JP2008111880A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus ensuring stable control of toner concentration by suppressing excessive supply of toner. <P>SOLUTION: When toner is supplied to a developing unit that develops images with two-component developer, concentration is controlled by performing a supply operation on the basis of a detection output from a concentration detection sensor, which detects the toner concentration of developer conveyed within the developing unit. In this case, the supply operation is performed in a regular supply mode from a time t1 at which the detection output exceeds a reference threshold AS, and a quantity of toner to be supplied is increased from a time t2 at which the detection output exceeds an intermediate threshold AT1. Then, the regular supply mode switches to a forcible supply mode from a time t3 at which the detection output exceeds a set threshold AT2, thereby decreasing the detection output. The regular supply mode is entered at a time t4 at which the detection output falls below the intermediate threshold AT3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image using a two-component developer in an image forming apparatus such as a copying machine, a printer, or a facsimile machine.

  As an electrophotographic image forming apparatus, for example, a photosensitive drum is used as an image carrier, the surface is charged and exposed to form an electrostatic latent image, and toner is attached to the electrostatic latent image. An image forming apparatus is known that forms a visible image and transfers it onto a sheet of paper.

As a developer used for image formation, two types have been conventionally used: a two-component developer containing a carrier composed of toner and magnetic particles, and a one-component developer using only the toner. In the case of the two-component developer, the toner is favorably charged by frictional charging with the carrier, and high-resolution image formation can be stably performed. In such an image forming apparatus using a two-component developer, in order to keep the mixing ratio of the toner and carrier of the developer constant, the toner concentration is constantly detected and the toner concentration is adjusted to a predetermined range. Replenishment is to be performed. For example, in Patent Document 1, a toner concentration control method in which the toner concentration of a two-component developer is detected by the output of a magnetic permeability sensor and the toner is replenished into the developing device when the output exceeds a certain level. The toner is replenished based on the output value of the sensor and the output increase rate of the sensor, and after the toner replenishment, only the developer agitation operation is executed according to the output increase change rate without executing the image forming cycle for a predetermined time. Has been.
JP 2004-317960 A

  As described in the above-mentioned patent document, when the toner density of the developer is detected while conveying a two-component developer (hereinafter referred to as “developer”), a rapid toner consumption occurs. There is a problem that the toner density becomes non-uniform and the toner density control becomes unstable. Such toner density control becomes unstable even when toner is replenished rapidly. In the case of toner replenishment, if the toner replenishing port is away from the toner density detection position, the toner replenishment operation is continued while the replenished toner is transported to the detection position, and the toner density is detected. The output becomes unstable and toner density control cannot be performed stably. As described in the patent document, it is conceivable that the image forming cycle is not executed until the toner density is stabilized. However, limiting the image forming cycle every time the toner is replenished reduces the operation efficiency of the apparatus. There is a fear.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of performing stable toner density control while suppressing excessive supply of toner.

  An image forming apparatus according to the present invention includes an image carrier, a charging unit that charges the surface of the image carrier, and an exposure unit that exposes the charged surface of the image carrier to form an electrostatic latent image. Developing means for storing the two-component developer and visualizing the electrostatic latent image formed on the surface of the image carrier with the two-component developer; and a replenishing means for supplying toner to the developing means. And an image forming apparatus comprising: a control unit that controls the respective units so as to control the rotation of the image carrier and form an image on a sheet; and the toner concentration of the two-component developer conveyed by the developing unit. Density detecting means for detecting, and when the detection output from the density detecting means exceeds a reference threshold, the detection output indicates a normal supply mode for performing toner supply control and a set threshold exceeding the reference threshold. Beyond By limiting the toner consumption if, characterized in that it comprises a concentration control means for controlling the toner concentration by forced supply mode for toner replenishment control. Further, the density control unit increases the toner replenishment amount per unit time when the detection output exceeds at least one intermediate threshold set between the reference threshold and the set threshold. To do. Further, when the toner density is controlled in the forced replenishment mode, the density control unit is configured to supply the normal replenishment when the detection output falls below an intermediate threshold set between the reference threshold and the set threshold. It is characterized by shifting to the mode. Further, the concentration control means outputs an error when the forced supply mode continues for a predetermined time or more.

  With the above configuration, the toner supply is performed when the detection output exceeds the normal supply mode in which toner supply control is performed when the detection output from the density detection unit exceeds the reference threshold and the set threshold exceeding the reference threshold. Since the toner density is controlled by the forced supply mode in which toner supply control is performed with the toner density being restricted, stable toner density control can be performed without abruptly changing the toner density.

