JP3211106B2 - Image forming device - Google Patents

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 such as a copying machine, a facsimile, a printer, and the like. More specifically, the present invention forms a pulse width and a signal for modulating the output of each pulse width based on an image signal. The present invention relates to an image forming apparatus that forms an image by modulating a laser based on a signal.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus,
After the photosensitive member is uniformly charged, a latent image is formed by irradiating light such as a laser beam, and the latent image is developed by a developer to be visualized. As a multi-level writing method of a laser used when forming a latent image on the photosensitive member, a pulse width modulation method for changing a laser emission time and a power modulation method for changing a laser output are representative. Things. The pulse width modulation method is an area gradation method for changing the laser emission time to change the area of a latent image in a unit pixel , and finally changing the area to which toner adheres, to produce gradation. On the other hand, the power modulation method is
It is a method similar to the analog method, in which the laser intensity is changed to change the surface potential of the photoreceptor, thereby changing the amount of adhered toner to produce a gradation. Comparing both methods has the following advantages and disadvantages. That is, since the former pulse width modulation method basically does not use the potential of the intermediate portion of the photoconductor, there is an advantage that the latent image potential is more stable than the power modulation method. However, the higher the required number of gradations, the higher the resolution of the area of the latent image formed in one pixel is required. For this reason, it is necessary to reduce the beam diameter to a small value (for example, in the case of 400 dpi and a pixel of 63.5 μm, the spot in the main scanning direction (when the laser energy is 1).
/ E2 (the width of e being a common logarithm) is 30 to 40 .mu.m.
m, 80 to 85 μm in the sub-scanning direction), the depth of focus of the beam on the photoreceptor becomes shallow, the focus of the laser beam tends to fluctuate, and a mechanism for adjusting the focus is required.
Also, because the changing light emission time in one pixel, use of multi-value write
The high-speed response is required for the modulation circuit, and it is difficult to increase the writing speed. Also, in terms of image quality, characters at intermediate density tend to be cut off. Further, there is a disadvantage that the substantial image density reproducibility is controlled by frequency characteristics of development, toner particle size, and the like. On the other hand, the latter power modulation method is
In general, it is not necessary to reduce the laser beam diameter as much as the pulse width modulation method (for example, 400 dpi, one pixel 6 pixels).
In the case of 3.5 μm, spots 70 to 80 in the main scanning direction
μm, 80 to 85 μm in the sub-scanning direction). For this reason, halftone characters are less likely to be cut off, and the responsiveness of the modulation circuit is not required to be as responsive as the pulse width modulation method, and the speeding up is relatively easy. However, since the potential of the intermediate portion where the potential of the photoconductor easily fluctuates is used,
It has the disadvantage that the image density tends to fluctuate.

Therefore, as a method for improving the disadvantages of both the pulse width modulation method and the power modulation method, a laser modulation method for modulating a pulse width and power has been developed and put into practical use. This method is superior to the pulse width modulation method in terms of high-speed responsiveness and character reproducibility at intermediate densities. Excellent in terms of stability.

[0004]

However, in the conventional laser modulation system for modulating the pulse width and power,
It has been found that there is a problem that the image density jumps when the pulse width changes. Hereinafter, this problem will be described. FIG. 1 shows the upper 2 bits of an 8-bit output signal among laser modulation schemes that modulate pulse width and power.
A diagram showing an apparent light attenuation characteristic (attenuation characteristic with respect to an irradiation light amount of a photosensitive member charging potential) of a photosensitive member when a laser modulation method in which a pulse width is modulated by bits and power is modulated by lower 6 bits is used. It is. Here, the “apparent light attenuation characteristic” is a light attenuation characteristic using a measured value of the charged potential of the photoconductor measured by the potential sensor. That is, since the area of the sensor part of the potential sensor is usually larger than the area of the dot part whose potential has been attenuated by light irradiation, the output of the potential sensor is affected by both the dot part and the surrounding photoconductor part. It has to be something. Therefore, it is referred to as “apparent light potential characteristic” to distinguish it from ideal light attenuation characteristics using the potential of only the dot portion. Specifically, the characteristics in FIG.
K) The electric potential measured by a surface electrometer MODEL 344 (sensor area is 1 mm ² , and the electric potential is measured at a distance of 1 mm from the object to be measured) manufactured by K) is used. In addition, the light irradiation amount (laser output) of the laser in the same figure used the light amount measured by TQ8215 made by Advantest. In addition, the laser beam diameter (laser power is 1 /
The diameter) becomes e ^2, primary scanning direction 50 [mu] m, was used in the sub-scanning direction 80 [mu] m. Characteristic curves a, b, c in FIG.
Indicates that the maximum value of the laser light amount is 1.1, 1..
This shows an apparent optical attenuation characteristic when the pulse width and the power are modulated so as to be 5, 2.4 [mW]. A characteristic curve d in the figure shows, for comparison, an apparent optical attenuation characteristic when only the power is modulated while the pulse width is constant. As can be seen from the comparison of the characteristic curves a, b, and c, when the maximum value of the laser output is different, the apparent light attenuation characteristic is different, and the linearity is also different. In addition,
When only the laser power is modulated as can be seen from the characteristic curve d, a constant apparent light attenuation characteristic is obtained irrespective of the maximum value of the laser output.

