Patent Publication Number: US-11046081-B2

Title: Printer

Description:
The present application is based on, and claims priority from JP Application Serial Number 2019-022317, filed Feb. 12, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a printer and the like. 
     2. Related Art 
     In the related art, there is known a method for determining whether ink is present in an ink container in a printer that performs printing by using ink. For example, in JP-A-2001-105627, an ink supply device that detects a liquid level of ink by receiving light emitted from a light emitter and passing through an ink bottle by using a light receiver is disclosed. 
     Further improvements of the printer have been required. 
     SUMMARY 
     An aspect of the present disclosure relates to a printer including an ink tank, a print head performing printing by using ink in the ink tank, a light source irradiating the ink tank with light, a photoelectric conversion device detecting light incident from the ink tank in a period during which the light source emits light, and a processing unit determining ink characteristics of ink in the ink tank based on characteristics of a light amount detected by the photoelectric conversion device. In this way, the ink characteristics in the ink tank can be determined by using the light source and the photoelectric conversion device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective diagram illustrating a configuration of an electronic apparatus. 
         FIG. 2  is a diagram for explaining an arrangement of ink tanks in the electronic apparatus. 
         FIG. 3  is a perspective diagram of the electronic apparatus in a state where a lid of an ink tank unit is opened. 
         FIG. 4  is a perspective diagram illustrating a configuration of the ink tank. 
         FIG. 5  is a diagram illustrating a configuration example of a printer unit and the ink tank unit. 
         FIG. 6  is an exploded diagram of a sensor unit. 
         FIG. 7  is a diagram illustrating a positional relationship between a substrate, a photoelectric conversion device, and a light source. 
         FIG. 8  is a sectional diagram of the sensor unit. 
         FIG. 9  is a diagram for explaining a positional relationship between the ink tank, the light source, and the photoelectric conversion device. 
         FIG. 10  is a diagram for explaining a positional relationship between the light source and a light guide. 
         FIG. 11  is a diagram for explaining a positional relationship between the light source and the light guide. 
         FIG. 12  is a diagram for explaining a positional relationship between the light source and the light guide. 
         FIG. 13  is a diagram illustrating a configuration example of the sensor unit and a processing unit. 
         FIG. 14  is a diagram illustrating a configuration example of the photoelectric conversion device. 
         FIG. 15  is a perspective diagram of an electronic apparatus including a window portion. 
         FIG. 16  is a schematic diagram when a lens array is provided as an optical separator. 
         FIG. 17  is a schematic diagram when a resin slit is provided as an optical separator. 
         FIG. 18  is a schematic diagram when an optical separator is provided on a side surface of an ink tank. 
         FIG. 19  is a diagram illustrating a configuration example of an optical separator provided on a side surface of an ink tank. 
         FIG. 20  is a diagram illustrating a configuration example of an optical separator provided on a side surface of an ink tank. 
         FIG. 21  is a diagram illustrating a configuration example of an optical separator provided on a side surface of an ink tank. 
         FIG. 22  is a schematic diagram when an optical separator is omitted. 
         FIG. 23  is a diagram for explaining a positional relationship between a light source and a light guide. 
         FIG. 24  is a diagram for explaining a positional relationship between a light source, a light guide, and a photoelectric conversion device. 
         FIG. 25  is a diagram for explaining a positional relationship between an ink tank, a light source, and a photoelectric conversion device. 
         FIG. 26  is an exploded diagram of a light receiving unit. 
         FIG. 27  is an exploded diagram of a light emitting unit. 
         FIG. 28  is a diagram for explaining a positional relationship between an ink tank, a light source, and a photoelectric conversion device. 
         FIG. 29  is an exploded diagram illustrating another configuration of a sensor unit. 
         FIG. 30  is a sectional diagram illustrating another configuration of a sensor unit. 
         FIG. 31  is a diagram illustrating an example of output data of a photoelectric conversion device. 
         FIG. 32  is a flowchart for explaining ink amount detection processing. 
         FIG. 33  is a schematic diagram illustrating an ink tank to which an ink droplet is attached and output data at that time. 
         FIG. 34  is a flowchart for explaining ink amount detection processing in consideration of an ink droplet. 
         FIG. 35  is a diagram for explaining correction processing with respect to output data. 
         FIG. 36  is a schematic diagram for explaining an assembly error. 
         FIG. 37  is a diagram for explaining ink amount detection processing based on a mark. 
         FIG. 38  is a schematic diagram illustrating an ink tank with a mark and output data. 
         FIG. 39  is a diagram illustrating an example of a relationship between a slit and a mark provided on a side surface of an ink tank. 
         FIG. 40  is a schematic diagram when a photoelectric conversion device is inclined with respect to an ink tank. 
         FIG. 41  is a schematic diagram when a plurality of photoelectric conversion devices are provided in a horizontal direction with respect to one ink tank. 
         FIG. 42  is an explanatory diagram of a method for detecting an inclination of a photoelectric conversion device with respect to an ink tank. 
         FIG. 43  is an explanatory diagram of a method for detecting an inclination of an ink tank with respect to a horizontal plane. 
         FIG. 44  is a diagram illustrating a relationship between output data of yellow ink and output data of magenta ink. 
         FIG. 45  is a diagram illustrating a relationship between output data of magenta dye ink and output data of magenta pigment ink. 
         FIG. 46  is a perspective diagram of an electronic apparatus when a scanner unit is used. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, the present embodiments will be described. The present embodiments described below do not unduly limit the content described in claims. Also, not all configurations described in the present embodiment are essential configuration requirements. 
     1. Configuration Example of Electronic Apparatus 
     1.1 Basic Configuration of Electronic Apparatus 
       FIG. 1  is a perspective diagram of an electronic apparatus  10  according to the present embodiment. The electronic apparatus  10  is a multifunction peripheral (MFP) including a printer unit  100  and a scanner unit  200 . The electronic apparatus  10  may have other functions such as a facsimile function in addition to a printing function and a scanning function. Alternatively, only the printing function may be provided. The electronic apparatus  10  includes an ink tank unit  300  that accommodates ink tanks  310 . The printer unit  100  is an ink jet printer which executes printing by using ink supplied from the ink tanks  310 . Hereinafter, the description of the electronic apparatus  10  can be appropriately replaced with a printer. 
       FIG. 1  illustrates a Y-axis, an X-axis orthogonal to the Y-axis, and a Z-axis orthogonal to the X-axis and the Y-axis. In each of the XYZ axes, a direction of an arrow indicates a positive direction, and a direction opposite from the direction of the arrow indicates a negative direction. Hereinafter, the positive direction of the X-axis is described as +X direction and the negative direction is described as −X direction. The same applies to the Y-axis and the Z-axis. The electronic apparatus  10  is disposed on a horizontal plane defined by the X-axis and the Y-axis in a use state, and the +Y direction is the front of the electronic apparatus  10 . The Z-axis is an axis orthogonal to the horizontal plane, and −Z direction is vertically downward direction. 
     The electronic apparatus  10  has an operation panel  101  as a user interface unit. The operation panel  101  is provided with buttons for performing, for example, an ON/OFF operation of a power supply of the electronic apparatus  10 , an operation related to printing using the printing function, and an operation related to reading of a document using the scanning function. The operation panel  101  is also provided with a display unit  150  for displaying an operating state of the electronic apparatus  10  and a message or the like. Further, the display unit  150  displays the ink amount detected by the method described later. Further, the operation panel  101  may be provided with a reset button for the user to replenish ink in the ink tank  310  to execute reset processing. 
     1.2 Printer Unit and Scanner Unit 
     The printer unit  100  performs printing on a printing medium P such as printing paper by ejecting ink. The printer unit  100  has a case  102  which is an outer shell of the printer unit  100 . On a front side of the case  102 , a front cover  104  is provided. Here, the “front” represents a face on which the operation panel  101  is provided and represents a face in +Y direction of the electronic apparatus  10 . The operation panel  101  and the front cover  104  are pivotable around the X-axis with respect to the case  102 . The electronic apparatus  10  includes a paper cassette (not illustrated), and the paper cassette is provided in the −Y direction with respect to the front cover  104 . The paper cassette is coupled to the front cover  104  and detachably attached to the case  102 . A paper discharge tray (not illustrated) is provided in the +Z direction of the paper cassette, and the paper discharge tray can be expanded and contracted in the +Y direction and the −Y direction. The paper discharge tray is provided in the −Y direction with respect to the operation panel  101  in the state illustrated in  FIG. 1 , and exposed to the outside by the pivoting of the operation panel  101 . 
     The X-axis is a main scanning axis HD of a print head  107 , and the Y-axis is a sub-scanning axis VD of the printer unit  100 . A plurality of printing media P are placed in a stacked state on the paper cassette. The printing media P placed on the paper cassette are supplied one by one into the case  102  along the sub-scanning axis VD, printed by the printer unit  100 , discharged along the sub-scanning axis VD, and placed on the paper discharge tray. 
     The scanner unit  200  is mounted on the printer unit  100 . The scanner unit  200  has a case  201 . The case  201  constitutes the outer shell of the scanner unit  200 . The scanner unit  200  is of a flat bed type and has a document table formed of a transparent plate-like member such as glass and an image sensor. The scanner unit  200  reads an image or the like recorded on a medium such as paper as image data via an image sensor. The electronic apparatus  10  may be provided with an automatic document feeder (not illustrated). The scanner unit  200  sequentially feeds a plurality of stacked documents while reversing them one by one by the automatic document feeder, and reads them by using the image sensor. 
     1.3 Ink Tank Unit and Ink Tank 
     The ink tank unit  300  has a function of supplying ink IK to the print head  107  included in the printer unit  100 . The ink tank unit  300  includes a case  301 , and the case  301  has a lid  302 . A plurality of ink tanks  310  are accommodated in the case  301 . 
       FIG. 2  is a diagram illustrating a state of the ink tanks  310  being accommodated. A portion indicated by a solid line in  FIG. 2  represents the ink tanks  310 . A plurality of inks IK of different kinds are individually accommodated in the plurality of ink tanks  310 . That is, different kinds of inks IK are accommodated in the plurality of ink tanks  310  for each ink tank  310 . 
     In the example illustrated in  FIG. 2 , the ink tank unit  300  accommodates five ink tanks  310   a ,  310   b ,  310   c ,  310   d , and  310   e . In the present embodiment, five kinds of inks are adopted, as the kinds of inks: two kinds of black inks, color inks of yellow, magenta, and cyan. Two kinds of black inks are pigment ink and dye ink. Ink IKa which is black pigment ink is accommodated in the ink tank  310   a . The respective color inks IKb, IKc, and IKd of yellow, magenta, and cyan are accommodated in the ink tanks  310   b ,  310   c , and  310   d . Ink IKe which is a black dye ink is accommodated in the ink tank  310   e.    
     The ink tanks  310   a ,  310   b ,  310   c ,  310   d , and  310   e  are arranged side by side in this order along the +X direction, and fixed in the case  301 . Hereinafter, when the five ink tanks  310   a ,  310   b ,  310   c ,  310   d , and  310   e  and the five kinds of inks IKa, IKb, IKc, IKd, and IKe are not distinguished, they are simply expressed as the ink tank  310  and the ink IK. 
     In the present embodiment, ink IK is configured to be able to be filled into the ink tank  310  from the outside of the electronic apparatus  10  for each of the five ink tanks  310 . Specifically, the user of the electronic apparatus  10  fills to replenish ink IK accommodated in another container into the ink tank  310 . 
     In the present embodiment, the capacity of the ink tank  310   a  is larger than the capacities of the ink tanks  310   b ,  310   c ,  310   d , and  310   e . The capacities of the ink tanks  310   b ,  310   c ,  310   d , and  310   e  are the same as each other. In the printer unit  100 , it is assumed that the black pigment ink IKa is consumed more than that of the color inks IKb, IKc, and IKd and the black dye ink IKe. The ink tank  310   a  accommodating the black pigment ink IKa is disposed at a position close to the center of the electronic apparatus  10  on the X-axis. In this way, for example, when the case  301  has a window portion  103  as illustrated in  FIG. 15  described later, the remaining amount of ink that is frequently used is easily confirmed. However, the arrangement order of the five ink tanks  310   a ,  310   b ,  310   c ,  310   d , and  310   e  is not particularly limited. When any one of the other inks IKb, IKc, IKd, and IKe is consumed more than the black pigment ink IKa, the ink IK may be accommodated in the ink tank  310   a  of a large capacity. 
       FIG. 3  is a perspective diagram of the electronic apparatus  10  in a state where the lid  302  of the ink tank unit  300  is opened. The lid  302  is pivotable with respect to the case  301  via a hinge portion  303 . When the lid  302  is opened, five ink tanks  310  are exposed. More specifically, five caps corresponding to each ink tank  310  are exposed by opening the lid  302 , and a portion of the ink tank  310  in the +Z direction is exposed by opening the caps. A portion of the ink tank  310  in the +Z direction is an area including an ink filling port  311  of the ink tank  310 . When the ink IK is filled into the ink tank  310 , the user accesses the ink tank  310  by pivoting the lid  302  and opening it upward. 
       FIG. 4  is a diagram illustrating the configuration of the ink tank  310 . Each axis of X, Y, and Z in  FIG. 4  indicates an axis in a state where the electronic apparatus  10  is used in a normal posture and the ink tank  310  is appropriately fixed to the case  301 . Specifically, the X-axis and the Y-axis are axes along the horizontal direction, and the Z-axis is an axis along a vertical direction. For each axis of XYZ, unless otherwise specified, the same shall apply in the following drawings. The ink tank  310  is a three-dimensional body in which the ±X direction is a short side direction and the ±Y direction is a longitudinal direction. Hereinafter, of the surfaces of the ink tank  310 , a surface in the +Z direction is referred to as an upper surface, a surface in the −Z direction is referred to as a bottom surface, and surfaces in the ±X direction and ±Y direction are referred to as side surfaces. The ink tank  310  is formed of a synthetic resin such as nylon or polypropylene, for example. 
     When the ink tank unit  300  includes a plurality of ink tanks  310  as described above, each of the plurality of ink tanks  310  may be configured separately or may be configured integrally. When the ink tank  310  is integrally configured, the ink tank  310  may be integrally formed, or a plurality of ink tanks  310  formed separately may be integrally bundled or coupled together. 
     The ink tank  310  includes the filling port  311  into which ink IK is filled by the user, and a discharging port  312  for discharging the ink IK toward the print head  107 . In the present embodiment, the upper surface of the portion on the +Y direction side that is a front side of the ink tank  310  is higher than the upper surface of the portion on the −Y direction side that is a rear side. The filling port  311  for filling ink IK from the outside is provided on the upper surface of the portion on the front side of the ink tank  310 . The filling port  311  is exposed by opening the lid  302  and the cap as described above with reference to  FIG. 3 . The ink IK of each color can be replenished to the ink tank  310  by filling the ink IK from the filling port  311  by the user. The ink IK for the user to replenish the ink tank  310  is accommodated and provided in a separate replenishing container. The discharging port  312  for supplying ink to the print head  107  is provided on the upper surface of the portion on the rear side of the ink tank  310 . Since the filling port  311  is provided on the side close to the front of the electronic apparatus  10 , filling of the ink IK can be facilitated. 
     1.4 Other Configurations of Electronic Apparatus 
       FIG. 5  is a schematic configuration diagram of the electronic apparatus  10  according to the present embodiment. As illustrated in  FIG. 5 , the printer unit  100  according to the present embodiment includes a carriage  106 , a paper feed motor  108 , a carriage motor  109 , a paper feed roller  110 , a processing unit  120 , a storage unit  140 , the display unit  150 , an operation unit  160 , and an external I/F unit  170 . In  FIG. 5 , the specific configuration of the scanner unit  200  is omitted.  FIG. 5  is a diagram exemplifying a coupling relationship between each part of the printer unit  100  and the ink tank unit  300 , and does not limit the physical structure or the positional relationship of each part. For example, in the arrangement of members such as the ink tank  310 , the carriage  106 , and a tube  105  in the electronic apparatus  10 , various embodiments can be considered. 
     The print head  107  is mounted on the carriage  106 . The print head  107  has a plurality of nozzles for ejecting ink IK in the −Z direction on the bottom surface side of the carriage  106 . The tube  105  is provided between the print head  107  and each ink tank  310 . Each ink IK in the ink tank  310  is sent to the print head  107  via the tube  105 . The print head  107  ejects each ink IK sent from the ink tanks  310  to the printing medium P from the plurality of nozzles as ink droplets. 
     The carriage  106  is driven by the carriage motor  109  to reciprocate along the main scanning axis HD on the printing medium P. The paper feed motor  108  rotationally drives the paper feed roller  110  to transport the printing medium P along the sub-scanning axis VD. The ejection control of the print head  107  is performed by the processing unit  120  via a cable. 
     In the printer unit  100 , printing is performed on the printing medium P by the carriage  106  ejecting the ink IK from the plurality of nozzles of the print head  107  to the printing medium P transported to the sub-scanning axis VD while moving along the main scanning axis HD, based on the control of the processing unit  120 . 
     One end portion of the carriage  106  on the main scanning axis HD in a moving area is a home position area where the carriage  106  stands by. In the home position area, for example, a cap or the like (not illustrated) for performing maintenance such as cleaning the nozzle of the print head  107  is disposed. Also, a waste ink box for receiving waste ink when flushing or cleaning of the print head  107  is performed is disposed in the moving area of the carriage  106 . The flushing means that ink IK is ejected from each nozzle of the print head  107  regardless of printing during printing of the printing medium P. The cleaning means cleaning the inside of the print head by sucking the print head by a pump or the like provided in the waste ink box, without driving the print head  107 . 
     Here, an off-carriage type printer in which the ink tank  310  is provided at a location different from the carriage  106  is assumed. However, the printer unit  100  may be an on-carriage type printer in which the ink tank  310  is mounted on the carriage  106  and moved along the main scanning axis HD together with the print head  107 . For example, in a printer for monochrome printing having one ink tank  310 , the amount of ink IK to be accommodated is small, and even when the ink tank  310  is mounted on the carriage  106 , the carriage is easily driven. 
     The operation unit  160  and the display unit  150  as a user interface unit are coupled to the processing unit  120 . The display unit  150  is for displaying various display screens and can be realized by, for example, a liquid crystal display or an organic EL display. The operation unit  160  is for the user to perform various operations and can be realized by various buttons, GUI, or the like. For example, as illustrated in  FIG. 1 , the electronic apparatus  10  includes the operation panel  101 , and the operation panel  101  includes the display unit  150  and a button or the like as the operation unit  160 . The display unit  150  and the operation unit  160  may be integrally configured by a touch panel. When the user operates the operation panel  101 , the processing unit  120  operates the printer unit  100  and the scanner unit  200 . 
     For example, in  FIG. 1 , the user operates the operation panel  101  to start operation of the electronic apparatus  10  after setting a document on a document table of the scanner unit  200 . Then, the document is read by the scanner unit  200 . Subsequently, based on the image data of the read document, the printing medium P is fed from the paper cassette into the printer unit  100 , and printing is performed on the printing medium P by the printer unit  100 . 
     An external device can be coupled to the processing unit  120  via the external I/F unit  170 . The external device here is, for example, a personal computer (PC). The processing unit  120  receives the image data from the external device via the external I/F unit  170 , and performs control for printing the image on the printing medium P by the printer unit  100 . In addition, the processing unit  120  controls the scanner unit  200  to read the document and transmit the image data as a reading result to the external device via the external I/F unit  170 , or to print the image data as the reading result. 
