JP2002055496A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of easily grasping the characteristic of the lowering of density caused in the image forming device, performing correction so as to prevent the lowering of the density at a boundary part where a halftone part is shifted to a background part or a boundary part where a low density part is shifted to a high density part by such grasping, and easily coping with a machine difference between the image forming devices, the difference and the change of environment and the secular change of the device and parts. SOLUTION: The image forming device is provided with a density control part detecting the density at the trailing edge of a toner patch image formed on a photoreceptor drum as reflected light quantity and setting a specified difference between the first rotation and the second and succeeding rotation of the photoreceptor drum in cleaning field being a difference between the grid applied voltage of an electrifier and developing bias voltage in accordance with a sensor output value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control technique for an image forming apparatus, and more particularly, to image density control in an image forming apparatus such as a copying machine, a printer, and a facsimile apparatus for forming an image by an electrophotographic process.

[0002]

2. Description of the Related Art Many image forming apparatuses, such as digital copiers and printers, which are currently commercialized, use an electrophotographic system capable of obtaining a high-quality image at a high speed as an image output section (image output apparatus). Has been widely adopted. In the electrophotographic method, as the developing means, the insulating toner and the magnetic particles are mixed and rubbed in a developing device to charge the insulating toner, and the developer is formed into a brush shape by a magnetic force on the developing roll. A two-component magnetic brush developing system that develops an electrostatic latent image on a photoconductor by supplying a developer onto the photoconductor by rotation is widely used.
In particular, color image forming apparatuses are more widely used.

[0003] However, this electrophotographic image output unit,
Especially in the image output unit using the two-component magnetic brush development method,
Due to the non-linear and asymmetric output characteristics, when two image portions having different densities are continuous, a phenomenon occurs in which the density of a boundary portion of one image portion with the other image portion decreases.

First, when the output image changes from the halftone portion to the background portion in the sub-scanning direction, the density of the rear end portion of the halftone portion in contact with the background portion decreases. That is,
As shown in FIG. 14A, the output image is in a direction opposite to the paper transport direction orthogonal to the main scanning direction which is the scanning direction of the light beam for forming the electrostatic latent image on the photoconductor. When the halftone portion changes from the halftone portion to the background portion in the sub-scanning direction, the density of the rear end portion of the halftone portion in contact with the background portion decreases.

Second, when an output image changes from a low-density portion to a high-density portion in the sub-scanning direction, the density at the rear end portion of the low-density portion that contacts the high-density portion decreases. That is, as shown in FIG. 14B, when the output image changes from the low-density portion to the high-density portion in the sub-scanning direction, the density of the rear end portion in contact with the high-density portion of the low-density portion decreases. .

The reduction in the density at the rear end also differs depending on the state of the surface charge of the photosensitive drum. In particular,
Since the surface charge at the time of image formation differs between the first rotation and the second rotation of the photosensitive drum, the lowering of the density at the rear end occurs more remarkably.

In the electrophotographic system using the two-component magnetic brush developing system, as shown in FIG. 15, the photosensitive drum is charged by a charger for forming an electrostatic latent image by rotation of the photosensitive drum in the direction of the arrow. The charged photosensitive drum is irradiated with a laser beam L modulated by an image signal to form an electrostatic latent image on the photosensitive drum, and the photosensitive member on which the electrostatic latent image is formed. When the drum comes into contact with the developer layer on the surface of the developing roller rotating in the direction of the arrow at a peripheral speed of about twice the peripheral speed of the photosensitive drum, the toner in the developer layer becomes a latent image on the photosensitive drum. And the electrostatic latent image on the photosensitive drum is developed into a toner image.

FIG. 15A shows a moment when a latent image portion of a halftone portion is formed on the photosensitive drum by irradiation of the laser beam L, and a front edge of the latent image portion contacts the developer layer.
(B) shows the moment when the portion slightly before the rear edge of the latent image portion contacts the developer layer, and FIG. 15 (C) shows the moment when the rear edge of the latent image portion contacts the developer layer.

The developing roller is supplied with a developing bias having a potential of, for example, -500 V. The photoreceptor drum is charged by the charger to a potential having a larger absolute value than the developing bias potential, for example, a potential of -650 V, and the latent image portion of the halftone portion has a smaller absolute value than the developing bias potential, for example, 200 V.
It is said. Further, the portion corresponding to the background portion behind the halftone portion has a charging potential of −650 V, which is larger in absolute value than the developing bias potential. When the front edge of the latent image portion contacts the developer layer as shown in FIG. 15A, a forward developing electric field is applied to the toner tq existing at the position Q where the photosensitive drum and the developer layer contact. As a result, the toner tq is attracted to the surface of the developer layer and adheres to the latent image portion. However, FIG.
When the portion corresponding to the background portion behind the halftone portion approaches the developer layer as shown in FIG. 5B, the toner tb existing in the portion facing the developer layer portion is developed by the developing electric field in the opposite direction. The developer is moved away from the surface of the developer layer and sunk deep into the developer layer.

When the developing roller rotates in the direction of the arrow, the toner tb approaches the position Q where the photosensitive drum and the developer layer are in contact with each other, and the low potential of the latent image portion causes the toner tb to reach the surface side of the developer layer. , But a time delay occurs to reach the surface of the developer layer. Therefore, FIG.
Since the portion slightly before the rear edge of the latent image portion comes into contact with the developer layer as shown in FIG. 5 (B), the amount of toner adhered to the photosensitive drum decreases, as shown in FIG. 14 (A). like,
The density of the rear end portion of the halftone portion in contact with the background decreases.

When the front of the halftone part is also the background part,
Even when the front edge of the latent image portion contacts the developer layer as shown in FIG. 14A, the toner tf is contained in the toner in the developer layer.
As shown by, some portions on the photosensitive drum corresponding to the front background portion are separated from the surface of the developer layer.

