JPH07333922A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device having stable gradation and image density. CONSTITUTION:When power is supplied at the time of starting copy, a photoreceptor preparation process 1 for electrifying an image carrier twice or more, a developer preparation process 2 for stirring a developer and making the electrostatic charge quantity of toner sufficient and an image formation preparation process 3 for attaining corrections for maintaining the maximum density of an image >=1.4 and the gradation of the image are prepared in advance. Moreover, a set temperature T1 (0-150 deg.C, preerably 50 deg.C) lower than the fixing control temperature Tc of a fixing unit 37 is set and when a temperature Tx at the time of supplying the power of the fixing unit 37 is Tx<=T1 (1), all the processes 1-3 are executed, when the temperature Tx is T1<Tx<=Tc (2), the processes 1 and 2 are executed and when the temperature Tx is Tx>Tc (3), only the process 1 is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus utilizing an electrostatic transfer process such as an electrophotographic copying machine, a laser beam printer, an electrostatic recording device and the like.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus utilizing an electrostatic transfer process requires a warming-up time until the fixing device rises to a fixing temperature after power is turned on to start copying. Nothing was done inside.

[0003]

In the conventional image forming apparatus as described above, if a copying operation is performed after the copying apparatus is left without copying, the charging potential of the charging device of the image carrier is 1%.
In the charging of the first time (first round), there is a property that the absolute value becomes lower as the standing time becomes longer. Therefore, the charging potential of the first rotation of the image carrier and the charging potential of the second rotation are different. Since the normal image forming area is formed over the first and second laps as shown in FIG. 16, the potential of A in FIG. 16 becomes smaller in absolute value as the standing time becomes longer as shown in FIG. However, when the copy image has uneven density and is left for a long time, fogging occurs in the first half of the image.

Further, the charge amount of the toner of the developer also has a property that the charge amount becomes low as shown in FIG. 18, so that the image density of the copy image becomes high and fog occurs when the leaving time is long. There was a point.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide an image forming apparatus which can always obtain a copy image having stable gradation and image density.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to form an electrostatic latent image on a uniformly charged image carrier and develop the latent image with a developing device to obtain a toner image. In an image forming apparatus that obtains a copy image by fixing an image on a transfer material and then fixing the image with a fixing device, when the power of the image forming apparatus is turned on, a photoconductor preparing step for the image carrier is performed in advance.
A developer preparation step and an image formation preparation step are prepared, a preset temperature T ₁ lower than the fixing control temperature Tc of the fixing device is determined, and the temperature Tx when the fixing device is turned on is (1) Tx ≦
If T ₁ , then do all of the above, (2) T ₁
If <Tx ≦ Tc, perform the above, and (3) Tx
In the case of> Tc, it is achieved by the image forming apparatus characterized in that only the above is performed.

The image forming apparatus is a preferable image forming apparatus, wherein the writing unit for forming the electrostatic latent image is a digital writing system.

Further, an electrostatic latent image is formed on a uniformly charged image carrier, the latent image is developed by a developing device to form a toner image, and the toner image is transferred to a transfer material, and then the fixing device. In an image forming apparatus for fixing a copy image to obtain a copy image, a photoconductor preparation step, a developer preparation step, and an image formation preparation step of the image carrier are prepared in advance when the image forming apparatus is powered on. When the stand-by time after turning off the power and turning on the power is tx, and the set times are t ₁ and t ₂ (t ₁ <t ₂ ), if (1) tx ≧ t ₂ , , And (2) If t ₁ ≤tx <t ₂ , then the above-mentioned preparatory steps are performed and (3) tx <t
_When it is ₁ , only the preparation step is performed.

This is achieved by an image forming apparatus characterized by the above.

[0010]

As described above, the so-called warming-up time until the temperature of the fixing device of the image forming apparatus rises is used to prepare the photosensitive member, the developer and the image forming. It is possible to obtain stable gradation and image density.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure and operation of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention, and FIG. 2 is a block diagram showing a control system of the apparatus of FIG.

First, a normal copy operation of this image forming apparatus will be described. This image forming apparatus is composed of an image reading unit 10, a writing unit 20 which is a digital writing system, an image forming section 30, a paper feeding section 40, a document placing section 50 and the like.

