JPH10181927A - Belt device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt device without generating a bending habit and settling in an endless belt even in a stop condition for a long period. SOLUTION: In full color printing, in a motor 85, through a drive gear 84, one-way gear 83, clutch gear 82, electromagnetic clutch 81, drive shaft 78, turn arm 79 and an intermediate connecting lever 77, a turn arm 57 is turned upward with backup rollers 56a to 56c, a belt 45 is brought into contact with all four photosensitive drums 48a to 48d. In monochrome printing, the turn arm 57 is turned to an intermediate position, the belt 45 is brought into contact with only the photoreceptor drum 48d, to be separated from the three photoreceptor drums 48a to 48c in the upstream. At operation recess time, the electromagnetic clutch 81 is released, the turn arm 57, by its own weight, is turned downward till coming into contact with a stopper 88, the three backup rollers 56a to 56c and three transfer brushes 54 are separated from the belt, further, energizing of a tension roller 58 is suppressed, the belt 45 is placed in almost a free condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a belt device which relaxes an endless belt which is stretched and stretched when driven.

[0002]

2. Description of the Related Art Conventionally, there have been various electrophotographic image forming apparatuses, as shown in FIGS. Same figure
(a), (b), and (c) show only the main part of each image forming apparatus.

FIG. 6A shows an image forming apparatus for performing monochrome printing. An endless belt 1 is stretched between a driving roller 2a and a driven roller 2b with a predetermined tension. A suction roller 3 is in pressure contact with the driven roller 2b via an endless belt 1, whereby the sheet P is nipped and conveyed in the left direction indicated by an arrow A in the figure.

The endless belt 1 is generally formed of a film-like member having a thickness of about one hundred and several tens μm. A photosensitive drum 4-1 is pressed against the outer peripheral surface of the endless belt 1 for conveying the paper P, and a transfer brush 4-2 is placed on the upper inner peripheral surface of the endless belt 1 opposite to the photosensitive drum 4-1. Is in sliding contact. Cleaner 4-1 surrounds the peripheral surface of photoconductor drum 4-1.
3, an initialization charging brush 4-4, a recording head 4-5, and a developing unit 4-6.

The initialization charging brush 4-4 is connected to a high-voltage power supply and applies a negative high voltage to the photosensitive drum 4-1 to change the photosensitive layer on the peripheral surface of the photosensitive drum 4-1 to a negative high potential. To be uniformly charged. The recording head 4-5 includes a predetermined light source, and performs selective exposure according to image information on a peripheral surface of the photosensitive drum 4-1 charged to a negative high potential to form a negative low potential portion whose potential is attenuated. Then, an electrostatic latent image composed of the low potential portion and the high potential portion is formed on the peripheral surface of the photosensitive drum 4-1.

The developing device 4-6 contains a non-magnetic toner T inside a housing, and supports a developing roller 4-7 at a lower opening. A developing bias is applied to the developing roller 4-7 from a developing bias power supply. The developing roller 4-7 attaches the toner T charged to a weak negative charge to the surface thereof by the friction of rotation, and conveys the toner T to a portion facing the photosensitive drum 4-1.

At the opposing portion between the photosensitive drum 4-1 and the developing roller 4-7, a potential difference is formed between the low potential portion of the electrostatic latent image and the developing roller 4-7, and the electrostatic latent image is formed. The low potential portion forms a positive potential relative to the developing roller 4-7. The non-magnetic toner T charged to the negative polarity by the electric field due to the potential difference is transferred to the low potential portion of the positive electrostatic latent image on the photosensitive drum 4-1 to form a toner image (reversal development). The photoconductive drum 4-1 conveys the toner image to a portion facing the endless belt 1 while rotating. The endless belt 1 conveys the paper P while circulating in a counterclockwise direction.

The transfer brush 4-2 is connected to a transfer bias power supply that outputs a positive current, and applies a positive charge to the endless belt 1. This electric charge is applied to the paper P by the dielectric effect of the endless belt 1, and the electric field of this electric charge transfers the negative toner image on the photoconductor drum 4-1 to the paper P in contact with the photoconductor drum 4-1. Is done.

A separation claw 5 is provided at the downstream end (left side in the figure) of the endless belt 1, and the tip of the separation claw 5 is urged to lightly contact the endless belt 1. The leading end of the sheet P to which the toner image has been transferred is scooped by the separation claw 5 and guided to the fixing device 6.

