JPH11196273A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate an image with excellent gradation by executing output density correction that takes into account a difference from the effect of changes in sensitivity performance and charging performance due to film thickness fluctuation of an image medium by each signal generating means onto gradation characteristic. SOLUTION: A gamma conversion section 34, that converts an output characteristics of an image signal generated from any of pluralities of signal generating means such as a PWM circuit 35 and a binary processing circuit 36 based on a film thick detection result of a photoreceptor drum, is controlled optimally by a CPU 25 in response to any signal generating means such as the PWM circuit 35 and the binary processing circuit 36 that generates an image signal.

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 that forms an image on a recording medium by exposing and scanning an image carrier on the basis of input image information.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, when the use condition or the use environment of a photosensitive drum or the like as an image carrier changes, the characteristics of the photosensitive drum change, which is significant for an output image. It is well known that change occurs.
For example, when the temperature of the photoconductor drum increases, the sensitivity of the photoconductor increases, and the output density changes. In addition, as the photoconductor drum is used, the photoconductor film thickness gradually decreases, and as a result, the charging performance decreases and the sensitivity deteriorates, and the output density changes.

Further, the reproducibility of minute dots changes due to a change in the characteristic of scattering of irradiation light on the photosensitive drum due to a decrease in the thickness of the photosensitive drum, and the charging performance and sensitivity of the photosensitive drum are changed. Changes in the output density characteristics which cannot be explained by the changes in the output density characteristics.

It is known that a change in the use environment of the apparatus affects not only the photosensitive drum but also the developing apparatus. That is, it is known that when the humidity of the use environment changes, the charging performance of the developer in the developing device changes, and as a result, a significant change occurs in the output density characteristics.

In order to solve these problems, various measures have conventionally been used.

For example, with respect to the change in the thickness of the photosensitive drum, a detecting means for detecting the thickness of the photosensitive drum is provided, and the voltage supplied to the charging device is changed in accordance with the detection signal. A method for correcting a change in the charging performance of the drum has been proposed.

Similarly, the voltage applied to the lamp for illuminating the original is changed in accordance with the detection signal for detecting the film thickness.
A method for correcting a change in the sensitivity of the photosensitive drum is also known.

Further, with respect to changes in the temperature and humidity of the use environment, the temperature around the photosensitive drum is detected, and the voltage supplied to the charging device is changed in accordance with the temperature and humidity, so that the performance of the photosensitive drum according to the temperature is changed. There has been proposed a method for compensating for the change in the distance.

There is also known a method in which an image signal is changed so as to maintain gradation characteristics in accordance with a detection signal which detects the thickness of the photosensitive drum.

By adopting such a method, it is possible to stabilize the output density characteristics with respect to changes in sensitivity characteristics and charging performance due to variations in the thickness of a medium such as a photosensitive drum.

On the other hand, recent electrophotographic printers,
Copiers are often provided with a mode called character mode or text / photo mode, which prioritizes character quality, and a mode called photo mode, which gives priority to gradation images such as photographs. In this case, the image processing method is often changed between the character mode and the photo mode.

For example, in the case of a 600 dpi printer,
In the character mode, a 600 dpi binarization process is used to reproduce the gradation characteristics while maintaining the resolution. In the photographic mode, a 200 dpi PWM is used to obtain the gradation characteristics and the smoothness of the image. Method may be used.

As described above, when a plurality of signal generating means are provided, the effect of the change in the film thickness of the medium, such as the photosensitive drum, on the sensitivity characteristic and the change in charging performance on the gradation characteristic are different in each of the signal generating means. There are many.

For example, as the character mode described above, 600d
pi binarization processing and 200dp as photo mode
FIGS. 17 and 18 show output density characteristic results in the case of a printer using the PWM method i.

FIG. 17 shows that the thickness of the photosensitive member is 30 μm, 2 μm,
600 when changing to 0 μm, 16 μm, 13 μm
FIG. 18 shows a change in output density characteristics when the binarization process of dpi is used.
m, 16 μm, and 13 μm.
The change of the output density characteristic when the 0 dpi PWM method is used is shown. This data indicates through data that has not been subjected to γ conversion. 17 and 18, the horizontal axis represents video data, and the vertical axis represents the output density of the conventional image forming apparatus.

As described above, the 600 dpi shown in FIG.
18 differs from the case of the 200 dpi PWM method shown in FIG. 18 in that the sensitivity characteristics due to the film thickness variation of the medium such as the photosensitive drum and the effect of the change in the charging performance on the gradation characteristics are different. I understand.

Even in such an image forming apparatus having a plurality of signal generating means, a method for optimizing an image signal conversion method and maintaining a gradation characteristic is used in accordance with the above-mentioned detection signal for detecting the film thickness. be able to.

