JPH11133791A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which makes a quantity of heat supplied to a transfer material from a fixing means even, and prints an image which is less in irregularity in gloss obtained after fixing. SOLUTION: A motor control means 41 for a driving means which rotates and drives a fixing roller 1 is provided with a transfer-material-carrying adjustment means which is operated at least one and after the second rotation of the fixing means 2 and decreases carrying speed in a fixing process. After the transfer material enters a fixing nip and the fixing roller 1 makes one rotation to apply heat and pressure to toner on the transfer material at the fixing nip while carrying the transfer material at the speed corresponding to the peripheral speed of the fixing roller 1, the transfer-material-carrying adjustment means is turned on to decrease the speed at which the fixing roller 1 is rotated by the driving means 40 and hence the speed at which the transfer material is carried is made slow, thereby increasing a quantity of heat supplied to the transfer material. Thus, irregularity in the gloss of the front and rear parts of the transfer material is reduced.

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 having a fixing device for fixing a toner image on a transfer material such as an electrophotographic apparatus.

[0002]

2. Description of the Related Art Conventionally, an image carrier having an electrostatic latent image on the surface thereof, a developing device for developing the electrostatic latent image on the image carrier with a toner as a developer to visualize the image, and a developed device have been developed. 2. Description of the Related Art An image forming apparatus having a transfer device for transferring a toner image on an image carrier onto a transfer material, a fixing device for fixing the toner on the transfer material by heating and pressing the transfer material on which the toner image has been transferred, and the like are known. The image forming apparatus includes an electrophotographic printer, a copying machine, a facsimile, and the like.

FIG. 11 shows a schematic configuration diagram of a color image forming apparatus as an example of the above image forming apparatus. FIG.
As shown in the figure, the photosensitive drum 101 serving as an image carrier, a roller charger 34 for uniformly charging the surface of the photosensitive drum 101, a charged photosensitive drum 101
Exposure means 35 for irradiating a laser L thereon to form an electrostatic latent image on the photosensitive drum 101,
01, a developing device 31 for developing the electrostatic latent image with four color toners, an intermediate transfer body 32 as a transfer device for temporarily carrying one or four colors of the toner image developed by the developing device 31, and an intermediate transfer A secondary transfer roller 33 serving as a transfer device for transferring the toner image on the body 32 to the surface of the transfer material, and heating and pressing the transfer material on which the toner image has been transferred to transfer the toner image on the transfer material to the transfer material A fixing device 25 for fixing, a transport guide (not shown) for transporting the transfer material to a predetermined position, and the like are provided.

The developing device 31 for developing the electrostatic latent image on the photosensitive drum 101 has four developing units 30a, 30b, 30
c and 30d are supported by a rotatable support 31a, and a developing opening surface of each developing unit is provided on the same circumference centered on the rotation axis of the support 31a. Further, each developing unit 30a,
Yellow toner, magenta toner, and cyan toner, which are non-magnetic toners, are stored in 30b and 30c, respectively, and black toner, which is a magnetic toner, is stored in the developing device 30d.

In the development by the developing devices containing the four color toners, one of the developing devices containing the toners of the respective colors contains one of the photosensitive drums 1 containing the color corresponding to the image signal.
The electrostatic latent image on the photosensitive drum 101 is developed by a predetermined color toner by being moved to the opposite portion of the photosensitive drum 101. The developed toner image on the photosensitive drum 101 is temporarily transferred to the intermediate transfer body 32. If the image to be printed is a full color image, development and transfer to the intermediate transfer body 32 are performed in accordance with the image signal for each of the developing devices containing the toners of four colors or three primary colors.

When the image to be printed on the intermediate transfer member 32 is transferred, the toner image on the intermediate transfer member 32 is transferred by the secondary transfer roller 33 at a transfer nip where the intermediate transfer member 32 and the secondary transfer roller 33 face each other. The image is transferred onto a transfer material (not shown). The transfer material onto which the toner image has been transferred by the secondary transfer roller 33 is conveyed in the direction of the fixing device 25 via a predetermined conveyance guide (not shown). FIG. 1 is a schematic configuration diagram of a heat roller type fixing device conventionally used as a toner image fixing device in the apparatus. As shown in FIG. 12, the fixing device 25 includes a fixing roller 1 which comes into contact with a transfer material carrying a toner image and is rotated by a driving unit (not shown) using a motor or the like, and a pressing unit (not shown). And a pressure roller 2 that is pressed against the fixing roller 1 and rotates in accordance with the rotation of the fixing roller 1, and the fixing roller 1 is rotated by rotating the fixing roller 1.
The pressure roller 2 is driven to rotate while forming a nip at the pressure contact portion between the pressure roller 2 and the pressure roller 2.

The fixing roller 1 has, for example, a silicon rubber layer on a metal core formed in a substantially hollow cylindrical body, and a halogen heater 3 is built in a hollow space of the metal core. By driving, the fixing roller is heated and heat required for fixing is supplied. Also,
The pressure roller 2 has a silicon rubber layer on a metal core formed in a substantially hollow cylindrical body similarly to the fixing roller 1, and a halogen heater 3 ′ is built in the hollow space of the metal core. When the heater 3 ′ is driven, the pressure roller is heated to supply heat necessary for fixing, and the transfer material carrying the toner is fixed to the fixing roller 1 and the pressure roller 2.
By passing the toner through the nip formed by the above, the toner can be heated and pressed at the nip to fix the toner on the transfer material.

A thermistor 4 as a temperature detecting means for detecting the surface temperature of the fixing roller 1 is brought into contact with the surface of the fixing roller 1, and a temperature for detecting the surface temperature of the pressing roller is provided on the surface of the pressing roller 2. A thermistor 4 'is abutted as a detecting means, and the two thermistors 4, 4' are connected to a control device (not shown). In addition, the surface temperature of the pressure roller 2 can be detected. The control device, which detects the surface temperatures of the fixing roller 1 and the pressure roller 2, controls on / off of the two halogen heaters 3, 3 'so that the temperatures detected by the two thermistors 4, 4' reach a predetermined temperature. , The temperature of both rollers can be controlled.

Further, an oil application roller 12 is brought into contact with the surface of the fixing roller 1, and the oil application roller 12 rotates in contact with the surface of the fixing roller 1 so that the surface of the fixing roller 1 is subjected to oil application. The offset of the toner on the surface of the roller 1 can be prevented. Silicon oil is suitable as the oil used when applied to the surface of the fixing roller 1 from the viewpoint of releasability.

As the above-mentioned silicone oil, methylphenyl silicone oil was used. It is desirable to use a phenyl group content of 5 mol% or more from the viewpoint of preventing swelling. On the other hand, if the viscosity is too low, the swelling property becomes large, and the in-machine contamination due to volatilization also worsens. On the other hand, if the viscosity is too high, the adhesion to the roller deteriorates.
A value of about 00 cs is desirable.

In an oil supply device for supplying oil to the oil application roller 12, an oil tank 18, which is a replaceable oil container, is connected to an oil pump 16 via joints 17, 17 'by a tube of silicone resin or the like. Have been. The configuration of the oil tank 18 has oil contained in an aluminum pack in a rigid case. The joints 17, 17 'are composed of a combination of a rubber seal, a spring, and the like, and when the A oil tank 18 is detached, the oil seals from both are made. The oil pump 16
It serves to send oil to the oil supply nozzle 13 in the application section. On the other hand, the oil remaining in the application section is once collected in the oil tank 18 from the oil case 15 and reused.

The type of pump for pumping oil from the oil tank 18 preferably employs a system in which the amount of oil is controlled by a pulse signal using an electromagnetic pump. Also, a gear pump may be used, in which case it is cheap and inexpensive. The pump may be provided with a check valve.

The oil supply device having the above configuration is a completely closed system and has no fear of leakage. Therefore, the oil supply device may be provided on the main body side of the image forming apparatus or on the fixing unit side. .

As for the oil application section, the oil supplied from the oil supply nozzle 13 is used for holding a very small amount of replenished oil closely or extremely close to the oil application roller 12 having silicone rubber as a surface layer. 1
After the oil is supplied by the oil application roller 4, oil is held between the oil application roller 12 and the oil application roller 12 for a short period of time. A homogeneous thin layer application is made on top. The surplus oil falls from the plate 14 for oil and travels along the bottom surface of the oil case 15 to be collected again by the oil pump 16.

The fixing roller 1 is controlled by the oil application roller 12.
The oil applied above absorbs or adheres to the paper as the paper passes, and goes out of the machine. However, the oil applied during the non-paper-passing portion of the fixing roller 1 or at the time of front / rear rotation is pressurized. Adhering and transferring to the roller 2, the cleaning blade 5
As a result, the toner is scraped off from the pressure roller 2 together with the paper dust and toner, falls below the cleaning blade 5, and is promptly absorbed by the oil absorption band 10 in the oil pan 6 which is a waste oil recovery container. . The oil pan 6 containing the oil absorber 10 can be detached and replaced from the fixing unit. In addition to the oil recovery by the oil absorber 10, a method of solidifying the oil by a chemical change is also conceivable.

