JPH11305591A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a proper and efficient fixing process on a storage medium of poor fixation, while avoiding enlargement of a device. SOLUTION: During a fixing process for a storage medium of poor fixation, such as OHP paper, the storage medium is reciprocated and clamped and conveyed plural times by a heat roller 28 and a pressure roller 29 to apply sufficient heat to the storage medium to fix a toner image to the storage medium. When the storage medium is conveyed in the direction indicated by the arrow C, a conveyor belt 26 is separated from a photoconductor drum 16 and the storage medium is guided to a conveying path 33 without touching the photoconductor drum 16. Therefore, interval between a fixing device 27 and a transfer device 20 can be set at not more than a length along the conveying direction of the storage medium, and the next toner image can be formed on the photoconductor drum 16 immediately after a transfer process has been finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus, and more particularly, to transferring a toner image formed on an image carrier to a recording medium by a transfer means, and transferring the toner image to the recording medium. The present invention relates to an image forming apparatus that is conveyed to a fixing unit by a conveying unit and fixes a toner image on a recording medium by the fixing unit.

[0002]

2. Description of the Related Art In a color image forming apparatus such as a copying machine or a printer, when a toner image is fixed on a recording medium having poor fixability such as OHP paper or thick paper, a larger number of fixing processes are performed than in a fixing process on plain paper. You need to give heat. As one of techniques for applying such a large amount of heat, there has been proposed a method of increasing a fixing nip time by reciprocating a recording medium with a fixing device (Japanese Patent Laid-Open No. 2-109).
064, JP-A-5-11655).

In this method, a recording medium 100 on which a toner image has been transferred as shown in FIG.
After passing in the recording medium discharge direction (arrow B direction) at 7, the transport direction is reversed in the arrow C direction as shown in FIG. Further, as shown in FIG. 8C, the conveyance direction is switched again to the recording medium discharge direction (arrow B direction), and the recording medium 100 is caused to pass in the arrow B direction to perform the third fixing process.

[0004]

However, when the above-described method is used, in a configuration in which the reversely conveyed recording medium 100 contacts the image carrier 16 as shown in FIG. Until the sheet 100 is separated from the image carrier 16 again, the next image cannot be formed on the image carrier 16. In addition, since the fixing operation of the recording medium having the poor fixing property takes longer than the fixing operation on the plain paper, the printing speed is reduced.

[0005] The printing speed when the recording medium is plain paper and when the recording medium is a recording medium having poor fixability (such as OHP paper) will be specifically described with reference to FIG. 9. FIG. 9A shows a time chart of various processes for plain paper. In this case, while transferring the first toner image onto plain paper, charging, exposure, and the like for forming the second toner image are performed.
Put in development.

However, when the recording medium is reversely conveyed in a fixing process on paper having poor fixability, the recording medium conveyed in the reverse direction comes into contact with the image carrier, and therefore, the recording medium is removed from the image carrier again. Cannot be used for charging, exposure and development for forming a second toner image. Therefore, the print speed is reduced as shown in FIG. To solve this, as shown in FIG. 9C, the fixing process and the charging on the image carrier are performed.
It is necessary to execute exposure and development independently and simultaneously.
This can be realized by setting the interval L2 between the transfer nip portion TR and the fixing nip portion FX longer than the length L1 along the transport direction of the recording medium 100 as shown in FIG. The device becomes large.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and performs a proper and efficient fixing process on a recording medium having low fixability while avoiding an increase in the size of the apparatus. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

[0008]

According to another aspect of the present invention, there is provided an image forming apparatus, comprising: a transfer unit configured to transfer a toner image formed on an image carrier to a recording medium; Conveying means for transferring the transferred recording medium in a predetermined direction away from the image carrier, and conveying means for conveying the recording medium in a direction opposite to the predetermined direction so that the recording medium does not touch the image carrier, On the downstream side of the transfer unit in the predetermined direction, the transfer unit is disposed so that the distance from the transfer unit is equal to or less than the length of the recording medium along the predetermined direction, and includes a roller pair including a heating roller. Fixing means for fixing the transferred toner image to the recording medium by nipping and conveying the recording medium while heating the recording medium in the predetermined direction or the opposite direction by the pair of rollers; When fixing the toner image on a recording medium having a low fixing property, while the recording medium is conveyed at least once in the predetermined direction by the conveyance unit and the roller pair and conveyed at least once in a direction opposite to the predetermined direction, And control means for controlling the toner image to be fixed on the recording medium.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, when the recording medium is conveyed in the reverse direction, the recording medium can be moved toward and away from the image carrier. The image forming apparatus further includes a separating unit that separates the provided conveying unit from the image carrier.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, when the recording medium is conveyed in the reverse direction, the recording medium is adsorbed by the conveying means. Is further provided.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the operation mode of the image forming apparatus is set to the recording medium having the low fixing property. And a mode setting unit for setting a mode for fixing the toner image on the paper or a normal mode for fixing the toner image on plain paper.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the roller is provided in accordance with a fixing processing time required for the recording medium. The apparatus further comprises setting means for setting a conveying speed of the recording medium by each of the pair and the conveying means and a number of times of fixing processing on the recording medium.

In the above-described image forming apparatus, the toner image formed on the image carrier is transferred to a recording medium by a transfer unit, and the recording medium on which the toner image has been transferred is transported by the transport unit. Transported in a predetermined direction away from the printer.

On the downstream side of the transfer unit in a predetermined direction, a fixing unit including a roller pair including a heating roller is provided so that a distance from the transfer unit is equal to or less than a length of the recording medium along the predetermined direction. It is arranged to become. The fixing unit fixes the toner image to the recording medium by nipping and conveying the recording medium conveyed by the conveying unit while heating the recording medium in a predetermined direction by a pair of rollers.

In a normal case, the fixing process is completed only once, but when a toner image is fixed on a predetermined recording medium having low fixability, the control unit controls the recording medium by a conveying unit and a pair of rollers. The toner image is fixed on the recording medium by the fixing unit while being conveyed at least once in the predetermined direction and conveyed at least once in the direction opposite to the predetermined direction.

When a toner image is fixed on a recording medium having such a low fixability, the recording medium is conveyed at least once in a normal conveying direction (predetermined direction), and is conveyed at least once in the opposite direction. Is performed, a plurality of fixing processes are performed on the recording medium, and the toner image can be sufficiently fixed on the recording medium.

When the recording medium is conveyed in a direction opposite to the predetermined direction, the conveying means conveys the recording medium so as not to touch the image carrier. That is, as described above, the distance between the fixing unit and the transfer unit is set to be equal to or less than the length of the recording medium along the predetermined direction, but as described above, the transport unit contacts the image carrier with the recording medium. The recording medium is conveyed in a direction opposite to the predetermined direction so that the next toner image can be formed on the image carrier immediately after the end of the transfer by the transfer unit, and the recording medium having a low fixability can be used. The processing time of the image forming process can be reduced.

Further, since the fixing means is arranged so that the distance between the fixing means and the transfer means is equal to or less than the length along the predetermined direction of the recording medium, it is possible to avoid an increase in size of the apparatus.

When a toner image is fixed on a recording medium having a low fixing property, the control means conveys the recording medium in a predetermined direction by, for example, a conveying means and a pair of rollers, and conveys the recording medium in a direction opposite to the predetermined direction. Then, the sheet may be conveyed again in a predetermined direction. In this case, the fixing process is performed three times on the recording medium. Further, for example, the recording medium may be conveyed in a predetermined direction, conveyed in a direction opposite to the predetermined direction, and then discharged. In this case, the fixing process is performed twice on the recording medium.

In this way, by setting the number of times the recording medium is reciprocated and whether or not the recording medium is finally conveyed in a predetermined direction, it is possible to set the number of times of performing the fixing process on the recording medium to a desired number.

In order to convey the recording medium in a direction opposite to the predetermined direction so that the recording medium does not touch the image carrier as described above, the separating means according to claim 2 moves the recording medium relative to the image carrier. The transport means provided so as to be able to approach and separate from the image carrier may be separated from the image carrier when the recording medium is transported in the opposite direction. That is, if the transporting means is separated from the image carrier, the recording medium transported by the transporting means can be separated from the image bearing body, and the contact of the recording medium with the image bearing body can be reliably avoided. it can.

At this time, it is desirable that the recording medium be adsorbed to the conveying means by the adsorbing means according to the third aspect. This allows the recording medium to be attracted to the conveying means separated from the image carrier, so that the contact of the recording medium with the image carrier can be more reliably avoided.

The operator of such an image forming apparatus is:
The operation mode of the image forming apparatus can be set to a mode in which a toner image is fixed on a recording medium having low fixability or a normal mode in which a toner image is fixed on plain paper. .

The quality of the fixing property differs depending on the material of the recording medium such as plain paper and OHP paper, and the required fixing processing time also varies. Therefore, the setting unit according to the fifth aspect sets the conveying speed of the recording medium by each of the roller pair and the conveying unit and the number of times of the fixing process on the recording medium according to the fixing processing time required for the recording medium. It is desirable. That is, when a fixing process is performed on a recording medium that requires a long fixing processing time, the conveyance speed of the recording medium by the roller pair and the conveyance unit may be reduced or the number of times of the fixing process may be increased. On the other hand, when the fixing process is performed on a recording medium having a short required fixing time, the number of times of the fixing process is set to one, and the conveying speed of the recording medium by the roller pair and the conveying unit is set to be high. And the fixing processing time can be shortened.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a color laser beam printer will be described below.

[Schematic Configuration of Color Laser Beam Printer] FIG. 1 shows a schematic configuration of a color laser beam printer 10 of the present embodiment. First, an outline of the structure and operation of the color laser beam printer 10 will be described with reference to FIG.

The color laser beam printer 10 is provided with a laser scanning device 11, and a semiconductor laser (not shown) that modulates and emits a laser beam in accordance with image information is arranged in the laser scanning device 11. ing. The laser beam emitted from the semiconductor laser enters the polygon mirror 12 and is deflected in accordance with the rotation of the polygon mirror 12. The deflected laser beam 13 is the fθ lens 1
4, the traveling direction is changed by the mirror 15, and the output is output from the laser scanning device 11.

On the extension of the laser beam 13 output from the laser scanning device 11, a photosensitive drum 16 is arranged. The photosensitive drum 16 is moved in the direction of arrow A at a constant speed by the photosensitive drum drive motor 8. It is driven to rotate.
Laser beam 13 output from laser scanning device 11
Scans a predetermined exposure position 17 repeatedly in the axial direction of the photosensitive drum 16, that is, in the main scanning direction. This exposure position 1
A charging device (charge corotron) 18 is disposed before the photosensitive drum 16 in the rotation direction of the photosensitive drum 16, and the charging device 18 uniformly charges the surface of the photosensitive drum 16.
By irradiating the laser beam 13 to the charged photosensitive drum 16, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 16.

This electrostatic latent image is developed by the color developing device 19. The color developing device 19 is capable of full-color image recording, and has a developing device 19Y for developing yellow toner and a developing device 19 for developing magenta toner.
M, a developing device 19C for developing cyan toner, and a developing device 19K for developing black toner. Hereinafter, the step of full-color development will be described.

The photosensitive drum 1 is irradiated with the laser beam 13.
The electrostatic latent image formed on 6 is first visualized on the photosensitive drum 16 by the yellow toner developing device 19Y. At this time, a visible bias image is formed by applying a developing bias only to the yellow toner developing device 19Y and attaching the yellow toner to the electrostatic latent image. At this time, no developing bias is applied to the other developing devices 19M, 19C, and 19K, so that toner of a color other than yellow does not fly onto the photosensitive drum 16.

When the development of the yellow toner is completed, in order to draw a magenta image next, after the charge on the photosensitive drum 16 is removed by the charge removing device 31, charging by the charging device 18 and the laser scanning device 11 is performed again. Exposure is performed. Since this operation is performed on the photosensitive drum 16 on which the yellow toner has already been developed, it is important to adjust the exposure timing to the yellow toner image. At this time, a developing bias is applied only to the magenta toner developing device 19Y, and the visible image of magenta is superposed by attaching the magenta toner from above the yellow toner.

Similarly, cyan and black toners are also superimposed on the photosensitive drum 16 and the photosensitive drum 16
When the toner is rotated and the four color toners are overlapped, the developing process is completed.
Note that the above is the developing process in full-color printing. However, in the case of performing single-color printing, each of the charging, exposing, and developing processes may be performed once.

A transfer device (transfer belt) 20 integrated with a conveyor belt 26 is disposed downstream of the color developing device 19 in the rotation direction of the photosensitive drum 16. During execution of the charging, exposure, and development steps, the toner image is at a position away from the photosensitive drum 16 so as not to disturb the developed toner image.

However, when transferring the toner image, the transfer device 20 contacts the photosensitive drum 16 and
A transfer bias is applied via OA. That is, the transfer device 20 sandwiches and conveys a recording medium (recording paper, OHP sheet, or the like) between the photoconductor drum 16 and draws the toner image toward the transfer device 20 by applying the transfer bias. Then, the toner image is transferred to a recording medium. In the case of monochromatic printing, the transfer device 20 does not need to be separated from the photosensitive drum 16.

Next, the transport path of the recording medium will be briefly described. A recording medium (not shown) is a recording medium feeding device 2.
1 are stacked on a detachable cassette tray 22 inserted into the cassette tray 22. The recording medium positioned on the uppermost layer of the cassette tray 22 is sent out one by one as the half-moon roll 23 rotates.

The fed recording medium is transported by the transport roll 24 as shown by the broken line P, and stops once it reaches the registration roll 25. Photoconductor drum 1
After the toner image to be transferred is formed on 6, an electromagnetic clutch (not shown) starts rotating the registration roll 25 in synchronization with the rotation position of the photosensitive drum 16. Thus, the recording medium is conveyed stably at a constant speed and passes between the photosensitive drum 16 and the transfer device 20 at a predetermined timing. During this passage, the transfer device 20 transfers the toner image on the photosensitive drum 16 onto a recording medium.

The recording medium to which the toner image has been transferred is conveyed by a conveying belt 26 along a path of a predetermined length, and then reaches a fixing device 27. In addition, holes (not shown) are provided at predetermined intervals on the surface of the transport belt 26 so that the recording medium is attracted to the transport belt 26 when the fan 41 described later blows air.

The fixing device 27 is provided with two rolls of a heat roll 28 and a pressure roll 29 with a predetermined nip width. The recording medium is conveyed such that the surface on which the toner image has been transferred faces the heat roll 28, and the pressure roll 29 presses the recording medium against the heat roll 28 to enable efficient heat conduction. The heat roll 28 is controlled at a constant high temperature, and heat-fixes the toner image on the recording medium to the recording medium surface.

A recording medium passage sensor 32B for detecting that the trailing end of the recording medium has passed is provided upstream of the nip portion of the two rolls in the recording medium conveyance direction. A recording medium passage sensor 32A that detects that the leading end of the recording medium has passed is provided downstream of the recording medium in the transport direction.

The recording medium that has passed through the fixing device 27 is conveyed along the conveyance path P by the discharge roll 30 and discharged to the upper portion of the color laser beam printer 10. On the other hand, the toner image remaining on the photosensitive drum 16 without being transferred to the recording medium is removed from the surface of the photosensitive drum 16 by the cleaning device 40. In the cleaning device 40, a built-in blade is applied to the surface of the photosensitive drum 16, and the blade removes toner. In the cleaning device 40, the toner on the photosensitive drum 16 may be electrically removed by applying a cleaning bias to the built-in brush.

The color laser beam printer 10 is equipped with a microcomputer (microcomputer) 50 for controlling various operations of the printing process. On the upper surface of the color laser beam printer 10, an operator starts the image forming process. A start button 47 for giving an instruction and an operation unit 48 for an operator to set a print mode, an OHP mode speed in the case of an OHP mode, a number of reciprocating conveyances, and the like, which will be described later, are provided.

The transfer belt 2 integrated with the transfer device 20
Numeral 6 is provided so as to be vertically movable between a position indicated by a solid line and a position indicated by a two-dot chain line in FIG. Hereinafter, a mechanism for moving the transport belt 26 up and down will be described with reference to FIGS.

The shafts 36 and 37 shown in FIGS. 6A and 6B are shafts for rotating the conveyor belt 26, and the shaft 36 serves as a fulcrum when the belt is moved up and down. The shaft 37 is urged in the direction of arrow D by a spring (not shown).
The movement of 7 in the direction of arrow D is suppressed by the belt up-down control part 38. The conveyor belt 26 moves up and down as the cam 39 built in the belt up / down control part 38 rotates 180 degrees about the shaft 39A. The cam 39 is provided with an electromagnetic clutch (not shown) controlled by the microcomputer 50, and the cam 39 rotates 180 degrees by one operation of the electromagnetic clutch.

FIG. 6A shows a state in which the conveyor belt 26 is at a position shown by a two-dot chain line in FIG. 1, and FIG.
Indicates a state in which the conveyor belt 26 is at a position indicated by a solid line in FIG.

When the cam 39 is rotated by 180 degrees from the state shown in FIG. 6A, the belt up / down control part 38 moves in the direction of arrow E shown in FIG. 6B, and the urging force in the direction of arrow D is applied by the spring. The conveyor belt 26 is pushed down in the direction of the arrow E against this. Further, the cam 39 is moved from the state shown in FIG.
When rotated by 0 degrees, the conveying belt 26 is pushed up in the direction of the arrow D by the urging force of the spring in the direction of the arrow D, and returns to the state of FIG.

As described above, the operation of the electromagnetic clutch controlled by the microcomputer 50 causes the cam 39 to rotate by 180 degrees, so that the conveyor belt 26 moves to the position shown by the solid line and the position shown by the two-dot chain line in FIG. Move up and down between

By the way, as shown in FIG.
6, a plurality of fans 41 whose operation is controlled by the microcomputer 50 are installed. When the recording medium is conveyed along the conveyance belt 26, the fan 41 is driven to blow air in the arrow F direction. In addition, it is possible to generate a negative pressure on the side of the transport belt 26 so that the recording medium is attracted to the transport belt 26.

[Configuration Related to Control of Fixing Process] Next, a configuration related to control of the fixing process will be described.

The color laser beam printer 10 includes:
As the print mode, there are provided two modes: a normal mode using plain paper as a recording medium, and an OHP mode using a recording medium having poor fixability such as an OHP sheet. Mode can be set. However, the default print mode is the normal mode, and if there is no setting by the operator, the normal mode is set as the print mode.

It is assumed that the recording medium is either plain paper or OHP paper, and the light reflectance on the surface of the recording medium is detected. Is set as the normal mode as the print mode automatically assuming that it is plain paper, and if the light reflectance is less than the predetermined value, the recording medium is regarded as OHP paper and the OHP mode is automatically set as the print mode. good.

FIG. 2 shows a procedure for conveying the recording medium in the fixing operation in the OHP mode. FIG. 2A shows a state where the toner image formed on the photosensitive drum 16 is transferred onto the OHP sheet 100 by the transfer device 20. The OHP sheet 100 onto which the toner image has been transferred is transported by the transport belt 26 as it is in the direction of arrow B.
8 and the pressure roll 29 to convey the sheet.

When the OHP paper 100 passes the position shown in FIG. 2B and the rear end of the OHP paper 100 is detected by the recording medium passage sensor 32A, the discharge roll 30, the fixing device 27, and the transport belt 26 are transported. The direction is reversed in the direction of arrow C, and the OHP paper 100 is again held and transported by the heat roll 28 and the pressure roll 29. OH
The timing of reversing the transport direction of the P paper 100 may be obtained by measuring a predetermined time corresponding to the length of the recording medium in the transport direction with a timer.

FIG. 2C shows the OHP sheet 100 being reversely conveyed in the direction of arrow C. At this time, the shaft 37 in FIG. 6A is moved downward so that the OHP sheet 100 conveyed in the direction of arrow C does not contact the photosensitive drum 16, and the conveying belt 26 is separated from the photosensitive drum 16.
The downward movement of the conveyance belt 26 may be performed after the transfer is completed and the recording medium is separated from the photosensitive drum 16, but before the recording medium conveyed in the reverse direction reaches the photosensitive drum 16.

The OHP recording medium 100 conveyed in the reverse direction in the direction of arrow C passes between the transfer device 20 and the photosensitive drum 16 and passes through the conveyance path 33 for the OHP mode fixing operation as shown in FIG. Get in. By doing so, a length equal to or longer than the length of the recording medium in the transport direction is provided between the transfer position by the transfer device 20 (= the nip portion between the transfer device 20 and the photosensitive drum 16) and the nip portion of the fixing device 27. Thus, the next image can be formed on the photosensitive drum 16 during the fixing operation.

When the leading edge of the OHP paper 100 passes through the position shown in FIG. 2D and is detected by the recording medium passage sensor 32B, the transport direction of the discharge roll 30, the fixing device 27, and the transport belt 26 is performed. Is reversed in the direction of arrow B, and the OHP paper 100 is again held and transported by the heat roll 28 and the pressure roll 29.

FIG. 2E shows the OHP sheet 100 being conveyed in the direction of arrow B (the direction in which the recording medium is discharged). Thereafter, the OHP sheet 100 is discharged out of the image forming apparatus. However, if the above process is repeated a plurality of times without discharging the sheet, more heat can be applied.

In this embodiment, when the OHP paper 100 is reciprocated by the transport belt 26 in the OHP mode to perform the fixing process a plurality of times, the microcomputer 50 drives the fan 41 during the reciprocating transport to blow air in the direction of arrow F. Then, the OHP paper 100 is attracted to the transport belt 26. This makes it possible to more reliably prevent the OHP sheet 100 from touching the photosensitive drum 16 during reciprocating conveyance. OH
As a method of adsorbing the P paper 100 to the transport belt 26, a method of electrically charging the OHP paper 100 by charging the transport belt 26 to a polarity opposite to the charging polarity of the OHP paper 100 may be adopted.

In the present embodiment, the transport speed of the recording medium and the number of reciprocating transports by the transport belt 26 and the fixing device 27 can be changed. For example, when performing a fixing process on a recording medium that requires a fixing process time that is about twice as long as the fixing process time of plain paper (= fixing process time in the normal mode),
The fixing process may be performed while setting the conveyance speed of the recording medium to 1.4 times that of the normal mode, and reciprocating the recording medium once. That is, by making the one-way transport time about 0.7 times longer than in the normal mode, and performing one reciprocating transport (= performing one-way transport three times), it is possible to secure about 2.1 times the fixing processing time in the normal mode. Can be. By setting the transport speed and the number of reciprocating transports according to the fixing processing time required for each recording medium in this manner, appropriate fixing processing can be performed with a necessary and sufficient fixing processing time while eliminating unnecessary fixing processing time. be able to.

[Control Process of Image Formation by Microcomputer 50] Next, a control process of image formation by the microcomputer 50 will be described with reference to FIG.

When the operator operates the operation unit 48 as necessary, the transport speed of OHP sheets in the print mode and the OHP mode (hereinafter referred to as OHP mode speed),
When the number of reciprocating conveyances and the like are specified and the start of the image forming process is instructed by the start button 47, the microcomputer 50 starts execution of the control routine of FIG.

In step 102 of FIG. 3, the print mode is set to either the normal mode or the OHP mode based on the contents specified by the operator. In the case of the OHP mode, the transport speed of the OHP sheet (hereinafter referred to as the OHP mode speed) is set. ) And the number of reciprocating conveyances.

Here, for example, as the speed for the OHP mode, a speed that is 1.4 times the speed in the normal mode (normal speed) is set, and the number of times of reciprocating conveyance is set to 1 (= fixing process is performed three times). To set). As a result, a fixing processing time approximately 2.1 times that of the normal mode is secured. In step 102, a counter N for counting the number of reciprocations is initialized to zero.

In the next step 104, an image forming process on the recording medium is performed. That is, the surface of the photosensitive drum 16 is uniformly charged by the charging device 18, and the charged photosensitive drum 16 is irradiated with the laser beam 13 by the laser scanning device 11, so that the surface of the photosensitive drum 16 is electrostatically charged. Form an image. Then, the electrostatic latent image is developed by the color developing device 19 to form a toner image, and the formed toner image is transferred to a recording medium by the transfer device 20.

In the next step 106, it is determined whether or not the print mode is the OHP mode. If the print mode is not the OHP mode but the normal mode, the process proceeds to step 108, in which the transport belt 26 and the fixing device 27 are moved at the normal speed until the recording medium passage sensor 32A detects the passage of the rear end of the recording medium. While rotating forward
The fixing device 27 performs a fixing process. When the passage of the rear end of the recording medium is detected by the recording medium passage sensor 32A, the process proceeds to step 132, where the recording medium is ejected by the ejection roll 30, and the process ends.

On the other hand, if the print mode is the OHP mode in step 106, the process proceeds to step 112, where the transport belt 26 and the fixing device 27 are turned off until the recording medium passage sensor 32A detects the passage of the rear end of the recording medium.
The fixing process is performed by the fixing device 27 while rotating forward at the P mode speed.

When the passage of the rear end of the recording medium is detected by the recording medium passage sensor 32A, step 11 is executed.
Then, the conveyor belt 26 is moved downward by rotating the cam 39 by 180 degrees from the state shown in FIG.

In the next step 118, fixing is performed by the fixing device 27 while rotating the conveyor belt 26 and the fixing device 27 in the reverse direction at the OHP mode speed until the recording medium passage sensor 32B detects the passage of the leading end of the recording medium. Perform processing. At this time, the fan 41 is driven to blow air in the direction of arrow F, and the OHP paper 100 is transported by the transport belt 26.
To be absorbed. This makes it possible to more reliably prevent the OHP sheet 100 from touching the photosensitive drum 16.

When the passage of the leading end of the recording medium is detected by the recording medium passage sensor 32B, step 12 is executed.
2 while rotating the conveyor belt 26 and the fixing device 27 at the OHP mode speed until the recording medium passage sensor 32A detects the passage of the rear end of the recording medium.
The fixing device 27 performs a fixing process. At this time, the fan 41 is driven to blow air in the direction of arrow F, so that the OHP paper 100 is attracted to the transport belt 26, and the OHP paper 100 is more reliably prevented from touching the photosensitive drum 16 as described above. I do.

When the passage of the trailing end of the recording medium is detected by the recording medium passage sensor 32A, the counter N is counted up by one at step 126, and then at the next step 12
In step 8, it is determined whether the counter N has reached the number of reciprocations set in step 102. If the counter N has not yet reached the set number of round trips, step 11
8, the fixing process is performed while the recording medium is reciprocated again.

On the other hand, if the counter N has reached the set number of reciprocations in step 128, it can be considered that the fixing process has been completed, so the process proceeds to step 130 and the cam 39 is turned 180 degrees from the state of FIG. After rotating the transport belt 26 upward to return it to the original position, the recording medium is discharged by the discharge roll 30 in step 132, and the process ends.

According to the embodiment described above, in the OHP mode, the fixing process is performed on the OHP sheet 100 a plurality of times by reciprocating the OHP sheet 100 at least once. Even if it is low, the toner image can be sufficiently fixed on the OHP sheet 100.

In the color laser beam printer 10, in the OHP mode, the transport belt 26 is separated from the photosensitive drum 16, and the OHP paper 100 is normally transported so that the OHP paper 100 does not touch the photosensitive drum 16. Since the sheet is transported in the opposite direction, the distance between the transfer position by the transfer device 20 (= the nip portion between the transfer device 20 and the photosensitive drum 16) and the nip portion of the fixing device 27 is set to the OHP paper 1.
00, the size of the apparatus can be avoided, and the next toner image can be formed on the photoconductor drum 16 immediately after the transfer process. It is possible to reduce the processing time of the image forming process for a low recording medium.

When the OHP paper 100 is transported in the direction opposite to the normal transport direction, the fan 41 is driven to attract the OHP paper 100 to the transport belt 26 by the negative pressure. 100 contact can be avoided more reliably.

In the OHP mode, the operator can set the transport speed of the recording medium and the number of reciprocating transports to desired values according to the fixing processing time required for the recording medium by using the operation unit 48. The fixing process can be performed for a fixing process time suitable for the recording medium.

In the above embodiment, the OHP paper 10
0 when transporting 0 in the opposite direction to the normal transport direction.
Although the example in which the paper 100 is adsorbed to the transport belt 26 has been described, it is not essential that the paper 100 be adsorbed in this way. If the possibility that the OHP paper 100 contacts the photosensitive drum 16 is extremely low without being adsorbed, the fan 41 Is omitted and OH
The P paper 100 does not have to be adsorbed on the transport belt 26.

It is not essential to provide a mechanism for separating the transport belt 26 from the photosensitive drum 16 when the OHP paper 100 is transported in the direction opposite to the normal transport direction in the image forming apparatus, as shown in FIG. , OHP paper 100
When the OHP paper 100 is transported in the direction opposite to the normal transport direction, the guide member 90 is moved in the direction of arrow G to enter the transport path, and the OHP paper 100 transported in the reverse direction is transported to the transport path 33 for the OHP mode fixing operation. By guiding, the contact of the OHP sheet 100 with the photosensitive drum 16 may be avoided.

In the above-described embodiment, an example in which the present invention is applied to a color laser beam printer has been described. However, the present invention is applicable to other image forming apparatuses such as a copying machine and a facsimile apparatus and a monochromatic image forming apparatus. Needless to say, this can also be applied.

Hereinafter, the OHP paper 100 in the OHP mode will be described.
The following describes two configuration examples in which the transfer route is different from the above.

FIG. 4 shows a configuration example in which the transfer device is constituted by a transfer corotron 34 to which the transfer device is fixed.
In this case, when the OHP paper 100 is transported in a direction opposite to the normal transport direction, the OHP paper 100 is prevented from touching the photosensitive drum 16 by moving the shaft 42 around which the transport belt 26 is wound downward. It can be guided to the transport path 33. As a result, the next image can be formed on the photosensitive drum 16 even while the OHP sheet 100 is being reciprocated.

FIG. 5 shows an example of a configuration in which the transport path for the OHP mode fixing operation is not provided. In this example, as shown in FIG. 5A, the pre-transfer chute 35 is separated from the photosensitive drum 16. OHP
When the paper 100 is conveyed and enters the transfer process, the conveyance belt 26 is moved in a direction approaching the photosensitive drum 16 so as to lift the conveyed OHP paper 100, and the transfer is performed as shown in FIG. The OHP sheet 100 is nipped and transported between the apparatus 20 and the photosensitive drum 16 to perform a transfer process. During the fixing process in the OHP mode after the transfer process is completed, the transport belt 26 is moved to the photosensitive drum 16.
In the direction away from, as shown in FIG.
The OHP sheet 100 is separated from the photosensitive drum 16.
As a result, the fixing process in the OHP mode and the formation of the next image on the photosensitive drum 16 can be performed simultaneously in parallel without providing a special conveyance path.

[0081]

As described above, according to the first aspect of the present invention, when a toner image is fixed on a recording medium having low fixability, the recording medium is moved at least once in the normal transport direction (predetermined direction). Since the fixing process is performed while transporting the recording medium in the reverse direction, the fixing process is performed on the recording medium a plurality of times, and the toner image can be sufficiently fixed on the recording medium. Further, since the fixing unit is arranged so that the distance between the fixing unit and the transfer unit is equal to or less than the length along the predetermined direction of the recording medium, it is possible to avoid an increase in the size of the apparatus.
Since the recording medium is conveyed in a direction opposite to the predetermined direction so that the recording medium does not touch the image carrier, immediately after the transfer by the transfer unit is completed, the next toner image can be formed, and the recording medium having low fixability can be used. The processing time of the image forming process can be reduced.

According to the second aspect of the present invention, when the recording medium is conveyed in the reverse direction, the conveyance means can be separated from the image carrier by the separation arrangement means, so that the recording medium conveyed by the conveyance means Can be reliably prevented from contacting the image carrier.

According to the third aspect of the present invention, when the recording medium is conveyed in the reverse direction, the recording medium can be adsorbed by the conveying means separated from the image carrier by the adsorbing means. The contact of the recording medium with the recording medium can be avoided more reliably.

According to the fourth aspect of the invention, the operator of the image forming apparatus changes the operation mode of the image forming apparatus to the mode for fixing the toner image on the recording medium having low fixability or the normal mode by the mode setting means. A normal mode for fixing a toner image on paper can be set.

According to the fifth aspect of the present invention, the setting means sets the conveying speed of the recording medium by each of the roller pair and the conveying means and the speed of the recording medium in accordance with the fixing processing time required for the recording medium. Since the number of times of the fixing process is set, the fixing process can be performed for a fixing process time suitable for the recording medium.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a color laser beam printer according to an embodiment of the present invention.

2A and 2B are diagrams for explaining a flow of a fixing process in an OHP mode, in which FIG. 2A is a diagram illustrating a state of a transfer process before a fixing process, and FIG. FIG. 9C is a diagram illustrating a state immediately after the second fixing process is performed while the OHP sheet is being transported in the reverse direction, and FIG. 9D is a diagram illustrating the state of the second fixing process. FIG. 10E is a diagram illustrating a state immediately before the end, and FIG. 10E is a diagram illustrating a state when the third fixing process is being performed while the OHP sheet is transported again in the forward direction.

FIG. 3 is a flowchart illustrating a processing routine of an image forming process according to the embodiment of the present invention.

FIG. 4 is a schematic configuration diagram when a transfer device is configured by a fixed transfer corotron.

FIG. 5 is a diagram for explaining a configuration in which a transport path for an OHP mode fixing operation is not provided and a recording medium is prevented from coming into contact with a photosensitive drum during reverse transport only by vertical movement of a transport belt. (A) is a diagram showing a state immediately before the transfer process, (B) is a diagram showing a state during the transfer process,
FIG. 6C is a diagram illustrating a state where the second fixing process is performed while the OHP sheet is being transported in the reverse direction.

6A and 6B are explanatory diagrams of a mechanism for moving the transport belt up and down, wherein FIG. 6A is a diagram illustrating a state when the transport belt is moved to an upper position, and FIG. It is a figure showing the state at the time of moving to the position.

FIG. 7 is a diagram illustrating an example of a configuration in which a recording medium is prevented from coming into contact with a photosensitive drum during reverse conveyance while the conveyance belt is fixed.

8A and 8B are diagrams for explaining the flow of a conventional fixing control for a recording medium having poor fixability, where FIG. FIG. 7B is a diagram illustrating a state immediately before the second fixing process is started by conveying the recording medium in the reverse direction, and FIG. 8C is a diagram illustrating the state immediately before the second fixing process is started; FIG. 10 is a diagram showing a state immediately before the third fixing process is started.

9A is a time chart showing the progress of various processes when an image is formed on plain paper, and FIG. 9B is a conventional various process for forming an image on a recording medium having poor fixability. 7C is a time chart showing the progress of various processes when the fixing process and the image forming process on the next recording medium are performed in parallel.

FIG. 10 is a diagram illustrating a configuration in which a fixing device and a transfer device are arranged at intervals longer than a length along a conveyance direction of a recording medium.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Color laser beam printer 16 Photoreceptor drum 20, 34 Transfer device 26 Conveyor belt 27 Fixing device 28 Heat roll 29 Pressure roll 33 OHP mode fixing operation conveyance path 38 Belt up / down control parts 39 Cam 41 Fan 48 Operation unit 50 Microcomputer 100 OHP Paper

Claims (5)

[Claims] A transfer unit configured to transfer a toner image formed on an image carrier to a recording medium; a recording medium on which the toner image has been transferred is transported in a predetermined direction away from the image carrier; Transport means for transporting the recording medium in a direction opposite to the predetermined direction so that the recording medium does not touch the image carrier; and a distance between the transfer means and the transfer means downstream of the transfer means in the predetermined direction. The recording medium is arranged so as to have a length equal to or less than the length along the predetermined direction, and includes a roller pair including a heating roller. A fixing unit for fixing the transferred toner image to the recording medium by fixing the toner image to a recording medium having a low fixability predetermined by the fixing unit. Control means for controlling the toner image to be fixed on the recording medium while the recording medium is conveyed at least once in the predetermined direction by the pair of rollers and conveyed at least once in a direction opposite to the predetermined direction. Forming equipment. 2. The image forming apparatus according to claim 1, further comprising: a separating unit configured to separate the transport unit provided to be able to approach and separate from the image carrier when transporting the recording medium in the reverse direction. The image forming apparatus according to claim 1, further comprising: 3. The image forming apparatus according to claim 2, further comprising suction means for sucking the recording medium onto the conveyance means when conveying the recording medium in the reverse direction. 4. A mode setting means for setting an operation mode of the image forming apparatus to a mode for fixing a toner image on the recording medium having low fixability or a normal mode for fixing a toner image on plain paper. The image forming apparatus according to claim 1. 5. A setting unit for setting a conveying speed of the recording medium by each of the roller pair and the conveying unit and a number of times of fixing processing on the recording medium according to a fixing processing time required for the recording medium. The image forming apparatus according to claim 1, further comprising: