JP2007190919A - Liquid detection device and liquid amount detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a change in liquid properties by preventing electrolysis of the liquid. <P>SOLUTION: The device comprises a liquid detection circuit 20 and a judgement means 31. The liquid detection circuit 20 comprises an electrode part 26 (26a-26e), impedance 22 and an alternating current signal source 21. The electrode part 26 is disposed so as to contact a liquid inside the containers T1 and T2. The liquid detection circuit 20 outputs a signal indicating an energizing state of the electrode part 26 by inputting an alternating current signal which does not contain direct current components by way of the impedance 22 from the AC signal source 21 and a binary signal to indicate whether the electrode part 26 is energized or not, based on the output signal. The judgment means 31 determines as to the presence or absence of the liquid in the electrode part 26 from the binary signal output from the liquid detection circuit 20. The frequency of the alternating current signal is a frequency which produces an impedance at least three orders smaller than the impedance in the case where an alternating current signal at 100 Hz is input to the electrode part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is used, for example, when detecting the remaining amount of ink in an ink tank of an ink jet printer, and detects a liquid or a liquid amount in a container that contains a conductive liquid inside. It relates to the device.

  In an ink jet printer, ink is stored in an ink tank, and ink is sent from the ink tank to an ink discharge section (head) through an ink flow path to discharge ink droplets. Here, the ink jet printer needs to be able to detect the presence or absence of ink with relatively high accuracy. The first reason is that it is difficult to visually determine the remaining amount of ink from the appearance of the ink tank.

  Second, if the ink is discharged until the ink is completely removed, the ink as “priming water” disappears (that is, air is mixed into the ink flow path, and as a result, the ink enters the nozzle portion). This is because the ink cannot be ejected unless the ink filling operation is performed again, or the ink ejection portion may be deteriorated. Here, as one of ink ejection methods in an ink jet printer, a thermal method is known in which ink in an ink chamber is rapidly heated by a heating element to eject ink droplets. If the heating element is heated, the heating element may be deteriorated. Therefore, it is necessary to stop ink ejection (printing) when the ink level reaches a certain level.

Third, when printing on large photographic paper, if the remaining amount of ink cannot be detected with high accuracy, ink may be lost during printing, and the previous print may be wasted. Because you get.
From the viewpoints of safety and economy, it is necessary to accurately detect the remaining amount of ink.

As a method for detecting the remaining amount of ink, (1) mechanical type, (2) optical detection type, (3) electrical resistance change detection type, (4) capacity change detection type, (5) discharge amount count type, etc. It has been known.
For example, the electrical resistance change detection type of (3) includes a) Japanese Patent Laid-Open No. 6-226990 (Patent Document 1), b) Japanese Patent No. 27772015 (Patent Document 2), and c) Japanese Patent No. 2798948 (Patent Document). 3), d) JP-A-11-179936 (Patent Document 4), and the like.

  Among these electrical resistance change detection types, the methods of Patent Documents 1 to 3 provide a pair of electrodes in a liquid, and a current flows from the DC power source through a high resistance to these electrodes. Then, the fact that the potential applied to the pair of electrodes changes depending on the presence or absence of the liquid at the pair of electrodes, that is, the liquid is used as a resistor having a high conduction resistance. Moreover, the method of patent document 4 uses alternating current for the detection of a liquid.

However, the above-described conventional technology has the following problems.
First, when a direct current is applied to a liquid as in Patent Documents 1 to 3, electrolysis occurs depending on the type of electrode and the components of the liquid, the electrode surface is likely to change, and metal ions are eluted in the liquid. Therefore, there is a problem that the liquid (ink) characteristics may change. Further, the method of flowing a direct current will be described in detail in the embodiments of the invention described later, but there is a problem that it is difficult to increase the detection speed as a result of the increased impedance as a circuit system.

  In Patent Document 3, a method of reversing the direction of the current flowing through the electrode at every measurement time is adopted in order to eliminate this drawback, but this method performs the measurement itself with a direct current, In order to erase the ions generated by the direct current measurement, a method of returning the generated ions by flowing a direct current in the opposite direction for the same time causes a problem that the measurement speed is slow.

  Furthermore, in the above-mentioned Patent Document 4, since alternating current is used, problems such as electrolysis do not occur, but the liquid is detected by an analog method of detecting the amount of change of the liquid based on the capacitance change of the capacitance. Therefore, there is a problem that the detection level is unstable and the reliability of the detection result is lacking.

  Therefore, the problem to be solved by the present invention is to prevent liquid electrolysis (ionization) so that the characteristics of the liquid do not change and to perform highly reliable detection.

The present invention solves the above-described problems by the following means.
The invention according to claim 2, which is one of the present invention, is a liquid amount detection device for detecting the amount of liquid in one or more containers containing therein a conductive liquid, and at least a part thereof. Is composed of a pair of electrodes arranged so as to be in contact with the liquid in the container, and has an electrode portion, an impedance and an AC signal source in which the pair of electrodes are energized by contact with the liquid, An AC signal that does not include a DC component is input from the AC signal source to the electrode unit via the impedance, and a signal indicating the energization state between the pair of electrodes is output, and the pair of electrodes is output based on the output signal. And a liquid detection circuit configured to output a binarized signal indicating the presence / absence of energization between them, and a judgment for determining the presence / absence of liquid in the electrode unit based on the binarized signal output from the liquid detection circuit. Wherein the frequency of the AC signal that does not include a DC component is a frequency that is at least three orders of magnitude lower than the impedance when the AC signal at 100 Hz is input to the electrode unit. It is characterized by being.