When such a method is employed, usually, the optimization of the image signal conversion method according to the detection signal for detecting the film thickness is not continuously performed due to the cost of the image forming apparatus or the like. In addition, a method of switching an image signal conversion method before and after a threshold value of a detection signal that detects a plurality of film thicknesses is used.

[0019]

However, in the conventional image forming apparatus having a plurality of signal generating means as described above, the threshold value of the detection signal for detecting the film thickness is the same in the plurality of signal generating means. As described above, since the influence of the change in the film thickness on the sensitivity characteristics and the change in the charging performance on the gradation characteristics differs depending on the signal generation means, the gradations before and after the threshold value may differ depending on the signal generation means. There has been a problem that a difference in characteristics may increase or a problem such as generation of a pseudo contour immediately before the threshold may occur.

The present invention has been made to solve the above problems, and an object of the first to sixth inventions according to the present invention is to provide a method for detecting the thickness of an image bearing member, Each signal generation is performed by optimizing the conversion means for converting the output characteristic of the image signal generated by any of the plurality of signal generation means in accordance with the signal generation means for generating the image signal. Means for performing output density correction in consideration of the difference in sensitivity characteristics due to variations in the thickness of the image carrier and the effects of changes in charging performance on gradation characteristics, thereby enabling image formation with excellent gradation characteristics to be performed. An object of the present invention is to provide an image forming apparatus.

[0021]

According to a first aspect of the present invention, there is provided an image carrier (photosensitive drum 6 shown in FIG. 1) for carrying an image to be formed on a recording medium, and an input image. A plurality of generating means for generating different image signals based on the information (γ conversion unit 34 and PWM circuit 35, binarization processing circuit 36 shown in FIG. 3, PWM circuit 35, binarization processing circuit 36 shown in FIG. 11) Detecting means for detecting the film thickness of the image carrier (the detecting section 13 shown in FIG. 1); and an image signal generated by any of the generating means based on a detection result (detection signal TD) of the detecting means. (A CPU 25 shown in FIG. 3 converts the γ conversion unit 3 shown in FIG. 4 based on a program stored in a ROM 26) into image signals having different output characteristics.
4 is controlled by the CPU 25 shown in FIG. 11 based on the program stored in the ROM 26. The primary conversion unit 1302 shown in FIG.
Switching between the primary conversions L1 to L4), and exposing and scanning the image carrier on the basis of the image signal converted by the conversion means to form an image on a recording medium. Control means for optimizing and controlling the conversion means in accordance with any of the generation means for generating the gamma conversion (the CPU 25 shown in FIG. 3 performs the γ conversion of the γ conversion section 34 shown in FIG. 4 based on the program stored in the ROM 26) The CPU 25 shown in FIG. 11 controls the change of the switching points of the tables 401 to 404 based on the program stored in the ROM 26.
2 primary conversions L1 to L4 to change and control the switching point).

According to a second aspect of the present invention, the conversion means (γ conversion section 34 shown in FIG. 4) is based on a detection result (detection signal TD) of the detection means (detection section 13 shown in FIG. 1). And any one of the generating means (the γ conversion unit 34 shown in FIG. 3).
And γ by the PWM circuit 35 and the binarization processing circuit 36)
The conversion characteristic of the conversion processing (γ conversion tables 401 to 404 of the γ conversion unit 34 shown in FIG. 4) is switched to convert the output characteristic of the image signal generated by the generation unit.

According to a third aspect of the present invention, the conversion means (primary conversion unit 1302 shown in FIG. 12) is configured to detect the detection result (detection signal TD) of the detection means (detection unit 13 shown in FIG. 1).
A primary conversion process that is switched based on the
The primary transformations L1 to L4) of the primary transformation unit 1302 shown in FIG.
Any of the generating means (the PWM circuit 3 shown in FIG. 11)
5, which is applied to the image signal generated by the binarization processing circuit 36).

According to a fourth aspect of the present invention, the image bearing member is a photosensitive member (the photosensitive drum 6 shown in FIG. 1).

According to a fifth aspect of the present invention, the detecting means (the detecting section 13 shown in FIG. 1) applies a voltage (the voltage Vpp0 shown in FIG. 2) to the image carrier (the photosensitive drum 6 shown in FIG. 1). By measuring the current (current i shown in FIG. 2) flowing on the image carrier when the voltage V0) is applied, the film thickness of the image carrier is detected.

According to a sixth aspect of the present invention, the conversion means (the γ conversion unit 34 shown in FIG. 4 and the primary conversion unit 1 shown in FIG. 12)
The detection unit 302 detects a detection result (detection signal TD) of the detection unit (the detection unit 13 shown in FIG. 1) and a predetermined threshold (for example, a switching point of 20 μm) (the CPU shown in FIGS. 3 and 11).
25) performs a comparison, and converts the output characteristic of the image signal generated by the generating means based on the comparison result (selection signal). The control means (CP shown in FIGS. 3 and 11)
U25) controls the threshold value to be changed according to any of the generating means for generating the image signal (for example, the switching point for the binarization processing circuit 36 shown in FIGS. 3 and 11 is set to 20 μm, The switching point for the PWM circuit 35 shown in FIG.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIG. 1 is a schematic sectional view illustrating the structure of an image forming apparatus according to a first embodiment of the present invention.

