Liquid dispensing device

Abstract

To detect that continuous short-circuit and temporal short-circuit occur between a liquid discharge head and an electrode.SOLUTION: A voltage supply circuit 51 generates a potential difference between an inkjet head 4 and an electrode. To an inkjet head 4, a first output part 58 to which a first signal according to a change in a voltage when driving for inspection is performed by the inkjet head 4 is output is connected. To the inkjet head 4, a second output part 60 is connected through low-pass filters 59 and 71. To the inkjet head 4, a third output part 62 is connected through a high-pass filter 56. It is determined whether ink has been normally discharged from a nozzle by driving for inspection on the basis of the first signal. It is determined whether the continuous short-circuit is generated on the basis of a second signal output from the second output part 60. It is determined whether the temporal short-circuit is generated on the basis of a third signal output from the third output part 62.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a liquid ejection device that ejects liquid from a nozzle. [Background technology]

[0002] As an example of a liquid ejection device that ejects liquid from nozzles, Patent Document 1 describes an inkjet printer that performs recording by ejecting ink from nozzles. The inkjet printer described in Patent Document 1 has a test area including an electrode member in a capping member that covers the nozzles. Then, while generating a potential difference between the print head and the test area, the print head is operated to eject ink from the nozzles toward the test area, and the ink is inspected to determine whether the nozzles are ejecting ink normally based on the change in voltage in the test area. Furthermore, Patent Document 1 also measures the actual voltage between the print head and the test area when performing the test. If the actual measured voltage is below the test tolerance range, it is determined that the print head and the electrode member are short-circuited, causing a leak current to flow. The printer then separates the print head from the capping member and uses a suction pump to drain the ink accumulated in the capping member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-136858 Summary of the Invention [Problem to be solved by the invention]

[0004] In the inkjet printer of Patent Document 1, when a continuous short circuit occurs between the print head and the inspection area, a leakage current continuously flows between the print head and the inspection area, causing the voltage between the print head and the inspection area to remain below the inspection tolerance range. Patent Document 1 then determines whether a continuous short circuit occurs between the print head and the inspection area based on whether the voltage between the print head and the inspection area is below the inspection tolerance range. Meanwhile, a temporary short circuit between the print head and the inspection area may also occur due to, for example, a temporary discharge between the print head and the inspection area. In this case, only a temporary leakage current flows between the print head and the electrode member, so it is necessary to detect the temporary voltage change. However, the configuration for detecting a continuous short circuit between the print head and the inspection area described in Patent Document 1 may not be able to detect such a temporary voltage change. If a temporary short circuit occurs between the print head and the inspection area, similar temporary short circuits may occur repeatedly or may develop into a continuous short circuit between the print head and the inspection area. Therefore, it is preferable to be able to detect the occurrence of a short circuit between the print head and the inspection area not only when a continuous short circuit occurs between the print head and the inspection area, but also when a temporary short circuit occurs between the print head and the inspection area.

[0005] An object of the present invention is to provide a liquid ejection device that can more accurately detect both the occurrence of a continuous short circuit and the occurrence of a temporary short circuit between a liquid ejection head and an electrode that receives liquid ejected from a nozzle. [Means for solving the problem]

[0006] a first output section electrically connected to either the electrode or the liquid ejection head and configured to output a first signal corresponding to an electrical change when the liquid ejection head is driven for testing to eject liquid from the nozzle toward the electrode while the liquid ejection head is facing the electrode; a low-pass filter electrically connected to the liquid ejection head; a second output section electrically connected to the liquid ejection head via the low-pass filter; a high-pass filter electrically connected to the liquid ejection head; a third output section electrically connected to the liquid ejection head via the high-pass filter; and a control section. The control section determines whether liquid has been ejected normally from the nozzle based on the first signal, and determines whether a short circuit has occurred between the liquid ejection head and the electrode based on the second signal output from the second output section and the third signal output from the third output section. [Effects of the Invention]

[0007] According to the present invention, it is possible to determine whether liquid is being ejected normally from the nozzle based on the first signal output from the first output unit. Furthermore, when a continuous short circuit occurs between the liquid ejection head and the electrode, the DC component of the voltage of the liquid ejection head changes. In this invention, the second output unit is connected to the liquid ejection head via a low-pass filter, so the second signal output from the second output unit is a signal corresponding to the DC component of the voltage of the liquid ejection head. This makes it possible to detect a continuous short circuit between the liquid ejection head and the electrode based on the second signal. Furthermore, when a temporary short circuit occurs between the liquid ejection head and the electrode, the voltage of the liquid ejection head changes suddenly, generating a high-frequency component in the voltage of the liquid ejection head. In this invention, the third output unit is connected to the liquid ejection head via a high-pass filter, so the third signal output from the third output unit is a signal corresponding to the high-frequency component of the voltage of the liquid ejection head. This makes it possible to detect a temporary short circuit between the liquid ejection head and the electrode based on the third signal. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a printer according to an embodiment of the present invention. [Figure 2] 4A and 4B are diagrams for explaining electrodes and the like arranged inside the cap. [Figure 3] FIG. 2 is a block diagram showing the electrical configuration of the printer. [Figure 4] FIG. 2 is a block diagram showing the configuration of an inspection circuit; [Figure 5] (a) is a diagram for explaining the signal sent from the high-pass filter to the first output unit when ink is not ejected from the nozzle during test drive, and the signal output from the first output unit; (b) is a diagram for explaining the signal sent from the high-pass filter to the first output unit when ink is ejected from the nozzle during test drive; and (c) is a diagram for explaining the signal output from the first output unit when ink is ejected from the nozzle during test drive. [Figure 6]10 is a diagram illustrating a signal output from a second output unit. FIG. [Figure 7] (a) is a diagram for explaining a signal received by the latch circuit when no temporary short circuit occurs, (b) is a diagram for explaining a signal received by the latch circuit when a temporary short circuit occurs, and (c) is a diagram for explaining a signal output from the latch circuit (third output section). [Figure 8] 10 is a flowchart showing a process flow when an inspection instruction signal is received. [Figure 9] 10 is a block diagram showing a configuration of an inspection circuit in an example in which a discharge instruction signal is output from a control unit to a discharge circuit. FIG. [Figure 10] 10 is a flowchart showing a process flow when an inspection instruction signal is received in the example of FIG. 9. [Figure 11] 10 is a diagram illustrating an example in which an electrode and a first output section are electrically connected. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the present invention will now be described.

[0010] <Overall printer configuration> As shown in FIG. 1, the printer 1 (the "liquid ejection device" of the present invention) according to this embodiment includes a carriage 2, a subtank 3, an inkjet head 4 (the "liquid ejection head" of the present invention), a platen 5, conveying rollers 6 and 7, a maintenance unit 8, etc.

[0011] The carriage 2 is supported by two guide rails 11 and 12 extending in the scanning direction. The carriage 2 is connected to a carriage motor 36 (see FIG. 3) via a belt or the like (not shown), and when the carriage motor 36 is driven, the carriage 2 moves in the scanning direction along the guide rails 11 and 12. In the following description, the right and left sides of the scanning direction are defined as shown in FIG. 1.

[0012] The subtank 3 is mounted on the carriage 2. The printer 1 is equipped with a cartridge holder 13, in which four ink cartridges 14 are removably attached. The four ink cartridges 14 are aligned in the scanning direction, and store black, yellow, cyan, and magenta inks ("liquids" according to the present invention) in that order, from the one located on the right side of the scanning direction. The subtank 3 is connected to the four ink cartridges 14 attached to the cartridge holder 13 via four tubes 15. This allows the four colors of ink to be supplied from the four ink cartridges 14 to the subtank 3.

