JP5369786B2 - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate uneven toner concentration without increasing size or cost of an apparatus. <P>SOLUTION: The image forming apparatus includes: an optical writing unit which forms a latent image corresponding to image information on an image carrier; a convey screw which circulates and conveys a two-component developer on a convey path; a toner replenishing device which replenishes toner to the two-component developer at a predetermined replenishment place on the convey path; a developing unit which develops the latent image formed on the image carrier by the two-component developer; an image information obtaining section 2103 which obtains the image information; and a replenishment control section 2102 which calculates a toner replenishment amount so as to eliminate the toner concentration change with time by performing filter calculation for the image information using either a first filter or a second filter having higher accuracy than the first filter and controls the toner replenishing device to replenish the toner in the calculated toner replenishment amount. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method for forming an image by transferring a toner image obtained by developing a latent image on a latent image carrier with a two-component developer onto a recording material.

  When the two-component developer circulated and conveyed in the developing device (developing unit) along the developer circulation conveyance path consumes toner due to image formation, the consumed toner is replenished to the two-component developer by the toner replenishing unit. The As conventional toner replenishing methods employed for this toner replenishment, the following two replenishing methods are known.

  In the first method, for example, when the latent image is consumed by developing the latent image from pixel writing information (image information) used when the exposure device (latent image forming means) forms the latent image on the latent image carrier. Calculate the expected toner consumption. Then, an amount of toner corresponding to the calculated toner consumption is supplied to the two-component developer all at once or at a constant interval.

  In the second method, a toner concentration sensor (toner concentration detecting means) is provided at a predetermined position (predetermined detection position) on a conveying screw (developer conveying means) for circulating and conveying the two-component developer in the developing device. Is provided. The toner density sensor measures the toner density at the predetermined detection location, and replenishes the two-component developer all at once or at regular intervals so that the toner density becomes the target toner density. .

  However, in any of the toner replenishing methods, toner is replenished to the two-component developer all at once or at regular intervals. For this reason, it has been difficult to eliminate toner density unevenness (hereinafter simply referred to as “toner density unevenness”) in the circulation direction of the two-component developer circulated through the developing device. Hereinafter, it will be described in detail with reference to the drawings.

  FIG. 30 is an explanatory diagram showing an example of a developing device that circulates and conveys the two-component developer along the developer circulation and conveyance path.

  In this developing device, the two-component developer is circulated and conveyed in the direction indicated by the arrow A in the figure by the two conveying screws 8 and 11. The developing roller 12 faces the portion of the developer circulation conveying path where the second conveying screw 11 is installed. In this portion, the two-component developer is pumped up to the surface of the developing roller and passes through the developing region. The two component developer is returned. In addition, a toner replenishing port 17 is provided at an upper portion of the developer circulation conveying path where the second conveying screw 11 is installed, and toner is replenished through the toner replenishing port 17 by a toner replenishing means (not shown). Is done. Further, a portion indicated by B in the figure is a measurement portion where the toner density unevenness is measured by the toner density sensor.

  FIG. 31 is a graph showing the relationship between toner replenishment and toner density unevenness when toner is replenished to the two-component developer. FIG. 32 is a graph showing the relationship between toner replenishment and toner density unevenness when toner is replenished to the two-component developer intermittently at regular intervals.

  In these graphs, the waveform (consumption waveform) indicated by a thin solid line indicates that the two-component developer after developing a predetermined latent image using the two-component developer without toner density unevenness is not replenished with toner. 6 is a waveform showing a result of measuring a toner density by the toner density sensor. That is, this consumption waveform shows an example of toner density unevenness that occurs after development.

  A waveform indicated by a dotted line (replenishment waveform) indicates the toner concentration of the two-component developer after toner replenishment is performed with respect to the two-component developer without toner density unevenness by the toner concentration sensor. It is a waveform which shows the result of having measured. Note that each waveform indicated by a two-dot chain line in FIG. 32 indicates an individual supply waveform of each toner supply intermittently performed, and a waveform obtained by synthesizing each individual supply waveform indicated by a two-dot chain line indicates a supply indicated by a dotted line. It becomes a waveform.

  The waveform indicated by the thick solid line is a composite of the consumption waveform and the replenishment waveform, and the toner density after replenishing toner by each replenishment method for the two-component developer after developing a predetermined latent image. It shows unevenness.

  As shown by the thick solid lines in FIGS. 31 and 32, the toner is supplied to the two-component developer all at once (the first method) or the toner is supplied to the two-component developer intermittently at regular intervals. In the method (the second method), it can be seen that there is toner density unevenness in the two-component developer after toner replenishment.

  In particular, the consumption waveform in actual image formation is not constant because it varies depending on the image to be formed, specifically the position and size of the latent image to be developed. Therefore, as with conventional replenishment methods, when toner is replenished at a constant timing and at a constant speed regardless of the difference in consumption waveform, the toner density unevenness of the two-component developer after toner replenishment is eliminated. I can't do it.

  This point will be further described. In the developing device shown in FIG. 30, the two-component developer conveyed by the second conveying screw 11 is conveyed along the developer circulation conveying path in a direction orthogonal to the developer conveying direction by the developing roll 12, It is carried on the surface of the developing roll 12 and conveyed to the developing area. Then, after contributing to development in the development region, the developer is returned again to the developer circulation conveyance path and conveyed by the second conveyance screw 11.

  If the position of the latent image is unevenly distributed on the latent image carrier, the developed two-component developer may have a portion that consumes a large amount of toner and a portion that consumes little toner. Then, the two-component developer in such a state is returned to the developer circulation conveyance path. In this case, toner density unevenness occurs in the two-component developer after being returned to the developer circulation conveyance path. In addition, the toner density unevenness varies depending on the uneven distribution of the latent image on the latent image carrier.

  FIG. 33 is an explanatory diagram showing the relationship between the uneven distribution of latent images on the latent image carrier and the state of uneven toner density. Note that an arrow A in the figure indicates the direction in which the two-component developer is conveyed by the second conveying screw 11. In the figure, an arrow C indicates the direction of surface movement of the latent image carrier.

  The upper part of the figure shows three image patterns formed on the recording material. The lower part of the figure shows the toner density sensor without replenishing toner for the two-component developer after developing the latent image corresponding to each image pattern using the two-component developer in a state where there is no toner density unevenness. 6 is a graph showing a measurement result (consumption waveform) when the toner density is measured by the method of FIG.

  As shown in the figure, it can be seen that the consumption waveform, that is, the state of toner density unevenness varies depending on the uneven distribution of the latent image on the latent image carrier. In addition, when the image pattern drawn on the left in the figure is compared with the image pattern drawn on the right in the figure, the latter has a broader consumption waveform than the former. This is because the latter has a longer developer conveyance distance from the position where the toner-consumed two-component developer part is returned to the developer circulation conveyance path to the measurement point B by the toner density sensor, and the agitation by the conveyance screw is increased. It is a difference by receiving. That is, in the latter case, the toner density is more uneven than the former because the two-component developer that has consumed the toner is more agitated by the conveying screw until it is conveyed to the measurement location B of the toner concentration sensor. As a result of canceling the part, the consumption waveform becomes broad.

  FIG. 34 is an explanatory diagram showing in more detail the relationship between the position of the latent image on the latent image carrier and the state of toner density unevenness.

  The figure shows three image patterns in which latent images are formed at three different positions in the transport direction of the two-component developer by the second transport screw 11 and two different positions in the latent image carrier surface movement direction. Two image patterns in which a latent image is formed are drawn. Note that some image patterns overlap. In addition, the image area is the same for all image patterns.

  In the lower part of the figure, the latent image corresponding to each of the three image patterns is developed using a two-component developer in a state where there is no toner density unevenness, and then the toner density sensor does not supply toner. It is a graph which shows the measurement result (consumption waveform) when measuring the toner density of a component developer. Further, the left part of the figure shows the latent image corresponding to each of the two image patterns developed by using the two-component developer without toner density unevenness, and then the toner density sensor does not supply the toner. It is a graph which shows the measurement result (consumption waveform) when measuring the toner density of a two-component developer.

  When latent images of the same area are formed at different positions in the two-component developer conveying direction by the second conveying screw 11, as shown in the lower part of the figure, the consumption waveform corresponding to each image pattern has its peak time and The half width (broad state) and the minimum toner density are different. As described above, this is due to the difference in the developer conveyance distance from the position where the portion of the two-component developer that has consumed the toner is returned to the developer circulation conveyance path to the measurement location B by the toner density sensor. Specifically, the difference in peak time is simply due to the difference in time until the portion of the two-component developer that has consumed the toner reaches the measurement location B by the toner density sensor. Further, the difference between the half-value width (broad state) and the minimum toner concentration is due to the difference in the amount of stirring received until the portion of the two-component developer that has consumed the toner reaches the measurement position B by the toner concentration sensor. .

