KR20080103782A - Image forming apparatus for controlling image density and image density control method thereof - Google Patents

Abstract

An image forming apparatus and a method for controlling image density thereof are disclosed. The sensor detects the first image concentration and the second image concentration from the image region in which the test pattern is formed and the non-image region in which the test pattern is not formed, respectively, and the controller detects the suitability of the detected first image concentration and the first image concentration. Compare the first criterion for judging, compare the detected second image density with the second criterion for judging suitability of the second image concentration, and based on the comparison result, at least one of the first image concentration and the second image concentration Increase or decrease one.

Description

Image forming apparatus for controlling image density and its image density controlling method

1 is a perspective view showing an image forming apparatus for controlling image density according to a preferred embodiment of the present invention;

2A to 2C are diagrams for explaining changes in exposure potential and surface potential formed on the photoconductor according to image density;

3 is a flow chart for explaining the image density control method according to FIG. 1, and

4 is a perspective view schematically illustrating an image forming apparatus according to another embodiment of the present invention.

Explanation of symbols on the main parts of the drawings

100: image forming apparatus 105: charging roller

110: photosensitive member 115: exposed portion

120: developer 125: intermediate transfer belt

135: first transfer roller 140: second transfer roller

145 sensor 150 voltage supply

155 storage unit 160 control unit

The present invention relates to an image forming apparatus for controlling image density and an image density control method thereof. More particularly, the present invention relates to an image density control for adjusting an image density based on an image density detected from an image area and a non-image area, respectively. An image forming apparatus and an image density control method thereof.

An image forming apparatus using a two-component developer composed of a magnetic carrier and a nonmagnetic toner develops an electrostatic latent image formed on a photosensitive member using charged toner. Therefore, an image forming apparatus using a two-component developer needs to adjust the toner concentration, that is, the amount of toner relative to the carrier, in accordance with the amount of toner consumed.

To this end, a conventional image forming apparatus uses an image density method of controlling a toner concentration by forming a reference image pattern on a photosensitive member or an intermediate transfer member, detecting an image density of the formed reference image pattern, and determining whether toner is supplied.

However, this image density method has the following problems. When continuously outputting images with low coverage, the toner consumption is low and the charge amount of the toner (Q / M, Q is the actual charge amount, M is the mass of the toner) is increased, thereby decreasing the density of the image. Phenomenon occurs. At this time, more toner is supplied to match the density of the image. Even though there is a sufficient amount of toner, additional toner is added to generate an uncharged toner. It causes problems such as scattering. Here, coverage means the degree to which the A4 paper is filled with toner and printed.

This is because the toner concentration and the charge amount of the toner are inversely related, the charge amount of the toner is inversely related to the image density, and the toner concentration and the image concentration are in proportional relationship, so the image density is influenced by the charge amount as well as the toner concentration Because I receive. Toner scattering is contaminating the print engine without developing toner sufficiently charged on the photoconductor. Background contamination is toner developing in an area where an image should not be formed, thereby forming unnecessary images on the paper.

Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to control the image density by accurately adjusting the exposure potential or the surface potential or to identify the situation in which toner is additionally supplied. An image forming apparatus and a method for controlling the image density thereof for maintaining the image density at the highest level are provided.

The image forming apparatus for controlling the image density according to an embodiment of the present invention for achieving the above object, the first image density and the first image density from the image region in which the test pattern is formed and the non-image region in which the test pattern is not formed, respectively. A sensor for detecting the image density; And comparing the detected first image density with a first criterion for determining the suitability of the first image concentration, and comparing the detected second image density with the second standard for determining the suitability of the second image concentration. And a controller configured to increase or decrease at least one of the first image concentration and the second image concentration based on the comparison result.

In detail, when the first image concentration is smaller than the first criterion and the second image concentration is larger than the second criterion, the control unit adjusts the potential of the image region so that the first image concentration is the first image concentration. The first image is reached, and the potential of the non-image area is adjusted so that the second image concentration is less than or equal to the second standard.

If the first image concentration is less than the first criterion and the second image concentration is less than the second criterion, the controller determines that the developer is insufficient and notifies the outside that the developer needs to be supplied.

