JPH11338280A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an excellent-quality image extending over a long term by surely energizing a transfer roller. SOLUTION: A bearing unit 131 is composed of a bearing 132 formed of a conductive material and a compression spring 133 which is made of the conductive material and which elastically supports the bearing 132. Besides, it is slidably housed in a side plate 78 of a transfer belt unit and a bearing housing groove 134 of an elevating/lowering plate 93. Then, a projection 135 engaged with the upper end part of the spring 133 is formed at the lower end of the bearing 132 so that the spring 133 and the bearing 132 are always brought into contact with each other. Besides, a conductive part 137 connected to an outside power source through a wire 136 is arranged at the lower end of the spring 133. Then, the rotary shaft 130a-130d of transfer rollers 41a-41a are rolled in a bearing hole 138 of the bearing 132.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile for forming an image on a transfer member such as paper or a plastic sheet.

[0002]

2. Description of the Related Art For example, a printer for forming a color image on a transfer member such as a sheet of paper generally has a transfer drum system,
It is classified into four types of recording systems: an intermediate transfer system, a tandem system, and a multiple developing system. Of these, in response to the recent demand for high-speed recording, a tandem method that is superior to other methods in recording speed has been often adopted. This tandem printer uses black, black,
Cyan, magenta, and yellow photoconductors are appropriately arranged,
The transfer body is sequentially conveyed to each of the photoconductors by the transfer belt unit, and the toner images of each color formed on each of the photoconductors are sequentially transferred to the transfer body. Then, a desired color image is formed by a fixing device (fixing unit). It is designed to be fixed on a transfer member.

In a transfer belt unit used in such a tandem type printer, a plurality of photosensitive members are arranged in a line in a sheet conveying direction, so that a sheet fed from a sheet feeding section is driven by a driving roller and a driven roller. It is electrostatically attracted by an endless transfer belt wound around a roller, and is conveyed to each photoconductor. Here, since the transfer roller conveyed to each photoreceptor is provided with a charge having a polarity opposite to that of the charged toner by the transfer roller on the back side, the toner image on the photoreceptor side is transferred to the front surface.

[0004]

As described above, a transfer roller for applying a charge having a polarity opposite to that of the charged toner to the back side of the transfer body generally has a flat conductive brush at the end of its rotating shaft. The electric brush is brought into contact with the electric power source, and the electric power is supplied from an external power source through the electric brush. However, in a conventional example in which a flat conductive brush is brought into contact with the end of the rotating shaft,
Since the contact portion of the flat conductive brush with the rotating shaft is always a fixed portion, the contact portion may be worn, causing a phenomenon called so-called burn-in, which may result in poor current supply. When such an energization failure to the transfer roller occurs, noise is generated to cause a malfunction of the machine or transfer is not performed accurately, so that a high-quality image cannot be formed on the transfer body.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus capable of stably energizing a transfer roller for a long time and forming a high-quality image on a transfer body.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a transfer roller which presses a transfer member against a photoreceptor having a toner image formed thereon and applies a transfer charge having a polarity opposite to that of the charged toner to the back surface of the transfer member. A conductive bearing that rotatably supports the roller, and a conductive spring that urges the transfer roller toward the photoconductor through the conductive bearing; and a conductive spring that is provided through the conductive spring and the conductive bearing. It is characterized in that the transfer roller is energized.

According to the present invention having such a configuration, the transfer roller rotatably supported by the bearing comes into rolling contact with the bearing, and the contact surface between the bearing and the transfer roller changes. Therefore, the contact surface between the bearing and the transfer roller does not cause a problem of so-called seizure, and it is unlikely that the current supply failure occurs, so that the transfer roller is reliably energized through the conductive spring and the conductive bearing for a long time. You. In the prior art in which the end of the rotating shaft and the plate-shaped contact terminal are always in sliding contact at one place, the sliding contact portion of both is worn out early,
There is a possibility that a problem such as so-called burn-in may occur, and a current supply failure may occur.

The present invention also relates to a black-and-white and a plurality of color photoconductors arranged in a transfer body transport direction, and a drive roller and a tension roller arranged at predetermined intervals in the transfer body transport direction. And an endless transfer belt that electrostatically attracts the transfer body and conveys the transfer body to the photoconductor, and is disposed between the drive roller and the tension roller and at a position corresponding to the photoconductor, and is disposed via the transfer belt. A transfer roller that presses the transfer member against the photoreceptor on which the toner image is formed, and that applies a charge having a polarity opposite to that of the charged toner to the back surface of the transfer member via a transfer belt; Transfer roller lifting / lowering means for retracting the transfer roller corresponding to the photoconductor for use from the transfer work position separately from the transfer roller corresponding to the photoconductor for black and white. And
The transfer roller is rotatably supported by a conductive bearing, and the transfer roller is urged toward the photoreceptor by a conductive spring via the conductive bearing. And energizing the transfer roller. Here, the photoconductor for black and white refers to a photoconductor using black toner. The photoconductor for color is a photoconductor using magenta, cyan, yellow or other color toner.

