JP5692643B2 - Image forming apparatus - Google Patents

Description

  The present invention provides an image forming apparatus for a copying machine, a printer, a facsimile machine, or the like that corrects a toner density target value in a developer based on a toner adhesion amount of a test toner image formed at a regular timing during a continuous image forming operation. It relates to the device.

  Conventionally, in an image forming apparatus such as a copying machine, a printer, or a facsimile, a latent image formed on the surface of a latent image carrier such as a photoconductor is developed with a developer containing a magnetic carrier and toner to obtain a toner image. Things are known. In this type of image forming apparatus, it is easy to cause insufficient image density or excessive image density during a continuous image forming operation in which images are continuously formed on a plurality of recording sheets. Specifically, when images with a relatively low image area ratio are output continuously, the amount of toner replenished to the developer due to toner consumption is small despite the developer being stirred for a long time. Therefore, the charge amount of the toner in the developer becomes excessive. Then, since it becomes difficult for the toner particles to be detached from the surface of the magnetic carrier, the transfer of the toner from the developer to the latent image is not performed well, resulting in insufficient image density. In addition, if images with a relatively high image area ratio are output continuously, a large amount of new toner is replenished to the developer in a short time, so the charge amount of the toner in the developer seems to be insufficient. become. Then, since the toner particles easily come off from the surface of the magnetic carrier, a large amount of toner is transferred from the developer to the latent image, resulting in excessive image density.

  Therefore, the image forming apparatus described in Patent Document 1 detects the toner adhesion amount of the test toner image formed at regular timing during the continuous image forming operation, and based on the result, detects the amount of toner in the developer. The density target value is corrected. Specifically, when the toner adhesion amount of the test toner image is smaller than the target adhesion amount, the target density value of the toner in the developer is set higher than before. As a result, by increasing the toner concentration of the developer, excessive charging of the toner in the developer is reduced, and the image density is increased. On the other hand, when the toner adhesion amount of the test toner image is larger than the target adhesion amount, the target density value of the toner in the developer is set lower than before. Thereby, by lowering the toner density of the developer, the charging failure of the toner in the developer is reduced and the image density is lowered. In this way, the image density is stabilized during the continuous image forming operation.

  However, this image forming apparatus has a problem that it is difficult to stabilize the image density with high accuracy because the development density unevenness of the test toner image is caused due to the fluctuation of the development gap. Specifically, in this image forming apparatus, a drum-shaped photoreceptor as a latent image carrier and a developing sleeve as a developer carrier are opposed to each other with a predetermined development gap. Then, the developer carried on the surface of the developing sleeve is conveyed into the developing gap by the rotation of the developing sleeve and brought into contact with the surface of the photosensitive member to develop the latent image on the surface of the photosensitive member. In such a configuration, in the process in which the photosensitive member and the developing sleeve rotate, the developing gap periodically varies due to the eccentricity of the photosensitive member, the eccentricity of the developing sleeve, and the straightness error of the photosensitive member and the developing sleeve. Causes uneven development density of the toner image. Due to the periodic fluctuation of the development gap, when the test toner image is developed at a higher density than the original, the toner adhesion amount of the test toner image becomes larger than the original. Then, the target density value of the toner in the developer is corrected to a value lower than the appropriate value, and the image density is insufficient. In addition, when the test toner image is developed at a lower density than the original, the toner adhesion amount of the test toner image becomes smaller than the original. Then, the target density value of the toner in the developer is corrected to a value higher than the appropriate value, and an excessive image density occurs.

  The present invention has been made in view of the above background, and an object of the present invention is to provide an image forming apparatus capable of correcting the target density value of toner in a developer more appropriately than in the past. It is.

To achieve the above object, a first aspect of the invention, at least a latent image carrier for carrying a latent image on an endless moving surface, comprising a carrying toner and carrier to an endless moving surface of the developer carrying member Developing means for developing a latent image on the latent image carrier with a developer to obtain a toner image, and transfer means for transferring the toner image on the latent image carrier to a recording member directly or via an intermediate transfer member An image forming means having toner density detecting means for detecting the toner density of the developer in the developing means,
A toner replenishing unit that replenishes the developer in the developing unit and brings the detection result of the toner density detecting unit closer to a predetermined density target value; and a continuous image that continuously forms images on a plurality of recording members. Based on the result of forming a test toner image by the imaging means at a regular timing during the forming operation and detecting the toner adhesion amount per unit area of the test toner image by the adhesion amount detection means. In an image forming apparatus including a density target correction unit that corrects a target value, when an image forming operation based on an image forming instruction from a user is not performed, the peripheral length of the latent image carrier and the developer carrier is determined. A long target area determining test toner image is formed by the image forming means, and a plurality of target area determining test toner images in the circumferential direction of the latent image carrier are formed. The lower limit value of the toner adhesion amount of the test toner image formed during the continuous image forming operation and the upper limit value larger than this are determined based on the results of detection of the toner adhesion amount by the adhesion amount detection means. the range determining means is provided, the toner adhering amount of the test toner image is detected by the deposited amount detecting means, only if it does not fit within the target range from the lower limit up to the upper limit value, the density target value The density target correction means is configured to perform the process of correcting the above .
Also, the invention of claim 2, the image forming apparatus according to claim 1, the pre-Symbol target range determined for the test toner image multiple imaging, the deposited toner adhesion amount in their target range determined for the test toner image, respectively The range determination unit is configured to perform a process of determining the lower limit value and the upper limit value based on a result detected by the amount detection unit.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the target range determining test toner is performed prior to performing an image forming operation based on an initial image forming instruction by a user after factory shipment. The range determining means is configured to perform processing for forming an image and determining the lower limit value and the upper limit value.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the target range determination test toner image is created based on the maintenance performed on the imaging means. The range determining means is configured to perform processing for determining the lower limit value and the upper limit value.

  In these inventions, the toner adhesion amount of the test toner image periodically varies due to the periodic variation of the development gap. At this time, if the toner in the developer is not excessively charged or insufficiently charged, the variation is within a predetermined range. In other words, if the toner in the developer is not overcharged or insufficiently charged, the periodic variation in the toner adhesion amount of the test toner image due to the periodic variation in the development gap falls within a predetermined range. is there. By utilizing this, in the present invention, when the toner adhesion amount of the test toner image is within the target range from the predetermined lower limit value to the upper limit value, the developer toner density target value is set. By not correcting the toner density, it is possible to prevent the toner density target value from being inappropriately corrected due to the periodic fluctuation of the development gap. On the other hand, if the toner in the developer is overcharged or insufficiently charged due to continuing to output an image with a low image area ratio or an image with a high image area ratio, toner adhesion to the test toner image The quantity deviates greatly from the target range. In this case, by correcting the target density value of the toner in the developer so that the toner adhesion amount falls within the target range, fluctuations in the image density due to excessive toner charging or insufficient charging are suppressed. As described above, the toner density target value can be corrected more appropriately than in the past.