If the first image concentration is greater than the first criterion, the controller adjusts the absolute value of the potential of the image area to increase or decreases the amount of developing of the developer with the photosensitive member to reduce the first image concentration. .

The control unit forms the image region and the non-image region in at least one of a photosensitive member and an intermediate transfer member.

On the other hand, the image density control method according to an embodiment of the present invention, the step of detecting the first image concentration and the second image concentration from the image region in which the test pattern is formed and the non-image region in which the test pattern is not formed; Compare the detected first image concentration with a first criterion for determining the suitability of the first image concentration, and compare the detected second image density with a second criterion for determining the suitability of the second image concentration. Doing; And increasing or decreasing at least one of the first image concentration and the second image concentration based on the comparison result.

In the comparing step, if the first image concentration is smaller than the first reference and the second image concentration is larger than the second reference, the step of increasing or decreasing the first image concentration by adjusting the potential of the image area. To reach the first criterion and adjust the potential of the non-image area so that the second image concentration is less than or equal to the second criterion.

In the comparing step, if the first image concentration is less than the first criterion and the second image concentration is less than the second criterion, the step of increasing or decreasing determines that the developer is insufficient, and the developer is determined from the outside. Increasing the first image concentration is supplied.

In the comparing step, if the first image concentration is greater than the first criterion, the increasing or decreasing step may be adjusted to increase the absolute value of the potential of the image area or to reduce the amount of the developer developed by the photosensitive member. Thereby reducing the first image concentration.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, in describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, a detailed description thereof will be omitted.

1 is a perspective view showing an image forming apparatus for controlling image density according to a preferred embodiment of the present invention.

Referring to FIG. 1, the image forming apparatus 100 according to the present invention includes a charging roller 105, a photosensitive member 110, an exposure unit 115, a developing unit 120, an intermediate transfer belt 125, and a supporting roller ( 130, a first transfer roller 135, a second transfer roller 140, a sensor 145, a voltage supply unit 150, a storage unit 155, and a controller 160.

The charging roller 105 charges the surface of the photoconductor 110 to a uniform electric potential with a high voltage negative voltage (for example, -700V) while rotating in contact or non-contact state with the surface of the photoconductor 110.

When the surface is charged by the charging roller 105, the photoconductor 110 forms an electrostatic latent image on the portion where light is scanned by the exposure unit 115, and causes a developer such as toner to adhere to the formed electrostatic latent image.

The exposure unit 115 scans the light corresponding to the image information to the charged photoconductor 110 to have a uniform potential so that an electrostatic latent image of a predetermined pattern is formed. The exposure unit 115 uses a laser scanning unit (LSU) using a laser diode as a light source.

The developing unit 120 develops the electrostatic latent image formed on the photoconductor 110 with a developer. The developing unit 120 includes a container 120a for receiving a developer having a negative charge (-) and a nonmagnetic developer, for example, a toner and a positive charge (+), and a carrier mixed with a magnetic carrier, and a photosensitive member. The developing roller 120b is provided to face the 110, and supplies the toner to the photosensitive member 110 to form an electrostatic latent image as a toner image, and the developing roller 120b by using an electrostatic force acting between the developing roller 120b. A developer is attached to the surface thereof, and a feed roller 120c for forming a developer layer, that is, a toner layer, and a trimmer (not shown) for uniformizing the developer layer formed on the surface of the developing roller 120b. Since the developing roller 120b has a magnetic roller, the carrier with the toner, that is, the developer is attached to the developing roller 120b to form a developer layer.

When the image forming apparatus 100 performs only mono printing, the developing unit 120 includes only black toner K. FIG. In addition, when the image forming apparatus 100 performs color printing, four developing apparatuses (not shown) for accommodating toner of each of the YCMK colors are provided around one photoreceptor 110.

The intermediate transfer belt 125 is driven in one direction by the support rollers 130 formed at both ends thereof, and the toner image formed on the photosensitive member 110 is applied to the intermediate transfer belt 135 by a bias applied to the first transfer roller 135. 125). When a developer for each of the YCMK toners is provided, the toner image of each YCMK color may be transferred to the intermediate transfer belt 125 to form a multi-color toner image.

