Image formation device

Abstract

To provide an image formation device capable of making proper density correction with a cost-reduced constitution.SOLUTION: A control part of an image formation device can execute a density correction mode for correcting toner density on the basis of, detection results of toner density of a plurality of reference images formed while having density gradations changed sequentially in a plurality of stages, detects variation in a voltage applied to a density detection part 14 or each of density gradations on the basis of detected values of toner density detected in the density detection mode, and corrects toner density of a specific density gradation using detected values of density gradations higher and lower than the specific density gradation if the specific density gradation at which the variation in a voltage is detected is present among the density gradations.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] In electrophotographic image forming devices such as copiers and printers, a device is widely used that supplies toner to an electrostatic latent image formed on the outer peripheral surface of a photosensitive drum, which is an image carrier, and develops it to form a toner image that is later transferred to paper. The density of the toner image formed by the image forming device changes over time for various reasons. For this reason, it is common to form a toner image (reference image) for density correction on the outer peripheral surface of the photosensitive drum or intermediate transfer belt, and perform calibration to detect the toner density of the toner image with a sensor and perform density correction.

[0003] The conventional image forming apparatus disclosed in Patent Document 1 detects the density of a toner patch (density adjustment pattern) formed on an image carrier, which serves as a density reference, by an optical density sensor, and adjusts image forming conditions based on the detection result (detected density). The density sensor has a light receiving element for detecting regular reflected light and a light receiving element for detecting diffuse reflected light. The density sensor makes it possible to detect low to high densities of black and color. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-155856 A Summary of the Invention [Problem to be solved by the invention]

[0005] When a density sensor has a light receiving element for detecting specular reflection light and a light receiving element for detecting diffuse reflection light, the toner concentration is determined by the ratio of the detection values ​​related to the toner concentration output by the two light receiving elements. In the case of two light receiving elements, even if the power supply voltage applied to the density sensor fluctuates, the ratio of the detection values ​​does not change, so the fluctuation is not affected by the detection value of the toner concentration. However, there is a concern that such a density sensor will increase costs by having two light receiving elements.

[0006] In order to reduce costs, it is preferable that the concentration sensor output a detection value related to the toner concentration using a single light receiving element. However, in the case of a single light receiving element, if a fluctuation occurs in the power supply voltage applied to the concentration sensor, the effect of the fluctuation is reflected in the detection value, and there is a problem in that it is not possible to obtain an appropriate toner concentration.

[0007] The present invention has been made in consideration of the above-mentioned points, and has an object to provide an image forming apparatus capable of realizing appropriate density correction with a configuration that achieves low cost. [Means for solving the problem]

[0008] In order to solve the above problems, the image forming apparatus of the present invention includes an image carrier, a charging unit, an exposure unit, a developing unit, a density detection unit, and a control unit. The image carrier has a photosensitive layer formed on its outer peripheral surface. The charging unit charges the outer peripheral surface of the image carrier to a predetermined surface potential. The exposure unit exposes the outer peripheral surface of the image carrier charged by the charging unit to form an electrostatic latent image in which the charge is attenuated. The developing unit supplies toner to the electrostatic latent image of the image carrier to form a toner image. The density detection unit outputs a detection value related to the toner density of the toner image of the image carrier. The control unit controls the image carrier, the charging unit, the exposure unit, and the developing unit. The density detection unit includes a light emitting unit that irradiates light toward the toner image by application of a predetermined voltage, and a single light receiving unit that receives reflected light reflected by the toner image. The control unit is capable of executing a concentration correction mode in which a reference image, which is the toner image for concentration correction, is formed by sequentially changing the concentration gradation in multiple stages, the toner concentration of each of the formed multiple reference images is detected by the concentration detection unit, and the toner concentration is corrected based on the detection result, and based on the detection value of the toner concentration detected in the concentration correction mode, the presence or absence of voltage fluctuation at each of the concentration gradations is detected, and when a specific concentration gradation exists in which the voltage fluctuation has been detected, the toner concentration of the specific concentration gradation is corrected using the detection values ​​of the density gradations before and after the specific concentration gradation. Effect of the Invention

[0009] According to the configuration of the present invention, the density detection unit having a single light receiving unit detects the fluctuation of the voltage applied to the density detection unit, and the toner density of the specific density gradation where the fluctuation of the voltage is detected can be corrected. Therefore, it is possible to realize appropriate density correction with a configuration that achieves low cost. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic sectional front view of an image forming apparatus according to an embodiment of the present invention; [Diagram 2]FIG. 2 is a block diagram showing a configuration of the image forming apparatus in FIG. [Diagram 3] 2 is a schematic cross-sectional front view of the periphery of an image forming unit of the image forming apparatus of FIG. 1. [Figure 4] 4 is a partial side view of the concentration detection unit in FIG. 3. [Diagram 5] 2 is an explanatory diagram showing a reference image group for density correction and detection values ​​of a density detection unit of the image forming apparatus of FIG. 1. [Figure 6] 4 is a graph showing the relationship between the detection value of a concentration detection unit of the image forming apparatus of FIG. 1 and the toner concentration. [Figure 7] 6 is an explanatory diagram showing a reference image group for density correction in FIG. 5 and detection values ​​of a density detection unit, showing a state in which a fluctuation occurs in the applied voltage to the density detection unit. FIG. [Figure 8] 1. FIG. 4 is a graph showing the relationship between the detection value of the density detection unit and the toner density of the image forming apparatus of FIG. 1, showing a state in which a fluctuation occurs in the applied voltage to the density detection unit. [Figure 9] 4 is a graph showing the relationship between the detection value of a concentration detection unit of the image forming apparatus of FIG. 1 and the toner concentration, showing a state in which a discrepancy occurs between the two detection values. FIG. [Figure 10] 4 is a flowchart showing a process in a density correction mode in the image forming apparatus of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following.