The fixing device 6 includes a heat generating roller and a pressure roller surrounded by a heat insulating plate. The rotating heat roller and the pressing roller hold the sheet P discharged from the endless belt 1 on the sheet P while nipping and conveying the sheet. Is thermally fixed on the paper surface, and the paper P is discharged out of the apparatus (left side in the figure).

FIG. 6B shows a tandem-type printer that performs full-color printing. In this case, the somewhat long endless belt 11 is stretched between the driving roller 12a and the driven roller 12b with a predetermined tension. In the driven roller 12b,
The suction roller 13 is pressed into contact with the endless belt 11 via the endless belt 11 to cause the sheet P to be sucked to the endless belt 11. The endless belt 1 circulates in a counterclockwise direction indicated by an arrow B in FIG.
Is transported.

Four photosensitive drums 14-1 are pressed against the upper and outer peripheral surfaces of the endless belt 11, and these photosensitive drums 14-1
, Four transfer brushes 14-2 slidably contact the upper inner peripheral surface of the endless belt 11. Around the photosensitive drums 14-1, a cleaner 14-3 and an initialization charging brush 14 are respectively provided.
-4, a recording head 14-5, and a developing device 14-6. The developing device 14-6 contains a nonmagnetic color toner Tx inside the housing, and supports a developing roller 14-7 at a lower opening. Each developing unit 14-6 stores, for example, color toners Tx of mass center, cyan, yellow, and black sequentially from the upstream side (right side in the figure). Although not particularly shown, a separation claw is provided downstream of the endless belt 1, and a fixing device 16 is provided a little further downstream.

The above-mentioned endless belt 11 and drive roller 12
a, driven roller 12b, suction roller 13, photosensitive drum 14-1, transfer brush 14-2, cleaner 14-3, initialization charging brush 14-4, recording head 14-5, developing unit 14-6, developing roller 14-7, toner Tx, separation claw,
And the fixing device 16 includes the endless belt 1 described in FIG.
A driving roller 2a, a driven roller 3b, a suction roller 3, a photosensitive drum 4-1, a transfer brush 4-2, a cleaner 4-3,
Initializing charging brush 4-4, recording head 4-5, developing unit 4
-6, developing roller 4-7, non-magnetic toner T, separation claw 5,
And has the same function as that of the fixing device 6. The sheet is conveyed while being inverted from the lower side into a U-shape as shown by a dashed arrow C, and four color toners Tx are sequentially transferred to the paper surface, and the full-color image is heat-fixed by the fixing unit 16, and the dashed arrow in the figure It is discharged outside the machine as shown by D.

FIG. 6C shows a space-saving (vertical type) printer for performing monochrome printing. This printer is provided with a paper feeding device at an upper part, and a paper conveying path 21 is disposed inside from the upper left to the lower right. A pair of standby rolls 22 for temporarily stopping the fed sheet and starting to convey the sheet at the timing of transfer and fixing is disposed upstream of the conveying path 21 (obliquely upper left in the figure). Downstream of the standby roll pair 22, a transfer roller 23 and a transfer path 2
A heating roller 24 that is in pressure contact with the heating roller 24 is disposed inside the heating roller 1. Further downstream, a paper discharge roll pair 25 is arranged.

An intermediate transfer roller 26 is disposed at a position slightly diagonally lower left of the heat roller 24, and an endless belt 27 is stretched between the intermediate transfer roller 26 and the heat roller 24 as an intermediate transfer belt. You. The endless belt 27 is formed of a member having an adhesive surface, and circulates and carries a toner image described later due to the adhesiveness.

A cylindrical transparent photosensitive member 28 is rotatably disposed in pressure contact with the intermediate transfer roller 26 via an endless belt 27. Inside the transparent photoreceptor 28, a recording head 29 is provided in a position fixed independently of the transparent photoreceptor 28 in parallel with the axial direction along the inner peripheral surface. At a position facing the recording head 29 outside the transparent photosensitive member 28, a developing roller 31 is disposed with a slight gap from the peripheral surface of the transparent photosensitive member 28, and the developing roller 31 is rotatably held in the lower opening. Then, a developing device 32 is provided. The developing device 32 has a toner replenishing container 33 detachably mounted on an upper portion thereof, and the toner T
Feed to 1.

The transparent photoreceptor 28 rotates counterclockwise as shown by the arrow E in the figure, and is exposed from the back (inside) by the recording head 29 based on image information. With this exposure, an electrostatic latent image is formed on the outer peripheral surface. Form. At the same time, the transparent photoconductor 2
A developing roller 31 rotating in the same direction as the transparent photoconductor 28 on the surface facing the photoconductor 8 sequentially transfers the toner T supplied from the developing device 32 to an electrostatic latent image on the transparent photoconductor 28 to develop a toner image. I do. The developed toner image is conveyed with the rotation of the transparent photoconductor 28, and is adhesively transferred to the endless belt 27 at a pressure contact portion between the transparent photoconductor 28 and the intermediate transfer roller 26.

