JP5683505B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a photosensitive drum and a developing device.

  Among image forming apparatuses using a developer such as a printer, there is a model that employs a touch-down developing device.

  In the touch-down developing device, a magnetic brush is formed on the surface of the magnetic roller by a magnetic force, and a toner layer is formed on the surface of the developing roller with toner supplied from the magnetic brush to the developing roller. The developing device develops the electrostatic latent image formed on the surface of the photosensitive drum by supplying the toner layer formed on the developing roller to the photosensitive drum.

  In a touch-down developing device, a two-component developer (hereinafter also referred to as “developer”) including a toner and a carrier is used as a developer. The toner used for the developer deteriorates as it is stirred in the developing device, and the toner becomes overcharged or the toner external additive is buried in the toner. As a result, an appropriate amount of toner does not adhere to the electrostatic latent image formed on the surface of the photosensitive drum, and problems such as a decrease in the density of the image formed on the paper occur.

  Therefore, a technique relating to so-called refresh operation is proposed in which deteriorated toner is forcibly supplied to a photosensitive drum and discharged, and a new developer is replenished in the developing device (see Patent Document 1). Further, as a technique related to the refresh operation described above, the development time is extended or the development bias voltage is increased compared to the normal operation. The development bias voltage is a potential difference between a voltage applied to the magnetic roller and a voltage applied to the development roller.

Japanese Patent Laid-Open No. 5-72850

  However, if the development time is extended in the refresh operation as compared with the normal operation, the printing speed as a whole decreases. Even if the developing bias voltage is increased, the deteriorated toner may not be consumed stably. Therefore, the toner cannot be sufficiently replaced, and as a result, the toner and the carrier may be further deteriorated.

  An object of the present invention is to provide an image forming apparatus that can stably consume deteriorated toner by a refresh operation.

  In the present invention, a developer containing portion containing at least a toner and a carrier containing a two-component developer, and the two-component developer are magnetically held, and a magnetic brush is formed on the surface by the carrier contained in the two-component developer. A developer carrier, a toner carrier on which a toner layer is formed by the toner supplied from the magnetic brush of the developer carrier, and a toner supplied from the toner layer of the toner carrier. An image bearing member on which an image along the electrostatic latent image formed on the surface is formed, a laser beam continuously irradiated on the surface of the image bearing member to form a 100% solid image of a predetermined area, and a laser An exposure unit that forms an electrostatic latent image in a non-100% dot image having a predetermined area and a predetermined toner density by intermittently irradiating light, and a 100% solid image for detecting a deterioration state of the toner. An image formation control unit for forming a small image and a second small image based on a non-100% dot image on the exposure unit, and toner concentrations of the first small image and the second small image formed on the surface of the image carrier A toner density detecting unit for detecting toner, and a target consumption amount of toner in a predetermined first area based on information on the toner density of the first small image and the second small image detected by the toner density detecting unit The present invention relates to an image forming apparatus comprising: a refresh operation control unit that causes the exposure unit to form the dummy image having a toner density suitable for the above.

  According to the present invention, it is possible to provide an image forming apparatus that can stably consume deteriorated toner by a refresh operation.

1 is a diagram for describing an overall configuration of a printer 1 according to an embodiment. 2 is a block diagram illustrating a functional configuration of the printer. FIG. (A) and (B) are schematic views showing first and second small images formed on the photosensitive drum 31. (A) and (B) are graphs showing the relationship between the developing bias voltage and the toner consumption. (A) and (B) are schematic diagrams showing regions in the photosensitive drum 31 where a dummy image is formed. It is a flowchart which shows the process sequence in case the control part 90 determines the image density of a dummy image. 6 is a graph showing transition of image density when a document with a low printing rate is continuously printed.

  Hereinafter, a printer 1 which is an embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. First, the overall configuration of the printer 1 will be described. FIG. 1 is a diagram for explaining the overall configuration of the printer 1 according to the present embodiment.

  As shown in FIG. 1, the printer 1 of the present embodiment includes a paper transport unit 10, an image forming unit 30, and a fixing unit 40 as main components.

  The paper transport unit 10 includes a first feed roller 11, a second feed roller 12, a registration roller pair 13, a first roller pair 14, a second roller pair 15, and a paper discharge unit 16. The conveyance path L through which the paper T is conveyed includes a first conveyance path L1 from the first feeding roller 11 or the second feeding roller 12 to the image forming unit 30 (a transfer nip N described later), and the image forming unit 30 ( A second conveyance path L2 from a transfer nip N), which will be described later, to the fixing unit 40, a third conveyance path L3 from the fixing unit 40 to the paper discharge unit 16, and the paper T discharged from the fixing unit 40 are registered with the registration roller pair 13. And a fourth transport path L4.

  The first feed roller 11 supplies the paper T (transfer material) stored in the paper feed cassette 17 to the first transport path L1. The second feed roller 12 supplies the paper T (transfer material) placed on the manual feed tray 18 to the first transport path L1. The registration roller pair 13 is formed on the photosensitive drum 31 by supplying the sheet T conveyed through the first conveyance path L1 to a transfer nip N formed between the photosensitive drum 31 and the transfer roller 38. In order to transfer the toner image onto the paper T, the transport of the paper T or the transport of the paper T is stopped.