FIG. 2 shows a sensitometry chart (conceptual diagram) when the above-mentioned laser modulation method is used. In the first quadrant, the horizontal axis represents the image input signal (the amount proportional to the density of the original image), and the vertical axis represents the amount of laser light, and shows the characteristics of the gradation correction table. The second quadrant shows the apparent light attenuation characteristics by taking the surface potential of the photoreceptor on the horizontal axis and the amount of laser light on the vertical axis. The pulse width used in each laser light amount area is represented by the pulse width. It is noted as 1 to 4. In the third quadrant, the difference between the surface potential of the photoreceptor and the DC component of the developing bias, that is, the developing potential is plotted on the horizontal axis, and the image density is plotted on the vertical axis, showing the development characteristics. In the fourth quadrant, an image input signal (an amount proportional to the density of a document image) is plotted on the horizontal axis, and the image density is plotted on the vertical axis, and the image density reproducibility characteristics are shown. As can be seen from the characteristic curve of the apparent light attenuation characteristic in the second quadrant, the slope of the characteristic curve differs depending on the region of each pulse width (pulse width 1 to 4). Therefore,
The slope of the characteristic curve of the image density reproducibility characteristic in the fourth quadrant differs depending on the region of the pulse width (pulse width 1 to 4) used for forming the latent image. For this reason, the image density jumps when the pulse width changes.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus having an image exposing means employing a laser modulation system for modulating a pulse width and a power. It is an object of the present invention to provide an image forming apparatus capable of preventing a jump in image density from occurring at the time when the image density changes.

[0007]

According to one aspect of the present invention, a laser drive signal having a pulse width and a power modulated based on an image signal is formed on a charged photosensitive member. and an image exposing means for forming a latent image is subjected to exposure with a laser, an image forming apparatus for forming an image by developing the latent image, the light attenuation characteristics of the apparent sensitive light body
The first control for switching the laser output so as to be substantially linear through each pulse width region and the second control for switching the charge amount of the photoconductor so as to maintain the development potential at the target potential are performed. Things.

[0008]

[0009]

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, latent images for detection are respectively formed by two predetermined image signals, and their potentials are detected. A linear correspondence between the image signal and the latent image potential within a range having the upper and lower limits of one image signal is obtained, a detection latent image is formed by a predetermined image signal within the range, and the potential is detected. The image exposure means is used with a laser output such that a difference between a detected potential and a latent image potential corresponding to the predetermined image signal based on the correspondence relationship is equal to or less than a predetermined value. .

Further, the invention of claim 3, the image forming apparatus according to claim 2, for controlling the charging potential of the laser output and the photosensitive member on the basis of the potential of the at least two latent images were formed at different pulse widths It is characterized by the following.

According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, based on the potentials of at least two latent images respectively formed under power modulation conditions under which laser outputs with different pulse widths are maximized. The laser output and the charging potential of the photoconductor are controlled.