  On the other hand, when latent images of the same area are formed at different positions in the surface movement direction of the latent image carrier, as shown in the left part of the figure, the consumption waveform corresponding to each image pattern has only a different peak time. There is no difference in the half width (broad state) and the minimum toner density. This is because each image pattern has the same position where the portion of the two-component developer that has consumed toner is returned to the developer circulation conveyance path, and differs in the developer conveyance distance to the measurement point B by the toner density sensor. Because there is no. Accordingly, there is no difference in the amount of agitation received before reaching the measurement location B by the toner concentration sensor. That is, no difference occurs in the half width (broad state) and the minimum toner density. However, since the time when the two-component developer that has consumed the toner is returned to the developer circulation conveyance path is different, the peak time is different.

  As described above, the consumption waveform varies depending not only on the size of the latent image on the latent image carrier but also on the position of the latent image, and thus does not become constant in actual image formation. Therefore, the conventional replenishment method can maintain the average toner concentration of the entire two-component developer existing in the developing device at the target toner concentration, but cannot eliminate the uneven toner concentration of the two-component developer. .

  Patent Document 1 discloses a toner that suppresses toner density unevenness in a developing device by a histogram analysis of the density distribution of image data and a configuration in which the replenishment amount can be controlled independently from a plurality of toner replenishment ports based on the analysis result. A replenishment method has been proposed. According to this method, it is possible to eliminate toner density unevenness of the two-component developer.

  Further, in Japanese Patent Laid-Open No. 2004-260688, image density is divided into a finite number of sections, and toner density unevenness in the developing device is configured by supplying toner from a toner replenishing unit corresponding to each section based on the number of dots in each section. A toner replenishing method that suppresses toner is proposed.

  However, the toner replenishing method described in Patent Document 1 requires a configuration in which the replenishing amounts can be controlled independently from each other from a plurality of toner replenishing ports in order to eliminate toner density unevenness. Specifically, the embodiment of Patent Document 1 employs a configuration in which the replenishment amount can be controlled simultaneously from the six toner replenishing ports independently of each other. The toner density unevenness cannot be solved without a configuration capable of performing independent replenishment control at the same time.

  In order to simultaneously perform independent replenishment control for each of the plurality of toner replenishing ports, a drive source for driving a toner replenishing member for replenishing toner from each toner replenishing port is individually provided for each toner replenishing port. Necessary. For this reason, compared to a conventional general apparatus having only one drive source for supplying toner, a space for arranging a plurality of drive sources is required. There is a problem that the cost increases due to the cost of parts.

  Note that the toner replenishing method of Patent Document 2 also requires the same control as that of Patent Document 1 because it is necessary to control a plurality of toner replenishing ports independently.

  The present invention has been made in view of the above, and provides an image forming apparatus and an image forming method capable of eliminating toner density unevenness of a two-component developer without increasing the size and cost of the apparatus. The purpose is to do.

In order to solve the above-described problems and achieve the object, the present invention provides a latent image forming unit that forms a latent image by irradiating a light beam corresponding to image information onto a rotating or moving image carrier, and a toner. A conveying unit that circulates and conveys a two-component developer including a carrier and a carrier on a conveying path; a toner replenishing unit that can replenish toner to the two-component developer at a predetermined replenishment location on the conveying path; A developing unit that develops the latent image formed on the image carrier with the two-component developer, an acquisition unit that acquires the image information in units obtained by dividing the image information at least in the main scanning direction, and the image information. By performing a filter operation, it is possible to calculate a toner replenishment amount that eliminates a temporal change in the toner concentration of the two-component developer at a specific location on the transport path by developing a latent image according to the image information. Such a first filter means, from the first filter means to said image information, and a second filter means capable of calculating the toner supply amount by performing high precision filter operation to eliminate the time change, the main scanning direction The toner replenishment amount is calculated using the first filter means for the division unit corresponding to the upstream side of the replenishment location of the transport path as the starting point, and the position in the main scanning direction is the transport position. A replenishment amount calculating means for calculating the toner replenishment amount using the second filter means for the divided unit corresponding to the downstream side starting from the replenishment location of the road; and the toner of the calculated toner replenishment amount And a replenishment control means for controlling the toner replenishing means so that the toner is replenished at the replenishment location.

The present invention also provides a latent image forming means for forming a latent image by irradiating a rotating or moving image carrier with a light beam according to image information, and a two-component developer including a toner and a carrier on a conveyance path. A conveying unit that circulates and conveys the toner, a toner replenishing unit that can replenish toner to the two-component developer at a predetermined replenishment location on the conveying path, and a latent image formed on the image carrier. Developing means for developing with a two-component developer, and toner of the two-component developer at a specific location on the conveyance path by developing a latent image according to the image information by performing a filter operation on the image information A first filter means capable of calculating a toner replenishment amount that eliminates a change in density with time, and a filter operation with higher accuracy to eliminate the time change than the first filter means on the image information. An image forming method implemented by an image forming apparatus including a second filter means can be calculated, the the toner supply amount, acquisition means, the image division unit that the image information is divided in at least the main scanning direction An acquisition step for acquiring information; and a replenishment amount calculating means , wherein the first filter means is applied to the division unit corresponding to the upstream side where the position in the main scanning direction starts from the replenishment location of the transport path. The toner replenishment amount is calculated using the second filter means for the division unit corresponding to the downstream side where the position in the main scanning direction starts from the replenishment location of the transport path. A replenishment amount calculating step for calculating an amount, and a replenishment control step for controlling the toner replenishing unit so that the replenishment control unit replenishes the calculated toner replenishment amount of toner at the replenishment location; Characterized in that it comprises a.

  According to the present invention, a toner replenishment operation that eliminates a change in toner density over time is determined using a filter that outputs a waveform that indicates a toner replenishment amount according to image information, and toner replenishment is performed using the determined toner replenishment operation. The amount can be controlled. For this reason, there is an effect that the toner density unevenness of the two-component developer can be eliminated without increasing the size and cost of the apparatus.

FIG. 1 is a schematic configuration diagram illustrating a printer according to the first embodiment. FIG. 2 is a schematic diagram showing the configuration of the process unit. FIG. 3 is a perspective view showing an appearance of the process unit. FIG. 4 is an explanatory diagram showing the configuration of the developing unit around the developer circulation conveyance path. FIG. 5 is a functional block diagram of a mechanism that performs toner supply control. FIG. 6 is a diagram illustrating a flow of image information acquired by the image information acquisition unit. FIG. 7 is a block diagram illustrating a detailed configuration of the scanner correction unit. FIG. 8 is a block diagram illustrating a detailed configuration of the printer correction unit. FIG. 9 is a diagram illustrating an example of the image information acquisition area. FIG. 10 is a diagram illustrating an example of the image information acquisition area. FIG. 11 is a graph illustrating a supply basic pattern of the toner supply device according to the first exemplary embodiment. FIG. 12 is a graph showing the relationship between the basic consumption waveform and the basic supply waveform. FIG. 13 is a graph showing the relationship between the arbitrary consumption waveform K and the replenishment waveform. FIG. 14 is a diagram illustrating an example of the image information acquisition area. FIG. 15 is a block diagram illustrating a configuration of a modified printer correction unit. FIG. 16 is a functional block diagram of a mechanism that performs toner supply control according to the second embodiment. FIG. 17 is a diagram illustrating the relationship between the divided areas, the toner supply waveform, and the consumption waveform. FIG. 18 is an explanatory diagram showing the relationship between the antiphase filter and other waveforms. FIG. 19 is an explanatory diagram showing the relationship between the anti-phase filter (supplement signal), the supplement waveform, and the anti-phase waveform. FIG. 20 is an explanatory diagram showing image information and antiphase filters for consumption waveforms for each region in the main scanning direction. FIG. 21 is a diagram illustrating an example of the relationship between the control sampling period and the pseudo impulse signal. FIG. 22 is an explanatory diagram when the replenishment amount is calculated from the image information using the antiphase filter. FIG. 23 is a diagram illustrating the relationship between the supply waveform and the consumption waveform. FIG. 24 is a diagram illustrating an example of the impulse response of the antiphase filter with respect to the consumption waveform. FIG. 25 is a diagram illustrating an example of the impulse response of the antiphase filter with respect to the consumption waveform. FIG. 26 is a diagram illustrating an example of the impulse response of the antiphase filter with respect to the consumption waveform. FIG. 27 is a diagram illustrating an example of the impulse response of the antiphase filter with respect to the consumption waveform. FIG. 28 is a diagram illustrating an example of a result of superposing the consumption waveform and the supply waveform. FIG. 29 is a diagram illustrating an example of the result of superposing the consumption waveform and the supply waveform. FIG. 30 is an explanatory diagram showing an example of a developing device that circulates and conveys the two-component developer along the developer circulation and conveyance path. FIG. 31 is a graph showing the relationship between toner replenishment and toner density unevenness when toner is replenished to the two-component developer. FIG. 32 is a graph showing the relationship between toner replenishment and toner density unevenness when toner is replenished to the two-component developer intermittently at regular intervals. FIG. 33 is an explanatory diagram showing the relationship between the uneven distribution of latent images on the latent image carrier and the state of uneven toner density. FIG. 34 is an explanatory diagram showing in more detail the relationship between the position of the latent image on the latent image carrier and the state of toner density unevenness.

