Abstract:
A liquid measuring device to detect an amount of liquid contained in a container, having a weight detecting system to detect weight of the container including the liquid contained in the container, and an amount determining system configured to determine the amount of the liquid contained in the container based on the weight detected by the weight detecting system, is provided.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a liquid measuring device for developing solution of a wet type image forming apparatus.  
         [0002]     Apparatuses that transfer toner to a recording sheet to thereby form an image include, for example, a dry type image forming apparatus, which applies powder toner to a surface of a developing roller to form an image, and a wet type image forming apparatus, which applies developing solution containing toner in carrier solution to a surface of a developing roller to form an image. The toner employed in the latter apparatus is finer than that employed in the former. Accordingly, the latter provides an image of a higher quality.  
         [0003]     A conventional wet type image forming apparatus is generally equipped with a developing solution container, and developing solution therein is supplied to a developing device during an image forming operation. In such a wet type image forming apparatus, color density of an image being formed depends on density of the toner in the developing solution. Therefore, in order to maintain the toner density to be constant, the developing solution is occasionally stirred and adjusted with additional carrier solution. Further, as the image is formed, an amount of the developing solution in the container decreases. Therefore, as disclosed in Registered Japanese Utility Model Publication No. 2556068, for example, the wet type image forming apparatus is provided with a liquid measuring unit for the developing solution so that the amount of the developing solution in the container is detected.  
         [0004]     In the above-referenced publication, a liquid measuring unit with a liquid container, a frame that holds the container, and a platform that resiliently supports the frame is disclosed. The frame is adapted to be uplifted by expanding force of the platform according to weight of the container, and is provided with a sensor and a contacting member, which become in contact with each other when the frame is uplifted, and are released when the frame is depressed in an initial position with a substantial amount of liquid in the container. Thus, based on the contact of the sensor and the contacting member, the amount of the liquid in the container is detected. In this method, however, a level of merely one predetermined kind of liquid can be exclusively measured, and other kinds of liquid with different specific gravities cannot be measured.  
         [0005]     In another example, a method to detect a level of the liquid in a container by having an object to be detected float on a surface of the liquid so that a level thereof is detected by a plurality of vertically aligned sensors is known. In many cases in this method, however, the object does not float properly when the developing solution adheres to a surface of the object. Further, when the developing solution is stirred in the container and a swirl occurs, the level of the liquid may not accurately be detected. Moreover, in this method, a plurality of sensors for each of the levels to be detected are required, therefore the measuring unit tends to be greater in size as the number of the detection levels increases.  
       SUMMARY OF THE INVENTION  
       [0006]     In view of the foregoing drawbacks, the present invention is advantageous in that an improved liquid measuring device for developing solution, which is capable of accurately detecting an amount of the developing solution is provided.  
         [0007]     According to an aspect of the invention, there is provided a liquid measuring device to detect an amount of liquid contained in a container, having a weight detecting system to detect weight of the container including the liquid contained in the container, and an amount determining system configured to determine the amount of the liquid contained in the container based on the weight detected by the weight detecting system.  
         [0008]     Optionally, the weight detecting system may include a guide member allowing the container to be shifted in vertical directions so that the container is restricted in moving in directions other than the vertical directions, and a weight sensor to resiliently hold the container and to sense the weight of the container including the liquid contained in the container.  
         [0009]     According to another aspect of the invention, there is provided a liquid containing unit, including a liquid measuring device, which is adapted to detect an amount of liquid contained in a container, with a weight detecting system to detect weight of the container including the liquid contained in the container, and an amount determining system configured to determine the amount of the liquid contained in the container based on the weight detected by the weight detecting system.  
         [0010]     Optionally, the weight detecting system may include a guide member allowing the container to be shifted in vertical directions so that the container is restricted in moving in directions other than the vertical directions, and a weight sensor to resiliently hold the container and to sense the weight of the container including the liquid contained in the container.  
         [0011]     Optionally, the liquid containing unit may further include a stirring system, which is adapted to stir the liquid contained in the container.  
         [0012]     Optionally, the stirring unit may include a screw to be rotated by a motor so that the liquid contained in the container is stirred thereby.  
         [0013]     Optionally, the stirring system may be fixed to a mechanism being provided independently from the container.  
         [0014]     Optionally, the motor may be activated at predetermined intervals.  