1 is a schematic configuration diagram showing a copying machine according to a reference embodiment. FIG. 3 is a partially enlarged configuration diagram illustrating an enlarged part of an internal configuration in a printer unit of the copier. FIG. 2 is an enlarged configuration diagram illustrating a process unit for Y in the printer unit. FIG. 2 is a block diagram showing a part of an electric circuit in the copier. FIG. 2 is a perspective view showing a transfer unit of the copier. FIG. 4 is a schematic plan view showing an intermediate transfer belt of the transfer unit and test toner images of respective colors formed in an inter-paper corresponding area A2. FIG. 3 is a schematic plan view showing the intermediate transfer belt and test toner images of respective colors formed on the side of the paper corresponding area A1. FIG. 6 is a schematic plan view showing the intermediate transfer belt, an experimental K image formed in the paper corresponding area A1, and a K test toner image formed in the paper corresponding area A2 of the belt. 6 is a graph showing a change with time of a detection result of an amount of K toner adhesion in Experiment 1. 6 is a graph showing a change with time of a detection result of an amount of adhesion of K toner in Experiment 2. 6 is a graph showing an example of the relationship between the number of continuous prints during a continuous image forming operation based on a user image formation command and the detection result of the toner adhesion amount of a test toner image formed every 10 prints. 6 is a graph showing a change with time of the toner adhesion amount of a test toner image when an experiment similar to Experiment 1 is performed using the copying machine individual A; 6 is a graph showing a change with time of a toner adhesion amount of a test toner image when an experiment similar to Experiment 1 is performed using the copying machine individual B; 10 is a graph showing a change with time in the amount of K toner attached to a K test toner image in Experiment 3. 10 is a graph showing a change with time in the amount of K toner attached to a K test toner image in Experiment 4. 10 is a graph showing a change with time in the amount of K toner attached to a K test toner image in Experiment 5. 10 is a graph showing a change with time of a target density correction amount for K developer in Experiment 5. FIG. 14 is a graph showing a change with time of a toner developer target cumulative correction amount of K developer in Experiment 3. FIG. 6 is a schematic plan view showing Y, M, C, and K test toner images MTy, MTm, MTc, and MTk formed on the intermediate transfer belt 61 in order to determine a target range. 6 is a graph showing an example of sampling data regarding the amount of K toner attached to a K test toner image MTk.

Hereinafter, as an image forming apparatus to which the present invention is applied, a copying machine according to a reference form that is helpful in understanding the present invention will be described before describing an embodiment of a copying machine that forms an image by an electrophotographic method. .
First, the basic configuration of the copying machine according to the reference embodiment will be described. FIG. 1 is a schematic configuration diagram showing a copying machine according to a reference embodiment. The copying machine includes a printer unit 1, a blank paper supply device 200, and a document conveyance reading unit 150.

  The document conveyance reading unit 150 includes a scanner 160 as a document reading device fixed on the printer unit 1 and an ADF 170 as a document conveyance device supported by the scanner 160.

  The blank paper supply apparatus 200 has two paper feed cassettes 202 and 203 arranged in multiple stages in the paper bank 201, two pairs of separation rollers 204 and 205, a paper feed path 206, a plurality of transport roller pairs 207, and the like. doing. Each of the two paper feed cassettes 202 and 203 is housed in the form of a paper bundle in which a plurality of recording papers (not shown) as recording bodies are stacked. Based on the control signal from the printer unit 1, the sending rollers 202 a and 203 a are driven to rotate, and the uppermost recording paper in the paper bundle is sent out toward the paper feed path 206. The fed recording paper is separated into one sheet by the pair of separation rollers 204 and 205 and then reaches the inside of the paper feed path 206. Then, the paper is fed to the first receiving branch path 30 of the printer unit 1 through the conveyance nips of the plurality of conveyance roller pairs 207 provided in the paper supply path 206.

  The printer unit 1 includes four process units 2C, M, Y, and K for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. Also, the first receiving branch path 30, the receiving conveyance roller pair 31, the manual feed tray 32, the manual separation roller pair 33, the second receiving branch path 34, the manual conveyance roller pair 35, the pre-transfer conveyance path 36, the registration roller pair 37, the conveyance A belt unit 39, a fixing unit 43, a switchback device 46, a discharge roller pair 47, a discharge tray 48, a switching claw 49, an optical writing unit 50, a transfer unit 60, and the like are also provided. The process units 2C, M, Y, and K have drum-shaped photoreceptors 3C, M, Y, and K that are latent image carriers.

  A pre-transfer conveyance path 36 for conveying a recording sheet immediately before a secondary transfer nip, which will be described later, is branched into a first reception branch path 30 and a second reception branch path 34 on the upstream side in the paper conveyance direction. After the recording paper fed out from the paper feed path 206 of the blank paper supply device 200 is received by the first receiving branch path 30, the recording paper passes through the transport nip of the receiving transport roller pair 31 disposed in the first receiving branch path 30. Then, it is sent to the pre-transfer conveyance path 36.

  A manual feed tray 32 is disposed on the side surface of the housing of the printer unit 1 so as to be openable and closable with respect to the housing. The uppermost recording paper in the manually fed paper bundle is sent out toward the second receiving / branching path 34 by the feed roller 32 a of the manual feed tray 32. After being separated into one sheet by the manual feed separation roller pair 33 and sent to the second receiving branch path 34, it passes through the transport nip of the manual feed roller pair 35 disposed in the second receiving branch path 34. Then, it is sent to the pre-transfer conveyance path 36.

  The optical writing unit 50 includes a laser diode, a polygon mirror, various lenses (not shown), etc., and is based on image information read by a scanner 160 described later or image information sent from an external personal computer. Drive the laser diode. Then, the photoconductors 3C, M, Y, and K of the process units 2C, M, Y, and K are optically scanned. Specifically, the photosensitive members 3C, M, Y, and K of the process units 2C, M, Y, and K are respectively driven to rotate counterclockwise in the drawing by a driving unit (not shown). The optical writing unit 50 performs optical scanning processing by irradiating the driven photosensitive members 3C, 3M, 3Y, and 3K while deflecting laser light in the direction of the rotation axis. Thereby, electrostatic latent images based on the C, M, Y, and K image information are formed on the photoreceptors 3C, M, Y, and K.

  FIG. 2 is a partially enlarged configuration diagram illustrating a part of the internal configuration of the printer unit 1 in an enlarged manner. The process units 2K, Y, M, and C for the respective colors support the photosensitive member as a latent image carrier and various devices arranged around it on a common support as a unit. It is detachable from the printer unit main body. The configuration is the same except that the colors of the toners used are different. Taking the process unit 2Y for Y as an example, this has a developing device 4Y as developing means for developing an electrostatic latent image formed on the surface of the photoreceptor 3Y into a Y toner image in addition to the photoreceptor 3Y. Yes. Further, it also includes a drum cleaning device 18Y that cleans transfer residual toner adhering to the surface of the photoreceptor 3Y after passing through a Y primary transfer nip described later. The copying machine has a so-called tandem configuration in which four process units 2C, M, Y, and K are arranged along an endless movement direction with respect to an intermediate transfer belt 61 described later.

  FIG. 3 is an enlarged configuration diagram showing the Y process unit 2Y. As shown in the figure, the process unit 2Y includes a developing device 4Y, a drum cleaning device 18Y, a charge eliminating lamp 17Y, a charging roller 16Y, and the like around the photoreceptor 3Y.