  Exemplary embodiments of an image forming apparatus according to the present invention will be explained below in detail with reference to the accompanying drawings.

(Embodiment 1)
Hereinafter, an embodiment (hereinafter, this embodiment is referred to as “embodiment 1”) in which the present invention is applied to an electrophotographic printer (hereinafter simply referred to as “printer”) as an image forming apparatus will be described. .

  First, the basic configuration of the printer according to the first embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a printer according to the first embodiment.

  The printer includes four process units 1Y, 1C, 1M, and 1K for yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K). These use Y, C, M, and K toners of different colors as image forming substances for forming an image, but the other configurations are the same.

  FIG. 2 is a schematic diagram showing a configuration of a process unit 1Y for generating a Y toner image. FIG. 3 is a perspective view showing an appearance of the process unit 1Y. The process unit 1Y includes a photoreceptor unit 2Y and a developing unit 7Y. As shown in FIG. 3, the photoconductor unit 2Y and the developing unit 7Y are configured to be detachably attached to the printer body as a process unit 1Y. However, the developing unit 7Y can be attached to and detached from the photoreceptor unit 2Y in a state where it is detached from the printer body.

  The photoreceptor unit 2Y includes a drum-shaped photoreceptor 3Y as a latent image carrier, a drum cleaning device 4Y, a static eliminator (not shown), a charging device 5Y, and the like. The charging device 5Y, which is a charging unit, uniformly charges the surface of the photoreceptor 3Y, which is driven to rotate clockwise in FIG. 2 by a driving unit (not shown), by the charging roller 6Y. Specifically, a charging bias is applied from a power source (not shown) to the charging roller 6Y that is driven to rotate counterclockwise in FIG. 2, and the charging roller 6Y is brought close to or in contact with the photosensitive member 3Y, whereby the photosensitive member 3Y. Is uniformly charged. Instead of the charging roller 6Y, another charging member such as a charging brush may be used in proximity or contact. Further, a charger that uniformly charges the photosensitive member 3Y by a charger method, such as a scorotron charger, may be used. The surface of the photoreceptor 3Y uniformly charged by the charging device 5Y is exposed and scanned by a laser beam emitted from an optical writing unit 20 serving as a latent image forming unit, which will be described later, and carries an electrostatic latent image for Y.

  FIG. 4 is an explanatory diagram showing the configuration of the developing unit around the developer circulation conveyance path in which the two-component developer circulates in the developing unit. As shown in FIGS. 2 and 4, the developing unit 7 </ b> Y that is a developing unit includes a first agent containing portion 9 </ b> Y in which a first conveying screw 8 </ b> Y as a developer conveying unit is disposed. Further, it also has a second agent storage portion 14Y in which a second conveying screw 11Y as a developer conveying means, a developing roll 12Y as a developer carrying member, a doctor blade 13Y as a developer regulating member, and the like are disposed. . In these two agent storage portions, a Y developer (not shown) which is a two-component developer composed of a magnetic carrier and a negatively chargeable Y toner is included. The first transport screw 8Y is rotationally driven by a driving unit (not shown) to transport the Y developer in the first agent storage portion 9Y to the front side in FIG. 2 (in the direction of arrow A in FIG. 4). Then, the Y developer conveyed to the end of the first agent accommodating portion 9Y by the first conveying screw 8Y enters the second agent accommodating portion 14Y through the communication port 18Y.

  The second conveying screw 11Y in the second agent accommodating portion 14Y is rotationally driven by a driving means (not shown) to convey the Y developer in the rear side in FIG. 2 (in the direction of arrow A in FIG. 4). In this way, the developing roll 12Y is arranged in a posture parallel to the second conveying screw 11Y above the second conveying screw 11Y that conveys the Y developer in FIG. The developing roll 12Y includes a magnet roller 16Y fixedly disposed in a developing sleeve 15Y made of a non-magnetic sleeve that is driven to rotate counterclockwise in FIG. A part of the Y developer conveyed by the second conveying screw 11Y is pumped up to the surface of the developing sleeve 15Y by the magnetic force generated by the magnet roller 16Y. Then, after the layer thickness is regulated by a doctor blade 13Y disposed so as to maintain a predetermined gap from the surface of the developing sleeve 15Y, the layer is conveyed to a developing region facing the photosensitive member 3Y, and is transferred onto the photosensitive member 3Y. Y toner is adhered to the electrostatic latent image for Y. This adhesion forms a Y toner image on the photoreceptor 3Y. The Y developer that has consumed Y toner by the development is returned onto the second conveying screw 11Y as the developing sleeve 15Y rotates. Then, the Y developer conveyed to the end of the second agent accommodating portion 14Y by the second conveying screw 11Y returns to the first agent accommodating portion 9Y through the communication port 19Y. In this way, the Y developer is circulated and conveyed in the developing unit.

  Here, an outline of toner replenishment control for replenishing consumed toner will be described. FIG. 5 is a functional block diagram of a mechanism that performs toner supply control. In the first embodiment, the control unit 100 is provided with an image information acquisition unit 103 as an image information acquisition unit that acquires image data (image information) from a personal computer or an image reading apparatus. The image information acquisition unit 103 sends the acquired image information to the prediction data calculation unit 101 as a prediction data calculation unit. The prediction data calculation unit 101 calculates, from the received image information, a change in toner density over time (prediction data) at the measurement location B generated in the developer that has consumed toner by developing a latent image based on the image information. .

  In the first embodiment, image information is input from a personal computer or an image reading apparatus, and prediction data is calculated based on the image information. The number of laser beams (number of dots) emitted from the optical writing unit 20 is calculated. ) May be used as image information, and prediction data may be calculated based on the image information.

  The replenishment control unit 102 functioning as a replenishment control unit is one of the toner replenishing devices 70 as toner replenishing units based on the prediction data calculated by the prediction data calculation unit 101 of the control unit 100 functioning as a prediction data calculation unit. The drive source 71Y is controlled. Here, based on the image information, the prediction data calculation unit 101 calculates prediction data of the temporal change in the Y developer toner concentration at the measurement location B using a calculation program or calculation table stored in the ROM. Then, the replenishment control unit 102 eliminates toner density unevenness by performing drive control of one drive source 71Y with a combination of various basic replenishment patterns described later based on the prediction data calculated by the prediction data calculation unit 101. . The toner replenishment control in the first embodiment is performed so as to cancel out the toner density unevenness, and details thereof will be described later.

  Next, processing after forming a Y toner image on the photoreceptor 3Y will be further described. The Y toner image formed on the photoreceptor 3Y is intermediately transferred to an intermediate transfer belt 41 that is an intermediate transfer body. The drum cleaning device 4Y of the photoreceptor unit 2Y removes toner remaining on the surface of the photoreceptor 3Y after the intermediate transfer process. As a result, the surface of the photoreceptor 3Y subjected to the cleaning process is neutralized by a neutralizing device (not shown). By this charge removal, the surface of the photoreceptor 3Y is initialized and prepared for the next image formation. Similarly, in the process units 1C, 1M, and 1K for other colors, C toner images, M toner images, and K toner images are formed on the photoreceptors 3C, 3M, and 3K, and the intermediate transfer belt 41 is subjected to intermediate transfer. Is done.

  An optical writing unit 20 is disposed below the process units 1Y, 1C, 1M, and 1K in FIG. The optical writing unit 20 irradiates the photoconductors 3Y, 3C, 3M, and 3K of the process units 1Y, 1C, 1M, and 1K with the laser light L emitted based on the image information. As a result, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 3Y, 3C, 3M, and 3K, respectively. The optical writing unit 20 deflects the laser light L emitted from the light source by the polygon mirror 21 that is rotationally driven by a motor, and passes through the photoreceptors 3Y, 3C, 3M, and 3K via a plurality of optical lenses and mirrors. Is irradiated. Instead of such a configuration, an LED array may be used.

  A first paper feed cassette 31 and a second paper feed cassette 32 are disposed below the optical writing unit 20 so as to overlap in the vertical direction. In each of these paper feed cassettes, a plurality of recording papers P, which are recording materials, are stored in a stack of recording papers, and a first paper feed roller is placed on the top recording paper P. 31a and the second paper feed roller 32a are in contact with each other. When the first paper feed roller 31a is driven to rotate counterclockwise in FIG. 1 by driving means (not shown), the uppermost recording paper P in the first paper feed cassette 31 is vertically oriented on the right side of the cassette in FIG. The paper is discharged toward the paper feed path 33 arranged so as to extend. When the second paper feed roller 32a is rotated counterclockwise in FIG. 1 by driving means (not shown), the uppermost recording paper P in the second paper feed cassette 32 is discharged toward the paper feed path 33. The A plurality of transport roller pairs 34 are arranged in the paper feed path 33, and the recording paper P fed into the paper feed path 33 is sandwiched between the rollers of the transport roller pair 34 while being fed between the paper feed paths 33. 1 is conveyed from the lower side to the upper side in FIG. A registration roller pair 35 is disposed at the end of the paper feed path 33. The registration roller pair 35 temporarily stops the rotation of both rollers as soon as the recording paper P sent from the conveyance roller pair 34 is sandwiched between the rollers. Then, the recording paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.

