention includes an image forming unit and an intermediate transfer unit arranged so as to be in contact with each other, and transfers an image formed on the image forming unit to the intermediate transfer unit at a contact portion between the two units. And a printing device that is set to perform printing using the image transferred to the intermediate transfer unit, wherein one of the two units has a protrusion while the other unit has a protrusion. Is provided with a locking piece having a locking groove, and is configured to connect both units by inserting a projection into the locking groove of the locking piece. The pressing force acting on the unit having the protrusion from the unit having the locking piece has a component in the same direction as the insertion direction of the protrusion into the locking groove. It can also be present.

Further, in the image forming apparatus, if the positional relationship between the photoreceptor and the intermediate transfer member is not correctly mounted, a good image cannot be formed after maintenance work or replacement work is performed. Are unitized so that they can be mounted in a precise positional relationship using a positioning member, or have an integral structure so that they can be attached to and detached from the image forming apparatus. Further, if the positional relationship between the respective units is not accurately performed at the time of mounting, it can be said that there is a problem that not only deterioration of image forming quality is caused but also a failure occurs in the worst case. It can also be stated that the object of the present invention is to provide a positioning mechanism that is configured to be separated into a photoreceptor unit and an intermediate transfer unit, and that maintains the positional relationship between both units with high accuracy.

In this printer, the photosensitive belt 1
It can be said that the roller 3 is rotatably supported by the rollers 14 and 15. In addition, it can be said that the charger 4, the first cleaner unit 5, and the intermediate transfer belt 20 are arranged to face the surface of the photoreceptor belt 13. A light beam irradiator is provided downstream of the charger 4 in the photoreceptor belt 13, and a light beam is radiated by the optical unit 1 located at the upper part of the printer, so that the surface of the photoreceptor belt 13 Can be said to form an electrostatic latent image. Downstream of the light beam irradiating section of the photoconductor belt 13, a plurality of color developing units 16a to 16d for visualizing according to a plurality of component color image signals given to the optical unit 1 are provided. 13 are arranged. These developing units 16a to 16d are brought into contact with or separated from the photoreceptor belt 5 by separation / contact cams 17a to 17d arranged on the side opposite to the photoreceptor belt 13 in accordance with the formation of images of the respective color components. Thus, toner images of each color are sequentially formed.

Further, in the present printer, the toner images of each color formed on the photoreceptor belt 13 are sequentially transferred onto the intermediate transfer belt 20 in a superimposed manner. A multicolor toner image may be formed. Further, in the present printer, the sheet picked up by the pickup roller 22 is moved by the registration roller 23 by the registration roller 23.
The toner image formed on the intermediate transfer belt 20 may be conveyed to a transfer point (that is, between the intermediate transfer belt 20 and the sheet transfer roller 24 opposed thereto) in synchronization with the timing. At the transfer point, the intermediate transfer belt 20 and the sheet transfer roller 2
The multi-color toner image formed on the intermediate transfer belt 20 may be collectively transferred to the sheet sandwiched therebetween.

In the present printer, the fixing unit 8
In the above, the toner on the sheet may be melted and pressed by heating and pressing to fix the color image on the sheet. Furthermore, the sheet after fixing is
The paper may be discharged to the upper discharge section of the color printer through a reverse discharge path arranged in the latter half of the sheet transport path L and on the back side of the separation / contact cams 17a to 17d.

In this printer, the intermediate transfer belt 20 is composed of a transfer belt driving roller 18, a transfer belt tension roller 19, and a frame 5 of the intermediate transfer unit 6.
1. Two transfer rollers 21a rotatably supported by one
The intermediate transfer belt 20 is supported by the transfer belt tension roller 19 and tensioned by the transfer tension SP provided at both ends of the transfer belt tension roller 19 to enable the rotation operation without slipping.
May be set so that the pressing force acts. Further, the pressing transfer roller 21c described in the second embodiment may be set so that pressing (SP) is provided at the bearing support portions at both ends to apply a pressing force of 500 to 1000 g from the back side of the intermediate transfer belt 20.

