JP4682661B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a technique for forming an electrostatic latent image by irradiating light on the surface of a charged photoreceptor.

An electrophotographic image forming apparatus irradiates light on a charged photoreceptor to form an electrostatic latent image, and attaches toner to the electrostatic latent image to form a toner image. An image is formed by transferring and fixing to a recording sheet. In such an image forming apparatus, even if the same amount of light is applied to the photosensitive member, the potential of the electrostatic latent image varies due to a decrease in the photosensitive layer of the photosensitive member or a temperature change around the photosensitive member. For this reason, the amount of light applied to the photoconductor is corrected so that the potential of the electrostatic latent image becomes a target potential. In addition, in order to prevent unevenness in the density of the toner image caused by unevenness in the photosensitivity of the photoconductor and unevenness in the exposure of the surface of the photoconductor, the amount of light irradiated to the photoconductor is corrected (see Patent Document 1). ).
JP 2002-86800 A

  By the way, the image forming apparatus detects the amount of light output from the light source to form an electrostatic latent image, controls the light source based on the detected amount of light, and outputs a target amount of light. Some have automatic light control (APC). The range of the amount of light that can be controlled automatically is determined in advance, and the image forming apparatus performs automatic light amount control for the amount of light within the determined range. If the light amount is corrected so that the light amount is corrected or the light amount is corrected in consideration of the photosensitive member film thickness, the temperature around the photosensitive member, and density unevenness, the amount of light in the upper limit of the predetermined range may be insufficient. In some cases, the light amount must be reduced from the lower limit light amount of the determined range, and the light amount of the output light may be out of the automatic light amount control range. In such a case, Patent Document 1 discloses a technique in which, in such a case, the amount of light to be output is corrected, the amount of light to be output falls within the range of the upper limit light amount to the lower limit light amount, and priority is given to obtaining the target potential. In this technique, the amount of light set in order to prevent uneven density is changed, so that good image quality cannot be obtained.

  The present invention has been made under the above-described background, and an object of the present invention is to prevent the light amount of light forming an electrostatic latent image from being outside the range of automatic light amount control.

In order to solve the above-described problems, the present invention detects a charging unit for charging an image carrier, a light output unit for variably outputting a light amount of output light, and a light amount of light output from the light output unit. When the light quantity detected by the light quantity detection means and the light quantity detected by the light quantity detection means are within the light quantity control range in the automatic light quantity control and are different from the preset set light quantity, the light having the set light quantity is output. In this way, the light output means is controlled by the automatic light quantity control so that the light quantity of the output light is corrected, and the light output from the light output means is irradiated to the image carrier charged by the charging means. A latent image forming means for forming an electrostatic latent image on the surface of the image carrier , a color material attached to the electrostatic latent image formed by the latent image forming means, and transferring the attached color material. An image that forms an image on a recording medium And forming means reads an image formed on a recording medium by the image forming means, and density unevenness detecting means for detecting the density unevenness of the read image, a temperature detecting means for detecting the temperature of the image carrier near, When the potential of the electrostatic latent image formed by the latent image forming unit is detected and there is a difference between the detected potential and the target potential of the electrostatic latent image, the potential of the electrostatic latent image is set to the target potential. the amount of light determined, the amount of light determined corrected based on the temperature detected by said temperature detecting means and the detected density unevenness in the density unevenness detecting unit, a setting unit of the quantity of light after corrected to the set amount of light, is set If the ratio of the set light amount obtained by the setting means with respect to the upper limit of the control range is substantially the same as the predetermined ratio or does not reach the ratio, the upper limit of the control range after the change Set light intensity ratio To provide an image forming apparatus and a changing means for changing the control range by lowering the upper and lower limits of the control range to exceed the predetermined ratio.

  According to the present invention, it is possible to prevent the amount of light forming an electrostatic latent image from being outside the range of automatic light amount control.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
[Configuration of the embodiment]
FIG. 1 is a diagram illustrating a configuration of a main part of an image forming apparatus according to an embodiment of the present invention. As shown in FIG. 1, the image forming apparatus that employs the intermediate transfer method includes a control unit 100, an image reading unit 110, and an image processing unit 120. The control unit 100 includes a CPU, a ROM, a RAM, and the like, and controls each unit of the image forming apparatus according to a program stored in the ROM. The control unit 100 is connected to various buttons (not shown) for operating the image forming apparatus. When a button is operated by the user of the image forming apparatus, the control unit 100 controls each part of the image forming apparatus to perform processing such as copying of a document.

