JP4595460B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an electrostatic latent image, develops it with toner, and finally forms an image composed of a fixed toner image on a recording medium.

  In recent years, with the development of information technology, the need to print information on paper is also increasing, and image forming apparatuses centering on printers and technologies relating to various elements constituting such image forming apparatuses have been developed. Widely used. Many of these image forming apparatuses include an exposure device that forms an electrostatic latent image that is a pattern to be printed on a photosensitive member by irradiating a photosensitive member such as a photosensitive drum with light such as laser light. Since the amount of toner adhering to the electrostatic latent image is determined by the amount of exposure light emitted by the exposure device, this method of controlling the amount of exposure light is one element for maintaining the image density at an appropriate density. Become.

Since the image density fluctuates due to the influence of environmental changes and changes over time, in such an image forming apparatus, a toner patch is created at a predetermined timing during image formation, and exposure is performed according to the measurement result of the patch density of the toner patch. Control for returning the image density to an appropriate value is performed by correcting the amount of exposure light emitted by the device. If the amount of exposure light is greatly changed at one time when performing such correction, the image density of the image formed before the change of the amount of exposure light and the image density of the image formed after the change of the amount of exposure light are changed. There arises a problem that the difference is conspicuous. To solve this problem, a method for controlling the amount of exposure light that does not make the difference in image density before and after the correction of the amount of exposure light intensify by gradually correcting the amount of exposure light in multiple stages has been proposed. (For example, refer to Patent Document 1).
JP 2003-131448 A

  However, according to the control method described in Patent Document 1, depending on the nature of the job for performing image formation and the timing for measuring the patch density, the correction of the amount of exposure light is delayed and an image whose density deviates from an appropriate value is formed. And the problem that the measurement result of the patch density is not sufficiently reflected.

  This is not limited to the control of the amount of exposure light, but is a problem common to all the controls performed by the image forming apparatus, such as charging, transfer, fixing, toner supply, and control relating to the gradation of image data.

  In view of the above circumstances, the present invention makes an image density difference inconspicuous before and after changing a control value for an image forming condition, and measures an accurate patch density to form an image with an accurate image density. An object is to provide a forming apparatus.

In order to achieve the above object, a first image forming apparatus of the present invention is a method in which a rotating image carrier is primarily charged and an electrostatic latent image is formed on the image carrier by exposure to form a toner. In an image forming apparatus that forms an image composed of a fixed toner image on a recording medium by developing and finally transferring and fixing the toner image on the recording medium.
A patch density measuring unit that forms a toner patch and measures the patch density of the toner patch;
Based on the patch density measurement value obtained by the patch density measurement unit, a control target value is calculated for a predetermined image forming condition that affects the density of the image formed on the recording medium, and the current image forming condition is Image formation condition control that obtains each control value that changes sequentially so as to reach the above control target value during multiple image formation from the set control value, and sets each control value according to the progress of image formation With
The image formation condition control unit sets the control target value as a control value for the next image formation when image formation of the current job is completed before setting the control target value. Features.

  When forming dissimilar images that do not care about the difference in density in human perception, during the transition from image formation to image dissimilar image formation, Even if the control value for the image forming condition is changed, the difference in image density that occurs before and after the change does not become a serious problem. Therefore, the control method described in Patent Document 1 is adopted when such image forming is performed. In such a case, the problem of forming an image whose density deviates from an appropriate value due to a delay in necessary correction becomes a more serious problem. The first image forming apparatus of the present invention sets a control target value, which is a final target value, as a control value for the next image formation when image formation for one job is completed. The control value suitable for the image density is set during the transition from the image formation to the image formation of an image that is dissimilar to the image. Image formation of similar images can be performed with accurate image density. In addition, in order to set each control value according to the progress of image formation so as to reach the control target value during the formation of a plurality of images until image formation of one job is completed, It is possible to suppress the occurrence of a difference in image density between a plurality of continuous images in one job.

In order to achieve the above object, a second image forming apparatus of the present invention forms a latent electrostatic image on the image carrier by first charging a rotating image carrier and exposing it with toner. In an image forming apparatus that forms an image composed of a fixed toner image on a recording medium by developing and finally transferring and fixing the toner image on the recording medium.
A patch density measuring unit that forms a toner patch and measures the patch density of the toner patch;
Based on the patch density measurement value obtained by the patch density measurement unit, a control target value is calculated for a predetermined image forming condition that affects the density of the image formed on the recording medium, and the current image forming condition is Image formation condition control that obtains each control value that changes sequentially so as to reach the above control target value during multiple image formation from the set control value, and sets each control value according to the progress of image formation With
The image forming condition control unit sets the control target value as a control value for forming the toner patch when the next toner patch forming timing is reached before setting the control target value. It is characterized by that.