(Function)
In the said invention, the alternating current signal which does not contain a direct current component is input into an electrode part via an impedance from an alternating current signal source.
When an AC signal is input to the electrode unit, a signal indicating the energization state between the pair of electrodes of the electrode unit is output, and further, based on the output signal, a binary signal indicating the presence / absence of energization between the pair of electrodes is output. Is output. Based on this binarized signal, the presence or absence of liquid in the electrode portion is determined.

Therefore, since an AC signal that does not include a direct current component is input to the electrode portion, direct current does not flow through the liquid, and the liquid characteristics do not change. In addition, the conduction resistance is reduced, and the detection speed is also increased.
Furthermore, since the binarized signal is output to determine the presence or absence of liquid, digital processing can be performed, and the detection reliability can be improved.

According to the present invention, since direct current does not flow in the liquid, it is possible to prevent the characteristics of the liquid from changing. In addition, the conduction resistance can be reduced. Furthermore, the detection speed can be increased.
Furthermore, since a binarized signal is output to determine the presence or absence of a liquid, digital processing can be performed and detection reliability can be improved.
The frequency of the AC signal that does not include a DC component is a frequency that is at least three orders of magnitude lower than the impedance when an AC signal at 100 Hz is input to the electrode section. When an AC signal is applied to the switch through a series resistor from the side, a switch with a large short-circuit ratio can be obtained. Furthermore, since the difference in resistance value sharply appears depending on the distance even in the liquid, it is not affected by the electrodes that are slightly apart. In particular, if the detected output value is binary, this tendency becomes even stronger.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In the present invention, a pair of electrodes is placed in a liquid, and the presence or absence of the liquid is determined by the flow of current between the pair of electrodes. However, the current used here is alternating current instead of direct current. The reason will be described below.

  When the electrical resistance between the electrodes in contact with the liquid is measured with a tester or the like, the distance between the electrodes is not greatly affected, and initially shows a large resistance value. To go. This phenomenon varies greatly depending on the electrode material, surface treatment condition, contact surface area, liquid properties, etc., but this phenomenon occurs because the electrolysis progresses as a result of current flowing between the electrodes. It is explained that ions are increasing. Here, when L is the distance between the electrodes and A is the cross-sectional area of the electrode through which the current passes, L / A becomes a constant value (= K) in a certain container. The resistance R of the liquid between the electrodes is R = K / k, where k is the conductivity of the liquid.

  In view of the impedance (Zx) between the electrodes, it is considered that the impedance equivalent circuit shown in FIG. 1 is appropriate. In FIG. 1, a resistance Rdc is the resistance of a liquid when measured for a short time with a direct current. Furthermore, the capacitor Cx is the capacitance of the liquid, and the resistance Rac is the resistance of the liquid when measured by alternating current. Here, since measurement values differ between direct current measurement and alternating current measurement, a capacitor Cx is connected in series to the resistor Rac.

FIG. 2 is a diagram showing a simulation result of the impedance equivalent circuit of FIG. In FIG. 2, ink for an inkjet printer is used as the liquid. In FIG. 2, the horizontal axis represents frequency, and the vertical axis represents resistance value (ohms). In the circuit shown in FIG. 2, the signal source V1 is an AC signal source, and the resistor R2 is a signal source resistor.
It is clear from FIG. 2 that in the situation of the liquid and electrode used in this simulation, the AC resistance value shows several megohms that are almost equivalent to the resistance value measured by DC when the frequency is 100 Hz or less. It decreases dramatically around 1 kHz (from 3 megohms to 500 ohms), and depending on the conditions of the liquid and the electrode, it has a characteristic of decreasing to about 1/10000.

This means the following.
(1) When the electrical resistance (conductivity) of the liquid is used as a switch in the detection of the conductive liquid, if a direct current is used, only a high conduction resistance can be obtained in a conductive state (a state where liquid exists between the electrodes). However, if an alternating current of several kHz or more is used, the overall impedance can be lowered by 3 to 4 digits.

(2) From the above simulation, the resistance value of the liquid at the time of AC use shows a low constant value over a wide band, so when an AC signal is applied to the switch through the series resistance from the signal source side in this frequency band, A switch with a large short-circuit ratio can be obtained.
(3) Since the difference in resistance value is sharp depending on the distance even in the liquid, it is not affected by the electrodes at a distance from each other. In particular, if the detected output value is binary, this tendency becomes even stronger.

  FIG. 3 is a diagram specifically showing a difference in circuit impedance due to a difference between the DC detection method and the AC detection method. In the figure, the upper figure is a DC detection model, and the lower figure is an AC detection model. In FIG. 3, V1 and V2 are signal sources, respectively, and the resistor Rg is a signal source resistor. Cs is a stray capacitance between the electrodes. Further, S-Sw is an electrode selection switch, and W-Sw is a switch based on liquid conduction.

The main difference between DC detection and AC detection is that in the case of DC, there is one decision line (whether it exceeds a certain level), whereas in AC detection, there are generally two locations around 0. A judgment line is necessary.
In DC detection, in order to reduce the ionization problem, it is required that the current flowing through the electrode be as low as possible.
For this reason, as seen in the DC detection model of FIG. 3, the signal source resistance Rg and the interelectrode resistance Rdc need to be extremely large values. For this reason, the influence of the stray capacitance Cs caused by the wiring from the signal source resistance Rg to the electrode and the electrode itself is greatly affected.
In the example of FIG. 3, the signal source resistance Rg is different by 3 digits between the DC detection method and the AC detection method. This difference is a time difference until the measurement of the electrode can be stably started.