  The image reading unit 110 includes an image scanner, reads a document image, and outputs an image signal under the control of the control unit 100. The image processing unit 120 receives the image signal output from the image reading unit 110 and performs image processing such as gradation correction and screen processing on the image represented by the image signal. Then, color conversion is performed on the image that has been subjected to image processing, image signals of each color Y, M, C, and K are generated, and the generated image signals are supplied to image forming units corresponding to the respective colors.

  Further, the image forming apparatus includes an intermediate transfer belt 20 and four systems of image forming units 10Y, 10M, 10C, and 10K corresponding to colors of Y (yellow), M (magenta), C (cyan), and K (black). A belt cleaning unit 30 for cleaning the intermediate transfer belt 20 is provided upstream of each image forming unit that transfers the toner image to the intermediate transfer belt 20.

  Each image forming unit has the same configuration except that the color of the toner image to be formed is different. Here, one of the image forming units 10K will be described. For each part of the image forming units 10Y, 10M, and 10C, the letters Y, M, and C representing the respective colors are replaced with K representing black and the end of the code. The description is omitted.

  The image forming unit 10K includes a photosensitive drum 11K as an image carrier on which a black (K) toner image is formed, a charger 12K that charges the photosensitive drum 11K to a constant potential, and supply of a black image signal. When receiving the light, the photosensitive drum 11K is irradiated with light modulated using the image signal to form an electrostatic latent image.

As shown in FIG. 2, the exposure unit 13K includes a light source unit 60, a half mirror 61, a polygon mirror 62, an f-theta lens 63, a mirror 64, a light amount sensor 65, and a light source control unit 66. I have. The light source unit 60 outputs laser light for forming an electrostatic latent image on the photosensitive drum 11K. The laser light output from the light source unit 60 is divided into light that passes through the half mirror 61 in the direction of the polygon mirror 62 and light that reflects in the direction of the light quantity sensor 65. The polygon mirror 62 is rotated by a motor (not shown) and guides the light that has passed through the half mirror 61 to the f-theta lens 63 while scanning. The light guided to the f-theta lens 63 is reflected by the mirror 64 and guided to the photosensitive drum 11K, and an electrostatic latent image is formed by the photosensitive drum 11K. On the other hand, the light reflected by the half mirror 61 enters the light quantity sensor 65. The light quantity sensor 65 is a sensor that detects the quantity of incident laser light, and outputs a signal indicating the detected quantity of light to the light source controller 66.
The light source control unit 66 controls the amount of laser light output from the light source unit 60. The light source control unit 66 controls the light source unit 60 according to the image signal output from the image processing unit 120 and causes the light source unit 60 to output light for forming an electrostatic latent image. The light source control unit 66 sets the light amount and the light amount range of the light output from the light source unit 60 based on the control from the control unit 100, and sets the light amount of the set light amount based on the signal output from the light amount sensor 65. Automatic light quantity control is performed so that light is output.

  Returning to FIG. 1, the image forming unit 10 </ b> K includes a two-component developing type developing device 14 </ b> K that forms a toner image by attaching black toner to the photosensitive drum 11 </ b> K on which the electrostatic latent image is formed, and an intermediate toner image. A primary transfer roll 16K to be transferred to the transfer belt 20 and a cleaning device 17K that removes toner remaining on the photosensitive drum 11K after the primary transfer are provided.

  Further, in the image forming unit 10K, a potential sensor 19K and a temperature sensor 18K are provided in the vicinity of the photosensitive drum 11K. The potential sensor 19K is a sensor that detects the potential of the surface of the photosensitive drum 11K, and outputs a signal indicating the detected potential to the control unit 100. The temperature sensor 18K is a sensor that detects the temperature near the photosensitive drum 11K, and outputs a signal indicating the detected temperature to the control unit 100.