  As the photoreceptor 3 </ b> Y, a drum-like member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to a raw tube such as aluminum. However, an endless belt may be used.

  The developing device 4Y develops a latent image using a two-component developer (hereinafter simply referred to as developer) containing a magnetic carrier (not shown) and non-magnetic Y toner. And it has the stirring part 5Y which conveys the developer accommodated in the inside while stirring, and the developing part 9Y which develops the electrostatic latent image on the photoreceptor 3Y.

  The agitating unit 5Y is provided at a position lower than the developing unit 9Y. The first conveying screw 6Y and the second conveying screw 7Y are arranged in parallel to each other, a partition plate provided between these screws, and the bottom surface of the casing. The toner density sensor 8Y and the like provided in the printer.

  The developing unit 9Y includes a developing roll 10Y that faces the photoreceptor 3Y through the opening of the casing, a doctor blade 13Y that makes its tip close to the developing roll 10Y, and the like. The developing roll 10Y includes a cylindrical developing sleeve 11Y made of a nonmagnetic material, and a magnet roller 12Y provided inside the developing roll 11Y so as not to rotate. The magnet roller 12Y has a plurality of magnetic poles arranged in the circumferential direction. Each of these magnetic poles applies a magnetic force to the developer on the sleeve at a predetermined position in the rotational direction. As a result, the developer sent from the stirring unit 5Y is attracted and carried on the surface of the developing sleeve 11Y, and a magnetic brush along the magnetic field lines is formed on the sleeve surface.

  The magnetic brush is transported to a developing region facing the photoreceptor 3Y after being regulated to an appropriate layer thickness when passing through a position facing the doctor blade 13Y as the developing sleeve 11Y rotates. Then, Y toner is transferred onto the electrostatic latent image by the potential difference between the developing bias applied to the developing sleeve 11Y and the electrostatic latent image on the photoreceptor 3Y, thereby contributing to development. Further, as the developing sleeve 11Y rotates, the developing sleeve 9Y returns to the developing portion 9Y again, and after the release from the sleeve surface due to the influence of the repulsive magnetic field formed between the magnetic poles of the magnet roller 12Y, the developing sleeve 11Y returns to the stirring portion 5Y. An appropriate amount of toner is supplied to the developer in the stirring unit 5Y based on the detection result of the toner density sensor 8Y.

  As the drum cleaning device 18Y, a system that presses the cleaning blade 20Y made of polyurethane rubber against the photoreceptor 3Y is used, but another system may be used. For the purpose of improving the cleaning property, this copying machine employs a system having a fur brush 19Y whose outer peripheral surface is in contact with the photoreceptor 3Y so as to be rotatable in the direction of the arrow in the figure. The fur brush 19Y also serves to apply the lubricant to the surface of the photoreceptor 3Y while scraping the lubricant from a solid lubricant (not shown) into a fine powder.

  The toner attached to the fur brush 19Y is transferred to the electric field roller 21Y to which a bias is applied while rotating in contact with the fur brush 19Y in the counter direction. And after scraping off from the electric field roller 21Y by the scraper 22Y, it falls on the collection | recovery screw 23Y.

  The collection screw 23Y conveys the collected toner toward the end of the drum cleaning device 18Y in the direction perpendicular to the drawing surface, and delivers it to an external recycling conveyance device. A recycle conveyance device (not shown) sends the delivered toner to the developing device 4Y for recycling.

  The neutralization lamp 17Y neutralizes the photoreceptor 3Y by light irradiation. The surface of the photoreceptor 3Y that has been neutralized is uniformly charged by the charging roller 16Y, and then subjected to optical scanning by the optical writing unit described above. The charging roller 16Y is rotationally driven while receiving a charging bias from a power source (not shown). Instead of the charging method using the charging roller 16Y, a scorotron charger method in which charging processing is performed in a non-contact manner on the photoreceptor 3Y may be employed.

  In FIG. 2 described above, C, M, Y, and K toner images are formed on the surfaces of the photosensitive members 3C, M, Y, and K of the four process units 2C, M, Y, and K by the processes described above. Is formed.

  Below the four process units 2C, M, Y, and K, a transfer unit 60 as transfer means is disposed. The transfer unit 60 rotates in the clockwise direction in the figure by rotating the drive roller 67 while bringing an endless intermediate transfer belt stretched by a plurality of rollers into contact with the photoreceptors 3C, M, Y, and K. Move endlessly. As a result, primary transfer nips for C, M, Y, and K in which the photoreceptors 3C, M, Y, and K contact the intermediate transfer belt 61 are formed.

  In the vicinity of the primary transfer nips for C, M, Y, and K, the intermediate transfer belt 61 is moved to the photoreceptors 3YC, M, Y, and K by primary transfer rollers 62C, M, Y, and K disposed inside the belt loop. Pressing toward K. A primary transfer bias is applied to the primary transfer rollers 62C, M, Y, and K by a power source (not shown). As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 3C, M, Y, and K toward the intermediate transfer belt 61 is formed in the primary transfer nips for C, M, Y, and K. Has been.

In the drawing, a toner image is formed on each of the primary transfer nips on the front surface of the intermediate transfer belt 61 that sequentially passes through the primary transfer nips for C, M, Y, and K along with the endless movement in the clockwise direction. Are sequentially superimposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface of the intermediate transfer belt 61.

  A secondary transfer roller 72 is disposed below the intermediate transfer belt 61 in the drawing. The secondary transfer roller 72 contacts the secondary transfer backup roller 68 on the intermediate transfer belt 61 from the belt front surface. A secondary transfer nip is formed. As a result, a secondary transfer nip where the front surface of the intermediate transfer belt 61 and the secondary transfer roller 72 abut is formed.

  A secondary transfer bias is applied to the secondary transfer roller 72 by a power source (not shown). On the other hand, the secondary transfer backup roller 68 in the belt loop is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip.

  A pair of registration rollers (37 in FIG. 1) is disposed on the right side of the secondary transfer nip in the drawing, and the recording paper sandwiched between the rollers can be synchronized with the four-color toner image on the intermediate transfer belt 61. It is sent out to the secondary transfer nip at the timing. In the secondary transfer nip, the four-color toner image on the intermediate transfer belt 61 is secondarily transferred onto the recording paper under the influence of the secondary transfer electric field and the nip pressure, and becomes a full color image combined with the white color of the recording paper.

  The transfer residual toner that has not been transferred to the recording paper at the secondary transfer nip adheres to the front surface of the intermediate transfer belt 61 that has passed through the secondary transfer nip. This transfer residual toner is cleaned by a belt cleaning device 75 in contact with the intermediate transfer belt 61.

  In FIG. 1 described above, the recording paper that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and transferred to the transport belt unit 39. The transport belt unit 39 moves the endless transport belt 40 endlessly in the counterclockwise direction in the figure by the rotational drive of the drive roller 41 while being stretched by the drive roller 41 and the driven roller 42. The recording paper delivered from the secondary transfer nip is conveyed along with the endless movement of the belt while being held on the belt upper tension surface, and delivered to the fixing unit 43.

