JP2008111996A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which performs control operation, based on a stable detection output by avoiding a period such as the time of starting developer-conveyance where the toner concentration detection output is not stabilized. <P>SOLUTION: Regarding the image forming apparatus, in the case of starting a control of the toner concentration in a developing unit using two-component developer, a main motor 60 starts to be driven (S100a), the developer conveyance stop period in the developing unit counted from when the drive of the motor is stopped last is calculated (S100b), and a delay time TD corresponding to the calculated conveyance stop period is read from a set value table 102, and the delay time TD is set (S100c). A counting operation is started by a timer T(S101), whether the counted value by the timer T is exceeding the delay time TD is checked (S102), When being equal to or exceeding the delay time TD, the concentration control is started, and the sampling processing of the detection outputs from the concentration detecting sensor 44 is started (S103). <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, Patent Document 1 describes that the toner replenishment amount is corrected according to a change in toner fluidity in order to keep the toner concentration of the two-component developer within an allowable range. Further, in Patent Document 2, each time the developer in the developing device is agitated during the image forming operation, the detection output of the toner concentration sensor or the toner concentration control is performed according to the time from the agitation start to the detection start by the toner concentration sensor. The point is provided with a correction means for calculating the correction amount of the reference value.
JP-A-10-78696 Japanese Patent No. 3542148

  As described in the above-mentioned patent document, when the toner concentration of the developer is detected while conveying a two-component developer (hereinafter referred to as “developer”), the detection is performed by a change in toner fluidity. Since the output becomes unstable, improvements have been made so that the unstable detection output does not affect other control operations.

  It is known that when the detection output becomes unstable in this way, it occurs immediately after the developer transport operation in the developing device starts from the stopped state, but the period during which the detection output becomes unstable Therefore, even if the detection output is corrected as in Patent Document 2, there is a possibility that a deviation from the actual toner density occurs.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of performing a control operation based on a stable detection output while avoiding an unstable period of a toner density detection output at the start of developer conveyance. To do.

  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. A start timing for measuring a two-component developer conveyance stop time in the developing unit and acquiring a detection output of the concentration detection unit based on the conveyance stop time; Setting to set Characterized in that it comprises means, and a density control means for controlling the developing means and the feeding means based on the obtained and the detection output of the detection output at the set start timing. Further, the density control means is characterized in that the detection output is obtained by sampling every predetermined time and controlled based on an average value of a predetermined number of sampling times.

  Another image forming apparatus according to the present invention includes an image carrier, charging means for charging the surface of the image carrier, and exposure for forming an electrostatic latent image by exposing the charged surface of the image carrier. Means for storing the two-component developer and developing the electrostatic latent image formed on the surface of the image carrier with the two-component developer, and supplying the developer with toner. In the image forming apparatus, comprising: a means; a paper conveying means for feeding and conveying the paper; and a control means for controlling the rotation of the image carrier and controlling the means so as to form an image on the paper. The control means measures the transport stop time of the two-component developer in the developing means and sets the paper feed start timing of the paper transport means based on the transport stop time, and the set paper feed Before feeding at the start timing It characterized in that it comprises a conveyance control means for controlling the sheet conveying means.

  As a result of earnestly examining the phenomenon that the detection output of the density detection sensor that detects the toner density of the developer becomes unstable when the developer starts to be transported, the length of the unstable period is It was found that there is a correlation with the length of the conveyance stop time. For example, when the conveyance stop time is short, the unstable period also becomes short, and when the conveyance stop time becomes long, the unstable period tends to become long.

  Therefore, based on such knowledge, in the present invention, the start timing for measuring the transport stop time of the two-component developer in the developing unit and acquiring the detection output of the density detector based on the transport stop time is set. By providing the setting means, it is possible to set a start timing for acquiring the detection output in accordance with the conveyance stop time, and to reliably acquire a stable detection output while avoiding an unstable period. Therefore, stable toner density control can be performed by acquiring the detection output at the set start timing and controlling the developing means and the replenishing means based on the detection output to perform density control. In particular, when the conveyance stop time is short, the start timing for acquiring the detection output can be set earlier, so that the image forming process can be started earlier.

  In addition, when the detection output is sampled and acquired every predetermined time and density control is performed based on the average value of the predetermined number of times of sampling, the sampling process in which the influence follows when the unstable detection output is acquired and sampled There is a possibility that the period of instability will be extended, but the start timing is set so as to acquire stable detection output, so that stable sampling processing can be performed. It becomes possible.

  And a setting unit configured to measure a conveyance stop time of the two-component developer in the developing unit and set a sheet feeding start timing of the sheet conveying unit based on the conveyance stop time. By controlling the paper transporting unit so as to feed the paper, the paper can be fed in synchronization with the above-described density control to perform stable image forming processing, and the developer transport stop time is further increased. If the length is short, the paper feeding operation is started earlier, and the efficiency of the image forming process can be improved.

  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 the toner cartridge 30 through the toner delivery path 52 to a hopper 54 having a built-in transport 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 voltage applied to the corona charger 21, the developing roller 40, and the transfer roller 23 is controlled by the control unit 100 controlling the developing voltage application circuit 62, the charging voltage application circuit 63, and the transfer voltage application circuit 64, respectively. Done.

  The control unit 100 includes a setting unit 101, a setting value table 102, and a timer 103. The setting unit 101 starts timing by the timer 103 at the timing of stopping the conveying operation of the augers 41 and 42 in the developing device 19, The conveyance stop time until the start of the next conveyance operation is measured. Based on the measured conveyance stop time, the acquisition start timing data of the detection output of the density sensor 44 is read from the set value table 102 and the start timing is set. Since the transport operations of the augers 41 and 42 are synchronized with the rotational drive of the main motor 60, the transport stop time can be measured at the start and stop timing. As the acquisition start timing data, a delay time from when the main motor 60 starts to rotate until the acquisition starts can be registered in the set value table 102 in correspondence with the conveyance stop time. In this example, the acquisition start timing data is registered in advance in the set value table. However, an equation for calculating data based on the measured conveyance stop time is set, and the acquisition start timing is calculated using the equation. May be requested.

  FIG. 3 is a graph showing the temporal transition of the detection output of the density detection sensor 44 immediately after the developer transport is stopped in the developing device 19 from the transport stop state. FIG. 3A shows the transition of the detection output when the conveyance stop time is short, and FIG. 3B shows the transition of the detection output when the conveyance stop time is long. Comparing the time when the detection output immediately after the start of both conveyances is unstable, the unstable time T1 shown in FIG. 3 (a) is shorter than the unstable time T2 shown in FIG. 3 (b). I understand. Therefore, by setting the detection output acquisition start timing corresponding to the conveyance stop time based on such correlation, it is possible to reliably acquire a stable detection output, and early timing when the conveyance stop time is short. You can start acquisition.

  FIG. 4 is an explanatory diagram regarding sampling processing of detection output from the density detection sensor 44. The detection signal of the density detection sensor 44 causes periodic amplitude fluctuations as shown in FIG. 4 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 interval synchronized with the rotation period of the auger and using the average value of the sampled history data as a detection output.

  In the example shown in FIG. 4, when the drive of the main motor is turned on, a detection output is generated from the density detection sensor 44, but sample data is not acquired during the delay time TD set corresponding to the conveyance stop time. . Then, detection output is sequentially started from the sample timing S1 after the delay time TD has elapsed. In this example, since the average value of the history data for 10 times is used as the detection output, the average value for 10 times from S1 to S10 is obtained at the sample timing S10, and output of data used for density control is started. The Then, at the sample timing S11, the average value for 10 times from S2 to S11 is obtained, and the average value for 10 times is obtained while being sequentially shifted one by one.

  FIG. 5 is a processing flow when density control is started at the time of power-on or operation from a standby state. When the power is turned on or during operation from the standby state, the main motor 60 starts driving (S100a), calculates the developer conveyance stop time in the developer measured from the previous driving stop (S100b), and calculates The delay time TD corresponding to the transport stop time is read from the set value table 102 and set (S100c). Then, the timer T starts counting (S101), and it is checked whether or not the timer T has reached the delay time TD or more (S102). If the delay time TD or more is reached, density control is started and sampling processing of detection output from the density detection sensor 44 is started (S103).

  In the embodiment described above, the start timing of density control is controlled based on the transport stop time of the developer in the developing device. However, the start timing of paper feed control is controlled based on the transport stop time. It may be. That is, a series of process processes such as charging-exposure-development-transfer and sheet conveyance control cannot be performed in precise synchronization, and high-quality image forming processing cannot be performed on the sheet. As described above, since the image forming process is performed by performing the density control stably in the developing process using the two-component developer, the developer transport that is an index for starting the stable density control is performed. If the paper feed start timing is controlled based on the stop time, stable image forming processing can be performed.

  The paper feed start timing data may be registered in advance in the setting value table 102 shown in FIG. 2 in association with the conveyance stop time. When the setting unit 101 calculates the conveyance stop time, the setting unit 101 reads the corresponding paper feed start timing data and sets the start timing. As the paper feed start timing data, a delay time from when the main motor 60 starts to rotate to when paper feed is started may be set.

  FIG. 6 is a processing flow in the case of starting paper conveyance control when the power is turned on or during operation from the standby state. When the power is turned on or during operation from the standby state, the main motor 60 starts driving (S200a), calculates the developer conveyance stop time in the developer measured from the previous driving stop (S200b), and calculates The delay time TD corresponding to the transport stop time is read from the set value table 102 and set (S200c). Then, the timer T starts counting (S201), and it is checked whether or not the timer T has reached the delay time TD or more (S202). If the delay time TD or more is reached, the paper conveyance control is started and the paper feed process is started (S203).

  The paper conveyance control start process described above can be performed in parallel with the above-described density control start process, and a more stable image forming process can be realized.

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 explanatory drawing regarding the sampling process of the detection output of a density | concentration detection sensor. It is a flow regarding the start processing of density control. It is a flow regarding the start process of paper conveyance control.

Explanation of symbols

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

Claims (3)

  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 means is set with setting means for measuring a transport stop time of the two-component developer in the developing means and setting a start timing for acquiring a detection output of the density detection means based on the transport stop time. Started Thailand Image forming apparatus characterized by to obtain the detection output ring and a density control means for controlling the developing means and the feeding means based on the detection output.   The image forming apparatus according to claim 1, wherein the density control unit samples and acquires the detection output at predetermined time intervals and controls the detection output based on an average value of a predetermined number of sampling times.   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 paper is fed and conveyed. In the image forming apparatus, comprising: a sheet conveying unit; and a control unit that controls the rotation of the image carrier and controls the units so as to form an image on the sheet. Setting means for measuring the transport stop time of the developer and setting the paper feed start timing of the paper transport means based on the transport stop time; and the paper so as to feed paper at the set paper feed start timing Transport control to control transport means An image forming apparatus characterized by comprising a stage.

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