JP2009169317A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device such as a printer, capable of determining properly a toner density in a developing device in an initial stage of starting stirring to control replenishment of toner to the developing device. <P>SOLUTION: A laser printer 1 detects the toner density in the developing device 31 with a developer stirred by a conveying screw 35 executing stirring and stopping thereof at prescribed timing, by a toner density sensor 36, stores a toner density value detected by the toner density sensor 36 as a storage toner density value Vtp in a RAM 43 or an NVRAM 44, and calculates a toner replenishing amount, based on the storage toner density value Vtp (as an estimated toner density value), in a detection unstable period from the start of the stirring until the toner density value detected by the toner density sensor 36 gets stable. Consequently, the toner density in the developing device 31 is controlled precisely from just after the start of the stirring. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more specifically, a printer apparatus, a facsimile apparatus, and a copying machine that control toner replenishment to a developing device by detecting a toner concentration in a developing device with a toner concentration detecting means such as a magnetic permeability sensor. The present invention relates to an image forming apparatus such as an apparatus or a composite apparatus.

  About.

  In image forming apparatuses, so-called electrophotographic image forming apparatuses have been used because of their good print quality, but in recent years, as image forming apparatuses, higher image quality is required, and at the same time, high durability, High stability has also been desired, and there has been a demand for forming a stable image with little change in image quality due to environmental fluctuations.

  In such image forming apparatuses such as electrophotographic copying machines, facsimile machines, printers, and composite machines, an electrostatic latent image is formed on a photosensitive member by light modulated based on image data, and the electrostatic latent image is formed. A toner image is formed by applying toner to the photoconductor on which the image is formed and developing the photoconductor. The image forming apparatus transfers the toner image on the photosensitive member to a sheet by a transfer unit, and conveys the sheet on which the toner image is transferred to a fixing member (such as a fixing roller and a pressure roller) heated by a fixing heater. Then, the sheet is conveyed while being heated by the fixing member to fix the unfixed toner image on the sheet.

  In such an image forming apparatus, conventionally, a two-component developer composed of a non-magnetic toner and a magnetic carrier is held on the developing sleeve in the developing device, and the developing sleeve takes a magnetic pole. There is a known two-component development system in which a magnetic brush is formed and a developing bias is applied to the developing sleeve at a position facing the photosensitive member to develop the electrostatic latent image on the photosensitive member with toner to form a toner image. This two-component development system has been widely used because it is easy to colorize. In this two-component development system, the developer is transported to the developing area as the developing sleeve rotates, and as the developer is transported to the developing area, many developers in the developer follow the magnetic field lines of the developer. The magnetic carriers gather together with non-magnetic toner to form a magnetic brush. The formed magnetic brush moves while the tip of the magnetic brush is rubbed against the photoconductor to attach toner to the electrostatic latent image on the photoconductor. Due to the adhesion of the toner, a toner image is formed on the photoreceptor.

  In the two-component development method, unlike the one-component development method, it is important to improve the stability of the image quality to accurately control the weight ratio (toner concentration) of the toner and the carrier in the developing device. For example, if the toner density is too high, background stains occur on the image, and the resolution of details is reduced. Further, in the two-component development method, when the toner density in the developing device is low, there is a problem that the density of the solid image portion is reduced and carrier adhesion occurs.

  Therefore, it is necessary to control the toner replenishment amount to the developing unit and adjust the toner density in the developing unit to an appropriate range.

  Conventionally, the toner density in the developing device is detected using a magnetic permeability sensor, the output value of the magnetic permeability sensor is compared with a reference value of the toner density in the developing device, and based on the comparison result. The toner replenishment amount is controlled.

  As described above, the toner concentration detection method generally uses a magnetic permeability sensor, and this magnetic permeability sensor is used to measure the magnetic permeability of the developer by changing the toner concentration in the developing device. By detecting the change and comparing the output of the magnetic permeability sensor with the output of the magnetic permeability sensor at the reference density, the current toner density of the developer is detected.

  By the way, the magnetic permeability of the developer depends on the density of the magnetic material in the developer, and when the ratio of the non-magnetic toner is high, the ratio of the carrier (magnetic carrier) that is a magnetic material is low and the magnetic permeability is low. However, even if the density of the developer in the developing device changes due to causes other than the toner concentration, the magnetic permeability changes. That is, when the developer is stirred, the density of the developer decreases, and the magnetic permeability decreases even if the toner concentration does not change. On the contrary, when the developer is allowed to stand for a long time, the density of the developer increases, and the magnetic permeability increases even if the toner concentration does not change.

  In the control of the toner concentration in the developing device, when the toner concentration is controlled immediately after the start of the developing operation, the toner concentration immediately after the start of the developing operation, that is, immediately after the start of the developer stirring is required. However, as described above, the magnetic permeability does not change even if the toner concentration does not change immediately before stopping stirring of the developer (immediately before stopping stirring) and immediately after starting stirring of the next developer (immediately after restarting stirring). Is different. In this case, the toner concentration sensor immediately before the developer stirring is stopped has a stable output, whereas the toner concentration sensor immediately after the developer stirring is restarted (immediately after the stirring is restarted) is unstable. Output. That is, when the toner density is controlled immediately after the development operation starts, how to process the toner density while the output of the toner density sensor is unstable immediately after the development operation starts is an important issue.

