JPH10293514A - Carrying belt unit and image forming device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrying belt unit capable of being largely away from a photoreceptor drum and preventing the possibility of causing carrying defect at the time of carrying paper sheet. SOLUTION: As shown in Figure (a), the long-radius peripheral surface of a cam plate 61 is made in contact with a supporting pin 58 when a lever 62 is erected, a carrying mechanism 43 is positioned upward, and the upper surface of the carrying belt 46 is made in contact with photoreceptor drums 11B, 11M, 11C, and 11Y. When the erected lever 62 is rotated clockwise and brough down, cam shafts 59 and 60 rotate in accordance with the rotation of the lever 62, and four cam plates 61 are rotated clockwise. In accordance with this, as show in Figure (b), the pin 58 is relatively moved on the peripheral surface of the plate 61, and made in contact with the short-radius position of the board 61, so that the mechanism 43 is displaced downward.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transport belt unit for transporting a sheet, and more particularly, to a transfer belt unit for transferring a toner image formed on the surface of a photoreceptor to a sheet while transporting the sheet. It relates to a suitable transport belt unit. Further, the present invention relates to an image forming apparatus including the transport belt unit.

[0002]

2. Description of the Related Art Conventionally, a full-color image forming apparatus is provided with four image forming units for black, magenta, cyan, and yellow along a linear conveying path formed by a conveying belt. A so-called tandem-type image forming apparatus is known, in which a toner image formed by each image forming unit is sequentially superimposed on a sheet and transferred while the sheet is linearly conveyed by a conveying belt.

In a tandem-type full-color image forming apparatus, a transfer roller is disposed below an upper conveyor belt so as to face a photosensitive drum included in each image forming unit. The transport belt is pressed against the photosensitive drum by the transfer roller, and the paper enters between the photosensitive drum and the transfer roller in a state of being placed on the transport belt. The image is transferred.

[0004]

When the transport belt is replaced with a new one due to dirt or wear, it is necessary to separate the transport belt from the photosensitive drum. Because
This is because the conveyor belt is in contact with the photosensitive drum, and if the conveyor belt is pulled out as it is, the surface of the photosensitive drum will be damaged. In addition, even when a paper conveyance failure (paper jam) occurs between the conveyance belt and the photoconductor drum, it is necessary to separate the conveyance belt from the photoconductor drum in order to remove the paper having the conveyance failure. is there.

[0005] As shown in FIG. 7, a structure in which the transport belt is separated from the photosensitive drum is one roller 105.
A configuration is conceivable in which the conveyor belt 100 is rotated in the direction of the arrow 110 around the center. However, in the case of the configuration shown in FIG.
Since there is no sufficient space between the belt 1 and the conveyor belt 100, it is difficult to pull the conveyor belt 100 forward.

[0008] As shown in FIG. 8, it is conceivable to lower the four transfer rollers 106 to 109 to separate the conveyor belt 100 from the photosensitive drums 101 to 104. However, in this configuration, the steep slope is formed near the upstream end and the downstream end of the conveyor belt 100 in a state where the conveyor belt 100 is in contact with the photosensitive drums 101 to 104. Then, the leading end of the paper P sent on the conveyor belt 100 hits the inclined portion of the conveyor belt 100, and this may cause a conveyance failure, which is not preferable. Further, the leading end of the sheet P after the transfer may be pulled downward due to the attraction force acting between the transport belt 100 and the sheet P, and the sheet P may not be supplied to a fixing device (not shown) satisfactorily.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned technical problems, and to provide a transport belt unit in which a transport belt can be largely separated from a photosensitive drum and a transport failure is less likely to occur during paper transport. That is. Another object of the present invention is to provide an image forming apparatus provided with such a transport belt unit.

[0008]

According to a first aspect of the present invention, there is provided a transport belt unit provided in a unit case and a unit case. A second roller provided at a predetermined distance in the horizontal direction, and a transport having an endless transport belt wound around the first roller and the second roller to form a transport path whose upper surface extends in the horizontal direction. And a lifting mechanism for horizontally moving the transport mechanism up and down with respect to the unit case.