  In the second image forming apparatus of the present invention, when the control value for a predetermined image forming condition reaches the control target value that is the final target value of the control value, the next toner patch formation timing is reached. Since the control target value is set as the control value for forming the toner patch, the patch density is measured after the necessary correction for a predetermined image forming condition is completely performed. Therefore, it is possible to improve the accuracy of the correction amount grasped by the patch density measurement.

In order to achieve the above object, a third image forming apparatus of the invention forms a latent image with a toner by first charging a rotating image carrier and exposing it to exposure with toner. In an image forming apparatus that forms an image composed of a fixed toner image on a recording medium by developing and finally transferring and fixing the toner image on the recording medium.
A patch density measuring unit that forms a toner patch and measures the patch density of the toner patch;
Based on the patch density measurement value obtained by the patch density measurement unit, a control target value is calculated for a predetermined image forming condition that affects the density of the image formed on the recording medium, and the current image forming condition is Image formation condition control that obtains each control value that changes sequentially so as to reach the above control target value during multiple image formation from the set control value, and sets each control value according to the progress of image formation With
The image forming apparatus, wherein the patch density measurement unit forms a next toner patch after the control target value is set by the image forming condition control unit.

  According to the third image forming apparatus of the present invention, until the control value for a predetermined image forming condition reaches the control target value which is the final target value, the toner patch is not detected even when the next toner patch formation timing is reached. Since the image is not created, a new patch density measurement is not performed with a necessary correction being left, and an efficient and highly productive image can be formed without consuming excess toner.

The image forming apparatus according to any one of the first image forming apparatus, the second image forming apparatus, and the third image forming apparatus of the present invention has a light amount based on a set light amount control value and an image signal. An exposure unit that forms an electrostatic latent image on the image carrier by exposing the image carrier with a light beam modulated according to
The image forming condition control unit may set a control value for controlling a light amount of a light beam emitted from the exposure device to the exposure device.

  Among the means for controlling the image density, the control of the amount of exposure light is the most effective means. By controlling the amount of exposure light, an image with a more accurate image density can be formed.

  According to the image forming apparatus of the present invention, the difference in image density is not noticeable before and after changing the control value for the image forming condition, and an accurate patch density is measured to form an image with an accurate image density. be able to.

[First embodiment]
Hereinafter, an image forming apparatus that controls the amount of exposure light, which is an embodiment of the first and second image forming apparatuses of the present invention, will be described as a first embodiment. First, the configuration of the image forming apparatus of this embodiment will be described.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment.

  The image forming apparatus of this embodiment is a full-color image forming apparatus having a tandem configuration using an intermediate transfer belt. The image forming apparatus according to the present embodiment rotates in the direction of arrow R in the drawing, and forms yellow (Y), magenta (M), cyan (C), and black (K) toner images. The four photosensitive drums 1Y, 1M, 1C, and 1K are provided. An intermediate transfer belt 8 is provided that contacts these four photosensitive drums 1Y, 1M, 1C, and 1K and circulates in the direction of arrow A. The intermediate transfer belt 8 is stretched around path rolls 9a and 9b. ing. Around the photosensitive drums 1Y, 1M, 1C, and 1K, the chargers 2Y, 2M, 2C, and 2K that perform primary charging on each photosensitive member, and the photosensitive members after the primary charging are modulated based on image data. ROS 30 which is a kind of exposure apparatus for forming an electrostatic latent image on each photosensitive member by irradiating the laser exposure light is provided. This ROS is an abbreviation taken from the acronym of “Raster Output Scanner”. Further, around each photoreceptor, potential sensors 90Y, 90M, 90C, and 90M that measure the potential of the electrostatic patch when an electrostatic patch is formed as an electrostatic latent image for control, and each photoreceptor drum Developing units 3Y, 3M, 3C, and 3K are provided for developing the electrostatic latent images formed thereon with respective color toners of Y, M, C, and K to form toner images on the respective photoreceptors. Yes. Adjacent to these developing units 3Y, 3M, 3C, and 3K, a developing bias applying unit (not shown) that applies a developing bias to each developing unit is provided in order to set the potential at the developing position of each developing unit to a predetermined potential. It has been. Further, toner density sensors 7Y, 7M, 7C, and 7K for detecting the toner density are also provided in the developing units 3Y, 3M, 3C, and 3K. The toner density sensors 7Y, 7M, 7C, and 7K are provided. The detection results are sent to the TC control unit 70, and based on the detection results, the TC control unit 70 rotates the dispense motors 8Y, 8M, 8K, and 8Y so as to maintain the target toner density, and the toner boxes 5Y, 5M. The toners corresponding to the respective colors are supplied to the developing units 3Y, 3M, 3C, and 3K from 5K and 5Y, respectively.