As the material of the cleaning blade 5, it is preferable to use a material having excellent releasability, such as fluoro rubber, and non-attachment sliding property. The material of the oil absorber 10 is preferably one that absorbs oil mainly by natural or natural fibrous or porous material by capillary action. For example, a nonwoven fabric processed by laminating fibers having a diameter of several to several tens of μm such as polyester, polypropylene, and polyethylene to a thickness of several cm or less is preferable. The surface may be treated so as to increase lipophilicity.

In order to fix the toner on the transfer material by the fixing device 25 having the above-described configuration, the transfer material having an unfixed toner image carried in a nip portion between the fixing roller 1 and the pressure roller 2 heated to a predetermined temperature. Is guided by a guide 8, and the transfer material is conveyed by the rotation of the fixing roller 1 rotated at a predetermined peripheral speed by the driving means, and the toner on the transfer material is heated and pressed at the nip. It has become. At this time, the oil is uniformly applied to the surface of the fixing roller 1 with which the toner comes into contact by the above-described oil application device, and the offset of the toner is prevented.

The toner on the transfer material that has entered the nip portion is
The fixing roller 1 is heated while being in contact with the fixing roller 1, and is pressed by both rollers to be fused and fixed on the transfer material, thereby forming an image on the transfer material. The transfer material to which the toner has been fixed is
The sheet is guided out of the apparatus by being guided by the guide 8 '. The surface of the fixing roller 1 on which the fixing has been performed is rubbed again by the cleaning web 7 during rotation, so that the offset toner is removed and oil is applied at the same time, while excess oil is stripped off. The fixed recording material and the pressure roller 2
And a separation claw 9 for separating the transfer material from the pressure roller 2 is prevented.

The fixing roller 1 of the fixing device 25 has a thickness (multiple to several tens μm) of multicolor toner of a single color to four colors of a color image.
In order to follow m), it is necessary to provide an elastic layer on the core shaft of aluminum or the like with several tens μm or more. If the elasticity is low, the toner concave portions are not fixed, and the resolution is reduced due to the collapse of the toner.

The material of the elastic layer is preferably a liquid silicone rubber RTV or LTV type of methyl or methyl vinyl type having elasticity. In particular, RTV has a high affinity with silicone oil. It is preferable because oil can be easily applied. On the surface layer of the fixing roller 1, the above R
It is also possible to use a TV or LTV, provide a heat resistant HTV layer below the TV, and form a multilayer structure in which thermal degradation and peeling of the back surface of the surface layer are prevented.

The configuration of the pressure roller 2 may be simplified because it may have less elasticity than the fixing roller 1, and may be simply provided with a layer of HTV, fluoro rubber, etc. on the aluminum core shaft, and PFA on the surface. Alternatively, a PTFE coat or the like may be applied to prevent oil swelling. Further, an RTV may be used. Of course, a roller having substantially the same configuration as the fixing roller may be used. In addition, as the rubber used for the fixing roller and the pressure roller, methylphenyl silicone rubber may be used.

When the toner is fixed in the nip formed by the fixing roller 1 and the pressure roller 2 having the above-described configuration, the surface of the toner image is smoothed, and an image having a high gloss (usually, a gloss value) is easily formed. . If a large amount of release agent such as silicone oil is applied to the fixing roller to prevent the toner from being offset to the surface of the fixing roller by heating the toner, the silicone oil may be transferred to the transfer material. Since the toner was absorbed or adhered to the toner, the glossiness of the toner was further increased, and the fixing device was easily contaminated by oil.

Further, in recent years, as color copiers permeate the general society, not only full-color images but also mono-color and black-and-white images may be printed by the same apparatus. When a black-and-white print is performed by an image forming apparatus capable of printing, an image having a higher gloss is obtained as compared with an image forming apparatus that performs only a black-and-white print (a device that performs only monochrome printing).

Therefore, a configuration is generally used in which the temperature adjustment target value is changed in order to adjust the glossiness by using the fact that the glossiness of the transfer material after fixing changes depending on the temperature at the time of fixing. FIG. 13 shows the relationship between the temperature of the fixing roller and the gloss. As can be seen from FIG. 13, when the temperature at the time of fixing is high, an image with high gloss is obtained, and when the temperature at the time of fixing is low, an image with low gloss is obtained. As a result, the target temperature adjustment value is set higher (about 180 ° C.) when outputting a highly glossy image, and the target temperature adjustment value is set lower than the standard value (170 ° C.) when outputting a weak glossy image.
Degree) to adjust the temperature during fixing.

An OHP sheet is an important material in print output of a color image. OHP
When printing using a transfer material such as a sheet,
Normal (plain paper) to supply more heat to the toner than usual to satisfy the transparency of the OHP sheet
Is conveyed at a lower speed than the conveyance speed. More specifically, in the case of printing using an OHP sheet, the driving of the driving unit for rotating the fixing roller 1 is controlled to slow down the rotation of the fixing roller 1 and conveyed by the rotation of the fixing roller and the pressure roller. Reduce the transfer speed of the transfer material
That is, the heating time of the P sheet is increased. At this time, it is general to set the transport speed of the OHP sheet to about 50% of the normal speed.

[0026]

However, the fixing device used in the conventional image forming apparatus has the following disadvantages. The fixing roller 1 is covered with a silicone rubber elastic layer in order to fix multiple toners of a single color to four colors of a color image. The thermal conductivity of this silicone rubber is about 1 W / mK, and the release layer on the surface, for example, PF
The thermal conductivity of A is about 0.5 W / mK, which is much smaller than the thermal conductivity of an aluminum core (about 200 W / mK). Therefore, the transfer of heat from the core metal heated to a predetermined temperature by the halogen heater to the surface of the fixing roller becomes slower, and the fixing roller rotates from the surface of the fixing roller every time the fixing roller rotates when the transfer material is passed through the nip portion. The amount of heat deprived is larger than the amount of heat supplied from the halogen heater via the cored bar, and the surface temperature of the fixing roller is reduced, and the surface of the fixing roller is smaller than the amount of heat required to be supplied to the transfer material during the fixing process. Was sometimes lowered. If the surface temperature of the fixing roller decreases, the glossiness of the image after fixing decreases, and if the fixing temperature further decreases, fixing failure or the like occurs.

Since the amount of heat supplied from the fixing roller to the transfer material decreases with the number of rotations of the fixing roller due to the decrease in the temperature of the fixing roller, one fixing step is completed by rotating the fixing roller a plurality of times. For example, when the length of the transfer material in the transport direction is longer than the outer circumference of the fixing roller, as shown in FIG. There was a problem that the appearance of the camera became poor. This change in gloss
Because it appears as a sudden change in each cycle of the fixing roller,
The variation in gloss of the print was conspicuous.

When an OHP sheet is used as the transfer material, the transfer speed is higher than the normal (plain paper) transport speed in order to supply more heat than usual to the toner in order to satisfy the transparency of the OHP sheet. Although the sheet is conveyed at a low speed, in this case, the amount of heat supplied to the OHP sheet itself becomes excessive, and the rigidity of the sheet is lost. It was difficult to satisfy both.

Accordingly, the present invention reduces the temperature drop of the fixing unit by lowering the conveying speed of the fixing unit, thereby uniformizing the amount of heat supplied from the fixing unit to the transfer material, and causing variation in gloss after fixing. It is an object of the present invention to provide an image forming apparatus capable of printing an image with few images. OHP
It is an object of the present invention to provide an image forming apparatus that can satisfy both the transportability and transparency of an OHP sheet when a sheet is used.

[0030]

According to a first aspect of the present invention, there is provided an image carrier for forming an electrostatic latent image on a surface thereof, and a method for forming an electrostatic latent image on the image carrier into a toner. A transfer device for transferring the developed toner image on the image carrier to a transfer material, a fixing device for fixing the toner transferred to the transfer material onto the transfer material, and transporting the transfer material. An image forming apparatus provided with a conveying unit and at least a speed changing unit that can change a conveying speed of a transfer material at the time of fixing, wherein the fixing device contacts a transfer material carrying a toner image and heats the toner. A fixing unit rotatably disposed with the fixing unit, a pressing unit pressed against the fixing unit and rotatably disposed, and a fixing unit and a heating unit connected to one or both of the fixing unit and the pressing unit. Rotating the pressure means Forming an image by passing the transfer material through a pressure contact portion between the fixing unit and the pressing unit, heating and pressing the toner on the transfer material, and fixing the toner on the transfer material. In the image forming apparatus, the image forming apparatus includes a transfer material transport adjusting unit that operates in response to a temperature drop of the surface temperature of the fixing unit and reduces a transport speed of the transfer material in the fixing process. Is
When the surface temperature of the fixing unit drops by a predetermined temperature, the rotation speed of the fixing unit and the pressurizing unit that are driven to rotate by the driving unit is reduced by the speed changing unit to reduce the conveyance speed in the fixing step after the temperature of the fixing unit drops. This can be achieved by lowering the temperature of the fixing unit before the temperature drops.

