JP3309306B2 - Digital image forming equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital image forming apparatus using an electrophotographic process such as a copying machine or a printer, and more particularly, to controlling the amount of toner adhered to an image carrier to improve the stability of color and density. It relates to the technology to be improved.

[0002]

2. Description of the Related Art In recent years, digital and reversal image forming apparatuses have been put into practical use. For example, a color electrophotographic copying machine and a color recording apparatus constituting an output section of a personal computer, a facsimile or the like are known. In such an image forming apparatus, it is necessary to perform an adjustment operation in order to obtain a recorded image with good reproducibility even during continuous operation, but this adjustment operation is complicated and complicated. Had. In order to solve this problem, an image density control technique using a patch detection method is currently employed.

[0003] Japanese Patent Application Laid-Open No. 63-113568 discloses this patch detection technique. That is, in this apparatus, before forming a digital image, a gradation density pattern for each color is formed on a photoreceptor, and a correction amount is obtained by measuring the pattern density by a detection sensor to form a digital image. At this time, the density adjustment process is performed by variably controlling the exposure amount of a laser beam or the like based on the correction amount.

However, in such a technique, the types and quantity of the measurement data of the gradation density pattern for each color become enormous, the program relating to the adjustment processing becomes complicated, the correction data to be prepared increases, and the design cost becomes too enormous. Therefore, a technique has been developed in which a control coefficient is read from a memory and the number of revolutions of the developing sleeve is feedback-controlled at a variable speed so as to control the amount of toner adhesion in accordance with the fluctuation of the detected density data value. (Japanese Patent Application No. 6-189
No. 211).

Further, in this apparatus, when the amount of toner is small, the detection signal value of the patch image fluctuates due to a slight increase or decrease in the amount of toner adhesion, and when the toner covers the photosensitive member 1, the detection signal value increases even if the amount of toner adhesion increases. Because the value does not change,
The number of rotations of the developing sleeve is reduced to one third of that in the image recording mode so that the amount of the detection signal falls within the stable area excluding the unstable area, and the amount of toner adhered to the color patch image on the photoconductor is reduced by one. / 3 to detect the color patch image,
After accurately setting the toner adhesion amount, the toner adhesion amount at the time of forming a print image is predicted based on FIG. 10, and the rotation number of the developing sleeve is controlled.

[0006]

In the conventional image forming apparatus, various problems occur due to environmental changes during image formation. First, the relationship between the number of rotations of the developing sleeve (transport speed) and the amount of adhered toner is known. In a conventional image forming apparatus, as shown in FIG. Is approximated by a straight line, but if the environment during image formation changes, such as temperature, humidity, and aging of the photoconductor, the relationship between the toner adhesion amount and the sleeve rotation speed also changes. In addition, the relationship between the rotation speed of the developing sleeve and the amount of adhered toner may not be linear due to the influence of the characteristics of the toner.

Next, regarding the adjustment of the detection signal of the detection sensor, usually, in order to accurately detect the signal output of the patch image, the photosensitive drum is idled before detecting the patch image. Baseline correction for adjusting the detection signal of the detection sensor is performed. However, when the photoconductor drum is used for a long time, the surface state of the photoconductor drum changes due to stains or scratches on the surface. When the surface state changes, the detection signal of the detection sensor fluctuates greatly, making this adjustment difficult, and in order to obtain a good image signal output,
Baseline correction takes time.

The present invention has been made in view of such conventional problems, and has as its object to provide a digital image forming apparatus capable of obtaining appropriate image forming conditions in response to various environmental changes. I do.