The toner image formed on the intermediate transfer belt 125 is transferred to the printing paper P by a bias applied to the second transfer roller 140, and to a fixing unit such as a heating roller (not shown) and a pressure roller (not shown). Is fixed to the printing paper P.

The sensor 145 detects the first image concentration and the second image concentration, respectively, from an image region in which a test pattern for detecting an image density is formed and a non-image region in which a test pattern is not formed. To this end, the sensor 145 includes a light emitting unit 145a such as a porter diode and a light receiving unit 145b.

First, the test pattern is formed as an electrostatic latent image on the surface of the photosensitive member 110 when the printed matter is output by the set number of sheets or when the control unit 160 determines that the image density is required, and then the intermediate transfer belt 125. Is transferred. The test pattern is formed in the image area predetermined on the intermediate transfer belt 125. The image area is an area set as a part where an image is formed when the user actually prints, and the non-image area is an area set as a part where the image is not formed when the user actually prints, that is, a part where no toner is to be attached.

The light emitter 145a irradiates light to the image area and the non-image area, and the light receiver 145b receives the light reflected from the image area and the non-image area and outputs the light to the controller 160. The test pattern is a pattern formed by transferring the image toner formed on the photosensitive member 110 to the intermediate transfer belt 125.

The sensor 145 may be provided near the photosensitive member 110 as well as the intermediate transfer belt 125 to detect the first image concentration and the second image concentration from the test pattern formed on the photosensitive member 110.

The voltage supply unit 150 supplies high voltage to the charging roller 105, the exposure unit 115, the developing roller 120b, and the supply roller 120c, respectively, under the control of the controller 160. The portion where the electrostatic latent image is formed may be an image region or a non-image region in which a test pattern is formed.

Each voltage supplied from the voltage supply unit 150 adaptively increases or decreases according to the detected first image concentration and the second image concentration.

The storage unit 155 stores a first criterion for determining the suitability of the first image density detected by the sensor 145, and stores a second criterion for determining the suitability of the detected second image concentration. The first criterion and the second criterion are criteria for determining whether the toner accommodated in the developing unit 120 is provided at an appropriate density for outputting printed matter or for determining whether the toner contained in the developer 120 is suitable for image formation. The first criterion and the second criterion may have one fixed value or a specific range calculated in the step of designing the image forming apparatus 100.

The controller 160 controls the overall operation of each block described above using a control program, firmware, and the like stored in an inactive memory such as a ROM (not shown). As an example, the controller 160 controls the voltage supply unit 150 to perform the image operation as shown in FIG. 2A so that the exposure unit 115 scans light at an exposure potential such as -60V, and the charging roller 105 By supplying a negative voltage, such as -700V, the photosensitive member 110 is charged to a surface potential of -700V. As a result, the negatively charged toner is attached to an image region having an exposure potential of -60V in the photoconductor 110 to form an electrostatic latent image corresponding to an image or a test pattern. In addition, the portion of the non-image area where the image is not formed has a surface potential of -700V.

In addition, the controller 160 controls the voltage supply unit 150 to supply a negative voltage such as -500V to the supply roller 120c and a negative voltage such as -300V to the developing roller 120b. As a result, the developing roller 120b receives the developer attached to the supply roller 120c by the potential difference between the supply roller 120c and the developing roller 120b, and the toner is applied to the electrostatic latent image of the photosensitive member 110. To be attached to the formed part.

In addition, the controller 160 forms a predetermined test pattern on the photosensitive member 110 or the intermediate transfer belt 125 when printing is performed by a predetermined number of sheets, and controls the sensor 145 to control the first image from the test pattern. Process to detect light corresponding to the concentration and the second image concentration.

That is, the controller 160 controls the exposure unit 115 to scan the light corresponding to the image information for forming the test pattern to the designated image region of the photosensitive member 110 to form an electrostatic latent image, and to develop the electrostatic latent image. Toner is attached from the roller 120b, and the toner image formed by attaching the toner is transferred to the intermediate transfer belt 125. The controller 160 controls the light emitter 145a to scan light into the test pattern and the non-image area transferred to the intermediate transfer belt 125, and receives the light received from the light receiver 145b.

The controller 160 detects the first image density by converting the light reflected from the image region among the light input from the light receiving unit 145b into a digital signal, and converts the light reflected from the non-image region into a digital signal to convert the second image. Detect concentration. Then, the controller 160 compares the detected first image concentration with the stored first reference to control whether the first image concentration is increased or decreased based on the comparison result and the toner is supplied. The criteria are compared to control the increase or decrease of the second image concentration or the supply of the toner based on the comparison result.

In more detail, if the first image concentration is less than the first criterion and the second image concentration is greater than the second criterion, the controller 160 adjusts the potential of the image region to which the toner is attached to adjust the first image concentration to the first image concentration. The first image is reached, and the potential of the non-image area is adjusted so that the second image concentration is lower than the second standard.

That is, if the first image concentration is less than the first criterion and the second image concentration is greater than the second criterion, the controller 160 does not have a low toner supply amount due to insufficient supply of the toner in the developing unit 120, and the toner concentration is appropriate. This means that the toner adheres to the non-image area where it is judged to be at a level and it is preferable that an image is not formed because the toner that is not sufficiently charged is present in the photoconductor 110. This means that the second image concentration is larger than the second standard, so that the toner is provided to be suitable for printing so that the toner that is not sufficiently charged is also attached to the non-image area of the photosensitive member 110 and transferred to the intermediate transfer belt 125. It means.

Therefore, the controller 160 performs a latent image condition that increases the first image concentration and maintains or decreases the second image concentration. In order to increase the first image concentration while maintaining the second image concentration, the controller 160 reduces the exposure potential of the photoconductor 110 as shown in FIG. 2B and the controller 160 to reduce the second image concentration. Controls the voltage supply unit 150 to increase the surface potential of the photosensitive member 110.

That is, the controller 160 controls the voltage supply unit 150 to reduce the power of the exposure unit 115 to reduce the exposure potential, and to increase the voltage supplied to the charging roller 105 to increase the surface potential. The voltage supply unit 150 is controlled. The exposure potential may be performed by adjusting the on-time to which the voltage is supplied as well as the power.

Here, decreasing the exposure potential means adjusting the absolute value of the exposure potential to the smaller side, and increasing the surface potential means adjusting the absolute value of the surface potential to the larger side. This means that if the absolute value of the exposure potential is adjusted small, the force to send the toner from the developing roller 120b to the photoconductor 110 increases, so that the first image density can also be increased. If the absolute value of the surface potential is large, the toner is increased. This is because the force from the developing roller 120b to the photosensitive member 110 can be reduced.

On the other hand, if the first image concentration is less than the first criterion and the second image concentration is less than the second criterion, the controller 160 determines that the toner supply amount of the developing unit 120 is insufficient and the image concentration is small. Inform the outside world via alarm or warning message that the supply is necessary. When the user supplies the toner in the developing unit 120, the controller 160 may selectively reform the test pattern. This is to confirm whether the toner concentration is properly adjusted and may be selectively applied by the user or the designer.

On the other hand, if the first image concentration is greater than the first criterion, the controller 160 executes a latent image condition or developing condition that reduces the first image concentration regardless of the size of the second image concentration. The latent image condition is to control the exposure potential or surface potential so that toner does not adhere to the non-image area or toner adheres to the image area less. Accordingly, the controller 160 controls the voltage supply unit 150 to increase the exposure potential on the photoconductor 110 as shown in FIG. 2C to reduce the first image concentration. That is, the controller 160 controls the voltage supply unit 150 to increase the power of the exposure unit 115 to increase the exposure potential.

When the developing condition is performed to reduce the first image concentration, the controller 160 reduces the amount of development developed from the developing roller 120b to the photosensitive member 110 by reducing the size of the developing electric field. Alternatively, the controller 160 reduces the on-duty in which the toner is developed and increases the off-duty in which the toner is recovered from the photosensitive member 110 to the developing roller 120b, thereby reducing the amount of development. Alternatively, the controller 160 may increase the developing frequency so as to reduce the developing amount.