  In the fixing unit 43, a fixing belt stretched by a driving roller and a heating roller containing a heat generation source is moved endlessly in the clockwise direction in the drawing as the driving roller is driven to rotate. The pressure roller 45 disposed below the fixing belt is brought into contact with the lower tension surface of the fixing belt to form a fixing nip. The recording paper received by the fixing unit 43 is pressed or heated in the fixing nip, whereby the full-color image on the surface is fixed. Then, it is sent out from the fixing unit 43 toward the switching claw 49.

  The switching claw 49 is swung by a solenoid (not shown), and the recording paper conveyance path is switched between the paper discharge path and the reversing path with the swing. When the paper discharge path is selected by the switching claw 49, the recording paper fed out from the fixing unit 43 passes through the paper discharge path and the paper discharge roller pair 47 and is then discharged to the outside of the apparatus and discharged to the paper discharge tray. 48 is stacked.

  A switchback device 46 is disposed below the fixing unit 43 and the conveyor belt unit 39. When the switchback path is selected by the switching claw 49, the recording paper fed out from the fixing unit 43 is turned upside down via the reversing path and then sent to the switchback device 46. Then, the image enters the secondary transfer transfer nip again, and the secondary transfer processing and fixing processing of the image are performed on the other surface.

  In the printer unit 1 configured as described above, a combination of the Y, M, C, and K process units 2Y, M, C, and K, the optical writing unit 50, the transfer unit 60, and the like functions as an image forming unit. Yes.

  The scanner 160 fixed on the printer unit 1 has a fixed reading unit 161 and a moving reading unit 162 as reading means for reading an image of a document (not shown). A fixed reading unit 161 having a light source, a reflection mirror, an image reading sensor such as a CCD, and the like is disposed immediately below a first contact glass (not shown) fixed to the upper wall of the casing of the scanner 160 so as to contact the document. . Then, when the document conveyed by the ADF 170 passes over the first contact glass, the light emitted from the light source is sequentially reflected by the document surface and is received by the image reading sensor via the plurality of reflection mirrors. Thus, the original is scanned without moving the optical system including the light source and the reflecting mirror.

  On the other hand, the moving reading unit 162 is disposed directly below a second contact glass (not shown) fixed to the upper wall of the casing of the scanner 160 so as to come into contact with the document, and an optical system including a light source, a reflection mirror, and the like. It can be moved in the left-right direction in the figure. Then, in the process of moving the optical system from the left side to the right side in the figure, the light emitted from the light source is reflected by a document (not shown) placed on the second contact glass and then passed through a plurality of reflecting mirrors. The image is received by an image reading sensor fixed to the scanner body. Accordingly, the original is scanned while moving the optical system.

  This copying machine has a function as a copying machine and a function as a printer and a facsimile in addition to a function as a copying machine that forms an image based on image information of an original read by a scanner 160 on a recording sheet. Specifically, the printer unit 1 includes a LAN (Local Area Network) connector (not shown), and a LAN cable is connected to the printer unit 1 to enable communication with a personal computer (not shown). Then, an image based on image information sent from a personal computer via a LAN cable and a LAN connector can be formed on a recording sheet by the printer unit 1 (printer function). In addition, the printer unit 1 includes a modem (not shown), and a telephone line is connected thereto, so that an image based on image information transmitted via the telephone line can be output to a destination facsimile ( Facsimile function). At this time, the image information that is the source of the image to be transmitted to the transmission destination can be acquired by reading the document with the scanner 160 as information acquisition means. It is also possible to acquire image information that is the source of an image to be transmitted by receiving image information sent from a personal computer through a LAN connector as information acquisition means.

  The copier includes a toner supply device (not shown). This toner replenishing device uses Y, M, C, and K process units 2Y, M, C, and K based on detection results of a toner density sensor (for example, 8Y in FIG. 3), respectively. Y, M, C, and K toners are individually supplied to the K developing device. Hereinafter, the toner concentration sensor is also referred to as a T sensor.

  An optical sensor unit 101 is disposed on the right side of the transfer unit 60 in the drawing. The optical sensor unit 101 includes a Y adhesion amount sensor and an M adhesion amount sensor that are opposed to a portion where the intermediate transfer belt 61 is wound around the drive roller 67 through a predetermined gap in the entire region in the circumferential direction. , C adhesion amount sensor, and K adhesion amount sensor. These adhesion amount sensors are made up of reflective optical sensors, and detect the toner adhesion amount per unit area in a test toner image (not shown) formed on the surface of the intermediate transfer belt 61.

  FIG. 4 is a block diagram showing a part of an electric circuit in the copying machine. In the figure, a control unit 100 as a calculation means includes a CPU 100a, a ROM 100c that stores a control program and various data, and a RAM 100b that temporarily stores various data. Various devices are connected to the control unit 100 via an I / O interface 114. The Y, M, C, and K T sensors 8Y, M, C, and K detect the Y, M, C, and K toner concentrations of the developer contained in the Y, M, C, and K developing devices. To do. The optical writing control circuit 205 controls driving of the optical writing unit 50 that performs optical writing on the Y, M, C, and K photoconductors. The toner replenishing circuit controls driving of the toner replenishing device that replenishes Y, M, C, and K toners to the Y, M, C, and K developing devices. The power supply circuit 146 outputs the developing bias of each color developing unit, the primary transfer bias of each color, the secondary transfer bias, and the like. The motor drive circuit 112 controls driving of various types of motors such as process drive motors for each color for individually driving the process units for each color and belt drive motors for driving the intermediate transfer belt 61. It is. The unit detection circuit 110 individually detects Y, M, C, and K process units. The operation display unit includes a plurality of touch keys, a touch panel, and the like, and receives a user's touch operation and sends it to the control unit 100, or displays an image on the touch panel based on a command from the control unit 100. is there. Further, as shown in FIG. 5, the optical sensor unit 101 includes Y, M, C, and K per unit area of Y, M, C, and K test toner images Ty, Tm, Tc, and Tk formed on the surface of the intermediate transfer belt. Y, M, C, and K adhesion amount sensors 101Y, M, C, and K for detecting C and K toner adhesion amounts are provided.

  FIG. 6 is a schematic plan view illustrating the intermediate transfer belt 61 and the test toner images of the respective colors formed in the inter-paper corresponding area A2. The intermediate transfer belt 61 has an endless belt shape as described above, but in the drawing, the intermediate transfer belt 61 is shown as one elongated shape for convenience. During the image forming operation, the area in the circumferential direction of the intermediate transfer belt 61 is roughly divided into a paper corresponding area A1 and a paper gap corresponding area A2. The paper corresponding area A1 is an area where the recording paper is brought into close contact with the above-described secondary transfer nip, and carries a toner image for secondary transfer onto the recording paper. The inter-paper correspondence area A2 is an area interposed between the paper correspondence area A1 and the paper correspondence area A1, and does not carry a toner image for secondary transfer onto the recording paper. During the continuous image forming operation for continuously forming images on a plurality of recording sheets, the control unit (100) of the copying machine performs a paper interval every time the image forming operation for ten recording sheets is performed. Y, M, C, and K test toner images Ty, Tm, Tc, and Tk are formed side by side in the belt width direction with respect to the corresponding area A2. Each of these test toner images has a square patch shape and is formed under the condition that the toner adhesion amount in the square is uniform. During the continuous image forming operation, the control unit (100) performs the process of forming such Y, M, C, and K test toner images Ty, Tm, Tc, and Tk for every 10 prints. .