The endless belt 27 carries the adhered toner image and circulates clockwise as indicated by arrow F in FIG.
The toner image is transported to a portion where the transfer roller 23 and the heat roller 24 face each other. The transfer roller 23 transfers the sheet conveyed in the conveyance path 21 to the heat roller 2 via the endless belt 27.
4, the heat generating roller 22 transfers and thermally fixes the toner image conveyed by the endless belt 27 onto the sheet.

As shown in FIGS. 6 (a), 6 (b) and 6 (c), endless belts are used in various forms in electrophotographic image forming apparatuses.

[0020]

As described above, the conventional belt device is always stretched between a plurality of rolls. Therefore, if the main body device is not used for a long period of time and the endless belt is in a stopped state, a bending habit is formed at both ends where the main body device is stretched. If the endless belt is bent in this way, the state of the surface to be flattened changes when the endless belt circulates, and the conveyance of the paper, the conveyance or transfer of the toner image, etc. are performed well. The problem of disappearing occurred.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional circumstances,
An object of the present invention is to provide a belt device which does not bend even when the endless belt is in a long-term stopped state.

[0022]

The construction of the belt device according to the present invention will be described below. The belt device of the present invention includes an endless belt stretched between a plurality of rollers, driving means for driving the endless belt to circulate, and tensioning the endless belt at a predetermined tension when the driving means drives the belt. When the driving by the driving means is stopped, the tension of the endless belt is reduced from the predetermined tension to relax the belt and the belt tension switching means is provided.

The belt tension switching means may include, for example, one of the plurality of rollers, a supporting member for movably supporting the tension roller, and a support member for movably supporting the tension roller. An urging member that urges the tension roller to move in a direction in which the endless belt is tensioned, and the endless belt is connected to the tension roller via the support member when driving by the driving unit is stopped. And a belt relaxing means for moving in a relaxing direction.

According to a third aspect of the present invention, in the image forming apparatus, the endless belt is circulated by adsorbing the transfer material on an outer peripheral surface thereof so that the transfer material is brought into contact with the image carrier on which the toner image is formed. Is configured as a transfer / conveying belt disposed in the printer.

According to a fourth aspect of the present invention, the image forming apparatus is a tandem type color image forming apparatus in which a plurality of image carriers are arranged side by side in the transport direction of the transfer transport belt. The belt tension degree switching means includes a position where the transfer conveying belt is brought into contact with the transfer material with respect to the entire image carrier, a position where the transfer material is brought into contact only with the image carrier of a predetermined color, and a position where the belt is relaxed. It is configured to be moved to three modes. Further, for example, an intermediate transfer provided in the image forming apparatus so as to convey the toner image transferred from the image carrier to the outer peripheral surface and circulate to transfer the toner image to the transfer material. Configured as a belt.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side sectional view schematically showing an internal configuration of an image forming apparatus according to an embodiment, and FIG. 2 is a perspective view showing only a belt device portion thereof.

As shown in FIGS. 1 and 2, the image forming apparatus (main body apparatus) 40 has a paper cassette 41 at its lower part which is detachable from the front of the apparatus (right side in the figure). A large number of sheets 42 are placed and stored in the sheet cassette 41. An upper lid 43 is provided on the upper surface of the main unit 40. A power switch, a liquid crystal display, a plurality of input keys, and the like are arranged on the front side of the upper lid 43, which are not visible in the drawing. The upper lid 43 forms a paper discharge tray 44 at a rear portion thereof together with a rear upper surface of the main device 40.

A transfer / transport belt (hereinafter, simply referred to as a belt) 45 is disposed substantially in the center of the main unit 40 in a front and rear flat loop shape, and both ends of the loop in the horizontal direction are connected to a drive roller 46. It is held by a driven roller 47. The belt 45 is driven by a driving roller 46 and circulates in a counterclockwise direction indicated by an arrow H in the figure.
In the upper circulation portion of the belt 45, four photosensitive drums 48
(48a, 48b, 48c, 48d) are arranged side by side in a multi-stage manner in the sheet conveying direction (from right to left in the drawing).