Further, according to the second aspect of the present invention, the above object is achieved when the fixing means rotates a plurality of times in one fixing step, and the transfer material transport adjusting means adjusts the surface temperature of the fixing means to a predetermined value. In place of the case where the temperature drops, this is achieved by operating at least in the second and subsequent rounds of the fixing unit to lower the transport speed in the fixing step.

Further, according to the third aspect of the present invention, the above object is achieved when the fixing means rotates a plurality of times in one fixing step, and the transfer material transport adjusting means sets the surface temperature of the fixing means to a predetermined value. In place of the case where the temperature drops, it is achieved by lowering the conveying speed in the fixing step by operating according to the increase in the number of rotations of the fixing unit.

Further, according to the fourth aspect of the present invention, the object is to set the length in the transport direction of the transfer material to A, the outer circumference of the fixing means to R, and the distance between the transfer position and the fixing position. When the distance is H, the respective relations are H <A−R
When the relationship of A−R ≧ 2R is satisfied and the transfer speed in the fixing step is reduced by the transfer material transfer adjusting means, the image forming apparatus responds to the decrease in the transfer speed in the fixing step. This is achieved by providing a transfer changing means for lowering the transfer speed at the time of transfer and changing the transfer conditions according to the decrease in the transfer speed.

Further, according to the fifth aspect of the present invention, the object is to set the length of the transfer material in the transport direction to A, the outer circumference of the fixing means to R, and the distance between the transfer position and the fixing position. When the distance is H, the respective relations are H <A−R
When the relationship of A−R ≧ 0.5R is satisfied, the transfer material transport adjusting means operates after the end of the transfer process and performs the fixing operation in place of the case where the surface temperature of the fixing means drops by a predetermined temperature. This is achieved by reducing the transfer speed of the transfer material in the process.

According to the sixth aspect of the present invention, the above object is attained by reducing the reduction of the transport speed in the fixing step by the transfer material transport adjusting means at a predetermined rate per unit time. You.

Further, according to the seventh aspect of the present invention, the object is to reduce a decrease in the transport speed in the fixing step by the transfer material transport adjusting means by reducing the transport speed to an arbitrary value as the transport time elapses. Is achieved by

Further, according to the eighth aspect of the present invention, the above-described object is achieved, when an OHP sheet is used as a transfer material, in a fixing step until a range within 50 mm from the leading end of the OHP sheet passes through a fixing nip. The transport speed of the OHP sheet at 50 m from the leading end of the OHP sheet
This is achieved by making the transport speed higher than the transport speed when transporting the OHP sheet in a range excluding the range within m.

According to a ninth aspect of the present invention, there is provided an image carrier for forming an electrostatic latent image on a surface thereof, and a developing device for developing the electrostatic latent image on the image carrier with toner. An apparatus, a transfer device that transfers the developed toner image on the image carrier to a transfer material, a fixing device that fixes the toner transferred to the transfer material onto the transfer material, and a conveyance unit that conveys the transfer material, An image forming apparatus provided with at least a speed changing unit for changing a transfer speed of the transfer material at the time of fixing, wherein the fixing device abuts on the transfer material carrying the toner image to heat the toner and to be rotatable. A fixing unit disposed, a pressing unit that is pressed against the fixing unit and rotatably disposed, and is connected to one or both of the fixing unit and the pressing unit to rotate the fixing unit and the pressing unit. Drive means for driving An image forming apparatus that forms an image by passing a transfer material through a pressure contact portion between a fixing unit and a pressing unit to heat and pressurize the toner on the transfer material to fix the toner on the transfer material, When an OHP sheet is used as the transfer material, the speed changing means is O
The transport speed of the OHP sheet during the fixing process until the area within 50 mm from the leading edge of the HP sheet passes through the fixing nip is the transport speed when transporting the OHP sheet within the range excluding the area within 50 mm from the leading edge of the OHP sheet. This is achieved by changing the rotation speed of the fixing member by the driving means so as to be faster.

In other words, according to the first aspect of the present invention, when the surface temperature of the fixing means decreases in the fixing step, the transfer material transport adjusting means operates and the fixing means which is driven to rotate by the driving means and The amount of heat supplied to the transfer material is made uniform by lowering the rotation speed of the pressurizing unit by the speed changing unit and lowering the conveyance speed in the fixing step after the temperature of the fixing unit lowers than before the fixing unit lowers the temperature. Thus, an image having less variation in gloss after fixing is provided.

According to the second aspect of the present invention, when the fixing means rotates a plurality of times in one fixing step, the transfer material transport adjusting means operates at least in the second and subsequent rounds of the fixing means. Since the transport speed in the fixing step is reduced, the amount of heat supplied to the transfer material is made uniform, and an image having less variation in gloss after fixing is provided.

According to the third aspect of the present invention, when the fixing means rotates a plurality of times in one fixing step, the transfer material transport adjusting means operates according to an increase in the number of rotations of the fixing means. As a result, the transfer speed in the fixing step is reduced, so that even when a transfer material having a long length in the transfer direction is used, an image having less variation in gloss after fixing is provided.

According to the fourth aspect of the present invention, the length of the transfer material in the transport direction is A, the outer circumference of the fixing means is R, and the distance between the transfer position and the fixing position is H.
When the respective relations satisfy the relationship of H <AR and satisfy the relation of AR ≧ 2R, the transfer material transport adjusting means operates to reduce the transport speed in the fixing process. When the transfer rate is decreased, the transfer changing means reduces the transfer speed at the time of transfer in accordance with the decrease in the transport speed in the fixing step, and by providing the transfer change means for changing the transfer condition in accordance with the decrease in the transfer speed, Transfer of the transfer material between the transfer position and the fixing position is performed favorably,
An image having less variation in gloss after fixing is provided.

According to the fifth aspect of the present invention, the length of the transfer material in the transport direction is A, the outer circumference of the fixing means is R, and the distance between the transfer position and the fixing position is H.
When the respective relations are in the relation of H <A−R and satisfy the relation of A−R ≧ 0.5R, the transfer material conveyance adjusting means is operated after the end of the transfer process to perform the fixing process. By reducing the transfer speed of the transfer material, an image having less variation in gloss after fixing can be provided without complicating the transfer process.

According to the sixth aspect of the present invention, the transfer speed in the fixing step by the transfer material transfer adjusting means is reduced at a predetermined rate per unit time, so that a rapid temperature change can be prevented. And smooth images are provided.

Further, according to the seventh aspect of the present invention, the transfer speed in the fixing step by the transfer material transfer adjusting means can be reduced abruptly by reducing the transfer speed to an arbitrary value as the transfer time elapses. A smooth image without temperature change is provided.

According to the eighth aspect of the present invention, in the image forming apparatus of the first to seventh aspects, when an OHP sheet is used as a transfer material,
The transport speed of the OHP sheet in the fixing process until the area within 50 mm from the leading edge of the HP sheet passes through the fixing nip is set to the transport speed for transporting the OHP sheet in the range excluding the range within 50 mm from the leading edge of the OHP sheet. By making it faster, the rigidity of the leading end of the OHP sheet is secured, and both the transportability and the transparency are satisfied.

According to the ninth invention of the present application, when an OHP sheet is used as a transfer material, the OHP sheet in the fixing step until a range within 50 mm from the leading end of the OHP sheet passes through the fixing nip. The conveying speed of the OHP sheet is made faster than the conveying speed when conveying the OHP sheet in a range excluding the range within 50 mm from the front end of the OHP sheet. Both are satisfied.

[0048]

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

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram of a fixing device used in the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a graph showing a change in the conveyance speed of the fixing roller. FIG. 3 is a graph showing a change in the surface temperature of the fixing roller when the transfer paper passes through the fixing nip when the transfer paper is conveyed in A4 size. 3 shows a graph representing.