[0013]

In the present invention, a latent image is formed by irradiating a photoreceptor with a laser beam based on an image signal by an image exposing means after charging the photoreceptor to a predetermined potential by a charger. This image exposure means drives a laser with a laser drive signal whose pulse width and power are modulated based on the image signal. The output of this laser is such that the apparent light attenuation characteristic of the photoreceptor is substantially linear, thereby preventing the image density from jumping when the pulse width changes.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) as an image forming apparatus will be described. First, an outline of the entire copying mechanism will be described with reference to FIG. In FIG. 3, around a 120 mm diameter organic photosensitive drum 102 serving as a latent image carrier, which is disposed at a substantially central portion of a copying machine main body 101, a charger 103 for charging the surface of the photosensitive member is uniformly charged. A laser optical system 104 that irradiates a laser beam onto the surface of the photoconductor to form an electrostatic latent image, and supplies and develops each color toner to the electrostatic latent image to obtain a toner image for each color. 105, a yellow developing device 106, a magenta developing device 107, a cyan developing device 108 (all adopt a reversal developing method in this example), an intermediate transfer belt 109 for sequentially transferring toner images of respective colors formed on a photoconductor, A part of the intermediate transfer belt 109 is brought into contact with the surface of the photoreceptor to form a transfer region, and a bias roller 110 to which a transfer voltage is applied to form a transfer electric field in the transfer region is applied. A cleaning device 111 for removing the toner remaining on the body surface, neutralization apparatus 112 for removing the charges remaining on the photoreceptor surface after transfer are arranged. On the surface of the intermediate transfer belt 109,
A transfer bias roller 113 that forms a transfer area for transferring the toner image transferred to the belt 109 to transfer paper and applies a transfer voltage that forms a transfer electric field to the transfer area, and transfers the toner image to the transfer paper A belt cleaning device 114 for cleaning the residual toner after the cleaning is provided. Then, a transport belt 115 for transporting the transfer paper separated from the intermediate transfer belt 109, and
A fixing device 11 that heats and pressurizes the toner on the transfer paper conveyed from the conveyance belt 115 and fixes the toner.
6. Discharge tray 1 for receiving transfer paper from fixing device 116
17 is also provided. Above the laser optical system 104, an exposure lamp 119 for irradiating scanning light to a document on a contact glass 118 serving as a document mounting table provided on the top of the copying machine main body 101, and reflecting light from the document to a photoelectric conversion element A reflection mirror 121 and an imaging lens 122 for forming an image on a CCD image sensor array 123
Is provided. Then, the image sensor array 1
At 23, an image signal obtained by converting the document information into an electric signal is processed by an image
4 is used for controlling the laser oscillation of the semiconductor laser.

Next, the electrical components of the copying machine will be schematically described with reference to FIG. In FIG. 4, the main control unit (CP
U) 130 is provided with a ROM 131 and a RAM 132 in which predetermined programs and the like are stored.
The main control unit 130 has an interface (I /
O) The laser optical system control unit 134, power supply circuit 135, optical sensor 136, toner density sensor 137, environment sensor 138, photoconductor surface potential sensor 139, toner supply circuit 140, intermediate transfer belt driving unit 141, etc. It is connected. Although only the magenta developing device 107 is shown as a developing device in the same drawing, other developing devices 105, 106, and 108 are similarly connected to the interface 133 via the toner density sensor 137, the power supply circuit 135, and the toner replenishing circuit 140, respectively. It is connected. The laser optical system controller 134 adjusts the laser output of the laser optical system. The power supply circuit 135 applies a predetermined charging discharge voltage to the charger 113 and develops the developing devices 105, 106, and 10.
7 and 108, and a predetermined transfer voltage to the bias roller 110 and the transfer bias roller 113. The optical sensor 136 includes a light-emitting element such as a light-emitting diode and a light-receiving element such as a photosensor that are disposed in proximity to the surface of the photoconductor that has passed through the transfer area, and a reference toner pattern formed on the photoconductor as described later. In addition to detecting the toner adhesion amount and the toner adhesion amount of the background portion for each color, the residual potential after the photoconductor is neutralized is detected. The detection signal from the photoelectric sensor 136 is applied to a photoelectric sensor control unit (not shown). The photoelectric sensor control unit obtains a ratio between the toner adhesion amount of the reference toner pattern and the toner adhesion amount of the background portion, compares the ratio value with a reference value to detect a change in image density, and detects a change in image density. Is corrected. The toner density sensor 137 is provided in each of the developing devices 105, 106, 107, and 108, and detects the toner density based on a change in the magnetic permeability of the developer contained in each of the developing devices. The toner density sensor 137 compares the detected toner density value with a reference value, and when the toner density falls below a certain value and becomes in a toner shortage state, a toner replenishment signal of a magnitude corresponding to the shortage is supplied to the toner replenishment signal. Applied to the circuit 140. The potential sensor 139 detects the photoconductor surface potential, and the detection result is used for output control of the charging charger 103 and the laser optical system 104. The intermediate transfer belt driving section 141 controls driving of the intermediate transfer belt.

Next, the image processing section will be described. FIG.
, 401 is a scanner, 402 is a shading correction circuit, 403 is an RGBγ correction circuit, 404 is an image separation circuit, 405 is an MTF correction circuit, and 406 is color correction-U
CR processing circuit, 407 is an image processing circuit (create), 408 is a scaling circuit, 409 is an MTF filter circuit, 410 is a gamma correction circuit, 411 is a gradation processing circuit, 41
Reference numeral 2 denotes a printer. A document to be copied is read by being separated into R, G, and B colors by a color scanner 401. In the shading correction circuit 402, unevenness of the image sensor, illumination unevenness of the light source, and the like are corrected. γ correction circuit 40
In step 3, the input data is corrected or converted so as to have predetermined desirable characteristics such as linear reflectance and linear density. The MTF correction circuit 405 corrects the deterioration of the MTF characteristics of the input system, particularly in a high frequency range. Image separation circuit 4
In 04, character images, halftone images,
A photographic image, a chromatic color, an achromatic color, and the like are determined, and a coefficient of the MTF filter, gradation processing, and the like are determined based on the determination results. A color correction-UCR processing circuit 405 corrects the difference between the color separation characteristics of the input system and the spectral characteristics of the output color material, and calculates the amount of the color material YMC necessary for faithful color reproduction. , YMC and a UCR processing unit for replacing a portion having three different colors with Bk (black). The color correction process can be realized by performing a matrix operation as in the following equation. Here, r, g, and b indicate the complements of R, G, and B. The matrix coefficient a _ij is determined by the spectral characteristics of the input system and the output system (color material). Here, the first-order masking equation is used as an example, but color correction can be performed with higher accuracy by using a second-order term such as b ² or bg or a higher-order term. Further, the arithmetic expression may be changed depending on the hue, or the Neugebar equation may be used. In any method, Y, M, and C are b, g, and r (or B,
G or R). on the other hand,
UCR processing is calculated using the following equation. Y ′ = Y−α · min (Y, M, C) M ′ = M−α · min (Y, M, C) C ′ = C−α · min (Y, M, C) Bk = α · min (Y, M, C) In the equation, α is a coefficient for determining the amount of UCR, and α = 1
At this time, 100% UCR processing is performed. α may be a constant value.
For example, by setting α close to 1 in a high density portion and close to 0 in a highlight portion, an image in the highlight portion can be smoothed. The scaling circuit 407 performs enlargement and reduction, and uses a three-point convolution method or the like. In the image processing, processing such as repeating (repeat) or erasing an image in a designated area is performed. The MTF filter 409 performs a process of changing the frequency characteristics of the image signal, such as edge enhancement and smoothing, such as a sharp image and a soft image, according to the user's level. The gamma correction circuit 410 corrects the image signal in accordance with the development characteristics and the light attenuation characteristics of the photoconductor, and the gradation processing circuit 411 performs dither processing. The scanner 401
The image data read by
Interface I / F 41 for processing and outputting image data from an external image device by printer 412
3,414 are provided. CPU 415, ROM 416, RAM 4 for controlling the above image processing circuit
17 is connected by BUS418. CPU 415
Is the system controller 4 through the serial I / F
19, a command from an operation unit (not shown) or the like is transmitted.

