Image forming apparatus

Abstract

To more accurately calculate a setting value of a control amount related to an image forming operation to stabilize image quality.SOLUTION: An image forming apparatus 1 detects the relationship (approximate line L1) between a control amount CV related to an image forming operation and the density D of an image formed on a photoreceptor drum that is an image carrier, and on the basis of the relationship, calculates a setting value CV_TD of the control amount CV corresponding to a target density TD. The image forming apparatus forms patch images on the photoreceptor drum by using the setting value CV_TD, corrects the relationship on the basis of the difference ΔD between the density D10 of the patch images and the target density TD, and corrects the setting value CV_TD on the basis of the corrected relationship.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a calibration function. [Background technology]

[0002] Some image forming devices, such as printers, have a calibration function. For example, Patent Document 1 below describes forming a patch image on an image carrier and performing calibration to maintain image quality based on the density of the patch image. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5806985 Summary of the Invention [Problem to be solved by the invention]

[0004] During calibration, a setting value of a control variable corresponding to a predetermined target density is calculated based on the density of multiple patch images of different densities formed on an image carrier and on the relationship between the control variable (e.g., bias or light amount) related to the image formation operation and the density of the image (development process characteristics).

[0005] However, since the density of each patch image varies depending on the formation position on the image carrier, even if calibration is performed, the calculated setting values ​​may not be sufficiently accurate, and image quality may not be stable. Furthermore, with regard to the development process characteristics, the required setting values ​​may change as the development process deteriorates over time.

[0006] The present invention has been made in view of the above circumstances, and has as its object to more accurately calculate the set values ​​of the control variables related to the image forming operation and stabilize the image quality. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided an image forming apparatus including: an image forming unit having an image carrier, forming an image on a surface of the image carrier, and transferring the image to a recording medium to form an image on the recording medium; a control unit changing a control variable related to an image formation operation in the image forming unit to control the operation of the image forming unit and form a plurality of first patch images having different densities on the image carrier; a density measurement unit measuring the density of the image formed on the image carrier; and a calculation unit calculating a setting value of the control variable corresponding to a predetermined target density based on the control variable when each of the first patch images is formed and the density of each of the first patch images measured by the density measurement unit. The control unit uses the setting value calculated by the calculation unit to control the operation of the image forming unit to form a second patch image on the image carrier, and the calculation unit corrects the setting value based on a difference between the density of the second patch image measured by the density measurement unit and the target density. The control unit uses the setting value corrected by the calculation unit as a control variable during normal image formation operation by the image forming unit. [Effects of the Invention]

[0008] According to the present invention, it is possible to more accurately calculate the set values ​​of the control variables related to the image forming operation, thereby stabilizing the image quality. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a front cross-sectional view showing the structure of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a functional block diagram illustrating a schematic main internal configuration of an image forming apparatus according to an embodiment of the present invention; [Figure 3] 1A is a graph showing an example of the relationship between the control amount related to the image forming operation and the image density, and FIG. 1B is a diagram illustrating the relationship between the control amount and the image density. [Figure 4] 10 is a flowchart illustrating an example of processing performed by a control unit in the image forming apparatus. [Figure 5] 10A and 10B are diagrams illustrating the difference between the density of a second patch image and a target density. [Figure 6] 10A and 10B are diagrams illustrating an example of a method for correcting the relationship between the control amount and the image density. DETAILED DESCRIPTION OF THE INVENTION

[0010] An image forming apparatus according to one embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a front cross-sectional view showing the structure of an image forming apparatus according to one embodiment of the present invention. Fig. 2 is a functional block diagram showing the main internal configuration of an image forming apparatus according to one embodiment of the present invention.

[0011] The image forming apparatus 1 is a multifunction device that combines multiple functions, such as a copy function, a printer function, a scanner function, and a facsimile function. The image forming apparatus 1 includes a control unit 10, a document feed unit 6, a document reading unit 5, an image forming unit 12, a fixing unit 13, a paper feed unit 14, a density sensor 130, an operation unit 47, a communication unit 9, and a memory unit 8.

