Patent Abstract:
An image forming apparatus includes an image bearer bearing a static image and an exchangeable type developing apparatus for developing the static image on the image bearer. The developing apparatus includes a developing chamber having a developing roller in an opening opposite to the image bearer, and a containing chamber containing a developer to be supplied to the developing chamber. A detection electrode is disposed outside the developing device and in which a voltage is induced. A detection device detects an amount of the developer in the containing chamber on the basis of an induced voltage in the detection electrode.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image forming apparatus such as a copier, printer, and the like using an electrophotographic system or a static recording system. 
     2. Related Background Art 
     In the image forming apparatus using an electrophotographic system, for example, a static latent image is formed on a surface of a photosensitive drum or a photosensitive belt, which is an image bearer, and the static image on the image bearer is developed by a developer, such as toner, to visualize an image as a toner image. The developed image is transferred to a transferring material by a transferring apparatus, to cause the toner image to be borne by the transferring material, and the toner image is fixed to the transferring material by heating and pressing by a fixing apparatus. By sequentially carrying out these steps, the image is formed. 
     Meanwhile, toner is consumed as the image forming apparatus is used and hence, a user should supply toner. Known methods for supplying toner include charging only toner in the image forming apparatus, replacing the developing apparatus including a toner container, or replacing a unit including the photosensitive drum. 
     There are methods for detecting of the amount of unused toner to inform the user of the time to replace toner. Conventional methods for residual toner detection are as follows. 
     In developing the static latent image formed on the image bearer by powder toner, toner is adsorbed and transferred by a static force. Toner is previously magnetized and then an electrostatic force is applied to the developing roller in the developing apparatus caused by a voltage difference to cause the toner to be adsorbed to the surface of the developing roller. The developing roller is disposed opposite to the image bearer and an electrostatic force stronger than that of the developing roller is applied to the image bearer. Then, toner is transferred and adsorbed from the developing roller to the image bearer and the latent image on the image bearer is visualized by toner. 
     Thus, the method for detecting a residual toner amount employs the voltage to be applied to the developing roller. Voltage is applied to the developing roller in order to adsorb and transfer toner as described above and the voltage and the electrostatic force are effective to all radial directions of the developing roller. For example, when an antenna, which is made of a conductive material is disposed in a position distant from the developing roller, an electric charge is generated in the antenna side by an electric potential difference. Hence, if toner which is a dielectric material exists between the developing roller and the antenna, the electric charge changes compared with absence of toner. As the amount of toner differs, the magnitude of the electric charge also differs and thus, the residual amount of toner can be detected by measuring the electric potential according to the electric charge to know relative comparison with the amount of toner. 
     However, there are problems in the conventional residual toner detection method as follows. 
     As shown in FIG. 4, the antenna  30  for measurement of the electric charge is disposed in the toner container  31  and thus, disturbs replacement of the toner container  31  (or, the developing apparatus or a process cartridge) for toner supply. In FIG. 4, a reference numeral  6  denotes a drum unit having a photosensitive drum  1 . 
     In addition, as shown in FIG. 5, a contact  34  of antenna side in the toner container  31  should be attached to and detached from a contact  35  of main body side of the image forming apparatus. However, the conventional residual toner detection method is the detection method by measuring a micro voltage and therefore, a low reliability of the contact point does not allow for detection of a correct residual toner amount. Particularly, in a color image forming apparatus, as shown in FIG. 6, having a plurality of developing apparatus  4 BK,  4 Y,  4 M, and  4 C, antennas  30 BK,  30 Y,  30 M, and  30 C are disposed in developing apparatus  4 BK,  4 Y,  4 M, and  4 C, respectively, and hence, the increased number of the contact points results in lower reliability of the image forming apparatus and also a plurality of  30 BK,  30 Y,  30 M, and  30 C are necessary and hence, the cost increases. For information, in FIG. 6, the reference numeral  6  denotes a photosensitive drum unit having a photosensitive drum  1 . 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an image forming apparatus of high reliability of the contact point for detecting an amount of the developer. 
     Another object of the present invention is to provide an image forming apparatus comprising: an image bearer for bearing a static image; an exchangeable type developing for developer the static image on the image bearer, the developing apparatus comprising, a developing chamber having a developing roller in an opening opposite to the image bearer, and a containing chamber for containing a developer to be supplied to the developing chamber; a detection electrode disposed outside the developing apparatus and in which a voltage is induced; and detection means for detecting an amount of the developer in the containing chamber on the basis of an induced voltage of the detection electrode. 