According to the present invention, the transfer roller corresponding to the plurality of color photoconductors among the plurality of transfer rollers can be moved up and down separately from the transfer roller corresponding to the black and white photoconductor. Even with this configuration, the transfer roller is reliably brought into contact with the photosensitive member via the transfer belt, and the transfer roller is reliably energized via the conductive spring and the conductive bearing.
Therefore, according to the present invention, the occurrence of transfer unevenness is effectively prevented, and a high-accuracy image is formed over a long period of time.

According to a third aspect of the present invention, there is provided a photosensitive drum for black and white and a plurality of colors arranged in the transfer body conveying direction, and a driving roller and a tension roller arranged at a predetermined interval in the transfer body conveying direction. And an endless transfer belt for electrostatically adsorbing and transferring the transfer body to the photoconductor, and a transfer belt disposed between the drive roller and the tension roller and at a position corresponding to the photoconductor drum. A transfer roller that presses the transfer body against the photosensitive drum on which the toner image has been formed via the transfer belt, and that applies a charge of a polarity opposite to that of the charged toner to the back surface of the transfer body via the transfer belt; A transfer roller that presses and retreats the transfer roller corresponding to the plurality of color photoconductor drums to the color photoconductor drum separately from the transfer roller corresponding to the black and white photoconductor drum And a means. Further, according to the present invention, both ends of the outer periphery of the photosensitive drum are rotatably supported by bearings, the transfer roller is rotatably supported by conductive bearings, and the transfer roller is supported via the conductive bearings. The present invention is characterized in that the transfer roller is energized by biasing the photosensitive member side with a conductive spring and passing through the conductive spring and the conductive bearing.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

<Schematic Configuration of Color Printer> FIG. 1 is a schematic configuration diagram of a color printer (image forming apparatus) according to a first embodiment of the present invention.

First, a schematic configuration of the color printer 2 will be described with reference to FIG. The color printer 2 includes a sheet feeding unit 4 that feeds sheets 3 as transfer members one by one, a conveying unit 6 that conveys the sheet sent from the sheet feeding unit 4 to an image forming unit 5 described below, An image forming unit (image forming unit) 5 for forming a toner image to be transferred onto the sheet conveyed by the sheet 6, and a sheet conveyed by the conveying unit 6, and the sheet conveyed in a predetermined direction;
A transfer / conveying unit 7 for transferring the toner image formed by the image forming unit 5 to the sheet, a fixing unit 8 for fixing the toner image on the sheet conveyed by the transfer / conveying unit 7 to the sheet,
The paper discharge unit 1 that receives the sheet discharged from the fixing unit 8
0 and an optical unit 11 for irradiating the image forming section 5 with laser light for exposure.

The paper feed unit 4 feeds the sheets 3 stacked on the first paper feed tray 12 to a paper feed roller 13 and a reverse roller 14.
And a second paper feed unit 18 for feeding sheets (not shown) on the manual feed tray 16 by the paper feed roller 17.

The conveying section 6 includes a conveying path 20 for guiding the movement of the sheet 3 sent from the first sheet feeding section 15, a conveying roller 21 disposed in the middle of the conveying path 20, A pair of registration rollers 22 that receives the sheet, corrects the skew of the sheet, and feeds the sheet to the image forming unit 5, and a manual conveyance path 23 that is connected to the conveyance path 20 upstream of the registration roller pair 22 in the sheet conveyance direction. Has become.

The image forming unit (image forming unit) 5 includes a first image forming unit 24 having a black toner (hereinafter, abbreviated as black) and a toner containing a cyan pigment (hereinafter, abbreviated as black). A second image forming unit 25 having cyan (abbreviated as cyan), a third image forming unit 26 having magenta pigment-containing toner (hereinafter abbreviated as magenta), and a yellow pigment-containing toner (hereinafter abbreviated as yellow). And a fourth image forming unit 27. And the first to fourth
Each of the image forming units 24 to 27 includes a cylindrical photosensitive drum (photosensitive member) 28, a developing device 30 for forming a toner image on the outer peripheral surface of the photosensitive drum 28, and a residual toner on the photosensitive drum 28. Device 33 including fur brush 31 and cleaning blade 32 for removing dust
To charge the photosensitive drum 28 to charge the photosensitive drum 2
And a charging device 34 for charging. still,
The image forming unit 5 can be pulled out of the color printer main body 36 integrally with the support frame 35. Each of the photosensitive drums 28 sequentially arranged in the sheet conveying direction is supported so that both ends of the outer periphery can be rotated by the image forming frame 35 by bearings (not shown). Each of the photosensitive drums 28 is driven to rotate with high precision by a driving unit (not shown) (for example, a servo motor with a planetary roller speed reducer).

