JP2010048859A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus capable of always detecting toner density accurately with prevention of erroneous detection of toner density by an inductance detection sensor.
A vertical stirring type developing device has a test mode for determining whether or not a detection value of an inductance detection sensor 20 detected at the time of image formation is appropriate, and in the test mode, the speed of a developing sleeve 28 is determined. The detection value detected by the inductance detection sensor 20 is monitored while changing the rotation speed of the first and second conveying screws 26 and 25 arranged above and below with a constant value. Based on the result of the above, based on the result of determining whether or not the detection value detected at the time of image formation is appropriate, control is performed so that the toner density detected at the time of image formation becomes an appropriate value.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a recorded image display device, a facsimile, or the like, which is equipped with a developing device using a two-component developer.

  In general, in an image forming apparatus such as a copying machine using an electrophotographic system, a developer is attached to an electrostatic latent image formed on an image carrier such as a photosensitive drum to form a visible image. As a developing device used for such development, one using a two-component developer composed of a toner and a carrier is known.

  In many developing apparatuses using the two-component developer, two first and second conveying screws that convey the two-component developer while stirring are arranged in the horizontal direction.

  The first conveying screw is used to supply a developer to a developer carrying member (hereinafter referred to as a developing sleeve) and collect the developer after passing through the developing region.

  The second conveying screw is used for mixing and stirring the developer collected from the developing sleeve and the newly supplied developer.

  In recent years, in an image forming apparatus using an electrophotographic method such as a copying machine or a printer, there has been a strong demand for downsizing the apparatus body in order to achieve space saving. There is a strong demand for miniaturization in order to arrange a plurality of devices.

  Therefore, a vertical stirring type developing device having a configuration shown in FIG. 11 is known. This developing device is characterized in that a conveying screw for stirring and mixing the two-component developer is arranged above and below.

  That is, in FIG. 11, the developing device 1 has a developing container 2, in which first and second conveying screws 5, 6 are arranged vertically via the partition wall 7 and have a predetermined distribution. A developing sleeve 8 having a magnetic force of about 5 mm and having a rotating outer periphery is fixed. The first conveying screw 5 is used for conveying the developer in the developing chamber 3 above the developing container 2 and supplying it to the developing sleeve 8.

  The second conveying screw 6 mixes and stirs the developer collected from the developing sleeve 8 and the newly replenished developer while conveying the developer in the stirring chamber 4 below the developing container 2. Used for. The developer on the developing sleeve 8 develops the photosensitive drum 10, and the remaining developer is reduced to the second conveying screw 6 (see Patent Document 1).

  As described above, the vertical stirring type developing device 1 has an advantage that the developing chamber 3 and the stirring chamber 4 are arranged in the vertical direction, and the occupied space in the horizontal direction can be small. Therefore, for example, a tandem color image forming apparatus in which a plurality of developing devices 1 are arranged in parallel in the horizontal direction can be downsized.

  By the way, in the development method using the two-component developer as described above, the toner is charged by friction charging between the carrier and the toner, and the charged toner is electrostatically attached to the latent image. This is a method for forming an image.

  In such a two-component development system, in order to provide an image satisfying high durability and high stability, it is important to provide a stable toner charge amount (hereinafter referred to as tribo). It is necessary that the charge imparting ability of the carrier is stable before and after durability.

  However, in practice, the toner is consumed by the developing operation as needed, whereas the carrier is not consumed and remains in the developing device. For this reason, when used for a long time, the carrier is agitated with the toner for a long time, and the surface is contaminated by the external additive of the toner and the adhesion of the toner.

  As a result, the carrier's ability to impart tribo is lowered, and tribo is lowered, resulting in image degradation such as scattering fogging. In view of this, there has been proposed an apparatus that can suppress deterioration in charging performance by supplying developer to the developing apparatus.

  As this type of apparatus, a trickle developing type has been proposed. That is, a new developer or carrier replenishing device is provided in the developing device. The developer in the developing device that has become excessive due to replenishment of new developer or carrier by the replenishing device overflows from the developer discharge port provided on the wall surface of the developing device and is discharged (see Patent Document 2). ).

  In such an apparatus, replenishment of new developer or carrier and discharge of the developer are sequentially repeated so that the deteriorated developer in the developing apparatus is replaced with newly supplied toner and carrier. It has become.

