Abstract:
There is provided a toner supply method in a picture image forming system having a plurality of picture image forming parts, each of which is designed to supply a toner from a toner cartridge to a developing part, the toner supply method having the steps of: detecting a cartridge empty when the level of the toner in the toner cartridge of any one of the picture image forming parts becomes an empty level; introducing a toner, which remains in the toner cartridge of each of the plurality of picture image forming parts, from the toner cartridge of a corresponding one of the plurality of picture image forming parts into a reserve tank portion, which is provided so as to correspond to each of the toner cartridges for housing therein a predetermined quantity of toner, when the cartridge empty is detected in any one of the picture image forming parts; detecting a toner empty when the level of the toner in the developing part becomes an empty level in any one of the picture image forming parts; and inspiring to replace all of the toner cartridges, for which a cartridge empty has been detected, with new cartridges when the toner empty is detected in any one of the picture image forming parts.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a toner supply method in a picture image forming system, and a picture image forming system. More specifically, the invention relates to a toner supply method in a picture image forming system, which enables replacement of not only a toner cartridge running short of toner in a picture image forming system for making copies with toners of a plurality of colors, but also, simultaneously, a toner cartridge for a toner which is running short, and to the picture image forming system itself. 
     2. Related Background Art 
     In a picture image forming system for making copies with toners of a plurality of colors, the quantities of toners consumed by making several copies vary depending on the colors of the toners. For example, a picture image forming system for making copies with toners of four colors including Y (yellow), M (magenta), C (cyanogen) and K (black) is considered. After such a picture image forming system makes several copies, a toner cartridge for, e.g., a toner Y, becomes empty (a toner cartridge empty). Then, when the toner specific concentration thereof lowers to a level which is not suitable for copying (a toner empty), the toner cartridge for the toner Y is replaced. Similarly, when the state of a toner M is changed from “toner cartridge empty” to “toner empty”, the toner cartridge for the toner M must be replaced. 
     There are some cases where the toner cartridge for the toner M must be replaced immediately after the toner cartridge for the toner Y is replaced. In such cases, the replacing operation is very complicated. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to do away with the complicated replacing operation for a toner cartridge for each color, which is caused by replacing a toner cartridge separately from and independently of other toner cartridges for the respective colors. 
     It is another object of the present invention to prevent the complicated replacing operation by simultaneously replacing toner cartridges for a plurality of colors. 
     It is a further object of the present invention to prevent a toner cartridge from being disposed with the a toner remaining in the toner cartridge. 
     It is a still further object of the present invention to easily recognize time to replace toner cartridges for toners of a plurality of colors, by displaying the time to replace the toner cartridges. 
     In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, there is provided a toner supply method in a picture image forming system having a plurality of picture image forming parts, each of which is designed to supply a toner from a toner cartridge to a developing part, the toner supply method comprising the steps of: detecting a cartridge empty when the level of the toner in the toner cartridge of any one of the picture image forming parts reaches an empty level; introducing a toner, which remains in the toner cartridge of each of the plurality of picture image forming parts, from the toner cartridge of a corresponding one of the plurality of picture image forming parts into a reserve tank portion, which is provided so as to correspond to each of the toner cartridges for housing therein a predetermined quantity of toner, when the cartridge empty is detected in any one of the picture image forming parts; detecting a toner empty when the level of the toner in the developing part reaches an empty level in any one of the picture image forming parts; and exchanging all of the toner cartridges, for which a cartridge empty has been detected, for new cartridges when the toner empty is detected in any one of the picture image forming parts. 