The transfer conveyance section 7 includes an endless transfer belt 37 made of a fluorine resin material, a driving roller 38 around which the transfer belt 37 is wound, and a tension roller (follower roller) 4.
0, and transfer rollers 41a, 41b, 41c, and 41d disposed at positions facing the respective photosensitive drums 28. Then, these transfer rollers 41a to 41
The transfer belt 37 is sandwiched between d and each photosensitive drum 28. Further, a belt guide roller 43 is disposed at an appropriate position on the inner peripheral side of the transfer belt 37. The transfer conveyance section 7 includes a photosensitive drum 28, a transfer roller 41
In order to prevent deterioration of the transfer belts 37a to 41d and the transfer belt 37, the transfer rollers 41a to 41d and the transfer belt 3
7 is lowered to the position indicated by the two-dot chain line, and the tension roller 40 is slightly moved to the drive roller side so that the photosensitive drum 28 and the transfer roller 41 are moved.
The pressure acting on the transfer belt 37 and the tension acting on the transfer belt 37 are released. When only a black-and-white image is to be created, the transfer / conveyance section 7 has other transfer rollers 41b to 41c for cyan, magenta, and yellow.
A mechanism (not shown) for separating d from the photosensitive drum 28
It has. Here, the drive roller 38 is connected to a drive motor (not shown) via a torque limiter (not shown), and causes a slip on the drive motor when a predetermined torque or more acts. Therefore,
The transfer belt 37 is given a driving force by a driving roller 38, but follows the rotation of the photosensitive drum 28.

The fixing unit 8 includes a heating roller 44 having a built-in heater, a fixing roller 45, and a metal endless belt 4 wound around the heating roller 44 and the fixing roller 45.
6, and a pressure roller 47 pressed against the fixing roller 45
And Then, a donor roller 48 for supplying oil to the outer surface of the endless belt 46 and the donor roller 4
An oil roller 50 and a cleaning roller 51 that are in rolling contact with the roller 8 are arranged.

The paper discharge section 10 guides the sheet discharged from the fixing section 8 to an upper portion of the color printer main body 36 through a discharge path 53, and a discharge tray 54 on which the image forming surface is stacked.
And The paper ejection cover 52 can be pulled out of the color printer main body 36 when the jam is cleared, and can be stored in the color printer main body 36 when the jam is not cleared.

The optical unit 11 has a polygon scanner mirror 55, image forming lenses 56, 57 and a mirror 58 arranged corresponding to each photosensitive drum 28, and a laser beam is formed on an optical unit support plate 60. Slit 61
Irradiates the photosensitive drum 28 toward the photosensitive drum 28.

The color printer 2 configured as described above
When a sheet is sent out from the first sheet supply unit 15 or the second sheet supply unit 18, the sheet is transferred to the photosensitive drum 28 of the first image forming unit 24 and the transfer belt 37 of the transfer transfer unit 7 by the transfer unit 6. Sent between. Then, while the sheet is conveyed by the transfer belt 37 between the photosensitive drum 28 and the transfer rollers 41a to 41d, the toner images formed on the black, cyan, magenta, and yellow photosensitive drums 28 are sequentially formed. Transcribed. Then, the sheet on which the transfer of the color image has been completed is sent by the transfer belt 37 between the fixing roller 45 and the pressure roller 47 of the fixing unit 8, where the sheet is heated and pressed to fix the color toner image. . The sheet on which the fixing operation has been completed is discharged to the discharge tray 54.

<Details of Transfer Conveying Unit> Next, details of the transfer conveying unit 7 will be described with reference to FIGS.

FIG. 2 is a front view showing a part of the transfer conveyance section 7 when printing is stopped (at a position where the transfer belt unit is lowered). FIG. 3 is a front view showing a part of the transfer conveyance section 7 in a printing state (up position of the transfer belt unit) with a part omitted. Further, FIG.
FIG. 4 is a sectional view taken along line AA of FIG. 3.

As shown in these figures, the transfer conveying section 7
Is a transfer belt unit support frame 70 fixed to the printer main body 36, elevating means 71 attached to the transfer belt unit support frame 70, and a transfer belt unit 72 supported by the elevating means 71 so as to be able to move up and down.
And

(Elevating means) Of these, the elevating means 71
The rotating shaft 73 rotatably supported by the transfer belt unit support frame 70, a cam 74 fixed to the rotating shaft 73, and a motor 75 for driving the rotating shaft 73 to rotate. The rotating shafts 73 are arranged in a pair at predetermined intervals in the transfer body transport direction of the transfer belt unit support frame 70 (direction B in FIG. 3). As shown in FIG. 4, a pair of cams 74 are fixed to both ends of the rotating shaft 73, and move the transfer belt unit 72 up and down between the lower position in FIG. 2 and the upper position in FIG. It has become. Further, the motor 75 is connected to a controller 76 as control means, and operates based on a control signal output from the controller 76. The controller 76 outputs a control signal to the motor 75 based on a signal from a switch (not shown) attached to the printer main body 36 or a switch of a drawer lever (not shown) of the image forming unit 5. I have.

(Transfer Belt Unit) The transfer belt unit 72 rotatably supports the drive roller 38, the tension roller 40, and the transfer rollers 41a to 41d by a pair of side plates 78, 78 of a base plate 77. (See FIG. 4). The tension roller 41
b to 41d are supported by side plates 78, 78 via elevating plates 93, 93 described later. An overhang portion 80 is formed on the side plate 78 of the base plate 77,
A support leaf spring 81 is attached to the lower surface 80a side of the overhang portion 80. The support leaf spring 81 includes a base portion 81a fixed to the base plate 77 and a flexible portion 81b that bends and deforms. As shown in FIG. It is mounted open. The flexible portion 81b of the support leaf spring 81 is supported by the cam 74. Therefore, the transfer belt unit 72 is elastically supported on the transfer belt unit support frame 70.