  As a result, the developing characteristics of the developer in the developing device can be maintained constant, and the charging characteristics of the developer can be maintained to suppress a reduction in copy image quality. As a result, the serviceman or the like can extend the developer replacement frequency or eliminate the replacement.

  Further, as is well known, the toner concentration of the two-component developer, that is, the ratio of the toner particle weight to the total weight of the carrier particles and the toner particles is an extremely important factor in stabilizing the image quality.

  The toner particles of the developer are consumed during development, and the toner density changes. For this reason, an automatic toner replenishment control device (ATR) is used to accurately detect the toner concentration of the developer in a timely manner, replenish the toner in accordance with the change, control the toner concentration constantly, and improve the image quality. Need to hold.

  In order to correct the change in the toner density in the developing device due to the development as described above, that is, to control the amount of toner replenished to the developing device, various methods have conventionally been used as toner density detecting means in the developing container. Have been put to practical use.

  For example, an optical toner density detecting means for detecting the toner density by utilizing the fact that the reflectance when light is applied to the developer on the developing sleeve varies depending on the toner density is used. Inductance detection toner concentration detection that detects the toner concentration in the developing device based on a detection signal from an inductance detection sensor that detects the magnetic permeability based on the mixing ratio of the magnetic carrier and non-magnetic toner of the developer and converts it into an electrical signal. Means are used.

  The inductance detection type toner density control device determines that the toner density has decreased when, for example, the magnetic permeability of the developer is high, that is, when the sensor output is higher than the reference value, and starts toner supply. To do.

  Conversely, when the magnetic permeability decreases, that is, when the sensor output becomes lower than the reference value, it is determined that the toner concentration has increased, and the toner concentration is controlled based on such control as stopping the toner supply. (See Patent Document 3).

Japanese Patent Laid-Open No. 5-333691 Japanese Patent Publication No. 2-21591 Japanese Patent Laid-Open No. 5-61353

  However, in the image forming apparatus in which the trickle developing method is applied to a vertical stirring type developing device, when discharging the developer, a developer discharging port is provided on the container wall surface on the downstream side of the developing chamber, and this discharging port A configuration for discharging and collecting the overflowed developer is conceivable.

  If a discharge port is provided in a place other than this, for example, a stirring chamber, a new carrier just replenished may be discharged immediately. If a discharge port is provided on the upstream side of the developing chamber, this part is the place immediately after the developer is pumped from the stirring chamber to the developing chamber. I can't.

  Therefore, when the developer discharge port is installed on the downstream side of the developing chamber, it is most suitable as the installation location of the discharge port. If the height of the discharge port exceeds the level of the developer, the developer overflows and is discharged. The developer is not discharged unless the surface of the developer exceeds the discharge port.

  The trickle development system is configured to discharge and collect the developer overflowed from the discharge port, and thus has a feature that the amount of developer in the developing device changes.

  For example, when the state of the developer changes and the pumping property of the developer from the stirring chamber to the developing chamber is lowered, the height of the developer surface in the developing chamber is lowered, and the developer is not easily discharged from the discharge port. As a result, the amount of developer in the developing device increases.

  On the other hand, as a means for controlling the toner concentration of the two-component developer in the vertical stirring type developing device, an inductance detection type toner density control means is used. In this case, the inductance detection sensor is often installed in a pumping unit for pumping the developer from the stirring chamber to the developing chamber.

  In this pumping unit, pressure is always applied to the developer in order to pump up the developer from the bottom to the top. However, particularly when the amount of developer in the developing device exceeds a certain amount, the pressure rapidly increases. It became clear.

  This is shown in FIG. In the region where the amount of developer is a certain amount or less, the developer that has been conveyed through the stirring chamber by the first conveying screw is delivered to the developing chamber side relatively smoothly in the pumping portion. On the other hand, it is considered that when the developer amount exceeds a certain amount, the conveyed developer becomes clogged at the pumping portion, and the pressure rapidly increases as the developer amount increases.

    The inductance detection sensor detects the toner concentration by detecting the magnetic permeability of the two-component developer. However, as the pressure applied to the developer increases as described above, the developer is compressed and the bulk density increases. For this reason, the apparent magnetic permeability becomes high, and even if the toner density is not changed, it is detected as if the toner density is low.

