JP2020034485A - Capacitive sensor, and printing apparatus - Google Patents

Abstract

To provide a capacitive sensor capable of accurately and easily obtaining the correlation between the liquid level in a liquid storage unit and the capacitance value, and a printing apparatus.SOLUTION: A capacitive sensor S is disposed in a negative pressure tank 19 and a pressure tank 11 as an example of a liquid storage unit that stores ink IK as an example of a liquid for detecting the capacitance value C for detecting the liquid level H of ink IK. The capacitive sensor includes an electrode 100, 200 that has at least one of a width change portion where widths W1 and W2 change discontinuously over height direction of the liquid level H and a thickness change portion where the thicknesses t1, t2 change discontinuously.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a capacitance sensor and a printing device including the capacitance sensor.

  2. Description of the Related Art Conventionally, there is known an ink circulation type ink jet printing apparatus which discharges ink from an ink jet head while circulating ink to perform printing. As this ink circulation type ink jet printing apparatus, a pressurized tank arranged upstream of the ink jet head, a negative pressure tank arranged downstream of the ink jet head, and a device for sending air from the negative pressure tank to the pressurized tank. Some include an air pump and a pump that sends ink stored in a negative pressure tank to a pressurized tank (for example, see Patent Document 1).

  Such an ink circulation type ink jet printing apparatus discharges ink in an ink jet head while circulating ink by a pressure difference between a pressurized tank and a negative pressure tank. As a pressure control method for the pressurized tank and the negative pressure tank, a pressure follow-up control method is known. In this system, the pressure in the ink path is monitored at regular intervals by a pressure sensor, and air supply and deaeration are repeated so as to maintain the pressure to be maintained. In this method, the pressure is maintained while repeating a certain degree of pressure fluctuation, so that the pressure fluctuation needs to be controlled in order to keep the pressure within the specified value range of the head.

  The magnitude of the pressure fluctuation depends on the volume of air in the ink path. Since the air volume changes depending on the liquid level in the ink tank, it is necessary to control the liquid level to control the magnitude of the pressure fluctuation. In order to control the liquid level, it is necessary to detect the liquid level. Therefore, a liquid level detection sensor is attached to the pressurized tank and the negative pressure tank. This liquid level detection sensor has a plurality of functions, such as liquid level height control, abnormality detection of the ink jet printing apparatus, and ink replacement notification. In order to perform these functions, the liquid level detection sensor needs to detect a plurality of liquid level heights. As a method of detecting a plurality of liquid level heights with one sensor, a capacitance type is used. Are known.

  The capacitance method is a method using the fact that the capacitance value of an electrode mounted on a sensor changes (increases) with the proximity of a substance. This method is used for liquid level detection, and the correlation between the liquid level and the capacitance value is obtained in advance, and the value of the liquid level is obtained to detect multiple liquid level with one sensor. It is possible to do.

JP 2017-226097 A

  However, the capacity of the liquid container such as the pressurized tank and the negative pressure tank for storing the ink, which is detected by the capacitance sensor due to the dimensional variation at the time of manufacture or the variation of the position where the capacitance sensor is attached, is considered. Values vary.

  For example, even in the same liquid storage unit that differs only in the color of the ink to be stored, the liquid level height of the liquid storage unit is different due to individual dimensional variations and variations in the positions where the capacitance sensors are attached. Even if they are the same, the same capacitance value is not necessarily detected.

  For this reason, the liquid level cannot be accurately detected, so that the magnitude of the pressure fluctuation as described above cannot be accurately controlled, resulting in an increase in the pressure fluctuation and a range of the specified value of the head. Can no longer hold pressure. In addition, there is a possibility that the accuracy of abnormality detection and the notification of ink replacement may be reduced. Therefore, there is a need for a method for easily and accurately obtaining a correlation between the liquid level and the capacitance value for each liquid storage unit.

  An object of the present invention is to provide a capacitance sensor and a printing apparatus that can accurately and easily obtain a correlation between a liquid level in a liquid container and a capacitance value.

  In one aspect, the capacitance sensor is a capacitance sensor that is disposed in a liquid storage unit that stores a liquid and detects a capacitance value for detecting a liquid level of the liquid. An electrode having at least one of a width change portion whose width changes discontinuously in the height direction of the liquid level and a thickness change portion whose thickness changes discontinuously is provided.

  According to the above aspect, it is possible to accurately and easily obtain the correlation between the liquid level in the liquid storage unit and the capacitance value.

1 is a configuration diagram illustrating an inkjet printing apparatus according to one embodiment. FIG. 2 is a block diagram illustrating a control configuration of the inkjet printing apparatus according to one embodiment. It is a front view showing the electrode of the capacitance sensor concerning one embodiment. It is a side view showing the electrode of the capacitance sensor concerning a modification of one embodiment. 5 is a flowchart illustrating a process of an initial ink filling operation according to the embodiment. 5 is a graph showing a correlation between a liquid level and a capacitance value.

  Hereinafter, a capacitance sensor and an inkjet printing apparatus (an example of a printing apparatus) according to an embodiment of the present invention will be described with reference to the drawings.

<About the configuration of the inkjet printing apparatus 1>
FIG. 1 is a configuration diagram illustrating an inkjet printing apparatus 1 according to an embodiment. The vertical direction and the height direction in the following description are vertical directions.