  Conventionally, during the predetermined initial control time from the start of the developing operation, the toner density control is performed by obtaining the predicted toner consumption amount from the image signal. A technique has been proposed in which toner density control is performed based on this, and the initial control time is determined at the start of the developing operation based on environmental conditions (see Patent Document 1). In this prior art, a count value obtained by pixel counting from a scanned image signal is stored in a counter memory, a predicted consumption amount of toner for one scan is calculated, and the calculation result is held in the memory, and the timing of toner consumption is calculated. The toner density is controlled in accordance with the above.

  Also, every time the developer in the developing device is started to stir during the image forming operation, the correction amount of the output fluctuation of the toner density sensor is adjusted according to the time from the start of stirring to the start of detection by the toner density sensor. Has been proposed (see Patent Document 2).

Japanese Patent Laid-Open No. 11-202605 Japanese Patent No. 3542148

  However, in the conventional technique described in Patent Document 1, since the estimated toner consumption is calculated based on the scanned image signal, it can be applied only during a copying operation and can be applied during a printer function. This is not possible and is not versatile, and requires storage means for storing the calculated estimated toner consumption until the toner density control timing, resulting in high costs.

  In the prior art described in Patent Document 2, every time the developer in the developing device is started to be stirred, the output fluctuation of the toner concentration sensor is changed according to the time from the start of stirring to the start of detection by the toner concentration sensor. As a result, the output of the toner density sensor after correction also varies, and how much error the output value of the toner density sensor at the start of developer stirring has. This is not taken into consideration, and there is a need for improvement in controlling the toner density in the developing unit with high accuracy.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of improving the image quality by controlling the toner density in the developing device with high accuracy.

  In order to achieve the above object, the image forming apparatus of the present invention detects the toner concentration in the developing device in which the developer is stirred by the stirring unit that performs stirring and stirring stop at a predetermined timing, and detects the toner concentration in the developing unit. The toner supply amount is calculated by the toner supply amount calculation means based on the toner density value detected by the toner concentration detection means, and the toner supply control means supplies toner to the developing device based on the toner supply amount. The toner density value detected by the toner density detecting means is stored as a stored toner density value in the storage means, and the estimated toner density value generating means stores the toner density value in the storage means before the stirring of the stirring means is stopped. An estimated toner density value in the developing unit is generated based on the stored toner density value stored in the toner, and the toner replenishment amount calculation control means starts the stirring of the stirring means from the start of the stirring means. Toner density value to detect the degree detecting means is characterized in that to calculate the toner supply amount to the toner supply amount calculating unit based on the estimated toner density value in the detection unstable period to stabilize.

  In the image forming apparatus of the present invention, the estimated toner density value generation unit may generate the stored toner density value as the estimated toner density value.

  Furthermore, in the image forming apparatus of the present invention, the estimated toner density value generation unit sets a predetermined constant, and adds, subtracts, multiplies, and divides the constant to the stored toner density value. An arithmetic process may be performed to generate the estimated toner density value.

  In the image forming apparatus of the present invention, the estimated toner density value generating unit is configured to mix the temperature and humidity outside the developing unit and / or outside the developing unit, and stirring from the stirring stop immediately before the stirring unit to the start of stirring. The constant may be set based on at least one of the stop periods.

  Furthermore, in the image forming apparatus of the present invention, the storage unit stores a plurality of stored toner density values until immediately before the stirring unit stops stirring, and the estimated toner density value generation unit includes a plurality of stored toners. The constant may be set based on a change gradient of the density value.

  In the image forming apparatus of the present invention, the storage unit stores a plurality of stored toner density values until immediately before the stirring of the stirring unit is stopped, and the estimated toner density value generation unit stores the plurality of stored toners. The estimated toner density value may be generated based on the density value.

  Further, in the image forming apparatus according to the present invention, the image forming apparatus includes a stirring speed detecting unit that detects a stirring speed by the stirring unit, a stirring speed before the stirring of the stirring unit is stopped, and the detection failure after the stirring is started. Correction means for correcting the estimated toner density value based on the stirring speed during the stable period may be provided.

  According to the present invention, the toner density in the developing device in which the developer is stirred is detected by the toner density detecting means by the stirring means that performs stirring and stirring stop at a predetermined timing, and the toner density value detected by the toner density detecting means is detected. Is stored in the storage means as the stored toner concentration value, and the estimated toner concentration is detected in the unstable detection period from the start of the next agitation until the toner concentration value detected by the toner concentration detection means becomes stable. Since the toner replenishment amount to the developing device is calculated based on the value, the toner density in the developing device can be controlled with high accuracy immediately after the start of stirring, and the image quality can be improved.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, since the Example described below is a suitable Example of this invention, various technically preferable restrictions are attached | subjected, However, The range of this invention is unduly limited by the following description. However, not all the configurations described in the present embodiment are essential constituent elements of the present invention.

  1 to 7 are views showing an embodiment of the image forming apparatus of the present invention, and FIG. 1 is a schematic front view of a laser printer 1 to which an embodiment of the image forming apparatus of the present invention is applied. .