  In this way, if the inductance detection sensor erroneously detects that the toner concentration has decreased due to the increase in the developer amount in the developing device, the toner is replenished excessively. For this reason, the actual toner density increases excessively, and fogging and toner scattering occur.

  The technical problem of the present invention has been made in view of the circumstances as described above, and an object thereof is to prevent erroneous detection of toner concentration by an inductance detection sensor and to always detect toner concentration with high accuracy. An object is to provide an image forming apparatus.

    In order to achieve the above object, a typical configuration according to the present invention includes an image carrier and a developer carrier that carries a developer including a toner and a carrier, and a static image formed on the image carrier. A developing device that develops an electrostatic latent image; a first conveying member that is provided in a first chamber in the developing device and conveys a developer toward a second chamber provided above the first chamber; A second conveying member that is provided in the second chamber and conveys the developer toward the first chamber; a detecting unit that detects information related to the magnetic permeability of the developer in the developing device; and A replenishment control means for controlling the amount of toner to be replenished to the developing device based on a detection result, a drive means for driving the first transport member and the second transport member, and when the image is not formed, The first conveying member or the first conveying member with respect to the rotation speed of the developer carrier. The rotational speed of the first transport member or the second transport member during image formation is corrected based on a plurality of detection values detected by the detection means when the rotational speed of the transport member is changed. Correction means.

  A developing device for developing an electrostatic latent image formed on the image carrier, and a developer carrier for carrying a developer including a toner and a carrier; A first conveying member provided in the first chamber for conveying developer toward a second chamber provided above the first chamber; and provided in the second chamber; A second conveying member that conveys the toner toward the surface, a detecting unit that detects information on the magnetic permeability of the developer per unit volume in the developing device, and a detection result of the detecting unit becomes a predetermined reference value. A replenishment control means for controlling the amount of toner to be replenished to the developing device, a driving means for driving the first transporting member and the second transporting member, and the developer carrying member when the image is not formed. The first conveying member or the second conveying member with respect to the rotational speed Based on the plurality of detection values detected by the detection means when changing the rotational speed, and having a correction means for correcting the predetermined reference value.

  According to the present invention, it is always possible to accurately determine whether or not the detection value of the inductance detection sensor at the time of image formation is appropriate, and an excessive increase in toner density can be prevented.

[Embodiment 1]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic longitudinal sectional view of a full-color image forming apparatus employing an electrophotographic system as an embodiment of the present invention. 2 and 3 show a vertical stirring type developing device installed in the image forming apparatus of FIG. 1, FIG. 2 is a longitudinal sectional view of the developing device, and FIG. 3 is a transverse sectional view.

  The image forming apparatus shown in FIG. 1 includes four image forming portions Pa, Pb, Pc, and Pd, and each image forming portion Pa to Pd is a drum shape that rotates in an arrow direction (counterclockwise direction) as an image carrier. Electrophotographic photosensitive members, that is, photosensitive drums 1a, 1b, 1c, and 1d.

  Around the photosensitive drums 1a to 1d, there are chargers 2a, 2b, 2c and 2d, and laser beam scanners 3a, 3b, 3c and 3d as exposure means. Further, the image forming apparatus includes developing devices 4a, 4b, 4c, and 4d, transfer rollers 6a, 6b, 6c, and 6d, and cleaning units 19a, 19b, 19c, and 19d.

  The image forming units Pa to Pd have the same configuration, and the photosensitive drums 1a to 1d arranged in the image forming units Pa to Pd have the same configuration. Accordingly, the photosensitive drums 1a to 1d are collectively referred to as “photosensitive drum 1”. Similarly, the chargers 2a to 2d, the laser beam scanners 3a to 3d, the developing devices 4a to 4d, the transfer rollers 6a to 6d, and the cleaning means 19a to 19d are the charger 2, the laser beam scanner 3, the developing device 4, and the transfer roller. 6. Collectively called cleaning means 19.

  Next, an image forming sequence in the normal mode of the entire image forming apparatus will be described. First, the photosensitive drum 1 is uniformly charged by the charger 2. In the normal mode, the photosensitive drum 1 rotates at a process speed (circumferential speed) of 286 mm / sec in the clockwise direction indicated by the arrow.

  Next, the uniformly charged photosensitive drum 1 is subjected to scanning exposure with the laser beam modulated by the image signal by the laser beam scanner 3.