  In other words, when the detection output exceeds the reference threshold, toner supply control is performed in the normal supply mode, so that toner supply is performed while the toner is consumed by the image forming process, and when the detection output exceeds the set threshold. By performing toner supply control in the forced supply mode, toner supply is limited and toner supply is performed. Therefore, the normal supply mode is used as a pre-stage of the forced supply mode in which a rapid change in toner density is likely to occur. Replenishment of toner can be performed to suppress a rapid change in toner density.

  In addition, even if the detection output exceeds the reference threshold, if the toner concentration is stabilized by the normal replenishment mode and the detection output does not exceed the set threshold, a forced change in toner concentration is likely to occur. It is not necessary to shift to the replenishment mode, and the operation efficiency of the apparatus can be maintained without performing the toner consumption restriction associated with the forced replenishment mode.

  If the toner replenishment amount per unit time is increased when the detection output exceeds at least one intermediate threshold set between the reference threshold and the set threshold, the change in the detection output in the normal replenishment mode. By increasing the toner replenishment amount in accordance with this, it is possible to further suppress a rapid change in the toner density.

  In addition, when the toner density is controlled by the forced supply mode, if the detection output falls below the intermediate threshold set between the reference threshold and the set threshold, the normal threshold supply mode can be entered. The toner consumption restriction associated with the forced replenishment mode is canceled at an early stage before the detection output falls below, and the reduction in the operation efficiency of the apparatus due to the restriction of the image forming process can be recovered early. If the transition to the normal replenishment mode is made at an early stage, it becomes easy to stabilize the detection output near the reference threshold by gradually changing the toner density when the detection output approaches the reference threshold. If the forced replenishment mode is continued until the detection output falls below the reference threshold, toner oversupply is likely to occur, but it must first shift to the normal replenishment mode before the detection output drops to the reference threshold. Thus, the excessive supply of toner can be suppressed.

  In addition, if the forced replenishment mode continues for a predetermined time or more, it is suspected that the density control is not normally performed, and therefore an error is output to reliably prevent abnormal density control from being performed. It becomes possible.

  Hereinafter, embodiments according to the present invention will be described in detail. The embodiments described below are preferable specific examples for carrying out the present invention, and thus various technical limitations are made. However, the present invention is particularly limited in the following description. Unless otherwise specified, the present invention is not limited to these forms.

  FIG. 1 is a schematic cross-sectional view of the entire image forming apparatus according to the present invention. A paper discharge tray 10 is provided in the upper part of the image forming apparatus 1, and a recording unit 2 and a paper supply unit 3 are arranged in the lower part thereof.

  In the paper feed unit 3, a paper feed cassette 11 is arranged, and a plurality of sheets of a predetermined size are stacked on the flapper 12. The flapper 12 is rotated upward in conjunction with the rotation of the arm 13 by the rotation of the arm 13 by the motor. A pickup roller 14 is disposed at the right end of the paper feed cassette 11. The flapper 12 is supported by the arm 13 so that the upper surface of the stacked paper is pressed against the pickup roller 14. When the pickup roller 14 is rotationally driven in this state, the sheets are fed one by one to the sheet conveyance path by the frictional force, and are nipped and conveyed by the feed roller 15 and the press roller 16.

  The fed paper is conveyed to the recording unit 2 by the registration roller 17 and the press roller 18. The recording unit 2 includes a developing device 19, a cleaning mechanism 20, a corona charger 21, a photosensitive drum 22, a transfer roller 23, an exposure head 24, and a fixing roller 25 for recording on the conveyed paper.

  As will be described later, the developing unit 19 incorporates a pair of augers having spiral blades, and the developer is conveyed by the pair of augers so as to circulate in a predetermined direction. The developer conveyed in a circulating manner is supplied to the developing roller through a rotating paddle. The developing roller is composed of an internal magnet roller and a cylindrical developing sleeve disposed on the outer peripheral surface of the magnet roller, and the carrier of the developer is attracted to the surface of the developing sleeve by the magnetic force of the magnet roller to form carrier spikes. Then, the toner is attached to the formed carrier ear. In this case, since the carrier and the toner are charged with opposite polarities due to frictional charging while being conveyed, the toner is held in a stable state by the electric attraction force on the carrier ear. Further, a density detection sensor for detecting the toner density of the conveyed developer is attached in the vicinity of the developer conveyance path by the auger, and toner is replenished based on an output signal from the density detection sensor. As the concentration detection sensor, a known sensor that detects the toner concentration by measuring the magnetic permeability of the developer can be used. When a magnetic permeability sensor is used, the density of the carrier, which is a magnetic material, increases as the toner concentration decreases. Therefore, the magnetic permeability increases and the output of the sensor increases. Conversely, when the toner concentration increases, the corresponding amount increases. The density of the carrier is reduced and the output of the sensor is lowered. The toner is supplied from the toner cartridge 30 to the developing unit 19 through a supply mechanism (not shown).