     The processing unit  120  performs, for example, drive control, consumption calculation processing, ink amount detection processing, and ink characteristics determination processing. The processing unit  120  of the present embodiment is configured by the following hardware. The hardware can include at least one of a circuit for processing a digital signal and a circuit for processing an analog signal. For example, the hardware can be configured by one or more circuit devices mounted on the circuit substrate or one or more circuit elements. The one or more circuit devices are, for example, ICs or the like. The one or more circuit elements are, for example, resistances, capacitors, or the like. 
     The processing unit  120  may be realized by the following processor. The electronic apparatus  10  of the present embodiment includes a memory that stores information, and a processor that operates based on information stored in the memory. The information is, for example, a program and various kinds of data. The processor includes hardware. As the processor, various processors such as a central processing unit (CPU), graphics processing unit (GPU), digital signal processor (DSP), or the like can be used. The memory may be semiconductor memory such as static random access memory (SRAM), dynamic random access memory (DRAM), or the like, and may be a register, or a magnetic storage device such as a hard disk device, or may be an optical storage device such as an optical disk device or the like. For example, the memory stores an instruction that can be read by a computer, and the function of each unit of the electronic apparatus  10  is realized as processing by executing the instruction by the processor. The instruction here may be an instruction of an instruction set constituting the program or an instruction for instructing the operation to the hardware circuit of the processor. 
     The processing unit  120  controls the carriage motor  109  to perform drive control for moving the carriage  106 . Based on the drive control, the carriage motor  109  drives to move the print head  107  provided on the carriage  106 . 
     The processing unit  120  performs the consumption calculation processing of calculating a consumption of ink consumed by ejecting the ink IK from each nozzle of the print head  107 . The processing unit  120  starts the consumption calculation processing with the state where each ink tank  310  is filled with the ink IK as an initial value. More specifically, when the user replenishes the ink IK to the ink tank  310  and presses a reset button, the processing unit  120  initializes a count value of the ink consumption with respect to the ink tank  310 . Specifically, the count value of the ink consumption is set to 0 g. The processing unit  120  starts the consumption calculation processing with the pressing operation of the reset button as a trigger. 
     The processing unit  120  performs ink amount detection processing of detecting the amount of ink IK accommodated in the ink tank  310 , based on the output of a sensor unit  320  provided corresponding to the ink tank  310 . The processing unit  120  performs ink characteristics determination processing of determining the characteristics of the ink IK accommodated in the ink tank  310 , based on the output of the sensor unit  320  provided corresponding to the ink tank  310 . Details of the ink amount detection processing and ink characteristics determination processing are described later. 
     1.5 Detailed Configuration Example of Sensor Unit 
       FIG. 6  is an exploded perspective diagram schematically illustrating the configuration of the sensor unit  320 . The sensor unit  320  includes a substrate  321 , a photoelectric conversion device  322 , a light source  323 , a light guide  324 , a lens array  325 , and a case  326 . 
     The light source  323  and the photoelectric conversion device  322  are mounted on the substrate  321 . The photoelectric conversion device  322  is a linear image sensor in which, for example, photoelectric conversion elements are arranged in a predetermined direction. The linear image sensor may be a sensor in which photoelectric conversion elements are arranged in one row or a sensor in which photoelectric conversion elements are arranged in two or more rows. The photoelectric conversion element is, for example, a photodiode (PD). A plurality of output signals based on a plurality of photoelectric conversion elements are acquired by using the linear image sensor. Therefore, not only whether the ink IK is present but also the position of the interface can be estimated. 
     The light source  323  has, for example, R, G, and B light emitting diodes (LED: Light emitting diode) and emits light sequentially while switching the R, G, and B light emitting diodes at high speed. The light emitting diode of R is represented as a red LED  323 R, the light emitting diode of G is represented as a green LED  323 G, and the light emitting diode of B is represented as a blue LED  323 B. The light guide  324  is a rod-like member for guiding light, and the cross-sectional shape may be a square shape, a circular shape, or another shape. The longitudinal direction of the light guide  324  is a direction along the longitudinal direction of the photoelectric conversion device  322 . Since light from the light source  323  goes out from the light guide  324 , the light guide  324  and the light source  323  may be collectively referred to as a light source when it is not necessary to distinguish the light guide  324  and the light source  323 . 
     The light source  323 , the light guide  324 , the lens array  325 , and the photoelectric conversion device  322  are accommodated between the case  326  and the substrate  321 . The case  326  is provided with a first opening portion  327  for a light source and a second opening portion  328  for a photoelectric conversion device. Light emitted from the light source  323  enters the light guide  324 , thereby the entire light guide emits light. Light emitted from the light guide  324  is emitted to the outside of the case  326  through the first opening portion  327 . Light from the outside is inputted to the lens array  325  through the second opening portion  328 . The lens array  325  guides the input light to the photoelectric conversion device  322 . Specifically, the lens array  325  has a Selfoc lens array (Selfoc is a registered trademark) in which many refractive index distribution type lenses are arranged. 
       FIG. 7  is a diagram schematically illustrating the arrangement of the photoelectric conversion devices  322 . As illustrated in  FIG. 7 , n, n being an integer of 1 or more, photoelectric conversion devices  322  are arranged along a given direction on the substrate  321  side by side. Here, n may be 2 or more as illustrated in  FIG. 7 . That is, the sensor unit  320  includes a second linear image sensor provided on the longitudinal direction side of the linear image sensor. The linear image sensor is, for example,  322 - 1  in  FIG. 7 , and the second linear image sensor is  322 - 2 . Each photoelectric conversion device  322  is a chip having many photoelectric conversion elements arranged side by side as described above. By using a plurality of photoelectric conversion devices  322 , a reading range for detecting incident light is widened, thereby a target range for detecting the ink amount can be widened. However, the number of linear image sensors, that is, the setting of the target range for detecting the ink amount can be performed in various ways, and it is not hindered that there is only one linear image sensor. 
       FIG. 8  is a sectional diagram schematically illustrating the arrangement of the sensor units  320 . As can be seen from  FIGS. 6 and 7 , although the positions of the photoelectric conversion device  322  and the light source  323  do not overlap in the Z-axis, for convenience of describing the positional relationship with other members, the light source  323  is illustrated in  FIG. 8 . As illustrated in  FIG. 8 , the sensor unit  320  includes a light shielding wall  329  provided between the light source  323  and the photoelectric conversion device  322 . The light shielding wall  329  is, for example, a portion of the case  326  and formed by extending a beam-like member between the first opening portion  327  and the second opening portion  328  to the substrate  321 . The light shielding wall  329  shields direct light from the light source  323  toward the photoelectric conversion device  322 . Since incidence of the direct light can be suppressed by providing the light shielding wall  329 , detection accuracy of the ink amount can be enhanced. It is preferable that the light shielding wall  329  is capable of shielding direct light from the light source  323  toward the photoelectric conversion device  322 , and the concrete shape is not limited to that in  FIG. 8 . A member separate from the case  326  is preferably used as the light shielding wall  329 . 
       FIG. 9  is a diagram for explaining the positional relationship between the ink tank  310  and the sensor unit  320 . As illustrated in  FIG. 9 , the sensor unit  320  is fixed to any wall surface of the ink tank  310  in such a posture that the longitudinal direction of the photoelectric conversion device  322  is the ±Z direction. That is, the photoelectric conversion device  322  as the linear image sensor is provided so that the longitudinal direction goes along the vertical direction. Here, the vertical direction represents the gravity direction and the reverse direction when the electronic apparatus  10  is used in a proper attitude. 
     In the example illustrated in  FIG. 9 , the sensor unit  320  is fixed to the side surface of the ink tank  310  in the −Y direction. That is, the substrate  321  provided with the photoelectric conversion device  322  is closer to the discharging port  312  than the filling port  311  of the ink tank  310 . Whether printing in the printer unit  100  can be executed depends on whether the ink IK is supplied to the print head  107 . Therefore, by providing the sensor unit  320  on the discharging port  312  side, the ink amount detection processing can be performed for a position where the ink amount is particularly important in the ink tank  310 . 
     As illustrated in  FIG. 9 , the ink tank  310  may include a main container  315 , a second discharging port  313 , and an ink flow path  314 . The main container  315  is a portion of the ink tank  310  that is used for accommodating the ink IK. The second discharging port  313  is, for example, an opening provided at a position in the most −Z direction in the main container  315 . However, various modifications can be performed for the position and shape of the second discharging port  313 . For example, when suction by a suction pump or supply of pressurized air by a pressure pump is performed on the ink tank  310 , ink IK accumulated in the main container  315  of the ink tank  310  is discharged from the second discharging port  313 . The ink IK discharged from the second discharging port  313  is guided in the +Z direction by the ink flow path  314 , and discharged from the discharging port  312  to the outside of the ink tank  310 . In this case, as illustrated in  FIG. 9 , detection processing of the proper ink amount can be performed by setting the positional relationship in which the ink flow path  314  and the photoelectric conversion device  322  do not face each other. For example, the ink flow path  314  is provided at the end of the ink tank  310  in the −X direction, and the sensor unit  320  is provided in the +X direction from the ink flow path  314 . In this way, the decrease in accuracy of the ink amount detection processing can be suppressed by the ink in the ink flow path  314 . 
     As described above, the “discharging port” in the present embodiment includes the discharging port  312  for discharging ink IK to the outside of the ink tank  310 , and the second discharging port  313  for discharging ink IK from the main container  315  to the discharging port  312 . Among them, the second discharging port  313  is more strongly related to whether ink IK is supplied to the print head  107 . As illustrated in  FIG. 9 , the substrate  321  provided with the photoelectric conversion device  322  is closer to the second discharging port  313  than the filling port  311  of the ink tank  310 . Thus, the ink amount detection processing can be performed for a position where the ink amount is particularly important. However, as the distance between the discharging port  312  and the second discharging port  313  becomes longer, it is necessary to lengthen the ink flow path  314 , and the arrangement of the ink flow path  314  may become complicated. That is, it is desirable that the discharging port  312  and the second discharging port  313  are provided at positions close to each other. Therefore, as described above, by providing the substrate  321  at a position closer to the discharging port  312  than to the filling port  311 , the ink amount detection processing can be performed for a position where the ink amount becomes important. The same applies to the following description. In the expression that a given member is “closer to the filling port  311  than to the discharging port  312  of the ink tank  310 ” or similar expressions, the discharging port  312  can be appropriately replaced with the second discharging port  313 . 
     The sensor unit  320  may be bonded to the ink tank  310 , for example. Alternatively, the sensor unit  320  may be mounted on the ink tank  310  by providing fixing members respectively to the sensor unit  320  and the ink tank  310  and fixing the members by fitting or the like. Various modifications can be performed in the shape, material, or the like of the fixing member. 
     The photoelectric conversion device  322  is provided in the range of z1 to z2, for example, in the Z-axis. The z1 and z2 are coordinate values in the Z-axis, and z1&lt;z2. When the ink tank  310  is irradiated with light from the light source  323 , absorption and scattering of light occur by the ink IK filled in the ink tank  310 . Therefore, the portion of the ink tank  310  not filled with the ink IK becomes relatively bright, and the portion filled with the ink IK becomes relatively dark. For example, when the interface of the ink IK exists at the position of the coordinate value of z0 in the Z-axis, in the ink tank  310 , the area of the Z coordinate value of z0 or less becomes dark and the area of the Z coordinate value of greater than z0 becomes bright. 
     As illustrated in  FIG. 9 , the position of the interface of the ink IK can be appropriately detected by providing the photoelectric conversion device  322  so that the longitudinal direction is the vertical direction. Specifically, in the case of z1&lt;z0&lt;z2, the photoelectric conversion elements arranged at a position corresponding to the range of z1 to z0 out of the photoelectric conversion device  322  has a relatively small amount of light to be inputted. Therefore, the output value becomes relatively small. The photoelectric conversion elements arranged at a position corresponding to the range of z0 to z2 has a relatively large amount of light to be inputted, so that the output value becomes relatively large. That is, z0 which is the interface of the ink IK can be estimated based on the output of the photoelectric conversion device  322 . That is, it is possible to detect not only binary information relating to whether the ink amount is equal to or more than a predetermined amount but also a specific interface position. When the position of the interface is known, the ink amount can be estimated in units of milliliters or the like based on the shape of the ink tank  310 . When the output value of the entire range of z1 to z2 is large, the interface can be determined to be lower than z1, and when the output value of the entire range of z1 to z2 is small, the interface can be determined to be higher than z2. The range where the ink amount can be detected is a range of z1 to z2 which is a range where the photoelectric conversion device  322  is provided. Therefore, the detection range can be easily adjusted by changing the number of photoelectric conversion devices  322  and the length per chip. The resolution of ink amount detection is determined based on the longer pitch between the pitch of the photoelectric conversion device  322  and the pitch of the lens array  325 . For example, when photoelectric conversion elements of the photoelectric conversion device  322  are provided at intervals of 20 micrometers and lenses of the lens array  325  are provided at intervals of 300 micrometers, the ink amount detection is performed in units of 300 micrometers. The specific resolution can be variously modified. However, according to the method of the present embodiment, it is possible to detect the ink amount with higher accuracy than the related art. 
     In consideration of the accurate detection of the ink amount, it is preferable that light emitted to the ink tank  310  be made to be approximately the same degree regardless of the position in the vertical direction. As described above, since whether the ink IK is present appears as a difference in brightness, variation in light amount of the irradiation light leads to reduction in accuracy. Therefore, the sensor unit  320  has a light guide  324  disposed so that the longitudinal direction is the vertical direction. The light guide  324  here is a rod-shaped light guide as described above. In consideration of uniformly illuminating the light guide, the light source  323  preferably causes the light to enter the light guide from the longitudinal direction, that is, the direction along the longitudinal direction of the light guide. Since the incident angle becomes large in this way, total reflection is easily generated. 
       FIGS. 10 to 12  are diagrams for explaining the positional relationship between the light source  323  and the light guide  324 . For example, as illustrated in  FIG. 10 , the light source  323  and the light guide  324  may be provided so as to be aligned in the Z-axis. The light source  323  can guide light in the longitudinal direction of the light guide  324  by emitting light in the +Z direction. Alternatively, as illustrated in  FIG. 11 , the end of the light guide  324  on the light source side may be bent. In this way, the light source  323  can guide light in the longitudinal direction of the light guide  324  by emitting light in the direction perpendicular to the substrate  321 . Alternatively, as illustrated in  FIG. 12 , a reflective surface RS may be provided at the end of the light guide  324  on the light source side. The light source  323  emits light in a direction perpendicular to the substrate  321 . Light from the light source  323  is guided in the longitudinal direction of the light guide  324  by being reflected on the reflective surface RS. The light guide  324  according to the present embodiment can be widely applied to a known configuration such as providing a reflective plate on the −Y direction surface of the light guide  324  and changing the density of the reflective plate in accordance with the position from the light source  323 . The light source  323  may be provided in the +Z direction from the light guide  324 , or light sources  323  of the same color may be provided at both ends of the light guide  324 , or the configuration of the light source  323  and the light guide  324  may be variously modified. 
     It is desirable that at least a portion of the inner wall of the ink tank  310  that faces the photoelectric conversion device  322  is higher in ink repellency than the outer wall of the ink tank  310 . Of course, the entire inner wall of the ink tank  310  may be processed to enhance the ink repellency in comparison with the outer wall of the ink tank  310 . The portion facing the photoelectric conversion device  322  may be the entire inner wall in the −Y direction of the ink tank  310  or a portion of the inner wall. Specifically, in the inner walls of the ink tank  310  in the −Y direction, the portion of the inner wall is an area including a portion where the position on the XZ plane overlaps the photoelectric conversion device  322 . As will be described later with reference to  FIG. 33 , when an ink droplet adheres to the inner wall of the ink tank  310 , the portion of the ink droplet becomes darker than a portion where no ink is present. Therefore, there is a possibility that the ink amount detection accuracy may be lowered due to the ink droplet. By enhancing the ink repellency of the inner wall of the ink tank  310 , the adhesion of ink droplets can be suppressed. 
     1.6 Detailed Configuration Example of Sensor Unit and Processing Unit 
       FIG. 13  is a functional block diagram relating to the sensor unit  320 . The electronic apparatus  10  includes a second substrate  111  provided with the processing unit  120  and an analog front end (AFE)  130 . The processing unit  120  outputs a control signal for controlling the photoelectric conversion device  322  corresponding to the processing unit  120  illustrated in  FIG. 5 . The control signal includes a clock signal CLK and a chip enable signal EN 1  described later. The AFE  130  is a circuit having at least a function of analog-to-digital (A/D) converting an analog signal from the photoelectric conversion device  322 . The second substrate  111  is, for example, a main substrate of the electronic apparatus  10 , and the substrate  321  is a sub-substrate for a sensor unit. 
     In  FIG. 13 , the sensor unit  320  includes a red LED  323 R, a green LED  323 G, a blue LED  323 B, and n photoelectric conversion devices  322 . As described above, n is an integer of 1 or more. The red LED  323 R, the green LED  323 G, and the blue LED  323 B are provided in the light source  323 , and a plurality of photoelectric conversion devices  322  are arranged on the substrate  321 . A plurality of red LEDs  323 R, green LEDs  323 G, and blue LEDs  323 B may exist, respectively. The AFE  130  is realized by, for example, an integrated circuit (IC). 
     The processing unit  120  controls the operation of the sensor unit  320 . First, a processing unit  120  controls operations of the red LED  323 R, the green LED  323 G, and the blue LED  323 B. Specifically, the processing unit  120  supplies a drive signal DrvR to the red LED  323 R at a fixed period T for a fixed exposure time Δt and causes the red LED  323 R to emit light. Similarly, the processing unit  120  supplies the green LED  323 G with a drive signal DrvG for the exposure time Δt at the period T to cause the green LED  323 G to emit light, and supplies the blue LED  323 B with a drive signal DrvB for the exposure time Δt at the period T to cause the blue LED  323 B to emit light. The processing unit  120  causes the red LED  323 R, the green LED  323 G, and the blue LED  323 B to emit light exclusively one by one in order during the period T. 
     The processing unit  120  controls the operation of the n photoelectric conversion devices  322 - 1  to  322 - n . Specifically, the processing unit  120  supplies the clock signals CLK in common to the n photoelectric conversion devices  322 . The clock signal CLK is an operation clock signal of the n photoelectric conversion devices  322 , and each of the n photoelectric conversion devices  322  operates based on the clock signal CLK. 
     Each photoelectric conversion device  322 - j  (j=1 to n) generates and outputs a signal OS based on light received by each light receiving element in synchronization with the clock signal CLK when receiving a chip enable signal ENj after the light receiving element receives light. 
     The processing unit  120  causes the red LED  323 R, the green LED  323 G, or the blue LED  323 B to emit light, generates a chip enable signal EN 1  that is active only until the photoelectric conversion device  322 - 1  finishes outputting the output signal OS, and supplies it to the photoelectric conversion device  322 - 1 . 
