JP2002357963A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of realizing excellent color copying by a simple control process. SOLUTION: This image forming device having a double-sided image forming mode and an OHT image forming mode and equipped with a fixing device for thermally fixing a toner image formed on a sheet is equipped with a circular sheet passing path for thermally fixing the image on a sheet on which the image is thermally fixed by the fixing device by the fixing device again in the double-sided image forming mode and the OHT image forming mode, a transmittance detection means arranged on the paper ejection side of the fixing device and detecting the transmittance of an OHT sheet on which the color toner image is formed, and a control means for controlling so that the transmittance of the OHT sheet may be a specified value by making the OHT sheet circulate repeatedly in the circular sheet passing path including the transmittance detection means and thermally fixing the image thereon.

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, a printer, a facsimile, etc., having a fixing device for thermally fixing a toner image on a sheet by a heating roller and a pressure roller.

[0002]

2. Description of the Related Art <Prior Art 1> When an OHT sheet of a color original is color-copied, light is sufficiently transmitted. Therefore, when changing from the normal sheet image forming mode to the color OHT image forming mode, the process speed of the entire image forming process is changed to a low speed,
When the OHT image forming mode is changed, the heating temperature of the fixing device is changed.

<Prior art 2> In an image forming apparatus having an OHT image forming mode and a normal sheet image forming mode, it is known that one oil application roller is brought into contact with a heating roller of a fixing device to apply oil. Have been.

<Prior art 3> In a normal sheet image forming mode and an OHT image forming mode, an oil application roller impregnated with oil is always pressed against and applied to a heating roller to improve the separation between the sheet and the heating roller. Forming devices are known.

[0005] <Prior art 4> In the heat fixing by a roller having an elastic layer provided in a fixing device, for example, as described in JP-A-9-305056, JP-A-11-95603, etc. 2. Description of the Related Art There is known an image forming apparatus that detects a peripheral speed of a heating roller formed in an apparatus and drives the heating roller to a predetermined speed to stabilize a sheet conveying speed.

[0006]

However, as the problem of <Prior Art 1>, if the process speed of the entire image forming process is changed, control becomes complicated, and it takes time to change the heating temperature of the fixing device. In other words, there is a problem that operability is poor.

An object of the first invention is to provide an image forming apparatus capable of copying an OHT sheet by mode switching and capable of performing high-quality color copying of an OHT sheet by a simple control process. is there.

[0008] As a problem of <Prior art 2>, when an OHT sheet is used, the transmittance of a color changes due to a difference in viscosity of oil used for an oil application roller.
When a normal sheet is used, the separability between the normal sheet and the heating roller and the adhesion rate of the toner to the heating roller change due to the difference in oil viscosity. Therefore, when the heat fixing is performed using the OHT sheet and the ordinary sheet with one oil viscosity, the allowable range of the oil viscosity that satisfies both the transparency of the OHT sheet and the separation property of the ordinary sheet is narrow, and the accuracy is maintained. There is a problem that it is difficult to do.

A second object of the present invention is to provide an OHT image forming mode and a normal sheet image forming mode. In the case of an OHT sheet, an image having good color transparency is provided, and in the case of an ordinary sheet, an image having good separation properties is provided. An object of the present invention is to provide a forming apparatus.

[0010] The problem of <Prior art 3> is that the oil application roller is constantly pressed against the heating roller in the normal sheet image forming mode and the OHT image forming mode.
There is a problem that the durability of the oil application roller is short.

A third object of the present invention is to provide an image forming apparatus provided with a fixing device having good durability for an oil application roller for applying oil to a heating roller.

[0012] The problem of <Prior art 4> is that the sheet conveyance speed itself in the nip portion of the fixing device depends on the distortion of the elastic layer formed on the roller, and the circumferential length and the number of revolutions of the heating roller, and other than the nip portion, It cannot be accurately estimated from the peripheral speed. For example, when there are physical property values such as hardness of the elastic layer formed on the roller under constant load conditions, and dimensional variations such as the thickness of the elastic layer, the amount of distortion of the elastic layer formed on the roller changes, and the sheet conveying speed changes. There is a problem. If the sheet conveyance speed in the fixing device is not stabilized to a predetermined value in relation to the sheet conveyance speed of the transfer roller unit and the registration roller unit, a problem such as transfer deviation and image expansion and contraction may occur. It is important to control accurately.

A fourth object of the present invention is to provide an image forming apparatus having good sheet conveyance accuracy and good heat fixing.

[0014]

The above object of the first invention can be achieved by any of the following means.

(1) In an image forming apparatus having a double-sided image forming mode and an OHT image forming mode and including a fixing device for thermally fixing a toner image formed on a sheet, the double-sided image forming mode and the OHT image forming In the mode, the sheet thermally fixed by the fixing device is again circulated by the fixing device, and a sheet circulation path for the sheet, and an OH disposed on the discharge side of the fixing device to form a color toner image.
Transmittance detecting means for detecting the transmittance of the T sheet;
Control means for repeatedly circulating the HT sheet through the circulating paper path including the transmittance detection means and thermally fixing the HT sheet so that the transmittance of the OHT sheet becomes a predetermined value. Image forming apparatus.

(2) In an image forming apparatus having a double-sided image forming mode and an OHT image forming mode and including a fixing device for thermally fixing a toner image formed on a sheet, the double-sided image forming mode and the OHT image forming In a mode, the sheet heat-fixed by the fixing device is re-fixed by the fixing device again.
A transmittance detecting means for detecting the transmittance of the HT sheet, and a transmittance after the first heat fixing of the color toner image formed on the OHT sheet is measured by the transmittance detecting means;
Determine the number of circulations of the circulation paper path based on the value of the transmittance,
An image forming apparatus comprising: a control unit configured to control the OHT sheet to circulate through the circulating paper path by the circulating number of times so as to thermally fix the OHT sheet.

The object of the second invention can be achieved by the following means. (3) An image forming apparatus having an OHT image forming mode and a normal sheet image forming mode, and having a fixing device that heats and presses a toner image on a sheet by a heating roller and a pressure roller to thermally fix the toner image. A first oil application unit having a first oil application roller for applying oil for a normal sheet so as to be able to come and go on the surface; and a second oil application roller for applying oil for an OHT sheet so as to be able to come and go on the heating roller. The second oil application unit presses only the first oil application roller against the heating roller in the normal sheet image forming mode, and presses only the second oil application roller against the heating roller in the OHT image forming mode. An image forming apparatus, comprising: a control unit that performs control as described above.

