JP2011252709A - Liquid detecting device and liquid detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the detection accuracy of the presence/absence of liquid, by accurately detecting changes of output characteristics accompanied with a discharge phenomenon of a liquid detection sensor.SOLUTION: A liquid detecting device comprises a voltage applying portion applying voltage to a first electrode of a liquid detection sensor, and generating electric potential difference between the first electrode and a second electrode of the liquid detection sensor; a voltage measuring portion measuring the voltage of the second electrode; a characteristics measuring portion measuring output characteristics of the liquid detection sensor according to change amount of the measured voltage of the second electrode; and a liquid detection controlling portion drive-controlling the liquid detection sensor for detecting the presence/absence of liquid in a liquid container, according to the measured output characteristics. The voltage measuring portion has a voltage measurement possible range, and the voltage applying portion adjusts the voltage applied to the first electrode of the liquid detection sensor so as to make the voltage of the second electrode be within the measurement possible range of the voltage measuring portion.

Description

  The present invention relates to a technique for detecting a liquid in a liquid container.

  Conventionally, a technique using a piezoelectric element as a liquid detection sensor for detecting the presence or absence of a liquid in a liquid container such as an ink cartridge is known (for example, see Patent Document 1). In this technique, a predetermined waveform is applied to a piezoelectric element to cause electrostriction, and the presence or absence of liquid can be detected based on a waveform generated by residual vibration after electrostriction.

  However, in the piezoelectric element, self-discharge may occur due to a decrease in insulation resistance caused by external humidity change or the like, or natural discharge may occur like a capacitor. When these discharge phenomena occur, the potential difference between the electrodes of the piezoelectric element gradually decreases, and there is a problem that the change in the potential difference affects the output waveform from the piezoelectric element. Such a problem is not limited to ink cartridges, but is a problem common to techniques for detecting the presence or absence of liquid using a liquid detection sensor.

JP 2009-255418 A JP 2009-274438 A

  In view of the above-described problems, the problem to be solved by the present invention is to accurately detect a change in output characteristics associated with a discharge phenomenon of a liquid detection sensor and improve the detection accuracy of the presence or absence of liquid.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A liquid detection apparatus for detecting the presence or absence of liquid in a liquid container using a liquid detection sensor including a piezoelectric element, and applying a voltage to the first electrode of the liquid detection sensor to detect the liquid According to a voltage application unit that generates a potential difference with the second electrode of the sensor, a voltage measurement unit that measures the voltage of the second electrode, and a measured change amount of the voltage of the second electrode A characteristic measurement unit that measures output characteristics of the liquid detection sensor, and liquid detection control that controls driving of the liquid detection sensor for detecting the presence or absence of liquid in the liquid container based on the measured output characteristics The voltage measuring unit has a measurable range of the voltage to be measured, and the voltage applying unit has the voltage of the second electrode within the measurable range of the voltage measuring unit. The liquid detection sensor Adjusting the voltage applied to the first electrode Sir, liquid detection device.

  In the liquid detection device having such a configuration, the voltage applied to the first electrode of the liquid detection sensor is set so that the voltage of the second electrode of the liquid detection sensor falls within the voltage measurable range of the voltage measurement unit. adjust. Therefore, even if the voltage measurement unit has a dead band in voltage measurement, it is possible to accurately measure the change in output characteristics due to the discharge phenomenon of the liquid detection sensor. As a result, it is possible to accurately detect the presence or absence of liquid.

[Application Example 2] In the liquid detection device according to Application Example 1, in the case where the voltage of the second electrode is less than the lower limit of the measurable range, the voltage application unit A liquid detection device that increases the voltage applied to the liquid.

  With such a configuration, by increasing the voltage applied to the first electrode of the liquid detection sensor, even if the voltage output from the second electrode is low, the voltage is measured by the voltage measuring unit. It becomes possible to pull in within the possible range. Therefore, it becomes possible to accurately measure the output characteristics of the liquid detection sensor.

[Application Example 3] In the liquid detection device according to Application Example 1 or Application Example 2, the voltage application unit may be configured such that the voltage of the second electrode exceeds the upper limit of the measurable range. A liquid detection apparatus for reducing a voltage applied to one electrode.

  With such a configuration, by reducing the voltage applied to the first electrode of the liquid detection sensor, even if the voltage output from the second electrode is high, the voltage is It becomes possible to draw within the measurable range. Therefore, it becomes possible to accurately measure the output characteristics of the liquid detection sensor.

