Image forming apparatus

Abstract

The invention provides an image forming apparatus. A controller of an image forming apparatus is capable of executing a density correction mode for correcting a toner density based on a detection result of the toner density of each of a plurality of reference images formed by sequentially changing a density level in a plurality of stages, and correcting the density of the toner based on a detection value of the toner density detected in the density detection mode. The detection unit detects the presence or absence of a change in the voltage applied to the concentration detection unit at each of the concentration levels, and detects the presence or absence of a change in the voltage applied to the concentration detection unit when a specific concentration level in which the change in the voltage is detected exists among the concentration levels. The toner concentration of the specific concentration level is corrected using the detected values of the concentration levels before and after the specific concentration level.

Description

Technical Field

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

[0002] In electronic photographic image forming devices such as copiers and printers, devices that supply toner to an electrostatic latent image formed on the peripheral surface of a photosensitive drum as an image carrier and develop it to form a toner image to be transferred to a sheet of paper are widely used. The density of the toner image formed by the image forming device changes over time for various reasons. Therefore, calibration is usually performed, in which a toner image (reference image) for density correction is formed on the peripheral surface of a photosensitive drum or an intermediate transfer belt, and the toner density of the toner image is detected by a sensor to perform density correction. Summary of the invention

[0003] An object of the present invention is to provide an image forming apparatus capable of realizing appropriate density correction with a structure that realizes cost reduction.

[0004] The image forming device of the first structure of the present invention comprises an image carrier, a charging unit, an exposure unit, a developing unit, a concentration detection unit and a control unit. The image carrier has a photosensitive layer formed on the 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 that attenuates the charging. The developing unit supplies colorant to the electrostatic latent image of the image carrier to form a toner image. The concentration detection unit outputs a detection value related to the toner concentration 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 concentration detection unit has a light emitting unit that irradiates light to the toner image by applying a predetermined voltage, and a single light receiving unit that receives reflected light reflected by the toner image. The control unit forms a reference image of the colorant image for concentration correction in such a manner that the concentration level changes sequentially in multiple stages. The control unit detects the colorant concentration of each of the multiple reference images formed by the concentration detection unit, and is capable of executing a concentration correction mode for correcting the colorant concentration based on the detection result. The control unit detects whether the voltage at each concentration level has changed based on the detection value of the colorant concentration detected in the concentration correction mode. When there is a specific concentration level among the concentration levels at which the voltage change is detected, the control unit corrects the colorant concentration of the specific concentration level using the detection values ​​of the concentration levels before and after the specific concentration level.

[0005] According to the first structure of the present invention, the density detection unit having a single light receiving unit can detect the change in the voltage applied to the density detection unit and correct the toner density of the specific density level detected by the voltage change. Therefore, appropriate density correction can be achieved with a low-cost structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a schematic cross-sectional front view of an image forming apparatus according to one embodiment of the present invention. Figure 2 Yes means Figure 1 A block diagram of a structure of an image forming apparatus. Figure 3 yes Figure 1 A schematic cross-sectional front view of the periphery of an image forming unit of an image forming apparatus. Figure 4 yes Figure 3 A partial side view of the concentration detection section. Figure 5 Yes means Figure 1 An explanatory diagram of a reference image group for density correction of an image forming apparatus and a detection value of a density detection section. Figure 6 Yes means Figure 1 A coordinate graph showing the relationship between a detection value of a density detection portion of an image forming apparatus and a toner density. Figure 7 Yes means Figure 5 The diagram is an explanatory diagram of a reference image group for density correction and a detection value of a density detection unit, and is a diagram showing a state in which a voltage applied to the density detection unit varies. Figure 8 Yes means Figure 1 The present invention is a graph showing the relationship between the detection value of the density detection section of the image forming apparatus and the toner density, and is a graph showing a state in which the applied voltage of the density detection section varies. Fig. 9 Yes means Figure 1 The present invention is a graph showing the relationship between the detection value of the density detection section of the image forming apparatus and the toner density, and is a graph showing a state in which a deviation occurs between the two detection values. Fig.10 Yes means Figure 1 Flowchart of processing of the density correction mode in the image forming apparatus. DETAILED DESCRIPTION

[0007] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the present invention is not limited to the following contents.

[0008] Figure 1It is a schematic cross-sectional front view of the image forming apparatus 1 according to the embodiment. Figure 2 Yes means Figure 1 FIG. 1 is a block diagram showing a structure of an image forming apparatus 1 . Figure 3 yes Figure 1 1 is a schematic cross-sectional front view of the image forming unit 20 and its surroundings of the image forming apparatus 1. An example of the image forming apparatus 1 of the present embodiment is a tandem color printer that transfers a toner image to a sheet S using an intermediate transfer belt 31. The image forming apparatus 1 may be, for example, a so-called multifunction printer having functions such as printing, scanning (image reading), and fax transmission.

