JP2001324890A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that improves the ability to fix image to an OHP sheet or cardboard, can obtain a satisfactorily fixed image free from image irregularity, image slippage, and muddy color, and can be made smaller in the size of its outer shape. SOLUTION: In the image forming device 1 having a specific recording mode for decreasing the paper carrying speed of a fixing device 217, a carrying distance L between a transfer point of a transfer part, which transfers a toner image formed on a photoreceptor 222d, and a fixing point of the fixing device 2, which fixes the toner image transferred to the recording medium to the recording medium by a heat roller 71, is shorter than the length Lp of the recording medium in the recording medium carrying direction. Further, the carrying distance L is longer than a difference between the length Lp of the recording medium in the carrying direction and the circumference πD of the heat roller 71. When the heat roller 71 makes one rotation, the recording medium is separated from the transfer point of the transfer part. Therefore, the toner is satisfactorily fixed to the recording medium despite a decrease in the fixing speed of the heat roller 71.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic color image forming apparatus for forming a color image on a recording medium using a plurality of color toners, and more particularly, to a method for forming a toner image on a transparent member for an overhead projector or a thick sheet of paper. The present invention relates to an image forming apparatus to be formed.

[0002]

2. Description of the Related Art In an electrophotographic color image forming apparatus for forming a color image on a recording medium using toners of a plurality of colors, an overhead projector is used.
ctor) (hereinafter referred to as OHP sheet)
When forming an image on thick paper or thick paper, by sufficiently melting the toner of each color, the reflection at the boundary surface of the toner can be reduced and the transparency of the toner can be increased, and the color turbidity can be improved. And a vivid color image without blemishes can be obtained. In order to form such a good color image on an OHP sheet or cardboard, a technique relating to the following apparatus has been disclosed.

[0003] That is, Japanese Patent Application Laid-Open No. 49-73141 discloses a structure in which the running speed of a recording sheet is controlled in accordance with the thickness of the recording sheet, so that the recording sheet can be satisfactorily fixed from a thin recording sheet to a thick recording sheet. A technique relating to a fixing device is disclosed. This fixing device controls the running speed according to the thickness of the recording paper and feeds the recording paper at a constant speed.

However, when a toner image is fixed on a recording sheet, the fixing roller usually rotates on the recording sheet a plurality of times. Therefore, the surface temperature of the fixing roller changes. Therefore, even though the toner image can be fixed satisfactorily in the first half of the recording paper conveyance direction, the fixing temperature of the fixing roller decreases in the second half of the recording paper conveyance direction. is there.

[0005] In order to solve the above problem, Japanese Utility Model Publication No.
Japanese Patent Application Laid-Open Publication No. H11-163,086 discloses a technique relating to a fixing device of a copying machine in which the rotation speed of a fixing roller is reduced in a predetermined shift pattern within one copy cycle.

However, in the fixing device of this copying machine, the relationship between the rotation amount of the fixing roller and the temperature drop has not been considered. That is, when the fixing roller fixes the toner image on the recording paper, the fixing roller rotates two or more times.
No consideration was given to the fact that the temperature drop becomes significant after the rotation.

Therefore, Japanese Patent Application Laid-Open No. 8-95422 discloses that after the recording paper enters the fixing roller,
There is disclosed a technology relating to an image forming apparatus in which the rotation speed of a fixing roller is reduced as the recording paper passes after rotation. In this image forming apparatus, in the first rotation after the recording paper with little decrease in the surface temperature of the fixing roller enters the fixing roller, the fixing roller is driven at a constant speed, and the conveyance of the recording paper is unnecessarily delayed. There is no. Further, since the subsequent rotation speed is reduced as the recording paper passes, even if the temperature of the fixing roller surface decreases, the amount of heat required for fixing is given to the toner image over the entire surface, and good fixing is achieved. The processing is performed over the entire surface of the recording paper, and the gloss of the image is also uniform over the entire surface.

[0008]

However, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 8-95422,
A transport means such as a transport deck is required for transporting the sheet between the transfer section and the fixing section, and there has been a problem that the apparatus is complicated and the cost is increased. Further, since the distance between the transfer portion and the fixing portion was not taken into consideration, the distance between the two was unclear. Furthermore, it is unclear about the case of transferring an image to a special recording material such as an OHP sheet or cardboard.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to improve the fixability of an image on an OHP sheet or a thick paper, and to provide a good fixed image free from image unevenness and image shift without color turbidity. And an image forming apparatus capable of reducing the external size of the apparatus.

[0010]

The present invention has the following arrangement as means for solving the above-mentioned problems.

(1) a transfer section for transferring the toner image formed on the photoreceptor to a recording medium; and a fixing section for fixing the toner image transferred to the recording medium onto the recording medium by a fixing roller. In an image forming apparatus having a specific recording mode in which a conveyance speed of a recording medium in a fixing unit is reduced, a conveyance distance interval L between a transfer point of the transfer unit and a fixing point of the fixing unit, and a length of the recording medium in a conveyance direction. Lp and the circumference πD of the fixing roller have a relationship represented by Lp>L> (Lp−πD).

