JPH0359583A - Fusing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixing device for an image forming apparatus capable of monochrome copying and multicolor copying.

Multicolor image forming devices such as multicolor electrophotographic copying machines and multicolor printers that use electrophotography are equipped with a black developer and a color developer around a photoreceptor, and are capable of forming multicolor images. Sometimes, toner images of multiple colors are sequentially formed on a photoreceptor, and after being superimposed and transferred onto a transfer paper carried on a transfer belt and conveyed along the transfer position of the photoreceptor, the transfer paper is fixed to form a multicolor image. An overlapping transfer type apparatus is known.

Since it is impossible for the transfer paper that is attracted and carried by the transfer belt to be deflected together with the transfer belt at the support roller of the transfer belt due to the stiffness of the paper, the transfer belt is reciprocated and When the toner image is transferred and the transfer belt moves backward, it is necessary to separate the transfer belt from the photoreceptor so as not to disturb the already transferred toner image, which has the drawback of complicating the apparatus.

Therefore, rather than using the transfer belt as a transfer paper conveyance means,
A method has been considered in which a toner image is used as an intermediate transfer material, rotated in the same direction multiple times to transfer a plurality of toner images in a superimposed manner, and then transferred to transfer paper to form an image. In this case, even in the case of black-and-white copying, since the image is intermediately transferred to the transfer belt and then transferred to the transfer paper, the time required for image formation becomes longer and the image quality may deteriorate.

Therefore, in the case of a single-color image forming bag, the toner image formed on the photoconductor is transferred to the surface of the transfer paper that contacts the photoconductor conveyed by the transfer belt, separated from the transfer belt, and fixed by a fixing device. During color image formation, a plurality of toner images formed sequentially on a photoreceptor are superimposed and transferred onto a rotating transfer belt, and then the surface of the transfer paper conveyed by the transfer belt that is opposite to the side that contacts the photoreceptor is transferred to the surface,
The applicant has separately proposed an image forming apparatus that is separated from a transfer belt and fixed by a fixing device.

In this case, the side on which the toner image is transferred of the transfer paper introduced into the fixing device is reversed when forming a monochrome image and when forming a multicolor image.

In a heat roller fixing device that is widely used as a fixing device and consists of a pair of a fixing roller and a pressure roller, a heater is usually built into the fixing roller that contacts the toner image bearing side of the transfer paper, and a heater is installed on the back side of the fixing roller. The contact pressure roller is a core roller with an elastic layer laminated on its surface in order to obtain a nip width.

Therefore, in order to be able to handle the case where a toner image is carried on either the front or back of the transfer paper, both rollers must each have a built-in heater of a wattage that enables fixing. If a heater with the wattage required for fixing is built into the core of an elastic roller such as rubber, adhesion at the interface between the core roller and the elastic layer becomes a technical problem, resulting in roller punctures due to thermal expansion. may occur, and there is a problem with reliability. Further, temperature control means and safety means are required for each roller, and since one side is a rubber roller made of silicone rubber, the warm-up time becomes long, which is disadvantageous in terms of cost and specifications.

In addition, when one is an elastic roller such as silicone rubber and the other is a metal roller coated with a releasable layer such as tetrabutylene, as in a conventional general heat roller fixing device, it is difficult to determine which side the toner layer is on. There is a difference in image quality depending on the location.

Therefore, if both rollers are provided with an elastic layer such as silicone rubber, they will expand due to oil impregnation, and the linear speed at the nip will change, causing problems in conveying the transfer paper and in image quality. .

The present invention provides a heat roller fixing device as a fixing device for an image forming apparatus in which the toner image-bearing surfaces of transfer paper are reversed when forming a monochrome image and when forming a multicolor image. To provide a heat roller fixing device which solves the above-mentioned problems when using a transfer paper, has a simple configuration, and can always obtain good fixing quality even when a toner image is carried on either side of a transfer paper. That is the issue.

for The fixing device of the present invention solves the above problems.

A fixing roller with a built-in heater that can be rotated in forward and reverse directions.

It has two pressure rollers that are in contact with each other on both sides to form a nip portion and are rotated following the rotation of the fixing roller, and the transfer paper separated and discharged from the transfer belt has an unfixed toner image bearing surface. It is inserted into the nip in contact with the fixing roller,
The fixing roller is characterized in that it is rotationally driven in a direction to convey and discharge the inserted transfer paper in a predetermined direction.

Since the fixing device of the present invention is configured as described above, the surface carrying the unfixed toner image is inserted into the nip portion on the side where the surface carrying the unfixed toner image is in contact with the fixing roller, both when forming a monochrome image and when forming a multicolor image. Like a normal heat roller fixing device, the toner image has an internal heater, contacts a rigid fixing roller, and presses the opposite side with an elastic pressure roller to obtain the required nip width. Good fixing takes place. The fixing roller can rotate in forward and reverse directions, so no matter which nip the transfer paper is inserted into, the fixing roller and the two pressure rollers that come into pressure contact with it rotate in a direction that allows the transfer paper to be conveyed in the normal ejection direction. The transfer paper is conveyed and discharged in a predetermined direction.

It is also possible to switch between forward and reverse rotation of the fixing roller using a clutch, but if a drive source capable of forward and reverse rotation, such as a forward and reverse rotation motor, is used, a forward/reverse switching clutch is not required, the configuration is simple, and the device can be combined. It can be set to 1-.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a diagram showing the arrangement of equipment around a photoreceptor in an example of a two-color black and red laser printer equipped with a fixing device according to the present invention.

A charger 2, a laser beam writing unit 3, a black developer 4, a red developer 5, a first transfer charger 6, and a cleaning unit 7 are provided around the photoreceptor drum l in the order of the rotation direction indicated by the arrow. ing. A transfer belt 7 formed as an endless belt is hung between a drive roller 8 and a support roller 9 so that one side of the belt loop passes through a transfer portion formed between the photoreceptor drum 1 and the first transfer charger 6. Passed out. A fulcrum roller 10 for changing the transfer belt angle is provided downstream of the first transfer charger 6 along the inner surface of the transfer belt 7 in contact with the photosensitive drum 1, and the upper support roller 9 is shown by a solid line in the figure. A solenoid 11 is provided for displacement between the first transfer position and the second transfer position indicated by a chain line in the figure. When the support roller 9 is in the first transfer position, both running portions of the transfer belt 7 take the linear I position, and the transfer belt angle changing fulcrum roller 10 simply contacts the inner surface of the transfer belt 7. There is only one. On the other hand, when the support roller 9 is at the second transfer position, the side of the transfer belt 7 in contact with the photoreceptor drum is supported around the transfer belt angle changing fulcrum roller 10 and bent, as shown by the chain line in the figure. On the opposite side, a tighter roller 12 for taking up slack is pressed by a spring 13 and assumes a second position in a bent state. The tighter roller 12 and the spring 13 are displaced by the solenoid 14, and the tighter roller 12 is held at a position spaced apart from the transfer belt 7 at the first position of the transfer belt 7.

The transfer belt 7 is driven only in the direction shown by the arrow by a drive source (not shown). A transfer belt cleaning unit 15 is provided so as to be able to come into contact with and separate from the transfer belt, facing the outside of the transfer belt wrapped around the drive roller 8, and a transfer belt cleaning unit 15 is provided on the running part of the transfer belt on the side that contacts the photoreceptor on the downstream side thereof. Registration roller pair 1 that feeds the transfer paper in a direction tangent to the
6 and a transfer hole guide plate F are provided. A charger 18 for adhering the transfer paper is provided opposite to the outer side of the transfer paper feeding position of the transfer belt 7 . Further, a second transfer charger 19 is provided opposite to the outside of the point where the straight portion of the running portion of the transfer belt in the I-th position that contacts the photosensitive drum 1 contacts the support roller 9 .