However, the rotation of the developing roller in the direction of the arrow causes the toner tf to rapidly move away from the position Q where the photosensitive drum and the developer layer are in contact with each other. Attracted toner t
q immediately approaches the position Q and is deposited on the latent image portion. Therefore, even if the output image changes in the sub-scanning direction, or conversely, from the background portion to the halftone portion, the density of the front end portion of the halftone portion in contact with the background portion does not decrease.

FIG. 16A shows that the latent image portion of the low density portion is formed on the photosensitive drum by the irradiation of the laser beam L, and the front edge of the latent image portion is developed. FIG. 16B shows the moment when the rear edge of the latent image portion comes into contact with the developer layer, and FIG.
FIG. 6 (C) shows the moment when the high-density latent image portion, slightly behind the rear edge of the latent image portion, comes into contact with the developer layer.

The latent image portion of the low density portion has an absolute value smaller than the developing bias potential, for example, -300 V. Also,
The latent image portion of the high density portion behind the low density portion has an absolute value smaller than the potential of the latent image portion of the low density portion, for example, -200V. As shown in FIG. 16A, when the front edge of the latent image portion comes into contact with the developer layer, a forward developing electric field is applied to the toner ta located at the position Q where the photosensitive drum and the developer layer come into contact. Then, the toner ta adheres to the latent image portion. Since then
As shown in FIG. 16B, the toner adheres to the low-density portion of the latent image until the rear edge of the latent image contacts the developer layer. The toner tc is toner attached to a rear end portion of the latent image portion, which is in contact with the latent image portion, corresponding to a rear end portion of the low density portion in contact with the high density portion.

However, after the point of FIG. 16B, the latent image portion of the high density portion comes into contact with the developer layer.
The potential of the latent image portion has a smaller absolute value than the potential of the latent image portion, and a larger developing electric field in the forward direction is applied between the latent image portion and the developer layer. A large amount of toner is deposited. Therefore, in the portion of the developer layer near the position Q where the photosensitive drum and the developer layer are in contact, the magnetic particles covered with the toner are exposed, and the potential of the magnetic particles causes the magnetic particles shown in FIG. As shown in ()), the toner tc once attached to the rear end portion of the latent image portion in contact with the latent image portion is pulled back into the developer layer.

For this reason, as shown in FIG. 16C as a portion where no toner is present, the rear end of the latent image portion which is in contact with the latent image portion is not necessarily completely eliminated but is simplified. 14 (B), the amount of toner in the portion decreases.
As shown in (1), the density at the rear end portion of the low density portion that contacts the high density portion decreases. It should be noted that the toner te attached to the latent image portion of the high density portion is the same as the toner t attached to the latent image portion of the low density portion.
Although it is larger than a, it is shown as the same amount in FIG.

The decrease in the density at the rear end of the low-density portion, that is, the decrease in the toner amount at the rear end of the latent image portion, is caused by the absolute value of the latent image portion of the high-density portion immediately following the low-density portion. The small potential causes the toner tc adhered to the rear end of the latent image portion to be drawn back into the developer layer, so that the output image changes from the high density portion to the low density portion in the sub-scanning direction. Even if the density changes, the density of the front end portion in contact with the high density portion of the low density portion does not decrease.

As described above, in the electrophotographic system based on the two-component magnetic brush developing system, when the output image changes from the halftone portion to the background portion in the sub-scanning direction, the rear end portion of the halftone portion which comes into contact with the background portion. The density of the halftone area where the density of
When the output image changes from a low-density portion to a high-density portion in the sub-scanning direction, two densities having different densities, such as a low-density portion density decrease in which the rear end portion in contact with the high-density portion of the low-density portion decreases. When the image portions are continuous, a phenomenon occurs in which the density of the boundary portion between one image portion and the other image portion decreases.

JP-A-5-281790 and JP-A-6-87234 disclose that a laser beam scanner for writing an electrostatic latent image on a photoreceptor by a laser beam has been improved in accuracy.
By adjusting the parameters of the developing means that develops the electrostatic latent image, the contrast of the developing electric field is increased, and the density at the boundary where the transition from the halftone portion to the background portion is reduced, and the density is shifted from the low density portion to the high density portion The idea is to prevent the lowering of the density at the boundary portion. That is, due to the maintenance of the accuracy of each image forming component, for example, the high-voltage power supply unit, the cartridge, the density adjusting unit for the user, etc., even if environmental fluctuations such as temperature, humidity, and atmospheric pressure occur, they are allowed depending on the design margin. It was configured to be absorbed in the range.

[0020]

However, the method of increasing the contrast of the developing electric field by increasing the accuracy of the laser beam scanner, which is a means for writing an electrostatic latent image, increases the size and cost of the image output section. become. Moreover,
When increasing the number of screen lines at the image output unit to increase the resolution of the output image, the contrast of the developing electric field decreases, and the density of the boundary that shifts from the halftone part to the background part decreases, and the density decreases from the low density part. Since the lowering of the density at the boundary that shifts to the high-density portion is more likely to occur, it is difficult to achieve a high resolution of the output image.

In recent years, there has been a tendency to increase the chance of printing graphic images created on a host such as a personal computer. In such a graphic image, the above-described decrease in density is more noticeable than in a natural image such as a photograph. Therefore, in an image forming apparatus such as a computer printer or a network printer, the above-described reduction in density becomes more problematic than in an image forming apparatus such as a copying machine.

Since the image forming process of the image forming apparatus is quite complicated, it is quite difficult to elucidate the physical characteristics of the image forming apparatus and determine the characteristics of the density reduction that occurs there from theoretical calculations. Accompany. Also, directly measuring the physical characteristics of the image forming apparatus using a measuring instrument,
It's not easy. Moreover, between the individual image forming apparatuses,
In addition to variations in characteristics due to machine differences, the characteristics of the image forming apparatus also change due to environmental conditions such as temperature and humidity, and aging of the apparatus and components.

