Patent Publication Number: US-2023135411-A1

Title: Liquid ejection apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a liquid ejection apparatus universally applicable as, for example, an inkjet printing apparatus comprising a print head capable of ejecting ink under an inkjet system. 
     Description of the Related Art 
     Japanese Patent Laid-Open No. 2019-25818 discloses a technique of including a member comprising a float in a storage chamber storing ink such that the member is pivotally movable and detecting the pivot motion of the member with a sensor, thereby detecting the remaining amount of ink in the storage chamber. According to the technique disclosed in Japanese Patent Laid-Open No. 2019-25818, a buoyancy exerted on a float by a stored ink is used to pivot the pivot member depending on the remaining amount of ink. In order to exert the buoyancy on the float, the specific gravity of the float is designed to be lower than the specific gravity of the stored ink. 
     Incidentally, in a printing apparatus which ejects multiple types of inks, the storage chamber disclosed in Japanese Patent Laid-Open No. 2019-25818 is provided for each of the inks. The buoyancy exerted on the float differs according to the specific gravity of an ink. Thus, in the case of using multiple types of inks which have specific gravities greater than that of the float and different from one another, the buoyancy exerted on the float varies according to whether an ink has a high or low specific gravity. Hence, the amount of pivot motion of the pivot member corresponding to the remaining amount of ink differs according to the type of ink, which may inhibit correct detection of the remaining amount of ink. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished in consideration of the above problem and provides a technique that enables correct detection of the remaining amount of liquid such as ink. 
     In the first aspect of the present invention, there is provided a liquid ejection apparatus including: 
     a liquid ejection head configured to eject a liquid; and 
     a plurality of storage units configured to store a liquid to be supplied to the liquid ejection head, 
     each of the storage units comprising: 
     a pivot member immersed in a stored liquid and pivotally movable according to an amount of the liquid; and 
     a detection unit configured to detect an amount of the liquid stored in the storage unit using the pivot member, 
     wherein at least one of a specific gravity and size of the pivot member comprised in each of the storage units differs according to a specific gravity of a liquid stored in each of the storage units. 
     According to the present invention, the remaining amount of ink can be correctly detected. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A and  1 B  are schematic diagrams of a configuration of a printing apparatus as an example of a liquid ejection apparatus according to an embodiment; 
         FIGS.  2 A and  2 B  are diagrams showing a motion of a pivot member in a case where an ink storage chamber is supplied with ink; 
         FIGS.  3 A and  3 B  are diagrams showing a motion of the pivot member in a case where the stored ink is reduced in the ink storage chamber; 
         FIGS.  4 A to  4 C  are diagrams showing heights of ink liquid surfaces in a case where the remaining amounts of inks different in specific gravity are determined to be equal to or less than a predetermined amount; 
         FIGS.  5 A and  5 B  are diagrams showing pivot members to provide a constant liquid surface height of an ink according to the specific gravity of the ink; and 
         FIGS.  6 A to  6 C  are diagrams showing other embodiments of the pivot member. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An example of a liquid ejection apparatus according to the present invention will be hereinafter described in detail with reference to the accompanying drawings. It should be noted that the embodiments described below do not limit the present invention and not all combinations of features described in the embodiments are necessarily essential for solving the problem to be solved by the present invention. Further, the relative positions, shapes, and the like of constituents described in the embodiments are merely shown as examples unless otherwise specified and are not intended to limit the scope of the invention to these examples. 
     First Embodiment 
     First, a liquid ejection apparatus according to a first embodiment will be described with reference to  FIGS.  1 A to  5 B . An example of the liquid ejection apparatus described herein is a printing apparatus which performs printing by ejecting ink to a print medium.  FIGS.  1 A and  1 B  are diagrams schematically illustrating the printing apparatus according to the embodiment;  FIG.  1 A  is a perspective view of an appearance of the apparatus and  FIG.  1 B  is a diagram showing a configuration of a printing portion inside the apparatus. It should be noted that the printing apparatus  10  of  FIGS.  1 A and  1 B  is an example of the printing apparatus to which the present embodiment is applicable; the printing apparatus to which the present embodiment is applicable is not limited to the printing apparatus  10  shown in  FIGS.  1 A and  1 B . 
