JP2968310B2 - Background density control copying machine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic copying apparatus, and more particularly, to detecting a background density of a document and controlling a developing bias voltage in accordance with the density to obtain an image on a copy. And a background density control for suppressing the original background toner density.

[Conventional technology]

Background toner on the copy image is called so-called background stain. If the background color of the document (color or discoloration of the original paper or overall stain) is dark, the background stain becomes large. Conventionally, in order to suppress this, the background density of the original is detected by an optical sensor and the developing bias voltage is controlled in accordance with the detected density (for example, JP-A-54-36725 and JP-A-63-10047).
No. 4).

[Problems to be solved by the invention]

However, not only the background of the document but also a background stain is caused by a change in the characteristics of the copying function element such as deterioration of the photosensitive member or the exposure lamp. The background contamination due to the deterioration of the photoreceptor or the exposure lamp is reduced to a standard reflection density surface (white surface).
The photoreceptor is exposed to the reflected light of the photoreceptor, the resulting electrostatic latent image is developed, and the development density at that portion on the photoreceptor is detected by an optical sensor. This is prevented or suppressed by adjusting the voltage of the exposure lamp so that the value of the exposure lamp becomes zero.

However, when the voltage of the exposure lamp is adjusted, the light receiving level of the above-described optical sensor that detects the background density of the document changes, and the detection signal level shifts even at the same background density.
As a result, the background density control by the above-described development bias control is disturbed, and background contamination appears even though the development bias control is performed due to the voltage adjustment of the exposure lamp.

SUMMARY OF THE INVENTION It is an object of the present invention to simultaneously suppress the background stain on a copy caused by the background color of a document and the background stain caused by deterioration of a photoconductor and an exposure lamp.

[Means for solving the problem]

The background density control copying apparatus of the present invention comprises a photosensitive member (2), a means (3) for uniformly charging the photosensitive member (2), an illumination light source (31) for illuminating a document, and a photoconductor ( An optical unit (30) for exposing 2) to form an electrostatic latent image corresponding to a document image on a photoreceptor (2), a developing unit (5) for developing the electrostatic latent image with toner, and an illumination light source (31). First detecting means (22) for detecting the background density of the illuminated document and generating a density signal indicating the density.
0,225) and developing means (5) according to the density signal.
First control means (100) for controlling the developing bias voltage of
An image forming apparatus including: a second detecting unit (6,230) for detecting the density of the toner image on the photoconductor (2);
A reference density surface (16); a toner image of the reference density surface (16) is formed on the photoreceptor (2) by the image forming apparatus, and the density of the toner image detected by the second detecting means (6,230) is used as a reference. Second control means (100) for correcting the applied voltage (V _L ) of the illumination light source (31) so as to fall within the range; and
When the control means (100) corrects the applied voltage ( _VL ) of the illumination light source (31), the first detection means (220, 225) detects the reflected light of the reference density surface (16) illuminated by the illumination light source (31) Third control means (100) for correcting the relationship of the density signal level to the light receiving level of the first detection means (220, 225) so that the level indicated by the density signal (Vo _D1 ) becomes the reference value (2.0). ;

Symbols in parentheses indicate corresponding elements or items in the embodiment shown in the drawings and described later.

[Action]

The second control means (100) is an image forming apparatus, which forms a toner image on the reference density surface (16) on the photoreceptor (2), and determines the density of the toner image detected by the second detection means (6,230) as a reference range. The applied voltage (V _L ) of the illumination light source (31) to be within
Is corrected, the background contamination due to a change in the characteristics of the copying function element such as the deterioration of the photosensitive member or the exposure lamp is prevented or suppressed.