Further, even if the pressing force of the pressing transfer roller 62 (the force received by the photoreceptor unit 3 due to the tension of the intermediate transfer belt 20) is directed toward the center of the central shaft 14a, the positioning is performed by the component force F2a in FIG. Becomes unstable. That is, when the position of the pressure transfer roller 62 is on the L side with respect to a line (line segment X) perpendicular to the insertion direction W, the component force acts in a direction opposite to the insertion direction W as indicated by F2a, so that it is unstable. Become. Further, as shown in FIG. 10, when the pressing force acts in a direction at an acute angle to the insertion direction W (when the position of the pressing transfer roller 62 is on the R side), the positioning is stable. Therefore, the photoconductor unit 3
The position is determined by the position of the contact point between the sheet and the intermediate transfer unit 6 and the insertion direction and the direction in which the pressing force acts, and it can be said that the positioning is stable when the acute angle condition is satisfied on the R side.

FIGS. 9 and 11 are diagrams for explaining the situation due to the difference in the position of the contact portion (the contact portion of the pressure transfer roller 62 with the photoconductor unit 3) when the direction of the pressure force F2 is 90 degrees. You can say that. In these figures,
The stability of positioning is determined by the component forces F2c and F2e.
In other words, as shown in FIG. 9, when the position of the pressure contact transfer roller 62 is on the L side and the pressure force acts like F2 on a line (line segment X) perpendicular to the insertion direction, the center axis to be positioned is positioned. The force indicated by F2b acts in the direction, and the component force acts in the direction opposite to the insertion direction W as in F2c, so that the positioning becomes unstable. Further, as shown in FIG. 11, when the position of the pressure contact transfer roller 62 is the R side, the component force F2e is in the same direction as the insertion direction W, and the positioning is stable.

The image forming apparatus (printing apparatus) of the present invention
Can also be expressed as the following first to fifth image forming apparatuses. That is, the first image forming apparatus is a unit that is later mounted on a frame member that forms a unit that is mounted first among an intermediate transfer unit and an image carrier unit that are detachably provided in the image forming apparatus main body. And the angle between the direction of the force acting on the unit mounted first and the unit mounted later and the direction of insertion when the unit is mounted on the positioning unit later is 90 degrees or less. According to this, the unit to be mounted later is pressed by the force from the previously mounted unit acting on the unit to be mounted later, so that the unit to be mounted later is pressed down in a direction in which it does not come off (the direction in which it does not come off), and is reliably positioned.

The second image forming apparatus of the first image forming apparatus is configured such that the unit to be mounted first is an intermediate transfer unit, and the unit to be mounted later is an image carrier unit. According to this, since the intermediate transfer body of the intermediate transfer unit applies a pressing force to the photosensitive body of the photosensitive body unit for transfer, the photosensitive body unit is reliably positioned to the intermediate transfer unit by this force.

The third image forming apparatus is the same as the first or second image forming apparatus, except that the photoreceptor unit mounted later on the positioning section provided on the intermediate transfer unit mounted earlier. The configuration is such that a rotating shaft for rotating and moving the photoreceptor is engaged. According to this, the positioning is performed so that the photoconductor of the photoconductor unit can accurately and reliably contact the intermediate transfer body of the intermediate transfer unit.

Further, the fourth image forming apparatus comprises first to third
In any one of the image forming apparatuses, the direction in which the force acts is directed substantially toward the center of the positioning section.
According to this, since a stable force acts on the unit to be positioned and no force for pushing the positioned unit acts, an accurate and reliable positional relationship between the two can be maintained.

Further, the fifth image forming apparatus is mounted later on a frame member forming a unit to be mounted first of the intermediate transfer unit and the image carrier unit detachably provided in the main body of the image forming apparatus. A positioning unit for the unit to be mounted is provided, and the direction of the rotating member of the unit to be mounted first is substantially the same as the direction of insertion of the unit to be mounted later. According to this, since the rotation direction at the time of operation of the rotating member acts on the unit to be mounted later,
It is possible to reliably maintain an accurate positional relationship between a unit mounted first and a unit mounted later.

[0105]

As described above, the printing apparatus according to the present invention (the present printing apparatus) includes the image forming unit and the intermediate transfer unit arranged so as to be in contact with each other. A printing device which is set to perform printing using an image transferred to an intermediate transfer unit after transferring to an intermediate transfer unit at a contact portion between both units, wherein one of the two units has a protrusion. The other unit is provided with a locking piece having a locking groove, and is configured to connect both units by inserting a projection into the locking groove of the locking piece. Further, in the contact portion between the two units, the direction of the pressing force acting on the unit having the projection from the unit having the engagement piece and the direction of inserting the projection into the engagement groove are described. Angle, a configuration that is set below 90 degrees.