Above each process unit 1Y, 1C, 1M, and 1K in FIG. 1, a transfer unit 40 is disposed to endlessly move the intermediate transfer belt 41 counterclockwise in FIG. In addition to the intermediate transfer belt 41, the transfer unit 40 includes a belt cleaning unit 42, a first bracket 43, a second bracket 44, and the like. Also provided are four primary transfer rollers 45Y, 45C, 45M, 45K, a secondary transfer backup roller 46, a drive roller 47, an auxiliary roller 48, a tension roller 49, and the like. The intermediate transfer belt 41 is endlessly moved counterclockwise in FIG. 1 by the rotational driving of the driving roller 47 while being stretched around these rollers. The four primary transfer rollers 45Y, 45C, 45M, and 45K sandwich the intermediate transfer belt 41 that moves endlessly between the photoreceptors 3Y, 3C, 3M, and 3K to form primary transfer nips, respectively. Yes. Then, a transfer bias having a polarity opposite to that of the toner (plus polarity in the first embodiment) is applied to the inner peripheral surface of the intermediate transfer belt 41. The intermediate transfer belt 41 is
In the process of sequentially passing through the primary transfer nips for Y, C, M, and K along with the endless movement, the respective color toner images on the photoreceptors 3Y, 3C, 3M, and 3K are formed on the outer peripheral surface. Primary transfer is performed so as to overlap. As a result, a four-color superimposed toner image (hereinafter referred to as “four-color toner image”) is formed on the intermediate transfer belt 41.

  The secondary transfer backup roller 46 sandwiches the intermediate transfer belt 41 with the secondary transfer roller 50 disposed outside the loop of the intermediate transfer belt 41 to form a secondary transfer nip. The registration roller pair 35 described above feeds the recording paper P sandwiched between the rollers toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 41. The four-color toner image on the intermediate transfer belt 41 is affected by the secondary transfer electric field formed between the secondary transfer roller 50 to which the secondary transfer bias is applied and the secondary transfer backup roller 46, and the influence of the nip pressure. The secondary transfer is batch-transferred onto the recording paper P in the secondary transfer nip. Then, combined with the white color of the recording paper P, a full color toner image is obtained.

  Untransferred toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 41 after passing through the secondary transfer nip. This is cleaned by the belt cleaning unit 42. In the belt cleaning unit 42, the cleaning blade 42a is brought into contact with the front surface of the intermediate transfer belt 41, whereby the transfer residual toner on the belt is scraped off and removed.

  The first bracket 43 of the transfer unit 40 swings at a predetermined rotation angle about the rotation axis of the auxiliary roller 48 as the solenoid (not shown) is turned on / off. In the case of forming a monochrome image, the printer of the first embodiment rotates the first bracket 43 a little counterclockwise in the drawing by driving the solenoid described above. By this rotation, the Y, C, and M primary transfer rollers 45Y, 45C, and 45M are revolved counterclockwise in the drawing around the rotation axis of the auxiliary roller 48, whereby the intermediate transfer belt 41 is moved to the Y direction. , C and M photoconductors 3Y, 3C and 3M. Of the four process units 1Y, 1C, 1M, and 1K, only the K process unit 1K is driven to form a monochrome image. Accordingly, it is possible to avoid exhaustion of the process units due to wastefully driving the process units for Y, C, and M during monochrome image formation.

  A fixing unit 60 as a fixing unit is disposed above the secondary transfer nip in the figure. The fixing unit 60 includes a pressure heating roller 61 that includes a heat source such as a halogen lamp, and a fixing belt unit 62. The fixing belt unit 62 includes a fixing belt 64, a heating roller 63 containing a heat source such as a halogen lamp, a tension roller 65, a driving roller 66, a temperature sensor (not shown), and the like. Then, the endless fixing belt 64 is endlessly moved in the counterclockwise direction in FIG. 1 while being stretched by the heating roller 63, the tension roller 65, and the driving roller 66. In the process of endless movement, the fixing belt 64 is heated from the back side by the heating roller 63. A pressure heating roller 61 that is driven to rotate in the clockwise direction in FIG. 1 is in contact with the surface of the fixing belt 64 that is heated in this manner. Thereby, a fixing nip where the pressure heating roller 61 and the fixing belt 64 abut is formed.

  Outside the loop of the fixing belt 64, a temperature sensor (not shown) is disposed so as to face the front surface of the fixing belt 64 with a predetermined gap, and the fixing belt 64 just before entering the fixing nip. Detect surface temperature. This detection result is sent to a fixing power supply circuit (not shown). The fixing power supply circuit performs on / off control of power supply to the heat generation source included in the heating roller 63 and the heat generation source included in the pressure heating roller 61 based on the detection result of the temperature sensor. As a result, the surface temperature of the fixing belt 64 is maintained at about 140.degree. The recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 41 and then fed into the fixing unit 60. Then, in the process of being conveyed from the lower side to the upper side in the drawing while being sandwiched by the fixing nip in the fixing unit 60, the full-color toner image is applied to the recording paper P by being heated or pressed by the fixing belt 64. To settle.

  The recording paper P subjected to the fixing process in this manner is discharged outside the apparatus after passing between the rollers of the paper discharge roller pair 67. A stack unit 68 is formed on the upper surface of the housing of the printer main body, and the recording paper P discharged to the outside by the discharge roller pair 67 is sequentially stacked on the stack unit 68.

  Above the transfer unit 40, toner cartridges 72Y, 72C, 72M, and 72K, which are four toner containers that respectively store Y toner, C toner, M toner, and K toner, are disposed. The color toners in the toner cartridges 72Y, 72C, 72M, and 72K are appropriately supplied to the developing units 7Y, 7C, 7M, and 7K of the process units 1Y, 1C, 1M, and 1K by the toner replenishing device 70, respectively. The toner cartridges 72Y, 72C, 72M, and 72K are detachable from the printer main body independently of the process units 1Y, 1C, 1M, and 1K.

  Next, details of the image information acquired by the image information acquisition unit 103 will be described with reference to FIG. For convenience of explanation, FIG. 5 shows the flow of image information when the image forming apparatus is realized as an MFP including a copy function, a scanner function, and the like in addition to a printer function. First, a copy image flow will be described.

  When reading a document, a reading unit 611 in the engine unit 610 reads image information from the set document. Then, the reading unit 611 sends image information read as data separated into RGB colors to the scanner correction unit 612. The engine controller 616 controls processing of each component in the engine unit 610.

  FIG. 7 is a block diagram illustrating a detailed configuration of the scanner correction unit 612. As shown in the figure, the scanner correction unit 612 includes a scanner γ processing unit 612a that performs scanner gamma correction, a filter processing unit 612b that performs filter processing, a scaling processing unit 612c that performs scaling processing, and color correction processing. A color correction processing unit 612d. With these processes, RGB color signals (image information) are converted into CMYK color signals (image information).

  Returning to FIG. 6, the color data (image information) of CMYK 8 bits (4 × 8 bits) for each color after scaling is converted into n bits (n ≦ 8) for each color by a color multivalue data compressor 613 that compresses the data to a fixed length. It is converted into color data (image information).

  The CMYK image information compressed by the color multi-value data compressor 613 is sent to the printer controller 604 through the general-purpose bus 620. The printer controller 604 has an independent semiconductor memory 605 for each color, and stores sent image information.

  The stored image information is written to a hard disk (HDD) 606 as needed. This is for avoiding rereading the original again or performing electronic sorting even when the paper is clogged at the time of printout, that is, when the printing has not ended normally. Further, the read original may be stored in the hard disk 606 and re-output when necessary.

  When outputting image information, the image information in the hard disk 606 is once expanded in the semiconductor memory 605 and then sent to the engine unit 610 through the general-purpose bus 620. The sent image information is converted again into CMYK 8-bit image information by a color multi-value data decompressor 614 that decompresses the image at a fixed length in the engine unit 610. Then, the converted image information is sent to the printer correction unit 615.

  FIG. 8 is a block diagram illustrating a detailed configuration of the printer correction unit 615. As shown in the figure, the printer correction unit 615 performs a printer gamma correction unit 615a that performs printer gamma correction on each color of CMYK and halftone processing according to the characteristics of the process units 1Y, 1C, 1M, and 1K. A halftone processing unit 615b. The image information subjected to the halftone processing is modulated into laser light by the optical writing unit 20 and output to the transfer paper.

  The above is the case of copy processing. In the case of printer processing, the printer controller 604 directly draws a bitmap image (image information) on the semiconductor memory 605. Image information, which is bitmap data, passes through the general-purpose bus 620 and is directly sent to the optical writing unit 20 for printing without passing through the color multilevel data decompressor 614 and the printer correction unit 615.