  As shown in FIG. 1, the inkjet printing apparatus 1 includes an inkjet head 2, an ink circulation unit 3, and an ink supply unit 4. 2, the inkjet printing apparatus 1 includes a control unit 61, a storage unit 62, an operation panel unit 63, a document reading unit 64, and a capacitance sensor S. Further, the inkjet printing apparatus 1 may include a transport unit that transports a sheet, which is an example of a print medium, a paper feed unit that feeds the paper, a paper discharge unit that discharges the paper, and the like.

  As shown in FIG. 1, the inkjet head 2 has a plurality of head modules 31 and discharges the ink IK supplied by the ink circulation unit 3. The head module 31 has an ink chamber (not shown) for storing the ink IK, and a plurality of nozzles (not shown) for discharging the ink IK. A piezo element (not shown) is arranged in the ink chamber. By driving the piezo element, ink IK is ejected from the nozzle.

  The ink circulation unit 3 supplies the ink IK to the inkjet head 2 while circulating the ink IK. The ink circulating unit 3 includes a pressurized tank 11, a pressurized tank air release valve 12, a pressurized tank air open pipe 13, a pressurized tank pressure control valve 14, a pressurized tank pressure control pipe 15, and a pressurized side. A pressure sensor 16, a distributor 17, a collector 18, a negative pressure tank 19, a negative pressure tank atmospheric release valve 20, a negative pressure tank atmospheric release pipe 21, a negative pressure tank pressure regulating valve 22, a negative pressure A tank pressure adjusting pipe 23, a negative pressure side pressure sensor 24, an ink pump 25, an air pump 26, an air pump pipe 27, and ink circulation pipes 28 to 30 are provided.

  The collector 18, the ink circulation pipe 29, the negative pressure tank 19, the ink circulation pipe 30, the pressure tank 11, the ink circulation pipe 28, and the distributor 17 transfer the ink IK not consumed by the inkjet head 2 to the inkjet head 2. It is an example of a circulation path for resupply.

  As will be described in detail later with reference to FIG. 3, electrodes 100 (shown by two-dot chain lines in FIG. 1) of the capacitance sensor S are arranged in the negative pressure tank 19 and the pressurized tank 11. The negative pressure tank 19 and the pressurized tank 11 are examples of a liquid storage unit that stores the ink IK (liquid). The ink supply unit 4 (ink supply valve 42) is an example of a liquid supply unit that supplies ink IK (liquid) to the negative pressure tank 19 (liquid storage unit), and the ink circulation unit 3 (ink pump 25) Is an example of a liquid supply unit that supplies ink IK (liquid) to the pressurized tank 11 (liquid storage unit). The liquid storage unit is not limited to the negative pressure tank 19 and the pressurized tank 11, and may be, for example, a sub-tank disposed between the ink cartridge 41 and the negative pressure tank 19, and stores the liquid. I just need.

  The pressurized tank 11 stores (contains) the ink IK supplied to the inkjet head 2. The ink IK in the pressurized tank 11 is supplied to the inkjet head 2 via the ink circulation pipe 28 and the distributor 17. In the pressurized tank 11, an air layer is formed on the liquid surface of the ink IK. The pressurized tank 11 is arranged at a lower position (below) than the inkjet head 2.

  The pressurized tank air release valve 12 is provided inside the pressurized tank air release pipe 13 to switch the pressurized tank 11 between a closed state (a state in which the pressurized tank is cut off from the atmosphere) and an open state to the atmosphere (a state open to the atmosphere). Open and close the air flow path. The pressurized tank atmosphere release valve 12 is arranged in the middle of the pressurized tank atmosphere release pipe 13.

  The pressurized tank open-to-air tube 13 forms an air flow path for releasing the pressurized tank 11 to the atmosphere. The pressurized tank atmosphere open pipe 13 has one end connected to the air layer of the pressurized tank 11 and the other end connected to the atmosphere.

  The pressurized tank pressure adjusting valve 14 opens and closes a flow path of air in the pressurized tank pressure adjusting pipe 15 in order to adjust the pressure in the pressurized tank 11. The pressure tank pressure adjusting valve 14 is provided in the middle of the pressure tank pressure adjusting pipe 15.

  The pressurized tank pressure adjusting pipe 15 forms an air flow path for adjusting the pressure in the pressurized tank 11. The pressurized tank pressure adjusting pipe 15 is a pipe having a larger flow path resistance than the pressurized tank atmospheric release pipe 13. Specifically, the pressurized tank pressure adjusting pipe 15 is a pipe that is thinner than the pressurized tank atmospheric release pipe 13. One end of the pressurized tank pressure adjusting pipe 15 is connected to the air layer of the pressurized tank 11, and the other end communicates with the atmosphere.

The pressure side pressure sensor 16 detects the pressure in the pressure tank 11.
The distributor 17 distributes the ink IK supplied from the pressurized tank 11 via the ink circulation pipe 28 to each head module 31 of the inkjet head 2.

  The collector 18 collects the ink IK not consumed by the inkjet head 2 from each head module 31. The ink IK collected by the collector 18 flows through the ink circulation pipe 29 to the negative pressure tank 19.