FIG. 6 shows a block diagram of the laser modulation circuit. The writing frequency is 18.6 [MHz], and the scanning time of one pixel is 53.8 [nsec]. 8-bit image data can be subjected to gamma conversion using a look-up table (LUT) 451. Pulse width modulation circuit (PWM) 4
At 52, the signal is converted into a quaternary pulse width based on the upper 2 bits of the 8-bit image signal, and the power modulation circuit (P
In M) 453, 64-level power modulation is performed with the lower 6 bits, and the laser diode (LD) 454 emits light based on the modulated signal. Photo detector (PD) 45
In step 5, the emission intensity is monitored, and correction is performed for each dot.
As shown in FIG. 7, the laser light is applied to a pixel a. From the beginning, b. From inside, c. The three values can be arbitrarily selected later. The figure shows an example of a pulse width of 4 values and a power of 64, and shows the relationship between the pulse width for image data n and the light amount of each pulse width.

Here, the laser modulation method in this embodiment will be described in detail. As described above, the laser modulation system of the present embodiment is a laser modulation system in which the pulse width is modulated by the upper 2 bits and the power is modulated by the lower 6 bits of the 8-bit image signal. In addition, there is a possibility that the image density jumps when the pulse width changes. For example, FIG. 8 shows the relationship between the image signal and the surface potential of the photosensitive member when the laser modulation method for modulating the pulse width and power of the laser is used. b, c, d, and e correspond to a laser output in which the later characteristic curve has a larger maximum value of the laser output in this order. As can be seen from this figure, the characteristic curves a and b have good linearity of the surface potential with respect to the image signal, whereas the other characteristic curves c, d and e have poor linearity. As can be seen from the latter characteristic curves c, d, and e, if the linearity of the light attenuation is poor, there arises a problem that the gradation reproducibility and stability of the image density deteriorate. Therefore, it is necessary to use a laser output having good linearity such as the characteristic curves a and b.

Therefore, in this embodiment, a laser output is used in which the apparent light attenuation characteristic on the photoreceptor is almost linear. First, a method of determining whether or not a laser output has good linearity will be described. As image signal levels a and b (where a <b), a = 0
5 (H) (5), b = F0 (H) (240) (where (H) indicates a hexadecimal number), and the corresponding surface potentials V (a), V (b) of the photoreceptor are Measure. Then, a straight line L passing through the two points is defined as L (n) = V (a) + {V (b) -V (a)} / (ba) × n (1). Surface potential V detected corresponding to each pulse width
(Ni) (i = 1, 2,..., NPW, nPW is the number of pulse widths,
Here, the absolute value | V (n) of the difference between nPW = 4) and L (ni)
i) -L (ni) | is a predetermined reference value △ VGAP (for example, 8
It is determined that the linearity is good when it is 0 [V] or less. FIG.
Here, the measurement result of the characteristic curve e is represented by V (n), and the straight line of the above equation (1) obtained from the result is shown as a straight line f in the figure. In this case, the absolute value | V (n
i) -L (ni) | is | V (150) -L (150) |
Which corresponds to the size indicated by g in FIG.

In order to determine whether or not the linearity is good, the following may be performed. That is, the detection value VD _D in the potential of the photosensitive _{member, VL iD (i = 1,2,} ..., nPW) by the least square method from determined tilt and residuals when the linear, or standard error, the standard error Is smaller than the reference value, it is determined that the linearity is good. The characteristic curves a and c and b and d in FIG. 9 have the same maximum value of the laser output, the charging potential (a and b are −600 [V], and c and d are the same). −800 [V]). From the graph, it can be seen that the linearity of a and c and b and d does not depend much on the charging potential. FIG. 10 shows the result of calculating the linearity by this determination method. In the figure, the horizontal axis is the laser output, and the vertical axis is the amount representing the deviation from the straight line (here, the standard error is used). In the figure, a is the charging potential VD = -600 [V], and b is the charging potential VD = -800.
It is obtained from the measurement result of [V]. From this graph, it can be seen that the dependence of the deviation amount (standard error) on the charging potential is small, and that the deviation amount increases as the laser output increases. For this reason, when the developing potential is set to a predetermined value, it is desirable to adjust the charging potential without significantly changing the laser output in order to maintain the linearity of the apparent light attenuation characteristic of the photoconductor. I understand. In this case, it is desirable that the value (standard error) on the vertical axis be about 20 [V] or less.