[0009] like Figure 1 , Figure 2 and Figure 3 As shown, the image forming apparatus 1 includes a paper supply unit 3, a paper conveying 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 storage unit 9 which are provided in its main body 2.

[0010] The paper supply unit 3 is arranged at the bottom of the main body 2. The paper supply unit 3 stores a plurality of sheets of paper S before printing, and separates and delivers the sheets of paper S one by one during printing. The paper conveying unit 4 extends in the vertical direction along the side wall of the main body 2. The paper conveying unit 4 conveys the sheets of paper S delivered from the paper supply unit 3 to the secondary transfer unit 33 and the fixing unit 6, and then discharges the sheets of paper S after fixing from the paper discharge port 4a to the paper discharge unit 7. The exposure unit 5 is arranged above the paper supply unit 3. The exposure unit 5 irradiates the image forming unit 20 with laser light controlled based on image data.

[0011] The image forming unit 20 is arranged 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. The basic structure of these four image forming units 20 is the same. Therefore, in the following description, the identification symbols "Y", "C", "M", and "B" representing each color are sometimes omitted except for the case where they are particularly required.

[0012] The image forming unit 20 includes a Figure 1 and Figure 3 The image forming unit 20 further includes a charging unit 22, a developing unit 23, and a drum cleaning unit 24, which are arranged around the photosensitive drum 21 along the rotation direction of the photosensitive drum 21. In addition, a primary transfer unit 32 is arranged between the developing unit 23 and the drum cleaning unit 24.

[0013] The photosensitive drum 21 has a photosensitive layer formed on the outer peripheral surface. The charging unit 22 charges the outer peripheral surface of the photosensitive drum 21 to a predetermined surface potential. The exposure unit 5 exposes the outer peripheral surface of the photosensitive drum 21 charged by the charging unit 22, and forms an electrostatic latent image of the original image on the outer peripheral surface of the photosensitive drum 21 to attenuate the charge. The developing unit 23 supplies colorant to the electrostatic latent image on the outer peripheral surface of the photosensitive drum 21 and develops it to form a toner image. The four image forming units 20 form toner images of different colors respectively. The drum cleaning unit 24 removes the toner remaining on the outer peripheral surface of the photosensitive drum 21 after the toner image is transferred to the outer peripheral surface of the intermediate transfer belt 31 once, and cleans the photosensitive drum 21. In this way, the image forming unit 20 forms an image (toner image) to be transferred to the paper S later.

[0014] The transfer unit 30 includes an intermediate transfer belt 31, a primary transfer unit 32Y, a primary transfer unit 32C, a primary transfer unit 32M, a primary transfer unit 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 an endless intermediate transfer body supported so as to be movable in a predetermined direction ( Figure 1 and Figure 3 The intermediate transfer belt 31 rotates in the counterclockwise direction (in the middle) to transfer the toner images formed by the four image forming units 20 one after another in a superimposed manner. The four image forming units 20 are arranged in a row from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 31 in a so-called tandem manner.

[0015] The primary transfer sections 32Y, 32C, 32M, and 32B are arranged above the image forming sections 20Y, 20C, 20M, and 20B of the respective colors with the intermediate transfer belt 31 interposed therebetween. The secondary transfer section 33 is arranged on the upstream side of the fixing section 6 in the paper conveying direction of the paper conveying section 4, and is arranged on the downstream side of the four image forming sections 20Y, 20C, 20M, and 20B in the rotation direction of the intermediate transfer belt 31. The belt cleaning section 34 is arranged on the downstream side of the secondary transfer section 33 in the rotation direction of the intermediate transfer belt 31.

[0016] The primary transfer section 32 transfers the toner image formed on the outer peripheral surface of the photosensitive drum 21 to the intermediate transfer belt 31. In other words, the toner image is primarily transferred by the primary transfer sections 32Y, 32C, 32M, and 32B of each color to the outer peripheral surface of the intermediate transfer belt 31. Then, as the intermediate transfer belt 31 rotates, the toner images of the four image forming sections 20 are continuously transferred to the intermediate transfer belt 31 in an overlapping manner at a predetermined timing, thereby forming a color toner image in which the toner images of four colors, namely yellow, cyan, magenta, and black, are overlapped on the outer peripheral surface of the intermediate transfer belt 31.