The photoconductor drums 48 are respectively surrounded (hereinafter, only the peripheral devices of the photoconductor drums 48a are denoted by reference numerals), and a cleaner 49,
An initialization charging brush 51, a recording head 52, a developing unit 53, and a transfer brush 54 are arranged. Transfer brush 54
Is pressed against the photosensitive drum 48 via the belt 45 to form a transfer portion. The developing device 53 has a developing roller 55 rotatably supported by a lower opening thereof in contact with the peripheral surface of the photosensitive drum 48, and forms a developing section there.

The recording head 52 is disposed on the back surface of the upper cover 43, descends as the upper cover 43 is closed, and is positioned between the initialization charging brush 51 and the developing roller 55 of the developing device 53. Here, a recording unit is formed.

The backup rollers 56 (56a, 56b, 56) are located near the photosensitive drums 48 (48a to 48d) on the upstream side of the transfer brushes 54 in the transport direction.
c, 56d). In response to the fact that the belt 45 is charged with electric charges for electrostatically attracting and transporting the sheet, these backup rollers 56 are
It is formed of an appropriate insulator so that the charge does not flow through the backup roller 56. These backup rollers 56 are supported by a rotating arm 57 (see FIG. 2) to form a special belt device, and do not loosen the upper circulation portion of the belt 45 while the main device 40 is operating. The photosensitive drum 48 and the belt 4 are supported from below.
5 is maintained.

On the downstream back surface of the lower circulation portion of the belt 45,
A tension roller 58 is disposed in contact with the back surface. The tension roller 58 is rotatably supported at one end of a key-shaped member 61 supported at a fulcrum 59. The key-shaped member 61 is urged to rotate clockwise around the fulcrum 59 by the urging force of the urging member 62 engaged with the other end. With this rotating power, the tension roller 58 presses the belt 45 downward as indicated by the arrow J in FIGS. 1 and 2 to absorb the bending of the belt 45, and the entire belt 45 is driven by the driving roller 46 and the driven roller with a predetermined tension. It is stretched between 47.

At the upstream end of the upper circulation portion of the belt 45,
The suction roller 64 is driven by the driven roller 47 via the belt 45.
To form a paper carry-in port. The suction roller 64 is a sheet (transfer material) that is carried into the sheet carry-in port.
Is pressed against the belt 45 while applying a suction bias to
The sheet is electrostatically attracted to the belt 45.

The photosensitive drum 4 at the uppermost stream in the paper transport direction.
8a to the most downstream photosensitive drum 4 from the developing device 53 corresponding to
8d, each developing device 53 has M
Each toner contains a (magenta) toner, a C (cyan) toner, a Y (yellow) toner, and a Bk (black) toner dedicated to printing black portions of characters and images.

A pair of standby rolls 65 is disposed further upstream (to the right in the drawing) in the transport direction than the belt 45, and a paper feed guide path 66 is disposed below the standby roll pair. A roll pair 67 is provided. Feeding roll pair 67
The paper feed end of the paper cassette 41 described above is located upstream (below). A paper feed roller 68 is arranged above the paper feed end of the paper cassette 41. The paper feed roller 68 takes out one topmost sheet stored in the paper cassette 41 and feeds it to the pair of feed rolls 67 for each rotation.

On the other hand, a fixing device 69, a pair of paper discharge rolls 71, and a switching lever 72 are provided downstream of the belt 45 in the paper transport direction (left side in the drawing). The fixing device 69 includes a pressure contact roller, a fixing roller, a heating roller, a peripheral surface cleaner, an oil application member, a thermistor, and the like assembled in a heat-insulating housing, and heats the toner image transferred on the paper to the paper surface. Fix it.

When the switching lever 72 is at the lower position as shown in the figure, it guides the paper to the paper discharge tray 44 via the upper discharge path 73 and the paper discharge roll pair 74, and rotates upward. When the sheet is being fed, the sheet is guided to the opening / closing tray 75 that is opened outward from the rear side.

Between the belt 45 and the paper cassette 41,
An electrical component 76 is provided. An appropriate number of circuit boards on which a control device including a plurality of electronic components is mounted are mounted on the electrical unit 76. The control device is composed of a controller and an engine, and the controller is a CPU (Central Processing Unit), ROM (Read Only Memory), EEPROM
(Rewritable read memory), frame memory,
It includes an image data transfer circuit and the like, analyzes print data input from a host computer or the like, creates print data, and transfers it to the engine unit.