[0012] Fig. 1 is a schematic sectional front view of an image forming apparatus 1 of an embodiment. Fig. 2 is a block diagram showing the configuration of the image forming apparatus 1 of Fig. 1. Fig. 3 is a schematic sectional front view of the periphery of an image forming unit 20 of the image forming apparatus 1 of Fig. 1. One example of the image forming apparatus 1 of this embodiment is a tandem type color printer that transfers a toner image to paper S using an intermediate transfer belt 31. The image forming apparatus 1 may be a so-called multifunction machine equipped with functions such as printing, scanning (image reading), and facsimile transmission.

[0013] As shown in Figures 1, 2 and 3, the image forming apparatus 1 includes a paper supply unit 3, a paper transport unit 4, an exposure unit 5, an image forming unit 20, a transfer unit 30, a fixing unit 6, a paper discharge unit 7, a control unit 8 and a memory unit 9, which are provided in a main body 2.

[0014] The paper supply unit 3 is disposed at the bottom of the main body 2. The paper supply unit 3 stores multiple sheets of paper S before printing, and separates and sends out the sheets S one by one when printing. The paper transport unit 4 extends in the vertical direction along the side wall of the main body 2. The paper transport unit 4 transports the paper S sent out from the paper supply unit 3 to the secondary transfer unit 33 and the fixing unit 6, and further ejects the paper S after fixing from the paper ejection port 4a to the paper ejection unit 7. The exposure unit 5 is disposed above the paper supply unit 3. The exposure unit 5 irradiates the image forming unit 20 with laser light controlled based on image data.

[0015] The image forming unit 20 is disposed above the exposure unit 5 and below the intermediate transfer belt 31. The image forming unit 20 includes an image forming unit 20Y for yellow, an image forming unit 20C for cyan, an image forming unit 20M for magenta, and an image forming unit 20B for black. These four image forming units 20 have the same basic configuration. Therefore, in the following description, the identification symbols "Y", "C", "M", and "B" representing each color may be omitted unless there is a particular need to limit it.

[0016] The image forming unit 20 includes a photoconductor drum (image carrier) 21 that is supported so as to be rotatable in a predetermined direction (clockwise in Figs. 1 and 3). The image forming unit 20 further includes a charging unit 22, a developing unit 23, and a drum cleaning unit 24 that are arranged around the photoconductor drum 21 along the direction of rotation of the photoconductor drum 21. A primary transfer unit 32 is arranged between the developing unit 23 and the drum cleaning unit 24.

[0017] The photosensitive drum 21 has a photosensitive layer formed on its outer circumferential surface. The charging section 22 charges the outer circumferential surface of the photosensitive drum 21 to a predetermined surface potential. The exposure section 5 exposes the outer circumferential surface of the photosensitive drum 21 charged by the charging section 22, and forms an electrostatic latent image of the original image with the charge attenuated on the outer circumferential surface of the photosensitive drum 21. The developing section 23 supplies toner to the electrostatic latent image on the outer circumferential surface of the photosensitive drum 21 to develop it and form a toner image. Each of the four image forming sections 20 forms a toner image of a different color. The drum cleaning section 24 removes toner and the like remaining on the outer circumferential surface of the photosensitive drum 21 after the toner image is primarily transferred to the outer circumferential surface of the intermediate transfer belt 31, and cleans it. In this way, the image forming section 20 forms an image (toner image) to be transferred to the paper S later.

[0018] The transfer unit 30 includes an intermediate transfer belt 31, primary transfer units 32Y, 32C, 32M, and 32B, a secondary transfer unit 33, and a belt cleaning unit 34. The intermediate transfer belt 31 is disposed above the four image forming units 20. The intermediate transfer belt 31 is supported so as to be rotatable in a predetermined direction (counterclockwise in FIGS. 1 and 3), and is an endless intermediate transfer body onto which the toner images formed in each of the four image forming units 20 are sequentially superimposed and primarily transferred. The four image forming units 20 are disposed in a so-called tandem manner, lined up in a row from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 31.

[0019] The primary transfer units 32Y, 32C, 32M, and 32B are disposed above the image forming units 20Y, 20C, 20M, and 20B of the respective colors, with the intermediate transfer belt 31 sandwiched therebetween. The secondary transfer unit 33 is disposed upstream of the fixing unit 6 in the paper conveying direction of the paper conveying unit 4, and downstream of the four image forming units 20Y, 20C, 20M, and 20B in the rotation direction of the intermediate transfer belt 31. The belt cleaning unit 34 is disposed downstream of the secondary transfer unit 33 in the rotation direction of the intermediate transfer belt 31.