According to the first aspect of the present invention, the transport mechanism is moved up and down horizontally with respect to the unit case by the elevating mechanism. Therefore, for example, as compared with a configuration in which the transport mechanism is rotated about the first roller or the second roller as described with reference to FIG. it can. According to a second aspect of the present invention, there is provided a conveyance belt unit for conveying a sheet, and an image for forming an image to be transferred to the sheet conveyed by the conveyance belt unit, the image being provided in association with the conveyance belt unit. And a forming unit, wherein the conveying belt unit according to claim 1 is used as the conveying belt unit.

According to the second aspect of the present invention, since the transport belt unit is configured to vertically move the transport mechanism relative to the unit case, for example, the photosensitive member provided in the image forming unit is a bearing. , Or even if the frame for holding the photoconductor is deeply lowered, the conveying mechanism can be lowered to below the bearing or the frame. Therefore, when a paper jam or the like occurs between the photoconductor and the transport belt, the paper can be easily removed.

When the transfer belt is provided with a transfer roller in the image forming apparatus as the transfer belt unit, the transfer belt is separated from the photoreceptor by lowering only the transfer roller. 8
), When the conveyor belt is in contact with the photoconductor,
There is a possibility that the sheet is steeply inclined near the upstream end and the downstream end of the transport belt, and the sheet hits the inclined portion to cause a transport failure.

However, according to the present invention, since the entire transport mechanism moves up and down, the upstream end and the downstream end of the transport belt are not inclined, and the above-described poor transport of the paper is less likely to occur. . According to a third aspect of the present invention, there is provided the image forming apparatus according to the second aspect, further comprising a slide mechanism for slidably holding the unit case in a direction orthogonal to the sheet conveying direction.

According to the third aspect of the present invention, the unit case is slidable in a direction orthogonal to the sheet conveying direction by the slide mechanism. Therefore, when replacing the transport belt, lower the transport mechanism below the bearings and frame for holding the photoconductor, and then slide the unit case to hook the transport belt on the bearing and frame. And the transport mechanism can be pulled out.

According to a fourth aspect of the present invention, a plurality of the image forming units are provided along a conveying path formed by a conveying belt, and the plurality of image forming units form images of different colors. 3. The method according to claim 2, wherein
An image forming apparatus according to claim 3. According to the configuration of the fourth aspect, even in a tandem-type image forming apparatus in which a plurality of image forming units are arranged along the transport path, each of the photoconductors provided in each image forming unit is used. The transport mechanism can be largely separated. Therefore, unlike the configuration in which the transport mechanism is rotated around the first roller or the second roller (see FIG. 7), there is not sufficient space between the photosensitive member closest to the rotation center and the transport belt. There is no difficulty in pulling out the conveyor belt to the near side.

[0015]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a sectional view schematically showing the internal configuration of a digital full-color printer in which a transport belt unit according to an embodiment of the present invention is provided as a transfer belt unit.

Referring to FIG. 1, this digital full-color printer is arranged in a line along a paper transport path formed by transport mechanism 43 for transporting paper P in a substantially straight line, and a paper transport path formed by transport mechanism 43. Four image forming units 10B for black, magenta, cyan and yellow
10M, 10C, 10Y (hereinafter collectively referred to as
This is referred to as “image forming unit 10”. ), And the photosensitive drums 11B, 11M,
Black, magenta, cyan, and yellow toner images formed on the respective photoconductors 11C and 11Y (hereinafter, collectively referred to as “photosensitive drums 11”) are sequentially superimposed and transferred onto one sheet of paper P. This is a so-called tandem-type full-color printer that obtains a full-color image.

The transport mechanism 43 includes a drive roller 44 disposed downstream with respect to the sheet transport direction, a driven roller 45 disposed upstream, and an endless roller wrapped between the drive roller 44 and the driven roller 45. Conveyor belts 46 and auxiliary rollers 47 to 4 for suppressing bending of the conveyor belt 46.
9 are included. When the drive roller 44 is driven to rotate, the paper P on which the toner image is transferred is conveyed linearly in the direction of arrow 98 while being placed on the upper surface of the conveyance belt 46.

Inside the conveyor belt 46, a black transfer roller 50B, a magenta transfer roller 50M, a cyan transfer roller 50C, and a yellow transfer roller 50Y are arranged at positions facing the photosensitive drums 11B, 11M, 11C, and 11Y, respectively. ing. These transfer rollers 50
B, 50M, 50C, and 50Y have functions of pressing the conveyor belt 46 against the photosensitive drums 11B, 11M, 11C, and 11Y from below and transferring the toner image on the photosensitive drum 11 to paper. .