FIG. 3 is a flowchart for explaining an image density control method according to FIG. 1.

1 to 3, when a test pattern is formed to reach a condition for detecting the first image concentration and the second image concentration, the control unit 160 controls the test pattern to the photosensitive member 110 or the intermediate transfer belt 125. ), The charging roller 105, the photosensitive member 110, the exposure unit 115, the developer 120, the intermediate transfer belt 125, the support roller 130, the first transfer roller 135, the second transfer The roller 140 and the voltage supply unit 150 are controlled (S305).

When the test pattern is formed, the controller 160 controls the light emitter 145a to irradiate light to the image area and the non-image area where the test pattern is formed, and the light reflected from the image area among the light input from the light receiver 145b. The first image density is detected by converting the signal into a digital signal, and the second image concentration is detected by converting the light reflected from the non-image area into the digital signal (S310).

After the step S310, the controller 160 compares the detected first image concentration with the stored first criterion to determine whether the first image concentration is included in the first criterion (S315).

If the first image concentration is not included in the first criterion and is smaller than the first criterion (S320), the controller 160 compares the second image concentration and the second criterion (S325).

If the second image concentration is greater than the second criterion in step S325, the controller 160 determines that the toner concentration is an appropriate level for printing (S330). That is, the controller 160 determines that the first image concentration is not smaller than the first criterion because the toner supply amount is insufficient, and the toner that is not sufficiently charged is adhered to the non-image area of the photoconductor 110 as a result. In step 145, it is determined that the second image concentration is sensed.

Therefore, the controller 160 adjusts the exposure potential on the photoconductor 110 to increase the first image concentration (S335), and adjusts the surface potential on the photoconductor 110 to reduce the second image concentration. (S340). In operation S335 and S340, the controller 160 decreases the exposure potential of the photoconductor 110 to increase the first image concentration, and increases the surface potential of the photoconductor 110 to increase the second image concentration. The voltage supply unit 150 is controlled to reduce the voltage.

On the other hand, if it is determined in step S325 that the second image concentration is less than or equal to the second criterion, the controller 160 determines that the image concentration is low due to insufficient amount of toner supply of the developing unit 120, and that the supply of toner is necessary. Notify the user through an alarm or warning message (S345).

When the toner is supplied into the developer 120 by the user or the designer (S350), the controller 160 controls each block to reconstruct the test pattern (S355).

The controller 160 redetects the first image concentration and the second image concentration from the image region and the non-image region on which the test pattern is formed using the sensor 145 (S360).

If the first image concentration is within the first criterion (S365), the controller 160 determines that an amount of toner suitable for image formation is supplied in step S350. On the other hand, if it is determined in step S365 that the first image concentration deviates from the first standard, the controller 160 compares the second image concentration with the second standard (S370).

If the second image concentration is greater than the second criterion in step S370, the controller 160 enters step S330 to process steps S330 to S340. In addition, if the second reference is greater than the second image concentration in step S370, the controller 160 enters step S345.

On the other hand, if it is determined in step S320 that the first image concentration is greater than the first criterion, the controller 160 determines that the toner is sufficiently supplied, and the toner concentration is suitable for image formation (S375).

However, since the first image concentration is greater than the first criterion, the controller 160 reduces the amount of development that is developed from the developing roller 120b onto the photoreceptor 110, resulting in a latent image condition or development condition in which the first image concentration is reduced. To execute (S380). That is, in step S370, the controller 160 controls the voltage supply unit 150 to increase the exposure potential on the photoconductor 110 as shown in FIG. 2C to reduce the first image concentration. Alternatively, in step S370, the controller 160 may reduce the amount of development by reducing the size of the developing electric field, reducing the on-duty in which the toner is developed, or increasing the developing frequency.

In FIG. 3, steps S355 to S370 may be selectively performed. That is, the designer or the user can selectively perform or cancel the steps S355 to S370 by setting as an option.