     Further objects of the present invention will be apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of an image forming apparatus (a laser beam printer) according to the present invention; 
     FIG. 2 is a side view of a developing apparatus and a photosensitive drum unit of a monochromatic color image forming apparatus according to embodiment 1 of the present invention; 
     FIG. 3 is a side view of the developing unit and the photosensitive drum unit of a color image forming apparatus according to embodiment 2 of the present invention; 
     FIG. 4 is a side view of the developing apparatus and the photosensitive drum unit of the monochromatic color image forming apparatus; 
     FIG. 5 is a front view of the developing apparatus of the monochromatic color image forming apparatus; and 
     FIG. 6 is a side view of the developing unit and the photosensitive drum unit of the color image forming apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described below with reference to the drawings attached herewith. 
     FIG. 1 is the sectional view of the laser beam printer as an embodiment of the image forming apparatus, according to the present invention using electrophotography and the laser beam printer can form a tetrachromatic full-color image. 
     The image forming apparatus A, which forms image by fixing an image visualized by the developing to the transfer material by heating, comprises a photosensitive drum  1  which is an electrophotographic photosensitive member of a drum type as a first image bearer. The photosensitive drum  1  is incorporated into the photosensitive drum unit  6  and rotatively driven by driving means, not illustrated, in a direction (counterclockwise) of an arrow illustrated. 
     Around the above-described photosensitive drum  1 , sequentially in a rotational direction of the photosensitive drum  1 , a charging apparatus  2  for charging evenly a surface of the photosensitive drum  1 , an exposing apparatus for forming a static latent image on the photosensitive drum  1  by radiating a laser beam based on an image information, the developing unit  4  for developing the latent image as a toner image by attaching toner to the latent image on the photosensitive drum  1 , an intermediate transfer unit  5  as a second image bearer on which the toner image on the photosensitive drum  1  is primarily transferred, and the like are disposed. 
     The developing unit  4  for developing the static latent on the photosensitive drum  1  has four developing apparatus, i.e.,  4 BK,  4 Y,  4 M, and  4 C, containing four color toners and these developing apparatus,  4 BK,  4 Y,  4 M, and  4 C, are disposed concentrically around a rotating shaft  4   a . In respective developing apparatus,  4 BK,  4 Y,  4 M, and  4 C, the developing rollers  4   b  are respectively disposed to bear toner, which is the developer, on the surface thereof and to be positioned opposite to the photosensitive drum  1  when the developing apparatus,  4 BK,  4 Y,  4 M, and  4 C, are faced to the photosensitive drum  1 . The static latent image on the photosensitive drum  1  is developed by the developing roller  4   b  to be visualized as the toner image. 
     The above-described intermediate transfer unit  5  as a second image bearer primarily transfers the toner image on the photosensitive drum  1  and then, secondarily transfers the toner image to the surface of the transferring material S fed to the intermediate transfer unit  5 . The transferring material S is carried from a cassette  14  to the intermediate transfer unit  5  by carrying means in predetermined timing. 
     In the image forming apparatus A, the fixing apparatus  8  is disposed to fix the toner image to the transferring material S by heating toner on the transferring material S after secondary transfer. The transferring material S passed through the fixing apparatus  8  is discharged to a sheet discharging tray  10  by a carrying unit  9 . The fixing apparatus  8  has a fixing roller  8   a  and a pressing roller  8   b , which are a pair of rolling bodies, and by passing the transferring material S bearing the toner image between the fixing roller  8   a  and the pressing roller  8   b  with the surface of the fixing roller  8   a  heated to a predetermined temperature by a heater (not illustrated) in the fixing roller  8   a , heats and presses the transferring material S to fix the toner image to the transferring material S. The heater may be disposed inside the pressing roller  8   b.    
     In this embodiment, the static latent image is developed by electrostatic adsorption of toner to the photosensitive drum  1 . In case of a monochromatic color image forming apparatus, there is single developing apparatus, the intermediate transfer unit is not necessary, and the toner image is directly transferred from photosensitive drum bearing a developed image to the transferring material. 
     &lt;Embodiment 1&gt; 
     Embodiment 1 according to the present invention will be described with reference to FIG.  2 . FIG. 2 is a side view of a developing apparatus and a photosensitive drum unit of a monochromatic color image forming apparatus. 
     The photosensitive drum unit  6  shown in FIG. 2 has the photosensitive drum  1  as an image bearer and in developing the static latent image formed on the photosensitive drum  1 , unused toner  22  contained in the toner container  21  of the developing unit  4  is rotatively carried to the developing roller  4   b  by the carrying roller  4   d  to make toner  22  to be electrostatically adsorbed to the surface of the developing roller  4   b  by applying voltage to the developing roller  4   b . And, to the photosensitive drum  1  opposed to the developing roller  4   b , the voltage is applied to generate an adsorbing force larger than the electrostatic adsorbing force of the developing roller  4   b . As a result, by a bias formed by the photosensitive drum  1  and the developing roller  4   b , toner on the developing roller  4   b  is transferred to the photosensitive drum  1 . 
     Now, the detection method for the residual toner amount will be described below. 
     By the voltage applied to the developing roller  4   b , the antenna  20  disposed previously in the main body of the image forming apparatus is electrically charged to cause an electric current to flow to the main body. Between the developing roller  4   b  and the antenna  20 , unused toner  22  is interposed and unused toner  22  becomes a dielectric material and hence, according to the change of residual amount of the unused toner  22 , electric charge on the antenna  20  changes to change the electric current and voltage. Consequently; on the basis of the change of the electric current and voltage, the residual amount of the unused toner  22  can be detected. The antenna  20  comprises a linear or plate-like metal. 
     Therefore, according to the present invention, by disposing the antenna  20  in the main body side of the image forming apparatus, the contact point becomes unnecessary, which allows the developing apparatus to be attached and detached for toner replacement between the antenna  20  and the image forming apparatus and hence, reliability and detection precision of the contact point of a detection current are increased in detecting the residual toner amount. 
     &lt;Embodiment 2&gt; 
     Next, The embodiment 2 according to the present invention will be described with reference to FIG.  3 . FIG. 3 is a side view of the developing unit and the photosensitive drum unit of the color image forming apparatus. 
     In FIG. 3, reference numerals  4  and  6  denote the developing unit having a plurality of developing apparatus  4 BK,  4 Y,  4 M, and  4 C and the photosensitive drum unit having the photosensitive drum  1 , respectively. Development of the static latent image on the photosensitive drum  1  in the color image forming apparatus having the developing unit  4  and photosensitive drum unit  6  is similar to the monochromatic color image forming apparatus according to the above-described embodiment 1. 
     For example, in the case where development is carried out by using the developing apparatus  4 Y of a yellow color, unused toner  22 Y contained in the toner container  21 Y is rotatively carried to the developing roller  4   b Y by the carrying roller  4   d Y. And then, the voltage is applied to the developing roller  4   b Y to cause toner  22 Y to be statically adsorbed to the surface of the developing roller  4   b Y. To the photosensitive drum  1  opposite to the developing roller  4   b Y, the voltage is applied to generate the adsorbing force larger than static adsorption force of the developing roller  4   b Y in order to transfer toner  22 Y on the developing roller  4   b Y to the photosensitive drum  1  by the bias formed by the photosensitive drum  1  and the developing roller  4   b Y. In the developing apparatus  4 M,  4 C, and  4 BK of magenta, cyan and black colors, respectively, the same development as above-described is carried out and in the toner containers  21 M,  21 C, and  21 BK,  22 M,  22 C, and  22 BK are disposed, respectively. 
     Subsequently, the method for detection of residual toner amount will be described below. 
     By the voltages applied to respective developing rollers  4   b Y,  4   b M,  4   b C, and  4   b BK, the antenna  24 , disposed in the main body of the image forming apparatus, is electrically charged to make the electric current flow to the main body. Between the respective developing rollers  4   b Y,  4   b M,  4   b C, and  4   b BK and the antenna  24 , unused toners  22 Y,  22 M,  22 C, and  22 BK are interposed and these kinds of unused toners  22 Y,  22 M,  22 C, and  22 BK become dielectric and hence, according to the change of the residual amount of toner, the electric charge on the antenna  24  changes to change the electric current and voltage. Consequently, on the basis of the change of the electric current and voltage, the residual toner amount of the unused toners  22 Y,  22 M,  22 C, and  22 BK can be detected. 
     Therefore, in the case of this color image forming apparatus where selection and switching of a plurality of the developing apparatus,  4 Y,  4 M,  4 C, and  4 BK is performed by a rotational mechanism, by disposing the antenna  24  in a center  4 f of the rotating shaft  4   a , the contact point becomes unnecessary which allows the developing apparatus  4 Y,  4 M,  4 C, and  4 BK to be attached and detached for toner replacement, between the antenna  24  and the image forming apparatus and hence, as with the above described embodiment 1 reliability and detection precision of the contact point of detection current are increased in detecting the residual toner amount. 
     In addition, installing the single antenna  24  in the center  4   f  of the rotating shaft  4   a  simply allows for detection of residual toner in the plurality of developing apparatuses and hence reduction of a number of the antenna. 
     The embodiments above described should be considered in all respects as illustrative and not restrictive; any modification can be made within the technical concept.

Technology Classification (CPC): 6