  The image information of CMYK 2 bits × 4 channels before being sent to the optical writing unit 20 is sent to the image information acquisition unit 103. In this way, the image information acquisition unit 103 acquires image information after gradation processing. The number of bits of the image information after gradation processing is reduced in accordance with the capability of the image forming engine. For this reason, the amount of calculation when counting image information is small.

  The image information acquisition unit 103 divides the range of at least one of the effective range of image information in the main scanning direction (main scanning effective range) and the effective range of image information in the sub scanning direction (sub scanning effective range). Image information is acquired for each region. FIG. 9 is a diagram illustrating an example of the image information acquisition area.

  As shown in the figure, the image information is transmitted in parallel with the image information by a signal XLGATE indicating the main scanning effective range, a signal XFGATE indicating (sub-scanning effective range), and a pixel clock (not shown). It has been. For example, by counting the pixel clock after each signal is asserted, it is possible to specify which part of the pixel on the two-dimensional plane (the image information acquisition region in the figure) is being sent.

  Note that the size of the area into which the image information acquisition area is divided is limited by the resolution of the sensor, the influence of noise, or the minute amount replenishment performance of the toner replenishing device 70 as will be described later, but depends on the size of the output image. It is not a thing. For this reason, as shown in FIG. 10, the size of the divided area is always constant regardless of the size of the transfer paper at the time of printing. As a result, it is possible to obtain the maximum effect for stabilizing the toner density while suppressing the calculation amount.

  The image information acquisition unit 103 passes the image information of each region to the prediction data calculation unit 101 when XFGATE is negated. When the transfer speed of the developer in the developing unit is slow and the length of the transfer paper in the sub-scanning direction is short, the toner amount to be replenished after XFGATE is negated is calculated, and the toner replenishing device 70 Even if the toner is replenished by this, the replenishment can be performed in time for the next toner consumption. The details of the toner supply amount calculation method will be described later.

  Next, a basic supply pattern used when the supply control unit 102 controls the drive source 71 will be described. The basic replenishment pattern can be obtained by conducting an experiment or the like in advance. Hereinafter, a specific procedure for creating a basic supply pattern will be described.

  First, a toner concentration sensor for detecting the toner concentration of the Y developer passing through the measurement point B (see FIG. 4) located downstream of the toner supply port 17Y in the first agent storage unit 9Y in the developer circulation direction is disposed. To do.

  First, a basic pattern of toner supply operation by the toner supply device 70 (hereinafter referred to as “replenishment basic pattern”) is measured. FIG. 11 is a graph showing a basic supply pattern of the toner supply device 70 according to the first exemplary embodiment.

  The waveforms H1, H2, H3, H4, and H5 indicate the amount of toner that is replenished by a single drive operation of the drive source 71Y (hereinafter referred to as “replenishment operation”) for the Y developer in a state where there is no toner density unevenness. (Hereinafter referred to as “unit replenishment amount”) A waveform (hereinafter ““ unit replenishment amount ”) indicating a result of detecting a change in toner density over time at a measurement location B by a toner density sensor when toner replenishment is performed with five different replenishment patterns. It is called “Replenishment basic waveform”. The unit replenishment amount increases in the order of the replenishment basic waveforms H1, H2, H3, H4, and H5. The unit replenishment amount can be varied by changing the drive time and drive speed of the drive source 71Y in one replenishment operation.

  Next, the surface of the photoreceptor 3Y is divided into a plurality of regions in a direction orthogonal to the direction of movement of the photoreceptor surface (hereinafter referred to as “photoreceptor axial direction”), and each region has a unit area for toner density detection. The Y developer after forming each corresponding latent image of the same unit image and developing each latent image using the Y developer in a state where there is no toner density unevenness is measured at the location B without toner replenishment. The toner concentration sensor measures the change in toner concentration over time (basic consumption waveform). As a unit area for toner density detection when obtaining a basic consumption waveform, one dot area of image information is ideal, but in reality, the influence of sensor resolution and noise or a minute amount of the toner replenishing device 70 Since it is limited by the replenishment performance or the like, it is preferable to determine a unit area for toner density detection that can be set as small as possible in consideration of these. Further, the division interval when the surface of the photoreceptor 3Y is divided into a plurality of regions as described above is appropriately set according to the unit area for toner density detection. The basic consumption waveform measured in this way is as shown in the graph shown in the lower part of FIG. However, only the two regions located at both ends and the one region located at the center of the plurality of regions described above are depicted in the lower graph of FIG.

  In the graph shown in the lower part of FIG. 30, when the basic consumption waveforms of three latent images having different positions on the surface of the photosensitive member in the axial direction of the photosensitive member are compared with each other, the half width (broad state) and the minimum toner density are different from each other. ing. This is because the Y developer portion that has developed the latent image and consumed the toner is different in distance from the position where the Y developer portion is returned to the developer circulation conveyance path to the measurement location B, so that the returned Y developer is measured at the measurement location B. This is because the amount of agitation received from the first conveying screw 8Y is different while being conveyed.

  As described above, the consumption waveform after developing the latent images formed at different positions in the direction of movement of the surface of the photosensitive member has a full width at half maximum (broad state) and a minimum toner density, as the peak time is different. There is no difference. Therefore, if the basic consumption waveform for the latent images formed at the same position in the photoconductor axis direction is grasped, the consumption waveforms for the latent images formed at different positions in the photosensitive body surface movement direction It can be obtained simply by advancing or delaying the phase of the waveform by a predetermined time. Therefore, it is only necessary to measure each basic consumption waveform for the latent image of the unit image in each region obtained by dividing the surface of the photosensitive member 3Y in the photosensitive member axial direction, and the latent image formed at all positions on the photosensitive member 3Y. The consumption waveform can be grasped.

  Next, a basic replenishment waveform for canceling toner density unevenness due to each basic consumption waveform Kn is obtained. FIG. 12 is a graph showing a certain basic consumption waveform Kn and a basic supply waveform Jn ′ that cancels toner density unevenness due to the basic consumption waveform Kn.

  From the basic consumption waveform Kn and each supply basic waveform H1, H2, H3, H4, and H5, a waveform that cancels the basic consumption waveform Kn is created by combining each supply basic waveform H1, H2, H3, H4, and H5. The waveform is obtained as a basic supply waveform Jn ′. By performing the toner replenishment operation so as to obtain the basic replenishment waveform Jn ′ thus obtained, the toner density unevenness due to the development of the latent image corresponding to the basic consumption waveform Kn is eliminated at least at the measurement location B. be able to. Each toner supply pattern (toner supply amount control pattern) corresponding to each combination of the supply basic waveforms H1, H2, H3, H4, and H5 constituting each basic supply waveform Jn 'becomes each basic supply pattern.

  Next, specific contents of toner replenishment control in the first exemplary embodiment will be described. FIG. 13 is a graph showing an arbitrary consumption waveform K when an arbitrary image described in the upper part of the figure is formed, and a replenishment waveform J that cancels toner density unevenness due to the arbitrary consumption waveform K.

  When an arbitrary image is formed during actual image formation, the image information is sent to the prediction data calculation unit 101 of the control unit 100. The predicted data calculation unit 101 decomposes the latent image based on this image information into each position on the photoreceptor 3Y, and obtains a basic consumption waveform Kn corresponding to each separated latent image. A combination of the basic consumption waveforms Kn thus obtained is a waveform (predicted value) that approximates the arbitrary consumption waveform K shown in the figure, that is, a developer that develops a latent image based on the image information. It approximates a consumption waveform indicating a change in toner density over time when passing through the location B.

  Note that the unit image for obtaining the basic consumption waveform Kn is an image in which the pixel value is the maximum at each pixel within the unit area corresponding to the decomposed region. In the first embodiment, as described above, the pixel value takes a value of 2 bits (0 to 3). Therefore, when a pixel whose pixel value is smaller than the maximum value is included in the unit area, it is necessary to change the predicted value accordingly. That is, the prediction data calculation unit 101 first calculates the average value of the pixel values of each pixel in the divided area, and obtains the basic consumption waveform Kn by multiplying the ratio of the calculated average value to the maximum pixel value (for example, 3). The predicted data is calculated by synthesizing the obtained waveforms. Instead of the value obtained by dividing the average pixel value by the maximum pixel value, a value obtained by dividing the number of pixels having a pixel value other than 0 by the total number of pixels in the unit area may be used.

  As described above, the prediction data calculation unit 101 executes a predetermined calculation program, and based on the mechanism described above, the developer that develops the latent image based on the image information passes through the measurement location B based on the image information. A combination of a plurality of basic consumption waveforms Kn that is a decomposition component of the arbitrary consumption waveform K, which is a change in toner density with time, is calculated as prediction data.

  The prediction data (the combination data of a plurality of basic consumption waveforms Kn) calculated by the prediction data calculation unit 101 in this way is sent to the supply control unit 102. The replenishment control unit 102 combines a plurality of basic replenishment waveforms Jn ′ respectively corresponding to these basic consumption waveforms Kn, so that a replenishment waveform that cancels the toner density unevenness indicated by the arbitrary consumption waveform K as shown in FIG. A supply waveform J close to J, that is, a waveform having an opposite phase to the arbitrary consumption waveform K can be created. Therefore, the replenishment control unit 102 obtains a combination of basic replenishment waveforms Jn ′ corresponding to the combination of the plurality of basic consumption waveforms Kn based on the prediction data. Next, by combining various basic supply patterns previously stored in the RAM so as to correspond to the obtained combination of basic supply waveforms Jn ′, a toner supply operation (toner supply pattern) corresponding to the predicted data is performed. decide.