     The photoelectric conversion device  322 - j  generates a chip enable signal ENj+1 before the output of the output signal OS is finished. The chip enable signals EN 2  to ENn are supplied to photoelectric conversion devices  322 - 2  to  322 - n , respectively. 
     Thus, after the red LED  323 R, the green LED  323 G, or the blue LED  323 B emits light, the n photoelectric conversion devices  322  sequentially output the output signals OS. Then, the sensor unit  320  outputs the output signal OS sequentially output by the n photoelectric conversion devices  322  from a terminal (not illustrated). The output signal OS is transferred to the second substrate  111  through wiring (not illustrated) that electrically couples the sensor unit  320  and the second substrate  111 . 
     The AFE  130  sequentially receives the output signals OS outputted in order from the n photoelectric conversion devices  322 , performs amplification processing and A/D conversion processing with respect to each output signal OS to convert into digital data including a digital value corresponding to the amount of light received by each light receiving element, and sequentially transmits each digital data to the processing unit  120 . The processing unit  120  receives each digital data sequentially transmitted from the AFE  130 , and performs ink amount detection processing and ink characteristics determination processing described later. The processing unit  120  may perform correction processing using a first correction parameter or the like described later, before the ink amount detection processing or the like. 
       FIG. 14  is a functional block diagram of the photoelectric conversion device  322 . The photoelectric conversion device  322  is provided with a control circuit  3222 , a boosting circuit  3223 , a pixel drive circuit  3224 , p pixel units  3225 , a correlated double sampling (CDS) circuit  3226 , a sample hold circuit  3227 , and an output circuit  3228 . The photoelectric conversion device  322  is supplied with a power supply voltage VDD and a power supply voltage VSS from the two power supply terminals VDP and VSP, respectively. The photoelectric conversion device  322  operates based on a chip enable signal EN_I, a clock signal CLK, and a reference voltage VREF supplied from a reference voltage supply terminal VRP. The power supply voltage VDD corresponds to a high potential side power supply, and is 3.3 V, for example. The VSS corresponds to a low potential side power supply, and is 0 V, for example. The chip enable signal EN_I is any one of chip enable signals EN 1  to ENn in  FIG. 13 . 
     The chip enable signal EN_I and the clock signal CLK are inputted to the control circuit  3222 . The control circuit  3222  controls operations of the boosting circuit  3223 , the pixel drive circuit  3224 , the p pixel units  3225 , the CDS circuit  3226 , and the sample hold circuit  3227  based on the chip enable signal EN_I and the clock signal CLK. Specifically, the control circuit  3222  generates a control signal CPC that controls the boosting circuit  3223 , a control signal DRC that controls the pixel drive circuit  3224 , a control signal CDSC that controls the CDS circuit  3226 , a sampling signal SMP that controls the sample hold circuit  3227 , a pixel selection signal SEL 0  that controls the pixel unit  3225 , a reset signal RST, and a chip enable signal EN_O. 
     The boosting circuit  3223  boosts the power supply voltage VDD based on the control signal CPC from the control circuit  3222 , and generates a transfer control signal Tx that sets the boosted power supply voltage to a high level. The transfer control signal Tx is a control signal for transferring electric charges generated during exposure time Δt based on photoelectric conversion by the light receiving element and is commonly supplied to the p pixel units  3225 . 
     The pixel drive circuit  3224  generates a drive signal Dry for driving the p pixel units  3225  based on the control signal DRC from the control circuit  3222 . The p pixel units  3225  are arranged side by side in a one-dimensional direction, and the drive signal Dry is transferred to the p pixel units  3225 . When the drive signal Dry is active and a pixel selection signal SELi−1 is active, an i-th, i being any one of 1 to p, pixel unit  3225  activates a pixel selection signal SELi and outputs a signal. The pixel selection signal SELi is outputted to an i+1th pixel unit  3225 . 
     The p pixel units  3225  include photoelectric conversion elements that receive light and perform photoelectric conversion, and based on the transfer control signal Tx, the pixel selection signal SEL (any one of SEL 0  to SELp−1), the reset signal RST, and the drive signal Dry, respectively, output a signal having a voltage corresponding to light received by the light receiving element during the exposure time Δt. Signals outputted from the p pixel units  3225  are sequentially transferred to the CDS circuit  3226 . 
     The CDS circuit  3226  receives a signal Vo sequentially including the signals respectively output from the p pixel units  3225 , and operates based on the control signal CDSC from the control circuit  3222 . The CDS circuit  3226  removes noise generated by the characteristics variation in the amplification transistors of the p pixel units  3225  and superimposed on the signal Vo by correlated double sampling with the reference voltage VREF as a reference. That is, the CDS circuit  3226  is a noise reduction circuit for reducing noise included in the signals outputted from the p pixel units  3225 . 
     The sample hold circuit  3227  samples the signal from which noise is removed by the CDS circuit  3226  based on the sampling signal SMP, holds the sampled signal, and outputs it to the output circuit  3228 . 
     The output circuit  3228  amplifies the signal outputted from the sample hold circuit  3227  to generate the signal OS. As described above, the signal OS is outputted from the photoelectric conversion device  322  via an output terminal OP 1  and supplied to the AFE  130 . 
     The control circuit  3222  generates a chip enable signal EN_O which is a high pulse signal shortly before the output of the signal OS from the output circuit  3228  is finished, and outputs it from an output terminal OP 2  to a next-stage photoelectric conversion device  322 . The chip enable signal EN_O here is any one of chip enable signals EN 2  to ENn+1 in  FIG. 13 . Thereafter, the control circuit  3222  causes the output circuit  3228  to stop outputting the signal OS and sets the output terminal OP 1  to high impedance. 
     As described above, the electronic apparatus  10  according to the present embodiment is a printer, and the printer includes the ink tank  310 , the print head  107 , the substrate  321 , the light source  323 , the photoelectric conversion device  322 , and the processing unit  120 . The print head  107  performs printing by using ink IK in the ink tank  310 . The light source  323  is provided on the substrate  321  and irradiates the ink tank  310  with light from the side of the ink tank  310 . The side is specifically the horizontal direction and includes both the direction along the X-axis and the direction along the Y-axis. In the present embodiment, light is emitted from the direction along the Y-axis. The photoelectric conversion device  322  is provided on the substrate  321  and detects light incident from the ink tank in a period during which the light source  323  emits light. The processing unit  120  detects the amount of ink in the ink tank  310  based on the output of the photoelectric conversion device  322 . In this way, the amount of ink in the ink tank  310  can be detected by using the light source  323  and the photoelectric conversion device  322  provided on the same substrate  321 . The sensor unit  320  including the light source  323  and the photoelectric conversion device  322  can be integrally configured, and the arrangement is easily optimized. 
     2. Modifications Related to Configuration of Electronic Apparatus 
     The configuration of the electronic apparatus  10  is not limited to that described above, and various modifications can be made for each portion. 
     2.1 Window Portion 
     The electronic apparatus  10  may include ink viewing window portions  103  in the ink tank  310 . For example, the case  301  is provided with the window portions  103  corresponding to each of the five ink tanks  310 . The window portions  103  may be opening portions formed in the case  301 , or may be a light transmissive member. The user can visually recognize the five ink tanks  310  through the window portions  103 . 
       FIG. 15  is a perspective diagram of the electronic apparatus  10  including the window portions  103 . In the example illustrated in  FIG. 15 , the window portions  103  are provided on a surface in the +Y direction that is the front side of the case  301  of the ink tank unit  300 . By providing the window portions  103 , the user can visually recognize a portion of the side surface of the ink tank  310  in the +Y direction, specifically a portion of the ink tank  310  facing the window portion  103 . 
     Further, a portion of each ink tank  310  facing the window portion  103  has light transmittance. Therefore, the user can visually recognize the amount of ink IK included in the ink tank  310  through the window portion  103 . The window portion  103  which is a member having light transmittance may be provided with a scale. The user can grasp the amount of ink IK in each ink tank  310  by using the scale as a mark. The scale may be provided on the side surface of the ink tank  310  instead of the window portion  103 . 
     As can be seen from  FIGS. 9 and 15 , the window portion  103  is closer to the filling port  311  than to the discharging port  312  of the ink tank  310 . In other words, the window portion  103 , the filling port  311 , and the discharging port  312  are arranged in this order along the −Y direction. As described above with reference to  FIG. 9 , the sensor unit  320  is provided at a position closer to the discharging port  312  than to the filling port  311  of the ink tank  310 . That is, when the ink tank  310  is used as a reference, the window portion  103  is positioned in the +Y direction, and the sensor unit  320  is positioned in the −Y direction. Thus, it is possible to suppress the visual recognition of the ink amount by the user from being hindered by the sensor unit  320 , and to efficiently arrange each part of the electronic apparatus  10 . 
     2.2 Modifications Related to Optical Separator 
     As illustrated in  FIG. 9 , in the method of the present embodiment, the amount of ink is detected by arranging the linear image sensors in the vertical direction. In the ink amount detection processing, each photoelectric conversion element included in the photoelectric conversion device  322  is required to detect light from a facing position in the ink tank  310 . For example, it is desirable that the photoelectric conversion element provided at a position where the Z coordinate value is z3 mainly detects light from a position where the Z coordinate value is z3 in the ink tank  310 , which is ideal. In other words, when the photoelectric conversion element provided at the position where the Z coordinate value is z3 detects light from a position where the Z coordinate value is not z3, the detection accuracy may be reduced. Therefore, the sensor unit  320  desirably includes an optical separator for separating light in the vertical direction. 
       FIG. 16  is a schematic diagram illustrating the relationship between the ink tank  310 , the optical separator, and the photoelectric conversion device  322  when the lens array  325  is included as the optical separator as in the example illustrated in  FIG. 6 . In  FIG. 16 , the shape of the ink tank  310  is simplified. From this point onward, the description of the drawings is simplified with respect to the portion of the ink tank  310  that does not require a detailed shape. The drawing is an example in which the lower end of the photoelectric conversion device  322  is located below the lower end of an ink chamber of the ink tank  310  so that the ink amount can be detected until the ink almost runs out. Although the lower end of the ink tank  310  and the lower end of the photoelectric conversion device  322  have substantially the same height in the drawing, the lower end of the photoelectric conversion device  322  may be positioned further below the lower end of the ink tank  310 . 
     Each lens included in the lens array  325  collects light incident on the lens at a predetermined position. Therefore, each photoelectric conversion element included in the photoelectric conversion device  322  mainly receives light transmitted through a given lens and also suppresses reception of light transmitted through another lens. For example, the photoelectric conversion element provided in the range illustrated by A0 mainly receives light from the lens illustrated by A1 and suppresses reception of light from the lens provided A2 and the lens provided in the −Z direction from A2. By using the lens array  325 , since light is separated in the vertical direction, the accuracy of ink amount detection can be improved. 
     However, although the method of the present embodiment can use a linear image sensor the same as that in the image reading in the scanner unit  200 , the ink amount detection processing does not necessarily require the same accuracy as in the image reading processing. When the ink amount detection processing requires lower accuracy, it is possible to use a simple optical separator having a light separation performance lower than that of the lens array  325 . 
       FIG. 17  is a schematic diagram for explaining another example of the optical separator. As illustrated in  FIG. 17 , the optical separator may be an optical slit provided between the photoelectric conversion device  322  and the ink tank  310 . The optical slit is, for example, a resin slit  330  formed of a resin material. 
     Slits are formed by alternately providing areas having relatively high light transmittance and areas having relatively low light transmittance in the Z-axis. The area having high light transmittance and the area having low light transmittance are areas having a width of several hundred micrometers in the Z-axis respectively, for example. The resin slit  330  may be provided in the case  326  of the sensor unit  320 . A member having low light transmittance is used for the case  326  for suppressing the incidence of environmental light to the photoelectric conversion device  322 . Therefore, the resin slit  330  can be formed by providing the case  326  with openings having a pitch of several hundred micrometers. For example, in  FIG. 6 , the second opening portion  328  is illustrated as one continuous opening in a given range of the Z-axis, the resin slit  330  is realized by changing this to a plurality of openings provided at intervals of several hundred micrometers within a given range of the Z-axis. The area having high light transmittance is not limited to the opening, and may be formed of a light transmitting member having higher light transmittance than that of the case  326 . The resin slit  330  illustrated in  FIG. 17  is not limited to the one formed in the case  326 , and may be provided as a separate body from the case  326 . For example, the resin slit  330  separated from the case  326  is provided at a position corresponding to the lens array  325  in  FIG. 6  or  FIG. 8 . 
     Among a plurality of photoelectric conversion elements included in the photoelectric conversion device  322 , a photoelectric conversion element corresponding to an area with high light transmittance detects light from the ink tank  310 . On the other hand, among the plurality of photoelectric conversion elements included in the photoelectric conversion device  322 , a photoelectric conversion element corresponding to an area with low light transmittance has very little incidence of light from the ink tank  310 . In order to suppress misidentifying an area where light is not incident due to the optical separator as an area where the ink IK exists, in the ink amount detection processing and the like to be described later, processing of extracting a portion corresponding to an area having a high light transmittance from a signal output from the photoelectric conversion device  322  is performed. For example, since the pitch of the resin slit  330  is known in design, the processing unit  120  extracts data corresponding to the opening portion of the slit from the signal OS as a set of output data of a plurality of photoelectric conversion elements, and performs ink amount detection processing based on data after the extraction processing. For example, a waveform described later with reference to  FIG. 31  is data after the extraction processing. 
     The optical separator may be provided on the side surface of the ink tank  310 . In this case, the electronic apparatus  10  includes the ink tank  310  provided with an optical separator that separates light in the vertical direction on the side surface, the print head  107  that performs printing by using ink IK in the ink tank  310 , the photoelectric conversion device  322  that detects light incident from the ink tank  310  through the optical separator, and the processing unit  120  that detects the amount of ink in the ink tank  310  based on the output of the photoelectric conversion device  322 . As described above, by providing the optical separator on the side surface of the ink tank  310 , the configuration on the sensor unit  320  side can be simplified. Specifically, since the lens array  325  illustrated in  FIG. 16  and the resin slit  330  illustrated in  FIG. 17  can be omitted, the sensor unit  320  can be miniaturized. 
       FIG. 18  is a schematic diagram for explaining the optical separator provided on the side surface of the ink tank  310 . The optical separator is an optical slit. This makes it possible to separate light in the vertical direction by using the slits provided in the ink tank  310 . 
     The optical separator separates light in a vertical direction by passing the first light through a first transmission area between the first layer and the second layer and passing the second light through a second transmission area between the second layer and the third layer. The layer here represents any one of the structures in which a plurality of layers overlap each other in a predetermined direction. In this way, an optical slit can be formed by sandwiching an area having relatively high light transmittance by two layers having relatively low light transmittance. Since the ink tank  310  needs to accommodate ink IK which is a liquid, it is necessary to use a light transmissive member instead of an opening in an area where the light transmittance is relatively high. Various specific methods for forming layers are conceivable. 
       FIG. 19  is a schematic diagram illustrating a configuration of the ink tank  310  having the optical slits on the side surface.  FIG. 19  illustrates a configuration of a side surface of the ink tank  310  in the −Y direction. The optical separator is formed by coating the outer wall of the ink tank  310  having light transmittance with a member having low light transmittance. Thus, the first layer, the second layer, and the third layer of the optical separator are coating layers. The coating layers are stacked in the −Y direction with respect to the outer wall of the ink tank  310 . That is, in the configuration illustrated in  FIG. 19 , the ink tank  310  and the coating layers are stacked along the Y-axis. The thickness in the Y-axis is emphasized in  FIG. 19 , but the coating layers can be formed very thin. The second layer is a coating layer adjacent to the first layer in the Z-axis, and the third layer is a coating layer adjacent to the second layer in the Z-axis. For example, B1 in  FIG. 19  is a first layer, B2 is a second layer, B3 is a third layer, B4 is a first transmission area, and B5 is a second transmission area. 
     Since the coating layers are easy to form, the pitch of the optical separator can be narrowed. For example, when the resin slits  330  illustrated in  FIG. 17  or two-color molding described later is used, the pitch of the optical separator is on the order of several hundreds micrometers to several millimeters, which is a factor that makes it impossible to increase the resolution of ink amount detection. In this regard, it is considered that the ink amount can be detected with a resolution of the order of several tens of micrometers by using the coating layers. 
     The area where the light transmittance is relatively low is not limited to the coating layer. The first layer, the second layer, and the third layer are layers of one color of two-color molding, and the first transmission area and the second transmission area may be layers of the other color of two-color molding. A member having low light transmittance constituting the first to third layers is described as a first member and a member having high light transmittance constituting the first transmission area and the second transmission area is described as a second member of two members used for the two-color molding. Thus, the ink tank  310  having the optical separator on the side surface can be formed by using two-color molding using the two members having different light transmittances. 
       FIGS. 20 and 21  are schematic diagrams illustrating the configuration of the ink tank  310  in which the optical slits are provided on the side surface by two-color molding. The structure in the XZ plane is the same as the example in  FIG. 19  which uses the coating layer. However, various configurations in the YZ plane are conceivable. 
     For example, as illustrated in  FIG. 20 , the first to third layers may be formed on the surface portion of the ink tank  310 . That is, the second member and the first member are laminated along the Y-axis as indicated by C1, and the first member does not penetrate the side surface of the ink tank  310  on the Y-axis. In  FIG. 20 , the first to third layers may be considered to be layers stacked on the Z-axis. Specifically, the first member and the second member are alternately stacked in the direction indicated by C2 in  FIG. 20 . 
     Alternatively, as illustrated in  FIG. 21 , the first member may be provided so as to penetrate the side surface of the ink tank  310  on the Y-axis. The first member and the second member are alternately stacked on the Z-axis in  FIG. 21 . 
     As described above with reference to  FIG. 4 , the ink tank  310  includes the filling port  311  into which ink IK is filled by the user and the discharging port  312  for discharging the ink IK toward the print head  107 . The optical separator is provided on the side surface of the ink tank  310  in the −Y direction closer to the discharging port  312  than to the filling port  311 . Thus, light directing from the ink tank  310  to the photoelectric conversion device  322  can be separated in the vertical direction. 
     In addition, although the example in which the optical separator is a slit has been described above, the present disclosure is not limited thereto, and other configurations capable of separating light in the vertical direction may be used. Specifically, the optical separator may be an optical pinhole. In  FIGS. 19 to 21 , the first layer and the second layer are rectangles having the ±X direction as the longitudinal direction and the ±Z direction as the short side direction in the XZ plane, and the first transmission area is an area between the first layer and the second layer. When the optical pinhole is used, the first transmission area may be formed into a minute circular shape, and the first layer may be provided in the +Z direction and the second layer may be provided in the −Z direction so as to surround the circular shape. In this case, the first layer and the second layer are continuous at positions deviated from the pinhole in the X direction or the −X direction. 