  The laser beam scanner 3 incorporates a semiconductor laser, and this semiconductor laser is controlled in response to an original image information signal output from an original reading apparatus having a photoelectric conversion element such as a CCD, and emits laser light.

  As a result, the surface potential of the photosensitive drum 1 charged by the charger 2 changes in the image portion, and an electrostatic latent image is formed on the photosensitive drum 1. The electrostatic latent image is reversely developed by the developing device 4 to be a visible image, that is, a toner image. In this case, the developing device 4 uses a two-component developing system that uses a developer in which a toner and a carrier are mixed as a developer.

  The above-described steps are performed for each of the image forming portions Pa to Pd, and toner images of four colors of yellow, magenta, cyan, and black are formed on the photosensitive drum 1.

  In addition, an intermediate transfer member 5 serving as an intermediate transfer belt is disposed below each of the image forming units Pa to Pd. The intermediate transfer belt 5 is suspended by rollers 51, 52, 53 and is movable in the direction of the arrow.

  The toner image on the photosensitive drum 1 is once transferred to an intermediate transfer belt 5 as an intermediate transfer member by a transfer roller 6 as a primary transfer unit.

  As a result, toner images of four colors of yellow, magenta, cyan, and black are superimposed on the intermediate transfer belt 5 to form a full color image. Further, the toner remaining without being transferred onto the photosensitive drum 1 is collected by the cleaning means 19.

  The full-color image on the intermediate transfer belt 5 is taken out from the feeding cassette 12 and transferred to a transfer material S such as paper that has advanced via a feeding roller 13 and a feeding guide 11 as a secondary transfer means. Transfer is performed by the action of the transfer roller 10.

  The toner remaining on the surface of the intermediate transfer belt 5 without being transferred is collected by the intermediate transfer belt cleaning means 18. On the other hand, the transfer material S onto which the toner image has been transferred is sent to a fixing device (heat roller fixing device) 16 where the image is fixed and discharged to a discharge tray 17.

  In the present embodiment, the photosensitive drum 1 that is a drum-shaped organic photosensitive member that is usually used is used as the image carrier, but it is of course possible to use an inorganic photosensitive member such as an amorphous silicon photosensitive member. .

  It is also possible to use a belt-like photoreceptor. The charging method, transfer method, cleaning method, and fixing method are not limited to the above methods.

  Next, the developing device 4 will be specifically described with reference to FIGS. That is, the developing device 4 includes a developing container 22 in which a two-component developer containing toner and a carrier as a developer is accommodated. Further, the developing container 22 has a developing sleeve 28 as a developer carrying member driven by a driving motor M1, and a panning member 29 for regulating the ears of the developer carried on the developing sleeve 28. ing.

  The interior of the developing container 22 is divided into a developing chamber (second chamber) 23 and an agitating chamber (first chamber) 24 by a partition wall 27 having a substantially central portion extending in a direction perpendicular to the paper surface. The developing chamber 23 is located above the stirring chamber 24, and the developing chamber 23 and the stirring chamber 24 contain a developer.

  In the stirring chamber 24 and the developing chamber 23, a first conveying screw (first conveying member) 26 and a second conveying screw (second conveying member) 25 are arranged as developer agitating and conveying means, respectively. .

  The second conveying screw 25 is disposed substantially parallel to the bottom of the developing chamber 23 along the axial direction of the developing sleeve 28, and rotates to allow the developer in the developing chamber 23 to move in one direction along the axial direction. Transport.

  The first conveying screw 26 is disposed at the bottom of the stirring chamber 24 substantially in parallel with the second conveying screw 25, and conveys the developer in the stirring chamber 24 in the opposite direction to the second conveying screw 25. .

  As described above, the developer is circulated between the developing chamber 23 and the agitation chamber 24 through the openings 11 and 12 at both ends of the partition wall 27 by the conveyance by the rotation of the first and second conveyance screws 26 and 25. .

  The first and second conveying screws 26 and 25 have a diameter of 18 mm and a pitch of 20 mm, and are rotated at a rotation speed of 390 rpm by the drive motor M2 in the normal mode.

  Openings 11 and 12 are formed at positions corresponding to the developing region of the developing container 22 facing the photosensitive drum 1, and a developing sleeve 28 is partially exposed to the photosensitive drum 1 side at the openings 11 and 12. It is provided so that it can rotate.

  Here, the diameter of the developing sleeve 28 is 20 mm, the diameter of the photosensitive drum 1 is 40 mm, and the closest region between the developing sleeve 28 and the photosensitive drum 1 is a distance of about 400 μm. As a result, development can be performed in a state where the developer conveyed to the developing unit is in contact with the photosensitive drum 1.

  The developing sleeve 28 is made of a nonmagnetic material such as aluminum or stainless steel, and a magnet roller 28m as a magnetic field means is installed in a non-rotating state therein. The magnet roller 28m has a developing pole S2 disposed facing the photosensitive drum 1 in the developing section, and a magnetic pole S1 disposed facing the ear cutting member 29. Furthermore, it has a magnetic pole N1 arranged between the magnetic pole S1 and the developing pole S2, and magnetic poles N2 and N3 arranged to face the developing chamber 23 and the stirring chamber 24, respectively. The rotation speed of the developing sleeve is set to 250 rpm.

  The developing sleeve 28 rotates in the direction indicated by the arrow (counterclockwise) during development, and carries a two-component developer whose layer thickness is regulated by the earbrushing of the magnetic brush by the earbrushing member 29, and this is loaded on the photosensitive drum. 1 is conveyed to the development area facing 1. Then, a developer is supplied to the electrostatic latent image formed on the photosensitive drum 1 to develop the latent image.

  The ear cutting member 29 is composed of a nonmagnetic member 29a formed of plate-like aluminum or the like extending along the longitudinal axis of the developing sleeve 28, and a magnetic member 29b such as an iron material. The ear cutting member 29 is disposed upstream of the photosensitive drum 1 in the developing sleeve rotation direction, and both the developer toner and the carrier pass between the tip of the ear cutting member 29 and the developing sleeve 28. And sent to the development area.

  By adjusting the gap between the head cutting member 29 and the surface of the developing sleeve 28, the amount of developer magnetic brush carried on the developing sleeve 28 is regulated and the amount of developer conveyed to the developing area is adjusted. The

  In the present embodiment, the amount of developer coat per unit area on the developing sleeve 28 is regulated to 30 mg / cm 2 by the ear cutting member 29. The gap between the ear cutting member 29 and the developing sleeve 28 is set to 200 to 1000 μm, preferably 400 to 700 μm. In this embodiment, it is set to 600 μm.

  On the developing container 22, a hopper 31 for storing a two-component developer for replenishment in which toner and a carrier are mixed is disposed. The hopper 31 constitutes a developer replenishing means, and includes a screw-like conveying member 32 at the lower portion. One end of the conveying member 32 extends to a developer replenishing port 30 provided at the front end of the developing device 4. Yes.

  In addition, an inductance detection sensor 20 for detecting the toner concentration of the two-component developer is provided on the stirring chamber 24 side of an opening 11 (hereinafter referred to as a pumping portion) for transferring the developer from the stirring chamber 24 to the developing chamber 23. Is installed. In accordance with the detection output of the inductance detection sensor 20, the developer is supplied into the developer container 22 by the developer supply means.

  In the present embodiment, the carrier mixing ratio in the replenished developer is adjusted to 15% by weight. A specific toner supply control method by the inductance detection sensor 20 will be described in detail below. The inductance detection sensor 20 of this embodiment detects information related to the magnetic permeability of the developer per unit volume in the developing container 22.

  Since the two-component developer contains a magnetic carrier and a non-magnetic toner as main components, when the toner concentration of the developer (ratio of the toner particle weight to the total weight of the carrier particles and the toner particles) changes, the magnetic carrier and the non-magnetic toner The magnetic permeability varies depending on the mixing ratio.

  When this magnetic permeability is detected by the inductance detection sensor 20, the detection output (Vsig) changes substantially linearly according to the toner concentration (T / D ratio) as shown in FIG. That is, the detection output of the inductance detection sensor 20 corresponds to the toner concentration of the two-component developer present in the developing container 22.

  That is, as the toner concentration increases, the proportion of non-magnetic toner in the developer increases, so the permeability of the developer decreases and the detection output decreases.

  On the contrary, when the toner concentration is lowered, the magnetic permeability of the developer is increased, so that the detection output is increased. In this way, the toner density of the developer can be detected using the inductance detection sensor 20.

  The detected Vsig is compared with a toner density reference value Vref recorded in advance in a non-volatile memory means (not shown), and the toner replenishment time is controlled based on the calculation result of the difference (Vsig−Vref).

  Since the toner density reference value Vref is an output value corresponding to the target toner density, Vsig is controlled so as to approach this toner density reference value.

  For example, when Vsig−Vref> 0, the toner density of the developer is in a state lower than the target toner density, and therefore the necessary toner replenishment amount is determined according to the difference.

  Therefore, the larger the difference between Vsig and Vref, the more toner is supplied. Further, when Vsig−Vref ≦ 0, the toner concentration is higher than the target, so that the toner supply is stopped and the toner concentration is lowered by the toner consumption by the image forming operation. The toner replenishment control is performed as described above.

  The initial toner concentration of the developer used in this embodiment is 7%, and the toner concentration target value Vref of the inductance detection sensor 20 is adjusted so that the output when the toner concentration is 7% is 2.5V. Yes. However, other adjustment values for the initial toner density and the initial reference signal Vref may be used.

  On the wall surface on the downstream side of the developing chamber 23, a developer discharge means is formed, and a developer discharge port 40 for discharging the deteriorated developer is formed upstream of the developer supply port 30 in the developer transport direction and supplied. The new developer is not discharged immediately, but is discharged at a place where the surface height is stable.

  When the developer in the developer container 22 increases in the developer replenishment process, the developer is discharged so as to overflow (overflow) from the developer discharge port 40 according to the increase amount. The discharged developer is transported to a recovered developer storage by a recovery screw (not shown) that is a transport member. Note that the position and size of the developer discharge port 40 are appropriately determined by the image forming apparatus.

  By the way, depending on the state of the developer, the pumping ability of the developer from the agitating chamber 24 to the developing chamber 23 is lowered, so that the height of the developer surface in the developing chamber 23 is lowered and the developer is discharged from the developer discharge port 40. The amount of developer in the developing container 22 may increase.

  For example, immediately after being left in a high humidity environment for a long period of time, the charge amount of the developer is in a reduced state. Therefore, the fluidity of the developer is increased, and the pumping performance in the pumping unit is greatly decreased.

  This is because the developer with high fluidity becomes slippery because the frictional resistance with the surfaces of the first and second conveying screws 26 and 25 becomes small, and as a result, it is difficult to draw up from below. It is thought to be. When such a phenomenon occurs, the developer discharge amount decreases, and as a result, the developer amount in the developing device 4 increases.

  Then, as described above, when the amount of developer exceeds a certain amount, the pressure applied to the developer increases rapidly, so that the output of the inductance detection sensor 20 greatly changes even if the toner concentration does not change. (See FIG. 5).

    In order to prevent such problems, the test mode for judging whether the detected output value of the inductance detection sensor 20 is appropriate or not is obtained. As a result of this test mode, the output value is judged to be inappropriate. Then, control for correcting the image forming condition is performed. Specifically, in this embodiment, the image forming condition is a control for correcting a reference value, which is a target value for controlling the toner supply amount. A specific method of the control will be described with reference to the flowchart of FIG.

  In the present embodiment, the test mode is executed during post-rotation after a total of 500 prints have elapsed (step S1). When the test mode execution timing is reached (step S2), the rotation speed of the first and second conveying screws 26 and 25 is set to normal image formation while maintaining the rotation speed of the developing sleeve 28 at the time of normal image formation. It is changed step by step around the speed in time.

  The rotational speed of the first and second conveying screws 26 and 25 during image formation is 390 rpm. As shown in FIG. 7, the nine-stage speed is changed, and the output value (V1) of the inductance detection sensor 20 at that time is changed. ˜V9) are monitored (step S3).

  Here, when the rotational speeds of the first and second conveying screws 26 and 25 are decreased, the pumping performance of the developer in the pumping unit is lowered. For this reason, when the rotational speed is slowed below a certain fixed speed, the pressure applied to the developer in the pumping-up portion suddenly increases in the same manner as when the fluidity of the developer is increased.

  Therefore, when the output value of the inductance detection sensor 20 when the rotational speed of the first conveying screw 26 is changed is plotted on a graph, it is as shown in FIG. This graph is approximated by two straight lines having different inclinations, and a rotational speed S1 that is the intersection of the two approximate straight lines is obtained.

  In the case of FIG. 8, S1 is 354 rpm. The speed of S1 is compared with the rotation speed (390 rpm) during normal image formation. If the rotational speed at the time of normal image formation is larger than S1, the output value of the inductance detection sensor 20 detected at the time of normal image formation is an area where the output is almost flat even if the conveying screw speed is changed. It is. From this, it is determined that the pressure on the developer is not so high (step S4), and the test mode is terminated without performing any particular correction (step S7).

  On the other hand, when the amount of the developer in the developing device 4 increases to some extent, the pressure on the developer in the pumping portion is likely to increase, so that V1 to V9 are plotted as shown in FIG. 9 in the test mode. In such a case, for example, the rotational speed S1 that is the intersection of two approximate lines is 425 rpm.

  When S1 is larger than the rotation speed at the time of normal image formation, the output value of the inductance detection sensor 20 detected at the time of normal image formation is a flat area of the output, that is, the pressure on the developer is not so high. It is higher than the output in the area. For this reason, it is determined that the detected value is higher than the appropriate output value, and the toner density reference value of the inductance detection sensor 20 is corrected accordingly.

  That is, the difference ΔV (step S5) between the output value V0 in the flat output region and the output value V5 at the conveying screw rotation speed during normal image formation is set as the correction value. Then, by adding the difference ΔV to the toner density reference value (Vref), the corrected toner density reference value (Vref_adj) is determined (step S6), and the test mode is ended (step S7). If it is not the test mode execution timing, the post-rotation is terminated (step S8).

  In this embodiment, the difference ΔV is corrected by adding it to the toner density reference value (Vref). However, the present invention is not limited to this, and it may be added to the toner density reference value (Vref) obtained by multiplying the difference ΔV by a correction coefficient.

  Thereafter, until the next test mode is executed, toner density control during normal image formation is performed using the corrected toner density reference value determined here.

  As described above, in this embodiment, even when the pressure in the pumping portion increases because the amount of developer in the vertical stirring type developing device 4 increases, the output value of the inductance detection sensor 20 during normal image formation is It is judged whether or not it is appropriate. If it is determined that the toner density is not appropriate, the toner density reference value is corrected accordingly, so that an excessive increase in the toner density of the developer is avoided.

  The embodiment of the present invention has been described in detail above, but the present invention is not limited to the above-described embodiment, and the scope does not depart from the spirit of the invention described in the claims of the present invention. Thus, various changes can be made.

[Embodiment 2]
For example, as shown in FIG. 10, when it is determined that the output value of the inductance detection sensor 20 at the time of normal image formation is not appropriate as a result of the test mode, the first and second conveying screws at the time of normal image formation The rotational speeds 26 and 25 may be controlled. That is, in this embodiment, the rotation speeds of the first and second conveying screws 26 and 25 are used as the image forming conditions to be corrected when it is determined that the output value of the inductance detection sensor 20 is not appropriate.

  In FIG. 10, steps S1 to S4 are the same as those in FIG. That is, when the result of the test mode is FIG. 9, the closest and faster speed than the intersection S1 of the two approximate lines is selected from the nine speeds in FIG.

  If S1 is 425 rpm, 470 rpm, which is faster than this and the closest rotation speed, is set as the rotation speed of the normal first and second conveying screws 26, 25 (step S5). Then, the test mode (step S6) and the post-rotation are finished (step S7). Here, the reason why the rotational speeds of the first and second conveying screws 26 and 25 are set to the speed closest to S1 is to avoid as much as possible the temperature rise and wear of the rubbing portion due to the increase in the rotational speed.

  In this way, by increasing the rotation speed of the conveying screw, the output of the inductance detection sensor 20 becomes an appropriate output value (a region where the output is flat in FIG. 9), and an excessive increase in toner density is prevented.

  Further, by increasing the rotational speed of the first and second conveying screws 26 and 25, the developer pumping performance at the pumping section is improved, so the developer discharge amount from the developer discharge port 40 is increased. The amount of developer in the developing container 22 can be optimized.

1 is a schematic longitudinal sectional view of an image forming apparatus according to an embodiment of the present invention. It is a longitudinal cross-sectional view of the developing device shown in FIG. It is a cross-sectional view of the developing device shown in FIG. It is a figure which shows the relationship between the toner density | concentration of a developing agent, and an inductance detection sensor output. It is a figure which shows the relationship between the developer amount in a developing device, and an inductance detection sensor output. 4 is a flowchart showing control of the developing device of FIGS. It is a figure which shows the rotational speed value of 9 steps | paragraphs of a conveyance screw. It is a figure explaining the result when the output value of the inductance detection sensor at the time of normal image formation is appropriate in the test mode. It is a figure explaining the result when the output value of the inductance detection sensor at the time of normal image formation is not appropriate in the test mode. 4 is a flowchart showing another control of the developing device of FIGS. It is a schematic sectional drawing of the conventional vertical stirring type developing apparatus. FIG. 12 is a diagram showing the relationship between the developer amount in the developing device shown in FIG. 11 and the pressure applied to the developer in the pumping unit.

Explanation of symbols

1 Photosensitive drum 4 Developing device
20 Inductance detection sensor
22 Developer container
23 Development chamber
24 Mixing chamber
25 Second conveying screw
26 First conveying screw (developer stirring / conveying means)
28 Development sleeve (developer carrying means)
30 Developer supply port
31 Toner hopper (replenishment means)
32 Conveying material
40 Developer outlet (discharge means)
M1, M2 drive motor

Claims (6)

An image carrier;
A developing device having a developer carrying member carrying a developer containing toner and a carrier, and developing an electrostatic latent image formed on the image carrier;
A first conveying member that is provided in a first chamber in the developing device and conveys the developer toward a second chamber provided above the first chamber;
A second conveying member provided in the second chamber, for conveying the developer toward the first chamber;
Detecting means for detecting information on the magnetic permeability of the developer in the developing device;
Replenishment control means for controlling the amount of toner replenished to the developing device based on the detection result of the detection means;
Drive means for driving the first transport member and the second transport member;
When the image is not formed, a plurality of detection values detected by the detection unit when the rotation speed of the first transport member or the second transport member is changed with respect to the rotation speed of the developer carrier. Based on the correction means for correcting the rotational speed of the first conveying member or the second conveying member during image formation;
An image forming apparatus comprising:   The correction means includes the first transport when the plurality of detection values detected when the rotational speed of the first transport member is decreased with respect to the rotational speed of the developer carrier. 2. The rotational speed of the first transport member during image formation is corrected based on the rotational speed of the member and the rotational speed of the first transport member during image formation. Image forming apparatus.   The correction means includes the second transport when the plurality of detection values detected when the rotational speed of the second transport member is decreased with respect to the rotational speed of the developer carrier start to increase. 2. The rotational speed of the second transport member during image formation is corrected based on the rotational speed of the member and the rotational speed of the second transport member during image formation. Image forming apparatus. An image carrier;
A developing device having a developer carrying member carrying a developer containing toner and a carrier, and developing an electrostatic latent image formed on the image carrier;
A first conveying member that is provided in a first chamber in the developing device and conveys the developer toward a second chamber provided above the first chamber;
A second conveying member provided in the second chamber, for conveying the developer toward the first chamber;
Detecting means for detecting information on the magnetic permeability of the developer per unit volume in the developing device;
Replenishment control means for controlling the amount of toner to be replenished to the developing device so that the detection result of the detection means becomes a predetermined reference value;
Drive means for driving the first transport member and the second transport member;
When the image is not formed, a plurality of detection values detected by the detection unit when the rotation speed of the first transport member or the second transport member is changed with respect to the rotation speed of the developer carrier. Correction means for correcting the predetermined reference value based on:
An image forming apparatus comprising:   The correction means includes the first transport when the plurality of detection values detected when the rotational speed of the first transport member is decreased with respect to the rotational speed of the developer carrier. The image forming apparatus according to claim 4, wherein the predetermined reference value is corrected based on information relating to a difference between a rotation speed of the member and a rotation speed of the first conveying member at the time of image formation. .   The correction means includes the second transport when the plurality of detection values detected when the rotational speed of the second transport member is decreased with respect to the rotational speed of the developer carrier start to increase. 5. The image forming apparatus according to claim 4, wherein the predetermined reference value is corrected based on information on a difference between a rotation speed of the member and a rotation speed of the second conveying member at the time of image formation. .

Images