JP2009168906A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of minimizing a solid patch density difference and obtaining a preferable image by suppressing a change in transfer rate depending on an image area ratio in a main scanning direction.
Image forming means for forming at least two solid patches for detecting the amount of adhesion of toner having different image area ratios in the main scanning direction on a photoconductor, and an intermediate transfer member with the same transfer output. And a transfer unit 57 that transfers to a recording medium, a control unit 56 that performs image density control, and a toner adhesion amount detection sensor S that is used for image density control. The toner adhesion amount of the solid patch is detected by the toner adhesion amount detection sensor S. I read.
[Selection] Figure 5

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a printer, and a facsimile machine.

In such an image forming apparatus, it is known that when the image area ratio in the main scanning direction (longitudinal direction of the photoconductor) is different, the impedance of the photoconductor is different and the transfer rate is changed accordingly. When the change in the transfer rate is large, a phenomenon occurs in which the density is different between solid patches having different image area ratios in the main scanning direction. Specifically, the density tends to decrease as the image area in the main scanning direction increases (an image like a horizontal band).
As a solution to this problem, it is known in the prior art to change the transfer energy based on image area ratio data (see, for example, Patent Document 1).
Patent Document 1 discloses a method for automatically and satisfactorily controlling the image density on the recording paper by changing the transfer energy based on the data of the image area ratio (expressed as the surplus ratio in Patent Document 1). Has been.
JP 2001-331005 A

However, the image area ratio in the main scanning direction changes between 0% and 100%, and the change may appear for each scanning. In Patent Document 1, image area ratio data for each scan is reflected in the transfer energy amount.
It is very difficult to change the amount of transfer energy corresponding to the process line speed that has been increased due to the recent increase in speed and size required for image forming apparatuses.
Actually, Patent Document 1 does not describe a method for forming a pattern that causes a difference in adhesion amount or a method for detecting the adhesion amount of the pattern, and the image area in the main scanning direction obtained from image data. The method of predictive control inferred from the rate is taken. Because of the predictive control, the amount of adhesion that actually changes depending on the image area ratio in the main scanning direction cannot be grasped.

Patent Document 1 does not describe a method for detecting a change in transfer output due to a change in the image area ratio in the main scanning direction. As described above, Patent Document 1 cannot grasp the amount of adhesion that actually changes depending on the image area ratio in the main scanning direction because of predictive control.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of obtaining a preferable image by minimizing a solid patch density difference by suppressing a change in transfer rate depending on an image area rate in the main scanning direction in consideration of the above-described situation. Is to provide.

In order to solve the above problems, the invention described in claim 1 is to develop and visualize an electrostatic latent image formed on a photoreceptor with toner, transfer the toner image onto a recording medium, and In the image forming apparatus for fixing an image on the recording medium, an image forming unit that forms on the photosensitive member at least two or more solid patches for detecting the amount of toner adhesion having different image area ratios in the main scanning direction; A transfer unit that transfers the solid patch to the intermediate transfer member and the recording medium with the same transfer output; a control unit that performs image density control; and a toner adhesion amount detection sensor that is used in the image density control. The toner adhesion amount of the solid patch is read by a detection sensor.
According to a second aspect of the present invention, the electrostatic latent image formed on the photoconductor is visualized by developing with toner, the toner image is transferred onto a recording medium, and the toner image is transferred onto the recording medium. In an image forming apparatus to be fixed, at least two toner adhesion amount detection solid patches having different image area ratios in the main scanning direction are formed on the photosensitive member, and the solid patch is output with the same transfer output. A transfer unit that transfers to an intermediate transfer body and a recording medium; a control unit that controls image density; and a detection unit that detects a difference in transfer output, the detection unit transferring the solid patch to the intermediate transfer body The difference in transfer output caused by the difference in image area ratio in the main scanning direction is detected as a change in transfer output.

The invention according to claim 3 is the image forming apparatus according to claim 2, wherein the detecting means detects a voltage value when the transfer output is a constant current output.
According to a fourth aspect of the present invention, in the negative development method, when a predetermined difference is detected in each toner adhesion amount with the two or more solid patches having different image area ratios in the main scanning direction, the photoconductor 2. The image forming apparatus according to claim 1, wherein the photosensitive member is subjected to potential control for lowering the absolute value of the charging potential from a standard value.
According to a fifth aspect of the present invention, when a predetermined difference is detected in each transfer output between the two or more solid patches having different image area ratios in the main scanning direction, the absolute potential of the charging potential of the photosensitive member is determined. 4. The image forming apparatus according to claim 2, wherein the photosensitive member is subjected to electric potential control that lowers the value from a standard value.
According to a sixth aspect of the present invention, in the image formation according to the fourth or fifth aspect, when the potential control for lowering the charging potential is performed, the potential control of the photosensitive member is also performed so that the development potential is also lowered. Features the device.

According to a seventh aspect of the present invention, in the quadruple tandem system in which a plurality of photoconductors are used, when the charging / developing potential is lowered for at least one of the photoconductors, the remaining photoconductors 7. The image forming apparatus according to claim 6, wherein the charging / developing potential is similarly lowered to control the potential of the photosensitive member.
According to an eighth aspect of the present invention, in the two-component development method, after the charging / developing potential is lowered by the potential control, a toner adhesion amount control mode including toner replenishment is executed, and the charging / developing potential is set. 8. The image forming apparatus according to claim 4, wherein control is performed to change the charging potential to a value that is not changed or lower than a set value set by the potential control. And
According to a ninth aspect of the present invention, in the detection of the transfer output change, when a predetermined difference is detected in each transfer output with two or more solid patches having different image area ratios in the main scanning direction, the tension roller 4. The image forming apparatus according to claim 2, wherein control is performed to increase the pressure applied to the image forming apparatus.