[0013] The inkjet head 4 is mounted on the carriage 2 and connected to the lower end of the subtank 3. The inkjet head 4 is supplied with the four colors of ink from the subtank 3. The inkjet head 4 ejects ink from multiple nozzles 10 formed on its lower surface, the nozzle face 4a. More specifically, the multiple nozzles 10 are arranged in a transport direction perpendicular to the scanning direction to form nozzle rows 9, and four nozzle rows 9 are aligned in the scanning direction on the nozzle face 4a. The multiple nozzles 10 eject black, yellow, cyan, and magenta inks, starting from the nozzles constituting the nozzle row 9 on the right side of the scanning direction. The inkjet head 4 is also connected to an inspection circuit 27 (see FIGS. 3 and 4). The inspection circuit 27 is controlled by a control unit 30 (see FIGS. 3 and 4). The inspection circuit 27 and the control unit 30 will be described in detail later.

[0014] The platen 5 is disposed below the inkjet head 4 and faces the multiple nozzles 10. The platen 5 extends across the entire length of the recording paper P in the scanning direction and supports the recording paper P from below. The transport roller 6 is disposed upstream of the inkjet head 4 and platen 5 in the transport direction. The transport roller 7 is disposed downstream of the inkjet head 4 and platen 5 in the transport direction. The transport rollers 6 and 7 are connected to a transport motor 37 (see FIG. 3) via gears and the like (not shown). When the transport motor 37 is driven, the transport rollers 6 and 7 rotate and the recording paper P is transported in the transport direction.

[0015] The maintenance unit 8 includes a cap 21, a suction pump 22, and a waste liquid tank 23. The cap 21 is disposed to the right of the platen 5 in the scanning direction. When the carriage 2 is positioned at a maintenance position to the right of the platen 5 in the scanning direction, the multiple nozzles 10 face the cap 21.

[0016] The cap 21 can be raised and lowered by a cap lifting mechanism 38 (see FIG. 3). When the carriage 2 is positioned at the maintenance position so that the plurality of nozzles 10 and the cap 21 face each other, and the cap 21 is raised by the cap lifting mechanism 38, the upper end of the cap 21 comes into close contact with the nozzle surface 4a, and the plurality of nozzles 10 are covered by the cap 21. When the cap 21 is lowered by the cap lifting mechanism 38, the plurality of nozzles 10 are uncovered by the cap 21 and are in an uncapped state. Note that the cap 21 does not necessarily have to cover the plurality of nozzles 10 by coming into close contact with the nozzle surface 4a. The cap 21 may, for example, cover the plurality of nozzles 10 by coming into close contact with a frame (not shown) or the like that is arranged around the nozzle surface 4a of the inkjet head 4.

[0017] The suction pump 22 is a tube pump or the like, and is connected to the cap 21 and the waste liquid tank 23. In the maintenance unit 8, when the suction pump 22 is driven in the above-mentioned capped state, it is possible to perform a so-called suction purge, which discharges ink from inside the inkjet head 4 through the multiple nozzles 10. The ink discharged by the suction purge is stored in the waste liquid tank 23.

[0018] For convenience, the cap 21 has been described as covering all of the nozzles 10 together, and ink in the inkjet head 4 is discharged from all of the nozzles 10 during suction purging. However, this is not limiting. For example, the cap 21 may have separate portions covering the nozzles 10 constituting the rightmost nozzle row 9 that ejects black ink and the nozzles 10 constituting the three leftmost nozzle rows 9 that eject color inks (yellow, cyan, and magenta ink), so that either the black ink or the color ink in the inkjet head 4 can be selectively discharged during suction purging. Alternatively, for example, a separate cap 21 may be provided for each nozzle row 9, so that ink can be discharged from the nozzles 10 for each nozzle row 9 individually during suction purging.

[0019] Furthermore, in the maintenance unit 8, when the suction pump 22 is driven in the uncapped state, ink accumulated in the cap 21 can be discharged by suction purging, inspection driving (described later), or the like, thereby performing so-called idle suction. The ink discharged from the cap 21 by idle suction is also stored in the waste liquid tank 23.

[0020] 2, an electrode 26 having a rectangular planar shape is disposed within the cap 21. The electrode 26 is connected to ground. In this embodiment, with the cap in the above-described state and a potential difference being generated between the inkjet head 4 and the electrode 26 as described below, it is possible to determine whether ink has been ejected from the nozzle 10 based on a change in voltage of the electrode 26 when the inkjet head 4 is driven for testing to eject ink from the nozzle 10.

[0021] <Printer electrical configuration> Next, the electrical configuration of the printer 1 will be described. As shown in Fig. 3, the printer 1 includes a control unit 30. The control unit 30 includes a central processing unit (CPU) 31, a read-only memory (ROM) 32, a random access memory (RAM) 33, a memory 34, and an application-specific integrated circuit (ASIC) 35. The control unit 30 controls the operation of a carriage motor 36, an inkjet head 4, a transport motor 37, a cap lifting mechanism 38, a suction pump 22, an inspection circuit 27, and the like. The control unit 30 also receives signals from the inspection circuit 27.

[0022] The control unit 30 may be configured such that only the CPU 31 performs various processes, or such that only the ASIC 35 performs various processes, or such that the CPU 31 and the ASIC 35 work together to perform various processes. The control unit 30 may be configured such that one CPU 31 performs processes independently, or such that multiple CPUs 31 share the processes. The control unit 30 may be configured such that one ASIC 35 performs processes independently, or such that multiple ASICs 35 share the processes.

[0023] <Test circuit> Next, we will explain the inspection circuit 27. As shown in Fig. 4, the inspection circuit 27 includes a voltage supply circuit 51 (the "voltage supply unit" of the present invention), a main circuit 52, a voltage dividing circuit 53, a comparison voltage generating circuit 54, a comparison circuit 55, a high-pass filter 56, an amplifier circuit 57, a first output unit 58, a low-pass filter 59 (the "other low-pass filter" of the present invention), a second output unit 60, a latch circuit 61, a third output unit 62, and a discharge circuit 63 (the "discharge unit" of the present invention).

[0024] The voltage supply circuit 51 applies a voltage to the inkjet head 4 to generate a potential difference between the inkjet head 4 and the electrodes 26. As will be described later, the voltage supply circuit 51 adjusts the output voltage by switching between boosting the output voltage and stopping the boost. The operation of the voltage supply circuit 51 will be described in detail later.

[0025] The voltage supply circuit 51 also includes a comparison signal receiving section 51a, an enable signal receiving section 51b, and an on / off signal receiving section 51c.

[0026] The comparison signal receiving unit 51a is a unit that receives a comparison signal output from the comparison circuit 55, as will be described later. The permission signal receiving unit 51b is a unit that receives a permission signal output from the control unit 30. The permission signal is a signal that indicates whether or not to permit voltage boosting in the voltage supply circuit 51. The on / off signal receiving unit 51c is a unit that receives an on / off signal output from the control unit 30. The on / off signal is a signal that indicates whether the voltage supply circuit 51 should be in an on state in which voltage boosting is possible, or an off state in which voltage boosting is not possible.

[0027] The main circuit 52 is a circuit that connects the voltage supply circuit 51 and the inkjet head 4. A low-pass filter 71 is connected to a portion of the main circuit 52 between the voltage supply circuit 51 and the inkjet head 4. The low-pass filter 71 is a filter that reduces frequency components higher than the cut-off frequency of voltage fluctuations on the inkjet head 4 side, which is downstream of the low-pass filter 71 in the voltage supply, relative to the voltage supply circuit 51 side, which is upstream of the low-pass filter 71 in the voltage supply of the main circuit 52. In other words, mainly the DC component of the voltage input from the downstream side of the voltage supply is output from the low-pass filter 71 to the upstream side of the voltage supply.

[0028] The voltage dividing circuit 53 is connected to a connection 52a between the voltage supply circuit 51 and the low-pass filter 71 of the main circuit 52. The voltage dividing circuit 53 outputs a voltage Vd obtained by dividing the voltage V output from the voltage supply circuit 51 at a predetermined ratio. The voltage Vd output from the voltage dividing circuit 53 is a voltage having a magnitude that can be input to the comparison circuit 55.

[0029] The comparison voltage generation circuit 54 generates a comparison voltage Vda to be compared with the voltage Vd output from the voltage divider circuit 53. The comparison voltage Vda is a voltage corresponding to a predetermined voltage Va. More specifically, the magnitude |Vda| of the comparison voltage Vda is the magnitude |Vd| of the voltage Vd output from the voltage divider circuit 53 when the magnitude |V| of the voltage V output from the voltage supply circuit 51 is the magnitude |Va| of the predetermined voltage Va. In other words, the magnitude |Vda| of the comparison voltage Vda is set so that the magnitude |V| of the voltage V output from the voltage supply circuit 51 becomes the predetermined voltage Va. The comparison voltage generation circuit 54 has a PWM signal receiving unit 54a that receives a PWM (Pulse Width Modulation) signal output from the control unit 30. The comparison voltage generation circuit 54 generates a comparison voltage based on the PWM signal received by the PWM signal receiving circuit 54a. Specifically, the comparison voltage generation circuit 54 generates a comparison voltage Vda with a larger magnitude as the proportion R of the PWM signal that is set to High increases.

[0030] The comparison circuit 55 is electrically connected to the voltage divider circuit 53, the comparison voltage generation circuit 54, and the voltage supply circuit 51. The comparison circuit 55 compares the magnitude |Vd| of the voltage Vd output from the voltage divider circuit 53 with the magnitude |Vda| of the comparison voltage Vda output from the comparison voltage generation circuit 54, and outputs a comparison signal according to the result to the voltage supply circuit 51. In other words, the comparison signal is a signal that indicates whether the magnitude |Vd| of the voltage Vd output from the voltage divider circuit 53 is greater than the magnitude |Vda| of the comparison voltage Vda. The comparison signal output from the comparison circuit 55 is received by a comparison signal receiving unit 51a of the voltage supply circuit 51.

[0031] Here, the operation of the voltage supply circuit 51 will be described. When the permission signal received by the permission signal receiver 51b indicates that the voltage supply circuit 51 is permitted to boost the voltage, and the on / off signal received by the on / off signal receiver 51c indicates that the voltage supply circuit 51 should be turned on, the voltage supply circuit 51 switches between boosting the voltage or stopping the boosting based on the comparison signal. Specifically, the voltage supply circuit 51 boosts the voltage when the comparison signal indicates that |Vd| is equal to or smaller than |Vda|. On the other hand, when the comparison signal indicates that |Vd| is greater than |Vda|, the voltage supply circuit 51 stops boosting the voltage. As a result, the magnitude |Vd| of the voltage Vd output from the voltage divider circuit 53 is maintained at the magnitude |Vda| of the comparison voltage Vda. Furthermore, the magnitude |V| of the voltage V output from the voltage supply circuit 51 is maintained at the magnitude |Va| of the predetermined voltage Va.

[0032] Here, the predetermined voltage Va is, for example, a positive voltage of about 500V, and the comparison voltage Vda is, for example, a positive voltage of about 1.7V. In this case, the voltages V and Vd are voltages of 0V or higher. Alternatively, the predetermined voltage Va may be, for example, a negative voltage of about -500V, and the comparison voltage Vda may be, for example, a negative voltage of about -1.7V. In this case, the voltages V and Vd are voltages of 0V or lower.

[0033] The high-pass filter 56 is connected to a connection 52b (the "second connection" of the present invention) between the inkjet head 4 of the main circuit 52 and the low-pass filter 71. The amplifier circuit 57 is connected to the high-pass filter 56. The first output section 58 is connected to the amplifier circuit 57. That is, the amplifier circuit 57 is connected between the high-pass filter 56 and the first output section 58. Furthermore, the high-pass filter 56 is connected between the voltage supply circuit 51 and the first output section 58.

[0034] When a voltage fluctuation occurs in the inkjet head 4 located upstream of the high-pass filter 56 in the voltage supply, the DC component of the voltage (the high voltage component applied by the voltage supply circuit 51) is removed by the high-pass filter 56 downstream of the high-pass filter 56 in the voltage supply. The voltage that has passed through the high-pass filter 56 is amplified by the amplifier circuit 57 and output from the first output unit 58. As a result, the signal output from the first output unit 58 is a signal in which the high-frequency component of the voltage of the inkjet head 4 has been amplified.

[0035] Here, the voltage of the inkjet head 4 will be described when the inkjet head 4 is driven for testing to eject ink from the nozzles 10 while in the capped state and with a voltage applied to the inkjet head 4 by the voltage supply circuit 51 to generate a potential difference between the inkjet head 4 and the electrodes 26. When ink is not ejected from the nozzles 10 by the testing drive, the voltage of the inkjet head 4 hardly changes. When ink is ejected from the nozzles 10 by the testing drive, the voltage of the inkjet head 4 changes. Furthermore, this change in the voltage of the inkjet head 4 is sudden. Therefore, the high-frequency component of the voltage of the inkjet head 4 differs depending on whether or not ink is ejected from the nozzles 10 by the testing drive.

[0036] Thus, when ink is not ejected from nozzle 10 by the inspection drive, the signal output from the high-pass filter 56 toward the amplifier circuit 57 and the signal output from the first output unit 58 are signals whose voltage hardly changes from V0 as shown in FIG. 5(a). Here, V0 is a voltage close to, for example, the ground potential.

[0037] On the other hand, when ink is ejected from nozzle 10 by the inspection drive and the voltage of the inkjet head 4 changes, the signal output from the high-pass filter 56 toward the amplifier circuit 57 is a signal whose voltage changes with respect to V0 as shown in FIG. 5(b). However, the amount of change in the voltage of the inkjet head 4 when ink is ejected from nozzle 10 by the inspection drive is smaller than the amount of change in the voltage of the inkjet head 4 when a temporary short circuit occurs between the inkjet head 4 and the electrode 26 as will be described later. Therefore, the signal output from the high-pass filter 56 toward the amplifier circuit 57 when ink is ejected from nozzle 10 by the inspection drive is also a signal with a small amount of voltage change as shown in FIG. 5(b).

[0038] Also, the signal output from the first output unit 58 is a signal obtained by amplifying the signal in FIG. 5(b) as shown in FIG. 5(c). Therefore, the signal output from the first output unit 58 has a larger voltage change than the signal output from the high-pass filter 56 toward the amplifier circuit 57. Specifically, the signal output from the first output unit 58 when ink is ejected from nozzle 10 by the inspection drive is a signal whose maximum value Vh of the voltage V1 is larger than Vh1 (>V0) and whose minimum value Vm of the voltage V1 is smaller than Vm1 (<V0).

[0039] In this way, the signal output from the first output unit 58 is a signal indicating whether ink is ejected from nozzle 10 by the inspection drive. Also, since the signal output from the first output unit 58 is a signal amplified by the amplifier circuit 57, it is a signal with a certain amount of voltage change when ink is ejected from nozzle 10 by the inspection drive.

[0040] The low-pass filter 59 is connected to a connection portion 52c (the "first connection portion" of the present invention) of the main circuit 52 between the voltage supply circuit 51 and the low-pass filter 71. Here, the connection portion 52c is also a portion of the main circuit 52 between the voltage supply circuit 51 and the inkjet head 4. The second output portion 60 is connected to the low-pass filter 59. As a result, in this embodiment, the second output portion 60 is connected to the connection portion 52c, and the low-pass filter 59 is connected between the connection portion 52c and the second output portion 60.

[0041] The second signal output from the second output unit 60 is a signal in which high frequency components have been removed by the low pass filters 59 and 71 in response to fluctuations in the voltage of the inkjet head 4. In other words, the second signal output from the second output unit 60 is mainly a signal of the DC component of the voltage of the inkjet head 4.

[0042] Here, for example, connection between the inkjet head 4 and the electrode 26 via the ink in the cap 21 may cause a continuous short circuit between the inkjet head 4 and the electrode 26. A continuous short circuit between the inkjet head 4 and the electrode 26 means that the inkjet head 4 and the electrode 26 remain shorted, causing a leak current to continue to flow between the inkjet head 4 and the electrode 26. When a continuous short circuit occurs between the inkjet head 4 and the electrode 26, a leak current continues to flow between the inkjet head 4 and the electrode 26, causing the magnitude of the voltage of the inkjet head 4 to decrease.

[0043] Therefore, as shown in FIG. 6, when there is no continuous short circuit between the inkjet head 4 and the electrode 26, the magnitude |V2| of the voltage V2 of the second signal output from the second output unit 60 is about the voltage V2a (V2a>0). When there is a continuous short circuit between the inkjet head 4 and the electrode 26, the magnitude |V2| of the voltage V2 of the second signal output from the second output unit 60 becomes smaller than the voltage V2b (<V2a). Thus, the second signal becomes a signal indicating whether there is a continuous short circuit between the inkjet head 4 and the electrode 26. Note that FIG. 6 shows a case where there is no continuous short circuit between the inkjet head 4 and the electrode 26 until time T1, and a continuous short circuit occurs between the inkjet head 4 and the electrode 26 from time T1.

[0044] The latch circuit 61 is connected in parallel with the amplifier circuit 57 to the high-pass filter 56. The third output unit 62 is connected to the latch circuit 61. Thus, the third output unit 62 is connected to the high-pass filter 56 without passing through the amplifier circuit 57, and the latch circuit 61 is connected between the high-pass filter 56 and the third output unit 62. The latch circuit 61 receives a signal from which the DC component (the high voltage component applied by the voltage supply circuit 51) has been removed by the high-pass filter 56 from the voltage of the inkjet head 4. The latch circuit 61 is configured to output a signal when a voltage of a predetermined voltage or higher is input, and not to output a signal when a voltage lower than the predetermined voltage is input. Further, the latch circuit 61 has a circuit that maintains its output once it has output a signal. The latch circuit 61 includes a release signal receiving unit 61a that receives a release signal instructing the release of the output from the control unit 30, and the maintenance of the output of the latch circuit 61 continues until a release command is received from the control unit 30.

[0045] If a temporary short circuit occurs between the inkjet head 4 and the electrode 26, for example, due to a temporary discharge occurring in the gap between the ink in the cap 21 and the nozzle surface 4a, a temporary voltage change occurs in the inkjet head 4. A temporary short circuit occurs between the inkjet head 4 and the electrode 26 when a temporary short circuit occurs between the inkjet head 4 and the electrode 26, causing a temporary leakage current to flow between the inkjet head 4 and the electrode 26. The temporary voltage change in the inkjet head 4 when a temporary short circuit occurs between the inkjet head 4 and the electrode 26 is sudden. Therefore, the high-frequency component of the voltage of the inkjet head 4 differs depending on whether or not a temporary short circuit occurs between the inkjet head 4 and the electrode 26. The amount of change in the voltage of the inkjet head 4 at this time is greater than the amount of change in the voltage of the inkjet head 4 when ink is ejected from the nozzle 10 by test driving.

[0046] Therefore, when no temporary short circuit occurs between the inkjet head 4 and the electrode 26, the voltage of the signal output from the high-pass filter 56 and received by the latch circuit 61 changes very little, as shown in FIG. 7(a). In other words, the latch circuit 61 does not output a signal. On the other hand, when a temporary short circuit occurs between the inkjet head 4 and the electrode 26, the voltage of the signal received by the latch circuit 61 changes temporarily, as shown in FIG. 7(b). However, this voltage change lasts only a short time.

[0047] When a voltage change occurs in the signal received by the latch circuit 61 due to a temporary short circuit occurring between the inkjet head 4 and the electrode 26, the latch circuit 61 outputs a signal. Furthermore, since the latch circuit 61 includes a circuit for maintaining the output, the signal continues to be output. As a result, the latch signal output from the latch circuit 61 has a voltage of V0 when no temporary short circuit occurs between the inkjet head 4 and the electrode 26, as shown in FIG. 7(c), for example. When a temporary short circuit occurs between the inkjet head 4 and the electrode 26, the voltage becomes V3a (>V0), and the output of this signal is maintained. That is, the latch signal output from the latch circuit 61 indicates whether or not a temporary short circuit has occurred between the inkjet head 4 and the electrode 26. Note that FIGS. 7(b) and 7(c) illustrate the case where a temporary short circuit occurs between the inkjet head 4 and the electrode 26 at time T2. Furthermore, when temporary short circuits occur repeatedly between the inkjet head 4 and the electrode 26, the latch signal output from the latch circuit 61 maintains a voltage of V3a. The control unit 30 outputs a release signal when it determines that it is not necessary to maintain the output from the latch circuit 61, and the latch circuit 61 receives the release signal from the control unit 30 at the release signal receiving unit 61a. The latch circuit 61 receives the release signal and stops outputting the latch signal. Note that FIG. 7(c) shows a case where the latch circuit 61 receives the release signal at time T3, which is after time T2. The third signal output from the third output unit 62 connected to the latch circuit 61 is the same signal as the latch signal.

[0048] The discharge circuit 63 is connected to a connection 52d (referred to as a "third connection" in the present invention) between the inkjet head 4 and the connection 52b of the main circuit 52. The connection 52d is also a portion of the main circuit 52 between the inkjet head 4 and the low-pass filter 71. The connection 52d is closer to the inkjet head 4 than the connection 52c of the main circuit 52, to which the second output section 60 is connected, and the connection 52b of the main circuit 52, to which the third output section 62 is connected. The discharge circuit 63 discharges at a position close to the inkjet head 4 in order to rapidly reduce the voltage of the inkjet head 4 without waiting for the voltage supplied from the voltage supply circuit 51 to drop.

[0049] The discharge circuit 63 has a second signal receiving unit 63a that receives the second signal output from the second output unit 60, and a latch signal receiving unit 63b that receives the signal output from the latch circuit 61. The second signal receiving unit 63a is electrically connected to the second output unit 60. The latch signal receiving unit 63b is electrically connected to the latch circuit 61. The discharge circuit 63 discharges the inkjet head 4 when the second signal received by the second signal receiving unit 63a indicates that a continuous short circuit has occurred between the inkjet head 4 and the electrode 26. The discharge circuit 63 also discharges the inkjet head 4 when the latch signal received by the latch signal receiving unit 63b indicates that a temporary short circuit has occurred between the inkjet head 4 and the electrode 26.

[0050] <Processing when receiving an inspection instruction signal> Next, a description will be given of the flow of processing by the control unit 30 when an inspection instruction signal is received instructing the control unit 30 to inspect whether ink is being ejected from the nozzles 10. In this embodiment, for example, when a user operates an operation unit (not shown) of the printer 1 or a PC connected to the printer to issue an instruction to inspect whether ink is being ejected normally from the nozzles 10, an inspection instruction signal is sent from the operation unit or PC of the printer 1, and the control unit 30 receives this inspection instruction signal. Then, when the control unit 30 receives the inspection instruction signal, it performs processing according to the flow of FIG.

[0051] 8 starts, the on / off signal output from the control unit 30 indicates that the voltage supply circuit 51 is to be turned off. The permission signal output from the control unit 30 indicates that the voltage supply circuit 51 is not permitted to boost. At this point, the control unit 30 is not outputting a PWM signal.

[0052] 8 in more detail, the control unit 30 first executes the capping process (S101). In the capping process, the control unit 30 controls the carriage motor 36 and the cap lifting mechanism 38 to establish the capped state described above. Note that if the capped state is established at the time when the inspection instruction signal is received, the capped state is maintained in S101.

[0053] Next, the control unit 30 switches the ON / OFF signal it is outputting to one indicating that the voltage supply circuit 51 is turned on (S102). Next, the control unit 30 switches the permission signal it is outputting to one indicating that the voltage boost is permitted (S103). Next, the control unit 30 starts outputting the PWM signal (S104). Through the processes of S102 to S104, the voltage supply circuit 51 switches between boosting and stopping the voltage boost based on the comparison signal, as described above.

[0054] As a result, the voltage supply circuit 51 continues to boost the voltage until the magnitude |Vd| of the voltage Vd output from the voltage divider circuit 53 becomes equal to the magnitude |Vda| of the comparison voltage Vda, i.e., until the magnitude |V| of the voltage V output from the voltage supply circuit 51 becomes equal to the magnitude |Va| of the predetermined voltage Va. Then, upon receiving a comparison signal indicating that the magnitude |Vd| of the voltage Vd output from the voltage divider circuit 53 has reached the magnitude |Vda| of the comparison voltage Vda, the voltage supply circuit 51 stops boosting the voltage. In this way, the voltage supply circuit 51 repeatedly boosts and stops boosting the voltage based on the comparison signal so that the magnitude |Vd| of the voltage Vd output from the voltage divider circuit 53 is maintained at the magnitude |Vda| of the comparison voltage Vda. In other words, the magnitude |V| of the voltage V output from the voltage supply circuit 51 is maintained at the magnitude |Va| of the predetermined voltage Va.

[0055] Next, the control unit 30 starts the ejection detection process after the voltage supplied to the inkjet head 4 reaches a predetermined voltage Va (S105). In the ejection detection process, the control unit 30 sequentially performs a test drive on each of the multiple nozzles 10 of the inkjet head 4. Then, based on the first signal output from the first output unit 58 when the test drive is performed, the control unit 30 determines whether ink has been ejected normally from the nozzle 10, and stores the result in the memory 34.

[0056] If a continuous short circuit has not occurred between the inkjet head 4 and the electrode 26 (S106: NO) and a temporary short circuit has not occurred between the inkjet head 4 and the electrode 26 (S107: NO), the control unit 30 continues the ejection detection process until the ejection detection process is completed (S108: NO). Here, in S106, the control unit 30 determines whether a continuous short circuit has occurred between the inkjet head 4 and the electrode 26 based on the second signal output from the second output unit 60. Furthermore, in S107, the control unit 30 determines whether a temporary short circuit has occurred between the inkjet head 4 and the electrode 26 based on the third signal output from the third output unit 62.

[0057] When the ejection detection process is completed (S108: YES), the control unit 30 stops outputting the PWM signal (S109). This reduces the magnitude |Vda| of the comparison voltage Vd (for example, to ground potential). As a result, the voltage supply circuit 51 no longer boosts the voltage, and the magnitude |Va| of the voltage V output from the voltage supply circuit 51 gradually decreases and finally reaches, for example, ground potential. In other words, the output of voltage from the voltage supply circuit 51 is stopped.

[0058] Next, the control unit 30 switches the output permission signal to one indicating that boosting is not permitted (S110), and then switches the output ON / OFF signal to one indicating that the voltage supply circuit 51 is turned off (S111).

[0059] On the other hand, if a continuous short circuit occurs between the inkjet head 4 and the electrode 26 during the ejection inspection process (S106: YES), or if a temporary short circuit occurs between the inkjet head 4 and the electrode 26 during the ejection inspection process (S107: YES), the control unit 30 interrupts the ejection detection process (S112), performs an uncap process (S113), and then performs the processes of S109 to S111. In the uncap process of S113, the control unit 30 controls the cap lifting mechanism 38 to lower the cap 21, thereby setting the cap 21 in an uncapped state. This makes it difficult for leakage current to flow between the inkjet head 4 and the electrode 26, preventing damage to the nozzle 10.

[0060] Furthermore, if a continuous short circuit occurs between the inkjet head 4 and the electrode 26 during the ejection inspection process, the second signal received by the second signal receiving unit 63a of the discharge circuit 63 indicates that a continuous short circuit has occurred between the inkjet head 4 and the electrode 26. This causes the discharge circuit 63 to discharge from the inkjet head 4. Furthermore, if a temporary short circuit occurs between the inkjet head 4 and the electrode 26 during the ejection inspection process, the latch signal received by the latch signal receiving unit 63b of the discharge circuit 63 indicates that a temporary short circuit has occurred between the inkjet head 4 and the electrode 26. This causes the discharge circuit 63 to discharge from the inkjet head 4. While the discharge circuit 63 is discharging from the inkjet head 4, leakage current is less likely to flow between the inkjet head 4 and the electrode 26, thereby preventing damage to the nozzle 10.

[0061] Furthermore, if the discharge inspection process is not interrupted after the process of S111, i.e., if the discharge inspection process is completed (S114: NO), the control unit 30 ends the process. If the discharge inspection process is interrupted (S114: YES), the control unit 30 executes an idle suction process (S115) and returns to S101. In the idle suction process, the control unit 30 performs idle suction by driving the suction pump 22 in an uncapped state. Note that in the discharge inspection process that starts in S105 after the idle suction process of S114, it may be determined whether ink is being ejected normally only for nozzles 10 other than the nozzles 10 for which it was determined whether ink was being ejected normally before the interruption, or it may be determined whether ink is being ejected normally for all nozzles 10 of the inkjet head 4.

[0062] <Effects> According to this embodiment, it is possible to determine whether or not liquid has been ejected normally from the nozzles 10 based on the first signal output from the first output section 58 when the test drive is performed.

[0063] Furthermore, when a continuous short circuit occurs between the inkjet head 4 and the electrode 26, the DC component of the voltage of the inkjet head 4 changes. In this embodiment, the second output unit 60 is connected to the inkjet head 4 via the low-pass filters 59 and 71, and therefore the second signal output from the second output unit 60 is a signal containing a DC component in response to voltage fluctuations of the inkjet head 4. This makes it possible to more accurately detect the occurrence of a continuous short circuit between the inkjet head 4 and the electrode 26 based on the second signal.

[0064] Furthermore, when a temporary short circuit occurs between the inkjet head 4 and the electrode 26, the voltage of the inkjet head 4 changes suddenly, generating high-frequency components in the voltage of the inkjet head 4. In this embodiment, the third output unit 62 is connected to the inkjet head 4 via the high-pass filter 56, and therefore the third signal output from the third output unit 62 is a signal containing high-frequency components in response to voltage fluctuations of the inkjet head 4. As a result, it is possible to detect the occurrence of a temporary short circuit between the inkjet head 4 and the electrode 26 based on the third signal.

[0065] Furthermore, in this embodiment, a low-pass filter 71 that has an effect in the direction from the inkjet head 4 to the voltage supply circuit 51 is connected between the voltage supply circuit 51 and the inkjet head 4. Therefore, even if voltage fluctuations occur in the inkjet head 4 due to a temporary short circuit or ejection, these voltage fluctuations are unlikely to be transmitted to the voltage supply circuit 51. This makes it possible to suppress fluctuations in the voltage Vd output from the voltage divider circuit 53, thereby stabilizing the voltage V supplied from the voltage supply circuit 51.

[0066] In this embodiment, a low-pass filter 71 and a low-pass filter 59 are connected between the inkjet head 4 and the second output unit 60. As a result, these two low-pass filters 59 and 71 can effectively remove high-frequency components from the voltage of the inkjet head 4.

[0067] In this embodiment, the third output unit 62 is electrically connected to a connection unit 52b of the main circuit 52 between the inkjet head 4 and the low-pass filter 71, and the high-pass filter 56 is connected between the third output unit 62 and the connection unit 52b. This allows for a structure in which the high-pass filter 56 is connected between the inkjet head 4 and the third output unit 62.

[0068] Furthermore, by connecting the third output unit 62 and the high-pass filter 56 in this manner, the inkjet head 4 and the third output unit 62 can be connected without the intervention of the low-pass filter 71. This makes it possible to accurately determine whether or not a temporary short circuit has occurred between the inkjet head 4 and the electrode 26, based on the third signal output from the third output unit 62.

[0069] Furthermore, when a temporary short circuit occurs between the inkjet head 4 and the electrode 26, the voltage of the inkjet head 4 changes for only a short time. Therefore, unlike this embodiment, if the latch circuit 61 is not connected between the high-pass filter 56 and the third output unit, when a temporary short circuit occurs between the inkjet head 4 and the electrode 26, the third signal output from the third output unit 62 will also be a signal whose voltage changes for only a short time. As a result, there is a risk that the control unit 30 will not be able to detect the occurrence of a temporary short circuit between the inkjet head 4 and the electrode 26 based on the third signal.

[0070] In contrast, in this embodiment, a latch circuit 61 is connected between the high-pass filter 56 and the third output section. Therefore, when a temporary short circuit occurs between the inkjet head 4 and the electrode 26 and a short-term change occurs in the voltage of the inkjet head 4, information indicating the occurrence of such a short-term voltage change is stored in the latch circuit 61. The third signal output from the third output section 62 is a signal corresponding to the information stored in the latch circuit 61. This allows the control section 30 to accurately detect the occurrence of a temporary short circuit between the inkjet head 4 and the electrode 26 based on the third signal.

[0071] Furthermore, once a temporary short circuit has occurred, it is highly likely that it will occur again unless the state of the ink between the electrode 26 and the inkjet head 4 changes. In this case, the presence of the latch circuit 61, which can maintain output even after a temporary short circuit has occurred, makes it possible to continue outputting a latch signal until the state of the ink between the electrode 26 and the inkjet head 4 is improved. This makes it possible to prevent the recurrence of a temporary short circuit.

[0072] Furthermore, in this embodiment, in order to generate a detectable voltage change in the inkjet head 4 when ink is ejected from the nozzles 10 toward the electrodes 26 by the test drive, it is necessary to increase the potential difference generated between the inkjet head 4 and the electrodes 26 by the voltage supply circuit 51. Therefore, the DC component of the voltage output from the inkjet head 4 becomes a high voltage, for example, about 500 V. On the other hand, the amount of change in the voltage of the inkjet head 4 when ink is ejected from the nozzles 10 by the test drive is smaller than the magnitude of the DC component of the voltage of the inkjet head 4.

[0073] In this embodiment, the high-pass filter 56 is connected between the inkjet head 4 and the first output unit 58, so that the voltage of the inkjet head 4 from which the DC component (high voltage component) has been removed is sent to the first output unit 58. Therefore, the first signal output from the first output unit 58 makes it easy to determine whether ink has been normally ejected from the nozzles 10 by the test drive. Furthermore, because the first output unit 58 and the third output unit 62 are connected to a common high-pass filter 56, the circuit configuration of the test circuit 27 can be simplified.

[0074] Furthermore, in this embodiment, the amount of change in voltage of the inkjet head 4 when ink is ejected from the nozzle 10 toward the electrode 26 by test driving is smaller than the amount of change in voltage of the inkjet head 4 when a temporary short circuit occurs between the inkjet head 4 and the electrode 26.

[0075] Therefore, in this embodiment, an amplifier circuit 57 is connected between the high-pass filter 56 and the first output section 58. This prevents the magnitude of the voltage of the first signal output from the first output section 58 from becoming too small when ink is ejected from the nozzle 10 toward the electrode 26 by the test driving, and makes it possible to accurately determine, based on the first signal, whether or not ink has been ejected normally from the nozzle 10 by the test driving.

[0076] On the other hand, the third output section 62 is connected to the high-pass filter 56 without passing through the amplifier circuit 57. This prevents the voltage of the third signal output from the third output section 62 from becoming too large.

[0077] Furthermore, in this embodiment, when a continuous or temporary short circuit occurs between the inkjet head 4 and the electrode 26, the discharge circuit 63 discharges the inkjet head 4. This makes it possible to suppress leakage current flowing between the inkjet head 4 and the electrode 26, thereby preventing damage to the nozzles 10 due to leakage current. Furthermore, because the discharge circuit 63 is connected to the connection portion 52d of the main circuit 52 between the inkjet head 4 and the low-pass filter 71, which is close to the inkjet head 4, it is possible to discharge the inkjet head 4 as quickly as possible when a continuous or temporary short circuit occurs between the inkjet head 4 and the electrode 26.

[0078] Furthermore, the connection portion 52d to which the discharge circuit 63 is connected is closer to the inkjet head 4 than the connection portion 52c to which the second output portion 60 is connected and the connection portion 52b to which the third output portion 62 is connected, of the main circuit 52. This also makes it possible to discharge from the inkjet head 4 as quickly as possible when a continuous or temporary short circuit occurs between the inkjet head 4 and the electrode 26.

[0079] In this embodiment, the latch circuit 61 and the discharge circuit 63 are electrically connected, and the discharge circuit 63 switches whether or not to discharge the inkjet head 4 based on a latch signal output from the latch circuit 61. As a result, when a temporary short circuit occurs between the inkjet head 4 and the electrode 26, discharge from the inkjet head 4 can be performed as quickly as possible based on the latch signal output from the latch circuit 61. Furthermore, when a temporary short circuit occurs between the inkjet head 4 and the electrode 26, there is a high possibility that such a temporary short circuit will occur again. In this embodiment, by directly inputting the latch signal output from the latch circuit 61 to the discharge circuit 63, discharge from the inkjet head 4 can be continued until the fluctuation in voltage of the inkjet head 4 caused by the temporary short circuit subsides.

[0080] In this embodiment, the second output unit 60 and the discharge circuit 63 are electrically connected, and the discharge circuit 63 switches whether or not to discharge the inkjet head 4 based on the second signal output from the second output unit 60. This allows the inkjet head 4 to discharge as quickly as possible based on the second signal output from the second output unit 60 when a continuous short circuit occurs between the inkjet head 4 and the electrode 26.

[0081] <Modification> Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims.

[0082] In the above-described embodiment, the second signal receiving section 63a of the discharge circuit 63 is electrically connected to the second output section 60, and the latch signal receiving section 63b of the discharge circuit 63 is electrically connected to the latch circuit 61. The discharge circuit 63 is configured to discharge the inkjet head 4 when the second signal received by the second signal receiving section 63a indicates that a continuous short circuit has occurred, and when the latch signal received by the latch signal receiving section 63b of the discharge circuit 63 indicates that a temporary short circuit has occurred, but the present invention is not limited to this.

[0083] In the first modification, as shown in FIG. 9 , the control unit 30 can output a discharge instruction signal to the discharge circuit 101, instructing the discharge circuit 101 to discharge the inkjet head 4. The discharge circuit 101 has a discharge instruction signal receiving unit 101a that receives the discharge instruction signal. The discharge circuit 101 is configured to discharge the inkjet head 4 when the discharge instruction signal receiving unit 101a receives the discharge instruction signal. That is, in the above-described embodiment, the discharge circuit 63 receives the signal indicating the occurrence of a short circuit, which is output from the second output unit 60 and the latch circuit 61, without going through the control unit 30. In contrast, in the first modification, the control unit 30 receives the signal indicating the occurrence of a short circuit, which is output from the second output unit 60 and the latch circuit 61, and outputs a discharge instruction signal indicating the occurrence of a discharge to the discharge circuit 101 based on the signal.

[0084] In Modification 1, when an inspection command signal is received, the control unit 30 performs processing in accordance with the flow of Fig. 10. More specifically, when an inspection command signal is received, the control unit 30 executes the same processes of S101 to S115 as in the above-described embodiment. However, in Modification 1, unlike the above-described embodiment, when the control unit 30 receives a signal in S106 or S107 in response to the occurrence of a short circuit between the inkjet head 4 and the electrode 26, it outputs a discharge command signal to the discharge circuit 101 (S201) and then proceeds to S112.

[0085] In the first modification, when the control unit 30 determines that a continuous or temporary short circuit has occurred between the inkjet head 4 and the electrode 26, it outputs a discharge instruction signal to the discharge circuit 101. Then, when the discharge circuit 101 receives the discharge instruction signal, it causes discharge from the inkjet head 4. This allows discharge from the inkjet head 4 to occur when a continuous or temporary short circuit has occurred between the inkjet head 4 and the electrode 26.

[0086] The discharge circuit may also include both the second signal receiving unit 63a and the latch signal receiving unit 63b of the above-described embodiment and the discharge instruction signal receiving unit 101a of Modification 1. The discharge circuit 63 may be configured to discharge ink from the inkjet head 4 when the second signal received by the second signal receiving unit 63a indicates that a continuous short circuit has occurred, when the latch signal received by the latch signal receiving unit 63b of the discharge circuit 63 indicates that a temporary short circuit has occurred, and when the discharge instruction signal receiving unit 101a receives a discharge instruction signal. The discharge circuit may also include either the second signal receiving unit 63a or the latch signal receiving unit 63b of the above-described embodiment and the discharge instruction signal receiving unit 101a of Modification 1.

[0087] In the above embodiment, the discharge circuit 63 is connected to the connection portion 52d of the main circuit 52, which is between the inkjet head 4 and the low-pass filter 71. The connection portion 52d is closer to the inkjet head 4 than the connection portion 52c to which the second output portion 60 is connected and the connection portion 52b to which the third output portion 62 is connected, of the main circuit 52. However, this is not limiting.

[0088] For example, the discharge circuit 63 may be connected to a connection part of the main circuit 52 between the inkjet head 4 and the low-pass filter 71, and which is farther from the inkjet head 4 than at least one of the connections 52b and 52c (the "third connection part" of the present invention).

[0089] Also, for example, the discharge circuit 63 may be connected to a connection part (the "third connection part" of the present invention) in a part of the main circuit 52 other than the part between the inkjet head 4 and the low-pass filter 71, which is closer to the inkjet head 4 than the connection parts 52b and 52c.

[0090] Also, for example, the discharge circuit 63 may be connected to a connection part of the main circuit 52 other than the part between the inkjet head 4 and the low-pass filter 71, and farther from the inkjet head 4 than at least one of the connections 52b and 52c. The discharge circuit 63 may also be connected to the inkjet head 4 without going through the main circuit 52. Furthermore, a discharge circuit that discharges electricity from the inkjet head 4 need not be provided.

[0091] In the above embodiment, the high-pass filter 56 and the first output section 58 are connected via the amplifier circuit 57, and the high-pass filter 56 is connected to the third output section 62 without via the amplifier circuit 57. However, this is not limiting. For example, if the control section 30 can detect small voltage changes in the first output section 58, the amplifier circuit 57 does not need to be connected between the high-pass filter 56 and the first output section 58.

[0092] Furthermore, in the above-described embodiment, the high-pass filter 56 is connected between the first output unit 58 and the connection unit 52, thereby connecting the high-pass filter 56 to the first output unit 58 and the third output unit 62. However, this is not limiting. For example, the inkjet head 4 and the third output unit 62 may be connected via the high-pass filter 56, and the inkjet head 4 and the first output unit 58 may be connected without the high-pass filter 56. In this case, a high-pass filter other than the high-pass filter 56 may be connected between the inkjet head 4 and the first output unit 58. That is, the high-pass filter connected between the inkjet head 4 and the first output unit 58 and the high-pass filter connected between the inkjet head 4 and the third output unit 62 may be separate. Alternatively, a high-pass filter may not be connected between the inkjet head 4 and the first output unit 58.

[0093] In addition, in the above-described embodiment, the latch circuit 61 is connected between the high-pass filter 56 and the third output unit 62, but this is not limiting. For example, if the discharge circuit 63 and the control unit 30 can accurately detect short-term voltage changes received, the latch circuit 61 does not need to be connected between the high-pass filter 56 and the third output unit 62.

[0094] In the above embodiment, the third output unit 62 is connected to the connection unit 52b of the main circuit 52, and the high-pass filter 56 is connected between the connection unit 52b and the third output unit 62. However, this is not limiting. For example, the inkjet head 4 and the third output unit 62 may be connected without going through the main circuit 52, and the high-pass filter 56 may be connected between the inkjet head 4 and the third output unit 62.

[0095] In the above embodiment, the low-pass filter 71 provided in the main circuit 52 and the low-pass filter 59 provided outside the main circuit 52 are connected between the inkjet head 4 and the second output unit 60, but this is not limiting. Only the low-pass filter 71 provided in the main circuit 52 may be connected between the inkjet head 4 and the second output unit 60. Alternatively, only the low-pass filter 59 provided outside the main circuit 52 may be connected between the inkjet head 4 and the second output unit 60.