In FIG. 1, reference numeral 2 denotes a document illumination lamp for illuminating image information on the document 1 with light. Reference numeral 3 denotes a CCD image sensor (hereinafter referred to as a CCD) which receives reflected light from the original 1 and
Convert to image signal. 4 is an image signal processing circuit, which is a CCD
Subjecting the image signal output from 3 to predetermined image processing,
It is output as a drive signal for driving the laser driver 5. The laser driver 5 performs image exposure according to image information on the document 1 on the uniformly charged photosensitive drum 6 by a drive signal output from the image signal processing circuit 4.

Reference numeral 7 denotes a charging member which is disposed in contact with the photosensitive drum 6 and receives a predetermined voltage from a high voltage power supply 11 to uniformly charge the photosensitive drum 6 before exposure. Reference numeral 8 denotes a developing device, which is a photosensitive drum 6 formed by the laser driver 5.
A developing step of developing the upper electrostatic latent image with toner is performed.

Reference numeral 9 denotes a transfer device which performs a transfer process of transferring the toner image formed on the photosensitive drum 6 through the developing process onto the transfer paper P fed in synchronization. Reference numeral 10 denotes a fixing unit that fixes the toner image on the transfer paper P transported by the transport belt to the transfer paper P through a transfer process. A cleaner 12 removes residual toner on the photosensitive drum 6 after transfer.

Reference numeral 13 denotes a detection unit which detects the amount of current flowing through the photosensitive drum 6 when a constant voltage is applied to the photosensitive drum 6 by the high voltage power supply 11 through the charging member 7 and detects the amount of current flowing through the photosensitive drum 6. A detection signal corresponding to the film thickness is output. The CPU 25 shown in FIG. 2, which will be described later, corrects an output density characteristic due to a change in the thickness of the photoconductor based on a detection signal output from the detection unit.

The operation of each section will be described below.

First, the photosensitive drum 6 is uniformly charged by applying a predetermined voltage to the charging member 7 from the high voltage power supply 11. The light illuminated by the document illumination lamp 2 is C
The information is guided to the CD 3 and the image information on the document 1 is converted into an image signal. This image signal is processed by the image signal processing circuit 4 and output as a drive signal for driving the laser driver 5. Thus, image exposure according to image information on the original 1 is performed on the uniformly charged photosensitive drum 6.

Next, the photosensitive drum 6 on which an electrostatic latent image has been formed
Is subjected to a developing process of developing with the toner of the developing device 8, and further, the photosensitive drum 6 formed through the developing process is formed.
The upper toner image is the transfer paper P fed synchronously.
Is transferred by the transfer device 9, and the transfer paper P having passed through the transfer process is transported to the fixing device 10 by the transport belt.
The toner on the transfer paper P is fixed on the transfer paper P by the fixing device 10. Further, the cleaner removes residual toner on the photosensitive drum 6 after fixing.

The amount of current flowing through the photosensitive drum 6 when a constant voltage is applied to the photosensitive drum 6 by the high-voltage power supply 11 through the charging member 7 is detected, so that the amount of current flowing through the photosensitive drum 6 is adjusted. A detection signal is obtained, and the output density characteristic due to a change in the photoconductor thickness is corrected in accordance with the detection signal.

FIG. 2 is a diagram showing a configuration of the detecting unit 13 for detecting a value corresponding to the photoconductor thickness of the photoconductor drum 6 shown in FIG. 1, and the same components as those in FIG. Are attached.

In the figure, reference numeral 21 denotes a source of an AC voltage,
While the photosensitive drum 6 is rotating, a predetermined voltage V0 is applied to the voltage VPP.
Superimpose on O. 24 is an analog / digital converter (A / D)
Converter) converts the voltage across the detection resistor 23 according to the current i into a detection signal TD which is a 6-bit digital signal. The detection signal TD is a signal corresponding to the thickness of the photosensitive member, which is a measure for measuring the newness of the drum.

A CPU 25 controls the entire image forming apparatus based on a program stored in the ROM 26. Further, the CPU 25 classifies the photoreceptor film thickness based on a predetermined criterion based on the detection signal TD output from the detection unit 13, and stores a γ conversion table corresponding to a plurality of γ conversion characteristics γ1 to γ4 shown in FIG. One of them is selected, and control is performed so as to switch the method of converting the output (density) characteristics of the image signal.