     The printing apparatus  10  shown in  FIGS.  1 A and  1 B  is a so-called multifunction peripheral comprising a reading portion  12  capable of reading a document set on a document plate and a printing portion  14  which performs printing on a print medium based on information read by the reading portion  12 , information input from an external apparatus, or the like. 
     The reading portion  12  is located at the top of the printing apparatus  10  and the printing portion  14  is located at the bottom of the printing apparatus  10 . The printing portion  14  comprises an accommodating tray  16  which accommodates a print medium M, a feeding roller  18  which feeds the print medium M accommodated in the accommodating tray  16 , and a guide portion  20  which guides the fed print medium M to a position of printing by a print head  26  (described later). The printing portion  14  also comprises a conveying roller  22  which conveys the print medium M fed through the guide portion  20 , a platen  24  which supports the print medium M conveyed by the conveying roller  22 , and the print head  26  which ejects ink to the print medium M supported by the platen  24 . The printing portion  14  further comprises a discharge roller  30  which discharges the printed print medium M to a discharge tray  28  and an ink storage portion  32  as a storage unit to store an ink to be supplied to the print head  26  through a tube (not shown). 
     The print head  26  may be configured to eject inks of a plurality of colors or eject only an ink of a single color. The print head  26  may also be configured to eject a processing liquid to give a predetermined effect to an image after printing. In a case where multiple types of inks (including a processing liquid) are ejected, a plurality of ink storage portions  32  are provided to store the different types of inks. The print head  26  is mounted on a carriage  34 . The carriage  34  is configured to move reciprocally in an X direction. The print medium M accommodated in the accommodating tray  16  is conveyed in a −Y direction by the feeding roller  18 , turned around by the guide portion  20 , and conveyed in a +Y direction by the conveying roller  22 . 
     In the printing apparatus  10 , the print head  26  performs a print operation of ejecting ink to the print medium M supported by the platen  24  while moving in the X direction via the carriage  34  to make print corresponding to a single scan on the print medium M. Next, a conveyance operation is performed by conveying the print medium by a predetermined amount in the +Y direction to locate an area of the print medium M on which no print is made at a position facing the print head  26 . After that, the print operation is performed again. In this manner, the printing apparatus  10  alternately repeats the print operation and the conveyance operation, thereby printing an image on the print medium M. 
       FIGS.  2 A and  2 B  are schematic configuration diagrams of the ink storage portion  32 ;  FIG.  2 A  shows a state in which the ink accommodating member  36  is not yet mounted on the ink storage chamber  38  and  FIG.  2 B  shows a state in which the ink accommodating member  36  has been mounted on the ink storage chamber  38 . 
     The ink storage portion  32  comprises an ink accommodating member  36  which accommodates ink and an ink storage chamber  38  which stores the ink accommodated in the ink accommodating member  36 . The ink accommodating member  36  is attachable to and detachable from the ink storage chamber  38 . In the printing apparatus  10 , in a case where the remaining amount of ink in the ink storage chamber  38  reaches a certain amount, a user makes a replacement with a new ink accommodating member  36 . 
     The ink storage portion  32  is provided for each type of ink ejected from the print head  26 . Incidentally, the ink storage portions  32  have the same configuration irrespective of the type of ink except for part of the configuration of a pivot member  48  (described later). In the ink storage portion  32 , ink stored in the ink storage chamber  38  is supplied to the print head  26  through the tube (not shown). In a case where the ink is supplied from the ink storage chamber  38  to the print head  26  and the amount of ink is reduced in the ink storage chamber  38 , the ink storage chamber  38  is supplied with ink from the connected ink accommodating member  36 . 