  The Y, M, C, and K toner adhesion amounts per unit area in the Y, M, C, and K test toner images Ty, Tm, Tc, and Tk are as shown in FIG. It is detected by the sensor, the M adhesion amount sensor, the C adhesion amount sensor, and the K adhesion amount sensor. The control unit (100) performs target value correction processing for correcting the toner density target values of the Y, M, C, and K developers based on the detection results of the respective adhesion amount sensors. Specifically, in this copying machine, the Y T sensor 8Y, the M T sensor 8M, the C T sensor 8C, and the K T sensor 8K shown in FIG. ing. The magnetic permeability of the Y, M, C, K developer changes according to the Y, M, C, K toner density. The Y T sensor 8Y, the M T sensor 8M, the C T sensor 8C, and the K T sensor 8K increase the output voltage VT [V] as the toner concentration in the developer decreases. That is, the higher the output voltage VT of these T sensors, the lower the toner concentration in the developer. The toner replenishing device 51 uses the output target value VTref [V] as the density target value for each of the output voltages VT from the Y T sensor 8Y, the M T sensor 8M, the C T sensor 8C, and the K T sensor 8K. It is memorized individually. For example, when Y is taken as an example, based on the comparison between the output voltage VT from the Y T sensor 8Y and the Y output target value VTref, it is determined that the Y toner concentration of the developer is lower than the target. In this case, a toner replenishing process for replenishing the Y toner in the Y developing device and recovering the Y toner density is performed for each print. Thereby, the Y toner density of the developer is maintained within a certain range. For M, C, and K, the same toner replenishment processing as that for Y is performed.

  The example in which the Y, M, C, and K test toner images Ty, Tm, Tc, and Tk are formed side by side in the belt width direction with respect to the inter-paper corresponding area A2 of the intermediate transfer belt 61 has been described. It may be formed. That is, as shown in FIG. 7, the Y, M, C, and K test toner images Ty belong to the paper corresponding area A1 in the belt circumferential direction but are out of the paper corresponding area A1 in the belt width direction. , Tm, Tc, Tk may be formed side by side in the belt moving direction. In this case, the Y, M, C, and K toner adhesion amounts of the Y, M, C, and K test toner images Ty, Tm, Tc, and Tk can be detected by one adhesion amount sensor.

Next, an experiment conducted by the inventor will be described.
[Experiment 1]
A continuous print test for continuously forming predetermined experimental images on 1100 sheets of recording paper was performed. As an experimental image, an experimental K image Ek made of only K toner as shown in FIG. 8 and extending over the entire paper corresponding area A1 of the intermediate transfer belt 61 is detected by a K adhesion amount sensor (101K). Formed in the position to get. Similarly to the normal continuous image forming operation, the K test toner image Tk is formed in the inter-paper corresponding area of the intermediate transfer belt 61 every 10 prints. During the continuous image forming operation of 1100 sheets, the K toner adhesion amount of the experimental K image Ek and the K toner adhesion amount of the K test toner image Tk were detected by the K adhesion amount sensor (101K). The width W1 (dimension in the belt width direction) of the experimental K image Ek was set to a length that does not cause excessive charging or insufficient charging of the K toner in the K developing device during the continuous image forming operation. Specifically, if an image with a relatively low image area ratio is continuously output or an image with a relatively high image area ratio is continuously output, toner is excessively charged or insufficiently charged in the developing device. In Experiment 1, the width W1 of the Experiment K image Ek is adjusted so that the image area ratio does not cause such overcharging or insufficient charging. Therefore, theoretically, during the continuous image forming operation of 1100 sheets, the K toner adhesion amount of the experimental K image and the K toner adhesion amount of the K test toner image Tk are stably set to the same value as the target adhesion amount. Should continue to detect.

  FIG. 9 is a graph showing the change with time of the detection result of the K toner adhesion amount in Experiment 1. FIG. The output voltage from the K adhesion amount sensor has a value corresponding to the amount of light received by the light receiving element for the reflected light reflected on the belt surface. In the figure, as the vertical axis item of the graph, not the output voltage itself from the K adhesion amount sensor but the toner adhesion amount obtained by converting the output voltage into the K toner adhesion amount is employed. As shown in this graph, originally, the detection result of the K toner adhesion amount of the experimental K image and the detection result of the K toner adhesion amount of the K test toner image are indicated by a predetermined target adhesion amount (indicated by a dotted line in the figure). It should be stable in the vicinity of (position), but it can be seen that the position is not stable but fluctuates greatly. This indicates that image density unevenness occurs in the experimental K image and the K test toner image. As shown by the white circles and black circles in the figure, the image density unevenness has a characteristic in which a sine wave synchronized with one rotation cycle of the photosensitive member and a sine wave synchronized with one rotation cycle of the developing sleeve are superimposed. Yes. The image density unevenness having such characteristics occurs for the reason described below. That is, eccentricity and roundness error are inevitably generated in the photosensitive member and the developing sleeve. As a result, the development gap fluctuates in a sine wave shape in synchronization with one rotation cycle of the photosensitive member and one rotation cycle of the developing sleeve, thereby causing image density unevenness corresponding to each sine wave. is there.

[Experiment 2]
A continuous print test for continuously forming predetermined experimental images on 1100 sheets of recording paper was performed. As an experiment image, the same experiment K image as experiment 1 was formed. The difference from Experiment 1 is that a K test toner image Tk is formed in the inter-paper corresponding area A2 of the intermediate transfer belt 61 for each print. FIG. 10 shows changes with time in the detection result of the K toner adhesion amount in Experiment 2. In FIG. As shown in the drawing, the K toner adhesion amount of the K test toner image formed in each inter-paper corresponding area A2 varies greatly. Depending on the timing at which the K test toner image is formed, the K toner adhesion amount of the K test toner image greatly exceeds the target adhesion amount as indicated by a point S2 in the figure, or the target adhesion as indicated by a point S4. It may be far below the amount. Since the K toner is not excessively charged or insufficiently charged, and the average toner adhesion amount is in the vicinity of the target adhesion amount indicated by the dotted line in the figure, the K toner concentration of the developer is normally assumed. VTref for K, which is the target value, need not be corrected. However, conventionally, for example, when the K toner adhesion amount indicated by the point S2 is detected, the K VTref is corrected to a larger value (decreasing the density target value), and the K toner density of the developer is corrected. Was lowering. This promotes excessive charging of the K toner and causes insufficient image density. For example, when the K toner adhesion amount indicated by the point S4 is detected, the K VTREF is corrected to a smaller value (increasing the density target value) to increase the K toner density of the developer. It was. As a result, insufficient charging of the K toner is promoted to cause excessive image density.