  In FIG. 1, a laser printer (image forming apparatus) 1 includes a paper conveyance path 3 formed in a main body housing 2, and along the paper conveyance path 3, a conveyance roller 4, a registration roller 5, a guide plate 6, and the like. Is arranged. In the laser printer 1, a fixing unit 7 is disposed on the downstream side of the sheet conveyance path 3 in the main body housing 2.

  In the laser printer 1, a conveyance roller 8 and a switching claw 9 are disposed on the downstream side of the fixing unit 7 in the main body housing 2, and the switching claw 9 causes the face-down conveyance path 10 side and the face-up discharge tray. The discharge direction of the paper P (see FIG. 2) that has passed through the fixing unit 7 is switched to the 11th side. The laser printer 1 is provided with a paper discharge roller 12 and a face-down paper discharge tray 13 on the face-down conveyance path 10 side, and an image has been recorded in a face-down state with the image recording surface down from the paper discharge roller 12. Sheet P is discharged onto the face-down sheet discharge tray 13. The laser printer 1 discharges the image-recorded sheet P discharged toward the face-up discharge tray 11 onto the face-up discharge tray 11 in a face-up state with the image recording surface facing up.

  In the laser printer 1, a paper feed cassette 14 is slidably housed in the lower part of the main body housing 2. In the paper feed cassette 14, various types of paper (paper types) such as paper P and various types are provided. A plurality of sheets P of the sheet size can be stored. A paper feed roller 15 is disposed on the upper side of the paper feed cassette 14 on the paper feed side. The paper feed roller 15 separates the paper P in the paper feed cassette 14 one by one and sends it to the transport roller 4. .

  Further, the laser printer 1 has a writing unit 16 disposed in the main body housing 2. The writing unit 16 is not numbered, but includes a polygon motor, a polygon mirror, an Fθ lens, a laser diode as a light source, A mirror is provided. The writing unit 16 emits a laser beam modulated by performing laser diode lighting control for each pixel in the main scanning direction based on the image signal, and performs lighting control for one line. The process of performing the lighting control is sequentially repeated to control the lighting of the laser diode by the image signal for one page.

  The laser printer 1 has an endless belt-like photoconductor 21 in the clockwise direction indicated by an arrow in FIG. 1 in a state where the upper side of the paper transport path 3 is formed on the paper transport path 3 in the main body casing 2. The charging unit 22, the developing unit 23, the transfer charger 24, the cleaning unit 25, and the charge removing unit 26 are disposed around the photosensitive member 21 in the order of the rotation direction. The laser printer 1 is disposed in the main body housing 2 with the photosensitive member 21 facing and in contact with the transfer charger 24, and feeds paper from the paper cassette 14 between the photosensitive member 21 and the transfer charger 24. The paper P separated and sent one by one by the roller 15 and sent to the registration roller 5 by the conveyance roller 4 is conveyed after the timing adjustment by the registration roller 5.

  In the laser printer 1, the photosensitive member 21 is rotationally driven in a clockwise direction in FIG. 1 by a driving mechanism (not shown), and at that time, the surface is uniformly charged by the charging charger 22. The laser printer 1 irradiates the uniformly charged photosensitive member 21 with laser light from the writing unit 16 to form an electrostatic latent image on the photosensitive member 21, and develops it when passing through the developing unit 23. Toner is supplied from the unit 23 to visualize the electrostatic latent image as a toner image. When the laser printer 1 further rotates the photoconductor 21 and opposes the transfer charger 24, the toner image on the photoconductor 21 is conveyed between the transfer charger 24 and the photoconductor 21 by the transfer charger 24. The paper P on which the toner image has been transferred is transferred to the fixing unit 7. The laser printer 1 further rotates the photoconductor 21 that has been transferred to remove residual toner in the cleaning unit 25, and again uses it for image formation.

  As shown in FIG. 2, the developing unit 23 includes a developing device 31, a developing sleeve 32, a toner replenishing unit 33, a toner bottle 34, and the like. The toner bottle 34 stores toner to be replenished to the developing device 31. Has been. The toner replenishing section (toner replenishing means) 33 is connected to the toner bottle 34 by a replenishing tube 34 and to the replenishing port 31 a of the developing device 31, and acquires toner in the toner bottle 34 through the replenishing tube 34. Then, the developer 31 is supplied from the supply port 31a. The toner replenishing section 33 may be of any mechanism as long as it can transport toner from the toner bottle 34 to the developing device 31 and replenish it. For example, the toner is supplied by rotating a screw by a motor. A mechanism for transporting toner may be used, or a mechanism for transporting toner by air force by a pump may be used.

  The developing device 31 includes a conveying screw 35, a toner concentration sensor 36, and a temperature / humidity sensor 37 inside. The conveying screw (stirring means) 35 is disposed in a state where a part of the developing sleeve 32 is accommodated. Yes. The conveying screw 35 is disposed over the entire length direction of the developing device 31, and is rotated by a motor (not shown) or the like to supply toner supplied into the developing device 31 from the supply port 31 a. The toner is conveyed to the developing sleeve 32 while stirring with a two-component developer composed of toner and carrier. The developing sleeve 32 is rotated in a state in which the developer ears are in contact with the surface of the photosensitive member 21 by applying a developing bias at a position facing the photosensitive member 21, and the toner in the developing device 31 is transferred to the photosensitive member. Then, the electrostatic latent image on the photosensitive member 21 is developed to form a toner image. The laser printer 1 transfers the toner image formed on the photoreceptor 21 onto the paper P by the transfer charger 24.