In this configuration, in an image forming apparatus having a specific recording mode in which the conveyance speed of the recording medium at the fixing unit is reduced, the transfer point of the transfer unit for transferring the toner image formed on the photoreceptor to the recording medium is determined. The distance L between the fixing point and the fixing point of the fixing unit for fixing the toner image transferred to the recording medium onto the recording medium by the fixing roller is smaller than the length Lp of the recording medium in the conveying direction. It is larger than the difference between the length Lp and the circumference πD of the fixing roller.
Therefore, when the fixing roller rotates at least one time, the recording medium separates from the transfer point of the transfer unit. Therefore, even if the fixing speed is reduced after one rotation of the fixing roller, the fixing of the toner to the recording medium can be performed without transfer deviation. Can do it. In addition, since the distance between the fixing unit and the transfer unit can be shorter than the length of the recording medium in the conveyance direction, there is no need to provide a recording medium conveyance mechanism for conveyance, and the size of the image forming apparatus can be reduced. It is possible to minimize a decrease in image forming speed when executing the specific mode.

(2) Length Lp of the recording medium in the transport direction
Is the length in the widthwise direction of a standard size recording medium used in the specific recording mode.

In this configuration, the length in the short direction of the standard size recording medium used in the specific recording mode is the length Lp in the transport direction of the recording medium. Therefore, the distance between the fixing unit and the transfer unit can be further reduced, the size of the image forming apparatus can be reduced, and the reduction in image forming speed in the specific recording mode can be minimized.

(3) Length detecting means for detecting the length Lp of the recording medium in the transport direction, type detecting means for detecting the type of the recording medium, notifying means for notifying the state of the apparatus, and each means of the apparatus And a controller for controlling the length L of the recording medium in the transport direction when the specific recording mode is executed.
When it is detected that p is equal to or longer than the length in the short direction of the standard size recording medium used in the specific recording mode, and when the type detecting unit detects the standard size recording medium used in the specific recording mode, The notifying unit notifies the user of the fact, and the control unit prohibits image formation in the specific recording mode.

In this configuration, when the specific recording mode is executed, the length Lp of the recording medium in the image forming apparatus in the transport direction is equal to or longer than the length of the standard size recording medium used in the specific recording mode in the transverse direction. Is detected by the length detecting means for detecting the length Lp of the recording medium in the transport direction, and the standard size recording medium used in the specific recording mode is detected by the type detecting means for detecting the type of the recording medium. And a notifying unit for notifying the state of the apparatus that the length Lp of the standard size recording medium used in the specific recording mode in the transport direction is equal to or greater than the length of the recording medium in the width direction. The control unit that controls each unit prohibits image formation in the specific recording mode. Therefore, it is possible to prevent the formation of a poor image in which transfer deviation has occurred due to an incorrectly set recording medium.

(4) When the specific recording mode is executed, the length Lp of the recording medium in the transport direction by the length detecting means is longer than the length of the standard size recording medium used in the specific recording mode in the transverse direction. When detecting that the type detection unit detects a recording medium other than the standard size recording medium used in the specific recording mode, the control unit,
In addition to prohibiting image formation in the specific recording mode, the image forming apparatus waits until input of execution of image formation in another mode is input to the input unit, and the notification unit determines whether image formation in another mode is executable. In this case, it is notified that the input standby state has been entered.

In this configuration, when the specific recording mode is executed, the length Lp of the recording medium in the transport direction by the image forming apparatus is equal to or greater than the length in the transverse direction of the standard size recording medium used in the specific recording mode. Is detected by the length detecting means, and when the type detecting means detects a recording medium other than the standard size recording medium used in the specific recording mode, the image formation in the specific recording mode is prohibited, and in another mode, The control unit waits until the execution of the image formation is input to the input unit, and the notification unit notifies the input standby state of the image formation execution in another mode. Therefore, when using a recording medium other than the standard size recording medium used in the specific recording mode, the recording mode can be selected according to the size of the recording medium.

(5) In the configurations of (2) to (4), the standard size recording medium used in the specific recording mode can be an OHP sheet.

In this configuration, the OHP sheet is a recording medium of a standard size used in a specific recording mode.
Therefore, an image can be reliably formed on the OHP sheet. In addition, since the OHP sheet does not generally have a size other than the standard size, it can be prohibited to use the OHP sheet in a direction other than the specified conveyance direction.

[0021]

FIG. 1 is a schematic configuration diagram of a digital color copying machine 1 which is an image forming apparatus according to an embodiment of the present invention. A document table 111 and an operation panel are provided on an upper surface of the copying machine main body 1, and an image reading unit 110 and an image forming unit 210 are provided inside the copying machine main body 1. The upper surface of the platen 111 is supported so as to be openable and closable with respect to the platen 111, and has a predetermined positional relationship with respect to the upper surface of the platen 111.
ADF; Recirculating Automatic Document Feeder)
112 is mounted.

