Image forming apparatus

Abstract

Regardless of the type of paper used to adjust the density of the image formed by ink ejection from the ink head, the density adjustment of the output image can be performed as desired by reading the output image. [Solution] The image forming apparatus 1 includes a control unit 100 that ejects ink from multiple ink heads to create a test chart, a density calculation unit 101 that analyzes the image of the read test chart and calculates the density of the image formed by each of the multiple ink heads for each image, a determination unit 103 that determines whether the density of each image falls within a threshold range from the average density of images formed by ink heads of the same color, and an adjustment value calculation unit 104 that calculates an adjustment value to adjust the reference voltage to the drive unit that drives the ink head so that the density of the formed image of the ink head that has formed an image whose density does not fall within the above range approaches the average density.

Description

Technical Field

[0001] The present invention relates to an inkjet type image forming apparatus.

Background Art

[0002] Inkjet type image forming apparatuses are known that include a plurality of ink heads for each color that eject ink to form an image on a recording paper.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the image forming apparatus as described above, even when the ink heads are driven with the same driving voltage, there may be variations in the ink ejection amount between the ink heads due to individual differences. If there are variations in the ink ejection amount, density unevenness may occur in the image formed on the recording paper.

[0005] Patent Document 1 described above describes correction of density unevenness due to variations in the ink ejection amount between nozzles provided in an ink head, but a method of outputting a sample for a predetermined density target value, reading it, and adjusting it is described. However, in this case, since the density of the image formed on the paper may vary depending on the type of paper used for image formation, density adjustment by reading the output image cannot be performed as desired, or it is necessary to use a specific paper for the density adjustment.

[0006] This invention has been made in view of the above circumstances, and aims to enable density adjustment of an image formed by ink ejection from an ink head to be performed as desired, regardless of the type of paper used for density adjustment. [Means for solving the problem]

[0007] An image forming apparatus according to one aspect of the present invention includes a head unit equipped with multiple ink heads for each color of color image formation, which eject ink to form an image on recording paper; multiple drive units that drive each of the multiple ink heads that eject ink of the same color and eject ink from the ink heads; an output tray from which the recording paper on which the image has been formed by the ink heads is discharged; a control unit that controls the drive of the drive units based on a predetermined reference voltage to eject ink from the multiple ink heads and form a test chart consisting of a predetermined image pattern on the recording paper, and discharges the recording paper after the image has been formed into the output tray; and a document reading unit that reads an image of a document. The system includes: a density calculation unit that analyzes the image of the test chart obtained by reading the recording paper after the image has been formed by the document reading unit and calculates the density of each image formed by each of the plurality of ink heads for each image; a determination unit that determines whether the density of each of the plurality of ink heads falls within a predetermined threshold range based on the average density of the images formed by the plurality of ink heads of the same color; and an adjustment value calculation unit that calculates an adjustment value for adjusting the reference voltage to the drive unit that drives the ink head so that the density of the formed image of the ink head that the determination unit has determined to have formed an image whose density does not fall within the range approaches the average density. [Effects of the Invention]

[0008] In this invention, regardless of the type of paper used to adjust the density of the image formed by ink ejection from the ink head, the density can be adjusted as desired by reading the output image. As a result, according to this invention, it is not necessary to use a specific type of paper for density adjustment. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view showing the external appearance of an image forming apparatus according to one embodiment of the present invention. [Figure 2] This is a functional block diagram schematically showing the main internal configuration of an image forming apparatus according to one embodiment of the present invention. [Figure 3] (A) is a schematic diagram of a head unit with an ink head viewed from below, and (B) is a schematic diagram of a head unit with an ink head viewed from the front. [Figure 4] This diagram schematically shows a part of the image forming section. [Figure 5] This figure shows an example of a test chart formed on recording paper. [Figure 6] This figure shows an example of a test chart formed on recording paper. [Figure 7] An example flowchart of density adjustment processing by an image forming apparatus. [Modes for carrying out the invention]

[0010] Hereinafter, an image forming apparatus according to one embodiment of the present invention will be described with reference to the drawings. Figure 1 is a perspective view showing the external appearance of the image forming apparatus according to one embodiment of the present invention. Figure 2 is a functional block diagram schematically showing the main internal configuration of the 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 is composed of a control unit 10, a document feeding unit 6, a document reading unit 5, an image forming unit 12, a paper feeding unit 14, an operation unit 47, a network interface unit 9, and a storage unit 8.