Next, a characteristic configuration of the copying machine will be described.
FIG. 11 is a graph showing an example of the relationship between the number of continuous prints during a continuous image formation operation based on a user image formation command and the detection result of the toner adhesion amount of a test toner image formed for every 10 prints. . In the continuous image forming operation on which the graph is based, an image having a relatively low image area ratio is continuously output. For this reason, if the toner density target value is not corrected, the image density continues to decrease over time. However, in this copying machine, the toner density target value is corrected based on the result of detecting the toner adhesion amount of the test toner image formed for every 10 prints for each of the colors Y, M, C, and K. Thus, a decrease in image density over time is suppressed. What should be noted is how to correct the density target value. In this copying machine, for each of the colors Y, M, C, and K, the toner adhesion amount target value Ma, the adhesion amount lower limit value Mb, and the adhesion amount upper limit value Mc of the test toner image are individually set. Yes. The adhesion amount target value Ma is a substantially central value between the adhesion amount lower limit value Mb and the adhesion amount upper limit value Mc. When the detection result of the toner adhesion amount of the test toner image falls within the target range from the adhesion amount lower limit value Mb to the adhesion amount upper limit value Mc, the control unit (100) is a toner density target value T. The output target value VTref from the sensor is not corrected. On the other hand, when the detection result of the toner adhesion amount of the test toner image is smaller than the adhesion amount lower limit value Mb, the output target value VTref [V is set by a value corresponding to the difference between the adhesion amount target value Ma and the detection result. ] Is increased by a value corresponding to the difference. This suppresses excessive charging of the developer toner, thereby increasing the image density to near the target density. If the detection result of the toner adhesion amount of the test toner image is larger than the adhesion amount upper limit Mc, the output target value VTref [V] is set to a value corresponding to the difference between the adhesion amount target value Ma and the detection result. By increasing, the toner density of the developer is decreased by a value corresponding to the difference. This suppresses charging failure of the developer toner, thereby reducing the image density to near the target density. Such correction of the output target value VTref is performed individually for each color of Y, M, C, and K. In the illustrated example, during the long-term continuous image forming operation, there are four cases where the detection result of the toner adhesion amount of the test toner image falls below the adhesion amount lower limit Mb. The output target value VTref is corrected only four times.

  In such a configuration, even if the toner adhesion amount of the test toner image periodically fluctuates within a certain range due to the cyclic fluctuation of the developing gap due to the eccentricity of the photosensitive member or the developing sleeve, the toner of the developer If no excessive charging or insufficient charging occurs, the fluctuation range falls within the target range from the adhesion amount lower limit value Mb to the adhesion amount upper limit value Mc. In this case, the control unit (100) does not correct the toner density target value VTref, thereby correcting the VTrfe excessively high or correcting it excessively low due to the periodic fluctuation of the development gap. Avoid doing that. On the other hand, when an image with a low image area ratio is continuously output during continuous image forming operation or an image with a high image area ratio is continuously output, excessive toner charging or insufficient charging occurs in the developer. The toner adhesion amount of the test toner image deviates greatly from the target range. In this case, the control unit (100) corrects the output target value VTref as described above, thereby suppressing fluctuations in image density due to excessive charging or insufficient charging of toner. As described above, the output target value VTref can be corrected more appropriately than in the past for each of the colors Y, M, C, and K.

  When the toner in the developer is excessively charged or insufficiently charged, the toner adhesion amount of the test toner image greatly deviates from the target range. As described above, when the toner adhesion amount deviates from the target range, the toner density target value in the developer is corrected so that the toner adhesion amount falls within the target range. Suppresses fluctuations in image density. As described above, the toner density target value can be corrected more appropriately than in the past.

Next, it describes the copier Nitsu according to the embodiment.
FIG. 12 is a graph showing the change over time in the toner adhesion amount of the test toner image when the same experiment as Experiment 1 was performed using the copying machine individual A having the same configuration as the copying machine according to the reference embodiment. FIG. 13 is a graph showing the change over time in the toner adhesion amount of the test toner image when an experiment similar to Experiment 1 was performed using a copier B different from the copier B. The variation width of the toner adhesion amount with time (see the arrow in the figure) shown in FIG. 13 is larger than the variation width of the toner adhesion amount with time shown in FIG. This is because the period fluctuation amount of the development gap in the copying machine individual B is larger than the period fluctuation amount of the development gap in the copying machine individual A. As described above, in the image forming apparatus, since the fluctuation amount of the development gap varies from one individual to another, the fluctuation width of the toner adhesion amount caused by the fluctuation in the development gap varies from one individual to another. Nevertheless, when the same value is used for all individuals as the adhesion amount lower limit value Mb and the adhesion amount upper limit value Mc, depending on the individual, the target range from the adhesion amount lower limit value Mb to the adhesion amount upper limit value Mc is appropriate. May be larger or smaller than range.

[Experiment 3]
The inventor conducted an experiment for determining the target range of the toner adhesion amount using a test machine having the same configuration as the copying machine according to the reference embodiment. Specifically, an experimental image having the same width W1 as the experimental K image shown in FIG. 8 and extending over the entire circumference of the intermediate transfer belt (61) is formed. The toner adhesion amount was sampled by a K adhesion amount sensor (101K) at predetermined time intervals. And the minimum value of sampling data was set as adhesion amount lower limit Mb. The maximum value of the sampling data was set as the adhesion amount upper limit value Mc.

  Next, the inventor conducted a continuous image forming operation test in which a predetermined experimental image was continuously formed on a plurality of recording papers under the conditions of the adhesion amount lower limit value Mb and the adhesion amount upper limit value Mc. As an experimental image, an image composed only of K toner and having a width W1 smaller than the experimental K image Ek shown in FIG. 8 was formed. Since the width W1 is smaller than that shown in FIG. 8, the ratio of the toner that is continuously consumed without being consumed for a long time in the developing device for K becomes larger than that in Experiment 1. For this reason, during the continuous image forming operation, excessive charging of K toner proceeds in the K developing device.

  The control unit (100) of the testing machine was controlled as follows. That is, every 10 prints, a K test toner image Tk is formed in the inter-paper corresponding area A2 of the intermediate transfer belt (61), and the K toner adhesion amount is detected by the K adhesion amount sensor (101K). When the detection result of the K toner adhesion amount falls within the target range from the adhesion amount lower limit value Mb to the adhesion amount upper limit value Mc, the K output target value VTref is not corrected. On the other hand, when the detection result of the K toner adhesion amount is smaller than the adhesion amount lower limit value Mb, the output target value VTref [V] is decreased by a value corresponding to the difference between the adhesion amount target value Ma and the detection result. Let When the detection result of the K toner adhesion amount is larger than the adhesion amount upper limit value Mc, the output target value VTref [V] is increased by a value corresponding to the difference between the adhesion amount target value Ma and the detection result.

  FIG. 14 is a graph showing the change with time of the K toner adhesion amount of the K test toner image in Experiment 3. In FIG. As shown in the figure, the K toner adhesion amount may be slightly lower than the adhesion amount lower limit value Mb, or may slightly exceed the adhesion amount upper limit value Mc. However, the K output target value VTref is appropriately corrected each time, so that the K toner adhesion amount does not greatly fall below the adhesion amount lower limit value Mb and does not greatly exceed the adhesion amount upper limit value Mc. It is within the target range from the amount lower limit value Mb to the adhesion amount upper limit value Mc or in the vicinity thereof.