Here, the CPU 25 determines that the larger the value of the detection signal TD is, the newer the photoconductor drum 6 is, the thicker the photoconductor drum is, and the smaller the value of the detection signal TD is, the larger the photoconductor drum 6 is.
It is determined that the photoreceptor film thickness is small due to deterioration of the photoconductor, and a control signal for selecting the γ conversion characteristic is output.

FIG. 3 shows the image signal processing circuit 4 shown in FIG.
3 is a block diagram illustrating the configuration of FIG. 1, and the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals.

In the figure, reference numeral 31 denotes an analog processing unit,
Gain adjustment and shading correction are performed on the analog signal from the CD sensor 3. Reference numeral 32 denotes an analog-to-digital converter (A / D converter), which converts an analog signal output from the analog processor 31 into an 8-bit digital signal.

Reference numeral 33 denotes a logarithmic converter which converts a digital signal output from the A / D converter 32 into a density signal. 34
Is a γ conversion unit that performs γ conversion of one of γ conversion characteristics γ1 to γ4 on the density signal output from the logarithmic conversion unit 33 to convert the output (density) characteristics of the image signal. A PWM circuit 35 converts the density signal output from the gamma converter into a pulse width signal for driving the laser 5. Reference numeral 36 denotes a binarization processing circuit serving as a signal transmission unit, which binarizes the density signal output from the γ conversion unit. An operation unit 50 includes a display screen and various setting keys, and can perform various settings including an image forming mode (photo mode, character mode, and the like).

The PWM circuit 35 and the binarization processing circuit 3
In step 6, the CPU 25 controls the selection based on the image forming mode (photo mode, character mode) set by the operation unit 50.

Each part of the image signal processing circuit 4 including the γ conversion part 34 is controlled by the CPU 25. CPU2
Reference numeral 5 receives a value corresponding to the film thickness from the A / D converter 24 and performs control according to the value. 40 is a printer control unit,
A charging voltage control circuit 41 for controlling a charging voltage by the high voltage power supply 11; a developing bias control circuit 42 for controlling a developing bias of the developing device 8; a laser light amount adjusting circuit 43 for adjusting the laser light amount of the laser 5; And a fixing temperature control circuit 44 for controlling the temperature.

FIG. 4 is a block diagram for explaining the configuration of the gamma converter 34 shown in FIG. 3, and the same components as those in FIG. 3 are denoted by the same reference numerals.

In the figure, reference numerals 401 to 404 denote γ conversion tables which use input γ conversion tables 401 to 404 respectively corresponding to γ conversion characteristics γ1 to γ4 shown in FIG. Perform the conversion.

Note that the γ conversion section 34 performs the γ conversion tables 401 to 404 according to the selection signal output from the CPU 25.
Is a table conversion circuit for selecting one of the γ conversion tables (switching the γ conversion table).

The γ conversion section 3 as the table conversion circuit
4 can be realized, for example, by providing the ROM with input / output characteristics (γ conversion tables 401 to 404) of γ conversion characteristics γ1 to γ4. In the case of using a RAM, the CPU 25 may set a set of table data of characteristics to be selected in the RAM to create a γ conversion table according to the film thickness.

FIG. 5 shows the γ conversion table 40 shown in FIG.
6 is a characteristic diagram showing γ conversion characteristics γ1 to γ4 of Nos. 1 to 404, and (a) to (d) correspond to the γ conversion characteristics γ1 to γ4, respectively. The horizontal axis indicates input data to the γ conversion unit 34 (data before γ conversion), and the vertical axis indicates output data from the γ conversion unit 34 (data after γ conversion).

As shown in FIGS. 5A to 5D, the slope of the curve of the γ conversion characteristic increases as the value changes from γ1 to γ4.

That is, the γ conversion characteristics are γ1 to γ4 ((a)
(D)), the conversion characteristic corresponds to the conversion characteristic at the time of γ conversion to the photoreceptor having the deteriorated thin photoreceptor film thickness.

Hereinafter, a method of selecting the γ conversion characteristic by the CPU 25 will be described.

First, a predetermined threshold value (switching point) A,
B and C (for example, A>B> C) are signal generation units (FIG. 3) in advance.
Are individually set for each of the PWM circuit 35 and the binarization processing circuit 36) and stored in the ROM 26.

The CPU 25 selects a γ conversion characteristic γ1 when a predetermined reference for classifying the photoconductor film thickness, for example, when the detection signal TD is “TD> A (for example, 20 μm)”,
If “A ≧ TD> B”, select the γ conversion characteristic γ2,
In the case of “B ≧ TD> C”, select the γ conversion characteristic γ3,
If “C ≧ TD”, the γ conversion characteristic γ4 is selected.

Hereinafter, the correction (conversion) of the output density characteristic of the image signal according to the photoconductor thickness of the photoconductor drum 6 will be described with reference to FIGS.