[0017] The color toner image on the outer peripheral surface of the intermediate transfer belt 31 is transferred to the paper S synchronously conveyed by the paper conveying section 4 at the secondary transfer nip formed in the secondary transfer section 33. The belt cleaning section 34 removes the toner and other attached materials remaining on the outer peripheral surface of the intermediate transfer belt 31 after the secondary transfer and cleans the intermediate transfer belt 31. In this way, the transfer section 30 transfers (records) the toner image formed on the outer peripheral surface of the photosensitive drum 21 to the paper S.

[0018] The fixing section 6 is disposed above the secondary transfer section 33. The fixing section 6 heats and presses the paper S to which the toner image has been transferred, thereby fixing the toner image to the paper S.

[0019] The paper discharge section 7 is disposed above the transfer section 30. The paper S on which the toner image is fixed and printed is conveyed to the paper discharge section 7. The printed paper (printed material) is taken out from above the paper discharge section 7.

[0020] The control unit 8 includes a CPU, an image processing unit, and other electronic circuits and electronic components (all not shown). The CPU controls the operation of each component provided in the image forming apparatus 1 according to the control program and data stored in the storage unit 9, and performs processing related to the function of the image forming apparatus 1. The paper supply unit 3, the paper conveying unit 4, the exposure unit 5, the image forming unit 20, the transfer unit 30, and the fixing unit 6 receive instructions from the control unit 8 separately, and perform printing on the paper S in conjunction.

[0021] The storage unit 9 is composed of, for example, a combination of a nonvolatile storage device (not shown) such as a program ROM (Read Only Memory) and a data ROM, and a volatile storage device (not shown) such as a RAM (Random Access Memory).

[0022] Next, use Figure 3 The image forming unit 20 and its peripheral structure will be described. Since the basic structure of the image forming unit 20 of each color is the same, the description and description of the identification symbols representing each color will be omitted for the components unless otherwise specified.

[0023] The image forming section 20 includes a photosensitive drum 21 , a charging section 22 , a developing section 23 , and a drum cleaning section 24 .

[0024] The photosensitive drum 21 is cylindrical in shape and supported to be rotatable with its central axis horizontal. It is rotated at a constant speed around the central axis by a driving unit (not shown). The photosensitive drum 21 has a photosensitive layer composed of an inorganic photosensitive body such as amorphous silicon on the outer peripheral surface of a drum tube blank made of metal such as aluminum. An electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 21.

[0025] The charging section 22 includes, for example, a charging roller 221. The charging roller 221 extends parallel to the axial direction of the photosensitive drum 21 and is supported so as to be rotatable with the central axis being horizontal. The charging roller 221 rotates as the photosensitive drum 21 rotates by contacting the outer peripheral surface of the photosensitive drum 21. The charging roller 221 includes, for example, a conductive layer composed of a cross-linked rubber mixed with an ion conductive material on the outer peripheral surface of a core shaft. If a predetermined charging voltage is applied to the charging roller 221, the outer peripheral surface of the photosensitive drum 21 is also charged.

[0026] The developing section 23 is arranged downstream of the charging section 22 in the rotation direction of the photosensitive drum 21. The developing section 23 includes a developing container 231, a first conveying member 232, a second conveying member 233, a developing roller (developer carrier) 234, and a regulating member 235.

[0027] The developing container 231 is arranged along the axial direction of the photosensitive drum 21 ( Figure 3 The developing container 231 has an elongated shape extending in the paper depth direction and is arranged with its long side in the horizontal direction. The developing container 231 contains, for example, a two-component developer containing a toner and a magnetic carrier as a developer containing a toner supplied to the photosensitive drum 21.

[0028] The first conveying member 232 and the second conveying 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 conveying member 232 and the second conveying member 233 rotate about their respective axes to stir and convey the developer in opposite directions along the axis direction of the rotation.

[0029] The developing roller 234 is located above the second conveying member 233 in the developing container 231 and is arranged opposite to the photosensitive drum 21. The developing roller 234 is supported by the developing container 231 in a manner that allows rotation around an axis extending parallel to the axis of the photosensitive drum 21. A portion of the outer peripheral surface of the developing roller 234 is exposed from the developing container 231, and the developing roller 234 is opposite to the photosensitive drum 21 and close to the photosensitive drum 21. The developing roller 234 carries the developer containing the 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 peripheral surface of the photosensitive drum 21 to form a toner image.

[0030] The restricting member 235 is arranged on the upstream side of the developing roller 234 in the rotation direction of the developing roller 234 in the opposing region where the developing roller 234 and the photosensitive drum 21 are opposed to each other. The restricting member 235 is arranged close to the developing roller 234 and opposed to the developing roller 234, and a predetermined gap is provided between the top end thereof and the outer peripheral surface of the developing roller 234. The restricting member 235 extends over the entire region of the developing roller 234 in the axial direction.

