Abstract:
This invention relates to a toner replenishing method including the steps of conveying, from a toner storing section which forms a fluid mixture of toner and air, the fluid mixture to a toner separating section provided away from the toner storing section through toner supplying fluid conveying system, separating the toner from air in the toner separating section, and supplying the toner from the toner separating section to a developing unit, and a toner replenishing unit which practices the toner replenishing method. The toner replenishing method of the invention further includes the step of returning part of air separated from the toner from the toner separating section to the toner storing section by using a returning fluid conveying system. The toner replenishing unit of the present invention includes a returning fluid conveying system between the toner storing section and the toner separating section. A path through which the fluid mixture meanders in the toner separating section is formed in the toner separating section.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electro-photographic image forming apparatus and, more particularly, a toner replenishing method and unit. 
     2. Description of the Prior Art 
     In a high-speed image forming apparatus and color image forming apparatus, the toner storing section for storing toner has a large capacity, sometimes making it difficult to put it in the vicinity of a developing unit. 
     As a countermeasure against such a case, a toner replenishing technique is developed which conveys toner from a toner storing section to a developing unit in accordance with a toner conveying method called air conveyance that can convey the toner to a remote place (see Japanese Unexamined Patent Publication Nos. 7-219329, 10-97130, 10-268641, 10-299672, and the like). 
     The basic constituent elements of a toner replenishing unit utilizing air conveyance include a toner storing section, a fluid conveying means for conveying a fluid mixture of toner and air from the toner storing section, and a toner separating section for separating the toner from the conveyed fluid mixture. 
     In many toner replenishing units, part of the air separated from the toner is returned to the fluid conveying means without being discharged to the outside. In order to separate the toner, a filter that does not allow the toner to scatter to the outside is provided. 
     According to the toner replenishing technique disclosed in the above references and other Japanese Unexamined Patent Publications, the fluid mixture of the toner and air is conveyed from the toner storing section to the developing unit by a fluid conveying means such as a pump. In the prior art, a fluid conveying means comprised of a pump, which conveys the fluid mixture of air and toner from the toner storing section to the toner separating section is merely provided, and the toner conveying performance is not sufficiently high. When the toner storing section as the conveyance origin is located at a position far from the toner separating section as the conveyance destination, toner conveyance becomes difficult. Therefore, it is difficult to arrange the toner storing section at a position sufficiently away from the developing unit. In order to solve this problem, the pump must be large. When the pump is large, however, the exhaust air amount to the outside through the filter provided to the toner separating section increases. The amount of toner attaching to the filter increases, and the filter tends to undesirably clog at an early stage. 
     According to the conventional toner replenishing technique, as the interior of the toner separating section is in direct contact with the outside through the filter, the amount of toner filtered by the filter is large. This can cause the filter to clog at an early stage. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in order to solve the problems of the toner replenishing technique utilizing conventional air conveyance, and has as its object to provide a toner replenishing method and unit with which a filter provided to a toner separating section causes less clogging and accordingly the performance of the filter can be maintained well over a long period of time, so that the storing section can be arranged away from the developing unit, and an image forming apparatus having such a toner replenishing unit. 
     In order to achieve the above object, according to the first aspect of the present invention, there is provided a toner replenishing method comprising the steps of conveying, from a toner storing section which forms a fluid mixture of toner and air, the fluid mixture to a toner separating section provided away from the toner storing section through toner supplying fluid conveying means, separating the toner from air in the toner separating section, and supplying the toner from the toner separating section to a developing unit, wherein the toner replenishing method further comprises the step of returning part of the air separated from the toner from the toner separating section to the toner storing section by using returning fluid conveying means. 
     According to the second aspect of the present invention, when the toner is to be separated from the air in the toner separating section, the fluid mixture of the toner and air is caused to meander in the toner separating section. 
     According to the third aspect of the present invention, there is provided a toner replenishing unit comprising a toner storing section which forms a fluid mixture of toner and air, toner supplying fluid conveying means for conveying the fluid mixture from the toner storing section, and a toner separating section which is provided away from the toner storing section and separates the fluid mixture into the toner and air, wherein the toner replenishing unit further comprises returning fluid conveying means for returning part of the air separated from the toner from the toner separating section to the toner storing section. 
     According to the fourth aspect of the present invention, each of the toner supplying fluid conveying means and the returning fluid conveying means according to the third aspect comprises a transport pipe and a pump provided midway along the transport pipe. 
     According to the fifth aspect of the present invention, the toner storing section according to the third aspect comprises a toner hopper which is connected to a toner container for storing the toner, and a mixing chamber which is connected to the toner hopper so as to mix the toner and air. 
     According to the sixth aspect of the present invention, the toner storing section according to the fourth aspect comprises a toner hopper which is connected to a toner container for storing the toner, and a mixing chamber which is connected to the toner hopper so as to mix the toner and air. 
     According to the seventh aspect of the present invention, there is provided a toner replenishing unit comprising a toner storing section which forms a fluid mixture of toner and air, toner supplying fluid conveying means for conveying the fluid mixture from the toner storing section, and a toner separating section which is provided away from the toner storing section and separates the fluid mixture into the toner and air, the toner separating section comprising an introducing chamber where the fluid mixture is introduced and separated into the toner and air, an exhaust chamber which communicates with the introducing chamber so as to discharge air separated from the toner, and a filter which is provided to a filter chamber communicating with the exhaust chamber, wherein the introducing chamber and the exhaust chamber communicate with each other through a meandering path. 
     According to the eighth aspect of the present invention, the toner replenishing unit according to the seventh aspect further comprises returning fluid conveying means which returns part of the air separated from the toner from the toner separating section to the toner storing section. 
     According to the ninth aspect of the present invention, there is provided an image forming apparatus comprising a developing unit which performs developing by using the toner replenishing unit according to any one of the third to eighth aspects and the toner replenished by the toner replenishing unit. 
     According to the tenth aspect of the present invention, there is provided an image forming apparatus comprising an image forming section which has a developing unit, a sheet feeding section which is provided below the image forming section, a toner storing section which is arranged below the image forming section and on a side of the sheet feeding section and forms a fluid mixture of toner and air, a toner separating section which is arranged away from the toner storing section and in the vicinity of the developing unit, a first transport pipe which transports the fluid mixture from the toner storing section to the toner separating section, a second transport pipe which returns part of the air separated from the toner in the toner separating section to the toner storing section, a fluid mixture conveying pump which is provided midway along the first transport pipe, and a returning air conveying pump which is provided midway along the second transport pipe. 
     As is apparent from the above aspects, according to the present invention, the following effects which are expected to contribute to this technical field remarkably can be obtained. 
     The fluid is circulated between the toner storing section and the toner separating section which separates the toner from the fluid mixture conveyed from the toner storing section, by the toner supplying fluid conveying means and the returning fluid conveying means. This increases the conveying performance of the toner. 
     Even when the toner storing section as the toner conveyance origin is arranged away from the toner separating section as the conveyance destination, the toner can be conveyed smoothly. 
     In the toner separating section, the amount of air flowing to the outside decreases, so that filter clogging is suppressed effectively. As a result, the service life or cleaning period of the filter can be prolonged. In addition, since air is circulated within the toner replenishing unit, it becomes possible to be unnecessary to discharge air outside, in other words, it becomes possible to disuse any filter. 
     The amount of toner in the fluid mixture in a flow path extending from the toner separating section to the outside is decreased, and after that air used for conveyance of the toner is discharged to the outside through the filter. Therefore, the amount of toner deposited on the filter can be decreased. As a result, the service life or cleaning period of the filter can be prolonged. 
     As the toner storing section can be arranged away from the developing unit, it can store a large amount of toner. A large-capacity toner storing section, which is necessary for a high-speed image forming apparatus or color image forming apparatus, can thus be provided. 
     The above and many other objects, features and advantages of the present invention will become apparent to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which a preferred embodiment incorporating the principle of the present invention is shown by way of an illustrative example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view showing the schematic overall arrangement of an image forming apparatus having a toner replenishing unit of the present invention; 
     FIG. 2 is a schematic view showing a fluid circulating path in the toner replenishing unit of the present invention; 
     FIG. 3 is a partial sectional side view of a toner storing section in the toner replenishing unit of the present invention; 
     FIG. 4 is a longitudinal sectional view of a pump in the toner replenishing unit of the present invention; and 
     FIG. 5 is a longitudinal sectional view of a toner separating section in the toner replenishing unit of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described with reference to the accompanying drawings. 
     (1) Image Forming Apparatus 
     Referring to FIG. 1, in an automatic document feeder  20 , the documents placed on a document table are conveyed one by one to a reading position, and the documents after reading are stacked on a document delivery tray. 
     A document reading section  21  reads the image of the document and forms digital image data. 
     An image forming section  22  forms an image on a recording sheet by electrophotographing. 
     In the image forming section  22 , a charging unit  2 , exposure unit  3 , developing unit  4 , transfer unit  5 , separation unit  6 , and cleaning unit  7  are arranged around a drum-like photosensitive body  1 . A sheet feeding section  23  having a plurality of recording sheet storing portions is formed below the image forming section  22 , and feeds a recording sheet to the image forming section  22 . Reference numeral  10  denotes a manual sheet feeding section. A recording sheet fed from the sheet feeding section  23  or manual sheet feeding section  10  is supplied to a portion between the photosensitive body  1  and transfer unit  5  by registration rollers  11 , undergoes image fixing by a fixing unit  8 , and is delivered to a delivery tray  12 . 
     As the photosensitive body  1  rotates clockwise, a toner image is formed on the photosensitive body  1  by charging of the charging unit  2 , image exposure of the exposure unit  3 , and development of the developing unit  4 . The formed toner image is transferred to the recording sheet by the transfer unit  5 . The toner-image-bearing recording sheet is subjected to a fixing process by the fixing unit  8 , and is delivered to the delivery tray  12 . 
     The developing unit  4  develops an electrostatic latent image on the photosensitive body  1  with a two-component developing agent containing toner and carrier, or a one-component developing agent not containing a carrier but containing toner, or toner and an additive. The developing unit  4  stores a predetermined amount of developing agent. When a two-component developing agent is to be used, the toner consumed by development is replenished by a toner storing section  24  (to be described next), so that the toner concentration of the developing agent in the developing unit  4  always maintains a predetermined value. In a developing unit  4  using a one-component developing agent, the amount of developing agent in it always maintains a predetermined amount by similar toner replenishing. 
     A toner container  31  is mounted in the toner storing section  24 . The toner storing section  24  has a toner hopper  30  and a funnel-like mixing chamber  35 . A toner separating section  60  arranged in the vicinity of the developing unit  4  and the toner storing section  24  formed at a position away from the developing unit  4  are connected to each other through transport pipes  40  to  43 . 
     (2) Toner Replenishing Unit 
     The toner storing section  24  will be described first with reference to FIGS. 2 and 3. 
     The toner replenishing unit is comprised of the toner storing section  24  (constituted by the toner hopper  30  and mixing chamber  35 ), pumps  501  and  502  serving as a fluid conveying means, the toner separating section  60 , and the transport pipes  40  to  43 . 
     The toner storing section  24  has the toner hopper  30  and the funnel-like mixing chamber  35 . The cylindrical toner container  31  is mounted in the toner storing section  24 . When the toner container  31  is driven to rotate by a motor  38 , the toner drops from the toner container  31  into the toner hopper  30  through an opening  30   a . The toner hopper  30  has a rod-like stirring member  32  with a plurality of U-shaped portions, and a screw  34  at its lower portion. 
     When the motor  39  rotates, the stirring member  32  and screw  34  rotate, and the toner drops from the toner hopper  30  into the mixing chamber  35  through an opening  30   b.    
     Air is sent into the mixing chamber  35  through the transport pipe  43  as will be described later. Hence, a fluid mixture of the toner and air is formed. 
     As the fluid conveying means, the pumps  501  and  502  formed of diaphragm pumps shown in FIG. 4 are used. Alternatively, any known arbitrary pump such as the screw pump and fan disclosed in Japanese Unexamined Patent Publication Nos. 7-219329 and 8-6368 can be used. The pump  501  forms a toner supplying fluid conveying means which conveys the fluid mixture of the toner and air from the toner storing section  24  to the toner separating section  60 . The pump  502  forms a returning fluid conveying means which returns air from the toner separating section  60  to the toner storing section  24 . In FIG. 4, the pumps  501  and  502  having the same structure are used. Alternatively, different pumps may be used as the toner supplying fluid conveying means and the returning fluid conveying means. 
     The pumps  501  and  502  will be described with reference to FIG.  4 . The pumps  501  and  502  have the same structure shown in FIG.  4 . 
     The intake port of the pump  501  is connected to the transport pipe  40 , and its exhaust port is connected to the transport pipe  41 . The intake port of the pump  502  is connected to the transport pipe  42 , and its exhaust port is connected to the transport pipe  43 . A pump chamber formed by an outer wall  50  is partitioned by an inner wall  51  into an intake chamber  50   a  and an exhaust chamber  50   b . A valve  53  is provided to the intake port of the intake chamber  50   a , and a valve  54  is provided to the vent hole (vent hole formed in the inner wall  51 ) of the exhaust chamber  50   b.    
     The outer shape of each of the pumps  501  and  502  is partly formed of a diaphragm  52  formed by an elastic body made of rubber. The diaphragm  52  is driven by an eccentric rotary member  56  driven by a motor  55 , and deforms into a state indicated by a solid line and a state indicated by a broken line. 