     The ink accommodating member  36  comprises a main body portion  40  and a lid portion  42 . The main body portion  40  accommodates ink therein. The bottom of the main body portion  40  is provided with a supply portion  44  connected to a connecting member  47  (described later) in the ink storage chamber  38  and capable of supplying ink to the ink storage chamber  38 . That is, in the present embodiment, the ink accommodating member  36  is attachable to and detachable from the ink storage chamber  38  via the supply portion  44 . The supply portion  44  comprises an open/close mechanism such as a valve spring structure. In the lid portion  42  is formed an air communication port  46  which allows communication between the inside and outside of the ink accommodating member  36 . 
     The ink storage chamber  38  comprises the connecting member  47  connected to the ink accommodating member  36  via the supply portion  44 . The pivot member  48  is provided at a bottom  38   a  in the ink storage chamber  38 . The pivot member  48  is pivotally supported by the support member  50  at the bottom  38   a.  Accordingly, in a case where the ink storage chamber  38  is supplied with ink, the pivot member  48  is immersed in the ink. In the ink storage chamber  38 , a sensor  52  capable of detecting the pivot motion of the pivot member  48  is also provided above the pivot member  48 . Incidentally, the sensor  52  is provided in the ink storage chamber  38  but is not limited to this and may be provided separately from the ink storage chamber  38  as long as the pivot motion of the pivot member  48  can be detected. In the ink storage chamber  38 , an air communication port  54  which allows communication between the inside and outside of the ink storage chamber  38  is formed at a position not reached by a liquid surface of the stored ink. 
     The pivot member  48  comprises a float  56  which extends in the Y direction, an arm portion  58  which extends upward (substantially in a Z direction) from the float  56 , and a detection target portion  60  located at the end of the arm portion  58 . The float  56  is formed of a material lower in specific gravity than an ink stored in the ink accommodating member  36 . The float  56  is pivotally supported by a shaft  62  extending in the X direction in the support member  50  at the bottom of one side in the extending direction (Y direction). The detection target portion  60  is located above the float  56  via the arm portion  58 . Thus, the detection target portion  60  is movable according to the pivot motion of the float  56 . The detection target portion  60  is formed of a material detectable by the sensor  52 . Incidentally, as will be described later, since the sensor  52  of the present embodiment is an optical sensor comprising a light emitting portion and a light receiving portion, the detection target portion  60  is formed of a material which shields or attenuates light from the light emitting portion. 
     The sensor  52  is a detection unit which detects the pivot motion of the pivot member  48  and thereby optically detects that the height of the liquid surface of the ink stored in the ink storage chamber  38  becomes lower than a predetermined position. In a case where the height of the liquid surface of the ink becomes lower than the predetermined position, the printing apparatus  10  determines that the ink stored in the ink storage chamber  38  becomes equal to or less than a predetermined amount. More specifically, the sensor  52  comprises a light emitting portion (not shown) and a light receiving portion (not shown). In  FIGS.  2 A and  2 B , the light emitting portion and the light receiving portion are arranged so as to face each other with an interval in the X direction. In a case where the pivot member  48  pivots, the detection target portion  60  passes between the light emitting portion and the light receiving portion. The sensor  52  outputs a detection signal which differs according to reception of light output from the light emitting portion by the light receiving portion. 
     More specifically, for example, in a case where light output from the light emitting portion cannot be received by the light receiving portion, that is, in a case where a received light intensity is less than a predetermined intensity, the sensor  52  outputs a low-level signal indicating a signal having a signal level lower than a threshold level. The output low-level signal is accepted by a control portion (not shown) mounted on a main board (not shown). On acceptance of the low-level signal, the control portion detects that the height of the liquid surface of the ink is equal to or higher than the predetermined position. 
     On the other hand, in a case where light output from the light emitting portion can be received by the light receiving portion, that is, in a case where a received light intensity is equal to or greater than a predetermined intensity, the sensor  52  outputs a high-level signal indicating a signal having a signal level equal to or higher than a threshold level. The output high-level signal is accepted by the control portion and the control portion detects that the height of the liquid surface of the ink is lower than the predetermined position. 