[0020] The primary transfer unit 32 transfers the toner image formed on the outer circumferential surface of the photoconductor drum 21 onto the intermediate transfer belt 31. In other words, the toner image is primarily transferred onto the outer circumferential surface of the intermediate transfer belt 31 at the primary transfer units 32Y, 32C, 32M, and 32B of each color. Then, as the intermediate transfer belt 31 rotates, the toner images of the four image forming units 20 are successively superimposed and transferred onto the intermediate transfer belt 31 at a predetermined timing, so that a color toner image in which the toner images of four colors, yellow, cyan, magenta, and black, are superimposed on each other is formed on the outer circumferential surface of the intermediate transfer belt 31.

[0021] The color toner image on the outer peripheral surface of the intermediate transfer belt 31 is transferred to the paper S, which is synchronously fed by the paper transport unit 4, at a secondary transfer nip portion formed in the secondary transfer unit 33. The belt cleaning unit 34 removes and cleans the toner and other deposits remaining on the outer peripheral surface of the intermediate transfer belt 31 after the secondary transfer. In this way, the transfer unit 30 transfers (records) the toner image formed on the outer peripheral surface of the photoconductor drum 21 onto the paper S.

[0022] The fixing unit 6 is disposed above the secondary transfer unit 33. The fixing unit 6 fixes the toner image to the paper S by applying heat and pressure to the paper S onto which the toner image has been transferred.

[0023] The paper discharge section 7 is disposed above the transfer section 30. The paper S on which the toner image has been fixed and printing has been completed is transported to the paper discharge section 7. The paper discharge section 7 takes out the printed paper (printed matter) from above.

[0024] The control unit 8 includes a CPU, an image processing unit, and other electronic circuits and electronic components (none of which are shown). The CPU controls the operation of each component provided in the image forming apparatus 1 based on control programs and data stored in the storage unit 9 to perform processing related to the functions of the image forming apparatus 1. The paper supply unit 3, the paper transport unit 4, the exposure unit 5, the image forming unit 20, the transfer unit 30, and the fixing unit 6 each receive instructions individually from the control unit 8 and print on the paper S in cooperation with each other.

[0025] The storage unit 9 is configured by combining a non-volatile storage device (not shown) such as a program ROM (Read Only Memory) or a data ROM, and a volatile storage device (not shown) such as a RAM (Random Access Memory).

[0026] Next, the configuration of the image forming unit 20 and its surroundings will be described with reference to Fig. 3. Since the image forming units 20 of each color have the same basic configuration, the description and explanation of the identification symbols representing each color of the components will be omitted unless there is a particular need to limit the same.

[0027] The image forming unit 20 includes a photoconductor drum 21, a charging unit 22, a developing unit 23, and a drum cleaning unit 24.

[0028] The photoconductor drum 21 has a cylindrical shape that is rotatably supported with its central axis horizontal, and is rotated at a constant speed about the central axis by a drive unit (not shown). The photoconductor drum 21 has a photosensitive layer made of an inorganic photoconductor such as amorphous silicon on the outer circumferential surface of a drum tube made of a metal such as aluminum. An electrostatic latent image is formed on the outer circumferential surface of the photoconductor drum 21.

[0029] The charging unit 22 has, for example, a charging roller 221. The charging roller 221 extends parallel to the axial direction of the photoconductor drum 21 and is rotatably supported with its central axis horizontal. The charging roller 221 rotates in accordance with the rotation of the photoconductor drum 21 by contacting the outer circumferential surface of the photoconductor drum 21. The charging roller 221 has, for example, a conductive layer made of crosslinked rubber or the like containing an ion conductive material on the outer circumferential surface of a core metal. When a predetermined charging voltage is applied to the charging roller 221, the outer circumferential surface of the photoconductor drum 21 is uniformly charged.

[0030] The developing unit 23 is disposed downstream of the charging unit 22 in the rotation direction of the photoconductor drum 21. The developing unit 23 includes a developer container 231, a first transport member 232, a second transport member 233, a developing roller (developer carrier) 234, and a regulating member 235.

[0031] The developing container 231 has an elongated shape extending along the axial direction of the photoconductor drum 21 (the depth direction of the paper in FIG. 3) and is disposed with its longitudinal direction horizontal. The developing container 231 contains, as the developer containing toner to be supplied to the photoconductor drum 21, for example, a two-component developer containing toner and a magnetic carrier.

[0032] The first transport member 232 and the second transport member 233 are supported by the developing container 231 so as to be rotatable about an axis extending parallel to the photosensitive drum 21. The first transport member 232 and the second transport member 233 rotate about their axes, thereby transporting and stirring the developer in opposite directions along the axis of rotation.

[0033] The developing roller 234 is located above the second transport member 233 in the developing container 231 and disposed to face the photosensitive drum 21. The developing roller 234 is supported by the developing container 231 so as to be rotatable about an axis extending parallel to the axis of the photosensitive drum 21. A part of the outer circumferential surface of the developing roller 234 is exposed from the developing container 231 and faces the photosensitive drum 21 in close proximity. The developing roller 234 carries a developer including toner in the developing container 231 and supplies it to the photosensitive drum 21. In other words, the developing roller 234 causes the toner in the developing container 231 to adhere to the electrostatic latent image on the outer circumferential surface of the photosensitive drum 21 to form a toner image.