For example, in the case of the direct current detection method, assuming that the stray capacitance Cs is 5 (PF), a large value of about Tdc = 50 (usec) is obtained, and there are few electrodes (coarse detection is sufficient, or the number of containers to be monitored is small). In the case of a small number of cases, or when the entire detection operation cycle may be delayed, one detection circuit can cope with this.
However, when there is a condition that the distance from the electrode to the container may be increased by detecting the remaining amount of ink in different containers of 4 to 7 colors at high speed and with high accuracy, such as an inkjet printer, each color There is a possibility that a detection circuit is required every time, so that one detection circuit is not sufficient, or the circuit structure is complicated.

  Furthermore, in the direct current method, in order to see how far the voltage applied to the electrode rises within a given time, it is important to measure the spire value (peak value), and a peak detector is usually used. In principle, the peak detection holds the detected value until the value is taken out as valid data, and needs to be cleared in the next measurement. In other words, in the DC method, not only does it take time to rise, but also the measurement takes extra time due to the analogy of the delay of the stray capacitance and the previous value clearing operation of the peak detector. It takes time to measure.

On the other hand, in the AC detection method, as a result of the original circuit impedance being lowered due to the conductivity characteristics of the liquid, the time for convergence to the peak value is much faster than in the DC detection method, and the timing for detecting the peak is accurately determined by the given signal. Can be predicted.
For example, in the case of a sine wave, the maximum is obtained at a position of 90 degrees, and in the case of a rectangular wave that has passed through a primary integration circuit, the maximum amplitude at each pole (+/−) is immediately before the change in polarity of the waveform.
As described above, in detecting liquid, it is more advantageous to use alternating current than to use direct current. Therefore, in the present invention, alternating current is used.

Next, the liquid amount detection device in the present embodiment will be described.
(First embodiment)
FIG. 4 is a configuration diagram illustrating the liquid amount detection device 10 of the present embodiment. As shown in FIG. 4, a liquid (conductive liquid) that is a detection target of the liquid amount detection device 10 is accommodated in a container T (T1 and T2).
If the liquid amount detection device 10 is used in, for example, an ink jet printer, the container T is an ink tank, and the liquid in the container T is ink for an ink jet printer. In the case of a color ink jet printer using a plurality of colors of ink, a container T (ink tank) for each color is provided.

The liquid amount detection device 10 according to the present embodiment includes a liquid detection circuit 20, a control unit 30, and a remaining amount display unit 40.
The liquid detection circuit 20 includes an AC signal source (V1) 21, an impedance (Zs) 22, a changeover switch (SW) 23, a threshold detection unit 24, a data extraction unit 25, and electrode units 26 (26a to 26e). 27. A specific circuit configuration of the liquid detection circuit 20 will be described later.
The AC signal generated by the AC signal source 21 is supplied to the electrode unit 26 side as an AC signal not including a DC component through the impedance 22, and a sufficient potential difference depends on whether or not the electrode unit 26 is in contact with the liquid. Comes to occur.

The changeover switch 23 is a switch that is controlled so as to input an AC signal sent from the AC signal source 21 via the impedance 22 to any one of the selected electrode portions 26.
The electrode portion 26 is composed of a pair of electrodes 26a to 26e arranged so that at least a part thereof is in contact with the liquid in the container T, and the liquid is in contact with each other so that the pair of electrodes 26a to 26e is in an energized state. It will be. In the present embodiment, the electrode unit 26 is provided on the detection substrate 27, and the detection substrate 27 is disposed in the container T.
In the present embodiment, the electrode part 26 is disposed in the container T, and the part other than the electrode part 26 of the liquid detection device 10 is disposed outside the container T.

  In the present embodiment, a pair of electrodes (26a to 26d and 26e) are provided in one container T (in FIG. 4, the pair of electrodes are surrounded by an elliptical dotted line). The pair of electrodes includes detection electrodes 26a to 26d and a common electrode 26e. The detection electrode 26a and the common electrode 26e, the detection electrode 26b and the common electrode 26e, the detection electrode 26c and the common electrode 26e, and the detection electrode 26d and the common electrode 26e are arranged close to each other to form a pair of electrodes. Yes.

Each detection electrode 26a-26d is arranged in parallel at equal intervals in the vertical direction in the figure. Here, when the liquid in the container T decreases due to use, the liquid level moves from the upper side to the lower side in the drawing. That is, the vertically downward direction is the direction in which the liquid level decreases when the liquid is decreasing.
The detection electrode 26a is disposed on the uppermost side among the detection electrodes 26a to 26d. This position is a position that contacts when the liquid in the container T is full. In addition, the detection electrode 26d is disposed in the vicinity of the bottom surface in the container T.

Furthermore, one common electrode 26e is provided on one detection substrate 27, and is one common electrode 26e corresponding to all four detection electrodes 26a to 26d. Further, the common electrode 26e is grounded to the ground (GND) (not necessarily ground if no direct current flows through the electrode, but normally the ground is taken as a reference point of potential, and thus such a configuration is adopted. ).
All the detection electrodes 26a to 26d and the common electrode 26e are formed with substantially the same surface area, shape and the like so that the impedance characteristics are common. This is because if the impedance characteristic differs for each electrode section 26, the correct detection range with respect to the amplitude of the detection signal is reduced accordingly.

  In FIG. 4, two containers T1 and T2 are illustrated, but the number of containers T may be any number. When the container T is further provided, the above-described detection substrate 27 is provided for each container T. And what is necessary is just to provide the contact 23a of the changeover switch 23 corresponding to the detection electrodes 26a-26d, as shown in FIG. The common electrode 26e may be connected to the wiring to which the common electrode 26e of the containers T1 and T2 is connected and grounded to the ground.