Below the side plate 78 of the base plate 77,
A guide pin 82 is attached, and the guide pin 82 is slidably engaged with the elevating guide groove 83 of the transfer belt unit support frame 70. Therefore, the transfer belt unit 72 is
Can be moved up and down accurately.

(Positioning pin) Also, as shown in FIG.
Upper surface 8 of overhang 80 of transfer belt unit 72
0b, positioning holes 84, 85,
A positioning pin 87 made of a resin material that engages with 86 is attached. Therefore, when the transfer belt unit 72 is lifted to the state shown in FIG. 3 by the cam 74, the transfer belt unit 72 is pressed toward the image forming unit 5 by the elastic force of the support plate spring 81 and is positioned on the image forming unit 5 side. The positioning pin 87 is engaged with the holes 84, 85 and 86, and is accurately positioned with respect to the image forming unit 5.

The positioning pin 87 is, as shown in FIG.
A pair is arranged on the upstream side in the transfer body transport direction and in a direction orthogonal to the transfer body transport direction, and a pair is arranged on the downstream side in the transfer body transport direction and in a direction orthogonal to the transfer body transport direction. As shown in FIGS. 2 to 5, the positioning pin 87 includes a flat board portion 87a.
The upper surface of 7 a contacts the positioning surface 88 on the image forming unit 5 side, and also functions as a stopper surface or a positioning surface that regulates the rising end position of the transfer belt unit 72 (see FIG. 3). By forming the positioning pins 87 from the resin material in this manner, when the transfer belt unit 72 is pressed against the image forming unit 5, the substrate portion 87a of the positioning pins 87 is pressed.
The transfer belt unit 72 can absorb the impact.
Can be quietly positioned with respect to the image forming unit 5. Further, by forming the positioning pins 87 from a resin material, the positioning pins 87 can be smoothly engaged with the positioning holes 84, 85, 86 on the image forming unit 5 side, and the transfer belt unit 72 and the image forming unit 5 are formed. Can be performed smoothly.

Here, as shown in FIG. 5, the first to third three types of positioning holes 84 which engage with the positioning pins 87 of the overhang portion 80 are formed on the positioning surface 5a at the bottom of the image forming unit 5. To 86 are formed. Of these, the first positioning hole 84 is a round hole that engages with a small gap with one of the positioning pins 87 on the upstream side in the transfer body transport direction. The second positioning hole 85 is engaged with the other positioning pin 87 on the upstream side in the transfer body transport direction with a slight gap in the transfer body transport direction, while the second positioning hole 85 is in a direction orthogonal to the transfer body transport direction. Is an elongated hole that engages with a sufficient gap. Furthermore, the third positioning hole 86 is a round hole that engages with a sufficient gap with the pair of positioning pins 87 on the downstream side in the transfer body transport direction, and does not have the original function of the positioning hole. This is because a pair of positioning pins 87 on the upstream side in the transfer body transport direction and positioning holes 84 and 8 on the image forming unit 5 side.
This is because positioning with the image forming unit 5 and the transfer body belt unit 72 can be reliably performed by engagement with the transfer member 5.

As described above, in the present embodiment, the positioning pins 87, 87 and the positioning holes 84, which are arranged in a pair on the upstream side in the transfer body transport direction and in the direction orthogonal to the transfer body transport direction.
85, the transfer body belt unit 72 is positioned with respect to the image forming unit 5, so that the transfer start position of the transfer body by the transfer belt unit 72 is accurately positioned upstream in the transfer body transfer direction, and the transfer body Is accurately positioned, and the transfer of the transfer body to the image forming unit 5 is always accurately performed. as a result,
The toner image of the image forming unit is accurately transferred to the transfer body conveyed by the transfer belt unit, and color misregistration during color image formation is more effectively suppressed.

In this embodiment, as described above, a pair of positioning pins 8 are arranged on the upstream side in the transfer body transport direction.
One of the positioning pins 87 and the positioning holes 84 is formed so as to engage with a slight gap in the transfer body transport direction and a direction orthogonal to the transfer body transport direction. Further, the other positioning pin 87 and the positioning hole 85 are formed so as to engage with a slight gap in the transfer body transport direction, while engaging with a sufficient gap in a direction orthogonal to the transfer body transport direction. Therefore, a dimensional error between the pair of positioning pins 87, 87 and a dimensional error between the pair of positioning holes 84, 85 can be absorbed by the gap between the other positioning pin 87 and the other positioning hole 85, The positioning between the transfer belt unit 72 and the image forming unit 5 can be performed smoothly.

In this embodiment, the reason for adopting the configuration in which the pair of positioning pins 87 on the downstream side in the transfer body transport direction is engaged with the positioning holes 86 on the image forming unit 5 is as follows.
By commonly using four positioning pins 87 that also function as stoppers or positioning surfaces at the rising end position of the transfer belt unit 72, the number of components is reduced, component management is facilitated, and component costs are reduced. That's why.