     In a case where the ink accommodating member  36  is connected to the connecting member  47  of the ink storage chamber  38  with no ink stored (see  FIG.  2 A ) via the supply portion  44 , ink in the ink accommodating member  36  flows into the ink storage chamber  38  through the supply portion  44  and the connecting member  47 . In a case where a certain amount of ink is stored in the ink storage chamber  38 , the buoyancy acting on the float  56  lower in specific gravity than the ink exceeds the gravity and the pivot member  48  (float  56 ) pivots in an arrow A direction. This pivot motion of the pivot member  48  in the arrow A direction moves the detection target portion  60  in an arrow B direction. 
     In a case where ink further flows in and the height of the liquid surface of the ink thereby becomes equal to or higher than the predetermined position in the ink storage chamber  38 , the detection target portion  60  moves in the arrow B direction to a position between the light emitting portion and light receiving portion of the sensor  52 . The height of the liquid surface of the ink being equal to or higher than the predetermined position in the ink storage chamber  38  means that a predetermined amount or more of ink is stored in the ink storage chamber  38 . Incidentally, while the height of the liquid surface of the ink is equal to or higher than the predetermined position, the detection target portion  60  remains in between the light emitting portion and the light receiving portion (see  FIG.  2 B ). As stated above, in a case where the height of the liquid surface of the ink is equal to or higher than the predetermined position, since light output from the light emitting portion is prevented from being received by the light receiving portion (or attenuated before reaching the light receiving portion) by the detection target portion  60 , the sensor  52  outputs a low-level signal to the control portion. The control portion thus detects that the height of the liquid surface of the ink is equal to or higher than the predetermined position. 
       FIGS.  3 A and  3 B  are diagrams illustrating a motion of the pivot member  48  in a case where ink is reduced in the ink storage chamber  38 .  FIG.  3 A  is a diagram showing the pivot member  48  in a case where the liquid surface of the ink in the ink storage chamber  38  is equal to or higher than the predetermined position.  FIG.  3 B  is a diagram showing the pivot member  48  in a case where the liquid surface of the ink in the ink storage chamber  38  is lower than the predetermined position. 
     Ink is supplied from the ink storage chamber  38  to the print head  26 , whereby ink is reduced in the ink storage chamber  38  and the ink accommodating member  36  and the liquid surface of the ink is lowered in the ink storage chamber  38  (see  FIG.  3 A ). In a case where the amount of ink is reduced in the ink storage chamber  38  and the stored ink becomes less than a certain amount, the gravity exceeds the buoyancy acting on the float  56 . This causes the pivot member  48  (float  56 ) to pivot in an arrow C direction. This pivot motion of the pivot member  48  in the arrow C direction moves the detection target portion  60  in an arrow D direction. 
     In a case where the print head  26  is further supplied with ink and the height of the liquid surface of the ink thereby becomes lower than the predetermined position in the ink storage chamber  38 , the detection target portion  60  moves in the arrow D direction to a position away from between the light emitting portion and light receiving portion of the sensor  52 . Incidentally, while the height of the liquid surface of the ink is lower than the predetermined position, the target portion  60  remains at the position away from between the light emitting portion and light receiving portion, that is, stays away from the sensor  52  (see  FIG.  3 B ). Accordingly, in case where the height of the liquid surface of the ink is lower than the predetermined position, since light output from the light emitting portion can be received by the light receiving portion (or can reach the light receiving portion without attenuation), the sensor  52  outputs a high-level signal to the control portion. The control portion thus detects that the height of the liquid surface of the ink is lower than the predetermined position. 