[0034] The regulating member 235 is disposed upstream in the rotation direction of the developing roller 234 in the opposing region between the developing roller 234 and the photoconductor drum 21. The regulating member 235 is disposed closely opposed to the developing roller 234 with a predetermined gap between its tip and the outer circumferential surface of the developing roller 234. The regulating member 235 extends over the entire area of ​​the developing roller 234 in the axial direction.

[0035] The developer in the developing container 231 is circulated, stirred, and charged by the rotation of the first transport member 232 and the second transport member 233, and is carried on the outer circumferential surface of the developing roller 234. The layer thickness of the developer carried on the outer circumferential surface of the developing roller 234 is regulated by a regulating member 235. When a predetermined developing voltage is applied to the developing roller 234, the toner in the developer carried on the outer circumferential surface of the developing roller 234 moves to the outer circumferential surface of the photoconductor drum 21 in the opposing region with the photoconductor drum 21 due to the potential difference with the surface potential of the outer circumferential surface of the photoconductor drum 21. As a result, the electrostatic latent image on the outer circumferential surface of the photoconductor drum 21 is developed by the toner.

[0036] The drum cleaning unit 24 is disposed downstream of the primary transfer unit 32 with respect to the rotation direction of the photoconductor drum 21. The drum cleaning unit 24 includes a collection container 241, a cleaning blade 242, and a collection spiral 243.

[0037] The collection container 241 has an elongated shape extending along the axial direction of the photoconductor drum 21 (the depth direction of the paper in FIG. 3) and is disposed with its longitudinal direction horizontal. The collection container 241 stores residual matter such as toner removed from the outer circumferential surface of the photoconductor drum 21 by the cleaning blade 242.

[0038] The cleaning blade 242 has a plate shape extending along the axial direction of the photoreceptor drum 21, and is formed of an elastic member such as polyurethane rubber. The cleaning blade 242 is disposed downstream of the contact point with the photoreceptor drum 21 in the drum rotation direction so as to form a predetermined angle with respect to the tangent direction of the photoreceptor drum 21 at the contact point. The cleaning blade 242 comes into contact with the outer circumferential surface of the photoreceptor drum 21 with a predetermined pressure. The cleaning blade 242 removes residues, including toner, remaining on the outer circumferential surface of the photoreceptor drum 21 after primary transfer.

[0039] The recovery spiral 243 is disposed in a lower portion of the recovery container 241, in an area separated from the photosensitive drum 21 across the cleaning blade 242. The recovery spiral 243 is supported by the recovery container 241 so as to be rotatable about an axis extending parallel to the rotation axis of the photosensitive drum 21. The recovery spiral 243 has, for example, a spiral transport blade extending in the axial direction. The recovery spiral 243 transports residual matter such as toner removed from the outer circumferential surface of the photosensitive drum 21 to a waste container for recovered matter (not shown) provided outside the drum cleaning unit 24.

[0040] The image forming apparatus 1 further includes a density detection unit 14. The density detection unit 14 is disposed upstream of the secondary transfer unit 33 with respect to the rotation direction of the intermediate transfer belt 31 and downstream of the black image forming unit 20B which is the most downstream of the four image forming units 20. The density detection unit 14 faces the outer circumferential surface of the intermediate transfer belt 31.

[0041] Fig. 4 is a partial side view of the density detection unit 14 in Fig. 3. Fig. 4 is a view of the density detection unit 14 shown in Fig. 3, seen from the side in Fig. 3 along the rotation direction of the intermediate transfer belt 31.

[0042] The concentration detection unit 14 includes a reflective optical sensor having a light-emitting unit 141 including a light-emitting element such as an LED (Light Emitting Diode) and a light-receiving unit 142 including a light-receiving element such as a photodiode. The light-emitting unit 141 irradiates detection light at a predetermined angle toward the toner image primarily transferred onto the outer circumferential surface of the intermediate transfer belt 31. The light-receiving unit 142 receives the detection light that is irradiated by the light-emitting unit 141 toward the toner image and reflected by the toner image.

[0043] In addition, there are two methods for detecting the toner concentration of a toner image: a method for receiving detection light of specular reflection and a method for receiving detection light of diffuse reflection. In this embodiment, the method for detecting specular reflection will be described.

[0044] The concentration detection unit 14 outputs the level of the detection light received by the light receiving unit 142 as a detection value (voltage value) related to the toner concentration, thereby deriving the toner amount of the toner image primarily transferred onto the outer peripheral surface of the intermediate transfer belt 31, and can detect the toner concentration of the toner image. When there is no toner on the outer peripheral surface of the intermediate transfer belt 31, the detection light irradiated from the light emitting unit 141 is specularly reflected without being diffusely reflected by the toner, and a large amount of the light is incident on the light receiving unit 142. This increases the detection value (voltage value) related to the toner concentration. Then, as the amount of toner on the outer peripheral surface of the intermediate transfer belt 31 increases, more light is diffusely reflected by the toner, and the amount of light incident on the light receiving unit 142 gradually decreases. That is, the detection value (voltage value) related to the toner concentration gradually decreases.

[0045] In this way, concentration detection unit 14 irradiates detection light from light-emitting unit 141 toward the toner image, and detects the toner concentration of the toner image transferred to the outer circumferential surface of intermediate transfer belt 31 based on the detection light reflected by the toner image and received by light-receiving unit 142. In other words, concentration detection unit 14 detects the toner concentration by outputting a detection value related to the toner concentration of the toner image formed on the outer circumferential surface of photoconductor drum 21 in image forming unit 20.