First, the double-sided automatic document feeder 112 conveys a document such that one side of the document faces the image reading unit 110 at a predetermined position on the document table 111. Then, after the image reading on one side is completed, the document is inverted so that the other side faces the image reading unit 110 at a predetermined position on the document table 111 and the document table 1
11 is conveyed. Then, after the two-sided image reading for one document is completed, the double-sided automatic document feeder 112 discharges this document and performs a double-sided conveyance operation for the next document.

The above-described operation of conveying the document and reversing the front and back is as follows.
It is controlled in relation to the operation of the entire copying machine.

The image reading unit 110 is arranged below the document table 111 for reading an image of a document conveyed onto the document table 111 by the automatic duplex document feeder 112. The image reading unit 110 includes the platen 11
Document scanning body 11 reciprocating in parallel along the lower surface of document 1
3, 114, an optical lens 115, and a CCD line sensor 116 as a photoelectric conversion element.

The original scanning bodies 113 and 114 are composed of a first scanning unit 113 and a second scanning unit 114. The first scanning unit 113 has an exposure lamp for exposing the surface of the original image, and a first mirror for deflecting the reflected light image from the original in a predetermined direction. Are reciprocated in parallel at a predetermined scanning speed while maintaining the above distance. The second scanning unit 114 is the first scanning unit 113
It has second and third mirrors for deflecting the reflected light image from the original deflected by the mirror in a predetermined direction, and reciprocates in parallel with the first scanning unit 113 while maintaining a constant speed relationship. Things that move.

The optical lens 115 forms a reflected light image from the document deflected by the third mirror of the second scanning unit 114 at a predetermined position on the CCD line sensor 116.

The CCD line sensor 116 sequentially converts the formed light images into photoelectric signals and outputs them as electric signals. The CCD line sensor 116 is a three-line color CCD capable of reading a black-and-white image or a color image and outputting line data separated into R (red), G (green), and B (blue) color components. . The document image information converted into an electric signal by the CCD line sensor 116 is further transferred to an image processing unit (not shown) and subjected to predetermined image data processing.

Next, the configuration of the image forming unit 210 and the configuration of each unit related to the image forming unit 210 will be described.

Below the image forming section 210, there is provided a sheet feeding mechanism 211 for separating the sheets (recording media) P stored and stored in the sheet tray one by one and supplying them to the image forming section 210. Have been. Then, the sheets P separated and supplied one by one are conveyed to the image forming unit 210 at a controlled timing by a pair of registration rollers 212 disposed in front of the image forming unit 210. Further, the sheet P on which an image is formed on one side is re-supplied and conveyed to the image forming unit 210 in synchronization with the image formation of the image forming unit 210.

On one side of the copying machine body 1, a manual feed tray 201 is provided with one end extending outside the apparatus so that the paper P can be manually fed. The paper placed on the manual tray 201 is conveyed to the image forming unit 210. The manual feed tray 201 is provided with a sensor A202 for detecting the presence or absence of a sheet placed thereon, a sensor B203 for detecting the type of sheet, and a sensor C204 for detecting the direction of the sheet with respect to the transport direction.

Below the image forming section 210, a transfer and transport belt mechanism 213 is disposed. The transfer / transport belt mechanism 213 is provided between the drive roller 214 and the driven roller 215 to extend substantially in parallel to the transfer / transport belt 2.
The sheet P is electrostatically attracted to the sheet 16 and transported.

Further, a fixing device 21 for fixing the toner image transferred and formed on the sheet P to the sheet P downstream of the transfer and conveyance belt mechanism 213 in the sheet conveyance path.
7 are arranged. The sheet P having passed through the nip between the pair of fixing rollers of the fixing device 217 passes through a conveyance direction switching gate 218 and is discharged by a discharge roller 219 onto a discharge tray 220 attached to the other side surface of the copying machine main body 1. Is discharged.

The switching gate 218 is connected to the sheet P after fixing.
Is selectively switched between a path for discharging the sheet P to the copying machine main body 1 and a path for re-supplying the sheet P toward the image forming unit 210. The sheet P whose transport direction has been switched again toward the image forming unit 210 by the switching gate 218 is turned upside down via the switchback transport path 221, and then the image forming unit 210 is turned over.
Is supplied again.

Above the transfer belt 216 in the image forming section 210, a first image forming station Pa, a second image forming station Pb, and a third image forming station are disposed adjacent to the transfer belt 216. P
c and a fourth image forming station Pd are arranged in order from the upstream side of the sheet transport path.

The transfer conveyance belt 216 is driven by the driving roller 21.
1, the sheet P is frictionally driven in the direction indicated by the arrow Z in FIG.
Conveyed sequentially to Pd.

Each of the image forming stations Pa to Pd has substantially the same configuration. Each of the image forming stations Pa, Pb, Pc, and Pd is a photosensitive drum 222a, 222 that is driven to rotate in the direction of arrow F shown in FIG.
b, 222c and 222d, respectively.

