JPH1010891A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a fixing-irregularity phenomenon and a fixing-gloss- irregularity phenomenon which are caused by wrinkle in a fixing film specific to a film fixing system. SOLUTION: A toner image on transfer paper 18 is fixed by a fixing device 19 provided with a heater 20, a pressure roller 28, opposite the heater 20, and the fixing film 25, so held between the heater 20 and pressure roller 28 as to surround the heater 20. In the case, the fixing conditions of the heater 20 are altered based on the range of the medium density of an output image or its ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer, and more particularly to an image forming apparatus having a fixing device having a fixing film for fixing a toner image to a transfer material. It is.

[0002]

2. Description of the Related Art In a conventional image forming apparatus, an electrostatic latent image is formed by irradiating an image exposure light corresponding to an original image or an image signal input from a computer onto the surface of an image carrier uniformly charged by charging means. And developing the electrostatic latent image with a developing unit to form a toner image, transferring the toner image to a transfer material by a transfer unit, fixing the toner image on the transfer material by a fixing unit, and outputting the toner image. There are electrophotographic copying machines and printers.

In a fixing device for fixing a toner image on a transfer material, a heat-resistant fixing film is provided so as to be slidable on a heat generating member, and a pressing member is connected to the heat generating member via the fixing film. There is a film fixing method of a configuration in which the transfer member is pressed against the transfer material, and the fixing device applies heat energy from a heat generating member through the fixing film to the transfer material conveyed with the movement of the fixing film while being nipped. The fixing is performed.

FIG. 6 is a schematic diagram showing an example of a film fixing type fixing device. In the figure, reference numeral 20 denotes a heater which is a heating member supported by a stay 21 as a support. The heater 20, the driving roller 26, and the driven roller 27 are formed of a material having high heat resistance. An endless belt-shaped fixing film 25 is wound and stretched.

On the lower surface of the heater 20, a pressure roller 28 as a pressure member opposed to the fixing film 25 so as to sandwich the fixing film 25 is biased by, for example, a total pressure of 5 mm.
It is pressed against the fixing film 25 with a contact pressure of about kg weight. The pressure roller 28 has a rubber elastic layer of silicone rubber or the like with good releasability.
Is formed.

When the drive roller 26 is driven to rotate in the clockwise direction indicated by an arrow in the figure by a drive motor M as a rotary drive means, the driven roller 2 serving as a tension roller is also driven.
Fixing film 2 given a predetermined tension by 7
5 rotates at a predetermined peripheral speed in the direction of arrow a in the figure, and the pressure roller 28 is also driven to rotate counterclockwise with the rotation of the fixing film 25 so as to pinch and convey the transfer material P. ing.

Therefore, the transfer material P after the transfer of the toner image T is sequentially sent to the fixing device by the transfer material supply means (not shown), and when the transfer material P enters the fixing portion N, the transfer material P is The toner image T on the transfer material P is fixed to the transfer material P while being conveyed while being pinched and conveyed by the rotation of the pressure roller 28, and the thermal energy generated by the heater 20 is applied.

In this type of film fixing type fixing device, the heat capacity of the heater 20 as a heat generating member and the fixing film 25 as a member for transmitting the heat energy of the heater 20 to the transfer material P can be reduced. This has the advantage that the weight time can be reduced (quick start property).

[0009]

However, the above-mentioned conventional fixing device has the following problems.

That is, in the fixing device of the film fixing system, the thickness of the fixing film 25 is set to 50 μm in order to efficiently transmit the heat energy of the heater 20 to the transfer material P.
m or less. However, the thickness is 50 μm
Since the following fixing film 25 has extremely low rigidity, wrinkles may be generated in the fixing film 25 during rotation.

When wrinkles occur on the fixing film 25,
In the fixing portion N, distribution of thermal energy transmitted to the transfer material P occurs in accordance with the wrinkles of the fixing film 25.
As a result, in the output image after the fixing process corresponding to the wrinkle pattern generated on the fixing film 25, a portion where sufficient fixing has been performed and a portion where only insufficient fixing has been performed are generated, so-called. An uneven fixing phenomenon due to wrinkles of the fixing film 25 occurs. In the output image in which the fixing unevenness phenomenon due to the wrinkles of the fixing film 25 has occurred, such a problem that a part thereof easily peels off occurs.

Further, in the case of an output image in which a toner image includes a large area intermediate density (halftone) portion, the fixing film 25 has a so-called fixing gloss unevenness phenomenon caused by wrinkles of the fixing film 25. An image having gloss unevenness corresponding to the wrinkle pattern generated in the image 25 occurs.

The fixing gloss unevenness phenomenon caused by wrinkles of the fixing film 25 is caused by a difference in the degree of melting of toner for forming an image due to a slight uneven distribution of heat applied to the toner on the transfer material P at the fixing portion N. When the fixing unevenness phenomenon due to the wrinkling of the fixing film 25 occurs, the phenomenon can occur even when the wrinkling of the fixing film 25 is not generated at such a bad level that a part of the image is peeled off.

[0014] Further, a digital image forming apparatus for forming an electrostatic latent image on an image carrier with a laser scanner controlled to emit light in accordance with a digital image signal and visualizing the electrostatic latent image to form an image. Since the apparatus has good reproducibility of the intermediate density, it frequently outputs a toner image including many intermediate density portions. As a result, in a digital image forming apparatus, wrinkling of the fixing film 25 often leads to a defect in an output image.

For this reason, the present inventor has repeatedly studied the causes of the occurrence of the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon due to the wrinkles of the fixing film 25, and ascertained the cause.

According to this, wrinkles generated in the fixing film 25 are caused by the heater 20 and the stay 21 being temporarily expanded and deformed by rapidly heating and increasing the temperature of the heater 20 at the start of image formation. It has been found that this occurs due to unstable applied tension.

If the temperature of the heater 20 and the stay 21 has already risen to a certain temperature at the time of starting the image formation, the range of the temperature increase applied to the heater 20 and the stay 21 may be small. If the control temperature of the heater 20 is low, the heater 20 or the stay 21
The width of the temperature rise to be added may be small. In such a case, it was found that the temporary expansion deformation of the heater 20 and the stay 21 was small, and that the fixing film 25 was hardly wrinkled.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and it is intended to minimize the reduction in productivity of image formation without deteriorating the fixing characteristics of the entire image, and to further reduce the film fixing. It is an object of the present invention to provide an image forming apparatus which does not cause a fixing unevenness phenomenon and a fixing gloss unevenness phenomenon due to a wrinkle of a fixing film peculiar to a method, and always maintains a high quality image of a toner image having an intermediate density. And

[0019]

According to another aspect of the present invention, there is provided an image forming apparatus, comprising: an image carrier configured to transfer a toner image corresponding to an original image or an input multi-valued image signal; And an image forming means for transferring the toner image on the image carrier onto a transfer material, and a fixing device for fixing the toner image formed on the transfer material by the image forming means. The fixing device may further include a heating member, a pressing member disposed to face the heating member, and a fixing member sandwiched between the heating member and the pressing member so as to include the heating member. And a fixing condition changing means for changing the fixing condition of the heat generating member based on the width or ratio of the intermediate density portion in the output image.

According to the second aspect of the present invention, the fixing condition changing means selects the fixing condition of the heating member based on the width or ratio of the intermediate density portion in the output image; Power control means for controlling the temperature of the heat-generating member so as to attain a set temperature according to the characteristic selected by the selection means.

According to the third aspect of the present invention, the fixing condition changing means selects the fixing condition of the heat generating member based on the width or ratio of the intermediate density portion in the output image; Power control means for controlling the temperature of the heat generating member so as to be a set temperature according to the characteristic selected by the selection means, and a pre-rotation time of the fixing film until the transfer material reaches the fixing device. And changing means for changing.

According to the fourth aspect of the present invention, the fixing condition changing means includes a temperature detecting means for detecting the temperature of the heat generating member at the time of starting the image formation, and the fixing condition changing means according to a detection result by the temperature detecting means. Changing means for changing at least one of a set temperature of the fixing device and a pre-rotation time of the fixing film until the transfer material reaches the fixing device.

According to the fifth aspect of the present invention, the fixing condition changing means includes a temperature detecting means for detecting the temperature of the heat generating member at the time of starting the image formation, and a fixing means for detecting the temperature of the input multi-valued image signal. A counting means for counting the number of image signals corresponding to densities in a predetermined density range; and a ratio of a count value counted by the counting means to an entire image signal and a temperature at the start of image formation detected by the temperature detecting means. And a changing means for changing a set temperature of the heat generating member from the temperature of the heat generating member and changing a pre-rotation time of the fixing film until the transfer material reaches the fixing device.

According to a sixth aspect of the present invention, the fixing condition changing means includes a temperature detecting means for detecting a temperature of the heat generating member at the time of starting the image formation, and a temperature detecting means for detecting a temperature of the input multi-valued image signal. A counting means for counting the number of image signals corresponding to densities equal to or lower than a predetermined density range; a ratio of a value obtained by subtracting a count value counted by the counting means from the entire image signal to the entire image signal; The set temperature of the heating member is changed based on the temperature of the heating member at the start of image formation detected by the detection unit, and the pre-rotation time of the fixing film until the transfer material reaches the fixing device is changed. And changing means.

According to the seventh aspect of the present invention, the counting means corresponds to a density in a predetermined density range in the image signal after performing the image signal processing on the input multi-valued image signal. The number of image signals is counted.

According to the invention described in claim 8, the fixing condition changing means sets the time until the transfer material reaches the fixing device based on the width or ratio of the intermediate density portion in the output image. There is a changing means for changing a pre-rotation time of the fixing film and a set temperature of the heat generating member.

According to the ninth aspect of the present invention, the fixing condition changing means is configured such that the temperature of the heat generating member detected by the temperature detecting means is equal to or lower than a predetermined set temperature and the mode selected by the mode selecting means is the heat generating member. The operation is performed in a mode in which the set temperature is changed and the pre-rotation time of the fixing film is extended.

[Operation] Based on the above configuration, a first aspect of the present invention will be described.
In the described invention, the fixing condition of the heat generating member is changed by the fixing condition changing means based on the width or ratio of the intermediate density portion occupying in the output image.

