Patent Publication Number: US-10761456-B2

Title: Developing device and image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2018-091470, filed on May 10, 2018, which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technological Field 
     A developing device and an image forming apparatus of the present disclosure relate to a developing device and an image forming apparatus in which an image is formed by electrophotography. The image forming apparatus includes an electrophotographic apparatus such as a digital copying machine, a facsimile machine, or a printer, a recording apparatus, a display device, and the like regardless of color or monochrome. 
     Description of the Related Art 
     JP 2010-210697 A relates to a developing device and an image forming apparatus, and discloses a structure of the developing device capable of reducing a difference in bulk density on a detection surface of a toner density detection sensor during stirring operation while preventing erroneous detection caused by accumulation of developer on the detection surface. 
     According to JP 2010-210697 A, a detection surface stirring member capable of stirring developer while rubbing a detection surface of a toner density detection sensor is provided at a position located in an axial direction of a conveyance screw and facing the detection surface in order to stabilize detection by a toner density detection sensor. This detection surface stirring member is formed in a rectangular waveform and includes, at each protrusion of the waveform, an elastic sheet that is flexible and deformable while contacting the detection surface. 
     The toner density detection sensor is fixed to the outside of a developing device, and reads toner density of the developer inside the developing device by using a non-contact type toner density detection sensor for the developer. The toner density detection sensor is made by combining a coil and a capacitor, and reads magnetic permeability of a carrier inside the developer. To accurately detect the toner density inside the developing device, an amount of the developer existing at the position of the toner density detection sensor is required to be constant all the time. 
     However, since force pushed by a screw blade acts on the developer, in a case where a rotation speed of the conveyance screw is accelerated, conveyance force acting on the developer becomes larger. In a case where the screw blade has a continuous shape, the developer existing at the position facing the toner density detection sensor is conveyed as it is, a constant amount of the developer hardly exists, and it is difficult to accurately detect the toner density. 
     On the other hand, in a case where the amount of the developer is reduced, the amount of the developer at the position of the toner density detection sensor is also reduced, and therefore, a sparse space is increased and a detection error is likely to occur. 
     SUMMARY 
     The present disclosure may be directed to: solving one or more of the above-described problems; and providing a developing device and an image forming apparatus both including a structure in which toner density of a developer inside the developing device may be accurately detected. 
     To achieve the abovementioned object, according to an aspect of the present disclosure, a developing device reflecting one aspect of the present disclosure comprises: a casing that stores developer containing toner; and a screw arranged inside the casing, wherein the screw includes: a rotary shaft; and a screw blade that is spirally arranged around the rotary shaft and conveys the toner from an upstream side to a downstream side by rotation of the rotary shaft, the screw blade includes a discontinuous region, a paddle extending in a radial direction of the rotary shaft is provided along an axial direction of the rotary shaft on a surface of the rotary shaft located in the discontinuous region, and a recess and a protrusion are provided at an edge side in a radial direction of the paddle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages and features provided by one or more embodiments of the disclosure will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present disclosure: 
         FIG. 1  is a diagram illustrating a schematic structure of an image forming apparatus according to an embodiment; 
         FIG. 2  is a diagram illustrating a schematic structure of a developing device of the embodiment; 
         FIG. 3  is a schematic diagram to describe a circulation time in the developing device of the embodiment; 
         FIG. 4  is a partially enlarged perspective view illustrating a specific structure of a stirring screw of the embodiment; 
         FIG. 5  is a diagram illustrating an arrangement ration between a developing roller, a supply screw, and the stirring screw of the embodiment; 
         FIG. 6  is a schematic diagram illustrating an arrangement relation between the stirring screw, a wall surface, and a toner density detection sensor of the embodiment; 
         FIG. 7  is a schematic diagram illustrating a relation between a paddle and a liquid level height of developer of toner of the embodiment; 
         FIG. 8  is a diagram illustrating a stirring state of the developer by the paddle in a discontinuous region of the embodiment; 
         FIG. 9  is a schematic diagram in a case where a space between a screw blade and the paddle of the embodiment is larger on an upstream side; 
         FIG. 10  is a schematic diagram in a case where a space between the screw blade and the paddle of the embodiment is larger on a downstream side; 
         FIG. 11  is a diagram illustrating another form of the paddle of the embodiment; 
         FIG. 12  is a schematic diagram in a case where one paddle is provided in the discontinuous region of the embodiment; and 
         FIG. 13  is a schematic diagram in a case where two paddles are provided in the discontinuous region of the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one or more embodiments of the present disclosure will be described with reference to the drawings. However, the scope of the disclosure is not limited to the disclosed embodiments. In a case of referring to number, an amount, and the like in each of the embodiments described below, the scope of the present disclosure is not necessarily limited by the number, the amount, and the like, unless otherwise particularly specified. Identical components or equivalent components are denoted by the same reference signs, and there may be a case where the same description is not repeated. In the drawings, there may be a part illustrated in a manner not conforming to a ratio of an actual dimension, and the ratio is changed to clarify a structure for easy understanding 
     The image forming apparatus includes: an MFP having a scanner function, a copying function, a function as a printer, a facsimile function, a data communication function, and a server function; a facsimile machine; or a copying machine. 