Application Example 4 In the liquid detection device according to Application Example 1 or Application Example 2, in the case where the voltage application unit exceeds the upper limit of the measurable range when the voltage of the second electrode exceeds the upper limit of the measurable range, A liquid detection apparatus, wherein a voltage applied to one electrode is a voltage that gradually decreases from a predetermined voltage.

  With such a configuration, by gradually decreasing the voltage applied to the first electrode of the liquid detection sensor, even if the voltage output from the second electrode is high, the voltage is It becomes possible to draw within the measurable range. Therefore, it becomes possible to accurately measure the output characteristics of the liquid detection sensor.

  The present invention can be configured as a liquid detection method and a computer program for detecting a liquid, in addition to the configuration as the liquid detection apparatus described above. The computer program may be recorded on a computer-readable recording medium. As the recording medium, various media such as a flexible disk, a CD-ROM, a DVD-ROM, a magneto-optical disk, a memory card, and a hard disk can be used.

1 is an explanatory diagram showing a schematic configuration of a printing apparatus as an embodiment of the present invention. It is explanatory drawing which shows the internal structure of an ink cartridge and a control unit. It is a flowchart of a characteristic measurement process. It is explanatory drawing which shows the example of the waveform for characteristic measurement, and the leak voltage component according to it. It is a figure which shows the method of measuring a leak voltage component with the waveform for characteristic measurement which raised. It is a figure which shows the method of measuring a leak voltage component with the waveform for characteristic measurement lowered | hung. It is a figure which shows the other aspect of the volume reduction of the waveform for a characteristic measurement. It is a flowchart of a liquid detection process. It is explanatory drawing which shows the example of the waveform for liquid detection, and the response waveform according to it.

Hereinafter, embodiments of the present invention will be described in the following order based on examples.
A. Device configuration:
B. Characteristic measurement process:
C. Liquid detection process:
D. Variations:

A. Device configuration:
FIG. 1 is an explanatory diagram showing a schematic configuration of a printing apparatus as an embodiment of the present invention. The printing apparatus 10 includes a carriage 12 on which an ink cartridge 80 containing ink such as cyan, magenta, and yellow is mounted, a carriage motor 14 that drives the carriage 12 in the main scanning direction, and a printing paper PA in the sub scanning direction. The overall operation of the paper feed motor 16 that transports, the print head 18 that is mounted on the carriage 12 and ejects ink supplied from the ink cartridge 80, the operation unit 20 that performs setting operations related to printing, and the overall operation of the printing apparatus 10. And a control unit 50 for controlling.

  The control unit 50 has a function of controlling the carriage motor 14, the paper feed motor 16, and the print head 18 to perform printing based on print data received from a computer 90 or the like connected via a predetermined interface 22. . In the present embodiment, the control unit 50 further has a function of detecting the presence or absence of ink in the ink cartridge 80 and a function of measuring the output characteristics of the liquid detection sensor provided in the ink cartridge 80. Hereinafter, the configuration and processing contents for realizing these functions will be described in detail.

  FIG. 2 is an explanatory diagram showing the internal configuration of the ink cartridge 80 and the control unit 50. The ink cartridge 80 includes an ink storage chamber 82 in which ink is stored, an ink supply port 83 for supplying the ink stored in the ink storage chamber 82 to the print head 18, and the presence or absence of liquid in the ink storage chamber 82. A liquid detection sensor 84 for detection and a nonvolatile semiconductor memory 87 in which various kinds of information are recorded are provided.

  The liquid detection sensor 84 includes a piezoelectric element, and includes a first electrode 85 and a second electrode 86 for driving the piezoelectric element. The first electrode 85, the second electrode 86, and each electrode of the semiconductor memory 87 are provided in the control unit 50 through terminals on a circuit board (not shown) provided on the outer surface of the ink cartridge 80. It is electrically connected to each circuit.

  The control unit 50 includes a drive waveform generation unit 52, an EEPROM 54, a sensor control unit 56, a voltage measurement unit 60, and a main control unit 70.

  The drive waveform generation unit 52 generates a drive waveform (voltage waveform) for driving the liquid detection sensor 84 in response to a command from the main control unit 70. Specifically, the drive waveform generation unit 52 reads a drive waveform stored as a digital signal in the EEPROM 54, and generates a drive waveform as an analog signal by performing D / A conversion on the drive waveform. The drive waveform generation unit 52 can output not only the liquid detection sensor 84 but also a drive waveform for driving the piezo elements provided in the print head 18.