  The toner images formed by the image forming units are transferred to the intermediate transfer belt 20 so that the toner images of the respective colors overlap. The intermediate transfer belt 20 onto which the toner image is transferred is stretched between a drive roll 40 that rotates in one direction and a tension roll 41 that applies tension to the intermediate transfer belt 20, and the arrow in FIG. It is moved in the A direction. When the intermediate transfer belt 20 is moved, the toner image transferred to the intermediate transfer belt 20 moves to the position of the transfer unit 42 for transferring the toner image onto the recording paper P.

  The transfer unit 42 includes a backup roll 42A and a secondary transfer roll 42B, and the backup roll 42A is provided at a position facing the secondary transfer roll 42B with the intermediate transfer belt 20 interposed therebetween. Further, the backup roll 42A forms a transfer electric field for transferring the toner image onto the recording paper P. A voltage source (not shown) is connected to the backup roll 42A, and a voltage is applied thereto. When the secondary transfer roll 42B comes into contact with the intermediate transfer belt 20, a potential difference is generated between the secondary transfer roll 42B and the grounded secondary transfer roll 42B, and a transfer electric field corresponding to the applied voltage is formed. The secondary transfer roll 42B contacts the intermediate transfer belt 20 immediately before the recording paper P is conveyed between the backup roll 42A and the secondary transfer roll 42B, and the toner image on the intermediate transfer belt 20 is transferred onto the recording paper P. Let them transcribe. When the transfer of the toner image is completed, the toner image is separated from the intermediate transfer belt 20.

  The fixing device 43 includes a heating roll 43A that applies heat to the recording paper P and a pressure roll 43B that applies pressure to the recording paper P. The fixing device 43 conveys the recording paper P, onto which the toner image has been transferred in the transfer unit 42, in the direction of arrow B in the drawing while being sandwiched between the heating roll 43A and the pressure roll 43B. Then, heat and pressure are applied to the toner image transferred to the recording paper P by a heating roll and a pressure roll to fix the toner image on the recording paper P.

  The image forming apparatus also includes a density sensor 50. The density sensor 50 is a sensor that detects the density of the toner image fixed on the recording paper P, and outputs a signal indicating the detected density to the control unit 100. Although not shown, the image forming apparatus also includes a density sensor that detects the density of the toner image transferred onto the intermediate transfer belt 20.

[Operation of the embodiment]
Next, the operation of this embodiment will be described with reference to FIG. Since the operations of the respective image forming units are the same, the operation of the image forming unit 10K will be described below, and the description of the operations of the other image forming units will be omitted.

  First, the control unit 100 detects the surface potential of the photosensitive drum 11K by a signal output from the potential sensor 19K (step SA1). Next, the control unit 100 obtains a potential difference between the detected potential and a target charging potential. Then, the photosensitive drum 11K is rotated and the charger 12K is controlled to charge the photosensitive drum 11K so that this potential difference is eliminated (step SA2).

  Next, the control unit 100 controls and controls the image processing unit 120 so that the image signal of the test patch is output to the exposure unit 13K. When this control is performed, the image signal of the test patch is output from the image processing unit 120 to the exposure unit 13K. Upon receiving this image signal, the exposure unit 13K irradiates the photosensitive drum 11K with light based on this image signal, and forms an electrostatic latent image of a test patch on the surface of the photosensitive drum 11K (step SA3).

  Next, the control unit 100 detects the potential of the electrostatic latent image portion of the test patch based on a signal output from the potential sensor 19K (step SA4). The control unit 100 obtains a potential difference between the detected potential and the target potential of the electrostatic latent image, and obtains the amount of light irradiated to the photosensitive drum 11K from the potential difference in order to obtain the target potential. Then, the light source control unit 66 is set so that the obtained light amount (hereinafter referred to as a set light amount) is output (step SA5).

  Next, the control unit 100 determines whether or not the set light amount set in step SA5 is a light amount around 30% of the maximum light amount in the automatic light amount control, and when the light amount is around 30% of the maximum light amount (step SB1). : YES), the setting of the maximum light amount output from the light source unit 60 is lowered (step SB2). Specifically, for example, when the maximum light amount in the output light amount range is set to 100 and the set light amount is 30, the maximum light amount is reduced to 87. Then, the reduced light amount is set in the light source control unit 66 as the maximum light amount output from the light source (step SB3).