The threshold detection unit 24 outputs a signal representing an energization state between the pair of electrodes 26a to 26d and 26e.
Further, the data extraction unit 25 outputs a binarized signal that indicates the presence / absence of energization between the pair of electrodes 26a to 26d and 26e based on the output signal from the threshold detection unit 24.

The control unit 30 includes a CPU and a memory (storage unit), and includes a determination unit 31 that determines the presence or absence of liquid in the electrode unit 26 based on the binarized signal output from the liquid detection circuit 20. Further, the control unit 30 has a function of controlling switching of the contact 23a of the changeover switch 23 (Node Select).
The remaining amount display unit 40 displays the remaining amount of liquid in the container T based on the determination result of the determination unit 31 of the control unit 30, and in this embodiment, performs a five-step display.

When an AC signal is output from the AC signal source 21, the AC signal passes through the impedance 22. Thereby, the direct current component of the alternating current signal is cut. Then, this AC signal is sent to the changeover switch 23 side.
The AC switch 21 electrically connects the AC signal source 21 and any one of the detection electrodes 26a to 26d. That is, the changeover switch 23 sends an AC signal that has passed through the impedance 22 to any one of the selected detection electrodes 26a to 26d.

  When a liquid is present between the pair of electrodes 26a to 26d and 26e, the detection electrodes 26a to 26d and the common electrode 26e are electrically connected, so that current flows from the detection electrodes 26a to 26d to the common electrode 26e and is grounded. Therefore, the input to the threshold detection unit 24 is a signal with almost no voltage change. On the other hand, when there is no liquid between the pair of electrodes 26a to 26d and 26e, the detection electrodes 26a to 26d and the common electrode 26e are not electrically connected, so that current flows from the detection electrodes 26a to 26d to the common electrode 26e. Does not flow. Therefore, the input to the threshold detection unit 24 is a signal having a voltage change.

  When the signal is input to the threshold detection unit 24, the threshold is detected and the output value is input to the data extraction unit 25. The data extraction unit 25 performs synchronous detection. A clock signal for detection, which is controlled to synchronize with the signal input from the threshold detection unit 24, is input from the AC signal source 21 to the data extraction unit 25. Here, since the clock signal and the AC signal are originally the same signal emitted from the AC signal source 21, the periods of both signals are synchronized, and therefore both the signals are in a synchronized state. As a result of the synchronous detection, the measurement speed can be increased. Of course, it is also possible to emit the clock signal from a signal source different from that of the AC signal. In this case, by synchronizing the two signals, the synchronous detection can be easily performed. It is possible to obtain the same effect as when the AC signal is the same signal generated from the same signal source.

  Then, the data extraction unit 25 outputs a binarized signal indicating the presence / absence of energization between the pair of electrodes 26a to 26d and 26e. The binarized signal is input to the determination unit 31. And the determination part 31 determines the presence or absence of the liquid in the electrode part 26 based on the combination of this binarization signal.

  Further, the result (signal) determined by the determination unit 31 is input to the remaining amount display unit 40. The remaining amount display unit 40 has, for example, a display, and performs step display in five steps for the remaining amount of liquid for each container T. For example, regarding the remaining amount of liquid in one container T, “4” is displayed when liquid is detected in all four electrode portions 26. Further, when no liquid is detected in the uppermost electrode portion 26 (detection electrode 26a and common electrode 26e), “3” is displayed when liquid is detected in the three electrode portions 26 below it. . In this way, when no liquid is detected in all four electrode portions 26, “0” is displayed.

FIG. 5 is a waveform diagram for explaining the detection operation of this embodiment. Note that the detection operation example shown in FIG. 5 is merely an operation example for understanding the detection operation, and the correlation between the position of each electrode portion 26 in the container T and the ink amount shown in FIG. 4 is considered. Absent. That is, in the detection operation example shown in FIG. 5, for the sake of explanation, the case where ink is present → no ink → ink present → no ink is used.
5A is a waveform diagram of an AC signal output from the AC signal source 21. FIG. The AC signal is a rectangular wave having a period of 2 (usec), and indicates that the amplitude is +5.0 (V) to 0 (V).
Moreover, (B) is a waveform diagram when the DC component is cut from the AC signal. The AC signal from the AC signal source 21 is obtained by cutting the DC component through the impedance 22 and has an amplitude of +2.5 (V) to -2.5 (V).

  In (B), as indicated by P1, the connection between the changeover switch 23 and the contact 23a is switched in the cycle (2 (usec)) of this AC signal. Further, the connection between the changeover switch 23 and the contact 23a is switched at the position indicated by the arrow P2, that is, at the timing of the falling edge of the rectangular wave.

  Thereby, in the first period (0 to 2 (usec)) of the AC signal, the changeover switch 23 is connected to the contact 23a of the detection electrode 26a of the container T1. At the time of 2 (usec), the changeover switch 23 is switched from the contact 23a to the contact 23a of the detection electrode 26b of the container T1. Thereby, in the next second period (2 to 4 (usec)), the AC signal from the AC signal source 21 is sent to the detection electrode 26b side. In this way, if the changeover switch 23 is controlled to be synchronized with the AC signal from the AC signal source 21, the connection with the electrode unit 26 can be switched efficiently.

  Further, not only the detection of the liquid in one container T1, but also one liquid detection circuit if the connection with the electrode unit 26 is sequentially switched for all the containers T1, T2,. 20, the connection with the electrode portions 26 of all the containers T can be performed in a time-sharing manner.

5C is a waveform diagram showing an input signal from each electrode unit 26 (an input signal to the threshold detection unit 24). The first 0 to 2 (usec) represents an energization state between the detection electrode 26a and the common electrode 26e of the container T1. The next 2 to 4 (usec) represents the energization state between the detection electrode 26b and the common electrode 26e of the container T1.
The input signal from each electrode unit 26 is input to the threshold detection unit 24, and the threshold is detected.

  (D) is a waveform diagram showing an output signal from the threshold detector 24. In this example, a threshold value P3 (in this example, approximately −1 (V)) is provided on the − (minus) side, and the signal attenuation state of the electrode unit 26 is output. That is, the input value from each electrode section 26 is in the range of +2.5 (V) to −2.5 (V), but is a value when the value is further on the − (minus) side than the threshold ((C)). In the middle, see the part enclosed by the elliptical dotted line).

  (E) is a waveform diagram showing an output signal from the data extraction unit 25. In the waveform diagram of (D), synchronous detection is performed in accordance with the cycle of the clock signal, and whether or not it has a voltage of about +5 (V) is output as a binarized signal. In the example of FIG. 5, the determination (detection) is performed at the timing of 1, 3, 5,... (Usec) (arrow P4). For example, in the first cycle of 0 to 2 (usec), the determination is made at 1 (usec). Here, in the waveform diagram of (D), since it has a voltage of about +5 (V), a signal indicating “with voltage” is output. This signal is maintained until the next determination.

  The next determination is at 3 (usec). At this timing, the waveform diagram of (D) does not have a voltage of about +5 (V), so a signal indicating “no voltage” is output. . In the same manner as described above, it is maintained until 5 (usec), which is the next determination time. In this manner, by performing determination (detection) in synchronization with the clock signal, the output result can be performed at a stable timing.

Next, a specific circuit configuration of the liquid detection circuit 20 described above will be described. FIG. 6 is a circuit diagram of the liquid detection circuit 20 of the present embodiment.
In this embodiment, the AC signal source V1 (21) uses signals of 0-5 (V) and 250 (kHz) used for the CMOS logic circuit.
The capacitor C1 is a capacitor that cuts the DC component of the AC signal transmitted from the AC signal source V1, and is grounded to the ground via a resistor R1 (4.7 k ohm). A signal is sent to the changeover switch 23 side via a resistor R4 (22 k ohms). That is, in this circuit diagram, the impedance network Zs is a T-type circuit including a capacitor C1 and resistors R1 and R4.

The transistors Q1 and Q2 constitute a differential amplifier with the transistors Q3 and Q4, and a detection threshold connected to the base of the transistor Q3 and a threshold value preset at the base of the transistor Q4 (approximately −1 (V)). A signal change at the electrodes (26a to 26d) is detected by comparison.
In addition, with this connection, a current flows through the collector of the transistor Q4 only when the base potential of the transistor Q3 is lower than that of the transistor Q4. In effect, in this state, a current flows only when the signal applied to the detection is swung to the minus side and is lower than the threshold value (when no liquid is in contact with the electrode portion 26).

  Transistors Q5 and Q6 invert the collector current of transistor Q4 and flow it through the collector of transistor Q6, generating a voltage across resistor R5 (3.3 k ohms). The voltage is generated in the resistor R5 only when it is determined that the electrode part 26 that has detected is not in contact with the liquid.

Note that the voltage generated by the resistor R5 has a relationship between the collector current of the transistor Q6 and the resistor R5 so that the transistor Q6 is in a saturated state (about 5 (V) which is the highest potential), and thus the resistor R5 When a voltage is generated, a signal sufficient for determination by a CMOS DFF (D type flip-flop) that performs the next synchronous detection is applied to the D input terminal.
The DFF receives the same clock (detection signal) as the above-mentioned AC signal from the AC signal source V1 from the CLK input terminal and makes a determination.

  In FIG. 6, the AC signal output from the AC signal source V1 and input to the capacitor C1 and the clock signal input to the CLK input terminal of the DFF correspond to the waveform diagram (A) in FIG. Is. The AC signal that does not include a DC component after passing through the capacitor C1 corresponds to the waveform diagram (B) in FIG.

  Furthermore, an input signal (Detector-Input) from the electrode unit 26 corresponds to the waveform diagram (C) of FIG. Furthermore, a signal (Detector-Output) sent to the D input terminal of the DFF corresponds to the waveform diagram (D) of FIG. An output signal (Phase-Detector-Output) from the DFF corresponds to the waveform diagram (E) in FIG.

(Second Embodiment)
FIG. 7 is a waveform diagram showing the second embodiment of the present invention, and corresponds to FIG. 5 of the first embodiment.
In the first embodiment, the AC signal from which the DC component is cut is a rectangular wave, but in the second embodiment, a sine wave (sin wave) is used.
In FIG. 7, the first signal output from the AC signal source 21 is a rectangular wave as shown in (A). This signal is converted into a sine wave shown in (B) through a low-pass filter, for example. is there.

In (B), the rectangular wave is converted into a sine wave, but the DC component is further removed. In (A), the phase is shifted by ¼ compared to (A) in FIG. 5 (see P5). As a result, the sine wave passes through the point of 0 (V) at 1, 2, 3,... (Usec).
Then, determination (detection) is performed at the rising edge of the clock signal (the point at which the sine wave has the minimum potential) (the determination timing is indicated by an arrow P4 as in FIG. 5).