Around the photosensitive drums 222a to 222d, chargers 223a, 223b, 223c, 22 for uniformly charging the photosensitive drums 222a to 222d, respectively.
3d and developing devices 224a and 224 for developing electrostatic latent images formed on the photosensitive drums 222a to 222d, respectively.
4b, 224c, 224d and transfer dischargers 225a, 225b, 225c, 225d for transferring the developed toner images on the photosensitive drums 222a to 222d to the paper P.
Cleaning devices 226a, 226b, and 2 for removing toner remaining on photoconductor drums 222a to 222d.
26c and 226d are the photosensitive drums 222a to 222d.
They are sequentially arranged along the rotation direction of d.

Each of the photosensitive drums 222a to 222d
Above the laser beam scanner unit 227a,
227b, 227c and 227d are provided respectively. Laser beam scanner units 227a-22
Reference numeral 7d denotes a semiconductor laser element (not shown) for emitting dot light modulated in accordance with image data, and polygon mirrors (deflecting devices) 240a to 240d for deflecting a laser beam from the semiconductor laser element in the main scanning direction.
Lenses 241a to 241d, 2 for imaging the laser beams deflected by the polygon mirrors 240a to 240d on the surfaces of the photosensitive drums 222a to 222d.
42a to 242d and mirrors 243a to 243d.

The laser beam scanner 227a receives a pixel signal corresponding to the black component image of the color original image, and the laser beam scanner 227b receives a pixel signal corresponding to the cyan component image of the color original image.
A pixel signal corresponding to the magenta component image of the color original image is input to 7c, and a pixel signal corresponding to the yellow component image of the color original image is input to the laser beam scanner 227d.

As a result, the electrostatic latent images corresponding to the color-converted original image information are transferred to the respective photosensitive drums 222a to 222a.
d. The developing device 227a contains a black toner, the developing device 227b contains a cyan toner, the developing device 227c contains a magenta toner, and the developing device 227d contains a yellow toner. . Then, the photosensitive drums 222a to 222d
The upper electrostatic latent image is developed with each of these color toners. As a result, the document image information color-converted by the image forming unit 210 is reproduced as a toner image of each color.

Further, between the first image forming station Pa and the paper feeding mechanism 211, a paper suction (brush) charger 228 is provided. This adsorption charger 228
Charges the surface of the transfer conveyance belt 216. Then, the sheet P supplied from the sheet feeding mechanism 211 is moved from the first image forming station Pa to the fourth image forming station Pd without being displaced in a state where the sheet P is securely attracted onto the transfer conveyance belt 216. Conveyed.

On the other hand, a static eliminator 229 is provided almost directly above the drive roller 214 between the fourth image forming station Pd and the fixing device 217. An AC current for separating the paper P electrostatically attracted to the transport belt 216 from the transfer transport belt 216 is applied to the neutralizer.

In the digital color copying machine 1 having the above configuration, cut sheets of paper stored in a paper cassette are used as the paper P. Further, OHP sheets or cardboard of a predetermined size can be used by setting the tray on the manual feed tray 201. The paper P is sent out from the paper feed cassette or the manual feed tray 201 and is fed to the paper feed mechanism 211.
Is fed into the guide of the paper feed conveyance path of the
Is detected by a sensor (not shown), and is temporarily stopped by a pair of registration rollers 212 based on a detection signal output from the sensor.

Then, the paper P is fed onto the transfer / conveying belt 216 rotating in the direction of the arrow Z shown in FIG. 1 at the timing of each of the image forming stations Pa to Pd.
At this time, since the transfer / transport belt 216 is given a predetermined charge by the attraction charger 228 as described above, the paper P is stably transported and supplied while passing through the image forming stations Pa to Pd. Is done.

In each of the image forming stations Pa to Pd, a toner image of each color is formed, and is superposed on the support surface of the paper P conveyed by being electrostatically attracted and conveyed by the transfer conveyance belt 216. When the transfer of the image by the fourth image forming station Pd is completed, the sheet P is sequentially transferred from the leading end portion thereof by the neutralizer 229 to the transfer / conveying belt 2.
16 and is guided to the fixing device 217. The sheet P on which the toner image has been fixed by the fixing device 217
Is discharged onto a paper discharge tray 220 from a paper discharge port (not shown).

In the above description, the laser beam is scanned and exposed by the laser beam scanner units 227a to 227d to write light on the photosensitive member. However, the laser beam scanner unit 22
Instead of 7a to 227d, a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used. The LED head is smaller in size than the laser beam scanner unit and operates silently because there is no movable part. Therefore, an LED head can be suitably used in an image forming apparatus such as a tandem digital color copying machine that requires a plurality of optical writing units.