[0012] The document feeder 6 is configured to be openable and closable by a hinge or the like (not shown) on the top surface of the document reading unit 5, and functions as a document pressing cover when reading a document placed on a platen glass (not shown). The document feeder 6 is also an ADF (Auto Document Feeder), and includes a document placement tray 61, and supplies documents placed on the document placement tray 61 to the document reading unit 5.

[0013] The document reading unit 5 includes a scanner and the like, and reads a document fed from a document feeding unit 6, or reads a document placed on a platen glass.

[0014] The following describes the case where a document is read by the image forming apparatus 1. The document reading unit 5 optically reads an image of a document supplied to the document reading unit 5 by the document feeding unit 6 or a document placed on the platen glass, and generates image data. The image data generated by the document reading unit 5 is stored in an image memory (not shown) or the like.

[0015] An image forming operation performed by the image forming apparatus 1 will now be described. The image forming section 12 includes image forming units 120B, 120Y, 120C, and 120M (hereinafter collectively referred to as "image forming units 120") for each color (black, yellow, cyan, and magenta). Each image forming unit 120 includes a photosensitive drum 121 as an image carrier that carries a toner image, a charging device 122, an exposure device 123, a developing device 124, and a primary transfer device (primary transfer roller 126). The image forming units 120 are configured to form an image on recording paper as a recording medium by secondary transfer via an intermediate transfer belt 125 stretched around a driving roller 125A and a driven roller 125B. The photosensitive drum 121 is an example of an image carrier as defined in the claims.

[0016] The charging device 122 charges the surface of the photosensitive drum 121. The exposure device 123 exposes the charged surface of the photosensitive drum 121 to light to form an electrostatic latent image on the surface of the photosensitive drum 121. The developing device 124 contains toner for developing the electrostatic latent image and develops the electrostatic latent image formed on the surface of the photosensitive drum 121.

[0017] The image forming units 120 for each color form a toner image on the photosensitive drum 121 through the processes of charging, exposing, and developing based on an image made up of the respective color components, and the toner image is transferred onto the intermediate transfer belt 125 by the primary transfer roller 126. The intermediate transfer belt 125 is an example of an image carrier in the claims.

[0018] Intermediate transfer belt 125 has an image bearing surface on its outer circumferential surface onto which a toner image is transferred, and is driven by drive roller 125A while in contact with the circumferential surfaces of photosensitive drums 121. Intermediate transfer belt 125 travels endlessly between drive roller 125A and driven roller 125B in synchronization with each photosensitive drum 121.

[0019] The toner images of each color transferred onto the intermediate transfer belt 125 are superimposed on each other on the intermediate transfer belt 125 to form a color toner image. The secondary transfer roller 127 transfers the color toner image formed on the surface of the intermediate transfer belt 125 onto the recording paper P conveyed from the paper feed unit 14 by a conveying roller pair 191 provided at an appropriate position on the conveying path 190, at a nip portion N between the secondary transfer roller 127 and the driving roller 125A, with the intermediate transfer belt 125 sandwiched therebetween.

[0020] Image forming unit 12 includes density sensor 130 that measures the density of the toner image transferred to intermediate transfer belt 125. Density sensor 130 is disposed upstream of the position of secondary transfer roller 127 in the movement direction of intermediate transfer belt 125, and measures the density of a first patch image PT1 and a second patch image PT2, which will be described later.

[0021] The density sensor 130 is an optical sensor. The density sensor 130 includes a light-emitting unit (not shown) that emits light toward the intermediate transfer belt 125, and a light-receiving unit (not shown) that receives reflected light of the light emitted by the light-emitting unit. The density sensor 130 is an example of a density measurement unit in the claims.

[0022] Under the control of the control unit 100, the image forming unit 12 forms a toner image on recording paper fed from the paper feed unit 14 based on image data generated by the document reading operation, image data stored in an image memory, etc., image data received from a computer connected to the network, etc., to create a printed matter.

[0023] The paper feed unit 14 includes a paper feed cassette 141, a pickup roller that picks up recording paper P from the paper feed cassette 141 and feeds it to the image forming unit 12, a transport roller, a transport path, and a rotation drive mechanism for each roller.