The object of the third invention can be achieved by any of the following means. (4) An image forming apparatus having at least an OHT image forming mode and including a fixing device that heat-presses a toner image on a sheet with a heating roller and a pressure roller to thermally fix the sheet,
Oil applying means having an oil applying roller capable of being pressed against or released from the heating roller, and when using an OHT sheet,
Control means for controlling the oil application roller to be released from the heating roller.

(5) In an image forming apparatus having at least a thick paper image forming mode and having a fixing device for heating and pressing a toner image on a sheet with a heating roller and a pressure roller to thermally fix the toner image, the image forming apparatus is pressed against the heating roller or Oil application means having a releasable oil application roller, thick paper detection means for detecting thick paper having a mass per unit area of 105 g / m ² or more, and when the thick paper is detected, the oil application roller is connected to the heating roller An image forming apparatus, comprising: a control unit configured to perform control to further cancel the image forming apparatus.

(6) An image forming apparatus provided with a fixing device for thermally fixing a toner image on a sheet by applying heat and pressure by a heating roller and a pressure roller, wherein an oil application roller is provided which can be pressed against or released from the heating roller. Coating means;
Detection means for detecting a normal sheet having a mass per unit area of 75 g / m ² or less; and control means for controlling the oil application roller to press against the heating roller when the normal sheet is detected. An image forming apparatus comprising:

The object of the fourth invention can be achieved by any of the following means. (7) In an image forming apparatus provided with a fixing device that heats and presses the toner image on the sheet by pressing and rotating at a nip portion between a heating roller and a pressure roller, and heat-fixes the toner image on the sheet, a predetermined amount is preliminarily set on the test sheet in the sheet conveying direction. Mark detecting means for detecting a plurality of marks provided in isolation, passing time measuring means for measuring the passing time of the plurality of mark intervals while the test sheet passes through the nip portion, and measuring the passing time An image forming apparatus comprising: control means for controlling the number of rotations or the rotation speed of a drive source of the heating roller or the pressure roller based on a result.

(8) In an image forming apparatus provided with a fixing device that heats and presses a toner image on a sheet at a nip portion between a heating roller and a pressure roller that are pressed and rotated, and heat-fixes the sheet, the sheet is transported in advance to a test sheet. Mark forming means for forming a plurality of marks provided at predetermined intervals in a direction, mark detecting means for detecting the plurality of formed marks, and the plurality of marks while the test sheet passes through the nip portion. A transit time measuring means for measuring transit time of an interval, and a driving source of the heating roller or the pressure roller when passing a sheet having the same configuration as a subsequent test sheet based on the measurement result of the transit time. An image forming apparatus comprising: control means for controlling a rotation speed or a rotation speed.

(9) In an image forming apparatus provided with a fixing device that heats and presses the toner image on the sheet at a nip portion between a heating roller rotated by pressing and rotating and a pressure roller to thermally fix the toner image, the toner image is transferred onto the sheet. A sheet conveyance path between the transfer section and the nip section, a sheet conveyance speed detection roller that contacts and follows a sheet in the sheet conveyance path, and detects a conveyance speed based on a rotation amount of the sheet conveyance speed detection roller. Transport speed detecting means, and control means for controlling the number of rotations or the rotational speed of the drive source of the heating roller or the pressure roller based on the sheet transport speed detected by the transport speed detecting means. Image forming apparatus.

(10) In an image forming apparatus provided with a fixing device for heat-pressing and thermally fixing the toner image on the sheet by pressing and rotating the nip portion between the heating roller and the pressure roller, the surface temperature of the heating roller First temperature detection means for detecting, second temperature detection means for detecting the surface temperature of the pressure roller, and mark detection means for detecting a plurality of marks provided on the test sheet at predetermined intervals in the sheet conveying direction. A passing time measuring unit that measures a passing time of the plurality of mark intervals while the test sheet passes through the nip portion; a calculating unit that calculates a sheet conveying speed based on a measurement result of the passing time; Storage means for passing a test sheet and storing a relationship between a surface temperature of the heating roller, a surface temperature of the pressure roller, and a sheet conveying speed; Thereafter, when a sheet having the same configuration as the test sheet is passed, rotation of the drive source of the heating roller or the pressure roller is performed based on the detection result of the surface temperature of the heating roller and the surface temperature of the pressure roller. An image forming apparatus, comprising: control means for controlling the number or rotation speed.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a schematic configuration of an image forming apparatus common to the image forming apparatuses of the inventions will be described. FIG. 1 is a schematic sectional view of a color image forming apparatus showing an embodiment of the image forming apparatus according to the present invention.

This color image forming apparatus is called a tandem type color image forming apparatus, and a plurality of sets of image forming sections 10Y, 10M, 10C, 10K arranged in tandem.
And a semiconductive endless belt-shaped intermediate transfer member 7 wound around a plurality of rollers and rotatably supported, a sheet feeding and conveying means, and a fixing device 8.

Image forming section 1 for forming a yellow image
0Y includes a charging unit 2Y, an exposing unit 3Y, a developing unit 4Y, a primary transfer unit 5Y, and a cleaning unit 6Y arranged around the image carrier (photoconductor) 1Y. The image forming unit 10M that forms a magenta image includes an image carrier (photoconductor) 1M, a charging unit 2M, an exposure unit 3M, and a developing unit 4.
M, a primary transfer unit 5M, and a cleaning unit 6M. An image forming unit 10C for forming a cyan image includes an image carrier (photoconductor) 1C, a charging unit 2C, an exposure unit 3C,
Developing unit 4C, primary transfer unit 5C, cleaning unit 6
C. The image forming unit 10K for forming a black image includes:
Image carrier (photoconductor) 1K, charging unit 2K, exposure unit 3
K, a developing unit 4K, a primary transfer unit 5K, and a cleaning unit 6K.

The image forming units 10Y, 10M, 10C, 10
The image of each color formed from K is transferred to primary transfer units 5Y and 5Y.
M, 5C, and 5K successively transfer the image onto the rotating intermediate transfer body 7 to form a combined color image. The sheet P stored in the sheet cassette 20 is fed to the sheet feeding unit 21.
And a plurality of intermediate transfer rollers 22A, 22A
B, 22C, 22D, and the registration roller 23, and is conveyed to a secondary transfer unit (also referred to as a transfer unit) 5A, and the sheet P
A color image is collectively transferred on the top. The sheet P to which the color image has been transferred is subjected to a fixing process by the fixing device 8, and is held by a sheet discharging roller 24 and placed on a sheet discharging tray 25 outside the apparatus. The details of the fixing device 8 will be described later.

At the time of double-sided image formation, the sheet P formed on the first surface and discharged from the fixing device 8 is
6, the sheet is branched from the sheet discharge path, passes through the lower circulating paper paths 27A, 27B, and 27C, and passes through the intermediate transfer roller 2
Merge in 2D. The sheet P that has been reversely conveyed is conveyed to the secondary transfer unit 5A via the registration roller 23, and the color image is collectively transferred onto the second surface of the sheet P. The sheet P to which the color image has been transferred is subjected to fixing processing by the fixing device 8. The details of the fixing device will be described later. Next, the sheet is nipped by a sheet discharge roller 24 and placed on a sheet discharge tray 25 outside the apparatus.

On the other hand, after the color image is transferred onto the sheet P by the secondary transfer means 5A, the residual toner is removed by the cleaning means 6A from the intermediate transfer body 7 from which the sheet P is separated by curvature.

During the image forming process, the primary transfer means 5K is always in pressure contact with the photosensitive member 1K. Other primary transfer means 5
Y, 5M, and 5C are in pressure contact with the corresponding photoconductors 1Y, 1M, and 1C only during color image formation. The secondary transfer unit 5A comes into pressure contact with the intermediate transfer member 7 only when the sheet P passes through the second transfer unit and secondary transfer is performed.

(First Embodiment) The image forming apparatus of the first invention has the configuration of the image forming apparatus shown in FIG. 1 except for the configuration shown in FIG. FIG. 2 is a cross-sectional view of a main configuration showing a fixing device of the image forming apparatus, a sheet circulation path, a transmission detection unit, a control unit, and the like. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is partially omitted.

As shown in FIG. 2, the image forming apparatus is an OHT
It has an image forming mode and a double-sided image forming mode. O
The color toner used for the HT sheet is thermoplastic, for example, a styrene acrylic toner. Also, O
The amount of attached color toner on the HT sheet is smaller than the amount of attached toner on the normal sheet.

The fixing device 8A has a heating roller 82 and a pressure roller 83, and thermally fixes a color toner image on the sheet P.

The transmittance detecting means 92 measures the transmittance of the OHT sheet, on which the color toner image is formed, which is disposed on the paper discharge side of the fixing device 8A.

The circulating paper passages 27A, 27B, and 27C are paths for heat-fixing the sheet P, which has been thermally fixed on one surface by the fixing device 8A, to the other surface again by the fixing device 8A in the duplex image forming mode. In the OHT image forming mode, the OHT sheet P is also used as a path for repeatedly circulating and thermally fixing the OHT sheet.

The control means 100A transmits the OHT sheet P to the circulating paper paths 27A, 27B, 27 including the transmittance detecting means 92.
C is repeatedly circulated and thermally fixed so that the transmittance of the OHT sheet P is controlled to a predetermined value.

Next, the operation in the OHT image forming mode will be described. First, a color toner image is formed on the OHT sheet P, and the image is thermally fixed by the fixing device 8A.
The transmittance of the HT sheet is measured by the transmittance detecting means 92. If the OHT sheet transmittance does not reach the predetermined transmittance, the OHT sheet P is branched from the sheet discharge path by the branching unit 26, and the lower circulation paper paths 27A, 27B,
The OHT sheet P conveyed through the sheet 7C passes through the intermediate transfer roller 22D and the registration roller 23, and the OHT sheet P is heat-fixed again by the fixing device 8A.
The transmittance of the sheet is measured again by the transmittance detecting means 92,
Repeat this. When the transmittance of the OHT sheet reaches a predetermined value, the OHT sheet is nipped by the discharge rollers 24 and placed on a discharge tray 25 outside the apparatus.

With the above arrangement, the OHT sheet can be repeatedly and thermally fixed with a simple arrangement to obtain an appropriate color transmittance so that a high-quality color copy can be obtained.

(Second Embodiment) The other image forming apparatus of the first invention has the configuration of the image forming apparatus shown in FIG. 1 except for the configuration shown in FIG. FIG. 3 is a cross-sectional view of a main configuration showing a fixing device of the image forming apparatus, a sheet circulation path, a control unit, and the like.

As shown in FIG. 3, the image forming apparatus is an OHT
It has an image forming mode and a double-sided image forming mode. O
The color toner used for the HT sheet is thermoplastic, for example, a styrene acrylic toner. Also, O
The amount of attached color toner on the HT sheet is smaller than the amount of attached toner on the normal sheet.

The fixing device 8B has a heating roller 82 and a pressure roller 83, and thermally fixes the color toner image on the sheet P.

The transmittance detecting means 92 measures the transmittance after the first heat fixing of the OHT sheet P, which is disposed on the sheet discharging side of the fixing device 8B and on which a color toner image is formed.

The circulating paper passages 27A, 27B and 27C are paths for heat-fixing the sheet P on one surface by the fixing device 8B again on the other surface by the fixing device 8B in the double-sided image forming mode. In the OHT image forming mode, the OHT sheet P is also used as a path for repeatedly circulating and thermally fixing the OHT sheet P.

The control means 100B measures the transmittance of the color toner image formed on the OHT sheet after the first heat fixing by the transmittance detecting means, and determines the number of circulations in the circulating paper path based on the value of the transmittance. , OHT sheet P in circulation paper path 27A, 27B, 27C including transmittance detecting means 92
Are repeatedly circulated and thermally fixed so that the transmittance of the OHT sheet P is controlled to a predetermined value.

Next, the operation in the OHT image forming mode will be described. First, a color toner image is formed on the OHT sheet P, and the image is thermally fixed by the fixing device 8B.
The transmittance of the HT sheet is measured by the transmittance detecting means 92, and the number of circulations of the OHT sheet is determined based on the measured value.
The OHT sheet P is branched from the sheet discharge path by the branching unit 26, and the lower circulating paper paths 27A, 27B, 27C.
Pass through. The conveyed OHT sheet P passes through the intermediate transfer roller 22D and the registration roller 23, and the OHT sheet P is heat-fixed again by the fixing device 8B. This is repeated. And is placed on a discharge tray 25 outside the apparatus.