  The toner concentration sensor (toner concentration detection means) 36 uses a magnetic permeability sensor, and detects the toner concentration in the developing device 31 based on the magnetic permeability of the developer in the developing device 31. The temperature / humidity sensor 37 detects the temperature and humidity in the developing device 31.

  The laser printer 1 includes a toner density control unit 40 as shown in FIG. 3, and the toner density control unit 40 includes a CPU (Central Processing Unit) 41, a ROM (Read Only Memory) 42, and a RAM (Random Access). Memory (RAM) 43, NVRAM (Non-Volatile Random Access Memory) 44, RTC (Real Time Clock) 45, and the like.

  The ROM 42 stores a basic program of the laser printer 1, a toner density control program for executing the toner density control process of the present invention, and necessary data, and a CPU (toner replenishment amount calculation means, toner replenishment control means, estimated toner density). (Value generation means, toner replenishment amount calculation control means, correction means) 41 uses the RAM 43 as a work memory based on a program in the ROM 42 to control each part of the laser printer 1 and perform basic processing as the laser printer 1. At the same time, a toner density control process to be described later is executed based on the toner density control program.

  That is, the laser printer 1 includes ROM, EEPROM, EPROM, flash memory, flexible disk, CD-ROM (Compact Disc Read Only Memory), CD-RW (Compact Disc Rewritable), DVD (Digital Video Disk), SD (Secure Digital ) A toner density control program for executing the toner density control process of the present invention recorded on a recording medium readable by a laser printer 1 such as a card or MO (Magneto-Optical Disc) is read and introduced into the ROM 42 or the like. Thus, the laser printer 1 is configured to execute the toner density control process. This toner density control program is a computer-executable program written in a legacy programming language such as assembler, C, C ++, C #, Java (registered trademark) or an object-oriented programming language, and is stored in the recording medium. And can be distributed.

  The NVRAM 44 is a memory that retains the stored contents even when the power of the laser printer 1 is turned off. Data that needs to be stored even when the power of the laser printer 1 is turned off is written under the control of the CPU 41. Also read. In particular, the NVRAM 44 stores a temperature / humidity-constant correspondence table Tb1 as shown in FIG. 4 and a developer continuous stop time-constant correspondence table Tb2 as shown in FIG. . This temperature / humidity-constant table Tb1 stabilizes the output of the toner concentration sensor 36 in consideration of the fact that the magnetic permeability of the developer changes due to the temperature / humidity in the developing device 31 and the substantial toner concentration changes. A table for setting a constant K corresponding to the temperature T and the humidity H for optimizing the estimated toner density based on the temperature T and the humidity H by estimating the toner density in the developing device 31 during the unstable detection period until It is. In the developer continuous stop time-constant table Tb2, since the developer in the developer 31 is not stirred by the transport screw 35, the developer permeability changes, and the toner density changes. In consideration of this, the estimated toner concentration value Vs obtained by estimating the toner concentration in the developing device 31 during the unstable detection period until the output of the toner concentration sensor 36 is stabilized is used to drive the conveying screw 35 in the developing device 31. This is a table for setting a constant K for optimization based on the continuous stop time (developer continuous stop time: TM) corresponding to the continuous developer stop time (TM).

  The RTC 45 includes an oscillation circuit, a frequency dividing circuit, etc., and measures the current time, and is used by the CPU 41 to control the laser printer 1. In particular, in the toner density control described later, the developer continuous stop time is used. Used to find etc.

  The CPU 41 receives detection signals from the toner concentration sensor 36 and the temperature / humidity sensor 37 provided in the developing device 31 of the developing unit 23, and the CPU 41 is based on the detection signal (detection value) from the toner concentration sensor 36. Then, the toner replenishment amount to the developing device 31 is obtained, and in the unstable detection period of the toner density sensor 36, the estimated toner density value Vs is generated in consideration of the detection signal of the temperature / humidity sensor 37, and the estimated toner density value A toner replenishment amount is obtained based on Vs, and based on the toner replenishment amount, driving of the toner replenishment unit 33 is controlled to replenish toner from the toner bottle 34 to the developing device 31 and a developer by the conveying screw 35. Controls conveyance and agitation.

  Next, the operation of this embodiment will be described. The laser printer 1 of this embodiment appropriately estimates the toner concentration in the developing device 31 during the unstable detection period of the toner concentration sensor 36 for a predetermined time after the rotation and driving of the developing screw 35 are started during image formation. Then, toner supply is performed, and toner density control processing for controlling the toner density in the developing device 31 to a predetermined toner density is performed.

  That is, when performing image formation, the laser printer 1 starts the rotation drive of the conveying screw 35 to stir the developer in the developing device 31 as shown in FIG. Start (step S101). When the agitation is started, the laser printer 1 detects the toner density by the toner density sensor 36, controls the driving of the toner replenishing unit 33 based on the toner density, and transfers the toner from the toner bottle 34 to the developing device 31. The toner supply is controlled, and the toner density in the developing device 31 is controlled to a predetermined toner density (step S102). The CPU 41 starts image formation at a predetermined timing, performs image formation, and controls the driving of the toner replenishing unit 33 based on the toner density detected by the toner density sensor 36, so that the developing device 31 starts from the toner bottle 34. The toner supplied to the developing device 31 is controlled, the toner consumed in the image formation is supplied to the developing device 31, and the toner concentration in the developing device 31 is controlled to a predetermined toner concentration. In this toner density control, the CPU 41 obtains the toner density value detected by the toner density sensor 36 at regular time intervals (for example, 300 msec) or every variable time, and uses the obtained toner density value. The stored toner density value Vtp is stored in the RAM 43 or the NVRAM 44, and the stored toner density value Vtp stored in the RAM 43 or the NVRAM 44 is rewritten with a new toner density value every time the toner density sensor 36 acquires the toner density value. . In the RAM 43 or NVRAM 44, only one stored toner density value Vtp may be stored, or as will be described later, a plurality of stored toner density values Vtp may be sequentially rewritten and stored.

  When the image forming operation is completed, the CPU 41 stops the rotation / drive of the conveying screw 35. The CPU 41 stops the rotation / driving of the conveying screw 35, and finally starts from the toner density sensor 36 before stopping the driving of the conveying screw 35. The acquired toner density value or the past several toner density values including the last acquired toner density value are stored in the RAM 43 or NVRAM 44 as the stored toner density value Vtp as it is, and the basic operation is terminated.

  Then, when the operation of the developing unit 23 is started, the CPU 41 performs a toner density control process as shown in FIG. That is, in FIG. 6, the CPU 41 starts the operation of the developing unit 23 and also starts stirring the developer by the transport screw 35. When the developer stirring is started, the toner density in the developing device 31 starts to change. Therefore, as shown in FIG. 7, detection of toner density by the toner density sensor 36 is started, and toner density control is started (step S201). However, since the magnetic permeability in the developing device 31 is not stable for a predetermined period after starting the stirring of the developer, if the magnetic permeability sensor is used as the toner concentration sensor 36, the toner concentration sensor 36 is used during this period. Output is not stable, and an accurate toner density cannot be detected. Therefore, the CPU 41 checks whether the output of the toner density sensor 36 is stable in order to appropriately control the toner density in the developing device 31 even during such an unstable detection period (step S202). The CPU 41 determines the stability of the toner density sensor 36 by checking the passage of a predetermined stabilization waiting time, or whether the output of the toner density sensor 36 has settled within a predetermined stability threshold range, or the like. To do. For example, when the determination is made using the stabilization waiting time, the stabilization waiting time is stored in advance in the ROM 42 or the NVRAM 44, and after the CPU 41 starts driving the conveying screw 35 and starts stirring the developer, Whether the stable waiting time has elapsed is checked based on the time measured by the RTC 45, and when the stable waiting time has elapsed, it is determined that the toner density sensor 36 has become stable. When the determination is made using the stable threshold, the CPU 41 detects the detection value acquired from the toner concentration sensor 36 at every predetermined timing and the stored toner concentration value Vtp in the RAM 43 or NVRAM 44 as shown in the following equation (1). Alternatively, the absolute value of the difference from the average value of a plurality of past detection values is calculated, and when the absolute value becomes smaller than a preset stability threshold, it is determined that the toner density sensor 36 is stable.

| Vtp−Vtr | ≦ Lt or | Vtp−Vtr | <Lt (1)
Here, Vtp is the stored toner density value Vtp or its average value, Vtr is the actual detection value of the toner density sensor 36, and Lt is the stability threshold.

  If the toner density sensor 36 is not stable in step S202, the CPU 41 performs an estimated toner density value generation process for generating an estimated toner density value Vs that is an estimated value of the current toner density value of the developing device 31. (Step S203).

  In this estimated toner density value generation process, the CPU 41 generates the stored toner density value Vtp stored in the RAM 43 or NVRAM 44 as it is as the estimated toner density value Vs as shown in the following equation (2).

Vs = Vtp (2)
Further, in this estimated toner density value generation process, the CPU 41 sets a predetermined constant K, and adds, subtracts, multiplies and multiplies the constant K to the stored toner density value Vtp as shown in the following equation (3). The estimated toner density value Vs may be generated by performing one arithmetic processing of the division.

Vs = Vtp + K
Vs = Vtp-K
Vs = Vtp × K
Vs = Vtp ÷ K (3)
In this way, the current toner density value of the developing device 31 can be estimated with higher accuracy, and the estimated toner density value Vs can be generated.

  Further, the CPU 41 takes this constant K into the developing unit 31 that is detected by the temperature / humidity sensor 37 in consideration of the fact that the toner density changes under the influence of the temperature T and the humidity H in the estimated toner density value generation process. The temperature / humidity-constant correspondence table Tb1 shown in FIG. 4 stored in the NVRAM 44 may be set based on the temperature T and the humidity H. For example, in the temperature-humidity-constant correspondence table Tb1 in FIG. 4, when the temperature T is in the range of 0 ≦ T <10 and the humidity H is in the range of 30 ≦ H ≦ 70, “0.02” is set as the constant K. Set.

