Liquid level detection circuit, liquid discharging device, control method of liquid level detection circuit, and control program of liquid level detection circuit

Abstract

To provide a circuit for generating an appropriate threshold voltage according to a resistance value detected so as to set the threshold voltage.SOLUTION: A liquid level detection circuit includes: a pair of electrodes disposed in a tank; a voltage application circuit for applying a voltage to one of the pair of electrodes; a voltage determination circuit for determining a value of a voltage appearing in a voltage detection node on the basis of a voltage applied from the voltage application circuit when a liquid level is at a reference height; a reference voltage generation circuit for generating a reference voltage in a connection node by connecting one of multiple first resistors in parallel with a second reference resistor connected in series with a first reference resistor via the connection node on the basis of a voltage value determined by the voltage determination circuit; a voltage comparison circuit for comparing a voltage appearing in a voltage detection node according to a resistance value between the pair of electrodes with the reference voltage; and a determination circuit for determining whether or not a liquid level is at a lower-limit height or less that is less than the reference height on the basis of a comparison result by the voltage comparison circuit.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a liquid level detection circuit, a liquid ejection device, a control method for the liquid level detection circuit, and a control program for the liquid level detection circuit. [Background technology]

[0002] A method is known for detecting the ink level in a subtank based on a threshold voltage and a voltage value obtained in response to a change in resistance between multiple electrode pins arranged in the subtank while immersed in the ink (see, for example, Patent Document 1). In this type of method, a main tank is provided in which ink to replenish the subtank is filled, and the resistance between multiple electrode pins arranged in the main tank while immersed in the ink is detected, and a threshold voltage used for detecting the ink level is set in response to the detected resistance. Summary of the Invention [Problem to be solved by the invention]

[0003] However, there is no suggestion as to how to generate a threshold voltage in response to a sensed resistance value to set the threshold voltage.

[0004] In view of the above problems, an object of the present invention is to generate a reference voltage used for determining whether or not the liquid level is equal to or lower than a lower limit height, without increasing the circuit scale. [Means for solving the problem]

[0005] In order to solve the above technical problems, one embodiment of the liquid level detection circuit of the present invention is characterized in that it comprises a pair of electrodes arranged at a distance from one another in a tank containing a conductive liquid, a voltage application circuit that applies a voltage to one of the pair of electrodes via a voltage detection node, a voltage judgment circuit that determines a value of a voltage that appears at the voltage detection node based on the voltage applied from the voltage application circuit when the liquid level in the tank is at a reference height, a reference voltage generation circuit that has a second reference resistor connected in series with a first reference resistor via a connection node and a plurality of first resistors having different resistance values, and that generates a reference voltage at the connection node by connecting one of the plurality of first resistors in parallel with the second reference resistor based on the voltage value determined by the voltage judgment circuit, a voltage comparison circuit that compares the voltage that appears at the voltage detection node with the reference voltage in accordance with the resistance value between the pair of electrodes, which varies depending on the type of the liquid and the height of the liquid in the tank, and a judgment circuit that determines whether the liquid level is below a lower limit height that is lower than the reference height based on a comparison result by the voltage comparison circuit. Effect of the Invention

[0006] The reference voltage used to determine whether the liquid level is equal to or lower than the lower limit height can be generated without increasing the circuit scale. [Brief description of the drawings]

[0007] [Figure 1] 1 is a block diagram showing an example of a liquid ejection device including a liquid level detection system according to a first embodiment of the present invention. [Diagram 2] 2 is a block diagram showing an example of a hardware configuration of the liquid ejection device of FIG. 1. [Diagram 3] 2 is a block diagram showing an outline of the liquid level detection circuit of FIG. 1. [Figure 4] FIG. 4 is a circuit diagram showing an example of a liquid level detection circuit in FIG. [Diagram 5] 5 is a circuit diagram showing an example of a voltage determination circuit of FIG. 4. [Figure 6] 5 is a diagram showing an example of detecting a liquid level by the liquid level detection circuit of FIG. 4. [Figure 7] 5 is a flow chart showing an example of a method for generating a threshold voltage by the liquid level detection circuit of FIG. 4. [Figure 8] 1. FIG. 4 is a circuit block diagram showing an example of another liquid level detection system mounted on the liquid ejection device of FIG. [Figure 9] FIG. 11 is a block diagram showing an example of a liquid ejection device including a liquid level detection system according to a second embodiment of the present invention. [Figure 10] 10 is a flow chart showing an example of a method for generating a threshold voltage by the liquid level detection circuit of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, the embodiments will be described with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicated descriptions may be omitted. In the following, the same reference numerals as the voltage names are used for voltage lines through which voltages are transmitted, and the same reference numerals as the signal names are used for signal lines through which signals are transmitted.

[0009] In this application, a "liquid ejection device" is a device that includes a liquid ejection head or a liquid ejection unit and ejects liquid by driving the liquid ejection head. Devices that eject liquid include not only devices that can eject liquid onto objects to which the liquid can adhere, but also devices that eject liquid into air or liquid.

[0010] This "liquid ejection device" can also include means for feeding, transporting, and discharging objects onto which liquid can be attached, as well as pre-processing devices and post-processing devices.

[0011] For example, examples of "liquid ejection devices" include image forming devices that eject ink to form an image on paper, and three-dimensional modeling devices that eject modeling liquid onto a powder layer formed by layering powder in order to create a three-dimensional object (a three-dimensional model).

[0012] Furthermore, the term "liquid ejection device" is not limited to devices that visualize meaningful images such as characters and figures by ejecting liquid. For example, the term also includes devices that form patterns that have no meaning in themselves and devices that create three-dimensional images.

[0013] The above-mentioned "object to which liquid can adhere" means an object to which liquid can adhere at least temporarily, and to which the liquid adheres and sticks, or to which the liquid adheres and penetrates, etc. Specific examples include media such as paper, recording paper, film, cloth, and other recording media, electronic boards, electronic components such as piezoelectric elements, powder layers, organ models, and test cells, and unless otherwise specified, includes all objects to which liquid can adhere.

[0014] The material of the above-mentioned "object to which liquid can adhere" may be any material to which liquid can adhere even temporarily, such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, and ceramics.

[0015] The "liquid" may be any liquid having a viscosity and surface tension that allows it to be discharged from the head, and is not particularly limited, but is preferably one whose viscosity becomes 30 mPa·s or less at room temperature and pressure, or by heating or cooling. More specifically, it is a solution, suspension, emulsion, etc. containing a solvent such as water or an organic solvent, a colorant such as a dye or pigment, a functionalizing material such as a polymerizable compound, a resin, or a surfactant, a biocompatible material such as DNA, amino acids, proteins, calcium, etc., an edible material such as a natural dye, etc., and these can be used for applications such as inkjet ink, surface treatment liquid, a liquid for forming a component of an electronic element or a light-emitting element, an electronic circuit resist pattern, a material liquid for three-dimensional modeling, etc.

[0016] Furthermore, the term "liquid ejection device" includes devices in which a liquid ejection head and an object to which liquid can be attached move relatively, but is not limited to this. Specific examples include serial type devices in which a liquid ejection head moves, and line type devices in which a liquid ejection head does not move.