A color printer as an image forming apparatus capable of forming a full-color image with four color toners is a photosensitive drum which is an image carrier which rotates and carries an electrostatic latent image on its surface, and an electrostatic latent image on the photosensitive drum. A developing device that develops the image with a toner as a developer to visualize the image, an intermediate transfer body that once carries the developed image on the photosensitive drum and rotates, and a toner image that is carried on the intermediate transfer body. It has a secondary transfer roller that rotates while transferring to the transfer material, a fixing device that heats and pressurizes the transfer material on which the toner image has been transferred, and fixes the toner on the transfer material. The developed electrostatic latent image is developed with a toner of a predetermined color to transfer a developed image to an intermediate transfer body. After transfer from development to the intermediate transfer body for each color, the intermediate transfer is performed at a predetermined timing. An image is formed by transferring the toner image on the intermediate transfer member to the transfer material conveyed to a position facing the secondary transfer member by a secondary transfer roller, and fixing the toner image on the transfer material by a fixing device. You can do it. The structure and operation of the photosensitive drum and the developing device, which are image carriers of the image forming apparatus, are shown in FIG.
And the detailed description is omitted.

As shown in FIG. 1, the fixing device 25 for fixing the toner image on the transfer material includes a fixing roller 1 which is brought into contact with the transfer material carrying the toner image and is rotated by the driving means 40. The fixing roller 1 is pressed against the fixing roller 1 by pressing means (not shown).
And a pressure roller 2 that rotates in accordance with the rotation of the fixing roller 1. The driving unit 40 rotates the fixing roller 1 to form a nip at a pressure contact portion between the fixing roller 1 and the pressure roller 2. The pressure roller 2 can perform a driven rotation. In the fixing device 25, the pressure roller 2 rotates following the fixing roller 1 rotated by the driving unit 40, and the transfer material is transferred to a fixing nip, which is a nip formed by both rollers in a state where both rollers are rotated. By being guided, the transfer material can be transported in the discharge direction at a transport speed corresponding to the peripheral speed of the fixing roller 1.
Note that an oil application device that applies oil to the surface of the fixing roller may be provided to prevent offset of the toner to the fixing roller.

The fixing roller 1 according to this embodiment follows the thickness (several μm to several tens μm) of a multicolor toner of a single color to four colors of a color image on the outer periphery of a core metal formed of, for example, aluminum in a substantially hollow cylindrical body. A Φ40 mm roller formed by providing an HTV type dimethyl silicone rubber of 1.5 mm as an elastic layer and a 250 μm LTV type of dimethyl silicone rubber as a release layer on the outer periphery of the elastic layer was used.

For the pressure roller 2, for example, an HTV type of dimethyl silicone rubber is provided as an elastic layer on the outer periphery of a metal core having aluminum formed substantially in the hollow like the fixing roller 1. A φ40 mm roller formed by providing an LTV type dimethyl silicone rubber of 250 μm on the outer periphery was used. In addition, as the rubber used for the fixing roller and the pressure roller, a methylphenyl-based silicone rubber can also be used. Further, the pressure roller 2 may be a roller having the same configuration as the fixing roller 1.

A halogen heater 3 is built in the hollow space of the metal core of the fixing roller 1, and the fixing roller 1 is heated by the driving of the halogen heater 3 to supply heat necessary for fixing to the fixing roller 1. It has become. Further, a halogen heater 3 ′ is built in the hollow space of the metal core of the pressure roller 2, and the pressure roller 2 is heated by the heating drive of the halogen heater 3 ′, and heat required for fixing is applied to the pressure roller 2. The transfer material carrying the toner is passed through a fixing nip formed by the fixing roller 1 and the pressure roller 2, so that the toner on the transfer material is heated and heated by the fixing nip. The toner can be fixed on the transfer material by pressing.

A heater control means (not shown) is connected to the two halogen heaters 3 and 3 ', and a thermistor as a temperature detecting means is provided on the surfaces of the fixing roller 1 and the pressure roller 2. 4, 4 'are brought into contact with each other, and the heater control means turns on / off the two halogen heaters 3, 3' at a predetermined timing in accordance with the temperature detected from each thermistor 4, 4 ', thereby fixing the image. Roller 1
Further, the pressure roller 2 can be heated to a temperature required for fixing. In this embodiment, the temperature of the fixing device is controlled by setting the surface temperature of the fixing roller 1 to 170 ° C. as a normal fixing temperature, and the fixing temperature can be changed in a range of 160 to 180 ° C.

The driving means 40 for rotating the fixing roller 1 at a predetermined peripheral speed is connected to a DC motor via a gear, for example, to the rotating shaft of the fixing roller, and the DC motor is connected to the motor control means 41 to control the motor. D by means 41
The rotation of the C motor can be controlled to rotate the fixing roller at a predetermined peripheral speed.

The motor control means 41 is disposed in the control means 50 provided in the image forming apparatus and controlling each step of image formation, and the control section 51 in the control means 50 is provided.
By turning on the DC motor by a drive signal transmitted from the control unit 50 at a predetermined timing to rotate the fixing roller 1 at a predetermined rotation speed,
The fixing can be performed while the transfer material guided to the fixing nip is conveyed in the discharge direction of the transfer material by the rotation of the fixing roller 1. In order to smoothly transfer the transfer material between the position of the transfer nip where the intermediate transfer member and the secondary transfer member face each other and the position of the fixing nip where the fixing roller and the pressure roller face each other, for example, A transfer unit for transferring the transfer material such as a transfer belt may be provided. In this case, the transfer unit is driven by a DC motor provided in the driving unit, and the transfer speed of the transfer material by the fixing roller is adjusted. The transfer speed of the transfer material by the transfer means is synchronized.

Further, the motor control means 41 is provided with a reference which is set when a predetermined clock frequency is set in advance and which is referred to when supplying power to the DC motor, and supplies a power according to the clock frequency set in the reference. The speed at which the transfer speed of the transfer material at the time of fixing by the fixing roller can be changed by changing the peripheral speed of the fixing roller by increasing or decreasing the rotation speed of the DC motor by changing the reference clock frequency supplied to the DC motor and changing the reference clock frequency. In this embodiment, the fixing roller has a peripheral speed of 100 mm / sec.
It can be changed within the range of 10 to 120 mm / sec.

Further, in the motor control means 41, there is provided a transfer material conveyance adjusting means for reducing the rotation speed of the fixing roller by the DC motor of the driving means in response to the decrease in the surface temperature of the fixing means. The transfer material transport adjusting means operates at least at the timing when the fixing roller makes two rotations in one fixing process, so that the transfer material transport adjusting means appropriately changes the clock frequency of the reference of the DC motor. The rotation frequency of the DC motor can be reduced by changing the clock frequency of the power supplied to the DC motor. This is because when the fixing roller rotates a plurality of times in one fixing process, the surface temperature of the fixing roller decreases in accordance with the rotation of the fixing roller. Then, the transfer material transport adjusting means is operated.

Here, the timing when the fixing roller 1 makes two rotations is determined by the fact that the fixing roller 1 makes two rotations after a lapse of a predetermined time from the transmission of the image writing timing signal to the length corresponding to the outer periphery of the fixing roller 1. Or the timing when the fixing roller 1 makes two rotations in the arithmetic processing unit in the control means based on the timing of the secondary transfer start (timing at which the toner is transferred to the transfer material) and the transport speed in the transfer process of the transfer material. The control unit transmits an ON operation signal to the transfer material transport adjusting means at the timing when the fixing roller 1 makes two rotations. The transfer material conveyance adjusting unit that receives the ON operation signal changes the clock frequency of the power supply supplied to the DC motor to reduce the peripheral speed of the fixing roller. further,
The timing at which the speed of the transfer roller is reduced may be determined based on the output of a sensor used for jam detection or the like.

In the image formation by the image forming apparatus using the above-described fixing device, the electrostatic latent image formed on the photosensitive drum is developed by the toner of the developing device into a visible image in accordance with the image signal. The transferred toner image on the photosensitive drum is transferred to a transfer material via an intermediate transfer member and a secondary transfer member. The transfer material carrying the toner image has a leading end at the fixing device 25.
The toner on the transfer material is heated and pressed while being conveyed in the discharge direction in accordance with the rotation of the fixing roller 1 and guided by a fixing nip formed by The toner is fixed on the transfer material. In addition,
When the transfer material is guided to the fixing nip, the fixing roller 1
Are heated to 170 ° C., which is the fixing temperature.

In the present embodiment, the transfer material enters the fixing nip, and while the transfer material is being conveyed at a speed corresponding to the peripheral speed of the fixing roller 1, the toner on the transfer material is heated and pressed at the fixing nip to fix the toner. After the roller 1 completes one rotation, the transfer material transport adjusting means is turned on to reduce the rotation speed of the DC motor to reduce the transport speed of the fixing roller 1 from 100 mm / sec to 90 mm.
/ Sec. By lowering the transport speed,
The amount of heat supplied from the fixing roller 1 to the transfer material is increased, and the variation in gloss at the front and rear positions with respect to the transfer direction of the transfer material can be reduced.