[0024] The fixing unit 13 is a fixing device equipped with a heat roller, a pressure roller, and a drive mechanism for rotating these rollers. The fixing unit 13 heats and presses the recording paper P on which a toner image has been formed by the image forming unit 12 at the nip between the two rollers, fixing the toner image to the recording paper P. The recording paper P that has undergone the fixing process is discharged to the discharge tray 151.

[0025] The operation unit 47 includes various hard keys that are operated by the user, and receives instructions from the user, such as an instruction to execute an image forming operation, regarding various operations and processes that the image forming apparatus 1 can execute in response to the operation of the hard keys.

[0026] The operation unit 47 includes a display unit 473 that displays operation guides and the like to the operator. The operation unit 47 also receives input of instructions from the user based on the user's operation (touch operation) on the screen displayed on the display unit 473 via a touch panel that the display unit 473 has.

[0027] The display unit 473 is composed of an LCD (Liquid Crystal Display) or the like. When the operator touches a button or key displayed on the screen, the touch panel receives an instruction associated with the touched position. In this case, the touch panel functions as an operation unit.

[0028] The communication unit 9 is a communication interface for transmitting and receiving various data to and from external devices (for example, personal computers) within a local area or on the Internet.

[0029] The storage unit 8 is a large-capacity storage device such as a hard disk drive (HDD) or a solid state drive (SSD), and stores various control programs and the like.

[0030] The control unit 10 includes a processor, a RAM (Random Access Memory), a ROM (Read Only Memory), and a dedicated hardware circuit. The processor is, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), or an MPU (Micro Processing Unit). The control unit 10 includes a control unit 100 and a calculation unit 101.

[0031] The control unit 10 functions as a control unit 100 and a calculation unit 101 by the operation of the processor in accordance with a control program, etc. stored in the storage unit 8. However, the control unit 100, etc. may also be configured by hardware circuits, without relying on the operation in accordance with a control program by the control unit 10. Unless otherwise specified below, this applies to each embodiment.

[0032] The control unit 100 is responsible for overall operational control of the image forming apparatus 1. The control unit 100 is connected to the document feed unit 6, the document reading unit 5, the image forming unit 12, the fixing unit 13, the paper feed unit 14, the density sensor 130, the operation unit 47, the communication unit 9, and the storage unit 8, and controls the driving of each of these units. For example, the control unit 100 executes various processes required for image formation by the image forming apparatus 1.

[0033] Furthermore, the control unit 100 controls the operation of the image forming unit 12 using a control amount CV related to the image forming operation in the image forming unit 12, thereby forming an image on a recording medium. The control amount CV is, for example, one or more values ​​of the charging bias applied to the photosensitive drum 121 by the charging device 122, the exposure amount irradiated onto the photosensitive drum 121 by the exposure device 123, and the developing bias applied to the developing device 124. It is possible to arbitrarily set which of these is the control amount CV.

[0034] Next, a case will be described in which a plurality of first patch images PT1 with different densities are formed on intermediate transfer belt 125, the densities D of these plurality of first patch images PT1 are measured, and calibration is performed based on the measured densities D.

[0035] When performing calibration, control unit 100 uses a plurality of different (e.g., four) control variables CV related to the image formation operation in image forming unit 12 to cause image forming unit 12 to form the plurality of first patch images PT1 with different densities D on intermediate transfer belt 125. For example, control unit 100 changes control variable CV in a stepwise manner within a range between an upper limit value and a lower limit value, and causes the plurality of first patch images PT1 with different densities D to be formed on intermediate transfer belt 125.

[0036] Fig. 3(A) is a graph showing an example of the relationship between the control amount CV and the density D. In Fig. 3(A), the horizontal axis represents the control amount CV, and the vertical axis represents the density D measured by the density sensor 130. Fig. 3(A) shows four points of data, each corresponding to four first patch images PT1 formed on the intermediate transfer belt 125. Fig. 3(A) shows that the densities of the first patch images PT1 formed on the intermediate transfer belt 125 with the control amounts CV1 to CV4 are densities D1 to D4, respectively.