     In the printing apparatus  10 , at the time of detecting that the height of the liquid surface of the ink becomes lower than the predetermined position, for example, a display portion  17  (see  FIG.  1 A ) provided in the printing apparatus  10  makes a notification to prompt a user to replace the ink accommodating member  36 . A user generally checks the notification displayed on the display portion  17  and replaces the ink accommodating member  36 . However, a small amount of ink still remains in the ink storage chamber  38  and a certain number of sheets can be printed even after it is detected that the height of the liquid surface of the ink becomes lower than the predetermined position. Thus, the printing apparatus  10  counts the number of ink droplets ejected from the time of detecting that the height of the liquid surface of the ink becomes lower than the predetermined position and notifies that ink has run out at the timing when it becomes likely that ink cannot be supplied from the ink storage chamber  38  to the print head  26 . 
     Incidentally, in recent years, types of inks for use in a printing apparatus have been used in multiple ways and a single printing apparatus has been configured to use multiple types of inks. Accordingly, in a case where the printing apparatus comprises a plurality of ink storage portions  32  completely identical in configuration for respective inks, some inks may be different in specific gravity, which may make a difference in buoyancy acting on the float. As a result, it may be impossible to correctly detect that the height of the liquid surface of ink becomes lower than the predetermined position. 
     It will be explained in detail with reference to  FIGS.  4 A to  4 C  that a difference in specific gravity between inks makes it impossible to correctly detect that the height of the liquid surface of ink becomes lower than the predetermined position.  FIGS.  4 A to  4 C  are diagrams showing differences in the state of the pivot member and the remaining amount of ink in the case of using inks different in specific gravity.  FIG.  4 A  shows the case of using an ink having a specific gravity a certain amount less than a reference specific gravity.  FIG.  4 B  shows the case of using an ink having the reference specific gravity.  FIG.  4 C  shows the case of using an ink having a specific gravity a certain amount greater than the reference specific gravity. Incidentally, the pivot member is a pivot member  48 R having such a specific gravity that in the case of using a reference ink  400 , it can be correctly detected that the height of the liquid surface of the ink  400  in the ink storage chamber  38  becomes lower than the predetermined position. The specific gravity of the pivot member  48 R is less than a specific gravity of an ink  402 , which is a certain amount less than that of the reference ink  400 . 
     In the case of using the ink  400  having the reference specific gravity, if a liquid surface Ls of the ink  400  reaches a height hr in the ink storage chamber  38 , the detection target portion  60  of the pivoting pivot member  48 R gets away from the sensor  52  (see  FIG.  4 B ). At this time, the printing apparatus  10  detects that the height of the liquid surface of the ink becomes lower than the predetermined position. That is, in this case, the buoyancy exerted on the pivot member  48 R is less than the gravity acting on the pivot member  48 R at the height hr. 
     In the case of using the ink  402  having the specific gravity lower than the reference specific gravity of the ink  400 , if the liquid surface Ls of the ink  402  reaches a height hl in the ink storage chamber  38 , the detection target portion  60  of the pivoting pivot member  48 R gets away from the sensor  52  (see  FIG.  4 A ). That is, the buoyancy exerted on the pivot member  48 R (float  56 R) is less than the gravity acting on the pivot member  48 R at the height hl higher than the height hr. Accordingly, the printing apparatus  10  detects that the height of the liquid surface of the ink becomes lower than the predetermined position in a case where the liquid surface Ls reaches the height hl. The ink  402  is lower in specific gravity than the ink  400 . Thus, in the ink storage chamber  38 , the buoyancy exerted on the pivot member  48 R (float  56 R) by the ink  402  is less than the buoyancy exerted on the pivot member  48 R by the ink  400 . As a result, in a case where the liquid surface height reaches the height hl at which a greater amount of ink remains, the detection target portion  60  gets away from the sensor  52 . 
     In the case of using an ink  404  having a specific gravity higher than the reference specific gravity of the ink  400 , if the liquid surface Ls of the ink  404  reaches a height hh in the ink storage chamber  38 , the detection target portion  60  of the pivoting pivot member  48 R gets away from the sensor  52  (see  FIG.  4 C ). That is, the buoyancy exerted on the pivot member  48 R is less than the gravity acting on the pivot member  48 R at the height hh lower than the height hr. Thus, in a case where the liquid surface Ls reaches the height hh, the printing apparatus  10  detects that the height of the liquid surface of the ink becomes lower than the predetermined position. The ink  404  is higher in specific gravity than the ink  400 . Thus, in the ink storage chamber  38 , the buoyancy exerted on the pivot member  48 R by the ink  404  is greater than the buoyancy exerted on the pivot member  48 R by the ink  400 . As a result, in a case where the liquid surface height reaches the height hh at which a less amount of ink remains, the detection target portion  60  gets away from the sensor  52 . 