     (Image Forming Apparatus) 
     In the following, an image forming apparatus  1  according to the present embodiment will be described with reference to  FIG. 1 .  FIG. 1  is a diagram illustrating a schematic structure of the image forming apparatus  1  according to the present embodiment. 
     The image forming apparatus  1  forms an image on a recording medium by a known electrophotographic system. The image forming apparatus  1  includes an image processor  10 , a transfer part  20 , a sheet feeder  30 , a fixing device  40 , and a controller  45 . The image forming apparatus  1  selectively executes color and monochrome printing based on a print job received from an external terminal device (not illustrated) via a network (such as a LAN). 
     The image processor  10  includes image forming units  10 Y,  10 M,  10 C, and  10 K corresponding to developing colors of yellow (Y), magenta (M), cyan (C), and black (K). The image forming unit  10 Y includes: a photoreceptor drum  11  that is an electrostatic latent image carrier; an electric charger  12 ; an exposure device  13 ; a developing device  14 ; a primary transfer roller  15 ; a cleaner  16 ; and the like which are arranged around the photoreceptor drum  11 . The electric charger  12  charges a peripheral surface of the photoreceptor drum  11  that is rotated in a direction indicated by an arrow A. 
     The exposure device  13  exposes and scans the charged photoreceptor drum  11  with laser light to form an electrostatic latent image on the photoreceptor drum  11 . The developing device  14  stores developer containing toner inside thereof and develops the electrostatic latent image on the photoreceptor drum  11  with the toner, thereby forming a toner image Y on the photoreceptor drum  11 . In other words, the toner image is carried on the electrostatic latent image carrier. 
     The primary transfer roller  15  transfers, onto the intermediate transfer body  21 , the Y color toner image that has been formed on the photoreceptor drum  11  by electrostatic action. In other words, the toner image is primarily transferred to the intermediate transfer body. The cleaner  16  cleans residual toner remaining on the photoreceptor drum  11  after the transfer. Other image forming units  10 M,  10 C, and  10 K also have structures similar to the structure of the image forming unit  10 Y, and the reference signs therein are omitted in the drawing. The transfer part  20  includes the intermediate transfer body  21  which is stretched around a drive roller  24  and a driven roller  25  and circulated in a direction indicated by an arrow. 
     In a case of executing color printing (color mode), an image of toner of a corresponding color is formed on the photoreceptor drum  11  in each of the image forming units  10 M,  10 C, and  10 K, and each of the formed toner images is transferred onto the intermediate transfer body  21 . Image forming operation of each of the colors Y to K is executed by deviating timing sequentially from an upstream side to a downstream side such that the toner images of the respective colors are superimposed and transferred onto the same position of the intermediate transfer body  21  that is traveling. 
     The sheet feeder  30  feeds sheets S that are recording media one by one from a sheet feeding cassette in accordance with the above-described image forming timing, and conveys the fed sheet S to a secondary transfer roller  22  on a conveyance path  31 . When the sheet S conveyed to the secondary transfer roller  22  passes between the secondary transfer roller  22  and the intermediate transfer body  21 , the respective color toner images that have been formed on the intermediate transfer body  21  are collectively secondarily transferred to the sheet S by electrostatic action of the secondary transfer roller  22 . In other words, the toner image is secondarily transferred from the intermediate transfer body to the recording medium. 
     The sheet S onto which the respective color toner images have been secondarily transferred is conveyed to the fixing device  40  and subjected to heating and pressing in the fixing device  40 . Consequently, the toner on the surface is fused and fixed to a surface of the sheet S, and then the sheet S is ejected onto a sheet ejection tray  33  by a sheet ejection roller  32 . Thus, an image corresponding to the toner image is formed on the recording medium. 
     In the above description, operation in the case of executing the color mode has been described, but in a case of executing monochrome printing such as in black (monochrome mode), only the image forming unit  10 K for the black color is driven to execute image forming (printing) on a sheet S in the black color through the respective steps including electric charging, exposing, developing, transferring, and fixing for the black color. 
     The toner and a toner pattern on the intermediate transfer body  21 , which has not been transferred to the sheet S, are removed by a cleaning blade  26  arranged at a position facing the driven roller  25  interposing the intermediate transfer body  21 . On the downstream side of the image forming unit  10 K in a travel direction of the intermediate transfer body  21 , for example, a density detection sensor  23  including a reflection photoelectric sensor is arranged to detect density of a toner pattern formed on the intermediate transfer body  21 . 
     For example, the controller  45  controls the respective components based on data of a print job received from the external terminal device via the network to execute smooth printing operation. An operation panel  35  is arranged on a front side and an upper side of an apparatus body of the image forming apparatus  1  and also at a position where a user can easily operate the operation panel. The operation panel  35  includes: buttons to receive various commands from the user; a touch panel type liquid crystal display; and the like, and can notifies the controller  45  of content of the received command. 
     As the above-describe image forming apparatus, an electrophotographic image forming apparatus such as a copying machine, a printer, a digital printing machine, and a simple printing machine can be exemplified, and either a dry type or a wet type may be applied, but using the dry type image forming apparatus is particularly effective. 
     (Developing Device  14 ) 
     The developing device  14  will be described with reference to  FIGS. 2 and 3 .  FIG. 2  is a diagram illustrating a schematic structure of the developing device  14 , and  FIG. 3  is a diagram illustrating an arrangement relation between a developing roller  17 , a supply screw  18 , and a stirring screw  19 . 
     The developing device  14  is provided corresponding to each photoreceptor drum  11 , and is arranged in a manner facing a surface of the photoreceptor drum  11 . The developing device  14  is applied with charging bias, thereby supplying toner to the photoreceptor drum  11 . The developing device  14  makes toner of a predetermined color adhere to an electrostatic latent image formed on the photoreceptor drum  11 , and forms a toner image on the surface of the photoreceptor drum  11 . 
     The developing device  14  includes the developing roller  17 , the supply screw  18 , and the stirring screw  19  which are arranged in a manner facing the surface of the photoreceptor drum  11 . The toner cartridge  5  is provided corresponding to each developing device  14 , and stores the toner to be supplied to the developing device  14 . The developing roller  17 , the supply screw  18 , and the stirring screw  19  are housed inside the casing (wall surface W). 
     The toner supply device  6  is provided corresponding to each toner cartridge  5  and each developing device  14 , and supplies the developing device  14  with the toner stored in the toner cartridge  5 . The toner supply device  6  and the developing device  14  are connected by a toner supply path (not illustrated). 
     The developing device  14  includes a charging bias application device  100  in addition to the above-described components. The charging bias application device  100  executes a command from the controller  45 . The charging bias application device  100  applies predetermined charging bias to the developing device  14 . Specifically, the charging bias application device  100  applies the predetermined charging bias to the developing roller  17 . The charging bias application device  100  adjusts the charging bias under the control of the controller  45 . The charging bias is bias obtained by superimposing AC bias on DC bias. 
     Referring to  FIG. 3 , supply toner to be supplied from the toner cartridge  5  is firstly injected into one end side (right side in the drawing) of the stirring screw  19 . The injected toner is stirred by the stirring screw  19  with existing developer while being transferred to the other end side (left side in the drawing). 