(Transfer Belt Unit Support Frame) As shown in FIG. 4, the transfer belt unit support frame 70 has a pair of side plates 70a and a bottom plate 70b connecting the pair of side plates 70a, and has a sufficient strength. Have. As shown in FIG. 4, the base plate 77 is sized to be accommodated inside the transfer belt unit support frame 70, and similarly to the transfer belt unit support frame 70, the base plate 77 has a pair of side plates 78, 78 and the pair of side plates 78, 78. Side plate 78,
And a bottom plate 79 for connecting the driving roller 3.
8 and the transfer roller 41a.

<Transfer roller lifting / lowering means and tension release means of transfer belt unit>
2 is a transfer roller 41b corresponding to the second image forming unit 25, a transfer roller 41c corresponding to the third image forming unit 26, and a transfer roller corresponding to the fourth image forming unit 27, as shown in FIGS. Transfer roller lifting / lowering means 9 for raising / lowering only 41d at the same time
0 is provided. Further, the transfer belt unit 72 moves the tension roller 40 toward the drive roller 38 when the print belt unit 72 is lowered to the retracted position (the position shown in FIG. 2) when printing is stopped, and releases the tension of the transfer belt 37. It has.

(Transfer Roller Elevating Means) First, the transfer roller elevating means 90 will be described with reference to FIGS. 4, 6 and 7. FIG. As shown in these figures, the transfer rollers 41b to 4b
1d, both ends of the rotating shaft 92 are rotatably supported by the lifting plate 93, respectively. A pair of cam grooves 94 having the same shape are formed at predetermined intervals in the longitudinal direction (C1 direction in FIG. 6) on the pair of elevating plates 93 supporting both ends of the transfer rollers 41b to 41d. As shown in FIGS. 6 and 7, the cam groove 94 includes a horizontal groove 95 extending in the C1 direction and a diagonal groove 96 extending diagonally rightward and upward from the horizontal groove 95, and is supported by the base plate 77. Guide shaft 97 is slidably engaged. Of the guide shaft 97 engaged with the pair of cam grooves 94, FIG.
The middle right guide shaft 97 has an eccentric disk cam 98 that rotates integrally with the guide shaft 97 at a position near the side surface of the elevating plate 93. The guide shaft 97 having the eccentric disk cam 98 is connected to a motor 100 and is driven to rotate by the motor 100. An eccentric disk cam 98 is provided on a side surface of the lifting plate 93.
A pair of guide ribs 101 are formed so as to sandwich them with a gap. The plate-like spring member 102 is attached so as to project toward the eccentric disk cam 98 so that a predetermined gap is formed between the plate-like spring member 102 and the guide rib 101. Therefore, when the right plate spring member 102 in FIG. 6 is pressed by the eccentric disk cam 98, the plate spring member 102 urges the elevating plate 93 in the direction C1 in FIG.
Further, the plate-like spring member 102 on the left side in FIG.
8, the plate-like spring member 102 urges the elevating plate 93 in the direction C2 in FIG.

In the transfer roller elevating means 90 having the above-described structure, in the state shown in FIG. 6, an operation control signal is output from the controller 76 to the motor 100, and the motor 100 rotates based on the operation control signal. When the plate spring member 102 on the middle right is pressed and deformed by the eccentric disk cam 98, the elevating plate 93 is urged by the plate spring member 102 in the direction C1 in the drawing. As a result, the guide shaft 97
Slides in the oblique groove portion of the cam groove 94, and the elevating plate 9
3 rises obliquely upward. When the guide shaft 97 contacts the lower wall 95a of the lateral groove 95, the elevating plate 93
Is further urged by the plate spring member 102 in the direction C1 in the figure. As a result, the guide shaft 97 and the lateral groove 95 of the cam groove 94 are completely engaged (see FIG. 7), and the transfer roller 41b
Even if .about.41d is pressed from the image forming unit 5 side (upper side in FIG. 7), the elevating plate 5 does not descend. That is, the lifting plate 93 is locked by the guide shaft 97 at the upper end position shown in FIG.

On the other hand, in the state shown in FIG. 7, when the plate spring member 102 on the left side in FIG. 7 is pressed and deformed by the eccentric disc cam 98 in the state of FIG. Is urged in the direction C2 in the figure. As a result, the engagement between the guide shaft 97 and the lateral groove 95 of the cam groove 94 is released, and the locked state of the elevating plate 93 is released. Thereafter, when the plate spring member 102 on the left side in FIG. 7 is further pressed by the eccentric disk cam 98, the guide shaft 97 slides in the oblique groove 96 of the cam groove 94, and the elevating plate 93 is moved by two points. Go down diagonally to the dashed line. As a result, the transfer rollers 41b to 41d corresponding to the second image forming unit 25 to the fourth image forming unit 27
Moves down to a predetermined retracted position shown in FIG. 6 (the position indicated by the two-dot chain line in FIG. 7).