  When a sine wave is used, there is an advantage that a band required for a signal may be narrower than a rectangular wave. And since the band may be narrow, there is little worry about unnecessary radiation. In addition, since the waveform is not significantly affected by the environment and conditions in the middle of detection, even a large apparatus having a long distance to the detection point can be applied without problems. Furthermore, the detection speed can be increased as compared with the case where a rectangular wave is used. However, as described above, a sine wave synchronized with the system is required.

  It is also possible to use a rectangular wave obtained by applying a certain low-pass filter. In this case, the impedance (Zs) 22 is obtained by adding a resistance for impedance adjustment to a low-pass filter.

(Third embodiment)
FIG. 8 is a circuit diagram showing a third embodiment of the present invention, and corresponds to FIG. 6 of the first embodiment. FIG. 9 is a waveform diagram corresponding to the circuit diagram of FIG. 8 and corresponding to FIG. 5 of the first embodiment.
As shown in FIG. 6, in the first embodiment, ± 5 (V) power supply is required, but in the third embodiment, as shown in FIG. 8, only +5 (V) power supply V2 is used. The same function as in the first embodiment can be achieved.

  In this circuit, since the average voltage of the measurement is the same as the DC component of the clock signal, when 5V is used as the power supply, the measurement is performed around 2.5V, but is used for comparison. This is a DC power supply V3 (2.2V) connected to the base of the transistor Q2.

Furthermore, in the first embodiment, all the contacts 23a of the changeover switch 23 are connected to the detection electrodes 26a to 26d. However, in the third embodiment, one of the contacts is grounded to the common electrode 26e, that is, the ground. The contact 23a 'is newly provided.
For example, when the power supply of the liquid detection device 10 is turned off, the contact 23a ′ is selected as the contact to which the changeover switch 23 is connected.

  For example, when the power source of the liquid detection device 10 is turned on or shut off, the contact 23a ′ is selected so that the capacitor C1 is charged and discharged in a short time and does not flow to the electrode portion 26 that is in contact with the liquid. It is a thing. That is, a residual potential difference is generated between the pair of electrodes (between the detection electrodes 26a to 26d and the common electrode 26e) immediately after the liquid detection device is turned on or when it is not in operation. This residual potential difference attenuates over time, but if this is repeated many times, the electrolysis of the liquid may proceed. Therefore, in the third embodiment, in order to avoid such a situation, the changeover switch 23 is connected to the contact 23a 'when the power is turned on or off.

(Fourth embodiment)
FIG. 10 is a circuit diagram showing a fourth embodiment of the present invention, and corresponds to FIG. 6 of the first embodiment. FIG. 11 is a waveform diagram corresponding to the circuit diagram of FIG. 10 and corresponding to FIG. 5 of the first embodiment.
The circuit of the fourth embodiment is a single power supply V2 of +5 V, as in the third embodiment. In the third embodiment, the comparison of detection is performed using the DC power source V3 of 2.2V. However, in the fourth embodiment, the threshold value detection unit maintains the DC component of the clock signal passing through the resistors R2 and R5. In addition to the bases of the transistors Q1 and Q2 serving as the 24 input units, the threshold value detection is performed at about 1/2 power supply voltage (2.5 V).

  Furthermore, since it is necessary to keep the base potential of the transistor Q1 high by the threshold value (in this embodiment, it is determined only by the signal on the minus side from the intermediate point), the voltage is slightly divided by the resistor R4 (220 k ohms). The base potential of Q2 is lowered.

  With such a circuit configuration, stable detection can be performed even if the power supply voltage fluctuates. Further, the signal voltage remaining on the base side of the transistor Q1 when the electrode portion 26 is in contact with the liquid can be made substantially equal to the signal voltage applied to the base side of the transistor Q2, and hardly appears in the output. be able to. That is, the S / N ratio of detection can be increased (dynamic range can be increased).

In the waveform diagram of FIG. 11, as can be seen from (B) (Vb (Q1) −Vb (Q2)), the clock signal (signal source resistance R2 (20 k ohms) appearing at V (Detector-Input) immediately below it. ) And the conduction resistance at the alternating current of the liquid (a value that attenuates in this example calculated as 500 ohms) is almost canceled (see P6 portion surrounded by an elliptical dotted line in FIG. 5B).
In principle, if the total value of the resistance of the changeover switch 23 and the conduction resistance when the electrode portion 26 is in contact with the liquid is equal to the resistance R1 (820 ohms in this example), the clock signal Since the attenuated value can be almost canceled, the resistor R1 may be a variable resistor and adjusted according to the actual state.

Since the present embodiment is configured as described above, the following effects are obtained.
(1) Since a complete alternating current of one cycle or several cycles always flows through the detection electrodes 26a to 26d, ionization of the liquid can be prevented and the characteristics of the liquid are not changed.
(2) The electrical signal processing is performed at a place separated from the container T, and since direct current does not flow and alternating current flows only weak current, it is highly safe as a system that handles an aqueous liquid.

(3) Since the measurement at the individual electrode portions 26 is not the measurement of the analog amount but the determination of presence / absence, it can be made unadjusted, the reliability is high, and the measurement accuracy is the number of the electrode portions 26 installed. It can be decided only by.
(4) If the electrode part 26 for measurement is provided, the number of the liquid detection circuits 20 may be one, so that the liquid amount detection device 10 can be configured simply and inexpensively.
(5) Since the conduction resistance is smaller than that of the direct current method, the area of the electrode portion 26 can be reduced. As a result, high-precision detection can be performed without taking up space, and a large number of electrode portions 26 can be provided.