     As explained above, in a case where the ink storage chambers  38  of the same configuration comprising the pivot member  48 R are used for the inks different in specific gravity, the liquid surface height at which it is detected that the liquid surface becomes lower than the predetermined position, that is, the liquid surface height at which the detection target portion  60  gets away from the sensor  52 , differs according to the specific gravity of an ink. The printing apparatus  10  is configured to count the number of ink droplets ejected after making a notification to prompt replacement of the ink accommodating member  36  and, in a case where the count reaches a predetermined number, notify that the ink has run out. Accordingly, there is a possibility that the ink runs out before the timing of notifying that the ink has run out or a printable amount of ink still remains even at that timing. 
     Therefore, in the present embodiment, the specific gravity of the pivot member  48 , more specifically the specific gravity of the float  56  is changed according to the specific gravity of an ink. This will be described below in detail with reference to  FIGS.  5 A and  5 B .  FIGS.  5 A and  5 B  are diagrams showing a change of specific gravity of the float according to the specific gravity of an ink;  FIG.  5 A  shows the case of storing an ink lower in specific gravity than the reference ink and  FIG.  5 B  shows the case of storing an ink higher in specific gravity than the reference ink. 
     In the ink storage chamber  38  storing the ink  402  low in specific gravity, a pivot member  48 L with a float  56 L low in specific gravity is used as the pivot member  48  (see  FIG.  5 A ). The float  56 L is lower in specific gravity than the float  56 R of the pivot member  48 R capable of appropriately detecting that the liquid surface height of the reference ink  400  becomes lower than the predetermined position. The specific gravity of the float  56 L is adjusted to such a specific gravity as to appropriately detect that the liquid surface height of the ink  402  becomes lower than the predetermined position. That is, the specific gravity of the float  56 L is adjusted to such a specific gravity that the detection target portion  60  gets away from the sensor  52  in a case where the liquid surface height of the ink  402  reaches the height hr. More specifically, the specific gravity of the float  56 L is adjusted such that a difference in specific gravity between the ink  402  and the float  56 L is equal to a difference in specific gravity between the ink  400  and the float  56 R. Incidentally, the equality of the difference in specific gravity between the ink  402  and the float  56 L with the difference in specific gravity between the ink  400  and the float  56 R is not limited to exact equality between these differences and includes a case where they are both within a predetermined range. 
     In the ink storage chamber  38  storing the ink  404  high in specific gravity, a pivot member  48 H with a float  56 H high in specific gravity is used as the pivot member  48  (see  FIG.  5 B ). The float  56 H is higher in specific gravity than the float  56 R of the pivot member  48 R capable of appropriately detecting that the liquid surface height of the ink  400  becomes lower than the predetermined position. The specific gravity of the float  56 H is adjusted to such a specific gravity as to appropriately detect that the liquid surface height of the ink  404  becomes lower than the predetermined position. That is, the specific gravity of the float  56 H is adjusted to such a specific gravity that the detection target portion  60  gets away from the sensor  52  in a case where the liquid surface height of the ink  404  reaches the height hr. More specifically, the specific gravity of the float  56 H is adjusted such that a difference in specific gravity between the ink  404  and the float  56 H is equal to a difference in specific gravity between the ink  400  and the float  56 R. Incidentally, the equality of the difference in specific gravity between the ink  404  and the float  56 H with the difference in specific gravity between the ink  400  and the float  56 R is not limited to exact equality between these differences and includes a case where they are both within a predetermined range. 