Further, in the invention according to claim 10, in the detection of the transfer output change, when a predetermined difference is detected in each transfer output with two or more solid patches having different image area ratios in the main scanning direction, 4. The image forming apparatus according to claim 2, wherein control is performed to reduce a pressing force for pressing the primary transfer roller toward the intermediate transfer member.
According to an eleventh aspect of the present invention, after performing the control to increase the pressure applied to the tension roller and the control to decrease the pressure to press the primary transfer roller toward the intermediate transfer body, 11. The image forming apparatus according to claim 9, wherein image density adjustment process control is performed.
According to a twelfth aspect of the present invention, when the tension of the intermediate transfer member or the pressing force of the primary transfer roller is changed, the image density control is performed at the time of the image density control at the next timing following the change. 12. The image forming apparatus according to claim 9, wherein before the change, the tension of the intermediate transfer member or the pressure applied to the primary transfer roller is controlled to the level before the change.

According to the present invention, a change in the transfer rate due to a change in the image area ratio in the main scanning direction is accurately detected by forming a plurality of solid patches having different image area ratios in the main scanning direction and detecting the adhesion amount. be able to.
Further, according to the present invention, a plurality of solid patches having different image area ratios in the main scanning direction are imaged, and a difference in transfer output caused by a difference in image area ratios in the main scanning direction of the solid patches transferred to the intermediate transfer member is detected. By doing so, it is possible to accurately detect a change in the transfer rate due to a change in the image area rate in the main scanning direction.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the description, specific member names are used to facilitate understanding of the invention, but it should be clearly stated that the scope to which the present invention can be applied is not limited thereby.
In particular, an image forming apparatus using a tandem type intermediate transfer system is taken up as an application example, and secondary transfer from an intermediate transfer body to a secondary transfer roller is described. However, the present invention is limited to an intermediate transfer system. It is not done. For example, the same operation and effect can be obtained even in a mode in which a direct transfer method is employed in which the image carrier is a photoconductor.

FIG. 1 is a cross-sectional view showing a schematic configuration of a color printer which is an example of an image forming apparatus according to the present invention. FIG. 2 is an enlarged schematic view showing the periphery of the image forming unit in FIG. The illustrated image forming apparatus 1 is a tandem type intermediate transfer color printer, and includes an image forming unit 10, a writing optical unit 11, a paper feeding unit 12, a fixing unit 13, a double-side unit 14, and the like.
As shown in FIG. 1 and FIG. 2 showing an enlarged image forming section, in the color printer 1 employing the tandem type intermediate transfer system, an intermediate transfer belt 15 that is an intermediate transfer member that is rotationally driven in the direction of arrow A in the drawing. The four image forming process units 2 to 5 corresponding to the respective color toners of yellow (Y), cyan (C), magenta (M), and black (K) are arranged along the lower traveling side.
The intermediate transfer member 15 made of rubber or resin having a single layer or a multilayer structure is stretched by a secondary transfer counter bias applying roller 16 and support rollers 17, 18, and 19, and in the illustrated example, the intermediate transfer member 15 is rotated counterclockwise. It is rotationally driven in the direction. A secondary transfer roller 20 is disposed opposite to the secondary transfer counter bias applying roller 16 on the opposite side of the intermediate transfer body 15.
The secondary transfer counter bias applying roller 16 can form an electric field having the same polarity as that of the toner by a secondary transfer electric field forming unit (not shown). The toner can be secondarily transferred to the recording paper.

FIG. 3 is a schematic enlarged view showing the intermediate transfer member cleaning device of FIG. 2 and 3, an intermediate transfer body cleaning device 21 for removing residual toner remaining on the intermediate transfer body 15 after image transfer is provided on the left side of the support roller 19.
The intermediate transfer member cleaning device 21 includes a blade member 22 for removing a toner image, a lubricant 23, a coil member 24 for conveying the removed toner image to a waste toner tank of the main body, and a lubricant application brush. 25 and a spring 26 that is an elastic member that biases the lubricant 23.
The contact angle, position, pressure, and the like of the blade member 22 are appropriately set depending on the toner used, the image forming speed of the apparatus, and the like. The lubricant 23 is pressed against the lubricant application brush 25 by means such as a spring or a weight, and the lubricant application brush 25 scrapes the lubricant 23 while rotating to apply the lubricant 23 to the intermediate transfer member 15. Perform the action.

Referring again to FIG. 2, primary transfer bias rollers 27, 28, 29, and 30 in which an electric field is formed at the time of primary transfer are disposed inside the intermediate transfer body 15 between the support roller 17 and the support roller 18. The intermediate transfer member 15 is disposed so as to be in contact with the intermediate transfer member 15.
Then, on the opposite side of the primary transfer rollers (primary transfer bias rollers) 27, 28, 29, 30 across the intermediate transfer body 15, four photosensitive materials of yellow, cyan, magenta, and black are arranged along the conveyance direction. The image forming process units 2, 3, 4, and 5 having the bodies 31, 32, 33, and 34 as the center are arranged in parallel to constitute a tandem type image forming apparatus. Around each of the photoconductors 31 to 34, photoconductor charging means 35 to 38, photoconductor cleaning means 39 to 42, and developing means 43 to 46 are arranged, respectively.

FIG. 4 is an enlarged schematic view showing the photoconductor cleaning means of FIG. The photoreceptor cleaning means 39 to 42 include a blade member 47 for removing the toner image, a coil member 48 for conveying the removed toner image to a waste toner tank of the main body, a lubricant 49, and a lubricant application brush. 50 and a spring 51 which is an elastic member for urging the lubricant 49.
The contact angle, position, pressure, and the like of the blade member 47 are appropriately set depending on the toner used, the image forming speed of the apparatus, and the like. The lubricant 49 is pressed against the lubricant application brush 50 by means such as the spring 51 or the weight described above, and the lubricant application brush 50 scrapes the lubricant 49 while rotating, and applies the lubricant to the photoreceptors 31 to 34. 49 is applied.

