JPH08297384A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of exactly performing toner sticking amount control from the halftone to the solid. CONSTITUTION: This is an image forming device performing the image forming by making the toner stick on the image carrier 1. The image carrier 1 is provided thereon, with a patch forming means for forming the test solid patch and the test halftone patch, and an image density detection means 15 for detecting the image density of the test solid patch and the test halftone patch formed by the patch forming means. The device is constituted so that firstly the control of the solid density is performed by controlling circumferential speed ratio of the developer carrier 13 based on the image density detection by the test flat patch, and secondly the control of the half tone density is performed by controlling laser power based on the image density detection by the test half tone patch.

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.

[0002]

2. Description of the Related Art FIG. 12 is a conceptual diagram of the structure of an image forming apparatus. In the figure, 1 is a photoconductor drum which is an image carrier,
The drum is coated with an OPC photoconductor, which is grounded in terms of electric potential and is driven and rotated by a main motor (not shown) in a clockwise direction (arrow direction in the drawing). 2 is a charger,
The peripheral surface of the photosensitive drum 1 is uniformly charged with the potential VH by the corona discharge by the grid held at the potential VG and the corona discharge wire. Prior to the charging by the charging device 2, an exposure device using a light emitting diode or the like (for example, P
CL) 3 is used to remove the charge from the peripheral surface of the photoconductor.

After the photosensitive member 1 is uniformly charged, the laser optical system 4 performs image exposure based on an image signal. The laser optical system 4 uses a laser diode (not shown) as a light emitting source, and performs scanning by bending the optical path by a reflecting mirror 5 through a rotating polygon mirror, fθ lens, etc., and by rotating the photosensitive drum 1 (sub scanning). An electrostatic latent image is formed. Here, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential VL.

A developing device 1 in which a two-component developer composed of toner and carrier is built in the periphery of the photosensitive drum 1
0 is provided, and the development is performed by a developing sleeve (not shown) that has a magnet built therein and holds the developer and rotates. The developer is a carrier in which a metal oxide is used as a core and an insulating resin is coated around the core, and a pigment is a polymer as a main material and a charge control agent, silica,
The developer is composed of toner to which titanium oxide or the like is added. The developer is regulated by the layer forming means to have a certain layer thickness (developer) of about several hundred μm and is conveyed to the developing area.

The gap between the developing sleeve and the photosensitive drum 1 in the developing area is 0.2 mm, which is larger than the layer thickness (developer).
.About.1.0 mm, during which the AC bias of the voltage value VAC and the DC bias of the voltage value VDC are superimposed and applied. 11 is an AC power supply that gives an AC bias voltage value VAC,
Reference numeral 12 is a DC power supply that gives a DC bias voltage value. V
Since DC and VH and the toner are charged with the same polarity, the toner that is triggered by VAC to leave the carrier is
It does not adhere to the portion of VH having a potential higher than VDC, but adheres to the portion of VL having a potential lower than VDC, and visualization (reversal development) is performed.

On the other hand, the recording paper P carried out from the paper feed cassette 6 is temporarily stopped and is fed to the transfer area when the transfer timing is adjusted. In the transfer area, the transfer unit 7 transfers the toner image formed on the surface of the photosensitive drum 1. Then, the recording paper P is discharged at almost the same time by a separating brush (not shown) that is brought into a pressure contact state, separated by the peripheral surface of the photosensitive drum 1, and conveyed to the fixing unit 8.
After the toner is fused by heating and pressurizing the heat roller and the fixing roller (not shown), the toner is discharged to the outside of the apparatus through the paper discharge roller.

On the other hand, the photosensitive drum 1 from which the recording paper P is separated
Removes and cleans the residual toner by pressing the cleaning blade 9 and again receives the charge removal by the exposure device 3 and the charge by the charging device 2, and the next image forming process starts. The cleaning blade 9 moves immediately after cleaning the surface of the photoconductor and retracts from the peripheral surface of the photoconductor drum 1.

Although the case of forming a monochrome image with one developing device 10 has been described above, a plurality of developing devices 10 may be provided to form a color image. In that case, the developing device 10 is set to Y (yellow), M (magenta),
By providing four C (cyan) and BK (black) toner images of four types on the photosensitive drum 1 and transferring them onto the recording paper P, a color image can be formed.