     Accordingly, in a case where the printing apparatus  10  is configured to use a plurality of inks different in specific gravity, each ink storage chamber  38  is provided with a pivot member  48  comprising a float  56  having a specific gravity adjusted according to the specific gravity of a stored ink. At this time, all the ink storage chambers  38  are equal to one another in a difference in specific gravity between the stored ink and the float  56  (including a case where the differences are all within a predetermined range). 
     As explained above, in the printing apparatus  10 , the specific gravity of the float  56  in the pivot member  48  is changed according to the specific gravity of an ink stored in the ink storage chamber  38 . This makes it possible to appropriately detect that the liquid surface height of an ink stored in the ink storage chamber  38  becomes lower than the predetermined position. As a result, depending on the type of ink, a notification that the ink has run out can be made at an appropriate timing after the issuance of a notification to prompt replacement of the ink accommodating member  36 . 
     Second Embodiment 
     Next, a liquid ejection apparatus according to a second embodiment will be described with reference to  FIGS.  6 A to  6 C . The following description shows an example of a printing apparatus which performs printing by ejecting ink to a print medium like the first embodiment described above. Further, a detailed description of constituents identical or corresponding to those of the printing apparatus according to the first embodiment will be omitted as appropriate by using the same reference numerals. 
     A liquid ejection apparatus  10  according to the second embodiment is different from that of the first embodiment in that the size of the float  56  is changed according to the specific gravity of an ink. 
       FIGS.  6 A to  6 C  are diagrams showing a change of size of a float according to the specific gravity of an ink;  FIG.  6 A  shows the case of storing an ink lower in specific gravity than the reference ink,  FIG.  6 B  shows the case of the reference ink, and  FIG.  6 C  shows the case of storing an ink higher in specific gravity than the reference ink. 
     In the case of using the ink  400  having the reference specific gravity, if the liquid surface Ls of the ink  400  reaches a height hr in the ink storage chamber  38 , the detection target portion  60  of the pivoting pivot member  48 R gets away from the sensor  52  (see  FIG.  6 B ). At this time, the printing apparatus  10  detects that the height of the liquid surface of the ink becomes lower than the predetermined position. That is, in a case where the liquid surface height is the height hr, the buoyancy exerted on the pivot member  48 R is less than the gravity acting on the pivot member  48 R. In the description with reference to  FIGS.  6 A to  6 C , it is assumed that the detection can be made appropriately at this time. 
     In the ink storage chamber  38  storing the ink  402  low in specific gravity, a pivot member  48 Sm with a small-sized float  56 Sm is used as the pivot member  48  (see  FIG.  6 A ). The float  56 Sm is smaller in size than a float  56 Me of a pivot member  48 Me capable of appropriately detecting that the liquid surface height of the reference ink  400  becomes lower than the predetermined position. The float  56 Sm is adjusted to such a size as to appropriately detect that the liquid surface height of the ink  402  becomes lower than the predetermined position. That is, the float  56 Sm is adjusted to such a size that the detection target portion  60  gets away from the sensor  52  in a case where the liquid surface height of the ink  402  reaches the height hr. More specifically, the size of the float  56 Sm is adjusted such that a buoyancy experienced by the float  56 Me in a case where the liquid surface height of the ink  400  is the height hr is equal to a buoyancy experienced by the float  56 Sm in a case where the liquid surface height of the ink  402  is the height hr. Incidentally, the equality of the buoyancy experienced by the float  56 Me in the case where the liquid surface height of the ink  400  is the height hr with the buoyancy experienced by the float  56 Sm in the case where the liquid surface height of the ink  402  is the height hr is not limited to exact equality between these buoyancies and includes a case where the buoyancies are both within a predetermined range. 