[0009]

Therefore, in the digital image forming apparatus according to the present invention, as shown in FIG. 1, a detecting means for outputting a patch image on an image carrier and performing photoelectric conversion is used. Optically detects the image on the image carrier, and variably sets a peripheral speed ratio of the developer transport carrier to the image carrier based on a signal output value of the detection means so that appropriate image forming conditions can be obtained. In a digital image forming apparatus, before forming a digital image, a signal output value of a patch image forming means for setting a peripheral speed ratio to form a patch image on an image carrier, and a detecting means for detecting a patch image is used. A patch image toner adhesion amount calculating means for inputting and calculating a toner adhesion amount on the patch image based on the signal output value; and a bias voltage and an image on the surface of the developer carrying carrier based on the patch image toner adhesion amount. On carrier Based on the surface potential of the image display area, the toner of the toner adhesion amount estimating means for estimating the amount of toner adhesion of the image bearing member corresponding to the circumferential speed ratio, the peripheral speed ratio estimated
Peripheral speed when forming a digital image based on the amount of adhesion
Peripheral speed ratio setting means for setting the ratio.

In the digital image forming apparatus according to a second aspect of the present invention, the toner adhering amount estimating unit is a unit for estimating the toner adhering amount by the equation (1). In the digital image forming apparatus according to the third aspect of the present invention, the peripheral speed ratio when forming the patch image is set such that the signal output value of the detection means in the patch image forming region has a fluctuation tendency as an upper limit, Is set so as to be a value within a region having a lower limit at a point at which is generated.

[0011] In the digital image forming apparatus according to the invention of claim 4, wherein the detection means detects the peripheral area of the patch image formation area patch image formation region and a toner which the toner is adhered is not attached, the patch image The toner adhesion amount calculation unit inputs a ratio of a signal output value when the patch image formation region is detected to a signal output value when a peripheral region of the patch image formation region is detected as a signal output value of the detection unit. It was configured as follows .

[0012]

According to the configuration of the digital image forming apparatus according to the first aspect of the present invention, when the environment at the time of image formation changes, for example, the temperature, humidity, change with time of the image carrier, etc.
The amount of toner adhered to the patch image is a value according to the environment at that time, and the amount of toner adhered according to the peripheral speed ratio is estimated based on the amount of toner adhered to the patch image. Can be variably set in accordance with the conditions, and an appropriate image forming condition can be obtained.

According to the configuration of the digital image forming apparatus according to the second aspect of the invention, specifically, the number of times the toner has been refreshed n and the toner adhesion amount M ₍₁₎ at the peripheral speed ratio set at the time of patch detection ₎ , The bias voltage _{VDC on the} surface of the developer carrying carrier, the writing potential _VL on the image carrier, and the toner charge amount Q, and the peripheral speed ratio and the toner adherence are determined by the equation (1) based on the patch image toner attached amount It is possible to estimate the relationship with the quantity in a series.

According to the digital image forming apparatus of the present invention, the peripheral speed ratio is set so that the signal output value of the detecting means in the patch image forming area is within the area. Since the signal output value is not detected in the unstable detection area, it is possible to accurately estimate the toner adhesion amount. According to the configuration of the digital image forming apparatus according to the fourth aspect of the present invention, for example, the surface state of the image carrier changes using the image carrier for a long period of time, and the baseline of the detection signal of the detection unit changes. Also, the signal output value at the time of detecting the patch image forming area to which the toner adheres and the signal output value at the time of detecting the peripheral area of the patch image forming area to which the toner does not adhere fluctuate in the same manner. The value ratio is not affected by the surface condition of the image carrier. Therefore, the detection accuracy of the patch image is improved, and the output value of the patch image can be accurately obtained even when the baseline correction is completed at a certain level. Adjustment time can be reduced.

[0015]

An embodiment of the present invention will be described below. FIG.
1 is a schematic control block diagram of a digital color image forming apparatus according to the present embodiment. In FIG. 2, the operation of the normal image recording mode will be described.

A charging unit 2, a developing unit 3, a transfer roller 4, a neutralizing brush 5, and a cleaning unit 6 are arranged opposite to a photosensitive drum 1 as an image carrier rotating in the direction of the arrow. When a laser beam corresponding to an image is emitted from an exposure unit (not shown) onto the photosensitive drum 1 charged by the charger 2, toner adheres to the irradiated portion of the surface of the photosensitive drum 1 by the developing unit 3. Then, the electrostatic latent image is visualized.
The developing device 3 includes four developing sleeves 3a, 3b, and 3 as developer transport carriers for each of the primary colors Y, M, C, and Bk.
c, 3d and a developing sleeve drive motor (not shown). When an image of a specific color is formed, a direct current (D
C) biased developing sleeves 3a, 3b, 3
By superimposing an alternating current (AC) bias on a specific developing sleeve from among c and 3d, toner particles on the developing sleeve rotated by a developing sleeve driving motor fly and adhere to the photosensitive drum 1 to form an image of a specific color. Is formed. A desired color can also be formed for the secondary colors by a combination of the developing sleeves 3a, 3b, 3c, and 3d.

When the toner image formed on the photosensitive drum 1 by the developing device 3 reaches the transfer position of the transfer roller 4,
A recording sheet (not shown) whose timing is controlled is also conveyed to the transfer position, a transfer bias having a polarity opposite to that of the toner is applied from the back surface of the recording sheet, and an electrostatic attractive force acts on the photosensitive drum 1. The toner image is transferred to the surface of the recording paper, and the charge removing brush 5 removes unnecessary electric charges.

When a color image is formed, the charging, exposing, and developing steps are performed for the Y color, and the above-described series of steps are sequentially repeated for the M, C, and Bk colors. The recording paper is separated from the photosensitive drum 1 by a known separation means such as a separation claw or a curvature separation, and is thermally fixed by a fixing device (not shown) and discharged from the apparatus. Then, the cleaning unit 6 cleans the residual toner on the photosensitive drum 1 to prepare for the next recording.

The developing conditions are as follows. (1) Charge potential (V _H ) of the photosensitive drum 1: −750 V (2) DC bias voltage (V _DC ) of the developing sleeve: −650
V (3) AC bias voltage (V _AC ) of the developing sleeve: 1.7 kV
_PP (4) Frequency of developing sleeve: 8 kHz (5) Amount of developer transport (D _WS ): 20 to 30 mg / cm ² (6) Image writing potential (V _L ): -40 to -50 V () (7) Photosensitivity Line speed of the drum 1: 100 mm / sec (8) Line speed when forming a test patch on the developing sleeve: 70 mm / sec (9) Developer used: two-component developer (Bk) (10) Charge variation: ± 3 μC / g (humidity: 20 to 80%) Next, a configuration for performing image adjustment using a color patch image will be described.

The color patch image data is stored in a memory 7 in advance.
In the image adjustment mode, the control unit 8 sequentially reads out the color patch image data of each color from the memory 7 and outputs the color patch image data to the exposure unit, so that the charged photosensitive drum 1 is exposed, and the electrostatic latent image is visualized by the developing device 3. On the other hand, as shown in FIG. 3, a detection sensor 9 as a detection means provided between the neutralization brush 5 and the cleaning unit 6 has an angle of 40 ° with respect to a virtual perpendicular line (dotted line) of the photosensitive drum 1. It comprises a pair of photodiodes (LEDs) and phototransistors (PtTr) installed at an angle of ° and receives reflected light according to the amount of toner forming a color patch image. In this embodiment,
The distance between each element of the detection sensor 9 and the photosensitive drum 1 is 6 mm.
Set to.

The control unit 8 sets the peripheral speed ratio of the developing sleeve to the photosensitive drum 1, inputs a detection signal from the detection sensor 9, and estimates the relationship between the peripheral speed ratio and the amount of adhered toner to obtain a digital signal. Set the peripheral speed ratio at the time of image formation. next,
The operation of the control unit 8 will be described based on the flowchart of FIG. In step (denoted by “S” in the figure, the same applies hereinafter) 1, the rotation speed of the developing sleeve is reduced from that in the image recording mode so that the detection signal of the detection sensor 9 enters the stable detection region. Control.

FIG. 5 is a diagram showing the relationship between the detection signal value and the amount of adhered toner. As shown in FIG.
When there is no toner adhesion, the amount of light received by the PtTr becomes maximum and the detection signal also becomes maximum. The detection signal decreases as the toner adhesion amount increases until the toner covers the photosensitive drum 1. However, in a region where the amount of toner is small, the received light amount of PtTr varies due to a slight increase or decrease in the amount of toner adhesion. Therefore, the detection signal indicates the upper limit of the stable region, and thereafter, the fluctuation tendency becomes large. Further, even if the toner adhesion amount increases after the toner covers the photosensitive drum 1, PtTr
Since the amount of received light does not change, the detection signal indicates the lower limit and becomes saturated. Such a fluctuation region and a saturation region are unstable regions, and a stable output voltage with respect to the toner adhesion amount cannot be obtained.

The toner adhesion amount at the upper limit of the detection signal is 0.
1 mg / cm ² , the toner adhesion amount at the lower limit was determined to be 0.4 mg / cm ² as a measurement result, and the toner adhesion amount was 0.1 mg / cm ^2.
An area of about 0.3 mg / cm ² is a stable detection area of the detection signal of the detection sensor 9. Specifically, if the peripheral speed ratio of the developing sleeve to the photosensitive drum 1 is set to 0.7, the amount of toner adhered becomes about 0.2 mg / cm ² .

This step corresponds to the patch image forming means. In step 2, a detection signal when a color patch image is detected by the detection sensor 9 is input. Before the detection of the patch image, a baseline correction for adjusting the detection signal of the detection sensor 9 by idling the photosensitive drum 1 is performed, which will be described later.

In step 3, the patch image toner adhering amount is calculated from the above-described FIG. 5 based on the input detection signal. Steps 2 and 3 correspond to a patch image toner adhesion amount calculation unit. In step 4, the amount of toner adhered according to the peripheral speed ratio is estimated. The relationship between the toner adhesion amount and the peripheral speed ratio is estimated by generating a series based on the following equation (1).

M _(n) = M ₍₁₎ × (V _DC −V _L −Q × k × M _(n−1) ) / V _DC + M _(n−1) (1) , M _(n): the peripheral speed ratio 0.7 × n (n: integer) toner adhesion amount when the ^{(kg · m -2) M (} 1): toner adhesion amount when the peripheral velocity ratio 0.7 (kg · m ^{- 2} ) _VDC : bias voltage on the developing sleeve surface _VL : writing potential on the photosensitive drum 1 Q: toner charge (A · skg ⁻¹ ) k: coefficient for potential conversion [1.5 × 10 ² (A ^{− 2} s ^-4 m
⁴ kg) That is, the toner amount M of the patch image when the peripheral speed ratio is 0.7
_{Using (1)} as a reference toner adhesion amount, toner adhesion amounts M ₍₂₎ , M ₍₃₎ ,..., M _(n) are sequentially estimated based on this equation (1).

Note that the coefficient k is a value determined by the toner characteristics, and is a constant experimentally obtained based on the toner adhesion amount and the toner charge amount. Explaining the contents of the equation (1), the toner adhesion amount M ₍₁₎ is an actual measurement value of patch image detection, and therefore, the toner adhesion amount M ₍₁₎ is a value corresponding to the environment at that time. When the environment at the time of image formation changes, such as temperature, humidity, time-dependent change of the photoconductor 1, the toner adhesion amount M ₍₁₎ also changes.

FIG. 6 is a diagram for explaining the equation (1). As shown in FIG. 6, if toner does not adhere to the image forming area on the photosensitive drum 1, the surface of this area is The potential is the writing potential _VL . When the toner flies from the developing sleeve and adheres to the image area of the photosensitive drum 1, the surface potential of the image forming area of the photosensitive drum 1 decreases by the amount of the toner. (Q × k × M _(n-1) )
Is a value corresponding to the total toner charge amount.
The above actual surface potential is a potential including the charge amount. That is, it is assumed that as the toner adheres to the image area on the photoconductor drum 1, the amount of toner adhering to the image area on the photoconductor drum 1 also decreases. FIG. 7 is a diagram in which the relationship between the toner adhesion amount and the peripheral speed ratio is estimated based on the above equation (1). Even if the peripheral speed ratio increases, the toner adhesion amount does not linearly increase accordingly. That is why.

Step 4 corresponds to a toner adhesion amount estimating means for estimating the toner adhesion amount with respect to the peripheral speed ratio. In step 5, based on FIG. 7, the developing sleeves 3a, 3
The peripheral speeds and rotation speeds of b, 3c and 3d are determined. Step 5 corresponds to the peripheral speed ratio setting means.

According to this configuration, even if the environment during image formation changes, for example, the temperature, humidity, and the aging of the photoconductor 1, the toner adhesion amount M (1) corresponds to the change. Since the toner adhesion amount is estimated based on the peripheral speed ratio based on the image toner adhesion amount, even if the environment during image formation changes, the proper image forming conditions are not affected by the toner performance and the like. The peripheral speed ratio can be variably controlled so as to obtain

Next, the baseline correction will be described. As described above, before the detection of the patch image, the baseline correction for adjusting the light amount of the detection sensor 9 by idling the photosensitive drum 1 is performed. If the surface of the photosensitive drum 1 becomes dirty or scratched, the detection sensor 9 will be described below.
Also greatly fluctuates.

V _LED M / A V ₁ V ₂ (V ₁ / V ₂ ) ---------------------------------------------------- −−− 5 0.19 0.2460 0.06153 2.00 6 0.19 0.3965 0.1015 2.04 8 0.19 0.6104 0.1589 2.08 where V _LED : applied voltage to the detection sensor 9 (see FIG. 8) M / A: toner adhesion amount V ₁ : baseline output value V ₂ : Output value when patch image is detected However, even if the baseline output value fluctuates, the output value when a patch image is detected fluctuates in the same manner. The ratio to the output value is not affected by changes in the surface state.

In this embodiment, by paying attention to this point, an accurate detection output value of a patch image can be obtained even when used for a long time. Next, this processing content will be described based on the flowchart of FIG. In step 11, the photosensitive drum 1
The peripheral speed ratio of the developing sleeves 3a, 3b, 3c, 3d to 0.7 is controlled to 0.7.

In step 12, the unit of the patch detection sensor 9 is operated. In step 13, the photosensitive drum 1 is idled. In step 14, the light amount of the light emitting element (LED) of the detection sensor 9 is adjusted so that the detection signal value becomes ± 2% of the designated baseline output. Thereby, before detecting an actual patch image, the state of the surface of the photosensitive drum 1 and the state of the detection sensor 9 are considered.

Up to this point, the baseline correction that is usually performed. Next, in step 15, the patch detection sensor 9
Activate the unit again. In step 16, a patch image is formed on the photosensitive drum 1. In step 17, the photosensitive drum 1 is idled. In step 18, measuring the output value V ₂ of the detection sensor 9, based on the test patch image.

In step 19, the output value of the detection sensor 9 at the periphery of the test patch image is measured. This value corresponds to the baseline output value V _1. In step 20,
The value obtained by the following equation (3) is used as the detection output. Detection output = V ₂ / V ₁ (3) According to this configuration, the detection accuracy of the patch image is improved,
Even if the baseline correction is finished at a certain level, accurate patch image output values can be obtained.
Baseline correction is simplified, and the adjustment time for detecting a patch image can be reduced.

[0037]

As described above, according to the digital image forming apparatus of the first aspect, for example, the temperature,
The peripheral speed ratio can be variably set so that an appropriate image forming condition can be obtained even when the environment during image formation such as humidity, change over time of the image carrier, or the like changes.

According to the digital image forming apparatus of the second aspect of the present invention, the proper toner adhesion amount based on the patch image toner adhesion amount and the peripheral speed for achieving the proper toner adhesion amount are obtained by the equation (1). The ratio can be estimated in a series. According to the digital image forming apparatus of the third aspect, since the patch image is not detected in the unstable detection area, it is possible to accurately estimate the toner adhesion amount.

According to the digital image forming apparatus of the present invention, the detection accuracy of the patch image is improved, and the output value of the patch image can be accurately obtained even when the baseline correction is completed at a certain level. Is obtained, the baseline correction is simplified, and the adjustment time at the time of patch detection can be shortened.

[Brief description of the drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of the present invention.

FIG. 2 is a schematic control block diagram of a digital color image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of the detection sensor of FIG. 2;

FIG. 4 is a flowchart showing the operation of the control unit in FIG. 2;

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

FIG. 6 is an explanatory diagram of a bias voltage and a write voltage.

FIG. 7 is a diagram illustrating a relationship between a toner adhesion amount and a rotation number of a developing sleeve according to the present exemplary embodiment.

FIG. 8 is a circuit diagram of a detection sensor according to the present embodiment.

FIG. 9 is a flowchart of image adjustment processing at the time of baseline correction.

FIG. 10 is a diagram illustrating a relationship between a conventional toner adhesion amount and a developing sleeve rotation speed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Developing device 7, 21 Memory 8 Control part 9 Detection sensor 10 Color patch image detection circuit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/08 G03G 15/00

Claims (4)

(57) [Claims] 1. A patch image is output on an image carrier, and the image on the image carrier is optically detected by using a detecting means for photoelectrically converting the patch image.
A digital image forming apparatus for variably setting a peripheral speed ratio of a developer carrying carrier to an image carrier based on a signal output value of the detection means so as to obtain an appropriate image forming condition. Before, a patch image forming means for setting a peripheral speed ratio to form a patch image on the image carrier, and a signal output value of the detecting means at the time of detecting the patch image are inputted, and the patch image is formed based on the signal output value. A patch image toner adhesion amount calculating means for calculating the above toner adhesion amount, and based on the bias voltage on the surface of the developer carrying carrier and the surface potential of the image display area of the image carrier based on the patch image toner adhesion amount. a toner deposition amount estimating means for estimating the amount of toner adhesion of the image bearing member corresponding to the circumferential speed ratio, based on the toner adhesion amount of each tip speed ratio estimated, digital
A digital image forming apparatus comprising: a peripheral speed ratio setting unit that sets a peripheral speed ratio when forming an image. 2. The toner adhesion amount estimating means calculates the following equation (1): M (n) = M (1) × (VDC−VL−Q × k × M (n−1)) / VDC + M (n−1) ) (1) where M (1) is the toner adhesion amount at the peripheral speed ratio set at the time of detection of the patch image (kg · m ^-2 ) M (n) is the circumference set at the time of detection of the patch image Speed ratio xn
(N = integer) Amount of toner attached (kg · m ^-2 ) VDC: Bias voltage on the surface of developer carrying carrier VL: Writing potential of image display area on image carrier Q: Toner charging amount (A skg ^-1 ) k: coefficient for potential conversion [1.5 × 10 ² (A ^-2 s ^-4 m ⁴
2. The digital image forming apparatus according to claim 1, wherein the unit is a unit for estimating a toner adhesion amount based on (kg). 3. The peripheral speed ratio when forming the patch image is defined as an area in which the signal output value of the detecting means in the patch image forming area has an upper limit at which a fluctuation tendency occurs and a lower limit at a point at which a saturation tendency occurs. The digital image forming apparatus according to claim 1, wherein the digital image forming apparatus is configured to set a value within the range. 4. The patch image forming apparatus according to claim 1, wherein said detecting means detects a patch image forming area to which toner has adhered and a peripheral area of the patch image forming area to which toner has not adhered. It is configured to input a ratio of a signal output value when detecting an area and a signal output value when detecting a peripheral area of the patch image forming area as a signal output value of the detection unit. The digital image forming apparatus according to claim 1.