With the above configuration, the OHT sheet can be repeatedly subjected to thermal fixing with a simple configuration to obtain an appropriate color transmittance so that a high-quality color copy can be performed.

(Third Embodiment) The image forming apparatus of the second invention has the configuration of the image forming apparatus shown in FIG. 1 except for the configuration shown in FIG. FIG. 4 is a cross-sectional view of a main configuration showing a fixing device, a first oil applying unit, a second oil applying unit, a control unit, and the like of the image forming apparatus. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is partially omitted.

As shown in FIG. 4, the image forming apparatus is an OHT
It has an image forming mode and a normal sheet image forming mode. The color toner used is a styrene acrylic toner.

The fixing device 8C has a heating roller 82 and a pressure roller 83, and thermally fixes the color toner image on the sheet P.

The first oil applying means 85 is configured so that the first oil applying roller 85a is rotated by the rotation of the cam 85b.
2 can be approached and separated. First oil application roller 85
a applies oil for a normal sheet to the heating roller 82. As a preferable oil for a normal sheet, for example, there is dimethyl silicone oil having a viscosity of 100 cs.

The second oil applying means 86 is configured such that the second oil applying roller 86a is rotated by the cam 86b to rotate the heating roller 8a.
2 can be approached and separated. Second oil application roller 86
“a” applies oil for the OHT sheet to the heating roller 82. Preferred oils for the OHT sheet include, for example, dimethyl silicone oil and a viscosity of 1000 cs (centi-those).

In the normal sheet image forming mode, the control means 100C controls only the heating roller 8 for the first oil application roller 85a.
In the OHT image forming mode, only the second oil application roller 86a is controlled to press against the heating roller 82.

Next, the operation of the ordinary sheet image forming mode will be described with reference to FIG. 4. First, the first oil application roller 85a is rotated by the rotation of the cam 85b.
, And conversely, the second oil application roller 86a is
It is separated from the heating roller 82 by the rotation of 6b. Thereafter, a color toner image is formed on the ordinary sheet P, and is thermally fixed by the fixing device 8C. Then, as shown in FIG. 1, the image is sandwiched by sheet discharge rollers and placed on a sheet discharge tray outside the apparatus.

Next, the operation in the OHT image forming mode will be described. First, the first oil application roller 85a is separated from the heating roller 82 by the rotation of the cam 85b, and conversely, the second oil application roller 86a is rotated by the rotation of the cam 86b. Is pressed against the heating roller 82. Thereafter, a color toner image is formed on the OHT sheet, and is thermally fixed by the fixing device 8C. Then, as shown in FIG. 1, the color toner image is sandwiched by paper discharge rollers and placed on a paper discharge tray outside the apparatus.

With the above configuration, in an image forming apparatus provided with the OHT image forming mode and the normal sheet image forming mode, the OHT sheet has good color transparency and the normal sheet has good transportability.

(Fourth Embodiment) This embodiment is a modification of the second embodiment and will be described with reference to FIG. The description of the parts that are the same mechanically will be omitted, and the description will focus on the parts that are different from the third embodiment.

The first oil applying means 85 applies ordinary sheet oil to the heating roller 82. The second oil applying means 86 applies oil for the OHT sheet to the heating roller 8.
Apply to 2.

In the ordinary sheet image forming mode, the control means controls the first oil application roller 85a to be in pressure contact with the heating roller 82 only when the ordinary sheet P passes through the heating roller 82. Further, in the OHT image forming mode, the control unit controls the second oil application roller 86 a to be in pressure contact with the heating roller 82 only when the OHT sheet P passes through the heating roller 82.

Next, the operation in the normal sheet image forming mode will be described.
a, the sheet is pressed against the heating roller 82 only when the sheet is passed, and the second oil application roller 86 a is separated from the heating roller 82.

Next, the operation in the OHT image forming mode will be described. First, the first oil application roller 85a is separated from the heating roller 82, and the second oil application roller 86a
Makes the sheet press against the heating roller 82 only when the sheet is passed.

With the above configuration, in an image forming apparatus provided with the OHT image forming mode and the ordinary sheet image forming mode, the OHT sheet has good color transparency and the ordinary sheet has good transportability. Further, the oil application roller is pressed against the heating roller only when necessary, so that the durability of the oil application roller is improved.

(Fifth Embodiment) An image forming apparatus according to a third aspect of the present invention has the same configuration as the image forming apparatus shown in FIG. 1 except for the configuration shown in FIG. FIG. 5 is a cross-sectional view of a main configuration showing a fixing device, an oil application unit, a control unit, and the like of the image forming apparatus. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is partially omitted.

As shown in FIG. 5, the image forming apparatus is an OHT
It has an image forming mode, a cardboard image forming mode, and a normal sheet image forming mode.

The fixing device 8D fixes the toner image on the sheet P by applying heat and pressure by the heating roller 82 and the pressure roller 83.

The oil applying means 87 applies oil to the heating roller 82 so as to press or release the oil applying roller 87a. The oil application roller 87a is pressed against only the normal sheet. The oil impregnated in the oil application roller 87a is dimethyl silicon, and the viscosity is preferably 100 cs (centi-stroth) or more and 1000 cs or less. Within this range, the separation performance of the ordinary sheet is improved. The amount of oil applied to a normal sheet is preferably from 0.1 mg to 0.3 mg for A4 size or larger. In the case of A4 size or less, 1.5 mg to 3 mg is preferable. The separation performance is improved by setting the above range.

The normal sheet detecting means 88 measures the curl state of the sheet P while conveying the normal sheet, and detects a sheet having a mass per unit area of 75 g / m ² or less.

During the conveyance of the sheet P, the cardboard detecting means 89 measures the curl state of the sheet P and detects a cardboard having a mass per unit area of 105 g / m ² or more.

When the control means 100D detects the ordinary sheet, it controls the oil application roller 87a to the heating roller 82.
Is controlled so as to be pressed against. Further, when the thick paper is detected, and in the OHT image forming mode, the oil application roller 87a is controlled to be released from the heating roller 82.