[0031] The developer in the developing container 231 circulates by the rotation of the first conveying member 232 and the second conveying member 233, is stirred and charged, and is carried on the outer peripheral surface of the developing roller 234. The developer carried on the outer peripheral surface of the developing roller 234 has a layer thickness restricted by the restricting member 235. When a predetermined developing voltage is applied to the developing roller 234, the toner in the developer carried on the outer peripheral surface of the developing roller 234 moves to the outer peripheral surface of the photosensitive drum 21 in the opposing area with the photosensitive drum 21 due to the potential difference between the surface potential of the outer peripheral surface of the photosensitive drum 21. As a result, the electrostatic latent image on the outer peripheral surface of the photosensitive drum 21 is developed by the toner.

[0032] The drum cleaning section 24 is arranged on the downstream side of the primary transfer section 32 in the rotation direction of the photosensitive drum 21. The drum cleaning section 24 includes a recovery container 241, a cleaning blade 242, and a recovery screw 243.

[0033] The recovery container 241 is arranged along the axial direction of the photosensitive drum 21 ( Figure 3 The recovery container 241 is an elongated shape extending in the paper depth direction and is arranged with its long side direction horizontal. The recovery container 241 contains the residual toner and the like removed from the outer peripheral surface of the photosensitive drum 21 by the cleaning blade 242.

[0034] The cleaning blade 242 is in the shape of a plate extending along the axial direction of the photosensitive drum 21, and is formed of an elastic member such as polyurethane rubber. The cleaning blade 242 is arranged on the downstream side of the drum rotation direction with respect to the contact point with the photosensitive drum 21 so as to form a predetermined angle with respect to the tangential direction of the photosensitive drum 21 at the contact point with the photosensitive drum 21. The cleaning blade 242 contacts the outer peripheral surface of the photosensitive drum 21 with a predetermined pressure. The cleaning blade 242 removes the residue including the toner remaining on the outer peripheral surface of the photosensitive drum 21 after the primary transfer.

[0035] The spiral recovery device 243 is arranged in the lower part of the recovery container 241 and is separated from the photosensitive drum 21 by the cleaning blade 242. The spiral recovery device 243 is supported by the recovery container 241 in a manner that it can rotate around an axis extending parallel to the rotation axis of the photosensitive drum 21. The spiral recovery device 243 has, for example, a spiral conveying blade extending in the axial direction. The spiral recovery device 243 conveys the residual toner and the like removed from the outer peripheral surface of the photosensitive drum 21 to a recycling waste container (not shown) provided outside the drum cleaning unit 24.

[0036] The image forming apparatus 1 further includes a density detection section 14. The density detection section 14 is arranged upstream of the secondary transfer section 33 in the rotation direction of the intermediate transfer belt 31 and downstream of the image forming section 20B for black, which is the most downstream side among the four image forming sections 20. The density detection section 14 faces the outer peripheral surface of the intermediate transfer belt 31.

[0037] Figure 4 yes Figure 3 A partial side view of the concentration detection unit 14. Figure 4 is along the rotation direction of the intermediate transfer belt 31 from Figure 3 Side view Figure 3 A diagram of the concentration detection unit 14 is shown.

[0038] The density 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 the toner image primarily transferred to the outer peripheral surface of the intermediate transfer belt 31 with detection light at a predetermined angle. The light receiving unit 142 receives the detection light irradiated by the light emitting unit 141 to the toner image and reflected by the toner image.

[0039] As a method for detecting the toner density of a toner image, two methods can be used: a method of receiving specularly reflected detection light and a method of receiving diffusely reflected detection light. In this embodiment, a method of detecting specular reflection is described.

[0040] The density 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 density, thereby being able to derive the toner amount of the toner image that is primarily transferred to the outer peripheral surface of the intermediate transfer belt 31 and detect the toner density 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 not diffusely reflected by the toner but is reflected by the mirror surface and enters the light receiving unit 142 in large quantities. As a result, the detection value (voltage value) related to the toner density becomes higher. Then, as the toner amount 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 entering the light receiving unit 142 gradually decreases. That is, the detection value (voltage value) related to the toner density gradually becomes lower.

[0041] In this way, the density detection unit 14 irradiates the toner image with detection light from the light emitting unit 141, and detects the toner density of the toner image transferred to the outer peripheral surface of the intermediate transfer belt 31 based on the detection light reflected by the toner image and received by the light receiving unit 142. In other words, the density detection unit 14 detects the toner density by outputting a detection value related to the toner density of the toner image formed on the outer peripheral surface of the photosensitive drum 21 in the image forming unit 20.