[0037] The calculation unit 101 detects a relationship RA between the control variable CV and the density D of the image formed on the photosensitive drum 121 based on the control variables CV1 to CV4 used to form each first patch image PT1 and the densities D1 to D4 of each first patch image PT1 measured by the density sensor 130, and calculates a setting value CV_TD of the control variable CV corresponding to a predetermined target density TD based on the detected relationship RA.

[0038] 3(B) is a diagram illustrating the relationship RA between the control variable CV and the concentration D. The relationship RA is expressed by an approximation line L1 that passes through the vicinity of all four data points. The calculation unit 101 calculates, for example, an arithmetic formula F1 (an arithmetic formula that shows the relationship RA between the control variable CV and the concentration D) that shows the approximation line L1 using the least squares method, and calculates the set value CV_TD of the control variable CV that corresponds to the target concentration TD using the calculated arithmetic formula F1, as shown in FIG. 3(B).

[0039] The formation of each first patch image PT1 and the calculation of the set value CV_TD are performed for each of the image forming units 120B, 120Y, 120C, and 120M of each color.

[0040] Next, correction of the set value CV_TD will be described. For calibration, the control unit 100 uses the set value CV_TD calculated by the calculation unit 101 to control the operation of the image forming unit 12 and further form a second patch image PT2 on the photosensitive drum 121. For example, the control unit 100 forms the second patch image PT2 on the photosensitive drum 121 at a timing other than the normal image forming operation executed based on a print job (when an image to be transferred to a recording medium is not formed on the photosensitive drum 121 and intermediate transfer belt 125) (Method 1). Alternatively, when forming an image to be transferred to a recording medium on the photosensitive drum 121 and intermediate transfer belt 125 during the normal image forming operation, the control unit 100 forms the second patch image PT2 in an area on the intermediate transfer belt 125 where an image to be transferred to a recording medium is not formed (Method 2). The density sensor 130 measures the density of each second patch image PT2.

[0041] The calculation unit 101 corrects the relationship RA based on the difference ΔD between the density D10 of the second patch image PT2 measured by the density sensor 130 and the target density TD, and corrects the setting value CV_TD when each of the second patch images is formed based on the corrected relationship RA.

[0042] The control unit 100 uses the set value CV_TD thus corrected by the calculation unit 101 as a control amount during the normal image forming operation by the image forming unit 12.

[0043] The formation of second patch image PT2 and the correction of setting value CV_TD are performed for each of image forming units 120B, 120Y, 120C, and 120M of each color. Control unit 100 uses setting value CV_TD for each of image forming units 120B, 120Y, 120C, and 120M corrected by calculation unit 101 as a control amount during the normal image formation operation by each of image forming units 120B, 120Y, 120C, and 120M.

[0044] Next, an example of a process for correcting the set value CV_TD in the image forming apparatus 1 will be described with reference to the flowchart shown in Fig. 4. This process is performed after the calculation unit 101 calculates the set value CV_TD.

[0045] First, control unit 100 uses set value CV_TD calculated by calculation unit 101 to control the operation of image forming unit 12, causing second patch image PT2 to be formed on intermediate transfer belt 125 (S1).

[0046] Calculation unit 101 acquires information indicating density D10 of second patch image PT2 measured by density sensor 130 (S2), calculates a difference ΔD (see FIG. 5) between density D10 of second patch image PT2 indicated by the acquired information and target density TD (S3), and calculates a ratio R of the difference ΔD to the target density TD (S4). FIG. 5 is a diagram illustrating the difference ΔD between density D10 of second patch image PT2 and target density TD.

[0047] Next, the calculation unit 101 corrects the relationship RA based on the ratio R calculated from the target concentration TD and the difference ΔD (S5). Figures 6(A) and (B) are diagrams for explaining an example of a method for correcting the relationship RA.

[0048] The four data points indicated by circles in Figure 6(A) are the same as the four data points shown in Figure 3(A), and the four data points indicated by crosses in Figure 6(A) are corrected by adding the densities D1 to D4 of these data by a ratio R. For example, density D14 is density D4 plus ratio R, and can be expressed by the formula D14 = D4 + D4 × R. Note that if density D10 is smaller than the target density TD, ratio R is subtracted rather than added, so density D14 becomes D14 = D4 - D4 × R.