  Similar to the prediction data calculation unit 101, the supply control unit 102 obtains a waveform obtained by multiplying the basic supply waveform Jn ′ by a value obtained by dividing the average pixel value of each pixel in the divided area by the maximum pixel value. The toner replenishment operation is determined by obtaining the toner replenishment pattern in combination.

  Then, the replenishment control unit 102 performs drive control of the drive source 71Y with the determined toner replenishment operation (toner replenishment pattern). Since the replenishment waveform obtained by such a toner replenishment operation is a combination of the basic replenishment waveforms Jn ′ according to the basic replenishment patterns, the replenishment waveform J shown in FIG. Therefore, the toner density unevenness indicated by the arbitrary consumption waveform K is sufficiently eliminated at the measurement location B as shown by the thick solid line in FIG.

  In the first embodiment, as described above, the image information acquisition unit 103 acquires image information in units of divisions corresponding to regions obtained by dividing the image information acquisition region into a plurality of regions. The toner replenishment control as described above can be executed based on each of the divided image information. For this reason, it is possible to calculate the toner replenishment amount with higher accuracy than the method of acquiring image information in a lump without dividing and calculating the toner replenishment amount based on the acquired image information. .

(Modification 1)
In the above-described embodiment, as shown in FIG. 9, the image information is divided in both the main scanning direction and the sub-scanning direction of the image information acquisition region. On the other hand, the image information may be acquired by dividing the region only in the sub-scanning direction. FIG. 14 is a diagram illustrating an example of an image information acquisition region configured as described above. With such a configuration, the number of divisions can be reduced, so that it is possible to reduce the calculation amount for determining the toner replenishment amount.

  In the above-described embodiment, the image information acquisition unit 103 passes the image information of each region to the prediction data calculation unit 101 when XFGATE is negated. On the other hand, the writing may be performed by the optical writing unit 20, and the image information may be transferred to the prediction data calculation unit 101 immediately after the image information of the written part is obtained. FIG. 14 also shows how image information is acquired in such a configuration.

  That is, when the image information acquisition area is divided into four areas 1 to 4 as shown in the figure, when the acquisition of the image information of each area is completed, the image information for each acquired area is calculated as predicted data. Sent to the unit 101.

  With such a configuration, even when the developer advancing speed is high, replenishment of consumed toner can be performed without delay if a predetermined condition is satisfied.

(Modification 2)
In the above-described embodiment, as shown in FIG. 8, image information after gradation processing is output to the image information acquisition unit 103 by the halftone processing unit 615 b in the printer correction unit 615. In contrast, the image information before performing the printer gamma correction may be output to the image information acquisition unit 103. FIG. 15 is a block diagram showing the configuration of the printer correction unit 2015 of the present modification configured as described above. As shown in the figure, in this modification, image information before γ conversion is sent to the image information acquisition unit 103. In the image information before γ conversion, the value of the image information corresponds to the density value of the final image. Since the density value and the toner consumption amount are proportional, by using the image information before γ conversion, the consumed toner amount can be obtained more accurately and an image forming apparatus with a stable density can be obtained.

  As described above, in the image forming apparatus according to the first exemplary embodiment, the prediction data of the temporal change in the toner density generated at the specific location by the development is calculated, and the toner at the predetermined supply location is calculated based on the prediction data. Adjust the replenishment amount. Since the two-component developer circulates in the developer circulation conveyance path, the toner concentration unevenness of the two-component developer can be grasped as a change with time in the toner concentration of the two-component developer passing through a specific location. Then, based on the prediction data, which is a predicted value of the change in toner density over time, the toner supply amount at a predetermined supply point is set so as to eliminate the change in toner concentration over time of the two-component developer passing through the specific part. Since the adjustment is performed, toner density unevenness of the two-component developer at least at a specific location can be eliminated.

  In addition, the control target of the replenishment control unit according to the first exemplary embodiment is one (single) drive source of the toner replenishment unit. For this reason, only one drive source for replenishing toner is required to cancel out the toner density unevenness. Therefore, the problem of the increase in the size of the device and the increase in the cost of the devices described in Patent Documents 1 and 2, which require a plurality of drive sources in order to cancel the toner density unevenness, do not occur.

  In the first embodiment, since the toner replenishment amount can be calculated based on each of the divided image information and the toner replenishment control can be executed, more accurate control can be realized.

(Embodiment 2)
In the second embodiment, the supply waveform is considered in advance as a method for obtaining the same effect as the method of performing the decomposition using the supply waveform on the prediction data calculated by the prediction data calculation unit 101 of the first embodiment as described later. Then, by using an anti-phase filter that indicates the amount of toner replenishment that generates a replenishment waveform that is in reverse phase with respect to the consumption waveform, a control sampling period (replenishment control period) for the replenishment result to be in the reverse phase of the predicted data The replenishment amount for each is calculated directly from the image information.

  FIG. 16 is a functional block diagram of a mechanism that performs toner supply control according to the second embodiment. As shown in the figure, as in the first embodiment, the control unit 2100 is provided with an image information acquisition unit 2103 as an image information acquisition unit that acquires image data (image information) from a personal computer or an image reading apparatus. Yes.

  The replenishment control unit 2102 that functions as the first filter unit, the second filter unit, the replenishment amount calculation unit, and the replenishment amount control unit includes an antiphase filter (not shown) that directly calculates the replenishment amount from the image information. The image information acquisition unit 2103 sends a pseudo impulse signal (described later) corresponding to the acquired image information to the antiphase filter. The antiphase filter generates a replenishment pattern whose replenishment result has an antiphase waveform from the received pseudo impulse signal, and calculates a replenishment amount for each control sampling period based on the replenishment pattern based on the image information. Also in the second embodiment, image information from a personal computer or an image reading apparatus is input and the replenishment amount is calculated based on the image information. However, the number of laser beams (dots) emitted from the optical writing unit 20 (Number) may be used as image information, and the replenishment amount may be calculated based on the image information.

  The antiphase filter can be obtained by conducting an experiment or the like in advance. Hereinafter, a procedure for creating an antiphase filter will be described.

  First, a toner concentration sensor for detecting the toner concentration of the developer passing through the measurement point B (see FIG. 4) located downstream of the toner supply port 17Y in the first agent storage unit 9Y in the developer circulation direction is disposed. . Then, toner is replenished from the toner replenishing port 17Y, and a change in toner concentration with time (a replenishment waveform) is measured by the toner density sensor at the measurement location B. The replenishment waveform measured and measured in this way is as shown in the graph of FIG. In the second embodiment, only one pattern generated when toner is replenished with a typical replenishment amount is measured as a unit replenishment waveform.

  Next, the surface of the photosensitive member 3 is divided into a plurality of regions in a direction orthogonal to the moving direction of the photosensitive member surface (hereinafter referred to as “main scanning direction”), and each region corresponds to a unit area for toner density detection. A latent image of the same unit image is formed. Then, the developer after developing each latent image using a developer in a state where there is no toner density unevenness is a time change (consumption waveform) of the toner density by the toner density sensor at the measurement location B without replenishing the toner. Measure.

  Here, as a unit area for toner density detection when obtaining a consumption waveform, one dot area of image information is ideal. However, it is actually limited by the resolution of the sensor, the influence of noise, or the minute amount replenishment performance of the toner replenishing device 70. Therefore, it is preferable to determine a unit area for toner density detection that can be set as small as possible in consideration of these. For example, when the resolution of the image information is low or the processing speed of the controller is limited, the minimum unit of the unit area is set to the entire printing paper, and the amplitude of the consumption waveform is approximated as the total image area for each printing. You may do it.

  Further, the division interval when the surface of the photoreceptor 3Y is divided into a plurality of regions as described above is appropriately set according to the unit area for toner density detection.

  The consumption waveform measured in this way is like the graph shown in FIG. However, the graph of the consumption waveform depicted in FIG. 7B is only for the region A of the plurality of regions shown in FIG.

  An antiphase filter that satisfies the relationship of FIG. 18 is constructed from the supply waveform and the consumption waveform obtained as described above. The vertical axis of the antiphase filter shown in the figure is a replenishment amount instruction value (toner amount [mg], motor drive time conversion value [msec], etc.) for each control sampling period. The horizontal axis of the antiphase filter is the control sampling period (the interval between bars shown in the antiphase filter graph is one sample period, which is usually a fixed value, for example, 200 [msec]). .