At the upper part of the image forming apparatus, there is a document table 51 made of a transparent glass plate or the like, and a document placing section 50 having a document cover 52 for covering the document D placed on the document table 51. Below the table 51, inside the apparatus main body, a first mirror unit 12, a second mirror unit 13, an imaging lens 14,
An image reading unit 10 including an image pickup device 15 such as a CCD array is provided.

The image of the document D on the document table 51 is moved parallel to the position shown by the broken line from the solid line of the first mirror unit 12 including the illumination lamp 12A and the first mirror 12B of the image reading unit 10, and the second The entire surface is illuminated and scanned by the second mirror unit 13 that integrally includes the mirror 13A and the third mirror 13B facing each other at a speed of 1/2 of that of the first mirror unit 12, and the image is captured by the imaging lens 14. Thus, an image is formed on the image sensor 15 via the first mirror 12B, the second mirror 13A and the third mirror 13B. After scanning, the first mirror unit 12 and the second mirror unit 13
Returns to the original position and waits for the next image formation.

The image data obtained by photoelectric conversion by the image pickup device 15 is converted into a digital signal, and then subjected to MTF correction, γ correction and the like by the image signal processing unit 60 and temporarily stored in a memory as an image signal. To be done. Next, the image signal is read from the memory under the control of the CPU 90, pulse width modulated, and then input to the writing unit 20.

Under the control of the CPU 90, the image forming section 30 outputs the image signal to the drive motor 21, the polygon mirror 22, and the f.
When input to the writing unit 20 including the θ lens 23, mirrors 24, 25 and 26 and a semiconductor laser, a correction lens and the like (not shown), the image recording operation is started. That is, the photosensitive drum 31, which is an image carrier, rotates clockwise as shown by the arrow,
Since the charge is given by the charger 32 after the charge is removed by the charge remover 36 that performs precharge exposure and removes the charge, the laser beam L from the writing unit 20 corresponds to the image of the document D on the photosensitive drum 31. Electrostatic latent image is formed. After that, the electrostatic latent image on the photosensitive drum 31 is
Reversal development is carried out by the developer carried on the developing sleeve 33A, which is the developer carrying body to which the DC bias voltage of the developing device 33 is applied, to form a visible toner image.

On the other hand, the paper feed cassette loaded in the paper feed unit 40
Transfer paper P of a designated size is unloaded one by one from 41A or 41B by unloading roller 42A, and is fed toward the image transfer section via unloading roller 43 and guide member 42. The transferred transfer paper P is transferred to the photosensitive drum by the registration roller 44 which operates in synchronization with the toner image on the photosensitive drum 31.
Dispatched on 31. The toner image on the photoconductor drum 31 is transferred to the transfer paper P by the action of the transfer device 34, separated from the photoconductor drum 31 by the charge removal action of the separator 35, and then fixed via the conveyor belt 45. The sheet is sent to a container 37, melted and fixed by a heating roller 37A and a pressure roller 37B, and then discharged to a tray 54 outside the apparatus by paper discharge rollers 37D and 46. 53 is a paper feed table for manual feeding.

The photosensitive drum 31 continues to rotate,
The toner remaining on the surface without being transferred is removed and cleaned by the cleaning blade 39A in pressure contact with the cleaning device 39, discharged again by the charge eliminator 38, and then uniformly charged by the charger 32, and next time. Enter the process of image formation.

The magnetic permeability sensor TS provided at the bottom of the stirring screw 33C of the developing unit 33 utilizes the fact that the magnetic permeability changes when the toner concentration of the developing agent changes, so that the toner of the developing agent in the developing unit 33 is changed. It is a sensor that monitors the density and sends the toner density information of the developer to the CPU 90. The CPU 90 sends a toner replenishment instruction to the toner replenishing unit 33T to replenish the toner when the toner concentration decreases below a certain value based on the information of the magnetic permeability sensor TS, so that the toner concentration of the developer can always be kept constant. it can.