The operation of each mode will be described. In the OHT image forming mode, the oil application roller 87a is released from the heating roller 82 to prevent the transmittance from lowering, and the toner image on the OHT sheet is heated. Press and fix. When the thick paper is detected, the oil application roller 87a is released from the heating roller 82 and the toner image on the sheet P is fixed by heating and pressing because the thick paper has good separability. Further, when a normal sheet having a mass per unit area of 75 g / m ² or less is detected, the oil application roller 87a is pressed against the heating roller 82 to fix the toner image on the sheet by heating and pressing.

With the above configuration, the oil application roller is pressed against the heating roller only when necessary in various modes, so that the durability of the oil application roller is improved. Also, OH
Since the T sheet releases the oil application roller, the transparency of the color is good, and the separation property of the ordinary sheet is good.

(Sixth Embodiment) An image forming apparatus according to a fourth aspect of the invention has the configuration of the image forming apparatus shown in FIG. 1 except for the configuration shown in FIG. FIG. 6A shows a fixing device, a mark detecting unit, a passing time measuring unit of the image forming apparatus of the present invention,
FIG. 2 is a cross-sectional view of a main part configuration showing a control unit and the like, and FIG. 2B is a plan view of a test sheet previously marked. In addition,
The same components as those in FIG. 1 are denoted by the same reference numerals and the description thereof is partially omitted.

As shown in FIG. 6, the fixing device 8E heats and presses the toner image on the sheet P at the nip between the heating roller 82 and the pressing roller 83 which are pressed and rotated.

The mark detecting means 95 detects a plurality of marks M1 and M2 which are provided on the test sheet P on which marks are preliminarily provided at a predetermined interval L in the sheet conveying direction. The mark detection means 95 is disposed near the discharge side of the nip portion N between the heating roller 82 and the pressure roller 83.

The passage time measuring means 96 measures the passage time of the interval L between the marks M1 and M2 attached to the test sheet P while the pre-marked test sheet P passes through the nip portion N. .

The control means 100E obtains the sheet conveying speed from the measurement result of the passage time, and adjusts the number of rotations or the rotating speed of the driving source (not shown) of the heating roller 82 or the pressing roller 83 so as to obtain an appropriate sheet conveying speed. Control.

A plurality of marks M1 and M2 are provided on the test sheet P at a predetermined interval L in the sheet conveying direction. Further, the test sheet P used has a contraction ratio due to thermal fixing smaller than a predetermined contraction ratio.

With the above arrangement, the number of rotations or the rotation speed of the driving source can be accurately controlled, and excellent heat fixing can be achieved by accurate sheet conveyance.

(Seventh Embodiment) The other image forming apparatus of the fourth invention has the configuration of the image forming apparatus shown in FIG. 1 except for the configuration shown in FIG. FIG. 7A is a cross-sectional view of a main configuration showing a fixing device, a mark forming unit, a mark detecting unit, a passage time measuring unit, a control unit, and the like of the image forming apparatus;
(B) It is a top view of the test sheet in which the mark was formed later. The same parts as those in FIG.

As shown in FIG. 7, the fixing device 8F heats and presses the toner image on the sheet P at the nip portion N between the heating roller 82 and the pressure roller 83 which are pressed and rotated.

The mark forming means 97 is means for forming a plurality of marks on the test sheet.
From the image carriers 1Y to 1K, the charging units 2Y to 2K
K, exposure units 3Y to 3K, primary transfer units 5Y to 5K, and image forming units 10Y to 10K.

The mark detecting means 95 detects a plurality of marks M3 and M4 transferred to the test sheet P by the mark forming means at a predetermined interval L in the sheet conveying direction. The mark detection means 95 is disposed near the discharge side of the nip portion N between the heating roller 82 and the pressure roller 83.

The passage time measuring means 96 is used for the test sheet P
Measures the passage time of the interval L between the marks M3 and M4 attached to the test sheet P while passing through the nip N.

The control means 100F determines the sheet conveying speed based on the measurement result of the passing time, and adjusts the number of rotations or the rotating speed of the driving source (not shown) of the heating roller 82 or the pressure roller 83 so that the sheet conveying speed becomes appropriate. Control. Also,
When controlling the drive source of the heating roller or the pressure roller based on the measurement result of the passing time, the expansion and contraction rate of the sheet due to the heat fixing is corrected in advance.

The test sheet P is used for actual copying, and marks M3 and M4 are formed later.

With the above configuration, the number of rotations or the rotation speed of the drive source can be accurately controlled, and good heat fixing can be achieved by accurate sheet conveyance. Further, it is easy to provide feedback on the fluctuation of the sheet conveying speed.

(Eighth Embodiment) Another image forming apparatus according to the fourth invention has the configuration of the image forming apparatus shown in FIG. 1 except for the configuration shown in FIG. FIG. 8 is a cross-sectional view of a main configuration showing a fixing device, a sheet conveyance path, a sheet conveyance speed detection roller, a conveyance speed detection unit, a control unit, and the like of the image forming apparatus. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is partially omitted.

In FIG. 8, the fixing device 8 G heats and presses the toner image on the sheet P at the nip N between the heating roller 82 and the pressure roller 83, which are pressed and rotated.

The sheet conveying path 93 is a sheet conveying path provided between the transfer section 5A for transferring the toner image onto the sheet P and the nip section N.

The sheet conveying speed detecting roller 98 is provided in the sheet conveying path 93 and presses against the guide plate 99 to contact the sheet P.
The rollers are driven to rotate together with the rollers.

The conveying speed detecting means 94 detects the conveying speed of the sheet P based on the rotation amount of the sheet conveying speed detecting roller 98. The detection is performed when the sheet P is sandwiched between the nip portions N and the sheet P does not exist in the transfer portion 5A.

The control means 100G includes the transport speed detecting means 9
The number of rotations or the rotation speed of a drive source (not shown) of the heating roller 82 or the pressure roller 83 is controlled so as to obtain an appropriate sheet conveyance speed based on the sheet conveyance speed obtained in step 4.

With the above configuration, the number of rotations or the rotation speed of the drive source can be accurately controlled, and good heat fixing can be achieved by accurate sheet conveyance. By performing the measurement at the above timing, the sheet conveyance speed can be accurately detected.