A fixing device 21 is provided on the downstream side of the exit side of the transfer belt 7 via a fixing entrance guide plate 20 . As shown in FIG. 2, the fixing device 21 consists of one fixing roller 23 having a built-in heater 22, and two pressure rollers 24, 25 in contact with both sides of the fixing roller 23, respectively. The fixing roller 23 is made of a metal roller coated with tetrafluoroethylene resin or thin silicone rubber, and the pressure rollers 24 and 25 are made of a metal core bar coated with thick silicone rubber.

The fixing roller 23 is driven by a drive motor 40 that rotates in forward and reverse directions.
It is rotatable in both directions, a first direction indicated by a solid line in the figure and a second direction indicated by a broken line, through gear trains 41 and 42,
The pressure rollers 24 and 25 are rotated following the rotation of the fixing roller 23. The fixing entrance guide plate 20 transfers the transfer paper separated from the transfer belt 7 at the first position to the fixing roller 23.
The first guide plate 27 guides the transfer paper separated from the transfer belt 7 at the second position to the first fixing nip 26 formed between the fixing roller 23 and the pressure roller 24. and second guide plates 29 and 29' that guide the second fixing nip portion 28 formed between the two guide plates 29 and 29'. The inner guide plates 27' and 29' are integrally formed in a V-shape, and a spur 30 having sharp teeth around the periphery is rotatably provided at the tip facing the fixing roller 23.

A first separating pawl 31 and a second separating pawl 32 are provided on the downstream side of each of the I and second fixing nip portions of the fixing roller, and the first separation pawl 31 and the second separation pawl 32 are provided so that the fixing roller can be discharged to the outside of the machine via a fixing exit guide plate 33. There is.

The operation of this device will be explained below.

Two-color print mode> First, a black toner image is formed on the photoreceptor drum 1 by a known electrophotographic process, and the transfer belt 7 is moved to the support roller 9 for the first transfer without feeding the transfer paper to the transfer belt 7. The first transfer charger 6 transfers a black toner image from the photoreceptor drum 1 to the transfer belt 7, and then forms a red toner image on the photoreceptor; Align the position with the black toner image and overlay and transfer. red·
The order of transferring the black image may be reversed. At this time, the tight narrow roller 12 is pulled by the solenoid 14 and is separated from the outer circumferential surface of the transfer belt, and the cleaning unit 15 is also retracted from the transfer belt 7, so it is undetermined. The registration roller 12 and the cleaning unit 5 do not disturb the registration roller 12 and the cleaning unit 5 at the timing when the leading edge of the portion of the transfer belt 7 to which the two-color toner images have been transferred aligns with the leading edge of the transfer paper. When the transfer paper is fed to the transfer belt 7 by the transfer paper 16, the transfer paper is conveyed in close contact with the transfer belt by the transfer paper adhesion charger 18, and at the exit of the transfer belt 7, the toner image on the transfer belt is transferred to the second transfer belt. Due to the action of the charger 19, the image is transferred from the transfer belt 7 to the side of the transfer paper that is in contact with the transfer belt. After the transfer, the transfer paper is separated from the transfer belt 7 due to the stiffness of the paper, and is moved to the entrance guide plate 2.
7, 27', the first nip portion 26 of the fixing device
The side on which the toner image has been transferred is connected to the fixing roller 23
is held in contact with the pressure roller 24 and is conveyed and fixed,
It is separated from the fixing roller 23 by the separating claw 31 and discharged outside the machine.

Monochrome print mode> The support roller 9 is moved to the second transfer position by the solenoid 11, and the tight roller 12 is moved by the solenoid 14 to press against the belt, and the transfer belt 7 is held at the second position. Then, a toner image of one color, black or red, is formed on the photoreceptor drum l, and the transfer belt 7 is rotated so that the leading edge of the toner image on the photoreceptor and the leading edge of the transfer paper are aligned with the first transfer charger 6. The transfer paper is fed to the transfer belt 7 by the registration roller 16 at a timing that should coincide with the transfer position between the transfer paper and the photoreceptor 1 . Under the action of the first transfer charger 6, the toner image is transferred from the photoreceptor drum 1 to the surface of the transfer paper that contacts the photoreceptor. The transfer paper is bent at the transfer belt angle changing fulcrum roller 10, and is adsorbed and conveyed by the transfer belt moving in the direction of the support roller 9 displaced to the second transfer position.