  Further, the registration roller pair 13 performs skew (oblique feeding) correction of the paper T. The first roller pair 14 is provided in the third transport path L3 and transports the paper T discharged from the fixing unit 40 to the paper discharge unit 16 side. The second roller pair 15 carries the paper T transported to the paper discharge unit 16 side by the first roller pair 14 into the fourth transport path L4. The paper discharge unit 16 discharges the paper T on which the toner image is fixed to the outside of the printer 1. A paper discharge stacking unit 19 is formed outside the printer 1 in the paper discharge unit 16. In the paper discharge stacking unit 19, the paper T discharged from the paper discharge unit 16 is stacked.

  The image forming unit 30 is a device for forming a toner image. The image forming unit 30 includes a photosensitive drum 31 as an image carrier, a charging unit 32, a laser scanner unit 33 as an exposure unit, a developing unit 34, a static eliminator 35, a cleaning unit 36, and a developer container. A toner cartridge 37 as a unit, and a transfer roller 38. In the present embodiment, the laser scanner unit 33 operates as a part of the image forming unit 30.

  An image (toner image) along the electrostatic latent image formed on the surface of the photosensitive drum 31 is formed by the toner supplied from the toner layer of the developing roller 343 (toner carrier). Around the photosensitive drum 31, a charging unit 32, a laser scanner unit 33, a developing device 34, and a toner concentration sensor 39 as a toner concentration detection unit are sequentially arranged from the upstream side to the downstream side along the rotation direction of the photosensitive drum 31. And the cleaning part 36 is arrange | positioned.

  The charging unit 32 uniformly charges the surface of the photosensitive drum 31 negatively (minus polarity) or positively (plus polarity).

  The laser scanner unit 33 is disposed away from the surface of the photosensitive drum 31. The laser scanner unit 33 continuously irradiates the surface of the photosensitive drum 31 with laser light based on image data (original image) transmitted by an external device (for example, a personal computer) arranged outside, and has a predetermined area. The electrostatic latent image in the 100% solid image and the electrostatic latent image in the non-100% dot image (described later) having a predetermined area and a predetermined toner density are formed by intermittent irradiation with laser light. By irradiating the photosensitive drum 31 with laser light from the laser scanner unit 33, the charge on the exposed portion is removed on the surface of the photosensitive drum 31, and an electrostatic latent image corresponding to the document image is formed. .

  The laser scanner unit 33 of the present embodiment continuously irradiates the surface of the photosensitive drum 31 (image carrier) with laser light, and intermittently irradiates the electrostatic latent image and laser light in a 100% solid image of a predetermined area. An electrostatic latent image is formed in a non-100% dot image having a predetermined area and a predetermined toner density. Specifically, the laser scanner unit 33 includes a first small image based on a 100% solid image and a second image based on a 70% half image (non-100% dot image) for detecting toner deterioration in addition to a normal document image. A small image and a dummy image (area A or B described later) for consuming toner are formed. Note that normal document images and dummy images are formed in the print area (image formation area) of the photosensitive drum 31. Further, the first small image and the second small image are formed outside the printing area of the photosensitive drum 31.

  The developing device 34 forms a toner image on the surface of the photosensitive drum 31 by attaching a single color (usually black) toner to the electrostatic latent image formed on the surface of the photosensitive drum 31. The developing device 34 includes a stirring roller 341, a magnetic roller 342 as a developer carrier, a developing roller 343 as a toner carrier, and the like.

  The developing device 34 is a touch-down developing device. The developing device 34 forms a magnetic brush by the magnetic force on the surface of the magnetic roller 342, and forms a toner layer on the surface of the developing roller 343 with the toner supplied from the magnetic brush to the developing roller 343. Then, the electrostatic latent image formed on the surface of the photosensitive drum 31 is developed by supplying the toner layer formed on the developing roller 343 to the photosensitive drum 31. As a result, a toner image is formed on the surface of the photosensitive drum 31.

  The agitation roller 341 agitates the developer supplied by a toner supply unit 371 (described later). The developer stirred by the stirring roller 341 generates static electricity due to friction. As a result, the carrier is negatively charged and the toner is positively charged. Further, the toner adheres to the carrier due to electrostatic force.

  The magnetic roller 342 includes a magnetic sleeve made of a cylindrical nonmagnetic member. The magnetic sleeve is supported so as to be rotatable in a predetermined direction, and a plurality of magnetic members (not shown) are disposed therein. The magnetic roller 342 holds the two-component developer by a magnetic force, and a magnetic brush is formed on the surface by the carrier contained in the two-component developer. A first bias voltage V <b> 1 is applied to the magnetic roller 342 by a first voltage application unit 101 (described later).

  The developer supplied from the toner cartridge 37 (described later) to the developing device 34 is stirred by the stirring roller 341, and a part of the developer is held on the surface of the magnetic roller 342 by magnetic force. Part of the developer held on the surface of the magnetic roller 342 forms a magnetic brush (developer layer) (not shown).

  The developing roller 343 is configured by a developing sleeve made of a cylindrical nonmagnetic member. A plurality of magnetic members are disposed inside the developing roller 343. The developing roller 343 is driven so that the rotation direction of the developing sleeve is opposite to the rotation direction of the magnetic roller 342 at a position facing the surface of the photosensitive drum 31.