         [0015]     Optionally, the amount of the liquid contained in the container may be detected whilst the motor is inactive.  
         [0016]     Optionally, the stirring system may be located integrally with the container.  
         [0017]     Optionally, the amount of the liquid contained in the container is detected whilst the motor is inactive.  
         [0018]     According to another aspect of the invention, there is provided a wet type image forming appratus, including a liquid measuring device to detect an amount of developing solution contained in a container, with a weight detecting system to detect weight of the container including the developing solution contained in the container, and an amount determining system configured to determine the amount of the liquid contained in the container based on the weight detected by the weight detecting system.  
         [0019]     According to another aspect of the invention, there is provided a wet type image forming apparatus, including a liquid containing unit with a liquid measuring device, which is adapted to detect an amount of developing solution contained in a container and has a weight detecting system to detect weight of the container including the developing solution contained in the container, an amount determining system configured to determine the amount of the liquid contained in the container based on the weight detected by the weight detecting system,  
     
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS  
       [0020]      FIG. 1  is a cross-sectional side view showing a structure of a wet type printer according to an embodiment of the present invention.  
         [0021]      FIG. 2  is another cross-sectional side view of the wet type printer taken from a rear side thereof according to the embodiment of the present invention.  
         [0022]      FIG. 3  is an illustrative diagram of a solution container of the wet type printer according to the embodiment of the present invention.  
         [0023]      FIG. 4  is a flowchart to illustrate a developing solution supplying process to adjust a liquid level in the solution container according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0024]     Referring to the accompanying drawings, a wet type printer according to an embodiment of the present invention will be described in detail.  
         [0025]      FIG. 1  is a cross-sectional side view showing a structure of a wet type printer  100  according to an embodiment of the present invention. The wet type printer  100  in the present embodiment is an apparatus that receives print information (i.e., character and/or image information) from an external apparatus such as a computer, and prints out the characters or the images on a sheet of recording paper P 1  in accordance with a so-called electrophotographic imaging process by using developing solution with carrier solution and toner therein.  
         [0026]     The wet type printer  100  includes a laser scanning unit (hereinafter abbreviated as “LSU”)  30  that outputs a laser beam modulated according to the print information, a developing unit  50  that develops a latent image formed on a photoconductive drum  55  according to the print information with the developing solution in the electrophotographic method, a feeding unit  90  that feeds the recording paper P 1 , a transfer unit  70  that transfers a toner image developed by the developing unit  50  at a transfer position onto the recording paper P 1 , and a fixing unit  80  that permanently fixes the toner image that has been transferred on the recording paper P 1 .  
         [0027]     The developing unit  50  includes an add roller  51 , a measuring roller  52 , an adjusting blade  52   a , a developing roller  53 , a developing roller cleaning blade  53   a , a developing roller corona charger  54 , the photoconductive drum  55 , a photoconductive drum corona charger  57 , a solution pipe  49 , and a screw  59 . The measuring roller  52  is provided to measure an amount of the developing solution on a surface thereof. The adjusting blade  52   a  evenly adjusts thickness of the developing solution on the surface of the measuring roller  52 . The developing roller  53  carries the developing solution supplied from the measuring roller  52 . The developing roller cleaning blade  53   a  scrapes off an excessive amount of the developing solution from the surface of the developing roller  53 . The developing roller corona charger  54  charges the surface of the developing roller  53 . A surface of the photoconductive drum  55  has a latent image formed by the laser beam from the LSU  30 . The photoconductive drum corona charger  57  uniformly charges the surface of the photoconductive drum  55 . The squeeze roller  58  collects used developing solution from the surface of the photoconductive drum  55 . And the screw  59  transmits residual developing solution collected in the developing unit  50  to a solution container  3  (see  FIG. 2 ). All of rotation axes of the respective rollers are in parallel with each other and are perpendicular to a direction parallel to a plane of  FIG. 1 , although rotating directions of the respective rollers may vary.  