[0046] The control unit 8 of the image forming apparatus 1 of this embodiment executes a density correction mode, which is a calibration for correcting the density of a toner image, during non-image formation, periodically, for example, every predetermined number of printed sheets, or at any timing selected by a user or manager. In this density correction mode, a reference image (patch image), which is a toner image for density correction, is formed on the outer peripheral surface of the photoconductor drum 21 by sequentially changing the density gradation in multiple steps, and is transferred to the outer peripheral surface of the intermediate transfer belt 31, and the toner density of each of the multiple reference images is detected by the density detection unit 14. Based on the detection result, the control unit 8 compares the density (actual measurement value) of each of the multiple reference images for density correction with a predetermined target density (ideal value), and corrects the toner density by, for example, adjusting the developing bias or the like.

[0047] FIG. 5 is an explanatory diagram showing the reference image group P1 for density correction and the detection value of the density detection unit 14 of the image forming apparatus 1 of FIG. 1. Two reference image groups P1 for density correction are drawn in the upper part of FIG. 5. A graph represented by the detection value of the toner density for the reference image group P1 is drawn in the lower part of FIG. 5. The graph shown in FIG. 5 is a line graph of the ideal toner density for the reference image group P1. The left and right horizontal directions of the reference image group P1 in FIG. 5 are the circumferential direction of the photoconductor drum 21 (= the rotation direction of the intermediate transfer belt 31), and the detection time and timing of the toner density, which is the horizontal axis of the graph, coincide with each other. The vertical axis of the graph is the detection value (voltage value) of the toner density output by the density detection unit 14. The "belt surface detection value" is the detection value v10 output by the density detection unit 14 in a state where there is no toner on the outer peripheral surface of the intermediate transfer belt 31.

[0048] The reference image group P1 for density correction is a strip-like shape in which rectangular reference images extending in the axial and circumferential directions of the photoconductor drum 21 are successively formed in the circumferential direction of the photoconductor drum 21 by sequentially changing the density gradation in multiple steps. In this embodiment, the reference image group P1 has four reference images P1a, P1b, P1c, and P1d.

[0049] The four reference images P1a, P1b, P1c, and P1d have an increased amount of toner per unit area and a higher toner concentration as they proceed downstream in the circumferential direction of the photoconductor drum 21 (= the rotation direction of the intermediate transfer belt 31), i.e., toward the right in FIG. 5. That is, the toner concentration increases in the order of the reference images P1a, P1b, P1c, and P1d. Compared to the belt surface detection value v10 output by the concentration detection unit 14, the detection values ​​in the four reference images P1a, P1b, P1c, and P1d decrease in the order of the detection values ​​v1a, v1b, v1c, and v1d because the detection light is absorbed by the toner image.

[0050] Then, the control unit 8 detects the toner concentration of each of the multiple reference images P1a, P1b, P1c, and P1d for density correction formed as shown in FIG. 5 by the density detection unit 14. FIG. 6 is a graph showing the relationship between the detection value of the density detection unit 14 of the image forming apparatus 1 of FIG. 1 and the toner concentration. In FIG. 6, the horizontal axis shows the toner concentration of the image, and the vertical axis shows the detection value (voltage value) of the density detection unit 14 corresponding to the toner concentration. The line graph shown in FIG. 6 is the actual measurement value of the toner concentration by the density detection unit 14 for the reference image group P1 (FIG. 5 is an example of ideal values). The two-dot chain line shown in FIG. 6 is the ideal slope of the detection value of the toner concentration with respect to the density gradation. Ideal slope data 91 related to the ideal slope is stored in advance in the storage unit 9 (see FIG. 2).

[0051] Furthermore, the control unit 8 analyzes a plurality of toner concentration detection values ​​based on the detection result of the concentration detection unit 14, and corrects the toner concentration. At this time, the control unit 8 calculates the slope of the detection values ​​(actual measurement values) from toner concentration 1 to toner concentration 5 shown in FIG. 6, which are detected by the concentration detection unit 14. Then, the control unit 8 calculates the difference between the slope of the calculated detection values ​​(actual measurement values) and, for example, an ideal slope of the detection values ​​stored in the storage unit 9 (two-dot chain line in FIG. 6). If the difference is less than a predetermined value, the control unit 8 determines that there has been no fluctuation in the voltage applied to the concentration detection unit 14 that would prevent the acquisition of an appropriate toner concentration, and corrects the toner concentration based on the concentration correction mode.

[0052] Next, the process of the density correction mode when a fluctuation occurs in the voltage applied to the density detection unit 14 will be described.

[0053] Fig. 7 is an explanatory diagram showing the reference image group P1 for density correction in Fig. 5 and the detection values ​​of the density detection unit 14, and shows a state in which a fluctuation occurs in the applied voltage of the density detection unit 14. The configuration and format of Fig. 7 are generally the same as those of Fig. 5, so their description will be omitted here. Note that the output value indicating the applied voltage to the density detection unit 14 is drawn as a line below the line graph represented by the detection values ​​of the toner concentration for the reference image group P1.