  The developing roller 343 has a toner layer (not shown) formed on the surface by toner supplied from the magnetic brush of the magnetic roller 342 (developer carrier). Specifically, on the surface of the developing roller 343, only the toner moves from the magnetic brush whose layer thickness is regulated by a layer thickness regulating blade (not shown) of the magnetic roller 342, and a toner layer is formed. A second bias voltage V2 is applied to the developing roller 343 by a second voltage application unit 102 (described later).

  The static eliminator 35 irradiates the surface of the photosensitive member with light, thereby neutralizing the surface of the photosensitive drum 31 after the transfer is performed (removing the electric charge).

  The cleaning unit 36 removes the toner remaining on the surface of the photosensitive drum 31 after the surface of the photosensitive drum 31 is neutralized by the static eliminator 35.

  The toner cartridge 37 contains a two-component developer including at least toner and a carrier as a developer supplied to the developing device 34. A toner supply unit 371 is provided inside the toner cartridge 37. The toner supply unit 371 supplies the developer stored in the toner cartridge 37 to the developing device 34. The toner supply unit 371 and the developing device 34 are connected by a toner supply path (not shown).

  The transfer roller 38 transfers the toner image formed on the surface of the photosensitive drum 31 onto the paper T by sandwiching the paper T between the photosensitive drum 31 and the transfer roller 38. A transfer bias for transferring the toner image formed on the surface of the photosensitive drum 31 onto the paper T is applied to the transfer roller 38 by a transfer bias applying unit (not shown).

The toner density sensor 39 is disposed to face the surface of the photosensitive drum 31. The toner density sensor 39 detects the toner density (image density) of a normal document image formed on the surface of the photosensitive drum 31. The toner density sensor 39 detects the toner density of the first small image and the second small image formed on the surface of the photosensitive drum 31 (image carrier). The toner density sensor 39 detects the toner density based on the reflectance of light emitted from the toner density sensor 39 to the image formed on the surface of the photosensitive drum 31. The toner density is represented by Log ₁₀ (1 / R). Here, R represents reflectance (%). Information about the toner density detected by the toner density sensor 39 (hereinafter also referred to as “detected toner density value”) is transmitted to the control unit 90.

  The fixing unit 40 includes a heating rotator 41 and a pressure rotator 42. The heating rotator 41 and the pressure rotator 42 sandwich the paper T on which the toner image is transferred, melt and press the toner, and fix the toner to the paper T.

  Next, a functional configuration of the printer 1 according to the present embodiment will be described. FIG. 2 is a block diagram illustrating a functional configuration of the printer 1. In addition, about the structure demonstrated using FIG. 1, the description is abbreviate | omitted suitably.

  The printer 1 includes an operation unit 50, a display unit 60, an interface unit 70, a storage unit 80, in addition to the above-described components (such as the paper transport unit 10, the image forming unit 30, and the fixing unit 40). And a control unit 90. The printer 1 includes a first voltage application unit 101, a second voltage application unit 102, and a third voltage application unit 103.

  The operation unit 50 has a plurality of keys (not shown). These plurality of keys are operated, for example, when changing the setting of the printer 1 or resetting the job. The operation unit 50 transmits a signal corresponding to the operated key to the control unit 90 when any key is operated.

  In addition to the setting mode, the paper size, the number of printed sheets, and the output destination, the display unit 60 has a small amount of developer stored in the toner cartridge 37 and that the paper T is not stored in the paper feed cassette 17. Various kinds of information are displayed.

  The interface unit 70 is connected to an external device (for example, a personal computer) installed outside the printer 1.

  The storage unit 80 includes a hard disk, a semiconductor memory, and the like. The storage unit 80 stores image data supplied from the external device described above. The storage unit 80 stores a control program used in the printer 1 and data used by the control program.

  The control unit 90 includes a CPU, a RAM, and a ROM. The RAM is a storage device having a function of temporarily storing various data and a function of a work area during calculation. The ROM is a storage device having a function as a flash memory for storing various programs. The CPU is an arithmetic device that reads and executes a program from a ROM. The CPU, the RAM, and the ROM transmit and receive data via a data bus (not shown). By executing the program read from the ROM, the CPU executes processing according to the contents of the program.

  The control unit 90 controls the paper transport unit 10, the image forming unit 30, the fixing unit 40, and the display unit 60. The control unit 90 controls the first voltage application unit 101, the second voltage application unit 102, and the third voltage application unit 103. The control unit 90 includes a normal operation control unit 91, a test image formation control unit 92 as an image formation control unit, and a refresh operation control unit 93.

  The control unit 90 (normal operation control unit 91) controls each unit of the printer 1 when a normal document image is formed. The control unit 90 (test image formation control unit 92) also uses a 100% solid image for detecting toner deterioration and a 70% half image (non-100% dot image) second small image. Is formed in the laser scanner unit 33. Further, the control unit 90 (refresh operation control unit 93) causes the laser scanner unit 33 to form a dummy image suitable for the target consumption amount of toner. The functions of the normal operation control unit 91, the test image formation control unit 92, and the refresh operation control unit 93 will be described later.

  First, the operation when the control unit 90 (normal operation control unit 91) performs normal operation of the printer 1 will be described. In the following description, a case where a toner image is formed on one side of the paper T is taken as an example.