In this printing apparatus, one of the two units has a projection. Further, the other unit is provided with a locking piece having a locking groove. Then, when installing these units in the printing apparatus, by inserting the protrusions into the locking grooves of the locking pieces,
Both units can be connected.

Further, in this printing apparatus, since both units are in contact with each other to transfer an image to the intermediate transfer member, a pressing force acts between the two units at the contact portion. Therefore, in order to prevent the displacement of the unit due to the pressing force, in the present printing apparatus, the direction of the pressing force acting on the unit having the protrusion from the unit having the locking piece, and the projection with respect to the locking groove, Angle with the insertion direction of the part,
It is set to 90 degrees or less.

That is, the above two units, the contact portion,
By adjusting the positions of the locking pieces, the protrusions, and the like, the pressure contact force is set so as not to act in a direction opposite to the insertion direction of the protrusions (a direction in which both units are separated). This allows
The two units can be firmly fixed without shifting their positional relationship.

In general, the image forming unit is mounted later on the printing apparatus than the intermediate transfer unit. Further, when the unit having the protruding portion is mounted after the unit having the locking piece, the two units can be connected smoothly. For this reason, in the present printing apparatus, it is preferable that the unit having the protruding portion be the image forming unit and the unit having the locking piece be the intermediate transfer unit.

The image forming unit in the printing apparatus includes an image forming belt as an image forming body for forming an image, and a roller pair for stretching and rotating the image forming belt on a frame or the like. It can be configured by fixing. Similarly, the intermediate transfer unit can be configured by fixing an intermediate transfer belt as an intermediate transfer body for holding an image and a roller pair for stretching and rotating the intermediate transfer belt to a frame or the like. .

In this case, it is preferable to use the central axis of one of the rollers of the image forming unit as the projection. Preferably, the locking piece having the locking groove is formed on the frame of the intermediate transfer unit. In this case, the projections and the locking pieces can be easily formed. In the image forming unit, it is preferable to use a driven roller whose central axis does not rotate as a roller that uses the central axis as a protrusion (hereinafter, referred to as a fixed roller).

Further, in the above configuration, the intermediate transfer belt of the intermediate transfer unit is provided at the contact portion between the two units.
It is preferable that the setting is such that the image forming belt is pressed against the fixed roller of the image forming unit. In this configuration, the projection of the image forming unit, which is the connecting portion between the two units, is made adjacent to the contact portion between the units. Thereby, the contact portion can be stabilized, and the image transfer from the image forming belt to the intermediate transfer belt can be favorably performed.

In this configuration, it is preferable that a contact portion for pressing the intermediate transfer belt against the image forming belt is provided at a contact portion between the two units. As a result, the two belts can be reliably brought into contact with each other, so that the image transfer from the image forming belt to the intermediate transfer belt can be performed more favorably.

Further, the pressure contact portion can be constituted by a pair of pressure contact rollers for supporting the intermediate transfer belt with the contact portion between the two units interposed therebetween. In this case, it is preferable that the line connecting the two rollers in the pressure roller pair is substantially parallel to the insertion direction of the projection into the locking groove. With this configuration, the pressure contact can be performed without hindering the rotation of the intermediate transfer belt.

In this case, the substantially middle portion of the pressing roller pair is positioned at the same position as the projection (the contact portion of the unit) in the insertion direction of the projection into the locking groove.
Alternatively, it is preferable to be located on the upstream side of the projection (the insertion opening side of the locking groove is the upstream side, and the deep side of the locking groove is the downstream side). In this case, there is no component for moving the protrusion to the upstream side. This allows both units to
It is possible to firmly fix without shifting the mutual positional relationship.

Further, a pressure roller for supporting the intermediate transfer belt at the contact portion between the two units may be used as the pressure contact portion. In this case, it is preferable that the pressing roller be located at the same position as the protrusion (contact portion) or at the upstream side of the protrusion (contact portion) in the insertion direction of the protrusion. In this case, there is no component for moving the protrusion to the upstream side, so that both units can be firmly fixed without displacing the mutual positional relationship.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a pressing force applied from an intermediate transfer unit to a photoconductor unit in a color printer according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a configuration of the color printer.

FIG. 3 is an explanatory diagram showing a configuration of an intermediate transfer unit and a photoreceptor unit provided in the color printer shown in FIG.