As a method for solving the above problem, there is, for example, an image processing apparatus described in Japanese Patent Application Laid-Open No. H10-65920. In the above-described apparatus, measurement data in which a plurality of toner patches having different numbers of pixels to be corrected (the range of the rear end where the density is reduced) and pixel value correction amounts (a correction amount corresponding to the density reduction amount) are arranged. Is output, and the optimum correction target pixel number and the pixel value correction amount are obtained from the output result, and are stored in the characteristic description unit. Then, from the input image data, a rear edge portion where image missing can occur is extracted,
In the extracted rear edge area, the image data is corrected based on the number of correction target pixels and the pixel value correction amount held in the characteristic description unit, thereby preventing image loss in the area.

However, in the apparatus disclosed in the above publication, a plurality of toner patches (1 to 225) are
Step) The problem is that it takes time to measure the image and calculate the amount of density reduction at the rear end of the image at each step, and the amount of toner consumption increases because multiple toner patches are formed. Had occurred.

The present invention has been made in view of such circumstances, and it is possible to easily grasp the characteristics of density reduction occurring in an image forming apparatus. The correction can be made so that the density drop at the boundary where the transition from the density portion to the high density portion is prevented, and it can be easily performed due to differences in the image forming apparatus, differences and changes in the environment, and aging of the device and parts over time. It is an object of the present invention to provide an image forming apparatus capable of coping with the above.

[0026]

According to the present invention, means for solving the above-mentioned problems are constituted as follows.

(1) The density at the rear end of the toner patch image formed on the photosensitive drum is detected as the amount of reflected light, and the difference between the grid applied voltage of the charger and the developing bias voltage according to the sensor output value. In the cleaning field,
A density controller is provided for setting a predetermined difference between the first rotation of the photosensitive drum and the second rotation and thereafter.

According to this configuration, since the change in the waveform output of the toner patch image is detected and fed back, the control can be performed by utilizing the existing means without changing the structure of the mechanical part of the image forming apparatus. By changing the contents of the system, it is possible to prevent the occurrence of a missing image at the rear end and improve the image quality.

(2) When the sensor output value is between the first reference value on the low output side and the second reference value on the high output side, the photosensitive member is increased as the sensor output value increases. The cleaning field is reduced after the first and second rotations of the drum, and when the sensor output value is equal to or less than a first reference value or equal to or greater than a second reference value, the cleaning field is reduced to the first reference value and the second reference value. The potential difference corresponding to the second reference value is fixed, and the value of the cleaning field is not changed in a range outside the first reference value and the second reference value.

According to this configuration, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both low cost and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the cleaning field is fixed at a potential difference corresponding to the first reference value, so that it is possible to prevent the high voltage power supply from becoming excessive in capacity. it can.

In a region where the sensor output value is equal to or larger than the second reference value, the cleaning field is fixed at a potential difference corresponding to the second reference value, so that it is possible to prevent image fog from deteriorating.

(3) The density at the rear end of the toner patch image formed on the photosensitive drum is detected as the amount of reflected light,
The method is characterized in that the LSU light amount at the rear end of the image is changed in the first and second rotations of the photosensitive drum according to the sensor output value.

According to this configuration, since the change in the waveform output of the toner patch image is detected and fed back, the existing system is utilized without changing the structure of the mechanical part of the image forming apparatus. By changing the contents of (1), the occurrence of a rear end missing image can be prevented, and a good image can be obtained.

(4) When the sensor output value is between the first reference value on the low output side and the second reference value on the high output side, the photosensitive drum is increased as the sensor output value increases. In the first and second rotations, the LSU light amount is increased, and when the sensor output value is equal to or less than the first reference value or equal to or greater than the second reference value, the LSU light amount is increased to the first reference value. And the LSU light amount is not changed in a range outside the first reference value and the second reference value.

According to this configuration, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both cost reduction and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the LSU light amount is fixed as the light amount corresponding to the first reference value, thereby preventing the image density from becoming insufficient.

In a region where the sensor output value is equal to or larger than the second reference value, the LSU light amount is fixed as the light amount corresponding to the second reference value, so that the performance deterioration due to light fatigue of the photoconductor is prevented.

(5) The change in the LSU light amount after the first and second rotations of the photosensitive drum is caused by a change in laser output value, a change in laser PWM value, a length of laser irradiation time, and a laser beam aperture diameter. Characterized in that at least one of the magnitudes is controlled.

According to this configuration, the control contents for changing the LSU light amount can be simplified.

(6) When the sensor output value is between the first reference value on the low output side and the second reference value on the high output side, the photosensitive member is increased as the sensor output value increases. The laser output value is increased after the first and second rotations of the drum, and when the sensor output value is equal to or less than the first reference value or equal to or greater than the second reference value, the laser output value is increased. The laser output value is fixed as a value corresponding to the first reference value and the second reference value, and the laser output value is not changed in a range outside the first reference value and the second reference value.

According to this configuration, the occurrence of the trailing edge missing image can be stopped within an allowable range, and both low cost and improvement in image quality can be achieved.

Further, in a region where the sensor output value is equal to or less than the first reference value, the laser power is fixed as an output value corresponding to the first reference value.

In a region where the sensor output value is equal to or larger than the second reference value, the laser power is fixed as an output value corresponding to the second reference value, so that performance degradation due to light fatigue of the photosensitive drum can be prevented. it can.

(7) When the sensor output value is between the first reference value on the low output side and the second reference value on the high output side, the photosensitive member is increased as the sensor output value increases. The laser PWM value is increased after the first and second rotations of the drum, and when the sensor output value is equal to or less than the first reference value or equal to or more than the second reference value, the laser PWM value is increased. The laser PWM value is fixed as a value corresponding to the first reference value and the second reference value, and the laser PWM value is not changed in a range outside the first reference value and the second reference value.

According to this configuration, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both low cost and improvement in image quality can be achieved.

Further, in a region where the sensor output value is equal to or less than the first reference value, the laser PWM value is fixed as an output value corresponding to the first reference value, thereby preventing image density from becoming insufficient.

In a region where the sensor output value is equal to or more than the second reference value, the laser PWM value is fixed as an output value corresponding to the second reference value, so that performance degradation due to light fatigue of the photosensitive drum can be prevented. Can be.

(8) When the output value of the sensor is between the first reference value on the low output side and the second reference value on the high output side, the photosensitive member is increased as the sensor output value increases. Increasing the number of revolutions of the rotating polygonal mirror after the first and second rotations of the drum, and when the sensor output value is equal to or less than the first reference value or equal to or greater than the second reference value, the rotating polygonal mirror; Is fixed as the rotation speed corresponding to the first reference value and the second reference value, and the rotation speed of the rotary polygon mirror is not changed in a range outside the first reference value and the second reference value. It is characterized by.

According to this configuration, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both low cost and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the rotation speed of the rotary polygon mirror is fixed as an output value corresponding to the first reference value, thereby preventing image density from becoming insufficient. Can be.

In a region where the sensor output value is equal to or more than the second reference value, the rotation speed of the rotary polygon mirror is fixed as an output value corresponding to the second reference value, so that the performance deterioration due to light fatigue of the photosensitive drum is prevented. Can be prevented.

(9) When the sensor output value is between the first reference value on the low output side and the second reference value on the high output side, the photosensitive member is increased with an increase in the sensor output value. The aperture diameter of the laser beam is increased after the first rotation and the second rotation of the drum, and when the sensor output value is equal to or less than the first reference value or equal to or more than the second reference value, the aperture diameter is increased. The aperture diameter is fixed as a value corresponding to the first reference value and the second reference value, and the aperture diameter is not changed in a range outside the first reference value and the second reference value.

According to this configuration, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both cost reduction and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the aperture diameter of the laser beam is set to the first reference value.
Since the output value is fixed as the output value corresponding to the reference value, it is possible to prevent the image density from becoming insufficient.

In a region where the sensor output value is equal to or larger than the second reference value, the aperture diameter of the laser beam is fixed as an output value corresponding to the second reference value. Can be prevented.

(10) The density of the trailing edge of the toner patch image formed on the photosensitive drum is detected as the amount of reflected light, and the amount of charge elimination at the trailing edge of the image is determined based on the sensor output value. It is characterized in that it is changed after the second rotation.

According to this configuration, since the change in the waveform output of the toner patch image is detected and fed back, the existing means is utilized without changing the structure of the mechanical part of the image forming apparatus, and the control system can be utilized. By changing the contents of the above, the generation of the rear end missing image can be prevented, and the image quality can be improved.

(11) When the sensor output value is between the first reference value on the low output side and the second reference value on the high output side, the photosensitive drum 1 is increased as the sensor output value increases.
In the case where the sensor output value is equal to or less than the first reference value or equal to or greater than the second reference value, the amount of charge removal is increased in the first and second rotations. It is characterized in that it is fixed as a value corresponding to a reference value, and that the amount of static elimination light is not changed in a range outside the first reference value and the second reference value.

According to this configuration, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both cost reduction and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the amount of static elimination is fixed as the amount of static elimination corresponding to the first reference value, thereby preventing the occurrence of a photoconductor memory (charging memory). be able to.

Then, in a region where the sensor output value is equal to or more than the second reference value, the light elimination light amount is fixed as the light elimination light amount corresponding to the second reference value, so that the performance deterioration due to light fatigue of the photosensitive member can be prevented. .

(12) The density of the rear end of the toner patch image formed on the photosensitive drum is detected as the amount of reflected light, and the peripheral speed ratio is determined at the first and second rotations of the drum according to the sensor output value. Is changed.

According to this configuration, since a change in the waveform output of the toner patch image is detected and fed back, the existing system is utilized without changing the structure of the mechanical part of the image forming apparatus, and the control system is utilized. By changing the contents of the above, the occurrence of the rear end missing image rubber can be prevented, and the image quality can be improved.

(13) When the sensor output value is between the first reference value on the low output side and the second reference value on the high output side, the photosensitive drum is increased as the sensor output value increases. When the sensor output value is equal to or less than a first reference value or equal to or greater than a second reference value, the peripheral speed ratio is decreased after the first and second rotations. And a fixed value corresponding to the second reference value, and the peripheral speed ratio is not changed in a range outside the first reference value and the second reference value.

According to this configuration, the generation of the trailing edge missing image can be stopped within an allowable range, and both low cost and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the peripheral speed ratio (the number of rotations of the developing roller) is fixed as the peripheral speed ratio corresponding to the first reference value. Can be prevented.

In a region where the sensor output value is equal to or larger than the second reference value, the peripheral speed ratio is fixed as the peripheral speed ratio corresponding to the first reference value, so that it is possible to prevent the image density from becoming insufficient. .

[0069]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described in detail.

In this image forming apparatus, the same conditions as those in the process control are used to determine the conditions for correcting the missing image at the trailing edge. For this reason, in the present image forming apparatus, a toner patch image is formed on a photoconductor (photoconductor drum), the toner patch image is read by a reflection type optical sensor, and image missing at a rear edge is detected. The toner patch image formed here is an image that satisfies the conditions for image chipping as described in the related art,
That is, an image that moves from the halftone portion to the background portion, an image that moves from the low density region to the high density region, and the like. The detection of the missing image is performed by the method shown in FIG.

As shown in FIGS. 1A and 1B, when a rear end chip is generated in the toner patch image, a shake is generated in a sensor output that reads this. The amplitude ΔV of the fluctuation of the sensor output increases as the level of the rear end chipping increases. That is, the rear end chipping level can be detected by the sensor output.

When the level of the rear end chipping is detected, image forming conditions such as the difference between the grid applied voltage and the developing bias (cleaning field), the LSU light amount, the charge elimination light amount, or the peripheral speed ratio between the photosensitive member and the developing roller. Is changed, the above-mentioned rear end chipping is suppressed. Here, the portions where image correction is performed by changing the image forming conditions are only portions where rear end chipping is expected to occur, and such portions are similar to those in JP-A-10-65920. It is analyzed from the input image data.

