JPH10123795A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To output an image having high transmittance to a transparent member for overhead projector (OHT), to output images having mutually different glossiness so as to miniaturize and speeding-up an image forming device by turning a photoreceptor at a first specified sped of an image carrier and forming the toner image of plural colors on the image carrier, then switching the speed to a second specified speed of the image carrier, and transferring the toner image of plural colors to a recording material. SOLUTION: In the case of forming the image, the photoreceptor 2 turns at the same rotational speed as a speed in a low speed mode, a latent image is formed by an electrifying device, developing is performed by a developing device, and the color toner image is obtained on the photoreceptor 2. The developing is performed by the developing device 13K, and the color toner image is completed on the photoreceptor 2, then the turning speed of the photoreceptor 2 is switched. When the leading end of the toner image formed on the photoreceptor 2 comes close to a transfer area, a transfer roller 10 and a cleaning blade 19a are brought into press-contact with the photoreceptor 2, a resist roller 16 feeds a recording paper at a speed synchronized with the turning speed of the photoreceptor 2 whose speed has been changed, and the toner image is transferred.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of arranging a plurality of chargers, an exposing device and a developing device around an image carrier, and superimposing a toner image during one rotation of the image carrier to form a color image. More particularly, the present invention relates to an image forming apparatus capable of forming a toner image on a transparent member for an overhead projector (hereinafter, also referred to as OHT).

[0002]

2. Description of the Related Art A method of forming a multicolor image is to form a color image at high speed by sequentially performing charging, image exposure and development for each color within one rotation of one image carrier. Methods and the like are known. An apparatus for realizing such an image forming method includes a charger,
It is necessary to arrange a plurality of sets of the exposure unit and the development unit, and there is a possibility that the optical system for performing image exposure may be stained with toner leaking from the adjacent development unit and deteriorate the image quality. Since it is necessary to increase the interval, there is a contradiction that the diameter of the image carrier is inevitably increased and the apparatus is enlarged. For the purpose of avoiding this drawback, a device in which the base of the image carrier is formed of a transparent material, a plurality of exposure devices are accommodated therein, and the photosensitive layer formed on the outer periphery thereof is exposed through the base, For example, JP-A-5-30
No. 7307.

[0003] In order to form a toner image on a transparent member for an overhead projector or on high gloss paper, it is necessary to increase the fixing nip time as compared with plain paper. Color image formation that runs at the same process speed as plain paper and reduces the OHT conveyance speed when the leading edge of the OHT reaches the transfer area to increase the fixing nip time to obtain a vivid color image A method has been proposed (see JP-A-60-80885 and JP-A-60-86574).

[0004]

However, a conventional color image forming method (Japanese Patent Application Laid-Open No. 60-80885,
Japanese Unexamined Patent Publication No. Sho 60-86574) discloses that a transport path longer than the length of the OHT must be provided between the transfer section and the fixing section in order to reduce the transport speed of the OHT. Was invited.

An object of the present invention is to solve the above technical problems,
It can output vivid and high transparency images to OHT,
An object of the present invention is to provide an image forming apparatus capable of outputting images having different gloss levels according to a user's request and paper quality, and being small and capable of high-speed processing.

[0006]

The above object is achieved by the following constitution.

(1) A plurality of sets of charging means and developing means are provided facing the image carrier, and a plurality of latent image forming means are provided in the vicinity of the image carrier to charge the image carrier. ,exposure,
An image forming apparatus for forming a color image on the recording material by forming a plurality of color toner images by sequentially repeating development, transferring the plurality of color toner images to a recording material, and fixing the image; After rotating the carrier at a first predetermined speed to form a plurality of color toner images on the image carrier, the image carrier is switched to a second predetermined speed, and the image carrier is switched at a second predetermined speed. An image forming apparatus, wherein the plurality of color toner images are transferred from the image carrier to the recording material. With the above configuration, it is possible to output a bright high-transparency image to the OHT, and it is possible to perform small-sized and high-speed processing.