[0042] Furthermore, the control unit 8 of the image forming apparatus 1 of the present embodiment executes a density correction mode during non-image forming, for example, periodically, such as when a predetermined number of printed sheets is reached, or at an arbitrary timing by a user or an administrator. The density correction mode is a calibration for density correction of a toner image. In the density correction mode, a reference image (color patch image) as a toner image for density correction is formed on the outer peripheral surface of the photosensitive drum 21 in such a manner that the density level changes sequentially in a plurality of stages, and is transferred to the outer peripheral surface of the intermediate transfer belt 31, and the toner density of each of the plurality of reference images is detected by the density detection unit 14. The control unit 8 compares the density (actually measured value) of each of the plurality of reference images for density correction with a predetermined target density (ideal value) based on the detection result, and adjusts, for example, the development bias voltage, thereby correcting the toner density.

[0043] Figure 5 Yes means Figure 1 FIG. 1 is an explanatory diagram of a reference image group P1 for density correction of an image forming apparatus 1 and a detection value of a density detection unit 14. Figure 5 Two reference image groups P1 for density correction are depicted in the upper part of FIG. Figure 5 The lower part of is a graph showing the detected values ​​of the toner concentration detected for the reference image group P1. Figure 5 The graph shown is a line graph of ideal toner density for the reference image group P1. Figure 5 The left and right lateral directions of the reference image group P1 in the figure are the circumferential direction of the photosensitive drum 21 (= the rotation direction of the intermediate transfer belt 31), and the timing is consistent with the detection time of the toner concentration as the horizontal axis of the coordinate graph. The vertical axis of the coordinate graph is the detection value (voltage value) of the toner concentration output by the concentration detection unit 14. The "belt surface detection value" is the detection value v10 output by the concentration detection unit 14 when there is no toner on the outer peripheral surface of the intermediate transfer belt 31.

[0044] The reference image group P1 for density correction is in the form of a belt, and is a rectangular reference image extending along the axial direction and the circumferential direction of the photosensitive drum 21. The density level is sequentially changed in multiple stages, and the reference image group P1 is continuously formed in the circumferential direction of the photosensitive drum 21. In this embodiment, the reference image group P1 includes four reference images P1a, P1b, P1c, and P1d.

[0045] The four reference images P1a, P1b, P1c, and P1d are formed as they move toward the downstream side in the circumferential direction of the photosensitive drum 21 (= the rotation direction of the intermediate transfer belt 31), that is, Figure 5As the toner amount per unit area increases, the toner density increases. That is, the toner density increases in the order of the reference images P1a, P1b, P1c, and P1d. With respect to the belt surface detection value v10 output by the density detection unit 14, in the four reference images P1a, P1b, P1c, and P1d, the detection light is absorbed by the toner image, and thus the value decreases in the order of the detection values ​​v1a, v1b, v1c, and v1d.

[0046] Then, the control unit 8 detects through the concentration detection unit 14 whether Figure 5 The toner density of each of the plurality of reference images P1a, P1b, P1c, and P1d for density correction formed in this manner. Figure 6 Yes means Figure 1 A graph showing the relationship between the detection value of the density detection unit 14 of the image forming apparatus 1 and the toner density. Figure 6 In FIG. 1 , the horizontal axis represents the toner density of the image, and the vertical axis represents the detection value (voltage value) of the density detection portion 14 corresponding to the toner density. Figure 6 The line graph shown is the actual measured value of the toner density detected by the density detection unit 14 for the reference image group P1 ( Figure 5 is an example of an ideal value). Figure 6 The double-dashed line is the ideal slope of the detected value of the toner concentration with respect to the concentration level. The ideal slope data 91 related to the ideal slope is pre-stored in the storage unit 9 (refer to Figure 2 ).

[0047] Furthermore, the control unit 8 analyzes the detection values ​​of the plurality of toner densities based on the detection result of the density detection unit 14 and corrects the toner density. Figure 6 The control unit 8 then compares the calculated slope of the detected value (measured value) with the ideal slope (measured value) of the detected value stored in the storage unit 9, for example. Figure 6 When the difference is smaller than a predetermined value, the control unit 8 determines that there is no change in the voltage applied to the density detection unit 14 that prevents the acquisition of an appropriate toner density, and corrects the toner density according to the density correction mode.

[0048] Next, the process in the density correction mode when the voltage applied to the density detection unit 14 varies will be described.

[0049] Figure 7 Yes means Figure 5 1 and 2 are diagrams for explaining the reference image group P1 for density correction and the detection value of the density detection unit 14 , and are diagrams showing a state in which the applied voltage of the density detection unit 14 varies. Figure 7The composition and format of Figure 5 In addition, below the line graph representing the detected values ​​of the toner density detected for the reference image group P1 , the output value representing the voltage applied to the density detection section 14 is plotted in a linear form.