     In the ink storage chamber  38  storing the ink  404  high in specific gravity, a pivot member  48 La with a large-sized float  56 La is used as the pivot member  48  (see  FIG.  6 C ). The float  56 La is larger in size than the float  56 Me of the pivot member  48 Me capable of appropriately detecting that the liquid surface height of the ink  400  becomes lower than the predetermined position. The float  56 La is adjusted to such a size as to appropriately detect that the liquid surface height of the ink  404  becomes lower than the predetermined position. That is, the float  56 La is adjusted to such a size that the detection target portion  60  gets away from the sensor  52  in a case where the liquid surface height of the ink  404  reaches the height hr. More specifically, the size of the float  56 La is adjusted such that the buoyancy experienced by the float  56 Me in the case where the liquid surface height of the ink  400  is the height hr is equal to a buoyancy experienced by the float  56 La in the case where the liquid surface height of the ink  404  is the height hr. Incidentally, the equality of the buoyancy experienced by the float  56 Me in the case where the liquid surface height of the ink  400  is the height hr with the buoyancy experienced by the float  56 La in a case where the liquid surface height of the ink  404  is the height hr is not limited to exact equality between these buoyancies and includes a case where the buoyancies are both within a predetermined range. 
     Accordingly, in a case where the printing apparatus  10  is configured to use a plurality of inks different in specific gravity, each ink storage chamber  38  is provided with a pivot member  48  comprising a float  56  having a size adjusted according to the specific gravity of a stored ink. At this time, all the ink storage chambers  38  are equal to one another in a buoyancy acting on the float  56  (including a case where the buoyancies are all within a predetermined range). 
     As explained above, in the printing apparatus  10  according to the second embodiment, the size of the float  56  in the pivot member  48  is changed according to the specific gravity of an ink stored in the ink storage chamber  38 . As a result, the printing apparatus  10  according to the second embodiment can produce the same advantageous result as the printing apparatus  10  according to the first embodiment. 
     Other Embodiments 
     The embodiments described above may be modified as stated in (1) to (4) below. 
     (1) In the above embodiments, the pivot member  48  is provided in the ink storage chamber  38 , but is not limited to this. That is, the pivot member  48  may be provided in the ink accommodating member  36 . In this case, the sensor  52  is provided such that the pivot member  48  provided in the ink accommodating member  36  can be detected with the ink accommodating member  36  connected to the ink storage chamber  38 . In the above embodiments, only one of the specific gravity and size of the float  56  is changed according to the specific gravity of an ink, but the target to be changed is not limited to this. That is, both of the specific gravity and size of the float  56  may be changed. It is only necessary to change at least one of the specific gravity and size of the float  56  according to the specific gravity of an ink. 
     (2) The above embodiments are not only applied to a printing apparatus which performs printing on a print medium by ejecting ink from a print head but also universally applicable to a liquid ejection apparatus which performs various types of processing by ejecting various liquids from an liquid ejection head. In addition, the printing apparatus  10  is a so-called serial scan type printing apparatus which ejects ink from a print head moving in the X direction to a print medium conveyed in the Y direction in the above embodiments, but is not limited to this. That is, it is also possible to use a so-called full line type print head using an elongate print head covering the entire width of a print area of a print medium. 
     (3) In the above embodiments, the pivot member  48  and the sensor  52  are used to determine whether the liquid surface height of the ink stored in the ink storage chamber  38  is lower than the predetermined position. However, the configuration to detect the amount of ink in the ink storage chamber  38  is not limited to this. That is, a sensor capable of detecting a pivot angle of the pivot member  48  from a reference position may be provided such that the remaining amount of ink stored in the ink storage chamber  38  is gradually or continuously detected based on the pivot angle of the pivot member  48 . Further, although not particularly described in the above embodiments, a printing apparatus configured to eject only an ink of a single color uses an ink storage portion  32  comprising a pivot member  48  with a float  56  of a specific gravity corresponding to the specific gravity of an ink to be ejected. Alternatively, the printing apparatus uses an ink storage portion  32  comprising a float  56  of a size corresponding to the specific gravity of the ink. 
     (4) The above embodiments and various forms shown in (1) to (3) above may be combined as appropriate. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2021-176496, filed Oct. 28, 2021, which is hereby incorporated by reference wherein in its entirety.