     According to another aspect of the present invention, there is provided a toner supply method in a picture image forming system including first and second picture image forming parts, the toner supply method comprising the steps of: detecting a cartridge empty of the first picture image forming part when the level of a toner in the toner cartridge of the first picture image forming part reaches an empty level; introducing a toner, which remains in each of the toner cartridges of the first and second picture image forming parts, from each of the toner cartridges of the first and second picture image forming parts into a reserve tank, which is provided so as to correspond to each of the toner cartridges for housing therein a predetermined quantity of toner, when the cartridge empty is detected in the first picture image forming parts; detecting a cartridge empty of the second picture image forming part when the level of a toner in the toner cartridge of the second picture image forming part reaches an empty level; introducing a toner, which remains in each of the toner cartridges of the first and second picture image forming parts, from each of the toner cartridges of the first and second picture image forming parts into a reserve tank, which is provided so as to correspond to each of the toner cartridges for housing therein a predetermined quantity of toner, when the cartridge empty is detected in the second picture image forming parts; detecting a toner empty of a corresponding one of the first and second image forming parts when the level of the toner in the developing part of any one of the first and second picture image forming parts reaches the empty level; and inspiring to replace the toner cartridges of the first and second picture image forming parts with new cartridges when the toner empty is detected in any one of the first and second picture image forming parts. 
     According to another aspect of the present invention, there is provided a picture image forming system comprising: a plurality of developing means, each of which houses toner therein, for forming a developer image with the toner; a plurality of toner cartridges, each of which is provided so as to correspond to a corresponding one of the plurality of developing means, for supplying the toner to the corresponding one of the plurality of developing means; a plurality of reserve tank portions, each of which is provided between the corresponding one of the plurality of developing means and a corresponding one of the plurality of toner cartridges, for housing therein a predetermined quantity of toner to supply the toner to the corresponding one of the plurality of developing means; a plurality of cartridge empty detecting means, each of which is provided in the corresponding one of the plurality of toner cartridges, for detecting that the level of the toner in the corresponding one of the plurality of toner cartridges reaches an empty level; a plurality of toner empty detecting means, each of which is provided in the corresponding one of the plurality of developing means for detecting that the level of the toner in the corresponding one of the plurality of developing means reaches an empty level; introducing means for introducing a toner, which remains in a corresponding one of the plurality of toner cartridges, from the corresponding one of the plurality of toner cartridges to a corresponding one of the reserve tank portions when a cartridge empty of any one of the plurality of toner cartridges is detected by a corresponding one of the plurality of cartridge empty detecting means; and display means for displaying to inspire to exchange one or more toner cartridges of the plurality of toner cartridges, the level of which has reached the cartridge empty, when a toner empty of any one of the plurality of developing means is detected by a corresponding one of the plurality of toner empty detecting means after the toner is introduced by the introducing means. 
     According to another aspect of the present invention, there is provided a toner supply method in a picture image forming system having a plurality of picture image forming parts, each of which is designed to supply a toner from a toner cartridge to a developing part, the toner supply method comprising the steps of: detecting a toner empty when the level of the toner in the developing part in any one of the picture image forming parts reaches an empty level; supplying a toner to a developing part from a reserve tank portion, which is provided in each of the picture image forming parts and which stores therein a predetermined quantity of toner, via a reserving supply passage in a corresponding one of the picture image forming parts, when the toner empty is detected in the corresponding one of the picture image forming parts; and inspiring to replace with new ones toner cartridges of all of picture image forming parts, in which the toner empty has been detected, when a toner empty is detected again in any one of the picture image forming parts after the toner is supplied from the reserve tank to the developing part. 
     According to a further aspect of the present invention, there is provided a toner supply method in a picture image forming system having first and second picture image forming parts, the toner supply method comprising the steps of: detecting a toner empty in the first picture image forming part; discontinuing forming a picture image when the toner empty is detected in the first picture image forming part, and resuming forming a picture image after a toner is supplied to a corresponding developing part from a reserve tank portion which is provided in the first picture image forming part; detecting a toner empty in the second picture image forming part; discontinuing forming a picture image when the toner empty is detected in the second picture image forming part, and resuming to form a picture image after a toner is supplied to a corresponding developing part from a reserve tank portion which is provided with the second picture image forming part; and inspiring to replace toner cartridges of the first and second picture image forming parts with new ones when a toner empty is detected again in the first or second picture image forming part. 
     According to a still further aspect of the present invention, there is provided a picture image forming system comprising: a plurality of developing means, each of which houses therein a toner, for forming a developer image with the toner; a plurality of toner cartridges, each of which is provided so as to correspond to a corresponding one of the plurality of developing means, for supplying the toner to the corresponding one of the plurality of developing means; a plurality of reserve tank portions, each of which is provided so as to correspond to the corresponding one of the plurality of developing means, for housing therein a predetermined quantity of toner to supply the toner to the corresponding one of the plurality of developing means; a plurality of toner empty detecting means, each of which is provided in the corresponding one of the plurality of developing means, for detecting that the level of the toner in the corresponding one of the plurality of developing means reaches an empty level; supply means for supplying a toner from a corresponding one of the reserve tank portions to the corresponding one of the plurality of developing means when a toner empty of any one of the plurality of developing means is detected by a corresponding one of the plurality of toner empty detecting means; and display means for displaying a message to inspire to replace with new ones all of corresponding cartridges of the plurality of toner cartridges, which correspond to one or more of the plurality of developing means in which a toner empty has been detected, when a toner empty of any one of the plurality of developing means is detected by a corresponding one of the plurality of toner empty detecting means after the toner is supplied by the supply means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention. However, the drawings are not intended to imply limitation of the invention to a specific embodiment, but are for the purpose of explanation and understanding only. 
     In the drawings: 
     FIG. 1 is a side view of a principal part of a picture image forming system to which the present invention is applied; 
     FIG.  2 ( a ) is a perspective view of a principal part of a preferred embodiment of the present invention, 
     FIG.  2 ( b ) is a schematic diagram showing an optical toner detecting mechanism, and 
     FIG.  2 ( c ) is a schematic diagram showing an operation panel; 
     FIG. 3 is a side view of a principal part of a preferred embodiment of the present invention; 
     FIG. 4 is a flow chart of an example of an operation in a preferred embodiment of the present invention; 
     FIG. 5 is a graph showing an example of an operation in a preferred embodiment of the present invention; 
     FIG. 6 is a perspective view of a principal part of another preferred embodiment of the present invention; 
     FIG. 7 is a perspective view of a principal part of another referred embodiment of the present invention; 
     FIG. 8 is a part of a flow chart of an example of an operation in another preferred embodiment of the present invention; 
     FIG. 9 is a part of the flow chart of the example of the operation in another preferred embodiment of the present invention; 
     FIG. 10 is a graph showing the example of the operation in another preferred embodiment of the present invention; 
     FIG. 11 is a graph showing an example of an operation in a conventional picture image forming system; 
     FIG. 12 is a graph showing an example of the variation in toner specific concentration in a picture image forming system; and 
     FIG. 13 is a block diagram for explaining the function of a toner specific concentration detecting sensor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention are described below. 
     FIG. 1 shows a principal part of a color picture forming system to which the present invention is applied. As can be seen from FIG. 1, picture image forming units  101 Y,  101 M,  101 C and  101 K for the four colors Y, M, C and K are provided. To these units, read picture signals are inputted as laser light beams of four colors  103 Y,  103 M,  103 C and  103 K from a polygon mirror  102  and a reflecting mirror  102 A of an exposure device. On the basis of these laser beams, a picture image is formed in each of the picture image forming units, so that the picture images of Y, M, C and K are sequentially transferred to recording paper (not shown) which is conveyed by a conveyance belt  100  in a direction of arrow “a” in the figure. Although this structure is not described in detail, it will be briefly described below. In each of the picture image forming units, reference number  105  denotes a photosensitive material drum; reference number  106  denotes an electrifying device for electrifying the photosensitive material drum  105 ; reference number  107  denotes a developing device for developing a toner image in accordance with a latent image which is drawn on the photosensitive material drum  105  by laser beams; reference number  108  denotes a transferring device for transferring the toner image to recording paper; reference number  109  denotes a cleaning device; and reference number  110  denotes a de-electrifying device. To each of the developing devices  107 , toners Y, M, C and K are supplied from toner cartridges  8 , specifically toner cartridges  8 Y,  8 M,  8 C and  8 K. 
     In a picture image forming system with the above described construction, the toners Y, M, C and K in the toner cartridges  8  decrease as copies are continuously made. According to the present invention, instead of replacing a single toner cartridge each time, a plurality of toner cartridges can be simultaneously replaced, so that it is possible to keep the exchanging operation of the toner cartridges from being complicated. 
