JP2008256929A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and an image forming method by which time related to toner concentration control of two-component developer including time for securing toner electrifying amount of the developer can be shortened, and waiting time required until image forming operation is started is shortened all the more, and also the deterioration of the developer is suppressed when the toner concentration control of the developer is performed. <P>SOLUTION: The image forming apparatus 100 which performs the toner concentration control so as to keep the toner concentration of the developer E fixed on the basis of the result of measurement by a toner concentration sensor 243 detecting the toner concentration of the developer E is equipped with a surface potential sensor 40 and a toner image density sensor 50. When the toner concentration control is to be performed, if the decision is made that image density based on the result of measurement by the toner image density sensor 50 is within a predetermined range in a state that the surface potential of the photoreceptor 21 is within the predetermined range, the toner concentration control of the developer E is finished. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to an electrophotographic image forming apparatus and an image forming method for controlling toner density so as to keep the toner density of a two-component developer constant.

  In a conventional electrophotographic image forming apparatus, generally, the surface of a latent image carrier (for example, a photoreceptor) is charged, and an electrostatic latent image is formed by exposing the charged area to an image. The latent image is visualized (developed) as a toner image by a developing device, and the visualized toner image is electrostatically transferred to a recording material such as recording paper and then transferred to the recording material. The toner image is fixed to the recording material by a fixing device.

  In this type of image forming apparatus, when development is performed using a two-component developer including toner and carrier, only the toner out of the toner and carrier in the developer is attached to the image carrier and consumed. Generally adopted. Therefore, in the image forming apparatus, toner density control is performed so as to keep the toner density of the developer constant based on the measurement result of the toner density sensor that detects the toner density of the developer.

  In the conventional image forming apparatus, in order to maintain the toner concentration of the two-component developer, the toner concentration of the developer is periodically controlled. However, the control time is long (for example, see Patent Document 1 below).

  In addition, the toner concentration control is usually performed in a state where the developer is circulated (stirred and mixed) for a certain period of time (for example, about 2 minutes) and the toner charge amount of the developer is stabilized. That is, a time for ensuring the toner charge amount of the developer is set in advance, and the toner density of the developer is controlled after the time has elapsed.

  As described above, in the conventional image forming apparatus, it takes a long time to control the toner density and it takes time to secure the toner charge amount. Therefore, it takes time until the image forming operation is started. There is a problem that the waiting time until image formation becomes long. In addition, while the developer is being stirred and mixed, there is a problem that the developer is loaded and the developer is deteriorated.

On the other hand, in Patent Document 2 below, based on the deviation of the measured value of the image density of the reference toner image (toner patch) from the predetermined target value and the conversion coefficient corresponding to the predetermined region of the measured value, An image forming apparatus that controls the toner density of a developer is disclosed. However, this image forming apparatus is effective in that the control time at the time of toner density control can be shortened, but the shortening of the time for securing the toner charge amount of the developer is not taken into consideration, and the above-mentioned problem is caused. The cancellation is not enough.
JP-A-4-246672 JP 2002-196552 A

  Therefore, the present invention aims at shortening the time related to the toner concentration control of the developer including the time for securing the toner charge amount of the developer when the toner concentration control of the two-component developer is performed. An object of the present invention is to provide an image forming apparatus and an image forming method capable of reducing the waiting time until the image forming operation is started and suppressing the deterioration of the developer.

  In the conventional image forming apparatus, as described above, the toner density control of the two-component developer is usually performed by stirring and mixing the developer for a certain time (for example, about 2 minutes) to stabilize the toner charge amount of the developer. The time is set as the maximum time for securing the toner charge amount by stirring and mixing the carrier and toner in the developer.

  FIG. 8 is a graph showing an example of the relationship between developer agitation time and toner charge amount. As shown in FIG. 8, the toner charge amount is stabilized in a relatively short time (for example, about 20 seconds). In other words, in the remaining time, the developer is excessively stirred and mixed even though the toner charge amount has already been stabilized. Therefore, it is not necessary to secure the developer agitation time so much.

  Therefore, the present inventor has found the following. That is, when controlling the toner density of the two-component developer, without providing time for securing the toner charge amount of the developer that has been provided in the past, that is, without waiting for the toner charge amount securing time, When a reference toner image is formed on the latent image carrier every predetermined time (for example, 10 seconds) and the image density of the reference toner image is within a predetermined range, the toner charge amount of the developer is stabilized In addition, it can be determined that the toner density of the developer is a predetermined value.

  As a premise for making this determination, it is necessary to ensure a constant surface potential of the latent image carrier that affects the toner image density. That is, when the surface potential on the latent image carrier is within a predetermined range and the image density of the reference toner image formed on the latent image carrier is within the predetermined range, the developer toner concentration The toner density of the developer is maintained without control.

The present invention is based on such knowledge, and provides the following image forming apparatus and image forming method in order to solve the above problems.
(1) Image forming apparatus The surface of the latent image carrier is charged, and an image is exposed to the charged area to form an electrostatic latent image. On the latent image carrier, a developer carrier carrying a two-component developer is used. An image forming unit that develops the electrostatic latent image formed on the toner as a toner image, and based on the measurement result of a toner concentration sensor that detects the toner concentration of the developer, the toner is kept constant. An image forming apparatus that controls density, a surface potential sensor that detects a surface potential on the latent image carrier, and a toner image density sensor that detects an image density of a toner image formed on the latent image carrier A charging means for charging the surface of the latent image carrier, a surface potential measuring means for measuring a surface potential on the latent image carrier with the surface potential sensor, and the surface. Measurement with potential sensor A potential determination is made as to whether or not the surface potential based on a predetermined result is within a predetermined range, and when it is determined that the surface potential exceeds the predetermined range as a result of the potential determination, the surface potential is within the predetermined range. A surface potential adjusting means for adjusting to enter, and a reference toner image for forming a reference toner image on the latent image carrier every predetermined time when it is determined that the potential is within the predetermined range as a result of the potential determination Forming means, image density measuring means for measuring the image density of the reference toner image formed on the latent image carrier by the toner image density sensor, and an image density based on a measurement result by the toner image density sensor. An image forming apparatus comprising: a determination unit that terminates the toner density control when it is determined that the toner density is within a predetermined range.