  When image data is input to the image forming apparatus from the outside, the input image data is subjected to image processing by the image processing unit 41 of the controller 40 and then input to the ROS 30. In the ROS 30, each pulse width modulation signal for modulating the pulse width of each laser exposure light for exposing the photosensitive drums 1Y, 1M, 1C, and 1K is generated based on the image data. Based on the generated pulse width modulation signal, a laser diode (LD) provided in the ROS 30 is driven to irradiate the exposure light and statically irradiate the photosensitive drums 1Y, 1M, 1C, and 1K. An electrostatic latent image is formed. Hereinafter, the amount of light by such exposure light is referred to as LD light amount. The electrostatic latent images thus formed on the respective photosensitive drums are developed by the developing devices 3Y, 3M, 3C, and 3K, respectively, and toner images are formed on the respective photosensitive drums. These toner particles are transferred so as to be sequentially superimposed on the intermediate transfer belt 8 by the action of the transfer rolls 4Y, 4M, 4C, and 4K. The image transferred to the intermediate transfer belt 8 is transferred to a recording medium by the action of a secondary transfer roll (not shown), and fixed on the recording medium by heat and pressure of a fixing device (not shown).

  Next, components that detect various physical quantities in the image forming apparatus of the present embodiment and a control unit that performs control based on the detection results will be briefly described.

  The measurement results of the potentials of the electrostatic patches measured by the potential sensors 90Y, 90M, 90C, and 90K are output to the charging voltage control unit 80. The charging voltage control unit, based on the potential measurement results. The chargers 2Y, 2M, 2C, and 2K are controlled.

  When the toner patch 20 that is a control toner image is formed on the intermediate transfer belt 8, the patch density of the toner patch 20 is measured by the density sensor 10. The patch density measurement result by the density sensor 10 is transmitted to the gradation control unit 50, the TC control unit 70, and the LD light amount control unit 60. Based on the measurement result of the patch density, the gradation control unit 50 controls the image processing unit 41, and the TC control unit 70 controls the dispense motors 8Y, 8M, 8K, and 8Y. The LD light amount control unit 60 controls the LD light amount through the ROS 30 based on the patch density measurement result, thereby controlling the image density. Details of the control method by the LD light quantity control unit 60 will be described later. Further, a temperature sensor 100 and a humidity sensor 110 for measuring temperature and humidity are provided in parallel with the concentration sensor 10, and the detection results of these sensors are a charging voltage control unit 80, a TC control unit 70, and an LD light quantity. It is transmitted to the control unit 60.

  In the image forming apparatus shown in the present embodiment, the density sensor 10 used to measure the density of the toner patch 20 includes a light receiving sensor, two types of light emitting diodes for black K, and a light emitting diode for YMC. I have.

  FIG. 2 is a configuration diagram of a density sensor used in the image forming apparatus shown in the present embodiment.

  As shown in FIG. 2, the density sensor 10 is provided with LEDs 11 and 12 that are light emitting diodes, and a light receiving sensor 13, and the LED 11 is used for black and the LED 12 is used for YMC. The light receiving sensor 13 is used in common for both the LED 11 and the LED 12. Since black does not diffusely reflect, the specularly reflected light emitting diode is more sensitive to the patch density of the toner patch 20 on the intermediate transfer belt 8 than the diffusely reflected light emitting diode, and emits light for black. As the diode, a specular reflection type light emitting diode is adopted as the LED 11. The color is less sensitive at high density in the specular reflection method and more sensitive in the diffuse reflection method. For this reason, a diffuse reflection type light emitting diode is adopted as the LED 12 as a light emitting diode for YMC. The light emitted from these two types of light emitting diodes, LED 11 and LED 12, is detected by the light receiving sensor 13, and the detected image density data is output to the above-mentioned LD light quantity control unit 60, and these image density data. Based on the above, the LD light quantity control unit 60 corrects the LD light quantity.

  The above is the description of the configuration of the image forming apparatus of the present embodiment. Next, an image density control method using the LD light quantity control unit of the image forming apparatus according to the present embodiment will be described with reference to a flowchart.

  FIG. 3 is a flowchart showing a method for controlling the LD light quantity based on the patch density of the toner patch.

  First, the description will be given assuming that it is the timing for creating a toner patch at the time of START (step S1; Yes). If the correction of the LD light amount is not completed at this time, that is, the current LD light amount control value reaches the control target value of the LD light amount determined to be appropriate from the patch density measurement result performed before this time. If not, the control target value is set as the LD light quantity control value (step S2).

  Before creating a toner patch in this way, by setting the LD light quantity control value so that the LD light quantity correction is completed, the patch density is measured after the necessary LD light quantity correction has been completed. Thus, it is possible to improve the accuracy of the correction amount of the LD light amount grasped by the current patch density measurement.

  When the LD light quantity is changed, the potential of the electrostatic latent image on each of the photosensitive drums 1Y, 1M, 1C, and 1K shown in FIG. 1 changes, and the amount of toner attached to the electrostatic latent image also changes accordingly. At this time, in order to make such a change amount of the toner appropriate, the LD light amount is changed and the developing bias applied to each of the developing devices 3Y, 3M, 3C, and 3K shown in FIG. It is known that it is necessary to change according to. For this reason, in the image forming apparatus of the present embodiment, when the above-described LD light quantity control target value is set in the step S2, a developing bias that matches the LD light quantity control target value is calculated. The development bias that matches the LD light quantity control target value is the development bias control target value.

  After setting the LD light quantity and developing bias in this way, a toner patch is created and the patch density is measured using the density sensor 10 (step S3). Then, from this patch density measurement result, a control target value of the LD light amount necessary for setting the image density to an appropriate value is calculated (step S4). In the image forming apparatus according to the present embodiment, at the stage of step S4, the control target value for the LD light quantity is calculated, and the control target value for the developing bias that matches the control target value for the LD light quantity is also calculated. Then, the LD light amount and the development bias control value for each page are calculated so that the LD light amount and the development bias control target values are reached while a predetermined number of pages are formed. As a method for calculating the LD light amount and the developing bias control value for each page, the method described in Patent Document 1 is used, and a specific description thereof is omitted here.

  When the calculation of the LD light amount and the development bias control value for each page is completed, the process returns to START again. At this point in time, the description will proceed assuming that it is not time to create a toner patch (step S1; No). If it is not time to create a toner patch, the control is performed for the LD light amount and the developing bias for each page determined in step S4, and the job is executed (step S5). If the toner patch creation timing is reached before the job is completed, No is selected in step S6, the process returns to START again, and Yes is selected in step S1, and the operations described in steps S2 to S4 are repeated. Do. When the job is finished (step S6; Yes), the aforementioned LD light quantity control target value and development bias control target value are set as the LD light quantity and development bias control values (step S7).

When the job is completed in this way, the difference in image density that occurs before and after the change of the LD light quantity is set by setting the LD light quantity control target value and the development bias control target value as the LD light quantity and development bias control value. Therefore, the light quantity control value suitable for the appropriate image density is set between the two jobs so that the image is not a problem. Compared with the control method of Patent Document 1, image formation of such dissimilar images is performed. It can be performed with an accurate image density.
[Second Embodiment]
Hereinafter, an image forming apparatus that controls the amount of exposure light, which is an embodiment of a third image forming apparatus of the present invention, will be described as a second embodiment.

  The configuration of the image forming apparatus according to the present embodiment is the same as that of the image forming apparatus according to the first embodiment shown in FIG. The creation of the patch itself is controlled in accordance with the control value of the LD light quantity at that time. In the following, the control method that is the difference will be described in detail, and a duplicate description of the overall configuration of the image apparatus will be omitted.

  FIG. 4 is a flowchart showing a control method for controlling the toner patch creation as well as the LD light quantity.

  First, the description will proceed assuming that the start point is the timing for creating a toner patch (step S11; Yes). If the correction of the LD light quantity has been completed at this point, that is, the current LD light quantity control value reaches the control target value of the LD light quantity determined to be appropriate from the patch density measurement result performed before this point. If YES in step S12, it is determined Yes in step S12, a toner patch is created, and the patch density is measured using the density sensor 10 (step S13). Then, from the patch density measurement result, a control target value of the LD light quantity and a control target value of the developing bias that matches the control target value are calculated (step S14). Then, the LD light amount and the development bias control value for each page are calculated so that the LD light amount and the development bias control target values are reached while a predetermined number of pages are formed. As a method for calculating the LD light amount and the developing bias control value for each page, the method described in Patent Document 1 is used, and a specific description thereof is omitted here. After calculating the LD light amount and development bias control values for each page, the process returns to START, and the LD light amount and development bias control values for each page determined in this way until the next toner patch creation timing is reached. The job is executed (step S15).

  When the toner patch creation timing is reached, if the LD light quantity control value has not reached the LD light quantity control target value at that time, it is determined No in step S12, and the toner patch is not created. Image formation is continued until the LD light quantity control value reaches the LD light quantity control target value.

  Thus, until the LD light quantity control value reaches the LD light quantity control target value, the toner patch is not created even when the toner patch formation timing is reached, so that the necessary LD light quantity correction is performed by the previous patch density measurement. Therefore, a new patch density measurement is not performed with the toner remaining, and an image can be formed efficiently and with high productivity without consuming excess toner.

  The above is the description of the embodiment of the image forming apparatus of the present invention.

  In the image forming apparatus described in the first embodiment and the second embodiment, the LD light amount and the LD light amount in each page are determined after the number of pages until the LD light amount and the development bias control value reach the respective control target values is determined. Although the control method for determining the developing bias is employed, the image forming apparatus of the present invention determines the LD light amount and the developing bias for each page in advance, and then the LD light amount and the developing bias control values are set to the respective control target values. You may employ | adopt the control method which determines the number of pages until it arrives.

  The image forming apparatus described in the first embodiment and the second embodiment corrects the LD light amount and the developing bias based on the detection result of the density sensor. The image forming apparatus of the present invention further includes a temperature sensor. Further, the LD light quantity and the developing bias may be corrected in consideration of the detection results of the humidity sensor, the surface potential sensor, and the toner density sensor.

  The image forming apparatus described in the first embodiment and the second embodiment employs a control method for the LD light amount and the developing bias. However, the image forming apparatus of the present invention limits the control target to these. Alternatively, a control method for charging, transfer, fixing, toner supply, and gradation of image data may be employed.

1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment. It is a block diagram of a density sensor used in the image forming apparatus shown in the present embodiment. 6 is a flowchart illustrating a method for controlling the LD light amount based on the patch density of a toner patch. 6 is a flowchart showing a control method for controlling toner patch creation as well as LD light quantity.

Explanation of symbols

1Y, 1M, 1C, 1K Photosensitive drum 2Y, 2M, 2C, 2K Charger 3Y, 3M, 3C, 3K Developer 4Y, 4M, 4C, 4K Transfer roll 5Y, 5M, 5K, 5Y Toner box 7Y, 7M, 7C, 7K toner density sensor 8 Intermediate transfer belts 8Y, 8M, 8K, 8Y Dispense motors 9a, 9b Path roll 10 Density sensor 20 Toner patch 30 ROS
40 controller 50 gradation control unit 60 LD light quantity control unit 70 TC control unit 80 charging voltage control unit 90Y, 90M, 90C, 90M potential sensor 100 temperature sensor 110 humidity sensor

Claims (2)

The rotating image carrier is primarily charged, and an electrostatic latent image is formed on the image carrier by exposure, developed with toner, and finally the toner image is transferred and fixed on the recording medium to be fixed on the recording medium. In an image forming apparatus for forming an image composed of a toner image,
An exposure device that forms an electrostatic latent image on the image carrier by exposing the image carrier with a light beam that is based on a set light amount control value and modulated according to an image signal;
A patch density measuring unit that forms a toner patch and measures the patch density of the toner patch;
A control value setting unit for setting the light amount control value,
The control value setting unit calculates a light quantity control target value based on the patch density measurement value obtained by the patch density measurement by the patch density measurement unit, and sets the set light quantity control value on a predetermined number of recording media. In the course of image formation, the light intensity control value set at the time of patch density measurement is gradually changed in a plurality of stages from the light intensity control value to the light intensity control target value.
If the light amount control value set at the end of image formation of the job started after the patch density measurement by the patch density measuring unit does not reach the light amount control target value, the control value setting unit An image forming apparatus characterized in that a light amount control value set at the end is changed to the light amount control target value at a time before image formation of the next job is started. A developing device that develops an electrostatic latent image on the image carrier with toner in response to application of a bias voltage;
A developing bias application unit that applies a developing bias having a voltage value based on a set developing bias control value to the developing device;
The control value setting unit is for setting a development bias control value,
The control value setting unit calculates a development bias control target value based on the patch density measurement value obtained by the patch density measurement by the patch density measurement unit, and sets the set development bias control value to the patch density measurement. toward the developing bias control values that are set at the time of the developing bias control target value state, and are not gradually changed in plural steps,
The control value setting unit, when the development bias control value set at the end of image formation of the job started after the patch density measurement by the patch density measurement unit has not reached the development bias control target value, 2. The development bias control value set at the end of image formation is changed to the development bias control target value at a time before image formation of the next job is started. Image forming apparatus.

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