         [0028]     When the image is formed, the developing solution stored in the solution container  3  is injected and the injected developing solution is transitionally pooled in a pit portion formed by the add roller  51  that rotates in a clockwise direction in  FIG. 1  and the measuring roller  52  that rotates in a counterclockwise direction in  FIG. 1 . Thereafter, the developing solution is supplied to a surface of the measuring roller  52  by the rotation of the measuring roller  52 . The supplied developing solution is partially scraped off and thereby adjusted by the adjusting blade  52   a , of which an edge is in contact with the surface of the measuring roller  52  so that excessive amount of the developing solution is removed. Thus, the remaining developing solution on the surface of the measuring roller  52  is transferred evenly to a surface of the developing roller  53 , which is in contact with the measuring roller  52 . The photoconductive drum  55  has the surface constituted of a conductive material, so that such surface is uniformly charged by a corona charging effect of the developing roller corona charger  57 . On the surface of the photoconductive drum  55 , a latent image corresponding to the print information is formed, by the laser beam emitted from the LSU  30 . The photoconductive drum  55  is charged so as to gain a higher potential than that of the developing roller  53 , by the photoconductive drum corona charger  57 . However, the region where the latent image is formed gains a lower potential than the developing roller  53 , due to an effect of the laser beam. Accordingly, between the region excluding the latent image on the photoconductive drum  55  and the surface of the developing roller  53 , the toner remains closely stuck to the lower-potential region, i.e. the surface of the developing roller  53 , without being transferred to the region where no latent image exists. Consequently, the region excluding the latent image is not developed. By contrast, between the latent image region on the surface of the photoconductive drum  55  and the surface of the developing roller  53 , the toner performs electrophoresis toward the lower-potential region, i.e. the latent image region on the surface of the photoconductive drum  55 , thus to adhere thereto. That is how the latent image on the photoconductive drum  55  is developed, to turn into a toner image.  
         [0029]     The toner image developed on the surface of the photoconductive drum  55  is transferred to the recording paper P 1  by the transfer unit  70 . The transfer unit  70  includes an intermediate transfer roller  71  and a secondary transfer roller  73 . To the intermediate transfer roller  71 , a transfer bias of a reverse polarity to the toner is applied, so that the toner image developed on the surface of the photoconductive drum  55  is transferred as a primary step to the intermediate transfer roller  71 , at the interface between the photoconductive drum  55  and the intermediate transfer roller  71 . The intermediate transfer roller  71  and the secondary transfer roller  73  are disposed so as to be opposed to each other across a paper path for the recording paper P 1 , and mutually abut at a predetermined nip pressure. The toner image transferred to the surface of the intermediate transfer roller  71  is transferred to the recording paper P 1  being carried along the paper path at the interface with the secondary transfer roller  73 , by the effect of a transfer electric field, the nip pressure and so on.  
         [0030]     The recording paper P 1  on which the toner image has been transferred is carried to the fixing unit  80  along the paper path. The fixing unit  80  serves to apply heat and pressure to the recording paper P 1 , so as to fix the toner image onto the recording paper P 1 , and includes a heat roller  81  that heats up the recording paper P 1 , and a press roller  82  located opposite to the heat roller  81  across the paper path, so as to hold the recording paper P 1  in cooperation with the heat roller  81 , thus to apply a pressure to the recording paper P 1 .  
         [0031]     The feeding unit  90  includes a core roller  91 , around which the recording paper P 1  as a continuous form recording sheet is rolled, a feed roller  93 , which carries the recording paper P 1 , a subsidiary feed roller  94 , which is rolled accordingly to rotation of the feed roller  93  to carry the recording paper P 1 , and a drive motor  95 , which supplies rotating force to the feed roller  93 .  
         [0032]     Next, referring to  FIG. 2 , the solution container  3 , to store the developing solution therein will be described. The wet type printer  100  in the present embodiment includes the solution container  3 , wherein the developing solution is stored, a preparatory solution container  5 , a preparatory carrier solution container  7 , a supplier pump unit  9 , and a conveyer pump unit  11 . The preparatory solution container  5  stores therein preparatory developing solution, which is supplied to the solution container. Carrier solution is stored in the preparatory carrier solution container  7 , and is supplied to the solution container  3 . The supplier pump unit  9  is used to transmit the preparatory developing solution in the preparatory solution container  5  to the solution container  3 .  