The image forming condition correction processing (to be described below) performed based on the above method is described with reference to FIG.
This is executed according to a command from the concentration control unit constituting the control system as shown in FIG. The density control unit includes a CPU having various arithmetic functions, a ROM having a storage function, and a ROM.
The input side is connected to a low output side reference voltage circuit, a high voltage side reference voltage circuit, and a reflection type sensor output voltage (reflection type sensor). A circuit, a pulse width modulator, a rotating polygon mirror driving unit, a projection optical device, and a developing device driving unit are connected, and a CPU is controlled based on a program stored in a ROM.
Controls the respective units to execute the correction processing.

Hereinafter, a method of correcting image forming conditions at a correction position detected based on input image data will be described.

[Changing the difference (cleaning field) between the grid application voltage of the charger and the developing bias voltage] A change in the waveform output of the toner patch image is detected by a reflective sensor used for process control, and the cleaning field (V _g− V _B ).

[0076] (V _g -V _B) If the varied inhibit rear chipping, it is necessary to be determined according to the level of the rear end missing change amount generated of (V _g -V _B). However, as shown in FIG. 2, the level of the rear end chipping corresponds to the sensor shake due to the change in the waveform output of the toner patch image, and is based on the change in the waveform output of the toner patch image (V _g −V _B ). Can be determined.

Next, the cleaning field (V _g −
The process of determining the amount of change in V _B ) will be described with reference to the flow in FIG. First, it is determined whether the input image data is a color image (S1). This is because whether the image output by the image forming apparatus is a color image or a monochrome image, the correction state of the image forming conditions to be corrected is different, and another program is required. The color adhesion amount control program is read (S2), and in the case of a monochrome image, the monochrome adhesion amount control program is read (S3).

Then, a toner patch image is formed on the photosensitive drum, and in order to detect a rear end chipping level in a rear edge region of the image, the amount of reflected light at the rear end notch is measured by a reflection type optical sensor. (S4). The output voltage (sensor output value) of the sensor corresponding to the amount of reflected light measured by the optical sensor is two threshold values, namely, a first reference value Va on the low output side, and _a threshold value on the high output side. is compared V _b and (V _a <V _b) is a second reference value.

If the sensor output is larger than the threshold value _Vb (NO in S5), a target value corresponding to the output voltage _Vb is read (S6). If the sensor output is smaller than the threshold value V _a (NO in S7), the reading of the target value is performed corresponding to the output voltage V _a (S8). And V _a ≦
When the (output voltage) ≦ V _b is between the sensor main and a (V _g -V _B) satisfied the relationship shown in FIG. 4, based on this, (V _g -V _B) Is calculated (S9).

[0080] Thus, when the target value of the cleaning field (V _g -V _B) is determined, the target value is stored in the memory (S10), further, the photosensitive drum 1
A final output value is determined by a predetermined table (see FIG. 13) for correcting a potential difference generated in the rotation and the second and subsequent rotations, and correction of a rear end chip is performed in a subsequent image forming operation (printing process). Is performed.

In the above process, the sensor output value is low.
Output-side threshold (first reference value) V_aIs set to 0.5V
And V_a (V_g -V_B ) Target value is 300
V is set. The threshold value on the high output side of the sensor output value
2) V_b Is set to 0.75V and V_b Compatible with
Yes (V_g -V_B ) Is set to 100V
You. Normally, the charging grid bias: V_g = -50
0V, developing bias: V _B = About -300V.

[0082] In the image forming apparatus according to this embodiment, in order to change the cleaning field (V _g -V _B), and one that changes the charging grid bias V _g,
When the sensor output value is 0.5V to 0.75V,
The (V _g -V _B) reducing at between 300V for 100 V. When the sensor output value is 0.5V or less is fixed to the corresponding to the sensor output value 0.5V (V _g -V _B). When the sensor output value is greater than 0.75V is fixed to correspond to the sensor output value 0.75V (V _g -V _B).

[0083] The reason why the variable width of the cleaning field (V _g -V _B) is restricted as described above is as follows. That is, if to be controlled beyond 300V corresponding to the sensor output value 0.5V to (V _g -V _B), becomes a capacity shortage of the high-voltage power supply, the burden of the circuit is increased. Further, the sensor output value (V _g -V _B) 0.75V
If control is attempted with a value smaller than 100 V corresponding to the above, it is expected that the state of image fogging will deteriorate.

[Case of Changing LSU Light Amount] (See FIG. 5) A change in the waveform output of the toner patch image is detected by a reflection type sensor used for process control, and the LSU light amount is changed. The process in this case, similarly to the Agego changing the above-described (V _g -V _B), is intended to be performed based on the flow of FIG. 3, the cleaning field (V _g as a target value to be set - A parameter for changing the LSU light amount is set instead of V _B ).

In the same manner as (V _g -V _B ), the variable width corresponding to the sensor output value is limited.
Sensor output value of the low output side of the threshold value (first reference value) V _a
Is small, and the LSU light amount corresponding to the high-output-side threshold value (second reference value) _Vb is large.

To change the LSU light amount, for example, a method of changing a laser output value, a laser PWM value, a laser irradiation time (the number of rotations of a polygon mirror), or a laser spot diameter (a laser beam aperture area) is used. Conceivable.

(1) When changing the laser output value (see FIG. 6) If the low output side of the sensor output value is 0.5 V, the laser output value is set to 0.23 mW. If the high output side of the sensor output value is 0.75 V, the laser output value is set to 0.37 mW. If the sensor output value is 0.5V to 0.75V, the laser output value is increased between 0.23mW and 0.37mW. If the sensor output value is 0.5 V or less, the laser output value is fixed at 0.23 mW corresponding to the sensor output value of 0.5 V. If the sensor output value is 0.75 V or more, it is fixed at 0.37 mW corresponding to the sensor output value of 0.75 V.

If the laser output value deviates from the predetermined range, the following adverse effects are expected to occur. That is,
When (laser output value) ≧ 0.37 mW, photo fatigue of the photoconductor occurs. When (laser output value) ≦ 0.23 mW, the image density becomes insufficient.

(2) When changing the laser PWM value (see FIG. 7) If the low output side of the sensor output value is 0.5 V, the laser PWM value is set to 50 counts. If the high output side of the sensor output value is 0.75 V, the laser PWM value is set to 100 counts. If the sensor output value is between 0.5V and 0.75V, the laser PWM value is increased between 50 and 100 counts. If the sensor output value is 0.5V or less, laser P
The WM value is fixed at 50 counts corresponding to a sensor output value of 0.5V. If the sensor output value is 0.75 V or more, the laser PWM value is set to 100 corresponding to the sensor output value of 0.75 V.
Fix to count. If the laser PWM value deviates from the predetermined range, the following adverse effects are expected to occur. That is, (Laser P
When (WM value) ≧ 100 counts, light fatigue of the photoconductor occurs. (Laser PWM value) ≦ 50 counts results in insufficient image density.

(3) Changing laser irradiation time (rotation speed of polygon mirror) (see FIG. 8) If the low output side of the sensor output value is 0.5 V, the rotation speed of the polygon mirror is set to 18000 RPM. If the high output side of the sensor output value is 0.75 V, the rotation speed of the polygon mirror is set to 25000 RPM. When the sensor output value is 0.5V to 0.75V, the polygon mirror rotation speed is increased from 18000 RPM to 25,000.
Increase between RPMs. If the sensor output value is 0.5 V or less, the rotation speed of the polygon mirror is set to 18 corresponding to the sensor output value of 0.5 V.
Fix to 000 RPM. If the sensor output value is 0.75 V or more, the rotation speed of the polygon mirror is fixed at 25000 RPM corresponding to the sensor output value of 0.75 V.

If the laser PWM value deviates from the predetermined range, the following adverse effects are expected. That is,
(Polygon rotation speed) ≧ 25000 RPM causes photo fatigue of the photoconductor. In addition, the burden on the rotation mechanism increases.
If (polygon rotation speed) ≦ 18000 RPM, the image density is insufficient. (4) Changing the laser spot diameter (aperture area of the laser beam) (see FIG. 9) If the low output side of the sensor output value is 0.5 V, the aperture area is 2.5 mm ² . If the high output side of the sensor output value is 0.75 V, the aperture area is set to 3.2 mm ² . If the sensor output value is 0.5V～0.75V, increases in the range of Apachiya area of 2.5mm ² ~3.2mm ^2. If the sensor output value is 0.5 V or less, the aperture area is set to 2.5 m corresponding to the sensor output value of 0.5 V.
It is fixed to the m ^2. 2. If the sensor output value is 0.75V or more, the aperture area corresponds to the sensor output value of 0.75V.
Fixed to 2mm ^2.

If the laser beam diameter (aperture area) deviates from a predetermined range, the following adverse effects are expected to occur. That is, (aperture area) ≧ 3.2 m
At m ² , light fatigue of the photoconductor occurs.

If (aperture area) ≦ 2.5 mm ² , the image density becomes insufficient.

[Case of Changing Light Elimination Light Amount] (Refer to FIG. 10) A change in the waveform output of the toner patch image is detected by a reflection type sensor used for process control, and the light elimination light amount (voltage applied to the charge eliminator) is changed. Processing in this case is intended to be performed based on the flow of FIG. 3 as in the case of changing the cleaning field as described above _{(V g -V B), (} V g -V B as a target value to be set ) Is set instead of the voltage applied to the static eliminator for changing the amount of static elimination.

If the low output side of the sensor output value is 0.5V, the voltage applied to the static eliminator is set to 18V. If the high output side of the sensor output value is 0.75V, the voltage applied to the static eliminator is set to 24V. If the sensor output value is 0.5V to 0.75V, the static eliminator applied voltage is increased in the range of 18V to 24V. If the sensor output value is 0.5V or less, the static eliminator applied voltage is fixed at 18V corresponding to the sensor output value of 0.5V. If the sensor output value is 0.75 V or more, the static eliminator applied voltage is changed to 24 V corresponding to the sensor output value of 0.75 V.
Fixed to.

If the amount of static elimination (voltage applied to the static eliminator) deviates from a predetermined range, the following adverse effects are expected to occur. That is, when (applied voltage of the static eliminator) ≧ 24V, photo fatigue of the photoconductor occurs. In addition, power supply capacity is insufficient.
When (applied voltage of the static eliminator) ≦ 18 V, the photoconductor memory remains.

[Case of Changing Peripheral Speed Ratio] (See FIG. 11)
See) Toner with reflective sensor used for process control
-Changes in the patch image waveform output are detected and the peripheral speed ratio (developing low
Rotation speed). The processing in this case is described above.
Cleaning field (V_g -V_B Place to change)
In the same way as in the case, it is executed based on the flow of FIG.
The target value to be set is (V_g -V _B )Instead of
The number of rotations of the developing roller for changing the peripheral speed ratio (K) is set.
Is determined.

If the low output side of the sensor output value is 0.5 V, the peripheral speed ratio is set to 2.4. If the high output side of the sensor output value is 0.75 V, the peripheral speed ratio is set to 1.8. If the sensor output value is 0.5V to 0.75V, the peripheral speed ratio is reduced in the range of 1.8 to 2.4. If the sensor output value is 0.5 V or less, the peripheral speed ratio is fixed at 2.4 corresponding to the sensor output value of 0.5 V. If the sensor output value is 0.75 V or more, the peripheral speed ratio is fixed at 1.8 corresponding to the sensor output value of 0.75 V. If the peripheral speed ratio (developing roller rotation speed) deviates from a predetermined range, the following adverse effects are expected to occur. That is,
When (peripheral speed ratio) ≧ 2.4, the developer stress increases. Further, the thickness of the photoreceptor decreases. (Peripheral speed ratio) ≦ 1.
8, the image density is insufficient.

[0099]

The present invention configured as described above has the following effects.

According to the first aspect, the feedback is performed by detecting the change in the waveform output of the toner patch image, so that the existing means can be utilized without changing the structure of the mechanical part of the image forming apparatus. By changing the contents of the control system, it is possible to prevent the occurrence of a missing image at the rear end and improve the image quality.

According to the second aspect, the generation of the rear end missing image can be stopped within an allowable range, and both low cost and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the difference between the grid applied voltage of the charger and the developing bias voltage is fixed as a potential difference corresponding to the first reference value. Excessive capacity can be prevented.

In a region where the sensor output value is equal to or larger than the second reference value, the difference between the grid applied voltage of the charger and the developing bias voltage is fixed as a potential difference corresponding to the second reference value. Deterioration can be prevented.

According to the third aspect, since the change in the waveform output of the toner patch image is detected and fed back, the existing means can be utilized without changing the structure of the mechanical part of the image forming apparatus. By changing the contents of the control system, it is possible to prevent the occurrence of the rear end missing image and obtain a good image.

According to the fourth aspect, it is possible to prevent the occurrence of a rear end missing image within an allowable range, and to achieve both low cost and improvement in image quality.

In the region where the sensor output value is equal to or less than the first reference value, the LSU light amount is fixed as the light amount corresponding to the first reference value, thereby preventing the image density from becoming insufficient.

Then, in a region where the sensor output value is equal to or more than the second reference value, the LSU light amount is fixed as the light amount corresponding to the second reference value, thereby preventing performance degradation due to light fatigue of the photoconductor.

According to the fifth aspect, the content of the control for changing the LSU light amount can be simplified.

According to the sixth aspect, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both cost reduction and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the laser power is fixed as an output value corresponding to the first reference value, so that it is possible to prevent the image density from becoming insufficient.

In a region where the sensor output value is equal to or larger than the second reference value, the laser power is fixed as an output value corresponding to the second reference value, so that performance deterioration due to light fatigue of the photosensitive drum can be prevented. it can.

According to the seventh aspect, the generation of the rear end missing image can be stopped within an allowable range, and both low cost and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the laser PWM value is fixed as an output value corresponding to the first reference value, thereby preventing image density from becoming insufficient.

In a region where the sensor output value is equal to or larger than the second reference value, the laser PWM value is fixed as an output value corresponding to the second reference value, so that performance degradation due to light fatigue of the photosensitive drum can be prevented. Can be.

According to the eighth aspect, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both cost reduction and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the rotation speed of the rotary polygon mirror is fixed as an output value corresponding to the first reference value, thereby preventing image density from becoming insufficient. Can be.

In a region where the sensor output value is equal to or larger than the second reference value, the rotation speed of the rotary polygon mirror is fixed as an output value corresponding to the second reference value, so that the performance deterioration due to light fatigue of the photosensitive drum is prevented. Can be prevented.

According to the ninth aspect, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both cost reduction and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the aperture diameter of the laser beam is set to the first reference value.
Since the output value is fixed as the output value corresponding to the reference value, it is possible to prevent the image density from becoming insufficient.

In a region where the sensor output value is equal to or larger than the second reference value, the aperture diameter of the laser beam is fixed as an output value corresponding to the second reference value, so that the performance deterioration due to light fatigue of the photosensitive drum is prevented. can do.

According to the tenth aspect, since the change in the waveform output of the toner patch image is detected and fed back, the existing means is utilized without changing the structure of the mechanical part of the image forming apparatus. By changing the contents of the control system, it is possible to prevent the occurrence of a rear end missing image, and to improve the image quality.

According to the eleventh aspect, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both low cost and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the amount of static elimination is fixed as the amount of static elimination corresponding to the first reference value, thereby preventing the occurrence of photoconductor memory (charging memory). be able to.

In a region where the sensor output value is equal to or greater than the second reference value, the light elimination light amount is fixed as the light elimination light amount corresponding to the second reference value. .

According to the twelfth aspect, since the change in the waveform output of the toner patch image is detected and fed back, the existing means can be utilized without changing the structure of the mechanical part of the image forming apparatus. By changing the contents of the control system, it is possible to prevent the occurrence of a missing image at the rear end and improve the image quality.

According to the thirteenth aspect, the occurrence of a trailing edge missing image can be stopped within an allowable range, and both cost reduction and improvement in image quality can be achieved.

In a region where the sensor output value is equal to or less than the first reference value, the peripheral speed ratio (the number of rotations of the developing roller) is fixed as the peripheral speed ratio corresponding to the first reference value. Can be prevented.

In a region where the sensor output value is equal to or more than the second reference value, the peripheral speed ratio is fixed as the peripheral speed ratio corresponding to the first reference value, so that it is possible to prevent the image density from becoming insufficient. .

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an image missing detection method in an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a touch of an output value of the sensor and a level of chipping at a rear end of an image.

FIG. 3 is a flowchart for explaining a process of determining a difference between a grid applied voltage and a developing bias of the charger.

FIG. 4 is a graph showing a relationship between the output of the sensor, a difference between a grid applied voltage of a charger, and a developing bias.

FIG. 5 is a graph showing the relationship between the sensor output and the LSU light amount.

FIG. 6 is a graph showing the relationship between the sensor output and the laser output value.

FIG. 7 is a graph showing a relationship between the sensor output and a laser PWM output value.

FIG. 8 is a graph showing the relationship between the sensor output and the polygon rotation speed.

FIG. 9 is a graph showing the relationship between the sensor output and the aperture area.

FIG. 10 is a graph showing the relationship between the sensor output and the amount of static elimination light.

FIG. 11 is a graph showing the relationship between the sensor output and the peripheral speed ratio.

FIG. 12 is a block diagram of the control system.

FIG. 13 is a table for the same potential difference correction.

FIG. 14 is an explanatory diagram showing a conventional density reduction phenomenon.

FIG. 15 is an explanatory diagram of a conventional phenomenon of density reduction in a halftone portion in contact with a background portion.

FIG. 16 is an explanatory diagram of a conventional low-density density reduction phenomenon in contact with a high-density portion.

Continuation of front page (72) Inventor Takayuki Yamanaka 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka F-term (reference) 2H027 DA04 DA10 DE02 DE07 EA01 EA02 EA05 EA10 EC03 EC06 EC15 EC20 ED06 ED08 EE04 EE07 EF10 EG06 2H035 AA11 AB02 AC02 AC06 AZ09 2H076 AB05 AB12 AB16 AB22 CA02 CA09 CA16 CA18 DA06 DA08 DA14 DA17 DA19

Claims (13)

[Claims] 1. A cleaning device which detects a density of a rear end portion of a toner patch image formed on a photosensitive drum as a reflected light amount, and determines a difference between a grid applied voltage of a charger and a developing bias voltage according to a sensor output value. An image forming apparatus, wherein a density controller for setting a predetermined difference between a first rotation of the photosensitive drum and a second rotation and thereafter of the photosensitive drum is provided in a field. 2. When the sensor output value is between a first reference value on a low output side and a second reference value on a high output side,
When the cleaning field is reduced after the first and second rotations of the photosensitive drum with the increase in the sensor output value, and the sensor output value is equal to or less than the first reference value or equal to or more than the second reference value, And fixing the cleaning field as a potential difference corresponding to the first reference value and the second reference value, and does not change the value of the cleaning field in a range outside the first reference value and the second reference value. The image forming apparatus according to claim 1, wherein: 3. A density of a rear end portion of the toner patch image formed on the photosensitive drum is detected as a reflected light amount, and an LSU light amount of the rear end portion of the image is determined according to the sensor output value.
3. The image forming apparatus according to claim 1, wherein the first and second rotations of the photosensitive drum are changed. 4. When the sensor output value is between a first reference value on a low output side and a second reference value on a high output side, the sensor output value of the photosensitive drum is increased with an increase in the sensor output value. 1
In the second and subsequent rotations, the LSU light amount is increased,
When the sensor output value is equal to or less than the first reference value or equal to or greater than the second reference value, the LSU light amount is fixed as a light amount value corresponding to the first reference value and the second reference value, The image forming apparatus according to claim 3, wherein the LSU light amount is not changed in a range outside the first reference value and the second reference value. 5. A change in the LSU light amount after the first and second rotations of the photosensitive drum is caused by an increase or decrease in a laser output value.
5. The image forming apparatus according to claim 3, wherein at least one of the increase / decrease of the laser PWM value, the length of the laser irradiation time, and the size of the aperture of the laser beam is controlled. 6. When the sensor output value is between a first reference value on the low output side and a second reference value on the high output side, the photosensitive drum is increased with an increase in the sensor output value. The laser output value is increased in the first and second rotations and thereafter, and when the sensor output value is equal to or less than the first reference value or equal to or more than the second reference value, the laser output value is increased to the second reference value. 6. The image according to claim 5, wherein the laser output value is fixed as a value corresponding to the first reference value and the second reference value, and the laser output value is not changed in a range outside the first reference value and the second reference value. Forming equipment. 7. When the sensor output value is between a first reference value on a low output side and a second reference value on a high output side, the photosensitive drum is increased with an increase in the sensor output value. The laser PWM value is increased in the first rotation and the second rotation and thereafter, and when the sensor output value is equal to or smaller than the first reference value or equal to or larger than the second reference value, the laser P is increased.
The WM value is fixed as a value corresponding to the first reference value and the second reference value, and the laser PWM value is not changed in a range outside the first reference value and the second reference value. Item 6. The image forming apparatus according to Item 5. 8. When the sensor output value is between a first reference value on a low output side and a second reference value on a high output side, the photosensitive drum is increased with an increase in the sensor output value. Increasing the number of rotations of the rotating polygonal mirror after the first and second rotations, and when the sensor output value is equal to or less than the first reference value or equal to or greater than the second reference value, A rotation speed is fixed as a rotation speed corresponding to the first reference value and the second reference value, and a rotation speed of the rotary polygon mirror is not changed in a range outside the first reference value and the second reference value. The image forming apparatus according to claim 5, wherein 9. When the sensor output value is between a first reference value on a low output side and a second reference value on a high output side, the photosensitive drum is increased with an increase in the sensor output value. When the aperture diameter of the laser beam is increased after the first and second rotations, and the sensor output value is equal to or less than the first reference value or equal to or more than the second reference value,
The aperture diameter is fixed as a value corresponding to the first reference value and the second reference value, and the aperture diameter is not changed in a range outside the first reference value and the second reference value. Item 6. The image forming apparatus according to Item 5. 10. A method for detecting the density of a rear end portion of a toner patch image formed on the photosensitive drum as a reflected light amount, and detecting the amount of charge removal at the rear end portion of the image based on the sensor output value. 3. The image forming apparatus according to claim 1, wherein the change is performed after the rotation. 11. The sensor output value is a first output value on a low output side.
And the second reference value on the high output side, the amount of charge removal is increased at the first and second rotations of the photosensitive drum with an increase in the sensor output value, and the sensor output is increased. When the value is equal to or less than the first reference value or equal to or greater than the second reference value, the amount of static elimination is changed to the first reference value and the second reference value.
The image forming apparatus according to claim 10, wherein the static elimination light amount is not changed in a range outside the first reference value and the second reference value, the value being fixed as a value corresponding to the reference value. 12. A density of a rear end portion of the toner patch image formed on the photosensitive drum is detected as a reflected light amount, and a peripheral speed ratio is determined in the first and second rotations of the drum according to the sensor output value. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed. 13. The method according to claim 1, wherein the sensor output value is a first output value on a low output side.
When the sensor output value is between the reference value and the second reference value on the high output side, the peripheral speed ratio is reduced after the first rotation and the second rotation of the photosensitive drum, When the sensor output value is equal to or less than a first reference value or equal to or more than a second reference value, the peripheral speed ratio is fixed as a value corresponding to the first reference value and the second reference value, and the first reference value is set. 13. The image forming apparatus according to claim 12, wherein the peripheral speed ratio is not changed in a range outside the value and the second reference value.