In this embodiment, a two-component developer comprising a polyester-based toner having a weight average particle size of 8.5 μm and a carrier having a resin coating on ferrite and a weight average particle size of 60 μm is used as a developer having a toner concentration of 5%. However, the toner density fluctuation is ± 0.3 due to the above toner density control.
It was able to fall within the range of%.

37A and 37B of the fixing device 37 are an upper roller and a lower roller which are a pair of rotating members for fixing.

A heater 37D (upper roller 1,100 W, lower roller 200 W) composed of a halogen lamp or the like is provided at the inner core of the upper roller 37A and the lower roller 37B. The ambient temperature of the upper roller 37A and the lower roller 37B is detected by a temperature sensor 37C such as a thermistor and sent to the CPU 90, and the CPU 90 controls the heater 37D by this detection signal to allow a predetermined temperature Tc which is the fixing control temperature. Keep within range.

The lower roller 37B is pressed against the upper roller 37A with a linear pressure of 3.7 kg / cm by a biasing member such as a spring (not shown). The upper roller 37A rotates clockwise, and the lower roller 37B comes into pressure contact with the upper roller 37A and is driven to rotate.

The upper roller 37A and the lower roller 37B are composed of a metal pipe covered with an elastic layer. The elastic layer is coated with a PFA coating layer having a thickness of 20 μm in the upper roller 37A and the lower roller 37B. Then, the lower layer: LTV rubber layer with a thickness of 0.5 mm (rubber hardness 30 °) Surface layer: covered with a PFA tube with a thickness of 70 μm.

In the image forming apparatus described above, the photosensitive drum 31 is a drum coated with an OPC photosensitive member that is negatively charged, and the image forming conditions when the writing density is 400 dpi (Dot per inch) are shown in Table 1 below. Is.

[0027]

[Table 1]

An encoder (not shown) is provided on the rotary shaft of the photosensitive drum 10. The phase signal from this encoder is sent to the CPU 90 and is used for process control that requires accurate knowledge of the image position.

P located upstream of the cleaning device 39
C is a concentration detection sensor of the concentration detection device. The concentration detecting sensor PC of this concentration detecting device emits infrared light with an incident angle of 0 ° or about 40 ° attached to two attaching holes formed in the casing CK as shown in FIGS. 3 and 4, for example. About the light emitting diode LED which is a light emitting element to irradiate,
The phototransistor PT is a light-receiving element that receives light at a reflection angle of 40 °, and a dust-proof member BG such as glass for preventing dirt from toner. The infrared ray has no sensitivity to the photosensitive layer of the image carrier, for example, a wavelength of 900
Infrared at ~ 980 nm is used. The phototransistor PT may use a photodiode instead. LN66 manufactured by Kagoshima Matsushita Electronics Co., Ltd. was used for the light emitting diode LED, and PN101 manufactured by Kagoshima Matsushita Electronics Co., Ltd. was used for the phototransistor PT. FIG. 5 is a circuit diagram showing an example of the circuit of the concentration detecting device used in this embodiment.

The concentration detecting sensor PC is combined with the electric circuit shown in FIG. 5 to form a concentration detecting device. A variable DC power supply Ve having a maximum output of 10 V is connected to the anode terminal of the light emitting diode LED, which is a light emitting element, and the amount of light emitted from the light emitting diode LED can be changed. The light emitting diode LED has a resistor R ₈ for current control and a semi-fixed resistor V.
Is connected to R ₁ in series have a voltage of 10V is applied from the DC power source, the light emitting diode L by the semi-fixed resistor VR ₁
It can be fixed after adjusting the variation in the resistance value of the ED. The light emitting diode LED is turned on when the terminal Te is connected to ground.

The phototransistor PT, which is a light-receiving element, is connected in series with the load resistor R _7, and a power source of 10 V is applied from the DC power source. A phototransistor PT that receives the reflected light from the toner image illuminated by the light of the light emitting diode LED.
Output current changes according to the intensity of the reflected light, and the load resistance R
A voltage proportional to the output current of the phototransistor PT is generated at both ends of ₇ . This voltage is input to the (+) input terminal of IC1 which is an operational amplifier and amplified. As a result, when the resistance connected between the output terminal and the (−) input terminal is R _5, and the resistance connected between the (−) input terminal and the ground is R ₆ , the resistance R ₅ is Output terminal O connected to both ends
A voltage of Vout = R ₅ / R ₆ × Vin is output between a and Ob. Here, Vin is a voltage applied to the (+) input terminal of IC1, and is the voltage gain (voltage gain) V of the amplifier circuit in this case.
out / Vin becomes R ₅ / R ₆ . C1 is a capacitor for bypassing surge voltage and other noises.

In the image forming apparatus of the present invention, when the power is turned on at the start of copying, a photoconductor preparation step for the image carrier, a developer preparation step, and an image formation preparation step are prepared in advance, and the fixing device 37 A preset temperature T ₁ lower than the fixing control temperature Tc is set in advance, and the temperature Tx when the fixing device 37 is powered on is set.
If (1) Tx ≤ T ₁ , then all of the above are performed, (2) If T ₁ <Tx ≤ Tc, then perform the above, and (3) If Tx> Tc, Only do the above.

Here, the set temperature T ₁ is 0 to 150 ° C., preferably 50 ° C.

The photosensitive member preparing step for the image bearing member is
Under the control of the CPU 90, the charging of the photoconductor drum 31, which is an image carrier, is performed twice or more by the charging device 32 so that the photoconductor drum 31 is uniformly charged to a specified potential (-750 V) without uneven charging. When the diameter of the photosensitive drum 31 is 80 mm, the required time is about 2 seconds.
As a result, the image area is uniformly charged to the specified potential as shown in FIG.

In the developer preparing step, the charge amount of the toner of the developer decreases with the standing time as described above. When the developer whose charge amount has been lowered is stirred, the charge amount increases as it is stirred as shown in FIG. 11. When the developer is stirred until time k, the charge amount returns to almost the original value. Is to operate above,
k is about 4 minutes. However, when T ₁ <Tx ≤ Tc, it is performed until the warming up of the fixing device 37 is completed.

Further, the image forming preparation step is the maximum density control and gradation correction of the copy image, which will be described below. This image formation preparation process requires about 30 seconds.

The maximum density control of the copy image is a preparatory process for always maintaining the maximum density of the copy image. In this embodiment, the maximum density of the copy image is controlled by selecting the rotation speed (linear velocity) of the developing sleeve 33A. The maximum density of the copy image is controlled. This maximum density control will be described.

When the image forming apparatus is shipped, each light emitting diode LED is made to emit light at a standard voltage with the density detection sensor PC free from dirt and fatigue, and the density is measured in a state where toner does not adhere to the photosensitive drum 31. The detected value is stored in the memory 91 as initial data.

Next, when the maximum density control is performed, the density when the toner does not adhere to the photosensitive drum 31 is detected by the density detection sensor PC. This data is compared with the previously stored initial data in the comparison circuit 92. If the detected data is darker (higher density) than the initial data, CP
U90 controls the output voltage of the variable DC power supply Ve to be high and increases the amount of light emitted from the light emitting diode LED. The density of the surface of the photosensitive drum 31 in the state where the toner is not attached again is detected with the amount of light increased and is compared with the initial data.
When the detected data is brighter than the initial data (the density is lower), the CPU 90 controls the variable DC power supply Ve to lower the output voltage and lower the amount of light emitted from the light emitting diode LED. By repeating this, the output voltage of the variable DC power supply Ve is fixed to the voltage when the difference between the detected data and the initial data is within the allowable range. As a result, an output change due to dirt or performance deterioration of the density detection sensor PC is corrected. After this, the CPU 90 detects the reflection density of the maximum density control test patch image.

The above-mentioned reflection density means that when the amount of light projected onto the test object is I ₀ and the amount of light reflected from the test object is I, D =
-D is represented by the formula of log I / I ₀ . When the amount of reflected light is proportional to the output voltage of the density detection sensor PC, the output voltage of the density detection sensor PC for a surface having a reflectance of 100% (density 0) is V _100, and the output voltage for the object m is V m. Then, the concentration Dm of the test object m is -log
It becomes Vm / V ₁₀₀ . Hereinafter, the reflection density is simply referred to as density. A method of obtaining the density from the output of the density detecting device of the test patch image on the photosensitive drum 31 will be described later.

To detect the density of the test patch image for maximum density control, following the completion of image formation, the photosensitive drum 31 is charged by the control of the CPU 90 in a state where there is no toner on the photosensitive drum 31, as in the case of the image formation. Then, the test pattern signal of the maximum density control patch image is sent from the image signal processing unit 60 to the writing unit 20 so that the photosensitive drum 31 has a size of about 30 mm × 20 mm as shown in FIG. 6A. The latent images of multiple maximum density control test patches are 2 to 5 mm in the sub-scanning direction.
It is written every other time. At this time, the exposure level is constant, and for example, in the case of an 8-bit digital signal by pulse width modulation (PWM), the exposure is performed at level 255 corresponding to solid black. CP
U90 detects the phase of the photoconductor drum 31 based on the phase signal from the encoder, and then drives the developing device 33 at a position synchronized with the latent image to perform reversal development. Developing device 33 during this development
The number of rotations of the developing sleeve 33A is changed for each test patch latent image by the control of the CPU 90 of the developing drive unit 33M that drives the developing sleeve 33A, developed and visualized, and the density shown in FIG. It becomes a plurality of test patch images. The maximum density control test patch image passes through the retracted transfer device 34 and separator 35 positions and is detected and amplified by a density detection sensor PC provided on the upstream side of the cleaning device 39 to be used as patch density data. CPU90
Are sequentially sent to. After this, the test patch image is cleaned by the cleaning device 39.

The CPU 90 detects the number of rotations (linear velocity) of the developing sleeve 33A which is within the preset density range set in advance in the patch density data, and stores this rotation speed in the built-in RAM. At the time of subsequent image formation, a designation signal is sent to the developing drive unit 33M so as to use this rotation speed (linear speed) to fix the rotation speed (linear speed) of the developing sleeve 33A. As a result, changes in the maximum density of the copy image due to environmental conditions, deterioration of the photosensitive layer of the photosensitive drum 31, and the like are corrected. Usually the specified concentration is
Set to 1.4. This is because if the density is 1.35 or higher, the quality of the copied image is sufficient. This maximum density correction control can also be performed by changing the toner density (mixing ratio) of the developer or changing the amount of the developer conveyed on the developing sleeve 33A. However, the method of changing the rotation speed of the developing sleeve 33A causes toner contamination. It is excellent in that it does not cause fogging.

After the maximum density of the copy image is corrected to the specified density as described above, the gradation is further corrected.

FIG. 7 is a four-quadrant chart showing printer characteristics and gradation.

In the figure, the density signal level is the writing unit 20.
The emission time of the semiconductor laser is, for example, 8-bit 256 (0
Up to 255) level is represented by the level of pulse width modulation (PWM).

The curve in the second quadrant of the figure is a γ curve of an ideal shape showing the relationship between the original image density and the density signal level, and shows the design value of the γ curve. Point A has a maximum image density of 1.
4 indicates that if the maximum image density is 1.4 or more, it is considered as an excellent image.

The first quadrant shows that the density signal level (PWM level) is a through that directly shifts to the input level to the image signal processing circuit 60 described later.

The curve of the third quadrant is the image signal processing circuit 60.
Output signal level (input level to writing unit 20)
Shows the printer characteristics, which is the relationship between the image density and the image density.
If the printer characteristic is a, the image density is 0 to 1.
An excellent image can be obtained if the gradation is expressed up to 5 and the gradation correction is properly performed, but if the gradation is deteriorated and the maximum density is lowered as shown by the b curve, no matter how many gradation corrections are performed. The density of the copy image is low as a whole, and the image has a gradation different from that of the original image. Since this apparatus corrects the maximum density as described above, an excellent image can be obtained if the gradation correction is appropriately performed. The curve of the fourth quadrant shows an example of a gradation correction curve selected according to the printer characteristics in the image signal processing circuit 60.

In the gradation correction, similarly to the above, the photosensitive drum 31 is charged by the control of the CPU 90 in a state where there is no toner on the photosensitive drum 31, and the image signal processing unit is provided in the writing unit 20 in the same manner as the image formation. A test pattern signal for gradation correction is sent from 60 to the semiconductor laser of the writing unit 20. As described above, this test pattern is 8 level jumps when the 8-bit digital signal is 0 to 255 levels.
The WM signal is sent to the semiconductor laser of the writing unit 20, and on the photosensitive drum 31, almost 30 as shown in FIG.
The latent images of multiple test patches of mm x 20 mm are 2 in the sub-scanning direction.
It is written every 5 mm. This latent image is reverse-developed by the developing device 33 whose rotation speed is fixed to be a plurality of tone correction test patch images having different densities shown in FIG. After passing, the density is detected by the density detection sensor PC. A series of detected density data is sent to the CPU 90 and the image signal processing circuit 60 as gradation correction data.

A method of converting the output of the test patch image density detecting device into the density of the patch image will be described.

The output voltage of the density detecting device of the patch image is set to ₀ , ₈ , 16, 24 ... N ... 255 for the gradation correcting test patch image, and the output voltage is V ₀ , V ₁ , V _2. , V ₃ ...
・ When Vn ・ ・ ・ V ₃₁ is set, each temporary density is D
When _Pn the _{D P0 = -logV 0 / V 0} D P8 = -logV 8 / V 0 D P16 = -logV 16 / V 0 Dn = -logVn / V 0 as _{D P31 = -logV 255 / V 0} D Pn Then, all D _Pn are normalized so that D _P31 becomes 1.4 which is the maximum density. Further, since the density of the transfer paper P is 0.08, 0.08 is added to all D _Pn . In this way, the density of the patch image on the fixed transfer paper as a copy image is converted.

In the image processing circuit 60, the gradation correction data is interpolated by the control of the CPU 90 to form a continuous curve shown in FIG. 9A, and this curve represents the printer characteristic. As the interpolation method, linear interpolation can be sufficiently used.
When this inverse function is taken, the curve shown in FIG. 9B is obtained, and this curve becomes the gradation correction curve. With the curve in (a) of FIG. 9 above
When the product of the curves in (b) is taken, it becomes a straight line of 45 ° shown in (c). The image signal is corrected according to such a gradation correction curve and then input to the writing unit 20 to form a latent image, so that the deterioration of the photoconductor of the photoconductor drum 31 in use of the apparatus or the change of the environmental condition may occur. Tone changes due to changes in printer characteristics are corrected.

Here, the gradation correction curve is created from the density data of the test patch image on the photosensitive drum 31, but ideally it is desirable to create it from the density data of the copied image after fixing.

The two types of test patch images are formed in the image area of the photosensitive drum 31 because it is desired to directly obtain the printer characteristics. However, the present invention is not limited to this, and may be formed in the non-image area. Good.

In the above embodiment, the execution of the preparatory process is changed depending on the fixing temperature of the fixing device when the power is turned on at the start of copying. However, after the previous copying is completed and the power is turned off, The purpose can be achieved by changing the preparatory process as described below depending on the waiting time until the power is turned on for the next copy.

The above leaving time is tx, and the set time is t ₁ ,
When t ₂ is set, (1) When tx ≧ t ₂ , all of the preparation steps are performed, and when (2) t ₁ ≦ tx <t ₂ , the preparation step is performed. , (3) When tx <t ₁ , only the preparation step is performed.

The above t ₁ and t ₂ are, for example, t ₁ is 10 seconds, t ₂
Is set to 4 minutes.

Due to such control correction, in the image forming apparatus of the present invention, as shown in FIG. 12, the fluctuation of the maximum density of the image during copying of 50,000 sheets becomes extremely small as shown in FIG.
On the other hand, in the copy by the conventional apparatus which is not corrected, the change in the maximum density is large as shown in FIG. 14, and it was confirmed that it was significantly improved.

Further, in the conventional apparatus, the fluctuation of the gradation is largely changed when 50,000 copies are made as shown in FIG. 15, but in the apparatus of the present invention, there is almost no change from the start as shown in FIG. Even with this, a copy image having excellent gradation could be obtained.

Although the above embodiments have been described by taking the image forming apparatus having the image reading unit as an example, the present invention is not limited to this, and the electrophotographic printer without the image reading unit and the electrostatic recording. It goes without saying that the present invention is also applied to the image forming apparatus of the system.

[0061]

As described above, in the present invention, the so-called warming-up time until the temperature of the fixing device of the image forming apparatus rises is utilized to prepare the photosensitive member, the developer and the image forming. Therefore, it is possible to provide an excellent image forming apparatus capable of obtaining a copy image having extremely stable gradation and image density without providing special time.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus of the present invention.

2 is a block diagram showing an example of a control system of the image forming apparatus in FIG.

FIG. 3 is a diagram showing an example of a density detection sensor of this embodiment.

FIG. 4 is a diagram showing another example of the density detection sensor of the present embodiment.

FIG. 5 is a diagram showing an electric circuit of the concentration detecting device of the present embodiment.

FIG. 6 is a diagram showing a test patch image for maximum density correction on an image carrier.

FIG. 7 is a four-quadrant chart showing gradation reproduction characteristics.

FIG. 8 is a diagram showing a tone correction test patch image on an image carrier.

FIG. 9 is a diagram illustrating how to obtain a correction γ characteristic.

FIG. 10 is a diagram showing a charging potential waveform in an image area of the device of the present invention.

FIG. 11 is a graph showing the relationship between the developer stirring time and the toner charge amount.

FIG. 12 is a graph showing changes in the maximum density of a copy image of the apparatus of the present invention.

FIG. 13 is a graph showing the relationship between the gradation of a copied image and the number of times of copying in the apparatus of the present invention.

FIG. 14 is a graph showing changes in the maximum density of a copy image of a conventional apparatus.

FIG. 15 is a graph showing the relationship between the gradation of a copy image and the number of copies made by the conventional apparatus.

FIG. 16 is a diagram showing a charging potential waveform in an image area of a conventional device.

FIG. 17 is a graph showing a standing time of the image bearing member and a charging potential after charging once after the standing.

FIG. 18 is a graph showing the relationship between the developer standing time and the toner charge amount.

[Explanation of symbols]

 20 Writing unit 30 Image forming unit 31 Photoreceptor drum (image bearing member) 32 Charging device 33 Developing device 33A Developing sleeve 33C Stirring screw 34 Transfer device 35 Separator 37 Fixing device 37C Temperature sensor 37D Heating heater 39 Cleaning device 40 Paper feeding unit 50 Document Placer 90 CPU IC1 Operational Amplifier LED Light Emitting Diode (Light Emitting Element) P Transfer Paper PC Density Detection Sensor PT Phototransistor (Light Sensing Element) TS Permeability Sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Takahashi 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Stock Company

Claims (3)

[Claims] 1. A fixing device after forming an electrostatic latent image on a uniformly charged image bearing member, developing the latent image by a developing device into a toner image, and transferring the toner image to a transfer material. In the image forming apparatus for fixing and obtaining a copy image, a photoconductor preparation step, a developer preparation step, and an image formation preparation step of the image carrier are prepared in advance when the power of the image forming apparatus is turned on. If a preset temperature T ₁ lower than the fixing control temperature Tc of the fixing device is determined and the temperature Tx when the fixing device is powered on is (1) Tx ≦ T ₁ , all of the above are performed and (2) ) If T ₁ <Tx ≤ Tc, the above is performed. (3) If Tx> Tc, only the above is performed. 2. The image forming apparatus according to claim 1, wherein the writing unit for forming the electrostatic latent image is a digital writing system. 3. An electrostatic latent image is formed on a uniformly charged image carrier, the latent image is developed by a developing device into a toner image, and the toner image is transferred to a transfer material, and then the fixing device. In an image forming apparatus for fixing a copy image to obtain a copy image, a photoconductor preparation step, a developer preparation step, and an image formation preparation step of the image carrier are prepared in advance when the image forming apparatus is powered on. When the set time is set to t ₁ and t ₂ after the power is turned off and the set time is set to t ₁ and t ₂ , provided that t ₁ <t ₂ and (1) tx ≧ t ₂ , 、、
(2) If t ₁ ≦ tx <t ₂ , then in the preparatory step,
And (3) when tx <t ₁ , the image forming apparatus is characterized in that only the preparation step is performed.