According to a second aspect of the present invention, the fixing condition of the heat generating member is selected by the selecting means based on the width or ratio of the intermediate density portion occupying in the output image. And
The power control unit is controlled so that the temperature of the heat generating member becomes a predetermined temperature according to the characteristic selected by the selection unit.

According to the third aspect of the present invention, the fixing condition of the heat generating member is selected based on the width or ratio of the intermediate density portion in the output image by the selection means. And
The power control unit is controlled so that the temperature of the heat generating member becomes a predetermined temperature according to the characteristic selected by the selection unit, and the pre-rotation of the fixing film until the transfer material reaches the fixing device. Change the time.

According to a fourth aspect of the present invention, the temperature of the heat generating member is detected when the image formation is started by the temperature detecting means, and the set temperature of the fixing device and the temperature of the fixing device are determined in accordance with the detection result by the temperature detecting means. At least one of a pre-rotation time of the fixing film until the transfer material reaches the fixing device is changed.

According to a fifth aspect of the present invention, the temperature of the heating member is detected at the time when the image formation is started by the temperature detecting means, and the predetermined density is included in the multi-valued image signal input by the counting means. The number of image signals corresponding to the density of the area is counted. And changing the set temperature of the heating member from the ratio of the count value counted by the counting unit to the entire image signal and the temperature of the heating member at the start of image formation detected by the temperature detection unit, and changing the fixing temperature. The pre-rotation time of the fixing film until the transfer material reaches the apparatus is changed.

According to a sixth aspect of the present invention, the temperature of the heating member is detected at the time when the image formation is started by the temperature detecting means, and a predetermined density is included in the multi-valued image signal input by the counting means. The number of image signals corresponding to the density below the range is counted. Then, the ratio of the value obtained by subtracting the count value counted by the counting means from the entire image signal to the total image signal and the temperature of the heat generating member at the start of image formation detected by the temperature detecting means are determined based on the temperature of the heat generating member. In addition to changing the set temperature, the pre-rotation time of the fixing film until the transfer material reaches the fixing device is changed.

According to a seventh aspect of the present invention, the counting means includes:
The number of image signals corresponding to densities in a predetermined density region is counted in the image signals obtained by performing image signal processing on the input multi-valued image signals.

According to an eighth aspect of the present invention, the pre-rotation time of the fixing film until the transfer material reaches the fixing device based on the width or ratio of the intermediate density portion occupied in the output image by the changing means. And changing the set temperature of the heating member.

According to a ninth aspect of the present invention, the temperature of the heat generating member detected by the temperature detecting means is equal to or lower than a predetermined set temperature, the mode selected by the mode selecting means changes the set temperature of the heat generating member, and the fixing is performed. The fixing condition changing means is operated in a mode in which the pre-rotation time of the film is extended.

[0037]

Embodiments of the present invention will be described below in detail with reference to the drawings. <First Embodiment> FIG. 1 is a schematic structural view showing an image forming apparatus according to a first embodiment of the present invention, and FIG. 2 is a view showing an image forming operation according to the first embodiment. 6 is a flowchart illustrating control of a fixing temperature.

First, a first embodiment of the present invention will be described with reference to FIGS. In FIG. 1, reference numeral 10 denotes a drum-type electrophotographic photosensitive member (hereinafter, referred to as a “photosensitive drum”) as an image bearing member.
C photosensitive drum and the like.

Above the photosensitive drum 10, a primary charging device 11 as charging means is provided. The primary charging device 11 uniformly charges the surface of the photosensitive drum 10 during image formation. On the charged surface of the photosensitive drum 10, an image exposure light 12 corresponding to an image signal such as a document image is formed. Irradiation results in the formation of an electrostatic latent image. Then, the developing device 13 includes the photosensitive drum 10
The toner image is formed by developing the above electrostatic latent image. The transfer charging device 14 serving as a transfer unit includes the photosensitive drum 1
The transfer paper 18 on which the toner image on the photosensitive drum 10 has been transferred is transferred to the fixing device 19 by the transfer material transfer device 32. The fixing device 19 fixes the toner image, forms an output image, and discharges the image. In addition,
The photosensitive drum 10, the primary charging device 11, the developing device 13, and the transfer charging device 14 constitute an image forming unit.

The fixing device 19 in the image forming apparatus according to the present embodiment is a film fixing type fixing device as shown in FIG. 1, and is an endless belt-shaped fixing film 25 formed of a material having high heat resistance. Is wound and wound between the heater 20, the driving roller 26, and the driven roller 27 so as to be in sliding contact with the heater 20, which is a heat generating member supported by a support (not shown).

On the lower surface of the heater 20, a pressing roller 2 as a pressing member is interposed with a fixing film 25 interposed.
8 are pressed against each other by a biasing means (not shown) at a contact pressure of, for example, about 5 kg weight. Pressure roller 28
Has a rubber elastic layer of silicone rubber or the like with good releasability, and forms a fixing portion by being pressed against the heater 20.