(2) A toner image of a plurality of colors is formed on the image carrier during the first rotation of the image carrier, and the rotation speed of the image carrier is reduced from the first predetermined speed after the second rotation. The image forming apparatus according to (1), wherein the plurality of color toner images are transferred from the image carrier to the recording material at the second predetermined speed by switching to the second predetermined speed.

(3) A toner image of a plurality of colors is formed on the image carrier in the first cycle of the image carrier, and the rotation speed of the image carrier is increased to the first predetermined speed in the second cycle. And switching to the second predetermined speed, and transferring the plurality of color toner images from the image carrier to the recording material at the second predetermined speed after the third round. (2) Image forming apparatus.

(4) Plural sets of charging means and developing means are provided to face the image carrier, and plural sets of latent image forming means are provided near the image carrier, and charged on the image carrier. , Latent image formation and development are sequentially repeated to form a toner image of a plurality of colors,
In the image forming apparatus for obtaining a color image on a recording material by transferring the toner images of the plurality of colors onto a recording material and then fixing the image, the image carrier is rotated at a first predetermined speed. Forming a plurality of color toner images thereon, transferring the plurality of color toner images from the image carrier to the recording material, and rotating the image carrier at a first predetermined speed. After forming a multi-color toner image on the image carrier,
Switching the rotation speed of the image carrier to a second predetermined speed,
A shift mode for transferring the plurality of color toner images from the image carrier to the recording material at the second predetermined speed. With the above configuration, images having different gloss levels can be output according to the user's request and paper quality, and small-sized and high-speed processing can be performed.

(5) In the shift mode, the fixing temperature for fixing the toner images of the plurality of colors on the recording material is switched to a temperature different from the fixing temperature in the constant speed mode. Image forming device.

[0012]

FIG. 1 is a sectional view showing a schematic configuration of an image forming apparatus according to the present embodiment.

The color image forming process in the constant speed mode will be described.

At the start of image recording, the photosensitive drum 2
Is rotated to rotate the photosensitive drum 2 clockwise, and at the same time, a potential is applied to the photosensitive drum 2 by the charging action of the scorotron charger 11Y.

After the photosensitive drum 2 is applied with a potential,
The exposure unit 12Y starts exposure with an electric signal corresponding to the yellow image signal, and forms an electrostatic latent image corresponding to the yellow image on the photosensitive layer of the photosensitive drum 2 by rotating and scanning the photosensitive drum 2. Such a latent image is reversely developed by the developing device 13Y in a non-contact state with the developer on the developing sleeve 131Y, and is visualized as a yellow toner image according to the rotation of the photosensitive drum 2.

Next, the photosensitive drum 2 is further provided with a potential on the yellow toner image by the charging action of the scorotron charger 11M, and the exposure unit 12M performs exposure with an electric signal corresponding to the magenta image signal. 13M forms a magenta toner image on a yellow toner image by non-contact reversal development.

By the same process, a cyan toner image corresponding to the cyan image signal is further formed by the scorotron charger 11C, the exposure unit 12C and the developing unit 13C, and is further formed by the scorotron charging unit 11K, the exposure unit 12K and the developing unit 13K. A black toner image corresponding to the black signal is formed so as to be superimposed, and a color toner image is formed on the peripheral surface of the photosensitive drum 2 within one rotation.
During the above-described four color exposure and development processes, the transfer roller 1
0 and the blade 19a are in a non-contact state.

The exposure of the organic photosensitive layer of the photosensitive drum 2 by the exposure devices 12Y, 12M, 12C and 12K is performed through a transparent substrate from the inside of the drum. In order to stabilize the temperature in the photosensitive drum 2 and prevent the temperature from rising due to the heat generated by the exposure units 12Y, 12M, 12C and 12K, a material having good heat conductivity is used for the support member 20, and a heater is used when the temperature is low. In the case of a high temperature, measures such as radiating heat to the outside through a heat pipe can be suppressed to a level that does not cause any trouble.

The replenishing developer of each color is supplied to a replenishing tank 21.
From Y, 21M, 21C and 21K to developing units 13Y, 1
Replenished to 3M, 13C and 13K. Developing device 13
In the developing operation by Y, 13M, 13C, and 13K, the developing sleeves 131Y, 131M, and 13K are used, respectively.
A developing bias in which a direct current or a further alternating current is applied to 1C and 131K is applied, jumping development is performed by a two-component developer contained in the developing device, and toner is applied to the photosensitive drum 2 that grounds the transparent conductive layer. By applying a DC bias of the same polarity, non-contact reversal development is performed in which toner is attached to the exposed portion.

As shown in FIG. 1, a paper feed cassette 15 in which a plurality of recording papers P are built in the main body is detachably provided. A half-moon-shaped feeding roller for feeding the recording paper P is provided on the paper feeding cassette 15, and a push-up plate for pressing the uppermost recording paper P against the separation claw is provided in the paper feeding cassette 15. The recording paper P placed on the push-up plate is constantly pushed upward by a spring (not shown), the leading end of the recording paper P is locked by a separation claw, and fed by the operation of an electromagnetic clutch (not shown). The roller is driven, and the uppermost sheet of recording paper P is separated by a separation claw and fed. The fed recording paper P is driven and conveyed by an intermediate paper feed roller, and is guided to a registration roller 16. A registration shutter that opens and closes a registration unit in accordance with a control signal from the engine controller 100 is provided downstream of the registration roller 16 in sheet feeding. The detection member 219 is operated by the engine controller 100,
When the recording sheet P is detected by the detection member 219, the recording sheet P directly enters the registration roller 16 and stops at the registration shutter. Further, a sensor 3 for detecting the transparency or gloss of the recording paper P surface is provided on the upstream side of the registration roller 16 in the paper supply. At that time, the guide member 213
On the upper part of the sensor 3 is a sensor 3 rotatably fixed to a part of the main body.
After the leading end of the recording paper P abuts on a protrusion provided on a part of the recording paper P and the sensor 3 is arranged at a predetermined position along the image forming surface of the recording paper P, the transparency of the image forming surface formed on the recording paper P Alternatively, the glossiness is detected, and the CPU 130 identifies plain paper or OHT.

A detecting member for detecting the recording paper P is provided above the paper feed cassette 15. The intermediate paper feed roller is provided between the paper feed cassette 15 and the curved reverse guide member.

Thus, the color toner image formed on the peripheral surface of the photosensitive drum 2 is
The sheet is fed out of the sheet cassette 15 and is
The recording paper P is conveyed to the recording roller P and fed in synchronization with the toner image on the photosensitive drum 2 by driving the registration roller 16.
Is transferred to

The recording paper P to which the toner image has been transferred is separated from the peripheral surface of the drum by the charge removing brush 14b after the charge is removed, and then the fixing device 1 is transported by the transport belt 14e.
7 is conveyed. The fixing device 17 fuses and fixes the toner on the recording paper P by applying heat and pressure, and then discharges the toner onto a tray on the side of the device via a discharge roller 18.

On the other hand, the photosensitive drum 2 from which the recording paper has been separated is rubbed against the surface of the photosensitive drum 2 by a blade 19a in a cleaning device 19 to remove residual toner, and is cleaned to continue forming a toner image of a document image. Alternatively, the image forming apparatus temporarily stops and starts forming a toner image of a new document image.
The waste toner scraped off by the blade 19a and the roller 19b is discharged to the waste toner container 22 through the toner conveying screw 19c and the toner conveying pipe 19d. After the cleaning, the blade 19a and the roller 19b are kept in contact with each other at a pressure lower than that of the photosensitive drum 2 in order to prevent damage to the photosensitive drum 2.

Next, the color image forming process in the shift mode will be described.

Prior to the start of image formation, the transfer roller 1
0 and the cleaning blade 19a are separated from the photosensitive drum 2, and if necessary, a fixing heater (not shown) is turned on / off so as to set the fixing temperature of the fixing device to a temperature different from the constant speed mode.

Subsequently, image formation is started, and the photosensitive drum 2 is rotated at the same rotation speed as in the above-described constant speed mode, so that charging by the charger, formation of a latent image by the exposure device, and development by the developing device are performed. As a result, a color toner image is obtained on the photosensitive drum 2. Further, the recording paper P sent out from the paper feed cassette 15 is
Stops at the registration shutter in the same manner as in the constant speed mode.

After the development by the developing unit 13K is completed and a color toner image is completed on the photosensitive drum 2, the rotation speed of the photosensitive drum 2 is switched. The speed after the switching may be faster or slower than in the constant speed mode. However, if the rotation speed is changed while the toner image is being formed on the photosensitive drum 2, the image density fluctuates. Therefore, it is preferable to start acceleration or deceleration after completion of the formation of the color toner image.

After the switching of the rotation speed of the photosensitive drum 2 is completed, when the leading end of the toner image formed on the photosensitive drum 2 approaches the transfer area, the transfer roller 10 and the cleaning blade 19a are pressed against the photosensitive drum 2. Then, the registration roller 16 sends out the recording paper P to the transfer area at a speed synchronized with the changed rotation speed of the photosensitive drum 2, and the toner image is transferred onto the recording paper P. Following static elimination, separation,
The fixing is performed at a speed synchronized with the process speed after the shift, and the transfer roller 10 and the cleaning blade 19a are separated from the photosensitive drum 2 again in preparation for the next image formation. After the switching of the rotation speed of the photosensitive drum 2 is completed, the transfer roller 10 and the cleaning blade 1
9a is pressed in order to prevent image fluctuation due to transfer during acceleration / deceleration of the photosensitive drum 2.

In the shift mode, the toner image on the photosensitive drum 2 before the transfer is transferred to the cleaning blade 19.
In order to prevent the toner image from being cleaned by a, a non-image area on the circumference of the photosensitive drum 2 that is longer than the separation distance between the transfer roller 10 and the cleaning blade 19a is preferably provided between the front end and the rear end of the toner image.

The photosensitive drum 2 has, for example, a cylindrical substrate formed of a transparent member such as optical glass or transparent acrylic resin on the inner side, and a transparent conductive layer and an organic photosensitive layer (OPC) formed on the outer periphery of the substrate. A photosensitive layer is formed on the drum and grounded. The organic photoreceptor is provided with an intermediate layer on a conductive support, if necessary, and is formed on the intermediate layer.
The organic photoreceptor layer may have a single-layer structure in which a charge generation material (CGM) and a charge transport material (CTM) are contained in one layer, or a charge generation layer (CGL) containing CGM as a main component and a CTM. And a charge transport layer (CTL) mainly composed of a CTL. In addition,
The single-layer or two-layer photosensitive layer usually contains a binder resin.

The photosensitive layer of the organic photoreceptor has a thickness of 480 as described above.
It is only necessary to have sensitivity at a wavelength of at most 430 nm, and depending on the emission wavelength of the exposure device, it is sufficient to have sensitivity at at most 430 nm. Good. That is, 43
A photoconductor having a light-transmitting property in a green or red region of 0 nm or 480 nm to 700 nm can be used. Therefore, it is possible to visually check the state of the LED inside the photosensitive drum 2 and the state of the light detecting means described later.

In the present embodiment, the photoconductor layer of the photosensitive drum 2, which is the image forming point of the exposure beam for image exposure, is suitable for the light attenuation characteristics (photocarrier generation) of the photoconductor layer. What is necessary is that it has an exposure light amount of a wavelength that can provide contrast. Therefore, the light transmittance of the transparent substrate of the photosensitive drum in the present embodiment does not need to be 100%, and may have a characteristic that a certain amount of light is absorbed when the exposure beam is transmitted. As the material of the light-transmitting substrate, various light-transmitting resins such as soda glass, Pyrex glass, borosilicate glass, and fluorine, polyester, polycarbonate, and polyethylene terephthalate used for general optical members can be used.

As the light-transmitting conductive layer, a light-transmitting conductive layer made of indium tin oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, Au, Ag, Ni, Al or the like is used. Is used, and a vacuum deposition method, an active reaction deposition method, various sputtering methods, various CVD methods, a dip coating method, a spray coating method, or the like is used as a film forming method. Various organic photosensitive layers (OPC) can be used as the photoconductor layer.

Scorotron chargers 11Y, 11M, 11
C and 11K are used in an image forming process of each color of yellow, magenta, cyan and black. Corona discharge by a control grid and a discharge wire maintained at a predetermined potential with respect to the above-mentioned organic photoconductor layer of the photoconductor drum 2 is performed. As a result, the photosensitive drum 2 is given a uniform potential.

Exposure units 12Y, 12M, 12C and 12
K is a support member 2 provided inside the photosensitive drum 2.
0, and is formed as a unit by a linear LED (light emitting diode) in which light emitting elements arranged in the axial direction of the photosensitive drum 2 are arranged in an array and a selfoc lens as an equal magnification imaging element. It is configured by a laser light emitting element and an optical system, and emits light by using electric signals sequentially read out of a memory from image signals of respective colors read by a separate image reading device.

For example, an LED or a laser light-emitting element uses Zn-doped InGaN for the light-emitting layer,
It employs a double hetero structure sandwiched between lGaN layers, and has an emission wavelength of a monochromatic light having a peak at 450 nm of blue and a half-value width of 70 nm.

The toner of the developer is yellow, magenta,
Since the cyan and black toners having spectral reflectances are used, the spectral reflectance of the color toner is determined by the image exposure light passing through the photosensitive drum 2 and being reflected by the toner attached to the photosensitive drum 2. The condition is set to 25% or less as a condition for reducing the influence of the disturbance of the latent image by re-entering the photosensitive drum 2. LED light emitting element without Zn doping I
The emission wavelength of nGaN is 400 nm. For a light emitting element having a blue emission wavelength of 480 nm or less, the spectral reflectance of yellow, magenta, and black toners is 25% or less. For example, the reflectance of yellow toner is low, that is, the light absorption is high. Therefore, when irradiating exposure light for forming a next latent image by a light emitting element provided inside the photosensitive drum 2, irregular reflection due to yellow toner on the outer peripheral surface of the photosensitive drum 2 is small, and the above color image The order of formation can be yellow, magenta, black → cyan. It is not the best to set the order of color image formation from yellow, magenta → cyan → black, but it is preferable because color mixing in the developing device is not noticeable. In addition, 430n
m or less, the spectral reflectances of all the yellow, magenta, cyan and black toners are 25% or less. Therefore, the order of the toner used for color image formation does not depend on the order of yellow, magenta, cyan and black. You may go in. This tendency is more preferable at 300 nm or more and 400 nm or less.

Developing units 13Y, 13M, 13C and 13
K contains a two-component developer consisting of yellow, magenta, cyan, and black carriers and toner, respectively, and makes the electrostatic latent image on the photosensitive drum 2 non-contact by applying a developing bias voltage. The developing sleeves 131Y, 1 rotate in the same direction while maintaining a predetermined gap with respect to the peripheral surface of the photosensitive drum 2 in each state.
31M, 131C and 131K. The developing sleeves 131Y, 131M, 131C, and 131K have a power supply (not shown) for applying a DC bias and an AC bias set for each color, and individually turn on / off the DC bias and the AC bias under the control of an engine controller. be able to.

The spectral reflectance of the yellow toner, the magenta toner, the cyan toner, and the like is obtained by measuring the spectral reflectance of a white substrate rubbed with each of the toners, and the reflectance is low. This indicates that the absorption rate of the measurement light in the toner layer is large, and that the reflectance is high indicates that the transmittance of the toner itself to the measurement light is large.

The image of the original is read by an image reading apparatus separate from the present apparatus, and the image read by the image pickup device or the image edited by the computer is once converted into image signals for respective colors of Y, M, C and K. Stored and stored in memory.

The toner concentration detecting sensor S2 is fixed to a support member 20 provided inside the photosensitive drum 2, provided after the developing unit 13K, and formed on the outer peripheral surface of the photosensitive drum 2. For example, a photocoupler using an LED as a light-emitting element for detecting the reflection density of the light-emitting element is used. Similarly, a jam detection sensor S1 fixed to a support member 20 provided inside the photosensitive drum 2 detects a jam of a recording sheet based on the presence or absence of the recording sheet after passing through the transfer roller 10 and the discharging brush 14b. For example, LE
It is composed of a photocoupler in which D is a light emitting element. For example, the emission wavelength of the light detection means is longer than the image exposure light and the image carrier has no spectral sensitivity so that potential change or light fatigue does not occur for the organic photoreceptor having a spectral sensitivity of 500 nm or less. Monochromatic light on the long wavelength side that passes through the photosensitive drum 2 including visible light of 560 nm or more and infrared light is used.

When the sensor 3 detects the glossiness of the recording paper P, the sensor 3 is provided with a light emitting element installed so as to have an incident angle of 60 degrees or more with respect to the recording paper P, and records the light emission of the light emitting element. When the sensor 3 detects the transparency of the recording paper P, the sensor 3 includes a light-emitting element and a light-receiving element provided so as to face each other with the recording paper P interposed therebetween. Consists of

The fixing device 17 is a device for fixing the image transferred onto the recording paper P, and comprises a fixing heating roller 171 and a pressure roller 172. The fixing heating roller 171 has a thickness of 455.7 mm on a substrate having a diameter of 245.7 mm and an outer diameter of 1.6 mm.
It has a 0 μm silicone rubber layer and a 50 μm thick PFA layer. A fixing heater 174 is inserted through the base of the fixing heating roller 171. The surface temperature of the fixing heating roller 171 is controlled by the fixing temperature control unit 120 so that the surface temperature is detected by the fixing temperature sensor Th and is always constant. The fixing temperature control unit 120 detects the surface temperature of the fixing heat roller 171 and detects the surface temperature of the fixing heat roller 171.
The first fixing heater 174 is turned on and off, and the surface temperature of the fixing heating roller 171 is detected, and when the temperature becomes abnormally high, the power supply to the fixing heater 174 is stopped. The fixing temperature sensor Th is provided in a non-transfer material area where the recording paper P does not contact the fixing heating roller 171 when the recording paper P passes (an area which is not affected by toner, paper dust, etc.), so that the paper passing time is reduced. Irrespective of the above, the initial detection accuracy can be maintained. The pressure roller 172 has a surface layer such as rubber. The discharge roller 173 discharges the recording paper P from the fixing device 17, and the discharged recording paper P is
4 to be transported upward. The recording paper P conveyed upward by the conveyance rollers 174 is discharged by a discharge roller 18 provided in a paper discharge passage formed in the main body with a recording surface facing down onto a discharge tray provided on almost the entire upper portion of the main body. Paper. A paper discharge detection sensor is provided in the paper discharge path of the fixing device 17.

The driving force is transmitted by a motor (not shown) to the paper feed roller 202 via a speed reduction mechanism (not shown), and to the intermediate paper feed roller via a toothed pulley and an intermediate gear group. . The paper feed roller is driven intermittently by an electromagnetic clutch (not shown). On the other hand, the registration roller 16 and the intermediate sheet feeding roller are configured to be driven and rotated at all times.

Next, FIG. 1 shows a schematic configuration of an engine controller 100 employed in the image forming apparatus according to the present embodiment.
This will be described with reference to FIG.

The engine controller 100 includes a CPU 1
30, fixing temperature control means 120, speed control means 140,
The image forming is performed by the CPU 130 which includes a transfer cleaning pressure control unit 150 and a transfer roller voltage switching unit 160 and controls these units in accordance with an engine control sequence programmed in advance.

The recording material detecting means 110 identifies plain paper or OHT based on the transparency or glossiness of the recording paper P detected by the sensor 3 and transmits the identification result to the CPU 130. When the operator manually designates the recording paper mode, the user selects the mode of plain paper or OHT using the mode selection key 111, and the recording material detecting means 110 detects the transparency or gloss of the recording paper P detected by the sensor 3. The mode selection result is identified with higher priority than the
The identification result is transmitted to 30.

The above-mentioned switching between the constant speed mode and the shift mode is preferably performed by the CPU 130 based on the identification result transmitted from the recording material detecting means 110.

Switching between the constant speed mode and the shift mode is performed when the amount of light received by the light receiving element of the sensor 3 becomes equal to or greater than a predetermined threshold, and image formation is performed in the shift mode. Mode. When plain paper is selected by the mode selection key 111, image formation is performed in the constant speed mode, and when OHT is selected, image formation is performed in the shift mode.

The fixing temperature control means 120 includes a CPU 130
The fixing temperature of the fixing device 17 is controlled on the basis of the instruction from the printer, and the optimum fixing temperature condition is set. Such setting is performed before the start of printing, and printing is started after the temperatures of the fixing heating roller 171 and the pressure roller 172 reach desired temperature regions. In this embodiment, the set temperature for fixing a toner image on plain paper is from 165 ° C. to 1
70 ° C., the set temperature for fixing the toner image on the OHT is in the range of 180 ° C. to 185 ° C., and the set temperature during the period when the recording paper is not passed is 135 ° C. to 145 °.
In the range of ° C, the set temperature in the standby state is 120 ° C.

The speed control means 140 controls the photosensitive drum 2,
The image forming speed is controlled by controlling the driving source of each member that affects the image forming speed, such as the sheet feeding roller, the registration roller 16, the transfer roller 10, the fixing heating roller 171, the pressure roller 172, and the sheet discharging roller 18. doing.

The transfer cleaning pressure contact control means 150
Based on an instruction from the CPU 130, the pressure control of the transfer roller 10 and the cleaning blade 19 a to the photosensitive drum 2 and the release of the pressure bonding are controlled.

The transfer roller voltage switching means 160 is a CPU
The voltage supplied to the transfer roller 10 is controlled based on an instruction from 130, and optimal transfer conditions are provided according to the situation.

Next, the process timing in this embodiment will be described with reference to FIGS.

FIG. 2 is a timing chart showing the process timing for obtaining a full-color image in the constant speed mode.

When the start signal is issued, the rotation of the photosensitive drum 2 starts at time t1. Speed control means 14
0 keeps the process speed at 75 mm / sec. In addition, the transfer roller 10 and the cleaning blade 19 a, which have been in contact with the photosensitive drum 2 with the pressure reduced by the transfer cleaning pressure contact control unit 150, are pressed against the photosensitive drum 2, and the fixing temperature control unit 120 controls the temperature of the fixing device 17. Is a 170 for fixing a toner image on plain paper.
Set to ° C. Note that such setting is preferably performed before the start of printing.
Arrives shortly after the start of printing, so that the set temperature is reached in accordance with the timing at which the recording paper P arrives at the fixing device 17 in consideration of the heat capacities of the fixing heating roller 171 and the pressure roller 172. Control of the heater can be performed.

Each time the leading end of the image on the photosensitive drum 2 passes through the charging device, exposure device and developing device of each color, charging, exposure and development are performed to form a color toner image. In the present embodiment, the scorotron chargers 11Y, 11M,
The grid voltages of 11C and 11K are -550V, and the surface potential of the photosensitive drum 2 is -600V.

Before time t2 when the leading edge of the image on the photosensitive drum 2 reaches the transfer area, the voltage applied to the transfer roller 10 is maintained at +2 kV by the transfer roller voltage switching means 160, and the recording paper P is transferred from the photosensitive drum 2 in the transfer area. The transfer of the toner image to is performed. The recording paper P separated from the photoconductor drum 2 is conveyed to a fixing device 17 maintained at a fixing set temperature at a process speed of 75 mm / sec, and the toner image has a length corresponding to two rotations of the photoconductor drum 2. Image
When the image formation for the circumference of the photosensitive drum 2 is completed, the operation is sequentially stopped from the yellow charger to prepare for the next image formation.

FIG. 3 is a time chart showing a process timing for obtaining a full-color image in the shift mode.

When a start command is issued, the rotation of the photosensitive drum 2 is started at time t1 as in the case of the constant speed mode. The transfer roller 1 that has been in contact with the photosensitive drum 2 by reducing the pressure by the transfer cleaning pressure control unit 150
0 and the cleaning blade 19 a are completely separated from the photosensitive drum 2, and the temperature of the fixing device 17 is adjusted by the fixing temperature control means 120 to 18 to fix the toner image on the OHT.
The heater is controlled so that the timing at which the recording paper P reaches the fixing device 17 set at 0 ° C. is reached.

At time t3 immediately after the trailing edge of the image has passed the developing unit 13K in the second rotation from the start of printing, the process speed is increased from 75 mm / sec to 15 mm by the speed control means 140.
/ Sec, the transfer roller 10 is pressed against the photosensitive drum 2 at time t4 when the leading edge of the image reaches the transfer area in the third rotation from the start of printing, and the cleaning blade 19a is pressed at time t5 with a slight delay. Before time t4, the voltage applied to the transfer roller 10 is
At 0, the voltage is maintained at +1 kV, and the transfer of the toner image from the photosensitive drum 2 to the recording paper P is performed in the transfer area.
The recording paper P separated from the photosensitive drum 2 has a thickness of 15 mm /
With the process speed of 2 seconds, the sheet is conveyed to the fixing device 17 maintained at the fixing set temperature of 180 ° C. to fix the toner image, thereby completing a full-color image.

[0063]

According to the present invention, by providing the above-mentioned structure, it is possible to output a bright image with high transparency to an OHT, and to output an image having a different glossiness according to a user's request or paper quality. It is small and can be processed at high speed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment.

FIG. 2 is a timing chart showing a process timing for obtaining a full-color image in a constant speed mode.

FIG. 3 is a time chart showing a process timing for obtaining a full-color image in a shift mode.

[Explanation of symbols]

 2 Photoconductor drum (corresponding to image carrier) 3 Sensor 11Y, 11M, 11C, 11K Scorotron charger 12Y, 12M, 12C, 12K Exposure unit 13Y, 13M, 13C, 13K Developing unit 100 Engine controller 130 CPU 150 Transfer cleaning Crimping control means 160 Transfer roller voltage switching means

Claims (5)

[Claims] 1. A plurality of sets of charging means and developing means are provided to face an image carrier, and a plurality of sets of latent image forming means are provided in the vicinity of the image carrier. The image forming apparatus obtains a color image on the recording material by forming a plurality of color toner images by sequentially repeating exposure and development, transferring the plurality of color toner images onto a recording material, and fixing the image. After rotating the carrier at a first predetermined speed to form a plurality of color toner images on the image carrier, the image carrier is switched to a second predetermined speed, and the image carrier is switched at a second predetermined speed. An image forming apparatus, wherein the plurality of color toner images are transferred from the image carrier to the recording material. 2. A toner image of a plurality of colors is formed on the image carrier in a first cycle of the image carrier, and the rotation speed of the image carrier is reduced from the first predetermined speed after a second cycle. 2. The image forming apparatus according to claim 1, wherein the second predetermined speed is switched, and the plurality of color toner images are transferred from the image carrier to the recording material at the second predetermined speed. 3. A plurality of color toner images are formed on the image carrier in a first cycle of the image carrier, and a rotation speed of the image carrier is reduced from the first predetermined speed in a second cycle. The second
3. The image forming apparatus according to claim 2, wherein the plurality of color toner images are transferred from the image carrier to the recording material at the second predetermined speed after the third round. apparatus. 4. A plurality of sets of charging means and developing means are provided in opposition to the image carrier, and a plurality of latent image forming means are provided in the vicinity of the image carrier. An image forming apparatus for forming a color image on a recording material by forming a plurality of color toner images by sequentially repeating latent image formation and development, transferring the plurality of color toner images to a recording material, and fixing the same. A constant speed mode in which a plurality of color toner images are formed on the image carrier by rotating the image carrier at a first predetermined speed, and the plurality of color toner images are transferred from the image carrier to the recording material; And after rotating the image carrier at a first predetermined speed to form a plurality of color toner images on the image carrier, switching the rotation speed of the image carrier to a second predetermined speed, The plurality of color toner images are transferred from the image carrier to the recording material at the second predetermined speed. An image forming apparatus comprising: a shift mode for photographing. 5. The fixing mode according to claim 4, wherein in the shift mode, a fixing temperature for fixing the plurality of color toner images onto a recording material is changed to a temperature different from a fixing temperature in the constant speed mode. Image forming device.