  The EEPROM 54 stores a plurality of types of drive waveforms in accordance with the purpose for operating the liquid detection sensor 84. Specifically, a drive waveform for detecting the presence or absence of liquid in the ink cartridge 80 and a drive waveform for measuring the output characteristics of the liquid detection sensor 84 are stored. Hereinafter, the former waveform is referred to as “liquid detection waveform”, and the latter waveform is referred to as “characteristic measurement waveform”.

  The sensor control unit 56 includes a plurality of switches S1 to S6 therein, and outputs from the drive waveform generation unit 52 by switching the open / close state of these switches S1 to S6 in accordance with a command from the main control unit 70. The transmitted drive waveform is transmitted to the liquid detection sensor 84 and the response waveform output from the liquid detection sensor 84 is received. As the switches S1, S2, S5, and S6, for example, analog switches can be used, and as the switches S3 and S4, for example, NMOS transistors can be used.

  When the switch S <b> 1 is turned on, the drive waveform generation unit 52 and the first electrode 85 of the liquid detection sensor 84 are connected. Further, the switch S2 connects the drive waveform generation unit 52 and the second electrode 86 of the liquid detection sensor 84 when turned on.

  The switch S3 grounds the first electrode 85 of the liquid detection sensor 84 when turned on. In addition, the switch S4 grounds the second electrode of the liquid detection sensor 84 when turned on.

  When the switch S5 is turned on, the switch S5 connects the first electrode 85 of the liquid detection sensor 84 and the voltage measurement unit 60. Further, the switch S6 connects the second electrode 86 of the liquid detection sensor 84 and the voltage measurement unit 60 when turned on.

  The voltage measurement unit 60 has a function of receiving the response waveform output from the liquid detection sensor 84 through the sensor control unit 56 and measuring the voltage of the waveform. The voltage measurement unit 60 includes a voltage conversion circuit 62 composed of an operational amplifier and the like, and an A / D conversion circuit 64. The voltage conversion circuit 62 converts a voltage range (for example, 0 to 5 V) of a response waveform that is an analog signal into a voltage range (for example, 0 to 3.3 V) that can be measured by the A / D conversion circuit 64. The A / D conversion circuit 64 converts the analog signal whose voltage range has been converted in this way into a digital signal. The voltage measuring unit 60 measures the voltage of the received waveform based on this digital signal.

  In the voltage measuring unit 60 of this embodiment, the range (measurable range) in which the voltage can be measured with high accuracy is limited by the electrical characteristics of the operational amplifier or the like constituting the voltage conversion circuit 62. That is, the voltage measuring unit 60 of the present embodiment has a lower limit value and an upper limit value of a measurable voltage. In this embodiment, the lower limit value of the voltage that can be measured by the voltage measuring unit 60 is 1V, and the upper limit value is 5V. That is, 0 V to 1 V is a dead zone in the voltage measurement of the voltage measuring unit 60.

  The main control unit 70 is configured as a computer including a CPU, RAM, and ROM. The CPU functions as the characteristic measurement unit 72 and the liquid detection control unit 74 by loading the control program stored in the ROM into the RAM and executing it.

  The characteristic measurement unit 72 has a function of measuring the output characteristic of the liquid detection sensor 84 in cooperation with the drive waveform generation unit 52, the sensor control unit 56, and the voltage measurement unit 60. In this embodiment, “leak voltage component” output from the liquid detection sensor 84 is measured as the output characteristic of the liquid detection sensor 84. The piezoelectric element has a property that the insulation resistance between the first electrode 85 and the second electrode 86 decreases as the humidity of the external environment increases. Therefore, the higher the surrounding humidity is, the more self-discharge proceeds, and the potential difference between the first electrode 85 and the second electrode 86 becomes smaller. This amount of decrease in potential difference corresponds to the “leak voltage component” in the present embodiment. When the characteristic measurement unit 72 measures the leakage voltage component, it records the measurement value (voltage change amount per unit time) in the EEPROM 54. Specific processing contents for measuring the leakage voltage component will be described later.

  The liquid detection control unit 74 has a function of detecting the presence or absence of liquid in the ink cartridge 80 in cooperation with the drive waveform generation unit 52, the sensor control unit 56, the voltage measurement unit 60, and the liquid detection sensor 84. The liquid detection control unit 74 detects the presence or absence of liquid in consideration of the leakage voltage component measured by the characteristic measurement unit 72. Specific processing contents for detecting the liquid will be described later.

B. Characteristic measurement process:
FIG. 3 is a flowchart of the characteristic measurement process executed by the characteristic measurement unit 72 described above. FIG. 4 is an explanatory diagram showing an example of a characteristic measurement waveform for measuring the characteristic of the liquid detection sensor 84 and a leak voltage component corresponding thereto. The characteristic measurement process shown in FIG. 3 is executed, for example, when a new ink cartridge 80 is mounted on the carriage 12. Whether or not a new ink cartridge 80 has been installed can be determined by, for example, reading the serial number of the ink cartridge 80 from the semiconductor memory 87 provided in the ink cartridge 80. Note that this characteristic measurement process may be executed not only when a new ink cartridge 80 is installed, but also when the printing apparatus 10 is started up or during the printing process.

  When the execution of the characteristic measurement process is started, first, the characteristic measurement unit 72 gives an instruction to the sensor control unit 56 to perform initial setting of the switch (step S10). Specifically, the switches S1, S4 are turned on, and the switches S2, S3, S5, S6 are turned off. By doing so, the drive waveform generation unit 52 and the first electrode 85 of the liquid detection sensor 84 are connected, and the second electrode 86 of the liquid detection sensor 84 is grounded.

  Next, the characteristic measurement unit 72 gives a command to the drive waveform generation unit 52 to output the characteristic measurement waveform W1 (see FIG. 4) and apply it to the first electrode 85 of the liquid detection sensor 84 (step S12). ). As shown in FIG. 4, the characteristic measurement waveform W1 is formed so that the initial voltage is 0 V, and then the voltage is raised to a predetermined voltage and then maintained. This voltage can be set to, for example, an intermediate value (for example, about 15 V) between the maximum voltage and the minimum voltage of the liquid detection waveform described later.

  The characteristic measuring unit 72 gives a command to the sensor control unit 56 to disconnect the switch S4 from the ground at a time T0 after the voltage of the first electrode 85 becomes constant by the application of the characteristic measuring waveform W1. Then, the switch S6 is turned on to connect the second electrode 86 of the liquid detection sensor 84 and the voltage measuring unit 60 (step S14). At this time, the characteristic measuring unit 72 keeps the voltage of the first electrode 85 constant by keeping the switch S1 in the ON state. As described above, when the second electrode 86 is disconnected from the ground while the first electrode 85 is kept at a constant voltage, when the insulation resistance of the piezoelectric element is reduced, as shown in FIG. A leak voltage component is generated, and the voltage of the second electrode 86 gradually increases from the ground potential (0 V). The voltage measurement unit 60 measures the voltage of the second electrode 86.

  After switching the connection state of the switch in step S14, the characteristic measuring unit 72 uses the first voltage of the second electrode 86 at the first time point T1 and the second electrode 86 at the subsequent second time point T2. The second voltage is acquired from the voltage measuring unit 60 (step S16). The interval from the first time point T1 to the second time point T2 is, for example, about several tens of μsec. FIG. 4 shows the voltage measurable range MR of the voltage measuring unit 60, its upper limit value UL (5V), and its lower limit value LL (1V). As shown in “Case 1” in FIG. 4, when both the first voltage and the second voltage fall within the measurable range MR of the voltage measuring unit 60, the leakage voltage component of the piezoelectric element Can be measured normally. However, depending on the insulation resistance of the piezoelectric element (that is, the humidity of the external environment), the first voltage and the second voltage are both within the measurable range MR, as shown as “Case 2” in FIG. It may be below the lower limit value LL. Further, as indicated by “Case 3”, the first voltage may fall below the lower limit value LL, but the second voltage may fall within the measurable range MR. In addition, as indicated by “Case 4”, the first voltage falls within the measurable range MR, but the second voltage may exceed the upper limit value UL. In these cases 2 to 4, the characteristic measuring unit 72 cannot normally measure the leakage voltage component of the piezoelectric element by the voltage measuring unit 60. Therefore, in the present embodiment, processing described below is executed.

  In step S16 (FIG. 3), when the first voltage and the second voltage are acquired from the voltage measurement unit 60, the characteristic measurement unit 72 determines whether or not the first voltage cannot be measured (step S18). ). In the present embodiment, the characteristic measurement unit 72 cannot measure the first voltage when the first voltage acquired from the voltage measurement unit 60 is less than the lower limit value LL of the measurable range MR of the voltage measurement unit 60. Judge that it was. When the first voltage cannot be measured, the first voltage can be measured because the amount of decrease in insulation resistance is small and the leakage voltage component is small, as in case 2 and case 3 of FIG. It can be determined that the lower limit value LL of MR is not reached. Therefore, the characteristic measurement unit 72 raises the voltage of the characteristic measurement waveform W1 (step S20) and executes the characteristic measurement process again. The characteristic measurement waveform W1 may be raised by performing voltage conversion by the drive waveform generation unit 52, or the characteristic measurement waveform that has been raised is recorded in the EEPROM 54 in advance, and the drive waveform generation unit 52 stores the waveform. 52 may be read out.