Next, the fixing device 2 in the image forming apparatus 1
17 will be described. FIG. 2 is a cross-sectional view illustrating a schematic configuration of the fixing device 217. The fixing device 217 includes a heating roller 71 that is a pair of rollers that press against each other with a predetermined nip pressure.
And a pressure roller 72. Heating roller 71
The pressure roller 72 rotates in directions opposite to each other as indicated by arrows in the figure, and heats and presses a recording material P, which is a recording medium passing between the two. The heating roller 71 located on the upper side has a hollow cylindrical shape and includes an upper heater lamp 73 inside. The pressure roller 72 also has a hollow cylindrical shape, and includes a lower heater lamp 74 inside.

On the upstream side of the fixing device 217 in the conveying direction of the recording material P, fixing is performed to guide the recording material P conveyed from the image forming station Pd to the nip portion of the heating roller 71 and the pressure roller 72. A front guide 70 is provided.

A pressure roller 7 is provided around the heating roller 71.
2, the upper peeling claw 81, the upper cleaning roller 79, the upper thermistor 75, and the upper oil application roller 77 contact the surface of the heating roller 71 from the upstream side to the downstream side. Is provided.
Further, around the pressure roller 72, with the pressure contact portion with the heating roller 71 as the upstream side, from the upstream side to the downstream side,
The lower peeling claw 82, the lower cleaning roller 80, and the lower thermistor 76 are provided in contact with the surface of the pressure roller 72, respectively.

The upper peeling claw 81 is provided with its acute-angled tip abutting on the surface of the heating roller 71, and the lower peeling claw 82 is provided with its acute-angled tip abutting on the surface of the heating roller 71. The upper peeling claw 81 and the lower peeling claw 82 are formed such that the recording material P having completed the fixing is heated roller 71 or pressure roller 72.
When the recording material P adheres to the surface of the recording material P, the recording material P is peeled off.

The upper cleaning roller 79 and the lower cleaning roller 80 clean the surfaces of the heating roller 71 and the pressure roller 72, respectively.

Upper thermistor 75 and lower thermistor 7
6 is for measuring the surface temperature of the heating roller 71 and the pressure roller 72, respectively.

The oil application roller 77 includes a heating roller 71
This is for applying oil to the surface of the recording medium, and prevents the toner on the recording material from adhering to the surface of the heating roller 71.

Next, control of each section in the image forming apparatus 1 will be described. FIG. 3 is a block diagram showing the relationship between the control unit 31 and each unit. The components described below are connected to the control unit 31, and the components are controlled by exchanging signals. That is, the image reading unit 110, the display / input unit 41, the sensor A202, the sensor B203, the sensor C204, the image processing unit 51, the image memory 52, the main motor drive circuit 66, the fixing motor drive circuit 65, the lower heater lamp power supply 64, the lower The thermistor 76, the upper heater lamp power supply 63, and the upper thermistor 75 are connected to the controller 31 respectively.

The image processing section 51 includes an image forming section 21.
0, the main motor drive circuit 66 has a main motor 86
However, the fixing motor drive circuit 65 includes a fixing motor 85, the lower heater lamp power supply 64 includes a lower heater lamp 74,
The upper heater lamp power supply 63 includes an upper heater lamp 73.
Are connected respectively.

Next, the distance relationship between the fixing device in the image forming apparatus 1 of the present invention and the transfer section of the image forming station will be described. FIG. 4 is an arrangement diagram showing a relationship between the fixing device and a transfer unit of the image forming station.

When the fixing device 217 fixes the toner image on the recording material P, the surface temperature of the heating roller 71 is substantially constant at the first rotation. However, if the heating roller 71 is 1
When the heating roller 71 rotates, the surface temperature of the heating roller 71 decreases after the second rotation since heat is taken off by contact with the recording material P. Therefore, after the second rotation of the heating roller 71, the feeding speed of the recording material P by the fixing device 217, that is, the heating roller 7
By reducing the rotation speed of the recording medium P, the toner image is reliably fixed on the recording material P.

In the present invention, in order to reliably fix a color image on an OHP sheet or cardboard as a specific recording mode, the fixing device 217 and the transfer section of the image forming station Pd are used in addition to the above-described method. The arrangement is as shown in FIG. That is, the photosensitive drum 222d which is the transfer point of the transfer unit in the fourth image forming station Pd which is the most downstream of the image forming unit in the image forming apparatus 1.
Contact portion between the transfer device 225 d and the transfer discharge device 225 d, and the fixing device 217
Heating roller 71 and pressure roller 72 as fixing points
And L, the transport distance interval, which is the distance between the contact portion and the contact portion. Further, when the length of the recording material P, which is a recording medium, in the transport direction is Lp, and the circumferential length of the heating roller 71 is πD, the heating roller 71 is arranged so as to maintain the relationship represented by Lp>L> (Lp−πD). Further, when the toner image is fixed, when the heating roller 71 makes one rotation, the paper conveying speed of the fixing device 217 is reduced to a predetermined speed.

The transport distance L between the transfer point of the transfer section at the fourth image forming station Pd and the fixing point of the fixing device 217 is smaller than the length Lp of the recording material P in the transport direction. It is not necessary to provide a movable transfer device, and only a guide or the like may be provided.