     The motor  55  rotates the eccentric rotary member  56 . Due to the rotation of the eccentric rotary member  56 , the diaphragm  52  deforms between the state indicated by the solid line and the state indicated by the broken line. Thus, the capacity of the intake chamber  50   a  changes, and the pressure in the intake chamber  50   a  accordingly increases or decreases. Due to this increase or decrease of the pressure, the valves  53  and  54  deform into the state indicated by a solid line and a state indicated by a broken line, to convey the fluid in one direction indicated by arrows. 
     The toner separating section  60  will be described with reference to FIG.  5 . 
     The toner separating section  60  is comprised of an outer wall  61  which limits the outer shape of the toner separating section  60 , and inner walls  64  and  65  and a vertical section  65 A of an inner wall  65  which separate the interior of the toner separating section  60  into an introducing chamber  60 A and an exhaust chamber  60 B. The exhaust chamber is formed of an exhaust portion  60 B and a filter chamber  60 C. 
     The introducing chamber  60 A has an air inlet port  62 , and the exhaust chamber  60 B has an air discharge port  63 . The auxiliary inner wall  66  guides dropping toner, and suppresses any upward movement of the toner. Stirring members  67  having blades and a screw  68  for conveying the toner in the axial direction are formed in the lower portion of the toner separating section  60 . The air mixture of the toner and air is introduced from the air inlet port  62  into the introducing chamber  60 A as indicated by an arrow W 1 , and drops as indicated by arrows W 2 . The fluid mixture fills the introducing chamber  60 A. The fluid mixture receives the negative pressure of the fluid conveying force generated by the pump  502 , and partly moves upward as indicated by arrows W 3  and is conveyed to the exhaust chamber  60 B. The toner concentration in the fluid mixture which moves upward decreases due to the specific gravity of the toner and the operation of the auxiliary inner wall  66 , and the fluid mixture becomes a fluid mostly comprised of air. The fluid mixture in the exhaust chamber  60 B is discharged from the air discharge port  63  as indicated by an arrow W 4 . Part of the fluid mixture in the exhaust chamber  6 GB enters the filter chamber  60 C as indicated by an arrow W 5 , and is filtered by a filter  69  and is discharged as indicated by arrow W 6 . 
     As shown in FIG. 5, a vertical portion  65 A of the inner wall  65  and a vertical portion  64 A of the inner wall  64  form a communicating path through which the fluid mixture meanders. Because of this meandering communication path, the toner content in the air to be discharged and that in the discharge fluid to be processed by the filter  69  are low. The vertical portions  65 A and  64 A are cylindrical, and the cylinder of the vertical portion  64 A is arranged inside the cylinder of the vertical portion  65 A. 
     As shown in FIG. 2, the toner hopper  30 , pumps  501  and  502 , and toner separating section  60  are connected to each other through the transport pipes  40 ,  41 ,  42 , and  43 . 
     Due to the operation of the pump  501 , the fluid mixture is conveyed from the toner hopper  30  to the pump  501  as indicated by an arrow X 1  and from the pump  501  to the toner separating section  60  as indicated by an arrow X 2 , so that the toner is supplied. Due to the operation of the pump  502 , air returns from the toner separating section  60  to the pump  502  as indicated by an arrow X 3 , and from the pump  502  to the toner hopper  30  as indicated by an arrow X 4 . The toner is then separated by the toner separating section  60 , and the separated toner is supplied to the developing unit  4  by the screw  68 . 
     The toner replenishing unit shown in FIGS. 2 to  5  operates in the following manner. 
     The toner amount in the toner hopper  30  is detected by a toner sensor  33  using a piezoelectric element. If the toner level becomes lower than that detected by the toner sensor  33  (see FIG.  2 ), the motor  38  is actuated to replenish more toner from the toner container  31  to the toner hopper  30 . 
     A replenish signal from a control means (not shown), which replenishes toner to the developing unit  4 , actuates the motor  39  shown in FIG.  3 . Thus, the stirring member  32  is driven to stir the toner in the toner hopper  30 , and the screw  34  is driven so that the toner drops into the mixing chamber  35 . The replenish signal actuates the motor  55 , and the pumps  501  and  502  are actuated accordingly. When the pumps  501  and  502  are actuated, an air current occurs in the mixing chamber  35 , and the toner and air are mixed. The fluid mixture is conveyed to the toner separating section  60  through the transport pipes  40  and  41  by the conveying force of the pump  501 . 
     As shown in FIG. 5, the toner separated by the toner separating section  60  is supplied to the developing unit  4  by the screw  68 . The separated air returns to the mixing chamber  35  through the transport pipes  42  and  43  by the conveying force of pump  502 .