     As described above, the photoelectric conversion device  322  has a plurality of photoelectric conversion elements. The arrangement pitch of the plurality of photoelectric conversion elements is narrower than the pitch of the optical separation by the optical separator. The arrangement pitch of the photoelectric conversion elements is an interval at which the photoelectric conversion elements are provided. The optical separation pitch is an interval between members having low light transmittance or an interval between members having high light transmittance. For example, the optical separation pitch is an interval between the first layer and the second layer or an interval between the first transmission area and the second transmission area. 
     When the resin slit  330  illustrated in  FIG. 17  and the two-color molding illustrated in  FIGS. 20 and 21  are used, it is not easy to form the minute structure and it is difficult to narrow the optical separation pitch. Further, it is not necessary to narrow the optical separation pitch than a pitch of the photoelectric conversion elements. For example, when the light separation pitch is narrow enough to allow both light transmitted through the first transmission area and light from the second transmission area to enter one photoelectric conversion element, the significance of light separation by the second layer is damaged. Furthermore, a signal value of the photoelectric conversion element is lowered when light is blocked by the second layer. That is, by making the arrangement pitch of the plurality of photoelectric conversion elements narrower than the optical separation pitch by the optical separator, the formation of the optical separator is facilitated and the efficient configuration can be realized. 
     Further, the example of providing an optical separator on one of the side surfaces of the sensor unit  320  and the ink tank  310  has been described above. However, when the ink amount detection processing does not require accuracy compared to the image reading processing in the scanner unit  200 , the optical separator can be omitted.  FIG. 22  is a schematic diagram describing the relationship between the photoelectric conversion device  322  and the ink tank  310  when the optical separator is omitted. 
     2.3 Modifications Related to Light Source 
     2.3.1 Relationship with Light Guide 
     In the example illustrated in  FIG. 6 , the sensor unit  320  includes the light guide  324 . The light source  323  irradiates the light guide  324  with light. As described above, in order to make the light guide  324  emit light uniformly, light from the light source  323  needs to be incident in a direction along the longitudinal direction of the light guide  324 . Specific methods can be considered in various ways as illustrated in  FIGS. 10 to 12 . In the examples illustrated in  FIGS. 10 to 12 , the position of the light source  323  in the Z-axis does not overlap the photoelectric conversion device  322 . However, the relationship between the light guide  324  and the light source  323  is not limited thereto. 
       FIGS. 23 and 24  are schematic diagrams illustrating other configurations of the light source  323  and the light guide  324 . As illustrated in  FIG. 23 , the light source  323  may irradiate the light guide  324  with light from a direction intersecting the longitudinal direction of the light guide  324 . The longitudinal direction of the light guide  324  is a direction along the longitudinal direction of the photoelectric conversion device  322  and a direction along the Z-axis. The light source  323  is provided in the −Y direction with respect to the light guide  324 , and emits light in the +Y direction. More preferably, the light source  323  is provided near the center of the light guide  324  in the Z-axis. For example, as illustrated in  FIG. 24 , the photoelectric conversion device  322  and the light guide  324  are provided in the same range on the Z-axis, and the light source  323  is disposed at the center of the range. 
     When the configuration illustrated in  FIG. 23  is used, light from the light source  323  is less likely to propagate inside the light guide  324  as compared with  FIGS. 10 to 12 . It is because that, in the configuration in  FIG. 23 , an incident angle when light enters an interface from an inside to an outside of the light guide  324  is small and total reflection is difficult to occur. Therefore, the light incident on the light guide  324  is emitted in the +Y direction before sufficiently propagating inside the light guide  324 . As a result, the light emitted from the light guide  324  toward the ink tank  310  is more likely to cause intensity variation in the Z-axis than in the configurations of  FIGS. 10 to 12 . 
     In the scanner unit  200 , the image sensor needs to read an image of a document of a predetermined size, for example, A4 size or A3 size, so that a certain length is required in the longitudinal direction. Therefore, in the scanner unit  200 , it is required to emit light uniformly over a wide range to some extent. On the other hand, the photoelectric conversion device  322  of the present embodiment is used for detecting the ink amount and does not require a length in comparison with the scanner unit  200 . This is because there are many cases where the side surface of the ink tank  310  itself is not so long in the vertical direction, and the ink amount may be detected only in a portion of the side surface. For example, in the case of detecting an ink end or an ink near end, a problem hardly occurs even if only a range of several centimeters close to the bottom surface of the ink tank  310  is an object of the ink amount detection. The ink end represents a state where the amount of ink is small and it is difficult to continue printing, and the ink near end is a state in which it is determined that printing can be continued but the amount of ink is small. 
     When the photoelectric conversion device  322  is short, since the area to be irradiated with light is also shortened, the light guide  324  can be shortened accordingly. Therefore, even if the light source  323  is disposed in a positional relationship in which total reflection is hard to occur, since an area of a sufficient proportion of the light guide  324  emits light, accuracy deterioration caused by unevenness of luminance hardly occurs. That is, even if the configurations of  FIGS. 23 and 24  are used, the ink amount can be detected with sufficient accuracy. In this case, since processing of bending the light guide  324  as illustrated in  FIG. 11  and processing of providing a reflective surface RS as illustrated in  FIG. 12  become unnecessary, mounting is facilitated. The light source  323  is disposed in the horizontal direction with respect to the photoelectric conversion device  322 . The horizontal direction here is specifically the +X direction or the −X direction. In other words, the positions of the light source  323  and the photoelectric conversion device  322  in the Z-axis overlap each other. That is, unlike the example illustrated in  FIG. 10 , it is not necessary to arrange the light guide  324  and the light source  323  in the longitudinal direction, and the size of the substrate  321  and the sensor unit  320  in the vertical direction can be reduced. 
     The light guide  324  may be omitted from the sensor unit  320 . In this case, the light source  323  is disposed at a position illustrated in  FIG. 24 , for example, and the light guide  324  is omitted in  FIG. 24 . Light from the light source  323  passes through the first opening portion  327  of the case  326  and is emitted to the ink tank  310 . In this case, the light emitted to the ink tank  310  is likely to have uneven brightness on the Z-axis. However, as described above, when the photoelectric conversion device  322  is short, ink detection may be performed with sufficient accuracy even if the light guide  324  is omitted. 
     As described above, in the example when the light source  323  and the photoelectric conversion device  322  are provided on the same substrate  321 , various modifications can be performed for the configuration of the optical separator and the configuration of the light guide  324 . For example, when accuracy is important, the configuration in which the lens array  325  is provided as the optical separator, and the light source  323  and the light guide  324  are likely to generate total reflection as illustrated in  FIGS. 10 to 12  is used. When it is important to simplify the configuration, both the optical separator and the light guide  324  are omitted. In addition, various modifications can be implemented for specific combinations such as omitting the light guide  324  and providing the optical separator. 
     2.3.2 Location of Light Source 
     The light source  323  and the photoelectric conversion device  322  are not limited to those arranged on the same substrate.  FIG. 25  is another diagram for explaining the positional relationship between the light source  323 , the photoelectric conversion device  322 , and the ink tank  310 . As illustrated in  FIG. 25 , the photoelectric conversion device  322  may be provided in a given direction with respect to the ink tank  310 , and the light source  323  may be provided in an opposite direction from the given direction. In the example illustrated in  FIG. 25 , the photoelectric conversion device  322  is provided on the side surface of the ink tank  310  in the −Y direction, and the light source  323  is provided on the side surface of the ink tank  310  in the +Y direction. In the example illustrated in  FIG. 9 , the photoelectric conversion device  322  detects reflected light of light emitted from the light source  323  in the ink tank  310 , but in the example illustrated in  FIG. 25 , the photoelectric conversion device  322  detects transmitted light that is emitted from the light source  323  and transmitted through the ink tank  310 . 
       FIG. 26  is an exploded diagram illustrating the configuration of the light receiving unit  340  including the photoelectric conversion device  322 . The light receiving unit  340  includes a sensor substrate  341 , the photoelectric conversion device  322 , the lens array  325  as the optical separator, and a sensor case  342 .  FIG. 27  is an exploded diagram illustrating the configuration of a light emitting unit  350  including the light source  323 . The light emitting unit  350  includes a light source substrate  351 , the light source  323 , the light guide  324 , and a light source case  352 . In  FIGS. 26 and 27 , the same components as those in  FIG. 6  are denoted by the same reference numerals. As can be seen from  FIGS. 26 and 27 , the light receiving unit  340  has a configuration in which a portion of the sensor unit  320  in  FIG. 6  is extracted, and the light emitting unit  350  has a configuration in which the remaining portion of the sensor unit  320  is extracted. In the case of the configurations illustrated in  FIGS. 26 and 27 , since direct light from the light source  323  to the photoelectric conversion device  322  is not required to be taken into consideration, it is not necessary to provide a light shielding wall. 
     As illustrated in  FIGS. 16 to 22 , modifications such as changing the lens array  325  to the resin slit  330 , providing an optical separator on the side surface of the ink tank  310 , and omitting the optical separator can be executed. Further, as described above with reference to  FIGS. 23 and 24 , modifications such as changing the positional relationship between the light source  323  and the light guide  324  and omitting the light guide  324  can be executed. 
     The light receiving unit  340  in  FIG. 26  and the light emitting unit  350  in  FIG. 27  are respectively arranged on different side surfaces of the ink tank  310  as illustrated in  FIG. 25 . By aligning positions of the light receiving unit  340  and the light emitting unit  350  in the Z-axis and X-axis, ink amount detection using transmitted light becomes possible. Even in the case of using the transmitted light, since the transmitted light easily reaches the photoelectric conversion device  322  in the area where the ink IK does not exist, the output value of the photoelectric conversion element corresponding to the area increases. Since absorption and scattering of light in the ink IK occur in the area where the ink IK exists, transmitted light reaching the photoelectric conversion device  322  is weak and the output value of the photoelectric conversion element corresponding to the area is small. Therefore, even in the configuration of  FIG. 25 , the ink amount can be detected by the same method as in  FIG. 9 . Specific processing is described later. 
       FIG. 28  is another diagram for explaining the positional relationship between the light source  323 , the photoelectric conversion device  322 , and the ink tank  310 . The photoelectric conversion device  322  and the ink tank  310  are the same as those in  FIG. 25 . That is, the light receiving unit  340  illustrated in  FIG. 26  is provided on the side surface of the ink tank  310  in the −Y direction.  FIG. 28  illustrates an example of providing the light source  323  on the upper surface of the ink tank  310 . However, the light source  323  can be provided at an optional position when the light source  323  is at a position capable of irradiating the inside of the ink tank  310  with light. In  FIG. 28 , the substrate provided with the light source  323  is omitted. In  FIG. 28 , although the provision of the light guide  324  and the light source case  352  is not hindered, these can be omitted. 
     The light source  323  irradiates the inside of the ink tank  310  with light. When a certain amount of light enters the inside of the ink tank  310 , reflection occurs at the inner wall of the ink tank  310  and the interface of the ink IK, and the entire inside of the ink tank  310  emits light. Hereinafter, light illuminating the entire inside of the ink tank  310  is described as spatial light. By using the spatial light, even if the positional relationship between the light emitting side and the light receiving side is not exactly aligned as illustrated in  FIG. 9  or  FIG. 25 , it is possible to realize a state where the area where the ink IK does not exist becomes bright and the area where the ink IK exists becomes dark. When spatial light emitted from the side surface of the ink tank  310  is detected by using the photoelectric conversion device  322 , the output value of the photoelectric conversion element changes in accordance with whether ink is present. Therefore, the ink amount can be detected by the same method as in  FIG. 9  or  FIG. 25 . 
     The configuration illustrated in  FIG. 28  has an advantage that the degree of freedom of the position of the light source  323  is high. On the other hand, since the irradiation direction of light from the light source  323  cannot be limited in the configuration illustrated in  FIG. 28 , the amount of light incident on the photoelectric conversion device  322  is considered to be small as compared to the configuration of  FIG. 9  or  FIG. 25 . Therefore, it is considered that the ink amount detection accuracy is higher by using the configuration of  FIG. 9  or  FIG. 25  than by using the configuration of  FIG. 28 . 
     2.3.3 Type of Light Source 
     In the above, three of the red LED  323 R, the green LED  323 G, and the blue LED  323 B are provided as the light source  323 , and an example in which these emit light sequentially has been illustrated. In this case, the photoelectric conversion device  322  sequentially outputs a signal corresponding to red, a signal corresponding to green, and a signal corresponding to blue. However, the type and the number of light sources  323  are not limited thereto. 
     For example, the light source  323  may be a white LED. The white LED may be realized by a method of mixing each light of the red LED  323 R, the green LED  323 G, and the blue LED  323 B. Alternatively, the white LED may be realized by a method of combining the LED of a given wavelength band and a phosphor. For example, the white LED can be realized by combining a blue LED and a yellow phosphor, and combining a blue LED, and a red phosphor and a green phosphor. 
     Light emitted from the light source  323  is not limited to the wavelength band of visible light. For example, the electronic apparatus  10  includes the light source  323  that irradiates the ink tank  310  with infrared light. The light source  323  that emits infrared light may be an LED or other light sources. Hereinafter, it is assumed that the light source  323  that emits infrared light is an LED, and the LED is referred to as an infrared LED. The photoelectric conversion device  322  detects light based on infrared light emitted from the light source  323  to the ink tank  310 . The light source  323  that emits infrared light has high affinity with the ink viewing window portion  103  in the ink tank  310 . 
     The window portion  103  has light transmittance for visually recognizing ink IK. Therefore, when the light source  323  that emits visible light is used, the light from the light source  323  may be visually recognized by the user. When the light emitted from the light source  323  is visually recognized every time ink amount is detected, it is troublesome for the user and there is a possibility that the use of the electronic apparatus  10  is hindered. In that respect, when the light source  323  that emits infrared light is used, since the light emitted from the light source  323  is not visually recognized by the user, it is possible to suppress discomfort to the user. The light source  323  that emits ultraviolet light may be used. However, it is preferable to use infrared light having a low frequency in consideration of the deterioration of the ink IK due to the light energy. 
     Even when infrared light is used, as in the example illustrated in  FIGS. 9 and 15 , the photoelectric conversion device  322  is provided on the side surface among the side surfaces of the ink tank  310  in the −Y direction that is the horizontal direction, and the window portion  103  is provided in the +Y direction, which is the opposite direction from the −Y direction, with respect to the ink tank  310 . In this way, the visual recognition of the ink IK by the user can be suppressed from being hindered by the photoelectric conversion device  322 . 
     The thing that ink tank  310  includes the filling port  311  and the discharging port  312 , the window portion  103  is closer to the filling port  311  than to the discharging port  312 , and the photoelectric conversion device  322  is closer to the discharging port  312  than to the filling port  311  are the same as the above-described example. 
     Heretofore, five of red LED, green LED, blue LED, white LED, and infrared LED have been exemplified. The light source  323  may be one of these or a combination of two or more. When a plurality of light sources are used, it is not always necessary to use all the light sources. For example, although all the light sources are used immediately after the power source is turned on, only the infrared LED may be used in a normal state thereafter. Further, the light source  323  is not limited to the LED, and may be a light source using other methods such as a xenon lamp, a semiconductor laser, or the like. 
     Further, the method for detecting a plurality of light beams having different wavelength bands in the photoelectric conversion device  322  is not limited to those using a plurality of LEDs. For example, the sensor unit  320  may include a light source  323  having a wide wavelength band and a filter (not illustrated). The photoelectric conversion device  322  detects light passing through the filter. The light source  323  here is, for example, a white LED. By providing a red filter that allows red light to pass through, a green filter that allows green light to pass through, and a blue filter that allows blue light to pass through as filters, the photoelectric conversion device  322  can respectively detect red light, green light, and blue light. By changing the wavelength band of the light source  323  and a pass band of the filter, the photoelectric conversion device  322  can detect light in various wavelength bands. 
     2.4 Modifications of Ink Tank 
     The number of ink tanks  310  included in the electronic apparatus  10  is not limited to a plurality, and may be one. For example, when the electronic apparatus  10  includes a printer unit  100  dedicated to monochrome printing, the printer unit  100  includes one ink tank  310  for accommodating black ink. In this case, the ink amount can be detected by applying any of the configurations in  FIG. 9 ,  FIG. 25 , and  FIG. 28  to the one ink tank  310 . 
     The electronic apparatus  10  may include a plurality of ink tanks  310  as illustrated in  FIG. 2 . In this case, the ink amount detection processing is executed for a plurality of ink tanks  310 , for example. Hereinafter, an example in which all of the plurality of ink tanks  310  are subjected to ink amount detection will be described, but some of the plurality of ink tanks  310  may be excluded from the targets of ink amount detection. 
     The electronic apparatus  10  includes a first ink tank, a second ink tank, a first photoelectric conversion device, and a second photoelectric conversion device. The first ink tank is, for example, the ink tank  310   a , and the second ink tank is the ink tank  310   b . The second ink tank is provided in the horizontal direction relative to the first ink tank. The horizontal direction is specifically the +X direction. 
     The first photoelectric conversion device is provided on the side surface of the first ink tank in a direction orthogonal to the +X direction, specifically in the −Y direction, and detects light incident from the first ink tank. The second photoelectric conversion device is provided on the side surface of the second ink tank in the −Y direction and detects light incident from the second ink tank. 
     When a plurality of ink tanks  310  are provided, it is efficient to arrange the plurality of ink tanks  310  adjacent to each other. Therefore, it is difficult to arrange the photoelectric conversion devices  322  on the side surface of the first ink tank on the second ink tank side and on the side surface of the second ink tank on the first ink tank side. When there are three or more ink tanks  310 , excluding the ink tanks  310  at both ends, the side surface in the +X direction and the side surface in the −X direction of the given ink tank  310  are in contact with the side surfaces of other ink tanks  310 , it is difficult to dispose the photoelectric conversion device  322  on the side surface. That is, it is desirable that the photoelectric conversion device  322  is provided on the side surface in the +Y direction or the side surface in the −Y direction. As illustrated above, in  FIG. 9  or the like, the photoelectric conversion device  322  is provided in the −Y direction with respect to the ink tank  310 . 
     The print head  107  performs printing by using the ink IKa in the first ink tank and the ink IKb in the second ink tank. The processing unit  120  detects the amount of ink in the first ink tank based on the output of the first photoelectric conversion device and detects the amount of ink in the second ink tank based on the output of the second photoelectric conversion device. In this way, when the electronic apparatus  10  includes a plurality of ink tanks  310 , the ink amount detection processing for the plurality of ink tanks  310  can be performed. 