         [0033]     During a printing operation of the wet type printer  100 , the developing solution in the solution container  3  is conveyed to the developing unit  50  by the conveyer pump unit  11 . An outlet of the conveyer pump unit  11  is connected to the solution pipe  49 . When the level of the developing solution in the solution container  3  becomes too low, the developing solution is not supplied to the developing unit  50 . Therefore, in the present embodiment, the preparatory developing solution stored in the preparatory solution container  5  is supplied to the solution container  3  when the level of the developing solution in the solution container becomes as low as a predetermined lower limit. Further, toner density of the developing solution in the solution container  3  tends to be concentrated over image forming operations. Therefore, the toner density is monitored by a density sensor (not shown) so that the carrier solution is supplied from the preparatory carrier solution container  7  if necessary.  
         [0034]     As mentioned above, color density of an image to be formed depends on toner density of the developing solution. That is, the image is printed in higher density when the toner density of the developing solution is high, and in lower density when the toner density is low. In the wet type printer  100  in the present embodiment, the toner density in the developing solution in the solution container  3  is adjusted with the supplemental carrier solution from the preparatory carrier solution container  7  so that the toner density (i.e., the color density of the image) is maintained constant. More specifically, the developing solution in the solution container  3 , as well as the developing solution in the preparatory solution container, is composed in a weight ratio of approximately 30% as toner and the remaining 70% as carrier solution.  
         [0035]     As viscosity of the developing solution is generally high, in order to avoid coagulation, the developing solution requires occasional stirring so that fluidity of the developing solution is maintained. The solution container  3  is provided with a stirring unit  4 , which stirs the stored developing solution, and a lateral opening  6 . The lateral opening  6  is connected to a pipe (not shown), which is further connected to an opening (not shown) provided on an extended line (not shown) of an axis of the screw  59  (see  FIG. 1 ). The developing solution carried by the screw  59  is returned to the solution container  3  via the lateral opening  6 .  
         [0036]     When a level of the developing solution in the solution container  3  is as low as or lower than a level L 1  shown in  FIG. 2 , a substantial amount of the developing solution may not be supplied to the developing unit  50 . As the amount of the developing solution decreases and when the level of the developing solution reaches to a level L 2 , a predetermined amount of supplemental developing solution is added to the developing solution in the solution container  3 . That is, the level L 2  is a threshold to determine whether the supplemental developing solution should be added to the solution container  3 . A level L 3  of the developing solution indicates an average level of the developing solution when the amount of the developing solution is adjusted. In a normal operation of the wet type printer  100 , it is preferable that the level of the developing solution is maintained in a range from the level L 2  to a level L 4 . It should be noted that a level L 5  indicates that the developing solution is excessive and the developing solution may overflow during the normal operation.  
         [0037]     As mentioned above, the used developing solution that is residual from the developing unit  50  is returned to the solution container  3  by the screw  59 . Thus, the amount of the developing solution in the solution container  3  decreases during the printing operation of the wet type printer  100 , whilst the toner density therein increases gradually. Therefore, the toner density is monitored by a density sensor (not shown) so that the carrier solution is supplied from the preparatory carrier solution container  7  if necessary.  
         [0038]      FIG. 3  is an illustrative diagram of the solution container  3  of the wet type printer  100  according to the embodiment of the present invention. The solution container  3  is formed to be, for example, cylindrical with a bottom thereof being closed and a top thereof being open. On top of the solution container  3 , a cover  103   a  is provided. A stirrer unit  4  and a weight sensor unit  110  are provided in a vicinity to the solution container  3 . The stirrer unit  4  includes a drive motor  119 , a stirrer  111 , and a rotary shaft  113 . The stirrer  111 , for example a screw, is adapted to stir the developing solution by rotating. The rotary shaft  113  is coupled to the drive motor  119  at one end, and is coupled to the stirrer  111  at the other end, so that rotating force of the drive motor  119  is transmitted to the stirrer  111 . The drive motor  119  is fixed to a top of the cover  103   a , which is fixed to a body of the wet type printer  100 . The drive motor  119  is activated when the developing solution is stirred, and as the stirrer  111  is rotated by the rotating force of the drive motor, the developing solution is stirred.  
         [0039]     On a circumferential surface of the solution container  3 , a guide member  108  is provided. The guide member  108  is fixed to the body of the wet type printer  100 , and is configured to guide the solution container  3  to be shifted only in vertical directions, which is perpendicular to the surface of the developing solution in the solution container  3 . The guide member  108 , for example, may be provided with a plurality of bearings on an inner circumference thereof, so that the bearings may be engaged with grooves extended vertically on the circumferential surface of the container  3 . (It should be noted that the grooves may be provided to the circumferential surface of the container  3  if the guide member  108  is configured to have the bearings.) In this configuration, the solution container  3  is allowed to be shifted vertically, whilst the solution container  3  is restricted from rotating in circumferential directions.  