The transport distance L between the transfer point of the transfer section at the fourth image forming station Pd and the fixing point of the fixing device 217 is determined by the length Lp of the recording material P in the transport direction and the length of the heating roller 71. Because of the difference from the circumference πD, when the heating roller 71 makes one rotation, the recording material P is not sandwiched between the photosensitive drum 220d and the transfer discharger 225d. Therefore, even if the rotation speeds of the heating roller 71 and the pressure roller 72 are reduced, there is no fixing device 217 that sandwiches the recording material P, so that image unevenness and image displacement do not occur.

By setting the length Lp of the recording material P in the conveying direction to the widthwise direction of the recording material P, the transfer point of the transfer section in the fourth image forming station Pd and the fixing device 2
It is possible to further reduce the transport distance interval L between the fixing point 17 and the fixing point 17.

The effect of the configuration shown in FIG. 4 was confirmed by conducting an experiment with the following configuration. An OHP sheet was used as a standard size recording medium used in the specific recording mode. OHP sheet is letter size (8.5 inch)
X 11 inch) and A4 size (210mm x 297m)
m) are generally commercially available sizes.

The temperature of the heating roller 71 of the fixing device 217 is determined based on the temperature detected by the upper thermistor 75 provided in contact with the heating roller 71, based on the temperature of the upper heater lamp power supply 6.
The control was performed by energizing the upper heater lamp 73 and the lower heater lamp 74 by the power source 64 and the lower heater lamp 64. When the fixing operation is on standby, the upper heater lamp 73 is set at 650 W, and the lower heater lamp 74 is set at 650 W.
Was turned on and off at 450 W, and was controlled so that the surface temperature of the heating roller 71 became 180 ° C. Further, during the fixing operation, the upper heater lamp 73
On-off control is performed at 950 W, and the lower heater lamp 74 is controlled.
The energization to was stopped. Then, the surface temperature of the heating roller was controlled to 180 ° C., the same as during standby.

The diameter of the heating roller 71 and the pressure roller 72 was 40 mm. Therefore, the circumference is 40π (12
5.7 mm). Further, the image forming station Pd
The distance L between the transfer point and the fixing point of the fixing device 271 was 120 mm. This is a letter size O
8.5 inches (216 inches) in the widthwise direction of the HP sheet
mm) and the circumference πD of the heating roller 71 (125.7 mm)
Is 90.3 mm, so that 216 mm and 90.
It was 120 mm, which was between 3 mm.

[0065]

[Table 1]

Table 1 is a table showing the relationship between the conditions of the fixing device and the transparency of OHP in each recording mode. In the experiment under the above conditions, the fixing device 21 in the normal recording mode was used.
7, the first rotation of the heating roller 71 is 117 m.
m / s and the second rotation were also 117 mm / s. In the specific recording mode, the transport speed of the fixing device 217 is set to
The first rotation of the heating roller 71 was 117 mm / s, and the second rotation was 104 mm / s. In this case, in both the normal recording mode and the specific recording mode, the surface temperature of the fixing roller is 180 ° C. at the first rotation of the heating roller 71 and 2 degrees.
The number of revolutions was 164 ° C.

As a result of fixing the color image on the OHP sheet, in the normal recording mode, the first rotation of the heating roller 71 was good, but the transparency gradually deteriorated at the second rotation, and the transparency near the terminal end. Became bad.

On the other hand, in the specific recording mode, OHP
The transparency of the sheet was good at both the first rotation and the second rotation of the heating roller 71.

The letter-sized OHP used in the experiment was used.
Since the length of the sheet in the width direction is 216 mm, in the fixing device 217, the fixing is completed when the heating roller 71 makes two turns.

As described above, the surface ambient temperature of the heating roller 71 decreases by 13 ° C. in the second rotation of the heating roller 71 with respect to the first rotation. However, as shown in FIG. 4, the transport distance L between the transfer point of the transfer unit in the fourth image forming station Pd and the fixing point of the fixing device 217 is set, and the transport speed of the fixing device 271 is set to 1
When the heating roller 71 is reduced by about 11% from 17 mm / s to 104 mm / s, good transparency can be obtained in the second rotation of the heating roller 71 as in the first rotation.

Although the experimental results are shown only for the OHP sheet, similarly, good permeability can be obtained even with a cardboard having a predetermined thickness.

Next, an image forming procedure in the image forming apparatus 1 will be described. FIG. 5 is a flowchart illustrating an image forming procedure of the image forming apparatus 1. When an image is formed on an OHP sheet or thick paper in the specific recording mode in the image forming apparatus 1, the OHP sheet or thick paper is set on the manual feed tray 201. Also,
The image forming apparatus 1 can execute a normal recording mode in which the sheet conveyance speed of the fixing device 217 is not reduced halfway in addition to the specific recording mode.