When the driving roller 26 is driven to rotate clockwise by a driving motor (not shown) as a rotation driving means, the fixing film 25 given a predetermined tension by a driven roller 27 also serving as a tension roller is removed.
The motor rotates at a predetermined peripheral speed in the clockwise direction. Then, as the fixing film 25 circulates, the pressure roller 28 is also driven to rotate in the counterclockwise direction.
Is transported while being sandwiched between the fixing film 25 and the pressure roller 28.

The fixing film 25 circulated in this way
Is a film having excellent heat resistance, releasability, and abrasion resistance, and generally has a total thickness of 100 μm or less, preferably 4
Use a thin material of 0 μm or less. Therefore, as the film material, for example, a single layer or a composite layer of a heat-resistant resin such as polyimide, polyetherimide, or polyethersulfone may be used.

The heater 20 has a thickness of 1.0 mm and a width of 1 mm.
A good heat conductor of 0.0 mm and length of 350 mm is coated with an electric resistance material to a width of 2.5 mm and a length of 300 mm on a substrate such as alumina or aluminum nitride. To generate thermal energy.

Further, a temperature sensor 29 as temperature detecting means is mounted on the back surface of the substrate of the heater 20. The temperature sensor 29 is provided with a predetermined substrate during the image forming operation. A power control unit 30 is connected as power control means for controlling power supplied to the heater 20 in accordance with the temperature detected by the temperature sensor 29 so that the temperature reaches a set temperature (temperature controlled temperature). Further, the power supply control unit 30 is connected to a density output characteristic selection switch 31 described later as selection means for selecting a photograph mode or a character mode, and controls the temperature control temperature by a detection signal selected by the density output characteristic selection switch 31. It is supposed to change.

Further, in the image forming apparatus of the present embodiment, the relationship between the density of the original image and the density of the image output by the image forming apparatus (hereinafter referred to as "density output characteristics") is shown in FIG.
The characteristic shown in FIG. 3A or the characteristic shown in FIG. 3B can be selected by the density output characteristic selection switch 31.

In this embodiment, the fixing condition changing means is constituted by the density output characteristic selection switch 31 and the power supply control unit 30.

If the characteristic shown in FIG. 3A is selected by the density output characteristic selection switch 31, the background (white background) of the original image reproduces completely white, and the character portion of the original image has the density. Since a high density capable of clearly recognizing a low fine line or the like is reproduced, an output image with high contrast can be obtained (hereinafter, a mode suitable for reproducing a character portion of a document image is referred to as a character mode).

If the characteristic shown in FIG. 3B is selected by the density output characteristic selection switch 31, the intermediate density portion of the original image is reproduced with a faithful density, so that an image with rich gradation can be output (FIG. 3B). Hereinafter, a mode suitable for reproduction of a photo original requiring the gradation expression is referred to as a photo mode).

When the character mode is selected, due to its characteristics, the width of the intermediate density portion in the output image is significantly smaller than the width of the intermediate density portion in the original image. Furthermore, the selection of the character mode itself means that the original image does not include many intermediate densities that require gradation expression. That is, when the character mode is selected, it can be determined that the width or ratio of the intermediate density portion in the output image is very small.

On the other hand, when the photograph mode is selected, due to its characteristics, the width of the intermediate density portion in the output image matches the width of the intermediate density portion included in the document density. Further, the selection of the photograph mode itself means that the original image contains many intermediate density portions requiring gradation expression. That is, it can be determined that the width or ratio of the intermediate density portion in the output image is large when the photograph mode is selected.

Therefore, in this embodiment, the mode selected by the density output characteristic selection switch 31 is detected, and the temperature of the substrate of the heater 20 during the image forming operation is changed according to the mode. Then, the power supplied to the heater 20 via the power supply control unit 30 is controlled based on the set temperature control temperature.

FIG. 2 shows a flowchart of the image forming operation in this embodiment. First, it is determined whether the selected density output characteristic is a photograph mode characteristic or a character mode characteristic (step S1). If the selected density output characteristic is a photograph mode characteristic, the heater 20 is turned on.
The temperature control temperature of the substrate is set to 200 ° C., and the toner image on the transfer paper 18 is fixed (step S2). on the other hand,
If the selected density output characteristic is the character mode characteristic, the temperature of the substrate of the heater 20 is set to 230 ° C. and the toner image is fixed on the transfer paper 18 (step S3). After the fixing according to the density output characteristic selected as described above, the supply of the electric power to the heater 20 is stopped (step S4).

According to the present embodiment, when the photograph mode is selected (ie, when the width or ratio of the intermediate density portion in the output image is large), the temperature of the substrate of the heater 20 is controlled. By changing the temperature to a lower temperature, the width of the temperature increase applied to the heater 20 and the stay at the start of image formation is reduced, so that the temporary expansion and deformation of the heater 20 and the stay can be reduced, and even in the case of a toner image including many intermediate density portions. It is possible to obtain an output image of high quality without any uneven fixing phenomenon and uneven fixing gloss due to wrinkles of the fixing film 25.

In this embodiment, when the photograph mode is selected, the temperature of the substrate of the heater 20 is changed to a lower temperature, so that the fixing characteristics may be slightly deteriorated. Is of a practically acceptable degree. <Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG.

In the present embodiment, the occurrence of the uneven fixing phenomenon and the uneven fixing gloss phenomenon in the intermediate density portion is prevented, and at the same time, the fixing characteristics when the photograph mode is selected are improved.

Since the image forming apparatus of the second embodiment has the same configuration as the image forming apparatus shown in FIG. 1, the description of the configuration of the image forming apparatus is omitted.

Also, in the image forming apparatus of this embodiment, similarly to the first embodiment, the density output characteristic can be selected from a text mode and a photograph mode.

In this embodiment, the mode selected by the density output characteristic selection switch 31 is detected, and the temperature of the substrate of the heater 20 during the image forming operation is changed in accordance with the mode. The pre-rotation time of the fixing film 25 is extended by the changing means.

FIG. 4 is a flowchart illustrating control of the fixing temperature during the image forming operation according to the present embodiment. First, it is determined whether the selected density output characteristic is a photograph mode characteristic or a character mode characteristic (step S5). If the selected density output characteristic is a photograph mode characteristic, the heater 20 is turned off. Temperature of the substrate
After setting the temperature to 00 ° C. and extending the pre-rotation time of the fixing film 25 by 10 seconds from the normal (character mode), the toner image on the transfer paper 18 is fixed (step S).
6). The pre-rotation time of the fixing film 25 refers to the fixing device 1
This is the time during which the fixing film 25 is rotated before the transfer paper 18 reaches 9. During this pre-rotation, power is supplied to the heater 20 so that the temperature of the substrate of the heater 20 becomes a predetermined temperature regulation temperature.

On the other hand, if the selected density output characteristic is a character mode characteristic, the transfer temperature is set after the temperature of the substrate of the heater 20 is set to 230 ° C. and the pre-rotation is performed for a normal time. The toner image on the paper 18 is fixed (step S7). After the fixing according to the density output characteristic selected in this way, the supply of the electric power to the heater 20 is stopped (step 8).

According to the present embodiment, when the photograph mode is selected (that is, when the width or ratio of the intermediate density portion in the output image is large), the temperature of the substrate of the heater 20 is adjusted. By changing the temperature to a lower temperature, the range of temperature increase applied to the heater 20 and the stay at the start of image formation becomes smaller, so that temporary expansion and deformation of the heater 20 and the stay can be reduced. Further, by extending the pre-rotation time of the fixing film 25, the transfer paper 18 on which the toner image is transferred is formed.
When the heater 20 and the stay arrive at the fixing device 19, the heater 20 and the stay are uniformly heated, and the temporary expansion and deformation of the heater 20 and the stay are recovered. The fixing unevenness phenomenon and the fixing gloss unevenness phenomenon due to wrinkles of the film 25 are improved as compared with the first embodiment, and an output image of high quality image can be obtained.

Further, according to the present embodiment, when the photograph mode is selected, the entire fixing device 19 (heater 20, stay, driving roller 26, driven roller 27, pressure roller 28) is performed in a warmed state, so that sufficient fixing characteristics can be obtained even when the temperature of the substrate of the heater 20 is slightly lower.

However, in the present embodiment,
When the photograph mode is selected, the pre-rotation time of the fixing film 25 is extended, so that the productivity of the image forming apparatus is slightly reduced. <Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIG.

In the present embodiment, the occurrence of the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the intermediate density portion is prevented, and at the same time, the reduction in productivity due to the extension of the pre-rotation time of the fixing film 25 is improved.

Since the image forming apparatus of the third embodiment has the same configuration as the image forming apparatus shown in FIG. 1, the description of the configuration of the image forming apparatus is omitted.

Also, in the image forming apparatus of the present embodiment, similarly to the first embodiment, the density output characteristic can be selected from a character mode and a photograph mode.

In this embodiment, at the time when the image formation is started, the temperature sensor 2 for detecting the temperature of the substrate of the heater 20 is used.
9 detected temperature (hereinafter referred to as "temperature at start of rotation")
And the mode selected by the density output characteristic selection switch 31 and changes the temperature of the substrate of the heater 20 during the execution of the image forming operation in accordance with the value of the rotation start temperature and the selected mode. At the same time, the pre-rotation time of the fixing film 25 is extended by the changing means.

FIG. 5 shows a flowchart of the image forming operation in the present embodiment. First, it is determined whether the selected density output characteristic is a photograph mode characteristic or a character mode characteristic (step S9). If the selected density output characteristic is the characteristic of the Bunu mode, the heater 20
After the temperature control temperature of the substrate is set to 230 ° C. and the pre-rotation is performed for a normal time, the fixing of the toner image on the transfer paper 18 is executed (step S12). If the selected density output characteristic is the characteristic of the photograph mode, it is determined whether the rotation start temperature detected at the time of starting the image formation is 100 ° C. or less (step S10). If the rotation start temperature is higher than 100 ° C., the temperature of the substrate of the heater 20 is set to 230 ° C., and after performing the pre-rotation for a normal time, the fixing of the toner image on the transfer paper 18 is performed. Is executed (step S12). The detected rotation start temperature is 1
If the temperature is not higher than 00 ° C., the temperature of the substrate of the heater 20 is set to 200 ° C., and the pre-rotation time of the fixing film 25 is extended by 10 seconds from normal (character mode).
The toner image on the transfer paper 18 is fixed (step S11). Even during the pre-rotation of the fixing device 19, the heater 20 is energized so that the temperature of the substrate of the heater 20 becomes a predetermined temperature regulation temperature. After the fixing is performed in accordance with the value of the rotation start temperature and the selected mode, the supply of the electric power to the heater 20 is stopped (step 13).