A belt cleaner 17 is provided below the drive roller 44 to remove dirt such as toner and paper powder attached to the surface of the conveyor belt 46. In this embodiment, the transport mechanism 43, the transfer rollers 50B, 50
M, 50C, 50Y and the belt cleaner 17 are held by a unit case 41 to form a transfer belt unit 40. The transfer belt unit 40 can be moved back and forth with respect to the printer main body 2 by slide mechanisms 42 provided on both right and left sides of the unit case 41 in FIG.

On the other hand, below the transfer belt unit 40, a paper feed tray 3 for accommodating a plurality of sheets P is provided. In connection with the paper feed tray 3, a paper feed roller 5 for feeding the paper P from the paper feed tray 3 to the transport path 4 one by one
Is provided. The sheet P sent to the conveyance path 4 by rotating the sheet supply roller 5 is conveyed by the conveyance roller 6 toward the registration roller 7. Registration roller 7
Is the transfer belt unit 40 in the transport direction of the paper P.
After temporarily stopping the conveyed sheet P, the sheet P is sent out onto the conveying belt 46 in synchronization with the toner image forming operation (described later) in the image forming unit 10. .

Above the image forming unit 10, a black laser scanning unit 2 for irradiating the photosensitive drums 11B, 11M, 11C and 11Y with laser beams respectively.
0B, a magenta laser scanning unit 20M, a cyan laser scanning unit 20C, and a yellow laser scanning unit 20Y. The printer body 2 is connected to an external device (not shown) such as a microcomputer. Image data input from an external device is separated into color image data of each color component of black, magenta, cyan, and yellow, and is provided to laser scanning units 20B, 20M, 20C, and 20Y corresponding to each color.

When the black image data is supplied to the black laser scanning unit 20B, a laser beam corresponding to the supplied black image data is generated from a laser light source (not shown). This laser beam is reflected by a polygon mirror 21 rotating at a predetermined high speed, and guided to a first reflecting mirror 23 via a lens 22. The light path of the light guided to the first reflecting mirror 23 is turned back by the first reflecting mirror 23 and the second reflecting mirror 24 and guided to the third reflecting mirror 25. Then, the optical path is bent downward by the third reflecting mirror 25 and is incident on the black image forming unit 10B.

The black image forming unit 10B includes:
A photosensitive drum 11B is provided which rotates at a constant speed in the direction of an arrow (clockwise in FIG. 1) during image formation.
Around the photosensitive drum 11B, the main charger 12 and the black developing device 1 are sequentially arranged along the rotation direction.
3 and a cleaner 14 are arranged. The laser beam incident from the black laser scanning unit is applied to the surface of the photosensitive drum 11B between the main charger 12 and the black developing device 13.

After the surface of the photosensitive drum 11B is uniformly charged by the discharge of the main charger 12, it is exposed to a laser beam incident from the black laser scanning unit 20B to form an electrostatic latent image. . Next, the surface of the photosensitive drum 11B on which the electrostatic latent image has been formed is developed by the black developing device 13 with black toner.
The black developing device 13 includes a developing roller 15, a sub-roller 16, and a blade 86. In the black developing device 13, one-component black toner is stored, and the developing roller 15 and the sub-roller 1 are stored.
When each of the rollers 6 is rotated in a predetermined direction, the toner is supplied to the developing roller 15 by the sub-roller 16. And
By the action of the blade 86, a thin layer of toner is formed on the developing roller 15, and the toner is charged.

A reversal developing bias is applied to the developing roller 15, and when the electrostatic latent image on the photosensitive drum 11B comes into contact with the toner layer on the developing roller 15, the photosensitive drum 1
The toner is transferred to the exposed portion 1B, and the electrostatic latent image is visualized as a toner image. When the photosensitive drum 11B is further rotated, the black toner image formed on the surface of the photosensitive drum 11B faces the transfer belt unit 40. On the other hand, at the timing synchronized with the toner image facing the transfer belt unit 40, the paper P
Is sent. A predetermined transfer voltage is applied to the black transfer roller 50B disposed inside the conveyor belt 46, and the black toner on the surface of the photosensitive drum 11B moves to the upper surface of the paper P and is transferred. The toner remaining on the surface of the photosensitive drum 11B after the transfer is collected by the cleaner 14.