[Experiment 4]
Next, the present inventors set the adhesion amount lower limit value Mb to a value slightly lower than in Experiment 3 and the adhesion amount upper limit value Mc to a value slightly higher than in Experiment 3, That is, the continuous image forming operation was performed in the same manner as in Experiment 3 under the condition that the target range was wider than that in Experiment 3. FIG. 15 is a graph showing the change with time of the K toner adhesion amount of the K test toner image in Experiment 4. As shown in the figure, it can be seen that the K toner adhesion amount fluctuates mainly in a region having a value lower than the adhesion amount target value Ma. For this reason, the average value of the K toner adhesion amount is far below the adhesion amount target value Ma. According to Experiment 4, when the target range of the toner adhesion amount of the test toner image is set wider than the appropriate range, the average value of the toner adhesion amount may be significantly lower than the adhesion amount target value Ma, or vice versa. I understood that.

[Experiment 5]
Next, the present inventors set the adhesion amount lower limit value Mb to a value slightly higher than that in Experiment 3, and the adhesion amount upper limit value Mc to a value slightly lower than in Experiment 3, That is, the continuous image forming operation was performed in the same manner as in Experiment 3 under the condition that the target range was narrower than that in Experiment 3. FIG. 16 is a graph showing the change with time of the K toner adhesion amount of the K test toner image in Experiment 5. As shown in the figure, it can be seen that the K toner adhesion amount fluctuates in a considerably wider range than the target range from the adhesion amount lower limit value Mb to the adhesion amount upper limit value Mc.

  FIG. 17 is a graph showing a change with time in the target toner toner cumulative correction amount of Experiment K in Experiment 5. In Experiment 5, since the experiment K images having a relatively low image area ratio are continuously output, the toner tends to be overcharged. Then, the VTref for K tends to be lowered and the toner concentration of the K developer tends to increase with time. However, as shown in the figure, it can be seen that the graph of the density target cumulative correction amount sometimes drops. This means that insufficient charging of the toner sometimes occurs due to excessive increase in the toner density. On the other hand, in Experiment 3, as shown in FIG. 18, the density target cumulative correction amount does not decrease and continues to increase gently. From this, it can be seen that if the target range of the toner adhesion amount of the test toner image is set narrower than the appropriate range, the output target value VTref is too low or too high, causing a shot of image density. It was.

From the above, it has been found that for each individual copying machine, a range corresponding to that individual must be individually set as the target range of the toner adhesion amount of the test toner image. Therefore, in the copying machine according to the embodiment, to implement the following processes and constitute a control unit (100). That is, when a predetermined target range determination timing comes, first, a test toner image for determining the target range of the toner adhesion amount is formed for each of the colors Y, M, C, and K. FIG. 19 is a schematic plan view showing Y, M, C, and K test toner images MTy, MTm, MTc, and MTk formed on the intermediate transfer belt 61 in order to determine the target range. As illustrated, the Y, M, C, and K test toner images MTy, MTm, MTc, and MTk are formed side by side in the belt width direction so as to be detected by an unillustrated Y, M, C, and K adhesion amount sensor. The Each of them has an elongated shape extending in the belt circumferential direction. The lengths of the Y, M, C, and K test toner images MTy, MTm, MTc, and MTk are at least larger than the photosensitive member circumferential length and the developing sleeve circumferential length. More specifically, at least the image portion developed at the timing when the minimum diameter portion due to the eccentricity of the photosensitive member and the minimum diameter portion due to the eccentricity of the developing sleeve are synchronized, the maximum diameter portion due to the eccentricity of the photosensitive member, and the developing sleeve The length is set to include the image portion developed at the timing synchronized with the maximum diameter portion due to the eccentricity. For such length, the circumference of the photosensitive member, the circumferential length of the developing sleeve, their linear velocity, and can be identified based on a belt linear speed.

  When such Y, M, C, and K test toner images MTy, MTm, MTc, and MTk are formed, the detection results of the toner adhesion amounts are sampled at predetermined intervals and stored in the RAM (101b). .

  FIG. 20 is a graph showing an example of sampling data of the K toner adhesion amount of the K test toner image MTk. As shown in the figure, the sampling data includes fluctuations corresponding to one rotation cycle of the photosensitive member and one rotation cycle of the developing sleeve. The control unit (100) specifies the minimum value among these sampling data, and sets the adhesion amount lower limit Mb to the same value as the minimum value. Moreover, the thing of the maximum value is specified among several sampling data, and the adhesion amount upper limit Mc is set to the same value as the maximum value. In this way, the target range of the toner adhesion amount is determined.

In the copying machine according to the embodiment, as the target range determining when to implement such a range determination process employs the time during initial operation and maintenance performed. The initial operation is the timing before performing the image forming operation based on the first image forming command by the user after shipment from the factory. By performing the range determination process during such initial operation, the output target value VTref is corrected under the conditions of an appropriate target range from the initial continuous image forming operation under the user after shipment from the factory. can do.

In addition, the maintenance is performed before the image forming operation based on the first image forming instruction by the user after the maintenance is performed on the process units 2Y, 2M, 2C, and 2K. The control unit (100) determines whether or not maintenance has been performed on the process units 2Y, 2M, 2C, and 2K based on the attachment / detachment operation of the process units 2Y, 2M, 2C, and 2K. Specifically, the copying machine according to the embodiment includes a unit detection circuit 110 as shown in FIG. The unit detection circuit 110 includes detection sensors that individually detect the process units 2Y, M, C, and K of the respective colors set in the casing of the printer unit 1. The control unit (100) determines that maintenance has been performed on the process unit that is sent again after the detection signal is not sent from the unit detection circuit 110. If such a determination is made, then the range determination process is performed before the image forming operation based on the first image forming instruction by the user. In this way, when the range determination process is performed during maintenance, if the development gap fluctuation pattern changes from the factory default state due to parts replacement, etc., it matches the development gap fluctuation pattern after the change. The target range can be set appropriately.

  At the time of maintenance, the range determination process is performed only for the colors for which the process unit is maintained among the four colors Y, M, C, and K. On the other hand, the range determination process is performed for all four colors during the initial operation.

  So far, the example of detecting the toner adhesion amount of the test toner image transferred to the intermediate transfer belt has been described, but the adhesion amount to each color process unit is detected so as to detect the toner adhesion amount of the test toner image on the photoreceptor. A sensor may be provided.

As described above, in the copying machine according to the reference embodiment, the latent image on the photosensitive member is formed by at least the photosensitive members 3Y, 3M, 3C, and 3K that are latent image carriers that carry the latent image and the developer containing toner and carrier. Development means 4Y, M, C, and K as developing means for developing and obtaining a toner image, and transfer means for transferring the toner image on the photosensitive member to a recording sheet as a recording member via an intermediate transfer belt 61 as an intermediate transfer body. The image forming means having the transfer unit 60 is provided. Further, in the Y T sensor 8Y, the M T sensor 8M, the C T sensor 8C, and the K T sensor 8K as toner density detecting means for detecting the toner density of the developer in the developing devices 4Y, M, C, and K. A toner replenishing device 51 is provided as toner replenishing means for replenishing Y, M, C, and K toners to the developer and bringing the T sensor detection result close to the Y, M, C, and K VTref that is a predetermined density target value. Yes. In addition, the Y, M, C, and K test toner images Ty, T, Tm, Tc, and Tk are imaged, and Y, M, C, and K toner adhesion amounts per unit area in the respective areas are measured by Y, M, C, and K adhesion amount sensors 101Y, M, C, and K serving as adhesion amount detection means. Based on the detected result, the control unit 100 is configured to function as a density target correction unit that corrects VTref for Y, M, C, and K. The Y, M, C, and K toner adhesion amounts detected by the Y, M, C, and K adhesion amount sensors 101Y, M, C, and K are more than the predetermined adhesion amount lower limit value Mb to the adhesion amount lower limit value Mb. The control unit 100 is configured to perform the process of correcting the VTref for Y, M, C, and K only when it does not fall within the target range up to the large predetermined adhesion amount upper limit Mc. . In such a configuration, as already described, VTref can be corrected more appropriately than in the past.

In the copier according to the embodiment , when an image forming operation based on an image forming instruction from the user is not performed, Y, M, C for determining a target range of the toner adhesion amount by the image forming unit. , K test toner images MTy, MTm, MTc, and MTk are formed, and Y, M, C, and K toner adhesion amounts are detected by Y, M, C, and K adhesion amount sensors 101Y, M, C, and K, respectively. Based on the result, the control unit 100 is configured to function as range determining means for determining the adhesion amount lower limit value Mb and the adhesion amount upper limit value Mc. In such a configuration, the target range of the toner adhesion amount can be set to an appropriate range corresponding to the development gap fluctuation pattern of each individual copying machine.

In the copying machine according to the embodiment , as the photosensitive members 3Y, 3M, 3C, and 3K as latent image carriers, those that carry a latent image on a surface that moves endlessly are used. Further, as a developing means, a developing device 4Y that develops a latent image on the photoreceptors 3Y, 3M, 3C, and 3K with a developer carried on the surface of the developing sleeves 11Y, 11M, 11C, and 11K, which is a developer carrying member, that moves endlessly. , M, C, K are used. Further, Y, M, C, and K test toner images Ty, Tm, Tc, and Tk for determining the target range of the toner adhesion amount are respectively formed longer than the circumference of the photosensitive member and the developing sleeve, Based on the results of detecting the Y, M, C, and K toner adhesion amounts at a plurality of locations in the respective photoreceptor circumferential length directions by the Y, M, C, and K adhesion amount sensors 101Y, M, C, and K, respectively. The control unit 100 is configured to perform processing for determining the adhesion amount lower limit value Mb and the adhesion amount upper limit value Mc for M, C, and K, respectively. In such a configuration, for each of the colors Y, M, C, and K, periodic fluctuations in the toner adhesion amount due to periodic fluctuations in the development gap are detected, and the adhesion quantity lower limit value Mb and the adhesion quantity upper limit value are detected. Each Mc can be determined to an appropriate value.

  In the range determination process, instead of forming one elongate test toner image for each of the colors Y, M, C, and K, a plurality of short test toner images are formed, and the toner adhesion amount in each is detected. Based on the result, the adhesion amount lower limit value Mb and the adhesion amount upper limit value Mc may be determined.

Further, in the copying machine according to the embodiment, prior to performing an image forming operation based on the image formation instruction in the first by the user after the factory shipment, to perform a range determination process, constitute a controller 100 Yes. In such a configuration, the output target value VTref can be corrected under conditions of an appropriate target range from the first continuous image forming operation under the user after shipment from the factory.

Further, in the copying machine according to the embodiment, the process unit 2Y is part of the imaging means, M, C, based on the fact that maintenance is performed on the K, so as to implement the target determining process, The control unit 100 is configured. In such a configuration, when the development gap fluctuation pattern changes from the factory default state due to parts replacement or the like, the target range can be appropriately set in accordance with the development gap fluctuation pattern after the change.

2Y, M, C, K: Process unit (part of image forming means)
3Y, M, C, K: photoconductor (latent image carrier)
4Y: developing device (developing means)
8Y: toner density sensor (toner density detection means)
11Y: Development sleeve (developer carrier)
51: Toner supply device (toner supply means)
60: Transfer unit (transfer means)
61: Intermediate transfer belt (intermediate transfer member)
100: Control unit (density target correction means, range determination means)
101: Optical sensor unit 101Y, M, C, K: Adhesion amount sensor (adhesion amount detection means)

JP 2008-15260 A

Claims (4)

The latent image on the latent image carrier is developed by at least a latent image carrier that carries the latent image on the surface that moves endlessly, and a developer containing toner and carrier carried on the endlessly moving surface of the developer carrier. Developing means for obtaining a toner image, and transfer means for transferring the toner image on the latent image carrier to a recording member directly or via an intermediate transfer member;
Toner density detecting means for detecting the toner density of the developer in the developing means;
Toner replenishing means for replenishing the developer in the developing means and bringing the detection result by the toner density detecting means closer to a predetermined density target value;
A test toner image is formed by the image forming means at a regular timing during a continuous image forming operation in which images are continuously formed on a plurality of recording members, and toner adheres per unit area of the test toner image. In an image forming apparatus comprising: a density target correction unit that corrects the density target value based on a result of detecting an amount by an adhesion amount detection unit;
When the image forming operation based on an image forming command from the user is not performed, the image forming unit forms a test toner image for determining a target range longer than the circumference of the latent image carrier or the developer carrier. The target range determination test toner image is formed during the continuous image forming operation based on the result of detection of the toner adhesion amounts at a plurality of locations in the latent image carrier circumferential length direction by the adhesion amount detection means. A range determining means for determining a lower limit value of the toner adhesion amount of the test toner image and an upper limit value larger than the lower limit value;
The toner adhering amount of the test toner image is detected by the adhesion amount detection means, only if it does not fit within the target range from the lower limit up to the upper limit value, carries out a process of correcting the density target value Thus, an image forming apparatus comprising the density target correcting means. The image forming apparatus according to claim 1 .
Multiple imaging previous SL target range determined for the test toner image, based on a result detected by each of the adhesion amount detection unit of the toner adhesion amount in their target range determined for the test toner image, the lower limit and the upper limit value An image forming apparatus characterized in that the range determining means is configured to execute a determining process. The image forming apparatus according to claim 1 or 2 ,
Prior to performing an image forming operation based on an initial image forming instruction by a user after shipment from the factory, a process for forming the target range determining test toner image and determining the lower limit value and the upper limit value is performed. As described above, an image forming apparatus comprising the range determining means. The image forming apparatus according to any one of claims 1 to 3 ,
The range determination is performed such that the lower limit value and the upper limit value are determined by forming the target range determination test toner image based on the maintenance performed on the image forming unit. An image forming apparatus comprising a means.

Images