JPH1115331A - Image forming device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an image without deteriorating the image density to the level to prevent omission of information at higher image forming speed than the default image forming speed. SOLUTION: The image forming speed is switched to be V2 by a speed switching part 306 and when printing is started, speed control of a driving motor 310 is started at V2 by an operation controlling part 307, and a nip is set to be wide by a controlling fixing part conditions part 309. Then, respective latent images are formed on two different photoconductive drums by a known method and the latent images formed on these two photoreceptor drums are respectively developed by two black developing apparatuses selected by a developing apparatus selection part 308. After that, a toner image on the photoconductive drum in the upstream side is at first transferred to a fed transfer material and a toner image on the photoconductive drum in the downstream side is then transferred to the resultant transfer material and the transfer material on which the toner images are multi-transferred is sent between a fixing roller and a pressurizing roller of a fixing apparatus to fix the toner images on the transfer material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus and method for forming an image by an electrophotographic recording method or the like.

[0002]

2. Description of the Related Art As an image forming apparatus for forming an image by an electrophotographic recording method or the like, a personal, low-speed machine, medium-speed machine,
Diversified with high-speed machines, colors, special applications, etc.
The cost of an image forming apparatus is related to the image forming speed (also called print speed) when the resolution is the same. In general, a low-speed machine with a low image forming speed is cheap and a high-speed machine with a high image forming speed is cheap. Therefore, image forming apparatuses from low-medium-speed machines to high-speed machines are selected and used according to various applications.

[0003]

Although images for long-term storage require sufficient fixability, images for short-term storage do not always require a high level of fixability. It may be enough if there is no information missing. In the case of a graphic image, the recording speed may be reduced because the image is desired to be sharp, but in the case of a character image, the image does not need to be so high in quality.
There is a demand to increase the recording speed. Also, in the case of a color image, the recording speed may be slow, so a clear and high-quality image is demanded. In the case of a monochrome image such as a black-and-white image, the image need not be so high in quality. There is a demand for speed.

In order to meet such a demand, when the image forming speed of an image forming apparatus (low, medium, high speed machine) is increased,
In the obtained image, the density is reduced, information is lost, and in order to correspond to a plurality of image forming speeds, the setting conditions in each step of image forming, developing, transferring, fixing, etc., are largely changed. It has to be changed, and there has been a problem that the apparatus becomes complicated and the apparatus cost increases.

[0005] A laser printer having two types of image forming speeds by one laser printer is also known. The laser printer has one developing device, but when printing at 600 dpi, the printing speed is 16 sheets / min, and only when printing at 1200 dpi, the process speed is reduced by half. Print speed 8
Sheets / minute. In general, the printing speed of this laser printer is 16 sheets / min. However, at this printing speed, printing is performed at 600 dpi, so that sufficient image characteristics can be obtained, and high resolution is required for special applications. In this case, printing can be performed at 1200 dpi.

[0006] In the case of this laser printer as well, when the image forming speed is increased in order to meet the above demands,
In the obtained image, the density is reduced, information is lost, and in order to correspond to a plurality of image forming speeds, the setting conditions in each step of image forming, developing, transferring, fixing, etc., are largely changed. It has to be changed, and there has been a problem that the apparatus becomes complicated and the apparatus cost increases.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to form an image at an image forming speed higher than the default image forming speed without lowering the image density to the extent that information is not lost. It is an object of the present invention to provide an image forming apparatus and method capable of performing the above.

[0008]

According to a first aspect of the present invention, there is provided at least two image forming units, a moving speed switching unit for switching a moving speed of an image carrier, and a moving speed for setting a moving speed of the image carrier. When the moving speed is set to the first moving speed by the setting device and the moving speed setting device, an image is formed using only one of the two image forming devices, and the moving speed setting is performed. Means for forming a latent image on an image carrier on the upstream side of the two image forming means, and developing and transferring the latent image when the second moving speed is set to a predetermined second moving speed higher than the first moving speed by the means; Means for forming a latent image on the downstream image carrier of the two image forming means, developing the latent image, developing the latent image, and transferring the latent image to the transfer material.

According to a second aspect of the present invention, there is provided an image forming means having a plurality of developing devices, a moving speed switching means for switching a moving speed of an image carrier, and a moving speed setting means for setting a moving speed of the image carrier. Forming an image using only one of the plurality of developing devices when the moving speed is set to the first moving speed by the moving speed setting means;
When the moving speed is set to a predetermined second moving speed higher than the first moving speed by the moving speed setting means, one image carrier is used by using at least two developing devices of the plurality of developing devices. Means for multiple development on the body and transferring to a transfer material.

3. The image forming apparatus according to claim 1, further comprising a fixing unit capable of switching to a plurality of fixing capacities, wherein when the moving speed is set to the first moving speed by the moving speed setting unit, the fixing unit is set to the first moving speed. When the second moving speed is set by the moving speed setting unit, the fixing unit controls the fixing capability to a predetermined second fixing capability higher than the first fixing capability. be able to.

According to a third aspect of the present invention, the fixing unit is configured to perform fixing using a thermal unit, and when the moving speed is set to the first moving speed by the moving speed setting unit, the fixing unit is fixed to the fixing unit. A first heat quantity is supplied, and when the moving speed is set to the second moving speed by the moving speed setting means, a predetermined second heat quantity larger than the first heat quantity is supplied to the fixing means. be able to.

In any one of the first to fourth aspects, there is provided a means for inputting image information, and the moving speed can be controlled to be switched to the first moving speed or the second speed based on the input means.

According to a sixth aspect of the present invention, when the moving speed is set to a predetermined second moving speed higher than the first moving speed, the image forming means is disposed on the upstream image carrier of at least two image forming means. Forming a latent image, developing and transferring the latent image to a transfer material, and forming a latent image on a downstream image carrier of the two image forming units, developing the latent image, and transferring the latent image to the transfer material. And characterized in that:

According to a seventh aspect of the present invention, when the moving speed is set to a predetermined second moving speed higher than the first moving speed, one of the plurality of developing devices is used for one of the developing devices. A step of performing multiple development on the image carrier and transferring the image to a transfer material.

The step of controlling the fixing ability of the fixing means to a predetermined second fixing ability higher than the first fixing ability when the moving speed is set to the second moving speed. Can be further provided.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

<First Embodiment> FIG. 1 shows a first embodiment of the present invention.
An embodiment will be described. This is an example of a digital electrophotographic mono-color copying machine, and the structure of this copying machine is shown in FIG.

The digital electrophotographic monocolor copying machine shown in FIG. 2 includes an image scanner 1 and a printer 2. The image scanner unit 1 will be described. The image scanner unit 1 has a resolution of 400 dpi. The image scanner unit 1 includes a document table 3 on which a document is placed, and a scan unit 4 that scans a document G placed on the document table 3. The scanning unit 4 includes a document illumination lamp, a short focus lens array, and a CCD (charge couple).
d device) a sensor is integrated, the document G placed on the document table 3 is scanned by a document irradiating lamp, and reflected light from the document G is imaged on a CCD sensor by a short focus lens array. . The CCD sensor has a light receiving section, a transfer section, and an output section, converts a light signal into an electric signal by the light receiving section, and sequentially transfers the obtained electric signal to the output section in synchronization with a clock pulse by the transfer section. Then, the output section converts the charge signal into a voltage signal, amplifies the voltage signal, reduces the impedance, and outputs the signal. The obtained analog signal is a signal for mono-color, is subjected to well-known image processing, is converted into a digital signal, and is sent to the printer unit 2.

The printer section 2 will be described. The printer unit 2 includes image forming units P1 and P2, a transfer belt 70, a transport belt 72, a paper feed cassette 52, and a paper feed roller 54.
, A registration roller 55, a fixing device 76, and a paper discharge roller 77.

The image forming unit P1 includes a laser beam scanner 10, an electrophotographic photosensitive drum (hereinafter referred to as a photosensitive drum) 11, a charger 12, and developing devices 13K and 13
R, 13B, a transfer discharger 15, and a cleaning unit 16. The charger 12 charges the photosensitive drum 11. The laser beam scanner 10 includes the charger 1
2, a photosensitive drum 11 having a semiconductor laser, a polygon mirror, an fθ lens, and the like, and driven to rotate in the direction of the arrow shown in FIG.
Scanning is performed by a laser beam modulated based on an electric digital pixel signal (monocolor signal).
The developing devices 13K, 13R, and 13B develop latent images on the photosensitive drum 11 into toner images.
3K contains black toner, developing device 13R contains red toner, and developing device 13B contains blue toner. Developing devices 13K, 13R, 13
B is a two-component magnetic brush developing device, in which an oscillating bias voltage obtained by superimposing a direct current on an alternating current is applied to a developing sleeve. The developer is a two-component developer composed of non-magnetic toner and magnetic particles (carrier). Developing devices 13K, 13
R and 13B are arranged so as to be close to and separated from each other, and one of them is configured to contribute to development. As a means for approaching / separating, for example, a known method such as by energizing and deenergizing a solenoid can be used. Transfer discharger 15
Is for transferring the toner image on the photosensitive drum 11 to a transfer material. The cleaning means 16 is for cleaning the photosensitive drum 11.

The image forming unit P2 has substantially the same structure as the image forming unit P1, and includes a laser beam scanner 20, a photosensitive drum 21, a charger 22, developing devices 23K, 23R, 23B, and a transfer device. It has a discharger 25 and cleaning means 26. The charger 22 charges the photosensitive drum 21. Laser beam scanner 2
0 is provided between the charger 22 and the developing device 23K,
A photosensitive drum 21 having a semiconductor laser, a polygon mirror, an fθ lens, and the like, and driven to rotate in the direction of the arrow shown in FIG. 2, modulates a laser beam modulated based on an electric digital pixel signal (monochromatic signal). Is to be scanned. The developing devices 23K, 23R and 23B develop latent images on the photosensitive drum 21 into toner images. The developing device 23K contains black toner, and the developing device 23R contains red toner. The developing device 23B contains blue toner. Developing device 23
K, 23R and 23B are two-component magnetic brush developing devices, and an oscillating bias voltage obtained by superimposing a direct current on an alternating current is applied to the developing sleeve. The developer is a two-component developer composed of non-magnetic toner and magnetic particles (carrier). The developing devices 23K, 23R, and 23B are arranged so as to be able to approach and separate from each other, and one of them contributes to development. As a means for approaching / separating, for example, a known method such as by energizing and deenergizing a solenoid can be used.
The transfer discharger 25 transfers the toner image on the photosensitive drum 21 to a transfer material. The cleaning means 26 is for cleaning the photosensitive drum 21.

The image forming units P1 and P2 perform reversal development by image exposure. Photosensitive drum 1
The dark part potential (background part potential) of 1, 21 is -700V,
The bright portion potential (visible portion potential) was -150V. The peripheral speed of the photosensitive drums 11 and 21 is V1 (= 100 mm / se
c) and V2 (= 300 mm / sec) at high speed. Developing devices 13K, 13R, 13B, 23K, 23R, 23
The vibration bias voltage applied to the sleeve B has a frequency of 2 kHz and is obtained by superimposing a DC of -550 V on an AC of 2000 V peak-to-peak voltage Vp-p. The long distance between the photosensitive drums 11 and 21 and the developing sleeve is 0.5.
mm. The peripheral speed ratio between the developing sleeve and the photosensitive drums 11 and 21 was 1.75. That is, the peripheral speed at a low speed of the developing sleeve is 175 mm / sec (when V1 = 100 mm / sec), and the peripheral speed at a high speed is 525 mm / sec (V2 = 300 mm / sec).
Case). The peripheral speed of the fixing roller 81 at low speed is 10
0 mm / sec (when V1 = 100 mm / sec), and the peripheral speed at high speed was 300 mm / sec (when V2 = 300 mm / sec).

The paper supply cassette 52 is for storing a transfer material 53, and the transfer material 53 is fed to a registration roller 55 by a paper supply roller 54. The transfer belt 70 is wound around a driving roller and an idle roller, is an endless belt whose tension can be adjusted by an adjusting roller, and sequentially transfers the transfer material 53 fed by the registration roller 55 to the image forming units P1 and P2. Is what you do. The transport belt 72 is wound around a drive roller and an idle roller, is an endless belt whose tension can be adjusted by an adjusting roller, and transports the transfer material 53 onto which the toner image has been transferred. The fixing device 76 transfers the transfer material 53 transported by the transport belt 72.
Is applied with heat and pressure to fix the toner image on the transfer material 53. The discharge roller 77 discharges the transfer material 53 fixed by the fixing device 76 to a discharge stacker 78. The image formed by the printer unit 2 is 400 dpi
With a resolution of

FIG. 3 shows the structure of the fixing device 76 shown in FIG. A fixing roller 81 and a pressure roller 82 are provided to face each other. The fixing roller 81 has a heat source 83 inside,
The pressure roller 82 has a surface elastic layer 97 and
Both ends are supported by an arm 87 having one end pivotally supported at point a. The other end of the arm 87 is connected via a compression spring 88 to one end of a lever 89 pivotally supported at the point b, and the other end of the lever 89 is engaged with a pin 90 ′ of the cam 90. The thermistor 85 detects the surface temperature of the fixing roller 81.

The heat source 83 is turned on and off by a control unit (not shown) based on the temperature detected by the thermistor 85.

A concave portion 92 and a concave portion 93 provided on the outer peripheral portion of the cam 90 are detected by a sensor 91 provided near the cam 90.
Is to be detected. The angle between the concave portion 92 and the center of the cam 90 of the pin 90 ′ is determined by the concave portion 93
The angle between the center of the cam 90 and the 0 'is smaller than that of the cam 90.

The state of the fixing unit 76 shown in FIG. 3 is a state in which no paper is passed, and the lever 89 is not biased by the cam 90.
Therefore, the pressure roller 82 is separated from the fixing roller 81.

The fixing device 76 rotates the cam 90 in the state shown in FIG.
Is locked at one of two stop positions. That is, when the cam 90 is rotated by the pressurizing motor, the lever 89 is deflected (oscillated in the direction A) by the pin 90 ′. As a result, the arm 87 is rotated about the axis a by the spring force of the compression spring 88. The pressure roller 82 is rotated clockwise, and the pressure roller 82 is pressed against the fixing roller 81. Then, when the concave portion 92 is detected by the sensor 91, the rotation of the cam 90 is stopped (hereinafter, this stop position is referred to as “first
Position)), locked by the brake mechanism of the pressure motor itself, and fixed by the fixing roller 81 and the pressure roller 8.
The pressurized state of No. 2 is maintained.

On the other hand, when the concave portion 92 is detected by the sensor 91 and then the concave portion 93 is detected, the rotation of the cam 90 is stopped (hereinafter, this stop position is referred to as a "second position"), and the pressing motor itself Locked by the brake mechanism. Since the cam 90 is further rotated than the first position, the arm 87 is further rotated clockwise about the axis a, and the pressing roller 82 is further pressed against the fixing roller 81, so that the nip is further increased.

As the nip increases, the amount of heat supplied to the transfer material 53 passing between the fixing roller 81 and the pressure roller 82 increases.

Further, in order to increase the amount of heat supplied to the transfer material 53 by the fixing device 76, the power supplied to the heat source of the fixing roller 81 of the fixing device 76 is increased. You may make it switch to 800W. Furthermore, while increasing the nip,
The power supplied to the heat source of the fixing roller 81 of the fixing device 76 may be increased.

Referring to FIG. In FIG. 1, an operation unit 300 includes a print mode setting unit 301 and various function setting units 302, and the print mode setting unit 301 associates a print mode setting button pressed with a print mode setting button in advance. Are set, and the various function setting unit 302 sets a function associated in advance with the pressed function setting button. A control unit 305 includes a speed switching unit 306 and a developing device selection unit 308 according to the print mode set by the print mode setting unit 301.
And controls the fixing device condition control unit 309. The speed switching unit 306 sets the image forming speed to either V1 or V2 according to the print mode.
Reference numeral 310 denotes a drive motor, which includes photosensitive drums 11 and 21;
This is for driving the transfer belt 70, the transport belt 72, and the fixing device 76. An ultrasonic motor is used as the drive motor 310, and the ultrasonic motor has an advantage that speed control can be performed with high accuracy. The speed of the ultrasonic motor is controlled to a constant speed by applying a PLL to the ultrasonic motor based on the signal of the encoder, and is controlled by a known method of changing by changing the amplitude of the piezoelectric element. Detailed description of the method is omitted. A drive control unit 307 controls the drive of the drive motor 310 at the image forming speed switched by the speed switching unit 306. Reference numeral 308 denotes a developing device selection unit, which selects the developing device 13 according to the set print mode.
The selection of use of K, 13R, and 13B is switched, and the selection of use of developing devices 23K, 23R, and 23B is switched. The fixing condition control unit 309 moves the cam 90 of the fixing unit 76 to the first position or the second position in accordance with the print mode.
It locks in one of the positions.

FIG. 6 shows an operation panel provided on the operation unit 300 shown in FIG. In FIG. 6, reference numeral 340 denotes a display for displaying a mono-color type as a menu item. Reference numeral 350 denotes an equal-size button, which is used when making an image equal-size. A reduction button 351 is used to reduce an image. An enlargement button 352 is used to enlarge an image. 35
A zoom button 3 is used to zoom an image. A paper selection button 354 is used to select a paper size. Reference numeral 355 denotes an automatic density setting button for automatically setting the image density.

A low-speed print mode select button 342 is used to select a "low-speed print mode". A high-speed print mode select button 343 is used to select the "high-speed print mode". A two-color print mode select button 344 is used to select the "two-color print mode".

Reference numeral 345 denotes a developing device select switch for the image forming unit P1 for selecting the developing devices 13K, 13R, and 13B corresponding to black, red, and blue. When the developing device select switch 345 is pressed, the developing devices 13K, 13R, and 13B are selected in the order of black->red-> blue. When the high-speed print mode select button 343 is pressed and the “high-speed print mode” is set, the developing device select switch 345 sets the developing devices 13K and 23K, the developing devices 13R and 23R, and the developing devices 13B and 23B. To select one of the three pairs. When the developing device select switch 345 is pressed, the pair of developing devices is selected in the order of black->red-> blue. Reference numerals 347a, 347b, and 347c are display lamps that indicate the developing device selected by operating the developing device select switch 345 among the developing devices 13K, 13R, and 13B. A developing device select switch 346 for the image forming unit P2 is used to select the developing devices 23K, 23R, and 23B corresponding to black, red, and blue. Reference numerals 347d, 347e, and 347f are display lamps that indicate a developing device selected by operating the developing device select switch 346 among the developing devices 23K, 23R, and 23B.

Reference numeral 348 denotes a character button, which is used for a character original. Reference numeral 349 denotes a photo button, which is used when the document is a photo document. Reference numeral 356 denotes a reset button for resetting. A stop button 357 is used to stop the apparatus. Numeral 358 is a numeric keypad having a clear key for entering a numeral. A print button 341 is used to start printing.

FIG. 7 is a flowchart showing an example of a control procedure by the control unit 305 shown in FIG. When the power of the laser printer is turned on, the print mode setting unit 301
To set the "low speed black and white print mode" of the default print mode (S701), and the image forming unit P1
Is selected (S702), and the black developing device 13K of the image forming unit P1 is selected by the developing device selecting section 308 (S7).
03), the black lamp 347a is turned on. The image forming speed is switched to V1 by the speed switching unit 306 (S704),
The transfer step and the cleaning step are appropriately set according to the image forming speed V1. Fixing roller 8 of fixing device 76
1 and the pressure roller 82 are in a separated state as shown in FIG. Here, by pressing the developing device select button 345, the developing devices 13K, 13R, 13B
Can be selected.

To simplify the description, the black developing device 13K
The case where the print button 341 is pressed after various settings such as the magnification and the number of prints are performed in the state where the “low speed monochrome print mode” in which is selected is set will be described. When the print button 341 is pressed, control of the speed of the drive motor 310 is started by the drive control unit 307 at the image forming speed V1 switched by the speed switching unit 306, and the process is started. The cam 90 of the fixing device 76 is rotated clockwise by a pressure motor (not shown), the lever 89 is biased by the pin 90 ′ (oscillated in the direction A in FIG. 3), and the arm 87 is resiliently moved by the compression spring 88. By
The pressure roller 82 is rotated clockwise around the axis a.
Is pressed against the fixing roller 81. Then, when the concave portion 92 is detected by the sensor 91, the rotation of the cam 90 is stopped, that is, stopped at the first position, locked by the brake mechanism of the pressing motor itself, and fixed to the fixing roller 81.
And the pressure state of the pressure roller 82 is maintained (S70).
5). This state is shown in FIG. Therefore, the nip is set small.

When the print button 341 is pressed, the document G on the document table 3 is scanned, and a latent image is formed on the photosensitive drum 11 of the image forming unit P1 by a known method (S706). Then, the formed latent image is developed into a toner image by the black developing device 13K of the image forming unit P1 (S707). This toner image is transferred by the transfer discharger 15 onto the transfer material 53 fed by the registration roller 55 (S708), and the transfer material 53 on which the toner image has been transferred is fixed by the transfer belt 76 by the transport belt 72. The toner image is transferred between the roller 81 and the pressure roller 82 to fix the toner image on the transfer material 53 (hereinafter, “fixing at the first position”).
(S709), and the fixed transfer material 53 is
The paper is discharged to the paper discharge stacker 78 (S710). When the printing is completed, the print mode is set to the "low-speed black-and-white print mode". Thereafter, the cam 90 of the fixing device 76 is rotated in the reverse direction, and the fixing roller 81 and the pressure roller 82 are separated from each other as shown in FIG. I do.

In this low-speed print mode, the print speed was low, but a clear and high-quality print image could be obtained.

FIG. 8 is a flowchart showing an example of a control procedure by the control unit 305 shown in FIG. 1 when the high-speed print mode is set. When the high-speed print mode select button 343 of the operation unit 300 is pressed, the print mode is set to “high-speed print mode” by the print mode setting unit 301 (S801), and the image forming units P1 and P2 are selected (S802). , Developing device selecting section 3
08, the black developing device 13K of the image forming unit P1 is selected, and the black developing device 23K of the image forming unit P2 is selected (S803).
Turn on 7d. Further, the image forming speed is switched to V2 (> V1) by the speed switching unit 306. Then, the transfer step, the cleaning step, and the like are appropriately set according to the image forming speed V2. Here, by pressing the developing device select button 345, the developing devices 13K, 23K
And developing devices 13R and 23R and developing devices 13B and 23
Any of the three pairs of B can be selected.

To simplify the description, the black developing device 13
A case where the print button 341 is pressed after various settings such as the magnification and the number of prints are performed in a state in which the “high-speed monochrome print mode” in which a pair of K and 23K is selected is set will be described. When the print button 341 is pressed, control of the speed of the drive motor 310 is started by the drive control unit 307 at the image forming speed V2 that has already been switched, and processing is started. The cam 90 is rotated clockwise by a pressure motor (not shown), the lever 89 is biased by the pin 90 ′ (oscillated in the direction of A in FIG. 3), and the arm 8 is moved.
7 is rotated clockwise about the axis a by the spring force of the compression spring 88, and the pressing roller 82 is pressed against the fixing roller 81. Then, when the concave portion 92 is detected by the sensor 91 and then the concave portion 93 is detected, the rotation of the cam 90 is stopped, that is, the cam 90 is stopped at the second position, and the brake mechanism of the pressure motor itself is used. The locking is performed, and the pressing state of the fixing roller 81 and the pressing roller 82 is maintained (S805). This state is shown in FIG. Therefore, the nip is set large.

When the print button 341 is pressed, the document G on the document table 3 is scanned, and the document G is placed on the photosensitive drum 11 of the image forming unit P1 and the photosensitive drum 21 of the image forming unit P2 by a known method. A latent image is formed (S806). The latent image on the photosensitive drum 11 is developed into a toner image by the black developing device 13K of the image forming unit P1, and the latent image on the photosensitive drum 11 is developed by the black developing device 23K of the image forming unit P2. A toner image is formed (S807). Then, first, the toner image on the photosensitive drum 11 is transferred by the transfer discharger 15 onto the transfer material 53 fed by the registration roller 55, and then the toner image on the photosensitive drum 21 is transferred by the transfer discharger 25. (S808), the transfer material 53 on which the toner image is multiplex-transferred is sent between the fixing roller 81 and the pressure roller 82 of the transfer device 76 by the transport belt 72, and the transfer material 5 is transferred.
The fixing transfer material 53 is discharged to the discharge stacker 78 (S810), and the toner image on the third transfer material 53 is fixed (hereinafter, referred to as “fixing at the second position”) (S809). After the printing is completed, the print mode is set to the “low-speed black-and-white print mode”, and then the cam 90 of the fixing device 76 is rotated in the reverse direction so that the fixing roller 81 and the pressure roller 82 are moved as shown in FIG.
Set to the separated state.

In this high-speed print mode, although the image forming speed is faster than in the low-speed print mode, the same toner image
Since multiple transfer is performed on the transfer material 53 of the sheet, twice as much toner is used as the transfer material 5 as compared with the case where image formation is performed only once.
Thus, an image having a sufficiently high density can be obtained.

FIG. 9 is a flowchart showing an example of a control procedure by the control unit 305 shown in FIG. 1 when the two-color print mode is set. When the two-color print mode select button 344 of the operation unit 300 is pressed, the “two-color print mode” is set by the print mode setting unit 301 (S901), and the black developing device 13K of the image forming unit P1 is selected. Then, the red developing device 23R of the image forming unit P1 is selected (S902), and the black lamp 34 is selected.
7a and the red lamp 347e are turned on. The image forming speed is switched to V1 by the speed switching control unit 306. The transfer step and the cleaning step are appropriately set according to the image forming speed V1. Here, the developing device select button 3
By pressing the button 45, the developing devices 13K, 13R and 13B of the image forming unit P1 can be selected, and by pressing the developing device select button 346, the developing devices 23K, 23R and 23B of the image forming unit P2 are selected. It is possible.

To simplify the description, the black developing device 13K
The case where the print button 341 is pressed after various settings such as the magnification and the number of prints are performed in a state where the default mode in which the red developing device 23R is selected and the red developing device 23R is set will be described. When the print button 341 is pressed, the image forming speed V switched by the speed switching control unit 306.
In step 1, the control of the speed of the drive motor 310 is started by the drive control unit 307, and the process is started. The rotation of the cam 90 of the fixing device 76 is controlled in the same manner as in the "low-speed print mode" described above, and the cam 90 is locked at the first position (S9).
05), set the nip small. This state is shown in FIG.

When the print button 341 is pressed, the original G on the original platen 3 is scanned, and the photosensitive drum 11 of the image forming unit P1 and the photosensitive drum 21 of the image forming unit P2 are scanned by a known method. A latent image is formed (S906). The latent image formed on the photosensitive drum 11 is developed by the black developing device 13K of the image forming unit P1 to form a toner image, and the latent image on the photosensitive drum 21 is developed by the red developing device 23R of the image forming unit P2. An image is formed (S907). Then, first, the black toner image on the photosensitive drum 11 is transferred by the transfer discharger 15 onto the transfer material 53 fed by the registration roller 55, and then,
The red toner image on the photosensitive drum 21 is transferred by the transfer discharger 25 (S908), and the transfer material 53 on which the black and red toner images are multiplex-transferred is fixed by the conveyance belt 72 to the fixing roller 81 and the pressure roller of the transfer device 76. 82 and transfer material 53
“Fixing at the first position” is performed on the upper toner image (S
909). Then, the fixed transfer material 53 is discharged to the discharge stacker 78 (S910). When the printing is completed, the print mode is set to the “low-speed black-and-white print mode”, and then the cam 90 of the fixing device 76 is rotated in the reverse direction so that the fixing roller 81 and the pressure roller 82 are moved as shown in FIG.
Set to the separated state.

In the "two-color print mode", a clear, high-quality desired print image can be obtained although the print speed is slow.

Since a single-color or two-color image was formed by setting the image forming speed to V1, a clear, high-quality image with sufficiently high image density, no fogging was obtained. Of course, the fixability was sufficiently good. Further, since the image formation was performed with the image forming speed set to V2 (> V1), the printing speed was high, and although the image density was slightly lower and the image quality was slightly inferior to that when the image forming speed was set to V1, the image was formed. The density was sufficiently high, there was no fog, and a relatively good image was obtained. The fixability of the obtained image was good.

<Second Embodiment> FIG. 10 shows a second embodiment of the present invention. This is an example of a digital electrophotographic full-color copying machine, and the structure of this copying machine is shown in FIG.

In FIG. 11, reference numerals 76, 77 and 78 correspond to those in FIG.
The same parts are shown. The digital electrophotographic full-color copying machine shown in FIG. 11 includes an image scanner unit 601 and a printer unit 602. Image scanner unit 60
1 will be described. The image scanner unit 601 is 400 dpi
Having a resolving power of The image scanner unit 601 includes a document table 603 on which a document is placed, and a scan unit 604 that scans the document G placed on the document table 603. The scanning unit 604 includes a document illumination lamp, a short-focus lens array, and a CCD sensor, and scans the document G placed on the document table 603 with the document irradiation lamp. Is imaged on a CCD sensor by a short focus lens array.
The CCD sensor has a light receiving unit, a transfer unit, and an output unit,
The optical signal is converted to an electric signal by the light receiving unit, the obtained electric signal is sequentially transferred to the output unit in synchronization with the clock pulse by the transfer unit, and the charge signal is converted to a voltage signal by the output unit, amplified, and Output as impedance. The obtained analog signal is a signal for full color (magenta, cyan, yellow, and black), is subjected to well-known image processing, is converted into a digital signal, and is sent to the printer unit 602.

The printer section 602 will be described. The printer unit 2 includes image forming units P601 and P602, a transfer belt 670, a sheet feeding cassette 652, and a feeding roller 657.
, A registration roller 655, a fixing device 676, and a paper discharge roller 77.

The image forming unit P601 includes a laser beam scanner 610, a photosensitive drum 611, and a charger 612.
, A rotary developing device 614, a transfer drum 660, a transfer charger 615, a static eliminator 617, a cleaning unit 616, and a separation claw 666. The charger 612 charges the photosensitive drum 611. The laser beam scanner 610 includes a charger 612 and a rotary developing device 614.
The photosensitive drum 611 having a semiconductor laser, a polygon mirror, an fθ lens, and the like, and being driven to rotate in the direction of the arrow shown in FIG. 11 is modulated based on an electric digital pixel signal. It scans with a laser beam. The rotary developing device 614 includes the photosensitive drum 61
The developing unit 614M, 614C, 614Y, and 614K are used to develop the latent image on the developing unit 1 into a toner image. The developing device 614M contains magenta toner, the developing device 614C contains cyan toner, the developing device 614Y contains yellow toner, and the developing device 614K contains black toner. is there.
The developing devices 614M, 614C, 614Y, and 614K are 2
This is a component magnetic brush developing device, and an oscillating bias voltage in which a direct current is superimposed on an alternating current is applied to a developing sleeve.
The developer is a two-component developer composed of non-magnetic toner and magnetic particles (carrier). The transfer charger 615 transfers the toner image on the photosensitive drum 611 to a transfer material. The cleaning unit 616 cleans the photosensitive drum 611.

The image forming unit P602 includes a laser beam scanner 620, a photosensitive drum 621, and a charger 622.
, A developing device 624, a transfer discharger 625, and a cleaning unit 626. The charger 622 charges the photosensitive drum 621. The laser beam scanner 620 is provided between the charger 622 and the developing device 624, and has a semiconductor laser, a polygon mirror, an fθ lens, and the like, and is driven to rotate in the arrow direction shown in FIG. 621 is scanned by a laser beam modulated based on an electric digital pixel signal. The developing device 624 develops the latent image on the photosensitive drum 621 into a toner image, and is a non-contact one-component developing device using magnetic toner, a so-called jumping developing device. The developing material used for the developing device 624 is an inexpensive one.
Since it is a component developer, the apparatus configuration can be simplified, so that the running cost can be reduced.
An oscillating bias voltage in which a direct current is superimposed on an alternating current is applied to the developing sleeve. The transfer discharger 625 transfers the toner image on the photosensitive drum 621 to a transfer material. The cleaning unit 626 is for cleaning the photosensitive drum 621.

The fixing device 676 differs from the fixing device 76 shown in FIG. 2 in that a heat source is also provided inside the pressure roller 682. Since the fixing device 676 has a heat source inside the fixing roller 81 and a heat source inside the pressure roller, it is possible to completely melt and mix colors of toners of a plurality of colors.

The dark portion potential (background portion potential) of the photosensitive drum 611 is -700 V, and the bright portion potential (visible portion potential) is -1.
50 V was applied. The peripheral speed of the photosensitive drum 611 at low speed is V1
= 100mm / sec and the peripheral speed at high speed is V2 = 240mm / s
ec. Developing devices 614M, 614C, 614Y, 6
The vibration bias voltage applied to the 14K sleeve has a frequency of 2 kHz, and a DC voltage of 550 V is superimposed on an AC voltage having a peak-to-peak voltage Vp-p of 2000 V.
The closest distance between the photosensitive drum 611 and the sleeve was 0.5 mm. The peripheral speed ratio between the developing sleeve and the photosensitive drum 611 is set to 1.
75. That is, the peripheral speed at the low speed of the developing sleeve is 175 mm / sec (when V1 = 100 mm / sec), and the peripheral speed at the high speed is 420 mm / sec (when V2 = 240 mm / sec)
And

The vibration bias voltage applied to the sleeve of the developing device 624 has a frequency of 2 kHz, and the peak-to-peak voltage V
It is obtained by superimposing a DC voltage of -550 V on an AC voltage having pp of 1800 V. The closest distance between the photosensitive drum 621 and the sleeve was 0.3 mm. The peripheral speed ratio between the developing sleeve and the photosensitive drum 621 was 1.25. That is, the peripheral speed of the developing sleeve at a low speed is set to 125 mm / sec (V1 = 100 mm / s).
ec) and the peripheral speed at high speed is 300 mm / sec (V2 =
240 mm / sec). The peripheral speed of the fixing roller 81 at low speed is 100 mm / sec (when V1 = 100 mm / sec), the nip setting is small, and the peripheral speed at high speed is 240 mm / sec.
(When V2 = 240 mm / sec), and the nip setting was large.

Referring to FIG. In FIG. 10, 80
An operation unit 0 includes a print mode setting unit 801 and various function setting units 802.
Reference numeral 1 denotes a function for setting a print mode associated with the pressed print mode setting button in advance, and a function setting unit 802 for setting a function associated in advance with the pressed function setting button. is there. A control unit 805 controls the developing device selection unit 808, the speed switching unit 806, and the fixing unit condition control unit 809 according to the print mode set by the print mode setting unit 8. The speed switching unit 306 sets the image forming speed to either V1 or V2 according to the set print mode. 810 is a drive motor,
This is for driving the photosensitive drums 611 and 621, the transport belt 670, and the fixing device 76. Drive motor 8
As 10, an ultrasonic motor is used. A drive control unit 807 controls the drive of the drive motor 810 at the image forming speeds V1 and V2 switched by the speed switching unit 806. The developing device selecting unit 808 includes the developing device 6
14M, 614C, 614Y, and 614K are selected and switched. The fixing unit condition control unit 809 sets the cam 90 of the fixing unit 676 according to the print mode.
It locks in the first position or the second position.

FIG. 12 shows an operation panel provided on the operation section 800 shown in FIG. In FIG. 12, 340, 34
1,348-351,353-358 show the same parts as FIG. Reference numeral 1359 denotes an auto color print button for selecting an auto color print mode. 1360 is a full color print button,
This is for selecting the full color print mode. Reference numeral 1361 denotes a monochrome print button for selecting a monochrome print mode. 1
A black print button 362 is used to select a black and white print mode. Reference numeral 1363 denotes a high-speed black print mode button for selecting a high-speed black print mode.

FIG. 13 is a flowchart showing an example of a control procedure by the control unit 805 shown in FIG. After power on and device stable, full color button 1360
When is pressed, the print mode is set to the "full color print mode" by the print mode setting unit 801 (S1301), the image forming unit P601 is selected (S1302), and the developing device 614M is fixed at the developing position (S1303). . Next, the image forming speed is switched to V1 by the speed switching unit 806 (S1304).

When the print button is pressed, the cam 90 of the fixing device 676 is positioned at the first position by the fixing device condition control section 809 (S1305). And the drive control unit 8
07, the drive motor 810 is driven and controlled at the image forming speed V1, and the photosensitive drum 611 of the image forming unit P601 is controlled.
Is uniformly charged by the charger 612. On the other hand, the original G on the original platen 603 is scanned by the scan unit 604, and first, image exposure is performed by a laser beam modulated based on a magenta image signal.
An electrostatic latent image is formed on the image 11 (S1306). A magenta developing device 61 in which the formed latent image is fixed at a developing position in advance.
The image is developed by 4M to form a visible image (magenta toner image) (S1307).

On the other hand, the transfer material 653 of the paper feed cassette 652
Is fed to the registration roller 655, and is held at an appropriate timing by the gripper 661. The transfer roller 6 is electrostatically charged by the contact roller 662 and its opposite pole.
60, and the transfer drum 660 is
Rotating in the direction of the arrow shown in FIG.

Then, the magenta toner image on the photosensitive drum 611 is transferred to the transfer drum 66 by the transfer charger 615.
Then, the image is transferred to the transfer material 653 on the image No. 0 (S1308). The transfer drum 660 keeps rotating as it is, and prepares for transfer of the toner image of the next color (cyan). On the other hand, the photosensitive drum 61
1 is discharged by the discharging charger 617 and is cleaned by the cleaning means 616. Since the transfer for one color is completed (S1309), the process returns to step S1306. Hereinafter, steps S1306 to S130
Repeat step 9.

That is, the photosensitive drum 611 is connected to the charger 61.
2, the photosensitive drum 6 performs image exposure with a laser beam modulated based on a cyan image signal.
11, an electrostatic latent image is formed. Next, the formed latent image is developed by a cyan developing device 614M previously set at a developing position to be a cyan toner image. Then, the cyan toner image on the photosensitive drum 611 is transferred to the transfer material 653 on the transfer drum 660 by the transfer charger 615.
The transfer drum 660 keeps rotating, and prepares for the transfer of the next yellow toner image.

Next, the photosensitive drum 611 is uniformly charged by the charger 612, and image exposure is performed by a laser beam modulated based on a yellow image signal.
An electrostatic latent image is formed on the developing device 1, and the formed latent image is developed into a yellow toner image by a yellow developing device 614Y fixed at a developing position in advance. Then, the photosensitive drum 611
The upper yellow toner image is transferred to the transfer material 653 on the transfer drum 660 by the transfer charger 615. The transfer drum 660 keeps rotating, and prepares for the transfer of the next black toner image.

Further, the photosensitive drum 611 is connected to the charger 612.
And the image is exposed to light by a laser beam modulated based on a black image signal.
11, an electrostatic latent image is formed. Next, the formed latent image is developed by a black developing device 614K which is previously set at a developing position to be a black toner image. Then, the black toner image on the photosensitive drum 611 is transferred to the transfer charger 615.
Is transferred onto the transfer material 653 on the transfer drum 660.

When the transfer of the four colors to the transfer material 653 is completed (S1309), the four-color visible image on the transfer material 653 is neutralized by the neutralizing charger, the gripper 661 is released, and the transfer material is separated by the separating claw 666. 653 to transfer drum 6
60 and a fixing device 676 by a conveyor belt 670.
Send to In the toner image on the transfer material 653 sent between the fixing roller 81 and the pressure roller 682, four color toners are completely melted and mixed by the heat and nip pressure of the fixing roller 81 and the pressure roller 682. Then, fixing at the first position is performed (S1310). After the fixing, the transfer material 653 is discharged onto the discharge stacker 78 by the discharge roller 77 (S1311).

In the "full-color print mode", a desired full-color print image having a high print density, a sufficiently high image density, no fog, and a clear, high-quality image was obtained. Of course, the fixability was sufficiently good.

FIG. 14 is a flowchart showing an example of a control procedure by the control unit 805 shown in FIG. 10 when the mono color print mode is set. When the mono color button 1361 is pressed, the print mode setting unit 801
Print mode to "Mono-color print mode"
(S1401), the image forming unit P601 is selected (S1402), and the type of mono color is displayed on the display 340. Then, when, for example, magenta is selected from the displayed monocolor type, the selected magenta developing device 614M is fixed to the developing position (S1403). Next, the image forming speed is switched to V1 by the speed switching unit 806 (S1404).

When the print button 341 is pressed, the cam unit 90 of the fixing unit 676 is positioned at the first position by the fixing unit condition control unit 809 (S1405). The drive control unit 807 controls the drive motor 810 to control the image forming speed V1.
And the photosensitive drum 611 of the image forming unit P601 is uniformly charged by the charger 612. On the other hand, the original G on the original platen 603 is scanned by the scanning unit 60.
4 and performs image exposure with a laser beam modulated based on a black and white image signal.
An electrostatic latent image is formed thereon (S1406). A magenta developing device 614M in which the formed latent image is set at a developing position in advance.
To form a magenta toner image (S140
7).

On the other hand, the transfer material 653 of the sheet cassette 652
Is fed to the registration roller 655, and is held at an appropriate timing by the gripper 661. The transfer roller 6 is electrostatically charged by the contact roller 662 and its opposite pole.
60, and the transfer drum 660 is
Rotating in the direction of the arrow shown in FIG.

Then, the magenta toner image on the photosensitive drum 611 is transferred to the transfer drum 66 by the transfer charger 615.
Then, the image is transferred to the transfer material 653 on the image No. 0 (S1408). When the transfer to the transfer material 653 is completed, the gripper 661 is released, the transfer material 653 is separated from the transfer drum 660 by the separation claw 666, and sent to the fixing device 676 by the transport belt 670. The toner image on the transfer material 653 sent between the fixing roller and the pressure roller is fixed at the first position (S1409). Then, the transfer material 653 after fixing is discharged onto the discharge stacker 78 by the discharge roller 77 (S1410).

In the "mono-color print mode", a desired mono-color print image having a high print density, a sufficiently high image density, no fog, and a clear, high-quality image was obtained. Of course, the fixability was sufficiently good.

FIG. 15 is a flowchart showing an example of a control procedure by the control unit 805 shown in FIG. 10 when the black image print mode is set. Black button 136
When button 2 is pressed, the print mode is set to “black image print mode” by print mode setting section 801 (S1501), image forming unit P602 is selected (S1502), and developing device 624 is selected (S150).
3) The image forming speed is switched to V1 by the speed switching unit 806 (S1504).

When the print button 341 is pressed, the cam unit 90 of the fixing unit 676 is positioned at the first position by the fixing unit condition control unit 809 (S1505). The drive control unit 807 controls the drive motor 810 to control the image forming speed V1.
And the photosensitive drum 621 of the image forming unit P602 is uniformly charged by the charger 622. On the other hand, the original G on the original platen 603 is scanned by the scanning unit 60.
4 to perform image exposure using a laser beam modulated based on a black and white image signal.
An electrostatic latent image is formed thereon (S1506). The formed latent image is developed by the developing device 624 into a toner image (S
1507).

Then, the toner image on the photosensitive drum 621 is transferred onto the transfer material 653 by the transfer charger 625 (S1508). When the transfer to the transfer material 653 is completed, the transfer material 653 is transported by the transport belt 670 to the fixing device 6.
The toner image is fed between the fixing roller 81 and the pressure roller 682 at 76 and the toner image on the transfer material 653 is fixed at the first position (S1509). Then, the transfer material 65 after the fixing is performed.
3 is discharged onto the discharge stacker 78 by the discharge roller 77 (S1510).

In the "black image print mode", although the printing speed is slow, the image density is sufficiently high, there is no fog,
A clear, high-quality desired black-and-white print image was obtained. Of course, the fixability was sufficiently good.

FIG. 16 is a flowchart showing an example of a control procedure by the control unit 805 shown in FIG. 10 when the high-speed black print mode is set. High-speed black mode button 1
When the button 363 is pressed, the print mode is set to the “high-speed black print mode” by the print mode setting unit 801 (S1601). The image forming units P601 and P602 are selected (S1502), and the image forming units P
A developing device 614K for the image forming unit P602 and a developing device 624K for the image forming unit P602 are selected (S160).
3) The image forming speed is switched to V2 by the speed switching unit 806 (S1604).

When the print button is pressed, the cam 90 of the fixing device 676 is moved to the second position by the fixing device condition control section 809 (S1605). And the drive control unit 8
07, the drive motor 810 is drive-controlled at the image forming speed V2, and the photosensitive drum 611 of the image forming unit P601 is controlled.
Is uniformly charged by the charger 612, and the photosensitive drum 621 of the image forming unit P602 is charged by the charger 6
22 evenly charges. On the other hand, the scanning unit 604 scans the document G on the document table 603, performs image exposure with a laser beam modulated based on a monochrome image signal, and forms an electrostatic latent image on the photosensitive drums 611 and 621 (S1606). ). Next, the latent image formed on the photosensitive drum 611 is developed into a black toner image by a developing device 614K fixed at a developing position in advance, and the latent image formed on the photosensitive drum 621 is
The black toner image is developed by the developing device 624 (S1607).

On the other hand, the transfer material 653 of the paper cassette 652
Is fed to the registration roller 655, and is held at an appropriate timing by the gripper 661. The transfer roller 6 is electrostatically charged by the contact roller 662 and its opposite pole.
60, and the transfer drum 660 is
Rotating in the direction of the arrow shown in FIG.

Then, the black toner image on the photosensitive drum 611 is transferred to the transfer drum 66 by the transfer charger 615.
The image is transferred to the transfer material 653 on the “0”. When the transfer is completed, the gripper 661 is released, the transfer material 653 is separated from the transfer drum 660 by the separation claw 666, and is conveyed to the image forming unit P602 by the conveyance belt 670. Next, the black toner image on the photosensitive drum 621 is multiplex-transferred onto the transfer material 653 by the transfer charger 625 (S1608). When the transfer to the transfer material 653 is completed,
The transfer material 653 is sent between the fixing roller 81 and the pressure roller 682 of the fixing device 76 by the transport belt 670, and the toner image on the transfer material 653 is fixed at the second position (S1609). Then, the transfer material 653 after the fixing is discharged onto the discharge stacker 78 by the discharge roller 77 (S1).
610).

In the "high-speed black print mode", the toner image was transferred by multiple transfer, and the toner image transferred with weight was fixed by sufficiently applying heat and nip pressure, so that a sufficiently high density image could be obtained. .

<Third Embodiment> FIG. 17 shows a third embodiment of the present invention. This is an example of a digital electrophotographic copying machine, and its structure is shown in FIG.

Referring to FIG. In FIG. 18, FIG.
The same reference numerals indicate the same parts. The digital electrophotographic copying machine includes an image scanner unit 1401 and a printer unit 1402. The image scanner unit 1401 will be described. The image scanner unit 1401 includes a document table 1403 for placing a document, and a scan unit 1404 for scanning a document G placed on the document table 1403. A scan unit 1404 includes a document illumination lamp,
The short focus lens array and the CCD sensor are integrated, and the document G placed on the document table 1403 is scanned by the document irradiation lamp, and the reflected light from the document G is imaged on the CCD sensor by the short focus lens array. It is to let. C
The CD sensor has a light receiving unit, a transfer unit, and an output unit. The light receiving unit converts an optical signal into an electric signal, and the obtained electric signal is sequentially transferred to the output unit in synchronization with a clock pulse by the transfer unit. The output unit converts the charge signal into a voltage signal,
Amplify, lower impedance and output. The obtained analog signal is a black and white image signal, is subjected to well-known image processing, is converted into a digital signal, and is converted into a digital signal.
Sent to 2.

The printer section 1402 will be described. The printer unit 1402 includes an image forming unit P1401, a transfer belt 1470, a paper feed cassette 1452, a registration roller 1455, a fixing device 76, and a paper discharge roller 77.

The image forming unit P1401 performs regular development by background exposure, and includes a laser beam scanner 1410, a photosensitive drum 1411, a charger 1412, developing devices 1413 and 1414, a charger 1
418, a full-surface charger 1419, and a transfer charger 1415
And a cleaning unit 1416. Charger 14
Numeral 12 charges the photosensitive drum 1411. The laser beam scanner 1410 is provided between the charger 1412 and the developing device 1413, has a semiconductor laser, a polygon mirror, an fθ lens, and the like, and is driven to rotate in the direction of the arrow shown in FIG. 1411 is scanned by a laser beam modulated by an electric digital pixel signal. The transfer charger 615 transfers the toner image on the photosensitive drum 611 to a transfer material. The cleaning unit 616 cleans the photosensitive drum 611.

The developing devices 1413 and 1414 are non-contact one-component developing devices using magnetic toner, so-called jumping developing devices, which contain black toner and develop a latent image on the photosensitive drum 1411 into a toner image. Is what you do. An oscillating bias voltage in which AC is superimposed with DC is applied to the developing sleeve of the developing device 1413, and a DC bias voltage is applied to the developing sleeve of the developing device 1414.

(Normal Speed Print Mode) Photosensitive Drum 1
The peripheral speed of 411 was set to 100 mm / sec.

First image forming step (developing device 1413)
In this case, the dark portion potential (first latent image portion potential Vi1) of the photosensitive drum 1411 was -700V, and the bright portion potential (background portion potential Vbg1) of the photosensitive drum 1411 was -150V. The vibration bias voltage applied to the sleeve (DC superimposed on AC)
The frequency is 2 kHz and the peak-to-peak voltage Vp-p is 1800
V AC voltage, developing bias potential Vb1 (DC voltage)-
300 V was superimposed. The contrast potential (| Vi1-Vb1 |) of the first latent image portion was set to 400V. The peripheral speed of the developing sleeve was 125 mm / sec, and the closest distance between the photosensitive drum 1411 and the sleeve was 0.3 mm. The peripheral speed of the fixing roller 81 at a low speed was set to 100 mm / sec, and the nip setting of the fixing roller 81 was reduced.

(High Speed Print Mode) Photosensitive Drum 14
The peripheral speed of No. 11 was 200 mm / sec.

First image forming step (developing device 1413)
In this case, the dark portion potential (first latent image portion potential Vil) of the photosensitive belt was -700 V, and the bright portion potential (background portion potential Vbg1) of the photosensitive drum 1411 was -150 V. The vibration bias voltage applied to the sleeve (DC voltage superimposed on AC voltage)
The frequency is 2 kHz and the peak-to-peak voltage Vp-p is 1800
V AC voltage, developing bias potential Vb1 (DC voltage)-
300 V was superimposed. The contrast potential (| Vi1-Vb1 |) of the first latent image portion was 400 V, and the peripheral speed of the developing sleeve was 250 mm / sec. The closest distance between the photosensitive drum 1411 and the sleeve was 0.3 mm.

Second image forming step (developing device 1414)
In this case, the dark portion potential (second latent image portion potential Vi2) of the photosensitive drum 1411 was -750V, and the bright portion potential (background portion potential Vbg2) of the photosensitive drum 1411 was -150V. The developing bias potential Vb2 (DC voltage) was -250V. The contrast potential (| Vi2-Vb2 |) of the second latent image portion is set to 500 V
The peripheral speed of the developing sleeve was 250 mm / sec, and the closest distance between the photosensitive drum 1411 and the sleeve was 0.3 mm. The peripheral speed of the fixing roller 81 at a low speed was 200 mm / sec. The nip setting of the fixing roller 81 was increased.

Referring to FIG. In FIG. 17, 12
Reference numeral 00 denotes an operation unit, and a print mode setting unit 1201
And a various function setting unit 1202, the print mode setting unit 1201 sets a print mode in which the pressed button is related in advance, and the various function setting unit 1202 preliminarily relates to the pressed button. This is for setting the function. Reference numeral 1203 denotes an image determination unit which determines whether the obtained image is a character image or a graphic image when the “automatic speed print mode” is set by the print mode setting unit 1201. 1
Reference numeral 204 denotes a speed mode setting unit, and an image determination unit 1203
When the image is determined to be a character image, the "high-speed print mode" is set, and when the image is determined to be a graphic image, the "normal speed print mode" is set. Reference numeral 1205 denotes a control unit which controls the developing device selecting unit 1208 and the speed switching unit 1 according to the set print mode.
The control unit 206 controls the fixing unit condition control unit 1209. The speed switching unit 1206 switches the image forming speed to either V1 or V2. The developing device selection unit 1208 selects either the single use of the developing device 1413 or the combined use of the developing devices 1413 and 1414. The fixing unit condition control unit 1209 positions the cam 90 of the fixing unit 76 at the first position when the “normal speed printing mode” is set, and sets the cam 90 of the fixing unit 76 when the “high speed printing mode”. At the second position. Reference numeral 1210 denotes a drive motor, which includes a photosensitive drum 1411, a conveyance belt 1470, and a fixing device 76.
And for driving. As the drive motor 1210, an ultrasonic motor is used. A drive control unit 1207 controls the drive of the drive motor 1210 according to the image forming speeds V1 and V2 switched by the speed switching unit 1206.

Referring to FIG. 340, 341, 34
8 to 351, 353, 355 to 358 indicate the same parts as in FIG. A normal speed button 1401 is used to set a "normal speed print mode". 140
Reference numeral 2 denotes a high-speed mode button, which is a "high-speed print mode".
It is for setting. Reference numeral 1403 denotes an automatic mode button for setting an “automatic print mode”. Reference numeral 1404 denotes a display lamp which is turned on when the normal speed button 1401 is pressed. Reference numeral 1405 denotes a display lamp which is turned on when the high-speed mode button 1402 is pressed. Reference numeral 1406 denotes a display lamp, which is an automatic mode button 1
Lights up when 403 is pressed.

FIG. 20 is a flowchart showing an example of a control procedure by the control unit 1205 shown in FIG. When the normal speed button 1401 of the operation unit 300 is pressed, the print mode is set to “normal speed print mode” by the print mode setting unit 1201 (S2001), and only the developing device 1413 is selected by the developing device selecting unit 1208 (S2001). In step S2002, the image forming speed is switched to V1 by the speed switching unit 1206 (S2003).
According to 1, the transfer step and the cleaning step are appropriately set.

When the print button is pressed, the cam 90 of the fixing device 76 is moved to the first position by the fixing device condition control section 1209 (S2004). And the drive control unit 1
The drive of the drive motor 1210 is controlled by the image forming speed V1 by 207, and the photosensitive drum 1411 of the image forming unit P1401 is uniformly charged by the charger 1412. On the other hand, the scanning unit 1404 scans the document G on the document table 1403, performs image exposure with a laser beam modulated based on a black and white image signal, and forms an electrostatic latent image on the photosensitive drum 1412 (S2005). The formed latent image is developed into a toner image by the developing device 624 (S2006).

Then, the toner image on the photosensitive drum 1411 is transferred onto the transfer material 1453 by the transfer charger 1415 (S2007). When the transfer to the transfer material 1453 is completed, the transfer material 1453 is sent by the conveyor belt 1470 between the fixing roller 81 and the pressure roller 82 of the fixing device 76, and the toner image on the transfer material 1453 at the first position. Fixing is performed (S2008). Then, the transfer material 1453 after the fixing is discharged by a discharge roller 77 to a discharge stacker 78.
The sheet is discharged upward (S2009). Then, after a lapse of a predetermined time, the print mode is set to the automatic speed print mode.

In the normal speed print mode, although the printing speed was slow, the image density was sufficiently high, no fogging was observed, and a clear and high quality desired black and white print image was obtained. Of course, the fixability was sufficiently good.

FIG. 21 is a flowchart showing an example of a control procedure by the control unit 1205 shown in FIG. 17 when the high-speed print mode is set. When the high-speed mode button 1402 of the operation unit 1200 is pressed, the print mode is set to “high-speed print mode” by the print mode setting unit 1201 (S2101), and the developing device selection unit 12
08, the developing devices 1413 and 1414 are selected (S2102), and the image forming speed is switched to V2 by the speed switching unit 1206 (S2103).

When the print button 341 is pressed, the cam 90 of the fixing unit 76 is locked at the second position by the fixing unit condition control unit 1209 (S2104), and the drive motor 1210 is turned on by the drive control unit 807 at the image forming speed. V2
To start the first image forming process.

The first image forming step will be described. The photoconductor drum 1411 is uniformly charged by the charger 1412 (see FIG. 22A), and the white background W on the photoconductor drum 1411 is neutralized by image exposure using a laser beam modulated based on a black and white image signal. Then, a positive latent image of a black portion (latent image portion potential Vi1) is formed (S2105). Next, the potential Vi 1 of the latent image portion of the black portion
A developing bias potential Vb1 is applied between the developing device 141 and the background potential Vbg1 of the white background W (see FIG. 22C).
3 to develop the positive charge with the black toner (FIG. 22).
(See (c)) (S2106). At this time, since the positively charged black toner adheres only to the portion of the latent image portion potential Vi2, a black toner image is obtained.

When the development in the first image forming step is completed, the second image forming step is started and the photosensitive drum 141 is started.
In the state where a black toner image exists on the
8 (see FIG. 22D), and then the entire surface is exposed by the entire surface exposure means 1419. At this time, the white portion W (background portion) is neutralized, but the black portion BK
Since the (image portion) is blocked by the toner image and light does not pass through, the charge is not removed, and a positive latent image is formed on the black portion BK (latent image portion potential Vi2) (see FIG. 22E) (S2107). . The latent image portion potential Vi2 of the black portion BK and the background portion potential Vbg of the white background portion W
22 is applied with the developing bias potential Vb2 (FIG. 22).
(See FIG. 22F), and the developing device 1414 develops with positively charged toner (see FIG. 22F) (S210).
8). At this time, the toner adheres to the portion of the latent image portion potential Vi2. As a result, a toner image is further formed on the already formed toner image, and a multi-toner image is obtained.

Next, the multi-toner image is transferred by the transfer discharger 1415 onto the transfer material 1453 fed by the registration roller 1455 (S2109), and the transfer material 1453 on which the multi-toner image has been transferred is transferred to the conveyor belt. 14
70, the fixing roller 81 and the pressure roller 8 of the fixing device 76.
2 and performs “fixing at the second position” on the toner image on the transfer material 1453 (S 2110), and discharges the fixed transfer material 1453 to the paper discharge stacker 1478 (S 2110).
2111). Then, after a lapse of a predetermined time, the print mode is set to the automatic speed print mode.

In the "high-speed print mode", the printing speed is high, and although the image quality is slightly inferior to that in the "normal speed print mode", the image density is sufficiently high, there is no fog, and a relatively good image is obtained. Obtained. The fixability of the obtained image was good.

On the other hand, when the automatic mode button 1403 of the operation unit 1200 is pressed and then the print button 341 is pressed, the document G placed on the document table 1403 is scanned by the document irradiation lamp, The image determination unit 1 determines whether the document G is a character image or a graphic image based on the image information of
The determination is made by 203. If the image is a graphic image, the "normal speed print mode" is set by the speed mode setting unit 1204, and if the image is a character image, the "high speed print mode" is set by the speed mode setting unit 1204. The control procedure by the control unit 1205 in the “normal speed mode” and the “high-speed print mode” has already been described, and thus redundant description will be omitted.

In the present embodiment, the print mode is set to the "automatic speed print mode" after the image formation is completed. Therefore, even if the operator does not frequently set the speed mode, the print mode is often used. Printing can be started in the mode, and operability is improved. Of course, the default print mode can be set to a desired print mode.

[0107]

As described above, according to the present invention,
With the above configuration, one type of image forming apparatus can be used.
Although the recording speed is low, a clear and high-quality image can be obtained, and the recording speed can be increased.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating the structure of the device according to the first embodiment.

FIG. 3 is a diagram showing a structure of a fixing device 76 shown in FIG.

FIG. 4 is an explanatory diagram for explaining an operation of the fixing device 76.

FIG. 5 is an explanatory diagram for explaining an operation of the fixing device 76.

6 is a diagram showing an operation panel of the operation unit 300 shown in FIG.

FIG. 7 is a flowchart illustrating an example of a control procedure performed by a control unit 305 illustrated in FIG.

FIG. 8 is a flowchart illustrating an example of a control procedure performed by the control unit 305 illustrated in FIG. 1 when a high-speed print mode is set.

FIG. 9 is a flowchart illustrating an example of a control procedure by the control unit 305 illustrated in FIG. 1 when a two-color print mode is set.

FIG. 10 is a block diagram showing a second embodiment of the present invention.

FIG. 11 is a cross-sectional view illustrating the structure of a digital electrophotographic full-color copying machine according to a second embodiment.

12 is a diagram showing an operation panel of the operation unit 800 in FIG.

13 is a flowchart illustrating an example of a control procedure performed by a control unit 805 illustrated in FIG.

14 is a flowchart illustrating an example of a control procedure performed by the control unit 805 illustrated in FIG. 10 when a mono-color print mode is set.

15 is a flowchart illustrating an example of a control procedure performed by a control unit 805 illustrated in FIG. 10 when a black image print mode is set.

16 is a flowchart illustrating an example of a control procedure performed by the control unit 805 illustrated in FIG. 10 when a high-speed black print mode is set.

FIG. 17 is a block diagram showing a third embodiment of the present invention.

FIG. 18 is a cross-sectional view illustrating a structure of a digital electrophotographic copying machine according to a third embodiment.

19 is a diagram illustrating an operation panel of the operation unit 1200 in FIG.

20 is a flowchart illustrating an example of a control procedure performed by a control unit 1205 illustrated in FIG.

FIG. 21 illustrates a case where a high-speed print mode is set.
9 is a flowchart illustrating an example of a control procedure performed by a control unit 1205 illustrated in FIG.

FIG. 22 is an explanatory diagram for describing an image forming process in a high-speed print mode.

[Explanation of symbols]

11, 21 photosensitive drum 13K, 13R, 13B, 23K, 23R, 23B developing device 53 transfer material 55 registration roller 70 transfer belt 72 transport belt 76 fixing device P1, P2 image forming unit 300 operation unit 301 print mode setting unit 302 various functions Setting unit 305 Control unit 306 Speed switching unit 307 Drive control unit 308 Developing device selection unit 309 Fixing unit condition control unit 310 Drive motor 341 Print button 342 Low speed print mode select button 343 High speed print mode select button 344 Two color print mode Select button

Claims (8)

[Claims] At least two image forming units, a moving speed switching unit for switching a moving speed of an image carrier, a moving speed setting unit for setting a moving speed of the image carrier, and a moving speed set by the moving speed setting unit When the speed is set to the first moving speed, an image is formed using only one of the two image forming units, and the moving speed setting unit determines the image faster than the first moving speed. When the second moving speed is set, a latent image is formed on the image carrier on the upstream side of the two image forming units, developed, and transferred to a transfer material. Means for forming a latent image on the downstream image carrier of the forming means, developing the latent image, and transferring the latent image to the transfer material. 2. An image forming means having a plurality of developing devices; a moving speed switching means for switching a moving speed of an image carrier; a moving speed setting means for setting a moving speed of the image carrier; When the moving speed is set to the first moving speed by the means, an image is formed using only one of the plurality of developing devices, and the moving speed is set to the first moving speed by the moving speed setting means. Means for performing multiple development on one image carrier using at least two of the plurality of developing devices when the second moving speed is set to a higher predetermined second moving speed, and transferring the image to a transfer material; An image forming apparatus comprising: 3. The fixing device according to claim 1, further comprising a fixing unit that can be switched to a plurality of fixing capacities, wherein when the moving speed is set to the first moving speed by the moving speed setting unit, the fixing unit operates. When the second fixing speed is controlled by the first fixing ability and the second fixing speed is set by the moving speed setting means, the fixing means changes to a predetermined second fixing ability having a higher fixing ability than the first fixing ability. An image forming apparatus characterized by being controlled. 4. The fixing device according to claim 3, wherein the fixing unit performs fixing using a thermal unit, and when the moving speed is set to the first moving speed by the moving speed setting unit, the fixing unit performs the fixing. Means for supplying a first amount of heat to the means, and when the moving speed is set to the second moving speed by the moving speed setting means, a predetermined second amount of heat larger than the first heat amount is supplied to the fixing means. An image forming apparatus characterized by supplying. 5. The method according to claim 1, wherein
An image forming apparatus, comprising: means for inputting image information, and switching and controlling a moving speed to the first moving speed or the second speed based on the inputting means. 6. When a moving speed is set to a second predetermined moving speed higher than the first moving speed, a latent image is formed on an upstream image carrier of at least two image forming means. Developing, transferring to a transfer material; and forming a latent image on a downstream image carrier of the two image forming units, developing, and transferring the latent image to the transfer material. An image forming method comprising: 7. When a moving speed is set to a predetermined second moving speed higher than the first moving speed, at least two developing devices out of a plurality of developing devices are used to mount on one image carrier. An image forming method, comprising a step of performing multiple development and transferring to a transfer material. 8. The fixing device according to claim 6, wherein when the moving speed is set to the second moving speed, the fixing capability of the fixing unit is controlled to a predetermined second fixing capability higher than the first fixing capability. An image forming method, further comprising the step of: