Abstract:
A developing device includes N number of containers, N number of conveying members, N number of first sensors, stirring portions, a switching unit, and a control unit. The N number of conveying members stir and convey respective developers inside the N number of containers. The N number of first sensors are located at the N number of containers to detect toners remaining amount inside of the N number of containers. The stirring portions are located at the respective N number of conveying members to stir the developers at detecting regions opposed to detecting surfaces of the N number of first sensors by rotations of the N number of conveying members. The switching unit selects any one of outputs of the N number of first sensors to output. The control unit receives the selected output to detect the remaining amounts of the developers inside the N number of containers.

Description:
INCORPORATION BY REFERENCE 
     This application is based upon, and claims the benefit of priority from, corresponding Japanese Patent Application No. 2015-147232 filed in the Japan Patent Office on Jul. 24, 2015, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     Unless otherwise indicated herein, the description in this section is not prior art to the claims in this application and is not admitted to be prior art by inclusion in this section. 
     Some typical electrophotographic-method image forming apparatuses use a two-component-development-method developer. The two-component-development-method developer is made of magnetic powder, which is referred to as a magnetic carrier, and toner, which is colorant. At a development process when forming an image, since only the toner is consumed, the toner is supplied to the developer, and then the magnetic powder and the toner are stirred. Thus, in order to replenish the toner with an amount consumed at the development process, a toner density detecting sensor, which measures toner density in the developer, is equipped with an image forming apparatus. At a color image forming apparatus, for example, since cyan, magenta, yellow, and black toners are used for development, four toner density detecting sensors are used to detect respective remaining amounts of four color toners. 
     SUMMARY 
     A developing device according to one aspect of the disclosure includes N (N is an integer equal to or greater than two) number of containers, N number of conveying members, N number of first sensors, stirring portions, a switching unit, and a control unit. The N number of containers each house a developer including a toner. The N number of conveying members stir and convey the respective developers inside the N number of containers. The N number of first sensors are located at the N number of containers each to detect a toner remaining amount inside each of the N number of containers. The stirring portions are located at the respective N number of conveying members to stir the developers at detecting regions opposed to detecting surfaces of the N number of first sensors by rotations of the N number of conveying members. The switching unit selects any one of outputs of the N number of first sensors to output. The control unit receives the selected output to detect the remaining amounts of the developers inside the N number of containers. 
     These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description with reference where appropriate to the accompanying drawings. Further, it should be understood that the description provided in this summary section and elsewhere in this document is intended to illustrate the claimed subject matter by way of example and not by way of limitation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross section of an overall configuration of an image forming apparatus including a developing device according to one embodiment of the disclosure; 
         FIG. 2  illustrates a cross section of a side surface of a construction of the developing device according to the one embodiment; 
         FIGS. 3A and 3B  illustrate a conveying member that the developing device according to the one embodiment has; 
         FIG. 4  illustrates a NAND oscillator circuit of a density sensor that the developing device according to the one embodiment has; 
         FIG. 5  illustrates a relation between a rotation angle of the conveying member and a detecting state of the density sensor that the developing device according to the one embodiment has; and 
         FIG. 6  illustrates a toner density detecting system of the developing device according to the one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Example apparatuses are described herein. Other example embodiments or features may further be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. In the following detailed description, reference is made to the accompanying drawings, which form a part thereof. 
     The example embodiments described herein are not meant to be limiting. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the drawings, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     The following describes a configuration to execute the disclosure (hereinafter referred to as “embodiment”) with reference to the drawings. 
       FIG. 1  illustrates a cross section of an overall configuration of an image forming apparatus  1  including a developing device according to one embodiment of the disclosure. The image forming apparatus  1  according to the embodiment is a tandem-type color printer. The image forming apparatus  1  includes a housing  10  where photoreceptor drums (image carriers)  30   m ,  30   c ,  30   y , and  30   k  are arranged in a row corresponding to respective colors: magenta, cyan, yellow, and black. Adjacent to the photoreceptor drums  30   m ,  30   c ,  30   y , and  30   k , developing devices  100   m ,  100   c ,  100   y , and  100   k  are arranged respectively. 
     To the photoreceptor drums  30   m ,  30   c ,  30   y , and  30   k , laser beams Lm, Lc, Ly, and Lk for the respective colors are irradiated from an exposure unit  50 . This irradiation forms electrostatic latent images on the photoreceptor drums  30   m ,  30   c ,  30   y , and  30   k . The developing devices  100   m ,  100   c ,  100   y , and  100   k , while stirring toner, attach the toner to the electrostatic latent images formed on surfaces of the photoreceptor drums  30   m ,  30   c ,  30   y , and  30   k . This completes a development process to form toner images of the respective colors on the surfaces of the photoreceptor drums  30   m ,  30   c ,  30   y , and  30   k.    
     The image forming apparatus  1  includes an endless intermediate transfer belt  20 . The intermediate transfer belt  20  is stretched to a tension roller  24 , a drive roller  22 , and a driven roller  21 . The intermediate transfer belt  20  is driven in cycles by rotation of the drive roller  22 . 
     For example, a black toner image on the photoreceptor drum  30   k  is primarily transferred to the intermediate transfer belt  20  such that the photoreceptor drum  30   k  and a primary transfer roller  23   k  sandwich the intermediate transfer belt  20  to drive the intermediate transfer belt  20  in cycles. In this respect, the same applies to the three colors: cyan, yellow, and black. On a surface of the intermediate transfer belt  20 , the primary transfers mutually superimposed at a predetermined timing form a full-color toner image. Afterward, the full-color toner image is secondarily transferred to a printing paper sheet P supplied from a sheet feed cassette  60  to be fixed to the printing paper sheet P at a well-known fixing process. 
       FIG. 2  illustrates a cross section of a side surface of a construction of the developing device  100   k  according to the one embodiment. The developing devices  100   m ,  100   c , and  100   y  have configurations identical to the developing device  100   k , and are simply referred to as a developing device  100  (see  FIG. 2 ). The developing device  100  includes a developing roller (a developer support)  144 , a magnetic roller  143 , a regulating blade  146 , two conveying members  141  and  142 , and a container  145 . 
     The container  145  constitutes an outside of the developing device  100 . The container  145  includes a lower portion where a partition portion  145   b  is located. The partition portion  145   b  separates an inside of the container  145  into a first conveying chamber  145   a  and a second conveying chamber  145   c . The first conveying chamber  145   a  and the second conveying chamber  145   c , which cylindrically extend in a direction perpendicular to  FIG. 2 , house two-component developer (simply referred to as developer) made of magnetic carrier and black toner. At the first conveying chamber  145   a  and the second conveying chamber  145   c , the conveying members  141  and  142  are rotatably arranged respectively to stir the developer. 
     The container  145  further, rotatably holds the magnetic roller  143  and the developing roller  144 . At the container  145 , an opening  147 , which exposes the developing roller  144  to a photoreceptor drum  30  ( 30   k ), is formed. The two conveying members  141  and  142 , while stirring the developer inside the first conveying chamber  145   a  and the second conveying chamber  145   c  respectively, cyclically move the developer. 
     The conveying member  142 , as a magnetic brush, supplies electrostatic-charged developer to the magnetic roller  143 . The regulating blade  146  adjusts the magnetic brush at a predetermined height preliminarily set. The magnetic roller  143  supplies only the toner from the developer to the developing roller  144  in a well-known method. The developing roller  144  attaches the toner to a latent image formed on a surface of the photoreceptor drum  30  to form a visible image of an inverted image on a surface of the photoreceptor drum  30 . 
       FIG. 3A  obliquely illustrates the conveying member  141  of the developing device  100  according to the one embodiment.  FIG. 3B  illustrates a cross section of a side surface illustrating equipping states of the conveying member  141  and a density sensor  150  of the developing device  100  according to the one embodiment. The conveying member  141 , which includes a rotation shaft  141   b , a spiral blade  141   a , and a rib  141   r , is integrally constituted with them. The rotation shaft  141   b  is rotatably driven by a motor (not illustrated). The spiral blade  141   a  is formed in a spiral pattern with a constant pitch in an axial direction of the rotation shaft  141   b . The rib  141   r  is a member to adjust conveying speed of the developer. 
     The conveying member  141  further, includes a scraper  141 S at a region opposed to the density sensor  150  (referred to as a detecting region). The scraper  141 S, which includes a nonwoven fabric  141 S 1  and a polyethylene sheet  141 S 2  having identical shapes, is bonded to the spiral blade  141   a  with an adhesive layer (not illustrated). The scraper  141 S has a length to be able to clean a detecting surface  150   a  when the conveying member  141  rotates. 
     The conveying member  141 , while stirring the developer by rotating, can remove the developer being deposited on the detecting surface  150   a  by the scraper  141 S to reduce accumulation of the developer. This can reduce misdetections (errors) due to the accumulation of the developer (for example, attachment or deposition to the detecting surface  150   a ) at the detecting region. The scraper  141 S is also referred to as a stirring portion. 
       FIG. 4  illustrates a NAND oscillator circuit  151  of the density sensor  150  that the developing device  100  according to the one embodiment has. The density sensor  150  includes the NAND oscillator circuit  151  using a NAND gate (for example, 74HC00). The NAND oscillator circuit  151  includes two inverters N 1  and N 2 , two resistors Rf and Rd, a coil L, and two capacitors C 1  and C 2 . The two inverters N 1  and N 2  are connected in series. The inverter N 2  has an output that is an output of the NAND oscillator circuit  151  (an output of the density sensor  150 ). 
     The NAND oscillator circuit  151  is constituted of connections as follows. To the inverter N 1 , the resistor Rf is connected in parallel. To the inverter N 1 , further, a series circuit of the resistor Rd and the coil L is connected in parallel. The resistor Rd and the coil L have a connecting point that is grounded via a capacitor C 2 . The coil L and an input of the inverter N 1  have a connecting point that is grounded via a capacitor C 1 . The NAND oscillator circuit  151  causes the inverter N 1  to repeat inversion of a logical value together with charge and discharge of the two capacitors C 1  and C 2  as well known, to oscillate. 
     The coil L is arranged so that an inductance changes corresponding to the toner density in the developer on the detecting surface  150   a . Specifically, the coil L is arranged so that magnetic flux generated by the coil L passes through the developer on the detecting surface  150   a . At the coil L, since as the toner density increases, proportion of the toner, where magnetic against the magnetic carrier does not pass through, increases, magnetic permeability decreases to decrease the inductance. On the other hand, at the coil L, since as the toner density decreases, the proportion of the toner, where magnetic against the magnetic carrier does not pass through, decreases, the magnetic permeability increases to increase the inductance. 
     Thus, at the density sensor  150 , resonant frequency of the NAND oscillator circuit  151  changes corresponding to change of the inductance of the coil L. Specifically, if the toner density increases to decrease the inductance of the coil L, the resonant frequency increase, and if the toner density decreases to increase the inductance of the coil L, the resonant frequency decreases. The density sensor  150  is referred to as a first sensor. 
       FIG. 5  illustrates a relation between a rotation angle of the conveying member  141  and a detecting state of the density sensor  150  that the developing device  100  according to the one embodiment has.  FIG. 5  illustrates the conveying member  141  in four states S 1  to S 4  with different rotation angles and waveforms at the respective states detected by the density sensor  150 . The four states S 1  to S 4  illustrate states of the developer stirred by the scraper  141 S of the conveying member  141 . In the four states S 1  to S 4 , developer states D 1  and D 2  (simply referred to as developers D 1  and D 2 ) are also illustrated. The developer state D 1  illustrates a state of relatively dense developer in a state being pressed by the scraper  141 S. The developer state D 2  illustrates a state of relatively low-density developer being deposited. 
     In the state S 1 , the relatively dense developer D 1  is detected by the density sensor  150 . The developer D 1  has higher magnetic permeability than a magnetic permeability of air to decrease a detecting frequency. In the state S 2 , the relatively dense developer D 1  is separating from the density sensor  150  to increase the detecting frequency such that the magnetic permeability of air becomes gradually dominant. In the state S 3 , the relatively dense developer D 1  separates significantly from the density sensor  150  to increase further the detecting frequency. In the state S 4 , the relatively low-density developer D 2  starts flowing into an upper side of the density sensor  150  to shift the detecting frequency to decrease. 
     The present inventor found that the detecting frequency of the density sensor  150  thus changes at a constant stirring cycle. Furthermore, the present inventor also found that since in the state S 1 , the relatively dense developer D 1  is detected by the density sensor  150 , the state S 1  has an angle where the change of the magnetic permeability of the developer can be most remarkably detected. 
     Thus, the present inventor found that the detecting frequency of the density sensor  150  has following features. 
     Feature 1: The detecting frequency of the density sensor  150  decreases by reduction of the toner. 
     Feature 2: The detecting frequency of the density sensor  150  changes at the constant stirring cycle. 
     Considering Feature 1 and Feature 2, the reduction of the toner density can be detected by whether or not the detected lowest frequency within the stirring cycle becomes lower than a preliminarily set threshold value. The frequency can be detected, for example, by using a counter, as a count value of pulses at regular time intervals within the stirring cycle. 
       FIG. 6  illustrates a toner density detecting system  170  of the developing devices  100   m ,  100   c ,  100   y , and  100   k  according to the one embodiment. The toner density detecting system  170  includes a control unit  171 , a rotation angle sensor  172 , four density sensors  150   m ,  150   c ,  150   y , and  150   k , and a switching device  174 . The rotation angle sensor  172  is also referred to as a second sensor. The rotation angle sensor  172  can use, for example, a rotary encoder or a rotatable switch to measure a rotation angle, which is an angle of a conveying member  141   m  with respect to the detecting surface  150   a  of the developing device  100   m . The four density sensors  150   m ,  150   c ,  150   y , and  150   k  have identical configurations to detect toner densities of magenta, cyan, yellow, and black respectively as described above. 
     Four conveying members  141   m ,  141   c ,  141   y , and  141   k  stir the developers of magenta, cyan, yellow, and black respectively. The conveying members  141   m ,  141   c ,  141   y , and  141   k , while maintaining following relations, are synchronously driven. Specifically, this is achievable by driving the conveying members  141   m ,  141   c ,  141   y , and  141   k  by, for example, a gear drive (not illustrated) or a chain drive. 
     The four conveying members  141   m ,  141   c ,  141   y , and  141   k  have phase differences at regular intervals (or angle differences at preliminarily set unequal intervals), and in the embodiment, have mutually following phase relationships (phase differences). That is, the conveying member  141   c  puts the phase to 90 degrees in a clockwise direction with respect to the conveying member  141   m . The conveying member  141   y  puts the phase to 90 degrees in a clockwise direction with respect to the conveying member  141   c . The conveying member  141   k  puts the phase to 90 degrees in a clockwise direction with respect to the conveying member  141   y . The conveying member  141   m  puts the phase to 90 degrees in a clockwise direction with respect to the conveying member  141   k.    
     The switching device  174  is switched based on a switch timing signal Ts from the control unit  171 . The switch timing signal Ts is output from the control unit  171  to the switching device  174  when the control unit  171  determines that angles against the detecting surface  150   a  of the four conveying members  141   m ,  141   c ,  141   y , and  141   k  have become a preliminarily set angle (a setting angle). The determinations that these angles have become the setting angle are performed based on an output of the rotation angle sensor  172  input to the control unit  171 . 
     Specifically, when the control unit  171  determines that any of the angles of the four conveying members  141   m ,  141   c ,  141   y , and  141   k  is positioned at the proximity of the state S 1  in  FIG. 5 , the control unit  171  connects to an output signal of an object determined among the density sensors  150   m ,  150   c ,  150   y , and  150   k . The control unit  171  is constituted of a CPU (not illustrated). The density sensors  150   m ,  150   c ,  150   y , and  150   k  have output signals that are input to a digital port (not illustrated) of the CPU as pulses. The control unit  171  detects the toner density as the number of pulses per unit time. 
     Thus, the toner density detecting system of the embodiment can detect angles of the four conveying members  141   m ,  141   c ,  141   y , and  141   k  by the single rotation angle sensor  172  and also perform processing by one digital port of the CPU. Since the four conveying members  141   m ,  141   c ,  141   y , and  141   k  rotate at the phase differences preliminarily known, the detection of any one angle of them ensures detections of all angles. Thus, the toner density detecting system of the embodiment can detect remaining amounts of the developers of the four colors by the reduced hardware. 
     The disclosure can be performed not only in the above-described embodiment, but also in following modifications. 
     Modification 1 
     While in the above-described embodiment, the remaining amounts of the developers of the four colors are detected, the disclosure can be applied as long as N number of colors. N is an integer equal to or greater than two. 
     Modification 2 
     While in the above-described embodiment, the conveying member includes a scraper, the stirring/conveying member does not necessarily include the scraper and only have to include a stirring portion that changes a developer state at a constant cycle at the detecting region. However, including the scraper can reduce the misdetections (the errors) due to the accumulation of the developer (for example, attachment or deposition to a detecting surface) at the detecting region. 
     Modification 3 
     While in the above-described embodiment, a switching device switches an output to a control unit based on the angle measured by a rotation angle sensor, the switching device does not necessarily use the rotation angle sensor. The switching device may detect the lowest-frequency phase for one angle of a plurality of stirring portions and switch based on preliminarily set phase differences also for the other stirring portions. The switching device is also referred to as a switching unit. 
     Modification 4 
     While in the above-described embodiment, the plurality of stirring portions are configured to synchronously rotate at the preliminarily set phase differences, the plurality of detecting region stirring portions does not necessarily have phase differences and may have identical phase differences. However, while when having the identical phase differences, one-color detection is performed at one rotation, the above-described embodiment has an advantage that all-color detection can be realized at one rotation. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.