FIGS. 6 and 7 are characteristic diagrams showing output density characteristics when the photosensitive drum thickness of the photosensitive drum 6 shown in FIG. 1 is 30 μm, 20 μm, and 13 μm, respectively. FIG. FIG. 7 corresponds to a state before the output density characteristic is corrected by the conversion unit 34, and FIG. 7 corresponds to a state after the output density characteristic is corrected by the γ conversion unit 34.

In FIGS. 6 and 7, the horizontal axis represents the document density, and the vertical axis represents the output density of the image forming apparatus of the present invention. Further, this output density characteristic is 600 d
This corresponds to the case where the binarization method of pi is used.

The output density characteristic shown in FIG. 6 changes remarkably when the thickness of the photosensitive drum of the photosensitive drum 6 changes.

In the output density shown in FIG. 7, a constant output density characteristic is obtained regardless of the film thickness (30 μm, 20 μm, 13 μm) of the photosensitive drum 6.

The corrected output density characteristic shown in FIG. 7 is based on a threshold (switching point) set to be optimal in the binarization method of 600 dpi, based on γ.
Select the conversion characteristic (switch γ conversion table),
This corresponds to the case where the output density characteristic is corrected by the γ conversion unit 34.

Hereinafter, the optimization of the output density characteristic correction of the image signal for each signal generating means will be described with reference to FIGS.

FIGS. 8 and 9 are characteristic diagrams showing output density characteristics immediately before (for example, detected film thickness> threshold) and immediately after (for example, detected film thickness ≦ threshold) before switching of the γ conversion table. 8 corresponds to a binarization method of 600 dpi (for example, photograph mode), and FIG. 9 corresponds to a PWM method of 200 dpi (for example, character mode).

The output density characteristic correction in FIG. 8 and FIG. 9 is a threshold value (switching point, for example, the film thickness is “20 μm”) set to be optimal in the 600 dpi binarization method shown in FIG. Γ conversion table is switched based on

In FIGS. 8 and 9, the horizontal axis represents the document density, and the vertical axis represents the output density of the image forming apparatus of the present invention.

As shown in FIGS. 8 and 9, as shown in FIG.
As compared with the output by the binarization method of 00 dpi, the output by the PWM method of 200 dpi shown in FIG. 9 has a larger difference in the output density characteristics between immediately before and after the switching of the γ conversion table.

Further, the 200 dpi PW shown in FIG.
The output by the M method has a large deviation from the ideal output density characteristic in the low-density region in the output density characteristic immediately before switching of the γ conversion table, and in this case, the possibility of occurrence of a pseudo contour is large.

FIG. 10 is a characteristic diagram showing the output density characteristics immediately before (for example, the detected film thickness> threshold) and immediately after (for example, the detected film thickness ≦ threshold) before switching the γ conversion table, and shows the 200 dpi PWM method. (For example, character mode).

The output density characteristic correction in FIG. 10 is performed by using a threshold (switching point, for example, when the film thickness is “2”) set to be optimal in the 200 dpi PWM method.
4 .mu.m ").

As shown in the figure, by setting the film thickness as a switching point to “24 μm”, the difference between the output density characteristics immediately before and immediately after the switching of the γ conversion table is obtained.
This is almost the same as the 600 dpi binarization method (shown in FIG. 8) when the γ conversion table is switched with the film thickness as the switching point being “20 μm”.

Also, the deviation from the ideal output density characteristic in the low density range is small, and the occurrence of a false contour can be prevented.

As described above, the image forming apparatus according to the embodiment switches the γ conversion table when the image is formed by the binarization processing circuit 36 that generates the image signal by the binarization method of 600 dpi (for example, the photograph mode). A point is set to, for example, “20 μm”, and a gamma conversion table switching point is set to, for example, “24 μm” when an image is formed by the PWM circuit 35 that generates an image signal by the 200 dpi PWM method (character mode). Processing circuit 36 and the PWM circuit 35).
The PU 25 is configured to optimize the switching point of the γ conversion table.

As described above, the point of change of the output density characteristic before and after the switching of the γ conversion table (thickness before and after the threshold) is optimized by optimizing the switching point of the γ conversion table according to the signal generating means. It is possible to reduce the size and to prevent the occurrence of a defective image such as a false contour.

[Second Embodiment] In the first embodiment,
The gamma conversion characteristic (γ
(Conversion table) is switched to correct the output density characteristic of the image signal (non-linear conversion of the output (density) characteristic of the image signal). However, the primary conversion is performed according to the photoconductor thickness of the photoconductor drum 6. May be switched to correct the output density characteristic of the image signal (linear conversion of the output (density) characteristic of the image signal). Hereinafter, the embodiment will be described.

FIG. 11 is a block diagram illustrating the configuration of an image signal processing circuit 4 according to a second embodiment of the present invention.
The same components as those in FIG. 3 are denoted by the same reference numerals.