Paper P on which a black toner image has been transferred
Is transported by the transport belt 46 toward the magenta image forming unit 10M on the downstream side. Hereinafter, in the same manner as in the case of black,
Magenta, cyan, and yellow toner images are formed on the photosensitive drums 11M, 11C, and 11Y.
And are sequentially transferred.

As described above, since each color toner image is superimposed and transferred onto the sheet P, if a transfer deviation occurs in each color toner image, a color deviation occurs in a formed image.
Therefore, in the digital full-color printer according to this embodiment, various measures are taken to prevent color shift due to transfer shift. For example, by making the interval between adjacent photosensitive drums (interval between transfer positions) equal to the outer diameter of the photosensitive drum, the drum drive system for rotating the photosensitive drum 11 and rotating the photosensitive drum 11 In this case, the phase of the transfer deviation due to the drive unevenness can be made uniform, and the apparent color deviation during the transfer of each color can be reduced. Further, a driving roller 44 for moving the transport belt 46 is provided.
Is substantially equal to the outer diameter of the photoconductor drum, and the interval between the photoconductor drums is the same as the distance that the conveyance belt 46 travels by one rotation of the drive roller 44, so that the deflection of the conveyance belt 46 can be reduced. The color shift due to the driving unevenness of the transport belt 46 can be reduced.

As described above, the sheet P on which the toner images of the respective colors are transferred in a superimposed manner has a weaker adhesion to the conveyor belt 46 due to the discharge of the separation charger 19, and the conveyor belt 4
6 and is guided to the fixing unit 80. The fixing unit 80 includes a heat fixing belt 83 wound around two rollers 81 and 82, an oil application roller 84
, A pressure roller 85 provided below the roller 81, and a heater 90 provided inside the roller 82.

The heat fixing belt 83 is arranged so as to extend toward the upstream side in the sheet conveying direction 98. As a result, each color toner on the sheet P conveyed toward the fixing unit 80 is transferred to the heat fixing belt 83 and the pressure roller 8.
Before reaching the nip position with No. 5, the sheet is heated in advance by the heat of the heat fixing belt 83, and then heated and pressed by the heat fixing belt 83 and the pressure roller 85 to be fixed on the sheet P. The paper P after the fixing process is discharged by discharge rollers 8 and 9 to a discharge section 18 formed on the upper surface of the printer main body 2.

The above is one cycle of the image forming operation when the full-color image is formed on the paper P. As a means for fixing the toner to the paper, a heat roller and a pressure roller, which have been widely used, may be adopted. However, in order to obtain the same effect as described above, the diameter of the heat roller is increased. There is a need.

FIG. 5 is a plan sectional view schematically showing the image forming unit 10. FIG. 6 is a view of the image forming unit 10 as viewed from the front side of the printer main body 2. With reference to FIGS. 5 and 6, a predetermined interval is provided between the front side and the back side (the left-right direction in FIG. 5) of the printer main body 2.
A pair of drum unit side plates 124 and 125 are provided so as to face each other. Drum unit side plates 124, 12
5, bearings 126, 1 are provided at opposing positions, respectively.
27 is fitted. The photoreceptor drum 11 is rotatably held by the peripheral surfaces of both end portions thereof being received by bearings 126 and 127.

Thus, as compared with a configuration in which the drum shaft serving as the center of rotation is passed through the photosensitive drum 11 and both ends of the drum shaft are held by bearings,
Runout can be reduced. Therefore, it is possible to reduce the possibility that a problem such as color shift occurs in the formed image. However, in the case of the configuration in which the photosensitive drum 11 is held by the bearings 126 and 127, when the transport belt 46 is replaced with a new one due to dirt or abrasion, or when the paper is transported between the transport belt 46 and the photosensitive drum 11, When the transport failure occurs, it is necessary to lower the transport belt 46 at least below the bearings 126 and 127. Therefore, compared to a configuration in which the drum shaft passed through the photosensitive drum 11 is received by the drum unit side plate,
The conveyor belt 46 must be largely separated from the photosensitive drum 11.

Therefore, in the printer device 2 according to this embodiment, the entire transport mechanism 43 is configured to be able to move up and down substantially horizontally with respect to the unit case 41, and the transport belt 46 is largely separated from the photosensitive drum 11. I can do it. FIG. 2 is a perspective view showing the configuration of the transfer belt unit 40. In the following description, when viewed in the direction of arrow 99 in FIG.

Referring to FIG. 2, transfer belt unit 40
Are a unit case 41, a slide mechanism 42 (see FIG. 1), a transport mechanism 43, and four transfer rollers 50B and 50.
In addition to the M, 50C, 50Y and the belt cleaner 17 (see FIG. 1), an elevating mechanism 51 for moving the entire transport mechanism 43 up and down, and transporting the magenta, cyan, and yellow photosensitive drums 11M, 11C, 11Y. A pressure release mechanism 52 for releasing the pressure-contact state of the belt 46 is provided.

The unit case 41 is elongated in the left-right direction (paper transport direction), and is formed in a box shape having an open upper surface. Two guide grooves 55 are formed in each of the front plate 53 and the rear plate 54 of the unit case 41. The guide groove 55 includes a front plate 53 and a rear plate 54.
It is formed by notching a rectangular shape extending downward from the upper end of the. The guide groove 55 guides a vertical slide of a support pin 58 described later, and the groove width (width in the left-right direction) of the guide groove 55 corresponds to the outer diameter of the support pin 58.

The transport mechanism 43 is provided with a front support plate 56 and a rear support plate 57 that are opposed to each other at a predetermined interval in the front-rear direction (the direction orthogonal to the paper transport direction). Thus, the driving roller 44, the driven roller 45, and the auxiliary roller 47 (see FIG. 1) are rotatably held. The front support plate 56 has a 2
The two support pins 58 are projected, and two support pins 5 are provided.
8 are fitted into guide grooves 55 formed in the front side plate 53 of the unit case 41, respectively. The rear support plate 57 also has two support pins 5 extending rearward.
8, and the tip portions of the two support pins 58 are fitted in guide grooves 55 formed in the rear plate 54 of the unit case 41, respectively. Thus, the transport mechanism 43 is slidable in the up-down direction while being positioned in the left-right direction with respect to the unit case 41.

The elevating mechanism 51 is mounted on two cam shafts 59 and 60 rotatably held by a front plate 53 and a rear plate 54 of the unit case 41, and two cam shafts 59 and 60 are mounted on the cam shafts 59 and 60, respectively. A total of four cam plates 61,
And a lever 62 attached to one end of one cam shaft 59. The lever 62 is attached to a portion of the camshaft 59 protruding forward from the front plate 53 of the unit case 41, and is provided outside the unit case 41 so that an operator can easily operate it.

The two camshafts 59 and 60 are mounted at predetermined intervals in the left-right direction, and are rotated in synchronization with each other by an interlocking mechanism (not shown). Four cam plates 6 attached to cam shafts 59 and 60
Numerals 1 denote plate-like bodies all having the same shape, and more specifically, are formed in a substantially quarter elliptical planar shape. Front support plate 5
6 and the support pins 58 projecting from the rear support plate 57
The outer peripheral surfaces of the cam plates 61 are respectively circumscribed from above, and the transport mechanism 43 is supported by the four cam plates 61.

FIG. 3 is a view for explaining the function of the lifting mechanism, and is a schematic front view of the transfer belt unit 40. FIG. 3A illustrates a state in which the transport mechanism 43 is displaced upward, and FIG. 3B illustrates a state in which the transport mechanism 43 is displaced downward. As shown in FIG. 3A, when the lever 62 is in the upright state, the long radius peripheral surface of the cam plate 61 is in contact with the support pin 58 and the transport mechanism 43
Are located above, and the upper surface of the transport belt 46 is in contact with the photosensitive drum 11.

If a sheet conveyance failure occurs between the photosensitive drum 11 and the conveyance belt 46 while the image forming operation is being performed in the state shown in FIG. Person) is a front door (not shown) of the printer main body 2.
Is released, and the standing lever 62 is rotated clockwise to fall down. Then, the cam shafts 59 and 60 rotate with the rotation of the lever 62, and the four cam plates 61 rotate clockwise. With the rotation of the cam plate 61, the support pins 58 in contact with the long radius position of the cam plate 61
Relatively moves on the outer circumference of the cam plate 61 and comes into contact with the short radius position of the cam plate 61. Further, when the support pin 58 is moved to the short radius position, the support pin 58 is guided by the guide groove 55, and the transport mechanism 43 moves downward.

Thus, the transport belt 46 is separated from the photosensitive drum 11 (see FIG. 3B). Therefore,
The operator can easily remove the sheet having the conveyance failure from between the photosensitive drum 11 and the conveyance belt 46. Then, after removing the paper, the lever 6
When 2 is rotated counterclockwise and raised, the transport mechanism 43 is lifted by the four cam plates 61, and the transport belt 46 is pressed against the photosensitive drum 11.

When the transport belt 46 is to be replaced, for example, the lever 62 in the upright state is lowered to displace the transport mechanism 43 downward, and then the transport mechanism 43 is pulled out together with the unit case 41 to the near side. Then, the transport mechanism 43
Is taken out of the unit case 41 and the transfer belt 46 is
Can be replaced with a new one. In this manner, the conveyor belt 46 can be separated from the photosensitive drum 11 only by rotating the lever 62, so that the operability at the time of jam clearance and the exchange of the conveyor belt 46 is improved as compared with the related art. .

In this embodiment, when the operator manually operates the lever 62, the transport mechanism 43 is moved up and down. For example, when a stepping motor is mounted on the cam shaft 59, the front door of the printer body is opened. If the transport mechanism 43 is automatically moved up and down in response to the opening and closing of the, the workability can be further improved.

The transport mechanism 43 includes a unit case 41.
7, the transport mechanism is rotated around the drive roller 105 to separate the transport belt 100 from the photosensitive drums 101 to 104 (FIG. 7).
The transfer belt 46 can be largely separated from the photosensitive drum 11 as compared with the above-described method. Therefore, even if the photosensitive drum 11 is the bearings 126 and 127 (see FIG. 5), the transport belt 46 is connected to the drum unit side plate 12
4, 125 (see FIG. 5), so that the transport mechanism 43 can be pulled out without being hooked on the drum unit side plates 124, 125.

Further, as in a configuration in which the transfer belt 100 is separated from the photosensitive drums 101 to 104 by lowering only the transfer rollers 106 to 109 (see FIG. 8), near the upstream end and the downstream end of the transfer belt. There is no steep slope. Therefore, the transport belt 4
There is no possibility that the sheet supplied to the sheet 6 collides with the upstream end of the conveyor belt 46 to cause a conveyance failure. Also,
The attraction force acting between the transport belt 46 and the sheet does not cause the leading end of the sheet after the transfer to be drawn downward, and the sheet not to be supplied to the fixing unit 80 (see FIG. 1) well.

Referring again to FIG. 2, the pressure release mechanism 52
A swing plate 63 provided in parallel with the front support plate 56 at a predetermined distance behind the front support plate 56, and a predetermined distance between the rear support plate 57 and the rear support plate 57. And a pair of oscillating plates 63, 64, which are provided in parallel with each other. The magenta transfer roller 50M,
Cyan transfer roller 50C and yellow transfer roller 50
Y and auxiliary rollers 48 and 49 (see FIG. 1) are held.

At the right ends (upstream ends in the sheet transport direction) of the swing plates 63 and 64, swing pins 65 project outward. The tip portion of the swing pin 65 is rotatably received by the front support plate 56 and the rear support plate 57, respectively, and the swing plates 63 and 64 rotate with respect to the front support plate 56 and the rear support plate 57, respectively. It is movably held.

The rocking plates 63 and 64 have three notches 66 at positions facing each other. Each of these notches 66 has a coil spring 67
A bearing 68 is attached via the .magenta transfer roller 50M, the cyan transfer roller 50C and the yellow transfer roller 50Y are rotatably held by bearings 68 facing each other. Thus, the magenta transfer roller 50M and the cyan transfer roller 50
C and the yellow transfer roller 50Y apply a suitable force to the photosensitive drum 11
They are pressed in the M, 11C, and 11Y directions, respectively.

On the other hand, the front support plate 56 and the rear support plate 57 are also formed with notches 69 at positions facing each other, and bearings 71 are attached to the notches 69 via coil springs 70. I have. The rotating shaft of the black transfer roller 50B is rotatably held by the pair of bearings 71, and the black transfer roller 50B is always pressed against the black photosensitive drum 11B with an appropriate force. I have.

The oscillating plates 63 and 64 are further provided with rectangular hollow holes 72 between the cyan transfer roller 50C and the yellow transfer roller 50Y, and at positions facing each other. Eccentric cams 73 are fitted into the hollow holes 72, respectively. Two eccentric cams 7
3 is attached to a common rotation shaft 74, and the rotation shaft 74 is rotatably held by a front support plate 56 and a rear support plate 57. Therefore, when the rotation shaft 74 is rotated, the two eccentric cams 73 are rotated in synchronization with each other. In FIG. 2, the hollow hole 72 and the eccentric cam 73 are shown only on the rocking plate 63 side.

FIGS. 4A and 4B are illustrative views for explaining the function of the pressure releasing mechanism. FIG. 4A shows a state in which the conveying belt 46 is pressed against the photosensitive drum 11, and FIG.
Cyan and yellow photosensitive drums 11M, 11C,
This shows a state in which the pressing state of the conveyor belt 46 against 11Y has been released. In this digital full-color printer, when forming a full-color image, as shown in FIG. 4A, the transfer belt 46 is moved by the black transfer roller 50B, the magenta transfer roller 50M, the cyan transfer roller 50C, and the yellow transfer roller 50Y. The photosensitive drums 11B, 11M, 11C, and 11Y are pressed against each other. At this time, the high position peripheral surface of the eccentric cam 73 is in contact with the upper side of the hollow hole 72.

When a monochrome image is formed, the rotating shaft 74 of the eccentric cam 73 is rotated by, for example, a stepping motor (not shown). Then, the upper side of the hollow hole 72 is separated from the high position peripheral surface of the eccentric cam 73 and comes into contact with the low position peripheral surface of the eccentric cam 73. Thus, the swing plates 63 and 64 are rotated counterclockwise around the swing pin 65. Therefore, as shown in FIG. 4B, the magenta transfer roller 50 held by the swing plates 63 and 64
The M, cyan transfer roller 50C, and yellow transfer roller 50Y are moved downward, and the pressure contact between the conveyor belt 46 and the photosensitive drums 11M, 11C, 11Y is released.

On the other hand, since the black transfer roller 50B is held by the front support plate 56 and the rear support plate 57, the oscillating plates 63 and 64 are turned to rotate the magenta transfer roller 50M, the cyan transfer roller 50C, and the yellow transfer roller. Even if the roller 50Y is displaced, the black transfer roller 50B
Is not displaced, and the pressure contact state between the conveyor belt 46 and the black photosensitive drum 11B is not released. That is, at this time, the transfer belt 46 is
Only B comes into contact.

When a full-color image is to be formed again, the rotation shaft 74 of the eccentric cam 73 is further rotated to bring the high-peripheral surface of the eccentric cam 73 into contact with the upper side of the hollow hole 72. Then, the oscillating plates 63 and 64 are lifted by the eccentric cam 73, and the conveying belt 46 is moved by the magenta transfer roller 50M, the cyan transfer roller 50C and the yellow transfer roller 50Y to the photosensitive drums 11M, 11C and 1Y.
Pressed again to 1Y.

As described above, in the transfer belt unit 40 according to this embodiment, when forming a monochrome image,
The photosensitive drums 11M of the magenta transfer roller 50M, the cyan transfer roller 50C, and the yellow transfer roller 50Y,
The state of pressure contact with 11C and 11Y is released, and the conveyor belt 46 contacts only the black photosensitive drum 11B. Then, the operations of the laser scanning units 20M, 20C, and 20Y and the image forming units 10M, 10C, and 10Y are stopped, and a monochrome image can be formed.

When the monochrome image is formed, the transport belt 46 is separated from the photosensitive drums 11M, 11C, and 11Y.
11Y, the photosensitive drums 11M,
The life of 11C and 11Y is not shortened. Although the description of one embodiment of the present invention is as described above, the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the case where the transfer belt unit according to the present invention is provided in a digital full-color printer is described as an example. It may be provided in a full-color image forming apparatus such as a full-color copying machine of the type or an analog type, or a mono-color image forming apparatus that forms only a single-color image.

As a means for transferring the toner image on the photosensitive drum to the sheet, a transfer charger for discharging the photosensitive drum from below the transport belt may be provided instead of the above-described transfer roller. At this time, the pressure release mechanism only needs to be configured so that the transport belt comes into contact with / separates from the photosensitive drum, and there is no need to press the transfer charger against the photosensitive drum.