[0096] In the above-described embodiment, the first output unit 58 is electrically connected to the electrode 26, but this is not limiting. For example, in Modification 2, as shown in Fig. 11, the first output unit 111 is connected to the electrode 26, and an amplifier circuit 112 is connected between the first output unit 111 and the electrode 26. The electrode 26 is also connected to ground. Although not shown in the drawings, in Modification 2, the first output unit and the amplifier circuit are not connected to the inkjet head 4.

[0097] When the inkjet head 4 is driven for testing while a potential difference is generated between the inkjet head 4 and the electrode 26, a voltage change occurs in both the inkjet head 4 and the electrode 26. Therefore, even when the first output unit 111 is connected to the electrode 26, it is possible to determine whether ink has been ejected normally from the nozzle 10 based on the first signal output from the first output unit 111. As described above, in the second modification, the amplifier circuit 112 does not have to be connected between the electrode 26 and the first output unit 111. A filter may be connected between the electrode 26 and ground. This filter prevents the amplitude of the signal resulting from ink ejection during testing by the inkjet head 4 from becoming smaller in a configuration in which a voltage is supplied to the inkjet head 4 and the first output unit 111 is connected to the electrode 26. By providing the filter, the signal output from the first output unit 111 can be made larger.

[0098] In the above embodiment, the comparison circuit 55 outputs a comparison signal based on the magnitude relationship between the magnitude |Vd| of the voltage Vd output from the voltage divider circuit 53 and the magnitude |Va| of the comparison voltage Va generated by the comparison voltage generation circuit 54. Then, based on the comparison signal, the voltage supply circuit 51 switches between boosting and not boosting, thereby outputting a voltage from the voltage supply circuit 51 and applying the voltage to the inkjet head 4. However, this is not limiting. A voltage may be applied to the inkjet head 4 by a voltage supply unit having a configuration different from that described above.

[0099] In the above embodiment, the test drive is performed on all the nozzles 10 of the inkjet head 4 to determine whether ink is ejected normally from the nozzles 10, but this is not limiting. For example, the test drive may be performed on only some of the nozzles 10 of the inkjet head 4, such as every other nozzle 10 in each nozzle row 9, to determine whether ink is ejected normally from the nozzles 10. Then, for the other nozzles 10, it may be estimated whether ink is ejected normally from the nozzles 10 based on the determination results for the some of the nozzles 10.

[0100] In the above example, the first signal output from the first output unit is a signal indicating whether or not ink has been ejected from the nozzle 10. When the first signal indicates that ink has been ejected from the nozzle 10, it is determined that ink has been ejected normally from the nozzle 10. However, this is not limited to this. The first signal may be a signal indicating an ejection mode other than whether or not ink has been ejected, such as the ink ejection direction or ejection speed. When the first signal indicates that ink has been ejected from the nozzle 10 in a predetermined ejection mode, it may be determined that ink has been ejected normally from the nozzle 10.

[0101] In the above, an example has been described in which the present invention is applied to a printer equipped with a so-called serial head that ejects ink from multiple nozzles while moving in the scanning direction together with the carriage, but the present invention is not limited to this. For example, the present invention can also be applied to a printer equipped with a so-called line head that extends across the entire length of the recording paper in the scanning direction.

[0102] Although the above description has been given of an example in which the present invention is applied to a printer that ejects ink from nozzles to record on recording paper P, the present invention is not limited to this. The present invention can also be applied to printers that record images on recording media other than recording paper, such as T-shirts, outdoor advertising sheets, cases for mobile devices such as smartphones, cardboard, and resin materials. The present invention can also be applied to liquid ejection devices that eject liquids other than ink, such as liquid resins and metals. [Explanation of symbols]

[0103] 1: Printer 4: Inkjet head 26: Electrode 51: Voltage supply circuit 52: Main circuit 56: High-pass filter 57: Amplification circuit 58: First output section 59: Low-pass filter 60: Second output section 61: Latch circuit 62: Third output section 63:Discharge circuit 71: Low-pass filter 101:Discharge circuit 111: First output unit 112: Amplification circuit

Claims

1. a liquid ejection head having nozzles for ejecting liquid; an electrode arranged so as to be able to face the nozzle; a voltage supply unit that applies a voltage to the liquid ejection head to generate a potential difference between the liquid ejection head and the electrode; a first output section electrically connected to either the electrode or the liquid ejection head, and configured to output a first signal corresponding to an electrical change when the liquid ejection head is driven for testing to eject liquid from the nozzle toward the electrode in a state where the liquid ejection head and the electrode are opposed to each other; a low-pass filter electrically connected to the liquid ejection head; a second output section electrically connected to the liquid ejection head via the low-pass filter; a high-pass filter electrically connected to the liquid ejection head; a third output section electrically connected to the liquid ejection head via the high-pass filter; a control unit, The control unit determining whether or not the liquid has been ejected normally from the nozzle based on the first signal; A liquid ejection device characterized by determining whether a short circuit has occurred between the liquid ejection head and the electrode based on a second signal output from the second output section and a third signal output from the third output section.

2. a main circuit that electrically connects the voltage supply unit and the liquid ejection head, the low-pass filter is provided in the main circuit, 2. The liquid ejection device according to claim 1, wherein the second output section is electrically connected to a first connection section of the main circuit between the voltage supply section and the low-pass filter.

3. a low-pass filter separate from the low-pass filter; 3. The liquid ejection device according to claim 2, wherein the other low-pass filter is connected between the first connection portion and the second output portion.

4. the third output portion is electrically connected to a second connection portion of the main circuit between the liquid ejection head and the low-pass filter; 4. The liquid ejection device according to claim 2, wherein the high-pass filter is connected between the third output portion and the second connection portion.

5. The liquid ejection device according to claim 4, further comprising a latch circuit connected between the high-pass filter and the third output section.

6. the first output portion is electrically connected to the second connection portion; 6. The liquid ejection device according to claim 4, wherein the high-pass filter is connected between the first output portion and the second connection portion.

7. an amplifier circuit connected between the high-pass filter and the first output section; 7. The liquid ejection device according to claim 6, wherein the third output section is connected to the high-pass filter without passing through the amplifier circuit.

8. a discharge unit that discharges the liquid ejection head, A liquid ejection device according to any one of claims 2 to 7, characterized in that the discharge section is electrically connected to a third connection section of the main circuit between the liquid ejection head and the low-pass filter.

9. a main circuit that electrically connects the voltage supply unit and the liquid ejection head; a discharge unit that discharges the liquid ejection head, the second output section and the third output section are each electrically connected to the main circuit; A liquid ejection device as described in any one of claims 1 to 8, characterized in that the discharge section is electrically connected to a third connection section of the main circuit that is closer to the liquid ejection head than the section to which the second output section and the third output section are connected.

10. a discharge unit that discharges the liquid ejection head, The discharge unit is 6. The liquid ejection device according to claim 5, further comprising: a latch circuit electrically connected to said latch circuit, said latch circuit being configured to switch whether or not to perform discharge from said liquid ejection head based on a signal output from said latch circuit.

11. a discharge unit that discharges the liquid ejection head, The discharge unit is A liquid ejection device as described in any one of claims 1 to 10, characterized in that it is electrically connected to the second output section and is configured to switch whether or not to discharge from the liquid ejection head based on the second signal.

12. a discharge unit that discharges the liquid ejection head, The control unit when it is determined based on the second signal and the third signal that the liquid ejection head and the electrode have been short-circuited, outputting a discharge instruction signal to the discharge unit to instruct the liquid ejection head to discharge, The discharge unit is 12. The liquid ejection apparatus according to claim 1, wherein the liquid ejection head is configured to perform discharge when the discharge instruction signal is received.

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