[0017] Other examples of "liquid ejection devices" include a treatment liquid application device that ejects a treatment liquid onto paper to apply the treatment liquid to the surface of the paper for purposes such as modifying the surface of the paper, and an injection granulation device that ejects a composition liquid in which raw materials are dispersed through a nozzle to granulate fine particles of the raw materials.

[0018] (First embodiment) Fig. 1 is a block diagram showing an example of a liquid ejection device including a liquid level detection system according to a first embodiment of the present invention. The liquid ejection device 100 shown in Fig. 1 has a main tank 10, a sub tank 20, a liquid level detection system 30, a supply pump 40, a recovery pump 42, a pressure reducing valve 50, and an inkjet head 60. The liquid level detection system 30 has a pair of rod-shaped electrode pins 31a, 31b arranged in the main tank 10, and a liquid level detection circuit 32. The inkjet head 60 has a head nozzle 61, a charged electrode plate 62, and a deflection electrode plate 63. The inkjet head 60 is an example of a liquid ejection head.

[0019] 1, double lines indicate pipes through which a conductive liquid flows. Arrows beside the pipes indicate the direction in which the liquid flows within the pipes. In this embodiment, an example is shown in which the liquid ejection device 100 ejects ink 70, but the liquid ejected by the liquid ejection device 100 is not limited to ink 70 and may be, for example, an undercoat liquid that is ejected onto a paper medium or the like before the ink 70 is ejected.

[0020] The main tank 10 contains the ink 70 used for printing. The subtank 20 contains the ink 70 to replenish the main tank 10. The liquid level detection system 30 detects the remaining amount of ink 70 in the main tank 10. The liquid level detection system 30 detects when the remaining amount of ink 70 in the main tank 10 falls below a predetermined amount, and controls the refilling of the ink 70 from the subtank 20 to the main tank 10. Note that the electrical characteristics, such as resistance value, of the ink 70 contained in the main tank 10 and the subtank 20 differ depending on the type of ink.

[0021] The electrode pins 31a, 31b are arranged vertically in the main tank 10 at horizontal intervals, with their upper ends protruding from the upper surface of the ink 70 in the main tank 10 and their lower ends disposed in the ink 70 in the main tank 10. Electrode pin 31b is longer than electrode pin 31a, and the lower end of electrode pin 31b is located deeper in the main tank 10 than the lower end of electrode pin 31a.

[0022] The upper end of the electrode pin 31a is connected to the liquid level detection circuit 32. The upper end of the electrode pin 31b is connected to a ground line GND and fixed to the ground voltage GND. The liquid level detection circuit 32 applies a voltage to the electrode pin 31a and detects, as a voltage, the resistance value of the ink 70 present between the electrode pins 31a and 31b, which changes depending on the length of the opposing portions of the electrode pins 31a and 31b immersed in the ink 70. The liquid level detection circuit 32 then detects that the remaining amount of ink 70 in the main tank 10 is low, based on the detected voltage.

[0023] The supply pump 40 supplies the ink 70 under pressure from the main tank 10 to the inkjet head 60. The pressure reducing valve 50 adjusts the pressure of the ink 70 supplied to the inkjet head 60. The recovery pump 42 returns the ink 70 recovered from the inkjet head 60 to the main tank 10.

[0024] The head nozzle 61, the charging electrode plate 62, and the deflection electrode plate 63 are arranged in this order along the ejection direction of the ink 70. The head nozzle 61 ejects the ink 70 supplied via the pressure reducing valve 50 in the form of droplets. The charging electrode plate 62 charges the droplets of the ink 70 that have been ejected from the head nozzle 61 and turned into particles. The deflection electrode plate 63 bends the charged droplets of the ink 70 according to the amount of charge, and causes them to land on the printing target 80, such as a paper medium, thereby printing on the printing target 80 using the ink 70. Note that the printing on the printing target 80 is not limited to characters, and may be figures, images, or the like. The printing target 80 is an example of a discharge target.

[0025] 1 shows a so-called continuous type inkjet head 60 in which ink 70 is continuously ejected even when not printing on a print target 80. However, the liquid ejection device 100 may also have an inkjet head of a piezo type or the like that ejects ink 70 when printing on a print target 80.

[0026] Fig. 2 is a block diagram showing an example of a hardware configuration of the liquid ejection device 100 of Fig. 1. As shown in Fig. 2, the liquid ejection device 100 has a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, an NVRAM (Non-Volatile Random Access Memory) 104, an external device connection interface 108, a network interface 109, and a bus line 110. The CPU 101 is an example of a computer.

[0027] The liquid ejection device 100 also includes a paper transport unit 111, a sub-scanning driver 112, a main-scanning driver 113, a carriage 120, and an operation panel 130. The carriage 120 corresponds to the inkjet head 60 in FIG.

[0028] The CPU 101 controls the overall operation of the liquid ejection device 100. The ROM 102 stores programs such as an IPL (Initial Program Loader) used to drive the CPU 101. The RAM 103 is used as a work area for the CPU 101. The NVRAM 104 stores various data such as programs, and retains the various data even when the power to the liquid ejection device 100 is cut off.

[0029] The external device connection interface 108 is connected to a PC (Personal Computer) via a USB (Universal Serial Bus) cable or the like, and communicates control signals and data to be printed with the PC. The network interface 109 communicates data using a communication network such as the Internet. The bus line 110 includes an address bus and a data bus for electrically connecting each component such as the CPU 101.

[0030] The paper transport unit 111 is, for example, a roller and a motor that drives the roller, and transports print paper in the sub-scanning direction along a transport path within the liquid ejection device 100. The sub-scanning driver 112 controls the movement of the paper transport unit 111 in the sub-scanning direction. The main scanning driver 113 controls the movement of the carriage 120 in the main scanning direction.

[0031] 1, the liquid ejection head 121 of the carriage 120 has a plurality of nozzles for ejecting liquid such as ink 70, and is mounted on the carriage 120 so that its ejection surface (nozzle surface) faces the print paper. The liquid ejection head 121 ejects liquid onto the print paper that is intermittently transported in the sub-scanning direction while moving in the main scanning direction, thereby ejecting liquid onto a predetermined position on the print paper to form an image. A liquid ejection head driver 122 controls the driving of the liquid ejection head 121.

[0032] The operation panel 130 displays current settings, a selection screen, and the like, and has a touch panel for receiving input from an operator, an alarm lamp, and the like.

[0033] Fig. 3 is a block diagram showing an outline of the liquid level detection circuit 32 in Fig. 1. The liquid level detection circuit 32 has a control circuit 321, a voltage application circuit 322, a rectifier circuit 323, a feedback line 324, a resistance switching circuit 325, and a level comparison circuit 326. The control circuit 321 controls the overall operation of the liquid level detection circuit 32.

[0034] The control circuit 321 includes a CPU1, a pulse generating circuit PLSGEN, a voltage determination circuit VJDG, and a memory MEM. For example, the control circuit 321 may control the operation of the liquid level detection circuit 32 by executing a liquid level detection program using the CPU1. The CPU1 may be the CPU101 in FIG. 2. The liquid level detection program is an example of a control program for the liquid level detection circuit. The CPU1 is an example of a computer.