When an image is formed by the image forming apparatus 1,
First, the user performs a specific recording mode for forming an image on an OHP sheet or a cardboard from the display / input unit 41,
Or, select the normal recording mode (step 30).
1). When performing the normal recording mode, the image forming apparatus 1
The original is set on the original platen 111 or the automatic two-sided automatic document feeder 112, and a start button (not shown) is pressed to form a normal image (step 316). The control unit 31 of the image forming apparatus 1 checks whether or not the sheet has been discharged (step 317). Since the sheet conveying speed of the fixing device 217 has not been reduced, nothing is performed (step 318), and the image formation is performed as it is. To end.

On the other hand, when the user selects the specific recording mode, the user sets an OHP sheet or cardboard on the manual feed tray. The control unit 31 detects whether or not there is a sheet in the manual feed tray by the sensor A202 (step 302). If paper is set on the manual feed tray 201, whether or not the paper is an OHP sheet is detected by the sensor B203 as type detection means (step 303). The paper set in the bypass tray 201 is
If the sheet is an HP sheet, then OH
Whether or not the short direction of the P sheet is set is detected by the sensor C204 as the length detecting means (step 304). When the longitudinal direction of the OHP sheet is set in the sheet conveyance direction, the control unit 31 prohibits image formation and displays “OH” on the display / input unit 41 that is a notification unit.
Change the direction of the P sheet. Is displayed (step 305). And step 3 again
02 is performed.

On the other hand, if the short direction of the OHP sheet is set in the paper transport direction, and if the above-mentioned warning message is displayed, a warning message is displayed on the display unit display input unit 41 (step 306). . Then, the control unit 31 confirms whether or not the user has pressed the start button (step 307). When the display / input unit 41 notifies that the start button has been pressed, the control unit 31 forms an image (step 308). Then, the control unit 31 checks whether or not the transfer of the image has been completed (step 309).

Next, in the fixing device 217, the control section 31 checks whether or not the heating roller has made one rotation from the start of fixing (step 310). When the heating roller 71 makes one rotation, the controller 31 sends a signal to the fixing motor driving circuit 65 to reduce the rotation speed of the fixing motor 85 and
The paper transport speed of No. 17 is reduced (step 311). Then, the control unit 31 checks whether or not the sheet has been discharged from the image forming apparatus 1 (step 317).
Since the sheet conveyance speed of No. 7 has been reduced, the speed is returned to the original speed (step 318), and the image formation ends.

On the other hand, in step 303, the sensor B
If the sheet detected in 203 is not an OHP sheet, the sensor C204 detects whether or not the length of the sheet in the transport direction is equal to or greater than the length of the OHP sheet in the short direction (step 312). If the length of the sheet in the transport direction is equal to or less than the length of the OHP sheet in the width direction, the above-described step 3 is performed.
07 and subsequent processes are performed.

On the other hand, if the length of the sheet in the transport direction is equal to or longer than the width of the OHP sheet, the control unit 31 prohibits image formation in the specific recording mode and displays " Copy in normal recording mode.
If you like, press the start button. Is displayed (step 313).

Here, when the user presses the start button, an image is formed on thick paper whose transport direction is longer than the length of the OHP sheet in the short direction, so that the paper transport speed of the fixing device 217 is not reduced on the way. Image formation is performed in the recording mode. In this case, the surface temperature of the heating roller 71 decreases from the second rotation of the heating roller 71, and the melting property of the toner decreases. In the case of the OHP sheet, when the melting property of the toner is reduced, the reflection at the boundary surface of the toner is increased, and the transparency of the toner is reduced. Therefore, if this OHP sheet is used in the OHP, a color image cannot be displayed, and the OHP sheet may be displayed as a black and white image. However, when the recording medium is thick paper, even if the meltability of the toner is reduced, the image formed on the thick paper hardly causes image unevenness or color turbidity. Therefore, in the step 313, the warning sentence B is displayed for confirmation.

The control unit 31 confirms whether or not the start button has been pressed (step 314), turns off the display of the warning message B (step 315), and performs normal image formation (step 316). The control unit 31 checks whether or not the sheet has been ejected (step 317). Since the sheet conveyance speed of the fixing device 217 has not been reduced, the control unit 31 does nothing (step 318) and ends the image formation as it is. I do.

The present invention can be applied not only to a specific recording medium such as an OHP sheet or cardboard, but also to a recording medium such as a plain paper.

[0082]

According to the present invention, the following effects can be obtained.

(1) In an image forming apparatus having a specific recording mode in which the conveyance speed of a recording medium at a fixing unit is reduced, a transfer point of a transfer unit for transferring a toner image formed on a photoreceptor to a recording medium, and recording The conveyance distance interval L from the fixing point of the fixing unit for fixing the toner image transferred to the medium onto the recording medium by the fixing roller is the length Lp of the recording medium in the conveyance direction.
Is smaller than the difference between the length Lp of the recording medium in the transport direction and the circumferential length πD of the fixing roller, so that when the fixing roller rotates at least one turn, the recording medium separates from the transfer point of the transfer unit. Even if the fixing speed is reduced after one rotation, the toner can be fixed to the recording medium satisfactorily without transfer deviation. In addition, since the distance between the fixing unit and the transfer unit can be shorter than the length of the recording medium in the conveyance direction, there is no need to provide a recording medium conveyance mechanism for conveyance, and the size of the image forming apparatus can be reduced. It is possible to minimize a decrease in image forming speed when executing the specific mode.