Meanwhile, the above-described present invention has been described taking the case where the image forming apparatus 100 performs only mono printing as an example. When the image forming apparatus 100 performs color printing, four YCMK developer (not shown) for accommodating toner of each of the YCMK colors is provided around one photoreceptor 110 or as shown in FIG. 4. YMCK developer 120Y, 120C, 120M, 120K may be provided around each photosensitive member 110. Since only the color of the toner provided in each developing unit 120 is different, the operation of the toner is almost the same, and thus the detailed description and the reference numerals are omitted. However, in steps S305 and S355 of FIG. 3, the controller 160 controls the photosensitive member 110 or the intermediate transfer belt to the Y pattern test pattern, the M color test pattern, the C color test pattern, and the K color test pattern, respectively. It is preferable to form at 125 to detect and control image density.

As described above, according to the image forming apparatus and the image density control method for controlling the image density according to the present invention, even though the toner is sufficiently provided, it is determined that the toner is not enough and is caused by additional supply of the toner. Toner scattering or background contamination can be prevented.

In particular, the present invention can more accurately prevent toner from being supplied by judging whether the toner concentration is insufficient by using the first image concentration detected from the image region and the second image concentration detected from the non-image region.

In addition, the present invention determines that background contamination occurs when the first image concentration is smaller than the previously stored reference and the second image concentration is larger than the previously stored reference, and determines the amount of toner adhered to the photoconductor without further supply of toner. By increasing the image quality can be improved.

While the above has been shown and described with respect to preferred embodiments of the present invention, the present invention is not limited to the specific embodiments described above, it is usually in the technical field to which the invention belongs without departing from the spirit of the invention claimed in the claims. Various modifications may be made by those skilled in the art, and these modifications should not be individually understood from the technical spirit or the prospect of the present invention.

Claims (10)

A sensor for detecting a first image concentration and a second image concentration from an image region in which a test pattern is formed and a non-image region in which the test pattern is not formed; And Compare the detected first image concentration with a first criterion for determining the suitability of the first image concentration, and compare the detected second image density with a second criterion for determining the suitability of the second image concentration. And a controller configured to increase or decrease at least one of the first image concentration and the second image concentration based on the comparison result. The method of claim 1, If the first image concentration is less than the first criterion, and the second image concentration is greater than the second criterion, The control unit adjusts the potential of the image region so that the first image concentration reaches the first reference, and adjusts the potential of the non-image region so that the second image concentration is equal to or less than the second reference. And an image forming apparatus for controlling the image density. The method of claim 1, If the first image concentration is less than the first criterion, and the second image concentration is less than the second criterion, The controller determines that the developer is insufficient and notifies the outside that the supply of the developer is necessary. The method of claim 1, If the first image concentration is greater than the first criterion, And the controller is configured to reduce the first image density by adjusting the absolute value of the potential of the image region to increase or by decreasing the amount of the developer developed by the photosensitive member to reduce the first image density. The method of claim 1, And the control unit forms the image region and the non-image region in at least one of a photosensitive member and an intermediate transfer member. Detecting a first image concentration and a second image concentration from an image region in which a test pattern is formed and a non-image region in which the test pattern is not formed; Compare the detected first image concentration with a first criterion for determining the suitability of the first image concentration, and compare the detected second image density with a second criterion for determining the suitability of the second image concentration. Doing; And Increasing or decreasing at least one of the first image concentration and the second image concentration based on the comparison result. The method of claim 6, In the comparing step, if the first image concentration is less than the first criterion and the second image concentration is greater than the second criterion, In the increasing and decreasing step, the potential of the image area is adjusted so that the first image concentration reaches the first standard, and the potential of the non-image area is adjusted so that the second image concentration is less than or equal to the second standard. How to adjust the image density, characterized in that. The method of claim 6, In the comparing step, if the first image concentration is less than the first criterion, and the second image concentration is less than the second criterion, The increasing and decreasing step is determined that the developer is insufficient, the image density control method characterized in that for increasing the first image concentration by receiving the developer from the outside. The method of claim 7, wherein In the comparing step, if the first image concentration is greater than the first reference, The increasing and decreasing of the image density control method may include adjusting the absolute value of the potential of the image area to increase or decreasing the amount of the developer developed by the photosensitive member to reduce the first image density. The method of claim 6, And the image region and the non-image region are formed in at least one of a photosensitive member and an intermediate transfer member.

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