     Each of the preferred embodiments will be described in detail below. 
     First Preferred Embodiment 
     First, the first preferred embodiment of the present invention will be described. 
     One feature of the first preferred embodiment is as follows. When a toner cartridge for a toner of a certain color becomes empty, toner outlets to the reserve tank portions of toner cartridges for the toners of all of colors are forced to be open, so that the remaining toners are introduced into the reserve tank portions. This operation is repeated every time the toner cartridges for any one of toners of all of colors become empty. Thereafter, when a toner of a certain color is determined to be in a toner empty on the basis of a toner specific concentration, the toner cartridges having been empty are simultaneously replaced so as to avoid the complicated replacing process that each time a toner is running short, the toner cartridge therefor is replaced. 
     Referring to the accompanying drawings, the first preferred embodiment of the present invention will be described in detail below. FIG. 3 is a sectional side view of a principal part of a system according to the present invention, and FIG.  2 ( a ) is a perspective view of the system. FIGS.  2 ( b ) and  2 ( c ) show an optical toner detecting mechanism and operation panel of the system, respectively. As can be seen from FIG. 3, a toner tank  1  is divided into a tank body portion la serving as a usual toner tank, and a reserve tank portion  1   b  which is arranged on the tip side (on the left in the figure) and which serves as a place for temporarily storing therein a toner remaining in a toner cartridge. In the toner tank  1 , a toner conveying auger  3  rotated by a developing device motor  4  is provided. By the rotation of the auger  3 , the toner is conveyed in a direction of arrow AR 1  to be fed to a developing part while a developer is agitated. In the toner tank  1 , a well-known sensor for detecting a toner specific concentration in the developer is provided. This toner specific concentration detecting sensor will be described later. In a usual state, the toner is supplied from the toner cartridge  8  to the tank body portion  1   a  via a usual supply passage, but no toner is supplied to the reserve tank portion  1   b . Therefore, the reserve tank portion  1   b  is emptied by the rotation of the auger  3 . 
     The top face of the tank body portion la of the toner tank  1  is formed with a tank body inlet  1 A and a reserve tank inlet  1 B. The reserve tank inlet  1 B is provided with a shutter  6  for opening and closing the inlet  1 B. The shutter  6  is usually closed, but is opened when the toner is supplied to the reserve tank portion  1   b . By opening and closing the shutter  6 , a reserve supply passage between the reserve tank portion  1   b  and the toner cartridge  8  is established and blocked, respectively. 
     The bottom face of the toner cartridge  8 , which is detachably mounted on the toner tank  1  with the above described construction, is provided with a first opening  8 A and a second opening  8 B. The first opening  8 A faces the tank body inlet  1 A of the toner tank  1 , and the second opening  8 B faces the reserve tank inlet  1 B. The first and second openings  8 A and  8 B are provided with first and second lids  10 A and  10 B, respectively. 
     The lids  10 A and  10 B are open when the toner cartridge  8  is attached, and closed when the toner cartridge  8  is detached. Thus, the usual supply passage between the first opening  8 A and the tank body inlet  1 A, and the reserve supply passage between the second opening  8 B and the reserve tank inlet  1 B are automatically established and blocked in accordance with the attachment and detachment of the toner cartridge  8 . However, the shutter  6  exists in the reserve tank inlet  1 B as described above. 
     In such a toner cartridge  8 , an auger  12  for conveying a toner in a direction of arrow AR 2  is provided on the bottom side thereof. By this auger  12 , the toner in the toner cartridge  8  is efficiently conveyed therein to drop from the first opening  8 A to be introduced into the toner tank  1 . In the vicinity of the first opening  8 A, a cartridge sensor  14  is provided. This sensor  14  detects the presence of the toner in the cartridge  8 . That is, when the toner conveyed by the anger  12  to drop from the first opening  8 A runs short, the sensor  14  detects that the toner cartridge  8  is empty (a cartridge empty). The auger  12  is rotated by a toner motor  15  which is provided outside of the toner cartridge  8 . 
     In place of the sensor  14 , a light emitting part  14   a  and a light receiving part  14   b  may be provided so as to face to each other via the usual supply passage of the toner cartridge  8 , as shown in FIG.  2 ( b ), to optically detect the presence of the toner. 
     The toner specific concentration detecting sensor  16  described by referring to FIG. 13 will be described below. The toner specific concentration detecting sensor  16  is provided in each of the developing devices  107  for the respective colors, and detects the concentration of the toner in a developer consisting of a carrier and the toner. The detection principle is as follows. The toner specific concentration detecting sensor  16  forms a magnetic circuit in the developer to detect the variation in magnetic resistance in the developer. That is, if the quantity of the toner with respect to the carrier in the developer decreases, the magnetic resistance decreases, and, on the contrary, if the quantity of the toner increases, the magnetic resistance increases. Such variation in magnetic resistance is detected by a detecting part (not shown) and fed to a main CPU  18  as a toner specific concentration signal. The main CPU  18  receives the toner specific concentration signal and drives the toner motor  15  via a gate array  20  in accordance with the contents of the signal. 
     Accordingly, the toner is supplied from the toner cartridge to the developing device so that the concentration of the toner in the developing device  107  is maintained constant. 
     As shown in FIG.  12 ( c ), a general purpose display device is provided for displaying a message indicating a near empty or a toner empty. This display device is provided on an operating part of the picture image forming system body, and has a liquid crystal panel portion L on which various messages are displayed. Specifically, the main CPU  18  receives output signals from the cartridge sensor  14  and the toner specific concentration detecting sensor  16  to control the liquid crystal panel L to display a message indicating near empty or an empty. 
     Referring to FIG. 5, an example of the operation of the system with the above described construction will be described below. There will be herein described a case where the toner Y first runs short and where the residual quantity of the toner M, which is low at this time, is smaller than that in the reserve tank portion. From time t 0 , the toners Y and M are decreasing in accordance with the copying operation. At time t 1 , the toner Y runs short in the toner cartridge  8 . At this time, a slight amount of the toner M remains in the toner cartridge  8  although the residual quantity of the toner M is smaller than the volume r of the reserve tank portion  1   b . At this time t 1 , the shutters  6  for all of the toners Y, M, C and K are open. All of the toner M in the toner cartridge  8  drops into the reserve tank portion  1   b . Thus, the residual quantity of the toner M in the toner cartridge becomes zero at a time (time t 1 ). It is assumed that by the subsequent copying operation, a toner empty is detected from the toner concentration ratio with respect to, e.g., the toner Y. In response thereto, the toner cartridges  8  for the toners Y and M are replaced at time t 2 . Thus, the quantities of the toners Y and M increase. Thus, by simultaneously replacing the toner cartridge  8  for the toners M and Y, it is possible to void replacing the cartridge  8  for the toner M immediately after the cartridge  8  for the toner Y is replaced. 
     Referring to FIG. 4, the above described operation will be described in more detail below. 
     Until a cartridge empty is detected in the toner cartridges for the toners Y, M, C and K by the cartridge sensor  14 , a copying operation continues (NO of step S 1 , step S 2 ). 
     For example, it is assumed that a cartridge empty is detected by the cartridge sensor  14  for the toner Y (YES of step S 1 ). In this case, a control signal is outputted to open the shutters  6  of the reserve tanks  1   b  for all the colors of the toners Y, M, C and K (step S 3 ). Simultaneously, a near empty is displayed with respect to the toner Y (step S 4 ). That is, it is displayed that with respect to the toner Y, the toner cartridge  8  is empty, and there is only the toner remaining in the toner tank  1 . 
     Thereafter, a copying operation is carried out with the toner Y remaining in the toner tank  1  and other toners in both of the toner cartridges  8  and toner tanks  1  (NO of step S 5 , step S 6 ). 
     If a cartridge empty is detected by the cartridge sensor  14  for the toner M (YES of step S 5 ), a control signal is outputted again. By this control signal, the shutters  6  of the reserve tank portions  1   b  for the toners Y, M, C and K of all of colors are open. In practice, the opening operation is not carried out again since the shutters  6  have been opened at the preceding step S 3 . The technical significance herein is that the shutters  6  of the reserve tanks  1   b  for all of the toners Y, M, C and K are open even if the toner cartridge  8  for the toner M becomes empty before the toner cartridge  8  for the toner Y becomes empty, although in the example described herein, the toner cartridge  8  for the toner M becomes empty after the toner cartridge for the toner Y becomes empty. Simultaneously, a near empty is displayed with respect to the toner M (step S 8 ). 
     Thereafter, the copying operation continues (NO of step S 9 , step S 10 ). After this copying operation, if it is determined on the basis of the toner specific concentration that the toner Y is in a toner empty (YES of step S 9 ), the copying operation discontinues (step S 11 ). Simultaneously, the shutters  6  for all of the toners Y, M, C and K are closed (step S 12 ), and a message indicating a toner empty is displayed to indicate that the toners Y and M do not exist in the toner cartridges  8  (step S 13 ). 
     The user looks at this toner empty display to simultaneously replaces the toner cartridges  8  for the toners Y and M. At this time, the toners in the toner cartridges  8  are introduced into the tank body portions  1   a . In this state, the augers  12  are rotated by the toner motors  15  for a predetermined period of time to efficiently supply the toners Y and M (step S 14 ). The toners introduced into the tank body portions la are also conveyed by the augers  3 . Then, the toners Y and M are supplied until the concentration of the toner Y, the toner concentration ratio of toner Y having fallen to the empty state once, reaches a predetermined empty clear level (see level L 1  in FIG. 12 which will be described later) (NO of step S 15 , step S 14 ). Then, when the concentration of the toner Y reaches the release level (YES of step S 15 ), the toner empty displays for the toners Y and M are cleared, and a copying operation is resumed (step S 16 ). 
     Second Preferred Embodiment 
     Another preferred embodiment will be described below. 
     One feature of this second preferred embodiment is as follows. A toner supplied from a toner cartridge is previously stored in a reserve tank so that the toner stored in the reserve tank is discharged when the toner in the cartridge runs short. Thus, toner cartridges for toners of colors, which run short, are simultaneously exchanged to decrease the number of exchanging operations. 
     That is, the toner specific concentration gradually falls from a level higher than a level L 1  by continuing to carry out a copying operation. Referring to FIG. 12, in relation to this process, the definition of each level for toner supply will be described as follows. When the toner specific concentration falls to a level between levels L 1  and L 2  (part A), the copying operation is not discontinued, and the toner is supplied for a predetermined period of time while the copying operation is carried out. When the toner specific concentration is at a level between the levels L 2  and L 3  (part B), the toner is always supplied while the copying operation is carried out. When the toner specific concentration falls to a level which is slightly less than the level L 3  (part C), the copying operation is discontinued, and the toner is supplied for a predetermined period of time. Thus, the toner specific concentration returns to a level which is higher than the level L 3 , so that a copying operation is thereafter resumed. When the toner specific concentration falls to a level which is greatly less than the level L 3  (part D), the copying operation is discontinued, and the toner is supplied for a predetermined period of time. However, since the toner specific concentration does not return to the level L 3  even if the toner is supplied for the predetermined period of time, the toner empty is determined while the copying operation discontinues, and a toner empty is displayed. The part E shows that the user has replaced the toner cartridge and the toner has been supplied for the predetermined period of time, so that the toner specific concentration has returned to the level L 1 . 
     An example of the operation of this preferred embodiment will be described below. FIG. 10 shows the variations in toner specific concentration. In FIG. 10, the above described three levels L 1  through L 3  are shown. 
     In FIG. 10, a dotted line shows the level of the toner Y, and a solid line shows the level of the toner M. The level of the toner Y falls below the level L 3  at time t 1  (a first toner empty determination(Y)). At this time, the toner is supplied from the reserve tank, and the level rises to the level L 2 . The concentration level of the toner M falls below the level L 3  at time t 2  (a first toner empty determination(M)). Similar to the toner Y, the toner M is supplied from the reserve tank, so that the level of M rises to the level L 2 . At time t 3 , the level of the toner Y falls below the level L 3  again (a second toner empty determination (Y)). At this time, the level of the toner M does not yet fall below the level L 3 . However, since the reserve tank for the toner M has also been used, a message indicating the toner empty is displayed with respect to both of the toners Y and M to have the user replace the toner cartridges. Thus, the concentration levels of the toners Y and M rise to the level L 1 . 
     A principal part of a system for realizing the above described operation according to the present invention is shown in FIGS. 6 and 7. The entire constitution of a picture image forming system is the same as that described by referring to FIG. 1, so that the description thereof is omitted. This system is similarly formed with respect to each color of the toners Y, M, C and K. 
     In FIGS. 6 and 7, reference number  31  denotes a toner tank which has a toner conveying auger  32  therein. This auger  32  is rotated by a developing device motor  33 . By the rotation of the auger  32 , a toner, together with a developer, is agitated, and the toner is conveyed in a direction of arrow AR 3  to be fed to a developing part. In the toner tank  31 , a sensor for detecting a toner concentration ratio is provided. 
     On the toner tank  31 , a toner cartridge  35  is detachably mounted. In the bottom face of the toner tank  35 , a first opening  35 A is provided. The opening  35 A has a lid  36 . The lid  36  opens the opening  35 A when the cartridge  35  is attached to the toner tank  31 , and closes the opening  35 A to prevent the leakage of the toner when the cartridge  35  is detached from the toner tank  31 . A first toner inlet  31 A is formed in the toner tank  31  so as to face the first opening  35 A. A usual toner supply passage is formed therein. 
     A part of the toner cartridge  35  is an expanded portion  35   a  protruding so as to have a pent-roof shape. Between the expanded portion  35   a  and the toner tank  31 , a reserve tank  37  for connecting them is provided. The top face of the reserve tank  37  is provided with a top opening  37 A for receiving a toner, and the bottom face of the reserve tank  37  is provided with a bottom opening  37 B for releasing the toner. The bottom opening  37 B has a shutter  38 . The shutter  38  is usually closed, and is opened when discharging the toner to the toner tank  31 . Such a reserve tank  37  is attached between the expanded portion  35   a  of the toner cartridge  35  and the toner tank  31 . In this state, a second opening  35 B is provided on the bottom face of the expanded portion so as to face the top opening  37 A of the reserve tank  37 . The opening  35 B has a lid  39  which closes the opening  35 B when the cartridge  35  is detached. The toner tank  31  is formed with a second toner inlet  31 B which faces the bottom opening  37 B of the reserve tank  37 . A reserving supply passage is formed therein. 
     In the toner cartridge  35  and the reserve tank  37 , augers  41  and  42  are provided on the bottom portions thereof, respectively. The augers  41  and  42  are integral with each other so as to rotate simultaneously. The augers  41  and  42  are connected to a toner motor  43  to be rotated by the motor  43 . A general purpose display device (not shown) is provided for displaying messages indicating a near empty and a toner empty. 
     In the above described system, when the toner cartridge  35  is attached to the toner tank  31 , the two lids  36  and  39  are open, so that the first opening  35 A and the second opening  35 B are communicated with the first inlet  31 A and the top opening  37 A, respectively. However, the bottom opening  37 B and the second inlet  31 B are in a non-communication state by the shutter  38 . Then, if the toner runs short in the toner cartridge  35 , the shutter  38  is opened to supply the toner from the reserve tank  37  to the toner tank  31 . 
     Referring to the flow charts of FIGS. 9 and 10, an example of an operation shown in FIG. 11 will be described below. 
     As shown in FIG. 11, an example of a state that the toner Y first runs out and then the toner M decreases will be described herein. 
     When the toners Y, M, C and K sufficiently remain (when toner specific concentrations are sufficiently high), a copying operation continues as shown at steps S 21  and S 22 . 
     When the toner specific concentration of the toner Y decreases to reach the toner empty state, i.e., to reach the toner supply level L 3  (YES of step S 21 ), a near empty message is displayed with respect to the toner Y to discontinue the copying operation (step S 23 ). At this time, the shutter  38  of the reserve tank  38  for the toner Y is open (step S 24 ). Thereafter, the toner motor  43  for the toner Y is rotated for a predetermined period of time to rotate the auger  42  in the reserve tank  37  to supply the toner Y from the reserve tank  37  to the toner tank  31  via the second inlet  31 B (step S 25 ). The developing device motor  33  is also rotated to convey the toner from the toner tank  31  to the developing device. This operation is repeated until the toner specific concentration of the toner Y reaches the toner supply level (the empty release level  2 ) L 2 . Thus, the toner specific concentration of the toner Y is increasing (see t 1  of FIG.  10 ). 
     When the toner specific concentration of the toner Y reaches the empty release level L 2  (YES of step S 26 ), the near empty message continues to be displayed, and a copying operation is resumed (step S 27 ). 
     The copying operation continues until, e.g., the level of the toner M gets becomes lower due to the subsequent continuous copying operation (NO of step S 28 , step S 29 ). 
     For example, when the copying operation continues and the toner empty is determined (YES of step S 28 ), i.e., when the toner specific concentration of the toner M reaches the toner supply level L 3  (see t 2  of FIG.  11 ), an near empty message is displayed with respect to the toner M to discontinue the copying operation (step S 30 ). Simultaneously, the shutter  38  of the reserve tank  38  for the toner M is opened (step S 31 ). At this time, the toner motor  43  is rotated to rotate the auger  42  in the reserve tank  37  to supply the toner M from the reserve tank  37  to the toner tank  31  via the second inlet  31 B (step S 32 ). This operation continues with respect to the toner M until the toner specific concentration of the toner M reaches the empty removed level  2  (step S 32 , NO of step S 33 ). When the concentration of the toner M reaches the empty removed level L 2  (YES of step S 33 ), a copying operation is resumed while the toner empty message is displayed (step S 34 ). 
     This copying operation continues until a specific state occurs in which any one of the toners Y, M, C and K decreases (step S 35 , NO of step S 36 ). 
     When the toner empty for the toner Y is determined (second time) by the continuous copying operation (YES of step S 35 ), the copying operation discontinues (step S 37 ). At this time, the shutters  38  of the reserve tanks for the toners Y and M are closed (step S 38 ). The near empty message for each of the toners Y and M, which has been displayed, is cleared, and a toner empty message for each of the toners Y and M is newly displayed (step S 39 ). 
     Thereafter, the user can simultaneously replace the toner cartridges  35  for the toners Y and M. 
     When the toner cartridges for the toners Y and M are attached, the lids  39  of the toner cartridges  35  are automatically opened to open the second opening  35 B. Thus, the toners Y and M in the toner cartridges  35  are introduced into the reserve tanks  37  via the top openings  37 A (step S 40 ). At this time, as described above, the lids  36  are open to introduce the toners from the toner cartridges  35  to the toner tanks  31 . 
     Thereafter, the toner motors  43  for the toners Y and M are rotated for a predetermined period of time to supply the toners (step S 41 ). This operation continues until the toner level of the toner Y reaches the empty release level L 1  (NO of step S 42 , step S 41 ). 
     When the toner level of each of the toners Y and M reaches the empty release level L 1  (YES of step S 42 ), the toner empty display for each of the toners Y and M is cleared, and a copying operation is resumed (step S 43 ). 
     In the above described second preferred embodiment, the relationship between the toner specific concentration and the replacement of the cartridge has been described by referring to FIG.  10 . Referring to FIG. 11, in response to this, an example of a conventional case will be described below. That is, in FIG. 11, toner supply levels L 1  through L 3  are the same as those in FIG.  10 . In FIG. 11, the toner specific concentration of the toner Y is the toner supply level L 3  at time t 11 . That is, the toner empty for the toner Y is determined (first time) at time t 11 , so that the toner cartridge is replaced. At time t 12 , the toner specific concentration of the toner M is below the level L 3 . Therefore, the toner empty for the toner M is determined (first time), so that the toner cartridge is replaced. That is, it is necessary to perform two separate toner cartridge replacement operations in a short time. The toner specific concentration for the toner Y is below at time t 13  again. At this time, the toner cartridge for the toner Y is replaced. 
     While the present invention has been disclosed in terms of the preferred embodiment in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modification to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in the appended claims.