[0035] The pulse generation circuit PLSGEN outputs a voltage pulse, which is a pulse-shaped signal having a predetermined amplitude, to the voltage application circuit 322. The voltage application circuit 322 applies a voltage generated according to the amplitude and frequency of the voltage pulse from the pulse generation circuit PLSGEN to the electrode pin 31a. By applying a voltage pulse to the electrode pin 31a, wear of the electrode pin 31a due to electrolysis of the ink 70 or the like can be prevented more effectively than when a DC voltage is applied. A voltage Va0 is generated at the node between the voltage application circuit 322 and the electrode pin 31a, which is divided by the internal resistance of the voltage application circuit 322 and the resistance of the ink 70 present between the electrode pins 31a and 31b.

[0036] The rectifier circuit 323 rectifies the pulsating voltage Va0 and converts it into a DC component to generate a voltage Va1. The generation node of the voltage Va0 and the generation node of the voltage Va1 are examples of voltage detection nodes. The rectifier circuit 323 is an example of a voltage conversion circuit that converts an AC voltage appearing at the voltage detection node into a DC voltage. The voltage Va1 is output to a voltage judgment circuit VJDG of the control circuit 321 via a feedback line 324, and is then output to a level comparison circuit 326.

[0037] The voltage determination circuit VJDG determines the voltage level of the voltage Va1 received via the feedback line 324, and outputs a voltage level signal VLVL indicating the determined voltage level to the CPU 1. Based on the voltage level signal VLVL from the voltage determination circuit VJDG, the CPU 1 determines the value of the threshold voltage Vb used to determine whether or not there is any ink 70 remaining in the main tank 10. The threshold voltage Vb is an example of a reference voltage.

[0038] The length (impedance) of the wiring that transmits the voltage Va1 from the output of the rectifier circuit 323 to the input of the voltage evaluation circuit VJDG is set to be approximately equal to the length (impedance) of the wiring that transmits the voltage Va1 from the output of the rectifier circuit 323 to the input of the level comparison circuit 326. In other words, the wiring load from the electrode pin 31a to the voltage evaluation circuit VJDG is set to be approximately equal to the wiring load from the electrode pin 31a to the level comparison circuit 326. This makes it possible to determine the threshold voltage Vb using approximately the same circuit conditions as when detecting the remaining amount of ink 70, and to generate a more appropriate threshold voltage Vb.

[0039] For example, the control circuit 321 outputs a pulse signal when the liquid level of the ink 70 in the main tank 10 is at the liquid level determination reference (hx in FIG. 6). The control circuit 321 acquires the electrical characteristics of the ink 70 contained in the main tank 10 based on the voltage value Va1 received via the feedback line 324.

[0040] The CPU1 stores the determined value of the threshold voltage Vb in the memory MEM, and outputs a resistance switching signal RCNG for switching the resistance value to generate the threshold voltage Vb to the resistance switching circuit 325. The resistance switching circuit 325 switches the resistance value of the internal resistor based on the resistance switching signal RCNG from the CPU1, and generates the threshold voltage Vb. The CPU1 and the resistance switching circuit 325 are an example of a reference voltage generating circuit.

[0041] From the above, the threshold voltage Vb corresponding to the type (electrical characteristics) of the ink 70 in the main tank 10 is generated, completing preparations for determining whether or not there is any ink 70 remaining in the main tank 10. The threshold voltage Vb may be generated by voltage division using the internal resistance of the resistance switching circuit 325 and the internal resistance of the level comparison circuit 326.

[0042] 1 is repeatedly performed, and the ink 70 in the main tank 10 gradually decreases. The level comparison circuit 326 compares the voltage Va1 output from the rectifier circuit 323 with the threshold voltage Vb, and outputs the comparison result as a voltage comparison result signal VRSLT to the CPU 1. The level comparison circuit 326 is an example of a voltage comparison circuit.

[0043] The CPU 1 judges whether the remaining amount of ink 70 in the main tank 10 is low or has plenty of ink, based on the voltage comparison result signal VRSLT received from the level comparison circuit 326. If the CPU 1 judges that the remaining amount of ink 70 in the main tank 10 is low, it carries out a process of refilling the main tank 10 with ink 70 from the sub tank 20. The CPU 1 is an example of a liquid level judgment circuit that judges whether the liquid level of the ink 70 in the main tank 10 is below a predetermined height.

[0044] Fig. 4 is a circuit diagram showing an example of the liquid level detection circuit 32 of Fig. 3. The voltage application circuit 322 has a buffer BUF1, resistors R6, R7, R8, and a capacitor C1. The buffer BUF1, the capacitor C1, and the resistor R8 are connected in series between the pulse generation circuit PLSGEN and the electrode pin 31a. The resistor R6 connects the power supply line VCC to a node between the output of the buffer BUF1 and one end of the capacitor C1. The resistor R7 connects a node between the other end of the capacitor C1 and one end of the resistor R8 to a ground line GND.

[0045] The buffer BUF1 outputs a pulsed signal output from the pulse generating circuit PLSGEN of the control circuit 321 to one end of the capacitor C1. Then, the voltage application circuit 322 outputs an analog voltage corresponding to the pulsed signal received by the buffer BUF1 to the electrode pin 31a. The node Va0 between the voltage application circuit 322 and the electrode pin 31a is divided by the resistors R6, R7, and R8 of the voltage application circuit 322 and the capacitor C1, and the resistance rink of the ink 70 between the electrode pins 31a and 31b, and is set to a voltage Va0 (analog voltage). For example, the resistance value rink of the ink 70 is unique for each ink 70. Therefore, when the liquid level of the ink 70 in the main tank 10 is the same, the voltage Va0 differs for each type of ink 70. For example, when the liquid level is the same, the higher the electrical resistance of the ink 70, the higher the voltage Va0.

[0046] The rectifier circuit 323 includes a diode D1, a resistor R9, a capacitor C2, and a comparator CMP1. The anode of the diode D1 is connected to the node Va0, and the cathode is connected to the + input of the comparator CMP1. The resistor R9 and the capacitor C2 are connected in parallel between the + input of the comparator CMP1 and the ground line GND. The - input of the comparator CMP1 is connected to the output of the comparator CMP1.

[0047] The output of the comparator CMP1 is connected to a feedback line 324 and a negative input of a comparator CMP2 of the level comparison circuit 326. The rectifier circuit 323 half-wave rectifies the voltage Va0 (analog voltage) by a diode D1, and smoothes the voltage by a resistor R9, a capacitor C2, and a comparator CMP1 to generate a DC voltage Va1.

[0048] The CPU1 outputs selection signals SEL1-SEL3 having logical values ​​corresponding to the value of the threshold voltage Vb determined based on the voltage level signal VLVL from the voltage judgment circuit VJDG to the resistance switching circuit 325. For example, when the CPU1 determines the threshold voltage Vb to be a value Vb1, it outputs selection signals SEL1-SEL3 indicating a value 0 that turns on the switch SW1. When the CPU1 determines the threshold voltage Vb to be a value Vb2, it outputs selection signals SEL1-SEL3 indicating a value 1 that turns on the switch SW2.