  FIG. 5 is a diagram showing a method of measuring a leakage voltage component by using the raised characteristic measurement waveform W2. In the example shown in FIG. 5, at the time T1 and the time T2, the characteristic measurement waveform W1 is raised so that the voltage of the characteristic measurement waveform W2 increases by Δv with respect to the voltage of the characteristic measurement waveform W1. Yes. When such a characteristic measurement waveform W2 is applied to the first electrode 85 of the liquid detection sensor 84, the second electrode 86 is disconnected from the ground, and at the same time, follows the raised characteristic measurement waveform W2. The voltage of the second electrode 86 is also raised. As a result, the first voltage and the second voltage can be drawn into the measurable range MR of the voltage measurement unit 60. Note that the voltage Δv to be raised increases the characteristic measurement waveform W1 by the voltage Δv even when the leakage voltage component is zero, so that the potential of the second electrode 86 becomes the lower limit value LL of the measurable range MR. It is set to a voltage that will exceed. In the present embodiment, since the lower limit value of the measurable range MR of the voltage measuring unit 60 is 1V, the raised voltage Δv can be set to 1.5 to 2.0V, for example.

  In step S18 (FIG. 3), when it is determined that the first voltage is normally measured, the characteristic measurement unit 72 determines whether or not the second voltage cannot be measured (step S22). In the present embodiment, the characteristic measurement unit 72 cannot measure the second voltage when the second voltage acquired from the voltage measurement unit 60 is the upper limit value UL of the measurable range MR of the voltage measurement unit 60. Judge that there is. The voltage value that becomes the upper limit value UL is actually included in the measurable range MR, but as a result of voltage conversion and A / D conversion by the voltage measuring unit 60, all voltages that are higher than the upper limit value UL are the values of the upper limit value UL. May be fixed. Therefore, in this embodiment, when the voltage acquired from the voltage measurement unit 60 is the upper limit value UL of the measurable range MR of the voltage measurement unit 60, it is determined that the second voltage cannot be measured. . If it is determined in step S22 that the second voltage cannot be measured, the second voltage cannot be measured even though the first voltage is normally measured. . That is, as in the case 4 shown in FIG. 4, since the amount of decrease in insulation resistance is large and the leakage voltage component is large, it can be determined that the second voltage has exceeded the upper limit value UL of the measurable range MR. Therefore, the characteristic measurement unit 72 lowers the voltage of the characteristic measurement waveform W1 (step S24), and executes the characteristic measurement process again. The lowering of the characteristic measurement waveform W1 may also be performed by performing voltage conversion by the drive waveform generation unit 52, or the characteristic measurement waveform subjected to the lowering is recorded in the EEPROM 54 in advance, and this is driven. The waveform generation unit 52 may read out.

  FIG. 6 is a diagram illustrating a method of measuring a leakage voltage component by using the characteristic measurement waveform W3 that has been reduced in volume. In the example shown in FIG. 6, at time T1 and time T2, the characteristic measurement waveform W1 is reduced in bulk so that the voltage of the characteristic measurement waveform W3 is lower than the voltage of the characteristic measurement waveform W1 by −Δv. It is carried out. If such a characteristic measurement waveform W3 is applied to the first electrode 85 of the liquid detection sensor 84, the voltage of the second electrode 86 is also lowered so as to follow the lowered characteristic measurement waveform W3. It will be. As a result, the first voltage and the second voltage can be drawn into the measurable range MR of the voltage measurement unit 60.

  If it is determined in step S22 (FIG. 3) that the second voltage has been normally measured, both the first voltage and the second voltage have been normally measured. Based on the measured first voltage and second voltage, the measurement unit 72 calculates the value of the leakage voltage component (voltage change amount per unit time) (step S26). Then, the calculated value of the leakage voltage component is recorded in the EEPROM 54 as the output characteristic value of the liquid detection sensor 84 (step S28). The characteristic measurement process is completed by the series of processes described above.

  In this embodiment, this characteristic measurement process is performed individually for all ink cartridges 80 mounted on the carriage 12, and in the liquid detection process described later, the value of the individual leak voltage component is used for each ink cartridge 80. To detect the presence or absence of ink. On the other hand, for example, the characteristic measurement process is performed only for the representative ink cartridge 80, and in the liquid detection process described later, the liquid leakage is measured for each ink cartridge 80 using the value of the representative leak voltage component. The presence or absence may be detected.