According to the present embodiment, even when the photograph mode is selected, if the temperature of the substrate of the heater 20 at the start of image formation exceeds 100 ° C., the width of the temperature rise required at the start of image formation Therefore, even if the temperature of the substrate of the heater 20 is set higher and the pre-rotation time is short, the uneven fixing phenomenon and the uneven fixing gloss due to the wrinkles of the fixing film do not occur.

According to the present embodiment, even when the photograph mode is selected, the pre-rotation time of the fixing film 25 is extended only when the temperature of the substrate of the heater 20 at the start of image formation is 100 ° C. or less. A decrease in productivity of the image forming apparatus is minimized. <Fourth Embodiment> Next, a fourth embodiment of the present invention will be described.

In the present embodiment, a case where a toner image corresponding to a multi-valued image signal is formed as in an image forming apparatus such as a digital copying machine or a digital laser printer will be described.

In this embodiment, the structure other than the counting means for detecting the width or ratio of the intermediate density portion in the output image of the image forming apparatus is the same as that of the third embodiment.

The image exposure light 12 is 0 at a resolution of 400 dpi.
To 255 multilevel image signals having 256 gradation levels. Therefore, about 15 million pixels exist in the A4 size image.

A counter as a counting means is provided in a predetermined density range (for example, 0.3 to 0.3 in logarithmic reflection density) in the multi-valued image signal to be subjected to image formation at least before execution of fixing of the toner image. 1.0) is counted. Assuming that the multi-valued image signal from 0 to 255 represents a density value from 0.05 to 1.50, the number of pixels whose signal value is 44 or more and 168 or less may be counted.

If the number of intermediate-density pixels counted in this way exceeds 30% of the total number of pixels of 15 million, the intermediate-density portion of the output image corresponding to this image signal is The ratio is determined to be large, and if it does not exceed 30%, the ratio of the intermediate density portion is determined to be small.

In this embodiment, at the time when the image formation is started, the temperature sensor 2 for detecting the temperature of the substrate of the heater 20 is used.
9 detects the temperature at the start of rotation and the magnitude of the ratio of the intermediate density portion determined based on the ratio of the intermediate density occupying in the output image described above, and based on the result, the heater during the execution of the image forming operation is detected. At the same time as changing the temperature of the substrate 20
The pre-rotation time of the fixing film 25 is extended by the changing means.

In the above configuration, pixels corresponding to the background portion (white background portion) of the toner image are also counted as a part of the image.
Since no toner adheres to the background portion, the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon due to wrinkles of the fixing film 25 do not occur. Therefore, if the counting method described below is used, it is possible to accurately determine the ratio of the intermediate density portion in only the toner image portion where the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon due to the wrinkles of the fixing film 25 occur.

The number of pixels of the signal value corresponding to the intermediate density is counted in the same manner as in the above configuration, and the number of pixels of the signal value corresponding to the background portion (white background portion) of the image is counted. For example, the number of pixels having a logarithmic reflection density of 0.2 or less, that is, a signal value of 26 or less is counted. Next, when the number of pixels of the intermediate density exceeds 30% with respect to the number obtained by subtracting the number of pixels corresponding to the background portion of the image from the total number of pixels, the output image corresponding to this image signal is occupied. It is determined that the ratio of the intermediate density parts is large, and if it does not exceed 30%, it is determined that the ratio of the intermediate density parts is small.

In the present embodiment, the intermediate density range is not limited to 0.3 to 1.0, but may be determined according to the fixing characteristics of the toner used in the image forming apparatus and the configuration of the fixing apparatus. In this case, it is desirable to regard the density region where the fixing characteristics are clearly worse than that of the solid black image as the intermediate density.

In the present embodiment, the ratio used as a reference for judging the ratio of the intermediate density portion is not limited to 30%. If the criterion for determination is set between 20% and 80% according to the preference of the operator of the image forming apparatus, the effect of the present invention can be sufficiently obtained.

The count of the pixels of the intermediate density is determined by image signal processing for converting an image signal value such as gamma conversion (image signal processing for converting the density of an image) or original image processing such as shadowing processing. The effect of the present invention can be further enhanced by performing the processing on an image signal after performing image signal processing for adding a new intermediate-density image portion to the signal. <Fifth Embodiment> Next, a fifth embodiment of the present invention will be described.

The image forming apparatus according to the fifth embodiment has the same configuration as that of the image forming apparatus shown in FIG. 1, and a description of the configuration of the image forming apparatus will be omitted.

In the present embodiment, a mode selection switch (not shown) as mode selection means is provided on an operation panel (not shown), and the temperature control temperature of the substrate of the heater 20 during the image forming operation is operated by the selection switch. And at the same time, one of two types of fixing conditions is selected: a mode in which fixing is performed under conditions in which the pre-rotation time of the fixing film 25 is extended by the changing unit, and a mode in which fixing is performed under normal conditions. It is something to do.