[0049] 6(B), the corrected relationship RA between the control variable CV and the concentration D can be expressed by an approximation line L2 that passes as close as possible to the four data points indicated by x marks. The calculation unit 101 calculates an arithmetic formula F2 (an arithmetic formula that indicates the relationship RA between the control variable CV and the concentration D) that indicates the approximation line L2 using the least squares method.

[0050] The calculation unit 101 corrects the set value CV_TD based on the corrected relationship RA (S6). After that, the processing ends. The calculation unit 101 calculates the set value CV_TD of the control variable CV corresponding to the target concentration TD using the calculated arithmetic expression F2, as shown in FIG. 6(B), and corrects the set value CV_TD.

[0051] According to the above embodiment, the relationship RA between the control variable CV and the density D of the image formed on the photosensitive drum 121 is corrected, and the set value CV_TD of the control variable CV corresponding to the target density TD is corrected based on the corrected relationship RA. This makes it possible to appropriately correct the set value CV_TD and use the corrected set value CV_TD as the control variable SV. This makes it possible to more accurately calculate the set value of the control variable SV related to the image forming operation and stabilize image quality.

[0052] In the above embodiment, the case where control unit 100 forms only one second patch image PT1 on photoconductor drum 121 has been described, but in another embodiment, control unit 100 may form multiple second patch images PT2 on photoconductor drum 121, and calculation unit 101 may calculate the average value of densities D10 of the multiple second patch images PT2 measured by density sensor 130, and correct the relationship RA based on the difference between the average value and target density TD. This allows the setting value CV_TD to be corrected more appropriately.

[0053] The present invention is not limited to the configuration of the above embodiment, and various modifications are possible. In addition, in the above embodiment, the configuration and processing shown in the above embodiment using Figures 1 to 6 are merely one embodiment of the present invention, and it is not intended that the present invention be limited to these configurations and processing. [Explanation of symbols]

[0054] 1. Image forming device 12 Image forming unit 100 control section 101 Calculation Unit 121 Photosensitive drum 122 Charging device 123 Exposure equipment 124 Developing device 130 Concentration sensor

Claims

1. an image forming unit having an image carrier, forming an image on the surface of the image carrier, and transferring the image onto a recording medium to form the image on the recording medium; a control unit that changes a control amount related to an image forming operation in the image forming unit to control the operation of the image forming unit and causes a plurality of first patch images with different densities to be formed on the image carrier; a density measuring unit for measuring the density of an image formed on the image carrier; a calculation unit that calculates a set value of the control amount corresponding to a predetermined target density based on the control amount when each of the first patch images is formed and the density of each of the first patch images measured by the density measurement unit, the control unit controls an operation of the image forming unit using the setting value calculated by the calculation unit to form a second patch image on the image carrier; the calculation unit corrects the set value based on a difference between the density of the second patch image measured by the density measurement unit and the target density; The control unit uses the setting value corrected by the calculation unit as a control amount during a normal image forming operation by the image forming unit.

2. 2. The image forming apparatus according to claim 1, wherein the control unit forms the second patch image on the image carrier at a timing other than when the normal image forming operation is being performed, or forms the second patch image in an area of ​​the image carrier where an image to be transferred to the recording medium is not formed when the normal image forming operation is being performed.

3. the control unit causes the image carrier to form a plurality of the second patch images; 3. The image forming apparatus according to claim 1, wherein the calculation unit calculates an average value of the densities of the plurality of second patch images measured by the density measurement unit, and corrects the setting value based on a difference between the average value and the target density.

4. the image forming unit includes a charging device that charges the surface of the image carrier, an exposure device that exposes the charged surface of the image carrier to light to form an electrostatic latent image on the surface of the image carrier, and a developing device that develops the electrostatic latent image formed on the surface of the image carrier; 2. The image forming apparatus according to claim 1, wherein the control amount is at least one of a charging bias applied to the image carrier by the charging device, an exposure amount irradiated to the image carrier by the exposure device, and a development bias applied to the development device.

Images