In the drawing, reference numeral 1301 denotes a γ conversion unit which performs γ conversion on the density signal output from the logarithmic conversion unit 33. Reference numeral 1302 denotes a primary conversion unit that performs a primary conversion on the density signal output from the γ-number conversion unit 1301 to convert the output (density) characteristics of the image signal.

FIG. 12 is a block diagram showing the primary conversion unit 13 shown in FIG.
FIG. 4 is a block diagram for explaining the configuration of No. 02, and the same components as those in FIG. 3 are denoted by the same reference numerals.

In the figure, L1 to L4 are primary conversion units.
A predetermined primary conversion is performed on each of the input density signals.

Note that the primary conversion unit 1302
One of the primary conversion units L1 to L4 is selected according to the selection signal output from.

First, the primary conversion Ln of the density signal (where n
Is an integer of 1 to 4).

Doutn is a density signal after the primary conversion Ln,
Using Din as the density signal before the primary conversion and An and Bn as coefficients, the primary conversion Ln of the density signal is expressed as “Doutn = an ×
(Din + bn). " Here, n is an integer of 1 to 4.

Note that the primary conversion Ln is represented by “an =
1 ”and“ bn = 0 ”, that is, the case where the primary conversion is not performed.

The primary conversion section 1302 can be realized by, for example, providing ROM with primary conversion coefficients a1 to a4 and b1 to b4. In the case of using a RAM, a set of coefficient data to be selected may be set in the RAM by the CPU 25 to realize a primary conversion unit corresponding to the film thickness.

Hereinafter, the primary conversions L1 to L by the CPU 25 will be described.
The method of selecting No. 4 will be described.

First, a predetermined threshold value (switching point) A,
B and C (for example, A>B> C) are signal generation units (FIG. 1) in advance.
It is assumed that each of the PWM circuit 35 and the binarization processing circuit 36 shown in FIG. 1 is individually set and stored in the ROM 26.

The CPU 25 selects the primary conversion L1 when a predetermined reference for classifying the photoreceptor film thickness, for example, when the detection signal TD is "TD> A (for example, 20 μm)", and "A≥
If "TD>B", the primary conversion L2 is selected and "B≥T
In the case of “D> C”, the primary conversion characteristic L3 is selected, and “C ≧ C”
In the case of "TD", the primary conversion characteristic L4 is selected.

Hereinafter, referring to FIG.
The correction (primary conversion) of the output density characteristic of the image signal according to the photoconductor film thickness will be described.

FIG. 13 is a characteristic diagram showing output density characteristics after the primary conversion when the photoconductor thickness of the photoconductor drum 6 shown in FIG. 1 is 30 μm, 20 μm, and 13 μm.

In the figure, the horizontal axis represents the original density, and the vertical axis represents the output density of the image forming apparatus of the present invention. Further, this output density characteristic indicates that the signal generation means has a resolution of 600 dpi.
This corresponds to the case where the binarization method is used.

As shown in the figure, almost constant output density characteristics are obtained irrespective of the photoconductor thickness.

The output density characteristics after the primary conversion shown in FIG. 13 are obtained by converting the primary conversions L1 to L4 based on threshold values (switching points) set to be optimum in the binarization method of 600 dpi. This corresponds to a case where selection (switching) is performed and the output density characteristic is corrected by the primary conversion unit 1302.

Hereinafter, the optimization of the output density characteristic correction of the image signal for each signal generating means will be described with reference to FIGS.

FIGS. 14 and 15 are characteristic diagrams showing output density characteristics immediately before the primary conversion switching (for example, detected film thickness> threshold) and immediately after (for example, detected film thickness ≦ threshold).
FIG. 14 corresponds to a binarization method of 600 dpi (for example, a photograph mode), and FIG. 15 corresponds to a PWM method of 200 dpi (for example, a character mode).

Note that the output density characteristic correction in FIGS. 14 and 15 is a threshold value (switching point, for example, the film thickness is “20 μm”) set to be optimal in the 600 dpi binarization method shown in FIG. Γ conversion table is switched based on

14 and 15, the horizontal axis represents the document density, and the vertical axis represents the output density of the image forming apparatus of the present invention.

As shown in FIGS. 14 and 15, compared with the output by the 600 dpi binarization method shown in FIG.
The output by the 200 dpi PWM method shown in FIG. 5 has a large difference in output density characteristics between immediately before and after the primary conversion switching.

Further, the P of 200 dpi shown in FIG.
The output by the WM method has a large deviation from the ideal output density characteristic in the low-density region in the output density characteristic immediately before switching of the primary conversion, and in this case, the possibility of occurrence of a pseudo contour is large.

FIG. 16 is a characteristic diagram showing output density characteristics immediately before (for example, detected film thickness> threshold) and immediately after (for example, detected film thickness ≦ threshold) before the primary conversion switching.
It corresponds to the 00 dpi PWM method (for example, character mode).

The output density characteristic correction in FIG. 16 is performed using a threshold value (switching point, for example, when the film thickness is “2”) set to be optimal in the 200 dpi PWM method.
4 μm ”).

As shown in the figure, by setting the film thickness as the switching point to “24 μm”, the difference between the output density characteristics immediately before and immediately after the primary conversion switching is determined by the film thickness as the switching point. This is almost the same as the 600 dpi binarization method (shown in FIG. 14) when the γ conversion table is switched to “20 μm”.

Also, the deviation from the ideal output density characteristic in the low density range is small, and the occurrence of false contour can be prevented.

As described above, in the image forming apparatus according to the embodiment, the primary conversion switching point in the case where the image formation is performed by the binarization processing circuit 36 which generates the image signal by the binarization method of 600 dpi (for example, photograph mode). To "2
0 μm ”, the gamma conversion table switching point when image formation is performed by the PWM circuit 35 that generates an image signal by the PWM method (character mode) of 200 dpi is set to, for example,“ 2 ”.
4 μm ”and the signal generation means (binary processing circuit 36,
PWM circuit 35).
Is configured to optimize the point of switching the primary conversion.

As described above, by optimizing the point of the primary conversion switching according to the signal generating means, the difference in the change of the output density characteristics before and after the primary conversion switching (thickness before and after the threshold) is reduced. In addition, it is possible to prevent the occurrence of a defective image such as a false contour.

The conversion of the output (density) characteristic of the image signal may be a conversion method other than the γ conversion and the primary conversion.

As described above, the storage medium storing the program codes of the software for realizing the functions of the above-described embodiments is supplied to the system or the apparatus, and the computer (or CPU or MP) of the system or the apparatus is supplied.
It goes without saying that the object of the present invention is also achieved when U) reads out and executes the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, C
DR, magnetic tape, nonvolatile memory card, RO
M, EEPROM and the like can be used.

The functions of the above-described embodiments are implemented when the computer executes the readout program codes, and the OS (Operating System) running on the computer is executed based on the instructions of the program codes. ) And the like perform part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instruction of the program code, The CPU provided in the function expansion board or function expansion unit performs part or all of the actual processing,
It goes without saying that a case where the function of the above-described embodiment is realized by the processing is also included.

Further, the present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Needless to say, the present invention can be applied to a case where the present invention is achieved by supplying a program to a system or an apparatus. In this case, by reading a storage medium storing a program represented by software for achieving the present invention into the system or the apparatus, the system or the apparatus can enjoy the effects of the present invention. .

Further, by downloading and reading out a program represented by software for achieving the present invention from a database on a network by a communication program, the system or apparatus can be
It is possible to enjoy the effects of the present invention.

[0111]

As described above, the first embodiment according to the present invention is described.
According to the invention of the above, based on the thickness detection result of the image carrier,
The conversion means for converting the image signal generated by any of the plurality of generation means into image signals having different output characteristics is optimized and controlled according to the one of the generation means for generating the image signal. This makes it possible to perform the output density correction in consideration of the difference in the effect of the change in the sensitivity characteristic and the change in the charging performance on the gradation characteristic due to the change in the film thickness of the image carrier.

According to the second invention, the conversion means switches the conversion characteristic of the γ conversion processing by the generation means based on the detection result of the detection means, and the image generated by any of the generation means is switched. Because it converts the output characteristics of the signal,
With a simple configuration, it is possible to perform output density correction according to the film thickness of the image carrier.

According to the third aspect, the conversion means performs a predetermined primary conversion process which is switched based on the detection result of the detection means, to the image signal generated by any of the generation means. Therefore, it is possible to perform output density correction according to the thickness of the image carrier with a simple configuration.

According to the fourth aspect, since the image bearing member is a photosensitive member, it can be widely applied to the most general image forming apparatus.

According to the fifth aspect, the detecting means detects the film thickness of the image carrier by measuring a current flowing on the image carrier when a voltage is applied to the image carrier. Therefore, it is possible to reliably detect the thickness of the image carrier with a simple configuration.

According to the sixth aspect, the conversion means compares the detection result of the detection means with a predetermined threshold, and converts the output characteristic of the image signal generated by the generation means based on the comparison result. The control means controls the change of the threshold value according to any one of the generation means for generating the image signal. Therefore, with a simple configuration, the film of the image carrier is controlled by each signal generation means. It is possible to perform output density correction in consideration of differences in sensitivity characteristics due to thickness variations and changes in charging performance on gradation characteristics.

Therefore, the output density correction is performed in consideration of the difference between the sensitivity characteristics due to the variation in the film thickness of the image carrier and the effect of the change in the charging performance on the gradation characteristics by each signal generating means, thereby providing excellent gradation characteristics. This has the advantage that an image can be formed in an improved manner.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating a configuration of an image forming apparatus according to a first exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a detection unit for detecting a value corresponding to a photoconductor thickness of the photoconductor drum illustrated in FIG.