[0054] When a fluctuation occurs in the voltage applied to the concentration detection unit 14, the applied voltage changes suddenly as shown in Fig. 7 (inside the dashed circle in Fig. 7). At this time, as shown in the line graph in Fig. 7, a similar fluctuation occurs in the detected value of the toner concentration, and an appropriate toner concentration cannot be obtained.

[0055] For this reason, in the density correction mode, the control unit 8 detects whether or not there is a voltage fluctuation at each density gradation based on the detection value of the toner density. If there is a voltage fluctuation, the control unit 8 sets the density gradation at which the voltage fluctuation is detected as a specific density gradation. Then, if there is a specific density gradation at which the voltage fluctuation is detected among the density gradations, the control unit 8 corrects the toner density of the specific density gradation using the detection values ​​of the density gradations before and after the specific density gradation.

[0056] According to the above configuration, the concentration detection unit 14 having a single light receiving unit 142 detects the fluctuation in the voltage applied to the concentration detection unit 14, and corrects the toner concentration of the specific concentration gradation where the voltage fluctuation is detected. Therefore, it is possible to realize appropriate concentration correction with a configuration that achieves low cost.

[0057] Fig. 8 is a graph showing the relationship between the detection value of the density detection unit 14 of the image forming apparatus 1 in Fig. 1 and the toner concentration, and shows a state in which fluctuations occur in the voltage applied to the density detection unit 14. The configuration and format of Fig. 8 are generally the same as those of Fig. 6, so their explanation will be omitted here. As shown in Fig. 8, the detection value of the toner concentration 4 is affected by the fluctuations in the voltage applied to the density detection unit 14.

[0058] As described with reference to Fig. 6, the control unit 8 calculates the slope of the detection values ​​(actual measurements, dashed lines in Fig. 8) from toner density 1 to toner density 5 shown in Fig. 8, detected by the density detection unit 14. At this time, the control unit 8 calculates the slope of the detection values ​​using detection values ​​at two or more successive density gradations.

[0059] In detail, the control unit 8 calculates the slope of the detection values ​​(dashed line in FIG. 8) using the detection values ​​of toner concentration 1 and toner concentration 2, the detection values ​​of toner concentration 2 and toner concentration 3, the detection values ​​of toner concentration 3 and toner concentration 4, the detection values ​​of toner concentration 1 and toner concentration 3, the detection values ​​of toner concentration 2 and toner concentration 4, the detection values ​​of toner concentration 1 and toner concentration 4, etc. Also, the detection values ​​at three or four density gradations may be used.

[0060] Then, control unit 8 calculates the difference between the slope of the calculated detection value (actual measurement value, dashed line in FIG. 8) and the ideal slope of the detection value stored in memory unit 9 (two-dot chain line in FIG. 8). According to FIG. 8, at toner concentration 4 where a fluctuation occurs in the applied voltage to concentration detection unit 14, a difference occurs between the slope of the calculated detection value (dashed line in FIG. 8) and the ideal slope (two-dot chain line in FIG. 8), and control unit 8 calculates this difference.

[0061] Furthermore, when the difference between the slope of the calculated detection value (actual measurement value) and the ideal slope is equal to or greater than a predetermined value, the control unit 8 determines that there has been a fluctuation in the voltage applied to the concentration detection unit 14. Information related to the predetermined value (threshold value) is stored in advance in the storage unit 9. The control unit 8 determines that the concentration gradation indicating the toner concentration 4 in FIG. 8 is the specific concentration gradation at which a voltage fluctuation has occurred.

[0062] According to the above configuration, it is possible to recognize that a fluctuation has occurred in the voltage applied to the concentration detection unit 14, based on the detection value (voltage value) of the toner concentration detected by the concentration detection unit 14. Then, based on the difference between the calculated slope of the detection value (actual measurement value) and the ideal slope, the toner concentration can be corrected in the concentration correction mode.

[0063] When a specific density gradation exists, the control unit 8 corrects the toner density of the specific density gradation using the detection values ​​of the density gradations before and after the specific density gradation. That is, the control unit 8 corrects the toner density 4, which is the specific density gradation, using the detection values ​​of the toner density 3 and the toner density 5.

[0064] At this time, the control unit 8 calculates, for example, an intermediate value between the detection values ​​of the density gradations before and after the specific density gradation, and corrects the toner density of the specific density gradation using the intermediate value. With reference to FIG. 8, the control unit 8 calculates an intermediate value Dm between the detection values ​​of the toner density 3 and the toner density 5. Then, the control unit 8 corrects the toner density 4 of the specific density gradation using the intermediate value Dm. By correcting the toner density 4 with the intermediate value Dm calculated using the detection values ​​of the toner density 3 and the toner density 5, which are the actual measured values, it is possible to perform density correction corresponding to the characteristics of the actual machine and the usage environment. In other words, it is possible to realize appropriate density correction that is compatible with the image forming apparatus 1.

[0065] It is also possible to determine the presence or absence of a specific density gradation without using the ideal slope of the detection values ​​(ideal slope data 91) stored in the memory unit 9. In this case, the control unit 8 calculates a pseudo slope of the detection values ​​using a plurality of detection values ​​detected by the density detection unit 14. With regard to Fig. 8, the control unit 8 calculates a pseudo slope corresponding to the two-dot chain line in Fig. 8 by using detection values ​​from toner density 1 to toner density 5.

[0066] In detail, the control unit 8 calculates the pseudo slope (two-dot chain line in FIG. 8) using the detection values ​​of toner concentration 1 and toner concentration 2, the detection values ​​of toner concentration 2 and toner concentration 3, the detection values ​​of toner concentration 3 and toner concentration 4, the detection values ​​of toner concentration 1 and toner concentration 3, the detection values ​​of toner concentration 2 and toner concentration 4, the detection values ​​of toner concentration 1 and toner concentration 4, etc. Also, detection values ​​at three or four density gradations may be used. According to the example of FIG. 8, the detection values ​​of toner concentration 1, toner concentration 2, toner concentration 3, and toner concentration 5 are used to calculate the pseudo slope of the detection values ​​(two-dot chain line in FIG. 8).

[0067] Then, when there is a detection value whose difference from the pseudo slope (two-dot chain line in FIG. 8) is equal to or greater than a predetermined value, the control unit 8 determines that the density gradation at which the detection value is detected is a specific density gradation. According to FIG. 8, when the difference between the detection value of toner density 4 in which a fluctuation in the applied voltage of the density detection unit 14 occurs and the pseudo slope (two-dot chain line in FIG. 8) is equal to or greater than a predetermined value, the density gradation indicating the toner density 4 is determined to be a specific density gradation in which a fluctuation in voltage occurs.

[0068] According to the above configuration, it is possible to determine that the density gradation indicating toner concentration 4 is the specific density gradation by using the pseudo slope of the detection values ​​calculated using the detection values ​​of toner concentration 1, toner concentration 2, toner concentration 3, and toner concentration 5, which are actual measured values, instead of the ideal slope stored in advance. This makes it possible to perform density correction corresponding to the characteristics of the actual machine and the usage environment. In other words, it becomes possible to realize appropriate density correction suited to the image forming apparatus 1.

[0069] Fig. 9 is a graph showing the relationship between the detection value of the concentration detection unit 14 of the image forming apparatus 1 in Fig. 1 and the toner concentration, and shows a state in which a discrepancy occurs between the two detection values. The configuration and format of Fig. 9 are generally the same as Fig. 6 and Fig. 8, so their explanation will be omitted here. As shown in Fig. 9, the detection values ​​of toner concentration 3 and toner concentration 5 are affected by the fluctuation of the applied voltage of the concentration detection unit 14.

[0070] Based on the pseudo slope of the detection values ​​indicated by the two-dot chain line in Fig. 9, the control unit 8 determines that the density gradations indicating toner concentration 3 and toner concentration 5 are the specific density gradations where a voltage fluctuation has occurred. Note that the pseudo slope of the detection values ​​is calculated using the detection values ​​of toner concentration 1, toner concentration 2, and toner concentration 4.

[0071] When there are two or more detection values ​​whose difference from the pseudo inclination is equal to or greater than a predetermined value, the control unit 8 executes the density correction mode again. With this configuration, it is possible to prevent the density correction mode from being executed based on detection values ​​with low reliability, and toner density correction from being performed. In other words, it is possible to realize appropriate density correction.

[0072] Next, there will be described a process flow of the density correction mode in the image forming apparatus 1. Fig. 10 is a flowchart showing the process of the density correction mode in the image forming apparatus 1 in Fig. 1.

[0073] The image forming apparatus 1 executes the density correction mode, for example, every time a predetermined number of sheets are printed. That is, when the predetermined number of sheets is printed ("START" in FIG. 10), the control unit 8 forms a reference image group P1 during non-image formation (step S101). The reference image group P1 is a toner image for density correction, and has four reference images P1a, P1b, P1c, and P1d. The reference image group P1 is formed on the outer circumferential surface of the photoconductor drum 21, and is then transferred to the outer circumferential surface of the intermediate transfer belt 31.

[0074] Next, the control unit 8 detects the toner concentration of the reference image group P1 (reference images P1a, P1b, P1c, and P1d) transferred onto the outer circumferential surface of the intermediate transfer belt 31 by the concentration detection unit 14 (step S102).

[0075] The image forming apparatus 1 may include a plurality of density detection units 14, and each of the plurality of density detection units 14 may detect the toner concentration of the reference image group P1 individually. For example, the plurality of density detection units 14 are arranged side by side along the axial direction of the photoconductor drum 21 and the intermediate transfer belt 31. By detecting the toner concentration at a plurality of locations, it is possible to improve the reliability of both the density correction and the detection of the fluctuation in the voltage applied to the density detection unit 14.

[0076] Next, the control unit 8 analyzes a plurality of detection values ​​of toner concentration based on the detection result of the concentration detection unit 14 (step S103). For example, as described with reference to Fig. 6, the control unit 8 calculates the difference between the slope of the detection value calculated using the detection value (actual measurement value) detected by the concentration detection unit 14 and the ideal slope of the detection value stored in the storage unit 9. Also, for example, as described with reference to Fig. 8, the control unit 8 calculates the difference between the detection value and the pseudo slope of the detection value calculated using the detection value (actual measurement value) detected by the concentration detection unit 14.

[0077] Next, the control unit 8 determines whether or not a change has occurred in the voltage applied to the concentration detection unit 14 (step S104). If a change has occurred in the voltage (Yes in step S104), the process proceeds to step S105, and if no change has occurred in the voltage (No in step S104), the process proceeds to step S107.

[0078] When a change occurs in the voltage applied to the density detection unit 14, the control unit 8 judges whether or not there are two or more detection values ​​whose difference from the pseudo slope is equal to or greater than a predetermined value (step S105). If there are two or more detection values ​​(Yes in step S105), the control unit 8 returns to step S101 and executes the density correction mode again. If there is one or less detection value (No in step S105), the control unit 8 proceeds to step S106.

[0079] In addition, when the ideal slope is used to detect the fluctuation in the voltage applied to the concentration detection unit 14, the process of step S105 is not executed. That is, in step S104, when the ideal slope is used and a fluctuation occurs in the voltage applied to the concentration detection unit 14, the process proceeds to step S106.

[0080] Next, the control unit 8 calculates the median value of the detection values ​​of the density gradation for the specific density gradation where the applied voltage to the density detection unit 14 has fluctuated (step S106).

[0081] Then, the control unit 8 corrects the toner concentration (step S107). If there is no fluctuation in the voltage applied to the concentration detection unit 14, the control unit 8 corrects the toner concentration so that it matches the ideal slope or pseudo slope of the detection value of the concentration gradation. If there is a fluctuation in the voltage applied to the concentration detection unit 14, the control unit 8 corrects the toner concentration of the specific concentration gradation using the intermediate value of the detection value of the concentration gradation. Then, the control unit 8 ends the process shown in FIG. 10.

[0082] Although an embodiment of the present invention has been described above, the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

[0083] For example, in the above embodiment, the concentration detector 14 is configured to include a light receiving element for detecting specularly reflected light, but instead, it may be configured to include a light receiving element for detecting diffusely reflected light.

[0084] In the above embodiment, the image forming apparatus 1 is a so-called tandem type image forming apparatus for color printing that sequentially overlaps and forms images of multiple colors, but the image forming apparatus is not limited to this type. The image forming apparatus may be a non-tandem type image forming apparatus for color printing or a monochrome image forming apparatus. [Industrial Applicability]

[0085] The present invention can be used in an image forming apparatus. [Explanation of symbols]

[0086] 1. Image forming device 5 Exposure section 6 Fixing section 8. Control Unit 9 Memory section 14 Concentration detection unit 20 Image forming section 21 Photoconductor drum 22 Charging section 23 Development section 30 Transcription section 31 Intermediate transfer belt 91 Ideal slope data 141 Light emitting part 142 Light receiving part Dm Midpoint P1 Reference images P1a, P1b, P1c, P1d Reference images

Claims

1. an image carrier having a photosensitive layer formed on an outer peripheral surface thereof; a charging section for charging an outer peripheral surface of the image carrier to a predetermined surface potential; an exposure unit that exposes the outer peripheral surface of the image carrier charged by the charging unit to form an electrostatic latent image by attenuating the charge; a developing unit that supplies toner to the electrostatic latent image on the image carrier to form a toner image; a concentration detection unit that detects a toner concentration of the toner image on the image carrier and outputs the detected value; a control unit that controls the image carrier, the charging unit, the exposure unit, and the developing unit; Equipped with the density detection unit has a light emitting unit that irradiates light toward the toner image when a predetermined voltage is applied thereto, and a single light receiving unit that receives light reflected by the toner image; The control unit is forming a reference image, which is the toner image for density correction, by sequentially changing the density gradation in a plurality of steps; a density correction mode in which the toner density of each of the plurality of reference images formed is detected by the density detection unit and the toner density is corrected based on the detection result; detecting whether or not the voltage fluctuates in each of the density gradations based on the detected value of the toner density detected in the density correction mode; An image forming apparatus characterized in that, when a specific density gradation exists among the density gradations in which a fluctuation in the voltage is detected, the toner concentration of the specific density gradation is corrected using the detection values ​​of the density gradations before and after the specific density gradation.

2. a storage unit that stores an ideal gradient of the detected value of the toner concentration with respect to the density gradation; The image forming apparatus according to claim 1, characterized in that the control unit determines that a fluctuation in the voltage has occurred when a difference between the ideal slope of the detection value stored in the memory unit and the slope of the detection value detected by the concentration detection unit is equal to or greater than a predetermined value.

3. The image forming apparatus according to claim 2, characterized in that the control unit calculates a slope of the detection value using the detection values ​​at two or more consecutive density gradations, and calculates the difference between the calculated slope of the detection value and the ideal slope.

4. The image forming apparatus according to claim 1, characterized in that the control unit calculates a pseudo slope of the detection values ​​using the multiple detection values ​​detected by the density detection unit, and if there is a detection value whose difference from the pseudo slope is equal to or greater than a predetermined value, determines that the density gradation at which the detection value was detected is the specific density gradation.

5. 5. The image forming apparatus according to claim 4, wherein the control unit executes the density correction mode again when there are two or more detected values ​​whose difference from the pseudo inclination is equal to or greater than a predetermined value.

6. The image forming apparatus according to claim 1, characterized in that, when the specific density gradation exists, the control unit calculates an intermediate value of the detection values ​​of the density gradations before and after the specific density gradation, and corrects the toner concentration of the specific density gradation using the intermediate value.

Images