  The range of light quantity that can be controlled automatically by the light quantity sensor 65 and the light source control unit 66 is such that when the maximum light quantity in the light quantity range is set, the minimum light quantity in the light quantity range is relatively determined, and the light quantity is the maximum light quantity. Since the automatic light amount control cannot be performed with high accuracy when the light amount is 30% or less of the above, the light amount of about 30% of the upper limit becomes the minimum light amount. If the maximum light amount is 100 and the set light amount is 30, for example, when light amount correction is performed to prevent density unevenness, the light amount becomes 30 or less, and automatic light amount control cannot be performed with high accuracy. May occur. However, when the maximum light amount is reduced to 87, the relatively determined minimum light amount becomes 26. Even if the density unevenness is corrected from 30 of the set light amount, the light amount does not fall below the minimum light amount of 26. Control can be performed with high accuracy.

  As described above, according to the present embodiment, the light of the set light amount is accurately output by the automatic light amount control, so that the potential of the electrostatic latent image can be accurately maintained at the target potential. Further, since the maximum light amount in the automatic light amount control is changed, it is possible to secure the light amount when correcting the density unevenness.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The second embodiment of the present invention is different from the first embodiment in that light amount correction for preventing the occurrence of density unevenness is taken into account when setting the maximum light amount for performing automatic light amount control. Since the configuration of the present embodiment is the same as that of the first embodiment, description of the configuration is omitted.

  Hereinafter, the operation of the present embodiment will be described with reference to FIGS. 5 and 6. Since the operations of the respective image forming units are the same, the operation of the image forming unit 10K will be described below, and the description of the operations of the other image forming units will be omitted. Further, in the following description, the description will be made assuming that the processing shown in FIG. 2 has already been performed.

  First, the control unit 100 controls the image processing unit 120 and the image forming unit 10K to form a toner image having the same density on the entire surface on the recording paper P (step SC1). Specifically, the image processing unit 120 and the image forming unit 10 </ b> K are controlled to form toner images having the same density on the entire surface on the intermediate transfer belt 20. Next, the control unit 100 controls the transfer unit 42 to transfer the toner image transferred to the intermediate transfer belt 20 onto the recording paper P. When the transfer of the toner image onto the recording paper P is completed, the control unit 100 conveys the recording paper P to the fixing device 43 and fixes the toner image on the recording paper P.

  When the fixing of the toner image is completed, the control unit 100 detects the entire density of the toner image formed on the recording paper P based on the signal output from the density sensor 50B (step SC2). Then, the density unevenness of the toner image is detected from the detected density. In order to prevent the density unevenness, the light amount is increased by correcting the set light amount for the portion where the density is low, and the light amount is decreased by correcting the set light amount for the portion where the density is high. Based on the detected density unevenness, the control unit 100 obtains a correction amount for the set light amount for each pixel (step SC3).

  Next, the control unit 100 obtains the correction amount having the largest value among the correction amounts for reducing the light amount, and adds the obtained correction amount and the light amount set in step SA5 to obtain the corrected minimum light amount (step SD1). Then, it is determined whether or not the light amount as a result of the addition is approximately 30% of the maximum light amount in the automatic light amount control, and when the light amount is approximately 30% of the maximum light amount (step SD2: YES), the light source unit 60. Is lowered (step SD3). Specifically, for example, the maximum light amount in the range of the output light amount is set to 100, the set light amount set in step SA5 is 32, and the largest correction amount among the correction amounts for reducing the light amount is -3. In this case, the maximum light amount in the light amount range is reduced to 87. Then, the reduced light amount is set in the light source control unit 66 as the maximum light amount output from the light source (step SD4).