FIG. 4 is an explanatory view showing the intermediate transfer unit in a state where it is detached from the color printer shown in FIG. 2;

FIG. 5 is an explanatory diagram showing an operation of removing the intermediate transfer unit and the photoconductor unit shown in FIG. 3 from the color printer shown in FIG. 2;

FIG. 6 is an explanatory view showing a state in which the photoconductor unit is attached so that the central shaft is engaged with the groove of the locking piece in the intermediate transfer unit.

FIG. 7 is an explanatory diagram illustrating a configuration of an intermediate transfer unit and a photoconductor unit in a color printer according to a second embodiment of the invention.

FIG. 8 is an explanatory diagram illustrating a pressing force that acts between the intermediate transfer unit and the photoconductor unit when the pressure transfer roller of the intermediate transfer unit is disposed off the center of the driven roller.

FIG. 9 is another explanatory diagram showing the pressing force acting between the intermediate transfer unit and the photoconductor unit when the pressure transfer roller of the intermediate transfer unit is disposed off the center of the driven roller.

FIG. 10 illustrates a case where the pressure transfer roller of the intermediate transfer unit is disposed off the center of the driven roller.
FIG. 9 is a further explanatory view showing a pressing force acting between the intermediate transfer unit and the photoconductor unit.

FIG. 11 illustrates a case where the pressure transfer roller of the intermediate transfer unit is disposed off the center of the driven roller.
FIG. 9 is a further explanatory view showing a pressing force acting between the intermediate transfer unit and the photoconductor unit.

[Explanation of symbols]

Reference Signs List 3 photoconductor unit (image forming unit) 6 intermediate transfer unit 13 photoconductor belt (image forming belt) 14 photoconductor driven roller 14a central axis 15 photoconductor driving roller 18 transfer belt driving roller 19 transfer belt tension roller 20 intermediate transfer belt 21a・ 21b Transfer roller (pressing portion; press-contact roller pair) 41 Frame 42 Tension roller 43 Auxiliary roller 51 Frame 52 Locking piece 53 ・ 54 High voltage power supply 61a ・ 61b Followed roller 62 Press-contact transfer roller (Press-contact portion; pressing roller) H Lock Groove F1 ・ F2 Pressure contact P Contact part

Claims (7)

[Claims] An image forming unit and an intermediate transfer unit are provided so as to be in contact with each other. An image formed on the image forming unit is transferred to an intermediate transfer unit at a contact portion between the two units, and then transferred to the intermediate transfer unit. A printing apparatus configured to perform printing using a transferred image, wherein one of the two units has a protrusion, and the other unit has a locking groove. It is provided with a stop piece, and it is set so as to connect both units by inserting a protrusion into the lock groove of the lock piece, and further, from a unit having a lock piece at a contact portion of both units. An angle between the direction of the pressing force acting on the unit having the projection and the direction of insertion of the projection into the locking groove is set to 90 degrees or less. Apparatus. 2. The printing apparatus according to claim 1, wherein the unit having the projection is an image forming unit, and the unit having the locking piece is an intermediate transfer unit. 3. The image forming unit includes an image forming belt for forming an image, and a roller pair for stretching and rotating the image forming belt, and one of the rollers in the roller pair. The central axis of the roller is the protrusion, and the intermediate transfer unit includes an intermediate transfer belt for holding an image, and a roller pair for stretching and rotating the intermediate transfer belt. The printing apparatus according to claim 2, wherein the printing apparatus is formed on a frame having a locking piece. 4. An image forming apparatus according to claim 3, wherein the intermediate transfer belt is set so as to press the image forming belt against a roller having a central axis serving as the projection at a contact portion between the two units. A printing device according to claim 1. 5. The printing apparatus according to claim 4, further comprising a pressing portion for pressing the intermediate transfer belt against the image forming belt at a contact portion between the two units. 6. The pressure contact portion is a pair of pressure contact rollers that support the intermediate transfer belt with the contact portion interposed therebetween, and a line connecting the two rollers in the pair of pressure contact rollers is the insertion of the protrusion into the locking groove. And a substantially middle portion between these two rollers is located at the same position as the protrusion or in the upstream of the protrusion in the direction of insertion of the protrusion into the locking groove. The printing device according to claim 5, wherein: 7. The pressure contact portion is a pressure contact roller that supports the intermediate transfer belt at the contact portion, and is located at the same position as the protrusion or in the direction of insertion of the protrusion into the locking groove. The printing apparatus according to claim 5, wherein the printing apparatus is located on an upstream side.