[0050] like Figure 7 As shown in FIG. 1 , when the voltage applied to the concentration detection unit 14 changes, the voltage applied changes rapidly ( Figure 7 At this time, if Figure 7 As shown in the line graph, the detected value of the toner density also fluctuates in the same manner, and an appropriate toner density cannot be obtained.

[0051] Therefore, the control unit 8 detects whether the voltage at each density level changes based on the detected value of the toner density in the density correction mode. If the voltage changes, the control unit 8 sets the density level at which the voltage change is detected as a specific density level. Then, if there is a specific density level at which the voltage change is detected, the control unit 8 corrects the toner density of the specific density level using the detected values ​​of the density levels before and after the specific density level.

[0052] According to the above configuration, the density detection unit 14 having the single light receiving unit 142 can detect the change in the voltage applied to the density detection unit 14 and correct the toner density at a specific density level where the voltage change is detected. Therefore, appropriate density correction can be achieved with a low-cost configuration.

[0053] Figure 8 Yes means Figure 1 1 and 2. The graph is a graph showing the relationship between the detection value of the density detection unit 14 of the image forming apparatus 1 and the toner density, and is a graph showing a state in which the applied voltage of the density detection unit 14 varies. Figure 8 The composition and format of Figure 6 The above are roughly the same, so the description is omitted here. Figure 8 As shown, the variation in the applied voltage of the density detection unit 14 affects the detected value of the toner density 4 .

[0054] If used Figure 6 As described above, the control unit 8 calculates the concentration detected by the concentration detection unit 14. Figure 8 The detected values ​​(actually measured values, Figure 8 At this time, the control unit 8 calculates the slope of the detection value using the detection values ​​at two or more consecutive concentration levels.

[0055] Specifically, the control unit 8 calculates the detection value ( ) using the detection values ​​of the toner density 1 and the toner density 2, the detection values ​​of the toner density 2 and the toner density 3, the detection values ​​of the toner density 3 and the toner density 4, the detection values ​​of the toner density 1 and the toner density 3, the detection values ​​of the toner density 2 and the toner density 4, and the detection values ​​of the toner density 1 and the toner density 4. Figure 8 In addition, the detection values ​​at three or four concentration levels can also be used.

[0056] Then, the control unit 8 calculates the detection value (actual measurement value, Figure 8 The slope of the dashed line) is the same as the ideal slope of the detection value stored in the storage unit 9 ( Figure 8 The difference between Figure 8 , at a toner concentration 4 where the applied voltage of the concentration detection unit 14 varies, the calculated detection value ( Figure 8 The slope of the dotted line) is the same as the ideal slope ( Figure 8 The control unit 8 calculates the difference.

[0057] Furthermore, when the difference between the calculated detection value (actual measurement value) and the ideal slope is greater than a predetermined value, the control unit 8 determines that the applied voltage to the concentration detection unit 14 has changed. Information related to the predetermined value (threshold value) is pre-stored in the storage unit 9. The control unit 8 Figure 8 The density level indicating the toner density 4 in FIG. 1 is determined to be a specific density level at which a voltage variation occurs.

[0058] According to the above configuration, it is possible to recognize that the applied voltage of the density detection section 14 has changed based on the detection value (voltage value) of the toner density detected by the density detection section 14. Then, based on the difference between the calculated slope of the detection value (actual value) and the ideal slope, the toner density can be corrected in the density correction mode.

[0059] When there is a specific density level, the control unit 8 uses the detection values ​​of the density levels before and after the specific density level to correct the toner density of the specific density level. That is, for the toner density 4 as the specific density level, the control unit 8 uses the detection values ​​of the toner density 3 and the toner density 5 to correct the toner density 4.

[0060] At this time, the control unit 8 calculates, for example, an intermediate value of the detection values ​​of the density levels before and after the specific density level, and corrects the toner density of the specific density level using the intermediate value. Figure 8For example, the control unit 8 uses the detected values ​​of the toner density 3 and the toner density 5 to calculate the intermediate value Dm thereof. Then, the control unit 8 corrects the toner density 4 of a specific density level using the intermediate value Dm. By correcting the toner density 4 using the intermediate value Dm calculated using the detected values ​​of the toner density 3 and the toner density 5 as actual measured values, it is possible to perform density correction corresponding to the characteristics of the actual machine and the use environment. That is, it is possible to realize appropriate density correction suitable for the image forming apparatus 1.

[0061] In addition, the presence or absence of a specific concentration level can be determined without using the ideal slope (ideal slope data 91) of the detection value stored in the storage unit 9. In this case, the control unit 8 calculates the pseudo slope of the detection value using the plurality of detection values ​​detected by the concentration detection unit 14. Figure 8 For example, the control unit 8 calculates the toner density by using the detected values ​​from toner density 1 to toner density 5. Figure 8 The double-dotted line is equivalent to the pseudo slope.

[0062] Specifically, the control unit 8 calculates the pseudo slope ( ) using the detected values ​​of toner density 1 and toner density 2, the detected values ​​of toner density 2 and toner density 3, the detected values ​​of toner density 3 and toner density 4, the detected values ​​of toner density 1 and toner density 3, the detected values ​​of toner density 2 and toner density 4, the detected values ​​of toner density 1 and toner density 4, and the like. Figure 8 In addition, the detection values ​​at three or four concentration levels can also be used. Figure 8 For example, using the detection values ​​of toner density 1, toner density 2, toner density 3, and toner density 5, the pseudo slope of the detection value is calculated ( Figure 8 double-dotted line).

[0063] Then, in the presence of a pseudo slope ( Figure 8 When the difference between the detection value (the double-dashed line) and the detection value is greater than the predetermined value, the control unit 8 determines that the concentration level at which the detection value is detected is a specific concentration level. Figure 8 The detected value of the toner concentration 4 that has changed due to the applied voltage of the concentration detection unit 14 and the pseudo slope ( Figure 8 When the difference between the two dotted chain lines (shown by the double-dashed line) and the toner concentration 4 is equal to or greater than a predetermined value, it is determined that the density level indicating the toner density 4 is a specific density level at which a voltage change occurs.

[0064] According to the above configuration, it is possible to determine that the density level indicating the toner density 4 is a specific density level by using a pseudo slope of a detection value calculated using the detection values ​​of the toner density 1, toner density 2, toner density 3, and toner density 5, which are actual measured values, instead of using a pre-stored ideal slope. This makes it possible to perform density correction corresponding to the characteristics of the actual machine and the use environment. That is, it is possible to implement appropriate density correction suitable for the image forming apparatus 1.

[0065] Fig. 9 Yes means Figure 1 1 is a graph showing the relationship between the detection value of the density detection unit 14 of the image forming apparatus 1 and the toner density, and is a graph showing a state where a deviation occurs between the two detection values. Fig. 9 The composition and format of Figure 6 and Figure 8 The above are roughly the same, so the description is omitted here. Fig. 9 As shown, the variation of the applied voltage of the density detection unit 14 affects the detection values ​​of the toner density 3 and the toner density 5 .

[0066] The control unit 8 is based on Fig. 9 The pseudo slope of the detection value indicated by the double-dashed line in FIG. 1 is used to determine that the density levels indicating toner density 3 and toner density 5 are specific density levels at which voltage fluctuations occur. In addition, the pseudo slope of the detection value is calculated using the detection values ​​of toner density 1, toner density 2, and toner density 4.

[0067] If there are two or more detection values ​​that differ from the pseudo slope by a predetermined value or more, the control unit 8 executes the density correction mode again. This configuration can prevent the toner density from being corrected by executing the density correction mode based on a detection value with low reliability. That is, appropriate density correction can be achieved.

[0068] Next, the flow of the process in the density correction mode in the image forming apparatus 1 will be described. Fig.10 Yes means Figure 1 Flowchart of the process of the density correction mode in the image forming apparatus 1.

[0069] The image forming apparatus 1 executes the concentration correction mode every time a predetermined number of prints is reached. 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, which are sequentially formed on the outer peripheral surface of the photosensitive drum 21 and then transferred to the outer peripheral surface of the intermediate transfer belt 31.

[0070] Next, the control unit 8 detects the toner density of the reference image group P1 (reference images P1a, P1b, P1c, and P1d) transferred to the outer peripheral surface of the intermediate transfer belt 31 by the density detection unit 14 (step S102).

[0071] In addition, the image forming apparatus 1 may include a plurality of density detection units 14, and the toner density of the reference image group P1 is detected in each of the plurality of density detection units 14. For example, the plurality of density detection units 14 are arranged along the axial direction of the photosensitive drum 21 and the intermediate transfer belt 31. By detecting the toner density at a plurality of locations, the reliability of density correction and the detection of the change in the applied voltage to the density detection unit 14 can be improved.

[0072] Next, the control unit 8 analyzes the detection values ​​of the plurality of toner densities based on the detection results of the density detection unit 14 (step S103). Figure 6 As described above, the control unit 8 calculates the difference between the slope of the detection value calculated using the detection value (actual value) detected by the concentration detection unit 14 and the ideal slope of the detection value stored in the storage unit 9. Figure 8 As described above, the control unit 8 calculates the difference between the pseudo slope of the detection value calculated using the detection value (actual measurement value) detected by the concentration detection unit 14 and the detection value.

[0073] Next, the control unit 8 determines whether the voltage applied to the concentration detection unit 14 has changed (step S104). If the voltage has changed ("Yes" in step S104), the process moves to step S105, and if the voltage has not changed ("No" in step S104), the process moves to step S107.

[0074] When the applied voltage to the concentration detection unit 14 changes, the control unit 8 determines whether there are two or more detection values ​​whose difference from the pseudo slope is greater than a predetermined value (step S105). If there are two or more such detection values ​​("Yes" in step S105), the control unit 8 returns to step S101 and executes the concentration correction mode again. If there are less than one such detection value ("No" in step S105), the control unit 8 moves to step S106.

[0075] When the ideal slope is used to detect the change in the voltage applied to the concentration detection unit 14, the process of step S105 is not performed. That is, in step S104, when the ideal slope is used and the voltage applied to the concentration detection unit 14 changes, the process proceeds to step S106.

[0076] Next, the control unit 8 calculates a median value of the detection values ​​of the density level for a specific density level at which the voltage applied to the density detection unit 14 varies (step S106 ).

[0077] Then, the control unit 8 performs correction of the toner concentration (step S107). When the applied voltage applied to the concentration detection unit 14 does not change, the control unit 8 corrects the toner concentration so that it conforms to the ideal slope or pseudo slope of the detection value of the concentration level. In addition, when the applied voltage applied to the concentration detection unit 14 changes, the control unit 8 corrects the toner concentration of a specific concentration level using the intermediate value of the detection value of the concentration level. Then, the control unit 8 ends. Fig.10 processing.

[0078] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and the present invention can be implemented with various modifications without departing from the gist of the invention.

[0079] For example, in the above-described embodiment, the density detection unit 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.

[0080] In the above embodiment, the image forming apparatus 1 is a so-called tandem color printing image forming apparatus that sequentially and overlappingly forms images of multiple colors, but the present invention is not limited to such a type. The image forming apparatus may also be a non-tandem color printing image forming apparatus or a black-and-white printing image forming apparatus.

Claims

1. An image forming device, characterized in that: have: An image carrier having a photosensitive layer formed on the outer peripheral surface; A charging unit, which charges the outer peripheral surface of the image carrier to a predetermined surface potential; an exposure section for exposing the outer peripheral surface of the image carrier charged by the charging section to form an electrostatic latent image for attenuating the charge; a developing section that supplies toner to the electrostatic latent image on the image carrier to form a toner image; a density detection section that outputs a detection value related to the toner density of the toner image on the image carrier; as well as a control unit that controls the image carrier, the charging unit, the exposure unit, and the developing unit, The density detection section includes a light emitting section that irradiates light toward the toner image when a predetermined voltage is applied, and a single light receiving section that receives reflected light from the toner image. The control unit forms a reference image of the toner image for density correction in such a manner that the density level changes sequentially in a plurality of stages. The control unit detects the toner density of each of the plurality of reference images formed by the density detection unit, and can execute a density correction mode for correcting the toner density based on the detection result, and the control unit detects whether the voltage at each density level changes based on the detection value of the toner density detected in the density correction mode. When there is a specific density level at which the voltage variation is detected among the density levels, the control unit corrects the toner density at the specific density level using the detection values ​​of the density levels before and after the specific density level.

2. The image forming apparatus according to claim 1, wherein: A storage unit is provided for storing an ideal slope of the detected value of the toner density with respect to the density level, The control unit determines that the voltage has changed when a difference between the ideal slope of the detection value stored in the storage unit and the slope of the detection value detected by the concentration detection unit is equal to or larger than a predetermined value.

3. The image forming apparatus according to claim 2, wherein: The control unit calculates a slope of the detection value using the detection values ​​at two or more consecutive concentration levels, and calculates a difference between the calculated slope of the detection value and the ideal slope.

4. The image forming apparatus according to claim 1, wherein: The control unit calculates a pseudo slope of the detection value using the plurality of detection values ​​detected by the concentration detection unit, and determines the concentration level of the detected detection value as the specific concentration level when there is a detection value whose difference from the pseudo slope is greater than a predetermined value.

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 detection values ​​that differ from the pseudo slope by a predetermined value or more.

6. The image forming apparatus according to claim 1, wherein: When the specific density level exists, the control section calculates a median value of the detection values ​​of the density levels before and after the specific density level, and corrects the toner density of the specific density level using the median value.

Images