  In the above description, the temperature / humidity sensor 37 is disposed in the developing device 31 to detect the temperature T and humidity H in the developing device 31, but the temperature / humidity sensor 37 is disposed outside the developing device 31. For example, the constant K may be set based on the temperature T and humidity H outside the developing device 31 by being disposed on the outer wall portion of the developing device 31. Also in this case, the constant K may be determined with reference to a preset temperature / humidity-constant correspondence table. Further, a temperature / humidity sensor may be provided in both the developing device 31 and the outside of the developing device 31, and the constant K may be set based on the temperature T and humidity H inside and outside the developing device 31. Furthermore, in setting the constant K based on temperature and humidity, the constant K may be set only by the temperature T or only by the humidity H.

  Further, in the estimated toner density value generation process, the CPU 41 continuously stops the developing device, which is a stationary period from when the developer in the developing device 31 by the conveying screw 35 is stopped immediately before the stirring of the developer is started this time. This constant K is stored in the NVRAM 44 based on the developer continuous stop time TM in consideration of a substantial change in toner density due to the change in the magnetic permeability of the developer under the influence of the time TM. You may set with reference to the developing device continuous stop time-constant correspondence table Tb2 shown in FIG. For example, in the case of the developer continuous stop time-constant correspondence table Tb2 in FIG. 5, if the developer continuous stop time TM is in the range of 20 ≦ TM <30, “0.04” is set as the constant K.

  Further, the CPU 41 may set the constant K by applying a combination of the temperature and humidity and the developing device continuous stop time TM in the estimated toner density value generation process.

  Further, in the estimated toner density value generation process, when the plurality of stored toner density values Vtp before the developer agitation stop is stored in the RAM 43 or the NVRAM 44 in time series, the plurality of stored toner density values Vtp are used. Thus, the estimated toner density value Vs may be generated. In this case, the CPU 41 may generate the estimated toner density value Vs based on the gradient of the time change of the plurality of stored toner density values Vtp. For example, the displacement of the plurality of stored toner density values Vtp using the least square method. And an approximate toner density value Vs is generated by applying the approximate expression to the plurality of stored toner density values Vtp.

  Then, when the CPU 41 generates the estimated toner density value Vs as described above, the CPU 41 detects the stirring speed of the immediately preceding conveying screw 35 and the stirring speed before the developer stirring stop by the immediately preceding conveying screw 35 and the current stirring are performed. It is checked whether the stirring speed at the start is different (step S204). The stirring speed of the conveying screw 35 is detected by, for example, the number of driving steps per unit time of the drive signal when the conveying screw 35 is rotationally driven by a step motor and the CPU 41 controls the driving signal of the step motor. Or it detects by the method of calculating from the detection result of the rotation sensor which detects rotation of the rotating shaft of the conveyance screw 35, etc.

  If it is determined in step S204 that the stirring speed before the previous stirring stop is different from the stirring speed after the start of stirring, it is determined whether to correct the generated estimated toner density value Vs (step S204). That is, the magnetic permeability of the developer in the developing device 31 changes according to the stirring speed of the developer by the conveying screw 35, and the toner concentration changes with the change in the magnetic permeability. Therefore, in step S204, the CPU 41 It is determined whether the stirring speed before the stirring of the stirring speed is different from the stirring speed after the start of the current stirring. Furthermore, in order to prevent the correction process from frequently occurring and to make the processing efficiency appropriate, the CPU 41 determines that the correction is necessary when the change in the stirring speed is large to some extent.

  If the CPU 41 determines in step S205 that the estimated toner density value Vs needs to be corrected, the CPU 41 corrects the estimated toner density value Vs (step S206), and the toner bottle 34 is based on the corrected toner density value Vs. The toner replenishment amount supplied to the developing device 31 is calculated (step S207).

The CPU 41 corrects the estimated toner density value Vs by setting a predetermined correction constant Kh, as shown in the following equation (4), and adding or subtracting the correction constant Kh to the estimated toner density value Vs. Then, the corrected estimated toner density value Vsh is calculated by performing one arithmetic processing of multiplication and division. Vsh = Vs + Kh
Vsh = Vs−Kh
Vsh = Vs × Kh
Vsh = Vs ÷ Kh (4)
In the above description, after the estimated toner density value Vs is generated based on the stored toner density value Vtp, the corrected estimated toner density value Vsh is calculated by performing correction based on the stirring speed. However, the stored toner density value Vtp is calculated. May be calculated based on the stirring speed, and then the estimated toner density value Vs may be calculated. As a calculation method for calculating the toner replenishment amount from the corrected estimated toner density value Vsh, a known calculation method can be applied.

  After calculating the toner supply amount, the CPU 41 controls the driving of the toner supply unit 33 based on the calculated toner supply amount, and supplies toner from the toner bottle 34 to the developing device 31 by the toner supply amount (step S209). ), It is checked whether or not the development operation is stopped (step S210).

  If the image forming operation is not continued and the developing operation is not stopped in step S210, the CPU 41 returns to step S202, and determines whether or not the output of the toner density sensor is stable at predetermined time intervals (for example, every 300 msec). From above, the same processing as described above is repeatedly executed (steps S202 to S209). It should be noted that the interval between the repetition processes may be changed as appropriate by operating the operation panel of the laser printer 1 or the like.

  If the stirring speed before stopping stirring is the same as the current stirring speed in step S204, it is determined that there is no need to correct the estimated toner density value Vs estimated in step S203, the process proceeds to step S207, and the estimated toner is unchanged. The toner replenishment amount is calculated using the density value Vs (step S207), and toner replenishment is performed based on the calculated toner replenishment amount (step S209), and it is checked whether the development operation is stopped (step S210).

  If the CPU 41 determines in step S204 that the agitation speed before the agitation stop is different from the current agitation speed and that the correction of the estimated toner density value Vs is not necessary in step S205, the CPU 41 proceeds to step S207. The estimated toner density value Vs estimated in step S203 is used as it is without correction (step S207), and toner is replenished based on the calculated toner replenishment amount (step S209). Then, it is checked whether or not the development operation is stopped (step S210).

  When the output of the toner density sensor 36 is stabilized in step S202, the CPU 41 performs processing from the toner density control process using the estimated toner density value Vs to the toner density control process using the detection value detected by the toner density sensor 36. The mode is switched, the process proceeds to step S207, and the toner replenishment amount is calculated based on the detected toner density value (step S207), and the toner replenishment is performed based on the calculated (step S208). Check (step S209).

  If it is determined in step S209 that the developing operation is not stopped, the CPU 41 returns to step S202 and performs the same processing from the output stability check of the toner density sensor 36 as long as the output of the toner density sensor 36 is stable. The toner replenishment amount is calculated based on the detection value output from the density sensor 36, and the toner density control process for replenishing the toner is repeated (steps S202 to S209). If the development operation is stopped in step S209, the development is performed. The operation of the unit 23 is stopped and the process is terminated (step S210).

  As described above, the laser printer 1 according to the present embodiment detects the toner concentration in the developing device 31 in which the developer is stirred by the conveying screw 35 that performs stirring and stirring stop at a predetermined timing, and detects the toner density sensor 36. The toner density value detected by the density sensor 36 is stored in the RAM 43 or NVRAM 44 as a stored toner density value Vtp, and the toner density value detected by the toner density sensor 36 is stabilized until the toner density value detected by the toner density sensor 36 becomes stable. Based on the estimated toner density value Vtp, the toner replenishment amount to the developing device 31 is calculated.

  Therefore, the toner concentration in the developing device 31 can be controlled with high accuracy immediately after the start of stirring, and the image quality can be improved.

  In the laser printer 1 of this embodiment, the CPU 41 generates the stored toner density value Vtp stored in the RAM 43 or the NVRAM 44 as the estimated toner density value Vs.

  Therefore, the estimated toner density value Vs can be generated easily and accurately, and the toner density in the developing device 31 can be controlled easily and accurately immediately after the start of stirring, thereby improving the image quality at low cost.

  Further, in the laser printer 1 of this embodiment, the CPU 41 sets a predetermined constant K, and adds, subtracts, multiplies, and divides the constant K with respect to the stored toner density value as shown in the equation (3). The estimated toner density value Vs is generated by performing at least one calculation process.

  Therefore, the toner concentration in the developing device 31 during the unstable detection period can be estimated more accurately, and the toner concentration in the developing device 31 can be controlled with higher accuracy immediately after the start of stirring to further improve the image quality. This can be further improved.

  Further, in the laser printer 1 of this embodiment, the CPU 41 has a stirring stop period from the stirring stop immediately before the temperature T, the humidity H, and the conveying screw 35 in the developing device 31 to the stirring start (developing device continuous stop time: TM). The constant K is set based on at least one of the above.

  Therefore, the toner concentration in the developing device 31 during the unstable detection period can be estimated more accurately in consideration of changes in the magnetic permeability of the developer due to the temperature and humidity and the stirring stop period. The toner density in the toner 31 can be controlled with higher accuracy, and the image quality can be further improved.

  Furthermore, the laser printer 1 of the present embodiment sets the constant K by combining these temperature and humidity and the stirring stop period.

  Therefore, the toner concentration can be estimated more accurately than the constant K is set based on the temperature and humidity and the stirring stop period alone.

  Further, the laser printer 1 of the present embodiment stores a plurality of stored toner concentration values Vtp before the developer agitation stop in the RAM 43 or the NVRAM 44 in time series, and the CPU 41 follows a change gradient of the plurality of stored toner concentration values Vtp. A constant K is set based on this.

  Therefore, the toner concentration in the developing device 31 can be estimated more accurately based on the change state of the toner concentration value, and the toner concentration in the developing device 31 can be controlled with higher accuracy immediately after the start of stirring. The image quality can be further improved.

  Further, the laser printer 1 of this embodiment stores a plurality of stored toner concentration values Vtp before the developer agitation stop in the RAM 43 or the NVRAM 44 in time series, and the CPU 41 estimates based on the plurality of stored toner concentration values Vtp. A toner density value Vs is generated.