The engine unit includes a CPU, a ROM, and the like.
On the input side, data and command signals from the controller unit, outputs of various sensors, outputs of paper detection sensors, and the like are input, and on the output side, a motor driver that drives a motor and the like described later;
A clutch driver for switching a drive system of a drive device, which will be described later, in which the rotary arm 57 shown in FIG. 2 is set by rotating the rotary arm 57 to one of three states, and a drive system for transmitting the drive of the motor to other units. A clutch driver for switching, a print driver for driving the recording head 52 based on the print data, an initialization charging brush 51, a developing roller 55,
A bias power supply driver or the like that supplies a predetermined bias current to the transfer brush 54, the suction roller 64, and the like is connected. The engine unit controls the driving of each unit based on data and command signals from the controller unit, the output of the sheet detection sensor, and the like.

FIGS. 3 (a), 3 (b) and 3 (c) are side views showing in detail the belt device portion of FIG. 2, and show the state of the operation changing in three stages. The configuration will be further described with reference to FIG. 3A together with FIG. As shown in FIGS. 2 and 3 (a), the rotating arm 57 in the belt device section
The downstream end is rotatably supported and fixed at the frame of the main unit 40 coaxially with the backup roller 56d. The backup roller 56d is a drive roller 4
6, that is, near the upstream side of the most downstream photosensitive drum 48d. This backup roller 56d
Is arranged in contact with the inner circumferential surface of the belt 45 so that the belt 45 is always in contact with the photosensitive drum 48d at the most downstream position.

The free end side (right side in the figure) of the rotating arm 57 is rotated vertically about the same support shaft as the backup roller 56d. A backup roller 56a is supported at its free end. Backup roller 56a
Is in contact with the inner peripheral surface of the belt 45 and supports the belt 45 between the photosensitive drum 48 a closest to the driven roller 47, that is, between the most upstream photosensitive drum 48 a and the driven rotating roller 47. And
The backup roller 56a and the backup roller 5
In the middle of 6d, backup rollers 56b and 56c are supported by a rotating arm 57, and contact the inner peripheral surface of the belt 45 near the upstream side of the photosensitive drums 48b and 48c to support the belt 45.

The upper end of the intermediate connecting rod 77 is connected to the rotation arm 57 near the upstream end thereof, and the lower end of the intermediate connecting rod 77 is perpendicular to the shaft from the end of the drive shaft 78. Is connected to the tip of a rotating arm 79 protruding from the arm. The drive shaft 78 is engaged with a clutch gear 82 via an electromagnetic clutch 81. The clutch gear 82 is driven by a driving gear 84 of a motor 85 via a one-way rotating gear (one-way gear) 83.
Is engaged.

FIGS. 1, 2 and 3 (a) show the motor 85 in the counterclockwise direction indicated by the arrow K in FIG. 3 (c) from the reference state of FIG. The clutch gear 82 is driven through the one-way gear 83
Is driven to rotate the drive shaft 78, and the rotating arm 79 fixed thereto is rotated in the counterclockwise direction indicated by the arrow L in FIG. Is rotated upward, and the state when the whole is set to the full color print mode is shown. In this state, the position detecting projection 79-1 formed integrally with the tip of the rotating arm 79 is detected by the full-color sensor 87, and the motor 85 is stopped in accordance with this detection, and the position is determined.

Next, the operation of the image forming apparatus 40 having the above configuration will be described with reference to FIGS. 1, 2 and 3 (a), (b) and (c) again. First, the processing operation in the full-color print mode will be described. The apparatus main body 4 shown in FIG.
When the power is turned on to 0, and the paper quality, the number of sheets to be used, the print mode, and other designations are input as a key input or a signal from a connected host device, the electromagnetic clutch 81 shown in FIGS. Driven by the drive shaft 78
And the clutch gear 82, and subsequently the motor 8
5, the rotating arm 57 is rotated upward, whereby the backup rollers 56a, 56b and 56c are moved upward, and the belt 45 is moved to all four photosensitive drums 48 (48a, 48b, 48c, 48d).

Subsequently, the paper feed roller 68 is moved to the paper cassette 41.
One of the sheets 42 placed and accommodated in the tray is taken out, and a pair of feeding rolls 67 is moved through a paper feeding guide path 66 to a pair of standby rolls 65.
Feed to The standby roll pair 65 has stopped rotating,
The advance of the sheet 42 is stopped by bringing the leading end of the sheet 42 into contact with the holding portion, and the transfer timing is awaited.

The driving roller 46 rotates in the counterclockwise direction, and the driven roller 47 is driven to rotate in the same counterclockwise direction. As a result, the upper circulating portion of the belt 45 abuts on the four photosensitive drums 48, and the entire belt 45 circulates counterclockwise.