  In the characteristic measurement process described above, the characteristic measurement waveform can be reduced as shown in FIG. FIG. 7 is a diagram illustrating another aspect of reducing the bulk of the characteristic measurement waveform. In the example shown in FIG. 7, the bulk reduction is performed from the time point T1 to the time point T2 so that the slope of the characteristic measurement waveform W4 decreases. By doing so, the first voltage and the second voltage can be more reliably within the measurable range MR. In this case, when calculating the leakage voltage component, a voltage value corresponding to the lowered slope is added to each of the first voltage and the second voltage.

C. Liquid detection process:
FIG. 8 is a flowchart of the liquid detection process executed by the liquid detection control unit 74 described above. FIG. 9 is an explanatory diagram showing an example of a liquid detection waveform for detecting ink in the ink cartridge 80 and a response waveform corresponding thereto. The liquid detection process illustrated in FIG. 8 is executed, for example, when the printing apparatus 10 is activated or during the printing process.

  When the liquid detection process is started, the liquid detection control unit 74 first gives a command to the sensor control unit 56 to perform initial setting of the switch (step S50). Specifically, the switches S1, S4 are turned on, and the switches S2, S3, S5, S6 are turned off. By doing so, the drive waveform generation unit 52 and the first electrode 85 of the liquid detection sensor 84 are connected, and the second electrode 86 of the liquid detection sensor 84 is grounded.

  Next, the liquid detection control unit 74 gives a command to the drive waveform generation unit 52 to generate a liquid detection waveform W5 (see FIG. 9) corresponding to the leakage voltage component of the liquid detection sensor 84 measured in advance (see FIG. 9). Step S52). Upon receiving this command from the liquid detection control unit 74, the drive waveform generation unit 52 reads the original data of the liquid detection waveform and the value of the leak voltage component from the EEPROM 54, and generates a liquid detection waveform W5 as shown in FIG. Generate. Specifically, the drive waveform generation unit 52 has a pulse-like waveform in which two trapezoids in opposite directions are combined in the piezoelectric element drive periods T3 to T4 for driving the piezoelectric element. In the response waveform reception periods T4 to T5 for receiving the response waveform W6, even if the potential difference between the first electrode 85 and the second electrode 86 decreases due to the leakage voltage component, the center of vibration of the response waveform W6 A waveform W5 for liquid detection having an inclination that keeps the angle constant is generated.

  When the liquid detection waveform W5 is generated as described above, the drive waveform generation unit 52 applies the liquid detection waveform W5 to the first electrode 85 of the liquid detection sensor 84 (step S54). Thereafter, the liquid detection control unit 74 gives a command to the sensor control unit 56 at the end point T4 of the piezoelectric element driving period, disconnects the switch S4 from the ground while keeping the switch S1 in the on state, and switches the switch S6. In the on state, the second electrode 86 of the liquid detection sensor 84 and the voltage measuring unit 60 are connected (step S56). Then, as shown in FIG. 9, the response waveform W6 is applied to the first electrode 85 of the liquid detection sensor 84 even if the potential difference between the first electrode 85 and the second electrode 86 decreases due to the leakage voltage component. A voltage waveform having a slope that keeps the center of vibration of the liquid crystal constant is applied, and a response waveform W6 that vibrates at a predetermined cycle is output from the second electrode 86 of the liquid detection sensor 84. In the present embodiment, since the voltage waveform having the above-described slope is applied to the first electrode 85 of the liquid detection sensor 84 during the response waveform reception period, the potential increase of the response waveform W6 due to the leak voltage component is suppressed. As a result, a stable response waveform W6 in which the influence of the leakage voltage component is suppressed is output from the second electrode 86 of the liquid detection sensor 84. On the other hand, for example, when a leakage voltage component is superimposed on the response waveform W6, the waveform gradually increases as shown in the broken line in FIG.