Due to the correction of the applied voltage (V _L ) of the illumination light source (31), the level of the density signal (Vo _D1 ) of the first detection means (220, 225) shifts even if the original has the same background density. ) Is the reference density surface (1) illuminated by the illumination light source (31).
The reflected light of 6) is detected by the first detecting means (220, 225), and the density of the first detecting means (220, 225) with respect to the received light level is adjusted so that the level indicated by the density signal (Vo _D1 ) becomes the reference value (2.0). Since the signal level relationship is corrected, the illumination light source (3
Regardless of the change in the amount of emitted light in 1), the first detecting means (22
0,225) is indicated by the level indicated by the density signal (Vo _D1 ) (2.
0), and the control of the developing bias voltage of the developing means (5) according to the density signal by the first control means (100) is such that no background stain appears on the copy in spite of the stain on the original background. .

As a result, at the same time as the background contamination on the copy due to deterioration or contamination of the photoreceptor or the exposure lamp is prevented or suppressed,
Background dirt on a copy due to the color or dirt of the original background is prevented or suppressed.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

〔Example〕

FIG. 1 shows an outline of a mechanism configuration of an embodiment of the present invention.

This copying apparatus includes a copying machine main body and optional units such as an ADF (automatic document feeder / discharge device) 60, a sorter 70, an automatic duplexing unit 80, and paper feeding units 170 and 180.

The paper feeding system for supplying the recording sheets has five stages. That is, the first paper supply system and the second paper supply system are provided in the main body of the copying apparatus, and the third paper supply system including the second paper supply unit and the fourth paper supply system and the fifth paper supply system. The paper feeding unit is connected to the copying machine main body.

Reference numerals 21, 22, 23 and 24 denote a first sheet feeding system, a second sheet feeding system,
Cassettes provided in the third paper supply system and the fourth paper supply system, and 25 is a tray of the fifth paper supply system.

A contact glass 1 on which a document is placed is provided at the uppermost part of the main body of the copying apparatus. An optical scanning system 30 is provided below the contact glass 1.

The optical scanning system 30 includes an exposure lamp 31, a reflector 13, a first mirror,
32, second mirror 33, third mirror 34, lens 35, fourth mirror 3
6, which is composed of slits 37 and the like.

When scanning a document, the first carriage on which the exposure lamp 31, the reflection plate 13, and the first mirror 32 are mounted and the second carriage on which the second mirror 33 and the third mirror 34 are mounted have a 2: 1 ratio. , And the optical path length is kept constant. The moving direction of the first and second carriages, that is, the sub-scanning direction is the horizontal direction in FIG. 1, and the sub-scanning start position is the left end. At the sub-scanning start position, a home position sensor (not shown) detects the second carriage and turns on.

The lens 35 is a zoom lens, and can be driven by a motor to change the copy magnification. The light emitted from the exposure lamp 31 is reflected on the surface of the original, and passes through the first mirror 32, the second mirror 33, the third mirror 34, the lens 35, the fourth mirror 36, and the slit 37 onto the photosensitive drum 2. It is imaged.

Around the photosensitive drum 2, a main charger 3, an eraser 4, a developing cartridge 5, and a reflection type photo sensor (hereinafter referred to as P
6, a transfer charger 7, a separation charger 8, a kneeling unit 9, and the like.

 The copying process will be briefly described.

The photoreceptor drum 2 rotates in the direction indicated by the arrow in the figure, and its surface is uniformly charged to a predetermined high potential by the discharge when passing immediately below the main charger 3 and when passing immediately below the eraser 4. The electric charge in a portion not used for making a copy is erased. On the charged surface of the photosensitive drum 2,
When the reflected light (latent image forming light) from the document is irradiated, the potential of that portion changes (exposure and static elimination) according to the intensity of the irradiated light.

Since the optical scanning system 30 sequentially scans the document surface in synchronization with the peripheral surface speed of the photosensitive drum 2, the potential distribution corresponding to the density (light reflectance) distribution of the document image is formed on the surface of the photosensitive drum 2. ,
That is, an electrostatic latent image is formed. When the portion on which the electrostatic latent image is formed passes near the developing cartridge 5, the toner in the developing cartridge 5 is electrostatically attracted to the surface of the photoconductor 2 in accordance with the potential distribution, and the toner corresponding to the electrostatic latent image is formed. Visual image is photosensitive drum 2
Formed on (development).

On the other hand, in synchronization with the progress of the copy process, a recording sheet is supplied from any one of the five paper feeding systems. The recording sheet is fed via a registration roller 27 so as to overlap the surface of the photosensitive drum 2 at a predetermined timing, and is transferred by the transfer charger 7 to the photosensitive drum 2.
The upper visible image (toner image) is transferred, and the recording sheet onto which the visible image has been transferred is separated from the photosensitive drum 2 by the separation charger 8. The separated recording sheet is transported to the fixing device 12 by the transport belt 11. After passing through the fixing unit 12, the toner image on the recording sheet is fixed on the recording sheet by heat in the fixing unit 12. The fixed recording sheet is discharged to the sorter 70 or the automatic duplex unit 80 through a predetermined discharge path.

The first carriage has a light receiving end 14, to which light emitted from the exposure lamp 31 through the slit 13a and reflected from the document arrives. This light is optical fiber 15
The light is led to the light receiving element 225 (FIG. 2). When copying a document, the light receiving element detects the density of the document before exposing the document image to the photoconductor. This concentration background density of the document on the basis of the detection signal developing bias voltage V _B relative to the background density on the basis of the same are detected and corrected (automatic background density adjustment: ADS). Automatic background density adjustment (ADS) is, for example, 12 mm from the leading edge of the original with the original density sensor 14 at the same magnification.
From the start, the range up to a distance of 50 mm is detected by the movement of the carriage, and the voltage Vo _D (ADS data value) based on the light amount detected most (the cleanest background portion of the original) is detected. a developing bias voltage V _B is corrected as shown in FIG. 5b, thereby obtaining a clean copy of the background area (at this time, the exposure lamp voltage V _L is fixed). For example the development bias voltage V _B If the original reflection density of 0.2 is set to 380V.

In addition, one reference white plate 16 (reflection density = 0.2) is disposed in front of the contact glass 1. Reference white plate 1
6 and for the voltage correction of the exposure lamp 31 to be described later, for signal level calibration of the original density sensor (ADS reference data value Vo _D1 setting) is shared use.

FIG. 2 schematically shows an electric circuit configuration of the copying apparatus shown in FIG. The main control board 100 includes a CPU 110, a RAM 120, and a clock 130. The RAM 120 and the clock 130 are always backed up by a battery, and the clock 130 keeps measuring time even while the copier power is off, and the RAM 120 retains memory data.

The main control board 100 includes an exposure lamp voltage controller 210, A
GC circuit 220, A / D converter 230, developing bias power supply 240, scanner drive controller 250, other inputs 260 and outputs 2
70 is installed.

The exposure lamp voltage controller 210 sets the applied voltage V _L (exposure lamp voltage) of the exposure lamp 31 to a value specified by the main control board 100.

The AGC circuit 220 is a circuit that amplifies the detection signal of the document density sensor 14, but has a built-in gain adjustment circuit, and the amplification gain is adjustable. As will be described later, when calibrating the density detection signal level of the document density sensor (light receiving element 225 + AGC circuit 220), the carriage is moved to the light receiving end as shown in FIG. 4b.
14 is driven to a position for receiving the reflected light of the reference white plate 16, whereby the light receiving element 225 generates an electronic signal of a level corresponding to the level of the reflected light of the reference white plate 16, and the AGC circuit 220
Output signal level Vo _D1 is the reference voltage (ADS reference data value)
The gain of the AGC circuit 220 is set to 2.0 V. When scanning an image to obtain a copy of an original, the AGC circuit 2
The gain of 20 is fixed at the set value.

The P sensor 6 detects the toner density on the photosensitive drum 2, and the A / D converter 230 outputs the output voltage Vsp of the P sensor 6 as a digital signal (toner density data on the photosensitive drum 2).
Convert to

Developing bias power supply 240, defined in the developing bias voltage V _B that the main control board 100 instructs.

The scanner drive control device 250 controls the drive of the first and second carriages.

3a and 3b show the main control board shown in FIG.
The outline of the control operation of 100 CPUs 110 is shown.

When the power is turned on (Step 1: hereinafter, the word “step” is omitted in parentheses), the CPU 110 performs initialization to clear internal registers, flags, and the like (2). CP
U110 is then powered by a battery-backed watch 13
Read the timekeeping data of 0, and 2
It is checked whether or not the time has elapsed (3). The reason for this is that the sensitivity characteristic of the photoconductor 2 depends on the downtime and is stabilized at a downtime of 2 hours or more, and that the
The correction of the exposure lamp voltage _VL for the sensitivity correction should not be performed many times during one day, but once every day is sufficient, and it is efficient to perform it after turning on the power.

If the power-off time of the copying machine is 2 hours or more in step 3, the exposure lamp voltage _VL written in the RAM 120 backed up by the battery is called (4), and the exposure lamp voltage control is performed based on the data. The apparatus 210 is driven to turn on the exposure lamp 31 (5).

Next, as shown in FIG. 4a, the carriage is driven to a position where the light projected on the photosensitive drum 2 becomes the reflected light of the reference white plate 16. Then, the reference white plate 16 is projected onto the photosensitive drum 2 via the optical scanning system 30 to form an electrostatic latent image thereof, and the "image forming process" (7) is performed in the same manner as when copying a document. When the "image forming process" (7) is executed and the electrostatic latent image on the reference white plate 16 is developed, the density is read by the P sensor 6 (8).

Here, the relationship among the data Vsp read by the P sensor 6, the photoconductor surface potential Vs, and the exposure lamp voltage _VL has the characteristics shown in FIG. 5A. For example, the relationship between the initial state (when newly installed in the copying machine) When the approximate exposure lamp voltage V _L = 60 V, the surface potential Vs = 200 V, Vsp = 2.0 V (when the reflection density of the reference white plate 16 = 0.2) is applied to the photosensitive drum 2 Since the sensitivity or the light amount of the exposure lamp 31 deteriorates with time, the surface potential Vs increases with time, and a copy in which a so-called background stain appears appears.

To automatically prevent this background stain, the exposure lamp voltage _VL is adjusted so that Vsp falls within a predetermined range (1.9 to 2.1 V). That is, it is checked whether Vsp is in the range of 1.9 to 2.1 V (9), and if not, it is checked whether Vsp is smaller than 1.9 V (10). In this case, the exposure lamp voltage _VL is updated by 1V higher (11), and when Vsp is higher than 2.1V, _VL is updated lower by 0.5V (12). Then, the flag F indicating that the exposure lamp voltage _VL has been corrected is set to 1 (the flag F has been cleared in the initialization (2)) (13), and the above-mentioned "image forming process" ( 7) is carried out, Vsp is read, and it is checked again whether it is in the range of 1.9 to 2.1 V (8, 9). Then, if it falls within the range, a loop consisting of steps 10 → 11 (or 12) → 13 → 7 → 8 → 9 → 10... Is repeated until Vsp falls within the range of 1.9 to 2.1V.

As described above, when Vsp is within the predetermined range, or
When the value falls within the predetermined range, it is checked whether the flag F is set to 1 (14). When the exposure lamp voltage _VL is updated, the flag F is set to 1 (1
3) Write the exposure lamp voltage _VL at this time to RAM 120 (1
5) When this is completed, the "image forming process" for adjusting the lamp voltage is completed (16).

Note that the correction value in step 12 is 0.5 V (step 11
Is 1/2 of the correction value of 1V when Vsp is 1.9V, for example.
When the correction in step 11 is continued when the value is smaller than the above, since the exposure lamp voltage _VL is added by 1 V at a time, Vsp is 1.9 to 2.1 V
May be outside the range, and this is to prevent this.

As described above, when the exposure lamp voltage _VL changes due to the adjustment of the exposure lamp voltage _VL , the original density sensor (the light receiving element 225 + A
The GC circuit 220), the density detection signal level relationship to the light receiving level is changed, the correction of the developing bias voltage V _B in accordance with an original reflection density shown in FIG. 5b is no longer appropriate. Therefore, the relationship between the light reception level and the density detection signal level is calibrated.

That is, first, as shown in FIG. 4b, the carriage is driven to a position (ADS correction position) at which the light receiving end 14 (light receiving element 225) detects the reflected light of the reference white plate 16 (17). Then, the light-receiving element 225 detects and amplifies it with the AGC circuit 225, and the CPU 110 converts the digitally-converted and read-in density detection data Vo _D1 to a reference value of 2.0 V (18). If the value is less than the allowable value, the gain of the AGC circuit 220 is updated by one step,
2.0V + If it exceeds the permissible value, it will be updated one step lower, and the detection signal of the light receiving element 225 will be converted to digital and read,
o Check that _D1 is within 2.0 ± tolerance. In this way, the gain of the AGC circuit 220 is
Update Vo _D1 to a value within the range of 2.0V ± allowable value.

That is, when the exposure lamp voltage _VL is changed, the light receiving level of the light receiving element 225 is changed even if the original density is the same, and the developing bias voltage control is disturbed. Therefore, the gain is adjusted to compensate for this. Thus, even if the exposure lamp voltage _VL is adjusted, the developing bias voltage characteristic shown in FIG. 5b is maintained.

Next, the exposure lamp 31 is turned off (20), and the scanner is returned to the copy preparation position (home position) (21). After that, it waits until the copy operation is enabled (22), and when the copy operation is enabled and a copy start instruction is issued (23), the automatic background density adjustment (ADS) described above is performed so that a clear copy of the background can be obtained for the document. I do. That is, the developing bias voltage from the ADS data Vo _D obtained from the document of the reflected light
The V _B set from the relation of FIG. 5b performs normal copying operation to copy end (24, 25).

In step 3, when the power-off time is less than 2 hours, or when the exposure lamp voltage _VL is not changed even if it is 2 hours or more (14), the gain of the AGC circuit 220 is adjusted (19). ) Is not performed.

In the above embodiment, the carriage position for adjusting the lamp voltage (FIG. 4a) and the carriage position for calibrating the detection signal level of the document density sensors (225, 220) (FIG. 4b)
Is different. This is to shorten the required movement area of the carriage. If this area can be slightly widened, the carriage position for lamp voltage adjustment (Fig. 4a)
In this embodiment, the reference white plate 16 is preferably arranged up to the position where the light receiving end 14 faces. In this case, when the lamp voltage adjustment is completed, the calibration of the detection signal level of the document density sensors (225, 220) can be started immediately without driving the carriage (to the position shown in FIG. 4b).

〔The invention's effect〕

As described above, according to the present invention, the second control means (100)
Is an image forming apparatus that forms a toner image on one reference density surface (16) on the photoreceptor (2) so that the density of the toner image detected by the second detecting means (6,230) falls within the reference range. Since the applied voltage (V _L ) of the illumination light source (31) is corrected,
The aforementioned background contamination due to a change in the characteristics of the copying function element such as deterioration of the photoconductor or the exposure lamp is prevented or suppressed.

Due to the correction of the applied voltage (V _L ) of the illumination light source (31), the level of the density signal (Vo _D1 ) of the first detection means (220, 225) shifts even if the original has the same background density. ) Is the reference density surface (1) illuminated by the illumination light source (31).
The reflected light of 6) is detected by the first detecting means (220, 225), and the density of the first detecting means (220, 225) with respect to the received light level is adjusted so that the level indicated by the density signal (Vo _D1 ) becomes the reference value (2.0). Since the signal level relationship is corrected, the illumination light source (3
Regardless of the change in the amount of emitted light in 1), the first detecting means (22
0,225) is indicated by the level indicated by the density signal (Vo _D1 ) (2.
0), and the control of the developing bias voltage of the developing means (5) according to the density signal by the first control means (100) does not show background stain on the copy despite the fact that the background of the original is stained. Becomes

As a result, at the same time as the background contamination on the copy due to deterioration or contamination of the photoreceptor or the exposure lamp is prevented or suppressed,
Background dirt on a copy due to the color or dirt of the original background is prevented or suppressed.

Since the voltage adjustment of the exposure lamp (31) and the detection characteristics of the original density sensors (225, 220) corresponding to the adjustment of the voltage of the exposure lamp (31) are performed based on the reflection density of one reference original surface (16), the number of additional patterns (16) is small. I can do it.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a mechanism configuration of an embodiment of the present invention. FIG. 2 is a block diagram showing a schematic configuration of an electric system of the copying machine shown in FIG. FIGS. 3a and 3b are flowcharts showing the control operation of the microcomputer 110 shown in FIG. FIG. 4a is an enlarged cross-sectional view showing the position of the carriage on which the exposure lamp 31 is mounted when the microcomputer 110 adjusts the exposure lamp voltage. FIG. 4b is an enlarged cross-sectional view showing the position of the carriage on which the exposure lamp 31 is mounted when the microcomputer 110 calibrates the relationship between the light receiving level of the document density sensor (225, 220) and the detection signal level. FIG. 5a is a graph showing the relationship between the voltage applied to the exposure lamp 31 and the density detection voltage Vsp of the toner image on the first reference white plate 16a formed on the photosensitive drum 2 by the exposure lamp 31. FIG. 5B is a graph showing the relationship between the reflection density of the background of the document and the corresponding development bias voltage applied to the development cartridge 5. 1: Contact glass, 2: Photoconductor drum (Photoconductor) 3: Main charger (Charging means) 4: Eraser, 5: Developing cartridge (Developing means) 6: P sensor (6,230: Second detecting means) 7: Transfer Charger, 8: Separate charger 12: Fixer, 13: Reflector 13a: Slit, 14: Light receiving end 15: Optical fiber, 16: Reference white plate (reference density surface) 21 to 24: Paper feed cassette, 25: Paper feed Tray 27: Registration roller, 30: Optical scanning system (optical means) 31: Exposure lamp (illumination light source), 32, 33, 34: Mirror 35: Lens, 60: Automatic document feeder 70: Sorter, 80: Automatic duplex Processing device 100: main control board (first control means, second control means, third control means)
Control means) 110: CPU, 120: RAM 130: Clock, 170, 180: Paper feed unit 210: Exposure lamp voltage controller 220: AGC circuit, 225: Light receiving element (220, 225: First detection means) 230: A / D converter , 240: Development bias power supply 250: Scanner drive controller

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G03G 15/00 303 G03G 15/04-15/04 120 G03G 21/00 370-520 G03G 21/14

Claims (1)

(57) [Claims] 1. A photosensitive member, means for uniformly charging the photosensitive member, an illumination light source for illuminating a document, and an optical device for exposing the photosensitive member with reflected light of the document to form an electrostatic latent image corresponding to a document image on the photosensitive member. means,
Developing means for developing the electrostatic latent image with toner, first detecting means for detecting a background density of a document illuminated by an illumination light source and generating a density signal indicating the density, and developing means for developing means in response to the density signal An image forming apparatus including: a first control unit that controls a developing bias voltage; a second detecting unit that detects a density of a toner image on a photoconductor; one reference density surface outside a document area; A second control unit for forming a toner image on a reference density surface on the photoconductor, and correcting an applied voltage of the illumination light source such that a density of the toner image detected by the second detection unit is within a reference range; and When the second control means corrects the applied voltage of the illumination light source, the reflected light of the reference density surface illuminated by the illumination light source is detected by the first detection means, and the level indicated by the density signal becomes a reference value. The first detecting means, A third control means for correcting the relationship between the light receiving level and the density signal level;