The paper is separated from the transfer belt 7 at the position of the support roller 9 by using the stiffness of the paper, guided by the entrance guide plate 29, 29', and inserted into the second nip section 28 of the fixing device 21, where the toner image is transferred. The paper is conveyed and held between the fixing roller 23 and the pressure roller 25 so that its side is in contact with the fixing roller 23, is fixed, is separated by the separation claw 32, and is carried out of the machine.

In the above embodiment, a gear train was used to transmit the rotation of the forward/reverse motor 40 to the fixing roller.

Many known means can be employed, such as a combination of a chain and a sprocket wheel, a combination of a timing belt and a timing pulley, etc.

Also, instead of using a forward/reverse motor, it is possible to use a motor that rotates in one direction and insert a forward/reverse clutch in the middle of the transmission system, but this would require more complicated equipment and is not advantageous in terms of cost. Not. Furthermore, when a clutch is used, there is a risk of slippage occurring during high-torque fixing drive, which also poses a problem in terms of reliability.

Furthermore, in the above embodiment, as shown in FIGS. 1 and 2, the fixing roller is placed in the center and the pressure rollers are placed on both sides to form two nip portions in which the heating sides are opposite to each other. However, in another embodiment shown in FIG. 3, one pressure roller 24 is arranged at the center, and fixing rollers 23a,
23b to form two nips with heating sides opposite each other. In this case, the heater 22a provided in each fixing roller 23a, 23b,
The wattage of the 22b and the control temperature of the surface of the fixing roller can be changed, and the fixing temperature can be set to the optimum temperature for each of the monochrome print mode and the multicolor print mode.For example, by superimposing three colors. When printing in full color, the toner layer becomes thicker, requiring a higher fixing temperature. In this configuration, in the monochrome print mode in which a toner image is formed on the side of the transfer paper in contact with the photoreceptor, the transfer belt 7 is kept in a straight line as shown by the solid line in FIG. Since the transfer paper is inserted into the nip between the transfer paper and the pressure roller 24, it has the advantage that in the case of monochromatic printing, which is frequently produced, conveyance is performed smoothly and a good image can be obtained.

However, in the multicolor print 1-mode in which toner images of multiple colors are superimposed and transferred onto the transfer belt 7, the tight narrow roller 12 is placed in a state where the transfer belt is at a bending position and carrying toner images as shown by the broken line in FIG. Since the transfer belt must be tensioned, the tighter roller 12 must be provided inside the belt loop. Another problem is that the transmission means for separately driving the two fixing rollers in opposite directions using a single drive motor is complicated.

Various examples of such transmission means are shown in FIGS. 4 to 8.

In the example shown in FIG. 4, the pressure roller 24 is moved by the forward and reverse motor 4.
0, the two fixing rollers 23a, 2 rotate through a gear train in either the forward or reverse direction depending on the fixing roller used.
3b is rotated as a result of this rotation.

In another example of the transmission mechanism shown in FIG.
Accordingly, one of the fixing rollers (23a in this example) is rotated via a gear train, and the pressure roller 24 and the other fixing roller 23b are rotated by being driven by this.

In another example shown in FIG. 6, two clutches 43 are inserted in parallel in the transmission system between a motor 40' that rotates only in one direction and one fixing roller (23a in this example). By selecting and intermittent rotation, the direction of rotation transmitted to the fixing roller 23a is switched, and the fixing roller 23a is driven to rotate the pressure roller 24 and the other fixing roller 23b.