[0012] The document feeding unit 6 is configured to open and close on the upper surface of the document reading unit 5 by a hinge (not shown), and functions as a document holder cover when reading a document placed on a platen glass (not shown). The document feeding unit 6 is also called an ADF (Auto Document Feeder) and includes a document tray 61 on which documents are placed and a document output tray 62 located below the document tray 61. The document feeding unit 6 supplies documents placed on the document tray 61 to the document reading unit 5 one by one and outputs the documents to the document output tray 62.

[0013] The document reading unit 5 is equipped with a scanner and reads documents fed from the document feeding unit 6, or documents placed on the platen glass. The document reading unit 5 is also capable of sequentially reading multiple document images sent from the document feeding unit 6.

[0014] The process of reading a document in the image forming apparatus 1 will now be explained. The document reading unit 5 optically reads the image of the document supplied to the document reading unit 5 by the document feeding unit 6, or the 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] A case where an image forming operation is performed by the image forming apparatus 1 will be described. The image forming unit 12 includes an ink head 122 (see FIG. 3) that discharges ink onto a recording sheet to form an image on the recording sheet, a printing conveyance unit, and a drying conveyance unit. The image forming unit 12 forms an image on a recording sheet, which is a recording medium fed from a paper feeding unit 14, by an inkjet method using ink as a recording agent based on image data generated by a document reading operation, image data stored in an image memory or the like, image data received from a computer connected to a network, and the like.

[0016] The printing conveyance unit has an endless conveyance belt 125 (see FIG. 3), and conveys the recording sheet facing the ink head 122 using the conveyance belt 125. Similarly to the printing conveyance unit, the drying conveyance unit also has an endless conveyance belt, and conveys the recording sheet on which an image is formed using the conveyance belt to naturally dry the ink adhering to the recording sheet.

[0017] As shown in FIGS. 3(A) and (B), the image forming unit 12 includes a head unit 121 having a plurality (here, 12) of ink heads 122C, 122M, 122Y, 122K (hereinafter also collectively referred to as "ink head 122") for each of the colors cyan (C), magenta (M), yellow (Y), and black (K) which is a key plate. The ink head 122 is disposed to face the conveyance belt 125 that conveys the recording sheet. In addition, the plurality of ink heads 122C, 122M, 122Y, 122K for each color are arranged side by side in a direction (main scanning direction) orthogonal to the conveyance direction of the recording sheet, and are arranged with a shift in the conveyance direction every other one.

[0018] Further, as shown in FIG. 4, the image forming unit 12 includes a plurality of drive units 123C, 123M, 123Y, 123K (hereinafter also collectively referred to as "drive unit 123") that drive each of the plurality of ink heads 122 that discharge the same color ink and cause the ink to be discharged from the ink head 122.

[0019] The paper feeding unit 14 includes a paper feeding cassette 141, and further includes a pickup roller, a conveyance roller, a conveyance path, and a rotation drive mechanism for each roller that pick up recording paper from the paper feeding cassette and feed it to the image forming unit 12.

[0020] The operation unit 47 includes various hard keys 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, according to the operation of the hard keys.

[0021] The operation unit 47 includes a display unit 473 that displays operation guidance and the like to the operator. Further, the operation unit 47 receives an input of an instruction from the user based on an operation (touch operation) by the user on the screen displayed on the display unit 473 via the touch panel that the display unit 473 has.

[0022] The display unit 473 is composed of an LCD (Liquid Crystal Display) or the like. When the operator performs an operation of touching a button or a key displayed on the screen, an instruction associated with the touched position is received by the touch panel. In this case, the touch panel functions as an operation unit.

[0023] The network interface unit 9 is a communication interface that performs transmission and reception of various data with an external device (for example, a personal computer) within a local area or on the Internet.

[0024] The storage unit 8 is a large-capacity storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive), and stores various control programs and the like.

[0025] The control unit 10 comprises a processor, RAM (Random Access Memory), ROM (Read Only Memory), and dedicated hardware circuitry. 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, a concentration calculation unit 101, a determination unit 103, and an adjustment value calculation unit 104.

[0026] The control unit 10 functions as a control unit 100, a concentration calculation unit 101, a determination unit 103, and an adjustment value calculation unit 104, through operation by the processor in accordance with the control program stored in the memory unit 8. However, the control unit 100 and the others can also be configured by hardware circuits, rather than operating according to the control program of the control unit 10. The same applies to each embodiment below unless otherwise specified.

[0027] The control unit 100 is responsible for the overall operation control of the image forming apparatus 1. The control unit 100 is connected to the document feeding unit 6, document reading unit 5, image forming unit 12, paper feeding unit 14, operation unit 47, network interface unit 9, and storage unit 8, and performs drive control and other operations on each of these units, and executes various processes necessary for image forming by the image forming apparatus 1.

[0028] For example, the control unit 100 controls the drive of the drive unit 123 and increases or decreases the drive voltage supplied to the drive unit 123 based on a predetermined reference voltage RV, according to the density indicated by the print data. In other words, the control unit 100 adjusts the amount (density) of ink ejected from the ink head 122 by changing the drive voltage supplied to the drive unit 123.

[0029] Furthermore, the control unit 100 controls the drive of the drive unit 123 using a reference voltage RV to eject ink from multiple ink heads 122 to form a predetermined image pattern on the recording paper P1 as a test chart TC, and then discharges the recording paper P1 into the output tray 151.

[0030] Figure 5 shows an example of a test chart TC formed on recording paper P1. The test chart TC formed on recording paper P1 includes density calculation areas A1 and A2 for calculating the density of the image formed by the ink head 122, and position detection areas A3 to A5 for detecting the position of the ink head 122 that formed the image.

[0031] Furthermore, as shown in Figure 6, each image enclosed by the dashed line L1 within the density calculation region A1 is an image formed by each of the 12 cyan ink heads 122C. In Figure 6, the images formed by each of the 12 cyan ink heads 122C are arranged in order from top to bottom within the density calculation region A1.

[0032] Each image enclosed by the dashed line L1 within the density calculation area A2 is an image formed by each of the 12 magenta ink heads 122M. In Figure 6, the images formed by each of the 12 magenta ink heads 122M are arranged in order from top to bottom within the density calculation area A2.

[0033] The density calculation unit 101 analyzes the image of the test chart TC obtained by reading by the document reading unit 5 and calculates the density of each image portion formed by each of the multiple ink heads 122 for each respective image portion.

[0034] For example, the density calculation unit 101 detects the pixel value of each pixel constituting the image of the test chart TC obtained by reading by the document reading unit 5, and based on this, calculates the sum of the pixel values ​​of all pixels in each image portion formed by each of the multiple ink heads 122 (12 ink heads 122 of the same color) as the density DS of that image portion. Furthermore, based on the density of each image portion, the density calculation unit 101 calculates the average value of the above sums of all image portions formed by each of the multiple ink heads 122 as the average density AV. In this case, the density calculation unit 101 has in advance stored the positions of the regions that make up each image portion formed by each of the multiple ink heads 122 in the entire image of the test chart TC. Alternatively, the density calculation unit 101 may calculate the density by counting the density of the image.

[0035] The determination unit 103 determines whether the density DS of each image portion falls within the range WR, which is a predetermined threshold TH derived from the average density AV.

[0036] The adjustment value calculation unit 104 calculates an adjustment value for the reference voltage RV to the drive unit 123 that drives the ink head 122, for which the judgment unit 103 has determined that the density of the image portion formed is not within the range WR, so that the density DS of the formed image portion approaches the average density AV. For example, the adjustment value calculation unit 104 calculates the adjustment value by multiplying the difference between the density DS of the image portion and the average density AV by a predetermined adjustment coefficient that changes the reference voltage RV.

[0037] Furthermore, the control unit 100 controls the drive of the drive unit 123 for each of the multiple ink heads 122 using a reference voltage RV, or using the adjustment value if the reference voltage RV is adjusted to the adjustment value, causing ink to be ejected from the multiple ink heads 122 to form the image pattern on the recording paper as a second test chart, and then ejects the recording paper on which the second test chart has been formed into the output tray 151.

[0038] The density calculation unit 101 analyzes the image of the second test chart obtained by reading by the document reading unit 5, similar to when the test chart TC is read, and calculates the density DS and the average density AV for each image portion formed by each of the multiple ink heads 122.

[0039] The determination unit 103 determines whether the density DS of each image portion falls within the threshold range WR, which is the average density AV of the image formed by the same color ink head 122.