  First, the control unit 90 (normal operation control unit 91) temporarily stores in the storage unit 80 image data input from the external device via the interface unit 70. The control unit 90 (normal operation control unit 91) is configured to form a toner image on the paper T based on the image data temporarily stored in the storage unit 80, the paper transport unit 10, the image forming unit 30, and the fixing unit 40. To control each. That is, the control unit 90 (normal operation control unit 91) drives the first feed roller 11 or the second feed roller 12 to transport the paper T to the image forming unit 30.

  In addition, the control unit 90 (normal operation control unit 91) supplies data for forming a toner image generated based on the image data to the laser scanner unit 33, and the laser light emitted from the laser scanner unit 33 is used. An electrostatic latent image is formed on the photosensitive drum 31. The control unit 90 (normal operation control unit 91) causes the developing device 34 to form a toner image on the photosensitive drum 31 and transfers the toner image onto the paper T by the transfer roller 38. The control unit 90 (normal operation control unit 91) controls the heating rotator 41 to be heated to a predetermined temperature, melts the toner of the toner image transferred to the paper T by the heating rotator 41, and The toner is fixed on the paper T by the pressure rotator 42 pressed against the heating rotator 41. Further, the control unit 90 (normal operation control unit 91) causes the paper transport unit 10 to discharge the paper T on which the toner image is fixed from the paper discharge unit 16.

  The control unit 90 (normal operation control unit 91) controls the bias voltage applied to each roller from the first voltage application unit 101, the second voltage application unit 102, and the third voltage application unit. The first voltage application unit 101 applies the first bias voltage V <b> 1 to the magnetic roller 342 based on the control signal output from the control unit 90. The second voltage application unit 102 applies the second bias voltage V <b> 2 to the developing roller 343 based on the control signal output from the control unit 90. The third voltage application unit 103 applies the third bias voltage V <b> 3 to the photosensitive drum 31 based on the control signal output from the control unit 90.

  Due to the potential difference between the first bias voltage V1 applied to the magnetic roller 342 and the second bias voltage V2 applied to the developing roller 343 (hereinafter, also referred to as “developing bias voltage”), the magnetic roller 342 adhered to the surface of the magnetic roller 342. The toner moves to the developing roller 343. The amount of toner movement from the magnetic roller 342 to the developing roller 343 increases in proportion to the developing bias voltage generated between the magnetic roller 342 and the developing roller 343.

  Further, the toner attached to the surface of the developing roller 343 moves to the surface of the photosensitive drum 31 due to a potential difference generated between the photosensitive drum 31 and the developing roller 343. Thereby, the electrostatic latent image formed on the surface of the photosensitive drum 31 is developed (visualized) with the toner. The amount of toner movement from the developing roller 343 to the photosensitive drum 31 increases in proportion to the voltage difference generated between the developing roller 343 and the photosensitive drum 31.

  In the touch-down developing device 34, the second bias voltage V <b> 2 supplied to the developing roller 343 is controlled to a fixed value and supplied to the first bias voltage V <b> 1 supplied to the magnetic roller 342 and the photosensitive drum 31. Control is performed such that the potential difference from the third bias voltage V3 is constant. The controller 90 (normal operation controller 91) can adjust the amount of toner movement by controlling the potential difference between the developing roller 343 and the magnetic roller 342.

  In general, large-diameter toner has high chargeability and low adhesion to the developing roller 343 (easy to move to the photosensitive drum 31), and thus developability is good. For this reason, in the touch-down type developing device 34, a phenomenon in which large-diameter toner selectively moves to the photosensitive drum 31 tends to occur. Such a phenomenon becomes more prominent as the toner deteriorates. For this reason, when printing is performed continuously, small-diameter toner remains on the developing roller 343, and the density of the image decreases. Therefore, the control unit 90 (normal operation control unit 91) executes a calibration process for correcting the image density by adjusting the developing bias voltage at a constant period in the normal operation. However, when the deterioration of the toner progresses, it is difficult to correct the image density even if such a calibration process is executed.

  Therefore, the control unit 90 (refresh operation control unit 93) forcibly supplies the deteriorated toner to the photosensitive drum 31 for consumption during normal operation, and replenishes the developer 34 with a new developer. Run the operation. Specifically, the control unit 90 (refresh operation control unit 93) performs predetermined processing based on information on the toner density of the first small image and the second small image detected by the toner density sensor 39 (toner density detection unit). The dummy image of the toner having the first area and suitable for the target consumption of toner is formed on the laser scanner unit 33 (exposure unit). The control unit 90 (refresh operation control unit 93) causes the toner to be consumed by developing a dummy image on the surface of the photosensitive drum 31. In the refresh operation, the toner that has moved to the surface of the photosensitive drum 31 is removed from the surface of the photosensitive drum 31 by the cleaning unit 36 without being transferred to the paper T. As the deteriorated toner is consumed in this way, a new developer is supplied from the toner cartridge 37 to the developing device 34. The refresh operation in this embodiment will be described later.

  Next, the operation of the control unit 90 when the printer 1 is refreshed will be described. FIGS. 3A and 3B are schematic diagrams showing first and second small images formed on the photosensitive drum 31. FIG. 4A and 4B are graphs showing the relationship between the developing bias voltage and the toner consumption. FIGS. 5A and 5B are schematic diagrams illustrating regions on the photosensitive drum 31 where a dummy image is formed. FIG. 6 is a flowchart illustrating a processing procedure when the control unit 90 determines the image density of the dummy image.