         [0040]     The weight sensor unit  105  is configured to support the solution container  3  from the bottom. The weight sensor unit  105  may include, for example, a known weight sensor with an LC resonant circuit. The weight sensor unit  105  in the present embodiment includes a pushrod  107 , a spring  109 , the LC resonant circuit  122  with a coil  115  (the LC resonant circuit  122  excluding the coil  115  is referred to as an LC resonant circuit  121 ), and a solution amount detecting unit  123 . The pushrod  107 , which is in contact with the bottom surface of the solution container, is formed to be cylindrical, and is adapted to be shifted vertically according to weight of the solution container. The spring  109  is adapted to apply an expanding force to the pushrod so that the pushrod  107  is pressed against the bottom surface of the solution container  3 . The coil  115 , as an inductance component L of the LC resonant circuit, is arranged around a lower portion of the pushrod  107 . The solution amount detecting unit  123  is adapted to judge the amount of the developing solution in the solution container  3  based on a resonant frequency of current obtained from the LC resonant circuit  122 . The solution amount detecting unit  123  is further adapted to control power supply to the supplier pump  9  based on the amount of the developing solution detected, so that the preparatory developing solution is supplied to the solution container  3  when required.  
         [0041]     The pushrod  107  is adapted to be shifted vertically according to transition of the weight of the solution container  3 , which decreases as the developing solution therein is used during the printing operation, and increases as the supplemental developing solution is added. A lower portion of the pushrod  107  is made of, for example, a ferromagnetic material, so that the inductance of the coil  115  is altered according to the vertical movement of the pushrod  107 , and thus the resonant frequency of the LC resonant circuit  122  is altered.  
         [0042]     In the above-described configuration of the present embodiment, the weight of the solution container  3  with the developing solution therein is proportional to the resonant frequency of the current output from the LC resonant circuit  122 . That is, the weight of the solution container  3  including the developing solution can be obtained from the resonant frequency of the current from the LC resonant circuit  122 . As described above, the toner density of the developing solution in the solution container  3  is maintained to be substantially constant. Therefore, with a specific gravity corresponding to the density of the developing solution and the weight of the developing solution in the solution container  3  (obtained by subtracting weight of the solution container  3  from the total weight of the solution container  3  including the developing solution), the amount (i.e., a volume) of the developing solution in the solution container  3  can be detected. It should be noted that the weight sensor unit is not limited to a sensor unit with an LC resonant circuit as described above, but may be any weight sensor unit, for example using a strain gauge, as long as the weight sensor unit is capable of holding and measuring weight of the solution container  3 .  
         [0043]     It should be noted that, in the measuring unit with the weight sensor unit  105  as described above, the weight sensor unit  105  is prevented from being in contact with the developing solution in the solution container  3  even when the amount of the developing solution is measured. Therefore, the measuring accuracy of the weight sensor unit  105  will not be affected by the high viscosity of the developing solution, as the developing solution will not adhere to the weight sensor unit  105 . Further, as the measuring is based on the weight of the developing solution in the solution container  3 , the weight sensor unit  105  can avoid measuring erroneously the surface level of the developing solution that may be unevenly fluctuated due to the high viscosity thereof during a stirring operation. It should be further noted that, with the weight sensor unit  105 , different kinds of developing solutions with different specific gravities can be measured. When an interrelation between weight of the solution container  3  including developing solution and an amount (i.e., a volume) of the developing solution to be included in the solution container  3  is defined, i.e., when a specific gravity for each kind of the developing solution to be used is defined, the amount of the developing solution can be accurately measured by the same weight sensor unit  105  regardless of the difference in specific gravities of developing solution. Thus, the wet type printer  100  can be configured in a more simplified design. Furthermore, as the weight sensor unit  105  does not require a sensor and the like to be arranged on top of the solution container  3  and other peripheral space, the wet type printer  100  can be downsized.  
         [0044]     In the present embodiment, the weight sensor unit  105  is adapted to measure the amount of the developing solution whilst the developing solution is maintained still and the drive motor  119  of the stirrer unit  4  is inactivated, as the developing solution may be fluctuated vertically by external force from the stirrer  111  when the drive motor  119  is activated and the stirrer  111  is rotated. The stirrer unit  4  is activated and stirs the developing solution at predetermined intervals of time. Therefore, the weight of the solution container  3  including the developing solution is measured whilst the stirrer  111  is motionless, so that the amount of developing solution can be accurately measured. More specifically, for example, the drive motor  119  may be controlled to be activated at the predetermined interval.  
         [0045]     Next, referring to  FIG. 4 , a developing solution supplying process to adjust the level of the developing solution in the solution container  3  according to the embodiment of the present invention will be described. In the developing solution supplying process, the supplemental developing solution is added when the amount of the developing solution measured is less than a predetermined level, whilst an error-handling process is conducted when the measured amount is over a predetermined level, The developing solution supplying process shown in  FIG. 4  is repeatedly executed by a control unit (not shown) at a predetermined interval during a normal operation of the wet type printer  100 . As the developing solution supplying process starts, the control unit examines whether the stirrer unit  4  is in a stirring operation (S 0 ). When the stirrer unit  4  is not in the stirring operation (S 0 : NO), the weight sensor unit  105  measures the amount of the developing solution in the solution container  3  (S 1 ). When the measured amount indicates that the surface level of the developing solution is in a range from the level L 1  to the level L 2  (more specifically, higher than the level L 1  and lower than or equal to the level L 2 ) (S 1 : ML), the amount of the developing solution in the solution container  3  is considered to be low, and the process proceeds to S 2 . In S 2 , the control unit activates the supplier pump  9  to supply the supplemental developing solution to the solution container  3 . As an amount of the developing solution to be supplied by the supplier pump  9  in a unit of time is constant, operation time of the supplier pump  9  is set based on the amount of the developing solution before the supplying operation (i.e., the measured amount). When the operation time elapses (S 3 : YES), the control unit inactivates the supplier pump  9  (S 4 ). Thereafter, the process ends.  
         [0046]     When the measured amount of the developing solution indicates that the surface level is in a range from the level L 4  to the level L 2  (more specifically, the surface level is lower than the level L 4  and higher than the level L 2 ) (S 1 : d), and when the measured amount indicates the surface level is lower than the level L 5  and higher than or equal to the level L 4  (S 1 : MH), the process ends, as the amount is in a preferable level.  
         [0047]     When the measured amount of the developing solution indicates that the surface level is higher than or equal to the level L 5  (S 1 : H), and when the surface level is lower than or equal to the level L 1  (S 1 : L), the control unit executes the error-handling process, in which for example a notification is given to a user by generating an error sound and/or by displaying an error-notifying message (S 5 ), and the control unit stops the operation of the wet type printer  100  (S 6 ).  
         [0048]     Although the present invention has been described based on the foregoing embodiment, it is to be understood that the present invention is not limited thereto, but various modifications may be made without departing from the scope of the present invention.  
         [0049]     For example, the cover  103   a  may have the stirrer unit  4  thereon and may be fixed to the solution container  3 , instead of having the stirrer unit  4  fixed to the cover  103   a  that is fixed to the body of the wet type printer  100 . In this configuration, weight to be measured by the weight sensor unit  105  is a sum of the solution container  3  with the developing solution, the cover  103   a , and the stirrer unit  4 . Therefore, when the amount of the developing solution is measured, the weight of the developing solution is obtained by subtracting the weight of the solution container  3 , the cover  103   a , and the stirrer unit  4  from the sum. It should be noted in this configuration that the weight of the developing solution does not change even when the developing solution is fluctuated vertically by rotation of the stirrer  111 . Therefore, the step S 0  in the developing solution supplying process can be omitted.  
         [0050]     As described above, with the weight sensor unit  105  of the wet type printer  100 , the amount of the developing solution in the solution container  3  can be accurately measured as the weight sensor unit  105  is not affected by the developing solution. Further, different kinds of developing solution with different specific gravities can be measured in the same weight sensor unit  105 .  
         [0051]     The present disclosure relates to the subject matter contained in Japanese Patent Application No. 2005-145095, filed on May 18, 2005, which is expressly incorporated herein by reference in its entirety.