Further, in the above-described embodiment, the case where the transport belt unit according to the present invention is used as a transfer belt unit including four transfer rollers has been described as an example. The image forming apparatus may include a transport belt unit. In addition, various changes can be made within the scope described in the claims.

[0059]

According to the first aspect of the present invention, since the transport mechanism is moved up and down horizontally with respect to the unit case by the elevating mechanism, the transport mechanism is rotated around the first roller or the second roller, for example. The moving amount of the transport mechanism can be increased as compared with the configuration in which the transport mechanism is moved.

According to the second aspect of the present invention, even if the photosensitive member is held by the bearing or the frame for supporting the photosensitive member is lowered deeply, the moving amount of the transport mechanism is large. Alternatively, the transport mechanism can be lowered to below the frame. Therefore, when a paper jam occurs between the photosensitive member and the transport belt, the paper can be easily removed.

According to the third aspect of the present invention, when the transport belt is replaced, the transport mechanism is lowered to a position below the bearing or the frame for holding the photoreceptor, and then the unit case is slid so as to be transported. The transport mechanism can be pulled out without hooking the belt on the bearing or the frame. According to the fourth aspect of the present invention, even in a tandem type image forming apparatus in which a plurality of image forming units are arranged along the transport path, each of the photoconductors provided in each image forming unit has The transport mechanism can be largely separated. Therefore, unlike the configuration in which the transport mechanism is rotated around the first roller or the second roller, there is no sufficient space between the photosensitive member closest to the center of rotation and the transport belt, so that the transport belt is moved forward. There is no such thing as it becomes difficult to pull out.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing the internal configuration of a digital full-color printer in which a transport belt unit according to an embodiment of the present invention is provided as a transfer belt unit.

FIG. 2 is a perspective view illustrating a configuration of a transfer belt unit.

FIG. 3 is a diagram for explaining a function of a lifting mechanism;
(A) shows the transfer belt unit when the transport mechanism is displaced upward, and (b) shows the transfer belt unit when the transport mechanism is displaced downward.

FIG. 4 is an illustrative view for explaining a function of a pressure release mechanism, wherein (a) shows a state in which a conveying belt is pressed against all photosensitive drums, and (b) shows magenta, cyan and yellow photosensitive drums; The state where the pressure contact state of the transport belt to the body drum is released is shown.

FIG. 5 is a plan sectional view schematically showing an image forming unit.

FIG. 6 is a diagram of the image forming unit as viewed from the front side of the printer body.

FIG. 7 is a schematic diagram illustrating a configuration example of a conventional transport belt unit.

FIG. 8 is a schematic view showing another example of the configuration of a conventional conveyor belt unit.

[Explanation of symbols]

 2 Printer body 10B, 10M, 10C, 10Y Image forming unit 11B, 11M, 11C, 11Y Photoconductor drum 40 Transfer belt unit 41 Unit case 42 Slide mechanism 43 Transport mechanism 44 Drive roller 45 Follower roller 46 Transport belt 51 Lifting mechanism

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Kazuya Uehira, 1-2-28 Tamazuki, Chuo-ku, Osaka-shi, Osaka Prefecture Inside Mita Kogyo Co., Ltd. Mita Kogyo Co., Ltd. (72) Inventor Noriaki Miyamoto 1-2-28 Takumazo, Chuo-ku, Osaka-shi, Osaka Mita Kogyo Co., Ltd.

Claims (4)

[Claims] 1. A unit case, and a first roller, a first roller,
A second roller provided at a predetermined distance in the horizontal direction with respect to the roller, and an endless transport that is hung between the first roller and the second roller to form a transport path whose upper surface extends in the horizontal direction. A transport belt unit comprising: a transport mechanism having a belt; and an elevating mechanism for vertically moving the transport mechanism relative to a unit case. 2. A transport belt unit for transporting a sheet, and an image forming unit provided in association with the transport belt unit and for forming an image to be transferred onto the sheet transported by the transport belt unit. An image forming apparatus, comprising: the transport belt unit according to claim 1 as a transport belt unit. 3. An image forming apparatus according to claim 2, further comprising a slide mechanism for holding said unit case slidably in a direction perpendicular to a sheet conveying direction. 4. A plurality of image forming units are provided along a transport path formed by a transport belt, and the plurality of image forming units form images of different colors. The image forming apparatus according to claim 2 or 3.