As described above, according to the transfer roller elevating means 90 of the present embodiment, the elevating plate 93 is
7 and the cam groove 94 move up and down in parallel, and the transfer rollers 41b to 41d move up and down in the same manner. Therefore, according to the present embodiment, the retracted amount (downward dimension) of the transfer rollers 41b to 41d is smaller than a configuration in which a support shaft is provided at one end of the elevating plate 93 and the other end is rotated downward. Since the height dimension (direction dimension) of the transfer belt unit 72 can be reduced, the size of the transfer belt unit 72 can be reduced. Therefore, the color printer 2 using the transfer belt unit 72 can be reduced in size.

Here, the transfer roller lifting / lowering means 90 controls the motor from the controller 76 to the motor 100 when the transfer belt unit 72 is separated from the image forming unit 5 and descends to the position shown in FIG. A signal is output to lower the elevating plate 93 from the upper end position shown in FIG. 7 to the lower end position shown in FIG. Further, the transfer roller elevating means 90 lowers the elevating plate 93 from the upper end position shown in FIG. 7 to the lower end position shown in FIG. 6 even when only the first image forming section 24 is used and only a monochrome image is created. Therefore, as shown in FIG. 7, when the lifting plate 93 is raised to the upper end position, it is at the time of printing a color image.

(Tension Releasing Means) Next, the tension releasing means 91 of the transfer belt 37 will be described with reference to FIGS. FIG. 8 shows a state in which the tension roller 40 is held at a position where tension is applied to the transfer belt 37. FIG. 9 shows a state where the tension roller 40 is held at a position where the tension of the transfer belt 37 is released.

The tension releasing means 91 shown in these figures
Is a tension roller support plate 110 slidably engaged with the base plate 77 of the transfer belt unit 72 shown in FIGS. 2 and 3, and a direction in which the tension roller support plate 110 is separated from the drive roller 38 (D in the drawings). Tension spring 1 that always urges
11 are provided.

The tension roller support plate 110 rotatably supports both ends of the rotation shaft 40a of the tension roller 40. Therefore, the tension roller support plate 110 guides the side plates 78 on both sides of the base plate 77 shown in FIG. Guide plate 113 fixed via pin 112
Are slidably engaged with each other, and slidably engage with the pair of guide pins 112.
Are formed.

One end of the tension spring 111 is engaged with the tension roller support plate 110, and the other end is connected to the base plate 77 of the transfer belt unit 72.
And a tension spring that constantly urges the tension roller support plate 110 in a direction (D direction) that applies tension to the transfer belt 37. As shown in FIG. 8, the tension roller support plate 110 is pulled in the right direction (D direction) by the tension spring 111 until the guide pin 112 contacts the left end of the elongated hole 114. I have.

Here, when the cam 74 rotates in the direction of arrow E in FIG. 8 and the transfer belt unit 72 descends from the position shown in FIG. 3 to the position shown in FIG.
Hook 1 at tip of tension roller support plate 110
15 engages the arm 116 of the cam 74. Then, the tension roller support plate 110 is moved by a predetermined amount L1 against the spring force of the tension spring 111 by an arm 116 which rotates together with the cam 74, as shown in FIG. As a result, the tension of the transfer belt 37 is released.

On the other hand, the tension roller support plate 11
When the transfer belt unit 72 is moved toward the image forming unit 5 by rotating the cam 74 clockwise (direction F in FIG. 9) by a predetermined angle (from the position in FIG. 2 to the position in FIG. 3). Position, the arm 116 of the cam 74 is disengaged from the hook 115 of the tension roller support plate 110, and the tension spring 1
By means of 11, it is moved to the position shown in FIG. As a result, the tension roller 40 rotatably supported by the tension roller support plate 110 is moved to the transfer belt 3.
7 will be tensioned.

The tension releasing means 91 having such a configuration is described.
Accordingly, when the transfer belt unit 72 is lowered, the tension of the transfer belt 37 is automatically released, and when the transfer belt unit 72 is raised, the tension is automatically applied to the transfer belt 37. Therefore, the color printer 2 including the tension releasing unit 91 can release the tension of the transfer belt 37 when the transfer belt unit 72 is lowered, that is, when the machine is stopped, and can improve the durability of the transfer belt 37. , It is possible to perform smooth image printing, so that the reliability of the color printer 2 can be significantly improved.

(Another Embodiment of Tension Release Means)
FIG. 10 shows another embodiment of the tension release means. Tension release means 121 shown in this figure
In the state where the machine is stopped, that is, when the transfer belt unit 72 is lowered to the lowermost position (the state shown in FIG. 2), the cam 74 is further rotated from the position shown in FIG. I have. Then, when the image forming unit 5 is pulled out from the printer main body 36 shown in FIG. 1 and the sensor 122 detects the operation of pulling out the image forming unit 5, a detection signal is output from the sensor 122 to the controller 76 and the controller 76 rotates the image forming unit 5. A control signal is output to a motor 75 that drives the shaft 73. Then, the motor 75 rotates the rotary shaft 73 by a predetermined angle based on a control signal from the controller 76, and rotates the cam 74 from the retracted position to the intermediate position. As a result, the tension roller support plate 123 is urged by the tension spring 124 and moves rightward (H direction) in FIG. 10 by a predetermined dimension L2, and the transfer belt 37 is moved by the tension roller 40 so that the slack of the transfer belt 37 is reduced. Give 37 a tension. Here, the cam surface 125 is in contact with the supporting plate spring 81 about the center of rotation of the rotating shaft 73 so that the position of the transfer belt unit 72 does not change even when the cam 74 rotates from the intermediate position to the retracted position. Is formed in an arc shape with a radius dimension R.