Referring again to FIG. 1 and FIG. 2, the writing exposure to the photosensitive members 31 to 34 is performed at the position between the photosensitive member charging units 35 to 38 and the developing units 43 to 46, as shown in FIG. This is performed by laser irradiation from an exposure apparatus 11.
Under the secondary transfer roller 20, a registration roller 52 that feeds recording paper as a recording medium to the secondary transfer unit is installed. A fixing device 13 for fixing the toner image on the recording paper is provided above the secondary transfer roller 20. Furthermore, a paper feed cassette 54 and a paper feed roller 55 are arranged in the paper feed unit 12 of FIG.
A printing operation in the color printer 1 configured as described above will be briefly described. First, an image signal is input from an external device (not shown) such as a personal computer or a scanner. After the signal is input, the photosensitive members 31 to 34 and the intermediate transfer member 15 are rotated by a driving motor (not shown) at a predetermined timing.
Simultaneously with the photoconductors 31 to 34, a precleaning operation by the photoconductor cleaning means 39 to 42 is performed, and thereafter, a charging operation by the photoconductor charging means 35 to 38, an exposure operation by the writing optical unit 11, and a developing means using toner. Development operations 43 to 46 are performed.

The toner images formed on the photoreceptors 31 to 34 in this way are subjected to primary transfer onto the intermediate transfer member 15 by forming an electric field having a polarity opposite to that of the toner on the primary transfer rollers 27 to 30 at predetermined timings, respectively. As a result, a monochromatic or multicolored visible image is formed. At that time, the toner images remaining on the photoreceptors 31 to 34 without being completely transferred onto the intermediate transfer member 15 are cleaned by the photoreceptor cleaning means 39 to 42, respectively.
On the other hand, after the input of the image signal, the recording paper is fed out from the paper supply unit 12 at a predetermined timing, and is abutted against the registration roller 52 and temporarily stopped. Then, the registration roller 52 is rotated in synchronization with the visible image on the intermediate transfer member 15, and the recording paper is fed between the intermediate transfer member 15 and the secondary transfer roller 20.
At the same time, an electric field having the same polarity as the toner is formed on the secondary transfer counter bias applying roller 16 by a secondary transfer electric field forming means (not shown), and the visible image on the intermediate transfer body 15 is secondarily transferred onto the recording paper.

Thereafter, the recording paper passes through the fixing unit 13, and heat and pressure are applied to fix the visible image on the recording paper. After fixing, the recording paper is discharged and stacked on a discharge tray 53 on the upper surface of the apparatus, or if printing on the back side is necessary, after fixing, the recording paper is returned to the registration roller 52 through the double-sided portion 14 and printed on the back side. The visible image is fixed on the recording paper by passing through the fixing unit 13 and applying heat and pressure.
On the other hand, the toner image remaining on the intermediate transfer member 15 without being completely transferred onto the recording paper during the secondary transfer is removed by the intermediate transfer member cleaning device 21 to prepare for the image formation again.
Further, a reflection type photosensor S (FIG. 2) as image density detecting means is disposed above the secondary transfer counter bias applying roller 16 with the intermediate transfer body 15 interposed therebetween. A signal corresponding to the reflectance is output. The reflection type photosensor S is either a diffused light detection type or a regular reflection light detection type that can make the difference between the amount of reflected light on the surface of the intermediate transfer body 15 and the amount of reflected light of a reference pattern image to be described later sufficient. A photo sensor is used.

FIG. 5 is a block diagram showing a part of an electric circuit of a color printer embodying the present invention. In this figure, a control unit 56 including a CPU 56a and a RAM 56b, a reflection type photosensor S connected to the control unit 56, a writing optical unit 11, a paper feeding unit 12, a registration roller 52, a transfer unit 57, and an image forming unit. Shown are toner image forming portions 43 to 46 as developing means of the image forming process units 2 to 5.
The control unit 56 controls the toner image forming units 43 to 46, the writing optical unit 11, the paper feeding unit 12, the registration roller 52, the transfer unit 57, and the reflective photosensor S, which are electrically connected to each other. In the control unit 56, the CPU 56a mainly controls the calculation unit, and the RAM 56b stores data.

Next, detection of the toner adhesion amount using the reflective photosensor S and normal image density control using the toner adhesion amount detection will be described.
In the color printer 1 of the present embodiment, the control unit 56 described above has a predetermined timing such as when the main power is turned on, when waiting after a predetermined time has elapsed, or when waiting for a predetermined number of prints to be output. The image forming performance such as the image forming performance in each of the image forming process units 2 to 5 is tested.
Specifically, when the predetermined timing comes, first, the reflection type photosensor S is calibrated. In a state where no image is formed, the amount of light emitted from the reflective photosensor S is sequentially changed to obtain the amount of light emitted so that the detection voltage is 4.0 V ± 0.2 V. This emitted light quantity is used when detecting the toner adhesion amount of the solid patch reference pattern image.

Next, the photosensitive members 31 to 34 (FIG. 2) are uniformly charged while rotating. This charging is different from the uniform charging (for example, −700 V) during normal printing, and the potential is gradually increased. Then, development is performed by the developing means 43 to 46 while forming an electrostatic latent image for a reference pattern image by scanning with the laser beam. By this development, bias development pattern images of the respective colors are formed on the photoreceptors 31 to 34.
At the time of development, the control unit 56 of the printer controls so that the value of the developing bias applied to the developing roller of each developing means 43 to 46 is gradually increased. In this way, a pattern image having a low image density is formed, and a gradually dark pattern image is formed. A method for creating this pattern image will be described later.

On the contrary, if both the charging and developing bias are gradually lowered, a pattern image having a high image density is formed and a thin pattern image is formed gradually. However, in general, a high-voltage power supply has a drawback that it takes longer time to form a pattern image because lowering the voltage takes longer than raising the voltage.
The bias development pattern images of these colors are transferred as reference pattern images so as to be arranged on the intermediate transfer body 15 (FIG. 2) without overlapping. When this reference pattern image passes through a position facing the reflection type photosensor S along with the endless movement of the intermediate transfer member 15, the amount of reflected light is detected and output as an electric signal to the control unit 56.
The control unit 56 calculates the light reflectance of each reference pattern image based on the output signals sequentially sent from the reflection type photosensor S, and stores it as density pattern data in the RAM 56b as storage means. The reference pattern image that has passed the position facing the reflective photosensor S is cleaned by the intermediate transfer member cleaning device 21.

FIG. 6 is a schematic diagram showing a reference pattern image P. In the figure, the above-mentioned reference pattern images P (Py (not shown), Pm (not shown), Pc, Pk) are composed of ten reference images arranged at an interval of 13 mm. In the color printer 1 of FIG. 1, each reference pattern image P is 13 mm long × 15 mm wide and is formed through a gap of 13 mm.
Therefore, the lengths of the reference pattern images Pk, Pm, Pc, and Py on the intermediate transfer body 15 are L2 = 247 mm, respectively. The reference pattern images Pk, Pm, Pc, and Py are different from the toner images of the respective colors that are formed during the printing process, and are arranged so that they are arranged in the order of Py, Pm, Pc, and Pk without overlapping on the intermediate transfer body 15. Are formed and transferred onto the intermediate transfer member 15.
The reflective photosensor S detects the amount of reflected light from each reference image constituting the reference pattern images Pk, Pc, Pm, and Py in the following order. That is, detection is performed in the order of 10 reference images of the reference pattern image Pk, 10 reference images of the reference pattern image Pc, 10 reference images of the reference pattern image Pm, and 10 reference images of the reference pattern image Py. To do.
At this time, the reflective photosensor S detects a voltage signal corresponding to the light reflection amount of each reference image by a method described later, and sequentially outputs the voltage signal to the control unit 56. The control unit 56 sequentially calculates the image density of each reference image based on the voltage signals sequentially sent from the reflection type photosensor S and stores them in the RAM 56b. The image density of each reference image is converted into a toner adhesion amount by the following method.

FIG. 7 is a graph showing the relationship between the toner adhesion amount and the sensor detection output. The detection output of 10 reference pattern images of each color is converted into the toner adhesion amount of the reference image from the relationship between the sensor detection output (voltage) and the toner adhesion amount shown in FIG. 7, and stored in the RAM 56b (FIG. 5). .
Here, the toner adhesion amount is stored in the RAM 56b, and at the same time, the development potential of the reference pattern image is estimated from the image forming conditions of the reference pattern image of each color, and the reference pattern image information is also stored in the RAM 56b.
The above steps are sequentially performed in the order of Pk1, Pc1, Pm1, and Py1. FIG. 8 is a plot of the relationship between the development potential of each reference pattern image and the toner adhesion amount obtained here on the XY plane.

FIG. 8 is a graph showing the relationship between the development potential and the toner adhesion amount. In FIG. 8, the developing potential (difference between developing bias and reference pattern image potential: VB−VD [unit V]) is plotted on the X axis, and the toner adhesion amount M / A [mg / cm ² ] per unit area is plotted on the Y axis. Allocated.
A straight line area is selected from the data plotted as described above, a straight line approximation is performed by applying the least square method to the data in the section, and the resulting straight line equation is calculated for each color. Image density control, so-called process control (process control), is performed by calculating the development potential at which a target adhesion amount can be obtained by this linear equation and feeding back to the image forming conditions.

FIG. 9 is a diagram showing the formed solid image pattern for image widths of 5% and 80%. FIG. 10 is a graph showing the relationship between the transfer rate and the transfer current. FIG. 11 is a graph showing the relationship between the transfer voltage and the transfer current.
Regarding the following specific values and graphs, in the A4 size image forming apparatus of the two-component development / four-drum tandem type intermediate transfer method with a process linear speed of 150 mm / sec, the primary transfer roller resistance: 7.0 LogΩ, intermediate transfer This is an example in which body surface resistance: 11.0 LogΩ is used. When the method and member resistance change, the numerical value naturally changes, but the effect of the present invention does not change.

Explaining the present invention, a plurality of reflective photosensors S (FIG. 6) may be arranged in parallel in the main scanning direction so as to face the intermediate transfer belt 15 (FIG. 6) as an intermediate transfer member. However, the number of the reflection type photosensors S is often one for the purpose of cost reduction.
When there is one reflective photosensor S, it is usually installed at the center of the effective image width (FIG. 9). A toner adhesion amount detection pattern in a normal process control is formed on a portion where the reflective photosensor S faces.

In the toner adhesion amount detection according to the present invention, at least two or more toner adhesion amount detection solid patches having different image area ratios in the main scanning direction are formed on the photoconductors 31 to 34 as image carriers. This solid patch for toner adhesion amount detection is transferred to the intermediate transfer member 15 which is an image carrier with the same transfer output.
The toner adhesion amount of the solid patch for toner adhesion amount detection is read by a toner adhesion amount detection sensor S used in a normal image density control process computer that feeds back the read data to image forming conditions.
In this toner adhesion amount detection, two types of patterns having different image area ratios in the main scanning direction are formed so as to cover the position where the reflective photosensor S faces (the center of the effective image width). Here, as shown in FIG. 9, a solid image pattern having an image width of 5% and 80% is formed.

The graph of FIG. 10 shows the result of measuring the transfer rate of these two solid image patterns, which are reference pattern images, while changing the transfer current. Here, the transfer rate is a value obtained by dividing the toner adhesion amount on the intermediate transfer belt 15 (FIG. 2), which is an intermediate transfer body after the transfer, by the toner adhesion amount on the photosensitive members 31 to 34.
The 80% reference pattern image having a wider image width has the transfer rate curve shifted to the lower current side. This is because the ratio of the background portion of the photoconductors 31 to 34 (the portion where the charged potential is held without being exposed) is smaller at the image width of 80% than the image width of 5%. This is because the impedance of 34 is high.
Actually, the VI (transfer voltage-transfer current) characteristic measured under these conditions is shown in FIG. 11. With the same transfer current, the voltage with an image width of 80% is higher than the voltage with an image width of 5%. That is, it can be seen that the transfer section resistance is high because the photoconductors 31 to 34 have high impedance.
By reading the difference in transfer rate with the reflection type photosensor S, it is possible to detect whether the transfer rate is affected by the size of the image area rate in the main scanning direction, that is, whether the image density varies. it can.

A plurality of solid patches with different image area ratios in the main scanning direction are imaged, and these solid patches are transferred to an intermediate transfer member to detect the amount of toner adhesion, so that the transfer rate due to the change in the image area ratio in the main scanning direction is detected. Changes can be detected accurately.
This is because the impedance of the photoconductors 31 to 34, which are image carriers, changes depending on the image area ratio in the main scanning direction, and this is because the image portion potential is lower (as an absolute value) than the charged potential of the non-image portion. This is because the toner on the photoconductors 31 to 34 behaves as a resistor.
This effect is more noticeable with a solid image than with a dot image. Therefore, by comparing a solid patch with a low image area ratio and a high solid patch in the main scanning direction, a difference in impedance → a difference in transfer ratio → a difference in toner adhesion amount on the intermediate transfer body 15 can be detected with a high SN ratio. it can.

Further, from the relationship between FIG. 10 and FIG. 11, a difference in transfer rate can also be detected by providing a detection mechanism (not shown) that detects a current value at a constant voltage output or a voltage value at a constant current output. Can do.
By detecting the difference in transfer output caused by the difference in the image area ratio in the main scanning direction, a sensor is arranged opposite to the photoreceptors 31 to 34 instead of the intermediate transfer member 15 to detect the toner adhesion amount. Even in the configuration, there is an advantage that a difference in transfer rate can be detected.
By forming a plurality of solid patches with different image area ratios in the main scanning direction and detecting the transfer output at that time, the change in the impedance of the photoconductors 31 to 34 due to the change in the image area ratio in the main scanning direction can be accurately captured. Thus, a change in the transfer rate can be detected.
That is, if the impedance of the photoconductors 31 to 34 changes, the transfer output also changes. In the case of constant current output, the voltage value changes, and in the case of constant voltage output, the current value changes. Since the change leads to a change in the transfer rate, as described above, the change in the transfer rate can be detected by detecting the change in the transfer output.
According to this detection, an image forming apparatus that is not equipped with a toner adhesion amount detection sensor or an image forming apparatus (a monochrome machine or the like) in which the toner adhesion amount detection sensor is disposed to face the photoreceptors 31 to 34 can be used. It is possible to detect a change in transfer rate.

FIG. 12 is a circuit diagram showing the transfer part as a series circuit model of resistors. In FIG. 12, the series circuit includes a resistance R ₁ such as a transfer belt and a transfer roller, a transfer portion R _2, and a power source V ₁ .
As described above, when the difference in transfer rate is detected using the VI characteristic, it is preferable that the transfer output is a constant current output. That is, the transfer output change detection detects a voltage value at which the output method of the transfer output is a constant current output.
This is because when the transfer portion is considered as a series circuit model of resistance as shown in FIG. 12, the transfer electric field V ₂ applied to the transfer portion resistance R ₂ is expressed as R ₂ / (R ₁ + R ₂ ) × V when the voltage output is constant. This is because the transfer unit resistor R2 even if you want to apply the same transfer field not changed, it takes place such same field by varying the resistance R ₁ such as a transfer roller is not applied. In the case of constant current output, the transfer electric field V ₂ applied to the transfer portion resistance R ₂ is expressed as R ₂ × I, and R ₁ does not affect.

In this manner, a stable transfer electric field can be formed regardless of the resistance of a member related to transfer, and a stable transfer voltage change can be detected. When the transfer output is a constant voltage output, when the resistance of the transfer member other than the impedance of the photoconductors 31 to 34, which is a problem here, varies, the actual transfer between the photoconductors 31 to 34 and the transfer target is performed. The electric field (transfer electric field) formed on the substrate is likely to change greatly.
For example, when the resistance of the transfer member is increased, the partial pressure to the transfer member is increased, so that the transfer electric field is decreased. Since the change is small at the constant current output, a more stable transfer electric field can be obtained even when the resistance of the transfer member fluctuates.

FIG. 13 is a graph showing the results of examining the relationship between the charging potential and the VI characteristic.
The difference in the image area ratio in the main scanning direction is noticeably manifested as a change in the transfer ratio when the impedance of the photoreceptor background is low.
FIG. 13 shows the results of examining the relationship between the charging potential (Vd) and the VI (voltage-current) characteristics. It can be seen from FIG. 13 that the higher the charging potential, the lower the impedance. Therefore, it can be expected that reducing the charging potential is effective in suppressing the change in the transfer rate.
In the negative development method, at least two or more solid patches having different image area ratios in the main scanning direction in the toner adhesion amount detection described above have a certain difference (a predetermined value provided as a reference) in each toner adhesion amount. When detected, in this potential control, the absolute value of the charging potential of the photoconductor as the image carrier is lowered from the standard value.

FIG. 14 is a graph showing the relationship between the image width and the transfer rate. FIG. 14 shows the result of actually measuring the transfer rate of 5% and 80% of the image width at Vd = 580V and Vd = 480V. The development potential was 430V. When the charging potential is lower, Vd = 480 V, the difference between the transfer rate of 5% and 80% of the image width is reduced. That is, it can be seen that the difference in image density can be reduced.
In the negative development method, the charging polarity of the toner and the polarity of the charging potential are the same. Since the transfer output is applied with a bias having a polarity opposite to that of the toner, the impedance decreases as the absolute value of the charging potential increases.
Therefore, by utilizing this, by increasing the overall impedance of the photoconductor as an image carrier, the change in impedance due to the size of the image area ratio in the main scanning direction is relatively reduced, and the image area in the main scanning direction is reduced. The change of the transfer rate due to the rate can be suppressed.
However, if only the charging potential is lowered, the potential between charge and development becomes small, and the phenomenon of background smearing in which toner adheres to the background portion may become serious.

FIG. 15 is a graph showing the relationship between the charge-development potential and the background stain. FIG. 15 shows the result of measuring the amount of background contamination by changing the charging potential when the development potential is 430 V.
The amount of scumming is measured by transferring the scumming toner on the photoconductors 31 to 34 with a transparent tape, affixing the tape onto paper, and then a spectrocolorimeter manufactured by X-Rite. Image ID was measured with Model 938 (the vertical axis of the graph is the value obtained by subtracting the ID for paper and tape).
When Vd = 580V, the potential is 150V, and the dirt at that point is at a low level. However, when Vd = 480V, since the potential is 50V, the amount of background contamination increases. In order to prevent this background stain, the development potential is lowered to increase the charge-development potential.
In this example, if the charge-development potential is at least 100 V or more, a stable region with little background stain is obtained. Therefore, by changing the development potential from 430 V to about 380 to 330 V, an image with little background stain can be obtained. That is, when performing control to lower the charging potential, the developing potential is also lowered in conjunction with it.
In this way, if the charging potential is lowered without changing the development potential, the difference between the development potential and the charging potential is reduced, so that an abnormal image such as a background stain in which the toner is originally developed on the background portion where the toner is not attached is generated. It tends to occur. By reducing the development potential in conjunction with the decrease in the charging potential so as to keep the difference between the development potential and the charging potential substantially constant, an image free from background contamination can be obtained.

By the way, the quadruple tandem type color image forming apparatus illustrated here has four photosensitive members. If the development potential is lowered as described above in one of them, the toner adhesion amount for only that color is reduced and the density becomes light, and the density balance of the four colors is lost.
Therefore, in a system using a photoconductor as a plurality of image carriers (such as a quadruple tandem system), the potential control remains when the charging / developing potential of at least one of the photoconductors is lowered. Similarly, the charging / developing potential of the photosensitive member is also lowered.
Since color image processing is designed on the assumption that the toner adhesion amount of each color is almost the same, if the density decreases by one color, various colors expressed by mixing the four colors There is a risk that it will not be possible to correctly express the color tone.

Therefore, when the development potential is reduced by controlling the development potential in conjunction with the reduction of the charging potential in any one color, the development potential is set so that the density of the other colors is reduced to the same extent. By reducing it, the color balance can be maintained and the color tone can be expressed correctly.
As described above, when the development potential is lowered, the toner adhesion amount on the photoreceptor is lowered, and the image density on the recording paper is also lowered. If the charging / developing potential is lowered for only one of the plurality of photosensitive members by the potential control described above, the image density is lowered for only that color, and the density balance with other colors is lost.
Furthermore, a color imaging system expresses various colors by superimposing a plurality of colors. However, a target color cannot be expressed if the density of a specific color is low (for example, if only the density of cyan is reduced, blue (Cyan + Magenta) becomes reddish and Green becomes yellowish).
Therefore, when the development potential is lowered by the above-described potential control in any one of the plurality of photoreceptors, the density balance is maintained in the color image by reducing the charging / development potential of all the remaining photoreceptors. It is possible to suppress the change in hue and express the correct color. However, in this case, there may be a side effect that the concentration becomes lower overall.

FIG. 16 is a flowchart showing the control operation having the toner adhesion amount control mode. When the charging / developing potential of at least one of the photosensitive members is lowered, the charging / developing potential of the remaining photosensitive members is also lowered in the same manner as described above. Is lower than intended.
Therefore, by inserting the toner adhesion amount control mode as shown in the block diagram of FIG. 16, a target image density can be obtained while maintaining a charged potential that does not change the density depending on the image area ratio in the main scanning direction. .

In the flowchart of FIG. 16, first, control for lowering the charging potential / developing potential is executed (S1). Next, a normal process control including potential adjustment is executed (S2). It is determined whether or not the charged potential to be updated is equal to or less than the preset value x (V) from the program control result (S3).
If it is equal to or less than the preset value x (V), the charging potential / developing potential setting value is updated and the process ends (S4). If it is not less than the preset value x (V), toner replenishment is executed, and the flow returns to step (S2) to repeat the flow.
According to the examples described so far, the target charging potential x = 480 V and the control in FIG. 16 can be performed to obtain the target image density with a charging potential of 480 V or less. As shown in FIG. 14, at Vd = 480 V, the change in transfer rate due to the image area rate in the main scanning direction is small, so that an image with suppressed density variation can be obtained.

In the two-component development method, the toner adhesion amount control including toner replenishment after the charging / developing potential is lowered by the potential control for lowering the developing potential as well as the charging potential and the potential control for lowering the charging / developing potential of all the photoconductors. In the toner adhesion amount adjustment mode in which the mode is executed, the charging / developing potential is not changed, or the charging potential is changed to a value lower than the set value set by the potential control described above.
If the developing potential is changed by the potential control for reducing the developing potential as well as the charging potential and the potential control for reducing the charging / developing potential of all the photoconductors as it is, the image density naturally decreases.

However, if a toner adhesion amount adjustment mode (so-called procomputer) is entered, a target toner adhesion amount can be obtained, but the charging / developing potential rises as a means for adjustment.
Therefore, in this toner adhesion amount control mode, the toner density of the developer is increased by supplying toner. As a result, the development γ decreases, and as a result, a target toner adhesion amount can be obtained at a low charging / developing potential.
The charging / developing potential at this time is set to the same potential as or lower than the value set by the potential control for decreasing the developing potential as well as the charging potential and the potential control for decreasing the charging / developing potential of all the photoconductors.

With such a determined charging potential, a high photoconductor impedance necessary to suppress a change in transfer rate due to an image area rate in the main scanning direction is realized. Accordingly, it is possible to suppress a change in the transfer rate due to the image area ratio in the main scanning direction while maintaining a state in which no background contamination occurs and no change in image density or color.
In the toner adhesion amount adjustment mode for executing the toner adhesion amount control mode including toner replenishment described above, the charging / developing potential is not changed or the charging potential is set to a value lower than the set value set by the potential control described above. The changing control is a method of keeping the impedance high by keeping the charging / developing potential low by raising the toner density and developing γ.
For this reason, when the toner density is already high, there is a case where it cannot be executed due to being caught by the upper limit value in toner density control. Even when the toner adhesion amount adjustment mode cannot be controlled, a means that can achieve the object and that is effective even when used alone is required.

FIG. 17 is a schematic view showing a pressure mechanism for applying pressure to a tension roller as a support roller. FIG. 17 is an enlarged view of the vicinity of one end of a tension roller 19 (FIG. 2) as a support roller. A similar pressurizing mechanism is arranged at the other end.
The mandrel 19a of the tension roller 19 is fitted to a bearing 58, and the bearing 58 is pressed in a direction to apply tension to the intermediate transfer belt 15 (FIG. 2) by a tension spring 59 that urges the bearing 58. Further, the movement of the bearing 58 is restricted by the bracket 60 in the left-right direction in FIG.
The eccentric cam 61 is adjacent to the bracket 60, and its axis is fixed so as to penetrate a side wall (not shown) of the intermediate transfer unit. In the normal state, unlike FIG. 17, it contacts on the short side. When the eccentric cam 61 is rotated 90 degrees from the state where it is in contact with the short side, the bracket 60 moves to the left in FIG. 17 and comes into contact with the long side of the eccentric cam 61. Thereby, the tension of the intermediate transfer belt 15 can be increased.
In order to increase the pressing force of the primary transfer rollers 27 to 30 (FIG. 2), the pressing force of the primary transfer rollers 27 to 30 is increased by the same operation as the method of increasing the tension of the intermediate transfer belt 15. can do. In this case, the core 19a of the tension roller 19 may be considered as the core of the primary transfer rollers 27-30.

In this way, at least two or more toner adhesion amount detection solid patches having different image area ratios in the main scanning direction are formed on the photoconductors 31 to 34 (FIG. 2) as image carriers, and the same transfer output is obtained. Transfer to an intermediate transfer belt, which is an intermediate transfer body, a recording paper carrier (not shown), recording paper, etc., and detect the difference in transfer output caused by the difference in image area ratio in the main scanning direction. When a voltage value that is a constant current output is detected, the pressure applied to the tension roller 19 is increased.
When the tension of the intermediate transfer belt 15 is increased by increasing the applied pressure, the intermediate transfer belt 15 is stretched with a small amount of deflection. Since the deflection is reduced between the stretching roller 17 and the stretching roller 18, which are the support rollers shown in FIG. 2, the pressure for pressing the primary transfer rollers 27 to 30 against the photoreceptors 31 to 34 becomes weak, and the primary transfer nip width. Becomes narrower. For this reason, the impedance of the transfer portion becomes high, and therefore it is difficult to be affected by the size of the image area ratio. That is, it is possible to suppress a variation in the transfer rate due to the image area rate.

In addition, at least two or more toner adhesion amount detection solid patches having different image area ratios in the main scanning direction are formed on the photosensitive members 31 to 34, and the intermediate transfer member, the recording paper transport member, and the recording paper are produced with the same transfer output. Transcript to etc.
During this transfer, each transfer is detected by detecting a difference in transfer output caused by a difference in image area ratio in the main scanning direction, and detecting a transfer output change in which the output method of the transfer output is a constant current output. When a difference greater than a certain value (a predetermined value provided as a reference) is detected in the output, the pressure applied to pressurize the primary transfer rollers 27 to 30 in the direction is reduced.
In this way, the pressure applied to press the primary transfer rollers 27 to 30 against the intermediate transfer body 15 is weakened, so that the primary transfer nip width is narrowed. Therefore, since the impedance of the transfer portion becomes high, it is difficult to be affected by the size of the image area ratio, and fluctuations in the transfer ratio due to the image area ratio can be suppressed.

Further, after performing control to increase the pressure applied to the tension roller 19 and control to decrease the pressure to press the primary transfer rollers 27 to 30 in the direction of the intermediate transfer body 15, a normal image density control protocol is implemented. .
By doing so, both of the above-described controls increase the impedance of the primary transfer portion, so that the transfer electric field changes at the same transfer output. If it is left as it is, the transfer rate of primary transfer and the reverse transfer rate also change, resulting in fluctuations in image density.
For this reason, the image density can be appropriately maintained by executing the process control. Accordingly, it is possible to obtain an appropriate image density while suppressing fluctuations in the transfer rate due to the image area rate.
When the above-described control is performed to change the tension of the intermediate transfer belt 15 or the pressurizing force of the primary transfer rollers 27 to 30, the tension or primary of the intermediate transfer belt 15 is performed before the execution of this control at the next timing. The transfer pressure is configured to return to the level before the change.

In the two-component development method, the potential control includes a control for lowering the development potential in conjunction with the above-described charging potential, and a toner adhesion amount control mode including toner replenishment after lowering the charging / developing potential of all the photoconductors. And the charging potential is changed to a value lower than the set value set by these potential controls.
In the case of such control, if a problem occurs with the tension or the pressure increased, it is difficult to further improve the control. Therefore, the control for changing the tension of the intermediate transfer belt and the pressure of the primary transfer roller is not recommended. It is desirable to execute a toner adhesion amount control mode including the above and to provide a backup of control for changing the charging potential to a value lower than the set value set by these potential controls. As a result, it is possible to continuously suppress fluctuations in the transfer rate due to the image area rate.

1 is a cross-sectional view illustrating a schematic configuration of a color printer which is an example of an image forming apparatus according to the present invention. It is the schematic which expands and shows the image formation part periphery of FIG. FIG. 3 is a schematic enlarged view showing the intermediate transfer body cleaning device of FIG. 2. FIG. 3 is an enlarged schematic view illustrating a photosensitive member cleaning unit in FIG. 2. It is a block diagram which shows a part of electric circuit of the color printer which implements this invention. 5 is a schematic diagram showing a reference pattern image P. FIG. It is a figure which shows the relationship between a toner adhesion amount and a sensor detection output with a graph. FIG. 6 is a graph showing the relationship between development potential and toner adhesion amount. It is a figure which shows the imaged solid image pattern about image width 5% and 80%. It is a figure which shows the relationship between a transfer rate and a transfer current with a graph. It is a figure which shows the relationship between a transfer voltage and a transfer current with a graph. It is a circuit diagram which shows a transcription | transfer part as a series circuit model of resistance. It is a figure which shows the result of having investigated the relationship between a charging potential and VI characteristic by a graph. It is a figure which shows the relationship between an image width and a transfer rate with a graph. It is a figure which shows the relationship between the charge-development potential and background stain | pollution | contamination with a graph. 6 is a flowchart illustrating a control operation having a toner adhesion amount control mode. It is the schematic which shows the pressurization mechanism which applies a pressure to the tension roller which is a support roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus, 2 Image forming process unit, 10 Image forming means (image forming part), 15 Intermediate transfer body (intermediate transfer belt), 19 Tension roller (support roller), 31 Image carrier (photosensitive body), 35 Photosensitive Body charging means, 43 developing means (toner image forming section), 56 control section, 56a CPU, 56b RAM, 57 transfer unit, 58 pressure mechanism (bearing), 59 pressure mechanism (tension spring), 60 pressure mechanism ( Bracket), 61 pressurization mechanism (eccentric cam), S toner adhesion amount detection sensor (reflection photosensor)

Claims (12)

In an image forming apparatus for developing and visualizing an electrostatic latent image formed on a photoconductor with toner, transferring the toner image onto a recording medium, and fixing the toner image on the recording medium.
Image forming means for forming on the photosensitive member at least two solid patches for detecting the amount of adhered toner having different image area ratios in the main scanning direction, and the solid patch on the intermediate transfer member and the recording medium with the same transfer output A transfer unit for transferring, a control unit for performing image density control, and a toner adhesion amount detection sensor used for the image density control, wherein the toner adhesion amount of the solid patch is read by the toner adhesion amount detection sensor. An image forming apparatus. In an image forming apparatus for developing and visualizing an electrostatic latent image formed on a photoconductor with toner, transferring the toner image onto a recording medium, and fixing the toner image on the recording medium.
Image forming means for forming on the photosensitive member at least two solid patches for detecting the amount of adhered toner having different image area ratios in the main scanning direction, and the solid patch on the intermediate transfer member and the recording medium with the same transfer output A transfer unit that performs transfer, a control unit that performs image density control, and a detection unit that detects a difference in transfer output, and the detection unit includes an image area in the main scanning direction of the solid patch transferred to the intermediate transfer member. An image forming apparatus, wherein a difference in transfer output caused by a difference in rate is detected as a change in transfer output.   The image forming apparatus according to claim 2, wherein the detection unit detects a voltage value when the transfer output is a constant current output.   In the negative development method, the absolute value of the charging potential of the photoconductor is lowered from the standard value when a predetermined difference is detected in the amount of toner adhesion between the two or more solid patches having different image area ratios in the main scanning direction. 2. The image forming apparatus according to claim 1, wherein the potential of the photosensitive member is controlled.   In the two or more solid patches having different image area ratios in the main scanning direction, when a predetermined difference is detected in each transfer output, the absolute value of the charging potential of the photosensitive member is decreased from a standard value. 4. The image forming apparatus according to claim 2, wherein potential control is performed.   6. The image forming apparatus according to claim 4, wherein when performing the potential control for reducing the charging potential, the potential control of the photoconductor for decreasing the developing potential is also performed. In the quadruple tandem system in which multiple photoconductors are used,
7. The potential control of the photoconductor is performed so that, when the charging / developing potential of at least one of the photoconductors is lowered, the charging / developing potential of the remaining photoconductors is similarly lowered. Image forming apparatus.   In the two-component development system, after the charging / developing potential is lowered by the potential control, the toner adhesion amount control mode including toner replenishment is executed, and the charging / developing potential is not changed or is set by the potential control. 8. The image forming apparatus according to claim 4, wherein control is performed to change the charging potential to a value lower than the set value.   In the detection of the transfer output change, when a predetermined difference is detected in each transfer output with two or more solid patches having different image area ratios in the main scanning direction, control is performed to increase the pressure applied to the tension roller. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus.   In the detection of the transfer output change, when a predetermined difference is detected in each transfer output with two or more solid patches having different image area ratios in the main scanning direction, the primary transfer roller is pressed toward the intermediate transfer body. 4. The image forming apparatus according to claim 2, wherein control is performed to reduce the applied pressure.   A normal image density adjustment process control is performed after the control to increase the pressure applied to the tension roller and the control to decrease the pressure to press the primary transfer roller toward the intermediate transfer body. The image forming apparatus according to claim 9 or 10.   When the tension of the intermediate transfer member or the pressing force of the primary transfer roller is changed, the tension or the intermediate transfer member before the image density control is performed at the time of the image density control at the next timing following the change. 12. The image forming apparatus according to claim 9, wherein control is performed to return the pressure applied to the primary transfer roller to a level before the change.

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