  The control unit 90 (test image formation control unit 92) controls the image forming unit 30 before the refresh operation, so that the first small image (hereinafter referred to as a 100% solid image) outside the print area of the photosensitive drum 31 is obtained. A second small image (hereinafter also referred to as a “70% half image”) is formed by a 70% half image. Image data for forming these small images is stored in the storage unit 80 in advance. The control unit 90 (test image formation control unit 92) supplies image data for forming toner images of the first and second small images to the laser scanner unit 33, and the laser light emitted from the laser scanner unit 33 is used. Then, an electrostatic latent image of 100% solid image and 70% half image is formed on the surface of the photosensitive drum 31.

  3A shows a 100% solid image, and FIG. 3B shows a 70% half image. These small images are formed as a collection of dots by laser light. The image density of a small image can be adjusted by irradiating dots with laser light continuously or intermittently.

  A 100% solid image is formed by continuously irradiating laser light from the laser scanner unit 33. In a 100% solid image, since the irradiated laser light continuously moves, the charges formed on the surface of the photosensitive drum 31 are likely to move. Therefore, in a 100% solid image, the latent image potential of 1 dot becomes shallow.

  The 70% half image is formed by intermittently irradiating laser light from the laser scanner unit 33. In the 70% half image, since the irradiated laser light moves intermittently, the charge formed on the surface of the photosensitive drum 31 is difficult to move. Therefore, in a 70% half image, the latent image potential of 1 dot is deeper than that of a 100% solid image.

  In a normal refresh operation, a toner consumption amount is set in advance, and a development bias voltage corresponding to the toner consumption amount is set. However, when the toner deteriorates, even if the development bias voltage is raised to the maximum value, the target toner consumption is not reached, and it becomes difficult to stably consume the deteriorated toner.

  Here, the relationship between the development bias voltage and the toner consumption accompanying the toner deterioration will be described with reference to FIGS.

  FIG. 4A shows the toner consumption when the dummy image is formed with the toner density of 100% solid image in the refresh operation because the toner movement amount from the developing roller 343 to the photosensitive drum 31 decreases due to the deterioration of the toner. The case where the amount is reduced is shown. In a state where the toner is not deteriorated, a sufficient amount of toner moves from the developing roller 343 to the photosensitive drum 31, so that both 100% solid image and 70% half image can be developed with the original toner density. Therefore, as shown in FIG. 4A, before the toner is deteriorated, the toner consumption increases substantially in proportion to the developing bias voltage in both the 100% solid image and the 70% half image. In this case, the toner consumption during the refresh operation is larger when the dummy image is formed with the toner density of the 100% solid image than when the dummy image is formed with the toner density of the 70% half image.

  On the other hand, when the toner deteriorates, the amount of toner movement from the developing roller 343 to the photosensitive drum 31 decreases, so even if a dummy image is formed with a toner density of 100% solid image, the toner consumption during the refresh operation is Lower. Therefore, even if the development bias voltage is set to the maximum value (500 V), the target toner consumption may not be consumed.

  When the toner deteriorates, the movement amount of the toner from the developing roller 343 to the photosensitive drum 31 is reduced because the latent image potential of the 100% solid image is shallow, so that the toner moves from the developing roller 343 to the photosensitive drum 31. This is because the amount of toner used for developing the electrostatic latent image is reduced. On the other hand, since the latent image potential of the 70% half image is deep, the amount of toner used for developing the electrostatic latent image is not decreased unless the toner further deteriorates. Therefore, in the 70% half image, even if the toner deteriorates, as shown in FIG. 4A, the target toner consumption is consumed by setting the development bias voltage to the maximum value (500 V). Can do.

  In FIG. 4B, the toner further deteriorates, the amount of toner movement from the magnetic roller 342 to the developing roller 343 decreases, and a dummy image is formed with a toner density of 70% half image in the refresh operation. In this case, the toner consumption is reduced. If the toner further deteriorates, the amount of toner consumption decreases even if a dummy image is formed with a toner density of 70% half image. Therefore, even if the development bias voltage is set to the maximum value (500 V), the target toner consumption may not be consumed. This is because when the toner further deteriorates, the toner is overcharged and the amount of toner that moves from the magnetic roller 342 to the developing roller 343 decreases.

  Similarly, when toner deterioration further progresses, the amount of toner consumption decreases even if a dummy image is formed with a toner density of 100% solid image. This is because the deterioration of the toner further progresses, the toner external additive is buried in the toner, and the adhesion force between the developing roller 343 and the toner increases, so that the amount of toner moving from the developing roller 343 to the photosensitive drum 31 is reduced. This is thought to be less.

  As described above, the control unit 90 (refresh operation control unit 93) receives information on the detected toner density values of the 100% solid image and the 70% half image formed on the surface of the photosensitive drum 31 from the toner density sensor 39. get. Then, the control unit 90 (refresh operation control unit 93) compares the acquired detected toner density value with a toner target density value (described later) to obtain 100% as a toner density suitable for the target toner consumption amount. The toner density of the solid image or the 70% half image is selected, and a dummy image having the toner density is formed on the surface of the photosensitive drum 31 by the image forming unit 30. The toner target density value is a toner density value that can consume a target toner consumption amount by forming a dummy image of the toner density value during the refresh operation. A process for determining the image density (toner density) of the dummy image based on the detected toner density value acquired from the toner density sensor 39 in the control unit 90 will be described later.

  That is, the control unit 90 (refresh operation control unit 93) causes the amount of toner consumed when the dummy image is formed with the toner density of the 100% solid image (first small image) to reach the target consumption amount of toner. In this case, a dummy image having the same toner density as the 100% solid image is formed on the laser scanner unit 33 (exposure unit) regardless of the toner density of the 70% half image (second small image), and the 70% half image is formed. When only the consumption amount of toner consumed when the dummy image is formed with the toner density of (second small image) has reached the target consumption amount of toner, the dummy image having the same toner concentration as the 70% half image Is formed in the laser scanner unit 33.

  Here, the dummy image and its area will be described with reference to FIG. 5A and 5B are schematic views in which the photosensitive drum 31 is developed in the circumferential direction. FIG. 5A is a schematic diagram showing a dummy image 110 formed with an area A, and FIG. 5B is a schematic diagram showing a dummy image 120 formed with an area B. In FIGS. 5A and 5B, the range in which the dummy image is formed is indicated by hatching. 5A and 5B, a rectangular frame denoted by reference numeral 130 indicates a print area.

  The control unit 90 (refresh operation control unit 93), when any of the detected toner density values of the 100% solid image and the 70% half image acquired from the toner density sensor 39 is equal to or higher than the target density value (described later) of the toner. Then, as shown in FIG. 5A, the image forming unit 30 forms a dummy image having an area A in the print area 130 (photosensitive drum 31).

  On the other hand, the control unit 90 (refresh operation control unit 93) controls the image forming unit 30 when the detected toner density values of the acquired 100% solid image and 70% half image are both lower than the toner target density value. As shown in FIG. 5B, a dummy image having an area B (> area A) is formed in the print area 130 (photosensitive drum 31). As described above, in the printer 1 according to the present embodiment, when both the detected toner density values of the 100% solid image and the 70% half image are less than the toner target density value, the dummy image formed in the print area 130 is displayed. Therefore, a larger amount of toner can be consumed.

  That is, the control unit 90 (refresh operation control unit 93) is consumed when dummy images are formed with toner densities of 100% solid image (first small image) and 70% half image (second small image), respectively. When none of the toner consumption amounts has reached the target toner consumption amount, the laser scanner unit 33 is configured such that the area of the dummy image becomes a second area (area B) larger than the first area (area A). To control.

  Next, processing for determining the image density of the dummy image in the control unit 90 (the test image formation control unit 92 and the refresh operation control unit 93) will be described with reference to the flowchart of FIG.

  In step ST <b> 101 shown in FIG. 6, the control unit 90 (test image formation control unit 92) controls the image forming unit 30 to form a 100% solid image and a 70% half image on the surface of the photosensitive drum 31. These images are formed outside the printing area of the photosensitive drum 31.

  In step ST <b> 102, the control unit 90 (refresh operation control unit 93) acquires information regarding the detected toner density values of the 100% solid image and the 70% half image formed on the surface of the photosensitive drum 31 from the toner density sensor 39. .

  In step ST103, the control unit 90 (refresh operation control unit 93) determines whether or not the detected toner density value of the 100% solid image is equal to or higher than the toner target density value. If a dummy image having the same toner density as the toner target density value can be formed, the target toner consumption (see FIG. 3) can be consumed. Therefore, if the detected toner density value is equal to or higher than the target toner density value, a target toner consumption amount can be consumed by forming a dummy image with the detected toner density value in the refresh operation.

  In step ST103, when the control unit 90 (refresh operation control unit 93) determines that the detected toner density value of the 100% solid image is equal to or higher than the toner target density value (YES), the process proceeds to step ST104. In Step ST103, when the control unit 90 (refresh operation control unit 93) determines that the detected toner density value of the 100% solid image is less than the target toner density value (NO), the process proceeds to Step ST105. .

  In step ST104 (step ST103: YES determination), the control unit 90 (refresh operation control unit 93) causes the image forming unit 30 to form a dummy image having the same image density as the 100% solid image on the surface of the photosensitive drum 31. . At this time, the dummy image formed on the photosensitive drum 31 has a size of an area A shown in FIG. The dummy image is formed in the print area 130 (see FIG. 5A) of the photosensitive drum 31.

  As described above, when the detected toner density value of the 100% solid image is equal to or higher than the target toner density value, the control unit 90 (refresh operation control unit 93) regardless of the detected toner density value of the 70% half image. A dummy image having the same toner density as the 100% solid image is formed on the surface of the photosensitive drum 31 by the image forming unit 30. This is because a dummy image having the same toner density as the 100% solid image can be formed with a lower developing bias voltage than a dummy image having the same toner density as the 70% half image (see FIG. 3).

  When the process of step ST104 ends, the process of this flowchart for determining the toner density of the dummy image ends. The 100% solid image, the 70% half image, and the dummy image formed on the surface of the photosensitive drum 31 are removed from the surface of the photosensitive drum 31 by the cleaning unit 36.

  On the other hand, in step ST105 (step ST103: NO determination), the control unit 90 (refresh operation control unit 93) determines whether or not the detected toner density value of the 70% half image is equal to or higher than the toner target density value. In step ST105, when the control unit 90 (refresh operation control unit 93) determines that the detected toner density value of the 70% half image is equal to or higher than the toner target density value (YES), the process proceeds to step ST106. In Step ST105, when the control unit 90 (refresh operation control unit 93) determines that the detected toner density value of the 70% half image is less than the target toner density value (NO), the process proceeds to Step ST107. .