  The liquid detection control unit 74 receives the response waveform W6 from the liquid detection sensor 84 through the sensor control unit 56 and the voltage measurement unit 60 (step S58). The frequency is measured (step S60), and the presence or absence of liquid in the ink cartridge 80 is determined according to the measured frequency (step S62). Although not shown in detail, the liquid detection sensor 84 forms a cavity (resonance unit) that forms a part of the ink flow path from the ink storage chamber 82 to the ink supply port 83 and a part of the wall surface of the cavity. A diaphragm and a piezoelectric element disposed on the diaphragm are provided. When the liquid detection waveform W5 is supplied to the piezoelectric element, the diaphragm vibrates through the piezoelectric element. And the frequency of the residual vibration of the subsequent diaphragm becomes the frequency of the response waveform W6. Since the frequency of residual vibration of the diaphragm varies depending on the presence / absence of ink in the cavity, the liquid detection control unit 74 measures the frequency of the response waveform W6 to determine the presence / absence of ink in the ink cartridge (more precisely, in the cavity) The presence or absence of ink) can be detected. The liquid detection control unit 74 displays the determination result on the display unit and the computer 90 provided in the printing apparatus 10 (step S64).

  In the printing apparatus 10 of the present embodiment described above, the characteristic measurement waveform is applied to the first electrode 85 in order to measure the value of the leakage voltage component included in the output from the second electrode 86 of the liquid detection sensor 84. Apply W1. Then, when the waveform W1 for characteristic measurement is applied, the measured value of the leak voltage component is drawn into the measurable range MR of the voltage measuring unit 60 by raising or lowering the voltage of the waveform. Therefore, even when the leakage voltage component is small or large, the value can be measured accurately. As a result, since the liquid detection waveform W5 taking into account the accurately measured leakage voltage component can be applied to the liquid detection sensor 84, the liquid detection sensor 84 has a stable response in which the influence of the leakage voltage component is suppressed. Waveform W6 is output. Therefore, the frequency of the response waveform W6 can be accurately measured, and the presence or absence of liquid can be detected with high accuracy.

D. Variations:
As mentioned above, although one Example of this invention was described, this invention is not limited to such an Example, A various structure can be taken in the range which does not deviate from the meaning. For example, the following modifications are possible.

・ Modification 1:
In the above embodiment, the leakage voltage component of the liquid detection sensor 84 is measured, but the “return component” generated by the natural discharge of the voltage applied to the liquid detection sensor 84 is measured in the same manner. Is also possible. For this return component, for example, in an environment where a leakage voltage component does not occur (for example, a dry environment), the interval from time T1 to time T2 shown in FIG. It is possible to perform measurement by executing the same process as the characteristic measurement process described above.

Modification 2
In the above embodiment, the characteristic measurement waveform is applied to the first electrode 85 of the liquid detection sensor 84 and the leakage voltage component is measured based on the voltage value output from the second electrode 86. On the other hand, for example, a characteristic measurement waveform may be applied to the second electrode 86 of the liquid detection sensor 84 and the leakage voltage component may be measured based on the voltage value output from the first electrode 85. By doing so, it is possible to measure the leakage voltage component by reversing the polarity of the liquid detection sensor 84. In addition, a liquid detection waveform based on the leakage voltage component at the time of polarity reversal is applied to the second electrode 86, and the presence or absence of ink in the ink cartridge 80 is detected based on the vibration waveform output from the first electrode 85. It is also possible. The reversal of the polarity of the liquid detection sensor 84 can be easily performed only by controlling the switches S1 to S6 in the sensor control unit 56.

・ Modification 3:
In the above embodiment, a stable response waveform W6 is output from the liquid detection sensor 84 by generating the liquid detection waveform W5 taking into account the measurement value of the leakage voltage component of the liquid detection sensor 84. On the other hand, for example, the response waveform on which the leakage voltage component is superimposed is directly received from the liquid detection sensor 84 without adding the leakage voltage component to the liquid detection waveform W5, and the voltage measurement unit 60 or the liquid detection control unit is received. In 74, the value of the leakage voltage component may be subtracted from the response waveform. This also makes it possible to accurately measure the frequency of the response waveform.