(2) The distance between the fixing unit and the transfer unit can be increased by setting the length in the short direction of the standard size recording medium used in the specific recording mode to be the length Lp in the transport direction of the recording medium. The image forming apparatus can be shortened, the size of the image forming apparatus can be reduced, and a decrease in image forming speed in the specific recording mode can be minimized.

(3) When the specific recording mode is executed, the length Lp of the recording medium in the image forming apparatus in the transport direction may be longer than the length of the standard size recording medium used in the specific recording mode in the transverse direction. When the length is detected by the length detecting means for detecting the length Lp of the recording medium in the transport direction, and the standard size recording medium used in the specific recording mode is detected by the type detecting means for detecting the type of the recording medium, The notifying unit for notifying the state of the apparatus notifies that the length Lp of the standard size recording medium used in the specific recording mode in the transport direction is equal to or greater than the length of the recording medium in the width direction. Since the control unit that controls the unit prohibits the image formation in the specific recording mode, it is possible to prevent the formation of a poor image having a transfer deviation due to the erroneous setting of the recording medium.

(4) During execution of the specific recording mode, the length Lp of the recording medium in the transport direction of the recording medium by the image forming apparatus is longer than the length in the widthwise direction of the standard size recording medium used in the specific recording mode. If the recording medium other than the standard size recording medium used in the specific recording mode is detected by the type detecting means and the type detecting means detects the recording medium, the image forming in the specific recording mode is prohibited and the image in another mode is The control unit waits until the execution of the formation is input to the input unit, and the notification unit notifies that the image formation is in the input standby state of the execution of the image formation in another mode. Therefore, the standard size used in the specific recording mode is used. When using a recording medium other than the recording medium, the recording mode can be selected according to the size of the recording medium.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a digital color copying machine 1 which is an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of a fixing device 217.

FIG. 3 is a block diagram illustrating a relationship between a control unit 31 and each unit.

FIG. 4 is a layout diagram illustrating a relationship between a fixing device and a transfer unit of an image forming station.

FIG. 5 is a flowchart illustrating an image forming procedure of the image forming apparatus 1.

[Explanation of symbols]

 1-Image Forming Apparatus 71-Heating Roller 217-Fixing Apparatus 222d-Photoconductor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasunori Mizuguchi 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside (Sharp) (72) Inventor Atsushi Ide 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka (72) Inventor: Toshiya Mikita 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside (72) Inventor Kazuhiro Matsuyama 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka F term (reference) 2H027 DA36 DC02 DC10 EC20 ED16 ED25 EE07 EF06 EF09 FA30 FA35 FB07 FB17 GA47 GB05 GB16 2H033 AA02 AA47 BA08 BA11 BA59 BB01 BB28 BB37 CA16 CA17 CA36 CA57

Claims (4)

[Claims] An image forming apparatus comprising: a transfer unit configured to transfer a toner image formed on a photoconductor to a recording medium; and a fixing unit configured to fix the toner image transferred to the recording medium onto the recording medium by a fixing roller. An image forming apparatus having a specific recording mode for reducing the transport speed of a recording medium in a unit, a transport distance interval L between a transfer point of the transfer unit and a fixing point of the fixing unit, and a length Lp of the recording medium in a transport direction. ,
And a peripheral length πD of the fixing roller has a relationship represented by Lp>L> (Lp−πD). 2. The length Lp of the recording medium in the transport direction is:
2. The image forming apparatus according to claim 1, wherein the length is a length in a width direction of a standard size recording medium used in the specific recording mode. 3. A length detecting means for detecting a length Lp of a recording medium in a conveying direction, a type detecting means for detecting a type of the recording medium, a notifying means for notifying a state of the apparatus, and each means of the apparatus. And a control unit for controlling the length of the recording medium in the transport direction of the recording medium when the specific recording mode is executed. In addition to detecting the above, when the type detecting unit detects a standard size recording medium used in the specific recording mode, the notifying unit notifies the fact, and the control unit performs image forming in the specific recording mode. The image forming apparatus according to claim 2, wherein the image forming apparatus prohibits the image forming apparatus. 4. When executing the specific recording mode, the length detecting means sets the length Lp of the recording medium in the transport direction to be equal to or greater than the length in the short direction of the standard size recording medium used in the specific recording mode. When the type detection unit detects a recording medium other than the standard-size recording medium used in the specific recording mode, the control unit prohibits image formation in the specific recording mode and sets another mode. Waits until input of the execution of image formation in the input unit is input to the input unit, and the notifying unit notifies that it is in an input standby state of execution of image formation in another mode. The image forming apparatus according to claim 3.