  In step ST106 (step ST105: YES determination), the control unit 90 (refresh operation control unit 93) causes the image forming unit 30 to form a dummy image having the same toner density as the 70% half image on the surface of the photosensitive drum 31. . At this time, the dummy image formed on the photosensitive drum 31 has a size of an area A shown in FIG. When the process of step ST106 is finished, the process of this flowchart for determining the toner density of the dummy image is finished.

  As described above, when the toner moves from the developing roller 343 to the photosensitive drum 31 due to the deterioration of the toner and the toner density of the 100% solid image becomes less than the target toner density value, the 100% solid image is obtained. Even if a dummy image having the same toner density is formed on the surface of the photosensitive drum 31, the target toner consumption cannot be achieved. In that case, a target toner consumption amount can be achieved in the printer 1 by forming a dummy image having the same toner density as the 70% half image on the surface of the photosensitive drum 31.

  In step ST107 (step ST105: YES determination), the control unit 90 (refresh operation control unit 93) causes the image forming unit 30 to apply a dummy image having the same toner density as the 100% solid image on the surface of the photosensitive drum 31. Let it form. At this time, the dummy image formed on the photosensitive drum 31 has a size of an area B (> area A) shown in FIG.

  In this way, when toner deterioration further progresses, the amount of toner movement from the magnetic roller 342 to the developing roller 343 decreases, and the toner density of the 70% half image becomes less than the toner target density value, 70 Even if a dummy image having the same toner density as that of the% half image is formed on the surface of the photosensitive drum 31, the target toner consumption cannot be consumed. In that case, a larger amount of toner can be consumed in the printer 1 by increasing the area of the dummy image having the same toner density as the 100% solid image. When the process of step ST107 ends, the process of this flowchart for determining the toner density of the dummy image ends.

  Next, the results of measuring the transition of image density (toner density) using a conventional printer and the printer 1 according to the present embodiment will be described. Here, in each printer, an A4 size document having a printing rate of 1% was continuously printed, the image density was measured every 1000 sheets, and a refresh operation was performed.

  When an image of a document having an extremely low printing rate is continuously printed in the printer, the toner in the developing device 34 is hardly consumed, and only the stirring is repeated, so that the deterioration of the toner proceeds.

  FIG. 7 is a graph showing changes in image density when an image of a document having a printing rate of 1% is continuously printed. In FIG. 7, black circles (in the figure, the present invention) indicate measurement results when images of a document having a printing rate of 1% are continuously printed by the printer 1 according to the present embodiment, and white triangles (in the figure, the conventional ones). Example) shows a measurement result when an image of a document having a printing rate of 1% is continuously printed by a conventional printer. Further, the level of the image density 1.2 indicated by a broken line in FIG. 7 is a target image density at which a target toner consumption amount can be consumed by forming a dummy image. Therefore, if the detected image density is equal to or higher than the target image density (1.2), the target toner consumption can be achieved when the printer is refreshed.

Further, the conventional printer formed a dummy image having the same image density as the 100% solid image and the toner consumption amount per sheet being 0.3 [mg / cm ² ] × 29.7 [cm ² ]. In the printer 1 according to the present embodiment, the toner consumption per sheet is 0.3 [mg / cm ² ] × 29.29 at the same image density as the 100% solid image or the 70% half image (see FIG. 3). A dummy image of 7 [cm ² ] was formed. Here, 29.7 [cm ² ] is the area of the dummy image.

  As shown in FIG. 7, in the conventional printer, the detected image density is lower than the target image density (1.2) from around 7000 sheets. This is because in a conventional printer, the toner deteriorates and the amount of toner transferred from the developing roller to the photosensitive drum decreases, so that the toner consumption in a 100% solid image is reduced and the developing bias voltage is set to the maximum value. (500V) is considered to be because the target toner consumption cannot be achieved (see FIG. 4A).

  On the other hand, the printer 1 according to the present embodiment exceeds the target image density (1.2) even when the detected image density exceeds 7000 sheets. This is because a dummy image having the same image density as that of a 70% half image is formed when the toner consumption of a 100% solid image decreases after 7000 sheets due to toner deterioration. This is considered to be because the printer 1 continued to achieve the target toner consumption even after the time passed.

  According to the printer 1 according to the above-described embodiment, for example, the following effects are achieved.

  In the printer 1 according to the present embodiment, the control unit 90 (refresh operation control unit 93) performs a 100% solid image and a 70% half image formed on the surface of the photosensitive drum 31 by the image forming unit 30 during the refresh operation. The toner density is acquired from the toner density sensor 39, and based on the toner density, a dummy image having an image density suitable for the target consumption of toner is formed on the surface of the photosensitive drum 31 by the image forming unit 30.

  According to this, since a dummy image having an image density suitable for the target consumption of toner is formed during the refresh operation, the printer 1 can extend the development time or increase the development bias voltage more than necessary during the normal operation. The toner consumption can be optimized without increasing it. Therefore, the deteriorated toner can be stably consumed by the refresh operation.

  Further, when the detected toner density value of the 100% solid image is equal to or higher than the target toner density value, the control unit 90 (refresh operation control unit 93) 100% regardless of the detected toner density value of the 70% half image. A dummy image having the same image density as the solid image is formed on the surface of the photosensitive drum 31.

  A dummy image having the same image density as the 100% solid image can be formed with a lower developing bias voltage than a dummy image having the same image density as the 70% half image. Therefore, the printer 1 can consume the target toner consumption with less power.

  Further, the control unit 90 (refresh operation control unit 93), when both the detected toner density value of the 100% solid image and the detected toner density value of the 70% half image are less than the target toner density value, is the photosensitive drum 31. The image forming unit 30 is controlled so that the area of the dummy image formed on the surface of the image becomes larger.

  According to this, even when a dummy image having the same image density as the 100% solid image or the 70% half image is formed, even if the target toner consumption cannot be consumed, the printer 1 increases the area of the dummy image. As a result, more toner can be consumed. In particular, when a dummy image having the same image density as a 100% solid image is formed as a dummy image having an increased area, the printer 1 is compared with a dummy image having the same image density as a 70% half image. A larger amount of toner can be consumed.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above, It can implement with a various form.

  In the present embodiment, an example in which a 70% half image is used as the non-100% dot image has been described. For example, the printer 1 may use an 80% to 60% half image as the non-100% dot image.

  In this embodiment, an example in which a 100% solid image and a 70% half image are formed on the photosensitive drum 31 as a small image for detecting toner deterioration has been described. Not limited to this, the printer 1 may form three or more kinds of small images having different image densities on the photosensitive drum 31.

  In this embodiment, an example in which a small image for detecting toner deterioration is formed outside the print area of the photosensitive drum 31 has been described. For example, in the case of a printer including an intermediate transfer belt, the printer 1 may form a small image outside the toner image transfer region on the intermediate transfer belt.

  In the present embodiment, an example in which the area of the dummy image formed on the photosensitive drum 31 is increased when the detected toner density values of the 100% solid image and the 70% half image are less than the target toner density value has been described (FIG. 5). reference). In this case, the area of the dummy image may be increased stepwise in proportion to the decrease in the detected toner density value of the 100% solid image and the 70% half image. Alternatively, a plurality of dummy image areas may be set in advance, and the dummy image area may be selected according to the detected toner density values of the 100% solid image and the 70% half image.

  The image forming apparatus according to the present invention is not limited to the printer 1 described above. In other words, the image forming apparatus according to the present invention may be a copier, a facsimile or a copier, a multifunction machine having functions of a facsimile and a printer.

  DESCRIPTION OF SYMBOLS 1 ... Printer (image forming apparatus), 30 ... Image forming part, 31 ... Photosensitive drum (image carrier), 33 ... Laser scanner unit (exposure part), 34 ... Developer, 37 ... Toner cartridge (developer storage part) , 39... Toner density sensor (toner density detection unit), 80... Storage unit, 90... Control unit, 91 .. normal operation control unit, 92 .. test image formation control unit (image formation control unit), 93. , 101 ... first voltage application unit, 102 ... second voltage application unit, 103 ... third voltage application unit, 341 ... stirring roller, 342 ... magnetic roller (developer carrier), 343 ... development roller (toner carrier) , 371... Toner supply unit

Claims (3)

A developer accommodating portion for accommodating a two-component developer containing at least toner and a carrier;
A developer carrier that holds the two-component developer by a magnetic force, and a magnetic brush is formed on the surface by a carrier contained in the two-component developer;
A toner carrier having a toner layer formed on the surface by toner supplied from the magnetic brush of the developer carrier; and
An image carrier on which an image along an electrostatic latent image formed on the surface is formed by toner supplied from a toner layer of the toner carrier;
The surface of the image carrier is continuously irradiated with laser light to electrostatically latent image in a 100% solid image of a predetermined area, and the laser beam is intermittently irradiated to electrostatic in non-100% dot image of a predetermined area and predetermined toner density. An exposure unit for forming a latent image;
An image formation control unit that forms a first small image based on a 100% solid image and a second small image based on a non-100% dot image on the exposure unit for detecting the deterioration state of the toner;
A toner density detector for detecting the toner density of the first small image and the second small image formed on the surface of the image carrier;
Based on information on the toner density of the first small image and the second small image detected by the toner density detection unit, a dummy image having a predetermined first area and a toner density suitable for the target consumption of toner is obtained. A refresh operation control unit to be formed in the exposure unit;
An image forming apparatus comprising: The refresh operation control unit
When the amount of toner consumed when the dummy image is formed with the toner density of the first small image has reached the target consumption of toner, the toner is consumed regardless of the toner density of the second small image. When the dummy image having the same toner density as that of the first small image is formed in the exposure unit and the dummy image is formed with the toner density of the second small image, only the amount of toner consumed is the target consumption of toner. When the amount has reached, the dummy image having the same toner density as the second small image is formed on the exposure unit.
The image forming apparatus according to claim 1. The refresh operation control unit
If any of the toner consumptions consumed when the dummy images are formed with the toner densities of the first small image and the second small image, respectively, the dummy consumption is reached. Controlling the exposure unit so that the area of the image becomes the first area;
The first when the amount of toner consumption to be consumed in the case of forming each said dummy image at a toner density of the small image and the second sub image is not either reaches the target amount of toner consumption, the dummy image Controlling the exposure unit so that the area of the second area is larger than the first area,
The image forming apparatus according to claim 1.

Images