That is, the mode selection switch allows the operator to select two types of fixing conditions for each type of output image.

When the output image contains many intermediate density portions, the operator operates the heater 20 during the image forming operation to prevent the occurrence of the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the intermediate density portion. At the same time as changing the temperature of the substrate, the mode for executing the fixing under the condition that the pre-rotation time of the fixing film 25 is extended is selected by the mode selection switch.

On the other hand, when the output image does not include any intermediate density portion like a character image, the operator selects a mode in which fixing is performed under normal conditions with high productivity by using a mode selection switch.

In this embodiment, the occurrence of the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the intermediate density portion can be prevented without adopting the complicated structure described in the first to fourth embodiments.

Further, when the image formation is started,
When the temperature detected by the temperature detection sensor 29 is 100 ° C. or less,
Only when the mode selected by the mode selection switch is a mode in which the temperature of the substrate of the heater 20 is changed while the image forming operation is being performed and the pre-rotation time of the fixing film 25 is extended. And the pre-rotation time can be changed, the reduction in productivity can be minimized.

[0090]

As described above, according to the first aspect of the present invention, the fixing condition of the heating member is changed by the fixing condition changing means based on the width or ratio of the intermediate density portion in the output image. With this configuration, it is possible to prevent the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the intermediate density portion due to wrinkles of the fixing film specific to the film fixing method.

According to the second aspect of the present invention, the fixing means selects the fixing condition of the heat generating member based on the width or ratio of the intermediate density in the output image, and selects the fixing condition by the selecting means. The power control means is controlled so that the temperature of the heat generating member becomes a predetermined temperature according to the characteristics thus obtained, so that it is possible to detect the width or ratio of the intermediate density portion included in the image with a simple configuration. at the same time,
The fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the intermediate density portion due to wrinkles of the fixing film specific to the film fixing method can be prevented.

According to the third aspect of the present invention, the fixing condition of the heat generating member is selected by the selection means based on the width or ratio of the intermediate density in the output image, and the characteristic selected by the selection means is selected. In addition to controlling the power control means so that the temperature of the heat generating member becomes a predetermined temperature in accordance with, the pre-rotation time of the fixing film until the transfer material reaches the fixing device is changed. The width or ratio of the intermediate density contained therein can be accurately detected, and the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the intermediate density portion due to wrinkles of the fixing film peculiar to the film fixing method can be prevented.

According to the fourth aspect of the present invention, the temperature of the heat generating member is detected at the time when the image formation is started by the temperature detecting means, and the setting of the fixing device is performed according to the detection result by the temperature detecting means. Since at least one of the temperature and the pre-rotation time of the fixing film until the transfer material reaches the fixing device is changed, a decrease in productivity of the image forming apparatus can be minimized. Further, it is possible to more accurately detect the width or ratio of the intermediate density contained in the image, and at the same time, it is possible to prevent the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the intermediate density portion due to wrinkles of the fixing film specific to the film fixing method.

According to the fifth aspect of the present invention, the temperature of the heat generating member is detected at the time when the image formation is started by the temperature detecting means, and a predetermined value is included in the multi-valued image signal input by the counting means. The number of image signals corresponding to the density of the density region is counted, and the set temperature of the heating member is calculated from the ratio of the counted value to the entire image signal and the temperature of the heating member at the start of image formation detected by the temperature detection means. In addition to the change, the pre-rotation time of the fixing film until the transfer material reaches the fixing device is changed, so that the width or ratio of the intermediate density portion included in the image can be accurately detected, and the film fixing is performed. The fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the intermediate density portion due to the wrinkling of the fixing film specific to the system can be prevented.

According to the present invention, the temperature of the heat generating member is detected at the time when the image formation is started by the temperature detecting means, and the multi-valued image signal inputted by the counting means is used. The image signal corresponding to a density equal to or less than a predetermined density is counted, the ratio of the value obtained by subtracting the counted value from the entire image signal to the total image signal, and the heating member at the start of image formation detected by the temperature detecting means are detected. In addition to changing the set temperature of the heat generating member from the above temperature, and changing the pre-rotation of the fixing film until the transfer material reaches the fixing device, the width of the intermediate density portion included in the image or The ratio can be detected more accurately, and the fixing unevenness phenomenon and fixing gloss unevenness phenomenon in the intermediate density part due to wrinkles of the fixing film peculiar to the film fixing method can be prevented. .

Further, according to the seventh aspect of the present invention, the counting means includes an image signal corresponding to a density in a predetermined density range in the input image signal after the multivalued image signal processing. The number or the number of intermediate counts can be counted, so that the width or ratio of the intermediate density included in the image can be detected more accurately. The fixing gloss unevenness phenomenon can be prevented.

Further, according to the present invention, the pre-rotation time of the fixing film until the transfer material reaches the fixing device based on the width or ratio of the intermediate density in the output image by the changing means. Further, since the set temperature of the heat generating member is changed, it is possible to prevent the fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the intermediate density portion due to wrinkles of the fixing film specific to the film fixing method with a simple configuration.