  When the upper limit value of the light amount is 100, the set light amount is 32, and the correction amount is -3, if the light amount is corrected in order to prevent the occurrence of density unevenness, the light amount becomes 30 or less, and automatic light amount control is performed. Cannot be performed accurately. However, when the maximum light amount is reduced to 87, the relative minimum light amount is about 26. Even if the density unevenness is corrected from the light amount 30 set in step SA5, the light amount is below the minimum light amount 26. Therefore, automatic light quantity control can be performed with high accuracy.

  As described above, according to the present embodiment, the light of the set light amount is accurately output by the automatic light amount control, so that the potential of the electrostatic latent image can be accurately maintained at the target potential. Further, since the maximum light amount in the automatic light amount control is changed, it is possible to secure the light amount when correcting the density unevenness.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. The third embodiment of the present invention is different from the first embodiment in that light amount correction performed according to the temperature in the vicinity of the photosensitive drum is taken into consideration when setting the maximum light amount for performing automatic light amount control. Since the configuration of the present embodiment is the same as that of the first embodiment, description of the configuration is omitted.

  Hereinafter, the operation of the present embodiment will be described with reference to FIG. Since the operations of the respective image forming units are the same, the operation of the image forming unit 10K will be described below, and the description of the operations of the other image forming units will be omitted. Further, in the following description, the description will be made assuming that the processing shown in FIG. 2 has already been performed.

  When the process shown in FIG. 2 is completed, the control unit 100 detects the temperature in the vicinity of the photosensitive drum 11K based on the signal output from the temperature sensor 18K (step SE1). When the temperature of the photoconductor drum 11K is low, the photosensitivity of the photoconductor becomes low. Therefore, when an electrostatic latent image is formed, it is necessary to increase the amount of light according to a decrease in temperature. Since the photosensitivity of the photoconductor increases, it is necessary to reduce the amount of light as the temperature rises when forming an electrostatic latent image. Therefore, the control unit 100 corrects the set light amount obtained in step SA5 in accordance with the temperature detected in step SE1 so that an electrostatic latent image of the target potential is formed (step SE2).

  Next, the control unit 100 determines whether or not the light amount set in step SE2 is approximately 30% of the maximum light amount in the automatic light amount control, and when the light amount is approximately 30% of the maximum light amount (step SE3: YES), the setting of the maximum light quantity to be output is lowered (step SE4). Specifically, for example, when the maximum light amount in the output light amount range is set to 100 and the set light amount set in step SE2 is 30, the maximum light amount in the light amount range is reduced to 87. Then, the reduced light amount is set in the light source control unit 66 as the maximum light amount output from the light source (step SE5).

  The range of light quantity that can be controlled automatically by the light quantity sensor 65 and the light source control unit 66 is such that when the maximum light quantity in the light quantity range is set, the minimum light quantity in the light quantity range is relatively determined, and the light quantity is the maximum light quantity. Since the automatic light amount control cannot be performed with high accuracy when the light amount is 30% or less of the above, the light amount of about 30% of the upper limit becomes the minimum light amount. If the maximum light amount is 100 and the set light amount is 30, for example, when light amount correction is performed to prevent density unevenness, the light amount becomes 30 or less, and automatic light amount control cannot be performed with high accuracy. End up. However, when the maximum light amount is reduced to 87, the relatively determined minimum light amount becomes 26. Even if the density unevenness is corrected from 30 of the set light amount, the light amount does not fall below the minimum light amount of 26. Control can be performed with high accuracy.

  As described above, according to the present embodiment, the light of the set light amount is accurately output by the automatic light amount control, so that the potential of the electrostatic latent image can be accurately maintained at the target potential. Further, since the maximum light amount in the automatic light amount control is changed, it is possible to secure the light amount when correcting the density unevenness.

[Modification]
As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above, It can implement with another various form. For example, the present invention may be implemented by modifying the above-described embodiment as follows.

In the above-described embodiment, the maximum light amount is reduced by one step. However, if the set light amount is not more than the minimum light amount even if it is reduced by one step, the correction table stored in the ROM (see FIG. 8) is referred to. The maximum light amount may be lowered step by step. For example, when the maximum light amount of the automatic light control is set to the maximum light amount of the light source and the set light amount is 24% of the maximum light amount of the light source, the maximum light amount of the automatic light control is set to the maximum light amount of the light source. Even if it is lowered to 87%, the set light amount is not more than the minimum light amount of automatic light amount control. In this case, referring to the table shown in FIG. 8, the maximum light amount of the automatic light amount control is reduced to another level, that is, 74% of the maximum light amount of the light source. When the maximum light amount of the automatic light amount control is lowered to 87% of the maximum light amount of the light source, the set light amount becomes equal to or more than the minimum light amount of the automatic light amount control, and the automatic light amount control can be performed with high accuracy.
In the embodiment described above, the process of reducing the maximum light amount when the set light amount is near the minimum light amount has been described. However, when the set light amount is near the maximum light amount, the maximum light amount may be increased.

  The light source unit 60 may be a surface emission type light source including a plurality of laser diodes as shown in FIG. Further, when the light source unit 60 is a surface emission type light source, the exposure method may be either a multiple exposure method or an adjacent exposure method.

1 is a main part configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is the schematic diagram which showed the structure of the exposure part. It is a flowchart of the process which calculates | requires setting light quantity. It is a flowchart of the process which sets the maximum light quantity of automatic light quantity control. It is a flowchart of the process which calculates | requires the correction amount which correct | amends density unevenness. It is a flowchart of the process which sets the maximum light quantity of automatic light quantity control. It is a flowchart of the process which sets the maximum light quantity of automatic light quantity control. It is the figure which illustrated the correction table memorize | stored in ROM. It is the schematic of a surface emitting type light source.

Explanation of symbols

  10K: Image forming unit, 11K: Photosensitive drum, 12K: Charger, 13K: Exposure unit, 18K: Temperature sensor, 19K: Potential sensor, 42: Transfer unit , 43... Fixing device, 50... Density sensor, 60... Light source unit, 61... Half mirror, 62 ... polygon mirror, 63. 65... Light quantity sensor, 66... Light source control unit, 100... Control unit, 110.

Claims (4)

Charging means for charging the image carrier;
Light output means for variably outputting the amount of light to be output;
A light amount detecting means for detecting a light amount of light output from the light output means;
When the light quantity detected by the light quantity detection means is within a light quantity control range in automatic light quantity control and is different from a preset set light quantity, the automatic light quantity control is performed so that the set light quantity is output. and correcting means for controlling the light output means, for correcting the light amount of the light output by,
A latent image forming means for irradiating the image carrier charged by the charging means with the light output from the light output means to form an electrostatic latent image on the surface of the image carrier;
Image forming means for attaching a color material to the electrostatic latent image formed by the latent image forming means, and transferring the attached color material to form an image on a recording medium;
Density unevenness detecting means for reading an image formed on the recording medium by the image forming means and detecting density unevenness of the read image;
Temperature detecting means for detecting the temperature in the vicinity of the image carrier;
When the potential of the electrostatic latent image formed by the latent image forming unit is detected and there is a difference between the detected potential and the target potential of the electrostatic latent image, the potential of the electrostatic latent image is set to the target potential. A setting means for correcting the calculated light quantity based on the density unevenness detected by the density unevenness detection means and the temperature detected by the temperature detection means, and setting the corrected light quantity as the set light quantity;
When the ratio of the set light amount obtained by the setting means with respect to the set upper limit of the control range is substantially the same as or not reached the predetermined ratio, the upper limit of the control range after the change An image forming apparatus comprising: a changing unit that changes the control range by lowering an upper limit and a lower limit of the control range so that the ratio of the set light amount exceeds the predetermined ratio . When the ratio of the set light amount obtained by the setting means with respect to the upper limit of the set control range is substantially the same as or exceeds the predetermined ratio, the control means after the change The control range is changed by increasing the upper limit and the lower limit of the control range so that the ratio of the set light amount obtained by the setting means with respect to the upper limit of the control range does not exceed the predetermined ratio. Item 2. The image forming apparatus according to Item 1. A plurality of the control range, the changing means, the image forming apparatus according to claim 1, characterized in that to change the control range by selecting one of the plurality of control range.   The image forming apparatus according to claim 1, wherein the light output unit includes a plurality of laser diodes, and outputs light from the plurality of laser diodes.

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