  The negative pressure tank 19 receives and stores (contains) the ink IK not consumed by the inkjet head 2 from the collector 18. The negative pressure tank 19 stores ink IK supplied from an ink cartridge 41 of the ink supply unit 4 described later. In the negative pressure tank 19, an air layer is formed on the liquid surface of the ink IK. The negative pressure tank 19 is arranged at the same height as the pressurized tank 11.

  The negative pressure tank air release valve 20 opens and closes the air flow path in the negative pressure tank air release pipe 21 to switch the negative pressure tank 19 between a closed state and an atmosphere open state. The negative pressure tank air release valve 20 is provided in the middle of the negative pressure tank air release pipe 21.

  The negative pressure tank atmospheric release pipe 21 forms an air flow path for releasing the negative pressure tank 19 to the atmosphere. One end of the negative pressure tank atmosphere opening pipe 21 is connected to the air layer of the negative pressure tank 19, and the other end communicates with the atmosphere.

  The negative pressure tank pressure adjusting valve 22 opens and closes the air flow path in the negative pressure tank pressure adjusting pipe 23 in order to adjust the pressure in the negative pressure tank 19. The negative pressure tank pressure adjusting valve 22 is provided in the middle of the negative pressure tank pressure adjusting pipe 23.

  The negative pressure tank pressure adjusting pipe 23 forms an air flow path for adjusting the pressure in the negative pressure tank 19. The negative pressure tank pressure adjusting pipe 23 is formed of a pipe having a larger flow path resistance than the negative pressure tank atmosphere opening pipe 21. Specifically, the negative pressure tank pressure adjusting pipe 23 is formed of a pipe which is thinner than the negative pressure tank atmosphere opening pipe 21 and has a thickness approximately equal to that of the pressurized tank pressure adjusting pipe 15. One end of the negative pressure tank pressure adjusting pipe 23 is connected to the air layer of the negative pressure tank 19, and the other end communicates with the atmosphere.

The negative pressure side pressure sensor 24 detects the pressure in the negative pressure tank 19.
The ink pump 25 sends (supplies) the ink IK from the negative pressure tank 19 to the pressurized tank 11. The ink pump 25 is provided in the middle of the ink circulation pipe 30.

  The air pump 26 sends air from the negative pressure tank 19 to the pressurized tank 11. The air pump 26 is arranged in the middle of the air pump pipe 27.

  The pressure (positive pressure) is generated in the pressurized tank 11 by closing the pressurized tank air release valve 12 and closing the pressurized tank 11 when the air pump 26 is driven. Further, the pressure (negative pressure) is generated in the negative pressure tank 19 by closing the negative pressure tank air release valve 20 and closing the negative pressure tank 19 when the air pump 26 is driven. At the time of purging, in order to generate the purge set pressures Pkp and Pfp in the pressurized tank 11 and the negative pressure tank 19, respectively, the pressurized tank atmospheric release valve 12 is closed, and the air pump 26 is driven. The purging is a process of supplying the ink IK from the pressurized tank 11 to the inkjet head 2 and forcibly discharging the ink IK from the nozzle.

  The air pump pipe 27 forms a flow path for air sent from the negative pressure tank 19 to the pressurized tank 11 by the air pump 26. One end of the air pump pipe 27 is connected to the air layer of the negative pressure tank 19, and the other end is connected to the air layer of the pressurized tank 11.

  The ink circulation pipe 28 connects the pressurized tank 11 and the distributor 17. The ink IK flows from the pressurized tank 11 to the distributor 17 through the ink circulation pipe 28. The ink circulation pipe 29 connects the collector 18 and the negative pressure tank 19. The ink IK flows through the ink circulation pipe 29 from the collector 18 toward the negative pressure tank 19. The ink circulation pipe 30 connects the negative pressure tank 19 and the pressure tank 11. The ink IK flows through the ink circulation pipe 30 from the negative pressure tank 19 toward the pressurized tank 11.

  The ink supply unit 4 supplies (supplies) the ink IK to the negative pressure tank 19 of the ink circulation unit 3. The ink supply unit 4 includes an ink cartridge 41, an ink supply valve 42, and an ink supply tube 43.

  The ink cartridge 41 contains the ink IK used for printing by the inkjet head 2. The ink IK in the ink cartridge 41 is supplied to the negative pressure tank 19 of the ink circulation unit 3 via the ink supply pipe 43.

  The ink supply valve 42 is an electromagnetic valve that opens and closes an ink flow path in the ink supply pipe 43. When the ink IK is supplied to the negative pressure tank 19, the ink supply valve 42 is opened under the control of the control unit 61.

  The ink supply tube 43 connects the ink cartridge 41 and the negative pressure tank 19. The ink IK flows from the ink cartridge 41 to the negative pressure tank 19 through the ink supply pipe 43.

  The control section 61 shown in FIG. 2 controls the operation of each section of the inkjet printing apparatus 1. The control unit 61 has a processor (for example, a CPU: Central Processing Unit) that functions as an arithmetic processing unit that controls the operation of the entire inkjet printing apparatus 1.

  The control unit 61 performs a printing process by discharging the ink IK from the inkjet head 2 while circulating the ink IK in the ink circulating unit 3. Further, the control unit 61 performs drive control of the ink pump 25 and the like, opening and closing control of the ink supply valve 42 and the like.

  As will be described in detail later, the controller 61 detects the liquid level H of the ink IK in the negative pressure tank 19 and the pressurized tank 11 based on the capacitance value C detected by the capacitance sensor S. For example, the control unit 61 calculates the correlation between the liquid level height H and the capacitance value C as described later, and calculates the liquid level height H corresponding to the capacitance value C based on the correlation. The liquid level height H is detected by the calculation. However, using the correlation between the liquid level height H and the capacitance value C calculated by the control unit 61, the capacitance sensor S calculates the liquid level height H based on the capacitance value C. In such a case, the controller 61 detects the liquid level H by acquiring the liquid level H calculated by the capacitance sensor S.

  The storage unit 62 is, for example, a ROM (Read Only Memory), which is a read-only semiconductor memory in which a predetermined control program is recorded in advance, and a work storage area as needed when the processor executes various control programs. A random access memory (RAM), which is a semiconductor memory that can be written and read at any time, and a hard disk device are used.

  The operation panel section 63 has an operation key for performing various operations of the inkjet printing apparatus 1, a liquid crystal display section, and the like, and thus functions as an example of an input section and a display section of the inkjet printing apparatus 1. When the operation panel unit 63 has a display with a touch panel, the display with the touch panel functions as an example of the input unit and the display unit of the inkjet printing apparatus 1.

The document reading unit 64 has a scanner that reads image data from a document (paper).
Although the configuration of the inkjet printing apparatus 1 has been described above, this configuration is merely an example, and the printing apparatus according to the present embodiment includes a liquid storage unit (for example, the pressurized tank 11 and the A negative pressure tank 19), a liquid supply unit (for example, an ink circulation unit 3 (ink pump 25) and an ink supply unit 4 (ink supply valve 42)) for supplying liquid to the liquid storage unit, and a liquid supply unit. A capacitance sensor S for detecting a capacitance value C, and a control unit 61 for detecting a liquid level H of the liquid based on the capacitance value C detected by the capacitance sensor S. I just need.

  For example, the inkjet printing apparatus 1 does not need to perform the ink circulation without including the ink circulation unit 3. When an air chamber is provided in the air pump pipe 27 between the negative pressure tank 19 and the air pump 26, the air chamber is provided with a negative pressure tank air release valve 20, a negative pressure tank air release pipe 21, and a negative pressure tank. A tank pressure adjusting valve 22, a negative pressure tank pressure adjusting pipe 23, and a negative pressure side pressure sensor 24 may be provided. Similarly, when an air chamber is provided in the air pump pipe 27 between the air pump 26 and the pressurized tank 11, the pressurized tank air release valve 12, the pressurized tank air open pipe 13, The pressure tank pressure adjustment valve 14, the pressure tank pressure adjustment pipe 15, and the pressure side pressure sensor 16 may be provided. Further, an ink heater for heating the ink IK, a heat sink, a heater temperature sensor, an ink temperature sensor, and the like may be arranged in the ink circulation pipe 28 between the pressurized tank 11 and the distributor 17.

<About the configuration of the capacitance sensor S>
FIG. 3 is a front view showing the electrode 100 of the capacitance sensor S according to the present embodiment.

  The electrode 100 is disposed in both the negative pressure tank 19 and the pressurized tank 11, and the negative pressure tank 19 will be described as an example.

  The electrode 100 is fixed to the front surface (outer wall surface) of the negative pressure tank 19 by, for example, attaching. The electrode 100 has a narrow portion 101 and a wide portion 102 which are arranged integrally in the height direction. The narrow portion 101 is located on the lower side of the electrode 100, and the wide portion 102 is located on the upper side of the electrode 100. The width W2 of the wide portion 102 is preferably at least twice the width W1 of the narrow portion 101. The height of the step between the narrow portion 101 and the wide portion 102 is the step height Hc. When the electrode 100 is fixed to the inner wall surface of the negative pressure tank 19, the electrode 100 may deteriorate or the ink IK may deteriorate due to contact with the electrode 100, particularly when the ink IK is a magnetic ink. Therefore, it is desirable to be arranged on the outer wall surface of the negative pressure tank 19.

  Here, the step portion between the narrow portion 101 and the wide portion 102 is an example of a width change portion in which the widths W1 and W2 change discontinuously in the height direction of the liquid level H. The width change portion is not limited to the step portion, and may be, for example, a boundary portion between a portion having a constant width in the height direction and a portion in which the width gradually increases or decreases, or may have a width in the height direction. May be a boundary between a part where the width gradually increases or decreases and a part where the width gradually increases or decreases by a different amount from the part.

  Note that the electrode 100 has a width change portion only in the step portion between the narrow portion 101 and the wide portion 102, but may have a plurality of width change portions. The electrode 100 has an L shape by having the narrow portion 101 and the wide portion 102, but may have another shape such as a cross shape. The width change portion (step height Hc) is desirably the same as or close to the liquid level height H in the negative pressure tank 19 (pressurized tank 11) when the inkjet printing apparatus 1 is moving. The electrode 100 may be arranged on the back surface (outer wall surface) of the negative pressure tank 19 so as to face the electrode 100 on the front side.