     The toner having reached the other end of the stirring screw  19  is moved to one end side of the supply screw  18 . The developer having reached the one end side of the supply screw  18  is moved to the other end side of the supply screw  18  while being passed over to the developing roller from the supply screw  18 . After that, residual developer is returned to the one end side of the stirring screw  19  again. Thus, the toner injected into the one end side of the stirring screw  19  is circulated through a circulation path in which the stirring screw  19  and the supply screw  18  of the developing device  14  are arranged. 
     (Specific Structure of Stirring Screw  19 ) 
     A specific structure of the stirring screw  19  in the present embodiment will be described with reference to  FIG. 4 .  FIG. 4  is a partially enlarged perspective view illustrating the specific structure of the stirring screw  19 . 
     The stirring screw  19  includes a rotary shaft  19   a  and a screw blade  19   b  spirally provided around the rotary shaft  19   a.    
     The screw blade  19   b  at a position facing the toner density detection sensor  50  is provided with a discontinuous region  19   d  not including the screw blade  19   b  and having a length L 1 . Additionally, a surface of the discontinuous region  19   d  of the rotary shaft  19   a  is provided with two paddles  60  at positions facing each other by 180 degrees, and each of the paddles extends in the radial direction of the rotary shaft  19   a  along an axial direction of the rotary shaft  19   a . Three protrusions  61  and two recesses  62  are provided on an edge side of each paddle  60 , and the paddle  60  has a comb-tooth shape as a whole. The number of the paddles  60  can be appropriately changed. 
     Furthermore, the paddles  60  facing each other are arranged in a manner such that phases of the recesses  62  are deviated from each other. Specifically, one recess  62  of one paddle is arranged at a position facing one recess of the other paddle position, and the other recess  62  of the one paddle is arranged at a position not facing any recess of the other paddle. In the one paddle  60  (on an upper side in  FIG. 4 ), a large space S is provided in a space with the upstream-side screw blade  19   b . In the other paddle  60  (on a lower side in  FIG. 4 ), a large space S is provided in a space with the downstream-side screw blade  19   b.    
     Thus, in the stirring screw  19  of the present embodiment, the screw blade  19   b  facing the toner density detection sensor  50  is formed discontinuous, and the comb-tooth shaped paddles  60  are arranged in the discontinuous region. The space is provided between the paddle  60  and the upstream-side edge of the screw blade  19   b  (on the upstream side of the discontinuous region), and similarly, the space is also provided between the paddle  60  and the downstream-side edge of the screw blade  19   b  (on the downstream side of the discontinuous region). 
     With this structure, the developer is accumulated in the discontinuous region  19   d  of the screw blade  19   b  even in a case where operation speed is accelerated and an amount of developer is reduced. A density difference in the accumulated developer is eliminated before and after passage of the paddles  60 , and the density of the developer can be kept constant because of the comb-tooth shape of each of the paddles  60 . 
     Furthermore, since the space is also provided between the screw blade  19   b  and each paddle  60 , it is possible to more effectively eliminate the density difference in the developer. Even in a case where a conveying speed is accelerated, conveying force is lost between each paddle  60  and the edge of the screw blade  19   b  in the discontinuous region  19   d , and the developer can be easily accumulated at the position facing the toner density detection sensor  50 . 
     &lt;Discontinuous Region  19   d /Arrangement Position of Toner Density Detection Sensor  50 &gt; 
     Preferable arrangement positions of the discontinuous region  19   d  and the toner density detection sensor  50  in the case of adopting the stirring screw  19  having the above-described structure will be described with reference to  FIGS. 5 and 6 .  FIG. 5  is a diagram illustrating an arrangement relation between the developing roller  17 , the supply screw  18 , and the stirring screw  19 , and  FIG. 6  is a schematic diagram illustrating an arrangement relation between the stirring screw  19 , the wall surface W, and the toner density detection sensor  50 . White arrows in  FIG. 5  represent moving directions of the toner, and a place marked by “x” represents an arrangement position of the toner density detection sensor  50 . 
     The toner that has been supplied to the stirring screw  19  is stirred by the stirring screw  19  and conveyed to the supply screw  18 . The toner that has been conveyed to the supply screw  18  is conveyed to the developing roller  17  together with a carrier. 
     Referring to  FIG. 6 , the discontinuous region  19   d  is preferably provided at a position on the downstream side of the stirring screw  19  immediately before conveyance to the supply screw  18  (region where the developer is received), and it is preferable to provide the toner density detection sensor  50  on an outer side of the wall surface W facing a position on the downstream side of the stirring screw  19 . 
     The supplied toner is stirred by the stirring screw  19 , and the developer is accumulated in the discontinuous region  19   d  of the screw blade  19   b . Since the toner density detection sensor  50  is arranged at this facing position, it is possible to stably and highly accurately measure the toner density immediately before conveyance to the supply screw  18 . In a case of providing this structure in the supply screw  18 , a liquid level height of the developer may be changed, and an image may be defected due to existence of the discontinuous region in the supply screw  18 . 
     &lt;Length (L 1 ) of Discontinuous Region  19   d  and Length of Toner Density Detection Sensor  50 &gt; 
     The length (L 1 ) of the discontinuous region  19   d  and a length of the toner density detection sensor  50  will be described with reference to  FIG. 7 .  FIG. 7  is a schematic diagram illustrating a relation between a paddle  60  and a liquid level height (WL) of the developer of the toner. 
     The region having the constant density of the developer is widened by setting the length (L 1 ) of the discontinuous region  19   d  longer than a length (L 2 ) of the toner density detection sensor  50 . Therefore, detection accuracy by the toner density detection sensor  50  can be improved. Here, the length (L 2 ) of the toner density detection sensor  50  represents a length of a sensor coil included in the toner density detection sensor  50 . 
     &lt;Positional Relation&gt; 
     As for a positional relation between the protrusions  61  of each paddle  60  and the wall surface W, it is preferable that the protrusions  61  of the paddle  60  do not contact an inner side of the wall surface W of the casing. In the case where the protrusions contact the wall surface W, the toner is rubbed against the inner wall surface by the paddle  60 , and a phenomenon called spent in which a toner component transitions into a carrier and charging failure is caused occurs. 
     As illustrated in  FIG. 7 , as for the positional relation between the paddle  60  and the coil provided inside the toner density detection sensor  50 , an arrangement in which a center of the toner density detection sensor  50  (indicated by “x” in  FIG. 7 ) overlaps a center of a recess  62  of the paddle  60  (located on the same line CL) is preferable. Since the developer is accumulated in the recess  62  and the density is kept constant, the detection accuracy can be improved. 
     &lt;Positional Relation Between Recess  62  of Paddle  60  and Liquid Level Height of Developer&gt; 
     It is preferable that a bottom portion  62   b  of a recess  62  of each paddle  60  be arranged closer to the wall surface W side inside the casing than a liquid height (WL) of the developer. Here, the liquid level height (WL) of the developer represents a height of the developer from the wall surface W of the casing of the developing device. 
     A stirring state of the developer will be described with reference to  FIG. 8 .  FIG. 8  is a diagram illustrating the stirring state of the developer by one paddle  60  in the discontinuous region  19   d . As illustrated in  FIG. 8 , since there are: non-movable developer T 2  on a bottom surface; and developer T 1  that is movable by being pushed by the recesses  62  of the paddle  60  in the discontinuous region  19   d , a speed difference is caused in the developer. Since the developer is further stirred due to such a speed difference, supplied toner is conveyed without being superficially slipped, and the toner density can be accurately detected. 
     (Space (S) Magnitude Relation Between Screw Blade  19   b  and Each of Paddles  60 &gt; 
     A space (S) magnitude relation between the screw blade  19   b  and each of the paddles  60  will be described with reference to  FIGS. 9 and 10 .  FIG. 9  is a schematic diagram in a case where a space (S) between the screw blade  19   b  and the paddle  60  is larger on the upstream side, and  FIG. 10  is a schematic diagram in a case where a space (S) between a screw blade  19   b  and the paddle  60  is larger on the downstream side. 
     Referring to  FIG. 9 , in a case where the toner density detection sensor  50  is arranged more on the upstream side than a center (CL 2 ) of the discontinuous region  19   d , it is preferable that the space (S 1 ) between the paddle  60  and the upstream-side screw blade  19   b  be set larger than the space (S 2 ) between the paddle  60  and the downstream-side screw blade  19   b  (S 1 &gt;S 2 ). The larger the accumulated amount of the developer is, the more constant the density of the developer is kept. Therefore, the detection accuracy by the toner density detection sensor  50  can be improved. 
     Referring to  FIG. 10 , in a case where the toner density detection sensor  50  is arranged more on the downstream side than the center (CL 2 ) of the discontinuous region  19   d , it is preferable that the space (S 2 ) between the paddle  60  and the downstream-side screw blade  19   b  be set larger than the space (S 1 ) between the paddle  60  and the upstream-side screw blade  19   b  (S 1 &lt;S 2 ). The larger the accumulated amount of the developer is, the more constant the density of the developer is kept. Therefore, the detection accuracy by the toner density detection sensor  50  can be improved. 
     (Number of Protrusions  61  Provided in Paddle  60 ) 
     The number of protrusions  61  provided in one paddle  60  will be described with reference to  FIG. 11 .  FIG. 11  is a diagram illustrating another form of the paddle  60 . 
     The above-described paddle  60  is illustrated to have a structure including the three protrusions  61  and the two recesses  62 . The developer is pushed by the protrusions of the paddle  60 , the developer is stirred due to a speed difference of the developer caused in the discontinuous region  19   d . Accordingly, stirring performance for the developer accumulated in the discontinuous region  19   d  is improved by having the plurality of protrusions, and the detection accuracy is improved. Therefore, as illustrated in  FIG. 11 , a structure including four protrusions  61  and three recesses  62  may also be adopted, or a paddle  60  including the number of protrusions  61  equal to or more than four and the number of recesses  62  equal to or larger than three may also be adopted. 
     (Number of Paddles  60 ) 
     The number of paddles  60  provided in the discontinuous region  19   d  of the stirring screw  19  will be studied with reference to  FIGS. 12 and 13 .  FIG. 12  is a schematic diagram in a case where one paddle  60  is provided in the discontinuous region  19   d , and  FIG. 13  is a schematic diagram in a case where two paddles  60  are provided in the discontinuous region  19   d.    
     The stirring screw  19  illustrated in  FIG. 4  has the discontinuous region  19   d  in which the two paddles  60  extending in the radial direction of the rotary shaft  19   a  are provided at the positions facing each other by 180 degrees along the axial direction of the rotary shaft  19   a . Now, referring to  FIG. 12 , in a case where the one paddle  60  is provided in the discontinuous region  19   d , a density difference in the developer having passed through the recesses  62  is eliminated between before and after passage of the paddle  60 . However, since the developer is dense in a part pushed by the protrusions  61  of the paddle, the density difference remains between before and after passage through the paddle. 
     By providing the two paddles  60  as illustrated in  FIG. 13 , the developer existing in the discontinuous region  19   d  is easily stirred, the density difference in the developer is eliminated, and the density of the developer can be made constant. As a result, the detection accuracy of the toner density by the toner density detection sensor  50  can also be improved. Note that, in the present embodiment, the case of providing the two paddles  60  has been described, but a plurality of paddles  60 , that is, three or more paddles may also be provided. In such a case, the developer existing in the discontinuous region  19   d  is more easily stirred by arranging the protrusions and the recesses of the respective paddles  60  in a manner such that mutual phases are deviated from each other as described in  FIG. 4 . 
     Although embodiments of the present disclosure have been described and illustrated in detail, the disclosed embodiments are made for purposes of illustration and example only and not limitation. The scope of the present disclosure should be interpreted by terms of the appended claims. 
     As used throughout this application, the words “can” and “may” are used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). The words “include”, “including”, and “includes” and the like mean including, but not limited to. As used herein, the singular form of “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality). 
     Unless specifically stated otherwise, as apparent from the discussion, it is appreciated that throughout this specification discussions utilizing terms such as “processing,” “computing,” “calculating,” “determining” or the like refer to actions or processes of a specific apparatus, such as a special purpose computer or a similar special purpose electronic processing/computing device.