Incidentally, it is necessary to set the width of decrease in the transport speed in accordance with the thermal conductivity of the fixing roller, the transport speed, and the like. In particular, when the fixing roller has a release layer on the surface layer, the temperature characteristics of the fixing roller greatly differ depending on the thickness of the release layer, and also vary depending on the thermal conductivity depending on the amount of the filler with respect to the silicone rubber. It is necessary to consider the thermal conductivity superimposed.

If it is expected that the fixing roller will rotate a plurality of times in one fixing step due to the length of the transfer material used for printing in the transport direction, etc., the transfer is performed every rotation of the fixing roller. The material conveyance adjusting means is turned ON, and the clock frequency of the reference referred to when supplying power to the DC motor is appropriately changed every rotation of the fixing roller, and the rotation speed of the fixing roller is changed every rotation of the fixing roller. May be reduced.

As an example of the present embodiment, A is used as a transfer material.
The transfer speed of the fixing roller when the transfer paper is laterally fed using four sizes of transfer paper will be described. Since the length of the A4 size transfer paper in the horizontal direction is 210 mm, the fixing roller 1 of φ40 mm in this embodiment makes about 1.68 turns in one fixing process. Causes a difference in gloss before and after the transfer material.

FIG. 2 is a graph showing a change in the conveying speed of the fixing roller when the A4 size is fed laterally. As shown in FIG. 2, after the transfer material enters the fixing nip set at the set temperature of 170 ° C., the fixing roller 1 makes one rotation (in the present embodiment, since the fixing roller is a φ40 mm fixing roller, the transfer paper (At a position of 125.6 mm from the front end), and the conveyance speed of the fixing roller 1 is set to 100 mm / sec to 90 mm.
/ Sec. The conveyance speed of the fixing roller 1 changed to 90 mm / sec is changed to a normal 1 by changing the reference clock frequency when the temperature detected by the thermistor 4 at the fixing roller 1 returns to the predetermined fixing temperature.
It is better to return to 00 mm / sec.

FIG. 3 is a graph showing the surface temperature of the fixing roller when the transfer material passes through the fixing nip when the A4 size transfer paper is fed laterally. As shown in FIG. 3, when the image forming apparatus of the present embodiment lowers the rotation speed of the fixing roller after the second rotation of the fixing roller to lower the transfer speed of the transfer material in the fixing process, the set temperature From 170 ° C. which is only about 5 ° C. In this manner, by reducing the conveyance speed of the fixing roller by about 10% in accordance with the temperature drop of the fixing roller, the change in the amount of heat applied from the fixing roller to the transfer paper is reduced, and the transfer amount in the forward direction of the transfer paper is reduced. The difference between the gross at the rear and the rear can be reduced. In comparison,
When the conveyance speed in the fixing step is constant as in the conventional case, the surface temperature of the fixing roller in one fixing step is
Since the temperature is lowered by about 10 to 15 ° C. from the set temperature of 170 ° C., a difference in gloss appears between the front and rear portions of the transfer paper.

As described above, in the present embodiment, by lowering the rotation of the fixing roller after the second rotation of the fixing roller where the surface temperature of the fixing roller decreases, the conveyance speed in the fixing step of the transfer material is reduced. In addition, it is possible to reduce the temperature drop of the fixing roller in the fixing process, to reduce the variation in gloss at the front and rear positions with respect to the transfer direction of the transfer material, and to prevent the fixing failure.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. In the present embodiment, when the rotation speed of the fixing roller is reduced and the rear end of the transfer material is in the transfer process, the transfer speed is reduced according to the rotation speed of the fixing roller and the transfer speed is reduced. The transfer timing is changed accordingly, and the rotation speed of the fixing roller is reduced according to the number of rotations of the fixing roller. Thus, an image having little variation in gloss can be obtained.

The transfer speed is reduced according to the decrease in the rotation speed of the fixing roller, and the transfer timing is changed according to the decrease in the transfer speed. The operation is the same as in the first embodiment. Further, as for the fixing device, other than reducing the rotation speed of the fixing roller according to the number of rotations of the fixing roller, the configuration and operation of the fixing roller and the pressure roller are the same as those in the first embodiment. It is.

In the present embodiment, when the transfer speed in the fixing step is reduced by the transfer material transfer adjusting means in the control means provided in the image forming apparatus to control each step of image formation, A transfer changing unit is provided for reducing the transfer speed at the time of transfer in accordance with a decrease in the transport speed and changing transfer conditions in accordance with the decrease in the transfer speed.

That is, the length of the transfer material used for printing in the transport direction is A, the outer circumference of the fixing roller is R, and the transfer position (the position of the transfer nip where the intermediate transfer member and the secondary transfer roller face each other). Is the distance between the fixing position and the fixing position (the position of the fixing nip where the fixing roller and the pressure roller face each other).
When the respective relations are in the relation of H <(A−R) and in the relation of A−R ≧ 2R, and when the transport speed in the fixing step is reduced, The transfer speed is reduced in accordance with the decrease in the transport speed in the fixing process, and the application timing of the transfer bias is changed in accordance with the decrease in the transfer speed. This is because when the rotation of the fixing roller in one fixing step enters the second rotation, if the rear end of the transfer material is in the middle of the secondary transfer, if only the conveyance speed of the fixing roller is reduced, the paper is formed. This is because the medium is slack and the transportability is impaired.

In addition, when H <(A−R) and A
When a transfer material having a length in the transport direction that satisfies the condition of −R ≧ 2R is used, the fixing roller often rotates a plurality of times in one fixing process. The transfer speed of the transfer material is reduced stepwise by reducing the rotation speed of the roller. Specifically, the transfer material transport adjusting means is turned on for each rotation of the fixing roller.
At the same time, the clock frequency of the reference referred to when supplying power to the DC motor is changed for each rotation of the fixing roller, so that the rotation speed of the fixing roller is reduced for each rotation of the fixing roller.

The decrease in the transfer speed is caused by rotating the intermediate transfer member and the secondary transfer member when the intermediate transfer member once carrying the toner image and the secondary transfer member are rotated by independent drive motors. The rotation speed of the driving motor is reduced by, for example, changing the frequency of a power supply supplied to the driving motor, and the rotation speed of a registration roller that guides the transfer material to the transfer nip is also reduced. The timing of applying the transfer bias is changed so that the toner can be appropriately transferred to the transfer material in accordance with the decrease in the transfer speed in step (1). If the toner image is being transferred from the photosensitive drum to the intermediate transfer body when the transfer speed is reduced, the rotation speed of the drive motor that rotates the photosensitive drum is also reduced and the exposure speed is reduced. The timing is also changed according to the decrease in the rotation speed of the photosensitive drum.

Further, when rotating members such as a photosensitive drum, an intermediate transfer member, and a secondary transfer roller and a conveying roller are rotated by one driving motor, the rotation speed of the motor is reduced. In that case,
The timing of charging and exposure and the timing of development are reduced at the same time.

As an example of the present embodiment, A is used as a transfer material.
The conveyance speed of the fixing roller when three sizes of transfer paper are used will be described. In the case where the length of the transfer material in the transport direction is 420 mm in the longitudinal direction of the A3 size paper, the outer circumference of the fixing roller is about 125.6 mm, and the distance between the transfer nip and the fixing nip is 200 mm. Will be described.

FIG. 4 is a graph showing the positional relationship between the length of the transfer paper, the rotation of the fixing roller, and the fixing and transfer nips in this embodiment. FIG. 5 is a graph showing a change in the conveyance speed of the fixing roller when printing is performed on A3-size transfer paper. As shown in FIG. 4, the length of the A3-size transfer paper in the longitudinal direction is 420 m.
m, the fixing roller having a diameter of 40 mm according to the present embodiment makes about 3.34 rotations in one fixing step. Causes a difference in gloss.

Here, when the fixing roller enters the second round on the transfer paper in the fixing step, the distance between the transfer nip and the fixing nip is 200 mm. If the rear end of the transfer paper has not passed through the transfer nip position), and only the conveyance speed of the fixing roller is reduced by, for example, 10% after the fixing roller makes one rotation,
The transfer paper becomes slack between the fixing nip and the transfer nip, and the transportability is impaired. Therefore, after the fixing roller makes one rotation in one transfer step, when the conveyance speed of the fixing roller is changed from 100 mm / sec to 90 mm / sec as in the first embodiment, the transfer speed is increased by 10%. %
By changing the transfer bias in accordance with the decrease in the transfer speed, the transfer bias is maintained even after one rotation of the fixing roller, even when the rear end of the transfer material in the fixing process is at the transfer position. The transfer material can be prevented from sagging between the nip and the transfer nip, and good transportability can be ensured. The reduced speed of the fixing roller or the like may be returned to the normal speed by changing the reference clock frequency or the like when the temperature detected by the thermistor at the fixing roller returns to the predetermined fixing temperature.