(2) Image forming method The surface of the latent image carrier is charged, and an image is exposed to the charged area to form an electrostatic latent image. The developer carrier carrying the two-component developer is used to form a latent image on the latent image carrier. An image forming unit that develops the electrostatic latent image formed on the toner as a toner image, and based on the measurement result of a toner concentration sensor that detects the toner concentration of the developer, the toner is kept constant. An image forming method of an image forming apparatus for performing density control, wherein a surface potential sensor for detecting a surface potential on the latent image carrier and an image density of a toner image formed on the latent image carrier are detected. In performing toner density control using a toner image density sensor, a charging step for charging the surface of the latent image carrier, and a surface potential for measuring the surface potential on the latent image carrier with the surface potential sensor Measuring steps and If the surface potential based on the measurement result by the surface potential sensor is determined as to whether or not the surface potential is within a predetermined range, and the surface potential is determined to exceed the predetermined range as a result of the potential determination, A surface potential adjusting step for adjusting the reference toner image so as to fall within the predetermined range, and if the potential determination results in the predetermined range, the reference toner image is placed on the latent image carrier every predetermined time. A reference toner image forming step for forming the reference toner image, an image density measuring step for measuring the image density of the reference toner image formed on the latent image carrier by the toner image density sensor, and a measurement by the toner image density sensor. And a determination step of ending the toner density control when it is determined that the image density based on the result is within a predetermined range.

  In the image forming apparatus and the image forming method according to the present invention, when the toner density control of the developer is performed, a time for securing the toner charge amount of the developer that has been provided in the past is not provided. Without waiting for the toner charge amount securing time, the image density of the reference toner image formed on the latent image carrier with the surface potential on the latent image carrier within the predetermined range is set as the toner image. When it is measured by the density sensor and it is determined that the image density based on the measurement result by the toner image density sensor is within a predetermined range, it is determined that the toner charge amount of the developer is in a stable state. To do. As a result, useless time for stirring and mixing the developer can be reduced, and excessive stirring and mixing of the developer can be prevented. Further, since the image density based on the measurement result by the toner image density sensor is within a predetermined range, it is determined that the toner density of the developer is a predetermined value, and the toner density control is terminated.

  As a result, the control time for controlling the toner concentration can be shortened, and the stirring and mixing time of the developer can be reduced accordingly, and therefore deterioration of the developer can be suppressed.

  As described above, according to the image forming apparatus and the image forming method according to the present invention, in controlling the toner density of the two-component developer, the developer toner including the time for securing the toner charge amount of the developer is included. Time required for density control can be shortened, waiting time until the image forming operation is started can be reduced, and deterioration of the developer can be suppressed.

  By the way, the developer is generally easily affected by the surrounding environment, and the image density of the toner image formed on the latent image carrier is likely to change due to a change in the environmental state of the surrounding environment. Therefore, in the image forming apparatus according to the present invention, the image forming apparatus includes an environmental state detection unit that detects a state of the surrounding environment, and the image density measurement unit is configured to change the environmental state based on the measurement result of the environmental state detection unit. It is preferable that the measurement sensitivity of the toner image density sensor is changed. A typical example of the surrounding environment is temperature and / or humidity. In this case, examples of the environmental state detection device include a temperature sensor and / or a humidity sensor.

  In general, the developer tends to change the image density of the toner image formed on the latent image carrier depending on the lifetime. In view of this, the image forming apparatus according to the present invention includes a lifetime measuring device that measures the lifetime level of the developer, and the image density measuring unit includes the toner according to the lifetime level based on the measurement result of the lifetime measuring device. It is preferable that the measurement sensitivity by the image density sensor is changed. The “lifetime degree” refers to a use situation from the initial state to the life, and can include a use period, for example.

  Examples of the lifetime measuring device include a counting device that counts the number of image formations and the drive time of the image forming device.

  In the image forming apparatus according to the present invention, when the reference toner image forming unit determines that the reference toner image forming unit is within the predetermined range as a result of the potential determination, the reference toner image forming unit has two types of image densities different from each other on the latent image carrier. A reference toner image is formed at each predetermined time, and the image density measuring means measures the image density of the two types of reference toner images formed on the latent image carrier with the toner image density sensor. The determination means includes: one of the image densities of the two types of reference toner images based on the measurement result of the toner image density sensor is within a predetermined first range, and the other is the first range. May be configured to end the toner density control when it is determined that they are within a different predetermined second range. By doing so, it is possible to accurately determine the developability based on the image densities of the two types of reference toner images, and it is possible to more accurately determine whether or not to perform the toner density control.

  In the image forming apparatus according to the present invention, it is preferable that the toner density control is not performed immediately after toner replenishment. By so doing, fluctuations in the toner charge amount of the developer can be suppressed, and it is possible to more accurately determine whether or not to perform the toner density control.

  In the image forming apparatus according to the present invention, the peripheral speed of the latent image carrier is not less than 300 mm / sec and less than 350 mm / sec, and the peripheral speed ratio of the developer carrier to the peripheral speed of the latent image carrier is 2. 0.0 or less is preferable. In this case, the lower limit value of the peripheral speed ratio of the developer carrier relative to the peripheral speed of the latent image carrier is not limited to this, but may be about 0.8, for example.

  In the image forming apparatus according to the present invention, examples of the peripheral speed of the latent image carrier include 350 mm / sec or more. The upper limit value of the peripheral speed of the latent image carrier is not limited thereto, but can be exemplified by about 540 mm / sec.

  In this case, as the image forming speed of the image forming apparatus (that is, the peripheral speed of the latent image carrier) increases, development by high-speed rotation of the developer carrier is required. The peripheral speed ratio of the developer carrying member to the speed is preferably 1.2 or more and 2.0 or less.

  In the image forming apparatus according to the present invention, as the two-component developer, a carrier having an average particle diameter of about 30 μm to 60 μm can be used. By using a developer having a carrier having an average particle diameter in this range, it is possible to show an excellent charge rise in stabilizing the toner charge amount of the developer, and the time for stabilizing the toner charge amount accordingly. Can be reduced.

  The image forming apparatus according to the present invention may be configured to issue an alarm when a surface potential based on a measurement result by the surface potential sensor exceeds a predetermined range. In this configuration, it is possible to notify the user of an abnormality of a member related to the surface potential (for example, the latent image carrier or the surface potential sensor).

  As described above, according to the present invention, when controlling the toner concentration of the two-component developer, the time related to the toner concentration control of the developer including the time for securing the toner charge amount of the developer is included. It is possible to provide an image forming apparatus and an image forming method that can be shortened, reduce the waiting time until the image forming operation is started, and suppress deterioration of the developer.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

  First, the overall configuration of the image forming apparatus 100 shown in FIG. 1 will be described. FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus according to an embodiment of the present invention.

  An image forming apparatus 100 shown in FIG. 1 forms an image by an electrophotographic image forming process. The image forming apparatus 100 charges a latent image carrier (here, a photosensitive drum) 21 and the surface of the photosensitive drum 21. A charging device 22, an exposure device (here, an optical writing unit) 23 for forming an electrostatic latent image on the photosensitive drum 21, and developing the electrostatic latent image with a developer to form the electrostatic latent image on the photosensitive drum 21. A developing device 24 for forming a toner image, a transfer device (here, a transfer unit) 25 for transferring the toner image on the photosensitive drum 21 to a transfer sheet such as a recording paper, and a transfer image on the sheet. A fixing device (here, a fixing unit) 27 for fixing on the sheet, and a cleaning for removing residual toner remaining on the surface of the photosensitive drum 21 without being transferred by the transfer device 25 And location 26 (cleaning unit in this case), and a neutralization device for neutralizing the remaining residual charge on the surface of the photosensitive drum 21 (not shown).

  Specifically, the image forming apparatus 100 acquires image data read from a document, or acquires image data received from the outside, and forms a monochrome image indicated by the image data on a sheet. The configuration is roughly divided into a document conveying unit (ADF) 101, an image reading unit 102, an image forming unit 103, a sheet conveying unit 104, and a sheet feeding unit 105.

  When at least one document is set on the document setting tray 11, the document conveying unit 101 pulls out the document one by one from the document setting tray 11, conveys the document to the image reading unit 102, and passes the document. The original is discharged to the paper discharge tray 12.

  The image reading unit 102 reads a document image from the document conveying unit 101 and transmits image data corresponding to the document image to a control unit 200 including a microcomputer.

  The image data transmitted from the image reading unit 102 to the control unit 200 is subjected to various image processing by the control unit 200 and then output to the image forming unit 103.

  The image forming unit 103 records a document image based on the image data on a sheet. The photosensitive drum 21, the charging device 22, the exposure device 23, the developing device 24, the transfer device 25, and the cleaning device 26 described above. And a fixing device 27 and a charge eliminating device.

  The surface of the photosensitive drum 21 moves in a predetermined direction (rotates in the direction of arrow A in the figure), the surface is cleaned by the cleaning device 26, and the cleaned surface is uniformly charged by the charging device 22. In the present embodiment, the peripheral speed of the photosensitive drum 21 is set to 350 mm / sec or more in order to realize high-speed image forming processing.

  In the present embodiment, the charging device 22 is a scorotron charger having a grid electrode. Specifically, the charging device 22 is of a charger type, and a grid electrode is provided between the corona wire and the photoconductor 21. Under the instruction of the control unit 200, the grid voltage is adjusted to adjust the photoconductor 21. The upper surface potential can be adjusted.

  The optical writing unit 23 acting as an exposure apparatus is a laser scanning unit (LSU) including a laser irradiation unit 28 that is a laser light source and a mirror group 29. The optical writing unit 23 receives image data from the control unit 200, emits laser light corresponding to the image data from the laser irradiation unit 28, and outputs the laser light via the mirror group 29 to the photosensitive drum. 21, the surface of the photosensitive drum 21 that is uniformly charged is exposed, and an electrostatic latent image is formed on the surface of the photosensitive drum 21. The laser irradiation unit 28 can adjust the light amount and the irradiation diameter of the laser light on the surface of the photoconductor 21 under the instruction of the control unit 200.

  The developing device 24 supplies toner to the surface of the photosensitive drum 21 to visualize (develop) the electrostatic latent image formed on the photosensitive drum 21. The developing device 2 will be described in detail later.

  The transfer unit 25 transfers the toner image formed on the surface of the photosensitive drum 21 to the sheet conveyed by the sheet conveying unit 104.

  Specifically, the transfer unit 25 has an elastic conductive roller 34. The elastic conductive roller 34 presses the sheet conveyed from the sheet conveying unit 104 against the surface of the photosensitive drum 21. In addition, an electric field having a polarity opposite to the charge of the toner image on the surface of the photosensitive drum 21 is applied to the elastic conductive roller 34, and the toner image on the surface of the photosensitive drum 21 is transferred onto the sheet by the electric field having the opposite polarity. The For example, when the toner image has a (−) polarity charge, the polarity of the electric field applied to the elastic conductive roller 34 is set to the (+) polarity.

  The cleaning unit 26 removes and collects toner remaining on the surface of the photosensitive drum 21 after development and transfer.

  The fixing unit 27 heats and pressurizes the sheet on which the toner image is transferred by the transfer unit 25 to fix the toner image on the sheet.

  Specifically, the fixing unit 27 includes a pair of fixing rollers (here, a heating roller 35 and a pressure roller 36). Inside the heating roller 35, a heat source (not shown) for setting the surface of the heating roller 35 to a predetermined temperature (fixing temperature: approximately 160 to 200 ° C.) is provided. Further, pressure members (not shown) are arranged at both ends of the pressure roller 36 so that the pressure roller 36 is pressed against the heating roller 35 with a predetermined pressure. In the fixing unit 27 having such a configuration, when a sheet is conveyed to a pressure contact portion (referred to as a fixing nip portion) between the heating roller 35 and the pressure roller 36, the sheet is conveyed by the rollers 35 and 36. Meanwhile, the unfixed toner image on the sheet is heated and melted and pressed to fix the toner image on the sheet.

  The sheet conveyance unit 104 includes a plurality of pairs of conveyance rollers 41, a pair of registration rollers 42, and a conveyance path 43 for conveying the sheet from the sheet feeding unit 105.

  The paper feed unit 105 includes a plurality of paper feed trays 51. Each paper feed tray 51 is for storing sheets, and is provided below the image forming apparatus 100. Each paper feed tray 51 is provided with a pickup roller for pulling out the sheets one by one, and the sheet pulled out by the pickup roller is sent out to the transport path 43 of the sheet transport unit 104. Since the image forming apparatus 100 of the present embodiment is intended for high-speed image forming processing, each paper feed tray 51 has a capacity capable of storing 500 to 1500 sheets of standard size sheets.

  The conveyance path 43 conveys the sheet received from the sheet feeding unit 105 to the transfer unit 25 in synchronization with the toner image on the photosensitive member 21 rotated by the registration roller 42, and further to the fixing unit 27. It is designed to be transported. In addition, the sheet fixed by the fixing unit 27 is further conveyed to the sheet discharge tray 47 by the sheet conveying unit 104 and discharged.

  Next, the developing device 24 will be described. FIG. 2 is a side view schematically showing the developing device 24 shown in FIG. As shown in FIG. 2, the developing device 24 includes a developer carrier 241, a developing tank 242, and a toner concentration sensor 243.

  The developer carrier 241 carries a two-component developer E mainly composed of toner and carrier, and is here a developing roller. The developer carrying member 241 is disposed in the developing tank 242 and carries the developer E on the surface and is driven to rotate. As a result, the developer carrying member 241 conveys the developer E carried on the surface thereof to a developing region where the electrostatic latent image on the photosensitive drum 21 is developed.

  Specifically, the developer carrying member 241 has a cylindrical developing sleeve 241a that carries the developer E accommodated in the developing tank 242 on the outer peripheral surface and transports it to the developing region, and the inside of the developing sleeve 241a. Is provided with a magnet roll 241b. The developing sleeve 241a is rotatable relative to the magnet roll 241b and is driven to rotate in a predetermined rotation direction (the direction of arrow B in the figure).

  The developing tank 242 contains the developer E. In the present embodiment, the developing tank 242 is provided with a first transport member 242a and a second transport member 242b. The first conveying member 242a conveys the developer E in the developing tank 242 from one side in the axial direction to the other side. The second transport member 242b transports the developer E in the developing tank 242 from the other side in the axial direction to one side.

  Specifically, here, the first conveying member 242a is a first conveying screw for conveying the developer E in the developing tank 242 from one side to the other side in the axial direction while supplying the developer E to the developer carrier 241. It is said that. Here, the second transport member 242b is a second transport screw for transporting the developer E in the developing tank 242 from the other side in the axial direction to one side while supplying the developer E to the first transport member 242a. The first and second conveying screws 242a and 242b are provided with helical fins 242a 'and 242b' for conveying the developer E and mixing the toner and the carrier, respectively. In the present embodiment, the toner is charged with the same polarity as the polarity of the surface potential charged on the surface of the photoreceptor 21. A developing bias voltage is applied to the developing sleeve 241a by a developing bias applying device 244. As a result, the electrostatic latent image formed on the photosensitive member 21 is reversely developed by electrostatically attracting the toner charged to the same polarity by the developing bias voltage.

  The toner density sensor 243 detects the toner density of the developer E. The toner concentration sensor 243 is disposed at a predetermined detection position of the developing tank 242.

  The image forming apparatus 100 further includes a toner supply device 30 that supplies toner to the developer E in the developing device 24 (see FIG. 1). The toner replenishing device 30 is configured to replenish toner as necessary to the developer E from a supply port 242c in the developing tank 242.

  A toner replenishing device 30 is connected to the developing tank 242 of the developing device 24 so that the developing tank 242 can be replenished by an operation signal from the control unit 200. That is, the toner replenishing device 30 replenishes toner to the developing tank 242 as necessary by toner density control based on the sensor output value of the toner density sensor 243 provided in the developing tank 242 under the instruction of the control unit 200. It is like that.

  Next, the control unit 200 will be described. FIG. 3 is a schematic block diagram of a control system mainly showing the control unit 200 of the image forming apparatus 100 shown in FIG.

  The control unit 200 illustrated in FIG. 3 includes a CPU (Central Processing Unit) 201 and a storage unit 202. The storage unit 202 stores various control programs and necessary functions, and includes a ROM (Read Only Memory) and a RAM (Random Access Memory).

  The control unit 200 is configured to control the image forming process by reading various control programs from the storage unit 202 by the CPU 201 and executing the read control programs.

  The toner concentration sensor 243 is electrically connected to the input system of the control unit 200 so that the sensor output value is transmitted to the control unit 200. The toner replenishing device 30 is electrically connected to the output system of the control unit 200 so that the operation signal is received from the control unit 200.

  The image forming apparatus 100 includes a surface potential sensor 40 and a toner image density sensor 50 in addition to the above configuration.

  The surface potential sensor 40 detects the surface potential on the photoconductor 21. The surface potential sensor 40 may be disposed at any position around the photoconductor 21. Here, the surface potential sensor 40 is disposed downstream of the transfer unit 25 and upstream of the cleaning unit 26 in the rotation direction A of the photosensitive member 21 (see FIG. 1). The surface potential sensor 40 is electrically connected to the input system of the control unit 200 so that the sensor output value is transmitted to the control unit 200.

  The toner image density sensor 50 detects the image density of the toner image formed on the photoconductor 21. The toner image density sensor 50 may be disposed at any position around the photoreceptor 21. The toner image density sensor 50 is disposed downstream of the developing device 24 and upstream of the transfer unit 25 in the rotation direction A of the photosensitive member 21 (see FIG. 1). The toner image density sensor 50 is electrically connected to the input system of the control unit 200 so that the sensor output value is transmitted to the control unit 200.

  The surface potential sensor 40 and the toner image density sensor 50 can be the same as those used in the conventional image forming apparatus. Therefore, the description of the detailed configuration of these members is omitted.

  The charging device 22 is electrically connected to the output system of the control unit 200 so that an operation signal for adjusting the grid voltage is received from the control unit 200. The development bias applying device 244 is electrically connected to the output system of the control unit 200 so that an operation signal for adjusting the development bias voltage is received from the control unit 200. The laser irradiation unit 28 is electrically connected to the output system of the control unit 200 so that an operation signal for adjusting the amount of laser light and an operation signal for adjusting the irradiation diameter are received from the control unit 200.

  In the image forming apparatus 100 according to the embodiment of the present invention, the control unit 200 periodically controls the toner density of the developer E based on the measurement result of the toner density sensor 243 in order to maintain the toner density of the two-component developer E. However, the toner density control of the developer E is terminated under a predetermined condition without waiting for a time for securing the toner charge amount of the developer E, which has been set in advance.

  That is, here, the control program causes the control unit 200 to function as a unit including a charging unit, a surface potential measuring unit, a surface potential adjusting unit, a reference toner image forming unit, an image density measuring unit, and a determining unit, which will be described later. It is said that.

  When the toner density control is performed, the charging unit charges the surface of the photoreceptor 21 whose surface has been cleaned and discharged.

  Specifically, the charging means uniformly charges the surface of the photoreceptor 21 with the charging device 22.

  The surface potential measuring means measures the surface potential on the photoconductor 21 with a surface potential sensor 40.

  Specifically, the surface potential measuring means measures the surface potential uniformly charged on the photosensitive member 21 by the surface potential sensor 40 and transmits the measurement result to the control unit 200.

  When the surface potential adjusting means performs a potential determination as to whether or not the surface potential based on a measurement result by the surface potential sensor 40 is within a predetermined range, and determines that the surface determination result exceeds the predetermined range The surface potential is adjusted to fall within the predetermined range.

  Specifically, the surface potential measuring means determines whether or not the surface potential based on the measurement result by the surface potential sensor 40 is within a predetermined range. If the surface potential exceeds the predetermined range, the surface potential is measured. The grid voltage of the charging device 22 is adjusted to enter.

   When the reference toner image forming unit determines that the potential is within the predetermined range as a result of the potential determination, a reference toner image (hereinafter referred to as a toner patch) P is placed on the photoreceptor 21 for a predetermined time (for example, 10 seconds). ) Every time. That is, the reference toner image forming unit develops the latent image forming unit for irradiating the photosensitive member 21 with predetermined light to form a toner patch electrostatic latent image, and developing the toner patch electrostatic latent image. Latent image developing means for forming the toner patch P.

  Specifically, the latent image forming means forms a toner patch electrostatic latent image by irradiating the photosensitive member 21 with laser light from the laser irradiation unit 28 in the optical writing unit 23. Further, the latent image developing means forms the toner patch P by developing the electrostatic latent image for toner patch with the developing device 24. Here, the toner patch P is a high density image (so-called solid image) on the entire surface.

  The image density measuring means measures the image density of the toner patch P formed on the photosensitive member 21 by the toner image density sensor 50.

  Specifically, the image density measuring means measures the image density of the toner patch P formed on the photosensitive member 21 by the latent image developing means by the toner image density sensor 50, and sends the measurement result to the control unit 200. It is supposed to send.

  When the determination unit determines that the image density based on the measurement result by the toner image density sensor 50 is within a predetermined range, the toner density control of the developer E is terminated. The predetermined range is stored in the storage unit 202 in advance.

  Further, the image density with respect to the measurement result by the toner image density sensor 50 and the surface potential with respect to the measurement result by the surface potential sensor 40 can both be obtained by using a predetermined conversion table or a predetermined conversion formula. This conversion table or conversion formula is stored in advance in the storage unit 202 in the present embodiment.

  Then, after the toner density control of the developer E is completed, the control unit 200 makes the image forming operation possible state.

  As described above, according to the image forming apparatus 100 according to the embodiment of the present invention, the toner density of the developer E is controlled without waiting for the time for securing the toner charge amount of the developer E. The image density of the toner patch P formed on the photoconductor 21 is measured by the toner image density sensor 50 in a state where the upper surface potential is within the predetermined range, and an image based on the measurement result by the toner image density sensor 50 is measured. When it is determined that the density is within the predetermined range, it is determined that the toner charge amount of the developer E is in a stable state. As a result, useless time for stirring and mixing the developer E can be reduced, and excessive stirring and mixing of the developer E can be prevented. Further, since the image density of the toner patch P is within the predetermined range, it is determined that the toner density of the developer E is a predetermined value, and the toner density control of the developer E is terminated. Therefore, since the toner density control of the developer E, which conventionally takes a long time, can be completed in a short time, it is possible to realize a user-friendly image forming apparatus that reduces the waiting time until image formation. Furthermore, the deterioration of the developer E due to excessive stirring can be suppressed.

  Note that the image forming apparatus 100 of the present embodiment is a relatively high-speed image forming apparatus in which the peripheral speed of the photosensitive drum 21 is 350 mm / sec or more. However, the present invention has such an image forming speed as described above. This is particularly effective for a fast image forming apparatus.

  Next, the flow of processing for controlling the toner concentration of developer E will be described. FIG. 4 is a flowchart showing a processing flow for controlling the toner density of the developer E.

  In this process, as shown in FIG. 4, first, the surface of the photoconductor 21 is uniformly charged by the charging device 22, and then the surface potential of the photoconductor 21 is measured by the surface potential sensor 40 (step S1). If it is determined that the surface potential based on the measurement result by the surface potential sensor 40 exceeds the predetermined range (step S2: No), the grid voltage is adjusted so that the surface potential falls within the predetermined range (step S3). ), And proceeds to step S1. On the other hand, if it is determined that the surface potential based on the measurement result by the surface potential sensor 40 is within the predetermined range (step S2: Yes), the toner patch P is placed on the photoreceptor 21 every predetermined time (for example, 10 seconds). Then, the image density of the toner patch P is measured by the toner image density sensor 50 (step S5).

  When it is determined that the image density based on the measurement result by the toner image density sensor 50 exceeds the predetermined range (step S6: No), toner density control is performed. That is, based on the sensor output value of the toner density sensor 243, toner is supplied from the toner supply device 30 to the developing tank 242 as necessary (step S7). On the other hand, when it is determined that the image density is within the predetermined range (step S6: Yes), the toner density control is terminated and the normal image forming process is started (that is, the image forming operation is started).

  As described above, when the toner patch P is created on the photosensitive member 21 and the toner image density is read by the toner image density sensor 50 at a predetermined time (for example, 10 seconds) at the stage of toner density control, the developer. It can be determined that the toner charge amount in E and the toner density are at a predetermined value.

  As a premise for making this determination, it is necessary that the surface potential of the photosensitive member 21 that affects the toner image density be kept constant. However, the image forming apparatus 100 includes the surface potential sensor 40 and is regularly Therefore, the toner patch P is created from a state in which the surface potential of the photosensitive member 21 is within the predetermined range. When it is confirmed that the image density of the created toner patch P is within the predetermined range, the toner density control can be stopped and the normal image forming process can be started.

  As described above, in the image forming apparatus 100 according to the embodiment of the present invention, the toner density can be controlled in a short time, and the waiting time can be reduced for the user, and the developer E is excessively stirred. Therefore, deterioration of the developer E can be suppressed.

  FIG. 5 is a graph showing the stability of the toner charge amount of the developer due to changes in the surrounding environment. In FIG. 5, the developer is the initial one. L / L represents low temperature and low humidity, N / N represents normal temperature and normal humidity, and H / H represents high temperature and high humidity.

  As shown in FIG. 5, the toner charge amount in a stable state is changed by fluctuations in the surrounding environment (for example, high temperature and high humidity (H / H), low temperature and low humidity (L / L), and normal temperature and normal humidity (N / N)). fluctuate. Due to the change in the toner charge amount, the image density of the toner patch P formed on the photoreceptor 21 changes. For this reason, the toner density control of the developer E may not be finished accurately.

  Therefore, in the present embodiment, the image forming apparatus 100 includes environmental state detection devices 60 and 70 that detect the state of the surrounding environment. Here, the environmental state detection devices 60 and 70 are a temperature sensor that detects temperature and a humidity sensor that detects humidity.

  The temperature sensor 60 and the humidity sensor 70 may be disposed at any position in the image forming apparatus 100. Here, the temperature sensor 60 and the humidity sensor 70 are disposed in the vicinity of the toner image density sensor 50 (see FIG. 1). Further, the temperature sensor 60 and the humidity sensor 70 are electrically connected to the input system of the control unit 200 so that the sensor output value is transmitted to the control unit 200 (see FIG. 3).

  The image density measuring unit changes the measurement sensitivity of the measurement value measured by the toner image density sensor 50 in accordance with the change in temperature and / or humidity based on the measurement result of the temperature sensor 60 and / or the humidity sensor 70. It is supposed to be. As a result, the toner density control of the developer E can be accurately terminated regardless of changes in the surrounding environment.

  Specifically, the image forming apparatus 100 includes a measuring unit that measures the ambient temperature and / or humidity with the temperature sensor 60 and / or the humidity sensor 70, and a temperature and / or humidity (here, based on the measurement result of the measuring unit). Changing means for changing the center value of the sensor output value of the toner image density sensor 50 in accordance with changes in temperature and humidity.

Specifically, since the toner charge amount changes as the ambient environment changes, for example, the central value of the sensor output value of the toner image density sensor 50 at 2.10 V (toner at normal temperature and normal humidity (N / N)). When the adhesion amount is 0.525 mg / cm ² ), the center value of the sensor output value is 2.20 V (toner adhesion amount 0.550 mg / cm ² ) at high temperature and high humidity (H / H). On the other hand, at low temperature and low humidity (L / L), the center value of the sensor output value is set to 2.00 V (toner adhesion amount 0.500 mg / cm ² ). Here, the toner image density sensor 50 is a diffuse reflection type photodiode GP2TC1J000F (manufactured by Sharp Corporation).

  In addition, low temperature can illustrate about 5 to 10 degreeC, normal temperature can illustrate about 20 to 25 degreeC, and high temperature can illustrate about 30 to 35 degreeC. Moreover, low humidity is about 20% to 40%, normal humidity is about 50% to 65%, and high humidity is about 70% to 90%.

  FIG. 6 is a graph showing the stability of the toner charge amount according to the life of developer E. In FIG. 6, the environmental condition is normal temperature and normal humidity (N / N). Initial represents initial, 50k represents 50,000 counts, and 100k represents 100,000 counts.

  As shown in FIG. 6, the toner charge amount in the stable state varies depending on the lifetime of the developer E. Due to the change in the toner charge amount, the image density of the toner patch P formed on the photoreceptor 21 changes. For this reason, the toner density control of the developer E may not be finished accurately.

  Therefore, in the present embodiment, the image forming apparatus 100 includes a lifetime measuring device 80 that measures the lifetime level of the developer E instead of / in addition to the above configuration. Here, the life measuring device 80 is a counting device 80 that counts the number of image formations. Here, the counting device 80 is provided in the control unit 200 (see FIG. 3).

  The image density measuring means changes the measurement sensitivity of the toner image density sensor 50 in accordance with the lifetime based on the measurement result of the counting device 80. As a result, the toner density control of the developer E can be accurately terminated regardless of the lifetime of the developer E.

  Specifically, the image forming apparatus 100 uses the life measuring device 80 to measure the life degree of the developer E, and the toner image according to the life degree (here, the count number) based on the measurement result of the measuring means. Changing means for changing the center value of the sensor output value of the density sensor 50.

Specifically, since the toner charge amount changes as the life level of the developer E changes, for example, the center value of the sensor output value of the toner image density sensor 50 is initially set to 2.20 V (toner adhesion amount 0). .550 mg / cm ² ), the center value of the sensor output value is 2.10 V at 50,000 counts (toner adhesion amount 0.525 mg / cm ² ), and the center value of the sensor output value is 2.100 V at 100,000 counts. 0 V (toner adhesion amount 0.500 mg / cm ² ).

  In the present embodiment, when the reference toner image forming unit determines that the potential is within the predetermined range as a result of the potential determination, two types of toner patches having different image densities are respectively provided on the photosensitive member 21. It may be formed every predetermined time. In this case, the reference toner image forming unit forms a latent image forming unit that irradiates predetermined light onto the photoconductor 21 to form two types of electrostatic latent images for toner patches having different surface potentials; And latent image developing means for developing two types of toner patches P having different image densities by developing different types of toner patch electrostatic latent images.

  Specifically, the latent image forming unit irradiates the photosensitive member 21 with the laser beam from the laser irradiation unit 28 by the optical writing unit 23, whereby the first toner patch electrostatic latent image and the first toner are formed. The electrostatic latent image for the second toner patch is formed so as to have an image density lower than the image density of the patch. The latent image developing means develops the electrostatic latent images for the first and second toner patches by the developing device 24 to form first and second toner patches, respectively.

  The image density measuring means measures the two types of image densities formed on the photosensitive member 21 with a toner image density sensor 50, respectively.

  Specifically, the image density measuring means measures the image density of the first and second toner patches formed on the photosensitive member 21 by the latent image developing means by the toner image density sensor 50, and the measurement result. Is transmitted to the control unit 200.

  Then, the determination unit is configured such that one of the image densities of the two types of toner patches based on the measurement result by the toner image density sensor 50 is within a predetermined first range and the other is the first range. When it is determined that it is within a different predetermined second range, the toner density control of the developer E is terminated.

  Specifically, the determination means has a second image density based on the measurement result by the toner image density sensor 50 and the image density of the first toner patch based on the measurement result by the toner image density sensor 50 is within a predetermined first range. When it is determined that the image density of the toner patch is within a predetermined second range that is smaller than the first range, the toner density control of the developer E is terminated. The predetermined first and second ranges are stored in advance in the storage unit 202.

  Thus, by making a determination based on the determination results at two different image densities, the developability can be accurately determined. As a result, the toner density control of the developer E can be completed more accurately.

  By the way, from the viewpoint that the toner chargeability of the developer E becomes unstable immediately after the toner replenishment, in this embodiment, the toner density control of the developer E is not performed immediately after the toner replenishment. .

  Specifically, the image forming apparatus 100 determines whether or not the toner replenishing device 30 is immediately after the operation ends, and prohibits toner density control of the developer E when it is determined that the operation is immediately after the operation ends. A determination unit is provided.

  In the present embodiment, it is assumed that the surface potential of the photoconductor 21 falls within the predetermined range. However, if this cannot be ensured, trouble has occurred in the photoconductor 21 or the surface potential sensor 40. is assumed. Therefore, an alarm is issued when the measured potential based on the measurement result by the surface potential sensor 40 exceeds a predetermined range. As an embodiment for performing the alarm, an alarm device for displaying a warning on a display unit (not shown) of the operation unit provided in the image forming apparatus 100 and a measurement potential based on a measurement result by the surface potential sensor 40 are used. It is possible to exemplify an aspect provided with a determination unit that determines whether or not exceeds the predetermined range and, when it is determined that the determination exceeds the predetermined range, issues an alarm signal to the alarm device.

In this embodiment, the control for ending the toner density control of the developer is applied to the image forming apparatus that performs monochrome image formation. However, the control is similarly applied to the image forming apparatus that performs color image formation. be able to.
(Example)
Examples will be described below. However, the present invention is not limited to the following examples.

  First, the density of the developed image and toner scattering were examined based on the relationship between the peripheral speed of the photosensitive member 21 and the peripheral speed ratio of the developer carrier 241. The results are shown in Table 1 below. In Table 1, the evaluation “◯” indicates “no problem”, the evaluation “Δ” indicates “no problem in actual use”, and the evaluation “×” indicates “problem occurs”.

表１に示すように、感光体２１の周速度が３００ｍｍ／ｓｅｃ以上３５０ｍｍ／ｓｅｃ未満且つ現像剤担持体２４１の周速比が２．０以下で良好な結果が得られた。

As shown in Table 1, good results were obtained when the peripheral speed of the photosensitive member 21 was 300 mm / sec or more and less than 350 mm / sec and the peripheral speed ratio of the developer carrier 241 was 2.0 or less.

  Further, good results were obtained when the peripheral speed of the photosensitive member 21 was 350 mm / sec or more and the peripheral speed ratio of the developer carrier 241 was 1.2 or more and 2.0 or less.

  Next, the relationship between the average particle diameter of the carrier of the two-component developer E and the stability of the toner charge amount was examined. The result is shown in FIG. In FIG. 7, the environmental condition is normal temperature and normal humidity (N / N).

  As shown in FIG. 7, the carrier E of the developer E has an excellent toner charge amount in the range of 30 μm to 60 μm, and the carrier E of the developer E has an average particle size of 30 μm to 60 μm. It turned out to be preferable.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a side view schematically showing the developing device shown in FIG. 1. FIG. 2 is a schematic block diagram of a control system mainly showing a control unit of the image forming apparatus shown in FIG. 1. 6 is a flowchart showing a flow of processing for controlling toner density of a developer. 6 is a graph showing the stability of the toner charge amount of a developer due to changes in the surrounding environment. 6 is a graph showing the stability of the toner charge amount according to the life of the developer. It is a graph shown in the result of investigating the relationship between the average particle diameter of the carrier of the two-component developer and the stability of the toner charge amount. 6 is a graph showing an example of the relationship between developer agitation time and toner charge amount.

Explanation of symbols

21 Latent image carrier (photosensitive drum)
40 Surface potential sensor 50 Toner image density sensor 60, 70 Environmental state detection device (temperature sensor, humidity sensor)
80 Lifetime measuring device (counter)
100 Image forming apparatus 103 Image forming unit 241 Developer carrier 243 Toner density sensor E Developer P Reference toner image (toner patch)

Claims (10)

The surface of the latent image carrier is charged, and an image is exposed to the charged area to form an electrostatic latent image, and the electrostatic image formed on the latent image carrier by the developer carrier carrying the two-component developer. An image forming unit that includes an image forming unit that develops a latent image as a toner image, and controls toner density so that the toner density of the developer is kept constant based on a measurement result of a toner density sensor that detects the toner density of the developer. A device,
A surface potential sensor for detecting a surface potential on the latent image carrier;
A toner image density sensor for detecting an image density of a toner image formed on the latent image carrier;
In performing the toner density control, charging means for charging the surface of the latent image carrier,
Surface potential measuring means for measuring the surface potential on the latent image carrier with the surface potential sensor;
A potential determination is made as to whether or not the surface potential based on the measurement result by the surface potential sensor is within a predetermined range, and when it is determined that the surface potential exceeds the predetermined range as a result of the potential determination, the surface potential is Surface potential adjusting means for adjusting so as to fall within the predetermined range;
A reference toner image forming means for forming a reference toner image on the latent image carrier every predetermined time when it is determined that the potential is within the predetermined range as a result of the potential determination;
Image density measuring means for measuring the image density of the reference toner image formed on the latent image carrier with the toner image density sensor;
An image forming apparatus comprising: a determination unit that terminates the toner density control when it is determined that an image density based on a measurement result by the toner image density sensor is within a predetermined range. Environmental condition detection means for detecting the state of the surrounding environment,
2. The image forming apparatus according to claim 1, wherein the image density measuring unit changes measurement sensitivity of the toner image density sensor in accordance with a change in an environmental state based on a measurement result of the environmental state detecting unit. . Comprising a lifetime measuring means for measuring the lifetime of the developer,
The image forming apparatus according to claim 1, wherein the image density measuring unit changes measurement sensitivity of the toner image density sensor in accordance with a life degree based on a measurement result of the life measuring unit. When the reference toner image forming unit determines that the potential is within the predetermined range as a result of the potential determination, two types of reference toner images having different image densities are respectively displayed on the latent image carrier at the predetermined time. Formed into
The image density measuring means measures the image densities of the two types of reference toner images formed on the latent image carrier with the toner image density sensor,
The determination means has one of the image densities of the two types of reference toner images based on the measurement result of the toner image density sensor within a predetermined first range and the other being different from the first range. 4. The image forming apparatus according to claim 1, wherein the toner density control is terminated when it is determined that the toner density is within a predetermined second range.   5. The image forming apparatus according to claim 1, wherein the toner density control is not performed immediately after toner replenishment.   The peripheral speed of the latent image carrier is 300 mm / sec or more and less than 350 mm / sec, and the ratio of the peripheral speed of the developer carrier to the peripheral speed of the latent image carrier is 2.0 or less. The image forming apparatus according to claim 1.   The peripheral speed of the latent image carrier is 350 mm / sec or more, and the peripheral speed ratio of the developer carrier to the peripheral speed of the latent image carrier is 1.2 or more and 2.0 or less. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein an average particle diameter of the carrier of the two-component developer is 30 μm to 60 μm.   The image forming apparatus according to claim 1, wherein an alarm is issued when a surface potential based on a measurement result by the surface potential sensor exceeds a predetermined range. The surface of the latent image carrier is charged, and an image is exposed to the charged area to form an electrostatic latent image, and the electrostatic image formed on the latent image carrier by the developer carrier carrying the two-component developer. An image forming unit that includes an image forming unit that develops a latent image as a toner image, and controls toner density so that the toner density of the developer is kept constant based on a measurement result of a toner density sensor that detects the toner density of the developer. An image forming method for an apparatus, comprising:
Using a surface potential sensor that detects a surface potential on the latent image carrier and a toner image density sensor that detects an image density of a toner image formed on the latent image carrier,
In performing the toner density control, a charging step for charging the surface of the latent image carrier,
A surface potential measurement step of measuring the surface potential on the latent image carrier with the surface potential sensor;
A potential determination is made as to whether or not the surface potential based on the measurement result by the surface potential sensor is within a predetermined range, and when it is determined that the surface potential exceeds the predetermined range as a result of the potential determination, the surface potential is A surface potential adjusting step for adjusting to fall within the predetermined range;
A reference toner image forming step of forming a reference toner image on the latent image carrier every predetermined time when it is determined that the potential is within the predetermined range as a result of the potential determination;
An image density measuring step of measuring an image density of the reference toner image formed on the latent image carrier with the toner image density sensor;
And a determination step of ending the toner density control when it is determined that the image density based on the measurement result by the toner image density sensor is within a predetermined range.

Images