  The negative pressure tank 19 has a base 19a (11a) that protrudes horizontally in the peripheral direction. The upper surface of the base 19a is an abutting surface 19b (11b) against which the bottom of the electrode 100 (the narrow portion 101) abuts. The abutment surface 19b has, for example, a liquid level height H of zero, that is, the same height as the bottom surface of the ink IK storage portion in the negative pressure tank 19. In addition, since the bottom of the electrode 100 is abutted against the abutting surface 19b (11b), it is possible to prevent the displacement of the position where the electrode 100 is attached to the negative pressure tank 19 or the pressurized tank 11 from occurring. Therefore, the height of the width changing portion of the electrode 100 can be made to match the desired height.

FIG. 4 is a side view showing an electrode 200 of a capacitance sensor S according to a modification.
Similarly to the electrode 100, the electrode 200 is disposed in both the negative pressure tank 19 and the pressurized tank 11, but the negative pressure tank 19 will be described as an example.

  The electrodes 200 have, for example, the same shape on each of the front surface and the back surface (outer wall surface) of the negative pressure tank 19, but may be disposed only on a single outer wall surface.

  The electrode 200 has a thin portion 201 and a thick portion 202 which are provided integrally on the outer wall surface of the negative pressure tank 19 in the height direction. The thin portion 201 is located on the lower side of the electrode 200, and the thick portion 202 is located on the upper side of the electrode 200. The thickness t2 of the thick portion 202 is preferably at least twice the thickness t1 of the thin portion 201. The height of the step between the thin part 201 and the thick part 202 is the step height Hc.

  Here, the step portion between the thin portion 201 and the thick portion 202 is an example of a thickness change portion in which the thicknesses t1 and t2 change discontinuously in the height direction of the liquid level H. The thickness change portion is not limited to the step portion, and may be, for example, a boundary between a portion having a constant thickness in the height direction and a portion in which the thickness gradually increases or decreases, or may extend in the height direction. It may be a boundary between a portion where the thickness gradually increases or decreases and a portion where the thickness gradually increases or decreases by a different amount from the portion.

  The electrode 200 has a thickness change portion only at the step portion between the thin portion 201 and the thick portion 202, but may have a plurality of thickness change portions, or may further have the above-described width change portion. May be provided. Further, the shape of the electrode 200 is not particularly limited. Note that the thickness change portion (step height Hc) is desirably equal to or close to the liquid level height H in the negative pressure tank 19 (pressurized tank 11) when the inkjet printing apparatus 1 is movable.

  As described above, in the negative pressure tank 19, the base portion 19a (11a) protrudes to the periphery in the horizontal direction. The upper surface of the base 19a is an abutting surface 19b (11b) against which the bottom of the electrode 200 (the thin portion 201) abuts. The abutment surface 19b has, for example, a liquid surface height H of zero, that is, the same height as the bottom surface of the ink IK storage portion in the negative pressure tank 19.

  The electrode 100 shown in FIG. 3 and the electrode 200 shown in FIG. 4 have higher detection accuracy of the liquid level H as the area of attachment to the negative pressure tank 19 or the pressurized tank 11 increases. It is desirable that the adhesive be applied to the outer wall surface of the pressurized tank 11 over as wide a range as possible.

<About the initial ink filling operation of the inkjet printing apparatus 1>
FIG. 5 is a flowchart showing a process of an initial ink filling operation in the present embodiment.

  Note that the processing illustrated in FIG. 5 is performed by the control unit 61 illustrated in FIG. At the start of the process shown in FIG. 5, the ink IK is not stored in the negative pressure tank 19 and the pressure tank 11.

  First, the control unit 61 causes the capacitance sensor S (electrode 100) arranged in the negative pressure tank 19 to start measurement (detection of the capacitance value C) and record the detection result in the storage unit 62. Start (step S1).

  Next, the control unit 61 starts the ink supply operation from the ink cartridge 41 to the negative pressure tank 19 by opening the ink supply valve 42 (step S2). At this time, the controller 61 opens the ink supply valve 42 by a fixed amount so that the ink IK is supplied to the negative pressure tank 19 at a constant speed. Since the supply of the ink IK from the ink cartridge 41 to the negative pressure tank 19 is performed by the head pressure from the ink cartridge 41 located above the negative pressure tank 19, the ink IK is supplied to the negative pressure tank 19 at a constant speed. Can be supplied.

  After a lapse of a predetermined time, the control unit 61 closes the ink supply valve 42 to end the ink supply operation from the ink cartridge 41 to the negative pressure tank 19 (Step S3). The time for performing the ink supply operation is determined in advance as a time during which the ink IK does not overflow from the negative pressure tank 19.

  Further, the control unit 61 terminates the measurement by the capacitance sensor S arranged in the negative pressure tank 19 and terminates the recording of the detection result in the storage unit 62 (step S4).

  Here, the capacitance value C detected by the capacitance sensor S increases as the liquid level H increases, as shown in FIG. The capacitance value C is proportional to the area of the electrode 100 facing the ink IK when viewed from the thickness direction of the electrode 100 (see FIG. 3). That is, when the liquid level height H is 1 mm higher, the amount of change (inclination) of the capacitance value C is larger when the liquid level height H is at the height of the wide portion 102. H is larger than when H is at the height of the narrow portion 101. Since the ink IK is supplied to the negative pressure tank 19 at a constant speed, the amount of change in the capacitance value C with respect to the supply amount of the ink IK depends on the height at which the narrow portion 101 (or the thin portion 201) is located. The rise is gradual when the liquid level height H is at the liquid level height H, whereas the rise is sharp when the liquid level height H is at the height where the wide portion 102 (or the thick portion 202) is located. Therefore, when the liquid level height H is at the step height Hc of the step portion between the narrow portion 101 (or the thin portion 201) and the wide portion 102 (or the thick portion 202), the capacitance C Changes. That is, the capacitance value C when the liquid level height H is equal to the step height Hc is the change point Cc.

  As described above, the height of the abutting surfaces 19b, 11b of the negative pressure tank 19 or the pressurized tank 11 against which the bottoms of the electrodes 100, 200 abut, is such that the liquid level H is zero or a negative height. In this case, the value of the capacitance value C is easily obtained from when the liquid level H at the start of the ink supply operation is zero. Therefore, it is easy to obtain a correlation between the liquid level height H and the capacitance value C described later.

  The control unit 61 calculates the change amount and the change point Cc of the capacitance value C based on the capacitance value C measured and recorded as described above, and records the change amount and the change point Cc in the storage unit 62 (step S5). ).

  Further, since the control unit 61 can acquire the step height Hc in the pressurized tank 11 in advance, the control unit 61 determines the liquid level in the pressurized tank 11 based on the step height Hc, the amount of change in the capacitance value C, and the change point Cc. The relative relationship between the surface height H and the capacitance value C (for example, a relational expression for specifying the liquid surface height H corresponding to the capacitance value C as shown in FIG. 6) is calculated, and the storage unit 62 (Step S6).

  Next, the control unit 61 causes the capacitance sensor S (electrode 100) arranged in the pressurized tank 11 to start measurement (detection of the capacitance value C) and record the detection result in the storage unit 62. Is started (step S7).

  Next, the control unit 61 starts the ink feeding operation from the negative pressure tank 19 to the pressurized tank 11 by driving the ink pump 25 (step S8). At this time, the control unit 61 drives the ink pump 25 so that the ink IK is supplied to the pressurized tank 11 at a constant speed.

  After a certain period of time, the control section 61 stops driving the ink pump 25 and ends the operation of feeding the ink from the negative pressure tank 19 to the pressurized tank 11 (step S9). The time during which the ink is supplied is determined in advance as a time during which the ink IK does not overflow from the pressurized tank 11.

  Further, the control unit 61 terminates the measurement by the capacitance sensor S arranged in the pressurized tank 11 and terminates the recording of the detection result in the storage unit 62 (step S10).

  The control unit 61 calculates the change amount and the change point Cc of the capacitance value C based on the capacitance value C measured and recorded as described above, and records the change amount and the change point Cc in the storage unit 62 (step S11). ).

  Further, as described above, the control unit 61 determines the liquid level height H and the capacitance value C in the pressurized tank 11 based on the step height Hc, the amount of change in the capacitance value C, and the change point Cc. Is calculated and recorded in the storage unit 62 (step S12).

  Although the relative relationship between the liquid level H and the capacitance value C in the initial ink filling operation has been described with reference to FIG. 5, the negative pressure tank may be used in situations other than the initial ink filling operation, for example, during maintenance. The liquid level height H and the capacitance value C are also changed by changing the liquid level height H so as to straddle the step height Hc while supplying or discharging the ink IK to or from the pressure tank 19 or the pressure tank 11. Can be calculated.

<Operation of the inkjet printing apparatus 1 during printing>
Next, an operation during printing of the inkjet printing apparatus 1 in a state where the ink IK is supplied to the negative pressure tank 19 and the pressurized tank 11 by the above-described ink initial filling operation will be described.

  When a print job is input, first, the control unit 61 closes the pressurized tank atmospheric release valve 12 and the negative pressure tank atmospheric release valve 20. As a result, the pressurized tank 11 and the negative pressure tank 19 are closed. During the standby time when the inkjet printing apparatus 1 does not operate, the pressurized tank atmospheric release valve 12 and the negative pressure tank atmospheric release valve 20 are opened, and the pressurized tank 11 and the negative pressure tank 19 are released to the atmosphere. The pressurized tank pressure regulating valve 14 and the negative pressure tank pressure regulating valve 22 are closed from standby.

  Next, the control unit 61 starts the air pump 26. Thereby, the pressurized tank 11 starts to be pressurized, and the negative pressure tank 19 starts to be depressurized. Thus, a flow of the ink IK from the pressurized tank 11 to the negative pressure tank 19 via the inkjet head 2 occurs, and the circulation of the ink IK starts. After the activation of the air pump 26, the control unit 61 drives the air pump 26 so that the pressures in the pressurized tank 11 and the negative pressure tank 19 reach the respective circulating set pressures Pk and Pf and maintain them. The opening and closing of the pressurized tank pressure regulating valve 14 and the negative pressure tank pressure regulating valve 22 are controlled.

  The circulating set pressures Pk and Pf are preset as pressure values for adjusting the nozzle pressure of the inkjet head 2 to an appropriate value while circulating the ink IK. The set pressure Pk for circulation of the pressurized tank 11 is a positive pressure, and the set pressure Pf for circulation of the negative pressure tank 19 is a negative pressure. The set pressure for circulation Pf of the negative pressure tank 19 is larger in absolute value than the set pressure for circulation Pk of the pressurized tank 11. As a result, the nozzle pressure of the inkjet head 2 becomes a negative pressure suitable for discharging the ink IK.