  Here, FIG. 18 will be briefly described with reference to FIG. When consumption of an arbitrary image area ratio is performed once, a pseudo impulse signal corresponding to the image area ratio is given to the antiphase filter. Note that the image area ratio represents the ratio of pixels whose pixel values are not 0 within a unit area. When the pixel value is binary (0 or 1), the image area ratio corresponds to the average value of the pixel values. When the pixel value is multivalued (for example, 0 to 3), a value obtained by dividing the average value of the pixel values by the maximum pixel value may be used instead of the image area ratio. Hereinafter, a case where the image area ratio is used will be described as an example.

  The anti-phase filter creates an impulse response for each control sampling period using this pseudo impulse signal, and creates an anti-phase waveform indicating the replenishment amount according to the amplitude of the impulse response. By replenishing the replenishment amount indicated by the reverse phase waveform, the reverse phase waveform is the reverse phase of the consumption waveform, and thus the consumption waveform is canceled.

  In addition, when a time lag occurs between the consumption waveform and the replenishment waveform, a time delay element may be separately provided before and after the antiphase filter.

  The minimum unit area for each region in the main scanning direction of the image formed on the surface of the photoreceptor 3 in which the main scanning direction is divided into regions A, B, C, and D based on the image information as shown in FIG. When the anti-phase filters A, B, C, and D for the consumption waveforms A, B, C, and D are created by the above-described method, the result is as shown in FIG.

  Here, when the image position or the image area changes, the toner replenishment amount can be obtained by superimposing the output results (basic replenishment amount) of the antiphase filter having the minimum unit area, and an arbitrary antiphase waveform can be created. it can. In other words, when a pseudo impulse signal having an arbitrary amplitude is input at an arbitrary time, the antiphase filter automatically outputs an amplitude proportional to the input amplitude thereafter. The shape and number of anti-phase filters in each region in the main scanning direction is only one. When different pseudo impulse signals are sequentially input to the anti-phase filter, they are automatically proportional to the input amplitude. In addition, an antiphase waveform superimposed with a time lag shift is output.

  When the actual image area ratio is smaller than the minimum unit area, the amplitude of the pseudo impulse signal given to the antiphase filter is multiplied by the image area ratio with respect to the minimum unit area. As a result, the output value of the antiphase filter is automatically changed to the image area ratio times the minimum unit area.

  When there are a plurality of areas divided in the sub-scanning direction during the control sampling period, the image information acquisition unit 2103 adds a value (total value) obtained by adding all the amplitudes corresponding to those areas alone. The amplitude value of the pseudo impulse signal given to the anti-phase filter is assumed to be. FIG. 21 is a diagram illustrating an example of the relationship between the control sampling period and the pseudo impulse signal.

  As shown in the figure, when the amplitudes Skb and Skc corresponding to the image area ratios of the regions having different positions in the sub-scanning direction are obtained during the same control sampling period for the same main scanning direction region, the anti-phase filter is used. The amplitude of the pseudo impulse signal to be given is Skb + Skc. Thus, the replenishment amount for each control sampling period can be calculated without losing image information regardless of the relationship between the control sampling period and the division size in the sub-scanning direction.

  Next, from the image information shown in FIG. 22, an antiphase filter is used to calculate an antiphase waveform having an antiphase with respect to the consumption waveform, and toner is replenished with a replenishment amount based on the calculated antiphase waveform. A case of eliminating the toner density unevenness in B will be described.

  When the user performs printing based on the image information shown in the figure, the image information acquisition unit 2103 at the position of each minimum unit area for each of the regions A, B, C, and D in the main scanning direction on the surface of the photoreceptor 3. An image area ratio is calculated. Then, in consideration of a printing time lag, the image information acquisition unit 2103 gives a pseudo impulse signal having an amplitude corresponding to the image area ratio to each antiphase filter for each region in the main scanning direction. Each anti-phase filter generates an impulse response for each control sampling period by this pseudo impulse signal, and the replenishment result is an anti-phase waveform with respect to the consumption waveform for each region in the main scanning direction instructing the replenishment amount according to the amplitude of the impulse response. The replenishment pattern is calculated. The replenishment amount (basic replenishment amount) for each region in the main scanning direction thus calculated is summed up every control sampling period, and the toner concentration of the developer when toner replenishment is performed when the replenishment result passes the measurement location B. The replenishment amount that is the opposite phase of the time variation prediction data is calculated.

  Note that the replenishment control unit 2102 is configured to calculate a toner replenishment amount by summing values obtained by multiplying the replenishment amount generated by the anti-phase filter by individual weights determined in advance for each region in the main scanning direction. May be. As a result, when the toner consumption for the same image is different from the toner consumption assumed when the antiphase filter is created at a certain rate, the difference can be adjusted for each region in the main scanning direction. It becomes possible.

  The toner replenishing device 70 whose toner replenishment operation is controlled by the replenishment control unit 2102 based on this replenishment amount replenishes toner with a predetermined replenishment amount every control sampling period. Since the waveform obtained by superimposing the anti-phase waveform for each region in the main scanning direction related to the replenishment is the anti-phase waveform of the consumption waveform, the toner replenishing device 70 replenishes the toner according to the replenishment amount, so that the image It is possible to cancel the consumption waveform when printing is performed based on the information. Therefore, the toner density unevenness at the measurement location B can be sufficiently eliminated.

  The antiphase filter can be obtained as, for example, either an FIR filter or an IIR filter. However, there is usually a difference in accuracy and calculation amount as an antiphase filter between them. An example will be shown and described below.

  FIG. 23 is a diagram illustrating the relationship between the supply waveform and the consumption waveform. As shown in FIG. 23, it is assumed that the supply waveform and the consumption waveform 1 and the consumption waveform 2 of the divided regions having different positions are obtained. The divided area means an area obtained by dividing the image information acquisition area into a plurality of areas as shown in FIG. 9, for example.

At this time, anti-phase filters for the respective consumption waveforms are created as FIR filters and IIR filters. The FIR filter and IIR filter calculation are expressed by the following equation (1), where u (t) and y (t) are input and output at time t (n) = nT discretized in the control cycle T, respectively. .
y (t) =
[{B1 + B2 * q ^ -1 +... + Ba * q ^ (-a + 1)} /
{1 + F1 * q ^ −1 + F2 * q ^ −2 +... + Fb * q ^ −b}] ×
u (t−k * T) (1)

  Here, a, b, and k take integer values such that a ≧ 1, b ≧ 0, and k ≧ 0. Further, q is a phase shift operator, and (q ^ -m) f (t) = f (t-m * T) for the function f (t).

  If b = 0 in the equation (1), it is an FIR filter. Further, if a = 2, b = 2, and k = 0 in the expression (1), it is an IIR filter.

  If a, b, and k are given, the filter coefficients B1,..., Ba, F1,. If the anti-phase filter which is an FIR filter and an IIR filter is calculated | required with respect to the consumption waveform 1 and the consumption waveform 2, each impulse response will become like FIG. 24-28, for example. Furthermore, the result of superimposing the response waveform and the consumption waveform with respect to the replenishment signal of these filters is as shown in FIGS. 28 and 29, for example.

  24 and 25 show examples of impulse responses of the FIR and IIR antiphase filters for the consumption waveform 1, respectively. FIG. 26 and FIG. 27 show examples of impulse responses of the FIR and IIR antiphase filters for the consumption waveform 2, respectively. Further, FIGS. 28 and 29 show the results of superposing the consumption waveform 1 and the consumption waveform 2 of FIG. 23 and the supply waveform, respectively.

  For example, for the consumption waveform 2, as shown in FIG. 29, the FIR filter is a more accurate antiphase filter than the IIR filter. However, as shown in FIG. 26, about 40 filter taps are required in this case. This means that about 40 product-sum operations are required for one filter operation. On the other hand, since the IIR filter only requires a + b = 4 product-sum operations, the use of the IIR filter is advantageous in terms of calculation speed when the accuracy of the IIR filter is acceptable.

  The advantages and disadvantages of accuracy and speed of the created FIR filter and IIR filter can be obtained at the time of design. For this reason, switching may be performed so that the filter operation is performed using one of the anti-phase filters of the designed FIR filter and IIR filter in accordance with the requirements of accuracy and speed in actual use.

  Therefore, in the second embodiment, as shown in FIG. 22, two types of anti-phase filters, an IIR filter (first filter means) and an FIR filter (second filter means) are provided, and one of the anti-phase filters is provided. To perform the filter operation. The two types of antiphase filters are not limited to the FIR filter and the IIR filter. A plurality of filters in any combination can be used as long as the plurality of antiphase filters have different accuracy and processing speed. For example, two anti-phase filters of an FIR filter with a limited number of taps and an FIR filter without a limited number of taps may be used. In this case, the former is faster in processing speed than the latter, but is less accurate.

  Note that Num _ * (q) and Den _ * (q) (* = A to D) described in the IIR filter in FIG. 22 represent a numerator coefficient and a denominator coefficient that define the IIR filter, respectively.

  In the present embodiment, an FIR filter and an IIR filter are prepared as anti-phase filters for each position in the main scanning direction of the divided area, and the replenishment control unit 2102 uses any of the anti-phase filters to perform the filter operation. Can be switched independently. This is schematically shown in FIG.