  The cleaning mechanism 20 cleans the surface of the photoconductor drum 22 by scraping off foreign matters such as residual toner and paper dust attached to the surface of the photoconductor drum 22 after transfer with a cleaning blade. Foreign matter such as residual toner collected by the cleaning mechanism 20 is transported to the waste toner reservoir 31 and discharged.

  The corona charger 21 uniformly charges the surface of the photosensitive drum 22 by corona discharge from the discharge wire. An electrostatic latent image is formed on the uniformly charged photosensitive drum 22 by exposure according to the image recording signal by the exposure head 24. Then, the developing sleeve in the developing device 19 rotates and the carrier ears formed on the surface thereof approach the surface of the photosensitive drum 22 and the toner adhering to the carrier ears is transferred to the electrostatic latent image. Visualize the image. The transfer roller 23 is installed at a position facing the photosensitive drum 22 with the paper interposed therebetween, and a toner image formed on the surface of the photosensitive drum 22 is transferred to the paper when a predetermined voltage is applied. In this way, a series of processes necessary for image formation is performed, and the transferred toner image is sandwiched between the fixing roller 25 and the press roller 26 and heated and pressed to be fixed on the paper. The fixed sheet is sent to the discharge path by the feed roller 27 and the press roller 28, and is carried out to the sheet discharge tray 10 by the discharge roller 29.

  Further, a manual paper feed mechanism and a reverse conveyance mechanism are provided on the side surface of the apparatus main body. When manual paper feed is performed, the manual feed tray 32 is opened and the paper is inserted into the paper feed roller 33. . The inserted paper is conveyed to the feed roller 17 and the press roller 18 by the paper feed roller 33, and a recording operation is performed. Also, when performing reverse conveyance, the paper recorded on one side is once carried out by the discharge roller 29, then reversely rotates the discharge roller 29 and is conveyed to the reverse conveyance path, and is conveyed downward by the conveyance roller 34. . Then, the paper is transported upward along the transport path, transported again to the feed roller 17 and the press roller 18, and the recording operation is performed on the other surface to record on both surfaces of the paper.

  FIG. 2 is a schematic block diagram of the image forming apparatus shown in FIG. Around the photosensitive drum 22, a corona charger 21, an exposure head 24, a developing device 19, a transfer roller 23, a cleaning mechanism 20, and a static elimination lamp 36 are disposed, and the surface of the photosensitive drum 22 is rotated while rotating. On the other hand, after a series of process processes such as charging-exposure-development-transfer are performed, the surface is cleaned and the remaining charge is neutralized.

  In the developing unit 19, the developing roller 40 described above is disposed to face the photosensitive drum 22, and a developer storage portion is formed on the opposite side of the developing roller 40 from the photosensitive drum 22. A pair of augers 41 and 42 are arranged in the storage part. The rotation shafts of the augers 41 and 42 are linearly extended in the direction perpendicular to the paper surface, and a partition wall 43 is provided therebetween. Then, the augers 41 and 42 convey the developer in opposite directions so that the developer is circulated and conveyed around the partition wall in the reservoir.

  A density detection sensor 44 is disposed on the bottom surface corresponding to the storage portion of the developing device 19 so as to detect the toner density of the developer that is circulated and conveyed as described above. The developer conveyed in a circulating manner is supplied to the developing roller 40 by the supply paddle 45, and the developer supplied to the surface of the developing sleeve of the developing roller 40 is leveled into a uniform layer by the blade 46.

  The toner replenishing mechanism 50 delivers toner from a bottle holder 51 that holds the toner cartridge 30 through a toner delivery path 52 to a hopper 54 that incorporates a conveyance spiral 53. Toner is replenished from the hopper 54 to the storage portion of the developing device 19 through the toner conveyance path 55 containing the conveyance spiral 56. The toner cartridge 30 is rotated by a toner supply motor 61 to discharge toner.