     The electronic apparatus  10  may include a first light source for irradiating the first ink tank with light, and a second light source different from the first light source for irradiating the second ink tank with light. The first photoelectric conversion device detects light from the first ink tank in a light emitting period of the first light source. The second photoelectric conversion device detects light from the second ink tank in a light emitting period of the second light source. In this way, since the plurality of ink tanks  310  can be irradiated with light by using respective dedicated light sources, the accuracy of ink amount detection can be improved. 
     For example, the first light source irradiates a side surface of the first ink tank with light in the −Y direction, and the second light source irradiates a side surface of the second ink tank with light in the −Y direction. In other words, the first light source and the second light source emit light on the side surfaces of the ink tank  310  in the direction in which the first photoelectric conversion device and the second photoelectric conversion device are provided, respectively. For example, the electronic apparatus  10  includes a plurality of sensor units  320  illustrated in  FIGS. 6 to 8 , and the sensor units  320  are respectively fixed to the side surfaces in the −Y direction of the plurality of ink tanks  310 . In this way, the amounts of the ink IK included in the plurality of ink tanks  310  can be detected based on the reflected light from the ink tanks  310 . 
     Alternatively, the first light source may emit light on the side surface of the first ink tank in the +Y direction, and the second light source may emit light on the side surface of the second ink tank in the +Y direction. In other words, the first light source and the second light source emit light on the side surface of the ink tank  310  in the direction opposite from the side surfaces provided with the first photoelectric conversion device and the second photoelectric conversion device. For example, the electronic apparatus  10  includes a plurality of light receiving units  340  illustrated in  FIG. 26  and a plurality of light emitting units  350  illustrated in  FIG. 27 . In each ink tank  310  of the plurality of ink tanks  310 , the light receiving unit  340  is fixed to the side surface in the −Y direction, and the light emitting unit  350  is fixed to the side surface in the +Y direction. In this way, the amount of the ink IK included in the plurality of ink tanks  310  can be detected based on the transmitted light transmitted through the ink tanks  310 . 
     The electronic apparatus  10  is not limited to the configuration in which the light source is provided for each ink tank  310 . For example, the electronic apparatus  10  includes one light source that irradiates the first ink tank and the second ink tank with light. For example, the electronic apparatus  10  includes a plurality of light receiving units  340  illustrated in  FIG. 26 , and the light receiving units  340  are respectively fixed to the side surfaces of the plurality of ink tanks  310  in the −Y direction. Similarly to the example illustrated in  FIG. 28 , the light source  323  causes the entire ink tank  310  to emit light by irradiating each ink tank  310  with light from an optional position. In this case, one light source  323  irradiates the plurality of ink tanks  310  with light. In this way, the amounts of ink IK included in the plurality of ink tanks  310  can be detected based on spatial light of the ink tanks  310 . As described above, in the method using spatial light, it is sufficient that the entire ink tank  310  emits light, and it is not necessary to set the light irradiation direction strictly. Therefore, one light source can be shared by the plurality of ink tanks  310 . However, it is not hindered to provide a plurality of light sources in the method using spatial light. For example, the electronic apparatus  10  may include a first light source for supplying spatial light to the first ink tank and a second light source for supplying spatial light to the second ink tank. 
     The first ink tank includes a first filling port and a first discharging port, and the second ink tank includes a second filling port and a second discharging port. The first discharging port is provided in the −Y direction with respect to the first filling port, and the second discharging port is provided in the −Y direction with respect to the second filling port. Thus, it is possible to detect the ink amount at a position close to the discharging port  312  for each ink tank  310  by using the photoelectric conversion device  322 . 
     The electronic apparatus  10  may include the ink viewing window portion  103  in the first ink tank as described above with reference to  FIG. 15 . The window portion  103  is closer to the first filling port than to the first discharging port. This makes it possible for the user to visually recognize the ink amount for at least one of the plurality of ink tanks  310 . As illustrated in  FIG. 15 , a plurality of the window portions  103  corresponding to all of the plurality of ink tanks  310  may be provided. A large window portion including an area corresponding to the side surfaces of the plurality of ink tanks  310  may be provided. The window portion  103  may be provided in an area corresponding to some of the ink tanks  310  among the plurality of ink tanks  310 . 
     Heretofore, a method of using a plurality of sensor units  320  illustrated in  FIG. 8  or a method of using a plurality of light receiving units  340  illustrated in  FIG. 26  has been described. However, the arrangement of the photoelectric conversion device  322  is not limited to this in a case of detecting the amounts of ink in the plurality of ink tanks  310 . For example, on one substrate, both the photoelectric conversion device  322  for detecting light from the first ink tank and the photoelectric conversion device  322  for detecting light from the second ink tank may be provided. 
       FIG. 29  is an exploded diagram illustrating the configuration of the sensor unit  360  that detects the ink amounts of the plurality of ink tanks  310 , and  FIG. 30  is a sectional diagram of the sensor unit  360 . The sensor unit  360  includes a substrate  361 , a photoelectric conversion device  322   a , a photoelectric conversion device  322   b , a light source  323   a , a light source  323   b , a light guide  324   a , light guide  324   b , a lens array  325   a , a lens array  325   b , and a case  365 . The photoelectric conversion device  322   a  and the photoelectric conversion device  322   b  are the same as the photoelectric conversion device  322 , respectively. The light source  323   a  and the light source  323   b  are the same as the light source  323 , respectively. The light guide  324   a  and the light guide  324   b  are the same as the light guide  324 , respectively. The lens array  325   a  and the lens array  325   b  are the same as the lens array  325 , respectively. 
     As illustrated in  FIGS. 29 and 30 , the case  365  is provided with four openings  366  to  369 . The photoelectric conversion device  322   a  and the lens array  325   a  are provided at a position corresponding to the opening  366 . The light guide  324   a  and the light source  323   a  are provided at a position corresponding to the opening  367 . The photoelectric conversion device  322   b  and the lens array  325   b  are provided at a position corresponding to the opening  368 . The light guide  324   b  and the light source  323   b  are provided at a position corresponding to the opening  369 . Light shielding walls are respectively provided between the photoelectric conversion device  322   a  and the light source  323   a , between the light source  323   a  and the photoelectric conversion device  322   b , and between the photoelectric conversion device  322   b  and the light source  323   b . In the examples of  FIGS. 29 and 30 , the light shielding wall is a part of the case  365 . 
     Light is emitted from the light source  323   a  to the first ink tank via the light guide  324   a , and reflected light of the light is detected by the photoelectric conversion device  322   a  via the lens array  325   a . Light is emitted from the light source  323   b  to the second ink tank via the light guide  324   b , and reflected light of the light is detected by the photoelectric conversion device  322   b  via the lens array  325   b . The size of the ink tank  310  and the positional relationship between the plurality of ink tanks  310  are known in the design of the electronic apparatus  10 . Thus, proper positional relationship between the light source  323   a , the light source  323   b , the photoelectric conversion device  322   a , and the photoelectric conversion device  322   b  is also known. By making the substrate  361  common, the production of the unit for detecting the ink amount and the arrangement in the electronic apparatus  10  can be made efficient. 
     In  FIGS. 29 and 30 , the sensor unit  360  for detecting the amounts of ink in two ink tanks  310  is exemplified. However, a sensor unit for detecting the amounts of ink in three or more ink tanks  310  may be realized by using one substrate. In  FIGS. 29 and 30 , only one case  365  is provided, but only the substrate  361  may be shared and one case may be provided for each ink tank  310  as in  FIG. 8 . 
     In the light receiving unit  340  illustrated in  FIG. 26  and the light emitting unit  350  illustrated in  FIG. 27 , the substrate can be shared. For example, a light receiving unit in which a plurality of photoelectric conversion devices  322  for detecting the amounts of ink in a plurality of ink tanks  310  are provided on one substrate may be used. Alternatively, a light emitting unit in which a plurality of light sources  323  for irradiating the plurality of ink tanks  310  with light are provided on one substrate may be used. 
     3. Ink Amount Detection Processing Based on Output of Photoelectric Conversion Device 
     Next, processing of estimating the amount of ink IK accommodated in the ink tank  310  based on the output of the photoelectric conversion device  322  will be described. In the following description, any of the various embodiments described above may be used for the arrangement of the photoelectric conversion device  322  and the like. 
     3.1 Basic Ink Amount Detection Processing 
       FIG. 31  is a waveform representing output data of the photoelectric conversion device  322 . As described above with reference to  FIG. 13 , the output signal OS of the photoelectric conversion device  322  is an analog signal, and output data as digital data is acquired by A/D conversion by the AFE  130 . In order to simplify the description, digital data that is a result of A/D conversion performed on the output signal OS is referred to as “output data of the photoelectric conversion device  322 ”. 
     The horizontal axis of  FIG. 31  represents a position of the photoelectric conversion device  322  in the longitudinal direction, and the vertical axis represents a value of output data corresponding to the photoelectric conversion element provided at the position. The numerical values of the horizontal axis of  FIG. 31  represent the distances from the reference position in unit of millimeters.  FIG. 31  illustrates examples in which the red LED  323 R, the green LED  323 G, and the blue LED  323 B are provided as the light source  323 . The processing unit  120  acquires three pieces of output data of RGB as output data of the photoelectric conversion device  322 . 
     When the longitudinal direction of the photoelectric conversion device  322  is the vertical direction, the left end of the horizontal axis is a position corresponding to the photoelectric conversion element provided at the end of the photoelectric conversion device  322  in the +Z direction, and the right end of the horizontal axis is a position corresponding to the photoelectric conversion element provided at the end of the photoelectric conversion device  322  in the −Z direction. If the positional relationship between the photoelectric conversion device  322  and the ink tank  310  is known, the horizontal axis can be replaced with the distances from the reference position of the ink tank  310 . The reference position of the ink tank  310  is, for example, a position equivalent to the bottom surface of the ink tank  310 . 
     The output data is, for example, 8-bit data, and has a value in the range of 0 to 255. However, the values of the vertical axis can be replaced with data after the normalization processing or the like described later is performed. The  FIG. 31  does not need to include output data corresponding to all photoelectric conversion elements included in the photoelectric conversion device  322 , and may be a result of extracting data corresponding to some of the photoelectric conversion elements, for example, according to the pitch of the optical separator. 
     As described above, regardless of the configuration of reflected light, transmitted light, or spatial light, the photoelectric conversion element corresponding to the area where the ink IK does not exist has relatively large amount of light received, and the photoelectric conversion element corresponding to the area where the ink IK exists has relatively small amount of light received. In the example illustrated in  FIG. 31 , the value of output data is large in the range indicated by D1, and the value of output data is small in the range indicated by D3. The value of the output data is greatly changed with respect to the change of the position in the range indicated by D2 between D1 and D3. That is, the range of D1 is an ink non-detection area having a high probability that the ink IK does not exist. The range of D3 is an ink detection area having a high probability that the ink IK exists. The range of D2 is an ink boundary area representing a boundary between an area where the ink IK exists and an area where the ink IK does not exist. 
     The processing unit  120  performs the ink amount detection processing based on the output data of the photoelectric conversion device  322 . Specifically, the processing unit  120  detects the position of the interface of the ink IK based on the output data of the photoelectric conversion device  322 . As illustrated in  FIG. 31 , the interface of the ink IK is considered to exist at any position of the boundary area D2. Therefore, the processing unit  120  detects the interface of the ink IK based on a given threshold Th smaller than the value of the output data in the ink non-detection area and greater than the value of the output data in the ink detection area. 
     For example, the processing unit  120  specifies the maximum value of the output data of the photoelectric conversion device  322  as the value of the output data in the ink non-detection area. The processing unit  120  determines a value smaller than the specified value by a predetermined amount as the threshold Th. Alternatively, the processing unit  120  specifies the minimum value of the output data of the photoelectric conversion device  322  as the value of the output data in the ink detection area. The processing unit  120  determines a value greater than the specified value by a predetermined amount as the threshold Th. Alternatively, the processing unit  120  may determine the threshold Th based on the average of the maximum value and the minimum value of the output data of the photoelectric conversion device  322 . 
     However, when the type of the ink IK and the type of the light source  323  are determined, the value of the output data corresponding to the ink interface can be determined in advance. Therefore, the processing unit  120  may perform processing of reading out the predetermined threshold Th in advance from the storage unit  140  without obtaining the threshold Th each time. 
     When the threshold Th is acquired, the processing unit  120  detects a position where the output value becomes Th as an interface position of the ink IK. In this way, the amount of ink included in the ink tank  310  can be detected by using the photoelectric conversion device  322  which is a linear image sensor. Information obtained directly by using Th is a relative position of the ink interface with respect to the photoelectric conversion device  322 . Therefore, the processing unit  120  may perform calculation for obtaining the remaining amount of the ink IK based on the position of the interface. 
     When all the output data is larger than Th, the processing unit  120  determines that ink does not exist in the target range of ink amount detection, that is, the interface is located at a position lower than the end point of the photoelectric conversion device  322  in the −Z direction. When all the output data is smaller than Th, the processing unit  120  determines that the target range of ink amount detection is filled with ink, that is, the interface is at a position higher than the end point of the photoelectric conversion device  322  in the +Z direction. If it is not possible that the interface is located at a higher position than the end point of the photoelectric conversion device  322  in the +Z direction, it may be determined that an abnormality has occurred. 
     The ink amount detection processing is not limited to processing using the threshold Th in  FIG. 31 . For example, the processing unit  120  performs processing for obtaining an inclination of the graph illustrated in  FIG. 31 . The inclination is specifically a differentiation value and more specifically, a differential value between adjacent output data. When some of the output data are extracted in accordance with the pitch of the optical separator, the adjacent output data represent the adjacent data in the extracted data string. The processing unit  120  detects a point where the inclination is larger than a predetermined threshold, more specifically, a position where the inclination becomes maximum, as the position of the interface. If the maximum value of the obtained inclination is a given inclination threshold or less, the processing unit  120  determines that the interface is at a position lower than the end point of the photoelectric conversion device  322  in the −Z direction or a position higher than the end point in the +Z direction. Which side the interface is on can be identified from the value of the output data. 
     When a plurality of output data are acquired as illustrated in  FIG. 31 , the ink amount detection processing may be performed based on any one of the output data. Alternatively, the processing unit  120  may specify the positions of respective interfaces using respective output data, and determine the final position of the interface based on the specified positions. For example, the processing unit  120  determines, as the interface position, an average value or the like of an interface position obtained based on output data of R, an interface position obtained based on output data of G, and an interface position obtained based on output data of B. Alternatively, the processing unit  120  may obtain composite data obtained by combining three pieces of output data of RGB and obtain the position of the interface based on the composite data. The composite data is average data obtained by averaging output data of RGB at each point, for example. 
       FIG. 32  is a flowchart for explaining processing including the ink amount detection processing. When the processing is started, the processing unit  120  performs control for causing the light source  323  to emit light (S 101 ). Then, in the period during which the light source  323  emits light, reading processing using the photoelectric conversion device  322  is performed (S 102 ). When the light source  323  includes a plurality of LEDs, the processing unit  120  sequentially performs processing of S 101  and S 102  for each of the red LED  323 R, the green LED  323 G, and the blue LED  323 B. Through the above processing, three pieces of output data of RGB illustrated in  FIG. 31  are acquired. 
     Next, the processing unit  120  performs detection processing of the ink amount based on the acquired output data (S 103 ). As described above, the specific processing of S 103  can be variously modified such as comparison processing with the threshold Th and detection processing of the maximum value of the inclination. 
     The processing unit  120  determines the amount of the ink IK in the ink tank  310  based on the detected position of the interface (S 104 ). For example, the processing unit  120  sets ink amounts in three stages of “large remaining amount”, “small remaining amount”, and “ink end” in advance, and determines whether the current ink amount corresponds to which one of them. The large remaining amount represents a state in which a sufficient amount of the ink IK is left and no user action is required for continuing printing. The small remaining amount represents a state in which the continuation of printing itself is possible but the amount of ink is reduced and replenishment by the user is desirable. The ink end represents a situation where the ink amount is markedly reduced and the printing operation should be stopped. 
     When it is determined that the remaining amount is large in processing of S 104  (S 105 ), the processing unit  120  ends the processing without performing notification or the like. When it is determined that the remaining amount is small in the processing of S 104  (S 106 ), the processing unit  120  performs notification processing for urging the user to replenish the ink IK (S 107 ). The notification processing is performed by displaying a text or an image on a display unit  150 , for example. However, the notification processing is not limited to displaying, and may be notification by emitting light from a light emitting unit for notification, notification by sound using a speaker, or notification by combining these. When the ink end is determined in the processing of S 104  (S 108 ), the processing unit  120  performs notification processing of urging the user to replenish the ink IK (S 109 ). The notification processing of S 109  may be the same as the notification processing of S 107 . However, as described above, it is difficult to continue the printing operation in the ink end, which is a serious state as compared with the small remaining amount. Thus, the processing unit  120  may perform notification processing in S 109  different from that of S 107 . Specifically, the processing unit  120  may execute, in S 109 , processing of changing the text to be displayed to a content that strongly prompts the user to replenish ink IK, increasing the light emission frequency, increasing the sound, or the like compared to the processing of S 107 . The processing unit  120  may perform processing (not illustrated) such as printing operation stop control after the processing of S 109 . 
     The execution trigger for the ink amount detection processing illustrated in  FIG. 32  can be set in various ways. For example, the execution start of a given print job may be used as the execution trigger or a lapse of a predetermined time may be used as the execution trigger. 
     The processing unit  120  may store the ink amount detected by in the ink amount detection processing to the storage unit  140 . The processing unit  120  performs processing based on the time series change of the detected ink amount. For example, the processing unit  120  obtains an ink increase amount or an ink decrease amount based on a difference between the ink amount detected at a given timing and the ink amount detected at a timing before the given timing. 
     Since the ink IK is used for printing, head cleaning, or the like, the reduction of the ink amount is natural in consideration of the operation of the electronic apparatus  10 . However, the amount of ink IK consumed per unit time in printing and the amount of ink IK consumed per head cleaning are determined to some extent, and if the amount of consumption is extremely large, there may be some abnormality such as ink leakage. 
     For example, the processing unit  120  obtains a standard ink consumption assumed in printing or the like in advance. The standard ink consumption may be obtained based on the estimated ink consumption per unit time or based on the estimated ink consumption per job. The processing unit  120  determines that there is an abnormality when the ink reduction amount obtained based on the time-series ink amount detection processing is equal to or larger than the standard ink consumption by a predetermined amount or more. Alternatively, the processing unit  120  may perform consumption calculation processing of calculating the amount of ink consumption by counting the number of times of ejection of the ink IK as described above. In this case, the processing unit  120  determines that there is an abnormality when the ink decrease amount obtained based on the time series ink amount detection processing is larger than the ink consumption calculated by the consumption calculation processing by a predetermined amount or more. 
     The processing unit  120  sets an abnormality flag to be ON when the abnormality is determined. In this way, when the ink amount is excessively reduced, some kind of error processing can be executed. Various processing can be considered when the abnormality flag is set to ON. For example, the processing unit  120  may re-execute the ink amount detection processing illustrated in  FIG. 32  with the abnormality flag as a trigger. Alternatively, the processing unit  120  may perform notification processing for urging the user to check the ink tank  310  based on the abnormality flag. 
     The ink amount increases by replenishing the ink IK by the user. However, it is conceivable that the ink amount increases even when the ink IK is not replenished, such as temporary interface change due to shaking of the electronic apparatus  10 , backflow of ink IK from the tube  105 , detection error of the photoelectric conversion device  322 , or the like. Therefore, when the ink increase amount is a given threshold or less, the processing unit  120  determines that the ink IK is not replenished and the increase width is within an allowable error range. In this case, since it is determined that the change in the ink amount is in a normal state, no additional processing is performed. 
     On the other hand, when the ink increase amount is larger than the given threshold, the processing unit  120  determines that the ink is replenished and sets an ink replenishment flag to ON. The ink replenishment flag is used as a trigger for executing ink characteristics determination processing which will be described later, for example. The ink replenishment flag may be used as a trigger for processing of resetting an initial value in the consumption calculation processing. 
     However, when the ink increase amount is larger than the given threshold, there may be a possibility of an unacceptably large error due to some abnormality. Thus, the processing unit  120  performs notification processing for requesting the user to input whether the ink has been replenished, and may determine whether to set the abnormality flag or the ink replenishment flag based on the user input result. 
     3.2 Ink Droplet 
       FIG. 33  is a schematic diagram when an ink droplet adheres to the inner wall of the ink tank  310  in the −Y direction, and a schematic diagram of output data of the photoelectric conversion device  322  when an ink droplet adheres. The ink droplet represents a particle of ink which is a liquid. In  FIG. 33 , the graph is rotated and described so that the vertical axis represents the position and the horizontal axis represents the output data of the photoelectric conversion device  322  in consideration of the positional relationship between the photoelectric conversion device  322  and the ink tank  310 . 
     As described above, the photoelectric conversion device  322  is provided in the −Y direction with respect to the ink tank  310  and detects light from the side surface of the ink tank  310  in the −Y direction. When the ink droplet adheres to the inner wall in the −Y direction, since absorption and scattering of light are generated by the ink droplet, the portion corresponding to the ink droplet becomes relatively dark. As a result, as illustrated in  FIG. 33 , in the output data of the photoelectric conversion device  322 , the value decreases not only in the position E1 equivalent to the interface but also in the range from a position E2 to a position E3 equivalent to the ink droplet. 
     The processing unit  120  detects a point at which the output data is a given threshold Th as a position corresponding to the ink interface as described above, for example. As illustrated in  FIG. 33 , when an ink droplet adheres, there are a plurality of points at which the output data becomes the given threshold Th. 
     Therefore, the processing unit  120  detects the amount of ink in the ink tank based on the lowermost position among the positions where the amount of light detected by the photoelectric conversion device  322  satisfies a given condition. A position where the detected light amount satisfies the given condition is referred to as a candidate position of the ink interface. As described above, in the electronic apparatus  10  that is a printer includes the print head  107  that performs printing by using the ink IK in the ink tank  310 , the light source  323  that irradiates the ink tank  310  with light, the photoelectric conversion device  322  that detects light incident from the ink tank  310  in a period during which the light source  323  emits light, and the processing unit  120  that detects the amount of ink in the ink tank  310  based on the output of the photoelectric conversion device  322 . 
     Since the ink IK in the present embodiment is a liquid, in the normal usage mode of the electronic apparatus  10 , the ink moves in the −Z direction which is a vertically downward direction, in accordance with gravity and accumulates from the bottom surface of the ink tank  310 . Therefore, even if there is a dark area where output data decreases, when there is a brighter air layer vertically downward, it is assumed that the dark area is not the interface of the ink IK but the ink droplet. Thus, it is possible to appropriately detect the ink amount by estimating the position of the lowermost position among the candidate positions of the ink interface as the ink interface. In the case of the example illustrated in  FIG. 33 , the processing unit  120  determines that E3 is the ink droplet among E1 and E3 of which output value is Th or less, and determines that E1 is the ink interface. 
     The processing unit  120  determines that the given condition is satisfied when it is determined that the amount of change of the light amount is the first threshold or more. The amount of change of the light amount is, for example, the amount of change with respect to a given reference light amount. The reference light amount may be a light amount corresponding to the ink non-detection area as described above or a light amount corresponding to the ink detection area. The amount of change of the light amount may be the inclination of the graph. As described above, the method for estimating the candidate position of the ink interface can be variously modified. 
     When a plurality of candidate positions of the interface are detected based on the output of the photoelectric conversion device  322  at the given timing, the processing unit  120  may detect the lowermost candidate position directly as the position of the interface. However, when an ink droplet adheres to the inner wall of the ink tank  310 , it is considered that an event having a low occurrence frequency in the normal usage state of the electronic apparatus  10  has occurred, for example, electronic apparatus  10  is shaken. In this case, since there is a possibility that the state of the ink IK in the ink tank  310  may not be stable, the processing unit  120  may perform the ink amount detection processing again and determine the position of the interface of the ink IK based on the result of the re-detection. 
     Specifically, when a plurality of candidate positions satisfying the given condition are detected in the ink amount detection processing at the first timing, the processing unit  120  performs the ink amount detection processing again at the second timing after the lapse of a given period. The given period here is a short time of several seconds to several tens of seconds. For example, when the ink amount detection processing is performed for each execution of the print job, since the interval of the ink amount detection processing is longer than the execution time of the job, the given period here is shorter than that. Thus, when the adhesion of the ink droplet is suspected, the ink amount detection processing can be quickly executed again. 
     The processing unit  120  determines the lowermost position among the candidate positions detected at the first timing as a temporary interface, and determines whether the temporary interface is determined as the ink interface based on comparison processing between the detection result at the second timing and the detection result at the first timing. For example, when it is determined that the difference between the detection result at the second timing and the detection result at the first timing is small, the processing unit  120  determines that the state of the ink IK is stable and the temporary interface is determined as the ink interface. The small difference indicates, for example, that the change in the position of the point at which the output data is a given threshold in the Z-axis is small. In determining whether the temporary interface is reliable, it is important whether the state of ink IK is stable in the vicinity of the temporary interface. Therefore, it is not necessary to compare all of the detection results at the second timing and the detection results at the first timing, and for example, information on a position close to the temporary interface may be compared. 
       FIG. 34  is a flowchart for explaining the ink amount detection processing including processing related to the ink droplet. Processing of S 201  and S 202  in  FIG. 34  is the same as processing of S 101  and S 102  in  FIG. 32 . Next, the processing unit  120  performs the ink amount detection processing. Specifically, a point at which the output data becomes the threshold Th is detected (S 203 ). When the ink drop exists, there are a first feature point that changes from a value larger than the threshold Th to a threshold Th or less and a second feature point that changes from a value equal to or less than the threshold Th to a value greater than the threshold Th, in the −Z direction at the point where the output data becomes the threshold Th. In the example illustrated in  FIG. 33 , E1 and E3 are the first feature points, and E2 is the second feature point. Since the number of ink droplets is not limited to one, three or more first feature points and two or more second feature points may be detected. The processing unit  120  determines the first feature point as a candidate position of the interface. In the example illustrated in  FIG. 33 , the candidate positions of the interface are E1 and E3, and E1 is the lowermost candidate position between them. The processing unit  120  also stores the second feature point in the storage unit  140 . 
     Next, the processing unit  120  determines whether a plurality of candidate positions of the interface are detected (S 204 ). When there is one candidate position (Yes in S 204 ), the one candidate position is determined as the position of the interface (S 205 ). When a plurality of candidate positions are detected (No in S 204 ), detection processing is executed again after defining the lowermost position of the first feature points as the temporary interface. Specifically, the processing unit  120  performs control for causing the light source  323  to emit light (S 206 ), and performs light reception control of the photoelectric conversion device  322  during a light emission period of the light source  323  (S 207 ). The processing unit  120  detects the first feature point and the second feature point where the output data is the threshold Th (S 208 ). 
     The processing unit  120  performs processing of comparing the detection result in S 203  with the detection result in S 208  (S 209 ). For example, comparison of the lowermost points among the first feature points and comparison of the lowermost points among the second feature points are performed. The processing unit  120  determines whether the change between the two detection results is small based on the comparison processing (S 210 ). 
     When both the changes of the two points are a predetermined level or less (Yes in S 210 ), the degree of change in the vicinity of at least the temporary interface is small, and it is determined that the detection result is reliable. Therefore, the processing unit  120  detects the position of the interface based on the temporary interface detected in S 203  (S 211 ). Note that the processing unit  120  may directly use the position of the temporary interface as the position of the interface, may use the position of the lowermost first feature point detected in S 208  as the position of the interface, or may determine the position of the interface based on an average or the like of the two positions. In  FIG. 34 , the processing is finished after the determination of the position of the interface, but the processing may be shifted to the processing of S 104  in  FIG. 32 . 
     When it is determined that the change between the two detection results is large (No in S 210 ), the processing returns to S 204 , for example, and performs processing of determining the interface again. However, various modifications can be executed for the processing when No is determined in S 210 , for example, when the processing is finished without determining the position of the interface. 
     3.3 Shading Correction 
     The photoelectric conversion device  322  of the present embodiment includes a plurality of photoelectric conversion elements. Since the characteristics of the photoelectric conversion elements are varied, the output may vary depending on the photoelectric conversion elements even when light of the same intensity is incident. There is a possibility that the detection accuracy of the ink amount may be lowered due to this variation. For example, when the output of a given photoelectric conversion element is lowered compared with the output of a peripheral photoelectric conversion element, the processing unit  120  may not be able to determine whether the output is lowered due to the presence of ink IK or the output is lowered due to the variation in the photoelectric conversion elements. Therefore, preferably, the processing unit  120  performs the correction processing on the output data of the photoelectric conversion device  322 , and performs the ink amount detection processing based on the data after the correction processing. Similarly, regarding the ink characteristics determination processing which will be described later, there is a possibility that the processing accuracy may be lowered due to the characteristics variation in the photoelectric conversion elements. By performing the correction processing, the accuracy of the ink characteristics determination processing can be improved. 
     Shading correction is widely used in the linear image sensor used in a scanner. For example, the scanner incorporates a color reference plate used for shading correction. Specifically, the color reference plate is a white reference plate as a white reference. A white reference value is acquired by performing reading processing of a white reference plate in a state where the light source is turned on. A black reference value is acquired by performing reading processing in a state where the light source is turned off. The scanner performs shading correction processing based on the white reference value and the black reference value with respect to digital data being the reading result of the photoelectric conversion element, and outputs an image based on the corrected data. 
     In the present embodiment, by performing correction processing similar to that of the scanner, variation in photoelectric conversion elements can be suppressed. However, as illustrated in  FIG. 31 , the processing unit  120  of the present embodiment performs the ink amount detection processing based on the difference of brightness between the area where the ink IK is not filled and the area where the ink IK is filled. That is, it is not assumed that the photoelectric conversion device  322  used for the ink amount detection processing detects light having a larger amount of light than light from the area where the ink IK is not filled. The side surface of the ink tank  310  is formed of a light transmissive member such as a resin, and the reflectance is not as higher as that of the white reference plate. Therefore, in the case where the output data when the white reference plate is read is used as the white reference value, the area near the maximum value is not used in the actual ink amount detection processing. Since the data is processed using a narrow numerical range, the resolution is lowered, and the accuracy of the ink amount detection processing may be lowered. In the first place, the printer unit  100  and the ink tank unit  300  often do not include the white reference plate. 
     The method of the present embodiment is applicable to a production method of a printer which detects the ink amount in the ink tank  310  using the light source  323  and the photoelectric conversion device  322 . The production method includes a first step of irradiating the ink tank  310  with light from the light source  323  in a state where the ink IK is not filled in the ink tank  310 , and detecting light from the ink tank  310  using the photoelectric conversion device  322 . Also, the production method includes a second step of storing a first correction parameter of the output of the photoelectric conversion device  322  in a non-volatile storage unit of the printer, based on the output of the photoelectric conversion device  322  in the first step. The non-volatile storage unit is included in, for example, a storage unit  140 . The storage unit  140  may include a volatile storage unit in addition to the non-volatile storage unit. 
     In the first step, “unfilled” means that ink is not filled in an area facing the photoelectric conversion device  322  in the ink tank  310 . That is, the first step is not prevented from being executed in a state where the ink IK is filled in the area in the −Z direction with respect to the position where the photoelectric conversion device  322  is provided. Alternatively, the first step may be executed when the ink IK is once filled and the ink is discharged and not filled. The state at this time is also “unfilled” because the ink will be filled later. The processing unit  120  performs light emission control of the light source  323  and light reception control of the photoelectric conversion device  322 . When the light source  323  includes the red LED  323 R, the green LED  323 G, and the blue LED  323 B, the first correction parameter may be obtained by causing any one LED to emit light, but it is not hindered to obtain the first correction parameter individually for each emission color. The first correction parameter stored in the storage unit  140  is a set of values corresponding to the number of photoelectric conversion elements. 
     The first correction parameter is a white reference parameter. In this way, for each element of the plurality of photoelectric conversion elements, correction is performed so that the value of the output data in the ink non-detection area becomes a value near the maximum value. Thus, since variation in the photoelectric conversion elements is suppressed and the range of output data is effectively utilized, the accuracy of ink amount detection processing can be improved. 
     Further, the photoelectric conversion device  322  used for the ink amount detection processing is not assumed to receive light having a smaller amount of light than light from the area filled with the ink IK. When correction processing is performed with output data in a state where the light source  323  is turned off as a reference value, the area near the minimum value is not used in actual ink amount detection processing. Thus, the accuracy of ink amount detection processing may be reduced. 
     Therefore, the production method of the printer according to the present embodiment may include a third step of irradiating the ink tank  310  with light from the light source  323  and detecting light from the ink tank  310  using the photoelectric conversion device  322  in a state where the ink tank  310  is filled with the ink IK. The production method includes a fourth step of storing a second correction parameter of the output of the photoelectric conversion device in a non-volatile storage unit of the printer based on the output of the photoelectric conversion device  322  in the third step. 
     In the third step, “filling” means that at least an area of the ink tank  310  facing the photoelectric conversion device  322  is filled with ink, and the specific amount of ink IK can be variously modified. 
     The second correction parameter is a parameter of a black reference. In this way, for each element of the plurality of photoelectric conversion elements, correction is performed so that the value of the output data in the ink detection area becomes a value near the minimum value. By using both the white reference parameter and the black reference parameter, variation in the photoelectric conversion elements is further suppressed and the range of output data is effectively utilized, thereby improving the accuracy of ink amount detection processing. 
     When the photoelectric conversion device  322  is provided in each of the plurality of ink tanks  310 , ink IK corresponding to the target ink tank  310  may be filled in the third step for each photoelectric conversion device  322 . For example, in the third step for the photoelectric conversion device  322  for detecting the amount of yellow ink IK, in a state where the yellow ink IK is filled, the ink tank  310  is irradiated with light from the light source  323 , and light from the ink tank  310  is detected using the photoelectric conversion device  322 . In the third step for the photoelectric conversion device  322  for detecting the amount of the magenta ink, the magenta ink IK is filled. In this way, the data range can be appropriately expanded. However, filling of the same ink IK for inspection is not hindered for all the ink tanks  310  in consideration of a reduction in manufacturing burden. In this case also, the deterioration of accuracy caused by variation in the photoelectric conversion elements can be suppressed. 
     The correction processing using the first correction parameter and the second correction parameter is performed by equation (1). In equation (1), W represents the first correction parameter which is the parameter of the white reference. B represents the second correction parameter which is the parameter of the black reference. E is output data before the correction processing, and E′ is output data after the correction processing. 
     