  Therefore, the measurement error of the toner concentration sensor 36 can be suppressed, the toner concentration in the developing device 31 can be estimated more accurately, and the toner concentration in the developing device 31 can be controlled with higher accuracy immediately after the start of stirring. Thus, the image quality can be further improved.

  Further, in the laser printer 1 of the present embodiment, the CPU 41 performs a correction process in which the CPU 41 corrects the estimated toner density value Vs based on the stirring speed before stopping the stirring of the conveying screw 35 and the stirring speed in the detection unstable period after starting stirring. Is going.

  Accordingly, the toner concentration in the developing device 31 can be estimated with higher accuracy in consideration of the magnetic permeability variation due to the stirring speed of the developer, and the toner concentration in the developing device 31 can be further accurately determined immediately after the start of stirring. Control can further improve the image quality.

  The invention made by the present inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to that described in the above embodiments, and various modifications can be made without departing from the scope of the invention. It goes without saying that it is possible. Moreover, it is not limited to what was demonstrated in 1st Example and 2nd Example, The technique equivalent to these is also contained in the technical scope of this invention.

  The present invention relates to an image forming apparatus such as a printer device, a facsimile device, a copying device, and a composite device that detects toner concentration in a developing device with a toner concentration detecting means such as a magnetic permeability sensor and controls replenishment of toner to the developing device. Can be used.

1 is a schematic front view of a laser printer to which an embodiment of the present invention is applied. FIG. 2 is a schematic configuration diagram of a main part of a developing unit. FIG. 2 is a block configuration diagram of a toner density control unit of the laser printer in FIG. 1. The figure which shows an example of a temperature / humidity-constant correspondence table. The figure which shows an example of a developing device continuous stop time-constant correspondence table. 6 is a flowchart showing basic operations of the developing unit. 5 is a flowchart showing toner density control processing by a toner density control unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser printer 2 Main body housing | casing 3 Paper conveyance path 4 Conveyance roller 5 Registration roller 6 Guide board 7 Fixing part 8 Conveyance roller 9 Switching claw 10 Face down conveyance path 11 Face up paper discharge tray 12 Paper discharge roller 13 Face down paper discharge tray DESCRIPTION OF SYMBOLS 14 Paper feed cassette 15 Paper feed roller 16 Writing unit 21 Photoconductor 22 Charger charger 23 Developing unit 24 Transfer charger 25 Cleaning part 26 Electric discharge part 31 Developer 31a Replenishment port 32 Development sleeve 33 Toner replenishment part 33 Toner bottle 35 Conveying screw 36 Toner Concentration sensor 37 Temperature / humidity sensor 40 Toner concentration controller 41 CPU
42 ROM
43 RAM
44 NVRAM
45 RTC
P Paper Tb1 Temperature / humidity-constant correspondence table Tb2 Developer continuous stop time-constant correspondence table

Claims (7)

  Stirring means for stirring and stopping stirring of the developer in the developing device at a predetermined timing; toner concentration detecting means for detecting the toner concentration in the developing device; toner supplying means for supplying toner to the developing device; A toner replenishment amount calculating means for calculating a toner replenishment amount based on the toner density value detected by the toner density detecting means; a toner replenishment control means for controlling the driving of the toner replenishment means based on the toner replenishment amount; and the toner Storage means for storing the toner density value detected by the density detection means as a stored toner density value, and estimation in the developing unit based on the stored toner density value stored in the storage means before the stirring means stops stirring. An estimated toner density value generating means for generating a toner density value, and a detection unstable period from the start of stirring by the stirring means until the toner density value detected by the toner density detecting means becomes stable. An image forming apparatus characterized in that it comprises, a toner supply amount calculation control means for calculating the toner replenishing amount to the toner supply amount calculating unit based on the estimated toner concentration value each.   The image forming apparatus according to claim 1, wherein the estimated toner density value generation unit generates the stored toner density value as the estimated toner density value.   The estimated toner density value generation means sets a predetermined constant, and performs at least one of arithmetic processing of addition, subtraction, multiplication and division on the stored toner density value to obtain the estimated toner density value. The image forming apparatus according to claim 1, wherein:   The estimated toner density value generating means is based on at least one of a temperature, humidity outside the developing device and / or outside the developing device, and an agitation stop period from immediately before the agitation stop to the agitation start by the agitation unit. 4. The image forming apparatus according to claim 3, wherein a constant is set.   The storage means stores a plurality of stored toner density values until immediately before the stirring of the stirring means is stopped, and the estimated toner density value generating means calculates the constant based on a plurality of change gradients of the stored toner density values. The image forming apparatus according to claim 3, wherein the image forming apparatus is set.   The storage means stores a plurality of stored toner density values until immediately before the stirring means stops stirring, and the estimated toner density value generation means stores the estimated toner density values based on the plurality of stored toner density values. The image forming apparatus according to claim 1, wherein the image forming apparatus generates the image forming apparatus.   The image forming apparatus includes a stirring speed detecting unit that detects a stirring speed by the stirring unit, a stirring speed before the stirring of the stirring unit is stopped, and a stirring speed of the detection unstable period after the stirring is started. The image forming apparatus according to claim 1, further comprising a correcting unit that corrects the density value.

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