JPH1091033A - Fixing device for electrophotographic printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the fixing device of an electrophotographic printer where the control of an electrophotographic processing is easily made, whose image quality is stablized and which is miniaturized and at a low cost so as to obtain an image requiring translucency such as the image on a transparent sheet by performing heating fixing for plural times by normally and reversely rotating the fixing roller of the fixing device in the case that a photographic output medium is an OHP transparent sheet. SOLUTION: In the case of the OHP transparent sheet, a control part 15 is previously made to recognize as fixing for the transparent sheet by an another sensor or an input from a control condition setting part. When a sensor 20 detects the trailing end of the transparent sheet passing the fixing device 14, a heating roller 14b is reversely rotated so that the transparent sheet passes the inside of the fixing device 14 again and is heated again. The sensor 19 detects as second heating fixing is completed, and the heating roller 14b is reversely (normally) rotated again, so that the heating fixing is continuously executed. Thus, the melting of toner is made excellent, so that the image whose translucency is excellent is obtained on the OHP transparent sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device in a hard copy output device such as a printer or a copying machine for transferring a toner from an image bearing medium to a recording medium and then heating and fixing the toner image to the recording medium. is there.

[0002]

2. Description of the Related Art FIG. 7 is a sectional view of a conventional electrophotographic printing apparatus disclosed in, for example, Japanese Patent Application Laid-Open No. 4-75464. Such an electrophotographic printing apparatus is constituted by the following process means. A charging process for uniformly charging the surface of the photoconductor, an exposure process for forming a latent image corresponding to image information by partially erasing the charged charge by irradiating the photoconductor with light, and a developer for the latent image. A developing process of forming a toner image by attaching toner, a transfer process of transferring the toner image to a recording medium (hereinafter referred to as “paper”), a cleaning process of removing toner remaining on the photoconductor,
And a fixing process for fixing the transferred toner image to the paper by heating. In the figure, 1 is a photoconductor, 2
Is a charger for executing a charging process, 3 is an exposure bundle by light irradiation means of an optical system, and 4 is a developing device for attaching toner to an exposed latent image on the photoreceptor 1, and in this example, Y (yellow), M It has four colored toners of (magenta), C (cyan) and BK (black). Reference numeral 5 denotes a cleaner, 6 denotes a belt-shaped image carrier, and a first transfer unit 7 which rotates in synchronization with the photoconductor 1 and develops toner on the photoconductor 1 for each color.
And a color-colored toner image is generated.
Reference numeral 8 denotes a second transfer unit that transfers the color toner image of the image carrier 6 to the sheet P sent from the sheet feeding device by electrostatic action, and 9 denotes a toner image transferred on the sheet P on the sheet P. , A fixing belt for conveying the sheet P from the second transfer unit 8 to the fixing unit 9, and a re-conveying path 11 for passing the sheet P through the second transfer unit 8 a plurality of times. It is. Reference numeral 12 denotes a separator for distinguishing whether to return the sheet P to the re-conveying path 11 or to carry out the sheet P as a completed image.

In the above-described electrophotographic printing apparatus,
In addition to image printing on plain paper (opaque), image printing can be performed using a transparent sheet for an overhead projector (OHP). Here, when the toner image is fixed on the transparent sheet, in order to enhance the reproducibility of the hue, the colored toner image is completely melted on the transparent sheet, and the surface is flattened to secure the translucency. There is a need. As a method for completely melting the toner to secure the light-transmitting property, a method is generally used in which the fixing time in the fixing process is relatively longer than that for plain paper. By passing the toner through the container 9 a plurality of times, a time for completely melting the toner is obtained.

In addition to the above example, the fixing time is extended by detecting that the paper P is transparent and automatically lowering the fixing speed to be lower than the fixing speed of plain paper. There is also an electrophotographic printing device that has improved the condition.

[0005]

When a sheet is re-conveyed to the fixing unit and the fixing is performed a plurality of times, the length of the re-conveying path to the fixing unit corresponding to the sheet size must be provided. In other words, the re-conveying path requires a path length from the end of the sheet completely discharged from the fixing device to the end of the sheet entering the fixing device again. Therefore, there is a problem that a long conveyance path corresponding to the paper size is required, so that the apparatus main body becomes extremely large and costs increase.

When fixing is carried out at a low fixing speed, the conveying speed is made uniform over the entire surface of the paper in order to prevent the toner image from being disturbed (image deterioration) due to expansion and contraction in the paper conveying direction. Need to change. Therefore, when the fixing speed is reduced, the rotation speed of the belt of the image carrier needs to be reduced simultaneously with the rotation speed of the fixing roller. In other words, in each of the modes of fixing the color toner on the plain paper and the mode of fixing the transparent toner on the transparent sheet, the control of the entire electrophotographic process becomes complicated, and especially, immediately after the mode is switched, the mode is adjusted to each image forming speed. It is difficult to obtain the best electrophotographic process conditions (physical property values), and there is a problem that the stability of image quality is impaired.

In addition, since there are many types of transparent sheets for OHP which are generally available on the market, the fixing conditions for obtaining optimum transparency differ for each transparent sheet. Therefore, when fixing to a thick transparent sheet, the fixing operation must be repeated many times, three to four times, and the surface of the transparent sheet is scratched every time the sheet passes through a long paper conveyance path, and the image is deteriorated. was there.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and in obtaining an image which requires translucency such as an image on a transparent sheet, control of an electrophotographic process is easy and image quality is high. It is an object of the present invention to provide a small, low-cost fixing device for an electrophotographic printing apparatus, which is stable.

[0009]

According to a first aspect of the present invention, there is provided a fixing device for an electrophotographic printing apparatus, wherein the printing output medium is OH.
In the case of a transparent sheet for P, a reciprocating means for performing heat fixing a plurality of times by rotating a fixing roller of the fixing device in a normal direction and a reverse direction is provided.

According to a second aspect of the present invention, there is provided a fixing device for an electrophotographic printing apparatus, wherein the number of reciprocating fixing movements can be variably selected according to the type of transparent sheet.

According to a third aspect of the present invention, there is provided a fixing device for an electrophotographic printing apparatus, wherein the speed of the fixing roller can be variably selected only when the fixing roller reversely rotates in accordance with the type of the transparent sheet.

According to a fourth aspect of the present invention, there is provided a fixing device for an electrophotographic printing apparatus, wherein a sensor for detecting the presence or absence of an OHP transparent sheet disposed before and after the fixing roller is provided, and the sensor detects the absence of the OHP transparent sheet. After the fixing roller is fed from the fixing roller for a predetermined time during which the nipping of the OHP transparent sheet is not removed, the rotation direction of the fixing roller is changed.

According to a fifth aspect of the present invention, there is provided a fixing device for an electrophotographic printing apparatus, wherein the fixing device further comprises a sheet escape path provided in the middle of the sheet guide and following an opening through which the rear end of the print output medium is introduced when the fixing roller rotates in the reverse direction. Things.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is a diagram showing a main configuration of an electrophotographic printing apparatus according to the present invention. In the figure, reference numerals 1 to 7 are the same as those described in the above conventional example. Reference numerals 6a and 6b denote a driving roller for rotating the belt-shaped image bearing medium 6, and a driving motor for driving the driving roller 6a. Reference numeral 6c denotes a transfer backup roller, which is also one electrode of a transfer device to be described later for extending the image bearing medium 6. Reference numeral 13 denotes a transfer roller, which is provided so as to be able to contact and separate from the transfer backup roller 6c with the image carrying medium 6 and the paper P interposed therebetween, and this contact and separation operation is controlled by the control unit 15 of the electrophotographic printing apparatus. . Then, a DC voltage is applied between the transfer backup roller 6c and the second transfer device which transfers the toner by using the electric field of the DC voltage.
A fixing device 14 includes a heating roller 14b having a heating heater 14a as a fixing roller, and a heating roller 1b.
The heating roller 14b includes a fixing backup roller 14c that contacts the fixing roller 4b and a driving motor 14d that drives the heating roller 14b. The drive motor 14d controls the heating unit 14b to rotate the heating roller 14b in the forward / reverse rotation, rotation speed and rotation speed (rotation time).
Is controlled by Auxiliary rollers 16 and 17 are rotated in the same direction at the same peripheral speed as the heating roller 14b. The auxiliary roller 17 is configured to be able to contact and separate from the sheet P. Reference numeral 18 denotes a paper guide for guiding the paper P from the transfer roller 13 to the fixing device 14. Reference numerals 19 and 20 denote sensors for detecting the leading edge and the trailing edge of the sheet P or a transparent sheet Q described later.

In the electrophotographic printing apparatus configured as described above, when fixing plain paper, the paper P conveyed from a paper cassette (not shown) is passed between the transfer roller 13 and the transfer backup roller 6c, and is transferred. Roller 13
Is brought into contact with the transfer backup roller 6c side so that the image carrier 6
The upper toner is transferred onto the paper P by the force of the electric field. The sheet P to which the toner has been transferred passes through the sheet guide 18 while being heated between the heating roller 14b and the fixing backup roller 14c. During this time, the toner is melted and fixed on the sheet P. At this time, the auxiliary roller 17
, So that the unfixed toner is not disturbed by the auxiliary roller 17. Thus, the electrophotographic printing process on plain paper is completed.

However, in the case of the transparent sheet Q for OHP,
In order to enhance the reproducibility of hue, the toner must be completely melted on the transparent sheet, and the fixing process time is insufficient for the same fixing process time as that of the plain paper. Therefore,
In the present invention, the control unit 15 is made to recognize in advance that the fixing is performed on the transparent sheet by an input from another sensor or a control condition setting unit, and the fixing device 1 is temporarily stopped.
When the sensor 20 detects the rear end of the transparent sheet that has passed through 4, the heating roller 14b is rotated in the reverse direction, passes through the fixing device 14 again, and is heated again. The sensor 19 detects the completion of the second heat fixing, and the heat roller 14b is again rotated in the reverse direction (forward rotation) to continue the heat fixing.

This state will be described with reference to FIG. (a) The toner on the image carrier 6 is transferred to the transparent sheet Q by the transfer roller 13, the leading end is conveyed to the fixing device 14, and the toner is heated and melted by the normal rotation of the heating roller 14b. The auxiliary roller 17 is located away from the transparent sheet Q. (b) When the sensor 20 detects the rear end of the transparent sheet Q,
The rotation of the heating roller 14b is stopped and reversely rotated. (c) When the toner is heated and melted by the reverse rotation of the heating roller 14b and the sensor 19 detects the leading end of the transparent sheet Q, the reverse rotation of the heating roller 14b is stopped. At this time,
The auxiliary roller 17 is in contact with the transparent sheet Q, and the transfer roller 13 is separated from the image carrier 6. (d) Subsequently, the rotation of the heating roller 14b is returned to the normal rotation, and the toner on the transparent sheet Q is conveyed to the paper discharge side while being re-pressurized and re-heated, and the toner transferred on the transparent sheet Q is removed. It melts sufficiently to obtain the required permeability. And
The transparent sheet Q is discharged from the fixing device 14, and the fixing process ends. (e) The toner is completely melted by increasing the number of times of reciprocating fixing depending on the type and thickness of the OHP transparent sheet.

Embodiment 2 FIG. Since there are many types of OHP transparent sheets such as thickness, etc., the optimum toner fusion and fixation is not always achieved by an integral multiple of the uniform heating and fixing time described in the first embodiment. If anything, it is overheated, and in some cases, the transparent sheet Q may be deformed. Therefore, the rotation speed of the heating roller 14b may be changed according to the type of the transparent sheet Q. However, in order to reduce the size of the electrophotographic printing apparatus, the paper guide 18 is shorter than the transparent sheet Q, and the speed of one transparent sheet Q is reduced. The toner transfer by the transfer roller 13 and the heat fixing operation by the fixing device 14 are performed simultaneously. As described in the section of the related art, it is difficult to change the speed of the transfer roller because the image is disturbed. Therefore, by setting the speed only at the time of the reverse rotation of the heating roller 14b to the optimum rotation speed for the type of the transparent sheet Q,
Complete melting and fixing of the toner and deformation of the transparent sheet Q can be prevented. FIG. 3 shows an example of the relationship between the thickness of the transparent sheet and the speed at the time of reverse rotation of the heating roller.

Embodiment 3 FIG. 4 is a diagram showing an outline of a fixing device according to a third embodiment of the present invention. In the figure, 6, 13, 14, and 18 to 20 are the same as those described in the first embodiment. Reference numeral 21 denotes a discharge roller, which is not necessarily synchronized with the peripheral speed of the heating roller 14b. The sensors 19 and 20 are separated by distances L1 and L2 from the contact positions of the heating roller 14b and the fixing backup roller 14c, respectively. This is because the sensors 19 and 20 are
b to reduce the effect of heat from the heat roller 14
This is because b contains the heater 14a and therefore needs a certain diameter.

The operation of the third embodiment will be described with reference to FIG. FIG. 5A shows a state where the toner is transferred to the transparent sheet and the leading end of the transparent sheet enters the fixing device. FIG. 5B shows a state in which the transparent sheet Q is conveyed to the left in the figure from this state, and the rear end of the transparent sheet Q is detected by the sensor 19.
Since the distance L1 of the sensor 19 from the contact position between the heating roller 14b and the fixing backup roller 14c is known and the rotational speed of the heating roller 14b is known, the sensor 1
9 detects the rear end of the transparent sheet Q, sends the transparent sheet Q for a predetermined time, stops the heating roller 14b, and turns the heating roller 14b in the reverse direction. That is, the heating roller 14b
And the fixing backup roller 14c keeps the rear end of the transparent sheet Q barely pinched.
4b is reversed. FIG. 5 shows a state in which the heating roller 14b is reversed and the sensor 20 detects the leading end of the transparent sheet Q.
It is shown in (c). From this state, similarly to the above description, the heating roller 14b and the fixing backup roller 14c
Roller 1 where the tip of
The reverse rotation of 4b is stopped and the rotation is switched to the normal rotation.

As described above, since the transparent sheet Q is always held between the heating roller 14b and the fixing backup roller 14c and the transparent sheet Q is reciprocated, the auxiliary rollers 16 and 17 described in the first embodiment can be used. This is unnecessary, and the configuration of the device is simplified, which can contribute to downsizing of the device.

Embodiment 4 FIG. 6 is a diagram showing an outline of a fixing device according to a fourth embodiment of the present invention. In the figure, 6, 13, 14, 18 to 21 are the same as those described in the third embodiment. Reference numeral 22 denotes a paper escape path following the opening 18a provided in the middle of the paper guide 18. Next, the operation will be described. The transparent sheet Q, to which the toner has been transferred from the image carrier 6 by the transfer roller 13, has its leading end fixed to the fixing device 1.
4 FIG. 6A shows this state. At this time,
The opening 18a has a step so that the front end of the transparent sheet Q jumps over the opening 18a. Then, the heating roller 14
When the fixing by the reverse rotation of the heating roller 14b starts from the fixing by the rotation of the heating roller 14b in the forward direction, the rear end of the transparent sheet Q conveyed in the reverse direction enters the sheet retracting path 22 due to the step of the opening 18a.

As described above, when the heating roller 14b rotates in the reverse direction, the rear end of the transparent sheet Q is retracted to the sheet escape path 22, so that the rear end of the transparent sheet Q does not touch the image carrier 6, and the image carrier 6 6 can prevent the image from being stained due to the adhesion of the residual toner. Further, in the case where the sheet escape path 22 is not provided, if the fixing time to the transparent sheet Q is long, even if it is desired to develop the toner of the next image on the image carrier 6, the rear end of the transparent sheet Q is 6, the developed image is destroyed, so that the development of the next print must be started after the completion of fixing, and the print processing speed is reduced. By retreating to the sheet retreat path 22, the next image development process can be executed on the image carrier 6 regardless of the fixing process.

[0024]

According to the first aspect of the present invention, when the printing output medium is a transparent sheet for OHP, the fixing roller of the fixing device is rotated forward and backward to perform the heating and fixing a plurality of times, whereby the toner is removed. The melting is improved, and an image with good translucency is obtained on the transparent sheet for OHP.

According to the second aspect of the present invention, the number of reciprocating movements of the fixing can be variably selected in accordance with the type of the transparent sheet, so that the melting of the toner can be completed and the color appearance can be improved. An image is obtained.

According to a third aspect of the present invention, since the speed of the fixing roller is variably selected only when the fixing roller is rotated in reverse according to the type of the transparent sheet, overheating of the OHP transparent sheet during fixing is performed. And the thermal distortion of the OHP transparent sheet can be prevented.

According to the fourth aspect of the present invention, since the fixing reciprocating motion is performed while the OHP transparent sheet is always gripped by the sensor, an auxiliary roller for transporting the OHP transparent sheet in the reciprocating motion can be eliminated, and the apparatus can be used. Can be simplified.

According to the fifth aspect of the present invention, since the paper retraction path for introducing the rear end of the OHP transparent sheet when the fixing roller rotates in the reverse direction is provided, the rear end of the OHP transparent sheet comes into contact with the image carrier. As a result, contamination of the image carrier with the residual toner can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a main configuration of an electrophotographic printing apparatus according to the present invention.

FIG. 2 is a diagram illustrating the operation of the first embodiment of the present invention.

FIG. 3 is a table illustrating an example of a relationship between a thickness of a transparent sheet and a speed at the time of reverse rotation of a heating roller according to a second embodiment.

FIG. 4 is a diagram showing an outline of a fixing device according to a third embodiment of the present invention;

FIG. 5 is a diagram illustrating an operation of a third embodiment of the present invention.

FIG. 6 is a diagram showing an outline of a fixing device according to a fourth embodiment of the present invention.

FIG. 7 is a sectional view of a conventional electrophotographic printing apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photoreceptor, 2 Charger, 3 Exposure bundle by light irradiation means 4 Developing device, 5 Cleaner, 6 Image carrier 6c Transfer backup roller, 7 Transfer device 8 Second transfer device, 9 Fixing device, 13 Transfer roller 14 Fixing Equipment, 14a heater, 14b
Heating roller 15 control unit, 14c fixing backup roller,
16, 17 auxiliary roller, 18 paper guide,
18a opening, 19, 20 sensor 22 paper escape path, P paper, Q transparent sheet

Claims (5)

[Claims] 1. A fixing device of an electrophotographic printing apparatus for heating and fixing a toner image developed from an electrostatic latent image to a printing output medium after transferring the toner image, wherein the printing output medium is an overhead projector (O).
A fixing device for an electrophotographic printing apparatus, comprising reciprocating means for performing a plurality of heating and fixing operations by rotating a fixing roller of the fixing device in a normal direction and a reverse direction in the case of a transparent sheet for HP). 2. The fixing device for an electrophotographic printing apparatus according to claim 1, wherein the number of reciprocating fixing movements can be variably selected according to the type of the transparent sheet. 3. The fixing device for an electrophotographic printing apparatus according to claim 1, wherein the speed of the fixing roller is variably selected only when the fixing roller is rotated in reverse according to the type of the transparent sheet. 4. A sensor for detecting the presence or absence of a transparent sheet for OHP disposed before and after the fixing roller, and the sensor detects whether the transparent sheet for OHP is present or not and detects whether or not the transparent sheet for OHP is present. After sending the fixing roller for a predetermined time that does not remove the nipping,
4. The fixing device according to claim 1, wherein a rotation direction of the fixing roller is changed. 5. A paper guide for guiding the print output medium after transferring the toner to the print output medium to a fixing device, and a rear end of the print output medium provided in the middle of the paper guide is introduced when the fixing roller rotates in reverse. And a paper escaping path following the opening.
A fixing device for the electrophotographic printing apparatus according to the above.