[0040] The adjustment value calculation unit 104 calculates an adjustment value for the ink head 122 that has formed an image portion where the judgment unit 103 has determined that the density is not within the range WR. The adjustment value is used to readjust the reference voltage RV for the drive unit 123 that drives the ink head 122 so that the density DS of the formed image portion approaches the average density AV.

[0041] Furthermore, the control unit 100 sets the adjustment value as the reference voltage RV of the ink head 122 for the ink head 122 whose reference voltage RV has been adjusted to the adjustment value.

[0042] Then, if the number of adjustments made to the reference voltage RV by the adjustment value reaches a predetermined upper limit (for example, 5 times), and the determination unit 103 determines that there is an image portion in which the density is not within the above range, the control unit 100 performs an error determination for the ink head 122 corresponding to that image portion.

[0043] Furthermore, if the number of adjustments made to the reference voltage RV by the adjustment value is less than a predetermined upper limit, and if the judgment unit 103 determines that only image portions exist in which the density falls within the above range, the control unit 100 uses the reference voltage RV (or the adjustment value if it is set as the above adjustment value) set at this point to drive and control the drive unit 123 of each ink head 122, causing the head unit 121 to perform subsequent image formation.

[0044] Next, an example of the density adjustment process by the image forming apparatus 1 will be explained using the flowchart shown in Figure 7.

[0045] The control unit 100 sets a counter C for counting the number of adjustments to the reference voltage RV to 0 as an initial setting (S1). Then, the control unit 100 controls the drive of the drive unit 123 using a predetermined reference voltage RV (set value at this point) for each of the 12 ink heads 122 of two predetermined different colors (for example, cyan and magenta), causing ink to be ejected from each of the 12 ink heads 122 of the two predetermined colors, forming a predetermined image pattern on the recording paper as a test chart TC, and then ejecting the recording paper into the output tray 151 (S2).

[0046] The user picks up the recording paper on which the test chart TC has been imaged, which has been discharged into the output tray 151, and places the recording paper on the platen glass. When the user operates the operation unit 47 and a scan execution command is input to the operation unit 47, the control unit 100 causes the document reading unit 5 to read the image of the test chart TC on the recording paper placed on the platen glass (S3). If the image forming apparatus 1 has not yet left the factory, the user referred to here is the inspection personnel of the manufacturing company; if it has left the factory, the user is the end user.

[0047] After reading as described above, the density calculation unit 101 analyzes the image data of the test chart TC obtained by reading by the document reading unit 5 and calculates the density DS of the image portion formed by the 12 cyan and magenta ink heads 122C and 122M for each image (S4).

[0048] Next, the density calculation unit 101 calculates the average density AV_C for all image portions formed by the 12 cyan ink heads 122C from the density DS of each image portion formed by the 12 cyan ink heads 122C calculated by the density calculation unit 101, and further calculates the average density AV_M for all image portions formed by the 12 magenta ink heads 122M from the density DS of each image portion formed by the 12 magenta ink heads 122M calculated by the density calculation unit 101 (S5).

[0049] After S5, the determination unit 103 determines whether the counter C has reached a predetermined upper limit (S6). If it determines that the counter C has not reached the upper limit (NO in S6), it determines whether the density DS of each image portion formed by each of the 12 cyan (first color) ink heads 122C falls within the range WR_C of a predetermined threshold TH derived from the average cyan density AV_C (S7).

[0050] If the determination unit 103 determines that there is an image portion where the density does not fall within the range WR_C (NO in S7), the adjustment value calculation unit 104 calculates an adjustment value for the ink head 122C that formed the image portion where the determination unit 103 determined that the density does not fall within the range WR_C, so that the density of the formed image approaches the average density AV_C (S8). For example, if the density DS is not within the range WR_C and is darker than the average density AV_C, the adjustment value calculates a drive voltage value that reduces the amount of ink ejected from the corresponding ink head 122C by a predetermined amount. Also, if the density DS is not within the range WR_C and is lighter than the average density AV_C, the adjustment value calculates a drive voltage value that increases the amount of ink ejected from the corresponding ink head 122C by a predetermined amount.

[0051] On the other hand, for image portions where the density falls within the range WR_C, the determination unit 103 determines the reference voltage RV of the ink head 122C that formed the image portion at this point in time as the fixed value of the reference voltage RV (S9). In other words, the determination unit 103 does not calculate the above adjustment value for the reference voltage RV of the ink head 122C that formed the image portion at this point in time.