Along with this, the developing unit 53 and the photosensitive drum 4
8 are sequentially driven in accordance with the print timing. The photosensitive drum 48 rotates clockwise, the initialization charging brush 51 applies a uniform high negative charge to the peripheral surface of the photosensitive drum 48, and the recording head 52 applies an image to the peripheral surface of the photosensitive drum 48. Exposure is performed according to a signal to form a low potential portion. As a result, an electrostatic latent image composed of a high negative potential portion due to the initialization and a low negative potential portion due to exposure is formed. The developing roller 55 of the developing device 53 transfers the toner to the low potential portion of the electrostatic latent image to form a toner image on the peripheral surface of the photosensitive drum 48 (reversal development).

At the timing when the leading end of the toner image on the peripheral surface of the photosensitive drum 48a at the most upstream position is rotated and conveyed to the point facing the belt 45, the printing start position of the paper 42 coincides with the point. Then, the standby roll pair 65 starts rotating and feeds the sheet 42 to the sheet carrying-in section.

The driven roller 47 and the suction roller 64 hold and transport the fed sheet 42 together with the belt 45.
The paper 42 is attracted to the belt 45 and the photosensitive drum 48
a and the first transfer portion formed by the transfer brush 54. The transfer brush 54 applies a transfer current output from a transfer bias power supply (not shown) to the sheet 42 via the belt 45. The toner image on the photosensitive drum 48a is transferred to the sheet 42 by the applied transfer current, and a toner image is formed on the sheet 42.

Subsequently, a C (cyan) toner image is transferred at the second transfer portion from the upstream formed by the photosensitive drum 48b and the transfer brush 54, and further formed by the photosensitive drum 48c and the transfer brush 54. The Y (yellow) toner image is transferred at the third transfer portion from the upstream. Then, a Bk (black) toner image is sequentially transferred at the most downstream transfer portion formed by the photosensitive drum 48d and the transfer brush 54, and four color toner images are overlaid.

The sheet 42 onto which the four color toner images have been transferred in this manner is separated from the belt 45, and the fixing device 69
It is carried in. The fixing device 69 thermally fixes the toner image on the paper 42. After the image is fixed, the paper 42 is
1, the toner image is discharged from the rear paper outlet 72 with the toner image upward, or the toner image is discharged from the upper paper outlet with the paper discharge roll pair 74 downward.

Next, in the monochrome printing mode, the energization of the electromagnetic clutch 81 is temporarily interrupted, the connection between the drive shaft 78 and the clutch gear 82 is released, and the rotating arm 57 is rotated downward by its own weight, and It abuts at 88 and stops at the reference position. Thereafter, the electromagnetic clutch 81 is energized again to connect the drive shaft 78 and the clutch gear 82. The motor 85 is driven to rotate the drive shaft 78, and the projection 79-1 for detecting the position of the tip of the rotating arm 79 is detected by the monochrome sensor 89, and the motor 85 stops in response to this detection. Thus, the rotating arm 57 stops at the position shown in FIG.

As a result, when compared with FIG. 3A, the rotating arm 57 is set to be rotated downward from the position of FIG. 3A. In this state, the backup rollers 56a, 56b and 56c
5 is moved downward while being pressed against the photosensitive drum 5, whereby the upper circulating portion of the belt 45 is set to be separated from the three photosensitive drums 48a to 48c on the upstream side. Further, while the lowermost transfer brush 54 is fixed to the frame of the main body device 40, the other three transfer brushes 54 on the upstream side are fixed to the rotating arm 57 so that the transfer brush 54 is fixed to the belt 45. The transfer portion formed between the photosensitive drums 48a to 48c is moved downward together with the rotating arm 57 while being in sliding contact with the photosensitive drums 48a to 48c.

The belt 45 abuts only on the photosensitive drum 48d between the driving roller 46 and the backup roller 56d, thereby transferring the black toner formed by the most downstream photosensitive drum 48d and the transfer brush 54. Only the print mode is set to be operable, and the monochrome print mode is set. Note that the subsequent processing is substantially the same as that in the above-described full-color printing mode, and a description thereof will be omitted.

In the image forming apparatus of the present embodiment operating as described above, when the printing operation is stopped, the power supply to the electromagnetic clutch is cut off, and the belt device is moved to the reference position shown in FIG. Is maintained. Fig. 3 (a)
In the full-color print mode and the monochrome print mode in FIG.
6a to 56d are always in pressure contact with the belt 45,
All four transfer brushes 54 are always in sliding contact with the belt 45,
Then, the key-shaped member 61 is urged by the urging member 62, and the tension roller 58 constantly tensions the belt 45.
On the other hand, in FIG. 3C, the three backup rollers 56a to 56c are separated from the belt 45 to cancel the pressure contact with the belt 45, and the three transfer brushes 54 are also separated from the belt 45 and The sliding contact with has been released. Then, the other end of the key-shaped member 61 comes into contact with the stopper 89, and the urging by the urging member 62 is stopped.
Is stopped at a certain position.