Next, a neural network (hereinafter, referred to as a neural network)
NN) will be described. FIG. 11 is a schematic diagram of a configuration example of the NN. The NN 501 is made to previously learn data on the charging characteristics of the photoconductor and the latent image γ characteristics. At the time of control, the sensor output information, the current grid voltage VG0 of the charging charger 103, and the laser output L
Set value such as D0 and required development potential V
By inputting D0, the target exposure portion potential VL0, etc., the grid voltage VG1 of the charging charger 103 and the set value LD1 of the laser output are given. The sensor output information to be used includes the charging potential VD from the potential sensor 139,
The exposure portion potential VLi (i =
1,2,3,4), humidity H from environment sensor 138,
Enter the temperature T.

FIG. 12 is a schematic diagram of another configuration example of the NN. The NN 501 is made to previously learn data on the charging characteristics and the latent image γ characteristics of the photoconductor. At the time of control, the sensor output information, the current grid voltages VG0 and VG1 of the charger 103, and the set values LD1 such as the laser outputs LD0 and LD1 are given. The sensor output information to be used includes the charging potential VD and the exposure portion potential VL _iD (i = 1, 2, 3, 4, | VL _iD |> | VL) corresponding to each of the pulse widths 1 to 4.
_{(i + 1) D} |) from the potential sensor 139, the humidity H and temperature T from the environment sensor 138, and the current grid voltage value VG0 of the charging charger 103 to be controlled,
The value LD0 of the laser power, the value VG1 of the grid voltage of the charged charger 103 after the change, and the value L of the laser power
Entering a D0 (Note that all of the detected values of VL _iD is not necessary). The operation determining unit 502 determines the charging potential VD predicted by the NN 501 and the exposure unit potential VLi (i = 1,
2, 3, 4), target charging potential VD0 and exposure portion potential V
L0 and the grid voltage VG1 according to the comparison result.
And laser output LD1 are changed to | VD-VL4 | ≒ △ V,
In addition, VG1 and LD1 in which VL1 ≒ VL0 are output, and a latent image is formed using these values.

According to the control using the NN as described above,
Normally, the target image forming conditions (charge potential of the photoconductor, laser output) can be set accurately in a short time by shifting the grid voltage of the charging charger 103 and the like little by little.

A more specific example of the control using the NN will be described with reference to the flowchart of FIG. In FIG. 13, VG0 and VD0 are substituted for VG1 and VD1, respectively (step 1). Next, VD, VLi (i
= 1, 2, 3, 4) (step 2). Here, instead of using NN, a latent image of VD and VLi may be actually formed and the potential thereof may be measured. Next, it is determined whether or not the linearity is good by the above-described determination method (step 3).

If it is determined that the linearity is good (Y in step 3), then it is determined whether or not the predicted development potential VD-VL4 matches the target development potential ΔV. Is determined (step 4). Here, if it is determined that they match (Y in step 4), the control is terminated by setting VG1 and VL1 at that time to the set values of the grid voltage and the laser output, respectively (step 15 ). Conversely, if it is determined that they do not match (N in step 4), it is determined whether or not VL4 is higher than the target exposure portion potential VL0 (step 5).
(Y in step 5) After increasing the laser output by a predetermined amount ΔLD, if VL4 is not large (N in step 5)
It, and compares the development potential △ V step 10, the developing potential VD-VL4 and the target (step 1 1, 1 3). Here, the developing potential VD−VL
4 If is greater than the developing potential △ V of the target (Y in Step 1 1) a predetermined amount of the grid voltage VG1 △
After lowering VG only, if the developing potential VD-VL4 smaller than the developing potential △ V The targeted (and N, in Step 1 1, Step 1 3 Y) grid voltage VG1 predetermined amount △ VG enhanced After that, if they match (N in step 10 and N in step 11), the process returns to step 2 as it is.