-Modification 4:
In the above embodiment, an example in which the present invention is applied to a printing apparatus and an ink cartridge has been described. However, the present invention may be used for a liquid consuming apparatus that ejects or discharges liquid other than ink. Moreover, it is applicable also to the liquid container which accommodated such a liquid. In addition, the liquid container of the present invention can be used for various liquid consuming apparatuses including a liquid ejecting head that discharges a minute amount of liquid droplets. “Droplet” refers to the state of the liquid ejected from the liquid consuming apparatus, and includes those that have a tail in the form of particles, tears, or threads. In addition, the “liquid” referred to here may be a material that can be ejected by the liquid consuming device. For example, it may be in the state when the substance is in a liquid phase, and may be in a liquid state with high or low viscosity, sol, gel water, other inorganic solvents, organic solvents, solutions, liquid resins, liquid metals (metal melts) ) And a liquid as one state of the substance, as well as particles in which functional material particles made of solid materials such as pigments and metal particles are dissolved, dispersed or mixed in a solvent. Further, typical examples of the liquid include ink as described in the above embodiment, liquid crystal, and the like. Here, the ink includes general water-based inks and oil-based inks, and various liquid compositions such as gel inks and hot-melt inks. Specific examples of the liquid consuming device include, for example, a liquid containing dispersed or dissolved materials such as an electrode material and a color material used for manufacturing a liquid crystal display, an EL (electroluminescence) display, a surface emitting display, and a color filter. It may be a liquid consuming device for injecting a liquid, a liquid consuming device for injecting a bio-organic material used for biochip manufacturing, or a liquid consuming device for injecting a liquid as a sample used as a precision pipette. In addition, transparent resin liquids such as UV curable resin to form liquid consumption devices that pinpoint lubricant oil to precision machines such as watches and cameras, and micro hemispherical lenses (optical lenses) used in optical communication elements. A liquid consuming device that jets a liquid onto the substrate, or a liquid consuming device that jets an etching solution such as acid or alkali to etch the substrate or the like may be employed.

DESCRIPTION OF SYMBOLS 10 ... Printing apparatus 12 ... Carriage 14 ... Carriage motor 16 ... Motor 18 ... Print head 20 ... Operation part 22 ... Interface 50 ... Control unit 52 ... Drive waveform generation part 54 ... EEPROM
DESCRIPTION OF SYMBOLS 56 ... Sensor control part 60 ... Voltage measurement part 62 ... Voltage conversion circuit 64 ... A / D conversion circuit 70 ... Main control part 72 ... Characteristic measurement part 74 ... Liquid detection control part 80 ... Ink cartridge 82 ... Ink storage chamber 83 ... Ink Supply port 84 ... Liquid detection sensor 85 ... First electrode 86 ... Second electrode 87 ... Semiconductor memory 90 ... Computer S1-S6 ... Switch W1 ... Waveform for characteristic measurement W2 ... Waveform for characteristic measurement W3 ... Waveform for characteristic measurement W5 ... Liquid detection waveform W6 ... Response waveform PA ... Printing paper UL ... Upper limit value LL ... Lower limit value MR ... Measurable range

Claims (5)

A liquid detection device that detects the presence or absence of liquid in a liquid container using a liquid detection sensor including a piezoelectric element,
A voltage applying unit that applies a voltage to the first electrode of the liquid detection sensor to generate a potential difference with the second electrode of the liquid detection sensor;
A voltage measuring unit for measuring the voltage of the second electrode;
A characteristic measuring unit that measures the output characteristic of the liquid detection sensor according to the measured amount of change in the voltage of the second electrode;
A liquid detection control unit that performs drive control of the liquid detection sensor for detecting the presence or absence of liquid in the liquid container based on the measured output characteristics;
The voltage measuring unit has a voltage measurable range,
The voltage application unit adjusts the voltage applied to the first electrode of the liquid detection sensor so that the voltage of the second electrode falls within the measurable range of the voltage measurement unit;
Liquid detection device. The liquid detection device according to claim 1,
The voltage application unit increases the voltage applied to the first electrode when the voltage of the second electrode is less than the lower limit of the measurable range. The liquid detection device according to claim 1 or 2, wherein
The voltage application unit is a liquid detection device that reduces the voltage applied to the first electrode when the voltage of the second electrode exceeds the upper limit of the measurable range. The liquid detection device according to claim 1 or 2, wherein
When the voltage of the second electrode exceeds the upper limit of the measurable range, the voltage application unit sets the voltage applied to the first electrode to a voltage that gradually decreases from a predetermined voltage. . A liquid detection method for detecting the presence or absence of liquid in the liquid container using a liquid detection sensor including a piezoelectric element,
(A) applying a voltage to the first electrode of the liquid detection sensor to generate a potential difference with the second electrode of the liquid detection sensor;
(B) measuring the voltage of the second electrode by a voltage measuring circuit having a voltage measurable range;
(C) measuring an electrical characteristic of the liquid detection sensor in accordance with the measured change amount of the second voltage;
(D) performing drive control of the liquid detection sensor for detecting the presence or absence of liquid in the liquid container based on the measured electrical characteristics;
(E) adjusting the voltage applied to the first electrode of the liquid detection sensor so that the voltage of the second electrode falls within the measurable range of the voltage measurement circuit;
A liquid detection method comprising:

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