The color printer 2 provided with the tension releasing means 121 according to the above-described embodiment has the image forming unit 5
When the transfer belt 37 is pulled out, the loose transfer belt 37 is stretched, so that the transfer belt 37 does not catch on the image forming unit 5 from which the transfer belt 37 is pulled out. Therefore, the color printer 2 including the tension release unit 121 can reduce the amount of elevation of the transfer belt unit 72,
The height of the color printer 2 can be reduced,
The size of the color printer 2 can be reduced.

<Transfer Roller Support Bearing> FIGS. 11 and 12
Are rotating shafts 130a-13 of the transfer rollers 41a-41d.
It is a figure which shows the detail of the bearing unit 131 which supports 0d rotatably. As shown in these figures, the bearing unit 131 includes a bearing 132 formed of a conductive material, and a compression spring 133 made of a conductive material that urges the bearing 132 upward in the drawing. The belt unit 72 is slidably accommodated in the side plate 78 of the base plate 77 and the bearing accommodation groove 134 of the elevating plate 93, respectively. In the present embodiment, the bearing 132 made of a sintered alloy having conductivity is used. However, the present invention is not limited to this, and the bearing 132 may have any conductivity.

At the lower end of the bearing 132, a projection 135 is formed which engages with the upper end of the compression spring 133, so that the compression spring 133 and the bearing 132 can maintain a constant contact state. At the lower end of the compression spring 133, a conductive portion 137 connected to an external power supply (not shown) via a wire 136 is disposed. The transfer rollers 41a to 41d are made of a conductive sponge such as urethane, silicon, or EPDM or solid rubber, and their rotating shafts 130a to 130d are made of a conductive metal.

The thus constructed bearing unit 131
Are rotating shafts 130a-13 of the transfer rollers 41a-41d.
0d rolls in the bearing hole 138 of the bearing 132, and the contact surface between the bearing 132 and the rotating shafts 130a to 130d changes, so that the ends of the rotating shafts 130a to 130d and the plate-shaped contact terminals are always in contact. Compared with the related art in which the sliding contact is made at one place, the current supply failure is less likely to occur, and the transfer rollers 41a to 41d can be reliably energized for a long time. The conventional technology in which the end portions of the rotating shafts 130a to 130d and the plate-shaped contact terminal are always in sliding contact at one place, has a disadvantage that both sliding contact portions are worn out early or so-called seizure. Therefore, there is a fear that a current supply failure occurs.

Therefore, the color printer 2 including the bearing unit 131 of the present embodiment is provided with the transfer roller 41a.
To 41d, a charge having a polarity opposite to that of the charged toner is applied to the back surface of the transfer body via the transfer belt 37, and the charged toner can be reliably transferred to the transfer body. Image can be formed.

In this embodiment, since the transfer rollers 41a to 41d are energized via the conductive portion 137, the compression spring 133 and the bearing 132 as described above, the second image forming portion 25 is provided. When the transfer rollers 41b to 41d corresponding to the fourth image forming unit 27 are moved up and down, for example, the photosensitive drum 28, the transfer belt 37, and the transfer rollers 41b to 41d are moved.
After the pressure contact state of 41d is released, the transfer roller 4
Even when 1b-41d is raised again, the transfer rollers 41a-41d are always in contact with the bearing 132, and the transfer rollers 41b-41d are reliably energized. Therefore, the color printer 2 using the bearing unit 131 of the present embodiment has a plurality of transfer rollers 41b to 41b.
d, the transfer rollers 41b to 41b
1d can be reliably energized, and a high-quality image can be reliably formed. The transfer rollers 41b to 41b
The prior art in which the end portions of the rotating shafts 130b to 130d and the plate-shaped contact terminals are always in sliding contact at one place,
When the transfer rollers 41b to 41d move up and down with respect to the plate-shaped contact terminals, there is a problem that it is difficult to always reliably contact the transfer rollers 41b to 41d and the plate-shaped contact terminals.

According to the present embodiment, all the transfer rollers 41a to 41d are energized through the conductive portion 137, the compression spring 133 and the bearing 132, so that the transfer rollers 41a to 41d The configuration for energization may be the same, and the configuration is not complicated.

In the above embodiment, the bearing 132 is connected to an external power supply via the compression spring 133 and the conductive portion 137.
36 and the compression spring 133 may be connected, and the conductive portion 137 may be omitted. In the above embodiment, a color printer as an image forming apparatus has been described as an example. However, the present invention is not limited to this, and can be widely applied to facsimile machines, copiers, and the like. Further, in the above embodiment,
Although the drum-shaped photoconductor has been exemplified as the photoconductor, the present invention is not limited to this, and may be applied to a belt-shaped photoconductor.

[0057]

As described above, according to the present invention, the transfer roller rotatably supported by the conductive bearing rolls on the conductive bearing, and the contact surface between the conductive bearing and the transfer roller changes. However, since the contact surface between the conductive bearing and the transfer roller does not cause a problem of so-called burn-in, it is difficult to cause a power supply failure, and it is possible to reliably supply power to the transfer roller via the conductive spring and the conductive bearing. Can be. Therefore, according to the present invention, transfer unevenness can be effectively suppressed, and a high-quality image can be formed for a long period of time.

In the present invention, of the plurality of transfer rollers, the transfer roller corresponding to the photosensitive member for color is configured to be able to move up and down separately from the transfer roller corresponding to the photosensitive member for black and white. Is reliably energized through the conductive spring and the conductive bearing. Therefore, according to the present invention, even if the plurality of transfer rollers can be moved up and down, transfer unevenness can be effectively prevented, and a high-accuracy image can be formed for a long period of time. In addition, in the present invention, since all the transfer rollers are energized with the same configuration, the configuration for energizing the transfer rollers is not complicated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a front view (a state diagram illustrating a lowered position of a transfer belt unit) of a transfer conveyance unit according to an embodiment of the invention, with a part of the transfer conveyance unit omitted.

FIG. 3 is a front view (a state diagram illustrating a raised position of a transfer belt unit) of a transfer conveyance unit according to an embodiment of the invention, with a part of the transfer conveyance unit being omitted;

FIG. 4 is a sectional view taken along the line AA in FIG. 3;

FIG. 5 is a diagram illustrating a positioning state between an image forming unit and a transfer belt unit.

FIG. 6 is a diagram illustrating a first operation state (a lowered position) of a transfer roller elevating unit.

FIG. 7 is a diagram illustrating a second operation state (elevated position) of the transfer roller elevating unit.

FIG. 8 is a diagram showing a first operation state of the tension release means.

FIG. 9 is a diagram showing a second operation state of the tension release means.

FIG. 10 is an operation state diagram showing another embodiment of the tension release means.

FIG. 11 is a front view of a bearing unit of the transfer roller.

FIG. 12 is a side view of the transfer roller in which a bearing unit is partially cut away.

[Explanation of symbols]

2 ... color printer (image forming apparatus), 3 ... sheet (transfer body), 5 ... image forming unit (image forming unit), 71 ...
Elevating means, 72 Transfer belt unit, 84, 85,
86 positioning holes 87 positioning pins 87a
… Substrate

Claims (3)

[Claims] 1. A transfer roller for pressing a transfer member against a photoreceptor on which a toner image is formed, and applying a transfer charge having a polarity opposite to that of the charged toner to the back surface of the transfer member, and rotatably supporting the transfer roller. A conductive bearing, and a conductive spring that biases the transfer roller toward the photoconductor via the conductive bearing; and energizing the transfer roller via the conductive spring and the conductive bearing. Characteristic image forming apparatus. 2. A transfer member, which is wound around a black-and-white and a plurality of color photoconductors arranged in a transfer member transport direction, and a driving roller and a tension roller arranged at predetermined intervals in the transfer member transport direction. And an endless transfer belt that electrostatically attracts and conveys the transfer body to the photoconductor, and is disposed between the drive roller and the tension roller and at a position corresponding to the photoconductor, and transfers the transfer body via the transfer belt. A transfer roller that presses the photoreceptor on which the toner image is formed and applies a charge of opposite polarity to the charged toner on the back surface of the transfer body via a transfer belt; and a plurality of color photoreceptors among the plurality of transfer rollers. Transfer roller lifting / lowering means for retreating the transfer roller corresponding to the transfer roller from the transfer work position separately from the transfer roller corresponding to the photosensitive member for black and white, and rotatably supporting the transfer roller by a conductive bearing. An image is characterized in that the transfer roller is urged toward the photoreceptor by a conductive spring through the conductive bearing, and the transfer roller is energized through the conductive spring and the conductive bearing. Forming equipment. 3. A black and white and a plurality of color photosensitive drums arranged in the transfer body transport direction, and a drive roller and a tension roller arranged at predetermined intervals in the transfer body transport direction, and are transferred over the transfer body. And an endless transfer belt that electrostatically attracts and conveys the transfer member to the photoreceptor. The transfer member is disposed between the drive roller and the tension roller and at a position corresponding to the photoreceptor drum. A transfer roller that presses the photosensitive drum on which the toner image is formed, and that applies a charge of opposite polarity to the charged toner on the back surface of the transfer body via a transfer belt; and a plurality of color transfer rollers among the plurality of transfer rollers. A transfer roller corresponding to the photosensitive drum, and a transfer roller lifting / lowering unit for pressing and retracting the color photosensitive drum separately from the transfer roller corresponding to the monochrome photosensitive drum, Both ends of the outer periphery of the photoconductor drum are rotatably supported by bearings, the transfer roller is rotatably supported by conductive bearings, and the transfer roller is electrically conductive to the photoconductor side via the conductive bearings. An image forming apparatus, wherein the transfer roller is energized by a spring and is supplied with electricity through the conductive spring and the conductive bearing.