Conversely, if it is determined that the linearity is not good in the above-described determination of linearity (N in step 3),
Next, it is determined whether or not VL4 is smaller than VL0 (step 7). Here, if VL4 is small (Y in step 7), it is determined that the laser output is too large, the laser output is reduced by a predetermined amount ΔLD (step 8), and the above development potential VD−VL4 and the target development potential are determined. △ proceed to the comparison of the V (step 1 1). Conversely, V
If it is determined that L4 is equal to or higher than VL0 (N in step 7), it is determined whether or not the developing potential VD-VL4 is equal to or higher than the target developing potential {V (step 9). If it is not less than V (Y in step 9), the laser output is reduced by a predetermined amount ΔLD (step 8), and then the developing potential VD−
The process proceeds to the comparison between VL4 and the target development potential △ V (step 11 ), and conversely, the target development potential △
If it is smaller than V (N in step 9), the process returns to step 2 after increasing the grid voltage VG1 by a predetermined amount ΔVG.

[0027]

According to the first to fourth aspects of the present invention, the laser
Prevented by the first control of switching the over output, the light attenuation characteristics of the apparent photoreceptor to be substantially linear through each pulse width region, from flying to the image density when the pulse width is changed is generated it can. Also, is performed by switching the charge amount of the second control in For photoreceptor to maintain the current image potential target potential, said second control, as compared with the case where the switching of the laser output, the photosensitive It is difficult to impair the linearity of the apparent light attenuation characteristics of the body.

In particular, according to the invention of claim 4 , based on the latent image potential at the maximum value of the power at each pulse width where the slope of the apparent light attenuation characteristic of the photoreceptor may suddenly change. Since the tendency of the light attenuation characteristic is accurately detected, it is possible to particularly effectively prevent the image density from jumping when the pulse width changes.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram when a pulse width and power are modulated.

FIG. 2 is another characteristic diagram when a pulse width and power are modulated.

FIG. 3 is a front view showing a schematic configuration of the electrophotographic copying machine according to the embodiment.

FIG. 4 is a schematic configuration diagram of an electrical unit of the copying machine.

FIG. 5 is a block diagram of an image processing unit of the copying machine.

FIG. 6 is a block diagram of a laser modulation circuit of the copying machine.

FIG. 7 is an explanatory diagram of a relationship between a pulse width and a light amount of each pulse width.

FIG. 8 is still another characteristic diagram when modulating the pulse width and the power.

FIG. 9 is another characteristic diagram when modulating the pulse width and the power.

FIG. 10 is a graph for explaining a method of determining whether or not the laser output makes the apparent light attenuation characteristic substantially linear.

FIG. 11 is an explanatory diagram showing a configuration example of a neural network for control according to the embodiment.

FIG. 12 shows another neural network for control according to the embodiment.
FIG. 2 is an explanatory diagram illustrating a configuration example of a network.

FIG. 13 is a flowchart of control according to the embodiment.

[Explanation of symbols]

102 photoreceptor drum 103 charging charger 104 laser optical system 139 potential sensor 451 look-up table 452 pulse width modulation circuit 453 power modulation circuit 455 photodetector 454 laser diode 501 neural network

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/00 303 G03G 21/00 370-540 B41J 2/44 H04N 1/04-1/207 H04N 1/23-1 / 31 G03G 15/04-15/04 120

Claims (4)

(57) [Claims] An image exposing means for forming a laser drive signal having a pulse width and a power modulated based on the image signal, and exposing the charged photoreceptor with a laser to form a latent image; an image forming apparatus for forming an image by developing the latent image, the light attenuation characteristics of the apparent sensitive light body through the pulse width region
A first control for switching the laser output so as to be substantially linear, and a second control for switching the charge amount of the photoconductor so as to maintain the development potential at the target potential. Image forming device. 2. A latent image for detection is formed by each of two predetermined image signals and their potentials are detected. Based on the detection results, an image signal and a latent image within a range having the two image signals as upper and lower limits are detected. A linear correspondence between potentials is obtained, a latent image for detection is formed by a predetermined image signal within the range, the potential is detected, and the potential is detected based on the detected potential and the correspondence. 2. An image forming apparatus according to claim 1, wherein said image exposure means is used with a laser output such that a difference from a latent image potential to be applied is equal to or less than a predetermined value. 3. The image forming apparatus according to claim 2, wherein the laser output and the charging potential of the photosensitive member are controlled based on the potentials of at least two latent images formed with different pulse widths. 4. The laser output and the charging potential of the photosensitive member are controlled on the basis of the potentials of at least two latent images formed under power modulation conditions that maximize the laser output at different pulse widths. The image forming apparatus according to claim 3.