[0049] When the CPU1 determines the threshold voltage Vb to be value Vb3, it outputs selection signals SEL1-SEL3 indicating value 2 that turns on switch SW3. When the CPU1 determines the threshold voltage Vb to be value Vb4, it outputs selection signals SEL1-SEL3 indicating value 3 that turns on switch SW4. When the CPU1 determines the threshold voltage Vb to be value Vb5, it outputs selection signals SEL1-SEL3 indicating value 4 that turns on switch SW5.

[0050] The resistor switching circuit 325 includes a switch control circuit SWCNT, resistors R1, R2, R3, R4, R5, a reference resistor RrefA, and switches SW1, SW2, SW3, SW4, SW5. For example, the resistors R1, R2, R3, R4, R5 have higher resistance values ​​as their numbers increase. The resistors R1, R2, R3, R4, R5 are an example of a first resistor. The switches SW1, SW2, SW3, SW4, SW5 are an example of a connection circuit.

[0051] The switch control circuit SWCNT receives, for example, 3-bit selection signals SEL1-SEL3 from the CPU1 of the control circuit 321, and sets one of the switch control signals SCNT1-SCNT5 to an active level according to the logical values ​​of the selection signals SEL1-SEL3. The selection signals SEL1-SEL3 correspond to the resistance switching signal RCNG in FIG.

[0052] The resistor R1 and the switch SW1 are connected in series between the power supply line VCC and the node Vb. The switch SW1 is turned on while receiving the switch control signal SCNT1 of an active level, and connects the power supply line VCC to the node Vb via the resistor R1. The switch SW1 is turned off while receiving the switch control signal SCNT1 of an inactive level.

[0053] The resistor R2 and the switch SW2 are connected in series between the power supply line VCC and the node Vb. The switch SW2 is turned on while receiving the switch control signal SCNT2 of an active level, and connects the power supply line VCC to the node Vb via the resistor R2. The switch SW2 is turned off while receiving the switch control signal SCNT2 of an inactive level.

[0054] The resistor R3 and the switch SW3 are connected in series between the power supply line VCC and the node Vb. The switch SW3 is turned on while receiving the switch control signal SCNT3 of an active level, and connects the power supply line VCC to the node Vb via the resistor R3. The switch SW3 is turned off while receiving the switch control signal SCNT3 of an inactive level.

[0055] The resistor R4 and the switch SW4 are connected in series between the power supply line VCC and the node Vb. The switch SW4 is turned on while receiving the switch control signal SCNT4 of an active level, and connects the power supply line VCC to the node Vb via the resistor R4. The switch SW4 is turned off while receiving the switch control signal SCNT4 of an inactive level.

[0056] The resistor R5 and the switch SW5 are connected in series between the power supply line VCC and the node Vb. The switch SW5 is turned on while receiving the switch control signal SCNT5 of an active level, and connects the power supply line VCC to the node Vb via the resistor R5. The switch SW5 is turned off while receiving the switch control signal SCNT5 of an inactive level.

[0057] The level comparison circuit 326 includes a comparator CMP2, resistors R11, R12, R13, a reference resistor RrefB, and a buffer BUF2. The comparator CMP2 has a + input connected to a node Vb and one end of the reference resistor RrefB, and a - input connected to a node Va1. The output of the comparator CMP2 is connected to the input of the buffer BUF2, and is connected to the + input of the comparator CMP2 via the resistor R11.

[0058] The reference resistors RrefA and RrefB are connected in series between the power supply line VCC and the ground line GND. The reference resistor RrefA is an example of a second reference resistor, and the reference resistor RrefB is an example of a first reference resistor. The reference resistor RrefB may be provided outside the level comparison circuit 326. For example, the reference resistor RrefB may be included in the resistor switching circuit 325.

[0059] One end of the resistor R12 is connected to the input of the buffer BUF2, and the other end is connected to the power supply line VCC. The output of the buffer BUF2 is connected to a node VRSLT via a resistor R13. The comparator CMP2 compares the voltage Va1 with a threshold voltage Vb. The threshold voltage Vb is generated by resistance division using the combined resistance of the resistor switching circuit 325 and a reference resistor RrefB.

[0060] The comparator CMP2 outputs a high level when the voltage Va1 is lower than the threshold voltage Vb, and outputs a low level when the voltage Va1 is equal to or higher than the threshold voltage Vb. The buffer BUF2 converts the level output from the comparator CMP2 to a logical level and outputs it to the CPU1 of the control circuit 321 as a voltage comparison result signal VRSLT.

[0061] When the CPU 1 receives a high-level voltage comparison result signal VRSLT, it determines that there is sufficient ink 70 remaining in the main tank 10. When the CPU 1 receives a low-level voltage comparison result signal VRSLT, it determines that the ink 70 remaining in the main tank 10 is low and that replenishment from the subtank 20 is necessary.

[0062] When only the switch SWn (n is any of 1 to 5) is turned on in the resistance switching circuit 325, the value of the combined resistance RrefA' of the resistors Rn and RrefA is given by equation (1). From equation (1), the threshold voltage Vb generated at the node Vb when only the switch SWn (n is any of 1 to 5) is turned on is given by equation (2).

[0063] RrefA'=(Rn·RrefA) / (Rn+RrefA) ‥(1) Vb=(RrefB / (RrefA'+RrefB))·VCC =(RrefB / ((Rn·RrefA) / (Rn+RrefA)+RrefB))·VCC ‥(2)

[0064] The reference resistor RrefA is connected between the power supply line VCC and a node Vb. The resistor switching circuit 325 connects one of the resistors R1-R5 and the reference resistor RrefA in parallel between the power supply line VCC and a node Vb in response to a selection signal SEL1-SEL3 from the CPU1. This makes it possible to switch the combined resistance value of the parallel resistors in the resistor switching circuit 325 in response to the selection signals SEL1-SEL3, and to generate the threshold voltage Vb in stages. As a result, the threshold voltage Vb for determining whether the remaining amount of ink 70 is low can be appropriately generated in response to the type (electrical resistance value) of the ink 70.

[0065] 4, the combined resistance value can be switched between five values, but by increasing the number of resistors and switches, the combined resistance value can be switched between six or more values. When 3-bit selection signals SEL1-SEL3 are used, the combined resistance value can be switched between a maximum of eight values.

[0066] Fig. 5 is a circuit diagram showing an example of the voltage judgment circuit VJDG of Fig. 4. The voltage judgment circuit VJDG has a plurality of resistors connected in series between a reference voltage line Vref and a ground line GND, and a plurality of comparators that compare the voltages of the connection nodes of two adjacent resistors with the voltage Va1. For example, threshold voltages Vb5, Vb4, Vb3, Vb2, and Vb1 are generated at the connection nodes of the two resistors.

[0067] Each comparator outputs a logical value indicating the magnitude relationship between the voltage Va1 and the threshold voltages Vb5, Vb4, Vb3, Vb2, and Vb1 as a voltage level signal VLVL to the CPU1. Then, for example, when the voltage Va1 is between the threshold voltages Vb1 and Vb2, the CPU1 determines to generate the threshold voltage Vb1 at the node Vb. For example, when the voltage Va1 is between the threshold voltages Vb3 and Vb4, the CPU1 determines to generate the threshold voltage Vb3 at the node Vb.