(Ninth Embodiment) Another image forming apparatus according to the fourth aspect of the invention has the configuration of the image forming apparatus shown in FIG. 1 except for the configuration shown in FIG. FIG. 9 is a cross-sectional view of a main configuration of a fixing device, a first temperature detecting unit, a second temperature detecting unit, a mark detecting unit, a passing time measuring unit, a calculating unit, a storing unit, a controlling unit, and the like of the image forming apparatus. . FIG. 10 is a diagram showing the relationship between the stored heating roller temperature, the pressing roller temperature, and the sheet conveying speed. FIG. 11 is more preferable than the heating roller temperature, the pressing roller temperature, and the sheet conveying speed of the test sheet. In the explanatory diagram for obtaining the sheet conveyance speed,
FIG. 12 is a diagram showing the relationship between the stored surface temperature of the heating roller and the change ratio of the rotation speed of the motor to the surface temperature of the pressure roller. The same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is partially omitted.

As shown in FIG. 9, the fixing device 8H heats and presses the toner image on the sheet P at the nip N between the heating roller 82 and the pressing roller 83 which are rotated by pressing and pressing.

The first temperature detecting means TS1 has a heating roller 82
To detect the surface temperature. Further, the second temperature detecting means TS2
Detects the surface temperature of the pressure roller 83.

The mark detecting means 95 detects a plurality of marks M1 and M2 provided on the test sheet P in advance (see FIG. 6B). The mark detecting means 95 is arranged near the discharge side of the nip portion N.

The test sheet P has a plurality of marks M1 and M2 provided at predetermined intervals L in the sheet conveying direction. The passage time measuring means 96 measures the passage time of the interval L between the marks M1 and M2 attached to the test sheet P while the test sheet P passes through the nip portion N (see FIG. 6B). ).

The calculating means 91A calculates the sheet conveying speed based on the measurement result of the passing time. On the other hand, storage means 91B
Stores the relative relationship between the detected temperature of the heating roller and the detected temperature of the pressure roller, as shown in FIG. Further, the test sheet P is conveyed, and the surface temperatures of the heating roller 82 and the pressure roller 83 while the marks M1 and M2 (FIG. 6B) of the test sheet pass through the nip N are detected. The value of the sheet conveyance speed A shown in FIG. 10 is determined from the relationship with the sheet conveyance speed measured by the marks M1 and M2. Further, as shown in FIG. 12, the relationship between the detected temperature of the heating roller, the detected temperature of the pressure roller, and the rotational speed of the motor serving as the driving source so as to achieve the desired sheet conveyance speed is stored. When the temperature of the heating roller and the temperature of the pressure roller change, the rotation speed of the driving source (motor) is controlled based on FIG.

After the test using the test sheet, the control means 100H controls the surface temperature of the heating roller 82 and the pressure roller 8 when passing the sheet having the same configuration as the test sheet P.
3, for example, as shown in FIG.
The number of rotations or the rotation speed of a drive source (not shown) is controlled based on the relationship between the surface temperature of the heating roller 82 and the change ratio of the rotation speed of the motor to the surface temperature of the pressure roller.

Here, the operation will be described with reference to FIGS.
2 and FIG. 6 (b). Here, it is assumed that the desirable sheet conveyance speed is 180 mm / sec. 1) First, the test sheet P is conveyed, and the surface temperature of the heating roller 82 and the surface temperature of the pressure roller 83 while the marks M1 and M2 of the test sheet P are passing through the nip N are measured.
A detection temperature of 150 ° C. for the heating roller 82 and a detection temperature of 140 ° C. for the pressure roller 83 are obtained. 2) The mark detection means 95 detects a plurality of marks M1 and M2 attached to the test sheet P. 3) The transit time measuring means 96 determines the transit time of the interval L between the marks M1 and M2 attached to the test sheet P while the test sheet P passes through the nip N. 4) The sheet conveying speed is calculated from the passing time by the calculating means 91B, and the sheet conveying speed is 178.2 (mm / sec).
Obtain c). 5) The temperature of the heating roller is 150 ° C., the temperature of the pressure roller is 140 ° C., and the sheet conveying speed is 178.2 (mm / sec).
From c), as shown in FIG. 11, the detection temperature of the heating roller on the horizontal axis of FIG.
When the straight line d intersects with 40 ° C., the sheet conveying speed 17
Since 8.2 mm / sec, A = 180.0 (mm
/ Sec). Next, as shown in FIG.
A = 180.
0 (mm / sec) is applied. 6) As shown in FIG. 12, the heating roller or pressure roller motor rotation speed B is determined so that the desired sheet conveyance speed A in the fixing device becomes 180.0 (mm / sec), and the heating roller temperature and the heating roller temperature are calculated. FIG. 12, which is a diagram showing the relationship between the pressure roller temperature and the motor rotation speed, is created and stored. However, it is updated when a new test sheet P is passed. 7) Based on the data shown in FIG. 12, the desired sheet conveying speed 1 is obtained from the change ratio of the motor rotation speed to the detected temperature of the heating roller and the detected temperature of the pressure roller during actual copying.
The motor speed is determined to be 80 mm / sec, and the motor is controlled.

With the above configuration, the drive source (motor)
The rotation speed or the number of rotations can be accurately controlled, and good heat fixing can be achieved by accurate sheet conveyance.

In the embodiment, the color image forming apparatus of the present invention is not limited to the tandem type color image forming apparatus shown in FIG. 1, and the toner images formed on the plurality of image carriers are transferred to a sheet. The present invention is also applicable to a color image forming apparatus of a system in which a superimposed toner image is formed by directly transferring the toner image to P and the superposed toner image is fixed by a fixing device.

Further, in the color image forming apparatus of the present invention, each color toner image sequentially formed on the image carrier is superimposed, and then transferred onto the sheet P once at the transfer section to form a color image. After that, the sheet P is peeled from the image carrier surface,
The present invention is also applicable to a color image forming apparatus in which a superposed toner image is fixed by a fixing device.

[0105]

According to the above configuration, the following effects can be obtained.

According to the image forming apparatus of the first aspect, the OH
In an image forming apparatus capable of copying a T sheet by mode switching, good color copying can be performed with a simple control process. When the toner is made thermoplastic, OH
The transmittance of the T sheet is improved, and a good color copy is obtained.
Further, the amount of color toner adhered to the OHT sheet is made smaller than the amount of toner adhered to the ordinary sheet, so that the transmittance of the OHT sheet is improved and a good color copy is obtained.