In still another example shown in FIG. 7, one of the output shafts of a drive motor 40' that rotates only in one direction is connected to one of the fixing rollers 23b via a one-way clutch 44, and the output shaft The other one is connected to the other fixing roller 23a via a clutch 43. When fixing is performed by passing a sheet through the nip between the fixing roller 23a and the pressure roller 24, the clutch 43 is connected to rotate the fixing roller 23a in a predetermined direction, and the pressure roller 24 and the other fixing roller are connected. The roller 23b is driven to rotate. At this time, the fixing roller 23b is
Although the fixing roller is rotated in the opposite direction to the rotation direction when fixing is performed, since a one-way clutch 44 is inserted between the fixing roller and the drive motor 40', the rotation is performed without difficulty.

On the other hand, when fixing using the fixing roller 23b, the clutch 43 is disengaged and the fixing roller 23a is allowed to rotate freely. As a result, the other fixing roller 23b is driven by the drive motor 40.
' is rotated in a predetermined direction via the one-way clutch 44, and the pressure roller 24 and the other fixing roller 23a are driven to rotate.

In still another example shown in FIG. 8, each fixing roller 23a, 2
3b are rotatably driven by separate motors 40' that rotate in one direction via unidirectional clutches 44, and the motors for the fixing rollers to be used are selectively driven and the pressure rollers 24 and 3b are rotated. The other fixing roller is rotated in accordance with this rotation.

As described above, according to the present invention, whether the toner image is carried on the side of the transfer paper conveyed by the transfer belt that contacts the photoreceptor or the toner image is carried on the opposite side, It is transported through the nip section of the fixing device at a stable transport speed, which prevents failures such as peeling of the adhesive between the elastic layer of the pressure roller and the core metal, improving reliability and improving image quality. It is effective in improving

Furthermore, by using a motor capable of forward and reverse rotation as a drive source for the fixing roller, the drive device becomes simple, and costs can be reduced and the size of the device can be reduced.

[Brief explanation of drawings]

Fig. 2 is a sectional view showing the main parts of an image forming apparatus equipped with the fixing device of the present invention, Fig. 2 is a sectional view taken along a plane including the axes of the three rollers of the fixing device, and Fig. 3. 4 is a cross-sectional view showing a main part of an image forming apparatus having a fixing device with a different roller arrangement, and FIGS. 4 to 8 are cross-sectional views showing various configuration examples of a fixing roller driving device of the fixing device. 1...Photoreceptor 6...Transfer charger 7...Transfer belt 21...Fixing device 22, 22a, 22b-heater 23,
23a, 23b Constant fixing roller 24...Pressure roller 40...Forward and reverse rotation motor (drive source capable of forward and reverse rotation) 40'
... One-way rotational drive 41.42 ... Gear 43 ... Clutch 44 One-way clutch 3rd 4th snake 6th 4Q'

Claims (2)

[Claims] (1) A photoreceptor of transfer paper, which has a transfer belt that rotates in one direction in contact with a photoreceptor in a transfer section, and during monochrome image formation, the toner image formed on the photoreceptor is conveyed by the transfer belt. The toner images are transferred to the surface in contact with the photoconductor, separated from the transfer belt, and fixed by a fixing device. When forming a multicolor image, the plurality of toner images sequentially formed on the photoreceptor are transferred onto the rotating transfer belt in a superimposed manner. After that, the image is transferred to the surface of the transfer paper that is conveyed by the transfer belt, opposite to the surface that contacts the photoreceptor, and is fixed by a fixing device that is separated from the transfer belt. , a fixing roller that can be rotated in forward and reverse directions, and two pressure rollers that contact each side of the roller to form a nip and are rotated by the rotation of the fixing roller. A fixing device characterized in that the paper is inserted into a nip portion where the unfixed toner image bearing surface contacts the fixing roller, and the fixing roller is rotationally driven in a direction to convey and discharge the inserted transfer paper in a predetermined direction. . (2) The fixing device according to claim 1, wherein the fixing roller is driven by a drive source capable of forward and reverse rotation.