  After the pressures in the pressurized tank 11 and the negative pressure tank 19 reach the circulating set pressures Pk and Pf, the control unit 61 controls the inkjet head 2 based on the print job to perform printing. During the execution of the print job, the ink IK is supplied from the pressurized tank 11 to the inkjet head 2, and the ink IK not consumed by the inkjet head 2 is collected in the negative pressure tank 19.

  When performing ink circulation and printing in this manner, the control unit 61 performs liquid level maintenance control. This liquid level maintenance control is performed to maintain the liquid level of the pressurized tank 11 and the negative pressure tank 19 at the reference level and to circulate the ink while maintaining the liquid level of the pressurized tank 11 and the negative pressure tank 19. This is the control of the ink pump 25 and the ink supply valve 42 in response.

  When the print job is completed, the control unit 61 opens the pressurized tank atmospheric release valve 12 and the negative pressure tank atmospheric release valve 20. Here, when the ink pump 25 and the air pump 26 are being driven, the control unit 61 stops the driving. When the pressurized tank pressure adjusting valve 14, the negative pressure tank pressure adjusting valve 22, and the ink supply valve 42 are open, the control unit 61 closes them. Thus, the ink circulation operation ends, and the inkjet printing apparatus 1 enters a standby state.

  In the embodiment described above, the capacitance sensor S is disposed in the negative pressure tank 19 and the pressurized tank 11, which are an example of a liquid storage unit that stores the ink IK, which is an example of a liquid. A capacitance value C for detecting the surface height H is detected. Further, as shown in FIG. 3, the capacitance sensor S has a width changing portion (for example, a narrow portion 101 and a wide portion) in which the widths W1 and W2 change discontinuously in the height direction of the liquid level H. 102). In a modification of the present embodiment, as shown in FIG. 4, the capacitance sensor S has a thickness change in which the thicknesses t1 and t2 change discontinuously in the height direction of the liquid level H. The electrode 200 includes a portion (for example, a step portion between the thin portion 201 and the thick portion 202).

  In the present embodiment, the inkjet printing apparatus 1 as an example of a printing apparatus includes a negative pressure tank 19 and a pressure tank 11 as an example of a liquid storage unit that stores ink IK as an example of a liquid. The ink supply unit 4 (ink supply valve 42) and the ink circulation unit 3 (ink pump 25), which are examples of a liquid supply unit that supplies ink IK (liquid) to the tank 19 and the pressurized tank 11, the negative pressure tank 19 A capacitance sensor S that is disposed in the pressurized tank 11 and detects a capacitance value C, and a control unit 61 that detects a liquid level H based on the capacitance value C detected by the capacitance sensor S And Further, the capacitance sensor S includes at least one of a width change portion in which the width changes discontinuously and a thickness change portion in which the thickness changes discontinuously in the height direction of the liquid level H. The control unit 61 controls the ink supply valve 42 and the ink pump 25 so as to supply the ink IK (liquid) to the negative pressure tank 19 and the pressurized tank 11, and controls the liquid level H Calculates the change point Cc of the amount of change in the capacitance value C when it reaches the height (step height Hc) of at least one of the width change portion and the thickness change portion.

  By the way, the liquid storage units such as the pressurized tank 11 and the negative pressure tank 19 are the same liquids which differ only in the color of the ink IK to be stored, for example, due to dimensional variations at the time of manufacture and variations in the positions where the electrodes 100 and 200 are attached. Even in the storage section, the capacitance value C with respect to the liquid level Hc varies. In this regard, in the present embodiment and its modification, the electrodes 100 and 200 have the changing portions in which the widths W1 and W2 or the thicknesses t1 and t2 change discontinuously in the height direction. When the liquid level H reaches the point (C), the amount of change in the capacitance value C changes (change point Cc). Therefore, when the capacitance value C is at the change point Cc, it can be easily detected that the liquid level H is at the step height Hc. In addition, compared to the case where the capacitance value C is detected by arranging a plurality of electrodes in a single liquid storage unit, the capacitance value due to the positional deviation of the relative position between the plurality of electrodes is reduced. The detection accuracy of C can be prevented from lowering, and the configuration can be simplified.

  Therefore, according to the present embodiment and the modified example, the correlation between the liquid level height H and the capacitance value C in the liquid storage units (for example, the negative pressure tank 19 and the pressurized tank 11) can be accurately and easily determined. Obtainable. Further, since the liquid level height H can be accurately detected, the amount of the air layer in the liquid storage portion is accurately detected, and for example, the pressure fluctuation of the inkjet head 2 is kept within a specified range, and the printing accuracy is reduced. Can be increased. Further, since the liquid level height H can be accurately detected, the accuracy of detecting abnormalities such as leakage of ink IK (liquid) and the accuracy of notifying the replacement of the ink cartridge 41 (liquid supply unit) are improved. Can be increased.

  In the present embodiment, the electrode 100 (200) has a narrow portion 101 and a wide portion 102 (thin wall) provided integrally on the outer wall surfaces of the pressure tank 11 and the negative pressure tank 19 in the height direction. The width changing portion (thickness changing portion) is a step portion between the narrow portion 101 (thin portion 201) and the wide portion 102 (thick portion 202). Therefore, while using the electrode 100 (200) having a simple shape, the width (thickness) of the electrode 100 (200) at the step between the narrow portion 101 (thin portion 201) and the wide portion 102 (thick portion 202). Greatly changes, the controller 61 can easily calculate the change point Cc of the capacitance value C when the liquid level height H is at the step height Hc. Further, since the electrode 100 (200) detects the capacitance value C without contacting the ink IK (liquid), the electrode 100 (200) may be deteriorated, or the ink IK ( Of the liquid) can be prevented.

  Further, in the present embodiment, width W2 of wide portion 102 is at least twice as large as width W1 of narrow portion 101. Further, the thickness t2 of the thick portion 202 is at least twice the thickness t1 of the thin portion 201. Therefore, the width or thickness of the electrodes 100 and 200 greatly changes at the step between the narrow portion 101 and the wide portion 102 and at the step between the thin portion 201 and the thick portion 202. The change point Cc of the capacitance value C at the step height Hc can be easily calculated by the control unit 61.

  In the present embodiment, the control unit 61 controls the liquid supply unit (the ink supply valve 42 and the ink pump 25) so as to supply the ink IK (liquid) to the negative pressure tank 19 and the pressurized tank 11 at a constant speed. Control. Therefore, it is possible to easily detect the change point Cc at which the change amount of the capacitance value C changes when the liquid level height H reaches the step height Hc, and the ink IK (liquid) is discharged at a constant speed. By supplying, the correlation between the capacitance value C before and after the change point Cc and the liquid level H can be easily obtained.

  It should be noted that the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying constituent elements without departing from the scope of the invention at the stage of implementation. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above-described embodiments. For example, all components described in the embodiments may be appropriately combined. Of course, various modifications and applications are possible without departing from the spirit of the invention. Hereinafter, the inventions described in the claims at the time of filing the application of the present application are additionally described.

[Appendix 1]
A capacitance sensor that is disposed in a liquid storage unit that stores a liquid and detects a capacitance value for detecting a liquid level of the liquid,
An electrode having at least one of a width change portion whose width changes discontinuously in the height direction of the liquid level and a thickness change portion whose thickness changes discontinuously is provided. Capacitance sensor.

[Appendix 2]
The electrode has a narrow portion and a wide portion which are provided integrally with each other along the height direction on the outer wall surface of the liquid storage portion,
The capacitance sensor according to claim 1, wherein the width change portion is a step between the narrow portion and the wide portion.

[Appendix 3]
A liquid storage unit for storing a liquid,
A liquid supply unit that supplies the liquid to the liquid storage unit,
A capacitance sensor that is disposed in the liquid container and detects a capacitance value;
A control unit that detects a liquid level of the liquid based on a capacitance value detected by the capacitance sensor,
The capacitance sensor includes an electrode including at least one of a width change portion in which the width changes discontinuously and a thickness change portion in which the thickness changes discontinuously in the height direction of the liquid level. Have
The control unit controls the liquid supply unit so as to supply the liquid to the liquid storage unit, and the liquid level height is set to at least one of the width change unit and the thickness change unit. A printing apparatus for calculating a change point of a change amount of the capacitance value when the printing apparatus reaches the printing apparatus.

DESCRIPTION OF SYMBOLS 1 Ink-jet printing apparatus 2 Ink-jet head 3 Ink circulation part 4 Ink replenishment part 11 Pressurized tank 11a Base part 11b Abutment surface 19 Negative pressure tank 19a Base part 19b Abutment surface 25 Ink pump 41 Ink cartridge 61 Control part 62 Storage part 63 Operation panel section 64 Document reading section 100, 200 Electrode 101 Narrow section 102 Wide section 201 Thin section 202 Thick section C Capacitance value Cc Change point H Liquid level Hc Step height IK ink S Capacitance sensor t1 , T2 Thickness W1, W2 Width

Claims (3)

A capacitance sensor that is disposed in a liquid storage unit that stores a liquid and detects a capacitance value for detecting a liquid level of the liquid,
An electrode having at least one of a width change portion whose width changes discontinuously in the height direction of the liquid level and a thickness change portion whose thickness changes discontinuously is provided. Capacitance sensor. The electrode has a narrow portion and a wide portion which are provided integrally with each other along the height direction on the outer wall surface of the liquid storage portion,
The capacitance sensor according to claim 1, wherein the width change portion is a step portion between the narrow portion and the wide portion. A liquid storage unit for storing a liquid,
A liquid supply unit that supplies the liquid to the liquid storage unit,
A capacitance sensor that is disposed in the liquid container and detects a capacitance value;
A control unit that detects a liquid level of the liquid based on a capacitance value detected by the capacitance sensor,
The capacitance sensor includes an electrode including at least one of a width change portion in which the width changes discontinuously and a thickness change portion in which the thickness changes discontinuously in the height direction of the liquid level. Have
The control unit controls the liquid supply unit so as to supply the liquid to the liquid storage unit, and the liquid level height is set to at least one of the width change unit and the thickness change unit. A printing apparatus for calculating a change point of a change amount of the capacitance value when the printing apparatus reaches the printing apparatus.