According to the image forming apparatus of the second invention, OH
In an image forming apparatus provided with a T image forming mode and a normal sheet image forming mode, the OHT sheet has good color transparency and good separability of the normal sheet. Further, when the color toner used is a styrene acrylic toner, in the case of an OHT sheet, the transmittance is improved and a good color copy is obtained. Further, the oil application roller is pressed against the heating roller only when necessary, so that the durability of the oil application roller is improved.

According to the image forming apparatus of the third aspect of the present invention, since the coating is performed only when necessary, a fixing device having excellent durability of the oil application roller for applying oil to the heating roller can be obtained. When the oil impregnated in the oil application roller is dimethyl silicon and the viscosity is 100 cs or more and 1000 cs or less, the separation performance of the ordinary sheet is improved. If it exceeds this range, the separability of the sheet will decrease. In addition, the amount of oil applied on a normal sheet is 0.1 mg for A4 size or larger.
From 0.3 to 0.3 mg, and from 1.5 to 3 mg for A4 size or smaller, the sheet separation performance is improved. If it exceeds this range, the separability of the sheet will decrease.

According to the image forming apparatus of the fourth aspect, the rotation speed or the number of rotations of the driving source (motor) can be accurately controlled,
Good thermal fixing can be achieved by accurate sheet conveyance.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a cross-sectional view of a main configuration of a fixing device of the image forming apparatus, a sheet circulating path, a transmission detecting unit, a control unit, and the like.

FIG. 3 is a cross-sectional view of a main configuration showing a fixing device of the image forming apparatus, a sheet circulation path, a control unit, and the like.

FIG. 4 is a cross-sectional view of a main configuration showing a fixing device, a first oil application unit, a second oil application unit, a control unit, and the like of the image forming apparatus.

FIG. 5 is a cross-sectional view of a main part configuration showing a fixing device, an oil application unit, a control unit, and the like of the image forming apparatus.

FIG. 6A is a cross-sectional view of a main part configuration showing a fixing device, a mark detection unit, a passage time measurement unit, a control unit, and the like of the image forming apparatus, and FIG. 6B is a plan view of a pre-marked test sheet. FIG.

FIG. 7A is a sectional view of a main part showing a fixing device, a mark forming unit, a mark detecting unit, a passage time measuring unit, a control unit and the like of the image forming apparatus of the present invention, and FIG. It is a top view of the test sheet | seat which was done.

FIG. 8 is a cross-sectional view of a main configuration showing a fixing device, a sheet conveyance path, a sheet conveyance speed detection roller, a conveyance speed detection unit, a control unit, and the like of the image forming apparatus.

FIG. 9 illustrates a fixing device of the image forming apparatus, a first temperature detecting unit,
FIG. 4 is a cross-sectional view of a main configuration including a second temperature detecting unit, a mark detecting unit, a passing time measuring unit, a calculating unit, a storing unit, a controlling unit, and the like.

FIG. 10 is a diagram illustrating a relationship between stored heating roller temperature, pressing roller temperature, and sheet conveyance speed.

FIG. 11 is an explanatory diagram for obtaining a desirable sheet conveyance speed from a heating roller temperature, a pressure roller temperature, and a sheet conveyance speed of a test sheet.

FIG. 12 is a diagram illustrating a relationship between stored surface temperature of a heating roller and a change ratio of a rotation speed of a motor with respect to a surface temperature of a pressing roller.

[Explanation of symbols]

8, 8A to 8H Fixing device 27A, 27B, 27C Circulating paper path 82 Heating roller 83 Pressure roller 85 First oil application unit 86 Second oil application unit 87 Oil application unit 88 Normal sheet detection unit 89 Thick paper detection unit 92 Transmission Rate detecting means 93 Sheet conveying path 94 Conveying speed detecting means 95 Mark detecting means 96 Transit time measuring means 97 Mark forming means 98 Sheet conveying speed detecting rollers 100A to 100H Control means P sheet (test sheet, ordinary sheet, OHT sheet) TS1 First temperature detecting means TS2 Second temperature detecting means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 9/087 G03G 15/00 303 9/09 21/00 384 15/00 303 9/08 361 21/00 384 325 F-term (reference) 2H005 AA01 AA21 CA04 FB02 2H027 DA50 DC02 DE02 EC20 ED25 EE03 EE04 EE07 EF09 FA13 FA30 2H033 AA02 AA46 AA47 BA11 BA32 BA41 BA46 CA01 CA07 CA16 CA26 CA36 CA40 3F100 AAEA02

Claims (19)

[Claims] 1. An image forming apparatus having a double-sided image forming mode and an OHT image forming mode and including a fixing device for thermally fixing a toner image formed on a sheet, wherein the double-sided image forming mode and the OHT image forming mode are provided. Detecting the transmittance of the OHT sheet on which the color toner image is formed by circulating the sheet through which the sheet thermally fixed by the fixing device is again thermally fixed by the fixing device and disposed on the discharge side of the fixing device. Transmittance detecting means, and the OHT
Control means for repeatedly circulating the sheet through the circulating paper path including the transmittance detecting means and thermally fixing the sheet so that the transmittance of the OHT sheet becomes a predetermined value. Image forming device. 2. An image forming apparatus having a double-sided image forming mode and an OHT image forming mode and including a fixing device for thermally fixing a toner image formed on a sheet, wherein the double-sided image forming mode and the OHT image forming mode are provided. And an OHT on which a color toner image is formed by disposing the sheet thermally fixed by the fixing device again on the sheet circulation side of the sheet to be thermally fixed by the fixing device and the discharge side of the fixing device.
A transmittance detecting means for detecting the transmittance of the sheet;
The transmittance of the color toner image formed on the T sheet after the first heat fixing is measured by the transmittance detecting means, the number of circulations in the circulation paper passage is determined based on the value of the transmittance, and the OHT sheet is circulated. An image forming apparatus comprising: a control unit configured to control so as to circulate the circulating paper path by a number of times to perform heat fixing. 3. The color toner used for the OHT sheet is thermoplastic.
An image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 1, wherein the amount of color toner adhered on the OHT sheet is smaller than the amount of toner adhered on a normal sheet. 5. An image forming apparatus having an OHT image forming mode and a normal sheet image forming mode, and comprising a fixing device for thermally fixing a toner image on a sheet by heating and pressing the toner image with a heating roller and a pressure roller. A first oil application unit having a first oil application roller for applying an oil for a normal sheet so as to be able to contact and separate from the heating roller; and a second oil application roller for applying oil for an OHT sheet so as to be able to attach and detach to the heating roller. A second oil application unit having a first oil application roller pressed against the heating roller only in the ordinary sheet image forming mode, and only a second oil application roller applied to the heating roller in the OHT image formation mode. An image forming apparatus comprising: a control unit configured to perform pressure contact. 6. In a normal sheet image forming mode, only the first oil application roller is pressed against the heating roller while the normal sheet passes through the heating roller, and in the OHT image forming mode, the OHT sheet is in contact with the heating roller. The image forming apparatus according to claim 5, wherein only the second oil application roller is pressed against the heating roller during the passage through the heating roller. 7. The image forming apparatus according to claim 5, wherein the material of the toner used for the OHT sheet or the ordinary sheet is a styrene acrylic toner. 8. An image forming apparatus having at least an OHT image forming mode and having a fixing device for heat-pressing and thermally fixing a toner image on a sheet by a heating roller and a pressure roller, to press or release the heating roller. An image forming apparatus, comprising: an oil application unit having an oil application roller as much as possible; and a control unit controlling to release the oil application roller from the heating roller when an OHT sheet is used. 9. It has at least a cardboard image forming mode,
An image forming apparatus including a fixing device that heats and presses a toner image on a sheet by a heating roller and a pressure roller to thermally fix the toner image, comprising: an oil application unit having an oil application roller that can be pressed against or released from the heating roller; Thick paper detecting means for detecting thick paper having a weight per unit of 105 g / m ² or more; and control means for controlling the oil application roller to be released from the heating roller when the thick paper is detected. An image forming apparatus comprising: 10. An image forming apparatus having a fixing device for thermally fixing a toner image on a sheet by applying heat and pressure by a heating roller and a pressure roller, wherein an oil application roller having an oil application roller capable of being pressed against or released from the heating roller. Means, a detection means for detecting a normal sheet having a mass per unit area of 75 g / m ² or less, and a control means for controlling the oil application roller to press against the heating roller when the normal sheet is detected. An image forming apparatus comprising: 11. The amount of oil applied to the sheet is A4
For sizes larger than 0.1 mg to 0.3 mg, and A
The image forming apparatus according to claim 10, wherein the size of the image forming apparatus is 1.5 mg to 3 mg when the size is 4 or less. 12. The oil impregnated in the oil application roller is dimethyl silicone oil and has a viscosity of 10%.
The image forming apparatus according to claim 9, wherein the image forming apparatus has a length of 0 cs or more and 1000 cs or less. 13. An image forming apparatus provided with a fixing device for heat-pressing and thermally fixing a toner image on a sheet by pressing and rotating at a nip portion between a heating roller and a pressure roller, which presses and rotates the toner image on the test sheet in advance in a sheet conveying direction. Mark detecting means for detecting a plurality of marks separated by a predetermined distance from each other; passing time measuring means for measuring a passing time of the plurality of mark intervals while the test sheet passes through the nip portion; Control means for controlling the number of rotations or the rotation speed of the drive source of the heating roller or the pressure roller based on the measurement result of the above. 14. An image forming apparatus provided with a fixing device that heats and presses a toner image on a sheet by pressing and rotating at a nip portion between a heating roller and a pressure roller, and heat-fixes the toner image on the sheet. Mark forming means for forming a plurality of marks spaced apart from each other by a predetermined distance, mark detecting means for detecting the plurality of formed marks, and the plurality of mark intervals while the test sheet passes through the nip portion. And a rotation time of the drive source of the heating roller or the pressure roller when a sheet having the same configuration as the subsequent test sheet is passed based on the measurement result of the passage time. An image forming apparatus, comprising: control means for controlling the number or rotation speed. 15. The method according to claim 13, wherein the mark detecting means is disposed near the sheet discharge side of the nip portion, and a rate of expansion and contraction of the test sheet due to thermal fixing is smaller than a predetermined rate of expansion and contraction. The image forming apparatus as described in the above. 16. The image forming apparatus according to claim 1, wherein the mark detecting unit is disposed near the sheet discharge side of the nip portion, and when controlling a driving source of the heating roller or the pressure roller based on a measurement result of a passing time, the mark detection unit performs heat fixing. The image forming apparatus according to claim 14, wherein the expansion / contraction ratio of the sheet due to the correction is corrected in advance. 17. An image forming apparatus provided with a fixing device that heat-presses and thermally fixes a toner image on a sheet at a nip portion between a heating roller and a pressure roller that are pressed and rotated, and transfers the toner image onto the sheet. A sheet conveyance path between a transfer portion and the nip portion, a sheet conveyance speed detection roller that contacts and follows a sheet in the sheet conveyance path, and conveyance that detects a conveyance speed based on a rotation amount of the sheet conveyance speed detection roller. Speed detection means, and control means for controlling the number of rotations or the rotation speed of the drive source of the heating roller or the pressure roller based on the sheet conveyance speed detected by the conveyance speed detection means, Image forming apparatus. 18. When the sheet is nipped by the nip portion and the sheet does not exist in the transfer portion,
18. The method according to claim 17, wherein a sheet conveying speed is detected.
An image forming apparatus according to claim 1. 19. An image forming apparatus having a fixing device for applying heat and pressure at a nip portion of a heating roller and a pressure roller which presses and rotates a toner image on a sheet and thermally fixing the toner image, the surface temperature of the heating roller is detected. A first temperature detecting means for detecting the temperature of the pressure roller, a second temperature detecting means for detecting a surface temperature of the pressure roller, and a mark detecting means for detecting a plurality of marks provided on the test sheet at predetermined intervals in the sheet conveying direction. ,
Passing time measuring means for measuring a passing time of the plurality of mark intervals while the test sheet passes through the nip portion; calculating means for calculating a sheet conveying speed based on the measurement result of the passing time; A storage unit for storing the relationship between the surface temperature of the heating roller, the surface temperature of the pressure roller, and the sheet conveying speed after passing the sheet, and passing the sheet having the same configuration as the test sheet after the test using the test sheet. Control means for controlling the number of rotations or the rotation speed of a drive source of the heating roller or the pressure roller based on a detection result of the surface temperature of the heating roller and the surface temperature of the pressure roller when paper is formed. An image forming apparatus characterized in that: