JPH077219B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an image forming apparatus, and particularly, for example, charging, exposing, developing, etc. to an image carrier which is an image forming condition when an image is formed on the image carrier. It can be suitably applied to an electrophotographic copying machine provided with a control system for controlling.

2. Description of the Related Art Image forming apparatuses, particularly electrophotographic copying apparatuses, are generally provided with the measures described below so that a good quality copy can be stably obtained from the apparatus. That is, before an image forming process in which an image is formed on a photosensitive drum, which is an image carrier, provided in the image forming apparatus is performed, for example, a charging unit such as a primary charger or an exposure such as a laser beam scanner. Means for driving the means to form a light area and a dark area on the photosensitive drum, and a potential in the light area (ie, light area potential) and a potential in the dark area (ie, dark area potential) are known potentials. In order to make each detection value detected by the detection means and output from the detection means converge to a preset target value of the bright portion potential or the target value of the dark portion potential, the above-mentioned detection value is set in accordance with each detection value. This is the method of controlling the high voltage output and / or the grid bias voltage of the primary charger.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention By the above-mentioned potential detection means, the light potential and the dark potential on the photosensitive drum are detected to control the surface potential on the photosensitive drum to converge to a target value. In this method, the process of idly rotating the photosensitive drum a predetermined number of times is an essential condition.Therefore, the continuous image forming process in which images are continuously formed on the photosensitive drum is executed. The above control cannot be performed when Therefore, if the characteristics of the photosensitive drum are changed due to some factor while the image forming apparatus is performing the continuous image forming process, the light portion potential and the dark portion potential are also changed accordingly. There is a drawback in that the electrostatic latent image contrast voltage is changed, which changes the density of the image to be formed on the photosensitive drum.
Therefore, for the purpose of eliminating such drawbacks,
For example, a proposal was made as described in JP-A-58-145972. The outline of the proposal relates to an electrophotographic copying apparatus using a so-called reversal development method, and the apparatus uses a known potential detecting means on the photosensitive drum while the apparatus is executing the continuous image forming process as described above. A developing bias applied to the developing sleeve in the developing device that detects the light portion potential and visualizes the electrostatic latent image formed on the photosensitive drum according to the detection value output from the potential detecting means. It is designed to correct. For details of the above-mentioned proposal contents, refer to the above-mentioned publication. However, in the device according to the above proposal, the absolute value of the difference between the dark portion potential and the light portion potential on the photosensitive drum, that is, |
When the dark portion potential−the light portion potential | is changed, the absolute value of the difference between the dark portion potential and the developing bias applied to the developing sleeve, that is, | dark portion potential−developing sleeve | or the light portion potential and the developing bias. Absolute value of the difference with
Since either one of | light-area potential-developing sleeve | is variable, if the developing bias is corrected so as to maintain the electrostatic latent image contrast, fogging becomes easy, and conversely, the developing bias is used to suppress fogging. However, there is a problem in that the electrostatic latent image contrast may be changed by correcting the above.

The present invention was devised to improve the problems of the conventional image forming apparatus as described above, and its purpose is to provide the image forming apparatus when performing a continuous image forming process. In particular, it is an object of the present invention to provide an image forming apparatus in which the electrostatic latent image contrast does not change, fogging can be suppressed, and a high-quality and stable image can be obtained.

Means for Solving Problems The above object is achieved by the image forming apparatus according to the present invention.

In summary, the present invention provides: (a) a photoconductor drum; (b) a primary charger provided near the outer edge of the photoconductor drum, and a facing gap between the primary charger and the photoconductor drum. The grid provided, the exposure means for forming an electrostatic latent image on the photosensitive drum, and the electrostatic latent image formed on the photosensitive drum arranged near the outer edge of the photosensitive drum. (C) an image forming condition setting and changing means including at least one developing device for supplying a developing agent for visualizing onto the photosensitive drum by a developing bias voltage applied from the outside; The image forming condition setting, set by the variable means,
Surface potential detecting means for detecting and outputting a surface potential on the photosensitive drum which varies according to the varied image forming condition on the photosensitive drum; and (d) before the image forming process is executed. With the surface potential of each dark portion and light portion on the photoconductor drum output from the surface potential detecting means when the grid bias voltage applied to the grid is set to two control amounts of V _G1 and V _G2. Yes V _D (V _G1 ), V _L (V _G1 ), V _D (V _G2 ), V
Read _L (V _G2 ) to obtain these grid bias voltage V
_G1 , V _G2 and the surface potential V _D (V _G1 ), V _L (V _G1 ), V _D (V
_G2), from the V _L (V _G2), and a change rate α for glyceraldehyde each time the bias voltage V _G of the dark potential V _D by a relational expression stored in advance, changes to glyceraldehyde each time the bias voltage V _G of the light portion potential V _L The rate β is obtained by calculation, and then the difference value Vback between the preset dark portion potential V _D and the developing bias V _DC and the bright portion potential V _L , the developing bias V _DC and the difference value Vcont, and the grid bias. Voltage V _G1 , V _G2 and the surface potential V
_D (V _G1 ), V _L (V _G1 ) and the rate of change α, β obtained by the above calculation, the grid bias application voltage V _G and the developing bias voltage V _DC that are initial image forming conditions are determined, An operation for storing initial image forming conditions before the image forming process is executed; and (e) a continuous image forming process in which images are continuously formed on the photosensitive drum, the initial image forming condition During execution, the value of the surface potential in the non-image forming area on the photoconductor drum detected by the surface potential detecting means is read, and the difference value between the value and the surface potential at the time of initial image formation is set in advance. When the set reference value is exceeded, the grid bias voltage value V _G and the grid bias voltage value V _G in the initial image forming condition stored by the calculation and storage unit are set using the two difference values Vback and Vcont as target values. Development bias voltage V
An image forming apparatus comprising: a correction unit that corrects _DC ;

Embodiment Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a three-color image forming apparatus according to an embodiment of the present invention. An outline of an image forming apparatus according to an embodiment of the present invention includes an optical system for exposing given document information, a copying system for receiving and copying a document image exposed by the optical system, the optical system, and It comprises a drive system for supplying a drive power source for driving the copying system and a control system for controlling the drive of the drive system. As is apparent from FIG. 1, the optical system is composed of a scanning mirror 2 and an f-θ lens 3 which are arranged under a platen glass (not shown), and the copying system is an image carrier. That is, starting from the photosensitive drum 4, a cleaning device 13, a static eliminator 5, an image forming condition setting, a primary charging device 6 as a variable means, a grid 16, and a developing device arranged near the outer peripheral surface of the photosensitive drum 4. 9-1, 9-2, 9-3, transfer drum 11, transfer charger 10, cassette 18, separating means
19, a fixing device 20 and a tray 21, and the driving system includes developing bias voltage control circuits 8-1, 8-2, 8-3, a laser control unit 1, high voltage control units 15, 17, etc.
The control system comprises a surface potential detecting means, that is, a surface potential meter 14, an A / D converter 20, an electric potential controlling microcomputer 21 having functions as an arithmetic control means and a correcting means, and a D / A converter 22. The above-mentioned scanning mirror 2 receives the modulated laser beam output from the laser control unit 1 and the f-θ lens 3 along the longitudinal direction of the photosensitive drum 4 (that is, from the front side in FIG. 1). The scanning is performed along the direction toward the back side). Incidentally, in the laser beam exposure method in this type of image forming apparatus, a so-called image is formed in which toner is attached to a portion to which a light beam is applied by reversal development. Squaning method and so-called back ground in which a light beam is applied to the background area and toner is attached to the unexposed area by regular development. There is a skinning method. The photoconductor drum 4 having a photoconductor formed on its outer peripheral portion is rotatably supported by shaft means (not shown) so as to be rotatable only in the direction of arrow (clockwise direction) in FIG. As described above, in the peripheral portion of the photosensitive drum 4, the static eliminator 5 including the cleaning device 13 necessary for forming a visible image together with the photosensitive drum 4, the primary charger 6, the grid 16, Developing device 9-
1, 9-2, 9-3 and the like are provided. The cleaning device 13 scrapes and collects the developer (that is, toner) remaining on the photoconductor of the photoconductor drum 35. The static eliminator 5 is disposed on the downstream side of the cleaning device 13 in the rotation direction of the photoconductor drum 4, and is configured to remove the electric charge remaining on the photoconductor of the photoconductor drum 4. . The primary charger 6 is disposed on the downstream side of the static eliminator 5 in the rotation direction of the photoconductor drum 4, and the grid 16 is a facing gap formed by the primary charger 6 and the photoconductor drum 4. It is installed in. The primary charger 6 and the grid 16 described above uniformly charge the photoconductor after the toner is removed by the cleaning device 13 and the residual charge is removed by the static eliminator 5. It is configured. The peripheral edge of the photoconductor drum 4 in a section from the position where the primary charger 6 and the grid 16 are arranged to the position where the developing device 9-1 is arranged on the downstream side in the rotation direction of the photoconductor drum 4. The part is the scanning mirror 2
Also, the space is formed so that the f-θ lens 3 can scan the photosensitive drum 4. An electrostatic latent image formed by being exposed by a laser beam on the photoconductor is provided on the downstream side in the rotation direction of the photoconductor drum 4 with respect to the scanning portion of the space on the photoconductor drum 4 by the optical system. A probe 14a of a surface electrometer 14 for detecting the surface potential of an image is arranged close to the surface of the photosensitive drum 4. Developing devices 9-1, 9-2, and 9-3 are sequentially arranged on the downstream side of the probe 14a of the surface electrometer 14 in the rotation direction of the photosensitive drum 4. Inside the developing unit 9-1, the electrostatic latent image formed on the photoconductor is visualized (that is, developed).
In order to accommodate the yellow toner,
A developing sleeve 91 is provided for attaching the yellow toner onto the photosensitive drum 4 by the supplied developing bias voltage. A magenta toner for developing the electrostatic latent image formed on the photoconductor is accommodated inside the developing device 9-2, and the magenta toner is supplied by a supplied developing bias voltage. A developing sleeve 92 for adhering onto the photosensitive drum 4 is provided. Cyan toner for developing the electrostatic latent image formed on the photoconductor is accommodated inside the developing device 9-3, and the cyan toner is removed by a supplied developing bias voltage. The photoconductor drum 4
A developing sleeve 93 for adhering to the top is provided. The transfer drum 11 is arranged on the downstream side of the developing device 9-3 in the rotation direction of the photosensitive drum 4 so that the outer peripheral surface thereof can come into contact with the outer peripheral surface of the photosensitive drum 4. Is rotatably supported only by the shaft means (not shown) so as to be rotatable only in the direction of the arrow in FIG. 1 (counterclockwise direction). The transfer charger 10 described above is disposed near the position where the outer peripheral surface of the transfer drum 11 contacts the outer peripheral surface of the photosensitive drum 4, and the developed image on the photosensitive drum 4 is transferred to the transfer drum. It is for transferring to a transfer material such as a transfer paper adsorbed on the outer peripheral surface of 11. The cassette 18 is arranged upstream of the transfer charger 10 in the rotation direction of the transfer drum 11, and supplies the transfer material to the transfer drum 11. The separating means 19 is arranged in the vicinity of the outer peripheral surface of the transfer drum 11 on the downstream side in the rotation direction of the transfer drum 11 of the transfer charger 10, and the transfer attracted to the outer peripheral surface of the transfer drum 11 is performed. The material is separated from the transfer drum 11. The fixing device 20 receives the transfer material separated from the transfer drum 11 by the separating means 19 to form a final image, and then discharges the transfer material to the tray 21. The developing units 9-1, 9-2, 9-3 described above are used.
The process for developing the electrostatic latent image formed on the photoconductor 4 by the method is already known, but is as follows. First, an electrostatic latent image is formed on the photosensitive drum 4 by image exposure corresponding to the yellow development color described above, and a developing bias is applied to the corresponding developing sleeve 91 of the developing device 9-1. Then, the electrostatic latent image is developed to form a visible image, which is transferred to the transfer material on the transfer drum 11. The above operation is sequentially performed for each developing color (magenta, cyan), and finally the visible images of each color (three colors of yellow, magenta, and cyan in this embodiment) are multi-transferred onto the transfer material. .

The developing bias voltage control circuits 8-1, 8-2, 8 described above
-3 is placed under the control of a control system which will be described later in detail, and based on the output signal from the control system, the developing device 9
The developing bias voltages applied to the developing sleeves 91, 92, 93 incorporated in -1, 9-2, 9-3, respectively are controlled. The laser control unit 1 is
The laser light intensity supplied to the optical system is controlled based on the output signal from the control system and the image input signal given from the outside. The high-voltage control units 15 and 17 are also under the control of the control system, and the high-voltage control unit 15 supplies the charging current to be applied to the primary charger 6 based on the output signals from the control system. The high voltage control unit 17 controls the grid bias voltage applied to the grid 16. The surface electrometer 14 constituting the above-mentioned control system outputs the surface potential detection value on the photosensitive drum 4 detected via the probe 14a of the surface electrometer. The A / D converter 20 converts the surface potential detection signal (analog signal) output from the surface electrometer 14 into a digital signal and outputs it. Further, the D / A converter 22 converts the output signal (digital signal) from the potential controlling micro-computer 21 into an analog signal to drive the driving system including the developing bias voltage control circuit 8-1. It is designed to output. The potential controlling microcomputer 21 performs arithmetic operation and logical operation to store the operated data, and
The detection value data input from the surface electrometer 14 via the D converter 20 is stored. The potential controlling microcomputer 21 uses the D / A converter 2 based on various data after arithmetic processing according to an algorithm as described in detail later.
A predetermined signal is output to various drive systems as described above via 2.

The control of each drive system including the developing bias voltage control circuit 8-1 described above by the potential controlling microcomputer 21 is performed when the initial image forming condition is set before the image forming apparatus executes the image forming process. The control is roughly divided into a control and a control for correcting the initial image forming condition while the image forming apparatus is performing the continuous image forming process. The control process for setting the initial image forming conditions is the flow chart shown in FIG. 3A, and the control process for correcting the initial image forming conditions is the third process. Each is executed by the flow chart illustrated in FIG.

The process of setting the initial image forming conditions while using the flow chart shown in FIG. 3 (a) will be described below, and then the initial image forming condition will be shown while using the flow chart shown in FIG. 3 (b). A process of correcting the image forming condition will be described. Prior to executing the series of processes shown in FIG. 3 (a), for example, experimental data (grid bias voltage VG, dark part potential VD, bright part potential VL) as shown in FIG. 4 (a). And are respectively linear)
Variation amount of the grid bias voltage VG applied to the grid 16, the variation amount of the dark portion potential VD (VG) on the photosensitive drum 4 and the variation amount of the bright portion potential VL (VG) when the voltage VG is applied. A relational expression showing the relation with is derived, and the relational expression is stored in the memory of the potential controlling microcomputer 21. Immediately after shifting to the routine for setting the initial image forming condition, the potential controlling microcomputer 21 confirms that the photosensitive drum 4 is in the pre-rotation state (step 101) and shifts to step 103. The potential control micro computer 21 sets the grid bias voltage at VG ₁ (initial value) via the high voltage control unit 17, and then the A / D converter 20
The dark area potential VD (V
G ₁ ) and the bright part potential VL (VG ₁ ) output from the surface electrometer 14 via the A / D converter 20 after laser exposure via the laser control unit 1 are read respectively. (Step 103). At step 103, the grid bias voltage is
After reading VD (VG ₁ ) and VL (VG ₁ ) respectively when set to VG ₁ , set the grid bias voltage to VG 2 (VG ₂ ≠ VG
₁ ) and output from the surface electrometer 14 VD (V
G ₂ ) and VL (VG ₂ ) are read respectively (step 105). From the values of VD and VL read in steps 103 and 105, respectively, and the relational expression showing the relationship between VG and VD and VL stored in the memory in advance, the change rate α of VD with respect to VG and the change rate β of VL with respect to VG Is calculated.

From the above equation, the relational expression between VG and VD (VG) is VD (VG ₂ ) = α (VG ₂ −VG ₁ ) + VD (VG ₁ ) ・ ・ ・ ′, and from the above equation, VG and VL ( It can be seen that the relational expression with VG) is VL (VG ₂ ) = β (VG ₂ −VG ₁ ) + VL (VG ₁ ) ... ′ (step 107). Here, assuming that the image forming apparatus according to the embodiment of the present invention multiplex-transfers a color image using toners of three colors of yellow, magenta, and cyan to the transfer material as described above, the toners of the respective colors are transferred. Since the characteristics are different as shown in FIG. 2, for example, three types of electrostatic latent image contrast are prepared in order to obtain an image with good color balance.
The image forming density value in this case is shown in FIG. 7 (a) when the image scanning method exposure described above is adopted, when the developing bias voltage applied to each developing sleeve shown in FIG. 1 is VDC. Corresponds to Vcont (predetermined constant voltage value), that is, Vcont = VDC-VL, shown in Fig. 7 and does not cause fog in the non-exposed portion on the photosensitive drum 4 shown in Fig. 7B. Vback to do so
That is, it is necessary that the value of Vback = VD-VDC be equal to or greater than a preset constant voltage value. Therefore, in the image forming apparatus according to the embodiment of the present invention as described above, the target value data of Vcont and the target value data of Vback are input to the memory of the potential control micro-computer 21 in advance for three colors, for a total of three types. By the way, these three types of Vcont (i) and Vback
VG (i), VDC (i) corresponding to (i) (where i is the first color of yellow, the second color of magenta is the second color, and the third color of cyan is cyan. The following process for deriving an arbitrary integer value) by calculation is adopted. That is, from the above definition, VD (i) -VL (i) = Vcont (i) + Vback (i) ...
VDC (i) = VL (i) + Vcont (i) ...

Here, the target value of Vcont (i) corresponds to the target value of Vback (i), and VG (i) is an expression, an expression (also'expression, ')
Referring to equation), when _{VG 2 → VGi, V G (} i) = _{[V D (V G (i)} ) - V L (V G (i)) - {V D (V G1) -V L (V _G1 )}] / (α-β) + V _G1 ...
• From the formula, VD (VG (i))-VL (VG (i)) = Vcont (i) + Vback
(I) If 'because there is obtained the' ... Substituting equation in Equation, V _G (i) = [Vcont (i) + Vback (i ) - {V D (V G1) -V L (V _G1 )}] / (α-β) + V _G1・ ・
• will be obtained (step 109). Since all the values in the formula obtained in step 109 are known numbers, VG
(I) is uniquely determined, and if VG (i) is determined, the above equations, equations, VD (i), VL (i), VDC are derived from the equations.
(I) is obtained. Therefore, i is i = 1, 2, from the equation obtained in step 109 and the equation,
VG (i), VD (i) when an arbitrary integer value of 3 is taken,
After obtaining VL (i) and VDC (i) and obtaining the above values for the three colors of yellow, magenta, and cyan (step 11
1) are VG (i) and VDC (i) obtained in step 111 respectively.
Is read (step 113), and the image forming process is executed based on these values with the respective values read in step 113 as initial image forming conditions (step 115).

Next, the process illustrated in FIG. 3B will be described. It is an unavoidable fact that the characteristic change of the photoconductor occurs while the image forming apparatus executes the process of continuous image formation, and such characteristic change is remarkable especially when the organic photoconductor is used as the photoconductor. Is. Therefore, when the image forming apparatus performs the continuous image forming process and the light portion potential on the photoconductor rises (referred to as VL up) due to such a characteristic change of the photoconductor, as shown in FIG. By performing the process illustrated in (1), the electrostatic latent image contrast can be kept constant without hindering image formation. As described above, when VL is up, as shown in FIG. 4 (B), the value of the light potential is from VL (VG) to VL '(VG).
Therefore, the developing bias voltage
Vcont (= VDC-VL), which is the difference value between VDC and VL, becomes smaller, and accordingly the image density also decreases. Therefore, in the process shown in FIG. 3 (a), it was confirmed that the above-mentioned three colors of yellow, magenta, and cyan were used for image formation (step 131), and the image forming apparatus performs the continuous image forming process. If it is judged that the three-color image forming operation described in the above step 131 has been executed five times (step 135), it is determined through the surface electrometer 14 The light portion potential detection value VL '(i) in the non-image forming area on the photosensitive drum 4 given by the above is read (step 137). Step 137
For the voltage up of the bright part potential VL '(i) read in
When it is recognized that V ₁ exceeds a preset voltage that affects the image (here, it is assumed to be 10 V) (step 139), referring to FIG. 4B, V _D (V ' _{G (i)) - V L} (V 'G (i)) = Vcont (i) + Vback (i) + V 1 ···· V' DC (i) = V D (V 'G (i)) - Vback (I)
.. through the high-voltage control unit 17
Developing bias voltage control circuits 8-1, 8-2, 8-3 while increasing the grid bias voltage VG applied to
Vco by increasing the developing bias voltage VDC (i) applied to each developing sleeve 91, 92, 93 via
The initial image forming conditions set in the process shown in FIG. 3A are corrected so that nt (i) and Vback (i) always match their respective target values. (Step 141).

The above description relates to the image forming apparatus according to the embodiment of the present invention, and does not mean that the present invention is limited to the above description. The operation of measuring the light portion potential in the non-image forming area on the photoconductor drum 4 only once when recognizing that it has been executed once, or Vcont (i), Vback when the VL up becomes 10V or more. The operation of correcting the initial image forming condition so that (i) matches the target value is merely an example for explaining the content of the present invention, and does not limit the present invention at all. . In the above embodiment, only the countermeasure against the VL up during the continuous image formation was described, but the sequence according to the present invention (that is, the relational expression of VG and VD, VG and VL is derived, and the process of continuous image formation is described. The process of appropriately changing the value of VG according to the measured values of VD and VL during execution) can be applied to measures against changes in VD and / or VL during the continuous image formation process. Needless to say. As described above, in the image forming apparatus according to the embodiment of the present invention, the grid bias voltage VG is set at the beginning of the control sequence.
VG ₁ and VG ₂ are varied to measure the dark potential VD and bright potential VL at that time, and the relational expression with VG-VD and VL is derived. In order to compensate for local uneven surface potential due to factors such as the above, different sites on the photoconductor are measured multiple times under the same charging conditions and the same exposure conditions, and processing is performed to eliminate the effects of abnormal surface potentials. It is more desirable to derive the relational expression of VG-VD and VL based on the obtained data. As an example of such data processing, there is a method in which the lowest value of the measurement data of a plurality of times is truncated and the remaining data is averaged.

In the image forming apparatus according to the embodiment of the present invention described above, the grid bias voltage VG and the developing bias voltage VDC
However, when the laser light intensity and / or the charging current of the primary charger 6 is controlled by controlling the driving of the laser control unit 1 and the high voltage control unit 15, the laser light intensity and / or When controlling the charging current and / or the grid bias voltage and / or the developing bias voltage of the primary charger 6, the same process as above can be performed. When controlling the charging current or the laser beam intensity for the primary charger 6 described above, a pattern of a plurality of curves which is experimental data showing the relationship between the charging current and the surface potential shown in FIG. And a plurality of curved line patterns, which are experimental data showing the relationship between the laser light intensity (exposure amount) and the surface potential shown in FIG. 6, are stored in advance in the memory of the potential control microcomputer 21. The pattern of one curve is selected from the patterns of the plurality of curves according to the value of the detected surface potential to control the charging current value and the laser light intensity value. It is needless to say that the present invention can be applied not only to the image forming apparatus using the image scanning method described above but also to an image forming apparatus using the background ground scanning method, and further to an analog type image forming apparatus.

EFFECTS OF THE INVENTION As described above, according to the present invention, the surface potential detecting means is used during the continuous image forming process in which images are continuously formed on the image bearing member, which is a photosensitive drum. When the surface potential detection value in the non-image forming area on the image carrier detected as described above is read and the difference value between the surface potential and the surface potential at the time of initial image formation exceeds a preset reference value, Since the grid bias voltage value V _G and the developing bias voltage value V _DC under the initial image forming conditions are corrected using the two difference values Vback and Vcont as target values,
Even when the image forming apparatus is performing the process of continuous image formation, the electrostatic latent image contrast does not change and fogging can be suppressed, and a high-quality and stable image can be obtained. Can be provided.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a data diagram showing the relationship between the electrostatic latent image contrast and the optical density applied to the image forming apparatus according to the embodiment of the present invention. FIG. 3A is a flow chart showing a process for setting initial image forming conditions in the image forming apparatus according to the embodiment of the present invention. FIG. 3B is a flow chart showing a process in which the image forming apparatus according to the embodiment of the present invention corrects the initial image forming condition during the continuous image forming process. FIGS. 4 (a) and 4 (b) are diagrams showing the relationship between the grid bias voltage and the dark portion potential and the light portion potential, respectively. FIG. 5 is a diagram showing the relationship between the charging current for the primary charger and the surface potential on the image carrier. FIG. 6 is a diagram showing the relationship between the exposure amount on the image carrier and the surface potential on the image carrier. FIG. 7A is a diagram showing the relationship between the dark portion potential and the light portion potential formed on the image carrier and the developing bias. FIG. 7B is a diagram showing image densities in an exposed portion and a non-exposed portion on the image carrier. 1: Laser control unit 2: Scanning mirror 3: f-θ lens 4: Photosensitive drum 6: Primary charger 8-1, 8-2, 8-3: Development bias voltage control circuit 9-1, 9-2, 9-3: Developing device 14: Surface potential meter 14a: Surface potential meter probe 15: High voltage control unit 16: Grid 17: High voltage control unit 21: Potential control micro computer 91, 92, 93: Development sleeve

Continuation of the front page (56) Reference JP 58-145972 (JP, A) JP 60-52868 (JP, A) JP 58-120271 (JP, A) JP 58-120272 (JP , A) JP 54-17847 (JP, A) JP 58-172654 (JP, A) JP 53-112743 (JP, A) JP 54-73051 (JP, A) JP 4-15945 (JP, B2) Japanese Patent Publication 3-14187 (JP, B2)

Claims (1)

[Claims] 1. (a) a photoconductor drum; (b) a primary charger provided near an outer edge of the photoconductor drum, and provided in a facing gap between the primary charger and the photoconductor drum. Grid, an exposure unit that forms an electrostatic latent image on the photosensitive drum, and an electrostatic latent image formed on the photosensitive drum, which is disposed near the outer edge of the photosensitive drum. Image forming condition setting and changing means, comprising at least one developing device for supplying a developing agent to be turned on to the photosensitive drum by a developing bias voltage applied from the outside; (c) the image Forming condition setting, setting by variable means,
Surface potential detecting means for detecting and outputting a surface potential on the photosensitive drum which varies according to the varied image forming condition on the photosensitive drum; and (d) before the image forming process is executed. With the surface potential of each dark portion and light portion on the photoconductor drum output from the surface potential detecting means when the grid bias voltage applied to the grid is set to two control amounts of V _G1 and V _G2. Yes V _D (V _G1 ), V _L (V _G1 ), V _D (V _G2 ), V
Read _L (V _G2 ) to obtain these grid bias voltage V
_G1 , V _G2 and the surface potential V _D (V _G1 ), V _L (V _G1 ), V _D (V
_G2), from the V _L (V _G2), and a change rate α for glyceraldehyde each time the bias voltage V _G of the dark potential V _D by a relational expression stored in advance, changes to glyceraldehyde each time the bias voltage V _G of the light portion potential V _L The rate β is obtained by calculation, and then the difference value Vback between the preset dark portion potential V _D and the developing bias V _DC and the bright portion potential V _L , the developing bias V _DC and the difference value Vcont, and the grid bias. Voltage V _G1 , V _G2 and the surface potential V
_D (V _G1 ), V _L (V _G1 ) and the rate of change α, β obtained by the above calculation, the grid bias application voltage V _G and the developing bias voltage V _DC that are initial image forming conditions are determined, An operation for storing initial image forming conditions before the image forming process is executed; and (e) a continuous image forming process in which images are continuously formed on the photosensitive drum, the initial image forming condition During execution, the value of the surface potential in the non-image forming area on the photoconductor drum detected by the surface potential detecting means is read, and the difference value between the value and the surface potential at the time of initial image formation is set in advance. When the set reference value is exceeded, the grid bias voltage value V _G and the grid bias voltage value V _G in the initial image forming condition stored by the calculation and storage unit are set using the two difference values Vback and Vcont as target values. Development bias voltage V
An image forming apparatus comprising: a correction unit that corrects _DC ;