[0009]

In the above-mentioned image forming apparatus, a reference patch for controlling the image density of the photosensitive drum 1 is provided, the reference patch is read by the detection sensor, and the toner is read according to the read output. Generally, process control is performed to control the supply amount or laser power. The process control system, which reads the output of the reference patch with a detection sensor and controls the image forming conditions (for example, the developing sleeve rotation speed and laser power), is not only accurate in terms of operation accuracy but also the image density of the electrophotographic process (charging and exposure). -It is generally difficult to perform optimum control because it changes under the influence of variable factors such as development, transfer, and fixing. The reason is that, as described above, the materials and machines change moment by moment due to changes in the electrophotographic process, usage environment, number of prints, and the like. The effect of this process variation is particularly great for halftone images.

Therefore, in order to control the density of a halftone image, the applicant has developed a technique of first adjusting the image density of a solid patch, and then performing the halftone density control (Japanese Patent Application No. Hei.
No. 14211). The outline is as follows. First, after the solid density is properly adjusted, a Bayer type eighth gradation halftone patch is formed, and the image density is read by the image density detecting means, and the charging potential VH of the photosensitive drum is read.
Is gradually changed to bring VH to a predetermined voltage. After that, the laser power is controlled so that the output of the image density detecting means becomes a predetermined value when VH becomes a predetermined voltage.

However, this halftone density control method has a problem that the output method of the halftone patch is quite complicated and it takes time to output the test patch. The present invention has been made in view of such problems,
An object of the present invention is to provide an image forming apparatus capable of accurately controlling the amount of adhered toner from halftone to solid.

[0012]

SUMMARY OF THE INVENTION The present invention, which solves the above-mentioned problems, provides an image forming apparatus for forming an image by adhering toner onto an image carrier, and a test solid patch and a test intermediate on the image carrier. A patch forming means for forming a tonal patch, and a toner adhesion amount detecting means for detecting a toner adhesion amount of the test solid patch and the test halftone patch formed by the patch forming means. The feature is that the peripheral speed ratio of the developer carrier is controlled by density detection to control solid density, and then the laser power is controlled by image density detection by a test halftone patch to control halftone density. I am trying.

In this case, the patch forming means performs PW on the fourth step of the Bayer type of systematic dither.
It is preferable to output at M = 50% in order to appropriately control the halftone image density.

Further, it is preferable that the patch forming means outputs the second step of the Bayer type of systematic dither at PWM = 100% for stable halftone image density control.

[0015]

First, the peripheral speed ratio of the developer carrying member is controlled by the image density detection by the test solid patch to control the solid density, and then the laser power is controlled by the image density detection by the test halftone patch. The halftone density is controlled. As a result, it is possible to accurately control the image density from halftone to solid.

In this case, the patch forming means performs PW on the fourth step of the Bayer type of systematic dither.
By outputting at M = 50%, halftone image density control can be appropriately performed.

Further, the patch forming means outputs the second step of the Bayer type of systematic dither at PWM = 100%, so that the halftone image density control can be stably performed.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. The same parts as those in FIG. 12 are designated by the same reference numerals. In the figure, 13 is a developing sleeve provided in the developing device 10, and 15 is a photosensitive drum 1 as an image carrier.
It is a detection sensor that detects the amount of the toner image formed above. As the detection sensor, for example, L as a light emitting element is used.
A pair of ED and a phototransistor as a light receiving element is used.

FIG. 2 is a view showing an arrangement example of the detection sensor 15. As shown in the figure, the detection sensor 15 includes a light emitting diode (LED) 15a as a light emitting element and a phototransistor 15b as a light receiving element. In the figure, the light emitted from the LED 15a is incident on the photosensitive drum surface 1a at an angle of 40 ° with respect to a vertical line (shown by a broken line), and the reflected optical signal is arranged in a direction of 40 ° with respect to the vertical line. The light is received at 15b. LED15a
Alternatively, the distance from the phototransistor 15b to the light incident surface on the surface of the photosensitive drum is set to 6 mm here.

FIG. 3 is a diagram showing an example of the circuit configuration of the detection sensor 15. On the light emitting side, the voltage VLE is applied to one end of the LED 15a.
It is connected to D (adjusted between 5V and 20V), and the other end is grounded via a resistor R1 of 1 kΩ. On the light receiving side, the collector of the phototransistor 15b is connected to the voltage Vcc of 5V and the emitters of the resistors R2 and 6 of 36 kΩ.
It is connected to a series circuit of a resistor R3 of 8 kΩ. The other end of the resistor series circuit is grounded. And the output Vout
Is taken out from the connection point of the resistors R2 and R3.

In the circuit thus constructed, LE
The light emitted from D15a is incident on the photosensitive drum surface 1a. Then, reflected light according to the image density is reflected from the surface 1a of the photosensitive drum, and when the reflected light is applied to the base portion of the phototransistor 15b, the phototransistor 15b is turned on. The greater the reflected light,
The output Vout on the light receiving side becomes large. As a result, the image density on the surface 1a of the photosensitive drum can be detected.

Reference numeral 20 is a control unit for controlling the overall operation (image forming conditions) according to the density detected by the detection sensor 15. In the control unit 20, a table storage unit 21 stores a table indicating the relationship between the toner adhesion amount and the detection output, the relationship between the toner adhesion amount and the peripheral speed ratio, and the relationship between the image density and the detection output for each color (details). It will be described later).

The other parts are the same as in FIG. FIG.
The preferred operating conditions of the device shown in FIG. 2 are: the charging potential VH of the photosensitive drum surface = -750 V, the DC bias potential VDC =-
650 V, AC bias potential VAC = 1.7 kVpp (frequency 8 kHz), developer transport amount is 20 to 30 mg / cm
^{2. The} image writing potential is -30 to -40V (PWM = 1.
At 00%), -50V to -60V (PWM = 50%)
Image carrier line speed 100 mm / sec, developing sleeve line speed 180 to 480 mm / se
c (70 mm / sec when creating a solid test patch). The operation of the apparatus thus configured will be described below with reference to the flowchart of FIG.

(S1) Adjustment of Photoreceptor and Developer First, by detecting the magnetic permeability of the magnetic developer, the toner density ratio (toner and toner The carrier ratio) is set to a predetermined concentration. On the side of the photoconductor drum 1, the grid voltage of the charger 2 is adjusted according to the development environment, the charging potential VH of the photoconductor drum 1 is initialized, and the laser power (LD power) of the laser optical system 4 is initialized. Set.

(S2) Control start by patch detection Since the control of the photosensitive drum 1 and the developer is completed in the process of step S1, the control section 20 starts the control by patch detection.

(S3) Baseline Correction In a state where toner is not attached to the photoconductor drum 1, the photoconductor drum 1 is rotated, the output from the detection sensor 15 is read, and the present photoconductor drum in which toner is not attached The output from 1 is adjusted to a certain level.
Specifically, the voltage VLED applied to the LED 15a of the detection sensor 15 is changed to adjust the light amount of the LED 15a so that the output level (Vout) of the phototransistor 15b, which is the detection sensor output, is 0.4 ± 0.008V. Adjust (± 2% accuracy).

(S4) Solid Patch Detection Solid density control is performed by test solid patch detection. In this case, it is necessary to reduce the number of rotations of the developing sleeve 13 as compared with the normal image recording operation so that the output of the detection sensor 15 enters the stable detection area. FIG. 5 is a diagram showing the relationship between the output (detection signal value) of the detection sensor 15 and the toner adhesion amount. The vertical axis represents the detection signal value (V), and the horizontal axis represents the toner adhesion amount (m
g / cm ² ). When the toner does not adhere to the photosensitive drum 1, the amount of light received by the phototransistor 15b becomes maximum and the detection signal also becomes maximum. Then, as the toner adheres, the amount of light received by the phototransistor 15b also decreases, and the detection signal value thereof gradually decreases as shown in FIG.

By the way, in the region where the amount of toner adhered is small, the amount of light received by the phototransistor 15b varies due to a slight increase or decrease in the amount of adhered toner. Become. Further, since the amount of light received by the phototransistor 15b does not change even if the toner adhesion amount increases after the toner covers the photoconductor drum 1, the detection signal value reaches the lower limit and becomes saturated. Such a variation region and a saturation region are unstable regions, and stable output cannot be obtained with respect to the toner adhesion amount.

The toner adhesion amount at the upper limit of the detection signal value is 0.1 mg / cm ² , and the toner adhesion amount at the lower limit thereof is 0.
Since it can be seen that the amount is 4 mg / cm ² , the region where the toner adhesion amount is 0.2 to 0.3 mm / cm ² is the region where the output of the detection sensor 15 is stable. In this embodiment, the peripheral speed ratio of the developing sleeve 13 to the photosensitive drum 1 (vs /
A suitable value of vp) is 0.7, and the toner adhesion amount at this time was 0.2 mm / cm ² . The characteristics of FIG. 5 are stored in the table storage unit 21.

Therefore, the control unit 20 rotates the developing sleeve 13 at a peripheral speed ratio of 0.7 to form a test solid patch on the photosensitive drum 1. Then, the detection sensor 15 detects the density of the test solid patch. The control unit 20 receives the output of the detection sensor 15 and refers to the table storage unit 21,
The toner adhesion amount corresponding to the detection signal value is obtained from the characteristic curve of FIG. Next, when the toner adhesion amount is obtained, the patch image toner adhesion amount when the peripheral speed ratio is the same is used as a reference toner adhesion amount, and the toner adhesion amount when the peripheral speed ratio is changed is estimated by a predetermined arithmetic expression. The estimated characteristic curve is stored in the table storage unit 21. FIG. 6 is a diagram showing the relationship between the toner adhesion amount and the peripheral speed ratio thus obtained. The vertical axis represents the toner adhesion amount (mg / cm ² ), and the horizontal axis represents the peripheral speed ratio (vs / v).
p).

(S5) Solid adhesion amount control (peripheral speed ratio adjustment) Since the characteristics shown in FIG. 6 are obtained in step S4,
If the solid adhesion amount in the actual operation is determined, the peripheral speed ratio corresponding to it can be determined from the characteristics of FIG. For example, if the ideal value of the toner adhesion amount is 0.66 mg / cm ² , the toner adhesion amount of 0.66 mg is obtained from the characteristic curve of FIG.
The peripheral speed ratio Q1 corresponding to / cm ² is the optimum peripheral speed ratio.
According to the solid density control described above, the characteristics of FIG. 6 can be obtained even if the toner adhesion amount varies at the peripheral speed ratio of 0.7 due to the variation of the image forming process, etc. It is possible to determine the peripheral speed ratio required to obtain the desired toner adhesion amount in. With the above steps, the optimum density control of the solid image is completed.

(S6) Halftone Patch Detection The developing sleeve 13 is rotated at the peripheral speed ratio Q1 determined by the processing up to step S5, and the density control is performed by the halftone patch detection in the actual operating state. In this embodiment, a Bayer type dither matrix is used to form the test halftone patch, and the test halftone patch is formed using the fourth gradation pattern of PWM = 50%. For example, 4
Using a Bayer type dither matrix of × 4 (400 dpi), the pattern of the fourth gradation is output at PWM = 50%. FIG. 7 is a diagram showing the relationship between the gradation and the detection output of the detection sensor 15. The vertical axis represents detection output, and the horizontal axis represents gradation.
When the Bayer type threshold matrix is used, as shown in FIG. 7, the change in the detection output with respect to the gradation change is large up to around 10 gradations, which is convenient for matching the gradation of the halftone patch image. It can be seen that although the value is slightly different depending on the value of the charging potential VH of the photosensitive drum 1, it has the same characteristics.

Here, the detection output in the case of halftone density control will be defined. The detection output is the detection sensor 15
Is defined as V2 / V1 where V1 is the average output value of the baseline part and V2 is the average output value of the halftone patch part.
In general, as shown in FIG. 8, the baseline output average value V1 is larger than the halftone patch output average value V2, so the detection output becomes a value smaller than 1. In FIG. 8, the vertical axis represents the output of the detection sensor 15, and the horizontal axis represents the distance.

After forming the test halftone patch using the fourth gradation pattern of PWM = 50%, the detection sensor 15
The density (V2) of the halftone patch portion and the density (V1) of its peripheral portion are detected. The control unit 20 uses the detection sensor 1
Upon receiving the output of 5, the detection output V2 / V1 is obtained. Next, the control unit 20 obtains the corresponding image density from the obtained detection output. FIG. 9 is a diagram showing the relationship between the detection output and the image density when a halftone patch is formed using a fourth gradation pattern of PWM = 50% using a Bayer type threshold matrix. The vertical axis represents detection output and the horizontal axis represents image density. (A) shows the characteristics in the case of black (BK), (b)
Indicates the characteristics in the case of yellow (YELLOW). Since the characteristics of cyan (C) and magenta (M) are almost the same as those of black, the characteristic curve is omitted. It is assumed that the characteristics shown in this figure are stored in advance in the table storage unit 21. The image density corresponding to the detection output can be obtained from these characteristic curves. In addition,
In actual use, the envelope without the data can be interpolated by using the envelope showing the overall tendency as shown in (b). In the case of a slightly discontinuous characteristic as shown in (a), the respective data may be stored and the portion without the data may be interpolated by linear approximation.

(S7) Halftone Image Density Control (LD Power Adjustment) Since the image density of the halftone patch is obtained in step S6, the optimum laser diode (LD) is obtained from this image density.
Adjust the power of. There is a certain relationship between the image density and the laser power as shown in FIG. In the figure, the vertical axis represents image density and the horizontal axis represents laser power.
Now, let it be assumed that the image density obtained in step S6 is a point marked with X in the figure. If a straight line is drawn from the point marked with X to the origin, a characteristic straight line showing the relationship between the image density and the laser power can be obtained immediately. Therefore, if the ideal image density is N1, the laser power P1 corresponding to this N1 can be obtained. If the laser optical system 4 is driven by the obtained laser power P1,
The halftone image density control can be appropriately performed. The image density adjustment described above needs to be performed for each of Y, M, C, and BK.

In the above embodiment, the pattern of the fourth gradation of PWM = 50% is used as the test halftone patch to perform the halftone density control. If the halftone patch is controlled with PWM = 50%, the formation of the test halftone patch may become unstable in some cases. In this case, the second step of the Bayer type of systematic dither is PWM = 100%
It is also possible to form a test halftone patch by outputting at. At this time, the gradation of the formed halftone patch is almost the same as that in the case of outputting the pattern of the fourth gradation with PWM = 50%.

At this time, the diagram showing the relationship between the detection output and the image density used is shown in FIG. (A)
Shows the characteristics in the case of black (BK), and (b) shows the characteristics in the case of yellow (YELLOW). In addition,
The characteristics of cyan (C) and magenta (M) are almost the same as those of black (BK), as described above. Therefore, when controlling the halftone image density of the toner, the black (BK) characteristic shown in (a) can be substituted for the cyan (C) and magenta (M) characteristics.

By outputting the second step of the Bayer type of systematic dither at PWM = 100% to form a halftone patch, the laser power can be stably held,
A stable halftone patch can be obtained, and halftone image density control can be performed stably.

[0039]

As described in detail above, according to the present invention, first, the solid density is controlled by controlling the peripheral speed ratio of the developer carrying member by detecting the image density by the test solid patch. Further, by controlling the laser power by detecting the image density by the test halftone patch to control the halftone density, it is possible to accurately control the toner adhesion amount from halftone to solid.

In this case, the patch forming means PWs the fourth step of the Bayer type of systematic dither.
By outputting at M = 50%, halftone image density control can be appropriately performed.

Further, the patch forming means outputs the second step of the Bayer type of systematic dither at PWM = 100%, so that the halftone image density control can be stably performed.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating an arrangement example of detection sensors.

FIG. 3 is a diagram illustrating a circuit configuration example of a detection sensor.

FIG. 4 is a flowchart showing the operation of the present invention.

FIG. 5 is a diagram showing a relationship between a detection signal value and a toner adhesion amount.

FIG. 6 is a diagram showing a relationship between a toner adhesion amount and a peripheral speed ratio.

FIG. 7 is a diagram showing a relationship between gradation and detection output.

FIG. 8 is a diagram showing a relationship between a baseline output and a halftone patch output.

FIG. 9 is a diagram showing a relationship between detection output and image density.

FIG. 10 is a diagram showing the relationship between halftone image density and laser power.

FIG. 11 is a diagram showing a relationship between detection output and image density.

FIG. 12 is a conceptual diagram of a configuration of an image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charging device 3 Exposure device 4 Laser optical system 5 Mirror 6 Paper cassette 7 Transfer part 8 Fixing part 9 Cleaning blade 10 Developing device 11 AC voltage source 12 DC voltage source 13 Developing sleeve 15 Detection sensor 20 Control part 21 Table storage

Claims (3)

[Claims] 1. An image forming apparatus for forming an image by attaching toner to an image carrier, the patch forming unit forming a test solid patch and a test halftone patch on the image carrier, and the patch forming unit. The image density detecting means for detecting the image density of the test solid patch formed by the above method and the test halftone patch are provided. First, the solid speed is controlled by controlling the peripheral speed ratio of the developer carrier by the image density detection by the test solid patch. An image forming apparatus characterized in that the density is controlled, and then the laser power is controlled by detecting the image density by a test halftone patch to control the halftone density. 2. The image forming apparatus according to claim 1, wherein the patch forming unit outputs the Bayer type fourth step of systematic dither at PWM = 50%. 3. The image forming apparatus according to claim 1, wherein the patch forming unit outputs the Bayer type second step of systematic dither at PWM = 100%.