FIG. 3 is a block diagram illustrating a configuration of an image signal processing circuit illustrated in FIG.

FIG. 4 is a block diagram illustrating a configuration of a γ conversion unit illustrated in FIG.

FIG. 5 is a characteristic diagram showing a γ conversion characteristic of the γ conversion unit shown in FIG.

FIG. 6 shows a photoreceptor drum shown in FIG.
FIG. 9 is a characteristic diagram illustrating output density characteristics before γ conversion when the sizes are μm, 20 μm, and 13 μm.

FIG. 7 shows a photosensitive drum having a photosensitive drum thickness of 30 shown in FIG.
It is a characteristic view which shows each output density characteristic after gamma conversion in the case of micrometers, 20 micrometers, and 13 micrometers.

FIG. 8 shows a table immediately before and after the switching of the γ conversion table.
FIG. 10 is a characteristic diagram showing output density characteristics by a 00 dpi binarization method.

FIG. 9 shows two values immediately before and after switching of the γ conversion table.
FIG. 4 is a characteristic diagram showing output density characteristics by a 00 dpi PWM method.

FIG. 10 is a characteristic diagram showing output density characteristics by a 200 dpi PWM method immediately before and immediately after switching of the γ conversion table.

FIG. 11 is a block diagram illustrating a configuration of an image signal processing circuit according to a second embodiment of the present invention.

FIG. 12 is a block diagram illustrating a configuration of a primary conversion unit illustrated in FIG.

FIG. 13 shows a photosensitive drum thickness of the photosensitive drum shown in FIG.
1 for each of 0 μm, 20 μm, and 13 μm
FIG. 14 is a characteristic diagram illustrating output density characteristics after the next conversion.

FIG. 14 shows 600 dpi immediately before and after the primary conversion switching.
FIG. 6 is a characteristic diagram showing output density characteristics by the binarization method of FIG.

FIG. 15 shows 200 dpi immediately before and after the primary conversion switching.
FIG. 6 is a characteristic diagram showing output density characteristics according to the PWM method.

FIG. 16: 200 dp immediately before and after the primary conversion switching
FIG. 11 is a characteristic diagram showing an output density characteristic of the i-th PWM method.

FIG. 17 shows a photosensitive drum having a photosensitive drum thickness of 30 μm and 20 μm.
It is a characteristic view which shows each output density characteristic by 600 dpi binarization method in the case of micrometers, 16 micrometers, and 13 micrometers.

FIG. 18 shows a photoconductor drum having a photoconductor thickness of 30 μm and 20 μm.
It is a characteristic view which shows each output density characteristic by 200 dpi PWM method in the case of micrometers, 16 micrometers, and 13 micrometers.

[Explanation of symbols]

 Reference Signs List 6 photoconductor drum 13 detection unit 25 CPU 26 ROM 34 γ conversion unit 35 PWM circuit 36 binarization processing circuit 401-404 γ conversion unit table

Claims (6)

[Claims] 1. An image carrier for carrying an image to be formed on a recording medium, a plurality of generating means for generating different image signals based on input image information, and a film thickness of the image carrier. Detecting means for detecting, converting means for converting an image signal generated by any of the generating means into image signals having different output characteristics based on a detection result of the detecting means, and converting the image signal into an image signal converted by the converting means. An image forming apparatus that forms an image on a recording medium by exposing and scanning the image carrier on the basis of the image carrier, wherein a control unit that optimizes and controls the conversion unit according to any one of the generation units that generates the image signal An image forming apparatus comprising: 2. The image processing apparatus according to claim 1, wherein the conversion unit switches a conversion characteristic of a gamma conversion process by the generation unit based on a detection result of the detection unit, and converts an output characteristic of an image signal generated by any of the generation units. 2. The method according to claim 1, wherein
The image forming apparatus as described in the above. 3. The image processing apparatus according to claim 2, wherein the conversion unit performs a predetermined primary conversion process that is switched based on a detection result of the detection unit, to the image signal generated by any of the generation units. Item 2. The image forming apparatus according to Item 1. 4. The image forming apparatus according to claim 1, wherein the image carrier is a photoconductor. 5. The apparatus according to claim 1, wherein said detecting means detects a film thickness of said image carrier by measuring a current flowing on said image carrier when a voltage is applied to said image carrier. Item 2. The image forming apparatus according to Item 1. 6. The method according to claim 1, wherein the conversion unit compares a detection result of the detection unit with a predetermined threshold value, and converts an output characteristic of an image signal generated by the generation unit based on the comparison result. The image forming apparatus according to claim 1, wherein the control unit changes and controls the threshold value according to any one of the generating units that generates the image signal.