(6) Since measurement can be performed instantaneously compared to the direct current method, the overall measurement and display speed can be increased.
(7) Low power consumption and sufficient operation even when using a battery.
(8) Since signals in the audio frequency band to AM frequency band can be used, almost no unnecessary radiation countermeasures are required.

(9) Since only one liquid detection circuit 20 needs to be operated at all times for all the detection electrodes 26a to 26d, it is possible to eliminate the influence of mutual strokes at the time of observation / detection.
(10) Since only the electrode part 26 needs to be accommodated in the container T, the structure of the container T can be simplified.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications such as the following are possible.
(1) The liquid amount detection device 10 according to the present embodiment is not limited to the ink remaining amount detection of the ink jet printer, but is a device that detects and displays the presence or the remaining amount of various liquids contained in various containers T. Can be widely applied.

  (2) In the present embodiment, the remaining amount in the container T is displayed by numerical values of “0” to “4”. However, the display is not limited to this, and four LEDs may be provided for each container T, and the remaining amount of liquid may be displayed by turning on / off the LEDs. For example, when liquid is detected by all four electrode portions 26, all the LEDs are turned on. Also, no liquid was detected at the uppermost electrode part 26 (detection electrode 26a and common electrode 26e), but when the liquid was detected at the lower three electrode parts 26, three LEDs were turned on. One LED is turned off. Furthermore, when no liquid is detected by all four electrode portions 26, all the LEDs are turned off. The display method as described above is also possible.

  (3) In the third and fourth embodiments, one of the contacts of the changeover switch 23 is provided with a contact 23a 'grounded to the ground. However, the present invention is not limited to this. For example, the changeover switch 23 may not be connected to any contact. That is, any configuration may be used as long as the connection state with the detection electrodes 26a to 26d can be released.

  (4) In the present embodiment, the presence or absence of liquid is detected for all the electrode portions 26. However, for example, the uppermost electrode portion 26 (the detection electrode 26a and the common electrode 26e in one container T). ), And the electrode unit 26 disposed below the electrode unit 26 determined to have liquid may be passed without determining whether or not there is liquid.

  The detection of the presence / absence of the liquid or the remaining amount is not necessarily limited to the liquid in the container T, and the liquid in other portions can be detected together. For example, when this apparatus is applied to an ink jet printer, an electrode unit 26 may be provided in a chamber (ink reservoir) provided immediately before the printer head, and the presence or absence of ink in the chamber may be determined. Furthermore, when it is determined that there is no ink in the chamber, for example, control to stop printing can be performed together from the viewpoint of protecting the printer head.

  (5) The impedance 22 for cutting the DC component from the AC signal source 21 includes various ones such as one or two or more capacitors or resistors, or combinations thereof. In particular, when the signal generated from the AC signal source 21 does not include a DC component from the beginning, the impedance 22 consisting only of the resistance may be sufficient. Further, in order to cut the direct current component, it is sufficient if a capacitor is connected to the resistor in series or in parallel.

  (6) In this embodiment, a plurality of electrode portions 26 are provided in one container T so as to detect the remaining amount of liquid in the container T. For example, one electrode portion 26 is provided at the bottom in the container T. It is also possible to detect only the presence or absence of liquid in the container T.

It is a figure which shows an impedance equivalent circuit. It is a figure which shows the simulation result of the impedance equivalent circuit of FIG. It is a figure which shows concretely the difference in the circuit impedance by the difference between a direct current | flow detection system and an alternating current detection system. It is a block diagram which shows the liquid amount detection apparatus in this embodiment. It is a wave form diagram explaining the detection operation of 1st Embodiment. It is a figure which shows the liquid detection circuit of 1st Embodiment. It is a wave form diagram which shows 2nd Embodiment of this invention, and is a figure corresponding to FIG. 5 of 1st Embodiment. It is a circuit diagram which shows 3rd Embodiment of this invention, and is a figure corresponding to FIG. 6 of 1st Embodiment. FIG. 9 is a waveform diagram corresponding to the circuit diagram of FIG. 8 and corresponding to FIG. 5 of the first embodiment. It is a circuit diagram which shows 4th Embodiment of this invention, and is a figure corresponding to FIG. 6 of 1st Embodiment. FIG. 11 is a waveform diagram corresponding to the circuit diagram of FIG. 10 and corresponding to FIG. 5 of the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid amount detection apparatus 20 Liquid detection circuit 21 AC signal source (V1)
22 Impedance (Zs)
23 changeover switch 23a, 23a 'contact 24 threshold value detection part 25 data extraction part 26 electrode part 26a-26d detection electrode 26e common electrode 27 detection board 30 control part 31 determination part 40 remaining amount display part T (T1, T2) container

Claims (13)

A liquid detection device for detecting a liquid in one or more containers containing a liquid having conductivity therein,
It has a pair of electrodes that are arranged so that at least a part thereof is in contact with the liquid in the container, and has an electrode portion, an impedance, and an AC signal source that are energized between the pair of electrodes when in contact with the liquid. Then, an AC signal that does not include a DC component is input from the AC signal source via the impedance to the electrode unit to output a signal that indicates an energization state between the pair of electrodes, and based on the output signal, A liquid detection circuit configured to output a binarized signal indicating the presence / absence of energization between a pair of electrodes;
Determination means for determining the presence or absence of liquid in the electrode unit based on a binarized signal output from the liquid detection circuit;
Here, the frequency of the AC signal that does not include a DC component is a frequency that is at least three orders of magnitude lower than the impedance when the AC signal at 100 Hz is input to the electrode unit. Liquid detection device. A liquid amount detection device for detecting the amount of liquid in one or more containers containing therein a conductive liquid,
It has a pair of electrodes that are arranged so that at least a part thereof is in contact with the liquid in the container, and has an electrode portion, an impedance, and an AC signal source that are energized between the pair of electrodes when in contact with the liquid. Then, an AC signal that does not include a DC component is input from the AC signal source via the impedance to the electrode unit to output a signal that indicates an energization state between the pair of electrodes, and based on the output signal, A liquid detection circuit configured to output a binarized signal indicating the presence / absence of energization between a pair of electrodes;
Determination means for determining the presence or absence of liquid in the electrode unit based on a binarized signal output from the liquid detection circuit;
Here, the frequency of the AC signal that does not include a DC component is a frequency that is at least three orders of magnitude lower than the impedance when the AC signal at 100 Hz is input to the electrode unit. To detect the amount of liquid. A liquid detection device for detecting a liquid in one or more containers containing a liquid having conductivity therein,
It has a pair of electrodes that are arranged so that at least a part thereof is in contact with the liquid in the container, and has an electrode portion, an impedance, and an AC signal source that are energized between the pair of electrodes when in contact with the liquid. Then, an AC signal that does not include a DC component is input from the AC signal source to the electrode unit via the impedance, and a signal indicating the energization state between the pair of electrodes is output, and the output signal is set in advance. A liquid detection circuit configured to output a difference between the output signal and the threshold as a binarized signal indicating the presence / absence of energization between the pair of electrodes,
Determination means for determining the presence or absence of liquid in the electrode unit based on a binarized signal output from the liquid detection circuit;
Here, the frequency of the AC signal that does not include a DC component is a frequency that is at least three orders of magnitude lower than the impedance when the AC signal at 100 Hz is input to the electrode unit. To detect the amount of liquid. A liquid amount detection device for detecting the amount of liquid in one or more containers containing therein a conductive liquid,
It has a pair of electrodes that are arranged so that at least a part thereof is in contact with the liquid in the container, and has an electrode portion, an impedance, and an AC signal source that are energized between the pair of electrodes when in contact with the liquid. Then, an AC signal that does not include a DC component is input from the AC signal source to the electrode unit via the impedance, and a signal indicating the energization state between the pair of electrodes is output, and the output signal is set in advance. A liquid detection circuit configured to output a difference between the output signal and the threshold as a binarized signal indicating the presence / absence of energization between the pair of electrodes,
Determination means for determining the presence or absence of liquid in the electrode unit based on a binarized signal output from the liquid detection circuit;
Here, the frequency of the AC signal that does not include a DC component is a frequency that is at least three orders of magnitude lower than the impedance when the AC signal at 100 Hz is input to the electrode unit. To detect the amount of liquid. The liquid amount detection device according to claim 4,
The liquid quantity detection device characterized in that a binarized signal indicating the presence / absence of energization between the pair of electrodes is output based on a period of an AC signal generated from the AC signal source. The liquid amount detection device according to claim 4,
The liquid detection circuit generates a clock signal for outputting a binary signal indicating the presence / absence of energization between the pair of electrodes, and synchronizes the AC signal generated from the AC signal source with the clock signal. A liquid amount detection device characterized in that control is performed. The liquid amount detection device according to claim 4,
A plurality of the electrode portions are provided in one container, and are disposed at a plurality of positions in a liquid level lowering direction accompanying a decrease in the liquid in the container,
The liquid detection circuit outputs a binarized signal indicating the presence / absence of energization between each pair of electrodes, and the determination unit is configured to output a signal in the container based on the binarized signal between the pair of electrodes. A liquid amount detection device characterized by determining the remaining amount of liquid step by step. The liquid amount detection device according to claim 4,
The electrode portions are respectively disposed in the plurality of containers,
The liquid detection circuit is characterized in that the liquid detection circuit controls to sequentially output a signal representing an energization state between the pair of electrodes in each container in a time division manner. The liquid amount detection device according to claim 4,
The electrode part of the liquid detection circuit is disposed in the container,
A part of the liquid detection circuit other than the electrode part and the determination means are provided outside the container. The liquid amount detection device according to claim 4,
A plurality of the electrode portions are provided,
The liquid quantity detection device according to claim 1, wherein the impedance characteristics of the plurality of electrode portions are formed in common so as to facilitate determination of binarization. The liquid amount detection device according to claim 4,
The liquid detection circuit controls to output a binarized signal indicating the presence / absence of energization between the pair of electrodes, using at least one of the positive and negative electrodes of the AC signal. A liquid amount detection device characterized by the above. The liquid amount detection device according to claim 4,
The liquid detection circuit is configured to be capable of releasing a connection state between the AC signal source and a contact point to which the AC signal from the AC signal source is input in the electrode unit. To detect the amount of liquid. A liquid detection method for detecting a conductive liquid in a container,
From an alternating current signal source to an electrode portion that is at least partially composed of a pair of electrodes arranged so as to be in contact with the liquid in the container and in which the liquid is in contact between the pair of electrodes. A step of inputting an AC signal not including a DC component through impedance and outputting a signal representing an energization state between the pair of electrodes;
Comparing the output signal with a preset threshold value and outputting the difference between the output signal and the threshold value as a binarized signal indicating the presence or absence of energization between the pair of electrodes;
Determining the presence or absence of liquid in the electrode part based on a binarized signal,
Here, the frequency of the AC signal that does not include a DC component is a frequency that is at least three orders of magnitude lower than the impedance when the AC signal at 100 Hz is input to the electrode unit. Liquid detection method.

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