[0052] Next, the determination unit 103 determines, similar to the cyan color, whether the density DS of each image portion formed by each of the 12 magenta (second color) ink heads 122M falls within the range WR_M of a predetermined threshold TH derived from the average density AV_M of the magenta color (S10).

[0053] If the determination unit 103 determines that there is an image portion where the density does not fall within the range WR_M (NO in S10), the adjustment value calculation unit 104 calculates an adjustment value for the ink head 122M that formed the image portion where the determination unit 103 determined that the density does not fall within the range WR_M, so that the density of the formed image approaches the average density AV_M (S11). The method for calculating the adjustment value is the same as in the case of cyan.

[0054] On the other hand, for image portions where the density falls within the range WR_M, the determination unit 103 determines the reference voltage RV of the ink head 122M that formed the image portion at this point in time as a fixed value (S12). In other words, the determination unit 103 does not calculate the above adjustment value for the reference voltage RV of the ink head 122M that formed the image portion at this point in time.

[0055] Next, the control unit 100 determines, based on the determination results from the judgment unit 103 in S7 and S10, whether the density of the image formed by all ink heads 122 for both colors falls within the range WR, that is, whether there are any ink heads 122 for which an adjustment value has been calculated (S13). If it determines that the density of the image formed by all ink heads 122 for both colors falls within the range WR (i.e., there are no ink heads 122 for which an adjustment value has been calculated) (YES in S13), the control unit 100 sets the reference voltage RV (or the adjustment value if it is set as the above adjustment value) of each ink head 122 of the two colors set at this point as the reference voltage RV to be used during subsequent image formation (S25).

[0056] On the other hand, if the control unit 100 determines that the density of the image formed by all ink heads 122 for both colors is not within the range WR, that is, if there is at least one ink head 122 for which an adjustment value has been calculated (NO in S13), it sets the reference voltage RV of the ink head 122 for which an adjustment value has been calculated to the adjustment value (S14) and adds 1 to the counter C (S15). The process returns to S2.

[0057] Next, the control unit 100 controls the drive of the drive unit 123 using the respective reference voltage RV (or the adjusted value if adjusted) for the 12 cyan ink heads 122C and the 12 magenta ink heads 122M, causing ink to be ejected from the 12 cyan ink heads 122C and the 12 magenta ink heads 122M to form an image of the second test chart TC2, which consists of a predetermined image pattern, on the recording paper, and then ejects the recording paper into the output tray 151 (S2). Subsequently, processes S3 to S5 are performed in the same manner as described above.

[0058] In S6, if the determination unit 103 determines that the counter C has reached its upper limit (YES in S6), it determines whether the image forming apparatus 1 is set to a predetermined factory default state (S16). For example, the determination unit 103 determines whether the end user has completed the initial setup of the image forming apparatus 1 (such as setting the date and time) based on the setting values ​​of the setting items related to the operation of the image forming apparatus 1 stored in the built-in memory of the control unit 10, and determines that it is in the factory default state if the setting values ​​for which the initial setup has been completed are stored. If the built-in memory does not contain the setting values ​​for which the initial setup has been completed, the determination unit 103 determines that it is in the pre-factory default state.

[0059] If the determination unit 103 determines that the image forming apparatus 1 is in the state after leaving the factory (YES in S16), it changes the threshold TH to a predetermined relaxation threshold (S17). On the other hand, if the determination unit 103 determines that the image forming apparatus 1 is not in the state after leaving the factory (pre-factory state) (NO in S16), it does not change the threshold TH to a relaxation threshold. The relaxation threshold is, for example, a value obtained by increasing the threshold TH by 10%.

[0060] The determination unit 103 determines whether the density DS of each image portion falls within the threshold range WR, which is the average density AV of the image formed by the same color ink head 122.

[0061] Next, the determination unit 103 determines whether the density of each image portion formed by each of the 12 cyan (first color) ink heads 122C falls within the threshold range TH WR_C at this point, based on the average density AV_C (S18).

[0062] If the determination unit 103 determines that the densities of all 12 cyan ink heads 122C are within the range WR_C (YES in S18), it determines the current reference voltage RV as a fixed value (S19).

[0063] Next, the determination unit 103, similar to the cyan color, determines whether the density of each image portion formed by each of the 12 magenta (second color) ink heads 122M falls within the threshold range WR_M at this point, based on the average density AV_M (S20).

[0064] If the determination unit 103 determines that the density of all 12 magenta ink heads 122M is within the range WR_M (YES in S20), it determines the current reference voltage RV as a fixed value (S21).

[0065] Then, the control unit 100 sets the reference voltage RV of each of the two ink heads 122 set at this point as the reference voltage RV to be used during subsequent image formation (S26). After this, the process ends.

[0066] On the other hand, if the determination unit 103 determines that the density of at least one of the 12 cyan ink heads 122C is not within the range WR_C (NO in S18), or if it determines that the density of at least one of the 12 magenta ink heads 122M is not within the range WR_M (NO in S20), the control unit 100 performs an error determination on the ink head 122 and displays this fact on the display unit 473 (S22). The control unit 100 may also display a message on the display unit 473 indicating which color the error occurred in the ink head 122, based on the results of S18 and S20. After this, the process ends.

[0067] Furthermore, the same process shown in the flowchart in Figure 7 is performed for each of the 12 ink heads 122 of two colors different from the two colors mentioned above (cyan and magenta): yellow and black.

[0068] In the above embodiment, an adjustment value is calculated to adjust the reference voltage RV for the drive unit 123 that drives the ink heads 122 so that the density of each image formed by each of the multiple ink heads 122 falls within a predetermined threshold TH range WR, which is derived from the average density AV. By using the reference voltage RV adjusted with this adjustment value, it becomes possible to suppress variations in the amount of ink ejected between the ink heads 122. Therefore, it becomes possible to suppress the occurrence of density unevenness due to variations in the amount of ink ejected between the ink heads 122.

[0069] Furthermore, by repeating the adjustment of the reference voltage RV as described above a certain number of times, the image density will approach a value that falls within the range WR. If the image density does not fall within the range WR even after repeating the adjustment of the reference voltage RV several times, there is a high possibility that there is a problem with the ink head 122.

[0070] In the above embodiment, if the number of adjustments (counter C) based on the adjustment value of the reference voltage RV has reached a predetermined upper limit, but there are images in which the determination unit 103 determines that the density is not within the range WR, the control unit 100 performs an error determination on the ink head 122. This informs the user that there is a problem with the ink head 122.

[0071] The density of the image formed on the recording paper by the image forming apparatus 1 varies depending on the properties (paper characteristics) of the recording paper used. Within the factory, it is possible to inspect the image forming apparatus 1 using a specific type of paper, but after the product leaves the factory, it is not possible to identify the type of paper used, and inspections are performed using various types of recording paper. Furthermore, while inspections are performed within the factory in a controlled inspection environment (e.g., temperature and humidity), it is not easy to maintain a controlled inspection environment after the product leaves the factory. In addition, after the product leaves the factory, it is possible to reduce downtime and maintain convenience by not performing inspections as strictly as before the product leaves the factory.

[0072] In the above embodiment, if the number of adjustments (counter C) based on the adjustment value of the reference voltage RV reaches a predetermined upper limit, and the image forming apparatus 1 is in its factory-shipped state, the determination unit 103 relaxes the threshold TH and makes the above determination. After factory shipment, rather than causing downtime through adjustment work based on frequent error determinations, the threshold TH is relaxed and the above determination is made to reduce error determinations, ensuring convenience for the user by allowing the image forming apparatus 1 to operate normally even if there is some degradation in image quality.

[0073] Thus, according to the above embodiment, regardless of the type of paper used for adjusting the density of the image formed by the ink ejection from the ink head 122, the density can be adjusted as desired by reading the output image. As a result, according to this embodiment, there is no need to use a specific type of paper for density adjustment.

[0074] Furthermore, as described above, the density of the image formed on the recording paper by the image forming apparatus 1 varies depending on the properties (paper characteristics) of the recording paper used. Therefore, it is preferable that the adjustment coefficient used to calculate the above adjustment value is determined according to the paper characteristics of the recording paper that forms the image pattern. For this reason, the adjustment coefficient used to calculate the above adjustment value is one that has been predetermined according to the paper characteristics of the recording paper that forms the image pattern.

[0075] Furthermore, in the above embodiment, the control unit 100 is described as creating a test chart using two ink heads 122. However, in another embodiment, a test chart may be created using only one ink head 122 and the process shown in the flowchart in Figure 7 may be performed in the same manner, or a test chart may be created using three or more ink heads 122 and the process shown in the flowchart in Figure 7 may be performed in the same manner. In these cases, the processes S7 to S14 and S18 to S21 are performed in accordance with the number of colors used to create the test chart.

[0076] The present invention is not limited to the configuration of the above embodiments and various modifications are possible. Furthermore, the configuration and processing shown in the above embodiments using Figures 1 to 7 are merely one embodiment of the present invention and are not intended to limit the present invention to such configuration and processing. [Explanation of symbols]

[0077] 1. Image forming apparatus 5. Manuscript reading unit 100 Control Unit 101 Concentration calculation section 103 Judgment Department 104 Adjustment Value Calculation Unit 122 Inkhead 123 Drive unit 151 Discharge Tray

Claims

1. An image forming apparatus, A head unit is provided with multiple ink heads for each color used to form a color image, which eject ink to form an image on recording paper. Multiple drive units that drive each of the multiple ink heads that eject ink of the same color, and that eject ink from the ink heads, An output tray from which the recording paper on which the image has been formed by the ink head is ejected, A control unit controls the drive of the drive unit based on a predetermined reference voltage to eject ink from the plurality of ink heads to form a test chart consisting of a predetermined image pattern on the recording paper, and discharges the recording paper after the image has been formed into the output tray. A document reading unit that reads images from the document, A density calculation unit analyzes the image of the test chart obtained by reading the recording paper after the image has been formed by the document reading unit, and calculates the density of each image formed by each of the multiple ink heads for each image. A determination unit that determines whether the density of the image formed by each of the multiple ink heads falls within a predetermined threshold range based on the average density of the images formed by the multiple ink heads of the same color, An image forming apparatus comprising: an adjustment value calculation unit that calculates an adjustment value for adjusting the reference voltage to the drive unit that drives the ink head, so that the density of the formed image approaches the average density value, for the ink head that has formed an image determined by the determination unit to be outside the range.

2. The control unit controls the drive of the drive unit based on the reference voltage set to the adjustment value, to eject ink from the plurality of ink heads, to form an image of the second test chart consisting of the image pattern on the recording paper, and to discharge the recording paper after the image has been formed into the output tray. The density calculation unit analyzes the image data of the second test chart obtained by reading by the document reading unit and calculates the density of the image formed by each of the multiple ink heads for each image. The determination unit determines whether the density of the image formed by each of the multiple ink heads falls within the threshold range based on the average density of the images formed by the multiple ink heads of the same color. The adjustment value calculation unit calculates an adjustment value for the ink head that has formed an image in which the determination unit has determined that the density is not within the range, so that the density of the formed image approaches the average density value, thereby readjusting the reference voltage to the drive unit that drives the ink head. The image forming apparatus according to claim 1, wherein the control unit performs an error determination on the ink head when the number of adjustments of the reference voltage by the adjustment value reaches a predetermined upper limit and the determination unit determines that there is an image in which the density is not within the range.

3. The image forming apparatus according to claim 1 or 2, wherein, if the number of adjustments of the reference voltage by the adjustment value is less than a predetermined upper limit and only images in which the determination unit has determined that the density is within the range exist, the control unit drives the drive unit using the reference voltage consisting of the adjustment value set at this point, causing the head unit to perform subsequent image forming.

4. If the number of adjustments made to the reference voltage using the adjustment value reaches a predetermined upper limit, and the image forming apparatus is set to the factory default state, The image forming apparatus according to claim 2 or 3, wherein the determination unit performs the determination using a predetermined relaxation threshold that is relaxed from the threshold.

5. Equipped with the aforementioned ink heads of multiple colors, The image forming apparatus according to claim 1, wherein the control unit controls the drive to cause the head unit to form an image of the test chart using only one ink head or using two or more ink heads.

6. The image forming apparatus according to claim 1, wherein the adjustment value calculation unit calculates the adjustment value by multiplying the difference between the density of the image formed by each of the plurality of ink heads and the average density by a predetermined adjustment coefficient for adjusting the reference voltage.

7. The image forming apparatus according to claim 6, wherein the adjustment coefficient is determined according to the paper characteristics of the recording paper used to form the image pattern.

Images