As shown in FIG. 5, in the third rotation of the fixing roller, the rotation speed of the fixing roller is set to 90 mm.
/ Sec to about 5% (about 85 mm / sec)
After the rotation of the fixing roller has completed three revolutions, the rotation speed of the fixing roller is reduced by about 3% from 85 mm / sec, so that the rotation speed of the fixing roller is reduced stepwise with each rotation of the fixing roller. In addition, the transfer speed is reduced, and the application timing of the transfer bias is changed stepwise according to the decrease in the transfer speed. By reducing the rotation speed of the fixing roller for each rotation of the fixing roller in this manner, as shown in FIG. 6, a change in the amount of heat applied from the fixing roller to the transfer paper is reduced, and the length in the transport direction such as A3 is reduced. Even if the transfer material is long, it is possible to reduce the difference in gloss between the front and rear portions with respect to the transfer direction of the transfer paper.

Here, the reason why the decrease in the rotation speed in the third lap is set to be smaller than that in the second lap is that the transport speed is reduced in the second lap so that the temperature in the first and second laps is reduced. This is because the temperature drop in the second to third laps (about 3 ° C.) is smaller than the drop (about 5 ° C.). Similarly, by further reducing the transport speed by 3 mm / sec in the fourth round, it is possible to correct the variation in the gloss value at the front and rear ends of A3.

Incidentally, it is necessary to set the decrease in the transport speed in accordance with the thermal conductivity of the fixing roller, the transport speed, and the like. In particular, when the surface layer has a release layer, the temperature characteristics of the fixing roller greatly vary depending on the thickness of the release layer, and the thermal conductivity varies depending on the amount of the filler with respect to the silicone rubber. It is necessary to consider the rates in a superimposed manner.

If the image forming apparatus has a sufficient distance between the transfer and the fixation and does not need to perform the transfer process after the second rotation of the fixing roller, only the conveyance speed of the fixing roller may be changed. .

A transfer material detecting means for detecting the transfer material is provided upstream of the transfer nip in the transport direction, and the transfer material in the fixing process is kept in place even after one rotation of the fixing roller during the fixing process. H <
Assuming that (AR) and that the condition of AR ≧ 2R is met, the rotational speed of the fixing roller is decreased and the transfer speed is decreased at the same time, and the timing of applying the transfer bias is adjusted according to the decrease in the transfer speed. It may be changed.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. In this embodiment, when the rotation speed of the fixing roller is decreased, the rear end of the transfer material is in the transfer process, and the remaining portion of the transfer material in the transfer process is less than half of the outer circumference of the fixing roller. After the transfer step, the rotation speed of the fixing roller is reduced. In other words, when the transport speed is reduced in the second embodiment, if the range involving the change of the transfer process is equal to or less than half the circumference of the fixing roller, the speed of the transfer process is not reduced and the transfer bias is not changed. After the transfer to the rear end of the transfer material is performed, the rotation speed of the fixing roller is reduced.

In the present embodiment, when the length of the transfer material in the transport direction is A, the outer circumference of the fixing means is R, and the distance between the transfer position and the fixing position is H, the respective relations are H <H. In a relationship of AR, and AR ≧ 0.5R
When the relationship is satisfied, the transfer material transport adjusting means is operated after the end of the transfer process to reduce the transport speed of the transfer material in the fixing step.

As an example of this embodiment, L is used as a transfer material.
The conveying speed of the fixing roller when using EGAL size transfer paper will be described. A description will be given of a case where the length of the transfer material in the transport direction is 356 mm in the longitudinal direction, the outer circumference of the fixing roller is about 125.6 mm, and the distance between the transfer nip and the fixing nip is 200 mm.

FIG. 7 is a graph showing the relationship between the length of the LEGAL size transfer paper, the rotation of the fixing roller, and the positional relationship between the fixing nip and the transfer nip. As shown in FIG.
Since the length of the GAL size transfer paper in the longitudinal direction is 356 mm, the fixing roller having a diameter of 40 mm according to the present embodiment makes about 2.83 rotations in one fixing process, and the fixing roller after the second rotation of the fixing roller. The surface temperature of the roller is reduced, which causes a difference in gloss before and after the transfer material.

By the way, since the distance between the transfer nip and the fixing nip is 200 mm, when LEGAL (356 mm) is printed, when the fixing roller enters the second round on the transfer paper, the untransferred portion at the rear end of the transfer paper is removed. Only 30.4 mm remains. Here, when the transport speed is changed from the second rotation as in the first and second embodiments, the unfixed portions 30.
It is necessary to change the transfer speed and the like in the transfer step for only 4 mm. However, the change in gloss of the image after fixing is not greatly affected as long as the change in gloss on the actual image is not more than half a turn of the fixing roller, preferably not more than 1/3 turn.

Therefore, in the present embodiment, the transfer material transfer adjusting means is operated after the transfer process is completed, so that the transfer material transfer speed in the fixing step is reduced. That is,
The transport speed is changed when the transfer paper is transported by the fixing roller for one rotation of the fixing roller and 30.4 mm.
Therefore, in a color printer having a maximum paper size of LEGAL (216 mm × 356 mm), a device configuration that satisfies the above conditions can be easily realized. And the transfer process can be prevented from becoming complicated.

Of course, if the relationship of (distance between the transfer nip and the fixing nip) ≧ {(maximum sheet passing length) − (outer periphery of the fixing roller)} is satisfied, the fixing is performed after the second rotation of the fixing roller. Only the transport speed can be changed immediately.

Further, a transfer material detecting means for detecting a transfer material is provided at a position away from the transfer nip by a distance of の of the outer circumference of the fixing roller in an upstream side in the conveying direction, and the fixing roller is set to one during the fixing process. If the transfer material in the fixing process is still detected by the transfer material detecting means even after the rotation, H <A−
Assuming that the relationship of R and the relationship of A−R ≧ 0.5R are satisfied, the rotation speed of the fixing roller may be reduced after the end of the transfer process.

(Fourth Embodiment) A fourth embodiment of the present invention will be described with reference to FIG. In the present embodiment, instead of the DC motor rotating the fixing roller, the fixing roller is rotated by a stepping motor, and the rotation speed of the fixing roller is reduced stepwise rather than stepwise.
The speed can be changed smoothly.

In each of the above embodiments, an example has been described in which the transport speed is changed stepwise by changing the reference clock frequency for the DC motor. In the present embodiment, an example is shown in which a stepping motor is used as a driving motor for rotating the fixing roller and the speed is smoothly changed.

In this embodiment, as a driving means for rotating the fixing roller at a predetermined peripheral speed, a stepping motor is connected to a rotating shaft of the fixing roller via a gear, and the stepping motor is connected to a motor control means. The rotation of the stepping motor is controlled by a predetermined pulse signal from the control means, so that the fixing roller can be rotated at a predetermined peripheral speed.

The motor control means changes the peripheral speed of the fixing roller by appropriately increasing or decreasing the number of revolutions of the stepping motor by changing the pulse frequency for the stepping motor, and changing the peripheral speed of the fixing roller so as to convey the transfer material at the time of fixing by the fixing roller. In the present embodiment, the peripheral speed of the fixing roller is usually 100 mm / sec, and is in the range of 10 to 120 mm / sec, as in the above embodiments. Can be changed.

The motor control means is provided with a transfer material transport adjusting means for reducing the rotation speed of the fixing roller by the stepping motor of the driving means in response to the decrease in the surface temperature of the fixing means. The transfer material conveyance adjusting means operates at least at the timing when the fixing roller makes two rotations in one fixing step, so that the pulse frequency can be appropriately changed and the rotation speed of the stepping motor can be reduced. ing.

Specifically, as shown in FIG. 8, after one rotation of the fixing roller in one transfer step, the conveying speed of the fixing roller is increased by 10 mm / sec ² until the speed of the fixing roller becomes 90 mm / sec. The frequency of the stepping motor is changed and controlled so as to decelerate. By doing so, smoother image characteristics can be obtained. This takes into account the temperature mitigation of the roller surface from which heat has been removed during the first rotation, and the thermal conductivity and transport speed of the silicone rubber because the frequency for the stepping motor can be changed by software. This is because the rotation speed of the fixing roller can be set freely according to the temperature, and the temperature drop can be more precisely handled.

When the present embodiment is directly long in the transport direction such as A3 size and the fixing roller rotates three or more turns in the fixing step, the third turn of the fixing roller is also 10 mm, which is the same as the deceleration of the second turn. When deceleration is performed at an acceleration of / sec ^2, the conveyance speed is too low after the third round, and conversely, gloss may increase (gloss may increase). As described above, when the conveyance speed of the fixing roller is further changed after the third rotation, the deceleration is performed every rotation of the fixing roller such that the deceleration rate of the third rotation is smaller than that of the second rotation. It is good to

(Fifth Embodiment) A fifth embodiment of the present invention will be described with reference to FIGS. In this embodiment, the rotation speed of the fixing roller is reduced by an arbitrary value as the transfer time of the transfer material elapses by the driving unit using the stepping motor of the fourth embodiment.

In the present embodiment, as shown in FIG. 9, as an application of the fourth embodiment, the rotation speed of the fixing roller is changed with the lapse of the transfer time of the transfer material, and the transfer speed of the transfer material in the fixing process is changed to the transfer time. An example is shown in which the gloss change in one sheet is smoothed by decreasing the value by an arbitrary value as time elapses. In the present embodiment, it is possible to change the rotation speed of the stepping motor based on the conditional expression. However, the method of referring to the lookup table as shown in the table of FIG. Can be performed efficiently.

In the look-up table, for example, the rotation speed of the fixing roller by the stepping motor for each elapsed time is set in advance in a storage unit in the control unit, and when the transfer material conveyance adjustment unit is turned ON at a predetermined timing. Thus, the transfer material transport adjusting means can refer to the look-up table at predetermined intervals. The transfer material transport adjusting means with reference to the look-up table appropriately changes the frequency for the stepping motor so as to have a transport speed corresponding to the elapsed time since the transfer material transport adjusting means is turned ON, and the rotation speed of the stepping motor. Is changed to change the rotation speed of the fixing roller.

To change the transport speed in the fixing step in this embodiment, the rotation speed of the stepping motor is changed according to the transport speed at that time by referring to a lookup table every 100 msec. With this configuration, it is only necessary to input the data of the deceleration such as the transport speed with respect to the elapsed time into the lookup table, and if the data input to the lookup table is appropriately changed or replaced, the data can be used. It is possible to respond immediately according to the conditions such as the transfer material to be used.

In this embodiment, the change of the transport speed is set to 1
Although it was set to 00 msec, it differs depending on the size of the step angle of the stepping motor and the frequency division of the clock.
c or less, preferably 100 msec or less.

Further, the look-up table is set finely according to the paper size, the basis weight of the paper, and environmental conditions.
When used in the gross-up (high gloss) mode or the gloss-down (low gloss) mode, uniform gloss image output from high gloss images to low gloss images can be realized.

In each of the above embodiments, since the surface temperature of the fixing roller is reduced by the rotation of the fixing roller during fixing, the rotation speed of the fixing roller is reduced based on the number of rotations of the fixing roller. However, the present invention is not limited to this, and the rotation speed of the fixing roller may be reduced based on the temperature detected by the thermistor. In this case, when the temperature detected by the thermistor drops by a predetermined temperature, the transfer material conveyance adjusting means is turned on to reduce the rotation speed of the fixing roller, and when the temperature detected by the thermistor returns to the predetermined temperature, the rotation speed of the fixing roller is reduced. You may want to restore it.

(Sixth Embodiment) A sixth embodiment of the present invention will be described. In the present embodiment, when an OHP sheet is used as a transfer material, a certain length of time from the leading end of the OHP sheet after the OHP sheet is guided to the fixing nip is shorter than the normal OHP sheet conveyance speed. By transporting the OHP sheet at a higher rotation speed, the rigidity of the leading end of the OHP sheet in the transport direction is ensured, so that the transparency of the OHP sheet can be increased and the transportability can be satisfied. The components of the image forming apparatus may be the same as those in the above embodiments, except that the transport speed is increased for a predetermined time during the fixing of the OHP sheet.

In this embodiment, the motor control means and the driving means for rotating the fixing roller, which are described in the above embodiments and have a function as a speed changing means capable of changing the conveying speed of the transfer material at the time of fixing. Using a DC motor or a stepping motor) as the transfer material
When a P sheet is used, the rotation speed of the fixing roller is higher than a normal conveyance speed of the OHP sheet for a predetermined length from the leading end of the OHP sheet after the OHP sheet is guided to the fixing nip, and the conveyance is performed. It is characterized by doing so.

When printing is performed using an OHP sheet, it is necessary to sufficiently dissolve the toner on the sheet in the fixing step to satisfy the transparency, and therefore, the fixing is performed at a speed of 50% or less of plain paper in the fixing step. That is common. However, if the OHP sheet is excessively heated, the rigidity of the OHP sheet is lost, so that the conveyance of the OHP sheet after fixing is impaired.

Therefore, when the leading end portion of the OHP sheet along the transport direction is transported by the fixing roller, the transport speed of the OHP sheet is set higher than the speed at which the toner can be sufficiently dissolved so as to maintain the rigidity of the sheet. To be set.

In the present embodiment, the OHP sheet is conveyed at a rate of 70 mm / sec from the leading end of the OHP sheet in the conveying direction up to 50 mm, and 50 m from the leading end of the OHP sheet in the conveying direction.
m and later are conveyed at 30 mm / sec. As a result, not only can the leading end smoothly enter the paper discharge roller, but also the paper path can be prevented from being caught in the transport path. In the present embodiment, the transport speed is changed at the leading end of 50 mm, but is 30 m from the viewpoint of image transparency.
It is desirable to set m or less.

To detect 50 mm or 30 mm from the leading edge of the OHP sheet, a predetermined time after the transmission of the image writing timing signal is passed to the fixing nip.
Calculation processing in the control means based on the timing at which the HP sheet has been guided and has passed 50 mm or 30 mm, or the timing at which secondary transfer is started (timing at which toner is transferred to the transfer material) and the transport speed in the transfer process of the transfer material The timing at which the OHP sheet is guided by the fixing nip at the section and passes by 50 mm or 30 mm can be obtained.

Further, a transfer material detecting means for detecting the OHP sheet is provided upstream of the fixing nip in the transport direction,
When the transfer material detecting means detects the OHP sheet, the conveying speed is set to 70 mm / sec.
After detecting the sheet, a predetermined time (Omm at 70 mm / sec)
After the elapse of the time when the HP sheet is conveyed by 50 mm), the conveyance speed is set to 30 which is the conveyance speed during normal fixing.
It may be changed to mm / sec.

In the speed change in this embodiment, the fixing roller is changed by changing the reference clock frequency in the case of using the DC motor or changing the frequency of the stepping motor in the case of using the stepping motor. Of course, it is possible to use the change of the rotation speed. In this embodiment, the transfer material transfer adjusting means provided in the motor control means of each of the above embodiments may not be provided, and only the transfer speed when an OHP sheet is used may be changed.

[0114]

As described above, according to the first aspect of the present invention, when the surface temperature of the fixing means decreases in the fixing step, the transfer material conveyance adjusting means operates and the driving means rotates the transfer material. The rotation speed of the driven fixing unit and the pressurizing unit is reduced by the speed changing unit, and the conveyance speed in the fixing step after the temperature of the fixing unit is reduced is lower than that before the temperature of the fixing unit is reduced. Therefore, it is possible to provide an image having less variation in gloss after fixing.

Further, according to the second aspect of the present invention, when the fixing means rotates a plurality of times in one fixing step, the transfer material conveyance adjusting means operates at least in the second and subsequent rounds of the fixing means. Since the transport speed in the fixing step is reduced, the amount of heat supplied to the transfer material can be made uniform, and an image having less variation in gloss after fixing can be provided.

According to the third aspect of the present invention, when the fixing means rotates a plurality of times in one fixing step, the transfer material transport adjusting means operates according to the increase in the number of rotations of the fixing means. As a result, the conveyance speed in the fixing step is reduced, so that even when a transfer material having a long length in the conveyance direction is used, it is possible to provide an image with little variation in gloss after fixing.

According to the fourth aspect of the present invention, the length of the transfer material in the transport direction is A, the outer circumference of the fixing means is R, and the distance between the transfer position and the fixing position is H.
When the respective relations satisfy the relationship of H <AR and satisfy the relation of AR ≧ 2R, the transfer material transport adjusting means operates to reduce the transport speed in the fixing process. When the transfer rate is decreased, the transfer changing means reduces the transfer speed at the time of transfer in accordance with the decrease in the transport speed in the fixing step, and by providing the transfer change means for changing the transfer condition in accordance with the decrease in the transfer speed, The transfer material can be satisfactorily conveyed between the transfer position and the fixing position, and an image with less variation in gloss after fixing can be provided.

According to the fifth aspect of the present invention, the length of the transfer material in the transport direction is A, the outer circumference of the fixing means is R, and the distance between the transfer position and the fixing position is H.
When the respective relations are in the relation of H <A−R and satisfy the relation of A−R ≧ 0.5R, the transfer material conveyance adjusting means is operated after the end of the transfer process to perform the fixing process. By reducing the transfer speed of the transfer material, it is possible to provide an image with less variation in gloss after fixing without complicating the transfer process.

Further, according to the sixth aspect of the present invention, a decrease in the transport speed in the fixing step by the transfer material transport adjusting means is reduced at a predetermined rate per unit time, so that a rapid temperature change can be prevented. Thus, an image having a smooth change in gloss can be provided.

Further, according to the seventh aspect of the present invention, the transfer speed in the fixing step by the transfer material transfer adjusting means is reduced suddenly by arbitrarily decreasing the transfer speed as the transfer time elapses. It is possible to provide a smooth image with a simple configuration without a temperature change.

Further, according to the eighth aspect of the present invention, in the image forming apparatus of the first to seventh aspects, when an OHP sheet is used as a transfer material,
The transport speed of the OHP sheet in the fixing process until the area within 50 mm from the leading edge of the HP sheet passes through the fixing nip is set to the transport speed for transporting the OHP sheet in the range excluding the range within 50 mm from the leading edge of the OHP sheet. By making the speed higher than that, the rigidity of the leading end of the OHP sheet can be ensured, so that both sheet transportability and transparency can be satisfied.

According to the ninth invention of the present application, when an OHP sheet is used as a transfer material, the OHP sheet in the fixing step until a range within 50 mm from the leading end of the OHP sheet passes through the fixing nip is used. By making the conveying speed of the OHP sheet higher than the conveying speed when conveying the OHP sheet in the range excluding the range within 50 mm from the front end of the OHP sheet, the rigidity of the front end of the OHP sheet can be ensured. And an image forming apparatus that can satisfy both of the transparency.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a fixing device used in an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a graph showing a change in transport speed when printing on A4 size paper in the fixing device of the first embodiment.

FIG. 3 is a graph illustrating a change in the temperature of the surface of the fixing roller when A4 size paper is printed in the fixing device according to the first exemplary embodiment.

FIG. 4 is a graph showing the relationship between the length of a transfer sheet, the rotation of a fixing roller, and the positional relationship between a fixing nip and a transfer nip in a second embodiment.

FIG. 5 is a graph showing a change in transport speed when printing on A3-size paper in the fixing device of the second embodiment.

FIG. 6 is a diagram illustrating a temperature change on the surface of a fixing roller according to a second embodiment.

FIG. 7 is a graph showing the relationship between the length of the transfer paper, the rotation of the fixing roller, and the positional relationship between the fixing nip and the transfer nip in the third embodiment.

FIG. 8 is a graph showing a change in a conveyance speed in a fixing device according to a fourth embodiment.

FIG. 9 is a graph showing a change in a conveyance speed in a fixing device according to a fifth embodiment.

FIG. 10 is a table showing a setting example of a lookup table to be referred to when continuously changing the transport speed in the fifth embodiment.

FIG. 11 is a schematic configuration diagram illustrating a conventional color image forming apparatus.

FIG. 12 is a schematic configuration diagram illustrating a color fixing device in a conventional color image forming apparatus.

FIG. 13 is a graph showing a relationship between a fixing roller surface temperature and a gloss value.

FIG. 14 is a schematic diagram showing a gloss change for each fixing roller cycle when printing is performed by a conventional color fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller (fixing means) 2 Pressure roller (pressing means) 31 Developing device 32 Intermediate carrier (transfer device) 33 Secondary transfer roller (transfer device) 40 Drive means 41 Motor control means (speed changing means) 101 Photosensitivity Drum (image carrier)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G03G 21/14 G03G 21/00 372

Claims (9)

[Claims] An image carrier that forms an electrostatic latent image on a surface thereof;
A developing device for developing the electrostatic latent image on the image carrier with toner, a transfer device for transferring the developed toner image on the image carrier to a transfer material, and a toner device for transferring the toner transferred to the transfer material onto the transfer material; An image forming apparatus provided with a fixing device for fixing, a conveying unit for conveying a transfer material, and a speed changing unit for changing at least a conveying speed of the transfer material at the time of fixing, wherein the fixing device carries a toner image. A fixing unit that is rotatably disposed while heating the toner by contacting the transferred transfer material; a pressing unit that is rotatably disposed while being pressed against the fixing unit; and one of the fixing unit and the pressing unit. A driving unit connected to one or both of them for driving the fixing unit and the pressing unit to rotate, and passing the transfer material through a pressure contact portion between the fixing unit and the pressing unit to heat and transfer the toner on the transfer material; Pressurized In an image forming apparatus that forms an image by fixing an image onto a transfer material, the image forming apparatus operates in response to a temperature drop of the surface temperature of the fixing unit to reduce the transfer speed of the transfer material in the fixing process. A transfer material transport adjusting unit, wherein the transfer material transport adjusting unit lowers the rotational speeds of the fixing unit and the pressurizing unit that are rotationally driven by the driving unit when the surface temperature of the fixing unit drops by a predetermined temperature. An image forming apparatus, wherein the conveying speed in the fixing step after the temperature of the fixing unit is lowered is lower than that before the temperature of the fixing unit is lowered. 2. When the fixing unit rotates a plurality of times in one fixing step, the transfer material conveyance adjusting unit sets at least the second and subsequent rotations of the fixing unit in place of the case where the surface temperature of the fixing unit drops by a predetermined temperature. The image forming apparatus according to claim 1, wherein the image forming apparatus operates to reduce the transport speed in the fixing process. 3. When the fixing unit rotates a plurality of times in one fixing step, the transfer material conveyance adjusting unit increases the number of rotations of the fixing unit instead of when the surface temperature of the fixing unit drops by a predetermined temperature. The image forming apparatus according to claim 1, wherein the image forming apparatus operates in response to a reduction in a conveying speed in a fixing process. 4. When the length of the transfer material in the transport direction is A, the outer circumference of the fixing means is R, and the distance between the transfer position and the fixing position is H, the respective relations are H <AR.
When the relationship of A−R ≧ 2R is satisfied and the transfer speed in the fixing step is reduced by the transfer material transfer adjusting means, the image forming apparatus responds to the decrease in the transfer speed in the fixing step. 4. The method according to claim 1, further comprising a transfer changing means for reducing a transfer speed at the time of transfer and changing transfer conditions according to the decrease in the transfer speed. Image forming device. 5. When the length of the transfer material in the transport direction is A, the outer circumference of the fixing means is R, and the distance between the transfer position and the fixing position is H, the respective relations are H <AR.
When the relationship of A−R ≧ 0.5R is satisfied, the transfer material transport adjusting means operates after the end of the transfer process and performs the fixing operation in place of the case where the surface temperature of the fixing means drops by a predetermined temperature. The image forming apparatus according to claim 1, wherein a transfer speed of the transfer material in the process is reduced. 6. The image according to claim 1, wherein a reduction in the transport speed in the fixing step by the transfer material transport adjusting unit is reduced at a predetermined rate per unit time. Forming equipment. 7. The method according to claim 1, wherein the lowering of the transport speed in the fixing step by the transfer material transport adjusting means decreases the transport speed by an arbitrary value as the transport time elapses. The image forming apparatus as described in the above. 8. When an OHP sheet is used as a transfer material, the conveying speed of the OHP sheet in the fixing step until a range within 50 mm from the leading end of the OHP sheet passes through the fixing nip is 50 mm from the leading end of the OHP sheet.
The image forming apparatus according to any one of claims 1 to 7, wherein the conveying speed is higher than a conveying speed when conveying the OHP sheet in a range excluding the range of (1). 9. An image carrier for forming an electrostatic latent image on a surface thereof,
A developing device for developing the electrostatic latent image on the image carrier with toner, a transfer device for transferring the developed toner image on the image carrier to a transfer material, and a toner device for transferring the toner transferred to the transfer material onto the transfer material; An image forming apparatus comprising: a fixing device for fixing; a conveying unit for conveying a transfer material; and a speed changing unit for changing at least a conveying speed of the transfer material during fixing, wherein the fixing device carries a toner image. Fixing means arranged to be rotatable while heating the toner in contact with the transferred transfer material,
A pressure unit that is rotatably disposed while being pressed against the fixing unit; and a driving unit that is connected to one or both of the fixing unit and the pressing unit and rotationally drives the fixing unit and the pressing unit. An image forming apparatus that forms an image by passing a transfer material through a pressure contact portion between a fixing unit and a pressing unit to heat and pressurize the toner on the transfer material to fix the toner on the transfer material, O as transfer material
When an HP sheet is used, the speed changing means is OHP
The transport speed of the OHP sheet in the fixing process until the area within 50 mm from the leading edge of the sheet passes through the fixing nip is smaller than the transport speed when transporting the OHP sheet in the range excluding the area within 50 mm from the leading edge of the OHP sheet. An image forming apparatus capable of changing a rotation speed of a fixing member by a driving unit so that the rotation speed is also increased.