Thus, the tension of the belt 45 is released, and the belt 45 is only suspended in a substantially natural state between the driving roller 46, the backup roller 56d, and the driven roller 47. As described above, during the suspension of operation, the belt 45 is released from tension and becomes a natural state, so that there is no possibility that a curl will occur, and the printing process can always be restarted in the best state.

In the above-described embodiment, the belt is made of a hard material having a bending tendency. However, the belt may be made of a soft material such as rubber. Settling can be prevented.

In the above embodiment, the tension of the stretched belt 45 is released when it is not used by adding a further switching function to the rotating arm 57 for switching between full-color printing and monochrome printing. However, the tension release of the belt when not in use is not limited to this, and can be realized by other methods. This will be described below as a second embodiment.

FIGS. 4 (a) and 4 (b) are side views schematically showing the belt device according to the second embodiment, and show a tension state during operation and a tension release state during non-operation, respectively. I have. As shown in FIG. 9A, a belt 91 is suspended between a driving roller 92 and a driven roller 93, and its upper and outer peripheral surfaces are in contact with four photosensitive drums 94, and the upper inner peripheral surface is transferred by four transfer drums. Brush 95
Is driven by the drive roller 92 while sliding on
Circulates counterclockwise as indicated by.

A tension link gear 96 meshes with a gear 92-1 of the drive roller 92. A "-"-shaped tension link 98 is attached to the tension link gear 96 via a damper clutch 97. ing. The damper clutch 97 has a clutch mechanism of a multi-plate type, an oil type, a spring type, or the like, so that a torque greater than a predetermined torque is not applied.

When the tension link gear 96 rotates clockwise as indicated by the arrow N in the figure due to the rotation of the drive roller 92 (that is, the gear 92-1), the tension link 98 comes into contact with the stopper 101 and is stopped at the fixed position. To the same direction. While the tension link 98 is stopped, the damper clutch 97 is performing a slip rotation.

By rotating to the above-mentioned fixed position, the tension link 98 expands the tension spring 102 to generate a biasing force on the tension spring 102.
With this urging force, the key-shaped tension stay 103
Is urged to rotate clockwise about the fulcrum 104. As a result, the tension roller 105 disposed at the tip of the tension stay 103 presses the lower inner peripheral surface of the belt 91 downward as shown by the arrow P in the figure, and moves the belt 91 between the driving roller 92 and the driven roller 93. Stretch.

Next, as shown in FIG. 4B, when the operation of the apparatus stops, the drive roller 92 stops. As a result, the rotation of the tension link gear 96 also stops, and the torque inside the clutch decreases. The tension spring 102 retracts while sliding the damper clutch 97 via the tension link 98, and becomes almost free. Therefore, the urging force of the tension stay 103 also disappears, and the tension roller 105 simply comes into contact with the belt 91 and Only be. Thus, when the operation of the apparatus is stopped, the tension of the belt 91 is released.

In the above-described embodiment, the transfer unit including the four photosensitive drums and the transfer brush is described as a belt device of a tandem-type image forming apparatus in which the transfer units are arranged in multiple stages in the moving direction of the belt. However, the image forming apparatus is not limited to a tandem type, and may be an image forming apparatus for monochrome printing having only one photosensitive drum. Further, although the tension link is linked to the rotation of the drive roller, the present invention is not limited to this. For example, the tension link may be rotated by a solenoid independently of the drive roller.

FIGS. 5A and 5B are diagrams showing an example in which such a belt device is provided in an image forming apparatus for monochrome printing. 4A, parts having the same functions as those in FIGS. 4A and 4B are given the same numbers as in FIGS. 4A and 4B. FIG.
As shown in (a), during operation, the valve of the solenoid 107 is retracted to rotate the tension link 98 in the belt tension direction, and as shown in FIG. The tension link 98 is advanced to rotate in the belt tension releasing direction.

[0066]

As described above, according to the present invention,
By adding a further switching function to the switching mechanism between full-color printing and monochrome printing, the tension of the belt that is stretched and used is released when not in use. There will be no shortcomings and short-term
Processing can be resumed in a stable state, and therefore a high-quality image can always be formed, which is convenient.

Further, since the urging force of the tension roller for tensioning the belt is controlled by engaging with the belt drive system, the tensioning of the belt can be automatically released while the operation is stopped. If only a belt driven by the system and stretched by a tension roll is used, it is possible to easily release the tension when not in use and to prevent a bending habit or sagging, which is convenient.

[Brief description of the drawings]

FIG. 1 is a side sectional view schematically illustrating an internal configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is a perspective view showing only a belt device portion of the image forming apparatus.

FIG. 3 is a side view showing a belt device portion in detail;
(a) is a diagram showing full color printing, (b) is a monochrome printing, and (c) is a diagram showing a state when printing is stopped.

FIGS. 4A and 4B are side views schematically showing a belt device according to a second embodiment.

FIGS. 5A and 5B are diagrams showing another application example of the belt device according to the second embodiment.

FIGS. 6A, 6B, and 6C are diagrams showing examples of a conventional electrophotographic image forming apparatus.

[Explanation of symbols]

1, 11 Endless belt 2a, 12a Drive roller 2b, 12b Followed roller 3, 13 Suction roller P Paper 4-1, 14-1 Photoconductor drum 4-2, 14-2 Transfer brush 4-3, 14-3 Cleaner 4 -4, 14-4 Initializing charging brush 4-5, 14-5 Recording head 4-6, 14-6 Developing device 4-7, 14-7 Developing roller T, Tx Non-magnetic toner 5 Separating claw 6, 16 Fixing Device 21 Paper transport path 22 Standby roll pair 23 Transfer roller 24 Heating roller 25 Discharge roll pair 26 Intermediate transfer roller 27 Endless belt 28 Transparent photoreceptor 29 Recording head 31 Developing roller 32 Developing device 33 Toner replenishing container 40 Image forming device (main body) Apparatus) 41 paper cassette 42 paper 43 top cover 44 paper discharge tray 45 transfer / transport belt (belt) 46 drive roller 47 driven roller 4 8 (48a, 48b, 48c, 48d) Photoconductor drum 49 Cleaner 51 Initializing charging brush 52 Recording head 53 Developing unit 54 Transfer brush 55 Developing roller 56 (56a, 56b, 56c, 56d) Backup roller 57 Rotating arm 58 Tension Roller 59 fulcrum 61 key-shaped member 62 urging member 64 suction roller 65 standby roll pair 66 feed guide path 67 feed roll pair 68 feed roller 69 fixing device 71 discharge roll pair 72 switching lever 73 discharge path 74 discharge roll Pair 75 Open / close tray 76 Electrical unit 77 Intermediate connecting rod 78 Drive shaft 79 Rotating arm 79-1 Position detecting protrusion 81 Electromagnetic clutch 82 Clutch gear 83 One-way rotating gear (one-way gear) 84 Drive gear 85 Motor 87 Full color sensor 88, 89 Stopper 91 Belt Second drive roller 92-1 gear 93 driven roller 94 the photosensitive drum 95 transfer brush 96 tension link gear 97 damper clutch 98 tension link 101 stopper 102 tension spring 103 tension the stay 104 fulcrum 105 tension roller 107 solenoid

Claims (5)

[Claims] An endless belt extending between a plurality of rollers; driving means for driving the endless belt to circulate; and driving the endless belt at a predetermined tension when the driving means drives the belt. A belt tension switching unit configured to reduce the tension of the endless belt below the predetermined tension when the driving by the driving unit is stopped, and to relax the belt. 2. The belt tension degree switching means includes: a tension roller among the plurality of rollers; a support member that movably supports the tension roller; and the tension roller through the support member. An urging member for urging the endless belt to move in a direction in which the endless belt is tensioned; and a belt for moving the tension roller in a direction in which the endless belt relaxes via the support member when driving by the driving unit is stopped. The belt device according to claim 1, comprising a relaxation means. 3. The transfer belt provided in the image forming apparatus so that the transfer material is circulated by adsorbing the transfer material on an outer peripheral surface so that the transfer material is brought into contact with an image carrier on which a toner image is formed. The belt device according to claim 1, wherein the belt device is a belt. 4. The image forming apparatus is a tandem type color image forming apparatus in which a plurality of image carriers are arranged along a transfer direction of the transfer and transfer belt. Are moved in three forms: a position where the transfer material contacts the entire image carrier, a position where the transfer material contacts only the image carrier of a predetermined color, and a position where the belt relaxes. The belt device according to claim 3. 5. An intermediate transfer belt provided in an image forming apparatus so as to convey a toner image transferred from an image carrier to an outer peripheral surface and circulate to transfer the toner image to a transfer material. The belt device according to claim 1, wherein: