JPH0895425A - Image forming device - Google Patents

Abstract

PURPOSE: To always attain an excellent fixing by switching the quantity of heat supplied for fixing in accordance with an image forming mode and the kind of recording paper, etc. CONSTITUTION: At the time of copying in a monochrome image forming mode, a control signal is outputted to the driving circuit 104 of a fixing motor M2, to drive a fixing roller at the same speed as a system speed. At the time of copying in a multicolor image forming mode, it is judged whether to execute a copy in an OHP-gloss mode or in a normal mode. In the normal mode, a fixing initial speed and deceleration which are suitable to multicolor image formation are set, it is decided whether the leading edge of the recording paper has been detected or not by a paper detecting sensor S and when the leading edge has been detected, the driving speed of the fixing motor M2 is reduced to make speed slow over the total fixing process and supply a large quantity of heat to the recording paper. Then, the speed of the fixing roller is reduced according to the passage of the recording paper. In the OHP-gloss mode, the fixing initial speed and the deceleration are set to be lower than that in the normal mode, to obtain a glossy image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a heat fixing device for fixing a toner image on a recording paper by a pair of fixing rollers.

[0002]

2. Description of the Related Art An electrophotographic image forming apparatus, for example,
In a copying machine or a laser beam printer, a toner image on recording paper is fixed by a heat fixing device. The thermal fixing device has a pair of fixing rollers each having a heater built into both or one of them, and conveys the recording paper while nipping the recording paper in the nip portion of the fixing roller pair which is kept at a high temperature by the heater. It melts and fixes the toner image.

In this heat fixing device, heat is taken from the surface of the fixing roller by melting the toner, or heat is taken to the recording paper itself passing through the fixing roller. It decreases as the paper passes. Therefore, the amount of heat applied to the second half of the recording paper is reduced as compared with the first half of the recording paper, which causes defective fixing in the second half of the recording paper. Even if the fixing failure does not occur, the glossiness of the image in the first half of the recording paper and the glossiness of the second half of the recording paper differ from each other, and the image quality deteriorates. That is, a toner image that has been sufficiently melted by receiving a large amount of heat has high glossiness, and a toner image that has been melted with an insufficient amount of heat has low glossiness.

In order to solve such a problem, in Japanese Utility Model Publication No. 4-1564, the rotational speed of the fixing roller is gradually reduced while the recording paper is passing, and the fixing speed in the latter half of the recording paper is set to the first half of the recording paper. A thermal fixing device has been proposed in which the fixing speed is controlled so that the amount of heat given to the latter half and the amount of heat given to the first half are made slower than the latter.

[0005]

However, in the apparatus of Japanese Utility Model Publication No. 4-1564 described above, the fixing speed is uniquely controlled although it is more effective than the apparatus fixing at a constant speed. It was insufficient. That is,
In the case of forming a multi-color image by superimposing toner images of a plurality of colors, the amount of toner fixed becomes larger than that of a single-color image, so the above-mentioned decrease in the amount of heat in the latter half of the recording paper becomes remarkable. . Therefore, a multicolor image forming mode in which a plurality of developing devices having different developing colors are provided to form a multicolor image by superposing toner images of a plurality of colors, and only one of the developing devices is operated to supply a monochromatic toner In the full-color image forming apparatus capable of operating in the single-color image forming mode for forming an image, in the multi-color image forming mode and the single-color image forming mode, the fixing speed is uniquely controlled.
In either one of the modes, the image quality of the image is deteriorated. Furthermore, even in the multicolor image forming mode,
When forming an image on the HP film, or when forming an image having a particularly high glossiness, a larger amount of heat of fixing is required than in the normal multicolor image formation.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus which always performs good fixing by switching the amount of fixing heat to be applied according to the image forming mode, the type of recording paper and the like.

[0007]

In view of the above circumstances, the invention described in claim 1 is a heat for fixing a toner image on a recording paper by nipping and conveying the recording paper by a pair of fixing rollers pressed against each other. An electrophotographic image forming apparatus using a fixing device, comprising: an image forming unit that conveys a recording sheet to form a toner image on the recording sheet; and a recording sheet on which the toner image is formed by the image forming unit. Transporting means for transporting the recording paper to the recording paper, detecting means for detecting the position of the transported recording paper, driving means for changing the rotation speed of the fixing roller, and fixing roller for the recording paper based on the detection result by the detecting means. Control means for determining the time point of entry into the fixing roller and selectively setting the rotation speed of the fixing roller to one of a plurality of preset fixing initial speeds.

Further, according to the invention described in claim 2, in the image forming apparatus according to claim 1, the rotational speed of the fixing roller is decelerated as the recording sheet passes after the recording sheet has entered the fixing roller. It is characterized in that the rate of deceleration is changed according to the initial fixing speed set when the recording paper enters the fixing roller.

Further, the invention according to claim 3 is the image forming apparatus according to claim 1, wherein the image forming means comprises:
A multicolor image forming mode having a developing device for a plurality of developing colors and operating a plurality of developing devices to form a multicolor image, and a single color image forming for operating one of the developing devices to form a single color image Image formation is possible depending on the mode, and different initial fixing speeds are selected according to the switching of the mode.

[0010]

According to the image forming apparatus of the present invention, the rotation speed of the fixing roller is selectively set to one of a plurality of preset fixing initial speeds at the time when the recording paper enters the fixing roller. To be done.

Further, in the image forming apparatus of the second aspect, in addition to the operation of the first aspect, the rotational speed of the fixing roller is decelerated as the recording sheet passes after entering the fixing roller. The rate of such deceleration is changed according to the initial fixing speed set when the recording paper enters the fixing roller.

Further, in the image forming apparatus of the third aspect, in addition to the operation of the image forming apparatus of the first aspect, different initial fixing speeds are selected according to switching between the multicolor image forming mode and the single color image forming mode. It

[0013]

1 is a diagram showing a schematic configuration of a full-color copying machine 1 to which the present invention is applied. Reference numeral 10 in the drawing denotes a platen glass, and the document is placed with the image surface to be copied facing downward. A slider 11 capable of scanning and moving in the direction of arrow a is provided below the original platen glass 10, and the slider 11 includes an exposure lamp 12, a lens array 13, and a CCD.
The line sensors 14 are arranged with their longitudinal directions aligned with the main scanning direction (the direction in which the slider 11 moves is the sub-scanning direction and is orthogonal thereto).

The light emitted from the exposure lamp 12 is reflected by the image surface of the original on the original glass 10, is imaged on the line sensor 14 by the lens array 13, and the slider 11
By scanning and moving in the direction of arrow a, the image of the entire area of the document is read. Due to this scanning movement, R (red) corresponding to the image of the original is read from the line sensor 14.
G (green) and B (blue) color signals are output and input to the image processing circuit 15. In the image processing circuit 15,
The color signals of R, G, and B are converted into Y (yellow), M of the development color
The image signals are converted into four-color image signals of (magenta), C (cyan), and BK (black) and output to the laser optical system 20.

The laser optical system 20 is provided with a laser diode 21 for generating a laser beam, a scanning polygon mirror 22 for deflecting the laser beam, an fθ lens 23, a reflection mirror 24, etc., and the colors Y, M, C and BK. The image forming laser beam of each color modulated based on the signal is irradiated toward the photoconductor drum 30 to perform scanning exposure.

The photoconductor drum 30 is made of an organic optical semiconductor laminated on a conductor-based drum, and is driven to rotate counterclockwise in the figure. The surface of the photoconductor drum 30 is charged to a predetermined negative potential by the charging charger 31, and the charged surface of the photoconductor drum 30 receives the scanning exposure of the laser beam from the laser optical system 20 to form a latent image of each color. Is formed.

The latent image formed on the surface of the photosensitive drum 30 is developed by the developing devices 32Y, 32M, 32C and 32BK containing toners of Y, M, C and BK, respectively, and is held on the transfer drum 40. It is transferred by the transfer charger 33 onto the recording paper. The toner remaining on the photosensitive drum 30 without being transferred by this transfer is collected by the drum cleaner 34, and the cleaned surface of the photosensitive drum 30 is erased by the erase lamp 35 and charged again by the charging charger 31. .

Recording paper such as plain paper and OHP film is stored in a stacked state in the paper feed cassettes 51a and 51b, or
The sheets are set one by one in the manual feed cassette 51c and fed one by one toward the inside of the copying machine by the paper feed rollers 52a and 52b. The fed recording paper is conveyed by a pair of conveyance rollers 53.
When the leading edge of the recording paper is brought into contact with the registration roller pair 54 by the a, 53b, and 53c, the recording paper is temporarily stopped to correct the skew, and the photoconductor drum 30 is synchronized. And is conveyed to the transfer drum 40.

The recording paper conveyed to the transfer drum 40 is chucked on the transfer drum 40, and the suction charger 4
At 1, the toner is electrostatically adsorbed on the surface of the transfer drum 40 and is conveyed to the transfer portion facing the photoconductor drum 30 as the transfer drum 40 rotates.

At the transfer portion, the toner image on the photosensitive drum 30 is transferred onto the recording paper as described above. However, when a multicolor image (full color image) is formed, the transfer drum 40 is used for recording. With the paper held, rotate 4 times, and with each rotation,
The toner images of Y, M, C, and BK are sequentially transferred to the recording paper,
The toner images of the respective colors are superimposed on the recording paper to form a multicolor image. The recording paper on which the toner image is transferred is neutralized by the separation chargers 42 and 43, and separated from the transfer drum 40 by the separation claw 44.

The separated recording paper is conveyed to the conveyance deck 55 and then to the heat fixing device 60. Here, the transport deck 55 is a belt stretched between two rollers which are separated from each other. The belt is driven by rotating the rollers, and the recording paper is placed on the upper surface of the belt. Transport. Further, the transport deck 55 is provided with a sheet detection sensor S for detecting the position of the recording sheet.

As shown in FIG. 2, the heat fixing device 60 has an upper roller 61 and a lower roller 62 of the same diameter arranged in pressure contact with each other. The rollers 61 and 62 have heaters 63 and 62, respectively. 64 is built in and keeps the roller surface at a high temperature. Cleaning rollers 65 and 66 are arranged in pressure contact with the upper roller 61 and the lower roller 62,
The surfaces of the rollers 61 and 62 are cleaned.
Further, the upper roller 61 is provided with an oil application unit 67, which applies oil to the surface of the upper roller 61 to prevent toner from adhering thereto.

The thermal fixing device 60 thus constructed is
The lower roller 62 is rotated by being driven by the fixing motor M2 (see FIG. 3), and the upper roller 61 is driven to rotate accordingly, and the recording paper is pressed onto the pressure contact portion (nip portion) of both rollers 61 and 62. The toner image on the recording paper is heated and pressed to be fixed on the recording paper.

Further, the fixing motor M2 for driving the thermal fixing device 60 is provided independently of other driving systems, and is constructed so that the driving speed can be changed. That is, the photoconductor drum 30, the transfer drum 40, and the rollers for conveying the recording paper are driven by the main motor M1 (see FIG. 3) so as to keep the drive speed (system speed) constant. The speed (fixing speed) can be variably controlled independently of the system speed so that another fixing motor M can be used.
Driven by 2.

However, the transport deck 55 is a fixing motor M.
The fixing roller 6 is configured to be driven by
The speed switching of Nos. 1 and 62 is performed together with the transport deck 55 so that there is no problem in exchanging recording sheets with each other.

The recording paper on which the toner image is thus fixed is
The sheet is discharged onto the discharge tray 57 by the discharge roller 56.

The full-color copying machine 1 described above is capable of image formation in both the multi-color image forming mode and the single-color image forming mode, and further, in the multi-color image forming mode, the normal mode and the OHP / glossy mode. Can be selected. The OHP / glossy mode corresponds to a case where an image is formed on an OHP film and a case where an image having a particularly high glossiness is formed. The choice of these modes is
This is performed by operating a key on a control panel 102 (see FIG. 3) (not shown).

When the monochromatic image forming mode is selected, the original image is read by one scanning movement of the slider 11, and the monochromatic image signal designated by this (black BK is designated here). Will be generated). The laser beam output from the laser diode 21 is modulated according to this signal, and a latent image is formed on the photosensitive drum 30. The formed latent image is developed by the developing device 32BK, transferred onto recording paper, and fixed by the thermal fixing device 60. At this time, the thermal fixing device 60 is driven at the same speed (V0) as the system speed.

On the other hand, when the multicolor image forming mode is selected, the original image is read by four scanning movements of the slider 11, and Y, M, C and BK image signals are generated in each scanning. It The laser diode 21 is modulated in accordance with the Y image signal generated in the first scanning to move the photosensitive drum 30.
The latent image formed above is developed by the developing device 32Y and transferred onto the recording paper. Subsequently, the latent image based on the M image signal generated by the second scanning is the developing device 3
The image is developed at 2M and is transferred onto the recording paper on which the Y toner image has been transferred.

In this way, by four scans,
The recording paper on which the toner images of Y, M, C, and BK are superposed and transferred is fixed by the thermal fixing device 60. At this time, the driving speed of the fixing roller 62 when the recording paper enters the thermal fixing device 60 is a constant speed slower than the system speed. This is because fixing a multicolor image requires a larger amount of heat than fixing a single color image, so that the fixing speed is slowed down to give a large amount of heat to the recording paper. is there. Further, when the rollers 61 and 62 make one rotation and the temperature of the roller surface decreases, the fixing speed is further reduced as the recording paper passes, and the heat quantity shortage due to the temperature decrease of the rollers 61 and 62 is compensated.

FIG. 3 is a block diagram of a control circuit for controlling the operation of the full-color copying machine 1. In the figure, 100 is a microcomputer (CPU) that outputs a control signal to each part of the copying machine according to the state of each part of the copying machine by inputting a signal from a sensor of each part of the copying machine and executing a program stored in ROM 101. ). The CPU 100 has
Various key outputs including a signal for designating the image forming mode are input from the control panel 102, and outputs from the paper detection sensor S provided on the transport deck 55 are input.

On the other hand, from the CPU 100, the drive circuit 103 for controlling the drive of the main motor M1 is instructed to start / stop the drive of the main motor M1, and the fixing motor drive circuit 104 is instructed to the fix motor. A signal for instructing the start / stop of driving of M2 and the driving speed is output. As a result, the main motor M1 is controlled to start / stop the rotation drive at a constant speed, and the fixing motor M2 is
The start / stop of rotation drive and the rotation speed are controlled.

The CPU 100 receives inputs from other various sensors, switches, etc., and outputs a number of other control signals to each section of the copying machine. However, since they are not directly related to the present invention, the description thereof is omitted here. Omit it.

FIG. 4 is a flowchart showing a processing procedure of drive control of the thermal fixing device 60, which is executed by the CPU 100. First, in step S1, it is determined whether the copying is in the multi-color image forming mode or the single-color image forming mode. If it is determined that the copying is in the single color image forming mode, the process proceeds to step S20, a control signal is output to the drive circuit 104 of the fixing motor M2, and the fixing roller 62 is moved at the same speed as the system speed ( V0)
Drive with.

On the other hand, in the case of copying in the multicolor image forming mode, it is further determined in step S2 whether the copying is in the OHP / gloss mode or the normal mode.

When it is determined that the copying is in the normal mode, the initial fixing speed (Vb) and the deceleration (D2) suitable for the multicolor image formation are set in steps S11 and S12. Then, in step S13, it is determined whether or not the leading edge of the recording paper is detected by the paper detection sensor S. If detected, the driving speed of the fixing motor M2 is decelerated after the time t1, and the fixing roller 62 is moved to the fixing roller 62 in step S11. It is driven at the set initial fixing speed (Vb) (steps S14 and S1).
5).

Here, the time t1 corresponds to the time required to reach immediately before the thermal fixing device 60 after the recording paper is detected by the sensor S. The initial fixing speed (Vb) is
It is set lower than the system speed, but this is
This is because a multicolor image inevitably has a large amount of toner and a large amount of heat is required for fixing as compared with a single-color image, so that the fixing speed is slowed down throughout the fixing process to give a large amount of heat to the recording paper.

Next, in step S16, after a lapse of time t2, the driving speed of the fixing roller 62 is decelerated by the deceleration (D2) as the recording paper passes (step S17). Here, the time t2 corresponds to the time required for one rotation of the fixing rollers 61 and 62 after the recording paper has entered the nip portion of the fixing rollers 61 and 62. That is, the fixing roller 6
The first rotation of Nos. 1 and 62 is constantly driven at the above-described initial speed (Vb), and then the fixing speed is reduced as the recording paper passes.

Then, in step S18, the discharge tray 5
When it is confirmed that the recording paper has been discharged to the printer 7, the step S19
Then, the drive speed of the fixing roller 62 is set to the system speed (V0).
Accelerate to prepare for the next copy.

On the other hand, if it is determined in step S2 that the copying is in the OHP / gloss mode, step S3,
The initial fixing speed (Va) and the deceleration (D1) are set in S4.

Here, the initial fixing speed (Va) is set lower than the initial fixing speed (Vb) in the normal mode. This is because by providing a larger amount of fixing heat than in the case of forming a normal multicolor image, sufficient transparency on the OHP film is ensured or an image with gloss is obtained. .

The deceleration (D1) is set smaller than the deceleration (D2) in the normal mode. This is because in the OHP / glossy mode, the initial fixing speed is set low, so if the deceleration is increased, the amount of heat for fixing becomes excessive in the latter half of the recording paper, which may adversely affect the image such as offset. Is.

Further, when the detection of the leading edge of the recording paper by the paper detection sensor S is confirmed in step S5, thereafter, the initial fixing speed (Va) set in steps S3 and S4 is set in the same manner as in the normal mode. ) And deceleration (D1) to control the fixing speed (steps S6 to S9), and step S1
When it is confirmed that the recording paper is discharged at 0, the driving speed of the fixing roller 62 is returned to the system speed (V0) at step S19.

FIG. 5 shows the fixing rollers 61 and 6 described above.
6 is a graph showing a state of deceleration control of No. 2. The vertical axis of the graph shows the driving speed, and the horizontal axis shows the time. In the graph (1)
The deceleration control shown by means the normal mode of the present embodiment, and is maintained at the initial speed (Vb) during the time t2 (while the fixing rollers 61 and 62 make one rotation), and thereafter, as the recording paper passes, In the process of step S9 described above, the vehicle is decelerated at a constant rate (deceleration (D2)).

(2) in the graph shows the OHP / gloss mode of the present embodiment, and the initial velocity (V
It is maintained at a), and thereafter, as the recording paper passes, the speed is reduced at a constant rate (deceleration (D1)) in the process of step S17.

Further, (3) in the graph is a comparative example shown in comparison with the present embodiment, and in the OHP / gloss mode, after maintaining the initial speed (Va) for a time t2,
The case where the deceleration is performed at the same deceleration (D2) as in the normal mode of the present embodiment as the recording paper passes is shown.

FIG. 6 shows the present embodiment (1) shown in FIG.
6 is a graph showing the glossiness of the copied images obtained in (2) and Comparative Example (3), where the vertical axis represents the glossiness and the horizontal axis represents the length of the recording paper in the sheet passing direction. The gloss of the image here is MUR.
AKAMI COLOR RESEARCH LABOR
It was measured using a gloss meter manufactured by ATORY.

As is clear from the graph, this embodiment
(1) That is, in the normal mode, good gloss is stably obtained over the entire area of the recording paper. Further, it can be seen that in the present embodiment (2), that is, the OHP / glossy mode, the glossiness is higher than that in the normal mode, and is near the upper limit of the good region.

On the other hand, in Comparative Example (3), time t2
After the lapse of time, the amount of heat of fixing becomes excessive, and the image quality is deteriorated by exceeding the area where the gloss is good.

As described above, in the copying machine of this embodiment, the rotation speed of the fixing roller is selectively set to one of a plurality of preset initial speeds according to the switching of the image forming mode. The rate of deceleration of the fixing speed after that is set according to the set initial speed, so that an appropriate amount of fixing heat is given in any mode to always obtain a good image. You can

In the present embodiment, the rate of deceleration of the fixing speed is changed according to the initial fixing speed. However, for example, when the fixing pressure of the fixing roller pair is made variable, the recording paper is rushed into the fixing roller. That is, it is possible to change the rate of deceleration of the fixing speed thereafter according to the fixing pressure at the initial stage of fixing.

Finally, in this embodiment, a full color copying machine is shown, but the present invention is not limited to this.
The present invention can be applied to all electrophotographic image forming apparatuses, such as a printer.

[0053]

According to the first aspect of the present invention, the rotation speed of the fixing roller is one of a plurality of initial fixing speeds set in advance when the recording paper enters the fixing roller.
Since it is selectively set to one, it is possible to provide an appropriate amount of fixing heat according to various conditions, and it is possible to always obtain a good image.

Further, according to the invention described in claim 2,
In addition to the effect of claim 1, the rate of deceleration of the rotational speed of the fixing roller thereafter is changed according to the initial fixing speed set when the recording paper enters the fixing roller. Therefore, regardless of the initial fixing speed. Instead, an appropriate amount of heat for fixing is provided over the entire area of the recording paper.

Further, according to the invention described in claim 3,
In addition to the effect of claim 1, different fixing initial speeds are selected for the multi-color image forming mode that requires a large amount of heat for fixing and the single-color image forming mode that does not require a large amount of heat for fixing. A sufficient amount of fixing heat is given, and a good image can be obtained in any mode.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a full-color copying machine to which the present invention is applied.

FIG. 2 is a diagram showing a configuration of a heat fixing device.

FIG. 3 is a block diagram of a control circuit of a full-color copying machine.

FIG. 4 is a flowchart showing a procedure of drive control of the thermal fixing device.

FIG. 5 is a graph showing how the fixing roller is decelerated.

FIG. 6 is a graph showing the glossiness of an image.

[Explanation of symbols]

30: Photosensitive drum (image forming means) 55: Conveying deck (conveying means) 60: Thermal fixing device 61: Upper roller 62: Lower roller 100: CPU (control device) S: Paper detection sensor (detection device) M1: Main Motor M2: fixing motor (driving means)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 21/14

Claims (3)

[Claims] 1. An electrophotographic image forming apparatus using a heat fixing device for fixing a toner image on a recording paper by nipping and conveying the recording paper with a pair of fixing rollers pressed against each other. An image forming unit configured to convey a recording medium on which a toner image is formed on the recording sheet, and a conveyance unit configured to convey the recording sheet on which the toner image is formed by the image forming unit to a fixing device;
A detection unit that detects the position of the recording paper that is conveyed, a drive unit that drives the rotation speed of the fixing roller to be changeable,
Control means for determining a time point when the recording paper enters the fixing roller from the detection result of the detecting means, and selectively setting the rotation speed of the fixing roller to one of a plurality of preset fixing initial speeds; An image forming apparatus comprising: 2. After the recording paper enters the fixing roller, the rotation speed of the fixing roller is reduced as the recording paper passes, and the rate of such deceleration is set at the initial fixing time set when the recording paper enters the fixing roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed according to a speed. 3. The image forming means has a developing device for a plurality of developing colors, and a multicolor image forming mode for operating a plurality of developing devices to form a multicolor image, and one developing device. The image forming apparatus according to claim 1, wherein image formation is possible in a monochromatic image forming mode in which the image forming apparatus is operated to form a monochromatic image, and different initial fixing speeds are selected according to switching of the mode.