  As illustrated in FIG. 28 and FIG. 29, both the FIR filter and the IIR filter can obtain the accuracy as an antiphase filter due to the difference in the consumption waveform even if the filter is obtained with the same method for the same supply waveform. Usually makes a difference.

  Therefore, for example, the replenishment control unit 2102 performs the calculation using the FIR filter only in the region where the accuracy of the IIR filter is bad, and performs the calculation using the IIR filter otherwise. Thereby, it is possible to ensure the accuracy of the antiphase supply in the entire divided area in the main scanning direction with the minimum necessary amount of calculation. Note that the replenishment control unit 2102 may be configured to switch the filter in accordance with a design guideline with accuracy for each region. For example, if there is a design guideline that emphasizes the accuracy near the center in the main scanning direction, only the divided area near the center in the main scanning direction may be calculated by the FIR filter.

  Further, instead of including the FIR filter and the IIR filter for each of the divided regions, an antiphase filter that is predetermined for each divided region of the FIR filter and the IIR filter may be provided. For example, an optimum antiphase filter may be selected in advance for each position of the divided region in the main scanning direction, and provided as an antiphase filter for the divided region.

(Modification 3)
Normally, the change in toner density due to the consumption of the divided area located downstream of the developer circulation conveyance path in the main scanning direction reaches the measurement point B earlier than the fluctuation of the toner density due to the consumption of the divided area located upstream. To do. For this reason, depending on the configuration of the device, there may be a case where the image information of the divided areas is not obtained in time even if the toner is replenished at the same time. This corresponds to a state in which the fall of the supply waveform is delayed with respect to the rise of the consumption waveform in the divided area as shown in the consumption waveform 1 of FIG.

  In such a case, it is impossible to create an anti-phase filter having no fundamental error. However, in contrast to the IIR filter, the FIR filter can independently control the impulse response at each time and has a high degree of freedom in the antiphase supply pattern that can be generated. It is done. In particular, the difference in accuracy tends to increase when the supply waveform is delayed as described above.

  Therefore, in this modification, the anti-phase filter is switched depending on whether the position of the divided region in the main scanning direction is on the downstream side or the upstream side of the developer circulation conveyance path. For example, an FIR filter is used in the divided area where the position in the main scanning direction is downstream of the developer circulation conveyance path, and an IIR filter is used on the upstream side.

  The boundary between the region using the FIR filter and the region using the IIR filter may be obtained in advance by simulation or the like. For example, for a random image information, a consumption waveform and an antiphase waveform by an IIR filter may be obtained by simulation, and FIR may be used in a region where the matching rate of both falls below a predetermined threshold. Or, more simply, for each of the consumption waveform and the replenishment waveform, calculate the time when the absolute value of the fluctuation is greater than a certain value, and the time calculated for the replenishment waveform is greater than the time calculated for the consumption waveform, If it is not preceded by a predetermined threshold or more, FIR may be used.

  Further, an optimal antiphase filter is selected in advance according to whether the position of the divided region in the main scanning direction is the downstream side or the upstream side of the developer circulation conveyance path, and the selected antiphase filter is You may comprise so that it may provide as an antiphase filter of a division area.

(Modification 4)
In this modification, the FIR filter is used as the anti-phase filter when the image quality is important, and the IIR filter is used when the speed is important. Note that, as in Modification 3, the boundary between the divided region using the FIR filter and the divided region using the IIR filter is determined for each of the cases where the image quality is important and the speed is important. The filter may be switched for each divided region.

  This switching is performed, for example, when the mode that requires high image quality is selected by the user, the image quality is regarded as important, and otherwise the speed is regarded as important.

(Modification 5)
In this modification, the anti-phase filter is switched according to an increase in the color image or monochrome image to be formed. For example, an IIR filter is used if a sufficient time cannot be secured to perform the FIR filter calculation for each plate during color image formation. In addition, since only the K plate needs to be calculated when a monochrome image is formed, if the calculation time can be secured, the K plate is switched to use the FIR filter.

(Modification 6)
When the replenishment control period is shortened, not only the allowable calculation time is shortened, but the order of the FIR filter for expressing a replenishment pattern of the same length of time increases. That is, the order of the FIR filter that is almost inversely proportional to the replenishment control cycle is required. In this modification, the antiphase filter is switched according to the supply control cycle. For example, when the replenishment control cycle becomes short and sufficient time cannot be secured to perform the FIR filter calculation, the IIR filter is switched to use. For example, the replenishment control unit 2102 compares the designated replenishment control cycle with a predetermined threshold, and switches to use the IIR filter when the replenishment control cycle is shorter than the threshold.

  As described above, according to this modification, even when the linear velocity is high and the calculation time is insufficient for the calculation with the FIR filter, the IIR filter is replaced with the anti-phase filter when the calculation with the IIR filter is possible. The toner density fluctuation can be suppressed by replenishing toner in the opposite phase.

(Modification 7)
In the present modification, the anti-phase filter is switched according to the number of divisions in the main scanning direction. In general, the calculation time increases as the number of divisions increases. For example, the FIR filter is used when the number of divisions is smaller than a predetermined threshold, and the IIR filter is switched when the number of divisions is equal to or larger than the predetermined threshold. The division number threshold may be obtained in advance as the division number when the calculation amount when the FIR filter is used exceeds a predetermined threshold related to the calculation amount.

  As described above, according to the present embodiment, it is possible to switch between using the FIR filter and the IIR filter in calculating the replenishment amount in response to the request for speed and accuracy in the toner replenishment control.

1Y, 1C, 1M, 1K Process unit 3Y, 3C, 3M, 3K Photoconductor 7Y, 7C, 7M, 7K Development unit 8Y First transport screw 9Y First agent storage portion 11Y Second transport screw 12Y Developing roll 14Y Second agent Storage unit 17Y Toner supply port 20 Optical writing unit 40 Transfer unit 50 Secondary transfer roller 60 Fixing unit 70 Toner supply device 71Y Drive source 72Y, 72C, 72M, 72K Toner cartridge 100, 2100 Control unit 101 Prediction data calculation unit 102, 2102 Supply control unit 103, 2103 Image information acquisition unit 604 Printer controller 605 Semiconductor memory 606 Hard disk 610 Engine unit 611 Reading unit 612 Scanner correction unit 613 Color multi-value data compressor 614 Color multi-value data Data expander 615, 2015 Printer correction unit 616 Engine controller 620 General-purpose bus

JP-A-11-219015 JP 2006-171177 A

Claims (2)

A latent image forming means for forming a latent image by irradiating a rotating or moving image carrier with a light beam according to image information;
Conveying means for circulating and conveying a two-component developer containing toner and carrier on the conveying path;
Toner supply means capable of supplying toner to the two-component developer at a predetermined supply location on the transport path;
Developing means for developing the latent image formed on the image carrier with the two-component developer;
Acquisition means for acquiring the image information in a division unit obtained by dividing the image information in at least a main scanning direction ;
A toner replenishment amount that eliminates a temporal change in toner concentration of the two-component developer at a specific location on the transport path by developing a latent image corresponding to the image information by performing a filter operation on the image information. First filter means capable of calculating
Second filter means capable of calculating the toner replenishment amount by performing a filter operation with high accuracy to eliminate the time change from the first filter means to the image information;
The toner replenishment amount is calculated using the first filter means for the division unit corresponding to the upstream side where the position in the main scanning direction starts from the replenishment point of the transport path, and the position in the main scanning direction is calculated. Replenishment amount calculating means for calculating the toner replenishment amount using the second filter means for the division unit corresponding to the downstream side starting from the replenishment location of the transport path ;
Replenishment control means for controlling the toner replenishing means to replenish the calculated toner replenishment amount of toner at the replenishment location;
An image forming apparatus comprising: A latent image forming means for forming a latent image by irradiating a light beam according to image information onto a rotating or moving image carrier, and a two-component developer including toner and a carrier are circulated and conveyed on the conveyance path. A toner supply unit capable of supplying toner to the two-component developer at a predetermined supply point on the conveyance path, and a latent image formed on the image carrier is developed by the two-component developer. And developing the latent image according to the image information, thereby eliminating the temporal change in the toner concentration of the two-component developer at a specific location on the transport path by performing a filter operation on the image information. The first filter means capable of calculating the toner replenishment amount, and the toner replenishment amount is calculated by performing a high-accuracy filter operation to eliminate the time change from the first filter means on the image information. A second filter means capable, an image forming method implemented by an image forming apparatus equipped with,
An obtaining unit for obtaining the image information in a division unit obtained by dividing the image information in at least a main scanning direction ;
The replenishment amount calculation means calculates the toner replenishment amount using the first filter means for the division unit corresponding to the upstream side where the position in the main scanning direction starts from the replenishment location of the transport path. And a replenishment amount calculating step of calculating the toner replenishment amount using the second filter means for the division unit corresponding to the downstream side where the position in the main scanning direction starts from the replenishment point of the transport path. When,
A replenishment control step for controlling the toner replenishment means so that the replenishment control means replenishes the calculated toner replenishment amount of toner at the replenishment location;
Image forming method, which comprises a.

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