According to the ninth aspect of the present invention, the temperature of the heat generating member detected by the temperature detecting means is equal to or lower than a predetermined set temperature, and the mode selected by the mode selecting means changes the set temperature of the heat generating member. In addition, since the fixing condition changing means is operated in the mode in which the pre-rotation time of the fixing film is extended, the decrease in productivity is minimized, and the intermediate density due to wrinkles of the fixing film peculiar to the film fixing method. The fixing unevenness phenomenon and the fixing gloss unevenness phenomenon in the portion can be prevented.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating control of a fixing temperature during an image forming operation according to the first embodiment.

FIG. 3A is a diagram illustrating density characteristics in a character mode according to the first embodiment, and FIG. 3B is a diagram illustrating density output characteristics in a photograph mode.

FIG. 4 is a flowchart illustrating control of a fixing temperature during an image forming operation according to a second embodiment.

FIG. 5 is a flowchart illustrating control of a fixing temperature during an image forming operation according to a third embodiment.

FIG. 6 is a schematic sectional view showing an example of a conventional fixing device of a film fixing system.

[Explanation of symbols]

 Reference Signs List 10 image carrier (photosensitive drum) 11 image forming means (primary charging device) 12 image forming means (image exposure) 13 image forming means (developing device) 14 image forming means (transfer charging device) 18 transfer material 19 fixing device 20 Heating member (heater) 25 Fixing film 28 Pressure member (pressure roller)

Claims (9)

[Claims] An image forming means for forming a toner image corresponding to a document image or an input multi-valued image signal on an image carrier, and transferring the toner image on the image carrier onto a transfer material; An image forming apparatus comprising: a fixing device that fixes a toner image formed on the transfer material by a forming unit; wherein the fixing device includes: a heating member; and a pressing member disposed to face the heating member. A fixing film sandwiched between the heat-generating member and the pressure member so as to include the heat-generating member, and the heat generation based on the width or ratio of the intermediate density portion in the output image. An image forming apparatus comprising: a fixing condition changing unit configured to change a fixing condition of a member. 2. The image forming apparatus according to claim 1, wherein the fixing condition changing unit includes a selecting unit that selects a fixing condition of the heat generating member based on a width or a ratio of the intermediate density portion in the output image. 2. The image forming apparatus according to claim 1, further comprising: a power control unit configured to control a temperature of the heat generating member so that the temperature of the heat generating member becomes a set temperature corresponding to the temperature. 3. The fixing condition changing unit includes: a selection unit that selects a fixing condition of the heat generating member based on a width or a ratio of an intermediate density portion in an output image; and a characteristic selected by the selection unit. Power control means for controlling the temperature of the heat-generating member so that the temperature of the heat-generating member is adjusted to a set temperature according to the following conditions: and changing means for changing a pre-rotation time of the fixing film until the transfer material reaches the fixing device. The image forming apparatus according to claim 1, wherein: 4. The fixing condition changing unit includes: a temperature detecting unit configured to detect a temperature of the heat generating member when image formation is started; and a setting temperature of the fixing device according to a detection result by the temperature detecting unit. 2. The image forming apparatus according to claim 1, further comprising a change unit configured to change at least one of a pre-rotation time of the fixing film until the transfer material reaches the fixing device. 3. 5. A fixing condition changing unit, comprising: a temperature detecting unit for detecting a temperature of the heat generating member when image formation is started; and a density of a predetermined density range in an input multi-valued image signal. Counting means for counting the number of image signals corresponding to, and the ratio of the count value counted by the counting means to the entire image signal and the temperature of the heating member at the start of image formation detected by the temperature detection means. 2. The image according to claim 1, further comprising: changing means for changing a set temperature of the heat generating member and changing a pre-rotation time of the fixing film until the transfer material reaches the fixing device. Forming equipment. 6. A fixing condition changing means, comprising: a temperature detecting means for detecting a temperature of the heat generating member at the time of starting image formation; Counting means for counting the number of image signals corresponding to the density; a ratio of a value obtained by subtracting the count value counted by the counting means from the entire image signal to the entire image signal; and an image formation start detected by the temperature detecting means. Changing means for changing a set temperature of the heat generating member from a temperature of the heat generating member at the time, and changing a pre-rotation time of the fixing film until the transfer material reaches the fixing device. The image forming apparatus according to claim 1, wherein: 7. The image processing apparatus according to claim 1, wherein the counting unit counts the number of image signals corresponding to densities in a predetermined density region in the image signals obtained by performing image signal processing on the input multi-valued image signals. 7. The image forming apparatus according to claim 5, wherein: 8. The fixing condition changing means, comprising: a pre-rotation time of the fixing film until the transfer material reaches the fixing device, based on a width or a ratio of an intermediate density portion in an output image; The image forming apparatus according to claim 1, further comprising a mode selection unit that selects a set temperature of the heat generating member. 9. The fixing condition changing means, wherein the temperature of the heat generating member detected by the temperature detecting means is equal to or lower than a predetermined set temperature, the mode selected by the mode selecting means changes the set temperature of the heat generating member, and The image forming apparatus according to claim 1, wherein the apparatus operates in a mode in which a pre-rotation time of the fixing film is extended.