       
         
           
             
               
                 
                   
                     E 
                     ′ 
                   
                   = 
                   
                     
                       E 
                       - 
                       B 
                     
                     
                       W 
                       - 
                       B 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     The processing unit  120  acquires output data after A/D conversion from the AFE  130 , and performs correction processing using the above equation (1) on each output data. Then, the processing unit  120  performs the ink amount detection processing and the ink characteristics determination processing described later based on the output data after the correction processing. In the case of using the above equation (1), E′ is data of 0 or more and 1 or less. However, the numerical range of E′ may be changed by multiplying the right side of the equation (1) by a given coefficient. For example, when the output data is set to 8 bits, the processing unit  120  multiplies the right side by 255 and then converts it to an integer, and sets the result as corrected output data E′. 
       FIG. 35  is a schematic diagram for explaining a change in output data due to the correction processing. F1 in  FIG. 35  represents data before the correction processing, and F2 represents data after the correction processing. In both F1 and F2, the horizontal axis represents a position in the photoelectric conversion device  322 , and the vertical axis represents output data of the photoelectric conversion element corresponding to the position. 
     F11 is an example of output data detected in the first step, that is, the first correction parameter. Despite the incidence of light from an area that is not filled with ink IK on all the photoelectric conversion elements, values vary due to variation in the photoelectric conversion elements. F12 is an example of output data detected in the third step, that is, the second correction parameter. Despite the incidence of light from an area that is filled with ink IK on all the photoelectric conversion elements, values vary due to variation in the photoelectric conversion elements. Further, since the output data in the ink amount detection processing has a value between F11 and F12, for example, a range indicated by F13, the output data is narrower than F14, which is a numerical value range that the output data can take. 
     F21 is a correction result for the output data detected in the first step. As indicated by F21, since correction processing is performed so that output data corresponding to the area not filled with ink IK has the maximum value max, variation in data is suppressed. F22 is a correction result for the output data detected in the third step. As indicated by F22, since correction processing is performed so that output data corresponding to the area filled with the ink IK has the minimum value min, the variation in data is suppressed. Further, since the output data in the ink amount detection processing has a value between F21 and F22, a numerical range that the output data can take can be effectively utilized. 
     As illustrated in the above equation (1) and  FIG. 35 , the first correction parameter is a normalization parameter of the output of the photoelectric conversion device  322 . Similarly, the second correction parameter is a normalization parameter of the output of the photoelectric conversion device  322 . That is, correction processing in the present embodiment is normalization processing based on the first correction parameter. By using the output data after the normalization processing, the accuracy of ink amount detection processing or the like can be improved. 
     However, the production method of the printer according to the present embodiment is not limited to one including all the first to fourth steps. In the manufacturing step of the printer, it is considered normal that the ink tank  310  is not filled with ink IK. Thus, the first step is easily implemented. On the other hand, in the third step, it is necessary to fill the ink tank  310  with ink IK to the extent that the ink IK exists at least at a portion facing the photoelectric conversion device  322  of the ink tank  310 . Therefore, the case where the third step can be executed is limited, or the filling of ink IK is required only for executing the third step. 
     Therefore, the production method of the printer according to the present embodiment may include a fifth step of detecting light from the ink tank  310  using the photoelectric conversion device  322  in a state where the light source  323  is not caused to radiate light, and a sixth step of storing a third correction parameter of the output of the photoelectric conversion device  322  in the non-volatile storage unit of the printer based on the output of the photoelectric conversion device  322  in the fifth step. The third correction parameter is a parameter of the black reference. 
     The fifth step and the sixth step are performed in place of the third step and the fourth step. In this way, the parameter of the black reference can be easily acquired as compared with the case where the third step is performed. The processing unit  120  executes correction processing on the output data of the photoelectric conversion device  322  based on the first correction parameter and the third correction parameter. The third step is advantageous from the viewpoint of the range of the output data, and the fifth step is advantageous from the viewpoint of the easiness of measurement. 
     3.4 Correction Processing by Mark 
     As described above with reference to  FIG. 31 , what is required in the ink amount detection processing is information indicating which one of the plurality of photoelectric conversion elements included in the photoelectric conversion device  322  has a position corresponding to the ink interface. In order to specify the ink amount, the position of the ink interface in the ink tank  310  is required. That is, in order to specify the ink amount, the positional relationship between the ink tank  310  and the photoelectric conversion device  322  has to be known. 
     For example, the sensor unit  320  is fixed to a predetermined position of the ink tank  310  based on the design. Since the error in mounting of the photoelectric conversion device  322  on the substrate  321  is considered to be sufficiently small, when the sensor unit  320  is fixed to the ink tank  310  as designed, the positional relationship between the ink tank  310  and the photoelectric conversion device  322  also becomes as designed. However, the positional relationship between the sensor unit  320  and the ink tank  310  may not coincide with that of the design due to the assembly error. 
       FIG. 36  is a schematic diagram illustrating the assembly error of the sensor unit  320 . The sensor unit  320  is designed to be fixed at the position indicated by G1, but may be fixed at the position indicated by G2 that is shifted in the +Z direction due to the assembly error. When the sensor unit  320  is shifted in the +Z direction, the processing unit  120  detects the ink interface at the position of the photoelectric conversion element in the −Z direction rather than the photoelectric conversion element originally corresponding to the ink interface. Therefore, it is determined that the ink amount is smaller than the actual amount. On the contrary, when the sensor unit  320  is shifted in the −Z direction, the processing unit  120  detects the ink interface at the position of the photoelectric conversion element in the +Z direction rather than the photoelectric conversion element originally corresponding to the ink interface. Therefore, it is determined that the ink amount is larger than the actual amount. Thus, the assembly error in the Z-axis becomes a factor for lowering the accuracy of the ink amount detection processing. Although errors in the horizontal direction, particularly in the X-axis, can be generated, the assembly errors in the horizontal direction do not lead to erroneous determination of the interface position. The sensor unit  320  is illustrated in  FIG. 36 , but the same applies to the case of using the light receiving unit  340 . 
     The electronic apparatus  10  of the present embodiment includes the ink tank  310  with a mark MK attached to its side surface. The photoelectric conversion device  322  is provided outside the side surface to which the mark MK is attached out of the side surfaces of the ink tank  310 , and detects light from the ink tank  310  in a period during which the light source  323  emits light. The processing unit  120  determines the position of the interface of the ink IK based on the output of the photoelectric conversion device  322 , and detects the amount of ink in the ink tank  310  based on the position of the mark MK and the position of the interface. 
       FIG. 37  is a schematic diagram illustrating the relationship between the position of the mark MK and the assembly error of the photoelectric conversion device  322 . For example, the photoelectric conversion device  322  is provided in the −Y direction of the ink tank  310 , and the mark MK is attached to the side surface of the ink tank  310  in the −Y direction. Due to the assembly error, the sensor unit  320  may be fixed at the position indicated by H1, or may be fixed at the position indicated by H2. The position of the interface detected by the photoelectric conversion device  322  changes between H1 and H2. However, since the position of the mark MK detected by the photoelectric conversion device  322  is also changed, the difference between the position of the mark MK and the position of the interface is common between H1 and H2. Since the position of the mark MK in the ink tank  310  is known in design, the processing unit  120  can appropriately determine the position of the interface in the ink tank  310  even when the assembly error occurs. For example, if the distance from the bottom surface of the ink tank  310  to the mark MK is known, the processing unit  120  can calculate the distance from the bottom surface of the ink tank  310  to the interface based on the difference between the position of the mark MK and the position of the interface. 
     The mark MK is a member that is provided at a given position of the ink tank  310  in the Z-axis, and has a smaller light transmittance than the members constituting the ink tank  310 . For example, the mark MK is a coating layer provided on the outer wall of the ink tank  310 . Alternatively, when the ink tank  310  is formed by two-color molding, the mark MK is made of a member having relatively low light transmittance, and a portion other than the mark MK is made of a member having relatively high light transmittance. That is, the mark MK can be realized by the same configuration as the first layer to the third layer when the optical separator is provided on the side surface of the ink tank  310 . In this way, the positional relationship between the photoelectric conversion device  322  and the mark MK can be estimated based on the output of the photoelectric conversion device  322 . 
       FIG. 38  is a schematic diagram for explaining the relationship between the mark MK and the output data of the photoelectric conversion device  322 . Since the light emitted from the area to which the mark MK is attached to the photoelectric conversion device  322  becomes very weak light, the output data corresponding to the position of the mark MK is made smaller than the peripheral output data to the extent to be identifiable. Thus, the position of the mark MK in the photoelectric conversion device  322  can be specified by making the optical characteristics of the mark MK different from those of the wall surface of the ink tank  310 . 
     As described above, the processing unit  120  performs ink amount detection processing based on the relative position of the mark MK and the interface on the Z-axis. Therefore, the position of the mark MK on the Z-axis in the ink tank  310  needs to be a given fixed value. For example, the mark MK may be a point provided at a predetermined position on the side surface of the ink tank  310 . The point is, for example, a minute circular shape having a size capable of suppressing light incident on a given photoelectric conversion element. 
     However, the positional relationship between the photoelectric conversion device  322  and the ink tank  310  on the X-axis may change due to the assembly error. When the length of the mark MK on the X-axis is short, there is a possibility that the positional relationship in which the mark MK and the photoelectric conversion device  322  do not face each other may be caused by the assembly error. Therefore, the mark MK is preferably a shape including a line in the horizontal direction. 
     For example, the mark MK is a line segment extending in the horizontal direction as illustrated in  FIG. 38 , specifically, is a rectangle with the Z-axis as the short side direction and the X-axis as the longitudinal direction. By using such a mark MK, it is possible to appropriately detect the mark MK by the photoelectric conversion device  322  even when the assembly error in the horizontal direction occurs. However, the mark MK may include a line in the horizontal direction at a portion of a boundary between the area of the mark MK and an area other than the mark MK, and the shape thereof is not limited to a rectangle. For example, the mark MK may be a triangle provided so that any one side thereof is horizontal. In this case, the processing unit  120  uses the position of the horizontal side of the mark MK for the ink amount detection processing. The concrete shape of the mark MK can be variously modified. 
     As illustrated in  FIG. 38 , the mark MK can be detected as a position where the output data is locally decreased. Therefore, the processing unit  120  may perform processing of determining the position of the mark MK based on the output of the photoelectric conversion device  322 . For example, the processing unit  120  performs both the detection processing of the mark MK and the detection processing of the interface every time when performing the ink amount detection processing. 
     However, it is considered that, once the assembly is performed, the positional relationship between the ink tank  310  and the photoelectric conversion device  322  is not changed significantly thereafter. Therefore, the electronic apparatus  10  may include a non-volatile storage circuit for storing information representing the position of the mark MK. The processing unit  120  detects the ink amount by reading information indicating the position of the mark MK from the non-volatile storage circuit. In this case, since the information that has already been obtained can be used for the position of the mark MK, the processing unit  120  can detect the ink amount by detecting the interface of the ink IK from the output data. For example, the processing unit  120  obtains the mark MK in the first ink amount detection processing, and writes the obtained position of the mark MK in the storage unit  140 . In the subsequent ink amount detection processing, the processing unit  120  continuously utilizes the position of the mark MK that has been written. Thus, the position of the mark can be identified even in a situation where the identification of the mark is difficult because the interface of the ink exists above the position of the mark. 
     Alternatively, the position of the mark MK may be written in the storage unit  140  at the manufacturing stage. For example, the production method of the printer according to the present embodiment includes a seventh step of storing a fourth correction parameter representing the position of the mark MK in a non-volatile storage unit of the printer based on the output of the photoelectric conversion device  322  in the first step. Here, in the first step, an example of acquiring the fourth correction parameter together with the first correction parameter which is a parameter of white correction is exemplified, but it is not limited thereto. For example, the production method of the printer may include an eighth step, which is different from the first step, of irradiating the ink tank  310  with light from the light source  323  and detecting light from the ink tank  310  using the photoelectric conversion device  322 . In this case, the production method includes a seventh step of storing the fourth correction parameter representing the position of the mark MK in a non-volatile storage unit of the printer based on the output of the photoelectric conversion device  322  in the eighth step. 
     In the ink tank  310 , a slit which is an optical separator for separating light in the vertical direction may be provided on the side surface. In this case, since the optical separator includes an area with low light transmittance, the optical characteristics difference between the area and the mark MK is small. Therefore, in this case, it is preferable that the length of the mark MK in the vertical direction is longer than the pitch of the slit. 
       FIG. 39  is a schematic diagram illustrating the side surface of the ink tank  310  provided with both the optical separator and the mark MK. When the optical separator is provided, areas with a large amount of light reaching the photoelectric conversion device  322  from the ink tank  310  and areas with a small amount thereof appear alternately, in the Z-axis. As illustrated in  FIG. 38 , it is difficult to determine whether the reduction is caused by the optical separator or the mark MK, only by simply detecting the reduction of the output data. On the other hand, after changing the lengths of the optical separator and the mark MK, the processing unit  120  detects a range where the output data decreases. For example, in −Z direction, the processing unit  120  detects a point where the output data changes from a value larger than a given threshold to a value equal to or smaller than the threshold, and a point where the output data changes from a value equal to or smaller than the threshold to a value larger than the threshold, thereby obtaining the length between the two points. 
     In the example illustrated in  FIG. 39 , since the reduction range of the data caused by the mark MK is about three times as long as the reduction range of the data caused by the optical separator, the mark MK and the optical separator can be appropriately identified. As described above, the resolution in the ink amount detection processing is determined by the arrangement pitch of photoelectric conversion elements in the photoelectric conversion device  322  and the wider optical separation pitch of the optical separator. The pitch of the optical separator is preferably narrowed as much as possible, considering the resolution. Therefore, when a difference is provided between the lengths of the optical separator and the mark MK, it is easier to form the mark MK when the mark MK is made longer, and it is possible to suppress a decrease in resolution. 
     Heretofore, an assembly error in the translation direction of the photoelectric conversion device  322  has been described. However, the assembly errors can occur in the rotational direction.  FIG. 40  is a schematic diagram illustrating a relationship between the ink tank  310  and the photoelectric conversion device  322  when the photoelectric conversion device  322  rotates around the Y-axis by θ. As illustrated in  FIG. 40 , the distance between the mark MK and the interface on the Z-axis is H1. However, the processing unit  120  performs the ink amount detection processing on the assumption that the photoelectric conversion devices  322  are arranged along the Z-axis. Therefore, the processing unit  120  determines that the distance between the mark MK and the interface on the Z-axis is H2. By determining that the distance from the mark MK to the interface is excessively long, it is determined that the ink amount is smaller than the actual amount. Thus, the assembly error in the rotational direction also becomes a factor of lowering the accuracy of the ink amount detection processing. 
     The photoelectric conversion device  322  according to the present embodiment may include a first linear image sensor provided on the substrate  321  and a second linear image sensor provided on the substrate  321 . The processing unit  120  estimates the inclination of the photoelectric conversion device  322  with respect to the ink tank  310  based on the position of the mark MK determined from the first linear image sensor and the position of the mark MK determined from the second linear image sensor. 
       FIGS. 41 and 42  are diagrams for explaining the positional relationship between the ink tank  310 , the first linear image sensor, and the second linear image sensor.  FIG. 41  illustrates a positional relationship in a state where no assembly error occurs. For example, the first linear image sensor and the second linear image sensor are sensor chips having the same length and the same element pitch. In the example illustrated in  FIG. 41 , when no assembly error occurs, the position of the mark MK in the first linear image sensor coincides with the position of the mark MK in the second linear image sensor. The position of the interface in the first linear image sensor coincides with the position of the interface in the second linear image sensor. The positional relationship between the first linear image sensor and the second linear image sensor may be known, and the length, the element pitch, the position in the Z-direction, or the like are not limited to examples in  FIG. 41 . 
       FIG. 42  illustrates the positional relationship when the photoelectric conversion device  322  rotates by θ1 with respect to the ink tank  310 . The position of the mark MK in the second linear image sensor is shifted by I1 as compared with the position of the mark MK in the first linear image sensor. Since the distance I2 between the two linear image sensors is known, a rotation angle θ1 due to an assembly error is obtained by the following equation (2). When θ1 is obtained, the actual distance I4 between the mark MK and the interface is obtained by equation (3). 
     
       
         
           
             
               
                 
                   
                     θ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                   = 
                   
                     
                       tan 
                       
                         - 
                         1 
                       
                     
                     ⁡ 
                     
                       ( 
                       
                         
                           I 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         
                           I 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
             
               
                 
                   
                     I 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     4 
                   
                   = 
                   
                     I 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                     × 
                     cos 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     θ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     1 
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     Thus, by using two linear image sensors for one ink tank  310 , the inclination of the photoelectric conversion device  322  with respect to the ink tank  310  can be detected. Thus, even when the assembly error in the rotational direction occurs, the ink amount detection processing can be performed with high accuracy. The two linear image sensors need to be arranged not side by side in the longitudinal direction. More preferably, the second linear image sensor is disposed at a certain interval in a direction intersecting the longitudinal direction of the first linear image sensor. This is because even if the rotation angle θ1 is the same, the difference I1 between the detection positions of the two linear image sensors increases as the interval I2 increases. However, since the two linear image sensors need to detect the same ink tank  310 , the interval cannot be excessively widened. Therefore, it is desirable to set an appropriate value for the interval between the two linear image sensors based on the shape of the ink tank  310  or the like. 
     The processing unit  120  may estimate an inclination φ of the ink tank  310  with respect to the horizontal plane based on the position of the interface determined from the first linear image sensor and the position of the interface determined from the second linear image sensor. 
       FIG. 43  is a schematic diagram when the ink tank  310  is inclined with respect to an XY plane which is the horizontal plane.  FIG. 43  illustrates an example in which the photoelectric conversion device  322  is fixed at an appropriate angle with respect to the ink tank  310 . As illustrated in  FIG. 43 , when the ink tank  310  is inclined with respect to the horizontal plane, the line representing the mark MK rotates in accordance with the rotation of the ink tank  310 , but the ink interface coincides with the horizontal plane. 
     The position of the interface in the second linear image sensor is shifted by J1 as compared with the position of the interface in the first linear image sensor. Since the distance J2 between the two linear image sensors is known, the rotation angle θ2 of the photoelectric conversion device  322  with respect to the horizontal plane is obtained by the following equation (4). In  FIG. 43 , an example is considered in which the assembly error in the rotational direction of the ink tank  310  and the photoelectric conversion device  322  is not generated. Therefore, the inclination φ of the ink tank  310  with respect to the horizontal plane is equal to the rotation angle θ2 of the photoelectric conversion device  322  with respect to the horizontal plane. 
     
       
         
           
             
               
                 