[0068] Fig. 6 is a diagram showing an example of detecting the liquid level by the liquid level detection circuit 32 of Fig. 4. The left side of Fig. 6 shows the relationship between the liquid level height h of the ink 70 in the main tank 10 and the electrical resistance value rink of the electrode pins 31a, 31b. The liquid level height of the ink 70 when there is a sufficient amount of ink 70 remaining in the main tank 10 and both bottom ends of the electrode pins 31a, 31b are immersed in the ink 70 is indicated by the symbol hx. The liquid level height of the ink 70 when there is a small amount of ink 70 remaining in the main tank 10 and the electrode pin 31a is not immersed in the ink 70 is indicated by the symbol h1. The height hx is an example of a reference height, and the height h1 is an example of a lower limit height.

[0069] For example, assume that three types of ink 70 can be used for printing, and hereinafter, each ink 70 will be referred to as ink A, ink B, and ink C. The electrical resistance value rink of ink A is lower than the electrical resistance value rink of ink B, and the electrical resistance value rink of ink B is higher than the electrical resistance value rink of ink C.

[0070] As shown on the left side of Fig. 6, when the liquid levels of inks A, B, and C are lower than height h1, the lower end of electrode pin 31a is located above the liquid level. Therefore, the space between electrode pins 31a and 31b is electrically open, and the electrical resistance value becomes infinite (Fig. 6(a)).

[0071] When the liquid levels of the inks A, B, and C are higher than height h1, the lower end of the electrode pin 31a is located in the liquid. Therefore, the electrical resistance between the electrode pins 31a and 31b varies depending on the length of the opposing portions of the electrode pins 31a and 31b immersed in the inks A, B, and C. In other words, the electrical resistance between the electrode pins 31a and 31b decreases as the liquid level increases and the length of the opposing portions of the electrode pins 31a and 31b immersed in the inks A, B, and C increases (FIG. 6(b)).

[0072] The height hx is used as a criterion for determining the liquid level process. The control circuit 321 in FIG. 4 outputs a pulse-shaped signal when the liquid level of any of the inks A, B, and C is at height hx. The control circuit 321 determines a threshold voltage Vb based on a voltage value Va1 received via a feedback line 324, and sets a combined resistance value of the resistance switching circuit 325 according to the determined threshold voltage Vb. In the example shown in FIG. 6, the electrical resistance values ​​between the electrode pins 31a and 31b at height hx are, for example, rink-a, rink-b, and rink-c for the inks A, B, and C, respectively (FIG. 6(c)).

[0073] The right side of Fig. 6 shows the relationship between the electrical resistance value rink of the ink 70 and the voltage Va and threshold voltage Vb. The voltage Va is expressed by equation (3) assuming that the resistance value R of the resistance component in the voltage application circuit 322 in Fig. 4 and the resistance value rink of the ink 70 are connected in series. In equation (3), symbol V is the effective value of the high-level voltage output from the buffer BUF1 of the voltage application circuit 322.

[0074] Va = rink / (R + rink) V =1 / (R / rink+1)·V ‥(3)

[0075] 4, the voltage Va represents the effective value of the voltage Va0 and the voltage Va1. In the formula (3), the resistance value R and the high-level voltage V are fixed. Therefore, the voltage Va increases as the liquid level height h decreases and the resistance value rink of the ink 70 increases.

[0076] It is assumed that the electrical resistance value rink-a of ink A at height hx is between threshold voltages Vb1 and Vb2. It is assumed that the electrical resistance value rink-b of ink B at height hx is between threshold voltages Vb3 and Vb4. It is assumed that the electrical resistance value rink-c of ink C at height hx is between threshold voltages Vb4 and Vb5. It is not necessary for the electrical resistance values ​​rink-a, rink-b, and rink-c of inks A, B, and C to be known in advance. In other words, the liquid level detection circuit 32 does not need to know the type of ink 70 contained in the main tank 10.

[0077] When the voltage value Va1 generated on the feedback line 324 is between the threshold voltages Vb1 and Vb2, the control circuit 321 outputs selection signals SEL1-SEL3 that generate a threshold value Vb1 at the node Vb to the resistance switching circuit 325. When the voltage value Va1 generated on the feedback line 324 is between the threshold voltages Vb3 and Vb4, the control circuit 321 outputs selection signals SEL1-SEL3 that generate a threshold value Vb3 at the node Vb to the resistance switching circuit 325. When the voltage value Va1 generated on the feedback line 324 is between the threshold voltages Vb4 and Vb5, the control circuit 321 outputs selection signals SEL1-SEL3 that generate a threshold value Vb4 at the node Vb to the resistance switching circuit 325.

[0078] Fig. 7 is a flow diagram showing an example of a method for generating the threshold voltage Vb by the liquid level detection circuit 32 of Fig. 4. That is, Fig. 7 shows an example of a method for controlling the liquid level detection circuit. The flow shown in Fig. 7 is started when the power supply of the liquid ejection device 100 is turned on, when the ink 70 is replaced, or at any other necessary timing, and is executed by the CPU 1. For example, the flow shown in Fig. 7 may be realized by a control program for the liquid level detection circuit executed by the CPU 1.

[0079] First, in step S100, the CPU 1 controls the pulse generating circuit PLSGEN to apply a voltage pulse to the electrode pin 31a. Next, in step S102, the CPU 1 acquires a voltage Va1 via the voltage determining circuit VJDG when the liquid level of the ink 70 is at a height hx.

[0080] Next, in step S104, the CPU 1 determines whether the voltage Va1 is equal to or greater than the threshold voltage Vb1 and lower than the threshold voltage Vb2, and performs step S106 if the determination condition is satisfied, and performs step S108 if the determination condition is not satisfied. In step S106, the CPU 1 controls the resistance switching circuit 325 to turn on the switch SW1, and ends the operation of generating the threshold voltage Vb.

[0081] In step S108, the CPU 1 determines whether the voltage Va1 is equal to or greater than the threshold voltage Vb2 and lower than the threshold voltage Vb3, and performs step S110 if the determination condition is satisfied, and performs step S112 if the determination condition is not satisfied. In step S110, the CPU 1 controls the resistance switching circuit 325 to turn on the switch SW2, and ends the operation of generating the threshold voltage Vb.

[0082] In step S112, the CPU 1 determines whether the voltage Va1 is equal to or greater than the threshold voltage Vb3 and lower than the threshold voltage Vb4, and performs step S114 if the determination condition is satisfied, and performs step S116 if the determination condition is not satisfied. In step S114, the CPU 1 controls the resistance switching circuit 325 to turn on the switch SW3, and ends the operation of generating the threshold voltage Vb.

[0083] In step S116, the CPU 1 determines whether the voltage Va1 is equal to or greater than the threshold voltage Vb4 and lower than the threshold voltage Vb5, and performs step S118 if the determination condition is satisfied, and performs step S120 if the determination condition is not satisfied. In step S118, the CPU 1 controls the resistance switching circuit 325 to turn on the switch SW4, and ends the operation of generating the threshold voltage Vb.

[0084] In step S120, the CPU 1 determines whether the voltage Va1 is equal to or greater than the threshold voltage Vb5 and lower than the threshold voltage Vbmax, and if the determination condition is satisfied, the CPU 1 executes step S122, and if the determination condition is not satisfied, the CPU 1 executes step S124. In step S122, the CPU 1 controls the resistance switching circuit 325 to turn on the switch SW5, completing the operation of generating the threshold voltage Vb.

[0085] After completing the operation of generating the threshold voltage Vb, the CPU 1 detects whether the remaining amount of ink 70 in the main tank 10 has fallen below a predetermined amount (below the lower limit height h1) by comparing the voltage Va1 from the rectifier circuit 323 with the generated threshold voltage Vb.

[0086] In step S124, since the voltage Va1 is not within the range from the threshold voltage Vb1 to the threshold voltage Vbmax, the CPU 1 detects the occurrence of an abnormality and ends the operation of Fig. 7. For example, an abnormality occurs when the lower end of the electrode pin 31a is located above the upper surface of the ink 70 in the main tank 10, due to a disconnection or short circuit in the harness, damage to the electrode pins 31a and 31b, a malfunction of the liquid level detection circuit 32, etc. When the CPU 1 detects the occurrence of an abnormality, it notifies a higher-level block of the liquid ejection device 100 of the occurrence of the abnormality. Based on the notification of the occurrence of the abnormality, the higher-level block of the liquid ejection device 100 stops the printing operation and displays the occurrence of the abnormality on a display device or the like.

[0087] Fig. 8 is a circuit diagram showing an example of another liquid level detection circuit mounted on the liquid ejection device 100 of Fig. 1. Detailed description of the same elements as those in Fig. 4 will be omitted. The liquid level detection circuit 32A shown in Fig. 8 has a control circuit 321A, a voltage application circuit 322, a rectification circuit 323, and a level comparison circuit 326A. The voltage application circuit 322 and the rectification circuit 323 are the same as the voltage application circuit 322 and the rectification circuit 323 of Fig. 4.

[0088] The control circuit 321A has the same configuration and function as the control circuit 321 in Fig. 4, except that it does not have a voltage judgment circuit VJDG. The level comparison circuit 326A has the same configuration and function as the level comparison circuit 326 in Fig. 4, except that it has a reference resistor RrefA connected in series with the reference resistor RrefB between the power supply line VCC and the ground line GND.

[0089] The level comparison circuit 326A generates a fixed threshold voltage Vb using reference resistors RrefA and RrefB, which have fixed resistance values. For this reason, it is necessary to set the resistance value of the reference resistor RrefA in accordance with the resistance values ​​rink of the multiple types of ink filled in the main tank 10. When changing the type of ink, it is necessary to replace the reference resistor RrefA with, for example, another one having a different resistance value in order to change the threshold voltage Vb. For example, it is necessary to replace the board on which the level comparison circuit 326A is mounted.

[0090] As described above, in the first embodiment, the CPU 1 connects one of the resistors R1-R5, each having a different resistance value, in parallel to the reference resistor RrefA, which is connected in series with the reference resistor RrefB, based on the result of determining the voltage level of the voltage Va1 at the liquid level height hx. This makes it possible to generate an appropriate threshold voltage Vb in accordance with the resistance value of the ink 70 at the connection node Vb between the reference resistors RrefA and RrefB using the resistor switching circuit 325.

[0091] Therefore, without using a complex circuit such as an A / D converter, a simple resistance switching circuit 325 using switches SW1-SW5 and resistors R1-R5 can be used to generate a threshold voltage Vb1 of an appropriate value used to detect the presence or absence of remaining ink 70. As a result, the threshold voltage Vb used to determine whether the liquid level of the ink 70 in the main tank 10 is equal to or lower than the lower limit height h1 can be generated while suppressing an increase in circuit size. At this time, even if the type of ink 70 is unknown, a threshold voltage Vb1 of an appropriate value can be generated. Even if a liquid other than ink, such as an undercoat liquid, is placed in the main tank 10, a threshold voltage Vb1 of an appropriate value can be generated.

[0092] Furthermore, even if the resistance value changes due to changes in the volume, viscosity, etc. of the ink 70 caused by temperature or aging, an appropriate threshold voltage Vb1 can be generated by carrying out the flow of Fig. 7. As a result, the remaining amount of ink 70 in the main tank 10 can be accurately detected regardless of the type and condition of the ink.

[0093] The CPU1 controls the resistor switching circuit 325 to connect one of the resistors R1-R5 appropriate for the actual resistance value rink of the ink 70 contained in the main tank 10 in parallel with the reference resistor RrefA. This makes it possible to generate an appropriate value of the threshold voltage Vb1 depending on the ink 70 contained in the main tank 10, without replacing the board including the liquid level detection circuit 32.

[0094] Applying a voltage pulse to the electrode pin 31a can prevent wear on the electrode pin 31a due to electrolysis of the ink 70, compared to applying a DC voltage. By setting the wiring load from the electrode pin 31a to the voltage determination circuit VJDG to be approximately equal to the wiring load from the electrode pin 31a to the level comparison circuit 326, a more appropriate threshold voltage Vb can be generated using approximately the same circuit conditions as when detecting the remaining amount of ink 70.

[0095] As a result, the remaining amount of liquid in the main tank 10 of the liquid ejection device 100 can be accurately detected, and downtime due to insufficient remaining liquid can be reduced, thereby providing a liquid ejection device 100 with high processing performance.

[0096] Fig. 9 is a circuit diagram showing an example of a liquid level detection circuit mounted on a liquid ejection device according to a second embodiment of the present invention. The same elements as those in Fig. 4 are given the same reference numerals, and detailed description will be omitted. The liquid level detection circuit 32B shown in Fig. 9 constitutes a liquid level detection system together with rod-shaped electrode pins 31a and 31b arranged in the main tank 10. The liquid level detection system is mounted on the liquid ejection device 100, similar to Fig. 1.

[0097] The liquid level detection circuit 32B includes a control circuit 321B, a voltage application circuit 322, a rectifier circuit 323, a resistance switching circuit 325, and a level comparison circuit 326B. The control circuit 321B has the same configuration and function as the control circuit 321 in FIG. 4, except that it does not include the determination circuit VJDG.

[0098] When the liquid level of the ink 70 in the main tank 10 is at height hx, the CPU1 of the control circuit 321B causes the pulse generating circuit PLSGEN to generate a pulsed signal and applies a voltage pulse to the electrode pin 31a. While the voltage pulse is being applied to the electrode pin 31a, the CPU1 sequentially selects one of the resistors R1-R5 using selection signals SEL1-SEL3, connects it in parallel with the reference resistor RrefA, and sequentially generates threshold voltages Vb1-Vb5 shown in FIG. 6 at the node Vb.

[0099] Each time the CPU1 generates each of the threshold voltages Vb1-Vb5, it judges whether the voltage Va1 is larger than the threshold voltages Vb1-Vb5 based on the voltage comparison result signal VRSLT output from the level comparison circuit 326B. The CPU1 stores the judgment result in the memory MEM each time. Based on the five judgment results stored in the memory MEM, the CPU1 turns on one of the switches SW1-SW5 of the resistance switching circuit 325, and generates the threshold voltage Vb at the node Vb according to the electrical resistance value rink of the ink 70 filled in the main tank 10. After that, the CPU1 compares the voltage Va1 from the rectifier circuit 323 with the threshold voltage Vb to detect whether the remaining amount of ink 70 in the main tank 10 has fallen below a predetermined amount.

[0100] Fig. 10 is a flow diagram showing an example of a method for generating a threshold voltage by the liquid level detection circuit 32B of Fig. 9. That is, Fig. 10 shows an example of a method for controlling the liquid level detection circuit. The flow shown in Fig. 10 is started when the power supply of the liquid ejection device 100 is turned on, when the ink 70 is replaced, or at any other necessary timing, and is executed by the CPU1. The liquid level of the ink 70 is set to a height hx. For example, the flow shown in Fig. 10 may be realized by a control program of the liquid level detection circuit executed by the CPU1.

[0101] First, in step S200, the CPU 1 controls the pulse generating circuit PLSGEN to apply a voltage pulse to the electrode pin 31a. Next, in step S202, the CPU 1 sets the counter value n to "1." Next, in step S204, the CPU 1 controls the resistance switching circuit 325 to turn on the switch SWn and turn off the other switches SW.

[0102] Next, in step S206, the CPU 1 obtains the comparison result indicated by the n-th voltage comparison result signal VRSLTn indicating the magnitude relationship between the voltage Va1 and the threshold voltage Vb1 by the level comparison circuit 326B, and stores it in the memory MEM. Next, in step S208, the CPU 1 increments the counter value n by "1". Next, in step S210, if the counter value n is equal to or less than "5", the CPU 1 executes step S204, and if the counter value n exceeds "5", the CPU 1 executes step S212.

[0103] In step S212, the CPU 1 reads out the five comparison results indicated by the voltage comparison result signals VRSLT1-VRSLT5 from the memory MEM, and determines which switch SW to turn on. Next, in step S214, the CPU 1 controls the resistance switching circuit 325 to turn on the switch SW determined in step S212 and turn off the other switches SW, completing the operation of generating the threshold voltage Vb. This makes it possible to generate an appropriate threshold voltage Vb according to the electrical characteristics of the ink 70 contained in the main tank 10.

[0104] After completing the operation of generating the threshold voltage Vb, the CPU 1 compares the voltage Va1 from the rectifier circuit 323 with the threshold voltage Vb to detect whether the remaining amount of ink 70 in the main tank 10 has fallen below a predetermined amount.

[0105] In step S212, if the CPU 1 cannot determine which switch SW to turn on, it detects the occurrence of an abnormality, similar to step 124 in Fig. 7, and ends the operation in Fig. 10. When the CPU 1 detects the occurrence of an abnormality, it notifies the upper block of the liquid ejection device 100 of the occurrence of the abnormality. The upper block of the liquid ejection device 100 stops the printing operation based on the notification of the occurrence of the abnormality, and displays the occurrence of the abnormality on a display device or the like.

[0106] As described above, the second embodiment can achieve the same effects as the first embodiment. For example, the CPU 1 connects one of the resistors R1-R5, each having a different resistance value, in parallel to the reference resistor RrefA, which is connected in series with the reference resistor RrefB, based on the result of determining the voltage level of the voltage Va1 at the liquid level height hx. This makes it possible to generate an appropriate threshold voltage Vb at the connection node Vb between the reference resistors RrefA and RrefB in accordance with the resistance value of the ink 70.

[0107] Therefore, without using a complex circuit such as an A / D converter, a simple resistance switching circuit 325 using switches SW1-SW5 and resistors R1-R5 can be used to generate a threshold voltage Vb1 of an appropriate value used to detect the presence or absence of remaining ink 70. As a result, the threshold voltage Vb used to determine whether the liquid level of the ink 70 in the main tank 10 is equal to or lower than the lower limit height h1 can be generated without increasing the circuit size.

[0108] A threshold voltage Vb1 of an appropriate value used to detect the presence or absence of remaining ink 70 can be generated according to the type of ink 70 contained in the main tank 10. By applying a voltage pulse to the electrode pin 31a, wear on the electrode pin 31a due to electrolysis of the ink 70 or the like can be prevented compared to the case of applying a DC voltage. The remaining amount of liquid in the main tank 10 of the liquid ejection device 100 can be accurately detected, and downtime caused by a lack of remaining liquid can be suppressed, making it possible to provide a liquid ejection device 100 with high processing performance.

[0109] Furthermore, in the second embodiment, it is possible to generate a threshold voltage Vb1 of an appropriate value according to the type (electrical resistance value) of the ink 70 without providing the voltage judgment circuit VJDG in the control circuit 321B.

[0110] For example, aspects of the present invention are as follows. <1> A pair of electrodes spaced apart within a tank containing a conductive liquid; a voltage application circuit that applies a voltage to one of the pair of electrodes via a voltage detection node; a voltage determination circuit that determines a value of a voltage appearing at the voltage detection node based on a voltage applied from the voltage application circuit when the liquid level of the tank is at a reference height; a reference voltage generating circuit including a second reference resistor connected in series with a first reference resistor via a connection node and a plurality of first resistors having different resistance values, and which generates a reference voltage at the connection node by connecting any one of the plurality of first resistors in parallel with the second reference resistor based on a voltage value determined by the voltage determination circuit; a voltage comparison circuit that compares a voltage appearing at the voltage detection node with a reference voltage in response to a resistance value between the pair of electrodes that varies depending on the type of the liquid and the height of the liquid surface in the tank; a liquid level determination circuit that determines whether or not the liquid level is equal to or lower than a lower limit height that is lower than the reference height based on a comparison result by the voltage comparison circuit. A liquid level detection circuit comprising: <2> The voltage application circuit applies a voltage pulse to the one electrode. A liquid level detection circuit as described in <1>, characterized by: <3> a voltage conversion circuit that is disposed between the voltage detection node and an input of the voltage comparison circuit and converts an AC voltage appearing at the voltage detection node into a DC voltage; Characterized by <2> The liquid level detection circuit described in <4> The wiring for transmitting the voltage from the one electrode to the voltage judgment circuit has substantially the same length as the wiring for transmitting the voltage from the one electrode to the voltage comparison circuit. Characterized by <1> Or <3> 13. A liquid level detection circuit according to claim 12. <5> The liquid is ink to be discharged onto the discharge target, or an undercoat liquid to be discharged onto the discharge target before the ink is discharged. Characterized by <1> Or <4> 13. A liquid level detection circuit according to claim 12. <6> <1> Or <5> A liquid level detection circuit according to any one of claims 1 to 4, a liquid ejection head that ejects the liquid supplied from the tank. A liquid ejection device comprising: <7> A pair of electrodes spaced apart from each other in a tank containing a conductive liquid, and a voltage application circuit that applies a voltage to one of the pair of electrodes via a voltage detection node; A control method for a liquid level detection circuit having a reference voltage generation circuit including a second reference resistor connected in series with a first reference resistor via a connection node, and a plurality of first resistors having different resistance values, and a voltage comparison circuit that compares a voltage appearing at the voltage detection node with a reference voltage in accordance with the resistance value between the pair of electrodes that changes depending on the type of the liquid and the height of the liquid level in the tank, determining a value of a voltage appearing at the voltage detection node based on a voltage applied from the voltage application circuit when the liquid level in the tank is at a reference height; generating the reference voltage at the connection node by connecting any one of the plurality of first resistors in parallel with the second reference resistor based on the determined voltage value; determining whether the liquid level is equal to or lower than a lower limit height that is lower than the reference height based on a comparison result by the voltage comparison circuit; A control method for a liquid level detection circuit comprising: <8> A pair of electrodes spaced apart from each other in a tank containing a conductive liquid, and a voltage application circuit that applies a voltage to one of the pair of electrodes via a voltage detection node; A control program for a liquid level detection circuit having a reference voltage generation circuit including a second reference resistor connected in series with a first reference resistor via a connection node, and a plurality of first resistors having different resistance values, and a voltage comparison circuit that compares a voltage appearing at the voltage detection node with a reference voltage in accordance with the resistance value between the pair of electrodes that changes depending on the type of the liquid and the height of the liquid level in the tank, a process of determining a value of a voltage appearing at the voltage detection node based on a voltage applied from the voltage application circuit when the liquid level in the tank is at a reference height; generating the reference voltage at the connection node by connecting any one of the plurality of first resistors in parallel with the second reference resistor based on the determined voltage value; and determining whether or not the liquid level is equal to or lower than a lower limit height that is lower than the reference height based on a comparison result by the voltage comparison circuit. A control program for a liquid level detection circuit, characterized in that the program is executed by a computer.

[0111] Although the present invention has been described above based on the embodiments, the present invention is not limited to the requirements shown in the above embodiments. These points can be changed without departing from the spirit of the present invention, and can be appropriately determined according to the application form. [Explanation of symbols]

[0112] 10. Main Tank 20 Subtank 30 Liquid Level Detection System 31a, 31b Electrode pin 32, 32A, 32B Liquid level detection circuit 40 Supply Pump 42 Recovery pump 50 Pressure reducing valve 60 Inkjet head 61 Head nozzle 62 Charged electrode plate 63 Deflection electrode plate 70 Ink 100 Liquid dispensing device 101 CPU 102 ROM 103 RAM 104 NVRAM 108 External device connection interface 109 Network Interface 110 Bus Line 111 Paper transport section 112 Sub-scan driver 113 Main scanning driver 120 Carriage 121 Liquid ejection head 122 Liquid ejection head driver 130 Operation Panel 321, 321A, 321B Control circuit 322 Voltage application circuit 323 Rectifier circuit 324 Feedback Line 325 Resistor switching circuit 326, 326A, 326B Level comparison circuit CMP1, CMP2 comparators h1, hx Liquid level MEM Memory PLSGEN Pulse generation circuit RCNG Resistor switching signal rink Electrical resistance value RrefA, RrefB Reference resistors SCNT1-SCNT5 Switch control signals SEL1-SEL3 selection signal SW1-SW5 Switches SWCNT Switch control circuit Va0, Va1 voltage Vb Threshold voltage VJDG Voltage judgement circuit VLVL Voltage level signal VRSLT Voltage comparison result signal [Prior art documents] [Patent documents]

[0113] [Patent Document 1] JP 2009-172967 A

Claims

1. A pair of electrodes spaced apart within a tank containing a conductive liquid; a voltage application circuit that applies a voltage to one of the pair of electrodes via a voltage detection node; a voltage determination circuit that determines a value of a voltage appearing at the voltage detection node based on a voltage applied from the voltage application circuit when the liquid level of the tank is at a reference height; a reference voltage generating circuit including a second reference resistor connected in series with a first reference resistor via a connection node and a plurality of first resistors having different resistance values, the reference voltage generating circuit generating a reference voltage at the connection node by connecting any one of the plurality of first resistors in parallel with the second reference resistor based on a voltage value determined by the voltage determination circuit; a voltage comparison circuit that compares a voltage appearing at the voltage detection node with a reference voltage in response to a resistance value between the pair of electrodes that varies depending on the type of the liquid and the height of the liquid surface in the tank; a determination circuit that determines whether or not the liquid level is equal to or lower than a lower limit height that is lower than the reference height based on a comparison result by the voltage comparison circuit. A liquid level detection circuit comprising:

2. The voltage application circuit applies a voltage pulse to the one electrode.

2. The liquid level detection circuit according to claim 1 .

3. a voltage conversion circuit that is disposed between the voltage detection node and an input of the voltage comparison circuit and converts an AC voltage appearing at the voltage detection node into a DC voltage; 3. The liquid level detection circuit according to claim 2 .

4. The wiring for transmitting the voltage from the one electrode to the voltage judgment circuit has substantially the same length as the wiring for transmitting the voltage from the one electrode to the voltage comparison circuit.

2. The liquid level detection circuit according to claim 1 .

5. The liquid is ink to be discharged onto the discharge target, or an undercoat liquid to be discharged onto the discharge target before the ink is discharged.

2. The liquid level detection circuit according to claim 1 .

6. A liquid level detection circuit according to any one of claims 1 to 5, a liquid ejection head that ejects the liquid supplied from the tank. A liquid ejection device comprising:

7. A pair of electrodes spaced apart from each other in a tank containing a conductive liquid, and a voltage application circuit that applies a voltage to one of the pair of electrodes via a voltage detection node; A control method for a liquid level detection circuit having a reference voltage generation circuit including a second reference resistor connected in series with a first reference resistor via a connection node, and a plurality of first resistors having different resistance values, and a voltage comparison circuit that compares a voltage appearing at the voltage detection node with a reference voltage in accordance with the resistance value between the pair of electrodes that changes depending on the type of the liquid and the height of the liquid level in the tank, determining a value of a voltage appearing at the voltage detection node based on a voltage applied from the voltage application circuit when the liquid level in the tank is at a reference height; generating the reference voltage at the connection node by connecting any one of the plurality of first resistors in parallel with the second reference resistor based on the determined voltage value; determining whether the liquid level is equal to or lower than a lower limit height that is lower than the reference height based on a comparison result by the voltage comparison circuit; A control method for a liquid level detection circuit comprising:

8. A pair of electrodes spaced apart from each other in a tank containing a conductive liquid, and a voltage application circuit that applies a voltage to one of the pair of electrodes via a voltage detection node; A control program for a liquid level detection circuit having a reference voltage generation circuit including a second reference resistor connected in series with a first reference resistor via a connection node, and a plurality of first resistors having different resistance values, and a voltage comparison circuit that compares a voltage appearing at the voltage detection node with a reference voltage in accordance with the resistance value between the pair of electrodes that changes depending on the type of the liquid and the height of the liquid level in the tank, a process of determining a value of a voltage appearing at the voltage detection node based on a voltage applied from the voltage application circuit when the liquid level in the tank is at a reference height; generating the reference voltage at the connection node by connecting any one of the plurality of first resistors in parallel with the second reference resistor based on the determined voltage value; and determining whether or not the liquid level is equal to or lower than a lower limit height that is lower than the reference height based on a comparison result by the voltage comparison circuit. A control program for a liquid level detection circuit, characterized in that the program is executed by a computer.

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