  A series of operation control for performing the above-described process processing necessary for image formation is performed by the control unit 100. The photosensitive drum 22 and various rollers are driven to rotate by controlling a main motor 60 and a drive transmission mechanism such as a clutch mechanism (not shown). Further, the toner replenishment operation by the transport spiral of the toner replenishment mechanism 50 and the transport control of the developer such as the auger of the developing device 19 are also controlled by transmitting the rotational drive of the main motor 60, and the control unit 100 detects the density. Based on the detection signal from the sensor 44, toner replenishment control and developer density control are performed. The drive control of the toner supply motor 61 of the toner supply mechanism 50 is also performed by the control unit 100, and the supply operation from the toner cartridge 30 is controlled.

  The voltages applied to the corona charger 21, the developing roller 40, and the transfer roller 23 are controlled by controlling the developing voltage application circuit 62, the charging voltage application circuit 63, and the transfer voltage application circuit 64, respectively.

  FIG. 3 is a graph showing the temporal transition of the detection output when the control unit 100 performs density control in response to the detection output of the density detection sensor 44. The vertical axis represents detection output, and the horizontal axis represents time.

  The detection signal of the density detection sensor 44 causes periodic amplitude fluctuations because the auger blades periodically face the density detection sensor 44 as the auger rotates. Therefore, the detection output of the density detection sensor 44 may be obtained by, for example, sampling the detection signal at a sampling period synchronized with the rotation period of the auger and using the average value of the sampled history data as a detection output.

  In the graph shown in FIG. 3, since the toner in the developing device 19 is not consumed, the detection output A is density-controlled so as to fall below the reference threshold AS, as shown by the solid line. In this example, density control is performed using an intermediate threshold value AT1, a set threshold value AT2, and an intermediate threshold value AT3 as threshold values exceeding the reference threshold value AS. The intermediate threshold value AT1 is set between the reference threshold value AS and the set threshold value AT2, and the intermediate threshold value AT3 is set to a value smaller than the intermediate threshold value AT1 between the reference threshold value AS and the set threshold value AT2. Data relating to such threshold values is registered in the threshold value table 101 of the control unit 100 and used for density control.

  When the detection output A is within the detection range AD1 from the reference threshold value AS to the intermediate threshold value AT1, the density control is performed in the normal supply mode, and the toner supply operation by the conveying spiral of the toner supply mechanism 50 is executed. Then, a predetermined amount of toner is supplied into the developing device 19.

  When the detection output A is within the detection range AD2 from the intermediate threshold value AT1 to the set threshold value AT2, the density control is performed in the normal replenishment mode as in the detection range AD1, but the unit time is longer than that in the detection range AD1. The replenishment operation is performed by increasing the toner replenishment amount per unit. The increase in the toner replenishment amount may be performed by, for example, a method of setting the driving time of the conveyance spiral longer.

  When the detection output A is within the detection range AD3 that exceeds the set threshold value AT2, density control is performed in the forced supply mode, toner supply operation is performed, and image formation processing is restricted to limit toner consumption. Is done. By performing such density control, the toner amount in the developing device 19 is controlled to be rapidly increased so that the toner density is quickly restored.

  When density control is performed in the forced replenishment mode, if the detection output A falls below the intermediate threshold value AT3, the normal replenishment mode is entered and the restriction on toner consumption is released. By setting the intermediate threshold value AT3 to a value smaller than the intermediate threshold value AT1, a sufficient toner amount is supplied into the developing device 19 in the forced supply mode, and the detection output A can be lowered to the reference threshold value AS.

  FIG. 4 is a processing flow relating to density control, and FIG. 5 is a graph showing an example of temporal transition of the detection output A by density control. When the density control is started, it is checked whether the detection output A is equal to or less than the reference threshold AS (S100). If it is equal to or less than the reference threshold value AS, the same check is repeated. If the detection output A exceeds the reference threshold value AS, it is checked whether it is equal to or less than the intermediate threshold value AT1 (S101). If it is equal to or less than the intermediate threshold value AT1, the normal supply mode is entered, and the toner is supplied by driving the conveying spiral of the toner supply mechanism 50 (S102). Then, the process returns to step S100.

  If it is determined in step S101 that the detection output A has exceeded the intermediate threshold value AT1, it is checked whether it is equal to or less than the set threshold value AT2 (S103). When it is equal to or lower than the intermediate threshold value AT2, the normal supply mode continues, but the supply operation is performed by increasing the toner supply amount per unit time (S104). Then, the process returns to step S100.

  If it is determined in step S103 that the detection output has exceeded the set threshold value AT2, the timer T starts counting (S105), and the mode is shifted to the forced supply mode (S106). In the forced replenishment mode, the toner replenishing operation is performed by limiting the image forming process that consumes toner. Then, it is checked whether the count value of the timer T is equal to or longer than the predetermined time TL (S107). If the count value is smaller than the predetermined time TL, it is checked whether the detection output A is equal to or lower than the intermediate threshold value AT3 (S108). When the detection output A exceeds the intermediate threshold value AT3, the process returns to step S106, and the forced supply mode is continued.

  If it is determined in step S107 that the timer T is equal to or longer than the predetermined time TL, the process proceeds to error processing (S109). In error processing, concentration control is stopped and an alarm is displayed.

  If it is determined in step S108 that the detection output A has fallen below the intermediate threshold value AT3, the timer T is reset (S110) and the process returns to step S100. Then, whether or not the detection output A is less than or equal to the reference threshold AS is checked. If the detection output A exceeds the reference threshold AS, it is checked whether or not it is less than or equal to the intermediate threshold AT1 in step S101. Will come to do.

  When the time transition of the detection output A by the density control described above is taken as an example in FIG. 5, first, the transition to the normal replenishment mode is made from the time when the detection output A exceeds the reference threshold AS at time t1. Then, the toner replenishment operation is performed. When the detection output A further increases as in this example, the toner replenishment amount per unit time from the time when the detection output A exceeds the intermediate threshold value AT1 at time t2. To increase.

  When the detection output A further increases despite the increase in the toner replenishment amount, the forced replenishment mode is entered from the time when the detection output A exceeds the set threshold value AT2 at time t3. In the forced replenishment mode, toner replenishment is performed while restricting toner consumption, so that the toner density in the developing device increases and the detection output A decreases. If the forced replenishment mode continues for a predetermined time without the detection output A decreasing, the process proceeds to error processing and density control is stopped.

  Thus, instead of shifting to the forced supply mode when the reference threshold value AS is exceeded, it is possible to shift to the forced supply mode without causing a sudden change in toner density by shifting to the normal supply mode once. it can.

  Then, the transition to the normal replenishment mode starts from the time when the detection output A falls below the intermediate threshold value AT3 at time t4. By shifting to the normal replenishment mode, the restriction on toner consumption is lifted and the sudden increase in the toner amount in the developer as in the forced replenishment mode is suppressed, and the detection output gradually decreases. The normal replenishment mode is stopped when the detection output A falls below the reference threshold AS at t5. As described above, when the detection output A decreases due to the forced supply mode and approaches the reference threshold AS, the detection output A gradually changes, and the toner density rapidly increases. Destabilization of density control due to changes can be suppressed.

  As described above, when the detection output A exceeds the reference threshold value, the mode is temporarily shifted to the normal supply mode and then the forced supply mode. When the detection output A approaches the detection output A reference threshold value in the forced supply mode, Since the mode is shifted to the replenishment mode, a rapid change in toner density is suppressed, stable density control is performed, and occurrence of excessive toner replenishment is suppressed.

1 is a schematic sectional view of an entire image forming apparatus according to an embodiment of the present invention. It is a schematic block diagram regarding the embodiment concerning the present invention. It is a graph which shows the time transition of the detection output of a density | concentration detection sensor. It is a processing flow regarding density control. It is a graph which shows an example of the time transition regarding the detection output of a density | concentration detection sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Recording part 3 Paper feeding part

Claims (4)

  An image carrier, a charging unit for charging the surface of the image carrier, an exposure unit for exposing the charged surface of the image carrier to form an electrostatic latent image, and a two-component developer are stored. In addition, a developing unit that visualizes the electrostatic latent image formed on the surface of the image carrier with a two-component developer, a replenishing unit that replenishes toner to the developing unit, and rotation control of the image carrier. And a control unit that controls each of the units so as to form an image on a sheet. The image forming apparatus further includes a density detection unit that detects a toner density of a two-component developer conveyed by the development unit, The control unit restricts toner consumption when the detection output exceeds a normal supply mode in which toner supply control is performed when a detection output from the density detection unit exceeds a reference threshold and a set threshold exceeding the reference threshold. T An image forming apparatus characterized by comprising density control means for controlling the toner concentration by forced supply mode for over replenishment control.   The density control unit increases a toner replenishment amount per unit time when the detection output exceeds at least one intermediate threshold set between the reference threshold and the set threshold. Item 2. The image forming apparatus according to Item 1.   When the toner density is controlled by the forced replenishment mode, the density control unit switches to the normal replenishment mode when the detection output falls below an intermediate threshold set between the reference threshold and the set threshold. The image forming apparatus according to claim 1, wherein the image forming apparatus shifts.   The image forming apparatus according to claim 1, wherein the density control unit outputs an error when the forced supply mode continues for a predetermined time or more.

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