                   
                     θ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   = 
                   
                     
                       tan 
                       
                         - 
                         1 
                       
                     
                     ⁡ 
                     
                       ( 
                       
                         
                           J 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           1 
                         
                         
                           J 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     In the case of the state illustrated in  FIG. 43 , since the ink tank  310  itself is inclined, the ink amount cannot be specified only from the interface at one given point. In order to specify the ink amount, arithmetic processing using the position of the interface at the given point, the inclination angle φ of the ink tank  310 , and the shape of the ink tank  310  is required. The processing unit  120  may determine the ink amount by performing such a calculation. Alternatively, when the inclination of the ink tank  310  is detected, the processing unit  120  may perform processing for notifying the user of the fact and skip the calculation of the ink amount. 
     The processing unit  120  may obtain both the inclination θ1 of the photoelectric conversion device  322  with respect to the ink tank  310  and the inclination φ of the ink tank  310  with respect to the horizontal plane. That is, the situation that the photoelectric conversion device  322  rotates by θ1 with respect to the ink tank  310 , and the ink tank  310  inclines by φ with respect to the horizontal plane may be taken into consideration. 
     As illustrated in  FIGS. 42 and 43 , the inclination θ1 of the photoelectric conversion device  322  with respect to the ink tank  310  is obtained based on the difference in the positions of the marks MK in the two linear image sensors. Further, the inclination θ2 of the photoelectric conversion device  322  with respect to the horizontal plane is obtained based on the difference in the positions of the interfaces in the two linear image sensors. The inclination φ of the ink tank  310  with respect to the horizontal plane is obtained based on θ1 and θ2. For example, φ is a difference between θ1 and θ2. That is, even when both the inclination of the photoelectric conversion device  322  with respect to the ink tank  310  and the inclination of the ink tank  310  with respect to the horizontal plane are generated, the processing unit  120  can calculate each inclination based on two linear image sensors provided for the same ink tank  310 . 
     4. Determination Processing of Ink Characteristics Based on Output of Photoelectric Conversion Device 
     The electronic apparatus  10  according to the present embodiment is a printer including the ink tank  310 , the print head  107 , the light source  323 , the photoelectric conversion device  322 , and the processing unit  120 . The processing unit  120  determines the ink characteristics in the ink tank  310  based on the characteristics of the light amount detected by the photoelectric conversion device  322 . 
     As described above with reference to  FIGS. 2 and 3 , the electronic apparatus  10  may include a plurality of ink tanks  310  filled with different kinds of ink IK. In this case, there is a possibility that the user erroneously fills the other ink tank  310  such as the ink tank  310   b  with the ink IKa to be filled in the ink tank  310   a . Even if the electronic apparatus  10  is a monochrome printer having one ink tank  310 , if the user uses printers of different models together, there is a possibility that the ink IK used for another printer is erroneously filled. Furthermore, even when the user uses only one monochrome printer, since many different inks are distributed in the market depending on the model, the possibility that the user erroneously purchases and fills ink for the different model cannot be denied. 
     For example, when the ink tank  310  to be filled with yellow ink is filled with magenta ink, the color of the printing result largely deviates from the desired color. That is, in order to perform appropriate printing, it is necessary to appropriately detect the error of the color of the ink. Therefore, the processing unit  120  determines the color characteristics of the ink as the ink characteristics. 
       FIG. 44  is a diagram comparing output data of the photoelectric conversion device  322  for two inks IK having different color characteristics. K1 in  FIG. 44  is an example of output data of the photoelectric conversion device  322  when measurement is performed for the ink tank  310  filled with yellow ink. K2 is an example of output data of the photoelectric conversion device  322  when measurement is performed for the ink tank  310  filled with magenta ink. The horizontal axes of K1 and K2 represent positions in the photoelectric conversion device  322 , and the vertical axes represent output data corresponding to the positions. In  FIG. 44 , the position of ink interface is made common to K1 and K2. However, as will be described later, the output data in the ink boundary area or the ink detection area may be acquired in the ink characteristics determination processing, and the position of the ink interface is optional. 
       FIG. 44  illustrates the result of performing the correction processing indicated by the above equation (1) with the first correction parameter as the white reference parameter and the third correction parameter as the black reference parameter. The third correction parameter is a parameter acquired in a state where the ink IK is not filled. Therefore, as illustrated in  FIG. 44 , data in the ink detection area does not become a value close to 0, but becomes a different value depending on the color characteristics of the target ink IK. 
     In the example illustrated in  FIG. 44 , when yellow ink is the target, the signal value in the ink amount detection area is a value around 0.55 when any of RGB illumination light is used. On the other hand, when the magenta ink is the target, the signal value in the ink amount detection area is a value around 0.40 when any of RGB illumination light is used. 
     The processing unit  120  determines the ink characteristics based on the light amount in the ink detection area which is an area where it is determined that ink IK exists in the ink tank. In other words, the processing unit  120  uses the value of the output data in the ink detection area as a feature amount for determining the ink characteristics. As described above, the magnitude of the light amount is detected as the magnitude of the output data based on the photoelectric conversion device  322 . 
     The processing unit  120  first specifies an ink detection area. For example, the processing unit  120  specifies an area where the inclination is an inclination threshold or less and the data value is smaller than 1 by a predetermined amount or more as the ink detection area. The processing unit  120  obtains the minimum value of data in the ink detection area as the ink characteristics determination feature amount. In the example illustrated in  FIG. 44 , the processing unit  120  may use any of RGB data to obtain the minimum value. Alternatively, composite data obtained by combining two or more pieces of data among RGB may be obtained, and the minimum value in the ink detection area of the composite data may be obtained. The composite data is average data obtained by averaging RGB data at each point, for example. 
     In the example illustrated in  FIG. 44 , the processing unit  120  determines that the ink IK is yellow ink when the obtained minimum value is close to 0.55, and that the ink IK is magenta ink when it is close to 0.40. Although an example using the minimum value is exemplified here, other statistical values such as the average value and the median value of the output data in the ink detection area may be used. 
     As described above, in the ink characteristics determination processing, it is important to determine whether a given ink tank  310  is filled with an erroneous ink IK. Therefore, the processing unit  120  determines whether the ink IK other than the yellow ink is filled in the yellow ink tank  310 , and does not need to specify a specific color of the ink IK. For example, when the ink tank  310  for yellow ink is targeted, the processing unit  120  compares the output data in the ink detection area with 0.40 as a reference value of yellow ink, and determines abnormality when the difference is equal to or more than a given threshold. Similarly, when the ink tank  310  for magenta ink is targeted, the processing unit  120  compares the output data in the ink detection area with 0.55 as a reference value of magenta ink, and determines abnormality when the difference is equal to or more than a given threshold. 
     The processing unit  120  may also determine the ink characteristics based on the change characteristics of the light amount in the ink boundary area which is the boundary area between the area determined to have the ink IK in the ink tank and the area determined to have no ink. In other words, the processing unit  120  uses the change in the output data in the ink boundary area as the ink characteristics determination feature amount. 
     For example, the processing unit  120  obtains the maximum value of the inclination of the output data, and detects, as a boundary area, an area where the maximum value of the inclination is larger than the inclination threshold. The processing unit  120  obtains the maximum value of inclination in the boundary area as an ink characteristics determination feature amount. In the example illustrated in  FIG. 44 , the maximum value of inclination of yellow ink is relatively small, and the maximum value of inclination of magenta ink is large. Thus, the processing unit  120  can identify yellow ink and magenta ink by determining the maximum value of the inclination. Here, an example in which the maximum value of the inclination is used has been exemplified, but other statistical values such as an average value or a median value may be used. When using the inclination, the processing unit  120  may perform processing of specifying the color of ink IK, or may determine normality/abnormality. 
     In  FIG. 44 , the example in which the third correction parameter is used as the black reference parameter has been described. Thus, the reference value used for the ink characteristics determination processing is different according to ink IK, such as the reference value of the yellow ink is about 0.55 and the reference value of the magenta ink is about 0.40. However, the parameter of the black reference may be a second correction parameter. 
     For example, in the case of the photoelectric conversion device  322  corrected by the second correction parameter acquired in the state where the yellow ink is filled, the reference value of the yellow ink becomes a value close to zero. In the case of the photoelectric conversion device  322  corrected by the second correction parameter acquired in the state where magenta ink is filled, the reference value of the magenta ink becomes a value close to zero. In this case, the relationship in which the output data in the ink detection area when the appropriate ink IK is filled is close to 0, and the output data in the ink detection area when the different ink IK is filled deviates from 0 is established. 
     For example, when magenta ink is erroneously filled in the ink tank  310  corresponding to the photoelectric conversion device  322  corrected by using yellow ink, the output data in the ink detection area becomes a negative value which is small enough to be identified as compared with 0. When yellow ink is erroneously filled in the ink tank  310  corresponding to the photoelectric conversion device  322  corrected by using magenta ink, the output data in the ink detection area becomes a value which is large enough to be identified as compared with 0. Thus, even when correction processing using the second correction parameter is performed, ink characteristics determination processing can be appropriately executed. Since the reference value becomes a value close to zero, the numerical range of the output data may be expanded as necessary so that a negative value can be taken. Similarly, after performing the correction processing using the second correction parameter, the ink characteristics determination processing can be performed using the inclination in the ink boundary area. 
     The ink characteristics determined in the ink characteristics determination processing are not limited to color characteristics. For example, as described above with reference to  FIG. 2 , pigment ink and dye ink exist as the same black ink. The pigment ink has high color reproducibility and quick drying property. The dye ink has a vivid color and is easy to obtain a glossy feeling. Therefore, it is desirable to properly use inks of the same color according to the characteristics. In the printer, ink characteristics suitable for the printer are different according to various factors such as a physical structure of the print head  107 , an ink ejecting method, a printing speed, and a printing medium expected to be used. For this reason, there may be a case where suitable inks IK are different depending on the model even for pigment inks of the same color. Therefore, the processing unit  120  determines the color material characteristics of the ink as the ink characteristics. The color material represents a raw material of color and specifically represents a pigment or a dye. However, as organic pigments and inorganic pigments are known as pigments, the color materials here may represent more specific types and differences in properties. 
       FIG. 45  is a diagram comparing output data of the photoelectric conversion devices  322  for two inks IK having different color material characteristics. L1 in  FIG. 45  is an example of output data of the photoelectric conversion device  322  in the case of measuring the ink tank  310  filled with magenta dye ink. L2 is an example of output data of the photoelectric conversion device  322  in the case of measuring the ink tank  310  filled with magenta pigment ink. The horizontal axes of L1 and L2 represent positions in the photoelectric conversion device  322 , and the vertical axes represent output data corresponding to the positions. Similarly to  FIG. 44 ,  FIG. 45  illustrates the result of performing the correction processing indicated by the above equation (1) using the first correction parameter as the white reference parameter and the third correction parameter as the black reference parameter. 
     As illustrated in  FIG. 45 , output data of the photoelectric conversion device  322  based on light emission of the red LED  323 R is greatly different between magenta dye ink and magenta pigment ink. Therefore, the processing unit  120  determines the ink characteristics based on the light amount in the ink detection area or the change characteristics of the light amount in the ink boundary area. Specifically, the processing unit  120  determines that the ink is the dye ink when the R data in the ink detection area is small, and determines that the ink is the pigment ink when the data is large. Alternatively, the processing unit  120  determines that the ink is the dye ink when the inclination of the R data in the ink boundary area is large, and determines that the ink is the pigment ink when the data is small. 
     Alternatively, when the photoelectric conversion device  322  detects light of the first wavelength and light of the second wavelength, the processing unit  120  may determine the ink characteristics based on the first characteristics of the light amount of light of the first wavelength and the second characteristics of the light amount of light of the second wavelength. In other words, the processing unit  120  uses information representing the relationship between the first characteristics and the second characteristics as the ink characteristics determination feature amount. As described above, the configuration in which the photoelectric conversion device  322  detects light having a plurality of different wavelengths may be realized by a plurality of light sources  323  having different wavelength bands of irradiation light, or realized by a combination of a light source having a wide wavelength band and a filter. 
     In the example illustrated in  FIG. 45 , for the magenta dye ink, RGB data has the same characteristics in both the ink boundary area and the ink detection area. On the other hand, in the magenta pigment ink, the R data is larger than the G data and B data in the ink detection area. In the magenta pigment ink, the inclination of the R data is smaller than the inclination of the G data and B data in the ink boundary area. Therefore, the processing unit  120  determines that the ink is the magenta dye ink when a first characteristics related to red light and a second characteristics related to blue light or green light are similar, and determines that the ink is the magenta pigment ink when the first characteristics and second characteristics are not similar. 
     Specifically, the processing unit  120  obtains a ratio of the R data value to the B data value or the G data value in the ink detection area, as the ink characteristics determination feature amount. The processing unit  120  determines that the ink is the magenta dye ink when the determined ratio is close to 1, and determines that the ink is the magenta pigment ink when the difference from 1 is large. Alternatively, the processing unit  120  determines the ratio of the inclination of the R data to the inclination of the B data or the inclination of the G data in the ink boundary area. The processing unit  120  determines that the ink is the magenta dye ink when the determined ratio is close to 1, and determines that the ink is the magenta pigment ink when the difference from 1 is large. 
     The determination of the color characteristics and the determination of the color material characteristics have been described above respectively. However, the processing unit  120  of the present embodiment may perform the ink characteristics determination processing of determining both the color characteristics and the color material characteristics. 
     In the above, the example in which the determination based on the first characteristics relating to light of the first wavelength and the second characteristics relating to light of the second wavelength is used for the determination of the color material characteristics has been described. However, depending on the ink characteristics, determination based on the first characteristics and the second characteristics may be used for determination of color characteristics. In other words, the processing unit  120  can optionally select which one of the three ink characteristics determination feature amounts is used for each of the determination of the color characteristics and the determination of the color material characteristics. 
     In addition, the ink characteristics determination processing and the ink amount detection processing are not limited to those executed exclusively. The processing unit  120  detects the amount of ink in the ink tank based on the change in the light amount in the vertical direction detected by the photoelectric conversion device  322 . That is, both of ink amount detection processing and ink characteristics determination processing may be performed based on the output from the photoelectric conversion device  322 . 
     In the above, reference data representing the characteristics of the ink IK is known, and the method for determining the ink characteristics based on the comparison processing between the ink characteristics determination feature amount obtained from the output data of the photoelectric conversion device  322  and the given reference value in the processing unit  120  has been described. As illustrated with reference to  FIGS. 44 and 45 , the reference value here is a value of output data in the ink detection area, the inclination of the output data in the ink boundary area, the relationship between the plurality of characteristics corresponding to light of the plurality of wavelengths, or the like, which is obtained in advance for the ink IK to be determined. 
     However, the ink characteristics determination processing of the present embodiment is not limited to this. Specifically, the photoelectric conversion device  322  performs light detection at a first timing and light detection at a second timing different from the first timing. The processing unit  120  determines the ink characteristics based on the characteristics of the light amount detected at the first timing and the characteristics of the light amount detected at the second timing. 
     As described above, characteristics of the output data of the photoelectric conversion device  322  are different depending on the color characteristics and the color material characteristics of the ink IK. For this reason, it is estimated that the ink IK has changed between the two timings when the output data detected at the second timing changes significantly with respect to the output data detected at the first timing. The change of the output data here represents the change of the ink characteristics determination feature amount, and the change in the position of the interface is not included in the change of the output data. 
     Specifically, when the ink characteristics determination processing at the second timing is performed after the user filled the wrong ink IK in the ink tank  310  that has been filled with the appropriate ink IK at the first timing, the ink characteristics determination feature amount obtained from the output data changes greatly. Normally, the same ink tank  310  is continuously filled with ink IK having the same characteristics. That is, in the processing for a given ink tank  310 , it is not assumed that the ink characteristics determination feature amount will change significantly. Therefore, when such a change is detected, the processing unit  120  determines that it is abnormal. For example, the processing unit  120  performs processing of notifying the user that the wrong ink IK is filled by using a display unit  150  or the like. 
     The execution trigger for the ink characteristics determination processing of the present embodiment is optional. For example, the execution of printing processing may be used as the trigger similarly to the ink amount detection processing. However, as can be seen from the above-described example, it is considered that the situation where the inappropriate ink IK is filled occurs when the user performs the replenishment operation incorrectly. Therefore, the processing unit  120  may execute the ink characteristics determination processing using the determination that the user has replenished the ink IK as a trigger. For example, when it is determined that the ink amount is increased by a predetermined amount or more in the ink amount detection processing, the ink characteristics determination processing is started. 
     5. Electronic Apparatus as Multifunction Peripheral 
     The electronic apparatus  10  according to the present embodiment may be a multifunction peripheral having a printing function and a scanning function.  FIG. 46  is a perspective diagram illustrating a state in which the case  201  of the scanner unit  200  is pivoted with respect to the printer unit  100  in the electronic apparatus  10  of  FIG. 1 . In the state illustrated in  FIG. 46 , a document table  202  is exposed. The user sets a document to be read on the document table  202 , and then instructs the execution of scanning by using the operation unit  160 . The scanner unit  200  reads an image of the document by performing the reading processing while moving the image reading unit (not illustrated) based on an instruction operation by the user. The scanner unit  200  is not limited to a flat bed type scanner. For example, the scanner unit  200  may be a scanner having an auto document feeder (ADF) (not illustrated). The electronic apparatus  10  may be an apparatus having both the flat bed type scanner and a scanner having the ADF. 
     The electronic apparatus  10  includes the image reading unit including a first sensor module, the ink tank  310 , the print head  107 , the second sensor module, and the processing unit  120 . The image reading unit reads the document by using a first sensor module including m, m being an integer of two or more, linear image sensor chips. The second sensor module includes n, n being an integer of 1 or more and n&lt;m, linear image sensor chips, and detects light incident from the ink tank  310 . The processing unit  120  detects the amount of ink in the ink tank based on the output of the second sensor module. The first sensor module is a sensor module used for scanning an image in the scanner unit  200 , and the second sensor module is a sensor module used for the ink amount detection processing in the ink tank unit  300 . 
     Both the first sensor module and the second sensor module include a linear image sensor chip. The specific configuration of the linear image sensor chip is the same as that of the photoelectric conversion device  322  described above, and a plurality of photoelectric conversion elements are arranged side by side in a predetermined direction. Since the linear image sensor used for the image reading and the linear image sensor used for the ink amount detection processing can be used in common, it is possible to improve the manufacturing efficiency of the electronic apparatus  10 . 
     However, the first sensor module needs to have a length corresponding to the document size to be read. Since the length of one linear image sensor chip is about 10 mm, for example, the first sensor module needs to include at least two linear image sensor chips. On the other hand, the second sensor module has a length corresponding to the target range of ink amount detection. The target range of ink amount detection can be variously modified but is generally shorter than that of the image reading. That is, as described above, m is an integer of 2 or more, n is an integer of 1 or more, and m&gt;n. Thus, the number of linear image sensor chips can be appropriately set according to the application. 
     The difference between the first sensor module and the second sensor module is not limited to the number of linear image sensor chips. The m linear image sensor chips of the first sensor module are provided such that the longitudinal direction thereof corresponds to the horizontal direction. The n linear image sensor chips of the second sensor module are provided such that the longitudinal direction thereof corresponds to the vertical direction. Since the second sensor module needs to detect the interface of the ink IK as described above, the longitudinal direction corresponds to the vertical direction. 
     On the other hand, in consideration of reading the image of the document, the longitudinal direction of the first sensor module needs to be the horizontal direction. This is because when the longitudinal direction of the first sensor module is set to the vertical direction, it is difficult to stably set the document on the document table  202 , or it is difficult to stabilize the document posture when the document is transported by the ADF. By setting the longitudinal direction of the linear image sensor chip in accordance with the application, the ink amount detection processing and the image reading can be performed appropriately. 
     The image reading unit may include a third sensor module having k, k being an integer of k&gt;n, linear image sensor chips. The electronic apparatus  10  includes, as operation modes, a first mode for reading a document on the document table using the first sensor module and a second mode for reading the document while transporting the document using the third sensor module. In this way, it is possible to realize the electronic apparatus  10  having both the flat bed type scanner and the scanner having the feeder. At this time, it is possible to make the manufacturing of the electronic apparatus  10  more efficient by configuring both sensor modules of the two scanners with linear image sensor chips. Since the third sensor module is also used for image reading similarly to the first sensor module, the number of linear image sensor chips is larger than that of the second sensor module. 
     Alternatively, the image reading unit may use the first sensor module for reading by the ADF. Further, a fourth sensor module having a charge-coupled device (CCD) image sensor chip may be included. The linear image sensor chip included in the first sensor module and the linear image sensor chip included in the second sensor module are metal-oxide-semiconductor (MOS) image sensor chips. In this case, the electronic apparatus  10  includes, as operation modes, the first mode for reading the document on the document table by using the fourth sensor module and the second mode for reading the document while transporting the document by using the first sensor module. 
     Even in this case, it is possible to realize the electronic apparatus  10  having both the flat bed type scanner and the scanner having the feeder. At this time, the fourth sensor module for the first mode is a CCD system, so that an image with deep depth of field can be read. That is, as the fourth sensor module, the sensor module suitable for a method for reading the document on the document table can be used. 
     The first sensor module and the second sensor module have different configurations of optical separators. For example, the first sensor module has a first optical separator which is a lens module. On the other hand, in the ink tank  310 , a second optical separator for separating light incident on the second sensor module in the vertical direction is provided on the side surface. That is, the optical separator for the second sensor module may be a separator of a simple configuration provided on the wall surface of the ink tank  310  as described above with reference to  FIGS. 18 to 21 . In this way, it is possible to provide an appropriate optical separator according to the accuracy required for each sensor module. 
     Alternatively, the first sensor module may have the first optical separator as a lens module, and the second sensor module may have the second optical separator as a slit. The slit here is, for example, a resin slit  330  illustrated in  FIG. 17 . Even in this case, it is possible to provide an appropriate optical separator according to the accuracy required for each sensor module. 
     The first sensor module operates at a first operating frequency, and the second sensor module operates at a second operating frequency lower than the first operating frequency. In image reading, it is necessary to continuously acquire signals corresponding to many pixels and to form image data by performing A/D conversion processing, correction processing, or the like of the signals. Therefore, it is desirable to perform reading by the first sensor module at high speed. On the other hand, the ink amount detection is less likely to be a problem even when the number of photoelectric conversion elements is small and it takes a certain amount of time to detect the ink amount. By setting the operating frequency for each sensor module, each sensor module can be operated at an appropriate speed. 
     The position of the light source may be changed between the first sensor module and the second sensor module. For example, the first sensor module has a light source provided in a direction along the longitudinal direction of the m linear image sensor chips, and the second sensor module has a light source provided in a direction intersecting the longitudinal direction of the n linear image sensor chips. As described above, the length of the second sensor module in the longitudinal direction is shorter than that of the first sensor module, and the reading accuracy is not required as compared with the first sensor module. Therefore, as illustrated in  FIGS. 23 and 24 , the light source  323  and the photoelectric conversion device  322  can be arranged side by side in the direction along the X-axis. That is, an appropriate light source arrangement can be used according to the accuracy required for each sensor module. 
     The first sensor module includes a light guide and a light source provided at the end of the light guide. As illustrated in  FIGS. 10 to 12 , light from the light source corresponding to the first sensor module enters the light guide at an angle at which total reflection is likely to occur. Since the entire light guide can be uniformly illuminated, reading accuracy by the first sensor module can be enhanced. The second sensor module may include a light guide  324  as illustrated in  FIGS. 23 and 24 , or the light guide  324  may be omitted. 
     As described above, the printer according to the present embodiment includes an ink tank, a print head, a light source, a photoelectric conversion device, and a processing unit. The print head performs printing by using ink in the ink tank. The light source irradiates the ink tank with light. The photoelectric conversion device detects light incident from the ink tank in a period during which the light source emits light. The processing unit determines the ink characteristics of ink in the ink tank based on the characteristics of the light amount detected by the photoelectric conversion device. 
     In this way, the ink characteristics in the ink tank can be determined by using the light source and the photoelectric conversion device. Thereby, it can be detected that different specific ink is filled in an ink tank for filling ink having given characteristics. As a result, inappropriate printing can be suppressed. 
     Further, the ink characteristics may be color characteristics of ink. 
     In this way, the color of ink filled in the ink tank can be determined. 
     Further, the ink characteristics may be color material characteristics of ink. 
     In this way, the color material of ink filled in the ink tank can be determined. 
     Further, the processing unit may detect the amount of ink in the ink tank based on the change in the light amount, detected by the photoelectric conversion device, in the vertical direction. 
     In this way, the ink characteristics can be determined based on the characteristics of how the light amount changes in the vertical direction. 
     Further, the processing unit may also determine the ink characteristics based on the change characteristics of the light amount in the ink boundary area which is the boundary area between the area where it is determined that ink exists in the ink tank and the area where it is determined that ink does not exist. 
     In this way, by using information of the ink boundary area, the ink characteristics can be appropriately determined. 
     Further, the processing unit may also determine the ink characteristics based on the light amount in the ink detection area which is the area where it is determined that ink exists in the ink tank. 
     In this way, by using the information of the ink detection area, the ink characteristics can be appropriately determined. 
     Further, the photoelectric conversion device may detect light having a first wavelength and light having a second wavelength. The processing unit determines the ink characteristics based on first characteristics of the light amount of light having the first wavelength and second characteristics of the light amount of light having the second wavelength. 
     In this way, by detecting a plurality of light beams having different wavelength bands and comparing the detected results, it is possible to appropriately determine the ink characteristics. 
     Further, the photoelectric conversion device may detect light at a first timing and light at a second timing different from the first timing. The processing unit determines the ink characteristics based on the characteristics of the light amount detected at the first timing and the characteristics of the light amount detected at the second timing. 
     In this way, by detecting light at different timings and comparing the detected results, the ink characteristics can be appropriately determined. 
     Further, the photoelectric conversion device may be a linear image sensor. 
     In this way, by using a plurality of photoelectric conversion elements arranged in a predetermined direction, the ink characteristics can be accurately determined. 
     Further, the linear image sensor may be provided such that the long side direction of the linear image sensor corresponds to the vertical direction. 
     In this way, by using a plurality of photoelectric conversion elements arranged in the vertical direction, the ink characteristics can be accurately determined. 
     Although the present embodiment has been described in detail as described above, a person skilled in the art can easily understand that many modifications that do not substantially depart from the novel matters and effects of the present embodiment are possible. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. For example, a term described at least once together with a different term having a broader meaning or the same meaning in the specification or the drawings can be replaced with the different term anywhere in the specification or the drawings. All combinations of the present embodiment and the modifications are also included in the scope of the present disclosure. The configurations and operations of the electronic apparatus, printer unit, scanner unit, ink tank unit, and the like are not limited to those described in the present embodiment, and various modifications can be made. 
     For example, in the photoelectric conversion device, the linear image sensors may be arranged in the horizontal direction or obliquely from the horizontal direction. In this case, by arranging a plurality of linear image sensors in the vertical direction or moving them in the vertical direction relative to the ink tank, the same information as when the linear image sensors are arranged in the vertical direction can be obtained. The photoelectric conversion device may be one or more area image sensors. In this way, one image sensor may be straddled across a plurality of ink tanks. Also, in the photoelectric conversion devices, by disposing one linear image sensor in the vertical direction and moving it relative to the ink tank in a direction in which the ink tanks are arranged, information from all ink tanks may be obtained.